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Single Phase (single + phase)
Selected AbstractsEffects of annealing on structural, electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powderCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2009H. Karaagac Abstract The structural, electrical and optical properties of AgGa(Se0.5S0.5 )2 thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450,600 °C. X-ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 oC with mixed binary phases of Ga2Se3, Ga2S3, ternary phase of AgGaS2 and single phase of S. The compositional analysis with the energy dispersive X-ray analysis (EDXA) revealed that the as-grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as-grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250-430 K for all samples. The room temperature resistivity value of as-grown film was found to be 0.7x108 (,-cm) and reduced to 0.9x107 (,-cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth, structure and thermal properties of CuAlxGa1-xSe2 alloysCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2006J. Castro Abstract Ingots of the CuAlxGa1-xSe2 (0 , x , 1) alloys system were prepared by direct fusion of the stoichiometric mixture of the elements. The analysis of X-ray Powder Diffraction data showed the presence of one single phase with chalcopyrite tetragonal structure at room temperature for all the studied compositions. The lattice parameters, a and c, and the bond lengths were calculated. The phase transition temperatures were obtained by the onset method from Differential Thermal Analysis measurements performed on samples sealed in evacuated quartz ampoules. Fusion or transition enthalpies were determined from the area of the corresponding DTA peak. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal growth and structural refinement of NaMn7O12CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005E. Gilioli Abstract We report the crystal growth and the structural refinement of NaMn7O12, a manganite having a double perovskite structure. As in many similar compounds, there is coexistence of Mn3+ and Mn4+ but in this material they orderly occupy different sites for crystallographic reasons. Therefore, this peculiar structure can be considered as a model system for studying complex mechanisms such as charge, orbital and spin ordering. High purity bulk samples and "large" single crystals are needed to study tiny modifications in the crystallographic and magnetic structures associated to the ordering phenomena. Almost single phase (more than 96% pure) and single crystals (up to about 150 µm) of NaMn7O12 were synthesized by solid state reaction under pressure in a multi-anvil apparatus. Single crystal x-ray diffraction and SEM analysis have been used to characterize the crystals. The structure refinement indicates that NaMn7O12 crystallizes in the cubic Im3 space group, with a = 7.312 Å and Z = 2. Further studies are in progress to optimize the synthesis conditions, in order to grow larger crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermoelectric properties of RE2,xMxCuO4 oxide sintering bulksELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 12 2008Yusuke Ichino Abstract La2,xSrxCuO4 (LSCO) and Sm2,xCexCuO4 (SCCO) polycrystal bulks with x=0 to 0.10 were made by solid-phase reaction method. From the X-ray diffraction patterns, LSCO and SCCO were confirmed single phase. Seebeck coefficient, resistivity, and heat conductivity decreased with increasing amount of Sr2+ and Ce2+ substitution. We estimated ZT from these values and found that the highest value of ZT=0.034 at 323 K was achieved in the LSCO with x=0.02. As a result, we conclude that LSCO and SCCO showed high thermoelectric properties around room temperature. We can expect RE2,xMxCuO4 will be a very useful material for thermoelectric module operating at room temperature. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(12): 24,28, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10003 [source] Highly Crystalline, Idiomorphic Na2Ti6O13 Whiskers Grown from a NaCl Flux at a Relatively Low TemperatureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2010Katsuya Teshima Abstract Well-developed, highly crystalline Na2Ti6O13 whiskers were successfully grown by cooling a NaCl flux at a relatively low temperature of 700 °C. The obtained Na2Ti6O13 whiskers were colorless and transparent. The whiskers grown at 700 °C were single phase and exhibit the lowest sizes of up to about 3.5 ,m,×,0.1 ,m. From the results of SEM, XRD, and TEM, it was confirmed that the Na2Ti6O13 whiskers have very good crystallinity and elongated in the [lang]010[rang] directions. Furthermore, the whiskers exhibited good photocatalytic activity under ultraviolet light irradiation. It is reasonable to suppose