bluuebunny/crossref_metadata_2025 huggingface dataset:
The 12C(p,2p)11B Reaction at 100 MeV
Authors: Devins DW , Friesel DL , Jones WP , Attard AC , Svalbe ID , Officer VC , Henderson RS , Spicer BM , Shute GG
Published: June 2013

The 12C(p,2p)l1B reaction has been measured at 100 MeV in both symmetric and asymmetric geometries. Distorted wave impulse approximation calculations were used to obtain spectroscopic factors for all states of l1B below 7 MeV excitation. From these spectroscopic factors and the shapes of the measured angular correlations, it is concluded that (i) no large 1f components are present in the wavefunction of the ground state of 12C and (ii) this experiment gives no evidence for the formation of giant resonances as the intermediate step in multistep reaction processes to the 4�44 MeV (5/2-) and 6�74 MeV (7/2-) states of 11B.
Sea Level Muon Spectrum and Muon Charge Ratio derived from CERN Results for Nucleon?Nucleus Inelastic Interactions
Authors: Bhattacharyya DP , Roychoudhury RK
Published: June 2013

The sea level cosmic ray spectrum and muon charge ratio have been estimated by using the energy moments of the cross section for proton-air inelastic collisions. These energy moments have been determined by interpolation from CERN results for proton-nucleus inelastic interactions in pion production. The derived results are compared with previous work.
The Parkes 2700 MHz Survey (Fourteenth Part): Catalogue for Declinations ?4° to ?15°, Right Ascensions 10h to 15h
Authors: Bolton JG , E Wright Alan , Savage Ann
Published: June 2013

A catalogue of 278 radio sources is presented from a 2700 MHz survey of 0�247 sr. The catalogue is essentially complete for sources with S2700 ~ 0�25 Jy, corresponding to a source density in this area of 820 sources per steradian. The catalogue includes the results of examination of the Palomar Sky Survey prints at the positions of the sources.
New Optical Identifications from the Fourteenth Part of the Parkes 2700 MHz Survey: Declinations ?4° to ?15°, Right Ascensions 10h to 15h
Authors: Savage Ann , Bolton JG
Published: June 2013

Identifications are suggested for 36 radio sources from a survey of 0�247 sr of the southern sky, 14 with galaxies and 22 with possible quasi-stellar objects. The identifications were made from prints of the Palomar Sky Survey.
Electron Drift Velocities in Air
Authors: Hegerberg R , Reid ID
Published: June 2013

The drift velocities of electrons in dry CO2-free air at 293 K have been measured over the range 0�1 ~ Ej N ~ 1 Td for gas pressures between 0�4 and 1 �3 kPa.
The Drift Velocity of Electrons in Carbon Dioxide at Temperatures between 193 and 573 K
Authors: Elford MT , Haddad GN
Published: June 2013

The drift velocity of electrons in carbon dioxide has been measured at gas temperatures ranging from 193 to 573 Kand at EIN values up to 20 Td at 193 K, 50 Td at 293 K and 40 Td at 573 K. The measured drift velocities were found to decrease linearly with increasing gas number density at a given value of EIN for gas temperatures less than 293 K. This dependence has been attributed to multiple scattering and the data have been extrapolated to zero number density to correct for this effect. Comparisons are ,made with previous measurements where available. The present data for the variation of pN(thermal) with temperature agree to within the experimental error with the' data of Pack et at: (1962).
The Static Lattice Model of Hardy and Bullough Applied to the Noble Metals to Calculate Divacancy Interaction Energies and Relaxations
Authors: Richardson DD
Published: June 2013

The discrete lattice method of Hardy and Bullough (1967) and Bullough and Hardy (1968) is applied to the noble metals to obtain estimates of the relaxations around a vacancy and of the near neighbour divacancy interaction energy. Accuracy is improved on earlier work by use of a point-formula integration technique. It is found that the soft phonon spectrum of gold leads to large relaxations and a divacancy interaction energy which is about half the single vacancy formation energy. It is therefore concluded that the model is too simplistic to describe the single and divacancy situations in gold, and may also not be accurate for copper and silver, though for the lighter elements the results are better.
The Lost Neutrinos of the Sun
Authors: Peak LS
Published: June 2013

For the past decade there has been a discrepancy between the number of solar electron neutrinos predicted and observed. This paper discusses the magnitude of this discrepancy and the various ways by which the problem might be resolved.
Ion Scattering Spectrometry
Authors: MacDonald RJ
Published: June 2013

The scattering of ions from the surface and near surface region is a common method of analyzing solid surfaces. The basic principles of ion scattering spectrometry are reviewed with emphasis on those factors which affect the interpretation of the scattering measurements. In particular we emphasize the role of the interatomic potential and the neutralization factor involved in ion-surface scattering. Several aspects of ion scattering spectrometry are then outlined, including its application to studies of the composition and crystallographic structure of surfaces. Some factors of ion scattering spectrometry peculiar to surfaces are mentioned, e.g. the sequential 'double' collision event. The use of photon emission studies as a means of inferring something of the neutralization processes involved is briefly outlined, emphasizing the study of polarized emission from scattered ions at glancing incidence to the target surface.
Phonons, Lattice Instabilities and Superconductivity
Authors: G Smith Harold
Published: June 2013

