bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Approximations for Electron?Atom Direct Reactions
Authors: McCarthy IE , Stelbovics AT
Published: June 2013

The electron-hydrogen system is a true three-body system which provides an excellent test for theories of reactions in many-body systems that approximately involve only three-body degrees of freedom. The coupled-channels optical approximation reproduces experimental data in most cases within experimental error. The approximation may be extended to a larger space of coupled channels by various approximations which are tested with the example of 54�42 e V electron scattering on the Is, 2s and 2p space for hydrogen, extended by the addition of 3s and 3p channels. Channels outside this five-state space are treated by including the corresponding polarization potentials.
Quantum Electrodynamics in Strong Magnetic Fields. II. Photon Fields and Interactions
Authors: Melrose DB
Published: June 2013

A theory is developed which synthesizes the classical theory of wave-wave interactions in a medium and the QED theory of photon-photon interactions in a vacuum with or without static fields. First, a covariant version of the theory of wave dispersion in an arbitrary medium is outlined. Then the photon propagator is calculated both by solving the wave equation directly and from the vacuum expectation value, and the latter is generalized by introducing a statistically averaged propagator. The hierarchy of nonlinear responses of the medium is introduced and used to define a nonlinear interaction Hamiltonian. The expansion of the S matrix with this interaction Hamiltonian is re-ordered to correspond to a hierarchy of processes ordered according to the number of external photons. The theory is used to treat three-wave and four-wave interactions and both classical and QED applications are discussed. A covariant form of the Onsager relations and calculations of the hierarchy of response tensors using covariant classical kinetic theory and the Heisenberg-Euler Lagrangian are presented in appendices.
Radius Ratios of Argon Pinches
Authors: Lee S
Published: June 2013

According to a new theory based on energy balance, the radius ratio Yp/Yo of a constant-current plasma pinch depends only on the value of the effective specific heat ratio y of the pinched plasma. In this paper the value of y for argon is computed as a function of temperature. From these values the constant-current pinch ratios are computed. The results show argon pinch ratios of about o� 08 from (2-4) x 106 K, rising to 0�18 at 1�1 x 107 K and to O� 27 at 108 K. There is good agreement between this theory and an Imperial College measurement of Y o/ro ~ 0 �17 for a constant-current argon pinch at an estimated temperature of 1 keY.
A Deformation Dipole Model for Crystals: Application to NaCI
Authors: Richardson DD , Mahanty J
Published: June 2013

We present a deformation dipole model based on theoretical calculations of induced moments in ion pairs. The model is generally applicable and in this paper is applied to the calculation of the lattice dynamics of NaCI. Only a few parameters are required to give good agreement with experiment. Limitations of the approach are discussed.
Atomic X-ray Transition Probabilities: A Comparison of the Dipole Length, Velocity and Acceleration Forms
Authors: Quiney HM , Larkins FP
Published: June 2013

The length, velocity and acceleration forms of the dipole transition operator are examined in calculations of diagram and satellite X-ray emission probabilities in the Ne + to Ar 9 + isoelectronic series. All calculations are within the relaxed nonrelativistic Hartree-Fock framework, using separately optimized numerical wavefunctions for the initial and final electronic states. Divergence between the alternative forms of the transition moment, as the principal quantum 'number of the Rydberg electron and nuclear charge are increased, is discussed in the context of electron correlation differences between the initial and final states.
An Introduction to Mössbauer Studies of Magnetic Materials
Authors: Campbell SJ
Published: June 2013

A straightforward introduction to Mossbauer spectroscopy is presented along with a brief background to its discovery over 25 years ago. Several applications of Mossbauer spectroscopy in the study of condensed matter are described. The examples are based on recent investigations of the mixed magnetic AuFe system and amorphous alloys and show how Mossbauer spectroscopy can be used to obtain information on local atomic order, magnetic phases and texture. The diverse range of applications of Mossbauer spectroscopy is outlined, including a brief discussion of its use in topics of current interest in metal physics.
Electron Transport and Rate Coefficients in Townsend Discharges
Authors: Blevin HA , Fletcher J
Published: June 2013

Electron swarm parameters such as the drift velocity, diffusion coefficients and ionization rates have been calculated by many authors. However, the values obtained for most parameters depend upon the type of experiment under consideration, so that, for a given gas and a fixed value of E/ N, differences are obtained for steady-state Townsend, pulsed Townsend and time-of-flight experiments It is shown that this is an unnecessary complication since each experiment can be analysed in terms of time-of-flight parameters. It is proposed that calculated parameters should be presented in a manner which would assist not only in the analysis of the above experiments but also in other swarm studies in progress.
Dispersion in a Relativistic Quantum Electron Gas. I. General Distribution Functions
Authors: M Hayes Leith , Melrose DB
Published: June 2013

The covariant response tensor for a relativistic electron gas is calculated in two ways. One involves introducing a four-dimensional generalization of the electron-positron occupation number, and the other is a covariant generalization of a method due to Harris. The longitudinal and transverse parts are. evaluated for an isotropic electron gas in terms of three plasma dispersion functions, and the contributions from Landau damping and pair creation to the dispersion curve are identified separately. The long-wavelength limit and the non-quantum limit, with first quantum corrections, are found. The plasma dispersion functions are evaluated explicitly for a completely degenerate relativistic electron gas, and a detailed form due to Jancovici is reproduced.
The Experimental Value of f(220) for Copper
Authors: Mackenzie JK , McL Mathieson A
Published: June 2013