that NaCl can be adequately used to synthesize high quality and well-developed titanate whiskers in an environmentally friendly process of crystal growth. [source] Biomimetic Carbonate,Hydroxyapatite Nanocrystals Prepared by Vapor Diffusion,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Michele Iafisco Abstract Biomimetic carbonate,hydroxyapatite (HA) nanocrystals have been synthesized by using the sitting drop vapor diffusion technique, for the first time. The method consists of diffusing vapors of an aqueous solution of NH4HCO3 through drops containing an aqueous mixture of (CH3COO)2Ca and (NH4)2HPO4 in order to increase slowly their pH. This synthesis has been performed in a crystallization mushroom, a glass device developed for protein and small molecules crystallization. The concentrations of the reagents, the final pH and the crystallization time have been optimized to produce pure carbonate,HA as a single phase. X-Ray diffraction, Fourier transformed infrared spectroscopy, and transmission electron microscopy have been utilized to characterize the synthesized carbonated substituted HA crystals which display nanometric dimensions, plate-like morphology, and low crystallinity degree, closely resembling the inorganic phase of bones, teeth, and many pathological calcifications. This novel method may prove to be suitable for the study of the interactions and/or the co-crystallization of hydroxyapatite with minute amounts of biomolecules, polymers, or drugs. [source] Crystallization Kinetics of the (Zr58Ni13.6Cu18Al10.4)Nb1 Bulk Metallic Glass,ADVANCED ENGINEERING MATERIALS, Issue 8 2006D. Qiao The differential thermal analysis (DTA) curve of the (Zr58Ni13.6Cu18Al10.4)Nb1 bulk metallic glass (BMG) shows that there are two exothermic crystallization peaks and two endothermic melting peaks. The BMG has been completely crystallized in the first crystallization peak. X-ray shows that the quenched BMG only includes the glass single phase. The BMG heated to 823 K (between the first and the second crystallization peak) has the precipitation of the cubic NiZr2. The BMG heated to 1003 K (after the second crystallization peak) has the cubic NiZr2, bct NiZr2, and bct CuZr2. HRTEM shows that there are some nano-crystalline phases for the quenched BMG. [source] Barium Non-Stoichiometry Role on the Properties of Ba1+xCe0.65Zr0.20Y0.15O3,, Proton Conductors for IT-SOFCsFUEL CELLS, Issue 5 2008S. Barison Abstract Proton conducting perovskite oxides have been widely investigated because of their potential as electrolytes for intermediate temperature solid oxide fuel cells. Among them, BaCeO3 - based materials exhibit good proton conductivity under a humidified hydrogen-containing atmosphere, but rather poor chemical stability in CO2 atmosphere. The substitution with Zr for Ce improves the chemical stability but reduces proton conductivity due to difficulties in fabricating dense materials. In the present work, single phase nanostructured powders of Ba1+xCe0.65Zr0.20Y0.15O3,, (x,=,0, 0.05, 0.10) solid solutions have been prepared by a modified sol,gel Pechini method with the final aim of evaluating the role of barium on their chemical and electrical properties. A significant influence of barium excess on the preparation and on properties of these materials has been demonstrated. In fact, density measurements evidenced that a 5 or 10,mol% nominal barium excess sensibly favoured the sintering process. Impedance analyses of sintered pellets confirmed the necessity of barium excess in order to avoid the lowering of proton conductivity, which has been evidenced for samples having stoichiometric barium content. Moreover, an unforeseen increase in chemical stability in CO2 -containing atmosphere with the growth of the barium excess was detected by thermogravimetric analyses. [source] Gas breakthrough experiments on fine-grained sedimentary rocksGEOFLUIDS (ELECTRONIC), Issue 1 2002A. Hildenbrand Abstract The capillary sealing efficiency of fine-grained sedimentary rocks has been investigated by gas breakthrough experiments on fully water saturated claystones and siltstones (Boom Clay from Belgium, Opalinus Clay from Switzerland and Tertiary mudstone from offshore Norway) of different lithological compositions. Sand contents of the samples were consistently below 12%, major clay minerals were illite and smectite. Porosities determined by mercury injection lay between 10 and 30% while specific surface areas determined by nitrogen adsorption (BET method) ranged from 20 to 48 m2 g , 1. Total organic carbon contents were below 2%. Prior to the gas breakthrough experiments the absolute (single phase) permeability (kabs) of the samples was determined by steady state flow tests with water or NaCl brine. The kabs values ranged between 3 and 550 nDarcy (3 × 10,21 and 5.5 × 10,19 m2). The maximum effective permeability to the gas-phase (keff) measured after gas breakthrough on initially water-saturated samples extended from 0.01 nDarcy (1 × 10,23 m2) up to 1100 nDarcy (1.1 × 10,18 m2). The residual differential pressures after re-imbibition of the water phase, referred to as the ,minimum capillary displacement pressures' (Pd), ranged from 0.06 to 6.7 MPa. During the re-imbibition process the effective permeability to the gas phase decreases with decreasing differential pressure. The recorded permeability/pressure data were used to derive the pore size distribution (mostly between 8 and 60 nm) and the transport porosity of the conducting pore system (10 -5,10 -2%). Correlations could be established between (i) absolute permeability coefficients and the maximum effective permeability coefficients and (ii) effective or absolute permeability coefficients and capillary sealing efficiency. No correlation was found between the capillary displacement pressures determined from gas breakthrough experiments and those derived theoretically by mercury injection. [source] Developments and Perspectives of Iron-based High-Temperature Superconductors,ADVANCED MATERIALS, Issue 19 2008Hai-Hu Wen Abstract Since the first report on superconductivity at 26,K in F-doped LaOFeAs at the end of February 2008, the superconducting transition temperature has been quickly raised to about 55,K and many new superconductors have been found, and superconductors with a higher condensing temperature are expected in this system. In this brief Research News article, the author will relate the enormous interest that has been generated towards new superconductor exploration, the refinement and tailoring of the single phase of the available superconductors, the growth of single crystals, and the theoretical and experimental efforts toward targeting the mechanism. Finally, a preliminary comparison between the iron-based system and the cuprates is given, as well as perspectives on these new iron-based superconductors. [source] An integrated routing and admission control mechanism for real-time multicast connection establishmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2001Xiaohua Jia Abstract There are two major difficulties in real-time multicast connection setup. One is the design of an efficient distributed routing algorithm which optimizes the network cost of routing trees under the real-time constraints. The other is the integration of routing with admission control into one single phase of operations. This paper presents a real-time multicast connection setup mechanism, which integrates multicast routing with real-time admission control. The proposed mechanism performs the real-time admission tests on a cost optimal tree (COT) and a shortest path tree (SPT) in parallel, aiming at optimizing network cost of the routing tree under real-time constraints. It has the following important features: (1) it is fully distributed; (2) it achieves sub-optimal network cost of routing trees; (3) it takes less time and less network messages for a connection setup. Copyright © 2001 John Wiley & Sons, Ltd. [source] Structural characterization of manganese-substituted nanocrystalline zinc oxide using small-angle neutron scattering and high-resolution transmission electron microscopyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2009B. Roy A series of zinc oxide (ZnO) nanoparticles, substituted with manganese di-oxide, have been synthesized through a modified ceramic route using urea as a fuel. X-ray diffraction and high-resolution transmission electron microscopy studies indicate that the sizes of the ZnO particles are of nanometer dimension. Particles remain as single phase when the doping concentration is below 15,mol%. Small-angle neutron scattering indicates fractal-like agglomerates of these nanoparticles in powder form. The size distributions of the particles have been estimated from scattering experiments as well as microscopy studies. The average particle size estimated from small-angle scattering experiments was found to be somewhat more than that obtained from X-ray diffraction or electron microscopy measurement. [source] The effect of habitat management on home-range size and survival of rural Norway rat populationsJOURNAL OF APPLIED ECOLOGY, Issue 6 2008M. S. Lambert Summary 1Norway rat Rattus norvegicus populations are usually controlled with toxic baits, but this approach is increasingly recognized as having negative welfare and environmental impacts. An integrated strategy that relies less on rodenticides is therefore required. Here we investigate the possibility of using a resource-based approach to rat population management. 