Physical Sciences and Mathematics Commons^™

Fock-Tani Hamiltonian For Reactions Involving Two-Electron Atoms, Jack C. Straton

Physics Faculty Publications and Presentations

The Fock-Tani Hamiltonian is found for scattering processes involving up to two ions and two electrons. Possible bound-state species include one or two electrons bound on an ion fixed at the origin, and a one-electron projectile atom. A diagrammatic technique is illustrated that simplifies the algebra of the transformation. Coulomb- or plane-wave states are automatically generated by the same asymptotic Hamiltonian for all arrangement channels.

Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Bounded Systems, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

Linear hydrodynamics yields the onset of convection for ascending autocatalytic reaction fronts in laterally bounded geometries. The system is studied in the limit of infinite and zero thermal diffusivity. For convection in a vertical slab of thickness a or a long vertical cylinder of radius a, the appropriate dimensionless driving parameter scrS=δga³/νD_c involves the fractional density difference δ between the unreacted and reacted fluids, the acceleration of gravity g, the kinematic viscosity ν, and the catalyst molecular diffusivity D_c. Calculated critical values scrS_c for onset of convection agree with recent experiments on iodate–arsenous acid …

One- And Two-Photon Detachment Of H- With Excitation Of H(N=2), Chih-Ray Liu, Ning-Yu Du, Anthony F. Starace

Anthony F. Starace Publications

The cross sections for one- and two-photon detachment of H- with excitation of the degenerate H(2s) and H(2p) levels are calculated within an adiabatic hyperspherical representation. Both the partial cross sections, σ(2s) and σ(2s), and the photoelectron angular distribution asymmetry parameters are obtained. Our one-photon detachment results are dominated by the ¹P⁰ shape resonance feature above threshold, which is well known from prior theoretical and experimental work, with which our results are compared in detail. Our two-photon detachment cross sections and angular distribution asymmetry parameters exhibit a half-cycle of dipole-field-induced …

Behavior Of An Ion In A Bubble In The Ground State, Joung Hoon Oh

Dissertations and Theses

Deuterons might be trapped in a bubble embryo which occur s due to statistical fluctuation in heavy water. The size of the bubble embryo is expected to be an order of a small molecule. The ground state energy level which the deuteron may occupy in the bubble is calculated by solving the Schroedinger equation, and by considering the interaction between the trapped deuteron by a spherical bubble and the surrounding polarized liquid medium (heavy water). From the dependence of the energy eigenvalue of the ground state on the bubble radius, the pressure exerted on the bubble wall is obtained. It …

Abnormal Behaviour Of Zero Degree Δ-Electron Emission On The Projectile Ionic Charge, O. Jagutzkit, S. Hagtnanni, H. Schmidt-Bockingt, Ronald E. Olson, D. R. Schultz, R. Dornert, R. Kocht, A. Skutlartz, A. González, T. B. Quinterosi, C. Kelbcht, P. Richardt

Physics Faculty Research & Creative Works

The 0° δ-electron emission was investigated by an electron-projectile coincidence technique as a function of incoming and outgoing projectile charge state for 0.53 MeV u^-1Cu^q+ on He. The electron emission spectra vary strongly with initial and final projectile charge state. For pure ionization channels the cross sections follow for low electron energy the q²-scaling law whereas in the binary encounter regime the scaling is reversed. Ctmc calculations are in fair agreement with the experimental data. © 1991 IOP Publishing Ltd.

The Dimension Of A Chaotic Attractor, Roslyn Gay Lindquist

Dissertations and Theses

Tools to explore chaos are as far away as a personal computer or a pocket calculator. A few lines of simple equations in BASIC produce fantastic graphic displays. In the following computer experiment, the dimension of a strange attractor is found by three algorithms; Shaw's, Grassberger-Procaccia's and Guckenheimer's. The programs were tested on the Henon attractor which has a known fractal dimension. Shaw's and Guckenheimer's algorithms were tested with 1000 data points, and Grassberger's with 100 points, a data set easily handled by a PC in one hour or less using BASIC or any other language restricted to 640K RAM. …

Selective Decay And Coherent Vortices In Two-Dimensional Incompressible Turbulence, William H. Matthaeus, W. Troy Stribling, Daniel Martinez, Sean Oughton, David Montgomery

Dartmouth Scholarship

Numerical solution of two-dimensional incompressible hydrodynamics shows that states of a near-minimal ratio of enstrophy to energy can be attained in times short compared with the flow decay time, confirming the simplest turbulent selective decay conjecture, and suggesting that coherent vortex structures do not terminate nonlinear processes. After all possible vortex mergers occur, the vorticity attains a particlelike character, suggested by the late-time similarity of the streamlines to Ewald potential contours.

