Session VP05 - Postdeadline Poster Session I.
POSTER session, Thursday morning, March 25
Hallway, GWCC

[VP05.01] On the magneto-roton gap and the Laughlin state stability

It is argued that the Girvin, Mac Donald and Platzman (GMP) evaluation of the magneto-roton spectrum, in spite of being a sensible estimate of the excitation spectrum around the real FQHE ground state, does not imply the variational stability of the Laughlin state. The supplementary corrections needed to produce a variational calculation around the 1/3 filling factor Laughlin state, are evaluated approximately. These preliminary results indicate the existence of lower lying states for a range of wavevector values.

[VP05.02] Chain Dynamics at Polystyrene-Poly(bromo-styrene) Interfaces

The aim of this research is to understand the mechanism of interdiffusion at polystyrene (PS) - poly(bromo-styrene) (PBS) interfaces. PS/PBS bilayers were prepared and annealed at temperatures between the Tgs of the individual polymers. The polymers were characterized by NMR, UV-Vis spectroscopy, GPC, elemental analysis, thermogravimetric analysis, and differential scanning calorimetry. The interdiffusion across the welded bilayers was studied by using Rutherford backscattering spectroscopy (RBS). The bromine concentration profile across the interface was used to calculate the diffusion coefficient of PBS within PS. The RBS information is analyzed together with the fracture strength measurements available for this system and mechanisms for interdiffusion and adhesion are proposed. These mechanisms are compared to predictions from reptation theory, Rouse dynamics, and entropic barrier theory.

[VP05.03] Orbital effects of a magnetic field on weakly coupled two-leg Hubbard ladder.

By means of the multiplicative renormalisation group method with cut-off energies, we study the orbital effect of a magnetic field on the dimensional crossovers in two-leg Hubbard ladder. The ladders are weakly coupled via interladder one particle hopping process which generates a two particle hopping process. At zero field, the isolated ladders scale to a Spin Gap Metal phase (SGM). With applied pressure, the system undergoes a phase transition to a d-wave Superconducting phase (SCd) via two particle process. When the field is switched on, the SCd phase shrinks and disappears for the weak value of pressure where the SGM phase takes place. The interval of pressure on which the Scd phase appears is shifted to higher pessure with increasing field, at the expense of the two dimensional phase (2D), while its amplitude decreases. The critical temperature Tc at which occurs the SCd transition increases and falls to zero at a critical value Hc that increases with increasing pressure. For a field of about 20T the SCd phase and the 2D phase are completely destroyed. The ladder are in the SGM phase. The one particle and two particle motions are 'confined' within the ladder. Concerning the SGM phase, we find that the gap is reduced as the field is increased.

[VP05.04] Origin of anomalies observed in the thermal conductivity of high T_c superconductors under magnetic field

In this work we examine the magnetic field effects observed in high T_c superconductors, such as the kink in the thermal conductivity. So, we study a nearly square 2D Fermi surface with extremely good nesting properties and a Van Hove singilarity at the Fermi level such as Bi_2Sr_2CaCu_2O_8 + \delta. This model is consistent with recent photoemission data. We propose a mean field treatment which exhibit an effective coupling between electrons as well as an exchange coupling. When a magnetic field is applied perpendicularly to the electron plane, an orbital effect restores a 1D behaviour for the magnetic response,with

an effective exchange constant rapidly increasing with the field. Therefore, we expect, above a critical field, a new state caracterised by coexistence of superconductivity and spin density wave.This new symmetry breaking should open a gap on the whole Fermi surface.We propose to ascribe to this affect the anomalies observed in the thermal conductivity of Bi2212 and the apparent disappearence of the quasi-particles in an applied field.

[VP05.05] Selection Rules of Interface Modes in Ultrathin GaAs/AlAs Superlattice

All four interface (IF) modes were observed in both (XX) and (XY) geometries, contrary to the prediction of conventional theories, in the resonant Raman spectra of the ultra-thin (GaAs)_4 /(AlAs)_2 superlattice (SL). This violation has been interpreted to be a consequence of the deep penetration of the electron wavefunction in the GaAs wells into the AlAs barriers as well as a lack of definite parity of the electron wavefunction in such ultra-thin SL, i.e., violating the requirement of conventional theoreries. These indicate that conventional theory available to thicker systems need to be corrected and developed before it is applicable to ultra-thin systems.

[VP05.06] On the Application of the Two Temperature Model to Electron-Phonon Relaxation in Thin Metallic Films

The Two-Temperature Model (TTM) was developed in 1956 by Kaganov, Lifshits, and Tanatarov to describe the electron-phonon relaxation in metals. During the last decade the TTM has been widely used to explain the energy loss by electrons excited by femtosecond laser pulses. It is clear that the model is applicable in the picosecond time scale, when the electron temperature has already been established. We emphasize that in the application of the TTM two main approximations are used. The first one is that the phonon heat capacity is assumed to be independent of temperature, and the second that the energy transfer term is proportional to the difference T_e - T_ph . The first approximation corresponds to the classical limit of the lattice heat capacity and is obeyed if T_ph is much greater than the Debye temperature T_D . The second approximation, as it was mentioned by Kaganov et. al. is valid also when T_e is much greater than T_D , and when T_ph is much greater than T_D . Despite the fact that these conditions are not satisfied in the experiments with femtosecond pulsed laser excitation of electrons in thin metallic films, the results of the calculations based on the simplified version of the TTM equations demonstrate good agreement with experimental data. In this communication we analyze this contradiction and find the limits of applicability of the conventional approach based on the above mentioned approximations. We take into account the first corrections to the energy balance equations, which are of order of T_D / T_ph and T_D / T_e . The contribution to the phonon heat capacity as a result of this correction is found to be only 5T_ph = T_D. As for the contribution to the energy transfer term, it is multiplied by a factor which differs from unity by just 2.8take T_e = 2 T_D and T_ph = T_D . The numerical solution of the exact TTM equation with initial conditions T_ph = T_D , and T_e = 5 T_D show that the deviations caused by these corrections do not exceed 5-6

[VP05.07] Microscopic Identification of the Parameters in Cosserat Theory

The aim of this work is to verify a continuum theory for sheared granular systems. Therefore we are simulating a 2d shear cell using a molecular dynamics (MD) algorithm. The shear cell is built of an inner wheel and an outer ring. In order to parallel ongoing experiments in Durham NC (Prof. Behringer), the granular material consists of 2900 disks confined between the two cylindrical walls.

In our simulation we found a shear zone near the inner wheel where the tangential velocities show an exponential decay. Furthermore, the angular velocities of the grains are found to oscillate near the inner wheel from one disk layer to the next. To take this effect into account we are using the Cosserat theory to model the system (C. Veje, et al., Fluctuations and flow for granular shearing, in H. Herrmann, J.-P. Hovi, and S. Luding, editors, Physics of granular media), Kluwer, Dordrecht, 1998. Besides the kinematic quantities, we are interested in the stress, strain and fabric tensors of the disks in order to determine the classical elasticity theory coefficients and the Cosserat parameters as well. We found a dilatancy function which scales independent simulations with different densities onto one single master curve. Furthermore, one finds from simulations that the fabric tensor is strongly anisotropic, and that stress and strain are not colinear as often assumed.

[VP05.08] Manipulation of residual defects and transient-enhanced diffusion in solid-phase epitaxially grown Si

A method for preparing shallow dopant distributions via solid-phase epitaxial growth (SPEG) following amorphization by low-energy Si self-ion implantation leaves defects that can lead to unwanted dopant impurity diffusion. The double implant method for SPEG uses both low- and high-energy Si self-ion implantation to remove most of the inter- stitials. Nevertheless we find that measurable crystalline imperfections remain following the SPEG annealing step of both self-ion implanted Cz and float-zone silicon. Measurements of defect profiles using variable- energy positron spectroscopy show that there are divacancy-impurity complexes in the SPEG layer and V6 and larger vacancy clusters near the SPEG-crystalline interface. These measurements should be useful for modeling the diffusion of dopant atoms and for fine tuning the double implant parameters.

[VP05.09] Computational Modeling of Nanologic Circuit Molecules.

Nanomolecules and nanotechnology represent a new frontier in science that has potential application in engineering, chemistry, medicine, electronics, and many other fields. One such application is in design of miniature nanologic circuits, which can be composed of polymer based nanologic molecules. A perpendicular magnetic field can induce a current in a nanologic molecule, thus it can be used to construct a nanocircuit. We have studied various properties of some proposed nanomolecules, composed of available substituted conductive polymers, to determine their feasibility in use as nanologic circuits. We have also modeled these molecules, and the coupling of several other molecules to these nanomolecules using molecular dynamics simulations. Successful coupling of nanologic molecules can lead to the design of miniature electronic circuits, and eventually to nanoscale computer chips. We have also modeled some basic electronic circuits using nanologic molecules, and other organic polymeric molecules. By using different molecules to construct an electronic circuit, different excitation frequencies can be used to excite different parts of the circuit. This allows the construction of circuits that are similar in mechanism to brain function.

[VP05.10] Using Artificial Neural Networks to Predict Electronic Properties of Conjugated Polymers.

The use of artificial neural network's in chemistry, as well as in many other disciplines, has accelerated over the last ten years. The neural network's ability to predict properties of various systems has found applications in many different areas. Using the dipole moment, fifteen HOMOs and fifteen LUMOs we are training a neural network to predict the dielectric constant and conductivity of various polymers. The input information was obtained entirely from the Gaussian 94 ab initio program, using the Hartree Fock 6-31G* basis set. Through the training of the dielectric constants, we calculated an average error of about 16 percent. Since the net was only trained on 21 polymers, we believe increasing the number of polymers that we train on can significantly reduce the error. We are, therefore, in the process of adding more polymers to our training set. Our work on conductivities is still in progress and we plan on presenting both sets of data at the centennial APS meeting in March 1999.

[VP05.11] Using Artificial Neural Networks to Predict the Mutagenicity of Nitro Aromatic Compounds.

Research in artificial neural networks (ANN) has been active since the 1940's. In the 1980's, ANN experienced tremendous growth in many fields. Successful applications can be found in many areas including: business and finance, physics, astronomy, handwriting and speech recognition, medicine, chemistry, and biochemistry. The success of ANN is due to its ability to learn from examples and to generalize from learned information that is stored across network weights. Presently in our lab, mutagenicity of nitro aromatic compounds (NARs) is

being predicted by using ANN. The relation between eigenvalues, dipole moment, and mutagenecity is being explored. The eigenvalues have been calculated by both semi-empirical methods, using MOPAC, and ab-initio SCF-MO methods, using Gaussian. Preliminary results are being presented in this seminar. Planned studies include using Quantitative Structure- Activity Relationship (QSAR) methods to explore the relationship between eigenvalues, hydrophobicity, and mutagenicity. In addition, relationships involving the above variables will also be explored by way of bilinear regressions.

