bluuebunny/crossref_metadata_2025 huggingface dataset:
The far-infrared spectrum of OCCCS: high-resolution Fourier-transform measurements
Authors: Holland Frank , Winnewisser Manfred , Johns John W. C.
Published: April 2011

High-resolution far-infrared gas phase spectra of the linear cumulene-type molecule tricarbon oxide sulfide, OCCCS, have been measured between 50 and 660 cm−1 using a Bomem Fourier-transform spectrophotometer. Four band systems corresponding to the fundamental vibrations ν4, ν5, ν6, and ν7 were observed. Analysis of the rotational structure of the two fundamental transitions [Formula: see text] and [Formula: see text] yielded the band origins and rotational constants ν4 = 593.640 432 (270) cm−1, ν5 = 544.101 238 (210) cm−1, B4 = 1414.370 33 (36) MHz, and B5 = 1415.186 10 (13) MHz. The very weak absorption of the bending vibration ν6 was observed at lower resolution around 438 cm−1. The band system due to the low-lying CCC bending mode ν7 was found as a weak absorption near 80 cm−1. Despite the high resolution of 0.004 cm−1 (apodized), the rotational structure of this band was not completely resolved. However, the band contour is in good agreement with the expected harmonic character of the bending potential. The ν7 band systems of the three homologous molecules OCCCO, OCCCS, and SCCCS are compared in terms of their vibrational structure.
Large-amplitude ion-acoustic double layers in multispecies plasma
Authors: Jain S. L. , Tiwari R. S. , Sharma S. R.
Published: April 2011

We have investigated the effect of second-ion species on the characteristics of a large-amplitude ion-acoustic double layers (IADL) in a collisionless, unmagnetized plasma consisting of hot and cold Maxwellian populations of electrons and two cold-ion species with different masses, concentrations, and charge states. After deriving the criteria for the existence of large-amplitude IADL, we find that the presence of a positive-ion impurity does not modify considerably the characteristics of large-amplitude IADL. However, the presence of a negative-ion impurity changes significantly the characteristics of large-amplitude IADL. We have also presented an analytic discussion of small-amplitude IADL using a reductive perturbation method.
Configuration interaction study of the electronic spectrum of methinophosphide, HCP
Authors: Karna S. P. , Bruna P. J. , Grein F.
Published: April 2011

Ab initio configuration interaction (CI) studies were performed on low-lying linear and nonlinear states of methinophosphide (HCP), using large basis sets with polarization and s, p Rydberg functions, and extensive multireference CI wave functions. Potential curves for linear states of HCP as functions of RCP and RCH and for nonlinear states as functions of αHCP were obtained, from which spectroscopic constants Te, Re, and ωe were evaluated. For the X1Σ+ ground state, the energy of dissociation into H + CP and the dipole moment were also calculated. The assignment of states based on the observed spectrum had to be revised in several instances. The ã state remained 13Σ+ (or 13A′), but the [Formula: see text] state became 13A″, the [Formula: see text] state, 13Δ, the Ã and [Formula: see text] states remained 11A″ and 21A′, respectively, [Formula: see text] was not seen as a seperate state, and [Formula: see text] became 13Σ−. In the energy range from 0 to 8 eV, 22 linear and 11 nonlinear stable states were found. Nonlinear states were stabilized for excitations from π(9a′, 2a″) into the in-plane component of π*, 10a′. Several doubly excited states of the type π2 → π*2 were bound, lying at relatively small excitation energies.
Chemical exchange effects in spectral line shapes
Authors: Diaz M. A. , Veguillas J.
Published: April 2011

A theory of spectral-line shapes has been extended to the case in which relaxation broadening may be influenced by reactive interactions. This extension is valid for gaseous systems in the same way it is valid for condensed media, and particularly, for such chemical mechanisms as isomerizations. The dependence of the spectral rate on the chemical exchange rate is clarified. Finally, a discussion concerning the above aspects and their applications has been included.
Model-independent description of intermediate-range forces in static spherical bodies
Authors: Leon J. Ponce de
Published: April 2011

Recent experimental and theoretical investigations suggest the existence of fundamental intermediate-range forces. So far, the behaviour of such forces, in static spherical bodies, has been discussed using particular models, where the matter distribution is restricted to have some specific form. In this work we want to extend the discussion to an arbitrary matter distribution. With this aim, we solve the phenomenological equations that describe intermediate-range forces by quadratures. From the analysis of the physical properties of the solution, we show in detail how the shape of the matter distribution, as well as the range of the field, can influence the magnitude of intermediate-range forces. Our model-independent description allows us to generalize a number of particular results found previously.
The magnetic properties of the oxygen-hole aluminum centres in crystalline SiO2. IV. [AlO4/Na]+
Authors: Dickson R. S. , Weil J. A.
Published: April 2011

