Digital Commons Network^™

The Role Of Dephasing In Some Recent Theories Of Quantum Localization, Paul Ernest Parris, Philip W. Phillips

Physics Faculty Research & Creative Works

We consider the transport of electrons or excitons through a random environment in the presence of constant site off-diagonal dephasing processes. It is shown that dephasing of this form will always defeat Anderson localization at long times. Some recent theories of quantum localization which depend upon such dephasing processes are, therefore, seen to be inconsistent.

Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek

Physics

We present results of an investigation of the static magnetic susceptibility of Zn_1-xMn_xSe for x=0.05, 0.15, 0.30, and 0.45. From the Curie-Weiss behavior of the susceptibility at high temperatures, we determine the effective Mn-Mn exchange constant J₁ to be -13.5±0.95 K. By using the results of our study in conjunction with direct measurements of the nearest-neighbor exchange integral J_NN from inelastic neutron scattering by nearest-neighbor pairs, we obtain an estimate of the next-nearest-neighbor exchange constant J₂=-2.4 K.

Limitation Of The Semirelativistic Approach In Sum Rules And Related Calculations In Atomic Physics, M. L. Rustgi, P.T. Leung, S. A. Long

Physics Faculty Publications and Presentations

It is shown that the semirelativistic approach, when applied consistently to atomic calculations involving the Thomas-Reiche-Kuhn sum rule or its applications, may lead to very inaccurate results.

Effects Of Transport Coherence On The Mutual Annihilation Of Excitons, Demet Gulen, Vasudev M. Kenkre, Robert S. Knox, Paul Ernest Parris

Physics Faculty Research & Creative Works

We report results of a theoretical investigation into the mutual annihilation of tight-binding excitons. The results are in apparent contradiction with intuitive expectations and provide corrections to expressions given by one of the present authors (V.M.K.) in an earlier analysis. A part of that analysis was based on a mapping of the dynamics of two mobile, mutually annihilating excitons onto the dynamics of a single exciton migrating in the presence of a fixed trap. We find that while this equivalence is valid for incoherent, randomly walking particles in an ordered system, it does not hold for an arbitrary degree of …

Transitions And Modulated Phases In Centrosymmetric Ferroelectrics: Mean-Field And Renormalization-Group Predictions, George A. Hinshaw Jr., Rolfe G. Petschek

Faculty Scholarship

A variety of ferrodisplacive transitions have Landau expansions which involve terms proportional to p2(p), i.e., three powers of the order parameter (p) and one gradient (). Such expansions have also been suggested for polymeric liquid crystals. We have studied a rotationally invariant, centrosymmetric ferroelectric in which the order parameter is a vector. The pp term leads to modulated phases when it is large enough. The modulated phase close to the uniform-modulated transition and the location of the transition are discussed as a function of dimensionless parameters in a simple model for the free energy. Modifications expected from dangerous irrelevant variables …

Comparison Of Simultaneous Chatanika And Millstone Hill Temperature Measurements With Ionospheric Model Predictions, C. E. Rasmussen, Jan Josef Sojka, Robert W. Schunk, Vincent B. Wickwar, O. De La Beaujariere, J. Foster, J. Holt

All Physics Faculty Publications

As part of the MITHRAS program, the Chatanika and Millstone Hill incoherent scatter radars made coordinated observations of the polar ionosphere on June 27 and 28, 1981. The temperature data obtained during these days were compared with predictions made by a high-latitude ionospheric model. The comparison of the temperature measurements and the results of the ionospheric model depend on the assumptions made both in reducing the data and on the inputs that are needed by the model. The deduction of electron temperature from radar measurements depends upon a knowledge of the mean ion mass as a function of altitude. The …

A Photochemical Equilibrium Model For Ionospheric Conductivity, C. E. Rasmussen, Robert W. Schunk, Vincent B. Wickwar

