Home About us Contact
|
Home About us Contact | ||
|
|
||
Full Width (full + width)
Terms modified by Full Width Selected AbstractsTwo stage growth of microdiamond in UHP dolomite marble from Kokchetav Massif, KazakhstanJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2003H. Ishida Abstract The abundance and morphology of microdiamond in dolomite marble from Kumdy-kol in the Kokchetav Massif, are unusual; a previous study estimated the maximum content of diamonds in dolomite marble to be about 2700 carat ton,1. Microdiamond is included primarily in garnet, and occasionally in diopside and phlogopite pseudomorphs after garnet. They are classified into three types on the basis of their morphology: (1) S-type: star-shaped diamond consisting of translucent cores and transparent subhedral to euhedral very fine-grained outer parts; (2) R-type: translucent crystals with rugged surfaces; and (3) T-type: transparent, very fine-grained crystals. The S-type is the most abundant. Micro-Laue diffraction using a 1.6-µm X-ray beam-size demonstrated that the cores of the star-shaped microdiamond represent single crystals. In contrast, the most fine-grained outer parts usually have different orientations compared to the core. Laser,Raman studies indicate that the FWHM (Full Width at Half Maximum) of the Raman band of the core of the S-type diamond is slightly larger than that for the outer parts. Differences in morphology, crystal orientations, and in the FWHM of the Raman band between the core and the fine-grained outer-parts of S-type microdiamond suggest that the star-shaped microdiamond was formed discontinuously in two distinct stages. [source] In situ micro-Raman and X-ray diffraction study of diamonds and petrology of the new ureilite UAE 001 from the United Arab EmiratesMETEORITICS & PLANETARY SCIENCE, Issue 7 2008Dominik C. HEZEL This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8,81.8) and pyroxene (En73.9,75.2, Fs15.5,16.9, Wo8.8,9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1,96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro-Raman and in situ synchrotron X-ray diffraction. The main diamond Raman band (LO = TO mode at ,1332 cm,1) is broadened when compared to well-ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm,1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 ,m. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock-produced and natural diamonds. [source] Effect of AlN doping on the growth morphology of SiCCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009N. B. Singh Abstract AlN doped SiC films were deposited on on-axis Si-face 4H-SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 ,m range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X-ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1° indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 ,m in length and 40 to 50 ,m in width. It is clear that annealing of SiC-AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN-SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth, etching morphology and spectra of LiAlO2 crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2008Taohua Huang Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ligand-Driven Wavelength-Tunable and Ultra-Broadband Infrared Luminescence in Single-Ion-Doped Transparent Hybrid MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Shifeng Zhou Abstract Here, tuning of the optical properties of emission centers by tailoring the ligand fields is investigated. Experimentally, it is demonstrated that Ni2+ can act as a single emission species in multiple octahedral local environments. Nanocrystal-embedded hybrid materials are employed as hosts in order to take advantage of their convenience in local environment design for practical applications. Novel composite gain materials with high transparence are successfully made, and show interesting wavelength-tunable and ultra-broadband infrared luminescence covering the whole near-infrared region from 1,100 to 1,800,nm. The infrared luminescence peak positions can be finely tuned from 1,300 to 1,450 and to 1,570,nm, with the largest full width at half maximum being about 400,nm and covering the telecommunication bands at 1,200,1,500,nm. According to the results of characterization, the unusual luminescence, interestingly, originates from Ni2+ in nanocrystals and the doping efficiency of Ni2+ is surprisingly high. The results demonstrate that the method presented may be an effective way to fabricate multifunctional light sources with various fundamental multifunctional applications from efficient broadband optical amplifiers to bio-imaging. [source] Subtle myelin defects in PLP-null mice ,GLIA, Issue 3 2006Jack Rosenbluth Abstract This study explores