205093793
On p-Creative Sets and p-Completely Creative Sets
Abstract We study p-creative sets and p-completely creative sets. We first prove that for recursively enumerable sets, p-creativeness is equivalent to p-complete creativeness and Myhill's theorem still holds in the polynomial setting. We then consider p-creativity and p-complete creativity for time complexity classes. We prove that for P, p-creativeness is equivalent to p-complete creativeness. Moreover, we prove that a set A is p-m-complete for DEXT iff A is p-creative for P in DEXT. Since every p-m-complete set for DEXT is p-1-complete (Berman, 1977), we know that Myhill's theorem still holds for P in DEXT. These results can also be proved for NP in NEXT. k -creative sets and k -completely creative sets in NP are next studied. ( k,l )-creative sets and ( k,l )-completely creative sets in a more general setting are defined and shown to exist. It is known that k -completely creative sets are NP-complete (Joseph and Young, 1985), but it is not known whether the converse is true. We approach this problem based on our “double diagonalization” technique of showing that every p-m-complete set for DEXT is p-creative for P. A new class of k -completely creative sets is constructed as well.
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.
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 * .
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>>
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.
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.
5927994
A New Approach to Modeling Personal Office Documents
Abstract This paper proposes a new approach to modeling documents in a personal office environment. The proposed document model (called the D _model) combines the relational and object-oriented paradigms and adopts a very natural view for describing the office documents. Documents are grouped into classes. Each class is characterized by a frame template, which describes the type for the class of documents. A frame template is instantiated by providing it with values to form a frame instance, representing a synopsis of a particular document associated with the template. Based on the nature of their contents, different frame instances can be grouped into a folder. Thus, a folder is a set of frame instances which may or may not be associated with the same template. The D _model describes documents using dual hierarchies: a document type hierarchy, depicting the structural organization of the documents, and a folder organization, representing the user's logical file structure. The document type hierarchy exploits structural commonalities between frame templates. Such a hierarchy helps to classify various documents. The folder organization mimics the user's real-world document filing system and provides the user with an intuitively clear view of his/her file structure. Such a view facilitates document retrieval and filing activities. We also present an algebra (called the D _algebra) for manipulating frame instances contained in folders. In contrast to existing algebraic languages, the D _algebra provides operators for manipulating heterogeneous sets (i.e. sets with elements of different types). The proposed document model and algebraic language have been implemented as part of TEXPROS, a personal document processing system currently running in our laboratory.
16801882
Generalizations of Markov model to characterize biological sequences
BackgroundThe currently used kthorder Markov models estimate the probability of generating a single nucleotide conditional upon the immediately preceding (gap = 0) k units. However, this neither takes into account the joint dependency of multiple neighboring nucleotides, nor does it consider the long range dependency with gap>0.ResultWe describe a configurable tool to explore generalizations of the standard Markov model. We evaluated whether the sequence classification accuracy can be improved by using an alternative set of model parameters. The evaluation was done on four classes of biological sequences – CpG-poor promoters, all promoters, exons and nucleosome positioning sequences. Using di- and tri-nucleotide as the model unit significantly improved the sequence classification accuracy relative to the standard single nucleotide model. In the case of nucleosome positioning sequences, optimal accuracy was achieved at a gap length of 4. Furthermore in the plot of classification accuracy versus the gap, a periodicity of 10–11 bps was observed which might indicate structural preferences in the nucleosome positioning sequence. The tool is implemented in Java and is available for download at ftp://ftp.pcbi.upenn.edu/GMM/.ConclusionMarkov modeling is an important component of many sequence analysis tools. We have extended the standard Markov model to incorporate joint and long range dependencies between the sequence elements. The proposed generalizations of the Markov model are likely to improve the overall accuracy of sequence analysis tools.
15090515
Filling holes on locally smooth surfaces reconstructed from point clouds
Abstract Creating models of real scenes is a complex task for which the use of traditional modeling techniques is inappropriate. For this task, laser rangefinders are frequently used to sample the scene from several viewpoints, with the resulting range images integrated into a final model. In practice, due to surface reflectance properties, occlusions and accessibility limitations, certain areas of the scenes are usually not sampled, leading to holes and introducing undesirable artifacts in the resulting models. We present an algorithm for filling holes on surfaces reconstructed from point clouds. The algorithm is based on moving least squares and can interpolate both geometry and shading information. The reconstruction process is mostly automatic and the sampling rate of the given samples is preserved in the reconstructed areas. We demonstrate the use of the algorithm on both real and synthetic datasets to obtain complete geometry and plausible shading.
17750098
Lineage Path Integration for Phylogenetic Resources
With the increase of genome and proteome data, phylogenetic information and phylogenetic analysis tools are increasing greatly in current biological repositories. First, many repositories allow users to browse information about species through taxonomic tools. These tools present the species with its lineage path and links to the various types of information the repository provides about the species. Second, some multiple sequence alignment tools offer users basic phylogenetic data through applying basic reconstruction algorithms to the alignment. With the availability of this information in multiple locations, integrated tools are needed to allow the user to compare this data. This paper presents data integration research on lineage paths using the BIO-AJAX framework. It introduces BIO-AJAX for Lineage Paths, a tool that integrates lineage path information for NCBI Taxonomy Database [1] and the Integrated Taxonomic Information System (ITIS)[6].
2271365
Minimal period retiming under process variations
With aggressive scaling down of feature sizes in VLSI fabrication, process variations have become a critical issue in designs. With process variations, timing optimization should consider the randomness introduced in delays. This paper considers how to retime a circuit under process variations. A statistical retiming problem is defined on the concept of a disutility function. Based on a new minimal period retiming algorithm, two algorithms are presented for the statistical retiming problem. Both theoretical and experimental results are given.