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Silicon light-emitting diodes with luminescence associated with (113) defects are fabricated by the implantation of 350-keV oxygen ions at a dose of 3.7 × 1014 cm–2 and subsequent annealing at 700°C for 1 h in a chlorine-containing atmosphere. The electroluminescence is studied in wide temperature and excitation-power ranges. The line associated with the (113) defects is dominant in all the spectra. The temperature dependence of the line intensity depends on the excitation power at low temperatures: an increase in the intensity with an activation energy of 25 meV is observed at low current densities and no rise in the intensity is observed with increasing current density. At higher temperatures, an intensity with an activation energy of 59 meV is quenched irrespective of the current density. With increasing temperature, the peak of the line of the (113) defect shifts by the same energy as the energy-gap width, whereas the half width of the line grows linearly.

A detector for detection of beta-decay electrons in experiments on recording of a signal of sterile neutrinos is searched for. A set of parameters indicates that an avalanche silicon precision detector is a promising detector that allows electron counting rates of up to 2.5 × 107 s–1 for an active area of 0.785 mm2 at room temperature with a possibility of spectrometric detection.

An electron-spin resonance technique has been used to examine the influence exerted by the degree of compensation on spin effects in a set of nonmagnetic Ge:As semiconductor samples in the vicinity of the insulator–metal phase transition at temperatures 2 K ≤ T ≤ 80 K. It was found that the behavior of the paramagnetic susceptibility, specific to the Pauli paramagnetism and manifested in the spin density resonance, is drawn deep into the insulator state and is observed up to rather large degrees of compensation K ≈ 0.7 at temperature 20 K ≥ T ≥ 5–10 K. Outside this temperature range, both the quantities rapidly grow with increasing compensation and their behavior approaches the Curie law characteristic of the strong insulator state. The reason for this behavior is that the degeneracy is lifted at high temperatures and, at low temperatures, electron states are localized at the Fermi level as a result of the Coulomb blockade by compensating acceptors of the most closely lying donor states and the resulting formation of a narrow Coulomb band in the metallized impurity band. At temperature T ≥ 5–10 K, the gap is blurred by thermal excitations and has no effect on the manifestation of the Pauli paramagnetism. The behavior of the line width of the electron-spin resonance is determined by the scattering on quasi-stationary electric dipoles created by the Coulomb blockade at low temperatures and by the scattering on phonons at high temperatures. The behavior of the g-factor is qualitatively correlated with the specific features of the paramagnetic susceptibility and spin density: with decreasing temperature it weakly grows in the range of the Pauli paramagnetism and then rapidly increases in the range in which the Coulomb blockade is manifested and a transition occurs to the Curie law. By an analogy with ferromagnetic materials in which such a fast increase in the g-factor is observed, the possibility of a compensation caused ferromagnetic coupling of spins localized on donors. The microscopic model of such a coupling is discussed.

Introduction. In recent decades, in the field of photoelectronics, special attention has been paid to the development of semiconductor matrix photodetectors. These detectors have become an effective alternative to existing television receiving systems. Among such devices, linear position-sensitive sensors are used in cases where the rapid registration of changes to the environment is required (for instance, high-speed locators for flying vehicles).Aim. To develop a strip of silicon pin-diodes as part of a hybrid IR-detector for effective registration of photoelectrons with time resolution less than 10 ns, as well as to model the key electro-physical characteristics of the strip.Materials and methods. In the device under development, the registration of photoelectrons is achieved by the presence of a near-surface field using p ++–p junction formed by diffusion of boron into the silicon with resistivity of 3 kΩ · cm. The pulling field is also formed in the space charge region between p ++ - and n ++ -regions. Diffusion of phosphorus was carried out to create the n ++ -region. Numerical calculations of potential distribution, concentration of free charge carriers and currents were carried out using software for 1D- and 2D-modelling (SimWin and TCAD Synopsys).Results. 2D-calculation of charge carrier concentration and potential distribution was performed. The study determined the minimum bias for the complete depletion of the i-layer, including that for longitudinal grooves of various depths. The strip was tested as part of a hybrid photoelectric device by irradiating light pulses from IR LED. When the voltage on the diodes was reached –270 V, the duration of the signal front on all channels was 5…9 ns.Conclusion. For use in IR-hybrid detectors, a strip of 12 silicon pin-diodes was developed with a sensitive element of 24 × 0.2 mm in dimension. The study of pulse characteristics showed that the necessary duration of the front signal on all channels was achieved without thinning thus satisfying the requirements for high-speed position-sensitive sensor of the infrared radiation.

