反作用轮低速特性观测补偿方法

反作用轮在现代高精度卫星姿态控制中占据着重要的地位。但由于反作用轮工作于低速状态,其转速过零时摩擦力矩的非线性特征将会对姿态控制精度产生较大的影响,并影响卫星运行寿命。基于Dahl摩擦模型建立了直流电机驱动的反作用轮系统数学模型,在此基础上设计了用于改善反作用轮低速性能的补偿观测器,并将其应用于三正交结构姿态控制系统。数字仿真说明此方法可以有效地抑制反作用轮低速摩擦产生的扰动,从而大幅度改善卫星姿态控制精度及其姿态稳定性。最后探讨了该观测器方法同变结构控制方法的综合应用前景。     

Small world,big guns: globalization,interstate security networks and conventional weapons imports

With the burgeoning influence of emerging markets in Asia, a tectonic shift is taking place in the global security landscape. Asian states are concomitantly arming as their economic clout grows. In light of these developments, security analysts would benefit from a formal means of placing these arms acquisitions in a structural context. Are arms acquisitions on par with the expectations of Asian states, given their structural dispositions, or are recent acquisitions beyond anticipated levels? By using a dynamic panel regression of 187 states from 1950 to 2011, this research predicts arms import volume using the degree of interstate arms linkages, the size of a state's military, and its level of economic development. The technique offers analysts a formal means of distinguishing orthodox behavior in importing conventional weapons from extraneous security motivations. The article concludes by generating near-term forecasts of Asian arms imports and discussing the implications of the technique.     

伴随维修组维修模型聚合方法

面向装备维修保障系统的多分辨率建模问题,提出了一种装备维修模型的聚合方法,为装备维修保障系统模型的聚合研究提供了一种新的思路。该方法通过聚合故障输入和推理维修状态实现维修模型的聚合。最后通过基于MATLAB的仿真实验验证了该方法的可行性。通过实例验证可以看出,该方法缩短了仿真时间,减少了复杂系统底层建模的工作量。     

Formulations for dynamic lot sizing with service levels

In this article, we study deterministic dynamic lot‐sizing problems with a service‐level constraint on the total number of periods in which backlogs can occur over a finite planning horizon. We give a natural mixed integer programming formulation for the single item problem (LS‐SL‐I) and study the structure of its solution. We show that an optimal solution to this problem can be found in \begin{align*}\mathcal O(n^2\kappa)\end{align*} time, where n is the planning horizon and \begin{align*}\kappa=\mathcal O(n)\end{align*} is the maximum number of periods in which demand can be backlogged. Using the proposed shortest path algorithms, we develop alternative tight extended formulations for LS‐SL‐I and one of its relaxations, which we refer to as uncapacitated lot sizing with setups for stocks and backlogs. {We show that this relaxation also appears as a substructure in a lot‐sizing problem which limits the total amount of a period's demand met from a later period, across all periods.} We report computational results that compare the natural and extended formulations on multi‐item service‐level constrained instances. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013     

应用于四旋翼无人机角速度估计的几何滑模观测器设计

对四旋翼无人机的角速度进行估计时,传统的基于单位四元数的滑模观测器需要引入强制比例重调,因而影响了跟踪精度。本文提出一种基于数值积分的李群方法的滑模观测器设计框架。该算法基于等变映射思想,在齐性流形空间的等价李代数空间中设计滑模反馈,从而避免了直接在流形空间中设计反馈的复杂性,并消除了传统方法在每个积分步骤中强制加入的比例重调,提高了观测器的跟踪性能。仿真结果表明,几何滑模观测器算法可以有效的对四旋翼无人机的角速度进行估计。     

Empirical Investigation into the Determinants of Terrorism: Evidence from Fragile States

Abstract

This study investigates the determinants of terrorism in countries that are in the top category of the Fragile States Index (FSI), and are also prone to terrorism. Panel data for 38 countries mainly from Sub-Saharan Africa, the Middle East and North Africa, and South Asia for the years 2005–2014 are used. Findings from the negative binomial and fixed effects estimation show that fragile state, number of refugees and youth unemployment have positive and significant impacts on terrorism. Military spending is positive but less robust across models. Conversely, FDI and remittances have a negative impact on terrorism with the former less robust. Governance and foreign aid are negative and insignificantly related to terrorism. Policy implications follow from the findings.     

