bluuebunny/crossref_metadata_2025 huggingface dataset:
Tricritical phenomena in an Ising model with nearest- and next-nearest-neighbor interactions
Authors: Plischke M. , Zobin D.
Published: April 2011

We report on the analysis of low and high temperature series for the Ising model with nearest-neighbor antiferromagnetic and next-nearest-neighbor ferromagnetic interactions on the bcc lattice. The high temperature series are complete to β7, the low temperature series to u37. We determine the phase diagram, locate the tricritical point, and estimate the tricritical exponents. The tricritical exponents are only in fair agreement with the predictions of tricritical mean field theory.
Cross section for excitation of N2+ first negative bands in collisions between ground state N2+ ions and vibrationally excited N2 molecules
Authors: Anketell J.
Published: April 2011

A cross section [Formula: see text] has been derived for the excitation mechanism[Formula: see text]on the basis of a number of measurements of related quantities in the nitrogen pink afterglow.
Effects of temperature on the photovoltage of Au–InSb Schottky barriers
Authors: Rochon P. , Fortin E. , Woolley J. C.
Published: April 2011

The effect of temperature on the magnitude of the photovoltage ofa Au–InSb Schottky barrier is investigated in the range 60–250 K. Analysis of the variation of photo voltage with temperature shows that the barrier height [Formula: see text], which for Au–InSb is mostly determined by interface states, varies slowly with temperature. A model, taking into account the temperature dependence of the different components of the photovoltaic cell, is developed to explain the rapid increase in photovoltage with decreasing temperature, and its predictions are tested against experimental results.
Communications optiques par interférométrie à grande différence de marche en éclairement non parallèle
Authors: Cielo P. , Delisle C.
Published: April 2011

A generalisation of an optical wave communication system is proposed in which a wide band light source is modulated interferometrically using a path difference longer than the coherence length (Delisle and Cielo). The behaviour of the double interferometer system is studied theoretically and experimentally for the case of a non-parallel light beam. It is concluded that results similar to those obtained previously are applicable if the changes in direction of the light rays going through both interferometers obey an expression which we derive in terms of the path difference, the angle of the ray, and the wavelength. That same relation is equally useful for determining permissible misalignment between the two interferometers as well as the degree of turbulence of the medium between the two interferometers. Finally, the restrictions imposed on the system when light is transmitted between the two interferometers by means of an optical fiber are established. [Journal translation]
Beam-foil spectroscopy of neon in the wavelength range 209–602 Å
Authors: Kernahan J. A. , Donnelly K. E. , Pinnington E. H.
Published: April 2011

We have measured radiative mean lives from 24 transitions in Ne II–Ne VI in the wavelength range 209–602 Å using the beam-foil technique. We present the first experimental mean lives for nine levels, and our results are compared where possible with theoretical calculations and with other experimental values.
Analysis of singlet and triplet systems of yttrium hydride, YH and YD
Authors: Bernard A. , Bacis R.
Published: April 2011

Six new electronic band systems, ascribed to YH, have been observed in emission in the negative glow of a 'composite wall' hollow cathode lamp. Five of the similar systems of YD have also been observed. They appear between 4500 and 9000 Å. The vibrational analysis and observation of the related isotope effect permitted us to distinguish and partially classify these systems. Rotational analysis made it possible to identify the corresponding transitions as 3Φ → 3Δ, (1Π, 1Σ) → 1Σ, and (1Σ, 1Δ) → 1Π.Rotational constants of the ν = 0 states are given in this paper. Moreover, equilibrium molecular constants derived from the rotational study of a number of bands, namely (0, 0) and (1, 1) of YH and (1, 0), (2, 1), (3, 2), (0, 0), (1, 1), (2, 2), and (0, 1) of YD, are given for the states of the 1Σ → 1Σ transition. Franck–Condon factors of this system are estimated.
Nucleon separation and pairing energies, decay energies, and atomic masses for 68 ≤ Z ≤ 72
Authors: Sharma K. S. , Meredith J. O. , Barber R. C. , Kozier K. S. , Haque S. S. , Barnard J. W. , Southon F. C. G. , Williams P. , Duckworth H. E.
Published: April 2011

A set of 24 precise determinations of mass spectroscopic doublet spacings, including a new determination of the 176Hf35Cl – 174Hf37Cl mass difference, has been combined with nuclear reaction and decay Q values in a least squares adjustment of the atomic mass differences in the region 68 ≤ Z ≤ 72. The following quantities have been calculated for each nuclide: separation energies for the last neutron and last pair of neutrons (Sn, S2n), the neutron pairing energy (Pn), separation energies for the last proton and last pair of protons (Sp, S2p), the proton pairing energy (Pp), Q values for α and β− decays, and the mass defect. The systematic variations of these quantities with N and Z are discussed.
A new satellite in the L X-ray emission spectrum of lutetium-71
Authors: Nigam Anand N. , Mathur Rakesh B.
Published: April 2011

Using a 40 cm curved mica crystal spectrograph of the transmission (Cauchois) type, a new satellite β14 has been observed at λ = 1408.3 X unit (Xu) in the L X-ray emission spectrum of lutetium-71 for the first time. On the basis of Wentzel's multiple ionization theory the new satellite has been assigned to the transition L2M4 → M4M4. Further, the presence of the satellites αx, β21, and γ1′ in the spectrum of lutetium reported by earlier workers, has been confirmed and these satellites have been assigned to the transitions L3M2 → M2M5, L3M5 → M5N5, and L2M4 → M4N4, respectively.
Nuclear orientation of 54Mn in magnetically ordered MnCl2∙4H2O
Authors: Gorling R. L. A. , Turrell B. G. , Martin P. W.
Published: April 2011

