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221.
Emil Polturak Amit Kanigel Nir Gov Tuvy Markovich Joan Adler 《Physica B: Condensed Matter》2000,280(1-4):142-145
We have recently observed that the resistance to shear of solid 4He decreases dramatically near the first-order BCC–HCP transition. In our view, the solid shears via a diffusive counter-flow of atoms and point defects. The mechanism of self diffusion couples point defects with one specific phonon which softens as the transition is approached. Since such a scenario can possibly lead to melting, it is important to understand (a) which type of point defect is associated with the reduction of shear resistance, and (b) can the presence of point defects lead to the softening of phonons. We report here the results of numerical simulations and analytic modeling. Our results indicate that split interstitials are much more effective than vacancies in lowering the resistance to shear. We suggest that these excitations can be generated as a result of a “local mode” excited in the crystal. 相似文献
222.
Suppose G is a graph embedded in Sg with width (also known as edge width) at least 264(2g−1). If P ⊆ V(G) is such that the distance between any two vertices in P is at least 16, then any 5‐coloring of P extends to a 5‐coloring of all of G. We present similar extension theorems for 6‐ and 7‐chromatic toroidal graphs, for 3‐colorable large‐width graphs embedded on Sg with every face even‐sided, and for 4‐colorable large‐width Eulerian triangulations. © 2001 John Wiley & Sons, Inc. J Graph Theory 36: 105–116, 2001 相似文献
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225.
Víctor March Manuel Arrayás José Luis Trueba Joan Montanyà David Romero Glòria Solà Daniel Aranguren 《Journal of Electrostatics》2009,67(2-3):301-306
A numerical study of laser-triggered discharges in air at atmospheric pressure is presented for an ultraviolet laser in small gaps. Two models, one for the ionization of the air by the laser pulse and the second for the streamer evolution have been computed. From results of numerical simulations the influence of the laser parameters such as energy, pulse duration and beam radius is analyzed and electron distributions are obtained for different small gaps. Electric field, streamer velocity and evolution of the ionized volume are calculated by means of streamer simulations. This paper shows the main features of the laser-triggered discharges and also the importance of using numerical simulations in a laser-triggered experiment. 相似文献
226.
Anamika Das Christoph Marschner Joan Cano Judith Baumgartner Joan Ribas M. Salah El Fallah Samiran Mitra 《Polyhedron》2009
Two new dicyanamido-bridged di- and polynuclear complexes of Co(II), [Co(dca)(tptz)(H2O)]2·2(ClO4) (1) and [Co(dca)2(imz)2]n (2) [dca, dicyanamide; tptz, 2,4,6-tris(2-pyridyl)1,3,5-triazine; and imz, imidazole] have been synthesized and characterized structurally, as well as magnetically. The X-ray single crystal structure determination of complex 1 shows that two symmetry related octahedral Co(II) ions are separated by dca ligand and other coordination sites are satisfied by tptz and aquo ligands. Each dinuclear unit is associated with each other by intramolecular hydrogen bonding interactions, giving rise to a 1D chain structure. On the other hand complex 2 is a 1D coordination polymer having [Co(II)(imz)2] units connected by double bridging dca ligands. These 1D chains interact through face-to-face π–π stacking interactions of the imz rings extending the dimensionality to a 2D supramolecular network. The variable temperature (300–2 K) magnetic measurements of both compounds reveal that dicyanamide exhibits a weak antiferromagnetic interaction between the metal centers. 相似文献
227.
Reverse osmosis (RO) is a widely used and rapidly growing desalination technology. A major disadvantage of this process is that the concentrate from the RO process, which could be as much as 25% of the feed stream, represents a polluting stream. This waste stream could pose a significant challenge to the implementation of this process, particularly for inland communities which do not have the option of ocean disposal. An excellent environmentally benign approach to disposal could be beneficial reuse of the waste stream. This study presents two innovative beneficial reuse strategies for RO concentrate produced by an integrated membrane system (IMS) from a wastewater reclamation facility. The technologies evaluated in this study included bipolar membrane electrodialysis (BMED) for conversion of RO concentrate into mixed acid and mixed base streams, and electrochlorination (EC) for onsite chlorine generation. Bench-scale studies conducted with BMED demonstrated that RO concentrate could be desalted while producing mixed acids and mixed bases with concentrations as high as 0.2N. Similarly, the EC process was capable of producing a 0.6% hypochlorite solution from RO concentrate. The acids and bases as well as the hypochlorite produced could be directly applied to the RO process as well as upstream pre-treatment processes. A preliminary economic evaluation of the viability of these two approaches was conducted by conducting rough order of magnitude cost estimates based on the bench-scale performance of these processes on RO concentrate. A comparison of the overall costs of an Integrated Membrane System utilizing these innovative reuse strategies with conventional disposal options and thermal zero liquid discharge treatment is presented. This comparison indicates that a reuse approach might be economically viable for inland wastewater reuse facilities that utilize RO membranes and have limited options for concentrate disposal. 相似文献
228.