EDITOR'S NOTE

The Nonproliferation Review (NPR) recently interviewed Ambassador Sergio de Queiroz Duarte of Brazil, who presided over the 2005 Seventh Review Conference of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Ambassador Duarte discussed his views on the outcome of the conference and the future of the treaty. He provided NPR with valuable insights into the outcome of the conference and also shared his thoughts on some of the most pressing issues confronting the NPT today, including the Middle East, nuclear terrorism, elimination of the threat of highly enriched uranium in the civilian nuclear sector, proposals to limit access to the nuclear fuel cycle, nuclear disarmament, and negative security assurances. Blaming the failed conference on a general lack of political commitment among states parties and their unwillingness to negotiate common solutions, Ambassador Duarte stressed that “the conference should face squarely its own failure without my attempting to disguise or sugarcoat the deep differences of view, which must be resolved with courage and determination by the states parties if they want the treaty to remain effective.”?He emphasized that if states fail to act on their overriding interest in upholding the NPT, especially if states parties continue to ignore or disregard their nonproliferation and nuclear disarmament obligations, some states might come to believe that their security interests are no longer served by the treaty. The future prospects of the NPT would then “look dire indeed.”     

SPEED BUMP ON THE ROAD TO GLOBAL ZERO

The prospect of the United States continuing to reduce the size of its nuclear arsenal to “very low numbers” has raised questions in Japan and South Korea, where US extended deterrence guarantees are premised on the “nuclear umbrella.” In both countries, however, concerns focus less on numerical arsenal size than on the sufficiency of specific nuclear and non-nuclear capabilities to meet evolving threats and on the degree of broader US commitment to these alliances. This article assesses developments in US-Japan and US-South Korea relationships in response to the Obama administration's nuclear disarmament policies, focusing on how the evolutionary course of those relationships may in turn condition prospects for sustaining this US nuclear policy direction. The analysis finds that the challenges of deterrence credibility and allied reassurance are difficult and long-term, but also that US nuclear arsenal size is secondary to broader political, strategic, and military factors in meeting these challenges. The evaluation concludes that strong alliance relationships and strategic stability in East Asia can be maintained while the size of the US nuclear arsenal continues to decline, but also that deterioration of these relationships could imperil core US nuclear policy and nonproliferation objectives.     

MONGOLIA

Formed according to broad principles laid out by the United Nations, nuclear-weapon-free zones (NWFZs) play an important role in promoting nuclear nonproliferation, paralleling and complementing the Treaty on the Non-Proliferation of Nuclear Weapons. But the traditional regional treaty-based path to establishing NWFZs is not open to all states. Owing to various factors, some countries cannot realistically follow the path of states that have established traditional NWFZs. Mongolia, having declared itself a single-state NWFZ in 1992 and gained UN General Assembly recognition of this status in 1998, may provide an example for other countries to follow. This viewpoint presents Mongolia's case as a state seeking to acquire a nontraditional nuclear-weapon-free status despite unfavorable geopolitical circumstances. The case of Mongolia clearly demonstrates that the creation of a credible, single-state NWFZ status is possible, but demands the support and flexibility of both neighboring states and the nuclear weapon states.     

弹道导弹关机点状态估计的指数加权递归最小二乘方法

在双星预警条件下,将指数加权递归最小二乘算法应用于目标关机点状态估计问题中。通过引入加权因子对目标助推段运动的局部拟线性特性进行描述,从而在一定程度上克服了一般的线性多项式模型难以准确刻画整个助推段运动的难题。通过对助推段目标动力学特性的分析,考察了目标在垂直射面方向上的运动特性。在此基础上,提出了一种更为准确的助推段运动模型。仿真算例表明,所提出的关机点状态估计方法相对于传统的方法具有一定的优越性。