单峰高斯分布适应面上的误差阈

在Eigen的单峰适应面模型基础上,提出了生物体的适应值为高斯分布的随机适应面模型。 利用系综平均的方法, 计算了在单峰高斯分布适应面上准物种的浓度分布和误差阈。 结果表明, 对于小的适应面涨落, 准物种分布和误差阈与确定情形相比变化极小,误差阈对于小的涨落是稳定的。 然而, 当适应值涨落较大时,从准物种到误差灾变的转变不再明显。 误差阈变宽, 并且在涨落增加时向大的突变率方向移动。 Based on the Eigen model with a single peak fitness landscape, the fitness values of all sequence types are assumed to be random with Gaussian distribution. By ensemble average method, the concentration distribution and error threshold of quasispecies on single peak Gaussian distributed fitness landscapes were evaluated. It is shown that the concentration distribution and error threshold change little in comparing with deterministic case for small fluctuations, which implies that the error threshold is stable against small perturbation. However, as the fluctuation increases, the situation is quite different. The transition from quasi species to error catastrophe is no longer sharp. The error threshold becomes a narrow band which broadens and shifts toward large values of error rate with increasing fluctuation.     

Error Thresholds in Single-Peak Gaussian Distributed Fitness Landscapes

Based on the Eigen and Crow-Kimura models with a single-peak fitness landscape, we propose the fitness values of all sequence types to be Gausslan distributed random variables to incorporate the effects of the fluctuations of the fitness landscapes （noise of environments） and investigate the concentration distribution and error threshold of quasispecies by performing an ensemble average within this theoretical framework. We find that a small fluctuation of the fitness landscape causes only a slight change in the concentration distribution and error threshold, which implies that the error threshold is stable against small perturbations. However, for a sizable fluctuation, quite different from the previous deterministic models, our statistical results show that the transition from quasi-species to error catastrophe is not so sharp, indicating that the error threshold is located within a certain range and has a shift toward a larger value. Our results are qualitatively in agreement with the experimental data and provide a new implication for antiviral strategies.     

关于标准误差的估计

对实验教学中误差分析的重要性作了初步探讨 ,着重讨论了标准误差计算中用 1n - 1而不是 1n 问题。     

用动力学模型计算10.6MeV/u~(84)Kr(~(27)Al,准裂变)反应的裂变时间

用单体耗散模型对１０．６ＭｅＶ／ｕ８４Ｋｒ在２７Ａｌ上引起的准裂变反应进行了计算，结果表明该准裂变反应的准裂变时间大于２００×１０－２２ｓ．发现对本反应系统，准裂变的出现至少需要８ＭｅＶ／ｕ阈能     

用动力学模型计算10.6MeV/u 84Kr(27Al,准裂变)反应的裂变时间

用单体耗散模型对10.6MeV/u ⁸⁴Kr在²⁷Al上引起的准裂变反应进行了计算,结果表明该准裂变反应的准裂变时间大于200×10^－22s.发现对本反应系统,准裂变的出现至少需要8MeV/u阈能.     

94 GHz TE_(6,2)模式Denisov辐射器的研究

准光辐射器是回旋管内置准光模式变换器的重要组成部分.采用几何光学理论分析了圆波导中高阶旋转模式电磁波的准光传输特性,分析了螺旋非规则光滑圆波导中电磁波的传输和模式耦合机理,推导任意扰动的圆波导内模式间的耦合波方程及其相关系数.根据耦合波理论编制准光模式变换器的数值计算程序,分析了Denisov型辐射器内激励起的波导模式的功率分布规律和波导壁上的纵向磁场分布,以及辐射器螺旋切口的辐射场的分布和辐射波束的特征,并采用三维全波仿真软件进行对比模拟.优化了工作频率为94 GHz,TE6,2模式的Denisov型辐射器,其输出功率效率高达98%;加工成实物并内置于回旋振荡内进行热测实验,在回旋管的输出窗处获得了高斯分布的烧斑图.此结果表明测试结果与计算基本一致.     

大气环境下用于瞄准的激光波束传播特性研究

针对激光瞄准过程中的光斑偏移现象,结合修正的Von Karman谱的折射指数起伏和Hufnagel-Vally湍流模型上的近似积分,研究了高斯脉冲光束在湍流大气中远场水平以及斜程传播时的脉冲展宽和闪烁指数,分析了强湍流条件下1.06 μm准单色光斜程大气传输光强分布与脉冲展宽的关系,对数值结果进行比较,发现远距离传输中波长和距离对波束瞄准偏差影响较大.从理论和实验上对大气环境下激光光斑瞄准偏差进行了分析研究,研究结果表明:将激光光斑全场数据及分析结果应用到现有偏差补偿算法中,可以实现激光瞄准偏差的有效补偿,在大气能见度1 km～3 km范围内,激光瞄准偏差测量误差σA≤0.1 mrad.     

准高斯声束对超声造影剂的声辐射力研究*

超声造影剂的定向输运在超声医学成像领域有着极为重要的意义,而声辐射力作用是实现该过程的关键,相比于高斯声束,准高斯声束是无源亥姆霍兹方程的精确解,可以使用标准波分解法简化计算。因此,本文研究了准高斯声束对超声造影剂的声辐射力作用。文章首先分析了准高斯声束与高斯声束之间的相关性;随后通过数值计算求得了准高斯声束对超声造影剂模型的声辐射力函数与无量纲频率之间的关系;最后,本文研究了不同造影剂气泡情况下的声辐射力。研究结果表明:声辐射力函数随无量纲频率变化将在不同位置出现共振峰,不同的波束宽度值将改变辐射力强度,但不改变共振峰的位置。相关结果可为利用声辐射力定向输运超声造影剂至靶向位置提供理论参考。     

