Página 7 dos resultados de 2573 itens digitais encontrados em 0.079 segundos

‣ Bimetallic bars with local control of composition by three-dimensional printing

Techapiesancharoenkij, Ratchatee, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 112 p.; 1551479 bytes; 1998869 bytes; application/pdf; application/pdf
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Three Dimensional Printing (3DP) is a process that enables the fabrication of geometrically complex parts directly from computer-aided design (CAD) models. The success of 3DP as an alternative manufacturing technology to bulk machining of materials for complex parts has been demonstrated. By proof of concept, 3DP has demonstrated the ability to create parts with Local Control of the Composition (LCC). LCC allows tailoring the material properties in regions of a part for functional purposes. In this work, LCC was studied and demonstrated by fabricating bimetallic bars consisting of two layers of Fe-Ni alloys with different composition and, hence, different thermal expansion properties; the coefficient of thermal expansion (CTE) of Fe-Ni system is sensitive to its composition. Two types of the binder/dopant slurries were made for making the LCC bars. One type consisted of dispersions of Fe₂O₃ particles in water, and the other consisted of dispersion of NiO in water. The LCC bars were successfully made by printing the Fe₂O₃/NiO slurries into Fe-30Ni base powders. After heat treatment to impart strength to the printed bars, the bars were successfully retrieved from unbound powders. The bars, then, were annealed at 1400 ⁰C for 2 hours for sintering and homogenization. The final composition of the base powders were changed accordingly. In the layers on which an Fe₂O₃ slurry was printed...

‣ Grain size effects on the fatigue response of nanocrystalline materials

Hanlon, Timothy, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 158 p.; 5653368 bytes; 11346872 bytes; application/pdf; application/pdf
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The resistance of metals and alloys to fatigue crack initiation and propagation is known to be influenced significantly by grain size. Based on a wealth of experimental results obtained from microcrystalline metals, where the grain size is typically greater than 1 um, it is widely recognized that an increase in grain size generally results in a reduction in the fatigue endurance limit. On the other hand, a coarser grain structure can lead to an increased fatigue threshold stress intensity factor range, as well as a decrease in the rate of fatigue crack propagation. The relevance of these trends to ultra-fine-crystalline metals (grain size between 100 nm and 1000 nm) and nanocrystalline metals (grain size less than 100 nm) is relatively unknown. Such lack of understanding is primarily a consequence of the paucity of experimental data on the fatigue response of metals with very fine grains. In this work, the fatigue behavior of electrodeposited, fully dense, nanocrystalline pure Ni, with average and total range of grain sizes well below 100 nm, was examined. The fatigue response of nanocrystalline Ni was also compared with that of ultra-fine-crystalline and microcrystalline Ni wherever appropriate. It was found that grain refinement to the nanocrystalline regime generally leads to an increase in resistance to failure under stress-controlled fatigue whereas a deleterious effect was seen on the resistance to fatigue crack growth. To explore the generality of the above trends...

‣ The impact of improved materials in poly(vinyl chloride)-based endotracheal tubes

Domike, Kristin Rebecca, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 71 leaves; 4987553 bytes; 4994618 bytes; application/pdf; application/pdf
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Endotracheal tubes (ETs) are used to aid artificial ventilation in millions of medical patients every year and are known to invoke the proliferative phase in the cell linings. The technical objective of this work was to investigate in vitro the interaction between epithelial cells and current poly(vinyl chloride)-based ET materials, as well as some ET samples embedded with materials intended to improve biocompatibility properties of the tubes. Cells were grown in wells with small samples of ETs and proliferation and migration were observed using phase microscopy. ETs appeared to increase cell growth wherever cells came into contact with the material. The cell morphology altered once in contact with the ET sample. Cell growth on and around the ETs with embedded material appeared to slow, but had significant visible changes in cell morphology. The need for continued research in this area of research and development and future steps are addressed. A proposal for starting a company around a safer material for use in endotracheal tubes was developed and showed significant barriers to entry for a small medical device company with a single product. Subsequently, the most appropriate approach for bringing a new ET to the market would be by way of a licensing with an existing manufacturer.; by Kristin Rebecca Domike.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ MOCVD growth of In GaP-based heterostructures for light emitting devices; Metalorganic chemical vapor deposition growth of In GaP-based heterostructures for light emitting devices

