bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleus?Nucleus Elastic Scattering at Ultra-high Energies
Authors: Li Yang-guo , Lo Shui-yin
Published: June 2013

Nucleus-nucleus elastic scattering at ultra-high energy is studied within the scheme of Glauber multiple scattering and also within the geometrical picture of the Chou-Yang model. Both models offer a reasonable explanation of a recent CERN experiment on a-a elastic scattering and their differences are discussed. Results are presented for (X-a elastic scattering at ultra-high energies, and for a-9Be, a_1 2C, a_1 60 and a_24Mg elastic scatterings at currently accessible energies. The A dependence of the total cross section is approximately An with n ~ 0�55.
Comment on the Brans?Dicke?Kasner Solution
Authors: Lorenz-Petzold D
Published: June 2013

We point out that the Brans-Dicke-Kasner solution recently given by Johri and Goswami (1983) is nothing but the general Bianchi type-I vacuum solution first given by Ruban and Finkelstein (1972).
A New Look at Radio Supernova Remnants
Authors: Mills BY , Turtle AJ , Little AG , Durdin JM
Published: June 2013

Catalogues are presented of radio supernova remnants in both Large (LMC) and Small (SMC) Magellanic Clouds together with maps of the LMC remnants prepared at a frequency of 843 MHz and with a resolution of 43 x 45 arcsec. The 38 confirmed remnants are believed to represent a reasonably complete sample for diameters less than about 40 pc although the LMC catalogue is probably very incomplete for larger diameters. The supernova remnants (SNRs) are compared with the Galactic remnants in the catalogue of Clark and Caswell (1976) and they are found to be similar in many ways. In particular a distance scale derived from the Cloud SNRs reproduces well the mean distances of directly measured Galactic calibrators. The usual model of a SNR expanding adiabatically from a small diameter is not supported by the statistics of the numberdiameter relation which suggest that rapid expansion up to quite large diameters is common. The physical implications are discussed. A supernova rate of about four per century is derived for the Galaxy and about one per century for the two Magellanic Clouds combined.
Molecular Dynamics Simulations of Liquids
Authors: L Tallon Jeffery , MJ Cotterill Rodney
Published: June 2013

The atomic-level computer simulation technique of molecular dynamics is reviewed and its application is illustrated by the insights obtained in some current problems in the physics of liquids. These include melting in two and three dimensions.
Extinction in Polycrystalline Materials
Authors: Sabine TM
Published: June 2013

An expression is given for an extinction factor appropriate to powders composed of spherical perfect crystal grains or subgrains. This factor extrapolates to the dynamical theory value for the plane parallel plate in the symmetric Bragg case. Experimental tests of the theory have been made by nelitron diffraction experiments on polycrystalline specimens of MgO of controlled grain size. Agreement is excellent to an extinction level of y = 0�60.
Self-draining Manifolds for Solar Collectors
Authors: McPhedran RC , Onley IC , McKenzie DR , Collins RE
Published: June 2013

We consider manifolds for solar collectors capable of self-draining action as a means of freeze protection. We study a number of single- and double-header designs, both in the context of domestic and industrial installations. We present both simple theoretical models and experimental results for various promising manifold designs, indicating optimal choices for key design parameters.
The Formation Energy of Point Defects in Ionic Crystals
Authors: Runcima WA , Srinivasan B , Richardson DD
Published: June 2013

Simple calculations have been made of the formation energy of different types of defect centres such as those formed by hexavalent uranium introduced into lithium fluoride in an oxygen atmosphere. The Coulomb energies are compared for different configurations of the same defects. The method of calculation is described and results quoted for configurations including, in addition to oxygen ions, (a) a uranium ion and a divalent positive ion, (b) a uranium ion and a negative-ion vacancy and (c) two uranium ions.
Global Oscillations and Active Regions
Authors: Durrant CJ
Published: June 2013

We present further estimates of the amplitude of the modulation of the solar global velocity signal caused by the passage of active regions across the solar disc. Using measurements of the profile of the K I It 769�9 nm line in the quiet Sun and in plages we find a global velocity variation of ~ 2 m s - 1 during the transit of a typical active region of area 3300 millionths of the hemisphere. However, during the period in which a velocity amplitude of 6 m s - 1 was reported by Claverie et al. (1982), the sunspot areas were exceptionally large and we confirm Schroter's (1984) result that the combination of spot 'and plage contributions is sufficient to account for the observed signal. The velocity modulation is thus attributable to surface inhomogeneities, not to the structure of the solar core.
Experimental Aspects of the Electroweak Gauge Theory
Authors: G Clark Allan , N Tovey Stuart
Published: June 2013

A review is given of experimental tests that have been made on the validity of electroweak gauge theory and in particular on the validity of the Glashow-Salam-Weinberg model of the. weak and electromagnetic interactions. In addition to data from the CERN pp Collider, we briefly discuss tests of the model in neutrino-electron, neutrino-hadron and charged-lepton-hadron interactions
Polarisation and Angular Correlations of Excited P States of Helium and Hydrogen
Authors: Williams JF
Published: June 2013

