Investigation of an optimistic based concurrency control mechanism for parallel file systems

Parallel file systems offer improved performance over traditional file systems by allowing processes to access file data, stored over a number of disks, in parallel. When this file is to be accessed by many processes at the same time for reading and writing, the problem of maintaining file consistency is introduced. The general approach to maintaining file consistency is through the use locks which grant a single process exclusive access to the file. Existing studies have found parallel file systems and associated applications rarely experience conflict, resulting in unnecessary overheads from locks being acquired. This paper examines an alternate approach to maintaining file consistency, which is based on optimistic concurrency control. This approach was shown to have a much smaller overhead when compared with traditional lock-based approaches; especially in situations when there is little contention. This paper presents the design, implementation and initial testing results of an optimistic based concurrency control mechanism.

Comparison of cyclic fatigue and torsional resistance in reciprocating single-file systems and continuous rotary instrumentation systems

As compared with continuous rotary systems, reciprocating motion is believed to increase the fatigue resistance of NiTi instruments. We compared the cyclic fatigue and torsional resistance of reciprocating single-file systems and continuous rotary instrumentation systems in simulated root canals. Eighty instruments from the ProTaper Universal, WaveOne, MTwo, and Reciproc systems (n = 20) were submitted to dynamic bending testing in stainless-steel simulated curved canals. Axial displacement of the simulated canals was performed with half of the instruments (n = 10), with back-and-forth movements in a range of 1.5 mm. Time until fracture was recorded, and the number of cycles until instrument fracture was calculated. Cyclic fatigue resistance was greater for reciprocating systems than for rotary systems (P < 0.05). Instruments from the Reciproc and WaveOne systems significantly differed only when axial displacement occurred (P < 0.05). Instruments of the ProTaper Universal and MTwo systems did not significantly differ (P > 0.05). Cyclic fatigue and torsional resistance were greater for reciprocating systems than for continuous rotary systems, irrespective of axial displacement.

Reflections on five years of evaluating semantic search systems

Evaluations of semantic search systems are generally small scale and ad hoc due to the lack of appropriate resources such as test collections, agreed performance criteria and independent judgements of performance. By analysing our work in building and evaluating semantic tools over the last five years, we conclude that the growth of the semantic web led to an improvement in the available resources and the consequent robustness of performance assessments. We propose two directions for continuing evaluation work: the development of extensible evaluation benchmarks and the use of logging parameters for evaluating individual components of search systems.

Spatial indexing for scalability in FCA

The paper provides evidence that spatial indexing structures offer faster resolution of Formal Concept Analysis queries than B-Tree/Hash methods. We show that many Formal Concept Analysis operations, computing the contingent and extent sizes as well as listing the matching objects, enjoy improved performance with the use of spatial indexing structures such as the RD-Tree. Speed improvements can vary up to eighty times faster depending on the data and query. The motivation for our study is the application of Formal Concept Analysis to Semantic File Systems. In such applications millions of formal objects must be dealt with. It has been found that spatial indexing also provides an effective indexing technique for more general purpose applications requiring scalability in Formal Concept Analysis systems. The coverage and benchmarking are presented with general applications in mind.

A comparative study of multiple attribute tree and inverted file structures for large bibliographic files

A variety of data structures such as inverted file, multi-lists, quad tree, k-d tree, range tree, polygon tree, quintary tree, multidimensional tries, segment tree, doubly chained tree, the grid file, d-fold tree. super B-tree, Multiple Attribute Tree (MAT), etc. have been studied for multidimensional searching and related problems. Physical data base organization, which is an important application of multidimensional searching, is traditionally and mostly handled by employing inverted file. This study proposes MAT data structure for bibliographic file systems, by illustrating the superiority of MAT data structure over inverted file. Both the methods are compared in terms of preprocessing, storage and query costs. Worst-case complexity analysis of both the methods, for a partial match query, is carried out in two cases: (a) when directory resides in main memory, (b) when directory resides in secondary memory. In both cases, MAT data structure is shown to be more efficient than the inverted file method. Arguments are given to illustrate the superiority of MAT data structure in an average case also. An efficient adaptation of MAT data structure, that exploits the special features of MAT structure and bibliographic files, is proposed for bibliographic file systems. In this adaptation, suitable techniques for fixing and ranking of the attributes for MAT data structure are proposed. Conclusions and proposals for future research are presented.

An effective and efficient testing methodology for correctness testing for file recovery tools

We hereby develop an effective and efficient testing methodology for correctness testing for file recovery tools across different file systems. We assume that the tool tester is familiar with the formats of common file types and has the ability to use the tools correctly. Our methodology first derives a testing plan to minimize the number of runs required to identify the differences in tools with respect to correctness. We also present a case study on correctness testing for file carving tools, which allows us to confirm that the number of necessary testing runs is bounded and our results are statistically sound.

Semantic localization in the PCL library

The semantic localization problem in robotics consists in determining the place where a robot is located by means of semantic categories. The problem is usually addressed as a supervised classification process, where input data correspond to robot perceptions while classes to semantic categories, like kitchen or corridor. In this paper we propose a framework, implemented in the PCL library, which provides a set of valuable tools to easily develop and evaluate semantic localization systems. The implementation includes the generation of 3D global descriptors following a Bag-of-Words approach. This allows the generation of fixed-dimensionality descriptors from any type of keypoint detector and feature extractor combinations. The framework has been designed, structured and implemented to be easily extended with different keypoint detectors, feature extractors as well as classification models. The proposed framework has also been used to evaluate the performance of a set of already implemented descriptors, when used as input for a specific semantic localization system. The obtained results are discussed paying special attention to the internal parameters of the BoW descriptor generation process. Moreover, we also review the combination of some keypoint detectors with different 3D descriptor generation techniques.

