Influence Of Relaxation Processes Research Articles

The Influence of Relaxation Processes on the Thermoacoustics of Materials

The Influence of Relaxation Processes on the Thermoacoustics of Materials

Relaxation processes determining the electret stability of high-impact polystyrene/titanium-dioxide composite films

The influence of relaxation processes on the thermal electret stability of high-impact polystyrene (HIPS) free-standing films filled with titanium dioxide (TiO2) of the rutile modification are investigated by means of a combination of dielectric methods (dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and thermally stimulated surface-potential decay (TSSPD)), supplemented by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Films with 2, 4, 6 and 8 vol.% TiO2 are compared to each other and to non-filled samples. Filling HIPS with up to 8 vol.% of TiO2 enhances the elastic modulus below the glass transition and increases the thermal electret stability above the glass transition without significantly increasing the DC conductivity. The improvement of the electret stability is caused by the build-up of an interface polarization which decays only gradually if the glass transition is exceeded. Two kinds of Arrhenius processes are considered in order to explain the decay of the composite-polymer electrets: (1) charge release from chemical traps located at the phenyl rings of the polymer chain with an activation energy of Ea = 1.1 eV after passing the glass transition at about 100 °C and (2) charge release from traps formed by the TiO2 particles with Ea = 2.4 eV at temperatures above 130 °C. Finally, the activation energies are discussed with respect to their significance.

Influence of relaxation processes on the evaluation of the metastable defect density in Cu(In,Ga)Se2

In this contribution, we investigated by means of numerical simulations the influence of relaxation processes related to metastable defects on electrical characteristics of Cu(In,Ga)Se2. In particular, we analyzed the relaxation of a metastable state induced by illumination at a fixed temperature as well as the dependence of the hole concentration on the temperature during cooling. The knowledge of these two relaxation processes is crucial in the evaluation of the hole concentration in the relaxed state and after light soaking. We have shown that the distribution of the metastable defects can be considered frozen below 200 K. The hole capture cross section was estimated as ∼3 × 10−15 cm2. It was shown that the usually used cooling rates may lead to relevant changes of the hole concentration. We calculated the lower limit of the hole concentration after cooling, and we presented how it depends on densities of shallow acceptors and metastable defects. Moreover, we proposed a method which allows for the evaluation of shallow acceptor and metastable defect densities from two capacitance-voltage profiles measured in the relaxed and light soaking states. Finally, we indicated experimental conditions in which the influence of relaxation processes on the accuracy of this method is the smallest.

Spontaneous transfer of para-hydrogen induced polarization to 13C spins in symmetric molecules1

Experimental observations are found and explained for spontaneous transfer of para-hydrogen induced polarization at high (about 10 T) and ultralow (about 10 µT) magnetic fields. Polarization of 13C of 4% at high field and 8% at low field is achieved; the influence of relaxation processes on the spontaneous distribution of spin hyperpolarization is revealed.

Influence of relaxation processes on the wave dynamics of shock compression of solids

Nowadays, one obtains information about deformation and fracture strength at strain rates greater than 104 s−1 by analyzing the evolution of plane shock waves in the materials under study. This paper presents a short survey of methods for analyzing shock wave phenomena in relaxing media and recent observations of the evolution of elastoplastic shock compression waves in metals, some of which turned out to be unexpected.

Influence of relaxation processes on amplitude and shape of echo signals

A theory of signal-processing analog devices that use the phenomenon of spin, light, or nuclear quadrupole echo is considered with allowance for noise immunity. Main equations describing these phenomena are solved by multiplicative integration. Such an approach makes it possible to calculate echo signals of arbitrary amplitude and structure in a general form.