All Physics Faculty Publications

A photochemical equilibrium model of the high-latitude ionosphere has been developed. This model provides densities of the ionospheric constituents, N₂ ⁺, O₂ ⁺, O⁺, and NO⁺, from 85 km to approximately 220 km. These densities are then used to calculate Pedersen and Hall conductivities. A comparison of the model results with Arecibo and Chatanika radar observations was made, covering periods of solar minimum and solar maximum. The comparison showed the model to predict ionospheric densities to within 50% and conductivities to within 40% in the illuminated portion of the ionosphere. In regions …

Low-Temperature Ion Beam Mixing In Metals, S J. Kim, M A. Nicolet, R S. Averback, David Peak

All Physics Faculty Publications

A systematic study of ion-beam mixing of tracer impurities in thin metal films at low temperatures has been conducted. We have investigated the dependence of ion mixing on two matrix properties: atomic mass and cohesive energy. We have also studied the dependence of ion mixing on tracer impurity properties: its heat of mixing with the matrix and its thermal diffusivity in the matrix. The matrices investigated were thin films of C, Al, Ti, Fe, Ni, Cu, Mo, Ru, Ag, Hf, Ta, W, Pt, and Au. The tracer impurities, Al, Ti, Cr, Mn, Fe, Ni, Cu, Y, Nb, Mo, Ru, Ag, …

The Rainbow And The Achromatic Telescope: Two Case Studies, M. Eugene Rudd

M. Eugene Rudd Publications

From the history of science we can learn not only some science and some history, but also something about how science is done and how it interacts with technology.
The First case study chosen illustrates the development of an understanding of a phenomenon of nature-one that has been observed with awe and wonder for as long as man has walked the Earth, but has only been well understood in the last 200 years. Some of the greatest thinkers of all time have worked on the problems of the rainbow.
The second study shows how an important invention became possible only …

Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton

Faculty Publications

This study addresses the question, "How can the optical properties of matter in ultrathin amorphous nonmetallic films in multilayers best be determined from reflectance (R) and transmission (T) measurements?" A blue shift in the band gap of plasma CVD a-Si:H/a-SiNx:H multilayers was reported several years ago. It was suggested that the shift in the band gap, Eg, Relative to bulk a-Si:H as given by the Tauç plot was due to quantum confinement effects. The purpose of this study is to evaluate the usefulness of various effective media theories (EMT) for determining the optical constants of materials in a multilayer and …

Spin-Exchange Cross Section For Electron Excitation Of Na 3s 3p Determined By A Novel Spectroscopic Technique, Xianming Han, G. W. Schwinn, A. Gallagher

Scholarship and Professional Work - LAS

An experimental technique is described which enables determination of the partial cross sections for electron excitation of atoms as a function of changes in spin and orbital angular momentum. This method provides a good signal-to-noise ratio in the energy region near threshold, and could be used to study long- or short-lived excited states of many atomic systems. Measurements for Na 3S−3P, near-threshold excitation are reported here. The results are generally in good agreement with the close-coupling calculations of D. L. Moores and D. W. Norcross [J. Phys. B 5, 1482 (1972)] for the largest ΔmS and ΔmL components of …

The Spectroscopy And Molecular Dynamics Of The High Frequency Ν1 6 Intermolecular Vibrations In Hcn‐‐‐Hf And Dcn‐‐‐Df, B. A. Wofford, M. W. Jackson, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

Gas phase rovibrational analysis of the high frequency intermolecular hydrogen bonded bending overtone 2ν⁰ ₆ [ν₀=1132.4783(2) cm^{− 1}] in HCN‐‐‐HF and its corresponding perdeuterated fundamental ν¹ ₆ [ν₀=409.1660(2) cm^{− 1}] are reported. Evaluated rovibrational parameters provide the basis for quantitative modeling of the molecular dynamics associated with this vibration. A quantum mechanical calculation permits determination of the quadratic and quartic force constants K _{6 6}=537(17) and K _{6 6 6 6}=4.98(12) cm^{− 1} which in turn are used to estimate the pertinent cubic band stretching interaction constants …