The centre [AlO4/Na]+, formed in α-quartz by X irradiation at 77 K, contains an aluminum ion substituted for a silicon ion, with an electron hole on a nearest-neighbor oxygen ion, and an interstitial sodium ion, which acted as a charge compensator before loss of the electron. Electron paramagnetic resonance spectra of this centre at 35 K have yielded spin-Hamiltonian nuclear quadrupole and hyperfine parameter matrices [Formula: see text], Ā(23Na), and [Formula: see text], in addition to matrices [Formula: see text] and Ā(27Al) more accurate than those measured previously. The line width anisotropy is parameterized by an appropriate matrix W. Hartree–Fock molecular orbital geometry optimizations on a small model cluster, [Al(OH)4Na]+, and hyperfine matrices calculated for the lowest energy configuration, confirm that [AlO4/Na]+ has the same type of structure as [AlO4/H]+ and [AlO4/Li]+; the hole is on an oxygen ion linked to the aluminum ion by a "short" bond, and the sodium ion is in the nearby c-axis channel on the long-bond side of the aluminum ion. The thermal decay of [AlO4/Na]+ to [AlO4]0, measurable at 154 K and above, and the subsequent formation of centres [GeO4/Na]0 from [GeO4]− were studied.
Total energies in rubidium and cesium clusters
Authors: Onwuagba B. N.
Published: April 2011

The total energies in rubidium and cesium clusters are investigated as functions of the number of atoms in a cluster in the framework of the local spin density approximation to the density functional formalism. The computed results provide useful information regarding the role played by the shell structure and predict the experimental spectra in rubidium and cesium clusters.
Dipole–dipole interactions as the source of spin-glass behaviour in exchangewise two-dimensional ferromagnetic layer compounds
Authors: Rancourt D. G. , Lamarche G. , Tume P. , Lalonde A. E. , Biensan P. , Flandrois S.
Published: April 2011

We have studied magnetic layered materials that have in-plane ferromagnetic exchange interactions, and dipole–dipole only interplane interactions. These are biotite mica (including a nearly ideal annite end member) and new graphite bi-intercalation compounds that contain regularly stacked arrays of ferromagnetic and diamagnetic intercalates. All these strictly (exchangewise) two-dimensional materials exhibit hysteretic spin-glass magnetization cusps at temperatures up to 42 K. This proves that, in the presence of ferromagnetic correlations, classical dipole–dipole forces can play an important role in causing spin-glass behaviour at elevated temperatures. The layered materials described are ideal model systems for the study of a class of spin glasses that require only ferromagnetic exchange interactions. Below some characteristic temperature TFC, the latter interactions induce ferromagnetic correlations that give rise to significant dipole–dipole coupling leading to "domain configuration trapping" and an onset of temperature hysteresis at T ~ TFC.
Upper and lower bounds to multichannel-scattering parameters
Authors: Darewych J. W. , Schlifer I.
Published: April 2011

We derive rigorous calculable upper and lower bounds to the scattering parameters that arise in coupled channel problems. The method is based on integral identities and equations that are satisfied by the (unknown) exact and (approximate) trial solutions. We illustrate the method on the Huck model (coupled square wells) and the scattering of positrons by hydrogen atoms in a two-state (1s – 2s) approximation.
Correlations among relativistic charged secondaries produced in π−–nucleus interactions at 340 GeV/c
Authors: Ahmad Tauseef , Irfan M. , Ahsan M. Z.
Published: April 2011

Correlations amongst fast charged secondaries produced in 340 GeV π−–nucleus collisions are examined. The findings of these investigations reveal that strong short-range correlations occur in the central plateau region; there is, however, no evidence for the presence of intrinsic long-range correlations. A backward asymmetry in the case of a nuclear target, which increases with increasing target size, is also observed. There are strong two-particle correlations in both forward and backward hemispheres and the excess number of particles that appear in the backward hemisphere due to heavier targets are envisaged to be produced through the decay of clusters.
Relaxation constants in electron thermalization: Comparison of WKB and SWKB eigenvalues with exact results
Authors: Shizgal B.
Published: April 2011

The relaxation to equilibrium of a nonequilibrium distribution of electrons in gases is governed by a linear–Planck equation. The decay in time of the electron average energy as well as other transport properties can be expressed as a sum of exponential terms with each term characterized by an eigenvalue of the Fokker–Planck operator. This eigenvalue problem can be transformed into a Schrödinger equation with a potential function for which the Hamiltonian factors and belongs to the class of potentials encountered in supersymmetric quantum mechanics. The eigenvalues are calculated with the standard Wentzel–Kramers–Brillouin (WKB) semiclassical quantization condition as well as with a modified semiclassical quantization condition based on supersymmetric quantum mechanics (SWKB). The eigenvalues calculated in these ways are compared with the exact values obtained by the diagonalization of the operator in a large basis set. The applications considered are for the relaxation of electrons in the inert gases for which the electron–atom momentum transfer cross sections are available. The SWKB quantization condition gives results in much better agreement with the exact result (often within much less than 1%) than the WKB approximation.
A new path-integral solution to the Schwinger model
Authors: Skinner Ray , Wong Ken
Published: April 2011

It has been shown by the authors (see ref. 1) that it is necessary to supplement the conventional action of the Dirac fermion field with a boundary term. In this paper the Schwinger model (i.e., quantum electrodynamics in two space-time dimensions with massless fermions) is solved through the path integral with the boundary term included in the action. This considerably complicates the evaluation of the path integral so that only partial integrations over the field variables are attempted here. In the case of the integration over the electromagnetic potential Au, A0 will be set to zero based on arguments from a formulation of generalized Hamiltonian mechanics by one of the authors (Ray Skinner).
A Wiener–Hopf theory for a semi-infinite dielectric slab
Authors: Mitsioulis G.
Published: April 2011