2Structurally complex habitats provide rat populations with nest sites and opportunities to avoid predators; modifying habitats to reduce structural complexity might reduce their potential to support rat populations. As part of an integrated approach, this could be more sustainable than relying exclusively on lethal control. However, in order to target habitat management efforts most effectively with minimum impact on other species, an understanding of habitat utilization by Norway rats is required. 3In this study, rat populations on farms in the north-east of England were monitored by radio-tracking and population counts before and after a single phase of habitat modification. Rats living near farm buildings utilized areas with high levels of cover; habitat modification reduced the survival rate and size of these rat populations. Rats living in field margins also preferred areas with high levels of cover, but they had significantly bigger home ranges than rats living near farm buildings and were largely unaffected by small-scale habitat management. 4Synthesis and applications. Our results indicate that habitat management near farm buildings has the potential to reduce the size of rat populations. As part of an integrated approach, this technique offers a way of reducing reliance on rodenticides. Habitat use by rats within the wider farm landscape suggests that land management practices have the potential to influence the size and distribution of rat populations; many game-rearing practices and environmental policies designed to create habitats for ,desirable' farm wildlife, inadvertently create desirable habitats for rats. [source] Hydrothermal crystallization of carbonate-containing hydroxyapatite coatings prepared by radiofrequency-magnetron sputtering methodJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Satoshi Nakamura Abstract Carbonate-containing hydroxyapatite (HA) films were prepared by low-temperature hydrothermal annealing from carbonate-containing calcium phosphate amorphous coatings on titanium substrates. The biocompatibility of the carbonate-containing HA layers was estimated by in vitro tests using simulated body fluid (SBF). Precursory amorphous coatings were deposited with rf-magnetron sputtering apparatus, using calcium phosphate glass target in Ar/CO2 atmosphere. The carbonate-containing HA coatings were successfully formed by the annealing at above 130°C for 20 h. On the basis of SEM observation, about 2-,m thickness films coated rigidly were durable enough for the hydrothermal treatment. The coating layer was revealed to consist of single phase of PO4, and OH, partially carbonated HA by XRD and IR analyses. Overgrowing of bone-like apatite layers on the carbonate-containing HA surfaces in the SBF implied that the obtained films acquired a sufficient osteoconductivity, while it was still unclear that activity was enhanced, compared to pure HA coatings. The low-temperature hydrothermal annealing method was effective for preparation of rigid HA coatings on titanium as well as modification of their chemical compositions. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Driving force in first-order phase transitions and its application to gas hydrate nucleation from a single phaseAICHE JOURNAL, Issue 9 2009Bernardo Carreón-Calderón Abstract Classical nucleation theories of general application are taken as starting point to analyze the driving force for multicomponent gas hydrate nucleation from a single homogeneous phase. It is shown that the ratio between the specific surface energy and the critical radius of nucleation has a single value irrespective of the analyzed driving force expression. From this result, two driving force expressions for multicomponent gas hydrate nucleation are derived in the context of the so-called generalized nucleation theory, and it is demonstrated that the driving force for gas hydrates can be estimated using the same information given for the determination of the incipient formation points of the dispersed phase from a saturated phase. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Bi2O3,MoO3 Binary System: An Alternative Ultralow Sintering Temperature Microwave DielectricJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Di Zhou Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi2O3,MoO3 binary system. All materials have ultralow sintering temperatures <820°C. Eight different xBi2O3,(1,x)MoO3 compounds between 0.2,x,0.875 were fabricated and the associated microwave dielectric properties were studied. The ,-Bi2Mo2O9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/°C, with a permittivity ,r=38 and Qf=12 500 GHz at 300 K and at a frequency of 6.3 GHz. The ,-Bi2Mo3O12 and ,-Bi2MoO6 compounds both have negative temperature coefficient values of TCF,,215 and ,,114 ppm/°C, with permittivities of ,r=19 and 31, Qf=21 800 and 16 