subtle defects in the myelin of proteolipid protein (PLP)-null mice that could potentially underlie the functional losses and axon damage known to occur in this mutant and in myelin diseases including multiple sclerosis. We have compared PLP-null central nervous system (CNS) myelin with normal myelin using ultrastructural methods designed to emphasize fine differences. In the PLP-null CNS, axons large enough to be myelinated often lack myelin entirely or are surrounded by abnormally thin sheaths. Short stretches of cytoplasm persist in many myelin lamellae. Most strikingly, compaction is incomplete in this mutant as shown by the widespread presence of patent interlamellar spaces of variable width that can be labeled with ferricyanide, acting as an aqueous extracellular tracer. In thinly myelinated fibers, interlamellar spaces are filled across the full width of the sheaths. In thick myelin sheaths, they appear filled irregularly but diffusely. These patent spaces constitute a spiral pathway through which ions and other extracellular agents may penetrate gradually, possibly contributing to the axon damage known to occur in this mutant, especially in thinly myelinated fibers, where the spiral path length is shortest and most consistently labeled. We show also that the "radial component" of myelin is distorted in the mutant ("diagonal component"), extending across the sheaths at 45° instead of 90°. These observations indicate a direct or indirect role for PLP in maintaining myelin compaction along the external surfaces of the lamellae and to a limited extent, along the cytoplasmic surfaces as well and also in maintaining the normal alignment of the radial component. © 2006 Wiley-Liss, Inc. [source] Some Parameters of Correlated Current and Radiated Field Pulses from Lightning to the Gaisberg TowerIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 1 2010Hannes Pichler Non-member Abstract Simultaneous measurements of lightning current and associated radiated electromagnetic field are of fundamental interest for various applications in lightning research. These data can be used for the evaluation of return stroke (RS) models or to investigate the so-called tower effect when lightning hits an elevated object. In this paper, we show the results of simultaneous measurements of current pulses from lightning strikes on the instrumented Gaisberg tower (Austria) and the correlated vertical E-field components at a distance of 78.8 and 108.7 km, respectively. We have analyzed some main lightning current parameters (peak current Ip, 30,90% rise time TI_30-90, and full width at half maximum TI_FWHM and the time-correlated field waveform parameters (Ep, 30,90% rise time TE_30-90, TE_FWHM, and the peak-to-zero time TE_PTZ. With a geometric mean of TI_FWHM = 19 ,s and Ip = 9.6 kA (N = 73) of the RS current pulses used in this study, those strokes are very similar to the strokes in triggered lightning in Florida and Alabama1. With a TE_PTZ of about 10 µs, the zero-crossing time of the radiated E-fields from the tower strokes are significantly shorter than the typical values of 30 , 40 µs (e.g.2). Correlation between the current and field parameters TI_FWHM versus TE_FWHM and TE_PTZ, respectively, is low (R2 = 0.29 and 0.14). We assume that the relatively short lightning channel in the case of the RSs in object-triggered upward flashes is the main reason for the observed short zero-crossing time. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEMJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2006S. Parthiban To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 × 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source] Limitations of asymmetric parallel-beam geometryJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2004N. A. Raftery Bragg diffraction peak profiles and intensities in asymmetric (,,2,) diffraction using a mirror-based parallel-beam geometry were compared with symmetric parallel-beam (,,2,) and conventional Bragg,Brentano (,,2,) diffraction for a powdered quartz sample and the NIST standard reference material (SRM) 660a (LaB6, lanthanum hexaboride). A comparison of the intensities and line widths (full width at half-maximum, FWHM) of these techniques demonstrated that low incident angles (,,<,5°) are preferable for the parallel-beam setup. For higher , values, if 2,,<,2,, mass absorption reduces the intensities significantly compared with the Bragg,Brentano setup. The diffraction peak shapes for the mirror geometry are more asymmetric and have larger FWHM values than corresponding peaks recorded with a Bragg,Brentano geometry. An asymmetric mirror-based parallel-beam geometry offers some advantages in respect of intensity when compared with symmetric