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‣ Modelagem e projeto de módulos amplificadores e comparadores em tecnologia CMOS 0,35um; Analysis and design of amplifiers and comparators modules in cmos 0.35um technology

Cortes, Fernando da Rocha Paixao
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
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Diferente do projeto de sistemas digitais, no qual as técnicas de projeto e ferramentas CAD vêm apresentando uma crescente evolução acompanhada da redução de seus preços, o projeto de sistemas analógicos CMOS ainda apresenta uma forte correlação com a experiência do projetista. Dentro deste contexto, importantes fatores como caracterização de tecnologia, modelamento de dispositivos e metodologia de projeto devem ser considerados. Este trabalho apresenta um estudo destes importantes fatores necessários para se realizar o projeto de um sistema analógico com menor custo, bom desempenho e reduzido tempo de projeto. Primeiramente, é necessária uma extensa caracterização da tecnologia CMOS a ser usada, onde os parâmetros que descrevem as caracteristicas elétricas dos dispositivos são obtidos. A partir desta caracterização e das especificações requeridas para o circuito, é feita uma modelagem e sintese a fim de se obter as dimensões dos transistores. Ferramentas para a análise do desempenho elétrico são utilizadas a seguir, antes de se realizar a descrição geométrica (layout) do circuito. Com o layout pronto, uma nova simulação elétrica é feita incluindo os efeitos geométricos, incluindo-se os parasitas R...

‣ Characterization of mucosal dysplasia with ultraviolet resonance Raman spectroscopy; Characterization of mucosal dysplasia with UVRR

Boustany, Nada
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 160 leaves; 14429738 bytes; 14429493 bytes; application/pdf; application/pdf
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by Nada Boustany.; Thesis (Ph. D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 1997.; "August, 1997."; Includes bibliographical references.

‣ Stochastic characterization of chronic ventricular ectopic activity

Albrecht, Paul, 1956-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 289 leaves; 14695962 bytes; 14728873 bytes; application/pdf; application/pdf
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by Paul Albrecht.; Thesis (Ph.D.)--Harvard-Massachusetts Institute of Technology Division of Health Science and Technology Program in Medical Engineering and Medical Physics, 1986.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.; Bibliography: leaves 277-289.

‣ Characterization of a peptide biomaterial used for cell-seeded scaffolds with an analysis of relevant stem cell policy

Kim, Gina
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 7007829 bytes; 142 p.; 7015540 bytes; application/pdf; application/pdf
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(cont.) We describe the ethical debate and political climate that led to the decision. An examination of the publication data shows that researchers in the United States have in fact remained leaders in the field until this point, in part because U.S. federal funding has also been available to early mover international groups who appear to have abided by the restrictions.; Restoring damaged or diseased tissue in the body may involve the use of biomaterial scaffolds that provide a responsive environment for cell proliferation. Such scaffolds may be used for in situ cell regeneration, where an implanted scaffold incites cell growth in the body, as well as for growing artificial tissue in vitro by seeding cells in a scaffold that will be implanted at a later stage of development or used for physiological tissue models. The research outlined in this thesis describes two methods of characterizing the stiffness of a biomaterial scaffold. It is well known that cell growth in vitro is affected by the moduli of the surrounding scaffold. Stiffness is also cited as a major factor affecting angiogenesis, the formation of new blood vessels. We describe a new rheometric method to examine the bulk mechanical properties of a self-assembling peptide biomaterial that spontaneously forms a filament network in a physiological salt solution and supports cell attachment and differentiation. This method has two major advantages: first...

