550 research outputs found
Modeling the Field Emission Current Fluctuation in Carbon Nanotube Thin Films
Owing to their distinct properties, carbon nanotubes (CNTs) have emerged as
promising candidate for field emission devices. It has been found
experimentally that the results related to the field emission performance show
variability. The design of an efficient field emitting device requires the
analysis of the variabilities with a systematic and multiphysics based modeling
approach. In this paper, we develop a model of randomly oriented CNTs in a thin
film by coupling the field emission phenomena, the electron-phonon transport
and the mechanics of single isolated CNT. A computational scheme is developed
by which the states of CNTs are updated in time incremental manner. The device
current is calculated by using Fowler-Nordheim equation for field emission to
study the performance at the device scale.Comment: 4 pages, 5 figure
Oscillation of solar radio emission at coronal acoustic cut-off frequency
Recent SECCHI COR2 observations on board STEREO-A spacecraft have detected
density structures at a distance of 2.5--15~R propagating with periodicity of
about 90~minutes. The observations show that the density structures probably
formed in the lower corona. We used the large Ukrainian radio telescope URAN-2
to observe type IV radio bursts in the frequency range of 8--32~MHz during the
time interval of 08:15--11:00~UT on August 1, 2011. Radio emission in this
frequency range originated at the distance of 1.5--2.5 R according to the
Baumbach-Allen density model of the solar corona. Morlet wavelet analysis
showed the periodicity of 80~min in radio emission intensity at all
frequencies, which demonstrates that there are quasi-periodic variations of
coronal density at all heights. The observed periodicity corresponds to the
acoustic cut-off frequency of stratified corona at a temperature of 1~MK. We
suggest that continuous perturbations of the coronal base in the form of
jets/explosive events generate acoustic pulses, which propagate upwards and
leave the wake behind oscillating at the coronal cut-off frequency. This wake
may transform into recurrent shocks due to the density decrease with height,
which leads to the observed periodicity in the radio emission. The recurrent
shocks may trigger quasi-periodic magnetic reconnection in helmet streamers,
where the opposite field lines merge and consequently may generate periodic
density structures observed in the solar wind.Comment: 10 pages, 6 figures, accepted in A&
Radio seismology of the outer solar corona
Observed oscillations of coronal loops in EUV lines have been successfully
used to estimate plasma parameters in the inner corona (< 0.2 R_0, where R_0 is
the solar radius). However, coronal seismology in EUV lines fails for higher
altitudes because of rapid decrease in line intensity. We aim to use radio
observations to estimate the plasma parameters of the outer solar corona (> 0.2
R_0). We use the large Ukrainian radio telescope URAN-2 to observe type IV
radio burst at the frequency range of 8-32 MHz during the time interval of
09:50-12:30 UT in April 14, 2011. The burst was connected to C2.3 flare, which
occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio
emission shows clear quasi-periodic variations in the emission intensity at
almost all frequencies. Wavelet analysis at four different frequencies (29 MHz,
25 MHz, 22 MHz and 14 MHz) shows the quasi-periodic variation of emission
intensity with periods of 34 min and 23 min. The periodic variations can be
explained by the first and second harmonics of vertical kink oscillation of
transequatorial coronal loops, which were excited by the same flare. The apex
of transequatorial loops may reach up to 1.2 R_0 altitude. We derive and solve
the dispersion relation of trapped MHD oscillations in a longitudinally
inhomogeneous magnetic slab. The analysis shows that a thin (with width to
length ratio of 0.1), dense (with the ratio of internal and external densities
of > 20) magnetic slab with weak longitudinal inhomogeneity may trap the
observed oscillations. Seismologically estimated Alfv\'en speed inside the loop
at the height of 1 R_0 is 1000 km/s. Then the magnetic field strength at this
height is estimated as 0.9 G. Extrapolation of magnetic field strength to the
inner corona gives 10 G at the height of 0.1 R_0.Comment: 12 pages, 10 figures, Accepted in A&
Interventions for improving recovery from work
ObjectivesThis is a protocol for a Cochrane Review (intervention). The objectives are as follows:To compare the effectiveness of different individual interventions in recovery from work.info:eu-repo/semantics/publishedVersio
Tangling clustering of inertial particles in stably stratified turbulence
We have predicted theoretically and detected in laboratory experiments a new
type of particle clustering (tangling clustering of inertial particles) in a
stably stratified turbulence with imposed mean vertical temperature gradient.
