bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Isomers of the Benzene Dimer from Mass Selective Hole-Burning Spectroscopy
Authors: Scherzer W. , Krätzschmar O. , Selzle H. L. , Schlag E. W.
Published: February 2015

Mass selected hole-burning experiments in the gas phase are presented for the benzene dimer formed in a supersonic jet expansion. The observed spectra show three different ground state configurations for the dimer. From isotopically substituted dimers the structure of the most prominent conformer could be assigned to a very floppy T-shape like structure with two non-equivalent sites for the benzene molecules.
The v4 Rotation Vibration Band of Dicyanoacetylene
Authors: Winther Flemming , Ketelsen Maren , Niedenhoff Marion , Yamada Koichi M. T.
Published: February 2015

The v4 fundamental band of dicyanoacetylene has been recorded in a 60 m-Herriot cell with a PC-controlled diode laser spectrometer. Transitions were measured in the range from 2232 to 2250 cm-1 with a resolution of 0.005 cm-1 . Although the upper state is perturbed, v0 = 2245.374 (3) cm-1 and B'-B" = - 1.016 (10) • 10-4 cm-1 could be obtained.
An Effect of Deuteration on Ion Motions and Hydrogen Bondings in Guanidinium Tetrafluoroborate
Authors: Wąsicki J. , Grottel M. , Kozak A. , Pająk Z.
Published: February 2015

The fluorine spin-lattice relaxation time as well as NMR second moment for perdeuterated guanidinium tetrafluoroborate were studied over a wide range of temperature.

An analytical solution of a set of coupled differential equations describing the time variation of nuclear magnetisations for four unlike spin systems was applied to analyse all cross-relaxation effects in the compound. Activation parameters EF
a = 19.3 kJ/mole and τF
U= 9 • 10"14 s for the isotropic anion reorientation were derived.

A coupling of rotational modes of cation and anion was found. Significant lowering of the melting point explained by a weakening of the hydrogen bonds involves diminishing of the ion activation energies due to the large positive isotope effect
Phase Transitions of Scaling Functions Derived from Experimental Time Series
Authors: Stoop R. , Parisi J.
Published: February 2015

The occurrence of phase transitions in dynamical systems is intimately related to the analyticity properties of the thermodynamical functions. Such effects are believed to be of generic nature (for example, homoclinic tangency points). For one-dimensional maps, their existence has been proven for both the probabilistic and the dynamical scaling functions (that is, the / (a) and <P (A) spectra, respectively). With the help of simple model systems, we elucidate the different combinations in which the two types of phase transitions (namely, in the f(x) and <ϕ(λ) spectra) can appear. Moreover, we demonstrate the numerical evidence of phase-transition-like behavior in both spectra derived from experimental time series of laser and semiconductor systems. Finally, we discuss new aspects for the evaluation of the thermodynamic functions from time series
The Electric Field Gradient at the Site of the Halogen Ion and Structure of Amino Acid Hydrobromides and Hydroiodides
Authors: Kehrer Armin , Dou Shi-qi , Weiss Alarieh
Published: February 2015

The 79,81Br and 127I NQR spectra of several hydrobromides, respectively hydroiodides, of amino acides and dipeptides were studied, mostly as functions of temperature in the range 77 < T/K <420. The investigated compounds are: L-Arg • HBr • H2O, L-Cys • HBr • H2O , L - Cys - S - S - L - Cys • 2HBr, ethanolamine • HBr, L-Glu • HBr, L-His • HBr, L-His • 2HBr, L-Ile HBr • H2O , Sar • HBr, (Sar)2 • HBr, L-Val • HBr • H2O , Gly • LiBr, Gly-Gly • LiBr, ethanolamine HI, Sar • HI, (Sar)2 • HI, (Gly)2 • HI, (L-Val)2 • HI, Gly-L-Leu • HI • H2O . A phase transition with hysteresis was observed for L-Val • HBr • H2O (Tc.up = 318 K, Tc.down = 242 K). Two solid phases of Sar • HI have been studied by NQR, one crystallized from melt, the other one from aqueous solution.