The antiferromagnetic, spin-flop, and paramagnetic phases of MnCl2∙4H2O have been investigated by observing the nuclear orientation of radioactive 54Mn in a single crystal of the salt. The directions of the sublattice magnetizations in the absence of an external magnetic field were determined. The field dependence of the sublattice magnetizations in the spin-flop state indicated that second order anisotropy is significant in this system. Furthermore, the measurements allowed the determination of the molecular fields in the molecular field theory. The spin-flop transition region was found to be described adequately by a domain structure in which regions of antiferromagnetic phase and spin-flop phase co-exist in the crystal. The temperature dependence of the spin-flop field was determined by magnetic susceptibility measurements. It was found that the spin-flop field decreases with decreasing temperature down to temperatures less than 0.1 K contrary to previous reports. The cooling of the specimen in contact with a copper heat sink was investigated and the temperature dependence of the heat transfer is discussed. An attempt to observe magnetic resonance of the oriented nuclei was unsuccessful.
Photoelectric cross sections for 323 keV gamma rays in Cu, Zr, Ag, Sn, Ta, Au, and Pb
Authors: Ranganathaiah C. , Gowda Ramakrishna , Sanjeevaiah B.
Published: April 2011

Photoelectric cross sections for 323 keV gamma rays in Cu, Zr, Ag, Sn, Ta, Au, and Pb have been measured using a well-type plastic scintillation spectrometer. A comparison of these cross sections is made with the theoretical cross sections and the available measured values.
Phonon properties of niobium, molybdenum, and their alloys
Authors: Powell B. M. , Martel P. , Woods A. D. B.
Published: April 2011

Simple lattice dynamical models have been fitted to the experimental phonon dispersion curves of niobium, molybdenum, and their alloys. The 'best-fit' parameters are used to compute the phonon distribution functions, g(v), and several properties which depend on these functions.
Low temperature crystal structure of TbAsO4 and DyAsO4
Authors: Long F. G. , Stager C. V.
Published: April 2011

The crystal structures of TbAsO4 and DyAsO4 have been determined by X rays, using single crystal diffraction techniques. The structures have been determined both above and below the co-operative Jahn–Teller phase transition temperature. The structures at room temperature are in good agreement with previous results. The low temperature structures, below the phase transition temperature, are compared to the theory of Elliott, Harley, Hayes, and Smith.
Single proton states in odd holmium isotopes
Authors: Panar J. D. , Straume O. , Burke D. G.
Published: April 2011

The (3He,d) and (α,t) reactions have been used to study odd proton states in 157,159,161,163Ho. The beams were provided by tandem Van de Graaff accelerators and the light reaction products were analyzed with magnetic spectrographs and detected with photographic emulsions. Spectra were studied up to excitation energies of ~1.5 MeV for each nuclide with resolutions (FWHM) of ~14 keV for the (3He,d) reaction and ~12 keV for the (α,t) reaction. Information on the l-values was obtained from the ratios of (3He,d) and (α,t) cross sections and from (3He,d) angular distributions. The results are interpreted in terms of the Nilsson model with pairing and Coriolis mixing included. Nuclear structure factors were extracted from the experimental data with the aid of DWBA calculations. Nilsson assignments from previous gamma-ray studies have been confirmed for many low-lying rotational bands. In addition, many new assignments have been made, particularly in the lighter isotopes for which very little nuclear structure information existed previously. A relatively strong l = 0 transition is found in each nuclide and arguments are made to suggest these Iπ = 1/2+ states are gamma vibrations based on the 5/2+[402] states. Similarly, strong l = 2 transitions populate states which may be Iπ = 3/2+ gamma vibrations based on the 7/2+[404] orbitals. Some interesting systematics of the behaviour of single particle states in this region are presented and some anomalies in the populations of the 1/2+[411] and 3/2+[411] states are pointed out.
Développement complet de l'hamiltonien de vibration–rotation adapté à l'étude des interactions dans les molécules toupies sphériques. Application aux bandes ν2 et ν4 de 12CH4
Authors: Champion Jean-Paul
Published: April 2011

Using an unsymmetrized coupling scheme in the group Td, we determine all the vibration–rotation operators of the Hamiltonian of XY4 molecules, including all possible interactions, up to any order of approximation. We define a basis of Hamiltonian matrices of which the matrix elements are functions of coupling coefficients of the group chain [Formula: see text] only. Thus, we develop a general formalism available for any vibrational sublevels of whatever symmetry. The parameters relative to the different vibrational sublevels are known linear combinations of the coefficients of the Hamiltonian expansion. From these, we deduce simple relations between the parameters associated with the ground state, the fundamentals, and the harmonic and combination bands.We apply this formalism to the study of the Coriolis interaction between ν2 and ν4 of CH4. With only 21 parameters for the two bands, we obtain a standard deviation of 34 mK for 251 Raman transitions of ν2 and 20 mK for 243 ir transitions of ν4.
Détermination directe des coefficients du potentiel de Dunham par une méthode de moindres carrés non linéaire appliquée aux nombres d'ondes des raies. Application au cas de la molécule HBr
Authors: Niay P. , Bernage P. , Coquant C. , Fayt A.
Published: April 2011

