We study infix-free regular languages. We observe the structural properties of finite-state automata for infix-free languages and develop a polynomial-time algorithm to determine infix-freeness of a regular language u...
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We study infix-free regular languages. We observe the structural properties of finite-state automata for infix-free languages and develop a polynomial-time algorithm to determine infix-freeness of a regular language using state-pair graphs. We consider two cases: 1) A language is specified by a nondeterministic finite-state automaton and 2) a language is specified by a regular expression. Furthermore, we examine the prime infix-free decomposition of infix-free regular languages and design an algorithm for the infix-free primality test of an infix-free regular language. Moreover, we show that we can compute the prime infix-free decomposition in polynomial time. We also demonstrate that the prime infix-free decomposition is not unique.
Recent years have witnessed major advances in our understanding of the structural basis of protein aggregation on several fronts. Firstly, high-resolution structural information that remained elusive for many years wa...
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Recent years have witnessed major advances in our understanding of the structural basis of protein aggregation on several fronts. Firstly, high-resolution structural information that remained elusive for many years was provided by a series of studies of amyloid fibers using NMR, X-ray crystallography and electron microscopy, thereby confirming earlier models based on lower resolution observations. Secondly, studies of the sequence determinants of protein aggregation culminated in the development of computer algorithms that predict aggregation-prone sequences with good accuracy, allowing the design of mutations that reduce aggregation. Thirdly, based on the first results from such predictions and on statistical analysis of naturally occurring aggregating sequences, a picture is emerging in which aggregation-prone sequences are capped by gatekeeper residues that oppose aggregation. In addition to their aggregation-opposing function, it seems that gatekeeper residues are also important in determining chaperone selectivity for strongly aggregating regions. Finally, recent computational and experimental work shows that preventing aggregation does not necessarily mean that amyloid formation is prevented and vice versa. Thus, although aggregation and amyloidosis correlate to a certain extent, they are different processes and should be treated as such.
The systematic comparison of the atomic structure of solid compounds has become an important task in crystallography, chemistry, physics and materials science, in particular in the context of structure prediction and ...
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The systematic comparison of the atomic structure of solid compounds has become an important task in crystallography, chemistry, physics and materials science, in particular in the context of structure prediction and structure determination of crystalline solids. In this work, an efficient and robust algorithm for the comparison of periodic structures is presented, which is based on the mapping of the point patterns of the two structures into each other. This algorithm has been implemented as the module CMPZ in the structure visualization and analysis program KPLOT.
This is the English translation (by Michael P. Abramson) of the PhD thesis of Bruno Buchberger, in which he introduced the algorithmic theory of Grobner bases. Some comments by Buchberger on the translation and the th...
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This is the English translation (by Michael P. Abramson) of the PhD thesis of Bruno Buchberger, in which he introduced the algorithmic theory of Grobner bases. Some comments by Buchberger on the translation and the thesis are given in an additional short paper in this issue of the Journal of Symbolic Computation. (c) 2005 Published by Elsevier Ltd.
Load balancing is a critical issue for the efficient operation of peer-to-peer (P2P) networks. We give two new load-balancing protocols whose provable performance guarantees are within a constant factor of optimal. Ou...
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Load balancing is a critical issue for the efficient operation of peer-to-peer (P2P) networks. We give two new load-balancing protocols whose provable performance guarantees are within a constant factor of optimal. Our protocols refine the consistent hashing data structure that underlies the Chord (and Koorde) P2P network. Both preserve Chord's logarithmic query time and near-optimal data migration cost. Consistent hashing is an instance of the distributed hash table (DHT) paradigm for assigning items to nodes in a P2P system: items and nodes are mapped to a common address space, and nodes have to store all items residing closeby in the address space. Our first protocol balances the distribution of the key address space to nodes, which yields a load-balanced system when the DHT maps items "randomly" into the address space. To our knowledge, this yields the first P2P scheme simultaneously achieving O(log n) degree, O(log n) look-up cost, and constant-factor load balance (previous schemes settled for any two of the three). Our second protocol aims to balance directly the distribution of items among the nodes. This is useful when the distribution of items in the address space cannot be randomized. We give a simple protocol that balances load by moving nodes to arbitrary locations "where they are needed." As an application, we use the last protocol to give an optimal implementation of a distributed data structure for range searches on ordered data.
We address a hierarchical generalization of the well-known disk paging problem. In the hierarchical cooperative caching problem, a set of n machines residing in an ultrametric space cooperate with one another to satis...