For three of the title compounds the crystal structure was determined at room temperature: L-His - 2HBr, P212121 , Z = 4, aj pm = 1652, b/pm = 916, c/pm = 721; L-Cys HBr H2O , P212121 , Z = 4, a/pm = 1955, b/pm = 746, c/pm = 550; Gly-L-Leu • HI • H2O , P2X, Z = 2, a / p m = 1289, b/pm = 914, c/pm = 615, ß/° = 99.

In most cases the halogen ion in the studied hydrohalides is polycoordinated by hydrogen bonds of the type N - H • • • X⊖ and O - H • • • X⊖ , X = Br, I. The NQR frequencies and, for iodine, the nuclear quadrupole coupling constants depend on this coordination. A low frequency (coupling constant) region is found for pure N - H • • • X⊖ coordination. Replacing one N - H • • • X⊖ bond by O - H • • • X⊖ rises the electric field gradient, EFG, respectively the resonance frequencies.

The dependence of the EFG on the hydrogen bond coordination N - H • • • X⊖ plus O - H • • • X⊖ is discussed for the title compounds including information from literature
On Heisenberg's Uncertainty Principle and the CCR
Authors: Honegger Reinhard
Published: February 2015

Realizing the canonical commutation relations (CCR) [N, Θ] = - i as N = - i d/dϑ and Θ to be the multiplication by ϑ on the Hilbert space of square integrable functions on [0, 2π], in the physical literature there seems to be some contradictions concerning the Heisenberg uncertainty principle ⟨ΔN⟨ ⟨ΔΘ⟨ ≥ 1/4. The difficulties may be overcome by a rigorous mathematical analysis of the domain of state vectors, for which Heisenberg's inequality is valid. It is shown that the exponentials exp {i t N} and exp{i sΘ} satisfy some commutation relations, which are not the Weyl relations. Finally, the present work aims at a better understanding of the phase and number operators in non-Fock representations.
On Classical Representations of Convex Descriptions
Authors: Bugajski Slawomir
Published: February 2015

It is demonstrated that if V* is not a vector lattice, where V is a base norm Banach space, then there is no commutative observable providing a classical representation for V. This observation generalizes a similar result of Busch and Lahti, obtained for V - the trace class of operators on a separable complex Hilbert space.
Frequency-and Temperature-Dependence of Second Refractivity Virial Coefficients
Authors: Hohm Uwe
Published: February 2015

A reasonable heuristic extrapolation of a theory given by Buckingham is used to estimate the frequency-and temperature-dependence of the second refractivity virial coefficient. The calculations are carried out for the atoms He, Ne, Ar, Kr, Xe and the small molecules H2 , N2 , O2 , HCl, CO2 , N2O, NH3 , CH4 , C2H4 , and SF6 . In some cases the frequency-dependence of BR (ω, T) is compared with experimental values, showing sometimes considerable deviations between experiment and the heuristic approach used in this work.
The Centimeter and Millimeter Microwave Spectrum of 1,1-Difluoro-2-Chloroethylene
Authors: Leal Luis A. , López J. C. , Alonso J. L. , Guarnieri A.
Published: February 2015

The rotational spectra of both 35Cl and 37Cl 1,1-difluoro-2-chloroethylene isotopomers have been measured in the frequency range 12-225 GHz. A first order quadrupole coupling analysis has been performed for both isotopic species. The calculated quadrupole coupling constants for the 37Cl species not previously reported are χaa = - 49.2 (2), χbb = 14.2 (1), and χcc = 28.7 (1). Accurate rotational constants, quartic and some sextic centrifugal distortion constants have also been determined for both isotopomers from the fit to the observed central frequencies.
A Proton NMR Study of n-Decylammonium Chain Dynamics in the Perovskite-type Layered Compound (C10H21NH3)2CdCl4
Authors: Jurga Stefan , Jurga Kazimierz , Reynhardt Eduard C. , Katowski Piotr
Published: February 2015

