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1994

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Articles 1 - 30 of 245

Full-Text Articles in Physics

Formation Of Shape-Preserving Pulses In A Nonlinear Adiabatically Integrable System, R. Grobe, Foek T. Hioe, J. H. Eberly Dec 1994

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.


Discotic Micellar Nematic And Lamellar Phases Under Shear-Flow, J. T. Mang, Satyendra Kumar, B. Hammouda Dec 1994

Discotic Micellar Nematic And Lamellar Phases Under Shear-Flow, J. T. Mang, Satyendra Kumar, B. Hammouda

Physics Publications

Small-angle neutron scattering was employed to study the effect of shear flow on the nematic (N) and lamellar (L(alpha)) phases in aqueous solutions of cesium perfluoro-octanoate. Shear rates as high as similar to 4000 s(-1) were used. The N phase was found to align with the director in the direction of the gradient velocity. The L, phase oriented with lamellae parallel to the shear plane. This change in equilibrium orientation is attributed, primarily, to changes in the value of the Ericksen viscosity parameter at. Subtle shear-rate-dependent director reorientations were also observed in the proximity of the N-to-L(alpha ...


Low-Energy Differential Scattering Of Electrons And Positrons From Noble Gases, David D. Reid, J. M. Wadehra Dec 1994

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 electron and positron scattering ...


Portable, High-Bandwidth Frequency-Domain Photon Migration Instrument For Tissue Spectroscopy, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg Dec 1994

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.


Discrete Symmetries And Isosinglet Quarks In Low-Energy Supersymmetry, Diego Castano, Stephan P. Martin Dec 1994

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 ...


Calculus-Based Physics Exploratory Study: Summary Report, Illinois Mathematics And Science Academy Dec 1994

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

1990-2000 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.


Energy Spread And Ion Current Measurements Of Several Ion Sources, A. D. Gaus, W. T. Htwe, J. A. Brand, Timothy J. Gay, M. Schulz Dec 1994

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 ...


Magnetotaxis And Magnetic Particles In Bacteria, Richard B. Frankel, Dennis A. Bazylinski Dec 1994

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.


Mössbauer Spectroscopic And Magnetic Studies Of Magnetoferritin, Q. A. Pankhurst, S. Betteridge, D. P. E. Dickson, T. Douglas, Stephen Mann, Richard B. Frankel Dec 1994

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).


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 Dec 1994

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 ...


Further Thoughts On Newton's Zero-Order Rainbow, James A. Lock, Timothy A. Mccollum Dec 1994

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 ...


Electron-Beam-Induced Patterned Deposition Of Allylcyclopentadienyl Palladium Using Scanning Tunneling Microscopy, D.S. Saulys, A. Ermakov, E.L. Garfunkel, Peter A. Dowben Dec 1994

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 ...


Review Of "Modern Physics From Α To Z°" By J. W. Rohlf, Peter J. Collings Dec 1994

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

Physics & Astronomy Faculty Works

No abstract provided.


Small Polarons And The Electronic Properties Of Mo2S3, Adilgiry A. Kusov, Roger D. Kirby Dec 1994

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

Faculty Publications, Department of Physics and Astronomy

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 explain ...


Symmetry, Spin-Orbit Interactions, And Spin Anisotropies, Taner Yildirim, A. Brooks Harris, Ora Entin-Wohlman, Amnon Aharony Nov 1994

Symmetry, Spin-Orbit Interactions, And Spin Anisotropies, Taner Yildirim, A. Brooks Harris, Ora Entin-Wohlman, Amnon Aharony

Department of Physics Papers

The origins of anisotropy in the effective spin Hamiltonian, describing the ground manifold of Hubbard models with spin-orbit interactions, are critically discussed. For tetragonal symmetry, we show exactly that spin anisotropy can arise only if one includes both spin-orbit and Coulomb exchange interactions. For lower symmetries, additional anisotropies arise from terms which were hitherto neglected. Our analytic results are supported by numerical solutions for single bond clusters. These results can explain the easy plane anisotropy in the antiferromagnetic cuprates.