geometries, and hence may be well suited to quantitative studies, such as those involving Rietveld analysis. A trial Rietveld refinement of a 50% quartz,50% corundum mixture was performed and produced adequate results. [source] Bone marrow changes in adolescent girls with anorexia nervosaJOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2010Kirsten Ecklund Abstract Early osteoporosis is common among adolescent girls with anorexia nervosa (AN) and may result from premature conversion of red (RM) to yellow bone marrow. We performed right knee magnetic resonance imaging (MRI) on a 1.0 T extremity scanner in 20 patients and 20 healthy controls, aged 16.2,±,1.6 years (mean,±,SD). Coronal T1 -weighted (T1W) images and T1 maps were generated from T1 relaxometry images. Blinded radiologists visually assessed RM in the distal femoral and proximal tibial metaphyses in T1W images using a scale of signal intensity from 0 (homogeneous hyperintensity, no RM) to 4 (all dark, complete RM). Subjects with AN exhibited nearly twofold lower metaphyseal RM scores in both the femur (0.64 versus 1.22, p,=,.03) and tibia (0.54 versus 0.96, p,=,.08). In relaxometric measurements of four selected regions (femur and tibia amd epiphysis and metaphysis), subjects with AN showed higher mean epiphyseal but lower metaphyseal T1. The net AN-control difference between epiphysis and metaphysis was 70,ms in the femur (+31 versus ,35,ms, p,=,.02) and of smaller magnitude in the tibia. In relaxometry data from the full width of the femur adjacent to the growth plate, AN subjects showed mean T1 consistently lower than in controls by 30 to 50,ms in virtually every part of the sampling region. These findings suggest that adolescents with AN exhibit premature conversion of hematopoietic to fat cells in the marrow of the peripheral skeleton potentially owing to adipocyte over osteoblast differentiation in the mesenchymal stem cell pool. © 2010 American Society for Bone and Mineral Research [source] Highly porous elastomer-silsesquioxane nanocomposites synthesized within high internal phase emulsionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2008Jenny Normatov Abstract Highly porous elastomeric nanocomposites were successfully synthesized through copolymerization of 2-ethylhexyl acrylate (EHA), divinyl benzene (DVB), and up to 9 mol % of a polyhedral oligomeric silsesquioxane bearing one propylmethacryl group and seven cyclohexyl groups (MACH-POSS) within the external phase of high internal phase emulsions (HIPE). The chemical structures, morphologies, thermal properties, and mechanical properties of the polyHIPE were investigated. The mechanical loss peak temperature and full width at half maximum increased with increasing MACH-POSS content. These changes indicate that copolymerization with MACH-POSS limits segmental mobility and produces compositional distributions on the nanometer scale. At 9 mol % MACH-POSS, the reduction in segmental mobility produced a glass transition temperature above room temperature and a significant increase in modulus that can be ascribed to the relatively glassy nature of the polymer. Inorganic monoliths with porosities of around 86%, O/Si of about 1.6, and less than 10% carbon were produced on pyrolysis of the nanocomposite polyHIPE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2357,2366, 2008 [source] Raman spectroscopy of synthetic, geological and biological vaterite: a Raman spectroscopic studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2010U. Wehrmeister Abstract Raman spectroscopy was used to study vaterite samples of biological, geological and synthetic origin. The Raman band positions and the full width at half-maximum (FWHM) of the lattice modes and the internal modes of the carbonate ion of all specimens show no significant differences between vaterites of different origin. With increasing Mg concentrations, synthetic vaterite samples show increasing FWHM in the region of the lattice modes and the three ,1 bands, whereas no change in luminescence was detected. In contrast, in situ measurements of vaterite areas in freshwater cultured pearls (FWCPs) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) together with the Raman spectra obtained at the same points show that the luminescence intensity in biological samples is affected by the magnesium content. The Raman spectroscopic features of vaterite and parisite-(Ce) are compared, and their similarities suggest that the structure of vaterite contains at least three crystallographically independent carbonate groups and similar carbonate group layers. A band at 263 cm,1 is observed for the first time in this study, whereas it could be demonstrated that bands previously reported at 130 and 190 cm,1 