The relaxation of velocity-space-anisotropies due to Coulomb collisions is studied within the class of bi-Maxwellian distributions in the presence of an external homogeneous magnetic field, both analytically and numerically. It is found that the anisotropy dependence of the energy exchange collision frequency well separates from its magnetic field dependence. In a certain region of magnetic field strength, the latter can be approximated by a substitution of the thermal electron's Larmorradius for the Debye-length in the Coulomb-logarithm, as has been conjectured earlier.

Open Access June 2, 2014

The Viscosity Coefficients of Biaxial-Nematic Liquid Crystals. Phenomenology and Affine Transformation Model

Dieter Baalss

Page range: 7-13

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Abstract

The viscosity tensor of biaxial-nematic liquid crystals contains 16 independent elements. A complete set of these viscosity coefficients is introduced and related to experimentally accessible quantities. Furthermore, the flow alignment and its stability against an arbitrary infinitesimal disturbance are discussed. By the affine transformation model, formerly established for the uniaxial symmetric case, one can express the viscous anisotropy of perfectly ordered biaxial ellipsoids in terms of the two viscosities of an isotropic reference system and the axes ratios of the nonspherical particles.

Open Access June 2, 2014

Relativistic Energy States of the A-Particle in Hypernuclei Using Gaussian Potentials

C. G. Koutroulos

Page range: 14-16

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Abstract

The Dirac equation with scalar potential and fourth component of vector potential of the Gaussian form is solved numerically for potential parameters obtained by a least squares fitting of the ground state binding energies of the A in a number of hypernuclei. The binding energies in the ground and excited states for various hypernuclei are determined. The spacings between the various levels are also given

Open Access June 2, 2014

Decomposition of Positive Sesquilinear Forms and the Central Decomposition of Gauge-Invariant Quasi-Free States on the Weyl-Algebra

Reinhard Honegger

Page range: 17-28

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Abstract

A decomposition theory for positive sesquilinear forms densely defined in Hilbert spaces is developed. On decomposing such a form into its closable and singular part and using Bochner's theorem it is possible to derive the central decomposition of the associated gauge-invariant quasifree state on the boson C*-Weyl algebra. The appearance of a classical field part of the boson system is studied in detail in the GNS-representation and shown to correspond to the so-called singular subspace of a natural enlargement of the one-boson testfunction space. In the example of Bose-Einstein condensation a non-trivial central decomposition (or equivalently a non-trivial classical field part) is directly related to the occurrence of the condensation phenomenon.

Open Access June 2, 2014

Molecular Ordering in Nematic MBCA and EPAPU

S. Sreehari Sastry, V. Venkata Rao, P. Narayana Murty, G. Satyanandam, T. F. Sundar Raj

Page range: 29-32

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Abstract

By EPR, two nematic liquid crystals (MBCA and EPAPU) were investigated using a steroidal nitroxide spin probe. In both liquid crystals the isotropic-nematic phase transition is of first order. The observed variation of the order parameter with temperature is compared with predictions from the Maier-Saupe and Humphries-James-Luckhurst models and with results obtained by several other experimental techniques.

Open Access June 2, 2014

Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate

J. Wąsicki, Z. Pająk, A. Kozak

Page range: 33-36

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Abstract

Temperature dependences of 1 H and 19 F second moment and spin-lattice relaxation times for polycrystalline pyridinium tetrafluoroborate were measured. A phase transition was discovered at 202 K. A model of cation reorientation between inequivalent (low-temperature phase) and equivalent (high-temperature phase) equilibrium positions is proposed. Whether the anion reorients isotropically or about a symmetry axis cannot be decided. An analysis of cross-relaxation effects yielded activation parameters for cation and anion reorientation. The rotational correlation times for both ions converge just at the phase transition reaching the value of 10 -10 s.

