bluuebunny/crossref_metadata_2025 huggingface dataset:
Models for the bulk photovoltaic effect in ferroelectric crystals
Authors: Guibaly Fayez El
Published: April 2011

Three models for the bulk photovoltaic effect in electrooptic crystals are discussed. All models produce the same results. First, the photocurrent responsible for hologram storage is spatially shifted relative to the optical pattern that produced it. Second, the efficiency of hologram recording decreases with increases in the spatial frequency of the optical interference pattern. Third, the efficiency of hologram recording decreases for crystals exhibiting a strong bulk photovoltaic effect. The effect of finite electron transport length on volume-phase hologram storage is analyzed. It is shown that the resulting holograms are spatially shifted relative to the optical-intensity pattern that produced it. This phase shift affects beam coupling during hologram reading; it can be an aid in studying the bulk photovoltaic effect and the relative importance of the various mechanisms of hologram writing. The analysis also points out that the finite electron transport length reduces the ability of the crystal to store holograms if the spatial frequency of the optical interference pattern is increased.
Information storage in ferroelectrics: real-time monitoring of refractive indices
Authors: Guibaly Fayez El
Published: April 2011

An indirect experimental technique for real-time monitoring of electric fields in ferroelectric crystals is reported. Large electrostatic fields are observed in ferroelectrics exhibiting the bulk photovoltaic effect when they are exposed to light of an appropriate wavelength. It has been shown elsewhere that these fields are closely dependent on the light-intensity pattern that produced them, and that they strongly affect the holographic storage efficiency.
Rigorous analysis of an imperfectly conducting linear antenna
Authors: Saoudy S. A. , Hamid M.
Published: April 2011

A Wiener–Hopf type analysis is introduced to determine the radiation characteristics of an imperfectly conducting solid thin long dipole antenna. The analysis is applicable to dipoles with constant impedance per unit length. The input admittance of the infinitely long imperfectly conducting dipole is calculated and compared with available experimental and analytical data.
Comments on stochastic quantization and regularization of gauge theories
Authors: Pimentel B. M. , Kolck U. L. van
Published: April 2011

We discuss some aspects of stochastic quantization of gauge theories in the spirit of Parisi and Wu. We show that it is not compatible with dimensional regularization unless we suppress the noise associated with cyclic variables or fix the gauge in the action.
Raman spectroscopy of matrix-isolated hydrogen: I. Influence of matrices on defects
Authors: Bier K. D. , Jodl H. J. , Däufer H.
Published: April 2011

The hydrogen molecule is treated as a model substance for matrix-isolation effects. Raman investigations are made concerning the influence of matrix material on the various modes of hydrogen. The opposite interaction, how the defect influences modes of the matrix, is the object of the following paper.For the doublet in the vibrational range of hydrogen in rare-gas solids, an assignment to Q1(0) and Q2(1) is made and well substantiated. In addition to matrix-shift considerations, temperature influences, ortho–para investigations, and aggregation effects, different sites are observable in the nonspherical matrices, N2 and O2, with a restriction of free rotation in nitrogen.
Raman spectroscopy of matrix-isolated hydrogen. II. Influence of defects on matrices
Authors: Bier K. D. , Jodl H. J. , Däufer H.
Published: April 2011

The hydrogen molecule is treated as a model substance for matrix-isolation effects. Raman investigations are made concerning the influence of the defect on the matrix material Ar, Kr, Xe, N2, and O2. The influence of the matrix on the hydrogen impurities is investigated in the preceding paper.A detailed comparison of the spectra of pure molecular crystals with the spectra of doped crystals (1% H2 or 1% D2) shows distinct changes in the Raman spectra of the matrices. Weak influences of the impurity on site symmetry and on the vibron–phonon and phonon–phonon coupling mechanisms of the anisotropic matrices N2 and O2 are obtained. An additional line, observed in the vibron–phonon structure of N2 and O2, is interpreted as a coupled resonant mode. Direct evidence of a resonant mode at 39 cm−1 is only obtained in the system containing 1% D2 in N2.
A new biintercalation compound, FeCl3–NiCl2–graphite, studied by 57Fe Mössbauer effect spectroscopy and superconducting quantum interference device magnetization measurements: an ideally decoupled bimagnetic system
Authors: Rancourt D. G. , Hun B. , Flandrois S.
Published: April 2011

