bluuebunny/crossref_metadata_2025 huggingface dataset:
Yang–Mills theory and nonirreducible representations of the Lorentz group
Authors: McKeon D. G. C.
Published: April 2011

We start from an O(4) = SU(2) × SU(2) Yang–Mills theory and argue that the O(4) indices can, in fact, be space-time indices. The resulting theory is that of a tensor, Cμαβ = −Cμβα, which is in a reducible representation of the Lorentz group.fj This is a special case of the extended Yang–Mills formalism of Gabrielli. Some special solutions of the classical field equations are found.
Hydrogen-assisted reactive evaporation of quasi-stoichiometric polycrystalline InSb films
Authors: Leclerc G. , Beerens J. , Aktik C. , Paquin L. , Isai M.
Published: April 2011

We report here a new technique for evaporating polycrystalline InSb films, using hydrogen beams as carriers for each elemental source. The films obtained show X-ray diffraction patterns before annealing that are totally exempt from impurity peaks, unlike those other workers have previously reported for evaporated InSb.
Deriving gravitation from electromagnetism
Authors: Assis A. K. T.
Published: April 2011

We present a generalized Weber force law for electromagnetism including terms of fourth and higher orders in v/c. We show that these extra terms yield an attractive force between two neutral dipoles in which the negative charges oscillate around the positions of equilibrium. This attractive force can be interpreted as the usual Newtonian gravitational force as it is of the correct order of magnitude, is along the line joining the dipoles, follows Newton's action and reaction law, and falls off as the inverse square of the distance.
Electrophysical and photoelectrical properties of epitaxial films of Hg1−xCdxTe (x ≈ 0.2) after laser treatment
Authors: Kuźma M. , Abeynayake C. , Sheregii E. M. , Ugrin Y. O. , Virt I. S.
Published: April 2011

Changes in the electrophysical and photoelectrical properties of epitaxial films of Hg1−xCdxTe (x ≈ 0.2) due to laser annealing are studied. Experimental fits for the dependence of the resistance of the film to the energy density of the laser pulse, to the time, as well as to the temperature are obtained before and after laser annealing. Further, changes in the lifetime of minority nonequilibrium carriers of charge and the spectral dependence of the photoconductivity because of laser annealing are shown. Experimental results are interpreted on the basis of the two cluster model for electro- and photoconductivity.
Path integral on non-simply connected space and problem with zero boundary condition
Authors: Long Hoang Ngoc
Published: April 2011

In this paper a path integral formulation for various matrix elements of the evolution operator in a finite interval with zero boundary conditions is presented. Connection of these matrix elements with path integrals on a non-simply-connected space is given as well.
Massless particles with dependence on torsion
Authors: McKeon D. G. C.
Published: April 2011

In analogy with the treatment of a particle whose Lagrangian depends on the arc length and curvature of the path, we consider a particle whose Lagrangian depends on the arc length and torsion of the path. By introducing an auxiliary "einbein" field, the massless limit can be taken. The Dirac constraint formalism is used to cast the theory into Hamiltonian form. A solution to the equations of motion is obtained.
Bound and resonant relativistic two-particle states in scalar quantum field theory
Authors: Leo Leo Di , Darewych Jurij W.
Published: April 2011

We derive relativistic particle–antiparticle wave equations for scalar particles, [Formula: see text] and [Formula: see text], interacting via a massive or massless scalar field, χ (the Wick–Cutkosky model). The variational method, within the Hamiltonian formalism of quantum field theory is used to derive equations with and without coupling of this quasi-bound [Formula: see text] system to the χχ decay channel. Bound-state energies in the massless case are compared with the ladder Bethe–Salpeter and light-cone results. In the case of coupling to the decay channel, the quasi-bound [Formula: see text] states are seen to arise as resonances in the χχ scattering cross section. Numerical results are presented for the massive and massless χ case.
Induced absorption and stimulated emission in a driven two-level atom
Authors: Mavroyannis Constantine
Published: April 2011

We have considered the induced processes that occur in a driven two-level atom, where a laser photon is absorbed and emitted by the ground and by the excited states of the atom, respectively. In the low-intensity limit of the laser field, the induced spectra arising when a laser photon is absorbed by the ground state of the atom consist of two peaks describing induced-absorption and stimulated-emission processes, respectively, where the former prevails over the latter. Asymmetry of the spectral lines occurs at off-resonance and its extent depends on the detuning of the laser field. The physical, process where a laser photon is emitted by the excited state is the reverse of that arising from the absorption of a laser photon by the ground state of the atom. The former differs from the latter in that the emission of a laser photon by the excited state occurs in the low-frequency regime and that the stimulated-emission process prevails over that of the induced absorption. In this case, amplification of ultrashort pulses is likely to occur without the need of population inversion between the optical transitions. The computed spectra are graphically presented and discussed.
Does nature place a fundamental limit on strength?
Authors: Shiekh A. Y.
Published: April 2011

A fundamental limit on the stress to density ratio is determined solely from the theory of special relativity and the principle of the conservation of energy.
A method for generating exact solutions of the nonlinear Klein–Gordon equation
Authors: Grigorov A. , Martinov N. , Ouroushev D. , Georgiev Vl.
Published: April 2011

