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The operational problem of determining the shortest routes for a group of vessels that have received the task of achieving hypothetical target with certain coordinates located in a confined space is being solved. When controlling the process of vessels entering a desired area, time is an important indicator. The practical implementation of the modified Floyd-Warshall algorithm is demonstrated by calculating a network model with a complex topology, using an iterative procedure by means of a program in MATLAB codes. The computer model implemented on its basis is simple and compact. Unlike existing models, the suggested model allows one to eliminate the restrictions associated with the presence of negative weights and cycles in the network, to automate the calculation of the shortest paths at the nodes by means of the computer technology implemented in MATLAB.

Applicability of Spark Plasma Sintering has been studied for production of high-density (98.6–99.5%) composite ceramics Y2.5Nd0.5Al5O12 (YAG:Nd) – x MgO (x = 5, 10, 20 vol %). Powder YAG:Nd-MgO compositions have been obtained by precipitation of the MgO phase from Mg(NO3)2 water solution of magnesium nitrate onto the surface of garnet nanoparticles YAG:Nd. It has been demonstrated that the intensity of sintering fine-grained YAG:Nd-MgO composites is governed by volume diffusion at low temperatures and by grain boundary diffusion at high temperatures. Faster sintering at low temperatures is caused by formation of MgAl2O4 spinel particles and internal stress fields that are manifested as broadening and shifting of garnet peaks in the sintered composites.

Spark Plasma Sintering has been used to obtain first ever fine-grained SrWO4 and NaNd(WO4)2 ceramics with the scheelite structure and high density (95.8–99%) that are promising as materials for nuclear waste immobilization. It has been demonstrated that the densification intensity in tungstates at the initial sintering stage is determined by the agglomeration degree of input powders. The activation energy of fine-grained ceramics with the scheelite structure has been established to correlate at high temperatures with the activation energy of grain-boundary diffusion. Rapid sintering of fine-grained NaNd(WO4)2 ceramic results in internal tensile stress fields that lead to lowered hardness and fracture toughness of the ceramic.

This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and Spark Plasma Sintering (SPS) in a vacuum. The dependence of ultrafine-grained (UFG) alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has been shown that the optimal SPS temperature for mechanically activated nanopowders goes down by 350–400 °C in comparison with the optimal sintering temperature in hydrogen for coarse-grained 95W-Ni-Fe powder composition. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of nickel and iron in the surface layer of tungsten α-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of UFG tungsten alloys with high mechanical properties: macro-elastic limit – up to 2250 MPa, yield stress – up to 2500 MPa.

Powders of garnet-type complex oxide Y2.5Nd0.5Al5O12 (YAG:Nd) – x vol% W, Mo (x = 0, 10, 20) were obtained using wet chemistry techniques and precipitation of the metal phase from salt solutions. After synthesis, nanoparticles of YAG:Nd garnet cluster into submicron agglomerates. Spark Plasma Sintering (SPS) was used to obtain fine-grain ceramic-metal composites YAG:Nd – (W, Mo) with a relative density of ∼99%. The effect that metal concentration (tungsten, molybdenum) has on density, microstructure properties, and mechanical properties (microhardness, fracture toughness) of ceramics was studied. SPS activation energies were determined and it was demonstrated that the intensity of shrinkage of the fine-grained YAG:Nd – (W,Mo) ceramic-metal composites close to the activation energy of creep in tungsten (molybdenum). It has been demonstrated that the intensity of creep during SPS of fine-grained composites at medium temperatures is determined by the intensity of volume oxygen diffusion in the lattice of garnet nanoparticles, whereas at high temperatures it is determined by grain-boundary diffusion.

