Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Includes bibliographical references (leaves 190-194). / by Ng, Lee Hong. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006. / Includes bibliographical references (p. 133-142). / Coherence and entanglement in multi-spin systems are valuable resources for quantum information processing. In this thesis, I explore the manipulation of quantum information in complex multi-spin systems, with particular reference to Nuclear Magnetic Resonance implementations. In systems with a few spins, such as molecules in the liquid phase, the use of multi-spin coherent states provides a hedge against the noise, via the encoding of information in logical degrees of freedom distributed over several spins. Manipulating multi-spin coherent states also increases the complexity of quantum operations required in a quantum processor. Here I present schemes to mitigate this problem, both in the state initialization, with particular attention to bulk ensemble quantum information processing, and in the coherent control and gate implementations. In the many-body limit provided by nuclear spins in single crystals, the limitations in the available control increase the complexity of manipulating the system; also, the equations of motion are no longer exactly solvable even in the closed-system limit. Entanglement and multi-spin coherences are essential for extending the control and the accessible information on the system. I employ entanglement in a large ensemble of spins in order to obtain an amplification of the small perturbation created by a single spin on the spin ensemble, in a scheme for the measurement of a single nuclear spin state. I furthermore use multiple quantum coherences in mixed multi-spin states as a tool to explore many-body behavior of linear chain of spins, showing their ability to perform quantum information processing tasks such as simulations and transport of information. / (cont.) The theoretical and experimental results of this thesis suggest that although coherent multi-spin states are particularly fragile and complex to control they could make possible the execution of quantum information processing tasks that have no classical counterparts. / by Paola Cappellaro. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 221-226). / by Jimmy Kuo-Wei Chen. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / Disruptions, the sudden termination of tokamak fusion plasmas by instabilities, have the potential to cause severe material wall damage to large tokamaks like ITER.e mitigation of disruption damage is an essential part of any fusion reactor system. Massive gas injection (MGI) rapid shutdown is a technique in which large amounts of noble gas are injected into the plasma in order to safely radiate the plasma energy evenly over the entire plasma-facing first wall. However, it has been observed that this energy is not radiated evenly: it can have significant asymmetries, which could cause melting in large devices even in the case of a successful rapid shutdown. The first rapid shutdown experiments using multiple gas injectors on any tokamak were conducted on Alcator C-Mod. A dedicated toroidal array of fast ultraviolet photodiodes was installed in order to diagnose toroidal radiation asymmetries during the thermal quench (TQ). It is found that the radiation asymmetry is controlled by a low-n brightness mode in the TQ phase of rapid shutdowns. is mode sometimes rotates, and the rate of rotation sets the integrated radiation asymmetry in the TQ. It is proposed that this brightness feature is caused by the transport of energy from the hot plasma core to the radiative edge by the MHD flow at one phase of an n = 1 global MHD mode. is phenomenology is confirmed by extended MHD simulation using the NIMROD code. An exponentially growing n = 1 magnetic mode is observed during the pre-TQ phase of MGI rapid shutdowns; the saturation of this mode marks the beginning of the thermal quench. It is proposed that this mode is a magnetic island caused by a radiative tearing mode; the predicted growth rate is compared to the predictions of analytic theory. It is proposed that this mode is a magnetic island then couples to other global n = 1 MHD modes, causing the energy transport during the TQ. An important implication of this result is that simply adding more gas injectors cannot guarantee a symmetric rapid shutdown: the asymmetry is controlled by the behavior of the core MHD activity during the TQ. the implications of this rotating radiation asymmetry during the TQ of MGI rapid shutdown for the beryllium wall of ITER are discussed. / by Geoffrey Michael Olynyk. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 148-156). / Nanofluids, engineered colloidal dispersions of nanoparticles in fluid, have been shown to enhance pool and flow boiling CHF. The CHF enhancement was due to nanoparticle deposited on the heater surface, which was verified in pool boiling. However, no such work has been done for flow boiling. Using a cylindrical tube pre-coated with Alumina nanoparticles coated via boiling induced deposition, CHF of water was found to enhance up to 40% compared to that of the bare tube. This confirms that nanoparticles on the surface is responsible for CHF enhancement for flow boiling. However, existing theories failed to predict the CHF enhancement and the exact surface parameters attributed to the enhancement cannot be determined. Surface modifications to enhance critical heat flux (CHF) and Leidenfrost point (LFP) have been shown successful in previous studies. However, the enhancement mechanisms are not well understood, partly due to many surface parameters being altered at the same time, as in the case for nanofluids. Therefore, the remaining objective of this work is to evaluate separate surface effect on different boiling heat transfer phenomena. In the second part of this study, surface roughness, wettability and nanoporosity were altered one by one and respective effect on quenching LFP with water droplet was determined. Increase in surface roughness and wettability enhanced LFP; however, nanoporosity was most effective in raising LFP, almost up to 100°C. The combination of the micro posts and nanoporous coating layer proved optimal. The nanoporous layer destabilizes the vapor film via heterogeneous bubble nucleation, and the micro posts provides intermittent liquid-surface contacts; both mechanisms increase LFP. In the last part, separate effect of nanoporosity and surface roughness on pool boiling CHF of a well-wetting fluid, FC-72, was investigated. Nanoporosity or surface roughness alone had no effect on pool boiling CHF of FC-72. Data obtained in the literature mostly for microporous coatings showed CHF enhancement for well wetting fluids, and existing CHF models are unable to predict the enhancement. / by Bao Hoai Truong. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis introduces, demonstrates, and implements a unified computational design framework for material distribution modeling that enables the production of geometrically complex, materially heterogeneous, and functionally graded objects, across scales, media, and platforms. Receiving user-defined performance mappings as input, the workflow generates and evaluates instructions for designated fabrication systems, informed by the extrinsic constraints presented by the hardware and the intrinsic characteristics embedded in the materials utilized. As a proof of concept to the generalizable approach, three novel design-to-fabrication processes within the framework are introduced with material and materialization precedents and implemented through computational and robotic platforms: implicit modeling for the fabrication of photopolymers, trajectory optimizing for the fabrication of water-based material, and toolpath planning for the fabrication of fiber-based material. Titled Material-informed Tectonics, the framework extends the domain of parametric design processes from geometry to material, expands the potential application of volumetric material modeling techniques beyond high resolution multi-material 3D printing systems, and bridges between the virtual and the physical by integrating material information into the tectonic relationship between manufactured objects and manufacturing methods; thereby outlining an approach towards a synthesis of material properties, computational design, digital fabrication, and the environment. / by Yen-Ju Timothy Tai. / S.M.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 87-93). / A suspension of monodisperse colloids has an interesting property of self-assembling into a three-dimensional ordered structure. This crystalline material has attracted significant interest on the implementation of photonic crystals, which have practical applications in reflectors, filters, resonators, and waveguides. In this thesis, self-assembly of colloidal crystals and photonic crystal technologies are reviewed. Potential colloidal photonic and non-photonic devices were presented and their values/limitations were discussed. Colloidal photonic crystals were assessed on their technical capabilities, growth techniques and fabrication cost. In this assessment, the bulk colloidal photonic crystals are found to be inherently robust against stacking disorder, cracks and voids. The high reflectance performance and lattice parameter tailoring are useful for implementing reflectors, optical switch and sensors. Besides, the anomalous dispersion characteristic near to the band edges or near to flat bands of the photonic band diagram is suited for superprism and light harvesting applications. Potentially, the unique characteristics of colloidal photonic crystal could be capitalized in a low cost micro-fabrication model. Finally, the study has shown that it is more technically and commercially viable to implement bulk colloidal photonic crystal applications rather than lithographically-defined types. / by Chan Hoe Yip. / M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 191-193). / A new methodology has been developed that couples differential cross section data evaluation with integral benchmark analysis for improved uncertainty quantification. The new methodology was applied to the two new copper evaluations and resulted in an improved evaluation with smaller covariance data. Copper is a structural material in many nuclear applications, particularly those dealing with criticality safety. The current standard for the resonance evaluation of the two copper isotopes, ⁶³,⁶⁵Cu, has been determined to result in poor modeling performance. Therefore a new resonance evaluation of the two copper isotopes is vital to nuclear criticality safety applications. Performing a new resolved resonance region evaluation for copper