A simple method for generating the exact solutions of the nonlinear Klein–Gordon equation is proposed. The solutions obtained depend on two arbitrary functions and are in the form of running waves. An application of one of the solutions for the (2 + 1) – dimensional sine-Gordon equation is proposed. It concerns the selective properties of a two-dimensional semi-infinite Josephson junction with regard to an external electromagnetic field in the form of running waves with a phase velocity equal to the Swihart velocity. A method for measuring the Swihart velocity is presented.
Convex decomposition of the gauge field and background-field quantization
Authors: Hill N. C. A.
Published: April 2011

The 1PI (one-particle-irreducible) two-point function of a pure Yang–Mills gauge theory is computed. The background-field method is employed in a slightly altered form that makes use of the convexity of the space of gauge fields. It is shown how this avoids the singularity of the matrix ∂2S/∂V∂V thereby allowing the calculation of the Gaussian integral in the generating functional without having to fix the gauge. It is also shown how, when it comes to actually calculating the 1PI two-point function by a perturbative method, a singularity in a particular term, [Formula: see text] of the total matrix [Formula: see text] necessitates the introduction of a gauge-fixing term. The 1PI two-point function is shown to be identical to that of the conventional background-field method except for the presence of a new parameter, t, introduced by the convex decomposition of the gauge field.
Historical review of great auroras
Authors: Jones A. Vallance
Published: April 2011

Occurrences of great auroras of the past are discussed together with accounts of visual and instrumental observations. Earlier observations revealed the extraordinarily great heights and unusual spectral characteristics of such displays as well as documenting their penetration to low latitudes. Theoretical studies have led to an understanding of the observed unusual spectroscopic characteristics including their bright red colour and the abnormal vibrational and rotational structure in the molecular bands observed in high-altitude forms. As a result of the increasing sophistication of observing techniques, the phenomena associated with great auroras have passed beyond the characterization of optical and magnetic effects, to include information on associated changes in the composition of the neutral upper atmosphere and effects in the ionosphere. In more recent times, studies have led to increased understanding of the magnetospheric processes that produce these auroras.
Auroral ion composition during large magnetic storms
Authors: Yau A. W. , Whalen B. A.
Published: April 2011

Ion-composition measurements from the suprathermal mass spectrometer (SMS) on AKEBONO (EXOS-D) during large magnetic storms (minimum Dst < −50 nT) reveal substantial changes in the mass composition of the auroral ionosphere. At quiet times, H+ and O+ ions dominate the high-altitude (> 1000 km) polar (Λ > 70°) ionosphere, and the minor-ion species (He+, N+, and O++) typically constitute about 10% of the total ion population: N+/O+ ≈ 0.05–0.1 and O++/O+ ≈ 0.1–0.2. During magnetic storms, the relative abundance of minor ions increase substantially, and N+ becomes a significant, at times dominant, component. During the main phase of large storms, the N+/O+ ratio reaches peak values of unity in the dayside. Likewise, the peak O++/O+ ratio reaches 0.4–0.5 at storm time. In addition, molecular [Formula: see text] and NO+ ions are occasionally present, and constitute ~5% of the total ion flux. The observed ions typically have energies of 5–20 eV/q, and are moving upward along the field line. They are believed to originate from the topside ionosphere. The increased abundance of N+ ions during large magnetic storms is believed to be a direct result of the increase in molecular nitrogen density in the F-region and topside ionosphere due to thermospheric heating in the presence of prolonged auroral activity. This implies that N+ ions may possibly be the dominant plasma component in the magnetosphere during very large magnetic storms.
Photometric studies of the great red aurora March 13 and 14, 1989
Authors: McEwen D. J.
Published: April 2011

Extended photometric coverage of the great red aurora of March 13–14, 1989 was obtained at the Rabbit Lake observatory located in northern Saskatchewan, at an eccentric dipole latitude of 65.3°. The red aurora first appeared there about 0311 UT on March 13 and appeared to have run its course by about 0700 UT on March 14. During much of the two nights the observatory was near the poleward edge of the display; the aurora was active much of the time and its brightenings were accompanied by poleward expansions to as far north as the observatory. Combining these observations with those at low latitudes suggest a large auroral expanse from an equatorward edge of about 30° to a poleward edge of about 65° magnetic latitude. One key value of the optical data was the semicontinuous monitoring of major auroral emission intensities. The 01D emission at 630 nm reached 130 kR intensity shortly after onset, at about 0347 UT on March 13. Its intensity the following night was typically 35 kR or below. A HILAT satellite pass around 0415 UT March 14 indicated an electron influx of average energies varying between 150 and 800 eV. The excitation efficiency for the 630 nm emission, neglecting any collisional deactivation, was approximately 1 kR per erg cm−2 s−1 (1 erg = 10−7 J) of precipitating electron energy. These measurements along with related worldwide observations will assist in gaining a better understanding of the magnetospheric conditions producing such major widespread auroras.
Thermospheric heating away from the auroral oval during geomagnetic storms
Authors: Burns A. G. , Killeen T. L. , Roble R. G.
Published: April 2011

