Fluid analysis of arrival routing

In Hajek's arrival routing problem (1984), customers are routed to one of n queues to minimize average holding cost. Interarrival and service times are exponentially distributed. We solve the associated fluid model. The optimal fluid policy tells us the asymptotic slopes of the switching surfaces in the original problem when the queues are large. If these slopes are nonzero, then numerical tests indicate that the fluid policy performs well in the original stochastic network. The fluid policy also indicates the approximate path that will be taken to recover from large queues: Routing only switches to queues with larger holding cost and once a large queue empties it will remain approximately empty     

Inspection strategies for multistage production systems with time-varying quality

An economic, cost of quality model is formulated for a production system with multiple inspection locations and sampling. The model is applied to a thermal printer for digital photographs to determine when inspection of incoming material is appropriate. A simple dynamic model of quality is used, allowing for common-cause defects and the evaluation of sampling plans. The opportunity to correct quality problems more quickly when they are detected earlier is also considered. The cost structure used allows the costs of quality improvement, and not just that of defective units, to be considered.     

Just-in-time policies for single-machine manufacturing flowcontrollers

Single, unreliable machine producing n part types is considered. Using a continuous flow model, conditions are found for the optimality of a just-in-time, or zero-inventory, policy via a stochastic coupling analysis. These conditions are proven to be necessary and conjectured to be sufficient for optimality. This correspondence extends the results of Veatch and Caramanis, in which necessary and sufficient conditions are found for a single machine producing two part types, and it strengthens the results of Perkins and Srikant, in which sufficient conditions are found for n part types     

Optimal average cost manufacturing flow controllers: convexity anddifferentiability

The authors consider the control of a production facility consisting of a single workstation with multiple failure modes and part types using a continuous flow control model. Technical issues concerning the convexity and differentiability of the differential cost function are investigated. It is proven that under an optimal control policy the differential cost is C¹ on attractive control switching boundaries     

Egalitarian and maximin theories of justice: directed donation of organs for transplant

It is common to interpret Rawls's maximin theory of justice as egalitarian. Compared to utilitarian theories, this may be true. However, in special cases practices that distribute resources so as to benefit the worst off actually increase the inequality between the worst off and some who are better off. In these cases the Rawlsian maximin parts company with what is here called true egalitarianism. A policy question requiring a distinction between maximin and "true egalitarian" allocations has arisen in the arena of organ transplantation. This case is examined here as a venue for differentiating maximin and true egalitarian theories. Directed donation is the name given to donations of organs restricted to a particular social group. For example, the family of a member of the Ku Klux Klan donated his organs on the provision that they go only to members of the Caucasian race. While such donations appear to be discriminatory, if certain plausible assumptions are made, they satisfy the maximin criterion. They selectively advantage the recipient of the organs without harming anyone (assuming the organs would otherwise go unused). Moreover, everyone who is lower on the waiting list (who, thereby, could be considered worse off) is advantaged by moving up on the waiting list. This paper examines how maximin and more truly egalitarian theories handle this case arguing that, to the extent that directed donation is unethical, the best account of that conclusion is that an egalitarian principle of justice is to be preferred to the maximin.     

Medical ethics teaching. Report of a National Medical School Survey

Medical ethics teaching was surveyed at American medical schools. Of 107 schools that responded, 97 indicated some kind of medical ethics teaching. This included, however, 19 schools where teaching was only by discussion of ethical issues in courses not primarily identified as ethics courses. Fifty-six institutions (up from 17 in 1972) reported that they conducted special conferences, lectures, or seminars on issues in medical ethics. Specific medical ethics electives were offered in 47 schools; some kind of required course existed at six institutions. The number of faculties with major commitments to medical ethics teaching increased approximately 50% (from 19 to 31). Several schools now have departments or interdepartmental teaching programs with formal structure and permanent staff.     

Optimal manufacturing flow controllers: zero-inventory policies andcontrol switching sets

A continuous-flow control model of a single workstation with multiple failure modes and part types is considered. Although the general model is intractable, properties of the optimal control policy are identified that can be used to help formulate heuristic policies. Control switching sets are described and shown to have a threshold form. For a single machine with two part-types, conditions are found under which no inventory is held, analogous to the single-part-type result of Bielecki and Kumar (1988)     

Dynamic allocation of reconfigurable resources ina two-stage Tandem queueing system with reliability considerations

Consider a two-stage tandem queueing system, with dedicated machines in each stage. Additional reconfigurable resources can be assigned to one of these two stations without setup cost and time. In a clearing system (without external arrivals) both with and without machine failures, we show the existence of an optimal monotone policy. Moreover, when all of the machines are reliable, the switching curve defined by this policy has slope greater than or equal to -1. This continues to hold true when the holding cost rate is higher at the first stage and machine failures are considered.