Physical Sciences and Mathematics Commons^™

Recent Advances In The Comparison Of Matter— And Antimatter—Atom Collisions, D. R. Schultz, Ronald E. Olson, C. O. Reinhold

Physics Faculty Research & Creative Works

The relatively recent advent of low energy antimatter projectiles has spurred a rapid advance in the comparison of matter- and antimatter-atom collisions. These experimental studies have in turn stimulated a great deal of theoretical effort to explain their results, and together both theory and experiment have shed new light on the dynamics of ion-atom collisions. Here we review these developments with particular emphasis on the processes of ionization and charge transfer. © 1991 IOP Publishing Ltd.

Origins Of Compositional Order In Nipt Alloys, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy

Duane D. Johnson

We investigate the cause of compositional ordering in fcc Ni0.50Pt0.50 on the basis of a first-principles theory of electronic structure and finite-temperature concentration fluctuations. We treat the size effect, electronegativity, and band filling on an equal footing and find that the first of these dominates, leading to L10 ordering in agreement with experiment. An electronic origin is given for the metallurgical ‘‘rule of thumb’’ that alloys comprised of big atoms and little atoms tend to order into simple stuctures.

Selective Area Deposition Of Boron On Si(111) Induced By Synchrotron Radiation, R.A. Rosenberg, F.K. Perkins, D.C. Mancini, G.R. Harp, B.P. Tonner, S. Lee, Peter A. Dowben

Peter Dowben Publications

We have performed the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR). Contamination-free thin films were grown at room temperature using decaborane (B₁₀H₁₄) as the source gas. After deposition the films were examined using photoelectron microscopy, which showed that film growth was limited to the region illuminated by SR. The temperature of the substrate rose less than 10 K. These results indicate that gas-phase excitations are not important and that the films are deposited by a nonthermal, photoinduced mechanism. Masked exposures demonstrate the potential of this technique for patterned deposition.

Relativistic Approach For E± Scattering From Argon, Sultana N. Nahar, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Differential and integrated elastic, integrated total cross sections as well as various polarization parameters–the spin polarization P and the parameters T and U describing the change in the polarization vector during scattering–for the scattering of electrons and positrons from argon in the energy range of 3–300 eV are calculated using the relativistic Dirac equation. The real part of the projectile-target interaction is represented by a sum of model potentials. The phase shifts for large angular momenta ħl are calculated using the Born approximation. The relativistic calculations for the differential and integrated elastic cross sections obtained using the pure real potential …

The Interaction Between Dislocations And Intergranular Cracks, H. Zhang, Alexander H. King, R. Thomson

Alexander H. King

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in …

Substrate-Induced Magnetic Ordering Of Rare-Earth Overlayers, Peter A. Dowben, D. Lagraffe, Dongqi Li, A. Miller, Ling Zhang, L. Dottl, M. Onellion

Peter Dowben Publications

We have studied the magnetic ordering of terbium overlayers on Cu(100) and Ni(111), using angle-resolved photoemission. The 5p_3/2 to 5p_1/2 shallow-core-level branching ratios in different photoemission geometries provide a measure of the magnetic ordering in rare-earth-metal overlayers as a result of final-state effects in photoemission. We find that ferromagnetic substrates order paramagnetic terbium overlayers. This induced magnetic ordering is not a crystal-field effect and can be modeled by Ginzburg-Landau theory. Application of Ginzburg-Landau theory to our results suggests that the correlation length of paramagnetic terbium κ^-1 is between 2.5 and 3.5 Å. Reversible increases in …

The Jovian Ionospheric E Region, Y. H. Kim, Jane L. Fox

Physics Faculty Publications

We have constructed a model of the Jovian ionosphere that includes direct photoionization of hydrocarbon molecules. A high resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N) and high resolution cross sections for photoabsorption by H₂ bands in the range 842 to 1116 Å were constructed. Two strong solar lines and about 30% of the continuum flux between 912 and 1116 Å penetrate below the methane homopause despite strong absorption by CH₄ and H₂. We find that hydrocarbons (mainly C₂H₂) are ionized at a maximum rate of 55 cm^{−3 …}

First-Order Amplitude For General State-To-State Transitions In Hydrogen By Projectile Impact, Jack C. Straton

Physics Faculty Publications and Presentations

The closed analytic form for bound-state transitions due to projectile impact is found in the intermediate representation. The coordinate integral is obtained by evaluating the remaining two integrals in the general multicenter integral derived previously [J.C. Straton, Phys. Rev. A 41, 71 (1990)]. Evaluating the remaining time integral depends upon relating a sum of modified Bessel functions of the second kind K_N+1/2(z) to a simple polynomial in 1/z. The results of Van Den Bos and De Heer [Physica 34, 333 (1967)] are shown to be missing a phase factor of (-i)^(l′+l)

High-Resolution Photoelectron Spectrometry Study Of Conjugate Shakeup Processes In The Li 1s Threshold Region, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the ¹P and ³P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the ¹P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the ³P satellite correctly.

