Physical Sciences and Mathematics Commons^™

Nested Bars In Disk Galaxies : No Offset Dust Lanes In Secondary Nuclear Bars, Isaac Shlosman, Clayton Heller

Department of Physics and Astronomy Faculty Publications

Under certain conditions, subkiloparsec nuclear bars form inside large-scale stellar bars of disk galaxies. These secondary bars spend a fraction of their lifetime in a dynamically decoupled state, tumbling in the gravitational field of the outer bars. We analyze the flow pattern in such nested-bar systems under the conditions of negligible self-gravity and find that secondary bars differ fundamentally from their large-scale counterparts in gas flow pattern and other dynamical properties. In particular, the gas flow across the bar-bar interface in these systems can be more chaotic or more regular in nature and, contrary to predictions, has no difficulty in …

High-Energy Ion Generation In Interaction Of Short Laser Pulse With High-Density Plasma, Y. Sentoku, V. Y. Bychenkov, K. Flippo, Anatoly Maksimchuk, K. Mima, G. Mourou, Z. M. Sheng, Donald Umstadter

Donald Umstadter Publications

Multi-MeV ion production from the interaction of a short laser pulse with a high-density plasma, accompanied by an underdense preplasma, has been studied with a particle-in- cell simulation and good agreement is found with experiment. The mechanism primarily responsible for the acceleration of ions is identified. Comparison with experiments sheds light on the ion-energy dependence on laser intensity, preplasma scale length, and relative ion energies for a multi-species plasma. Two regimes of maximum ion-energy dependence on laser intensity, I, have been identified: subrelativistic, μ I ; and relativistic, μ √I. Simulations show that the energy of the …

Production Of Nitrogen Acceptors In Zno By Thermal Annealing, N. Y. Garces, N. C. Giles, L. E. Halliburton, G. Cantwell, D. B. Eason, D. C. Reynolds, David C. Look

Physics Faculty Publications

Nitrogen acceptors are formed when undoped single crystals of zinc oxide (ZnO) grown by the chemical-vapor transport method are annealed in air or nitrogen atmosphere at temperatures between 600 and 900 °C. After an anneal, an induced near-edge absorption band causes the crystals to appear yellow. Also, the concentration of neutral shallow donors, as monitored by electron paramagnetic resonance (EPR), is significantly reduced. A photoinduced EPR signal due to neutral nitrogen acceptors is observed when the annealed crystals are exposed to laser light (e.g., 364, 442, 458, or 514 nm) at low temperature. The nitrogens are initially in the nonparamagnetic …

The Intermediate-Period Cepheid Strip Stars, Edward G. Schmidt

Edward Schmidt Publications

To explore the population of variable stars that fall between RR Lyrae stars and classical Cepheids, we have obtained extensive photometric observations for 56 stars with periods between 0.6 and 1.0 days. For these stars and an additional 10, we have examined the form and stability of the light curves to explore the variety of types of stars in this period regime. We conclude that the majority of the sample are Bailey type ab RR Lyrae stars. However, a surprising number that possibly exhibit the Blazhko effect are found. There are a half-dozen other stars that do not appear to …

Electric Field Gradients In S-, P-, And D-Metal Diborides And The Effect Of Pressure On The Band Structure And TC In Mgb₂, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman, Dmitrii L. Novikov

Physics Faculty Research & Creative Works

Results of full-potential linear muffin-tin orbital generalized gradient approximation calculations of the band structure and boron electric field gradients (EFG's) for the new medium-T_c superconductor MgB₂ and related diborides MB₂, M = Be, Al, Sc, Ti, V, Cr, Mo, and Ta are reported. The boron EFG variations are found to be related to specific features of their band structure and particularly to the M-B hybridization. The strong charge anisotropy at the B site in MgB₂ is completely defined by the valence electrons - a property which sets MgB₂ apart from other diborides. The boron …

A Rf Discharge Cell For Saturated Absorption Spectroscopy Of Metastable Argon, C. I. Sukenik, H. C. Busch

Physics Faculty Publications

We have produced a rf discharge in 40Ar and used saturated absorption spectroscopy to offset lock a Ti:Sapphire laser to the absorption peak of the 43P243D3 cooling transition at 811 nm. We describe the procedure for fabrication of the cell and production of the discharge.

Modeling Hydrogen Diffusion For Solar Cell Passivation And Process Optimization, Yi Zhang

Dissertations

A diffusion model for hydrogen (H) in crystalline silicon was established which takes into account the charged state conversion, junction field, mobile traps, and complex formation and dissociation at dopant and trap sites. Carrier exchange among the various charged species is a "fast" process compared to the diffusion process. A numerical method was developed to solve the densities of various charged species from the Poisson's equation that involves shallow-level dopants and one "negative U" impurity, e.g., H. Time domain implicit method was adopted in finite difference scheme to solve the fully coupled equations.

