Abstract State Machines 1988-1998: Commented ASM Bibliography

An annotated bibliography of papers which deal with or use Abstract State Machines (ASMs), as of January 1998.Comment: Also maintained as a BibTeX file at http://www.eecs.umich.edu/gasm

Verification of Timed Automata Using Rewrite Rules and Strategies

ELAN is a powerful language and environment for specifying and prototyping deduction systems in a language based on rewrite rules controlled by strategies. Timed automata is a class of continuous real-time models of reactive systems for which efficient model-checking algorithms have been devised. In this paper, we show that these algorithms can very easily be prototyped in the ELAN system. This paper argues through this example that rewriting based systems relying on rules and strategies are a good framework to prototype, study and test rather efficiently symbolic model-checking algorithms, i.e. algorithms which involve combination of graph exploration rules, deduction rules, constraint solving techniques and decision procedures

Coloured Petri Nets - a Pragmatic Formal Method for Designing and Analysing Distributed Systems

The thesis consists of six individual papers, where the present paper contains the mandatory overview, while the remaining five papers are found separately from the overview. The five papers can roughly be divided into three areas of research, namely case studies, education, and extensions to the CPN method.The primary purpose of the PhD thesis is to study the pragmatics, practical aspects, and intuition of CP-nets viewed as a formal method for describing and reasoning about concurrent systems. The perspective of pragmatics is our leitmotif, but at the same time in the context of CP-nets it is a kind of hypothesis of this thesis. This overview paper summarises the research conducted as an investigation of the hypothesis in the three areas of case studies, education, and extensions.The provoking claim of pragmatics should not be underestimated. In the present overview of the thesis, the CPN method is compared with a representative selection of formal methods. The graphics and simplicity of semantics, yet generality and expressiveness of the language constructs, essentially makes CP-nets a viable and attractive alternative to other formal methods. Similar graphical formal methods, such as SDL and Statecharts, typically have significantly more complicated semantics, or are domain-specific languages.research conducted in this thesis, opens a new complex of problems. Firstly, to get wider acceptance of CP-nets in industry, it is important to identify fruitful areas for the effective introduction of the CPN method. Secondly, it would be useful to identify a few extensions to the CPN method inspired by specific domains for easier adaption in industry. Thirdly, which analysis methods do future systems make use of

Modeling of HVAC Configurations for De-Carbonization in a Mid-Size Hospital

As the threat of climate change becomes more imminent, there has been increasing emphasis on technologies that reduce carbon emissions in the HVAC sector. The clear path forward given existing technologies is electrification since electricity production has future potential to become cleaner. In terms of building type, high ventilation requirements and near continuous occupancy make healthcare facilities some of the highest energy users. HVAC equipment runs all day and night in these facilities with little change. Conventional HVAC equipment such as a boiler is proven to consume more energy than heat pump systems. More specifically, the Variable Refrigerant Flow (VRF) heat pump and the Ground Source Heat Pump (GSHP) are areas of ongoing research. This analysis included creating whole-building energy models using EnergyPlus and OpenStudio to compare the energy consumption for these heat pump configurations and some cheaper electrification alternatives. The results suggested that the GSHP system possessed the greatest potential for energy savings and thus decarbonization given its higher efficiency during times of extreme ambient temperatures compared to other options

Real-time power system dynamic simulation

The present day digital computing resources are overburdened by the amount of calculation necessary for power system dynamic simulation. Although the hardware has improved significantly, the expansion of the interconnected systems, and the requirement for more detailed models with frequent solutions have increased the need for simulating these systems in real time. To achieve this, more effort has been devoted to developing and improving the application of numerical methods and computational techniques such as sparsity-directed approaches and network decomposition to power system dynamic studies. This project is a modest contribution towards solving this problem. It consists of applying a very efficient sparsity technique to the power system dynamic simulator under a wide range of events. The method used was first developed by Zollenkopf (^117) Following the structure of the linear equations related to power system dynamic simulator models, the original algorithm which was conceived for scalar calculation has been modified to use sets of 2 * 2 sub-matrices for both the dynamic and algebraic equations. The realisation of real-time simulators also requires the simplification of the power system models and the adoption of a few assumptions such as neglecting short time constants. Most of the network components are simulated. The generating units include synchronous generators and their local controllers, and the simulated network is composed of transmission lines and transformers with tap-changing and phase-shifting, non-linear static loads, shunt compensators and simplified protection. The simulator is capable of handling some of the severe events which occur in power systems such as islanding, island re-synchronisation and generator start-up and shut-down. To avoid the stiffness problem and ensure the numerical stability of the system at long time steps at a reasonable accuracy, the implicit trapezoidal rule is used for discretising the dynamic equations. The algebraisation of differential equations requires an iterative process. Also the non-linear network models are generally better solved by the Newton-Raphson iterative method which has an efficient quadratic rate of convergence. This has favoured the adoption of the simultaneous technique over the classical partitioned method. In this case the algebraised differential equations and the non-linear static equations are solved as one set of algebraic equations. Another way of speeding-up centralised simulators is the adoption of distributed techniques. In this case the simulated networks are subdivided into areas which are computed by a multi-task machine (Perkin Elmer PE3230). A coordinating subprogram is necessary to synchronise and control the computation of the different areas, and perform the overall solution of the system. In addition to this decomposed algorithm the developed technique is also implemented in the parallel simulator running on the Array Processor FPS 5205 attached to a Perkin Elmer PE 3230 minicomputer, and a centralised version run on the host computer. Testing these simulators on three networks under a range of events would allow for the assessment of the algorithm and the selection of the best candidate hardware structure to be used as a dedicated machine to support the dynamic simulator. The results obtained from this dynamic simulator are very impressive. Great speed-up is realised, stable solutions under very severe events are obtained showing the robustness of the system, and accurate long-term results are obtained. Therefore, the present simulator provides a realistic test bed to the Energy Management System. It can also be used for other purposes such as operator training

