Optimization of multiclass queueing networks with changeover times via the achievable region approach: Part I, the single-station case

We address the performance optimization problem in a single-stationmulticlass queueing network with changeover times by means of theachievable region approach. This approach seeks to obtainperformance bounds and scheduling policies from the solution of amathematical program over a relaxation of the system's performanceregion. Relaxed formulations (including linear, convex, nonconvexand positive semidefinite constraints) of this region are developedby formulating equilibrium relations satisfied by the system, withthe help of Palm calculus. Our contributions include: (1) newconstraints formulating equilibrium relations on server dynamics;(2) a flow conservation interpretation of the constraintspreviously derived by the potential function method; (3) newpositive semidefinite constraints; (4) new work decomposition lawsfor single-station multiclass queueing networks, which yield newconvex constraints; (5) a unified buffer occupancy method ofperformance analysis obtained from the constraints; (6) heuristicscheduling policies from the solution of the relaxations.

Sign of the Times, January 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, February 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, March 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, April 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, May 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, June 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, July 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, August 2008

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, September 2008

Newsletter produced by Deaf Services Commission of Iowa

Serial defaults, serial profits: Returns to sovereign lending in Habsburg Spain, 1566-1600

Philip II of Spain accumulated debts equivalent to 60% of GDP. He also defaulted four times onhis short-term loans, thus becoming the first serial defaulter in history. Contrary to a commonview in the literature, we show that lending to the king was profitable even under worst-casescenario assumptions. Lenders maintained long-term relationships with the crown. Lossessustained during defaults were more than compensated by profits in normal times. Defaultswere not catastrophic events. In effect, short-term lending acted as an insurance mechanism,allowing the king to reduce his payments in harsh times in exchange for paying a premium intranquil periods. © 2010 Elsevier Inc. All rights reserved.

Retention half times in the skeleton of plutonium and 90Sr from above-ground nuclear tests: a retrospective study of the Swiss population.

Plutonium and (90)Sr are considered to be among the most radiotoxic nuclides produced by the nuclear fission process. In spite of numerous studies on mammals and humans there is still no general agreement on the retention half time of both radionuclides in the skeleton in the general population. Here we determined plutonium and (90)Sr in human vertebrae in individuals deceased between 1960 and 2004 in Switzerland. Plutonium was measured by sensitive SF-ICP-MS techniques and (90)Sr by radiometric methods. We compared our results to the ones obtained for other environmental compartments to reveal the retention half time of NBT fallout (239)Pu and (90)Sr in trabecular bones of the Swiss population. Results show that plutonium has a retention half time of 40+/-14 years. In contrast (90)Sr has a shorter retention half time of 13.5+/-1.0 years. Moreover (90)Sr retention half time in vertebrae is shown to be linked to the retention half time in food and other environmental compartments. These findings demonstrate that the renewal of the vertebrae through calcium homeostatic control is faster for (90)Sr excretion than for plutonium excretion. The precise determination of the retention half time of plutonium in the skeleton will improve the biokinetic model of plutonium metabolism in humans.

Optimization of multiclass queueing networks with changeover times via the achievable region method: Part II, the multi-station case

We address the problem of scheduling a multi-station multiclassqueueing network (MQNET) with server changeover times to minimizesteady-state mean job holding costs. We present new lower boundson the best achievable cost that emerge as the values ofmathematical programming problems (linear, semidefinite, andconvex) over relaxed formulations of the system's achievableperformance region. The constraints on achievable performancedefining these formulations are obtained by formulatingsystem's equilibrium relations. Our contributions include: (1) aflow conservation interpretation and closed formulae for theconstraints previously derived by the potential function method;(2) new work decomposition laws for MQNETs; (3) new constraints(linear, convex, and semidefinite) on the performance region offirst and second moments of queue lengths for MQNETs; (4) a fastbound for a MQNET with N customer classes computed in N steps; (5)two heuristic scheduling policies: a priority-index policy, anda policy extracted from the solution of a linear programmingrelaxation.

New findings regarding return autocorrelation anomalies and the importance of non-trading periods

In this paper, differences in return autocorrelation across weekdays havebeen investigated. Our research provides strong evidence of the importanceon non-trading periods, not only weekends and holidays but also overnightclosings, to explain return autocorrelation anomalies. While stock returnsare highly autocorrelated, specially on Mondays, when daily returns arecomputed on a open-to-close basis, they do not exhibit any significantlevel of autocorrelation. Our results are compatible with theinformation processing hypotheses as an explanation of the weekendeffect.