The cross section for absorption of neutrinos from the artificial neutrino sources
37
Ar,
51
Cr, and
65
Zn by
82
Se nuclei is calculated. The experimental data on
82
Se(
3
He,
t
)
82
Br ...charge-exchange reaction are used in calculations. It is shown that
82
Se is a perspective isotope for setting up the calibration experiments aimed at searching for new types of neutrinos.
The cross sections of neutrino absorption by the gallium-71 nucleus are obtained for neutrinos from artificial
37
Ar,
51
Cr, and
65
Zn sources. The calculations rely on the new measurement of the ...energy threshold of this absorption reaction, and contributions of germanium-71 excited states to the total cross section are estimated by invoking the data on the
71
Ga(
3
He,t)
71
Gе charge-exchange reaction. The results are important for searches for sterile neutrinos in calibration experiments.
The contributions of light sterile neutrinos to the properties of active-neutrino oscillations and the properties of double-beta decay are estimated under the assumption of the Majorana nature of ...neutrinos on the basis of a phenomenological model involving three active and three sterile neutrinos. The appearance and survival probabilities for active neutrinos are determined upon taking into account sterile-neutrino contributions in order to explain all known anomalies in neutrino data at short distances by employing the same test values of the model parameters. Modified graphical dependences of the survival and appearance probabilities for electron neutrinos/antineutrinos in beams of muon neutrinos/antineutrinos on the distance and other model parameters at various neutrino energies, as well as on the ratio of the distance to the neutrino energy, are presented. A significant distinction between the probability curves within the neutrino model being considered and the simple sinusoidal curves based on the neutrino model involving only one sterile neutrino is found. The effective electron-neutrino masses for beta decay and for neutrinoless double-beta decay are estimated in the presence of the sterile-neutrino contributions. In addition, the properties of selenium-82 two-neutrino double-beta decay are calculated. These results can be used in interpreting and predicting the results of ground-based experiments aimed at searches for sterile neutrinos and neutrinoless double-beta decay.
The energy and structure of two-dimensional domain walls under the action of an external magnetic field directed perpendicular to the easy axis of the film are investigated based on micromagnetic ...modeling. The transitions in the domain wall structure are considered in detail: with an increase in the external field, the transition of a single-vortex 180° Bloch DW to an intermediate two-dimensional Néel DW and, after removal of the external field, a transition to a 180° two-vortex structure.
The present study is focused on the problem of reconstruction of the magnetic configuration in the magnetic reconnection electron diffusion region (EDR). The problem is addressed in the frame of ...electron magnetohydrodynamics with kept electron inertia term. We introduce the new reconstruction model independent of divergence of the electron pressure tensor and reconnection electric field. The model is tested on the magnetotail reconnection event of July 11, 2017 observed by the Magnetospheric Multiscale (MMS) spacecraft in the course of crossing the very core part of the reconnection region, the internal EDR. This new model demonstrates considerably better accuracy of the longitudinal electron velocity reconstruction due to the lower sensitivity to the configuration deviation from the two‐dimensional time‐independent model adopted in our study. We suggest also a new technique to estimate the guide field, implementing the reconstruction of magnetic potential of the in‐plane magnetic field and relying on symmetric properties of magnetic reconnection.
Plain Language Summary
Magnetic reconnection is a fundamental plasma process responsible for the magnetic field reconfiguration and transforming magnetic energy to kinetic and thermal energy of plasma. In the Earth's magnetosphere, the magnetospheric conditions are monitored by several spacecraft missions. Among them, the NASA Magnetospheric Multiscale (MMS) mission is designed for exploring the process of reconnection. On July 11, 2017 at about 22:34 UT MMS was located in the magnetotail at a very fortunate position, intersecting the reconnection region in its very central part, the so‐called electron diffusion region (EDR).
Since MMS consists of four identical spacecraft, MMS provides an excellent tool for testing analytical models of reconnection. Taking the data of one probe as the boundary condition for the analytical model, one can compare the results of calculations with other probes data. In the present paper we suggest a new model of EDR, and compare it to the existing one using the data of 2017/07/11 event. This comparison has shown that the electron inertia term plays an important role in the EDR physics; the proper handling of this term allows considerable improvement of the EDR reconstruction accuracy.
Key Points
A model for electron diffusion region (EDR) reconstruction in electron magnetohydrodynamics (EMHD) approximation with kept electron inertia is developed
Reconstruction of the out‐of‐plane magnetic field is performed independent of the reconnection electric field and pressure anisotropy
Reconstruction is applied for self‐consistent estimate of the guide field value and local coordinate system orientation
Data‐Based Modeling of the Magnetosheath Magnetic Field Tsyganenko, N. A.; Semenov, V. S.; Erkaev, N. V.
