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Angular Dependence (angular + dependence)
Selected AbstractsCorrelations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen-free flame retardant polyolefin compoundsFIRE AND MATERIALS, Issue 1 2009Jeffrey M. Cogen Abstract Seven halogen-free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m2 during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no-burn) results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Symmetrization of diffraction peak profiles measured with a high-resolution synchrotron X-ray powder diffractometerJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2006H. Hibino The asymmetry of diffraction peak profiles observed with a high-resolution synchrotron powder X-ray diffractometer has been successfully removed by a double deconvolution method. In the first step, the asymmetry caused by the axial divergence aberration of the diffractometer is removed by a whole-pattern deconvolution method based on an a priori theoretical model for the aberration. In the second step, the residual asymmetry, the origin of which can be ascribed to the aberrations of the beamline optics, is also removed by a whole-pattern deconvolution method, based on an empirical model derived from the analysis of experimental diffraction peak profiles of a standard Si powder (NIST SRM640b). The beamline aberration has been modelled by the convolution of a pseudo-Voigt or Voigt function with an exponential distribution function. It has been found that the angular dependence of the asymmetry parameter in the exponential function is almost proportional to tan,, which supports the idea that the residual asymmetry should be ascribed mainly to the intrinsic asymmetry in the spectroscopic distribution of the source X-ray supplied by the beamline optics of the synchrotron facility. Recently developed procedures of whole-pattern deconvolution have been improved to treat the singularity of the instrumental function in the measured angular range. Formulae for the whole-pattern deconvolution based on the Williamson,Hall-type dependence of the width parameter of the instrumental function have also been developed. The method was applied to the diffraction intensity data of a standard ZnO powder sample (NIST SRM674) measured with a high-resolution powder diffractometer on beamline BL4B2 at the Photon Factory. The structure parameters of ZnO were refined from the integrated peak intensities, which were extracted by an individual profile fitting method applying symmetric profile models. The refined structure parameters coincide fairly well with those obtained from single-crystal data. [source] A Kirkwood-Buff derived force field for amidesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006Myungshim Kang Abstract A force field for the computer simulation of aqueous solutions of amides is presented. The force field is designed to reproduce the experimentally observed density and Kirkwood,Buff integrals for N -methylacetamide (NMA), allowing for an accurate description of the NMA activity. Other properties such as the translational diffusion constant and heat of mixing are also well reproduced. The force field is then extended to include N,N,-dimethylacetamide and acetamide with good success. Analysis of the simulations of low concentrations of NMA in water indicates a high degree of solvation with only 15% of the NMA molecules involved in solute,solute hydrogen bonding. There is only a weak angular dependence of the solute,solute hydrogen bonding interaction with a minimum at an angle of 65° for the NH and CO dipole vectors. The models presented here provide a basis for an accurate force field for peptides and proteins. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1477,1485, 2006 [source] Study of order and dynamic processes in tendon by NMR and MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2007G. Navon PhD Abstract Tendons are composed of a parallel arrangement of densely packed collagen fibrils that results in unique biomechanical properties of strength and flexibility. In the present review we discuss several advanced magnetic resonance spectroscopy (MRS) and imaging (MRI) techniques that have allowed us to better understand the biophysical properties of tendons and ligaments. The methods include multiple quantum and T2 filtering combined with NMR and MRI techniques. It is shown in detail how these techniques can be used to extract a number of useful parameters: 1) the 1H- 1H and 1H- 2H dipolar interactions; 2) the proton exchange rates between water and collagen, and between water molecules; 3) the distribution of fibril orientations; and 4) the anisotropy of diffusion. It is shown that relaxation data as a function of angular dependence can be obtained in vivo using mobile NMR sensors. Finally, this article describes how double quantum filtered (DQF) MRI can be used to image and monitor the healing process in injured tendons. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source] Phase Biaxility in Smectic-A Side-Chain Liquid Crystalline ElastomersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2009Rebekka Storz Abstract 2H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d6 and hexamethylbenzene-d18, at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase. [source] Cooling-field dependence of exchange bias and asymmetric reversal modes in a nanoparticles system with ferromagnetic core and antiferromagnetic matrix morphologyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009Yong Hu Abstract Interest in exchange bias (EB) in magnetic nanoparticles has increased in the past few years by virtue of its potential for application in fields such as ultrahigh-density magnetic recording. A modified Monte Carlo Metropolis method is performed to simulate the effect of cooling field on EB and asymmetric reversal modes of a granular system of ferromagnetic (FM) nanoparticles embedded in an antiferromagnetic (AFM) matrix, based on three-dimensional classical Heisenberg model. The results show that the EB first decreases slightly due to the energy barriers in the antiferromagnet, while the coercivity and vertical magnetization shift increase with the increase of cooling field, finally, they all level off as the cooling field is strong enough. Whereas the cooling- and measuring-field angular dependence of asymmetric reversal modes reveal asymmetric reversal mechanism and interesting rotation process of FM spins, confirming the existence of the net magnetization on the surface of AFM matrix. The reason may be due to the energy competition and geometric frustration of system. However, the strong interfacial coupling may change the intrinsic atomic configuration of antiferromagnet to influence the EB and reversal modes. [source] One- and two-dimensional porous silicon photonic crystals: momentum dispersion relations and stopbands analysisPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009Nadav Gutman Abstract We report on a novel approach to analyze and measure the optical properties of one- and two -dimensional photonic crystals (PCs) in all spatial directions inlcluding the symmetry axis of the PCs. The analysis is based on calculating momentum dispersion relations between the ordinary and the Bloch components of the wavevector and finding momentum stop-bands of the PC. This method provides a direct way to analyze the angular dependence of the reflection and the diffraction pattern of a monochromatic optical beam approaching the PC. Measurements have been performed on 1D PCs, e.g., 1D periodic structures of micro-porous silicon and 2D periodic arrays of macro-porous silicon. The periodicity of these PCs is about 2.5 to 4 ,m so that their momentum stop-bands fall in the mid-infrared (IR) wavelengths. We analyze several geometries, including slabs and prisms, to map the momentum dispersion relations and stopbands associated with guided and radiation modes. Angular reflection and diffraction measurements using a tunable CO2 laser showed a good agreement with the calculated momentum dispersion relations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Matrix isolation and magnetic parameters of septet 3,5-dicyanopyridyl-2,4,6-trinitreneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2010Sergei V. Chapyshev Abstract Septet 3,5-dicyanopyridyl-2,4,6-trinitrene was synthesized together with quintet 2-azido-3,5-dicyanopyridyl-4,6-dinitrene, quintet 4-azido-3,5-dicyanopyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-dicyanopyridyl-4-nitrene, and triplet 2,4-diazido-3,5-dicyanopyridyl-6-nitrene by photolysis of 2,4,6-triazido-3,5-dicyanopyridine in solid argon at 4,K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from spectral simulations. All signals in the EPR spectra of the nitrenes, randomly oriented in the solid phase, were unambiguously assigned based on eigenfield calculations of the Zeeman energy levels and angular dependences of resonance fields. Copyright © 2009 John Wiley & Sons, Ltd. [source] Lattice distortion (Peierls Transition) caused by spin interaction in the chaotic impurity system of a semiconductorANNALEN DER PHYSIK, Issue 12 2009A. Zabrodskii Abstract The effect of an elastic spontaneous distortion of the crystal lattice of a doped semiconductor Ge:As near the insulator,metal (IM) phase transition has been discovered. The effect is manifested in the electron spin resonance (ESR) of neutral As atoms as a splitting of the single resonance absorption line. It observed at electron concentrations in the range 0.8 < n/nC < 1 at low temperatures T < 100 K (nC = 3.7 × 1017 cm -3 is the critical electron concentration for the IM phase transition). The splitting is the strongest along each of the six [110] directions, which indicates that the local lattice distortion occurs just in these directions. As a result, a sample is possibly divided into separate domains differing in the directions of compressive or tensile deformations. A study of concentration, temperature, and angular dependences of the effect has shown that the phenomenon discovered can be understood in terms of the Peierls spin transition model. [source] | |||||||||||||