Near-Surface Electrical Discharge in Supersonic Airflow: Properties and Flow Control

The results of experimental and numerical investigations of the interaction between the near-wall electrical discharge and supersonic airflow in an aerodynamic channel with constant and variable cross sections are presented. Peculiar properties of the surface quasi-direct-current discharge generation in the flow are described. The mode with flow separation developing outside the discharge region is revealed as a specific feature of such a configuration. An interaction model is proposed on the basis of measurements and observations. A regime of gas-dynamic screening of a mechanical obstacle installed on the channel wall is studied. Variation of the main flow parameters caused by the surface discharge is quantified. The ability of the discharge to shift an oblique shock in an inlet is demonstrated experimentally. The influence of relaxation processes in nonequilibrium excited gas on the flow structure is analyzed. Comparison of the experimental data with the results of calculations based on the analytical model and on numerical simulations is presented.

Influence of the concentration of a dispersed phase and of the magnetic field on the attenuation of ultrasonic waves in magnetic fluids

The regularities of the propagation of elastic waves of ultrasonic range in magnetic fluids have been experimentally established. The influence of relaxation processes — nonlocal heat exchange and viscous dissipation — on the coefficient of attenuation of sound has been revealed and a comparison to the existing theoretical data has been made. The dependences (anisotropic in form) of the attenuation of the wave’s amplitude on the value and direction of the magnetic field have been determined and an interpretation of the results obtained has been proposed.

Influence of Relaxation Process on the Microstructure and Properties of Low Carbon Bainitic Steel

Influence of Relaxation Process on the Microstructure and Properties of Low Carbon Bainitic Steel

Effect of D 2O and cryosolvents on the redox properties of bacteriochlorophyll dimer and electron transfer processes in Rhodobacter sphaeroides reaction centers

Effects of environmental changes on the reaction pattern of excitation energy trapping and transformation into the “stable” radical pair P +Q A −. have been analyzed in isolated reaction centers of the anoxygenic purple bacterium Rhodobacter sphaeroides. The following results were obtained: (a) replacement of exchangeable protons by deuterons significantly retarded the electron transfer steps of primary charge separation, leading to the radical pair P +I − and of the subsequent reoxidation of I − by the quinone acceptor Q A but has virtually no effect on the midpoint potential of P/P + that was found to be 430±20 mV; (b) addition of 70% (v/v) glycerol causes a shift of E m by about 30 mV towards higher values whereas the kinetics of the electron transfer reactions remain almost unaffected; (c) in the presence of the cryoprotectant DMSO, a combined effect arises, i.e. a retardation of the electron transfer kinetics comparable to that induced by H/D exchange and simultaneously an upshift of the E m value to 475±20 mV, resembling the action of glycerol. These results are discussed within the framework of effects on the midpoint potential due to the dielectric constant of the medium and changes of the charge distribution in the vicinity of the redox groups and the influence of relaxation processes on electron transfer reactions.

Crystallization of (Fe, Co)78Si9B13 alloys: influence of relaxation processes

Crystallization of Fe78-xCoxSi9B13 amorphous alloys has been studied by differential scanning calorimetry (DSC), thermomagnetic gravimetry and X-ray diffraction techniques. Thermal stability of the amorphous alloy monotonically decreases with increasing cobalt content. The devitrification process as detected by DSC occurs in two main stages partially overlapping in temperature, but magnetic characterization reveals a third stage for cobalt-rich alloys. Primary precipitation of α-(Fe, Co) is followed by a polymorphic reaction to give (Fe, Co)2B phase. Fe3B-type phase is also detected at the end of the first crystallization stage for iron-rich alloys and β-Co(Si) and Co2B phases are found in fully crystallized samples for x=60. The influence of relaxation processes on the crystallization was investigated, but no significant effects of pre-annealing on the crystallization parameters resulted. © 1998 Chapman & Hall

Electron transport study of nanocrystallization in FeSiB based alloys

The influence of Cu, Nb and Ta additions on the crystallization of amorphous FeSiB based alloys was studied. For each alloy, coherent electrical resistivity and thermoelectric power behaviors were observed and related to the mean grain sizes. Anomalous electron transport parameters strongly influenced by the electron scattering at grain boundaries were explained using the Mayadas-Shatzkes model. From values of the local Avrami exponent, the nucleation rate and the growth kinetics were determined. The influence of relaxation processes on Avrami exponent was investigated.

