Session I38 - General Poster Session I.
MIXED session, Tuesday morning, March 17
Exhibit Hall,

[I38.01] COMPUTER DESIGN OF OPTICAL MOLECULAR SWITCHES USING A CONFORMATIONAL KINETIC TRAPPING MECHANISM

Some highly distorted porphyrins, including Ni(II) meso-tetra(tert-butyl)porphyrin (NiTtBuP), have been computer-designed and synthesized for optical memory applications. Molecular simulations show that these porphyrins possess several stable conformers, which can be used to trap electronic excited states as a means of storing information. For example, NiTtBuP has a (d,d) excited state lifetime about one hundred times longer than typical Ni porphyrins and this extended lifetime results from the conformational change following photoexcitation and the large energy barriers between the conformers. Halogenating NiTtBuP increases axial ligand affinity and energy barriers, giving a further extension of lifetime. (Supported by US DOE Contract DE-AC04-940AL85000.)

[I38.02] Laser PlasmaFormation at High Altitudes

Plasma production from solid targets starts at 10^8W/cm^2. Such fluxes can be realized at 10-100 km ranges with 10-100 J/pulse - one ns infra red solid state lasers when the output beam is expanded and focused by a 3 m diameter parabolic reflector. Raman shifting a 1.06\mu Nd^+ laser in H_2 gas to 1.9\mu minimizes atmospheric effects and results in a focal spot with a diffraction limited core. Natural (meteoric) dust and water droplets serve as the plasma sources. Proof of principal experiments are proposed with the UCLA 2.7 m diameter Liquid Mirror Telescope (LMT). Such plasmas offer new methods of stratosphere and ionosphere investigations; generating peroidic ELF radiation, launching plasma waves, and verifying conflicting theories of laser propagation through the atmosphere.

[I38.03] Behavior of Plastic Bonded Composite Explosives During High Acceleration

The mechanical behavior of plastic bonded composite explosives has been studied during high acceleration in an ultracentrifuge. The pressed explosives studied include LX-14 [95% HMX (cyclotetramethylene- tetranitramine), 5% Estane], Composition A3 type II [91% RDX (cyclotrimethylene-trinitramine), 99% BDNPF (bis-dinitropropyl acetal formal), 6% CAB (cellulose acetate butyrate)], and PAX-3 (85% HMX, 9% BDNPF, 6% CAB/25% Aluminum). The fracture strength of LX-14 is greater than all pressed explosives studied to date. The fracture strength of Composition A3 type II is smaller than all pressed explosives studied to date.

[I38.04]

This abstract was not submitted electronically.

[I38.05] Advanced Polymers PRT at NSLS - A Delicated Polymer Beamline

In January 1997, a newly established Advanced Polymers PRT (AP-PRT) constructed a x-ray scattering beamline (X27C) at the NSLS. The mission of this PRT

is to support continuing development and application of a dedicated facility at the NSLS for real time simultaneous small- and wide-angle x-ray scattering (SWAX) experiments with emphasis on structural and dynamical studies of polymer

materials. The primary focus of this PRT is to investigate polymer structure, morphology and dynamics from atomic (1-20 Åto nano/microscopic scales (20 1000 Åin real time and/or in-situ using simultaneous SAXS/WAXD techniques. Some examples of these studies that have been done during 1997 include characterizations of complex fluids (block copolymers, colloidal

systems, dendrimers, gels, ionomers); crystallization, melting and phase

transition of polymers and blends; polymer chemical reactions; polymer melts during shear; fiber and film formation and deformation; and polymers under high pressure and supercritical environment; etc.

[I38.06] Rapid manufacturing of metallic Molds for parts in Automobile

The recent research of RPM (Rapid Prototyping Manufacturing) in our lab has been focused on the rapid creation of alloyed cast iron (ACI) molds. There are a lot of machinery parts in an automobile, so a lot of mettallic molds are needed in automobile industry. A new mold manufacturing technology has been proposed. A new large scale RP machine has been set up in our lab now. Then rapid prototypes could be manufactured by means of laminated object manufacturing (LOM) technology. The molds for parts in automobile have been produced by ceramic shell precision casting. An example is a drawing mold for cover parts in automobile. Sufficient precision and surface roughness have been obtained. Itis proved that this is a vew kind of technology. Work supported by the Mational Science Foundation of China.

[I38.07] Casting Process Simulation Based of Interface Friction between Metallic Liquid and Die Wall

Rapid Tooling (RT) is a major field in rapid prototyping manufacturing (RPM). In order to obtain metallic molds for automobile industry, ceramic shell precision casting technology is being used. Models are used in this kind of casting technology in RT in our lab. Some main factors have been analysed and estimated. MARC nonlinear finite element analysis software has been used for calculation of size change in the casting process. Selection of boundary conditions in the solidification process is the most important. There is interface friction between metallic liquid and die wall. Except influence in size change due to phase transition and cooling process, this friction force in tangential direction could give severe influence on the size change. If this factor is not considered in the calculation for size change, there is a large difference between real value and calculated value. We use this new model instead of usual contact model, a better result has been obtained. Work supported by the National Natural Science Foundation of China.

[I38.08] Compositional Disorder in ZnSe Probed through Photoluminescence and Raman Spectroscopy

Temperature dependence of photoluminescence of single crystals of ZnSe with varying amounts of Cr doping, excited by 514.5 to 457.9nm has been studied.The discontinuties in the frequency, width, intensity and shape of the photoluminescence (and Raman) parameters around 200K are associated with the changes of the complex phonon-electron structure, as the excitation energy(457.9nm) approaches the energy difference between the valence and conduction band in the system. The anharmonic effects in the vibrational (transverse optic (TO), longitudinal optic(LO) and 2LO) bands could be explained by two different cubic anharmonic interaction in the crystal; one below 200K and another above 200K. It is seen that the long range order in the single crystals (ZnSe) is broken on Cr doping. The diminution of the overtone of the transverse acoustic mode in the Raman spectra is a clear evidence for this phenomena. The shift of LO phonon to lower energy in doped ZnSe has been attributed to the phonon confinement created by breaking the long-range order, on Cr doping. This work was supported by NASA-NCCW-0088 and NSF-OSR-9452893 Grants.

[I38.09] Resonant Raman effect in PPP-based carbon materials

Polyparaphenylene (PPP)- based carbon materials have attracted increasing attention in the last few years due to their potential application as host materials in Li-ion batteries. In particular, the PPP heat-treated at 700^\circC exhibits a very high lithium uptake capacity as a result of its particular structure. It consists of segments of the polymer PPP chain and some disordered carbon material associated with an early phase of the carbonization process. The Raman spectra from these heat-treated samples, collected using several laser excitation wavelengths, contain several low frequency peaks (1200 cm^-1 to 1400 cm^-1), and a higher frequency peak at \sim1600 cm^-1. Detailed lineshape analysis reveals that the low frequency band feature consists of contributions associated with PPP in its ground state (benzenoid configuration) and in an excited state (quinoid configuration). The lineshape analysis also gives evidence for a disorder-induced peak. The position and intensity of these low frequency peaks change as a function of the laser excitation energy. We attribute this effect to a resonant enhancement of their Raman cross-sections.

[I38.10] Molecular version of the resistive pulse technique: counting ATP by a single ion channel

The ``molecular Coulter counter'' concept has been used to study transport of ATP molecules through the nanometer-scale aqueous pore of the voltage-dependent mitochondrial ion channel, VDAC. We examine the ATP-induced current fluctuations and the change in average current through a single fully open channel reconstituted into a planar lipid bilayer. At high salt concentration (1M NaCl), the addition of ATP reduces both solution specific conductivity and channel conductance, but the effect on the channel is several times stronger and shows saturation behavior at 50 mM ATP concentration. ATP addition also generates an excess noise in the ionic current through the channel. By relating the low-frequency spectral density of the noise to the equilibrium diffusion of ATP molecules in the aqueous pore, we calculate a diffusion coefficient D = (1.6-3.3)x10^-11 m^2 /s. We show that the mesoscopic VDAC pore is a Coulter counter with the added features of attraction and diffusion.

[I38.11] Use of Designer Particles in Biolistics Plant-Transformation Studies

Designer particles provide a much more refined"tool" for biolistics studies than the typically used W or Au globular particles of nominal 1-um size. The extraordinary monodispersity, and unique shapes afforded by the designer particle synthesis technology, have led to high expectations for their use in plant and mammalian cell genetic transformation studies, where DNA or mRNA coated particles are literally fired by the gene gun into cells. Here, we discuss in broad terms some of the implications of these new particles for plant biolistics.

[I38.12] Ab initio calculation of ground and excited states in rhodopsin

We perform an all-electron ab initio calculation of the ground and excited states in rhodopsin. It is found that with respect to the ground state, the first-excited state has a minimum area in the regime with the dihedral angle around the bond C_11 - C_12, \theta_11,12=3D60^0-120^0. This area is much larger that found by Birge. A detailed comparison indicates that the first singlet in Birge's work is actually the third-excited state in our calculation. From the biological point view this is very desirable as one has a wider area to change the conformation during the excitation process. However concerning the response time of the surrounding proteins (such as Asp 85, Lysine 126) to the bathrhodopsin, one requires an excited state with a sufficiently long lifetime. From our calculations, we find that there are only limited number of configurations that allow an easy transition from the excited state back to the ground state, namely the dipole moment for many configurations is very weak. This helps one to understand a complete scenario how rhodopsin is excited and de-excited during isomerization.

[I38.13] DFT Equilibrium Geometry and Molecular Properties of Chiral Cyclo-Octapeptides

Cyclic peptides containing alternating D- and L-amino acids arranged in flat rings with C4 symmetry around the principal axis can self assemble into stacks forming peptide nanotubes in which the backbone strands of adjacent rings are arranged in an antiparallel beta sheet-like fashion. We report investigations of the dft optimized geometry and gas-phase, harmonic vibrational frequencies for the monomer as well as the energetics and configuration of the dimerization process. The polypeptides studied are among the largest investigated by ab initio calculations as well as being among the largest molecular systems investigated using dft methods and full size basis sets.

[I38.14] Ab initio calculation of ground and excited states in rhodopsin

We perform an all-electron ab initio calculation of the ground and excited states in rhodopsin. It is found that with respect to the ground state, the first-excited state has a minimum area in the regime with the dihedral angle around the bond C_11 - C_12, \theta_11,12=60^o-120^o. This area is much larger that found by Birge. A detailed comparison indicates that the first singlet in Birge's work is actually the third-excited state in our calculation. From the biological point view this is very desirable as one has a wider area to change the conformation during the excitation process. However concerning the response time of the surrounding proteins (such as Asp 212, Asp 85 and Lysine 126) to the bathrhodopsin, one requires an excited state with a sufficiently long lifetime. From our calculations, we find that there are only limited number of configurations that allow an easy transition from the excited state back to the ground state, namely the dipole moment for many configurations is very weak. This helps one to understand a complete scenario how rhodopsin is excited and de-excited during isomerization.

[I38.15] Critical demixing and the effect of electric fields on lipid bilayer membranes

Application of an electric field tangent to the plane of a fluid bilayer membrane can induce lateral reorganization of lipids. The resulting concentration profiles are readily observed in planar supported bilayers by epifluorescence microscopy. Using a fluorescently-labeled lipid to probe the field-induced separation of cardiolipin from egg-phosphatidylcholine, an enhanced sensitivity to the electric field is observed which is attributed to a critical demixing effect. A thermodynamic model of the system is used to analyze the results. The observed concentration profiles can be understood if the lipid mixture has a critical temperature equal to 75 K. This is in contrast to the behavior of membranes composed of phosphatidylserine and egg-phosphatidylcholine where nearly ideal mixing was observed. It appears to be an attribute of cardiolipin that causes the demixing and consequent increase in the sensitivity to an electric field. The steady state distribution of lipids under the influence of an electric field is very sensitive to demixing effects, even at temperatures well above the critical temperature for spontaneous phase separation.

[I38.16] Interactions determining phospholipid domain growth in monolayers: experimental results and computer simulations

Results are presented from a quantitative analysis of liquid condensed (LC) domain shapes in monolayers of the phospholipid dipalmitoylphosphatidylcholine (DPPC). Comparison with existing theory shows that the dominant dependence of LC domain shape factor on in-plane density is described well by electric dipole-dipole interactions; however, the detailed chirality of the LC domains remains unexplained. Also unaccounted for is the noncompact growth of LC domains either at electrolyte concentrations high enough to screen out electric dipole interactions, or in mixtures with anionic phospholipids. We have performed Monte Carlo simulations of domain growth using an Eden model with energetic contributions from line tension, dipole-dipole interactions, and a novel short-range chiral interaction term. We present results for the way in which these chiral interactions influence the geometry of the growing domains, yielding, e.g., noncompact domain growth even in the absence of dipole-dipole interactions.

[I38.17] Infrared Spectral Hole Burning and Change of Conformation in Amino Acid Salts

We have previously shown that we can hole-burn the simple amino acid salts, glycine and alanine hydrochlorides^1. We now apply hole-burning spectroscopy to study the vibrations of valine, tyrosine and glycylglycine hydrochlorides. These salts are doped with deuterium to form some NH_2D^+. Irradiation of the N-D stretching bands at low temperatures results in rotation of the NH_2D^+ moiety and forms spectral holes and antiholes. Due to the existence of combinations and Fermi resonance bands, the absorption spectra in 2000-3000 cm^-1 show complicated structure. By observing the pattern and relaxation of the holes and antiholes, the N-D and O-D stretching bands can be assigned, and this contributes to understanding the hydrogen-bonded environment of these biomolecules.

^1 G.-S. Yu, H.-W. Li and H. L. Strauss, J. Phys. Chem. B101, 5484 (1997); J. Phys. Chem. In press.

[I38.18] Reactions of Biomolecules to Alternative Methods of Energy Deposition

Ion induced fragmentation and polymerization of biomolecules is being investigated. Amino acids, which have been deposited on solid substrates, are bombarded with few-keV singly-charged ions. Ions ejected from the target are extracted with an electric field. Time-of-flight mass spectroscopy is then used to determine the degree of fragmentation and polymerization which has occurred. The mass spectra we observe indicate that slow, low-charged ions not ionize and fragment the biomolecules, but also catalyze a polymerization reaction. Data for various amino acids will be presented and discussed

[I38.19] Study of aortic matrix structure and molecular mobility by thermal analysis.

Aortic valves are complex materials primarily composed of different amounts of collagen and elastin. The aim of this work is to propose two techniques, the Differential Scanning Calorimetry (DSC) and the ThermoStimulated Currents spectroscopy (TSC) to characterize the structure and molecular mobility of the matrix. DSC thermograms indicate that pure collagen denaturation occurs at 230^\circC and that pure elastin undergoes a glass transition around 200^\circC; collagen and elastin TSC spectra reveal respectively four and three dielectric relaxation modes between -180^\circC and 220^\circC, attributed to localized and delocalized motions. These first studies were used as a reference for the characterization of the dynamic structure of aortic material itself. Aortic matrix DSC thermograms correspond to the superposition of collagen and elastin transitions. By TSC, four relaxation modes have been observed, confirming that elastin and collagen are the major factors of mobility. Analysis of the fine structure was necessary to separate the specific response of each constituent. Analysis of aortic matrix phase transition and dielectric relaxations of differently treated matrix has allowed us to precise the influence of the different treatments on the characteristic parameters of the dynamic structure.

[I38.20]

This abstract was not submitted electronically.

[I38.21] Two dimensional electron spin resonance: Structure and dynamics of biomolecules

The potential of two dimensional (2D) electron spin resonance (ESR) for measuring the structural properties and slow dynamics of labeled biomolecules will be presented. \par Specifically, it will be shown how the recently developed method of double quantum (DQ) 2D ESR (S. Saxena and J. H. Freed, J. Chem. Phys. 107), 1317, (1997) can be used to measure large interelectron distances in bilabeled peptides. The need for DQ ESR spectroscopy, as well as the challenges and advantages of this method will be discussed. \par The elucidation of the slow reorientational dynamics of this peptide (S. Saxena and J. H. Freed, J. Phys. Chem. A, 101) 7998 (1997) in a glassy medium using COSY and 2D ELDOR ESR spectroscopy will be demonstrated. The contributions to the homogeneous relaxation time, T_2, from the overall and/or internal rotations of the nitroxide can be distinguished from the COSY spectrum. The growth of spectral diffusion cross-peaks^2 with mixing time in the 2D ELDOR spectra can be used to directly determine a correlation time from the experiment which can be related to the rotational correlation time.

