bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Topography of Electron Momentum Densities of Linear Molecules
Authors: Kulkarni Sudhir A. , Gadre Shridhar R. 
Published: February 2015

Abstract
A topographical study of the electron momentum density (EMD) of some linear molecules is presented with special emphasis on the bond-directionality principle. A new approach to the bond-directionality (BD) principle has been proposed. This is based on the analysis of curvatures of critical points at p = 0 and elsewhere on the bonding axis. The linear molecules are classified into three broad categories: those which fully obey or disobey the BD principle as well as those which satisfy it only partly. The Laplacian of the EMD at p = 0 has been associated with the quality of the wavefunction via the electron density in the tail region. Also, the similarity in the critical structure of both the EMD and the spherically averaged EMD at the origin is brought out.
Core-Orthogonalization Effect in Pseudopotential Theory of the Charge Density Distribution of Valence Electrons in Semiconductors with Comments on the Effects in Momentum Space
Authors: Kobayasi Teiji , Nara Hisashi 
Published: February 2015

Abstract
A pseudopotential calculation has been performed for the charge density distribution in Si and Ge, with the core-orthogonalization terms fully included. The state of a positron subject to the Coulomb field of the resultant electron distribution in Si is also calculated. A possible improvement of the calculated distributions of electrons and positrons in momentum space is discussed.
Electron Momentum Densities by (y, e y)-Spectroscopy
Authors: Bell F. , Tschentscher Th. , Rollason A. J. 
Published: February 2015

Abstract
We report coincidence measurements of inelastically scattered 148 keV photons and the recoil electrons generated within thin Al and Cu foils. We have analyzed both the Doppler broadening of the scattered photon intensity and the angular correlation of the recoil electron. This corresponds to different scans through the three-dimensional electron momentum density of the target. Estimates of the triple-differential cross-section for Compton scattering are given. The experiment was performed with synchrotron radiation from a bending magnet of the DORIS storage ring at DESY, Hamburg.
Ultrahigh-Energy-Resolution Inelastic X-Ray Scattering Spectroscopy
Authors: Burkel E. 
Published: February 2015

Abstract
Very-high-energy-resolution measurements using X-rays can be achieved by extreme backreflection (Bragg angle close to 90°) from perfect crystals. This technique allowed the development of the instrument INELAX for inelastic scattering experiments at the HARWI wiggler at DORIS, DESY Hamburg. Recently, a high energy resolution of 9 meV could be achieved, and the instrument proved to be an excellent tool to investigate collective excitations in condensed matter. Energy transfers from 10 meV to 12 eV and wave vectors up to about 10 Â-1 are accessible.
The Anisotropy of the Reciprocal Form Factor and the Electronic Structure of Crystalline Lithium Hydride
Authors: Asthalter Tanja , Weyrich Wolf 
Published: February 2015

Abstract
New high-precision measurements of the isotropic as well as of three directional Compton spectra of lithium hydride have been carried out using241 Am as a γ-ray source. In order to account for the extreme sensitivity of LiH powder to atmospheric moisture, the final data (i.e. the reciprocal form factor) were corrected for the LiOH content determined by titrimetric analysis. For the interpretation of the data, theoretical calculations were carried out using a Hartree-Fock program for periodic systems (CRYSTAL). Basis sets published by Dovesi et al. were used, one of which allows for polarisation of both the hydride and lithium ions. Comparison of the theoretical data with the experiment shows much better agreement of the results of complete solid-state calculations that take into account higher-order effects (polarisation and covalency) than those obtained by Löwdin orthogonalisation of free-ion wave functions (which assumes pure ionicity, neglecting all but first-order effects). The influence of further polarisation functions on the reciprocal form factor is inves-tigated and discussed. The remaining discrepancies are attributed to electron-electron correlation.
Compton Profile of Boron Nitride
Authors: Ahuja B. L. , Gupta Anil , Department of Physics, M. Regional Engineering College, Jaip B. K. 
Published: February 2015

Abstract
The Compton profile of hexagonal boron nitride has been measured using 59.54 keV gamma rays and a planar Ge detector. The results are compared with theoretical Compton profiles calculated for various ionic arrangements and with those available from a bond orbital model, LCAO and SC canonical HF calculations. The LCAO calculation is in relatively good agreement with the present measurement.
The Electronic Structure of Hydrogen Bonding in a-Oxalic Acid Dihydrate
Authors: Weisser M. , Weyrich W. 
Published: February 2015

