bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientational ordering of hydrogen molecules adsorbed on graphite
Authors: Kubik P. R. , Hardy W. N. , Glattli H.
Published: April 2011

The orientational behaviour of ortho-H2 and para-D2 molecules adsorbed on graphite has been studied by NMR from 0.3 to 12 K at coverages where the molecules form a [Formula: see text] registered lattice. We have observed that for 90% ortho-H2, the splitting of the high-temperature NMR doublet increases rapidly near 0.6 K and additional structure appears. We have identified this as a transition to the orientationally ordered pinwheel phase: one of the phases predicted by the mean field theory of Harris and Berlinsky. In contrast, the spectrum of 90% para-D2 evolves smoothly to a broad, weak structure as the temperature decreases, showing no evidence of ordering down to 0.3 K. This very different behaviour is unexpected, given that in the bulk solid both isotopes order at comparable temperatures. From the splitting of the high-temperature NMR doublets, we have deduced the crystal fields Vc and the effective quadrupole coupling constants Γ. For D2, Γ is somewhat less than the rigid lattice value, as expected in the presence of translational zero-point motion. However, for H2, Γ is anomalously small. The ortho–para conversion rates of H2 and D2 on our Grafoil substrate have also been measured.
Radiation solution of the nonlinear Schrödinger equation
Authors: Enns R. H. , Rangnekar S. S.
Published: April 2011

The sine-Gordon, sinh-Gordon, modified Korteweg-deVries (KdV), and nonlinear (cubic) Schrödinger equations are four of the most important (from a physical point of view) nonlinear evolution equations that fit into the Ablowitz–Kaup–Newell–Segur (AKNS) inverse scattering framework. Historically, the soliton solutions of these equations have been exhaustively studied in the literature, the radiation solutions being almost entirely neglected. Using an expansion approach (expanding the reflection coefficient in powers of the area A of the input potential), we have previously studied the complete spatial and temporal evolution of the radiation solutions of the first three equations cited above. In this paper we demonstrate, using an illustrative example, that the expansion approach also works for the nonlinear Schrödinger equation. The qualitative features of the radiation solution thus obtained are easily understood in the physical context of the self-defocusing of an intense optical beam. Making use of numerical simulation, we show that the features persist as A is increased to very large values. The solution is also found to be analytically consistent with the asymptotic (t → ∞) form quoted in the literature for a general input profile.
Scattering phenomena in strong radiation fields II
Authors: Ehlotzky F.
Published: April 2011

By continuing previous work, several different scattering and absorption phenomena in the presence of a strong, coherent, electromagnetic background field are considered from a unifying point of view to elucidate the essential similarities of these processes, in particular, in the limit of low frequencies of the radiation field. The connection with corresponding classical processes is investigated. The limitations of the low-frequency approach are considered, and consequences are discussed with respect to the possible physical implications and conditions of experimental verification.
High-resolution studies of perturbations in the 410 band of thioformaldehyde
Authors: Fung K. H. , Petersen J. C. , Ramsay D. A.
Published: April 2011

The perturbations in the 41 level of the Ã1A2 excited state of thioformaldehyde (H2CS) are shown to be produced by interactions with the 2131, 4262, and 63 levels of the ã3A2 state.Some of these perturbations have been studied with megahertz resolution using the techniques of intermodulated fluorescence and microwave-optical double resonance. A particularly clear example involving hyperfine levels is found in the interaction of the 170.17 (41) level of the Ã1A2 state with the 17 181,18 (4262) level of the ã3A2 state.
Interference effects in the charge-induced spectrum of H2 at 4.2 K
Authors: Brooks R. L. , Hunt J. L. , MacDonald Jack R. , Poll J. D. , Waddington J. C.
Published: April 2011

The fundamental vibrational infrared-absorption spectrum of solid H2 at 4.2 K has been measured while the sample was irradiated with a 15-MeV proton beam. The Stark-shifted molecular transitions resulting from molecules that are the nearest neighbours of localized electrons have been observed and are contrasted with the same transition previously observed in solid D2. The differences are interpreted as evidence of an interference between the dipole of the localized electron and the charge-induced molecular dipole, a result of a coincidence in the frequencies of the molecular and electronic transitions.
Existence of resonances in positron scattering by hydrogen atoms
Authors: Treml T. F.
Published: April 2011

The method of coordinate rotation is used to study S-wave e+–H scattering near the H(n = 2) threshold. The rotated Weinberg – Van Winter equation is used to reduce the problem to the study of a coupled-channel integral equation with pseudo-local potentials. The existence, under certain restrictions, of an infinite sequence of resonances approaching the H (n = 2) threshold is established.
Precise atomic mass differences amongst isotopes of Hg, Tl, Pb, and Bi (and a least-squares mass evaluation for 78 ≤ Z ≤ 84)
Authors: Derenchuk V. P. , Ellis R. J. , Sharma K. S. , Barber R. C. , Duckworth H. E.
Published: April 2011

