Estimating component characteristics from system failure‐time data

Suppose that failure times are available from a random sample of N systems of a given, fixed design with components which have i.i.d. lifetimes distributed according to a common distribution F. The inverse problem of estimating F from data on observed system lifetimes is considered. Using the known relationship between the system and component lifetime distributions via signature and domination theory, the nonparametric maximum likelihood estimator _N(t) of the component survival function (t) is identified and shown to be accessible numerically in any application of interest. The asymptotic distribution of _N(t) is also identified, facilitating the construction of approximate confidence intervals for (t) for N sufficiently large. Simulation results for samples of size N = 50 and N = 100 for a collection of five parametric lifetime models demonstrate the utility of the recommended estimator. Possible extensions beyond the i.i.d. framework are discussed in the concluding section. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

Optimal search for a moving target with the option to wait

We investigate the problem in which an agent has to find an object that moves between two locations according to a discrete Markov process (Pollock, Operat Res 18 (1970) 883–903). At every period, the agent has three options: searching left, searching right, and waiting. We assume that waiting is costless whereas searching is costly. Moreover, when the agent searches the location that contains the object, he finds it with probability 1 (i.e. there is no overlooking). Waiting can be useful because it could induce a more favorable probability distribution over the two locations next period. We find an essentially unique (nearly) optimal strategy, and prove that it is characterized by two thresholds (as conjectured by Weber, J Appl Probab 23 (1986) 708–717). We show, moreover, that it can never be optimal to search the location with the lower probability of containing the object. The latter result is far from obvious and is in clear contrast with the example in Ross (1983) for the model without waiting. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009     

The ‘first’ surge: the repulse of the Easter Invasion in South Vietnam, 1972 – implications for Iraq and Afghanistan

In a military intervention, do surges work? I compare the failed ‘surge’ in Vietnam, the repulse of the Easter Invasion in 1972, as a means of assessing the more ambiguous surges in Iraq and Afghanistan. I identify four features of a surge for this analysis: the military dimensions and strategy of the surging forces, the military capabilities of the host forces, the political vitality and will of the host country, and the political commitment in the domestic politics of the intervener. I find that the last feature is the most critical; and, in all three surges, the American political commitment was lacking.     

Integrating the Services and Harnessing the Military Area Commands

ABSTRACT

The Chinese People’s Liberation Army (PLA) is halfway through a multi-decade modernization process. It has begun a major restructuring effort as it shifts its focus from a traditional continental defensive posture to a more maritime-oriented emphasis. In order to create more balanced joint force, it has adjusted the structure of its highest command organization, the Central Military Commission; abolished the former four General Departments and seven Military Regions; created five new joint Theater Commands and service-level commands for the Army and Rocket Force; and is reducing the size of its active duty force by 300,000 personnel. While seeking to overcome numerous internal obstacles, the PLA continues to develop and improve its capabilities to conduct integrated joint operations to deter a variety of threats to China’s sovereignty and territory and, if deterrence fails, to win informationized local war.     

Military expenditures,economic growth and spatial spillovers

The relationship between economic growth and military expenditure has been the subject of a large literature in defence economics. This study analyses the influence of military expenditures on economic growth in a global perspective for the time period 2000–2010 taking spatial dimension into account. The augmented Solow model is employed to investigate the defence-growth nexus using the cross-sectional data relating to 128 countries. Following a traditional regression analysis, spatial variations in the relationships are examined utilizing different spatial econometric specifications estimated by maximum likelihood. The regressions are compared with each other via likelihood ratio tests, and the spatial Durbin model is found to be the most appropriate one suggesting that the typical least-squares model is misspecified. Empirical evidence indicates that military expenditure has a positive effect on economic growth with a significant spatial dependence for the time period under consideration.     

Spatial Distribution of Minority Communities and Terrorism: Domestic Concentration versus Transnational Dispersion

Qualitative studies of terrorist movements frequently highlight the importance of diaspora communities as important factors in producing and sustaining terrorist activity in countries. The underlying theoretical argument is that bifurcation of tight-knit minority communities between countries nurtures separatist or irredentist sentiments among affected community members, thus prompting terrorist activity, while minority community members in other countries might mobilize financial and political resources to support terrorist activity among their compatriots. In this study, we empirically test whether transnational dispersion, versus domestic concentration, of minority communities in countries produces higher incidents of terrorism. Conducting a series of negative binomial estimations on a reshaped database of around 170 countries from 1981 to 2006, derived from the Minorities at Risk database and the Global Terrorism Database, we determine that both transnational dispersion of kin minority communities and domestic concentration of minorities within countries increase terrorism and that transnational dispersion is a particularly robust predictor of terrorist attacks.