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Stoichiometric
Terms modified by Stoichiometric Selected AbstractsBacterial energetics, stoichiometry, and kinetic modeling of 2,4-Dinitrotoluene biodegradation in a batch respirometerENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2004Chunlong Zhang Abstract A stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, ,max, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium. [source] Surface Physiochemistry Affects Protein Adsorption to Stoichiometric and Silicate-Substituted Microporous Hydroxyapatites,ADVANCED ENGINEERING MATERIALS, Issue 4 2010Katharina Guth An important factor in the bioactivity and success of a bone-graft substitute is the nature of the adsorbed protein layer, which plays a vital role in orchestrating cell attachment and development through the presence of adhesion proteins such as fibronectin (Fn) and vitronectin (Vn). In this study, microporous hydroxyapatite (HA) and silicate-substituted hydroxyapatite (SA) discs with matched porosity and surface morphology are developed to mimic the topography found in commercial bone-graft substitutes in order to identify whether the introduction of microporosity and associated surface roughness eliminates the beneficial effect that silicate substitution has on protein adsorption. The introduction of microporosity does not abolish the relative enrichment of the protein layer that is adsorbed to the microporous SA discs, as opposed to HA, but appears to accelerate it. Fibronectin and Vn adsorption in a range of competitive environments at physiological temperatures confirm that the microporous SA discs have a greater affinity for Fn and Vn compared with HA, suggesting differences in the mechanisms behind the surface affinity to SA. Thus, development of a surface protein layer on SA and HA is likely to be dependent on the nature of the local protein environment and a combination of factors that are associated with the addition of silicate: the surface charge, the nature of the ionic species at the interface and the resultant hydrophilicity of the surface. Total protein adsorption is not found to be a good indicator of potential implant performance, particularly at early time points. [source] Formation and Densification Behavior of MgAl2O4 Spinel: The Influence of Processing ParametersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Ibram Ganesh Different types of dense stoichiometric and nonstoichiometric magnesium aluminate (MgAl2O4) spinel (MAS) ceramics were prepared following a conventional double-stage firing process using different commercially available alumina and magnesia raw materials. Stoichiometric, magnesia-rich, and alumina-rich spinels were sintered at 1500°,1800°C for 1,2.5 h. The influence of the different processing parameters (average particle size, degree of spinel phase, green density, mass of the powder compact, sintering temperature, holding time at the peak temperature, and starting composition) on the densification behavior of MAS was assessed by measuring the bulk density, apparent porosity, and water absorption capacity, and microstructural observations. Most of the MAS compositions tested exhibited excellent sintering properties. [source] Rhodium-Mediated Decarboxylative Conjugate Addition of Fluorinated Benzoic Acids: Stoichiometric and Catalytic Transformations,ANGEWANDTE CHEMIE, Issue 36 2009Zhong-Ming Sun Dr. Je nach Bisphosphanligand entsteht bei der Decarboxylierung von 2,6-difluorierten Benzoesäuren mit einem RhI -Katalysator in Gegenwart eines Acrylesters oder Acrylamids bevorzugt das konjugierte Addukt 1 oder das Produkt der Heck-Mizoroki-Arylierung (2; Binap=2,2,-Bis(diphenylphosphanyl)-1,1,-binaphthyl, diop=4,5-Bis(diphenylphosphanylmethyl)-2,2-dimethyl-1,3-dioxolan). [source] ChemInform Abstract: Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis, Structure, and Activity in Stoichiometric and Catalytic C,C Bond-Forming Reactions of Alkyl Halides.CHEMINFORM, Issue 32 2009Oleg Vechorkin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Stoichiometric and Catalytic Reductive Aldol Cyclizations of Alkynediones Induced by Stryker,s Reagent.CHEMINFORM, Issue 13 2005Pauline Chiu Abstract For Abstract see ChemInform Abstract in Full Text. [source] Separating the influence of resource ,availability' from resource ,imbalance' on productivity,diversity relationshipsECOLOGY LETTERS, Issue 6 2009Bradley J. Cardinale Abstract One of the oldest and richest questions in biology is that of how species diversity is related to the availability of resources that limit the productivity of ecosystems. Researchers from a variety of disciplines have pursued this question from at least three different theoretical perspectives. Species energy theory has argued that the summed quantities of all resources influence species richness by controlling population sizes and the probability of stochastic extinction. Resource