bluuebunny/crossref_metadata_2025 huggingface dataset:
Conserved quantum probability currents on stochastic phase space
Authors: Ali S. T. , Gagnon R. , Prugovečki E.
Published: April 2011

It is shown that the continuity equation in stochastic phase space is satisfied if the configuration space representation ξ(x) of the resolution generator is real. It is also shown that the probability density and current merge into the standard ones if ξ(n)(x) is a sequence of real resolution generators which converges to the Dirac δ-function for n → x. A relation between the current on Γξ and the stochastic current in configuration representation is also derived.
Electric field effects on the ground state hyperfine structure of hydrogenic atoms
Authors: Weil John A.
Published: April 2011

The hyperfine structure of the ground state of the one-electron atom, with nuclear spin of 1/2, is discussed in terms of perturbation theory. The contact and dipolar hyperfine interactions plus the electric field effects from remote static charges are treated, performing exact summation over all discrete and continuum states, treating the second and third order mixed perturbation terms linear in the hyperfine Hamiltonian. Expressions for the energy terms, linear in the electric field gradient, quadratic in the electric field, and quadratic in the gradient are all derived, and their magnitudes evaluated for a simple field configuration.
Potential energies of one-dimensional systems at equilibrium
Authors: Ahmed Shafique
Published: April 2011

The equilibrium positions of some one-dimensional systems coincide with the zeros of Hermite, Laguerre, and Jacobi polynomials. Using the discriminants of these classical orthogonal polynomials it is then possible to calculate the values of the potential energies of the one-dimensional systems at equilibrium. It is also shown that the zeros of Bessel polynomials coincide with the equilibrium positions of certain dynamical systems.
An extended X-ray absorption fine structure study of amorphous and crystalline germanium
Authors: Crozier E. D. , Seary A. J.
Published: April 2011

Extended X-ray absorption fine structure (EXAFS) results are presented for amorphous and crystalline Ge at temperatures ranging from 83 to 1085 K. Specific tests for the detection of asymmetry in the distribution of atoms are examined. In amorphous Ge the distribution of nearest neighbours is found to be Gaussian. In crystalline Ge at the highest temperatures studied a small asymmetry in the distribution of nearest atoms, attributed to anharmonicity in the effective two-body potential, must be included explicitly in the EXAFS analysis to determine changes in nearest neighbour distances to an accuracy of ± 0.01 Å. The temperature dependence of the disorder parameter σ12 in crystalline Ge is found to obey an Einstein model, contrary to earlier work. The structure of amorphous Ge is found to be consistent with a continuous random network of distorted tetrahedra in which the dynamic contribution to σ12(T) is given by the same force-constant law as in crystalline Ge. The static structural disorder provides an additional contribution to a σ12(T) which decreases as the crystalline temperature is approached. Many-body contributions to the reduction of the amplitude of the EXAFS interference function in amorphous and crystalline Ge are also determined empirically.
The Curie–Weiss–Néel model of a ferrimagnet
Authors: Bowers R. G. , Schofield S. L.
Published: April 2011

An analogue, for ferrimagnetism, of the Curie–Weiss model ferromagnet is introduced. The resulting structure, the Curie–Weiss–Néel model, is based on a two sublattice description in which spins of one magnitude occupy one sublattice and spins of another magnitude occupy the other. Attention is concentrated on the case in which spins on the different sublattices tend to align in an anti-parallel fashion. Many properties of the new model are similar to those of the Curie–Weiss ferromagnet. Artificially long-ranged interactions connect spins on the different sublattices. The complete thermodynamics can be obtained exactly by relatively elementary methods. The exact solution of the model is essentially identical with the appropriate mean field results (of Néel). Attention is given to the Néel point and associated critical phenomena. Many standard critical exponents are calculated and, of course, classical exponent values result. Novel features of critical phenomena in ferrimagnets are considered. These are associated with the fact that, theoretically, the staggered magnetization and staggered fields are important while, experimentally, the total magnetization and uniform fields are usually employed. It is shown that, within the present context, corresponding staggered and uniform properties have identical exponent values.
A theoretical study of the Knight shift and its volume dependence for Li, Na, and K
Authors: Wilk L. , Vosko S. H.
Published: April 2011

The augmented plane wave method, in the muffin-tin approximation, was used to perform self-consistent spin-polarized calculations of the electron number densities, n(r), and spin magnetic moment densities, m(r), within the framework of the spin density functional formalism. For the exchange-correlation energy functional we used the new improved results of Vosko and coworkers in the local spin density approximation. The calculations were carried out for the range of volumes 0.9 ≤ V/V0 < 1. The contributions to the total Fermi contact term, m(0), relative to the Fermi surface contribution, were approximately −24, −2, and −2% from the core electron polarization and −0.7, −5, and −6% from the polarization of the valence electrons below the Fermi surface, for Li, Na, and K respectively. In Li the volume dependence of m(0) was strongly affected by the volume dependence of the core contribution, which differed markedly from that of the Fermi surface contribution. In both Li and K the calculated volume dependence for small volume changes was in good agreement with recent experiments, while in Na the trend was correct but the slope of the curve was too large. In all cases the results were very sensitive to achieving a high degree of self-consistency. The absolute values of m(0) are in excellent agreement with the measured Knight shifts.
Electrostatic disruption of a charged conducting spheroid
Authors: Hill Jay Roderick , Mendis D. A.
Published: April 2011

