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Tetrahedron
Selected AbstractsThe Inorganic,Organic Hybrid Compound {[Mn(trien)]2SnS4}·4H2O: Exhibiting a Hitherto Unknown Binding Mode of the [SnS4]4, TetrahedronEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2009Nicole Pienack Abstract The compound {[Mn(C6H18N4)]2SnS4}·4H2O (C6H18N4 = triethylenetetramine) was obtained under solvothermal conditions. In the structure of the {[Mn(C6H18N4)]2SnS4}, chain, two S atoms of the [SnS4]4, anion act in a hitherto never observed ,3 bridging mode that connects the Mn2S2N8 di-octahedra. The Mn2+ ions are octahedrally coordinated by four N and two S atoms, and two symmetry-related octahedra share a common S,S edge. Three of the H2O molecules are joined into chains through H-bonding interactions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Effects of climacostol on normal and tumoral mammalian cell linesTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005FEDERICO BUONANNO Climacostol, 1,3-dihydroxy-5-[(Z)-2,-nonenyl]benzene, is a natural toxin contained in the extrusomal cortical granules of the heterotrich ciliate Climacostomum virens. It is used for chemical defence against predators such as the raptorial ciliate Dileptus margaritifer and its cytotoxic activity has been assessed on several species of ciliates such as Didinium nasutum, Paramecium caudatum, and Blepharisma japonicum (Miyake et al. 2003, Europ. J. Protistol., 39:25,36). On the basis of its chemical structure, climacostol may be classified into the large group of natural compounds known as resorcinolic lipids, that show antimicrobial, antiparasitic, and antitumoral activities (Kozubek et al. 2003, Cell Moll. Biol. Lett., 6:351,355). To explore the possibility to use climacostol in medical applications, we examined the effects of chemically synthesized climacostol (Masaki et al. 2004, Tetrahedron, 60:7041,7048) on the growth and proliferation of tumoral and normal mammalian cell lines: (1) human promyelocytic leukaemia cells, HL60; (2) human squamous carcinoma cells, A431; and (3) non-tumoral cells derived from mice Leydig cells, TM3. It was observed that (1) a concentration of 10 ,g/ml of climacostol exerts a strong cytotoxic activity on all cell lines used; (2) at lower concentrations of 10 ng/ml and 1 ng/ml, the effect of climacostol is limited to the inhibition of the cell growth; and (3) the normal TM3 cells are more resistant to climacostol than the two tumoral HL60 and A431cell lines. The dose-dependent cytotoxic effects of climacostol encourage further investigation on the potential use of this ciliate toxin as an anti-cancer chemical. [source] (2S,3R,4S,5R)-Diethyl 2-(10,10-dimethyl-3,3-dioxo-3,6 -thia-4-azatricyclo[5.2.1.01,5]decan-4-ylcarbonyl)-5-phenylpyrrolidine-3,4-dicarboxylate: a novel isomorphous-by-addition compoundACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Graeme J. Gainsford The title compound, C27H36N2O7S, (I), is isomorphous by addition with the dimethyl ester analogue [Garner, Dogan, Youngs, Kennedy, Protasiewicz & Zaniewski (2001). Tetrahedron, 57, 71,85], (II), by replacing two methyl ester H atoms with two methyl groups. With the exception of the conformation of one of the ester groups, the molecules are almost superimposable. Likewise, apart from a slightly larger c axis in (I), few differences in the cell packing of (I) and (II) are found, with both dominated by the same C,H...O hydrogen bonds. Full synthetic and spectroscopic details of (I) are given. The molecular synthesis is important as an example of chiral auxiliary-assisted 1,3-dipolar cycloaddition of an azomethine ylid. [source] ChemInform Abstract: The Inorganic,Organic Hybrid Compound {[Mn(trien)]2SnS4}·4H2O: Exhibiting a Hitherto Unknown Binding Mode of the [SnS4]4- Tetrahedron.CHEMINFORM, Issue 29 2009Nicole Pienack 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] Accelerating Ray Tracing using Constrained TetrahedralizationsCOMPUTER GRAPHICS FORUM, Issue 4 2008Ares Lagae Abstract In this paper we introduce the constrained tetrahedralization as a new acceleration structure for ray tracing. A constrained tetrahedralization of a scene is a tetrahedralization that respects the faces of the scene geometry. The closest intersection of a ray with a scene is found by traversing this tetrahedralization along the ray, one tetrahedron at a time. We show that constrained tetrahedralizations are a viable alternative to current acceleration structures, and that they have a number of unique properties that set them apart from other acceleration structures: constrained tetrahedralizations are not hierarchical yet adaptive; the complexity of traversing them is a function of local geometric complexity rather than global geometric complexity; constrained tetrahedralizations support deforming geometry without any effort; and