Physics Commons^™

Critical Dynamics Of Nonconserved Ising-Like Systems, K. E. Bassler, Beate Schmittmann

Beate Schmittmann

We show that the dynamical fixed point of Ising-like models, characterized by a single scalar, nonconserved ordering field, is stable near four dimensions with respect to all dynamic perturbations, including those of a nonequilibrium nature.

Resolving A Conflict Between Coherence Theory And Classical Radiometry, Incoherent Planar Sources Are Lambertian, Dorothy M. Seitz

Honors Capstone Projects and Theses

No abstract provided.

Formation Of Shape-Preserving Pulses In A Nonlinear Adiabatically Integrable System, R. Grobe, Foek T. Hioe, J. H. Eberly

Physics Faculty/Staff Publications

No abstract provided.

Calculus-Based Physics Exploratory Study: Summary Report, Illinois Mathematics And Science Academy

Documents

During the 1992-1993 academic year a number of elements (national level surveys and research reports, IMSA’s professional development focus; a climate of reflective inquiry) focused attention on the participation and achievement of females in mathematics and science at a national level and, specifically, the participation and achievement of females in mathematics and science at the Illinois Mathematics and Science Academy. These elements served as the catalyst for the calculus-based physics exploratory study.

Mössbauer Spectroscopic And Magnetic Studies Of Magnetoferritin, Q. A. Pankhurst, S. Betteridge, D. P. E. Dickson, T. Douglas, Stephen Mann, Richard B. Frankel

Physics

Mössbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (γ-Fe₂O₃) rather than magnetite (Fe₃O₄).

Magnetotaxis And Magnetic Particles In Bacteria, Richard B. Frankel, Dennis A. Bazylinski

Physics

Magnetotactic bacteria contain magnetic particles that constitute a permanent magnetic dipole and cause each cell to orient and migrate along geomagnetic field lines. Recent results relevant to the biomineralization process and to the function of magnetotaxis are discussed.

Low-Energy Differential Scattering Of Electrons And Positrons From Noble Gases, David D. Reid, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Calculations of cross sections for electron (e⁻) and positron (e⁺) scattering from ground-state He, Ne, Ar, Kr, and Xe at projectile energies below the lowest inelastic thresholds are presented. The main focus in the present work is on the differential cross sections, since angular distributions depend sensitively on the choice of interaction potentials used in the calculations. A part of the interaction potential used in the calculations includes a parameter-free correlation-polarization potential which is (a) based on physical ideas of what a correlation-polarization potential should be, (b) different for various target gases, and (c) distinct for …

Kinetics Of Clustering In Traffic Flows, E. Ben-Naim, P. L. Krapivsky, S. Redner

Eli Ben-Naim

We study a simple aggregation model that mimics the clustering of traffic on a one-lane roadway. In this model, each ``car'' moves ballistically at its initial velocity until it overtakes the preceding car or cluster. After this encounter, the incident car assumes the velocity of the cluster which it has just joined. The properties of the initial distribution of velocities in the small velocity limit control the long-time properties of the aggregation process. For an initial velocity distribution with a power-law tail at small velocities, $\pvim$ as $v \to 0$, a simple scaling argument shows that the average cluster size …

Optical-Fiber Preamplifiers For Ladar Detection And Associated Measurements For Improving The Signal-To-Noise Ratio, Michael S. Salisbury, Paul F. Mcmanamon, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

In an effort to increase achievable postdetection signal-tonoise ratios (SNRs) of continuous-wave, 1-gm all-solid-state ladar systems, a prototype rare-earth-doped optical-fiber amplifier has been included in the optical return signal path of both a heterodyne and a directdetection ladar system. We provide numerical predictions for SNR increases according to our previously developed theory. We also detail our experimental efforts and provide the results of SNR measurements for four distinct cases: direct ladar detection with and without a fiber amplifier, and heterodyne ladar detection with and without a fiber amplifier. Experimentally measured increases in SNRs for ladar systems incorporating an optical-fiber amplifier …

Discrete Symmetries And Isosinglet Quarks In Low-Energy Supersymmetry, Diego Castano, Stephan P. Martin

