Dagestan Scientific Center of the Russian Academy of Sciences

We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I–V characteristics, with threshold voltage ∼3.2 V and low reverse leakage current ∼10−7 A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 nm is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500 K and shown to originate from recombination within the ZnO.

In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear behavior in the low current range with a slope 1.9 and a sublinear behavior with a slope 0.85 in the high current range are observed.

It is shown that the nonlocal nonlinear Schr\"odinger equation recently proposed by Ablowitz and Musslimani [Phys. Rev. Lett. 110, 064105 (2013)] is gauge equivalent to the unconventional system of coupled Landau-Lifshitz equations. The first integrals of motion and one-soliton solution of an obtained model are given. The physical and geometrical aspects of model and their effect on expected metamagnetic structures are studied.

For the first time the magnetocaloric properties of La0.9Ag0.1MnO3, La0.8Ag0.2MnO3, La0.85Ag0.15MnO3, La0.8Ag0.15MnO3 and La0.8Ag0.1MnO3 manganites have been investigated by direct and indirect measurement techniques. All samples showed almost the same relative cooling power (RCP). Temperatures of maxima of the magnetocaloric effect (MCE) are between a few degrees below freezing and the room temperature region. The compounds showed RCP values of about 100 J kg−1 at a field change of 2.6 T, which is about half the RCP of gadolinium. Because of considerable MCE and the Curie temperatures ranging from 269 to 303 K, these materials could be used as magnetic refrigerants for magnetic refrigeration in the sub-room and room temperature range.

The Yamnaya archaeological complex appeared around 3300 bc across the steppes north of the Black and Caspian Seas, and by 3000 bc it reached its maximal extent, ranging from Hungary in the west to Kazakhstan in the east. To localize Yamnaya origins among the preceding Eneolithic people, we assembled ancient DNA from 435 individuals, demonstrating three genetic clines. A Caucasus–lower Volga (CLV) cline suffused with Caucasus hunter-gatherer1 ancestry extended between a Caucasus Neolithic southern end and a northern end at Berezhnovka along the lower Volga river. Bidirectional gene flow created intermediate populations, such as the north Caucasus Maikop people, and those at Remontnoye on the steppe. The Volga cline was formed as CLV people mixed with upriver populations of Eastern hunter-gatherer2 ancestry, creating hypervariable groups, including one at Khvalynsk. The Dnipro cline was formed when CLV people moved west, mixing with people with Ukraine Neolithic hunter-gatherer ancestry3 along the Dnipro and Don rivers to establish Serednii Stih groups, from whom Yamnaya ancestors formed around 4000 bc and grew rapidly after 3750–3350 bc. The CLV people contributed around four-fifths of the ancestry of the Yamnaya and, entering Anatolia, probably from the east, at least one-tenth of the ancestry of Bronze Age central Anatolians, who spoke Hittite4,5. We therefore propose that the final unity of the speakers of ‘proto-Indo-Anatolian’, the language ancestral to both Anatolian and Indo-European people, occurred in CLV people some time between 4400 bc and 4000 bc. Ancient DNA reveals how the explosive expansion of Yamnaya steppe pastoralists began with a small community north of the Black Sea speaking ancestral Indo-European, and detects genetic links with Anatolian speakers, stemming from a common Indo-Anatolian homeland in the North Caucasus–lower Volga region.

Effective thermal conductivity (ETC) of five dry rocks (sandstone, limestone, amphibolite, granulite, and pyroxene−granulite) have been measured over a temperature range from (273 to 423) K and at pressures up to 350 MPa with a steady-state parallel-plate apparatus. It is an absolute, steady-state measurement device with an operational temperature range of (273 to 1273) K and hydrostatic pressures up to 1500 MPa. The estimated uncertainty of the method is 2 %. The porosity of the samples (sandstone, limestone, amphibolite, granulite, and pyroxene−granulite) was 5 %, 5 %, 1.0 %, 1.0 %, and 1.2 %, respectively. A sharp increase of ETC was found for rocks at low pressures between (0.1 and 100) MPa along various isotherms between (273 and 423) K. At high pressures (P > 100 MPa), a weak linear dependence of the ETC with pressure was observed. The measured values of ETC of rocks were used to test and confirm of applicability of the various theoretical and semiempirical models. The effect of structure (size, shape, and distribution of the pores), porosity, and mineralogical composition on temperature and pressure dependences of the ETC of various rocks types is discussed.

