美国在探讨分阶段部署SDI系统

美国战略防御计划管理局(SDIO)上周给国会1987年的报告说,初步部署一个分层的弹道导弹防御系统可能会给苏联的攻击时间表造成严重的限制,因为瞄准通道不灵活了,发射窗口有限,瞄准硬目标的武器分配也会发生混乱。 SDI负责人亚伯拉罕森说,采取逐步增加和完善武器系统的过程可能是唯一的部     

ANALYSIS OF DYNAMIC PRICING SCENARIOS FOR MULTIPLE-GENERATION PRODUCT LINES

In technology-intensive markets,it is a common strategy for companies to develop long-term multiple generation product lines instead of releasing consecutive single products.Even though this strategy is more profitable than sequentially introducing single product generations,it can also result in inter-product line cannibalization.Cannibalization of multiple-generation product lines is a complex problem that needs to be taken into account at the early product line planning stage in order to sustain long-term profitability.In this paper,we propose an agent-based model that can simulate the potential cannibalization scenarios within a multiple-generation product line.We view a multiple-generation product line(MGPL) as complex adaptive system where each product generation in the MGPL adjusts its sales price over time based on the shifts in the market demand.The proposed model provides insights into how various pricing strategies impact the overall lifecycle profitability of MGPL and can be used to assist companies in developing appropriate dynamic pricing strategies at the early product line planning stages.     

对称格路与恒等式

对一种简单而又重要的组合结构——对称格路进行了研究。记dn,mn,sn分别为长2n的对称Dyck格路,M otzkin格路,Schr¨oder格路的个数。利用Riordan阵理论得到了他们之间所满足的六个组合恒等式并给予两个组合解释。最后,得到了特殊Riordan阵系数所满足的恒等式。根据某些恒等式估计长为2n的对称Dyck路平均中间高度和平均落在x轴上的点的个数。     

基于灰色相似关联关系的灰色变精度粗糙集模型及应用

针对决策信息系统含有大量的灰信息、噪声数据且属性值为区间灰数,而利用传统的方法对其处理时易造成信息损失,鉴于此,本文利用灰色系统理论的思想方法构建了一种新的灰色变精度粗糙集模型。该方法,首先利用灰色相似关联度定义基于阀值λ的灰色相似关联关系、灰色相似关联类,而后以灰色相似关联关系代替灰色变精度粗糙集模型的等价关系,构建了一种基于灰色相似关联度的灰色变精度粗糙集模型,进而研究了模型的相关性质,并以实例验证了新模型的有效性与适用性。     

模拟结果为什么比实际更暖:简化气候模型结果（英文）

设计了一个非专业人士能够使用、最简化的气候敏感模型,用来研究人类活动所导致的全球变暖的幅度问题.在1990年的第一次IPCC评估报告中,IPCC对其报告中预测的未来全球变暖幅度很有信心,但是随后的观测结果显示全球的变暖幅度只有预测的一半.而自2001年起,全球变暖出现停滞,但是仅仅考虑到二氧化碳浓度的增加,很少有模型能够模拟出这一变化.在已出版的IPCC第五次评估报告的草稿中,IPCC大幅度削减了近期变暖的幅度,并以专家评估代替了模型预测.但是报告中关于未来气候长期变化的预测仍被保留.如果把IPCC模型的总反馈从1.9 W m–2 K–1调整到1.5 W m–2 K–1,气候敏感模型中模拟的温度将从3.2 K降至2.2 K.同时由于反馈很可能是净负反馈,更合适的估计应该是1.0 K.1.0 K是一个能够实现的增幅,21世纪的实际变暖将会小于1 K.即使燃烧所有可开采的化石燃料也不会使全球变暖的幅度超过2.2 K,这一增加幅度也将趋于平稳.本文认为解决IPCC第四、五次报告中评估方法的差异非常关键.一旦这些差异得到解决,人类活动导致的全球变暖在22世纪以及几个世纪以后的平稳态将有可能不会超过IPCC当前模型预测的1/3~1/2.     

Effect of equal channel angular pressing on aging treatment of Al-7075 alloy

The effect of aging treatment on microstructure and mechanical properties of equal channel angular pressed Al-7075 alloy was examined.Commercial Al-7075 alloy in the solid solution heat-treated condition was processed by equal channel angular pressing through route BCat both the room temperature and 120 1C. Only three passes of equal channel angular pressing was possible due to the low ductility of the alloy at both temperatures. Followed by equal channel angular pressing, the specimens have been aged at 120 1C for different aging times. Mechanical properties were measured by Vickers microhardness and tensile tests and microstructural observations were undertaken using transmission electron microscopy, X-ray diffractometer as well as optical microscopy. Microstructural investigations showed that ultrafine-grained materials with grain size in the range of 200–350 nm and 300–500 nm could be obtained after three passes of equal channel angular pressing at room temperature and 120 1C, respectively. Equal channel angular pressing of solid solution heat-treated Al-7075 alloy accelerates precipitation rate and subsequently leads to a significant decrease in aging time to attain maximum mechanical properties. Furthermore, it is possible to achieve maximum mechanical properties during equal channel angular pressing at 120 1C as a result of dynamic aging and formation of small η′ phase.     

