L’étude de la spéciation des actinides en solution revêt une importance particulière à la fois pour la compréhension et l’amélioration des procédés de séparation pour le cycle du combustible nucléaire ainsi que pour les problèmes de spéciation dans l'environnement. Toutefois, leur caractère radioactif associé à la complexité de leur chimie fait de l’étude de la spéciation des actinides un véritable challenge expérimental. C’est pourquoi le recours à la modélisation moléculaire peut s’avérer une aide déterminante pour progresser sur cette thématique. Dans ce travail, le couplage de calculs de chimie quantique et de données expérimentales (thermodynamique, EXAFS, spectroscopie UV-visible) pour étudier la spéciation du plutonium(IV) en phase organique après extraction par des ligands N,N-dialkylamides nous a permis d'identifier la formation de plusieurs complexes ayant des modes de coordination du ligand au plutonium différents. Parallèlement, aucun champ de force n'ayant été reporté pour décrire le plutonium(IV) par dynamique moléculaire classique, nous avons entrepris de développer un potentiel d'interaction classique pour cet élément. Ce développement a été initié par le paramétrage des interactions de la série d'actinides du thorium au berkelium au degré d'oxydation IV dans l'eau. L'approche ab initio retenue pour le paramétrage ainsi que le champ de force résultant sont exposés. Les premiers résultats de dynamique moléculaire sont comparés aux données expérimentales disponibles dans la littérature puis les limites et perspectives d'amélioration de la méthode de paramétrage ainsi que du potentiel sont discutées en détail. / The actinide speciation in solution is central to the understanding and improvement of separation processes for the nuclear fuel cycle as well as envirronmental speciation problems. However, the radioactivity of these elements combined with their chemical complexity make the study of their speciation a real experimental challenge. That is why, bringing into play the molecular modeling may be a key help in getting new insights on this issue. In this work, coupling quantum chemical calculations to experimental data (thermodynamics, EXAFS, UV-visible spectroscopy) for studying plutonium(IV) speciation in an organic phase containing N,N-dialkylamide ligands enabled us to identify the formation of several complexes having different coordination modes of the ligand to the plutonium. In parallel, as no force field has been reported for discribing plutonium(IV) by classical molecular dynamics, we decided to tackle the development of such a potential for this element. This development has been initiated with the parameterization of actinide - water interactions considering the series from thorium to berkelium at their +IV oxidation state. The chosen ab initio parameterization approach as well as the final force field are presented. Then, the first molecular dynamics results are compared to available experimental data. Finally, the limits and future developments concerning both the parameterization approach and the analytical potential are discussed in detail.

Tendons are collagen-based fibrous tissues that connect muscles to bones. Tendon injury is common, but currently available treatments for damaged tendons are limited, and often fail to restore pre-injury function. The cellular and molecular mechanisms underlying tendon formation are not completely understood, and a detailed understanding of the processes involved would facilitate new therapeutic strategies. Work presented in this thesis had two aims: to investigate the role and mechanisms of cell-generated force during tendon development, and to examine the effect of external force applied to tendon tissue. The rationale to investigate micro-mechanical aspects of tendon development came from observations that tendons are intrinsically tensioned, presumably to transmit force efficiently. Tension is also critical for the formation and regulation of the primary cell-matrix interaction structures seen in embryonic tendon, known as fibripositors. In initial experiments cell-generated force was disrupted with the non-muscle myosin II (NMII) inhibitor blebbistatin. NMII inhibition prevented formation of tendon tissue in a 3D cell culture system (tendon-construct). Cell-contraction was also shown to shape the ECM and generate a crimped collagen structure characteristic of tendon. These observations highlight the importance of cell-generated force in tendon development. Further investigation using novel microscopy techniques suggested that fibripositors contained newly formed collagen fibrils, and that fibrils in the ECM were internalised and fragmented in a NMII/MT1-MMP dependent pathway. It is proposed that these fragmented fibrils are re-secreted into the matrix, where they seed fibril growth. This pathway is disrupted in MT1-MMP deficient mice, which have half normal size tendons with fewer collagen fibrils. Investigations using a mechanical rig showed that external application of force to tendon-constructs stimulated matrix maturation that more closely mimicked embryonic development. Taken together these results show that both cell-generated force and external force have important roles during tendon development. Experiments in this thesis aimed to elucidate the role of force at the tissue level (generation of mechanical properties, crimp structure), the microscopic level (cell-matrix interactions) and the molecular level (role of NMII and MT1-MMP in ECM collagen fibril handling). Given the complexity of the developmental system being investigated the multi-level experimental approach used here is necessary to generate a holistic understanding of the important developmental processes involved. Therapeutic tissue regeneration may be facilitated by application of external force or modulation of cell-generated force. Furthermore, the identification of a fibril amplification pathway has implications for medical conditions characterised by excessive collagen fibril formation (fibrosis, some cancers) or by slow or inadequate fibril formation (tendon healing).

