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Unit Cell (unit + cell)
Kinds of Unit Cell Terms modified by Unit Cell Selected AbstractsChemInform Abstract: Sodium Etiobilirubin-IV,-C10-sulfonate: A Highly Solvated Bile Pigment Structure Containing Two Different Non-ridge-tile Conformers in the Unit Cell.CHEMINFORM, Issue 49 2001Mathias O. Senge Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Crystal structure of a tetrazole derivativeCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2006H. S. Yathirajan Abstract 5-(4'-Methyl-1,1'-biphenyl-2-yl)-1H-tetrazole(MBT), C28H24N8, CCDC: 223082, F.W.=472.55, triclinic, P1, a=4.99(1)Å, b=14.25(4)Å, c=16.63(5)Å, , = 90.27(5)°, , = 91.19(5)°, , = 90.64(5)°, V = 1182(6)Å3, Z = 4, Dcal = 1.327 Mgm -3, , = 0.084mm -1, F000 = 496, , (MoK,) = 0.71073Å, final R1 and wR2 are 0.0924 and 0.2309, respectively. There are two crystallographically independent molecules in the asymmetric unit. The dihedral angles between the two phenyl rings of the biphenyl ring system are 44.2(2)° and 44.3(2)° for the two molecules respectively. The molecules are stabilized by N-H,N and C-H,N types of intermolecular hydrogen bonds in the unit cell in addition to van der Waals forces. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Synthesis, structural and thermal studies of tetrathioureacopper(I) chloride crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2005M. Dhandapani Abstract Tetrathioureacopper(I) chloride, hereafter abbreviated as TCC, was synthesised and single crystals were obtained from saturated aqueous solution by slow evaporation (solution growth) method at room temperature. The crystals obtained are bright, colourless and transparent having well defined external faces. The grown crystals were characterized through elemental analysis, single crystal X-ray diffraction study, thermal analysis, electron spin resonance spectroscopy and Fourier Transform infrared spectroscopy. The elemental analysis confirms the stoichiometry of the compound. The single crystal diffraction studies indicate that TCC crystallises in the tetragonal lattice and the unit cell parameters are a = b = 13.4082 Å, c = 13.8074 Å, V = 2482.29 Å3, , = , = , = 90°. Space group and the number of molecules per unit cell (Z) are found to be P41212 and 8 respectively. The TG curve of the sample shows a prolonged decomposition from 210 to 628.3 °C, from which the decomposition pattern has been formulated. The endothermic peaks in the DTA curve indicate melting and decomposition of the compound at 165.2 and 633.8 °C respectively. An exothermic peak in high temperature DSC indicates a phase transition in the compound at 274.8 °C. Thermal anomalies observed in the low temperature DSC at ,163.3, ,152.0, ,141.5, ,108.3, 1.0 and 12.1 °C in the heating run and ,157.1 and ,153.9 °C in the cooling run reveal first order phase transitions in the crystal. The peaks observed at ,146.2 °C in both the heating and cooling runs suggest occurrence of a second order phase transition in this compound. The IR spectroscopic data were used to assign the characteristic vibrational frequencies of various groups present in the compound. The ESR study confirms that the copper is in the +1 oxidation state in the complex. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structures of two acridinedione derivativesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005K. Palani Abstract The crystal structures of two acridinedione derivatives, namely 10-(3,4-Dichloro-5-hydroxyphenyl)-3,4,6,7,9,10-hexahydro-1,8(2H, 5H) acridinedione (DHHA, CCDC 206440) and 10-(3,5-Dihydroxy-4-nitrophenyl)-3,4,6,7,9,10-hexahydro-1,8(2H, 5H) acridinedione (DHNA, CCDC206441) are reported here. Both the structures were solved by direct methods and refined by full-matrix least-squares procedures to final R- values of 0.073 and 0.076 respectively. In both the crystal structures, the central pyridine ring in the acridinedione moiety tends to be planar while the outer two rings adopt half-chair (sofa) conformation. The buckling angles 2.2(2)° and 11.0(1)° for DHHA and DHNA show the degree of planarity of the acridinedione moiety. The C-H,O types of hydrogen bonds help to stabilize the molecules in the unit cell in addition to van der Waals forces. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ca for Er substitution in tetragonal ErPO4 · H2O crystallised from phosphoric acid solutionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2004R. Kijkowska Abstract Erbium phosphate monohydrate with limited Ca for Er substitution, obtained through crystallisation from boiling phosphoric acid solution has been characterised by X-ray diffraction, Ir-spectroscopy and thermal analysis (TGA-DTA) methods. The difference in the electric charge between di-valent calcium and tri-valent erbium in the solid crystallised was compensated by simultaneous substitution of HPO42- for PO43- . Ca incorporation in erbium phosphate made expansion of tetragonal ErPO4 · H2O unit cell. After ignition at 900 °C the tetragonal crystal modification was maintained but the unit cell parameters of all the investigated phosphates, whether Ca-substituted or Ca-free, contracted to the same level. The unique contraction of the unit cell was resulted from recrystallisation of Ca-substituted into Ca-free erbium phosphate, while Ca was transferred into Ca(PO3)2 formed as a separate phase. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural Diversity in Organotin Compounds Derived from Bulky Monoaryl Phosphates: Dimeric, Tetrameric, and Polymeric Tin Phosphate ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2008Ramaswamy Murugavel Abstract Monoaryl phosphates with a bulky aryl substituent have been used to synthesize new organotin clusters and polymers. The equimolar reaction between 2,6-diisopropylphenylphosphate (dipp-H2) and Me2SnCl2 in ethanol at 25 °C leads to the formation of [Me2Sn(,3 -dipp)]n (1), while the reaction of 2,6-dimethylphenylphosphate (dmpp-H2) with Me2SnCl2 in either a 1:1 or 2:1 molar ratio proceeds to produce exclusively [Me2Sn(,-dmpp-H)2]n·nH2O (2). Compounds 1 and 2 are 1D polymers with different architectures. In compound 1, the tin atom is five-coordinate (trigonal bipyramidal). Each dipp ligand bridges three different tin atoms to form an infinite ladder-chain structure. In 2, each six-coordinate (octahedral) tin atom is surrounded by four phosphate oxygen atoms originating from four different bridging dmpp-H ligands, thus forming a spirocyclic coordination polymeric chain. The use of nBu2SnO as the diorganotin source in its reaction with dipp-H2 leads to the isolation of dimeric [nBu2Sn(,-dipp-H)(dipp-H)]2 (4), which contains a central Sn2O4P2 unit. There are two chemically different half molecules of 4 in the asymmetric part of the unit cell and hence it actually exists as a 1:1 mixture of [nBu2Sn(,-dipp-H)(dipp-H)]2 and [nBu2Sn(,-dipp)(dipp-H2)]2 in the solid state. The reaction of the monoorgano tin precursor nBuSn(O)(OH)·xH2O with dipp-H2 takes place in acetone at room temperature to yield the tetrameric cluster 5, which has different structures in the solution and in the solid state. 31P NMR spectroscopy clearly suggests that 5 has the formula [nBu4Sn4(,-O)2(,-dipp-H)8] in solution. The single-crystal X-ray diffraction studies in the solid state, however, reveal that compound 5 exists as [nBu4Sn4(,-OH)2(,-dipp-H)6(,-dipp)2]. The use of compounds 1,4 as possible precursors for the preparation of ceramic tin phosphate materials has been investigated. The thermolysis of 1 at 500 °C leads to the formation of quantitative amounts of Sn2P2O7, while the thermolysis of 2, 3, and 4 under similar conditions results in the formation of SnP2O7. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Breaking Infinite CuI Carboxylate Helix Held by Cuprophilicity into Discrete Cun Fragments (n = 6, 4, 2)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2008Yulia Sevryugina Abstract A new copper(I) carboxylate complex with 3,5-bis(trifluoromethyl)benzoate ligands, [Cu(O2C(3,5-CF3)2C6H3)] (1), has been prepared in high yield and fully characterized. An X-ray diffraction study revealed a remarkable infinite double-helical chain motif held together by cuprophilic interactions ranging from 2.69 to 3.14 Å. Both left- and right-handed helices are present in the unit cell of the centrosymmetric structure of 1 thus making the crystalline compound racemic. Complex 1 shows bright emission at ca. 594 nm upon UV/Vis radiation in the solid state (,ex = 350 nm). The Cu···Cu contacts in 1 are easily broken in the gas phase to afford copper clusters of ascertained nuclearity upon sublimation with various polyaromatic hydrocarbons. Several polyarenes such as fluoranthene (C16H10), pyrene (C16H10), and coronene (C24H12) were selected to cover a broad temperature range from 130 to 220 °C for the gas-phase co-deposition reactions. As a result of the successive temperature increase, cleavage of the infinite copper(I) chain into [Cun(O2C(3,5-CF3)2C6H3)n] fragments of decreasing nuclearity, n = 6, 4, and 2, has been achieved. The isolation of these units represents the first instance where various polynuclear copper(I) complexes are prepared and structurally characterized for the same carboxylate ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Trinuclear Aqua Cyano-Bridged Ruthenium Complex [{(,5 -C5H5)(PPh3)2Ru(,-CN)}2RuCl2(PPh3)(H2O)]PF6: Synthesis, Characterization and Crystal StructureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2007Viatcheslav Vertlib Abstract The organometallic trinuclear aqua cyano-bridged complex [{(,5 -C5H5)(PPh3)2Ru(,-CN)}2RuCl2(PPh3)(H2O)]PF6 (1), in which the fragment [RuCl2(PPh3)(H2O)] acts as a bridge and an acceptor