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991.
Crystal potentials are usually obtained through a combination of theoretical calculation and the fitting of crystal properties. Because of thermal expansion of the crystal, the equilibrium condition is not satisfied at all temperatures unless the crystal potential is made temperature-dependent. A quasiharmonic potential that satisfies the equilibrium condition at all temperatures is derived from KC1 and used to calculate temperature-dependent defect energies (at constant volume). Other thermodynamic defect parameters are then derived by combining these results with the experimental Gibbs energies. The temperature-dependence of these parameters is displayed. 相似文献
992.
993.
Masao Sumita Hibeki Abe Hiroyuki Kayaki Keizo Miyasaka 《Journal of Macromolecular Science: Physics》2013,52(1-2):171-184
The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point 相似文献
994.
Xiaoting Li Tao Hu Biao Wang Wenjian Weng Gaorong Han Chenglu Song Ning Ma Piyi Du 《Journal of Physics and Chemistry of Solids》2013
(100) Oriented (PbxSr1−x)TiO3 (PST) thin films were prepared on indium tin oxide coated glass substrates by sol–gel technique with rapid thermal processing. The dielectric permittivity and tunability of the thin films with different dispersion degrees of orientation were investigated in detail by characterizing the full width at half maximum of their (100) peak based on rocking curves at different annealing temperatures. Influence of orientation dispersion on dielectric properties was exhibited in the tunable dielectric thin films. It shows that the dielectric constant and hence the tunability of the sol–gel derived PST thin films are improved with the decrease in the dispersion degree of orientation of the perovskite phase other than the increase in the content of crystalline phase in the thin films. The dielectric constant (capacitance) and figure of merit of the oriented thin films are 3–6 times and 1 times higher than that of randomly oriented thin film respectively. 相似文献
995.
《Physics and Chemistry of Liquids》2012,50(4):239-247
Abstract The electrical conductance of KC1 in glycerol solutions has been measured at concentrations between 1.5 mol m?3 and 353 mol m?3 at 22°C. The results are compared with the Fuoss paired ion model and fits to the data are obtained assuming a Gurney co-sphere having a radius in the approximate range 6 ± 10?10 m to 9 ± 10?10 m. The model leads to an estimate of ionic association which is less than that given by the theory of Bjerrum. 相似文献
996.
《Analytical letters》2012,45(13):1367-1384
Abstract Interferences from small amounts of sea salt in the determination of cadmium and lead were investigated. Test samples were made to mimic solutions obtained after extraction of sea water for trace metal analysis. Sea salt concentrations in the range 0–400 mg/l were investigated. Background absorption from this salt was high but easily minimised through the addition of nitric acid (2 % v/v). Sensitivity reductions due to the salt were considerable and varied from one graphite tube to the other. This problem was overcome by the addition of 1000 mg lanthanum per litre of sample. The positive effect of the lanthanum matrix modification is thought to be due to a change of the graphite tube surface. 相似文献
997.
《Physics and Chemistry of Liquids》2012,50(3):209-219
Abstract The system of hard rods in an external, uniform gravitational field is studied and exact expressions obtained for the partition functions, and the one- and two-particle distributions. In principle all higher order distributions can be exactly expressed as finite sums and the Laplace transforms of the one-particle density and pressure for a semi-infinite system are reducible to single integrals. Limiting cases of weak field and small rod diameters are examined. In the former case, these results agree with Percus and Lebowitz's local density expansion. In the latter case, corrections to the barometric pressure and density laws are obtained. Finally some mathematical difficulties involved in the calculation of the virial expansion and distribution of roots of the grand partition function are mentioned. 相似文献
998.
《Physics and Chemistry of Liquids》2012,50(4):321-326
Abstract The optical absorption spectra of Nd3+ ion in glutamic, L-aspartic and maleic acids in UV-VIS and NIR regions have been recorded. From the spectral data thus obtained, various spectroscopic parameters are evaluated. The radiative lifetimes (γR) and branching ratios (β) for the excited states of Nd3+ ion in three acids have been computed. The relationship between the environment sensitive Judd-Ofelt parameter (ω2) and the intensities of hypersensitive level (4G5/2) is in good coincidence following the Judd-Ofelt theory. 相似文献
999.
《Physics and Chemistry of Liquids》2012,50(3):181-191
Abstract Les auteurs ont étudié par voie électroehimique l'influence de faibles additions d'or sur les propriétés thermodynamiques du zinc en solution diluée dans l'étain fondu. Le paramètre d'interaction de Wagner ?Zn Au et sa variation avec la température ont été déterminés dans l'intervalle de température 420–650°C: ?Zn Au = 2.71 – 5.92. 103/T. 相似文献
1000.
《Analytical letters》2012,45(20):2537-2549
Abstract The structure of the derivative formed during the reaction of 1,3-dimethyluric acid, the major metabolite of theophylline in humans, with iodopropane was elucidated. GC-MS analysis indicated the presence of a single dipropylated product even though three positional isomers are possible. The stability of the product was lower than anticipated since one of the alkyl groups added was readily removed by acid hydrolysis. Carbon-13 NMR proved to be the most useful technique for establishing the positions of alkylation. Assignment of carbon-13 resonances were consistent with placement of propyl groups on N-7 and on the oxygen at C-8. The structure of the product was assigned as 1,3-dimethyl-7-(1-propyl)-8-(1-propyloxy)xanthine. This O-alkylated structure is unusual since most heterocycles that can exist as lactim-lactam tautomers alkylate primarily on ring nitrogens. 相似文献