700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi2O3,2.2MoO3 at 620°C for 2 h, a composite dielectric containing both , and , phase can be obtained with a near-zero temperature coefficient of frequency TCF=,13 ppm/°C and a relative dielectric constant ,r=35, and a large Qf,12 000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi2O3,MoO3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application. [source] Preparation and Electrical Properties of New Oxide Ion Conductors Ce6,xGdxMoO15,, (0.0,x,1.8)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Defeng Zhou A series of oxide ion conductors Ce6,xGdxMoO15,, (0.0,x,1.8) have been prepared by the sol,gel method. Their properties were characterized by differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), Raman, IR, X-ray photoelectron spectroscopy (XPS), and AC impedance spectroscopy. The XRD patterns showed that the materials were single phase with a cubic fluorite structure. The conductivity of Ce6,xGdxMoO15,, increases as x increases and reaches the maximum at x=0.15. The conductivity of Ce4.5Gd1.5MoO15,, is ,t=3.6 × 10,3 S/cm at 700°C, which is higher than that of Ce4.5/6Gd1.5/6O2,, (,t=2.6 × 10,3 S/cm), and the corresponding activation energy of Ce4.5Gd1.5MoO15,, (0.92 eV) is lower than that of Ce4.5/6Gd1.5/6O2,, (1.18 eV). [source] Effect of Processing Parameters on Physical Properties of Cadmium Stannate Thin Films Prepared by a Dip-Coating TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Radhouane Bel Hadj Tahar Thin films of dicadmium stannate spinel (Cd2SnO4) were deposited on glass substrates using a dip-coating technique. The films were transparent to visible light (90%) and electrically conductive. X-ray diffractometry showed that annealed films consisted of a single cubic spinel phase only when they were prepared from a solution with the composition of Cd:Sn = 2.5 and fired at a temperature of 400°,500°C. The Cd:Sn ratio, the firing temperature, and the post-deposition annealing sequence were crucial for the formation of a single phase, which is vital to obtain optimal optical and electrical properties. A resistivity as low as 3.3 × 10,4,·cm could be obtained after annealing. [source] Optimization of a gastrointestinal model applicable to the evaluation of bioaccessibility in fish feedsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2009Mariam Hamdan Abstract BACKGROUND: Although several types of in vitro digestibility assays have been applied to nutritional evaluation of feeds for aquatic organisms, all of them are based on the use of closed reactors and do not simulate the gastric phase of the digestion. Our objective was to evaluate the suitability of a gastrointestinal model based on the use of a digestion cell provided by a semi-permeable reaction chamber, which allows continuous removal of digestion products as they are produced. We tested the effects of some factors, like the inclusion of a gastric phase, reaction temperature or bile salts on the hydrolysis of feed proteins by fish enzymes. RESULTS: We found that the most suitable operational conditions to simulate the digestion process must include a short acid pre-digestion as well as the use of bile salts in the reaction mixture. Acid pre-digestion resulted in a significant increase in the liberation of amino acids which represented more than twice that measured when using a single phase. The addition of two bile salts (45 µmol L,1 sodium taurocholate + chenodesoxycolate) resulted in almost a threefold increase in the hydrolysis of feed protein. The use of the described open system also allows the evaluation of carbohydrate hydrolysis as well as determination of residual undigested matter, in a similar manner to that carried out in ruminants with the DAISY system. CONCLUSION: Results suggest the system can be a very suitable model for evaluation of bioaccessibility in fish feeds. Copyright © 2009 Society of Chemical Industry [source] Cardiac diffusion MRI without motion effectsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Jiangang Dou Abstract We present a method for diffusion tensor MRI in the beating heart that is insensitive to cardiac motion and strain. Using a stimulated echo pulse sequence with two electrocardiogram (ECG) triggers, diffusion-encoding bipolar gradient pulses are applied at identical phases in consecutive cardiac cycles. In this experiment, diffusion is encoded at a single phase in the cardiac cycle of less than 30 ms in duration. This encoding produces no phase shifts for periodic motion and is independent of intervening strains. Studies in a gel phantom with cyclic deformation confirm that by using this sequence we can map the diffusion tensor free of effects of cyclic motion. In normal human subjects, myocardial diffusion eigenvalues