The 1.00-m radius, high resolution mass spectrometer at the University of Manitoba has been used to determine the spacings of a series of mass spectral doublets. These give improved values for the mass differences between the stable nuclides in Tl, Pb, and Bi and relate these values to previous atomic masses and mass differences for the isotopes of Hg. A least-squares adjustment has been performed on all available atomic mass data (including the mass spectroscopic results from this laboratory) for the region 78 ≤ Z ≤ 84.
Formation and dissociation of , , and ions by ruby laser radiation
Authors: Wagner G. S. , Isenor N. R.
Published: April 2011

Multiphoton ionization of K2, Rb2, and Cs2 in beam conditions by pulsed ruby laser radiation (λ = 6946.0 Å, pulse duration ~10 ns) and subsequent dissociation of the dimer ions by one or more additional photons have been observed. Ground-state dissociation energies of these ionic species have been determined directly from the time of flight of the dissociation fragment pairs, and from the use of retarding potentials, to be [Formula: see text], [Formula: see text], and [Formula: see text]. These observed values have been compared with the theoretical and experimental work of other authors. Our results for the [Formula: see text] and [Formula: see text] ions are the first direct measurements of their ground-state dissociation energies. The effect of laser polarization on the dissociation mechanism has also been experimentally investigated.
An examination of radio-auroral aspect sensitivity
Authors: Moorcroft D. R.
Published: April 2011

An attempt has been made to account for the experimental observations of scattering at angles away from perpendicularity to the earth's magnetic field (aspect sensitivity). First, it was necessary to develop a scattering model appropriate for the plasma waves generally assumed to be responsible for the scattering, consisting of an assembly of irregularities, each one a wave with a Gaussoidal envelope. Then, effects were included for off-perpendicular propagation of plasma waves, the perturbation of the magnetic field direction owing to the presence of auroral currents, and refraction of the radar wave in the E region. Even when possible effects from anomalous resistivity are included, many of the experimental observations require scattering models consisting of irregularities that are elongated along the direction of the earth's magnetic field by only a few plasma wavelengths (in some cases no more than one or two wavelengths). This is physically unreasonable and suggests that our understanding of auroral E-region irregularities and (or) the scattering processes responsible for auroral echoes is still incomplete.
Diffraction by an anisotropic impedance half plane
Authors: Hurd R. A. , Lüneburg E.
Published: April 2011

We solve a new canonical problem: that of a plane wave obliquely incident on an anisotropic imperfectly conducting half plane. An exact closed-form solution is obtained by factorizing a 2 × 2 Wiener–Hopf matrix. The problem had earlier been considered insoluble, but yields to a combination of new and old matrix-factorization techniques.
Radiative decay of unbound levels in 14N
Authors: Pruneau C. , Chatterjee M. B. , Rangacharyulu C. , St-Pierre C.
Published: April 2011

The gamma decay properties of 10.43-, 10.1-, 9.7-, 9.51-, and 8.91-MeV levels are studied by the 13C(p, γ) reaction. The natural widths, gamma decay widths, branching ratios, and multipole mixing ratios are determined. The gamma branching ratios are generally in good agreement with earlier works. However, it is found that the previous (p, γ) measurements overestimated the gamma transition strengths. The results are compared with shell model calculations. Also, a phenomenological description is attempted for a few 14N levels.
Matrix element calculation and a selection rule in the unitary group approach
Authors: Lev A. , Schlesinger M. , Drake G. W. F. , Kent R. D.
Published: April 2011

A closed form expression for the evaluation of many-electron matrix elements in the unitary group approach to the theory of atomic structure is presented in terms of simple factors. In addition, a new selection rule for nonvanishing matrix elements is given.
The D2Σ+ – A2Πi and C2Πr – A2Πi transitions of AlO
Authors: Singh M. , Saksena M. D.
Published: April 2011

Several bands of the D2Σ+ – A2Πi and C2Πr – A2Πi transitions of AlO have been photographed at high resolution and analyzed for the rotational structure. Rotational structure in the vibrational levels ν = 0, 1, 2, 3, and 4 of the common lower electronic state A2Πi has been investigated for the first time. Rotational perturbations have been observed in the A2Πi state. The equilibrium rotational constants of the A2Πi state are Be = 0.53705 cm−1 and αe = 0.00491 cm−1.
Three-beam grating interferometer
Authors: Kothiyal M. P. , Delisle C.
Published: April 2011

A conventional three-beam interferometric arrangement has been modified by introducing a grating in the setup. The grating is used for both fringe control and phase compensation.
Subnanosecond transient studies of intrinsic and extrinsic luminescence in CdSe
Authors: Steiner T. , Thewalt M. L. W.
Published: April 2011

The photoluminescence spectrum and transient behaviour of free and bound excitons in CdSe have been studied with both resonant and above band-gap excitation. The free- and bound-exciton lifetimes were found to be excitation-intensity dependent even at very low levels. In all cases, the free-exciton luminescence decayed more rapidly than that of the bound excitons. A comparison of the no-phonon and longitudinal-optic-phonon replicas of the free-exciton luminescence indicates that the observed doublet structure of the no-phonon spectrum arises from the two polariton branches. Resonant excitation of the donor and acceptor bound excitons revealed two-electron and two-hole replicas, respectively. We believe these to be the first reported two-hole transitions in CdSe. The initial rapid cooling of the free-exciton gas could be observed in a series of time-resolved spectra.
Variable scaling method and the Stark effect in the hydrogen atom
Authors: Roychoudhury R. K. , Roy Barnana
Published: April 2011

