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Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance, an unfavourable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. HgTe quantum wells close to the topological phase transition are a proven example of such gapped graphene-like materials. In this work we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by a magnetic field and gate voltage.

Abstract: The Fe–Cr–C–Ti–Al cored wire layers were cladded by laser, arc and hybrid methods. Mechanical tests have shown that the cladded layers strongly differ in wear resistance. The metallographic, X-ray diffraction and durometric studies were carried out to identify the reasons of such difference. The analysis of the study results showed that the main reason is the difference between the cooling rates of the cladded metal in the region of 1100–800 K. This difference provides the formation of the metastable austenitic structure, which significantly impacts the wear resistance of the cladded coatings.

The possibility of amplifying a THz hybrid surface plasmon in a structure with an Hg0.82Cd0.18Te epitaxial film grown on a GaAs substrate and covered with a metal layer is investigated. It is shown that for a film thickness of 100 nm and a temperature of 80 K, the hybrid surface plasmon mode gain can be greater than external losses at a pump radiation intensity with a wavelength of 2.3 ?m, exceeding 850 kW cm-2. Additional doping of the Hg0.82Cd0.18Te layer with a donor impurity having a concentration of 4 × 1017cm-3will lead to a 1.5-fold decrease in the threshold pump intensity.

Abstract: The original research results for thin disordered HTSC films based on YBCO are presented in this article. Several experiments have been carried out to confirm a theoretical prediction that the s-phase of superconducting pairing in disordered d-type superconductors can occur with a gradual decrease in the mean free path. The YBa2Cu3O7 – xfilms are used as samples which possess a d-type of superconducting state that was experimentally confirmed. A gradual decrease in the mean free path was achieved by both thermal annealing and ion irradiation. The experiments included measurements of temperature dependence of the London penetration depth λ and resistive studies.

Abstract: Phase transitions during crystallization and subsequent thermal and deformation effects under the influence of various mechanical loads in welded joints of the plates of medium carbon steel by a consumable electrode in shielding gases with a flux-cored wire based on Fe–C–Cr matrix are studied. The test results for weldability, abrasive wear resistance, and stress state formation and the results of metallographic, electron microscopic, and X-ray diffraction studies are analyzed. It is shown that the structure of welded seam consists of metastable austenite, δ-ferrite, and high-strength carbon–chromium martensite. Welded joints have a high capability of intense hardening under local deformation owing to the TRIP effect (transformation-induced plasticity).

An unusual decrease in the slope of the upper critical field near Tc0at a gradual increase in the ion implantation dose has been experimentally observed in narrow bridges formed on the base of thin HTSC YBa2Cu3O7 –xfilms, while an increase in the defect concentration usually leads to an increase in the local slope of the phase transition line Hc2(T). In addition, it has been found that the temperature dependence of the upper critical field has a positive curvature near Tc0. A possible theoretical interpretation of the results is proposed. It is based on the modified Ginzburg–Landau theory with a nonuniform length of superconducting correlations.

The threshold energy of Auger recombination in HgTe/CdxHg1-xTe heterostructures with quantum wells (QWs) is analysed numerically for different compositions of the solid solution in barriers. It is demonstrated that the threshold energy depends nonmonotonically on the cadmium content in barriers and reaches a maximum at x [?]0.6-0.7. A comparison of the results of numerical calculations with experimental data on the temperature quenching of stimulated emission in a Cd0.1Hg0.9Te/Cd0.65Hg0.35Te structure gives grounds to expect a more than twofold increase in the quenching temperature of stimulated emission in structures with pure HgTe QWs and barriers with a high ([?]0.6) cadmium content.

A class of multilayered functional materials has recently emerged in which the component atomic layers are held together by weak van der Waals forces that preserve the structural integrity and physical properties of each layer. An exemplar of such a structure is a transistor device in which relativistic Dirac fermions can resonantly tunnel through a boron nitride barrier, a few atomic layers thick, sandwiched between two graphene electrodes. An applied magnetic field quantizes graphene’s gapless conduction and valence band states into discrete Landau levels, allowing us to resolve individual inter-Landau-level transitions and thereby demonstrate that the energy, momentum and chiral properties of the electrons are conserved in the tunnelling process. We also demonstrate that the change in the semiclassical cyclotron trajectories, following an inter-layer tunnelling event, is analogous to the case of intra-layer Klein tunnelling.