A detailed proton second moment and spin-lattice relaxation time investigation of the bilayered compound (C10H21NH3)2 CdCl4 is reported. In the low temperature phase the methyl group exe-cutes a classical threefold reorientation, while the NH3 group is involved in a similar reorientation in an asymmetric potential well. Evidence for defect chain motions in this phase has been found, and infomation regarding the potential wells associated with these motions has been extracted from the data. In the high temperature phase, slow chain defect motions and fast fourfold reorientations of chains about their long axes, parallel to the normal to the bilayer, have been observed.
Generation of Diatomic Diabatic States by a General Multi-State Rotation
Authors: Metropoulos Aristophanes
Published: February 2015

We present a general multi-state orthogonal transformation program that generates a set of diatomic electronic diabatic states from a set of vibronically interacting adiabatic states of the same symmetry.
Effect of Cooling Rate on the Structure of Sodium Borate Glasses
Authors: Ennas G. , Musinu A. , Piccaluga G. , Pinna G.
Published: February 2015

Sodium borate glasses with two different compositions have been prepared using cooling rates in the range 7 • 10-3 ◦C/s-2 • 102 °C/s. Structural characterization has been carried out by X-ray diffraction, and glass transition temperatures have been measured by Differential Scanning Calorimetry. The samples exhibit slightly different density values and glass transition temperatures. However, radial distribution functions appear extremely similar and the sodium coordination shell does not change in going from fast to slowly quenched glasses, showing that the short and medium range order is not affected by thermal treatment.
X-Ray and Neutron Diffraction with Amorphous Ti67Si33, V67Si33, and Cr67Si33
Authors: Präffcke A. , Lamparter P. , Steeb S.
Published: February 2015

The amorphous alloys Ti67Si33 , V67Si33 , and Cr67Si33 were produced by sputtering. Their structure was investigated by X-ray and neutron diffraction. X-ray diffraction showed that the structure of the three metallic glasses is not isomorphous. Neutron diffraction showed that Si-Si atomic pairs occur preferentially with distances distinctly larger than the atomic diameter of the Si atoms. For T67Si33 partial pair correlation functions could be evaluated from combination of the X-ray and the neutron data.

The structural results are compared with the structure of amorphous Mn74Si23P3 .
p, T-Dependence of the Molecular Dynamics in a Hydrophobic Model System: 2,2-Dimethyl-1-propanol/D2O
Authors: Has M. , Lüdemann H.-D.
Published: February 2015

Aqueous solutions of 2,2-dimethyl-1-propanol were studied as a model system for the p, T-dependence of the hydrophobic interaction at pressures up to 200 MPa and between 273 K and 403 K. The liquid/liquid phase separation of this alcohol in light and heavy water is described. As expected for aqueous solutions of hydrophobic substances, the solubility of the alcohol is larger in light than in heavy water.

The p, T, c-dependence of the self diffusion coefficients and of the rotatoric mobility, as given by the deuteron spin lattice relaxation times, of the water and alcohol molecules are studied in the one phase region.

The translational and the rotational mobility of the water molecules in the binary solution show at low temperatures the anomalous pressure dependence typical for neat water.
Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. II. Diatomic Molecules
Authors: Koch Wolfhard , Neymeyr Klaus , Pernpointner Markus , Schaper Barbara , Strecker Klaus
Published: February 2015

A comparison of numerical Simplified Unrestricted Hartree-Fock (SUHF) results (electronic ground state configurations, total energies, first ionization potentials, atomic charges, atomic spin densities of diatomic molecules) with those of equivalent standard calculations suggests the applicability of the non-empirical but drastically simplified procedure. SUHF may even approach ab initio quality obtained with simple (STO-3G) contracted Gaussian basis sets.
Anomeric Effect and Charge Density of Dioxane and Dichlorodioxane
Authors: Buschmann Jürgen , Strümpel Marianna , Luger Peter
Published: February 2015

