Physical Sciences and Mathematics Commons^™

Chemical Bonding, Elasticity, And Valence Force Field Models: A Case Study For Α-Pt2si And Ptsi, Gus L. W. Hart, J. E. Klepeis, O. Beckstein, O. Pankratov

Faculty Publications

We have carried out a detailed study of the chemical bonding for two room-temperature stable platinum silicide phases, tetragonal α-Pt2Si. These elements of the bonding are further analyzed by constructing valence force field models using the results from recent first principles calculations of the six (nine) independent, nonzero elastic constants of α-Pt2Si (PtSi). The resulting volume-, radial-, and angular-dependent force constants provide insight into the relative strength of various bonding elements as well as the trends observed in the elastic constants themselves. The valence force field analysis yields quantitative information about the nature of the chemical bonding that is not …

Poynting's Theorem And Luminal Total Energy Transport In Passive Dielectric Media, Scott Glasgow, Michael Ware, Justin Peatross

Faculty Publications

Without approximation the energy density in Poynting's theorem for the generally dispersive and passive dielectric medium is demonstrated to be a system total dynamical energy density. Thus the density in Poynting's theorem is a conserved form that by virtue of its positive definiteness prescribes important qualitative and quantitative features of the medium-field dynamics by rendering the system dynamically closed. This fully three-dimensional result, applicable to anisotropic and inhomogeneous media, is model independent, relying solely on the complex-analytic consequences of causality and passivity. As direct applications of this result, we show 1 that a causal medium responds to a virtual, instantaneous …

Measurement Of DΣ/Dm And Forward-Backward Charge Asymmetry For High-Mass Drell-Yan E+E- Pairs From Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on a measurement of the mass dependence of the forward-backward charge asymmetry, A_FB, and production cross section dσ /dM for e⁺e^- pairs with mass M_ee> 40 GeV/c². The data sample consists of 108 pb^-1 of pp̅ collisions at √s= 1.8 TeV taken by the Collider Detector at Fermilab during 1992–1995. The measured asymmetry and dσ/dM are compared with the predictions of the standard model and a model with an extra Z′ gauge boson.

Threshold Effects On Angular Distributions For Multiphoton Detachment By Intense Elliptically Polarized Light, Bogdan Borca, M.V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Unusual threshold effects are found theoretically in the frequency and intensity dependence of angular distributions produced by an elliptically polarized laser as well as in the elliptic dichroism parameter, which measures the asymmetry of the angular distribution.

Fabrication Of Chromium Oxide Nanoparticles By Laser-Induced Deposition From Solution, Z.C. Zhong, R.H. Cheng, Jocelyn Bosley, Peter A. Dowben, David J. Sellmyer

David Sellmyer Publications

We have successfully deposited well-dispersed nanoscale chromium oxide particles by laser-induced solution deposition (LISD) from solution with CrCl₂ and organic solvents. The particles have narrow distributions about three sizes: 230, 350 and 400 nm and are uniform in composition and contain little contamination. We show that LISD is a new technique for producing nanoparticle chromium oxides with uniform composition, controllable size and high yield.

Three-Jet Production In Diffractive Deep Inelastic Scattering At Hera, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

Three-jet production in the reaction ep → eXp has been studied with the ZEUS detector at HERA using an integrated luminosity of 42.74 pb-1.The data were measured in the kinematic region 5 < Q2 < 100 GeV2, 200 < W < 250 GeV and 23 < MX < 40 GeV. The diffractive signal was selected by requiring a large rapidity gap in the outgoing proton direction. Jets were reconstructed in the centre-of-mass system of X using the exclusive kT-algorithm. A sample of three-jet events in diffraction has been identified. Differential cross sections were measured as a function of the jet pseudorapidity and jet transverse momentum with respect to the virtual photon-pomeron axis. The jets going in the pomeron direction are broader than those going in the virtual-photon direction. This is consistent with models predicting that gluons are predominantly produced in the pomeron direction and quarks in the virtual-photon direction. © 2001 Elsevier Science B.V. All rights reserved.