The techniques associated with angular and polarisation correlations have been used to study the electron impact excitation of the 21 P state of helium and the 2P state of hydrogen. The circular, and linear, polarisations of the 58�4 and 121�6 nm radiation have been measured with a double reflection analyser. The measurements have better statistical accuracy than previous work and, for helium at 81�2 eV and a large scattering angle of 108�, confirm that theoretical values are still outside the statistical accuracy of measurement. In hydrogen, the first complete determination of the elements of the 2P density matrix elements is reported. The parameters fl., Re, Im and the absolute value of 0'(2p) have been measured. No single theory is able to predict the scattering angle dependence above 70�.
Auger Electron?Ion Coincidence Studies to Determine the Pathways in Soft X-ray Induced Fragmentation of Isolated Molecules
Authors: Eberhardt W , Plummer EW , Whan Lyo In , Reininger R , Carr R , Ford WK , Sondericker D
Published: June 2013

We report a coincidence .experiment between energy selected Auger electrons and the ions produced in the events following the absorption of a soft X-ray photon by a CO molecule. This study allows us to correlate specific double hole final state configurations of the Auger decay of a core hole in this molecule with the production of fragment ions, thus giving new experimental insight into the potential energy curves of the doubly charged molecular ion and the involvement of individual valence electrons into the molecular bond in general.
X-ray Emission Spectra of Some Carbon-containing Molecules
Authors: Phillips RA , Larkins FP
Published: June 2013

Ab initio molecular orbital calculations for the energy and intensity of X-ray transitions associated with the carbon monoxide, hydrogen cyanide and carbon dioxide molecules have been calculated at the Hartree-Fock level. It is demonstrated that in general the absolute transition probabilities are sensitive to the inclusion of electronic relaxation effects and interatomic transition moment contributions. It is concluded that calculations for molecular X-r!ly emission henomena should be undertaken at least at the multicentre relaxed Hartree-Fock level to achieve a realistic basis for comparison with experiment. Total carbon-K X-ray rates do not show a strong variation with changes in the molecular environment. The total rates are of a similar magnitude to those reported for the atom. The calculated carbon-K fluorescence yield is also similar in both the carbon atom and the CO2 molecule.
Photoionisation of Unusual States of Matter: Atomic Ions, Excited States and Open-shell Atoms
Authors: T Manson Steven , K Bhattacharya Samir
Published: June 2013

Our understanding of the photoionisation of ground states of closed-shell atoms is fairly good. The situation is otherwise for open-shell atoms and for ions and excited states throughout the periodic table. Nevertheless, a number of interesting effects have been predicted theoretically in these unusual states of matter. In this paper, some of these predictions, not yet tested by experiment, shall be discussed, along with their implications.
Deexcitation Electron Spectroscopy: A Probe for the Localisation of Valence Wavefunctions in Free and Adsorbed Molecules
Authors: Eberhardt W , Plummer EW , Chen CT , Ford WK
Published: June 2013

Deexcitation electron spectroscopy (DES) is the measurement of the kinetic energy distribution of electrons emitted in the decay of highly excited states of molecules formed by core to bound resonant photon absorption. This spectroscopy has the potential of becoming a new probe of the localised properties of the valence electronic states in molecules as well as furnishing new insights into the dynamics of the electronic decay and screening processes. This paper describes the basic principles of DES by following the evolution of the DES spectra in CO, from the isolated CO molecule in the gas phase, through the transition metal carbonyls, to CO adsorbed on a surface. In all three cases the energetics, intensities and dynamics of DES will be compared with photoelectron spectroscopy (PES) and Auger electron spectroscopy (AES).
Magnetic Moments of Baryons in a Relativistic Constituent Quark Model
Authors: Tupper NE , McKellar BHJ , Warner RC
Published: June 2013

We utilise the light-front dynamical formalism to compute the magnetic moments of baryons in a relativistic constituent quark model, investigating the dependence of the results on the mass of the constituent quarks and on the size of the hadron.
Experimental Study of the Phase Transition in (CH2)8(NH3)2FeCl4-xBrx(x = 0, 1 and 2)
Authors: Ahmed MA , EI-Desoky MM , Radwan FA
Published: June 2013

The dielectric constant E and the pyroelectric current I p for the compounds (CH2)S(NH3hFeCI4_xBrx (x = 0, 1 and 2) have been measured in the range from the liquid nitrogen temperature up to near the melting points. Measurements of the dielectric constant have been carried out at various frequencies. A calculation of the electric dipole moments at the background and transition points is given. Calorimetric measurements have also been carried out and the values of the enthalpy change I::.H and entropy change I::.S are also reported.
Nonlinear Instability of Ion-cyclotron Whistlers in the Ionosphere
Authors: Chakraborty B , Sur AK , Paul SN
Published: June 2013

The papers in this special issue of the Australian Journal of Physics were presented at an International Symposium on X-ray Powder Diffractometry in Fremantle, Western Australia, in August 1987. The Symposium, with 160 participants, followed the Fourteenth Congress of the International Union of Crystallography in Perth.
Powder Diffractometry at the Tsukuba Photon Factory
Authors: Uno R , Ozawa H , Yamanaka T , Morikawa H , Ando M , Ohsumi K , Nukui A , Yukino K , Kawasaki T
Published: June 2013