The low-temperature molecular structure and electron density (ED) distribution of dioxane and trans-2,5-dichloro-l,4-dioxane were determined near 100 K from X-ray data. Deformation electron density maps were calculated by Fourier and multipole expansion techniques. The multipole model charge distribution of dioxane determined from experimental data was taken as a reference state, relative to which the ED of the substituted ring was analyzed. These fragment deformation density maps show quadrupolar deformations on atoms O, CI, and anomeric C only. The highly correlated orientation of the lobes at these atomic sites seems to indicate that the observed charge rearrange-ment is caused by three-center interactions.
Electrostatic Potential from High-Resolution X-Ray Diffraction. Application to a Pseudo-Peptide Molecule
Authors: Ghermani N. , Lecomte C. , Bouhmaida N.
Published: February 2015

The calculation of the electrostatic potential of a molecule removed from the crystal lattice is derived from the parameters obtained by a kappa refinement and by a Hansen-Coppens electron density model. These calculations in direct space are applied to N-acetyl-α,β-dehydrophenylalanine; deformation potentials calculated by Fourier transformation are compared to those obtained in direct space.
Electrostatic Properties of 3-(p-Ethoxyphenyl) sydnone
Authors: Fan Jumn-Min , Wang Yu , Ueng Chuen-Her
Published: February 2015

The bonding type and characteristic chemical reactions of the sydnone ring have been rationalized by examination of the deformation electron density distribution and electrostatic potential from both experiment and theory. The net atomic charges, bond lengths and bond orders of the title compound confirm the semiaromatic bonding type for the sydnone ring. The highly negative net atomic charge of C4 suggests its susceptibility to electrophilic substitution at this position. The well known 1,3-dipolar cycloaddition reaction of the sydnone ring can be understood by the analysis of the 7 t -o r b i t a l wavefunctions, which give rise to similar deformation densities as the experimental ones. The good agreement between the experimental and theoretical (ab initio calculation using 3-21G basis sets) deformation density distribution of the title compound justifies the use of the same basis set to derive the electrostatic potential. The electrostatic potential map reveals all the possible protonation sites of the sydnone ring at O1, N2 and O6 with the deepest hole at 06 (84.6 kcal/mole).
Ab initio Study of the Spin Density of Nitroxide Radicals
Authors: Wang Jiahu , Smith, Jr. Vedene H.
Published: February 2015

The spin densities of the nitroxides H2NO, (CH3)HNO and (CH3)2 NO have been studied by iterative CI methods. Calculations at different geometries with various basis sets were performed. It is found that the spin distribution is delocalized within the N-O group, and substitution of the hydrogen atoms on the nitroxyl group by methyl groups changes the spin distribution significantly. Electron correlation, as well as the basis-set quality, plays an important role for the fluctuation of spin populations in the nitroxide radicals. It has been found that the spin density map can be predicted fairly well when correlation was included at certain levels and reasonable quality basis sets were employed. The spin polarization mechanism has been studied through a core excitation method. The superiority of local-spin-density (LSD) theory over the unrestricted Hartree-Fock (UHF) method in spin property studies is discussed.
Visualization of Shapes of Molecular Anions
Authors: Gadre Shridhar R. , Kölmel Christoph , Ehrig Michael , Ahlrichs Reinhart
Published: February 2015

A recently formulated strict definition of the boundary surface of molecular anions has been employed for the visualization of some simple systems. The examples included are CN-, N-
3 , NO -
3 , ClO-
4, ClO-
3 , and BrO-
3 ions. A discussion on the anisotropy of electrostatic interaction of these anions is also presented.
On the Topography of Electron Momentum Densities of Linear Molecules
Authors: Kulkarni Sudhir A. , Gadre Shridhar R.
Published: February 2015

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Correlation between Colour and Fluorescence of Lapis lazuli
Authors: Banerjee A.
Published: February 2015

Colour and fluorescence of lapis lazuli depend on its mineral components. UV-VIS-and fluorescence-spectra of specimen rich in lazurite differ from those rich in haüyne.
Stabilization of Unstable Periodic and Aperiodic Orbits of Chaotic Systems by Self-Controlling Feedback
Authors: Pyragas K.
Published: February 2015

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.
Nucleation Rate of a Localized Structure in a Reaction-Diffusion System
Authors: Christen T.
Published: February 2015