‣ Characterization of human expired breath by solid phase microextraction and analysis using gas chromatography-mass spectrometry and differential mobility spectrometry

Merrick, William (William F. W.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95 leaves; 4181829 bytes; 4185745 bytes; application/pdf; application/pdf
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Breath analysis has potential to become a new medical diagnostic modality. In this thesis, a method for the analysis of human expired breath was developed using gas chromatography-mass spectroscopy. It was subsequently adopted for gas chromatography-differential mobility spectroscopy, a modality not previously applied to this problem. Tedlar bags and solid-phase microextraction were used for breath sampling and concentration prior to analysis. Four fiber coatings were evaluated with respect to selectivity and sensitivity; extraction time, gas chromatography temperature programming, and sample storage stability were explored for optimization. The method entails extraction and preconcentration with a polydimethylsiloxane-divinylbenzene coated fiber for 30 min at 37⁰C, and extraction profiles for several compounds demonstrate competitive adsorption. 120 compounds were identified in breath with response variability between 23 - 117% about mean values. Feasibility of differential mobility spectroscopy for breath analysis was established, and this method will be the basis for future investigations on the diagnostic potential of breath analysis.; by William Merrick.; Thesis (M. Eng.)--Harvard-MIT Division of Health Sciences and Technology...

‣ Characterization of Nb₃Sn superconducting strand under pure bending; Characterization of niobium-tin superconducting strand under pure bending

Harris, David L., S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 252 p.; 14298063 bytes; 14309789 bytes; application/pdf; application/pdf
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Characterizing the strain-dependent behavior of technological Nb₃Sn superconducting strand has been an important subject of research for the past 25 years. Most of the effort has focused on understanding the uniaxial tension and compression effects and applying this information to improve predictive scaling laws which are used for superconducting magnet design. However, the strain state of the strand in an actual magnet winding is often a complicated combination which includes uniaxial tension or compression, bending, and transverse compression. A bending mechanism was designed and used to characterize the bending strain behavior of two different types of Nb₃Sn superconducting strand at 4.2K in a magnetic field. Results showed that the critical current of the strand increased up to an applied bending strain between 0.2-0.3% and then decreased with continued applied strain.; by David L. Harris.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.; Includes bibliographical references (p. [247]-252).

‣ Metallurgical characterization of self catalytic structural materials for sulfuric acid decomposition

Rigual, David Andrés
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 279 p.; 23629038 bytes; 23628790 bytes; application/pdf; application/pdf
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Eight heats of material with base alloy chemistries of Alloys 800 HT or 617 with platinum additions of 2, 5, 15, or 30 wt% have been characterized according to their microstructural features. The goals of characterization were to determine metallurgical stability for service as self-catalytic structural materials. The results presented herein will be useful to the development of a material for the construction of a heat exchanger designed for sulfuric acid decomposition. This type of heat exchanger is a key component to hydrogen generation by the thermochemical sulfur-iodine water-splitting process, a future technology that promises efficient hydrogen production if coupled to a Generation IV nuclear reactor heat source. Characterization of each material was carried out in the cast and wrought conditions with optical and SE microscopy, electron dispersive spectrometry, chemical composition analysis, and thermodynamic modeling. Materials have been characterized according to grain size and morphology, precipitate features, twinning characteristics, and platinum composition effects. Results indicate that platinum and carbon compositions have the greatest effect on the development of microstructural features.; (cont.) Increasing platinum compositions in both base alloy chemistries fosters the presence of annealing twins...

‣ Process window and variation characterization of the micro embossing process

Wang, Qi, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 188 p.; 11875724 bytes; 11883666 bytes; application/pdf; application/pdf
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The micro embossing process on polymethylmethacrylate (PMMA) is demonstrated experimentally to be a useful process to produce micro fluidic and optical devices. Because this process is a one step thermoplastic deformation process, it is possible to reach high production rates and low cost in manufacturing compared to the standard clean room processes. Currently, the research about this process is still on the feasibility level, with not a quantitative work to optimize the process parameters and assure product quality. In this thesis, an experimental study on process window and variation of Micro Embossing is presented. This study includes the design and manufacturing of an embossing die, the development of an embossing product quality assessment protocol, the process window characterization and the process variation identification. The research results based on the experimental set up in this thesis show that we should apply constant 800N embossing force at an embossing velocity of 1000N/min in order to obtain well formed parts to maintain low process cycle time.; (cont.) An embossing temperature of 120°C and de-embossing temperature of 55°C are shown to be the optimal embossing condition to yield good replication and repeatability. These embossing parameters operating window can change with the variation of working piece material...