do not belong to vaterite. Copyright © 2009 John Wiley & Sons, Ltd. [source] Changes in spectral features with varying mole fractions of anisaldehyde in binary mixturesJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2007A. Anis Fathima Abstract Raman and IR spectra of neat anisaldehyde (4-methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic , (CH) and ring-breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute,solvent interaction is stronger in 2-propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, , (CO) in 2-propanol and aldehydic , (CH) in acetonitrile, gave a Gaussian-type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute,solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright © 2006 John Wiley & Sons, Ltd. [source] Demonstration of high lateral resolution in laser confocal microscopy using annular and radially polarized lightMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2009Jeongyong Kim Abstract The authors present the experimental result of improved lateral resolution in laser confocal microscopy (LCM) by using annular and radially polarized light as the input illumination of an existing LCM. The authors examined the lateral resolution of the LCM by imaging a single fluorescent bead and measuring the lateral width of the single bead profile appearing in the optical image. Compared to no aperture and linearly polarized light, the central peak of the single bead profile narrowed by ,40%, being as small as 122 nm in full width at half maximum using 405 nm laser excitation in a reflection imaging. In addition, the authors showed that radial polarization helps to preserve the circular shape of the single bead profile whereas linearly polarized light tends to induce an elongation along the polarization direction. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Experimental investigation into femtosecond fiber ring laser with passive mode lockingMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2009Xiaoping Xie Abstract A passively mode-locked Er3+ -doped fiber ring laser is experimentally investigated, with the emphasis on its practical design by considering the effects of ring cavity length, pumping light power, and optical amplification on the femtosecond optical pulses obtained. It is shown that the designed fiber ring laser can operate at the center wavelength of 1550 nm to produce a train of periodic optical pulses with full width at half maximum (FWHM) of 270 fs, repetition frequency of 20 MHz, and average output optical power of 146 ,W. The resulting femtosecond optical pulses are then amplified by using three kinds of Er3+ -doped optical fibers with different lengths and Er3+ -doped concentrations, respectively, while employing the same pumping laser. In the experiments, both the FWHM of amplified optical pulses and the amplifier gain are measured under different conditions. The optimization of optical pulse width is also carried out in terms of pumping light power. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 63,67, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23985 [source] Enhanced star formation in narrow-line Seyfert 1 active galactic nuclei revealed by SpitzerMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010E. Sani ABSTRACT We present new low-resolution Spitzer mid-infrared spectroscopy of a sample of 20 ROSAT -selected local narrow-line Seyfert 1 galaxies (NLS1s). We detect strong active galactic nucleus (AGN) continuum in all and clear polycyclic aromatic hydrocarbon (PAH) emission in 70 per cent of the sources. The 6.2 ,m PAH luminosity spans three orders of magnitude, from ,1039 to ,1042 erg s,1, providing strong evidence for intense ongoing star formation in the circumnuclear regions of these sources. Using the Infrared Spectrograph/Spitzer archive, we gathered a large number of additional NLS1s and their broad-line counterparts (BLS1s) and constructed NLS1 and BLS1 subsamples to compare them in various ways. The comparison shows a clear separation according to full width at half-maximum (H,) [FWHM(H,)] such that objects with narrower broad H, lines are the strongest PAH emitters. We test this division in various ways trying to remove biases due to luminosity and aperture size. Specifically, we find that star formation activity around NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above result seems to hold over the entire range of distance and luminosity. Moreover, the star formation rate is higher in low black hole mass and high L/LEdd systems indicating that black hole growth and star formation are occurring simultaneously. [source] H, long-term monitoring of the Be star , Cephei AaMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008G. Catanzaro ABSTRACT Papers