Molecular engineering and structural design of electrochemically active organic and organometallic materials for energy storage devices

In modern society energy and environmental issues are regarded as two grand challenges for human beings. Researchers are trying to utilize sustainable energy more efficiently without squandering resources or polluting the environment. However, the widespread application of conventional energy storage devices is limited by the uncompetitive performance, as well as the high cost and environmental concerns associated with the use of metal-based inorganic redox species. In consideration of advantageous features such as potentially low cost, vast molecular diversity, and highly tailorable properties, organic and organometallic molecules emerge as promising alternative electroactive species. In this dissertation, two families of materials, metallocene-based organometallics and quinone-based organic compounds are investigated comprehensively to build the high-performance redox flow batteries (RFB) for large-scale energy storage. Despite that metallocenes are also based on the redox reaction of metal centers, the cyclopentadienyl ring permits great flexibility to tune the electrochemical and physical properties through molecular engineering. Thanks to the fast reaction kinetics, the ferrocene-based membrane-free liquid battery delivers a superior power capability. Moreover, the vast family of metallocenes provides an opportunity to build an all-metallocene-based RFB. The prototype device exploits ferrocene and cobaltocene as the redox-active cathode and anode, respectively. In light of the Hammett equation, the output voltage can be finely tuned by introduction of methyl groups on the ligand rings of cobaltocene. We further investigated fundamental electrochemistry of quinones to enable heavy-metal-free, low-cost, environmental friendly energy storage devices. A bio-inspired, heavy-metal-free liquid battery has been built by directly using hydroquinone solution as catholyte and graphite as anode. The electrochemistry of hydroquinone is fundamentally studied in a broad pH range. By leveraging the knowledge of solubility enhancement techniques in pharmaceutical research, the solubility of hydroquinone in water is improved in the presence of urea as hydrotropic agent. Compared with arduous chemical functionalizations to improve the solubility of organic redox species, the hydrotropic solubilization method represents a sustainable and cost-effective approach to the design of grid-scale energy storage systems. Last but not least, the application of quinone family for energy systems is extended to non-aqueous electrolytes. By rational screening of different solvents and functionalization of electrochemically active molecules, the redox potential, solubility and molecular mobility of the redox species can be tuned systematically. Theoretical modeling is conducted to examine Li-binding characteristics, electronic properties, and structural stabilities of organic redox species that govern electrochemical performance of those novel energy systems. By integrating the function-oriented organic synthesis, detailed chemical characterizations, and advanced molecular dynamics simulations, we aim to provide a useful platform to design the next-generation of sustainable energy storage systems for grid-scale applicationsMaterials Science and Engineerin

Pairing Symmetry in Iron-Pnictide Superconductor KFe2_2As2_2

The pairing symmetry is one of the major issues in the study of iron-based superconductors. We adopt a low-energy effective kinetic model based on the first-principles band structure calculations combined with the $J_1$-$J_2$ model for KFe$_2$As$_2$, the phase diagram of pairing symmetries is constructed. Putting the values of $J_1$ and $J_2$ of the $J_1$-$J_2$ model obtained by the first-principles calculations into this phase diagram, we find that the pairing symmetry for KFe$_2$As$_2$ is a nodal $d_{xy}$-wave in the folded Brillouin zone with two iron atoms per unit cell. This is in good agreement with experiments observed a nodal order parameter.Comment: 5 pages, 4 figures (The pairing symmetry is dependent on choosing an effective tight-binding model. In the publication version, we adopt a ten-orbital model by using the maximally localized Wannier functions based on the first-principles band structure calculations, and give an s-wave pairing for KFe$_2$As$_2$

Aerodynamics and motor control of ultrasonic vocalizations for social communication in mice and rats.

BACKGROUND: Rodent ultrasonic vocalizations (USVs) are crucial to their social communication and a widely used translational tool for linking gene mutations to behavior. To maximize the causal interpretation of experimental treatments, we need to understand how neural control affects USV production. However, both the aerodynamics of USV production and its neural control remain poorly understood. RESULTS: Here, we test three intralaryngeal whistle mechanisms-the wall and alar edge impingement, and shallow cavity tone-by combining in vitro larynx physiology and individual-based 3D airway reconstructions with fluid dynamics simulations. Our results show that in the mouse and rat larynx, USVs are produced by a glottal jet impinging on the thyroid inner wall. Furthermore, we implemented an empirically based motor control model that predicts motor gesture trajectories of USV call types. CONCLUSIONS: Our results identify wall impingement as the aerodynamic mechanism of USV production in rats and mice. Furthermore, our empirically based motor control model shows that both neural and anatomical components contribute to USV production, which suggests that changes in strain specific USVs or USV changes in disease models can result from both altered motor programs and laryngeal geometry. Our work provides a quantitative neuromechanical framework to evaluate the contributions of brain and body in shaping USVs and a first step in linking descending motor control to USV production

