An approximate solution method for the fixed charge problem

In the absence, to date, of an exact method for solving the linear programming problem with fixed charges, two heuristic methods have been proposed and extensively investigated, computationally, for moderate sized problems. The results indicate that the heuristic methods produce optimal solutions in well over 90 percent of the several hundred problems investigated and very close to optimal (a few percent) in the remaining cases. Hence it should be of practical significance to practitioners in the field.     

旋转稳定塑料弹体工程设计计算研究

本文以实验结果为依据,首先分析了塑料弹体影响弹丸膛内运动的物理性能,然后结合旋转弹丸的膛内运动特征,经过模拟试验,采用数学拟合法,初步建立旋转稳定弹塑料弹体工程设计计算的数学模型(包括结构尺寸设计计算、强度计算和内弹道计算)。     

On failure modeling

A promising approach to failure modeling, in particular to developing failure-time distributions, is discussed. Under this approach, system state or wear and tear is modeled by an appropriately chosen random process—for example, a diffusion process—and the occurrences of fatal shocks are modeled by a Poisson process whose rate function is state dependent. The system is said to fail when either wear and tear accumulates beyond an acceptable or safe level or a fatal shock occurs. This approach has significant merit. First, it provides revealing new insights into most of the famous and frequently used lifetime distributions in reliability theory. Moreover, it suggests intuitively appealing ways for enhancing those standard models. Indeed, this approach provides a means of representing the underlying dynamics inherent in failure processes. Reasonable postulates for the dynamics of failure should lend credence to the prediction and estimation of reliability, maintainability, and availability. In other words, accuracy of representation could lead to better, more reliable prediction of failure.     

The Nuclear Peace Fallacy: How Deterrence Can Fail

Some scholars counter-intuitively argue that the proliferation of nuclear weapons increases international security by substantially reducing the chances for inter-state armed conflict. This school of thought draws heavily on the history of the American-Soviet Cold War rivalry to inform its analysis. The security dilemmas in the contemporary Middle East and South Asia where numerous states have or want nuclear weapons, however, are profoundly different than the competition between the United States and the Soviet Union. States in the Middle East and South Asia today may see nuclear weapons as usable instruments of warfare in contrast to conventional wisdom in the West that views them as weapons of deterrence and last resort. As common sense would have it, American and Allied policy designed to stem the proliferation of nuclear weapons is prudent. American diplomatic intervention, moreover, in regional crises as a third party may be needed in the future in the Middle East and South Asia to lessen the risks of nuclear warfare. Nevertheless, American policy-makers are likely in the future to find themselves facing a nuclear-armed nation-state-or soon to be nuclear weapons-capable state-in a crisis and will have to grapple with the risks of pre-emptive or preventive military action.     

Amidst the chaos a small force for stability: Somalia's business community

Though parts of Somalia appear mired in intractable conflict, both domestic and foreign trade continues. As a result amidst the conflict, corruption, and chaos Somalia's business community is a small force for peace and stability. Thus, efforts directed at enhancing the business community, possibly via the Transitional Federal Government or its successor, could play a small role in improving the situation in this strategically poised country with a very entrepreneurial population. However, such success is far from certain, and numerous other factors besides a strengthened business community would have to occur for Somalia even to begin the journey on the long road to recovery.     

A Novel Framework for Safeguarding Naval Nuclear Material

ABSTRACT

The present international standard allows non-nuclear weapon states (NNWS) to forego safeguards when nuclear material is used in a “non-proscribed military activity,” though no criteria have been established to determine when NNWS can remove naval nuclear material from safeguards. Though at present, only nuclear-armed states possess nuclear submarines, the global nuclear naval landscape may soon change with the advancement of Brazil's fledgling program and the possible precedent it would set for other NNWS. A framework is needed to shore up nuclear security and prevent nuclear material diversion from the nuclear naval sector. Proposed and existing nonproliferation frameworks, including a Fissile Material Cut-off Treaty and commitments through the nuclear security summits, are insufficient to close this loophole. A Naval Use Safeguards Agreement (NUSA), modeled after the Additional Protocol of the International Atomic Energy Agency, would provide a framework to remove the opacity surrounding nuclear material in the naval sector. Designed for NNWS and encouraged as confidence-building measures for nuclear weapon states, NUSA would explicitly outline those stages in the naval nuclear fuel cycle where safeguards are to be applied and in what context. This viewpoint also further provides direction for targeted research and development in technical naval nuclear safeguards solutions.     

多孔陶瓷膜双向过滤阻力试验分析

为研究多孔陶瓷膜过滤阻力,提出了多孔陶瓷膜双向过滤方式,分析了9通道多孔陶瓷膜在双向过滤时的有效过滤面积和通道截面积,建立了过滤阻力关系式。试验结果表明,跨膜压差0.05～0.10 MPa、错流速度1.8 m/s时,浓差极化阻力Rp为主要过滤阻力;跨膜压差0.10～0.25 MPa、错流速度1.0～2.2 m/s时,吸附沉积阻力Rd为主要过滤阻力;跨膜压差0.15 MPa、错流速度2.2～3.0 m/s时,膜自身阻力Rm是主要过滤阻力;增大错流速度能够有效延缓浓差极化的发生,减小吸附沉积层的厚度,减轻膜污染,延长过滤周期。     

What determines military allocations in Africa: Theoretical and empirical investigations

This paper investigates theoretically and empirically the determinants of military spending in Africa. It specifies a formal model and uses time‐series and cross‐sectional estimations to ascertain the reasons behind variations in military allocations across and within 40 African countries during 1960–1991. The differences in military expenditures appear to reflect a complex of economic, political, and strategic factors at both national and international levels. Strategic considerations are, however, found to be the most important factors in most African countries.