1,139 research outputs found
Quantum Transparency of Barriers for Structure Particles
Penetration of two coupled particles through a repulsive barrier is
considered. A simple mechanism of the appearance of barrier resonances is
demonstrated that makes the barrier anomalously transparent as compared to the
probability of penetration of structureless objects. It is indicated that the
probabilities of tunnelling of two interacting particles from a false vacuum
can be considerably larger than it was assumed earlier.Comment: Revtex, 4 pages, 4 figure
Mathematical modelling of liquid meniscus shape in cylindrical micro-channel for normal and micro gravity conditions
Mathematical model of liquid meniscus shape in cylindrical micro-channel of the separator unit of condensing/separating system is presented. Moving liquid meniscus in the 10 μm cylindrical microchannel is used as a liquid lock to recover the liquid obtained by condensation from the separators. The main goal of the liquid locks to prevent penetration of a gas phase in the liquid line at the small flow rate of the condensate and because of pressure fluctuations in the vapor-gas-liquid loop. Calculation of the meniscus shape has been performed for liquid FC-72 at different values of pressure difference gas - liquid and under normal and micro gravity conditions
Resonant enhanced diffusion in time dependent flow
Explicit examples of scalar enhanced diffusion due to resonances between
different transport mechanisms are presented. Their signature is provided by
the sharp and narrow peaks observed in the effective diffusivity coefficients
and, in the absence of molecular diffusion, by anomalous transport. For the
time-dependent flow considered here, resonances arise between their
oscillations in time and either molecular diffusion or a mean flow. The
effective diffusivities are calculated using multiscale techniques.Comment: 18 latex pages, 11 figure
A conserved alternative splice in the von Recklinghausen neurofibromatosis (NF1) gene produces two neurofibromin isoforms, both of which have GTPase-activating protein activity
Sequence analysis has shown significant homology between the catalytic regions of the mammalian ras GTPase-activating protein (GAP), yeast Ira1p and Ira2p (inhibitory regulators of the RAS-cyclic AMP pathway), and neurofibromin, the protein encoded by the NF1 gene. Yeast expression experiments have confirmed that a 381-amino-acid segment of neurofibromin, dubbed the GAP-related domain (GRD), can function as a GAP. Using the RNA polymerase chain reaction with primers flanking the NF1-GRD, we have identified evidence for alternative splicing in this region of the NF1 gene. In addition to the already published sequence (type I), an alternative RNA carrying a 63-nucleotide insertion (type II) is present in all tissues examined, although the relative amounts of types I and II vary. The insertion is conserved across species but is not present in GAP, IRA1, or IRA2. GenBank searches have failed to identify significant similarity between the inserted sequence and known DNA or protein sequences, although the basic amino acid composition of the insertion shares features with nuclear targeting sequences. Expression studies in yeasts show that despite the partial disruption of the neurofibromin-IRA-GAP homology by this insertion, both forms of the NF1-GRD can complement loss of IRA function. In vivo assays designed to compare the GAP activity of the two alternatively spliced forms of the NF1-GRD show that both can increase the conversion of GTP-bound ras to its GDP-bound form, although the insertion of the 21 amino acids weakens this effect. The strong conservation of this alternative, splicing suggests that both type I and II isoforms mediate important biological functions of neurofibromin
New Interstellar Extinction Maps Based on Gaia and Other Sky Surveys
We present new three-dimensional (3D) interstellar extinction maps in the
and Gaia filters within 2 kpc of the Sun, a 3D differential extinction
(dust spatial distribution density) map along the lines of sight in the same
space, a 3D map of variations in the ratio of the extinctions in the and
Gaia filters within 800 pc of the Sun, and a 2D map of total Galactic
extinction through the entire dust half-layer from the Sun to extragalactic
space for Galactic latitudes . The 3D maps have a transverse
resolution from 3.6 to 11.6 pc and a radial resolution of 50 pc. The 2D map has
an angular resolution of 6.1 arcmin. We have produced these maps based on the
Gaia DR3 parallaxes and Gaia, Pan-STARRS1, SkyMapper, 2MASS, and WISE
photometry for nearly 100 million stars. We have paid special attention to the
space within 200 pc of the Sun and high Galactic latitudes as regions where the
extinction estimates have had a large relative uncertainty so far. Our maps
estimate the extinction within the Galactic dust layer from the Sun to an
extended object or through the entire dust half-layer from the Sun to
