Página 1 dos resultados de 31 itens digitais encontrados em 0.004 segundos

Slicing the metric space to provide quick indexing of complex data in the main memory

CARELO, Caio Cesar Mori; POLA, Ives Rene Venturini; CIFERRI, Ricardo Rodrigues; TRAINA, Agma Juci Machado; TRAINA JR., Caetano; CIFERRI, Cristina Dutra de Aguiar
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
25.98%
Searching in a dataset for elements that are similar to a given query element is a core problem in applications that manage complex data, and has been aided by metric access methods (MAMs). A growing number of applications require indices that must be built faster and repeatedly, also providing faster response for similarity queries. The increase in the main memory capacity and its lowering costs also motivate using memory-based MAMs. In this paper. we propose the Onion-tree, a new and robust dynamic memory-based MAM that slices the metric space into disjoint subspaces to provide quick indexing of complex data. It introduces three major characteristics: (i) a partitioning method that controls the number of disjoint subspaces generated at each node; (ii) a replacement technique that can change the leaf node pivots in insertion operations; and (iii) range and k-NN extended query algorithms to support the new partitioning method, including a new visit order of the subspaces in k-NN queries. Performance tests with both real-world and synthetic datasets showed that the Onion-tree is very compact. Comparisons of the Onion-tree with the MM-tree and a memory-based version of the Slim-tree showed that the Onion-tree was always faster to build the index. The experiments also showed that the Onion-tree significantly improved range and k-NN query processing performance and was the most efficient MAM...

Slicing as a distributed systems primitive

Maia, Francisco; Matos, Miguel; Oliveira, Rui Carlos Mendes de; Rivière, Etienne
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Relevância na Pesquisa
26.55%
Large-scale distributed systems appear as the major in- frastructures for supporting planet-scale services. These systems call for appropriate management mechanisms and protocols. Slicing is an example of an autonomous, fully decentral- ized protocol suitable for large-scale environments. It aims at organizing the system into groups of nodes, called slices, according to an application-specific criteria where the size of each slice is relative to the size of the full system. This al- lows assigning a certain fraction of nodes to different task, according to their capabilities. Although useful, current slicing techniques lack some features of considerable practical importance. This pa- per proposes a slicing protocol, that builds on existing so- lutions, and addresses some of their frailties. We present novel solutions to deal with non-uniform slices and to per- form online and dynamic slices schema reconfiguration. Moreover, we describe how to provision a slice-local Peer Sampling Service for upper protocol layers and how to en- hance slicing protocols with the capability of slicing over more than one attribute. Slicing is presented as a complete, dependable and inte- grated distributed systems primitive for large-scale systems.

Dynamic assessment of high-resolution MRI with multi-planar reconstruction increases the yield of lesion detection in patients with partial epilepsy

Santos,Sérgio L. M.; Ghizoni,Enrico; Li,Li M.; Cendes,Fernando
Fonte: Liga Brasileira de Epilepsia (LBE) Publicador: Liga Brasileira de Epilepsia (LBE)
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 EN
Relevância na Pesquisa
26.16%
Objective: To investigate the presence and type of lesions associated with partial epilepsies by routine high resolution MRI and multi-planar reconstruction (MPR) and correlate the MRI abnormalities with semiology and EEG findings. Methods: We studied 100 consecutive patients followed in the epilepsy clinic of our Hospital with partial epilepsy who underwent MRI investigation. The MRI protocol included 6 mm sagittal T1-weighted, 3-4 mm axial T1 and T2-weighted, 3 mm coronal T1 inversion recovery and T2-weighted images that were printed on a radiographic film for routine analysis. In addition, all patients had a volume T1-gradient echo acquisition with isotropic voxels (1-1.5 mm) for multiplanar reconstruction (MPR). The MRIs were examined in two different occasions: first using only the images printed on films, without volume T1-gradiente echo acquisition and in a second occasion in a computer workstation when all the available images and MPR were analyzed blindly to the clinical information. The clinical and EEG findings were tabulated independently, and results were compared using Chi-square of Fisher exact test when appropriate. Results: The patients were divided into 10 groups according to their etiological classification (structural lesions) established by MRI. Mesial temporal sclerosis (MTS) was the largest group (40%). There were 65 women and 35 men. Mean age was 23.9 (± 5.7) years and mean age of onset of recurrent seizures was 9.9 (± 0.8) years. The most frequent risk factors were family history of seizures (23%)...