Journal of geophysical research. Space physics,
November 2023, 2023-11-00, 20231101, Letnik:
128, Številka:
11
Journal Article
Recenzirano
A quantitative model of the magnetosheath (MS) magnetic structure is developed, using a multi‐year set of Geotail, Themis, Cluster, and MMS magnetometer and plasma instrument data. The MS database is ...created using an identification algorithm, based on observed magnetic field magnitudes and proton densities, normalized by their concurrent interplanetary values, followed by additional filtering with the help of standard bow shock (BS) and magnetopause (MP) models. The model architecture is based on the toroidal/poloidal formalism and a coordinate system that naturally accounts for the tailward flaring of both boundaries. The magnetic field expansions include 960 free coefficients, derived by fitting the model to a grand data set, split into independent training and validation subsets with 1,291,380 and 411,933 1‐min records, respectively. The model faithfully reproduces basic types of the interplanetary magnetic field (IMF) wrapping around the MP. Regular IMF sectors result in strongly dawn‐dusk asymmetric draping, with much larger magnitudes at the quasi‐perpendicular dusk side of BS, and weaker at the quasi‐parallel dawn side, where the MS field lines are bent and dragged tailward. Except in the case of the flow‐aligned IMF orientation, the subsolar field steadily grows toward the MP, and the effect is clearly IMF Bz‐dependent: the field and its gradient are larger (smaller) for northward (southward) IMF Bz, implying a pile‐up of the magnetic flux in the first case and stronger reconnection in the second. Model distributions of the MS field magnitude reveal local depressions, associated with polar cusps near the high‐latitude limits of data coverage.
Plain Language Summary
The terrestrial magnetosheath is a relatively wide transition region, separating our planet’s magnetosphere from the undisturbed flow of magnetized solar wind. Due to the sudden compression of the incoming plasma flow at the bow shock and high conductivity of the magnetosheath medium, the relatively weak magnetic field of interplanetary origin undergoes abrupt compression and drapes around the magnetosphere boundary, the magnetopause. Huge amounts of archived spacecraft data accumulated in the world data centers during past decades of space flight made it possible to develop quantitative models of the magnetosheath magnetic field, based on direct in situ observations. This paper presents first results of such a modeling study, providing a closed analytical representation of the magnetosheath magnetic field, driven by input from upstream monitors of the interplanetary medium.
Key Points
A closed empirical model of the magnetosheath magnetic field is developed, based on satellite data and a flexible mathematical architecture
Driven by interplanetary parameters and dipole tilt, the model faithfully reproduces basic features of the IMF draping around the magnetopause
Northward (southward) IMF results in higher (lower) subsolar fields, indicating magnetic flux pile‐up (stronger reconnection), respectively
•The laser-induced thermocapillary deformation and rupture of liquid layer was investigated.•The experimental technique for measuring profile of the thermocapillary deformation of liquid layer was ...developed.•The optimal function for approximating the thermocapillary deformation was proposed.•The influence of conditions of radiative heat exchange in the system on the layer deformation was investigated numerically.
Characterizing the profile of the laser-induced thermocapillary deformation of a thin liquid layer on a laser absorbing solid is of great fundamental and applied importance. The thermocapillary effect is the basis of several non-contact methods for measuring the physicochemical and thermal properties of liquids and solids, and methods of non-destructive testing in material science and thermal physics. The study of the layer rupturing caused by laser beam heating could contribute to solving the problem of the dry spots formation in thin–film heat exchangers. In this regard, the development of physical and numerical tools to determine the thermocapillary profiles of thin liquid layers is of great interest to researchers. In the present work, we developed a home-made setup to scan a deformed surface of a liquid layer with a laser sheet. Its accuracy was verified by scanning the surface of a solid standard specimen with a given Gaussian profile. By scanning the thermocapillary deformed layers of silicone oil, we found that for the Gaussian distribution of the radiation intensity in the heating laser beam, the thermocapillary deformations are significantly not the Gaussian. A modified Agnesi function, which is characterized by high accuracy and allows defining the surface profile using a minimum of experimental data, is shown to be an optimal function for approximating the thermocapillary deformation. Using Agnesi approximation can significantly reduce the time of the experiment and the processing of results. To validate new experimental data, an axisymmetric numerical model of the thermocapillary convection in a thin liquid layer was developed using commercial software Comsol Multiphysics. It helped calculating the surface profile and the temperature field on the substrate for two boundary conditions of radiative heat exchange in the system corresponding to maximum and minimum radiation heat loss. For the case of the ebonite-silicone oil system, when the laser beam is absorbed by the ebonite surface, it was numerically shown that the difference between the types of boundary conditions becomes noticeable only on very thin layers close to the pseudo-rupture. In general, a comparison of the stationary profiles of the thermocapillary surface deformation and temperature distributions obtained experimentally and numerically for the entire range of the studied layer thicknesses shows satisfactory agreement between the physical and numerical results.
An analytical method for determining the vertical asymmetric magnetization distribution in a two-dimensional Bloch domain wall (DW) is proposed in this work. An asymmetric two-dimensional ...magnetization distribution in a DW is obtained using simple analytical dependences with a minimum number of variable parameters. The structure and energy of the Bloch DW in permalloy-type magnetic films are studied for a wide range of film thickness. The calculation results are compared with the calculation results of other authors.
•The M(H) magnetization curves of NiO nanoparticles (NPs) measured in pulsed fields of up to 250 kOe have been studied.•A model of NiO NP obtained from analysis of M(H) data have been ...proposed.•Surface and size effects as well as the origin and the magnitude of uncompensated magnetic moment have been revealed.
-The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun~ 3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.
We propose a modified extragradient method with dynamic step size adjustment to solve variational inequalities with monotone operators acting in a Hilbert space. In addition, we consider a version of ...the method that finds a solution of a variational inequality that is also a fixed point of a quasi-nonexpansive operator. We establish the weak convergence of the methods without any Lipschitzian continuity assumption on operators.
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