Challenges and New Trends in Power Electronic Devices Reliability

The rapid increase in new power electronic devices and converters for electric transportation and smart grid technologies requires a deepanalysis of their component performances, considering all of the different environmental scenarios, overload conditions, and high stressoperations. Therefore, evaluation of the reliability and availability of these devices becomes fundamental both from technical and economicalpoints of view. The rapid evolution of technologies and the high reliability level offered by these components have shown that estimating reliability through the traditional approaches is difficult, as historical failure data and/or past observed scenarios demonstrate. With the aim topropose new approaches for the evaluation of reliability, in this book, eleven innovative contributions are collected, all focusedon the reliability assessment of power electronic devices and related components

Reducing complexity in tree-like computer interconnection networks

Abstract The fat-tree is one of the topologies most widely used to build high-performance parallel computers. However, they are expensive and difficult to build. In this paper we propose two alternative tree-like topologies that are cheaper in terms of cost and complexity, because they are "thinner" than fat-trees: less switches, and less links. We test the performance of these narrowed trees, and compare it with that of the full-fledged fat-tree using a collection of synthetic patterns that emulate the behavior of well-known applications, including causal relationships among messages. Moreover, we do a performance/cost analysis of these networks. Our main conclusion is that, for the set of studied applications, performance of narrowed topologies is as high as that of fat-trees, with much less cost. Rearranging switch ports to use them as downward ports instead of upward ports do reduce bisection bandwidth, but also increases locality, which can be efficiently exploited by applications

Systems Engineering: Availability and Reliability

Current trends in Industry 4.0 are largely related to issues of reliability and availability. As a result of these trends and the complexity of engineering systems, research and development in this area needs to focus on new solutions in the integration of intelligent machines or systems, with an emphasis on changes in production processes aimed at increasing production efficiency or equipment reliability. The emergence of innovative technologies and new business models based on innovation, cooperation networks, and the enhancement of endogenous resources is assumed to be a strong contribution to the development of competitive economies all around the world. Innovation and engineering, focused on sustainability, reliability, and availability of resources, have a key role in this context. The scope of this Special Issue is closely associated to that of the ICIE’2020 conference. This conference and journal’s Special Issue is to present current innovations and engineering achievements of top world scientists and industrial practitioners in the thematic areas related to reliability and risk assessment, innovations in maintenance strategies, production process scheduling, management and maintenance or systems analysis, simulation, design and modelling

Constraint Programming-based Job Dispatching for Modern HPC Applications

A High-Performance Computing job dispatcher is a critical software that assigns the finite computing resources to submitted jobs. This resource assignment over time is known as the on-line job dispatching problem in HPC systems. The fact the problem is on-line means that solutions must be computed in real-time, and their required time cannot exceed some threshold to do not affect the normal system functioning. In addition, a job dispatcher must deal with a lot of uncertainty: submission times, the number of requested resources, and duration of jobs. Heuristic-based techniques have been broadly used in HPC systems, at the cost of achieving (sub-)optimal solutions in a short time. However, the scheduling and resource allocation components are separated, thus generates a decoupled decision that may cause a performance loss. Optimization-based techniques are less used for this problem, although they can significantly improve the performance of HPC systems at the expense of higher computation time. Nowadays, HPC systems are being used for modern applications, such as big data analytics and predictive model building, that employ, in general, many short jobs. However, this information is unknown at dispatching time, and job dispatchers need to process large numbers of them quickly while ensuring high Quality-of-Service (QoS) levels. Constraint Programming (CP) has been shown to be an effective approach to tackle job dispatching problems. However, state-of-the-art CP-based job dispatchers are unable to satisfy the challenges of on-line dispatching, such as generate dispatching decisions in a brief period and integrate current and past information of the housing system. Given the previous reasons, we propose CP-based dispatchers that are more suitable for HPC systems running modern applications, generating on-line dispatching decisions in a proper time and are able to make effective use of job duration predictions to improve QoS levels, especially for workloads dominated by short jobs

Network Simulation Cradle

This thesis proposes the use of real world network stacks instead of protocol abstractions in a network simulator, bringing the actual code used in computer systems inside the simulator and allowing for greater simulation accuracy. Specifically, a framework called the Network Simulation Cradle is created that supports the kernel source code from FreeBSD, OpenBSD and Linux to make the network stacks from these systems available to the popular network simulator ns-2. Simulating with these real world network stacks reveals situations where the result differs significantly from ns-2's TCP models. The simulated network stacks are able to be directly compared to the same operating system running on an actual machine, making validation simple. When measuring the packet traces produced on a test network and in simulation the results are nearly identical, a level of accuracy previously unavailable using traditional TCP simulation models. The results of simulations run comparing ns-2 TCP models and our framework are presented in this dissertation along with validation studies of our framework showing how closely simulation resembles real world computers. Using real world stacks to simulate TCP is a complementary approach to using the existing TCP models and provides an extra level of validation. This way of simulating TCP and other protocols provides the network researcher or engineer new possibilities. One example is using the framework as a protocol development environment, which allows user-level development of protocols with a standard set of reproducible tests, the ability to test scenarios which are costly or impossible to build physically, and being able to trace and debug the protocol code without affecting results

Law, regulation, and the promotion of renewable energy in South Africa

thesis submitted in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY (PhD) in the School of Law at the University of the WitwatersrandMany countries are under pressure to transition from fossil to renewable sources of energy. This pressure comes from multiple points including sustainable energy and climate change imperatives. The energy industry, especially electricity generation, is the main source of greenhouse gases, hence the significance of reductions in this industry. The purpose of this study was to conduct a legal analysis of the renewable energy law in the context of energy law generally in South Africa, to understand the regulatory function of law in promoting renewable energy. The study analysed government legal and policy positions, and the response by non-state actors to such policy positions and laws. Through a qualitative analysis of primary and secondary sources of law and public participation documents, the study found that; while South Africa is committed to renewable energy, its socio-economic, cultural, and environmental context superimposes other priorities that impede progress towards renewable energy. Several obstacles to renewable energy were identified, some internal to energy law and others external to it, coming from other areas such as environmental law, governance, economics, and behavioural sciences. Analysis at the convergence of environmental and energy law revealed misalignment and fragmentation as major obstacles to renewable energy. While barriers are common across the globe, countries cannot apply the same responses with the same results. Regulatory responses, beyond the traditional ‘command and control’ tools are context specific and tools that have worked, in other countries, may not be as effective in South Africa. Socio-economic dynamics determine the legal responses to the barriers to renewable energy or the efficacy of economic incentives to promote renewable energy. However, overall, law and regulation can, and must, play a crucial enabling role by removing barriers to renewable energy. Nevertheless, there are limits to the use law ‘as regulation.’ Renewables will not replace fossil sources yet; rather in the long-term, renewables should become a big part of the energy mix. Despite gaining price competitiveness, it is too early for renewables to displace conventional fossil sources in a context of entrenched structural and institutional obstacles. Concomitant technical, market, economic, and environmental and resource governance interventions are necessary to effectively promote an energy mix substantially composed of renewables. The study recommends that law should create an enabling regulatory environment for renewable energy. South Africa has not used law effectively enough to create this environment, thereby impeding the integration of renewable energy into its energy mix. Aligning energy and environmental law, among other incentives, can enhance this role of law. Legal reforms are necessary to remove the regulatory advantage afforded to conventional sources of electricity and level the playing field.MT201