By relating the Stark-effect problem in hydrogenlike atoms to that of the spherical anharmonic oscillator, we have found simple formulae for energy eigenvalues for the Stark effect. Matrix elements have been calculated using the properties of Laguerre polynomials, and then the variable scaling method has been used to find optimal solutions. Our numerical results are compared with those of Hioe and Yoo and also with the results obtained by Lanczos.
Kinetic Ising model on alternating linear chains
Authors: Gonçalves L. L. , Oliveira N. T. de
Published: April 2011

The kinetic Ising model on two alternating linear chains is considered. Exact expressions are obtained for the wave-vector frequency-dependent susceptibility and the time evolution of the magnetization. It is shown that the long-time behaviour of the magnetization in both systems is identical to the one in the uniform chain. Although they behave similarly as far as the relaxation of the magnetization is concerned, they have different dynamic magnetic responses at equilibrium. It is also shown that at T = 0 for a given set of parameters the static susceptibility diverges at a well-defined wave vector, which is a consequence of the ordering of the ground state.
Racah algebra of two-body double-tensor operators
Authors: Tuszyński J. A. , Chatterjee R. , Dixon J. M.
Published: April 2011

Two-body double-tensor (TBDT) operators are introduced in the LS- and jj-coupling schemes following Racah's definition of irreducible tensor operators. These operators are shown to contain well-known one-body double tensors as a subset. The result of applying parity, charge conjugation, and time reversal to the TBDT operators is investigated so as to obtain selection rules for their matrix elements. On the basis of their rotation properties, these Hermitian tensor operators are shown to satisfy an SU(2) algebra, and consequently the Wigner–Eckart theorem is applied to calculate their matrix elements. The derivation of the reduced matrix elements is provided. We show some examples of interactions investigated in the literature that can be represented as TBDT operators. For one such operator, the spin-correlated crystal field, a detailed numerical evaluation of its matrix elements is given.
Evidence for out-of-easy-plane solitons in CsMnBr3
Authors: Gaulin B. D. , Collins M. F.
Published: April 2011

CsMnBr3 is a quasi-one-dimensional antiferromagnetic insulator. The spin interactions are predominately of a Heisenberg nature, but at low temperatures the smaller dipolar interactions result in "easy-plane" one-dimensional antiferromagnetic ordering. We have examined the spin fluctuations at low energies, near the magnetic zone centre, with inelastic neutron scattering techniques. By means of a subtraction algorithm, we have separated intensities, as a function of the wave vector and energy, of the two polarizations of spin fluctuations (in-plane and out-of-plane). We report a strong qualitative difference between the energy dependence of the two polarizations, with the "out-of-plane" intensity exhibiting central-mode behaviour. A model of noninteracting Sine–Gordon solitons in the easy-plane antiferromagnet proposed by Mikeska provides an excellent qualitative and reasonable quantitative accounting of the polarization, wave vector, and energy dependence of the neutron scattering with low-energy transfer at 15 K. The model, however, cannot account for our elevated-temperature results. We have modified the theory using the phenomenological approach of ascribing an upwards renormalization of the soliton mass with temperature. The resulting comparison with our results is good.
1/N correction to the axial-coupling form factor gA in the Skyrme model
Authors: Zahir M. Sajjad
Published: April 2011

We explicitly calculate, in the Skyrme model, tree-level corrections of order 1/N to the axial-coupling form factor gA and find their contributions to be small and negative. This observation makes the agreement of gA with the experimental value worse. However, inclusion of the soft-pion – Skyrmion interaction brings in additional higher order corrections and the importance of their computation has also been schematically presented.
Alpha-decay widths and equivalence of optical potentials
Authors: Chaudhury M. L. , Agrawal S. K.
Published: April 2011

Decay widths and relative intensities of the alpha spectra of some rare-earth and heavy nuclei are calculated, taking the barrier, as in the previous treatments, to be the usual Coulomb potential superposed by a nonlocal alpha–nucleus potential with an exchange term. For the static part of the barrier, different forms of optical potentials are now used, and calculated relative intensities are in good agreement with the observed values. It is found that the exchange term is important in the odd-parity transitions, and the different optical potentials are equivalent for the cases considered.
A theoretical simulation of bulk water: the effect of the dispersion-energy contribution
Authors: Sordo J. A. , Klobukowski M. , Fraga S.
Published: April 2011

Inclusion of the dispersion-energy contribution, within the framework of a formulation developed at this laboratory for the study of molecular interactions, leads to an average potential energy of 39.3 kJ/mol for bulk water, in excellent agreement with the experimental value.
Molecular dynamics study of the alloy (N2)67(Ar)29
Authors: Nosé Shuichi , Klein Michael L.
Published: April 2011

Molecular dynamics calculations are used to investigate the effect of isobaric cooling on the hexagonal alloy (N2)67(Ar)29. Particular attention is given to the behavior of the reorientational motion of the N2 molecules. No orientational or structural transition was found to accompany the cooling from 60 to 10 K at either P = 4 × 103 or P = 1 × 103 bar (1 bar = 100 kPa). However, the power spectrum of the angular-velocity autocorrelation function clearly reveals the freezing out of rotational diffusion at low temperature.
Comments on rotational perturbations of Friedmann universes in Einstein zero-mass scalar theory
Authors: Bayin Selçuk Ş.
Published: April 2011

