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‣ How do mechanical engineering students see their training and learning at university? Findings from a case study

Flores, Paulo
Fonte: WIETE Publicador: WIETE
Tipo: Artigo de Revista Científica
Publicado em //2012 Português
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This article draws upon research aimed at investigating teaching and learning in higher education within the so-called Bologna Process. The author discusses the ways in which students acquire engineering education and analyses the implications of redesigning initial training and rethinking teachers’ role. Data were gathered through interviews and questionnaires. A questionnaire was designed including both closed and open-ended questions. Four levels of information were included: biographic data (gender, age, initial training, current job position, etc), academic education (reasons for choosing mechanical engineering, reasons for selecting the University of Minho, expectations about the mechanical engineering course, etc), transition from the university to the labour market (difficulties faced, scope and nature of the work, etc) and graduate and post-graduate interests (areas, type and organisation for high level courses, specific courses). Background characteristics, such as years of experience, academic years of experience at the current job were also included. Overall, findings suggest a positive evaluation of initial training, namely, the ways students adapted to the University, relationships between students and the length of their practicum. They also highlighted a number of issues to be improved: a more hands-on approach and a better pedagogical intervention from lecturers.

‣ Modeling, simulation, and control of a polypyrrole-based conducting polymer actuator

Bowers, Thomas A. (Thomas Alan), 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 181 p.; 1637652 bytes; 1682398 bytes; application/pdf; application/pdf
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A detailed model was developed for an ionic electro-active polymer (EAP) actuator. The electrical and chemical domains of the system were modeled using a simple electrical circuit. Ionic charge storage within the polymer was described using a linear reticulated model. This model improves upon the continuum diffusive model introduced in prior work by providing a low order model of diffusion that can be analyzed in the context of modern and classical control methods. Additionally, the reticulated diffusion model describes the dynamics of ionic charge distribution within the polymer, which enables a more precise calculation of electromechanical coupling. An interesting observation of ionic electro-active polymers is that they exhibit enormous asymmetry in coupling from electrical to mechanical domains. While electrical potentials produce large linear displacements (5% strain or greater), uniaxially-applied mechanical loads result in a negligible electrical back effect. This is surprising, suggesting that there are huge entropic losses when applying mechanical loads. After examining the mechanics of the system it was theorized that the apparent lack of coupling is actually the result of the Poisson Effect, which causes changes in the volume of an object when uniaxial loads are applied. A derivation of the stored electrical energy and strain energy led directly to a set of constitutive equations that are able to account for the asymmetric coupling observed in EAP. The solution to the uniaxial loading boundary condition was developed fully and compared to prior work. Experimental results from an EAP actuator composed of polypyrrole...

‣ Design, fabrication, and performance of a gas-turbine engine from an automobile turbocharger

Padilla, Jorge, 1983-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves; 2911971 bytes; 2913755 bytes; application/pdf; application/pdf
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Thermal-Fluids Engineering is taught in two semesters in the Department of Mechanical Engineering at the Massachusetts Institute of Technology. To emphasize the course material, running experiments of thermodynamic plants are integrated into the course as demonstrations. The aim of this thesis is to supplement the course demonstrations of thermodynamic plants through the design and fabrication of a gas-turbine engine. The engine operates on an open version of the Brayton cycle. Students will be able to evaluate the energy conversion efficiency and net work ratio from air temperature measurements in three stages of the cycle. The gas-turbine engine is made from an automobile turbocharger for its common shaft turbine and compressor. A combustion chamber was placed between the outlet of the compressor and the inlet of the turbine. The temperature measurement system was designed from the placement of thermocouples on the outside wall of a pipe leading from the compressor to the combustor, on the outside wall of a pipe leading from the combustor to the turbine, and on the outside wall of the turbine exhaust pipe. As the temperature measured by the thermocouple will be that of the outside walls of the engine, the model will depict the cross-sectional temperature profile so the students will know the actual bulk temperature of the working fluid...

‣ Design and performance of a gas-turbine engine from an automobile turbocharger

Tsai, Lauren (Lauren Elizabeth)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 46 leaves; 2125802 bytes; 2126005 bytes; application/pdf; application/pdf
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The Massachusetts Institute of Technology Department of Mechanical Engineering teaches thermodynamics and fluid mechanics through a pair of classes, Thermal Fluids Engineering I & II. The purpose of this project was to design and fabricate a gas-turbine engine for demonstration use in these two classes. The engine was built from an automobile turbocharger with a combustion chamber connected between its compressor and turbine. Pressure and temperature sensors at different points of the engine cycle allow students to monitor the performance of the individual engine components and the complete engine cycle.; by Lauren Tsai.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.; Includes bibliographical references (leaves 31-32).