Abstract
Compton spectra of a-oxalic acid dihydrate single-crystal slices and powder samples were measured in a helium atmosphere using 59.537 keV 241 Am radiation. In the anisotropic case, the scattering vector was oriented parallel to the shortest hydrogen bond, in the direction of the C = O bond, parallel to the C - O bond and perpendicular to the (a, c)-plane. The comparison of theoretical reciprocal form factors, calculated with a local density-approximation (LDA) method for an α-(COOH)2 • 2H2O cluster in triple-zeta basis-set quality, with the experimental data has demonstrated that there is a considerable influence of intermolecular interactions on the electronic structure. Further calculations including the intermolecular interactions of the first coordination sphere by symmetrical orthogonalisation of the LDA wave functions clearly improved the agreement of experiment and theory. A theoretical analysis of the reciprocal form factor Ba (s) in the direction of the three different hydrogen bonds of α-oxalic acid dihydrate on the basis of the cluster calculations has shown that in the region above s = 1.9 Å all these bonds are dominated by electrostatic attrac-tion and exchange repulsion of the donor and the acceptor system.
The Electron Momentum Distribution in Lead
Authors: Timms D. N. 
Published: February 2015

Abstract
Directional Compton profiles have been measured along the [100], [110] and [111] crystallographic axes in lead using 412 and 59.5 keV γ-radiation from 198 Au and 241 Am radioisotope sources, respectively. Both measurements are in mutual agreement and show a small anisotropy, which is just distinguishable within the statistical error. The spherically averaged data have been compared with the predictions of relativistic Hartree-Fock (RHF) and non-relativistic Hartree-Fock (HF) free atom calculations. As expected, the experiment clearly favours the RHF rather than the HF calculation.
Recent Advances in Electron Momentum Spectroscopy
Authors: Weigold Erich 
Published: February 2015

Abstract
The flexibility of the (e, 2e) technique or "electron momentum spectroscopy" (EMS) in obtaining information on the electronic structure of atoms, molecules, and solids is demonstrated. High-resolution EMS measurements for argon, including the first measurements of momentum profiles belonging to the 2P0 and 2De -manifolds, are used to demonstrate the technique for atomic targets. The d-wave transitions in argon are entirely due to initial-state correlations. The first (e, 2e) measurements on an excited target, and also on an oriented target, are discussed. Sodium atoms are pumped to the ml = +1 state of the excited 3p-state by σ+ -light from a laser. The (e, 2e) measurements on this excited state are in excellent agreement with the momentum density given by the 3p (ml - 1) Hartree-Fock wavefunction. The recent measurements of the valence-electron momentum distributions for ethyne, as well as some earlier results for water, are used as an example of the application of EMS to the study of molecules. The application of the EMS technique to measure spectral momentum densities in condensed-matter targets is demonstrated by some recent results on amorphous carbon.
What Can Positrons Contribute to High-Tc Superconductivity?
Authors: Peter M. , Jarlborg T. , Manuel A. A. , Barbiellini B. 
Published: February 2015

Abstract
The positron annihilation technique has made well-known contributions to the study of Fermi surfaces in "classical" superconductors, including A15 phases where the definition of the Fermi surface has been questioned on the grounds of Anderson localization. In the case of the superconducting oxides, even more far out models were proposed, which made the clear imaging of the Fermi surface by positrons desirable. The difficulties due to the predicted weakness of the signal, and the large possibility for trapping have now been surmounted and the Fermi surface has been seen; what more can we learn from positrons?
After presenting the actual situation with experiment, we will comment on enhancement and correlation and their effect on ACAR and lifetime studies. Then we explain the picture of Jarlborg and Singh of enhancement, with its recent tests for many substances. We conclude by asking the question of sensitivity of positrons to many-body effects. Ferromagnetism, antiferromagnetism, possibly charge density waves have been seen -superconductors, heavy fermions and spinons-holons would pose a problem.
Stephan Berko (1924-1991) was interested in these problems and knew that better machines and better detectors would open new possibilities.
Isomerization of Diphenyl Polyenes. Part VI. Properties of l,8-Diphenyl-l,3,5,7-octatetraene Fluorescence in Poly (vinyl alcohol) and other Polymer Films
Authors: Kawski A. , Kubicki A. , Kukliński B. , Piszczek G. 
Published: February 2015