Model predictions indicate that the high-latitude thermosphere near the F2 peak undergoes strong heating during geomagnetic storms. Experimental studies at middle and equatorial latitudes have indicated that heating occurs during geomagnetic storms, although the overall morphology of these temperature changes is not clear. In this paper we use data from the DE-2 (dynamics explorer) satellite to study this morphology at middle and high latitudes, and then use a simulation of the November 24, 1982 storm, by the NCAR–TIGCM, to compare model output and data on a "one-on-one" basis for an individual orbit in the middle of this storm. Agreement between model and data is good in the winter hemisphere, so we use a thermodynamic diagnostic processor to make a preliminary investigation of the mechanisms by which geomagnetic storms cause temperature increases at lower latitudes. The major conclusions from this work are (i) unlike compositional changes, thermospheric temperature changes do not display a long "tail" into the post-midnight, mid-latitude region; (ii) the pattern of heating during geomagnetic storms is complex, a result of the complicated physical processes that occur during geomagnetic storms; (iii) heating due to advection is approximately balanced by expansion of the gas and downward heat conduction in the postmidnight region; (iv) model predictions for this storm indicate that the greatest temperature increase at 40° N is seen in the dawn sector; (v) early in the storm the strongest compressional heating at latitudes near 40° N is found in the premidnight region, where parcels of air are slowed by sunward ion convection, and consequently converge causing downward winds; (vi) compressional heating also occurs in the afternoon, in a region where expansion of the gas, and hence cooling, occurs during quiet geomagnetic times.
Regional latitudinal magnetic and ionospheric effects of the March 13, 1989 storm over Italy
Authors: Bianchi C. , Santis A. De , Meloni A. , Zolesi B.
Published: April 2011

In March 1989, after a series of intense solar events, relevant effects on the Earth's magnetosphere and ionosphere were recorded. Astonishing phenomena (exceptional brilliant auroras, total blackouts of HF radio links, and one of the strongest magnetospheric and ionospheric storms ever recorded in this century) were observed in Italy during this month. In this paper the study of the main magnetic and ionospheric effects that occurred before and during the strong magnetospheric storm of March 13, as they were observed over Italy, is reported. Geomagnetic field elements from two Italian magnetic observatories L'Aquila, Castello Tesino and a temporary magnetic station (S. Nicolô Gerrei) as well as data scaled from two ionospheric stations, Rome and Gibilmanna, are discussed considering their latitudinal dependence and other different site characteristics.
The ionospheric response to perturbation electric fields during the onset phase of geomagnetic storms
Authors: Jakowski N. , Jungstand A. , Schlegel K. , Kohl H. , Rinnert K.
Published: April 2011

The generation and propagation of ionospheric storms are studied by analyzing EISCAT radar, and vertical-sounding and total-electron-content data obtained under different geophysical conditions. Both, case studies as well as the average storm pattern of percentage deviations of different ionospheric parameters from their corresponding reference values such as total electron content, F2-layer critical frequency foF2, F2-layer height hmF2, and slab thickness τ indicate the action of a perturbation electric field during the first few hours during the onset phase of geomagnetic storms. Considering the onset phase of the storm on July 28–29, 1987 evidence has been found that high-latitude electric fields may penetrate to lower latitudes before the ring current has developed. In most cases this process is accompanied by a positive phase in the upper ionosphere and F2-layer ionization. Different mechanisms are assumed to be responsible for the daytime and nighttime behaviour, respectively. The negative phase propagates equatorward with velocities in the order of 70–350 m s−1 following a strong heating of the thermosphere and ionosphere due to the auroral electrojet.
Medium-scale wave-like irregularities of electron density and electron temperature in the upper ionosphere at subauroral and high latitudes during different phases of the magnetic storm of January 1974
Authors: Förster M. , Fatkullin M. N. , Gasilov N. A. , Schwarz U.
Published: April 2011

Data obtained aboard the INTERCOSMOS-10 satellite during different phases of the geomagnetic storm in the last week of January, 1974, are used for the investigation of medium-scale wave-like irregularities of electron density and electron temperature in the upper ionosphere (altitudes from about 800 to about 1400 km) for high and subauroral latitudes. Daytime and nighttime conditions are analysed in detail. It is shown that independent of local time and of the degree of magnetic disturbance the spectra of medium-scale electron-density and electron-temperature fluctuations reveal equal characteristic wavelengths of l ≈ 130–150, 150–200, 210–240, 250–320, 340–400 km and so on. During nighttime conditions in the region of the main ionospheric trough the fluctuations of electron density (at the equatorward wall of the trough) and of electron temperature at the bottom of the trough) are separated in space. Later on it is shown that the intensity of the fluctuations of electron density and electron temperature at high and subauroral latitudes is dependent on the phase of magnetic storm.
Bäcklund transformations, truncated Painlevé expansions, and special solutions of nonintegrable long-wave evolution equations
Authors: Choudhury S. Roy
Published: April 2011