Lessons of Slicing Membranes: Interplay of Packing, Free Area, and Lateral Diffusion in Phospholipid/Cholesterol Bilayers

Falck, Emma; Patra, Michael; Karttunen, Mikko; Hyvönen, Marja T.; Vattulainen, Ilpo
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /08/2004 EN
Relevância na Pesquisa
26.1%
We employ 100-ns molecular dynamics simulations to study the influence of cholesterol on structural and dynamic properties of dipalmitoylphosphatidylcholine bilayers in the fluid phase. The effects of the cholesterol content on the bilayer structure are considered by varying the cholesterol concentration between 0 and 50%. We concentrate on the free area in the membrane and investigate quantities that are likely to be affected by changes in the free area and free volume properties. It is found that cholesterol has a strong impact on the free area properties of the bilayer. The changes in the amount of free area are shown to be intimately related to alterations in molecular packing, ordering of phospholipid tails, and behavior of compressibility moduli. Also the behavior of the lateral diffusion of both dipalmitoylphosphatidylcholine and cholesterol molecules with an increasing amount of cholesterol can in part be understood in terms of free area. Summarizing, our results highlight the central role of free area in comprehending the structural and dynamic properties of membranes containing cholesterol.

Information Slicing: Anonymity Using Unreliable Overlays

Katti, Sachin; Cohen, Jeffrey; Katabi, Dina
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 15 p
Relevância na Pesquisa
26.43%
This paper proposes a new approach to anonymous communication called information slicing. Typically, anonymizers use onion routing, where a message is encrypted in layers with the public keys of the nodes along the path. Instead, our approach scrambles the message, divides it into pieces, and sends the pieces along disjoint paths. We show that information slicing addresses message confidentiality as well as source and destination anonymity. Surprisingly, it does not need any public key cryptography. Further, our approach naturally addresses the problem of node failures. These characteristics make it a good fit for use over dynamic peer-to-peer overlays. We evaluate the anonymity ofinformation slicing via analysis and simulations. Our prototype implementation on PlanetLab shows that it achieves higher throughput than onion routing and effectively copes with node churn.

Multiprogramming on Multiprocessors

Crovella, Mark E. ; Das, P. ; Dubnicki, Cezary ; LeBlanc, Thomas J. ; Markatos, Evangelos P.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
ENG
Relevância na Pesquisa
26.47%
Several studies have shown that applications may suffer significant performance degradation unless the scheduling policy minimizes the overhead due to multiprogramming. This overhead includes context switching among applications, waiting time incurred by one process due to the preemption of another, and various migration costs associated with moving a process from one processor to another. Many different multiprogramming solutions have been proposed, but each has limited applicability or fails to address an important source of overhead. In addition, there has been little experimental comparison of the various solutions in the presence of applications with varying degrees of parallelism and synchronization. In this paper we explore the tradeoffs between different approaches to multiprogramming a multiprocessor. We modified an existing operating system to implement three different multiprogramming options: time-slicing, coscheduling, and dynamic hardware partitions. Using these three options, we implemented applications that vary in the degree of parallelism, and the frequency and type of synchronization. We show that in most cases coscheduling is preferable to time-slicing. We also show that although there are cases where coscheduling is beneficial...

A Security Domain Model to Assess Software for Exploitable Covert Channels

Auguston, Mikhail; Levin, Timothy; Shaffer, Alan; Irvine, Cynthia E.
Fonte: Association for Computing Machinery (ACM) Publicador: Association for Computing Machinery (ACM)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
25.98%
Within a multilevel secure (MLS) system, trusted subjects are granted privileges to perform operations that are not possible by ordinary subjects controlled by mandatory access control (MAC) policy enforcement mechanisms. These subjects are trusted not to conduct malicious activity or degrade system security. We present a formal definition for trusted subject behaviors, which depends upon a representation of information flow and control dependencies generated during a program execution. We describe a security Domain Model (DM) designed in the Alloy specification language for conducting static analysis of programs to identify illicit information flows, access control flaws and covert channel vulnerabilities. The DM is compiled from a representation of a target program, written in an intermediate Implementation Modeling Language (IML), and a specification of the security policy written in Alloy. The Alloy Analyzer tool is used to perform static analysis of the DM to detect potential security policy violations in the target program. In particular, since the operating system upon which the trusted subject runs has limited ability to control its actions, static analysis of trusted subject operations can contribute to the security of the system.