ratio theory has argued that the imbalance in the supply of two or more resources, relative to the stoichiometric needs of the competitors, can dictate the strength of competition and, in turn, the diversity of coexisting species. In contrast to these, the field of Biodiversity and Ecosystem Functioning has argued that species diversity acts as an independent variable that controls how efficiently limited resources are utilized and converted into new tissue. Here we propose that all three of these fields give necessary, but not sufficient, conditions to explain productivity,diversity relationships (PDR) in nature. However, when taken collectively, these three paradigms suggest that PDR can be explained by interactions among four distinct, non-interchangeable variables: (i) the overall quantity of limiting resources, (ii) the stoichiometric ratios of different limiting resources, (iii) the summed biomass produced by a group of potential competitors and (iv) the richness of co-occurring species in a local competitive community. We detail a new multivariate hypothesis that outlines one way in which these four variables are directly and indirectly related to one another. We show how the predictions of this model can be fit to patterns of covariation relating the richness and biomass of lake phytoplankton to three biologically essential resources (N, P and light) in a large number of Norwegian lakes. [source] Heteroleptic Guanidinate- and Amidinate-Based Complexes of Hafnium as New Precursors for MOCVD of HfO2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010Ke Xu Abstract The synthesis and characterization of four new heteroleptic complexes [Hf{,2 -(iPrN)2CNMe2}2Cl2] (1), [Hf{,2 -(iPrN)2CNMe2}2Me2] (2), [Hf{,2 -(iPrN)2CMe}2Cl2] (3), and [Hf{,2 -(iPrN)2CMe}2Me2] (4) are reported. All the complexes were characterized by spectroscopic methods, while compounds 1,3 were further examined by single-crystal X-ray diffraction, revealing that the complexes are monomers with the hafnium center in a distorted octahedral geometry. The thermal properties of the chlorine-free complexes (2, 4) were examined to determine their suitability for metalorganic chemical vapor deposition (MOCVD) applications, and compound 2 showed good volatility and thermal stability. On the basis of these results, compound 2 was selected for MOCVD of HfO2 with oxygen as oxidant. Depositions were carried out on Si(100) substrates in the temperature range 300,700 °C. The as-deposited HfO2 films crystallized in the monoclinic phase at temperatures above 500 °C, and the composition analysis determined by Rutherford back-scattering (RBS) and X-ray photoelectron spectroscopy (XPS) revealed that the films were stoichiometric and free of carbon. Thus, alkylguanidinatohafnium complex 2 is a promising precursor for growing HfO2 films in a wide temperature range with the desired stoichiometry, because of its adequate volatility, sufficient temperature window between vaporization and decomposition, as well as its ability to decompose cleanly in the presence of oxygen. [source] Structural Studies of the O-Chain Polysaccharide from Plesiomonas shigelloides Strain 302,73 (Serotype O1)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2008Giuseppina Pieretti Abstract Plesiomonas shigelloides is a Gram-negative bacterium belonging to the Enterobacteriaceae family. It has been found in an aquatic environment in the tropical and subtropical regions and is responsible for many gastrointestinal infections in humans, which take place from drinking untreated water or eating uncooked shellfish. Plesiomonas shigelloides has also been reported to provoke extraintestinal infections such as meningitis and bacteremia in immunocompromised adults and neonates. Despite the emerging importance of this pathogenic microorganism, only three different O-antigens have been characterised so far. The structure of the O-chain of the lipopolysaccharide (LPS) from Plesiomonasshigelloides strain 302,73 (serotype O1) was determined by chemical analysis, 1D and 2D NMR spectroscopy and MALDI-TOF mass spectrometry. The polysaccharide was constituted by a linear pentasaccharidic repeating unit as follows: ,3)-,- L -PneNAc4OAc(1,4)-,- L -FucNAc(1,4)-,- L -FucNAc(1,4)-,- L -FucNAc(1,3)-,- D -QuiNAc4NHb(1, (PneNAc = 2-acetamido-2,6-dideoxy-talose, Hb = (S)-3-hydroxybutanoyl) PneNAc O -acetylation was not stoichiometric and was found to be about 75,%. The position of the O -acetyl group and the amount of acetylation were deduced by NMR spectroscopic analysis. All the monosaccharides included in the repeating unit were deoxyamino sugars, which most probably, together with the presence of O -acetyl groups, were responsible for the recovery of the LPS in the phenol layer of the phenol/water extract of dried bacteria cells.