‣ Mechanics of deformation of carbon nanotubes

Garg, Mohit, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 191 p.; 9370369 bytes; 9378422 bytes; application/pdf; application/pdf
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The deformation mechanics of multi-walled carbon nanotubes (MWCNT) and vertically aligned carbon nanotube (VACNT) arrays were studied using analytical and numerical methods. An equivalent orthotropic representation (EOR) of the mechanical properties of MWCNTs was developed to model the anisotropic mechanical behavior of these tubes during various types of deformation. Analytical models of the micro-mechanical contact and deformation during nano-indentation and scratching of VACNTs were developed. The EOR model was developed based on finite element (FE) nested shell structural representation of MWCNTs. The EOR was used together with the FE method to simulate bending, axial compression and lateral compression. Results were compared with those of the nested shell model for 4-, 8-, 9-, 14-, and 19-walled carbon nanotubes. The comparison of axial and lateral compression results indicated that although MWCNTs have high strength and stiffness in the axial direction, they can exhibit significant radial deformability owing to their relatively compliant interwall normal and shear behaviors. The EOR results provide an improvement in computational efficiency as well as a successful replication of the overall deformation behavior including the initial linear elastic behavior and the onset of buckling of MWCNTs and the post-buckling compliance.; (cont.) The post-buckling progression in wavelength (a doubling of wavelength as deformation progresses) was not captured by the EOR model. Analytical predictions of the force-penetration depth during nano-indentation with a three-sided pyramidal shaped indentor tip were compared with results from macro-scale experiments...

‣ An enhanced propeller design program based on propeller vortex lattice lifting line theory

Chung, Hsin-Lung
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 112 p.
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A suite of propeller numerical design tools was developed in MATLAB®, a high-level technical computing language. The tools were based on the FORTRAN programs developed by Professor Justin Kerwin at MIT in 2001 and include enhanced parametric design capability, Graphical User Interfaces (GUIs) and enhanced graphics capability. The MIT Propeller Vortex Lattice Lifting Line Program (PVL) is an executable file written in FORTRAN language and serves as a preliminary propeller design tool. In this thesis, PVL was rewritten in MATLAB® and presented with the GUIs. The enhancements were incorporated in a revised propeller design program designated MPVL to distinguish it from PVL. Several new features such as the user-friendly GUIs and colorful graphs were included in MPVL in addition to the full functions of PVL. Moreover, MPVL was validated by comparing its outputs with PVL and MIT Propeller Lifting Line Program (PLL) and proved to be consistent with PVL. The advantages of MPVL were revealed in this thesis and enabled MPVL to replace PVL.; (cont.) MPVL was developed to serve as an open source code for propeller design. It is also a base program which can be extended to perform more sophisticated propeller design applications such as ducted propellers and contra-rotating propellers. A description of the development efforts for this revised propeller design program forms the basis of this thesis.; by Hsin-Lung Chung.; Thesis (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology...

‣ Cell-matrix interactions : collagen-GAG scaffold fabrication, characterization, and measurement of cell migratory and contractile behavior via confocal microscopy; Collagen-GAG scaffold fabrication, characterization, and measurement of cell migratory and contractile behavior via confocal microscopy

Harley, Brendan A. (Brendan Andrew), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (393 leaves)
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Three-dimensional, collagen scaffolds are an analog of the extracellular matrix and are used for many tissue engineering applications. While material and microstructural properties significantly affect overall scaffold bioactivity, the specific influence of construct mechanical properties, composition, and pore microstructure is unknown. In this thesis, experimental and theoretical approaches are employed to systematically examine the independent effect of extracellular features on cell behavior within a series of standardized, well-characterized, collagen-glycosaminoglycan (CG) scaffolds, providing valuable information for designing biomaterials with improved physiological relevance. This thesis also aims to provide experimental and theoretical approaches appropriate for characterizing and describing a wide range of porous biomaterials and for quantifying the effect of extracellular cues on cell behavior within these biomaterials. CG scaffolds are fabricated via freeze drying. Novel thermal processing conditions were developed to produce two homologous series of uniform, mechanically isotropic CG scaffolds, one with varying pore size and constant stiffness and the other with constant pore size and varying stiffness.; (cont.) The thermal processing conditions and the resultant scaffold microstructure have been modeled using an isothermal coarsening heat transfer model within a conductive mold with interface resistance...