The magnetostatic waves in ferrite film with losses

The influence of relaxation processes on dispersion equation solutions for surface and volume magnetostatic waves (MSW) propagating in a ferrite film is theoretically investigated. It is shown that dissipation is the main reason for the appearance of complementary MSW branches in frequency intervals which adjoin standard branches in spectra. The existence of threshold MSW wave numbers which upper bound the spectra of possible wave numbers is established. Asymptotic frequencies anf frequencies corresponding to the threshold values of wave numbers are calculated. The effects of dissipation on the ranges in which MSW exist are calculated. The frequency dispersion of the loss spectra is also calculated. >

Velocity redistribution of carriers in semiconductors induced by a laser beam and collisions

The velocity redistributions of carriers in two Landau bands interacting resonantly with a laser beam are investigated. Due to different collisional relaxation rates for holes in the ground and electrons in the excited state and velocity selective excitation the total carrier population velocity redistribution is asymmetrical. A method, based on the kinetic equation for the density matrix of the system, which allows one to describe the above effect is presented. The influence of relaxation processes and the pumping rate on the velocity distribution of the total population of carriers is discussed.

Influence of relaxation processes upon the polarization of the fluorescence of organic molecules adsorbed in porous glass

The goal of this research was to use polarized fluorescence to investigate the interactions of adsorbed molecules with the surface of a dielectric. The authors used porous glass into which organic dye molecules, including derivatives of phthalimide and rhodamine, had been introduced. Graphs illustrate the spectral and temperature and time dependences of the degrees of polarization of the fluorescence of the dyes in the matrix material and a rigorous description of these dependences is performed with the Fokker-Planck equation. It is found that the polarization factor for adsorbed molecules is much higher than for molecules in solution.

Memory effects in turbulent motions

The present state of the question of relaxation (memory) phenomena in turbulent wall and free boundary layers is reviewed. A simple derivation of the basic differential equation of the relaxation is proposed, and the region of applicability of this equation is extended to motion in the preseparation region of a boundary layer. The importance of taking into account the influence of relaxation processes is illustrated by a comparison with the available experimental data of calculations of the tangential Reynolds stresses in accordance with the relaxation theory and the local theory based on the Boussinesq hypothesis.

Influence of relaxation processes on the structure of a thermal boundary layer in partially ionized argon

A model for the unsteady thermal boundary-layer development at the end wall of a shock tube, in partially ionized atmospheric argon, is proposed. Consideration is given to ionization and thermal relaxation processes. In order to obtain some insight into the influence of the relaxation processes on the structure of the boundary layer, a study of the frozen and equilibrium limits has been carried out. The transition from a near-equilibrium situation in the outer part of the boundary layer towards a frozen situation near the wall has been determined numerically. Experimental data on the electron and atom density profiles obtained from laser schlieren and absorption measurements are presented. A quantitative agreement between theory and experiment is found for a moderate degree of ionization (3 %). At a higher degree of ionization the structure of the boundary layer is dominated by the influence of radiation cooling, which has been neglected in the model.

Influence of Relaxation Processes and Exciton Dispersion on Optical Characteristics of Crystals

AbstractThe exciton light absorption by a crystal is studied using the microtheory of electromagnetic and exciton field interaction. A comparison of the results obtained with the corresponding conclusions of earlier theoretical papers and experimental data is made.

Influence of relaxation processes on coherence of twophoton interaction between light pulses and resonant media

Numerical integration of a system of equations for a resonant medium and a field is used in a study of the influence of the relaxation of the phase memory of this medium on its coherent two-photon interaction with a light pulse. It is shown that the principal coherent effects occur right up to pulse durations equal to the phase relaxation time.