Powder dift"ractometry at the Photon Factory has been carried out with a diffractometer specially designed for measurements on molten salts, liquids, amorphous solids and polycrystalline materials. The main work done with the diffractometer has been structure analysis, and the study of phase transitions at high pressure and high temperature on Ge02' In 1986 a new powder diffractometer was designed and constructed. The aims of the new diffractometer are to allow easy alignment and provide sufficient accuracy for measurements taking advantage of anomalous dispersion and also to provide for energy dispersive diffractometry. The basic features are described.
Accurate Charge Density-Pendellosung Methods
Authors: Kato Norio
Published: June 2013

We review various Pendellosung methods for the determination of crystal structure factors. Historical matters and the methodological principles are emphasised. We also describe the current state for the case of Si. Some deformation maps based on our recent experiment (Saka and Kato 1986) are presented. It is pointed out that the real part of the anomalous dispersion term has to be determined more accurately.
Structure Factor Determination in Surface X-ray Diffraction
Authors: Robinson LK
Published: June 2013

A set of formulae is derived for correcting integrated diffraction intensities for surface structure analysis. These differ significantly from their bulk counterparts because of the diffuse nature of the peaks. In-plane and out-of-p1ane data collection are treated separately. Measurements of W(OOl) surface diffraction are used as a case study.
Accurate Determination of Structure Factors by Pendellosung Methods Using White Radiation
Authors: Takama T , Sato S
Published: June 2013

This paper describes two experimental techniques measuring the Pendellosung beats using white radiation, developed in the authors' laboratory. The intensity of a Laue spot diffracted from a parallel-sided single crystal is successively measured at different Bragg angles, i.e. with different wavelengths. The values of structure factors are evaluated from extremum positions in the measured beats on the basis of the dynamical diffraction theory. In the first method, the integrated intensity diffracted from the whole exit surface is measured, and in the second, the measurement is made only at the centre of the Borrmann fan on the exit surface of a specimen. A discussion is given on the accuracy associated with the following origins of errors: (1) polarisation of incident white radiation, (2) measurement of specimen thickness, (3) measurement of wavelength, (4) determination of extremum positions, and (5) effect of defects in the crystal.
Experimental Investigation and R-matrix Analysis of Low-lying Levels in 5He and 5Li
Authors: Woods CL , Barker FC , Catford WN , Fifield LK , Orr NA
Published: June 2013

The ~cle-unstable nuclei SHe and Su have been studied via the 4He<,U,6U)SHe and 4He( Li,6He)SU stripping reactions at beam energies of 50 MeV and the 6U(12C, 13N)SHe and 6Li(13C, 14C)SU pickup reactions at 90 MeV. The experimental data clearly demonstrate a dependence of the lineshapes on the method of production of the mass-5 nuclei (in this case pickup or stripping). The observed lineshapes were analysed using the R-matrix formalism in a two-level approximation for each r value, with parameter values deduced from fits to the available 4He + nucleon scattering data. A best channel radius of 5�5 � 1� 0 fm was determined from the stripping data, and the corresponding set of R-matrix parameters also provided a satisfactory description of the pickup data. This channel radius is significantly larger than that employed in most previous analyses. Properties of the lowest ~ - and ! - sta~s of SHe and sU, observed via direct reactions, ate deduced from the parameter values. These properties are compared with results from earlier experimental analyses and the inferred properties of positive-parity states are compared with the results of recent shell-model calculations.
Pseudopotential Calculations for Li2, Na2 and NaLi
Authors: Andriopoulos N , von Nagy-Felsobuki EI
Published: June 2013

A valence-electron only model potential (V ALMOP) pseudopotential method has been developed utilising the GAUSSIAN 76 integral packages. VALMOP and the reference ab initio potential energy curves have been calculated for the ground electronic state of Li2, Na2 and NaLi using a number of different basis sets. Comparisons indicate that V ALMOP accurately reproduces internuclear bondlengths, valence orbital eigenvalues and, moreover, the shape of the all-electron potential energy curves over a large range of bondlength R.
A Study of the Vibrational Excitation of H2 by Measurements of the Drift Velocity of Electrons in H2−Ne Mixtures
Authors: England JP , Elford MT , Crompton RW
Published: June 2013

Measurements of electron drift velocities have been made in 1�160% and 2�892% hydrogen-neon mixtures at 294 K and values of EI N from 0�12 to 1�7 Td. The measurements are highly sensitive to the region of the threshold of the v = 0 → 1 vibrational excitation cross section for hydrogen and have enabled more definitive tests of proposed cross sections to be made than was possible using drift velocity data for H2−He and H2−Ar mixtures. The theoretical v = 0 → 1 vibrational excitation cross section of Morrison et al. (1987) is shown to be incompatible with the present measurements. A new set of hydrogen cross sections has been derived from the available electron swarm measurements in pure hydrogen and hydrogen mixtures.
Renormalisation of g-boson Effects in an s-d-g Boson Model
Authors: Amos K , Chen XJ , Dieperink AEL , Morrison I
Published: June 2013