measured with the present method showed no significant change between acquisitions encoded at maximum contractile velocity (peak) vs. at myocardial standstill (end-systole), demonstrating motion independence of in vivo diffusion measurements. Diffusion tensor images acquired with the present method agree with registered data acquired with a previous cardiac diffusion MRI method that was shown to be valid in the normal heart, strongly supporting the validity of MRI diffusion measurement in the beating heart. Myocardial sheet and fiber dynamics measured during systole showed that normal human myocardial sheet orientations tilt toward the radial during systole, and fiber orientations tilt toward the longitudinal, in qualitative agreement with previous invasive studies in canines. These results demonstrate the technique's ability to measure myocardial diffusion accurately at any point in the cardiac cycle free of measurable motion effect, as if the heart were frozen at the point of acquisition. Magn Reson Med 48:105,114, 2002. © 2002 Wiley-Liss, Inc. [source] XMM,Newton observations of warm absorbers in PG quasarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004C. E. Ashton ABSTRACT We present XMM,Newton European Photon Imaging Camera observations of warm absorbers in the quasars PG 1114+445 and PG 1309+355, both of which exhibit evidence for absorption by warm material in the line of sight. We find the absorption in PG 1114+445 to be in two phases, a ,hot' phase with a log ionization parameter, ,, of 2.57, and a ,cooler' phase with log ,= 0.83; an unresolved transition array (UTA) of M-shell iron is observed in the cooler phase. The absorption in this quasar is similar to that observed in the Seyfert 1 NGC 3783. The absorption in PG 1309+355 consists of a single phase, with log ,= 1.87. The absorbing gas lies at distances of 1018,1022 cm from the continuum radiation sources in these active galactic nuclei (AGN), which suggests that it could originate in a wind emanating from a molecular torus. We derive distances assuming that these X-ray warm absorbers have the same velocity as the ultraviolet warm absorbers observed in these quasars. The distances to the warm absorbers from the central continuum source scale approximately with the square root of the AGN ionizing luminosity, a result consistent with the warm absorber originating as a torus wind. The kinetic luminosities of these outflowing absorbers represent insignificant fractions (<10,3) of the energy budgets of the AGN. [source] Electronic structure of TbBa2Cu3O7PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010Maciej, uszczek Abstract The full-potential linearized augmented plane wave (FP-LAPW) method was used for spin-polarized electronic structure calculations of stoichiometric TbBa2Cu3O7 (Tb123), not synthesized as a single phase yet. The generalized gradient approximation plus Hubbard correction (GGA,+,U) was employed for Tb4f electrons to prevented fractional occupation of states at Fermi level and hybridization with other electrons. The determined band structure is Y123-like with the metallic character as in the other superconducting R123 (R,=,rare earth). The presented results indicate that strong on-site spin moment of Tb could not effectively influence the neighbours and the induced magnetic interactions in the system are weak (CuO planes) or negligible (BaO planes and CuO chains). This appears to be the repercussion of the ,size effect' due to relatively small Tb+3 ionic radius. The predicted weak influence of magnetic moments of Tb on CuO states in the assumed (hypothetical) Fermi liquid phase of TbBa2Cu3O7 could favour the rise of superconductivity in this system. [source] Deficiency effects upon the physical properties of Pr0.8Sr0.2MnO3 manganite oxidePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006W. Cheikh-Rouhou Koubaa Abstract The effects of deficiency in praseodymium and in strontium upon the magnetic and magneto-transport properties of lacunar Pr0.8,x,xSr0.2MnO3 and Pr0.8Sr0.2,x,x MnO3 oxides have been investigated. Our synthesized samples have been elaborated using the conventional solid state reaction at high temperature. Crystallographic studies show that all our samples are single phase and crystallize in the orthorhombic system with Pnma space group. The praseodymium deficient samples Pr0.8,x,xSr0.2MnO3 exhibit three different regimes in the resistivity variation as a function of praseodymium deficiency amount: (i) at low concentration (0 , x , 0.1), a semiconductor behaviour is observed in the whole temperature range, (ii) at an intermediate amount (x = 0.15), a semiconductor-metallic transition is followed by a metallic-semiconductor one with decreasing temperature, and finally (iii) at x = 0.2 and 0.25, a metallic behaviour is observed below TC, whereas all the strontium deficient samples exhibit a semiconductor behaviour in the whole temperature range. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effect of nitrogen insertion on the magnetic and structural properties of Sm2,xGdxFe17 alloys (0 , x , 2)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. S. Ben Kraiem Abstract The effect of nitrogen insertion on the structural and magnetic properties of Sm2,xGdxFe17Ny compounds (x = 0-2) has been investigated. X-ray diffraction patterns at room temperature show that all our synthesized samples are single phase and crystallize in the rhombohedral Th2Zn17 -type structure with very small amount of impurity. Nitrogen insertion leads to a monotonic increase in the unit cell volume, it leads also to an increase in the Curie temperature Tc from 425 K for SmGdFe17 to 760 K for SmGdFe17N3. Moreover, the nitrogen insertion increases the saturated magnetization Ms. Ms increases from 17.9 µB/mole for SmGdFe17 to 32.7 µB/mole for SmGdFe17N3. X-ray diffraction measurements on magnetically aligned powder samples of Sm2,xGdxFe17Ny reveal a change in the easy magnetization direction from planar before nitrogen insertion to the c-axis after nitrogen insertion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Praseodymium deficiency effects on the physical properties of Pr1.2,x,xSr1.8Mn2O7 bilayer manganese oxidesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. Triki Abstract The praseodymium deficiency effects on the structural, magnetic and electrical properties of the lacunar bilayers manganese oxides Pr1.2,x,xSr1.8Mn2O7 (0 , x , 0.15) were studied. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the tetragonal structure with I4/mmm space group. All our samples exhibit a paramagnetic-ferromagnetic transition on cooling. The praseodymium deficiency leads to a decrease of the Curie temperature. Resistivity measurements as a function of temperature show that only the parent sample Pr1.2Sr1.8Mn2O7 exhibits a semiconducting-metallic transition with decreasing temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation of LaCuOS by solid phase reaction method using La2S3 and CuO starting materialsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006H. Matsushita Abstract We have developed the best method for synthesizing a single phase of LaCuOS, not using three starting materials, La2O3, La2S3 and Cu2S. If this method is possible, the LaCuOS thin film must be grown by the sputtering method with only two targets. The results of X-ray diffraction and diffuse reflective spectroscopy of LaCuOS samples prepared from the combination of La2O3+La2S3+4CuS and La2S3+2CuO at 600 °C for 6 hours under a vacuum show that the single phase of LaCuOS with a band gap of about 3.1 eV is obtained at lower temperature. The results on powder formation suggests a possibility that LaCuOS thin films can be prepared by the sputtering method by using La2S3 and CuO targets, by means of improving these preparation conditions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermally crosslinked polymer blends of polyurethane and chlorobutyl elastomers (sulfur cure)POLYMER INTERNATIONAL, Issue 5 2001B Khatua Abstract Blends of polyurethane with chlorobutyl elastomer prepared by three different blending techniques have been studied in the entire composition range. The properties of the blends showed that the blending technique plays an important role in determining the blend properties. IR spectral analysis revealed that interchain crosslinking is possible in this blend system upon heat treatment. Thermal stability of blends prepared by preheating the preblend was increased and the degradation process was retarded. Extractability of the single phase, by solvent, was also limited significantly in the case of the preheated preblended sample, probably due to phase adhesion. © 2001 Society of Chemical Industry [source] Corrosion inhibition of carbon steel under two-phase flow (water-petroleum) simulated by turbulently agitated systemTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2008Qasim J. M. Slaiman Abstract The corrosion of carbon steel in single-phase (water with 0.1N NaCl) and two immiscible phases (kerosene-water) using turbulently agitated system was investigated. The experiments were carried out for Reynolds number (Re) range of 38 000 to 95 000 using circular disc turbine agitator at 40°C. In two-phase system, test runs were carried out in aqueous phase (water) concentrations of 1% vol, 5% vol, 8% vol, and 16.4% vol mixed with kerosene at various Re. The effect of Re, percent of dispersed phase, dispersed droplet diameter, and number of droplets per unit volume on the corrosion rate were investigated and discussed. Test runs were carried out using two types of