Enhanced Double Ionization With Circularly Polarized Light, Glen D. Gillen, M. A. Walker, L. D. Van Woerkom

Physics

Using 120-fs, 800-nm Ti:sapphire laser pulses, ionic yields of singly and doubly charged magnesium ions were measured as a function of intensity and laser field ellipticity. A clear “nonsequential” enhancement of the doubly charged ion is observed for circularly polarized light in addition to linearly polarized light. Over the entire intensity range the double-ionization yield is considerably higher for linear polarization than it is for circular polarization.

Magnetic Properties Of The Mnbi Intermetallic Compound, Jinbo Yang, Kishore Kamaraju, William B. Yelon, William Joseph James, Qingsheng Cai, A. Bollero

Physics Faculty Research & Creative Works

A MnBi alloy containing over 90 wt% low-temperature phase (LTP) has been obtained by high-temperature sintering and magnetic purification. The coercivity of the bonded MnBi magnet increases with increasing temperatures. A coercivity of 2.0 T has been achieved at 400 K. The maximum energy product (BH)_max; of the magnet is 7.7 MGOe (61 kJ/m³) and 4.6 MGOe (37 kJ/m³) at room temperature and 400 K, respectively. Neutron diffraction and magnetic data reveal a spin reorientation, which gives rise to low anisotropy fields and coercivity at lower temperatures for the LTP MnBi alloy.

Recoil Momentum Spectroscopy Of Highly Charged Ion Collisions On Magneto-Optically Trapped Na, J. W. Turkstra, R. Hoekstra, S. Knoop, D. Meyer, R. Morgenstern, Ronald E. Olson

Physics Faculty Research & Creative Works

An attempt was made to derive new generation of cold targets for cold target recoil oil momentum spectroscopy (COLTRIMS) experiments. The ultracold targets were obtained by laser cooling and trapping in a magneto-optical trap (MOT). Impact parameter sensitive information about multielectron capture processes was obtained.

Universal Negative Poisson Ratio Of Self Avoiding Fixed Connectivity Membranes, Mark Bowick, Angelo Cacciuto, G. Thorleifsson, A. Travesset

Physics - All Scholarship

We determine the Poisson ratio of self-avoiding fixed-connectivity membranes, modeled as impenetrable plaquettes, to be sigma=-0.37(6), in statistical agreement with the Poisson ratio of phantom fixed-connectivity membranes sigma=-0.32(4). Together with the equality of critical exponents, this result implies a unique universality class for fixed-connectivity membranes. Our findings thus establish that physical fixed-connectivity membranes provide a wide class of auxetic (negative Poisson ratio) materials with significant potential applications in materials science.

Observation Of The Kapitza-Dirac Effect, Daniel L. Freimund, Kayvan Aflatooni, Herman Batelaan

Department of Physics and Astronomy: Faculty Publications

In their famous 1927 experiment, Davisson and Germer observed the diffraction of electrons by a periodic material structure, so showing that electrons can behave like waves. Shortly afterwards, Kapitza and Dirac predicted that electrons should also be diffracted by a standing light wave. This Kapitza-Dirac effect is analogous to the diffraction of light by a grating, but with the roles of the wave and matter reversed. The electron and the light grating interact extremely weakly, via the ‘ponderomotive potential,’ so attempts to measure the Kapitza-Dirac effect had to wait for the development of the laser. The idea that the underlying …

Quantal Density Functional Theory Of Excited States, Viraht Sahni, Lou Massa, Ranbir Singh, Marlina Slamet

Physics Faculty Publications

We explain by quantal density functional theory the physics of mapping from any bound nondegenerate excited state of Schrödinger theory to an S system of noninteracting fermions with equivalent density and energy. The S system may be in a ground or excited state. In either case, the highest occupied eigenvalue is the negative of the ionization potential. We demonstrate this physics with examples. The theory further provides a new framework for calculations of atomic excited states including multiplet structure.