We investigate the field distribution around a semi-infinite dielectric slab. The wave equation is transformed, through a Fourier transform, to the wave number domain. The boundary conditions are imposed and we end up with an equation of the Wiener–Hopf type. Certain functions are factorized and we find a system of equations for the unknown coefficients of the Fourier series expansion for the field at the mouth of the slab.
Characterization of the Tokamak de Varennes ohmic plasma in equilibrium
Authors: Boileau A. , Gregory B. C. , Abel G. , Bélanger C. , Boucher C. , Couture P. , Décoste R. , Haddad E. , Janicki C. , Kalnavarns J. , Lachambre J.-L. , Lafrance D. , Clair G. Le , MacLatchy C. , Pacher G. W. , Pacher H. D. , Ratel G. , Richard N. , Saint-Onge M. , Simm C. , Stansfield B. L. , Whyte D. , Zuzak W. , Rogister A. , Hasselberg G.
Published: April 2011

Experimental results obtained on the Tokamak de Varennes during a series of reproducible ohmic discharges are presented. Profiles of basic plasma parameters are constructed and compared with theoretical predictions. In particular, the measured plasma resistivity agrees with the neoclassical scaling rather than with Spitzer resistivity. The study of electron-density fluctuations indicates a linear dispersion relation with a propagation velocity of 3.0 × 104 cm s−1. Particle transport investigations are initiated, giving experimental diffusion and convection coefficients across the plasma radius for electrons and impurity ions.
A method for determination of the potential from the reaction matrix at fixed energy
Authors: Markushevich V. M. , Novikova N. N. , Razavy M.
Published: April 2011

The inverse problem at fixed energy, in the case of a central potential with finite range, is transformed to a form that is similar to the inverse problem for the S-wave scattering. Using a rational-function representation of the input data for the reaction matrix for different partial waves and a modified Gel'fand–Levitan formulation, one can construct the potential from the partial-wave phase shift at a given energy. In this formulation of the inverse problem the properties of the Cauchy matrix have been used to perform a number of operations analytically, thus reducing the sources of numerical round-off and truncation errors. The method has been applied to construct the potential for some simple scattering problems.
Two-photon absorption series of calcium
Authors: Makdisi Y. , Bhatia K. S.
Published: April 2011

Laser spectroscopy of calcium using two-photon absorption has produced the high Rydberg states of the 4nsn1S0 and 4snd1D21F3 series. The spectra recorded 1S0 states up to n = 35 while the nd1D2 transitions are extended to n = 86. A new series tentatively assigned as 4snf1F3 has been resolved up to n = 58. Comparison of the experimental values with the calculated values based on the multichannel quantum-defect theory developed by previous investigators has been presented.
Systèmes aux contraintes à température non-nulle et la recette de Dirac
Authors: Roberge André
Published: April 2011

We demonstrate how Dirac's method for constrained systems can be used to derive a partition function at finite temperature. We discuss some technical points regarding the symmetry properties of such theories.
Low-energy-ion shadow-cone calculations
Authors: Hird Brian
Published: April 2011

The usual momentum-approximation calculation of the shape of the shadow cone for ion–atom scattering is found to be surprisingly accurate at collision energies of a few keV and close atomic spacings, where the shadow-cone angles are not small. With a small modification to the Bessel-function argument this approximation is probably not the limiting factor in making fits to experimental shadow-cone measurements.
Semiclassical approximation for the isotopic shift of charge radii in Ca isotopes
Authors: Anagnostatos Gerassimos S. , Kosmas Theoharis S. , Hefter Ernst F. , Panos Constantine N.
Published: April 2011

The peculiar behavior of the rms-charge and mass radii of the Ca isotopes is explained by current approaches. Here these approaches are supplemented by microscopic calculations within the isomorphic shell model. The model verifies the trend of the data correctly, as a result of shell structure (particle–hole) and deformation effects. These results involve two numerical (not adjustable) parameters and are quantitatively at least equally as good as those of the best available theoretical calculations. In the case of 41Ca, however, a further investigation is required.
Détection galvanique de résonances dans une jonction polarisée
Authors: Ammari M. , Gire A. , Lomaglio G. , Theobald J. G. , Blanc F. , Fanguin R. , Raoult G.
Published: April 2011

The resonances observed in polarized junctions induce one current that can be detected. With a magnetic field, one can observe the nondiagonal component of the electrical conductivity, a sort of microwave Hall effect. It is also possible to perform a galvanic detection of cyclotron resonance within a polarized junction.
Exchange-correlation effects on the dynamical spin susceptibility of a homogeneous electron gas
Authors: Liu K. L.
Published: April 2011

We study the wavevector- and frequency- dependent exchange-correlation local-field factor, [Formula: see text], of the dynamical spin susceptibility, [Formula: see text], of a homogeneous electron gas. For high frequencies we calculate [Formula: see text] diagrammatically to second order in the Coulomb interaction, and consequently find that [Formula: see text] varies as q−2 ω−1/2 for large ω and finite q. We also consider an interpolation formula for [Formula: see text], that yields the exact small- and large- wave-number limits. Making use of these results and the Kramers–Kronig relation, we construct an approximate local-field factor that has the correct limiting behavior for both low and high frequencies.
Vibrational energy transfer in symmetric N2 charge transfer
Authors: Howard Stephen L.
Published: April 2011