A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) was held on February 27, 2008 in the conference hall of the Lebedev Physical Institute, RAS. The following reports were presented at the session: (1) Lozovik Yu E, Merkulova S P, Sokolik A A (RAS Institute for Spectroscopy, Troitsk, Moscow Region) "Collective electron phenomena in graphene"; (2) Morozov S V (RAS Institute for Problems in Micro-electronics Technology, Chernogolovka, Moscow Region), Novoselov K S, Geim A K (University of Manchester, Manchester, UK) "Electron transport in graphene." An abridged version of these reports is given below. * Collective electron phenomena in graphene, Yu E Lozovik, S P Merkulova, A A Sokolik Physics-Uspekhi, 2008, Volume 51, Number 7, Pages 727-744 * Electron transport in graphene, S V Morozov, K S Novoselov, A K Geim Physics-Uspekhi, 2008, Volume 51, Number 7, Pages 744-748

The dynamics of oxygen atoms in a Ta-O solid solution is studied. The vibrational energies of interstitial O impurities are determined, and the metal-impurity interaction constants are calculated. The experimental data obtained suggest that an oxygen atom is displaced from the center of the octahedral interstice of the crystal lattice. The oxygen vibrational energy in tantalum is shown to satisfy the relation between the localmode energy and the transition metal-interstitial impurity distance that is common for all M-O systems.

Abstract: The dynamics of hydrogen atoms in Ta-H and Ta-O-H interstitial solid solutions is analyzed. The vibrational energies of hydrogen interstitial impurity atoms are determined, and the metal-impurity interaction constants are calculated taking into account the atomic thermal vibrations in the host lattice. It is found that, in the Ta-O-H solid solution, as in the Ta-H solid solution, hydrogen atoms are located in relatively undistorted tetrahedra and the distance between the hydrogen and oxygen atoms is no shorter than that in the third coordination shell of the octahedral interstices.

No Heading Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity.

Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity.

Functional magnetic resonance tomography provides a non-invasive method for mapping the cerebral cortex. The aim of the present work was to assess the potential and suitability of this method in a series of brain disorders. Studies were performed on 32 volunteers (mean age 37.8 ± 20.9 years) and 16 patients with tumors of the cerebral cortex (mean age 36.2 ± 24.2 years). Initial functional images were processed by statistical methods. Computed activation maps were superimposed on anatomical images. In 89% of cases, functional magnetic resonance tomography allowed the motor cortex and Broca's area to be localized; in almost 69%, the method impinged on the therapeutic tactics used in patients with cerebral cortex lesions. Thus, functional magnetic resonance tomography can be used in clinical conditions to obtain information not yielded by other diagnostic methods and which can be used to plan the neurosurgical treatment of patients with supratentorial brain tumors with maximum preservation of cerebral cortex function. Assessments of the state of the motor and speech areas by this tomographic method has potential applications in neurosurgery and neurophysiology.

Abstract: The oxidation kinetics of Bi1.3Pb0.8Sr2Ca0.8Y0.2Cu2O8+δ solid solutions at different temperatures and $$p_{O_2 } = 0.21$$ atm is investigated by thermogravimetry. The results obtained are compared with the previously studied oxidation kinetics of Bi1.3Pb0.8Sr2Ca0.8Y0.2Cu2O8+δ solid solutions. It is found that the substitution of yttrium for calcium leads to an appreciable retardation of the initial oxidation stage associated with the oxygen diffusion. The phonon spectra of the solid solutions are examined using inelastic neutron scattering on a DIN-2PI direct-geometry spectrometer. The high-frequency (>50 meV) phonon densities of states for yttrium-containing and yttrium-free solid solutions are analyzed. The possible model is proposed for a correlation between the differences observed in the high-frequency phonon densities of states attributed to the vibrations of oxygen atoms and the differences in the oxidation kinetics of the solid solutions under consideration.

Incubation of rat liver microsomes with preparations of grape flavonoids, dihydroquercetin, and silibinin increased their resistance to lipid peroxidation induced by NADPH-Fe2++. This was manifested in less pronounced accumulation of lipid peroxidation products and changes in activity of microsomal enzymes induced by lipid peroxidation. In vitroantioxidant activity of grape flavonoids markedly surpassed that of dihydroquercetin and silibinin. Addition of flavonoids into fodder led to moderate, statistically significant, and similar increase in the resistance of rat liver microsomes to ex vivoinduced lipid peroxidation.

Lycopine in concentrations of 0.5-50 μM suppressed LPO in microsomes induced by NADPH-Fe2+and by ascorbic acid-Fe2+. Lycopine in a concentration of 20 μM completely prevented the decrease in the rate of benz[a]pyrene hydroxylation and activation of p-nitrophenyl-UDP-glucuronosyl transferase caused by LPO induction in microsomes.

