带有Fokker-Planck算子的BGK方程 [英文]

本文主要研究带有Fokker-Planck算子的BGK模型,即Fokker-Planck-BGK方程.首先,我们对线性方程?f/?t+v·▽_xf - σ?_vf = g(t, x, v), f (0, x, v) = f_0(x, v).建立了两个基本引理:速度矩引理和速度平均引理.然后通过渐近方法,在初始条件只有二阶矩的情形下得到Fokker-Planck-BGK方程经典解的存在性.     

磁性Gd3+离子对Chevrel相超导体PbMo6S8的临界电流和输运性质的影响

采用高温固态反应和均衡热压方法相结合,我们制备了一系列Gd掺杂的Chevrel相GdxPb1-xMo6S8超导样品.为了研究掺入的磁性Gd3+离子对于磁通线的钉扎作用和对临界电流及其它性质的影响,我们系统地测量了样品的电阻率,热电势,比热和临界电流密度.同时,我们计算了磁性Gd3+离子与磁通线之间的相互作用和这种作用可能导致的磁通钉扎及对临界电流的影响,并与实验结果进行了比较.结果显示除非Gd3+离子的分布是非常不均匀的,Gd3+离子所引起的钉扎是不重要的.另一方面,热电势和电阻率等输运性质及比热的结果显示由于Gd3+取代了Pb2+使载流子浓度降低了.载流子浓度的降低进而引起其它超导参数如热力学临界场Bc的变化,导致钉扎势的减小,最终降低了临界电流.     

Trend of extreme precipitation events over China in last 40 years

Using the daily precipitation data of 740 stations in China from 1960 to 2000, the analysis on the variations and distributions of the frequency and the percentage of extreme precipitation to the annual rainfall have been performed in this paper. Results indicate that the percentage of heavy rains （above 25mm/day） in the annual rainfall has increased, while on average the day number of heavy rains has slightly reduced during the past 40 years. In the end of 1970s and the beginning of 1980s, both the number of days with extreme precipitation and the percentage of extreme precipitation abruptly changed over China, especially in the northern China. By moving t test, the abrupt change year of extreme precipitation for each station and its spatial distribution over the whole country are also obtained. The abrupt change years concentrated in 1978-1982 for most regions of northern China while occurred at various stations in southern China in greatly different/diverse years. Besides the abrupt change years of extreme precipitation at part stations of Northwest China happened about 5 years later in comparison with that of the country＇s average.     

Intracavity optical parametric oscillator at 1.57-μm wavelength pumped by passive Q-switched Nd：GdVO4 laser

A high-repetition-rate eye-safe optical parametric oscillator （OPO）, using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd：GdVO4/Cr^4＋ ：YAG laser, is experimentally demonstrated. The conversion efficiency for the average power is 7% from pump diode input to OPO signal output and the slope efficiency is up to 10.3%. With an incident pump power of 7,3 W, the compact intracavity OPO （IOPO） cavity, operating at 15 kHz, produces an average power of 0.57 W at 1570 nm with a pulse width as short as 6 ns. The peak power at 1570 nm is higher than 6.3 kW.     

Dielectric Properties of Multilayered Ba0.5Sr0.5TiO3 Thin Films Deposited on ITO-Coated Corning 1737 Glass by rf Magnetron Sputtering

A new stacking method via variation ofsubstrate temperature in rfmagnetron sputter is used to fabricate polycrystalline/polycrystalline Ba0.5Sr0.5TiO3 thin films with higher dielectric constant, higher breakdown strength and lower leakage current densities than those prepared by a conventionM deposition method. The improved figure of merit G （ε0εrEb） of the Ba0.5Sr0.5TiO3 thin films implies that they are a feasible insulation layer for thin film electroluminescent devices.     

关于今年高考数学试题的若干思考

一年一度的高考结束了,对94年数学学科的(3 2)试卷及成绩会有各种评析。见解,冷静下来,想一想,做一番思考,对教学,对来年的备考都会是有益的。 1 几个数据 为了简单说明问题以近三年数据为主。 1.1 三年来试卷的题型和题量(理科)     

无约束连续最优控制问题的离散序列二次规划方法

其中f_0:R~n×R~m×R→R,g_0:R~n→R,f:R~n×R~m×R→R~n关于它们各自变量二次连续可微。终端时间T固定,初始状态已知,x(t)为状态变量,u(t)为控制变量,问题要求选择适当的 u(t)使目标函数(1.1)达到极小。 求解此类问题的一种途径是通过离散时间函数x(t),u(t)将它转化成传统的数学规划问题,然后,利用数学规划中已有的方法求得原问题的近似解。Cullum,Budak等在[1]和     

ON THE MULTIPLE-ATTRACTOR COEXSTING SYSTEM WITH PARAMETER UNCERTAINTIES USING GENERALIZED CELL MAPPING METHOD

I.IntroductionOneofthedolllinalltchaructcristicsofNon-lillcarsystemsistheboc-uniquenessoftherespollsef(7ragivensystemptlrallleter.Eacllsic'ldystiltcisallattrilctoj'baviilgitsownwalkinOf':lttrilCt1OllillpllaSCSpttCC.Allattl'tCtL)1'1flaybaflXCdl,Oillt,b1flitCyCIC,1llVIlriilllttol-uS,strtlbgeatti'ilctor.1b13riictlcLllifpl7llcatit)ns,oillyollcoj'theseb1uIti13Icattrilt')1-sisof'illtorestLllldcol'rcsl,olldstotilesalt,of>cl'iltlollilll'cglL)IIof'tilesystcllls,ifbdtileolll(:rstireustlilll…     

硬骨鱼类的细胞核移植——鲫鱼细胞核和鲤鱼细胞质配合的杂种鱼

本文用细胞核移植方法,获得了不同属淡水硬骨鱼类之间的核质杂种鱼,即鲫鱼细胞核和鲤鱼细胞质配合的杂种鱼.从观察到的形态特征来看,不论在口须、咽喉齿、侧线鳞片数目、脊椎骨数目等方面,基本上相似于供体细胞核鱼(鲫鱼)的性状.这种杂种鱼已能饲养到性成熟阶段。