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921.
Elastically coupled molecular motors 总被引:3,自引:0,他引:3
A. Vilfan E. Frey F. Schwabl 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):535-546
We study the influence of filament elasticity on the motion of collective molecular motors. It is found that for a backbone
flexibility exceeding a characteristic value (motor stiffness divided through the mean displacement between attached motors),
the ability of motors to produce force reduces as compared to rigidly coupled motors, while the maximum velocity remains unchanged.
The force-velocity-relation in two different analytic approximations is calculated and compared with Monte-Carlo simulations.
Finally, we extend our model by introducing motors with a strain-dependent detachment rate. A remarkable crossover from the
nearly hyperbolic shape of the Hill curve for stiff backbones to a linear force-velocity relation for very elastic backbones
is found. With realistic model parameters we show that the backbone flexibility plays no role under physiological conditions
in muscles, but it should be observable in certain in vitro assays.
Received: 27 November 1997 / Revised: 20 February 1998 / Accepted: 27 March 1998 相似文献
922.
A branch and bound method for stochastic global optimization 总被引:9,自引:0,他引:9
Vladimir I. Norkin Georg Ch. Pflug Andrzej Ruszczyński 《Mathematical Programming》1998,83(1-3):425-450
A stochastic branch and bound method for solving stochastic global optimization problems is proposed. As in the deterministic
case, the feasible set is partitioned into compact subsets. To guide the partitioning process the method uses stochastic upper
and lower estimates of the optimal value of the objective function in each subset. Convergence of the method is proved and
random accuracy estimates derived. Methods for constructing stochastic upper and lower bounds are discussed. The theoretical
considerations are illustrated with an example of a facility location problem. 相似文献
923.
Efficient Global Optimization of Expensive Black-Box Functions 总被引:41,自引:0,他引:41
Donald R. Jones Matthias Schonlau William J. Welch 《Journal of Global Optimization》1998,13(4):455-492
In many engineering optimization problems, the number of function evaluations is severely limited by time or cost. These problems pose a special challenge to the field of global optimization, since existing methods often require more function evaluations than can be comfortably afforded. One way to address this challenge is to fit response surfaces to data collected by evaluating the objective and constraint functions at a few points. These surfaces can then be used for visualization, tradeoff analysis, and optimization. In this paper, we introduce the reader to a response surface methodology that is especially good at modeling the nonlinear, multimodal functions that often occur in engineering. We then show how these approximating functions can be used to construct an efficient global optimization algorithm with a credible stopping rule. The key to using response surfaces for global optimization lies in balancing the need to exploit the approximating surface (by sampling where it is minimized) with the need to improve the approximation (by sampling where prediction error may be high). Striking this balance requires solving certain auxiliary problems which have previously been considered intractable, but we show how these computational obstacles can be overcome. 相似文献
924.
Traffic jams and ordering far from thermal equilibrium 总被引:3,自引:0,他引:3
The recently suggested correspondence between domain dynamics of traffic models and the asymmetric chipping model is reviewed. It is observed that in many cases traffic domains perform the two characteristic dynamical processes of the chipping model, namely chipping and diffusion. This correspondence indicates that jamming in traffic models in which all dynamical rates are non-deterministic takes place as a broad crossover phenomenon, rather than a sharp transition. Two traffic models are studied in detail and analyzed within this picture. 相似文献
925.
The linearization and correction method (LCM) proposed by He is a simple and effective perturbation technique to solve nonlinear equations. To analyze the random properties of rill erosion model, a new stochastic perturbation technique called linearized perturbation method is developed by combining the traditional stochastic perturbation method with the LCM. Comparisons between the numerical results obtained by the linearized perturbation method and those obtained by Monte Carlo method indicated an excellent agreement. However, the calculation efficiency of the linearized perturbation method is higher. 相似文献
926.
We give multi-stage stochastic programming formulations for lot-sizing problems where costs, demands and order lead times follow a general discrete-time stochastic process with finite support. We characterize the properties of an optimal solution and give a dynamic programming algorithm, polynomial in the scenario tree size, when orders do not cross in time. 相似文献
927.
E. Ben-Naim F. Vazquez S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):531-538
We model the dynamics of social structure by a simple interacting particle
system. The social standing of an individual agent is represented by an
integer-valued fitness that changes via two offsetting processes. When two
agents interact one advances: the fitter with probability p and the less
fit with probability 1-p. The fitness of an agent may also decline with
rate r. From a scaling analysis of the underlying master equations for
the fitness distribution of the population, we find four distinct social
structures as a function of the governing parameters p and r. These
include: (i) a static lower-class society where all agents have finite
fitness; (ii) an upwardly-mobile middle-class society; (iii) a hierarchical
society where a finite fraction of the population belongs to a middle class
and a complementary fraction to the lower class; (iv) an egalitarian
society where all agents are upwardly mobile and have nearly the same
fitness. We determine the basic features of the fitness distributions in
these four phases. 相似文献
928.
A new stochastic efficiency analysis approach, called stochastic efficiency with respect to a function (SERF), is applied to analyse optimal tree replanting on an area of recently harvested forest land. SERF partitions a set of risky alternative tree replanting strategies in terms of certainty equivalents (CEs) for a specified range of attitudes to risk. Both the entailed risk and the forest owner’s risk aversion are taken into account. The forest owner’s degree of risk aversion affects both the optimal tree replacement strategy and the reinvestment decision. The degree of risk aversion also needs to be taken into account when designing policy measures to affect forest investment. 相似文献
929.
930.
可违约债券在随机波动率假定下近似定价公式的求解 总被引:1,自引:0,他引:1
在假设标的资产价格的波动率是一个快速均值回复OU过程的函数的条件下,导出相应的可违约债券价格公式所应满足的偏微分方程,并利用Taylor级数展开得到一组Poisson方程.求解这些方程,得到非完全市场下固定补偿率的债券价格的近似表达式,然后在不同的补偿率规定上作了一些修正和推广. 相似文献