[I38.22] CONFORMATIONAL DIFFERENCES OF THE HEMES IN CYTOCHROMES C3 PROBED = BY RESONANCE RAMAN SPECTROSCOPY

The conformational differences in the hemes of four-heme cytochromes c3 have been investigated by resonance Raman (RR) spectroscopy. The frequencies of all of the structure-sensitive lines in the high-frequency region of the RR spectra are lower for the D. baculatum cytochromes c3 than for D. desulfuricans cytochrome c3, consistent with a more distorted heme. However, several or all of the four hemes may be more nonplanar. In addition, a shoulder appears on the low frequency side of v10 in the spectra of baculatum cytochromes c3, also consistent with a fraction of the hemes being significantly more nonplanar than the others. Further, a low-frequency subline of the macrocycle-breathing mode v8 of the spectrum of desulfuricans cytochrome c3 indicates a more planar heme than for the baculatum cytochromes c3. (Supported by US DOE contract DE-AC04-94AL85000.)

[I38.23] Nonplanarity of the Porphyrin in Nickel Cytochrome c Probed by = Resonance Raman Spectroscopy.

The influence of the protein on the nonplanarity of the porphyrin in Ni-reconstituted cytochrome c has been investigated with resonance Raman, absorption spectroscopy, and molecular simulations. The Raman results reveal that multiple conformers of the porphyrin exist at low pH. The amount of the nonplanar conformers decrease relative to the planar conformer as the pH is lowered. This change results from the disruption of the secondary structure and hydrogen-bonding network in the peptide backbone. Molecular simulations for Fe(III) and Ni(II) microperoxidase-5 show that the nonplanar distortion of the porphyrin is largely maintained by this particular covalently linked protein segment and that hydrogen bonding maintains this peptide's conformation and the porphyrin's distortion. (Supported by US DOE Contract DE-AC04-94AL85000)

[I38.24] A Detailed Model for Mg^2+-Actin Polymerization

A detailed model for actin polymerization is proposed in which the polymer size distribution is considered with cut-off mechanism. A closed set of coupled non-linear differential equations including total number concentration of polymers, polymerized actin concentration and all the intermediate polymer concentrations was obtained for describing the actin polymerization. This model gives a powerful tool to determine the rate constants for nucleation process. Dimer and trimer formation are quite unfavorable compare with elongation process. Trimer formation is however, much more favorable than dimer formation. It is also shown that the spontaneous fragmentation and annealing process are required for fitting the actin polymerization process. The dissociation constants obtained by fitting the experimental data to the model for dimer and trimer formation are (2.82 \pm 2.42) M and (3.23 \pm 0.93) X 10^-3 M respectively. The dissociation constant for elongation process obtained by fitting method is (0.11 \pm 0.02) \muM. The fitting rate constant for fragmentation is (1.10 \pm 1.26)x10^-7s^-1 and the annealing rate constant is obtained as (3.47 \pm 2.58)x10^6M^-1s^-1.

[I38.25] A Reaction-Diffusion Model for Microtubule Oscillations

Microtubules have been studied intensively in the past decades due to the many interesting properties they possess. The dynamics of microtubule assembly has been one key area of research and has yielded many interesting results, including that of microtubule oscillations. When a group of microtubules has the correct buffer conditions, they exhibit damped oscillations in terms of the amount of assembled tubulin. These oscillations are temporal as well as spatial. One successful method of modeling these oscillations is to use chemical reaction equations. If these equations are extended to include spatial dependence and diffusion, it is also possible to reproduce the spatial oscillations that are observed. The theoretical results are compared with those from experiment.

[I38.26] NORMAL-COORDINATE STRUCTURAL DECOMPOSITION OF HEME CONFORMATIONS = IN PROTEIN CRYSTAL STRUCTURES

All hemes from X-ray crystal structures in the Protein Data Bank have been analyzed using normal-coordinate structural decomposition(NSD). Complicated nonplanar heme distortions are caused by the asymmetric protein environment. NSD characterizes the out-of-plane and in-plane distortions of each heme by giving equivalent displacements along the normal coordinates of the D4h-symmetric porphyrin macrocycle. Even for highly distorted porphyrins, the macrocyclic structure can be accurately represented by displacements along only the lowest-frequency normal coordinates. The simplification of the structural description given by NSD reveals heme structural motifs for the proteins. These often conserved structural motifs were previously hidden in the complicated distortions of the hemes. The functional significance of the heme deformations is discussed. (Supported by US DOE Contract DE-AC04-94AL85000.)

[I38.27] How Fast is Collapse of Proteins During Folding?

Recent experiments in fast folding proteins are now starting to address the question of how fast is collapse relative to the total folding time. Using minimalist models, we are able to investigate the way in which different scenarios of folding can arise depending on the interplay between the collapse order parameter and the order parameter sensitive to specific tertiary contacts. Most of our earlier studies have focused on the limit that collapse is very fast compared to the total folding time. In this work we focus on the opposite limit, i.e., at the folding temperature, collapse and folding occurs simultaneously. The folding mechanism becomes very different in this limit. Particularly, the non-specific collapse transition, that occurs at temperatures higher than the folding temperature for the fast collapse limit, now occurs between the folding and the glass temperature. We show how this transition can be identified and its consequences for the folding kinetics.

[I38.28] A non-orthogonal basis analysis of two-state system in protein electron transfer reactions

In the protein-mediated electron transfer (ET) reactions, the electronic part of the Hamiltonian is partitioned into Donor-Acceptor(D-A) and protein bridge subspaces, and an effective two-state system is determined for the D-A subspace. We show that the effective D-A Hamiltonian obtained by the Löwdin diagonalization and the transformed propagator partition techniques are equivalent, and we extend the two-state analysis to explicitly account for non-orthogonal basis set effects on energy and time domains. The parameter that defines the two-state reduction validity is independent of the choice of basis set. However, the error of this approximation depends explicitly on the non-diagonal overlap elements, and we can investigate the difference between orbital basis sets. Typical values of this parameter for ET in biological systems and chemically modified proteins will be discussed.

[I38.29] Atomic Force Microscopy of DNA Helices Attached to Au(111)

Gold surfaces modified with thiol-derivatized DNA duplexes have been investigated. The densely packed DNA helices form a monolayer. The orientation of the DNA helices as a function of applied electrochemical potential is probed via atomic force microscopy (EC-AFM). At open circuit, the monolayer has a depth of 45 ÅThis film thickness implies an average 45^\circ orientation of the helical axis with respect to the gold surface. Under potential control, the monolayer thickness and hence the orientation of the helices changes dramatically with applied potentital. At potentials negative of approximately 0.45 V (vs. a Ag wire quasi-reference electrode) film thicknesses of approximately 60 Åare observed. At positive potentials, the monolayer thickness drops to a limiting value of approximately 20 ÅThese results are consistent with a morphology change in which the helices either stand straight up or lie flat down on the metal surface depending on the electrode potential relative to the potential of zero charge. In addition, preliminary results on the adsorption kinetics and film structure will be presented.

[I38.30] Thermodynamic Model of Spatial Memory

We develop and test a thermodynamic model of spatial memory. Our model is an application of statistical thermodynamics to cognitive science. It is related to applications of the statistical mechanics framework in parallel distributed processes research. Our macroscopic model allows us to evaluate an entropy associated with spatial memory tasks. We find that older adults exhibit higher levels of entropy than younger adults. Thurstone's Law of Categorical Judgment, according to which the discriminal processes along the psychological continuum produced by presentations of a single stimulus are normally distributed, is explained by using a Hooke spring model of spatial memory. We have also analyzed a nonlinear modification of the ideal spring model of spatial memory. This work is supported by NIH/NIA grant AG09282-06.

[I38.31] Nonlinear dynamics applied to the study of cardiovascular effects of stress

We study cardiovascular responses to emotional stresses in humans and rats using traditional physiological parameters and methods of nonlinear dynamics. We found that emotional stress results in significant changes of chaos degree of ECG and blood pressure signals, estimated using a normalized entropy. We demonstrate that the normalized entropy is a more sensitive indicator of the stress-induced changes in cardiovascular systems compared with traditional physiological parameters Using the normalized entropy we discovered the significant individual differences in cardiovascular stress-reactivity that was impossible to obtain by traditional physiological methods.

[I38.32] Extracting largest Lyapunov exponent from threshold-crossing interspike intervals

We take as initial data the time intervals between crossings by a realization of some threshold level. If this level defines the Poincare secant one is able to reconstruct a set looking similar to the chaotic attractor of the original system from the time series obtained by means of connecting the points of T-i's by a smooth curve. The use of technique of Wolf et al. allows us to extract the largest Lyapunov exponent (LE) from such time series which coincides with the largest LE of initial system attractor. We also recover the fractal dimension of original attractor by applying box-counting algorithm to the same realization. The method was tested on model systems with chaotic behavior (Rössler, Lorenz, Anishchenko-Astakhov oscillator). We show that an approximate value of largest LE can be obtained by this method for Hodgkin-Huxley neuron subjected to periodic stimulus even when the threshold level does not define the Poincare secant.

[I38.33] Storage capacities of two-layered networks

We have investigated the statistical mechanics of the storage capacities of the two types of two-layer feedforward neural networks, the committee and parity machines, by using the replica method. Networks are composed o f large K hidden units. Fully-connected and tree-like architectures bet ween input and hidden units are of typical interest. We have applied the well-known Gardner approach and also accompanied a recently developed app roach by Monasson and Zecchina. In the former approach, replica-symmetric assumption was found to lead to unstable results. Reliable results were obtained from one-step replica-symmetry-breaking scheme. On the other han d, in the latter approach, based on the analysis of internal representati ons on hidden units, only replica-symmetric calculation seemed to give eq uivalent results to those obtained from the former approach. The storage capacities of the fully-connected machines have been unknown until recent results on the committee machine(See references:R. Urbanzik, J. Phys A 30), L337 (1997); C. Kwon and J.-H. Oh, J. Phys. A 30, 6273 (1997); Y. S. Xiong, J.-H. Oh, and C. Kwon, Phys. Rev. E 56 4 540 (1997).. In this presentation we report our recent result on the par ity machine with fully-connected architechture. The value \alpha_c of t he storage capacity per input unit is found to be K\ln K/\ln 2.

[I38.34] Electronic Structure of Small Boron Clusters

Small Hartree-Fock clusters are considered for various geometries of boron (n = 2-7, 12), in preparation for calculations involving the structure of \alpha -rhombohedral boron ( 8 \times B_12 ), as well as embedded structures using arbitrary configurations (n = 13, 20, 32). The work was performed on Pentium PCs running UHF+MBPT2 FORTRAN codes under Windows 95/NT.

[I38.35] Solvation Dynamics of Ethanol in Porous Sol--Gel Glasses

The influence of confinement as well as surface effects on the interaction between chromophores and the surrounding solvent was investigated using solvation dynamics measurements on nile blue/ethanol solution. With the fluorescence up--conversion method both the solvation dynamics of the ethanol and the rotational dynamics of the chromophore were measured.

First there was a significant slowing down of the dynamics in comparison to the bulk solution. Second a reduction of the dynamic Stokes shift was observed in the porous medium. This indicates an enhancment of the reaction field in the liquid due to the effect of the pore walls. Additionally a loss of energy stabilisation of the chromophore is noticed, which is explained by a reduced solvation shell through the attachment at the surface.

[I38.36] The Mechanism of Formation of Type-I Xenon Hydrate Clathrate

The hydrate clathrates are a class of solids in which guest molecules occupy cages in a host structure formed from H-bonded water molecules. The normally unstable empty clathrate is stabilized by inclusion of the guest. While the general crystal structure of the type-I hydrate clathrates has already been established, the proposed mechanism for their nucleation and growth awaits experimental confirmation. This being our objective, we have studied both the melting and kinetics of formation of type I xenon hydrate clathrate using hyperpolarized ^129Xe NMR. The >2000 fold signal enhancement afforded by this method permits single scan observation of cage formation at less than parts-per-thousand levels. The signals arising from ^129Xe enclathrated in the tetrakaidecahedral (large) and dodecahedral (small) cages are well resolved, permitting the time dependence of each type to be measured independently.

Our kinetic model incorporates the time variations of the densities of the gaseous xenon, the xenon enclathrated into the small and large cages, and the ^129Xe magnetization of all three species. The pressure and NMR data at 223~K support a mechanism whereby the hydrate nucleates by first forming a small cage. This nucleation site then serves as a template for the formation of large and additional small cages. It turns out that this mechanism is consistent with recent molecular dynamics simulations of the formation process.

[I38.37] Memory Effect in Water and Sonoluminescence

Sonoluminescence (SL) may contain interesting informational and morphogenetic aspects. Memory effect in water (MEW) rests on selforganizational dynamics. Pattern proliferation is supported by strange attractor(s) acting as CPU of informational system. Critical for MEW succussion acts as pattern stabilization effect while in SL energy focusing fails to translate to sustained structural (informational) coherency. Coherency in MEW makes it conceptual relative of zero-phonon transitions and Moessbauer effect. Alternatively, MEW is antisonoluminescence in a sense that MEW dynamics is directed towards coherency enhancement rather than dissipation. Quest for coherent "messages" in SL signatures can be based on SL setting with informational modulation (Berezin and Nakhmanson, 1990). Possible link between Casimir pressure and SL (Eberlein, 1996) invokes analogy between Platonic pressure effect (Berezin, 1997) and MEW. Linking Casimir effect and gravity (Sakharov) and gravity and consciousness (Penrose) suggests possibility of SL acting as pre-biotic informational processing preceding quasi-biotic MEW stage.

[I38.38] A Quantum Statistical Mechanical Study of the Enthalpy of Formation of the Water Dimer

Monte Carlo simulations of quantum statistical mechanical properties using the Feynman path integral method were carried out over a temperature range from 50 to 400 K to study the energetics of the water dimer (H_2O)_2. These results were then used to understand the relation between estimates of the enthalpy of formation obtained from recent Ab initio electronic structure calculations and estimates of the enthalpy of formation deduced from experimental measurements of thermal conductivity, second virial coefficients and submillimeter spectroscopy. The full quantum mechanical and anharmonic theoretical results were compared to results obtained from classical mechanical simulation and those obtained from a quantum mechanical harmonic analysis. In performing the analysis for temperatures above 200K, the definition of a water dimer becomes poorly defined as thermal activation leading to dissociation becomes more probable. It is found that experimental observations are consistent with theoretical calculations only when a characteristic time scale for the experimental technique is identified.

[I38.39] Short Timescale Dynamics of a Protein Cylinder

Proteins adopt certain protein folds that can sometimes be connected with certain protein functions. Most important to perform its function is certainly the overall shape of a protein. Another important issue are its dynamical properties. A very useful tool to understand these relationships in atomic detail are molecular dynamics (MD) simulations. Yet, due to their complexity, MD simulations of biomolecular systems are currently limited to a length of ca. 1 ns. In a different context, we have performed 5 independent MD simulations of green fluorescent protein (GFP) fully solvated in a periodic box of 1 ns length each. GFP consists of a 11-stranded beta-barrel that forms a cylinder-like cage around its central chromophore, and during the MD simulations GFP was observed to be extraordinarily rigid. The simulations were performed for wild type protein and a S65T mutant with the chromophore in two protonation states. These minor modifications are unlikely to affect the inherent dynamics of the protein itself. Using essential dynamics analysis and cross-correlation analysis the protein motion during the 5 different simulations was carefully analyzed. It has been questioned previously whether these tools can reliably extract information about the underlying protein motion from MD simulations of relatively short length. Here, we will discuss their usefulness to characterize the dynamics of a protein cylinder.