Painlevé expansions, truncated at various stages, are constructed for the conditionally-Painlevé Benjamin–Bona–Mahoney (BBM), the modified Benjamin–Bona–Mahoney (MBBM), and the symmetric regularized long wave (SRLW) equations. Expansions truncated at the constant term lead to auto-Bäcklund transformations between two solutions of all three equations. Special solutions of the various equations, including a solitary-wave solution for the MBBM equation, and new one-parameter families of traveling-wave solutions for the BBM and SRLW equations are obtained using the truncated Painlevé expansions.
Calculation of the nucleon structure function in nuclei
Authors: Modarres Majid
Published: April 2011

We study the effect of nuclear structure on deep inelastic scattering, the EMC effect, in a quark cluster model. The cluster property is built in by increasing the MIT-bag radius for various nuclei that will be related to the two-body correlation function via a local density approximation. We show that we can well predict the experimental data and find that the cluster properties increase as we go from light nuclei to heavier ones.
Scattering of a plane wave by a hemispheroidal boss on an infinite plane
Authors: Ciric I. R. , Cooray M. F. R.
Published: April 2011

An analytic solution is presented for the problem of scattering of a plane wave by a hemispheroidal boss on a perfectly conducting plane. The solution is based on an image technique, by which the original problem is reduced to that of the scattering of two plane waves by a full spheroid, in the absence of the infinite plane. One of these waves is just the given incident plane wave and the other one is chosen such that the boundary conditions in the original problem are satisfied. The field scattered by the hemispheroidal boss on the infinite plane is obtained by the superposition of the fields scattered by the full spheroid in an unbounded space, due to each of the two plane waves. The theory is given for the scattering of both scalar and vector waves. Numerical results are presented for the normalized-scattering cross section in the electromagnetic case for various conducting and dielectric hemispheroidal bosses, of different sizes and axial ratios. From a practical point of view, the solution is significant for the wave scattering by metallic surfaces with various protuberances and by a variety of structures, towers, antennas, and artificial and natural formations on the ground plane.
Stimulation of nuclear transitions via resonance conversion in electromagnetic fields
Authors: Karpeshin F. F. , Listengarten M. A. , Zon B. A. , Band I. M. , Trzhaskovskaya M. B.
Published: April 2011

The feasibility of drastic acceleration in nuclear electromagnetic transitions is shown in the externally applied intense radiation of the appropriate frequency, which compensates for the energy difference of the electronic-shell and nuclear transitions. In the case of 235U the enhancement attains two orders of magnitude. Further applications of the effect for study of nuclear excitation through electronic transitions and for generating coherent X-ray beams are noted.
Path integral approach to the time-dependent quadratic Hamiltonian and coherent states
Authors: Xu Jing-Bo , Bao Ji-Ming , Gao Xiao-Chun
Published: April 2011

The exact propagator and invariant for the time-dependent quadratic Hamiltonian is found by a generalized canonical transformation and a path integral method. We then proceed to construct the coherent states for the system by making use of the propagator. The coherent states for the damped harmonic oscillator and variable mass or frequency harmonic oscillator are the special cases of the coherent states for the system studied in this paper.
Transition amplitudes in the Dirac–Fock approximation
Authors: Liaw Sy-Sang
Published: April 2011

Transition amplitudes for several iso-electronic sequences are computed on the frozen-core Dirac–Fock approximation using the B-spline method. The length and velocity forms of the oscillator strengths are shown to be equal numerically if the nonlocal effective vertex is used. These gauge-invariant values, when compared with other theoretical results aiming for the exact values of the oscillate strengths, show satisfactory quality. We also find a peculiar feature for some transitions.
Evaluation of loop diagrams using quantum mechanics
Authors: McKeon D. G. C.
Published: April 2011

In using the proper time formalism, Schwinger demonstrated that one-loop processes in quantum field theory can be expressed in terms of a matrix element whose form is encountered in quantum mechanics, and which can be evaluated using the Heisenberg formalism. We demonstrate how instead this matrix element can be computed using standard results in the path-integral formalism. The technique of operator regularization allows one to extend this approach to arbitrary loop order. No loop-momentum integrals are ever encountered. This technique is illustrated by computing the two-point function in [Formula: see text] theory to one-loop order.
Quadrature relations for finite-limit, principal-value integrals
Authors: Davies K. T. R. , Glasser M. L. , Davies R. W.
Published: April 2011

An intuitive expression is obtained for a general finite-limit, prinicipal-value (PV) integral containing a pole of arbitrary order. Such an integral is simply the difference between its "end-point quadratures," the quadrature being the result of the indefinite integral. This PV expression is fairly obvious for simple poles but requires careful justification for higher order poles. Moreover, quadratures are useful in evaluating related integrals that contain both poles and other singularities (e.g., step functions or logarithmic divergences). Then, for a certain type of finite-limit divergent integral, the PV is interpreted as its "convergent part." Also, for cases in which there are two PV's in a double integral, it is shown that the famous Poincaré–Bertrand theorem applies to finite-limit as well as infinite-limit integrals. Finally, an interesting quadrature relation is derived for such double integrals, and the validity of the Poincaré–Bertrand theorem is explicitly demonstrated for a simple finite-limit case.
Traveling-wave convection in a narrow rectangular cell
Authors: Liu Minghui , Bruyn John R. de
Published: April 2011

