Physical Sciences and Mathematics Commons^™

Far-Field Scattering Of An Axisymmetric Laser Beam Of Arbitrary Profile By An On-Axis Spherical Particle, James A. Lock, Joseph T. Hodges

Physics Faculty Publications

Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the TEM(00) laser mode. In order to take these deviations into account when calculating light scattering, we propose a method for approximating the beam shape coefficients in the partial wave expansion of an experimental laser beam. We then compute scattering by a single dielectric spherical particle placed on the beam's axis using this method and compare our results to laboratory data. Our model calculations fit the laboratory data well. (C) 1996 Optical Society of America

Θ Vacua In The Light-Cone Schwinger Model, Alex C. Kalloniatis, David G. Robertson

Physics Faculty Scholarship

We discuss the bosonized Schwinger model in light-cone quantization, using discretization as an infrared regulator. We consider both the light-cone Coulomb gauge, in which all gauge freedom can be removed and a physical Hilbert space employed, and the light-cone Weyl (temporal) gauge, in which the Hilbert space is unphysical and a Gauss law operator is used to select a physical subspace. We describe the different ways in which the θ vacuum is manifested depending on this choice of gauge, and compute the θ-dependence of the chiral condensate in each case.

Distribution Coefficients Of Ionized And Un-Ionized Halogenated Phenols In An Octanol-Water System And Their Relationship To Molecular Structure, Sven Hensler

Dissertations and Theses

Life supporting biological membranes are barriers to toxic chemicals. One of the factors determining the toxicity of chemical compounds is their distribution between membranes and their an environment. An octanol-water system is frequently used as a model for biological membranes to estimate the toxic potency of environmental pollutants. The distribution of a chemical between the octanol and the water phase is described by the octanol-water partition coefficient K_OW. This study is concerned with the relationship between K_OW and the molecular structure of the toxic chemical.

In the study the following trihalophenols were included: 2,4,6-trifluorophenol (TriFP), 2,4,6-trichlorophenol (TriCP); …

Phase Transitions In Driven Bilayer Systems: A Monte Carlo Study, C. C. Hill, R. K. P. Zia, Beate Schmittmann

Beate Schmittmann

We investigate the phase diagram of a system with two layers of an Ising lattice gas at half filling. In addition to the usual intralayer nearest neighbor attractive interaction, there is an interlayer potential J. Under equilibrium conditions, the phase diagram is symmetric under J→−J, though the ground states are different. The effects of imposing a uniform external drive, studied by simulation techniques, are dramatic. The mechanisms responsible for such behavior are discussed.

Anisotropy And Polarization In Charge Changing Collisions Of C⁴⁺ With Na(3s) And Laser Aligned Na(3p), S. Schippers, R. Hoekstra, R. Morgenstern, Ronald E. Olson

Physics Faculty Research & Creative Works

Absolute cross sections for C3+(6→5) emission at 465.7 nm after collisions of C4+ ions with ground state Na(3s) and laser excited aligned Na(3p) atoms are measured over the collision energy range of 3-7 keV amu-1. For Na(3s) polarizations are observed by measuring the linear polarization of the emitted light. In these collisions the polarization is found to be 0.33 and almost independent of the collision energy. Cross sections for collisions with the Na(3p) target are up to five times larger than for collisions with Na(3s). Slightly larger cross sections are measured when the laser excited Na(3p) target is Π-aligned as …

Design Of A Device Independent Computer Graphic Software Package, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the <110>, <112> and <111> direction, and each slab surfaces is extended in the <110>-<112> plane and normal to the <111> direction. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of …

Silcom Quantum Walls: Fabrication And Opticla Analysis, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the,anddirection, and each slab surfaces is extended in the-plane and normal to thedirection. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of the phonons is highly dependent on …

Measurement Of The Reaction Γ*P→Φp In Deep Inelastic E+P Scattering At Hera, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. R. Okrasinski, J. Repond, R. Stanek, R. L. Talaga, H. Zhang, Margarita C. K. Mattingly, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, R. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, R. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam

Faculty Publications

The production of φ mesons in the reaction e+p → e+φp (φ → K+K-), for 7 < Q2 < 25 GeV2 and for virtual photon-proton centre of mass energies (W) in the range 42-134 GeV, has been studied with the ZEUS detector at HERA. When compared to lower energy data at similar Q2, the results show that the γp → p0p cross section rises strongly with W. This behaviour is similar to that previously found for the γ*p → p0p cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small x. The ratio of σ(φ)/σ(p0), which has previously been determined by ZEUS to be 0.065 ± 0.013 (stat.) in photoproduction at a mean W of 70 GeV, is measured to be 0.18 ± 0.05 (stat.) ± 0.03 (syst.) at a mean Q2 of 12.3 GeV2 and mean W of ≈ 100 GeV and is thus approaching at large Q2 the value of 2/9 predicted from the quark charges of the vector mesons and a flavour independent production mechanism.

Atomic Data For Astrophysics. Ii. New Analytic Fits For Photoionization Cross Sections Of Atoms And Ions, D. A. Verner, Gary J. Ferland, K. T. Korista, D. G. Yakovlev

Physics and Astronomy Faculty Publications

We present a complete set of analytic fits to the nonrelativistic photoionization cross sections for the ground states of atoms and ions of elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization thresholds, the fits are based on the Opacity Project theoretical cross sections interpolated and smoothed over resonances. At higher energies, the fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.

Incoherent Scatter Radar, Ionosonde,And Satellite Measurements Of Equatorial F Region Vertical Plasma Drifts In The Evening Sector, Bela G. Fejer, E. R. De Paula, L. Scherliess, I. S. Batista

Bela G. Fejer

Studies of equatorial F region evening vertical plasma drifts using different measurement techniques have produced conflicting results. We examine the relationship of incoherent scatter radar and ionosonde drift observations over the Peruvian equatorial region, and AE-E satellite drifts for different geophysical conditions. Our data show that there is large day-to-day variability on the ratios of radar and ionosonde drifts, but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions. For high solar activity, however, the Jicamarca evening drifts during equinox and December solstice are significantly larger than the ionosonde …

Ground And Excited State Exciton Spectra From Gan Grown By Molecular-Beam Epitaxy, D. C. Reynolds, David C. Look, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç, D. N. Talwar

Physics Faculty Publications

The emission and reflection spectra of GaN have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Three intrinsic exciton transitions have been observed, one associated with each of the valence bands. Exciton excited states associated with the two top valence bands were also observed. The exciton binding energies, the band-gap energies, and the exciton Bohr radii are all reported along with the dielectric constant and the spin-orbit and crystal-field parameters for GaN.

Nickel Doping Of Boron Carbide Grown By Plasma Enhanced Chemical Vapor Deposition, Seong-Don Hwang, N.B. Remmes, Peter A. Dowben, D.N. Mcilroy

Peter Dowben Publications

We have nickel doped boron carbide grown by plasma enhanced chemical vapor deposition. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to grow the boron carbide, while nickelocene [Ni(C₅H₅)₂] was used to introduce nickel into the growing film. The doping of nickel transformed a p-type, B₅C material, relative to lightly doped n-type silicon, to an n-type material. Both n-n heterojunction diodes and n-p heterojunction diodes were constructed, using as substrates n- and p-type Si(111), respectively. With sufficient partial pressures of nickelocene in the plasma reactor, …

Structure, Dynamics, And Phase Transitions In The Fullerene Derivatives C_{60}O And C_{61}H_{2}, C. Meingast, G. Roth, L. Pintschovius, R. H. Michel, C. Stoermer, M. M. Kappes, Paul A. Heiney, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

The effect of perturbing the icosohedral symmetry of C₆₀ by the addition of the side groups -O and -CH₂ upon orientational order-disorder and glass transitions in solid C₆₀ has been studied by a combination of high-resolution capacitance dilatometry and single-crystal x-ray and powder inelastic neutron scattering. Both fullerene derivatives C₆₀O (epoxide) and C₆₁H₂ (6,5-annulene) are shown to undergo a sequence of transitions similar to that found in pure C₆₀, i.e., a first-order orientational ordering transition just below room temperature followed by an orientational glass transition at lower temperatures. Although the …

