Elastic properties of superionic cubic silver sulfide ß-Ag2S.

Measurement of heat capacity of superionic silver sulfide (argentite ß-Ag2S) revealed that nanocrystalline argentite has a higher heat capacity than coarse-crystalline argentite. It is shown that the heat capacity of nanocrystalline substances includes an additional positive contribution caused by the limitation of the phonon spectrum on the part of low and high frequencies due to a small particle size. The estimation of this contribution on the basis of experimental differences in the heat capacities of nano- and coarse-crystalline argentite ß-Ag2S in the region of its existence, 470-850 K, made it possible to determine for the first time the velocities of propagation of longitudinal and transverse elastic vibrations cl and ct and elastic stiffness constants c11, c12 and c44. It is established that with a rise in temperature the elastic characteristics of argentite decrease. The anisotropy of elastic properties of cubic argentite was analyzed, and the crystal lattice directions corresponding to the largest and the least values of elastic moduli were determined. An increase of the temperature from 470 to 850 K leads to a small decrease of the elastic anisotropy of cubic ß-Ag2S argentite.

Low-temperature decomposition and segregation on a surface in carbide-containing solid solutions of the zirconium-niobium-carbon system and in related ternary systems.

The crystal structure and microstructure of pseudobinary (ZrC0.96)1-x(NbC0.97)x carbide solid solutions has been studied. It was found that monocrystalline grains of zirconium carbide are spontaneously isolated on the surface of diluted solid solutions of the pseudobinary system ZrCy-NbCy' containing less than 2.0 mol% of zirconium carbide. It is shown that the appearance of zirconium carbide is a consequence of the solid-phase decomposition of these solid solutions and anisotropy of elastic properties of monocrystalline ZrC carbide grains. The model of subregular solutions was used in the temperature interval from 300 to 3900 K to calculate and plot an equilibrium phase diagram of the ternary Zr-Nb-C system. It is shown that at temperatures above 1210 K in the Zr-Nb-C ternary system, nonstoichiometric carbides ZrCy and NbCy' have unlimited mutual solubility and form a continuous series of (ZrCy)1-x(NbCy')x solid solutions with 0.6 ≤ y ≤ 0.98, 0.7 ≤ y' ≤ 1.0, and 0 ≤ x ≤ 1.0. At temperatures below 1200 K, under equilibrium conditions, a discontinuity of the miscibility of the solid solutions ZrCy-NbCy' is observed and there appears a region of solid phase decomposition. The anisotropy of elastic properties of monocrystalline grains of ZrC was considered. It is predicted that solid-phase decomposition and surface segregation can be observed in such related carbide systems as HfCy-NbCy', HfCy-TaCy', ZrCy-TaCy', VCy-TaCy' and VCy-NbCy'.

Disorder-order and order-order phase transformations in Ta5C4 phases predicted using the evolutionary algorithm and symmetry analysis.

A search for stable ordered phases in the nonstoichiometric cubic tantalum carbide TaC0.8 has been performed by use of the evolutionary algorithm and symmetry analysis. Four stable Ta5C4 superstructures with tetragonal, monoclinic, orthorhombic, and triclinic symmetry have been predicted for the first time. The DOS values of these Ta5C4 superstructures and stoichiometric TaC1.00 carbide have been calculated. All the tantalum carbide superstructures and stoichiometric TaC1.00 carbide have metal conductivity. The disorder-order phase transition channels TaCy → Ta5C4 associated with the formation of the considered model superstructures include superstructural vectors of non-Lifshitz stars {k1}, {k2}, and {k4}. The distribution functions of carbon atoms over the sites of the tetragonal, monoclinic, orthorhombic, and triclinic Ta5C4 superstructures have been calculated. For the first time, the physically permissible sequence of disorder-order and order-order phase transitions is established for the detected phases of the Ta5C4 family. Based on the formation enthalpy and the cohesion energy magnitudes, the triclinic Ta5C4 superstructure is the most favorable among all Ta5C4 phases predicted. The composition of the predicted Ta5C4 superstructures corresponds to TaC0.80 which possesses the highest melting temperature and hardness.

Correction: High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite ß-Ag2S.

Correction for 'High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite ß-Ag2S' by S. I. Sadovnikov et al., Phys. Chem. Chem. Phys., 2016, 18, 4617-4626.

High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite ß-Ag2S.