A novel situation in which long-range magnetic order coexists with (super)paramagnetism occurs in a new graphite biintercalation compound: FeCl3–NiCl2–graphite. Several compounds have been prepared by sequential intercalation of the two intercalates and have been characterized by powder diffractometry, X-ray precession photographs, high-precision X-ray single-crystal measurements, chemical analysis, and high-temperature susceptibility measurements. All measurements are consistent with the stacking sequence –C–NiCl2–C–FeCl3–C– and corroborate the crystallographic integrity of separate NiCl2 and FeCl3 sublattices. Since the in-plane magnetic interactions of the NiCl2 and FeCl3 layers are, respectively, ferromagnetic and antiferromagnetic, the two types of chloride layers have been probed independently by combining low-temperature superconducting quantum interference device magnetometry and 57Fe Mössbauer-effect spectroscopy. The NiCl2 layers order magnetically at 20.5 K, whereas the FeCl3 layers do not order down to 4.2 K. The drop of 1.5 K in the NiCl2-related ordering temperature, induced by the intercalation of FeCl3 into stage-2 NiCl2–graphite, is attributed to the increased NiCl2–layer separation, suggesting that the transition in NiCl2–graphite is not two-dimensional. Some of the FeCl3–NiCl2–graphite compounds show NiCl2-related transitions at temperatures lower than 20.5 K, which is explained in terms of lower in-plane NiCl2 concentrations. Partial oxidation and hydrolysis of in-gallery FeCl3 has been demonstrated and is found to depend strongly on the mean host-graphite-flake size. A charge transfer of 0.2 electrons per iron atom in the FeCl3 layers is inferred from the Mössbauer spectra collected at 4.2 K, which is the same as in singly intercalated FeCl3–graphite compounds of all known stages. Time and temperature-hysteresis effects in the magnetization have been measured and show distinct "re-entrant spin-glass" behaviour. Relevant aspects of the magnetism and structure of the related singly intercalated materials, the pristine chlorides, and the new biintercalation compounds are compared in detail. The overall features are consistent with a recent model based on interacting island supermoments.
Contour integral representation of the on-shell T matrix
Authors: Kröger Helmut
Published: April 2011

We suggest a contour integral representation for the on-shell T matrix in nonrelativistic N-body potential scattering with strong short range interactions. Results of a numerical calculation in the two-body system using a short range separable interaction of the Yamaguchi type are presented and show fast convergence towards the reference value.
Modal characteristics of a doubly clad step-index optical fibre: a general analytical approach
Authors: Chaubey V. K. , Dey K. K. , Ojha S. P. , Khastgir P.
Published: April 2011

Using a fairly rigorous approach, a general characteristic equation for a doubly clad step-index fibre has been derived under the assumption that the refractive-index difference between the inner and outer cladding is small. Two different profiles, i.e., the W profile and the staircase profile, have been treated together and a discussion of their common characteristics has been made. Cutoff conditions for low-order modes have been obtained. For a certain range of values of the transverse-phase parameter ratio, the singly-clad fibre has greater mode cutoff V numbers than those of a doubly clad fibre. The analysis anticipates the possibility of obtaining greater cutoff V numbers for W-profile fibres.
Cross sections for phosphorous negative-ion detachment in collisions with rare gas atoms
Authors: Hird B. , Bruyère M. , Fafard S. , Orakzai M. W.
Published: April 2011

Atomic cross sections for single and double electron detachment from P− in collisions with rare-gas atoms are reported at laboratory collision energies between 13 and 113 keV.
Antenna input impedance: experimental confirmation and geological application
Authors: Nicol J. L. , Ridd P. V.
Published: April 2011

Calculations and measurements of the input impedance of horizontal dipole antennas close to the Earth have been carried out, and the results have been compared with those of other workers. Antenna impedance measurements over both very highly and very poorly conducting ground planes were found to be consistent with theoretical calculations. Finally, a series of measurements traversing an interface between basalt and weathered granodiorite, both covered with soil, indicated that antenna input-impedance measurements can be useful for geological field surveys.
Dressed ion acoustic soliton in an ion-beam plasma system
Authors: Yashvir  , Tiwari R. S. , Sharma S. R.
Published: April 2011

Propagation of an ion-acoustic soliton in an ion-beam plasma system is studied using the renormalization procedure of Kodama and Taniuti in the reductive perturbation method and an alternative method. Expressions for the first- and second-order potentials are derived. The effects of beam velocity and beam density on the amplitude and the width of the solitons, for different ion-mass ratios, are considered. It is found that (i) the amplitude decreases with the increase of beam density, and (ii) there is a critical beam velocity, below which a stationary soliton cannot exist in an ion-beam plasma system.
Ultrasonic sensor using polarization-maintaining optical fiber
Authors: Takahara H. , Togashi F. , Aragaki T.
Published: April 2011

The interaction between an ultrasonic wave and the laser beam transmitted through a polarization-maintaining optical fiber is analyzed both theoretically and experimentally. An ultrasonic sensor using a polarization-maintaining optical fiber is optically simple; it is easily matched to the source and detection optics; and it has better stability than an optical configuration using two optical fibers.
High-resolution reconstruction of photon-limited stellar images using phase gradients
Authors: Aitken G. J. M. , Johnson R.
Published: April 2011

Phase-gradient and Knox–Thompson processes for determining the gradients of a stellar object's phase from speckle images are compared with respect to their behaviour at low photon levels. The phase-gradient process is immune to the degrading effects of image wandering and image recentering, and is computationally simpler and faster than the Knox–Thompson process. Examples of reconstructions from simulated and real speckle images are presented.
Nonlinear effects in the squeezing spectrum of a parametric amplifier
Authors: Zaidi H. R.
Published: April 2011

A general nonlinear theory is formulated for the calculation of the squeezing spectrum of a parametric amplifier. The lowest order nonlinear corrections are calculated for both modes below the threshold, and the results are compared with linear theory. The corrections to the spectrum are found to be significant.
Standardization and control of a dip-coating procedure for optical thin films prepared from solution
Authors: Hewak Daniel W. , Lit. John W. Y.
Published: April 2011