‣ Microstructure, residual stress, and mechanical properties of thin film materials for a microfabricated solid oxide fuel cell

Quinn, David John, Sc. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 184 p.
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The microstructure and residual stress of sputter-deposited films for use in microfabricated solid oxide fuel cells are presented. Much of the work focuses on the characterization of a candidate solid electrolyte: Yttria Stabilized Zirconia (YSZ). Stress and structure of reactive RF sputtered YSZ films are explored as a function of thickness (5nm - 1000nm), deposition pressure (5mtorr - 1OOmtorr), and substrate temperature (room temperature, 3000C and 6000C). Microstructure is characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Film composition, specifically impurity content, is investigated with secondary ion mass spectroscopy (SIMS). Results indicate that YSZ films likely have a columnar structure with fully cubic crystalline phases of (100) texture with mixed amorphous/crystalline phases. Residual stress is measured via substrate curvature techniques. Results indicate that the as-deposited residual stress of YSZ ranges from -1.4 GPa to 400MPa with variations in sputtering conditions. Transitions from compressive to tensile stress are identified with variations in working pressure and film thickness.; (cont.) The origins and variations in as-deposited stress are determined to be from two primary mechanisms: tensile stress due to grain coalescence/growth and compressive stresses due to forward sputtering of target atoms (also known as "atomic peening" stresses). Due to the expected high-temperature operation (-1 0000C) of microfabricated solid oxide fuel cells...

‣ Design and characterization of a compact voice coil for a needle-free injection device

Lui, Diana, S.B. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 50 leaves
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Conventional needle-free injection (NFI) devices are driven by a pressure source generated by either a compressed spring mechanism or compressed inert gas, which have fixed injection (pressure versus time) profiles. The NFI device developed at the Massachusetts Institute of Technology BioInstrumentation Laboratory (MIT BiLab) is novel in its use of a Lorentz force voice coil actuator as the pressure source. With servo-control, the applied pressure can be adjusted for injection conditions such as skin toughness and injection depth. The focus of this thesis was on designing, building and characterizing a more compact version of the current NFI device. The proposed design features a reduction of the diameter of the voice coil motor by packing empty space with an additional set of magnets. A prototype was built, and benchtop tests were conducted to characterize its force sensitivity, the stability of this force sensitivity, and the jet velocity from the syringe. The force sensitivity was found to be 8.3 N/A, and its consistency was shown to be remarkably stable throughout the stroke of the voice coil. It was found that, with a 200 V input, the voice coil exerted a force of 127 N on the syringe piston, which is equivalent to 12.7 MPa; this pressure produced a jet velocity of 162 m/s out of the syringe.; by Diana Lui.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Controlled synthesis and characterization of templated, magneto-responsive nanoparticle structures

Singh, Harpreet, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 230 leaves
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Magnetic fluids are colloidal dispersions of magnetic nanoparticles that are stable with respect to gravitational and moderate magnetic fields because of their small particle size, and to unbounded aggregation due to their surface coatings. The interaction between individual magnetic nanoparticles in a suspension is negligible even under applied magnetic fields. However, when they are incorporated into composite structures they act in concert to provide the desired magnetic response. The dynamic response of such composite structures can be exploited in a wide range of applications including high energy absorption scenarios. The goal of this thesis was to use magnetic nanoparticles as building blocks to create 3D magneto-responsive nanostructures and manipulate their behavior in the presence of an external magnetic field for various applications. Two approaches were followed to create composite structures. In the first approach, rigid magnetic chains composed of magnetic nanoparticles were synthesized. The layer-by-layer technique was used to coat polystyrene beads with magnetic nanoparticles to create novel core-shell structures. The behavior of these structures under an applied magnetic field was modeled and the results were verified experimentally.; (cont.) These magnetic polystyrene beads were then aligned within a microchannel by an external magnetic field and linked together using sol gel chemistry to yield rigid superparamagnetic chains. Linking the magnetically aligned beads with a flexible linker yielded flexible superparamagnetic chains. These permanently-linked magnetic chains can be used as micro-mixers in a microfluidic channel under a rotating magnetic field. The reorientation dynamics of these chains under an external magnetic field was modeled. Microcontact printing was employed to tether the flexible chains in a desired pattern on a glass surface. Tethered flexible magnetic chains have potential applications in microfluidics and separations. Rings and icosahedra shaped electrostatically charged templates were generated from the self-assembly of mixtures of surfactants in an aqueous solution and were investigated for their application in the synthesis of non-spherical magnetic structures. The magnetic response of the magnetic rings was modeled and the results were verified experimentally. "Templateless" aggregation of magnetic nanoparticles using radiation crosslinking was also investigated.; (cont.) Aqueous magnetic nanoparticles stabilized with a radiation crosslinkable polymer resulted in magnetic gels at high dosage amount of the ionizing radiation. Magnetic gels can have potential applications in biological areas. Different size monodisperse magnetic nanoparticles were synthesized via an organic synthesis route...