The relationship of phonon anomalies and lattice instabilities to high Tc superconductivity is explored. Inelastic neutron scattering studies have revealed an intimate and dramatic relation between certain phonons and lattice transformations, real or incipient, for moderate to high Tc superconductors, which are minimal or nonexistent in very low Tc or nonsuperconductors. Experimentalevidence is presented for a wide variety of superconducting materials and possible theoretical explanations for their behaviour are discussed.
Magnetic Order in Spatially Disordered Systems
Authors: Hicks TJ
Published: June 2013

Magnetic order in metallic and nonmetallic binary alloys is discussed. A recent model, in which the breakdown of long-range magnetic order in metallic alloys is due to the cooperative change of the moment magnitude with concentration, is illustrated with. examples from nickel alloy systems. Percolation at the critical concentration for long-range order plays a part in these alloy systems, as it does for nonmetallic alloys and metallic alloys in which the magnetic moment magnitude is not so environment dependent. Discussion of the magnetic state in the non long-range ordered composition range leads to a description of spin glasses. The results of recent experiments on the low temperature configuration, the AC susceptibility near the freezing temperature, and the dynamics at all temperatures are presented with the implications for the nature of the spin glass transition.
Progress in the Development of High Sensitivity Gravitational Radiation Antennas
Authors: Blair DG
Published: June 2013

This paper reviews the development of gravitational radiation antennas from the pioneering work of J. Weber during the 1960s to the present day. Major problems stilI to be overcome are outlined,and prospects for the detection of gravitational radiation from astrophysical sources are discussed. Major emphasis is placed on Weber bar antennas, with spacecraft Doppler ranging and laser interferometer antennas discussed briefly. (As this review is intended primarily for non-specialists, no attempt is made to cite all workers in the field.)
Frictional Force Exerted on Two Equal Spheres Situated Along the Axis of a Circular Cylinder Slowly Rotating About Axes Perpendicular to Their Line of Centres
Authors: Greenstein T , Zocco JG
Published: June 2013

Approximate expressions are presented and numerical values provided which enable the frictional force on the reference sphere to be computed for the case when two equally sized spheres situated along the axis of an infinitely long circular cylinder slowly rotate with equal and opposite angular velocities about axes perpendicular to their line of centres in a viscous fluid.
Inertial Development of Vorticity in Pulsar Magnetospheres
Authors: Burman RR
Published: June 2013

It is pointed out that inertial drift of a species will become important, corresponding to development of vorticity, as its number density becomes small. Hence, regions of inertial development of vorticity will form natural boundary layers to domains in which a species is concentrated.
Electron Vacancy Production in Near-symmetric Collisions of 100 MeV Copper Ions
Authors: Hay HJ , Pender LF , Treacy PB
Published: June 2013

With a high-resolution Si(Li) X-ray detector, characteristic K X rays have been detected with targets of Cr, Fe, Cu, Ge and Se ombarded by 100 MeV Cu ions, equilibrated by passing through carbon. Cross sections for X-ray production, target-to-projectile vacancy-sharing ratios and K, to K, ratios were measured and compared with predictions of molecular-coupling theories. The results show little greement with existing models based on rotational coupling in molecular-orbital states.
Compton Scattering of 279.1 and 661.6 keV Photons by K-shell Electrons
Authors: Whittingham IB
Published: June 2013

The spectral distributions of 279?1 and 661? 6 keY photons incoherently scattered by the K electrons of U, Pb, Ta and Sm are calculated for a point-Coulomb potential using a theory previously developed by the author which accounts completely for electron binding and relativistic effects. WKB treatments of the regular and irregular continuum Dirac wavefunctions have been developed and used to mprove the computation of the 'absorption-first' radial matrix elements. The scattered photon spectra for the four elements and scattering angles for which the free electron Compton energy lies below the high energy cutoff due to conservation of energy have broad peaks shifted by 3 to 18 and by 30 to 50 keY, for 279?1 and 661? 6 keY photons respectively, from the free electron Compton energy towards higher scattered photon energies. An infrared divergence, whose magnitude increases strongly with atomic number, commences at ~ 56 keV and is present in those spectra where there is no peak or where the peak lies significantly above 56 keY. Differential cross sections daK' computed using a low energy cutoff, are nonzero for zero-angle scattering and are lower than the Klein-Nishina cross section daF for scattering angles ~ 50� for 661?6 keV photons and for all scattering angles for 279?1 keY photons (with the exception of 80�-130� in the case of Sm). The cross section ratio daK/daF increases with increasing scattering angle until about 100� and 80� for 279?1 and 661? 6 keY photons respectively and then subsequently decreases slowly.
Corotation and Poloidal Flow in Pulsar Magnetospheres
Authors: Burman RR
Published: June 2013

In recent years, authors have recognized that it is essential to allow for the non-corotational part - '\l(/J of the electric field in pulsar magneto spheres, but have continued to neglect it .in zones of corotation. It is shown here that, in order to understand the flow dynamics and avoid absurdities, it is essential to use the correct functional form for (/J everywhere outside the star-without exception. Implications include a potential difference between zones of corotating electrons and ions, resulting in a large local 'V(/J field in vortical boundary layers separating those zones, directed so as to force a mixing of electrons and ions there. This result clashes sharply with a well-known conclusion of Holloway, based on use of the zero-inertia approximation with (/J piecewise constant on magnetic field lines: he found the electron and ion zones to be separated by evacuated regions. A further consequence of the present analysis is a possible mirroring of electrons between the northern and southern boundary layers, while they drift toward the star because of dissipative effects. These findings are not restricted to the usual axisymmetric case, but are valid for the oblique rotator, with non-aligned magnetic and rotation axes, so long as zones of corotation exist.
The Spectrum of 12C in a Multi-configuration Hartree-Fock Basis
Authors: Amos K , Morrison I , Smith R , Schmid KW
Published: June 2013

The energy level spectrum of 12C is calculated in a truncated but large shell model space of projected one particle-one hole Hartree-Fock determinants using a realistic g matrix. Predictions of electromagnetic decays and electron scattering form factors are compared with experimental values.
Rotating Strings, Glueballs and Exotic Mesons
Authors: Burden CJ , Tassie LJ
Published: June 2013

The relativistic string equation is solved for motion corresponding to rigid body rotation about the z-axis. One class of these solutions, namely the planar solutions, allows for the construction of two types of exotic meson and one type of glueball, all of which have asymptotically straight ChewFrautschi plots. The first type of meson only exists when the number of quarks or antiquarks is 4, 5, 6 or 7, whereas no such restriction applies to the second type. For each of these cases the first type of meson is energetically more favourable than the second type for a given angular momentum.
Effective Weak Non-Ieptonic Hamiltonians for Flavour Changing Processes
Authors: DC Miller Robert , HJ McKellar Bruce
Published: June 2013

We present a complete analysis of the W mediated effective weak non-leptonic theory for s, c, b and t flavour changing processes. Calculations are based upon the standard model with n generations. The theory is developed using a matrix formalism which leads to compact theoretical results and a simpler numerical analysis. In our analysis we take account of scheme and effective theory dependence of the QCD parameters. Explicit numerical calculations are performed for effective weak non-leptonic Hamiltonians describing s, c, band t decay, in both the penguin free and penguin generating sectors of the theory, for the modified minimal subtraction (ms) scheme and IX = 0 gauge. Our approach is to display the calculations as a detailed application of the Appelquist-Carazzone decoupling theorem incorporating some of the latest theoretical developments in this area.
GDR Contribution to Coulomb Excitation. I. 1p Shell Nuclei
Authors: Barker FC
Published: June 2013

The contributions to the Coulomb excitation of the first excited states of 6Li, 7Li, lOB and 12C due to virtual excitation of the giant dipole resonance (GDR) are calculated, using shell model wavefunctions for the ground and first excited states. When the radial integrals are renormalized in order to fit the experimental B(E2) values for the transitions between these states, the calculated GDR contributions agree reasonably with the measured values in 6Li, 7Li and lOB.
Recoil-distance Lifetime Measurements of 47SC Levels
Authors: Ohnuma H , Foot PB , Aoki T , Ryan CG , Bolotin HH
Published: June 2013

The mean lives of the first excited ~- and ~+ states at 808 and 1391 keV excitation energy in 47SC were measured using the recoil-distance method (RDM). The levels of interest were populated in the 44Ca(O(, py) reaction using 9 MeV 0( beams. The mean lives extracted from the p-y coincidence data were ,(808 keV, ~-) = 22� 5 ps and ,(1391 keV, ~+) = 13 �4 ps. These results are compared with similar prior measurements on other levels of interest in 47SC as well as with those in the other Sc isotopes, and are discussed in the light of the systematics displayed.
Electron?Hydrogen Elastic Scattering at Intermediate and High Energies
Authors: Das JN , Biswas AK , Saha N
Published: June 2013

Electron-hydrogen elastic scattering at intermediate and high energies (in the range 30-400 eV) is considered. The calculational method of Das is applied with improved input functions. Improvement is noticed in the results and, except around an energy of 100 eV, reasonable agreement is obtained with experiment.
The Loss-cone Driven Electron-cyclotron Maser
Authors: Hewitt RG , Melrose DB , Rönnmark KG
Published: June 2013

Electron-cyclotron instabilities may be classified in two ways depending on whether the relativistic correction to the gyrofrequency is important (class S) or not (class N), and whether the instability mechanism is of a maser type (class M) or due to bunching (class B). Renewed interest in class SM has followed the Wu and Lee application of it to the interpretation of terrestrial kilometric radiation. The maser is assumed to be driven by a one-sided loss-cone distribution of electrons. This mechanism seems particularly favourable for the interpretation of certain planetary, solar and stellar radio emissions
A New Class of Atomic States: The 'Wannier-ridge' Resonances
Authors: Read FH
Published: June 2013

The evidence for the existence of systems that are dominated by electron-electron correlations is briefly reviewed, with particular attention being paid to (i) the processes of near-threshold electronimpact ionization and excitation of atoms and (ii) the structure of atomic doubly excited states and Feshbach resonances. New evidence is then presented for the existence of atomic resonances in which two excited electrons both have high val. es of the principal quantum number n (up to n = 8), and in which these two electrons reside on or near the Wannier ridge (i.e. with r1 ~ -rz).
Thermal Electron Attachment to SF6 and CFCl3
Authors: Crompton RW , Haddad GN
Published: June 2013