McGill, Lisa Megan, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 205 p.; 9286017 bytes; 9285825 bytes; application/pdf; application/pdf
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In this work, we examine fundamental materials processes in the growth of indium gallium phosphide (InGaP) via metalorganic chemical vapor deposition (MOCVD). In particular, we realize improvements in the epitaxial integration of high-quality InGaP device materials on non-standard platforms, such as GeSi graded buffers orSi substrates, and InGaP or indium aluminum gallium phosphide (InAlGaP) graded buffers on GaP substrates. We apply these improvements to the design and implementation of strained-InGaP quantum-well light emitting diodes (LEDs) operating in the yellow-green region of the visible spectrum. The innovative use of these traditional materials is intended to provide a solution for bright green solid-state light emitters. Initial modes of InGaP lattice-matched epitaxy on GeSi were studied. Three- dimensional growth was observed over a wide range of deposition temperatures and V/III ratios. Pre-growth thermal cycling in a H2 plus PH3 ambient led to a large increase in surface roughness and the formation of surface mesas. Thermodynamic simulations suggest that these mesas may be P clusters or GeP solid complexes. They may also be surface oxides formed in conjunction with water vapor in the deposition chamber. Such surface degradation prior to the initiation of epitaxy is unfavorable for monolayer growth. The development and evolution of defect microstructures in relaxed...

‣ An investigation of the high cycle fatigue behavior of bovine trabecular bone

Hastings, Abel Z., 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 79 p.; 2385407 bytes; 2385215 bytes; application/pdf; application/pdf
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Fractures can be caused by fatigue loading due to prolonged exercise and age-related fragility. Fatigue loading causes microdamage in bone that leads to both a loss of stiffness and strength. Some engineering materials, such as steels, have a fatigue limit, which is represented by a stress plateau in the stress-life (S-N) curve. When loaded to levels below the stress plateau, these materials have an infinite fatigue life. Other materials, such as aluminum, do not exhibit a fatigue limit. For these materials, the endurance limit is defined as the stress amplitude corresponding to a somewhat arbitrary large number of cycles of fatigue (e.g. various texts suggest 10⁶ to 10⁸ cycles ). In previous work on compressive fatigue of bovine trabecular bone, it was hypothesized that there was a fatigue limit at a normalized stress, [Delta] [rho]/E₀, of approximately 0.0035. This study tested this hypothesis by fatigue testing bovine trabecular bone loaded to one of four normalized stresses ranging from 0.0015 to 0.0035. Failure was defined as a 10% loss in the secant modulus of the specimen. The data show that the rate of decrease of modulus reduction per cycle increased with increasing normalized stress. A fatigue limit in bovine trabecular bone was not found. While a threshold below which the fatigue life is infinite was not found...

‣ Sputtered silicon oxynitride for microphotonics : a materials study

Sandland, Jessica Gene, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 134 leaves; 5506996 bytes; 5524537 bytes; application/pdf; application/pdf
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Silicon oxynitride (SiON) is an ideal waveguide material because the SiON materials system provides substantial flexibility in composition and refractive index. SiON can be varied in index from that of silicon dioxide (n=1.46) to that of silicon-rich silicon nitride (n-2.3). This flexibility in refractive index allows for the optimization of device performance by allowing trade-offs between the advantages of low-index contrast systems (low scattering losses and easy fiber-to-waveguide coupling) and the benefits of high-index-contrast systems (small waveguide size and tight bending radii). This work presents sputter processing as an alternative to traditional CVD processing. Two room-temperature SiON sputter processes are explored. The first process is a co- sputtered deposition from a silicon oxide and a silicon nitride target. The second is a reactive sputtering process from a silicon nitride target in an oxygen ambient. Silicon nitride sputtered from a silicon nitride target is also investigated. Models are provided that predict the index and composition in both the reactive and co- sputtered depositions. The cosputtered deposition is shown to follow a mixture model, while the reactive sputter deposition is shown to be either Si-flux limited or O-flux limited...