An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide - monoclinic acanthite α-Ag2S and cubic argentite ß-Ag2S - has been carried out for the first time using the high-temperature X-ray diffraction method. The temperature dependencies of the unit cell parameters of acanthite and argentite in the interval of 300-623 K have been determined, and the thermal expansion coefficients of acanthite and argentite have been found. It is shown that the observed difference in the thermal expansion coefficients for nano- and coarse-crystalline acanthite is due to the small particle size of nanocrystalline silver sulfide leading to the growth of anharmonicity of atomic vibrations. It is established by differential thermal analysis that a reversible polymorphic acanthite-argentite phase transformation takes place at ∼449-450 K and the phase transformation enthalpy is equal to ∼3.7-3.9 kJ mol(-1).

An in situ high-temperature scanning electron microscopy study of acanthite-argentite phase transformation in nanocrystalline silver sulfide powder.

For the first time, the α-Ag2S (acanthite)-ß-Ag2S (argentite) phase transformation in nanocrystalline and coarse-crystalline powders of silver sulfide has been observed in situ by the scanning electron microscopy method in real-time. The argentite crystals are formed on the surface of acanthite particles as a result of electron-beam heating. According to the differential thermal analysis data, the transformation occurs at a temperature of ∼449-450 K, and the enthalpy of transformation is equal to ∼3.7-3.9 kJ mol(-1). The presence of α-Ag2S (acanthite)-ß-Ag2S (argentite) phase transformation is confirmed in situ by high-temperature X-ray diffraction data.

Nonstoichiometry of nanocrystalline monoclinic silver sulfide.

Powders of silver sulfide have been synthesized by chemical bath deposition from aqueous solutions of silver nitrate and sodium sulfide in the presence of sodium citrate or EDTA-H2Na2. Colloid solutions have been prepared by a chemical condensation method from the same aqueous solutions. Synthesized silver sulfide nanopowders have a monoclinic (space group P21/c) acanthite-type structure but the occupancy of the metal sublattice sites by Ag atoms is smaller than 1. Unlike coarse-crystalline silver sulfide Ag2S, silver sulfide nanopowders with particles sizes of less than ∼50 nm are nonstoichiometric, contain vacant sites in the metal sublattice and have a composition of ∼Ag1.93S.

Species-dependent hepatic metabolism of immunosuppressive agent tacrolimus (FK-506).

The current study aims to investigate species-related differences in the in-vitro hepatic metabolism of tacroliums using liver microsomes obtained from rat, hamster, guinea pig, rabbit, pig, dog, baboon and humans. Tacrolimus metabolism was characterized using high-performance liquid chromatography- ultraviolet light (HPLC-UV) and two soft ionization mass spectrometric techniques; matrix-assisted lasers desorption/ionization (MALDI) and time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The extent of tacrolimus metabolism, when normalized to the cytochrome P-450 content, was in the order: rat < hamster < rabbit < pig < guinea pig < dog < human < baboon. Tacrolimus metabolism exhibited significant qualitative and quantitative differences between the animal species tested. Desmethyl- (MI-MIII), didesmethyl- (MIV-MVI), monohydroxy- (MVII), dihydroxy- (MVIII), epoxide- (MIX), dihydrodiol- (MX), monodesmethyl and monohydroxy- (MXI-MXIII), and didesmethyl and monohydroxy- (MXIV-MXVI) tacroliums metabolites were identified in the species tested. MI-MX were identified in all the species tested; MXI-MXVI were identified in all species except rat, rabbit and guinea pig; and MXIV-MXVI were identified only in baboon. The current investigation was unable to detect any phase II metabolites due to the limitations of the test system used. The analytical methods were not able to differentiate optical and positional isomers of metabolites due to the nature of the analytical tools used, therefore groups of metabolites were identified based on their molecular weights and available information. From the current in-vitro metabolism studies, the pattern of tacroliums metabolism in baboons closely resembled that in humans and thus it is ideal for studying tacroliums metabolism-related work of clinical relevance.

Quasielastic neutron scattering study of hydrogen motion in NbC(0.71)H(0.28).

In order to study the mechanism and parameters of H jump motion in the nonstoichiometric Nb carbides, we have performed quasielastic neutron scattering (QENS) measurements for NbC(0.71)H(0.28) over the temperature range 11- 475 K. Our results indicate that about 30% of H atoms in this system participate in a fast diffusive motion. The temperature dependence of the corresponding H jump rate in the range 298-475 K follows the Arrhenius law with an activation energy of 328 ± 9 meV. The Q dependence of the QENS data suggests that the observed jump motion corresponds to long-range diffusion of H atoms along chains of the off-centre sites in carbon vacancies.