The value of the atomic form factor, /(220), for copper has been determined in recent years by a variety of methods. All the dynamical methods agree on a value in the region of 16'70-16�75. These methods include two X-ray methods, one involving measurement of intensity profiles and the other of Pendellosung beats, and also an electron diffraction measurement using a critical voltage procedure. By contrast, two recent kinematical measurements using y rays both report a distinctly different value of about 16�45. One of these determinations has already been re-examined by the present authors and the iscrepancy removed by an appropriate extrapolation to zero extinction.
Deconvolution in the Presence of Noise Using the Maximum Entropy Principle
Authors: Steenstrup S
Published: June 2013

The main problem in deconvolution in the presence of noise is non-uniqueness. This problem is overcome in the present work by the application of the maximum entropy principle. The way in which noise enters the formulation of the problem is examined in some detail and the final equations are derived in such a way that the various assumptions are made explicit. Some examples of the use of maximum entropy deconvolution on both simulated and real X-ray diffraction data are given.
Solid State Track Detectors: Applications to Fission Related Studies
Authors: L Koul Sohan
Published: June 2013

The passage of charged particles produces linear trails of damaged material in dielectric solids. These trails are frequently visible by transmission electron microscopy or can be chemically etched and observed with an optical microscope. This paper compares track registration and track retention behaviour of crystalline and non-crystalline track detectors such as stilbite, prehnite, cellulose nitrate CR-39 and LR115. The dependence on both the annealing temperature and time of the preferential track etch ratio Vt/Vg and also the track length and track density are discussed. The etching response is studied for fission fragments, alpha particles, protons and neutrons. Several useful applications of solid state track detectors in various fields are discussed.
Crystal Structure of Triclinic Colchiceine Hemihydrate
Authors: F Mackay Maureen , D Morrison James , M Gulbis Jacqueline
Published: June 2013

Triclinic crystals of colchiceine hemihydrate, C21H23N06.!H20, belong to the space group PI with a 8 .211(1), b 8�361(1), c16 �898(2) A, a 92 �35(1)", J3 93 �93(1)", l' 121�35(1)" and Z 2. The structure was solved by direct methods and successive difference syntheses with diffractometer data measured with CuKa radiation. Refinement converged at R 0�053 for 2798 observed reflections. The two tautomers, one of the isoco1chiceine and the other of the colchiceine form, exist as independent entities in the crystal; the angles between the normals to the plane of the benzene and troponoid rings are 44�5(4)" and 51� 5(5)" respectively. The hydroxyl and N-acetyl groups are oriented to form channels along the a-axis which accommodate the water molecules.
A Comparison of Methods for Calculating O(1S) Lifetimes
Authors: Burns GB , Reid JS
Published: June 2013

It is shown theoretically and with simulated data that O(lS) lifetimes determined by the cross-spectral method (Paulson and Shepherd 1965) are significant overestimates. A comparison is made of the cross-spectral and impulse function analysis (Burns and Reid 1984) methods using photometric data collected at Macquarie Island (54. 50S, l59�00E geographic). The results support the view that the O(lS) state is excited predominantly by an indirect process.
Low Energy Electron Collision Cross Sections for Methane
Authors: Haddad GN
Published: June 2013

Measurements of the drift velocity vdr and the ratio of the lateral diffusion coefficient to mobility D1/p. have been made in pure methane at 293 K. Measurements of vdr and D1/p. were made for values of E IN (the electric field strength divided by the number density) ranging from 0�03 to 14 Td and 0�02 to 12 Td respectively (1 Td == 10-21 Vm2). The estimated accuracy of the results is � 1 % for vdr and �2% for Dli p.. The data have been analysed by means of a multiterm solution of the Boltzmann equation to provide a set of low energy electron collision cross sections consistent with the transport data.
Recent Studies of Magnetic Canopies
Authors: P Jones Harrison
Published: June 2013

Two current studies are described which stem from Giovanelli's seminal studies of the spreading of chromospheric fields near active regions and active-region network. First, improved observ~tional techniques are described for obtaining magnetograms in the Ca II 8542 A, Fe I 8688 A, and C I 9111 A lines which at least in principle allow for more accurate treatment of instrumental noise and allow better inference of field .orientation. Second, a generalized response function is developed for calculating theoretical magnetograph signals from arbitrary line-of-sight variations of magnetic field, and initial applications to two-dimensional, potential-field models of network fields are described. Preliminary indications are that potential-field models can better explain the presence of low-lying, diffuse horizontal fields than can thin flux-tube models, but fail to predict a differential response between the different lines.
Numerical Simulations of Large-scale Solar Magnetic Fields
Authors: DeVore CR , Sheeley Jr NR , Boris JP , Young Jr TR , Harvey KL
Published: June 2013