We investigated the growth of III-N/graphene heterostructures as a single process in a MOVPE reactor. Raman spectra revealed that graphene can be successfully deposited on sapphire substrate by propane pyrolysis if temperature exceeds 1060 °C and hydrogen is used as a carrier gas. GaN epitaxial layers and heterostructures on such graphene using both high-temperature AlN buffer layer and low-temperature GaN nucleation layer was demonstrated. Analysis of surface morphology and X-Ray diffraction curves indicate that GaN quality depends on graphene thickness. Use of copper electroplated Ni-based contact layer combined with thermal shock allows exfoliation of large-area III-N LED structures from sapphire.

Fine-grained ceramics based on solid solutions of ZrO2-x-Ln2O3 (where Ln = Sm, Yb), which are used to simulate inert matrix fuel (IMF), were obtained by colloidal chemical synthesis of powders and their Spark Plasma Sintering (SPS). It has been established that the SPS activation energy (Qs) for fine-grain ceramics based on ZrO2 corresponds to the activation energy of oxygen diffusion on grain boundaries of zirconium oxide (zirconia). We have demonstrated that introducing oxides of samarium (Sm2O3) and ytterbium (Yb2O3) into zirconia decreases SPS activation energy and stabilizes the phase composition of zirconia. Ceramics with densities up to 100% were obtained by the following modes of SPS: sintering temperature 1000–1250 °C, sintering time 6–10 min. Hydrolysis testing in the static mode (Т = 20 °C, P = 1 atm) in distilled water revealed no leaching of lanthanide ions at detection thresholds of 5 ppm for Sm ions and 0.1 ppm for Yb ions.

Using wet chemistry techniques, ultrafine powders of complex oxides Y2.5Nd0.5Al5O12 (YAG) have been obtained with the garnet structure and coated with layers of nickel by means of precipitation from salt solutions. Spark Plasma Sintering (SPS) was used to obtain fine-grain ceramic composites YAG – Ni with 92–99% density. Sintering activation energies were determined and it was demonstrated that the intensity of high-rate sintering of the investigated ceramic composites is determined by the intensity of the nickel creep at lower heating temperatures, the intensity of oxygen diffusion in the garnet crystal lattice at average SPS temperatures, and the intensity of grain boundary diffusion at high SPS temperatures.

Spark Plasma Sintering (SPS) has been used to produce samples of fine-grained composites Y2.5Nd0.5Al5O12 + x wt.% α-SiC (x = 1020) with ∼98–99% density. The microstructure of the composites has been studied, as well as the impact of α-SiC particles on the mechanical properties and kinetics of composite sintering. The introduction of the α-SiC part has been demonstrated to form a more fine-grained structure and under the given SPS conditions change the sintering mechanism in ceramics. The study has also demonstrated that introduction of α-SiC particles into garnet results in formation of internal stress fields, which, in turn, leads to a decrease in the activation energy of sintering of fine-grained composites at high temperatures.

AFM study of surface morphology in green LED structures and multifractal analysis allowed us to reveal a relationship between step-meandering morphology quantitatively characterized by a multifractal parameter, the degree of disorder, and features of In incorporation in InGaN/GaN MQW structures. These features manifest themselves in a shape of the distribution of peak external quantum efficiency values with wavelengths (DPEW) in the current range of 0.1–1000 mA. High values of degree of disorder result in spinodal alloy decomposition and/or local In enriched regions in InGaN alloy and in a twofold decrease in EQE values in green LEDs.

Mineral-like matrix Na x (Ca/Sr) 1-2x Nd x WO 4 ( x = 0, 0.1 and 0.2) for radwaste is proposed. Powder samples of complex tungstates have been synthesized by coprecipitation from aqueous solutions of Na, Ca, Sr, Nd salts. Crystallographic characteristics of compounds have been calculated and a monotonous change observed in them along with some x value changes. Monophasic ceramics with high relative density (97–100%) from these powders have been obtained through Spark Plasma Sintering (SPS). SPS of tungstates has been shown to occur in multiple stages, with the sintering kinetics at the final stage of sealing controlled by diffusion both in the crystal lattice and along grain boundaries. Activation energies have been determined for sintering of tungstates at different x values. The reduced activation energy of sintering at the third heating stage (at high temperatures) could be ascribed to the grain growth.