Vertically aligned ZnO nanorods on porous silicon substrates: Effect of growth time

Vertically aligned ZnO nanorods were successfully grown on porous silicon(PS) substrates by chemical bath deposition at a low temperature.X-ray diffraction, field-emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM), and photoluminescence(PL)analyses were carried out to investigate the effect of growth duration(2 h to 8 h) on the optical and structural properties of the aligned ZnO nanorods. Strong and sharp ZnO(0 0 2) peaks of the ZnO nanorods proved that the aligned ZnO nanorods were preferentially fabricated along the c-axis of the hexagonal wurtzite structure. FESEM images demonstrated that the Zn O nanorod arrays were well aligned along the c-axis and perpendicular to the PS substrates regardless of the growth duration. The TEM image showed that the top surfaces of the ZnO nanorods were round with a smooth curvature. PL spectra demonstrated that the ZnO nanorods grown for 5 h exhibited the sharpest and most intense PL peaks within the ultraviolet range among all samples.     

Design of optimum solid oxide membrane electrolysis cells for metals production

Oxide to metal conversion is one of the most energy-intensive steps in the value chain for metals production. Solid oxide membrane (SOM) electrolysis process provides a general route for directly reducing various metal oxides to their respective metals, alloys, or intermetallics. Because of its lower energy use and ability to use inert anode resulting in zero carbon emission, SOM electrolysis process emerges as a promising technology that can replace the state-of-the-art metals production processes. In this paper, a careful study of the SOM electrolysis process using equivalent DC circuit modeling is performed and correlated to the experimental results. A discussion on relative importance of each resistive element in the circuit and on possible ways of lowering the rate-limiting resistive elements provides a generic guideline for designing optimum SOM electrolysis cells.     

MMC平均值模型在直流电网中的适用性分析

为了弥补原有AVM在仿真直流故障及换流器闭锁等方面精度不足的问题,研究了模块化多电平换流器(MMC)的平均值模型(AVM),在电压源换流器高压直流输电(VSC-HVDC)电网中的适用性.本文从MMC换流器拓扑的角度出发,提出了改进的AVM,采用MMC的电磁暂态(EMT)详细模型搭建的4端MMC型直流网络为基准,对比发现AVM有效的前提是MMC精确模型中的电容值足够大,以使得MMC中每个子模块(SM)的电容电压近似恒定.仿真证明:本文所提改进平均值模型能够精确仿真直流故障时换流器闭锁等工况,对MMC建模有着重要的工程指导意义.     

变化环境下乌伦古河径流序列变异特征诊断

研究变化环境下干旱区内陆河流以径流为主要指征的水文循环过程及其变化,对于认知水文机理,应对径流变化意义重大。选取乌伦古河二台水文站1959~2015年57年长系列实测月径流资料,采用年内分配完全调节系数C_r、年内分配不均匀系数C_n、相对变化幅度Cm、集中度Cd、集中期D、年际(年代际)径流均值、最大流量、最小流量、年际极值比以及C_v等多指标,运用Mann-Kendall法、累积距平法、R/S法等多方法,在揭示叶尔羌河径流长期演变规律基础上,采用非线性分析方法——启发式分割算法进行径流序列的变异特征诊断,并进行归因分析。结果显示:(1)乌伦古河径流受冰川融水影响年内分布呈"单峰型",主要集中于夏季5~8月,占年径流总量的70%,反映年内分配特征的各指标,如C_r、C_n、C_m、C_d和D,均呈下降趋势,特别是进入2000年后下降趋势较为明显,其中,C_r、C_d和D指标下降趋势显著,表明径流序列年内分配特征趋于均匀化;(2)乌伦古河径流序列年际变化趋势呈减少趋势,减少趋势不显著,且呈负持续性(Hurst=0.35),具有两个明显的丰枯交替周期,即1961~1973年及1974~1994年;(3)针对传统检验方法——Mann-Kendall法诊断乌伦古河二台站长系列(1959~2015年)径流突变点时出现多个虚假变异点的缺陷,采用非线性方法——启发式分割算法(BG法)诊断乌伦古河二台水文站长系列(1959~2015年)径流序列变异点,得出乌伦古河径流序列变异点为1962年。成果有助于了解变化环境下流域尺度的水文过程演变和水文响应规律,指导流域水资源规划与管理。