数值模拟气/气喷嘴速度比对燃烧性能的影响

为研究应用于全流量补燃循环发动机的不同气/气喷嘴得到的燃烧流场,通过求解NavierStokes方程组,对不同燃料与氧化剂速度比下的流动燃烧过程进行了数值计算,计算结果与实验结果吻合。仿真结果表明:增加速度比能使燃烧火焰面提前,燃烧效率变大。如果发动机的长度受到限制,可以适当增加速度比以实现高效燃烧。     

特征保持的视点相关三维矢量场流线简化方法

为了解决三维矢量场可视化中流线数量过多造成的遮挡与视觉混乱问题,同时保证流线能够准确描述矢量场变化规律与重要特征,提出了一种基于特征保持的视点相关三维矢量场流线简化方法。采用粒子跟踪生成3D矢量场流线集,并进行视点相关映射;对流线集进行特征保持计算;基于流线视觉效果度量对流线集进行迭代简化计算,从而实现流线集的有效简化。实验结果表明,能够有效保持矢量场的物理特征,且具有较好的流线视觉效果。     

They protect us,but are they using protection? The potential impact of HIV on the South African Police Service

The drivers of HIV/AIDS in the South African Police Service (SAPS) and impact of the disease on this workforce are neglected areas of research. Existing evidence suggests that while the occupational risk for contracting HIV is low, there are factors associated with the profession that, if left unmanaged, place police officers at risk of contracting HIV. This study's two aims are to identify the potential pathways of HIV infection within policing services and determine the probable impact of HIV/AIDS on SAPS. Through a systematic literature review on HIV/AIDS within police services, and by analysing selected SAPS human resource data, the causal pathways and impact of HIV/AIDS on police services are explored. The study finds that police officers (particularly male officers) are likely to be highly susceptible to HIV infection as a result of risky sexual behaviours born out of occupational characteristics such as high levels of stress, difficult working conditions, living away from home and interactions with sex workers. The problem is exacerbated by the ‘macho’ culture that often prevails among police officers. HIV/AIDS interventions within SAPS must focus on sustained behaviour change. Further, HIV programmes must equip officers with the knowledge and awareness to avoid engaging in high-risk sexual practices that may compromise their health and the effectiveness of the policing service.     

Defence R&D expenditure: The crowding-out hypothesis

The impact of defence expenditure on the economy has been widely studied through different types of models. However, the results from these studies have not reached definitive conclusions, and have left a gap in the analysis of the impact of defence R&D expenditure at the economy level. Defence R&D has specific characteristics, which lead to market failures: public good, high risk and uncertainty, national security. Also, defence R&D creates two types of externalities: negative (crowding-out), and positive (spin-off). Crowding-out is the major economic debate about defence R&D. This paper analyses the crowding-out hypothesis by applying three types of models for the UK case: supply, demand, and demand-supply models. From these three models the most reliable is chosen and applied to the individual cases of France, Germany, Japan and USA. The paper also reports the results for the pooled data of these five countries, and for four error component models. The results from estimating such models shed light on the defence R&D crowding-out hypothesis.     

ON THE CHOICE OF MULTI-TASK R&D DEFENSE PROJECTS: A CASE STUDY OF The ISRAELI MISSILE DEFENSE SYSTEM

Investments in R&D constitute a major share of the expenditures of the hi-tech industry since, generally, they enable firms to successfully compete in the rapidly and constantly changing markets for hi-tech products and services. The role of R&D projects is particularly important in the areas of defense and homeland security due to the nature of warfare and the continuous threats posed by arms races and by terror organizations. This study analyzes the choice of the R&D projects designed to counter multiple related military threats. It develops the methodology required to assess whether it is preferable to develop one project to thwart several related threats, or several distinct projects, each of which provides an answer to one specific threat or a partial set of the threats. An analytic solution is provided and assessed for two simple models with two related threats. A solution of the model is then provided for any number of related threats, using a dynamic programming methodology. Finally, we demonstrate the usefulness of our model and methodology to Israel’s missile defense problem; that is, we show how to optimally develop systems aimed at thwarting the multiple threats of short-, medium-, and long-range missiles.     

THE ‘EXPANDING TORRENT’: BRITISH MILITARY ASSISTANCE TO THE SOUTHERN AFRICAN REGION

In May 2012, Zambia's Inspector-General of Police announced a crackdown on sex workers. This commentary discusses the rationale behind this proposed crackdown and the problems associated with such a policy response.     

具有终端约束的制导炸弹模糊变结构制导律设计

针对INS/GPS制导炸弹对地面目标的精确打击问题,提出带落角约束的模糊变结构制导律。在变结构制导律的基础上,引入终端落角约束项,应用模糊规则对所设计制导律中的变结构开关项系数增益进行在线调节。仿真结果表明,在对地面目标进行攻击时,该制导律降低变结构控制系统的抖振,同时满足制导精度和期望落角的要求,具有有效性和鲁棒性。     

直接力/气动力复合控制系统鲁棒稳定性分析

脉冲发动机作为直接力与空气舵复合控制能有效提高导弹的快速性和末端大过载机动能力。由于脉冲发动机的喷流干扰会对复合控制系统的稳定性产生影响,本文在考虑脉冲发动机自身喷流因子效应以及对导弹气动干扰的情况下,把直接力喷流作用等效为弹体的气动力进行建模,并结合复合控制系统的性能指标以及稳定判据,对一类复合控制自动驾驶仪的鲁棒稳定性进行了分析,给出了直接力喷流作用下复合控制系统的满足性能要求的稳定边界。     

一种新的双输入多通道直流变换器

在传统的含储能单元分布式供电系统中,一般都需要多个单向直流变换器和双向直流变换器才能实现其功能。提出一种新的双输入多通道直流变换器,它的功能等效于一个单向直流变换器和一个双向直流变换器。分析了双输入多通道直流变换器的工作原理,给出了变换器的稳态关系式以及能量管理方法,并运用Saber软件进行仿真,验证了理论分析的正确性。该直流变换器除具有双输入Buck直流变换器的优点外,还能实现可再生能源向储电输入源充电。     

Review of the ordered and proportionate flow shop scheduling research

Ordered flow shop models have appeared in the literature since the mid‐1970s and proportionate flow shop models have appeared since the early 1980s. We provide a detailed review of these models along with some analysis and potential topics for future research. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2013