Chemistry and Physics Faculty Articles

Many extensions of the minimal supersymmetric standard model contain superfields for quarks which are singlets under weak isospin with electric charge -13. We explore the possibility that such isosinglet quarks have low or intermediate scale masses, but do not mediate rapid proton decay because of a discrete symmetry. By imposing the discrete gauge anomaly cancellation conditions, we show that the simplest way to achieve this is to extend the Z₃ “baryon parity” of Ibáñez and Ross to the isosinglet quark superfields. This can be done in three distinct ways. This strategy is not consistent with grand unification with a …

Review Of "Modern Physics From Α To Z°" By J. W. Rohlf, Peter J. Collings

Physics & Astronomy Faculty Works

No abstract provided.

Energy Spread And Ion Current Measurements Of Several Ion Sources, A. D. Gaus, W. T. Htwe, J. A. Brand, Timothy J. Gay, M. Schulz

Timothy J. Gay Publications

Energy spread and extracted current measurements are presented for five different types of ion sources: hot cathode, cold cathode, magnetron, microwave, and electron cyclotron resonance (ECR). The measurements were performed with a 45° parallel-plate energy analyzer with a resolution of better than 0.5 eV at 500 eV incident energy. Energy spreads ranged from 0.5 to 4 eV, while total extracted beam currents ranged from 2 to 30 μA. Beam currents due specifically to protons, ³He⁺⁺ ions, and H⁺₂ ions are also presented. The ECR and magnetron sources gave the best overall performance. These, along with the …

Electron-Beam-Induced Patterned Deposition Of Allylcyclopentadienyl Palladium Using Scanning Tunneling Microscopy, D.S. Saulys, A. Ermakov, E.L. Garfunkel, Peter A. Dowben

Peter Dowben Publications

Scanning tunneling microscopy has been used to study the electron-induced decomposition of allylcyclopentadienyl palladium [Pd(η³-C₃H₅)( η⁵-C₅H₅)] and subsequent deposition on a Si(111) surface. Deposition occurs via an electron impact mechanism on either the tip or surface, depending on the bias polarity, and is observed with voltages of 2.75 V. This is close to the predicted condensed phase dissociation energy of 2.3 eV for Pd(η³-C₃H₅)(η⁵-C₅H₅)→Pd+C₃H₅+C₅H₅. Metallic deposits of nanometer …

Portable, High-Bandwidth Frequency-Domain Photon Migration Instrument For Tissue Spectroscopy, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg

All HMC Faculty Publications and Research

We describe a novel frequency-domain photon migration instrument employing direct diode laser modulation and avalanche photodiode detection, which is capable of noninvasively determinating the optical properties of biological tissues in near real time. An infinite medium diffusion model was used to extract absorption and transport scattering coefficients from 300-kHz to 800-MHz photon-density wave phase data. Optical properties measured in tissue-simulating solutions at 670 nm agreed to within 10% of those expected.

Determination Of The Bulk Modulus Of A Lennard-Jones Solid, Spencer A. Van Roekel

Masters Theses

The quantum Monte Carlo method is used to determine the bulk modulus of a Lennard-Jones solid. The quantum Monte Carlo method is discussed in detail and is compared with other numerical methods used previously.

The zero pressure bulk modulus of a Lennard-Jones solid is computed at a number of different temperatures and compared with experimental data.

An Experimental Apparatus For Studying Double Differential Scattering By Low-Energy Multiply Charged Ions From Atomic Targets, Meenatchi S. Gopinathan

Masters Theses

A new differential energy-gain spectrometer with a movable parallel-plate electrostatic energy analyzer has been constructed and tested for the study of double differential (in energy and angle) cross sections for state-selective electron capture processes in collisions of low-energy multiply charged ions with atomic gases. The ion beam is produced by extracting recoil ions from a primary interaction region where these ions are generated in collisions between a neutral target gas and a fast fluorine beam from the WMU tandem Van de Graaff accelerator. An einzel lens is used to focus the ion beam extracted from the recoil-ion source into a …

Absolute Photonic Band Gaps Of Zincblende, Ulrich Bass

Masters Theses

One concept of examining the propagation of an electromagnetic wave through a periodic structure is the dispersion curve which relates the frequency of the propagating wave to its wave vector. In some cases frequency ranges occur where no propagation is possible. These ranges are called absolute photonic band gaps as far as periodic dielectric structures are concerned.