The application of the laser-aided diagnostic using the nanosecond laser for direct measurement of hydrogen concentration on the walls of the Globus-M2 tokamak is under discussion. The D release after the laser irradiation with the fluence in the range of 0.1 - 4 J/cm2 was measured in laboratory experiments at the Large MEPhI mass-monochromator facility for W-D, Ti-D films, and for the W tile exposed in the Globus-M tokamak. The desorption flux was high enough to be detected during similar measurements inside the Globus-M2 tokamak. TMAP 7 modeling of D release from W-D films was done for the relatively low laser fluence (

Powders based on the complex garnet-type oxide Y2.5Nd0.5Al5O12 - x wt. % Ni (x = 0, 10, 20) were prepared using wet chemistry methods. Ceramics based on these compounds were obtained by Spark Plasma Sintering (SPS) with a relative densities: 99%. 4% (TD = 4.77 g/cm3 (0%)), 97.6% (TD = 4.88 g/cm3 (10%)), 94.4% (TD = 5.06 g/cm3 (20%)). The influence of nickel concentration on the mechanical (fracture toughness, microhardness) and thermophysical (thermal conductivity) properties of the composites was studied.

The paper dwells on the research conducted into high-rate consolidation of pure tungsten carbide (WC) nanopowders using the Spark Plasma Sintering technology. Studies included the effect that the original size of WC nanoparticles and their preparation modes have on density, structure parameters, and mechanical properties of tungsten carbide. Samples of high-density nanostructured tungsten carbide characterized by high hardness (up to 31–34 GPa) and improved fracture toughness (4.3–5.2 MPa m 1/2 ) were obtained. It has been found that materials that show abnormal grain growth during sintering have lower values of sintering activation energy as compared to materials the structure of which is more stable during high-rate heating. A qualitative model is proposed that explains this effect through the dependence of the grain boundary diffusion coefficient on the grain boundary migration rate.

Temperature-dependent luminescent properties of dual-wavelength blue-cyan light emitting diodes (LEDs) based on InGaN quantum wells were investigated by means of photo- (PL) and electroluminescence (EL) spectroscopy techniques. The results showed that the thickness of the interwell GaN layer had a great impact on the spectra (especially on the EL ones) at room temperature. At low temperatures, however, the EL spectra are nearly identical for all the samples regardless the differences at room temperature. The differences in the temperature behavior of the above-bandgap PL spectra can be explained in terms of different areas of carrier collection region for the samples with different interwell barrier thickness, as evidenced by the below-bandgap PL spectra measurements as well as by the Beer's law calculations. Additionally, an anomalous increase of the above-bandgap PL intensity is observed at the temperature range of ~120–150 K, which is absent in the case of below-bandgap excitation.

This work was conducted to discover ways of processing high-paraffin oil residues using thermochemical processes to obtain binders. The principal purpose of such treatment of high-paraffinic residues is in the thermocatalytic process which consists of dehydroesterification via oxidation of paraffins which increase bitumen’s low-temperature stability (Fraass breaking point). Thus the n-alkanes, via our thermocatalytic process, can form several carbonyl compounds and oxidised compounds (such as alcohols, carboxylic acids, etc.). The thermocatalytic process of petroleum’s raw materials in our research carried out in two stages, including the catalytic process, as well as the thermal oxidation by air-blowing process. In this study, we used a biturox reactor. We evaluated the content of paraffin with GOST 33139 and low-field nuclear magnetic resonance (1H LF-NMR) relaxometry in high-paraffinic vacuum residues, and after our thermocatalytic process in the obtained product. Moreover, in order to ensure the reliability of results obtained through the processing of vacuum residues as well as the obtained product, various physicochemical methods were used. These investigation methods include SARA fractionation, Fourier-transform infrared spectroscopy, electron paramagnetic resonance (EPR), and VNII NP analysis. Furthermore, the colloidal structures were studied using the Gaestel and Asphaltene Index. The tests were carried out to determine the bitumen’s quality under the Russian interstate standard GOST 33133-2014 and the European standard EN 12591.