Binary Nucleation Kinetics. Iii. Transient Behavior And Time Lags, Barbara Ellen Wyslouzil, Gerald Wilemski

Physics Faculty Research & Creative Works

Transient binary nucleation is more complex than unary because of the bidimensionality of the cluster formation kinetics. To investigate this problem qualitatively and quantitatively, we numerically solved the birth-death equations for vapor-to-liquid phase transitions. Our previous work [J. Chem. Phys 103, 1137 (1995)] showed that the customary saddle point and growth path approximations are almost always valid in steady state gas phase nucleation and only fail if the nucleated solution phase is significantly nonideal. The current work demonstrates that in its early transient stages, binary nucleation rarely, if ever, occurs via the saddle point. This affects not only the number …

Nuclear Reaction Studies With Radioactive {Sup 18}F Beams At Atlas, K. E. Rehm, M. Paul, Andrew D. Roberts, C. L. Jiang, D. Blumenthal, C. N. Davids, P. Decrock, S. M. Fischer, J. Gehring, D. Henderson, C. J. Lister, Robert J. Nickles, J. Nolen, R. C. Pardo, J. P. Schiffer, R. E. Segel

Physics and Astronomy Department Publications

The contribution of the {sup 18}F(p,{gamma}) reaction to the production of {sup 19}Ne which is the crucial isotope for the breakout from the hot CNO cycle into the rp process, has been investigated in experiments with {sup 18}F beams. Measurements of the cross sections for the {sup 18}F(p,{alpha}){sup 15}O and the {sup 18}F(p,{gamma}){sup 19}Ne reactions indicate that the contribution from the (p,{gamma}) route to the formation of {sup 19}Ne is small.

Charge-Dipole Model For The Universal Field Dependence Of Mobilities In Molecularly Doped Polymers, David H. Dunlap, Paul Ernest Parris, Vasudev M. Kenkre

Physics Faculty Research & Creative Works

Using the general result that the mobility μ, of charge carriers driven in a spatially correlated random potential by an electric field E can be expressed in terms of the Laplace transform of a particular correlation function related to the random potential, we demonstrate that the exponential dependence of μ on √E universally observed in molecularly doped polymers arises naturally from the interaction of charge carriers with randomly distributed permanent dipoles.

Two-Dimensional Drift-Diffusion Simulations Of Silicon Avalanche Shaper (Sas) Devices For High Power Applications, Hamid Jalali

Electrical & Computer Engineering Theses & Dissertations

Silicon Avalanche Shaper devices have been projected as being important components of an inexpensive, semiconductor-based technology for high power switching applications. The primary advantage of this technology is that it is based on Silicon material which is easy to fabricate and has a well established processing technology. Unlike other high power technologies, the SAS devices do not rely on external optical triggering which eliminates the need for lasers and related optical circuitry.

The SAS based high power switching technology has been pioneered and tested by a Russian group. Though preliminary results have been very encouraging, the device reliability and its …

Light Front Qcd In (1+1)-Dimensions Coupled To Chiral Adjoint Fermions, David G. Robertson, Stephen S. Pinksy

Physics Faculty Scholarship

We consider SU(N) gauge theory in 1+1 dimensions coupled to chiral fermions in the adjoint representation of the gauge group. With all fields in the adjoint representation the gauge group is actually , which possesses nontrivial topology. In particular, there are N distinct topological sectors and the physical vacuum state has a structure analogous to a θ vacuum. We show how this feature is realized in light-front quantization for the case N = 2, using discretization as an infrared regulator. In the discretized form of the theory the nontrivial vacuum structure is associated with the zero momentum mode of the …

Evidence For Binary Orbital Motion Of A Quasar Broad-Line Region, C. Martin Gaskell

C. Martin Gaskell Publications

Analysis of spectra of the quasar 3C 390.3 covering a period of over 20 yr shows that the blueshifted peak of H beta has been changing its radial velocity at an almost constant rate during this time. The radial velocity has increased by over 1500 km/s. The lower limit to the period of radial velocity changes is 210 yr. Although very long periods cannot be excluded by the radial velocity curve alone, other considerations suggest that the period is about 300 yr. If the radial velocity changes are due to orbital motion, the radius of the orbit is about 0.3 …