‣ Operational sustainability metrics : a case of electronics recycling

Atlee, Jennifer Robinson
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 127 p.; 10729810 bytes; 10736001 bytes; application/pdf; application/pdf
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In the past 15 years corporations and governments have developed a growing appreciation of the need for "sustainability" and have worked the term into their goals, strategy and mission statements. Despite extensive efforts to define the term, there is still little clarity on how to move toward sustainability or measure improvements. Further advances toward sustainability will require system specific metrics to assess both current performance and the impact of operational, technological or regulatory changes on that performance. Not only are there currently few operational metrics by which to practically assess progress toward sustainability, there is also very little understanding of how to judge the effectiveness of such metrics. Electronics recycling is used in this thesis as a case problem in developing and evaluating system specific performance metrics for sustainability. Electronics recycling is a growing national and international concern due to the increasing volume of waste, the potential toxicity of the scrap, and reports of improper handling and disposal. Despite this concern, there is limited understanding about the electronics recycling system. There is a need for systematic ways to describe system functioning and quantitative methods to assess system performance. Existing evaluations of eco-efficiency or sustainability are either too aggregated to guide operational decisions or too complex and data intensive to be performed in the context of a low-margin system. A range of performance metrics were developed and assessed for several electronics recycling operators. These included measures of resource recovery and environmental performance.; (cont.) These metrics were assessed for their ability to provide insights on resource efficiency comparable to more complex indicators...

‣ Novel potentials for the simulation of polyethylene and other polymeric systems

Waksman, George
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 59 leaves; 1945360 bytes; 1946818 bytes; application/pdf; application/pdf
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Throughout the history of science, people have been developing models to explain reality. The advent of computer technology has made it possible to devise and implement incredibly complicated numerical models in a relatively short period of time; for example, three-body problems, impossible to solve analytically, becomes trivial to model with computers. Beyond three-body problems, computers have been instrumental in solving many-body problems, such as those encountered in the atomic interactions within materials. Since computer modeling of atomic systems does not predate computers, it is still in its childhood, requiring further investigations. In order to further the development of computer modeling and a general understanding of reality, novel model algorithms for the simulation of polymeric systems have been developed. The proposed algorithms are empirical in nature, having been derived from observed atomic and molecular behavior, owing little to subatomic theories. The algorithms were developed to model polyethylene but extensions are provided to allow possible generalization to any other polymeric system.; by George Waksman.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.; Includes bibliographical references (leaf 19).

‣ Development of bi-layer mineralized bone and cartilage regeneration template

Ott, Cassandra Holzgartner
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 94 leaves; 7061413 bytes; 7065297 bytes; application/pdf; application/pdf
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Porous collagen-glycosaminoglycan (CG) scaffolds have been studied extensively and proven to be capable of tissue regeneration in vivo for applications including skin regeneration templates, hollow nerve guides and conjunctiva regeneration. While the current CG scaffold has been thoroughly examined both mechanically and clinically, it has yet to prove appropriate for load- bearing applications. This study will investigate the mechanical properties of a mineralized CG scaffold and its application potential in a load-bearing environment. Through the introduction of calcium-phosphate mineral into the standard CG formulation the matrix analog will be available for bone regeneration. Utilizing a patented triple co-precipitation technique developed at Massachusetts Institute of Technology and Cambridge University, a homogeneous mineralized scaffold will be manufactured. Comparison to healthy trabecular bone as well as the selection of the most appropriate extracellular matrix analog will be presented. The key to commercial success is the introduction of a bi-layer bone and cartilage regeneration template to address concerns and difficulties in cartilage repair today. This dual combination is termed a layered osteochondral scaffold.; (cont.) The commercial viability of this product as well as the company founded on its inception...