they have the potential to unify several data structures currently used in global illumination. [source] Nickel Complexes and Cobalt Coordination Polymers with Organochalcogen (S, Se) Ligands Bearing an N -Methylimidazole Moiety: Syntheses, Structures, and Properties,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2008Wei-Guo Jia Abstract The organochalcogen ligands (S, Se) derived from 3-methylimidazole-2-thione/selone groups mbit (2a), mbis (2b), ebit (2c), and ebis (2d) [mbit = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-thione), mbis = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-selone), ebit = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-thione), ebis = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-selone)] were synthesized and characterized. Mononuclear NiII complexes NiBr2mbit (3a), NiBr2mbis (3b), NiBr2ebit (3c), and NiBr2ebis (3d) were obtained by the reactions of Ni(PPh3)2Br2 with 2a, 2b, 2c, and 2d, respectively. However, when the corresponding ligands 2a, 2b, 2c, and 2d were treated with CoCl2 in thf solution CoII 1D coordination polymers (CoCl2mbit)n (4a), (CoCl2mbis)n (4b), (CoCl2ebit)n (4c), and (CoCl2ebis)n (4d) were obtained. All compounds were fully characterized by IR spectroscopy and elemental analysis. The crystal structures of 2c, 3a, 3b, 3c, 4a, 4b, and 4c were determined by X-ray crystallography. The local geometry around the nickel atom in complexes 3a,c was distorted tetrahedron with coordinated S(Se) and two Br atoms, and the organochalcogen ligands form an eight- or a nine-membered ring with the nickel atom included. The cobalt atom coordination polymers 4a and 4b coexist as left-handed and right-handed helical chains, but 4c formed a zigzag chain with a CH3CN solvent molecule taken up in the channel structure. After activation with methylaluminoxane (MAO), the nickel complexes exhibited high activities for addition polymerization of norbornene (1.42,×,108 g,PNBmol,1,Nih,1 for 3a). The effects of the Al/Ni ratio, reaction temperature, and reaction time to norbornene polymerization were also investigated.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Hybrid 2D and 3D Frameworks Based on ,-Keggin Polyoxometallates: Experiment and SimulationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005Anne Dolbecq Abstract The ,-Keggin polyoxomolybdate {,-PMoV8MoVI4O40,x(OH)xM4} is a versatile building unit, with M being either a ZnII or a LaIII capping ion located at the vertices of a slightly distorted tetrahedron. The charge of the Keggin unit depends on the number of protonated oxo bridging ligands, which has been shown to vary from 0 to 5. The Keggin entity can thus be either an anion (M = Zn, x = 0) or a cation (M = La, x = 3,5). The Zn derivative has been generated in situ by hydrothermal synthesis and forms a 2D material built from the connection of the cations by 4,4'-bipyridine ligands linked to the capping ZnII ions. The reaction of the chloride salt of the La derivative with di-, tri- and tetrasubstituted benzenecarboxylate ligands has allowed us to isolate 2D and 3D materials. The 3D materials seem to be the first examples of hybrid open frameworks based on Keggin building blocks. The 3D framework built from the connection of ,-Keggin units by trimesate ions exhibits tunnels filled only by water molecules, which can be partly removed and reintroduced at room temperature. Besides these experimental results, simulation has allowed us to generate two virtual hybrid structures derived from those of known silicates by replacing the Si ions by hypothetical ,-Keggin cations and the O -bridging ligands by terephthalate ions, thus showing that 3D frameworks with large pores can be envisioned in the chemistry of hybrid organic,inorganic materials based on ,-Keggin units and motivating further experimental investigations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Directions of preferential flow in a hillslope soil, 1.HYDROLOGICAL PROCESSES, Issue 4 2005Quasi-steady flow Abstract Preferred infiltration is mainly perceived as vertically down whereas subsurface storm flow is thought to occur parallel to slopes. The transition from vertical to lateral flow in a layered hillslope soil is the focus of the contribution. Transient flow is assumed to move as a wetting front. Three time-domain reflectometry (TDR) wave-guides, each 0·15 m long, were mounted in the shape of a truncated tetrahedron with its peak pointing down. Each wave-guide focuses the front velocity along its axis. The three front-velocity vectors are decomposed into their x, y and z components, which are then assembled to the resultant velocity vector. The volume density flux of preferred flow is the product of the front velocity and the mobile water content. The latter is the amplitude of transient soil moisture measured with each wave-guide. The