An explosive growth of autonomous solar power plants is investigated. This growth takes a number of forms: technological, business, government, cultural, scientific and educational. The role of cash flows associated with the development of solar energy over the past two decades is studied. The tendencies influencing research developments and production of solar power plants are determined. These tendencies are manifested in a flow of scientific publications studying solar systems, especially the ones doing computer modelling. This fact makes bibliographic tools such as google scholar, web of science, scopus, etc., critically important for understanding the development. The usefulness of solar energy and possible scenarios for its development in the regions of Russia are discussed.

Cherenkov emission of extensive air showers (EAS) from cosmic gamma rays and cosmic-ray protons has been modelled. Spectral density of such emission in the 240–700 nm band has been determined for 3 GeV–10 TeV primaries of both sorts. It has been shown that the ratio of EAS Cherenkov emission fluxes in the optical and ultraviolet (UV) bands substantially depends on the sort of the primary, so the ratio can be employed to select gamma-ray events from the background produced by cosmic rays. Detection of EAS Cherenkov emission with specialized silicon photomultipliers sensitive in the UV band would allow one to substantially extend the duty cycle of a Cherenkov gamma-ray telescope, as it would be possible to observe the showers during moonlit nights. The UV-sensitive silicon photomultipliers developed at the Ioffe Institute would allow to detect gamma-ray-induced EAS at the Cherenkov gamma-ray observatory ALEGRO over a threshold of about 40 GeV at 5 km above sea level and about 80 GeV at 2 km above sea level.

Results are presented for a study on the development of methods to remove gum, sulfur, and other impurities from diesel fuels at the site of use. The removal of dissolved impurities in diesel fuel is possible by a physicochemical method, having first enlarged these impurities using coagulants. The introduction of carbamide dissolved in water into the fuel permits a reduction in the content of gum and sulfur and an increase in the anti-wear properties of diesel fuel. The use of monoethanolamine in a mixture with isopropyl alcohol in the following step of fuel treatment increases the efficiency of the impurity removal process and further reduces the fuel sulfur and gum impurity indices.

The sensitivity at wavelengths in the range 400–1150 nm, dark current, and dynamic characteristics of an silicon avalanche photodiode with an active region 1.5 mm in diameter that we developed have been examined. It has been shown that the avalanche photodiode has the following set of characteristics: sensitivity 80–85 A/W at wavelengths of 900–1010 nm, dark current 1.5 nA, and leading and trailing edges shorter than 2.5 ns at a reverse bias voltage of 350 V.

An avalanche silicon photodiode has been developed for the near IR, visible, UV and VUV light ranges. The external quantum efficiency has been studied in the 114-170 and 210-1100 nm ranges. It has been demonstrated that the avalanche photodiode reaches the quantum yield of 29 to 9300 electrons/photon at the 160 nm wavelength and bias voltage of 190-303 V, respectively. Keywords: avalanche photodiode, vacuum ultraviolet, visible light range, near IR, silicon

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic "kink" in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the majority shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator--metal concentration phase transition. Keywords: bulk crystals of germanium and silicon, hydrogen-like acceptors and donors, holes and electrons, band and hopping motion of charge carriers.

Experiments on random-bred albino mice showed that of β2-adrenoreceptor agonist hexaprenaline sulfate significantly reduced mortality of mice from experimental sepsis (intraperitoneal administration of E. coli) in 4 and 24 h after modeling by reducing blood levels of proinflammatory cytokines TNFα, IL-1β, and IL-6. The antagonist of β2AR ICI-118,551 eliminated this effect.

In experiments on outbred albino rats, it was established that subacute intoxication with ethylene chlorohydrin (0.2 LD50 daily for 4 days) causes a decrease in Th1 and Th2 lymphocytes function to the same extent, diminishes parameters of humoral and cellular immune responses and the content of immunoregulatory cytokines IFN- , IL-2, IL-4 in blood, increases concentrations of pro-inflammatory cytokine IL-6 and anti-inflammatory cytokine IL-10.

A brief overview of the history of atmospheric Cherenkov gamma-ray telescopes is given. Topical problems of modern astrophysics and fundamental physics to be solved with these instruments are listed. The ALEGRO project of a low-threshold gamma-ray observatory is characterized in detail. The aim of this project is to examine cosmic gamma-ray sources (especially the rapidly variable gamma-ray sources, gamma-ray transients) with high statistics of detected photons in the energy range of 5–50 GeV.

