Página 17 dos resultados de 10406 itens digitais encontrados em 0.015 segundos

‣ Evaluation of Non-Intrusive Load Monitoring for shipboard cycling system diagnostics; Evaluation of NILM for shipboard cycling system diagnostics

Mosman, James P. (James Paul)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 99 p.
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The Non-Intrusive Load Monitor (NILM) is a device that utilizes voltage and current measurements to determine the operating schedule of all of the major loads on an electrical service. Additionally, the NILM can use its electrical measurements to diagnose impending failures in the mechanical systems that are actuated by the electric loads. Ongoing NILM research conducted at Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES) is exploring the application of NILM technology in shipboard environments. For the current shipboard applications, diagnostic software development is in progress. To aid in that process, research was done to understand the dynamics of a shipboard cycling system. This thesis presents an in-depth examination of the development of diagnostic indicators for a shipboard vacuum assisted waste disposal system. Measurements and experimentation were conducted onboard USCGC SENECA (WMEC-906), a 270-foot Coast Guard Cutter. In order to better understand the system dynamics, a computer based model was developed to simulate the system.; (cont.) The intent of creating an in-depth model was to develop diagnostic methods that are applicable to any shipboard cycling systems. First...

‣ Determining the Preston constants of low-dielectric-constant polymers

Eusner, Thor
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 30 leaves
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An important step in the manufacture of integrated circuits (ICs) is the Chemical Mechanical Polishing (CMP) process. In order to effectively use CMP, the removal rates of the materials used in ICs must be known. The removal rate of a given material by CMP can be determined once its Preston constant is known. The objectives of this work were to develop a method to determine the Preston constants and to measure the Preston constants of four low-dielectric-constant (low-k) polymers, labeled A, B, C, and D, and Cu. A weight-loss method, which measures the weight difference between the initial wafer and the polished wafer, provided repeatable results. The Preston constants ranged from 1.01 to 5.96 x10-'3 m2/N. The variation in measurements of the Preston constant ranged from 16% to 31%. The Preston constant of Cu was found to be 1.60 + 0.50 x10-13 m2/N. Of the four polymers, Polymer A had the smallest Preston constant, 1.01 i- 0.30 x10-13 m2/N. It was also determined that there is an approximate inverse linear relationship between the Preston constant of the four low-k polymers and their Young's moduli of elasticity. An approximate inverse linear relationship between the Preston constant of the four low-k polymers and the hardness was also observed.; by Thor Eusner.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Dahl friction modeling

Chou, Danielle, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 60 p.; 3579118 bytes; 3580611 bytes; application/pdf; application/pdf
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The drive behind improved friction models has been better prediction and control of dynamic systems. The earliest model was of classical Coulomb friction; however, the discontinuity during force reversal of the Coulomb friction model has long been a point of contention since such a discontinuity does not accurately portray the behavior of real systems. Other models have been suggested, but variations of the Dahl solid friction model remain some of the simplest yet most useful. Dahl's original theory proposed that friction behaved as a stress acting upon the quantum mechanical bonds at the interface. Thus, the relationship between frictional force and position would be analogous to a stress-strain curve, complete with hysteresis should there be permanent displacement akin to plastic deformation in materials. This project reviews the variations of Dahl friction models popular in the literature and then demonstrates it both analytically via Matlab and Simulink simulations and experimentally by observing the behavior of a limited angle torque motor.; by Danielle Chou.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.; Includes bibliographical references (p. 22).

‣ Electrodeposition of conducting polymer fibers

Chen, Angela Y. (Angela Ying-Ju), 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 36 leaves; 1732193 bytes; 1731472 bytes; application/pdf; application/pdf
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Conducting polymers are materials that possess the electrical conductivity of metals while still retaining the mechanical properties such as flexibility of traditional polymers. Polypyrrole (PPy) is one of the more commonly studied electrically conducting polymers due to its high conductivity and stability in ambient conditions. A one step electrochemical process for growing macroscopic conducting polymer fibers previously described in Li et al's article (Science, 1993) was used to grow PPy fibers. Based on a schematic of the electrochemical flow cell used in the electrodeposition process, a physical electrochemical flow cell was constructed. Several trials were carried out in an attempt to repeatedly grow polymer fibers. The fibers grown from successful trials were analyzed and characterized by qualities such as length, diameter, surface texture, conductivity, and elasticity. There is room for further study involving optimization of parameters such as temperature, monomer concentration, and flow velocity of the monomer solution.; by Angela Y. Chen.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.; Includes bibliographical references (leaf 35).