Phenomena Relating To Charge In Insulators: Macroscopic Effects And Microscopic Causes, Jacques Cazaux, Claude Le Gressus

Scanning Microscopy

Conservation of current under steady-state conditions makes it possible to determine the sign of charges trapped in an insulator subjected to ionizing radiation. The maximum value of the surface potential can thus be estimated.

On the basis of a given trapped charge distribution, the pattern of the electrical field and of the potential can thus be established, and the influence of the shape of the sample and its environment can be clearly shown. Change of trapped charges with time (at the start and after irradiation) is then examined. Finally, the microscopic causes of trapping of charge is suggested by analogy …

Critical Properties Of A Randomly Driven Diffusive System, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We consider a system of interacting particles, diffusing under the influence of both thermal noise and a random, external electric field which acts in a subspace of m dimensions. In the nonequilibrium steady state, the net current is zero. When the interparticle interaction is short ranged and attractive, a second-order phase transition is expected. Analyzing this system in field-theoretic terms, we find the upper critical dimension to be 4-m and its behavior to fall outside the universality classes of the equilibrium Ising model and the usual driven diffusive system. A new fixed point and critical exponents are computed.

Radiative Transfer In Astronomical Masers. Iii. Filamentary Masers, Moshe Elitzur, Christopher F. Mckee, David J. Hollenbach

Physics and Astronomy Faculty Publications

This paper, the last in a series, presents the complete solution of a filamentary maser. The contribution of rays emanating from the filament sidewall is essential for the solution self-consistency during saturation. We develop an integral equation to calculate this contribution, devise an iteration scheme to solve it, and perform the first two iterations. The solution provides complete expressions for the distributions of intensity and flux across the source as functions of position and direction with regard to the axis. One consequence of radiation beaming, somewhat surprising at first, is that the filament appears smaller when viewed off-axis, at angles …

Gaussian Reference Auid And Interpretation Of Quantum Geometrodynamics, Karel V. Kucha, Charles G. Torre

Aerospace, Physics, and Space Science Faculty Publications

The of vacuum geometrodynamics is turned into a Schrödinger equation by imposing the normal Gaussian coordinate conditions with s and then restoring the coordinate invariance of the action by parametrization. This procedure corresponds to coupling the gravitational field to a reference fluid. The source appearing in the Einstein law of gravitation has the structure of a heat-conducting dust. When one imposes only the Gaussian time condition but not the Gaussian frame conditions, the heat flow vanishes and the dust becomes incoherent. The canonical description of the fluid uses the Gaussian coordinates and their conjugate momenta as the fluid variables. The …

Composite Operator Renormalization And The Trace Anomaly, David G. Robertson

Physics Faculty Scholarship

The general connection between the renormalization of elementary fields and couplings and of appropriate composite operators is discussed. A general method is presented for computing the anomalous dimension matrix of the lagrangian composite operators, to all orders in perturbation theory, in terms of the elementary beta functions and anomalous dimensions. The trace anomaly for a general field theory is determined.

A Search For Embedded Young Stellar Objects In And Near The Ic 1396 Complex, Richard Schwartz, Bruce Wilking, Armen Giulbudagian

Physics Faculty Works

The IRAS data base is used to locate young stellar object candidates in and near the IC 1396 complex located in the Cepheus OB2 association. Co-added survey data are used to identify all sources with a flux density Snu(100) greater than 10 Jy and with Snu(100) greater than Snu(60). The 15 sources located at the positions of globules and dark clouds are further analyzed using the in-scan slices to assess the source profiles

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom Ii: The Green Functions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

This is the second in a series of three papers in which it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. In this paper the nonrelativistic Green function is examined in detail; new functional forms are presented and a clear mathematical progression is shown to link these and most other known forms. A linear transformation of the four radial parts of the relativistic Green function is given which allows for the presentation of this function as a simple generalization of the non-relativistic Green function. …