The usability of semantic search tools:a review

The goal of semantic search is to improve on traditional search methods by exploiting the semantic metadata. In this paper, we argue that supporting iterative and exploratory search modes is important to the usability of all search systems. We also identify the types of semantic queries the users need to make, the issues concerning the search environment and the problems that are intrinsic to semantic search in particular. We then review the four modes of user interaction in existing semantic search systems, namely keyword-based, form-based, view-based and natural language-based systems. Future development should focus on multimodal search systems, which exploit the advantages of more than one mode of interaction, and on developing the search systems that can search heterogeneous semantic metadata on the open semantic Web.

Semantic annotation for knowledge management:requirements and a survey of the state of the art

While much of a company's knowledge can be found in text repositories, current content management systems have limited capabilities for structuring and interpreting documents. In the emerging Semantic Web, search, interpretation and aggregation can be addressed by ontology-based semantic mark-up. In this paper, we examine semantic annotation, identify a number of requirements, and review the current generation of semantic annotation systems. This analysis shows that, while there is still some way to go before semantic annotation tools will be able to address fully all the knowledge management needs, research in the area is active and making good progress.

The Design and Implementation of a SD Card File System

SD card (Secure Digital Memory Card) is widely used in portable storage medium. Currently, latest researches on SD card, are mainly SD card controller based on FPGA (Field Programmable Gate Array). Most of them are relying on API interface (Application Programming Interface), AHB bus (Advanced High performance Bus), etc. They are dedicated to the realization of ultra high speed communication between SD card and upper systems. Studies about SD card controller, really play a vital role in the field of high speed cameras and other sub-areas of expertise. This design of FPGA-based file systems and SD2.0 IP (Intellectual Property core) does not only exhibit a nice transmission rate, but also achieve the systematic management of files, while retaining a strong portability and practicality. The file system design and implementation on a SD card covers the main three IP innovation points. First, the combination and integration of file system and SD card controller, makes the overall system highly integrated and practical. The popular SD2.0 protocol is implemented for communication channels. Pure digital logic design based on VHDL (Very-High-Speed Integrated Circuit Hardware Description Language), integrates the SD card controller in hardware layer and the FAT32 file system for the entire system. Secondly, the document management system mechanism makes document processing more convenient and easy. Especially for small files in batch processing, it can ease the pressure of upper system to frequently access and process them, thereby enhancing the overall efficiency of systems. Finally, digital design ensures the superior performance. For transmission security, CRC (Cyclic Redundancy Check) algorithm is for data transmission protection. Design of each module is platform-independent of macro cells, and keeps a better portability. Custom integrated instructions and interfaces may facilitate easily to use. Finally, the actual test went through multi-platform method, Xilinx and Altera FPGA developing platforms. The timing simulation and debugging of each module was covered. Finally, Test results show that the designed FPGA-based file system IP on SD card can support SD card, TF card and Micro SD with 2.0 protocols, and the successful implementation of systematic management for stored files, and supports SD bus mode. Data read and write rates in Kingston class10 card is approximately 24.27MB/s and 16.94MB/s.

Navigating, recognizing and describing urban spaces with vision and lasers

In this paper we describe a body of work aimed at extending the reach of mobile navigation and mapping. We describe how running topological and metric mapping and pose estimation processes concurrently, using vision and laser ranging, has produced a full six-degree-of-freedom outdoor navigation system. It is capable of producing intricate three-dimensional maps over many kilometers and in real time. We consider issues concerning the intrinsic quality of the built maps and describe our progress towards adding semantic labels to maps via scene de-construction and labeling. We show how our choices of representation, inference methods and use of both topological and metric techniques naturally allow us to fuse maps built from multiple sessions with no need for manual frame alignment or data association.

Avaliação da extrusão bacteriana apical após instrumentação mecanizada com sistemas reciprocantes de instrumento único comparados a um sistema rotatório multi-instrumento

O objetivo deste estudo foi avaliar ex vivo a extrusão bacteriana apical após instrumentação mecanizada com sistemas reciprocantes de instrumento único e movimento reciprocante (WaveOne and Reciproc) comparados a um sistema multi-instrumentos (BioRaCe). Quarenta e cinco incisivos inferiores humanos unirradiculares, ovais e de anatomia semelhante foram utilizados. Os dentes foram acessados e seus canais radiculares foram contaminados com uma suspensão de Enterococcus faecalis e incubados por 30 dias possibilitando crescimento bacteriano em biofilme. Os dentes contaminados foram divididos em três grupos com 15 espécimes cada (RE - Reciproc, WO -WaveOne e BR - BioRaCe). Foram utilizados oito dentes para grupos controle de crescimento bacteriano positivo e negativo. As bactérias extruídas apicalmente durante a instrumentação foram coletadas em frascos de vidro contendo 0,9% de NaCl. As amostras microbiológicas foram retiradas dos frascos e incubadas em meio BHI ágar, durante 24 horas. O crescimento bacteriano foi contado e os resultados foram expressos em unidades formadoras de colônia (UFC). Os dados foram analisados pelos testes estatísticos de Wilcoxon e Kruskal-Wallis. Não houve diferença estatisticamente significante no número de UFC entre os dois sistemas reciprocantes (p>0,05). Em contrapartida, o sistema de instrumentos rotatórios mostrou uma quantidade de UFC significativamente maior do que os dois outros grupos (p <0,05). A partir da análise dos resultados e dentro das limitações deste estudo foi possível concluir que todos os sistemas de instrumentação testados extruem bactérias apicalmente. No entanto, ambos os sistemas de instrumento único e movimento reciprocante extruem menos bactérias apicalmente do que o sistema rotatório multi-instrumentos de referência.

Sistema de instrumentação mecanizada reciprocante

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária