427 research outputs found
Landau damping in thin films irradiated by a strong laser field
The rate of linear collisionless damping (Landau damping) in a classical
electron gas confined to a heated ionized thin film is calculated. The general
expression for the imaginary part of the dielectric tensor in terms of the
parameters of the single-particle self-consistent electron potential is
obtained. For the case of a deep rectangular well, it is explicitly calculated
as a function of the electron temperature in the two limiting cases of specular
and diffuse reflection of the electrons from the boundary of the
self-consistent potential. For realistic experimental parameters, the
contribution of Landau damping to the heating of the electron subsystem is
estimated. It is shown that for films with a thickness below about 100 nm and
for moderate laser intensities it may be comparable with or even dominate over
electron-ion collisions and inner ionization.Comment: 15 pages, 2 figure
A novel long non-coding natural antisense RNA is a negative regulator of Nos1 gene expression
Long non-coding natural antisense transcripts (NATs) are widespread in eukaryotic species. Although recent studies indicate that long NATs are engaged in the regulation of gene expression, the precise functional roles of the vast majority of them are unknown. Here we report that a long NAT (Mm-antiNos1 RNA) complementary to mRNA encoding the neuronal isoform of nitric oxide synthase (Nos1) is expressed in the mouse brain and is transcribed from the non-template strand of the Nos1 locus. Nos1 produces nitric oxide (NO), a major signaling molecule in the CNS implicated in many important functions including neuronal differentiation and memory formation. We show that the newly discovered NAT negatively regulates Nos1 gene expression. Moreover, our quantitative studies of the temporal expression profiles of Mm-antiNos1 RNA in the mouse brain during embryonic development and postnatal life indicate that it may be involved in the regulation of NO-dependent neurogenesis
ВЛИЯНИЕ ТЕПЛОВОЙ РАБОТЫ ФУТЕРОВКИ ЭЛЕКТРОДУГОВЫХ ПЕЧЕЙ НА ЭНЕРГОПОТРЕБЛЕНИЕ
The paper presents an analysis of specific features of lining thermal performance in electric-arc furnaces at various technological periods. It has been shown that on the basis of mathematical modeling methods for thermal processes it is possible to predict power consumption of furnaces at the operational split schedule with due account of such furnace characteristics as capacity, lining materials, furnace idle times under closed and open conditions etc. The paper shows distinctions in thermal performance of acid and the basic linings in the electric-arc furnaces. The proposed approach allows to analyze thermal losses by heat conductivity and on accumulation by a refractory lining and rather accurately to determine the required balance sheet items while calculating power consumption during various periods of scrap melting for furnaces of various capacity.Представлен анализ особенностей тепловой работы футеровки электродуговых печей в различные технологические периоды. Показано, что на основе методов математического моделирования тепловых процессов возможно прогнозировать энергопотребление печей при прерывистом графике работы с учетом таких характеристик печи, как емкость, материалы футеровки печи, время простоев печи в закрытом и открытом состояниях и т. д. Показаны различия в тепловой работе кислой и основной футеровок электродуговых печей. Представленный подход позволяет проанализировать тепловые потери теплопроводностью и на аккумуляцию кладкой и достаточно точно определять данные статьи баланса при расчете энергопотребления в разные периоды плавки для печей различной емкости
Electron-phonon scattering at the intersection of two Landau levels
We predict a double-resonant feature in the magnetic field dependence of the
phonon-mediated longitudinal conductivity of a two-subband
quasi-two-dimensional electron system in a quantizing magnetic field. The two
sharp peaks in appear when the energy separation between two
Landau levels belonging to different size-quantization subbands is favorable
for acoustic-phonon transitions. One-phonon and two-phonon mechanisms of
electron conductivity are calculated and mutually compared. The phonon-mediated
interaction between the intersecting Landau levels is considered and no avoided
crossing is found at thermal equilibrium.Comment: 13 pages, 8 figure
Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths
Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present SNSPDs embedded in nanophotonic integrated circuits which achieve internal quantum efficiencies close to unity at 1550 nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noise-equivalent powers in the 10-19 W/Hz-1/2 range and the timing jitter is as low as 35 ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms
Future of superheavy element research: Which nuclei could be synthesized within the next few years?
Low values of the fusion cross sections and very short half-lives of nuclei
with Z120 put obstacles in synthesis of new elements. Different nuclear
reactions (fusion of stable and radioactive nuclei, multi-nucleon transfers and
neutron capture), which could be used for the production of new isotopes of
superheavy (SH) elements, are discussed in the paper. The gap of unknown SH
nuclei, located between the isotopes which were produced earlier in the cold
and hot fusion reactions, can be filled in fusion reactions of Ca with
available lighter isotopes of Pu, Am, and Cm. Cross sections for the production
of these nuclei are predicted to be rather large, and the corresponding
experiments can be easily performed at existing facilities. For the first time,
a narrow pathway is found to the middle of the island of stability owing to
possible -decay of SH isotopes which can be formed in ordinary fusion
reactions of stable nuclei. Multi-nucleon transfer processes at near barrier
collisions of heavy (and very heavy, U-like) ions are shown to be quite
realistic reaction mechanism allowing us to produce new neutron enriched heavy
nuclei located in the unexplored upper part of the nuclear map. Neutron capture
reactions can be also used for the production of the long-living neutron rich
SH nuclei. Strong neutron fluxes might be provided by pulsed nuclear reactors
and by nuclear explosions in laboratory conditions and by supernova explosions
in nature. All these possibilities are discussed in the paper.Comment: An Invited Plenary Talk given by Valeriy I. Zagrebaev at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Three-loop verification of a new algorithm for the calculation of a -function in supersymmetric theories regularized by higher derivatives for the case of SQED
We verify a recently proposed method for obtaining a -function of
supersymmetric gauge theories regularized by higher derivatives by
an explicit calculation. According to this method, a -function can be
found by calculating specially modified vacuum supergraphs instead of a much
larger number of the two-point superdiagrams. The result is produced in the
form of a certain integral of double total derivatives with respect to the loop
momenta. Here we compare the results obtained for the three-loop
-function of SQED in the general -gauge with the help
of this method and with the help of the standard calculation. Their coincidence
confirms the correctness of the new method and the general argumentation used
for its derivation. Also we verify that in the considered approximation the
NSVZ relation is valid for the renormalization group functions defined in terms
of the bare coupling constant and for the ones defined in terms of the
renormalized coupling constant in the HD+MSL scheme, both its sides being
gauge-independent.Comment: 19 pages, 8 figures; title changed, minor corrections; the final
version to appear in Nuclear Physics
Melting Point and Lattice Parameter Shifts in Supported Metal Nanoclusters
The dependencies of the melting point and the lattice parameter of supported
metal nanoclusters as functions of clusters height are theoretically
investigated in the framework of the uniform approach. The vacancy mechanism
describing the melting point and the lattice parameter shifts in nanoclusters
with decrease of their size is proposed. It is shown that under the high vacuum
conditions (p<10^-7 torr) the essential role in clusters melting point and
lattice parameter shifts is played by the van der Waals forces of
cluster-substrate interation. The proposed model satisfactorily accounts for
the experimental data.Comment: 6 pages, 3 figures, 1 tabl
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