Traveling-wave convection in an ethanol–water mixture confined in a narrow rectangular cell of height:width aspect ratio 1:0.3 is studied using shadowgraph flow visualization. We are able to identify qualitatively the contributions to the shadowgraph intensity due to the concentration field in the convecting mixture. The measured shadowgraph intensities and traveling-wave frequencies share features with the results of numerical calculations, which assume an infinitely wide cell, and of experiments done in wider cells, but there are significant quantitative differences, apparently due to our highly constrained geometry.
Analytic solutions of the scattering by two multilayered dielectric spheres
Authors: Hamid A-K. , Ciric I. R. , Hamid M.
Published: April 2011

The problem of plane electromagnetic wave scattering by two concentrically layered dielectric spheres is investigated analytically using the modal expansion method. Two different solutions to this problem are obtained. In the first solution the boundary conditions are satisfied simultaneously at all spherical interfaces, while in the second solution an iterative approach is used and the boundary conditions are satisfied successively for each iteration. To impose the boundary conditions at the outer surface of the spheres, the translation addition theorem of the spherical vector wave functions is employed to express the scattered fields by one sphere in the coordiante system of the other sphere. Numerical results for the bistatic and back-scattering cross sections are presented graphically for various sphere sizes, layer thicknesses and permittivities, and angles of incidence.
An experimental observation of higher order radiative processes in π0 decays and π−p interactions at rest
Authors: Drees Reena Meijer , Waltham Chris
Published: April 2011

In this work we present techniques for dealing with radiative corrections in a precision π0 decay measurement. In this case these "corrections," due to processes involving additional photons, are as large as the effect being measured and so need to be approached with caution. Two methods are discussed, together with experimental evidence of their applicability.
Quantum tunneling in a dissipative environment
Authors: Hron M. , Razavy M.
Published: April 2011

A wave equation formulation of the problem of quantum tunneling in a dissipative medium is developed by considering a many-body system in which the central particle is subject to an arbitrary force law, and at the same time is coupled to a bath of noninteracting harmonic oscillators. For the motion of the central particle it is possible to obtain an effective Lagrangian and Hamiltonian by eliminating the degrees of freedom of the oscillators. However both of these operators are nonlocal, and it is difficult to derive a wave equation for this motion. As an alternative method one can write a many-body Schrödinger equation for the whole system, and then eliminate the wave functions of all of the oscillators. This result is a many-channel Schrödinger equation for the motion of the central particle. By truncating this set of coupled equations, one can solve the problem for different force laws. In particular, in this work, the cases of dissipative tunneling, hopping, and quantum coherence are studied in detail. It is also shown how this approach can be generalized to multidimensional dissipative systems.
Early era in a broken-symmetry theory of gravity
Authors: Krori K. D. , Chaudhury T. , Mahanta Chandra Rekha
Published: April 2011

We discuss in this paper the early era of Robertson–Walker, Kantowski–Sachs, and Bianchi type 1 cosmologies in the light of a broken-symmetry theory of gravity proposed by Chandra. The conclusions for all three cosmologies are briefly presented for comparison. Some results of Chandra's calculation on Robertson–Walker cosmology are corrected.
Gauge transformations in nonrelativistic quantum mechanics and different forms of the photon–electron interaction
Authors: Mu Xingdong
Published: April 2011

The properties of the Schrödinger equation under electromagnetic gauge transformations are investigated. A procedure to obtain gauge-invariant matrix elements and transition probabilities within perturbation theory is pointed out. Using this formalism, it is shown that the two commonly used photon–electron interaction Hamiltonians denoted as p∙A and r∙E cannot be connected by a gauge transformation and are therefore not necessarily equivalent. The conclusions are illustrated by an example from multiphoton ionization in strong radiation fields.
Energy levels of the Schrödinger equation for some rational potentials using the hypervirial method
Authors: Witwit M. R. M. , Killingbeck J. P.
Published: April 2011

The energy levels of a one-dimensional system are calculated for the rational potentials, [Formula: see text] and [Formula: see text], with (2L = 4, 6). We use the hypervirial method and Padé approximants over a wide range of values of the perturbation parameters (α, g, λ) and for various states. The numerical results agree with those of previous workers where they are available.
Influence of laser etching on the surface preparation of cadmium sulphide Schottky barrier
Authors: Al-Dhafiri A. M. , Al-Bassam A. A. I. , Al-Jaffali A. A.
Published: April 2011

Laser-etching techniques that induce different surface topographies for CdS were found to be an essential step for Schottky-diode fabrication. In this study, after a specific etching time, the CdS surfaces develops microscopic cones (pyramids). The density of the cones depends on the period of etching. The influence of these cones on the electrical properties of Schottky diodes (Au–CdS) are reported. The resulting changes in the I–V (current-voltage) characteristics and C−2–V measurements of the Au–CdS diodes are recorded. The barrier heights to these junctions were found to be strongly dependent on the topography of the CdS surfaces.
Doubly differential cross sections for electron impact ionization of atomic hydrogen
Authors: Ray H. , Roy A. C. , Werner U.
Published: April 2011