Complex studies of intentional GaN carbon doping from propane during MOVPE were performed in a wide range of growth conditions. A strong dependence of carbon doping efficiency on growth rate and ammonia flow is revealed, while dependence of carbon doping efficiency on reactor pressure is small. Atomic force microscopy confirms the good quality of the GaN:C layers for doping levels as high as 2*1019 cm−3 grown with growth rate up to 45 μm/h. The dependence of carbon incorporation into GaN is proportional to the propane concentration to the power 3/2 in most growth regimes, but for very high growth rate a linear or sub-linear component of the dependence becomes prominent.

Complex oxide Y 2.5 Nd 0.5 Al 5 O 12 with garnet structure and phosphates NdPO 4 and GdPO 4 with monazite structure were obtained by using precipitation methods. Ceramics Y 2.5 Nd 0.5 Al 5 O 12 and NdPO 4 were processed by Spark Plasma Sintering (SPS). Relative density more 98%, sintering time did not exceed 8 min, sintering temperature 1330–1390 °C. Leaching rates of elements from ceramics were 10 −6 –10 −7 g/(cm 2 d). The process of ceramics sintering has two-stage character: the first step of sintering-compaction process is related to the plastic flow of the material, the second step–to the process of grain boundary diffusion and grain growth.

In this study a new, fast and simple method based on low field NMR-relaxometry for in-situ determination of SARA (saturates, aromatics, resins and asphaltenes) composition of crude oils was proposed. This method was tested on 22 samples of crude oils with a wide range of SARA-composition and API gravity values (4.6–42.0°), including extra-heavy, heavy, medium and light crude oils. Results obtained by low-field nuclear magnetic resonance (LF-NMR) were compared with conventional SARA analysis method (ASTM D 4124). Comparison shows good coincidence between SARA values determined by LF-NMR and conventional method data for heavy fractions of asphaltenes and resins (R2 is equal to 0.98 and 0.91, respectively) and for the sum of light fractions including saturates and aromatics (R2 = 0.96). However, comparison for saturated and aromatic compounds separately gave low correlation coefficients (R2 ≤ 0.61 and 0.27, respectively) and relatively soaring standard deviation for individual correlations for saturates and aromatics (8.18 and 9.20). Consequently, LF- NMR relaxation as an alternative method for studying the composition of crude oil allows the determination of asphaltenes, resins and the sum of light fractions (saturates and aromatics) without their extraction (in-situ), which greatly simplifies and accelerates conventional chromatographic analysis. This method can be successfully applied for different types of crude oils with a wide range of API gravity and viscosity values.

Si3N4 deposition from silane and ammonia in a number of III-N MOVPE reactors of various sizes was studied in a wide range of reactor conditions. It was revealed that Si3N4 deposition rate depends on temperature, pressure, carrier gas type, and ammonia concentration. Deposition rate rises with temperature up to 1050–1100 °C in a manner typical for temperature-activated processes, but under any studied conditions, including the 800–850 °C range, it is strictly linear with SiH4 concentration indicating the absence of high-order parasitic reactions at high temperature and surface passivation at low temperature. For a low-volume reactor the higher the pressure is, the faster the deposition is both for N2 and H2 carrier gases. For large reactors the dependence is non-monotonic. At temperature above 900 °C using H2 as a carrier gas results in a higher Si3N4 deposition rate than when using N2. If nitrogen is used as a carrier gas, deposition rate gradually rises with ammonia concentration. If hydrogen is used, deposition rate rapidly rises with ammonia concentration and then gradually falls. If hydrogen-nitrogen mixture is used as a carrier gas, deposition rate changes in a linear manner with the mole fraction of hydrogen in the carrier gas.