resultant vector of the volume flux density is computed similarly to the velocity vector. The experimental approach allows for the rapid assessment of transient flows without relying on the variation of water potentials. The experiments indicate that the directions of the resultant vectors of velocity and volume flux density can be estimated if the moisture variations of the three TDR wave-guides are strongly correlated during the passing of the wetting front. Copyright © 2004 John Wiley & Sons, Ltd. [source] Modeling and simulation of bioheat transfer in the human eye using the 3D alpha finite element method (,FEM)INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 8 2010Eric Li Abstract Computational modeling is an effective tool for the detection of eye abnormalities and a valuable assistant to hyperthermia treatments. In all these diagnoses and treatments, predicting the temperature distribution accurately is very important. However, the standard finite element method (FEM) currently used for such purposes has strong reliance on element meshes and the discretized system exhibits the so-called ,overly stiff' behavior. To overcome this shortcoming, this paper formulates an alpha finite element method (,FEM) to compute two-dimensional (2D) and three-dimensional (3D) bioheat transfer in the human eyes. The ,FEM can produce much more accurate results using triangular (2D) and tetrahedron (3D) elements that can be generated automatically for complicated domains and hence is particularly suited for modeling human eyes. In the ,FEM, a scaling factor ,,[0, 1] is introduced to combine the ,overly stiff' FEM model and ,overly soft' node-based finite element method (NS-FEM) model. With a properly chosen ,, the ,FEM can produce models with very ,close-to-exact' stiffness of the continuous system. Numerical results have shown that the present method gives much more accurate results compared with the standard FEM and the NS-FEM. Copyright © 2010 John Wiley & Sons, Ltd. [source] Non-locking tetrahedral finite element for surgical simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2009Grand Roman Joldes Abstract To obtain a very fast solution for finite element models used in surgical simulations, low-order elements, such as the linear tetrahedron or the linear under-integrated hexahedron, must be used. Automatic hexahedral mesh generation for complex geometries remains a challenging problem, and therefore tetrahedral or mixed meshes are often necessary. Unfortunately, the standard formulation of the linear tetrahedral element exhibits volumetric locking in case of almost incompressible materials. In this paper, we extend the average nodal pressure (ANP) tetrahedral element proposed by Bonet and Burton for a better handling of multiple material interfaces. The new formulation can handle multiple materials in a uniform way with better accuracy, while requiring only a small additional computation effort. We discuss some implementation issues and show how easy an existing Total Lagrangian Explicit Dynamics algorithm can be modified in order to support the new element formulation. The performance evaluation of the new element shows the clear improvement in reaction forces and displacements predictions compared with the ANP element in case of models consisting of multiple materials. Copyright © 2008 John Wiley & Sons, Ltd. [source] A uniform nodal strain tetrahedron with isochoric stabilizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2009M. W. Gee Abstract A stabilized node-based uniform strain tetrahedral element is presented and analyzed for finite deformation elasticity. The element is based on linear interpolation of a classical displacement-based tetrahedral element formulation but applies nodal averaging of the deformation gradient to improve mechanical behavior, especially in the regime of near-incompressibility where classical linear tetrahedral elements perform very poorly. This uniform strain approach adopted here exhibits spurious modes as has been previously reported in the literature. We present a new type of stabilization exploiting the circumstance that the instability in the formulation is related to the isochoric strain energy contribution only and we therefore present a stabilization based on an isochoric,volumetric splitting of the stress tensor. We demonstrate that by stabilizing the isochoric energy contributions only, reintroduction of volumetric locking through the stabilization can be avoided. The isochoric,volumetric splitting can be applied for all types of materials with only minor restrictions and leads to a formulation that demonstrates impressive performance in examples provided. Copyright © 2008 John Wiley & Sons, Ltd. [source] Swift hopping gallium over [AlO4], tetrahedra in Ga/ZSM-5: A DFT studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2007Ilya V. Kusmin Abstract Density functional theory calculations were carried out to investigate gallium species (Ga+, [GaH2]+, and [GaO]+) stabilization in Ga-exchanged HZSM-5, using cluster modeling approach. Three isomeric gallium positions over [AlO4], zeolite fragment at T12 position were found. These isomers are turning into each over with low activation energy barrier and gallium fragment revolves around [AlO4], tetrahedron by hopping between cationic positions. Activation energies of gallium fragment hopping were computed and compared for different gallium containing cations. Those barriers were found to be times less than the activation energies of catalytic processes on gallium-exchanged zeolite. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Observation of orientational disorder in the hexagonal stuffed tridymite Sr0.864Eu0.136Al2O4 by the maximum-entropy methodJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2004H. Yamada The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4 tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gave Rwp = 2.99% and RB = 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased the R factors to Rwp = 2.81% and RB = 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4 tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along the c axis. These results suggest that AlO4 tetrahedra in Sr0.864Eu0.136Al2O4 are orientationally disordered. [source] The small-angle scattering structure functions of the single tetrahedronJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003W. Gille Basic properties of the SAS correlation function , (r) and related functions are represented for a tetrahedron of edge length a. An interval splitting into four basic r -intervals in a sequence of cases for averaging the intersection volume between two tetrahedrons has been performed. Remarkably simple analytic expressions result in the first r -interval. Indeed, ,(r) is a polynomial of degree three. The coefficients are given explicitly. The asymptotic expansion I(h) is compared with the exact scattering intensity I(h). [source] Algebraic solution to forward kinematics of a 3-DOF spherical parallel manipulatorJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 5 2001Ping Ji A three degree-of-freedom (3-DOF) spherical parallel manipulator consists of two tetrahedrons (pyramids). The base tetrahedron is fixed while the moving tetrahedron is rotating at the joint apex of the two tetrahedrons. This article studies the forward kinematics to a special 3-DOF spherical parallel manipulator, where the three apical angles of the moving tetrahedron are equal to their counterparts in the base tetrahedron, respectively. The final result of the forward kinematics to this parallel manipulator is a univariate quartic polynomial equation, which has a direct algebraic solution. In addition, a special right-angle case of the manipulator is investigated and its forward kinematics can be obtained directly. © 2001 John Wiley & Sons, Inc. [source] Atomistic characterization of structural and elastic properties of auxetic crystalline SiO2PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2007Hajime Kimizuka Abstract The structural and elastic changes with volume expansion in , -quartz and , -cristobalite, the typical polymorphs of silicon dioxide (SiO2), have been studied through first-principles calculations using the projector-augmented-wave (PAW) method, with particular emphasis on their negative Poisson's ratio behavior under negative pressure. The dominant mechanism of expansion is the increase of the Si,O,Si angles within their crystalline structures, whereas the SiO4 tetrahedron undergoes only a slight distortion. We provide theoretical ab initio results for a complete set of independent elastic constants of quartz and cristobalite with volume expansion. The present simulations confirm that the negative Poisson's ratio behavior is enhanced in the expansive phases of both polymorphs under negative pressures, with retaining strong elastic anisotropy. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modulation of primary and secondary infections in epidemics of carrot cavity spot through agronomic management practicesPLANT PATHOLOGY, Issue 1 2008F. Suffert The relative importance of primary and secondary infections (auto- and alloinfections) in the development of a carrot cavity spot (CCS) epidemic caused by Pythium spp. were investigated. Three cropping factors: fungicide application, soil moisture and planting density, were selected as the key variables affecting the disease tetrahedron. Their effects on: (i) disease measurements at a specific time, (ii) the areas under the disease progress curves (AUDPCs) and (iii) a time-dependent parameter in a pathometric incidence-severity relationship, were studied. Mefenoxam applications 5 and 9 weeks after sowing