‣ Design and fabrication of an optical pressure micro sensor for skin mechanics studies; Optical pressure micro sensor for skin mechanics studies

Kumar, Siddarth
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves
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The mechanics of skin is as central to touch as optics is to vision and acoustics is to hearing. With the advent of novel imaging technologies such as the Optical Coherence Tomography (OCT), we are now able to view structures within the skin to a resolution of a few microns in vivo and non-invasively. To fully understand the role of biomechanics of the skin in interpreting touch, we need to develop a quantitative understanding of how spatio temporal loads imposed on the surface of the skin are transmitted to mechanoreceptor locations within the skin. The following thesis presents a description of the design and fabrication of an Optical Pressure Sensor Device to be used in conjunction with an Optical Coherence Tomography Apparatus to quantify loads incident on the fingerpad surface. The Optical Pressure Sensor is a five layer PDMS based device having a total thickness of 150 microns. It consists of two layers of a textured pattern separated by a layer of "Soft" PDMS of thickness 100 microns. The top and bottom protective layers are of PDMS and have a thickness of 20 microns each. "Soft" PDMS is a combination of PDMS and the silicone oil "Fluid 200" and has a Young's Modulus less than that of Human Skin.; (cont.) The entire device is fabricated bottom up on a silicon wafer using soft lithography techniques and the textured pattern is imprinted onto the PDMS using photolithography techniques. This flexible pressure sensor is designed to be used on the fingerpad skin to determine the pressure distribution due to incident loads. The sensor is placed between the OCT head and the finger pad to be imaged. The OCT head (along with the indenter) acts as the mechanical stimulus and is used to indent the finger pad. As a result of this stimulus...

‣ Dielectric elastomer actuators for binary robotics and mechatronics

Plante, Jean-Sébastien, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 186 p.; 7102066 bytes; 7158412 bytes; application/pdf; application/pdf
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Future robotics and mechatronics applications will require systems that are simple, robust, lightweight and inexpensive. A suggested solution for future systems is binary actuation. Binary actuation is the mechanical analogy to digital electronics, where actuators "flip" between two discrete states. Systems can be simple since low-level feedback control, sensors, wiring and electronics are virtually eliminated. However, conventional actuators, such as DC motors and gearbox are not appropriate for binary robotics because they are complex, heavy, and expensive. This thesis proposes a new actuation technology for binary robotics and mechatronics based on dielectric elastomer (DE) technology. DE actuators are a novel class of polymer actuators that have shown promising low-cost performance. These actuators were not well understood and, as a result, faced major reliability problems. Fundamental studies conducted in this thesis reveal that reliable, high performance DE actuation based on highly viscoelastic polymers can be obtained at high deformation rates, when used under fast, intermittent motion.; (cont.) Also, analytical models revealed that viscoelasticity and current leakage through the film govern performance. These results are verified by an in-depth experimental characterizion of DE actuation. A new DE actuator concept using multi-layered diamond-shaped films is proposed. Essential design tools such as reliability/performance trade-offs maps...

‣ System identification and optimal control for mixed-mode cooling

Spindler, Henry C. (Henry Carlton), 1970-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 319 p.; 22793987 bytes; 22836775 bytes; application/pdf; application/pdf
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The majority of commercial buildings today are designed to be mechanically cooled. To make the task of air conditioning buildings simpler, and in some cases more energy efficient, windows are sealed shut, eliminating occupants' direct access to fresh air. Implementation of an alternative cooling strategy-mixed-mode cooling-is demonstrated in this thesis to yield substantial savings in cooling energy consumption in many U.S. locations. A mixed-mode cooling strategy is one that relies on several different means of delivering cooling to the occupied space. These different means, or modes, of cooling could include: different forms of natural ventilation through operable windows, ventilation assisted by low-power fans, and mechanical air conditioning. Three significant contributions are presented in this thesis. A flexible system identification framework was developed that is well-suited to accommodate the unique features of mixed-mode buildings. Further, the effectiveness of this framework was demonstrated on an actual multi- zone, mixed-mode building, with model prediction accuracy shown to exceed that published for other naturally ventilated or mixed-mode buildings, none of which exhibited the complexity of this building. Finally, an efficient algorithm was constructed to optimize control strategies over extended planning horizons using a model-based approach. The algorithm minimizes energy consumption subject to the constraint that indoor temperatures satisfy comfort requirements. The system identification framework was applied to another mixed-mode building...