Oral treatment with lycopene (per os) in doses of 10 or 50 mg/kg for 2 weeks led to accumulation of lycopene in the liver, liver microsomes, and blood plasma, increased total plasma antioxidant activity, inhibited LPO in the liver, and decreased solubilization of lysosomal enzymes. Lycopene had no effect on ex vivo resistance of liver microsomes to LPO and activities of antioxidant enzymes in the liver.

The interaction of titanium tetrachloride vapor with products formed in thermal decomposition of basic magnesium carbonate in the temperature range 200-800°C was studied.

Abstract: Phonon spectra of Bi2Sr2−y Ca1−x La x + y Cu2O8 + δ solid solutions (x=y=0; x=0, y=0.25; x=0.25, y=0; x=0, y=0.5) were measured by inelastic neutron scattering on a DIN-2PI direct-geometry spectrometer. A full-profile analysis of the x-ray diffraction data yielded an estimate of the distribution of alkaline-earth (AE) and La atoms over the Ca and Sr positions in the Bi2Sr2CaCu2O8 structure. An assignment of the main features in the phonon spectrum to dominant vibrations of certain atoms was made. In particular, the correlation of the x-ray structural data with spectroscopic data implies that the feature due to cation vibrations in the Sr crystallographic positions of the basic 2212 structure (near 11 meV) is single-mode in behavior. Substitution of La for an AE atom modifies the high-frequency part (>40 meV) of the phonon spectrum (which corresponds to vibrations of oxygen in the SrO and CuO2 layers of the Bi2Sr2CaCu2O8 structure) and affects the cut-off frequencies in the spectra of solid solutions of various compositions. A comparison of the results obtained in this study with earlier spectra of the 2212 compound, in which Ca was substituted for by Nd, indicates that the shape and intensity of the high-frequency vibration spectra of the samples studied are related to the average cation charge in the SrO layer of the Bi2Sr2CaCu2O8 structure.

Recent concepts of the mechanism of electrochemical ionization of metals and the part the electrolyte takes in it are analyzed. A comparison of electrochemical and topographic characteristics of iron in chloride and bromide media with different pH and concentrations of halide ions confirmed their intimate correlation. The microtopography of dissolution depends on the pH of the medium, concentration of halide ions, and anodic potential. General mechanisms of the formation of a surface structure are similar in both halide media. It is concluded that desorption of two-charge metal ions with their incorporation into the electrolyte structure is the rate-determining stage of anodic ionization. The overvoltage of this process may be considered as the overvoltage of discharge–ionization.

Application of various carbon materials as substrates for immobilizing hydrogenase and creating a hydrogen enzyme electrode is studied. A stable, highly-active electrocatalyst for mediatorless oxidation–evolution of hydrogen is obtained. The electrocatalyst uses hydrogenase from Th. roseopersicinaimmobilized on an inactive carbon material (based on carbon cloth TVSh-300M) and retains more than 50% of its initial activity after a half year in storage. An equilibrium hydrogen potential is established on enzyme electrodes made of a graphitized cloth and graphite rods with hydrogenase immobilized on them.

A comparative study of the surface morphology, photoluminescence, and photoelectric spectra of heterostructures with InAs/GaAs quantum dots (QDs) grown on the surface, uncovered by etching away the cladding layer, and built in the GaAs matrix is reported. The red-shift of the ground transition energy in the surface QDs compared to the built-in ones has been shown to be related not only to relaxation of the elastic strain, but also to the differences in size, shape, and chemical composition of the nanoclusters. The method of photoelectric spectroscopy in a semiconductor/electrolyte system has been applied to monitor the process of etching of the cladding layer in situ. Using this method, controlled uncovering of the buried QDs was shown to be possible. In turn, this makes it possible to study the actual morphology of the buried quantum-size layers by atomic force microscopy.

Experiments measuring the absolute power of the MATR-2 reactor by a modified frequency method are described. A theoretical substantiation of the method employed is given. Experimental results are presented. 3 figures, 1 table, 4 references.

Results of a complex study of 11 grades of periclase clinker are presented. Factors determining the possibility of their effective use as a raw material for fabrication of high-quality refractory parts are considered.