Electrostatic disruption of elongated or chain-like parent grains following sudden charging to high electrostatic potentials was recently offered as a specific mechanism for a certain cometary phenomenon, namely the appearance of the so-called striae or pseudosynchronic bands observed in several comets. Idealizing these grains as spheroids with greatest fragility at their centers, we have calculated the polar and equatorial electrostatic tension for axis ratios between 0.01 and 1000. We find that while the polar pressure is larger than the equatorial pressure for prolate spheroids, the opposite is true for oblate spheroids. This means that while prolate spheroids will split along the equatorial plane when charged to a high enough potential, oblate spheroids will split along a meridional plane.We have also calculated the electrostatic polar pressure profile along the polar axis for prolate spheroids. In all cases this pressure increases monotonically from a minimum at the center to maxima at the ends. The variation becomes less marked as the axis ratio decreases, becoming a constant for a sphere. This means that as a prolate spheroid of uniform tensile strength is charged up it will continue to chip off at its ends when the electrostatic pressure there exceeds the uniform tensile strength of the grain. During this chipping process the charge per unit length of the grain remains constant while it becomes less and less prolate. The final outcome could be one of two things: If the tensile strength of the grain is sufficiently large the end chipping process will eventually cease while the grain still remains prolate. Otherwise, it will continue chipping off until it becomes spherical, at which time it will explode in toto.
Propagation d'une onde électromagnétique à la surface d'un conducteur ou d'un supraconducteur de section circulaire
Authors: Fabre Georges , Wick Alain , Zepp Gérard
Published: April 2011

We are studying the electromagnetic wave (magnetic transverse mode) propagation on the surface of a circular cross section metallic cylinder coated with one or several dielectrics. The method we use allows us to study not only the case of ordinary metals, but also the case of superconductor metals. We determine the precise analytical expressions (for any kind of metal) of characteristic quantities: attenuation factor and phase shift.
The ultraviolet spectrum of AlO
Authors: Singh M. , Saksena M. D.
Published: April 2011

The E2Δi–A2Πi transition of AlO in the ultraviolet region has been excited in a high frequency discharge through a flowing mixture of AlCl3 vapour, argon, and oxygen and photographed at high resolution. The 0–0 and 0–1 bands of this transition at 2500.1 and 2545.9 Å respectively have been analysed for the rotational structure. Rotational perturbations and predissociation have been observed in the E2Δi state. Λ-doubling has been observed in both the bands for the transition E2Δ3/2–A2Π1/2. A weak rotational perturbation has been detected in the ν = 1 level of the A2Π3/2 state. In the same spectral region the 1–1, 2–2, 3–3 bands (observed for the first time) and the 1–2 band of the D2Σ+–X2Σ+ system have also been recorded and analysed for their rotational structure.
High-multipolarity magnetic sum rule
Authors: Montgomery John A. , Ertel John P. , Überall Herbert
Published: April 2011

We have derived a spin flip magnetic multipole sum rule for magnetic dipole (ML) transitions, L ≥ 2 of T = 1 type, valid in the long-wavelength limit. It is applied to known ML transitions in several light nuclei, including recently measured M6 and M8 transitions in inelastic electron scattering, and the degree of sum-rule exhaustion is determined.
Scattering phenomena in strong radiation fields
Authors: Ehlotzky F.
Published: April 2011

Several seemingly different scattering and absorption phenomena in the presence of a strong coherent electromagnetic background field are considered from a unifying point of view to elucidate the essential similarities and also the differences of these processes with regard to the induced nonlinear radiation effects. The consequences are discussed with respect to the possible physical implications and conditions of experimental verification.
The level structure of 142Pr deduced from the 141Pr(n,γ)142Pr reaction
Authors: Kennett T. J. , Prestwich W. V. , Islam M. A.
Published: April 2011

A study of the low lying levels of 142Pr observed via the 141Pr(n,γ)142Pr reaction has revealed this nuclide to possess a much more complex structure than previously reported. Acquiring high precision spectra, which readily permitted detection of transitions with intensities greater than 0.01% and employing deconvolution techniques to achieve an effective resolution of 1 keV, resulted in identification of 455 transitions in the range of excitation energy 0 to 3500 keV. A constant temperature level density model, for which losses due to intensity and resolution effects are included, was used to describe the present results. Computations were undertaken to explore the validity of the assumptions made regarding the primary or secondary nature of the observed transitions. The models used to describe the spacing and intensity distributions in order to account for losses were verified through an examination of the experimental data. In addition, consideration of the degree of E1 and M1 contributions has been included. A high degree of self consistency of all these factors is demonstrated. An examination of the reduced radiative widths strongly suggests the influence of the giant dipole resonance. The precision of the energy measurements permitted the derivation of level energies with an average uncertainty of less than 100 eV. In addition to obtaining a neutron separation energy of 5843.14(10) keV for 142Pr, precise values were determined for nuclides 144Nd, 156Gd, 158Gd, and 208Pb.
Electrointercalation of silver into 2H–NbSe2
Authors: Folinsbee J. T. , Jericho M. H. , March R. H. , Tindall D. A.
Published: April 2011