Limiting versions of the model were applied …

Consequence Of Superfluidity On The Expansion Of A Rotating Bose-Einstein Condensate, Mark Edwards, Charles W. Clark, P. Pedri, L. Pitaevskii, S. Stringari

Department of Physics and Astronomy Faculty Publications

We propose an easily detectable signature of superfluidity in rotating, vortex-free gaseous Bose-Einstein condensates. We have studied the time evolution of the expansion of such a condensate after it is released from the confining trap. We find that if such a condensate is not initially rotating, then at some moment it will instantaneously achieve a circular cross section. If the condensate is initially rotating its irrotational flow and the conservation of angular momentum prevent the released condensate from attaining a circular cross section, since the instantaneous moment of inertia is then proportional to the asymmetry of this cross section.

Structural Transitions In Biomolecules - A Numerical Comparison Of Two Approaches For The Study Of Phase Transitions In Small Systems, Nelson A. Alves, Ulrich H.E Hansmann, Yong Peng

Michigan Tech Publications

We compare two recently proposed methods for the characterization of phase transitions in small systems. The usefulness of these techniques is evaluated for the case of structural transition in alanine-based peptides.

Nontunneling High-Order Harmonics From Ultra-Intense Laser-Driven Tightly Bound Systems, S. X. Hu, Anthony F. Starace, W. Becker, W. Sandner, D. B. Milosevic

Anthony F. Starace Publications

High-order harmonic emission is investigated by numerical solution of the weakly relativistic, two-dimensional Schrödinger equation for the case of ultra-intense laser-driven tightly bound systems (for example, multiply charged ions such as O⁷⁺ exposed to laser fields of the order of 10¹⁸ W cm^-2 at 248 nm). In contrast to their usual substantial decrease, the low-order harmonics having an energy less than the ionization potential exhibit a high efficiency (i.e. intense) plateau with a well defined cutoff. The shape of this plateau is found to depend on the shape of the binding potential. A classical “surfing” mechanism for …

Observation Of Anomalous Spin-State Segregation In A Trapped Ultracold Vapor, Dwight L. Whitaker, H. J. Lewandowski, D. M. Harber, E. A. Cornell

Pomona Faculty Publications and Research

We observe counterintuitive spin segregation in an inhomogeneous sample of ultracold, noncondensed rubidium atoms in a magnetic trap. We use spatially selective microwave spectroscopy to verify a model that accounts for the differential forces on two internal spin states. In any simple understanding of the cloud dynamics, the forces are far too small to account for the dramatic transient spin polarizations observed. The underlying mechanism remains to be elucidated.

Search For Gluinos And Scalar Quarks In Pp̅ Collisions At √S = 1.8 Tev Using The Missing Energy Plus Multijets Signature, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have performed a search for gluinos (g̃) and scalar quarks (q̃,/i>) in a data sample of 84 pb^-1 of pp̅ collisions at √s =1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and three or more jets, a characteristic signature in R-parityconserving supersymmetric models. The analysis has been performed “blind,” in that the inspection of the signal region is made only after the predictions from standard model backgrounds have been calculated. Comparing the data with predictions of constrained supersymmetric models, we exclude gluino …

Measurement Of The Strong Coupling Constant From Inclusive Jet Production At The Tevatron P̅P Collider, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report a measurement of the strong coupling constant, α_s(M_z ), extracted from inclusive jet production in pp̅ collisions at √s =1800 GeV. The QCD prediction for the evolution of α_s with jet transverse energy E_T is tested over the range 40 TE_T for the renormalization scale. The data show good agreement with QCD in the region below 250 GeV. The value of α_s at the mass of the Z⁰ boson averaged over the range 40 < T < 250 GeV is found to be α_s(M_z )= 0.1178 ± 0.0001(stat)_-0.0095^+0.0081 (expt. syst). The associated theoretical uncertainties …

Stark Shifts And Transition Probabilities In The Ne Ii Spectrum, Stevan Djenize, Vladimir Milosavljevic, Milan S. Dimitrijevic

Articles

Stark shifts (d) and transition probabilities of the spontaneous emission (Einstein's A values) of forty two singly charged neon ( ) ion spectral lines have been measured in a linear, low pressure, pulsed arc at 35 300 K electron temperature and 1.83 10 ²³ m ^-3 electron density. Transition probabilities have been obtained using the relative line intensity ratio (RLIR) method. Stark shift values have also been calculated, using the semiclassical perturbation formalism (SCPF). The measured and calculated shift values and the measured A values have been compared to the existing data taken from available data sources.

