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

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

Draft genome sequence of Lactobacillus plantarum 2025

A draft genome sequence of Lactobacillus plantarum 2025 was derived using Ion Torrent sequencing technology. The total size of the assembly (3.33 Mb) was in agreement with the genome sizes of other strains of this species. The data will assist in revealing the genes responsible for the specific properties of this strain

Accounting for the influence of logging tool decentering in acoustic logging data processing

It was carried out the processing of research results of acoustic logging sector equipment. This processing was carried out taking into account the separate registration of wave patterns into four independent spatial sectors. It was detected the significant difference in the arrival times of acoustic waves to the different sectors of equipment. Such difference can be caused by differences in characteristics of environment for well diameter, changing of the wellbore shape or decentering of the logging tool. Authors propose a formation procedure of monopoly or dipole wave packets considering the separate registration on different sectors and shifts between wave patterns. The difference in the values of interval times obtained for the wave packets recorded by the classical method and calculated with allowance for shifts between sectors can result to differences in the calculation of porosity coefficient to 4 or more absolute percent. Apart from the formation of the correct wave packet processing of wave patterns on different sectors allows to reveal the occurrence of elastic anisotropy for well diameter. In addition, analysis of interval time curves allows to reveal areas with occurrence of inclined layers in relation to the well

Study of drying process in full-size core by nuclear magnetic resonance method

The paper describes the results of study of the nuclear magnetic resonance (NMR) signal distribution along the axis of full-size core depending on the time of its extraction from the core tube. It was detected the presence of thin interlayers characterized by the significant heterogeneity in the distribution of the NMR signal amplitude. This fact demonstrates the need to develop appropriate criteria when selecting the standard samples for the study of reservoir properties and creation of relationships between petrophysical parameters. It was conducted the study of kinetic of NMR signal loss during the period in about 20 days from the time of core material extraction from the well. The experiment showed the heterogeneity in the distribution of the characteristics of the fluid evaporation process along the core. Two types of kinetic dependencies were revealed. Form one of them is nearly exponential dependence. Another form characterized by anomalous behavior consisting in that at the initial time part the fluid evaporation from the core is carried out slowly and only after about 150 hours it is observed the acceleration of the evaporation process and the transition of the kinetic curve to exponential type. It is suggested that such behavior of the kinetic dependence may be due either to the heterogeneity in the distribution of pores by core volume in the study area or the shape of pores, for example, the presence of dead-end pores

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

'Porosity evaluation of the "archival" full-size core using nuclear magnetic resonance

Project devoted to the porosity definition of the full-size core which for a long time is stored in the core library using nuclear magnetic resonance. The paper describes an experiment of the full-size carbonate core saturation by mineralized water and the measurement of its voids ratio. The work shows the possibility of using the NMR method for assessing the porosity of the «archival» full-size carbonate core on condition of the correct saturation process by model of formation water. The study can be further used to conduct similar experiments with full-size core from the oil bearing horizons layers

Simulation design of PNL device for determining the spatial position of hydraulic fractures in three-dimensional space

The usage of modeling techniques allows to optimize the materials and construction of the neutron well logging apparatus and synthesized the recorded signal. This study focuses on modeling the construction of PNL device for determining the spatial position of hydraulic fractures in three-dimensional space. We used mathematical modeling by Monte Carlo method. PNL logs were synthesized, and it allowed to restore position of hydraulic fracture. The difference between angels simulated and the resulting equaled 3 degree, which confirms the possibility of using this technique

Stable Spin Precession at one Half of Equilibrium Magnetization in Superfluid 3He-B

New stable modes of spin precession have been observed in superfluid 3He-B. These dynamical order parameter states include precession with a magnetization S=pS_{eq} which is different from the equilibrium value S_{eq}. We have identified modes with p=1, 1/2 and \approx 0. The p=1/2 mode is the second member of phase correlated states of a spin superfluid. The new states can be excited in the temperature range 1-T/T_c \lesssim 0.02 where the energy barriers between the different local minima of the spin-orbit energy are small. They are stable in CW NMR due to low dissipation close to T_c.Comment: submitted to Physical Review Letters, 4 pages, revtex, 4 Figures in ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96005.p

Features of coupling between rheological properties of oil and natural bitumen and the self-diffusion data obtained by NMR method

This paper describes the features of translational characteristics of oil molecules by using nuclear magnetic resonance method with pulsed magnetic field gradient (gradient NMR). It is shown that the rheological properties of heavy oil samples (viscosity) do not completely correlate with the measurement of self-diffusion coefficient. It is caused by distribution of oil samples according to their molecular composition and molecular weight as well as their complex supramolecular organization. It is noted that the best agreement with the viscosity characteristics is achieved via the introduction of a new average coefficient, which is a weighted sum of the inverse of the partial self-diffusion coefficients