Consequences and conjectures in preordered sets

In a preordered set, or preset, consequence operators in the sense of Tarski, defined on families of subsets, are introduced. From them, the corresponding sets of conjectures, hypotheses, speculations and refutations are considered, studying the relationships between these sets and those previously defined on ortholattices. All the concepts introduced are illustrated with three particular consequence operators, whose behavior is studied in detail. The results obtained are applied to the case of fuzzy sets endowed with the usual pointwise ordering.     

Distributed speculative execution for reliability and fault tolerance: an operational semantics

This paper examines the use of speculations, a form of distributed transactions, for improving the reliability and fault tolerance of distributed systems. A speculation is defined as a computation that is based on an assumption that is not validated before the computation is started. If the assumption is later found to be false, the computation is aborted and the state of the program is rolled back; if the assumption is found to be true, the results of the computation are committed. The primary difference between a speculation and a transaction is that a speculation is not isolated—for example, a speculative computation may send and receive messages, and it may modify shared objects. As a result, processes that share those objects may be absorbed into a speculation. We present a syntax, and an operational semantics in two forms. The first one is a speculative model, which takes full advantage of the speculative features. The second one is a nonspeculative, nondeterministic model, where aborts are treated as failures. We prove the equivalence of the two models, demonstrating that speculative execution is equivalent to failure-free computation.     

In the Our Beautiful Future

Martha Rosler describes Oleanna, a collaborative project, manifested in part at the 2003 Venice Biennale, that joined together students and artists in imagining alternative publics to ‘rescue the utopian hopes of modernity’. Copyright © 2008 John Wiley & Sons, Ltd.     

国外电力市场的监管方法、指标与手段

文章在对美国加州，纽约州，PJM等电力市场，以及澳大利亚、阿根廷，新西兰等国电力市场监管调研的基础上，对电力市场监管分析、监管指标，重点监管的投机行为和监管手段等进行了分析和归纳，这些监管理论和实践对中国电力市场的建设和发展具有重要意义。