In this paper, the Dunham potential coefficients are numerically determined by using a nonlinear least squares routine applied directly to the line experimental wave numbers.The results are compared to the ones obtained when using the usual iterative process applied to the H81Br Yi0 and Yi1 equilibrium constants.The al determination new method assumes a theoretical framework (B.O., adiabatic or non-adiabatic) to be valid. One can test this assumption by comparing the experimental data to the calculated ones.
Librational motion in the α phase of solid nitrogen. III. Spin–Lattice relaxation
Authors: Dunmore Paul V. , Goodings D. A.
Published: April 2011

The theory of spin–lattice relaxation of Van Kranendonk and Walker is adapted to the α phase of solid nitrogen. The quadrupolar relaxation of the 14N nucleus by the 'anharmonic Raman process' is calculated for the cubic anharmonic terms obtained from the theory presented in the first paper of this series. Different approximations to the Raich–Mills intermolecular potential are employed. When the expansion of the potential in spherical harmonics is truncated at l = 2, the calculated temperature dependence of T1 is in satisfactory agreement with the experimental measurements of DeReggi, Canepa, and Scott between 20 and 35 K. Below 15 K the calculated results for T1, are too long, probably due to the neglect of mixing between the librons and acoustic phonons. When the Raich–Mills potential includes the spherical harmonic terms with l = 4 and l = 6, the relaxation is found to increase by more than a factor of 40, resulting in T1, becoming much shorter than the experimental results over the high-temperature region. This arises mainly from single-molecule terms of three-fold symmetry in the potential, leading to the suspicion that these terms are unrealistically large.
On the axial heating of magnetically confined plasma with CO2 lasers
Authors: Lai C. S. , Madan M. P.
Published: April 2011

The equations governing the electron–ion heating in a CO2 laser heated plasma column confined by a solenoidal magnetic field are solved for a laser intensity law I = I0t2/3. It is shown that in addition to a set of solutions obtained by Offenberger, one more set of solutions exists, which is of considerable interest if shorter confinement time is desirable.
Measurements of the structure of the convection sustained ion sheath
Authors: Smy P. R. , Noor A. I.
Published: April 2011

Probe measurements throughout a planar convection-sustained ion sheath reveal that upstream of the sheath: (a) no appreciable diminution of ionization density occurs, unlike the stationary continuum situation, and (b), there exists an electric field which is approximately equal to the ratio of the flow velocity to the electron mobility. Downstream of the sheath edge, measurements of the fall off of the ion and electron densities are reported. The above measurements are found to be in satisfactory agreement with the sheath convection theory of Smy.
Ionization and dissociative ionization of CO2 by electron impact
Authors: Bussières N. , Marmet P.
Published: April 2011

Using a very sensitive apparatus with a high signal-to-noise ratio, new structures are observed in the ionization curve of CO2 by electron impact in the first 10 V above the ionization threshold. Neutral and negative ion levels are observed and related to npσu and npπu series converging to Ā, [Formula: see text], and [Formula: see text] levels of CO2+. Data for the fragment ions CO+, O+, and C+ are also presented; it is shown that they can be formed with zero kinetic energy. No ion pair formation can be detected at threshold.
Rayleigh volume scattering coefficients for Freon-12, Freon-22, and sulphur hexafluoride
Authors: Harrison A. W.
Published: April 2011

Rayleigh volume scattering coefficients have been measured for Freon-12 (CCl2F2), Freon-22 (CHClF2), and sulphur hexafluoride (SF6) relative to air using an integrating spectronephelometer. The relative scattering ratios obtained are 15.78 ± 0.17, 7.69 ± 0.08, 6.79 ± 0.07, and 1.00, respectively, for CCl2F2, CHClF2, SF6, and air.
Dielectric dispersion and relaxation mechanism in some trichloro esters at microwave frequencies
Authors: Purohit H. D. , Sharma H. S. , Vyas A. D.
Published: April 2011

The permittivity and dielectric loss of three trichloro esters, namely methyl trichloroacetate, ethyl trichloroacetate, and n-propyl trichloroacetate have been measured at frequencies 1 MHz, 9.83, 18.26, 24.50 GHz, and optical frequency at 35 °C. The permittivity and dielectric loss at different frequencies have been plotted against concentration (weight fraction). The slopes of these straight lines have been used for complex plane plots (a″ vs. a′). There are two possible relaxation processes in these molecules, i.e. overall rotation of the molecule and intramolecular group rotation —CCl3 around C—C bond. Whereas the relaxation time for overall rotation is dependent on temperature the relaxation time for group rotation is practically independent of temperature.
Dielectric relaxation in CH3X molecules at radio frequencies
Authors: Struk Robert S. , Armstrong Robin L.
Published: April 2011

Measurements are reported of the dielectric susceptibility for the series of CH3X molecules with X ≡ F, Cl, Br, I, (CN). A differential type oscillator operating at 48.15 MHz with 1 part in 108 short term stability was constructed for the experiments. Data were taken at a temperature somewhat above ambient and for densities between 0.001 and 1.0 amagats. For each gas a Debye lineshape was observed. The effective diameters for molecular reorientation that were deduced are in reasonable agreement with earlier results obtained at microwave frequencies with the exception of that for CH3(CN). A theoretical prediction that the addition of a Stark field perpendicular to the radio frequency field would significantly modify the Debye lineshape was put to the experimental test. The result was negative.
A comparison of the spectral features of the collision-induced light scattering by the molecular gases CH4 and CF4 and by argon
Authors: Barocchi F. , Zoppi M. , Shelton D. P. , Tabisz G. C.
Published: April 2011

