Submonolayer InGaAs/GaAs Quantum Dots Grown by MOCVD

Semiconductors - The mode of the growth of InGaAs quantum dots by MOS-hydride epitaxy on GaAs substrates without a deviation and with a deviation of 2° is selected for laser structures...     

Magnetization of Manganese Perovskites

Temperature dependence of spontaneous magnetization at a separate site in the compounds La_1-xCa_xMnO₃ (0 ⩽ x ⩽ 1) is investigated in the molecular field approximation using a homogeneous model for the magnetic sub-lattice with allowance for the Heisenberg superexchange and double exchange between nearest neighbors. Unlike with the usual magnets having one type of magnetic ions, in this case there appears a system of equations with two unknowns, mean spins of ions Mn³⁺ and Mn⁴⁺. In the vicinity of the ordering temperature, this system can be solved analytically and the expression for the ordering temperature can be obtained as well. To find the temperature dependence of magnetization in the whole temperature range, we used the exact expression for the double exchange operator containing spin operators under the square root. The numerical solutions were found in this case.     

Investigation of the Electrophysical Characteristics of SF6Gas: The Effect of Electrode Layers on the Measurement Accuracy

The effect of the electrode layers of a space charge on the accuracy of determination of the intensity of the electric field in an ionization chamber described in [1] is treated. It is demonstrated that the measurement error at the SF₆gas pressure ranging from 10 to 100 torr does not exceed 3%.     

Boron and Gadolinium Loaded Fe3O4 Nanocarriers for Potential Application in Neutron Capture Therapy

In this article, a novel method of simultaneous carborane- and gadolinium-containing compounds as efficient agents for neutron capture therapy (NCT) delivery via magnetic nanocarriers is presented. The presence of both Gd and B increases the efficiency of NCT and using nanocarriers enhances selectivity. These factors make NCT not only efficient, but also safe. Superparamagnetic Fe₃O₄ nanoparticles were treated with silane and then the polyelectrolytic layer was formed for further immobilization of NCT agents. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), ultraviolet–visible (UV-Vis) and Mössbauer spectroscopies, dynamic light scattering (DLS), scanning electron microscopy (SEM), vibrating-sample magnetometry (VSM) were applied for the characterization of the chemical and element composition, structure, morphology and magnetic properties of nanocarriers. The cytotoxicity effect was evaluated on different cell lines: BxPC-3, PC-3 MCF-7, HepG2 and L929, human skin fibroblasts as normal cells. average size of nanoparticles is 110 nm; magnetization at 1T and coercivity is 43.1 emu/g and 8.1, respectively; the amount of B is 0.077 mg/g and the amount of Gd is 0.632 mg/g. Successful immobilization of NCT agents, their low cytotoxicity against normal cells and selective cytotoxicity against cancer cells as well as the superparamagnetic properties of nanocarriers were confirmed by analyses above.     

Russian grant-holders opinion on competitive funding: Results of a survey

This paper describes results of a survey conducted among the Russian Foundation for Basic Research (RFBR) grant-holders. The aim of this paper is to examine the attitude of grant holders to new multi-channel funding system and to assess its significance for Russian scientists involved in research in natural and applied sciences. It is a first attempt to get a fair and general picture of what scientists think about competitive funding. In 1999, 1440 questionnaires were distributed by mail. The response rate was 31.8%. The results of the survey clearly show that proposal writing has become a substantial part of research activity in Russia. Each respondent received more than 5 grants during 1993-1997. The RFBR and foreign funding agencies, particularly ISF, INTAS, and the Civilian Research and Development Foundation equally evaluated Russian scientists' performance: about 69.% of RFBR grant-holders were awarded a grant from foreign agencies. The present findings are being used, as a practical matter, to guide and inform the Ministry of Science and Technology Policy which is responsible for the promotion R in Russia to organize a special training for students and post docs on proposal writing. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sheep and goats raised in mixed flocks have diverse immune status around parturition