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We address a hierarchical generalization of the well-known disk paging problem. In the hierarchical cooperative caching problem, a set of n machines residing in an ultrametric space cooperate with one another to satisfy a sequence of read requests to a collection of read-only files. A seminal result in the area of competitive analysis states that the "least recently used" (LRU) paging algorithm is constant-competitive if it is given a constant-factor blowup in capacity over the offline algorithm. Does such a constant-competitive deterministic algorithm, with a constant-factor blowup in the machine capacities, exist for the hierarchical cooperative caching problem? In this paper we present a deterministic hierarchical generalization of LRU that is constant-competitive when the capacity blowup is linear in d, the depth of the cache hierarchy. Furthermore, we exhibit an infinite family of depth-d hierarchies such that any randomized hierarchical cooperative caching algorithm with capacity blowup b has competitive ratio Omega(log(d/b)) against an oblivious adversary. Thus, our upper and lower bounds imply a tight bound of Theta(d) on the capacity blowup required to achieve constant competitiveness.
We consider the problem of partitioning a graph into k components of roughly equal size while minimizing the capacity of the edges between different components of the cut. In particular we require that for a parameter...
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We consider the problem of partitioning a graph into k components of roughly equal size while minimizing the capacity of the edges between different components of the cut. In particular we require that for a parameter nu >= 1, no component contains more than. nu . n/k of the graph vertices. For k = 2 and nu = 1 this problem is equivalent to the well-known Minimum Bisection problem for which an approximation algorithm with a polylogarithmic approximation guarantee has been presented in [FK]. For arbitrary k and nu >= 2 a bicriteria approximation ratio of O(log n) was obtained by Even et al. [ENRS1] using the spreading metrics technique. We present a bicriteria approximation algorithm that for any constant nu> 1 runs in polynomial time and guarantees an approximation ratio of O(log(1.5) n) ( for a precise statement of the main result see Theorem 6). For nu = 1 and k >= 3 we show that no polynomial time approximation algorithm can guarantee a finite approximation ratio unless P = NP.
The Global Arrays (GA) toolkit provides a shared-memory programming model in which data locality is explicitly managed by the programmer. It inter-operates with MPI and supports a variety of language bindings. The Dis...
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The Global Arrays (GA) toolkit provides a shared-memory programming model in which data locality is explicitly managed by the programmer. It inter-operates with MPI and supports a variety of language bindings. The Disk Resident Arrays (DRA) model extends the GA programming model to secondary storage. GA and DRA together provide a convenient programming model that encourages locality-aware programming by the user, while presenting a high-level abstraction. High performance depends on the appropriate distribution of the data in the disk-resident arrays. In this paper, we discuss the addition of layout transformation support to DRA. The implementation of an efficient parallel layout transformation algorithm is done on top of existing GA/DRA functions;thus GA/DRA is itself used in implementing the enhanced DRA functionality. Experimental performance data is provided that demonstrates the effectiveness of the new layout transformation functionality.
The article briefly discusses research papers that are contained within the section, titled 'Algorithm Design and Scheduling Techniques (Realistic Platform Models) for Heterogeneous Clusters,' of this issue. T...
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The article briefly discusses research papers that are contained within the section, titled 'Algorithm Design and Scheduling Techniques (Realistic Platform Models) for Heterogeneous Clusters,' of this issue. The purpose of these papers is to explore the impact of platform heterogeneity on the design and evaluation of new algorithms, such as, distributed algorithms and scheduling algorithms. One paper by Ligang He and his colleagues discusses two new workload allocation strategies for large-scale heterogeneous platforms. The paper 'On the Distribution of Sequential Jobs in Random Brokering for Heterogeneous Computational Grids,' by Vandy Berten and colleagues, focuses on resource brokering for scheduling sequential jobs onto a grid platform. In their article, 'Multiple Job Scheduling in a Connection-Limited Data Parallel System,' authors Alessandro Amoroso and Keith Marzullo describe a new method for scheduling jobs in a distributed system.
Considering the special characteristic of a cable-mesh deployable antenna, the adjustment method for the cable-mesh reflector is studied in this paper. The cable-mesh model first is developed based on Lagrange princip...
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ISBN:
(纸本)0780393953
Considering the special characteristic of a cable-mesh deployable antenna, the adjustment method for the cable-mesh reflector is studied in this paper. The cable-mesh model first is developed based on Lagrange principle and its stiff matrix is deduced. Then, an adaptive control algorithm is presented based on the stiff matrix to only require coordinate values of part nodes. Finally, numeral result shows the validity and effectiveness of the algorithms.
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