The electrointercalation of Ag into single crystals of 2H–NbSe2 was studied. The distribution of Ag in the samples was measured with an electron beam probe. Intercalation generally proceeded in two stages, with the Van der Waals gaps, near the sample surface, appearing to intercalate first, while a critical concentration, [Formula: see text] of Ag, was required before intercalation in the bulk took place. The Ag concentration profiles were generally characterized by sharp fronts which remained stationary for long periods of time after intercalation was discontinued. Radioactive tracer measurements gave Ag self-diffusion coefficient of [Formula: see text] for [Formula: see text].
Ultrasonic attenuation and bulk viscosity of liquid xenon
Authors: Cowan J. A. , Leech J. W.
Published: April 2011

Ultrasonic attenuation measurements have been made for liquid xenon for temperatures between 165 and 288 K. and pressures between saturated vapor and 7 MPa. Values of the bulk viscosity were calculated and compared to theoretical results as well as previous argon and krypton results through the law of corresponding states.
Feedback non-linéaire dans un Fabry–Pérot bistable
Authors: Boulay Louis , Chrostowski Jacek , Delisle Claude , Beaudoin Gilles
Published: April 2011

A hybrid bistable Fabry–Perot interferometer with nonlinear feedback is described. One of the mirrors of the interferometer is mounted on piezoelectric crystals. The voltage driving these crystals is a nonlinear function of the interferometer luminous output. The theory and an experimental verification for the case where the nonlinearity is generated with a logarithmic amplifier is presented.[Journal translation]
Diffraction by an infinite set of hard and soft parallel half planes
Authors: Lüneburg E. , Hurd R. A.
Published: April 2011

We consider the diffraction of a plane wave by an infinite set of parallel half planes. On alternate half planes the total field or its normal derivative vanishes. An exact closed-form solution to this new canonical diffraction problem is presented. The problem also contains the solution to ten intrinsically different waveguide "bifurcation" problems.
Temperature variation of energy gap values in CuGaSnSe4
Authors: Lopez-Rivera S. Adan , Goodchild R. Gerald , Hughes Owain H. , Woolley John C. , Pamplin Brian R.
Published: April 2011

Measurements of reflectance as a function of temperature from 4 to 300 K have been made on a single crystal sample of CuGaSnSe4 using light polarised (a) perpendicular and (b) parallel to the c axis of the crystal. Values of the energy gaps EA, EB, and EC between the three valence bands and the conduction band have thus been determined as a function of temperature. The variation of these energy gaps with temperature has been fitted to the equation proposed by Manoogian and Leclerc, i.e., E0 − E = UTs + Vθ(coth (θ/2T) − 1). Values of spin–orbit splitting Δso and crystal field splitting Δcf have been determined and the temperature variation of these explained in terms of contributions from d orbitals to the valence band. Values of the various spin–orbit splittings and deformation potentials are discussed.
An improved method of representing and extrapolating diatomic molecule rotational constants
Authors: Tromp John W. , Roy Robert J. Le
Published: April 2011

It is shown that "near-dissociation expansions", empirical functions constrained to have the correct theoretically-predicted limiting behaviour at dissociation, provide representations of rotational and centrifugal distortion constants of diatomic molecules which are often much more compact, and which always provide much more reliable extrapolations beyond the range of available experimental data than comparable Dunham (ν + 1/2) expansions. The capabilities of these expansions are illustrated by applications to the extensive data for the [Formula: see text] state of I2.
Rotational analysis of hydroxyl vibration–rotation emission bands: Molecular constants for OH X2Π, 6 ≤ ν ≤ 10
Authors: Coxon J. A. , Foster S. C.
Published: April 2011

Seven vibration–rotation emission bands of the hydroxyl radical with 6 ≤ ν′ ≤10 have been recorded photoelectrically in the range λ6250–8500 Å. The first reliable constants for levels 6 ≤ ν ≤10 of OH X2Π are obtained by direct least-squares fitting of the measured line frequencies. The vibrational dependences of the Λ-doubling parameters (p and q) and the spin–orbit coupling constant (A) are well defined. A minimum value of Aν is found at ν = 7.
The critical curve for the quenched dilute random-bond Ising model
Authors: Frank B. , Cheung C. Y. , Barnea G.
Published: April 2011

The treatment by Frank and Barnea of the quenched dilute random-bond model for a system of Ising spins is improved by means of a more self-consistent calculation. This is done by relaxing one of their assumptions, which is replaced by an as yet unexploited identification, noted by Frank and Jan, with the coherent potential – random phase approximation formulation of Tahir-Kheli and Elliott. The results for the critical temperature as a function of the concentration of connected bonds are consequently better in relation to Rapaport's series values. However, at very low concentrations [Formula: see text], the theory remains inadequate.
The effect of static and modulated uniaxial constraint on impurity band conduction in p-type germanium
Authors: Lombos B. A. , Averous M. , Fau C. , Calas J. , Charar S.
Published: April 2011