Finger Formation In A Driven Diffusive System, D. H. Boal, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

A driven diffusive lattice gas is studied in a rectangular geometry: particles are fed in at one side and extracted at the other, after being swept through the system by a uniform driving field. Being periodic in the transverse direction, the lattice lies on the surface of a cylinder. The resulting nonequilibrium steady state depends strongly on this choice of boundary conditions. Both Monte Carlo and analytic techniques are employed to investigate the structure of typical configurations, the density profile, the steady-state current, and the nearest-neighbor correlations. As the temperature is lowered in a finite system, the simulations indicate a …

Anisotropic, Time-Dependent Solutions In Maximally Gauss-Bonnet Extended Gravity, T. Kitaura, James Thomas Wheeler

All Physics Faculty Publications

In an arbitrary number of dimensions, we find the full exact anisotropic, time-dependent, diagonal-metric solutions to maximally Gauss-Bonnet extended gravity theory. This class of theories, for which the lagrangian is an arbitrary linear combination of dimensionally extended Euler forms, is the most general gravitational theory in which the field equations contain no more than second derivatives of the metric.

We show that the space-time exponentially approaches an asymptotic state of constant, anisotropic curvature and prove three theorems concerning two generic types of singularities. The first theorem gives conditions for the existence of Kasner-like curvature singularities. For these the metric diverges …

Recoil Ions From Near-Zero-Impact-Parameter H+-Xe Collisions In The Range 20- 70 Kev, Wen-Qin Cheng, M. Eugene Rudd

M. Eugene Rudd Publications

Recoil ions from very small impact-parameter collisions of 20-70-keV protons with xenon atoms were selected by viewing only those ejected at 50° and 70° from the beam direction. These ions were charge-state analyzed and the cross sections determined for the production of charge states up to 6+. In such collisions, multiple ionization accounts for 60-80% of the ionizing collisions and 80-90 % of the total ionization.

Rbe Vs. Dose For Low Doses Of High-Let Radiations, Robert Katz, F. A. Cucinotta

Robert Katz Publications

(LET) radiations varies with cellular radiosensitivity parameters and the radiation environment. Of special interest is that the RBE varies as the dose of high-LET radiation to the power (1/m - 1) where /m is the “target number” parameter, which varies from 2-4 in different cell lines. This applies to neutrons as well as to heavy ions at sufficiently low doses such that cells are not activated in the γ-kill mode; that is, the tracks of single heavy ions are sufficiently far apart so that there are few cases of inter-track inactivation.

Comment On “Microdosimetry And Katz’S Track Structure Theory” By Marco Zaider, Robert Katz

Robert Katz Publications

To test radiobiological models one needs data from X- or γ-ray and HZE track segment irradiations of the widest possible dynamic range in dose, LET, end points, and test objects (enzymes, viruses, bacteria, cells, tissues, organs, and organisms). Some data are currently available. There are excellent data on the inactivation of dry enzymes and viruses which should serve as a test of every biophysical model. On many occasions Zaider has asserted the superiority of microdosimetric over track structure models, asserting that “radial dose distributions (on which track structure theory is based) are generally poor substitutes for exact microdosimetric distributions.” I …

Population Of Highly Excited Intermediate Resonance States By Electron Transfer And Excitation, Reinhold S. Schuch, Edson L B Justiniano, Michael Schulz, Sheldon Datz, Peter F. Dittner, J. P. Giese, Herbert F. Krause, Harald Schone, Charles Randy Vane, Stephen M. Shafroth

