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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 …

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 …

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.

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 …

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.

Quenching And Rotational Energy Transfer In Molecular Bromine: Br2(B), Dean A. Massman

Theses and Dissertations

This study investigates the rotational energy transfer processes of optically excited bromine molecules in the presence of several collision partners. Resolved laser induced fluorescence spectra of collisionally populated rotational states were analyzed by means of Stern Volmer analysis. Total rotational removal rate coefficients and state-to-state rotational removal rate coefficients for the v'=11,J'=35 level of Br₂(B) were obtained for collisions with Br₂(X), He, Ar and Xe. Rotational removal rate coefficients were also obtained for the v'11, J'=26 and 47; v'=14, J'=36 states of Br₂(B) with collisions with Ar. Total rotational removal rate for Br_{2 …}

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 …

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.

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 …

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.

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 …

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.

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.

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 …

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 …

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.

Fourier Transform Infrared (Ftir) Spectroscopy Analysis Of Combustion Aerosol, Gary Jacquin

Opportunities for Undergraduate Research Experience Program (OURE)

In conjunction with my co-op program at McDonnell-Douglas, my current OURE project is the analysis of combustion aerosols using Fourier Transform Infrared (FTIR) Spectroscopy. Aerosol science is a very important field as it is concerned with atmospheric chemistry, atmospheric physics, climate, public health, and environmental issues.

In the Cloud and Aerosol Sciences Laboratory (CASL) at UMR, combustion aerosols are generated by an in-house designed torch or burner. The fuels, JP4 and JP5, are provided by McDonnell-Douglas. Some other commercial fuels are also used. The primary objective of my OURE project was to generate and collect combustion aerosols for chemical analysis. …

Combustion Aerosol Morphology, Ronald P. Holland

Opportunities for Undergraduate Research Experience Program (OURE)

The following report entitled Carbon Aerosol Morphology is the result of research done through the University of Missouri--Rolla Graduate School program entitled Opportunities for Undergraduate Research Experience (OURE). My appointment was for the Summer - 1990 with the Cloud and Aerosol Sciences Laboratory, Department of Physics, located in Norwood Hall. The goal of this appointment was to study the size and morphology of combustion aerosols whose characteristics are dependent on the history of the particle, e.g. exposure to chemicals, scavenging effects, and other time dependent factors. Computer image processing software is available in the department for this purpose.

Synchrotron-Radiation-Induced Deposition Of Boron And Boron Carbide Films From Boranes And Carboranes: Decaborane, F. Keith Perkins, R.A. Rosenberg, Sunwoo Lee, Peter A. Dowben

Peter Dowben Publications

Boron has been deposited successfully on Si(111) from the synchrotron-radiation-induced decomposition of decaborane (14), i.e., B₁₀H₁₄. The rate of deposition is limited by the adsorption rate of decaborane (14) on the surface. In addition there is some indication that there is an activation barrier to dissociative adsorption. The synchrotron-radiation- induced growth rate of boron thin films from decaborane (14) is linear with coverage for a large range of thickness, suggesting a constant sticking coefficient for decaborane adsorption at room temperature.

Molecular-Orbital Studies Via Satellite-Free X-Ray Fluorescence: Cl-K Absorption And K–Valence-Level Emission Spectra Of Chlorofluoromethanes, Rupert C. Perera, P. L. Cowan, Dennis W. Lindle, R. E. Lavilla, T. Jach, R. D. Deslattes

Chemistry and Biochemistry Faculty Research

X-ray absorption and emission measurements in the vicinity of the chlorine K edge of the three chlorofluoromethanes have been made using monochromatic synchrotron radiation as the source of excitation. By selectively tuning the incident radiation to just above the Cl 1s single-electron ionization threshold for each molecule, less complex x-ray-emission spectra are obtained. This reduction in complexity is attributed to the elimination of multielectron transitions in the Cl K shell, which commonly produce satellite features in x-ray emission. The resulting "satellite-free" x-ray-emission spectra exhibit peaks due only to electrons in valence molecular orbitals filling a single Cl 1s vacancy. These …

A Mössbauer-Effect Study Of A Series Of R₂Fe₁₄C Hard Magnetic Materials, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, Fernande Grandjean, K. H. Buschow

Chemistry Faculty Research & Creative Works

The ⁵⁷Fe Mössbauer-effect spectra of the series of hard magnetic materials, R₂Fe₁₄C, where R is Nd, Gd, Tb, Dy, Ho, and Lu, have been measured at 295 K. All of these carbides exhibit uniaxial magnetic anisotropy. The spectra resemble those obtained for the related R ₂Fe₁₄B compounds and have been fit with the model used earlier for Nd₂Fe₁₄B. The magnitude of the hyperfine field on each site, as a function of rare earth, parallels the Curie temperature; the maximum hyperfine fields and the maximum Curie temperature are observed …

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 …

Degnerate Four-Wave Mixing In Rhodamine Doped Epoxy Waveguides, B. Rossi, Hugh Byrne, W. Blau

Articles

Self-diffraction from laser-induced gratings is observed in a 13 pm-thick film of rhodamine I3 doped epoxy. The decay of the grating is measured to be 2.05 ns. Degenerate forward four-wave mixing in a guided geometry is observed by coupling out all beams after nronagation over 1 mm. At 595 nm the third-order nonlinear susceptibility of the film is measured to be 1.5~10-‘~ m2Ve2.

Transport Anomalies In The High-Temperature Hopping Conductivity And Thermopower Of Sr-Doped La(Cr,Mn)O,₃, Ryne P. Raffaelle, Harlan U. Anderson, Don M. Sparlin, Paul Ernest Parris

Materials Science and Engineering Faculty Research & Creative Works

A minimum exists in the electrical conductivity of the perovskite-type ceramic LaCr_1-xMn_xO₃ as a function of Mn content near x=0.05. This minimum has been explained in terms of a crossover from multiple trapping to percolation among energetically lower Mn sites. In this paper electrical conductivity and Seebeck measurements are presented on a similar series in which 10 mol % Sr was substituted for La in order to increase the small polaron concentration through the compensation of Sr ions according to the Verway mechanism. The data suggests that there is an apparent suppression of the Verway …

Nonlinear Dynamics And The Lorenz Water Wheel, Richard Margis

Opportunities for Undergraduate Research Experience Program (OURE)

Undoubtedly one of the most exciting frontiers in physics today is the study of nonlinear systems, more popularly called chaos. Chaos is the key to many time-dependent processes in as varied fields as meteorology (such as weather modeling), mechanics (the three-body problem in gravitational fields), and economics (prediction of trends in the stock market).