The possibility to fabricate highly dense (95.3–95.8% of theoretical density) composite ceramics CeO2 – x α-SiC (x = 10, 20 vol %) as a promising mineral-like material for the inert fuel matrices (IFM) by Spark Plasma Sintering (SPS) has been explored. The kinetics of SPS of the CeO2 – SiC composites in the heating-up conditions was found to have a multi-stage character. The introduction of the α-SiC particles resulted in a shift of the characteristic sintering temperatures towards higher values, allows forming the highly dense fine-grained structure, and leads to increasing of the thermal conductivity of the cerium dioxide – based ceramics.

The paper describes the digital filter polychromator developed for Thomson scattering (TS) diagnostics. The device having ultra-low noise, high-speed detection system and up to 7 spectral channels is equipped with digitizer and single board computer for system control and data processing. The data acquisition system is capable to detect very short laser pulses of few ns width with low magnitude. This feature opens up new possibilities for the TS diagnostics design in modern fusion devices, which includes: operation with high background illumination, measurement of very low electron temperature and density at the plasma edge and scrape-off layer (SOL), separation of the TS signal and the stray light coming with a delay of several ns. The analysis of the TS signal waveform also gives a possibility to distinguish the TS and Mie scattering from the dust particles that is important for measurements in SOL. Owing to compactness and ultra-low energy consumption both optical and data processing units interfaced with optical Gigabit Ethernet were combined in a stand-alone device. Such all-in-one design with optical fiber input and optical digital output provides enhanced resistance to electromagnetic disturbances and simplify operation. A set of such polychromators can be mounted in a standard 19” rack and can be integrated with outer CODAC (Control, Data Access and Communication) system. Testing of the polychromators at the Globus-M2 tokamak has shown excellent performance of the developed serial devices.

This paper provides an overview of Spark Plasma Sintering (SPS), which is an advanced technology for high-speed sintering of powder materials by applying mechanical pressure to the powder compact and heating it using a pulsed direct current. Some examples of the successful application of the SPS technology in producing materials with high strength characteristics are shown. By optimizing the SPS regimes, the hardness of pure WC ceramics Hv=30÷31 GPa (20% higher than that of conventional materials), hardness of pure Al2O3 ceramics Hv=23.5 GPa (50% higher than that of conventional materials) and limit strength of the heavy alloy W–Ni–Fe σT=2500 MPa (2 times higher than that of conventional materials) are achievable.

The powder of phosphate Ca1/4Sr1/4Zr2(PO4)3 was synthesized by sol–gel processes in the presence of citric acid and ethylene glycol. Ceramic samples were prepared from this powder by Spark Plasma Sintering (SPS), their relative densities were found to be 99.5 ± 0.3% after the isothermal treatment at 860 °С for 3 min. Sintered disc-shaped ceramic samples (d = 10 mm, h = 4 mm) were bombarded at 300 K by 167 MeV Xe26+ ions with fluences ranging from 6 ⋅ 1010 to 1 ⋅ 1013 ions/cm2. It was found that exposure to the highest fluence (1013 ion/cm2) led to a complete amorphization of the irradiated layer. The observed phase transition is ascribed to the formation of amorphous latent tracks via dense electronic excitations. Postradiation heat treatment revealed that the transformation from metamict to crystalline form took place after annealing at T = 200, 300, 400, 500, 600 and 800 °С and t = 3, 13, 11, 5, 17 and 15 h, respectively.

Al-rich AlGaN layers and quantum well (QW) structures with a reasonable structural quality have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) under metal-rich stoichiometric conditions directly on c-sapphire. The bowing parameter of 1.1 eV for the compositional dependence of AlGaN band gap energy has been determined using an electron-probe microanalysis, Raman spectroscopy and optical transmission spectroscopy. A successful application of a sub-monolayer digital-alloying (SMDA) technique in PA-MBE for fabrication of AlGaN-based multiple QW structures, including deep-UV MQW light-emitting diodes, has been demonstrated for the first time. These structures exhibit both photo- and electroluminescence in the spectral range of 300–320 nm at room temperature.