published in recent years have contributed to resolve the enigma of the hypothetical Be nature of the hot pulsating star , Cephei. This star shows variable emission in the H, line, typical for Be stars, but its projected rotational velocity is very much lower than the critical limit, contrary to what is expected for a typical Be star. The emission has been attributed to the secondary component of the , Cephei spectroscopic binary system. In this paper, using both our and archived spectra, we attempt to recover the H, profile of the secondary component and to analyse its behaviour with time for a long period. To accomplish this task, we first derive the atmospheric parameters of the primary, Teff= 24 000 ± 250 K and log g= 3.91 ± 0.10, and then we use these values to compute its synthetic H, profile, and finally we reconstruct the secondary's profile disentangling the observed one. The secondary's H, profile shows the typical two-peak emission of a Be star with a strong variability. We also analysed the behaviour versus time of some linewidth parameters: equivalent width, ratio of blue to red peak intensities, full width at half-maximum, peak separation and radial velocity of the central depression. The projected rotational velocity (v sin i) of the secondary and the dimension of the equatorial surrounding disc have also been estimated. [source] Ly, leaks and reionizationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008Longlong Feng ABSTRACT Ly, absorption spectra of QSOs at redshifts z, 6 show complete Gunn,Peterson absorption troughs (dark gaps) separated by tiny leaks. The dark gaps are from the intergalactic medium (IGM) where the density of neutral hydrogen are high enough to produce almost saturated absorptions, however, where the transmitted leaks come from is still unclear so far. We demonstrate that leaking can originate from the lowest density voids in the IGM as well as the ionized apatches around ionizing sources using semi-analytical simulations. If leaks are produced in lowest density voids, the IGM must already be highly ionized, and the ionizing background should be almost uniform; in contrast, if leaks come from ionized patches, the neutral fraction of IGM should be still high, and the ionizing background is significantly inhomogeneous. Therefore, the origin of leaking is crucial to determining the epoch of inhomogeneous-to-uniform transition of the ionizing photon background. We show that the origin could be studied with the statistical features of leaks. Actually, Ly, leaks can be well defined and described by the equivalent width W and the full width of half-area WH, both of which are less contaminated by instrumental resolution and noise. It is found that the distributions of W and WH of Ly, leaks are sensitive to the modelling of the ionizing background. We consider four representative models: uniform ionizing background (model 0), the photoionization rate of neutral hydrogen ,H i and the density of IGM are either linearly correlated (model I), or anticorrelated (model II), and ,H i is correlated with high-density peaks containing ionizing sources (model III). Although all of these models can match to the mean of the observed effective optical depth of the IGM at z, 6, the distributions of W and WH are very different from each other. Consequently, the leak statistics provides an effective tool to probe the evolutionary history of reionization at z, 5,6.5. Similar statistics will also be applicable to the reionization of He ii at z, 3 [source] Spectral models for solar-scaled and ,-enhanced stellar populationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007P. Coelho ABSTRACT We present the first models allowing one to explore in a consistent way the influence of changes in the ,-element-to-iron abundance ratio on the high-resolution spectral properties of evolving stellar populations. The models cover the wavelength range from 3000 Å to 1.34 ,m at a constant resolution of full width at half-maximum (FWHM) = 1 Å and a sampling of 0.2 Å, for overall metallicities in the range 0.005 ,Z, 0.048 and for stellar population ages between 3 and 14 Gyr. These models are based on a recent library of synthetic stellar spectra and a new library of stellar evolutionary tracks, both computed for three different iron abundances ([Fe/H]=,0.5, 0.0 and 0.2) and two different ,-element-to-iron abundance ratios ([,/Fe]= 0.0 and 0.4). We expect our fully synthetic models to be primarily useful for evaluating the differential effect of changes in the ,/Fe ratio on spectral properties such as broad-band colours and narrow spectral features. In addition, we assess the accuracy of absolute model predictions in two ways: first, by comparing the predictions of models