Measurements of the attachment rate for thermal electrons to SF6 and CFCI3 have been made using the Cavalieri electron-density sampling technique. The largest single source of error was shown to be uncertainty in the composition of the gas mixtures used in the experiments which contained < 10 ppm of the attaching gases. By paying special attention to this problem, the overall uncertainty in the attachment rates was reduced to less than � 3 %.
Spin Glasses in Transition?
Authors: Hicks TJ
Published: June 2013

Spin glasses have variously been described as apparently frozen but very slowly relaxing spin systems, and also as magnetic phases below a second order transition. The structural and dynamic properties of metallic spin glasses are surveyed with emphasis on neutron scattering and low field magnetic measurements. Spin glass regions in phases with magnetic long range order are included, and an attempt is made to assess spin glass theories with respect to the various transitions.
The Spectroscopy of 198O11 and the 187N11 Ground State
Authors: K Sheline Raymond
Published: June 2013

The spectroscopies of 190 and 21 Ne (both eleven-neutron systems) are compared. The 1-+ [211 iJ, t+ [220il and t- [lOttl bands are observed in both nuclei. On the basis of these similarities 190 is assumed to be a prolate rotor like 21 Ne. If then the recently studied IBN ground state is also considered to be a deformed system (a one-proton hole in the 190 nucleus), both the 1- ground state spin and the sudden change in the systematics of the two-neutron binding energies can be understood.
Kinetic Theory Analysis of Electron Attachment Cooling in Oxygen
Authors: Skullerud HR
Published: June 2013

The attachment cooling effect observed by Hegerberg and Crompton (1983) has been analysed theoretically and numerically in a Boltzmann equation eigenvalue approach. The effect is highly sensitive to the shape and magnitude of the rotational excitation cross sections. When due account is taken of the rotational excitations associated with the (0‾2) negative ion resonances, good agreement between theory and experiment can be obtained with reasonable input cross-section data.
Low-lying Negative-parity Levels of 17N and 18N
Authors: Barker FC
Published: June 2013

On the basis of a weak-coupling model, adjustments are made to the interactions used in the full shell model calculations of Millener in order to fit the experimental energies of the low-lying negativeparity levels of 16N and of the low-lying positive-parity levels of 180 and 190 . The predicted energies of the low-lying negative-parity levels of 17N then agree better with experiment, while those for 18N lead to suggested spin assignments for the observed levels.
Cosmic Ray Anisotropy and the Knee of the Energy Spectrum
Authors: Clay RW
Published: June 2013

The knee of the cosmic:ray energy spectrum occurs at an energy slightly below 101 6 eV. At a similar energy significant changes are found in cosmic ray shower development and anisotropy. It is suggested that these changes can be understood if there is a general proton dominated cosmic ray flux along our spiral arm from outer galactic regions, which is exceeded by an iron dominated flux from the opposite spiral arm direction at energies between ~ 1014 and ~ 101 7 eV.
Coulomb Excitation of 7Li
Authors: Vermeer WJ , Baxter AM , Burnett SM , Esat MT , Fewell MP , Spear RH
Published: June 2013

Coulomb excitation of the 0�478 MeV, J1t = t-, first excited state of 7Li has been studied using beams of 7Li ions and targets of 138Ba and 208Pb. Spectra of the scattered particles were measured at 171� using an annular Si surface-barrier detector (l 38Ba and 208Pb targets) and at 90� using an Enge split-pole magnetic spectrometer (208Pb targets). For each experimental configuration, the bombarding energy at which nuclear interference became significant was determined experimentally. An analysis based upon the reorientation effect yielded the following results: the static electric quadrupole moment of the J1t = t- ground state (Q3/2-) is -4�0� 1�1 efm", the contribution of the giant dipole resonance (GDR) to the Coulomb-excitation cross section is 2�7 �0�2 times as great as would be calculated from the hydrodynamic model, and B(E2;t-~t-) is 7�42�0�14e2fm4 ? The value obtained for Q3/2- is in excellent agreement with results reported from atomic- and molecular-beam spectroscopy and from Coulomb scattering of aligned 7Li. Thus it provides a strong verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments, provided that the GDR effect is treated adequately.
Cross Sections for Electron Scattering in Nitrogen
Authors: Haddad GN
Published: June 2013

New measurements of electron drift velocities in mixtures of nitrogen and argon have been analysed to determine the normalization factor for the vibrational excitation cross sections for nitrogen. The validity of applying a two-term solution of the Boltzmann equation in these mixtures is demonstrated. The derived cross sections are shown to be consistent with earlier transport data in pure nitrogen.
An Absolute Measurement of Cherenkov Emission by Relativistic Muons in Pure Water
Authors: Bakich AM , Peak LS , Wearne NT
Published: June 2013

Relativistic cosmic ray muons passing through triple distilled water have been used to examine the absolute number of Cherenkov photons emitted between 250 and 650 nm. It is shown that almost all of the theoretically predicted photon number can be experimentally accounted for, provided that the apparatus is specifically designed to minimize losses due to reflection, absorption and coupling. It is noted that significant corrections need to be made for internal photomultiplier tube effects.
Ratio of the 4He(g, p)3H and 4He(g,n)3He Cross Sections
Authors: Barker FC
Published: June 2013

