217 research outputs found
Thermoelectric performance of weakly coupled granular materials
We study thermoelectric properties of inhomogeneous nanogranular materials
for weak tunneling conductance between the grains, g_t < 1. We calculate the
thermopower and figure of merit taking into account the shift of the chemical
potential and the asymmetry of the density of states in the vicinity of the
Fermi surface. We show that the weak coupling between the grains leads to a
high thermopower and low thermal conductivity resulting in relatively high
values of the figure of merit on the order of one. We estimate the temperature
at which the figure of merit has its maximum value for two- and
three-dimensional samples. Our results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays.Comment: 4 pages, 3 figure
Thermoelectric performance of granular semiconductors
We study thermoelectric properties of granular semiconductors with weak
tunneling conductance between the grains, g_t < 1. We calculate the thermopower
and figure of merit taking into account the shift of the chemical potential and
the asymmetry of the density of states in the vicinity of the Fermi surface due
to n- or p-type doping in the Efros-Shklovskii regime for temperatures less
than the charging energy. We show that for weakly coupled semiconducting grains
the figure of merit is optimized for grain sizes of order 5nm for typical
materials and its values can be larger than one. We also study the case of
compensated granular semiconductors and show that in this case the thermopower
can be still finite, although two to three orders of magnitude smaller than in
the uncompensated regime.Comment: 4 pages, 4 figure
Comparison of slowness estimation methods according to borehole acoustic waveform data
© Copyright 2016.Methods for estimating the slowness of elastic waves according to a multi-element acoustic logging are discusses in the paper. Compare slowness curves of longitudinal and transverse waves for carbonate deposits is held. Interval times curves estimated by Semblance and dispersion methods have better convergence with each other. The reason for this is that these methods estimate the group velocity, as opposed to the hodograph method, which gives an estimate of the phase velocity. Convergence of slowness curves for the transverse wave is generally belter than convergence of curves for the longitudinal wave. All methods yield similar values slowness estimation errors
Study of electromagnetic emissions associated with seismic activity in Kamchatka region
International audienceA review of data processing of electromagnetic emission observation collected at the Complex Geophysical Observatory Karimshino (Kamchatka peninsula) during the first 5 months (July?November, 2000) of its operation is given. The main goal of this study addresses the detection of the phenomena associated with Kamchatka seismic activity. The following observations have been conducted at CGO: variations of ULF/ELF magnetic field, geoelectric potentials (telluric currents), and VLF signals from navigation radio transmitters. The methods of data processing of these observations are discussed. The examples of the first experimental results are presented
Geophysical Observatory in Kamchatka region for monitoring of phenomena connected with seismic activity
Regular monitoring of some geophysical parameters in association with seismicity has been carried out since last year at the Japan-Russian Complex Geophysical Observatory in the Kamchatka region. This observatory was organized in connection with the ISTC project in Russia and was motivated by the results of the FRONTIER/RIKEN and FRONTIER/NASDA research projects in Japan. The main purpose of the observations is to investigate the electromagnetic and acoustic phenomena induced by the lithosphere processes (especially by seismic activity). The seismicity of the Kamchatka area is analyzed and a description of the observatory equipment is presented. At present, the activity of the observatory includes the seismic (frequency range ∆F = 0.5 – 40 Hz) and meteorological recordings, together with seismo-acoustic (∆F = 30 – 1000 Hz) and electromagnetic observations: three-component magnetic ULF variations ( ∆F = 0.003 – 30 Hz), three-component electric potential variations ( ∆F <u><</u> 1.0 Hz), and VLF transmitter’s signal perturbations ( ∆F ~ 10 – 40 kHz)
ВЛИЯНИЕ ТЕМПЕРАТУРЫ ОТЖИГА НА НЕКОТОРЫЕ ФИЗИЧЕСКИЕ СВОЙСТВА КНБ, ПОЛУЧЕННОГО ИЗ ПИРОЛИТИЧЕСКОГО НИТРИДА БОРА
The paper presents results of investigations on dependence of dielectric, electromechanical and elastic properties of BNпсф polycrystals (sphalerite) with texture axis [111]сф, obtained from pyrolitic boron nitride BNпг on annealing temperature up to 2173 К. Peculiar features concerning changes of the given properties in the zone of low-temperature annealing 700–773 К and phase transformation BNпг — BNпсф are shown in the paper.Приведены результаты исследования зависимости диэлектрических, электромеханических и упругих свойств поликристаллов кубического нитрида бора BNпсф (сфалерит) с осью текстур [111]сф, полученных из пиролитического нитрида бора BNпг , от температуры отжига до 2173 К. Показаны особенности изменения данных свойств в областях низкотемпературного отжига 700–773 К и фазового превращения BNпг — BNпсф
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Search for DCC in 158A GeV Pb+Pb Collisions
A detailed analysis of the phase space distributions of charged particles and
photons have been carried out using two independent methods. The results
indicate the presence of nonstatistical fluctuations in localized regions of
phase space.Comment: Talk at the PANIC99 Conference, June 9-16, 199
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