Theoretical study of the mechanism of dry oxidation of 4H-SiC

Possible defect structures, arising from the interaction of O-2 molecules with an ideal portion of the SiC/SiO2 interface, have been investigated systematically using density functional theory. Based on the calculated total energies and assuming thermal quasiequilibrium during oxidation, the most likely routes leading to complete oxidation have been determined. The defect structures produced along these routes will remain at the interface in significant concentration when stopping the oxidation process. The results obtained for their properties are well supported by experimental findings about the SiC/SiO2 interface. It is found that carbon-carbon bonds can explain most of the observed interface states but not the high density near the conduction band of 4H-SiC

MATHEMATICAL MODEL OF GRAIN MICRONIZATION

Summary. During micronisation grain moisture evaporates mainly in decreasing drying rate period. Grain layer located on the surface of the conveyor micronisers will be regarded as horizontal plate. Due to the fact that the micronisation process the surface of the grain evaporates little moisture (within 2-7 %) is assumed constant plate thickness. Because in the process of micronization grain structure is changing, in order to achieve an exact solution of the equations necessary to take into account changes thermophysical, optical and others. Equation of heat transfer is necessary to add a term that is responsible for the infrared heating. Because of the small thickness of the grain, neglecting the processes occurring at the edge of the grain, that is actually consider the problem of an infinite plate. To check the adequacy of the mathematical model of the process of micronisation of wheat grain moisture content must be comparable to the function of time, obtained by solving the system of equations with the measured experimental data of experience. Numerical solution of a system of equations for the period of decreasing drying rate is feasible with the help of the Maple 14, substituting the values of the constants in the system. Calculation of the average relative error does not exceed 7- 10 %, and shows a good agreement between the calculated data and the experimental values

Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study

A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface

Detection of an intergalactic meteor particle with the 6-m telescope

On July 28, 2006 the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences recorded the spectrum of a faint meteor. We confidently identify the lines of FeI and MgI, OI, NI and molecular-nitrogen N_2 bands. The entry velocity of the meteor body into the Earth's atmosphere estimated from radial velocity is equal to 300 km/s. The body was several tens of a millimeter in size, like chondrules in carbon chondrites. The radiant of the meteor trajectory coincides with the sky position of the apex of the motion of the Solar system toward the centroid of the Local Group of galaxies. Observations of faint sporadic meteors with FAVOR TV CCD camera confirmed the radiant at a higher than 96% confidence level. We conclude that this meteor particle is likely to be of extragalactic origin. The following important questions remain open: (1) How metal-rich dust particles came to be in the extragalactic space? (2) Why are the sizes of extragalactic particles larger by two orders of magnitude (and their masses greater by six orders of magnitude) than common interstellar dust grains in our Galaxy? (3) If extragalactic dust surrounds galaxies in the form of dust (or gas-and-dust) aureoles, can such formations now be observed using other observational techniques (IR observations aboard Spitzer satellite, etc.)? (4) If inhomogeneous extragalactic dust medium with the parameters mentioned above actually exists, does it show up in the form of irregularities on the cosmic microwave background (WMAP etc.)?Comment: 9 pages, 6 EPS figure