AlGaN with the Al content in the range of 10–30% is one of the key materials for production of the optoelectronic devices operating in the UV spectral range. At the same time there are well-known difficulties in growing such layers by MOVPE, associated with low efficiency of aluminum incorporation in AlGaN, caused by parasitic gas-phase reactions. In this paper, the results of a combined experimental and modeling study of AlGaN growth in a production scale multiwafer (6×2″) AIX2000HT Planetary Reactor are reported. The effects of reactor pressure, total flow rate and metalorganic flow rate variations on aluminum incorporation have been studied experimentally. Detailed simulations of flow dynamics and chemistry have enabled to identify the mechanisms responsible for aluminum losses in the gas phase. Model predictions have been found in good agreement with the experimental data in a wide range of growth conditions and AlGaN compositions. From the results obtained, possible strategies of growing high-Al content AlGaN are proposed.

Basic development steps towards the molecular beam epitaxy growth of AlGaAs/GaAs microcavity structures are presented, which contain self-organized InAs/GaInAs quantum dots as the active medium. The emission wavelength of these structures can be controllably adjusted within 1260–1340 nm by variation of the deposition parameters of the epitaxial layers without the use of any real-time monitoring technique. Based on quantum dot active material with optimized optical emission properties and accurately calibrated layer thicknesses microcavity light emitting diodes were fabricated. 40 μm diameter devices, as characterized on-wafer, showed narrow electroluminescence spectra (FWHM: 13–26 nm) centered at 1310–1325 nm and narrow circular beam widths of FWHM

Fluoride glasses, for the production of IR optical fibers, have a tendency to crystallization. The crystallization of fluoride glasses is one of the main reasons for non-intrinsic optical losses due to scattering in fibers. The crystallization kinetics of 53ZrF4–20BaF2–4LaF3–3AlF3–20NaF (ZBLAN), 53.8HfF4–20.1BaF2–5CeF3–3.1AlF3–17NaF–1.2InF3 (HBCANI), 12.3BaF2–12.3SrF2–12.3CaF2–12.3MgF2–36AlF3–12.3YF3–2.5LaF3 (BSCMAYL), 30InF3–10YF3–25BaF2–5SrF2–10ZnF2–10GaF3–6NaF–4PbF2 (InYBSNZnGaPb) fluoride glasses was investigated at the early stages of glass-to-crystal transformation. The experiment consisted in measuring the contents and sizes of microcrystals in glass interiors as a function of treatment time of the sample at constant temperature. The contents and sizes of crystals were determined by the method of laser ultramicroscopy. Investigations were carried out in the range between glass-forming and softening temperatures. The nucleation rate, W, the linear growth rate of crystals, V, and the temperature dependence of these kinetic parameters were found at the level of conversion of glass-crystal between 10−6% and 10−3%. The nucleation rate was maximum of ∼200 nuclei /( s cm 3 ) near 260°C in ZBLAN, ∼300 nuclei /( s cm 3 ) near 280°C in HBCANI, ∼280 nuclei /( s cm 3 ) near 400°C in BSCMAYL and ∼650 nuclei /( s cm 3 ) near 310°C in InYBSNZnGaPb glass. The results of investigation are useful for optimization of the heat treatment mode of fluoride glasses and to understanding of the processes critical to the optical homogeneity of these glasses.