A 30 GW subnanosecond solid-state pulsed power system based on generator with semiconductor opening switch and gyromagnetic nonlinear transmission lines.

This article describes a subnanosecond solid-state pulsed power system in which an input pulse from a generator with a semiconductor opening switch (generator) is amplified in power and is shortened in time by a two-stage magnetic compressor based on gyromagnetic nonlinear transmission lines. In this approach, the line of each stage operates as a magnetic compression line (MCL) which is realized when the duration of the input pulse is close to the period of oscillations generated by the line. The compression system contains two series connected lines MCL1 and MCL2 with a wave impedance of 40 Ω. The input pulse has a duration of 7 ns and an amplitude of 500 kV. After two compression stages, the pulse amplitude increases to 1.1 MV and the peak power increases from 6 to 30 GW, while the pulse duration transits into subnanosecond range (0.65 ns). In the burst mode, the system operates at a pulse repetition frequency up to 1 kHz.

Semiconductor opening switch generator with a primary thyristor switch triggered in impact-ionization wave mode.

The results of the investigation involving a thyristor switch triggered in the impact ionization wave mode are presented. This switch is intended for operation as a primary switch in a nanosecond pulse generator with a semiconductor opening switch (SOS). The thyristor switch is based on commercial low-frequency tablet thyristors stacked in a joint assembly of up to 6 pieces connected in series. At a charging voltage of 2-12 kV and switching energy of up to 16 J, the switch operates with a discharge current of up to 8 kA, a current rise rate in the range from 14 to 54 kA/µs, and a switching efficiency of ∼0.9. It is shown that an increase in a voltage rise rate on thyristors at the triggering stage reduces energy loss in the thyristor switch during the current flow. The SOS pumping circuit contains one magnetic element-a pulse transformer, which simplifies the generator and increases its efficiency. The SOS generator has an output voltage of up to 300 kV and a peak power of up to 250 MW with a pulse duration of ∼50 ns. The thyristor switch in the generator operates at a voltage of 12 kV and provides current flow with the amplitude of up to 7.5 kA with a duration of ∼500 ns and a current rise rate of ∼54 kA/µs. The pulse repetition frequency of the generator is 1 kHz in the burst mode of operation.

Solid-state repetitive generator with a gyromagnetic nonlinear transmission line operating as a peak power amplifier.

In this work, experiments were made in which gyromagnetic nonlinear transmission line (NLTL) operates as a peak power amplifier of the input pulse. At such an operating regime, the duration of the input pulse is close to the period of generated oscillations, and the main part of the input pulse energy is transmitted only to the first peak of the oscillations. Power amplification is achieved due to the voltage amplitude of the first peak across the NLTL output exceeding the voltage amplitude of the input pulse. In the experiments, the input pulse with an amplitude of 500 kV and a half-height pulse duration of 7 ns is applied to the NLTL with a natural oscillation frequency of ∼300 MHz. At the output of the NLTL in 40 Ω coaxial transmission line, the pulse amplitude is increased to 740 kV and the pulse duration is reduced to ∼2 ns, which correspond to power amplification of the input pulse from ∼6 to ∼13 GW. As a source of input pulses, a solid-state semiconductor opening switch generator was used, which allowed carrying out experiments at pulse repetition frequency up to 1 kHz in the burst mode of operation.

Semiconductor sharpeners providing a subnanosecond voltage rise time of GW-range pulses.

The article describes semiconductor sharpeners providing a subnanosecond voltage rise time of GW-range pulses. The sharpeners are made as stacks of series-connected dynistor structures built into an oil-filled coaxial line with 48 Ω wave impedance at the place of an inner conductor. Two sequential sections of pulse sharpening are used. An input voltage pulse has the amplitude of 540 kV with the rise time of ∼1.2 ns at 0.2-0.9 level from the amplitude and voltage rise rate of ∼0.3 MV/ns. After pulse propagation through the sharpening sections, its rise time is reduced down to 360 ps, and the voltage rise rate is increased up to ∼0.95 MV/ns. Peak power of the sharpened pulse is within the range of 4.5-5.5 GW. The sharpeners are tested at a pulse repetition frequency of up to 1 kHz. Sharpener operation is studied by numerical simulation methods. Experimental waveforms of output pulses and the corresponding calculated voltage-time dependences are in statistical agreement.

A 6 GW nanosecond solid-state generator based on semiconductor opening switch.