We have solved numerically a transport equation which describes the evolution of the large-scale magnetic field of the Sun. Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle. Our objective is to assess the ability of the model to reproduce the observed evolution of the field patterns. We discuss recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the Sun over sunspot cycle 21.
Solar Affinity of Sedimentary Cycles in the Late Precambrian Elatina Formation
Authors: Williams GE
Published: June 2013

Climatic cyclicity is recorded by regular variations in the thickness of siltstone-fine sandstone laminae interpreted as annual deposits (varves) within the Elatina Formation, a late Precambrian ( - 680 million years old) periglacial lake deposit in the Flinders Ranges, South Australia. Earlier conclusions, based on the study of limited rock outcrop, that the climatic cycles reflect solar variability are strongly supported by a complexity of periods revealed through study of drill cores of the - 10 m thick varved sequence. The wealth of new data generated by the drilling program, which was CSIRO-sponsored largely because of the support of R. G. Giovanelli, has application to solar physics and solar-planetary science.
Excitation of Swift Heavy Ions in Foil Targets. II. X-radiation from Br
Authors: Hay HJ , Pender LF , Treacy PB
Published: June 2013

An experimental arrangement is described to. detect delayed X-rays emitted fo.llo.wing fo.il excitatio.n o.f 130 MeV Br io.ns at distances to. 190 mm do.wnstream o.f a self-supPo.rting carbo.n target. The intensities o.f L X-rays at a number o.f distances were measured. The o.bservatio.ns are discussed in terms o.f the decay o.f high- n Rydberg io.ns. It is sho.wn that, in additio.n to. the expected yrast cascades, there are o.ther little-understo.o.d cascades with high intensities.
Enhancement of Parity Violation for Overlapping Nuclear Resonances
Authors: Awin AM
Published: June 2013

Proton scattering from a medium weight nucleus and the possibility of finding tWQ resonances, with the same spin but opposite parity, overlapping is studied. As a guide to the experimental study of this possibility we have constructed a simple separable potential model involving spin ~-spin 0 scattering that contains the required resonances for adjacent I values in the absence of a parity-violating (PV) interaction. A phenomenological PV interaction is then introduced and the magnitude of the longitudinal asymmetry is studied as a function of the model parameters. It is found that the magnitude of the asymmetry is greatest at zero separation for the case of narrow resonance levels.
The Determination of the Diffusion Coefficient for Thermal Electrons in Water Vapour by the Use of a Modified Blanc's Law Procedure
Authors: Lj Petrovic Zoran
Published: June 2013

The Cavalieri electron density technique has been used to measure the diffusion coefficient for thermal electrons in water vapour. When analysed by a straightforward application of Blanc's law to determine the diffusion coefficient for water vapour, the normalized coefficient ND showed an anomalous pressure dependence. The application of a modified procedure, in which these data were corrected using a calculated correction factor, removed the anomalous dependence and gave data which are in agreement with previously published data.
Excitation Function for 16O+24Mg Elastic Scattering at ?c.m. = 90°
Authors: Drumm PV , Hebbard DF , Ophel TR , Nurzynski J , Kondo Y , Robson BA , Smith R
Published: June 2013

The e C.m. = 90� excitation function for 160 + 24Mg elastic scattering, which is only sensitive to even partial waves, has been measured for energies 31�6..;; Ec.m . ..;; 45�2 MeV in an attempt to resolve an uncertainty in the sign and magnitude of a proposed parity-dependent term in the 160_24Mg interaction. The data have been analysed by an optical model potential, which includes both a real parity-dependent interaction and an angular momentum-dependent absorptive term. Both the measurements and calculations show some structure but, since this does not correlate with the energies of the even shape resonances in the 160_24Mg interaction, no conclusion can be drawn concerning the sign and magnitude of the parity dependence of the 160_24Mg potential.
Current Status and Future Directions of Atomic Studies by Electron Spectrometry with Synchrotron Radiation
Authors: Krause MO
Published: June 2013

Representative examples of recent work on the electronic structure and dynamics of atoms are discussed and new directions in studies by electron spectrometry with synchrotron radiation (ESSR) are indicated.
Relativistic Effects in the Photoionisation of Heavy Atoms: Cooper Minima
Authors: C Deshmukh Pranawa , Tambe BR , T Manson Steven
Published: June 2013

Cooper minima are known to profoundly affect photoionisation cross sections. They become particularly important in high-Z atoms where relativistic effects split each nonrelativistic Cooper minimum into three minima (two for s states). In addition, there are significant splittings in these 'triplets'. In this paper, the systematics of these relativistic Cooper minima are explored, over a broad range of elements, for 5p, 5d, 6s and 6p subshells. The phenomenology is presented and the physics behind the results discussed. In addition, the important implications for branching rates and photoelectron angular distributions are presented.
A Photodetector for Measurement of Metastable H(2S) in Ion-Atom Collisions
Authors: Williams DG , Lee AR , Butcher EC
Published: June 2013