In addition to the solutions given by Krori et al. for slowly rotating Friedmann models in Einstein zero-mass scalar theory, which correspond to separable w(r, t), we mention that there exists a special class of nonseparable w(r, t)'s that leads to soluble models. We present a particular integral representation of the general solution in terms of an auxiliary function along with two explicit analytic solutions.
A rocket measurement of the (0–0) atmospheric band in a pulsating aurora
Authors: McDade I. C. , Llewellyn E. J. , Harris F. R.
Published: April 2011

A rocket measurement of the [Formula: see text] (0–0) atmospheric-band emission profile in an IBC 1+ pulsating aurora is reported. The observed profile consists of a nightglow component of 4.5 kR and an auroral component of 2.0 kR. The relative intensity of the auroral component, compared with [Formula: see text] first negative emission measured on the same flight, is much weaker than the intensities reported from other rocket experiments.An auroral model calculation of the [Formula: see text] production rates from direct electron impact on O2, and from O(1D) produced by electron impact, predicts volume emission rates greater than those actually observed and reaffirms the suggestion that such models must overestimate the secondary electron flux. From an analysis of the possible contributions made to [Formula: see text] production by the reaction of N(2D) with O2, upper limits are placed on the yields of [Formula: see text] and O(1D) in this reaction of 0.02 and 0.1 respectively.It is concluded that mechanisms for the excitation of [Formula: see text] in the aurora, which can explain all of the observational data, have not yet been identified.
Beam-foil lifetime measurements for Ga II and Ga III using a field-emission ion source
Authors: Ansbacher W. , Pinnington E. H. , Bahr J. L. , Kernahan J. A.
Published: April 2011

A brief description is given of the modifications to a 2-MV Van de Graaff accelerator that are required to incorporate a field-emission ion source. The source is used to obtain a 1-μA beam of Ga+ ions. Lifetime measurements using the beam-foil technique are reported for the 4s5s1S, 4s4p1P, 4s4d1D, 4s5d1D, 4p21D, 4s5s3S, 4p23p, and 4s4d3D terms of Ga II and for the 5s2S, 4p2P, 4d2D, and 5f2F terms of Ga III. A detailed discussion is given of the cascading problem in the case of the Ga II resonance transition at 1414 Å.
A study of the path-integral quantization of Abelian gauge theories when no explicit gauge-fixing term is included in the bilinear part of the gauge-field action
Authors: Phillips Stephen
Published: April 2011

The mathematical problem of inverting the operator [Formula: see text] as it arises in the path-integral quantization of an Abelian gauge theory, such as quantum electrodynamics, when no gauge-fixing Lagrangian field density is included, is studied in this article.Making use of the fact that the Schwinger source functions, which are introduced for the purpose of generating Green's functions, are free of divergence, a result that follows from the conversion of the exponentiated action into a Gaussian form, the apparently noninvertible partial differential equation, [Formula: see text], can, by the addition and subsequent subtraction of terms containing the divergence of the source function, be cast into a form that does possess a Green's function solution. The gauge-field propagator is the same as that obtained by the conventional technique, which involves gauge fixing when the gauge parameter, α, is set equal to one.Such an analysis suggests also that, provided the effect of fictitious particles that propagate only in closed loops are included for the study of Green's functions in non-Abelian gauge theories in Landau-type gauges, then, in quantizing either Abelian gauge theories or non-Abelian gauge theories in this generic kind of gauge, it is not necessary to add an explicit gauge-fixing term to the bilinear part of the gauge-field action.
Several one-loop calculations in a formulation of massive quantum electrodynamics possessing only vacuum-polarization divergences
Authors: Phillips Stephen
Published: April 2011

An alternative formulation of path-integral quantization for gauge theories is proposed in which the gauge-fixing condition, normally imposed on just the gauge field itself, is imposed on the gauge-transformed gauge field, a continuous sum now being included over all configurations of the transformation field, Λ(x), that satisfy the gauge condition.It is shown, by explicit calculation, that when bilinear counterterms in the Lagrangian field density are included so as to render the two-point gauge- and fermion-field Green's functions finite, the fermion–fermion–gauge-field Green's function is divergence free. Unlike the more conventional approaches, there is no divergent vertex counterterm needed. Furthermore, the form of the fermion counterterm is a simple mass insertion only. There is no need for a divergent fermion wave-function renormalization. The cancellation of the divergences that are normally present is accomplished by the effect of, heretofor uncommon in perturbative quantum-field theory, infrared-divergent integrals. It is argued heuristically how these may be regulated by the same parameter, Λ, that is used for ultraviolet-divergent integrals, where now the cutoff is towards the lower limit of integration.
Becchi–Rouet–Stora invariance in the 't Hooft–Veltman gauge
Authors: McKeon G. , Phillips S. B. , Samant S. S. , Sherry T. N.
Published: April 2011

The Becchi–Rouet–Stora (BRS) invariance of quantum electrodynamics in the nonlineart' Hooft–Veltman gauge ∂∙A + λA2 = 0 is examined. It is the longitudinal contribution to the vacuum polarization in the t' Hooft–Veltman gauge that upholds BRS invariance.
Emission spectrum of the HCCS radical
Authors: Coquart Bernard
Published: April 2011