In this paper, a nanosecond all solid-state generator providing peak power of up to 6 GW, output voltage of 500-900 kV, pulse length (full width at half maximum) of ∼7 ns across external loads of 40-100 Ω, and pulse repetition frequency up to 1 kHz in burst operation mode is described. The output pulse is generated by a semiconductor opening switch (SOS). A new SOS pumping circuit based on a double forming line (DFL) is proposed and its implementation described. As compared with a lumped capacitors-based pumping circuit, the DFL allows minimization of the inductance and stray capacitance of the reverse pumping circuit, and thus, an increase in the SOS cutoff current amplitude and generator output peak power as a whole. The pumping circuit provides a reverse current increasing through the SOS up to 14 kA within ∼12 ns. The SOS cuts off the current in ∼2 ns; the current cutoff rate reaches 7 kA/ns. The SOS braking power (the product of peak voltage and cutoff current) for an external load above 100 Ω is 13 GW.

Effect of liquid chromatography separation of complex matrices on liquid chromatography-tandem mass spectrometry signal suppression.

The effect of liquid chromatography separation on liquid chromatography-tandem mass spectrometry (LC-MS-MS) signal response for the characterization of low-molecular-mass compounds in a complex matrix was investigated. Matrix induced signal suppression appears throughout the entire LC-MS-MS analysis of wheat forage extract, with greatest suppression occurring at early retention times. Experimental results show that co-elution of matrix components and analytes from the LC column may be most strongly attributed to column overloading rather than similar analyte and matrix retention behavior. As a result, two-dimensional (LC-LC) separation can be a highly effective approach to address signal suppression effects for the quantitative LC-MS-MS analysis of complex matrix samples.

Direct quantitative analysis of peptides using matrix assisted laser desorption ionization.

The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000-12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2-3 decades of analyte concentration. The relative error of the standard curve slope was 1.3-1.8% with correlation coefficients of 0.996-0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000-5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples.

[Alpha-fetoprotein in the liver of embryonic and newborn rats]. / Al'fa-fetoprotein v pecheni émbrionov i novorozhdennykh krys

The localization of alpha-fetoprotein in the liver of embryos and newborn Wistar rats was determined by the method of fluorescent antibodies. This protein was found in the cytoplasm of some hepatocytes, endothelium of blood vessels and erythroid blood cells of embryos and new born rats. It was never found in the blood-forming and Kupffer cells of the liver, as well as in the epithelium of bile ducts. The hepatocytes containing this protein were located in the liver lobes near the central veins. Their number and the intensity of fluorescence decreased with the age of animals.

[A method for plastic repair in oblique inguinal hernia]. / Sposob plastiki pri kosoi pakhovoi gryzhe.

Experimental and clinical investigations enabled the authors to develop a method of hernioplasty using a pi-shaped flap from aponeurosis of the external oblique abdominal muscle on the feeding pedicle. In this case the anatomo-functional interrelations of the tissues in the ilio-inguinal area get minimum injuries. It does not make a substantial obstacle for the following regeneration and restitution and so the method is rather efficient and can be used in the everyday practice.

[Analytical characteristics of commercial IRMA-AFP kit for determination of human alpha-fetoprotein]. / Analiticheskie kharakateristiki kommercheskogo nabora IRMA-AFP dlia opredeleniia al'fa-fetoproteina cheloveka.

Commercial polyclonal IRMA-AFP kit is manufactured by Radiopreparat in Tashkent since 1986. The kit has a range of 0 to 320 ng/ml. This report includes the data on AFP measurements in the sera of cancer patients, particularly at the lower part of the calibration curve. Within run precision studies yielded a CV of 7.7% at the 4.3-54.0 ng/ml interval. Between run precision was 8.6% at the 3.3-56.0 ng/ml interval. The recovery of AFP in the presence of matrix effects of 9 sera was 98% for mixtures at the 9.1-60.8 ng/ml range. The assay sensitivity was 0.6 ng/ml. In donor blood samples the AFP levels did not exceed 4 ng/ml.

[Effectiveness of nutritional support of elderly and senile of orthopedic traumatological profile]. / Effektivnost' nutritsionnoi podderzhki bol'nykh ortopedotravmatologicheskogo profilia pozhilogo i starcheskogo vozrasta.

An analysis of results of the operative treatment of 36 patients who received and did not receive nutritional support in the pre- and postoperative periods has shown that the nutritional support improves the course of the postoperative period.