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991.
Summary Against the background of the experimental reports obtained so far some very recent theoretical approaches to the understanding
of the exotic family events in cosmic-ray physics have been traced in a comprehensive manner. The main trends in the observations
have been highlighted and the limitations of the theoretical attempts have been pointed out. 相似文献
992.
993.
A comparative study of Gaussian geostatistical models and Gaussian Markov random field models 总被引:1,自引:0,他引:1
Gaussian geostatistical models (GGMs) and Gaussian Markov random fields (GMRFs) are two distinct approaches commonly used in spatial models for modeling point-referenced and areal data, respectively. In this paper, the relations between GGMs and GMRFs are explored based on approximations of GMRFs by GGMs, and approximations of GGMs by GMRFs. Two new metrics of approximation are proposed : (i) the Kullback-Leibler discrepancy of spectral densities and (ii) the chi-squared distance between spectral densities. The distances between the spectral density functions of GGMs and GMRFs measured by these metrics are minimized to obtain the approximations of GGMs and GMRFs. The proposed methodologies are validated through several empirical studies. We compare the performance of our approach to other methods based on covariance functions, in terms of the average mean squared prediction error and also the computational time. A spatial analysis of a dataset on PM2.5 collected in California is presented to illustrate the proposed method. 相似文献
994.
The reactions of p‐nitrophenyl acetate (PNPA) and p‐nitrophenyl benzoate (PNPB) with α‐nucleophile oximates, that is, butane 2,3‐dione monoximate, pralidoximate, and other oximates have been studied in the presence of different cationic surfactants. The first‐order rate constant increases with increasing surfactant concentration. The extent of acceleration is dependent on the head group structure of surfactants. The PNPA is more reactive than PNPB toward all the nucleophiles at higher concentration of surfactants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 57–64, 2009 相似文献
995.
996.
Voytas P. A. Behr J. A. Ghosh A. Gwinner G. Orozco L. A. Simsarian J. E. Sprouse G. D. Xu F. 《Hyperfine Interactions》1996,97(1):527-534
The techniques of laser cooling and trapping now make it possible to observe large samples of stable atoms in a small volume at low temperature. This capability was recently extended to radioactive isotopes. This opens up new opportunities for the investigation of fundamental symmetries through measurements using radioactive atoms. In this paper we will discuss several fundamental measurements in atomic systems and how the ability to trap radioactive atoms will play an important role in improving the precision of such measurements. Measurements of the effects of the weak interaction are of particular note since they are becoming quite precise. In particular, we will describe in detail the system developed at Stony Brook to trap radioactive alkali atoms and measure weak interaction effects in francium isotopes. 相似文献
997.
998.
The oscillatory wake potential for a slowly moving or static test dust particulate in a finite temperature, collisionless
and unmagnetized dusty plasma with a continuous flow of ions and dust particles has been studied. The collective resonant
interaction of the moving test particle with the low-frequency and low-phase-velocity dust-acoustic mode is the origin of
the periodic attractive force between the like polarity particulates along and perpendicular to the streaming ions and dust
grains resulting into dust-Coulomb crystal formation. This wake potential can explain the three-dimensional dust-Coulomb crystal
formation in the laboratory conditions. 相似文献
999.
1000.