‣ Latent heat fluxes through nano-engineered porous materials

Traum, Matthew J. (Matthew Jason), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 210 p.
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Micro- and nano-scale truss architectures provide mechanical strength, light weight, and breatheability in polymer barriers. Liquid evaporation and transport of resulting vapor through truss voids (pores) cools surfaces covered by the barriers, suggesting the possibility for simultaneous protection of humans from mechanical and thermal stresses. Design of real systems employing this technique requires quantitative understanding of vapor transport within the truss pores and accompanying latent heat lift under ambient temperature and pressure. One application is desert Soldier protection. Need exists to clarify whether smaller pore diameters affect surface cooling and water vapor transport owing to fluid rarefaction or surface interactions. Contrasting previous studies where pressure within capillaries of fixed diameter was modulated, in this thesis Knudsen Number (Kn) was systematically varied by changing pore diameter at constant pressure (one atmosphere). Cooling efficacy was assessed for porous membranes with pore diameters ranging from 39 to 14,400 nm, varied in regular increments. Evaporative cooling experiments simulated combined daytime desert solar and metabolic thermal load on humans by heating an evaporation chamber partially filled with liquid water and capped with a porous membrane.; (cont.) Hot...

‣ Extended tension leg platform design for offshore wind turbine systems

Parker, Nicholas W. (Nicholas William)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 85 p.
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The rise of reliable wind energy application has become a primary alternative to conventional fossil fuel power plants in the United States and around the world. The feasibility of building large scale wind farms has become increasingly dependent on location. The ideal locations require placement in desolate areas with limited or no visibility from surrounding communities, and with the presence of a consistent wind-enriched climate. Deployments of wind turbines in an offshore environment where water depths exceed 30 meters satisfy these requirements. Studies have shown that existing offshore wind turbine systems are limited to shallower coastal waters by the cost of constructing and installing the support structures. This thesis provides a continued parametric analysis of floating platforms for the support of offshore wind turbine systems. In particular, the Tension Leg Platform design will be optimized. Optimization is achieved through the coupling of wave-body interaction theory for the platform along with the aerodynamic performance of a 5-Megawatt wind turbine in the frequency domain. The study provides comparisons over a variety of initial tether tensions and the dynamic response and performance of the platform in several sea states.; (cont.) Statistical quantities are evaluated to ensure these tensions provide adequate forces in storms for various sea states where the significant wave heights can be expected to be 5 meters or greater. The Tension Leg Platform is substantially resistant to heave...

‣ CNC router modernization; Computer numerically controlled router modernization

Doody, Aaron L. (Aaron Lee)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 30 p.
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A large-format CNC router has been stored in the Pappalardo Laboratory wood shop for several years in an unusable state. A need assessment determined that it would be cost effective to bring the router online for use in the mechanical engineering curriculum. The router was cleaned and inspected; it was determined that the router was in sound mechanical condition. The stepper motors, control system, and power supply were also functional, but the CNC interface software was outdated. To ensure the long term viability of the router as an effective teaching tool the most cost effective solution was to upgrade the motors, control system, and CNC interface software using a package provided by the original supplier, Techno-Isel Inc. The motors, control system, and software were installed, bringing the router to a fully functional state. Dust and ejected cuttings cause a safety hazard and cleanliness problem when operating the router. An enclosure was designed and installed in order to trap the majority of debris and reduce noise levels in the workspace, and a brief user guide has been compiled to ensure safe and effective usage.; by Aaron L. Doody.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references.

‣ Skeletal muscle biomechanics drives intramuscular transport of locally delivered drugs

Wu, Peter I-Kung
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 97 leaves
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Introduction: Effective local drug delivery to contractile tissues such as skeletal muscle requires a thorough understanding of the impact of mechanical loads on intramuscular pharmacokinetics. Current preparations for studying skeletal muscle biomechanics typically use: mounting techniques that lead to mechanical disruption of the tissue, which can create drug transport artifacts. In order to accurately study mechanical influences on drug transport, experimental techniques and setups need to meet the particular design requirements of both biomechanical testing setups and local drug delivery preparations. Studies of intramuscular pharmacokinetics require anatomically physiologic and functionally viable conditions for accurate drug transport. In this study, we invent a method for the surgical isolation and mounting of whole skeletal muscles of small rodents that maintains the physiologic configuration of the tissue. We also invent a mounting assembly and dynamic loading system designed appropriately for in vitro drug transport studies. We present an effective protocol for tissue processing and visually quantifying intramuscular distribution of drug. With the primary objective of investigating muscle pharmacokinetics, we use these techniques in a study to elucidate the influence of mechanical loading on the intramuscular transport and distribution of locally delivered drug. Methods and Results: The dynamic loading system was characterized and used to investigate intramuscular transport of aqueous macromolecular drug. The loading system was designed to achieve a maximal force...

