We have simulated the uniquely interacting orbits of these fifth and sixth moons of Saturn. With a mean radial separation less than the diameter of either body, and nearly equal orbital velocities, the two satellites circle around Saturn relatively unaffected by each other until the inner satellite begins to ``catch up'' to the outer one. When this occurs, the inner satellite is boosted into a higher orbit, while the outer satellite is dropped into a lower orbit. For simplicity, a two--dimensional closed system was considered, with calculated interactions between Saturn and each satellite as well interactions between the two satellites. Various FORTRAN program--generated graphs demonstrate the interactive behavior. The two moons are visually recorded exchanging orbits in a time that agrees with mathematical calculations, providing support to the claim that the satellites do indeed maintain a co--orbital relationship.
[G.02] An N-Body Simulation of the Origin of the Oort Cloud Comets
Maureen E. Connolly, S.G. Alexander (Miami University)
We have simulated the ejection of planetesimals from the planetary region of the solar system by close encounters with the gas giant planets. Many of these planetesimals are ejected into orbits which have large semimajor axes that have aphelia in the region of the Oort Cloud. A two--dimensional gravitational N-body code has been modified so that the planetesimal orbits are perturbed only by the four gas giant planets; i.e. the planetesimals don't exert gravitational forces on each other. We present the results of two one million year simulations of the orbital evolution of identical planetesimals. The first simulation concentrates the planetesimals in initially circular orbits in the region of the terrestrial planets, and the second concentrates them near the gas giant planets. We find that after one million years of simulation time that many more planetesimals that started in the gas giant region are ejected into long semimajor axis orbits that will take them to the Oort Cloud than those planetesimals that were initially in the terrestrial region. This result is consistent with the fact that cometary bodies originating in the Oort cloud contain large concentrations of ices and could not have originated in the terrestrial region of the solar system.
[G.03] Branching Fractions and Oscillator Strengths for Astrophysical Modeling
F. S. Sultan, N. D. Gibson (Department of Physics and Astronomy, Denison University, Granville, OH 43023)
One of the fastest growing research areas today is the study and analysis of uv astrophysical data that has recently become available from new observational instruments unhampered by the earth's atmosphere. In order to model stellar spectra in astrophysics, high quality laboratory data on oscillator strengths and branching fractions are desperately needed. The branching fractions are measured by observing laboratory plasmas with a radiometrically calibrated 2 meter spectrometer equipped with a thermoelectrically cooled photodiode array. The direct oscillator strength measurements are performed on gaseous samples using the method of self-absorption of resonance radiation. An important overlap with research areas of industrial significance is found in new and efficient lighting systems and flat panel display screens.
[G.04] Spectroscopy of High-Redshift Quasars
Joseph Shields (Ohio U.), Fred Hamann (UC-San Diego)
The most distant known galaxies in the Universe are detected as quasars, which exhibit unusually luminous centers that are believed to be powered by massive black holes. A growing number of quasars are now known at redshifts z > 4, corresponding to an epoch when the Universe was less than 20% of its current size and age. This paper will present recent results from a program of optical (rest-frame ultraviolet) spectroscopy of z > 4 quasars conducted with the Multiple Mirror Telescope in Arizona. The results provide new insights into the small-scale structure of these energetic sources, as well as the evolution of the galaxies that host them.
[G.05] Reducing Instrument Baseline Fluctuations by Stabilizing Temperature in a Millimeter Wave SIS Receiver for Measuring Trace Gases in the Stratosphere
Jason Young (Allegheny College)
Several gases can deplete the amount of ozone in the stratosphere by acting as a catalyst in the ozone depletion reaction. Since these gases are not consumed by the reaction, a single molecule of a given trace gas can eliminate tens of thousands of ozone molecules. In reality, the amount of such unwanted gases in the stratosphere is very small, typically a few parts per billion. One method of remotely sensing these trace gases is to measure the faint but characteristic millimeter wave emission spectra given off by a particular trace gas. The millimeter wave receiver and spectrometer used for this purpose has an extremely high gain, and is subject to standing wave interference patterns, whose amplitude and phase are temperature dependent. In order to obtain stable performance, the operating temperature must be well controlled. We assembled and tested a temperature control circuit which is easily adjusted to produce a desired temperature, via a 50 watt heater. The circuit operates with a continuous feedback mode to allow constant control of the heater's thermal output. Unlike most ordinary thermostats in homes and businesses, the heater controls temperature with a continuous range of flow rather than simply by an on/off switch. By the nature of the feedback system, the temperature remains almost constant at some desired value, eliminating unwanted overshoot effects.
