Data taking has been started at the first stage of the polarization experiment SPASCHARM at U-70 accelerator. This report describes the detectors of the current experimental setup as well as the ...results of measurements of their characteristics during the beam data taking in the runs of 2018–2022.
The study of the decomposition process of gas hydrates at atmospheric pressure and temperatures below 0°C revealed that methanol could affect this process in different ways, depending on its ...saturation with environmental components. Indeed, due to the absorption of methane from the hydrate by methanol, the onset of its decomposition is observed at lower temperatures. Nevertheless, decomposition proceeds more slowly than with pure methane hydrate. When the methanol surrounding the methane hydrate is saturated with other medium components, the hydrate dissociation occurs at the equilibrium temperature (when intersecting the hydrate–ice–gas curve in a system without additives) regardless of the alcohol concentration. A similar situation is observed with hydrate obtained from a methane-propane gas mixture; however, under experimental conditions, ice begins to melt at a lower temperature compared to the dissociation point of methane-propane hydrate (in the case of methane hydrate, the situation is reversed: the hydrate is less stable). High concentrations of methanol (above 40 mass%) lead to a significant decrease in the temperature of hydrate decomposition. The data obtained show that methanol in low dosages (about 10 mass%) can be used for gas storage and transportation since, under certain conditions, it does not shift the equilibrium curve of hydrate formation and slows down the process of methane hydrate decomposition.
The effect of mixtures of fish gelatin (protein) from Atlantic cod skin and sodium alginate (polysaccharide) from brown algae on the nucleation of methane-propane hydrate with cubic structure II was ...studied. The rocking cell method with cooling at a constant rate was used to determine the supercooling required for the formation of hydrates both from solutions of the individual polymers and from their mixtures. It was shown that sodium alginate has practically no effect on the formation of the gas hydrates in contrast to gelatin, the inhibiting activity of which had an intermediate value between polyvinylpyrrolidone and polyvinylcaprolactam (commercial kinetic hydrate inhibitors). In the case of blends of the polymers, an insignificant effectiveness reduction was observed with a decrease in the sodium alginate concentration at a fixed gelatin content. The results indicate antagonism in the kinetic inhibition of methane–propane hydrate by mixtures of polyelectrolytes of biological origin. Intermolecular interactions in the polysaccharide–gelatin complexes inevitably affect the ability of the polymers to retard the nucleation process. A more detailed investigation of the hydrate formation kinetics in relation to the ratio of the polymers in the solution will make it possible to reveal the mechanism of their effect and propose mixed reagents to control the hydrate formation process.
Abstract
Problem of uncertainty of graph structure identification in random variable network is considered. An approach for the construction of upper and lower confidence bounds for graph structures ...is developed. This approach is applied for the construction of upper and lower confidence bounds for the threshold similarity graph. The stability of confidence bounds and gaps between upper and lower confidence bounds are investigated. Theoretical results are illustrated by numerical experiments.
Abstract
Two market network models are investigated. One of them is based on the classical Pearson correlation as the measure of association between stocks returns, whereas the second one is based on ...the sign similarity measure of association between stocks returns. We study the uncertainty of identification procedures for the following market network characteristics: distribution of weights of edges, vertex degree distribution in the market graph (MG), cliques and independent sets in the MG and the vertex degree distribution of the maximum spanning tree. We define the true network characteristics, the losses from the error of its identification by observations and the uncertainty of identification procedures as the expected value of losses. We use an elliptically contoured distribution as a model of the multivariate stocks returns distribution. It is shown that identification of statistical procedures based on the sign similarity are statistically robust in contrast to the procedures based on the classical Pearson correlation.
This work revealed that most water‑soluble compounds have a dual nature (thermodynamic promotion or hydrate inhibition) depending on thermobaric conditions. Indeed, by lowering the melting point of ...ice, water‑soluble organic compounds expand the region of water‑containing liquid phase existence below 0°C. This work considered typical thermodynamic hydrate inhibitors as alcohols (methanol, ethanol, and 2‑propanol). It turned out that even methanol does not exhibit inhibitory properties below the ice crystallization line, and it does not affect the equilibrium conditions of methane hydrate formation. In this case, the observed four-phase hydrate–ice–solution–gas equilibrium either corresponds to the hydrate–ice–gas line for the water-methane system (in the case of methanol) or lies at higher temperatures (in the case of ethanol and 2‑propanol). This allowed us to assume that practically any water‑soluble organic compounds will either exhibit the properties of thermodynamic hydrate promoters in a specific temperature range below 0°C or will not affect the hydrate–ice–gas equilibrium. In addition, the presence of the ice and an aqueous liquid mixture in the system accelerates the hydrate growth (compared to the hydrate growth from the bulk phase of ice). It should also be noted that, unlike conventional thermodynamic promoters, methanol does not alter the methane hydrate’s structure and gas capacity, which is more favorable. The data obtained can contribute to developing hydrate‑based technologies for gas storage and separation of gas mixtures.
