3,194 research outputs found
An Object-Oriented Model for Extensible Concurrent Systems: the Composition-Filters Approach
Applying the object-oriented paradigm for the development of large and complex software systems offers several advantages, of which increased extensibility and reusability are the most prominent ones. The object-oriented model is also quite suitable for modeling concurrent systems. However, it appears that extensibility and reusability of concurrent applications is far from trivial. The problems that arise, the so-called inheritance anomalies are analyzed and presented in this paper. A set of requirements for extensible concurrent languages is formulated. As a solution to the identified problems, an extension to the object-oriented model is presented; composition filters. Composition filters capture messages and can express certain constraints and operations on these messages, for example buffering. In this paper we explain the composition filters approach, demonstrate its expressive power through a number of examples and show that composition filters do not suffer from the inheritance anomalies and fulfill the requirements that were established
Scheduling real-time, periodic jobs using imprecise results
A process is called a monotone process if the accuracy of its intermediate results is non-decreasing as more time is spent to obtain the result. The result produced by a monotone process upon its normal termination is the desired result; the error in this result is zero. External events such as timeouts or crashes may cause the process to terminate prematurely. If the intermediate result produced by the process upon its premature termination is saved and made available, the application may still find the result unusable and, hence, acceptable; such a result is said to be an imprecise one. The error in an imprecise result is nonzero. The problem of scheduling periodic jobs to meet deadlines on a system that provides the necessary programming language primitives and run-time support for processes to return imprecise results is discussed. This problem differs from the traditional scheduling problems since the scheduler may choose to terminate a task before it is completed, causing it to produce an acceptable but imprecise result. Consequently, the amounts of processor time assigned to tasks in a valid schedule can be less than the amounts of time required to complete the tasks. A meaningful formulation of this problem taking into account the quality of the overall result is discussed. Three algorithms for scheduling jobs for which the effects of errors in results produced in different periods are not cumulative are described, and their relative merits are evaluated
SCADA System Testbed for Cybersecurity Research Using Machine Learning Approach
This paper presents the development of a Supervisory Control and Data
Acquisition (SCADA) system testbed used for cybersecurity research. The testbed
consists of a water storage tank's control system, which is a stage in the
process of water treatment and distribution. Sophisticated cyber-attacks were
conducted against the testbed. During the attacks, the network traffic was
captured, and features were extracted from the traffic to build a dataset for
training and testing different machine learning algorithms. Five traditional
machine learning algorithms were trained to detect the attacks: Random Forest,
Decision Tree, Logistic Regression, Naive Bayes and KNN. Then, the trained
machine learning models were built and deployed in the network, where new tests
were made using online network traffic. The performance obtained during the
training and testing of the machine learning models was compared to the
performance obtained during the online deployment of these models in the
network. The results show the efficiency of the machine learning models in
detecting the attacks in real time. The testbed provides a good understanding
of the effects and consequences of attacks on real SCADA environmentsComment: E-Preprin
Multifaceted Faculty Network Design and Management: Practice and Experience Report
We report on our experience on multidimensional aspects of our faculty's
network design and management, including some unique aspects such as
campus-wide VLANs and ghosting, security and monitoring, switching and routing,
and others. We outline a historical perspective on certain research, design,
and development decisions and discuss the network topology, its scalability,
and management in detail; the services our network provides, and its evolution.
We overview the security aspects of the management as well as data management
and automation and the use of the data by other members of the IT group in the
faculty.Comment: 19 pages, 11 figures, TOC and index; a short version presented at
C3S2E'11; v6: more proofreading, index, TOC, reference
Semileptonic Branching Fraction of Charged and Neutral B Mesons
An examination of leptons in events tagged by reconstructed
decays yields semileptonic branching fractions of for charged and for neutral mesons.
This is the first measurement for charged . Assuming equality of the charged
and neutral semileptonic widths, the ratio is
equivalent to the ratio of lifetimes. A postscript version is available through
World-Wide-Web in http://w4.lns.cornell.edu/public/CLNS/1994Comment: 9 pages (in REVTEX format) Preprint CLNS94-1286, CLEO 94-1
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