[I38.40] Small Water Islands in Proteins

Proteins often contain water-filled cavities. Their presence may have functional reasons or may be related to protein folding. In any case, they are integral parts of the protein. Here, results from molecular dynamics simulations for two systems are presented. First, we analyzed the hydration of an empty buried enzyme active site, cytochrome P450cam. A hydration free energy landscape was obtained by calculating free energy differences for hydrating the active site with 5 to 8 water molecules. In agreement with the crystal structure and with experiments performed under high hydrostatic pressure, 6 water molecules were found to be most favourable thermodynamically [Helms amp; Wade, Proteins, submited]. Long-lived hydrogen bond networks exist between the water molecules in the active site and result in a significant ordering. Secondly, results are presented from 5 simulations of green fluorescent protein (GFP) of 1 ns length each. The crystal structures of different forms of GFP contain a cluster of five water molecules next to the chromophore. The water cluster seems to play a crucial part in allowing the protein to switch between a fluorescent and a dark state [Dickson et al., Nature, 388, 385-8]. In the simulations, the water molecules are again strongly ordered by a long-lived hydrogen bond network. Both scenarios are discussed in the context of bulk liquid water.

[I38.41]

This abstract was not submitted electronically.

[I38.42] Confocal Microscopy of Single Molecules of Green Fluorescent Protein (GFP)

Single molecule detection has been extended into life sciences by use of strong fluorescent labels. GFP as a self fluorescent biomolecule has attracted great interest. Here, single molecules of the GFP-mutant Glu222Gln immobilized in PVA are detected by confocal microscopy. In this mutant the deprotonated form of the chromophore is stabilized which should result in the photocycle of excitation at 476 nm and emission at 506 nm of the equilibrated anion R^-_(eq.). However, dark states in the fluorescence time trace and blinking reveal reversible side reactions to e.g. the proton transfer cycle.

[I38.43] Solvation and Reorientation Dynamics of Rhodamine 700 in the Nematogenic Substance 8CB

The solvation and reorientation dynamics of rhodamine 700 as a function of temperature in the isotropic phase of octylcyanobiphenyl were investigated by time--resolved fluorescence spectroscopy. The solvation dynamics observed in the liquid crystal was characterized by two processes differing in their time scales. The faster process with a relaxation time of about 10 ps was temperature independent up to 20^oC above the nematic--isotropic phase transition. The temperature dependence of the second process with of an order of magnitude slower relaxation time can be well described by the theory of dielectric friction. This component is clearly not influenced by the phase transition. The reorientational dynamics of the chromophore shows the same temperature dependence as the slow solvation dynamics process.

[I38.44] Effects of Protein Dynamics on Biological Electron Transfer

We have recently developed techniques whereby the electronic coupling matrix element which is proportional to the electron tunneling probability can be calculated by semi-empirical means (Daizadeh, I., Gehlen, J. N., Stuchebrukhov, A. A. (1997) J. Chem. Phys.) 106, 5658. All of these methods that we have formulated as well as other researchers in the field depend on a static picture of the electronic coupling assuming conventional theory. Our current research casts some doubt as to the legitimacy of such approximations.

In fact, we have found a new aspect in long distance electron transfer reactions in proteins which reveals that the quantum mechanical tunneling process occuring at the transition state for electron transfer involves in an intricate way a non-linear dynamics of the protein medium in which the tunneling occurs (Daizadeh, I., Medvedev, E. S., Stuchebrukhov, A. A. (1997) Proc. Natl. Acad. Sci. USA) 94, 3703. It is the couplings of electron and vibrational degrees of freedom (phonons) that seem to be of critical importance for the dynamics of electron transfer in proteins. We calculate auto-correlation functions whose Fourier harmonics may elucidate certain couplings between the traveling charge and certain normal modes in the protein.

[I38.45] Mass Transfer Between Phases: From Molecular Simulations of Interfaces to Macroscopic Models of Transport

The transfer of molecules across interfaces is a fundamental process that directly controls the transport and indirectly can affect the fate of contaminants in the environment. The liquid/vapor interface of water is ubiquitous, being present in the unsaturated (vadose) zone of subsurface environments, on the surface of the earth, and in earth's atmosphere in the form of water droplets and aqueous aerosols. The goal of the present work is a detailed, molecular- scale understanding of the mass transfer process for a variety of molecular species and phases, with particular emphasis on liquid/vapor and liquid/liquid interfaces. Molecular dynamics computer simulations are used to examine the properties of interfaces, and the energetics and dynamics of the mass transfer process. The potential of mean force technique is used to explore the equilibrium free energy surface for inserting alcohols into bulk water from its vapor. The dynamic aspects of this process are explored using a Grote-Hynes approximation. Using the computed potential of mean force, the forced diffusion equation allows processes at molecular scales (nanometer lengths and nanosecond times) to be extended to macroscopic scales (centimeter lengths and millisecond times).

This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under Contract DE-AC06-76RLO 1830 with Battelle Memorial Institute which operates the Pacific Northwest Laboratory.

[I38.46] Energy Storage and Directed Motion in Enzymes: A Structural View

Energy storage and directed motion are key features of the well-known "rack" mechanism of enzyme function. In this mechanism, substrate binding energy is first stored as strain energy; it is then used to power a directed molecular motion that induces an oriented strain in the reactive bond of the substrate molecule. To gain physical insight into enzyme function, we adopt a structural view and focus on the role of geometric constraints within the enzyme-substrate complex. In particular, we view the initial steric misfit between enzyme and substrate as a type of incommensurate frustration and propose that the degree of this misfit determines the amount of stored strain energy. This amount is then taken to represent the distance of the complex from mechanical equilibrium and to thus govern the shape of its potential energy surface. Finally, we suggest that the directed motion responsible for producing oriented substrate strain represents the switching of the strained complex between the two wells of a strongly-anharmonic quartic potential.

[I38.47] Three Pulse Photon Echo Peak Shift Measurements of Water

An experimental study of the solvation dynamics in water is presented. Three pulse photon echo peak shift measurements have been used to investigate the solute/solvent interactions of a fluorescein derivative in water. The data reveals that 70% of the decay occurs under 20fs, while the remaining amplitude corresponds to longer time solvation components. Implications of the ultrafast dynamics resulting from water will be discussed.

[I38.48] Surface processes studied in a path integral approach in the wavelet space

We have developed a path integral formalism for studying the dynamics of adsorbates on crystal surfaces. A new algorithm based on wavelet functionals is employed for the numerical evaluation of the path integrals involved. This allows the efficient handling of the ubiquitous multiple time scales present in the surface dynamical processes. The implementation of this scheme is demonstrated for the evaluation of surface diffusion rate under equilibrium conditions. Applications to other surface dynamical processes such as nonequilibrium diffusion and femtosecond laser pulse induced desorption will also be discussed.

[I38.49] Hundred Years After Wilson: A Novel Technique for Ion Nucleation Using Resonance Ionization in Supersaturated Host Vapors

A new technique that allows the study of ion-induced nucleation by well defined ions is presented. The technique is based on Resonant Two-Photon Ionization (R2PI) of a chromophore molecule present in a small concentration within a supersaturated host vapor. With this method it is now possible, for the first time, to selectively and unambiguously generate specific ions of interest and study their nucleating behaviors during the process of condensation of different supersaturated vapors. The new method is demonstrated by studying the ion - induced nucleation of supersaturated methanol, acetonitrile and nonane vapors by benzene, toluene and other aromatic cations. The measurements are carried out in a thermal diffusion cloud chamber. The nucleation rate vs. wavelength exhibits the characteristic resonance peak for the R2PI of the chromophore molecule. The dependencies of the ion nucleation rates of different molecular ions in a given supersaturated vapor on the charge sign, polarizability and symmetry factors will be presented and compared to the predictions of different theoretical models.

[I38.50] SANS of Nanodroplet Aerosols II. Binary Droplet Studies

Droplet surfaces have considerable influence on multicomponent nucleation, droplet growth, and heterogeneous chemistry. These phenomena occur in many industrial and atmospheric processes such as cloud formation, air pollution, and ozone destruction. The new aerosol SANS technique permits study of the composition and structure of multicomponent droplets, particularly at the droplet/vapor interface. Aerosol SANS studies should therefore lead to a better understanding of many of these important phenomena. The results of our recent aerosol SANS measurements on water-alcohol nanodroplets produced in supersonic nozzle expansions will be reported.

[I38.51] A Scaled Form for the Binary Nucleation Formalism: Application to the Water-Sulfuric Acid System

A molecular statistical mechanical model [S. M. Kathmann and B. N. Hale, in Nucleation and Atmospheric Aerosols, edited by M. Kulmala and P. E. Wagner (Pergamon, New York, 1996), p. 30] for the concentration of binary clusters, N_km,m/V, with m molecules of species 2 and k\cdot m molecules of species 1 is discussed and used to develop a scaled form for J, the binary nucleation rate. \ This approach is an extension of the scaled form for the homogeneous unary nucleation rate [B. Hale, Phys. Rev. 33, 4156 (1986)] and allows one to express the binary nucleation rate as J=J_o\exp [-(x_o/x)^2] where J_o is the kinetic prefactor containing the flux of monomers to the critical cluster, x_o=2/[3\surd 3], \ and x =\ln S(k,T)/[A(k,T)^3/2] is the binary ''scaled supersaturation''. The S(k,T) =S_1^k/(k+1)S_2^1/(k+1) , S_i is the supersaturation ratio of species i and A(k,T)=[36\pi ]^1/3Ømega (k)[T_c(k)/T-1]. \ The applicability of Ømega (k), the critical temperature, T_c(k), and determination of the critical cluster composition, k=k^* will be discussed in the framework of Monte Carlo free energy difference calculations and applied to model binary water-sulfuric acid clusters. Deviations from the scaled form due to surface enrichment and/or small cluster size will be discussed.

[I38.52] Advanced Nucleation Study Using The Laminar Flow Tube Reactor (LFTR)

Quantitative measurements of homogeneous nucleation rates have been made using the laminar flow tube reactor experimental technique. Thorough computer calculations of the temperature, vapor concentration, supersaturation, and nucleation rate distributions in the reactor tube were made. The nucleation volume as well as the time of nucleation have been determined with high accuracy. The concentration of the particles formed in the LFTR was measured at the outlet of the reactor tube using the ultrafine CPC TSI-3025A. Comparison of experimental data with theoretical predictions based on SCC-model has been made.

[I38.53] The Geometry of Separation Processes: The Horse-Carrot Theorem for Steady Flow Systems

The horse-carrot theorem bounding the entropy production in processes with a fixed number of relaxations is extended to steady flow processes. The dissipation turns out to be related to a path of flows rather than states. The example of fractional distillation is presented and shows how null directions for the geometry turn out to be useful in the analysis. The implied distillation column design offers potentially significant energy savings. The distinguishability geometry of thermodynamic state space is reviewed.

[I38.54] New Functionals in Magnetic Field Density Functional Theory

Magnetic Field Density Functional Theory, allows one to construct magnetic responses, such as the magnetic susceptibility and chemical shielding tensor, which are universal functionals of the zero field electron density. This could, in principle, greatly simplify the computation and interpetation of NMR parameters. Local functionals, which, though gauge invariant, are unable to recover pure diamagnetism.(F.R. Salsbury, and R.A. Harris, J. Chem. Phys. 107 18 (Nov 8 1997)) We have constructed nonlocal density functionals for chemical shieldings and magnetic susceptibility which give the exact results for purely diamagnetic systems. We treat approximately only their paramagnetic components. The results are fully gauge inavariant. We discuss the nature of these functionals, and their potential applications.

[I38.55] Coherent Control via Photoselective Adiabatic Passage

The recently developed theory of Stimulated Raman Adiabatic Passage (StiRAP) is adapted for use in systems including degenerate target states. It is shown using a simple analytic theory that degenerate states may be selectively excited using a process similar to StiRAP. We present the results of calculations performed on a model of Na_2, and show that the technique is effective in a system including physically realistic parameters; we also compare the theory with the strong field Brumer-Shapiro approach, and demonstrate their equivalence in the limit of very strong fields.

[I38.56] Theory for the nonequilibrium dynamics of flexible polymers: relaxation of pentadecane from an all-trans conformation

A recent mode-coupling theory for the long time dynamics of flexible polymers based on an eigenfunction expansion of the diffusion equation is extended to treat nonequilibrium relaxations that occur during sudden transitions between two states. The theory is tested for the ``unfolding'' of pentadecane from a constrained all-trans state to a random-coil at 300K. The time evolution of the mean-square end-end distance \langle R_end^2(t) \rangle_neq after release of the constraints is computed both from the theory and from Brownian dynamics (BD) simulations. The lack of time translation symmetry for nonequilibrium processes requires that \langle R_end^2(t) \rangle_neq is obtained from an average over a huge number of independent BD trajectories (9000 are necessary to obtain adequate convergence for pentadecane), rather than over the successive configurations from a single trajectory used to compute equilibrium time correlation functions. In contrast, the theory requires only equilibrium averages for the initial and final states, which are readily obtained from a few BD trajectories. Hence, the new method produces enormous savings in computer time. Since both theory and simulations use identical potentials and solvent models the theory contains no adjustable parameters. There is very good agreement between theory and simulations.

[I38.57] Inelastic Multiphonon Helium Scattering from a Stepped Ni(977) Surface

This experiment examines how the presence of a regular array of atomic-scale steps on a surface modifies energy exchange in the inelastic multiphonon scattering regime. We have measured the multiphonon energy exchange between a neutral He atom beam and a stepped Ni(977) surface with scattering kinematics chosen to be both in- and out-of-phase with respect to the terraces. As the surface temperature is raised we observe the crossover from quantum single phonon exchange to the multiphonon exchange regime . At elevated substrate temperatures we examine the multiphonon scattering using the classical theory developed by Hofmann et al.(F. Hofmann, J. P. Toennies, and J. R. Manson J. Chem. Phys. 106, 1234 (1997)). In the classical limit, whether the surface behaves as a collection of discrete scattering centers or as a smooth vibrating continuum can be deduced from the temperature dependence of the multiphonon intensity. Previous studies on low Miller index surfaces indicate that the surface can be treated as smooth; this work examines whether there is modification in this behavior due to the presence of steps.

[I38.58] Critical parameters for few-electron systems: A phenomenological renormalization study

A mapping between the quantum few-body problem and its classical mechanics pseudo-system analog is used to study the critical parameters for the Helium isoelectronic sequence. The critical point is the critical value of the nuclear charge Z_c for which the energy of a bound state becomes degenerate with a threshold. A finite-size scaling ansatz in the form of a phenomenological renormalization equation is used to obtain very accurate results for the critical point of the ground state energy, \lambda_c=1/Z_c =1.0976 \pm 0.0004 , as well as for the excited 2p^2 \; ^3P state, \lambda_c=1.0058 \pm 0.0017. The results for the critical exponents \alpha and \nu and partial results for small molecular systems are also presented.

[I38.59] A Microscopic Model of the Inhomogeneous Broadening of Electronic Transitions in Solid Guest/Host Systems

In order to arrive at a microscopic picture of the inhomogeneous broadening of electronic transitions of guest molecules in solid hosts, the local environment of the guest molecule and the guest/host interaction mechanism(s) have to be known. To have a well-defined experimental situation, where changes to the local structure can be linked to the line broadening, we investigated octatetraene doped n-hexane and n-octane crystals, with n-alkane molecules replaced by matching halogenated alkanes in increasing concentrations. These (in effect) "atomic" substitutions cause additional inhomogeneous broadening. The changes to the local structure were modeled and the resulting inhomogeneous broadening calculated using electrostatic and dispersive interactions as well as effects from the distortion of the guest molecule. We found that the fluctuation of the guest molecules' bond-lengths is by far the dominant effect.

