太阳常数的微小变化在气候变化中的作用

将复杂的气候系统抽象为含有云辐射动态反馈过程的高度非线性气候模型,利用分岔理论,分析了该模型的平衡态及其稳定性。计算结果表明,云反照率反馈、地表反照率反馈和水汽反馈是气候系统呈现多平衡态结构的主要因素,是气候变化复杂性根源,而云放射率反馈对系统结构的影响,只有在强烈的水汽放射率反馈条件下才表现明显。较强的地表反照率反馈和水汽放射率反馈,均可在太阳常数仅有微小变化时就能导致全球气候突变。     

基于景观功能的生态风险评价关键科学问题探析

以人类福祉为导向的自然资源利用方式决定着景观及其功能的变化方向,进而加剧或缓解生态风险。科学量化景观功能及其与人类福祉之间的因果关系、异质过程和驱动机制,将为实现区域发展和生态保护双赢提供科学依据,也是当前制约相关研究从理论走向管理实践的难点。本文在查阅景观功能与生态风险相关文献的基础上,辨析景观变化、景观功能、人类福祉、生态风险间的反馈机制,构建基于景观功能的生态风险评价框架,梳理关键科学问题与研究难点。人类对景观功能的偏好和权衡是区域生态风险形成的重要原因,但对其时空权衡关系认识不足,景观功能的类型识别与综合评价缺乏系统规范方法。景观功能、人类福祉、生态风险三者之间的耦合关系是生态风险评价的重要科学问题。探索综合集成自然、人文两个过程的生态风险管理与方法体系,是未来研究的必然趋势。将景观结构、功能、过程等耦合到生态风险评价,并注重与人类福祉、多功能权衡决策和风险管控政策设计的结合,是亟待研究的重要方向。     

基于鲁棒线性二次算法的结构振动主动控制

线性二次控制算法在工程中得到了广泛的应用。本文提出了通过振型分解，赋予各阶振型不同权重，优化选择线性二次算法加权矩阵的方法，并采用回路传输恢复技术，设计了运用于土木工程结构主动减振的控制系统。仿真结果表明，本文方法能够有效地抑制高频噪声对输出控制力的影响。     

Predictive control of seismic structures with semi‐active friction dampers

In this paper a predictive control method especially suitable for the control of semi‐active friction dampers is proposed. By keeping the adjustable slip force of a semi‐active friction damper slightly lower than the critical friction force, the method allows the damper to remain in its slip state throughout an earthquake of arbitrary intensity, so the energy dissipation capacity of the damper can be improved. The proposed method is formulated in a discrete‐time domain and cast in the form of direct output feedback for easy control implementation. The control algorithm is able to produce a continuous and smooth slip force for a friction damper and thus avoid exerting the high‐frequency structural response that usually exists in structures with conventional friction dampers. Using a numerical study, the control performance of a multiple degrees of freedom (DOF) structural system equipped with passive friction dampers and semi‐active dampers controlled by the proposed method are compared. The numerical case shows that by merely using a single semi‐active friction damper and a few sensors, the proposed method is able to achieve better acceleration reduction than the case using multiple passive dampers. Copyright © 2004 John Wiley & Sons, Ltd.     

光学遥感成像半实物仿真中坐标系统转换

构建了一种以六自由度机器人为运动平台的光学遥感成像半实物仿真系统,利用共线条件方程的齐次坐标变换形式建立了仿真系统的成像模型,并对坐标系统转换问题进行了研究。提出一种利用全站仪确定沙盘坐标系与机器人基坐标系相互转换的"两步法";通过控制机器人旋转和平移运动,提出了一种单特征靶标测量模型,实现了摄像机坐标系与机器人工具坐标系的相互转换。最后通过空间前方交会计算多个靶标的物方坐标值,与物方真值进行比较,从而对系统精度进行评价。实验结果表明,立体定位误差优于0.5 mm,验证了提出的坐标转换方法的可行性与有效性,可为遥感成像仿真系统的设计与研究提供严密的空间基准和转换模型。     

OSB-Ⅱ型测浪浮标传感器及其接口

OSB-Ⅱ型测浪浮标以SZ-Ⅱ型力平衡伺服反馈式加速度计作为测浪传感器。文章介绍了该加速度计的设计原理、技术指标、检定及使用情况,同时还简介了传感器接口电路的设计。该传感器经3年多的海上连续工作,证实它具有稳定、精确、不易损坏等一系列优点。     