A hyperbolic slicing condition adapted to Killing fields and densitized lapses

Alcubierre, Miguel; Corichi, Alejandro; Gonzalez, Jose A.; Nunez, Dario; Salgado, Marcelo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.43%
We study the properties of a modified version of the Bona-Masso family of hyperbolic slicing conditions. This modified slicing condition has two very important features: In the first place, it guarantees that if a spacetime is static or stationary, and one starts the evolution in a coordinate system in which the metric coefficients are already time independent, then they will remain time independent during the subsequent evolution, {\em i.e.} the lapse will not evolve and will therefore not drive the time lines away from the Killing direction. Second, the modified condition is naturally adapted to the use of a densitized lapse as a fundamental variable, which in turn makes it a good candidate for a dynamic slicing condition that can be used in conjunction with some recently proposed hyperbolic reformulations of the Einstein evolution equations.; Comment: 11 pages

Dynamic Backward Slicing of Rewriting Logic Computations

Alpuente, María; Ballis, Demis; Espert, Javier; Romero, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.49%
Trace slicing is a widely used technique for execution trace analysis that is effectively used in program debugging, analysis and comprehension. In this paper, we present a backward trace slicing technique that can be used for the analysis of Rewriting Logic theories. Our trace slicing technique allows us to systematically trace back rewrite sequences modulo equational axioms (such as associativity and commutativity) by means of an algorithm that dynamically simplifies the traces by detecting control and data dependencies, and dropping useless data that do not influence the final result. Our methodology is particularly suitable for analyzing complex, textually-large system computations such as those delivered as counter-example traces by Maude model-checkers.; Comment: 17 pages, 1 figure, 5 extra pages for Appendix; Extended version of the CADE 23 paper Backward Trace Slicing for Rewriting Logic Theories

Originator usage control with business process slicing

Su, Ziyi; Biennier, Frédérique
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/03/2012
Relevância na Pesquisa
26.35%
Originator Control allows information providers to define the information re-dissemination condition. Combined with usage control policy, fine-grained 'downstream usage control' can be achieved, which specifies what attributes the downstream consumers should have and how data is used. This paper discusses originator usage control, paying particular attention to enterprise-level dynamic business federations. Rather than 'pre-defining' the information re-dissemination paths, our business process slicing method 'capture' the asset derivation pattern, allowing to maintain originators' policies during the full lifecycle of assets in a collaborative context. First, we propose Service Call Graph (SCG), based on extending the System Dependency Graph, to describe dependencies among partners. When SCG (and corresponding 'service call tuple' list) is built for a business process, it is analyzed to group partners into sub-contexts, according to their dependency relations. Originator usage control can be achieved focusing on each sub-context, by examining downstream consumers' security profiles with upstream asset providers' policies. Second, for analyzing SCG, we propose two 'slicing' strategies, namely 'asset-based' and 'request-based' slicing...

Distributed Slicing in Dynamic Systems

Fernandez, Antonio; Gramoli, Vincent; Jimenez, Ernesto; Kermarrec, Anne-Marie; Raynal, Michel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/12/2006
Relevância na Pesquisa
26.35%
Peer to peer (P2P) systems are moving from application specific architectures to a generic service oriented design philosophy. This raises interesting problems in connection with providing useful P2P middleware services that are capable of dealing with resource assignment and management in a large-scale, heterogeneous and unreliable environment. One such service, the slicing service, has been proposed to allow for an automatic partitioning of P2P networks into groups (slices) that represent a controllable amount of some resource and that are also relatively homogeneous with respect to that resource, in the face of churn and other failures. In this report we propose two algorithms to solve the distributed slicing problem. The first algorithm improves upon an existing algorithm that is based on gossip-based sorting of a set of uniform random numbers. We speed up convergence via a heuristic for gossip peer selection. The second algorithm is based on a different approach: statistical approximation of the rank of nodes in the ordering. The scalability, efficiency and resilience to dynamics of both algorithms relies on their gossip-based models. We present theoretical and experimental results to prove the viability of these algorithms.