The Stark effect is employed in the detection of fast metastable hydrogen in the energy range 4-24 keV. A consideration of the design of a detector is presented in the light of recent work describing the decay process.
The Rietveld Method ? A Historical Perspective
Authors: Rietveld HM
Published: June 2013

differences between observed and calculated values was already well established in crystallography. From there it was, in retrospect, only a small step to refrain from using the integrated intensities as observed values but to use the actual measured profile intensities obtained by step scanning the powder diagram. The Rietveld method was first reported at the I.U.Cr. congress in Moscow in 1966. However, it was not until 1975, when it was also applied to X-ray diffraction, that it became widely accepted. Nowadays its use is no longer confined to elastic neutron powder diffraction, but to all diffraction techniques producing complex diffraction diagrams.
Learned Peak Shape Functions for Powder Diffraction Data
Authors: Hepp A , Baerlocher Ch
Published: June 2013

An algorithm is described for the determination of an experimental (learned) peak shape function, which has been used succesfully in crystal structure refinements from powder data. The function gives an optimal fit to almost any peak shape since it is not based on an analytical expression. It is determined from a single peak in a pattern by first fitting this peak with the proposed algorithm which ensures that the function is smooth and has only one maximum and two inflection points. The learned function is then normalised and decomposed into a symmetric and an asymmetric part. These are stored in tabulated form, permitting linear interpolation. As with an analytical function, a FWHM and asymmetry function describing the 26 dependence of the peak shape can be applied.
Structure and Properties of Surface Layers: X-ray Diffraction Studies
Authors: Delhez R , de Keijser ThH , Mittemeijer EJ , Thijsse BJ , Hollanders MA , Loopstra OB , Sloof WG
Published: June 2013

Because X-rays are strongly absorbed on propagation through solid material, X-ray diffraction analysis can be fruitfully applied in the study of surface layers. After a brief discussion of some aspects of X-ray diffraction analysis of surface layers, attention is focussed on investigations of stress development and interdiffusion in surface layers. The behaviour of surface layers depends largely on their state of (residual) macro- and microstress. The development and possible relaxation of macrostress in surface layers can originate from the thermally imposed difference in shrink or expansion between layer and substrate, from developing concentration profiles and from structural changes, in particular phase transformations. Diffusion processes in multilayers, composed of alternately stacked sublayers of elements A and B, are highly affected by the multitude of interfaces and therefore differ from those in bulk material. The effective diffusion coefficients can be determined from the decrease of the intensity of the reflections corresponding to the composition-modulation period [so-called (000) satellites], and the change of the integrated intensities of reflections from produced or retained crystalline components. Examples of interdiffusion in an amorphous multilayer (in conjunction with structural relaxation) and in a crystalline multilayer (leading to amorphisation) are presented.
Computer Simulation of Positron Annihilation and Diffusion Characteristics in Kr and Xe
Authors: Singh Vikram
Published: June 2013

Analysis of spectra, annihilation rates, and drift and diffusion characteristics of slow positrons is carried out in the heavy gases Kr and Xe. These properties are quite sensitive to the external electric and magnetic fields. Comparison with experiment is made where measurements are available.
Motion of Charged Particles in a Homogeneous Reacting Medium with a One-dimensional Geometry
Authors: K Standish Russell
Published: June 2013

We study the approach to steady state of a system described by the Klein-Kramers equation with a COnstant source, to see how the source structure effects disappear away from the source. We link this to some earlier work on non-hydrodynamic effects in time-of-flight swarm experiments to show how this theory may be applied to the analysis of steady-state Townsend swarm experiments.
Neutron Kikuchi Effect and Practical Problems Associated with Its Observation
Authors: Town SL , Smith TF , Elcombe MM
Published: June 2013

The theory of the neutron Kikuchi effect has been re-examined and an exact formulation in reciprocal space derived. The conditions necessary for its observation have been considered and appropriate data from a lead single crystal have been collected on the triple-axis spectrometer at the HIFAR reactor in the laboratories of the Australian Nuclear Science and Technology Organisation. A series of constant-Q phonon scans across the predicted positions of the Kikuchi lines show reductions in the integrated phonon intensity, which appear to move as expected with changes in the scattered neutron wavevector.
Flux Penetration Effects in High-Tc SQUIDs
Authors: SIoggett GJ , Harvey lK , Wieczorek L , Binks RE , Driver R
Published: June 2013

Two experiments pertaining to the effects of intergranular flux penetration in high-Tc yttrium-barium-copper oxide (YBCO) SQUIDs are described. The first is a direct measurement of the flux noise of bulk YBCO exposed to the earth's magnetic field, and the second involves the fabrication and testing of break junction d.c. SQUIDs. Implications of a number of undesirable effects seen in these experiments are discussed.
Meson Mass Spectrum from First Order Static Cavity Wavefunctions
Authors: CL Hollenberg Lloyd , HJ McKellar Bruce
Published: June 2013

Large-basis O(g) static cavity wavefunctions, containing bremsstrahlung and quark-sea states, previously fitted to the light quark meson sector, are applied to the ground-state meson spectrum in general. The only parameters of the model in the heavy quark sector are the quark masses me and mb which we fit to D and B states. Predictions for the meson mass spectrum are given and are found to be a significant improvement over the predictions of the original. MIT model.
Correlation Effects of Third-order Perturbation in the Extended Hubbard Model
Authors: Wei CZ , Nie HQ , Li L , Zhang KY
Published: June 2013