Measurement Of The Top Quark PT Distribution, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have measured the p_T distribution of top quarks that are pair produced in pp̅ collisions at √s=1.8 TeV using a sample of tt̅ decays in which we observe a single high-p_T charged lepton, a neutrino, and four or more jets. We use a likelihood technique that corrects for the experimental bias introduced due to event reconstruction and detector resolution effects. The observed distribution is consistent with the standard model prediction. We use these data to place limits on the production of high-p_T top quarks suggested in some models of anomalous top quark pair production.

On Misorientation Distribution Evolution During Anisotropic Grain Growth, Elizabeth A. Holm, Gregory N. Hassold, Mark A. Miodownik

Physics Publications

In order to study the development of texture and boundary character during annealing, three-dimensional grain crystallography and crystallographically mediated grain boundary properties were incorporated into a finite temperature Monte Carlo model for grain growth. Randomly textured microstructures evolve normally, with growth exponent n=0.96. While texture remains random, the steady-state boundary misorientation distribution favors low-angle boundaries. To first order, low-angle boundaries increase by lengthening, not by proliferating. In contrast, microstructures with a strong single-component texture develop four-grain junctions and highly curved grain boundaries, which alter evolution. The boundary misorientation distribution narrows and shifts to low angles, and no steady state …

Off-Diagonal Exchange-Induced Transverse And Field-Induced Spin-Flop Order In The Diluted Metamagnet Fe0.85Mg0.15Br2, Wolfgang Kleeman, H. Aruga Katori, T. Kato, Christian Binek, K. Katsumata

Christian Binek Publications

Specific heat and Faraday rotation magnetometry were used to determine the axial magnetic phase diagram of the dilute hexagonal antiferromagnet Fe_0.85Mg_0.15Br₂. In contrast to metamagnetic pure FeBr₂, the first-order line of transverse phase transitions, H1(T), is disconnected with the antiferro-to-paramagnetic phase line H_c(T) and extends down to H_t=0 at T_t≈8.7 . This is attributed to symmetric off-diagonal exchange in the presence of structural disorder. Moreover, a spin-flop phase emerges beyond H_c(T) up to a bicritical point (T_b≈9.3 , μ_oH …

Seeding Effect On Micro- And Domain Structure Of Sol–Gel-Derived Pzt Thin Films, A. L. Kholkin, Alexei Gruverman, A. Wu, M. Avdeev, P. M. Vilarinho, I. M. Miranda Salvado, J. L. Baptista

Alexei Gruverman Publications

Current trend to miniaturization requires precise control of micro- and domain structure of ferroelectric materials at the nanoscale level. This is essential for future applications of ferroelectric thin films in non-volatile memories, microactuators and pyroelectric arrays. In this work, the seeding effect on the nanoscale properties of ferroelectric Pb(Zr,Ti)O₃ (PZT) thin films is investigated using scanning force microscopy (SFM) capable of simultaneously resolving topographic and domain features on the surface of the films. It is shown that the addition of 5 mol% seeds (fine PZT powder) into the sol–gel precursor solution completely modifies the film’s microstructure leading to the …

The Blazhko Effect Of The Rr Lyrae Star Dr Andromedae, Kevin M. Lee, Edward G. Schmidt

Edward Schmidt Publications

We have obtained 551 new V and R observations of the RR Lyrae star DR Andromedae. Our data set is consistent with a primary period of 0.563118 days; however, the light curve of DR And cannot be well described by a single period. We conclude that DR And demonstrates the Blazhko effect with a Blazhko period of approximately 57.5 days.

Strong Enhancement Of Superconducting TC In Ferromagnetic Phases, Theodore R. Kirkpatrick, Dietrich Belitz, Thomas Vojta, Rajesh S. Narayanan

Physics Faculty Research & Creative Works

It is shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of the magnons to the longitudinal magnetic susceptibility. Together with the tendency of the low-temperature ferromagnetic transition in very clean Heisenberg magnets to be of first order, this qualitatively explains the phase diagram recently observed in UGe₂.

