Abstract
An important quantity determining the choice of technical solutions in design of both surface and underground structures in the permafrost area is the thawing depth of the rocks. To obtain ...simple analytical relations to determine the thawing depth over time, a simple assumption is used: that the initial temperature of the rocks is equal to the melting temperature of ice. The aim of the present work was the assessment of impact of this assumption on the forecast precision. For a quantitative assessment, a simple typical formula recommended by construction norms was used. Functional dependence of the density of the rocks and their heat capacity on the fraction of ice content was considered in the formulas. A rock consisting of a combination of quartz sand and ice was used as an example.Multiple variant calculations were done according to the formulas and their results presented in the form of charts. It was shown that the relative error in determination of thawing depth depends solely on the Stefan criterion and is independent of the thawing duration, thermal conductivity coefficient of the thawing rocks and the air temperature during the thawing. A relation was obtained which allows to quickly assess at which initial values (temperature and ice content of the frozen rocks) it is possible to use the formulas obtained from the simplified calculation models with the assumption that the temperature of the rocks is equal to the melting temperature of ice.
Technical structures with a parallelepiped form are frequently used in various areas of industry. For example, as fluid containers, ice and minerals piles, underground and surface storages and ...cooling chambers. A task of determining the optimum dimensions of the structure to minimize the energy expenses to support a normative temperature in the structure arises. The minimum surface area of the structure at a given volume is accepted as a criterion of optimality. A problem of unconstrained optimization for a structure with a parallelepiped form was formulated and solved. Equations to determine the optimum dimensions of width, height and length of the structure were obtained. It was determined that a cube is the most optimal form.
The method of lifetime measurement is used to investigate the kinetics of spontaneous boiling-up of ethane-nitrogen solutions. Superheating temperatures T sub(n) of solutions have been determined in ...experiments at pressure p = 1.0, 1.6 MPa and nitrogen concentration in ethane x = 0.5, 1.5 mol% in the nucleation rate range J = 1 x 10 super(4)-2 x 10 super(8) s super(-1) m super(3). At J > 3 x 10 super(6) s super(-1) m super(-3) one can observe a satisfactory agreement between experimental data and homogeneous nucleation theory with respect to the temperature dependence of the nucleation rate and a systematic disagreement in the superheating temperature. At x = 0.5 mol% attainable superheating temperatures achieved by experiment coincide within the experimental error with theoretical values, and at x = 1.5 mol% exceed them by approximately 1.7 K. It is shown that one possible reason of such "excess superheating" of a solution beyond the theoretical value of T sub(n) may be the absence of adsorption equilibrium at the critical bubble-ambient solution interface.
The EAS Cherenkov light array Tunka-133, with ~ 3 km2 geometric area, is taking data since 2009.The array permits a detailed study of energy spectrum and mass composition of cosmic rays in the ...energy range from 6 · 1015 to 1018 eV. We describe the methods of time and amplitude calibration of the array and the methods of EAS parameters reconstruction. We present the all-particle energy spectrum, based on 7 seasons of operation.
Alumina ceramics doped with a different concentration of magnesium and manganese were synthesized at a different annealing temperature and medium. An increase in the dopant concentration leads to an ...increase in the pulsed cathodoluminescence intensity of impurity centers at 515 nm (Mg) and 678 nm (Mn). The concentration quenching of the luminescence in the 678 nm band occurs for Al2O3:Mn ceramics. The dopants affect the luminescence intensity in the F-center band differently. An increase in the concentration of an impurity from 0.001 to 18.77 wt % in Al2O3:Mn ceramics leads to a 4-fold decrease in the luminescence intensity of the F-center. On the other hand there is a maximum of the luminescence intensity of the F-center for Al2O3:Mg ceramics with a dopant concentration of 1 wt %. The luminescence bands of Cr3+ (687 nm) and most likely F-centers (670 nm) are dominated depending on the excitation energy in photoluminescence spectra of both Al2O3:Mg and Al2O3:Mn ceramics. The low luminescence intensity of the magnesium band (750 nm) is detected upon the excitation in the band of 325 nm. The luminescence bands of Mn2+ (540 nm) and Mn4+ (650 nm) with low intensity are found in the photoluminescence spectrum too.