[VP05.12] Theoretical Investigation of Locations of Implanted Fluorane Atoms and Associated ^19F^\ast Nuclear Quadrupole Interactions in Diamond, Silicon and Germanium

We have used the Hartree-Fock Cluster procedure to obtain the possible sites, for implanted ^19F^* and the nuclear quadrupole coupling constants e^2qQ and asymmetry parameter \eta. For the high frequency signals obtained by TDPAD measurements,(K. Bonde Nielsen et al. J. Phys. C 17, 3519 (1984)) (B. Roseler, Ph.D. Thesis, Universität Erlangen-Nürnberg(1984)) (S. H. Connell et al. Nucl. Instr. Meth. B35, 423(1988)) we were able to identity the Intraband site as the one responsible for all three systems, diamond, silicon and germanium. For Si and Ge, the assignment of the low-frequency signals is made to ^19F^\ast implants at dangling bonds resulting from damage generated in cascades during implantation. In diamond, none of the sites studied could explain the low-frequency signal and it is suggested that it is associated with ^19F^\ast adjacant to impurities.

[VP05.13] Investigation of Electronic Structure and Nuclear Quadrupole Interactions at Reconstructed Semiconductor Surfaces

Experimental Perturbed Angular Correlation studies(G. Krausch et al., Phys. Rev. Lett. 68, 377(1992)) of the nuclear quadrupole interaction of ^111Cd^\ast resulting from ^111In adsorbed on reconstructed <111> surface of silicon have led to the observation of two sets of quadrupole coupling constants e^2qQ and asymmetry parameters \eta in contrast to a single e^2qQ and \eta=0 from earlier Hartree-Fock Cluster investigations (S. M. Mohapatra et al., Revs. Solid State Sci. 4, 873(1990)) on the unreconstructed surface although the value of e^2qQ is close to the two experimental values of e^2qQ. We have carried out corresponding investigations of e^2qQ and \eta for ^111Cd^\ast on the reconstructed surface at the eclipsed position of ^111In adsorbed at the edge and corner sites in the dimer-adatom-stacking fault(DAS) model suggested^1 as responsible for the two observed sets of e^2qQ and \eta and have found satisfactory agreement with the observed data with the corner site exhibiting larger \eta as compared to the edge site. Relaxation effects associated with the ^111In atom at the surface are found to be rather important.

[VP05.14] Theory for Origin of Single Hyperfine Fields Observed for Muon in Antiferromagnetic NiO and MnO

The importance of tunneling and rotational diffusion of muon in antiferromagnetic(AF) NiO and MnO in leading to the single observed fields in muon spin rotation measurements is demonstrated. The results of first-principles investigation using unrestricted Hartree-Fock Cluster theory for studying the locations of muon, the hyperfine fields at these sites, the potentials governing the motions of the muon in AF NiO and MnO will be presented, providing very good agreement between theory and experiment (K.Nishiyama et al, Hyp. Int. \underline104), 349 (1997) (Y.J.Uemura et al, Hyp. Int. \underline17), 339 (1984) in both these systems.

[VP05.15] Theoretical and Experimental Investigations of Interaction of Negative Muon with LaSrCuO System

Theoretical unrestricted Hartree-Fock Cluster investigations are shown to demonstrate that the apical oxygen site with \mu^- attached to a paramagnetic O^- ion is much stabler than the (\mu^-O^2-) system and has a local moment of about 0.9 Bohr magneton in the LaCuO system, while for the planar case, the situation is not definitive. Our experimental muon spin rotation(\muSR) measurements in LaSrCuO have focused on the temperature and magnetic field direction dependences of the paramagnetic shifts for the muonic atom involving binding of \mu^- to oxygen, which clearly demonstrate the formation of a localized moment around \mu^- attached to an apical oxygen in agreement with theory. Quantitative comparisons will be made between theory and experiment.

[VP05.16] Anomalous Pseudogap Formation in a Non-superconducting Crystal of Nd_1.85Ce_0.15CuO_4+y : Implication of Charge Ordering

Nd_2-xCe_xCuO_4+y system is a well-known high-T_c superconductor, in which CuO_2 planes are doped with electrons. A unique feature of this system is complete absence of superconductivity in as-grown or oxygenated crystals irrespective of Ce concentration: The superconductivity shows up only when crystals are subject to an appropriate oxygen-reducing procedure. Recent neutron diffraction experiment has revealed that a minute amount of apical oxygens are removed by the reducing procedure. In this study, we have investigated temperature variation of optical spectra comparatively for both oxygenated non-superconducting crystal and reduced superconducting crystal in order to elucidate the charge dynamics in the non-superconducting crystal. We have found that only for the oxygenated crystal, conspicuous pseudogap structure emerges at around 0.3 eV in the optical conductivity spectrum at low temperatures, and concomitantly, Cu-O bending (infrared) and stretching (Raman) phonon mode increases in intensity. These anomalies are quite parallel with those observed in typical charge ordering transition systems, and can be accounted for in terms of charge ordering or its fluctuation, induced by the tiny amount of apical oxygens. We propose that the superconductivity is totally quenched by such charge ordering instability in this class of electron-doped cuprate compounds without appropriate reducing procedure.

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[VP05.17] Charge and Spin Dynamics in La_2-2xSr_1+2xMn_2O_7 Crystals at Low Temperatures

To investigate charge and spin dynamics in the ground state of La_2-2xSr_1+2xMn_2O_7 for x=0.3 and 0.4 which show quasi-two demensional ferromagnetic metal, we have measured resistivity and low-temperature specific heat in magnetic fields.

Low-temperature specific heat measurements suggest an enhancement of thermal exitations of spin-wave by reduction of demensionality. Estimated electronic specific heat coefficient \gamma is finite, about 2 - 4 mJ/K^2 mol, which is comparable with that of La_1-xSr_xMnO_3.

Resistivity measurements show T^1/2-dependence of conductivity and finite zero-temperature conductivity, which is characteristic of 3 dimensional localization effect and is not inconsistent with finite \gamma value. Furthermore, they show that negative magneto-resistance at low temperature is due to a combination of destruction of localization effect, spin-valve effect, spin-canting, and orbital variation by magnetic fields.

[VP05.18] From jump statistics to fractional Fokker--Planck equations: Anomalous diffusion in external fields

Anomalous diffusion is encountered in a large diversity of disciplines in physics, chemistry and biology. It comes about through the divergence of either the characteristic waiting time or the jump length variance, as viewed from a random walk standpoint. Continuous time random walk (CTRW) theory and fractional diffusion equations have been established to describe anomalous diffusion. Here, we develop a generalisation of the CTRW model from which we derive generalised Fokker--Planck equations of fractional order describing anomalous motion under the influence of an external field. Through this derivation the different versions of fractional equations discussed in literature are shown to emerge from a common underlying generalised master equation. We give special credit to subdiffusion close to thermal equilibrium, and Lévy flights in external fields. The first choice leads to generalised Einstein relations whereas the second case is far from equilibrium and allows for a comparison with Tsallis generalised theromostatistics.

[VP05.19] Mossbauer Effect in f.c.c. Fe-based Carbon-containing and Nitrogen-containing Alloys

The hyperfine interaction parameters obtained from Mossbauer pectra of the f.c.c. Fe-C, Fe-X-C and Fe-N, Fe-X-N (X = Ni, Mn, Cr) alloys are analyzed in order to determine a principle difference between the effect of carbon and nitrogen interstitial atoms on the electronic charge distribution.

A change of the s-electron density at the iron nuclei by the nearest nitrogen and carbon neighbours in austenite alloyed with Mn and Cr is shown in the same way it is observed in binary Fe-N and Fe-C alloys. The different effects of the nearest Mn and Cr neighbours on the change of charge density at the iron nuclei in nitrogen-containing and carbon-containing f.c.c.-iron are revealed. An alloying with Ni results in an appearance of magnetic ordering.

The quadrupole interaction parameter is analyzed. The distortion of the symmetry of the electronic charge distribution near iron atoms in both nitrogen-containing and carbon-containing alloys upon alloying with Ni, Mn, Cr is observed being less than that caused by C and N interstitial atoms.

[VP05.20] Local Environment Effects on Magnetic Structure at Interfaces

First principles local spin density calculations of the magnetic structure of interdiffused Cu/Py and Cu/Ni multilayers were performed. It was possible to solve the Kohn-Sham equations for both canted and collinear magnetic arrangements to a high level of convergence. We found multiple, metastable, non-collinear magnetic structures that showed a reduced contribution to the saturation magnetization consistent with roughly one ``magnetic dead'' layer per interface. These canted interface layers were stable with respect to collinear interfaces by about 2 mRy per atom at the interface. The correlation between local environments of atoms at the interface and their moment configurations will be discussed.

[VP05.21] Development of Radiation Tolerant Gb/s Optical Links for the Front-end Readout of the ATLAS Liquid Argon Calorimeter

In the baseline readout solution for the ATLAS liquid argon calorimeter, Gigabit/s data rate fiber-optic links are used to transfer data from the calorimeter front-end electronics board to the data acquisition electronics situated up to 200 m away. In an architecture currently under study, ``G-link'' serialiser chips from Hewlett-Packard are used to convert data words into 1.6 Gb/s serial data stream which is fed into a VCSEL based emitter system operating at 850 nm. Graded index multimode fibers are used to couple the on-detector emitter to PIN-photodiodes located in the receiver. We present the results from neutron irradiation of a complete G-link based demonstrator link, along with results from neutron and ionising irridiations of potential link components (packaged VCSELs and graded index fibers)

[VP05.22] On the role of Coulomb correlations and collective charge-density excitations in the mechanism of high-temperature superconductivity with d-wave symmetry of the order parameter

Many-body Coulomb correlations and low-frequency charge density excitations are shown to be a possible cause of the high critical temperature T_c of superconducting transition and d_x^2-y^2-wave symmetry of the order parameter in high-temperature cuprate hole-type superconductors with extended saddle points in the quasi two-dimensional spectrum. The d-wave symmetry of the gap, in this case, is a consequence of strong suppression of the screened Coulomb repulsion for small transferred momenta due to the exchange of the virtual Bose-type excitations with acoustic dispersion, appearing in the collective electron spectrum of layered crystals with pronounced anisotropy of the quasiparticle group velocity on the cylindrical Fermi surface. High values of T_c \ge 100~K are ensured by the high density of states in the vicinity of extended saddle points, as well as by the significant amplification of the effective electron-electron attraction in the d-wave channel of Cooper pairing due to the many-body correlations (Coulomb vertices).

[VP05.23] Theory of electromagnetic levitation of liquid metals

Recently, an increasing interest has arisen in the theory of electromagnetic control of fluid flows, with primary reference to metallurgical research. In this regard, a crucial aspect, particularly for its potential industrial applications, is played by the theoretical investigation of electromagnetic levitation of liquid metals, based on realistic physical models. In this work fundamental aspects of the problem will be analyzed and results will be presented in the physics of flow control produced by slowly varying external electric and magnetic fields.

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[VP05.24] Analysis of ponderomotive effects produced by turbulent eddies in a magnetofluid

A basic aspect of the MHD theory of incompressible conducting fluids immersed in an external magnetic field is the analysis of the Lorentz force acting on the fluid. In this regard, crucial is the effect produced by turbulence, either pre-existent, i.e., a result of initial and boundary conditions, or produced by the same Lorentz force. Purpose of the present work is to analyze basic properties of the self-consistent magnetic field produced by the fluid and to investigate the possible existence and role of ponderomotive effects produced by the turbulent eddies at low magnetic Reynolds number. Numerical results will be presented, based on (1+1/2) and (2+1/2)-dimensional finite-differences simulations of resistive viscous magnetofluids. \smallskip\

[VP05.25] Can one live without pseudopotentials?

