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Geometric Structure (geometric + structure)
Selected AbstractsTheoretical Investigation on the Electronic and Geometric Structure of GaN2+ and GaN4+CHEMINFORM, Issue 49 2007Demeter Tzeli 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, please click on HTML or PDF. [source] Ab initio Investigation of the Electronic and Geometric Structure of Magnesium Diboride, MgB2.CHEMINFORM, Issue 7 2006Demeter Tzeli Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF. [source] Relationship Between Geometric Structures of Catalyst Particles and Growth of Carbon Nanocoils,CHEMICAL VAPOR DEPOSITION, Issue 4-6 2010Da-Wei Li Abstract The relationship between the geometric structures of catalyst particles and the growth of carbon nanocoils (CNCs) is investigated. It is found that the CNCs usually consist of over two, but less than five tubules. The catalyst particles at the tips of CNCs are all polyhedron structures, in most cases, hexahedron. It is considered that a catalyst particle has two kinds of crystal facets, the catalytically active facet and the carbon precipitation facet. The active facet mainly plays the roles of decomposition of hydrocarbon and diffusion of the formed carbon atoms, while carbon tubules are grown from the precipitation facets and twisted to form a carbon coil. Catalysts with different numbers of active facets and geometric structures form different types of CNCs. [source] Spectroscopy of High-Energy States of Lanthanide IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Michael F. Reid Abstract We discuss recent progress and future prospects for the analysis of the 4fN,15d excited states of lanthanide ions in host materials. We demonstrate how ab initio calculations for Ce3+ in LiYF4 may be used to estimate crystal-field and spin-orbit parameters for the 4f1 and 5d1 configurations. We show how excited-state absorption may be used to probe the electronic and geometric structure of the 4fN,15d excited states in more detail and we illustrate the possibilities with calculations for Yb2+ ions in SrCl2. [source] How Do the Different Defect Structures and Element Substitutions Affect the Nonlinear Optical Properties of Lacunary Keggin Polyoxometalates?EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2006A DFT Study Abstract Systematic DFT calculations have been carried out on the lacunary ,-Keggin polyoxometalate derivatives [PW11O39]7,, [XW9O34]n, (X = AlIII, SiIV, GeIV, PV, AsV, and SbV), [XW9M2O39]n,, and [XW9M3O40]n, (X = PV and SiIV, M = MoVI, VV, NbV, and TaV) to investigate the geometric structure and element substitution effects on the molecular nonlinear optical response. Analysis of the computed static second-order polarizability (,0) predicts that the molecular nonlinear optical activity of lacunary Keggin polyoxometalate derivatives can be modified by replacing the central heteroatom and the addenda metal atom. Substitution of the central Al atom or the addenda V atom causes significant enhancement in the molecular nonlinearity. Moreover, the ,0 values are substantially dependent on the defect structures. This class of inorganic complexes possesses remarkably large molecular optical nonlinearity, especially for the partial substitution complex [SiW9Nb2O39]10, (IIIc), which has a computed ,0 value of 2071.0 a.u. Thus, lacunary Keggin polyoxometalates could become excellent candidates in the field of second-order NLO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The effective action of D-branes in Calabi-Yau orientifold compactifications,FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 10 2005H. Jockers Abstract In this review article we study type IIB superstring compactifications in the presence of space-time filling D-branes while preserving ,,=1 supersymmetry in the effective four-dimensional theory. This amount of unbroken supersymmetry and the requirement to fulfill the consistency conditions imposed by the space-time filling D-branes lead to Calabi-Yau orientifold compactifications. For a generic Calabi-Yau orientifold theory with space-time filling D3- or D7-branes we derive the low-energy spectrum. In a second step we compute the effective ,,=1 supergravity action which describes in the low-energy regime the massless open and closed string modes of the underlying type IIB Calabi-Yau orientifold string theory. These ,,=1 supergravity theories are analyzed and in particular spontaneous supersymmetry breaking induced by non-trivial background fluxes is studied. For D3-brane scenarios we compute soft-supersymmetry breaking terms resulting from bulk background fluxes whereas for D7-brane systems we investigate the structure of D- and F-terms originating from worldvolume D7-brane background fluxes. Finally we relate the geometric structure of D7-brane Calabi-Yau orientifold compactifications to ,,=1 special geometry. [source] Robust multiple-fault detection filterINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 8 2002Robert H. Chen Abstract A new robust multiple-fault detection and identification algorithm is determined. Different from other