Theoretical backgrounds of nonlinear THz spectroscopy of semiconductor superlattices

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.Comment: 14 page

Physical Principles of the Amplification of Electromagnetic Radiation Due to Negative Electron Masses in a Semiconductor Superlattice

In a superlattice placed in crossed electric and magnetic fields, under certain conditions, the inversion of electron population can appear at which the average energy of electrons is above the middle of the miniband and the effective mass of the electron is negative. This is the implementation of the negative effective mass amplifier and generator (NEMAG) in the superlattice. It can result in the amplification and generation of terahertz radiation even in the absence of negative differential conductivity.Comment: 5 pages, 3 figure

Interconnection of structural characteristics with dynamic properties of A5083 aluminum alloy

In this work, the resistance of high-strain rate deformation and fracture during shock-wave compression of aluminum alloy A5083 previously obtained in two structural states by torsion under high pressure or dynamic pressing is studied. It is shown by electron microscopy that sub-microcrystalline structures differ in the size of grain–subgrains, dislocation density, and ratio of low-angle and high-angle boundaries. It is established that, at the same grain size, the sub-microcrystalline alloy exhibits higher dynamic properties, and after dynamic pressing, it has higher spall strength

Russian Troops in the Badakhshan-Mountain Autonomous Region in 1992-1997

The study is devoted to the most dramatic period of the stay of Russian troops on the territory of Badakhshan-mountain - the era of the civil war in Tajikistan (1992-1997). The authors of the work tried to overcome the schematism and descriptive nature of the historiography of the topic. For this, documents from the archives of the Badakhshan mountain Autonomous Region (BMAR), data from the regional periodical press, and previously unpublished analytical materials and photographs from the funds of the Central Border Museum of the Federal Security Service of the Russian Federation were used. As a result of studying the opposing forces, instead of confronting the faceless, monolithic and mechanically opposed “Russians” and “fighters”, a complex picture of the interaction of various actors involved in the thick of events with the unpredictable dynamics of the context is formed. The authors conclude that the armed forces of the former “Center” at some point turned out to be the only significant economic agent, security guarantor and socialization institution that prevented the development of the region according to the “Afghan” scenario

Electrochemical synthesis of nickel-aluminium oxide system from metals obtained by ore processing

Separate and combined electrochemical oxidation of aluminium and nickel has been conducted by alternating current of industrial frequency. Concentration increase of electrolyte solution (sodium chloride) in the range from 3 to 25 wt. % and current density from 0.5 to 1.5 A/cm{2} was found to result in the increasing metal oxidation rate, excluding aluminium oxidation which oxidation rate is independent of the electrolyte solution concentration. At the current density of 1.5 A/cm{2} the products of separate oxidation of nickel and aluminium are nickel oxyhydroxides, nickel hydroxides and aluminium oxyhydroxide (boehmite), respectively. In addition to these compounds, the nickel-aluminium oxide hydrate is included in the products of nickel and aluminium co-oxidation. Its content grows with the increasing electrolyte solution concentration. Varying the concentration and current density within the limits indicated, the nickel-aluminium oxide system with nickel oxide content from 3 to 10 wt. % is produced

Body surface potential mapping in rats with stress-induce arterial hypertension

Studies on experimental animals allow us to approach the understanding of the mechanisms of changes in the electrical activity of the heart during morphofunctional rearrangements that occur as a result of the development of arterial hypertension (AH). Aim of the study was to investigate body surface potential mapping in young ISIAH rats with genetically determined stress-induced AH during ventricular depolarization. Material and methods. The study was carried out on 3-month-old ISIAH males (n = 10) weighing 250–300 g. Body surface potential mapping was performed using 64 electrodes evenly distributed around the chest of the animal. Results. Significantly higher systolic blood pressure was shown in ISIAH rats compared to Wistar rats (203 ± 14 and 125 ± 5 mm Hg, respectively), as well as heart relative mass, thickness of the left ventricle, right ventricle, and interventricular septum were significantly higher compared to Wistar. During the period of ventricular depolarization, a shift of the zone of negative cardiopotentials to the left-lateral region of the chest is shown in the period corresponding to the time the positive extremum reaches its maximum value in ISIAH rats compared to Wistar. An earlier time of formation, a significantly longer time to achieve the first and second inversion of cardiopotentials, a later time for the positive and negative extrema to reach their maximum values, a greater amplitude of the absolute value of the negative extremum, and a significantly longer total ventricular duration in ISIAH rats compared to Wistar rats were shown. Conclusions. The study give perspective to the use of body surface potential mapping for diagnosing the initial stages of the formation of myocardial hypertrophy in AH