has served as a backdrop to this work on developing new techniques for resolved resonance region evaluation. For the new evaluations, experimental cross section measurements have been carried out in the thermal energy region where no experimental data had previously been measured. Along the way, an automated routine was developed to aid with the determination of the quantum angular momentum of newly identified resonances. The impact of differential scattering cross sections with respect to angle was determined in the benchmarking process. The implications of the study of the impact of differential cross sections on criticality suggest a necessity for detailed treatment of the angular distributions during the evaluation process, as well as temperature broadening of the angular distributions for simulation applications. The formalism for temperature broadening of angular distributions has been derived and tested. The new evaluations were compared against the current ENDF/B-VII.1 standard on a set of 23 criticality safety benchmark models and displayed improved performance. In the new methodology developed for coupling of the differential and integral data evaluation, resonance parameters are directly and systematically adjusted based on feedback from integral benchmark experiments. Coupling this feedback directly to the resonance parameters gives the new method the advantage of implicitly adjusting all of the cross sections simultaneously, including the double differential cross sections. Based on integral feedback, the new methodology provides a way of updating the reported covariance of the resolved resonance region to reflect true state of knowledge. / by Vladimir Sobes. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 149-152). / In order to provide improved predictions of Pellet Cladding Mechanical Interaction (PCMI) for the FRAPCON nuclear fuel performance code, a new model, the FRAPCON Radial-Axial Soft Pellet (FRASP) model, was developed. This new model uses 1.5D structural mechanics to represent both the fuel pellet and cladding along with their interaction via interfacial forces. The fuel pellet and cladding are modeled as concentric annular cylinders using similar governing equations with slight differences to allow for cracking of the semi-brittle fuel matrix and plastic behavior in a ductile cladding. By accounting for the structural mechanics of the fuel pellet, FRASP allows for stress-induced deformations which were previously unattainable with the rigid pellet model used by FRAPCON. Because of the significant differences between FRAPCON's previous mechanical model, FRACASI, and FRASP, simply replacing the treatment of PCMI within the code was not a viable option. This led to a complete replacement of FRACAS-I and all associated fuel rod structural calculations. Feedback effects are likely to result from such a major change due to the complexity of nuclear fuel simulation. The potential for these feedback effects dictated a preliminary validation of FRASP against FRACAS-I for typical case. This evaluation was not limited to the investigation of mechanical parameters, but covered a wide variety of predicted parameters by the new and unaltered versions of FRAPCON. The differences which were found in this validation were limited in nature and easily attributable to the differing assumptions of FRASP and FRACAS-I. The newly developed mechanical model was used with the improved fuel behavior models of FRAPCON-EP (Enhanced Performance) to assess the mechanical behavior of fuel rods with a composite silicon carbide (SiC) cladding under Pressurized Water Reactor (PWR) conditions. The fuel rod designs were selected to match previously chosen values for both solid and annular fuel pellets under current and uprated power conditions. Unlike FRACAS-I, which is hindered by the rigid pellet model, FRASP was able to successfully analyze PCMI behavior with the more rigid SiC, even though "hard contact" of the fuel and cladding was encountered. Simulations using the improved models showed that the SiC clad fuel rods may not provide adequate safety margins at the desired burnup, or simply fail to achieve their desired final burnup. Previous analyses which relied on FRAPCON-3.3 may have been overly optimistic in this regard. The new, more conservative predictions are largely due to FRASP's treatment of the inner radius of the annular fuel pellets, which was assumed not to change in previous versions of FRAPCON. These new findings suggest that SiC fuel rod general design and operation require further optimization. / by Alexander James Mieloszyk. / S.M.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 86-88). / 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, OrthoCaP, Inc., is delivered as a start-up venture over the next eight to ten years. With several key patents already filed, an extensive patent search was completed to establish leading competitors and technology in the marketplace. Although still in the primary phases of development, short-term profitability can be seen through licensing the technology to larger more secure firms. Long-term profitability is realized through a more scientific approach of broadening the technology to other areas of tissue regeneration and modifying the mechanical and material characteristics associated with collagen based templates. / by Cassandra Holzgartner Ott. / M.Eng.