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Articles 331 - 360 of 772
Full-Text Articles in Computer Sciences
Relaxing The Problem-Size Bound For Out-Of-Core Columnsort, Geeta Chaudhry, Elizabeth A. Hamon, Thomas H. Cormen
Relaxing The Problem-Size Bound For Out-Of-Core Columnsort, Geeta Chaudhry, Elizabeth A. Hamon, Thomas H. Cormen
Computer Science Technical Reports
Previous implementations of out-of-core columnsort limit the problem size to $N \leq \sqrt{(M/P)^3 / 2}$, where $N$ is the number of records to sort, $P$ is the number of processors, and $M$ is the total number of records that the entire system can hold in its memory (so that $M/P$ is the number of records that a single processor can hold in its memory). We implemented two variations to out-of-core columnsort that relax this restriction. Subblock columnsort is based on an algorithmic modification of the underlying columnsort algorithm, and it improves the problem-size bound to $N \leq (M/P)^{5/3} / 4^{2/3}$ …
Stupid Columnsort Tricks, Geeta Chaudhry, Thomas H. Cormen
Stupid Columnsort Tricks, Geeta Chaudhry, Thomas H. Cormen
Computer Science Technical Reports
Leighton's columnsort algorithm sorts on an $r \times s$ mesh, subject to the restrictions that $s$ is a divisor of~$r$ and that $r \geq 2s^2$ (so that the mesh is tall and thin). We show how to mitigate both of these restrictions. One result is that the requirement that $s$ is a divisor of~$r$ is unnecessary; columnsort sorts correctly whether or not $s$ divides~$r$. We present two algorithms that, as long as $s$ is a perfect square, relax the restriction that $r \geq 2s^2$; both reduce the exponent of~$s$ to~$3/2$. One algorithm requires $r \geq 4s^{3/2}$ if $s$ divides~$r$ and …
Privacy-Enhanced Credential Services, Alex Iliev, Sean Smith
Privacy-Enhanced Credential Services, Alex Iliev, Sean Smith
Computer Science Technical Reports
The use of credential directories in PKI and authorization systems such as Shibboleth introduces a new privacy risk: an insider at the directory can learn much about otherwise protected interactions by observing who makes queries, and what they ask for. Recent advances in Practical Private Information Retrieval provide promising countermeasures. In this paper, we extend this technology to solve this new privacy problem, and present a design and preliminary prototype for a LDAP-based credential service that can prevent even an insider from learning anything more than the fact a query was made. Our preliminary performance analysis suggests that the complete …
Keyjacking: Risks Of The Current Client-Side Infrastructure, John Marchesini, S W. Smith, Meiyuan Zhao
Keyjacking: Risks Of The Current Client-Side Infrastructure, John Marchesini, S W. Smith, Meiyuan Zhao
Computer Science Technical Reports
In theory, PKI can provide a flexible and strong way to authenticate users in distributed information systems. In practice, much is being invested in realizing this vision via client-side SSL and browser-based keystores. Exploring this vision, we demonstrate that browsers will use personal certificates to authenticate requests that the person neither knew of nor approved (and which password-based systems would have defeated), and we demonstrate the easy permeability of these keystores (including new attacks on medium and high-security IE/XP keys). We suggest some countermeasures, but also suggest that a fundamental rethinking of the trust, usage, and storage model might result …
3d-Structural Homology Detection Via Unassigned Residual Dipolar Couplings, Christopher James Langmead, Bruce Randall Donald
3d-Structural Homology Detection Via Unassigned Residual Dipolar Couplings, Christopher James Langmead, Bruce Randall Donald
Computer Science Technical Reports
Recognition of a protein's fold provides valuable information about its function. While many sequence-based homology prediction methods exist, an important challenge remains: two highly dissimilar sequences can have similar folds --- how can we detect this rapidly, in the context of structural genomics? High-throughput NMR experiments, coupled with novel algorithms for data analysis, can address this challenge. We report an automated procedure for detecting 3D-structural homologies from sparse, unassigned protein NMR data. Our method identifies the 3D-structural models in a protein structural database whose geometries best fit the unassigned experimental NMR data. It does not use sequence information and is …
Tr-2003002: A Knowledge Based Semantics Of Messages, Rohit Parikh, R. Ramanujam
Tr-2003002: A Knowledge Based Semantics Of Messages, Rohit Parikh, R. Ramanujam
Computer Science Technical Reports
No abstract provided.
Tr-2003012: A Semantics For The Logic Of Proofs, Melvin Fitting
Tr-2003012: A Semantics For The Logic Of Proofs, Melvin Fitting
Computer Science Technical Reports
No abstract provided.
