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K. This (k + this)
Selected AbstractsInteraction between a dislocation and monovalent anion in various alkali halide crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010Y. KohzukiArticle first published online: 30 AUG 2010 Abstract It was investigated from (L0/L)2 versus ,0 curve that the Friedel relation between the effective stress and the average length of dislocation segments, L, is appropriate for the interaction between a dislocation and the monovalent anion in various alkali halides single crystals (NaCl: Br - , NaBr: Cl - or I - , KCl: Br - or I - , and RbCl: Br - or I - ). Here, L0 represents the average spacing of monovalent anions on a slip plane and ,0 is the bending angle at which the dislocation breaks away from the anion at the temperature of 0 K. This is because the anions are the weak obstacles such as impede the dislocation at ,0 above about 150 degrees, where the Friedel relation agrees with the Fleischer one (L02 = L2(,,,0)/2). Furthermore, the values of (L /L0) were found to be within 4.05 to 5.87 for the crystals. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The role of chlorine atoms and hydroxyl radicals in the formation of PCDDs from the oxidative pyrolysis of 2,4,6-trichlorophenolINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2010Lavrent Khachatryan A 132-step gas-phase reaction kinetic model has been combined with a four-step surface model for the formation of 1,3,6,8-tetrachlorodibenzo- p -dioxin (1,3,6,8-TCDD) from the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) in the presence of hexane. The revised model is based on a simpler model previously published in the literature and modified by adding Cl-releasing and the surface submodels, recalculating polynomial functions for thermodynamic parameters, and updating gas-phase submodels for (i) 1,3,6,8-TCDD formation, (ii) hydrogen oxidation, and (iii) hexane oxidation. The roles of the potential chain carriers, OH and Cl, in the formation of 1,3,6,8-TCDD were specifically addressed. In spite of the reported high reactivity of Cl, it was found that OH:Cl , 1, and OH is the dominant chain carrier from the apparent onset of purely gas-phase reactions at 750 K to 99% conversion of 2,4,6-TCP and hexane at 1075 K. This suggests that oxidation reactions are always dominant in realistic combustion systems, even where there are high concentrations of chlorine and relatively rich burning conditions. The update of the three gas-phase submodels as well as incorporation of Cl-releasing and the surface submodels resulted in improved agreement between calculated and experimental yields of 1,3,6,8-TCDD yields at temperatures as low as 800 K. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 90,97, 2010 [source] A solid-state NMR study of phase structure, molecular interactions, and mobility in blends of citric acid and paracetamolJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2009S. Schantz Abstract Citric acid anhydrate (CAA) and paracetamol (PARA), prepared as crystalline physical mixtures and as amorphous blends, were studied using 13C solid-state cross polarization magic angle spinning (CPMAS) NMR. Amorphous blends showed significant line broadening from the conformational distribution as compared to the crystalline samples. Also, chemical shift variations were observed between crystalline and amorphous blends, which were attributed to differences in intermolecular interactions. Averaging of proton rotating-frame spin-lattice relaxation times (T1,) probed via different 13C sites in the amorphous blends confirmed molecular level mixing. For some, initially amorphous, sample compositions the onset of crystallization was evident directly from spectra and from the significantly longer T1, relaxations. Thus, crystallization caused phase separation with properties of the two phases resembling those of pure CAA and PARA, respectively. 13C spectra of amorphous 50/50 (w/w, %) CAA/PARA recorded from above the glass transition temperature broadened as the temperature increased to a maximum at T,,,Tg,+,33 K. This was the result of a dynamic interference between the line narrowing techniques being applied and the time scale of molecular reorientation in the miscible melt. The derived average correlation time was found to correspond well with previous results from melt rheology. We conclude that the underlying reasons for physical instability (i.e., crystallization from the miscible melt, including molecular interactions and dynamics) of this class of amorphous binary mixtures can be effectively evaluated using NMR spectroscopy. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1862,1870, 2009 [source] Raman spectra of apatites: La10,x Si6,y (Al,Fe)y O26±,JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2007G. Lucazeau Abstract Raman spectra of eight polycrystalline apatites of the general formula La10,xSi6,yM,yO26 ± , with M, = Al or Fe were obtained at 300 K. Raman spectra of La10Si4Fe2O26 and La9.83Si4.5Al1.5O26 were investigated in the range 80,1000 K and 80,623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO4 tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm,1 when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al- and Fe-substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm,1 for La10Si4Fe2O26 is replaced by a strong band at 868 cm,1, suggesting that SiO4 tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so-called two-mode behavior. The occurrence of FeO stretching vibrations 150 cm,1 lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe4+ species. Copyright © 2006 John Wiley & Sons, Ltd. [source] Titan's damp ground: Constraints on Titan surface thermal properties from the temperature evolution of the Huygens GCMS inletMETEORITICS & PLANETARY SCIENCE, Issue 11 2006Ralph D. Lorenz The model parameters are adjusted to match the recorded temperature history of a nearby heater, taking into account heat losses by conduction to the rest of the probe and to Titan's cold atmosphere. The model suggests that after impact when forced convective cooling ceased, the inlet temperature rose from ,110 K to an asymptotic value of only ,145 K. This requires that the inlet was embedded in a surface that acted as an effective heat sink, most plausibly interpreted as wet or damp with liquid methane. The data appear inconsistent with a tar or dry, fine-grained surface, and the inlet was not warm enough to devolatilize methane hydrate. [source] Ground-based detection of thermal emission from the exoplanet WASP-19b,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010N. P. Gibson ABSTRACT We present an occultation of the newly discovered hot Jupiter system WASP-19, observed with the High Acuity Wide-field K -band Imager instrument on the VLT, in order to measure thermal emission from the planet's dayside at ,2 ,m. The light curve was analysed using a Markov Chain Monte Carlo method to find the eclipse depth and the central transit time. The transit depth was found to be 0.366 ± 0.072 per cent, corresponding to a brightness temperature of 2540 ± 180 K. This is significantly higher than the calculated (zero-albedo) equilibrium temperature and indicates that the planet shows poor redistribution of heat to the night side, consistent with models of highly irradiated planets. Further observations are needed to confirm the existence of a temperature inversion and possibly molecular emission lines. The central eclipse time was found to be consistent with a circular orbit. [source] Rigidity and gamma convergence for solid-solid phase transitions with SO(2) invarianceCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 6 2006Sergio Conti The singularly perturbed two-well problem in the theory of solid-solid phase transitions takes the form where u : , , ,n , ,n is the deformation, and W vanishes for all matrices in K = SO(n)A , SO(n)B. We focus on the case n = 2 and derive, by means of Gamma convergence, a sharp-interface limit for I,. The proof is based on a rigidity estimate for low-energy functions. Our rigidity argument also gives an optimal two-well Liouville estimate: if ,u has a small BV norm (compared to the diameter of the domain), then, in the L1 sense, either the distance of ,u from SO(2)A or the one from SO(2)B is controlled by the distance of ,u from K. This implies that the oscillation of ,u in weak L1 is controlled by the L1 norm of the distance of ,u to K. © 2006 Wiley Periodicals, Inc. [source] Multi-coloring the Mycielskian of graphsJOURNAL OF GRAPH THEORY, Issue 4 2010Wensong Lin Abstract A k -fold coloring of a graph is a function that assigns to each vertex a set of k colors, so that the color sets assigned to adjacent vertices are disjoint. The kth chromatic number of a graph G, denoted by ,k(G), is the minimum total number of colors used in a k -fold coloring of G. Let µ(G) denote the Mycielskian of G. For any positive integer k, it holds that ,k(G) + 1,,k(µ(G)),,k(G) + k (W. Lin, Disc. Math., 308 (2008), 3565,3573). Although both bounds are attainable, it was proved in (Z. Pan, X. Zhu, Multiple coloring of cone graphs, manuscript, 2006) that if k,2 and ,k(G),3k,2, then the upper bound can be reduced by 1, i.e., ,k(µ(G)),,k(G) + k,1. We conjecture that for any n,3k,1, there is a graph G with ,k(G)=n and ,k(µ(G))=n+ k. This is equivalent to conjecturing that the equality ,k(µ(K(n, k)))=n+k holds for Kneser graphs K(n, k) with n,3k,1. We confirm this conjecture for k=2, 3, or when n is a multiple of k or n,3k2/ln k. Moreover, we determine the values of ,k(µ(C2q+1)) for 1,k,q. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 311,323, 2010 [source] | ||||||||||||||||