Refinements to the microwave waveguide material parameters measurements. Case study

This work presents the results of experimental measurements of permittivity and permeability of materials (dried pine, paraffin, acrylic resin, bitumen, polypropylene and texolite) that has a comparative values. The laboratory installation compile from waveguides 23x10 mm that provides the frequency range 8 – 12 GHz. The results processing lay not only in comparison with the existing data, but also in investigation of physical conditions that should be taken into account for waveguide experiment setup. The main aim is to establish the variation of electro physical parameters of the material measured in waveguides and in free space. Selection of reference material samples is the main part of this work

Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature T_c=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at T_c and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure

COMPUTATIONAL INVESTIGATION OF THE INFLUENCE OF THE ENVIRONMENT ON MECHANICAL-PROPERTIES OF SOLIDS

Using modified MNDO and AM1 semiempirical self-consistent-field molecular orbital methods in the cluster approach, we investigated the environmental influence on the mechanical properties of solids. The computational approach of the chemical reaction coordinate was developed for the study of mechanical deformation. The modeling of different types of deformation was considered. To test the validity of the method, we investigated the mechanical properties of simple hydrocarbon chains and silica systems. Uniaxial deformation and bending were considered for the heptane molecule. Verification of the mechanochemical calculations for polypropylene was fulfilled by analyzing its vibrational spectra. It was found that the influence of active medium particles (water, hydroxonium ion, surfactant) may have caused a sharp decrease of the strength of silica and hydrocarbons. The atom-level mechanism and some qualitative characteristics of these processes were studied. (C) 1995 John Wiley & Sons, Inc

Computational investigation of the influence of the environment on mechanical properties of solids

Using modified MNDO and AM1 semiempirical self‐consistent‐field molecular orbital methods in the cluster approach, we investigated the environmental influence on the mechanical properties of solids. The computational approach of the chemical reaction coordinate was developed for the study of mechanical deformation. The modeling of different types of deformation was considered. To test the validity of the method, we investigated the mechanical properties of simple hydrocarbon chains and silica systems. Uniaxial deformation and bending were considered for the heptane molecule. Verification of the mechanochemical calculations for polypropylene was fulfilled by analyzing its vibrational spectra. It was found that the influence of active medium particles (water, hydroxonium ion, surfactant) may have caused a sharp decrease of the strength of silica and hydrocarbons. The atom‐level mechanism and some qualitative characteristics of these processes were studied. © 1995 John Wiley & Sons, Inc. Copyright © 1995 John Wiley & Sons, Inc

COMPUTATIONAL INVESTIGATION OF THE INFLUENCE OF THE ENVIRONMENT ON MECHANICAL-PROPERTIES OF SOLIDS

Using modified MNDO and AM1 semiempirical self-consistent-field molecular orbital methods in the cluster approach, we investigated the environmental influence on the mechanical properties of solids. The computational approach of the chemical reaction coordinate was developed for the study of mechanical deformation. The modeling of different types of deformation was considered. To test the validity of the method, we investigated the mechanical properties of simple hydrocarbon chains and silica systems. Uniaxial deformation and bending were considered for the heptane molecule. Verification of the mechanochemical calculations for polypropylene was fulfilled by analyzing its vibrational spectra. It was found that the influence of active medium particles (water, hydroxonium ion, surfactant) may have caused a sharp decrease of the strength of silica and hydrocarbons. The atom-level mechanism and some qualitative characteristics of these processes were studied. (C) 1995 John Wiley & Sons, Inc

Cross-relaxation and phonon bottleneck effects on magnetization dynamics in LiYF4:Ho3+

International audienceFrequency and dc magnetic field dependences of dynamic susceptibility in diluted paramagnets LiYF$_4$:Ho$^{3+}$ have been measured at liquid helium temperatures in the ac and dc magnetic fields parallel to the symmetry axis of a tetragonal crystal lattice. Experimental data are analyzed in the framework of microscopic theory of relaxation rates in the manifold of 24 electron-nuclear sublevels of the lowest non-Kramers doublet and the first excited singlet in the Ho$^{3+}$ ground multiplet $^5I_8$ split by the crystal field of S$_4$ symmetry. The one-phonon transition probabilities were computed using electron-phonon coupling constants calculated in the framework of exchange charge model and were checked by optical piezospectroscopic measurements. The specific features observed in field dependences of the in- and out-of-phase susceptibilities (humps and dips, respectively) at the crossings (anti-crossings) of the electron-nuclear sublevels are well reproduced by simulations when the phonon bottleneck effect and the cross-spin relaxation are taken into account