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom: Iii. The Reduced Green Functions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

The last in a series of three papers in which it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. The work presented here is concerned with the reduced Green functions which arise in second-order stationary state perturbation theory. Using a simple linear transformation of the four radial parts of the relativistic reduced Green function it is shown how the non-relativistic and relativistic functions are special instances of the solution of a general second-order differential equation. The general solution of this equation is exhibited in …

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom I: The Wavefunctions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

In this and the following two papers in this series it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. The angular part of such calculations, being well understood, is performed in the standard way. In this, the first paper, it is shown how a suitable linear transformation of the two relativistic radial wavefunctions allows the pair of relativistic coupled differential equations to be written as two uncoupled second-order equations which are simple generalizations of the corresponding non-relativistic equation. This transformation is presented in a …

Erratum: Expectation Values Of Rp For Arbitrary Hydrogenic States (Physical Review A (1991) 43, 11, (6432)), Gordon W. F. Drake, R. A. Swainson

Physics Publications

No abstract provided.

Variational Calculation For The Ground State Of Lithium And The Qed Corrections For Li-Like Ions, D. K. Mckenzie, Gordon W. F. Drake

Physics Publications

High-precision variational calculations using multiple basis sets in Hylleraas coordinates are presented for the 1s22s 2S state of lithium. The variational bound of -7.478 060 326(10) a.u. for the nonrelativistic energy is in good agreement with our revised experimental value of -7.47 806 034(20) a.u., thereby resolving a long-standing disrepancy. Two-electron calculations of the QED corrections are extended to three-electron systems and compared with other results. The comparison for Li-like ions up to U89+ suggests a simple interpretation for the ''screening of the Lamb shift'' recently calculated by Cheng, Johnson, and Sapirstein [Phys. Rev. Lett. 66, 2960 (1991)]. © 1991 …

Quantum Defects And The 1/N Dependence Of Rydberg Energies: Second-Order Polarization Effects, Gordon W. F. Drake, R. A. Swainson

Physics Publications

The principal result of this paper is a general expression for the second-order dipole polarization energy of a Rydberg electron resulting from the term -1/r4 in the asymptotic potential, where 1 is the core polarizability. It is shown that the second-order term contributes even as well as odd powers of 1/n in a 1/n expansion of the energies for Rydberg states. The results are used to extend the interpretation of the terms in a quantum-defect expansion. It is shown that the Ritz expansion for the quantum defect, which contains only even inverse powers of the effective quantum number n*, provides …

Measurement Of The N=2 Lamb Shift In He+ By The Anisotropy Method, A. Van Wijngaarden, J. Kwela, Gordon W. F. Drake

Physics Publications

A high-precision measurement of the 2s 2S1/22p 2P1/2 Lamb shift in He+ by the quenching-anisotropy method is reported. The theory and experimental method are described in detail. The measured value of 14042.520.16 MHz (11 parts per million) rivals the accuracy of Lamb-shift measurements in hydrogen by microwave resonance. By subtracting the known low-order terms in the Lamb shift, we interpret the results as a measurement of the order (Z)6mc2 and higher contributions to the electron self-energy GSE(Z). The various contributions to the Lamb shift are discussed, and a revised value for GSE(Z) at low Z is extracted from high-Z calculations. …

The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz

Physics - All Scholarship

The space of all solutions to the string equation of the symmetric unitary one-matrix model is determined. It is shown that the string equation is equivalent to simple conditions on points V 1 and V 2 in the big cell Gr (0) of the Sato Grassmannian Gr. This is a consequence of a well-defined continuum limit in which the string equation has the simple form [P; Q \Gamma ] = 1, with P and Q \Gamma 2 \Theta 2 matrices of differential operators. These conditions on V 1 and V 2 yield a simple system of first order differential equations …

Magnetic-Field-Induced Alignment-To-Orientation Conversion In Sodium, G. W. Schinn, Xianming Han

Scholarship and Professional Work - LAS

We report a detailed investigation of excited-state alignment-to-orientation conversion in the presence of an external magnetic field. This counterintuitive phenomenon occurs under intermediate-coupling conditions. A weak, linearly polarized, cw laser beam was used to excite and align the Na 3P3/2 state in an atomic beam along the z direction. The degree of circular polarization of the resulting fluorescence was detected along the z direction as a function of magnetic-field strength. The spectrally integrated transitions originating from individual F levels of the 3S1/2 state yield a maximum circular-polarization fraction of ∼40%; integrating the circular polarization over all the allowed 3S1/2-3P3/2 transitions …