High-frequency ultrasound has been shown to accelerate enzymatic fibrinolysis. One of the supposed mechanisms of this effect is the enhancement of mass transport by acoustic streaming, i.e., ultrasound-induced macroscopic flow around the clot. In this study, which is aimed at further elucidating the mechanisms of the acceleration of fibrinolysis by ultrasound, we investigated whether ultrasound would accelerate fibrinolysis if the flow around the thrombus is already present, as may occur in vivo. The effect of the ultrasound-induced temperature rise was also studied. In a model of a plasma clot submerged in plasma, containing tissue-type plasminogen activator, mild stirring of the outer plasma producing a shear rate of 40 seconds-1 at the surface of the clot resulted in a two-fold acceleration of lysis. A similar effect was obtained with ultrasound (1 MHz, 2 W/cm2). Furthermore, if ultrasound was applied together with stirring, only 30% acceleration by ultrasound was documented, fully attributable to the concomitant temperature rise. In a model with tissue-type plasminogen activator incorporated throughout a plasma clot, the effect of ultrasound (two-fold shortening of lysis time) was fully attributable to the concomitant temperature rise of a few degrees. We concluded that the acceleration of enzymatic plasma clot lysis by high-frequency ultrasound in the models we used can be largely explained by a combination of the effects of heating and acoustic streaming, equivalent to mild stirring. The thermal effects can hardly be utilized in vivo due to the danger of tissue overheat. The therapeutic advantage of transcutaneous high-frequency ultrasound as an adjunct to thrombolytic therapy may appear limited to the situations where there is no flow in the direct environment of the thrombus. Copyright (C) 2000 Elsevier Science Ltd. Chemicals/CAS: Tissue Plasminogen Activator, EC 3.4.21.68

We report on experimental and theoretical studies on a new type of quantum-dot (QD) structures obtained using ultrathin, i.e. below the critical thickness for 2D‐3D transition, strained narrow gap insertions in wide bandgap matrices. We concentrate on submonolayer (SML) or slightly above 1 ML CdSe insertions in a wide-gap II‐VI matrices and give the first results on ultrathin InGaN insertions in a GaN matrix. A discussion on detailed comparison of our original results with the results of other authors is presented. The formation of dense arrays (up to 10 12 cm 22 ) of nanoscale two-dimensional (2D) islands is revealed in processed high-resolution transmission electron microscopy images. In the case of stacked sheets of SML insertions, the islands in the neighboring sheets are formed predominantly in correlated or anticorrelated way for thinner and thicker spacer layers, respectively. Different polarization of photoluminescence (PL) emission recorded in edge geometry for vertically-uncoupled and coupled QDs confirms the QD nature of excitons. By monitoring of sharp lines due to single QDs using cathodoluminescence the 3D confinement is manifested. We demonstrate significant squeezing of the QD exciton wavefunction in the lateral direction using magneto-optical experiments. We point to complete suppression of lateral motion of excitons bound to islands in case of wide-gap (ZnMgSSe) matrices, as follows from PL excitation studies. A resonant (0-phonon) lasing is observed in ultrathin CdSe insertions and proves the lifting of the k-selection rule for QD excitons. We show that lack of exciton screening in QDs up to high excitation densities enables strong resonant modulation of the refractive index in stacked ultrathin insertions and allows realization of resonant (excitonic) waveguiding and lasing. This enables the realization of a new type of heterostructure laser operating without external optical confinement by layers having lower average refractive indices. Ultrahigh QD excitonic gain in dense arrays of stacked QDs allows a new type of surface-emitting laser. q 2000 Elsevier Science S.A. All rights reserved.

It is known that the critical temperature T c of ultrathin YBCO films is reduced to values far less than 77 K. To improve the superconducting properties of ultrathin YBCO films, we developed a new buffer layer which allowed an increase in the critical temperature of five-unit-cell-thick YBCO films to values above 77 K. Using atomic force microscopy (AFM) to study the growth modes of ultrathin YBCO films deposited on a SrTiO 3 substrate and on a YBaCuNbO buffer layer, we found that ultrathin YBCO films deposited on a SrTiO 3 substrate are formed due to 2D nucleation. The growth of ultrathin YBCO films deposited on YBaCuNbO buffer is governed by the step-flow mode. As a consequence of the different growth modes, the ultrathin films deposited on a SrTiO 3 substrate and a YBaCuNbO buffer layer have different surface morphologies and superconductive properties. We believe that the step-flow mode makes it possible to improve the ultrathin YBCO film structure and increase the critical temperature.