In this stratified turbulence a spatial distribution of the mean particle
number density is nonuniform due to the phenomenon of turbulent thermal
diffusion, that results in formation of a gradient of the mean particle number
density, \nabla N, and generation of fluctuations of the particle number
density by tangling of the gradient, \nabla N, by velocity fluctuations. The
mean temperature gradient, \nabla T, produces the temperature fluctuations by
tangling of the gradient, \nabla T, by velocity fluctuations. These
fluctuations increase the rate of formation of the particle clusters in small
scales. In the laboratory stratified turbulence this tangling clustering is
much more effective than a pure inertial clustering that has been observed in
isothermal turbulence. In particular, in our experiments in oscillating grid
isothermal turbulence in air without imposed mean temperature gradient, the
inertial clustering is very weak for solid particles with the diameter 10
microns and Reynolds numbers Re =250. Our theoretical predictions are in a good
agreement with the obtained experimental results.Comment: 16 pages, 4 figures, REVTEX4, revised versio
Peculiar Features of the Velocity Field of OB Associations and the Spiral Structure of the Galaxy
Some of the peculiar features of the periodic velocity-field structure for OB
associations can be explained by using the model of Roberts and Hausman (1984),
in which the behavior of a system of dense clouds is considered in a perturbed
potential. The absence of statistically significant variations in the azimuthal
velocity across the Carina arm, probably, results from its sharp increase
behind the shock front, which is easily blurred by distance errors. The
existence of a shock wave in the spiral arms and, at the same time, the
virtually free motion of OB associations in epicycles can be reconciled in the
model of particle clouds with a mean free path of 0.2-2 kpc. The velocity field
of OB associations exhibits two appreciable nonrandom deviations from an ideal
spiral pattern: a 0.5-kpc displacement of the Cygnus- and Carina-arm fragments
from one another and a weakening of the Perseus arm in quadrant III. However,
the identified fragments of the Carina, Cygnus, and Perseus arms do not belong
to any of the known types of spurs.Comment: 14 pages, 3 postscript figures, to be published in Astronomy Letter
Changes in composition and pore space of sand rocks in the oil water contact zone (section YU[1] {3-4}, Klyuchevskaya area, Tomsk region)
The article provides an analysis of specific features in changes of rocks in the oil water contact zone. The object of study is the formation YU[1] {3-4} (J[3]o[1]) of Klyuchevskaya oil deposit (West Siberian oil-gas province, Tomsk region). The research data allow the authors to determine vertical zoning of the surface structure and identify the following zones: oil saturation (weak alteration), bitumen-content dissolution, non-bitumen-content dissolution, cementation, including rocks not affected by hydrocarbon deposit. The rocks under investigation are characterized by different changes in composition, pore space, as well as reservoir filtration and volumetric parameters. Detection of irregularity in distribution of void- pore space in oil-water contact zones is of great practical importance. It helps to avoid the errors in differential pressure drawdown and explain the origin of low-resistivity collectors
Метаболічні ефекти карнітину, роль у розвитку патологій та перспективи клінічного застосування (огляд)
In the literature review the generalized data about the metabolic role of carnitine in the biochemical processes, the consequences of carnitine deficiency and its contribution to the pathogenesis of the development pathologies, prospects for the use of carnitine in clinical practice.В обзоре литературы приведены обобщенные данные о метаболической роли карнитина в биохимических процессах, проходящих в организме, последствия карнитиновой недостаточности и ее вклада в патогенез развития патологий различного генеза, перспектив применения препаратов карнитина в клинической практике.У огляді літератури наведені узагальнені дані щодо метаболічної ролі карнітину у біохімічних процесах, що проходять в організмі, наслідки карнітинової недостатності та її внеску у патогенез розвитку патологій різного генезу, перспектив застосування препаратів карнітину у клінічній практиці.
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