The collision-induced light scattering from compressed gaseous CH4 and CF4 has been observed at room temperature at densities up to 100 and 166 amagats, respectively. Absolute intensity measurements have been made and the two- and three-body components to the spectra have been identified. A detailed comparison is made with similar data on argon and significant differences emerge between the atomic and molecular cases. The two-body molecular spectra contain an excess of intensity over predictions of the dipole–induced-dipole (DID) model; the argon intensity is less than predicted. At low frequency, the two- and three-body spectra of all species are dominated by the DID interaction. At high frequency the two-body molecular spectra decay much more slowly than the profile due to argon. A moment analysis has been performed wherein the pair polarizability is assumed to be of the form, β(r) = 6α2/r3 + B/rp. The unknown parameters B and p are determined from the experimental zeroth and second moments of the spectra. For the molecules B is found to be greater than unity and p is 7.2 for CH4 and 8.5 for CF4. The difference in the values of B and p, together with the fact the shape of the high frequency tail is not consistent with pure translational broadening, lead to the suggestion that the internal degrees of freedom of the molecules are playing a role in the scattering process.
A classical field model for charged particles
Authors: Nash G. , Schiff H.
Published: April 2011

A classical field model is proposed, involving a scalar field interacting with the electromagnetic field, that has discrete particle-like solutions corresponding to any desired mass spectrum, all such solutions having exactly the same electric charge.
Electroproduction of low energy π+ from 3He
Authors: Asai J. , Tomusiak E. L.
Published: April 2011

A simple model is used to calculate cross sections and angular distributions for the reactions 3He(e,π+)e′T and 3He(e,T)e′π+. In addition to strictly numerical computations a test of the forward peaking approximation is made. Comparison with existing data shows that the threshold operator for π+ production appears as a good approximation (for 3He) for pion energies up to about 30 MeV.
Réactions 3He + 9Be, d + 10B → 3α et excitation du 12C dans la région 29–34 MeV
Authors: Goulard G. , Roy R. , Slobodrian R. J.
Published: April 2011

Excited states of 12C between 29 and 34 MeV are studied through the 3He + 9Be and d + 10B reactions leading to three α particles in the final state. Correlated energy spectra are analyzed with a two-stage process and new information is given about the studied excited energy region.
Non-pair forces and lattice dynamical properties of hexagonal close-packed lattice
Authors: Mishra S. K. , Kushwaha S. S.
Published: April 2011

Cadmium is a highly anisotropic hcp metal like zinc. It has an axial ratio (c/a = 1.8855) that is much higher than the ideal axial ratio for the hcp structure. The successful study of the lattice dynamical properties of Zn and Tl by the modified Cheveau model has created an interest in studying the phonon dispersion relations and specific heat of cadmium. The computed results are in reasonably good agreement with the experimental results.
On ion-acoustic plasma waves in radio aurora and the two-stream instability
Authors: Haldoupis Christos , Sofko George
Published: April 2011

Experimental results based on 42.1 MHz CW radio auroral backscatter and ground magnetograms are used to test the validity of the two-stream instability as a causal scattering mechanism in radio aurora. Spectral studies yield considerable evidence that the two-stream instability mechanism may operate to a limited extent (~ 10–15% of the echoes) in the auroral plasma. For these echoes, which last short periods of time (approximately a few minutes), averaged power spectra show that the Doppler spectrum is dominated by a strong narrow peak due to irregularities moving with a mean radial speed in the 380–510 m/s range. The position of the peak is found to be unchanged for different observation times and azimuth angles. Occasionally, the narrow peak can coexist with a broad long-lived spectral component centered closer to zero shift position. The vast majority of the ion-acoustic echoes occur around local midnight and are associated with strong scatterers moving southward. Ground magnetometer data indicates that (1) there are sudden current intensifications during the time the ion-acoustic echoes are observed, (2) the direction of the current is appropriate for generation of plasma waves propagating along the radio signal line-of-sight, (3) the echoes seem to originate from the vicinity of the Harang discontinuity. Finally, the experimental evidence suggests strongly that the linearized theory is inadequate in explaining the behaviour of the unstable plasma waves.
Band structures in 95Tc
Authors: Marshall K. A. , Thompson J. V. , Cook W. B. , Johns M. W.
Published: April 2011

The (α,2nγ) reaction has been used to study high momentum states in 95Tc. Gamma ray singles excitation functions, angular distribution functions, γ–γ coincidence probabilities, and internal conversion coefficients were determined for a large number of transitions. In addition to a number of low spin levels that are strongly populated in proton induced reaction, the alpha induced reaction populates a positive parity sequence levels at 882 (13/2), 857 (11/2), 1516 (17/2), 1550 (15/2), 2184 (19/2), 2548 (21/2), 2908 (23/2), 3517 (25/2), 3919 (29/2), and 4293 (27/2) keV together with a negative sequence of levels at 39 (1/2), 668 (5/2), 1214 (9/2), 1702 (13/2), 2213 (17/2), 3024 (21/2), 3822 (25/2), 4128 (27/2, 29/2), and 4972 (29/2). The spins are assigned on the basis of internal conversion measurements and angular distributions.
Calculations of the spin susceptibility and the electronic thermal effective mass of Be and Mg by spin density functional theory
Authors: Wilk L. , Fehlner W. R. , Vosko S. H.
Published: April 2011

