Search results for "Elastic"
showing 10 items of 2162 documents
Resonant Rayleigh scattering by confined two-dimensional excitonic states
1997
A systematic study of resonant Rayleigh scattering in semiconductor single quantum wells has been carried out. The dependence of the scattering efficiency on the well width and the temperature has been investigated. The behaviour observed in the resonant Rayleigh spectra can be explained in terms of the confinement of the excitonic states in the plane of the well due to fluctuations in the well width. A microscopic theoretical model for the elastic scattering of light by weakly confined two-dimensional excitonic states has been developed. The Rayleigh scattering efficiency has been calculated to the lowest-order of perturbation theory and the results found to be in good agreement with the e…
Polarization detection of trapped electrons via interaction with polarized atoms
1971
Electrons were trapped in an electrostatic quadrupole trap with superimposed homogeneous magnetic field. The electrons were polarized by spin exchange with a polarized atomic beam. The free trapped electron polarization was converted to a change in the electron translational energy via spin-dependent inelastic collisions with the atomic beam, and the electron translational temperature was monitored. Discussed are the development of this variation of the measurement technique, characteristics of electron storage, and the electron-polarized atom inelastic interaction as a function of electron temperature and time. The method has been applied to the detection of the (g-2) resonance of free, st…
Computer simulation study of a liquid crystal confined to a spherical cavity.
2007
The interplay of surface ordering and elasticity can be studied on the example of a liquid crystal confined to a cavity. We present a computer simulation study of a liquid of hard spherocylinders in a hard spherical cavity. With increasing density, first a uniaxial surface film forms and then a biaxial surface film, which eventually fills the entire cavity. We studied how the surface order, the adsorption, and the shape of the director field depend on the curvature of the wall. We find that orientational ordering at a curved wall is stronger than at a flat wall, while adsorption is weaker. For densities above the isotropic-nematic transition, we always find bipolar configurations.
Experimental determination of effective charges in aqueous suspensions of colloidal spheres
2003
Abstract We determined the low frequency conductivity σ , the phase behaviour and the shear modulus G of colloidal fluids, respectively solids prepared from deionised aqueous suspensions of highly charged spherical particles. Conductivity measures the number of freely moving small ions Z * σ and thus relates to the ion condensation process in the electric double layer under conditions of finite macro-ion concentrations. Phase behaviour and elasticity data are consistently described by a Debye–Huckel pair potential assuming pair-wise additive macro-ion interactions. Like Z * σ , also the effective charges Z * G derived from the elasticity data scales with the ratio of macro-ion radius to Bje…
Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constan…
2011
We investigate the low-frequency enhancement of vibrational excitations ('boson peak') in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150?cm ? 1. A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio.
Polyoxometalates: From Magnetic Models to Multifunctional Materials
2002
In this article we have presented some recent achievements of the polyoxometalates in the fields of molecular magnetism and functional molecular materials. In the context of the molecular magnetism we have shown that POMs provide ideal examples of magnetic clusters with coexisting ferro and antiferromagnetic exchange interactions which can be investigated using a variety of magnetic techniques, including the Inelastic Neutron Scattering spectroscopy, to get a thorough characterization of the magnetic levels in these large clusters, and to test the validity of the spin hamiltonians commonly used in magnetism.
Anomalous thermoelastic behavior of (KI)1-x(NH4I)x
1990
Abstract An anomalous softening of the shear mode c 44 is observed in (KI) 1- x (NH 4 I) x with Brillouin scattering (10 K ⩽ T ⩽ 300 K ). It is caused by the weak quadrupolar moment of the NH 4 + ion, induced by the C 3 v symmetry of the potential. A parallel decrease of the lifetime of this transverse phonon at lower temperatures is observed. Static random strain fields due to admixing KI with NH 4 I are small. The results have been treated in terms of a mean field theory. The c 11 elastic constant does not show any anomalous behavior. Also are given the elastic constants c 11 and c 44 for x =0.14, 0.43 and 1 and 1 at T = 300 K and 10 K .
Spin-polarization effects for electrons passing through thin iron and cobalt films
1993
Abstract Spin-dependent effects of the inelastic mean free path (IMFP) are evident for low-energy electrons passing through magnetized ferromagnetic films caused by a different attenuation within the layer. Values of IMFP for both spin components were determined for ultrathin iron and cobalt layers on W(1 1 0) by means of spin-resolving photoelectron spectroscopy.
EQCM and Quartz Crystal Impedance Measurements for the Characterization of Thiophene-Based Conducting Polymers
1999
AbstractEQCM was extensively used to investigate ion-transport phenomena during dopingundoping processes of electronically conducting polymers. Several early studies assumed that the polymer films were rigidly coupled to the quartz crystal so as to relate the mass change to the quartz crystal resonant frequency change via the Sauerbrey equation. However, the rigidity of electronically conducting polymer films is doubtful and it has to be demonstrated. Quartz crystal impedance analysis near the resonance is of paramount importance to get insight into the viscoelastic properties of the film [1] and to avoid misleading in the interpretation of EQCM data.This contribution presents and discusses…
Dynamic analysis for axially moving viscoelastic panels
2012
In this study, stability and dynamic behaviour of axially moving viscoelastic panels are investigated with the help of the classical modal analysis. We use the flat panel theory combined with the Kelvin–Voigt viscoelastic constitutive model, and we include the material derivative in the viscoelastic relations. Complex eigenvalues for the moving viscoelastic panel are studied with respect to the panel velocity, and the corresponding eigenfunctions are found using central finite differences. The governing equation for the transverse displacement of the panel is of fifth order in space, and thus five boundary conditions are set for the problem. The fifth condition is derived and set at the in-…