News: U.S.-Canada Commission criticizes Great Lakes research cuts

Government.     

基于LPV变换的变增益导弹自动驾驶仪设计

提出了纵向导弹自动驾驶仪的一种新的变增益设计方法,它不需对导弹动力学的配平状态进行线性化,而是通过状态变换表示成准线性参变系统的形式.线性参变系统(Linear Parameter Varying System)定义为一种线性系统,它的动力学取决于外部变量,其值预先未知,但通过系统的工作可对它进行测量.本文中这个变量就是迎角.实际上迎角是内部变量,因此是"准线性参变(准-LPV)系统".即可用μ综合法设计鲁棒控制器,用舵偏转完成迎角控制.最终的设计结果具有内/外回路结构,内回路为迎角控制,外回路为法向加速度控制.     

MRI/SPECT/Fluorescent Tri‐Modal Probe for Evaluating the Homing and Therapeutic Efficacy of Transplanted Mesenchymal Stem Cells in a Rat Ischemic Stroke Model

Quantitatively tracking engraftment of intracerebrally or intravenously transplanted stem cells and evaluating their concomitant therapeutic efficacy for stroke has been a challenge in the field of stem cell therapy. In this study, first, an MRI/SPECT/fluorescent tri‐modal probe (¹²⁵I‐fSiO4@SPIOs) is synthesized for quantitatively tracking mesenchymal stem cells (MSCs) transplanted intracerebrally or intravenously into stroke rats, and then the therapeutic efficacy of MSCs delivered by both routes and the possible mechanism of the therapy are evaluated. It is demonstrated that ⁽¹²⁵⁾I‐fSiO4@SPIOs have high efficiency for labeling MSCs without affecting their viability, differentiation, and proliferation capacity , and found that 35% of intracerebrally injected MSCs migrate along the corpus callosum to the lesion area, while 90% of intravenously injected MSCs remain trapped in the lung at 14 days after MSC transplantation. However, neurobehavioral outcomes are significantly improved in both transplantation groups, which are accompanied by increases of vascular endothelial growth factor, basic fibroblast growth factor, and tissue inhibitor of metalloproteinases‐3 in blood, lung, and brain tissue (p < 0.05). The study demonstrates that ¹²⁵I‐fSiO4@SPIOs are robust probe for long‐term tracking of MSCs in the treatment of ischemic brain and MSCs delivered via both routes improve neurobehavioral outcomes in ischemic rats.     

El Niño's Uneven Disruption of World's Electricity Systems

In a recent column in this journal, I discussed how in the early to middle nineteenth century Napoleon and Bismarck contributed to Europe's lack of any shale gas development compared to the shale boom in North America.¹ But that is rather recent business compared to those seventeenth-century fishermen off the coast of South America who noticed unusually warm waters that tended to occur every few years around Christmas—labelling the phenomenon El Niño.     

Distributed Energy and Low Carbon vs. Consumers,Regulators, and Tin Men

Economists, regulators, engineers, corporations, and climate activists all search for means to decarbonize the emissions footprint of the electric power industry. It is a pressing search as global electricity demand continues to grow quickly (particularly in the developing world) and fossil fuels continue to dominate generation. (See Exhibit 1 .)     

Effect of pulse scheme on the microstructural evolution,residual stress state and mechanical performance of resistance spot welded DP1000-GI steel

In the present study, the effect of resistance spot welding scheme (i.e. single and double pulse welding) on the mechanical behaviour of resistance spot-welded DP1000-GI steel is investigated. It is shown that double pulse welding at low welding current decreases the maximum cross-tension strength and mechanical energy absorption capability of the welds. The factors that lead to the lower mechanical performance of double pulse welds are scrutinised. Local residual stress mapping reveals that the compressive residual stress perpendicular to the plane of the pre-crack either decreases or is fully released at the weld edge of double pulse welds. Orientation imaging microscopy analyses show that the martensite formed in front of the pre-crack of double pulse weld has a lower fraction of high-angle grain boundaries and a coarser structure of Bain groups as opposed to the corresponding area of single pulse weld. Lower mechanical performance of double pulse welds produced at lower welding current is ascribed to the lower compressive residual stress normal to the plane of crack and the formation of martensitic structure in front of the pre-crack with a lower fraction of high-angle grain boundaries and coarser Bain groups.     

Sequential Exploration of Complex Surfaces Using Minimum Energy Designs

A new space-filling design, called minimum energy design (MED), is proposed to explore unknown regions of the design space of particular interest to an experimenter. The key ideas involved in constructing the MED are the visualization of each design point as a charged particle inside a box, and minimization of the total potential energy of these particles. It is shown through theoretical arguments and simulations that with a proper choice of the charge function, the MED can asymptotically generate any arbitrary probability density function. A version of the MED, which adaptively updates the design by “learning” about the unknown response surface sequentially, is proposed and implemented. Two potential applications of MED in simulation of complex probability densities and optimization of complex response surfaces are discussed and demonstrated with examples. This article has supplementary material online.