‣ An evaluation of cytokine-capture nanoparticle technology : stepping from bench-space into potential markets

Hong, Julee Y. (Julee Yang-A.), 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 66 leaves; 6528721 bytes; 6618022 bytes; application/pdf; application/pdf
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The feasibility of bringing a nascent technology for detection and quantification of local cytokine concentrations on cell surfaces to market is presented in this paper. Quantum dots or fluorochrome-loaded nanoparticles are conjugated with antibodies for target analytes and with proteins that allow nanoparticle attachment to the surface of T cells. A second labeled monoclonal antibody is introduced to detect the presence of any captured-cytokines using 3D fluorescent microscopy or flow cytometry. Microscopy of DO.ll cells labeled with cytokine-capture particles have shown successful detection of exogenous IL2. A comparison of existing patents with cytokine-capture technology revealed that although each aspect of the device is covered by prior IP, the capabilities of the technology exceed the claimed uses of the individual components. A preliminary market research for cytokine-capture technology applications resulted in dismissing the immunoassay industry as a target market. However, T cell monitoring was identified as a far more lucrative industry.; by Julee Y. Hong.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.; Includes bibliographical references (leaves 65-66).

‣ Advanced engineered substrates for the integration of lattice-mismatched materials with silicon

Isaacson, David Michael, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 171 p.
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The dramatic advances in Si/SiO2-based microelectronic processing witnessed over the past several decades can largely be attributed to relatively material-independent device scaling. However, with physical and economic limitations to the continued scaling of such devices appearing on the horizon, it is likely that near-term advances will come from the integration of novel and previously underrepresented materials. One of the most promising ways to enhance performance comes from the integration of judiciously chosen lattice-mismatched materials with Si. However, the integration of such structures typically poses significant technical challenges. The work contained in this thesis seeks to address several of these important issues, primarily through the use of relaxed, graded SiGe buffers on Si (i.e. Vx[Si1-xGex]/Si). Several new phenomena in relaxed graded SiGe buffers are developed in this thesis. A rise in threading dislocation density was observed in high-Ge content relaxed graded SiGe layers grown at relatively high temperatures, which was attributed to dislocation nucleation. This observation is contrary to conventional graded buffer theory in which high growth temperatures are expected to result in reduced threading dislocation densities (TDDs).; (cont.) Additionally...

‣ Development of monolithic CMOS-compatible visible light emitting diode arrays on silicon; Development of monolithic complementary metal oxide semiconductor-compatible visible LED arrays on silicon

Chilukuri, Kamesh
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 103 p.
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The synergies associated with integrating Si-based CMOS ICs and III-V-material-based light-emitting devices are very exciting and such integration has been an active area of research and development for quite some time now. SiGe virtual substrate technology presents one way to integrate these materials. A more practical approach to monolithic integration based on the SiGe virtual substrate technology was followed in this work which involves wafer bonding and hydrogen-induced exfoliation to transfer a thin layer of device-quality silicon on top of the SiGe graded buffers to produce Silicon on Lattice Engineered Substrate (SOLES). SOLES wafers are suitable for the practical fabrication of SOI CMOS circuits and III-V-based photonic devices on a common silicon substrate. A novel monolithic CMOS compatible AlGaInP visible LED array on the SOLES platform was developed, fabricated and demonstrated in this work. The prototype array is an important breakthrough in the realization of the ultimate objective - monolithically integrated optical interconnects in high speed digital systems.; by Kamesh Chilukuri.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.; Includes bibliographical references (p. 102-103).

‣ Applications of micromachined devices to malaria and cancer detection

Hardin, James O. (James Otey)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 51 p.
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Of the many micromachined diagnostic devices currently being developed, suspended microchannel resonator technology seems unique in that is not a scaling down of an existing technique and does not require labeling of the target cell. This technology has the potential to become an important diagnostic tool of diseases that cause a change in the mechanical properties of cells in blood. Malaria and cancer are good examples of this type of disease and both could benefit from more effective testing methods. For this to be accomplished, complementary technologies like filtration and microfluidic interconnects will also have to be developed. However, substantial funding will be required for this development. The cancer market appears to be the most favorable by an order of magnitude in terms of funding. There are many business strategies to take advantage of this technology. Each has its own set of risks and possible gains.; by James O. Hardin, IV.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.; "September 2006."; Includes bibliographical references (p. 49-51).