History effect in inhomogeneous superconductors

A model was proposed to account for a new kind of history effect in the transport measurement of a sample with inhomogeneous flux pinning coupled with flux creep. The inhomogeneity of flux pinning was described in terms of alternating weak pinning (lower jc) and strong pinning region (higher jc). The flux creep was characterized by logarithmic barrier. Based on this model, we numerically observed the same clockwise V-I loops as reported in references. Moreover, we predicted behaviors of the V-I loop at different sweeping rates of applied current dI/dt or magnetic fields Ba, etc. Electric transport measurement was performed in Ag-sheathed Bi2-xPbxSr2Ca2Cu3Oy tapes immersed in liquid nitrogen with and without magnetic fields. V-I loop at certain dI/dt and Ba was observed. It is found that the area of the loop is more sensitive to dI/dt than to Ba, which is in agreement well with our numerical results.Comment: To appear in Phys Rev B, October 1 Issu

Wideband THz time domain spectroscopy based on optical rectification and electro-optic sampling

We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement

Essays on financial market imperfections

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2007.Includes bibliographical references.This dissertation consists of three chapters on financial market imperfections, in particular, information imperfections. Chapter 1 studies how the existence of a fixed cost per transaction faced by uninformed investors hampers information revelation through price and exacerbates adverse selection. The exacerbated adverse selection explains one long-standing puzzle in finance - the momentum anomaly. Properly adjusting stock returns for adverse selection by using data on trading volume substantially mitigates momentum-based arbitrage profits for the sample period from 1983 to 2004. Chapter 2 studies how information asymmetry prevents perfect risk-sharing and offers insights on stock return behavior. Chapter 3 explores the idea of Tobin's tax in the context of an emerging market and in particular examines the cost effects on speculation in the Chinese stock market.by Ding Wu.Ph.D

AUV path planning and adaptive on-board routing for adaptive rapid environmental assessment

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 198-204).In shallow water, a large part of underwater acoustic prediction uncertainties are induced by sub-meso-to-small scale oceanographic variabilities. Conventional oceanographic measurements for capturing such ocean-acoustic environmental variabilities face the classical conflict between resolution and coverage. The Adaptive Rapid Environmental Assessment (AREA) project was proposed to resolve this conflict by optimizing the location of in-situ measurements in an adaptive manner. In this thesis, ideas, concepts and performance limits in AREA are clarified. Both an engineering and a mathematical model for AREA are developed. A modularized AREA simulator was developed and implemented in C++. Philosophies in AREA are discussed. Presumptions about the ocean are made to bridge the gap between the viewpoint in the oceanography community, where the ocean environment is considered to be a deterministic but very complicated system, and that of the underwater acoustic community, where the ocean environment is treated as a random system. At present, how to optimally locate the in-situ measurements made by a single AUV carrying a CTD (conductivity, temperature and depth) sensor is considered in AREA. In this thesis, the AUV path planning is modeled as a Shortest Path problem. However, due to the sound velocity correlation effect, the size of this problem can be very large. A method is developed to simplify the graph for a fast solution. As a significant step, a linear approximation for acoustic Transmission Loss (TL) is investigated numerically and analytically. In addition to following a predetermined path, an AUV can also adaptively generate its path on-board. This adaptive on-board AUV routing problem is modeled using Dynamic Programming (DP) in this thesis.(cont.) A method based on an optimized predetermined path is developed to reduce the size of the DP problem and approximately yet efficiently solve it using Pattern Recognition. As a special case, a thermocline- oriented AUV yoyo control and control parameter optimization methods for AREA are also developed.Finally, some AUV control algorithms for capturing fronts are developed. A frame-work for real-time TL forecasts is developed. This is the first time that TL forecasts have been linked with ocean forecasts in real-time. All of the above ideas and methods developed were tested in two experiments, FAF05 in the northern Tyrrhenian Sea in 2005 and MB06 in Monterey Bay, CA in 2006. The latter MB06 sea exercise was a major field experiment sponsored by the Office of Naval Research and the thesis compiles significant findings from this effort.by Ding Wang.Ph.D