inhibitors: sodium nitrite of concentrations 20, 40, and 60 ppm and sodium hexapolyphosphate of concentrations 485, 970, and 1940 ppm in a solution containing 8% vol aqueous phase (water) mixed with kerosene (continuous phase) at 40°C for the whole range of Re. It was found that increasing Re increased the corrosion rate and the presence of water enhanced the corrosion rate by increasing the solution electrical conductivity. For two-phase solution containing 8% vol and 16% vol of water, the corrosion rate was higher than single phase (100% vol water). The main parameters that play the major role in determining the corrosion rate in two phases were concentration of oxygen, solution electrical conductivity, and the interfacial area between the two phases (dispersed and continuous). Sodium nitrite and sodium hexapolyphosphate were found to be efficient inhibitors in two-phase solution for the investigated range of Re. On a étudié la corrosion de l'acier au carbone dans des conditions monophasiques (eau avec 0,1N de NaCl) et diphasiques immiscibles (kérosène-eau) à l'aide d'un système agité turbulent. Les expériences ont été menées pour une gamme de nombre de Reynolds (Re) de 38000 à 95000, avec un agitateur de type Rushton à 40°C. Des tests pour le système diphasique ont été effectuées dans des concentrations de phase aqueuse (eau) de 1%, 5%, 8% et 16,4% en volume, mélangée à du kérosène pour différentes valeurs de Re. L'effet du nombre de Reynolds (Re), le pourcentage de la phase dispersée, le diamètre des gouttelettes dispersées et le nombre de gouttelettes par unité de volume sur le taux de corrosion a été étudié et analysé. Les essais ont été réalisés avec deux types d'inhibiteurs: du nitrite de sodium à des concentrations de 20, 40 et 60 ppm et de l'hexapolyphosphate de sodium à des concentrations de 485, 970 et 1940 ppm dans une solution contenant 8% en volume de phase aqueuse (eau) mélangée à du kérosène (phase aqueuse) à 40°C pour la gamme complète de Re. On a trouvé que l'augmentation du Re augmentait le taux de corrosion et que la présence d'eau améliorait le taux de corrosion en augmentant la conductivité électrique des solutions. Pour la solution diphasique contenant 8% et 16% en volume d'eau, le taux de corrosion est plus grand qu'en monophasique (100% en volume d'eau). Les principaux paramètres qui jouent un rôle majeur dans la détermination du taux de corrosion dans la solution diphasique sont la concentration d'oxygène, la conductivité électrique de la solution et l'aire interfaciale entre les deux phases (dispersée et continue). On a trouvé que le nitrite de sodium et l'hexapolyphosphate étaient des inhibiteurs efficaces dans la solution diphasique pour la gamme de Re étudié. [source] Neutron and electron diffraction studies of La(Zn1/2Ti1/2)O3 perovskiteACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2006Yi Hu The crystallography and microwave dielectric properties of La(Zn1/2Ti1/2)O3 (LZT) ceramics prepared via the mixed-oxide route were investigated in this study. While samples were largely single phase, small amounts of ZnO impurity were detected in sintered pellets. Observed reflections in electron and neutron diffraction patterns indicate that the symmetry of LZT is P21/n. The B site is ordered on {110} or pseudocubic {111}, but the presence of the pseudocubic (111) reflection is in itself insufficient to indicate the existence of such order. Rietveld refinements of the neutron diffraction data yield an excellent fit for such a model. The structure is highly twinned, with variants related through common {211} composition planes and 90° rotations about ,011,. The microwave dielectric properties measured were ,r = 34, Qf = 36,090 and ,f = ,70,MK,1. [source] Vapor Condensation Heat Transfer in a Thermoplate Heat ExchangerCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007J. Mitrovic Abstract The heat transfer and pressure drop in a thermoplate heat exchanger operating as a condenser have been investigated experimentally. In order to separate the heat transfer resistances in the condensation process, the single phase forced convection has been studied using distilled water and Marlotherm oil in the thermoplate and correlations developed for the Nusselt number and the friction factor. For the condensation experiments, an apparatus has been constructed comprising two identical condensers composed of the same thermoplate type as employed in the single phase experiments. Isopropanol is used as a test fluid at pressures below atmospheric pressure. The heat transfer resistances in the condensation experiments are separated and expressions for the condensation heat transfer and pressure drop are developed with the aid of the results obtained in the single phase studies. [source] | ||||||||||||||||||||||