Blood flow in the rabbit aortic arch and descending thoracic aorta

The distribution of atherosclerotic lesions within the rabbit vasculature, particularly within the descending thoracic aorta, has been mapped in numerous studies. The patchy nature of such lesions has been attributed to local variation in the pattern of blood flow. However, there have been few attempts to model and characterize the flow. In this study, a high-order continuous Galerkin finite-element method was used to simulate blood flow within a realistic representation of the rabbit aortic arch and descending thoracic aorta. The geometry, which was obtained from computed tomography of a resin corrosion cast, included all vessels originating from the aortic arch (followed to at least their second generation) and five pairs of intercostal arteries originating from the proximal descending thoracic aorta. The simulations showed that small geometrical undulations associated with the ductus arteriosus scar cause significant deviations in wall shear stress (WSS). This finding highlights the importance of geometrical accuracy when analysing WSS or related metrics. It was also observed that two Dean-type vortices form in the aortic arch and propagate down the descending thoracic aorta (along with an associated skewed axial velocity profile). This leads to the occurrence of axial streaks in WSS, similar in nature to the axial streaks of lipid deposition found in the descending aorta of cholesterol-fed rabbits. Finally, it was observed that WSS patterns within the vicinity of intercostal branch ostia depend not only on local flow features caused by the branches themselves, but also on larger-scale flow features within the descending aorta, which vary between branches at different locations. This result implies that disease and WSS patterns in the vicinity of intercostal ostia are best compared on a branch-by-branch basis.     

On Homogeneous Nucleation of Dislocation Loops in Nanocrystalline Materials

In this article, we readdress the question of homogeneous nucleation of dislocation loops in the context of nanocrystalline materials. In this case, the commonly adopted assumption of an infinite medium is no longer valid, and image forces on dislocations must be accounted for in the analysis. An additional energy term associated with the presence of finite boundaries may act to promote homogeneous nucleation and growth of dislocation loops. Based on a simplified consideration of a circular dislocation loop in a spherical nanoparticle or nanosized grain in a polycrystal, energy calculations are carried out to estimate the activation energy for homogeneous nucleation of a dislocation loop in such a system. Two different cases are considered: (1) a single nanoparticle and (2) a grain in a polycrystalline nanomaterial. Based on simulations for aluminum, it is shown that this mechanism may be plausible in both cases, albeit only for small particles and grains in the nanometer range.     

Cell design in bacteria as a convex optimization problem

In this paper, we investigate the prediction of the cell composition of bacteria with respect to their medium. By modeling the bacterium as an interconnection of subsystems, the problem is written as a non-smooth convex optimization problem equivalent to a Linear Programming feasibility problem. We then obtain a new method, called Resource Balance Analysis (RBA), predicting the distribution of the available resources in the medium among the various cellular subsystems. Beyond its predictive capability, the proposed approach grasps some fundamental aspects of the bacterium physiology by including a refined model. This method reveals the existence of an intrinsic bottleneck in the system resource distribution of the bacterium, leading to the existence of a structural limitation of its growth rate which can be predicted. RBA is also able to predict the configuration of the metabolic network for a given medium at steady-state regimen which nicely fits the available experimental results for the gram-positive model bacterium Bacillus subtilis.     

Exact solution of a plastic hollow sphere with a Mises–Schleicher matrix

In this paper we establish the exact solution for a hollow sphere with a rigid-plastic pressure-sensitive matrix and subjected to hydrostatic tension or compression. The matrix is assumed to obey to a parabolic Mises–Schleicher criterion. The closed-form expressions of the velocity field and of the stress field are provided. These exact solutions, expressed by means of the Lambert W function, allow to assess and discuss existing results.     

Assessing the effect of nutrient mitigation measures in the watersheds of the Southern Bight of the North Sea

The Seine, Somme, and Scheldt Rivers (France, Belgium, and Netherlands) are the major delivering rivers flowing into the continental coastal zone of the Southern Bight of the North Sea, an area regularly affected by eutrophication problems. In the present work, the Seneque-Riverstrahler model was implemented in a multi-regional case study in order to test several planned mitigation measures aimed at limiting stream nutrient contamination and restoring balanced nutrient ratios at the coastal zone.This modeling approach, which is spatially distributed at the basin scale, allows assessing the impact of any change in human activities, which widely differ over the three basins. Here, we define realistic scenarios based on currently proposed measures to reduce point and non-point sources, such as the upgrading of wastewater treatment, the introduction of catch crops, and the development of extensive farming. An analysis of the current situation showed that a 47-72% reduction in P point-source emissions within the three basins could be reached if the intended P treatment was generalized to the largest treatment plants. However, only an overall 14-23% reduction in N could be achieved at the outlet of the three basins, by combining improved wastewater treatment and land use with management measures aimed at regulating agricultural practices. Nonetheless, in spite of these efforts, N will still be exported in large excess with respect to the equilibrium defined by the Redfield ratios, even in the most optimistic hypothesis describing the long-term response of groundwater nitrate concentrations.A comprehensive assessment of these mitigation measures supports the need for additional reductions of nutrient losses from agriculture to control harmful algae development. It also stresses the relevance of this mechanistic approach, in which nutrient transfers from land to sea can be calculated, as an integrated strategy to test policy recommendations.     

锂燃料电池的研究进展

高容量电池一直是研究的热点,锂燃料电池可能会突破电池体系的能量瓶颈.理论上,锂燃料电池的比能量高达11140 Wh/kg,高出现有商品电池体系1～2个数量级.但目前仍有不少问题需要解决,如寻找适用的电解质和空气电极.根据所用电解质的不同,将锂燃料电池分为三类:水溶性电解质电池、有机电解质电池和多相电解质电池.分别讨论了它们的优缺点和需要解决的难题,并综述了其研究进展.     

基于CORBA架构和LabVIEW的分布式电能质量在线监测系统

提出了一种基于CORBA架构和LabVIEW的分布式电能质量在线监测系统实现的框架结构来实现对电能质量的指标测量和监控。监测系统由数字测量仪器组成实现数据采集、分析处理、诊断和报警等功能。数字测量仪器采用虚拟仪器技术即LabVIEW软件开发实现硬件测量功能,在网络通信中采用CORBA架构技术实现异构环境下中心控制站与各个监测仪间的远程访问和控制。系统的仿真研究和现场测试均表明该系统能够基本实现电能质量各项指标的监测和分析功能。     

利用电弧动态数学模型的低压断路器开断过程仿真分析

低压断路器开断过程仿真的关键内容是如何建立开断过程的电弧数学模型,并将其与其它开断过程的物理现象相耦合。通过对虚拟样机软件ADAMS进行二次开发,将电弧动态数学模型应用到低压断路器的开断过程仿真,并结合有限元软件ANSYS,建立了耦合复杂机械运动﹑电路﹑磁场和电弧数学模型的低压断路器开断过程仿真模型。通过将建立的仿真模型应用到一带双向斥开触头系统的塑壳断路器,研究了静触头压力大小对该塑壳断路器开断性能的影响。实验结果表明,利用所提出的仿真模型研究低压断路器的开断过程是可行的。     

基于微波通信的新型小型化定向耦合器的设计

微机保护在电力系统中迅速发展,微波作为通信通道的通信方式也广泛应用,微带3dB分支线定向耦合器是微机保护微波通信设备的一个重要元器件,文章通过理论计算设计出新型梯形微带线小型化的定向耦合器,并在ADS仿真软件上进行仿真,分析仿真结果说明此方法的可行性.这种耦合器的低成本、高效、小型化等特点将在微机保护微波通信以及电力系统综合自动化领域微波通信方面发挥其巨大的潜能.