Physics Faculty Research & Creative Works

Coincidences between two sulfur K x rays were detected from collisions of hydrogenlike S ions with H₂ gas in the projectile energy range between 150 and 225 MeV. These K x rays are emitted in the decay of doubly excited states formed in the collisions via transfer and excitation. The excitation function for two coincident Kβ transitions peaks at about 175 MeV, slightly above the expected KMM resonance energy for resonant transfer and excitation (RTE). This demonstrates the occurrence of ΔN≥2 transitions (i.e., KMM and higher resonances) in the RTE process. The cross sections for the population of the …

Probing The Metal-Nonmetal Transition In Thin Metal Overlayers Using Resonant Photoemission, Peter A. Dowben, D. Lagraffe, Dongqi Li, G. Vidali, L. Zhang, L. Dottl, M. Onellion

Peter Dowben Publications

We have studied one and two monolayers of barium on Ni(111) and of mercury on Cu(100). Using resonant photoemission, we have found core excited electrons become delocalized with increasing barium coverage. Similarly, upon formation of the mercury bilayer (as determined by low-energy electron diffraction and by atom-beam scattering), there is a substantial increase in the screening of the photohole. A transition of the electronic structure akin to a metal-nonmetal (metal-insulator) transition is apparent in these final-state effects. The band structure for Hg is similar to the band structure expected for a free-standing film with a free-electron sd band. The delocalization …

Novel Methods For Deposition Of Boron Carbide Films, J. Mazurowski, S. Baral-Tosh, G. Ramseyer, J.T. Spencer, Yoon-Gi Kim, Peter A. Dowben

Peter Dowben Publications

By combining pentaborane (B₅H₉) and decarborane (B₁₀H₁₄) with methane in a plasma reactor, a variety of boron-carbides can be made over a wide range of compositions. The resulting thin films have uniform composition and appear to be polycrystalline.

The Deposition Of Nickel Boride Thin Films By Borane And Metallaborane Cluster Compounds, John A. Glass Jr., Shreyas Kher, Yoon-Gi Kim, Peter A. Dowben, James T. Spencer

Peter Dowben Publications

The deposition of high purity and controlled stoichiometry metal boride thin-film materials has recently received considerable interest. Borane clusters and their corresponding metal complexes are currently Wig investigated in our laboratories for their utility as unique source materials for the formation of metallic boride thin films by MOCVD. Variable composition nickel boride thin films ranging from 0.1 micron to several microns have been prepared. These new materials have been characterized by SEM, AES and XES. The magnetic properties of these new films have been investigated with torque magnetometry and magneto-optic Kerr effect magnetometry.

Thermal Desorption Of Hg Monolayers From Cu(100), Y.J. Kime, Jiandi Zhang, Peter A. Dowben

Peter Dowben Publications

A two dimensional phase transition from one adlayer structure to another is an inherent part of the thermal desorption of one monolayer of Hg on Cu(100). The energetics of this phase transition have been studied using thermal desorption spectroscopy (TDS). The TDS spectra reflect the coexistence of the two structural phases for a range of Hg exposures. The TDS spectra have been analyzed within a Polanyi-Wigner framework modified to account for the phase transition.

Double Excitation Of Helium By Fast Particles Of Charge Z, James H. Mcguire, Jack C. Straton

Physics Faculty Publications and Presentations

Results of calculations of double excitation of helium to n=2 states for fast projectiles of charge Z are presented. Nonzero Z³ contributions for single and double excitation occur only when time-ordering contributions from the second-order amplitude are nonzero. For double excitation, electron correlation must also be nonzero to obtain Z³ terms. The time-ordering effects arise from virtual off-energy-shell intermediate states. As with second-order amplitudes for Thomas singularities in electron capture, the energy-nonconserving amplitude is connected to the second-order energy-conserving amplitude by a dispersion relation. Comparison is made with experiment.