Abstract
Absorption, fluorescence and emission anisotropy spectra of l,8-diphenyl-l,3,5,7-octatetraene (DPO) in non-heated and heated polyvinyl alcohol) (PVA) films were measured at 296 and 87 K. Similar spectra to those of DPO in PVA heated to 423 K were observed for DPO in polymer films: polyvinyl chloride) (PVCh), polyvinyl formal) (PVF) and ethylacetate (EtA). Unusual photophysical properties of DPO fluorescence occur only in non-heated PVA. These are the increase in the absorbance and quantum yield at temperatures above 358 K and the change in the emission anisotropy, r, due to softening or stiffening of the PVA film. For DPO in PVCh and EtA, high values of r, close to 0.4, are observed (0.391 and 0.389, respectively), thus manifesting the stiffening of the microenvironment around the DPO molecule in these polymers. In the case of DPO in non-heated PVA film, strong temperature dependence of the intensity distribution in the fluorescence band and double exponential emission decay are observed. This proves that the fluorescence originates from two conformers: all-trans and s-eis.
Generation of Fullerenes by Circumscribing
Authors: Dias Jerry Ray 
Published: February 2015

Abstract
An algorithm for the generation of fullerenes with isolated pentagonal rings by successively circumscribing base excised internal structures with a combination of pentagonal and hexagonal rings is detailed. The presence of adjacent bay regions is a necesary and sufficient condition for preculding this circumscribing operation for a polypent/polyhex system.
Magnetism of Alkalitetrafluoromanganates (III) AMnF4 (A = K, Rb, Cs): Neutron Diffraction, Mössbauer and Magnetization Investigations
Authors: Molinier Michel , Frommen Christoph , Massa Werner , Pebler Jürgen , Roisnel Thierry 
Published: February 2015

Abstract
The magnetic properties of the d4 Jahn-Teller systems AIMnIIIF4 with layered structures were investigated. Neutron diffraction on powders of KMnF4 and RbMnF4 revealed different antiferro-magnetic spin arrangements below TN = 4.5 K and 2.3 K, respectively: for KMnF4 canted antiparallel along a and b, for RbMnF4 parallel along a and antiparallel along b, in both cases parallel along c, the stacking direction of layers. Mössbauer investigations on 57Fe doped KMnF4 confirmed a spin orientation approximately within the layer plane. A discussion is given of the contributions to the magnetic hyperfine field and the Mössbauer linewidth in quasi-two-dimensional antiferromagnets with Ising anisotropy due to thermal excitation of domain wall dynamics (solitons). The experimental data seem to confirm the predicted exponential temperature dependence of the linewidth. From magnetization measurements on powders and a single crystal of KMnF4 the 2-d exchange energy and the out-of-plane and in-plane anisotropies could be extracted. In addition, from susceptibility measurements the exchange energies of NaMnF4 , RbMnF4 and CsMnF4 were calculated. A linear dependence of these exchange energies (positive for ferromagnetic CsMnF4 , negative for the other AMnF4 compounds) on the cos2 of the Mn-F-Mn bridge angle is observed and compared with the behaviour of the AFeF4 compounds which is also linear but with reverse sign of the slope. The specific superexchange mechanisms active in Jahn-Teller systems with antiferrodistortively ordered layers are suggested to be responsible for these findings.
Modified 1/N Expansion for the Dirac Equation for Screened Coulomb Potential
Authors: Roychoudhury Rajkumar , Panchanan Swati 
Published: February 2015

Abstract
It is shown that if one chooses the shift parameter correctly then the lowest order term in the modified 1/N expansion for the Dirac equation as formulated by Stepanov and Tutik gives accurate results for Coulomb like potentials. Explicit eigenvalues have been obtained for the screened Coulomb potential

and these are compared with exact numerical results and the results obtained by the choice of shift suggested by Stepanov and Tutik.
Axisymmetric Magnetohydrodynamic Equilibria without a Wall
Authors: Lortz D. , Haimerl W. 
Published: February 2015