•The concentration quenching of the luminescence occurs for Al2O3:Mn ceramics.•A Mn concentration growth leads to a 4-fold decrease in a PCL intensity of F-center.•There is a maximum of the luminescence intensity of the F-center at 1 wt % of Mg.•The PL bands at 670 and 687 nm are dominated for Mg- and Mn-doped alumina ceramics.
Taxifolin is a natural polyphenol belonging to the class of flavonoids. The structure of this compound is characterized by the presence of two chiral centers. The spheroidal form of taxifolin (TAXs) ...has emerged as a promising modification due to enhanced solubility, higher safety profile, and long-term release from solid dosage forms. The study’s objective was to assess the diastereomeric content in TAXs and industrially produced samples of taxifolin. Considering the difference in the physico-chemical properties of diastereomers and based on the literature data, we developed a qualitative HPLC method. The chromatograms were recorded using a diode array detector at 290 nm and a mass spectrometer operated in negative ionization mode. Our data suggest that a biphenyl column and gradient elution using 0.1% formic acid in water and 0.2% formic acid in methanol, with the organic phase gradient from 7% to 21% and a flow rate of 0.65 mL/min for 15 min at 60 °C, provides the best conditions for the separation of taxifolin diastereomers. This method was validated for quantitative analysis. We discovered that the cis-isomer was present in all the analyzed samples, with its quantity ranging from 0.8% to 9.5%. TAXs can be considered a sample enriched with diastereomers.
Recent studies have shown that nitrogen-doped carbon nanotubes (N-CNTs) exhibit anomalous piezoelectric properties, which opens broad prospects for their use in the field of nanopiezotronics. In this ...work, we have demonstrated the effect of the material of the conducting sublayer (titanium, titanium nitride, molybdenum, and chromium) on the structural and piezoelectric properties of N-CNTs. It was found that the sublayer material significantly affects the nitrogen concentration and the type of defects formed in N-CNTs, which in turn has a decisive effect on the magnitude of the piezoelectric strain coefficient of N-CNTs. It is shown that the maximum piezoelectric strain coefficient is observed for CNTs grown on a molybdenum sublayer, which is associated with the active formation of pyrrolic nitrogen in the nanotube structure in the process of growth. The magnitude of the piezoelectric strain coefficient N-CNTs increases from 5.6 to 21.5 pm/V with an increase in the concentration of pyrrolic nitrogen from 10 to 39%. An increase in the piezoelectric strain coefficient of N-CNTs, in turn, leads to an increase in the generated current from 12 to 138 nA. The results obtained can serve as a basis for the development of energy-efficient nanogenerators based on nitrogen-doped CNTs.
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•The sublayer material affects the piezoelectric response of nitrogen-doped carbon nanotubes (N-CNTs).•The pyrrolic N concentration changes from 10 to 39% in N-CNTs on Cr, TiN, Ti and Mo sublayers.•Piezoelectric strain coefficient of N-CNTs increases with an increase in the pyrrolic N.•The maximum piezoelectric strain coefficient is observed for N-CNTs on a Mo sublayer.
New charged vector bosons W′ decaying into gauge boson pairs WZ are predicted in many scenarios of new physics, including models with an extended gauge sector (EGM). Due to the large variety of ...models (other unification groups, models with supersymmetry, little Higgs models, extra dimensions) the more general EGM approach is here considered. For what concerns W′-production, these models are parametrized by two parameters, the W′ mass MW′ and the W−W′ mixing parameter ξ. The diboson WZ production allows to place stringent constraints on this mixing angle and the W′ mass, which we determine and present for the first time by using data from pp collisions at √s = 13 TeV recorded by the ATLAS detector at the CERN LHC, with integrated luminosity of 36.1 fb−1. By comparing the experimental limits to the theoretical predictions for the total cross section of W′ resonant production and its subsequent decay into WZ pairs, we show that the derived constraints on the mixing angle are rather severe, between 10−4 and 10−3, i.e., greatly improved with respect to those derived from the global analysis of electroweak data which yield ξ≲10−2. We combine the limits derived from WZ production data with those obtained from the W′→eν process in order to significantly extend the exclusion region in the MW′−ξ parameter plane and obtain the most stringent exclusion limits to date. We present the combined allowed parameter space for the EGM W′ boson after incorporating indirect constraints from low energy electroweak data, direct search constraints from Tevatron and from the LHC Run I with 7 and 8 TeV as well as at Run II with 13 TeV data.
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