On the Viability of Gift Exchange in a Market Environment

Is gift-exchange inevitably to be crowded out by impersonal market exchange? The presence of a thick-market externality indicates that this is indeed likely to be the case. But reciprocity or gift-exchange induces social relations. The utility function is extended in order to take account of social relations in the form of symbolic utility or moral sentiments. As long as moral sentiments are valued high enough it is shown that both market and gift-exchange can coexist. The spontaneous order need not necessarily select the most efficient market size however.exchange;reciprocity;gifts;moral and extended preferences

Flux penetration and a.c. losses in type II superconductors: I. Model calculations

A numerical method is presented which allows the calculation of the a.c. response of type II superconductors under quasi-static conditions for arbitrary jc (B,x), Ben (Ba) and Bex (Ba) relations. Flux distributions, induced voltage waveforms, hysteresis loops and a.c. losses have been calculated. Deviations between experimental results and earlier calculations with respect to a minimum in the a.c. losses are explained by taking into account the finite thickness of the sample and realistic Ben (Ba) and Bex (Ba) relations

Modeling and solving the periodic maintenance problem.

We study the problem of scheduling maintenance services. Given is a set of m machines and integral cost-coefficients a(i) and b(i) for each machine i (1Branch-and-price; Column generation; Costs; Linear programming; Model; Models; Optimal; Scheduling; Structure; Studies; Time;

A note on a motion control problem for a placement machine.

Assembling printed circuit boards effciently using automated placement machines is a challenging task. Here, we focus on a motion control problem for a specific type of placement machines. More specifically,the problem is to establish movement patterns for the robot arm, the feeder rack,and -when appropriate- the work table, of a sequential, pick-and-place machine. In this note we show that a (popular) greedy strategy may not always yield an optimum solution. However, under the Tchebychev metric, as well as under the Manhattan metric, we can model the problem as a linear program, thereby establishing the existence of a polynomial time algorithm for this motion control problem. Finally, we give experimental evidence that computing optimal solutions to this motion control problem can yield significantly better solutions than those found by a greedy method.Algorithms; Computational complexity; Control; Printed circuit boards;

Telecommunication carrier selection under volume discounts: a case study.

During 2001 many of the European mobile phone markets have reached saturation, and hence mobile phone operators have shifted their attention from growth and market share to cutting costs. One way of doing so is to reduce spending on international calls which are routed via network operating companies (carriers). These carriers charge per call-minute for each destination and may use a joint business volume discount to price their services. We developed a software system that supports the decision of allocating destinations to carriers. The core of this system is a min-cost flow routine that is embedded in a branch-and-bound framework. Our system not only solves the operational problem to optimality, it is also capable of performing what-if analyses and sensitivity analysis. It has been implemented at a major telecommunication services provider. The main benefits realized are twofold: the business process of allocating carriers to destinations has been structured and the costs arising from routing international calls have significantly decreased.Selection; Case studies; Studies; Markets; Market; Costs; International; Companies; Software; Decision; Framework; Sensitivity; Processes;

Exact algorithms for procurement problems under a total quantity discount structure.

In this paper, we study the procurement problem faced by a buyer who needs to purchase a variety of goods from suppliers applying a so-called total quantity discount policy. This policy implies that every supplier announces a number of volume intervals and that the volume interval in which the total amount ordered lies determines the discount. Moreover, the discounted prices apply to all goods bought from the supplier, not only to those goods exceeding the volume threshold. We refer to this cost-minimization problem as the TQD problem. We give a mathematical formulation for this problem and argue that not only it is NP-hard, but also that there exists no polynomial-time approximation algorithm with a constant ratio (unless P = NP). Apart from the basic form of the TQD problem, we describe three variants. In a first variant, the market share that one or more suppliers can obtain is constrained. Another variant allows the buyer to procure more goods than strictly needed, in order to reach a lower total cost. In a third variant, the number of winning suppliers is limited. We show that the TQD problem and its variants can be solved by solving a series of min-cost flow problems. Finally, we investigate the performance of three exact algorithms (min-cost flow based branch-and-bound, linear programming based branch-and-bound, and branch-and-cut) on randomly generated instances involving 50 suppliers and 100 goods. It turns out that even the large instances of the basic problem are solved to optimality within a limited amount of time. However, we find that different algorithms perform best in terms of computation time for different variants.Algorithms; Approximation; Branch-and-bound; Complexity; Cost; Exact algorithm; Intervals; Linear programming; Market; Min-cost flow; Order; Performance; Policy; Prices; Problems; Procurement; Reverse auction; Structure; Studies; Suppliers; Time; Volume discounts;

X-ray and electron spin resonance on YBa2Cu3O7 prepared by citrate synthesis

YBa2Cu3O7 samples were prepared by a citrate synthesis technique. Powder X-ray diffraction and resistance measurements were performed for sample characterization. This single-phase material has a Tc(R=0) of 91.2 K. Electron spin resonance experiments indicate the presence of 10 to 15% of Cu3+