Recent measurements of the 4He(y, p)3H and 4He(y, n)3He cross sections suggest that their ratio in the giant dipole resonance region is approximately I . 6. This is in marked disagreement with detailed model calculations, which have given a ratio close to unity. We here explain why the calculations yielded this result, by using a simple argument based on independent experimental data and some apparently reasonable assumptions. In order to remove the discrepancy with experiment, it appears to be necessary to relax one of these assumptions and to include contributions from states of higher configurations
Higher Frequency Spectrum of a Diffuse Linear Pinch with Multiple Ion Species
Authors: Sy WN-C
Published: June 2013

A cold plasma model which takes into account finite ion cyclotron frequency effects and multiple ion species has been developed for wave propagation in arbitrary magnetic field geometries. This model has been used to derive an elegant system of normal mode equations for a 10w-fJ diffuse linear pinch. From a soluble model, general features of the spectrum are discussed up to and including the ion cyclotron range of frequencies. It is indicated that in the vicinity of the ion-ion hybrid cutoff frequency, there could exist global eigenmodes which might be useful for supplementary heating of diffuse linear pinches.
Two-dimensional Ising Model on a 4?6?12 Lattice
Authors: Lin KY , Huang WN
Published: June 2013

We have considered a two-dimensional Ising model on a 4-6-12 lattice. The partition function is evaluated exactly by the method of Pfaffian. The Ising model on a ruby lattice is a special case of our model.
On the Contribution of A McL Mathieson to Crystallography
Authors: L Mair Sylvia , W Wilkins Stephen
Published: June 2013

We briefly describe some of the main contributions of Dr A. McL. Mathieson to various aspects of X-ray crystallography, including his contributions to: (i) crystal structure determination; (ii) the development of X-ray diffraction instruments; and (iii) measurement procedures.
A Brief History of Fourier Methods in Crystal-structure Determination
Authors: Beevers CA , Lipson H
Published: June 2013

Fourier methods for the determination of crystal structures were first suggested by Bragg in 1929, and were then successfully used by Beevers and Lipson for determining the structure of CuS04.5H20 in 1934. It was necessary for methods of summation to be devised, and after some experimentation the Beevers-Lipson strips became established as the best device for the work. They enabled increasingly complicated structures to be derived, but ultimately more elaborate and automatic devices based on digital computers had to be introduced. At the same time, isomorphous-replacement, heavy-atom and direct methods were also developed and these have enabled structures of enormous complexity to be successfully determined.
Some Helical Structures Generated by Reflexions
Authors: Hurley AC
Published: June 2013

There has recently been a revival of interest in the helical structure built up as a column of face-sharing tetrahedra, because of possible applications in structural crystallography (Nelson 1983). This structure and its analogues in spaces of different dimensions are investigated here. It is shown that the only crystallographic cases are the structures in one- and two-dimensional space. For three and higher dimensional space the structures are all non-crystallographic. For the physically important case of three dimensions, this result is implicit in an early discussion by Coxeter (1969). Results obtained here include explicit formulae for the positions of all vertices of the simplexes for dimensions n = 1-4 and a demonstration that, for arbitrary n, the ratio of the translation component of the screw to the edge of the simplex is {6/ n(n+ I)(n+ 2)}1/2
Wavelength Dependence of Moderate Extinction Effects in an Extended-face Crystal of Cadmium Selenide
Authors: W Stevenson Andrew , Barnea Zwi
Published: June 2013

X-ray intensity measurements have been carried out with an extended-face single crystal of hexagonal CdSe using four different wavelengths. The wavelength dependence of moderate extinction effects (y > 0�7, where y is the secondary extinction factor) was investigated by analysing the Bragg intensities using Zachariasen's (1967) theory, with and without the sin 26 factor (6 being the Bragg angle), which was claimed to have been omitted from the original expression for the diffraction cross section in a perfect crystallite (Becker and Coppens 19740, 1974 b). The resulting Hamilton (1965) R factors for the different extinction models tested do not enable one to make conclusive statements in regard to the 'best' model, but the refined values of the domain radius r and the mosaic-spread parameter g suggest that the crystal is neither of type I (Le. r > Ag, where A is the wavelength) nor of type II (Le. r < Ag). The wavelength dependence of the extinction effects is adequately accounted for in terms of the models tested.
Technique and Performance of Powder Diffraction in Crystal Structure Studies
Authors: Taylor JC
Published: June 2013