Transport property measurements on p-type germanium, doped to be in the intermediate concentration region (1016 < NA < 1018 cm−3), were performed in the temperature range of 1.6–77 K under static (up to 337 MPa) and modulated (2.4 on 180 MPa) uniaxial compression. To elucidate the conduction mechanisms in this region the position of the Fermi level is calculated as a function of temperature and uniaxial stress and correlated to the variation of the measured transport properties. The analyses indicate an Anderson type metallic conduction, characteristic of random, amorphous systems, while the Fermi level is in the impurity band. Mott type metallic conduction, characteristic to periodic systems, determines the transport properties as the Fermi level moves out of the impurity band.
New analysis of the (0,0) band of the 2Π → 2Σ transition of TiN
Authors: Athénour C. , Féménias J.-L. , Dunn T. M.
Published: April 2011

From new spectra and by the use of a better computation procedure it has been possible to improve the rotational analysis of the (0,0) band of the red system of TiN. In particular, the spin doubling of the lower 2Σ state has been resolved and two new perturbations have been identified in the 2Π state. The inclusion of high values of J yields more accurate molecular constants.
Thermal fluctuations in the interface of an inhomogeneous fluid
Authors: Sobrino Luis de , Peternelj Jože
Published: April 2011

We use van Kampen's expression for the partition function of a van der Waals gas to investigate the effect of noncritical fluctuations on the interface of an inhomogeneous fluid. Such a procedure combines in a consistent manner the results of mean field theory and of capillary wave theory and, in addition, uncovers contributions due to fluctuations of the interface profile. Although the latter add negligibly to the interfacial width, they result in corrections to the mean field surface tension comparable to those resulting from capillary fluctuations. The effect of the walls in limiting the fluctuations is explicitly taken into account.
Optical mixing of frequencies of a strong bichromatic field interacting with a three-level atom. II. Numerical results
Authors: Mavroyannis Constantine , Woloschuk K. J. , Hutchinson D. A. , Downie Christine
Published: April 2011

We have numerically calculated the excitation spectra arising from the 3rd order mixing of the frequencies ωa and ωb of two laser fields interacting with a three-level atom, where each laser field resonantly couples the ground state with each excited state of the atom, respectively. In the limit of high photon densities, the excitation spectra near the reduced frequency X = (ω−ωa + 2ωb)/γ0 ≈ 0 are considered as a function of the reduced Rabi frequencies ηa and ηb of the two laser fields, respectively and γ0 is the spontaneous emission probability. For ηa < ηb the spectra consist of a doublet peaked at [Formula: see text] and its intensity is constant. When ηa = ηb, the spectra are composed of five pairs of bands peaked at [Formula: see text], and [Formula: see text]. When ηa < ηb the computed spectra consist of five pairs of bands, where the intensities of the peaks at [Formula: see text] and [Formula: see text] are positive indicating absorption, those at [Formula: see text] are negative implying amplification, and the two pairs of peaks at [Formula: see text] have positive and negative components describing the mixed process of absorption–amplification. The intensities of these bands are found to vary as (ηa/ηb)2 for (ηa/ηb) > 1 and, therefore, the intensities of the bands are immensely enhanced as the value of the ratio (ηa/ηb) increases. The computed spectra for a wide selection of Rabi frequencies are graphically presented and compared with those derived by analytical methods.
The hyperfine frequency shift of atomic hydrogen in the presence of helium buffer gas
Authors: Jochemsen R. , Berlinsky A. J.
Published: April 2011

A quantum mechanical thermal average is performed to obtain the temperature dependence of the hyperfine frequency shift (HFS) of hydrogen atoms in the presence of He buffer gas. The calculations are based on existing ab initio calculations of the hyperfine frequency shift as a function of internuclear separation and of the interatomic potential. We find that the HFS changes sign at fairly low temperature and has a small negative value at T = 1 K in agreement with recent measurements. The overall temperature dependence is shown to be quite sensitive to the interatomic potential.
Dipole moment and dielectric relaxation studies in some azo compounds
Authors: Sarma P. B. K. , Murthy P. V. G. K. , Murty C. R. K.
Published: April 2011

Dipole moments (μ) and relaxation times (τ) of seven azo central group liquid crystal compounds have been determined using the dilute solution method at radio and microwave frequencies. The results agree fairly well with the estimated values of the dipole moments. The angle, β, between the direction of the dipole moment and the long axis of the molecule, is determined for each molecule from structural considerations. The predicted sign of the dielectric anisotropy (Δε) from the estimated value of p is confirmed experimentally.
Prescission dissipation in nuclear fission from a microscopic point of view
Authors: Fontaine Marie , Amiot Pierre
Published: April 2011

We calculate the energy dissipated by the Landau–Zener mechanism from the collective into the intrinsic channels during nuclear fission. Our results are free of any externally adjusted viscosity coefficient such as Rayleigh's dissipation rate parameter. The high efficiency of the mechanism marks the collective motion as largely diabatic in the prescission stage of deformation. This diabaticity is large enough to be numerically describable by an enlarged class of parametrizations, including Rayleigh's.
Ginzburg–Landau theory of the Abrikosov vortex state near the upper critical field
Authors: Jacobs A. E.
Published: April 2011

A method which preserves the flux-quantization condition in all orders of perturbation theory is applied to the Ginzburg–Landau theory of type-II superconductors near the upper critical field. Expansions are obtained for the order parameter, the magnetic field, and the free energy; previous results are verified and extended to one higher order in Hc2 – Ha.
In situ X-ray diffraction experiments on lithium intercalation compounds
Authors: Dahn J. R. , Py M. A. , Haering R. R.
Published: April 2011