group between the two terminal cyclopentadienyl ruthenium cyano moieties, was isolated in moderate yield from the reaction of [(,5 -C5H5)(PPh3)2RuCN] with [RuCl2(PPh3)3] in THF. To the best of our knowledge, compound 1 is one of the few examples of a trinuclear array of ruthenium fragments bridged by the nitrogen atom of the,C,N, group (Ru,C,N,Ru,,N,C,Ru) with a Ru-coordinated water molecule. The new aqua complex was structurally characterized by FTIR, 1H, 13C, and 31P NMR spectroscopy, mass spectrometry, elemental analysis, single-crystal X-ray diffraction, and cyclic voltammetry. The title complex crystallizes in a triclinic unit cell a = 17.3477(6) Å, b = 17.8551(5) Å, c = 18.2460(7) Å, , = 95.693(2)°, , = 111.648(2)°, and , = 97.839(2)° in the space group P with Z = 2.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] X-ray Crystal Structure and Characterization in Aqueous Solution of{N,N,-Ethylenebis(pyridoxylaminato)}zinc(II)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006Isabel Correia Abstract The complexation of ZnII with H2Rpyr2en [H2Rpyr2en = N,N,-ethylenebis(pyridoxylaminato)] in aqueous solution has been studied by pH potentiometry and 1H NMR spectroscopy. Complex formation constants are determined and binding modes proposed. Complex formation starts at around pH 4, and several species with a 1:1 ligand-to-metal ratio with different protonation states form up to pH 12. Only above pH 10 does a hydrolytic species [ZnLH,1], become important. The crystal and molecular structures of [ZnCl(H2Rpyr2en)]+Cl,·1.5H2O (1) have been determined by X-ray diffraction. The coordination of the H2Rpyr2en ligand involves the two phenolate-O and two amine-N atoms in a distorted square-pyramidal geometry. The two pyridine-N atoms are protonated, and a Cl, atom completes the coordination sphere. Upon coordination, both N-amine atoms of H2Rpyr2en become stereogenic centres, and in both molecules of the unit cell of 1 one of the N-amine donors has an (R)-configuration, and the other an (S)-configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Non-Covalent Aggregation of Discrete Metallo-Supramolecular Helicates into Higher Assemblies by Aromatic Pathways: Structural and Chemical Studies of New Aniline-Based Neutral Metal(II) DihelicatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005Miguel Vázquez Abstract Neutral manganese(II), iron(II), cobalt(II), nickel(II), zinc(II) and cadmium(II) complexes with an N -tosyl-substituted N4 -donor Schiff base containing a 4,4'-methylenedianiline residue as spacer [H2La: N,N' -bis(2-tosylaminobenzylidene)-4,4'-methylenedianiline], and the zinc(II) complex with an analogous ligand [H2Lb: N,N' -bis(2-tosylaminobenzylidene)-4,4'-oxodianiline] have been prepared by an electrochemical procedure. FAB and ESI mass spectra of the complexes show peaks due to species corresponding to a general formula [M2(La,b)2 + H]+, thereby suggesting their dinuclear nature. A detailed study of the crystal packing in the unit cell of the zinc(II) complex with H2La shows that the helicates aggregate to form discrete prismatic moieties containing three molecules held together by ,,, and ,,, interactions. Moreover, the ZnII neutral dihelicate with H2Lb forms a 3D network in the solid state due to intermolecular ,-stacking interactions. 1H NMR studies of the diamagnetic compounds reported herein have been performed. Finally, the ligand H2La and its ZnII and CdII complexes have been studied by spectrophotometric and spectrofluorimetric techniques in order to get a better understanding of the formation mechanisms of the complexes and of the nature of their fluorescence emission. Emission studies show that the ZnII and CdII dihelicates with H2La display a green fluorescence in acetonitrile solution (, = 473 nm, , = 0.03 and , = 476 nm, , = 0.01, respectively). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] [Re6Q7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (Q = S, Se) , New Octahedral Rhenium Cluster Complexes with Organic Ligands: Original Synthetic Approach and Unexpected Ligand Exchange in the Cluster CoreEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005Yuri V. Mironov Abstract Two new octahedral rhenium cluster complexes, [Re6S7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (1) and [Re6Se7O(3,5-Me2PzH)6]Br2·3,5-Me2PzH (2), with the organic ligand 3,5-dimethylpyrazole (3,5-Me2PzH), have been synthesised by reaction of rhenium chalcobromides Cs3[Re6(µ3 -Q7Br)Br6] (Q = S, Se) with molten dimethylpyrazole. During the reaction, all six apical bromine ligands of the cluster complexes are substituted by the organic ligand, which is coordinated through the aromatic nitrogen atom N2. Additionally, the inner ligand µ3 -Br in the cluster core [Re6(µ3 -Q7Br)]3+ is substituted by oxygen, giving cluster cores [Re6(µ3 -Q7O)]2+ with mixed chalcogen/oxygen