Abstract
Starting from the ideal magnetohydrodynamic (MHD) equations, we consider the following axisymmetric configuration: a current-carrying plasma torus in a homogeneous magnetic field that is aligned parallel to the torus axis. At a certain field strength this configuration is in equilibrium without need of external current singularities such as wires or walls.The magnetic flux function is expanded in small inverse aspect ratio. The geometry of this configuration is completely determined to second order as a function of the profile parameters.
Anharmonic Self-Consistent Theory of Crystals. I. A 1 d Quartic Crystal Model
Authors: Soulayman S. Sh. , Marti C. Ch. , Guilpin Ch. Ch. 
Published: February 2015

Abstract
We apply the Unsymmetrized Self-Consistent-Field-Method (USCFM) to a linear infinite chain of identical atoms with a quartic pair interaction potential. We show that an exact solution of the USCFM can be found in terms of a single auxiliary function ℒ1 which is studied here in details. We use it to calculate the partition function, the energy and the free energy, the moments of the position, the corrections due to quantum effects and higher terms of the potential, the specific heat and the thermal expansion. An anharmonic approximative approach, based on the self-consistent potential of the used method, is developed also. We apply these two approaches to the study of the thermoelastic properties of a one dimensional system (krypton). It is demonstrated that the approximate approach is very effective when dealing with pairwise potentials of positive second derivative. The Lennard-Jones potential is used in our calculations.
Homogeneity Range, Hole Concentration, and Electrical Properties of the Bi2Sr3-x CaxCu2O8+y ,(1≦ x ≦ 2) Superconductors
Authors: Ghigna P. , Chiodelli G. , Anselmi-Tamburini U. , Spinolo G. , Flor G. 
Published: February 2015

Abstract
The homogeneity range of Bi-Sr-Ca-Cu oxides with two-layers ("2212") structure has been investigated with X-ray powder diffraction and electron microprobe determination on materials with nominal Bi2Sr3-xCaxCu2O8+y) , (x = 1÷ 2 in 0.1 steps) composition and being prepared at two different oxygen partial pressures. The results show Bi over-stoichiometry and a wide range of Sr/Ca substitution.
DC resistivity measurements indicate that the hole concentration is controlled by both oxygen non-stoichiometry and cation molecularity. It is shown that a single phenomenological relation between hole concentration and electrical properties can explain in a consistent way the complex behaviour of the whole set of materials with different oxygen non-stoichiometry and cation molecularity.
Stabilization of Unstable Periodic and Aperiodic Orbits of Chaotic Systems by Self-Controlling Feedback
Authors: Pyragas K. 
Published: February 2015

Abstract
The methods of stabilization of unstable periodic and aperiodic orbits of a strange attractor with the help of a small time-continuous perturbation are discussed. The perturbation is applied to the system in such a way that the desired periopdic or aperiodic orbits remain unperturbed. An experimental application of the methods can be carried out by a purely analogous technique without use of any computer.
Reaction Time to Voltage Pulses Applied to Semiconductor Impact Ionization Breakdown
Authors: Kittel A. , Rau U. , Hirsch M. , Richter R. , Huebener R. P. , Peinke J. , Parisi J. 
Published: February 2015

Abstract
The electric avalanche breakdown in semiconductors exhibits many features of a phase transition. In this paper, we introduce time-resolved measurements performed during the transition from a low to a high conducting state as reaction to a sudden change of the control parameter (i.e., the voltage bias).
On Complexity, Grammars and the Inferring of Models
Authors: Wagner Peter 
Published: February 2015

Abstract
Various measures of the physical complexity of a dynamical system are considered. Without question, these measures introduce a new quality in the description of nonlinear complex systems, but we think that their advantages have not yet been demonstrated in a convincing manner. We show that the estimation of the complexity of a given system is related to the extraction of models from real-world data.
Solvatochromic Fluorescence of 8-(Phenylamino)-1-naphthalene-ammoniumsulfonate (8,1 ANS) in 1,4-Dioxane/Water Mixtures, revisited
Authors: Hüttenhain Stefan H. , Balzer Wolfgang 
Published: February 2015

Abstract
The correlation of the solvatochromic fluorescence properties of 8-(phenylamino)-1-naphthalene-ammoniumsulfonate (8,1 ANS) in 1,4-dioxane/water mixtures with Eτ(30) and Δƒ values of the respective solvents shows that besides the polarity the nature of the solvent mixture determines the fluorescence intensity I and the Stokes shift Δv̅. Different amounts of hydrogen-bonding are suggested to be responsible for the different slopes of the correlation line plots. Key words: Solvatochromic fluorescence 8-(phenylamino)-1-naphthalene-ammoniumsulfonate (8,1 ANS); Semi-empiric polarity parameters 1,4-dioxane/water mixtures.
Proton Spin Lattice Relaxation in the Dimethylammonium Group
Authors: Venu K. , Sastry V. S. S. 
Published: February 2015