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Chromokinetics of metabolic pathwaysFEBS JOURNAL, Issue 13 2004Jörg W. Stucki Some methods to study and intuitively understand steady-state flows in complicated metabolic pathways are discussed. For this purpose, a suitable decomposition of complex metabolic schemes into smaller subsystems is used. These independent subsystems are then interpreted as basic colors of a chromatic coloring scheme. The mixture of these basic colors allows an intuitive picture of how a steady state in a metabolic pathway can be understood. Furthermore, actions of drugs can be more easily investigated on this basis. An anaerobic variant of pyruvate metabolism in rat liver mitochondria is presented as a simple example. This experiment allows measurement of the percentage that each basic color contributes to the steady states resulting from different experimental conditions. Possible implementations of existing algorithms and rational design of new drugs are discussed. A mathematica program, based on a new algorithm for finding all basic colors of stoichiometric networks, is included. [source] Pulsed Vapor-Liquid-Solid Growth of Antimony Selenide and Antimony Sulfide NanowiresADVANCED MATERIALS, Issue 31 2009Ren Bin Yang Antimony sulfide and antimony selenide nanowires are prepared in an original pulsed vapor-liquid-solid growth mode. The molecular precursors are not mixed together in the gas phase; therefore the chemical reaction forming the solid only occurs in the gold catalyst. The material is stoichiometric and highly crystalline. Wires consisting of Sb2S3 and Sb2Se3 segments can be obtained with the same process. [source] Hydrogen as burner fuel: modelling of hydrogen,hydrocarbon composite fuel combustion and NOx formation in a small burnerINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2005Mustafa Ilbas Abstract The objective of this work is to investigate numerically the turbulent non-premixed hydrogen (H2) and hydrogen,hydrocarbon flames in a small burner. Numerical studies using Fluent code were carried out for air-staged and non-staged cases. The effects of fuel composition from pure hydrogen to natural gas (100%H2, 70%H2+30%CH4, 10%H2+90%CH4, and 100%CH4) were also investigated. The predictions are validated and compared against the experimental results previously obtained and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation equations and reaction equations governing the problem. Although, three different turbulence models were tested, the standard k,, model was used for the modelling of the turbulence phenomena in the burner. The temperature and major pollutant concentrations (CO and NOx) distributions are in good agreement with the existing experimental results. Air staging causes rich and lean combustion regions thus lower NOx emissions through the combustor exit. Blending hydrogen with methane causes considerable reduction in temperature levels and thus NO emissions. Increasing the mixture ratio from stoichiometric to leaner mixtures also decreases the temperature and thus NO emissions. Hydrogen may be considered a good alternative fuel for burners, as its use reduces the emission of pollutants, and as it is a renewable synthetic fuel. Copyright © 2005 John Wiley & Sons, Ltd. [source] A Simple and Convenient Method for Epoxidation of Olefins without Metal CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2003Markus Klawonn Abstract An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non-activated olefins give epoxides in high yields and good selectivity at ambient conditions. [source] Sensitivity analysis in oxidation ditch modelling: the effect of variations in stoichiometric, kinetic and operating parameters on the performance indicesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2001A Abusam Abstract This paper demonstrates the application of the factorial sensitivity analysis methodology in studying the influence of variations in stoichiometric, kinetic and operating parameters on the performance indices of an oxidation ditch simulation model (benchmark). Factorial sensitivity analysis investigates the sensitivities in a region rather than in a point. Hence, it has the advantage of giving more information about parameter interactions (non-linearity). Short-term results obtained have shown the following. The index AE is not significantly affected by variations in the value of parameters of the activated sludge model (ASM) No 1. The index TSP is greatly influence by heterotrophic yield (YH), heterotrophic decay (bH) and specific hydrolysis (kh) and the index EQ is dominated by YH, Monod coefficient (KS), bH, kh, anoxic condition correction factors (,g, ,h), hydrolysis half-saturation coefficient (KX), autotrophs maximum specific growth rate (µA) and ammonia half-saturation coefficient (KNH). Furthermore, the index EQ has been shown to be very sensitive to parameter interactions, at certain regions. © 2001 Society of Chemical Industry [source] Modeling and simulation of the sequencing