14842083
The network communities of SeniorNet
With the explosion of participation on the Internet, there is increasing interest and speculation in extending its uses to support diverse online communities, and particular interest in using the Internet to combat loneliness and isolation amongst senior citizens For the past year, we have been investigating SeniorNet (SN), a 12 year old organization that attempts to bring seniors together via computer networking technologies. We found a rich tapestry of human relationships supported by various technical and social underpinnings. In this paper, we delve into the richness of an active community and describe the intertwining technical and social factors that make it valuable and useful for its members. An underlying question in these discussions is "If network communities have to be principally created and maintained by their members (as we posit), then how do designers help without getting in the way?".
5523130
Design for network communities
Collaboration has long been of considerable interest in the CHI community. This paper proposes and explores the concept of network communities as a crucial part of this discussion. Network communities are a form of technologymediated environment that foster a sense of community among users. We consider several familiar systems and describe the shared characteristics these systems have developed to deal with critical concerns of collaboration. Based on our own experience as designers and users of a variety of network communities. we extend this initial design space along three dimensions: the articulation of a persistent sense of location, the boundary tensions between real and virtual worlds, and the emergence and evolution of community.
40447136
On Designing Relational Database Schemes for Efficient Query Processing
In relational databases, operations including joins sometimes become a cause of performance problems. We study scheme transformations to reduce the number of joins used by a class of routine database activities whose access patterns are fixed. Two scheme operations, merge and copy, are defined to transform relation schemes. The former merges two relation schemes into one, and the latter copies a functional dependency of a relation scheme to its tightly related relation scheme. Necessary and sufficient conditions are shown for applying these operations to a database scheme such that no new anomalies occur. From the necessity of the conditions, the database scheme obtained by exhaustive applications of these operations as long as the conditions hold, is optimal in the sense that further application of one of the scheme operations to the database scheme would cause anomalies. It is also proved that the resulting view of a retrieval on the original database scheme is equivalent to that of the corresponding retrieval on the new database scheme.
23108457
On directable nondeterministic trapped automata
A finite automaton is said to be directable if it has an input word, a directing word, which takes it from every state into the same state. For nondeterministic (n.d.) automata, directability can be generalized in several ways. In [8], three such notions, D1-, D2-, and D3-directability, are introduced. In this paper, we introduce the trapped n.d. automata, and for each i = 1, 2, 3, present lower and upper bounds for the lengths of the shortest Di-directing words of n-state Di-directable trapped n.d. automata. It turns out that for this special class of n.d. automata, better bounds can be found than for the general case, and some of the obtained bounds are sharp.
29071607
Eigenvector Algorithms with Reference Signals for Frequency Domain BSS
This paper describes blind source separation (BSS) problems in the frequency domain using an eigenvector algorithm (EVA) with reference signals. The proposed EVA has such an attractive feature that all source signals are separated simultaneously from their mixtures. This is an advantage against the methods using deflation process (e.g., super-exponential method), because those methods sometimes do not work so as to converge to desired solutions, due to deflation failure. Computer simulation demonstrates the validity of the proposed EVA.
31816332
Source location problems considering vertex-connectivity and edge-connectivity simultaneously
Let G = (V, E) be an undirected multigraph, where V and E are a set of vertices and a set of edges, respectively. Let k and l be fixed nonnegative integers. This paper considers location problems of finding a minimum-size vertex-subset S ⊆ V such that for each vertex x ∈ V the vertex-connectivity between S and x is greater than or equal to k and the edge-connectivity between S and x is greater than or equal to l. For the problem with edge-connectivity requirements, that is, k = 0, an O(L(|V|, |E|, l)) time algorithm is already known, where L(|V|, |E|, l) is the time to find all h-edge-connected components for h = 1, 2, … , l and O(L(|V|, |E|, l)) = O(|E| + |V|2 + |V|min{|E|, l|V|}min{l, |V|}) is known. In this paper, we show that the problem with k ≥ 3 is NP-hard even for l = 0. We then present an O(L(|V|, |E|, l)) time algorithm for 0 ≤ k ≤ 2 and l ≥ 0. Moreover, we prove that the problem parameterized by the size of S is fixed-parameter tractable (FPT) for k = 3 and l ≥ 0. © 2002 Wiley Periodicals, Inc.
45793732
Adaptive Robust Super-exponential Algorithms for Deflationary Blind Equalization of Instantaneous Mixtures
The so called “super-exponential” algorithms (SEA’s) are attractive algorithms for solving blind signal processing problems. The conventional SEA’s, however, have such a drawback that they are very sensitive to Gaussian noise. To overcome this drawback, we propose a new SEA. While the conventional SEA’s use the second- and higher-order cumulants of observations, the proposed SEA uses only the higher-order cumulants of observations. Since higher-order cumulants are insensitive to Gaussian noise, the proposed SEA is robust to Gaussian noise, which is referred to as a robust super-exponential algorithm (RSEA). The proposed RSEA is implemented as an adaptive algorithm, which is referred to as an adaptive robust super-exponential algorithm (ARSEA). To show the validity of the ARSEA, some simulation results are presented.