Results of the crossed-beam investigation of the symmetric charge-transfer reaction of N2+ (X2Σg, ν = 0) with N2 (X1Σg, ν = 0) near 10 eV collision energy showed a symmetrically resonant channel with Δν = 0 as well as a series of inelastically scattered channels. Upon deconvolution to remove the Δν = 0 contribution, the inelastic Δν = 1, 2, and 4 channels were readily observed.
Analyse de surface d'échantillons exposés à des décharges luminescentes dans le Tokamak de Varennes
Authors: Thériault D. , Boucher C. , Paynter R. W. , Terreault B.
Published: April 2011

The effects of surface conditioning discharges were studied at the Varennes tokamak. Pre-analyzed samples were exposed to glow discharges in helium or hydrogen and then reanalyzed. Exposures to discharges took place in the vacuum chamber of the tokamak, and the analyses were carried out at INRS-Energie, by Auger electron spectroscopy with ionic etching (depth profile). Samples were transferred in vacuum. Chemical effects of hydrogen discharges and physical erosion effects of helium discharges were observed. We also observed that hydrogen and helium discharges produced graphite carbon (carbonization) or metallic carbide (carburization). These observations show the importance of the modifications of the discharge owing to its interaction with the wall and the graphite limiting devices in the Varennes tokamak.[Journal translation]
Surface photovoltage in a heavily doped high–low junction in equilibrium
Authors: De S. S. , Ghosh A. K. , Pattanayak T. K.
Published: April 2011

Surface photovoltage in a heavily doped high-low junction in equilibrium was investigated analytically taking into account the effects of band-gap narrowing. The dependence of the normalized surface photovoltage on surface potential for different values of the surface densities of states and also for various temperatures were studied. The results are shown graphically.
α spectra of deformed even–even nuclei and equivalence of optical model potentials
Authors: Chaudhury M. L. , Agrawal S. K.
Published: April 2011

The reduced transition probabilities of the α spectra of some deformed heavy even–even nuclei are calculated, taking the barrier to be the anisotropic electrostatic potential superposed by the deformed nonlocal α-nucleus potential. The latter is described by a deformation parameter, εl, as in our previous treatments and, for its static part, different optical model potentials are now used. Results show that the calculated values of the reduced transition probabilities are in good agreement with the observed values, taking the best-fit values of εl. It is also found, as in the case of spherical nuclei, that the different optical potentials are equivalent for the cases considered, and that the nonlocal effect is predominant.
Excited state hyperfine structures in 133Cs using quantum beat spectroscopy
Authors: Sagle J. , Wijngaarden W. A. van
Published: April 2011

Quantum beats arising from the hyperfine interaction were observed in the fluorescence produced when the 8D3/2, 9D3/2, and 10D3/2 states of 133Cs radiatively decayed to the 6P1/2 state. The period of the beats equals the reciprocal of the magnetic dipole coupling constant a since the 133Cs nucleus has a negligibly small electric quadrupole moment. The results are a = 3.95 ± 0.01, 2.38 ± 0.01, and 1.54 ± 0.02 MHz for the 8D3/2, 9D3/2, and 10D3/2 states, respectively.
Electric quadrupole transitions
Authors: Prestwich W. V. , Islam M. A. , Kennett T. J.
Published: April 2011

A data set has been compiled consisting of 101 E2 strengths observed in neutron radiative capture. The E2 strength function is found to be consistent with a fifth power energy dependence and mass dependence characterized by a power of n = 1.87 ± 0.07. The observed strengths are on average consistent with those predicted on the basis of the giant quadrupole resonance. A reduction in strengths is apparent near mass regions 28, 82, and 157. Evidence is cited for the possible existence of a direct capture mechanism.
An example of a general class of symmetries of Lagrangians and their equations of motion
Authors: Garcia-Sucre M. , Percoco U. , Núñez L.
Published: April 2011

Results on symmetries of equations of motion and equivalent Lagrangians are applied to obtain constants of motion of the two-dimensional isotropic and anisotropic oscillators. We find that the anisotropic case provides the first example of a general kind of Lagrangian symmetries.
Submillimetric and millimetric collision-induced absorption spectra in compressed gaseous nitrogen using very low-frequency optical source
Authors: Occelli R. , Chaaban H. , Moynault J. M. , Coulon R. , Balsamo A.
Published: April 2011

A (sub)millimetric source is obtained by difference-frequency mixing in a nonlinear crystal. It allows investigation of spectral absorption between 4 and 40 cm−1 with a new two-beam spectroscopic mounting. The complete mounting is described. The measurement method is given in detail. Compressed gaseous nitrogen-induced absorption measurements are used to calculate relaxation times and spectral moments. Comparisons are made with other measurements in close frequency regions, and theoretical models and an empirical line-shape model.
On an exit problem in a one-dimensional random walk in the diffusion approximation
Authors: Das Amal K.
Published: April 2011