Until such a time that computers are powerful enough to routinely perform ab initio simulation of large biomolecules, there will remain a demand for less expensive computational tools. Classical force field methods are widely used for the simulation of large molecules. However, their low computational cost comes at the price of introducing approximations to the description of the system, for example atomic point charges and Hooke type potentials. The quantum chemical topological force field, QCTFF, removes the classical approximations and uses a machine learning method, kriging, to build models that map ab initio atomic properties to changes in the internal coordinates of a chemical system. The atomic properties come from quantum chemical topology, QCT, and include atomic multipole moments and also energy terms from the interacting quantum atoms (IQA) energy decomposition scheme. By using atomic multipole moments, the electrostatic interactions between atoms is described in a more rigorous fashion than most classical force fields, and polarisation is captured through the use of kriging models. In this thesis, the QCTFF approach has been applied to a selection of test cases including small molecular dimers and amino acids. Kriging models are built using a “training set” of molecular geometries, and an investigation of different approaches for sampling amino acids is provided. The concept of the “atomic horizon sphere” is discussed, where the effect on the multipole moments of an atom in an increasingly large environment is investigated. This is an important investigation required to guide the development of future QCTFF training sets. Investigations into the effect of deprotonation of basic and acidic amino acids side chains is provided, as well as a study of the short range repulsion between atoms.

A dynamic three-dimensional volume element model (VEM) of a parabolic trough solar collector (PTC) comprising an outer glass cover, annular space, absorber tube, and heat transfer fluid is studied with detail. The model is coupled with an existing semi-finite optical model for the purpose of simulation and optimization. The spatial domain in the VEM is discretized with lumped control volumes (i.e., volume elements) in cylindrical coordinates according to the predefined collector geometry. Therefore, the spatial dependency of the model is taken into account without the need to solve partial differential equations. The proposed model combines principles of thermodynamics and heat transfer as well as empirical heat transfer correlations, to simplify the modeling and expedite the computations. The resulting system of ordinary differential equations is integrated in time, yielding temperature fields which can be visualized and assessed with scientific visualization tools. The current model is validated with experimental data provided in the literature. The model was employed to evaluate the sensitivity of the collector performance described by the first and second law efficiencies to receiver length, annulus gap spacing, concentration ratio, incidence angle, inlet fluid temperature, and flow rate. This work also examined the effects of inlet fluid temperature and temperature differential on dynamic collector performance in the transient case study. Results showed that the first law efficiency was most sensitive to the inlet fluid temperature with the maximum variation of 30%, whereas the incidence angle and concentration ratio affected the second law efficiency the most with the maximum variations of 375% and 300%, respectively. The effect of the remaining parameters were trivial in all cases. In the transient analysis, higher temperature differential and lower inlet fluid temperature yielded higher total heat gain while the total exergy gain was insensitive to both parameters. The first law efficiency should therefore be of greater importance than the second law efficiency in the control of dynamic collector performance based on these two parameters. Furthermore, a sensitivity analysis of vemPTC is done with the Fourier amplitude sensitivity testing (FAST) for selected nine parameters. Cover transmittance shows a highly sensitive parameter within the rest of the selected parameters. After this sensitivity analysis, a multi-objective sensitivity analysis is studied for different heat transfer fluids such as synthetic oils, molten salts, liquid metals, nanofluids, and gases. Sobol sampling method is used for a multi-objective sensitivity analysis of different heat transfer fluids except for nanofluids, because it is more accurate to use a different methodology for sensitivity analysis of nanofluids, due to the effects of specific parameters on both first and second law efficiency. The fluid inlet temperature is a common sensitive parameter for almost all heat transfer fluids. Therefore, a multi-objective optimization study is done with four parameters and the results of it are presented in Chapter Four. Moreover, Chapter Five shows enhancement of the efficiency of both traditional parabolic trough solar collector (PTC) and transparent insulation material integrated PTC in both one and two dimensional model. Altering model types, operating conditions, or making an assumption for some used correlations is studied in the last chapter of this dissertation. After comparing the 1D and the 2D model, the results show that the most promising model type of PTC is the 2D model with TIM integrated one with correlation due to its stability for predicted efficiency. That approved that simplifying the model types may affect the results even though sufficiently accurate results are obtained with a simplified model. Temperature-dependent parameters should be selected for temperature sensitive variable in order to reach precise results. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / October 18, 2018. / Optimization, Parabolic trough solar collector, Renewable energy, Solar energy, Sustainable energy / Includes bibliographical references. / Juan C. Ordóñez, Professor Directing Dissertation; Hui Li, University Representative; Wei Guo, Committee Member; Patrick J. Hollis, Committee Member.