‣ Effects of nanoscale film thickness on apparent stiffness of and cell-mediated strains in polymers

Oommen, Binu K
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves
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The mechanical properties of compliant materials such as polymeric films and biological membranes that are of nanoscale in thickness are increasingly extracted from scanning probe microscope-enabled nanoindentation. These films are applied in various fields that require multiaxial loading conditions. The Hertzian contact models developed for linear elastic materials of semi-infinite thickness fail to accurately predict the elastic modulus E for these compliant materials. This makes it necessary to understand the evolution of stress and strain fields of these nanoscale structures. In this thesis we employ computational simulations that are based on experimental parameters for contact based analysis of compliant polymer thin films, to decouple the effect of thickness and angle of indentation on calculated mechanical properties. Traction applied by living cells to these compliant films are studied in detail. We thus identify the range of strains and material thickness for which contact models could be used to accurately predict the elastic stiffness of these polymeric films of nanoscale (<100 nm) thickness using scanning probe microscope-enabled experiments, and the volumes over which adhered cells deform these films. The key results of this thesis enable accurate experimental analysis of polymeric thin film elastic properties...

‣ Effects of mechanical properties on the reliability of Cu/low-k metallization systems

Wei, Frank L. (Frank Lili), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 217 leaves
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Cu and low-dielectric-constant (k) metallization schemes are critical for improved performance of integrated circuits. However, low elastic moduli, a characteristic of the low-k materials, lead to significant reliability degradation in Cu-interconnects. A thorough understanding of the effects of mechanical properties on electromigration induced failures is required for accurate reliability assessments. During electromigration inside Cu-interconnects, a change in atomic concentration correlates with a change in stress through the effective bulk modulus of the materials system, B, which decreases as the moduli of low-k materials used as inter-level dielectrics (ILDs) decrease. This property is at the core of discussions on electromigration-induced failures by all mechanisms. B is computed using finite element modeling analyses, using experimentally determined mechanical properties of the individual constituents. Characterization techniques include nanoindentation, cantilever deflection, and pressurized membrane deflection for elastic properties measurements, and chevron-notched double-cantilever pull structures for adhesion measurements. The dominant diffusion path in Cu-interconnects is the interface between Cu and the capping layer...

‣ Multiscale chemomechanics of polymer deformation under contact : predicting structure-property correlations from the bulk to the interphase

Tweedie, Catherine Anne
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 181 p.
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The development of nanoscale polymeric materials for mechanical applications necessitates advances in small-volume experimental techniques and analyses that reflect the viscoelastoplastic behavior of such materials. In this thesis, the time-dependence and response of homogeneous engineering polymers under confined contact loading are characterized as a function of polymer physical and structural properties. The validity of the time-independent metric indentation hardness Hi is evaluated through the combination of nanoindentation and atomic force microscopy imaging. In addition, the classic, time-dependent metric creep compliance J(t) is used to establish the experimental conditions necessary for linear elastic behavior for a set of thermoplastic and thermoset materials. For large indentations (hmax > 1 um), properties are tacitly assumed to reflect the properties of bulk polymer; however, this assumption does not hold within 100 nm of a free surface or interface of amorphous polymers such as polystyrene and polycarbonate. The contact deformation mechanism near an amorphous polymer surface is found to scale with the surface area of contact, suggesting the dynamic formation of a structural interphase region. Chemical probe functionalization experiments are developed to explore the effects of probe surface charge on the probe-polymer interface and contribute to the understanding of the interphase that dominates nanocomposite material response. A technique to rapidly screen mechanical response of combinatorial polymer libraries is presented...

‣ Pottery engineering in ancient Guerrero, Mexico : the site of Las Fundiciones

Reitzel, Hannah Lynn
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 66 leaves
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This thesis examines ancient pottery from the site of Las Fundiciones, Guerrero, Mexico. Because this site provides the only documented evidence of prehispanic metal smelting in Mesoamerica it is critical to examine artifacts found there, in this case pottery, using the tools of materials science. These tools allow archaeologists to see past "stylistic preferences" to the design, functional, and compositional differences in artifacts that result from choices among a range of processing alternatives. Thus, this thesis seeks to show that potters at Las Fundiciones were engineering their pottery in their choices of materials and design processes. A selection of pottery sherds (representing different functional vessel types) from the site were petrographically analyzed, and nine clays collected in and around the site were petrographically analyzed and subjected to a variety of chemical, mechanical, and thermal tests to determine their material properties. Clays are matched with petrographic groupings of potsherds, showing that potters were using local clays. The clays are ranked according to their ability to withstand thermal shock, since this is an easily quantifiable measure of the viability of ancient pots for use in food preparation. Lastly...