We address a nonstandard random-walk problem in which the random walker, a Brownian particle, enters a linear chain at x = 0 and exits at x = L under the constraint that allows the particle to return to an arbitrarily close neighbourhood of the entrance point, but does not allow the entrance point to be touched back. In the diffusion approximation, the traversal time T*, calculated in an unconventional way, is found to be T/3, where T is the usual diffusion traversal time, L2/2D, D being the diffusion coefficient.
Statistics of contractive cracking patterns
Authors: Noever David A.
Published: April 2011

The statistics of convective soil patterns are analyzed using statistical crystallography. A underlying hierarchy of order is found to span four orders of magnitude in characteristic pattern length. Strict mathematical requirements determine the two-dimensional (2D) topology, such that random partitioning of space yields a predictable statistical geometry for polygons. For all lengths, Aboav's and Lewis's laws are verified; this result is consistent both with the need to fill 2D space and most significantly with energy carried not by the patterns' interior, but by the boundaries. Together, this suggests a common mechanism of formation for both micro- and macro-freezing patterns.
The statistical properties of Allan variance
Authors: Prestwich W. V. , Kennett T. J. , Kus F. W.
Published: April 2011

The probability density for the Allan variance of stochastic processes is derived. Numerical evaluation is performed for sample sets varying from three to eight members for white- and flicker-noise processes. Representation of the results by a chi-squared distribution is discussed. Effective degrees of freedom are established for each case.
Two-photon interference spectra induced by a bichromatic field in the excited state of a single three-level ion
Authors: Mavroyannis Constantine
Published: April 2011

We consider the interference spectra arising from the competition between a spontaneous process and two processes induced by two laser fields, which are coupled with a three-level atom in the "Λ" configuration. In the low-intensity limit of both laser fields and on two-photon resonance, the frequency profiles of the two peaks, which arise from the spontaneous and induced processes, cancel each other out completely at the center of the line for zero detuning and at the finite values of the detuning as well. At high intensities of the laser fields and on two-photon resonance, the dynamic Stark effect dominates the spectra of the excited state of the atom. Expressions for the interference spectra and correlation functions are derived, which describe the physical process of the absorption of a laser photon at two different times by the ground state of the atom. Interference spectra and correlation functions are calculated for the two-photon off-resonance and for the proces of the absorption of a photon by the ground state of the atom. In this case, the intensities of the frequency dips take negative values indicating that stimulated emission prevails for certain values of the detunings. Using values for the parameters involved close to those for Ba+, the computed two-photon resonance and off-resonance spectra are graphically presented and discussed.
The electrical conductivity of an amorphous Hubbard model
Authors: Liu K. L.
Published: April 2011

We study the frequency-dependent electrical conductivity of a structurally disordered single-band Hubbard model near half-filling and in the strong-correlation limit. The electronic transfer integral is assumed to have a quasi-exponential form as used in the impurity-band problem of doped semiconductors. The short-time expansion of the current correlation function is calculated diagrammatically to the second order in the inverse temperature β and up to the seventh order in electronic hopping. Based on this expansion an approximate current correlation function is constructed. By means of the Kubo formula, the configurational average of the electrical conductivity is then calculated to order β2 for various atomic densities. The validity of the high-temperature expansion is examined. We also study the effect of spin polarization on the absorption line shape and the dc resistivity at different temperatures.
Anharmonic perturbation theory to 0(λ4): Equation of state for Kr from the Aziz potential
Authors: Shukla Ramesh C. , Hübschle Hermann
Published: April 2011

We carry out a complete calculation of the thermodynamic properties of Kr from a potential function, the Aziz potential, including the three-body Axilrod–Teller contribution, and the (λ4) anharmonic perturbation theory proposed by Shukla and Cowley (Phys. Rev. B: Solid State, 3, 4055 (1971)), where λ is the Van Hove ordering parameter. Along with the λ4 results, in the high-temperature (HT) limit (T > θD, where θD is the Debye temperature), we also present the results for the quasi-harmonic (QH) theory (calculated for all temperatures), the lowest order (λ2) perturbation theory (PT), as well as results from those theories that involve a subset of diagrams (contributions) of 0(λ4), both in the HT limit. This work represents the first calculation of the thermodynamic properties of Kr with the λ2 and λ4 anharmonic PT from a potential function not fitted to the crystal data. The Aziz potential gives an excellent description of phonon-dispersion curves in the three principal symmetry directions. The QH results are in good agreement with the experimental values for most of the thermodynamic quantities for temperatures up to <Tm/3 (Tm is the melting temperature) except for the isothermal bulk modulus (BT) where the agreement is poor in 0 K < T < 25 K and good up to 2Tm/3. The λ2 PT results are only slightly better than the corresponding QH results in the temperature range of < Tm/2. The inclusion of the λ4 PT enhances the results for the Aziz potential significantly. The calculated lattice parameter (a0) is in excellent agreement with experimental values up to 3Tm/4. For T > 3Tm/4, a0 rises rapidly and there is an indication of the breakdown of the perturbation expansion. The values for specific heats at constant volume (Cv) and constant pressure (Cp) and volume expansion (β) are in very good agreement with experiment up to 60% of Tm. The other schemes (with the exception of Ladder) that utilize a subset of diagrams of 0(λ4), which were so successful for the model of a Lennard–Jones solid (viz., ISC (improved self-consistent), λ4-Ladder etc.), are not so useful for this potential. This is due to the heavy cancellation of diagrams in these sets. The ring diagram scheme proposed here for the Aziz potential gives better results than the ISC scheme.
Évaluation de l'approximation ion moyen pour un plasma de tokamak
Authors: Marchand R. , Fortin A. , Caillé S.
Published: April 2011

The average ion approximation, sometimes used to calculate atomic processes in plasmas, is assessed by computing deviations in various rates, over a set of conditions representative of tokamak edge plasmas. Conditions are identified under which the rates are primarily a function of the average ion charge and plasma parameters, as assumed in the average ion approximation.
Radiative corrections in two-dimensional gravity
Authors: McKeon D. G. C. , Wong C.
Published: April 2011

It is shown how one can do perturbative calculations about a flat background in two-dimensional models of quantum gravity. The Jackiw–Teitelboim model and the induced gravitational action of Polyakov are considered. A suitable choice of gauge allows one to employ operator regularization, a symmetry-preserving procedure that is particularly convenient as it does not alter the dimensionality of these models, allowing one to exploit some properties peculiar to two dimensions. A specific example is provided by the graviton two-point function.
Vacuum effects in a spatially homogeneous and isotropic cosmological background
Authors: Villalba Victor M. , Percoco Umberto
Published: April 2011

In this article we obtain, by separation of variables, an exact solution to the Klein–Gordon and Dirac equations in a cosmological, spatially-closed, Robertson–Walker space-time with a positive cosmological constant Λ. The model is associated with a universe filled with radiation. We analyze the phenomenon of particle creation for different values of the dimensionless coupling constant ξ.
Dirac quantization of higher order systems with odd variables
Authors: Campos R. de Azeredo
Published: April 2011

The canonical quantization of higher order constrained systems described by Grassmann variables is considered. We show that Dirac's method provides unambiguous quantum versions of classical models containing higher order derivatives.
String-modified four–dimensional cosmology
Authors: Krori K. D. , Purkayastha Anuradha Das
Published: April 2011

Recently Gegenberg proposed a string-modified four-dimensional gravity theory comprising gravity, electromagnetism, a dilaton field, and a Kalb–Ramond field. In this paper, some general cosmological aspects of this theory are discussed.
Second-order polarization energies for Rydberg states
Authors: Swainson R. A. , Drake G. W. F.
Published: April 2011

The energy level shifts for an electron in a high-nL Rydberg state of an atom such as helium are well described by an asymptotic potential with terms proportional to the multipole moments of the core. We obtain exact analytic expressions as a function of n and L for second-order perturbation corrections to the energy due to the asymptotic potential. The results are of importance in the analysis of high-precision variational calculations and experimental transition energies for Rydberg states.
Theoretical shell-model signatures in heavy-ion, coherent pion production
Authors: Maung Khin Maung , Deutchman P. A. , Buvel R. L.
Published: April 2011

A comprehensive summary of a many-body, microscopic, particle–hole formalism is presented that describes coherent, subthreshold, pion production in peripheral, heavy-ion collisions. The formalism uses a new separable model transition interaction that produces Δ-hole states in either the projectile or target nucleus. Shell-model states described by harmonic oscillator functions are used in the calculation of Δ formation and decay and Lorentz-contraction effects of the nucleus not at rest are included. An analytical expression to lowest multipole order for the differential cross section is examined. The sensitivity of the theoretical results to the shell-model states is determined with preliminary shape results compared with data. The effects of higher multipoles are examined with attention paid to the second-order multipole value.
Ion-energy measurements in a double plasma device
Authors: Schott L.
Published: April 2011

It is found that the ion-energy distribution in a quiescent low-pressure argon plasma that is produced in a double plasma device is anisotropic. More ions drift to the mesh separating the two plasmas than away from it. Ions travelling in these two directions have velocity distributions that approach half-Maxwellians with different temperatures for speeds above the mean speed. The mean-free paths for Coulomb and ion–neutral collisions exceed the plasma size, and the plasma-density fluctuation levels [Formula: see text] in the main body of the plasma are too small to explain the thermalization of the ion energy distribution. However, the larger fluctuation levels with δn/n ~ 0.1 that are observed close to the plasma boundaries and at the sheath at the separating mesh may play a role in the thermalization.
Effect of screening on the long-wavelength optical phonons in La1.85Sr0.15CuO4
Authors: Ramakrishnan Chellam , Navaneethakrishnan K. , Krishnamurthy N.
Published: April 2011

The lattice dynamics of La1.85Sr0.15CuO4 are studied with a rigid-ion model that takes into account the anisotropic screening of the Coulomb field by the charge carriers. The coupling coefficients for the screened potential are obtained using a generalized Ewald transformation that incorporates the Thomas–Fermi screening function. From the calculated phonons in the long-wavelength region it can be seen that the screening considerably reduces the longitudinal optical–transverse optical splitting of the polar modes. The nonpolar modes do not exhibit any changes in their behaviour with respect to that in the unscreened Coulomb potential.
On the thermodynamic and superconducting properties in the statistical model
Authors: Bhattacharya A. , Raichaudhuri Arati , Chakraborty B. , Banerjee S. N.
Published: April 2011