The Glauber approximation is used to calculate doubly differential cross sections (DDC's) for electron impact ionization of atomic hydrogen at incident energies of 100, 150, and 250 eV. The angular dependences of DDC's are presented for the scattered (primary) electrons. The energies of ejected (secondary) electrons were chosen to be 5, 10, and 14 eV. A comparison is made of the present DDC's with the results of other theoretical calculations.
Equilibrium for Compton-scattering media
Authors: Zhu Shao-Ping
Published: April 2011

The generalized H theorem is proved for Compton-scattering media. Using the H theorem, we discuss the equilibrium state for Compton-scattering media. We verify rigorously that Bose condensation, which was first found based on the Fokker–Planck equation, does exist for some initial data.
Tapered optical couplers with grating: Beyond the weak-guidance limit
Authors: Florjaāczyk M. , Tremblay R.
Published: April 2011

We describe the operation of a grating-assisted optical coupler consiting of two different curved slab wave guides. A version of vectorial, nonorthogonal coupled-mode theory based on local modes is applied. The coupled-mode equations contain mode overlap terms and coupling terms, which vary with distance. These equations are solved numerically for even-transverse magnetic modes propagating in the non-weakly guided slabs. We show output light powers as a function of the input wavelength assuming a condition of contradirectional coupling. For comparison we also show the result in the limit of weak guidance and a result from the vectorial theory without mode overlaps.
Analysis of the stability of multiple-phase-shift distributed-feedback semiconductor lasers
Authors: Champagne Yves , McCarthy Nathalie
Published: April 2011

The effects of the longitudinal spatial hole burning on the static lasing characteristics of a specific configuration of distributed-feedback semiconductor laser with three phase-shift regions are investigated using a numerical approach. A serious degradation of the stability of the optimum design, having the flattest axial intensity distribution at low output power, is predicted for drive levels beyond a critical value. The lasing wavelength exhibits a sudden shift (wavelength chirping), along with a significant degradation of the single-mode character of the longitudinal-mode spectrum. Thus, the potentialities of this multiple-phase-shift structure to provide a stable narrow-linewidth emission at high output power appear to be less than expected from results calculated for the near-threshold regime. Nevertheless, it is found that a multiple-phase-shift configuration that departs slightly from the optimum case suffices to recover most of the promises expected from this distributed-feedback laser design.
Surface second-harmonic susceptibility determined by noncollinear reflected second-harmonic generation
Authors: Provencher Pierre , Côté Christian-Yves , Denariez-Roberge Marguerite-Marie
Published: April 2011

We investigate the noncollinear reflected second-harmonic generation (SHG) for monolayers of Rhodamine 6G adsorbed on fused silica. We show that the ratios between the surface molecular χ(2) components can be related to the values of the polarization angles of the two incident beams when minima of the resulting SHG intensity are obtained.
Two-photon excitation and bleaching of the 400 nm luminescence band in germanium-doped-silica optical fibres
Authors: LaRochelle Sophie , Ouellette François , Lauzon Jocelyn
Published: April 2011

The 400 nm luminescence band of germanium-doped-silica optical fibres was excited via two-photon absorption of an argon ion laser beam. It was observed that the photoluminescence decreased by as much as 25% during the exposure of the fibres to several hundred milliwatts of optical power fora few hours. Surprisingly, the amount of bleaching is not a given proportion of the initial intensity of the luminescence band. These luminescence measurements are qualitatively related to the photosensitivity of the optical fibres. The saturation of two-photon absorption at relatively low power is also observed.
Glass-sandwich structure for one-step writing of optical wave guides in photopolymers
Authors: Carignan Claude , Duguay Michel A. , Ouellette François , Talon Marie-Hélène
Published: April 2011

By squeezing a few drops of UV-curing optical adhesive between two glass plates, a planar wave-guide sandwich structure is formed. Strip wave guides can then be written in one step by focussing a computer-controlled UV laser beam into the liquid adhesive layer and thereby solidifying it along a narrow path. Measured optical losses at 633 nm fall in the range 0.4–1.1 dB cm−1 for 12 μm wide wave guides.
Excitation function for α-particle-induced reactions in light-mass nuclei
Authors: Singh N. L. , Agarwal S. , Rao J. Rama
Published: April 2011

The excitation functions of 51V [(α, xn), x = 1.3; (α, p3n); (α, α3n) (α, 2α)] and 59Co[(α, 2n); (α, αxn); x = 1, 2] reactions were measured up to 50 MeV by the stacked-foil activation technique and high-resolution Ce(Li)–HPGe spectroscopy method. Of these 51V(α, xnypzα) reactions were studied for the first time with better accuracy than earlier measurements, which were done with a poor resolution scintillation–Ge(Li) detectors some 20 years ago. In the case of 59Co, existing data show large discrepancies at low energy. Comparisons are presented with the prediction of hybrid and exciton models. While for the (α, xn) type of reactions, reasonably explainable pre-equilibrium contributions are found, there seem to be indications of direct inelastic scattering effects in the (α, αxn) type of reactions.
Beam-foil lifetimes measured for intercombination transitions in Zn-like and Ga-like ions of Mo
Authors: Träbert E. , Pinnington E. H.
Published: April 2011

