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The cross sections and transverse spin asymmetries in the hard exclusive electroproduction of decuplet baryons are calculated in the large N(c) limit and found to be comparable to that of octet baryons. Large N(c) selection rules for the production amplitudes are derived, leading to new sensitive tests of the spin aspects of the QCD chiral dynamics both in the nonstrange and strange sectors. Importance of such studies for the reliable extraction of the pion form factor from pion electroproduction is explained. 相似文献
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符合Ore条件的简单图称为Ore图,Ore条件指图的两个不相邻的顶点的度数之和不小于图的顶点数。本文搞清了Ore图的泛连通性,同时得到了Ore图的点(边)泛圈性的结果,推广了Bondy的一个结论。 相似文献
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To calculate delta(13)C from raw CO(2) isotope data, the ion beam ratio of m/z 45 to 44 is corrected for the contribution arising from the contribution of (17)O-bearing molecules. First, a review on the current state of (17)O-corrections for CO(2) mass spectrometry is presented. The three correction algorithms that are generally in use, however, do produce biased delta(13)C values, and the bias is actually larger than the precision of modern isotope ratio mass spectrometers. The origin of this bias is twofold: different values for (17)R(VPDB-CO2) as well as different values for lambda are used in the correction algorithms. Despite both values being of high importance, large discrepancies between the absolute values published for (17)R(VPDB-CO2) appear to be the main reason for the delta(13)C biases. Next, the question of how to choose the value of lambda to best be used is considered. Natural (e.g. tropospheric) CO(2) as well as primary reference materials (PDB and NBS-19), having been in isotope exchange with water, are assumed to lie on the fractionation line for waters. On this ground, lambda = 0.5281 +/- 0.0015, as determined for waters (Meijer and Li, Isot. Environ. Health Stud., 1998; 34: 349-369), is suggested to be a base for the (17)O-correction algorithm. Finally, an approach to determine the absolute value for (17)R(VPDB-CO2), based on data of relative isotope measurements on two CO(2) gases having a large (17)O difference, is discussed and algebraic formulas are considered. Experimental data and new numerical values determined for (17)R(VPDB-CO2) and (17)R(VSMOW) are given in a companion paper. 相似文献
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T R?ckmann J Kaiser C A Brenninkmeijer W A Brand R Borchers J N Crowley M Wollenhaupt P J Crutzen 《Isotopes in environmental and health studies》2001,37(2):91-95
The position dependent 15N fractionation of nitrous oxide (N2O), which cannot be obtained from mass spectrometric analysis on molecular N2O itself, can be determined with high precision using isotope ratio mass spectrometry on the NO+ fragment that is formed on electron impact in the source of an isotope ratio mass spectrometer. Laboratory UV photolysis experiments show that strong position dependent 15N fractionations occur in the photolysis of N2O in the stratosphere, its major atmospheric sink. Measurements on the isotopic composition of stratospheric N2O indeed confirm the presence of strong isotope enrichments, in particular the difference in the fractionation constants for 15N14NO and 14N15NO. The absolute magnitudes of the fractionation constants found in the stratosphere are much smaller, however, than those found in the lab experiments, demonstrating the importance of dynamical and also additional chemical processes like the reaction of N2O with O(1D). 相似文献
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用描写相对论性核 核碰撞的LUCIAE模型及相应的MonteCarlo事例产生器分析了WA97最近发表的 1 5 8AGeVp Pb和Pb Pb碰撞中单奇异粒子 (Λ ,Λ)和多奇异粒子 (Ξ-,Ξ-,Ω-,Ω-)的多重数和横质量分布 .由于LUCIAE模型包含了弦碎裂微观过程中奇异夸克压低因子随碰撞体系的能量、中心度和质量的增大而增大 ,以及由它导致的相对论性核 核碰撞宏观过程中奇异粒子产额随上述三因素之增而增的物理机制 ;LUCIAE模型计算结果能较好描写WA97实验所揭示的相对论性核 核碰撞中奇异粒子产额随中心度之增而增和奇异粒子增强随奇异夸克数之增而增的实验事实 ,以及单奇异和多奇异粒子的横质量分布 . 相似文献
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We investigate the statistical properties of two single-mode dye-laser models-the colored-loss-noise model and the colored-gain-noise model. Analytic expressions of the probability,the mean and the variance of the steady-state laser intensity are obtained through the unified expansion theory [Phys. Rev. A43 (1991) 700]. By comparison we find that when the cavity decay rate for the electric field is large and the pump parameter a0 is small, the differences of the results of the two laser models are small. Otherwise, the differences are large. And the correlation time of the noise has very obvious influence on the results of the two models. 相似文献