Erratum: Determination Of Dissociation Energies And Thermal Functions Of Hydrogen Bond Formation Using High Resolution Ftir Spectroscopy [J. Chem. Phys. 8 7, 5674 (1987)], B. A. Wofford, M. E. Eliades, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

Erratum

Spectral Momentum Density From Graphite From (E,2e) Spectroscopy: Comparison With First Principles Calculations, Chao Gao, A. L. Ritter, Jr Dennison, N. A. W. Holzwarth

Journal Articles

We have measured the spectral momentum density p(E,q) of graphite by (e,2e) spectroscopy for momentum parallel and perpendicular to the crystal c axis. In the independent-electron approximation, p(E,q) = Σ_G |U_k(G)|² δ(q-k-G)δ(E-E(k)) where the one-electron wave function is Ψ_k(r) = e^ik•rΣ_GU_k(G)e^iG•r and G is a reciprocal-lattice vector. The measurements covered a range of momentum parallel to the c axis equal to 0 ≤ |q| ≤ 1.84Å^-1 and a …

Contact Resistance Measurements In Gaas Mesfet's And Modfet's By The Magneto‐Tlm Technique, David C. Look

Physics Faculty Publications

The standard transmission‐line model (TLM) for specific contact resistivity measurements of planar contacts is improved in two ways: (i) the addition of a magnetic field, which gives the mobility and carrier concentration of the bulk material, and the mobility of the material under the contact; and (ii) an extension to two layers, which makes the model applicable to MODFET structures. The results are applied to MESFET material, and MODFET material. One conclusion concerning the latter material is that the electrons directly beneath the annealed Au/Ge/Ni contacts have lower mobility than those in the bulk, but still …

Argon Metastable-Cadmium Dihalide Energy Transfer Collisions In A Flowing Afterglow, Christopher L. Bohler, Laird D. Schearer

Physics Faculty Research & Creative Works

The energy dependence of dissociating collisions between argon metastable atoms and cadmium dihalide molecules have been studied in a flowing afterglow apparatus. The fluorescence spectra obtained in the range of 3000-7600 Å which result from the Ar(3P2) + CdX2 interactions indicate a dominant dissociative excitation production mechanism. The emission spectra are used to narrow the uncertainty in the currently accepted values for the dissociation energy of the CdX2 molecules. The Wigner spin rule (conservation of total electronic spin) was verified for these processes as shown by the dominance of final state triplet production as compared to the virtual absence of …

Aerosol Evolution And Metamorphosis During And After Haze (Fog) Formation Over The Bay Of Naples, Josef Podzimek, H. Andriambeloma, A. De Maio, M. Ianniruberto, R. Montmory, E. Sansone, G. Spezie, G. Stowell

Physics Faculty Research & Creative Works

No abstract provided.

Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy James Gay, Jimmie Garwin Edwards, Edward Boyd Hale, M. L. Mckenzie, Ronald E. Olson

Physics Faculty Research & Creative Works

We have studied H⁺+He and He⁺+3+He ionizing collisions at intermediate energies (60 to 120 keV/amu) and have observed a significant shift in the velocity position of the maxima in forward-ejected electron spectra when changing projectiles from protons to particles. In ionizing collisions, a large portion of the ejected electrons are stranded near the transitory equiforce, or saddle point, position between the target ion and receding projectile. The shift in the electron spectra maxima to smaller velocities, due to changing projectiles from protons to particles, is consistent with the shift in the saddle-point velocity when the projectile …

Quantum Electrodynamics Based On Self-Fields, Without Second Quantization: A Nonrelativisitc Calculation Of G – 2, A. O. Barut, Jonathan P. Dowling, Jean F. Van Huele

Faculty Publications

Using a formulation of quantum electrodynamics that is not second quantized, but rather based on self-fields, we compute the anomalous magnetic moment of the electron to first order in the fine structure constant α. In the nonrelativistic (NR) case and in the dipole approximation, our result is a_e≡(g—2)/2=(4Λ/3m)(α/2π), where Λ is a positive photon energy cutoff and m the electron mass. A reasonable choice of cutoff, Λ/m=¾, yields the correct sign and magnitude for g—2 namely, a_e=+α/2π. . In our formulation the sign of a₃ is correctly positive, …