Program slicing techniques and its applications

Sasirekha, N.; Robert, A. Edwin; Hemalatha, Dr. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/08/2011
Relevância na Pesquisa
36.64%
Program understanding is an important aspect in Software Maintenance and Reengineering. Understanding the program is related to execution behaviour and relationship of variable involved in the program. The task of finding all statements in a program that directly or indirectly influence the value for an occurrence of a variable gives the set of statements that can affect the value of a variable at some point in a program is called a program slice. Program slicing is a technique for extracting parts of computer programs by tracing the programs' control and data flow related to some data item. This technique is applicable in various areas such as debugging, program comprehension and understanding, program integration, cohesion measurement, re-engineering, maintenance, testing where it is useful to be able to focus on relevant parts of large programs. This paper focuses on the various slicing techniques (not limited to) like static slicing, quasi static slicing, dynamic slicing and conditional slicing. This paper also includes various methods in performing the slicing like forward slicing, backward slicing, syntactic slicing and semantic slicing. The slicing of a program is carried out using Java which is a object oriented programming language.

An approach to find dynamic slice for C++ Program

Pani, Santosh Kumar; Arundhati, Priya
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/06/2010
Relevância na Pesquisa
26.57%
Object-oriented programming has been considered a most promising method in program development and maintenance. An important feature of object-oriented programs (OOPs) is their reusability which can be achieved through the inheritance of classes or reusable components.Dynamic program slicing is an effective technique for narrowing the errors to the relevant parts of a program when debugging. Given a slicing criterion, the dynamic slice contains only those statements that actually affect the variables in the slicing criterion. This paper proposes a method to dynamically slice object-oriented (00) programs based on dependence analysis. It uses the Control Dependency Graph for object program and other static information to reduce the information to be traced during program execution. In this paper we present a method to find the dynamic Slice of object oriented programs where we are finding the slices for object and in case of function overloading.; Comment: Submitted to Journal of Computer Science and Engineering, see http://sites.google.com/site/jcseuk/volume-1-issue-1-may-2010

Kernelet: High-Throughput GPU Kernel Executions with Dynamic Slicing and Scheduling

Zhong, Jianlong; He, Bingsheng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/03/2013
Relevância na Pesquisa
46.47%
Graphics processors, or GPUs, have recently been widely used as accelerators in the shared environments such as clusters and clouds. In such shared environments, many kernels are submitted to GPUs from different users, and throughput is an important metric for performance and total ownership cost. Despite the recently improved runtime support for concurrent GPU kernel executions, the GPU can be severely underutilized, resulting in suboptimal throughput. In this paper, we propose Kernelet, a runtime system with dynamic slicing and scheduling techniques to improve the throughput of concurrent kernel executions on the GPU. With slicing, Kernelet divides a GPU kernel into multiple sub-kernels (namely slices). Each slice has tunable occupancy to allow co-scheduling with other slices and to fully utilize the GPU resources. We develop a novel and effective Markov chain based performance model to guide the scheduling decision. Our experimental results demonstrate up to 31.1% and 23.4% performance improvement on NVIDIA Tesla C2050 and GTX680 GPUs, respectively.

Slicing of Constraint Logic Programs

Szilagyi, Gyongyi; Gyimothy, Tibor; Maluszynski, Jan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/12/2000
Relevância na Pesquisa
26.64%
Slicing is a program analysis technique originally developed for imperative languages. It facilitates understanding of data flow and debugging. This paper discusses slicing of Constraint Logic Programs. Constraint Logic Programming (CLP) is an emerging software technology with a growing number of applications. Data flow in constraint programs is not explicit, and for this reason the concepts of slice and the slicing techniques of imperative languages are not directly applicable. This paper formulates declarative notions of slice suitable for CLP. They provide a basis for defining slicing techniques (both dynamic and static) based on variable sharing. The techniques are further extended by using groundness information. A prototype dynamic slicer of CLP programs implementing the presented ideas is briefly described together with the results of some slicing experiments.; Comment: In M. Ducasse (ed), proceedings of the Fourth International Workshop on Automated Debugging (AADEBUG 2000), August 2000, Munich. cs.SE/0010035

A 3+1 Computational Scheme for Dynamic Spherically Symmetric Black Hole Spacetimes -- I: Initial Data

Thornburg, Jonathan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.1%
When using the black hole exclusion (horizon boundary condition) technique, $K$ is usually nonzero and spatially variable, so none of the special cases of York's conformal-decomposition algorithm apply, and the full 4-vector nonlinear York equations must be solved numerically. We discuss the construction of dynamic black hole initial data slices using this technique: We perturb a known black hole slice via some Ansatz, apply the York decomposition (using another Ansatz for the inner boundary conditions) to project the perturbed field variables back into the constraint hypersurface, and finally optionally apply a numerical 3-coordinate transformation to (eg) restore an areal radial coordinate. In comparison to other initial data algorithms, the key advantage of this algorithm is its flexibility: $K$ is unrestricted, allowing the use of whatever slicing is most suitable for (say) a time evolution. We have implemented this algorithm for the spherically symmetric scalar field system. We present numerical results for a number of Eddington- Finkelstein--like initial data slices containing black holes surrounded by scalar field shells. Using 4th order finite differencing with resolutions of $\Delta r/r \approx 0.02$ (0.01) near the (Gaussian) perturbations...

