Anticipating infectious disease re-emergence and elimination: a test of early warning signals using empirically based models

Timely forecasts of the emergence, re-emergence and elimination of human infectious diseases allow for proactive, rather than reactive, decisions that save lives. Recent theory suggests that a generic feature of dynamical systems approaching a tipping point—early warning signals (EWS) due to critical slowing down (CSD)—can anticipate disease emergence and elimination. Empirical studies documenting CSD in observed disease dynamics are scarce, but such demonstration of concept is essential to the further development of model-independent outbreak detection systems. Here, we use fitted, mechanistic models of measles transmission in four cities in Niger to detect CSD through statistical EWS. We find that several EWS accurately anticipate measles re-emergence and elimination, suggesting that CSD should be detectable before disease transmission systems cross key tipping points. These findings support the idea that statistical signals based on CSD, coupled with decision-support algorithms and expert judgement, could provide the basis for early warning systems of disease outbreaks.     

A new methodology for identification of critical lines using damping sensitivity analysis

When an inter-area mode dominates a low-frequency oscillation in a stressed condition, control of the active power flow of interface lines, with compensating devices, can effectively reduce the electromechanical power oscillations. In general, interface lines in which inter-area oscillations are large are considered to be good locations for installation of compensating devices. A sensitivity analysis with respect to change in active power flow can provide an important factor in electric power system operation. This paper proposes a new methodology to calculate the damping sensitivity with respect to change in active power flow, which can be useful for accurate selection of critical lines from the viewpoint of small-signal stability. In the proposed methodology, a damping sensitivity index is used to select the critical lines to damp power system oscillations. This paper describes how to derive the damping sensitivity for the selected mode and illustrates an example applying the proposed algorithm to a simple two-area system and the New England 39-bus test system.     

岩石切削过程中破坏机制的离散元分析

利用离散单元方法(DEM)对两种不同属性的花岗石样本模型进行了切割模拟,通过调整不同的切削参数计算并分析了岩石切削过程中的切削力、切削深度、切削比能及切削力倾角的变化规律,从细观上探讨了临界切深对岩石脆性破坏模式和塑性破坏模式及其转变的影响,指出了当切削深度逐渐增大时,破坏模式依次从塑性破坏模式到过渡破坏模式最后转变为脆性破坏模式,同时切削力倾角并不随切削深度变化。将离散单元法分析的结果与实际实验进行了比较,表明该方法是合理的。     

高速数字电路的FPGA实现技巧

高速数字电路是工程设计的一个难点和重点;FPGA和EDA工具提供了实现高速数字电路的资源和技术,把高速数字电路设计与FPGA技术相结合,依靠FPGA芯片和EDA工具所提供的功能来设计高速数字电路,将大大简化高速数字电路的设计难度和工程时间;在FPGA实现高速数字电路的过程中经常遇到的3个问题:时钟偏移、同步器的亚稳态性,以及高速传输接口的处理;在深入理解亚稳态,时钟偏移的产生机理和充分利用FPGA和EDA软件的基础上,可以比较快速地解决以上问题.     

基于时间约束的优化编码传输算法

考虑到对数据包延迟等服务质量要求比较高的流媒体应用,文章研究了在有记忆接收节点模型也即接收节点可以缓存多个数据包的前提下,数据包有延迟约束的无线网络中基于网络编码的广播调度问题,目标在于最小化超过延迟约束数据包的数目。本文提出一种利用着色图的方法来进行编码调度的算法,可以显著减少超过延迟约束数据包的数目,为以后针对QoS需求的网络编码问题提供了参考。模拟实验表明相比于接收节点丢弃暂时无用数据包的无记忆模型,在有记忆模型下我们的算法可以在很多情况下有效地降低超出延迟约束率,这对时间关键的应用非常重要。     

砂土强度和剪胀性的颗粒力学分析

基于广义塑性理论与临界状态概念,研究提出了一个统一三维砂土本构模型,通过一组参数实现了砂土由压缩至剪切过程中状态参量的统一表述。基于ABAQUS提供的用户自定义材料子程序UMAT接口,利用Fortran语言编程实现了该三维弹塑性本构关系模型在软件中的二次开发。分别利用Toyoura砂、Fuji River砂以及Tokachi砂的剪切试验数据与数值模拟结果进行对比,结果表明：提出的有限元计算模型可以有效反映加载过程中不同围压和砂土初始密度对应力-应变曲线的影响,能够准确描述密砂的剪胀特性与应变软化特性以及松砂的剪缩特性与应变硬化特性,从而更加真实地反映三维应力状态下土的变形和强度特性。研究成果进一步扩展了ABAQUS在岩土工程中的应用范围,能够为岩土工程领域的数值分析计算提供更加快捷的解决方案。     

基于最优乘子潮流估计的故障筛选与排序

提出了一种用于电压稳定安全评估的快速故障筛选和排序方法。该方法从故障前的临界点出发,通过最优乘子潮流法计算得到的故障后边界点来估计故障后临界点,当初始点接近临界点,通过一次迭代即可满足所需的计算精度,从而快速地识别出非严重故障。对于严重故障和某些特殊情况的故障进行了分析并提出了解决办法,保证了对严重故障的估计精度。通过某一实际703节点系统算例验证了该方法的有效性。     

使用后评估（POE）理论及案例研究——清华大学美术学院教学楼评价性后评估

使用后评估（post-ocupancy evaluation）是依据建筑性能标准对建筑环境进行评价与分析的操作。后评估以建筑使用者及其需求作为评价标准和依据,以期从评价中获取信息和经验为未来创造更好的建筑提供有益的借鉴。就当今建筑设计实践的全过程而言,使用后评估是建筑设计程序中的又一个重要的因素, 它的操作和研究使建成环境和设施更加完善,使建筑设计更加科学和合理。使用后评估分为三个层次,它们是指示性后评估、评价性后评估和诊断性后评估。本文通过对使用后评估理论的梳理,针对清华大学美术学院教学楼进行后评估,将后评估理论进行了实际程序的操作,为我国建筑环境后评估提供了案例研究。     

网络计划技术在暖通空调工程管理中的应用

结合实际工程,介绍了该应用的具体步骤。通过对工程的分析,绘制了网络图,找到了关键线路,并对工程计划进行了优化。     

High Tc Superconductor Theoretical Models and Electromagnetic Flux Characteristics

High Tc Superconductors (HTS) have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the applied HTS superconductivity and HTS behaviors for practical applications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS applications such as for HTS magnetic levitation application.