BACKGROUND: Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are used to reduce the risk of developing Coronavirus Disease 2019 (COVID-19). Despite the significant benefits in terms of reduced risk of hospitalization and death, different adverse events may present after vaccination: among them, headache is one of the most common, but nowadays there is no summary presentation of its incidence and no description of its main features. METHODS: , 2021, looking for record in English and with an abstract and using three main search terms (with specific variations): COVID-19/SARS-CoV-2; Vaccination; headache/adverse events. We selected manuscript including information on subjects developing headache after injection, and such information had to be derived from a structured form (i.e. no free reporting). Pooled estimates and 95% confidence intervals were calculated. Analyses were carried out by vaccine vs. placebo, by first vs. second dose, and by mRNA-based vs. "traditional" vaccines; finally, we addressed the impact of age and gender on post-vaccine headache onset. RESULTS: Out of 9338 records, 84 papers were included in the review, accounting for 1.57 million participants, 94% of whom received BNT162b2 or ChAdOx1. Headache was generally the third most common AE: it was detected in 22% (95% CI 18-27%) of subjects after the first dose of vaccine and in 29% (95% CI 23-35%) after the second, with an extreme heterogeneity. Those receiving placebo reported headache in 10-12% of cases. No differences were detected across different vaccines or by mRNA-based vs. "traditional" ones. None of the studies reported information on headache features. A lower prevalence of headache after the first injection of BNT162b2 among older participants was shown. CONCLUSIONS: Our results show that vaccines are associated to a two-fold risk of developing headache within 7 days from injection, and the lack of difference between vaccine types enable to hypothesize that headache is secondary to systemic immunological reaction than to a vaccine-type specific reaction. Some descriptions report onset within the first 24 h and that in around one-third of the cases, headache has migraine-like features with pulsating quality, phono and photophobia; in 40-60% of the cases aggravation with activity is observed. The majority of patients used some medication to treat headache, the one perceived as the most effective being acetylsalicylic acid.

The respiratory chain in the majority of organisms with aerobic type metabolism features the concomitant existence of the phosphorylating cytochrome pathway and the cyanide- and antimycin A-insensitive oxidative route comprising a so-called alternative oxidase (AOX) as a terminal oxidase. In this review, the history of AOX discovery is described. Considerable evidence is presented that AOX occurs widely in organisms at various levels of organization and is not confined to the plant kingdom. This enzyme has not been found only in Archaea, mammals, some yeasts and protists. Bioinformatics research revealed the sequences characteristic of AOX in representatives of various taxonomic groups. Based on multiple alignments of these sequences, a phylogenetic tree was constructed to infer their possible evolution. The ways of AOX activation, as well as regulatory interactions between AOX and the main respiratory chain are described. Data are summarized concerning the properties of AOX and the AOX-encoding genes whose expression is either constitutive or induced by various factors. Information is presented on the structure of AOX, its active center, and the ubiquinone-binding site. The principal functions of AOX are analyzed, including the cases of cell survival, optimization of respiratory metabolism, protection against excess of reactive oxygen species, and adaptation to variable nutrition sources and to biotic and abiotic stress factors. It is emphasized that different AOX functions complement each other in many instances and are not mutually exclusive. Examples are given to demonstrate that AOX is an important tool to overcome the adverse aftereffects of restricted activity of the main respiratory chain in cells and whole animals. This is the first comprehensive review on alternative oxidases of various organisms ranging from yeasts and protists to vascular plants.

Abstract Vanadium doped ZnO (VZO) thin films were grown by RF magnetron sputtering, starting from a ZnO:V ceramic target. The crystal structure, chemical composition, electric and piezoelectric properties of the films were investigated either on the as-grown thin films or after a post-deposition rapid thermal annealing (RTA) treatment performed at 600 °C for different lengths of time (1 and 5 min) in an oxygen atmosphere. Substitutional doping of Zn 2+ with V 3+ and V 5+ ions strongly deteriorated the hexagonal wurtzite ZnO structure of the as-grown thin films due to lattice distortion. The resulting slight amorphization led to a poor piezoelectric response and higher resistivity. After the RTA treatment, strong c -axis oriented VZO thin films were obtained, together with a partial conversion of the starting V 3+ ions into V 5+ . The improvement of the crystal structure and the stronger polarity of both V 3+ – O and V 5+ – O chemical bonds, together with the corresponding easier rotation under the application of an external electric field, positively affected the piezoelectric response and increased conductivity. This was confirmed by closed-loop butterfly piezoelectric curves, by a maximum d 33 piezoelectric coefficient of 85 pm·V −1 , and also by ferroelectric switching domains with a well-defined polarization hysteresis curve, featuring a residual polarization of 12.5 μC∙cm −2 .