We report the results of experimental studies of the photoelectric properties of a
p–i–n
GaAs photodiode with InAs/GaAs(001) double asymmetric quantum dots (DAQDs) grown by self-assembling in the ...metal–organic vapor-phase epitaxy process. Three peaks were observed in the dependence of the photocurrent on the reverse bias measured at monochromatic photoexcitation of the DAQDs at the wavelength corresponding to the energy of interband optical transitions between the ground hole and electron states in the larger quantum dots (QDs). These peaks were related to the tunneling of the photoexcited electrons between the QDs, including a dissipative one (with emission and absorption of optical phonons). The experimental results agree qualitatively with the theoretical field dependence of the probability of 1D dissipative tunneling between QDs.
ABSTRACT
Changes apparent in the arctic climate system in recent years require evaluation in a century‐scale perspective in order to assess the Arctic's response to increasing anthropogenic ...greenhouse‐gas forcing. Here, a new set of century‐ and multidecadal‐scale observational data of surface air temperature (SAT) and sea ice is used in combination with ECHAM4 and HadCM3 coupled atmosphere–ice–ocean global model simulations in order to better determine and understand arctic climate variability. We show that two pronounced twentieth‐century warming events, both amplified in the Arctic, were linked to sea‐ice variability. SAT observations and model simulations indicate that the nature of the arctic warming in the last two decades is distinct from the early twentieth‐century warm period. It is suggested strongly that the earlier warming was natural internal climate‐system variability, whereas the recent SAT changes are a response to anthropogenic forcing. The area of arctic sea ice is furthermore observed to have decreased ∼8 × 105 km2 (7.4%) in the past quarter century, with record‐low summer ice coverage in September 2002. A set of model predictions is used to quantify changes in the ice cover through the twenty‐first century, with greater reductions expected in summer than winter. In summer, a predominantly sea‐ice‐free Arctic is predicted for the end of this century.
Abstract The Preisach model is a well-known model of hysteresis in the modern nonlinear science. This paper provides an overview of works that are focusing on the study of dynamical systems from ...various areas (physics, economics, biology), where the Preisach model plays a key role in the formalization of hysteresis dependencies. Here we describe the input-output relations of the classical Preisach operator, its basic properties, methods of constructing the output using the demagnetization function formalism, a generalization of the classical Preisach operator for the case of vector input-output relations. Various generalizations of the model are described here in relation to systems containing ferromagnetic and ferroelectric materials. The main attention we pay to experimental works, where the Preisach model has been used for analytic description of the experimentally observed results. Also, we describe a wide range of the technical applications of the Preisach model in such fields as energy storage devices, systems under piezoelectric effect, models of systems with long-term memory. The properties of the Preisach operator in terms of reaction to stochastic external impacts are described and a generalization of the model for the case of the stochastic threshold numbers of its elementary components is given.
The factors affecting the experimental determination of the conditions of gas hydrates phase equilibria in various systems using the stepwise heating and constant-rate heating procedures in the ...GHA350 stirring autoclave or the RCS6 rocking cells were analyzed. It was found that more reliable results are obtained with the GHA350 autoclave, which gives more intense agitation of the fluids. The stepwise heating method is a priori a more reliable way for determination of the equilibrium conditions of hydrate formation suitable for any system. However, its use requires a greater expenditure of time. With the alternative method of heating at a constant rate of 0.1-1 deg/h it is possible to reduce the length of a single measurement considerably. Anyway, if it is used to obtain reliable experimental data it is necessary to select a heating rate in line with the mixing efficiency of the employed apparatus, the type of system being investigated, and other factors. For most systems the results of measuring the hydrate equilibrium temperatures by the stepwise method and by continuous heating at 0.1 deg/h using the GHA350 autoclave agree within the experimental error limits. Greater discrepancy between the results of the two methods is observed for gas hydrates in concentrated salt solutions that have high viscosity at low temperatures (below –25°C).
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