We make progress towards performing reliable solid-state calculations with true ionic potentials and plane-wave basis functions. The strategy proposed here can further simplify calculations based upon pseudopotentials and in addition enables one to abandon \emphnon-local pseudopotentials altogether. The ability to avoid non-local potentials is of fundamental interest in the contexts of the density functional theory, Green-function and diffusion quantum Monte-Carlo techniques.

[VP05.26] XANES and AC Impedance Measurements of Lithium Silicate Glasses

In this work, we study the effect of low temperature synthesis on the ionic transport and structural properties of Li silicate dried gels in order to improve the ionic conductivity. Li ion conducting Silica gels are becoming popular and increasingly useful as electrolytes for Li based high energy density batteries. We present our recent results of Li- silicate [ x Li_2O- (1-x)SiO_2; x = 0.1 to 0.9 in steps of 0.1 ] system using XANES, XRD, FTIR, SEM and ac Impedance techniques. The electrical behaviour and ionic transport of the LS system are estimated and compared with structural studies.

[VP05.27] Thresholds and Resonances in Superlattices

Threshold and resonances are studied for superlattices. We use the transfer matrix approach to compute the scattering amplitudes. Wigner cusps, well known in Nuclear Physics, are observed for superlattices with channels coupling. Also sharp resonaces, of Lorentzian shape, are obtained and explained in terms of singularities of the scattering amplitudes at complex energies.

[VP05.28] Time diffraction of evanescent electromagnetic waves

The concept of time diffraction of evanescent electromagnetic waves is proposed. Transient propagation of electromagnetic waves is studied in two forms: propagating and evanescent waves. The difference and resemblance between quantum particle tunneling and photon tunneling are clearly demonstrated. Traversal time cannot be accurately defined due to the diffraction in time. Nevertheless, a delay time is defined which counts the time between the time-of-fly and the peak time of the transient light. The delay time is found to increase linearly and slowly with the increase of the traversal distance. Superluminal tunneling is found possible only for evanescent waves, and however, the Einstein causality is not violated.

[VP05.29] AFM Study on Curing Behavior of Phenolic Resin/Rubber Adhesive Systems

The curing behavior of phenolic resin/rubber systems with different curing levels was investigated by Scanning Probe Microscopy (SPM) adhesion force measurements. Phenolic resin is one of the earliest synthetic resins to be used in construction, electric and other industries. However, unmodified phenolic resin is a brittle material with limited application. The addition of rubber to the phenolic has been used to improve its mechanical properties. The resulting reaction kinetics was compared with the adhesion force-distance curve data obtained via SPM. The SPM adhesion force approach is useful to elucidate the true curing behavior of this system and demonstrate the complimentary nature of the two techniques. As the cross-linking density of phenolic resins increases, the sample should becomes less flexible and the response to a deformation decreases. A force plot is an observation of the interaction between the SPM tip and the cured sample surface, which yields information regarding the degree of curing. The SPM results are compared to those obtained by other methods in order to yield a detailed description of the curing mechanism.

[VP05.30] Molecular Beam Epitaxial Growth of SrS:Cu Blue Phosphors

SrS:Cu is a possible candidate for blue electroluminescent (EL) material. Many progresses have been made for improving the efficiency and the color coordinates. However, some issues still remain. The EL efficiency of SrS:Cu is only half of the value expected for a bright VGA display. Low temperature process is another issue for the practical application to reduce the product costs. A systematic study of molecular beam epitaxial deposited SrS:Cu films will be presented. It was found that the grain size in the as-grown films was small and the luminescence very weak. Post-growth annealing in a H2S atmosphere effectively increased the grain size and dramatically improved the luminescent properties. It was proposed that the weak luminescence in the as-grown film was attributed to the Cu atoms segregated at the grain boundaries in the SrS films. The oxidation of atomic Cu by H2S and the diffusion of Cu+ into the SrS lattice during annealing were responsible for the grain growth and the improved luminescent properties.

[VP05.31] Analytical solutions of a spherically symmetric collapse of an anisotropic fluid body into a regular black hole.

Einstein's equations are investigated for a spherically symmetric anisotropic fluid body. Tolman-Bondi types of coordinates are employed. A class of exact solutions are found. On the boundary, both Synge-O'Brien and Israel junction conditions are satisfied. In the interior of the fluid, three energy conditions are satisfied. The interior metric is smoothly joined to the exterior Lemaître metric. (The Lemaître metric is known to correspond to domains I and II of the Kruskal chart.) -------------------------------------------------------------

[VP05.32] Chirial Electromagnetic Waves at the Boundary of gyrotropic media

We demonstrate that the boundary of two gyrotropic media with opposite directions of the gyration vectors can support propagation of electromagnetic wave in the direction perpendicular to the gyration axis (Cotton-Mouton geometry). The components of electromagnetic field in this wave decay exponentially into both media. The characteristic decay length is of the order of the Faraday rotation length in each medium. The remarkable property of this boundary wave is its chirality. Namely, the wave can propagate only in one direction determined by the relative sign of non-diagonal components of the dielectric tensor in contacting media. We find the dispersion law of boundary wave for the cases of abrupt and smooth boundaries. We also study the affects of asymmetry between the contacting media and generalize the results to the many-boundary case.

[VP05.33] Dipolar interactions and proteins: a model of anisotropic collapse

Protein folding is both a thermodynamical and dynamical problem. Protein collapse is usually described as a freezing transition of a random heteropolymer. We are here most interested in the structure of folded proteins. In order to understand the presence of secondary structures (such as \alpha-helices or \beta-sheets) in the folded phase of proteins, we have built a model of polymeric chain, where each monomer carries a dipolar moment. In order to respect the geometry of the peptidic bond, the dipoles are constrained to be locally perpendicular to the monomers. For chiral chains, and in a mean-field approach, an anisotropic collapse transition is observed before the usual \theta collapse takes place, which corresponds to the appearance of a compact phase of secondary structures.

[VP05.34] Chaos in a Two-Spin System with Applied Magnetic Field

We observe chaotic behavior in the dynamics of a system of two magnetic moments with a ferromagnetic XY-model interaction as a magnetic field is applied. In both a classical treatment, as seen in the Poincare surface of section, and a quantum treatment, as seen in the changes in the pattern of the quantum web, chaos is most widespread for an intermediate value of the applied field and then decreases at larger values of the field. The effects of an applied field on a two-by-two lattice of magnetic moments were also observed, and a proposal for the treatment of larger lattices is made. The results raise the question of how chaotic dynamics affect the behavior of macroscopic films.

[VP05.35] Andreev reflection and spin polarization in granular-gadolinium/Superconductor Josephson junctions

We report on transport measurements on Nb/Al/Gd/Al/Nb junctions. Bulk Gadolinium is a weakly polarized ferromagnet (5-7%), and is present in the junction in granular form, this magnetic layer behave like a superparamagnet. We show that Andreev reflection is strongly enhanced by a weak polarization, obtained by applying an external magnetic field parallel to the junction. Indeed, the junction resistance is substancially reduced (from 40 % to 1000 % depending of the sample) when the external magnetic field increases. A new model based on out-of-equilibrium process in S/FM/S junction is proposed that accounts for this effect. The transport is described in terms of ``hot'' carriers that experience Zeeman splitting due to the spin polarized background, this leads to the enhancement of the Andreev reflection.

[VP05.36] Optical properties of a mixed novel quaternary dielectric crystal

Is reported the growth and optical properties study of a novel quaternary dielectric crystal, that is a four alkali halide mixture. This could be useful in the finding of a mixed dielectric-semiconductor crystal. The quaternary crystal contains ternary crystals, one of these recently studied(R.R.Mijangos, A. Cordero,E.Camarillo, H.Riveros, V.M.Castaño. Physics Letter A, 245 (1998) 123-126.) and several known binaries. The study is preliminary, over two different concentrations, one of these in equal molar fraction of each component doped with europium, an impurity of high optical sensibility. We obtain the constant lattice by x ray diffractometry. The optical absorption spectra of the colored crystals, having one single F band, meaning one single electron trap. The vegard generalized law applieed to novel ternary system recently studied, was extended at the quaternary crystal. A good agreement with the experimental results was obtained.

[VP05.37] Momentum and Spin Relaxation of Hot Electrons in p-Doped GaAs: Electric Field Effects

This abstract not available.

[VP05.38] Origin of Ice Ages Solved by Correcting Mistakes in Applying Newtonian Dynamics in Initial Condition and Forcing

This abstract not available.

[VP05.39] Application of a Thermodynamical Model to Thermal Expansion in Barium Fluoride

This abstract not available.

[VP05.40] Stability of Elliptical Orbits of 2 Pointlike Noncomposite Constituents (PNCs) of Neo-Ritzian Photon Model (PM).

PM: stopped. PNCs: masses m, equal opposite charges Q = gm;(\itBulletin American Physical Society) \bf22, p. 447 (1977). g: large constant. Constrained speed c (from which the Lorentz transformation is derivable):(\itHadronic

Journal Supplement) \bf5, p. 103 (1990). acceleration solely normal to \bfc.(\itPhysics Essays) \bf5, p. 220 (1992). Nonaccelerative force component along \bfc: changes m, not "spin." Coulomb force: F' = (Q^2/4r^2) toward other PNC. Accelerative force: F'sinP, + mag. force F" = F', inwardly normal to \bfc. Stability: elliptical orbit due to central force 2F' = Q^2/2r^2, very small eccentricity e; perturbative force: F'(1 - sinP) inwardly normal to \bfc. P: angle between radius vector (extended) and \bfc. Perturbation theory:(E. J. Routh, \itDynamics of a Particle). NewYork:

Dover (1960) pp. 243-44. de/dt = 0. Change of m with r: negligible effect. Elliptical orbits: stable.

[VP05.41] A Search for B Decays to Two Charmless Vector Masons

We have searched for rare decays of the B meson to two charmless vector mesons, B \to VV. Using 5.57 fb^-1 of data collected in the region of the \Upsilon(4S) resonance with the CLEO-II detector, we obtain new results regarding the decay channels of B \to \rho^0 \rho^0, K^*0 \rho^0, K^*0\barK0, K^*0K^*0, K^*+\rho^0 and K^*+\barK^*0.

[VP05.42] Time Calibration of Sudbury Neutrino Observatory's PMT Array

The Sudbury Neutrino Observatory (SNO) is one of the next generations solar neutrino experiments designed to measure the ^8B neutrino flux. The detector consists of 1000 tonnes of heavy water shielded by 7500 tonnes of ultra-pure light water and viewed by about 9500 phototubes. The SNO collaboration has developed various calibration devices in order to determine the detector response. We have developed an independent light source to establish the time and optical calibration parameter. The light source consists of a set of 6 blue LEDs pulsed with a rise time comparable to the PMT time resolution and mounted on well-defined locations on the PMT support structure. We will present the calibration of the SNO detector achieved with the LED system and in combination with the laser calibration devices.