We report a method of profiled sapphire substrate preparation and growth of InGaAlN light-emitting diode (LED) structures over these substrates. Sapphire substrates with textured front surface were prepared by the simple method of nanoscale gold drops formation on sapphire surface followed by etching in hot H3PO4 acid. Comparison of blue LEDs grown on standard (flat) and profiled sapphire substrates in one epitaxial process shows significant increase in output power due to increased light extraction without deterioration of other LED characteristics.

Stimulated emission is studied in a hexagonal AlGaN/GaN/AlGaN double heterostructure grown on a (0 0 0 1) sapphire substrate by low pressure (200 mbar) metallorganic vapor phase epitaxy. A sharp increase in the edge emitted luminescence intensity is obtained above a threshold excitation density of 40 kW/cm2 and is accompanied by a strong narrowing of the luminescence line width. The specific surface morphology of the heterostructure is suspected to be responsible for an optical feedback in the sample. Although the surface is extremely smooth yielding roughness values of σRMS

Binding of components of the fibrinolytic system to fibrin is important for the regulation of fibrinolysis. In this study, decomposition of the fibrin network and binding of plasminogen and plasminogen activators (PAs) to fibrin during lysis of a plasma clot were investigated with confocal microscopy using fluorescein-labeled preparations of fibrinogen, plasminogen, tissue-type PA (t-PA), and two-chain urokinase-type PA (tcu-PA). Lysis induced by PAs present throughout the plasma clot was accompanied by a gradual loss of fibrin content of fibers and by accumulation of plasminogen onto the fibers. Two sequential phases could be distinguished: a phase of prelysis, during which the fibrin network remained immobile, and a phase of final lysis, during which fibers moved with a tendency to shrink and eventually disappeared. The two phases occurred simultaneously but in different locations when lysis was induced by PAs present in the plasma surrounding the clot. The zone of final lysis was located within a 5-8-μm superficial layer, where fibers were mobile, and surface-associated fibrin agglomerates appeared. Plasminogen accumulated in these agglomerates up to 30-fold as compared with its concentration in the outer plasma. t-PA was also highly concentrated in the agglomerates, and tcu-PA bound to them slightly. The zone of prelysis, where plasminogen was moderately accumulated on the immobile fibers, was located deeper in the clot. This zone was much thinner in the case of t-PA-induced lysis than in the case of tcu-PA-induced lysis, reflecting the difference in penetration of the two PAs into the clot. We conclude that under conditions of diffusional transport of fibrinolytic enzymes from outside a plasma clot, extensive lysis is spatially restricted to a zone not exceeding 5-8 μm from the clot surface. In this zone the structure of the fibrin network undergoes significant changes, and strikingly high accumulation of fibrinolytic components takes place.

The effects of hypertonic solutions and slow freezing to different temperatures in the range of 0 to -80 degrees C on the permeability of plasma membranes of reconstituted erythrocytes were investigated. It has been found that even increased concentrations of NaCl or KCl (1.2 to 4.2 M) do not change appreciably release of K+, [14C]sucrose and haemoglobin (by 8 to 20%), while leakage of markers into the supernatant fluid is essentially completed on freezing to -25 degrees C. If the content of mobile water in the sample of reconstituted erythrocytes is lower than 1 to 2%, the permeability of plasma membranes for [14C]sucrose and haemoglobin changes after freezing to -19 to -22 degrees C. These findings suggest that the existence of water-dependent structural changes in the membranes can be responsible for a primary mechanism of altering the permeability at low temperatures.