An expression is derived for the surface energy σ as a function of the size and shape of a nanocrystal. It is shown that the wider the deviation of the shape parameter f from unity, the more pronounced the decrease in the surface energy σ with a decrease in the number N of atoms in the nanocrystal. The dependences of the average coordination number, the surface energy, and the melting temperature on the number N exhibit an oscillatory behavior with maxima at points corresponding to numbers of atoms forming a defect-free cube. The surface energy decreases with an increase in the temperature T. It is found that the smaller the nanocrystal size or the greater the deviation of the nanocrystal shape from the thermodynamically most stable shape (a cube), the larger the quantity-(dσ/dT). It is established that the nanocrystal undergoes melting when the surface energy decreases to a value at which it becomes independent of the nanocrystal size and shape. The conditions providing fragmentation and dendritization of the crystal are discussed. It is demonstrated that, at N>1000, the dependence σ(N) coincides, to a high accuracy, with the dependence of the surface tension of the nanocrystal on N. The inference is made that bimorphism is characteristic of nanocrystals. This implies that nanocrystals can have platelike and rodlike shapes with equal probability.

Thermophysical, magnetic, and dielectric properties of multiferroic BiFeO3 and Bi0.95La0.05FeO3 ceramic compounds were comprehensively studied. Anomalies of the permittivity near an antiferromagnetic phase transition related to the structural variations were detected. The temperature T N was determined from the temperature dependences of the thermal expansion coefficient, heat capacity, and differential susceptibility. It is shown that the transition point is shifted to higher temperatures as the rare-earth La ion substitutes for Bi. It is established that an insignificant substitution of lanthanum for bismuth enhances the magnetic properties of bismuth ferrite and the magnetodielectric effect.

The interaction between ethoxyl groups of acrylate polymers and oxygen vacancies on the surface of ZnO nanoparticles is shown to produce resistive hysteresis according to a new interfacial phenomenon called interfacial coupling mechanism.

The constant volume and constant composition heat capacity CVX data for aqueous n-hexane mixtures are reported for seven compositions, (0.6146, 0.7965, 0.9349, 0.9775, 0.9858, 0.9892, and 0.9940) mol fraction of n-hexane, along seven near-critical isochores between 259.34 and 312.50 kg·m-3 in the temperature range from 463 to 522 K at pressures up to 6 MPa. All of these isochores display two features in the heat capacity as a function of temperature: the first peak appears when one of the liquid phases disappears, and the second peak appears when the vapor or liquid phase disappears. These features are interpreted in terms of the liquid−liquid−vapor, liquid−liquid, and liquid−vapor phase diagram, and their consistency is shown with earlier PTx measurements on the three-phase (L-L-G) boundary. Measurements of the isochoric heat capacity (CVVTx) of water + n-hexane mixtures were made in a spherical high-temperature, high-pressure nearly constant volume adiabatic calorimeter. The calorimeter was also used as a constant-volume piezometer to measure the PVTx properties. The uncertainties of the measurements are as follows: isochoric heat capacity, 1.0−1.5%; density, 0.1%; temperature, 10 mK; and pressure, 0.05%. The method of quasi-static thermograms was used to precisely measure the liquid−liquid−gas (L-L-G), liquid−liquid (L-L), and liquid−gas (L-G) phase transition temperatures at each fixed density, with an uncertainty of 0.02 K. New saturated densities and pressures are presented on the (L-L-G) and (L-G) phase boundaries. The values of temperature, pressure, and density of the upper critical end point (UCEP) in the water + n-hexane mixture were determined from the measurements. Results for the UCEP (TUCEP = 495.82 K; PUCEP = 5.25 MPa; ρUCEP = 259.9 kg·m-3) are in good agreement with the values reported by other authors. For the first time the temperature-dependent behavior of CVX near the UCEP is reported.

