Topological homogenization of metamaterial variability

With the proliferation of additive manufacturing and 3D printing technologies, a broader palette of material properties can be elicited from cellular solids, also known as metamaterials, architected foams, programmable materials, or lattice structures. Metamaterials are designed and optimized under the assumption of perfect geometry and a homogeneous underlying base material. Yet in practice real lattices contain thousands or even millions of complex features, each with imperfections in shape and material constituency. While the role of these defects on the mean properties of metamaterials has been well studied, little attention has been paid to the stochastic properties of metamaterials, a crucial next step for high reliability aerospace or biomedical applications. In this work we show that it is precisely the large quantity of features that serves to homogenize the heterogeneities of the individual features, thereby reducing the variability of the collective structure and achieving effective properties that can be even more consistent than the monolithic base material. In this first statistical study of additive lattice variability, a total of 239 strut-based lattices were mechanically tested for two pedagogical lattice topologies (body centered cubic and face centered cubic) at three different relative densities. The variability in yield strength and modulus was observed to exponentially decrease with feature count (to the power −0.5), a scaling trend that we show can be predicted using an analytic model or a finite element beam model. The latter provides an efficient pathway to extend the current concepts to arbitrary/complex geometries and loading scenarios. These results not only illustrate the homogenizing benefit of lattices, but also provide governing design principles that can be used to mitigate manufacturing inconsistencies via topological design.     

一种用于星载SAR天线的转动控制技术

针对星载合成孔径雷达（SAR）天线要求在超低转速下平稳转动，同时满足小型化轻量化的要求，本文提出一种基于微步距模式的天线转动控制技术，该技术使用两个带PWM电路的全桥驱动器通过微步距方式驱动步进电机。在给出系统架构、微步距控制原理后，进一步提出可靠性设计的具体措施。经测试和环境试验验证，该技术对同类应用具有一定的参考价值。     

Reliability Allocation for Series-Parallel Systems subject to Potential Propagated Failures

To analyze the dependent failures in the early stage of system development, this paper considers the potential propagated failures in the reliability allocation process. Factors which can be used to not only measure the component importance but also to reflect the influence brought by propagated failures are proposed. Specifically, cooperative game theory is introduced to explore how the propagated failures affect the failure severity level. Failure rates are obtained by using the Alpha Factor Model with the consideration of dependence among components. Reliability improvement rate is also developed to proportionally assign the target improvement of system reliability to the corresponding components. Furthermore, reliability allocation frameworks for series, parallel and series-parallel systems are designed respectively to make the proposed model meet a wide range of applications. An illustrative example of a hydraulic cooling system is presented to show how the proposed approach is applied. The allocation results demonstrate that the proposed method can achieve a valid reliability improvement with the minimum error.     

基于可靠度优化扭转梁系统开发成本

基于整车可靠度分解,在置信度、可靠度指标要求下,对系统进行可靠度框图分解,得出零部件级的可靠度要求。简要分析载荷谱的线性累加伪损伤,获取零部件一倍寿命伪损伤值,进而得出最优的样本量区间。根据扭转梁系统R97C50的案例要求,比较扭转梁的零件级试验开发成本、系统级试验开发成本、整车级试验开发成本之间的差异,由零部件试验成本固定为基础,得出系统试验的样本量应该控制为不大于2个样本量,达到优化系统试验成本的目的;使用整车级试验去验证系统级可靠度的成本是系统级试验开发成本的20倍。     

Analysis of robust optimization for decentralized microgrid energy management under uncertainty

The present paper provides an extended analysis of a microgrid energy management framework based on Robust Optimization (RO). Uncertainties in wind power generation and energy consumption are described in the form of Prediction Intervals (PIs), estimated by a Non-dominated Sorting Genetic Algorithm (NSGA-II) – trained Neural Network (NN). The framework is tested and exemplified in a microgrid formed by a middle-size train station (TS) with integrated photovoltaic power production system (PV), an urban wind power plant (WPP) and a surrounding residential district (D). The system is described by Agent-Based Modelling (ABM): each stakeholder is modeled as an individual agent, which aims at a specific goal, either of decreasing its expenses from power purchasing or increasing its revenues from power selling. The aim of this paper is to identify which is the uncertainty level associated to the “extreme” conditions upon which robust management decisions perform better than a microgrid management based on expected values. This work shows how the probability of occurrence of some specific uncertain events, e.g., failures of electrical lines and electricity demand and price peaks, highly conditions the reliability and performance indicators of the microgrid under the two optimization approaches: (i) RO based on the PIs of the uncertain parameters and (ii) optimization based on expected values.     

