Página 8 dos resultados de 100905 itens digitais encontrados em 0.085 segundos

‣ A PCI Express to PCIX Bridge optimized for performance and area

Chong, Margaret J. (Margaret Jane), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves; 1534220 bytes; 1611421 bytes; application/pdf; application/pdf
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This thesis project involves the architecture, implementation, and verification of a high bandwidth, low cost ASIC digital logic core that is compliant with the PCI Express to PCIX Bridge Specification. The core supports PCI Express and PCIX transactions, x16 PCI Express link widths, 32 and 64-bit PCIX link widths, all PCI Express and PCIX packet sizes, transaction ordering and queuing, relaxed ordering, flow control, and buffer management. Performance and area are optimized at the architectural and logic levels. The core is approximately 27K gate count, runs at a maximum of 250 MHz, and is synthesized to a current standard technology. This thesis explores PCI Express, PCIX, and PCI technologies, architectural design, development of Verilog and Vera models, thorough module-level verification, the development of a PCI Express/PCIX system verification environment, synthesis, static timing analysis, and performance and area evaluations. The work has been completed in IBM Microelectronics in Burlington, Vermont as part of the MIT VI-A Program.; by Margaret J. Chong.; Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, June 2004.; Includes bibliographical references (leaf 89).; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.

‣ Sparsely faceted arrays : a mechanism supporting the parallel allocation, communication, and garbage collection; SFAs : a mechanism supporting the parallel allocation, communication, and garbage collection

Brown, Jeremy Hanford, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 126 p.; 664152 bytes; 663501 bytes; application/pdf; application/pdf
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Conventional parallel computer architectures do not provide support for non-uniformly distributed objects. In this thesis, I introduce sparsely faceted arrays (SFAs), a new low-level mechanism for naming regions of memory, or facets, on different processors in a distributed, shared memory parallel processing system. Sparsely faceted arrays address the disconnect between the global distributed arrays provided by conventional architectures (e.g. the Cray T3 series), and the requirements of high-level parallel programming methods that wish to use objects that are distributed over only a subset of processing elements. A sparsely faceted array names a virtual globally-distributed array, but actual facets are lazily allocated. By providing simple semantics and making efficient use of memory, SFAs enable efficient implementation of a variety of non-uniformly distributed data structures and related algorithms. I present example applications which use SFAs, and describe and evaluate simple hardware mechanisms for implementing SFAs. Keeping track of which nodes have allocated facets for a particular SFA is an important task that suggests the need for automatic memory management, including garbage collection. To address this need, I first argue that conventional tracing techniques such as mark/sweep and copying GC are inherently unscalable in parallel systems. I then present a parallel memory-management strategy...

‣ Surface reflectance recognition and real-world illumination statistics

Dror, Ron O. (Ron Ofer), 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 150 p.; 3001789 bytes; 3001547 bytes; application/pdf; application/pdf
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Humans distinguish materials such as metal, plastic, and paper effortlessly at a glance. Traditional computer vision systems cannot solve this problem at all. Recognizing surface reflectance properties from a single photograph is difficult because the observed image depends heavily on the amount of light incident from every direction. A mirrored sphere, for example, produces a different image in every environment. To make matters worse, two surfaces with different reflectance properties could produce identical images. The mirrored sphere simply reflects its surroundings, so in the right artificial setting, it could mimic the appearance of a matte ping-pong ball. Yet, humans possess an intuitive sense of what materials typically "look like" in the real world. This thesis develops computational algorithms with a similar ability to recognize reflectance properties from photographs under unknown, real-world illumination conditions. Real-world illumination is complex, with light typically incident on a surface from every direction. We find, however, that real-world illumination patterns are not arbitrary. They exhibit highly predictable spatial structure, which we describe largely in the wavelet domain. Although they differ in several respects from the typical photographs...

‣ Interdigital dielectrometry based detection and identification of dangerous materials for security applications

Sears, Jason, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 137 p.; 2179275 bytes; 15358149 bytes; application/pdf; application/pdf
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Recent terrorist threats have increased the attention paid to searching airline passengers for dangerous and explosive materials. In particular, the possibility that terrorists might hide explosives in shoes has prompted most airline screening stations to require that shoes be removed for x-ray inspection. This thesis is a preliminary investigation of an interdigital dielectrometry based method that could safely and accurately determine the material content within shoes while they are worn. Theoretical modeling of the sensor and the representative materials under test were conducted with the finite element analysis package Maxwell from Ansoft Corp. and analytic/numerical mathematical models for material property estimation. The studies show that dangerous materials hidden in the sole of a shoe could be detected and identified if they lie within the penetration depth of the sensor and if they are sufficiently different in their complex dielectric properties from the normal shoe material. Preliminary finite element computer simulations were also performed to show the effects of sensing electrode segmentation on improving the penetration depth of the electric field, but at the cost of reduced signal strength. Experiments using interdigital sensors with wavelengths ranging from 1 mm to 40 mm in the frequency range of 0.005 Hz to 10 kHz first on homogeneous materials such as air...

‣ The eFacilitator : a meeting capture application and infrastructure; Meeting capture application and infrastructure

Fox, Harold, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves; 3647016 bytes; 3646821 bytes; application/pdf; application/pdf
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Meeting capture and support is an important research field in ubiquitous computing and human computer interaction. We have a built a note-taking application, which lets meeting facilitators and note takers organize the material they place on an electronic palette. This application stores all transactions, so that the note-taking process can be played back in real time along with the captured audio and video. Eventually, this captured note organization can be used for topic searches and information extraction. We have also built a browsing program to let users find meetings based on properties like time and location. This program can also create meetings which go into the same data space. The data space lets agents representing a meeting automatically find capture hardware to capture and index meetings without user intervention. The data space is enabled by a highly scalable distributed, object-oriented, semantic database.; by Harold Fox.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.; Includes bibliographical references (leaves 85-89).

‣ A forward model-based analysis of cardiovascular system identification methods

Mukkamala, Ramakrishna, 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 221 p.; 8339285 bytes; 8339092 bytes; application/pdf; application/pdf
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Cardiovascular system identification is a potentially powerful approach for intelligent patient monitoring of cardiovascular function. Rather than merely recording hemodynamic signals, the signals are mathematically analyzed so as to provide a dynamical characterization of the physiologic mechanisms responsible for generating them. The fundamental aim of this thesis is to develop and evaluate cardiovascular system identification methods based on a test bed of data generated from a forward model of the cardiovascular system whose dynamical properties are known. To this end, we developed a computer model of the human cardiovascular system which includes a lumped parameter model of the heart and circulation and a model of the short-term cardiovascular regulatory system continuously disturbed by resting physiologic perturbations. The short-term regulatory system consists of arterial and cardiopulmonary baroreflex systems and a direct neural coupling mechanism between respiration and heart rate. The resting physiologic perturbations include respiratory activity and stochastic disturbances to total peripheral resistance (TPR) and heart rate representing, for example, autoregulation of local vascular beds and higher brain center activity. We demonstrated that this model emulates experimental data in terms of steady-state pulsatility...

‣ MIT Automated Auscultation System; Massachusetts Institute of Technology Automated Auscultation System

Syed, Zeeshan Hassan, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 127 p.; 7383965 bytes; 7400200 bytes; application/pdf; application/pdf
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At every annual exam, the primary care physician uses a stethoscope to listen for cardiac abnormalities. This approach is non-invasive, inexpensive, and fast. It is also highly unreliable. Over 80% of the people referred to cardiologists as suffering from the most commonly diagnosed condition, mitral valve prolapse (MVP), do not have this condition. Working in conjunction with cardiologists at MGH, we developed a robust, low cost, easy to use tool that can be employed to diagnose MVP in the office of primary care physicians. The system fuses signals from an electronic stethoscope and a two-lead EKG, and uses software running on a desktop or laptop computer to make a diagnosis. We also provide a number of novel audiovisual diagnostic aids. These allow physicians to visualize both individual heart beats and a visual-prototypical heart beat constructed from a sequence of beats. They also permit doctors to listen to an audio-prototypical heart-beat, audio enhanced heart-beats that amplify clinically significant sounds, and slowed down heart-beats that make it easier to separate clinically relevant cardiac events. We tested our system on 51 patients. The number of false positives was reduced to approximately 10%. While there is no generally accepted statistic on false negatives...

‣ Design automation and analysis of three-dimensional integrated circuits

Das, Shamik, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 176 p.; 10090764 bytes; 10112999 bytes; application/pdf; application/pdf
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This dissertation concerns the design of circuits and systems for an emerging technology known as three-dimensional integration. By stacking individual components, dice, or whole wafers using a high-density electromechanical interconnect, three-dimensional integration can achieve scalability and performance exceeding that of conventional fabrication technologies. There are two main contributions of this thesis. The first is a computer-aided design flow for the digital components of a three-dimensional integrated circuit (3-D IC). This flow primarily consists of two software tools: PR3D, a placement and routing tool for custom 3-D ICs based on standard cells, and 3-D Magic, a tool for designing, editing, and testing physical layout characteristics of 3-D ICs. The second contribution of this thesis is a performance analysis of the digital components of 3-D ICs. We use the above tools to determine the extent to which 3-D integration can improve timing, energy, and thermal performance. In doing so, we verify the estimates of stochastic computational models for 3-D IC interconnects and find that the models predict the optimal 3-D wire length to within 20% accuracy. We expand upon this analysis by examining how 3-D technology factors affect the optimal wire length that can be obtained. Our ultimate analysis extends this work by directly considering timing and energy in 3-D ICs. In all cases we find that significant performance improvements are possible. In contrast...

‣ Red emitting photonic devices using InGaP/InGaAlP material system

Kangude, Yamini
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 58 leaves; 2677010 bytes; 2679333 bytes; application/pdf; application/pdf
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In this thesis, two red emitting photonic devices are presented using the InGaP/InGaAlP material system. InGaP/InGaAlP material system provides large flexibility in the band gap energy while being lattice matched to GaAs substrate. The devices consist of a quantum well active region and a distributed bragg reflector at the bottom to reduce loss of emitted light into the substrate. The first device emits at a wavelength of 650 nm and is intended to create a photonic crystal light emitting diode (PCLED). PCLEDs have been demonstrated to have higher efficiency compared to devices without the photonic crystal. The second device emits at 690 nm and is intended for integrating with an organic semiconductor to form a hybrid organic-inorganic emitter. The devices were grown using gas source molecular beam epitaxy (GSMBE) and then processed to form the final device. .; by Yamini Kangude.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (leaves 57-58).

‣ Propulsion mechanisms in a helicon plasma thruster

Sinenian, Nareg
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 110 p.
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Electric thrusters offer an attractive option for various in-space propulsion tasks due to their high thrust efficiencies. The performance characteristics of a compact electric thruster utilizing a helicon plasma source is investigated with the goal of identifying potential thrust mechanisms. Performance characteristics such as thrust, specific impulse, ion cost and thrust efficiency are discussed and related to plasma parameters. The design and fabrication of a prototype compact helicon thruster is presented, including design of a radio-frequency power delivery system, electromagnets and a propellant flow system. The design of plasma diagnostics and associated measurement techniques are discussed including a retarding potential analyzer, mach probes and langmuir probes. These diagnostics are used to measure plasma properties such as electron temperature, plasma density, and ion flow velocities. Thruster performance characteristics are then derived from these measurement results. Significant ion acceleration is demonstrated in both Argon and Nitrogen plasmas and potential mechanisms for this are discussed.; by Nareg Sinenian.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering; and, (S.M.)--Massachusetts Institute of Technology...

‣ The Profession of IT, Is Computer Science Science?

Denning, Peter J.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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Computer Science meets every criterion for being a science, but it has a self-inflicted credibility problem.

‣ Is Computer Science Science? (Spanish version)

Denning, Peter J.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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Computer Science meets every criterion for being a science, but it has a self-inflicted credibility problem. Spanish version. (Traducción por: Marco A. Alvarez)

‣ The Science in Computer Science

Denning, Peter J.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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The article of record as published may be found at http://doi.org/10.1145/2447976.2447988; Computer science is in a period of renaissance as it rediscovers its science roots.The article of record as published may be located at http://dx.doi.org/

‣ A cancer protocol writer's assistant

Masand, Brij, 1957-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 91 leaves; 6687167 bytes; 6686926 bytes; application/pdf; application/pdf
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by Brij Mohan Masand.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING; Bibliography: leaves 90-91.

‣ Fighting phishing at the user interface

Wu, Min, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 199 p.
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The problem that this thesis concentrates on is phishing attacks. Phishing attacks use email messages and web sites designed to look as if they come from a known and legitimate organization, in order to deceive users into submitting their personal, financial, or computer account information online at those fake web sites. Phishing is a semantic attack. The fundamental problem of phishing is that when a user submits sensitive information online under an attack, his mental model about this submission is different from the system model that actually performs this submission. Specifically, the system sends the data to a different web site from the one where the user intends to submit the data. The fundamental solution to phishing is to bridge the semantic gap between the user's mental model and the system model. The user interface is where human users interact with the computer system. It is where a user's intention transforms into a system operation. It is where the semantic gap happens under phishing attacks. And therefore, it is where the phishing should be solved. There are two major approaches to bridge the semantic gap at the user interface. One approach is to reflect the system model to the user.; (cont.) Anti-phishing toolbars and the browser's security indicators take this approach. User studies in this thesis show that this approach is not effective at preventing phishing. Users are required to constantly pay attention to the toolbar and are expected to have the expertise to always correctly interpret the toolbar message. Normal users meet neither of these requirements. The other approach is to let users tell the system their intentions when they are submitting data online. The system can then check if the actual submission meets the user's intention or not. If there is a semantic gap...

‣ Aural imaging from 3D vision; Aural imaging from three dimension vision

Vicenti, Jasper Fourways
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 60 p.
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Dense stereo maps have many useful applications in computer vision. They can help in performing such tasks as background separation, segmentation, and object recognition. Despite the continued exponential advances in the computational capacity of microprocessors, current personal computers are limited in their ability to adequately solve the dense stereo vision problem in realtime. Modern processors now contain a SIMD instruction set architecture that can provide substantial improvements in performance when working with specific data types. This program demonstrates a stereo vision algorithm that implements commonly known methods in computer vision and takes advantage of the Altivec instruction set to achieve realtime performance. Once the stereo data has been processed, the depth map that is produced can be used to provide an additional dimension of data to the user. The software demonstrates a possible use for this data, as an aural aid to people that are blind or vision impaired. The system uses the depth information to identify obstacles in a user's path and alert the user with aural feedback.; by Jasper Fourways Vicenti.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science...

‣ Sound propagation around underwater seamounts

Sikora, Joseph J., III
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 121 leaves
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This thesis develops and utilizes a method for analyzing data from the North Pacific Acoustic Laboratory's (NPAL) Basin Acoustic Seamount Scattering Experiment (BASSEX). BASSEX was designed to provide data to support the development of analytical techniques and methods which improve the understanding of sound propagation around underwater seamounts. The depth-dependent sound velocity profile of typical ocean waveguides force sound to travel in convergence zones about a minimum sound speed depth. This ducted nature of the ocean makes modeling the acoustic field around seamounts particularly challenging, compared to an isovelocity medium. The conical shape of seamounts also adds to the complexity of the scatter field. It is important to the U.S. Navy to understand how sound is diffracted around this type of topographic feature. Underwater seamounts can be used to conceal submarines by absorbing and scattering the sound they emit. BASSEX measurements have characterized the size and shape of the forward scatter field around the Kermit-Roosevelt Seamount in the Pacific Ocean. Kermit-Roosevelt is a large, conical seamount which shoals close to the minimum sound speed depth, making it ideal for study. Acoustic sources, including M-sequence and linear frequency-modulated sources...

‣ Auditing technology for electronic voting machines; voter verification audio audit transcript trail

Cohen, Sharon B
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 leaves; 5045752 bytes; 5050901 bytes; application/pdf; application/pdf
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Direct Recording Electronic (DRE) voting machine security has been a significant topic of contention ever since Diebold voting machine code turned up on a public Internet site in 2003 and computer scientists at Johns Hopkins University declared the machine "unsuitable for use in a general election." Since then, many people from computer scientists to politicians have begun to insist that DREs be equipped with a paper trail. A paper trail provides a paper printout for the voter to approve at the end of each voting session. Although there have been strong political efforts to place paper trails on DRE machines, there have not been any scientific studies to indicate that paper trails are effective audits. This work describes a user study done to compare paper trails to audio audits, a new proposal for DRE auditing. Participants in the study completed four elections on a voting machine with a paper trail and four elections on a machine with an audio trail. There were purposeful mistakes inserted into the audits on some of the machines. Results from the study indicated that participants were able to find almost 10 times as many errors in the audio audit then they were able to find in the paper trail. Voters' attitudes towards the paper audit were extremely apathetic...

‣ A serverless, wide-area version control system

Chen, Benjie, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 102 leaves; 4726852 bytes; 4738749 bytes; application/pdf; application/pdf
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This thesis describes Pastwatch, a distributed version control system. Pastwatch maintains versions of users' shared files. Each version is immutable: to make changes, a user checks out a version onto the user's computer, edits the files locally, then commits the changes to create a new version. The motivation behind Pastwatch is to support wide-area read/write file sharing. An example of this type of sharing is when loosely affiliated programmers from different parts of the world collaborate to work on open-source software projects. To support such users, Pastwatch offers three properties. First, it allows users who travel frequently or whose network connections fail from time to time to access historical versions of the shared files or make new versions while disconnected. Second, Pastwatch makes the current and historical versions of the shared files highly available. For example, even when their office building experiences a power failure, users can still create new versions and retrieve other users' changes from other locations. Supporting disconnected operation is not adequate by itself in these cases; users also want to see others' changes. Third, Pastwatch avoids using dedicated servers. Running a dedicated server requires high administrative costs...

‣ The assertive profile of the Bulgarian students in computer science and computer engineering

Peneva, Ivelina; Yordzhev, Krasimir
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/04/2014 Português
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Different points of view on the nature and content of the assertiveness are followed in this paper. The main purpose is to study the assertive profile of Bulgarian students in computer science and computer engineering by analyzing the components of assertiveness. Research was performed using testing methods. It was found that the level of expressivity of this personal quality among subjects were above-average level.