共查询到19条相似文献,搜索用时 162 毫秒
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研究利用Lie对称的生成元τ(t,q,q·)和ξs(t,q,q·)来构造广义H ojman守恒 量,并讨论三种特殊情况,研究表明:Hojman守恒量是该广义守恒量的特例,且在Lie对称 的生成元的形式为τ(t,q)和ξs(t,q)时,该广义Hojman守恒量可以导出Lu tzky守恒 量,此外,还给出一个排除平凡守恒量的条件.最后,给出两个简单例子,作为所获得结果 的说明.
关键词:
动力学系统
广义Hojman定理
Lie对称
守恒量 相似文献
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利用Larmor钟方法计算了一维复合势垒系统中的隧穿时间.从计算结果,对由Larmor钟所定义的Larmor时间在复合势垒中的有效性、可加性,以及它们与透射时间τT、反射时间τR、逗留时间τD的关系作了讨论.6个Larmor时间中,τxT,τxR,τyT和τyR都不是有效的时间量,它们不能为隧穿时间提供有效的描述,只有τyT和τyR满足可加性和判据τD=TτyT+RτyR,它们最有可能给出透射时间τT、反射时间τR.τyT,τyR与势垒的对称性有关,等式τyT=τyR是否成立与势垒是否对称有关.
关键词: 相似文献
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本文提出核与电子偶极相互作用和自旋扩散两种作用在被吸附到固体多电子表面上的分子弛豫起着重要作用,给出了自旋晶格弛豫时间(T1e)和相关时间(τc)的关系:T1e,-kτc/1+ω02τc2)1/2,式中k对给定固体是常数。吸附在硅胶上甲苯的弛豫数据可用此式描述。得到了甲苯中甲基在不同温度下的τc。,它们在374K到240K间的相关时间在3.56×10-9 s到5.76×10-8 s范围。由此计算出其活化能为15.0kJ/mol。 相似文献
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在采用自旋反转模型分析垂直腔面发射激光器(VCSELs)动力学行为的过程中,为了正确预测VCSELs的动力学行为,需要准确给出自旋反转模型中光场衰减速率k、总反转载流子衰减速率γN、线性二向色性系数γa、线性双折射系数γp、自旋反转速率γs和线宽增强因子α这6个特征参量.本文对1550 nm VCSELs在自由运行和平行光注入下的输出特性进行实验分析,获取了这6个特征参量的值,并着重研究了当激光器温度在10.00–30.00 ℃范围内变化时,这6个特征参量呈现的变化趋势.研究结果表明,随着温度的逐渐升高,γp整体呈现逐渐增加的趋势,γa,γs,γN和k呈现复杂的变化趋势,而α则呈现逐渐减小的趋势. 相似文献
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基于以前综合V-F模型(考虑施主受主(D-A)能量传递)和B模型(考虑施主施主(D-D)能量迁移)而提出的V-F-B综合模型,对La1-xErxF3体系中Er3+离子四种低掺杂浓度下(x=0.001,0.003,0.01,0.02)295K时4S3/2→4I15/2发光的时间演化曲线成功地重新进行了数值拟合.结果表明该体系内D-A间交叉弛豫能量传递是偶极-偶极作用,作用常数CDA为4.75×10-41cm6/s,与Okamoto等人原用YT扩散模型得到的结果一致.而拟合得到的四个D-D平均跳跃时间τ0粗略地与xDα次方(xD为D离子浓度)成正比(α≈-1.237),并不遵从τ0很小时与xD的-2次方成正比的理论关系.同时,通过把D-D迁移和D-A传递同时同样地纳入V-F模型还粗略估计了D-D平均跳跃时间τ0′的值,发现它与V-F-B给出的τ0拟合值比较一致,说明V-F-B模型在一定近似程度上是内部自恰的、合理的.