An Approach for Computing Dynamic Slice of Concurrent Aspect-Oriented Programs

Ray, Abhishek; Mishra, Siba; Mohapatra, Durga Prasad
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/04/2014
Relevância na Pesquisa
36.41%
We propose a dynamic slicing algorithm to compute the slice of concurrent aspect-oriented programs. We use a dependence based intermediate program representation called Concurrent Aspect-oriented System Dependence Graph (CASDG) to represent a concurrent aspect-oriented program. The CASDG of an aspect-oriented program consists of a system dependence graph (SDG) for the non-aspect code, a group of dependence graphs for aspect code and some additional dependence edges used to connect the system dependence graph for the non-aspect code to dependence graph for aspect code. The proposed dynamic slicing al-gorithm is an extended version of NMDS algorithm for concurrent object-oriented programs, which is based on marking and unmarking of the executed nodes in CASDG appropriately during run-time.; Comment: 20 pages. arXiv admin note: text overlap with arXiv:1403.0100

A Novel Approach for Computing Dynamic Slices of Aspect-Oriented Programs

Ray, Abhishek; Mishra, Siba; Mohapatra, Durga Prasad
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/03/2014
Relevância na Pesquisa
36.41%
We propose a dynamic slicing algorithm to compute the slices of aspect-oriented programs. We use a dependence based intermediate program representation called Aspect System Dependence Graph (AOSG) to represent aspect-oriented programs. Then, we propose the dynamic slicing algorithm for AOPs, which is an extended version of EMDS algorithm for object-oriented programs. Our algorithm is based on marking and unmarking of the edges of AOSG appropriately during runtime.; Comment: 7 Pages

Lessons of Slicing Membranes: Interplay of Packing, Free Area, and Lateral Diffusion in Phospholipid/Cholesterol Bilayers

Falck, Emma; Patra, Michael; Karttunen, Mikko; Hyvonen, Marja T.; Vattulainen, Ilpo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/02/2004
Relevância na Pesquisa
26.1%
We employ 100 ns molecular dynamics simulations to study the influence of cholesterol on structural and dynamic properties of dipalmitoylphosphatidylcholine (DPPC) bilayers in the fluid phase. The effects of the cholesterol content on the bilayer structure are considered by varying the cholesterol concentration between 0 and 50%. We concentrate on the free area in the membrane and investigate quantities that are likely to be affected by changes in the free area and free volume properties. It is found that cholesterol has a strong impact on the free area properties of the bilayer. The changes in the amount of free area are shown to be intimately related to alterations in molecular packing, ordering of phospholipid tails, and compressibility. Further, the behavior of the lateral diffusion of both DPPC and cholesterol molecules with an increasing amount of cholesterol can in part be understood in terms of free area. Summarizing, our results highlight the central role of free area in comprehending the structural and dynamic properties of membranes containing cholesterol.

Distributed Slicing in Dynamic Systems

Fernandez, Antonio; Gramoli, Vincent; Jimenez, Ernesto; Kermarrec, Anne-Marie; Raynal, Michel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/12/2007
Relevância na Pesquisa
26.35%
Peer to peer (P2P) systems are moving from application specific architectures to a generic service oriented design philosophy. This raises interesting problems in connection with providing useful P2P middleware services capable of dealing with resource assignment and management in a large-scale, heterogeneous and unreliable environment. The slicing service, has been proposed to allow for an automatic partitioning of P2P networks into groups (slices) that represent a controllable amount of some resource and that are also relatively homogeneous with respect to that resource. In this paper we propose two gossip-based algorithms to solve the distributed slicing problem. The first algorithm speeds up an existing algorithm sorting a set of uniform random numbers. The second algorithm statistically approximates the rank of nodes in the ordering. The scalability, efficiency and resilience to dynamics of both algorithms rely on their gossip-based models. These algorithms are proved viable theoretically and experimentally.