Magnetoresistance of p-GaAs/AlGaAs structures in the vicinity of metal-insulator transition: Effect of superconducting leads

Experimental and theoretical studies on transport in semiconductor samples with superconducting electrodes are reported. We focus on the samples close to metal-insulator transition. In metallic samples, a peak of negative magnetoresistance at fields lower than critical magnetic field of the leads was observed. This peak is attributed to restoration of a single-particle tunneling emerging with suppression of superconductivity. The experimental results allow us to estimate tunneling transparency of the boundary between superconductor and metal. In contrast, for the insulating samples no such a peak was observed. We explain this behavior as related to properties of transport through the contact between superconductor and hopping conductor. This effect can be used to discriminate between weak localization and strong localization regimes.Comment: 10 pages, 3 fi

Kharkiv incoherent scatter facility

The structure, parameters and operating modes of the incoherent scatter radar of the Institute of Ionosphere, Kharkiv are presented. Some results of the ionosphere research obtained by this facility are shown.Наведено структуру, параметри і режими роботи радара некогерентного розсіяння Інституту іоносфери (м. Харків). Показано деякі результати спостережень іоносфери за допомогою цього обладнання

Bending vibrations of stepped rods

Manufacturing stepped rods with segments of sizes proportional to stresses induced in operation is often used to reduce the material consumption in various fields of technology, for example, in the aircraft industry, where the requirements for the weight of structural elements are high. The vibration problems of continuous systems, i.e. systems which masses are considered distributed, are close to the resistance of materials and elasticity theory problems. They are described by partial differential equations. In this case, we consider a homogeneous isotropic material, obeying Hooke’s law. Of all the vibration problems of continuous systems, the transverse vibration problems of shafts and beams is of greatest practical importance. The simplest examples of vibrations of prismatic rods were studied in the 18th century in works on acoustics. But before solving problems of practical importance, the problems of stepped beams, it had taken another two hundred years and the development of approximate methods of solving differential equations. The paper presents a solution to the problem of determining the fundamental frequencies of bending vibrations of two-stepped rods with various boundary conditions, using the approximate Lagrange-Ritz method. The calculation error does not exceed 2.6 %. The fundamental frequency of vibration is defined considering different lengths and stiffness ratios of stepped rod segments. The obtained results can be used in solving practical problems in various fields of technology

The shape and size distribution of H II regions near the percolation transition

Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (H I) density fields, simulated using seminumerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the ‘largest cluster statistic’ (LCS), originally proposed in Klypin & Shandarin, to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction xHI≲0.728 (or equivalently z ≲ 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders – ‘thickness’ (T) and ‘breadth’ (B) – of the largest ionized region do not vary much, while the third Shapefinder – ‘length’ (L) – abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T × B, provides a measure of the ‘cross-section’ of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ∼7 Mpc2 (in comoving scale) while its length increases with time. Interestingly, all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V0.72, at the onset of percolation

Rhythmocardiography used to study the impact of validol and nitroglycerin on heart rate variability among patients with stable stenocardia