Esther Vizcaino Lourdes ArellanoPilar Fernandez Joan O. Grimalt 《Journal of chromatography. A》2009,1216(25):5045-5051
A sensitive and selective method for the determination of the whole congener distribution of polybromodiphenyl ethers in environmental and biological samples in one single instrumental run is described. The method is based on gas chromatography coupled to low-resolution mass spectrometry in negative ion chemical ionization mode. It allows determination of these compounds at concentration levels lower than 10−14 g. A programmed temperature vaporization injector has been used to ensure maximum compound transfer to the chromatographic column while maintaining low thermal degradation levels of the more brominated congeners. Selectivity was increased by modification of the MS source parameters for optimization of the abundance of the high mass fragment ions. Under optimized condition, good repeatability (1.7–9.1%) and reproducibility (4.1–20%), and low detection limits, ranging between 1.5 and 15 pg ml−1, were obtained. These features afforded reliable quantification of these compounds in snow and human samples at the concentrations in which these compounds are found. 相似文献
229.
Judit Rodríguez Joan Albert Jaume Granell Mercè Font-Bardia 《Journal of organometallic chemistry》2009,694(16):2467-2475
The reactions of [PtMe2(μ-SMe2)]2 with imines 4-ClC6H4CHNCHRCO2Me (R = H (1a), Me (1b), iPr (1c), CH2C6H4(4’-OH) (1d), C6H5 (1e), CH2C6H5(1f)) derived from natural amino acids produced under mild conditions cyclometallated platinum(II) compounds [PtMe{κ2-(C,N)-4-ClC6H3CHNCHRCO2Me}(SMe2)] (2a-2f). These compounds gave the corresponding phosphine derivatives [PtMe{κ2-(C,N)-4-ClC6H3CHNCHRCO2Me}(PPh3)] (3a-3f). The corresponding cyclometallated platinum(IV) compounds [PtMe2I{κ2-(C,N)-4-ClC6H3CHNCHRCO2Me}(PPh3)] (4) arising from intermolecular oxidative addition of methyl iodide were obtained with a high degree of stereo selectivity. Analogous results were obtained for imine 2,6-Cl2C6H3CHNCH(CH2C6H5)CO2Me (1g) in a process involving intramolecular oxidative addition of a C-Cl bond. The obtained compounds were fully characterized including structure determinations for compounds 3f, 4d and 4f. 相似文献
230.
Complex mixtures of polychlorostyrenes are produced and released into the environment by reaction of chlorine with graphite at high temperatures, e.g. in electrodes. The occurrence of these compounds in the environment or human tissues is often indicative of pollution from electrolytic processes. Combined gas chromatography coupled to electron impact and negative ion chemical ionization mass spectrometry is described here for the analysis of these compounds in sediments, human venous sera and cord sera. This method has allowed a specific congener identification and quantification of the chlorostyrene mixtures present in fluvial sediments polluted by effluents from a chlorine-alkali plant. Besides octachlorostyrene, the mixture of compounds identified involved the six possible heptachlorostyrenes, fifteen hexachlorostyrenes and seven pentachlorostyrenes, having concentrations in the range of 76–16 000 ng g−1 dry weight. In human sera from the population exposed to airborne emissions from this plant these compounds ranged between 17 and 63 ng L−1 and the distributions were dominated by octachlorostyrene, three heptachlorostyrenes, including β,β-2,3,4,5,6-heptachlorostyrene, and α-2,3,4,5,6-hexachlorostyrene. Both distribution patterns showed major differences in composition despite the common pollution source that was influencing both types of samples. The method also revealed qualitative differences between maternal and cord sera from the exposed population. 相似文献