关键词:
能量传递
能量迁移
跳跃时间
交叉弛豫 相似文献
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It is shown that, contrary to normal practice, the most appropriate criterion for distinguishing between lifetime and relaxation semiconductors in the presence of traps is the ratio of the screening length Ls, to the ambipolar diffusion length LDa,. Ls, is calculated. Its significance is not limited to zero current, even though it reduces to the conventional Debye length LD when the trap concentration is zero. (With traps, we always have Ls < LD.) The dielectric relaxation time itself is unaffected by traps, but in steady state situations, a material behaves as if it had an effective lifetime τ0s = τ0η, where η depends on the concentration and energetic position of the traps. τo, may be orders of magnitude greater than τ0, the conventional diffusion length lifetime. Typical values of Ls, are presented as a function of trapping parameters. Ls>LDa leads to relaxation behavior; Ls < LDa, to lifetime behavior. 相似文献
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本文计算了轴对称体系的引力辐射总功率。用胡宁的τ(n)αβ表达式和Bondi的柱面波解直接计算导出-(dE)/(dt)=1/2∫x0c02sinθdθ。这个结果与Bondi不用任何ταβ表达式得到的公式完全相同,并证明辐射总功率是恒正的。但是,由郑玉昆的ταβ表达式得到的结果与Bondi的公式不一致,并表明辐射总功率不是恒正的。
关键词: 相似文献
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H. Ez-Zahraouy A. Benyoussef 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(3-4):573-583
The effects of some disorders, on the traffic flow behavior, are studied numerically. Especially, the effect of mixture of vehicles of different velocities and/or lengths, the effects of different drivers reactions, the position and the extraction rate of off-ramp in the free way. Using a generalized optimal velocity model, for a mixture of fast and slow vehicles, we have investigated the effect of delay times τ f and τ s on the fundamental diagram. It is Found that the small delay times have almost no effect, while, for sufficiently large delay time τ s , the current profile displays qualitatively five different forms, depending on τ f , τ s and the fractions f f and f s of the fast and slow cars, respectively. The velocity (current) exhibits first-order transitions at low and/or high densities, from freely moving phase to the congested state, and from congested state to a jamming one, respectively. The minimal current appears in intermediate values of τ s . Furthermore there exist, a critical value of τ f above which the meta-stability and hysteresis appear. The effects of disorder due to drivers behaviors have been introduced through a random delay time τ allowing the car to reach its optimal velocity traffic flow models with open boundaries. In the absence of the variation of the delay time Δτ, it is found that the transition from unstable to meta-stable and from meta-stable to stable state occur under the effect of the injecting and the extracting rate probabilities α and β respectively. Moreover, the perturbation of the traffic flow behavior due to the off-ramp has been studied using numerical simulations in the one dimensional cellular automaton traffic flow model with open boundaries. When the off-ramp is located between two critical positions i c1 and i c2 the current remains constant (plateau) for β0c1 < β0 < β0c2, and the density undergoes two successive first order transitions: from high density to plateau current phase and from average density to the low one. In the case of two off-ramps, these transitions occur only when the distance between ramps, is smaller than a critical value. 相似文献
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The carrier concentration (Ns) dependence of electron mobility in Si (100) inversion layers has been measured at temperatures T = 1.5?70K for high- and low-mobility MOSFETs. An extrinsic term is observed in the T-dependent part of the scattering probability, τ?1T. At T = 4.4 K, τ?1T depends on Ns as N?1.9s in low mobility samples. In high-mobility samples, τ?1T increases with increasing Ns in high Ns region while τ?1T ∝ N?1.6s in low Ns region. The Ns-dependence of τ?1T becomes weaker with increasing T in both of low- and high-mobility samples. At Ns = 3 × 1012 cm?2, τ?1T depends on T as T1.8 in low-mobility samples and τ?1T ∝ T2.0 in high- mobility samples at T 5 K. 相似文献
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从速度v的傅里叶空间K的动力学方程出发,采用算子运算及变换方法,可较简便的算出静电湍流场中的重整化色散方程,在以有效关联时间代替湍流场的时、空关联的近似下,计算了有限关联时间效应的作用,表明它是削弱湍流场影响的。短关联时间极限可看成是湍流场影响的上限估计。讨论了湍流场对离声波、电子朗缪波和低频漂移波的影响。
关键词: 相似文献
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In this note radiative corrections to the total hadronic decay rate of the τ-lepton are studied employing perturbative QCD and the operator product expansion. We calculate quadratic quark mass corrections to the decay rate rationR τ to the order0(α s 2 m2) and find that they contribute appreciably to the Cabbibo supressed decay modes of the τ-lepton. We also discuss corrections of mass dimensionD=4, where we emphasize the need of a suitable choice of the renormalization scale of the quark and gluon condensates. 相似文献
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Experimental data are used to constrain the parameters of the six quark mixing model and of a composite quark model. A combined fit of the mixing angles in the Kobayashi-Maskawa scheme gives sinθ 1=0.228±0.011 and error contours around the best values sinθ 2=0.12 and sinθ 3≈0. From this, a limit of τ B >0.35×10?13 s for the mean lifetime of bottom-flavoured hadrons is obtained. For the composite quark model of Katsumata and Tomozawa, a value of τ B =(0.22?0.23)10?13 s is derived. 相似文献