Measurement Of The W Boson Mass With The Collider Detector At Fermilab, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present a measurement of the W boson mass using data collected with the CDF detector during the 1994–1995 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 30115 W→eν events recorded in an integrated luminosity of 84 pb^-1 gives a mass M_w=80.473±0.065(stat) ±0.092(syst) GeVc². A fit to the transverse mass spectrum of a sample of 14740 W→μν events from 80 pb^-1 gives a mass M_w=80.465±0.100(stat) ±0.103(syst) GeV/c². The dominant contributions to the systematic uncertainties are the …

Mev Magnetosheath Ions Energized At The Bow Shock, S. Chang, J. D. Scudder, K. Kudela, Harlan E. Spence, J. F. Fennell, R. P. Lepping, R. P. Lin, C. T. Russell

Physics & Astronomy

A causal relationship between midlatitude magnetosheath energetic ions and bow shock magnetic geometry was previously established for ion energy up to 200 keV e−1 for the May 4, 1998, storm event. This study demonstrates that magnetosheath ions with energies above 200 keV up to 1 MeV simply extend the ion spectrum to form a power law tail. Results of cross-correlation analysis suggest that these ions also come directly from the quasi-parallel bow shock, not the magnetosphere. This is confirmed by a comparison of energetic ion fluxes simultaneously measured in the magnetosheath and at the quasi-parallel bow shock when both regions …

Dynamical Relativistic Effects In Photoionization: Spin-Orbit-Resolved Angular Distributions Of Xenon 4d Photoelectrons Near The Cooper Minimum, H. Wang, G. Snell, Oliver Hemmers, M. M. Sant'anna, I. A. Sellin, N. Berrah, Dennis W. Lindle, P. C. Deshmukh, N. Haque, S. T. Manson

Environmental Studies Faculty Publications

Two decades ago, it was predicted [Y. S. Kim et al., Phys. Rev. Lett. 46, 1326 (1981)] that relativistic effects should alter the dynamics of the photoionization process in the vicinity of Cooper minima. The present experimental and theoretical study of the angular distributions of Xe 4d_3/2 and 4d_5/2 photoelectrons demonstrates this effect for the first time. The results clearly imply that relativistic effects are likely to be important for intermediate- Z atoms at most energies.

Development And Construction Of A White Light Profiler For Industrial Applications, Martin Somers

Masters

With the ever decreasing tolerances in modern manufacturing processes it has become more important to define surface topography measurements quickly and accurately. Though contact methods, using the stylus probe, have been used for a long time more optical techniques are being brought into the market place. The advantages in using optical methods is obvious; no contact with the surface eliminates damage due to a probing tip and also the surface may be scanned in a matter of seconds. Optical techniques also have the advantage that a full field of view may be acquired, unlike point measurement where the surface must …

Nature Of Charge Carriers In Disordered Molecular Solids: Are Polarons Compatible With Observations?, Paul Ernest Parris, Vasudev M. Kenkre, David H. Dunlap

Physics Faculty Research & Creative Works

Polaronic theories for charge transport in disordered organic solids, particularly molecularly doped polymers, have been plagued by issues of internal consistency related to the magnitude of physical parameters. We present a natural resolution of the problem by showing that, in the presence of correlated disorder, polaronic carriers with binding energies Δ ~ 50 - 500 meV and transfer integrals J ~ 1 - 20 meV are completely consistent with the magnitudes of field and temperature dependent mobilities observed.

Tunable Local Polariton Modes In Semiconductors, Michael G. Foygel, Alexey Yamilov, Lev I. Deych, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We study the local states within the polariton band gap that arise due to deep defect centers with strong electron-phonon coupling. Electron transitions involving deep levels may result in alteration of local elastic constants. In this case, substantial reversible transformations of the impurity polariton density of states occur, which include the appearance/disappearance of the polariton impurity band, and its shift and/or the modification of its shape. These changes can be induced by thermo- and photoexcitation of the localized electron states or by trapping of injected charge carriers. We develop a simple model, which is applied to the O_p center …

Comment On “Photodetachment In Combined Static And Dynamic Electric Fields”`, Ilya I. Fabrikant, M.V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