A Formal and Tool-Equipped Approach for the Integration of State Diagrams and Formal Datatypes

International audienceSeparation of concerns or aspects is a way to deal with the increasing complexity of systems. The separate design of models for different aspects also promotes a better reusability level. However, an important issue is then to define means to integrate them into a global model. We present a formal and tool-equipped approach for the integration of dynamic models (behaviors expressed using state diagrams) and static models (formal data types) with the benefit to share advantages of both: graphical user-friendly models for behaviors, formal and abstract models for data types. Integration is achieved in a generic way so that it can deal with both different static specification languages (algebraic specifications, Z, B) and different dynamic specification semantic

New electric utility management and control systems : proceedings of conference, held in Boxborough, Massachusetts, May 30-June 1, 1979

"This work was supported by the Center for Energy Policy Research and the Electric Power Systems Engineering Laboratory of the Massachusetts Institute of Technology.

Exploring the governance of private finance for the electricity sector in sub-Saharan Africa

My dissertation is a paper style thesis, which contains the following chapters: an introduction; a research design; three chapters, each derived from a different successful peer reviewed policy paper (there were corrections applied to each of the original papers); and a discussion and conclusions section. My thesis aims to answer the following research question: ‘What aspects of governance deter private investors from financing large-scale electricity network infrastructure in sub-Saharan Africa?’ My methodology utilises a Hypothetico-deductive approach: which focuses on the impact of risk surrounding the private financing process, when applied to electricity infrastructure development in the sub-Saharan region. My sources for evidence are mixed and multidisciplinary; and my analysis principally applies a governance lens. This is an important topic, as it is over 20 years since the multilateral development community re-focused its policy surrounding the improvement of electricity access in sub-Saharan Africa (SSA), to one that places private sector financing at the centre of its strategy (which transpired during the leadership of the World Bank by James Wolfensohn in the 1990s). Yet according to a recently published report by the IEA: ‘despite being home to 17% of the world’s population, Africa currently accounts for just 4% of global power supply investment’ – suggesting a significant policy failure for over twenty years. With SSA’s population forecast to double by the UN by 2050, it is imperative that the development community understands why such a policy is gaining so little traction. Affordable and reliable energy access is crucial for the economic growth that such a rapid population increase will require. If it is not delivered, excessive environmental damage will otherwise occur, as the enlarging population will have to continue to rely on unsustainably biofuel sources for its energy needs (mostly wood – causing deforestation); and ever increasing social problems will ensue, due to accelerating competition for scarce resources by this ever-growing population. My first paper has two functions: firstly, to reformulate the relevance of risk within the academic research community as an obstruction to the private financing of new SSA electricity infrastructure development. Secondly, to confirm and classify those risks that can be found in the greater interdisciplinary literature, which would negatively influence a private, financier’s willingness to invest in this type of infrastructure. To do this, I firstly analysed a manageable five-year sample of literature surrounding three African countries with a notable body of academic literature: Kenya, Mozambique, and Tanzania. To create my sample, I systematically interrogated the two principle academic libraries of Scopus and the Web of Science, using key terms. My secondary analysis then digs deeper, by including further interdisciplinary literature not specific to the first sample, drawing from the Project Management, Finance, and Innovation academic disciplines – to identify and classify all relevant and likely risks. My second paper is theoretical and utilises three separate perspectives to deliver a holistic and inclusive governance picture, to answer the following research question: ‘What aspects of governance deter private investors from financing large-scale electricity network infrastructure in sub-Saharan Africa?’ These perspectives comprise: 1) Financial Investment Governance, the private sector investor’s perspective, which focuses on the rules and institutions (or lack of) that directly influence the financial investment environment in SSA. 2) Political Governance, the political economy perspective, which relate to the negative, indirect investment consequences resulting from the way that SSA governments govern; and 3) Technical System Governance, a ‘systems’ perspective, which encompasses how the standard structure and organisation of the wider electricity delivery system in each country in SSA, negatively impacts such investment. My third paper focuses on the impact of governance surrounding large-scale electricity infrastructure development (megaprojects), by empirically analysing six case studies located in South Africa. My guide for my fieldwork was the following research question: ‘What aspects of project governance are important, to prevent time delays and cost overruns, when building large scale electricity infrastructure in South Africa?’ This research question is relevant to my thesis’ primary interrogation theme, as the adherence to schedules and budgets are of central importance to successful private financing of such infrastructure. My discussion and conclusions section commences with an explanation for why the multilateral development community should persevere with their policy of promoting private financing of electricity infrastructure development, in SSA. I do this by first explaining why access to affordable and reliable electricity services in Africa is crucial for promoting the meaningful economic growth in the region. I then discuss why the alternatives to this policy, are less inclusive and more exploitive. I then use this positioning to frame my key findings from my research, which I then clarify. Finally, I discuss policy implications surrounding my findings and possible policy solutions