Effects Of Surface Morphology On Magnetic Properties Of Ni Nanowire Arrays In Self-Ordered Porous Alumina, H. Zeng, Stevem A. Michalski, Roger D. Kirby, David J. Sellmyer, L. Menon, Supriyo Bandyopadhyay

David Sellmyer Publications

Ni nanowire arrays were produced by electrodeposition of Ni into self-assembled porous anodic alumina templates. With different anodization voltages, the wires show different surface morphologies. The temperature dependence of the coercivity and activation volume of wires with regular shape can be explained by thermal activation over an energy barrier with a 3/2 power dependence on the field. The wires with irregular surface morphologies show abnormal temperature dependences of the coercivity and activation volume. Possible mechanisms for these behaviors are discussed.

White-Light-Induced Fragmentation Of Toluene, A. M. Müller, B. Witzel, Cornelis J. Uiterwaal, J. Wanner, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

We investigate the influence of continuum generation on the photofragmentation dynamics of the toluene molecule. By sending an 80-fs Ti:sapphire laser beam through a 2-mm-thick CaF₂ plate we show that even moderately broadened laser frequency spectra considerably increase the degree of fragmentation, while it is nearly absent without continuum generation. The measured broadening of the frequency spectra and the known Raman-active vibrational modes of toluene afford an explanation in terms of a stimulated Raman scattering scheme, in which the molecule absorbs large amounts of vibrational energy.

Metallicities And Abundance Ratios From Quasar Broad Emission Lines, Fred Hamann, K. T. Korista, Gary J. Ferland, Craig Warner, Jack Baldwin

Physics and Astronomy Faculty Publications

The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs) are important diagnostics of the relative abundances and overall metallicity in the gas. Here we present new theoretical predictions for several UV BELs. We focus specifically on the relative nitrogen abundance as a metallicity indicator, based on the expected secondary enrichment of nitrogen at metallicities Z≳0.2 Z_☉. Among the lines we consider, NIII]λ1750/OIII]λ1664, NVλ1240/(CIVλ1549+OVIλ1034), AND NV/HeIIλ1640 are the most robust diagnostics. We argue, in particular, that the average N V BEL is not dominated by scattered Lyα photons from a broad absorption-line wind. We then …

Experimental Violation Of A Spin-1 Bell Inequality Using Maximally Entangled Four-Photon States, John C. Howell, Antia Lamas-Linares, Dik Bouwmeester

Mathematics, Physics, and Computer Science Faculty Articles and Research

We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.55 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27±0.02 using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.

Quantum-State Information Retrieval In A Rydberg-Atom Data Register, J. Ahn, Chitra Rangan, D.N. Hutchinson, P.H. Bucksbaum

Physics Publications

The connections between the phase retrieval protocol in a Rydberg data register were shown via an impulsive half-cycle pulse and the more general problem of constructing a database-search algorithm. The sensitivity of the phase retrieval to the peak HCP field was explained by multimode interference. By programming the initial wave packet and the HCP, it was possible to create the correct interference conditions to produce any desired energy eigenstates.

Lithium Transition Energies And Isotope Shifts: Qed Recoil Corrections, Z. C. Yan, Gordon W. F. Drake

Physics Publications

The quantum electrodynamic recoil correction for lithium in the 22S1/2, 32S1/2 and 22PJ states was evaluated, and its impact on lithium isotope shifts was examined. The nonrelativistic variational wave functions were constructed from fully correlated basis sets in Hylleraas coordinates. Results for the total transition frequencies were shown to be in good agreement with experiment, but there were discrepancies between theory and experiment for isotope shift in the fine structure splitting for 1s22p2P state.

Ground-State Energies For Helium, H-, And Ps-, Gordon W. F. Drake, M. M. Cassar, R. A. Nistor

Physics Publications

Nonrelativistic energy and other properties of He, H- and Ps- were discussed using a triple basis set in Hylleraas coordinates. The stability and efficiency of the computational method was compared with the quasirandom method. Results showed that the triple basis set in Hylleraas coordinates is capable of exceeding the accuracy of calculations for three-body system based on quasirandom Monte Carlo methods.

Determining The Locus For Photocarrier Recombination In Dye-Sensitized Solar Cells, Kai Zhu, Eric A. Schiff, N. G. Park, J. Van De Lagemaat, A. J. Frank

Physics - All Scholarship

We present intensity-modulated photocurrent and infrared transmittance measurements on dye-sensitized solar cells based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte. Under short-circuit conditions, we show that an elementary analysis accurately relates the two measurements. Under open-circuit conditions, infrared transmittance, and photovoltage measurements yield information on the characteristic depth at which electrons recombine with ions (the ‘‘locus of recombination’’). For one particular series of samples recombination occurred near the substrate supporting the titania film, as opposed to homogeneously throughout the film.

Infrared Charge-Modulation Spectroscopy Of Defects In Phosphorus Doped Amorphous Silicon, Kai Zhu, Eric A. Schiff, G. Ganguly

Physics - All Scholarship

We present infrared charge-modulation absorption spectra on phosphorus-doped amorphous silicon (a-Si:H:P) with doping levels between 0.17% - 5%. At higher doping levels (1% - 5%) we find a sharp spectral line near 0.75 eV with a width of 0.1 eV. We attribute this line to the internal optical transitions of a complex incorporating four fold coordinated phosphorus and a dangling bond. This line is barely detectable in samples with lower doping levels (below 1%). In these samples a much broader line dominates the spectrum that we attribute to uncomplexed dopants. The relative strength of the two spectral features is in …

Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff

Physics - All Scholarship

We present computer modeling for effects of the p/i interface upon the open-circuit voltage VOC in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensitydependence for the interface effect, and we present an interpretation for the modeling based on thermionic emission of electrons over the electrostatic barrier at the p/i interface. We present additional modeling of the relation of VOC with the intrinsic layer bandgap EG. The experimental correlation for optimized cells is VOC = (EG/e)-0.79. The correlation is simply explained if VOC in these cells is determined by the intrinsic …

Photocarrier Drift Mobility Measurements And Electron Localization In Nanoporous Silicon, P. N. Rao, Eric A. Schiff, L. Tsybeskov, P. Fauchet

Physics - All Scholarship

We report photocarrier time-of-flight measurements in diode structures made of highly porous crystalline silicon. The corresponding electron and hole drift mobilities are very small ð<104 cm2=V sÞ compared to homogeneous crystalline silicon. The mobilities are dispersive (i.e., having a power-law decay with time or length-scale), but are only weakly temperature-dependent. The dispersion parameter lies in the range 0.55–0.65 for both electrons and holes. We conclude that the drift mobilities are limited by the nanoporous geometry, and not by disorder-induced localized states acting as traps. This conclusion is surprising in the context of luminescence models based on radiative recombination of localized excitons.

Specification Of Jecp/Sp: Stereographic Projection With An Application For Specimen Orientation Adjustment Using Tem Holders, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

1. Purpose of the program 2. Graphic user interface and program design 3. Crystallographic principle and implementation 4. System requirement 5. Installation and user instruction 6. How to contact the author 7. References

1. Purpose of the program JECP/SP is a computer program in Java Electron Crystallography Package. JECP is developed for quantitative electron diffraction and image processing, the package is designed and written by Dr. XingZhong Li. JECP/SP provides the all necessary functions of stereographic projection for regular application and furthermore it can be used to minimized the difficulties encountered when tilting highly beam-sensitive, or small-grain-size specimens with known …

When Is Rain Steady?, A. R. Jameson, Alexander Kostinski

Department of Physics Publications

By definition, steady rain should have a nearly constant rainfall rate. Thus far, however, the criteria for determining when rain is steady remain qualitative and arbitrary. The authors suggest a definition for steadiness that can be used to quantify the elusive notion of natural variability. In particular, the logical criteria for steadiness imply statistical stationarity and lack of correlation between raindrops in neighboring volumes, requirements identical to those for the drops being distributed according to a Poisson process at all scales. Hence, steady rain is Poissonian. Explicit equations for the variance of the rainfall rates are developed. They show that, …

Thermoelectric Properties Of Bi2sr2co2o9 Whiskers Under Hydrostatic Pressure, F Chen, Kevin L. Stokes, Ryozi Funahashi

Physics Faculty Publications

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 {BC-222} single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of S and four-wire electrical conductivity (sigma) under high pressure. As a result, the power factor (S2sigma) was decreased less than 20% by pressure. From the temperature dependence of sigma, the band gap of BC-222 whiskers increase very slightly …

Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu

Physics Faculty Publications

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core’’ material and CoPt–PMMA …

Application Of Plasma Resonance Condition For Prediction Of Large Kerr Effects, A. De, A. Puri

Physics Faculty Publications

Resonance like enhancement of magneto-optic Kerr effects (MOKEs) have been attributed to numerous effects, one of them being plasma resonance of free charge carriers, which is analytically and numerically investigated here. Analytical expressions for frequency dependent enhancement of MOKE are obtained in the general framework of the Drude model, which are then applied to well known expressions describing MOKE. The derived expressions are numerically tested for various optical constants. It is known that for certain materials, the resonance like enhancements in the Kerr spectrum occur in the near vicinity of Re[ε_xx]=1, which is generally near the …