The anomalous behaviour of thermodynamic coordinates of a meson such as the free energy and specific heat in the statistical model is studied. The superconducting properties of the surrounding vacuum, which consist of the quark–antiquark pair condensates, are also investigated in the Ginzburg–Landau formalism.
Matter interactions of a three-dimensional gauge theory
Authors: McKeon D. G. C.
Published: April 2011

A recently introduced three-dimensional gauge theory involves a tensor field Tμν. In this paper we show how this field can interact with matter fields in a gauge-invariant fashion. The possibility of spontaneous breakdown of Lorentz symmetry is considered. An additional gauge-invariant interaction for Tμν is introduced. The field Tμν interacts with gravity; we compute the η function associated with the graviton propagator and show that it is proportional to the bilinear term in the Chem–Simons action for gravity in three dimensions.
Screening effects generated by a domain wall surrounding an Abelian dyon
Authors: Wolf C.
Published: April 2011

By considering a simple axion-like theory coupled to the electromagnetic field, we describe the screening and antiscreening properties that a domain wall will generate for a central dyon
Statistical nature of astrophysical maser radiation for linear masers
Authors: Wu Y. C.
Published: April 2011

The validity of the assumption of Gaussian statistics, a basis for the validity of use of the radiative transfer equation and for a lot of current astrophysical maser theories, is investigated. For tractability the investigation in this paper is confined to astrophysical linear masers, which are very important to astrophysical maser theories. It is found that for those masers the assumption of Gaussian statistics and therefore the use of the radiative transfer equation are not precise in saturated regions whereas they are valid in unsaturated ones. This will be very significant to the study of astrophysical masers.
The effective Lagrangian and the scale anomaly in the nonlinear σ model
Authors: McKeon D. G. C.
Published: April 2011

We compute the one-loop effective Lagrangian for the generally covariant nonlinear σ model in two dimensions, using a technique of Bukbinder et al. This circumvents the need to evaluate Feynman diagrams and eliminates having to introduce a mass to serve as an infrared regulator. The two-dimensional space is assumed to have Weyl geometry. In the limit that the Weyl geometry becomes Riemannian, the standard result for the anomaly in the trace of the stress tensor is recovered.
The global behavior of the March 1989 ionospheric storm
Authors: Yeh K. C. , Lin K. H. , Conkright R. O.
Published: April 2011

By any measure the magnetic storm beginning with a sudden storm commencement at 0128 UT March 13, 1989 must be classified historically as a great storm. Associated with this great magnetic storm was the drastic modification of the normal ionosphere lasting for several days. To study this abnormal behavior, ionospheric data collected at 52 ionosonde stations and 12 total electron content observing stations have been analyzed. The global data show a longitudinal dependence on the storm behavior; a pronounced worldwide depression in the diurnal maximum values of f0F2; the extreme depression of the diurnal-minimum in f0F2 to a frequency less than 2 MHz at many stations, sometimes accompanied by an unprecedented rise in h'F to 700 km or more; the presence of traveling ionospheric disturbances; the presence of large-scale standing oscillations; the development of hemispheric asymmetry; and the suppression of the equatorial anomaly. These and other unusual phenomena are described in this paper.
Plasmaspheric response to the geomagnetic storm period March 20–23, 1990, observed by the ACTIVNY (MAGION-2) satellite
Authors: Förster M. , Jakowski N. , Best A. , Smilauer J.
Published: April 2011

Langmuir probe data obtained during the storm period March 20–23, 1990, on board the MAGION-2 subsatellite of the ACTIVNY experiment are analyzed to study the plasmaspheric and ionospheric response to a magnetic storm. The data indicate a well-pronounced equatorward edge of the electron density trough in the afternoon (18:15 LT) at about 800 km height that moves towards lower latitudes during the course of the storm. It is interesting to note that the electron density inside the plasmasphere is increased by more than 20% in the morning shortly after sunrise (07:30 LT). This is due to enhanced O+ densities in the lower plasmasphere during the growth phase of the geomagnetic storm as measured by the ion mass spectrometer NAM-5 onboard the main satellite. It is suggested that the source for the increased density is thermospheric Joule heating at auroral latitudes with a commensurate increase in thermospheric pressure. This increased pressure causes the local thermosphere to expand both upward and equatorward. The increased atomic-oxygen scale height coupled with equatorward motion of fhermospheric perturbations results in an increased O density and resulting O+ density within the lower plasmasphere. The observations indicate a storm-induced compression of the plasmasphere that favourizes an enhanced outflow of plasma into the ionosphere leading to an increased nighttime F2-layer ionization and a depletion of the plasmasphere during the following hours.
A theoretical study of the structure and dynamics of amorphous Fe
Authors: Gupta Neelam , Jain Kamal C. , Pratap Arun , Saxena N. S.
Published: April 2011

