16968599
A New Variation of Chord with Novel Improvement on Lookup Locality
Distributed Hash Tables (DHT) are mechanisms used to locate data in P2P and Grid computing. Early DHT schemes, while providing lookups with optimal or near optimal efficiency at the overlay level, tend to neglect efficiency at the physical level. Although one may extend a DHT scheme by simply adding additional nodes in routing tables to provide extra locality choices, we note that there are intrinsically better ways. We illustrate this point using Chord as an example. We generalize Chord from one-sided lookups to two-sided lookups in a new variation called B-Chord. We show that B-Chord achieves substantially better lookup locality than Chord and 4-Extended Chord, a known variant that has approximately the same node degree of B-Chord. The improvement is achieved using a convex combination of finding a shorter physical path and finding a shorter overlay path. Simulating these protocols on common network models, we show that B-Chord, on average, incurs less than 35% and 25% of physical hops than Chord and 4-Extended Chord, respectively.
7902129
Efficient Minimization of Numerical Summation Errors
Given a multiset X={x 1,... x n } of real numbers, the floating-point set summation (FPS) problem asks for S n = x 1+...+ x n , and the floating point prefix set summation problem (FPPS) asks for S k =x 1+...+x k for all k = 1, ... n. Let E k * denote the minimum worst-case error over all possible orderings of evaluating S k . We prove that if X has both positive and negative numbers, it is NP-hard to compute S n with the worst-case error equal to E n * . We then give the first known polynomial-time approximation algorithm for computing Sn that has a provably small error for arbitrary X. Our algorithm incurs a worstcase error at most 2([log(n−1)]+1) E n * . After X is sorted, it runs in O(n) time, yielding an O(n 2)-time approximation algorithm for computing S k for all k = 1, ..., n such that the worst-case error for each S k is less than 2(⌈ log(k−1)⌋+ 1)E k * .
206565969
Immunity of Complete Problems
Abstract Two necessary and sufficient conditions for all E -complete sets to contain dense P subsets are shown. We then prove that every ≤ p m -hard for E set and its complement contain dense E ∩UP subsets. As a corollary, every NE -complete set and its complement contain dense E ∩UP subsets.
38052408
Towards a practical, secure, and very large scale online election
We propose a practical and secure electronic voting protocol for large-scale online elections. Our protocol satisfies a large set of important criteria that has never been put together in a single protocol before. Among all electronic voting schemes in the literature, Sensus, a security-conscious electronic voting protocol proposed by Cranor and Cytron (1997), satisfies most of our criteria. Sensus has been implemented and used in mock elections. However, Sensus suffers from several major drawbacks. For instance, we show that even if all voters follow the Sensus protocol honestly, some voters' votes may still be replaced with different votes without being detected. Our protocol overcomes these drawbacks.
32837558
On average P vs. average NP
Structures of polynomial-time computable distributions and polynomial-time many-one reductions on randomized decision problems are investigated. The scope is widened from the most studied class DNP (distributional-NP) to the class ANP (average-NP), which consists of randomized decision problems accepted by nondeterministic Turing machines in average polynomial time. Results indicate that the structures of average-case complexity classes are very different from their counterparts in worst-case complexity due to the complex structures of probability distributions and distribution functions.<<ETX>>
15313247
Performance of a MAC protocol for WDM networks with on-line scheduling
This paper investigates the performance of media access protocols based on on-line scheduling for an optically connected star-coupled system with wavelength division multiple access channels. Hybrid access protocols combining reservation and pre-allocation of receiver channels have been previously proposed. Transmission consisted of a reservation phase followed by a data phase. Each node was allowed to place a reservation for one WDM channel. This protocol is extended in this paper by allowing reservations on multiple channels and using simple on-line scheduling algorithms. Existing scheduling algorithms (all are off-line) for similar reservation problems tend to have high implementation and computational complexity. We require that scheduling algorithms be real-time and amenable to hardware implementation. The performance of the extended protocol incorporating two simple on-line scheduling algorithms is presented in this paper. We show that the slight increased computational overhead with scheduling is justified by reduced packet latency and higher utilization, especially for client-server traffic.
12667585
A novel self-configuration mechanism for heterogeneous P2P networks
We propose a simple and efficient mechanism to self-configure semi-structured overlay networks for heterogeneous peer-to-peer systems with no global knowledge. The overlay network is constructed as a hierarchical graph based on peer power which is an aggregate measure of available resources. We use index based, random walk JOIN and LEAVE protocols to build the overlay network in which node degree and workload correspond to its peer power. We also propose an index based query scheme for peers to search documents in the network. Performance studies demonstrate that the proposed self-configuration protocol and search scheme are efficient and viable. The self-configured P2P network has significantly lower query cost than traditional Gnutella-like P2P systems. We further propose a caching assisted query mechanism where query results are cached by intermediate nodes along the search path, thereby exploiting the surplus storage power of the peers and further improving query efficiency. Caching assisted query permits a quicker response to subsequent queries for popular data without incurring the excessive overhead of globally replicated directory information. Our experimental study reveals that the caching assisted query provides an additional reduction of up to 40% in messages needed per query.