A common use of powder diffraction data is for crystal structure studies. Since the pioneering papers of Rietveld (1967, 1969), powder diffraction has been improved in many ways. Some advances in powder diffraction techniques since an earlier review (Cheetham and Taylor 1977) are described, and an indication is given of how the Rietveld method is performing with X-ray and neutron diffraction. This method has been more popular with crystallographers than the integrated-intensity method since it attacks the superposition problem directly and allows more complex structures to be refined. It has been asserted (Sakata and Cooper 1969) that calculated e.s.d. values in the Rietveld method are low by a factor of about two, although the derived positional parameters have never been faulted. This does not negate the value of the method as corrections to the e.s.d. values can be computed (Cooper et aZ. 1981; Scott 1983). The problem of precision versus accuracy is universal; in fact most e.s.d. values published in single-crystal studies are probably low by a similar amount because of the widespread practice of omitting large amounts of 'weak' data in order to artificially lower the residuals and e.s.d. values. It is shown that powder methods, especially the Rietveld, have performed well in a variety of applications.
Electron Outflow in Axisymmetric Pulsar Magnetospheres
Authors: Burman RR
Published: June 2013

Mestel et al. (1985) have recently introduced an axisymmetric pulsar magnetosphere model in which electrons leave the star with speeds that are non-negligible, but not highly relativistic, and flow with moderate acceleration, and with poloidal motion that is closely tied to the poloidal magnetic field lines, before reaching a limiting surface, near which rapid acceleration occurs. This paper presents an analysis of flows which either encounter the limiting surface beyond the light cylinder or do not meet it at all.
A Bianchi Type V Universe with Stiff Fluid and Electromagnetic Radiation
Authors: Roy SR , Singh JP
Published: June 2013

This paper discusses the possibility of a Bianchi type V universe containing stiff matter and a source-free electromagnetic field which is, of necessity, found to be null. Physical and kinematical consequences of the model have also been considered.
The Influence of Magnetic Fields on Convective Motions in the Outer Layers of the Sun
Authors: Van der Borght R , Fox P
Published: June 2013

In this paper we make a preliminary investigation of the nonlinear equations of compressible convection under the influence of solar-type magnetic fields. A polytropic model of the basic structure is used and, although the model is somewhat restrictive, good agreement is obtained with general observations in both strong and weak field cases. The value and influence of the turbulent magnetic resistivity is investigated and the depth dependence of the vertical velocity within a given period is used to study the way in which the overstable oscillations change their direction of flow from positive to negative.
The Cancellation of Magnetic Flux. I. On the Quiet Sun
Authors: Livi SHB , Wang J , Martin SF
Published: June 2013

We studied the disappearance of magnetic flux in an area of the quiet Sun from digital and photographic magnetograms recorded at 2�5 min intervals for many hours on 9 July 1984 at the Big Bear Solar Observatory. We limited the quantitative part of the analyses to features which had a total of 1017 Mx (1 Mx "'" 10-8 Wb) or greater and at least a 20 G (1 G"", 10-4 T) contour, and which changed by more than 10% of the maximum measured flux during the 5�5 hours of most consistent image quality during the observing day. Sixteen examples of flux disappearance and three ephemeral regions met these criteria. The disappearance of flux in these examples occurred only in closely spaced features of opposite polarity. The mutual disappearance of magnetic flux in closely spaced features of opposite polarity is herein defined as 'cancellation'. The 16 examples of cancellation were observed in combinations of network features, intranetwork features, and ephemeral regions. In two of the three ephemeral regions, an imbalance of magnetic flux between the two poles within each of the ephemeral regions was created, at least in part, by the cancellation of one pole with an adjacent feature of opposite polarity. Many smaller cancellation are clearly recognized below the threshold that we established for our initial measurements. We conclude that cancellation is the dominant way in which magnetic flux is observed to disappear on the quiet Sun.
The Relationship Between Coronal Bright Points as Seen in He I ?10830 and the Evolution of the Photospheric Network Magnetic Fields
Authors: L Harvey Karen
Published: June 2013

Transient 'dark points' in He I,,10830 are found to be associated with small magnetic bipoles. The number of these dark points varies inversely with the sunspot number. Sampled over a solar cycle, about one-third of the dark points are associated with erupting magnetic flux (ephemeral regions) while the other two-thirds are associated with chance encounters of opposite magnetic polarity features. Since coronal bright points are associated with He I dark points, it is suggested that the inverse correlation of both of these events with the sunspot number results from the higher probability of chance encounters between magnetic network of opposite polarity (larger areas of mixed magnetic polarity) during low levels of solar activity.
The Cancellation of Magnetic Flux. II. In a Decaying Active Region
Authors: Martin SF , Livi SHB , Wang J
Published: June 2013

An active region was studied in detail during its period of decay from 3 to 8 August 1984 using Ha filtergrams and videomagnetograms acquired at the Big Bear Solar Observatory. The decay was initiated by a process of fragmentation in which very small knots of magnetic flux separated from larger concentrations of flux. The fragmentation was observed at discrete locations around the periphery of both the dominant areas of negative and positive field, but possibly occurred more frequently in the main polarity inversion zone. The fragmentation and migration of knots of magnetic flux were common predecessors to the disappearance of flux.
An Analytic Distorted Wave Approximation for Electropion and Photopion Production on 12C near Threshold
Authors: Di Marzio F , Amos K
Published: June 2013

An analytic distorted wave approximation (ADWA) that can be used to analyse photopion and electropion production cross sections is developed. An application is made to analyse data from 12C near threshold once the approximation scheme is established as a realistic replacement for the more usual, distorted wavefunctions given by the optical model for low energy pion scattering. The pion production data analyses made using a generalized Helm model for the transition densities clearly demonstrates the significant role of distortion effects and that the ADW A is a good and simple representation of these effects. Repeating the analyses using microscopic models of nuclear structure indicates inadequacies in those structure specifications.
EXAFS Spectroscopy by Continuum Soft X-ray Emission from a Short Pulse Laser-produced Plasma
Authors: Tallents GJ , Luther-Davies B , Horsburgh MA
Published: June 2013

