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971.
The probability density of the times for which the horizontal wind remains above or below a given threshold speed is of some interest in the fields of renewable energy generation and pollutant dispersal. However there appear to be no analytic or conceptual models which account for the observed power law form of the distribution of these episode lengths over a range of over three decades, from a few tens of seconds to a day or more. We reanalyze high resolution wind data and demonstrate the fractal character of the point process generated by the wind speed level crossings. We simulate the fluctuating wind speed by a Markov process which approximates the characteristics of the real (non-Markovian) wind and successfully generates a power law distribution of episode lengths. However, fundamental questions concerning the physical basis for this behavior and the connection between the properties of a continuous-time stochastic process and the fractal statistics of the point process generated by its level crossings remain unanswered. (c) 2001 American Institute of Physics. 相似文献
972.
Browder TE Li Y Rodriguez JL Yamamoto H Bergfeld T Eisenstein BI Ernst J Gladding GE Gollin GD Hans RM Johnson E Karliner I Marsh MA Palmer M Plager C Sedlack C Selen M Thaler JJ Williams J Edwards KW Janicek R Patel PM Sadoff AJ Ammar R Bean A Besson D Davis R Kwak N Zhao X Anderson S Frolov VV Kubota Y Lee SJ Mahapatra R O'Neill JJ Poling R Riehle T Smith A Stepaniak CJ Urheim J Ahmed S Alam MS Athar SB Jian L Ling L Saleem M Timm S Wappler F Anastassov A Duboscq JE Eckhart E Gan KK Gwon C 《Physical review letters》2001,86(14):2950-2954
We report results of a search for B-->tau(nu) in a sample of 9.7 x 10(6) charged B meson decays. We exclusively reconstruct the companion B decay to suppress background. We set an upper limit on the branching fraction B(B-->tau(nu))<8.4 x 10(-4) at 90% confidence level. We also establish B(B+/--->K+/-nu(nu))<2.4 x 10(-4) at 90% confidence level. 相似文献
973.
Pagba C Zordan G Galoppini E Piatnitski EL Hore S Deshayes K Piotrowiak P 《Journal of the American Chemical Society》2004,126(32):9888-9889
Novel ternary assemblies consisting of fully encapsulated host-guest complexes (hemicarceplexes) and wide band gap semiconductor nanoparticles were investigated. The water-soluble amphiphilic host (octacarboxyhemicarcerand) traps the hydrophobic chromophore within its cavity and binds to the surface of metal oxide nanoparticles. Fluorescence quenching and fast charge injection, kforward >/= 7 x 109 s-1, from the S2 state of encapsulated azulene were observed. Charge recombination proceeds at a much lower rate of 2 x 107 s-1. Interestingly, the recombination kinetics is homogeneous, suggesting that electron tunneling through the wall of the "molecular container" is the rate-limiting step of the process. 相似文献
974.
Readman JE Barker PD Gameson I Hriljac JA Zhou W Edwards PP Anderson PA 《Chemical communications (Cambridge, England)》2004,(6):736-737
We report the assembly of a cubic array of cationic cadmium clusters encapsulated in zeolite A, and its characterization through Rietveld analysis of powder synchrotron X-ray diffraction data and high resolution transmission electron microscopy. 相似文献
975.
The purpose of the present paper is to propose an idea to construct the volume function W for polymer glasses and calculate the volume of polymer glasses as a function of the compactivity X utilizing a statistical-mechanical method developed for semiflexible polymers. We also discuss the analogue for glasses of "tapping" experiments which show the validity of statistical mechanics and the entropy concept in powders. 相似文献
976.
Wagner GW O'Connor RJ Edwards JL Brevett CA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(17):7146-7150
The effect of drop size on the degradation rate of VX, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in fresh concrete has been examined using (31)P NMR. Drops of neat VX, ranging in size from 4 microL to 0.2 microL, applied to small concrete coupons (8 mm x 15 mm) were observed to degrade at different rates, with the 1 microL and smaller drops reacting in less than 4 days, and the larger droplets reacting in less than 11 days. Additionally, 4 microL VX predissolved in hexane to evenly spread it over the concrete coupon likewise reacted faster, degrading in less than 5 days. The fresh concrete, less than 2 months old, exhibited significantly faster VX degradation for all drop sizes than that observed for "aged" concrete in a previous study where VX persisted for months. The enhanced reactivity of the "fresh" concrete for VX was maintained for at least a 1-year period. The pH of water containing crushed "fresh" and "aged" concrete was 10.0 and 9.0, respectively. The higher pH of the "fresh" concrete is one reason for its enhanced reactivity toward VX. An additional contribution to the enhanced reactivity of the "fresh" concrete is suggested by the increased mobility of its sorbed VX as evidenced by its significantly narrower peak in (31)P NMR spectra. 相似文献
977.
In this note we prove the uniqueness of U in a group G with
a spherical split-BN-pair of rank
,i.e., if G has such a BN-pair with
a nilpotent normal subgroup of B,
and
, then
and
is a normal subgroup of G. Here
is the corresponding group of Lie-type and
the subgroup of
generated by all root-subgroups corresponding to positive roots.
Received: 19 May 2003 相似文献
978.
We investigate ionization and excitation of H(1s) in the limit of very short electric field pulses, analytically and numerically and both in the limit of small and extremely large peak electric fields. We identify a process of recombination akin to Rabi flopping from the continuum and give an analytic expression for this process after a single-cycle strong-field pulse. 相似文献
979.
We study analytically two of the central problems of colloid science: the structure of the double layer surrounding a charged particle and the forces between two such particles. Traditionally, these have been understood using a combination of electrostatic forces acting on the ions and the entropy of the same ions. Here we derive explicit formulas showing how the often dominant dispersion forces between ions and the surfaces can dramatically change the structure of the double layer and the forces. 相似文献
980.
Lu has shown that any dynamical r-matrix for the pair (
,
) naturally induces a Poisson homogeneous structure on G/U. She also proved that if
is complex simple,
is its Cartan subalgebra and r is quasitriangular, then this correspondence is in fact one-to-one. In this Letter we find some general conditions under which the Lu correspondence is one-to-one. Then we apply this result to describe all triangular Poisson homogeneous structures on G/U for a simple complex group G and its reductive subgroup U containing a Cartan subgroup. 相似文献