algorithms which explicitly force the geometric structure by using eigenstructure assignment or geometric theory, this algorithm is derived from solving an optimization problem. The output error is divided into several subspaces. For each subspace, the transmission from one fault, denoted the associated target fault, is maximized while the transmission from other faults, denoted the associated nuisance fault, is minimized. Therefore, each projected residual of the robust multiple-fault detection filter is affected primarily by one fault and minimally by other faults. The transmission from process and sensor noises is also minimized so that the filter is robust with respect to these disturbances. It is shown that, in the limit where the weighting on each associated nuisance fault transmission goes to infinity, the filter recovers the geometric structure of the restricted diagonal detection filter of which the Beard,Jones detection filter and unknown input observer are special cases. Filter designs can be obtained for both time-invariant and time-varying systems. Copyright © 2002 John Wiley & Sons, Ltd. [source] Time-dependent density functional theory study on the electronic excited-state geometric structure, infrared spectra, and hydrogen bonding of a doubly hydrogen-bonded complexJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2009Yufang Liu Abstract The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen-bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S1 state of this doubly hydrogen-bonded FN-2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen-bonded FN-2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm,1 observed in the IR spectra should be assigned as the doubly hydrogen-bonded FN-2MeOH complex from our calculated results. The electronic excited-state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S1 state of the doubly hydrogen-bonded FN-2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen-bonded FN-MeOH complex and play important role on the photophysics of fluorenone in solutions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source] The equivalent potential of water for electronic structure of aspartic acidJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2008Tian Zhang Abstract The equivalent potential of water for the electronic structure of aspartic acid (Asp,) in solution is constructed by the first-principles, all-electrons, ab initio calculations. Aspartic acid is a hydrophilic amino acid which is negatively charged in neutral water solution. The main process of calculation consists of three steps. Firstly, the geometric structure of the cluster containing Asp, and water molecules is calculated by the free cluster calculation. Then, based on the obtained geometric structure, the electronic structure of Asp, with the potential of water molecules is calculated using the self-consistent cluster-embedding method. Finally, the electronic structure of Asp, with the potential of dipoles is calculated. The results show that the major effect of water on Asp,'s electronic structure is lowering the occupied molecular orbitals by about 0.02 Ry on average, and narrowing energy gap by 10.8%. The effect of water on the electronic structure of Asp, can be simulated by dipoles potential. © 2008 Wiley Periodicals, Inc.J Comput Chem, 2008. [source] Equivalent potential of water molecules for electronic structure of glutamic acidJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2007Tian Zhang Abstract The fundamental importance of the electronic structure of molecules is widely recognized. To get reliable electronic structure of protein in aqueous solution, it is necessary to construct a simple, easy-use equivalent potential of water molecules for protein's electronic structure calculation. Here, the first-principles, all-electron, ab initio calculations have been performed to construct the equivalent potential of water molecules for the electronic structure of glutamic acid, which is a hydrophilic amino acid and is negatively charged (Glu,) in neutral water solution. The main process of calculation consists of three steps. Firstly, the geometric structure of the cluster containing Glu, and water molecules is calculated by free cluster calculation. Then, based on the geometric structure, the electronic structure of Glu, with the potential of water molecules is calculated using the self-consistent cluster-embedding method. Finally, the electronic structure of Glu, with the potential of dipoles is calculated. Our calculations show that the major effect of water molecules on Glu,'s electronic structure is lowering the occupied electronic states by about 0.017 Ry, and broadening energy gap by 12%. The effect of water molecules on the electronic structure of Glu, can be well simulated by dipoles potential. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Sex-related spatial patterns of Poa ligularis in relation to shrub patch occurrence in northern PatagoniaJOURNAL OF VEGETATION SCIENCE, Issue 1 2000Mónica B. Bertiller Correa (1969,1988) Abstract. Poa ligularis is a dioecious species and a valuable forage plant which is widespread in the arid steppe of northern Patagonia (Argentina). The vegetation in these areas consists of a system of perennial plant patches alternating with bare soil areas defining contrasting micro-environments. We hypothesized that (1) male and female individuals of P. ligularis are spatially segregated in different micro-environments, (2) the intensity of spatial segregation of sexes depends on plant structure and (3) spatial segregation of sexes is enhanced by competitive interactions between the sexes within the vegetation patches. We analysed the spatial distribution of female and male individuals in relation to the spatial pattern of vegetation in two areas differing in their vegetation structure. The location of P. ligularis within patches where either male, female or both sexes occurred was also analysed. The results indicate that different patterns of spatial distribution of sexes of P. ligularis may be found at the community level depending on the dominant life forms and geometric structure of plant patches. Where patches are of a lower height, with a high internal patch cover, individuals of both sexes are concentrated within patch canopies. In sites characterized by large, tall patches and less internal patch cover suitable microsites for female and male P. ligularis occur both within and outside the patch with males located at further distances from the patch edge. Where the patch is large and tall enough to allow the establishment of males and females at relatively high numbers, males occupy the patch periphery or even colonize the interpatch bare soil. These spatial patterns are consistent with selective traits in which females better tolerate intraspecific competition than males, while males tolerate wider fluctuations in the physical environment (soil moisture, nitrogen availability, wind intensity, etc.). [source] Mass-selective vibrational spectroscopy of vanadium oxide cluster ionsMASS SPECTROMETRY REVIEWS, Issue 4 2007Knut R. Asmis Abstract A corner stone in the study of the size-dependent properties of cluster ions in the gas phase is their structural characterization. Over the last 10 years, significant progress has been in this research field because of significant advances in the gas phase vibrational spectroscopy of mass-selected ions. Using a combination of modern experimental and quantum chemical approaches, it is now in most cases possible to uniquely identify the geometric structure of cluster ions, based on the comparison of the experimental and simulated infrared spectra. In this article, we highlight the progress made in this research area by reviewing recent infrared photodissociation (IR-PD) experiments on small and medium sized (up to 30 atoms) vanadium oxide ions. © 2007 Wiley Periodicals, Inc., Mass Spec Rev. [source] Picosecond and femtosecond X-ray absorption spectroscopy of molecular systemsACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Majed Chergui The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this true. X-ray absorption spectroscopy is ideal for the study of structural dynamics in liquids, because it can be implemented in amorphous media. Furthermore, it is chemically selective. Using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of the local geometric structure of the system under study, but also the underlying photoinduced electronic structure changes that drive the structural dynamics. Recent developments in picosecond and femtosecond X-ray absorption spectroscopy applied to molecular systems in solution are reviewed: examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. [source] Waddling and toddling: The biomechanical effects of an immature gaitAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Libby W. Cowgill Abstract Femoral shape changes during the course of human growth, transitioning from a subcircular tube to a teardrop-shaped diaphysis with a posterior pilaster. Differences between immature and mature bipedalism and body shape may generate different loads, which, in turn, may influence femoral modeling and remodeling during the course of the human lifespan. This study uses two different approaches to evaluate the hypotheses that differences in gait between young and mature walkers result in differences in ground reaction forces (GRFs) and that the differences in loading regimes between young children and adults will be reflected in the geometric structure of the midshaft femur. The results of this analysis indicate that GRFs differ between young walkers and adults in that normalized mediolateral (ML) forces are significantly higher in younger age groups. In addition, these differences between children and adults in the relative level of ML bending force are reflected in changes in femoral geometry during growth. During the earlier stages of human development, immature femoral diaphyses are heavily reinforced in approximately ML plane. The differences in gait between mature and immature walkers, and hence the differences in femoral shape, are likely partially a product of a minimal bicondylar angle and relatively broad body in young children. Am J Phys Anthropol 143:52,61, 2010. © 2010 Wiley-Liss, Inc. [source] A review on the use of the adjoint method in four-dimensional atmospheric-chemistry data assimilationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 576 2001K.