A renormalisation method is developed in which g-boson coupling effects in a transformed Hamiltonian are minimised. The unitary transformation upon which this is based is that proposed by Otsuka and Ginocchio (1985). The conditions under which the g-boson coupling is eliminated are specified under various approximations and resulting spectra are compared with the exact ones obtained from diagonalisation of an exact s-d-g boson Hamiltonian.
Lunisolar Atmospheric Tides: A New Approach
Authors: Brahde R
Published: June 2013

In records of the atmospheric pressure in Oslo, at 60' latitude, a one-day oscillation caused by the lunisolar tide has been detected. The amplitude has a mean value of O� 17 mb. This oscillation appears during intervals when the declination of the Moon has high numerical values. When the Moon passes through the equator, the one-day oscillation disappears and only the half-day mode continues. If a maximum coincides with upper culmination, it reappears during the next fortnight at lower culmination. This means that the phase changes approximately 180' or 12h every time the Moon crosses the equator, and this is the main reason why it has not been detected by means of traditional harmonic analysis of the atmospheric pressure oscillations. By means of the correlation between the pressure variation and the magnitude of the tidal acceleration, it was possible to separate the dynamic one-day oscillation from terms of thermal origin.
Characteristic Features of Vector Chaos
Authors: Delbourgo R , Zhang RB
Published: June 2013

Quadratic maps of a vector, depending on a vector parameter and any number of scalars, can be reduced to the transformation x ~ ax(l - x) + dy2 and y ~ h(c - x)y, where d = 0, 1 or -1. Such a (3-parameter) set of transformations possesses an extremely rich structure. We have determined the Julia and Mandelbrot sets of this system and have delineated the characteristic types of x-y motion as well as the transition from one regime to the next.
Raman Spectrum of Rubidium Thiocyanate at 37 K and Room Temperature
Authors: Joyce MJ , Ninio F
Published: June 2013

The single crystal Raman spectrum of RbSCN from 0 to 2200 cm-l was studied between 37 K and room temperature. A new eak was observed in the B2g polarisation and is believed to be an external mode. The low temperature data indicate that previous interpretations of the external modes are in error. A new classification of these modes is given. Further, whereas the internal modes are in agreement with previous studies, some multi phonon modes are not. The assumed isomorphism between bSCN and KSCN suggests a correction to the most recent interpretation of the spectrum
The Lyman a Forest in QSOs: A Window on Intergalactic Clouds at High Redshift
Authors: W Hunstead Richard , Pettini Max
Published: June 2013

It is now well established that the number density of Lya forest absorption lines evolves strongly with redshift. When combined with the observed exponential distribution of equivalent widths, this points to a steep dependence of H I column density on z. New information on the nature of the Lya clouds has recently been obtained from high-resolution AAT echelle observations (6.5 km S-l FWHM) of the QSO 2206-199N. Profile fits to unblended Lya lines in the interval Zabs = 2.103 - 2.587 have established a clear trend between the Doppler velocity dispersion b and column density N, suggesting that b is measuring large-scale motions within the Lya clouds rather than their temperatures. If correct, cloud temperatures (set by the lowest b values) are probably < 5000 K instead of the 30000 K usually assumed, implying that the clouds are predominantly neutral. Previous data at lower resolution are shown to be roughly consistent with the new b:N trend, after allowing for the evolutionary dependence of N on z. The new observations are difficult to accommodate within the conventional framework of pressure-confined, low-density, ionised clouds; instead, we suggest that the Lya clouds may be either in the form of dense, thin sheets or may be gravitationally confined.
Calculations on the Cosmic Ray Anisotropy above 1017 eV
Authors: Smith ACK , Clay RW
Published: June 2013

Possible trajectories of cosmic ray particles in our galactic magnetic field have been followed for various field models. It is found to be difficult to reconcile the observed low levels of cosmic ray anisotropy above 1018 eV with the modelled propagation. This strongly suggests a dominant extragalactic cosmic ray source at such high energies.
The General MCSCF Method with Full Symmetry Reduction
Authors: CJ Roothaan Clemens
Published: June 2013

A general multi-configuration self-consistent field (MCSCF) model is presented. The model permits the determination of wavefunctions for a collection of different physical states, achieves all possible group-theoretical reductions, and exhibits quadratic convergence.
Chiral Corrections for Lattice QCD
Authors: W Thomas Anthony
Published: June 2013

We show that in the quenched approximation, lattice QCD calculations miss important corrections to the mass of hadrons. For example, we argue that the nucleon mass is overestimated by up to 30% while the nucleon-delta mass splitting is underestimated by a similar amount. As the quenched approximation is relaxed, the quark mass decreased and the lattice size increased, these errors should go away. A systematic method of monitoring the size of the residual error is suggested.
Energy Dissipation Rates of Turbulence with an Airborne Microwave Refractometer
Authors: Sarma SBSS
Published: June 2013

Estimates of turbulence energy dissipation rates have been obtained in the free atmosphere of the planetary boundary layer. These are derived in terms of the variance of radio refractive index fluctuations {Lln2 }, the Brunt-Vaisala frequency N, the mean vertical gradient of generalised potential refractive index M, and the turbulence structure parameter C~, using an airborne microwave refractometer. The energy dissipation rates thus derived are comparable with the results from other experiments. The inferred energy dissipation rates (on a near real-time basis) from the airborne microwave refractometer. are useful for detection and warning of wind shears in the atmosphere.
Effect of Source Morphology on Thermal Radio Continuum Spectra
Authors: Calabretta Mark
Published: June 2013

The thermal radio continuum spectra derived from a selection of nebular models are compared. One class of models arises from three-dimensional distributions of emissivity, while the remainder are specified in a more abstract way. It is shown that the most important distinguishing feature between the models is the proportion of the nebular solid angle occupied by very faint emission. This finding is developed into a measure of nebular clumping. Practical aspects of the modelling are examined by applying a selection of the model spectra to the flux densities observed for the planetary nebula IC418.
Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model
Authors: McCann BT , Robson RE
Published: June 2013

A simplified, physically intuitive model of diffuse scattering of radio waves from a rough surface is used to present a self-contained derivation of first- and second-order cross sections, essentially in agreement with the standard expressions. Incoherent addition of the second-order contributions (electromagnetic and hydrodynamic) leads to a cross section which is slightly different from the more rigorously derived cross sections of Barrick (1972b) and Johnstone (1975). A surface current v has been incorporated in this model, with the main change to the cross section being a frequency shift of the entire spectrum by an amount Llw = -2ko . v.
Positronium Formation in e+ ?Na Scattering
Authors: Ranjit Singh N , Basu Choudhury Keka , Mazumdar PS , Brajamani S
Published: June 2013

The positronium formation cross section in positron-sodium scattering has been evaluated by employing a distorted wave approach in the low and intermediate energy region. The effect of the positronium� formation cross section on the total cross ection for positron-sodium scattering has also been discussed.
Nonlinear Wave Number Shift and Modulational Instability for Large Amplitude Waves in a Relativistic Magnetised Plasma
Authors: Mukhopadhyay J , Pakira G , Roy Chowdhury A
Published: June 2013

Properties of large amplitude waves in a relativistic magnetised plasma are studied using the method of reductive perturbation. The plasma under consideration consists of warm adiabatic ions and isothermal warm electrons, under the influence of a magnetic field. A onsideration of large amplitude waves demands study of the relativistic situation. In the present case we consider both the electrons and ions to be relativistic. A KdV equation is derived from which a nonlinear Schrodinger equation is deduced by further scaling. Lastly we derive an expression for nonlinear wave number shift, critical angle of propagation and the condition for modulational instability. Our analysis is applicable to both laboratory and space plasmas.
Determination of the Unit Cell for an Epitaxial Layer of Hg1-xCdxTe Deposited on GaAs
Authors: Nanchang Zhu , W Stevenson Andrew , Runshen Li
Published: June 2013

Stevenson et al. (1991) reported structural aspects of six metal organic chemical vapour deposition (MOCVD)-grown Hg1-xCdxTe epitaxial layers on novel GaAs substrates. Large layer miscuts (the angle between the surface and the Bragg planes of the nominal rientation) of 4�3� were reported for the samples of (311) and (3II) orientation, whereas the substrate miscuts were less than 1� (0�94� and 0�84� respectively).
Variational Wavefunctions for Non-compact U(1) Lattice Gauge Theory: Comparison with Exact Result
Authors: O'Shaughnessy D , Burden CJ
Published: June 2013

Estimates of the ground state wavefunction of (2+ 1 )-dimensional non-compact U (1) Hamiltonian lattice gauge theory are found in terms of variational wavefunctions with up to four parameters. These wavefunctions are compared with the exact ground state as a test of the accuracy of the method.
Minority Carrier Diffusion Lengths for High Purity Liquid Phase Epitaxial GaAs
Authors: Butcher KSA , Alexiev D , Tansley TL
Published: June 2013

Measurements of minority carrier diffusion lengths for p-type and n-type GaAs were carried out using an electron beam induced current (EBIC) technique. The GaAs material was grown by liquid phase epitaxy (LPE) at the Australian Nuclear Science and Technology Organisation. The diffusion lengths measured for high purity p-type and n-type LPE-GaAs samples were observed to be longer than any previously reported.
Lattice Dynamics of YBa2Cu3O6+x (x = 0·25, 0·5, 0.75)
Authors: Yim KK , Oitmaa J , Elcombe MM
Published: June 2013

The lattice dynamics of YBa2Cu306+x with partially filled 0(4) sites is investigated using a supercell method. The model used is the lattice-dynamical shell model, which incorporates the short-range interactions and the long-range Coulomb potential as well as the polarisabilities of ions. Varying the oxygen content produces small changes throughout the spectrum of normal modes, as well as major changes in those modes with large 0(4) amplitudes. Selected phonon dispersion curves are presented, with emphasis on the variation of frequency with oxygen concentration. The nature of new modes, which appear with an increase in oxygen concentration, is investigated. The overall phonon density of states is also presented.
Local-field Effects in the High-q-vector Dielectric Response of Si
Authors: Josefsson TW , Smith AE
Published: June 2013