Emission bands obtained in the region 3900–4500 Å by a radio-frequency discharge in thiophene are studied; they are assigned to the HCCS transient species whose absorption spectrum was recently observed. A rotational analysis is carried out for the strong bands, which are assigned to a 2Πi–2Πi transition in which both states are close to Hund's case (a). Vibrational assignments are discussed.
Further observations on the stability of low-energy electron diffraction fractional-order beam intensities: hexagonal close-packed (0001) surfaces with adsorption nets designated (2 × 1) and (2 × 2)
Authors: Hui K. C. , Mitchell K. A. R.
Published: April 2011

This paper concerns a problem in low-energy electron diffraction (LEED). Diffracted-beam intensity-versus-energy curves have been calculated with the renormalized forward-scattering method for (2 × 1) and (2 × 2) structures involving adsorption on (0001) surfaces of titanium and zirconium, and these data have been compared with the reliability indices of Zanazzi and Jona and of Pendry. This study establishes that LEED fractional-order beam intensities may be closely constant with changing coverage, even when, as for (2 × 1) structures, neighbouring adsorbed atoms are separated by just the substrate interatomic distance. This work confirms and extends an earlier observation by Yang et al., and it thereby provides further support for the neglect of the beam-set approximation, which was introduced by Van Hove et al. for making more tractable the calculation of LEED intensities from surfaces with large unit meshes.
Laser-induced fluorescence of MnS: rotational analysis of the A6Σ+ – X6Σ+ transition
Authors: Douay M. , Pinchemel B. , Dufour C.
Published: April 2011

Laser-excitation spectra of the rotational structure of the A6Σ+ – X6Σ+ transition of MnS has been performed. The combination of a single-mode dye laser and a high-resolution spectrometer have allowed analysis of a very congested spectrum in which the spin–rotation interaction completely dominates the spin–spin interaction. The (0,1) and (0,3) bands have been analyzed from laser-excitation spectra, and some information has been extracted from the emission spectrum of the (0,0) band. In addition, observation of a second band system confirms results already published by Monjazeb and Mohan.
Seebeck coefficient of quasi-two-dimensional SnSxSe2−x crystals
Authors: Frongillo Y. , Aubin M. , Jandl S.
Published: April 2011

We have measured the Seebeck coefficient of quasi-two-dimensional single crystals of SnSe2, SnS0.1Se1.9, and SnS0.3Se1.7, grown by the Bridgman technique, and SnSe2, grown by iodine transport, over a large temperature range varying from 15 (4.2 for SnSe2) to 300 K. To assist in the interpretation of these results, the Hall coefficient and resistivity were measured on SnSe2 and SnS0.1Se1.9 Bridgman samples. All these measurements were done in a plane perpendicular to the c axis. It was found that, as the temperature decreases, the absolute value of the Seebeck coefficient decreases slightly before a surprisingly large increase at the lowest temperatures. We interpret these results as the manifestation of two conduction mechanisms: electrons in the conduction band and hopping of electrons between impurities.
Attractive Casimir stress on a thin spherical shell
Authors: Brevik I. , Kolbenstvedt H.
Published: April 2011

The Casimir (i.e., zero-point) surface force on a spherical shell is calculated under the following conditions. (i) The material in the shell obeys the relation εμ = 1, ε being the permittivity and μ the permeability. To avoid great complications in the formalism, only the special cases μ → 0 or μ → ∞ are worked out. (ii) The thickness of the shell is small. Schwinger's source theory is used. The surface force turns out to be cutoff divergent. This contrasts with the case of a compact ball (instead of shell) made up of the same particular kind of material; in that situation, the surface force was shown to be cutoff independent (Brevik and Kolbenstvedt, 1982). If the cutoff term in the present calculation is omitted, the remaining finite term yields an attractive force. In the context of the Casimir semiclassical electron model, it gives the value α = 5/32 for the fine-structure constant. In relation to the bag model in quantum chromodynamics, our calculation corresponds to a gluonic zero-point energy of the right order of magnitude when compared with phenomenology.
Origin of the satellite Lγ10 in X-ray spectra
Authors: Nigam A. N. , Soni S. N.
Published: April 2011

It has been shown that the interaction between a 4p hole and an unfilled 4f subshell, as suggested by Sakellaridis, is not able to explain the presence of the satellite Lγ10 reported in the literature. This satellite has been observed in L-emission spectra of the elements with Z = 55–68, except for Z = 61 and 66. It has been further established that the transition L1M3 → M3N1, assigned earlier to this satellite by Deodhar and Rai, is also unacceptable. As a possible explanation, this satellite has now been assigned to the radiative Auger transition L1 → N4N41S0.
GA/GV in the quark model
Authors: Maltman Kim
Published: April 2011

It is shown that the naive nonrelativistic quark model, in the presence of pion emission and absorption, reproduces the usual Goldberger–Treiman relation for the nucleon axial–vector coupling constant.
Relation between bright nights and meteoritic showers
Authors: Herse M. , Rigaud P.
Published: April 2011