Using the local approach, we have performed a third�order perturbation calculation to investigate the effects of intra-atomic electron correlation and electron and spin correlation between nearest neighbour sites in the extended Hubbard model. We found that significant correction of the third order over the second order results and, in comparison with the results of the third-order perturbation where only the intra-atomic electron correlation is included, the influence of the electron and spin correlation between nearest neighbour sites on the correlation energy is non-negligible.
Deformation and Spin 1 Effects
Authors: Amos K , Raynal J
Published: June 2013

Elastic scattering measurables for 547 MeV proton scattering from l3C are calculated using a nonrelativistic optical model potential in which deformation of the conventional Woods-Saxon forms of the real and imaginary central potentials is allowed, as well as incorporating spin 1 transfer contributions. The latter are estimated from folding a simple two nucleon t-matrix with a Op-shell model wavefunction
Electron Transport Coefficients in Carbon Monoxide and Deuterium
Authors: Petrovic ZLj , Crompton RW
Published: June 2013

The drift velocity and the ratio of transverse diffusion coefficient to mobility have been measured for electrons in gaseous carbon monoxide and deuterium at 293 K. The measurements were made under conditions where vibrational excitation is the major energy loss in order to resolve some discrepancies that exist between published vibrational excitation cross sections for these gases. The results are in good agreement with the majority of the existing data where available, but the error bounds are reduced significantly in some cases.
Metal Enrichment, Dust and Star Formation in High-redshift Galaxies
Authors: Pettini Max , W Hunstead Richard
Published: June 2013

QSO absorption systems exhibiting a damped Lyoc line are thought to arise in the high�redshift progenitors of present-day disk galaxies. In order to clarify the evolutionary status of these absorbers and interpret the clues they provide to the process of galaxy formation in general, we have begun a programme of spectroscopic observations targeted at measuring their element abundances, dust concentration and star�formation rates. Abundance studies in the local interstellar medium (ISM) have identified Zn as a highly convenient species for surveying the overall level of metallicity of the damped systems, while a qualitative indication of the dust content can be obtained by consideration of the Zn�to�Cr ratio since, unlike Zn, Cr is readily bound to interstellar grains. In some favourable cases, higher�resolution observations of selected lines can provide additional information on abundance ratios of individual elements. Lastly, searches for weak emission in the black core of the damped Lyoc absorption line have so far provided the most stringent limits on the Lyoc luminosity of these supposedly young galaxies, and in one case led to a positive detection. The results obtained so far suggest that the damped Lyoc galaxies are indeed at an early phase of chemical evolution, with metal abundances 1 to 2 orders of magnitude below solar and with perhaps only 1/10 of the dust content of the local ISM. Lyoc fluxes are well below the predictions of many theoretical models, and star-formation rates < 10 MGl yr-1 seem to be typical. These properties are similar to those of present�day H II galaxies of which the Lyoc systems may therefore be high�redshift examples.
Spectroscopy and Structure of Aromatic?Rare Gas Cluster Ions
Authors: I McKay Ruth , J Bieske Evan , M Atkinson Ian , R Bennett Frederick , J Bradley Andrew , W Rainbird Mark , B Rock Andrew , S Uichanco Angelo , EW Knight Alan
Published: June 2013

Ionic clusters consisting of a polyatomic ion surrounded by a few 'solvent' atoms or molecules, provide a connecting link between the isolated gas phase ion and the ion solvated in a condensed medium. Analysis of the vibrational structure associated with the motion of the cluster atoms can reveal details concerning the intermolecular potential. However, for large polyatomic ions, information concerning the cluster vibrational motion has been difficult to obtain using conventional spectroscopic methods. We have developed a new combination of the previously available techniques of supersonic cooling, resonance-enhanced multi photon ionisation, timeof- flight mass spectroscopy, in concert with one-photon photodissociation spectroscopy. This new technique takes advantage of the facile predissociation of an electronically excited cluster and affords us a method of studying the previously unmeasurable vibrational structure associated with the motion of a molecular cluster ion. Using this technique we have obtained vibrationally resolved photodissociation spectra of a number of aromatic-rare gas cluster ions. Analysis of their vibrational structure permits structural details of the cluster cation to be deduced.
Ground State Positronium Formation Cross Sections for Scattering of Positrons from Li
Authors: Mukherjee KK , Ranjit Singh N , Basu Choudhury Keka , Mazumdar PS , Brajamani S
Published: June 2013

Total cross sections for positronium formation in e+-Li scattering have been studied in the framework of the distorted wave approximation in the energy range 1-50 eV by taking consistent account of the effect of the target distortion. The results are compared with existing theoretical predictions.
Imperfect Crystals and Dynamical X-ray Diffraction in the Complex Reflectance Plane
Authors: Davis TJ
Published: June 2013

A theoretical framework is developed to describe the dynamical diffraction of X-rays in perfect and imperfect crystals. The propagation of the X-ray beam inside the crystal is described by the evolution of a set of trajectories in the complex reflectance plane. The trajectory path is determined from a form of the Takagi-Taupin equations and leads naturally to simple forms for the crystal reflectivity for perfect crystals. A stochastic model for the effects of crystal defects is developed in terms of the Langevin equation which leads to a description of diffraction from imperfect crystals as the evolution of densities in a parameter space, described by a Fokker-Planck equation.
Position and Flux Density Calibration at Molonglo
Authors: W Hunstead Richard
Published: June 2013