The properties of dip-coated thin films prepared from colloidal silica and titania solutions have been examined. The effects of withdrawal rate, heat treatment, and solution concentration on film thickness, refractive index, and other properties have been studied. Results show that extremely uniform and reproducible thin films with refractive indices between 1.46 and 2.08 and thicknesses up to 0.25 μm can be produced with a single dip. The refractive index of the SiO2:TiO2 composite films varies linearly with the volume fraction of TiO2, and the thickness varies linearly with withdrawal rate. The effects of drying on the final thin film properties are minimal; however, baking conditions have a significant effect, with films shrinking up to 50% and the refractive index increasing 40% during baking. The resulting films are hard, durable, and of good optical quality. We have studied these films for use as planar optical waveguides; however, the results are also applicable to films made for various uses such as optical coatings, filters, or protective layers.
Polarimetric matched filter for coherent imaging
Authors: Kostinski Alexander B. , James Brian D. , Boerner Wolfgang-M.
Published: April 2011

In this paper we focus on image-contrast optimization between two rough-surface classes. Our approach is based strictly on polarimetric filtering, and therefore, no digital image-processing techniques are employed. The approach is tested on a complete polarimetric synthetic aperture radar (POL-SAR) image of the San Francisco Bay area. The data have been taken with the National Aeronautics and Space Administration – Jet Propulsion Laboratory CV-990L-band POL-SAR system, where eight real numbers (complex elements of a 2 × 2 polarization scattering matrix) are associated with each image pixel. Optimal transmitted polarizations (corresponding to maxima or minima of reflected energy) are found for each image pixel, and the results are analyzed statistically via a set of joint two-dimensional histograms. This is done for both of the rough-surface classes. The image response to the "optimal" incident polarization is then simulated digitally by adjusting the receiver polarization according to the modes of the histograms. The corresponding images are computed and displayed with significant image-contrast improvement.
Lifetime measurements for low-lying levels in Hg I and Hg II using the beam-foil technique
Authors: Pinnington E. H. , Ansbacher W. , Kernahan J. A. , Ahmad T. , Ge Z.-Q.
Published: April 2011

The techniques of beam-foil spectroscopy are applied to obtain measurements of the lifetimes of the 6s6p1P1, 3P1, 6s6d1D2, 3D1, 3D2, and 3D3 levels of Hg I and the 6p2P1/2, 2P3/2, 6d2D3/2, 2D5/2, and 7s2S1/2 levels of Hg II. The energy loss sustained by the ions in passing through the carbon foil is determined using an extended Doppler-shift technique. Constrained curve-fitting and arbitrarily normalized decay curve analyses are used to overcome problems caused by blending between transitions from the 6s6d1D2 and 3D1 levels of Hg I. The f values obtained from the resonance transitions are 1.14 ± 0.04 (Hg I) and 0.648 ± 0.022 (Hg II), in agreement with the trends found previously for higher Z ions in the Hg I and Au I isoelectronic sequences.
H216O: Line positions and intensities between 8000 and 9500 cm−1: the second hexad of interacting vibrational states: {(050), (130), (031), (210), (111), (012)}
Authors: Mandin J. -Y. , Chevillard J. -P. , Flaud J. -M. , Camy-Peyret C.
Published: April 2011

Water vapor Fourier-transform spectra (resolution = 0.010 cm−1) have been analyzed between 8000 and 9500 cm−1. Accurate values of 441 rotational energy levels, belonging to the vibrational states (050), (130), (031), (210), (111), and (012) of the second hexad of H216O, have been determined. Moreover, 500 line intensities have been accurately measured (uncertainty = 6%). To increase the number of experimental intensities (useful for atmospheric applications), we have set up a less sophisticated but faster method; this has led to the measurement of 1200 additional intensities, with an average uncertainty of about 10%.
Inflationary cosmological universe containing dark matter and many charged galaxies
Authors: Das A , Kay Daniel
Published: April 2011

Within the framework of Einstein's theory, cosmological universes are considered that contain three types of "fluids." A neutral cosmological fluid (dark matter), which is present everywhere, determines the overall time evolution of the universe. The second type consists of charged matter that constitutes the cores of galaxies. The electromagnetic fields generated by the charged matter make up the third kind of fluid, which is evidently null. An exact cosmological solution is furnished that provides for an early inflationary period and contains many charged black holes as galactic cores.
Quadrupolar spin relaxation mechanisms for 235U in liquid UF6
Authors: Ursu I. , Bogdan M. , Balibanu F. , Gulacsi Z. , Gulacsi M. , Tosa V. , Demco D. E.
Published: April 2011

The nuclear spin lattice relaxation time is calculated for 235U situated at the center of an octahedral 235UF6 molecule. Vibrational distortion, collisional deformation, and electric fields induced by neighbouring hexadecapole moments are considered as possible mechanisms that could account for the observed 235U quadrupolar relaxation rate. The efficiency of these mechanisms in causing relaxation is discussed by comparing the calculated value with the experimentally determined one.
Ortho–para conversion of positronium in some rare-earth ion aqueous solutions
Authors: Consolati G. , Quasso F.
Published: April 2011