Understanding of the transport phenomena in Li-air batteries is crucial for improving the performance and design of Li-air batteries. In this dissertation, the basic transport equations that govern the operation of Li-air batteries are derived by starting from the underlying mass and charge transport properties of the chemical species involved in the operation of the battery. Then, two approaches are presented to solve the transport equations. In the first approach, we use first-order approximations to derive a compact model for the discharge voltage of Li-air batteries with organic electrolyte. The model considers oxygen transport and volume change in the cathode, and Butler-Volmer kinetics at the anode and cathode electrodes, and is particularly useful to the fast prediction of the discharge voltage and specific capacities of Li-air batteries. In the second approach, we propose a finite-element model in which the basic transport equations are discretized over a finite space-time mesh and solved numerically to predict the battery characteristics under different discharge conditions and for different geometrical and physical parameters. Then, the transport equations are reexamined and improved to account for different pore microstructures, pore size distribution effects, and electron transport mechanisms through the discharge product. The different microstructures are simulated numerically and the performance of Li-air batteries is analyzed in each case. A novel hybrid model is introduced to explain the perceived transition from one microstructure to another. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2015. / July 13, 2015. / Cathode, Compact model, Energy density, Li-air, Microstrucuture, Nanofibers / Includes bibliographical references. / Petru Andrei, Professor Directing Dissertation; Anke Meyer-Baese, University Representative; Jim Zheng, Committee Member; Simon Foo, Committee Member.

Vertical jump performance is a key component of sporting success. In order to improve jump height, athletic assessments using constrained vertical jumps have been created to inform training decisions. The vertical force-velocity (FV) profile is a protocol that involves an athlete performing a series of squat jumps with multiple loads to create an athlete profile that is used to assess lower limb strength and speed performance and provide training recommendations. Yet, some practitioners avoid force-velocity profiling having expressed concerns about athlete safety during heavily loaded jumps, or the time cost of testing. As a simpler, faster and safer assessment, an unloaded squat jump, and a maximal voluntary isometric mid-thigh pull (IMTP) have been used to provide general training recommendations. These basic tasks have yet to provide the array of FV profile metrics or the accuracy of the training recommendations developed from the standard vertical FV profile protocol. Fortunately, due to the similarity of these IMTP and jump task metrics and the standard FV profile it may be possible to predict the same vertical FV metrics and training recommendations using multiple athlete measures, that include IMTP and jump task metrics and predictive modeling. Therefore, the purpose of this paper is to determine if an unloaded squat jump and an IMTP, alongside other athlete variables, can be used to create an athlete vertical FVP and training recommendation comparable to the standard protocol. / Graduate