Adaptive rapid environmental assessment system simulation framework

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (leaves 170-171).Adaptive Rapid Environmental Assessment (AREA) is a new concept for minimizing the non model-based sonar performance prediction uncertainty and improving the model-based sonar performance by adaptive and rapid in situ measurement in the ocean environment. In this thesis, a possible structure of the AREA system has been developed; an AREA System Simulation Framework has been constructed using C++, which can simulate how AREA system will work and be utilized to determine the optimal or sub-optimal sampling strategies. A user's manual for the simulation framework, and specifications of all important C++ classes are included.by Ding Wang.S.M

Occupational noise exposure is associated with hypertension in China: Results from project ELEFANT

OBJECTIVES: We investigated the association between occupational noise exposure and the risk of elevated blood pressure and hypertension by stage in young adults. METHODS: We utilized 124,286 young adults (18-40 years) from the Project ELEFANT study. We categorized occupational noise exposure as high (75 dBA noise exposure for more than 4 hours per day) or low, and measured blood pressure (mmHg) and categorized participants by hypertension stage (normal, elevated, Stage 1, Stage 2). We applied adjusted logistic regression models to identify associations with hypertension risk, and we further examined the noise-BMI, noise-gender, and noise-residence interactions on hypertension risk in separate models. RESULTS: High occupational noise exposure was associated with increases in blood pressure among participants with elevated blood pressure (Estimate = 0.23, 95% CI: 1.09, 1.46, p = 0.0009), in Stage 1 hypertension (Estimate = 0.15, 95% CI: 1.06, 1.25, p = 0.0008), and in Stage 2 hypertension (Estimate = 0.41 95% CI: 1.31, 1.73, p<0.0001). Likewise, noise exposure-BMI interaction was consistently positively associated with increases in blood pressure in participants with elevated blood pressure (Estimate = 0.71, 95% CI: 1.55, 2.69, p<0.0001), in Stage 1 hypertension (Estimate = 0.78, 95% CI: 1.82, 2.61, p<0.0001), and in Stage 2 hypertension (Estimate = 2.06, 95% CI: 5.64, 10.81, p<0.0001). The noise exposure-male interaction showed higher risk for hypertension compared to the noise exposure-female interaction in participants with elevated blood pressure (Estimate = 1.24, 95% CI: 2.56, 4.71, p<0.0001), Stage 1 (Estimate = 1.67, 95% CI: 4.34, 6.42, p<0.0001) and Stage 2 hypertension (Estimate = 1.70, 95% CI: 3.86, 7.77, p<0.0001). Finally, we found that noise exposure-urban interaction was consistently associated with an increase in blood pressure in elevated blood pressure (Estimate = 0.32, 95% CI: 1.19, 1.62, p<0.0001) and in Stage 2 hypertension (Estimate = 0.44, 95% CI: 1.31, 1.80, p<0.0001)

Associations between objectively assessed and questionnaire-based sedentary behaviour with body mass index and systolic blood pressure in Kuwaiti adolescents.

OBJECTIVE: Kuwait has one of the highest obesity rates in the world. This study examined the associations between sedentary behaviour (objectively measured and self-reported), adiposity and systolic blood pressure in a sample of adolescents residing in Kuwait. Data was obtained from the Study of Health and Activity among adolescents in Kuwait (2012-2013). The sample included a total of 435 adolescents (201 boys). Outcomes were age- and sex specific body mass index Z-scores and systolic blood pressure. Exposures were total sedentary behaviour measured by accelerometry and time spent in some sedentary behaviours (television viewing, video games, computer use and total screen-time). We used multiple linear regression analyses, adjusted for age, governorate, maternal education and physical activity, to examine associations between sedentary behaviour and adiposity and systolic blood pressure. RESULTS: Only 2 statistically significant associations were found between sedentary behaviour and the study outcomes: body mass in boys was directly associated with higher sedentary time [β (95% CIs) 0.003 (0.00 to 0.06)]; body mass index was inversely associated with videogames in both sexes [girls: β (95% CIs) - 0.17 (- 0.48 to - 0.04); boys: - 0.24 (- 0.57 to - 0.12)]. In this sample of Kuwaiti adolescents, sedentary behaviour showed limited deleterious associations with adiposity and systolic blood pressure