45976743
Improved lightpath (wavelength) routing in large WDM networks
We address the problem of efficient circuit switching in wide area networks. The solution provided is based on finding optimal routes for lightpaths and semilightpaths. A lightpath is a fully optical transmission path, while a semilightpath is a transmission path constructed by chaining several lightpaths together, using wavelength conversion at their junctions. The problem thus is to find an optimal lightpath/semilightpath in the network in terms of the cost of wavelength conversion and the cost of using the wavelengths on links. We first present fast, efficient algorithms both for the general problem and for a natural restricted version. The new algorithms outperform earlier work, providing time improvements amounting to an almost linear time factor in most cases. Also, all our algorithms can be implemented on the network in a distributed way.
6649930
Parallel integer sorting is more efficient than parallel comparison sorting on exclusive write PRAMs
We present a significant improvement for parallel integer sorting. On the EREW (exclusive read exclusive write) PRAM our algorithm sorts n integers in the range {0,1, . . . ,m-1 } in time O(log n) with $O(n \sqrt{\frac{\log n}{k}})$ operations using word length $k \log (m+n)$, where $1 \leq k \leq \log n$. In this paper we present the following four variants of our algorithm. 
\noindent (1) The first variant sorts integers in $\{ 0, 1, \ldots, m-1\}$ in time O(log n) and in linear space with O(n) operations using word length log m log n. 
(2) The second variant sorts integers in {0, 1, . . , n-1} in time O(log n) and in linear space with $O(n\sqrt{\log n})$ operations using word length log n. 
(3) The third variant sorts integers in {0, 1, . . . , m-1} in time O(log3/2 n) and in linear space with $O(n\sqrt{\log n})$ operations using word length log (m+n). 
(4) The fourth variant sorts integers in {0, 1, . . . ,m-1} in time O(log n) and space $O(nm^\epsilon )$ with $O(n\sqrt{\log n})$ operations using word length log (m+n). 
Our algorithms can then be generalized to the situation where the word length is k log (m+n), $1 \leq k \leq \log n$.
44902657
The 4-Star Graph is not a Subgraph of Any Hypercube
Abstract We prove that it is impossible to precisely embed any star graph S n ( n ⩾4) into a hypercube.
29710029
Covering convex sets with non-overlapping polygons
Abstract We prove that given n ⩾3 convex, compact, and pairwise disjoint sets in the plane, they may be covered with n non-overlapping convex polygons with a total of not more than 6 n −9 sides, and with not more than 3 n −6 distinct slopes. Furthermore, we construct sets that require 6 n −9 sides and 3 n −6 slopes for n ⩾3. The upper bound on the number of slopes implies a new bound on a recently studied transversal problem.
1982629
Efficient embedding K-ary complete trees into hypercubes
Dilated embedding and precise embedding of K-ary complete trees into hypercubes are studied. For dilated embedding, a nearly optimal algorithm is proposed which embeds a K-ary complete tree of height h, T/sub K/(h), into an (h/spl minus/1)/spl lsqb/logK/spl rsqb/+/spl lsqb/log(K+2)/spl rsqb/ dimensional hypercube with dilation max(2, /spl phi/(K)*), /spl phi/(K+2). For precise embedding, we show a (K/spl minus/1)h+1 dimensional hypercube is large enough to contain T/sub K/(h) as its subgraph for K/spl ges/3.<<ETX>>
7227837
Partitionability of k-Extra-Stage Omega Networks and an Optimal Task Migration Algorithm
In a large-scale parallel computing system, partitionability is an important feature that allows a large system to be partitioned into smaller subsystems so that multiple tasks can be run independently on different subsystems. In such a system, a task run on a subsystem may need to be migrated to another subsystem if the subsystem is faulty, if load balance is needed, or if subsystem restructuring is desired. This paper studies the partitionability of k-extra-stage Omega networks and presents an optimal task migration algorithm for k-extra-stage Omega networks.
9894542
Reliability optimization of distributed access networks with constrained total cost
In this paper, we study the system reliability optimization of distributed access networks subject to a constraint on the total cost. We first formulate the cost-constrained system reliability optimization problem as a searching process in a combinatorial tree, which enumerates all the possible solutions to the problem. Because the calculation of each possible solution for the reliability problem is extremely time-consuming, a novel algorithm, the Shrinking & Searching Algorithm (SSA), is proposed to speed up the searching process. SSA jointly considers the upper bound of the system reliability for each branch in the combinatorial tree, and the cost constraint on the possible solutions. It avoids most of the redundant calculations in the searching process by gradually shrinking the difference between lower & upper bounds of the length of a path in the corresponding combinatorial tree, which represents a feasible solution. Case study & simulation results are presented to demonstrate the performance of the SSA.
410513
Active Feedback - UIUC TREC-2003 HARD Experiments
In this paper, we report our experiments on the HARD (High Accuracy Retrieval from Documents) Track in TREC 2003. We focus on active feedback, i.e., how to intelligently propose questions for relevance feedback in order to maximize accuracy improvement in the second run. We proposed and empirically evaluated three different methods, i.e., top-k, gapped top-k, and k-cluster centroid, to extract a fixed number of text units (e.g. passage or document) for feedback. The results show that presenting the top k documents for user feedback is often not as beneficial for learning as presenting more diversified documents.
36077313
Developing High-Performance Parallel Applications Using EPAS
In spite of the advent of high performance parallel computers and commodity clusters, complexity of parallel application development remains one of the major obstacles towards the mainstream adoption of parallel computing. Researchers are constantly investigating different approaches to reduce parallel application development time and increase productivity. As re-usable components, patterns have gained popularity in the sequential programming domain. Subsequently, several pattern-based parallel programming environments (PPEs) have been proposed to facilitate parallel application development procedure. Unfortunately, most of these PPEs lack the required flexibility in order to develop real-life parallel applications. In this paper, we describe the features of the EPAS (Extended Parallel Architectural Skeleton) PPE that enables development of complex parallel applications. We investigate and design the required patterns, and then use them to develop a parallel data cube computing application. Finally, we present the performance of the developed applications and discuss the results.
872843
Active feedback in ad hoc information retrieval
Information retrieval is, in general, an iterative search process, in which the user often has several interactions with a retrieval system for an information need. The retrieval system can actively probe a user with questions to clarify the information need instead of just passively responding to user queries. A basic question is thus how a retrieval system should propose questions to the user so that it can obtain maximum benefits from the feedback on these questions. In this paper, we study how a retrieval system can perform active feedback, i.e., how to choose documents for relevance feedback so that the system can learn most from the feedback information. We present a general framework for such an active feedback problem, and derive several practical algorithms as special cases. Empirical evaluation of these algorithms shows that the performance of traditional relevance feedback (presenting the top K documents) is consistently worse than that of presenting documents with more diversity. With a diversity-based selection algorithm, we obtain fewer relevant documents, however, these fewer documents have more learning benefits.
11389576
Ultra-wideband wireless communications
Summary Ultra-wideband (UWB) communication techniques have attracted a great interest in both academia and industry in the past few years for applications in short-range wireless mobile systems. This is due to the potential advantages of UWB transmissions such as low power, high rate, immunity to multipath propagation, less complex transceiver hardware, and low interference. However, tremendous R&D efforts are required to face various technical challenges in developing UWB wireless systems, including UWB channel characterization, transceiver design, coexistence and interworking with other narrowband wireless systems, design of the link and network layers to benefit from UWB transmission characteristics. This paper is to provide an overview of UWB communications, summarize the previous research results, and identify further research issues that need to be tackled. The emphasis is placed on the commercial wireless communications. Copyright # 2003 John Wiley & Sons, Ltd.