Injection-induced terahertz electroluminescence from silicon p +–n structures is observed at helium temperatures. Structures fabricated by the diffusion of boron into a phosphorus-doped n-Si substrate are studied. Relatively narrow luminescence lines are observed in the luminescence spectra against a broad smooth background. The spectral position of a number of emission lines corresponds to optical transitions between excited donor states and the ground state of phosphorus donors. The intracenter optical transitions of electrons at phosphorus donors are excited as a result of recombination processes occurring in the n-type region of the structure under the injection of nonequilibrium holes. A number of other lines in the terahertz emission spectra are associated with intracenter transitions at acceptor centers, which are also excited as a result of injection. The structureless background in the electroluminescence spectra may be due to terahertz emission upon the intraband energy relaxation of “hot” carriers having an effective temperature exceeding the lattice temperature. These “hot” carriers appear in the structure under injection conditions.

For the first time, a quantitative model of the Curie–Weiss behavior of a low-temperature paramagnetic susceptibility of electrically neutral donors in n-type diamagnetic covalent semiconductors is proposed. The exchange interaction between nearest two neutral donors was calculated with the use of the Heitler–London model. In this model, we take into account the change in the thermal ionization energy of donors due to the shift of the bottom of the conduction band to the bandgap with doping and compensation. The energy of the exchange spin–spin interaction between electrons localized on donors is calculated as a function of the donor concentration and the degree of their compensation by acceptors. The broadening of the donor band due to the Coulomb interaction of the nearest impurity ions was taken into account. We considered crystals of n-type germanium doped with arsenic up to the concentration close to the insulator–metal phase transition (Mott transition) and compensated with gallium. The compensation ratio K is the ratio of the concentration of compensating acceptors KN to the concentration of doping donors N. The model predicts a change in the sign of the Curie–Weiss temperature from minus to plus (a transition from the antiferromagnetic to ferromagnetic local ordering of electron spins on donors) for K ≈ 0.15–0.3, reaching its maximum positive values of ≈1.3 K for K ≈ 0.5 with the following decrease (a transition to paramagnetism) for K > 0.85. The calculated behavior of the paramagnetic susceptibility of donors is consistent with the experimental data for compensated n-Ge:As,Ga samples close to the Mott transition.

Many advanced mathematical models of biochemical, biophysical and other processes in systems biology can be described by parametrized systems of nonlinear differential equations. Due to complexity of the models, a problem of their simplification has become of great importance. In particular, rather challengeable methods of estimation of parameters in these models may require such simplifications. The paper offers a practical way of constructing approximations of nonlinearly parametrized functions by linearly parametrized ones. As the idea of such approximations goes back to Principal Component Analysis, we call the corresponding transformation Principal Component Transform. We show that this transform possesses the best individual fit property, in the sense that the corresponding approximations preserve most information (in some sense) about the original function. It is also demonstrated how one can estimate the error between the given function and its approximations. In addition, we apply the theory of tensor products of compact operators in Hilbert spaces to justify our method for the case of the products of parametrized functions. Finally, we provide several examples, which are of relevance for systems biology.

An upper limit of absorption of the laser radiation in the plasma produced in a gas jet Xe target with the average density of (3–6) × 1018 cm–3 and the effective diameter of 0.7 mm is found. It is equal to ≈50% and remains constant under any variation in this range of densities. This result contradicts both theoretical assessments that have predicted virtually complete absorption and results of earlier experiments with the laser spark in an unlimited stationary Xe gas with the same density, where the upper limit of absorption was close to 100%. An analysis shows that nonlinearity of absorption and plasma nonequilibrium lead to the reduction of the absorption coefficient that, along with the limited size of plasma, can explain the experimental results.

The photoluminescence properties of (113) defects formed in a silicon structure after the implantation by oxygen ions with an energy of 350 keV and doses of 1.7 × 1013–1.7 × 1015 cm–2 and the subsequent annealing at a temperature of 700°C for 0.5–2.0 h in a chlorine-containing atmosphere have been investigated. Regardless of the implantation dose and annealing time, the photoluminescence spectra are dominated by the line at a wavelength of 1.37 μm, which is attributed to a (113) defect. The dependences of the line intensity on the implantation dose and annealing time are characterized by curves with maxima. As the measurement temperature increases in the range from 64 to 120 K, the line intensity decreases monotonically.