When the Molonglo Cross was brought into full operation its higher angular resolution and greater pointing accuracy posed special problems for position calibration. The development of a southern radio calibration grid is described, together with its extension for the MOST. The techniques developed in this program have found wide applicability in radio-source identification searches at other observatories. Calibration in flux density was based on absolute measurements at 408 MHz and transferred via secondary standards; at 843 MHz, the flux density calibration was based partly on absolute measurements and partly on the earlier 408 MHz data. The collection of data spanning several years led to the discovery of significant time variability at 408 MHz.
Drift Velocity, Longitudinal and Transverse Diffusion in Hydrocarbons derived from Distributions of Single Electrons
Authors: Schmidt Bernhard , Roncossek Michael
Published: June 2013

A time of flight method is described which allows the simultaneous measurement of drift velocity w and the ratios of the longitudinal and transverse diffusion coefficients to mobility (DL/JL, DT/JL) of electrons in gases. The accuracy achieved in this omnipurpose experiment is comparable with that of specialised techniques and is estimated to be �1 % for w and �5% for the D / JL measurements .. Results for methane, ethane, ethene, propane, propene and cyclopropane for values of E/N (the electric field strength divided by the number density) ranging from 0�02 to 15 Td are presented and discussed (1 Td = 10-21 Vm2 ).
Foreword
Authors: Melrose Don
Published: June 2013

A workshop on 'Star Formation in Different Environments' was held at the University of Sydney in October 1991. The workshop was sponsored by the Research Centre for Theoretical Astrophysics, which was set up in 1991 as a Special Research Centre of the Australian Research Council, with the primary objective of fostering theoretical astrophysics in Australia. The major part of the initial organisation of the workshop was carried out by Geoff Bicknell, who was co-opted to the Research Centre for several months from Mount Stromlo and Siding Spring Observatories. About fifty astrophysicists took part, including three distinguished overseas visitors, Leon Mestel, Colin Norman and Joe Silk, who took leading roles in the scientific discussions.
Star Formation in Cooling Flows
Authors: Nulsen PEJ
Published: June 2013

There is good evidence that the intracluster gas near the centres of many clusters of galaxies is cooling over at least a decade in temperature. This results in an inflow, which is approximately steady where the cooling time of the gas is shorter than the age of the flow. X-ray observations indicate that the cooling gas must have substantial inhomogeneities. Non-linear development of thermal instability causes cooled gas clouds to be deposited throughout the region of the steady cooling flow. The masses of these clouds will be small, typically a lot less than a Jeans mass when they first form. It is argued that the difficulty of forming large clouds in the bulk of a cooling flow inhibits high mass star formation there. There is evidence of some 'normal' star formation near to the centres of many cooling flows where conditions are more favourable for the formation of giant clouds. The initial mass function is strongly affected by the star formation environment in cooling flows.
Nonlocality and the D-state Probability of the Deuteron
Authors: M Mustafa Mustafa
Published: June 2013

Attractive short-range nonlocality incorporated only into the D state of the deuteron decreases the D-state probability Po. The variation of PD versus nonlocality strength is a characteristic curve.
Nonlinear Shifts of Refractive Indices from Obliquely Propagating Waves in a Magnetised Plasma in the Presence of Coriolis Rotation
Authors: Kashyapi PK , Paul SN , Chakraborty B
Published: June 2013

This paper provides an expression for the nonlinear shifts of refractive indices from obliquely propagating waves in a cold, homogeneous, magnetised rotating plasma in the presence of a Coriolis force. The effects of gyrofrequency, rotational frequency, and the amplitude of the waves on the nonlinear shifts of refractive indices are discussed. It is found that these parameters play a dominant role in the nonlinear shifts of refractive indices and the results are more general than those of earlier workers.
Effect of Short-range Repulsive Interactions on the Dynamics of the Methane Molecule
Authors: Kansal MK , Trikha SK
Published: June 2013

Using a computer simulation technique, an attempt has been made to explain the A-type transition in the specific heat of solid methane at around 20 K in terms of the changes in the dynamical behaviour of the methane molecule under the influence of its nearest neighbours. Different exponents of the short-range repulsive interaction occurring in the expression for the potential energy have been tried in order to select the appropriate value. The well known Lennard-Jones (6-12) and (6-15) potentials are found to reveal a phase transition in a well defined region. From an analysis of the direction cosine data, the three-dimensional motion of the central methane molecule has been visualised before and after the transition. Pertaining to the Lennard-Jones potential, the period of the torsional oscillation (libration) of the methane molecule comes out to be of the order of 0�3xlO-12 s. From the computed critical rotational kinetic. energy, the transition temperature is found to be 20�2 K which agrees well with experimental observations.
The Discrete Ordinate /Pseudo-spectral Method: Review and Application from a Physicist's Perspective
Authors: Robson RE , Prytz Arnstein
Published: June 2013