The use of a laser-produced plasma created by low ener~y (E :::;; 61), ps duration laser pulses as the X-ray source for EXAFS spectroscopy in the 3-8 A wavelength band is investigated. We consider the various factors that affect the X-ray flux at the detector plane and investigate ways of optimizing that flux. A simple qualitative model has been used to describe the way in which the source intensity scales with parameters�such as the laser intensity. Practical problems associated with the implementation of the various different X-ray dispersive elements and detectors are discussed.
Relativistic Electron Injection into Axisymmetric Pulsar Magnetospheres
Authors: Burman RR
Published: June 2013

A formalism introduced by Mestel, Robertson, Wang and Westfold for the description of electron outflow in axisymmetric pulsar magnetospheres, following injection with non-negligible speeds from the stellar surface, is extended here to incorporate emission with relativistic speeds. The formalism is then used to study the possible kinds of outflow. They are organized into five types, corresponding to differences in the emission speed and its variation with latitude, and into two classes according to whether or not they reach a region of rapid acceleration.
Scattering of Pulsar Radiation and Electron Density Turbulence in the Interstellar Medium
Authors: Alurkar SK , Slee OB , Bobra AD
Published: June 2013

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.
Numerical Simulation of Positron Diffusion in the Heavy Noble Gases Ar, Kr and Xe
Authors: Singh Vikram , Grover PS
Published: June 2013

Numerical simulation has been carried out of positron annihilation and diffusion under the influence of an external temperature and electric field in heavy noble gases. The electric field was varied over the range 0-200 V cm - 1 amagat - 1 (1 amagat ... 2.687 xl 019 atoms cm - 3), whereas the temperature was varied from 300 to 3000 K. It is observed that the decay constant ZeIT increases with increasing atomic mass of the interacting gases He, Ne, Ar, Kr and Xe, while the diffusion coefficient decreases except in the case of neon.
Electron Momentum Spectroscopy
Authors: McCarthy IE
Published: June 2013

For sufficiently high electron energies (greater than a few hundred eV) and sufficiently low recoil momenta Oess than a few atomic units) the differential cross section for the non-coplanar symmetric (e,2e) reaction on an atom or molecule depends on the target and ion structure only through the target-ion overlap. Experimental criteria for the energy and momentum are that the apparent structure information does not change when the energy and momentum are varied. The plane-wave impulse approximation is a sufficient description of the reaction mechanism for determining spherically averaged squares of momentum-space orbitals for atoms and molecules and for coefficients describing initial- and final-state correlations. For mainly uncorrelated initial states, spectroscopic factors for final states belonging to the same manifold are uniquely determined. For molecules, summed spectroscopic factors can be compared for different ion manifolds. For atoms, summed spectroscopic factors and higher-momentum profiles require the dist~rted-wave impulse approximation.
Recent Progress in a Green's Function Method for the Calculation of Ionisation Spectra
Authors: von Niessen W , Tomasello P , Schirmer J , Cederbaum LS
Published: June 2013

The ADC( n) approximation scheme to the one-particle Green function is briefly outlined [ADC( n) stands for algebraic diagrammatic construction accurate to nth order of perturbation theory]. The solution of the equations can be done either by a pole search algorithm (PSA) or by the Davidson diagonalisation approach CDDA) whose problems and advantages are discussed. The results obtained for N 2 are compared. The methods are applied to interpret the ionisation spectra of p-quinodimethane, p-benzoquinone and to calculate the lowest ionisation energies of the transition metal diatomics CU2, Ag2, Cr2 and M02. The ADC(4) equations are computationally very demanding and additional approximations need to be introduced in order to apply this method to any but the smallest systems. Such a simplified model is presented and applied to N2 and CS2.
Dynamics of Single­ and Multi-photon Ionisation Processes in Molecules
Authors: McKoy V , Dixit SN , Dubs RL , Lynch DL
Published: June 2013

Single-photon ionisation and resonant multiphoton ionisation studies, which can now be carried out using synchrotron radiation and pulsed dye lasers respectively, are providing important dynamical information on molecular photoionisation. In this paper we discuss some results of our recent studies of several, single- and multi-photon ionisation processes in molecules. The results will be taken from our studies of (i) single-photon ionisation of linear molecules with emphasis on the role of shape and autoionising resonances on these cross� sections, (ii) photoionisation from oriented NiCO as a simple but realistic model of photoemission in adsorbate-substrate systems, and (iii) resonant multiphoton ionisation of H2.
Photoelectron Spectroscopy using Pulsed Free Jets
Authors: Carnovale Frank , Barrie Peel J , G Rothwell Richard
Published: June 2013