We derive the nucleation rate of a localized structure of a one-dimensional, nonlocal, bistable reaction diffusion equation near instability of the uniform state.
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

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

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

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

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.
Notizen: An Automatic Scan Waveguide Microwave Fourier Transform Spectrometer
Authors: Krüger M. , Harder H. , Gerke C. , Dreizler H.
Published: February 2015

The design and performance of an automatic scan wave-guide microwave Fourier transform spectrometer is described, which is of great help in assigning microwave spectra.
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

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

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

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.
Solvation of Ions in Aqueous Solutions of Hydrophobic Solutes
Authors: Hawlicka Ewa , Grabowski Roman
Published: February 2015

The self-diffusion of Na+, Et4N+ and I- in mixtures of water with n-propanol at 25 °C and with lert-butanol at 30 °C was measured as function of salt concentration and solvent composition. The limiting self-diffusion coefficients of the ions were used to compute the ionic radii. The influence of the composition of the solvent on the solvation of the ions is discussed. In aqueous solutions of both alcohols the effective ionic radii are reduced. The strongest influence is found for the same solvent composition for which the highest concentration of the alcohol clusters has been reported. Hydra-tion of the clusters of n-propanol causes a vanishing of the second hydration shell of Na+ and the first one of Et4N+ and I-. In the case of terf-butanol even the first hydration shell of Na+ is partially reduced.
The Physical Interpretation of Special Relativity -a Vindication of Hendrik Lorentz
Authors: Prokhovnik S. J.
Published: February 2015

Modern astronomy has revealed the existence of a cosmologically-based fundamental reference frame associated with the distribution of matter in our universe. The existence of such a frame offers a firm basis to H. A. Lorentz's approach to the understanding of the relativistic effects associated with the transformation named after him.

Lorentz's approach and his notion of an "ether" evolved over a number of years, and it has been further refined as a result of our new view of the universe. It now provides a complete interpretation of Special Relativity based on a single assumption -that light-propagation takes place with respect to a unique, observable, fundamental reference frame. This interpretation links Einstein's theory with Lorentz's findings and so further develops our understanding of it; it also offers new insights for the better understanding of quantum and particle physics.
Inverse Isotope Effect on the Melting Temperature of LiNO3
Authors: Hidaka Takehiko , Lundén Arnold
Published: February 2015

An inverse isotope effect on the melting temperature, Tm, of lithium nitrate has been observed: Tm

is by 0.7 °C higher for a sample with 98.6% 6Li than for one with 92.6% 7Li. The abnormal sign of

the isotope effect on Tm has already previously been found in fractionation experiments. Our results

are in agreement with Holmberg’s finding for Tm of LiNO3 · 3H20 (30 °C) that the isotope effect is

inverse for 6Li- 7Li but normal for H-D. Different types of experimental methods have been compared

also for lithium sulfate, where a normal isotope effect has been found for both Tm (860 °C) and

Tc (577 °C), the temperature of a monoclinic-cubic phase transition. Otherwise, nonhydrogen isotope

effects at solid-solid transitions are usually inverse for displacive transitions, or nearly zero for

order-disorder transitions.
Graph-Theoretical Enumeration of Conjugated Patterns for Carbocyclic and Heterocyclic Compounds*
Authors: Morikawa Tetsuo
Published: February 2015

An algorithmic analysis of the existence of conjugated patterns for carbocyclic and heterocyclic compounds is presented. This graph theoretical method is applicable to the enumeration of Kekulé patterns for hydrocarbon benzenoids, as a special case.
Spectral Properties of Some Naphthalene Derivatives of Bicarboxylic Acid; Comparison of Experimental Results with Theoretical Predictions
Authors: Bauman Danuta , Hanemann Thomas , Wolarz Eryk
Published: February 2015