[VP05.43] The Year One Physics Capabilities of STAR

When the Relativistic Heavy Ion Collider (RHIC) at BNL begins operation in the Fall of 1999, heavy ions will be accelerated in collider mode for the first time, and a new energy regime will be entered for Heavy Ion Physics. The Solenoidal Tracker At RHIC ( STAR) detector is dedicated to taking hadronic measurements. STAR has a near 4\pi coverage and uses a large volume Time Projection Chamber placed in a solenoidal magnet at 0.5T to track and identify the many thousands of produced particles. STAR will measure many observables simultaneously on an event-by-event basis to study signatures of a possible QGP phase transition and the space-time evolution of the collision process. The goal is to obtain a fundamental understanding of the microscopic structure of hadronic interactions, at the level of quarks and gluons, at high energy densities. The physics capabilities of STAR in the first year of running will be presented.

[VP05.44] Measurement of the Weak Neutral Form Factor of the Proton at Jefferson Laboratory

The proton, a state of three quarks bound by the strong force of QCD, also has a ``sea'' of quark-antiquark pairs that includes strange quarks. A fundamental issue is how much these strange quarks contribute to the charge radius and magnetic moment of the proton. A particularly clean experimental technique for isolating these effects is measuring parity-violation asymmetry A_PV in the elastic scattering of polarized electrons from protons. From A_PV, we can cleanly extract the strangeness contributions to the elastic form factors, G_E^s and G_M^s. The strange form factors provide a direct measure of the strangeness contribution to the proton's radius and magnetic moment. In Hall A at the Thomas Jefferson National Accelerator Facility (JLab), the HAPPEX collaboration measured A_PV at the kinematic point (\langle\theta_\mathrm lab\rangle= 12.3^\circ and \langle Q^2\rangle=0.48 (GeV/c)^2). From our data, we can extract the combination G_E^_s+0.39 G_M^s=0.023\pm0.034(stat)\pm0.022(syst)\pm0.026(\delta G_E^n), where the last error results from the uncertainty in G_E^n. The result places a significant limit on the size of the effects of strangeness in the nucleon. The relative ease with which we were able to measure a small asymmetry at JLab bodes well for the future of experiments measuring parity-violating amplitudes.

[VP05.45] Order Parameter for Design of Proteinlike Copolymers

In simple models of neural networks, optimal storage for efficient recall is obtained when the stored patterns are uncorrelated. Earlier, we have shown that this effect leads to uncorrelated sequence familes with optimal folding properties in proteinlike copolymers. The natural motions of polymers, however, describe a more structured configurational envelope than spins in a neural network, so it is expected that certain dominant configurations exist for, say, designing an amino acid chain just by virtue of the fact that such chains are connected linear arrangements of similar units, with certain excluded volume restrictions. To explore this idea we study ``random'' copolymers with Mattis-like interactions. However, instead of uncorrelated patterns we consider a mixture of N orthogonal pattern vectors. This decomposition results in a set of order parameters Q_\nu for the copolymer which describe its motions. Computing Q_\nu, we find that the most designable shapes of an off lattice copolymer correspond to the most visited shapes of a uniformly attractive copolymer with the same connectivity and excluded volume conditions. The application to proteins will be discussed.

[VP05.46] Infrared spectroscopy of negatively charged water clusters: Evidence for a linear network

We report autodetachment spectra of the mass-selected, anionic water clusters, (H2O)n-, n = 2, 3, 5-9, 11 in the OH stretching region (3000-4000 cm-1), and interpret the spectra with the aid of ab initio calculations. For n>5, the spectra are structured and are generally dominated by an intense doublet, split by about 100 cm-1, which gradually shifts toward lower energy with increasing cluster size. This behavior indicates that the n = 5-11 clusters share a common structural motif. The strong bands appear in the frequency region usually associated with single donor vibrations of water molecules embedded in extended networks, and theoretical calculations indicate that the observed spectra are consistent with linear "chain-like" (H2O)n- species. A detailed isotopic substitution study explicitly records the couplings between OH oscillators in H-bonded networks.

[VP05.47] Membrane Fluctuations in Living Cells using Patterned Excitation Fluorescence Correlation Spectroscopy

We present measurements of mitochondrial membrane fluctuations inside intact living cells using a relatively new experimental approach: fluorescence correlation spectroscopy with patterned excitation. Our measurements reveal the wavevector-dependence of the mobility of fluorescently labeled mitochondria under physiological conditions. These fluctuation measurements are directly compared to analyzed trajectories from fluorescence video microscopy data of the same samples. We observe the signitures of random Brownian motion on submicron length scales, and the appearance of non-random directed motion on increasingly larger length scales. We interpret these motions in terms of their combined physiological and mechanical origins.

[VP05.48] Alternative CP Violation

We briefly review some new classes of models of soft CP violation recently proposed by us and by Georgi and Glashow(GG). We emphasize their interesting consequences in the B physics. Both classes of models use softly broken CP symmetry to suppress tree level KM phase as well as the strong CP phase. The observed CP-violation in the kaon system is accounted for by the contribution due to a new heavy sector of scalars and vectorial fermions. The models can be roughly classified as the righted-handed in our case, or the left-handed in GG's case depending on how the chiral light quark sector relate to the new sector. The models can be milliweak or superweak in nature depending on the scale of the heavy sector.

[VP05.49] Simulations of Fast Particle Behaviour During Fishbone Burst

Fishbones form the most proliferous fast particle driven instability seen in ASDEX Upgrade. Recent results show that they lead not only to an unfavourable loss of energy from the fast ion population but also affect the background temperature profiles [1], thus playing an important role in energy confinement.

The interaction between the fast particles and the electromagnetic component of the fishbones in ASDEX Upgrade is modelled using the \textscHagis code~[2]. This is a nonlinear \delta\!f code which follows the guiding centres of the fast particle distribution.

A comparison of the simulation results with the experimental observations is presented and discussed. [5mm]

[1] S.\ Günter et al. \emphMHD Phenomena in ASDEX Upgrade Submitted to Nucl.\ Fusion [2] S.\ D.\ Pinches et al., \emphThe HAGIS Self-Consistent Nonlinear Wave-Particle Interaction Model, CPC 111 (1998) 133

[VP05.50] Acceleration of Gamma-ray and Neutron Producing Particles in Impulsive and Long Duration Solar Flares

A major challenge in high energy solar physics is to identify the mechanism(s) that accelerate ions and electrons to energies as high as 1 GeV with initiation time scales as short as seconds, producing emissions that can extend from minutes to several hours. Therefore, we describe the characteristics of the accelerated particles which produce gamma-ray lines and continua, meson-decay gamma-rays, and high-energy neutrons as deduced from observations of several intense solar flares during solar sunspot cycles 22 and 23. Typically, the events consist of an impulsive gamma-ray burst or bursts lasting minutes, followed by an extended emission lasting up to hours. The extended emission often results from ions accelerated to at least several hundred MeV. Some general scenarios which have been considered to explain these high-energy flare phenomena are: acceleration of ions by 2nd order Fermi acceleration in a closed magnetic loop, acceleration of particles by transient reconnection in magnetic fields at the top of the loop, acceleration of ions at a coronal mass ejection (CME) shock front, and acceleration in a corona stressed by a passing CME. We confront theoretical scenarios with the observations, emphasizing ion acceleration, and mention additional observations and simulations necessary to advance our understanding of acceleration of high energy particles associated with flares.

[VP05.51] Precision Measurements of the Refractive Indices of Liquids with the Surface Plasmon Resonance Technique

The surface plasmon resonance (SPR) technique proved to be instrumental in measurements of the optical properties of metal films as well as dielectric media. Recent advances in this technique allow to measure the refractive indices of liquids with ppm accuracy. The method can be employed in real-time, thus providing a unique means for precision measurements of thermal and concentration variations of the refractive indices of liquid solutions. In this work the results of measurements performed with the SPR technique employing detection of the reflected light with a photodiode array are presented. The experimental results are compared with theoretical estimates of the shot noise limitation \footnote Al.A.Kolomenskii, P.D.Gershon, and H.A.Schuessler, Appl. Opt. 36, 6539 (1997)on the precision of the measurements. Different applications of the SPR method for chromatographic detection, to studies of chemical and biomolecular reactions, as well as to the observation of structural transitions have been demonstrated and are discussed.

[VP05.52] Electrostrictive Relaxations in Polyurethanes

This abstract not available.

[VP05.53] Double Length-Scale Ordered Nanoporous Structures of Silica

Preparation of ordered nanoporous materials has vitally practical interests in catalysis and phonotics. In this paper, a three-dimensional ordered nanoporous structure of silica at double length-scales have been prepared for the first time with the template assistance of polystyrene spheres. The first length-scale is in the order of the polystyrene spheres of mean size ~ 200 nm, which are packed into a face-centered cubic (fcc) or hexagonal-close-packed (hcp) lattice and extend to macroscopic sizes. The second length-scale order is formed by infiltrating the fcc/hcp assembly with surfactants, leading to nanopores of ~ 10 nm in diameter. The composites was treated in a furnace at 450oC for 6 hours to burn out the polystyrene and the co-polymer surfactant, while the porous structures in the two length-scales were preserved. Scanning electron microscopy and transmission electron microscopy have shown the ordered structures. A comparison is given on the low-loss EELS spectra recorded from solid silica spheres, mesoporous silica and double-length scale ordered porous silica. The plasmon energy of the porous silica structures shows a significant shift in comparison to that of the bulk, suggesting that the local density of the bound electrons in the porous structures is likely to be lower than that in the bulk. Therefore, the imaginary part of the dielectric function also drops, leading to even lower dielectric loss in addition to that induced by the volume porosity. With consideration the flexibility of tunable porosity of the silica by changing the sizes of the template PS spheres and the chain length of the co-polymer, this study provides a technique for tuning the electronic structure of silica by varying its porosity. The porous materials are expected to have not only large surface area for catalysis, but also low dielectric constant for high-frequency microelectronics. Research are undertaken in these directions.

[VP05.54] The Anisotropic Magnetic Exchange Interaction in Quaternary Intermetallic Compounds

The anisotropic magnetic exchange interaction constants in quaternary intermetallic compounds (RNi_2B_2C, where R stands for the rare earth element) are obtained from the magnetic susceptibilities with magnetic field H parallel and perpendicular to the c-axis at normal state. The anisotropy shows the maximum value for TbNi_2B_2C system and systematic change as R changes from Tm^+3 to Tb^+3. Our obtained values and signs are consistent with those from the neutron scattering measurement at low temperature. The magnetic structures at high temperature are discussed from the magnetic interaction constants.

[VP05.55] Escape Transition of a Polymer Chain: Phenomenological Theory and Monte Carlo Simulation

The escape transition of a polymer "mushroom" (i.e. flexible polymer chain of length N endgrafted on a flat repulsive surface), occuring when a piston (e.g. the tip of an Atomic Force Mictroscope) of radius R much larger than the size of the mushroom (R_0\approx aN^\nu, here a is the segment length and \nu\approx 3/5) but much smaller than the linearly stretched chain (R_max=aN) compresses the polymer to height H, is investigated for good solvent conditions.