From examination of published data, we find a strong correlation between the "bright-night" phenomenon and meteoritic showers. We show how the N atoms and nitric oxide molecules produced along meteor trails give a continuous emission due to NO2, the enhancement of which is at the origin of bright nights. At the same time the hydroxyl emission is enhanced.
Preregularization
Authors: Elias V. , Mann R. B. , Chowdhury A. M. , McKeon G. , Samant S. , Phillips S. B.
Published: April 2011

We describe and investigate the applicability of a recently proposed preregularization procedure in which arbitrary shift-of-integration-variable surface terms (in four dimensions) arising from loop-mementum ambiguities are constrained to absorb any contributions to unrenormalized Feynman amplitudes that violate Ward–Takahashi–Slavnov–Taylor (WTST) identities appropriate to the theory under consideration. Anomalies in WTST identities are shown to be the result of having insufficient arbitrariness in the loop momenta to accommodate the full set of Lagrangian symmetries. We demonstrate the utility of our procedure by analyzing the chiral anomaly in even dimensions, the supercurrent anomaly in N = 1 super Yang–Mills theory, and by calculations in quantum electrodynamics and Yang–Mills theory. We argue that the preregularization procedure should be particularly well suited to supersymmetric theories as a regularization-independent means of upholding super-WTST identities.
Alternative derivation of shift-of-integration-variable surface terms in n-dimensional Feynman integrals
Authors: Elias V. , McKeon G. , Mann R. B.
Published: April 2011

Differences of divergent n-dimensional Feynman integrals that are equivalent up to their shifts of integration variables are calculated without using Feynman parameters or symmetric-integration formulae. Nonzero values for such differences are obtained when n = 4 for linearly, quadratically, and cubically divergent Feynman integrals. Such differences are also shown to have a discontinuity in n at n = 4. Explicit values for the surface terms and for the magnitudes of the discontinuities at n = 4 are shown to agree with earlier calculations.
Temperature and pressure dependence of the electronic structure of tetracyanoquinodimethane crystals and the effect of impurities
Authors: Roubi L. , Cyr C. , Desgreniers S. , Carlone C. , Truong K. D. , Hota N. K. , Zauhar J.
Published: April 2011

The absorption spectrum (12 500–32 260 cm−1) of tetracyanoquinodimethane crystals has been obtained at 0 bars in the [001] and [010] direction at 84 and 300 K. The peak of the Ag → Bu transition has been identified at 21 370 cm−1 and that of the Ag → Au transition at 22 000 cm−1. The change with temperature of both transitions was −3.4 ± 0.1 cm−1∙K−1. The [001] absorption was also obtained at room temperature as a function of the pressure, up to 5.0 × 104 bar, for crystals grown in two different laboratories, giving the change with pressure as −0.037 ± 0.003 and −0.092 ± 0.010 cm−1∙bar−1, respectively. At ambient temperature the explicit contribution, which is a measure of the electron–phonon interaction, was negative and dominated the temperature dependence. The implicit contribution, which is a measure of the volume dilatation, contributed in the opposite way, i.e., positively. Working at room temperature, we observed on both samples irreversible effects at higher pressures. In the first case, a discontinuous change occurred at (12 ± 1) × 103 bar, with new peaks appearing both at higher energy (25 600 cm−1) and lower energy (12 500 cm−1). In the second case, the absorption peak shifted continuously towards lower energies, but it broadened abruptly above 1.3 × 104 bar. We believe that the differences in the pressure dependence of the optical properties are due to the presence of small amounts of impurities in the samples causing subtle structural differences and that the irreversible effects are due to pressure-induced chemical changes.
Two-level quantum mechanical system with decay: density matrix description and shifted frequency approximation
Authors: Morgan D. C. , Grindlay J.
Published: April 2011

The shifted frequency approximation is used to solve the equations of motion for the density matrix describing a quantum mechanical two-level system, with decay, in an applied monochromatic electric field. Expressions are obtained for the transient and the long-term linear electric dipole moment and occupation probability, and the long-term third-order dipole moment. The results are valid across the frequency spectrum, including resonance, provided the phenomenological decay times for the system are not too large or too close in value.
On the accuracy limits of different integral-equation formulations for numerical solution of dielectric bodies of revolution
Authors: Kishk A. A. , Shafai L.
Published: April 2011

In this paper, the numerical solution of electromagnetic scattering by lossless and lossy homogeneous bodies of revolution is investigated. Five different integral-equation formulations are considered, and the dependence of the accuracy of their solution on the object size and permittivity is examined. This is achieved by selecting spheres as the scattering objects and comparing the numerically generated data with analytic solutions.
A 57Fe Mössbauer study of Fe2As: a magnetically induced electric-field-gradient asymmetry
Authors: Rancourt D. G. , Daniels J. M. , Lam H-Y.
Published: April 2011