266135
Accuracy improvement for identifying translation initiation sites in microbial genomes
MOTIVATION
At present the computational gene identification methods in microbial genomes have a high prediction accuracy of verified translation termination site (3' end), but a much lower accuracy of the translation initiation site (TIS, 5' end). The latter is important to the analysis and the understanding of the putative protein of a gene and the regulatory machinery of the translation. Improving the accuracy of prediction of TIS is one of the remaining open problems.


RESULTS
In this paper, we develop a four-component statistical model to describe the TIS of prokaryotic genes. The model incorporates several features with biological meanings, including the correlation between translation termination site and TIS of genes, the sequence content around the start codon; the sequence content of the consensus signal related to ribosomal binding sites (RBSs), and the correlation between TIS and the upstream consensus signal. An entirely non-supervised training system is constructed, which takes as input a set of annotated coding open reading frames (ORFs) by any gene finder, and gives as output a set of organism-specific parameters (without any prior knowledge or empirical constants and formulas). The novel algorithm is tested on a set of reliable datasets of genes from Escherichia coli and Bacillus subtillis. MED-Start may correctly predict 95.4% of the start sites of 195 experimentally confirmed E.coli genes, 96.6% of 58 reliable B.subtillis genes. Moreover, the test results indicate that the algorithm gives higher accuracy for more reliable datasets, and is robust to the variation of gene length. MED-Start may be used as a postprocessor for a gene finder. After processing by our program, the improvement of gene start prediction of gene finder system is remarkable, e.g. the accuracy of TIS predicted by MED 1.0 increases from 61.7 to 91.5% for 854 E.coli verified genes, while that by GLIMMER 2.02 increases from 63.2 to 92.0% for the same dataset. These results show that our algorithm is one of the most accurate methods to identify TIS of prokaryotic genomes.


AVAILABILITY
The program MED-Start can be accessed through the website of CTB at Peking University: http://ctb.pku.edu.cn/main/SheGroup/MED_Start.htm.
2380687
Packet classification using multidimensional cutting
This paper introduces a classification algorithm called phHyperCuts. Like the previously best known algorithm, HiCuts, HyperCuts is based on a decision tree structure. Unlike HiCuts, however, in which each node in the decision tree represents a hyperplane, each node in the HyperCuts decision tree represents a k--dimensional hypercube. Using this extra degree of freedom and a new set of heuristics to find optimal hypercubes for a given amount of storage, HyperCuts can provide an order of magnitude improvement over existing classification algorithms. HyperCuts uses 2 to 10 times less memory than HiCuts optimized for memory, while the worst case search time of HyperCuts is 50--500% better than that of HiCuts optimized for speed. Compared with another recent scheme, EGT-PC, HyperCuts uses 1.8--7 times less memory space while the worst case search time is up to 5 times smaller. More importantly, unlike EGT-PC, HyperCuts can be fully pipelined to provide one classification result every packet arrival time, and also allows fast updates.
1925100
Self-configuration protocols for P2P networks
This paper proposes and evaluates different protocols for individual peers to self-configure the P2P overlay networks in various network environments. For small-scale homogeneous networks, an optimizer peer selection protocol is proposed and found to be superior to other peer selection protocols, including random, egoist, altruist and greedy protocols, in terms of network diameter and node eccentricity. For large-scale heterogeneous P2P systems, peer-power based peer selection protocols are proposed to self-configure semi-structured overlay networks for heterogeneous P2P systems. An index-based query mechanism is also proposed for peers to search documents in the P2P network. Performance studies demonstrate that the proposed self-configuration protocols and search scheme are efficient and viable, and the self-configured P2P network has a significantly lower query cost than traditional Gnutella-like P2P systems. In addition, a caching-assisted query mechanism is proposed to exploit the surplus storage power of the peers, improving further the query efficiency. Caching-assisted query permits a quicker response to subsequent queries for popular data without incurring the excessive overhead of globally replicated directory information.
2016479
Shape-Based Curve Growing Model and Adaptive Regularization for Pulmonary Fissure Segmentation in CT
This paper presents a shape-based curve-growing algorithm for object recognition in the field of medical imaging. The proposed curve growing process, modeled by a Bayesian network, is influenced by both image data and prior knowledge of the shape of the curve. A maximum a posteriori (MAP) solution is derived using an energy-minimizing mechanism. It is implemented in an adaptive regularization framework that balances the influence of image data and shape prior in estimating the curve, and reflects the causal dependencies in the Bayesian network. The method effectively alleviates over-smoothing, an effect that can occur with other regularization methods. Moreover, the proposed framework also addresses initialization and local minima problems. Robustness and performance of the proposed method are demonstrated by segmentation of pulmonary fissures in computed tomography (CT) images.