William E. Evenson

The effects of dissolved heavy metals on attached diatoms in the Uintah Basin of Utah, U.S.A.

The relationships of diatom species to dissolved heavy metals in the streams of the Uintah Basin of Utah were studied through four seasons of 1977–1978. Niche center gradient analysis, cluster analysis and correlation analysis were performed.Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta, Gomphonema parvulum, Navicula secreta var.apiculata, Nitzschia frustulum, Nitzschia frustulum var.perminuta, Nitzschia frustulum var.perpusilla, Nitzschia palea, andSynedra ulna appear to be indicator species of high or low heavy metal concentrations. Several other species also showed meaningful relationships to high or low heavy metal concentrations.

PAC analysis of defect motion by Blume's stochastic model forI=5/2 electric quadrupole interactions

Using Blumes stochastic model and the approach of Winkler and Gerdau, we have computed time-dependent effects on perturbed angular correlation (PAC) spectra due to defect motion in solids in the case ofI=5/2 electric quadrupole interactions. We report detailed analysis for a family of simple models: “XYZ+Z” models, in which the symmetry axis of an axial EFG is allowed to fluctuate among orientations alongx, y, andz axes, and a static axial EFG oriented along thez axis is added to the fluctuating EFGs. When the static EFG is zero, this model is termed the “XYZ” model. Approximate forms are given forG2(t) in the slow and rapid fluctuation regimes, i.e. suitable for the low and high temperature regions, respectively. Where they adequately reflect the underlying physical processes, these expressions allow one to fit PAC data for a wide range of temperatures and dopant concentrations to a single model, thus increasing the uniqueness of the interpretation of the defect properties. Application of the models is illustrated with data from a PAC study of tetragonal zirconia.

The effects of selected physical and chemical factors on attached diatoms in the Uintah Basin of Utah, U.S.A.

The relationships of diatom species to selected physical and chemical parameters in the streams of the Uintah Basin of Utah were studied through four seasons of 1977–1978. Niche center gradient analysis, cluster analysis and correlation analysis were performed.Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta var.latens, Fragilaria capucina, andNavicula secreta var.apiculata appear to be indicator species of high or low levels of certain water quality parameters. Several other species also showed meaningful relationships to selected physical and chemical parameters.

Theory of Itinerant Ferromagnets with Localized-Moment Characteristics: Two-Center Coupling in the Functional-Integral Scheme

The coupling between two magnetic centers in a band is discussed within the framework of the functional-integral scheme. The model used is the single-orbital Hubbard model with Coulomb repulsion only on the two magnetic sites. In lowest approximation, antiferromagnetic Ising coupling is obtained when the moments are nearest neighbors. When the moments are far apart, Ruderman-Kittel-Kasuya-Yosida coupling is the most important of several terms.

Surface alloying of indium on Cu(111)

An ultrathin film of indium deposited on Cu(111) has been studied by an in situ combination of medium-electron energy diffraction, low-energy electron diffraction, scanning tunnelling microscopy and Auger electron spectroscopy. The surface alloys, Cu2In and Cu3In, which do not exist in these structures in the bulk, have been found in this system.

Transition temperatures of Bose-Einstein condensation in traps

A careful study is made of the definitions of the transition temperature Tc of an ideal Bose system in traps. We review several physical quantities that are used to define the transition temperature, which corresponds to different kinds of Tc. The different definitions give different values for Tc and the differences are quite large for finite systems. This makes the comparisons of theoretical predictions of the transition temperature shift with experimental results quite difficult. We also find that the derivative of chemical potential with respect to temperature is nearly discontinuous. This implies that in the thermodynamic limit the system might undergo a first-order phase transition.

Cobalt growth on Cu(111) in the presence of indium surfactant

The effect of a pre-deposited ultrathin film of indium on the deposition of cobalt on Cu(111) has been studied by an in situ combination of medium energy electron diffraction, scanning tunneling microscopy, and Auger electron spectroscopy. Pre-deposited indium allows cobalt to deposit in layer-by-layer growth, in contrast to the three-dimensional growth observed without the indium surfactant. The surfactant effect is connected to the surface alloys, Cu2In and Cu3In, that form upon indium pre-deposition. Initial cobalt nucleation processes and indium segregation during cobalt deposition are also discussed.

Phonon spectrum of YBCO obtained by specific heat inversion method for real data

In this paper, the phonon spectrum of YBCO is obtained from experimental specific heat data by an exact inversion formula with a parameter for eliminating divergences. The results can be compared to those of neutron inelastic scattering, which can only be carried out in a few laboratories. Some key points of specific heat-phonon spectrum inversion (SPI) theory and a method of asymptotic behaviour control are discussed. An improved unique existence theorem is presented, and a universal function set for numerical calculation of SPI is calculated with high accuracy, which makes the inversion method applicable and convenient in practice. This is the first time specific heat-phonon SPI has been realized for a concrete system.

Stochastic hyperfine interactions modeling library—Version 2

The stochastic hyperfine interactions modeling library (SHIML) provides a set of routines to assist in the development and application of stochastic models of hyperfine interactions. The library provides routines written in the C programming language that (1) read a text description of a model for fluctuating hyperfine fields, (2) set up the Blume matrix, upon which the evolution operator of the system depends, and (3) find the eigenvalues and eigenvectors of the Blume matrix so that theoretical spectra of experimental techniques that measure hyperfine interactions can be calculated. The optimized vector and matrix operations of the BLAS and LAPACK libraries are utilized. The original version of SHIML constructed and solved Blume matrices for methods that measure hyperfine interactions of nuclear probes in a single spin state. Version 2 provides additional support for methods that measure interactions on two different spin states such as Mossbauer spectroscopy and nuclear resonant scattering of synchrotron radiation. Example codes are provided to illustrate the use of SHIML to (1) generate perturbed angular correlation spectra for the special case of polycrystalline samples when anisotropy terms of higher order than A22 can be neglected and (2) generate Mossbauer spectra for polycrystalline samples for pure dipole or pure quadrupole transitions.

CRITICAL PROPERTIES AND DISTRIBUTIONS OF TWO-DIMENSIONAL BOSE–EINSTEIN CONDENSATION

By studying the critical properties of a 2D Bose–Einstein condensation (BEC) in traps, we obtain the accurate analytic expressions of transition temperature, condensed fraction, and specific heat. The analytic results fit in fairly well with numerical results. We find that an isotropical potential favors most for condensation to occur. With the aid of Bloch summation, we study the distributions of coordinates and momenta of the system. Some clear physical pictures are presented.