The basic electronic quantities of some dichroic dyes, naphthalene derivatives of bicarboxylic acid, have been evaluated theoretically using a semi-empirical INDO (intermediate neglect of differential overlap) Cl (configuration interaction) approach. The theoretical data have been com­ pared with the experimental results obtained from the absorption and fluorescence measurements of the dyes dissolved in toluene and oriented in liquid crystal 8CB. Additionally, the order parame­ ters of the dyes in smectic A and nematic phases of 8CB have been determined.
Synthesis and Microwave Spectroscopic Study of Fluorinated Methyl Isocyanides
Authors: Krüger M. , Dreizler H. , Lentz D. , Preugschat D.
Published: February 2015

Difluoromethyl isocyanide has been generated by flash vacuum pyrolysis of pentacarbonyl (di-fluoromethyl isocyanide) chromium at 240 °C. Spectroscopic studies revealed the presence of several major and minor impurities like HCN, HCC -CN and HCC -NC . The pyrolysis of pentacarbonyl (fluoromethyl isocyanide)chromium did not lead to the observation of free fluoromethyl isocyanide. The rotational spectrum of difluoromethyl isocyanide has been recorded with a conventional continuous wave Stark spectrometer and a molecular beam Fourier transform microwave spectrometer resulting in A = 10.110841 (42), B = 4.550914 (19), C = 3.343550 (19) GHz, D′J = 0.41(13), D′JK = 26.72(36), D′J
= - 21.3 (18) kHz. The dipole moment components μa = 1.46(1), μc= 1.83 (1) and μtotal 2.34 (1) D were obtained from the second order Stark effect. The 14N nuclear quadrupole hyperfine structure in the rotational spectrum of CHF2-NC has been resolved and the 14N nuclear quadrupole coupling constants xaa = 599.0 (10), xbb = −406.5 (14), xcc= −192.6 (14) kHz have been obtained.
An EXAFS Investigation of Local Structure around Rb+ in Aqueous Solution
Authors: Kubozono Yoshihiro , Hirano Akiko , Maeda Hironobu , Kashino Setsuo , Emura Shuichi , Ishida Hiroyuki
Published: February 2015

EXAFS spectra have been measured in order to elucidate the local structure around Rb+ in aqueous solution. It has been found that the Rb+ is surrounded by ca. six O atoms of H2O molecules. The Rb -O distance was determined to be 2.90 (3) Å. The coordination number and Rb -O distance compare well with those of the other alkaline metal ions estimated by X-ray diffraction.
Notiz: A Molecular Source of CF2(X̃) at Room Temperature
Authors: Hack W. , Wagner M.
Published: February 2015

In the molecular system of F2 and C3O2 a fast formation of CF2 (X̃) was detected directly via LIF. The CF2 (X̃) production mechanism could be a single step process but also how­ ever a chain reaction via F atoms.
Transition to Higher Chaos in Diffusively Coupled Chemical Oscillators
Authors: Baier Gerold , Sahle Sven , Kummer Ursula , Brock Roland
Published: February 2015

A one-dimensional array of diffusively coupled identical oscillators is considered. It is demon­strated that coupling of two, three, four, and six oscillators can create chaos with one, two, three, and four positive Lyapunov characteristic exponents, respectively. We suggest that the turbulent behavior found with many coupled cells can be explained in terms of a high-order chaotic attractor.
The Velocity of Current Filaments in Weak Magnetic Fields
Authors: Christen Thomas
Published: February 2015

In the presence of a perpendicular weak magnetic field, current filaments in semiconductors can obtain a transverse drift. In the framework of a collective-coordinate ansatz, an expression for the velocity of the filament is derived for a simple type of extrinsic semiconductors. It turns out that the motion is caused by the coupling of the non-uniform Hall angle to the translational Goldstone mode of the current filament.
Universality in the One-Dimensional Self-Organized Critical Forest-Fire Model
Authors: Drossel Barbara , Clar Siegfried , Schwabl Franz
Published: February 2015

We modify the rules of the self-organized critical forest-fire model in one dimension by allowing the fire to jum p over holes of ≤ k sites. An analytic calculation shows that not only the size distribution of forest clusters but also the size distribution of fires is characterized by the same critical exponent as in the nearest-neighbor model, i.e. the critical behavior of the model is universal. Computer simulations confirm the analytic results.