9638835
Isolation and Lattice Embeddings
29806002
Prefix-Free Languages and Initial Segments of Computably Enumerable Degrees
We study prefix-free presentations of computably enumerable reals. In [2], Calude et. al. proved that a real α is c.e. if and only if there is an infinite, computably enumerable prefix-free set V such that α = Σσ∈V 2-|σ|. Following Downey and LaForte [5], we call V a prefixfree presentation of α. Each computably enumerable real has a computable presentation. Say that a c.e. real α is simple if each presentation of α is computable. Downey and LaForte [5] proved that simple reals locate on every jump class. In this paper, we prove that there is a noncomputable c.e. degree bounding no noncomputable simple reals. Thus, simple reals are not dense in the structure of computably enumerable degrees.
1961392
Degrees of Weakly Computable Reals
This paper studies the degrees of weakly computable reals. It is shown that certain types of limit-recursive reals are Turing incomparable to all weakly computable reals except the recursive and complete ones. Furthermore, it is shown that an r.e. Turing degree is array-recursive iff every real in it is weakly computable.
1638130
Bounding computably enumerable degrees in the Ershov hierarchy
Nanyang Technol Univ, Sch Math & Phys Sci, Div Math Sci, Singapore 639798, Singapore. Chinese Acad Sci, Inst Software, Beijing 100080, Peoples R China. Natl Univ Singapore, Dept Math, Singapore 119260, Singapore.
8102710
Degrees of d. c. e. reals
A real α is called a c. e. real if it is the halting probability of a prefix free Turing machine. Equivalently, α is c. e. if it is left computable in the sense that L(α) = {q ∈ ℚ : q ≤ α} is a computably enumerable set. The natural field formed by the c. e. reals turns out to be the field formed by the collection of the d. c. e. reals, which are of the form α—β, where α and β are c. e. reals. While c. e. reals can only be found in the c. e. degrees, Zheng has proven that there are Δ02 degrees that are not even n-c. e. for any n and yet contain d. c. e. reals, where a degree is n-c. e. if it contains an n-c. e. set. In this paper we will prove that every ω-c. e. degree contains a d. c. e. real, but there are ω + 1-c. e. degrees and, hence Δ02 degrees, containing no d. c. e. real. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
7723209
1-Generic splittings of computably enumerable degrees
Say a set G⊆ω is 1-generic if for any e∈ω, there is a string σ⊂G such that {e}σ(e)↓ or ∀τ⊇σ({e}τ(e)↑). It is known that 0′ can be split into two 1-generic degrees. In this paper, we generalize this and prove that any nonzero computably enumerable degree can be split into two 1-generic degrees. As a corollary, no two computably enumerable degrees bound the same class of 1-generic degrees.
8499708
Cooperation models for service oriented multi-agent system
In the paper, the cooperation models for service oriented multi-agent system are formally and rigorously investigated and put forward. According to the service request forces and service offer manners, a number of elementary cooperation models and their atomic communication acts are identified. The rigorous semantics of the communication acts and the cooperation models and their constraints are formally defined and analyzed.
1594579
GPSS Simulation Study of Quality Inspection System
4178545
Data placement and query processing based on RPE parallelisms
The basic idea behind parallel database systems is to perform operations in parallel to reduce the response time and improve the system throughput. Data placement is a key factor on the performance of parallel database systems. This paper proposes two data partition strategies to decluster XML documents with very large size, path schema based path instance balancing (PSPIB) strategy, in which all path instances with the same path schema in a data tree are declustered evenly over all sites, and node schema based node round-robin (NSNRR) strategy, in which all node objects with the same node schema in a data tree are declustered over all sites in a round-robin way. Accordingly, two query processing algorithms are proposed based on the two partition methods, parallel path merge (PPM) algorithm and parallel pipelining path join (PPPJ) algorithm. The performance analysis and evaluation on the two data placement strategies and corresponding query processing algorithms are given in this paper.
858614
Formulating context-dependent similarity functions
Tasks of information retrieval depend on a good distance function for measuring similarity between data instances. The most effective distance function must be formulated in a context-dependent (also application-, data-, and user-dependent) way. In this paper, we present a novel method, which learns a distance function by capturing the nonlinear relationships among contextual information provided by the application, data, or user. We show that through a process called the "kernel trick," such nonlinear relationships can be learned efficiently in a projected space. In addition to using the kernel trick, we propose two algorithms to further enhance efficiency and effectiveness of function learning. For efficiency, we propose a SMO-like solver to achieve O(N2) learning performance. For effectiveness, we propose using unsupervised learning in an innovative way to address the challenge of lack of labeled data (contextual information). Theoretically, we substantiate that our method is both sound and optimal. Empirically, we demonstrate that our method is effective and useful.
163515
Streaming stored video over AIMD transport protocols
We study the problem of using proxy servers to stream video stored at a geographically separate location. The separation of the server and the storage introduces a nonnegligible delay in retrieving video frames in real time. To ensure network stability we use an additive-increase and multiplicative-decrease transport protocol to support the streaming process. We develop an effective scheme, to achieve high, consistent streaming quality. The heart of the scheme is the control of buffer occupancy at the proxy server We model the buffer as a bilinear dynamical system with Poisson disturbance and develop three buffer controllers. Our empirical study proves the effectiveness of the streaming scheme. Moreover we find that the controllers exploiting the buffer model demonstrate performance significantly superior to that of model-free controllers in overcoming the adverse impact of the control delay.