DG planning with amalgamation of economic and reliability considerations

Distributed generation has been playing a vital role in dealing with issues related to distribution systems. This paper presents an approach which provides the distribution system operator with a set of solutions for DG placement to optimize reliability and total cost of power consumed by the distribution system. Optimal location of a Distributed Generator is evaluated based on the performance indices derived for reliability index and total cost of power consumed by the system. The proposed approach is applied to a 15-bus radial distribution system and a 18-bus radial distribution system and the results are analyzed.     

NBTI alleviation on FinFET-made GPUs by utilizing device heterogeneity

Recent experimental studies reveal that FinFET devices commercialized in recent years tend to suffer from more severe NBTI degradation compared to planar transistors, necessitating effective techniques on processors built with FinFET for endurable operations. We propose to address this problem by exploiting the device heterogeneity and leveraging the slower NBTI aging rate manifested on the planar devices. We focus on modern graphics processing units in this study due to their wide usage in the current community. We validate the effectiveness of the technique by applying it to the warp scheduler and L2 cache, and demonstrate that NBTI degradation is considerably alleviated with slight performance overhead.     

A knowledge-based archive multi-objective simulated annealing algorithm to optimize series–parallel system with choice of redundancy strategies

Redundancy allocation problem (RAP) is one of the best-developed problems in reliability engineering studies. This problem follows to optimize the reliability of a system containing s sub-systems under different constraints, including cost, weight, and volume restrictions using redundant components for each sub-system. Various solving methodologies have been used to optimize this problem, including exact, heuristic, and meta-heuristic algorithms. In this paper, an efficient multi-objective meta-heuristic algorithm based on simulated annealing (SA) is developed to solve multi-objective RAP (MORAP). This algorithm is knowledge-based archive multi-objective simulated annealing (KBAMOSA). KBAMOSA applies a memory matrix to reinforce the neighborhood structure to achieve better quality solutions. The results analysis and comparisons demonstrate the performance of the proposed algorithm for solving MORAP.     

Investigating software testing and maintenance reports: Case study

ContextAlthough many papers have been published on software development and defect prediction techniques, problem reports in real projects quite often differ from those described in the literature. Hence, there is still a need for deeper exploration of case studies from industry.ObjectiveThe aim of this study is to present the impact of fine-grained problem reports on improving evaluation of testing and maintenance processes. It is targeted at projects involving several releases and complex schemes of problem handling. This is based on our experience gained while monitoring several commercial projects.MethodExtracting certain features from detailed problem reports, we derive various measures and present analysis models which characterize and visualize the effectiveness of testing and problem resolution processes. The considered reports describe types of problems (e.g. defects), their locations in project versions and software modules, ways of their resolution, etc. The performed analysis is related to eleven projects developed in the same company. This study is an exploratory research with some explanatory features. Moreover, having identified some drawbacks, we present extensions of problem reports and their analysis which have been verified in another industrial case study project.ResultsFine-grained (accurate) problem handling reports provide a wider scope of possible measures to assess the relevant development processes. This is helpful in controlling single projects (local perspective) as well as in managing these processes in the whole company (global perspective).ConclusionDetailed problem handling reports extend the space and quality of statistical analysis, they provide significant enhancement in evaluation and refinement of software development processes as well as in reliability prediction.     

Food4Me study: Validity and reliability of Food Choice Questionnaire in 9 European countries

This analysis has been conducted to explore the validity and reliability of the Food Choice Questionnaire (FCQ) across 9 European countries. Variation in the factor structure and the perceived importance of food choice motives have been compared cross-nationally. Volunteers (N = 9381) were recruited from an existing panel of a social research agency to take part in the Food4Me survey in Germany, Greece, Ireland, Poland, Portugal, Spain, the Netherlands, the UK and Norway. The survey was administered on-line. Configural, metric and scalar invariance fell within acceptable limits and were consistent across the 9 countries. All reliability parameters were above acceptable levels. Factor analysis confirmed that all items loaded onto the same 9 factors established by Steptoe and Pollard (1995). There was highly significant agreement in the relative importance of food choice factors between countries. Price was ranked as most important food choice factor in five countries (Spain, Greece, Ireland, Portugal and the Netherlands), sensory appeal was ranked first for three countries (Norway, Germany and the UK) while natural content was ranked as the most important factor in Poland. Familiarity and ethical concern were consistently ranked as least important in all countries. These data suggest that the FCQ is a suitable tool for exploring food choice motives across different European populations. Differences in relative importance of factors within countries may need to be taken into account in dietary health intervention and food product development.