A discussion of the discrete ordinate method for solving differential equations is presented along with a number of examples that have application in various fields of physics. In particular, diffusion cooling, boundary layer meteorology and the diffusion of water in soils are studied. It is shown that the discrete ordinate method is considerably more accurate than finite difference methods of the same order. Results are presented for linear and nonlinear models, with a comprehensive analysis of the results and accuracies.
Preface
Authors: R Finlayson Trevor , J Morgan Michael , C Choy Tuck
Published: June 2013

On December 11, 1992 colleagues and friends of Geoffrey Charles Fletcher gathered at Monash University to honour him on the occasion of his 70th birthday. The photograph on the next page of those able to attend was taken during a pause for lunch during a busy day of formal presentations and fruitful discussion. The Festschrift Symposium ended with an evening dinner at which Professor Geoff Wilson presented his personal reflections on the beginnings of condensed matter physics at Monash University, and on Geoff Fletcher's emergence as an electron band theorist.
A Tight Binding Model for the Density of States of Graphite-like Structures, Calculated using Green's Functions
Authors: McKinnon BA , Choy TC
Published: June 2013

The electronic structure of graphite-like materials is investigated within the framework of the tight binding model. The densities of states of simple hexagonal and Bernal graphite are calculated, induding two layer (2D) and bulk (3D) cases. The calculation employs Green's function techniques, resulting in essentially analytic solutions in terms of elliptic integrals. The Bernal density of states is found to agree qualitatively with experimental measurements and the extension of our studies to surface effects and carbon fibre structures is also discussed.
On the Effects of Gravitational Fields on the Electrical Properties of Matter
Authors: I Opat Geoffrey
Published: June 2013

A discussion of the electrical state of a conducting solid in a static gravitational field is presented. The analysis of the stress-gravitational force balance inside the solid is complicated; however, outside the solid, in the evanescent electron field, the analysis of such a balance simplifies greatly. As a consequence of this external analysis, an expression for the electric field external to the body is presented which includes the direct effect of gravity on the electrons, as well as the indirect effect due to the stress induced by the action of gravity on the bulk solid. Such fields are an important determinant of the gravitational motion of charged particles within metallic shields.
A pilot study of paramagnetic resonance centres in selected Argyle diamonds
Authors: Hutton DR , Troup GJ
Published: June 2013

page missing 663
Space Charge Effects in the Cavalleri Determination of Electron Diffusion Coefficients in Gases
Authors: Liley BS
Published: June 2013

A theoretical analysis shows that positive ion space charge effects can dominate the Cavalleri experiment. It is, however, confirmed that on operating in a linear regime, corresponding to normal experimental conditions, very accurate values for the electron diffusion coefficient can be obtained by extrapolating to zero X-ray pulse intensity. Both primary effects, associated with ions produced by the initiating ray pulse, and secondary effects, associated with ions produced by the RF sampling pulse, are taken into account.
Effect of Streaming and Finite Geometry on a Resonance-like Phenomenon in Beam-Plasma Systems
Authors: Mukhopadhyay J , Roy Chowdhury K , Roy Chowdhury A
Published: June 2013

We have analysed the effect of finite geometry and streaming on a resonance-like phenomenon in a beam-plasma system placed in an infinite magentic field. The resonance-like phenomenon is displayed through a variation of the amplitude of the soliton with respect to a (the ratio of electron to ion density). It is shown that this event is very prominent in the case of an infinite plasma, but for a bounded system the effect is not so significant. As such, an effect of this type will be difficult to observe experimentally unless the dimension of the containment system is considerable. Furthermore, the peak of the resonance varies considerably with the streaming velocity and other parameters of the plasma. The whole phenomenon is crucially dependent on the phase velocity of the solitary wave, whose variation is also considered in detail. Lastly, it is demonstrated that the existence of a resonance-like phenomenon can also be ascertained from an analysis of the linear dispersion relation.
Reminiscences
Authors: Wild JP
Published: June 2013

I would like to take up something that John Whiteoak said at the symposium yesterday in relation to Cowra or Parkes as the possible site for the 64-m telescope. In my memory, what really happened was that E. G. (Taffy) Bowen was determined to locate the telescope on the Nepean River near Camden. It would have been a very beautiful, but very noisy site, and most people were resigned to having the telescope there. But I argued very strongly that it should go 'over the mountains'. Taffy was good enough to arrange a meeting of radio the result that a group, an unlikely team consisting of B. Y. (Bernie) Mills, W. N. (Chris) Christiansen and me, set out to look for an alternative site, and we finished up at Cowra. We were going to recommend Cowra but Chris had second thoughts, and said he would like to push on a little further-and he found this magnificent site near Parkes. So it was really Chris's discovery. was left to Kevin Sheridan, Frank Gardner and me, with the aid of a low-flying aircraft, to do some tests to make sure that the site did not suffer from interference from industrial noise from the town of Parkes itself.
Centaurus A, The Core of the Problem
Authors: J Tingay for the SHEVE team Steven
Published: June 2013

