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81.
The elastic constants of a nematic liquid crystal are calculated by means of a pseudo-molecular method that considers the quadrupolar intermolecular interaction with a screening length governing the range of the forces. The bulk as well as the surface-like elastic constants are determined as functions of the eccentricity of the interaction volume of ellipsoidal shape. It is shown that the elastic constants become negative for some values of the eccentricity, and, therefore, that the screened quadrupolar interaction could be the source of instabilities in the nematic phase and should be taken into account to interpret threshold phenomena in these systems. 相似文献
82.
The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N2 and O2 gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In2O3) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In2O3 with an increasing oxygen timing. The hexagonal structure of InN films with predominant (0 0 2) and (0 0 4) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In2O3 seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O2:N2 show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In2O3, the increase of optical bandgap from 1.4 to 3.4 eV and the rise of sheet resistance from 15 Ω/□ to insulator. 相似文献
83.
In this paper we study the macroscopic behavior of nematic side-chain liquid single crystal elastomers exposed to an external electric or magnetic field. For this purpose we use the framework of a continuum model. The geometries investigated comprise the bend and the twist geometry known from the classical Frederiks transition in low molecular weight liquid crystals. For the bend geometry we find a laterally homogeneous and a two-dimensional undulatory instability, which may compete at onset. In the case of the twist geometry three instabilities can occur at onset, two of which are two dimensional and clearly show undulations. As a major result we propose how the values of the twist coefficient K(2) and the values of the material parameters D(1) and D(2) connected to relative rotations between the director field and the polymer network can be determined from experimental observations. In addition, we explain why a twist experiment is probably the most suitable set-up in order to measure the material parameter D(1). 相似文献
84.
V. A. Seguin H. J. J. Seguin C. E. Capjack S. K. Nikumb 《Applied physics. B, Lasers and optics》1987,43(2):127-138
The operational characteristics of a convectively cooled Magnetically stabilized, Photo-initiated, Impulse-enhanced, Electrically-excited (MAGPIE) coaxial discharge system are described. terminal behavior is examined as a function of several parameters, such as gas flow, pulser ionization, and magnetic field strength. In-situ plasma potential measurements are also presented, which indicate that CO2 attachment effects have considerable influence on the spatial electrical characteristics of the gas discharge. 相似文献
85.
We report a quantitative study of temporal synchronization of two independently tunable, single longitudinal mode, hybrid CO2 lasers, sharing a common high pressure section. The theoretical estimates for the dependence of the laser pulse build up time on the cw section pressure are in satisfactory agreement with the experimental results. Further, we show that temporal synchronization over a larger frequency range with no significant degradation of peak power or longitudinal mode selection is possible, by utilising the cw section gain length and cavity Q as additional control parameters. 相似文献
86.
R. A. Rooth J. A. van der Pol E. H. Haselhoff 《Applied physics. B, Lasers and optics》1987,42(2):103-110
Analytical, experimental and numerical results concerning the influence of intramode and Fermi relaxation on multiple-pass, nanosecond-pulse energy extraction are presented. Multiple-pass energy extraction experiments show satisfactory agreement with the analytical and numerical calculations which predict a significant increase in extracted energy. In three passes, an amount of 9.7 J/l was extracted at an efficiency of 4.3%, These values are taken with respect to the volume of the beam inside the amplifier. In a single pass only 3.5 J/l was extracted. 相似文献
87.
Y.P. Varshni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):229-233
The effect of high pressures on an atom is frequently simulated by enclosing the atom in an impenetrable spherical box. The
spectrum of such a confined helium atom placed at the centre of a spherical box is investigated. A model potential is used
to calculate the energies of twelve excited states and thereby the transition wavelengths for a range of values of the radius
of the confining sphere. Applications of results are discussed.
Received 29 August 2002 Published online 10 December 2002
RID="a"
ID="a"e-mail: ypvsj@uottawa.ca 相似文献
88.
We demonstrate the sensitivity of X‐ray absorption fine‐structure (XAFS) measurements to the earliest stages of decomposition in Al alloys, i.e. just a few minutes after quenching. XAFS is one of the few applicable experimental approaches to this regime. Three different AlCu(Mg) samples were investigated by XAFS at the Cu K edge. Significant changes of the XAFS can be detected in the course of the decomposition in these alloys during the first 15 minutes. Actually, these changes correspond to relaxations of the nearest neighbours towards the absorbing Cu atoms. The Fourier transformation of the XAFS spectra thus leads to a pseudo radial distribution function which reflects this relaxation. In addition, XAFS measurements of the S‐phase of AlCuMg are used to decide in favour of the Perlitz and Westgren model for the S‐phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
89.
S. Saib N. Bouarissa P. Rodríguez-Hernández A. Muñoz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):435-438
We present a theoretical study of the structural properties, namely
lattice constant, bulk modulus and its pressure derivative of zinc-blende
GaxIn1-xN. The calculations are performed using first-principles
calculations in the framework of the density-functional-theory
within the local density approximation under the virtual
crystal approximation. The computed values are in good
agreement with the available experimental data. The composition dependence
of the studied quantities is examined. Besides, the deviation of the alloy
lattice constant from Vegard's law is evaluated. 相似文献
90.
W.D. Heiss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):1-4
Avoided level crossings are associated with exceptional points which are the singularities of the spectrum and eigenfunctions,
when considered as functions of a complex coupling parameter. It is shown that the wave function of one state changes sign but not the other, if the exceptional point is encircled in the complex plane. An experimental setup is
suggested where this peculiar phase change could be observed.
Received: 7 January 1999 / Received in final form: 15 March 1999 相似文献