In my thesis I am interested in the dispersion curve of a Zincblende type dielectric array. Zincblende is a diamond-like structure and it has been shown that diamond structures possess absolute photonic band gaps. In studying Zincblende we want to gain deeper insight …

Small Polarons And The Electronic Properties Of Mo2S3, Adilgiry A. Kusov, Roger D. Kirby

Department of Physics and Astronomy: Faculty Publications

We investigate the small-polaron mechanism as a possible explanation of electrical-conduction and electrical-noise properties of the linear chain material Mo₂S₃. Experimental conductivity and noise data obtained in earlier papers [Phys. Rev. B 38, 3973 (1988); Phys. Rev. B 39, 5139 (1989)] are analyzed in terms of a small-polaron mechanism and double-well potential model. We interpret the observed electronic properties in terms of kinetic equations describing the interaction of free carriers with fluctuations of density of the lattice. Appropriate kinetics equations to describe this interaction, which leads to small-polaron formation, are derived. These equations are found to …

Further Thoughts On Newton's Zero-Order Rainbow, James A. Lock, Timothy A. Mccollum

Physics Faculty Publications

A zero-order rainbow angle may be defined as the relative minimum angle of deviation of geometrical light rays transmitted without internal reflections through a transparent particle. If the incident rays are parallel and the particle is a sphere, such a minimum does not exist. But if the incident rays ale not parallel or if the particle has an elliptical rather than circular cross section, an angle of minimum deviation, hence a zero-order rainbow, can occur. For a spherical water droplet, the zero-order rainbow will occur when a point source is placed less than a droplet radius away from its surface. …

Frame Selection Performance Limits For Statistical Image Reconstruction Of Adaptive Optics Compensated Images, Stephen D. Ford

Theses and Dissertations

The U.S. Air Force uses adaptive optics systems to collect images of extended objects beyond the atmosphere. These systems use wavefront sensors and deformable mirrors to compensate for atmospheric turbulence induced aberrations. Adaptive optics greatly enhance image quality; however, wavefront aberrations are not completely eliminated. Therefore, post-detection processing techniques are employed to further improve the compensated images. Typically, many short exposure images are collected, recentered to compensate for tilt, and then averaged to overcome randomness in the images and improve signal-to-noise ratio. Experience shows that some short exposure images in a data set are better than others. Frame selection exploits …

Feasibility Exploration Of Throughfold As A Predictor For Target Loading And Associated Error Bounds, Kris G. Rongone

Theses and Dissertations

Various applications of the Fredholm integral equation appear m different fields of study. An application of particular interest to the Air Force arises in determination of target loading from nuclear effects simulations. Current techniques first unfold the incident spectrum then determine target loading; resulting spectrum and loading are assumed exact. This study investigates the feasibility of a new method, through-fold, for directly determining defensible error bounds on target loading. Through-fold uses a priori information to define input data and represents target response with a linear combination of instrument responses plus a remainder to derive a quadratic expression for exact target …

Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell

Theses and Dissertations

The research reported here investigated the use of a shearing interferometer (SI) wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SI's six cameras, …

Detecting Alpha Particles Through Scintillation In Porous Materials, Martin E. Keillor

Theses and Dissertations

This thesis presents the results of a preliminary study of parameters essential to the development of a scintillation flow-cell detector with improved characteristics over existing cells. Such a detector with better than 10% alpha energy resolution could provide in situ capability to detect and identify important alpha-emitting radionuclides in dilute aqueous solutions. Gel-silica is a potential candidate that may provide the needed improvement in resolution while maintaining 100% detection efficiency; however, gel-silica with useful light output is yet to be developed. As a step toward realizing the system described, the dependence of alpha detection efficiency and intrinsic energy resolution on …

Multispectral Detection Of Ground Targets In Highly Correlated Backgrounds, Jason E. Thomas

