A simheuristic algorithm to set up starting times in the stochastic parallel flowshop problem

This paper addresses the parallel flowshop scheduling problem with stochastic processing times, where a product composed of several components has to be finished at a particular moment. These components are processed in independent parallel factories, and each factory can be modeled as a permutation flowshop. The processing time of each operation at each factory is a random variable following a given probability distribution. The aim is to find the robust starting time of the operations at each factory in a way that all the components of the product are completed on a given deadline with a user-defined probability. A simheuristic algorithm is proposed in order to minimize each of the following key performance indicators: (i) the makespan in the deterministic version; and (ii) the expected makespan or a makespan percentile in the stochastic version. A set of computational experiments are carried out to illustrate the performance of the proposed methodology by comparing the outputs under different levels of stochasticity.     

A fast genetic algorithm for a critical protection problem in biomedical supply chain networks

In this paper, we present a new bilevel model for a biomedical supply chain network with capacity and budget constraint due to the protection and interdiction operations. The components considered in this model are biomedical devices, distribution centers (DCs), medical suppliers (MSs), and hospitals and patients as the demand points. On the other hand, two levels of decisions in the network planning is suggested: (1) the defender’s decision about protection operations of MSs and DCs, the assignment of clients to the DCs, and quantity of products shipped to DCs from MSs to minimize the demand-weighted traveling costs and transport costs and (2) the attacker’s decision about interdiction operations of MSs and DCs to maximize the capacity or service reduction and losses. Because of nondeterministic polynomial time (NP)-hardness of the problem under consideration, an efficient and fast approach based on a genetic algorithm and a fast branch and cut method (GA–FBC) was developed to solve the proposed model. Also, the efficiency via the comparison of results with the genetic algorithm based on CPLEX (GA-CPLEX) and decomposition method (DM) is investigated. In order to assess the performance of the presented GA–FBC, a set of 27 instances of the problem is used. Comprehensive analysis indicates that the proposed approach significantly solves the problem. In addition, the benefits and advantages of preference with running times and its accuracy is shown numerically. Simulation results clearly demonstrate that the defender’s objective effectively reduced and CPU time also within the large-sized instances of the problem in comparison with the GA-CPLEX and DM.     

The influence of temperature on the adhesion of mixed cultures of Staphylococcus aureus and Escherichia coli to polypropylene

The adhesion of Staphylococcus aureus and Escherichia coli, in mixed cultures, to polypropylene surfaces was evaluated at 12°C and 30°C. The micro-organisms were isolated from a chicken carcass and cultured in an aqueous extract, prepared from the same carcass, for the production of biofilms on polypropylene coupons. Adhered cells were counted by epifluorescence microscopy with acridine orange staining. Escherichia coli adhered in greater numbers to the coupons than S. aureus at both temperatures. Staphylococcus aureus adhered better at 12°C than at 30°C, while the reverse was true for E. coli. At 30°C, there was no increase in the number of adherent cells ofS. aureus over 8 h, while E. coli increased from a median of 5·0–19·0 per microscope field. At 12°C, the major increase in adherent cell numbers for both species occurred between 2 and 4 h, so that leaving cleaning until 8 h, as is common, would not result in greatly increased biofilms, 2-hourly cleansing is clearly unrealistic. However, total adherent cell numbers were the same at 12° and 30°C between 4 and 6 h incubation. Hence it seems that reduced temperature has little to offer for restricting biofilm formation on polypropylene work surfaces in a well-run food processing plant.     

Two 1-Server n-Unit Systems with Preventive Maintenance and Repair

This paper deals with the availability and reliability analysis of two different 1-server n-unit systems with preventive maintenance and repair. Initially, one unit operates and the remaining n - 1 units are kept as cold standbys. In the first system the time to failure and the time to preventive maintenance of a unit are arbitrarily distributed. In the second system, each unit consists of 2 components connected in series. When a unit fails, the failed component is taken up for repair while the other waits for preventive maintenance. Explicit expressions for the Laplace transform of the mean down-time of the system in [0, t] and for the mean time to system failure are obtained. Steady-state availability of the system is also discussed. A few special cases have been studied.     

A new thermodynamic function for phase‐splitting at constant temperature,moles, and volume

We introduce a new thermodynamic function for phase‐split computations at constant temperature, moles, and volume. The new volume function F_i introduced in this work is a natural choice under these conditions. Phase equilibrium conditions in terms of the volume functions are derived using the Helmholtz free energy. We present a numerical algorithm to investigate two‐phase equilibrium based on the fixed point iteration and Newton method. We demonstrate usefulness and powerful features of the new thermodynamic function for a number of examples in two‐phase equilibrium calculations. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

一类奇异LQ问题的Walsh级数分析法

利用Ｗａｌｓｈ级数的分析特性讨论了有限区间上奇异ＬＱ问题的解法。     

中立型方程的数值稳定性

主要研究中立型方程ｙ（ｔ）＝ａｙ（ｔ）＋ｂｙ（ｑｔ）＋ｃｙ（ｐｔ），ｙ（０）＝１，ｐ，ｑ∈（０，１，），ａ，ｂ，ｃ∈Ｃ的数值方法稳定性条件，给出了此方程当ｐ＝ｑ＝１／Ｌ，Ｌ≥２时为整数时的线性θ－方法渐近稳定充分条件，为「１／２，１」，／ｂ／－Ｒｅａ，Ｒｅａ〈０，／ｃ／〈１。     

对回归分析法的几点体会

通过科研实践，我们对线性回归分析方法的应用有几点新的体会     

控制系统的绝对稳定性

利用不等式分析技巧研究变系数控制系统的绝对稳定性,获得了系统的绝对稳定性条件。该条件均建立在系统本身的参数之上,故是实用的。用飞机纵向运动方程为例说明了所获结果的优越性。     

Reinhardt域上推广的Roper-Suffridge算子与Loewner链

研究了Roper-Suffridge算子与Loewner链的关系,利用Loewner链的定义及性质证明了推广的Roper-Suffridge算子在有界完全Reinhardt域上能嵌入Loewner链,从α次殆β型螺形映照与Loewner链的关系出发得到结论:推广后的Roper-Suffridge算子在有界完全Reinhardt域上保持α次殆β型螺形性,并作为特殊情况得出推广后的Roper-Suffridge算子在相应域上保持α次殆星形性及β型螺形性.