We describe powder X-ray diffraction experiments on lithium intercalation compounds. Using a unique electrochemical cell which incorporates a beryllium X-ray window we are able to monitor changes in the host lattice which occur when the lithium concentration is altered electrochemically. The detailed design of the cells and experimental problems which arise when using the in situ X-ray diffraction technique are discussed. Results of experiments on LixTiS2 are reported for 0 ≤ x ≤ 2.
Jahn–Teller interaction in ferricenium cation
Authors: Rai R.
Published: April 2011

Analysis of optical measurements on ferricenium cation (symmetry group D5d) suggests the existence of an isolated 2E2g ground level, the nearest excited level being about 2000–4000 cm−1 away from it. Efforts to explain magnetic resonance and susceptibility measurements on the ion, however, require a 2A1g level to be the lowest and a low lying 2E2g level at about 200 cm−1 above ground. Thus there exists an apparent inconsistency between the two sets of results. A possible model is suggested here to overcome this inconsistency. It is proposed that the electronic spectrum of the ion as suggested by the optical measurements is basically correct. However, there exists a Jahn–Teller induced coupling of the ground electronic 2E2g level with vibrational modes of the complex. The ground spectrum is found to consist of two vibronic Kramers' doublets lying close together, one of which has a negligible orbital contribution to the magnetic moment similar to that expected from a Kramers' doublet of 2A1g origin.
Irrotational core in deformed nuclei
Authors: Bishara B. A.
Published: April 2011

The construction of the "rotationally invariant core" (RIC) of the governor model for the deformed even–even nuclei has been studied for the rare earths. The comparison of the RIC nucleons with the shell model configurations shows that the model's assumption of "spherical" RIC is almost true only for the axially symmetric deformed nuclei. For asymmetric triaxial deformed nuclei, the study supports the assumption of the governor asymmetric rotator model, namely that the RIC is an axially symmetric prolate. The core shrinkage at higher rotational energies has been also calculated for several rare-earth nuclei.
Pure a-ZnTe and a-ZnSe: Reproducibility and deposition control
Authors: Moore C. J. L. , Brodie D. E.
Published: April 2011

Reproducible films of pure a-ZnTe and a-ZnSe have been prepared using a very high vacuum system and a complete microprocessor-based monitoring system. It is clear that not only must one reproduce every deposition parameter accurately, the anneal history of the sample must also be duplicated. The effect of a single parameter change, as well as the effect of a controlled gas leak which provides known ambients at 10−6 Torr during the sample deposition is reported.
Construction of angular momentum eigenstates in the unitary group formalism for many-electron atomic systems
Authors: Schlesinger M. , Kent R. D. , Drake G. W. F.
Published: April 2011

Efficient methods for the direct construction of angular momentum eigenstates in the unitary group approach to the theory of complex spectra are presented. We use raising/lowering operator techniques which avoid the need for more lengthy recursive formalisms.
The half-life of 176Lu by a γ–γ coincidence measurement
Authors: Sguigna A. P. , Larabee A. J. , Waddington J. C.
Published: April 2011

The half-life of 176Lu has been measured to be T1/2 = 3.59 ± 0.05 × 1010 years. Coincidences between pairs of Ge detectors were used to eliminate the uncertainties associated with detector efficiency, solid angle, and gamma ray absorption.
Propriétés des spectromètres électrostatiques à électrodes en spirale logarithmique
Authors: Tremblay D. , Roy D.
Published: April 2011

A study is presented of the properties of the electrostatic deflectors involving electrodes shaped like logarithmic spirals, both from the point of view of energy analysis and electron monochromatization. The optical constants of energy dispersion, angular aberration, and magnification are determined by means of numerical integration of the differential equation describing the electron motion. The maximum luminosity at fixed resolution and normalized dimensions is used as a criterion in order to achieve the definition of optimum conditions (for the beam-entrance parameters) and a figure of merit. Then it is found that the characteristics and the predicted performances do not strongly depend on the degree of curvature of spirals, while the optimum is obtained for the 127.3° cylindrical deflector, a particular case of the spiral deflector. From symmetry considerations, it is shown that for a given curvature the characteristics do not depend on the entrance direction (inward or outward with respect to the spiral center). The space charge limitations for an electron monochromator are discussed too. Then it is suggested that a monochromator involving a strong spiral curvature and outward electron injection could deliver a current of higher intensity than the conventional cylindrical deflector for the same resolution.
Strangeness-changing nonlepton decays of the kaons, hyperons, and the Ω− particle
Authors: Lee H. C. , Winterbon K. B.
Published: April 2011

We try to understand the strangeness changing nonleptonic decays of kaons, hyperons, and the Ω− particle in terms of the modern, renormalized weak Hamiltonian expressed as a sum of four-quark Wilson operators, including the so-called penguin operators c5O5 and c6O6 arising from gluon radiative corrections. It is found that these decays, including the long-standing s-wave/p-wave puzzle in hyperon decays, can be understood if the Wilson coefficient [Formula: see text] has a sign opposite to that obtained from short-distance perturbative quantum chromodynamics calculations and has an effective value such that [Formula: see text].
Gaseous positronics – past, present, and future
Authors: Massey H. S. W.
Published: April 2011