[I38.60] Accurate Zero Parameter Correlation Energy Functional Obtained from the Homogeneous Electron Gas with an Energy Gap

We have obtained an analytic approximation to E_c(r_g, \zeta,G) where G is an energy gap separating the occupied and unoccupied states of a homogeneous electron gas for \zeta=3D0 and \xi=3D1. When G=3D0, E_c(r_g, \zeta) reduces to the usual LSD result. This functional is employed in calculating correlation energies for unpolarized atoms and ions for Z \leq 18 by taking G[n]=3D1/8|\nabla \ln n|^2, which reduces to the ionization energy in the large r limit in an exact Kohn-Sham (KS) theory. The resulting functional is self-interaction-corrected employing a method which is invariant under a unitary transformation.

We find that the application of this approach to the calculation of the E_c functional reduces the error in the LSD result by more than 95%. When the value of G is approximately corrected to include the effect of higher lying unoccupied localized states, the resulting values of E_c are within a few percent of the exact results.

[I38.61] Experimental Observation of Solitary Waves in Capillary Electrophoresis

The experimental procedure used to observe solitary waves in capillary electrophoresis is described. The basic and most important analytical results found for this kind of nonlinear dynamics is also given as well as the numerical methods used to integrate the related system of coupled nonlinear partial differential equations. In the usual capillary electrophoresis running conditions the spatial variance of the bands (i.e., the Gaussian shape spatial concentration profile) grows linearly in time at a rate that is proportional to the diffusion coefficient. In the present experimental layout the nonlinear effect acts against diffusion, consequently the component (2-Naphthol) band evolves in a shape that remains constant during the running and has a constant variance.

[I38.62] Semi-Empirical Studies of Small Clusters of Inorganic Compou nds

This abstract was not submitted electronically.

[I38.63] Calculation of the Ionization Potentials and Electron Affinities for Atoms

The method employing the self-interaction-corrected correlation energy functional obtained from the homogeneous electron gas with a gap is extended to atoms and ions with non-zero spin polarization. As in the case for atoms and ions with \zeta=3D0, the error in the calculated E_c is significantly smaller than in the LSD approximation with zero gap for atoms and ions with Z\leq18. Comparison of the resulting ionization potentials and electron affinities with experimental values will also be presented. Finally, we will discuss the possibility of obtaining saturation for E_c for the He, Li, N, O, F and Ne isoelectronic series, but a divergent E_c for the Be, B and C isoelectronic series, in the large Z limit.

[I38.64] Mean Field Theory of Polynuclear Surface Growth

We study statistical properties of a continuum model of polynuclear surface growth on an infinite substrate. We develop a self-consistent mean-field theory which is solved to deduce the growth velocity and the extremal behavior of the coverage. Numerical simulations show that this theory gives an improved approximation for the coverage compare to the previous linear recursion relations approach. Furthermore, these two approximations provide useful upper and lower bounds for a number of characteristics including the coverage, growth velocity, and the roughness exponent.

[I38.65] Overtone Excitation of Multimode Systems using Chirped Laser Pulses

Earlier studies of multiphoton excitation and dissociation of diatomic molecules using IR chirped laser pulses show that these processes can be very efficient and highly selective. This is best understood in terms of "bucket dynamics", which can be used to explain its energy-transfer efficiency and good classical-quantum correspondence predicted. To extend such a study to polyatomic molecules, we investigate the dynamic behavior of an anharmonic oscillator coupled to a reservoir of harmonic oscillators. In particular, we study the selectivity and efficiency of the overtone excitation of the pumped mode as a function of relaxation times, chirping rates, laser intensity, frequency, and pulse duration.

[I38.66] Emission and absorption polarization study of single dye and conjugated polymer molecules

Polarization confocal microscopy was employed to study the dipole orientation of single molecules including 1,1-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and poly(p-phenylene vinlyene) and poly(p-pyridylene vinylene) derived conjugated copolymer (dPPV-PPyV). An electro-optical modulator produced linear polarized light with rotating frequency of 1Hz, which was used as excitation. The emission light passed through a polarizing beam-splitter and two avalanche photodiodes detected two perpendicular polarization components of the emission. The in plane absorption and emission dipole angle can be measured with error less than a few degrees. We found that both DiI and dPPV-PPyV's absorption and emission were strongly polarized with same orientation angles. Most molecules kept their dipole orientation until they were photobleached. A few molecules showed fast incidental rotation. dPPV-PPyV also showed discrete intensity jumps and the intensity jumps were not due to the incidental rotation.

[I38.67] Off--resonant fifth order responses of water and CS_2: Analysis based on normal modes

Off-resonant fifth order nonlinear response functions of liquid water and liquid CS_2 are analyzed based on two normal mode schemes, quenched and instantaneous normal modes. It was found that the fifth order response function is very sensitive to the mode mixing in polarization, arising from the quadratic term of polarization with respect to the different modes. The echo signal is drastically reduced by this off-diagonal mode mixing in polarization even without any rapid frequency modulation mechanism. The near absence of echo signal thus obtained for liquids is consistent with the recent experimental results for liquid CS_2. The present calculation yields the different fifth order signals for different polarization geometries, as experimentally shown by Tokmakoff and Fleming(J.Chem.Phys.106, 2569 (1997)).

[I38.68] The morphology and molecular orientation of Oligophenylene thin films by Organic Molecular Beam Deposition method

Organic thin films based on phenylene oligomers have potential for application to future opto-electronic devices such aslight-emitting diodes and field-effect transistor. To control morphology and molecular orientation of thin films is very important for improving the device characters. Here we report the morphology and molecular orientation of p-sexiphenyl(6P) thin film on glass substrate by Organic Molecular Beam Deposition(OMBD) and its dependence on the conditions of deposition. At the initial growth stage upon deposition at room temperature, islands of round shape (nearly 90nm in size) are observed and its height corresponds to one molecule. Taking acount of the results of X-ray diffraction analysis, these results show that 6P molecules are nealy aligned normal to the subsrate surface from the initial growth stage. An island size becomes larger as the substrate temperature increases. Especially, the large (several micrometers in size) dendritic island is formed upon deposition over 150.

The growth process of the organic thin films by OMBD and its structure are discussed from the view point of the substrate temperature.

[I38.69] Characterization of Active Sites in Pt Mono-crystalline Electrode Surfaces by Means of the Local Softness Function of Density Functional Theory.

The identification of active sites in metallic surfaces is a very important research topic in catalysis and electrochemistry, both experimentally and theoretically.

In this work we employ the local softness function of Density Functional Theory, computed from abinitio Hartree-Fock pseudopotential densities to characterize active sites in Pt fcc mono-crystalline electrode surfaces. The (1,0,0), (1,1,0) and (1,1,1) faces are modeled by means of suitable finite Pt clusters, where the crystalline geometries are used and fixed.

The results show that, in general, the most active sites reside in the more coordinated atoms in all faces and that the (1,1,1) face is the most reactive one.

[I38.70] Jet-cooled radicals in a supersonic slit discharge: infrared studies of the allyl and ethyl radicals

A supersonic slit jet discharge source has been recently constructed in our laboratory, which has proven to be a very efficient source of jet-cooled radicals and molecular ions. This capability enables us to investigate the spectroscopy and dynamics of a new class of fundamental transient species, among which are the allyl and the ethyl radicals, important intermediates in combustion processes. These two radicals were produced from their corresponding halides by dissociative electron attachment in the slit discharge, and detected via direct absorption infrared laser spectroscopy. The allyl and ethyl radicals are dynamically very dissimilar. Analysis of the CH_2 stretching vibrations of allyl confirms that it is essentially rigid, which is consistent with the delocalization of electrons over the C-C-C frame. In the ethyl radical, transitions due to internal rotation of the CH_2 subunit are observed; a preliminary analysis of these suggests a synchronous tilting of the CH_2 group above and below the C-C rotor axis with CH_3 rotation.

[I38.71] Fast Dynamics in the S1 and S0 States of Azulene in Solution

The transient absorption spectra with sub-picosecond resolution from the S1 state of azulene in different solvents (acetonitrile, cyclohexane, methanol) have been measuredin the range 350-700 nm. The spectrum is characterised by the presence of a strong peak at 380 nm and a weaker one at 440 nm. Small differences can be observed due to solvent effects.

The temporal behaviour of the spectrum is in agreement with previously reported measurements of the dynamics of the S1 state. Decay constants range from 1ps to 1.5 ps depending on the solvent. At 360 nm it is possible to observe a structure that grows with the decay constant of the S1 state and disappears with a time of approximately 3 ps.

This band is interpreted as due to a hot vibration in the ground state which is populatd by the relaxation process of S1 into S0 state.

By comparison of the transient spectral values to those of the ground state we concluded that the mode that accounts for this band is a 1580 wavenumbers vibration in the ground state. This observation confirms that the primary accepting modes in the intramolecular radiationless decay are those involving C-C stretching.

[I38.72] Photochemical Processing of NH_3/CO_2 and NH_3/H_2O Ices

The investigation of ices and their modification by photochemical processes have important applications in atmospheric physics and planetary astronomy. In this study, NH_3/CO_2 and NH_3/H_2O ice mixtures were formed at 77 K. These mixtures were then characterized using x-ray photoelectron spectroscopy (XPS). The chemical changes in the ices were monitored while the ices were continuously exposed to x-rays for several hours. Significant changes were observed in the XPS core level lines for the NH_3/CO_2 but not the NH_3/H_2O ice. A quadrupole mass spectrometer was also used to monitor the species evolving from the ice surface during the photoprocessing. The XPS and mass spectrometer results are correlated and the possible mechanisms associated with the photochemical processing of the ices are presented.

[I38.73] Characterization of the Electronic Wavefunction at Defect Sites in an GaAs/AlGaAs Heterostructure by Optical NMR

By combining optical nuclear polarization, Larmor-beat optical detection, and light-synchronized multiple-pulse line-narrowing, we have spectrally resolved the radial distribution of Knight shifts surrounding optically relevant point defects in an epitaxially grown GaAs/AlGaAs heterostructure. Multiple-pulse line-narrowing reduces dipolar, quadrupolar, and static Zeeman contributions to the linewidth to below 25 Hz, while pulses of circularly polarized light near the band gap supply spin-polarized electron density during appropriate intervals in the nuclear spin trajectory. The resulting asymmetric lineshape is consistent with identification of the defect sites observed as shallow donors, apparently present at concentrations below the limits of electrical detection. In contrast to earlier treatments, we find that the Knight shift at the maximum of the lineshape is not a reliable indicator of the spin-polarized electron density at the Bohr radius, but is sensitive to the underlying linewidth and the polarization dynamics, which together with the wavefunction determine the global fit.

[I38.74] Generation of Charged Droplets by Electrostatic Spraying of Liquid Helium

Positively charged helium droplets were produced by field ionization of liquid helium emerging from a thin glass capillary. Fine droplets (of approximately 10 microns in diameter) were produced in pulsed sprays with total currents as high as 0.4 microamperes. In contrast, liquid nitrogen formed a well-defined Taylor cone and a jet that broke up into droplets having diameters comparable to the jet diameter (approximately 100 microns), at much lower currents (10 nA). The mechanism for charging in these liquids was field ionization, identical to the processes leading to conduction in cryogenic insulating liquids observed by Gomer.(Gomer R., Acct. Chem. Res. 5 21 1972) The high currents resulting from field ionization in helium, together with the intrinsically low surface tension of He, led to charge densities that greatly exceeded the Rayleigh limit, thus preventing formation of a Taylor-cone and resulting in the coulomb explosion of the liquid.

[I38.75] A Small-Angle-Neutron-Scattering Study of a Synthetic Clay

The synthetic monodisperse model clay Laponite RD has been studied by means of Small-Angle-Neutron-Scattering (SANS). The investigated clay-water concentration regime include the reported(J-C P. Gabriel et.al., J.Phys.Chem. 100, 11139 (1996))transitions from isotropic liquid (IL) to isotropic gel (IG) to nematic gel (NG) in pure water. The present SANS data scale with the number of scatterers which is proportional to the clay concentration, and the SANS data are consistent with the scattering expected from randomly oriented thin platelets as reported earlier.(J.D.F. Ramsay and P. Lindner, J.Chem.Soc.Faraday Trans. 89, 4207 (1993); A. Mourchid et.al., Langmuir 11, 1942 (1995)) Thus the data show no detectable signs of the IL-IG-NG transtions. pH was not controlled during these experiments. The present analysis thus indicates that the SANS technique may not be sensitive to possible pH induced individual clay platelet distortions.(D.W. Thompson and J.T. Butterworth, J. Colloid and Interface Science 151, 237 (1992))

[I38.76] Metal Ammonia Solutions --- A Lattice Model Approach,

A generalized Falicov-Kimball model is applied to study the phase diagram of metal ammonia solutions. The model includes a fluid-fluid interaction term and an electron-fluid interaction with a hard core and an attractive tail. Mean field theories are derived for the localized and delocalized electron phases using ideas from the slave-boson approach to the Hubbard model. The attractive force stabilizes both the homogeneous delocalized electron phase and a regime where the electrons localize in cavities devoid of fluid particles. In its absence, the localized states are found to be unstable towards phase separation, in contrast to previous predictions. The Gaussian fluctuations and structure factors derived from this theory suggest the existence of bicontinuous channels percolating through the system. These findings agree qualitatively with experiments and computer simulations.

[I38.77] Probing Polar Ordering of Ferroelectric Liquid Crystals via Sum-Frequency Vibrational Spectroscopy

Infrared-visible sum-frequency generation (SFG) spectroscopy was used to study polar orientation of C=O groups on chiral molecules and hence polar ordering of molecules in a surface-stabilized ferroelectric liquid crystal cell. Two CO stretch peaks at 1760 cm^-1 and 1797 cm^-1 were observed and could be attributed to C=O groups attached to the chiral carbon center and to the linkage in the mesogen core, respectively. They showed strong temperature dependence near the smectic C->A transition. The signal strength of the chiral CO below the smectic C^*->A transition (T_AC) is proportional to the degree of hindered rotation and decreases with temperature as (T_AC^*-T)^1/3, with T_AC^*-T_AC=2.2 ^oK. Above T_AC, the signal decays exponentially with temperature indicating the presence of a residual surface-induced polar-ordered layer. The two CO modes also behave differently when circularly polarized visible input beam was used in the SFG measurement. The one connects to the chiral center exhibited circular dichroism as expected. The orientational distributions of the C=O groups in the smectic-C^* phase were deduced from the azimuthal dependence of SFG with different polarization combinations.

[I38.78] In-situ time response measurment of the microspheres dispersed in electrorheological fluids

The aggregations of different kinds of microspheres suspended in electrorheologial fluids have been observed in situ upon application of time-regulated electric field. It is found that both initial response time and chain's formation time depend on the conductivity of the microspheres. Water free, watered and metal coated glass microsphere together with SrTiO_3 and Cu m icrosphere were studied. Among them, water-free glass particle shows the longest initial response (chain formation) time of 16.7 ms (117.6 ms) under electric pulse strength V_p-p of 2.6 KV, while metal coated microsphere has the shortest initial response (chain formation) time of 0.5 ms (25.4ms). The overall trend is that the higher the microsphere's conductivity, the shorter the response time and the stronger the particles' interaction under the same external electric field. Moreover, it is found that the aggregation of the microspheres becomes faster if the applied field strength is increased.

[I38.79] Microscopic Structures under Shear in a Model Magnetorheological Fluid

This work is aimed to understand the rheological measurements of magnetorheological (MR) fluids based on structures formed. Particle structures affect the rheological properties of the fluids. In a magnetic field, induced dipole moment in each particle in MR fluids interacts to form large structures. The structures induced under quiescent condition are understood which shows either columnar or labyrinthine patterns. Under shear, the structures are much less understood. In this work we will use optical microscope to examine the effect of shear on structures by using a rotating plate-plate sample cell duplicating rheology measurements. This "micro-rheometer" allows direct observation of structures of the MR fluid while shearing occurs. We will report the structures observed under different shear rates, magnetic field strength and field ramping rates.