We argue that in the limit N\rightarrow \infty a sharp first-order type transition occurs, characterized in the isotherm force f versus height H by a flat region from H_esc,t=\hatH_1 (aN/R)^\nu/(1-\nu) to H_imp,t=\hatH_2 (aN/R)^\nu/(1-\nu), with (\hatH_2-\hatH_1)/\hatH_2\approx 0.26.

Monte Carlo methods are developed (combining configurational bias methods with pivot- and random hopping moves) which allow to study this transition for chain lengths up to N=1280. Even for such long chains some rounding of the transition due to finite-size effects is found. Nevertheless the expected scaling behavior of the transition heights with N and R is unambiguously established. Our simulational results demonstrate the escape transition via a double-peak structure of the radial distribution function of the monomers underneath the piston, and through a clear hysteresis in the force f versus height H isotherms for long enough polymer chains.

[VP05.56] A new fluid permeability estimation in nonoverlapping and overlapping spheres model porous media

We present a new fluid permeability estimation in nonoverlapping and overlapping monosized spheres porous media. The new method is based on the combination of Wiegel's translational diffusion coefficient of a uniform macromolecular spherical model and an excellent approximation for the translational scalar friction related to the electrical capacitance. For sphere packings, the random sequential addition is used. To get electrical capacitances, the first-passage algorithms by Given, Hubbard, and Douglas are used. Except for low porosities, the estimation is reasonably good.

[VP05.57] Atomic Force Microscopy Imaging of Defect Evolution and Domain Motion in Ultrathin Films of PS-b-PMMA Diblock Copolymers

We report the tracking of individual defects in the microdomain patterns of cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) films. 50nm thick films, containing a single layer of cylinders aligned parallel to the film plane, were repeatedly and non-destructively probed with atomic force microscopy (AFM) in an attempt to elucidate the evolution of the diblock domain topology between annealing treatments. We show explicitly that this evolution takes place through relinking, joining, clustering and annihilation of defects. We have also used AFM to observe directly the kinetics of domain mobility responsible for topological change. Domains of different thicknesses were monitored as a function of annealing temperature and time. The higher mobility and lower activation energy associated with the thicker domains are accounted for by the negligible substrate interactions where polymer-polymer rather than polymer-substrate interactions govern the dynamics.

[VP05.58] Kinetic energy effects on the oxidation of Ni(111) using molecular oxygen beams

The oxidation kinetics of the Ni(111) surface have been quantitatively examined utilizing kinetic energy selected supersonic beams of molecular oxygen. Using in situ high-resolution electron-energy-loss spectroscopy, we have observed notable differences in the oxidation mechanism for this interface as a function of incident beam kinetic energy. Exposure of a 300 K surface to a relatively low energy 60 meV O_2 beam leads to oxidation kinetics which follow an island growth model, qualitatively similar to what is seen with simple ambient gas dosing. In contrast to this, exposure to a relatively high energy 600 meV O_2 beam yields fundamentally different oxidation behavior: the kinetics of oxidation no longer follow an island growth model but rather behave with a Langmuir-like sticking model, implying key differences in the nucleation stage for interface oxidation. Cryogenically cooled Ni(111) could not be oxidized using either of these incident beam conditions, indicating that the energetic constraints needed to move from oxygen chemisorption to actual metallic oxidation could not be simply overcome using incident O_2 kinetic energy.

[VP05.59] The influence of steps on the interaction between hydrogen and a nickel surface

Defects play a vital role in surface phenomena, often initiating such processes as corrosion, chemical reaction, film nucleation, and embrittlement. These effects can be quantified with a surface that provides a regular and controllable source of defects. Using helium atom scattering and low energy electron diffraction, we have studied interaction of hydrogen with Ni(977). Deviations in H-uptake and phase behavior between the flat (111) and this stepped surface are observed. Most pronounced among these is the (2x2)-2H to (1x1) order-disorder transition at 0.5 ML. On Ni(111) this second-order transition occurs at a surface temperature of 270 K, however this transition on Ni(977) occurs at 310 K. This result will be discussed in terms of step density and pinning. Other results that will be presented include the cross section for the attenuation of He elastic scattering by adsorbed H, and the temperature-dependent domain size of ordered hydrogen.

[VP05.60] Large-Scale, Parallel Sparse Matrix Technique for Systems with \mathbf 10^15 Components

Many physical systems are analytically and numerically intractable because of the large number degrees of freedom involved. Examples are disordered interacting electronic systems, interacting spin systems, models for superconductivity, other cooperative phenomena and phase transitions (e.g. Anderson transition). For a number of these systems, it has been shown that quantities of physical interest can be extracted from distributions or the time-evolution thereof such as, for example, a projected density of states (PDOS) or density of transitions (PDOT). These quantities are local and therefore are exponentially insensitive to distant parts of the system---an expression of what is known as the black body theorem. We have developed a parallel implementation of the dynamic recursion method (Parallel Recursion Project) which is a powerful means to extract such local quantities from a sparse Hamiltonian matrix through tridiagonalization. The recursion method generates the transformation basis successively, requiring that only two vectors be stored at a time. In dynamic recursion, this basis is dynamic in that only the biggest components of these vectors are kept while the error remains bounded as a result of the black body theorem. This way, macroscopic systems with 10^15 states are accessible by microscopic simulations for the first time.

[VP05.61] Twist-bonded wafers - the perfect solid-solid contact?

Our phonon images of wafer-bonded GaAs demonstrate that phonons can propagate without scattering through a well-bonded region. Because of their high sensitivity to all types of imperfections, the ballistic (i.e., unscattered), gigahertz frequency phonons that form the phonon images are excellent probes of interface disorder on the smallest length scales. Thus, our measurements are a sensitive, non-destructive measurement of bond quality. Twist-bonded wafers, in which the two bonded pieces are deliberately oriented so that the lattice basis vectors are not parallel, have fewer and smaller voids at the interface but a larger number of crystalline defects at the interface (e.g., screw dislocations). In spite of these defects, we find measurable ballistic phonon propagation through twist-bonded interfaces. Our phonon images of twist-bonded wafers exhibit dramatic focusing features. Computer simulations of these features based on Snell's law scattering at the interface give new insights into appropriate models of lattice mismatch and interface scattering for these systems.

[VP05.62] The formation of nanostructured BaTiO_3 from monomer BaTi(methacryl)_6 observed by means of in situ X-ray absorption near edge structure (XANES) spectroscopy.

A phase transition from the paraelectric to the ferroelectric state occurs in BaTiO_3 with increasing particle sizes of nanostructured clusters. Monomer BaTi(methacr)_6 has been used as a precursor which upon heating reacts to form BaTiO_3. The particle size of the small BaTiO_3 crystals increases with a higher baking temperature. In situ X-ray absorption spectroscopy at the Ba L_III and Ti K edge has been used to visualize the kinetics of this reaction. The formation of nanostructured BaTiO_3 has been observed and the effect of the growing particle size is discussed. Furthermore, polymerization and pyrolysis of the precursor have been identified as different stages of this solid state reaction.

[VP05.63] Three dimensional mixing with natural convection

Natural convective mixing flows in closed containers can be achieved by imposing oscillating wall temperatures and using large enough Rayleigh numbers. In this investigation we present the numerical solution to the mass, momentum and energy transfer equations in a cubic box with oscillating wall temperatures. The relative phase of the oscillations has been chosen to generate two alternate corrotating vortices. The extent to which mixing can be achieved is described as a function of the Rayleigh number using Lagrangian tracking techniques. The stretching rate has been estimated by recording the growth of internal areas as functions of the oscillating cycles. Subregions of the integrated three dimensional volume have been identified where the flow can be considered two-dimensional. This work was partially financed by CONACyT-Mexico project number GE0044

[VP05.64] Using an atomic oxygen beam to achieve high oxygen coverages under UHV conditions

When dosing with molecular oxygen under ultra-high vacuum conditions, the saturation coverage of oxygen on Rh(111) is 0.5 monolayers. With further dosing, it is possible to slowly adsorb additional oxygen. Using an atomic oxygen beam, it is possible to grow a well-ordered (1x1) oxygen overlayer, which is quite stable for surface temperatures below ~400 K. This new structure leads to novel surface chemistry. Dosing with atomic oxygen also allows for the rapid absorption of oxygen, even at low temperatures. This latter observation has important implications for metallic oxidation and the growth of oxygen containing materials.

[VP05.65] Strongly Localized Amharmonic Modes

Studies of nonlinear vibrational dynamics lead to observation of long-living localized vibrations in perfect anharmonic lattices. The methods, used by a number of authors, so far, are based on direct numerical integration of classical equations of motions, being here the nonlinear differential equations. Due to the fast growth of the number of numerical operations and computational time with increase of the number degrees of freedom, the research is mainly focused on simple models: 1-D one- and two-atom lattices; only little have been done for real 3-D crystals. On the contrary, in harmonic approximation calculations can be performed also for macroscopically large pure and locally distorted crystals.

We present a method which makes use of harmonic approximation results for calculations of the anharmonic local modes. The developed techniques allow one to reduce the nonlinear problem to a properly formulated problem of linear local dynamics. It is applicable for lattices of arbitrary dimension, being especially efficient in the case of strongly localized modes, when it allows to obtain analytical solutions. Results of numerical calculations of anharmonic local vibrations of light ions in pure and impure alkali halide crystal are presented. It is found: in the case of amplitudes > 0.3Åthe vibrations depend very strongly on the crystallographic directions.

[VP05.66] Photoluminescence of Sub-Micron Structures Containing Self-Organised InAs Quantum Dots

A micro-photoluminescence (\muPL) technique was used in conjunction with sub-micron, e-beam lithography-created pillars (size range: -- \sim2.0 \mum) to study single InAs self-organised quantum dots over a four-order of magnitude variation of laser power. With decreasing laser power the background intensity decreases and the dot emission sharpens, reaching linewidths <80 \mueV (the system resolution).

The optical efficiency of sub-micron structures containing quantum dots was investigated by using e-beam lithography to fabricate 100 \mum square pads containing stripes or square mesas of sizes 0.1 -- 2.0 \mum. A study of PL efficiency, measured as a function of stripe or mesa size and temperature, will be reported.

[VP05.67] Raman and Brillouin Scattering in PEO-LiClO4 Polymer Electrolyte

Isotopically substituted samples were used to investigate ion-polymer and ion-ion interactions in PEO-LiClO4 polymer electrolyte by Raman and Brillouin scattering. The behavior of the hydrogen atoms of the polymer chains was examined by contrasting fully deuterated and hydrogenated polymers through the Raman and Brillouin shift. Ion-ion association, an important factor in reducing ionic conduction at high salt concentration, was investigated through the Raman scattering of the perchlorate anions. The results show that ion pairing in these samples are not as significant as other polymer electrolytes. The structural relaxation and its variation with isotope (i.e. D and H, Li6 and Li7) and phase (i.e. semi-crystalline and amorphous) are revealed by analyzing the scattering shift, line width and shape of the Brillouin scattering. This work was supported by Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract No. W-31-109-ENG-38.