reduced the intensity of a field CCS epidemic that involved both primary and secondary infections. In microcosm experiments, mefenoxam reduced secondary infections by Pythium violae obtained by transplanting infected carrot roots and slowed disease progress (1·6 lesions per root in treated versus 5·8 lesions in non-treated microcosms). A deficit of soil moisture limited the movement of Pythium propagules to host tissue, and thus reduced primary infections in the field; it also promoted the healing of lesions, limiting lesion expansion and the potential for alloinfections (6·8,7·5 lesions per root in irrigated plots compared with 2·4 lesions in non-irrigated plots). A negative relationship between the mean root-to-root distance and the rate of alloinfections was established in microcosms; a reduction in mean planting density was also effective in limiting CCS development (0·5, 1·6 and 2·0 lesions per root in microcosms containing 8, 16 and 31 roots, respectively). An integrated disease management system based on a combination of cultural methods, such as optimized fungicide application, date of harvest versus soil moisture content, and host density versus planting pattern, may make a useful contribute to the control of CCS. [source] Investigations of the bond-selective response in a piezoelectric Li2SO4·H2O crystal to an applied external electric fieldACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2009O. Schmidt Piezoelectric lithium sulfate monohydrate, Li2SO4·H2O, was analyzed with respect to the relationship between the static structural properties of the crystal and its response to an external electric field. The static electron density was determined via standard low-temperature X-ray data collection at 90,(5) K using an Enraf,Nonius CAD-4 diffractometer, Mo K, radiation and multipole model refinement. Then a synchrotron-radiation experiment using the D3 beamline at HASYLAB was conducted in order to investigate the structural deformations in Li2SO4·H2O caused by an applied external electric field. In particular, the shifts of Bragg-peak positions induced by the electric field were measured and the piezoelectric constants d211, d222, d233 and d213 of Li2SO4·H2O were obtained from the shifts. With the same experimental setup the variations of more than 100 Bragg intensities were measured under an applied electric field. The data were used to refine the corresponding displacements of individual atoms within the unit cell. The distortions of the cation,anion bond lengths in the LiO4, LiO3(H2O) and SO4 tetrahedra were evaluated and then analyzed in terms of the electron-density-related properties of the Li,O and S,O bonds. The two lithium structural units were found to be strongly deformed by the applied electric field, while the SO4 tetrahedron changed less. This is in agreement with the low bond strength of the Li,O bonds. [source] On a minimum tetrahedron in a three-dimensional lattice.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2009Part I. Lattices with a shortest basis fulfilling b The problem of a representative body of a three-dimensional lattice is considered. The cell fulfilling a + b + c = min is clearly not unique: even five mutually non-congruent such cells can exist in some lattices [Gruber (1973). Acta Cryst. A29, 433,440]. The idea that this number could be reduced by replacing the cell (i.e. a parallelepiped) by another, possibly more suitable, geometrical object is considered. For this object a lattice tetrahedron fulfilling the condition a + b + c + d + e + f = min is chosen, a to f being the lengths of its edges. It is called the minitetrahedron of the lattice. In this article, the problem is solved in detail for lattices that can be generated by a basis a, b, c fulfilling |a| + |b| + |c| = min, b,·,c, 0, a,·,c, 0, a,·,b, 0. It turns out that in this case not more than two mutually non-congruent minitetrahedra can exist. Necessary and sufficient conditions for the uniqueness are found. They have the form of inequalities between the lengths of the edges and diagonals of the parallelepiped formed by the vectors a, b, c. A procedure for determining all minitetrahedra of a given lattice is shown. Some results are illustrated graphically and all assertions are proved mathematically. [source] X-ray diffraction by a crystal in a permanent external electric field: electric-field-induced structural response in ,-GaPO4ACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2006Semen Gorfman For the first time, site-selective distortion has been investigated for two different structural units in the ternary compound ,-GaPO4 under the influence of a permanent external electric field. Based on 54 measured reflection intensities, the electric-field-induced distortion of PO4 and GaO4 tetrahedra in ,-GaPO4 crystals is evaluated using a model of pseudoatomic displacements