Dynamics Of Conversion Of Conduction Electrons Into A Collective Charge-Density-Wave Current, Alexander S. Kovalev, Yuriy V. Pershin Dr, Alexander S. Rozhavsky

Faculty Publications

The exactly solvable model which describes the dynamics of transformation of conduction electrons into nonlinear charge-carrying excitations of charge-density waves in quasi-one-dimensional Peierls-Frohlich conductors is formulated and studied by the inverse scattering transformation method. The pair of self-trapped conduction electrons transform into a charged 2π kink localized in a single conducting chain and surrounded by dipoles in neighboring chains.

The Spectral Function Of Random Resistor Networks, Anthony Day, M. Thorpe

Anthony Roy Day

The effective complex conductivity [...] of a two-component material can be conveniently expressed as an integral transformation of a spectral function. The spectral function depends only on the geometry of the material, and can be used to calculate [...] for any particular choice of component conductivities. This is a very useful feature if the component conductivities can be varied (by changing the temperature or frequency, for example) at a fixed geometry. We present a derivation of the spectral function that identifies it as a density of states. We have made direct numerical calculations of the spectral function of two-dimensional random …

Structural And Magnetic Studies On Prba2fe3o8, V. P.S. Awana, Latika Menon, S. K. Malik, Apurva Mehta, Sanjay Mishra, William B. Yelon

Physics Faculty Research & Creative Works

It is known that Fe moments order antiferromagnetically with Néel temperature, TN, above 700 K in RBa2Fe3O7-δ with R=Y and Eu, and Pr moments order antiferromagnetically in PrBa2Cu3,O7-δ, with TN of 17 K. We have synthesized PrBa2Fe3O8 to study the ordering of Pr and Fe moments. From X-ray and neutron diffraction studies, this compound is found to crystallize in the tetragonal structure (space group P4/mmm). 57Fe Mössbauer studies show a complex hyperfine split pattern at 77 K, but a doublet superimposed on a six-line pattern at 300 K implying that some of the Fe moments order magnetically between 77 and …

Построение Редуцированного Физического Гамильтониана Для Сферически-Симметричной Гравитации, Николай Заркевич

Nikolai A. Zarkevich

No abstract provided.

Charge Collection And Trapping In Low‐Temperature Silicon Detectors, M. J. Penn, Brian L. Dougherty, Blas Cabrera, R. M. Clarke, Betty A. Young

Physics

Charge collection efficiency measurements in silicon detectors at low temperature (T < 0.5 K) and low applied electric field (E=0.1–100 V/cm) were performed using a variety of high‐purity, p‐type silicon samples with room‐temperature resistivity in the range 2–40 kΩ cm. Good charge collection under these conditions of low temperature and low electric field is necessary for background suppression, through the simultaneous measurement of phonons and ionization, in a very low event rate dark matter search or neutrino physics experiment. Charge loss due to trapping during drift is present in some samples, but the data suggest that another charge–loss mechanism is also important. We present results which indicate that, for 60 keV energy depositions, a significant fraction of the total charge loss by trapping occurs in the initial electron‐hole cloud near the event location which may briefly act as a shielded, field‐free region. In addition, measurements of the lateral size, transverse to the applied electric field, of the initial electron‐hole cloud indicate large transverse diffusion lengths. At the lowest fields a lateral diameter on the order of 1 mm is found in a detector ∼5 mm thick.