Tr-2003005: Lambek Calculus Is Np-Complete, Mati Pentus
Tr-2003005: Lambek Calculus Is Np-Complete, Mati Pentus
Computer Science Technical Reports
No abstract provided.
Tr-2003006: Rijndael For Algebraists: An Expanded Version Of Lenstra's Manuscript, Hannes Moritz, Wei Zhu
Tr-2003006: Rijndael For Algebraists: An Expanded Version Of Lenstra's Manuscript, Hannes Moritz, Wei Zhu
Computer Science Technical Reports
No abstract provided.
Tr-2003009: A Hierarchical Projection Pursuit Clustering Algorithm, Jayson E. Rome, Alexei D. Miasnikov, Robert M. Haralick
Tr-2003009: A Hierarchical Projection Pursuit Clustering Algorithm, Jayson E. Rome, Alexei D. Miasnikov, Robert M. Haralick
Computer Science Technical Reports
No abstract provided.
Tr-2003004: Superfast Algorithms For Singular Toeplitz/Hankel-Like Matrices, Victor Y. Pan
Tr-2003004: Superfast Algorithms For Singular Toeplitz/Hankel-Like Matrices, Victor Y. Pan
Computer Science Technical Reports
No abstract provided.
Tr-2003003: Finite Information Logic, Rohit Parikh, Jouko Väänänen
Tr-2003003: Finite Information Logic, Rohit Parikh, Jouko Väänänen
Computer Science Technical Reports
No abstract provided.
Tr-2003008: Learning And Applying Temporal Patterns Through Experience, Esther Lock
Tr-2003008: Learning And Applying Temporal Patterns Through Experience, Esther Lock
Computer Science Technical Reports
No abstract provided.
Tr-2003011: Data Modelling And Description: A Guide To Using The Sylmodel Library, Jayson E. Rome, Alexei D. Miasnikov, Robert M. Haralick
Tr-2003011: Data Modelling And Description: A Guide To Using The Sylmodel Library, Jayson E. Rome, Alexei D. Miasnikov, Robert M. Haralick
Computer Science Technical Reports
No abstract provided.
Tr-2003013: Qr-Like Algorithms For Generalized Semiseparable Matrices, Dario A. Bini, Luca Gemignani, Victor Y. Pan
Tr-2003013: Qr-Like Algorithms For Generalized Semiseparable Matrices, Dario A. Bini, Luca Gemignani, Victor Y. Pan
Computer Science Technical Reports
No abstract provided.
Tr-2003001: States Of Knowledge And Group Action, Rohit Parikh
Tr-2003001: States Of Knowledge And Group Action, Rohit Parikh
Computer Science Technical Reports
No abstract provided.
Tr-2003007: On The Complexity Of The Reflected Logic Of Proofs, Nikolai V. Krupski
Tr-2003007: On The Complexity Of The Reflected Logic Of Proofs, Nikolai V. Krupski
Computer Science Technical Reports
No abstract provided.
Tr-2003010: A Semantic Proof Of The Realizability Of Modal Logic In The Logic Of Proofs, Melvin Fitting
Tr-2003010: A Semantic Proof Of The Realizability Of Modal Logic In The Logic Of Proofs, Melvin Fitting
Computer Science Technical Reports
No abstract provided.
Tr-2003014: A High-Performance Abstract Machine For Prolog And Its Extensions, Neng-Fa Zhou
Tr-2003014: A High-Performance Abstract Machine For Prolog And Its Extensions, Neng-Fa Zhou
Computer Science Technical Reports
No abstract provided.
Tr-2003015: Two Counterexamples In The Logic Of Dynamic Topological Systems, Sergey Slavnov
Tr-2003015: Two Counterexamples In The Logic Of Dynamic Topological Systems, Sergey Slavnov
Computer Science Technical Reports
No abstract provided.
Proofs Of Soundness And Strong Normalization For Linear Memory Types, Heng Huang, Chris Hawblitzel
Proofs Of Soundness And Strong Normalization For Linear Memory Types, Heng Huang, Chris Hawblitzel
Computer Science Technical Reports
Efficient low-level systems need more control over memory than safe high-level languages usually provide. As a result, run-time systems are typically written in unsafe languages such as C. This report describes an abstract machine designed to give type-safe code more control over memory. It includes complete definitions and proofs.
Exact Formulae For The Lovasz Theta Function Of Sparse Circulant Graphs, Valentino Crespi
Exact Formulae For The Lovasz Theta Function Of Sparse Circulant Graphs, Valentino Crespi
Computer Science Technical Reports
The Lovasz theta function has attracted a lot of attention for its connection with diverse issues, such as communicating without errors and computing large cliques in graphs. Indeed this function enjoys the remarkable property of being computable in polynomial time, despite being sandwitched between clique and chromatic number, two well known hard to compute quantities. In this paper I provide a closed formula for the Lovasz function of a specific class of sparse circulant graphs thus generalizing Lovasz results on cycle graphs (circulant graphs of degree 2).