The influence of microscopic or local fields on the full frequency- and wavevector-dependent dielectric loss function of Si has been calculated, based on accurate empirical pseudopotential calculations of the electronic structure. It is shown that local-field effects, dramatically significant at optical (q ~ 0) wavevectors, diminish with increasing magnitude of q to negligible proportions as q approaches the Brillouin zone boundary. In addition it is shown that the calculated volume-plasmon dispersion relation is improved in comparison with experimental results by the inclusion of local-field effects.
Consistent Treatment of Pion Exchange Force and Meson versus Quark Dynamics in the Nucleon?Nucleon Interaction
Authors: Liu GQ , Thomas AW
Published: June 2013

To distinguish explicit quark effects from meson exchange in the NN interaction, it is necessary to splice the long-range meson exchange forces and short-distance dynamics due to quarks. However, in most quark model studies the short-range part of the pion exchange is usually treated differently, which makes it difficult to get a uniform picture of the short-range dynamics. We make a comparison between meson exchange and quark-gluon dynamics using the same pion exchange potential based on a quark-pion coupling model. The roles of vector meson exchange and gluon exchange in the NN interaction are compared by calculating NN phase parameters. It is shown that, with this consistent one-pion exchange force, the vector meson exchange gives a better fit to the data. This suggests that non-perturbative mechanisms responsible for meson exchange may need more careful handling to supplement the usual one-gluon exchange mechanism in describing the NN interaction.
Staggered Magnetisation in the Heisenberg Antiferromagnet
Authors: CL Hollenberg Lloyd , J Tomlinson Michael
Published: June 2013

In the presence of a staggered magnetic field, the plaquette expansion of the Lanczos matrix elements are obtained for the antiferromagnetic 2D Heisenberg model up to order 1/Np (Np is the number of plaquettes on the lattice). The resulting approximate tri-diagonal form of the Hamiltonian is diagonalised for various values of the field strength in the -> 00 limit for the ground state energy density. From the behaviour of the ground-state energy density at weak fields, the staggered magnetisation at this order in the plaquette expansion is found to be 0�71 (in units where the Neel state staggered magnetisation is 1� 0).
The Early Years of Radio Astronomy at Caltech
Authors: L Greenstein Jesse
Published: June 2013

By the early 1950s astronomy in the United States was under pressure to embrace radio astronomy, which was being developed largely outside the USA. Much of the motivation derived from the need for accurate radio source positions, so that optical telescopes like the California Institute of Technology's giant Palomar Telescope and the nearby Mt Wilson Telescope could identify these sources with astronomical objects. To lead Caltech's move into radio astronomy its president, Lee DuB ridge, realised that he needed a leader from a country with more practical experience than the USA. He turned to his wartime friend E. G. 'Taffy' Bowen, chief of the CSIRO's Radiophysics Laboratory in Sydney, who 'loaned' him John Bolton. John stayed at Caltech for a bare five years, but it was a time of inspired guidance that helped to secure a place in radio astronomy, not only for Caltech, but for the USA.
John Bolton's Variable-baseline Interferometer and the Structure of Radio Galaxies
Authors: Ekers RD
Published: June 2013

John Bolton was a pioneer in the study of extragalactic radio sources, first at the CSIRO Radiophysics Laboratory and then at the California Institute of Technology's Owens Valley interferometer. I became his Ph.D. student after he returned to the Parkes Observatory from California, and I helped in the construction of the Parkes interferometer. This consisted of a 60-ft dish connected to the existing 210-ft dish by a flexible cable trailing from the 60-footer. The interferometer was used to observe continuously at 467 and 1401 MHz while the 60-ft dish was pulled along a track. The wisdom of the design is illustrated by comparing observations of Pictor A made at Parkes and at Owens Valley.
From the Parkes Catalogue to COMRAD
Authors: E Wright Alan
Published: June 2013

I present a brief description of John Bolton's work in establishing the Parkes Catalogue as the first of the major radio source databases. I also discuss how this Catalogue evolved over the years from a paper card format to a sophisticated computer database.
Cygnus A ? John Bolton?s First Cosmic Source
Authors: Harris DE
Published: June 2013

Using a sea interferometer, Bolton and Stanley isolated Cygnus A as a discrete source in 1948. It is a prime example� of a powerful radio galaxy and, in the last decade, has also been studied extensively in X-rays. In this paper I summarise the results from a ROSAT X-ray image.
Close Coupling Theory of Positron Scattering from Alkali Atoms
Authors: Mitroy Jim , Ratnavelu Kurunathan
Published: June 2013

The close coupling equatious for positron-alkali atom scattering are written as a set of coupled momentum-space Lippmann-Schwinger equations. The alkali atom is represented by a frozen-core model based upon the Hartree-Fock approximation. The interaction between the positronium and the residual ion is modified by the inclusion of a core potential. Similarly, a core term is present in the interaction describing the rearrangement process. Close coupling calculations of positron scattering from sodium are performed in a model containing multiple sodium (3s, 3p, 4s, 3d, 4p) and positronium (Is, 2s, 2p) states. Cross sections are reported for an energy range from threshold to 50�eV; the total cross sections are in agreement with experimental data.
The Pohang Light Source
Authors: Lee Tong-Nyong , Yoon Moohyun , Soo Kim Young , Kim Hogil
Published: June 2013