Open Access June 2, 2014

Elastic Constants of Nematic Phenylpyrimidines Determined by Two Different Methods

A. Scharkowski, H. Schmiedel, R. Stannarius, E. Weißhuhn

Page range: 37-42

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Abstract

A survey of various methods to measure the elastic constants K i of nematic liquid crystals is given. To determine K 1 , K 3 and the anisotropy of the diamagnetic susceptibility Δ x of two members of the 5n-hexyl-2-[4n-alkyloxy-phenyl]-pyrimidines and a mixture of both, we used a combined electromagneto- optical method, consisting in independent measurements of the optical phase difference in electric and magnetic fields acting on the same cell. The temperature dependence of the K 1- and K 3 -values for these phenylpyrimidines can be explained by common theories. The Δ x data show the same temperature dependence as the values of the orientational order parameter S obtained by 1 H-NMR.

Open Access June 2, 2014

The Influence of the Skin Effect on the Amplitude of Single Pulse Gamma Detected NMR on Oriented Nuclei Signals

D. J. Isbister, D. H. Chaplin

Page range: 43-49

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Abstract

The effects of skin depth on gamma detected single pulse Nuclear Magnetic Resonance on Oriented Nuclei (NMRON) signals are theoretically explored for narrow, intermediate and broad line metallic samples, using the density matrix approach describing a pure Zeeman system. It is shown that the skin effect distortion of the signal can dominate over intermediate to broadline distortions for that range of experimental conditions generally applicable to ferromagnetic hosts. In particular, the skin effect distortions of the first maximum, obtained when the excitation pulse width is lengthened, are significant and can determine the accuracy of calibration of the radiofrequency "(rf)" field amplitude at the resonating nuclei when assigning an average turn angle to this maximum.

Open Access June 2, 2014

Anomalous X-ray Scattering Study of the Quasi-crystalline Al₆₅Cu₂₀Fe₁₅ Alloy

E. Matsubara, Y. Waseda

Page range: 50-54

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Abstract

The environmental radial distribution functions (RDFs) around Cu and Fe as well as the ordinary RDF of an as-quenched Al 65 Cu 20 Fe 15 alloy have been determined by anomalous x-ray scattering (AXS) and conventional x-ray diffraction techniques. The experimental information indicates that a strong directional dependence along the symmetrical axes exists for the Cu atoms but not for the Fe atoms. Almost identical RDFs were also obtained in both the as-quenched and fully-annealed states of the Al 65 Cu 20 Fe 15 alloy. Thus, the small differences observed between diffraction profiles of the as-quenched and annealed samples of this alloy may be attributed to defects or strains introduced during the rapid quenching process.

Open Access June 2, 2014

A Deuterium NMR Study of some Ammonium Tetraphenylborates

Marco L. H. Gruwel, Roderick E. Wasylishen

Page range: 55-66

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Abstract

Deuterium nmr has been used to study the rotational dynamics of the ammonium ion in ammonium tetraphenylborate and of the cation in a series of methylammonium tetraphenylborates. The results of variable temperature 2 H relaxation measurements (T 1Z and T 1Q ) on the parent compound, ND 4 B(C 6 H 5 ) 4 , lead to a low activation energy for reorientation of the ND 4+ ion, 5.0 ± 0.5 kJ mol -1 , indicative of weak cation-anion interactions. Related studies of the tetramethyl-d 12 ammonium salt indicate rapid jumps of the whole cation (τ ≪ 10 -5 S) over the complete temperature range investigated, 137 to 385 K, with an activation energy of 14.1 + 0.5 kJ mol -1 . Deuterium nmr lineshape studies of the methylammonium salt indicate rapid reorientation of the CD 3 and ND 3 groups about their C 3 axes; however, the motion of the C - N axis is restricted to large amplitude librations. Similar studies of the dimethylammonium salt indicate methyl group jumps at 245 K; at temperatures above 320 K the cation also undergoes two-site jumps about the C 2 axis. In the case of the trimethylammonium salt, the nmr lineshapes indicate methyl group jumps superimposed on C 3 rotations of the complete cation about the N - H bond axis over the temperature interval 185-348 K. In all the tetraphenylborate salts studied, the 2 H nmr lineshapes indicate substantial librational motion of the cation at room temperature.