Model of heat and mass transfer in catalytic cathode layers of air–hydrogen fuel cells is developed on the basis of experimental data on the layers’ structure. The effect of carbon nanotubes is analyzed: their introducing into the catalytic layer increased the layer’s porosity. The derived analytical expressions allow estimating the carbon-nanotubes-content-dependence of the catalytic layer structure parameters, in particular, the gas channel characteristic dimensions and oxygen and water molecule diffusion coefficients. The simulation results showed that the adding of carbon nanotubes into the catalytic layer allows increasing the fuel cell power significantly, due to removal of limitations caused by water condensation process. The calculated results agree well with the previously obtained experimental data.

A quasi-classical method for calculating the narrowing of the Hubbard gap between the A 0 and A + acceptor bands in a hole semiconductor or the D 0 and D – donor bands in an electron semiconductor is suggested. This narrowing gives rise to the phenomenon of a semiconductor transition from the insulator to metal state with an increase in doping level. The major (doping) impurity can be in one of three charge states (–1, 0, or +1), while the compensating impurity can be in states (+1) or (–1). The impurity distribution over the crystal is assumed to be random and the width of Hubbard bands (levels), to be much smaller than the gap between them. It is shown that narrowing of the Hubbard gap is due to the formation of electrically neutral acceptor (donor) states of the quasicontinuous band of allowed energies for holes (electrons) from excited states. This quasicontinuous band merges with the top of the valence band (v band) for acceptors or with the bottom of the conduction band (c band) for donors. In other words, the top of the v band for a p-type semiconductor or the bottom of the c band for an n-type semiconductor is shifted into the band gap. The value of this shift is determined by the maximum radius of the Bohr orbit of the excited state of an electrically neutral major impurity atom, which is no larger than half the average distance between nearest impurity atoms. As a result of the increasing dopant concentration, the both Hubbard energy levels become shallower and the gap between them narrows. Analytical formulas are derived to describe the thermally activated hopping transition of holes (electrons) between Hubbard bands. The calculated gap narrowing with increasing doping level, which manifests itself in a reduction in the activation energy e2 is consistent with available experimental data for lightly compensated p-Si crystals doped with boron and n-Ge crystals doped with antimony.

We forecast 1,000,000 COVID-19 cases outside of China by March 31st, 2020 based on a heuristic and WHO situation reports. We do not model the COVID-19 pandemic; we model only the number of cases. The proposed heuristic is based on a simple observation that the plot of the given data is well approximated by an exponential curve. The exponential curve is used for forecasting the growth of new cases. It has been tested for the last situation report of the last day. Its accuracy has been 1.29% for the last day added and predicted by the 57 previous WHO situation reports (the date 18 March 2020). Prediction, forecast, pandemic, COVID-19, coronavirus, exponential growth curve parameter, heuristic, epidemiology, extrapolation, abductive reasoning, WHO situation report.

The method of superconducting quantum interference device (SQUID) magnetometry is used to measure and study low-temperature (T ≤ 100K) susceptibility in a series of samples of heavily doped Ge:As samples on the insulator side of the insulator–metal phase transition. Subtracting the known values of the magnetic susceptibility of the lattice from the measurement results, the values of the impurity magnetic susceptibility of the system are obtained. Using the method of electron spin resonance, the paramagnetic component of the impurity susceptibility is determined. Subtraction of the paramagnetic component from the total impurity susceptibility is used to obtain, for the first time, the values of the impurity diamagnetic susceptibility (~5 × 10–8 cm3/g). The obtained result is consistent with estimates obtained for the localization radius of an electron at an As donor. Lowering the temperature to T ≤ 4 K leads to an increase in the diamagnetic susceptibility, which is consistent with the observed increase in the paramagnetic susceptibility. The observed effect is accounted for by the transition of impurity electrons from the singlet state to the triplet one.

A number of proposed experiments aimed at dark matter studies are based on detection of luminescence in liquid argon at 128 nm. Existing solid-state photomultipliers do not have the capability to detect emission at 128 nm in the photon counting mode. Spectral properties of a new silicon photomultiplier prototype for vacuum ultraviolet registration are presented. The prototype demonstrates the photon detection efficiency about 1% in 112–182 nm range.

Electrical and spectrometric characteristics of 4H-SiC detectors with Cr Schottky barriers in the spectral ranges of 114–175 and 210–400 nm are studied. It is demonstrated that the quality of commercially available 4H-SiC layers is sufficient to construct UV radiation detectors with their external quantum efficiency exceeding 20% in the studied spectral ranges.