Theses and Dissertations

Multispectral detection methods attempt to discriminate targets in a dominant clutter background using multiple images of the same real-world scene taken in different narrow spectral bands in the infrared. Detection is possible due to the empirically observed phenomenon that the radiance of man-made objects, such as a tank or truck, often lies off the main spectral correlation axis of that of natural backgrounds. Radiometric measurements of several vehicles and a tree canopy background taken over three days in June. 1994 were used to examine the factors affecting multispectral detection. Results clearly showed that the processes which provide for higher spectral …

Generation Of A Single-Lobe, Far-Field Intensity Pattern From A Laser Diode Array Using An Optical Delay Line, Thomas A. Summers

Theses and Dissertations

A simple and practical technique is demonstrated to generate a stable, single-lobe, far-field intensity pattern from a one-dimensional, antiphased, laser diode array with gain-guided elements. The two far-field lobes of the array are combined after introducing an optical delay line into the path of one of the lobes to make the lobes mutually incoherent. The incoherent superposition of intensities produces a near-diffraction-limited, single-lobe, far-field intensity pattern containing 84% of the power, exceeding any previous (known) phase control experiments. This technique compares favorably with more elaborate schemes advanced previously using integrated phase plates, etc. The method is directly applicable to one-dimensional …

Laser Beam Propagation In Non-Kolmogorov Atmospheric Turbulence, Bruce E. Stribling

Theses and Dissertations

Several observations of atmospheric turbulence statistics have been reported which do not obey Kolmogorov's power spectral density model. These observations have prompted the study of optical propagation through turbulence described by non-classical power spectra. This thesis presents an analysis of optical propagation through turbulence which causes index of refraction fluctuations to have spatial power spectra that obey arbitrary power laws. The spherical and plane wave structure functions are derived using Mellin transform techniques and are applied to the field mutual coherence function (MCF) using the extended Huygens-Fresnel principle. The MCF is used to compute the Strehl ratio of a focused, …

Measurement Of N2+ Mobility In He Via Fourier Transform Emission Spectroscopy, Patrick D. Kee

Theses and Dissertations

Recently, Hong and Miller used Fourier Transform Emission (FTE) spectroscopy to determine the N₂⁺ mobility in helium by relating the observed Doppler shift of the N₂⁺ (B-X) transition to the measured electric field in the discharge as determined by probes. In order to establish the technique in-house, this effort duplicated that experiment and investigated the sensitivity and utility of the method. Doppler shift measurements in this experiment disagreed significantly with those reported by Hong and Miller. Attempts to reduce the data (and thus determine the mobility) using a model developed by Hong and Miller were unsuccessful. …

Analysis Of Instability Growth And Collisionless Relaxation In Thermionic Converters Using 1-D Pic Simulations, Bret B. Kreh

Theses and Dissertations

This work investigates the role that the beam-plasma instability may play in a thermionic converter. The traditional assumption of collisionally dominated relaxation is questioned, and the beam-plasma instability is proposed as a possible dominant relaxation mechanism. Theory is developed to describe the beam-plasma instability in the cold-plasma approximation, and the theory is tested with two common Particle-in- Cell (PIC) simulation codes. The theory is first confirmed using an unbounded plasma PIC simulation employing periodic boundary conditions, ES1. The theoretically predicted growth rates are on the order of the plasma frequencies, and ESl simulations verity these predictions within the order of …

The Photonic Band Structure Of Dielectric Systems With A Frequency Dependent Dielectric Function, Jiezhou Liu

Masters Theses

The concepts of band theory for electrons can be employed to describe the behavior of electromagnetic waves propagaiting in periodic dielectric structures with a frequency independent dielectric function. These periodic structures can produce photonic band gaps in which the propagation of electromagnetic waves is strictly prohibited. The introduction of a frequency dependent dielectric function in such systems gives rise to strong changes of the photonic bands in the neighborhood of the frequency resonance of the dielectric function.

In my thesis, the photonic band structure of a dielectric system with a frequency dependent dielectric function which undergoes a dielectric resonance will …

The Spectral Center Of Gravity Effect And Auditory Filter Bandwidth, Marc Fagelson, Linda M. Thibodeau

Marc A. Fagelson