Time-resolved EUV spectra of foil-excited 9.5 MeV Mo ions were recorded in the wavelength range of the ground state Δn = 0 intercombination lines in Zn I-, Ga I-, and Ge I-like spectra. Decay curves were obtained and analyzed; the results are compared with those of calculations.
Quasi-bound state calculations for several types of potential in one-, two-, and three-dimensional systems, using perturbative techniques
Authors: Witwit M. R. M.
Published: April 2011

The energy levels of the Schrödinger equation for various model potentials in one-, two-, and three-dimensional space are calculated using the hypervirial and inner product methods.
Gauge-fixing dependence of gluon and quark-damping rates in hot quantum chromodynamics
Authors: Baier R. , Kunstatter G. , Schiff D.
Published: April 2011

The recently observed gauge-fixing dependence in covariant gauges of the damping rates of the quantum chromodynamics (QCD) gluonic and fermionic excitations at high temperatures and long wavelengths is reviewed. The analysis is based on the method by Braaten and Pisarski for resumming hard thermal loops using the Ward identities satisfied by the effective propagators and vertex functions. A proposed resolution of the gauge problem by regularizing the mass singularities is also discussed.
Ring-diagram summations in the finite-temperature effective potential
Authors: Carrington M. E.
Published: April 2011

There has been much recent interest in the finite-temperature effective potential of the standard model in the context of the electroweak phase transition. We review the calculation of the effective potential with particular emphasis on the validity of the expansions that are used. The presence of a term that is cubic in the Higgs condensate in the one-loop effective potential appears to indicate a first-order electroweak phase transition. However, in the high-temperature regime, the infrared singularities inherent in massless models produce cubic terms that are of the same order in the coupling. In this paper, we discuss the inclusion of an infinite set of these terms via the ring-diagram summation, and show that the standard model has a first-order phase transition in the weak coupling expansion.
Thermal bosonic Green functions near zero energy
Authors: Evans T. S.
Published: April 2011

The properties of the various types of bosonic Green functions at finite temperature in the zero energy limit are considered in the light of recent work.
Damping of fermions in hot gauge theories
Authors: Kobes R. , Kunstatter G. , Mak K.
Published: April 2011

The calculation of the massless fermion damping rate to order g2T in the long-wavelength limit of hot gauge theories using the recently developed resummation methods in terms of hard thermal loops is reviewed. Ward identities between the effective propagators and vertices are used to formally prove the gauge independence of the damping rate to this order in a wide class of gauges. We also discuss some aspects of the cutoff dependence of the gauge-dependent terms proportional to the mass-shell condition.
Perturbation theory for nonequilibrium quantum fields
Authors: Lawrie Ian D.
Published: April 2011

Standard perturbation theory fails when applied to nonequilibrium processes. I explain why. To achieve sensible results, it is necessary to resum the absorptive parts of real-time self-energy corrections. Using the closed-time-path formalism, and in the context of scalar-field theory in an expanding universe, I show how a generalized renormalization technique can achieve this.
Medley in finite-temperature field theory
Authors: Pisarski Robert D.
Published: April 2011

Three subjects in thermal field theory are discussed; why in SU(N) gauge theories the Z(N) symmetry is broken at high (instead of low) temperature, the possible singularity structure of gauge-variant propagators, and the problem of how to compute the viscosity from the Kubo formula.
Optoneural system for invariant pattern recognition
Authors: Lejeune Claude , Sheng Yunlong
Published: April 2011

An optoneural system is developed for invariant pattern recognition. The system consists of an optical correlator and a neural network. The correlator uses Fourier–Mellin spatial filters (FMF) for feature extraction. The FMF yields an unique output pattern for an input object. The present method works only with one object present in the input scene. The optical features extracted from the output pattern are shift, scale, and rotation invariant and are used as input to the neural network. The neural network is a multilayer feedforward net with back-propagation learning rule. Because of substantial reduction of the dimension of feature vectors provided by optical FMF, the small neural network is simply simulated in a personal computer. Optical experimental results are shown.
Beam-laser lifetime measurements for low-lying levels in CrII
Authors: Pinnington E. H. , Ji Q. , Guo B. , Berends R. W. , Hunen J. van , Biémont E.
Published: April 2011

Lifetimes have been measured for 14 levels belonging to the z4P0, z4D0, z6P0, z6D0, and z6F0 terms of CrII using laser-induced fluorescence of a fast beam. The results are compared with earlier LIF and beam-foil measurements and with the calculations of Kurucz. An analysis of solar photospheric spectra, using the Kurucz branching-ratios renormalized by the new lifetime results, yields a solar photospheric abundance of chromium equal to ACr = 5.74 ± 0.06 on the usual logarithmic scale.
Born–Infeld solution for a point charge in D dimensions
Authors: Wolf C.
Published: April 2011

By considering the generalization to D space-time dimensions of the Born–Infeld Lagrangian we evaluate the electromagnetic field and gravitational field of a point charge and derive an expression for the total mass of a point charged particle in this theory.
Magnetostatics of a superconducting quark star
Authors: Chakrabarty Somenath
Published: April 2011