-Y. Wang Abstract In this paper we review a theoretical formulation of the adjoint method to be used in four-dimensional (4D) chemistry data assimilation. The goal of the chemistry data assimilation is to combine an atmospheric-chemistry model and actual observations to produce the best estimate of the chemistry of the atmosphere. The observational dataset collected during the past decades is an unprecedented expansion of our knowledge of the atmosphere. The exploitation of these data is the best way to advance our understanding of atmospheric chemistry, and to develop chemistry models for chemistry-climate prediction. The assimilation focuses on estimating the state of the chemistry in a chemically and dynamically consistent manner (if the model allows online interactions between chemistry and dynamics). In so doing, we can: produce simultaneous and chemically consistent estimates of all species (including model parameters), observed and unobserved; fill in data voids; test the photochemical theories used in the chemistry models. In this paper, the Hilbert space is first formulated from the geometric structure of the Banach space, followed by the development of the adjoint operator in Hilbert space. The principle of the adjoint method is described, followed by two examples which show the relationship of the gradient of the cost function with respect to the output vector and the gradient of the cost function with respect to the input vector. Applications to chemistry data assimilation are presented for both continuous and discrete cases. The 4D data variational adjoint method is then tested in the assimilation of stratospheric chemistry using a simple catalytic ozone-destruction mechanism, and the test results indicate that the performance of the assimilation method is good. [source] Effect of Electronic Structures of Enantiomers of Ruthenium(II) Polypyridyl Complexes on DNA Binding BehaviorsCHINESE JOURNAL OF CHEMISTRY, Issue 8 2010Haimei Luo Abstract A pair of Ru(II) complex enantiomers, , - and , -[Ru(bpy)2(p -mpip)]2+ {bpy=2,2,-bipyridine, p -mpip=2-(4-methylphenyl)imidazo[4,5-f]-1,10-phenanthroline} have been synthesized and structurally characterized. Both experimental results from crystallography, NMR, electrochemistry and theoretical calculations applying the density functional theory (DFT) method based on their crystal structures show that small difference in geometric structure existed can cause a considerable difference in electronic structure between enantiomers. In addition, the binding of the two enantiomers to calf thymus DNA (CT DNA) has been investigated with UV spectroscopy titration and viscosity measurements. It is very rare that the , enantiomer binds to DNA more strongly than the , enantiomer, which can be reasonably explained by their different electronic structures for the first time, suggesting that the dominant factor governing the stereoselectivity of DNA binding of Ru(II) complex may be the different electronic structures of its enantiomers. [source] Fractal dimension can distinguish models and pharmacologic changes in liver fibrosis in ratsHEPATOLOGY, Issue 4 2002Frédéric Moal Fractal analysis measures the complexity of geometric structures. The aim of this study was to evaluate the feasibility and accuracy of fractal analysis in liver fibrosis. A total of 77 rats were included: 10 sham, 46 with fibrosis secondary to bile duct ligation (BDL), and 21 with fibrosis due to CCl4 intoxication. Measurements included the fractal dimension of Kolmogorov (Dk), histologic lesions, the area of fibrosis by image analysis, liver hydroxyproline content, messenger RNA fibronectin, serum hyaluronate level, and portal pressure. Fibrotic rats were given placebo, octreotide, or O2 -vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO). Intraobserver agreement of Dk was excellent with the intraclass (ic) correlation coefficient ric = 0.91 (P < .0001) as well as the interobserver agreement with ric = 0.88 (P < .001). Dk was correlated with other measurements or markers of fibrosis: the area of fibrosis (r = 0.75; P < .0001), hydroxyproline content (r = 0.51; P < .001), serum hyaluronate level (r = 0.52; P < .001), and portal pressure (r = 0.52; P < .01). Dk was significantly different between the 2 models of fibrosis (P < .0001), unlike the area of fibrosis, and this relationship was independent of other histologic lesions. The significant decrease in fibrosis observed with octreotide or V-PYRRO/NO was similarly reflected by Dk or the area of fibrosis. The diagnostic accuracy for the fibrosis model was 97% with the 5 main measurements or markers of fibrosis studied, with Dk isolated at the first step by stepwise analysis. In conclusion, fractal analysis is suitable for analyzing liver fibrosis and has excellent reproducibility. This is the only quantitative morphometric method that can