Kähler-Chern-Simons Theory And Symmetries Of Anti-Self-Dual Gauge Fields, V. Parameswaran Nair, Jeremy Schiff

Publications and Research

Kähler-Chern-Simons theory, which was proposed as a generalization of ordinary Chern-Simons theory, is explored in more detail. The theory describes anti-self-dual in-stantons on a four-dimensional Kähler manifold. The phase space is the space of gauge potentials, whose symplectic reduction by the constraints of anti-self-duality leads to the moduli space of instantons. We show that infinitesimal Bäcklund transformations, previously related to "hidden symmetries" of instantons, are canonical transformations generated by the anti-self-duality constraints. The quantum wave functions naturally lead to a generalized Wess-Zumino-Witten action, which in turn has associated chiral current algebras. The dimensional reduction of the anti-self-duality equations leading to …

Observability Of The Anapole Moment And Neutrino Charge Radius, Mj Musolf, Br Holstein

Barry R Holstein

The properties of the neutrino charge radius (NCR) and anapole moments (AM's) of elementary fermions, nucleons, and nuclei are discussed. The dependence of these off-shell electromagnetic couplings on the weak gauge parameter is explicitly demonstrated by a calculation performed in the Rξ gauge. The gauge dependence of the AM's and NCR implies that they cannot be observed in isolation from other second-order, electroweak effects. It is shown, however, that the AM's of various hadronic systems having an SU(2)L quantum number TL3=0 can be considered ``observables'' in certain formal, though unphysical, limits. It is argued that, apart from these special limits, …

Effect Of Microstructure On Coercivity Of C-Axis In-Plane-Oriented Co/Cr Multilayered Films, D. Wang, David J. Sellmyer, George C. Hadjipanayis

David Sellmyer Publications

The effect of the insertion of nonmagnetic Cr planes on coercivities of thin Co films has been studied in Co/Cr multilayered films. The in-plane coercivity H_c║ can be as high as 1800 Oe and can be adjusted easily, ranging from 650 to 1800 Oe. The large H_c║ is related to the Co(110) in-plane orientation which is induced by a Cr(100) in-plane-oriented underlayer. In addition, it appears that a decreasing saturation magnetization M_s, a decreasing average structural coherence length D in the direction perpendicular to the film, and a narrowing distribution of D are correlated …

Magneto-Optic And Optical Characterization Of Tb/Co Compositionally Modulated Amorphous Films, Liang-Yao Chen, Ping He, S. Nafis, William A. Mcgahan, John A. Woollam, David J. Sellmyer

David Sellmyer Publications

Amorphous Tb/Co compositionally modulated films were deposited on Si substrates with different modulation layer thicknesses ranging from about 2.5 to 15 Å. The nominal Tb to Co layer thickness ratios were systematically varied and the complex refractive index (n and k) and polar magneto-optical Kerr effects (rotation and ellipticity) were measured in the 3000–8000-Å spectral range as well. The samples were divided into two groups. In one group, the thickness of the Co layers was fixed, the Tb layer thickness varied. In the second group, the thickness of the Tb layer was fixed, and that of the Co …

Magneto-Optical Properties Of Mnbial Thin Films, J. X. Shen, Roger D. Kirby, David J. Sellmyer, Y. J. Wang

Roger Kirby Publications

Mn-Bi-Al thin films. were produced by sequential evaporation of the constituents, followed by an anneal at 300 °C. The temperature and composition dependencies of the Kerr rotation angle, absolute reflectivity, and magnetic anisotropy were measured. The results show that, up to 30 at. % Al concentration, the thin films retain the pure MnBi hexagonal structure. Further, for suitable Al content, the films have the same large Kerr rotation as MnBi. Pure MnBi films exhibit perpendicular anisotropy at room temperature and in-plane anisotropy for temperatures below 142 K. In contrast,. the Al-doped films prepared here have perpendicular anisotropy down to at …

The Process-Controlled Magnetic Properties In Nanostructured Fe/Ag Composite Films, Y.Z. Zhang, Sy_Hwang Liou, R.J. Deangelis, K.W. Lee, C.P. Reed, A. Nazareth

Sy-Hwang Liou Publications

Nanostructured Fe/Ag composite films were prepared by magnetron sputtering using a single target. Correlations between the microstructure and magnetic properties, in particular the effects of cluster-size distribution in the films, are discussed. The cluster-size distribution was calculated by analyzing the width and shape of the x-ray-diffraction peaks. The average cluster size in the films increased from 42 to 295 Å and from 38 to 320 Å in the systems of 41 and 27 vol % of Fe, respectively, as the substrate temperature increased from 100 to 500 °C. The maximum magnetic coercivity, as high as 900 Oe, has been observed …