introduced recently [Gorfman, Tsirelson & Pietsch (2005). Acta Cryst. A61, 387396]. A stronger variation of the P,O bond lengths in the PO4 tetrahedron was found compared to the bonds in the GaO4 tetrahedron. The different distortions of the tetrahedra owing to the electric field were analysed in terms of the valence charge density of ,-GaPO4 and its topological characteristics. The larger charge of the P pseudoatom compared to the Ga atom was recognized as the main reason for the higher sensitivity of the PO4 tetrahedron to a permanent external electric field. [source] Diffraction line profiles from polydisperse crystalline systemsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2001Paolo Scardi Diffraction patterns for polydisperse systems of crystalline grains of cubic materials were calculated considering some common grain shapes: sphere, cube, tetrahedron and octahedron. Analytical expressions for the Fourier transforms and corresponding column-length distributions were calculated for the various crystal shapes considering two representative examples of size-distribution functions: lognormal and Poisson. Results are illustrated by means of pattern simulations for a f.c.c. material. Line-broadening anisotropy owing to the different crystal shapes is discussed. The proposed approach is quite general and can be used for any given crystallite shape and different distribution functions; moreover, the Fourier transform formalism allows the introduction in the line-profile expression of other contributions to line broadening in a relatively easy and straightforward way. [source] Rigorous solution of a Hubbard model extended by nearest-neighbour Coulomb and isotropic exchange interaction on a triangle and tetrahedronANNALEN DER PHYSIK, Issue 4 2009R. Schumann In connection with the study of the extended Hubbard model on an isosceles triangular cluster, we discovered a factor two error in the coding of the Ising part of the Heisenberg term in the Hamiltonian. In consequence the rigorous results remain valid, but not for the isotropic Heisenberg model, but for an anisotropic Heisenberg model. [source] Linkage Analysis of Affected Sib Pairs Allowing for Parent-of-Origin EffectsANNALS OF HUMAN GENETICS, Issue 1 2005Chih-Chieh Wu Summary Parent-of-origin effects, also known as genomic imprinting, exist for many mammalian genes. For imprinted genes the expression of an allele depends upon the sex of the transmitting parent. Here we have developed a method based on alleles that are shared identical by descent by affected sib pairs, that allows for parent-of-origin effects. Our method allows for sex-specific recombination rates, an important consideration in studying imprinted genes. We have also derived a tetrahedron for the true identical-by-descent frequencies accounting for parent-of-origin effects. Using this tetrahedron, we propose a robust generalized minmax test for linkage and discuss its properties in the presence of genomic imprinting. We have also performed power comparisons of various allele sharing tests and provide regions of the tetrahedron in which the different tests are optimal. We also provide useful strategies to determine the optimal tests to use while performing a genome scan. [source] Orthorhombic aluminium oxyfluoride, AlOFACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Alexander D. Vasiliev Crystals of the title compound were extracted from the bulk of grown SrAlF5 crystals as unexpected inclusions that were identified as the long sought after aluminium oxyfluoride. The structure of AlOF is built up from tetrahedral and octahedral polyhedra. Each tetrahedron is bisected by a mirror plane, with the Al atom and two vertex anions in the plane. All tetrahedral vertices are positions of competing oxide and fluoride ions and are shared with octahedra. These shared vertices belong to two octahedral edges which join the octahedra to form infinite zigzag chains. The chains are strung along twofold screw axes that run parallel to the unit-cell b axis. The remaining two octahedral vertices are occupied only by fluoride ions. A small deficiency in the occupation of the octahedral Al position was suggested by the refinement. However, the stoichiometry of the compound is AlOF within experimental uncertainty. The Al,F(O) distances are separated into three groups with average values of 1.652,(3) (tetrahedra), 1.800,(2) (octahedra) and 1.894,(2),Å (octahedra). This structure differs widely from the reported tetragonal phase Al1,xO1,3xF1+3x (x = 0.0886) [Kutoglu (1992). Z. Kristallogr.199, 197,201], which consists solely of octahedral structural units. [source] (Di- tert -butylmethylphosphane)(,2 -di- tert -butylphosphanylphosphinidene)(triphenylphosphane)platinum(0)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Antoni Konitz The crystal structure of the title