Karmel S. Shehadeh  Amy E. M. Cohn  Ruiwei Jiang 《海军后勤学研究》2021,68(1):89-111

We study a stochastic outpatient appointment scheduling problem (SOASP) in which we need to design a schedule and an adaptive rescheduling (i.e., resequencing or declining) policy for a set of patients. Each patient has a known type and associated probability distributions of random service duration and random arrival time. Finding a provably optimal solution to this problem requires solving a multistage stochastic mixed‐integer program (MSMIP) with a schedule optimization problem solved at each stage, determining the optimal rescheduling policy over the various random service durations and arrival times. In recognition that this MSMIP is intractable, we first consider a two‐stage model (TSM) that relaxes the nonanticipativity constraints of MSMIP and so yields a lower bound. Second, we derive a set of valid inequalities to strengthen and improve the solvability of the TSM formulation. Third, we obtain an upper bound for the MSMIP by solving the TSM under the feasible (and easily implementable) appointment order (AO) policy, which requires that patients are served in the order of their scheduled appointments, independent of their actual arrival times. Fourth, we propose a Monte Carlo approach to evaluate the relative gap between the MSMIP upper and lower bounds. Finally, in a series of numerical experiments, we show that these two bounds are very close in a wide range of SOASP instances, demonstrating the near‐optimality of the AO policy. We also identify parameter settings that result in a large gap in between these two bounds. Accordingly, we propose an alternative policy based on neighbor‐swapping. We demonstrate that this alternative policy leads to a much tighter upper bound and significantly shrinks the gap.  相似文献   

    

Joanna R.Hall  Olivia Matthews  Timothy N.Volonakis  Eric Liggins  Karl P.Lymer  Roland Baddeley  Innes C.Cuthill  Nicholas E.Scott-Samuel 《防务技术》2021,17(6):1833-1839

The human visual system is still an important factor in military warfare; military personnel receive training on effective search strategies, and camouflage that can effectively conceal objects and personnel is a key component of a successful integrated survivability strategy. Previous methods of camouflage assessment have, amongst others, used psychophysics to generate distinctiveness metrics. However, the population from which the human observers are drawn is often not well defined, or necessarily appropriate. In this experiment we designed a new platform for testing multiple patterns based on a camouflaged object detection task, and investigate whether trained military observers perform better than civilians. We use a two-alternative forced choice paradigm, with participants searching images of woodland for a replica military helmet displaying Olive Green, Multi Terrain Pattern, US Marine Pattern or, as a conspicuous control, UN Peacekeeper Blue. Our data show that there is no difference in detection performance between the two observer groups but that there are clear differences in the effectiveness of the different helmet colour patterns in a temperate woodland environment. We conclude that when tasks involve very short stimulus presentation times, task-specific training has little effect on the success of target detection and thus this paradigm is particularly suitable for robust estimates of camouflage efficacy.  相似文献   

    

Rubing Chen  Jinjiang Yuan  C.T. Ng  T.C.E. Cheng 《海军后勤学研究》2019,66(7):582-595

We consider scheduling a set of jobs with deadlines to minimize the total weighted late work on a single machine, where the late work of a job is the amount of processing of the job that is scheduled after its due date and before its deadline. This is the first study on scheduling with the late work criterion under the deadline restriction. In this paper, we show that (i) the problem is unary NP‐hard even if all the jobs have a unit weight, (ii) the problem is binary NP‐hard and admits a pseudo‐polynomial‐time algorithm and a fully polynomial‐time approximation scheme if all the jobs have a common due date, and (iii) some special cases of the problem are polynomially solvable.  相似文献   

    

B. M. T. Lin  T. C. E. Cheng 《海军后勤学研究》2011,58(1):17-27

This article considers batch scheduling with centralized and decentralized decisions. The context of our study is concurrent open shop scheduling where the jobs are to be processed on a set of independent dedicated machines, which process designated operations of the jobs in batches. The batching policy across the machines can be centralized or decentralized. We study such scheduling problems with the objectives of minimizing the maximum lateness, weighted number of tardy jobs, and total weighted completion time, when the job sequence is determined in advance. We present polynomial time dynamic programming algorithms for some cases of these problems and pseudo‐polynomial time algorithms for some problems that are NP‐hard in the ordinary sense. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 58: 17–27, 2011  相似文献   