Improved Frequency Response Measurements In The Human Visual System, Yuping Chen Nov 1994

Improved Frequency Response Measurements In The Human Visual System, Yuping Chen

FIU Electronic Theses and Dissertations

The temporal frequency response characteristics of the human visual system have been investigated by combining the increment threshold and sinusoidal flicker methods. Gain and phase spectra were obtained for two subjects using improved equipment and methodology compared with previous investigations. While the output of the system for sinusoidal input stimuli was generally also sinusoidal, as required for a linear system, other non-linearities emerged. Gain spectra for both subjects indicated a low-pass filtering action. Phase spectra showed a possible low frequency phase lead followed by a high frequency lag. Earlier studies suggested that the system might be a minimum phase system ...


Iron Core Formation In Horse Spleen Ferritin: Magnetic Susceptibility, Ph, And Compositional Studies, S. Hilty, B. Webb, Richard B. Frankel, G. D. Watt Nov 1994

Iron Core Formation In Horse Spleen Ferritin: Magnetic Susceptibility, Ph, And Compositional Studies, S. Hilty, B. Webb, Richard B. Frankel, G. D. Watt

Physics

Horse spleen ferritin (HoSF) reconstituted with small iron cores ranging in size from 8 to 500 iron atoms was studied by magnetic susceptibility and pH measurements to determine when the added Fe3+ begins to aggregate and form antiferromagnetically coupled clusters and also to determine the hydrolytic state of the iron at low iron loading. The Evans NMR magnetic susceptibility measurements showed that at iron loadings as low as 8 Fe3+/HoSF, at least half of the added iron atoms were involved in antiferromagnetic exchange interactions and the other half were present as isolated iron atoms with S = 5 ...


Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine Nov 1994

Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine

Ames Laboratory Publications

The effect of changing stress on the magnetization of ferromagnetic materials leads to behavior in which the magnetization may increase, or decrease, when exposed to the same stress under the same external conditions. A simple empirical law seems to govern the behavior when the magnetization begins from a major hysteresis loop. The application of the law of approach, in which the derivative of the magnetization with respect to the elastic energy supplied dM/dW is proportional to the magnetization displacement M anM, is discussed.


Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles Nov 1994

Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles

Ames Laboratory Publications

An extension of the hysteresis model has been developed that takes into account the effects on the hysteresis curves of eddycurrents in electrically conducting media. In the derivation presented it is assumed that the frequency of the applied field is low enough (or the thickness of the material medium small enough) that the skin effect can be ignored so that the magnetic field penetrates uniformly throughout the material. In this case, the dc hysteresis equation is extended by the addition of a classical eddy‐current‐loss term depending on (i) the rate of change of magnetization with time, (ii) the ...


Surface Core-Level Shifts And Atomic Coordination At A Stepped W(110) Surface, D. Mark Riffe, B. Kim, J. L. Erskine, N. D. Shinn Nov 1994

Surface Core-Level Shifts And Atomic Coordination At A Stepped W(110) Surface, D. Mark Riffe, B. Kim, J. L. Erskine, N. D. Shinn

All Physics Faculty Publications

Core-level 4f7/2 photoemission spectra have been measured from a single, bifacial W crystal, which has both a flat W(110) and a vicinal, stepped W(110) [W(320)] surface. This procedure reduces uncertainties in the quantitative description of peaks in the spectra from W(320). Various analyses, including nonlinear least-squares curve fitting, show that the average surface core-level shift (SCS) for W(320) is only ∼-140 meV, compared to -310 meV for W(110) and that, at a maximum, only two of five terrace rows are isoelectronic to W(110) surface atoms. The absence of a large SCS ...