The spin-density functional theory was used to calculate the electronic thermal effective masses (including electron–electron interactions) and the spin susceptibilities (via a variational principle) for beryllium and magnesium. The necessary exchange-correlation functionals were treated in the local-spin-density approximation. The single-particle electron states were calculated by the augmented-plane-wave method using a self-consistent muffin-tin potential. It was found that the calculated thermal effective masses agreed very well with semi-empirical results from fits to the Fermi surface. We conclude that the accepted values of the electron–phonon mass enhancement parameter λep are too large by approximately 50%. The theoretical spin susceptibiltiy for Be was found to be 0.47 × 10−6 (cgs volume units), in marked disagreement with the experimental values. For Mg we obtained the value 1.65 × 10−6 (cgs volume units).
Short term characteristics of ion-acoustic type radio auroral echoes
Authors: Haldoupis Christos , Sofko George
Published: April 2011

Digital demodulation techniques and spectral analysis are used to study the short term (<1 s) characteristics of the ion-acoustic radio auroral echoes. Examination of 0.4 s time sequences indicates that the signal amplitude undergoes a deep and quasi-periodic fading with strongly marked periodicities in the 2–10 Hz range. Evidence shows that the fading is not due to interference but to the appearance and disappearance of independent scatterers, causing a sequence of backscatter signal bursts. If the assumption is made that these scatterers are longitudinal plasma density waves, the observed signal fading can be interpreted in terms of the growth and decay of individual regions of plasma instability rather than as interference between signals from separated coexisting scattering regions. Investigation of a large number of records suggests the following features for the irregularities associated with the ion-acoustic echoes: (1) their lifetime is in the 0.05–0.25 s range. (2) their growth (or decay) rate is in the 10–60 s−1 range, (3) their velocity remains fairly constant, even during growth and decay, and is always within the ion-acoustic velocity range in the medium.
Essai sur les configurations d'équilibre des complexes moléculaires en phase gazeuse (HCl)2, HCl—DCl, HCl—HBr, HCl—DBr et HCl—HI, à partir de leurs spectres d'absorption au voisinage de 3.5 μm
Authors: Larvor M. , Houdeau J.-P. , Haeusler C.
Published: April 2011

Spectra observed, under certain conditions of temperature, pressure, and absorption path, between rotation–vibration lines of the fundamental band of HCl, either pure or mixed with DCl, HBr, DBr, or HI, can be assigned either to the dimer (HCl)2 or to the molecular complexes HCl—DCl, HCl—HBr, HCl—DBr or HCl—HI. The nature of the observed spectra, along with calculations of the energy of interaction between two associated molecules and of the shifts in the spectra of associated HCl vibrators allow us to propose models that correspond, for (HCl)2 and HCl—DCl, to 'orthogonal' and 'antiparallel' configuration, and only to 'orthogonal' configurations for the other complexes.[Journal translation]
Diffusive motions of water molecules near 1 °C
Authors: Irish J. D. , Graham W. G. , Egelstaff P. A.
Published: April 2011

Neutron (quasi-elastic) scattering experiments have been carried out to investigate the effects of temperature and pressure on the motion of molecules in liquid H2O. Spectra were obtained at several temperatures between −10 and +24 °C at atmospheric pressure, and also at +1 °Cand 1.42 × 108 Pa. The root-mean-square amplitude of proton motion in solid and liquid H2O at atmospheric pressure has been inferred from measurements of the Debye–Waller factor and is nearly constant at 0.07 nm for both the solid and liquid. A model in which the translational diffusion and rotational diffusion are based on Brownian motion was fitted to our data using published diffusion coefficient data. The structure breaking time was found to be very small at 1 and 10 °C. Both these conclusions are compared with those reported in several earlier papers, which gave varying results.The spectrum measured at 1.42 × 108 Pa was slightly broader than the corresponding spectrum at atmospheric pressure, probably indicating that the well-known minimum in the viscosity at this pressure is due to a structure breaking effect.
Evolution of stimulated Brillouin to stimulated ion Compton scattering in a CO2 laser – plasma interaction experiment
Authors: Offenberger A. A. , Ng A. , Cervenan M. R.
Published: April 2011

Strong backscatter [Formula: see text] has been observed in the interaction of focused CO2 laser radiation (I ~ 1012 W/cm2) with a hydrogen gas target plasma. Spectral measurements show it to arise from stimulated ion Compton scattering (SCS) at later times when the electron–ion temperature ratio is not large. The scattering growth rate γ was determined experimentally to be 3.4 × 1012 s−1, in good agreement with theoretical predictions for our plasma parameters. Temporal modulation of the backscatter clearly shows build-up and decay of SCS during the interaction time. It may be anticipated that such scattering will be important in laser–pellet fusion experiments.
Threshold conditions for the onset of cavitation
Authors: Wentzell R. A. , Lastman G. J.
Published: April 2011