Anodic behavior of iron in chloride solutions is studied in the pH range from 0 to 6 and at the concentration of chloride ions from 0.2 to 3 mol/l. Electrochemical measurements were supplemented with the raster electron microscopy studies, of electrode surfaces. The observed independence of the limiting dissolution current of pH is explained by a hypothesis that water does not participate in the anodic process at sufficiently large anodic overpotentials. Depending on the concentration of chloride ions, the continuity of the logia-pH dependence is first interrupted and the, restored; the reaction order in hydroxide ions changes from a positive value to zero. This is probably caused by the “dynamic passivation” of iron with the adsorbed oxygen atoms and their competitive replacement by chloride ions.

A new RNA of about 900 nt was found in the virions of cocksfoot mottle virus (CfMV) and in infected plants by RNA hybridization and RT-PCR. Structural features suggested that this RNA is a defective interfering RNA (diRNA). The CfMV diRNA was shown to consist of a 35-nt 5′-terminal genomic region, which formed a hairpin, and a 3′-terminal genomic region, which included the coat protein (CP) gene lacking the first 120 nt.In vitrotranslation of the diRNA started at the third Met codon to produce truncated CP. The CfMV diRNA was assumed totrans-activate synthesis of the CP subgenomic RNA (sgRNA).

Issues of the general architecture design for integrated applications of mathematical modeling and scientific visualization are considered. In line with the object-oriented methodologies of Bailin and Booch, a novel model for a visualization scene is described. The scene is a composition of interrelated, typed scientific data and algorithms. A systematic approach to developing applications based on the model is presented. Theoretical analysis is illustrated by various examples related to geometric modeling, numerical solution of ordinary differential equations, visualization, and rendering.

Natural autoantibodies of IgG class to proteins SlOOb, glial fibrillar acidic protein (GFAP), and nerve growth factor (NGF) are presented in serum of healthy adults and those levels/ affinities are relatively constant and may vary among individuals within narrow limits. In patients with depressive disorder, epilepsy, multiple sclerosis, and Parkinson's disease dispersion of such autoantibodies serum levels were often found beyond the normal ranges. Most of the patient groups include cases with significantly elevated as well as abnormally decreased immunoreactivity parameters. This leads us to assumption that changes in some basic mechanisms of individual immune state represent the common features of different forms of pathology of the nervous system.

The phenomenon of trans–complementation of cell–to–cell movement between plant positive–strand RNA viruses is discussed with an emphasis on tobamoviruses. Attention is focused on complementation between tobamoviruses (coding for a single movement protein, MP) and two groups of viruses that contain the triple block of MP genes and require four (potato virus X) or three (barley stripe mosaic virus) proteins for cell–to–cell movement. The highlights of complementation data obtained by different experimental approaches are given, including (i) double infections with movement–deficient (dependent) and helper viruses; (ii) infections with recombinant viral genomes bearing a heterologous MP gene; (iii) complementation of a movement–deficient virus in transgenic plants expressing the MP of a helper virus; and (iv) co–bombardment of plant tissues with the cDNAs of a movement–dependent virus genome and the MP gene of a helper virus.

Abstract: Experiments measuring the lifetime of prompt neutrons in the system BARS-6 reactor—laser unit by the statistical frequency method are described. A theoretical substantiation of the method employed is given on the basis of a point model of the kinetics. Experimental results are presented. 4 figures, 1 table, 13 references.

We establish the existence of discontinuous solutions for a positive definite, seminormal, quasiregular variational problem when the order of growth of the integrand of the functional is degenerate on lines parallel to the Oy axis.

Existence and uniqueness theorems for the solution of a mixed problem for a nonlinear nonstationary integrodifferential transfer equation of general form, as well as stability theorems for the solutions of this problem with respect to the perturbation of a parameter occurring in the equation and in the initial and boundary conditions, are established in the article.

Supported Ni/?-Al2O3 catalysts were studied in the gas phase hydrodechlorination of substituted chlorobenzenes. The catalytic properties of the catalysts were shown to be determined by the metal nickel. A correlation between the rate of the gas phase hydrodechlorination of substituted chlorobenzene and donor-acceptor properties of substituents was established. The electron-donor substituents increase and the electron-acceptor ones decrease their reactivity. The correlation analysis of data treated via the Hammett equation shows that hydrodechlorination on Ni/?-Al2O3 catalysts is a reaction of electrophilic type.

The protonation of 1-R-2,2,5,5-tetramethyl-3-imidazoline-3-oxides (R=OH, O) in superacid media was investigated with1H and13C NMR. The hydroxylamino dication forming on protonation can undergo imidazoline ring opening to form an isomeric mixture of diprotonated N-(2-hydroxyimino-1,1-dimethylethyl),a,a-dimethylnitrones.