The 57Fe Mössbauer spectrum of Fe2As has been measured in the temperature range 25–456 K. Evidence is found for two factors that affect the spectrum and that had been neglected in earlier investigations. These are (i) spin relaxation in a time period that is short compared with the characteristic Mössbauer measurement time and (ii) an anisotropy induced in the electric field gradient at the 57Fe nuclei, by the Weiss molecular field, via the spin orbit coupling. Taking these factors into account, we find that the Mössbauer spectra give consistent and physically reasonable parameters over the whole temperature range. There is also agreement with previous neutron-diffraction studies in that the spins in the antiferromagnetic phase are perpendicular to the c axis. The disagreements reported in earlier studies are seen to arise from a neglect of these factors.
The far-infrared collision-induced spectrum of liquid and near-critical CO2
Authors: Clouter M. J. , McKellar A. R. W.
Published: April 2011

Far-infrared (15–200 cm−1) absorption spectra of CO2 have been obtained (i) in the super-critical gas at 306 K with densities from 80 to 122 amagat, (ii) in the saturated liquid at 298, 272, and 236 K, and (iii) on the critical isochore in the temperature range 0.02 K < (T – Tc) < 2.0 K. The gas-phase measurements are in agreement with previous work, but an error in previously reported liquid-phase results is revealed. In contrast to the previous measurements of Mannik and Stryland on the ν1 band, the far-infrared spectra showed no measurable effects associated with density fluctuations in the critical region. A simple statistical theory is proposed to account for this result.
Vacuum ultraviolet laser spectroscopy III: laboratory sources of coherent radiation tunable from 105 to 175 nm using Mg, Zn, and Hg vapors
Authors: Herman P. R. , LaRocque P. E. , Lipson R. H. , Jamroz W. , Stoicheff B. P.
Published: April 2011

Nonlinear frequency mixing of laser radiation in Mg, Zn, and Hg vapors has produced coherent radiation, tunable over the range 175–104.5 nm in the vacuum ultraviolet. The resulting radiation is pulsed, monochromatic, and of sufficient intensity for use in high-resolution spectroscopy. Detailed descriptions are given of the dye oscillator–amplifier systems along with the heat-pipe ovens for producing stable densities of the metal vapors. Measurements of intensities, linewidths, and ranges of tunability are presented for each metal vapor.
Power counting in 1/Nc in the chiral soliton model
Authors: Bunens Johan , Sonoda Hidenori , Wise Mark B.
Published: April 2011

In the large Nc limit, the SU(3) flavor representations for the baryons are large. Naively this suggests that predictions for properties of hyperons and nucleons based on the semiclassical approximation in the chiral soliton model get corrections suppressed by only [Formula: see text]. In this paper it is shown by explicit computation that these corrections are actually suppressed by 1/Nc. We also predict relations between the structure functions of the proton that are valid in the large Nc limit.
The effects of incorporating water into vacuum-deposited amorphous silicon films
Authors: Audas R. , Brodie D. E. , Cowan J. A. , Moore C. J. L.
Published: April 2011

This paper describes the effects on some of the electrical and optical properties of a-Si: C films prepared by vacuum deposition in controlled ambient gases of N2, O2, H2, and water vapour. This stidy was initiated in an attempt to determine the role of a low-energy electron beam irradiating the substrate and film as the layer grows. We find that depositing an a-Si:C film in a water-vapour environment, at a partial pressure of only 4 × 10−8 Torr, will result in the film having a room-temperature resistivity two thousand times higher than that for "clean" films deposited in a good vacuum with a partial pressure of water vapour near 4 × 10−9 Torr (1 Torr = 133.3 Pa). If the partial pressure of the water vapour is increased, the film resistivity increases and it becomes photoconducting. By comparison, the other gases tested had no measurable effect on the properties of the films, with the exception of oxygen which increases the film resistance. None of these latter films were photoconducting. We conclude that the improvement observed in the film properties when samples are irradiated with low-energy electrons results more from the effects of water vapour and (or) oxygen which can be freed from cold surfaces near the substrate than from a possible restructuring of the film as postulated earlier (1).
Variational thermodynamic calculations for some liquid sd metals
Authors: Li D. H. , Moore R. A. , Wang S.
Published: April 2011

A tractable and reliable expression for the one valence-electron eigenenergies, required in calculating the total energy of a disordered sd-type metal, is formulated in the context of the model-potential theory. With the aid of this expression, the variational calculation of the Helmholtz free energy using the hard-sphere model as a reference system, as employed in ab initio calculations of the thermodynamic properties for the nearly-free-electron-like (NFE) liquid metals, can now be extended with reasonable accuracy to those liquid sd metals in which the d-like valence-electron states below the Fermi level are not very localized. Also, the ab initio-type pseudopotential calculation of the interionic pair potentials, as carried out for the NFE-like metals in the literature, is made practical for these sd metals in their disordered states.
The formation of black holes in nonspherical collapse and cosmic censorship
Authors: Israel Werner
Published: April 2011

Circumstantial evidence favouring the broad conjecture that event horizons always form in gravitational collapse is summarized along with the mounting counterevidence to a more restrictive cosmic censorship principle, which would compel every singularity formed in the collapse to be enclosed within a horizon. A confinement theorem is presented, stating that a closed, initially-trapped 2-surface of fixed area that remains regular will act as a wall that permanently seals off its interior contents from causal influence on the environment.
Why study quantum theory?
Authors: Unruh W. G.
Published: April 2011

It is argued that the study of the problems associated with quantum mechanics and gravity, and especially those arising from the role of measurement in quantum gravity, have led and will continue to lead to new insights even in ordinary quantum problems.
Approximation methods in gravitational-radiation theory
Authors: Will Clifford M.
Published: April 2011