A mathematical criterion for determination of the threshold radius for cavitation of a bubble within a viscous liquid is developed. This criterion leads to a difficult two-point boundary-value problem that cannot be solved in closed form. A lower bound on the threshold radius is computed by considering the special case of an inviscid fluid. By consideration of the equilibrium solution an approximate value of the threshold radius can be computed. These estimates agree well with the values determined by numerical integration of the differential equation describing the bubble's motion. They are also better estimates of the threshold radius than those previously obtained.
Absolute calibration of the helium gas jet noise source
Authors: McBride S. L. , Hutchison T. S.
Published: April 2011

A helium gas jet produces a convenient and reproducible localized (point source) displacement spectrum over the frequency range 0.2–1.0 MHz. The calibration spectrum has a maximum value of 10 Å at 200 kHz and decreases approximately logarithmically with increasing frequency to about 0.2 Å at 0.8 MHz. Comparison of a detected voltage spectrum for an acoustic emission event with the helium gas jet system spectrum permits the displacement amplitude spectrum of the acoustic emission source event to be determined using the calibration spectrum. The source event spectrum thus obtained can be transferred between different systems via the helium gas jet system spectra.The knowledge of the actual localized displacement spectrum associated with an acoustic emission source event should permit quantitative deductions to be made about the relation between the observed acoustic emission signals and the micro-failure processes that give rise to the acoustic emission events.
Raman scattering from impurities in semiconductors. I. General result
Authors: Barrie Robert , Sharpe I. W.
Published: April 2011

A mathematical technique previously used for studying absorption and emission from impurity centres in semiconductors is applied to Raman scattering from such centres. The usual adiabatic approximation is not made. The method makes use of the fact that at most one electron can be bound at the impurity site and reduces the problem in a systematic fashion to the evaluation of traces over only phonon states. These traces are evaluated for a particular type of electron–phonon coupling.
Excited states of positronium in positron–hydrogen charge exchange
Authors: Kulhar V. S. , Shastry C. S.
Published: April 2011

The two state approximation method for the study of the rearrangement collisions is applied to the process of positronium formation in excited states for positron–hydrogen charge exchange collisions. Differential and integrated cross sections are computed for positronium formation in 2S, 2P, and 3S excited states. The results obtained in the energy region 2 to 10 Ry are compared with positronium formation cross sections in ground state. Total positronium formation cross sections including the contributions of capture into all the higher excited states of positronium are also computed in the first Born approximation and the two state approximation in the energy region considered.
Vacancy doping by off-stoichiometry in mercury chalcogenides
Authors: Fau C. , Calas J. , Averous M. , Lombos B. A.
Published: April 2011

The influence of cation and anion vacancies on the transport properties of mercury telluride was investigated. The off-stoichiometry created vacancies were introduced by annealing the samples under controlled mercury vapor pressure. Transport property measurements between 1.6 and 300 K with magnetic field intensities, increasing up to0.6 Wb m−2, supplied the data to be analyzed using a two band model. The vacancies in turn introduced slow or heavy electrons and at high enough vacancy concentration, holes were also introduced. The mobilities, concentrations of the light and heavy electrons, or holes, and their influence on the electrical characteristics of mercury telluride could be quantitatively evaluated.
Energy dependence of quark line rules and the quark rearrangement model
Authors: Kogitz S. , Logan R. K. , Tanaka S.
Published: April 2011

We argue that the possible energy dependence of the suppression factor in the quark rearrangement model might explain the energy dependence of the violation of the quark line rule.
The ν5 and ν6 fundamental bands of HDCO in the 9–11 μm region
Authors: Allegrini M. , Johns J. W. C. , McKellar A. R. W.
Published: April 2011

The ν5 and ν6 fundamental bands of formaldehyde-d1 vapour have been recorded by conventional infrared absorption spectroscopy with a spectral resolution of ~0.05 cm−1. The excited vibrational levels are strongly coupled by a- and b-type Coriolis interactions and must be analysed simultaneously. Such an analysis has been performed using the present results and the excited state microwave data, and the resulting band origins, rotational, centrifugal distortion, and Coriolis coupling parameters are given. The HDCO spectrum in the 9–11 μm region is of special interest since deuterium isotope separation has been demonstrated using 10.6 μm CO2 lasers. Because of this interest, the complete observed spectrum, a listing of observed lines, and some other lengthy tables are collected in an appendix to this work.
The ground state of two quantum models of magnetism
Authors: Oitmaa J. , Betts D. D.
Published: April 2011

The ground state energy and pair correlations have been computed exactly for the spin [Formula: see text] XY magnet and isotropic Heisenberg antiferromagnet, for a sequence of finite cells on the square and honeycomb lattices. Precise estimates of the ground state energy of the infinite lattices are obtained by extrapolation. It is predicted that the XY magnet has a non-zero transverse magnetization and the Heisenberg antiferromagnet has a non-zero staggered magnetization in the ground state.
Variational study on the ground state of the spin XY magnet
Authors: Suzuki Masuo , Miyashita Seiji
Published: April 2011

An approximate wave function of the ground state of the spin [Formula: see text] XY magnet is derived using a variational method. This wave function yields estimates of the ground state energy and long-range order which agree very well with the results obtained by Betts and Oitmaa by a finite lattice method.
Empirical formulas for 14 MeV (n,p) cross sections
Authors: Pai H. L. , Andrews D. G.
Published: April 2011

