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Significant Anisotropy (significant + anisotropy)
Selected AbstractsAnisotropic Optical Properties of Semitransparent Coatings of Gold Nanocaps,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006J. Liu Abstract An ordered array of cap-shaped gold nanoparticles has been prepared by vapor deposition onto polystyrene nanospheres supported on a glass substrate. The method of fabrication used imparts a significant anisotropy to the geometric and optical properties of the coating. The optical-absorption properties of these deposits have been measured using UV-vis spectrometry and simulated using a code based on the discrete dipole approximation. Because the nanocaps are not interconnected, they interact with incident light as individual particles with a plasmon resonance that depends upon wavelength and the polarization vector of the light. The resulting extinction peaks manifest in the upper visible and near-infrared regions of the electromagnetic spectrum. Surprisingly, varying the angle of incidence of the light (for a fixed polarization) has no effect on the optical properties of individual nanocaps. Calculations show that these phenomena may be readily interpreted in terms of dipole resonances excited across the longitudinal, transverse, and short-transverse directions of the nanocaps. Coatings comprised of arrays of these particles have the potential to serve as angularly and spectrally selective filters. [source] Molecular dynamics simulations of fluid methane properties using ab initio intermolecular interaction potentialsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2009Shih-Wei Chao Abstract Intermolecular interaction energy data for the methane dimer have been calculated at a spectroscopic accuracy and employed to construct an ab initio potential energy surface (PES) for molecular dynamics (MD) simulations of fluid methane properties. The full potential curves of the methane dimer at 12 symmetric conformations were calculated by the supermolecule counterpoise-corrected second-order Møller-Plesset (MP2) perturbation theory. Single-point coupled cluster with single and double and perturbative triple excitations [CCSD(T)] calculations were also carried out to calibrate the MP2 potentials. We employed Pople's medium size basis sets [up to 6-311++G(3df, 3pd)] and Dunning's correlation consistent basis sets (cc-pVXZ and aug-cc-pVXZ, X = D, T, Q). For each conformer, the intermolecular carbon,carbon separation was sampled in a step 0.1 Å for a range of 3,9 Å, resulting in a total of 732 configuration points calculated. The MP2 binding curves display significant anisotropy with respect to the relative orientations of the dimer. The potential curves at the complete basis set (CBS) limit were estimated using well-established analytical extrapolation schemes. A 4-site potential model with sites located at the hydrogen atoms was used to fit the ab initio potential data. This model stems from a hydrogen,hydrogen repulsion mechanism to explain the stability of the dimer structure. MD simulations using the ab initio PES show quantitative agreements on both the atom-wise radial distribution functions and the self-diffusion coefficients over a wide range of experimental conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Hot Forging of a Textured ,-Sialon CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Andrew Carman A texture was introduced into an Sm-,-sialon ceramic by hot pressing, such that the c -axis was preferentially oriented normal to the pressing direction. The material was then uniaxially hot forged for up to 60 min, with the forging direction normal to the hot-pressing direction. The texture initially reduced to a one-dimensional preferential orientation in the direction normal to both the hot-pressing and hot-forging directions. Further deformation resulted in a two-dimensional texture normal to the hot-forging direction. The forging process was used to produce a strong one-dimensional texture by alternating between the hot-pressing and hot-forging directions, thereby producing a material with significant anisotropy in its properties. [source] Secondary Ion Mass Spectroscopy Study of Oxygen-18 Tracer Diffusion in 2/1-Mullite Single CrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001Peter Fielitz Oxygen 18O tracer diffusion in Czochralski-grown mullite single crystals is investigated along [010] and [001]. Oxygen diffusion coefficients range between ,5 × 10,20 m2/s (1250°C) and ,9 × 10,18 m2/s (1525°C). The data does not show any significant anisotropy. The values of the activation enthalpy (4.5 eV) and of the activation entropy ((3.4 ± 1.6)kB, where kB is the Boltzmann constant) suggest that the atomic transport occurs via thermally activated vacancies. [source] Longitudinal diffusion tensor imaging in a rat brain glioma modelNMR IN BIOMEDICINE, Issue 8 2008Silvia Lope-Piedrafita Abstract In order to investigate the properties of water motion within and around brain tumors as a function of tumor growth, longitudinal diffusion tensor imaging (DTI) was carried out in a rat brain glioma (C6) model. As tumors grew in size, significant anisotropy of water diffusion was seen both within and around the tumor. The tissue water surrounding the tumor exhibited high planar anisotropy, as opposed to the linear anisotropy normally seen in white matter, indicating that cells were experiencing stress in a direction normal to the tumor border. When tumors were sufficiently large, significant anisotropy was also seen within the tumor because of longer-range organization of cancer cells within the tumor borders. These findings have important implications for diffusion-weighted MRI experiments examining tumor growth and response to therapy. Copyright © 2008 John Wiley & Sons, Ltd. [source] Directed anisotropy in bis(acetato-,2O,O,)diaquazinc(II) at 110 and 250,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Martin Lutz The molecule of the title compound, [Zn(C2H3O2)2(H2O)2], is located on a twofold axis in the crystal structure. The displacement parameters and the thermal expansion of the crystal show significant anisotropy. This is explained by the two-dimensional hydrogen-bonded structure, with only very weak interactions perpendicular to it. Besides the overall molecular motion, there are internal vibrations, which cause the Zn,O(carboxylate) bonds to fail the Hirshfeld rigid-bond test. It is shown that this can be interpreted in terms of the steric strain in the four-membered chelate ring due to the bidentate carboxylate coordination. [source] Crystallization and preliminary crystallographic studies of MOMP (major outer membrane protein) from Campylobacter jejuniACTA CRYSTALLOGRAPHICA SECTION D, Issue 12-2 2004Jean Michel Bolla Campylobacter jejuni is the leading bacterial cause of human enteritis linked to ingestion of contaminated food or water. MOMP, the major outer membrane protein from these Gram-negative bacteria, belongs to the porin family. In order to determine the three-dimensional structure of this protein and to elucidate the underlying molecular mechanisms, the MOMP from C. jejuni strain 85H has been purified and crystallized by vapour diffusion. Two crystal forms were characterized for this membrane protein. X-ray diffraction data were collected to a resolution of 3.1,Å using a synchrotron-radiation source from the orthorhombic crystal form, which belonged to space group P21212 with unit-cell parameters a = 170.1, b = 101.9, c = 104.9,Å. With a trimer in the asymmetric unit, the solvent content is 64% (VM = 3.4,Å,Da,1). The other form exhibits trigonal symmetry (space group R3) with hexagonal unit-cell parameters a = b = 94.2, c = 161.2,Å, but diffracts X-rays poorly to about 4,Å with significant anisotropy. [source] | |||||||||||||