The bullwhip effect in supply chain networks

This paper analyzes the propagation and amplification of order fluctuations (i.e., the bullwhip effect) in supply chain networks operated with linear and time-invariant inventory management policies. The supply chain network is allowed to include multiple customers (e.g., markets), any network structure, with or without sharing information. The paper characterizes the stream of orders placed by any supplier for any stationary customer demand processes, and gives exact formulas for the variance of the orders placed and the amplification of order fluctuations. The paper also derives robust analytical conditions, based only on inventory management policies, to predict the presence of the bullwhip effect for any network structure, any inventory replenishment policies, and arbitrary customer demand processes. Numerical examples show that the analytical results accurately quantify the bullwhip effect; managerial insights are drawn from the analysis. The methodology presented in this paper generalizes those in previous studies for serial supply chains.     

Heterogeneous slow dynamics and the interaction potential of glass-forming liquids

The role of the intermolecular interaction potential on the dynamic and thermodynamic properties of model glass-forming mixtures is investigated through molecular dynamics simulations. Variations of the repulsive exponent m in the well-studied Lennard-Jones Kob-Andersen mixture are shown to have a negligible effect on the fragility and dynamic correlation volumes when quenches are performed at constant pressure. The number of dynamically correlated particles, estimated from the temperature derivative of a two-point dynamic correlation function, is approximately invariant to m at any fixed relaxation time. Further, the density scaling property of a model tetrahedral network glass-former, based on inverse power law and Lennard-Jones potentials, is investigated. The optimal scaling exponent γ is close to zero and does not superpose the data well. The breakdown of density scaling is consistent with the absence of correlation between fluctuations of the virial and the potential energy. These results emphasize the crucial role of structural many-body correlations in glass-forming systems and show the need of investigations of more complex and realistic model liquids.     

Optimal design of a manpower system

An equilibrium model of a manpower system is developed based on the notion of a career flow. Institutional constraints and measures of system performance are linear functions of the career flow. A typical optimal design problem is formulated and a solution procedure is developed. The optimization problem is a generalized linear program in which columns are generated by solving a shortest path problem. Upper and lower bounds on the optimal value function can be developed at each stage of the calculations.This research was supported by ONR grant N00014-75-C-0619.     

子句集的神经网络归结

给出基于神经网络的归结方法。首先将子句集S表示为δ形式，并且用算子对(⊙， )引入两种类型的神经元；然后用这两种神经元构造子句集S的神经网络结构；而后给出基于子句集的神经网络的归结算法；最后证明了该算法的完备性，并用实例进行了验证。     

光电混合MESH互连网络的研究

提出一种自由空间空分复用的光学MESH互连网络系统．该光学MESH互连网络系统是由N×4位相型计算全息傅里叶光栅分束器、高速多量子阱空间先调制器SEED器件和高速间接耦合光电探测器列阵组成,具有互连数大、数据通道同步性好、光学硬件少、系统简单等特性．     

On the computational behavior of a polynomial-time network flow algorithm

A variation on the Edmonds-Karp scaling approach to the minimum cost network flow problem is examined. This algorithm, which scales costs rather than right-hand sides, also runs in polynomial time. Large-scale computational experiments indicate that the computational behavior of such scaling algorithms may be much better than had been presumed. Within several distributions of square, dense, capacitated transportation problems, a cost scaling code, SCALE, exhibits linear growth in average execution time with the number of edges, while two network simplex codes, RNET and GNET, exhibit greater than linear growth.Our experiments reveal that median and mean execution times are predictable with surprising accuracy for all of the three codes and all three distributions from which test problems were generated. Moreover, for fixed problem size, individual execution times appear to behave as though they are approximately lognormally distributed with constant variance. The experiments also reveal sensitivity of the parameters in the models, and in the models themselves, to variations in the distribution of problems. This argues for caution in the interpretation of such computational studies beyond the realm in which the computations were performed.This work has been supported in part by NSF grants ENG-7910807, ECS-8313853, DMS-8706133, and DDM-8813054, and by AFOSR, NSF, and ONR under NSF grant DMS-8920550 to Cornell University, and by a Sloan Foundation research fellowship held by the first author.     

Complexity of some parametric integer and network programming problems

Two examples of parametric cost programming problems—one in network programming and one in NP-hard 0-1 programming—are given; in each case, the number of breakpoints in the optimal cost curve is exponential in the square root of the number of variables in the problem. This research is partially supported by the Air Force Office of Scientic Research. Air Force Number AFOSR-78-3646     

On equivalent representations of certain multicommodity networks as single commodity flow problems

Several classes of multicommodity networks have been shown to have the property that they can be transformed to equivalent uncapacitated single commodity flow problems. We show that many of these networks can be further reduced to smaller, semi-capacitated flow problems using the inverse of a result of Ford and Fulkerson. This appears to be a useful computationally-oriented tool for developing practically efficient algorithms. These concepts are also used to establish a generalization of a previous result concerning multicommodity transportation problems.     

苯乙烯─马来酸酐共聚物／聚硅氧烷纳米尺度复合材料的研究

用溶胶－凝胶方法制备了苯乙烯、马来酸酐和ｒ－缩水甘油丙基醚三甲氧基硅烷复合材料．利用红外光谱、动态力学分析、小角Ｘ－射线散射和原子力显微镜等手段研究了这种材料的结构与性能．结果表明，这种材料以三维网络和纳米微相分离的形式存在，其力学性能和耐热性能较苯乙烯－马来酸酐共聚物有大幅度提高，透明且不溶于丙酮．     

PROPERTIES AND MORPHOLOGY OF LIQUID CHLOROPRENE-METHACRYLIC ACID COPOLYMER MODIFIED EPOXY RESIN/POLY (BUTYL METHACRYLATE) SEMI-IPN

A series of liquid chloroprene-methacrylic acid copolymcr (CP--co-MAA) modified epoxy resin (ER)/poly (butyl methacrylate) (PBMA). semi-IPN were synthesized. Some physical properties were investigated. DSC diagrams showed two indistinct and inward endothermal transitions corresponding to the transitions of two networks in the semi-IPN system. By observing morphology with SEM technique it shows that there is a multiphase structure, in which CP-co-MAA's. domain sizes arc about 0.10--0.80μ. With increasing C/E ratio, the domain eizes are getting smaller, which is due to effect of mixing network of CP-co-MAA promoting entanglement and interpenetrating of PBMA and CP-co-MAA-ER network. In most of the semi-IPN's compositions, ER phase readily maintains its phase continuity while PBMA phase presents a band shape structure. Consequently, crosslinking network keeps in its continuous phase more readily than uncrosslinking one, thus it influences dominantly on the physical properties.