    

Lawrence E. Cline 《Small Wars & Insurgencies》2013,24(2):126-147

The northeast states of India have faced a series of insurgencies almost since independence. Most insurgent groups have been based on the competing demands of various ethnic groups, with conflicts not only between the insurgents and the government, but also between groups. The combination of anti-government and intercommunal violence shows little sign of ending. Although the Indian government has made progress in dealing with the largest groups, the continued existence of several dozen insurgent movements represents a significant security threat to internal stability in India.  相似文献   

    

Lawrence E. Cline 《Small Wars & Insurgencies》2013,24(2):275-287

The insurgency in southern Thailand has proven to be intractable over the last few years. The insurgents, who comprise several different groups, have largely retained the initiative in a series of relatively unsophisticated operations. Although involving ethnic Malay Muslims – and marked by an increasingly strong Islamist ideology – the insurgency has been predominantly ethnic rather than religious. External jihadist involvement has been minimal at best. The recent coup in Thailand may improve the odds of reaching some form of accommodation with the southern insurgents; but it is likely that the south will remain a continuing security problem for Bangkok.  相似文献   

    

Lawrence E. Cline 《Small Wars & Insurgencies》2013,24(3-4):574-591

Multiple ethnic insurgencies have existed in Myanmar since independence. The military junta's response has been extremely brutal at the tactical level, but has shown some political astuteness at the strategic level, with a series of ceasefires with most of the ethnic groups. Despite these ceasefires – most of which have resulted in the continued existence of quasi-independent armed groups – other ethnic movements have continued their armed operations. The overall strategic picture is one of stalemate, with the ethnic movements continuing to exist, but with few realistic prospects of expanding their operations.  相似文献   

    

Dr Sarah E. Kreps 《African Security Review》2013,22(4):65-79

With the security situation in Darfur remaining grim, the international community passed United Nations Security Resolution 1769 that authorised a more robust peacekeeping force. This article addresses the security concerns motivating the United Nations-African Union Mission in Darfur (UNAMID), highlights the mandate and implications of the force, and compares the potential command and control issues to the experiences of the Somalia intervention in the 1990s. It closes by analysing the prospects for success of the intervention and offering some limited recommendations on ways to mitigate the risks associated with the peacekeeping effort.  相似文献   

    

Janne E. Nolan 《The Nonproliferation Review》2013,20(2):273-277

ABSTRACT

Widespread and often exaggerated generalizations about the global spread weapons of mass destruction (WMDs) have proven to be not only misleading and technologically naïve, but also unhelpful in formulating effective policies to counter their threat. The new book by George Mason University's Sonia Ben Ouagrham-Gormley dispels the popular narrative that governments and terror groups can easily—and inevitably will—develop WMDs, particularly biological weapons, by exploring the complex external and internal conditions that such programs require, as demonstrated by the Cold War-era biological weapon programs of the superpowers. This empirically grounded and realistic assessment of how states try—and often fail—to develop such programs offers a more reliable basis to craft realistic counterproliferation policies that can elicit international support.  相似文献   

    

William E. Stein  Ronald Dattero  Roger C. Pfaffenberger 《海军后勤学研究》1984,31(4):647-651

Let {Xⁱ} be independent HNBUE (Harmonic New Better Than Used in Expectation) random variables and let {Yⁱ} be independent exponential random variables such that E{Xⁱ}=E{Yⁱ} It is shown that documentclass{article}pagestyle{empty}begin{document}$ Eleft[{uleft({mathop {min ,X_i}limits_{l le i le n}} right)} right] ge Eleft[{uleft({mathop {min ,Y_i}limits_{l le i le n}} right)} right] $end{document} for all increasing and concave u. This generalizes a result of Kubat. When comparing two series systems with components of equal cost, one with lifetimes {Xⁱ} and the other with lifetimes {Yⁱ}, it is shown that a risk-averse decision-maker will prefer the HNBUE system. Similar results are obtained for parallel systems.  相似文献