Research, both experimental and theoretical, concerning the interaction of positrons with atoms and molecules has progressed now to the stage where it is not only timely to reflect upon the historical development and to review our current knowledge of this subject but it is appropriate to speculate upon the challenges it presents to the future and to endeavor to chart that future.
The interaction of positrons and positronium with small atoms
Authors: Drachman Richard J.
Published: April 2011

This is a report on recent progress in the theory of small atomic systems including a positron. I have selected four main topics that seem interesting, instead of trying to cover the entire extensive subject. First, I consider the two-channel region in e+–H scattering which lies between 6.8 and 10.2 eV, and have reported the results of positronium-formation and resonant-scattering calculations. Second, I introduce the concept of "iso-leptonic families" with fixed electron and positron numbers and discuss in detail the two-electron, one-positron family. This family includes several interesting bound and resonant states. Next, I derive a new method of calculating positron annihilation rates and cross-sections from approximate wave functions. Although more difficult to apply than the direct method, this technique is more accurate. Finally, I show the applicability of many positron calculations to currently interesting astrophysical problems, especially the recent observations of annihilation radiation coming from the direction of the galactic center.
Slow positron beam design notes
Authors: Canter K. F. , Mills Jr. A. P.
Published: April 2011

Recent methods of producing high flux. (105–106) s−1 slow positron beams are briefly reviewed. Currently, slow positron beams are produced most efficiently using a single crystal Cu(111) + S backscatter geometry moderator for ultra-high vacuum (UHV) conditions and an annealed W-vane converter for non-UHV conditions. The respective fast positron to slow positron conversion efficiencies for the Cu(111) + S and W-vane converters are (9 ± 3) × 10−4 and (1.2 ± 0.2) × 10−4. A new figure of merit, the "normalized brightness-per-volt", for converters is introduced which takes into account the transverse energy spread as well as the conversion efficiency. The importance of the normalized-brightness-per-volt in beam design and future methods to improve this figure of merit are discussed.
Round-table discussion on future directions in positron-gas research
Authors: Fraser P. A. , Bransden B. H. , Coleman P. G. , Raith W.
Published: April 2011

The two days of review papers and of poster presentations of recent research results at the International Conference on Positron Scattering and Annihilation in Gases, York University. 10 and 11 July 1981, were concluded by a discussion during which panelists, and participants from the floor, gave their views on important and likely directions of positron-gas research.
Positron–hydrogen scattering with quadratic variational methods
Authors: Abdel-Raouf M. A.
Published: April 2011

New variational techniques in which the functional [Formula: see text] is minimized are used to calculate the S-wave phase shifts of e+–H elastic scattering. The convergence of these phases, as n increases, is precisely investigated.
A lower bound to the critical positron mass for binding to a hydrogen atom
Authors: Armour E. A. G. , Schrader D. M.
Published: April 2011

A lower bound value of 1.51 me, where me is the mass of the electron, is obtained for the critical mass at which a hydrogen atom will just form a bound state with a positron. This is slightly above the previous best lower bound value obtained by Aronson, Kleinman, and Spruch. The method used in the calculation is similar to that used by Aronson et al. except that a lower bound to the required adiabatic potential is calculated by the method of Temple and Kato.
Positronium formation in s-wave positron–hydrogen scattering
Authors: Humberston J. W.
Published: April 2011

A two channel version of the Kohn variational method is used with trial functions containing up to 120 linear variational parameters to calculate the R-matrix elements and the positronium formation cross section for the scattering of s-wave positrons by atomic hydrogen. Results are obtained in the energy range between the positronium formation threshold and the lowest excitation threshold of the atom. The positronium formation cross section rises very steeply to a value of [Formula: see text] just above the positronium formation threshold and then rises approximately linearly with positron energy to a value of [Formula: see text] just below the excitation threshold. Owing to the weakness of the coupling between the positron and positronium channels, the elastic scattering cross section for the positron continues smoothly across the positronium formation threshold.
Elastic scattering of intermediate-energy positrons and electrons by alkali atoms
Authors: Wadehra J. M.
Published: April 2011

In this paper we present the total elastic scattering cross section for collisions of intermediate energy (500–1000 eV) positrons and electrons by alkali atoms (Li, Na, K, Rb). Calculations are done by using the first Born approximation with polarization plus static interaction. The static interaction is obtained by using a Hartree–Fock–Slater type wave function for the target atom and the polarization interaction is modeled by using a pseudopotential.
Positron–hydrogen ionizing collisions in the presence of a laser field
Authors: Cavaliere P. , Leone C. , Ferrante G.
Published: April 2011