for scaled-solar metal abundances ([,/Fe]= 0.0) to those of existing models based on libraries of observed stellar spectra; and secondly, by comparing the predictions of models for ,-enhanced metal abundances ([,/Fe]= 0.4) to observed spectra of massive early-type galaxies in the Sloan Digital Sky Survey Data Release 4. We find that our models predict accurate strengths for those spectral indices that are strongly sensitive to the abundances of Fe and , elements. The predictions are less reliable for the strengths of other spectral features, such as those dominated by the abundances of C and N, as expected from the fact that the models do not yet allow one to explore the influence of these elements in an independent way. We conclude that our models are a powerful tool for extracting new information about the chemical properties of galaxies for which high-quality spectra have been gathered by modern surveys. [source] VIMOS-VLT spectroscopy of the giant Ly, nebulae associated with three z, 2.5 radio galaxies,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007M. Villar-Martín ABSTRACT The morphological and spectroscopic properties of the giant (>60 kpc) Ly, nebulae associated with three radio galaxies at z, 2.5 (MRC 1558,003, 2025,218 and 0140,257) have been investigated using integral field spectroscopic data obtained with the Visible Multi-Object Spectrograph (VIMOS) on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within ,30°. The total Ly, luminosities are in the range (0.3,3.4) × 1044 erg s,1. The Ly, spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range ,400,1500 km s,1 and velocity shifts Voffset, 120,600 km s,1. We present an infall model that can successfully explain the morphology, size, surface brightness distribution and the velocity field of the Ly, nebula associated with MRC 1558,003. It can also explain why Ly, is redshifted relative to other emission lines and the FWHM values of the non-resonant He ii line. This adds further support to our previous conclusion that the quiescent giant nebulae associated with this and other high-redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Ly, FWHM values, which might be the consequence of a different mechanism. We have discovered a giant (,85 kpc) Ly, nebula associated with the radio galaxy MRC 0140,257 at z= 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s,1 and Voffset, 120 km s,1), unique among high- z (,2) radio galaxies. [source] Atomic hydrogen in asymptotic giant branch circumstellar environments.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006A case study: X Her ABSTRACT We report the detection of the H i line at 21 cm from the circumstellar shell around the asymptotic giant branch star X Her using the position-switching technique with the Nançay Radio Telescope. At the star position, the line shows two components: (i) a broad one [full width at half-maximum (FWHM) , 13 km s,1] centred at ,72.2 km s,1 and (ii) a narrow one (FWHM , 4 km s,1) centred at ,,70.6 km s ,1. Our map shows that the source associated to the broad component is asymmetric with material flowing preferentially towards the north-east. This source extends to ,10 arcmin (,0.4 pc) from the star in that direction. On the other hand, the narrow component is detected only at the star position and indicates material flowing away from the observer. The total mass of atomic hydrogen is ,6.5 × 10,3 M, which, within a factor of 2, agrees with the estimate obtained from IRAS data at 60 ,m. [source] What controls the C iv line profile in active galactic nuclei?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005Alexei Baskin ABSTRACT The high-ionization lines in active galactic nuclei (AGN), such as C iv, tend to be blueshifted with respect to the lower-ionization lines, such as H,, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the H, profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C iv suggest that non-gravitational effects, such as obscuration and radiation pressure, may affect the line profile. We explore the relation between the H, and C iv profiles using the ultraviolet (UV) spectra available for 81 of the 87 z, 0.5 PG quasars in the Boroson & Green sample. We find the following. (1) Narrow C iv lines (full width at half-maximum, FWHM < 2000 km s,1) are rare (,2 per cent occurrence rate) compared with narrow H, lines (,20 per cent). (2) In most objects where the H, FWHM < 4000 km s,1 the C iv line is broader than H,, but the reverse is true when the H, FWHM > 4000 km s,1. This argues against the view that C iv generally originates closer to the centre, compared with H,. (3) C iv appears to provide a significantly less accurate, and possibly biased estimate of the black hole mass in AGN, compared