Introduction: One of the main reasons of frequent able-bodied citizens’ mortality is ischemic heart disease. Nitroglycerin is used for the reduction of stenocardia attacks, but in case of intolerance of the medication or if side effects appear, it may be substituted for validol. Nowadays peripheral vegetotropic effects of these medications are not completely studied, thus the research that is being carried out is of great topicality. Aims: The present research is aimed at studying the way nitroglycerin and validol affect heart rate variability among patients with stable stenocardia. In the research were included 32 patients with stable stenocardia of I (16%) %), II (56%) and III (28%) dynamic classes from the Cardiology department of outpatient clinic №8 (Chelyabinsk, Russia). The average age of the group is 54±6,2 years. Rhythmocardiography was realized on apparatus-program complex “Micor” (Russia) of high resolution in order to study heart rate variability. Rhythmocardiography was carried out 2 minutes before and 2 minutes after sublingual nitroglycerin intake and on the other day 10 minutes before and 10 minutes after sublingual validol intake. Heart rate variability was studied initially in lying position (ph) and also in 4 stimulating probes: Vm- Modified Valsalva Maneuver, pAAshner-Danjiny Test, AOP -Active Orthostatic Test, PWC120 -Loading Test Power Working Capacity simultaneously measured with EKG in real-time. Following findings were determined: RR - beat-to-beat interval; SDNN - Standard Deviation of Normal-to-Normal Intervals of sinus heart rate HR; ARA -Amplitude respiratory arrhythmia; separately were defined: quadratic dispersion of humoral-metabolic HR deflections (al), sympathetic HR deflections (am), parasympathetic fluctuations (as) and their spectral analogues for determination of control factors’ correlation in constitutional deflection spectrum BCP -VLF%, LF%, HF%. Statistics were elaborated with the help of StatPlus® program (2009). Results: It was proved from the realized research that with validol and nitroglycerin intake the total heart rate variability (SDNN) significantly increased in all probes. With nitroglycerin intake in comparison with the reference level the RR duration in the background probe fell (ph) (p<0,0001), humoral metabolic impact increased aloud: al b ph (p<0,05), Vm (p<0,001), pA (p<0,0001), VLF% b ph (p<0,01), pA (p<0,05); sympathetic manipulation: am b Vm (p<0,0001), pA (p<0,01), AOP (p<0,001), PWC (p<0,01), LF% b AOP (p<0,01); parasympathetic regulation fell: as b ph (p<0,01),HF% b ph (p<0,001), Vm (p<0,01), pA (p<0,0001); with nitroglycerin intake the response value to stimulus in AOP increased: d-a NN% (p<0,01), d-a NN, sec (p<0,05). In probe with validol significantly increased the RR range in all other probes: ph, AOP (p<0, 0001), Vm, pA (p<0,001), PWC (p<0, 01); humoral-metabolic and sympathetic impact increased in all probes, except PWC, the amount of parasympathetic deflections (as) increased in AOP (p<0, 01) and PWC (p<0, 05), meanwhile the percentage of parasympathetic impact (HF %) (p<0, 05) for certain reduced by ph. Thus, the prescription of these medications has both: positive aspects - SDNN increase after nitroglycerin and validol intake, with validol intake the RR increase in all probes may be observed, as in AOP and PWC and negative aspects-the increase of humoral-metabolic and sympathetic regulation under the impact of surveyed medications, as normally parasympathetic regulation should predominate. It brings about the necessity of specific control of the prescription and the individual selection of the medications even contrary to standard schemes

Analysis of the current state and modern trends in the development of the rocket and space complex of the Russian Federation

This article focuses on the analysis of the current state and modern development trends of the Russian Federation’s rocket and space complex under contemporary conditions. The relevance of the study is driven by the increasing complexity of geopolitical and sanctions policies, which affect technological development in the industry, as well as the significant role of the rocket and space complex in ensuring national security, scientific progress, and the country’s technological sovereignty. The research is aligned with the Russian Space Activity Development Strategy up to 2030 and beyond. The aim of the study is to conduct a comprehensive analysis of the current state of the Russian rocket and space complex, identify modern trends, and develop recommendations to enhance its competitiveness in the global market. The research employs methods such as a systematic approach, which allowed for the consideration of the rocket and space complex as a complex multi-level structure, encompassing a wide range of functions, products, and services provided by major enterprises, corporations, and other participants; a comparative analysis of the activities of leading global space powers; statistical analysis of reporting data, expert opinions, and more. The application of this comprehensive set of research methods provided a holistic understanding of the current state of the industry and its prospective areas for further development. The main results of the study include an assessment of the current state of the rocket and space industry, a comparative analysis of the activities of major players in the global market, which helped to identify the key problems, challenges, and specific features of the Russian Federation’s rocket and space complex at the current stage of economic development. The scientific novelty lies in identifying, substantiating, and systematizing the main trends occurring in the industry. Based on the data obtained, recommendations have been developed to improve the efficiency of the Russian rocket and space complex, with a focus on increasing innovation activity, upgrading key assets, and expanding international cooperation. The practical significance of the study is reflected in the potential use of its results to shape strategic development plans for the industry and to develop government policies in the field of space research and technology

The resonance phenomenon in the reaction–diffusion systems

A new mechanism of pattern formation different from the Turing and oscillatory instabilities in the reaction–diffusion systems was found. It is closely connected with the resonance phenomenon that appears in the models when Jacobi's matrix of the kinetic part is equivalent to Jordan cell and diffusion coefficients are cited. Some results of numerical calculations of the blood coagulation model are discussed. The pattern formation regimes that can be treated as the results from the resonance phenomenon were observed

Smart contract as a tool for digital transformation of penitentiary system economy

The Russian penitentiary system is a large diversified industry with a total annual output of goods, works and services worth more than 30 billion rubles. The process of integrating such a manufacturer into the national digital economic system requires a special set of tools, one of which, in the author’s opinion, is a smart contract. The object of the study is the sphere of labor adaptation of convicts, subject is digital tools to improve efficiency of production processes and relations in the penitentiary system. The article studies the use of smart contracts as one of the promising directions for improving economic activity of correctional institutions and optimizing the contracting system. As a result of the study, the author concluded that it is advisable to develop smart contracts as a tool to strengthen and develop economic potential of the penitentiary system, and also suggested possible directions of its practical application