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

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

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

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

QSOs Associated with Messier 82

The starburst / AGN galaxy M82 was studied by Dahlem, Weaver and Heckman using X-ray data from ROSAT and ASCA, as part of their X-ray survey of edge-on starburst galaxies. They found seventeen unresolved hard-X-ray sources around M82, in addition to its strong nuclear source, and other X-rays within the main body of M82. We have measured optical point sources at these positions, and have obtained redshifts of six candidates at the Keck I 10-m telescope, using the low-resolution imaging spectrograph (LRIS). All six are highly compact optical and X-ray objects with redshifts ranging from 0.111 to 1.086. They all show emission lines. The three with the highest redshifts are clearly QSOs. The others with lower redshifts may either be QSOs or compact emission-line galaxies. In addition to these six there are nine QSOs lying very close to M82 which were discovered many years ago. There is no difference between optical spectra of these latter QSOs, only two of which are known to be X-ray sources, and the X-ray emitting QSOs. The redshifts of all fifteen range between 0.111 and 2.05. The large number of QSOs and their apparent association with ejected matter from M82 suggest that they are physically associated with the galaxy, and have large intrinsic redshift components. If this is correct, the absolute magnitudes lie in the range -8 < M_v < -10. Also we speculate that the luminous variable X-ray source which has been detected by Chandra in the main body of M82 some 9 arcseconds from the center is another QSO in the process of ejection from the nucleus, and propose some observational tests of this hypothesis.Comment: 16 pages aastex, 3 eps figures, accepted for publication on Ap

Modulational instability of bright solitary waves in incoherently coupled nonlinear Schr\"odinger equations

We present a detailed analysis of the modulational instability (MI) of ground-state bright solitary solutions of two incoherently coupled nonlinear Schr\"odinger equations. Varying the relative strength of cross-phase and self-phase effects we show existence and origin of four branches of MI of the two-wave solitary solutions. We give a physical interpretation of our results in terms of the group velocity dispersion (GVD) induced polarization dynamics of spatial solitary waves. In particular, we show that in media with normal GVD spatial symmetry breaking changes to polarization symmetry breaking when the relative strength of the cross-phase modulation exceeds a certain threshold value. The analytical and numerical stability analyses are fully supported by an extensive series of numerical simulations of the full model.Comment: Physical Review E, July, 199

Determination of Redshifts for Selected IVS Sources. I

From observations with the 6-m BTA telescope at SAO RAS, we have determined spectroscopic redshifts of seven optical objects whose coordinates coincide with those of radio sources from the list of IVS (International VLBI Service for Geodesy and Astrometry). When compared to radio data, the obtained spectra and redshifts provide evidence for reliable identification of four observed objects; the other three require further study. The distances to the sources derived from our measurements will make it possible to refine the current estimates for parameters of cosmological models based on proper motions of these objects, which are determined from geodetic VLBI observations.Comment: 8 pp., submitted to Astrophysic

Analysis of Epidemiological Situation on Leptospiroses in the Amur-River Region. Operational Experience in the Flood Area in 2013, and Forecasting for 2014

For the first time ever mobile SAET units have performed complex investigation of epidemiological situation on leptospiroses in order to provide sanitary-epidemiological welfare of the population in the Amur-River region devastated by high water in 2013. Analyzed have been contemporary published and archival data on morbidity rate and epizootic activity of the natural leptospirosis foci in the Amur-River territory up to 2013. Summarized is the information concerning monitoring over natural focal infections (in particular leptospiroses) in the flooding area, obtained by specialized antiepidemic teams from Irkutsk Research Anti-Plague Institute of Siberia and Far East deployed in Belogorsk town of the Amur Region and Khabarovsk city in 2013. Epizootiological situation during the high water period in the Jewish Autonomous Region has been defined as an extremely adverse, unlike the Khabarovsk Territory and the Amur Region where epizootic process is less expressed. Therewith aggravation of epidemiological situation on leptospiroses in the Amur-River Region in 2014 is not ruled out