[VP05.68] Structure and Magnetic Phase Transition in the Dimer Phase of AC_60 (A=K, Rb, Cs): ab initio study

The peculiar change in magnetic property (from diamagnetic to paramagnetic) of the dianionic C_60-dimer phase in a rapidly cooled AC_60 sample has been investigated using first principles calculations. We find that two different states of (C_60)_2^2- are degenerate with a small transition barrier between them. This trend prevails in the lattice, and contrasts with the high barrier in the transition to the C_60^- monomer phase. Therefore, the observed susceptibility increase with an increase in temperature and the magnetic phase transition can be explained.

[VP05.69] New Theory

This abstract not available.

[VP05.70] Electron-Phonon Scattering In GaAs/AlAs Structurally Modified Quantum Wells

Theoretical studies of electron-phonon scattering in structurally modified semiconductor quantum wells will be presented. Electron-phonon scattering in these structures strongly influences carrier mobility. Phonon modes and potentials for the modified quantum wells were determined using the dielectric continuum model for long-wavelength longitudinal optical phonons. The effective-mass approximation was used to obtain the electronic states. We present results for simple quantum wells and quantum wells with thin layers of barrier material within the wells. Thin layers of barrier material in the quantum well modify the electronic states, phonon modes and potentials. Electron-phonon scattering contributions to carrier mobility are determined using the relaxation time approximation. Theoretical results suggest increased mobilities for some structurally modified quantum well widths.

[VP05.71] Observation of Parametric X-ray and Diffracted Transition Radiation from Crystalline Foils at REFER Electron Ring

X radiation generated by 150 MeV electrons passing through accurately aligned 1-100 layers of 16.4 micro-meter thick monocrystalline Is foils was measured. It was found that diffracted transition radiation intensity at 14.4 and 28.8 kV was higher than Parametric radiation from a Is crystal of equivalent thickness. We hope to show results for the 35.5 KV x-ray line as well.

[VP05.72] General Taylor Configuration Expansion and the Gibbs Phenomenon

A formalism for describing Taylor configurations for arbitrarily shaped conducting walls with a ``frozen-in'' perpendicular ``seed'' field component at the wall was given earlier.(T.H. Jensen and M.S. Chu, Phys.\ Fluids 27), 2881 (1984). Frozen-in fields can exist without normal field components at the wall if the volume enclosed is not singly connected. The formalism provided convenient ways of viewing methods for helicity injection or current drive into plasmas as well as useful relationships between total helicity K, energy E, and the helicity parameter \sigma. The formalism utilized an expansion in eigenfunctions of the curl operator. Recently an apparent paradox associated with the formalism has been noted. For helicity injection with perpendicular seed field, there must be a non-vanishing normal current density at the wall. But, paradoxically, all elements of the formal expansion have vanishing normal components of the current density. From an analysis of this phenomenon for simple analytically solvable examples, we conclude that the paradox is an example of the Gibbs phenomenon and that the proposed expansion is valid.

[VP05.73] A New Time-Dependent Quantum Approach to High-Resolution Spectroscopy: Application to 3D Rydberg Systems in Crossed Electric and Magnetic Fields

We present a new time-dependent approach for probing the dynamics and high-resolution spectroscopy of Rydberg systems in the presence of external fields(Shih-I Chu and Xiao-Min Tong, Chem. Phys. Lett. 294) (1998) 31. ^,(Xiao-Min Tong and Shih-I Chu, Phys. Rev. Lett. (submitted).). The procedure is based on the extension of a recent development of a generalized pseudospectral time-dependent method which allows for non-uniform spatial grid discretization, and long-time propagation of the time-dependent Schrödinger equation with both high accuracy and efficiency(Xiao-Min Tong and Shih-I Chu, Chem. Phys. 217) (1997) 119.. The method is demonstrated by a case study of the photoabsorption spectrum of atomic hydrogen in the presence of static magnetic fields^1 and crossed electric and magnetic fields^2. Excellent agreement of the time-dependent results with the high-resolution experimental spectrum is achieved line by line, covering both the classically regular and chaotic regimes. To our knowledge, this is the first ab initio\ 3D calculation of field-induced Rydberg dynamics and spectroscopy with spectral accuracy^2.

[VP05.74] Ion-Molecular-Ion collisions

We investigate the electron capture reaction H_2^+ + He^2+\rightarrow H^+ + H^+ + He^+ at keV collision energies. In particular we are looking for the effect of the alignment of the H_2^+ molecular ion on the capture cross section. This collision system is a true one-electron system and the experimental data should provide a stringent test of theoretical calculations.

The experiment will be performed at the ion-ion collision facility at KSU. The He^2+ ions will be produced in an 5 GHz ECR ion source while the H_2^+ molecular ions come from a PIG ion source. The two protons emerging from the capture reaction will have scattering angles up to a few degrees. An imaging lens will be added immediately following the collision region to project both protons onto a position sensitive detector with a fast anode. SIMION simulations of this setup have shown that all three momentum components of both protons may be extracted through the two-dimensional position information and the flight times of each of the particles.

This is a work in progress and results to date will be reported.

[VP05.75] Model Potentials for Group II Metal-atom -Rare-Gas atom Interaction

We have attempted to model the attractive part of the interaction of excited- metal atoms with an outer pp orbitals with rare gas atoms as combinations of several interactions: i) M*(npp)-RG long range dispersion interaction (~1/R6), ii) RG dipole induced by the point charge quadrupole of M*(npp) state at close range (~1/R4) and iii) "back-polarization" of the M+(ns) core (for group II metals) by the induced RG dipole (~1/R10). The RKR method is used to construct the potentials using experimentally determined spectroscopic constants. A fitting program is then used to fit the analytical model potential to the experimental RKR potential. The results will be discussed for Zn(4s4p1P1).R (R=Ar,Kr,Xe) ,Cd(5s5p 1P1).Ar , Mg(3s3p 1P1).Ar ,and HgAr potentials.

[VP05.76] Modeling of the Natural Gas Consumption in Argentina.

In the present work we present the basic characteristics of a model intended to predict the natural gas consumption of the major cities of Argentina. This type of prediction is crucial for a country such as Argentina, where the natural Gas production centers are far away (more than 2000 km) from the main consumption centers. Therefore a coordinated set of operations are required in order to respond to a large increase in demand. The model presented herein predicts, within a 10% of uncertainty, the consumption in 90% of the days of the year for all the cities studied. The model is very robust, since it depends on preexisting conditions and is only partially dependent on the temperature forecast. The model has 5 adjustable parameters that can be obtained for each city using the historical data of consumption and temperatures. The model has been successfully tested in 6 of the major cities of Argentina.

[VP05.77] Strange Behavior of Projectile Fragments of Gold Beam at the Highest Available Energy

By following along the primary tracks of a 197^Au beam at 10.6A GeV, we observed \sim 2000 nuclear interactions in nuclear emulsion (BNL Exp. No. 875). Charges of all the secondary fragments (SF's) were determined with great accuracy and were divided into four different groups with Z > 20. When these SF's were followed, their interacting behavior was different, especially the group with 30 < Z < 60. These exciting, new results will be presented with possible explanations.

[VP05.78] An impact oscillator

We suggest to study a 2-d piece-wise smooth mapping that can be qualitatively derived from the differential equations describing an impacting nonlinear oscillator. This map is interesting because it may show a kind of boundary collision bifurcation with some new behaviors. The bifurcation gradually leads a group of regular motion to chaotic ones. It seems that a general description can be found for all of the transition.

[VP05.79] Aging Dependence of Charge Injection, Transport and Recombination in MEH-PPV Polymer Light Emitting Diodes

We study the current-voltage and radiance-voltage characteristics of double carrier and single carrier polymer light emitting diodes as a function of aging with applied DC electric field in a nitrogen atmosphere. The quantum efficiency saturates with aging and electric field to a maximum value half that of the fresh device; no significant change in the quantum efficiency occurs after the first seven hours of aging. By modeling the current-voltage characteristics as single carrier space charge limited current, we observe a factor of 5 decrease in the zero field charge mobility after 60 hours and no significant change in the electric field dependence of the mobility. Double carrier devices show increasing single carrier behavior with aging. These results can be explained by the creation of single-carrier traps or scissoring of the polymer chains. We observe no formation of new shorts with aging. We also address the effects of temperature on the aging dependence of the charge transport properties. -------------------------------------------------------------

[VP05.80] Properties of Pr_1-xCa_x MnO_3 Films Prepared by Pulsed Laser Ablation

Perovskite manganese oxides exhibit a paramagnetic-to-ferromagnetic transition upon cooling, which is accompanied by a sharp drop in resistivity. The colossal magnetoresistance occurs as a result of a rapid shift of the ferromagnetic transition temperature to a higher temperature range in the presence of an applied magnetic field. Nd-YAG lasers were employed in a crossed-beam scheme for depositing Pr_1-xCa_xMnO_3 films with thicknesses of 10 - 200 nm. The prepared films showed excellently c-axis oriented microstructures and following lattice parameters : a = 0.542 nm, b = 0.545 nm and c = 0.767 nm. The electrical resistivity was measured as function of temperature between 4.2 and 300 K. The temperature variation illustrates that the films remain insulating down to the lowest temperature where the resistance can still be measured. The experimental data are well fitted by the adiabatic expression with E_0 (activation energy of electrons) = 158 meV, not by the Mott's law for variable-range hopping. We suggest that the activation mechanism of conductivity is connected with the phase separation of the electron subsystem and the formation of so-called "foggy" state which is accompanied by a subdivison of the sample into domains with different number of carriers.

[VP05.81] Electronic Structure, Optical and Transport Properties of \beta - Phase Co_0.50Ti_0.50 Alloy Films

The influence of the structural disorder on the electronic structures, and optical and transport properties of the Co_0.50Ti_0.50 alloy films has been investigated. The disordered state in the alloy films was obtained by using vapor quenching deposition onto glass substrates cooled by liquid nitrogen. The transport properties of the ordered and disordered alloy films have been measured in a temperature range of 4.2 - 300 K. The optical properties were investigated at 293 K by spectroscopic ellipsometry in an energy range of 0.5 - 4.7 eV. The experimental optical data for the ordered CoTi compound were compared with the results of ab initio calculations based on the linearized-augmented-plane-wave method with the local-density approximation, and explained in terms of the electronic energy band structures. A reasonable agreement was achieved between the experimental and calculated optical properties of the ordered compound with the inclusion of a quasiparticle self-energy correction in the calculations. The disordered state in Co_0.50Ti_0.50 alloy is ferromagnetically ordered at 100 K. The changes in electronic structure of the Co_0.50Ti_0.50 alloy caused by the order-disorder structural transformation are interpreted based on the analyses of the obtained optical and resistivity data.