Several physiological and metabolic changes take place in dairy ruminants around parturition (late pregnancy, parturition, and early lactation). Dairy species are genetically selected for their higher milk production compared with non-dairy species. This fact causes a constant stress that impairs the immune status of the animal, with consequences for its welfare and performance. In the present study, we assessed the immune status of high-yield dairy sheep and goats by quantifying IgG and IgM concentrations, as well as chitotriosidase (ChT) and complement system [total complement system (TC) and alternative complement pathway (AC)] activity in blood plasma around parturition. We also measured IgG and IgM concentrations and ChT activity in colostrum and milk during the first 40 d postpartum. The lowest blood IgG concentration was at parturition in both species. We detected no differences in blood IgG concentrations between species. Blood IgM concentrations were constant in both species throughout the study period. However, blood IgM concentrations were greater in sheep than in goats. Blood ChT activity was greater in goats than in sheep, and both species showed constant activity of this enzyme throughout the study period. We observed no differences in complement system (TC and AC) activity between sheep and goats. In addition, both TC and AC activity were constant in both species throughout the experiment. In general, IgG and IgM concentrations were greater in sheep colostrum than in goat colostrum, but these differences disappeared after d 4 (IgG) and d 3 (IgM) postpartum. In both species, the highest IgG and IgM concentrations were measured in colostrum, gradually decreasing during the first days postpartum. Chitotriosidase activity decreased in both species from colostrum to milk, although goats always showed greater ChT activity than sheep. Both sheep and goats seemed to be more susceptible to infectious diseases around parturition. As well, goats showed greater ChT activity in blood, colostrum, and milk than sheep. This fact may give these animals additional protection against parasite and fungal infections.     

Picosecond kinetics of photoexcited carriers in gallium arsenide containing aluminum nanoclusters

The kinetics of photoluminescence and reflectance of GaAs containing Al clusters is studied. The lifetime of photocarriers in the samples investigated was equal to ～15 ps. A simple model describing the kinetics of photoluminescence and the reflection coefficient is proposed.     

Stimulated emission from a metamorphic GaAsSb bulk layer on a GaAs substrate

The structural and optical properties of a metamorphic GaAsSb bulk layer grown on a GaAs substrate are studied. As the excitation power density (at a wavelength of 0.65 μm) reaches 9 kW cm^?2 at liquid-nitrogen temperature and 230 kW cm^?2 at room temperature, a superluminescence signal is observed at wave-lengths of 0.943 and 0.992 μm, respectively.     

Detection of polyomavirus DNA in human brain tumors

AIM: To investigate surgically resected human brain tumors for the presence of polyomavirus DNA. MATERIALS AND METHODS: 65 samples of surgically resected human brain tumors (57 tumors were of neuroectodermal genesis, 4--mesenchimal, 4--metastatic tumors) were examined for the presence of viral DNA by PCR analysis. RESULTS: DNA of polyomaviruses was found in oligodendroligomas (66.7% of cases), oligodendroastrocytomas (66.7% of cases) and glioblastomas (40% of cases). In metastatic tumors viral infection had not been detected. No correlation between the grade of brain tumors and infection with polyomavirus DNA has been revealed. CONCLUSION: Our data point to importance of investigation of the brain tumors and cerebrospinal fluid for determination of viral infection.     

A multifrequency interband two-cascade laser

Multifrequency lasing in a new class of injection heterolasers, i.e., in an interband two-cascade laser with a tunneling p-n junction separating two active regions of quantum wells located in the same waveguide is obtained and studied. The developed laser structure with pulsed pumping provided the simultaneous emission of two first-order modes with the wavelengths of 1.063 and 0.98 μm and two third-order modes with the wavelengths of 0.951 and 0.894 μm. Due to nonlinear mixing of the modes within the laser cavity, the generation of the second harmonics and sum frequencies was observed.