[G.06] Magnetic Anisotropy and Coupling in Epitaxial Co/Cr Trilayers on MgO(100) and MgO(110) Substrates
J. Zachary Hilt, Alexandra V. O'Brien, J. Johanna Picconatto, Michael J. Pechan (Miami University), Eric E. Fullerton (Argonne National Lab)
Trilayers of Co(15ÅCr(x)/Co(17Åhave been epitaxially sputtered onto MgO (100) and(110) substrates coated with epitaxial Cr(100) and (211) buffer layers. The Cr thickness x is varied from 6 to 50ÅOn the MgO(110)/Cr(211) substrates, coherent hcp-Co(1øverline100)/bcc-Cr(211) structures are formed. On MgO(100)/Cr(100) the trilayers grow in a strained hcp Co(11øverline20) / Cr(100) structure. Both of these structures result in the Co c-axis lying in the plane of the film, however, due to the four-fold symmetry of MgO(100), Co bicrystals exist in that system with perpendicularly orieted c-axes. Ferromagnetic resonance measurements clearly show two-fold magnetic in-plane anisotropy for all samples grown on MgO(110) and four-fold for those grown on MgO(100). Magnetization measurements indicate an interlayer coupling strength peaked at a Cr thickness of approximately 10ÅThe interlayer coupling strength fell off more rapidly with Cr thickness in the MgO(110) system than in the MgO(100).
[G.07] Magnetic Field Profiles obtained by means of a GMR-based Sensor
Christopher Baker, Heather Pounds, Joe Priest, Dan Lottis
An inexpensive and easily implemented way of measuring spatially-varying fields will be described. The technique utilizes a commercially available sensor that is based on an effect known as Giant Magnetoresistance (GMR) to provide a signal that, within a certain range, varies linearly with the magnetic field. Because of the small size of the sensor's active area, it can serve as a local probe of field strength in a sub-millimeter region. A sample placed on a translation stage can be scanned past the sensor, resulting in a B vs. position measurement. Profiles will be shown for fields produced by several types of permanent magnet as well as for a current-bearing wire. Results obtained using the GMR-based sensor will be compared to profiles obtained using a Hall probe. Suggestions will be made for the incorporation of this technique into instructional laboratories.
[G.08] Low Frequency Magnetic & Electrical Properties of Iron Microcomposites
Jacilyn Wilkins (Allegheny College)
Magnetic properties of iron microcomposites of varying concentrations of Fe mixed with a high performance, LARC SI, were studied from hysteresis measurements. The properties considered included the permeability, coercivity, and the saturation magnetization of each sample of the varying concentration Fe microcomposite. Although the primary focus of this research has been on the magnetic properties of iron microcomposites, the electrical properties are equally important. Further research is being done concerning these properties.
[G.09] Effects of external and anisotropy fields on the magnetization of two-dimensional q-state clock models
P. D. Scholten (Miami University, Oxford OH 45056)
Monte Carlo simulations were performed on two-dimensional q- state clock models subject to both an external field and a uniaxial anisotropy field. For temperatures below the paramagnetic transition the direction of the net magnetization was studied as a function of the angle and strength of the applied field. All angles were measured with respect to the anisotropy axis. Effects of temperature, lattice size, and number of spin states (q) were also examined. It was found in general that the relative angle between the magnetization and applied field increased smoothly as applied field angle increased. But as the applied field angle approached 90^o, the average relative angle dropped sharply to zero. The magnetization angle distribution function showed that this behavior was due to the uniaxial anisotropy. At large applied field angles it became more favorable for the magnetization to be an angle of 180^o-\theta as well as at \theta.