We have extended a previous investigation by studying the ortho–para conversion of positronium in aqueous solutions of some lanthanide ions (Yb3+, Tm3+, Er3+, Dy3+, and Tb3+). The corresponding cross sections were found to be proportional to the number of unpaired electrons in the ion. Furthermore, the contact density of the electron–positron pair in the origin was obtained for a 1 M aqueous solution of ErCl3.
Deconvolution of blurred images using photon counting statistics and maximum probability
Authors: Lloyd N. D. , Llewellyn E. J.
Published: April 2011

A method for the deconvolution of blurred images that uses photon counting Poisson statistics to determine the most probable solution is described. The method ensures that the final solution is physically meaningful and consistent with the observations. The developed algorithm is tested with real blurred data, and the result is compared with other methods. These tests show that the algorithm produces stable results that are in good agreement with the true answer.
High-resolution Fourier spectrometry of 14N2: analysis of the (0–0), (0–1), (0–2), (0–3) bands of the C3Πu – B3Πg system
Authors: Roux F. , Michaud F. , Vervloet M.
Published: April 2011

The C3Πu – B3Πg System of the 14N2 molecule has been recorded by high-resolution Fourier transform spectrometry between 20 000 and 32 000 cm−1. Four bands (0–0, 0–1, 0–2, 0–3) were analyzed initially. The whole set of wavenumbers has been fitted using a nonlinear procedure. The molecular constants for the ν = 0 level of the C3Πu state have been computed. Weak perturbations were detected unambiguously.
On the question of stability and disorder in icosahedral aluminum – transition metal alloys
Authors: Lawther D. W. , Dunlap R. A. , Srinivas V.
Published: April 2011

Through an X-ray diffraction and thermal analysis investigation of melt spun Al – transition metal (Al–TM) alloys, we report the formation of a highly stable and well-ordered pure icosahedral (i) phase in Al80TMl20−xTM2x(TM1 = V, Cr; TM2 = Fe, Co). The superior i-phase formation over that in the binary Al–TM alloys is interpreted in terms of the distribution of TM sites known to exist in this phase. A comparison of the i-phase formation ranges indicates the presence of two distinct classes of TM sites and a strong interaction between adjacent TM sites.
Symmetries and constants of motion of geodesic equations
Authors: Patino Alberto
Published: April 2011

Results for the symmetries of equations and equivalent Lagrangians are applied to the problem of geodesic motion in Riemannian space–times. These results are compared with those calculated previously, and the construction of conserved quantities is achieved.
Lattice dynamics of molybdenum and tungsten
Authors: Onwuagba B. N.
Published: April 2011

The directional properties of the Born–Mayer potential associated with the interaction of the s- and d- state wave functions are shown in the framework of the model potential theory for the lattice dynamics of molybdenum and tungsten. The numerical calculations give a better understanding of the occurrence of the soft modes in both metals.
A new interpretation of the wave function
Authors: Wassef Wafik A.
Published: April 2011

A memory is attributed to quantum systems. The time range of this memory is found to be inversely proportional to the energy of a system. The value of the wave function at any moment of time is the time average of its past values during the memory range. The formalism of quantum mechanics is reproduced in terms of integral operators and the time span of the memory of a system. The representation of the state of a quantum system at any moment of time is found to include an explicit representation of its past states as well. Measurement processes are explained from this point of view. Some experiments are analyzed using the present new interpretation.
Dimensional regularization and the path-integral approach to photon mass in the Schwinger model
Authors: Treml T. F.
Published: April 2011

The derivation of the photon mass in the Schwinger model (two-dimensional quantum electrodynamics) is studied in a path-integral approach that employs a coordinate-space form of dimensional regularization. The role of the antisymmetric epsilon pseudotensor in dimensional regularization is briefly discussed. It is shown that the correct photon mass may easily be recovered by a dimensionally regularized calculation in which the epsilon pseudotensor is taken to be a purely two-dimensional quantity.
Relativistic versus nonrelativistic Hartree–Fock calculations: solvable examples in one dimension
Authors: Mitchell D. B. , Nogami Y. , Whelan N. D.
Published: April 2011

Relativistic and nonrelativistic one-dimensional systems of particles of the same mass interacting through instantaneous contact interactions are considered. For the relativistic interaction, we assume a combination of a Lorentz scalar and a vector. The mass and interaction strength are chosen such that the deuteron is simulated; the relativistic and nonrelativistic "deuteron" models have the same binding energy and practically the same structure. The relativistic and nonrelativistic Hartree–Fock equations can both be solved analytically. For certain combinations of the Lorentz scalar and vector interactions, the difference between the relativistic and nonrelativistic results can be appreciable.
Electromagnetic scattering from a coated notched cylinder
Authors: Ruppin R. , Yatom H.
Published: April 2011

The problem of electromagnetic scattering of a normally incident plane wave from a coated conducting notched cylinder is solved. The coating material and the notch material are arbitrary dielectrics, and the incident wave is either transverse electric or transverse magnetic polarized. The numerical results of backscattering cross-section calculations are presented, and the dependence of the cross section on the various physical parameters is investigated. The coated notched cylinder system possesses characteristic electromagnetic resonances that manifest themselves in the scattering spectra.
A search for evidence of cold fusion in the direct implantation of palladium and indium with deuterium
Authors: Durocher J. J. G. , Gallop D. M. , Kwok C. B. , Mathur M. S. , Mayer J. K. , McKee J. S. C. , Mirzai A. , Smith G. R. , Yeo Y. H. , Sharma K. S. , Williams G.
Published: April 2011