Abstract
A model for the spin lattice relaxation time of the protons of dimethylammonium in the Redfield limit and common spin temperature approximation is developed. The three fold reorientations of the methyl groups, the rotation of the whole molecular group around its two fold symmetric axis and possible correlations among these motions are considered. The effect of these processes on the dipolar interactions among the protons within the same molecular group is taken into account. The resulting relaxation rate is powder averaged and used to explain the experimental data in literature on [NH2(CH3)2]3Sb2Br9 . The analysis shows that dynamically inequivalent groups exist in this compound and that the effect of proposed correlation among the different motions on the final results is negligible.
Isomerization of Diphenyl Polyenes. Part V. The Origin of Fluorescence of l,6-Diphenyl-1,3,5-hexatriene in Poly (vinyl alcohol) Films
Authors: Kawski A. , Kubicki A. , Kukliński B. , Piszczek G. 
Published: February 2015

Abstract
The effect of temperature on the absorption and fluorescence spectra of l,6-diphenyl-1,3,5-hexatriene (DPH) was investigated in three different polymer films: polyvinyl chloride) (PVCh), polyvinyl formal) (PVF) and polyvinyl alcohol) (PVA) in the temperature range 296-423 K. Anomalous behaviour of the fluorescence intensity was observed only for DPH in non-heated PVA film. The intensity distribution in the fluorescence band of DPH in both non-heated and heated PVCh and PVF films was found to be independent of the excitation light wavelength, λexc . The behaviour of DPH is similar in the PVA film heated to 423 K. For these samples, single exponential fluorescence decay was observed. The behaviour of non-heated DPH samples in PVA is quite different, the intensity distribution and the fluorescence band position depending strongly on λexc and the fluorescence decay being double exponential. It can be inferred that the fluorescence of DPH in a non-heated PVA sample consists of two components, the first originating from the all-trans conformer and the second from the ground-state s-cis conformer.
Molecular Dynamics in Tetramethyl Ammonium Hexabromo Selenate [N(CH3)4]2SeBr6. A Proton NMR Study
Authors: Murthy B. V. S. , Ramesh K. P. , Ramakrishna J. 
Published: February 2015

Abstract
spin-lattice relaxation time T1 and second moment M2 have been studied as a function of temperature over the temperature range 445 to 77 K. A discontinuous change in T1 at 365 K, indicates the presence of a phase transition, while the slope change at 152 K, is attributed to a change in the TMA ion dynamics from tumbling to torsion. The T1 results could be explained in terms of inequivalent TMA ions and their small angle torsional oscillations. A second moment (M2) transition occurs around 160 K and is ascribed to the freezing of TMA tumbling and CH3 reorientation.
Dielectric Properties of Mesomorphic n-TPEB's in Isotropic Phase
Authors: Jadżyn J. , Czechowski G. , Żywucki B. , Legrand C. , Bonnet P. , Dąbrowski R. 
Published: February 2015

Dielectric relaxation studies have been performed for the isotropic phase of a series of mesogenic
molecules of l-[3-n-alkyl-biphenyl]-2-[4-isothiocyanatophenyl]ethane, CnH2n+1-Φ-Φ-CH2CH2-Φ-NCS (n-TPEB), for n = 7, 8 and 9. Two Debye-type dielectric absorption bands have been
interpreted as corresponding to the rotation around the short and long molecular axis.
Towards a Fundamental Structure of Continuum Mechanics
Authors: Stuke Bernward 
Published: February 2015

Abstract
For a class of systems obeying Euler's equation of motion the existence of a quantity to be named "proper mechanical energy" (PME) is shown which, together with internal energy, results in a quantity to be named "proper energy" (PE), which is conserved under conditions of time-dependent potentials. The appertaining formal structure for the continuum mechanics of such systems is the counterpart to Gibbs' fundamental equation of thermodynamics and the relations deriving therefrom. Euler's equation of motion, in particular, corresponds to the Gibbs-Duhem equation of thermodynamics. The transport properties of PME and PE are different from those of the corresponding conventional energies. The results point to a general structure of this kind for continuum mechanics.