‣ High-precision position control of a heavy-lift manipulator in a dynamic environment

Garretson, Justin R. (Justin Richard)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 88 leaves; 4213321 bytes; 4217475 bytes; application/pdf; application/pdf
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This thesis considers the control of a heavy-lift serial manipulator operating on the deck of a large ocean vessel. This application presents a unique challenge for high- precision control because the system must contend with both high levels of joint friction and oscillatory motions in the manipulator's base. Due to the uncontrolled outdoor environment, the behavior of these disturbances in the field cannot be accurately predicted using models developed offline. To achieve high-precision control, the system must therefore be capable of effectively estimating and compensating for these disturbances online. This thesis presents the design of a position control system to allow high-precision control of the manipulator's payload by a human user. The design features a standard decentralized linear control architecture augmented by a combination of adaptive and sensor-based techniques to estimate and compensate for base-motions and joint friction. A procedure is also suggested by which a parametric friction model can be extracted from adaptive estimates recorded over a period of time. This extracted model can be used to temporarily replace the adaptive estimation in compensating for joint friction when the manipulator is in contact with the environment. Performance of the control methods developed here are evaluated using simulation studies conducted with a high-fidelity dynamic model of the mechanical system. These studies demonstrate the tracking capability of the control system for various representative tasks.; by Justin R. Garretson.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ The effects of glycosaminoglycan content on the compressive modulus of chondrocyte seeded type II collagen scaffolds; Effects of GAG content on the compressive chondrocyte seeded type II collagen scaffolds

Pfeiffer, Emily (Emily R.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 42 p.
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This study examines glycosaminoglycan (GAG) density and aggregate compressive modulus HA of engineered cartilaginous implants. Culture parameters were developed to cause the goat articular chondrocyte seeded type II collagen scaffolds to generate 25 and 50% of the natural biochemical content of articular cartilage, with an overall goal of identifying construct compositions that might provide the most favorable response when implanted into defects in articular cartilage. Several scaffold cross-link densities were compared across constructs cultured in vitro to several time-points. The compressive modulus HA was measured through unconfined compression. One group of scaffolds averaged a compressive modulus one order of magnitude below that of natural tissue. Histological analysis verified that a chondrogenic phenotype was maintained and revealed a concentration of tissue development in the center of most scaffolds. This work includes a design for an original mechanical test apparatus for measuring the Poisson's ratio of the samples, enabling meaningful interpretation of indentation test results.; by Emily Pfeiffer.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (p. 34-36).

‣ Critical temperatures of superconducting solders

Pavão, Erica Medeiros
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 30 p.
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Different magnetic strengths in MRIs produce different reactions and provide more insight into what being imaged. Being able to more quickly switch between two or more different magnet strengths would allow scientists in research to be able to gather more useful data. Replacing the persistent-current switch (PCS), which needs to be warmed beyond its critical temperature at times in order to charge or discharge the magnet, with a mechanical switch that can be kept at its superconducting stage may be able to speed up the charging/discharging process. A malleable superconductor would be needed for the current pending design of this switch. A superconducting solder with a critical temperature above 4.2K would be ideal. This experiment uses a bucket Dewar and a cryocooler to attempt to cool the solders to 4.2K and determine at which temperature they become superconducting. The setup, however, was not capable of measuring any of the four tested solders' critical temperature. Reasons for this may include poor thermal contact between the sample and the cryocooler and excessive noise that overpowers small voltages.; by Erica Medeiros Pavão.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (p. 30).

