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971.
A theoretical study of the electron dynamics in image potential states on Cu(1 0 0) surfaces with different types of adsorbates is presented. Scattering of the image state electron by an adsorbate induces inter-band and intra-band transitions leading respectively to the population decay and to the dephasing of the image state. We compare results obtained with low coverage (typically 1 adsorbate atom per 1000 surface atoms) Cs, Ar, and a model electronegative adsorbates. As follows from our results, Cs adsorbates lead to both appreciable dephasing and decay, while electronegative adsorbates mostly affect the dephasing rate. The effect of low coverage Ar adsorbates is small, consistent with their neutrality. 相似文献
972.
973.
Laura Montanaro K. Belgacem P. Llewellyn F. Rouquerol F. Merlo Paola Palmero 《Journal of Thermal Analysis and Calorimetry》2007,88(3):789-793
Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more
prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible
for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained
from aged precursors can reach a very low final density with respect to the theoretical value. A large degree of the original
sintering properties can be recovered after washing the aged powders with ethanol in a basic medium. 相似文献
974.
M. G. Voronkov S. G. D’yachkova I. P. Lebedeva A. V. Evart L. G. Shagun 《Russian Journal of General Chemistry》2007,77(4):604-606
Alkylthiochloroacetylenes react with geminal (in ether) and vicinal (in THF) dithiols to form, respectively, functional 1,3-dithiolenes (yield 43%) or 1,3-dithiolanes (yield 34%). 相似文献
975.
The present report describes a method suitable for the indirect assay of hydroxyl radical (OH.), which is likely to be produced during reperfusion of ischemic myocardium. Isolated rat heart perfused by the Langendorff technique was subjected to 30 min of ischemia, followed by 30 min of reperfusion. Salicylic acid (2 mM) was added to the perfusion circuit to trap any OH. radical generated during the experiment. 2,5- and 2,3-dihydroxybenzoic acids (hydroxylated products of salicylic acid) were identified by authentic standards as well as by pure OH.-generating system using high-performance liquid chromatography with electrochemical detection. In addition to serving as a chemical trap for the detection of OH., salicylate attenuated myocardial reperfusion injury as evidenced by reduced formation of creatine kinase, decreased lipid peroxidation, and improved myocardial contractile functions during reperfusion. These results thus provide direct evidence for the presence of OH. in heart and link it to the myocardial reperfusion injury. 相似文献
976.
977.
978.
In a seminal paper, Martin Clark (Communications Systems and Random Process Theory, Darlington, 1977, pp. 721–734, 1978) showed how the filtered dynamics giving the optimal estimate of a Markov chain observed in Gaussian noise can be expressed
using an ordinary differential equation. These results offer substantial benefits in filtering and in control, often simplifying
the analysis and an in some settings providing numerical benefits, see, for example Malcolm et al. (J. Appl. Math. Stoch.
Anal., 2007, to appear).
Clark’s method uses a gauge transformation and, in effect, solves the Wonham-Zakai equation using variation of constants.
In this article, we consider the optimal control of a partially observed Markov chain. This problem is discussed in Elliott
et al. (Hidden Markov Models Estimation and Control, Applications of Mathematics Series, vol. 29, 1995). The innovation in our results is that the robust dynamics of Clark are used to compute forward in time dynamics for a simplified
adjoint process. A stochastic minimum principle is established. 相似文献
979.
980.
E. S. Zhukova A. S. Prokhorov I. E. Spektor V. A. Karavanskiĭ N. N. Mel’nik T. N. Zavaritskaya B. P. Gorshunov 《Physics of the Solid State》2007,49(12):2242-2250
The dielectric response (conductivity and permittivity) spectra of a series of nanoporous silicon samples prepared by anodization of low-resistivity single-crystal silicon are measured, for the first time, using terahertz and IR spectroscopy in the frequency range 7–4000 cm?1 at room temperature. The spectra obtained are analyzed in terms of the effective medium theory with a size-dependent dielectric response function of nanoinclusions and averaged dielectric characteristics of the surrounding medium. The geometric and dielectric characteristics of silicon nanoinclusions are determined. The dielectric properties of inclusions are found to be affected by nanosize effects, namely, carrier scattering at crystallite boundaries and a broadening of the band gap due to quantum confinement. The spectra of the samples prepared by adding iodine to the electrolyte exhibit a resonance at frequencies of 150–300 cm?1. The nature of the resonance can be associated with the presence of chemisorbed iodine on the surface of porous silicon. Possible mechanisms responsible for the changes in broadband conductivity and permittivity spectra of single-crystal silicon upon transformation into a nanoporous structure are discussed. 相似文献