A high concentration of deuterium atoms was implanted into palladium and indium targets by means of a 60 keV, 100 μA [Formula: see text] beam. The motivation was to simulate the Utah electrolysis experiment in a nonequilibrium situation not involving heavy water as the intermediate material. The assumption was that the formation of a high concentration of deuterium nuclei in the surface region of the target material was a prerequisite for the demonstration of the so-called "cold fusion" effect. In experiments performed at the Accelerator Centre of the University of Manitoba, significant neutron production was observed for palladium and indium targets into which an excess of 1019 deuterons were implanted. Despite some initial surprise at the flux of neutrons generated at such low energies, the numbers observed seem consistent with known fusion cross sections and warm fusion calculations.
New relativistic crystalline electric field effective operators
Authors: Chatterjee R. , Buckmaster H. A.
Published: April 2011

This paper shows that the use of the Landau and Lifshitz definition of the Hermitian adjoint of a tensor operator combined with the triangular rule leads to new terms in the relativistic "effective operator technique" formulation of a crystalline electric field, and that the matrix elements of these terms are significant for S-state ions.
The Raman spectrum of Cs2SeO4 crystals
Authors: Ethier L. , Massa N. E. , Béliveau A. , Carlone C.
Published: April 2011

The Raman spectrum of Cs2SeO4 crystals has been obtained at T = 20 K. We have observed 23 of the 24 external modes predicted by a model with four formula units per unit cell. A comparison of the internal mode frequencies with those of the solution spectrum shows that the charge on the SeO4 tetrahedron is, in the crystal phase, less than two electrons. We have obtained the temperature dependence of the Raman spectrum from 20 to 650 K. For the internal modes only, we have observed the pressure dependence up to 25 kbars, and we have evaluated the volume dilatation and the interaction contributions to their total temperature dependence. (1 bar = 100 kPa.)
Mechanical and thermal properties of the glassy semiconductor chlorinated Se0 997As0 003 used as an X-ray imaging material
Authors: Kasap S. O. , Yannacopoulos S.
Published: April 2011

Mechanical and thermal properties of a typical X-ray imaging material amorphous Se0.997As0.003, chlorinated in the ppm range were investigated using thermal microhardness analysis (TμHA) and differential scanning calorimetry (DSC). The experiments were carried out over a temperature range encompassing the glass transformation to study the nature of structural changes controlling the mechanical and thermal properties. It is shown that the mechanical property microhardness when examined on an Itoh–Shishokin plot of log Vickers hardness number (VHN) vs. temperature (T) exhibits a hardness transition temperature, Tg*, in the glass transformation region. The rates of relaxation of the mechanical and thermal properties in the glass transformation region were studied by investigating the heating rate dependence of the glass transition temperatures, Tg* and Tg, defined empirically on the log VHN vs. T behavior and the DSC glass transformation endotherm, respectively. By applying the present thermoanalytical methods, it has proved possible to identify a typical Vogel–Tammann–Fulcher type of behavior in the mechanical and thermal relaxation times that correlates remarkably well with the viscosity–temperature data of M. Cukierman and D. R. Uhlmann (J. Non-Cryst. Solids, 12, 199 (1973)) as well as the dielectric loss experiments of M. Abkowitz, D. F. Pochan, and J. M. Pochan (J. Appl. Phys. 51, 1539 (1980)). The latter had previously exposed a Williams–Landel–Ferry relation for the Debye relaxation times in a-Se and a-Se: 1% As. It is therefore concluded that the behavior of mechanical, thermal, and dielectric properties of a-Se0997As0003 in the glass transformation region is inversely proportional to the viscosity, which in turn can be adequately described over a temperature range above ~30 °C by a Vogel expression.
Unitary-group canonical representations
Authors: Mirman R.
Published: April 2011

A procedure based on symmetric-group basis states is constructed to develop and justify the formalism for the computation of unitary-group canonical matrix elements and states, the quantities needed for physical applications to prepare for such applications. It is shown that this method does give the required canonical decomposition. This completes the preparation for the computation of these numerical quantities.
Unitary-group canonical states and matrix elements
Authors: Soto Jr. M. F. , Mirman R.
Published: April 2011

States of unitary groups are realized as multinomials in boson operators, symmetrized to give symmetric-group basis states. From these, matrix elements of the group generators are calculated using the procedures discussed here. A table of basis states and matrix elements of unitary-group representations, and the values of the invariants so generated, is given for SU(1) through SU(4), for all symmetric groups from S(1) through S(3).
Hydrogen interaction with oxidized Si(111) probed with positrons
Authors: Lynn K. G. , Nielsen Bent , Welch D. O.
Published: April 2011

A variable-energy positron beam was utilized to study the interface action of hydrogen with Si(111) covered by an ultrahigh-vacuum thermally grown oxide of 2–3 nm thickness. It was observed that positrons implanted at shallow depth (<100 nm) after diffusion are trapped either at the interface between the oxide and the Si or in the oxide. The positron-annihilation characteristics of these trapped positrons are found to be very sensitive to hydrogen exposure. The momentum distribution of the annihilating positron–electron pair, as observed in the Doppler broadening of the annihilation line, broadens considerably after exposure to hydrogen. The effect recovers after annealing at [Formula: see text], suggesting a hydrogen binding at the interface of ~3 ± 0.3 eV.
Deconvolution of noisy data using a priori constraints
Authors: McKee B. T. A.
Published: April 2011

