The authors present recent results obtained from simulating the action potential generation and propagation through a thin 3-D cylindrical heart muscle bundle. These results represent the first step towards obtaining a more accurate understanding of wave propagation properties through striated muscles. Using a 3-D computational grid of 32*32*128 cells, a single muscle bundle was modeled. The individual fibers and inter-fiber matter making up the bundle were treated homogeneously. Using a modified FitzHugh-Nagumo equation called the Epsilon-4 model, the authors obtained the relationship of propagation speed as a function of cross-sectional depth. The variations in speed that were observed can be explained in terms of the different wave curvatures arising from different types of boundary conditions and the geometry of the pathway. From these observations, the authors construct experiments where unidirectional blocks can occur in geometries with low excitability and no flux borders.>

Auditing capability is one of the requirements for secure databases. A secure database management system, among other things, has to provide not only facilities for recording the history of all updates and queries against the database but high-level support for querying this history as well. The authors present an audit model for object-oriented databases that satisfies both requirements. The model offers several additional advantages: (1) it imposes a uniform logical structure upon both the current and the audit data: (2) it results in zero-information loss, i.e. there is never any loss of historical or current information in this model; and (3) since it captures the entire database activity, a complete reconstruction of every action taken on the database is possible. They show how this third aspect can be exploited to provide high-level support for expressing audit and other database queries and therefore, they make a complete audit trail methodology available.>

In a multilevel secure database management system based on the replicated architecture, there is a separate database management system to manage data at or below each security level, and lower level data are replicated in all databases containing higher level data. In this paper, we address the open issue of concurrency control in such a system. We give a secure protocol that guarantees one-copy serializability of concurrent transaction executions and can be implemented in such a way that the size of the trusted code (including the code required for concurrency and recovery) is small.

A security model is presented for object-oriented database systems. This model is a departure from the traditional security models based on the passive-object active-subject paradigm. The model is a flow model whose main elements are objects and messages. An object combines the properties of a passive information repository with those of an active agent. Messages are the main instrument of information flow. The chief advantages of the proposed model are its compatibility with the object-oriented data model and the simplicity with which security policies can be stated and enforced.>

In a multilevel secure database management system based on the replicated architecture, there is a separate database management system to manage data at or below each security level, and lower-level data are replicated in all databases containing higher-level data. The issue of transaction processing in such a system is addressed. A synchronization protocol is given that guarantees one-copy serializability of concurrent transaction executions. It is secure since the information always flows in one direction-from databases at lower security classes to databases with higher security classes-and it can be implemented in such a way that the size of the trusted code (including the code required for concurrency and recovery) is small.>

The problem of implementing reliable broadcast in ARPA-like computer networks is studied. The environment is characterized by the absence of any multicast facility on the communication by the absence of any multicast facility on the communications subnetwork level. Thus, broadcast has to be implemented directly on hosts. A reliable broadcast protocol is presented and evaluated with respect to several important performance criteria.>

The authors consider the problem of reliable broadcast in a point-to-point asynchronous network. Such a network consists of host computers and a communication subnetwork. The latter, in turn, is a collection of switches (special-purpose computers that have the ability to store and forward messages), interconnected by point-to-point bidirectional communication links. The subnetwork is unreliable, i.e. a message is never guaranteed to be delivered in a finite interval of time. Broadcast is to be implemented among the hosts of the network. The basic mode of operation for the proposed broadcast mechanism is the posting by the source of multiply addressed data messages to be delivered to all participating hosts, combined with a distributed redelivery algorithm that ensures that those messages that were lost in transit do eventually arrive at all intended destinations. At the heart of the algorithm is a set of structures called priority lists. The use of the priority lists to encode topological information and the performance of the algorithm are discussed.>

An approach is presented for managing distributed database systems in the face of communication failures and network partitions. The approach is based on the idea of dividing the database into fragments and assigning each fragment a controlling entity called an agent. The goals achieved by this approach include high data availability and the ability to operate without promptly and correctly detecting partitions. A correctness criterion for transaction execution, called fragmentwise serializability, is introduced. It is less strict than the conventional serializability, but provides a valuable alternative for some applications.>

A new approach is presented for managing distributed database systems in the face of communication failures and network partitions. It offers high availability and, at the same time, guarantees some meaningful correctness properties. The approach is based on the idea of fragments and agents. It does not require prompt and correct detection of partitions and other failures.

Article Update propagation in Bakunin data networks Share on Authors: Boris Kogan Department of Computer Science, Princeton University, Princeton, N.J. Department of Computer Science, Princeton University, Princeton, N.J.View Profile , Hector Garcia-Molina Department of Computer Science, Princeton University, Princeton, N.J. Department of Computer Science, Princeton University, Princeton, N.J.View Profile Authors Info & Claims PODC '87: Proceedings of the sixth annual ACM Symposium on Principles of distributed computingDecember 1987 Pages 13–26https://doi.org/10.1145/41840.41842Online:01 December 1987Publication History 11citation172DownloadsMetricsTotal Citations11Total Downloads172Last 12 Months2Last 6 weeks2 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteGet Access