[VP05.82] Physical Properties and Electronic Structures of the B2 - Phase Co-Al Alloys

Spectroscopic ellipsometry measurements were performed to obtain the optical conductivity spectra of the ordered and disordered Co_1-xAl_x (x=0.5, 0.46 and 0.38) alloy films in the 0.5-5.5 eV range. A bulk polycrystalline equiatomic sample was also measured in the 1.5-5.4 eV range. Electronic structures, magnetic moments and optical conductivity spectra of Co_1-xAl_x (x=0.5, 0.4375 and 0.375) were calculated using tight-binding linear-muffintin-orbital method. The supercell method was employed to calculate the alloys with x different from 0.5. The equilibrium Wigner-Seitz radius decreases as x decreases. The decreasing equilibrium Wigner Seitz radius results in the band shifts. The unoccupied (occupied) bands moves toward the higher (lower) energy region. The calculated magnetic moments were in a reasonable agreement with experiment. A nonnegligible amount of charge transfer from the Al to Co atoms is important in determination of the stability and magnetic perperties. Both the antistructure Co atoms and their neighboring 8 Co atoms contribute to the magnetic moments. The inclusion of corrections for both the real and imaginary parts of self-energy markedly improves the agreement between experimental optical conductivity spectra and calculated ones.

[VP05.83] van der Waals and Casimir forces between quantum wells

We present results for the force between two quantum wells as function of separation. The force is determined in two different ways: In the first calculation it is obtained with many-body theory and the force is due to the correlation energy; in the second, the normal modes of the system are determined and the interaction energy is obtained as the total zero-point energy of these modes. Retardation is taken into account and one finds clear van der Waals and Casimir regions. We furthermore investigate the effects on the force from current flow in the wells.

[VP05.84] Magnons and solitons in the low-carrier density, one-dimensional S = 1/2 antiferromagnet Yb_4As_3

Upon cooling to below T_co \approx 293K, Yb_4As_3 undergoes a structural transition from a cubic high-temperature phase into a trigonal low-T structure. This transition is accompanied by a change in the electronic structure from a homogeneous intermediate-valence metallic state, with a Yb valence close to 2.25, to a low-T semimetallic phase, with a carrier concentration n \underline\sim 10^-3 / formula unit, characterized by a charge ordering of Yb^+3 ions along the <111> direction. As a result of a superexchange interaction among the Yb^+3 spins mediated by the surrounding As atoms, weakly coupled S = 1/2 antiferromagnetic (afm) Heisenberg chains are formed. Here we report measurements of the specific heat, thermal expansion and thermal conductivity of this compound aiming at an investigation of its low-temperature magnetic properties. A large linear in-T specific heat, C = \gammaT, \gamma\underline\sim 200mJ/K^2mole, is observed for B=0 and T<2K. This term is completely independent of the carrier concentration, which can be strongly modified by partial substitution of P or Sb for As. We attribute \gamma to the magnon excitations of afm Heisenberg chains. In finite magnetic fields, distinct anomalies were found in the above thermodynamic and transport quantities which are well described by the classical sine-Gordon soliton solutions for an easy-plane Heisenberg antiferromagnet. Our findings strongly suggest that Yb_4As_3 represents the first example of an afm S = 1/2 spin-chain system where this type of non-linear excitations could be identified.

[VP05.85] Magnetic Irreversibility and Relaxation in Assembly of Ferromagnetic Nanoparticles

Measurements of the magnetic irreversibility line and time-logarithmic decay of the magnetization are described for three Fe_2O_3 samples composed of regular amorphous, acicular amorphous and crystalline ferromagnetic nanoparticles. The relaxation rate is the largest and the irreversibility temperature is the lowest for the regular amorphous nanoparticles. The crystalline material exhibits the lowest relaxation rate and the largest irreversibility temperature. We develop a phenomenological model to explain the details of the experimental results. We propose that the time dependent barrier for magnetic moment reversal yields a natural explanation to the time-logarithmic decay of the magnetization. Interactions between particles as well as shape and crystalline magnetic anisotropies define a new energy scale that controls the magnetic irreversibility. Introducing this energy scale yields a self-consistent explanation of the experimental data.

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[VP05.86] Self-organization in type-II superconductors during magnetic relaxation

We revise applicability of the theory of self-organized criticality (SOC) to the process of magnetic relaxation in type-II superconductors. It is demonstrated that the driving parameter of self-organization of vortices is the energy barrier for flux creep and not the current density. Power spectrum of the magnetic noise due to vortex avalanches is calculated and is predicted to vary with time during relaxation.

[VP05.87] Models of Stress Propagation in Granular Media

We shall discuss some recent attempts to describe the stress propagation in granular media. Stress propagation appears to be fundamentally different in granular media and in usual elastic media, primarily due to the existence of stress paths, which collect, focuses and sometimes screens the stress field. We argue that a natural family of equations which account for these stress paths are wave like, hyperbolic equations. We establish the solution of these equations in several geometries, in particular that of the heap. We discuss the instabilities induced by small changes in boundary conditions or other perturbations, and argue that granular matter should be seen as `fragile', in a sense which we define.

[VP05.88] Detection of Magnetism in Atomic Clusters by Photon Scattering : A Theoretical Suggestion

Recent theoretical estimates indicating large magnetic moments may be carried by atomic clusters of manganese (for example, 25 Bohr magnetons for Mn_5 cluster) prompt us to suggest their detection by means of polarised optical spectroscopic methods. Our estimate for the magnetic part of the cross section for Mn_5 cluster is of the order of 10^-6, including possible resonance contribution from states near the highest occupied molecular orbital state of the cluster. This appears to be well within the accuracy of current spectroscopic techniques.

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[VP05.89] Infinite-disorder random quantum Ising critical fixed points

We implement numerically a generalization of the Ma-Dasgupta-Hu renormalization group for the random quantum Ising model in a transverse field in spatial dimensions d=2,\,3. The action of the RG is a novel aggregation/annihilation process. The quantum c ritical point is where the two balance. We found that the critical RG flows are toward strong disorder similar to d = 1. Several critical exponents characterizing the fixed point are measured and some consequences of strong disorder are also discussed. Fo r example, since frustration becomes unimportant at infinite-disorder, the same fixed point should also govern the quantum spin-glass critical point.

[VP05.90] UV Photodissociation Of Furan: Observation Of Three Primary Channels

Photodissociation dynamics of furan at 193 nm has been studied using photofragment translational spectroscopy. Three primary channels are observed two of which occur on the ground state potential energy surface

(PES) following internal conversion. One of the channels leads to the formation of free radicals and the dissociation is believed to occur from an excited PES. All channels exhibit a barrier for dissociation with the acetylene + ketene channel having the largest value at about 25

kcal/mol. Angular distribution measurements show anisotropy only for the radical channel with the other two channels exhibiting isotropic angular distributions. These findings are consistent with a rapid excited state dissociation for the radical channel and slow dissociation

for the other two pathways. The two ground state dissociation channels - propyne + CO and acetylene + ketene - should be important in the thermal decomposition of furan as was found by the pyrolytic studies of Lifshitz, et al. [A. Lifshitz, M. Bidani, and S. Bidani, J. Phys. Chem.,

90, 5373 (1986)] and the theoretical investigations of Liu, et al. [R. Liu, X. Zhou, and L. Zhai, J. Comput. Chem., 19, 240 (1998)].

Chemical Dynamics Group - LBNL

[VP05.91] Light Scattering by Landau-Quantized Electrons Driven by Intense Terahertz Radiation

Motivated by a recent experiment,^1 we investigated theoretically the scattering of weak NIR radiation (frequency Ømega) by Landau-quantized electrons in a GaAs quantum well driven by intense THz radiation (frequency ømega), treating the THz field non-perturbatively. The theory predicts a series of emission lines at Ømega \pm 2 n ømega (n=0,1,2, \dots). Their intensities I_n vary non-monotonously with the THz field E_THz: After the initial rise, they saturate, start to oscillate and eventually decay exponentially to zero. The decay is caused by the THz field driving the cyclotron centers of the electrons and holes in the opposite directions, reducing their overlap and therefore the recombination probability (dynamic electron-hole separation). This mechanism also causes I_n to oscillate with E_THz, similarly to the I-V characteristics of photon-assisted tunneling. I_n plotted against the magnetic field is peaked at a cyclotron resonance, but right at the center of the peak is a sharp cusp where I_n vanishes. This cusp also results from the dynamic electron-hole separation. ^1J.~Kono et al., PRL 79, 1758 (1997).

[VP05.92] Magnetoluminescence Investigations of the Charged Exciton in Undoped GaAs Multiple Quantum Wells

We have investigated the magnetoluminescence of the charged exciton in undoped GaAs multiple quantum wells (MQW) with different well sizes using a 60T quasi-continuous magnet. Because the radiative lifetime of the charged exciton is about ten times shorter than that of the neutral exciton (X), a slight charge imbalance due to a difference between the inter-well tunneling time of an electron and that of a heavy hole gives rise to a pronounced photoluminescence (PL) peak associated with the charged exciton. Both the negatively charged exciton (X^-) and the positively charged exciton (X^+) are identified from the laser-power dependence and circular polarization characteristics of the PL peaks originated from the MQWs. The PL intensities of the charged and neutral excitons oscillate with the magnetic field applied both parallel and perpendicular to the growth axis, but reveal opposite oscillation characteristics. These results may be explained by the magnetic-field induced changes in the density and screening effect of excess carriers in each well.

[VP05.93] Monte Carlo Simulations for the Spin-S Blume-Capel Model

The static critical properties of the two-dimensional spin S=3/2 Blume-Capel model is studied by using Monte Carlo simulations. The numerical results have been obtained from simulations on square lattices with L^2 sites where 8\le L \le 128. Long runs, about 2.4 \times 10^6 Monte Carlo steps per spins (MCS) were used to reduce the systematic and statistical errors arising due to the finite sample. The energy, magnetization and fourth-order cumulant have been obtained with the corresponding errors. Hystogram techniques, as well as finite size scaling analysis, have also been used in order to obtain the critical values. The results for the second-order phase transition show that the model is in the same universality class as the spin-1/2 Ising model, as expected. An isolated multiphase critical point is achieved at the terminus of a first-order transition line.

[VP05.94] Scaling and Universality of First Order Phase Transitions

The scaling law for first order phase transition (FOPT) is studied by using exactly solvable models and Monte Carlo simulations. We have found that the energy dissipation W during the FOPT can be scaled as W\sim R^b, where R is the varying rate of the external driving field and b is a new exponent governing the FOPT. We have proven that in mean field theory, kinetic Ising models, and N-vector models, the exponent b satisfies the scaling relation, b=1-(2z-\beta\nu)/(z+\beta\nu-1/\nu). The concenpt of scaling and universality are also shown by simulations in the Ising models. Furthermore, the rate dependent scaling for the FOPT is found by finite-size scaling of the Binder cumulant of order parameters in both the Ising and Potts model.

[VP05.95] Stepwise Electron Emission of Magnesium Autoionizing Stark States

We report on an investigation of autoionization of doubly excited magnesium atoms in a strong electric field. With a narrow band pulse one electron is excited towards a 3s16k Stark state and subsequently the second electron of the isolated core is excited with a short laser pulse. The autoionizing electron yield shows a stepwise decay which is detected by a streak camera with picosecond resolution. Full quantum calculations are in good agreement with the experimental results.

