Demand forecasting by temporal aggregation

Demand forecasting performance is subject to the uncertainty underlying the time series an organization is dealing with. There are many approaches that may be used to reduce uncertainty and thus to improve forecasting performance. One intuitively appealing such approach is to aggregate demand in lower‐frequency “time buckets.” The approach under concern is termed to as temporal aggregation, and in this article, we investigate its impact on forecasting performance. We assume that the nonaggregated demand follows either a moving average process of order one or a first‐order autoregressive process and a single exponential smoothing (SES) procedure is used to forecast demand. These demand processes are often encountered in practice and SES is one of the standard estimators used in industry. Theoretical mean‐squared error expressions are derived for the aggregated and nonaggregated demand to contrast the relevant forecasting performances. The theoretical analysis is supported by an extensive numerical investigation and experimentation with an empirical dataset. The results indicate that performance improvements achieved through the aggregation approach are a function of the aggregation level, the smoothing constant, and the process parameters. Valuable insights are offered to practitioners and the article closes with an agenda for further research in this area. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 60: 479–498, 2013     

Middle Powers And The Demand For Military Expenditures

This paper identifies and classifies middle power nations through the use of broad political science definitions, the demand for military expenditures models and gross domestic product (GDP) per capita. The latter is used as a simple quantifiable measure of relative and potential military power. The paper also develops and utilizes a threat variable that is applicable to middle power nations. The panel data analysis shows that the middle power nations react to threat variables that proxy global instability utilize foreign aid as a complementary policy tool along with military expenditures, and face significant trade-offs between military and non-military government spending.     

Approximation techniques in the solution of queueing problems

In the study of complex queueing systems, analysis techniques aimed al providing exact solutions become ineffective. Approximation techniques provide an attractive alternative in such cases. This paper gives an overview of different types of approximation techniques available in the literature and points out their relative merits. Also, the need for proper validation procedures of approximation techniques is emphasized.     

A note on the forecast performance of temporal aggregation

Earlier research on the effects of nonoverlapping temporal aggregation on demand forecasting showed the benefits associated with such an approach under a stationary AR(1) or MA(1) processes for decision making conducted at the disaggregate level. The first objective of this note is to extend those important results by considering a more general underlying demand process. The second objective is to assess the conditions under which aggregation may be a preferable approach for improving decision making at the aggregate level as well. We confirm the validity of previous results under more general conditions, and we show the increased benefit resulting from forecasting by temporal aggregation at lower frequency time units. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 489–500, 2014     

Class scheduling algorithms for Navy training schools

The problem of developing good schedules for Navy C-Schools has been modeled as a combinatorial optimization problem. The only complicating feature of the problem is that classes must be grouped together into sequences known as pipelines. An ideal schedule will have all classes in a pipeline scheduled in consecutive weeks. The objective is to eliminate the nonproductive time spent by sailors at C-Schools who are waiting for the next class in a pipeline. In this investigation an implicit enumeration procedure for this problem was developed. The key component of our algorithm is a specialized greedy algorithm which is used to obtain a good initial incumbent. Often this initial incumbent is either an optimal schedule or a near optimal schedule. In an empirical analysis with the only other competing software system, our greedy heuristic found equivalent or better solutions in substantially less computer time. This greedy heuristic was extended and modified for the A-School scheduling problem and was found to be superior to its only competitor. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 533–551, 1998     

A new importance sampling Monte Carlo method for a flow network reliability problem

The exact evaluation of the probability that the maximum st‐flow is greater than or equal to a fixed demand in a stochastic flow network is an NP‐hard problem. This limitation leads one to consider Monte Carlo alternatives. In this paper, we propose a new importance sampling Monte Carlo method. It is based on a recursive use of the state space decomposition methodology of Doulliez and Jamoulle during the simulation process. We show theoretically that the resulting estimator belongs to the variance‐reduction family and we give an upper bound on its variance. As shown by experimental tests, the new sampling principle offers, in many cases, substantial speedups with respect to a previous importance sampling based on the same decomposition procedure and its best performances are obtained when highly reliable networks are analyzed. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 204–228, 2002; DOI 10.1002/nav.10004     

Human Capital,Natural Resource Scarcity and the Rwandan Genocide

Many authors contend that ethnic extremism coupled with political manipulation were the primary factors behind the Rwandan genocide. Yet, to oversimplify the cause of this tragedy makes one blind to the complicated nexus that generated the outcome. Even though this genocide was quick in its execution, the events that lead to this massacre took years to unfold. We argue that the evolution of human capital and the competition for scarce resources contributed to the genocide.     

Building peace from the margins in Somalia: The case for political settlement with Al-Shabaab

The prevailing discourse in Mogadishu among the federal government of Somalia and the international community is that Al-Shabaab is no longer relevant in contemporary Somali political landscape. In the language of the government, Al-Shabaab is like a lost crocodile thrown out from the river. In the lexicon of the international community, Al-Shabaab is gradually receding. In fact, Al-Shabaab is actually puissant and potent in terms of social, political and military capabilities; not just in Somalia, but also in the wider East Africa region. Why is Al-Shabaab resilient and resistant? Why is it even more effective than the federal government? To answer these questions, this article reveals how Al-Shabaab is increasingly more legitimate than the federal government. In conclusion, the article proposes that negotiated settlement with the insurgency movement could lead to peace in war-torn southern Somalia.