‣ Optimal workloop energetics of muscle-actuated systems

Farahat, Waleed A. (Waleed Ahmed), 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 122 p.
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Skeletal muscles are the primary actuators that power, stabilize and control locomotive and functional motor tasks in biological systems. It is well known that coordinated action and co-activation of multiple muscles give rise to desirable effects such as enhanced postural and dynamic stability. In this thesis, we study the role of muscle co-activation from an energetics perspective: Are there situations in which antagonist co-activation leads to enhanced power generation, and if so, what is the underlying mechanism? The mechanical energetics of muscles are traditionally characterized in terms of workloop measures where muscles are activated against oscillating, zero-admittance motion sources. We extend these measures to more natural, "mid-range" admittance loads, actuated by multiple muscles. Specifically, we set up the problem of a second-order mechanical system driven by a pair of antagonist muscles. This is the simplest problem where the influences of load dynamics and muscle co-activation on the output energetics may be investigated. To enable experimentation, a muscle testing apparatus capable of real-time servo emulation of the load is developed and utilized for identification and workloop measurements.; (cont.) Using this apparatus...

‣ Multiscale simulations of the aortic heart valve : applications in disease and surgery

Weinberg, Eli, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 148 p.
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This thesis presents mathematical models describing the mechanical behavior of the human aortic heart valve over a range of length and time scales. In the human heart, the valves perform the vital function of controlling the direction of blood flow. Each valve is an intricate mechanical structure, with distinct features and functions at multiple scales. This effort first develops a framework of reference configurations that enables communication between simulations of the different length scales. Three simulations are created within that framework. At the cell scale, the interaction between a single valvular interstitial cell and its surrounding matrix is described. At the tissue scale, a model is created for the valve cusp tissue mechanical behavior, including the multilayered, nonuniform geometry and nonlinear, anisotropic material properties. At the organ scale, a dynamic, three-dimensional model with fluid-structure interaction predicts the motion of the valve, blood, and surrounding tissue. Each simulation is verified against a number of experimental measures. These three simulations together constitute a model for the dynamic, three-dimensional, multiscale mechanical behavior of the healthy human aortic heart valve throughout the cardiac cycle. The model is employed to perform multiscale investigation into the mechanisms of the disease calcific aortic stenosis in three ways. First...

‣ Redesign and shock analysis of HALIFAX class frigate gas turbine uptake structure

Summers, Simon A. (Simon Andrew)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 66 p.
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The gas turbine exhaust uptakes in the HALIFAX class frigates of the Canadian Navy have experienced thermally-induced fatigue cracking since soon after the commissioning of these ships. The uptake structure is heavily stiffened in order to meet shock resistance requirements. Unfortunately, the result has been that thermal expansion of the uptake shell is constrained, thus every flash-up and shut-down of a gas turbine results in a fatigue cycle of its uptake with extremely high stresses. Among the methods proposed to address the problem is the structural redesign of the uptakes within the constraints of the original mounting arrangements. Any such redesign would be required to reduce thermal stresses while still meeting the shock resistance requirements. This work presents the redesign of the uptakes such that they continue to meet shock requirements while incorporating design aspects, developed in the literature, which are anticipated to reduce thermal stresses. The original intention was to use the modal-based design response spectrum method to assess shock resistance. However, due to excessive stresses in the original model and in all subsequent modifications using this method, the less-rigorous base acceleration method was primarily used.; by Simon A. Summers.; Thesis (S.M. in Mechanical Engineering and Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology...

‣ Designing an alternative project for a product design curriculum for high school students

Kirby, Jeffrey (Jeffrey T.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 80 p.
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An alternative curriculum is designed for Engineering the Future, a high school level engineering curriculum developed by the Boston Museum of Science. It is designed on the premise that a hands-on curriculum providing an authentic engineering experience is the best method of teaching high school level engineering. The main design challenge the students are faced with is the design and manufacturing of a unique pinhole camera for a potential business they will be starting. The design challenge takes the student through the design process from the initial concept during brainstorming to a functional prototype. During the process, the students will validate their ideas with sketch models and investigate solutions to critical issues with mockup models. Throughout the project, the students will investigate solutions with the aid of the design process and make intelligent decisions based in reason. The curriculum offers an engaging opportunity for teachers to use within their high school engineering class at the beginning phase of a yearlong class on engineering.; by Jeffrey Kirby.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.; Includes bibliographical references (p. 23).

‣ 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...

