This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical ...activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and Spark Plasma Sintering (SPS) in a vacuum. The dependence of ultrafine-grained (UFG) alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has been shown that the optimal SPS temperature for mechanically activated nanopowders goes down by 350–400 °C in comparison with the optimal sintering temperature in hydrogen for coarse-grained 95W-Ni-Fe powder composition. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of nickel and iron in the surface layer of tungsten α-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of UFG tungsten alloys with high mechanical properties: macro-elastic limit – up to 2250 MPa, yield stress – up to 2500 MPa.
•Obtained ultrafine-grained tungsten alloys with high macroelastic limit and yield stress.•Dependence between density of tungsten alloys and sintering temperatures is non-monotonic.•Sintering activation energy of nanopowders is lower than that of coarse-grained powders.•Optimal sintering temperature of nanopowders is lower than that of coarse-grained alloys.•SPS activation energy is lower compared to sintering of powders in hydrogen.
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A combined passive shield of the RED-100 two-phase emission neutrino detector has been developed and built for suppressing the background of external γ rays and neutrons. The shield is composed of ...a 5‑cm-thick copper layer (the inner layer is adjacent to the detector) and a water layer with a total thickness of approximately 70 cm (including the water inside the copper shield). The Monte Carlo simulation of the shielding efficiency has been performed. The obtained attenuation factor of the copper shield for the γ-ray background has been experimentally verified in a laboratory test using a NaI(Tl) scintillator detector. The γ‑ray background rejection factor of the full shield has also been calculated.
We report simulation and resolution evaluation of monolithic position sensitive detectors with different surfaces. The best result was obtained using a combination of rough polishing of the crystal ...surface and a Teflon wrapper with a resolution in the interaction depth of
dZ
= 0.89 ± 0.01 mm. The best planar resolution
dX
= 0.53 ± 0.01 mm is obtained for a finely polished plate with an ESR film. The diffuse reflector also demonstrates an increase in light collection by 33% compared to the specular one.
The transformation of a subnanosecond ultrawideband electromagnetic pulse (UWB EMP) in a large-volume transparent plasma has been demonstrated experimentally using a large-scale KROT plasma device. ...The column of the plasma generated in the device chamber has a length of more than 4 m and a diameter of more than 1 m. This allows one to implement the regime of quasiuniform ionization, which is necessary to simulate UWB EMP propagation through the ionosphere. It is shown that the length of the wave propagation path in the plasma is sufficient for dispersion transformation of the pulse retaining the envelope of its frequency spectrum.
ABSTRACT
The paper discusses changes in various characteristics of the solar wind, interplanetary magnetic field, geomagnetic activity, and cosmic rays during the registration of paired interacting ...solar wind disturbances on the Earth using the data base of Forbush effects and interplanetary disturbances – FEID. The cases of pair interaction are considered for 1995–2020: (i) successive coronal mass ejections; (ii) coronal mass ejections and high-speed streams from coronal holes; (iii) successive high-speed streams from coronal holes. It is shown that for the first events from a pair, the times for reaching the maximum values of the interplanetary magnetic field and solar wind velocity are significantly reduced, and the amplitudes of the recorded Forbush decreases decline. It is also found that the presence of interaction enriches the second event at the expense of the resources of the first, increasing geomagnetic efficiency and the degree of cosmic ray modulation for the second event in comparison with isolated events, which is especially pronounced for a pair of interacting coronal mass ejections. The existence of the described effects can be explained by the observed increase in the interplanetary magnetic field magnitude in the second events due to the presence of interaction.
Statistical analysis is performed for the relationship of coronal mass ejections (CMEs) and X-ray flares with the fluxes of solar protons with energies >10 and >100 MeV observed near the Earth. The ...basis for this analysis was the events that took place in 1976–2015, for which there are reliable observations of X-ray flares on GOES satellites and CME observations with SOHO/LASCO coronagraphs. A fairly good correlation has been revealed between the magnitude of proton enhancements and the power and duration of flares, as well as the initial CME speed. The statistics do not give a clear advantage either to CMEs or the flares concerning their relation with proton events, but the characteristics of the flares and ejections complement each other well and are reasonable to use together in the forecast models. Numerical dependences are obtained that allow estimation of the proton fluxes to the Earth expected from solar observations; possibilities for improving the model are discussed.
On the approach to minimum of Solar Cycle 24, on 26 August 2018, an unexpectedly strong geomagnetic storm (GMS) suddenly occurred. Its
D
st
index reached
−
174
nT
, that is, the third most intense ...storm of the cycle. The analysis showed that it was initiated by a two-step long filament eruption, which occurred on 20 August in the central sector of the solar disk. The eruptions were accompanied by two large-scale divergent flare-like ribbons and dimmings of a considerable size and were followed by relatively weak but evident Earth-directed coronal mass ejections. In the inner corona, their estimated speed was very low, about
200
–
360
km
s
−
1
. The respective interplanetary transients apparently propagated between two high-speed solar wind streams originated from a two-component coronal hole and therefore their expansion was limited. The resulting ejecta arrived at Earth only on 25 August and brought an unexpectedly strong field of
B
t
≈
18.2
nT
with a predominantly negative
B
z
component of almost the same strength. The geospace storm also manifested itself in the form of a peculiar Forbush decrease (FD). Its magnitude was about 1.5%, which is rather small for the observed G3-class GMS. The main unusual feature of the event is that large positive bursts with an enhancement up to 3% above the pre-event level were recorded on the FD background. We argue that these bursts were mainly caused by an unusually large and changeable cosmic ray anisotropy combined with lowering of the geomagnetic cutoff rigidity in the perturbed Earth’s magnetosphere under cycle minimum-like conditions.
The article discusses an approach to building a system for generating a bank investment prediction with the technology of parallel computing. We develop a predictive model of the price of securities ...for the banking business on the stock market. For predictive analysis of investments, the choice of a mathematical model was justified using the Monte Carlo method. Computer simulation was carried out to form a forecast of securities prices based on historical data on securities of Goldman Sachs. Estimates of the execution time of the forecasting algorithm by the parallel programming method are obtained. The conclusion is made about the applicability of the proposed model when using the method of algorithmic trading in the stock market. The technical requirements for the development of a predictive analytics system for the Bank's investment portfolio are formulated.
We present recent results on the first experimental observation of the coherent elastic scattering of the neutrino on atomic nuclei and review other experiments related to the detection and ...investigation of this process.
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