355 research outputs found
Peculiarities of neutron waveguides with thin Gd layer
Peculiarities of the formation of a neutron enhanced standing wave in the
structure with a thin highly absorbing layer of gadolinium are considered in
the article. An analogue of the poisoning effect well known in reactor physics
was found. The effect is stronger for the Nb/Gd/Nb system. Despite of this
effect, for a Nb/Gd bilayer and a Nb/Gd/Nb trilayer placed between Al2O3
substrate and Cu layer, it is shown theoretically and experimentally that one
order of magnitude enhancement of neutron density is possible in the vicinity
of the Gd layer. This enhancement makes it possible to study domain formation
in the Gd layer under transition of the Nb layer(s) into the superconducting
state (cryptoferromagnetic phase).Comment: 5 pages, 2 figure
Method of Laser Cross-correlation Optical Spectroscopy for Investigation of Dispersion Medium
In the paper, we suggest one of the possible schemes of a cross-correlation optical spectroscopicdevice for investigation of turbid colloidal solutions and suspensions. This devise is designed fordeterminationof the hydrodynamic radii of nanoparticles. The cross-correlation function is constructed for two signals of light intensity scattered on a cuvette with the investigated dispersion medium. The construction of crosscorrelation optical spectroscopicdevice makes it possible to detect single scattered light by suppressing multiple scattering. We carried out an analysis of literature containing theory of light scattering and results of applying cross-correlation method for investigation of solutions and suspensions. Based on the analytical review, the scheme of cross-correlation optical spectroscopicdevice was developed and constructed.
Keywords: specklefield, cross-correlation, optical spectroscopy, size distribution, dispersion mediu
Manipulation of Microparticles By Bessel Light Beam
We consider perspectives of optical manipulation of microscopic objects in the area of biology, biophysics and medicine. The first part of the work is devoted to a brief review of the microparticles’ manipulation. The second part contains calculations of the focusing of laser radiation parameters and some results on the formation of Bessel light beams. The experimental setup based on the optical manipulation technique of micron-sized particles was developed
Thermalization of a nonequilibrium electron-positron-photon plasma
Starting from a nonequilibrium configuration we analyse the essential role of
the direct and the inverse binary and triple interactions in reaching an
asymptotic thermal equilibrium in a homogeneous isotropic
electron-positron-photon plasma. We focus on energies in the range 0.1--10 MeV.
We numerically integrate the integro-partial differential relativistic
Boltzmann equation with the exact QED collisional integrals taking into account
all binary and triple interactions in the plasma. We show that first, when
detailed balance is reached for all binary interactions on a timescale
sec, photons and electron-positron pairs establish
kinetic equilibrium. Successively, when triple interactions fulfill the
detailed balance on a timescale sec, the plasma reaches
thermal equilibrium. It is shown that neglecting the inverse triple
interactions prevents reaching thermal equilibrium. Our results obtained in the
theoretical physics domain also find application in astrophysics and cosmology.Comment: 4 pages, 3 figures, Phys. Rev. Lett., to appea
Numerical simulation in roll pass design for bar rolling
The application of finite element simulation to the problem of roll pass design for round bar rolling is considered. Two roll pass sequences were developed by analytical methods and then optimized using 2.5D Finite Element Method (FEM). The first one is a classical oval-round roll pass design. The second one is a combination of flat rolls and round roll passes. Relying on the simulation data obtained by FEM, the roll gaps were adjusted to achieve the required bar shape and the uniform distribution of rolling force between the passes. Advantages and disadvantages of each roll pass design were considered
Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers
We report on a study of the structural, magnetic and superconducting
properties of Nb(25nm)/Gd()/Nb(25nm) hybrid structures of a
superconductor/ ferromagnet (S/F) type. The structural characterization of the
samples, including careful determination of the layer thickness, was performed
using neutron and X-ray scattering with the aid of depth sensitive
mass-spectrometry. The magnetization of the samples was determined by SQUID
magnetometry and polarized neutron reflectometry and the presence of magnetic
ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The
analysis of the neutron spin asymmetry allowed us to prove the absence of
magnetically dead layers in junctions with Gd interlayer thickness larger than
one monolayer. The measured dependence of the superconducting transition
temperature has a damped oscillatory behavior with well defined
positions of the minimum at =3nm and the following maximum at =4nm;
the behavior, which is in qualitative agreement with the prior work (J.S. Jiang
et al, PRB 54, 6119). The analysis of the dependence based on Usadel
equations showed that the observed minimum at =3nm can be described by the
so called "" to "" phase transition of highly transparent S/F
interfaces with the superconducting correlation length nm in
Gd. This penetration length is several times higher than for strong
ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures
with which are of topical interest in superconducting
spintronics
A Rotating Collapsar and Possible Interpretation of the LSD Neutrino Signal from SN 1987A
We consider an improved rotational mechanism of the explosion of a collapsing
supernova. We show that this mechanism leads to two-stage collapse with a phase
difference of \sim 5 h. Based on this model, we attempt a new interpretation of
the events in underground neutrino detectors on February 23, 1987, related to
the supernova SN 1987A.Comment: 18 pages, 3 figures, 9 table
Magnetic proximity effect in [Nb/Gd] superlattices seen by neutron scattering
We have used spin-polarized neutron reflectometry to investigate the
magnetization profile of superlattices composed of ferromagnetic Gd and
superconducting Nb layers. We have observed a partial suppression of
ferromagnetic (F) order of Gd layers in [Gd()/Nb(25nm)]
superlattices below the superconducting (S) transition of the Nb layers. The
amplitude of the suppression decreases with increasing . By analyzing the
neutron spin asymmetry we conclude that the observed effect has an
electromagnetic origin - the proximity-coupled S layers screen out the external
magnetic field and thus suppress the F response of the Gd layers inside the
structure. Our investigation demonstrates the considerable influence of
electromagnetic effects on the magnetic properties of S/F systems
Seasonal Arctic sea ice forecasting with probabilistic deep learning
Anthropogenic warming has led to an unprecedented year-round reduction in Arctic sea ice extent. This has far-reaching consequences for indigenous and local communities, polar ecosystems, and global climate, motivating the need for accurate seasonal sea ice forecasts. While physics-based dynamical models can successfully forecast sea ice concentration several weeks ahead, they struggle to outperform simple statistical benchmarks at longer lead times. We present a probabilistic, deep learning sea ice forecasting system, IceNet. The system has been trained on climate simulations and observational data to forecast the next 6 months of monthly-averaged sea ice concentration maps. We show that IceNet advances the range of accurate sea ice forecasts, outperforming a state-of-the-art dynamical model in seasonal forecasts of summer sea ice, particularly for extreme sea ice events. This step-change in sea ice forecasting ability brings us closer to conservation tools that mitigate risks associated with rapid sea ice loss
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