extragalactic space with a precision mag. This
gives a high relative precision of extinction estimates even at high Galactic
latitudes, where, according to our estimates, the median total Galactic
extinction through the entire dust half-layer from the Sun to extragalactic
objects is mag. We have shown that the presented
maps are among the best ones in data amount, space size, resolution, precision,
and other properties.Comment: 15 pages, 4 table
On the characterisation of a Bragg spectrometer with X-rays from an ECR source
Narrow X-ray lines from helium-like argon emitted from a dedicated ECR source
have been used to determine the response function of a Bragg crystal
spectrometer equipped with large area spherically bent silicon (111) or quartz
(10) crystals. The measured spectra are compared with simulated ones
created by a ray-tracing code based on the expected theoretical crystal's
rocking curve and the geometry of the experimental set-up.Comment: Version acceptee (NIM
Examination of the astrophysical S-factors of the radiative proton capture on 2H, 6Li, 7Li, 12C and 13C
Astrophysical S-factors of radiative capture reactions on light nuclei have
been calculated in a two-cluster potential model, taking into account the
separation of orbital states by the use of Young schemes. The local two-body
potentials describing the interaction of the clusters were determined by
fitting scattering data and properties of bound states. The many-body character
of the problem is approximatively accounted for by Pauli forbidden states. An
important feature of the approach is the consideration of the dependence of the
interaction potential between the clusters on the orbital Young schemes, which
determine the permutation symmetry of the nucleon system. Proton capture on 2H,
6Li, 7Li, 12C, and 13C was analyzed in this approach. Experimental data at low
energies were described reasonably well when the phase shifts for
cluster-cluster scattering, extracted from precise data, were used. This shows
that decreasing the experimental error on differential elastic scattering cross
sections of light nuclei at astrophysical energies is very important also to
allow a more accurate phase shift analysis. A future increase in precision will
allow more definite conclusions regarding the reaction mechanisms and
astrophysical conditions of thermonuclear reactions.Comment: 40p., 9 fig., 83 ref. arXiv admin note: substantial text overlap with
arXiv:1005.1794, arXiv:1112.1760, arXiv:1005.198
СТРУКТУРНО-ВЕЩЕСТВЕННАЯ МОДЕЛЬ СТАНОВЛЕНИЯ КИМБЕРЛИТОВОЙ ТРУБКИ НЮРБИНСКАЯ (СРЕДНЕ-МАРХИНСКИЙ РАЙОН ЯКУТСКОЙ АЛМАЗОНОСНОЙ ПРОВИНЦИИ)
The paper presents the results of comprehensive study of the primary diamond deposit of the Nyurbinskaya pipe in the Yakutian diamondiferous province. It is established, that the pipe is confined to the fault junction of four directions and is composed of the kimberlite of four phases. Analysis of different faults and tectonic fracturing allowed to reconstruct the tectonic stress fields acting at the stage of the kimberlite body formation and to determine their occurrence sequence in time. The data obtained about regularities of the Nyurbinskaya pipe compositional structure and results of geologo-structural studies are combined in a single structural-compositional model of the deposit formation. Peculiarities of the fault network operation during the deposit formation stage are confirmed by experimental results using polarization-optical method. The model allowed to formulate the basic structural characteristics of the prospecting works object within which the formation of kimberlite body type of the Nyurbinskaya pipe is possible and to determine the elements of the fault network which are promising for the kimberlite pipes discovery.В статье представлены результаты комплексного изучения коренного месторождения алмазов трубка Нюрбинская. Установлено, что трубка приурочена к узлу разломов четырех направлений и сложена кимберлитами четырех фаз. Анализ разноранговых разрывных нарушений и тектонической трещиноватости позволил восстановить поля тектонических напряжений, действовавшие на этапе формирования кимберлитового тела и определить последовательность их проявления во времени. Полученные данные о закономерностях вещественного строения трубки Нюрбинской и результаты геолого-структурных исследований объединены в рамках единой структурно-вещественной модели формирования месторождения. Особенности функционирования разрывной сети на этапе формирования месторождения подтверждены результатами экспериментов с использованием поляризационно-оптического метода. Полученная модель позволила сформулировать признаки, определяющие основные структурные характеристики объекта поисковых работ, в пределах которого возможно формирование кимберлитовых тел типа трубки Нюрбинской, и на их основании выделить те элементы разломной сети (разломные узлы), которые являются перспективными для обнаружения кимберлитовых трубок
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