[VP05.96] A general formula for 1/f noise in homogeneous multi-terminal conductors

A general formula is derived for the power spectral densities of short-circuit 1/f noise currents for multi-terminal conductors with arbitrary geometry using the ``characteristic potentials'' (E. V. Sukhorukov and D. Loss, cond-mat/9809239). The derived formula tells us how much contribution a certain part of a homogeneous conductor makes to the terminal 1/f noise currents. For 2-terminal homogeneous resistors with uniform 1/f noise sources the derived formula reduces to the previously derived one. A direct experimental verification of the derived formula has been done using a 3-terminal polycrystalline silicon resistor.

[VP05.97] A Density Functional Study of Small Neutral and Cationic Vanadium Clusters V_n and V_n^+ (n=2-9)

All electron density functional theory with gradient corrections to the exchange and correlation functionals has been used to investigate the properties of small neutral and cationic vanadium clusters. The energetically favorable structures of vanadium clusters are found to be those with maximized average coordinations. The binding energy is found to increase monotonically with the number of atoms in the cluster and it is predicted that a significantly large number of atoms is needed to reproduce the bulk cohesive energy. Except for the neutral vanadium tetramer, the preferred decay channels for all the deutral and cationic clusters contain the vanadium atom. The average magnetic moment per atom is found to oscillate with cluster size, with an upper bound of 0.33\mu _B in the range from V_4 to V_9. Results will be compared, in detail, with available experimental and theoretical data.

[VP05.98] A New Evaluation of the Neutron Cross Section Standards

The measurements of most neutron cross sections are made relative to neutron cross section standards. These reference standards eliminate the need to measure the neutron fluence in a cross section measurement. Improvements in these standards increase the accuracy of all measurements made relative to them. The last evaluation of the standards, for ENDF/B-VI, took place over 10 years ago. At that time evaluations were produced for all the cross section standards, i.e. H(n,n), ^3He(n,p), ^6Li(n,t), ^10B(n,\alpha), C(n,n), Au(n,\gamma), and ^235U(n,f). Some additional important reactions were also evaluated. An international collaboration is now planning to update the previous work by including standards measurements made since that evaluation was completed. The work has begun with an investigation of the experiments to determine uncertainties and correlations within and among data sets. Following this work an evaluation of the H(n,n) cross section will begin. Then R-matrix evaluations, a simultaneous evaluation, and a combining procedure for these evaluations will be done, leading to final standard cross sections. The status of this work will be discussed.

[VP05.99] Effective Model of QCD in the Coulomb Gauge: Quark Sector

We model the behaviour of QCD at the hadronic scale by means of an effective Hamiltonian. As in the Nambu-Jona-Lasinio model, chiral symmetry is explicity broken, however our model contains confinement and is a priori renormalizable. Because the confining potential is linear, infrarred singularities arise in momentum space when applying many body techniques to approximately diagonalize the effective Hamiltonian. This work focuses upon the delicate numerical control of such singularities and how the hadronic mass scales are generated by chiral symmetry breaking in the vacuum of the theory. In particular we study the BCS gap equation and the Tamm-Dancoff truncation of the Fock space. The Hamiltonian is amenable to systematic improvements from further QCD refinements including effects from the gluonic sector.

[VP05.100] Phenomenological Fit of Double Pion Photoproduction

Double pion photoproduction off proton targets is studied, in the framework of Effective Lagrangian approach at tree level, based on the coupling of photons and pions to nucleons and resonances. We consider N, \Delta (1232), N(1440), N(1520) and N(1535) as intermediate baryonic states and \rho-meson as the intermediate 2 \pi resonance. The general form of the amplitude is presented and total cross sections of the \gamma p \to\pi^+\pi^- p, \gamma p \to\pi^0\pi^0 p and \gamma p \to\pi^+\pi^0 n processes are evaluated up to E_\gamma=800 MeV. We fit the experimental data to our theoretical calculation and extract some previously unknown parameters.

[VP05.101] On the Cosmological Aspects of the Observed High Energy Cosmic Phenomena

Super-high energy corpuscular and gamma rays as well as cosmic sources of high energy density (quasars, jetting objects, gamma bursts) are hard to be explained in a galaxy model framework. Attemts to include some of those phenomena in the Standard Cosmological Model also encounter serious difficulties. In the presented paper an alternative cosmological model is discussed. There are several features of the model. First of all, the whole Universe (Grand Universe) is a multitude of tipical universes, like ours, evenly made of either matter or antimatter, hence, there is no violation of barion symmetry on the largest scale. Second, high energy processes are the result of matter-antimatter annihilation processes during a tipical universe evolution. Finally, the Ground Universe is a self-creating due to a balance of annihilation and pair creation processes in a inter-universe infinite space. This model and its consistence with the major observational data are discussed in detail

[VP05.102] Universe as an Expanding Phase Boundary in a 4-d Euclidean Space

It is proposed that space is a four-dimensional Euclidean space with universal time. Originally this space was filled with a uniform substance, pictured as a liquid, which at some time became supercooled. Our universe began as a nucleation event initiating a liquid to solid transition. The universe we inhabit and are directly aware of consists of only the three-dimensional expanding phase boundary. Random energy transfers to the boundary from thermal fluctuations in the adjacent bulk phases are interpreted by us as quantum fluctuations. Fermionic matter is modeled as screw dislocations; gauge bosons as phonons. Minkowski space and special relativity emerge dynamically through redefining local time to be proportional to the spatial coordinate perpendicular to the boundary. Other features include a geometrical quantum theory of gravity, and an explanation of quantum measurement through classical symmetry breaking.

[VP05.103] Simulation of atomic ionization following \alpha decay

When the nucleus of an atom decays by emitting an \alpha particle, the surrounding electrons are perturbed and the atom may be ionized. We consider two schematic one-dimensional models that simulate the ionization process. In the first model the \alpha particle is treated as a classical point charge that is emitted by the nucleus at a certain time and travels out at constant speed. In the second model the \alpha particle is treated as a quantum mechanical wave that slowly leaks out from the nucleus. The first model simulates Migdal's method(A. Migdal, J. Phys. (U.S.S.R.) 4), 449 (1941). that has been adopted in practically all the calculations done so far for the ionization process and which gives reasonable agreement with experiment. The second model, which treats the \alpha particle quantum mechanically, is also expected to lead to correct results. The ionization probability calculated using the second model is, however, much smaller than that of the first. Implications of this difference are discussed.

[VP05.104] Cavity-QED Enhanced Morphology Dependent Resonances at Small Size Parameter

We report the observation of cavity-QED enhanced morphology dependent resonances (MDR) in micron-size optically trapped droplets. Ethylene glycol droplets doped with Rhodamine-590 dye are trapped by counter-propagating 800-nm laser beams in a 20-\mum inner diameter hollow-core fiber. A low power 532-nm laser is also directed into the fiber and excites the dye. Fluorescence light from the droplet is collected through the glass fiber's wall. A series of MDR increasing in width and eventually vanishing is observed as the droplet evaporates from size parameter 30 to 10. The spectrum between size parameter 26 and 10 clearly shows first and second order TE and TM sequences of MDR distinguished by narrow and broad peaks. At this size parameter the widths of the first and second mode orders differ by a factor 10^3. Below size parameter 15 the first orders MDR broaden and vanish at approximately size parameter 12. The experimental spectrum is compared to MIE scattering calculations, and the kinetic evaporation rate and droplet size determined.

[VP05.105] A New Eigenvalue Problem Associated with the Two Dimensional Newcomb Equation without Continuous Spectra

A new eigenvalue problem associated with the two-dimensional Newcomb equation in an axisymmetric toroidal plasma, such as a tokamak, has been posed. In the formulation of the eigenvalue problem, the weight functions (the kinetic energy integral) and the boundary conditions at rational surfaces are chosen such that the spectra of the eigenvalue problem are comprised of only the real and denumerable eigenvalues (point spectra) without continuous spectra. Applications to the ideal m = 1 mode have verified that this formulation is able to identify stable states as well as unstable states, and that the numerically obtained eigenfunctions show the singular behavior predicted by the theory at rational surfaces.

[VP05.106] Surface-Enhanced Electronic Raman Scattering from Self-Assembled Alkanethiol Monolayers on Gold Surfaces

A preliminary model is presented that describes the observed surface-enhanced electronic Raman scattering spectrum of self-assembled alkanethiol monolayers on roughened Au surfaces and Au colloidal films. At room temperature, a series of intense resonance Raman spectral lines, superimposed on the normal surface-enhanced Raman vibrational spectrum, are produced when monolayers of C_nH_2n+1SH, where n includes numbers from 9 to 18, are illuminated with laser radiation between 630 and 740 nm. We describe the effects of isotopic substitution, and of varying both the alkane chain length and temperature of the monolayer films.

[VP05.107] Stimulated Raman Scattering and Stimulated Emission Pumping Effects on Optical Pulse Propagation and Population Transfer in Molecular Vapor

It is generally understood that Stimulated Raman Scattering is the principle gain mechanism in diatomic alkali based optically pumped lasers. We discuss the different spatial regimes in which Stimulated Raman Scattering or Stimulated Emission Pumping dominate the gain mechanism as pump and probe laser emissions propagate through molecular potassium vapor. In a three level laser, the pump laser emission is tuned from a thermally populated level |1> in the K_2 X state to an unpopulated level |2> in the K_2 B state. The probe laser is tuned to the level |2> to level |3> transition in the K_2 X state. We also discuss the resulting linewidths of the optically pumped laser and the population transfer from |1> to |3>. Experimental and numerical results are included.

[VP05.108] Collective Amplified Emission of Light and Atoms from a Bose-Einstein condensate

When a cigar-shaped anisotropic Bose-Einstein condensate was exposed to a single near-resonant laser beam, we observed highly directional emission of light and atoms. This effect is explained by collective amplified Rayleigh scattering. In contrast to other stimulated processes, this effect does not rely on optical feedback, but is solely due to stimulation by the atomic field. Time-resolved signals reflect the spontaneous nature (quantum fluctuations) of the scattering process.

[VP05.109] The optical-mechanical analogy for stationary metrics in general relativity

The optical-mechanical analogy allows for a common description of the motion of particles in mechanics and for light in geometrical optics. Recently, it has been shown that the optical-mechanical analogy can be extended to general relativity for the case of static metrics expressible in isotropic coordinates. (J.Evans, K.K. Nandi and A. Islam, Am. J. Phys. \textbf64), 1404 (1996); Gen. Relativ. Gravit. \textbf28, 413 (1996). In this work we extend the optical-mechanical analogy in general relativity to the case of stationary metrics. (P.M. Alsing, Am. J. Phys. \textbf66), 779 (1998). A variational principle for the trajectories of both photons and particles is derived which takes the form of Fermat's principle or the principle of Maupertuis. When the (suitably defined) spatial portion of the metric is written as or restricted to an isotropic form, exact equations of motion for both massless and massive particles are obtained in the form of Newtonian mechanics, describing objects moving in a medium with a spatially varying index of refraction. Such restrictions of the metric commonly occur, for example, when orbital motion is considered in a plane perpendicular to the axis of rotation of a rotating black hole or spacetime. The Newtonian form of the equations of geodesic motion are illustrated by applications to a uniformly rotating reference system and a rotating black hole (the Kerr metric).

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