A 2 GeV synchrotron light source project is in progress in Pohang, Korea. The light source is designed to provide high brightness radiation with continuous wavelengths down to 1 A (10-8 em) with its peak at 4�43 A(Le. 2�8 keY). The project, consisting of a full energy injector linear accelerator and a 2 GeV storage ring, was launched in 1988 and is scheduled to be completed by the end of 1994. In this article, we introduce the main features and status of the storage ring components and the installation procedure. Radiation characteristics and beamline status are also described.
Technological Challenges in Thermal Plasma Production
Authors: Ramakrishnan S
Published: June 2013

Thermal plasmas, generated by electric arc discharges, are used in a variety of industrial applications. The electric arc is a constricted electrical discharge with a high temperature in the range 6000-25,000 K. These characteristics are useful in plasma cutting, spraying, welding and specific areas of material processing. The thermal plasma technology is an enabling process technology and its status in the market depends upon its advantages over competing technologies. A few technological challenges to enhance the status of plasma technology are to improve the utilisation of the unique characteristics of the electric arc and to provide enhanced control of the process. In particular, new solutions are required for increasing the plasma-material interaction, controlling the electrode roots and controlling the thermal power generated by the arcing process.
Electrical Breakdown in Air and in SF6
Authors: Morrow R , Lowke JJ
Published: June 2013

A theory is presented for the development of streamers from a positive point in atmospheric air. The continuity equations for electrons, positive ions, and negative ions are solved simultaneously with Poisson's equation. For an applied voltage of 20 kV across a 20 mm gap, streamers are predicted to cross the gap in 26 ns, and the calculated streamer velocities are in fair agreement with experiment. When the gap is increased to 50 mm for the same voltage, the streamer is predicted not to reach the cathode. In this case an intense electric field front rapidly propagates about 35 mm into the gap in 200 ns. For a further 9�5 �s the streamer slowly moves into the gap, until the electric field at the head of the streamer collapses, and the streamer front stops moving. Finally, only positive space-charge remains; this moves away from the point, allowing the field near the point to recover, giving rise to a secondary discharge near the anode. The electric field distribution is shown to be quite different from that found previously for SF6; this is explained by the much lower attachment coefficient in air compared with that in SF6. These results show that streamers in air have a far greater range than streamers in SF6. This greater range cannot be explained by comparison of the values of E*, the electric field at which ionisation equals attachment.
Dissociation Processes of SiCl4 and Plasma Parameters measured by Transient Spectroscopy at the Beginning of a SiCl4?Helium dc Discharge
Authors: Sakurai Takeki , Kobayashi Shigeru , Ogura Jun , Inoue Yukio , Hori Hirokazu
Published: June 2013

We propose that the excitation or the dissociation mechanism and plasma parameters in a discharge can be estimated by. spectroscopic methods, such as the measurement of the transient behaviour of fluorescences at the beginning of a pulsed de discharge. Fluorescences emitted from excited atoms and dissociated fragments from 270 to 640 nm in wavelength are measured as a function of time at the beginning of a discharge of a He-SiCl4 gas mixture. The transient waveform of fluorescence is calculated by considering the experimental results of discharge current and voltage between electrodes measured as a function of time. From a comparison of the experimental and calculated waveforms of fluorescence it is concluded that the fragment emitting the light, SiCb, is excited in a single-step from SiCl4 by electronic collisions and the fluorescence-emitting fragments of SiCI3, SiCI, C12, CI, Si and CI+ in a discharge can never be excited by electronic collisions in a single step. Furthermore, an average electron energy in the plasma at a steady state is simply estimated from a measurement of the transient behaviour of emission lines from helium excited states. The result is in fair agreement with the value measured by using an electric probe.
Velocity Distribution Functions and Transport Coefficients of Electron Swarms in Gases in the Presence of Crossed Electric and Magnetic Fields
Authors: Ness KF
Published: June 2013

A multi-term solution of the Boltzmann equation is used to calculate the spatially homogeneous velocity distribution function of a dilute swarm of electrons moving through a background of denser neutral molecules in the presence of crossed electric and magnetic fields. As an example, electron motion in methane is considered.
Geometrical Models of Elementary Particles
Authors: Smrz PK
Published: June 2013

A new concept of space and time, constructed from a de Sitter structured principal fibre bundle with a connection, is used to discuss a geometrical interpretation for the complex plane of the quantum theory and quantum behaviour of particles. In particular some features of a theory based on a torsion free metric linear connection in a five-dimensional base manifold are described.
The Electron - Atom Ionisation Problem
Authors: McCarthy IE
Published: June 2013

Methods of calculating electron–atom ionisation as a three-body problem with Coulomb boundary conditions are considered. In the absence of a fully-valid computational method for a time-independent experiment the approximation is made that the incident electron experiences a screened potential. Approximations involving a final state that obeys the three-body Coulomb boundary condition are compared with the distorted-wave Born approximation and the convergent close-coupling method.
Planck's Radiation Law: A Many Body Theory Perspective
Authors: Derlet PM , Choy TC
Published: June 2013