The deconvolution of experimental data with noise present is discussed with emphasis on the ill-conditioned nature of the problem and on the need for a priori constraints to select a solution. An analytical Fourier space deconvolution that selects the minimum-norm solution subject to a least-squares constraint is described. The cutoff parameter used in the constraint is evaluated from the statistical fluctuations of the data. This method is illustrated by its application to 3-d image reconstruction for positron emission tomography.
Quantum corrections to the geodesic equation
Authors: McKeon D. G. C.
Published: April 2011

The geodesic equation of motion for a particle moving in a background gravitational field can be derived from an action that is essentially that of a one-dimensional bosonic nonlinear sigma model. We quantize the particle, and obtain its effective action to lowest order in both the background curvature and the loop expansion, using the background quantization procedure appropriate to the nonlinear sigma model. Operator regularization is used to regulate the theory. Explicit calculation shows that these lowest order corrections vanish exactly.
Evolution of radiating viscous spheres and gravitational collapse
Authors: Herrera L. , Jiménez J. , Barreto W.
Published: April 2011

The effects of viscosity on the gravitational collapse of a radiating sphere are calculated by extending the Herrera–Jiménez–Ruggeri method to the case of viscous fluids. An explicit model is worked out, indicating that when both the shear and bulk viscosity are nonvanishing, the final configuration is less compact than that corresponding to a nonviscous fluid.
Isotopic mass dependence in the bound–free D–X fluorescence spectrum of Br2
Authors: Tellinghuisen Joel , Austin Derek , MacDonald Michael , Lawley Kenneth P. , Donovan Robert J.
Published: April 2011

The D → X transition is studied for both natural Br2 and 81Br2, using 1576-Å radiation from an F2 laser to excite the fluorescence. The characteristic interference structure at the long-wavelength end of the spectrum is found to be much more sensitive to changes in isotopic mass than to changes in the vibrational and rotational quantum numbers, when all three represent comparable changes in the energy of the excited state. These dependences are consistent with predictions from semiclassical theory.
Turbulent heating experiment in the STOR-1M tokamak
Authors: Sarkissian A. , Hirose A. , Mitarai O. , Wolfe S. , Skarsgard H. M.
Published: April 2011

In this paper the STOR-1M tokamak and its diagnostics are described. The plasma behavior before, during, and after turbulent heating is also discussed. Anomalously rapid current penetration has been observed during both the ohmic current-rise phase and the turbulent heating phase. The critical streaming parameter for the onset of current driven turbulence has been measured. Efficient electron and ion heating during turbulent heating has been observed. Plasma confinement properties show significant improvement, following the turbulent heating pulse, for a period much longer than the duration of the turbulent heating pulse.
Corrections to the tritium β decay spectrum arising from radiative and atomic effects and their relationship to neutrino mass experiments
Authors: Weisnagel S. , Law J.
Published: April 2011

The process of inner bremsstrahlung is examined for the β− decay of 3H. These radiative effects are then combined with atomic corrections in a more complete theoretical reference spectrum consisting of both light and heavy neutrino decay in accordance with recently published results of neutrino mass experiments. Due to the unusual nature of the experimental detector, final density of states is modified to provide a decay rate as a function of recorded energy. This reference spectrum is compared with experimental data using the exact method employed in the original analysis. It is found that previously reported low energy Kurie spectrum deviations are still present in the sample data, corresponding to a best fit for neutrino mass mν = 17.2 keV and mixing probability R = 2.5%. The origin of the difference between the conclusions reached here and those of earlier cited works is briefly discussed.
The ground state of Na2
Authors: Babaky O. , Hussein K.
Published: April 2011

The laser-induced fluorescence of the [Formula: see text] and [Formula: see text] transitions of Na2 are analysed, using high resolution Fourier transform spectroscopy. Fixed-frequency ion-laser lines (4880 and 4765 Å (1 Å = 10−10 m) from Ar+ and 6471 and 4762 Å from Kr+) together with laser frequencies from a ring dye laser, using rhodamine 6 G with λ = 5781.22 and 5796.80 Å, were used to excite Na dimer in the gas phase. Twenty-eight series of [Formula: see text] and [Formula: see text] systems have been assigned and analysed, and the strong transitions are accompanied by numerous rotational relaxation lines. Molecular constants of the [Formula: see text] state were calculated with high precision from simultaneous least-squares fits to 1410 lines assigned to the A–X and B–X systems. These constants have been used to determine the Rydberg–Klein–Rees potential curve of the X ground state for vibrational levels up to ν = 62.
Calculation of energy eigenvalues via supersymmetric quantum mechanics
Authors: Fernández Francisco M. , Ma Q. , DeSmet D. J. , Tipping R. H.
Published: April 2011