Open Access June 2, 2014

Luminescent Centres of T_d Symmetry in "Cold" Activated ZnS-Mn

K. Kynev, N. Maneva, S. Angelov

Page range: 67-68

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Abstract

By coprecipitation of ZnS and MnS in excess of Na 2 S, luminescent centres are built differing considerably from those in zinc salt excess. ESR data give evidence of centres of T d symmetry.

Open Access June 2, 2014

What do We Know about the Numbers of Benzenoid Isomers?

J. Brunvoll, S. J. Cyvin

Page range: 69-80

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Abstract

The numbers of benzenoid chemical isomers, represented by the formulas C n H s , are reviewed. The data which have been deduced from the available literature are supplemented.

About this journal

Objective
A Journal of Physical Sciences: Zeitschrift für Naturforschung A (ZNA) is an international scientific journal which publishes original research papers from all areas of experimental and theoretical physics. Authors are encouraged to pay particular attention to a clear exposition of their respective subject, addressing a wide readership. In accordance with the name of our journal, which means “Journal for Natural Sciences”, manuscripts submitted to ZNA should have a tangible connection to actual physical phenomena. In particular, we welcome experiment-oriented contributions.

Manuscripts considered for publication in A Journal of Physical Sciences: Zeitschrift für Naturforschung A undergo high-level refereeing. Mere formal correctness of a paper is not sufficient for its acceptance. Moreover, articles reporting a merely marginal extension of already existing knowledge are considered unsatisfactory. Instead, the key quality a publication in A Journal of Physical Sciences: Zeitschrift für Naturforschung A should possess is that it makes a genuine contribution to the advancement of its topic.

Topics

Atomic, Molecular & Chemical Physics
Dynamical Systems & Nonlinear Phenomena
Gravitation & Cosmology
Hydrodynamics
Quantum Theory
Solid State Physics & Materials Science
Thermodynamics & Statistical Physics

Article formats
Original research articles, research notes, letters and review articles from all areas of theoretical and experimental physics

Information on submission process

Volume 45 Issue 1

Issue of Zeitschrift für Naturforschung A

Titelei

Inhaltsverzeichnis

Magnetic Field Influence on Coulomb Relaxation of Anisotropic Electron-Ion-Plasmas

Abstract

The Viscosity Coefficients of Biaxial-Nematic Liquid Crystals. Phenomenology and Affine Transformation Model

Abstract

Relativistic Energy States of the A-Particle in Hypernuclei Using Gaussian Potentials

Abstract

Decomposition of Positive Sesquilinear Forms and the Central Decomposition of Gauge-Invariant Quasi-Free States on the Weyl-Algebra

Abstract

Molecular Ordering in Nematic MBCA and EPAPU

Abstract

Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate

Abstract

Elastic Constants of Nematic Phenylpyrimidines Determined by Two Different Methods

Abstract

The Influence of the Skin Effect on the Amplitude of Single Pulse Gamma Detected NMR on Oriented Nuclei Signals

Abstract

Anomalous X-ray Scattering Study of the Quasi-crystalline Al65Cu20Fe15 Alloy

Abstract

A Deuterium NMR Study of some Ammonium Tetraphenylborates

Abstract

Luminescent Centres of Td Symmetry in "Cold" Activated ZnS-Mn

Abstract

What do We Know about the Numbers of Benzenoid Isomers?

Abstract

Anomalous X-ray Scattering Study of the Quasi-crystalline Al₆₅Cu₂₀Fe₁₅ Alloy

Luminescent Centres of T_d Symmetry in "Cold" Activated ZnS-Mn