[I38.80] Experimental Study on Mechanisms of Colloidal Crystal Assembly at Electrode Interfaces

We made quantitative measurements on the clustering of colloidal particles that reversibly form two-dimensional gaseous, liquid, and crystalline structures at electrode interfaces under an electric field. Digitized images of video recordings have been used to trace out the coordinates and the movement of each particle. The analysis of the data supports previous observations on the long-range attraction (>10 particle diameters) between the particles. The motion of the particles and the clusters is dominated by fluid flow resulting from an electrohydrodynamic mechanism.

[I38.81] Far Infrared Optical Spectroscopy of Alkali Halide-Polymer= Composites

Composite samples of small (dimension < 10 =B5m) alkali halide crystallites in a polymer matrix (low density polyethylene and polytetrafluoroethylene) have been prepared. The far infrared optical spectra of these samples are presented, spanning a temperature range of 300 to <10 K, and a dominant absorption feature due to absorption by the transverse optic phonon of the alkali halide constituent is observed. An effective medium analysis of the samples, using the Maxwell-Garnett model, is shown to accurately reproduce the main absorption feature, but requires a shape factor for the inclusion geometry corresponding to flat, plate-like inclusions, and a plausible explanation for such a geometry is proposed. The temperature dependence of the frequency and linewidth of the absorption peak is presented. The temperature shift of the line-center-frequency is found to be adequately described by a quasiharmonic description of the transverse optic phonon energy shift of the alkali halide due to lattice thermal expansion, using published values for the mode Gruneisen parameter and the temperature dependence of the lattice thermal coefficient. In contrast, the linewidth (phonon lifetime) of the composite samples is roughly twice as large as that observed for thin film and bulk crystals, and has a much stronger temperature dependence as well.

[I38.82] Optical Properties of Cermets with Large Metallic Inclusions

We study the optical reflectance of cermets beyond the quasistatic limit using Monte Carlo multiple-scattering simulations as well as a radiative transfer method. Slabs of alumina with inclusions of Cu, Au, Co and Cr are studied; reflectance coefficients are calculated as a function of wavelength, considering metal inclusion diameters up to 2.0\mu m. We find that strong spectral selectivity is achieved by particle diameters around 0.2\mu m, even for very low metal concentrations.

[I38.83] Effects of a cavity in a spheroidal dielectrics

The effects of a cavity in a dielectric material on light scattering are presented. The light scattering by a spheroidal cavity embedded in a host of spheroidal dielectrics is studied within the framework of the generalized eikonal approximation (Applied Optics vol.28, 4096, 1989). The effects on the scattered light, especially on the diffraction minima, due to the location, shapes, size and refractive index of the cavity are studied.

[I38.84] Variational Calculation of Effective Parameters in Random Porous Media

Effective parameters are used in stochastic hydrology and petroleum engineering as estimates of the coarse-grained behavior of fluid flow and transport. Stochastic effective parameter estimation involves averaging over the local heterogeneity. Explicit evaluation methods are often based on low order perturbation expansions. We obtain more general estimates using a variational scheme that employs auxiliary probability measures. The average over the local fluctuations is evaluated by means of the logarithm transform and the replica trick. The equations satisfied by the effective parameters are obtained variationally from an effective free energy functional. We use this method for the evaluation of the effective permeability of random porous media with Gaussian local fluctuations. The resulting equations are solved explicitly in specific cases, and the results are compared with leading-order perturbation estimates and experimental data. Explicit finite-size expressions are obtained using momentum-space filters. The implications of the finite size behavior for the scaleup problem are discussed.

[I38.85] Reactive wetting and dewetting induced diffusion-limited aggregation

Diffusion-limited aggregation fractals, formed by the wetting of eutectic SnPb alloy ball on Au/Cu/Cr multi-layered thin films and the dewetting of SnPb from the Cr surface after the Au/Cu thin film underneath the wetting cap were consumed, have been observed experimentally. The wetting formed fractal locates near the edge of the SnPb wetting cap, while the dewetting formed fractal sits around the center of the SnPb cap. One uniqueness of the former is that its growth direction is opposite to the wetting direction of the SnPb. More interestingly the latter is a reverse process of the regular percolation phenomena. The dimensions of the two fractal patterns are measured to be 1.83 plus/minus 0.07 and 1.79 plus/minus 0.06, respectively.

[I38.86] Microscopic Dynamics in Glass-Forming Materials Revealed by Fluorescent Probe Molecules

The microscopic dynamics of several monomeric and polymeric glass forming materials has been investigated by the time-resolved fluorescence measurement of doped malachite green molecules in a wide temperature range. For monomers and a polymer without side chains, beside a kink around the calorimetric glass transition temperature Tg, another crossover at Tc about 30 - 50 K above Tg has been clearly observed, which is in agreement with the prediction of the mode-coupling theory. On the other hand, for the complex polymers with side chains, the crossover at Tg is less pronounced than those for the monomers and the polymer without side chains. Moreover, although we could not distinguish any singularities above Tg for the complex polymers, we observed another kink below Tg, which may be attributed to the side-chain motions.

[I38.87] Temporal Order and Dynamic Phase Transition in Sliding Charge-Density Wave Systems

The influence of randomly quenched impurities on the collective dynamics in charge-density wave systems (CDW's) has been a subject of intense study. Recent theoretical studies have suggested the possibility that CDW's exhibit novel dynamic phase transition between "Plastic flow" and "Fluid Solid" as a function of external driving force. We have investigated the transport properties of CDW's as a function of electric field in orthorhombic TaS_3 at 77.3K. We found that the power of fundamental component of narrow-band noise (NBN) has minimum value at a critical electric field V_c. Moreover, the field dependence of non-linear current abruptly changes at the same field V_c. We give the first evidence of novel dynamic phase transition between "Plastic Flow" and "Fluid Solid" in CDW's.

[I38.88] A New Real Space formulation for the Electronic Structure of Ordered and Disordered Binary Alloys.

We propose a new scheme for calculation of the electronic structure of binary alloys. The proposed scheme combines the coherent potential approximation (CPA) with the Spectral Density Approach (SDA), and explicitly includes the effect of alloy (short- or long-range) order on the electronic structure, in contrast to earlier CPA-like approaches. It can be used to compute k-dependent effects on the electronic structure of binary alloys. The theory is exact in the pure limit, valid for all alloy concentrations, and interpolates correctly between the completely disordered and fully ordered limits. The computed spectral density is always positive definite. Application of the method to the Anderson disorder problem with binary disorder yields better ground state energies compared to those computed from usual CPA, and reveals new features in the spectral density, which are completely missed by CPA.

[I38.89] Role of dielectric function in model GW calculations of structural and optical properties in semiconductors

Recently proposed nonlocal exchange potential methods such as screened exchange (sX-LDA)(Bylander, Kleinman, Phys. Rev. B 41, 7868 (1990)) and model GW(Gygi, Baldereschi, Phys. Rev. Lett. 62, 2160 (1989)) demonstrated successful extensions of LDA energy bands to treat excited states in semiconductors and insulators. While using different static dielectric functions - a Thomas-Fermi or a Hubbard screening function for the sX-LDA and a step function or an RPA for the model GW - those methods gave surprising agreement of the energy gaps with each other and with experiments. We have investigated semiconductor systems such as Si, Ge, and InSb using the full-potential linearized augmented plane wave (FLAPW) method(Wimmer, Krakauer, Weinert, Freeman, Phys. Rev. B 24, 864 (1981)) within the model GW method including the above dielectric functions. Our focus is on understanding the different results obtained for the structural properties (lattice constants and bulk moduli) and optical properties (band gaps and optical spectra). We find that the results can be interpreted by different long-range screening behavior corresponding to the different static dielectric functions employed in the model GW calculations.

[I38.90]

This abstract was not submitted electronically.

[I38.91] Electronic Tansport Properties of Liquid Cadmium-Germanium Alloys

The electrical resistivity and thermopower of liquid cadmium-germanium alloys have been measured as a function of temperature by 10 atomic percent steps over the composition range between pure cadmium and pure germanium. The experiment was difficult because of the high vapor pressure of cadmium at melting point of germanium. A new experimental cell has been used in order to make such measurements possible. The very high resolution of the thermopower measurements (better than 0.05 \muV/K), permits to observe a surprisingly non linear temperature dependence for the thermopower of pure cadmium and for divalent rich alloys. For pure cadmium, a drastic change of the thermopower temperature coefficient is observed; from positive near 400^oC it becomes negative at 800^oC. This can be qualitatively explained within the Ziman formalism. The isothermal concentration dependent resistivity and thermopower are discused in the framework of the extended Faber-Ziman theory by using energy dependent phase shifts in order to take into account the energy dependence of the thermopower.

[I38.92] some muffin-tin calculations of electrical resistivity and thermopower in molten germanium

Ab initio calculations of electrical resistivity and thermopower of liquid germanium as a fuction of energy are presented. The caculations are based on different muffin-tin potentials constructed with various exchange-correlation approximations. In order to satisfy the free boundary conditions for the single-site scattering, we are proposed a new method consisting to evaluate the Fermi energy self-consistently.

[I38.93] On the Nature of Cyclotron Resonance in Metals in a Normal Magnetic Field

The theory of electron Fermi-liquid has been used to calculate the surface impedance of a metal with an axially symmetric Fermi surface in a magnetic field applied perpendicularly to the boundary under the conditions of anomalous skin effect and specular reflection of electrons from the boundary. It has been shown that anomalous curvature of the effective strips of the Fermi surface may give rise to a resonance at the cyclotron frequency. The behavior of the impedance as a function of the field in the vicinity of the cyclotron resonance has been analyzed for various types of anomalous curvature of the effective cross sections of the Fermi surface.

[I38.94] Current noise in the transport through localized states with strong Coulomb interaction

We study the current noise in the transport through Anderson model out of equilibrium. This study may illuminate more on the Kondo physics in the transport through the quantum dot, which was realized recently. Current fluctuations are studied as a function of bias voltage, temperature for one-, and two-channel Anderson models. Zero-frequency noise shows a scaling behavior as a function of temperature or bias voltage.

[I38.95]

This abstract was not submitted electronically.

[I38.96]

This abstract was not submitted electronically.

[I38.97] A new light absorption mechanism in metals

We have investigated theoretically the light reflection from the metal under the condition, when 1/\tau<< \varpi << \varpi_p , where \varpi is the light frequency, \varpi_p is the plasma frequency of the metal and 1/\tau is the collision frequency. The electrons are described in the frame of the noninteractive degenerate Fermi-gas model. The electric field strength in the near surface region of metal decreases exponentially with penetration depth equal to the ratio of light speed in the vacuum and plasma frequency. This effect takes place due to the interference of the coherently scattered light waves without losses. For typical metals like Au or Cu, the value of penetration depth is about 10-15nm. Since the light dispersion law is governed by the temporal and the spatial dependence of the electric field strength in the medium, in the case discussed here, the light dispersion strongly differs from that in vacuum. Thus the energy-momentum conservation laws for light absorption by free electrons in the metal can be satisfied. Such an absorption can lead to acceleration of the electrons in the direction of the incidence of the light.

[I38.98] Quasiparticle Dynamics and Transport in Thin Ferromagnetic Nickel Films

It has recently been demonstrated that excitation of electronic carriers in thin metallic films by femtosecond duration laser pulses leads to non equilibrium particle dynamics and transport. The excited electronic carriers are generally referred to as quasiparticles and their dynamics have been shown to be governed by Fermi Liquid Theory. The quasiparticle transport occurs even in the absence of an external electric potential applied to the thin film. Instead, the transport is driven by a local concentration gradient of quasiparticles between the excited and non excited volumes of the film. We report here on the dynamics and transport of quasiparticles across itinerant ferromagnetic thin Nickel films of various thicknesses. We also report on the dynamics and transport of quasiparticles across thin Aluminum films of different thicknesses. We employed a front-back pump-probe excitation-detection technique to determine the dynamics and transport of the excited electronic carriers.

[I38.99] Microfabricated Torsional Oscillator Magnetometer

We have designed and fabricated a torsional oscillator magnetometer for use with microscopic samples. The oscillator is fabricated from a silicon-on-insulator substrate. The paddle has dimensions 200 \times 50 \mu m and is supported by two torsion bars of dimensions 25 \times 10 \times 1 \mu m. The paddle and rods are single crystal silicon to reduce dissipation. The paddle oscillator can be driven by coupling an external field either to the magnetic moment of the sample or to an integrated coil. The amplitude of the oscillation is detected with a fiber optic interferometer.

[I38.100] Random Motion of Paired Electrons and Positrons, Causing Diverse T= hermal Radiations of Some "Vacuum Space" Regions.

In the Electron Positron Lattice (EPOLA) model of space,(M. Simhony, The Epola Space, 1990, 160 pp (available from the author). Also, M.Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994 (292 pp).) the mysterious 3K blackbody radiation, reaching us from all directions in the sky, is the thermal radiation of our epola region, and is due to the random vibrations of epola particles (also causing the zero-point motion of helium atoms, analogous to Brownian motion). The temperature (T) of our epola region is therefore 3K. T is elevated in epola regions where there are more "hot" stars, more nuclear activity, more injected free nuclear particles and radiation. Epola regions of T>3K are observed as mysterious "dark matter", considered to "constitute 90% of the mass of the universe". 100K warm regions create the mystery of "gray matter'. Epola regions hotter than 800K emit visible radiation; at 3000K they glow like lamp filaments, and at 6000K - like the sun. Such very distant epola regions can be mistaken for stars and galaxies. At sufficiently high T, the epola "melts" into a liquid of electron positron (epo) pairs, in which the velocity of light is drastically reduced. At 6 billion K, it turns into a gaseous mixture of epo pairs and free electrons and positrons. In this "epogas", quantum radiation laws do not hold, there are no photons, just as there are no phonons in gases.

[I38.101] Can Spectroscopy Provide Means to Distinguish the Thermal Radiation of Extended Atomic Bodies from that of "Vacuum Space"?

Assuming a more or less uniform distribution of mass and energy in "vacuum space", one finds that the probability P of observing a "hot spot" in space should be proportional to the volume V of the bulk of space, onto which our optical instrument is "focused". The volume V is proportional to the "field of view" area A, multiplied by the supposed depth \Delta f of the bulk. Clearly, the uncertain value of \Delta f increases with distance d to the bulk under observation, and A is roughly proportional to d ^2, so that P increases very fast with growing distance d. The number of "hot spots", seen in the field of view, increases therefore very fast with increasing "penetration depth" of the instrument, e.g., of the Hubble telescope. The hot spots are presented to the public (and to NASA) as galaxies and stars, but they may just as well represent hot regions of the electron positron lattice (epola) space.(M.Simhony, The Epola Space, 1990, 160 pp, and The Story of Matter and Space, 1998, 70 pp (available from the author). Also, M.Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994 (292 pp).) It is therefore imperative to discuss and work out spectroscopic and other means that distinguish between hot epola regions and real galaxies and stars.

[I38.102] Thin film calibration specimens for light-element EDX analysis

Many transmission electron microscopes have been fitted with thin-window energy -dispersive X-ray (EDX) detectors capable of analysing light (4<Z<11) elements, but many of these systems are used only for qualitative or semi-quantitative measurements due to absence of accurate calibration factors. We have used reactive sputtering and e-beam evaporation to make free standing amorphous films which can be inserted into analytical TEM to routinely measure these k-factors. Elemental ratios in the films were measured by electron energy loss spectroscopy (EELS)

[I38.103] Near-Field Scanning Microwave Microscopy

We will present recent work on near-field scanning microwave microscopy. Our microscopes consist of an open-ended coaxial probe which forms one end of a transmission line resonator.(D.\ E.\ Steinhauer, et al.), Appl.\ Phys.\ Lett.\ 73 (1998).^,(D.\ E.\ Steinhauer, et al.), Appl.\ Phys.\ Lett.\ 72, 1736 (1997).^,( C.\ P.\ Vlahacos, et al.), Appl.\ Phys.\ Lett. 69, 3272 (1996).^,(See http://www.csr.umd.edu/research/hifreq/micr_microscopy.html) In one configuration, the microscope can be used to image electric and magnetic fields above operating microwave circuits. In a second configuration, a microwave source is coupled directly to the resonator, allowing quantitative imaging of sample properties such as surface resistance and complex dielectric constant. We will present results both at room temperature and at 77 K with various types of samples, including operating thin-film microwave circuits, conducting and superconducting thin-films, and dielectrics.