‣ Characterization in cochlea of KCTD12/PFET1, an intronless gene with predominant fetal expression

Kuo, Sharon Fan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: viii, 122 leaves
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The prevalence of severe to profound bilateral congenital hearing loss is estimated at 1 in 1000 births, at least half of which can be attributed to a genetic cause. To date, mutations in at least 67 genes have been associated with hearing loss. Discovery of these genes has revealed fundamental processes within the ear, and enabled diagnosis and implementation of genetic counseling in affected patients. As a part of the continuing effort to study genes important for hearing and deafness, a novel cochlear transcript with predominantly fetal expression containing a single tetramerization domain (PFET1, HUGO-approved symbol KCTD]2) was identified from the Morton fetal cochlear cDNA library. KCTD12/Kctd]2 is an evolutionarily conserved intronless gene encoding a 6 kb transcript in human and three transcripts of approximately 4, 4.5 and 6 kb in mouse. The protein, pfetin, is predicted to contain a voltage-gated potassium channel tetramerization (T1) domain. This thesis reports characterization of this novel human gene and its encoded protein pfetin in relation to its role in auditory function. Experimental data from tissue and cellular expression profiling, and genetic and functional analyses suggests KCTD12 and its orthologs playing a crucial role in the developmental of the auditory sense organ.; by Sharon Fan Kuo.; Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology...

‣ Biofuels supply chain characterization

Banerjee, Anindya, M. Eng. Massachusetts Institute of Technology; Noguer, José Luis
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 89 leaves
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Ethanol can be made from agricultural residues like wheat straw and from crops dedicated to energy use, like switchgrass. We study the logistics aspects of this transformation and determine the main characteristics of the supply chain making ethanol from cellulose. Important to the final acceptability of ethanol as a transportation fuel is both the economics as well as the environmental aspect of using ethanol. In this study we analyze the buildup of cost as biomass is transformed into fuel. We also look at all the steps involved and describe them from a supply chain perspective We have found that the main cost components in the cellulosic ethanol production are biomass production, harvesting and ethanol refining. We have also found that the main factor in reducing the overall production cost is the biomass to ethanol conversion factor. The development of new technologies to convert biomass into ethanol becomes a critical issue to achieve the cost targets imposed in order to make ethanol more competitive with other sources of energy such as fossil fuels. An increase in the current conversion factor of 42% could potentially yield to a decrease of nearly 15% in the: total production cost of cellulosic ethanol.; (cont.) Other factors such as increasing the refining plant size and biomass yield can also help to reduce the production cost but we found its impact to be lower than that of the conversion factor. Finally...