The Effectiveness Of Using Writing In The High School Biology Classroom, Lynne E. Kelly

Dissertations and Theses @ UNI

"Writing across the curriculum" programs have emerged throughout the United States during the last decade as an attempt to improve both writing skills and learning of today's youth. The purpose of this study was to determine if students learn and retain concepts of biology to a greater extent in a program using expressive writing than a program using traditional expository writing. The sample consisted of two high school biology classes from Fort Dodge Senior High School, Fort Dodge, Iowa. Expressive writing assignments were incorporated into the biology curriculum of the experimental group two to four times a week during the …

Electron Loss From Helium Atoms By Collisions With Fully Stripped Ions, A. E. Wetmore, Ronald E. Olson

Physics Faculty Research & Creative Works

Electron-loss cross sections have been calculated for fully stripped ions with charge states +1 to +100 colliding with helium atoms in the energy range 100 1000 kev/amu. The classical-trajectory Monte Carlo method was used along with a model of the helium atom with two active electrons. The reactions studied were single and double ionization, single- and double-electron capture, and electron capture plus ionization. Cross sections for the single-electron-removal reactions agree well with experimental data. Double-electron-removal cross sections are in qualitative agreement with experimental results. The n-level distributions following electron capture show that the electron-capture plus ionization and double electron-capture processes …

Single-Electron Removal Processes In Collisions Of Positrons And Protons With Helium At Intermediate Velocities, D. R. Schultz, Ronald E. Olson

Physics Faculty Research & Creative Works

Total cross sections for single ionization and charge transfer have been calculated using the classical-trajectory Monte Carlo (CTMC) technique for collisions of both positrons and protons with helium. Analysis of the classical trajectories has helped to explain the differences in the collision mechanisms responsible for the observed relative magnitudes of the positron and proton electron-removal cross sections. In the intermediate collision velocity range (1.5 a.u.

State-Selective Studies Of T→R, V Energy Transfer: The H+Co System, G. K. Chawla, George C. Mcbane, P. L. Houston, G. C. Schatz

Peer Reviewed Articles

Collisional energy transfer from H atoms to CO(v=0, J≈2) has been studied at a collision energy of 1.58±0.07 eV by photolyzing H₂S at 222 nm in a nozzle expansion with CO and probing the CO(v", J") levels using tunable VUV laser-induced fluorescence. The ratio CO(v"=1)/CO(v"=0) is found to be 0.1±0.008. The rotational distribution of CO(v"=0) peaks at J"gradually; population is still observed at J">45. The rotational distribution of CO(v"=1) is broad and peaks near J"=20. The experimental results are compared to …

Electrooptic And Piezoelectric Measurements In Photorefractive Barium Titanate And Strontium Barium Niobate, Stephen Ducharme, Jack Feinberg, R.R. Neurgaonkar

Stephen Ducharme Publications

We have measured the low-frequency ("unclamped") electrooptic and piezoelectric coefficients in undoped BaTiO₃and Sr_xBa_1-xNb₂O₆ (x = 0.61) crystals using interferometric techniques. The contribution of the piezoelectric effect to the Pockels measurements is discussed. For an applied ac electric field in the range 0.1-200 V/cm, the electrooptic and piezoelectric effects are linear in the magnitude of the applied field and independent of its frequency in the range 10 Hz-100 kHz. The unclamped electrooptic coefficients of poled BaTiO₃ single crystals are r₁₃= 19.5 pm ±1 pm/V and r₃₃ = …

Moment Analysis Of The Cluster-Size-Distribution Approach To Scaling During Coagulation, Thomas W. Taylor, C. M. Sorensen