МОРФОГЕНЕТИЧЕСКАЯ ДИФФЕРЕНЦИАЦИЯ БЕРЕГОВ КОНТАКТНЫХ ЗОН СЕВЕРНОЙ ПАЦИФИКИ

The results of the analysis of geospatial and geological-geomorphological information on the shores of the contact zones of the North Pacific are presented. An analysis of the maps of the morphogenetic types of coasts of the North Pacific revealed the specifics of the coastal morpholithogenesis of the seas of subarctic and moderate zones. It has been established that for the seas of the North Pacific, a two-modal distribution of the length of coasts of various types is characteristic. The first maximum relates to abrasion-denudation rocky shores, with a significant contribution to the destruction of physical weathering. The second peak is formed by abrasive-accumulative shores. A similar distribution of coast types along with structural and geological features of the coastal structure is probably associated with various stages of coastal maturity under conditions of intense denudation destruction of the coasts of the seas, characterized by a prolonged “open sea” period at negative air temperatures. The morphoclimatic position (geospatial parameters and the related differences in morpholithodynamic parameters) of Sakhalin Island and the island arc systems of the North Pacific allowed us to consider them as contact zones of different types of seas, as well as seas and oceans. The morpholithodynamic characteristics of the shores of contact zones along with the features of hydrodynamics and the thermal regime of the shared water areas also determine the morphoclimatic parameters of the contact zone itself. The Sakhalin shores of the moderately cold northern part of the Sea of Japan and the Subarctic Sea of Okhotsk are 30-140 km apart, while the oceanic and marine shores of large islands in island-arc systems separate the first kilometers. Thus, the windwave fields and their interaction with swell waves in the contact zones are very complex. The temperature regime of the coasts also largely depends on the geospatial parameters of the contact zones. Based on the map of morphogenetic types of coasts, the distribution features of coastal types from the sea and ocean side of island-arc systems are digitized and considered. Cartometric and morphometric studies in conjunction with the data of geological and geomorphological analysis revealed the peculiarities of development and modern dynamics of the sea and ocean coasts of island-arc systems. It is assumed that the longitudinal asymmetry of the low isthmus between the ocean and sea shores is due to tsunamigenic processes.Представлены результаты анализа геопространственной и геолого-геоморфологической информации о берегах контактных зон Северной Пацифики. Анализ карт морфогенетических типов берегов Северной Пацифики позволил выявить специфику берегового морфолитогенеза морей субарктической и умеренной поясности. Установлено, что для морей Северной Пацифики характерно двухмодальное распределение протяженности берегов различного типа. Первый максимум относится к абразионно-денудационным скалистым берегам, со значительным вкладом в процессы разрушения физического выветривания. Второй пик формируют абразионно-аккумулятивные берега. Подобное распределение типов берегов наряду со структурно-геологическими особенностями строения побережий вероятно связано с различными стадиями зрелости берегов в условиях интенсивного денудационного разрушения берегов морей, характеризующихся продолжительным периодом «открытого моря» при отрицательных температурах воздуха. Морфоклиматическая позиция (геопространственные параметры и связанные с ними различия морфолитодинамических показателей) острова Сахалин и островодужных систем Северной Пацифики позволили нам рассматривать их как контактные зоны морей разного типа, а также морей и океанов. Морфолитодинамические характеристики берегов контактных зон наряду с особенностями гидродинамики и термического режима разделяемых акваторий определяют также и морфоклиматические параметры собственно контактной зоны. Сахалинские берега умеренно холодной северной части Японского моря и субарктического Охотского моря расположены друг от друга в 30-140 км, в то время как океанские и морские берега крупных островов в островодужных системах разделяют всего несколько километров. Таким образом, ветроволновые поля и их взаимодействие с волнами зыби в контактных зонах имеют весьма сложный характер. Температурный режим побережий также в значительной степени зависит от геопространственных параметров контактных зон. На основе карты морфогенетических типов берегов оцифрованы и рассмотрены особенности распределения типов берегов с морской и океанской стороны островодужных систем. Картометрические и морфометрические исследования в комплексе с данными геолого-геоморфологического анализа позволили выявить особенности развития и современной динамики морских и океанских берегов островодужных систем. Предполагается, что продольная асимметрия низменных перешейков между океанскими и морскими берегами обусловлена цунамигенными процессами

Identification of intrinsic electron trapping sites in bulk amorphous silica from ab initio calculations

Using ab initio calculations we demonstrate that extra electrons in pure amorphous SiO2 can be trapped in deep band gap states. Classical potentials were used to generate amorphous silica models and density functional theory to characterise the geometrical and electronic structures of trapped electrons. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2 and produce ≈≈3.2 eV deep states in the band gap. These precursors comprise wide (⩾⩾130°°) O–Si–O angles and elongated Si–O bonds at the tails of corresponding distributions. The electron trapping in amorphous silica structure results in an opening of the O–Si–O angle (up to almost 180°°). We estimate the concentration of these electron trapping sites to be View the MathML source≈5×1019cm-3

Hydrogen-induced rupture of strained Si─O bonds in amorphous silicon dioxide

Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide (a−SiO2) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E′ centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of a−SiO2

Observations of Stellar Objects at a Shell Boundary in the Star-Forming Complex in the Galaxy IC1613

The single region of ongoing star formation in the galaxy IC 1613 has been observed in order to reveal the nature of compact emission-line objects at the edges of two shells in the complex, identified earlier in H-alpha line images. The continuum images show these compact objects to be stars. Detailed spectroscopic observations of these stars and the surrounding nebulae were carried out with an integral field spectrograph MPFS mounted on the 6m telescope of the Special Astrophysical Observatory. The resulting stellar spectra were used to determine the spectral types and luminosity classes of the objects. An Of star we identified is the only object of this spectral type in IC 1613. The results of optical observations of the multi-shell complex are compared to 21cm radio observations. The shells harboring the stars at their boundaries constitute the most active part of the star-forming region. There is evidence that shocks have played an important role in the formation of the shells.Comment: 10 pages, 5 PS and 1 color JPEG figur

Spectrum of Light in a Quantum Fluctuating Periodic Structure

We address the general problem of the excitation spectrum for light coupled to scatterers having quantum fluctuating positions around the sites of a periodic lattice. In addition to providing an imaginary part to the spectrum, we show that these quantum fluctuations affect the real part of the spectrum, in a way that we determine analytically. Our predictions may be observed with ultracold atoms in an optical lattice, on a J=0->J'=1 narrow atomic transition. As a side result, we resolve a controversy for the occurrence of a spectral gap in a fcc lattice.Comment: 4 pages, 1 figure; introduction, conclusion and title change