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1994

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Articles 1 - 30 of 350

Full-Text Articles in Physics

A High Temperature Pressure Sensor Based On Magnetic Coupling And Silicon Wafer Bonding, Deguang Zhu Dec 1994

A High Temperature Pressure Sensor Based On Magnetic Coupling And Silicon Wafer Bonding, Deguang Zhu

Theses

In this thesis, the design and fabrication of a bulk micromachined and wafer bonded pressure sensor for high temperature applications is described. The device design is based on the magnetic coupling principle as described by the Biot-Savart law. By combining the mechanical properties of single crystal silicon with magnetic coupling, the designed sensor can be operated up to 600°C. The key components within the sensor are two inductive coils, a silicon diaphragm and a hermetic vacuum cavity.

The modeling based on a nine-turn single level coil device and a 300 μm x 300 diaphragm indicates an output rms voltage ...


Silicon Optical Fiber Pressure Sensor, Jian Pan Dec 1994

Silicon Optical Fiber Pressure Sensor, Jian Pan

Theses

A novel optical fiber pressure sensor based on a micromachined thin silicon diaphragm is proposed. Detail descriptions of the sensor structure, modulation principle and fabrication process are given.

The device operates on the following principle: Pressure deflects a silicon diaphragm which moves the output end of a light source fiber. The emitted light intensity is picked up and shared by two receiving fibers placed side by side. The variation of the intensity ratio in the receiving fibers caused by the relative motion of the emitting fiber can be easily converted to a linear signal versus the deflection of the silicon ...


Ultra-Thin Silicon Wafer Bonding, Diyu Yan Dec 1994

Ultra-Thin Silicon Wafer Bonding, Diyu Yan

Theses

In this thesis the history and recent developments on the silicon direct bonding technique are reviewed. The growing applications of this technique in SOI, SOS and MEMS areas, difficulties and disadvantages of various bonding processes are discussed. A direct bonding procedure for attaching ultra-thin wafers less than 200 μm thick to substrate wafers is developed and described in detail. Difficulties in handling, aligning and annealing ultra-thin wafers are reported. Wafers of different doping concentration, thickness, surface roughness and chemical characteristics are tested for bondability. Methods to minimize voids and other failure mechanisms are proposed. A photodetector is designed based on ...


The Neutralino Sector In Strongly Interacting Supersymmetric Models, Tonnis Ter Veldhuis Dec 1994

The Neutralino Sector In Strongly Interacting Supersymmetric Models, Tonnis Ter Veldhuis

Tonnis ter Veldhuis

No abstract provided.


Critical Dynamics Of Nonconserved Ising-Like Systems, K. E. Bassler, Beate Schmittmann Dec 1994

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.


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.


Kinetics Of Clustering In Traffic Flows, E. Ben-Naim, P. L. Krapivsky, S. Redner Dec 1994

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 ...


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.


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 ...


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 ...


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 ...


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 ...


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.


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 ...


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 ...


Determination Of The Bulk Modulus Of A Lennard-Jones Solid, Spencer A. Van Roekel Jr. Dec 1994

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

Master's 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.


The Photonic Band Structure Of Dielectric Systems With A Frequency Dependent Dielectric Function, Jiezhou Liu Dec 1994

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

Master's 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 ...


An Experimental Apparatus For Studying Double Differential Scattering By Low-Energy Multiply Charged Ions From Atomic Targets, Meenatchi S. Gopinathan Dec 1994

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

Master's 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 Dec 1994

Absolute Photonic Band Gaps Of Zincblende, Ulrich Bass

Master's 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 ...


A Comparison Of Higgs Mass Bounds In The Sm And The Mssm, Tonnis Ter Veldhuis, T Weiler, M Diaz Nov 1994

A Comparison Of Higgs Mass Bounds In The Sm And The Mssm, Tonnis Ter Veldhuis, T Weiler, M Diaz

Tonnis ter Veldhuis

No abstract provided.


The Spectral Center Of Gravity Effect And Auditory Filter Bandwidth, Marc Fagelson, Linda M. Thibodeau Nov 1994

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

Marc A. Fagelson

The spectral center of gravity refers to a listener’s averaging of frequency and intensity components when formant peaks in a speechlike signal are separated by 3.5 Bark units or less. In this paper a total of 18 synthetic vowels whose spectra approximated /ae/ or /inverted vee/ were generated digitally; each stimulus contained the first 40 harmonics of a 100‐Hz fundamental. Nine spectra contained three formants, while the balance contained only two. Subjects with normal hearing and mild high‐frequency hearing loss above 3000 Hz were instructed to identify synthetic vowels as either /ae/ or /inverted vee/ as ...


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.