[I38.104] ANKA, a customer-oriented synchrotron radiation facility for microfabrication and analytical services

ANKA (Angströmquelle Karlsruhe) is a state-of-the-art synchrotron radiation facility under construction at the Forschungszentrum Karlsruhe. Based on a 2.5 GeV electron storage ring it will deliver photons predominantly in the hard X-ray range but it will also feature both XUV and infrared beamlines. In its first operational phase the radiation will be taken out of normal-conducting dipole bending magnets, while five free long straight sections are foreseen to accommodate insertion devices later on.

ANKA has a novel mission, namely to provide synchrotron-radiation based services to industrial and other customers, in the fields of microfabrication and materials analysis. A limited liability company, ANKA GmbH, is being founded to operate the facility. Although commercial services to customers will represent more than half of the overall activity, these services will be complemented by providing beam time for research users.

[I38.105] Nano-optical probe in a scanning near-field optical microscope (SNOM)

Evaluations of optical probe profiles in an SNOM using a knife edge method are described. The optical probe profiles were measured using various optical tungsten mask patterns, which were fabricated on a fused silica substrate using a commercial electron beam (EB) writing system, Hitachi's HL-750D. The line and space mask patterns were 50nm to 15m wide with a thickness of 30nm. The SNOM used here was Aurora from TopoMetrix with shear force detection for the gap control. The SNOM probe was a pipet-pulled optical fiber covered with a thin Al film. The evaluations were made by measuring the profile of the optical probe using an edge of the wide pattern and observing the 50nm-wide line and space patterns. We also evaluated the profile of the probe using the shear force image. Experimental results show that the SNOM probe has a dual optical feature with small- and large- diameter probes. One is a near-field optical feature, and its diameter is thought to be a few 10s nm. The other is a far-field probe with a diameter of a few 100s nm. The effective diameter of the SNOM optical probe as a far-field probe was larger than that of the shear force probe. This means that the metal-masking for forming small optical aperture is not perfect. Furthermore, this causes contrast of the SNOM image or signal-to-noise ratio in the recording to deteriorate.

[I38.106] Photoluminescence of Low Dimensional Electron Gases in Pulsed Magnetic Fields

We describe a facility for photoluminescence experiments in pulsed magnetic fields recently established at the K.U. Leuven. The system, which is presently capable of achieving 50T at temperatures down to 1.5K is being used to study low-dimensional semiconductor structures. State-of-the-art photon detectors in combination with an optical fibre bundle to transmit light to and from the cryostat allow us to record several spectra at different magnetic fields during each 20ms pulse. Future developments will include extending the temperature range down to 350mK, and the field up to 60T. We present results of recent experiments in which we have observed negatively charged excitons in the dense (1x10^11cm^-2) two-dimensional electron gas of a modulation doped single GaAs quantum well at Landau-level filling factors below 1/3.

[I38.107] Comparative Study of Vacancies in the b.c.c. and h.c.p. Phases of ^4He using Shadow Wave Functions

We use the shadow wave function formalism in Monte Carlo simulations to determine the energy of formation of single and double vacancies in ^4He crystals at T=0 K, at the bcc ^4He density. Data is presented for both the bcc and hcp phases. The activation energy for single vacancies in bcc ^4He was found to be 6.6\pm3.8 K, about 45% of that in the hcp ^4He, 14.9\pm4.0 K. By determining the occupation of the Voronoi regions of the crystal sites, over Monte Carlo time, we study the motion of the vacancies. We also present data on the correlations between vacancies, and between vacancies and ^3He impurities.

[I38.108] Comparative Study of Vacancies in the b.c.c. and h.c.p. Phases of >^4He using Shadow Wave >Functions

We use the shadow wave function formalism in Monte Carlo simulations to determine the energy of formation of single and double vacancies in ^4He crystals at T=0 K, at the bcc ^4He density. Data is presented for both the bcc and hcp phases. The activation energy for single vacancies in bcc ^4He was found to be 6.6\pm3.8 K, about 45% of that in the hcp ^4He, 14.9\pm4.0 K. By determining the occupation of the Voronoi regions of the crystal sites, over Monte Carlo time, we study the motion of the vacancies. We also present data on the correlations between vacancies, and between vacancies and ^3He impurities.

[I38.109] Path integral calculation of the 2D ^4He phase diagram

We present a set of Path Integral Monte Carlo calculations for 2D ^4He at temperatures lower than 1.5 K and for coverages in the range 0 < \sigma < 0.094 ÅThey were used to calculate the phase diagram of a perfect ^4He film. It shows a liquid-gas coexistence zone for temperatures lower than 0.87 K (the critical point) and \sigma < 0.044 ÅFrom that density to \sim 0.068 Åwe got a superfluid if the temperature is below the range 0.72-0.90 K, depending on the coverage. For \sigma > 0.07 Åthe stable phase is a triangular solid. These phase boundaries are comparable to the calculated previously with T=0 methods (DMC and GFMC), and very similar to the derived from experimental data of a second layer of helium absorbed on graphite.

[I38.110] Interaction of Two Vortices in Superfluid Helium

A straight wire can trap circulation in superfluid helium. In some cases, the trapped circulation can leave the wire and continue through the fluid as a free vortex line. The location of the detachment point and the position of the free vortex affect the wire's vibration frequencies, providing a rare opportunity to observe the motion of a single vortex line. In the simplest situation, the free end of the vortex is swept around the cell at the local superfluid velocity, and oscillations appear in the wire's beat frequency. Here we investigate signatures from more complicated fluid flow. We model interaction of the trapped circulation with another vortex, either a segment pinned to the cell wall or an additional free vortex. We discuss changes in the motion of the partially trapped vortex and how they affect the wire's vibration, with comparison to observed irregularities in the oscillation pattern.

[I38.111] Estimating Thermometry Noise and Systematic Error for a Low-Temperature Experiment in the Charged-Particle Radiation Environment of Low Earth Orbit

Heating due to the high ambient flux of charged particles above the earth's atmosphere is a problem for orbital low-temperature experiments with high energy sensitivity. Calorimetric measurements performed by the Lambda Point Experiment found the charged-particle heating to be complicated, varying with vehicle attitude and orbital position. The random timing of arrival of individual particles contributed significantly to thermometer noise. Future orbital experiments using high-resolution thermometry or ultralow temperatures will need to design to minimize these effects. We describe numerical calculations used to estimate temperature noise and systematic error due to charged particle heating for the planned DYNAMX experiment. A Monte Carlo method is used to generate a distribution of ionized particles of various orientations and species. Correct geometries are used to calculate track lengths through different parts. The resulting heat deposition time series for the different parts are used as input to a dynamic thermal network model of the thermometer. Intrinsic thermal fluctuations prescribed by the fluctuation-disspation theorem are added in. The overall approach is validated by comparison of these estimates to data from the Lambda Point Experiment.

[I38.112] Design considerations for an experimental cell used in thermal conductivity measurements near the superfluid transition in ^4He

A thermal conductivity cell typically includes a low-conductivity cylindrical sidewall with high conductivity probes protruding through the circumference at various axial positions. The thermal conductivity of the helium in the cell is measured by passing a heat current axially through the helium column and measuring the temperature at each probe. A slight excess of heat applied to the cold end of the cell causes the temperature profile to slowly scan by the probes. The cell geometry assures that the temperature profile is essentially one dimensional with only an axial variation. One systematic error inherent to this setup results from small heat currents present in the sidewall material. An appreciable radial heat flux at the interface between the liquid helium and a probe manifests as the apparent \emphearly arrival of the interface at that probe's position. We present the results of numerical modeling, including a comparison to some experimental data, to illustrate how the material physical properties such as thermal conductivity and the cell dimensions (wall and probe thickness in particular) influence the error between the measured and actual helium temperature profiles. Work sponsored by NASA under contract 957448.

[I38.113] Rapid vapor depostion of thick doped parahydrogen solids

We report the rapid vapor deposition of millimeters thick parahydrogen (pH2) solids of remarkable optical clarity. Characterization of pure pH2 samples by infrared (IR) and Raman spectra show a very low orthohydrogen and vacancy content, and a mixed hcp/fcc polycrystalline structure for as-deposited samples, which converts to hcp upon annealing. Efficient isolation of atomic and molecular dopants is achieved by conventional matrix isolation spectroscopy (MIS) techniques. The increased optical path lengths offer significant improvements in spectroscopic data quality, and reveal novel dopant-induced IR absorptions of the pH2 matrix host itself. Thus, while traditional MIS studies in rare gas hosts can only probe the influence of the matrix environment on the spectrum of the dopant "solute," in pH2 the response of the host "solvent" is directly observable as well. This complementary information may prove key to identifying conclusively the microscopic structures of dopant trapping sites.

[I38.114] Dielectric Investigations of \alpha-Relaxation of Polysulfone Model Molecules

Dielectric relaxation of five polysulfone model molecules have been examined from 50 ^oC below to 50 ^oC above the glass transition temperature in a frequency range of 10^-3 to 10^5 Hz. The model molecules are composed of a single repeat unit of polysulfone family and have a common structure of diphenyl sulfone group but with different end groups. The experimental results were well described by the empirical Cole-Davidson equation. The width parameter \beta can be described by Arrherius equation. Values of \beta range from 0.55 to 0.75 at temperatures studied indicating non-Debye relaxation behavior. The relaxation times can be represented by the Vogel-Tamman-Fulcher equation. The fragility parameters range from 67 to 87 indicating that the molecules exhibit intermediate glassy behavior between strong and fragile glass formers. The \alpha-relaxation for the five polysulfone model molecules, over the entire frequency and temperature range investigated, can be collapsed onto a single scaling curve with only two parameters, peak position and width.

[I38.115] Experiments to Observe Oscillatory Photodarkening in g-GeSe_2

We describe measurements made on glassy GeSe_2 films deposited on silica and other substrates to observe oscillatory photo-darkening under constant 655 nm (sub-bandgap) illumination. System parameters such as power-density, film characteristics and ambient temperature will be discussed.

[I38.116] Effects of Geometrical Frustration in the Hubbard Model

We have studied the effects of geometrical frustration in the Hubbard model defined on a two-dimensional lattice with adjustable degrees of frustration. Exact diagonalization techniques are applied to an eight-site cluster with periodic boundary conditions. Ground-state properties are calculated and analyzed to gain insight into the role of the geometrical frustration in determining the electronic and magnetic structures of the system.

[I38.117] Spin populations in mixed spin systems: A DMRG study

Spin density maps for both Mn^2+Cu^2+ pair and chain compounds have recently been reported. These studies provide the motivation for a detailed theoretical investigation of the spin populations in mixed spin systems. We have considered Heisenberg models for one-dimensional ferrimagnetic systems (S_A,S_B)_N, where the larger spin S_A takes on all integer and half-integer values from 1 to 7/2, while the smaller spin S_B remains equal to 1/2. Spin populations have been determined for systems with open and periodic boundary conditions using the density matrix renormalization group method. The evolution from pair to the Neel state is studied (O.Kahn, C.Mathoniere, B. Srinivasan, B. Gillon, V. Baron, A. Grand, L.Ohrstrom and S. Ramasesha, New J. Chem., \bf21), 1037 (1997). The effect of the value the larger spin on quantum fluctuations on both sub-lattices has been studied. End effects have been investigated in open chains. The behaviour of spin populations at finite temperetures in the presence of a magnetic field has been studied. High magnetic fields have been found to lead to interesting re-entrant behaviour. Working at low but finite temperatures does not significantly change the ratio of spin populations at the A and B sites( B. Srinivasan, S. Ramasesha and O.Kahn, to be submitted to J. Chem. Phys.).

[I38.118] Properties of low-lying excited states of Hubbard models: A multi-configuration symmetrized projector quantun Monte Carlo approach

We present in detail the multiconfigurational symmetrized-projector quantum Monte Carlo (MSPQMC) method for excited states of the Hubbard model, which is a novel development that allows us to obtain excited states for the first time from a PQMC-like scheme. We describe the implementation of the Monte Carlo method for a multiconfigurational trial wavefunction. We give a detailed discussion of issues related to the symmetry of the projection procedure which validates our Monte Carlo procedure for excited states. Various one- and two-dimensional systems are studied( B. Srinivasan, S. Ramasesha and H. R. Krishnamurthy, Phys. Rev. B, R 2276 (1996), B. Srinivasan, S. Ramasesha and H. R. Krishnamurthy, ibid., (in press (1997))). We study the ground state energy and correlation functions of the one-dimensional Hubbard model at half-filling to confirm these analyses. We then study the energies and correlation functions of excited states of Hubbard chains. Hubbard rings away from half-filling are also studied and the pair binding energies for holes of 4n and 4n+2 systems are compared with the Bethe ansatz results of Fye, Martins and Scalettar. Our study of the two-dimensional Hubbard model includes the 4 \times 2 ladder and the 3 \times 4 lattice with periodic boundary conditions. The 3 \times 4 lattice is non-bipartite and amenable to exact diagonalization studies and is therefore a good candidate for checks on the method. We are able to reproduce accurately the energies of ground and excited states, both at and away from half-filling. The method reproduces the correlation functions accurately. We also examine the severity of sign-problem for one- and two-dimensional systems.

[I38.119] Fractional entropy in the exactly solvable two-channel Kondo model

This work addresses the issue of fractional entropy for the two-channel Kondo model [1]. In an infinite system, a zero temperature residual entropy of 1øver 2\ln 2 is explained by the presence of a Majorana fermion [2]. For finite systems, this fractional entropy disappears [3] on a temperature scale T_L=v_F/L; for T

[I38.120] Metal-insulator transition in molecular conductors driven by the order-disorder transition of H-bond sublattice

The temperature dependencies of transport, infrared spectra and crystal structure have been investigated for a hydrogen-bonded molecular conductor, [Pd(H_2-xEDAG)(HEDAG)]TCNQ. HEDAG or H_2EDAG stands for hydro- or dihydro- ethylenediaminoglyoxime, respectively. This substance consists of segregated stacks of Pd complex and TCNQ, and shows a metal-to-insulator (M-I) transition around 180K. Below this temperature, commensurate superlattice reflections are observed with periods of c^*/2, c^*/3 and c^*/12 along the stacking axis, c. The full X-ray diffraction analyses except for the superlattice spots show remarkable increases of the temperature factors below 180K for several atoms which are associated with the intermolecular H-bonds between Pd complexes. This indicates that the M-I transition is driven by the order-disorder transition of the 1-D intermolecular H-bond sub-lattice. This transition is also confirmed by the splitting of B_1u CN stretching mode of TCNQ in IR spectra below 180K: The averaged valence state of TCNQ in the metallic state separates into the mixed-valence state of TCNQ^0 and TCNQ^-1, corresponding to localized carriers in the insulating phase. The substitution effect of deuterium for hydrogen will also be discussed.

[I38.121] Organic Superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br - A Tunable Electronic System across the Mott Transition -

k-(BEDT-TTF)2Cu[N(CN)2]Br, is an organic superconductor with the highest Tc of 11.6K at ambient pressure (A. M. Kini et al., Inorg. Chem. 29, 2555 (1990)). We have reported a normal isotope effect,when all the hydrogen atoms of BEDT-TTF are replaced with deuterium, in other words, Tc was depressed by as much as 0.9 K (M. Tokumoto et al., J. Phys. Soc. Jpn. 60, 1426 (1991)), in contrast to the "inverse isotope effect" commonly observed in organic superconductors (K. Oshima, et al., Synth. Metals 27, A473 (1988)) . Recently, it was reported that the deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br is of an insulating nature similar to k-(BEDT-TTF)2Cu[N(CN)2]Cl when cooled rapidly(Y. Nakazawa and K. Kanoda, Phys. Rev. B 53, R8875 (1996)). Here we report on the results of reexamination of the superconducting transition of deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br by SQUID measurements with special attention to the cooling speed ranging from 10K/min to less than 0.01K/min. We observed a significant effect not only on the superconducting transition temperature Tc but also on the superconducting volume fraction.