batch reactor at a full-scale municipal wastewater treatment plantAICHE JOURNAL, Issue 8 2009Bing-Jie Ni Abstract In this work, we attempted to modify the Activated Sludge Model No.3 and to simulate the performance of a full-scale sequencing batch reactor (SBR) plant for municipal wastewater treatment. The long-term dynamic data from the continuous operation of this SBR plant were simulated. The influent wastewater composition was characterized using batch measurements. After incorporating all the relevant processes, the sensitivity of the stoichiometric and kinetic coefficients for the model was thoroughly analyzed prior to the model calibration. The modified model was calibrated and validated with the data from both batch- and full-scale experiments. Model predictions were compared with routine data in terms of chemical oxygen demand, NH4+ -N and mixed liquid volatile suspended solids in the SBR, combined with batch experimental data under different conditions. The model predictions match the experimental results well, demonstrating that the model is appropriate to simulate the performance of a full-scale wastewater treatment plant even operated under perturbation conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Excess silica in omphacite and the formation of free silica in eclogiteJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2007H. W. DAY Abstract Silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite. However, mechanisms other than exsolution might produce free silica, and the possible mechanisms depend in part on the nature and definition of excess silica. ,Excess' silica may occur in both stoichiometric and non-stoichiometric pyroxene. Although the issue has been debated, we show that all common definitions of excess silica in non-stoichiometric clinopyroxene are internally consistent, interchangeable, and therefore equivalent. The excess silica content of pyroxene is easily illustrated in a three-component, condensed composition space and may be plotted directly from a structural formula unit or recalculated end-members. In order to evaluate possible mechanisms for the formation of free silica in eclogite, we examined the net-transfer reactions in model eclogites using a Thompson reaction space. We show that there are at least three broad classes of reactions that release free silica in eclogite: (i) vacancy consumption in non-stoichiometric pyroxene; (ii) dissolution of Ti-phases in pyroxene or garnet; (iii) reactions between accessory phases and either pyroxene or garnet. We suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility, but also of titanium solubility, and the possible roles of accessory phases and inclusions on the balance of free silica. [source] Bile acid sequestrants based on cationic dextran hydrogel microspheres.JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2001Abstract Cationic dextran hydrogel microspheres with pendant quaternary ammonium groups having alkyl substituents (C2,C12) at quaternary nitrogen were synthesized. The in vitro sorption of sodium salts of four bile acids (glycocholic, cholic, taurocholic, and deoxycholic acids) with these hydrogels was studied as a function of substituent alkyl chain length and bile acid hydrophobicity. Sorption experiments were performed in phosphate buffer solutions (pH 7.4) containing one bile salt (individual sorption) or mixtures of several bile salts (competitive sorption). Parameters for individual sorption were calculated taking into consideration the stoichiometric and cooperative binding of bile salts to oppositely charged polymer hydrogels. The results show that the increase in the length of the alkyl chain of the substituent leads to an increase in both ionization constant K0 and overall stability constant of binding K, but decreases the cooperativity parameter u. The competitive sorption studies indicate that the hydrogels display a good affinity for both dihydroxylic and trihydroxylic bile salts. The molar ratio of maximum amounts bound for the two types of bile acid is 2 to 1, which is much lower than those reported for other cationic polymers recommended as bile acid sequestrants. The binding constants for the sorption of bile salts by some dextran hydrogels are 20,30 times higher than those obtained for cholestyramine under similar sorption conditions. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:681,689, 2001 [source] Formation and Densification Behavior of MgAl2O4 Spinel: The Influence of Processing ParametersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Ibram Ganesh Different types of dense stoichiometric and nonstoichiometric magnesium aluminate (MgAl2O4) spinel (MAS) ceramics were prepared following a conventional double-stage firing process using different commercially available alumina and magnesia raw materials. Stoichiometric, magnesia-rich, and alumina-rich spinels were sintered at 1500°,1800°C for 1,2.5 h. The influence of the different processing parameters (average particle size, degree of spinel phase, green density, mass of the powder compact, sintering temperature, holding time at the peak temperature, and starting composition) on the densification behavior of MAS was assessed by measuring the bulk density, apparent porosity, and water absorption capacity, and microstructural observations. Most of the MAS compositions tested exhibited excellent sintering properties. [source] Effects of Oxidation Curing and Sintering Additives on the Formation of Polymer-Derived Near-Stoichiometric Silicon Carbide FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Lifu Chen The effects of oxygen pick-up and sintering additives on the formation of silicon carbide (SiC) fibers from polyaluminocarbosilane are studied. It has been found that the strict control of oxygen pick up during the oxidation curing is essential to produce near-stoichiometric SiC fibers. When the molar ratio of oxygen to excess carbon in the pyrolyzed fibers (SiCxOy) is slightly over 1 (O/CExcess=y/(x,1)>1), the excess carbon is eliminated during the subsequent sintering as CO and CO2 as a result of the decomposition of SiCxOy; the remaining oxygen is removed as SiO and CO vapor, leaving near-stoichiometric SiC as the residue. However, with still increasing oxygen pick up, the final ceramic fibers become more porous and rich in silicon. The evolution of CO, CO2, and SiO generates high porosity in the absence of a sintering additive, leading to low fiber density. The inter-connected and open porosity favors the formation of CO. In contrast, for the fibers containing aluminum (Al) or Al/B sintering additives, the pores are much smaller and essentially closed, favoring the formation of CO2. Therefore, after sintering at 1800°C, the fibers without sintering additives contain excess silicon, while those with sintering additives are near stoichiometric. Al is beneficial to the densification but it alone cannot produce fibers of high density. When B is added in addition to Al, the fibers can be sintered to nearly full density. [source] To be or not to be what you eat: regulation of stoichiometric homeostasis among autotrophs and heterotrophsOIKOS, Issue 5 2010Jonas Persson Homeostasis of element composition is one of the central concepts of ecological stoichiometry. In this context, homeostasis is the resistance to change of consumer body composition in response to the chemical composition of consumer's food. To simplify theoretical analysis, it has generally been assumed that autotrophs exhibit flexibility in their composition, while heterotrophs are confined to a constant (strictly homeostatic) body composition. Yet, recent studies suggest that heterotrophs are not universally strictly homeostatic. We examined the degree to which autotrophs and heterotrophs regulate stoichiometric homeostasis (P:C, N:C, N:P, or %P and %N). We conducted a quantitative review and meta-analysis using 132 datasets extracted from 57 literature sources which examined the dependence of organismal stoichiometry on resource stoichiometry. Among individual datasets, there was a wide range of responses from strictly homeostatic to non-homeostatic. Even within heterotrophic organisms, varying levels of homeostasis were observed. Comparing the degree of homeostasis between organisms based on large-scale habitat types using meta-analysis indicated some significant differences between groups. For example, aquatic macroinvertebrates were significantly more homeostatic in terms of P:C than terrestrial invertebrates. Our meta-analysis also confirmed that, with regard to N:P, heterotrophs are significantly more homeostatic than autotrophs. Furthermore, our analysis indicated that the homeostasis parameter 1/H, despite being a potentially useful predictive metric, has to be utilized with caution since it oversimplifies some important aspects of the responses of organisms to elemental imbalances. This critical evaluation of stoichiometric homeostasis contributes to a better understanding of many food-web interactions, which are commonly driven by elemental imbalances between consumers and their resources. [source] Electronic structure of GaN(0001)-2 × 2 thin films grown by PAMBEPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2008R. Gutt Abstract Gallium nitride thin films were grown on silicon carbide (0001) by plasma-assisted molecular beam epitaxy (PAMBE). The samples were cooled down in nitrogen plasma and characterized in situ by reflection high energy electron diffraction (RHEED), photoelectron spectroscopy (XPS/UPS), and atomic force microscopy (AFM) revealing stoichiometric and smooth GaN films virtually free of contaminations. We present valence band data obtained by UPS with strong emission from surface states inside the fundamental band gap. These states and the observed 2 × 2 surface reconstruction are highly sensitive towards residual molecules. Once these surface states have disappeared the original state could not be recovered by surface preparation methods underlining the necessity of in situ investigations on as-grown surfaces. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Blue-shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometryPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Toshihiro Moriga Abstract The perovskite-type oxynitride LaTiO2N was prepared by heating an oxide precursor at 950 °C for 5 hours under NH3 atmosphere at a flow rate of 1 dm3/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)2.9, with a reddish orange color. The oxynitride was successively annealed at 950 °C for 3 hours under a NH3 atmosphere at flow rates of 50 cm3/min, 30 cm3/min and 10 cm3/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)2.8 through green-yellow LaTi(O0.93N0.07)2.9 to light-blue LaTi(O0.98N0.02)2.9 in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green-yellow, to 3.44 eV for the light-blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue-shift of the absorption edge. DV-X, calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of the oxygen nonstoichiometry on the structure and magnetic properties of Nd2CoMnO6+, double perovskitesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2007A. P. Sazonov Abstract The properties of Nd2CoMnO6+, (, up to 0.12) were investigated by means of neutron powder diffraction and magnetization measurements. It is found that the samples exhibit partial ordering of Co and Mn ions which strongly affects the magnetic properties. Ionic disorder increases with the oxygen content. According to neutron diffraction the stoichiometric and nonstoichiometric samples show ferromagnetic components which decreases as the oxygen content increases. The magnetization study of the strongly oxidized sample reveals a metamagnetic behavior. It is assumed that metamagnetism results from clusters with short-range antiferromagnetic order. Enhancement of the oxygen content leads to a conversion of Co2+ into low spin Co3+ and the appearance of a cationic vacancy which destroys the ionic order and stabilizes the overall antiferromagnetic behavior. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-quality ZnO epilayers grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004Hiroyuki Kato Abstract High-quality ZnO epilayers have been grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy. With increasing O/Zn flux ratio from the stoichiometric to the O-rich, the growth mode changed from three- to two-dimensional growth and the line widths of (0002) and (10,10) ,-rocking curves showed dramatic narrowing from 471 to 42 arsec and from 1635 to 46 arcsec, respectively. These values are narrower compared to those of ZnO on sapphire and also those of device-grade MOCVD-grown GaN. Moreover, A-, B-excitons (FEA, FEB), and the n = 2 state of FEA at 3.378, 3.393, and 3.424 eV, respectively, were clearly observed in the low-temperature (4.2 K) photoluminescence spectrum of ZnO grown under O-rich flux conditions. Our results show that growth under high O-rich flux conditions is required to produce high-quality Zn-polar ZnO films. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of CuInS2 crystals from melt and their propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006N. Satoh Abstract CuInS2 crystals are grown from the melt with the typical compositions which are stoichiometric, In2S3 and Cu2S excess ones and the effect of the melt composition on the melt growth is examined. Large grain size crystals are grown for the melt compositions except the case of Cu2S excess one. It is found that a small amount of CuIn5S8 is precipitated in In2S3 excess crystals by forming thin film layers in the bulk. From electrical conductivity and photo-luminescence (PL) spectra of the grown crystals, predominant native point defects characterizing their semi-conducting properties are discussed. As a result, it is suggested that native vacancy and the interstitial Cu play an important roles and a tentative band-diagram is proposed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical properties of carbon doped EuB6PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006M. Bat'kovį Abstract We report results of electrical resistivity and tunnelling spectroscopy studies of carbon doped EuB6 showing a colossal magnetoresistance effect. Performed tunnelling spectroscopy studies confirm a metallic-like nature of the system. The electrical resistivity studies reveal, it is a spin-disorder scattering that dominates in the temperature region 10.3,20 K and the magnetic phase transition temperature is Tc = 4.1 K. Due to similarities of the temperature dependence of the resistivity with ones reported for stoichiometric and lanthanum substituted EuB6, the resistivity behavior in the intermediate temperature region is expected to be strongly influenced by the formation of magnetic polarons. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of Sb-doped CuInS2 crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003H. Komaki Abstract CuInS2 semiconductor crystals were successfully grown by a hot-press (HP) method at 400,700,°C for 1,h at growth pressures from 10 to 100 MPa. The samples were 20 mm in diameter. The samples grown at 700,°C were found to be of chalcopyrite structure, nearly stoichiometric and n-type by means of X-ray diffraction, electron probe microanalysis and thermoprobe analysis, respectively. A donor,acceptor pair emission band was observed in the photoluminescence spectra at 10 K, indicating that the samples had both donor and acceptor impurity types. It was also found that p-type CuInS2 crystals could be obtained by Sb doping. It was suggested that the Sb atoms in the S site might enhance p-type conductivity. [source] Structure and oxygen mobility in mayenite (Ca12Al14O33): a high-temperature neutron powder diffraction studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2007H. Boysen The structure of mayenite, Ca12Al14O33, was investigated by neutron powder diffraction up to 1323,K. It has been described previously as a calcium,aluminate framework, in which 32 of the 33 oxygen anions are tightly bound, containing large cages, 1/6 of them being filled randomly by the remaining `free' oxygen. At ambient temperature excess oxygen was found, corresponding to the composition Ca12Al14O33.5 which was attributed to the presence of hydroxide, peroxide and superoxide radicals in the cages. Above 973,K these are lost under vacuum conditions and the composition becomes stoichiometric. From the refined structural parameters it is concluded that the structure is more adequately described as a relatively stable aluminate framework consisting of eightfold rings of AlO4 tetrahedra with disordered Ca and `free' O distributed within. At high temperatures the density of the `free' oxygen is extremely spread out, with the expansion being related to the high ionic conductivity of this material. Since no continuous density distribution between adjacent cages was found and the `free' O forms bonds with part of the Ca, the diffusion proceeds via a jump-like process involving exchange of the `free' oxygen with framework oxygen. The results confirm the recent theoretical predictions of Sushko et al. [(2006), Phys. Rev. B, 73, 014101-1-10]. [source] A simple hydrogen-bonded chain in (3Z)-3-{1-[(5-phenyl-1H -pyrazol-3-yl)amino]ethylidene}-4,5-dihydrofuran-2(3H)-one, and a hydrogen-bonded ribbon of centrosymmetric rings in the self-assembled adduct (3Z)-3-{1-[(5-methyl-1H -pyrazol-3-yl)amino]ethylidene}-4,5-dihydrofuran-2(3H)-one,6-(2-hydroxyethyl)-2,5-dimethylpyrazolo[1,5- a]pyrimidin-7(4H)-one (1/1)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2010Jairo Quiroga (3Z)-3-{1-[(5-Phenyl-1H -pyrazol-3-yl)amino]ethylidene}-4,5-dihydrofuran-2(3H)-one, C15H15N3O2, (I), and the stoichiometric adduct (3Z)-3-{1-[(5-methyl-1H -pyrazol-3-yl)amino]ethylidene}-4,5-dihydrofuran-2(3H)-one,6-(2-hydroxyethyl)-2,5-dimethylpyrazolo[1,5- a]pyrimidin-7(4H)-one (1/1), C10H13N3O2·C10H13N3O2, (II), in which the two components have the same composition but different constitutions, are formed in the reactions of 2-acetyl-4-butyrolactone with 5-amino-3-phenyl-1H -pyrazole and 5-amino-3-methyl-1H -pyrazole, respectively. In each compound, the furanone component contains an intramolecular N,H...O hydrogen bond. The molecules of (I) are linked into a chain by a single intermolecular N,H...O hydrogen bond, while in (II), a combination of one O,H...N hydrogen bond, within the selected asymmetric unit, and two N,H...O hydrogen bonds link the molecular components into a ribbon containing alternating centrosymmetric R44(20) and R66(22) rings. [source] 3-[5-(4-Bromophenyl)-1H -pyrazol-3-ylamino]-5,5-dimethylcyclohex-2-en-1-one,(Z)-3-(4-bromophenyl)-3-chloroacrylonitrile (2/1): a stoichiometric cocrystal of a reaction product with one of its early precursorsACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2006Silvia Cruz The title compound, 2C17H18BrN3O·C9H5BrClN, was crystallized from the reaction between 5,5-dimethylcyclohexane-1,3-dione, triethyl orthoformate and 5-amino-3-(4-bromophenyl)pyrazole, which had itself been prepared from the reaction between (Z)-3-(4-bromophenyl)-3-chloroacrylonitrile and hydrazine. The compound is a stoichiometric 2:1 cocrystal of the reaction product 3-[5-(4-bromophenyl)-1H -pyrazol-3-ylamino]-5,5-dimethylcyclohex-2-en-1-one and the early reactant (Z)-3-(4-bromophenyl)-3-chloroacrylonitrile. The two independent molecules of cyclohex-2-en-1-one are linked by N,H,N and N,H,O hydrogen bonds into complex bilayers and the molecules of acrylonitrile are trapped within large cavities in the substructure formed by the cyclohex-2-en-1-one molecules. [source] | |||||||||||||||||||||||||||||||||||||||||||