1,721,014 research outputs found
Channel assignment with separation in wireless networks based on regular plane tessellations
No full textProc. of the 1st Advanced Research Workshop on Information Security in Wireless Networks (ARW),
NATO Security through Science Series D, vol. 13, éd. IOS Press, 2008
Channel assignment on strongly-simplicial graphs
No full textGiven a vector ( 1 � 2�::: � t) of non increasing positive integers, and an undirected graph G = (V�E), an L ( 1 � 2�::: � t)-coloring of G is a function f from the vertex set V to a set of nonnegative integers such that jf(u) ; f(v)j i, if d(u � v) = i � 1 i t� where d(u � v) is the distance (i.e. the minimum number of edges) between the vertices u and v. This paper presents e cient algorithms for nding optimal L(1�:::�1)-colorings of trees and interval graphs. Moreover, e cient algorithms are also provided for nding approximate L ( 1 � 1�:::�1)-colorings of trees and interval graphs, as well as approximate L ( 1 � 2)colorings of unit interval graphs.
Fault-tolerant rate-monotonic first-fit scheduling in hard-real-time systems
No full textHard-real-time systems require predictable performance despite the occurrence of failures. In this paper, fault tolerance is implemented by using a novel duplication technique where each task scheduled on a processor has either an active backup copy or a passive backup copy scheduled on a different processor. An active copy is always executed, while a passive copy is executed only in the case of a failure. First, the paper considers the ability of the widely-used Rate-Monotonic scheduling algorithm to meet the deadlines of periodic tasks in the presence of a processor failure. In particular, the Completion Time Test is extended so as to check the schedulability on a single processor of a task set including backup copies. Then, the paper extends the well-known Rate-Monotonic First-Fit assignment algorithm, where all the task copies, included the backup copies, are considered by Rate-Monotonic priority order and assigned to the first processor in which they fit. The proposed algorithm determines which tasks must use the active duplication and which can use the passive duplication. Passive duplication is preferred whenever possible, so as to overbook each processor with many passive copies whose primary copies are assigned to different processors. Moreover, the space allocated to active copies is reclaimed as soon as a failure is detected. Passive copy overbooking and active copy deallocation allow many passive copies to be scheduled sharing the same time intervals on the same processor, thus reducing the total number of processors needed. Simulation studies reveal a remarkable saving of processors with respect to those needed by the usual active duplication approach in which the schedule of the non-fault-tolerant case is duplicated on two sets of processors. © 1999 IEEE
Allocating Servers in Infostations for On-Demand Communications
No full textGiven a set of service requests, each characterized by a temporal interval and a category, an integer k , and an integer h_c for each category c , the Server Allocation with Bounded Simultaneous Requests problem consists in assigning a server to each request in such a way thatat most k mutually simultaneous requests are assigned to the same server at the same time, out of which at most hc are of category c , and the minimum number of servers is used. Since this problem is computationally intractable, a 2-approximation on-line algorithm is exhibited which asymptotically gives a (2 - \frac{h}{k})-approximation, where h = \min \{ h_c \}. Generalizations of the problem are considered, where each request r is also characterized by a bandwidth rate wr, and the sum of the bandwidth rates of the simultaneous requests is bounded, and where each request is characterized also by a gender bandwidth. Such generalizations contain Bin-Packing and Multiprocessor Task scheduling as special cases, and they admit on-line algorithms providing constant approximations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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