‣ The role of heat assisted magnetic recording in future hard disk drive applications

Méndez de la Luz, Diego A., 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves; 4175342 bytes; 4182241 bytes; application/pdf; application/pdf
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(cont.) portable consumer electronics, such as PDAs, cell phones, music players, digital cameras, etc. make a relatively modest but fast growing market for ultrahigh areal density HAMR-based HDDs. HAMR-based HDD for portable applications could very well be a disruptive technology in the magnetic recording industry. Companies that intend to profit from this technology need to invest on its development and must try to be first-to-volume production to benefit from economies of scale and to build the necessary expertise that could give them leadership roles in future magnetic recording.; The magnetic recording industry keeps up with the demand of high capacity hard disk drives by improving the areal recording density of these devices. The use of conventional longitudinally magnetized media will be truncated by the challenges it faces nowadays, which are related to the instability of the stored information, produced by the aggressive decrease in the volume of the grains in the media. To overcome this problem, the use of large magnetic anisotropy energy density alloys is necessary, but the write fields that are required by such alloys can be prohibitively large, rendering these media effectively unwritable. Fortunately, the magnetocrystalline anisotropy energy density decreases with increasing temperature and so does the required write field. Heat assisted magnetic recording allows the use of such magnetically hard alloys by using both a magnetic and a thermal field during the writing process. Research in HAMR is centered in three major fields: the heat delivery system...

‣ Investigation of bone response to implant materials by electron microscopy and computer simulation

Wang, Hao, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 148 p.; 8217464 bytes; 8237183 bytes; application/pdf; application/pdf
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(cont.) implementation of this scintigraphic method for quantitative studies of osteoblast-mediated mineralization in vitro. A 2-D truss finite element model is used to study the remodeling of trabecular bone. Using strain energy density (SED) as the optimization object and the trabecular width as the optimization variable, an optimal structure with minimum SED was achieved. This structure is similar to real bone in the dense outside, porous inside, and orientation of the trabeculae. The bone density distribution pattern also matched with previous result by other people. Different implants were introduced to simulate the replacement for the femoral head. It has been proved that the difference in Young's modulus between bone and implant materials is the main reason for the long-term bone loss (stress screening). This problem can be alleviated by proper implant design and resurfacing instead of replacing the whole femoral head.; Initial fixation with bone and the long term bone loss are two main problems associated with total hip replacement (THR), which are studied by electron microscope and computer simulation in this thesis. Bare Titanium-6 wt% Aluminum-4 wt% Vanadium (Ti64) implants, Ti64 implants with plasma-sprayed hydroxyapatite (PSHA)...

‣ Evaluation of nanoparticles-based thermotherapy for cancer

Wiryaatmadja, Edwina
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 88 p.
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Under alternating magnetic field, superparamagnetic iron oxide nanoparticles can be used to generate heat for the treatment of cancer. With suitable coating, these nanoparticles are biocompatible, stable in solution, and absorbed by tumor cells in good contrast. The mechanism of heating is mainly due to Neel relaxation process and a quantity called specific loss power (SLP) / specific absorption rate (SAR) is used to describe the heating effect. Past clinical studies have shown minimum side effects and proven the success of the new thermotherapy as a treatment modality in conjunction with chemo- or radiotherapy. Studies are in progress to improve the nanoparticles' heating power to enable treatment of small tumors and metastases, thermoablation as a monotherapy, and to achieve tumor-specific thermotherapy with the aid of tumor-finding molecules. This paper evaluates the novel technology that is magnetic nanoparticles-based thermotherapy and explores its commercialization potential. It explains the medical need driving the innovation, examines the technology in comparison with existing cancer therapies, identifies the strategic position the technology has in the present state of market for cancer therapies, and explores opportunities and Challenges in the introduction of the new therapy into the U.S. market.; by Edwina Wiryaatmadja.; Thesis (M. Eng.)--Massachusetts Institute of Technology...