Interface Alloying And Magnetic Properties Of Fe/Rh Multilayers, K. Hanisch, W. Keune, R.A. Brand, Christian Binek, Wolfman Kleemann Nov 1994

Interface Alloying And Magnetic Properties Of Fe/Rh Multilayers, K. Hanisch, W. Keune, R.A. Brand, Christian Binek, Wolfman Kleemann

Christian Binek Publications

Rh(20 Å)/57Fe(tFe) multilayers with Fe thicknesses tFe of 2, 5, 10, and 15 Å prepared by alternate evaporation in UHV have been investigated by x-ray diffraction (XRD), Mössbauer spectroscopy, and SQUID magnetometry. First- and second-order superstructure Bragg peaks (but no higher-order peaks) in small-angle XRD patterns suggest some compositional modulation. Mössbauer spectra taken at 4.2 K are characterized by a distribution P(Bhf) of hyperfine fields Bhf. Peaks observed in the P(Bhf) curves near 17 and 35 T are assigned to an fcc-RhFe interface alloy (~7–24 at. % Fe ...


Thickness Dependence Of The Magnetic And Electrical Properties Of Fe:Sio2 Nanocomposite Films, S.S. Malhotra, Yi Liu, J.X. Shen, Sy_Hwang Liou, David J. Sellmyer Nov 1994

Thickness Dependence Of The Magnetic And Electrical Properties Of Fe:Sio2 Nanocomposite Films, S.S. Malhotra, Yi Liu, J.X. Shen, Sy_Hwang Liou, David J. Sellmyer

Si-Hwang Liou Publications

Nanocomposite Fe80 (SiO2)20 films with thickness from 150 to 5000 Å have been prepared by rf magnetron sputtering from a composite target. The crystallites in the Fe80 (SiO2)20 films have a bcc structure with the average size of 46–66 Å which was determined by transmission electron microscopy. As indicated by the thickness dependence of resistivity, the stacking and connectivity of the crystallites depend on the thickness of the films. The magnetic properties also depend on the microstructure which changes with the thickness of the films. The magnetic coercivity of the films increases with ...


Mössbauer Study Of Permanent-Magnet Materials: Sm2Fe17-XAlX Compounds, I.A. Al-Omari, Sitaram Jaswal, A.S. Fernando, David J. Sellmyer Nov 1994

Mössbauer Study Of Permanent-Magnet Materials: Sm2Fe17-XAlX Compounds, I.A. Al-Omari, Sitaram Jaswal, A.S. Fernando, David J. Sellmyer

David Sellmyer Publications

The Fe57 Mössbauer spectra of Sm2Fe17-xAlx, where x=0, 1.0, 2.0, 3.0, and 4.0, have been measured at room temperature and analyzed. The ternary compounds Sm2Fe17-xAlx have the rhombohedral Th2Zn17 structure. Mössbauer measurements showed that all the compounds studied were ferromagnetic. The average hyperfine field was found to decrease with the increasing aluminum concentration, which is in qualitative agreement with magnetic measurements. The decrease in the average hyperfine field was from 224 kOe at x=0 to 174 kOe at x=4 ...


Sputtering Pressure Effects And Temperature-Dependent Magnetism Of Co/Pd Multilayers, S.Y. Jeong, Z.S. Shan, P. He, J.X. Shen, Y.B. Zhang, John A. Woollam, David J. Sellmyer Nov 1994

Sputtering Pressure Effects And Temperature-Dependent Magnetism Of Co/Pd Multilayers, S.Y. Jeong, Z.S. Shan, P. He, J.X. Shen, Y.B. Zhang, John A. Woollam, David J. Sellmyer

David Sellmyer Publications

The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the coercivity mechanism of Co(2 Å)/Pd(13 Å) multilayers were studied as the sputtering Ar pressure varied from 3–15 mTorr and the temperature from 300 to 35 K. It is found that the roughness of the interfaces or film surface increases with increasing sputtering pressure, the anisotropy increases with decreasing temperature and increasing Ar pressure and shows a maximum at PAr≃12 mTorr, and the coercivity increases with Ar pressure and shows stronger temperature dependence at higher Ar pressure. The coercivity mechanism was ...