A systematic procedure using supersymmetric quantum mechanics is presented for calculating the energy eigenvalues of the Schrödinger equation. Starting from the Hamiltonian for a given potential-energy function, a sequence of supersymmetric partners is derived such that the ground-state energy of the kth one corresponds to the kth eigen energy of the original potential. Various theoretical procedures for obtaining ground-state energies, including a method involving a rational-function approximation for the solution of the Ricatti equation that is outlined in the present paper, can then be applied. Illustrative numerical results for two one-dimensional parity-invariant model potentials are given, and the results of the present procedure are compared with those obtainable via other methods. Generalizations of the method for arbitrary power-law potentials and for radial problems are discussed briefly.
Quantum fluctuations near a space–time singularity
Authors: Krori K. D. , Borgohain P. , Kar Dipali Das
Published: April 2011

The well-known operator technique in quantum mechanics is used to study quantum fluctuations near the space–time singularity using Kantowski–Sachs and Bianchi type VIo metrics. In both cases the wave function of the universe is found to diverge near the space–time singularity, indicating the divergence of the quantum uncertainty near the initial epoch.
Finite-size scaling of O(n) models with singular behaviour
Authors: Allen Scott , Pathria R. K.
Published: April 2011

The finite-size scaling hypothesis of Privman and Fisher (Phys. Rev. B, 30, 322 (1984)) is applied to systems with O(n) symmetry [Formula: see text], confined to geometry Ld − d′ × ∞d′ (where d and d′ are continuous variables such that 2 < d′ < d < 4) and subjected to periodic boundary conditions. Predictions, involving amplitudes as well as exponents, are made on the singular part of the specific heat c(s), spontaneous magnetization m0, magnetic susceptibility χ0, and correlation length ξ0 in the region of the second-order phase transition [Formula: see text]. Analytical verification of these predictions is carried out in the case of the spherical model of ferromagnetism (n = ∞), which includes evaluation of the shift in the critical temperature of the system.
Anomalous effects of planar Hall voltage and magnetoresistance of m3m group (n-PbS, n-Ge, and n-Si cubic crystals) at different temperatures
Authors: Zaghloul M. S.
Published: April 2011

The planar magnetoresistance (PMR) and planar Hall voltage (PUH), of n-PbS, n-Ge, and n-Si forming m3m-group cubic crystals, were measured under weak electric and magnetic fields at different temperatures. Measurements were taken of the different angles (ϕ) of deviation of the current vector from the different crystallographic axes. The samples were doped with the same impurity concentration (1.2 × 1017 cm−3). Many types of anomalous effects of PMR and PUH were observed when the direction of magnetic field (B) was reversed. It was found that the positive and negative PMR and PUH are strongly dependent on the direction of weak B. This shows that the behaviours of PMR and PUH are dependent upon the angle of deviation of the current from the axis of symmetry with respect to the type of orientation of the sample. The contributions of PUH and PMR were calculated at different temperatures and values of ϕ. It is very clear that the anomalous terms of PUH and PMR are in good agreement with B1. The experimental data are illustrated and the results are discussed.
Core-polarization effects in subordinate series of the alkali atoms
Authors: Barrientos Carmen , Martin Inmaculada
Published: April 2011

The quantum defect orbital method, including core-polarization effects through an effective dipole-moment transition operator, has been followed to calculate oscillator strengths involving the sharp and diffuse series in the alkali atoms. Comparisons are made among various theoretical and experimental results and those predicted here. It is shown that the formalism adequately describes transitions in subordinate series of the alkali atoms.
Fisher-renormalized critical exponents by two hidden variables
Authors: Cordeiro C. E. , Wagner D.
Published: April 2011

The Fisher approach to obtain the critical exponents through the introduction of one hidden variable in the system is extended to the case where a physical system needs two or more hidden variables for its description.
The spectrum of gaseous methane at 77 K in the 1.1 – 2.6 μm region: a benchmark for planetary astronomy
Authors: McKellar A. R. W.
Published: April 2011

The spectrum of CH4 obtained in CH4 plus N2 mixtures at a temperature of 77 K has been recorded with a spectral resolution of 0.14 cm−1 in the region 3800 to 9100 cm−1. The experiments were performed with long paths (66 or 88 m) in a cooled absorption cell using a Fourier-transform spectrometer. Data are presented here at low and medium resolution, and examples of some spectral regions are also shown at high resolution. The complete results are available from the author in an Appendix. Comparisons are made with previous model calculations of CH4 absorption, and with the observed spectrum of Neptune's satellite, Triton. The results should be useful for the interpretation of the spectra of Triton, Titan, and Pluto. They will also be of value for testing model calculations of low-temperature CH4 absorption, which, thus verified, can be used with greater confidence to analyze observations of Jupiter, Saturn Uranus, and Neptune.
: line positions and intensities between 9500 and 11500 cm−1. The interacting vibrational states (041), (220), (121), (022), (300), (201), (102), and (003)
Authors: Chevillard J.-P. , Mandin J.-Y. , Flaud J.-M. , Camy-Peyret C.
Published: April 2011