ligands. Compounds 1 and 2 have been characterised by single-crystal X-ray diffraction analysis. They are isostructural and crystallise with four formula units in the unit cell. Absorption spectra and luminescence characteristics of these two cluster compounds have been investigated in methanol. Absorption starts below 400 nm. For both compounds, broad emissions were found. The fluorescence decays of the two compounds follow a diexponential decay behaviour. The main fluorescence intensity decays have longer fluorescence lifetimes of 3.07 ± 0.03 (1) and 3.96 ± 0.02 µs (2). Studying the thermal stability of both compounds in vacuo showed that the release of 3,5-dimethylpyrazole ligands begins near 200 °C, and decomposition, with the removal of 7 molecules of 3,5-Me2PzH, is complete at 330 °C. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Structural Study of Novel Graphite,Lithium,Calcium Intercalation CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Sébastien Pruvost Abstract Three new layered compounds were synthesised by immersing a pyrographite platelet in a molten Ca,Li alloy creating a new graphite intercalation compound family. The samples were studied by X-ray and neutron diffraction, revealing that the intercalated sheets are polylayered. The study of the 00l reflections allowed us to establish the c -axis stacking of these three phases. The ,-phase exhibits a five-layered intercalated sheet which has something in common with a Li,Ca,Li,Ca,Li slice cut in the CaLi2 structure (ThMn2 Laves phase type). The ,-phase, which is richer in metallic elements and with a greater repeat distance, possesses seven-layered intercalated sheets due to the splitting of the middle lithium plane in three. The third phase is a pseudo-binary compound, containing monolayered sheets and with a formula close to CaC6. Electron microdiffraction allowed us to determine the 2D unit cell for each compound, all of which were commensurate with that of graphite. Charge transfer from the intercalate to the host lattice was evaluated for the three phases from hk0 data, leading to high values. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Strain-Gradient Elasticity for Bridging Continuum and Atomistic Estimates of Stiffness of Binary Lennard-Jones CrystalsADVANCED ENGINEERING MATERIALS, Issue 6 2010Andrei A. Gusev Lagrangian variational approach is employed to derive the equations of equilibrium of strain-gradient elasticity. For a periodic lamellar-morphology strain-gradient medium, we present an exact formula for the overall, system stiffness. We compare the formula with direct atomistic estimates of stiffness of binary Lennard-Jones crystals. The comparison reveals that the strain-gradient formula remains fairly accurate for all the crystals studied, including those with order of unity atoms in the crystal unit cell. Thus, one can surmise that the strain-gradient correction alone can already be sufficient to extend the scope of validity of continuum-level elasticity to near atomistic length scales. [source] Damage analysis of laminated composites using a new coupled micro-meso approachFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2010A. FARROKHABADI ABSTRACT In this study, the simplicity and strong physical meaning of micromechanics approach and capability of mesomechanics approach for damage analysis of structures with complex loadings are employed to develop a new micro-meso approach. For this purpose, a new micromechanics model is developed to predict the matrix cracking initiation and evolution in laminated composites. These damage initiation and evolution are replaced with the damage criteria and flow rule in the continuum damage approach, respectively. The results of this procedure are used in the FEM damage analyses of laminated composites to predict constitutive response of layered composites. It is shown that, the predicted stress distribution and strain energy in a lamina unit cell are in good agreement with the finite element results. Furthermore, it is shown that the predicted stress,strain behaviours are in good agreement with the available experimental results for various laminates with different lay-ups. [source] Carbon Nanotubes: (Thermal and Structural Characterizations of Individual Single-, Double-, and Multi-Walled Carbon Nanotubes) Adv.ADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Funct. Here, M. T. Pettes and L. Shi report for the first time the thermal conductance, diameter, and chiral angle for a single single-walled carbon nanotube (SWCNT). A scanning electron micrograph of the suspended micro-thermometer device and transmission electron microscopy images used to determine the SWCNT's (22, 12) chirality are shown in this frontispiece image, along with the rendered unit cell. [source] A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by CrystallizationADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Yeo-Wan Chiang Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source] Probing the Anisotropic Field-Effect Mobility of Solution-Deposited Dicyclohexyl-,-quaterthiophene Single Crystals,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007Abstract Measuring the anisotropy of the field-effect mobility provides insight into the correlation between molecular packing and charge transport in organic semiconductor materials. Single-crystal field-effect transistors are ideal tools to study intrinsic charge transport because of their high crystalline order and chemical purity. The anisotropy of the field effect mobility in organic single crystals has previously been studied by lamination of macroscopically large single crystals onto device substrates. Here, a technique is presented that allows probing of the mobility anisotropy even though only small crystals are available. Crystals of a soluble oligothiophene derivative are grown in bromobenzene and drop-cast onto substrates containing arrays of bottom-contact gold electrodes. Mobility anisotropy curves are recorded by measuring numerous single crystal transistor devices. Surprisingly, two mobility maxima occur at azimuths corresponding to both axes of the rectangular cyclohexyl-substituted quaterthiophene (CH4T) in-plane unit cell, in contrast to the expected tensorial behavior of the field effect mobility. [source] Madelung Strain in Cuprate Superconductors , A Route to Enhancement of the Critical TemperatureADVANCED MATERIALS, Issue 36 2009Vladimir Y. Butko "Madelung Strain" in cuprate films containing metal (M,=,La1.56Sr0.44CuO4) and insulator (I,=,La2CuO4) layers: X-ray diffraction shows that, unexpectedly, the volume of unit cell of the top layer adjusts to that of the bottom layer. The effect is due to long-range Coulomb forces; it affects interfacial superconductivity because the critical temperature scales with the unit-cell height. [source] Dynamic numerical simulations of void growth and coalescence with stress triaxiality maintained constant,Application to ductile solids with secondary voidsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008L. Siad Abstract Dynamic explicit finite element analysis is used to investigate void growth and plastic collapse of an axisymmetric unit cell model with a primary spherical void imbedded in a porous matrix material. The Gurson,Tvergaard,Needleman homogenized model is used to describe the plastic behaviour of the matrix material. The simulations are performed under large strain conditions for varying secondary void volume fractions and quasi-static loading controlled by constant stress triaxiality. The proposed accomplishment of constant stress triaxiality associated with dynamic explicit computations provides a method allowing to trace the collapse of the unit cell from the onset of coalescence to practically its final failure. Consistent with experimental and theoretical results available in the literature, the obtained results substantiate the sensitivity of coalescence to the presence of secondary voids. Copyright © 2008 John Wiley & Sons, Ltd. [source] Polarization characteristics and property distributions of a proton exchange membrane fuel cell under cathode starvation conditionsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2010Dongsoo Ko Abstract Property distribution and polarization characteristics of a proton exchange membrane fuel cell (PEMFC) under cathode starvation conditions were investigated numerically and experimentally for a unit cell. The polarization curves of a lab-scale PEMFC were measured with increasing current density for different cell temperatures (40°C, 50°C, and 60°C) at a relative humidity of 100%. To investigate the local temperature, water content and current density on the membrane, and gas velocity in the channel of the PEMFC, numerical studies using the es-pemfc module of the commercial flow solver STAR-CD, which were matched with experimental data, were conducted. Temperature, current density on the membrane, and water content in the MEA were examined to investigate the effect of cell temperature on performance under the cathode starvation condition. At cathode starvation conditions, the performance of a higher cell temperature condition might drop significantly and the mean temperature on the membrane increase abruptly with increasing cell temperature or current density. Copyright © 2009 John Wiley & Sons, Ltd. [source] Molecular dynamics simulations of polarizable DNA in crystal environmentINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006Volodymyr Babin Abstract We have investigated the role of the electrostatic description and cell environment in molecular dynamics (MD) simulations of DNA. Multiple unrestrained MD simulations of the DNA duplex d(CCAACGTTGG)2 have been carried out using two