The superconducting properties of a strange quark star are investigated using the relativistic theory of superconductivity for a fermion system. A dynamical density-dependent quark mass model is used for confinement. The type of superconductivity and the magnetostatic properties for the material of the star are also studied.
Bound polaron in a narrow-band polar crystal
Authors: Lépine Y. , Schönborn O.
Published: April 2011

The ground-state energy of a bound polaron in a narrow-band polar crystal (such as a metal oxide) is studied using variational wave functions. We use a Fröhlich-type Hamiltonian on which the effective mass approximation has not been effected and in which a Debye cutoff is made on the phonon wave vectors. The wave functions that are used are general enough to allow the existence of a band state and of a self-trapped state and are reliable in the nonadiabatic limit. We find that three ground states are possible for this system. First, for small electron–phonon coupling, moderate bandwidth, and shallow impurities, the usual effective-mass hydrogenic ground state is found. For a narrow bandwidth and a deep defect, a collapsed state is predicted in which the polaron coincides with the position of the defect. Finally, for moderate electron–phonon coupling, narrow bandwidth, and a very weak defect, a self-trapped polaron in a hydrogenic state is predicted. Our conclusions are presented as asymptotic expansions and as phase diagrams indicating the values of the parameters for which each phase can be found.
Degenerate trajectories and Hamiltonian envelopes in the method of self-similar approximations
Authors: Yukalov V. I. , Yukalova E. P.
Published: April 2011

We study two new techniques for the approximate calculation of the eigenvalues of the Schrödinger equation. These techniques are variants of the method of self-similar approximations suggested recently by one of the authors. We illustrate the ideas by an anharmonic oscillator problem. We show that the precision of the method can be very high. For example, the ground-state energy of an anharmonic oscillator can be calculated with an error not exceeding 0.07% for all anharmonicity parameters ranging from zero to infinity.
Satellite airglow limb tomography: Methods for recovering structured emission rates in the mesospheric airglow layer
Authors: McDade Ian C. , Llewellyn Edward J.
Published: April 2011

In this paper, we investigate the possibility of using satellite airglow limb tomography to study spatial structures in the airglow emissions of the upper mesosphere and lower thermosphere. We describe inversion procedures for converting satellite airglow limb observations into two-dimensional distributions of volume emission rates. The performance of the inversion procedures is assessed using simulated limb observations and we demonstrate the potential of this tomographic technique for studying the horizontal and vertical characteristics of wave-driven disturbances in the 80–100 km region.
Nonlocal exchange contribution to the free energy of inhomogeneous many-fermion systems. II: Second-order gradient coefficient for a Coulomb system
Authors: Glasser M. L. , Geldart D. J. W. , Dunlap E.
Published: April 2011

The coefficient Bx(T), which determines the leading gradient contribution to the nonlocal free energy of an inhomogeneous many-fermion system, has been evaluated exactly to first order in the interparticle interaction, in the case of pure Coulomb interactions. The result is valid for all temperatures and is expressed in terms of Fermi–Dirac integrals having known properties. Explicit analytical results are given for the degenerate and nondegenerate limits and numerical results are given for the intermediate regime of temperature and density. The limiting value of Bx(T) at T → 0 differs from previous evaluations of this quantity based on ground-state perturbation theory. The reasons for this discrepancy are discussed.
Nonlocal exchange contribution to the free energy of inhomogeneous many-fermion systems. III: Numerical study for screened Coulomb interaction
Authors: Shegelski Mark R. A. , Geldart D. J. W. , Glasser M. L. , Neilson D.
Published: April 2011

The coefficient Bx(n; T) that determines the leading gradient contributions at finite temperature, T, to the nonlocal exchange free energy of a system of fermions interacting by a static screened Coulomb interaction u2(r) = (e2/r) e−λr has limiting behavior for small λ and T, which depends on the order in which the limits λ → 0 and T → 0 are taken. We isolate the quantity that is responsible for this nonuniformity of limits and present a numerical study of its dependence on λ and T. The physical reason for different limiting values of Bx(n; T) is given. We consider the applicability of these results to physical systems and also discuss the discrepancy between first principles and semiempirical determinations of the leading gradient expansion coefficient for the nonlocal ground-state exchange energy of atoms.
Mean dyadic Green's function of a randomly rough surface
Authors: Mudaliar Saba
Published: April 2011

The problem of wave propagation and scattering over a randomly rough surface is considered from a multiple-scattering point of view. Assuming that the magnitude of irregularities are small an approximate boundary condition is specified. This enables us to derive an integral equation for the dyadic Green's function (DGF) in terms of the known unperturbed DGF. Successive iteration of this integral equation yields the Neumann series. On averaging this and using a diagram method the Dyson equation is derived. Bilocal approximation to the mass operator leads to an integral equation whose kernel is of the convolution type. This is then readily solved and the results are presented in a simplified and useful form. It is observed that the coherent reflection coefficients involve infinite series of multiple scattering. Two special cases are considered the results of which are in agreement with our expectations.