次生悬浮颗粒物与海域生命元素的内循环

重点讨论近岸海域海洋资源开发过程中所诱发产生的次生悬浮颗粒物（Ｓ．Ｐ．Ｍ．）的产生机制，及其对近岸海域水体中生命元素（Ｃ．Ｎ．Ｐ．）的生物地球化学的行为、过程和内循环等诸环节的效应。该物质很大程度上决定了海域水体中的生命元素的存在形态、含量水平。因此，可能成为近岸水体富营养化的潜在威胁。     

A DIAGNOSTIC STUDY OF FEEDBACK MECHANISM IN GREENHOUSE EFFECTS SIMULATED BY NCAR CCM1

This paper describes a diagnostic study of the feedback mechanism in greenhouse effects of increased CO_2 and oth-er trace gases(CH_4,N_2O and CFCs),simulated by general circulation model.The study is based on two sensitivity exper-iments for doubled CO_2 and the inclusion of other trace gases,respectively,using version one of the community climatemodel(CCM1)developed at the National Centre for Atmospheric Research.A one-dimensional(1-D)and atwo-dimensional(2-D)radiative-convective models are used to diagnose the feedback effect.It shows that thefeedback factors in global and annual mean conditions are in the sequence of surface albedo,water vapor amount,watervapor distribution,cloud height,critical lapse rate and cloud cover,while in zonal and annual mean conditions in thetropical region the above sequence does not change except the two water vapor terms being the largest feedback compo-nents.Among the feedback components,the total water vapor feedback is the largest(about 50%).The diagnosis alsogives a very small feedback of either the cloud cover or the lapse rate,which is substantially different from the 1-Dfeedback analysis by Hansen et al.(1984).The small lapse rate feedback is considered to be partly caused by theconvective adjustment scheme adopted by CCM1 model.The feedback effect for doubled CO_2 is very different from that of the addition of other trace gases because of theirdifferent vertical distributions of radiative forcing although the non-feedback responses of surface air temperature forboth cases are almost the same.For instance,the larger forcing at surface by the addition of other trace gases can causestronger surface albedo feedback than by doubled CO_2.Besides,because of the negative forcing of doubled CO_2 in thestratosphere,cloud height feedback is more intense.The larger surface forcing in the case of other trace gases can also in-fluence atmospheric water vapor amount as well as the water vapor distribution,which will in turn have strongerfeedback effects.All these indicate that it is incorrect to use“effective CO_2”to replace other trace gases in the generalcirculation model.     

基于负μ传输线的电偶极子和环天线设计

负μ传输线是一种通过串联电容加载来获得等效负磁导率的人工电磁材料,利用其零传播常数的性质,可以设计具有无限大波长且谐振频率与尺寸无关的谐振器,从而实现天线的小型化和宽带化.本文以基于分段线结构的负μ传输线为例,分别设计了具有宽带特性的电偶极子和环天线.测试结果表明长度为107 mm（1.03λ₀@2.9 GHz）的电偶极子可获得的阻抗带宽约为1.4 GHz（2.2~3.6 GHz,48%）,并且该天线在工作带宽内具有稳定的E面方向图.直径为52 mm（0.5λ₀@2.9 GHz）的环天线可获得的阻抗带宽约为1 GHz（2.4~3.4 GHz,34%）,并且环上具有均匀的电流分布,从而具有磁偶极子的辐射特性.测试和仿真结果吻合较好.     

瞬变电磁中两种发射源的响应特征研究

大回线源作为一种快速有效的瞬变电磁观测方式,它的优点是铺设一次线框,在框内和框外都可以测量,空间采样率高、工作效率高和解释精度高,特别适合高密度、大深度的面积测量。目前针对矩形源计算有两种方式,1通过面积等效法用圆形发射源代替矩形发射源;2利用水平偶极子沿矩形回线做数值积分。这里计算了两种发射装置内二次场值,研究两种发射源内二次场的分布特征,证明对于中心回线装置、大定源装置,在晚期使用面积等效方法用圆型线框代替矩型线框计算视电阻率是有效的,在早期计算会引入较大误差,需要校正。