Physics Faculty Publications

We study the temporal approach of a cluster size distribution to its asymptotic scaling form. By enforcing consistency between the distribution’s zeroth moment derived from both the Smoluchowski equation and the scaling distribution ansatz, we find values for the scaling exponents w and z in terms of the scaling exponent τ and the kernel homogeneity λ which are not equivalent to their asymptotic, scaling forms. The predicted values do agree well, however, with intermediate time values found in simulations by Kang, Redner, Meakin, and Leyvraz [Phys Rev. A 33, 1171 (1986)]. By enforcing consistency between all moment orders, the asymptotic …

Ion-Ion Recombination In Mixtures Of Methane And Sulphur Hexafluoride, M. C. Cornell, Ian M. Littlewood

Physics Faculty Research & Creative Works

The authors have measured the recombination rate for positive and negative ions in Sulphur hexafluoride and in mixtures of methane and Sulphur hexafluoride in an electron beam sustained discharge. Measurements were made as a function of gas composition, gas pressure in the range 100 to 600 Torr, and reduced electric field strength in the range 12 to 150 Td. When plotted as a function of an effective ion temperature, defined by the drift velocities of the ions in the applied electric field, the rates in each of the gas mixtures follow the same Teff-1.6 power law. From comparisons with theories …

Hypernuclear Photoproduction Via (Γ,K*), Kimberly Ann Hodgkinson

Masters Theses

The nuclear (γ,K^*) reaction is studied using plane wave impulse approximation (PWIA) and a distorted wave impulse approximation (DWIA), which includes full Coulomb and optical distortions. The model and calculations for each model are presented. For ¹²C(γ K^*)¹²B, the two approximation methods are compared at 2 energies: 1.47 Gev/c and 1.84GeV/c. ²⁰⁸Pb(γ, K^*)²⁰⁸ i s a lso examined. Distortion effects are found to greatly alter the magnitude of the cross sections, but the shape of the angular distributions remains. the same. Conclusions suggest further study.

Theoretical Thermodynamic Properties Of Low Temperature Fluids, Zul Azhar Zahid Jamal

Masters Theses

The thermodynamic functions for low temperature fluids are computed using parametric integral equations and perturbation theory. Parametric integral equation N is applied to a low temperature Lennard-Jones gas. It is found that there is no significant improvement over the better known parametric integral equation C. The two parameter integral equation T is applied to a low temperature square-well potential and is found to be unsatisfactory at reduced temperatures of T*= 1.4 and 1.6, but quite accurate at T* = 2.2. The equation T results for T* = 2.2 are used as the reference system in perturbation theory computations. Tables of …

Effects Of A Magnetic Field On The Thermodynamics Of Dilute Classical Spin Chains, Guoqing Hu

Masters Theses

The thermodynamics of a diluted chain of ferromagnetic classical spin in the presence of an external magnetic field is determined in the limit of the continuum model. The magnetization, susceptibility, specific heat are determined for both the isotropic Heisenberg and the classical XY models as functions of temperature, magnetic field and magnetic concentration. Scaling law for the behavior of the thermodynamic quantities in field, temperature, and magnetic concentration are obtained.

The calculations will be based on the continuum model of classical spin which was solved for the infinite chain system by McGurn and Scalapino.

University Of Missouri-Rolla Cloud Simulation Facility: Proto Ii Chamber, Daniel R. White, James L. Kassner, John C. Carstens, Donald E. Hagen, John L. Schmitt, Darryl J. Alofs, Alfred R. Hopkins, Max B. Trueblood, Max W. Alcorn, William L. Walker

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Graduate Center for Cloud Physics Research at UMR Has Developed a Cloud Simulation Facility to Study Phenomena Occurring in Terrestrial Clouds and Fogs. the Facility Consists of a Pair of Precision Cooled-Wall Expansion Chambers Along with Extensive Supporting Equipment. the Smaller of These Chambers, Described in This Article, is Fully Operational, and is Capable of Simulating a Broad Range of In-Cloud Thermodynamic Conditions. It is Currently Being Used to Study Water Drop Growth and Evaporation for Drops Nucleated (Activated) on Well-Characterized Aerosol Particles. Measurements Have Been Made Not Only for Continuous Expansions (Simulated Updraft) But Also for Cyclic Conditions, …