‣ Design of reversible "smart" surfaces for biomedical and nanotechnological applications; Design of switchable "smart" surfaces for biomedical and nanotechnological applications

Tran, Thanh-Nga T. (Thanh-Nga Trinh)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 177 leaves
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Chapter 1. An Introduction to Self-Assembled Monolayers & Surface Characterization A brief summary of the formation, structure, and characterization techniques of self assembled monolayers (SAMs) is described. The characterization techniques include contact angle goniometry, ellipsometry, grazing-angle Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), sum-frequency generation spectroscopy (SFG), and atomic force microscopy (AFM). Chapter 2. A Reversibly Switching Surface The design of surfaces that exhibit dynamic changes in interfacial properties such as wettability in response to an electrical potential is described. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed both at a molecular level using sum-frequency generation spectroscopy and at a macroscopic level using contact angle measurements. This type of surface design enables amplification of conformational transitions at a molecular level to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open new opportunities in interfacial engineering.Chapter 3. A Synthetic Chemical Route for the Formation of Homogeneously- Mixed Self-Assembled Monolayers A novel way to produce self-assembled monolayers (SAMs) uniformly mixed on the molecular length scale is described.; (cont.) Initially...

‣ Assessing the economic case for stratified medicine; Economic case for stratified medicine

Goren, Amir, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 39 leaves
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The goal of this study is to explore the economic conditions that favor the joint development of therapeutics and companion diagnostics. I hypothesize that predictive biomarkers can generate economic value in drug development by increasing success rates. I construct an economic model of the development of a hypothetical new therapy, and devote particular attention to parameters regarding safety, efficacy, cost, and market size, within a decision-theoretic framework. The results include a characterization of the dynamic net present value trade-offs between stratum size and biomarker success, as well as the identification of two complementary concepts of stratified medicine, namely, disease reclassification and value-based reimbursement. I also identify a strong potential incentive mechanism in the hands of public policy makers that could facilitate a resolution of the tension between patient interests and the interests of pharmaceutical sponsors. The conclusion is that a biomarker can compensate for smaller stratum by increasing success probabilities. However, the effects of longer development time due to biomarker inclusion counter the effects of improved success probabilities. Longer exclusivity periods for stratified medicine may be required in order to resolve the tension between patient interests and the interests of pharmaceutical sponsors.; by Amir Goren.; Thesis (S.M.)--Harvard-MIT Division of Health Sciences and Technology...

‣ Electrospinning of polymeric nanofiber materials : process characterization and unique applications

Yu, Jian Hang, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 p.
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Electrospinning or electrostatic fiber spinning employs electrostatic force to draw a fiber from a spinneret. This fiber solidifies and lies down on a collector in the form of a non-woven fiber mat. Electrospinning has attracted much attention recently due to the ease with which fine fibers about 10 nanometers to 10 microns in diameter can be produced from both natural and synthetic polymers. Despite the large volume of publications on this technology, few publications discuss the mechanics of electrospinning. Most publications deal with the exploratory works on what material can be electrospun and the potential applications of the electrospun fibers. This work examined the electrohydrodynamics of the electrospinning process and developed this technology for making functional materials. The first part of this dissertation deals with the electrohydrodynamics of the process. The effects of processing parameters and material properties on the size and structure of electrospun fibers were studied. The experimental findings validated the analytical scaling model developed by Fridrikh and co-workers to predict how the final radius or "the terminal jet radius" of the electrospun fiber depends on the processing parameters.; (cont.) The scaling formula is derived from the force balance between surface tension and surface charge repulsion. The scaling model provides a powerful tool for controlling the fiber diameter just by adjusting the surface tension...

‣ Design and characterization of Hover Nano Aerial Vehicle (HNAV) propulsion system; Design and characterization of HNAV propulsion system

Sato, Sho, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 321 p.
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On October 4th 2005, DARPA released a request for proposals for a Nano-Air Vehicle (NAV) program. The program sought to develop an advanced urban reconnaissance vehicle. According the requirement imposed by DARPA, the NAV was to have dimensions smaller than 7.5 cm in diameter, and a weight of approximately 10 grams, to allow indoor operation. On top of these requirements, this vehicle was to operate for about 20 minutes, and have a low noise signature to avoid risk of detection. This thesis addresses the propulsion system required to enable the DARPA NAV. In particular, a rotary-wing vehicle is favored because of its high efficiency and simplicity. One large challenge faced for this design is the torque canceling mechanism to counter the torque produced by the rotating rotor. To provide a reasonable torque canceling, the solution proposed here is to use a rotating motor inside the vehicle. One rotor will be attached to the shaft of the motor and the other to a motor body that is left free to rotate inside the vehicle. By letting the motor rotate freely inside the body, the torque is cancelled automatically without a gearbox. In addition to this passive torque canceling mechanism, a novel approach is used in the fabrication approach of the motor in order to maximize the power density of this propulsion system. This new fabrication method involves the use of flexible printed circuit for the stator of the motor...

