Abstract
The effective mass at the Fermi level is measured in the strongly interacting two-dimensional (2D) electron system in ultra-clean SiGe/Si/SiGe quantum wells in the low-temperature limit in ...tilted magnetic fields. At low electron densities, the effective mass is found to be strongly enhanced and independent of the degree of spin polarization, which indicates that the mass enhancement is not related to the electrons’ spins. The observed effect turns out to be universal for silicon-based 2D electron systems, regardless of random potential, and cannot be explained by existing theories.
The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross section is by far the largest of all low-energy neutrino couplings. This ...mode of interaction offers new opportunities to study neutrino properties and leads to a miniaturization of detector size, with potential technological applications. We observed this process at a 6.7σ̃ confidence level, using a low-background, 14.6-kilogram CsINa scintillator exposed to the neutrino emissions from the Spallation Neutron Source at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the standard model for this process, were observed in high signal-to-background conditions. Improved constraints on nonstandard neutrino interactions with quarks are derived from this initial data set.
The work demonstrates the results of noise-like (spread-spectrum) signal application in oil industry. A functional practical scheme of information support in bottom-to-head communication channel is ...presented. Some of spread-spectrum signal noise resistance issues are described.
Well-known two-sided estimates for the Lebesgue constants of two classical trigonometric interpolation Lagrange polynomials are improved. Approximations of these Lebesgue constants are based on ...logarithmic functions with shifted arguments.
•Technique for determining rock thermal properties from logging data is enhanced.•New technique allows determining thermal conductivity accounting for anisotropy.•Technique was applied for two ...unconventional reservoirs.•Uncertainty in thermal conductivity determination is less than 12 %.•Uncertainty in volumetric heat capacity determination is less than 5 %.
The limitations of the existing techniques for in situ rock thermal property measurements and numerous cases with non-coring drilling determine the necessity for methods of rock thermal property determination based on well-logging data. Existing approaches for determining rock thermal properties from well-logging data are appropriate only for isotropic rocks. Since many rock types, especially organic-rich shales, exhibit a considerable degree of heterogeneity and anisotropy, advanced approaches for well log-based determination of rock thermal properties are highly desired. The implementation of the new thermal core logging technique, which provides continuous and high-precision measurements of the principal components of the thermal conductivity tensor and volumetric heat capacity from core samples, enabled the development of a new framework for the indirect determination of rock thermal properties. An enhanced technique for determining rock thermal conductivity and volumetric heat capacity from well-logging data accounting for thermal anisotropy and in situ thermobaric conditions is proposed and tested. This technique includes both the application of theoretical models and regression analysis of rock thermal properties, depending on the availability and quality of the input data. Three theoretical models involving a correction factor were compared to provide the best results. The experimental data of rock thermal properties inferred from the thermal core-logging and well-logging data from five wells (1630 samples) drilled through two highly anisotropic unconventional formations – the Bazhenov and the Domanic – were used as the basis of this newly developed approach. It is shown that rock thermal conductivity can be predicted from well-logging data accounting for thermal anisotropy with an uncertainty of less than 12 % and rock volumetric heat capacity with a total uncertainty of less than 5%.
The COHERENT Collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220 MeV/c^{2} using a CsINa scintillation detector sensitive ...to nuclear recoils above 9 keV_{nr}. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6 kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants α_{D}<0.64, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.
Features of obtaining fullerene-containing soot during combustion of gaseous and liquid hydrocarbons with the influence of an electric field on the flame are discussed. The characteristic voltage - ...current characteristics of the discharge created in the flame region and electron microscopic photographs of fullerene-containing soot were obtained.
A series of eight new phosphonamidates containing sterically hindered phenolic and N-heterocyclic fragments was obtained and characterized. The synthesis is based on the reaction of
O
-alkyl-3,5-di-
...tert
-butyl-4-hydroxybenzylchlorophosphonates with aliphatic amines.
At present, an urgent problem is the study of temporal variations of various types of nuclear radiation from the lithosphere in foothill and desert landscapes. This refers to the fluxes of neutrons, ...gamma quanta, beta particles, and emanations of heavy chemical elements. The problem of studying such distributions in the surface atmospheric layer of the Earth remains relevant, owing to the fact that they are concentrated in the human habitat and have a direct impact on the health of the population. This work is devoted to the study of beta spectra of the natural radiation background in the surface atmospheric layer of the Earth. The origin of the measured beta spectra is associated with the daughter products of the decay of radon isotopes
219
Rn,
220
Rn, and
222
Rn in three natural radioactive series. Measurements of the spectra were performed from October 2018 to October 2019 in the foothills of the Zailiysky Alatau of the Tien Shan in Almaty. The frequency of measurements, on average, was about 10 measurements per day with an exposure of at least 2000 s. A database of daily, seasonal, and annual variations in beta spectra has been accumulated. For the analysis of the data obtained, a special software program Analyzer of the Beta Spectra Array was developed, which made it possible to process the standard output files of the Sputnik spectrometric installation and to integrate each spectrum in a given time interval. Time variation over the measured period was described using a standard mathematical computer package for wavelet analysis. The wavelet spectra obtained as a result of integration are used to identify daily, seasonal, and annual effects in variations of beta emanations. Along with this, similar mathematical processing was performed to predict the impact of external factors in the temporal variations of beta particles.
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