[I38.122] Ferromagnetism in Organic Polymeric Hubbard Model: Quantum Monte Carlo Simulation

The magnetic properties of a organic polymer chain are studied by the quantum Monte Carlo simulation. Considering the polymer doped by transition-metal impurities situated at every other radical site of the chain, the electron hopping and electron-impurity coupling effect are described by the Hubbard Hamiltonian. The magnetization, magnetic susceptibility and spin density wave(SDW) are investigated for a half-filling chain at low temperatures. By finite size scaling analysis, we find that the polymer chain could exhibit ferromagnetic order. Moreover, the on-site Coulomb repulsion enhances ferromagnetic order and the SDW coexists with the ferromagnetic order. These results can be understood qualitatively by the mean field theory.

[I38.123] Point Contact Spectroscopy of URu_2Si_2 in the Superconducting State

Point contact spectroscopy (PCS) performed in single crystals of the heavy fermion superconductor URu_2Si_2 has been used to study the temperature behavior of the superconducting energy gap. The differential resistance dV/dI vs voltage V shows a depression around zero bias when the URu_2Si_2 transits from the normal to the superconducting state. This depression which arises from the opening of the superconducting energy gap, increases when the temperature decreases. The energy gap can be observed due to the Andreev reflections mechanism. The dV/dI vs V curves measured at different temperatures between 0.3 K and 2.5 K, show that the critical temperature is higher than that determined by resistance measurements. We propose that this increase of the critical temperature is due to the pressure applied on the URu_2Si_2 when the PC is made. The temperature behavior of the superconducting energy gap cannot be fitted by the BCS model.

[I38.124] The Specific Heat of La_1.85Sr_0.15CuO_4: d-Wave Scaling.

The specific heat (C) of two polycrystalline samples of La_1.85Sr_0.15CuO_4 (LSCO) is reported for 1 \le T \le 45 K and magnetic fields (H) to 9T. T_c for one sample was \sim36K and for the other \sim39K, with well-resolved anomalies in C at T_c. For both samples the concentrations of paramagnetic centers were unusually low, \le10^-4 moles/mole LSCO. This facilitated the identification of a well-defined \alphaT^2 term for H = 0 and 1 \le T \le 10 K, as expected for lines of nodes in the gap. For T/H^1/2 \le 10 K/T^1/2 the \alphaT^2 term was replaced by a \betaH^1/2T term, as predicted for d-wave superconductivity, with complex crossover behavior for T/H^1/2 \ge 10 K/T^1/2. Overall, the electron density of states contribution scales as predicted for d-wave pairing. This behavior is similar to that for YBCO reported elsewhere at this meeting.

[I38.125] Phase Transitions in Superconducting Cuprates by X-Ray Absorption Spectro scopy

We have measured the temperature dependence of the x-ray spectra for substituted cuprates undergoing phase transitions: YBa_2Cu_3O_7 (single crystal), Nd(Ba_0.95 Nd_0.05)_2Cu_3O_7 near the Nd L_3 edge and Ba L_2, L_3 and Cu K edges display increased transparency in the post edge region atT_c +/- 2 K. The XAFS spectrum (10% of the absorption) does not change. The increased transparency is due to the remaining 90% of the absorption. The XAFS analysis gives good results and will be shown. The increased transparency has been assigned to a change in the relaxation time of the sum of the continuous post edge absorbance giving rise to the total signal 1/2[\pi /2 + ATAN(4\pi T_if(\nu _if-\nu _0))] where T_if is the relaxation time of the final states and \nu _0 is the edge frequency. We show a change in T_if from 10^-16 to 10^-18 s near the transition temperature to superconductivity, even in single crystals with two transition temperatures (87-93.2 K and 59.4-69.5 K).

[I38.126] Collective Mode Dispersion in Electronic Bilayers with Strong Coupling

The collective mode dispersion in strongly coupled bilayers is calculated in the Quasi Localized Charge (QLC) Approximation using pair correlation function data from an earlier HNC calculation performed for the same system. Our results show qualitative new features, such as the emergence of an energy gap at zero wavenumber and the disappearance of the dynamical instability, when compared to previous studies done either in the STLS or in the weak interlayer coupling framework. Possible direct experimental verifications of the above findings are discussed also.

[I38.127] Structural and Magnetic Ordering of the Interface of Fe/Tb Multilayers

The interface of Fe/Tb multilayers was investigated using x-ray diffraction and Mösbauer spectroscopy. Structural and magnetic ordering of the interface and its dynamic of growth as function of Fe and Tb layer thicknesses was the focus of this study. Two groups of samples, one with fixed Tb lauer thickness and one with fixed Fe layer thickness, were prepared by planar magnetron sputtering. Two major structures were identified with x-ray diffraction, and two more minor structures were identified from Mössbauer measurement. The composition and the thickness of the interface change with both, Tb and Fe layer thickness. Results of Mössbauer measurements show that an amorphous Tb-Fe component at the interface with an average composition close to that of the intermetallic compound TbFe_2 is likely to be the origin of perpendicular magnetic anisotropy (PMA) of Fe/Tb multilauers. It is also suggested that PMA in multilayers and amorphous Tb-Fe films may have the same origin.

[I38.128] Comparison Between Lanczos and Linked Cluster Methods For The Heisenberg Antiferromagnet On A Square Lattice

The Lanczos tridiagonal scheme is applied to investigate the ground-state energy of the 2D anisotropic XXZ Heisenberg Model. Comparisons are made with connected moments and t-expansion methods as well as a recently developed plaquette expansion. A number of poles appear in each of the schemes, which has previously been unreported.

[I38.129] Quasi-Long-Range Order in Random-Anisotropy Magnets

Monte Carlo simulations have been used to study a discretized Heisenberg ferromagnet (FM) with random anisotropy on simple cubic lattices. The spin variable on each site is chosen from the twelve [110] directions. The random anisotropy has infinite strength and a random direction on a fraction x of the sites of the lattice, and is zero on the remaining sites. In most respects, the behavior of this model is qualitatively similar to that of the corresponding random-field model,(R. Fisch, Phys. Rev. B 57, XXX (Jan. 1, 1998).) except that one needs a substantially larger value of x to get a comparable result for the random anisotropy, as compared to the random field. Due to the discretization, for small x at low temperature there is a [110] FM phase. For x>0 there is an intermediate phase between the paramagnet and the ferromagnet, which is characterized by a |k|^-3 divergence of the magnetic structure factor S(k) for small k, but no true FM order. At the transition between the paramagnetic and quasi-long-range ordered phases S(k) diverges as |k|^-2. For x close to 1 the low temperature form of S(k) can be fit by a Lorentzian with a correlation length estimated to be 11 \pm 1 at x=1.0 and 25 \pm 5 at x=0.75.

[I38.130] High Field Mossbauer Evaluation of Cation Distribution In Titanomagnetites.

Peaks area analysis of Mossbauer spectra were often used to directly appraise models of cation distribution in synthetic titanomagnetites. However, large uncertainties arise from strong overlapping among peaks of sextets originating from Fe^3+ and Fe^2+ ions on both tetrahedral (A) and octahedral (B) sites of the cubic spinel structure. To alleviate such complication, fields up to 7 T were applied to Ti_xFe_3-xO_4 (0<x<1) in our Mossbauer study, which effectively isolated the signal from Fe3+ on A sites. Its fraction remains constant at 0.25 for 0<x<0.5, in disagreement with reports from Mossbauer measurements in zero field. In the range 0.5<x<1, this fraction decreases linearly toward zero with x. Based on these observations, a new model of cation distribution is proposed.

[I38.131] Specific Heat of LaCu_2O_4 and NdCu_2O_4 to 7T.

The isostructural monoclinic compounds LnCu_2O_4 are a new series of cuprates in which there are two inequivalent Cu sites, a magnetic Cu^2+ and a diamagnetic Cu^3+. The specific heat (C) was measured for 0.5 \le T \le 50 K and 0 \le H \le 7 T for polycrystalline samples with Ln = La and Nd. For LaCu_2O_4 and H = 0, Cu^2+ orders antiferromagnetically with a lambda-like anomaly at \sim17 K and an entropy of only \sim0.29Rln2, which indicates partial ordering at higher T. For H \neq 0 the anomalies in C are broadened and shifted to higher T, but maintain the same entropychange. For NdCu_2O_4 and H = 0, Cu^2+ orders at \sim22 K. The anomaly is broadened compared to that for the La analogue, and the \gamma(H)T term is increased by two orders of magnitude. A Schottky-like anomaly at \sim3 K is associated with Nd^3+ ordering. The combined entropy is \sim1.25Rln2, of which Rln2 is expected for the Nd^3+ ordering. Broadening of the Cu^2+ anomaly, the increase in \gamma(H)T, and the Schottky-like anomaly for Nd^3+ could reflect Cu^2+- Nd^3+ interactions as predicted and found for Nd_2CuO_4.

[I38.132] ``Inversion'' of Microwave Surface Resistance in Colossal Magnetoresistance Manganites

We have performed a comprehensive study (powders, ceramics, thin films, single crystals) of the microwave losses in colossal magnetoresistance (CMR) manganites using a cavity perturbation technique over a wide range of frequencies (3 - 60 GHz) and temperatures (77 - 400 K). For conducting samples with dimensions larger than the electromagnetic skin depth \delta = \sqrt\rho /\mu_0 ømega where \rho is the resistivity, the conventional result is that the surface resistance R_s \propto \rho^1/2. For thin films (thickness t \ll \delta), one would expect R_s \propto \rho while for small powders (radius < \delta) the anticipated effective R_s \propto \rho^-1. Further, the microwave losses should scale as R_s h^2 (e^2/R_s) for a specimen placed in an h (e) field. For many CMR samples, an inversion is observed, that is, the observed microwave losses for a sample placed at the maximal h field follow those expected of a sample placed in the maximal e field and vice versa. It seems that the apparent R_s is ``inverted'' from its conventional behavior. An interpretation of this anomalous phenomenon will be presented.

[I38.133] Microwave Transmission Through Colossal Magnetoresistance Manganites

We have recently investigated the microwave properties of bulk specimens of CMR manganites by a cavity perturbation technique and found several interesting results. In particular, it was found(M. Dominguez et al.), Europhys. Lett. 32, 349 (1995). that the low temperature dc and microwave resistivity can be quite different in some samples. Furthermore, although most samples showed a surface resistance R_s which follows \rho^1/2 with \rho being the dc resistivity, specimens with very high resistivities exhibited R_s values which were inverted,(S. E. Lofland, et al.), J. Phys: Cond. Matt., 9, 6697 (1997). i.e. R_s \propto \rho^-1/2. In an attempt to gain insight into this inversion phenomenon, we have constructed a transmission spectrometer for carefully prepared thin (< 0.3 mm) slabs of both ceramic and single crystal specimens and studied the transmission of 10 GHz microwave radiation through the sample at temperatures between 150 and 400 K and with applied fields of upto 5 kOe. The results of the transmission experiment will be discussed and compared with those of the reflection data of Refs. 1 and 2.

[I38.134] Magnetic Order in UO_2 and NpO_2, studied by Muon Spin Rotation

The magnetic behaviour of UO_2 and NpO_2 has been thoroughly studied in the past, yet no satisfying model for both compounds has been achieved. UO_2 becomes antiferromagnetic below 30.8~K. Neutron diffraction supports a non-collinear spin structure probably of 3k-type. Susceptibility, resistivity and specific heat data for NpO_2 indicate a phase transition at 25 K. Neither neutron diffraction nor Mössbauer spectroscopy could, however, prove the presence of ordered magnetic moments.

We have performed muon spin rotation experiments between 0.3~K and 300~K at the \mu\/E1 beam of PSI, Villigen, Switzerland. UO_2 reveals a clear magnetic transition at about 30~K with the appearance of spontaneous muon rotation frequencies. The temperature dependence follows that of the sublattice magnetization: after a quick rise below T_N a gradual saturation is achieved with \sim~57,~75 and 120~MHz, resp..

Below 25~K also in NpO_2 spontaneous rotation (\sim~6,~13~MHz) develops. These signals represents about \frac110 of the sample. The rest of the signal depolarises exponentially. Its damping scales with the spontaneous frequency. This is a prove of magnetic order though part of the moments may be frozen in an inhomogeneous surrounding.

[I38.135] Magnetotransport Properties of Nd_2Fe_14B Single Crystal

The electrical resistivity and Hall effect have been studied in a single crystal of Nd_2Fe_14B as a function of magnetic field, up to 12 T, and temperature, in the range 10 to 300 K. At 10 K, a positive (both transverse and longitudinal) magnetoresistance of 6% approximately is observed at highest fields for currents along the [1\bar1 0] crystalographic direction. This effect is less than 0.5% at 100 K and the magnetoresistance turns slightly negative at room temperature for magnetic fields along the easy magnetization axis [001]. Hall data for fields applied along the [110] direction are hole-like and follow the magnetization of the system at 100 and 280 K. The low-field Hall coefficient, R_H, peaks at about 120 K, slightly below the spin reorientation temperature in Nd_2Fe_14B. Away from the peak, R_H is roughly proportional to the total resistivity, as predicted for skew scattering in ferromagnetic materials.

[I38.136] Magnetostriction of Polycrystalline TbDy at Cryogenic Temperatures

At cryogenic temperatures, TbDy alloys exhibit giant magnetostriction, which makes these materials interesting for engineering service in cryogenic actuators, valves, and positioners. Saturation magnetostrictions of 5000 ppm are easily achieved for single crystals, but their preparation is difficult and costly. Textured polycrystalline materials are being developed for use in place of single crystals. Polycrystalline Tb_.6Dy_.4, cold rolled to induce crystallographic texture, shows magnetostrictions at 77 K which are a significant fraction of those obtained for single crystals. The correlation between rolling texture and bulk magnetostriction is presented. Polycrystalline samples show two major advantages over single crystals. They are easy to prepare, and large samples can be prepared at low cost. Second, it is not always necessary to apply a stress to return a polycrystalline TbDy alloy to its original unstrained state. The microstructural origin of this "internal spring" is under investigation, but it is likely related to elastic interactions between neighboring crystallites.

[I38.137] Magnetoelastic Properties of Magnetic Thin Films Using the Magnetooptic Kerr Effect

The magnetoelastic properties of Co and Fe thin films were measured using the magnetooptic Kerr effect (MOKE). Films were grown via magnetron sputtering on thin mica substrates. Magnetization loops were measured using MOKE with the magnetic field along different in-plane directions. Subsequently, the samples were mounted on a cylindrical sample holder, which imposed a well-defined strain to the film. This caused the magnetization loops to change dramatically due to the magnetoelastic coefficient of the thin film materials. The effects of the surface roughness and film thickness will also be discussed.

[I38.138] Muon Localization in Transition Metal Oxides: NiO, CoO and CuO

Transition metal oxides form the basis for many unique phenomena in magnetism, superconductivity and ferroelectricity. CuO forms the framework structure of the majority of the high-temperature superconductors. The experimental results of recent muon spin rotation measurements in antiferromagnetic CuO, CoO, and NiO have been modeled using a combination of potential energy calculations and magnetic dipole calculation. Based upon this model, the experimentally observed muon-spin frequencies are explained by a localized hopping of the muon among chemically equivalent sites. Although the structures of the antiferromagnetic lattices of NiO, CoO and CuO are vastly different, a consistent model is being developed to explain the diverse experimentally observed muon-spin frequencies. A model for muon localization in these oxides will also be discussed.