Observation Of A Large Parity Nonconserving Analyzing Power In Xe, J J. Szymanski, W M. Snow, J D. Bowman, B Cain, Bret E. Crawford, P P J. Delheij, R D. Hartman, T Haseyama, C D. Keith, J N. Knudsen, A Komives, M Leuschner, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, D Rich, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, Y-F Yen, V W. Yuan

Physics and Astronomy Faculty Publications

A large parity nonconserving longitudinal analyzing power was discovered in polarized-neutron transmission through Xe. An analyzing power of 4.3±0.2% was observed in a p-wave resonance at E_n=3.2 eV. The measurement was performed with a liquid Xe target of natural isotopic abundance that was placed in the polarized epithermal neutron beam, flight path 2, at the Manuel Lujan Neutron Science Center. This apparatus was constructed by the TRIPLE Collaboration, and has been used for studies of parity symmetry in compound nuclear resonances. Part of the motivation of the experiment was to discover a nucleus appropriate for a sensitive test …

Thermally Stimulated Current Trap In Gan, David C. Look, Z-Q. Fang, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç

Physics Faculty Publications

A thermally stimulated current peak, occurring at 100 K for a heating rate of 0.4 K/s, has been found in semi‐insulating GaN grown by molecular beam epitaxy. This peak has contributions from two traps, with the main trap described by the following parameters: emission thermal activation energy E≂90±2 meV, effective capture cross‐section σ≂3±1×10⁻²² cm⁻², and Nμτ≂3±1 × 10¹⁴ cm⁻¹ V ⁻¹, where N is the trap concentration, μ the mobility, and τ the free‐carrier lifetime. This trap is much deeper than the typical shallow donors in conducting GaN, but shallower than any …

Optical Properties Of Boron Carbide (B5C) Thin Films Fabricated By Plasma-Enhanced Chemical-Vapor Deposition, Ahmad A. Ahmad, N.J. Ianno, P.G. Snyder, D. Welipitiya, D. Byun, Peter A. Dowben

Peter Dowben Publications

Variable angle of incidence spectroscopic ellipsometry was used to determine the optical constants near the band edge of boron carbide (B₅C) thin films deposited on glass and n-type Si(111) via plasma-enhanced chemical-vapor deposition. The index of refraction n, the extinction coefficient k, and the absorption coefficient are reported in the photon energy spectrum between 1.24 and 4 eV. Ellipsometry analysis of B₅C films on silicon indicates a graded material, while the optical constants of B₅C on glass are homogeneous. Line shape analyses of absorption data for the films on glass indicate …

Multicomponent Diffusion In Two-Temperature Magnetohydrodynamics, John D. Ramshaw, C. H. Chang

Physics Faculty Publications and Presentations

A recent hydrodynamic theory of multicomponent diffusion in multitemperature gas mixtures [J. D. Ramshaw, J. Non-Equilib. Thermodyn. 18, 121 (1993)] is generalized to include the velocity-dependent Lorentz force on charged species in a magnetic field B. This generalization is used to extend a previous treatment of ambipolar diffusion in two-temperature multicomponent plasmas [J. D. Ramshaw and C. H. Chang, Plasma Chem. Plasma Process. 13, 489 (1993)] to situations in which B and the electrical current density are nonzero. General expressions are thereby derived for the species diffusion fluxes, including thermal diffusion, in both single- and two-temperature multicomponent magnetohydrodynamics (MHD). It …

Design Of Gradient Index Optical Thin Films, Jeffrey J. Druessel

Theses and Dissertations

Gradient index thin films provide greater flexibility for the design of optical coatings than the more conventional 'layer' films. In addition, gradient index films have higher damage thresholds and better adhesion properties. This dissertation presents an enhancement to the existing inverse Fourier transform gradient index design method, and develops a new optimal design method for gradient index films using a generalized Fourier series approach. The inverse Fourier transform method is modified to include use of the phase of the index profile as a variable in rugate filter design. Use of an optimal phase function in Fourier-based filter designs reduces the …

Electrical Characterization Of Gasb Based Semiconductors For 2-4 Micrometers Diode Laser Applications, Daniel K. Johnstone

Theses and Dissertations

Deep Level Transient Spectroscopy (DLTS) was used to characterize the band offsets and deep levels in MBE grown GaSb-based semiconductors that are used in 2-4 µm laser diode structures. One of several deep level traps found in Al_xGa_1-xAs_ySb_1-y (x=0, 0.5, 0.6, 1.0) is a GaSb double acceptor trap. Progress is also made in establishing the model for the DX center in this material. The degree of compensation of the donor related DX center by GaSb affect where donors are situated, giving preference to one configuration over the many other possible configurations. One minority …