The bright, peculiar elliptical galaxy Centaurus A (NGC 5128, PKS 1322-427) was one of the first extragalactic radio sources to be optically identified (Bolton et al 1949). At a distance of 4 Mpc, Centaurus A is the closest active radio galaxy and affords the highest linear imaging resolution (1 mas ~ 0�02 pc) and hence the best prospects for studying an active nucleus close to the central radio source. We present the results of multi-epoch, 8� 4-G Hz, very long baseline interferometry (VLBI), imaging observations of the nucleus made over the past three years. The nucleus possesses a core-jet structure where the inner portion of the jet shows apparent linear motion with a velocity substantially less than the speed of light.
Elastic Behaviour of Terbium Metaphosphate Glasses Under High Pressures
Authors: Senin HB , Sidek HAA , Saunders GA
Published: June 2013

The elastic and nonlinear acoustic vibrational properties of terbium metaphosphate glasses (Tb2O3)x(P2O5)1?x with x = 0�226,0�247,0�263 and 0�271 (x is the mole fraction) have been determined from measurements of the effects of temperature, hydrostatic pressure, and uniaxial stress on' ultrasonic wave velocity. At temperatures below about 140 K, the elastic stiffness of' (Tb2O3)x(P2O5)1?x glasses becomes anomalously dependent upon temperature, a behaviour usually associated with interactions between acoustic phonons and two-level systems. Except for the (Tb2O3)0�271(P205)0�729 glass, the hydrostatic pressure derivatives of the elastic stiffness and also of the bulk modulus BS of terbium metaphosphate glasses are small and negative. The third-order elastic stiffness tensor components CIJK of the (Tb2O3)0�247(P2O5)0�753 glass between 77 K and 400 K have also been determined. At room temperature, C112, C123 and C144 are positive while C111, C155 and C456 are negative. Both longitudinal and shear acoustic mode Gr�neisen parameters are small and negative: the application of pressure softens the long-wavelength acoustic phonon mode frequencies. The mode softening is enhanced as the temperature is reduced.
Recent Progress in High Field Magnetism
Authors: Date Muneyuki
Published: June 2013

Recent progress in high field magnetism performed mainly in the Research Centre for Extreme Materials, Osaka University, is reported, with a short survey of the Centre's history. The main activities are in the fields of magnetism and superconductivity where a common keyword is highly correlated electron physics. A rich variety of effects such as metamagnetism, field-induced electronic transitions etc. is summarised. High field studies are also effective in the fields of atomic and molecular sciences; for example, field-induced transparency in liquid oxygen, and diamagnetic orientation of organic and biological materials. New frontiers in high field technologies are discussed, including a highly sensitive magnetometer using the dynamical Faraday effect.
Silent Discharges in Ozonisers and CO2 Lasers
Authors: Yagi S , Kuzumoto M
Published: June 2013

Dielectric barrier ac discharges (silent discharges) have been developed to optimise the performance of ozonisers and C02 lasers. The characteristics and properties of the discharge are discussed and examined in the light of experimental results. The frequency of the applied voltage and gap length are around 1 kHz and 1 mm for the ozoniser and around 100 kHz and several em for the C02 laser. We have found that ozone is produced with high efficiency by using high energy electrons in a narrow gap. On the other hand, for C02 lasers, a high excitation efficiency is achieved by specifying the laser medium gas at very high N2 concentrations in a long gap.
Measurement of Electron Impact Ionisation and Attachment Coefficients in NO2/He Gas Mixtures and Estimated Electron Collision Cross Sections for NO2
Authors: Sakai Y , Okumura T , Tagashira H
Published: June 2013

The electron impact ionisation a/po and attachment coefficients r]/po in N02/He gas mixtures, where po is the gas pressure at O�C, are measured by a steady-state Townsend method over a wide range of compositions and E/po values. Based on the experimental values of a/po and r]/ po, a preliminary set of the cross sections for N02 is estimated by a Boltzmann equation analysis and values of the cross sections are discussed.
Calculation of Electron Scattering on Atoms and Ions
Authors: Bray Igor
Published: June 2013

We present an overview of the application of the convergent close-coupling (CCC) method to electron scattering on light atoms and ions. Particular emphasis is given to those areas where other theories have difficulty, e.g. total ionisation cross sections and the associated spin asymmetries. We begin with the simplest application to the Temkin–Poet model problem of electron-hydrogen scattering, which we use to validate the CCC approach. Subsequently, results are given for electron impact ionisation of various initial states of the targets H(1s, 2s), He(11S, 23,1S), He+(1s), Li(2s), 05+(2s) and Na(3s).
Ab initio Calculations on Excited Molecular Ions of Ethylene and Acetylene
Authors: R Davidson Ernest , A Wang Yan
Published: June 2013

Ab initio calculations of the energy and wave functions for neutral molecules and excited molecular ions are used to interpret the EMS and PES spectra of acetylene and ethylene. The five satellite regions of acetylene are assigned to intensity borrowed from 2σg, 3σg and 2σu primary hole states by ion states with configurations (πu)−2 (δg)1, (πu)−2 (3σg)−1 (πg)2, and (πu)−1 (3σg)−1 (πg)1. The Dyson orbitals for the satellite regions of acetylene and ethylene are shown to differ from the Dyson orbitals of the primary holes. The importance of choosing basis sets appropriate to the excited states of the ion is illustrated.