‣ Design of an autonomous underwater vehicle to evaluate the blazed array sonar and simultaneous localization and mapping algorithms; Design of an AUV to evaluate the blazed array sonar and simultaneous localization and mapping algorithms

Uhle, Matthew William
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 14 leaves
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This thesis has investigated aspects of the design of a new highly maneuverable Autonomous Underwater Vehicle - the XAUV. The overall goal for the design of this vehicle is to create a small, highly maneuverable AUV that can perform autonomous ship hull inspection. Our work towards this goal was targeted to three different aspects: (1) contributions to the conceptual design of the overall vehicle, (2) specification and acquisition of the electronic components of the vehicle, including its main CPU, and (3) mechanical design of selected components, including the ship's hull, servo-controlled fin system, and blazed array sonar nose cone. These contributions have helped to improve and realize the design of the first prototype XAUV, which is expected to be completed in May, 2007, through the work of other members of the design team.; by Matthew William Uhle.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (leaf 14).

‣ Integrated optical switching using titanium nitride micro electromechanical systems

Takahashi, Satoshi, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95, [32] p.; 5151871 bytes; 5157156 bytes; application/pdf; application/pdf
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This thesis reports an integrated optical wavelength specific switching device for applications in optical integrated circuits (OICs) based on micro electromechanical systems (MEMS). The device consists of a ring resonator add-drop filter and a conductive MEMS bridge which is actuated by electrostatic force. Introducing conductive material into the electromagnetic evanescent field of the ring waveguide results in loss in the propagating light within, disabling the resonance and the filtering capabilities of the ring resonator. Therefore, by actuating the MEMS bridge in and out of the waveguide's evanescent field, the filter can be toggled between the on and off states. One large problem that must be faced when fabricating and actuating a MEMS cantilever or bridge structure for this type of device is the residual stress that may deflect the structure in an undesired way. This is because the vertical displacement of the structure is crucial. In order to solve this problem, this thesis is based on the use of titanium nitride (TiN) as structural material for the bridge. Titanium nitride has very attractive mechanical properties as well as good conductivity, which makes it an ideal structural material for electrostatically actuated devices.; (cont.) Moreover...

‣ Simulation of actin cytoskeleton structure and rheology

Kim, Taeyoon, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 153 p.
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Structures consisting of G-actin or other filament-forming monomers show a variety of morphologies with widely different properties in regard to pore size, degree of isotropy, and extent of cross-linking. These characteristics are primarily determined by the concentration and feature of proteins which cross-link filaments, but little is known how the filament-forming monomers and cross-linking proteins are organized in order to produce various network morphologies. In addition, it's generally known that mechanical force plays an important role in the physiology of eukaryote cells whose major structural component in cortex is actin cytoskeleton. Thus, understanding the origin of viscoelasticity of cross-linked networks should be crucial to figure out the exact role of cytoskeletal behaviors in many cellular functions. Here, we introduce a Brownian dynamics (BD) simulation model in three dimensions in which actin monomers polymerize into a filament and become cross-linked by two types of cross-linking molecules that constitute either perpendicular or parallel cross-links. We evaluate the influences of system parameters on the morphology of resultant networks. Some scaling behaviors that are independent of the specific choice of most parameters appear.; (cont.) Additionally...

‣ Mechanics of inelastic deformation and delamination in paperboard

Xia, Qingxi, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 236 p.; 14268980 bytes; 14268735 bytes; application/pdf; application/pdf
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Paperboard is one of the most widely used materials. The inelastic deformation of paperboard plays a crucial role during many manufacturing processes (e.g., the converting process whereby paperboard is converted into a product such as a milk carton by punching and subsequent folding) and during in-service applications. There is a scarcity of constitutive models describing inelastic behavior of paperboard under complex loading, despite the paper industry's great need of analytical tools to aid the design and manufacturing of better paperboard products. In this thesis, two constitutive models are developed to model the highly anisotropic, elastic-plastic behavior of paperboard/paper: (1) A three-dimensional elastic-plastic interface constitutive model is developed to model the out-of-plane delamination behavior of paperboard. The onset of interface separation is controlled by a limit surface in the normal-shear traction space. The limit surface is taken to shrink with a monotonically-increasing scalar internal variable reflecting damage associated with the history of inelastic relative interface displacement. (2) A three-dimensional, anisotropic continuum constitutive model is developed to model the in-plane elastic-plastic deformation of paper and paperboard. The proposed initial yield surface is directly constructed from the yield strengths measured in various loading directions and the corresponding ratios of plastic strain components. An associated flow rule is used to model the plastic flow of the material. Anisotropic strain-hardening of yield strengths is introduced to model the evolution of the yield surface with inelastic strain.; (cont.) The two constitutive models are implemented into finite element software to enable the simulation of paperboard mechanical behavior under complex...