Levkovskii's and Gardner's empirical formulas for 14 MeV neutron (n,p) cross sections can be shown to be mainly equivalent to the following approximation: [Formula: see text]subject to modifications from direct interaction. Here T is the nuclear temperature, given by 10/A1/2 and Vp′ is Dostrovsky's value of the effective Coulomb barrier. Qnp′ is the effective Q value calculated using the mass formula [Formula: see text]in which B and Z0/A are shell-independent parameters.
The 4s2S–4p2P transition of the Al sequence
Authors: Fischer Charlotte Froese
Published: April 2011

In the Hartree–Fock approximation the f-value trend for the 4s2S–4p2P transition of the Al sequence varies smoothly as the nuclear charge increases. The effect of the core is primarily a screening effect. However, when correlation with the core is included, 'accidental' degeneracies with other configurations at selected Z-values destroy the usually smooth trend and dips appear.The f-values for these transitions are presented and the various effects illustrated.
Sur l'existence d'une longueur élémentaire et d'un intervalle de temps élémentaire
Authors: Lacroix Robert
Published: April 2011

We have briefly examined several studies which have been made concerning the introduction of an elementary length l0 and an elementary time interval t0 into physical theories. We have discussed the arguments which we have found, arguments formulated by other authors, and which support the hypotheses concerning the existence of l0 and of t0. A finite difference equation is proposed and the solutions of some problems of movement in one dimension are given.
Dynamical theory of neutron diffraction
Authors: Sears V. F.
Published: April 2011

We present a review of the dynamical theory of neutron diffraction by macroscopic bodies which provides the theoretical basis for the study of neutron optics. We consider both the theory of dispersion, in which it is shown that the coherent wave in the medium satisfies a macroscopic one-body Schrödinger equation, and the theory of reflection, refraction, and diffraction in which the above equation is solved for a number of special cases of interest. The theory is illustrated with the help of experimental results obtained over the past 10 years by a number of new techniques such as neutron gravity refractometry, Pendellösung interference, and neutron interferometry.
Nonlinear wave equation for quantized frictional forces
Authors: Razavy M.
Published: April 2011

The close connection between the Jacobi function for a velocity-dependent dissipative system and the nonlinear Schrödinger–Langevin equation is used to study some of the features of the latter equation. Starting with the Hamiltonian for a classical system, different forms of the Jacobi generating function are obtained. With the help of these, corresponding solutions of the nonlinear wave equation are studied. It is found that the solution of the wave equation is not unique, and that it admits quasi-stationary, decaying, and asymptotically stationary solutions. Since this nonlinear wave equation is derivable from a classical generating function, it preserves some of the characteristic properties of the linear quantum theory. Among these are: (a) the lack of any correlation between noninteracting particles moving in a viscous medium, (b) the gauge independence of the observable quantities, and (c) the constancy of the density of states in phase space. This discussion can also be extended to the problem of quantal description of a harmonically bound radiating electron.
The g-factors of cross-conjugate nuclei
Authors: Taylor T. , Cameron J. A.
Published: April 2011

The g-factors of cross-conjugate pairs of states are shown to be simply related. The data for 1f7/2 nuclei are consistent with theory except for the g-factor of the 308 keV 2+ state of 48V which has been remeasured by a time-integral perturbed angular distribution technique. The inconsistency is confirmed.
Massless fermions coupled to N-pseudoparticle field: isospin
Authors: Viswanathan K. S. , Yee Jae Hyung
Published: April 2011

Adapting the spinorial formalism of Jackiw and Rebbi, we treat the problem of massless fermions of isospin [Formula: see text] in an N-pseudoparticle field. The Atiyah–Singer index theorem, applied to this problem, indicates the existence of 10N zero energy normalizable solutions. 3N solutions are explicitly constructed. The remaining 7N solutions are reduced to quadratures. We demonstrate the regularity and normalizability of these solutions.
Electronic states of a semi-infinite crystal with a surface impurity
Authors: Modinos A. , Oxinos G.
Published: April 2011

The electronic states of a model Hamiltonian representing a single impurity atom adsorbed on the surface of a semi-infinite crystal are described in general terms. The model potential field is constructed by abruptly terminating the potential of the infinite crystal at the surface and by replacing the potential outside the crystal by a constant. The adsorbed atom is represented by a spherical potential of the muffin-tin type superimposed on the constant potential on the vacuum side of the metal–vacuum interface. A method for evaluating the eigenvalues and eigenfunctions of this model Hamiltonian is presented.
Partially coherent far-field diffraction in the presence of primary astigmatism
Authors: Gupta A. K. , Singh K.
Published: April 2011

This paper deals with the study of intensity distributions and the encircled energy in the Fraunhofer diffraction patterns formed by an optical system with a circular aperture afflicted with primary astigmatism under partially space coherent illumination. The besinc form of the correlation function has been assumed for the mutual coherence function. Computed results are presented graphically in the midfocal plane to illustrate the degrading effects of various amounts of astigmatism on the image quality for several values of the coherence parameter. Peak intensity as a function of coherence parameter is also plotted.
Hydrogen atoms in the presence of a homogeneous magnetic field: a variational approach
Authors: Brandi H. S. , Koiller Belita
Published: April 2011