The use of pulsed gaseous free jets in the study of atomic and molecular species by ultraviolet photoelectron spectroscopy (UPS) offers a number of advantages over the usual continuous flow room temperature technique. Pulsed free jet expansions provide, on the one hand, 'cold' molecules for which spectroscopy is simplified through the absence of hot band structure and, on the other hand, cluster species including dimers, trimers and higher clusters, as well as intermolecular species, all generally of low intermolecular binding energies. Furthermore a high pressure gas pulse is a suitable medium for the preparation, relaxation and transport of reactive species formed in processes such as pyrolysis, photodissociation or electrical discharge. This paper describes the modifications made to an ultraviolet photoelectron spectrometer to allow measurements on pulsed free jet expansions. The important features of the modified instrument concern the control of the gas beam and the timing electronics for photoelectron detection. Examples of He I photoelectron spectra presented include (a) the demonstration of hot band structure in the room temperature UPS of ammonia, (b) the preparation of the dimer (NOh and higher clusters (NO) n of nitric oxide, (c) the UPS of sulfur dioxide clusters (S02) n' and (d) the UPS of ammonia clusters (NH 3) n'
Particle?Hole Description of Dipole States in17O
Authors: Eden JA , Assafiri YI
Published: June 2013

The particle-hole model has been applied to the 170 nucleus to study the electric dipole states below the giant dipole resonance (GDR). Comparison is made with the most recent photonuclear data for this nucleus and an E 1 assignment for the observed strength at 15� 1 Me V in the photoproton cross section is discussed. The WMBH residual interaction used in this calculation produces more T> strength below the GDR than predicted in other calculations using the Tabakin, Soper or Kuo-Brown interactions.
Comptonisation of Radiation Below the Cyclotron Frequency in a Strong Magnetic Field
Authors: Melrose DB , Padden WEP
Published: June 2013

We present new equations describing the Thomson scattering of the o-mode and z-mode in a strongly magnetised plasma, valid below the fundamental cyclotron frequency. Scattering by nonrelativistic thermal electrons leads to a frequency diffusion equation for the more strongly scattered o-mode and this equation is effectively the Kompaneets equation with cross section 2/ 15th of the Thomson' cross section. Transfer of the photons tends to be dominated by the less strongly scattered z-mode; an o-mooe photon is scattered occasionally into a z-mode photon, which then diffuses rapidly due to its large mean free path before being scattered back into an o-mode photon. Our results should have applications in X-ray pulsars and 'Y-ray burst sources, as well as magnetic white dwarfs occurring in cataclysmic variables.
A Note on Lan's Generalised Theory of Gravitation
Authors: Beesham A
Published: June 2013

Lau has recently proposed a generalised theory of gravitation incorporating time-dependent cosmological and gravitational terms which is consistent with Dirac's large numbers hypothesis. It is shown that all vacuum solutions in this theory are identical to those of Einstein's theory with a cosmological constant. In particular, solar system experiments cannot be used to test the theory.
Quiet Ionospheric Currents and Earth Conductivity Profile Computed from Quiet-time Geomagnetic Field Changes in the Region of Australia
Authors: H Campbell Wallace , R Schiffmacher Edward
Published: June 2013

Equivalent ionospheric source currents representing the quiet-day geomagnetic field variations were established for a half-sector. of the Earth that included Australia. The analysis used a spherical harmonic separation of the external and internal fields for the extremely quiet conditions existing in 1965. Month-by-month behaviour of the current system indicated a clockwise vortex source with a maximum of 12.8xl04 A in January and a minimum of 4.4xl04 A in June. The focus location shifted from about -32�5� geomagnetic latitude in summer to about - 30.0� in winter. The separated external and internal field coefficients were used to estimate the Earth's upper mantle electrical conductivity (J" at a depth d from about 250 to 350 km as (J" =0�00067 exp(O� 012 d) S m - I and from about 350 to 550 km as (J" = 0�0014exp(0�0088d) Sm- I .
The Cubic Response Tensor for a Magnetised Plasma: A Covariant Forward-scattering Approach
Authors: Melrose DB
Published: June 2013

The quadratic and cubic nonlinear response tensors are calculated for an arbitrary magnetised plasma using a covariant forward-scattering method. Some relevant approximate forms for the response tensors are derived, and translated into 3-tensor notation in the Appendix. The general form of the tensors is used to re-enforce an argument for the non-existence of turbulent bremsstrahlung.
An Experimental Investigation of Low Power, Long Duration Rotamak Discharges
Authors: Jones IR , Turley MDE , Wedding JE , Durance G , Hogg GR , Tendys J
Published: June 2013

A rotamak device is described in which compact torus plasmas are generated using relatively low RF input powers (~ a few kW). Compact torus configurations are generated in both argon and hydrogen plasmas and are sustained for ~ 9 ms. These configurations appear to be grossly stable and show no tendency to disrupt even when subjected to large amplitude forced oscillations. A configuration incorporating a toroidal field is also investigated.
Magnetohydrodynamic Equilibrium Models for Rotamak Plasmas
Authors: Donnelly IJ , Rose EK , Cook JL
Published: June 2013

A semi-analytic method is used to solve the Grad-Shafranov equation for a range of compact torus plasma configurations which have ellipsoidal separatrices, zero toroidal magnetic field and pressure P proportional to the square of the poloidal flux function 1[1. The equilibria are compared with the analytic solutions of the Solov'ev model, for which P ex 1[1.