An exposition of Planck's Law of Radiation is presented within the context of modern quantum many body theory. In particular the generality of the Planck radiation law is demonstrated to be Valid to all orders of perturbation theory for an interacting system, regardless of the underlying statistics for the particles comprising the matter field and the precise nature of the interaction mechanism. This exposition justifies the use of Planck's law with minor modifications via the refractive index, in the optical properties of semiconductors and insulators. We conclude by clarifying when Planck's law is likely to fail.
Experiments in Atom Optics
Authors: GH Baldwin Kenneth
Published: June 2013

This article outlines experiments which have highlighted the rapid development of the field of atom optics since the mid 1980s. The distinguishing features of the components used in atom optics are compared with their conceptual analogues in light optics. The potential for atom optic devices, both demonstrated and predicted, are described. Experiments and applications of this new technology are reviewed, and the article concludes with a synopsis of work in this field currently being undertaken in Australasia.
Electron Impact Ionisation of Metastable 2s-state Hydrogen Atoms
Authors: Dhar Sunil
Published: June 2013

The triple differential cross section for ionisation of hydrogen atoms in the metastable 2s-state by electrons of 250 eV incidence energy has been calculated following the multiple scattering theory of Das and Seal (1993). The results are compared with the first Born results and with the results of some other theories. Additional features are noted in the cross section curves of the present calculation. These offer wider scope for the experimental study of ionisation of hydrogen atoms in their metastable states.
Understanding Multicentre Electron Orbitals by Electron Momentum Spectroscopy
Authors: McCarthy Ian E. , Vos Maarten
Published: June 2013

Electron momentum spectroscopy can investigate qualitative predictions based
on a physical understanding of the one-electron structure of a system. We
describe examples of this understanding for molecules and solids.
Two-dimensional Scattering by a Potential without a Classical Analogue
Authors: Ponomarev I. V.
Published: June 2013

A two-dimensional scattering potential represents the quantum extension of a
diffractive lattice: a Dirac delta function with a modulated permeability
along the y-axis. This model does not have an explicit
classical analogue and quantum effects such as tunneling and diffraction play
an important role. An analytical solution for the one-harmonic case is found.
For the general case of an arbitrary number of harmonics a simple criterion is
derived for the range of parameters where quantum chaos is permitted (but does
not necessarily occur). The statistical properties of the
S-matrix for the given model have been investigated. The
deviations from the usual predictions for irregular scattering in the random
matrix theory (RMT) framework have been found and are discussed.
Nonlinear Field-dependent Susceptibilities of C60 and Carbon Nanotubes
Authors: Ling M. F. , Finlayson T. R. , Raston C. L.
Published: June 2013

We have found strongly nonlinear, field-dependent magnetic susceptibilities in
a range of carbon-based materials such as C60, carbon
nanotubes, diamond and graphite. This nonlinear behaviour is prominent at low
fields and it vanishes at relatively high fields. We have interpreted this
phenomenon in terms of the field dependence of the spectral energy separations
of the van Vleck paramagnetic term of the susceptibility. Our results should
have significant bearing on the interpretation of the magnetic properties of
this class of materials.
Equation-of-Motion O(N) Electronic Structure Studies of Very Large Systems (N ~ 10 7 )
Authors: Michalewicz Marek T. , Nyberg Per
Published: June 2013

Extremely fast parallel implementation of the equation-of-motion method for
electronic structure computations is presented. The method can be applied to
non-periodic, disordered nanocrystalline samples, transition metal oxides and
other systems. It scales linearly,
O(N), runs with a speed of up to
43 GFLOPS on a NEC SX-4 vector-parallel supercomputer with 32 processors and
computes electronic densities of states (DOS) for multi-million atom samples
in mere minutes. The largest test computation performed was for the electronic
DOS for a TiO2 sample consisting of 7,623,000 atoms.
Mathematically, this is equivalent to obtaining the spectrum of an
n × n Hermitian operator
(Hamiltonian) where n = 38;115; 000. We briefly
discuss the practical implications of being able to perform electronic
structure computations of this great speed and scale.
Experimental Quantum Ratchets based on Solid State Nanostructures
Authors: Linke H.
Published: June 2013

Ratchets are spatially asymmetric devices in which particles can move on
average in one direction in the absence of external net forces or gradients.
This is made possible by the rectification of fluctuations, which also provide
the energy for the process. Interest in the physics of ratchets was revived in
recent years when it emerged that the ratchet principle may be a suitable
physical model for ‘molecular motors’, which are central to many
fundamental biological processes, such as intracellular transport or muscle
contraction. Most ratchets studied so far have relied on classical effects,
but recently ‘quantum ratchets’, involving quantum effects, have
also been studied. In the present article it is pointed out that semiconductor
or metal nanostructures are very suitable systems for the realisation of
experimental quantum ratchets. Recent experimental studies of a quantum
ratchet based on an asymmetric quantum dot are reviewed.
A Critique of the Gauge Technique
Authors: Delbourgo R.
Published: June 2013

A summary of the successes of and obstacles to the gauge technique (a
non-perturbative method of solving Dyson–Schwinger equations in gauge
theories) is given, as well as an outline of how progress may be achieved in
this field.