Distributed Algorithms For Guiding Navigation Across A Sensor Network, Qun Li, Michael Derosa, Daniela Rus
Distributed Algorithms For Guiding Navigation Across A Sensor Network, Qun Li, Michael Derosa, Daniela Rus
Computer Science Technical Reports
We develop distributed algorithms for self-reconfiguring sensor networks that respond to directing a target through a region. The sensor network models the danger levels sensed across its area and has the ability to adapt to changes. It represents the dangerous areas as obstacles. A protocol that combines the artificial potential field of the sensors with the goal location for the moving object guides the object incrementally across the network to the goal, while maintaining the safest distance to the danger areas. We report on hardware experiments using a physical sensor network consisting of Mote sensors.
Using The Emulab Network Testbed To Evaluate The Armada I/O Framework For Computational Grids, Ron Oldfield, David Kotz
Using The Emulab Network Testbed To Evaluate The Armada I/O Framework For Computational Grids, Ron Oldfield, David Kotz
Computer Science Technical Reports
This short report describes our experiences using the Emulab network testbed at the University of Utah to test performance of the Armada framework for parallel I/O on computational grids.
Heterogeneous Self-Reconfiguring Robotics: Ph.D. Thesis Proposal, Robert C. Fitch
Heterogeneous Self-Reconfiguring Robotics: Ph.D. Thesis Proposal, Robert C. Fitch
Computer Science Technical Reports
Self-reconfiguring robots are modular systems that can change shape, or "reconfigure," to match structure to task. They comprise many small, discrete, often identical modules that connect together and that are minimally actuated. Global shape transformation is achieved by composing local motions. Systems with a single module type, known as "homogeneous" systems, gain fault tolerance, robustness and low production cost from module interchangeability. However, we are interested in "heterogeneous" systems, which include multiple types of modules such as those with sensors, batteries or wheels. We believe that heterogeneous systems offer the same benefits as homogeneous systems with the added ability to …
Analysis Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien
Analysis Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien
Computer Science Technical Reports
Understanding usage patterns in wireless local-area networks (WLANs) is critical for those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings. Our study expands on those done by Tang and Baker, with a significantly larger and broader population. We …
Xslt And Xquery As Operator Languages, A Abram White
Xslt And Xquery As Operator Languages, A Abram White
Computer Science Technical Reports
Ubiquitous computing promises to integrate computers into our physical environment, surrounding us with applications that are able to adapt to our dynamics. Solar is a software infrastructure designed to deliver contextual information to these applications. Solar represents context data as events, and uses small programs called operators to filter, merge, aggregate, or transform event streams. This paper explores the possibility of using XSLT and XQuery to build language-neutral Solar operators.
Characterizing Usage Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien
Characterizing Usage Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien
Computer Science Technical Reports
Wireless local-area networks (WLANs) are increasingly common, but little is known about how they are used. A clear understanding of usage patterns in real WLANs is critical information to those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings. …
Context Aggregation And Dissemination In Ubiquitous Computing Systems, Guanling Chen, David Kotz
Context Aggregation And Dissemination In Ubiquitous Computing Systems, Guanling Chen, David Kotz
Computer Science Technical Reports
Many ``ubiquitous computing'' applications need a constant flow of information about their environment to be able to adapt to their changing context. To support these ``context-aware'' applications we propose a graph-based abstraction for collecting, aggregating, and disseminating context information. The abstraction models context information as events, produced by sources and flowing through a directed acyclic graph of event-processing operators and delivered to subscribing applications. Applications describe their desired event stream as a tree of operators that aggregate low-level context information published by existing sources into the high-level context information needed by the application. The operator graph is thus the dynamic …
Solar: A Pervasive-Computing Infrastructure For Context-Aware Mobile Applications, Guanling Chen, David Kotz
Solar: A Pervasive-Computing Infrastructure For Context-Aware Mobile Applications, Guanling Chen, David Kotz
Computer Science Technical Reports
Emerging pervasive computing technologies transform the way we live and work by embedding computation in our surrounding environment. To avoid increasing complexity, and allow the user to concentrate on her tasks, applications must automatically adapt to their changing \emph{context}, the physical and computational environment in which they run. To support these ``context-aware'' applications we propose a graph-based abstraction for collecting, aggregating, and disseminating context information. The abstraction models context information as \emph{events}, which are produced by \emph{sources}, flow through a directed acyclic graph of event-processing \emph{operators}, and are delivered to subscribing applications. Applications describe their desired event stream as a …