This dissertation is mainly focused on the investigation of cathode in Li-air batteries using organic electrolyte and the development of high-rate rechargeable Li-air flow batteries. A Li-air battery using organic electrolyte with an air electrode made with a mixture of carbon nanotube (CNT) and carbon nanofiber (CNF) is utilized to investigate the capacity limitation effects of cathode using a multiple-discharge method. Scanning electron microscopy (SEM) images show that the discharge product mainly forms at the air side of cathode due to low oxygen solubility and diffusivity in the organic electrolyte. This inhomogeneous distribution of discharge product indicates that the Li-air cell falls short of the maximum capacity of air electrode. Electrochemical impedance spectra (EIS) demonstrated that during discharge at high current density (1 mA/cm2) pore blocking is the major factor that limits capacity; however, during discharge at low current density (0.2 mA/cm2) both pore blocking and impedance rise contribute to the capacity limitation. It's been confirmed that cathode is the dominant limitation to the discharge capacity. Also, the gradient porosity structure of cathode is able to increase the capacity based on the weight of carbon, but the electrolyte loading needs to be optimized to achieve high energy density of cell. A novel rechargeable Li-air flow battery is demonstrated. It consists of a lithium-ion conducting glass-ceramic membrane sandwiched by a Li-metal anode in organic electrolyte and a carbon nanofoam cathode through which oxygen-saturated aqueous electrolyte flows. It features a flow cell design in which aqueous electrolyte is bubbled with compressed air, and is continuously circulated between the cell and a storage reservoir to supply sufficient oxygen for high power output. It shows high rate capability (5 mA/cm²) and renders a power density of 7.64 mW/cm² at a constant discharge current density of 4 mA/cm². Adding RuO² as a catalyst in the cathode, the battery showed a high round-trip efficiency (ca. 83%), with the overpotentials of 0.67 V between charge and discharge at a current of 1 mA/cm². A Li-air flow battery using graphite as anode is also demonstrated for several cycles. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2014. / October 10, 2014. / Li-air battery, Li-air flow battery / Includes bibliographical references. / Jim P. Zheng, Professor Directing Dissertation; Tao Liu, University Representative; Pedro Moss, Committee Member; Petru Andrei, Committee Member.

Thesis (M.S.)--Boston University

The ability to use force by police officers is one of their defining features. Police officers have a monopoly on the legitimate use of coercive force in the United States. A police officer’s decision to use force in an encounter depends on the behavior of both officer and citizen in an officer-citizen encounter. Each party interacts with, and responds to, the other over the course of the encounter, with each behavior and subsequent response drawing the encounter closer to its ultimate conclusion. As representatives of government, police officers have perhaps greater control in steering the interaction towards or away from a forceful conclusion. Using various techniques, police officers often can de-escalate an officer-citizen encounter before use of force is required. These techniques include things such as explaining the purpose of the interaction, keeping a respectful and safe distance from citizens, providing an introduction to citizens, exhibiting a calm and controlled demeanor, speaking directly and concisely, repeating important information, engaging in active listening, and clearly explaining the consequences of the offenders actions. The current study utilizes police officer body camera footage to examine if and how these eight officer de-escalation practices predict whether or not officers’ resort to using force in an officer-citizen encounter. Furthermore, the eight techniques are divided into proactive and reactive techniques in order to test whether a specific set of de-escalation techniques are more effective than another.

Wind energy has become one of the most important and thriving renewable energy resources in the world. Transforming the kinetic energy of wind into electric power is more environmentally friendly than traditional processes such as the combustion of fossil fuels. It provides independence from the limited fossil fuels reserves by using an unlimited resource. In order to develop a wind power facility, it is important to develop an initial wind resource assessment to guarantee the selected site will be profitable in terms of electric energy output. Several countries lack developed wind atlases that indicate a rough estimate of wind resource in their territories, which is an obstacle for inexpensive wind resource evaluations. In order to perform site evaluations generally an anemometer must be put in place to take wind measurements. This process is costly and time consuming since at least a year of data must be observed. The quality of wind resource depends on several geographic and atmospheric characteristics such as: air density, site location, site topography, wind speed and direction. This study was conducted to provide an initial wind resource assessment on three locations in Venezuela which do not have previous evaluations: Cerro Copey, Punta de Piedras and Los Roques. The assessment was done remotely based on the national meteorological service meteorological observations; wind resource and turbine power output uncertainties were taken into account. The wind assessment was done through Monte Carlo simulations mathematically considering several uncertainties with emphasis on surface roughness for vertical extrapolation. The results exhibit wind energy potential of the three sites and a throughout wind resource characterization of the site with the most potential: Cerro Copey. / A Thesis submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the Master of Science. / Spring Semester 2016. / April 8, 2016. / Assessment, Energy, Venezuela, Wind / Includes bibliographical references. / Sungmoon Jung, Professor Directing Thesis; Eren Erman Ozguven, Committee Member; Kamal Tawfiq, Committee Member; Raphael Kampmann, Committee Member.