Structural / thermodynamic studies of polyanionic melts

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A Formal Characterization of Epsilon Serializability

Epsilon Serializability (ESR) is a generalization of classic serializability (SR). ESR allows some limited amount of inconsistency in transaction processing (TP), through an interface called epsilon-transactions (ETs). For example, some query ETs may view inconsistent data due to non-SR interleaving with concurrent updates. In this paper, we restrict our attention to the situation where query-only ETs run concurrently with consistent update transactions that are SR without the ETs. This paper presents a formal characterization of ESR and ETs. Using the ACTA framework, the first part of this characterization formally expresses the inter-transaction conflicts that are recognized by ESR and, through that, defines ESR, analogous to the manner in which conflict-based serializability is defined. The second part of the paper is devoted to deriving expressions for: (1) the inconsistency in the values of data -- arising from ongoing updates, (2) the inconsistency of the results of a query ““ arising from the inconsistency of the data read in order to process the query, and (3) the inconsistency exported by an update ET - arising from ongoing queries reading uncommitted data produced by the update ET. These expressions are used to determine the preconditions that ET operations have to satisfy in order to maintain the limits on the inconsistency in the data read by query ETs, the inconsistency exported by update ETs, and the inconsistency in the results of queries. This determination suggests possible mechanisms that can be used to realize ESR

A virtual time CSMA protocols for hard real-time communication

We study virtual time CSMA protocols for hard real time communication systems where messages have explicit deadlines. In this protocol, each node maintains two clocks; a real time clock and a virtual time clock. Whenever a node finds the channel to be idle, it resets its virtual clock to be equal to the real clock. The virtual clock then runs at a higher rate than the real clock. A node transmits a waiting message when the time on the virtual clock is equal to the latest time to send the message. This protocol implements the minimum-laxity-first transmission policy. We compare the performance of our protocol with two baseline protocols both of which transmit messages according to the minimum-laxity-first policy. While both use perfect state information about the nodes and channel, the first is an idealized protocol which obtains this information without paying any cost and the second one pays a reasonable price for it. The simulation study shows that in most cases, our protocol performs close to the first one and better than the second one

Specifying and Proving Properties of Sentinels

This paper presents a technique for specifying and verifying properties of sentinels, a high-level language construct for synchronizing access to shared resources. Statements in the specification language possess formal temporal semantics. As a prelude to proving the correctness of sentinels, the semantics of constructs used in sentinels is given. The proof technique involves showing that the temporal behavior of a sentinel conforms to that defined by the specification. The methodology is illustrated by applying it to a typical synchronization problem

Specification of Synchronizing Processes

The formalism of temporal logic has been suggested to be an appropriate tool for expressing the semantics of concurrent programs. This paper is concerned with the application of temporal logic to the specification of factors affecting the synchronization of concurrent processes. Towards this end, we first introduce a model for synchronization and axiomatize its behavior. SYSL, a very high-level language for specifying synchronization properties, is then described. It is designed using the primitives of temporal logic and features constructs to express properties that affect synchronization in a fairly natural and modular fashion. Since the statements in the language have intuitive interpretations, specifications are humanly readable. In addition, since they possess appropriate formal semantics, unambiguous specifications result

Analysis of distributed multi-periodic systems to achieve consistent data matching

International audienceDistributed real-time architecture of an embedded system is often described as a set of communicating components. Such a system is data flow (for its description) and time-triggered (for its execution). This work fits in with these problematics and focuses on the control of the time compatibility of a set of interdependent data used by the system components. The architecture of a component-based system forms a graph of communicating components, where more than one path can link two components. These paths may have different timing characteristics but the flows of information which transit on these paths may need to be adequately matched, so that a component uses inputs which all (directly or indirectly) depend on the same production step. In this paper, we define this temporal datamatching property, we show how to analyze the architecture to detect situations that cause data matching inconsistencies, and we describe an approach to manage data matching that uses queues to delay too fast paths and timestamps to recognize consistent data