The observation of gravitational-radiation damping in the binary pulsar PSR 1913 + 16 and the ongoing experimental search for gravitational waves of extraterrestrial origin have made the theory of gravitational radiation an active branch of classical general relativity. In calculations of gravitational radiation, approximation methods play a crucial role. We summarize recent developments in two areas in which approximations are important: (a) the quadrupole approximation, which determines the energy flux and the radiation reaction forces in weak-field, slow-motion, source-within-the-near-zone systems such as the binary pulsar; and (b) the normal modes of oscillation of black holes, where the Wentzel–Kramers–Brillouin approximation gives accurate estimates of the complex frequencies of the modes.
General relativistic cosmological models and the cosmic microwave background radiation
Authors: Barrow John D.
Published: April 2011

We survey recent theoretical ideas regarding the possible value of the present total density of the Universe and show how physically realistic cosmological models containing small deviations from isotropy allow observations of intrinsically general relativistic effects on the microwave background to determine whether or not the Universe is open or closed no matter how close the total density lies to the critical value. Applications of these results to inhomogeneous cosmological models, cosmic vorticity, and observational studies of the microwave-background-radiation isotropy are also discussed.
Gravitational lenses and the inhomogeneous universe
Authors: Dyer Charles C.
Published: April 2011

The theory of static gravitatonal lenses is discussed using the optical scalar formalism and the ray-bending approximation to this formalism. The advantages of each approach are discussed, with particular emphasis on the use of the bending approximation for discretely observable lenses, say multiply imaged quasars, and the optical scalar equations for cumulative effects of inhomogeneities for distant objects in the universe.The effect of a locally lumpy distribution on the past null cone of a typical observer is discussed. This is of particular interest in deciding the limits to which one can hope to do cosmology through the use of optical and other telescopes. The optical-scalar-equation driving terms can be replaced by appropriately defined mean driving terms for subsets of observable objects, and coupled with corresponding probabilities, these calculations can yield estimates of the "thickness" of the observer's past null cone as a function of the red shift. This imposes a limit on the use of standard observations in determining the structure of the universe, simply owing to the "fuzzy" structure of the perceived past null cone.
Evolution of bubbles in vacuum
Authors: Lake Kayll , Wevrick Rachel
Published: April 2011

Pseudoeffective potentials are developed for the motion of spherical bubbles in vacuum within the context of the general relativistic thin-wall approximation. It is assumed that the intrinsic surface tension and density are proportional.
Lagrangian formalism for adiabatic fluids on five-dimensional space-time
Authors: Künzle H. P.
Published: April 2011

The recently developed Lagrangian formalism on extended five-dimensional space-time that permits a unified description of general relativistic and gravitating nonrelativistic classical fields is applied to a model of an adiabatic perfect fluid described in terms of Lagrangian coordinates. The Lagrangian density is chosen as an arbitrary Lorentz- (or Galilei-) invariant function of the 5-current vector and leads, by variation with respect to frame fields, to a 5-stress-energy tensor, whose additional components are naturally interpreted as an entropy-flux vector.
Shear-free fluids in general relativity
Authors: Collins C. B.
Published: April 2011

For a large class of shear-free general-relativistic perfect fluids that obey a barotropic equation of state, either the expansion or the rotation is zero; well-known examples include the Friedmann–Robertson–Walker (FRW) models, the Gödel solution, and stationary axisymmetric systems in rigid rotation. It has been conjectured that this is necessarily the case. Several results prove that restricted versions of this conjecture are valid, although no proof is known for the general case. A survey of these special results is given, together with physical and mathematical reasons for the study of shear-free fluids.If the conjecture is true, then there are three mutually exclusive subclasses, according to whether or not the expansion and the rotation are zero separately or simultaneously. Of these, the physically most interesting subclass is that in which the expansion is not zero, since this subclass might be thought to contain space-times that are suitable for the description of collapsing stars or expanding cosmologies. All space-times of this particular subclass are given, and their global properties are investigated. It turns out that the FRW models are the only ones in which the matter is physically reasonable on a global scale. This consequently provides a global uniqueness theorem for the FRW models.
An oscillatory big-bang singularity
Authors: Wainwright J.
Published: April 2011

The big-bang singularities in the exact cosmological solutions of the Einstein field equations that have been studied up to now are power asymptotes in the sense that all scalar polynomials in the curvature tensor diverge monotonically as a power of clock time along the fundamental world lines, as the singularity is approached. One can thus regard the solutions as being asymptotically self-similar near the singularity. In this paper, we illustrate a more complicated type of singularity by giving an example of an exact cosmological solution in which the big-bang singularity is of an oscillatory nature, so that the solution is not asymptotically self-similar.
Localized electronic states: the small-radius potential approximation
Authors: Steslicka Marie , Jurczyszyn Leszek
Published: April 2011

Using a quasi-three-dimensional crystal model, we investigate the localized electronic states generated by a crystal surface covered by foreign atoms. Two such states are found in the first forbidden energy gap and, because of their localization properties, called the Tamm-like and adsorptionlike states. Using the small-radius potential approximation, we discuss the properties of both types of states in detail.