‣ Design and construction of a human powered vehicle seating simulator for diagnostic testing

Lichter, Harry (Harry J.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 24 leaves
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A seating simulator was built to test the influence of various seating positions on human cycling power output. The simulator measures a rider's physical stress required to produce a certain power output. A heart rate monitor is used to find the rider's physical stress level. The theory is that the best shaped seat will allow the rider to pedal most efficiently. The seat of the simulator can easily be changed by connecting the seat's support strings to a square grid of holes. Mechanical power flows from the simulator's bike pedals through a chain drive to an electric motor. Electrical power flows from the electric motor through a rectifier to a variable bank of resistors. There were issues which came up involving the bike parts used and the dynamics of the chain drive system. The worst problem was that the supports would flex causing the chain to slacken and resonate under the changing forces of the pedaling motion. First a steel pipe was added to make the system more rigid. Then a sliding copper derailleur was used to allow the chain to stay on up to 213 watts. Finally the copper derailleur was replaced with a bike's derailleur which allows the simulator to operate in excess of 450 watts. Initial tests of several different seat configurations were completed with notable influence on the heart rate of the rider.; by Harry Lichter.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ A collagen based scaffold for the repair of annulus fibrosus defects

Saad, Leonide C. (Leonide Camile), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 162 p.
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The intervertebral disc (IVD) is the natural cartilaginous cushion found between the osseous vertebrae of the spinal column. It is an essential element for the flexibility of the spine but undergoes major degeneration with age, resulting in the loss of its functionality and in back and leg pain. Due to the large size of the IVD, its avascular nature and the difficulty for nutrients and waste particles to diffuse in or out of the IVD, damage and defects incurred by the IVD, be they natural or accidental, are very unlikely to heal and often trigger faster degeneration. The annulus fibrosus (AF) defines the outer boundaries of the disc and provides the structural integrity of the IVD. The purpose of this thesis was to evaluate the regenerative potential of a collagen type II scaffold on standardized defects of the AF. Specifically, this thesis evaluated in vitro the effects of the culture conditions, of a select group of growth factors, of the cross-linking method and of the biochemical composition of the scaffold, in the perspective of preparing a suitable autologous cell-seeded implant for a goat animal model. Cross-linking method and the presence of GAG dramatically affected cell proliferation and new tissue synthesis, with the most promising results obtained with dehydrothermal treatment (DHT) cross-linking and with scaffolds containing 5 to 10% of chrondroitin-6-sulfate.; (cont.) Autologous cells seeded in this promising scaffold and cultured in a serum-free environment supplemented with a mix of Transforming Growth Factor-[beta]1 and Fibroblast Growth Factor-2...

‣ Robotic technology to aid and assess recovery and learning in stroke patients

Palazzolo, Jerome J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 343 p.; 19214204 bytes; 19229359 bytes; application/pdf; application/pdf
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Each year, about 700,000 people in the United States have a stroke, making it a leading cause of serious, long-term disability. Modalities of therapy often assume the processes underlying motor recovery and motor learning are similar because both exhibit activity- dependent neural plasticity. However, the impact of other factors unique to recovery such as re-acquisition of muscle strength and resolution of abnormal muscle tone confounds the validity of this assumption. By implementing an adaptive impedance controller that collapses from a "virtual slot" between two targets to a "virtual spring" at the desired target, a new performance-based progressive therapy (PBPT) algorithm was developed to test whether recovery would be enhanced by incorporating learning strategies like repetition, goal specification, and positive reinforcement. A study of chronic stroke patients (8 to 95 months post-stroke) who were in a clinically verified "stable" phase of recovery was conducted with the PBPT protocol, in which patients made over 12,000 visually guided, point-to-point movements.; (cont.) Though prior clinical results suggested that recovery would plateau 6 months post-stroke, two studies using sensorimotor (SM) and progressive resistance (PR) therapy protocols achieved significant...

