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The emission angle and the transverse momentum distributions of projectile fragments produced in the fragmentation of 56Fe on CHs, C and A1 targets at 471 A MeV are measured. It is found that for the same target, the average value and width of the angular distribution decrease with an increase of the projectile fragment charge; for the same projectile fragment, the average value of the distribution increases and the width of the distribution decreases with increasing the target charge number. The transverse momentum distribution of a projectile fragment can be explained by a single Gaussian distribution and the averaged transverse momentum per nucleon decreases with the increase of the charge of projectile fragment. The cumulated squared transverse momentum distribution of a projectile fragment can be explained well by a single Rayleigh distribution. The temperature parameter of the emission source of the projectile fragment, calculated from the cumulated squared transverse momentum distribution, decreases with the increase of the size of the projectile fragment.  相似文献   
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the collision of very heavy nuclei ^197Au+^197Au at 15AMeV has been studied within the improved quantum molecular dynamics model. A class of ternary events satisfying nearly complete balance of mass numbers is selected. The experimental mass distributions for the system ^197Au+^197Au ternary fission fragments, the heaviest(A1), the intermediate (A2) and the lightest (A3), are reproduced well. The mean free path of nucleons in the reaction system is studied and the shorter mean free path is responsible for the ternary fission with three mass comparable fragments, in which the two-body dissipation mechanism plays a dominant role.  相似文献   
4.
Exploiting the nonlinear dynamics in the negative feedback loop, we propose a statistical signal-response model to describe the different oscillatory behaviour in a biological network motif. By choosing the delay as a bifurcation parameter, we discuss the existence of Hopf bifurcation and the stability of the periodic solutions of model equations with the centre manifold theorem and the normal form theory. It is shown that a periodic solution is born in a Hopf bifurcation beyond a critical time delay, and thus the bifurcation phenomenon may be important to elucidate the mechanism of oscillatory activities in regulatory biological networks.  相似文献   
5.
How ATP binding initiates the docking process of kinesin's neck linker is a key question in understanding kinesin mechanisms. By exploiting a molecular dynamics method, we investigate the initial conformation of kinesin's neck linker in its docking process. We find that, in the initial conformation, the neck linker has interactions with /30 and forms a 'cover-neck bundle' structure with/30. From this initial structure, the formation of extra turns and the docking of the cover- neck bundle structure can be achieved. The motor head provides a forward force on the initial cover-neck bundle structure through ATP-induced rotation. This force, together with the hydrophobic interaction of ILE327 with the hydrophobic pocket on the motor head, drives the formation of the extra turn and initiates the neck linker docking process. Based on these findings, a pathway from ATP binding-induced motor head rotation to neck linker docking is proposed.  相似文献   
6.
基于Skyrme能量密度泛函并对动能密度按扩展的Thomas-Fermi半经典近似展开到四阶项,探索了深度垒下熔合反应的熔合截面急剧下降现象。通过分析熔合反应的入射道势和熔合截面来选择Skyrme参数,进而探索了深度垒下熔合反应与核物质状态方程之间的关系。  相似文献   
7.
研究了15 Me V/u197Au+197Au体系三裂变反应过程中体系的集体运动动能、核-核相互作用势、集体运动总动能以及核子激发能的演化过程,并讨论了该反应过程的能量耗散问题。通过与两裂变时体系总动能εtot和Θc.m.关联图作对比,初步得出三裂变反应体系的第一次裂变是极端深度非弹性散射过程;进一步分析了三裂变与两裂变反应体系总动能与碰撞参数的关系,发现小碰撞参数下两裂变比三裂变反应耗散的能量多大约150 Me V,大碰撞参数下三裂变比两裂变反应多消耗300 Me V。  相似文献   
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通过CR-39 核径迹探测器对471 AMeV 56Fe 和400 AMeV 20Ne 诱发Al,C 和CH2 靶反应的弹核碎裂反应截面及出射角度进行了测量,并利用改进的量子分子动力学(ImQMD) 模型和描述统计衰变的GEMINI 模型对实验结果进行了分析和讨论。实验结果表明,总反应截面与弹核的能量无关,但随着靶核质量的增加而增加。这与其他的实验结果以及Bradt-Peters 的半经验理论公式所得结果一致。理论计算和实验测量结果中,分截面出现了明显的奇偶效应。理论计算结果表明,奇偶效应主要产生于受激碎块的衰变过程,其中对效应起着重要作用,而且,主要形成于擦边碰撞的反应中且多来自于同位旋为TZ = 0; ±0:5 的弹核碎块的贡献。产生碎块的同位素分布与弹核的种类有关,与入射能量和靶核的种类没有太大依赖性,其较小的偏转角大部分来自于擦边碰撞产生的较重的类弹碎块的贡献。We have measured the fragmentation cross sections and the emission angles for 471 AMeV 56Fe and 400AMeV 20Ne on Al, C and CH2 targets using CR-39 plastic nuclear track detector. The total charge changing cross sections agree well with other previous experimental results at different energies and the theoretical prediction of Bradt-Peters semiempirical formula, which are pproximately independent of the beam energy but increase with the increase of the target mass. The experimental results are compared with the prediction of the improved quantum molecular dynamical model (ImQMD) together with the GEMINI model. The odd-even effect of the partial cross sections observed in experiments is well produced. It is found that such effect is mainly formed in the grazing collisions and comes from the fragments with TZ = 0; ±0:5. The shape of the isotopic distribution is independent on the target mass and the incident energy but the projectile mass and charge, and the small angular distribution of all fragments comes from the heavier projectile-like fragments which produced in the peripheral collision.  相似文献   
9.
p53-Mdm2相互作用在DNA损伤的细胞响应方面起着非常重要的作用。最新实验结果表明,在受到各种辐射损伤而引起DNA损伤后,细胞中的p53蛋白浓度在单体细胞和群体细胞情况下,表现为非衰减振荡和衰减振荡两种不同的动力学行为。通过研究p53 -Mdm2负反馈回路的非线性动力学,分析了各种(特别是DNA损伤,p53和Mdm2浓度三者之间的)动力学关系,提出了一个能同时描述这两种不同动力学行为的非线性模型。 Exploring the nonlinear dynamics of the negative feedback loop composed of p53 and Mdm2 proteins, we propose a signal-response model to study the dynamical mechanism of the different oscillatory behaviors for the activities of p53 and Mdm2 proteins both in individual and population of cells. It is shown that the sustained and damped oscillatory dynamics could be described in a unified way when the dynamics of damage-derived signal is properly introduced.  相似文献   
10.
刘波  晏世伟  耿轶钊 《中国物理 B》2011,20(12):128702-128702
There have been many recent studies devoted to the consequences of stochasticity in protein circuitry. Stress conditions, including DNA damage, hypoxia, heat shock, nutrient deprivation, and oncogene activation, can result in the activation and accumulation of p53. Several experimental studies show that oscillations can be induced by DNA damage following nuclear irradiation. To explore the underlying dynamical features and the role of stochasticity, we discuss the oscillatory dynamics in the well-studied regulatory network motif. The fluctuations around the fixed point of a delayed system are Gaussian in the limit of sufficiently weak delayed feedback, and remain Gaussian along a limit cycle when viewed tangential to the trajectory. The experimental results are recapitulated in this study. We illustrate several features of the p53 activities, which are robust when the parameters change. Furthermore, the distribution in protein abundance can be characterized by its non-Gaussian nature.  相似文献   
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