[I38.139] Microwave Dynamics of the Manganite Oxide La_1-xCa_xMnO_3

Using a broadband technique,(J.C. Booth et al.), Rev. Sci. Intrum. 65, 2082 (1994). we have measured the complex microwave response of the manganite oxide La_1-xCa_xMnO_3 between 45~MHz and 45~GHz. For a range of calcium concentrations from x \approx 0.2-0.5, this material exhibits a high temperature, paramagnetic, insulating phase and a low temperature, ferromagnetic, metallic phase. For x=0.33, the Curie temperature is T_C\approx 265~K, and the dc resistivity has a maximum at approximately 270~K. We have studied the dynamical response, \hat\sigma(ømega), of thin film samples in the vicinity of this phase transition.

[I38.140] Mossbauer study of cation distribution in MnGa_xFe_2-xO_4

The authors have used ^57Fe Mossbauer spectroscopy to examine the cation distribution in the spinel system MnGa_xFe_2-xO_4 for gallium concentrations, 0.2, 0.4, 0.6, 0.8, and 1, and at temperatures between 20 and 295K. For x = 0, the room temperature Mossbauer spectra show about 77 % of the Mn cations on the tetrahedral A-site with the remaining ions on the octahedral B-site, consistent with the findings of Sawatzky, et al ^1. i.e., Mn_.77Fe_.23 (Mn_.23 Fe_1.77 O_4) , where ( ) represents the B-site occupation. With the addition of about 0.2 Ga, the local site configuration changed to Mn_.77Ga_.09Fe_.147(Mn_.23Ga_.11Fe_1.65) O_4 , which means that about half of the Ga ions went to the A-site with the remainder to the B-site. Increasing the Ga concentration to 0.4 and 0.6 changes the local configurations to Mn_.77Ga_.092Fe_.141(Mn_.23Ga_.3Fe_1.46)O_4 , and Mn_.77Ga_.054Fe_.18(Mn_.23Ga_.55Fe_1.22)O_4 , respectively; which means that 75 % and 90 %, respectively, of the Ga ions go on the B-site. The local configurations will be discussed within the context of a normal and inverted spinel along with their effects on the magnetization and Curie Temperature.

^1 Sawatsky et al., Phys. Rev. 187. 747(1969).

[I38.141] Ce M-edge x-ray absorption and Fe L-edge magnetic circular dichroism study of Ce_2Fe_17-xM_x solid solutions (M=Al,Si).

Ce M-edge x-ray absorption spectra and Fe L-edge magnetic circular dichroism spectra of Ce_2Fe_17-xM_x solid solutions, where M is Al and Si, have been measured at 295 K. The Ce M-edge spectra have been fit with a linear combination of CePO_4 and CeO_2 spectra in order to determine the valence of Ce. The resulting values, which range from 3.64 in Ce_2Fe_17 to 3.06 in Ce_2Fe_6Al_11, decrease linearly with x in both series, but the decrease is twice as large in Ce_2Fe_17-xSi_x. The Ce valence also correlates linearly with the Ce Wigner-Seitz cell volume, but with positive and negative slopes for the Si and Al solid solutions, respectively. These differences result from the more extensive Ce-Si covalent bonding interactions as compared to those of Ce-Al. The L-edge MXCD spectra indicate that the Fe orbital moments, which range from 0.0 to 0.2 \mu _B, are coupled parallel to the Fe spin moments.

[I38.142] Magnetization and compensation temperature in transition metal -- rare earth multilayers: a mean-field approach

Mean-field theory is used to explain the magnetization as a function of layer thickness in transition metal -- rare earth multilayers. Long-range dipole interactions are included along with FM nearest neighbor interactions within the layers and AF nearest neighbor interactions at the interface.

The obtained dependencies of saturation magnetization and compensation temperature on layer thickness agree with experimental data on Tb/Co multilayers( L.\ Ertl, G.\ Endl, and H.\ Hoffmann, J.\ Magn.\ Magn. Mater.\ 113, 227 (1992).). The saturation magnetization is constant for very thin films (the behavior characteristic to Tb - Co alloys) but it decreases with increase of layer thickness. At thick enough films the magnetization starts to increase again confirming the importance of the long - range forces. The compensation temperature also decreases with layer thickness. The proposed theory is extended to calculate the magnetization of FM/AFM layers with a spacer layer in between.

[I38.143] The exact transverse susceptibility of general Ising-type chains with uniform, periodic and random structures

The transverse susceptibility of general Ising-type chains at zero transverse field is exactly expressed in terms of an eigenvector of corresponding transfer matrix, and hence explicitly obtained for small spin values, generally obtained from the solution of eigenvalue problem of finite degree. Numerical calculations are easy for arbitrary spin values. This formula includes the spin-S transverse Ising model with vanishing or nonvanishing parallel external field, the Blume-Emery-Griffiths model and the Blume-Capel model, mixed spin and mixed bond periodic systems such as alternating Ising chains or Ising ferrimagnets and also includes Ising models with random structures. The susceptibility in parallel and other arbitrary directions, the specific heat, the energy and the magnetization are also obtained.

\beginflushleft K.Minami : J. Phys. A29 (1996) 6395-6405 K.Minami : submitted to J.Phys.Soc.Jpn. \endflushleft

[I38.144] Role of Spin-Orbit interaction in Magneto-optical Effect

Recently, we study for the magneto-optical enhancement of Ce in Ce-substituted iron garnets based on the quantum theory. In the study, special attention is paid to the possible different effects of the spin-orbit coupling of the ground and excited configurations. The relative spin-orbit interation constant \xi_1 and \xi_2 are defined as the ratio of assumed strength to the actual strength of the spin-orbit interaction in the ground configuration and excited configuration, respectively. So, for example, when we set \xi_1 to zero(or1), then the spin-orbit interaction in the ground configuration is assumed to be zero(or the normal value). In our calculations, we found, the variation of the Faraday rotation with \xi_1 when \xi_2 keeps constant 1 is very big. The spin-orbit interaction in the ground configuration plays a very important role in the MO effects, if there is no such an interaction, the Faraday rotation becomes very small. When \xi_1 increases from zero to 0.25 and approaches saturation when \xi_1 reaches 0.5, the Faraday rotation increases very rapidly. However, the spin-orbit interaction of the excited configuration has almost no effect on the magneto-optical effects.

[I38.145] The Action of Temperature on the Megneto-optic in Rare-Earth-Substituted Yttrium iron garnet

The dependence of Megneto-optic on temperature in Ce-substituted Yttrium iron garnet is calculated based on the quantum theory. You Xu, Jie-Hui Yang and Xi-Juan Zhang* have pointed out that the very large splitting of the states caused by the crystal field makes the MO effect vary with temperature. In this section, we found that the occupation probability (\rho_1,\rho_2) of the lowest two crystal feild and exchange-interaction-split levels of the ground configuration is another cause which makes the Megneto-optic effect vary with temperature. At the room temperature, the calculated values of \rho_1, \rho_2, are 0.5057743, 0.4523548 respectively, while the temperature at 40K, \rho_1 and \rho_2 are 0.6943162 0.3056838 respectively. To our knowledge, when a plane-polarized electromagnetic wave propagater through the medium, the transition probabilities for the right- and left-handed circularly polarized light between one crystal field and spin-orbit split 4f level and one crystal field and spin-orbit 5d level are the same. But the Zeeman splitting makes the occupation probabilities of the sublevels of one crystal field and spin-orbit split 4f level different. Now we found the values of \rho_1 and \rho_2 increase with the temperature bring low. So, the MO vary with temperature. *Physical Review B Vol.50,1994

[I38.146] Superfluid-Bose glass critical point in and between one and two dimensions

I study the disordered Bose-Hubbard model at a commensurate density of particles. Critical point controlling the superfluid-Bose glass (SF-BG) quantum phase transition in the system allows a simple description within the (dual) theory for topological defects of the superfluid phase in one and two dimensions. The similarity of the renormalization scenarios which lead to the SF-BG critical point in two cases are pointed out. The critical point is strongly coupled in d=2, but lays at zero disorder in d=1. I evaluate the critical exponents at the SF-BG transition by a new expansion in small parameter \epsilon=d-1: z=1+\epsilon and \nu=1/\sqrt3\epsilon, to the lowest order. An alternative calculation of the exponents and the universal conductivity by a less controlled perturbative renormalization group in fixed dimension in d=2 will also be discussed (I. F. Herbut, Phys. Rev. Lett.) 79, 3502 (1997).

[I38.147] Temperature-Independent Quantum Resistance of Ultrathin Superconducting Films

We have observed the superconductor-insulator (SI) transition of a set of Pb and Bi ultrathin films. For in-situ deposition of small increments of material onto substrates at 0.3K. Observed conductance above 4K can be described by a single parameter scaling function (\beta-function) with a self-consistent theory for fermion localization in two dimensions. In the low temperature region below 1.0K, we have observed the temperature-independent resistance (TIR) near the SI transition. We suggest that the TIR is a new macroscopic quantum effect from the results of the noise measurements and the Hall resistances.

[I38.148] Electro-optic effects in thin organic films

Thin organic films with thickness ranging from 5 to 20 micrometers of meta-nitroaniline and 2-cyclo-octylamino-5-nitropyridine were grown between two transparent fused quartz plates deposited with indium-tin-oxide layers. Pockel's and Kerr's effects were studied with an ac modulation method. It is suggested that a commercial electro-optic cell based on organic crystal could be fabricated.

[I38.149] Linear Jahn-Teller Effect: A Connected Moments Approach

The ground-state energy of the linear Eøtimes \epsilon Jahn-Teller effect is obtained using a connected-moments expansion. The calculation is straightforward and leads to a set of simple algebraic expressions for the connected moments of the Hamiltonian. This is then compared to a recent calculation wherein a coupled-cluster scheme has been applied resulting in a set of thirteen nonlinear coupled algebraic equations.

[I38.150] Optical and Electronic Properties of Oxide Spinels.

Optical spectroscopy can be used as a tool to study band structures and hence it motivated us to study the optical properties of the spinel samples experimentally and compare it with the theoretical band structure calculations performed. Oxide spinels of zinc are known to exhibit optical and semiconducting properties of practical importance and hence we chose to study the spinels of zinc, viz. zinc aluminate and zinc gallate. Zinc aluminate and zinc gallate are normal spinels with fcc structure and fd3m group symmetry. Zinc aluminate (ZnAl_2O_4) and zinc gallate (ZnGa_2O_4) were synthesized in the laboratory using conventional ceramic processing techniques. The cubic spinel structure was confirmed by X-ray powder diffraction. The UV-reflectance spectra reflects the fundamental band transition taking place and can shed information to determine the band gap of the material. This spectra can be used to explain the electronic band transitions. The optical band gap of zinc aluminates (as determined by the powder reflectance spectra) ranged from 320 nm to 325 nm, while it is 290 nm to 300 nm for zinc gallates. Further theoretical band structure calculations on our samples are being used to understand the optical spectra that we obtained.

[I38.151] Laser-ablation mechanism of alkaline earth metals.

In order to understand the nascent process of laser-ablation of metals, the amount of desorbed monovalent ions have been measured on the laser-ablation of alkaline earth metals. The relationship between the amount of the desorbed ion and the laser fluence is I^4.6\pm0.2, I^3.7\pm0.4 and I^2.9\pm0.3 for Ca, Sr and Ba, respectively when ArF excimer laser (6.4eV, 193nm) is used as a light source. Here, ''I'' represents the laser fluence. The result can be interpreted that the desorption is caused by 5-, 4- and 3-photon process for Ca, Sr and Ba, respectively because such nonlinear behavior is caused by a certain multiphoton process. Since the total photon energy of 3-, 4- and 5-ordered process well corresponds to the highest core electron level for each metal, a model has been proposed that the laser-ablation of the alkaline earth metal is triggered by excitation of the outermost core electron. The experiment using KrF excimer laser (5.0eV, 248nm) has been performed to give the more evidence for the above mentioned model. The relationship between the amount of desorbed ion and the laser fluence is I^6.4\pm1.0, I^5.3\pm1.2 and I^3.6\pm1.0 for Ca, Sr and Ba, respectively. Such values also correspond to the outermost core level of each metal.

[I38.152] Novel Block Copolymer Composites as Photonic Band Gap Materials

We explore the possibility of making photonic band gap materials using novel block copolymer based composites. Our experiments have shown that a block copolymer system self-assembles into periodic refractive index structures at a length scale of tens of nanometers. This may suggest the use of these block copolymer based composites as photonic band gap materials. We characterize microstructures using transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). We are in the process of determining experimentally the optical properties of the periodic refractive index structures, which are predicted to have photonic band gaps. We also discuss possible applications of such photonic band gap materials.

[I38.153] Progress in differential optical reflectivity on YBa_2Cu_3O_6+x untwinned crystals

We present differential optical reflectivity (DOR, or \frac\partial R\partial T) measurements obtained, as a function of temperature, with photothermal techniques using 633 nm (1.96 eV), 780 nm (1.6 eV), 830nm (1.49 eV), 1064 nm (1.16 eV), and 1310 nm (0.95 eV) probe lasers. The results were obtained on 2 samples at each wavelength and with the \textbfE field polarized either along the [100] or [010] axis. The DOR spectra show a large qualitative variation as a function of polarization, frequency, and across samples. General features of the background (far from T_\mathrmc response), such as the background sign frquency variation, are explainable in terms of a Drude plasma model. Other features, such as the frequency variation of the near-T_\mathrmc response, are not explainable within the same model.

We also present techniques for calibrating DOR measurements. These techniques permit the determination of the temperature modulation present durning the experiment, and its variation during the experiment. We can thus calibrate DOR spectra into \frac\partial R\partial T, permitting quantitative comparisons with theory.

[I38.154] Photoinduced dichroism in Bacteriorhodopsin and its application to optical computing and information processing

The intensity dependence of the photoinduced dichroism in Bacteriorhodopsin (bR) films has potential application in optical image processing and optical computing. Under the illumination of linearly polarized actinic light of 570 nm wavelength, the photoinduced dichroism in a Bacteriorhodopsin film induces polarization rotation for a probe beam of the same wavelength. This behavior is a function of the life time of the M state in the Bacteriorhodopsin photocycle. We studied the dependence of the photoinduced dichroism on the pH environment in which the bR molecules are and on genetic mutation by replacement of the Aspartic amino acid in position 96 by Asparagine. The photoinduced probe polarization rotation can be exploited for optical Fourier processing and logic operations. The intensity dependence of the photoinduced dichroism in the different films has important implications on the applications for which they are suitable.

[I38.155] A Novel Two Dimensional Z-Scan Technique

A novel two dimensional Z-scan technique has been used to study the nonlinear optical properties and beam profile evolution within optical limiting devices with arbitrary beam shape and sample thickness. Two dimensional far field patterns of both signal and reference beams are recorded by a CCD detector, and the evolution of the beam distribution inside the nonlinear optical medium can be extracted directly by the beam propagation method. We have used this method to study the optical nonlinearity of nonlinear materials such as zinc porphyrin and azulenic donor-acceptor molecules. This technique offers a simple and accurate means for optimizing the design of optical limiting devices.

[I38.156] Persistent spectral holeburning in CaF_2:Tm^3+:D^-

We report the observation of persistent spectral holeburning on the ^3H_6 \rightarrow ^3H_4 transition of the trivalent thulium ion at 800\,nm, with the goal of obtaining long-term persistence for optical storage, frequency references and signal processing.

Deuteration treatment of rare-earth doped calcium fluoride gives rise to a number of new spectroscopic centers in which a rare-earth ion is adjacent to one or more negative deuteride ions. Laser-induced migration of the deuteride ions associated with such centers gives rise to bleaching of the rare-earth absorption profile. In the case of Tm^3+, hole widths of 18\,MHz have been measured, and the holes show no measurable degradation 6 hours after burning.

The strong ^3H_6\rightarrow ^3H_4(1) transitions of these Tm^3+ centers are favorable for application as frequency references as they have no hyperfine structure, and diode lasers are available in this spectral region.

[I38.157] Photoemission calculations in crystals using Kronig-Penney model

Results for photoemission calculations has been performed using Kronig-Penney model. To do this we have included the photonic field and employed a simple model where the surface respond is the dielectric function obtained from a linear interpolation between the experimentally-determined dielectric function for bulk and vacuum dielectric function. In this work we have tested this model for different materials.

Part I of program listing