‣ An internal variable theory for isotropic visco-elastic-plastic solids : application to indentation of amorphous polymeric solids

Ames, Nicoli M. (Nicoli Margret), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 92 leaves; 6267944 bytes; 6273494 bytes; application/pdf; application/pdf
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A significant advance in modeling the plastic deformation of amorphous polymers has been made by Parks, Argon, Boyce, Arruda, and their co-workers (e.g. Parks, Argon, & Bagepalli, 1985; Boyce, Parks, & Argon, 1998; Arruda & Boyce, 1993), and by Wu and Van der Giessen (1993). Although these models phenomenologically capture the large deformation elastic-viscoplastic response of these materials in a reasonably accurate manner, they do not adequately account for the creep response of these materials at stress levels below those causing "macro-yield", as well as the Bauschinger-type reverse yielding phenomena at strain levels less than ~ 30% associated with the macro-yield transient. Anand (2003) has recently generalized the model of Anand and Gurtin (2003) to begin to capture these important aspects of these material's mechanical response. In this work, we summarize Anand's three-dimensional theory and then specialize the constitutive equations to an approximate one-dimensional form. Also, we describe our monotonic, cyclic and creep experiments on the amorphous polymeric solid poly(methyl methacrylate) (PMMA), at ambient temperature and stress states under which this material does not exhibit crazing, and we outline detailed procedures for material parameter determination from these experiments. We have implemented the three-dimensional constitutive equations in the finite-element computer program ABAQUS/Explicit (ABAQUS...

‣ Design and analysis of fingernail sensors for measurement of fingertip touch fouce and finger posture

Mascaro, Stephen A. (Stephen Austin)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 148 leaves; 10246167 bytes; 10245975 bytes; application/pdf; application/pdf
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A new type of wearable sensor for detecting fingertip touch force and finger posture is presented. Unlike traditional electronic gloves, in which sensors are embedded along the finger and on the fingerpads, this new device does not constrict finger motion and allows the fingers to directly contact the environment without obstructing the human's natural haptic senses. The fingertip touch force and finger posture are detected by measuring changes in the coloration of the fingernail; hence, the sensor is mounted on the fingernail and does not interfere with bending or touching actions. Specifically, the fingernail is instrumented with miniature light emitting diodes (LEDs) and photodetectors in order to measure changes in the reflection intensity when the fingertip is pressed against a surface or when the finger is bent. The changes in intensity are then used to determine changes in the blood volume under the fingernail, a technique termed "reflectance photoplethysmography." By arranging the LEDs and photodetectors in a spatial array, the two-dimensional pattern of blood volume can be measured and used to predict the touch force and posture. This thesis first underscores the role of the fingernail sensor as a means of indirectly detecting fingertip touch force and finger posture by measuring the internal state of the finger. Desired functionality and principles of photoplethysmography are used to create a set of design goals and guidelines for such a sensor.; (cont.) A working miniaturized prototype nail sensor is designed...

‣ Neural adaptive mechanisms in respiratory regulation : theory and experiments

Young, Daniel Laurence
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 215 p.; 9701899 bytes; 9701705 bytes; application/pdf; application/pdf
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The respiratory regulatory system is an example of a complex biological control system. The principle goal of the regulator is to preserve the chemical balance of 02, CO2 and pH in the body. Although much is known about the visceral aspects of the respiratory control system, such as lung anatomy, gas exchange, and the mechanics of breathing, considerably less is understood about the neural centers in the brainstem that give rise to known varied respiratory responses. A more complete understanding of respiratory regulation necessitates better knowledge of these underling brain mechanisms. While the task of breathing may seem straightforward, the respiratory system faces many challenges that threaten to perturb homeostasis. It has been shown that the respiratory system adapts itself to better meet changing conditions, for example to meet the stresses of high altitude or increased airway resistance. The question remains then: what neural processes in the brainstem controller participate to engender such sophisticated autonomic regulation? The primary aim of this thesis was to uncover and characterize the central adaptive mechanisms involved in modulating respiratory output. A series of in-vivo animal studies is presented that were designed to elucidate the organizational and functional principles of neural adaptation intrinsic to the respiratory control centers. In these open-loop experimental studies...