The theoretical analysis of C. Rangan and A. R. P. Rau [Phys. Rev. A 61, 033405 (2000)] on the process of photodetachment of H^- in a strong static electric field, which calls into question the predictions of B. Gao and A. F. Starace [Phys. Rev. A 42, 5580 (1990)] and also of M. Q. Bao et al. [Phys. Rev. A 58, 411 (1998)], is shown in this Comment to be incorrect. First, we point out that a number of assumptions of Rangan and Rau’s analysis rest on tenuous theoretical grounds. Second, we adduce two completely independent and different …

Invariant Spinor Representations Of Finite Rotation Matrices, N. L. Manakov, A. V. Meremianin, Anthony F. Starace

Anthony F. Starace Publications

Our recent results [N. L. Manakov et al., Phys. Rev. A 57, 3233 (1998); 61, 022103 (2000)] on the invariant representations of finite rotation matrices (FRM’s) of integer rank j (in terms of tensor products of vectors connected with a space-fixed reference frame) are generalized here for the general case of arbitrary (i.e., integer or half-integer) rank j. This extension is carried out by using new spinor representations of FRM’s in terms of specially introduced spinor-annihilation operators. We demonstrate that all widely used, standard representations of FRM’s follow as special cases of our invariant representation for particular parametrizations …

Thermal Activation Between Landau Levels In The Organic Superconductor Β″-(Bedt-Ttf)2sf5ch2cf2so3, Gary L. Gard, M. S. Nam, A. Ardavan, J. A. Symington, J. Singleton, N. Harrison, C. H. Mielke, J. A. Schlueter, Rolf Walter Winter

Chemistry Faculty Publications and Presentations

We show that Shubnikov–de Haas oscillations in the interlayer resistivity of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ become very pronounced in magnetic fields ~60T. The conductivity minima exhibit thermally activated behavior that can be explained simply by the presence of a Landau gap, with the quasi-one-dimensional Fermi surface sheets contributing negligibly to the conductivity. This observation, together with complete suppression of chemical potential oscillations, is consistent with an incommensurate nesting instability of the quasi-one-dimensional sheets.

Transport Properties Of Bi2−Xinxse3 Single Crystals., J. Navrátil, T. Plecháček, J. Horák, S. Karamazov, P. LošŤÁK, Jeffrey Dyck, W. Chen, C. Uher

Jeffrey Dyck

The paper reports on the temperature dependence of the electrical and thermal conductivity, Hall constant, and Seebeck coefficient of Bi2−xInxSe3 (x=0, 0.2, 0.4) single crystals measured over the temperature range from 2 to 300 K. One single-valley conduction band model is used to interpret relations among transport coefficients. The data analysis relies on the use of a mixed carrier scattering mechanism consisting of acoustic scattering and scattering on ionized impurities. The effect of In incorporation into the Bi2Se3 crystal lattice on the individual components of thermal conductivity is evaluated and discussed. Copyright 2001 Academic Press.

Structural, Transport And Magnetic Studies Of Perovskite Bi1-X Cax Mn O3, Hyungje Woo

Dissertations

This dissertation presents an investigation of the fundamental physics of the perovskite system Bi_1-xCa_xMn0₃. This material belongs to a group of simple perovskites called the manganites which are of technological importance for magnetic device applications as read-head sensors.

The Bi_1-xCa_xMnO₃ system is known to exhibit charge ordering (and high sensitivity to magnetic fields) for a much broader range of x than the well-characterized La_1-xCa_xMnO₃ system. However, the properties of Bi_1-xCa_xMnO₃ over the entire doping range are not well understood. …

Detection Of Vapor Phase Mercury Species By Laser Fluorescence Methods, Xiaomei Tong

Dissertations

Elemental and compound mercury are often both volatile and air stable. Several mercury species emissions have been identified in off-gases from industrial processes. The high toxicity of mercury species and the presence of mercury species in municipal waste and coal have prompted a demand for a cost-effective, accurate, and rugged technique for real-time, continuous detection of mercury species vapors. Real-time, continuous emission measurements are important for process control, monitoring, and remediation. At present, there is no commercial continuous emission monitoring (CEM) technique or instrumentation to reliably monitor volatile mercury species emissions from industrial stacks. Conventional measurement methods, such as cold …