Effect Of Interfacial Microstructure On Magnetic Properties Of Dysprosium Multilayers, Z.S. Shan, B. Jacobsen, Sy_Hwang Liou, David J. Sellmyer

Sy-Hwang Liou Publications

Nanostructured multilayers of Dy/M (M=Ta, Cu, Y, and Co) have been investigated. Correlations between the microstructure and the magnetic properties, in particular the effects of interfacial structure, are discussed. The temperature and layer-thickness dependences of anisotropy of these Dy/M multilayers can be interpreted reasonably in light of the model previously developed for the perpendicular anisotropy in amorphous multilayers.

Spacetime Dimension From A Variational Principle, D. Hochberg, James Thomas Wheeler

All Physics Faculty Publications

We consider spacetime as having an a priori arbitrary, possibly fractional dimension p>0 and propose a new variational principle for actions defined on p-dimensional spaces. Demanding that the action be stationary with respect to variations in p leads to a constraint equation whose solution yields an explicit determination of the dimension at the classical level. We illustrate these concepts by analyzing a model which reduces to free scalar field theory when p is any positive integer.

Transport Properties Of An Interacting Lattice Gas Model In A Charge Density Gradient By Monte Carlo Simulation, Ras B. Pandey, Songping Gao

Faculty Publications

A two-dimensional lattice is considered with a linear charge-density gradient produced by a charge source at one end and a sink at the opposite end. A fraction p of the lattice sites are occupied by mobile particles that interact only with neighboring particles and empty sites (the substrate) and carry charges from source to sink; the charge neutrality of the whole lattice is maintained. The root-mean-square (rms) displacement of the particles (i.e., the tracers) and their effective conductivity for the charge transport are studied as a function of temperature and concentration p. The rms displacement shows a crossover from diffusion …

Magneto-Optic Properties Of Uranium-Based Compounds, Roger D. Kirby, J. X. Shen, John A. Woollam, David J. Sellmyer

Roger Kirby Publications

Uranium-based compounds often show interesting magnetic properties and large polar Kerr rotations. Because of this, the wavelength and temperature dependencies of the polar Kerr rotation in several uranium-based compounds, including UMn₂Ge₂, UFe₂, and UGa₂, have been investigated. The Mn moments order ferromagnetically in UMn₂Ge₂ below 380 K, and while the U moments do not order ferromagnetically until the temperature is below 150 K. The measurements presented here show that the size of the Kerr rotation increases from 0.05° at room temperature to 0.15° when the U moments are ordered. …

Observation Of The Photorefractive Effect In A Polymer, Stephen Ducharme, J.C. Scott, R.J. Twieg, W.E. Moerner

Stephen Ducharme Publications

We report the first observation of the photorefractive effect in a polymeric material, the electro-optic polymer bisphenol-A-diglycidylether 4-nitro-1,2-phenylenediamine made photoconductive by doping with the hole-transport agent diethylamino-benzaldehyde diphenylhydrazone. The gratings formed exhibit dynamic writing and erasure, strong electric-field dependence, polarization anisotropy, and estimated space-charge fields up to 26 kV/cm at an applied field of 126 kV/cm. Application of similar concepts should provide a broad new class of easily fabricated photorefractive materials.

Removal Of Chlorine From Chlorine-Nitrogen Mixture In A Film Of Liquid Water, Sarwan S. Sandhu

Chemical and Materials Engineering Faculty Publications

In industry there are many examples of absorption of a gas with or without chemical reaction in the liquid phase. In physical absorption, a particular gaseous component is removed from a gas mixture due to its larger solubility in the liquid phase solvent. The removal of butane and pentane from a refinery gas mixture by a heavy oil in the liquid phase is an example of physical absorption. In absorption with chemical reaction, the gaseous component to be removed transfers across the gas-liquid interface due to a difference in the bulk chemical potentials or concentrations in the two phases. The …