discriminate among the models of fibrosis and is sensitive enough to detect pharmacologically induced changes in liver fibrosis. [source] Study of conformational and optical rotation for the alaninamideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2007Shulei Zhao Abstract Six stationary points of alaninamide have been located on the potential surface energy (PES) at the B3LYP/6-311++G(2d,2p) level of theory both in the gas phase and in aqueous solution. In the aqueous solution, to take the water solvent effect into account, the polarizable continuum model (PCM) method has been used. Accurate geometric structures and their relative stabilities have been investigated. The results show that the intramolecular hydrogen bond plays a very important role in stabilizing the global minimum of the alaninamide. Moreover, the consistent result in relative energy using high-level computations, including the MP2 and MP3 methods with the same basis set [6-311++G(2d,2p)], indicates that the B3LYP/6-311++G(d,p) level may be applied to the analogue system. More importantly, the optical rotation of the optimized conformers (both in the gas phase and in aqueous solution) of alaninamide have been calculated using the density functional theory (DFT) and Hartree,Fock (HF) method at various basis sets (6-31+G*, 6-311++G(d,p), 6-311++G(2d,2p) and aug-cc-pvdz). The results show that the selection of the computation method and the basis set in calculation has great influence on the results of the optical rotations. The reliability of the HF method is less than that of DFT, and selecting the basis set of 6-311++G(2d,2p) and aug-cc-pvDZ produces relative reliable results. Analysis of the computational results of the structure parameters and the optical rotations yields the conclusion that just the helixes in molecules caused the chiral molecules to be optical active. The Boltzmann equilibrium distributions for the six conformers (both in the gas phase and in the aqueous solution) are also carried out. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Blue-shifted and red-shifted hydrogen bonds: Theoretical study of the CH3CHO· · ·HNO complexesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006Yong Yang Abstract The blue-shifted and red-shifted H-bonds have been studied in complexes CH3CHO,HNO. At the MP2/6-31G(d), MP2/6-31+G(d,p) MP2/6-311++G(d,p), B3LYP/6-31G(d), B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) levels, the geometric structures and vibrational frequencies of complexes CH3CHO,HNO are calculated by both standard and CP-corrected methods, respectively. Complex A exhibits simultaneously red-shifted CH,O and blue-shifted NH,O H-bonds. Complex B possesses simultaneously two blue-shifted H-bonds: CH,O and NH,O. From NBO analysis, it becomes evident that the red-shifted CH,O H-bond can be explained on the basis of the two opposite effects: hyperconjugation and rehybridization. The blue-shifted CH,O H-bond is a result of conjunct CH bond strengthening effects of the hyperconjugation and the rehybridization due to existence of the significant electron density redistribution effect. For the blue-shifted NH,O H-bonds, the hyperconjugation is inhibited due to existence of the electron density redistribution effect. The large blue shift of the NH stretching frequency is observed because the rehybridization dominates the hyperconjugation. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Energies, structures, and electronic properties of molecules in solution with the C-PCM solvation modelJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2003Maurizio Cossi Abstract The conductor-like solvation model, as developed in the framework of the polarizable continuum model (PCM), has been reformulated and newly implemented in order to compute energies, geometric structures, harmonic frequencies, and electronic properties in solution for any chemical system that can be studied in vacuo. Particular attention is devoted to large systems requiring suitable iterative algorithms to compute the solvation charges: the fast multipole method (FMM) has been extensively used to ensure a linear scaling of the computational times with the size of the solute. A number of test applications are presented to evaluate the performances of the method. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 669,681, 2003 [source] Dehn surgeries on periodic linksMATHEMATISCHE NACHRICHTEN, Issue 5-6 2006E. Barbieri Abstract We consider orientable closed connected 3-manifolds obtained by Dehn surgeries with rational coefficients along the components of certain periodic links. These manifolds extend many classes of (hyperbolic) manifolds considered by several authors (see the references). We find geometric presentations of the fundamental group of such manifolds, and study some covering properties of them. Then we obtain results on their geometric structures in many cases. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic semiconductors in ternary Cd,Mn,Te compoundsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008Yong Liu Abstract Since Mn-doped CdTe in zincblende structure has been fabricated for Mn concentrations from 0 to 0.5, we use a first-principles full-potential method to study CdTe-based ternary Cd,Mn,Te compounds for possible magnetic semiconductors. The compounds are constructed by substituting Mn for some Cd atoms in zincblende CdTe. We optimize fully their geometric structures and internal atomic positions, and then study their electronic and magnetic properties. We find that the stable CdMnTe2 and Cd3MnTe4 are antiferromagnetic semiconductors with space groups 160 and 111, and the stable Cd7MnTe8 is a layered ferromagnetic semiconductor with space group 115. Their real lattice constants are a little smaller than CdTe's and an Mn atom contributes 5 Bohr magnetons to their total magnetic moments. The antiferromagnetism for the CdMnTe2 is attributed to the Te-based superexchange of Mn spins. For the other two, the MnMn spin interactions are dependent on the MnMn distance and the environment. The antiferromagnetism for the Cd3MnTe4 and the layered ferromagnetism for the Cd7MnTe8 can be attributed to two weaker indirect exchange interactions based on both Cd and Te. The Kohn,Sham gaps of the three magnetic semiconductors are 0.52 eV, 0.80 eV, and 1.23 eV, respectively. The real semiconductor gaps may be larger than 1 eV considering the fact that the Kohn,Sham gap of CdTe is 0.55 eV but the experimental semiconductor gap is 1.56 eV at 300 K. These magnetic semiconductors, compatible with semiconductors such as CdTe, could be useful in spintronics applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatial orientation of nanoclay and crystallite in microcellular injection molded polyamide-6 nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 6 2007Mingjun Yuan Three different types of characteristic structures-microcells, nanoclay, and crystallite lamella-exist in injection molded polyamide-6 microcellular nanocomposites. These structures are in completely different scales. The spatial orientation of these microscale structures crucially determines the material's bulk properties. Based on scanning electron microscopy, transmission electron microscopy, and two-dimensional X-ray diffractometry measurements, it was found that the nanoclay and the crystallite formed special geometric structures around the microcells and near the part skins. The nanoclay platelets lay almost parallel to the surfaces of the molded parts. Preferred orientation of the crystallites was induced by the presence of the nanoclay. A molecular-based model is proposed to describe the structural hierarchy and correlations among the microcells, nanoclay, and crystallite lamella. From the small-angle X-ray scattering experiments, it was found that microcellular injection molding produces relatively smaller crystallite lamella than that of conventional injection molding, and that for both solid and microcellular neat resin parts the crystallite lamella thickness at the part skin is smaller than that at the core. Polarized optical microscopy results also indicated that the size of crystallites in the microcellular neat resin and nanocomposite parts is smaller than that in the corresponding solid parts. POLYM. ENG. SCI., 47:765,779, 2007. © 2007 Society of Plastics Engineers [source] Structural comparison of three N -(4-halogenophenyl)- N,-[1-(2-pyridyl)ethylidene]hydrazine hydrochloridesACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Julia Heilmann-Brohl 2-{1-[(4-Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C13H13ClN3+·Cl,·CH3OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N,C,C,N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2-{1-[(4-fluoroanilino)methylidene]ethyl}pyridinium chloride, C13H13FN3+·Cl,, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N,C,C,N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak ,,, interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324,(3). 2-{1-[(4-Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C13H13FN3+·Cl,·2CH3OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry-equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C,H...O contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same. [source] Relationship Between Geometric Structures of Catalyst Particles and Growth of Carbon Nanocoils,CHEMICAL VAPOR DEPOSITION, Issue 4-6 2010Da-Wei Li Abstract The relationship between the geometric structures of catalyst particles and the growth of carbon nanocoils (CNCs) is investigated. It is found that the CNCs usually consist of over two, but less than five tubules. The catalyst particles at the tips of CNCs are all polyhedron structures, in most cases, hexahedron. It is considered that a catalyst particle has two kinds of crystal facets, the catalytically active facet and the carbon precipitation facet. The active facet mainly plays the roles of decomposition of hydrocarbon and diffusion of the formed carbon atoms, while carbon tubules are grown from the precipitation facets and twisted to form a carbon coil. Catalysts with different numbers of active facets and geometric structures form different types of CNCs. [source] | ||||||||||||||||||||||||||||||||||