The extended theory of transition-metal potential, which includes the transition-metal d states, is used to obtain the effective interatomic interactions in terms of pair potential for amorphous Fe. Pair potential for amorphous Fe is also computed using a simple approach for liquid metals given by de-Angelis and March. We employ the so obtained pair potentials to calculate the longitudinal- and transverse-phonon eigenfrequencies using the theory of phonons in amorphous solids. The results for the phonon eigenfrequencies obtained from these potentials are in good qualitative agreement with the molecular-dynamics results as well as with the theoretical results of Bhatia and Singh. Computation of the Debye temperature and the isothermal bulk modulus also shows a close agreement with other results.
The study of multiplicity characteristics and reduced entropy of particles produced by hadrons (70–400 GeV) and heavy ions (2.1–4.5 GeV)
Authors: Ghosh Dipak , Roy Jaya , Sengupta Alokananda Ghosh , Thakurata Argha Deb Tarit Guha , De Atanu , Hossain Sk. Anwar , Mukherjee Hiten , Halder Supria , Naha Sadhan , Halder D. , Lahiri Madhumita , Sen Sanjib , Basu Madhumita
Published: April 2011

This paper presents an analysis of the multiplicity characteristics in nucleus–nucleus (n–n) and hadron–nucleus (h–n) interactions in different pseudorapidity bins in terms of a new variable defined as the reduced entropy. The data includes n–n interactions (2.1–4.5 GeV) and h–n interactions (70–400 GeV). The data reveal some interesting features that have not so far been reported.
Charged solutions in higher dimensions
Authors: Krori K. D. , Chaudhury T. , Borgohain P. , Das Kanika , Mahanta Chandra Rekha
Published: April 2011

In this paper we derive spherically symmetric interior isotropic and anisotropic solutions in higher dimensions in Einstein–Maxwell theory. Some particular solutions are obtained from the general isotropic solution. The anisotropic solution is Schwarzschild-like. It reduces to the Krori–Borgohain–Das solution if the charge is zero and to the Krori–Paul solution if the number of dimensions is four.
Electronic shell structure of antimony cluster
Authors: Onwuagba B. N.
Published: April 2011

The ground-state properties of antimony clusters are investigated in the framework of density functional theory. The exchange correlation effects were included in the local spin density approximation and a spherical jellium model is used to calculate the total energy, binding energy, relative binding-energy change, and ionization potential with a view to understanding the mechanism leading to the magic-numbers exhibited by this class of higher valence clusters.
Calculation of the g-factors for the improvement of the theoretical treatment of the emission spectrum of the 3s,3d complex of H2
Authors: Bouchard R. , Alikacem A. , Larzillière M.
Published: April 2011

A calculation of the g-factors for the states of the 3s,3d complex of H2 is performed using a matrix model of the Hamiltonian that combines the rovibrational elements found earlier for the complex with Zeeman interactions between states with rotational levels where ΔN = 0, ± 1. The purpose of this calculation is to confirm the accuracy of the rovibronic Hamiltonian used by Alikacem and Larzillière for the 3s,3d complex of H2.
Restrictions on shape-coexistence descriptions of A ~ 150 nuclei from the 156Dy(p, t) 154Dy reaction
Authors: Qu Tao , Burke D. G.
Published: April 2011

The 156Dy(p, t),154Dy reaction was studied, using 20 MeV protons and a magnetic spectrograph to analyze the reaction products. This reaction on the "deformed" target 156Dy has three strong L = 0 transitions populating levels in the "spherical" nucleus 154Dy at 0, 661, and 1058 keV with relative strengths of 100:74:16, respectively. This population pattern is similar to those observed in the isotones 152Gd and,150Sm, in which the third 0+ bands have been interpreted as deformed bands coexisting in spherical nuclei. However, the third 0+ band in 154Dy has a rotational energy spacing as large as that for the ground-state band, which suggests that it does not have a large deformation, and its (p, t) strength is significantly less than those for the corresponding states in the samarium and gadolinium isotones. This restricts the shape-coexistence interpretation of excited 0+ states in 154Dy. The systematics suggest that,152Gd is probably also not as good an example of shape coexistence as 150Sm.
Theoretical and experimental investigation of radar scattering from conducting and dielectric targets in the resonance region
Authors: Moheb H. , Shafai L. , Mishra S. , Larose C.
Published: April 2011

A theoretical and experimental study is undertaken to investigate the radar scattering of various three-dimensional targets. The targets considered have prismatic structure and are made of either perfectly conducting or dielectric materials. The surface integral equations are formulated by the equivalence principle in terms of equivalent surface electric and magnetic currents. A moment method is then used to reduce the integral equations to a matrix equation to compute the current coefficients. Polarimetric measurements are carried out on a variety of targets at linear polarization. In order to determine the complex-scattering matrix, amplitude and phase of both co- and cross-polar returns are measured for linearly polarized signals. Good agreement between numerical and experimental results is obtained. Brief details of both measurement and theoretical methods are presented.
Multiple-scattering aerosol lidar inversion method
Authors: Bissonnette Luc R. , Hutt Daniel L.
Published: April 2011

The multiple-scattering contributions to lidar aerosol backscatter returns are measured by simultaneous detection at four concentric fields of view. A solution method is proposed to calculate, from the ratios of the lidar returns at the different fields of view, the range-resolved scattering coefficient. The method also provides the effective size of the aerosol particles responsible for the forward peak of the scattering phase function. Solutions from measurements performed in fog and clouds with a 1.054 μm lidar system are presented.