Water vapor Fourier-transform spectra (0.015 cm−1 resolution) were analyzed between 9500 and 11500 cm−1. Accurate values of 557 rotational energy levels, belonging to the interacting vibrational states (041), (220), (121), (022), (300), (201), (102), and (003) of the first decad of [Formula: see text], were determined. Moreover, 718 line intensities were accurately measured (7% uncertainty). To increase the number of experimental intensities (needed for atmospheric applications), a faster method, using the measured line depths, has made it possible to obtain 1695 additional intensities, with an average uncertainty of about 15%.
Rotational tunneling of methyl groups in a strong magnetic field: a path-integral approach
Authors: Peternelj J. , Kodeli I. , Pintar M. M.
Published: April 2011

The magnetic-flux splitting of the E levels of the methyl group in a threefold potential is analyzed using path-integral techniques. The results are in agreement with the conclusions obtained previously using the traditional methods of wave mechanics. The influence of the magnetic-flux splitting on the spin-lattice relaxation in single crystal samples is also discussed.
Remarks on the vacuum energy in interacting scalar field theory
Authors: Treml T. F.
Published: April 2011

The vacuum energy in interacting scalar field theory is computed in the case of the Casimir effect as a sum over zero-point energies and as a path-integral determinant, using both ζ-function regularization and dimensional regularization. Using a simple nonrecursive method of calculation, the two forms of the vacuum energy are shown to differ before renormalization by a scale-independent term when ζ-function regularization is used, but yield exactly the same result when dimensional regularization is used.
HgCl B2Σ+1/2 formation by low-energy electron impact dissociation of HgCl2 and(or) CH3HgCl molecules: applications to HgCl (B → X) laser
Authors: Mahmood Mohammad F.
Published: April 2011

An investigation was made of the process of dissociative excitation of a HgCl radical in the B2Σ+1/2 state due to collisions of low-energy electrons with HgCl2 and CH3HgCl molecules. Using the most intense band of the B2Σ+1/2 – X2Σ+1/2 system of the HgCl radical at 557 nm that corresponds to the ν′ = 0 to ν″ = 22 transition, emission cross sections were measured in the electron energy range 1–100 eV. The threshold electron energy for the observation of the B2Σ+1/2 – X2Σ+1/2 band system has been determined to be 7.0 and 8.0 eV for HgCl2 and CH3HgCl molecules, respectively.
Scattering of acoustic waves by an oscillating soft sphere
Authors: Razavy M.
Published: April 2011

The problem of the scattering of acoustic waves by an oscillating sphere with a perfectly reflecting surface is studied. Here, the scattering amplitude is expressible in terms of partial wave amplitudes and these depend on both the incident and the scattered wave frequencies, the difference between these two frequencies being an integral multiple of the frequency of oscillation of the sphere. The exact formulation leads to an infinite set of linear equations for the partial wave scattering amplitude of which only a finite number of terms are important. If the amplitude of oscillation of the sphere is small compared with the wavelength of the scattered wave and the radius of the sphere, a perturbation technique can be used to obtain the scattering amplitude.
Susceptibilités radiofréquence d'une jonction polarisée — effet d'une induction magnétique
Authors: Gire Alain , Lomaglio Germaine , Morand Serge , Théobald Jean-Gérard , Blanc François , Fanguin René , Raoult Gaston
Published: April 2011

Polarized junctions show an electric susceptibility toward a radiofrequency field E when it is parallel to the metallurgic plane of the junction, but also, in some circumstances, when E is perpendicular to the junction. Furthermore, a magnetic field modifies significantly the observed phenomena. The experiments give structural information about the local field.
Large-amplitude ion-acoustic double layers in a plasma with warm ions
Authors: Roychoudhury R. K. , Bhattacharyya Sikha , Varshni Y. P.
Published: April 2011

The conditions for the existence of an ion-acoustic double layer in a plasma with warm ions and two distinct groups of hot electrons have been studied using the Sagdeev potential method. A comparison is made with the published results of Bharuthram and Shukla for cold ions and a two-temperature electron population. Numerical studies have been made to find out the effect of a finite ion temperature on the Mach number of the double layers.
Surface Raman characterization of plasma-sprayed TiC coatings from the tokamak fusion reactor at Varennes, Quebec
Authors: Mathur M. S. , McKee J. S. C. , Ross G. G. , Marzouk H. A. , Bradley E. B.
Published: April 2011

TiC coatings deposited by a plasma spraying process were placed on the internal wall of the tokamak fusion rector at Varennes, Quebec and were subjected to repeated ~1500 hydrogen plasma discharges. X-ray photoelectron spectroscopy and unenhanced surface Raman scattering were used to investigate the possibility of the formation of C–H and Ti–H complexes on the TiC plasma sprayed surfaces.
A laser-excited three-level atom. II numerical results
Authors: Mavroyannis Constantine
Published: April 2011

Numerical calculations are presented for the interference spectra of a laser-excited three-level atom, where the strong and the weak atomic transitions are driven by resonant and nonresonant laser fields, respectively. The spectral functions describing the interference spectra for the electric dipole allowed excited state have been considered in the low- and high-intensity limit of the laser field operating in the strong transition. The interference spectra arise from the competition between short-lifetime spontaneous processes and short- and long-lifetime excitations induced by the strong and the weak laser fields, respectively. Both laser fields have been treated as quantized and as classical entities. The computed spectra have been presented graphically for different values of the Rabi frequencies and detunings of the weak laser field. It is shown that the decrease in the intensity of the short-lifetime excitation may provide a measure of the spectral width of the long-lifetime excitation.