‣ Development of an in-line putter for handicap friendly tabletop golf games

Berberian, Sam J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 57 leaves
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The market for handicapped tabletop games is severely untapped. The students of the Red Team in the course 2.009 (Product Engineering Processes, a capstone design project course in the Mechanical Engineering Department) at the Massachusetts Institute of Technology attempted to produce a tabletop golf game that would even the playing field between handicapped and able-bodied individuals. This game, Microgolf, was not received well by the faculty. One of the largest downfalls of Microgolf was an inherent lack of control over the putting aspect of the game. The putter designed by the 2.009 Red Team was difficult to use as it shot the ball perpendicular to the line of sight path between the ball and the hole used by the user to aim. The goal of this thesis is to design a user friendly putter that would provide a substantial amount of control over the shooting aspects of the game, thus truly leveling the playing field between handicapped and able-bodied individuals, and providing a more exciting playing environment. After several rounds of modeling and optimization, a final design is accomplished that accommodates all of the functional requirements desired by players.; (cont.) This putter is lightweight and could be used with one hand, aided by a set of legs near the front end that allowed it to rest on the table for support. The putter relies on user input for aim...

‣ The effect of the interstitial flow on the directional cell migration and sprouting of capillaries

Wan, Chen-rei
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 92 p.
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Development of functional endothelium in tissue engineering is both critical and challenging. It is critical because of its role in transporting nutrient and waste in tissues larger than the length scale of diffusion. It is challenging because of its complexity in both the chemical and mechanical environments actively evolving in both space and time. In addition to the signals from the microenvironment, cells are more than likely to receive global signaling as well. The goal of the overall project is to establish a functional endothelium for a long period of time under the optimal chemical and physical conditions. This master's thesis project focuses specifically on the effect of interstitial fluid flow on the capillary morphogenesis process. Interstitial fluid flow is defined as flow perpendicular to the endothelial monolayer, as opposed to shear flow which is parallel. Interstitial flow is an essential process in vivo both in normal physiology and pathology. Liver filtration system, angiogenesis during wound healing, vasculogenesis during fetal development and lymphoangiogenesis are a few examples that depend heavily on interstitial flow. Pathologically, interstitial flow is observed when the vessels are abnormally leaky, such as the case in tumor-induced angiogenesis.; (cont.) In vivo observations of angiogenesis suggest the nascent blood vessels sprout from the venous end. This indicates that the interstitial flow direction is opposite of the direction of sprouting. In vitro studies of interstitial flow on endothelial cells are not done until the recent development of three dimensional culture systems. The studies suggest that capillary branching is biased the direction of interstitial flow when VEGF is matrix-bound. The seemingly contradicting results ignite our interest in investigating whether the direction of interstitial flow has an impact on the directional migration or sprouting of endothelial cells or not in a device-independent method in vitro. Two different designs of 3D culture bioreactors were used...

‣ Non-linear rolling of ships in large sea waves

Vanden Berg, Scott M
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 66 leaves
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The United States Navy has taken a new interest in tumblehome hulls. While the stealth characteristics of these hull forms make them attractive to the Navy, their sea keeping characteristics have proven to be problematic. Normal approximations of sea keeping characteristics using linear differential equations with constant coefficients predict a very stable platform, while observations in model tests show a ship that is prone to extreme roll transients. This thesis examines a simple method of producing a non-linear simulation of roll motion using a tumblehome hull provided by the Office of Naval Research. This research demonstrates the significant difference that a variable restoring coefficient introduces into a hull's seakeeping characteristics.; by Scott M. Vanden Berg.; Thesis (S.M. in Naval Architecture and Marine Engineering and Mechanical Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (leaf 51).

‣ Mechanics of amorphous polymers and polymer nanocomposites during high rate deformation

Mulliken, Adam Dustin, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 290 p.
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It has been suggested that a polymer's macroscopic mechanical response to a general loading case is governed by its ability to access various primary and secondary molecular mobilities. Specifically, under conditions of high strain rate, restricted secondary molecular motions are thought to bring about enhanced stiffness and strength. In accordance with this theory, an experimental protocol and associated analytical techniques were established to better understand the rate- and temperature-dependent mechanical behavior of two exemplary amorphous polymers, PC and PMMA. The experiments included dynamic mechanical thermal analysis (DMTA), as well as uniaxial compression tests over a wide range of strain rates. In both cases, the polymer exhibited a distinct transition in the rate-dependent yield behavior, under the same temperature/strain rate conditions as the observed viscoelastic 0-transition. Drawing off of previous research in the field of polymer mechanics, a new continuum-level constitutive model framework is proposed to account for the contributions of different molecular motions which become operational in different frequency/rate regimes. This model is shown to capture well the unique rate-dependent yield behavior of PC and PMMA...