This paper investigates migratory patterns in the North Caucasian republic of Dagestan. It relies on prior literature, both in Russian and English, to establish the basic form of migration in the republic and recent census data to describe these patterns. The authors then analyze responses from a December 2005 survey of Dagestani residents about their migration intentions to investigate the motivations underlying these patterns. The paper investigates the extent to which economic incentives vis-à-vis other traditional assumptions associated with migration theory maintain in the case of Dagestan, and explores the impact of migration on interethnic relations in the republic. Journal of Economic Literature, Classification Numbers: I30, J61, O15, O18. 2 figures, 7 tables, 47 references.

It is shown that the Debye temperature as a function of temperature must satisfy certain equations in order for the thermodynamic functions calculated in terms of the Debye temperature to satisfy both the third law of thermodynamics and the law of equipartition of energy. A general expression for the Θ(T) function satisfying these thermodynamic laws is found.

We describe aspects of genetic diversity in several ethnic populations of the Caucasus Mountains of Daghestan using mitochondrial DNA sequences and a sample of 100 polymorphic Alu insertion loci. The mitochondrial DNA (mtDNA) sequences are like those of Europe. Principal coordinates and nearest neighbor statistics show that there is little detectable structure in the distances among populations computed from mtDNA. The Alu frequencies of the Caucasus populations suggest that they have undergone more genetic drift than most other groups since the dispersal of modern humans. Genetic differences among these populations are not large; instead, they are of the same order as distances among populations of Europe. We compare two methods of inference about the demography of ancient colonizing populations from Africa, one based on conventional FST statistics and one based on mean Alu insertion frequencies. The two approaches agree reasonably well if we assume that there was demographic growth in Africa before the diaspora of ancestors of contemporary regional human groups outside Africa.

The constant volume, constant composition heat capacity data for aqueous sodium sulfate show several interesting features: one peak or step when solid salt first precipitates and, on further heating, a λ-shaped peak when the vapor- or liquid-phase disappears. These features are interpreted in terms of the solid−liquid−vapor phase diagram, and their consistency is shown with earlier PVTx, phase boundary, and three-phase data from the literature. New data are presented on the density of liquid solutions saturated with respect to the vapor. New liquid compositions or densities supplement the three-phase data available in the literature, and new fluid densities are reported near the critical end point. For aqueous Na2SO4, we find Tcep = (648.2 ± 0.2) K, and for aqueous Na2CO3, Tcep = (649.0 ± 0.2) K. The present heat capacity data, as well as recent data for aqueous sodium carbonate, have sufficient resolution to distinguish, for the first time, the temperature of the critical end points in aqueous sodium sulfate and aqueous sodium carbonate from the critical temperature of pure water, Tc = (647.1 ± 0.1) K.

A model is proposed which treats network traffic as a stochastic process with an infinite mean delay. Such a model can be used to explain the appearance of long-range dependence and a fractal-like feature of network data flow. The heavy-tailed delay distributions, the hyperbolic decay of the packet delay auto-covariance function and fractional differential equations are shown to be formally related. The new interpretation of fractional calculus opens up a new area for using this well-developed mathematical tool to understand the local and global characteristics of the packet traffic behaviour.

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The expressions for the Debye temperature Θ as well as for the first (γ = −[∂ln(Θ)/∂ln(V)] T ) and second (q = [∂ln(γ)/∂ln(V)] T ) Grüneisen parameters are derived based on the Mie-Lennard-Jones pair atomic interaction potential. The conditions imposed on the Θ(V/V 0), γ(V/V 0), and q(V/V 0) dependences for V/V 0 → 0 and for V/V 0 → ∞ are analyzed. Here, V/V 0 is the ratio of the molar volumes for pressure P at temperature T and for P = 0 at T = 0 K. Calculations are performed for crystals of parahydrogen and orthodeuterium at T = 0 K for V/V 0 ranging from 1.30 to 0.01. Good agreement is reached between the calculated dependences and experimental data. The behavior of dependences Θ(V/V 0), γ(V/V 0), and q(V/V 0) upon a variation of the isotopic composition of the crystal is analyzed.