‣ Lorentz force actuator and carbon fiber co-winding design, construction and characterization

Chen, Yi, S. B. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 76 p.
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Carbon fiber composites are materials that present many benefits to engineering applications, ranging from aerospace to medicine. This thesis provides background on carbon fiber properties and manufacturing techniques, and outlines the methodology for manufacturing a co-wound carbon fiber and copper coil for use in linear Lorentz force actuators. A conventionally-wound, plastic-bobbin actuator coil and the new, co-wound coil were then tested to compare their electrical, thermal, and mechanical performance. In a needle-free injection application, the cowound coil demonstrated improved performance over the conventional coil configuration. The carbon fiber coil is lighter by 3.75 ± 0.155 grams, increases the transient heat transfer by 15.7 %, is 2.18 ± 0.13 times stiffer, and can survive a higher compressive force than the conventional plastic bobbin.; by Yi Chen.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.; Includes bibliographical references (p. 66-67).

‣ Characterization of macro-length conducting polymers and the development of a conducting polymer rotary motor

Schmid, Bryan D. (Bryan David), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 145 leaves; 7386032 bytes; 7393791 bytes; application/pdf; application/pdf
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Conducting polymers are a subset of materials within the electroactive polymer class that exhibit active mechanical deformations. These deformations induce stresses and strains that allow for conducting polymers to be used as an actuator for mechanical devices. Incorporation of conducting polymer actuators into mechanical devices requires electrochemical and mechanical characterization of varying polymer sample sizes and their active properties. Of particular interest, is the characterization of macro-length polymer samples, which have yet to be investigated. An understanding of conducting polymer films and their feasibility as an actuator in a mechanical device are required for the development of a conducting polymer based rotary motor. The conducting polymer, polypyrrole, was studied for its feasibility as an actuator for control surfaces on autonomous underwater vehicles. Enhancements to the actuator's performance were addressed following the feasibility study. The development of an electrochemical dynamic mechanical analyzer provides an instrument for characterization of the polymer's properties over a variety of sample sizes and actuation conditions. Finally, the application of polypyrrole as an actuator and possible enhancements combined with the characterization of macro-length polymers provides the necessary tools to develop a rotary motor. Enhancements to polypyrrole actuators in this study account for an increase in tip force of 350% and a seven fold increase in achievable strain.; (cont.) Completion of a novel electrochemical dynamic mechanical analyzer...

‣ Characterizing radio channels : the science and technology of propagation and interference, 1900-1935

Yeang, Chen-Pang.
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 429 p.
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Guglielmo Marconi's trans-Atlantic wireless experiment in 1900 marked the beginning of a communication revolution that transformed the open space above the earth into channels of information flow. This dissertation grapples with the historical conditions that gave rise to such a transformation: the studies of radio-wave propagation and the treatments of radio interferences in early twentieth-century America and Western Europe. The part on propagation examines the debate between the surface diffraction theory and the atmospheric reflection theory for long waves, the development of the ionic refraction theory for short waves, the evidential quests for the existence of the ionosphere, and the studies of the geomagnetic effects on propagation. The part on interferences focuses on the engineering efforts toward the characterization of atmospheric noise and signal-intensity fluctuations, the policies of radio-channel allocation for fighting man-made interference, and the scientific research into electronic tube noise. By the mid-30s, the results from these endeavors had considerably improved the quality of radio communication. Characterizing Radio Channels builds a bridge between the history of science and the history of technology by inspecting an immaterial engineering entity--radio channels--whose control required significant scientific research. In the history of science...