We propose a variational scheme to obtain the spectrum of the hydrogen atom in the presence of an external homogeneous magnetic field. We use two different sets of basis functions to diagonalize the Hamiltonian describing the system, namely, the eigenfunctions of the free hydrogen atom and of the three-dimensional harmonic oscillator, both having their radial coordinates properly scaled by a variational parameter. Because of its characteristics, the present approach is suited to describe the ground state as well as an infinite number of excited states for a wide range of magnetic field strengths.
Collision-induced microwave absorption in Ne–Xe and Ar–Xe gaseous mixtures at 2.3 cm−1
Authors: Dagg I. R. , Reesor G. E. , Wong M.
Published: April 2011

Collision-induced microwave absorption has been observed at 2.3 cm−1 for the inert gas mixtures Ne–Xe and Ar–Xe. The absorption coefficient has been measured at room temperature for a range of density products up to 15 000 amagat2 for different density ratios. The present results are compared with the results obtained earlier at 4.4 cm−1. The intracollisional absorption coefficient arising from two body interactions is approximately proportional to the square of the frequency for both mixtures. The intercollisional interference effects have led to a larger suppression of the absorption than was observed previously at 4.4 cm−1. An expression for the intercollisional line shape factor was used to fit the data. At high densities, there is observed a marked increase in the absorption which has also been observed at 4.4 cm−1 and which may be attributed to many body collisions.
Study of Hg6(3P0) → Hg6(3P1) excitation induced by collisions with N2, using a double modulation technique
Authors: Oka K. , Cvetanović R. J.
Published: April 2011

The 253.7 nm emission from N2 + Hg gaseous mixtures at 298 K, illuminated by double modulated 253.7 nm Hg resonance radiation, was measured by means of a photomultiplier coupled to a phase sensitive detector. The emission is composed of a fast and a slow decaying component. Since the 253.7 nm radiation was modulated simultaneously at two different frequencies, at 10 Hz and in the kilohertz region, it was possible to evaluate the fractional intensities of both the fast (DI) and the slow (DII) decaying component of the emission and, in particular, the decay rate (K) of the latter. Imprisonment of the 253.7 nm light affects both the decay rate of the slow decaying component of the emission and the ratio of the intensity of the total emission to that of its fast decaying component. However, the product of these two quantities, K(DI + DII)/DI, is independent of the light imprisonment effects and is directly related to the sum of the pseudo-first-order rate (k5[N2]) of the reaction Hg(3P0) + N2 → Hg(3P1) + N2 (reaction [5]) and of the rate (k′) of the consumption of Hg(3P0) in secondary processes. The latter appears to be very small since the total emission intensity is found to be independent of [N2]. The observed rate constants of the reaction Hg(3P2) + N2 → Hg(3P0) + N2 (reaction [3]) and of reaction [5] at 298 K are k3 = 4.1 × 10−12 and k5 = 2.1 × 10−15 cm3 molecule−1 s−1. The potential uncertainties in these values are estimated to be less than about 15%.
Méthode tensorielle de calcul des intensités de diffusion hyper-Raman d'une molécule XY4 tétraédrique
Authors: Pascaud E. , Poussigue G.
Published: April 2011

The development of high power pulsed lasers has permitted the observation of nonlinear light scattering phenomena, in particular the molecular hyper-Raman effect. The wave numbers of hyper-Raman transitions can be predicted simply from the energy differences between known levels. For the intensities, however, it is necessary to devise a well-adapted method of calculation.Hilico, Berger, and Loete have developed a tensor formalism in the (m)O(3) × (F)O(3) group, for the calculation of microwave, infrared, and Raman intensities from XY4 tetrahedral molecules. In this paper, we extend the formalism to a G × (F)O(3) subgroup and make it applicable to the case of hyper-Raman transitions.A general expression for the hyper-Raman intensities of any molecule is given. In the case of XY4 tetrahedral molecules, where a tensor extension to the (m)O(3) × (F)O(3) group is possible, we give the intensity formulas line by line and band by band for the simplest cases.[Journal translation]
Nonequilibrium ensembles of self-organizing systems: a simulation study
Authors: Lumsden Charles J. , Trainor L. E. H.
Published: April 2011

Ensemble methods from nonequilibrium statistical mechanics are applied to certain self-organizing models important in biological physics. The investigation uses computer simulation and graphics techniques to analyze the dynamical properties of the nonequilibrium ensembles. Both short- and long-term evolutions are studied. Qualitatively new features of the 'biological statistical mechanics' relevant to each model are characterized, and significant conclusions are obtained regarding the applicability of methods from physical statistical mechanics in cross-disciplinary fields. Of particular interest is the need in such applications for principles of preferred states to replace the axioms of conserved equal a priori probabilities.
Photoelectric cross sections derived from the total absorption cross sections in the energy range 5–130 keV
Authors: Puttaswamy K. S. , Gowda Ramakrishna , Sanjeevaiah B.
Published: April 2011

Total absorption cross sections in the elements C, Al, S, Cu, Zr, Ag, Sn, Ta, Au, and Pb for photons of energies 5.0, 5.9, 6.4, 8.1, 10.6, 14.4, 24.7, 32.9, 36.9, 66.6, and 129 keV are measured using a krypton-filled proportional counter in the energy range 5 to 25 keV and a thin NaI(Tl) detector in the energy range 30 to 130 keV. The measured total absorption cross sections are compared with those of Miller and Greening and McCrary, Plassman, Paekett, Conner, and Zimmermann. The scattering cross sections obtained by interpolation using the Atomic Data Tables are subtracted from the total cross sections to obtain the photoelectric cross sections and these are further compared with the recent theoretical values of Scofield.