Search results for " Geometry"
showing 10 items of 2294 documents
Crystal structure of ethyl 2-(di-eth-oxy-phosphor-yl)-2-(2,3,4-tri-meth-oxy-phen-yl)acetate.
2014
The title compound, C17H27O8P, was prepared by Michaelis–Arbuzov reaction of ethyl 2-bromo-2-(2,3,4-trimethoxyphenyl)acetate and triethyl phosphite. Such compounds rarely crystallize, but single crystals were recovered after the initial oil was left for approximately 10 years. The bond angle of thesp3-hybridized C atom connecting the benzene derivative with the phospho unit is widened marginally [112.5 (2)°]. The terminal P—O bond length of 1.464 (2) Å clearly indicates a double bond, whereas the two O atoms of the ethoxy groups connected to the phosphorous atom have bond lengths of 1.580 (2) Å and 1.581 (3) Å. The three methoxy groups emerge out of the benzene-ring plane due to steric hind…
Crystal structure of N-(tert-butoxycarbonyl)phenylalanyldehydroalanine isopropyl ester (Boc–Phe–ΔAla–OiPr)
2014
In the crystal structure of the dehydrodipeptide (Boc-Phe-ΔAla-OiPr), the molecule has a trans configuration of the N-methylamide group. Its geometry is different from saturated peptides but is in excellent agreement with other dehydroalanine compounds. In the crystal, an N—H⋯O hydrogen bond links the molecules in a herringbone packing arrangement.
Halogen...halogen interactions in pressure-frozen ortho- and meta-dichlorobenzene isomers.
2007
Isomers 1,2-dichlorobenzene (o-DCB) and 1,3-dichlorobenzene (m-DCB) were high-pressure frozen in-situ in a Merrill–Bassett diamond–anvil cell and their structures determined at room temperature and at 0.18 (5) GPa for o-DCB, and 0.17 (5) GPa for m-DCB by single-crystal X-ray diffraction. The patterns of halogen...halogen intermolecular interactions in these structures can be considered to be the main cohesive forces responsible for the molecular arrangements in these crystals. The molecular packing of dichlorobenzene isomers, including three polymorphs of 1,4-dichlorobenzene (p-DCB), have been compared and relations between their molecular symmetry, packing arrangements, intermolecular inte…
Minimal Supergravity Scalar Neutrino Dark Matter and Inverse Seesaw Neutrino Masses
2008
We show that within the inverse seesaw mechanism for generating neutrino masses minimal supergravity is more likely to have a sneutrino as the lightest superparticle than the conventional neutralino. We also demonstrate that such schemes naturally reconcile the small neutrino masses with the correct relic sneutrino dark matter abundance and accessible direct detection rates in nuclear recoil experiments.
Stochastic seismic analysis of multidegree of freedom systems
1984
Abstract A unconditionally stable step-by-step procedure is proposed to evaluate the mean square response of a linear system with several degrees of freedom, subjected to earthquake ground motion. A non-stationary modulated random process, obtained as the product of a deterministic time envelope function and a stationary noise, is used to simulate earthquake acceleration. The accuracy of the procedure and its extension to nonlinear systems are discussed. Numerical examples are given for a hysteretic system, a duffing oscillator and a linear system with several degrees of freedom.
Pieri and Projective Geometry
2021
Projective geometry can be described as the geometry of the straightedge, in comparison with Euclid’s geometry of straightedge and compass.
Surface Development of (As2S3)1–x (AgI)x Thin Films for Gas Sensor Applications
2011
Thin (As2S3)100−x(AgI)x (x = 0–40) films were deposited by thermal vacuum evaporation from the respective bulk glasses; their structure and morphology before and after illumination with light have been studied by scanning electron microscopy (SEM). As-deposited films show fractional evaporation and surface inhomogeneities but after illumination they become uniform on the surface and in the depth as revealed by SEM top-view and cross-section images. Mechanical parameters like stress and microhardness of as-prepared and illuminated films were also investigated. The results from the stress measurements show variation in both the sign and the magnitude of the values with increasing AgI content …
Filament sets and homogeneous continua
2007
Abstract New tools are introduced for the study of homogeneous continua. The subcontinua of a given continuum are classified into three types: filament , non-filament , and ample , with ample being a subcategory of non-filament. The richness of the collection of ample subcontinua of a homogeneous continuum reflects where the space lies in the gradation from being locally connected at one extreme to indecomposable at another. Applications are given to the general theory of homogeneous continua and their hyperspaces.
DNA cleavage reaction induced by dimeric copper(II) complexes of N-substituted thiazole sulfonamides
2005
A new dinuclear copper(II) complex has been synthesised and structurally characterised: [Cu2(tz-ben)4] (Htz-ben = N-thiazol-2-yl-benzenesulfonamide). Its crystal structure, magnetic properties and electronic paramagnetic resonance (EPR) spectra were studied in detail. In the compound the metal centres are bridged by four non-linear triatomic NCN groups. The coordination geometry of the copper ions in the dinuclear entity is distorted square pyramidal (4+1). Two thiazole N and two sulfonamido N atoms occupy the equatorial positions and one sulfonamido O atom is in the axial position. Magnetic susceptibility data show a strong antiferromagnetic coupling, -2J = 114.1 cm(-1). The EPR spectra of…
Structure and superconductivity in LnNi2B2C: comparison of calculation and experiment
2001
Abstract The experimental relation between the superconducting transition temperature ( T c ) and lattice size for the lanthanide nickel borocarbides is clarified. The electronic density of states (DOS) at the Fermi energy is calculated by the LMTO method for selected non-magnetic lanthanides. The T c and the DOS are both shown to scale in the same way with a structural parameter that characterizes the bond angle in the NiB 4 tetrahedra. The results strongly support arguments that the suppression of superconductivity on going from smaller to larger lanthanides in the quaternary nickel borocarbides is structurally driven. A structure– T c relationship of this type is unusual for intermetalli…