compound, [Pt(C8H18P2)(C9H21P)(C18H15P)] or [(Ph3P)(tBu2PMe)Pt(,2 - tBu2PP)], contains four molecules in the asymmetric unit with slightly different conformations. The P,P distances in the tBu2PP ligands are similar for all four molecules [2.0661,(13),2.0678,(13),Å] and indicate a multiple character of the P,P bond in the tBu2PP ligand. Molecules of the asymmetric unit can be assembled into a tetrahedron that fulfils the requirements for a rhombic disphenoid. The coordination of the Pt atom in all four molecules is square planar, with r.m.s. deviations from the PtP4 planes in the range 0.03,0.05,Å. All planes of the PtP4 groups are approximately parallel to the ab plane of the unit cell. The structure represents an unusual unsymmetrical platinum phosphinidene derivative. [source] Ce20Mg19Zn81: a new structure type with a giant cubic cellACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Volodymyr Pavlyuk Icosacerium nonadecamagnesium henoctacontazinc, Ce20Mg19Zn81, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F3m, a = 21.1979,(8),Å] and represents a new structure type among the technologically important family of ternary rare earth,transition metal,magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce20Mg19Zn81 structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+Zn4+Zn4+Zn12+Ce6), B (Mg+Zn12+Ce4+Zn24+Ce4), C (Zn4+Zn12+Mg6) and D (Zn4+Zn4+Mg12+Ce6), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic-type bonding. [source] Crystallographic report: Crystal structure of tris(2,6-di- tert -butyl-4-methylphenolato- O) (tetrahydrofuran- O) erbium toluene solvateAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2004Xiaoping Xu Abstract A low-coordinate aryloxo erbium complex, [(ArO)3Er(THF)](MePh), has been synthesized by the reaction of anhydrous ErCl3 with three equivalents of NaOAr in tetrahydrofuran. The central erbium atom is coordinated by three oxygen atoms of the aryloxo ligands and one oxygen atom of the tetrahydrofuran molecule, resulting in a distorted tetrahedron. Copyright © 2004 John Wiley & Sons, Ltd. [source] Crystallographic report: Ethyltriphenyltin(IV), Et(Ph)3SnAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2004José S. Casas Abstract The crystal lattice of the title compound comprises isolated molecules. The coordination polyhedron is a slightly distorted tetrahedron with C,Sn,C bond angles ranging from 106.62(17)° to 113.9(3)°. Copyright © 2004 John Wiley & Sons, Ltd. [source] Bis(azido-,N)[(6R,7S,8S,14S)-(,)-sparteine-,2N,N,]copper(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2003Yong-Kyu Kim In the title compound, [Cu(N3)2(C15H26N2)], the chiral alkaloid (,)- l -sparteine (Sp) acts as a bidentate ligand, with two azide ligands occupying the remaining coordination sites, forming a distorted CuN4 tetrahedron. The dihedral angle between the NSp,Cu,NSp and Nazide,Cu,Nazide planes is 55.3,(2)°. Principal dimensions include Cu,NSp,=,2.011,(6) and 2.025,(5),Å, and Cu,Nazide,=,1.939,(6) and 1.934,(7),Å. The mid-point of the NSp,NSp line does not lie exactly in the Nazide,Cu,Nazide plane, but is tilted towards one of the NSp atoms by 0.026,Å. [source] Synthesis and Crystal Structure of Two iso - closo 11-Vertex p -Bromobenzoate Ruthenoborane Clusters: [(PPh3)(p -BrC6H4CO2)2RuB10H8] and [(PPh3)2Ru(p -BrC6H4CO2)-(PPh3)RuB10H9]CHINESE JOURNAL OF CHEMISTRY, Issue 12 2006Qing-Liang Guo Abstract The title clusters [(PPh3)(p -BrC6H4CO2)2RuB10H8] (1) and [(PPh3)2Ru(PPh3)(p -BrC6H4CO2)RuB10H9] (2) have been prepared and characterized by elemental analysis, FT-IR, 1H, 13C NMR spectra and single-crystal X-ray diffraction analysis. The clusters crystallize in monoclinic system, space group C2/c, with a=2.569(4) nm, b=1.546(2) nm, c=1.927(3) nm, ,=95.11(2)°, Z=8, V=7.622(21) nm3, Dc=1.533 Mg/m3, F(000)=3472, S=1.009, R=0.0418, wR=0.0775 and triclinic system, space group P -1, with a=1.3142(3) nm, b=1.3761(3) nm, c=1.8503(4) nm, ,=90.445(4)°, ,=105.950(4)°, (=108.980(4)°, Z=2, V=3.0251(12) nm3, Dc=1.434 Mg/m3, F(000)=1316, S=1.007, R=0.0464, wR=0.1175, respectively for 1 and 2. In the structures, both of the clusters are based on a closo -type C2v 1:2:4:2:2 RuB10 stack with the metal occupying the unique six-connected apical position. In cluster 1, the metal center has three exo -polyhedral ligands:one triphenylphosphine and two dative oxygen atoms of p -bromobenzoates. The other oxygen atoms of two p -bromobenzoate are additionally bonded to B(2) and B(3) atoms respectively, resulting in two exo -cyclic five-membered Ru-O-C-O-B rings and engendering a symmetrical conformation. The cluster 2 is a bimetallic species in which the second ruthenium is bound to the {RuB10} center via one Ru,Ru bond and two {RuHµB} bridges resulting in one closo distorted exo -polyhedral Ru(1)- Ru(2)-B(3)-B(6) tetrahedron. [source] | ||||||||||||||||||||||||||||||||||