Triple differential cross sections (TDC) for positron–hydrogen ionization in the presence of a laser field are derived within a treatment which uses the Coulomb–Born wave approximation. The laser field is treated classically in the dipole approximation and taken to be homogeneous and single mode. Calculations are specialized to the case of a coplanar asymmetric geometry. The presence of the laser is found to alter significantly the shape of the angular distribution of the ejected electrons when photon exchanges occur. Laser electric fields parallel to the positron transferred momentum [Formula: see text] increase the number of electrons ejected in the forward direction, compared to the no-field case. Laser electric fields perpendicular to Kif double the peaks present in the field-free angular distribution and rotate them symmetrically in opposite directions from the Kif axis towards the EL axis. The results for ionization by positrons are compared to those for ionization by electrons (within the same theoretical treatment). Differences are found only for [Formula: see text]. The limits of validity of the model are discussed, together with simple physical arguments to explain the modifications to the shape of the TDC.
Positronium formation in gaseous ethane and ethane–Ne mixtures
Authors: Sharma S. C. , McNutt J. D. , Eftekhari A. , Ataiiyan Y. J.
Published: April 2011

The positronium yields have been measured in gaseous ethane at gas densities in the range 0.1–286 amagat at 256, 294, 306, 307, 310, 323, 343, and 377 K and in ethane–neon mixtures having neon concentrations from about 0.38 to 0.99 at 256, 294, and 306 K. The positronium yields in gaseous ethane are observed to vary with gas density in a complex manner and to remain independent of temperature for the range of temperatures investigated. The presence of neon in ethane–neon mixtures enhances the fraction of positrons forming positronium at low partial densities of ethane. These results are discussed in terms of the models for positronium formation.
The absorption spectrum of KBr:Sn2+
Authors: Scacco A. , Jacobs P. W. M.
Published: April 2011

Thorough annealing on crystals of KBr.Sn2+ results in significant changes in their absorption spectra. These changes have been interpreted as the effect of the annealing on the relative concentration of different types of Sn2+ centres: isolated Sn2+ substitutional ions ("cubic" centres) and Sn2+–cation vacancy complexes ("tetragonal" and "rhombic" centres). The line shape of the optical absorption has been calculated theoretically, by diagonalizing the complete 12 × 12 Hamiltonian matrix, for cubic centres only, for tetragonal centres only, and for different relative concentrations of cubic and tetragonal centres. The experimental absorption spectra of KBr:Sn2+ crystals that have undergone various annealing treatments are in good agreement with theoretical spectra calculated for appropriate mixtures of the above centres. These results confirm that thorough annealing increases the fraction of isolated Sn2+ substitutional ions at the expense of the Sn2+–cation vacancy complexes. The consistency of the theoretical model is demonstrated by the agreement of the calculated moments of the absorption bands of KBr:Sn2+ with the experimentally derived values.
Optical properties of plasma-polymerized organosilicone films
Authors: Wertheimer M. R. , Klemberg-Sapieha J. E. , Corriveau R.
Published: April 2011

The refractive index, n, of plasma-polymerized hexamethyldisiloxane and -silazane thin films has been measured by ellipsometry at 632.8 nm. For both types of films n was found to increase from about 1.4 to about 1.7, with increasing substrate temperature during film deposition, Ts. Using the Lorentz–Lorenz equation and our previously published density and infrared data for these thin film materials, it is shown that films produced at [Formula: see text] are essentially "inorganic." Calculated n values for hypothetical structures (Si2O)x and (Si2N)x (expected from the "monomer" compositions) agree to within a few percent with measured data.
Measurement of the total cross section of titanium with neutrons of 6–8 m/s
Authors: Gabriel P. , Robson J. M.
Published: April 2011

The sum of the absorption, incoherent, and thermal inelastic scattering cross sections of natural titanium has been measured at 293 K for three neutron velocities in the range 6–8 m/s. They agree with values to be expected on the basis of an inverse velocity extrapolation from measurements near thermal neutron velocities.
The nuclear relaxation rate for the itinerant-electron antiferromagnet
Authors: Crişan M. , Gulácsi Zs.
Published: April 2011

The relaxation rate in the nuclear magnetic resonance of the itinerant-electron antiferromagnet was calculated as a function of temperature. A good agreement with the experimental results obtained on CrB2 has been observed. The two band model for the itinerant-electron antiferromagnet for T < TN (TN is the critical temperature) and the mean field theory for the critical region have been used to calculate [Formula: see text] as a function of temperature.
Equations de bilan dépendentes du temps appliquées aux collisions inélastiques
Authors: Lupaşcu A. , Tudorache St. , Popescu I. M.
Published: April 2011

A general matrix method for the time dependent rate equations applied to inelastic collisions is presented. The minimal information needed to compute the collisional cross-sections is deduced and used to study the particular case of two excited levels.
The early universe in a generalized theory of gravitation
Authors: Moffat J. W. , Vincent D.
Published: April 2011

The standard Friedmann–Robertson–Walker (FRW) big-bang model of the universe requires special initial conditions: the early universe is highly homogeneous and isotropic even though there exist causally disconnected regions (horizon problem). A plane symmetric (anisotropic) solution of a system of field equations in a generalized theory of gravitation, predicts the beginning of the universe as a vacuum instability at a specific fundamental time (which can be associated with the Planck time (tp)), after which matter is created as the universe begins to expand. At a time t = tc there is a singular expansion, the anisotropy vanishes, and the physical horizon becomes infinite. Thereafter the solution of the field equations goes over into the FRW model. Thus the special initial conditions of the FRW model at the big-bang singularity t = tc are predicted by the theory.
Some characteristics of the medium energy particles produced in -nucleus collisions
Authors: Khan A. R. , Ali U. , Ahmad A. , Ahmad S. , Irfan M. , Zafar M. , Shafi M.
Published: April 2011