different force fields: a traditional description based on atomic point charges and a polarizable force field. For the time scales probed, and given the "right" distribution of divalent ions, the latter performs better than the nonpolarizable force field. In particular, by imposing the experimental unit cell environment, an initial configuration with ideal B-DNA duplexes in the unit cell acquires sequence-dependent features that very closely resemble the crystallographic ones. Simultaneously, the all-atom root-mean-square coordinates deviation (RMSD) with respect to the crystallographic structure is seen to decay. At later times, the polarizable force field is able to maintain this lower RMSD, while the nonpolarizable force field starts to drift away. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Adsorption of water in mordenite,An ab initio studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2001Th. Demuth Abstract The adsorption of water in mordenite has been investigated using density functional theory using gradient corrections to the exchange,correlation functional. In the neutral complex water is strongly physisorbed through two different hydrogen bonds, the stronger between the acid site and the water oxygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the question if a chemisorbed complex (creation of a hydroxonium ion) is possible, ab initio molecular dynamics have been performed, indicating that a protonation of water occurs even for the low coverage of one water molecule per unit cell. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 110,116, 2001 [source] Analysis and design of band-pass frequency-selective surfaces using the FEM CAD toolINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2004P. T. Teo Abstract Three-dimensional (3D) full-wave analysis and design of bandpass frequency-selective surfaces (FSSs) is presented. By using the unique features of a unit cell and the periodic boundary conditions, infinite FSSs can be simulated. Wave propagation through FSSs, which is otherwise difficult to quantify, can be visualised by using a commercial CAD tool. The creation of the simulation model, interpretation and analysis of the outcome, and comparison with experimental results are presented for the square-slot and the square-loop-slot band-pass FSS. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 391,397, 2004. [source] Cation distribution in spinel (Mn,Co,Cr)3O4 at room temperatureJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010A. Purwanto As part of a study of the long-term operation of solid-oxide fuel cells, three (Mn,Co,Cr)3O4 samples have been synthesized and characterized. X-ray and neutron diffraction patterns from the powder samples at room temperature were measured and the data were co-refined. The neutron data were indispensible in locating Mn, Co and Cr within the crystallographic unit cell with their respective atomic occupancies. Two of these samples have been identified as cubic Mn0.76Co0.58Cr1.66O4 and Mn1.28Co1.72O4. The third is a two-phase sample containing cubic Mn1.66Co1.34O4 and tetragonal Mn2.05Co0.91O4 in a 59.1,(6):40.9,(6)% mass fraction ratio. Cr, which might be introduced from reaction with chromia during oxidation of interconnect materials, exhibits a preference for the octahedral site rather than the tetrahedral site. Without Cr, Mn dominates the octahedral site. [source] Transformations for monoclinic crystal symmetry in texture analysisJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2009Siegfried Matthies Monoclinic crystals can be described in two settings: in the first setting the C2 rotation axis is parallel to the z axis and in the second setting it is parallel to the y axis. Transformations of lattice parameters, Miller and zone indices, and atomic coordinates is straightforward; the situation is far more complex for texture analysis with orientation distributions and corresponding representations. This article gives explicit transformations that need to be applied, not only for texture analysis but also for calculations of physical properties of materials with preferred orientation. In texture research the relationship between the Cartesian crystal coordinate system and the unit cell must be unambiguously defined and a uniform convention is desirable. [source] Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sitesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Xinguo Hong Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5,Å resolution (qmax = 1.25,Å,1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8,Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2, level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax = 0.25,Å,1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. [source] Application of small-angle scattering to study the effects of moisture content on a native soy proteinJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2008Catherine S. Kealley The nano- and microstructure of glycinin, a soybean protein, has been investigated as a function of moisture for moisture contents between 4 and 21,wt%. Glycinin exhibits peaks in the small-angle region whose positions show minimal change with X-rays for samples up to 13% moisture. However, the use of neutron scattering, and the associated enhancement in contrast, results in the Bragg peaks being well resolved up to higher moisture contents; the associated shift in peak positions between 4 and 21% moisture are consistent with the expansion of a hexagonal unit cell as a function of moisture content. A Porod slope of ,,4 indicates that the interface between the `dry' protein powder and the surrounding medium at a length-scale of at least 3,µm down to ,20,nm is smooth and sharp. Scanning electron microscopy indicates that the powders, with low moisture content, have a porous appearance, with the porosity decreasing and microstructure expanding as the moisture content increases. [source] New techniques for indexing: N-TREOR in EXPOJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2000Angela Altomare Indexing of a powder diffraction pattern is still a critical point in procedures aiming at solving crystal structures from powder data. New code has been associated to the program TREOR90 in order to define an efficient peak search procedure, to modify the crystallographic decisions coded into TREOR90 to make it more exhaustive, to refine the selected unit cell automatically, and to make the entire procedure user friendly, via a graphical interface. The new program, called N-TREOR, has been integrated into the package EXPO to create a suite of programs able to provide a structural model from the analysis of the experimental pattern. N-TREOR is also available as a stand-alone program. [source] Synthesis of higher soluble nanostructured polyaniline by vapor-phase polymerization and determination of its crystal structureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Sambhu Bhadra Abstract Higher soluble nanostructured polyaniline was prepared by vapor-phase polymerization after passing aniline vapor through an aqueous acidic solution of ammonium persulfate (PANI-V). Polyaniline was also synthesized by the conventional oxidative polymerization method (PANI-C) in an aqueous medium for the comparison of its properties with PANI-V. PANI-V exhibited lower conductivity but higher hydrophilicity and higher solubility (2,3 times) in different solvents, such as tetrahydrofuran, N -methyl-2-pyrrolidone, dimethylsulfoxide, N,N -dimethyl formamide, and m -cresol at room temperature compared with that of PANI-C. The thermal stability of PANI-V was higher than that of PANI-C. In-depth investigations of the crystal structures of PANI-C and PANI-V were performed through powder X-ray diffraction analysis. The PANI-V showed a less ordered structure with a lower crystallinity and crystallite size and with a higher d-spacing and interchain separation compared with PANI-C. The unit cell volume of PANI-V was significantly higher with a greater number of atoms in the unit cell than that of PANI-C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] In vitro evaluation of porous poly(L -lactic acid) scaffold reinforced by chitin fibersJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Xiaoming Li Abstract In this study, the previously reported porous three-dimensional poly(L -lactic acid) (PLLA) scaffolds reinforced by the chitin fibers (PLLA/CF) with and without the link were evaluated in vitro. Firstly, pH value of the phosphate buffered saline lixiviums of the PLLA/CF with different content of the chitin fibers was measured to get an appropriate content of the chitin fibers in the PLLA/CF. Then, the cell functions (attachment, proliferation, alkaline phosphatase per unit cell, total protein per unit cell, and osteonectin, osteopontin, and osteocalcin gene expression) of human osteoblast-like cells (SaOS2) cultured on the PLLA/CF with the link, PLLA/CF without the link and PLLA scaffold were compared. The results showed that the link treatment did not significantly influence the pH value of the lixiviums of the scaffolds, 30% volume content might be an appropriate content of the chitin fibers in PLLA/CF scaffold to keep the pH value of the lixiviums of the scaffolds between 7.0 and 7.2 during the lixiviation time of 16 weeks, the PLLA/CF scaffold was significantly better for the attachment, proliferation, differentiation, and mineralization of the osteoblast than PLLA, the link treatment did not significantly influence these cells activities, which further suggested that PLLA/CF with the link treatment might be an appropriate scaffold for tissue engineering. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] | |||||||||||||||||||