with H,. (4) All objects where C iv is strongly blueshifted and asymmetric have a high L/LEdd, but the reverse is not true. This suggests that a high L/LEdd is a necessary but not sufficient condition for generating a blueshifted asymmetric C iv emission. (5) We also find indications for dust reddening and scattering in ,normal' AGN. In particular, PG quasars with a redder optical,UV continuum slope show weaker C iv emission, stronger C iv absorption and a higher optical continuum polarization. [source] Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experimentMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007C. J. Phillips ABSTRACT Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975,1985 period of strong recurrent flaring activity. We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the ,2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system. [source] Low-temperature growth of high quality AlN films on carbon face 6H-SiCPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1 2008Myunghee Kim Abstract AlN films have been grown on atomically flat carbon face 6H-SiC (000) substrates by pulsed laser deposition and their structural properties have been investigated. In-situ reflection high-energy electron diffraction observations have revealed that growth of AlN at 710 °C proceeds in a Stranski,Krastanov mode, while typical layer-by-layer growth occurs at room temperature (RT) with atomically flat surfaces. It has been revealed that the crystalline quality of the AlN film is dramatically improved by the reduction in growth temperature down to RT and the full width at half maximum values in the X-ray rocking curves for 0004 and 102 diffractions of the RT-grown AlN film are 0.05° and 0.07°, respectively. X-ray reciprocal space mapping has revealed that the introduction of misfit dislocations is suppressed in the case of RT growth, which is probably responsible for the improvement in crystalline quality. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical, structural, and magnetic properties of p-type GaN implanted with Fe+ (5 and 10 at%)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007Yoon Shon Abstract p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+. The results of energy dispersive X-ray peak displayed the Fe-injected concentration of 5 and 10 at%, respectively. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 and 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak at 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K with the Fe concentration of 10 at% were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to 300 K. The systematic enhancement of ferromagnetic hysteresis loops for GaN implanted with high doses of Fe (5 , 10 at%) takes place with an increase in the annealing temperature from 700 to 850 °C. The trends of magnetic properties coincide with the results of the increased full width at half maximum of triple axis diffraction for GaN (0002) including the appearance of GaFeN, the enhanced Fe-related photoluminescence transitions, and the increased sizes of symmetric spin ferromagnetic domains GaFeN in atomic force microscopy and magnetic force microscopy systematically. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural defects in homoepitaxial diamond layers grown on off-axis Ib HPHT substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2006T. Bauer Abstract In the present study homoepitaxial diamond films have been grown by microwave plasma chemical vapour deposition (MWPCVD) on (001)-oriented Ib HPHT substrates with off-axis angles of up to 11°. Freestanding films of several hundred microns thickness were produced by removal of the Ib substrate and of the polycrystalline rim. In high resolution X-ray diffraction (HRXRD) rocking curve measurements the crystals showed a full width at half maximum (FWHM) between (2 × 10,3)°, which is close to the instrumental limit of our setup, and maximum values of (3 × 10,2)°. The structural quality is directly reflected in the strength of the birefringence observed in the optical microscope. While the high quality sample showed a weak birefringence with a couple of localized centres distributed over the whole sample surface, a tatami-like pattern is measured for the sample with the broad rocking curve. Identical defect structures with perfect correspondence are observed in X-ray topography images. Furthermore the X-ray topographs allow to identify isolated dislocation lines. Both characterisation methods show that the defect lines are aligned along the off-axis direction which allows conclusions on the mechanism of formation. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impact of nitridation on structural and optical properties of MOVPE-grown m-plane GaN layers on LiAlO2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009C. Mauder Abstract In this paper, we investigate the influence of the nitridation of LiAlO2 substrates on the growth of m-plane (1-100) GaN layers by metal-organic vapour phase epitaxy (MOVPE). Before thin film deposition, we performed an in-situ substrate pretreatment by exposing the wafer to NH3 for different times between no pretreatment and 300 s. The properties of subsequently grown layers show a significant dependency on this nitridation step. We find that this procedure is essential for obtaining pure m-plane GaN films and has a beneficial effect on the X-ray rocking curve (XRC) full width at half maximum (FWHM) value, which decreases by almost two orders of magnitude. Deposited layers with NH3 pretreatment also exhibit much smoother surfaces with a reduction of the root mean square (RMS) roughness value from ,20 to ,6 nm. Additionally, the nitridation greatly increases the GaN band edge emission intensity in room temperature (RT) photoluminescence (PL) spectroscopy. Furthermore, we compare the sensitivity of the substrate against water for uncoated LiAlO2 wafers with and without nitridation process. While the untreated surface shows a clear roughening when dipped into de-ionized (DI) water for 5 min, we can see no significant impact on the nitridated substrate surface. This indicates a change in surface composition which protects the sensitive substrate surface and provides good conditions for the nucleation of high-quality m-plane GaN films. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ga-doped ZnO transparent conducting films prepared by helicon-wave-excited plasma sputteringPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009Shingo Masaki Abstract Gallium-doped zinc oxide (ZnO:Ga) transparent conducting films were prepared by the helicon-wave-excited plasma sputtering (HWPS) method. The films exhibited a dominant [0001]-oriented growth with a small full width at half maximum of the (0002) ZnO diffraction peak (0.28 degrees). A high optical transmittance greater than 80% was achieved in the wavelength range between 400 and 1600 nm, because the HWPS method essentially does not damage the film surface. The results indicate that CdS-free Cu(In,Ga)Se2 -based solar cells may be fabricated by sputtering ZnO:Ga directly on the Cu(In,Ga)Se2 layer using the HWPS method. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 1.3 µm high indium content (42.5%) GaInNAs/GaAs quantum wells grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006Zhichuan Niu Abstract High structural and optical quality 1.3 µm GaInNAs /GaAs quantum well (QW) samples with 42.5% indium content were successfully grown by molecular beam epitaxy. The growth of well layers was monitored by reflection high-energy electron diffraction (RHEED). Room temperature photoluminescence (PL) peak intensity of the GaIn0.425NAs/GaAs (6 nm/20 nm) 3QW is higher than, and the full width at half maximum (FWHM) is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality due to strain compensation effects by introducing N to the high indium content InGaAs epilayer. The measured (004) X-ray rocking curve shows clear satellite peaks and Pendellösung fringes, suggesting high film uniformity and smooth interfaces. The cross sectional TEM measurements further reveal that there are no structural defects in such high indium content QWs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] n-Al0.75Ga0.25N epilayers for 250 nm emission ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005W. H. Sun Abstract We have developed a unique approach combining migration-enhanced metalorganic chemical vapor deposition (MEMOCVD) high temperature AlN buffer layers and AlGaN/AlN superlattices (SLs) to yield high quality ( HQ) AlGaN layers for 250 nm LEDs. Symmetric/asymmetric X-ray diffraction (XRD) and room temperature photoluminescence measurements were used to study the high-structural and optical quality. The (002) and (114) rocking curve full width at half,maximum (FWHM) of 1.4 µm n-Al0.75Ga0.25N grown over AlGaN/AlN buffer were 143 and 565 arcsec, respectively. Crack-free Al0.75Ga0.25N layers with electron concentration as high as 1 × 1018 cm,3 and Hall mobility about 50 cm2/V.s were successfully grown and used for sub-milliwatt power (0.12 mW at a pulse pump current of 300 mA) 250 nm deep ultraviolet light emitting diodes (UVLEDs). In addition, for comparison, we prepared n-AlGaN only using high temperature AlN without SLs inserted. The experiments show that the AlGaN/AlN SLs inserted play a crucial role in improving structural and optical quality of high Al-composition AlGaN epilayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||||||||