The effect of correlated exponential service times on single server tandem queues

An investigation via simulation of system performance of two stage queues in series (single server, first-come, first-served) under the assumption of correlated exponential service times indicates that the system's behavior is quite sensitive to departures from the traditional assumption of mutually independent service times, especially at higher utilizations. That service times at the various stages of a tandem queueing system for a given customer should be correlated is intuitively appealing and apparently not at all atypical. Since tandem queues occur frequently, e.g. production lines and the logistics therewith associated, it is incumbent on both the practitioner and the theoretician that they be aware of the marked effects that may be induced by correlated service times. For the case of infinite interstage storage, system performance is improved by positive correlation and impaired by negative correlation. This change in system performance is reversed however for zero interstage storage and depends on the value of the utilization rate for the case where interstage storage equals unity. The effect due to correlation is shown to be statistically significant using spectral analytic techniques. For correlation equal unity and infinite interstage storage, results are provided for two through twenty-five stages in series to suggest how adding stages affects system performance for ρ>0. In this extreme case of correlation, adding stages has an effect on system performance which depends markedly on the utilization rate. Recursive formulae for the waiting time per customer for the cases of zero, one, and infinite interstage storage are derived.     

Human Security and the State in Africa

The most recent major document on human security tells us more about the ideal of human security than how this worthy objective can best be achieved. This is a problem because most African states were created to serve as a bulwark against further colonial rule rather than provide domestic order and protection for their citizens. Many African states have since become battlegrounds for ethnic or economic struggles. Neither a new and committed African leadership, nor intervention by the international community, is likely to transcend this problem and effectively advance the human security agenda. A reformed African state—one which induces leaders to be more concerned with advancing the interests of their people more broadly—remains the only viable alternative. The problem is that any reform of African states will also involve difficult trade-offs and dilemmas.     

An alliance between Cyprus and Greece: assessing its partners’ relative security contribution

The issue that this paper tackles is the assessment of the relative security benefits that Cyprus and Greece derive in the context of their cooperation on defence matters. This form of cooperation, known as the ‘Integrated Defence Space Doctrine’, aims at defending their interests in the Aegean Sea and the broader East Mediterranean theatre. The paper relies heavily on earlier research on this topic, which deals with the Greek–Cypriot alliance facing an arms race against Turkey, and uses a coefficient especially designed to assess the optimal levels of security and the associated defence expenditure of the two allies. A comparison of the relative security coefficient values for the two allies suggests that the security benefit that Greece derives thanks to its alliance with Cyprus exceeds the corresponding Cypriot benefit by far. Given the importance assigned to human resources by this index, in conjunction with the demographic problems of Greece, this conclusion justifies the recent Greek defence policy revision, emphasizing quality, capital equipment and flexibility of forces. This revision aims at satisfying the security requirements of the alliance and the increasing demands of an arms race against Turkey.     

FINANCIAL VERSUS HUMAN RESOURCES IN THE GREEK–TURKISH ARMS RACE 10 YEARS ON: A FORECASTING INVESTIGATION USING ARTIFICIAL NEURAL NETWORKS

This paper looks into the Greek–Turkish arms race a decade after an earlier contribution to the issue that relied heavily on artificial neural networks. The time period between the two papers contributes to the reliability of the results derived, not just by increasing the number of observations, but also mainly by incorporating the progress made in the realm of artificial intelligence. The focus on the case of both countries unlike the paper mentioned above that dealt with just the Greek side provides ample room for comparative purposes regarding the determinants of defense expenditure on both sides. The results derived in terms of input significance estimation support the findings of the earlier research as indicated above, pointing to the leading role of the demographic preponderance of Turkey over Greece. The paper also points to the fact that 10 years later, Turkey continues to set the arms race rules against its rival by determining the defense expenditure of Greece, whereas the role of the latter in affecting the military spending of Turkey is non‐existent.     

EXTRAORDINARY VISITS

North Korea has the bomb but not much of a nuclear arsenal. For fifty years, it pursued the plutonium path to the bomb in parallel with its pursuit of nuclear electricity. My visits to North Korea's Yongbyon nuclear complex provided a window to its plutonium capabilities. After having made six visits to North Korea, Pyongyang surprised me during my seventh visit last November by showing me a small, modern uranium enrichment plant, which I was told was needed for its new indigenous light water reactor program. However, the same capabilities can be used to produce highly enriched uranium bomb fuel. Following a pattern of having made poor risk-management decisions during much of the past twenty years of diplomacy dealing with the North Korean nuclear threat, Washington remains in a standoff with Pyongyang.     

Acceptance sampling,imperfect production,and the optimality of zero defects

Acceptance sampling is often used to monitor the quality of raw materials and components when product testing is destructive, time-consuming, or expensive. In this paper we consider the effect of a buyer-imposed acceptance sampling policy on the optimal batch size and optimal quality level delivered by an expected cost minimizing supplier. We define quality as the supplier's process capability, i.e., the probability that a unit conforms to all product specifications, and we assume that unit cost is an increasing function of the quality level. We also assume that the supplier faces a known and constant “pass-through” cost, i.e., a fixed cost per defective unit passed on to the buyer. We show that the acceptance sampling plan has a significant impact on the supplier's optimal quality level, and we derive the conditions under which zero defects (100% conformance) is the policy that minimizes the supplier's expected annual cost. © 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 515–530, 1997     

Airpower in India's 1999 Kargil War

For 74 days in mid-1999, India waged an intense war against intruding Pakistani forces on the Indian side of the Line of Control dividing Kashmir in the Himalayas. The Indian Air Force (IAF) was a key contributor to India's eventual victory in that war. Among other things, the IAF's combat performance showed how the skillful application of air-delivered firepower, especially if unmatched by the other side, can shorten and facilitate the outcome of an engagement that might otherwise have persisted indefinitely. It also showed that a favorable position in the conventional balance remains strategically useful even in conditions of mutual nuclear deterrence.