耗散系统的准热力学模型

以具有自治系统一般形式的运动方程及其相应的Fokker-Planck方程为出发点,确立了一种适应面比较广的耗散系统的准热力学模型.定义了与驱动项f相共轭的函数X,取代作为上述运动方程的自田变量x(x可代表某种输出或化学反应的产物).以状态参量f,X,C(C为控制参量)对照参量p,V,T,得到一系列涉及准热力学函数及其导数的基本关系式,它们与传统热力学是一一对应的,最后给出一个应用范例. 关键词：     

Statistical mechanics of Eigen's evolution model

The correspondence between Eigen's model of macromolecular evolution and the equilibrium statistical mechanics of an inhomogeneous Ising system is developed. The free energy landscape of random Ising systems with the Hopfield Hamiltonian as a special example is applied to the replication rate coefficient landscape. The coupling constants are scaled with 1/l, since the maxima of any landscape must not increase with the length of the macromolecules. The calculated error threshold relation then agrees with Eigen's expression, which was derived in a different way. It gives an explicit expression for the superiority parameter in terms of the parameters of the landscape. The dynamics of selection and evolution is discussed.     

A stochastic theory for clustering of quenched-in vacancies—III. A continuum model

In continuation of our earlier investigation on the problem of clustering of quenched-in vacancies reported earlier, starting from the discrete model, we derive a second order partial differential equation for the growth of the clusters. The solution of this equation is shown to be in reasonable agreement with the solution of the discrete model proposed earlier. However, the total number of vacancies is not conserved under slightly less stringent conditions than the conditions dictated by the solution of the discrete model, suggesting a slightly modified differential equation for the concentration of the clusters. The solution of this modified differential equation has the required properties. The leading part of the distribution when transferred into the space designating the linear dimension of the cluster has a Gaussian form. This feature is shown to be consistent with writing a Langevin equation with the linear dimension of the cluster taking the role of the random variable. This permits the identification of the smallness of parameter. An alternate formulation is also given where the concentration of the vacancies stored in a cluster of a certain size is considered as the dynamical variable. The solution obtained in this alternate formulation is shown to be consistent with the other formulation.     

CARS技术中泵浦激光光场相干特性的研究

本文从理论上指出，在分子振动能级的横向弛豫时间远小于激光相干时间的条件下，相干反斯托克斯喇曼散射（ＣＡＲＳ）信号能够反映出激光光场的相干特性，据此可直接了解其相干时间并推算出激光的线宽。实验记录了苯、甲苯的ＣＡＲＳ光信号与激光延时时间的关系，得出了激光的相干时间和线宽。     

随机性对部分随机介质激光器阈值的影响

基于速率方程和Maxwell方程相结合的模型，采用时域有限差分法(FDTD)研究了介质的随机性和层数对部分随机介质激光器阈值的影响.模拟结果显示，当抽运速率超过阈值时，出现一个或者多个振荡模；随机性或者系统的尺度增加时，振荡模数量也增加；部分随机介质激光器的阈值在一定的随机强度和层数下将达到最小值，它与完全随机情况下的结论有所不同.对所得到的结论给出了物理解释.这些结果对于制作随机激光器和光集成潜在应用价值. 关键词： 激光物理 随机激光器 阈值 时域有限差分法     

位相畸变光束的聚焦特性与光束质量

针对高斯型随机位相畸变，应用夫琅和费衍射积分研究了畸变光束的聚焦特性和光束质量Ｍ＾２因子，给出子它们随位相畸变特征量主烨的近似分析和数计算结果，可为高功率激光器的设计提供理论依据。     

Emergence of species and punctuated equilibrium in the Tangle Nature model of biological evolution

We consider an individual-based model of evolution. Species emergence as segregation of the population on to discrete positions in a hyper-cubical genotype space. The model emphasises interaction between coexisting genotypes. Although the rate of the micro-dynamics, consisting of reproduction and killing of individuals is essentially constant, the macro-dynamics is punctuated. The macro-evolution consists of the creation and annihilation of configurations in genotype space equivalent to sequences of different ecosystems. We review the definition of the model and results concerning distribution lifetimes of individuals, genotypes and configurations. We discuss the non-stationarity of the model and how this agrees with the fossil record. Finally, we describe how the model is able to produce species abundance distributions of a form qualitatively in agreement with observation on real ecosystems.     

Investigations on order and width of RZ super Gaussian pulse in pre-, post- and symmetrical-dispersion compensated 10 Gb/s optical communication system using standard and dispersion compensating fibers

We show the effect of varied order and width of super Gaussian pulse at 10 Gb/s in dispersion compensated optical communication system. The optical communication system consists of standard single-mode fiber of 16 ps/nm/km of a certain length, whose dispersion is compensated using pre-, post- and symmetrical-dispersion compensation schemes with proportionate length dispersion compensating fiber of −80 ps/nm/km. Performance of these three compensation schemes is compared at 14 dBm values of Er-doped fiber amplifiers (EDFA) power at 1st, 2nd and 3rd order RZ super Gaussian optical pulse. The pulse width, full width at half maximum (FWHM) is also varied from 5 to 30 ps to highlight the optimum performance. The graphical results obtained show a relationship among the attributes pulse width, order of RZ super Gaussian optical pulse and dispersion compensation scheme implemented. It shows that to decrease BER and timing jitter in the system, smaller width and 3rd order super Gaussian pulse should be used. It is recommended that to decrease dependency of BER and timing jitter in the communication system on the pulse width i.e. FWHM, the symmetrical compensation scheme should be implemented.     

基于DFB-LD宏观电路模型的建立与讨论

建立了ＤＦＢ－ＬＤ的宏观电路模型,并对此模型进行了诸如效率带宽积等问题的深入讨论,指出提高效率有特别重要的意义。