Resistivity And Thermoelectric-Power Measurements Of PrXY1-XBa2Cu3O7-Δ Up To 1200 K And An Electronic-Structure Analysis, B. Fisher, J. Genossar, L. Patlagan, J. Ashkenazi

Physics Articles and Papers

We report measurements of absolute thermoelectric power and resistivity in Pr_xY_1-xBa₂Cu₃O_7-δ, as function of x and δ, over a wide temperature range. At high temperature, the substitution of Pr for Y does not affect the thermopower and resistivity; Pr behaves then as a trivalent ion: Pr³⁺. For small x and δ the effects of substitution of Y by Pr and of oxygen deficiency on the low-temperature resistivity are additive. A simple electronic-structure model is proposed to account for thermopower as function of temperature, x, and δ.

Flux States For The Infinite-U Limit Of The Hubbard Model, S. E. Barnes

Physics Articles and Papers

For finite doping, δ, relative to half filling, it is shown, within the confines of a mean-field auxiliary-operator formulation, for the strictly infinite-U, i.e., J=0, limit of the two-dimensional Hubbard model, that the spinons generate a fictitious magnetic flux to which holons are subject and vice versa. For small doping, a flux state is the absolute ground state and has 1-δ=2p/q, where p/q is a rational fraction and the flux per plaquette is Φ=(p/q)Φ₀, where Φ₀ is the flux quantum. This phenomenon can be viewed upon as an all-electron Peierls instability or as broken statistical symmetry.

Electronic Properties Of Monocapped Prismane And Basket Iron-Sulphur Clusters, B. S. Snyder, M. S. Reynolds, R. H. Holm, G. C. Papaefthymiou, R. B. Frankel

Physics

The ground state electronic properties of the mixed-valence clusters Fe₇S₆ (PEt₃)₄Cl₃ (1), Fe₆S₆(PEt₃)₄L₂ [L = Cl− (2), Br− (4), I− (5) and PhS− (6)], Fe₆Se₆ (PEt₃)₄Cl₂ (3) and [Fe₆S₆(PEt)₆]¹⁻ (9), have been investigated by magnetic susceptibility, magnetization and Mössbauer spectroscopic measurements. Cluster 1 has a (idealized C_3v) monocapped prismane structure and clusters 2–6 and 9 adopt the C_2v “basket” configuration based on the [Fe_{6 …}

Magnetic Fine Particles In Biological Systems, Dominic P.E. Dickson, Richard B. Frankel

Physics

Two examples of biological magnetic fine particles are considered: iron-storage proteins and magnetotactic bacteria. These cover many aspects of this field, including the use of well-defined biological systems for testing theoretical models, using magnetic properties to distinguish between different biological materials, producing magnetic materials by biological processes, and using optimised biological magnetic systems as a guide to the production of synthetic magnetic materials.

Diffuse Band Profiles In The Spectrum Of Hd 29647: Evidence For A Molecular Origin?, Theodore P. Snow, C G. Seab

Physics Faculty Publications

High signal-to-noise ratio spectra have been obtained of the diffuse interstellar bands at 5780 and 5797 Å in the spectrum of HD 29647, a heavily reddened star within or behind a portion of the Taurus dark cloud complex. The observations were made using the coudé spectrograph on the Canada-France-Hawaii Telescope. The Reticon detector combined with the coudé spectrograph and excellent observing conditions allowed S/N ratios as high as 200 for this star, which was V=8.37 and E(B–V)=1.03. In two separate exposures both bands were found to be narrower and weaker than normal values for …

The Photorefractive Effect In Batio3, Tom Savard

Honors Theses, 1963-2015

The photorefractive effect was observed in a sample of BaTiO, crystal. In two-beam coupling experiments, the crystal failed to amplify the signal beam even though experimental configurations that provided other researchers with large gains were used. However, beam fanning, a two-beam coupling effect, was observed. The unmeasurable gain of our crystal in twc-beam coupling experiments might be due to multiple domains in the crystal or competition between hole and electron charge carriers. In addition, a self-pumped phase conjugate mirror was made using the "cat" configuration. The formation of the phase conjugate mirror in the crystal was observed using the image …