Emission characteristics of 1083 interactions with Nh ≤ 2 produced in 50 GeV/c[Formula: see text]-nucleus collisions have been analysed with regard to the emission frequency, energy spectrum, angular distribution, and momentum distribution, etc., of grey pions, protons, douterons, and tritons. The variation of average emission frequencies of these particles with different parameters has been investigated. Further, an attempt has also been made to check whether the emission characteristics of these particles depend on the type of disintegration.
The open orbits of potassium
Authors: Overhauser A. W.
Published: April 2011

The high-field magnetoresistance of potassium, which fails to saturate, can be an intrinsic property only if the Fermi surface is multiply connected. Direct observation of open-orbit magnetoresistance peaks by Coulter and Datars confirms this theoretical principle. Since the Brillouin zone of potassium is only half full, and the Fermi surface is nearly spherical, open orbits can occur only if the translational symmetry of the crystal is broken by a charge-density-wave structure. The open-orbit distributions that result explain the observed magnetoresistance patterns.
Is potassium a simple metal?
Authors: Wisbr Nathan
Published: April 2011

The temperature-dependent part of the electrical resistivity ρ(T) of a metal consists of the sum of two terms, one term being due to electron–phonon scattering ρcp(T) and the other term being due to electron–electron scattering ρcc(T). One may write[Formula: see text]where θD, is the Debye temperature of the metal and the coefficients C and A give the magnitudes of ρcp(T) and ρcc(T), respectively. For a metal whose electrical resistivity exhibits "simple" behavior, it had been expected that the measured data for ρ(T) would have the following properties. (i) The function f(T/θD) should approach (T/θD) for [Formula: see text]. (ii) The magnitude of the coefficient C should be the same, or nearly so, for all measured samples. (iii) The magnitude of the coefficient A should be the same, or nearly so, for all measured samples.The low-temperature ρexpt(T) data for potassium, which has by now been measured for many samples, exhibit none of these three properties. A discussion will be presented of the reasons for this "non-simple" behavior of ρexpt(T) for potassium.
Electron–electron interactions in simple metals and transition metals
Authors: MacDonald A. H.
Published: April 2011

Approximate formulas have been suggested for the electron–electron scattering amplitude in crystalline metals. These formulas are based on a formal exact relationship between the scattering amplitude and the electronic response functions and on formulas for the response function within density functional theory. It is pointed out that these approximations suggest that a large contribution to the scattering amplitude from effective spin–spin interactions should be present in many transition metals. The formulas are simple enough to make a quantitative exploration of electron–electron scattering amplitudes in non-simple metals practical.
The electron–phonon interaction in simple metals
Authors: Taylor Roger
Published: April 2011

The ingredients necessary for a good description of the electron–phonon interaction in simple metals are discussed from the point of view of lattice dynamics and electron transport. Exchange and correlation effects in the electron gas are summarized and it is concluded that the local density approximation is satisfactory, as is Rasolt's formula for the vertex function. Particular emphasis is laid on the importance of nonlocality in the pseudopotential and it is pointed out that only Na can be adequately described by a local psuedopotential. Finally the calculations performed at NRC are summarized and it is concluded that they give a good description of electron transport in the alkalis.
Ideal transport in transition metals: the rigid-muffin-tin approximation and beyond
Authors: Butler W. H.
Published: April 2011

A recent calculation of the electrical and thermal resistivities of Nb and Pd due to electron–phonon scattering is reviewed. This calculation used the rigid-muffin-tin approximation and its results indicate that electron–phonon matrix elements calculated in this approximation are too weak at low momentum transfer. A formalism is developed for calculating the corrections to the rigid-muffin-tin approximation.
Localization and interaction effects in weakly disordered two-dimensional systems
Authors: Kaveh Moshe
Published: April 2011

The question of whether a two-dimensional metal can exist is discussed. The theoretical and experimental position is reviewed. Experimentally, the conductivity of a two-dimensional system (such as inversion layers or thin film metals) shows the following nonmetallic behavior: (i) logarithmic decrease of the conductivity as T → 0. (ii) negative magnetoresistance, (iii) logarithmic decrease of the Hall coefficient as T → 0, and (iv) nonohmic conductivity, increasing logarithmically with electric field.The nonmetallic behavior of the conductivity is discussed in view of two recent theoretical approaches, (i) The localization approach, which predicts that all electronic states in a two-dimensional system are localized, and (ii) the interaction approach which predicts a logarithmic decrease in the density of states as the temperature is decreased.Evidence for both theories is presented.
Dependence on the renormalization points in a simple scalar theory
Authors: McKeon Gerry
Published: April 2011

One loop corrections to the scalar potential in a simple theory involving two scalar fields [Formula: see text] and ψ are evaluated. The dependence of the renormalized coupling constants on the renormalization points [Formula: see text] and ψ0 are examined. It is found that under the change [Formula: see text], ψ0 → (1 + ε)ψ0, the coupling constants vary according to a set of equations that are independent of the ratio [Formula: see text]. It is shown that the coupling constants are not altered if [Formula: see text] is changed.