Aligned Two-Phase Magnets: Permanent Magnetism Of The Future? (Invited), Ralph Skomski Nov 1994

Aligned Two-Phase Magnets: Permanent Magnetism Of The Future? (Invited), Ralph Skomski

Ralph Skomski Publications

Micromagnetic calculations are used to investigate coercivity and energy products of magnets consisting of an aligned hard-magnetic skeleton phase and a soft-magnetic phase with high saturation magnetization. Compared to the present-day theoretical limit of 516 W/m3 for single-phase Nd2Fe14B, the energy product in suitable nanostructured Sm2Fe2N3/Fe65Co35 composites is predicted to be as high as 1090 kJ/m3. The influence of the skeleton’s texture and shape is discussed, and aligned nanocrystalline two-phase magnets are compared with remanence-enhanced isotropic magnets. In particular, it is shown how ...


Matched Optical Solitary Waves For 3-Level And 5-Level Systems, Foek T. Hioe, R. Grobe Nov 1994

Matched Optical Solitary Waves For 3-Level And 5-Level Systems, Foek T. Hioe, R. Grobe

Physics Faculty/Staff Publications

Exact analytic results are presented that give a general solution for a pair of solitary waves which can propagate through a three- and a five-level system with their shapes invariant. These solitary waves vary widely in shape and form: from ones for which the pulses have similar shape to ones which have very different but ''complementary'' shapes. A general type of solitary-wave pair which is insensitive to small perturbations is identified.


Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra Nov 1994

Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra

Chemistry Faculty Publications

Large basis set ab initio calculations have been carried out for a dense grid of points on the He, potential energy surface. Three-body contributions were extracted at every point, and a number of concise functional representations for the three-body potential surface were then examined. Three-body multipolar dispersion terms and other radial and angular terms were used in the representations, and an assessment of relative importance of the different terms is presented. Combined with a two-body He-He potential, the results of this work should offer a high quality interaction potential for simulations of aggregated helium.


Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon Nov 1994

Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon

Physics Faculty Publications

The Frenkel-Kontorova (FK) model of edge dislocation is analyzed. Solutions of the continuum limit of the FK model [the sine-Gordon (SG) equation] are obtained in a form convenient for investigation of dynamics of a large number of interacting dislocations. We consider, based on these solutions, some nonstationary processes: dislocation generation, diffusion of dislocations, and crack-dislocation interaction. Simple relations connecting the velocity of plastic deformation, density and velocity of dislocations, and the force of interaction between dislocations are obtained. The nucleation of dislocations at a moving crack tip is described.


Nanostructures Of Sm-Co On Cr Thin Films, Yi Liu, B. W. Robertson, Z.S. Shan, S. Malhotra, M.J. Yu, S.K. Renukunta, Sy_Hwang Liou, David J. Sellmyer Nov 1994

Nanostructures Of Sm-Co On Cr Thin Films, Yi Liu, B. W. Robertson, Z.S. Shan, S. Malhotra, M.J. Yu, S.K. Renukunta, Sy_Hwang Liou, David J. Sellmyer

Si-Hwang Liou Publications

The nanostructures of Sm-Co on Cr thin films prepared by dc magnetron sputtering were investigated by high resolution transmission electron microscopy (HRTEM) and diffraction techniques. HRTEM micrographs show that the crystallites in the Sm-Co films, as revealed by the lattice fringes, are distributed discontinuously in the matrix. The matrix is amorphous as indicated by the microdiffraction study. The size of the crystallites is in the range of 2~5 nanometers. The volume fraction of the crystallites in the film decreases from 91% to 54% as the argon pressure is increased from 5 mTorr to 30 mTorr. Micrographs recorded in a ...


A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of The Nd2Fe17-XAlX Solid Solutions, Gary J. Long, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean Nov 1994

A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of The Nd2Fe17-XAlX Solid Solutions, Gary J. Long, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The magnetic properties of a series of Nd2Fe17-xAlx solid solutions, with x equal to 2.04, 4.01, 5.97, 7.94, and 9.06, have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 330 K in Nd2Fe17 to a maximum of ~470 K at an x of 3.5. The compounds crystallize in the Th2Zn17 structure with lattice parameters and unit cell volumes which increase linearly with increasing aluminum content. The neutron diffraction results indicate that aluminum ...