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Open Access Publications from the University of California

Scholarly Works (13 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2015)

This dissertation includes three chapters: (1) Farmers' Information Management in Developing Countries - A Highly Asymmetric Information Structure. (2) Information Provision Policies for Improving Farmer Welfare in Developing Countries: Heterogeneous Farmers and Market Selection. (3) Role of Exchangeable Tickets in the Optimal Menu Design for Airline Tickets.

The first chapter studies farmers' information management and utilization problems in developing countries. In these countries, governments, non-governmental organizations, and social entrepreneurs are disseminating agriculture information to farmers to improve their welfare. However, instead of having direct access to the information, farmers usually acquire information from local social networks, and, thus, they may have very different information channels. In this paper, we establish a general framework that accommodates highly asymmetric information structures to capture the fact that information is transmitted indirectly through the social network. In our model, a bipartite graph describes which subset of signals is accessible to a farmer. We characterize a unique Bayesian Nash equilibrium and express farmers' strategies and expected profits in closed forms. We discuss properties of this equilibrium and show that asymmetric information structures can lead to various novel results. We also conduct comprehensive studies on the equilibrium in the "weak signal limit", where signals are subject to substantial noise. We examine the government's optimal information allocation in this limit when its goal is to maximize (1) farmers' total profits or (2) the social welfare.

In the second chapter, we examine the impact of information provision policies on farmer welfare in developing countries where farmers lack relevant and timely information for making informed decisions regarding which crop to grow and which market to sell in. In addition to heterogeneous farmers, we consider the case when farmers are price takers and yet the price of each crop (or the price in each market) is a linearly decreasing function of the total sales quantity. When market information is offered free-of-charge, we show that: (a) providing information is always beneficial to farmers at the individual level; and (b) providing information to all farmers may not be welfare maximizing at the aggregate level. To maximize farmer welfare, it is optimal to provide information to a targeted group of farmers who are located far away from either market. However, to overcome perceived unfairness among farmers, we show that the government should provide information to all farmers at a nominal fee so that the farmers will adopt the intended optimal provision policy willingly. We extend our analysis to examine different issues including: precision of market information, and information dissemination via a for-profit company.

The third chapter examines the optimal menu design problem with three types of tickets: refundable, nonrefundable, and exchangeable tickets. We identify the role of exchangeable tickets in trapping consumers and show that for the seller, it is inherently more profitable than the other two types of tickets. On the other hand, increasing the flexibility of exchangeable tickets may dampen the seller's profitability. The analysis also reveals that cancellation fees are used as instruments to adjust the differences between consumers' willingness to pay, and when they are adopted, the seller has less incentive to sell nonrefundable tickets. Our results also explain why menu offerings, while prevalent in the airline industry, are so scant in commodity goods markets.

    Cover page: Game Theory Applications in Socially Responsible Operations and Operations-Marketing Interface
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2018)
    Future energy applications rely on our ability to tune liquid intermolecular interactions and achieve designer electrolytes with highly optimized properties. In this work, we demonstrate rational, combined experimental-computational design of a new carba- closo-dodecaborate-based salt with enhanced anodic stability for Mg energy storage applications. We first establish, through a careful examination using a range of solvents, the anodic oxidation of a parent anion, the carba- closo-dodecaborate anion at 4.6 V vs Mg0/2+ (2.0 vs Fc0/+), a value lower than that projected for this anion in organic solvent-based electrolytes and lower than weakly associating bis(trifluoromethylsulfonyl)imide and tetrafluoroborate anions. Solvents such as acetonitrile, 3-methylsulfolane, and 1,1,1,3,3,3-hexafluoroisopropanol are shown to enable the direct measurement of carba- closo-dodecaborate oxidation, where the resultant neutral radical drives passive film formation on the electrode. Second, we employ computational screening to evaluate the impact of functionalization of the parent anion on its stability and find that replacement of the carbon-vertex proton with a more electronegative fluorine or trifluoromethyl ligand increases the oxidative stability and decreases the contact-ion pair formation energy while maintaining reductive stability. This predicted expansion of the electrochemical window for fluorocarba- closo-dodecaborate is experimentally validated. Future work includes evaluation of the viability of these derivative anions as efficient and stable carriers for energy storage as a function of the ionic transport through the resulting surface films formed on candidate cathodes.
      Cover page: Enhanced Stability of the Carba-closo-dodecaborate Anion for High-Voltage Battery Electrolytes through Rational Design
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2017)
      We used extreme ultraviolet (XUV) transient absorption spectroscopy to study the autoionizing Rydberg states of oxygen in an electronically- and vibrationally-resolved fashion. XUV pulse initiates molecular polarization and near-infrared pulse perturbs its evolution. Transient absorption spectra show positive optical-density (OD) change in the case of nsσg and ndπg autoionizing states of oxygen and negative OD change for ndσg states. Multiconfiguration time-dependent Hartree-Fock (MCTDHF) calculations are used to simulate the transient absorption and the resulting spectra and temporal evolution agree with experimental observations. We model the effect of near-infrared perturbation on molecular polarization and find that the laser-induced phase-shift model agrees with the experimental and MCTDHF results, while the laser-induced attenuation model does not. We relate the electronic-state-symmetry-dependent sign of the OD change to the Fano parameters of the static absorption line shapes.
        Cover page: Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modifications
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2022)
        The rational design of electrolytes has been a long-standing challenge in chemistry and materials science. In this work, we demonstrate a computational rationale for improving the performance of weakly coordinating electrolytes in currently challenging multivalent-ion battery applications, based on enhanced thermodynamic and kinetic stability against reductive decomposition. A series of fluorinated alkoxyborate and alkoxyaluminate salts are systematically examined based on their reduction and oxidation potentials and, motivated by NMR spectroscopy, detailed reductive decomposition pathways involving the breaking of Al/B-O, C-O, or C-F bonds are obtained. Based on the decomposition kinetics, the hexafluoro-tert-isopropoxy (hfip) ligand for borates and the trifluoro-tert-butoxy (tftb) ligand for aluminates are identified as promising ligands for constructing the salt anions. This borate prediction corroborates previous experimental work on Mg[B(hfip)4]2and Ca[B(hfip)4]2, in which excellent electrochemical properties were reported. We find that steric factors govern the B-O bond-breaking decomposition kinetics while electronic factors are more important for aluminate salts. There is more charge transfer character in the aluminate transition states compared with borates for Al/B-O bond-breaking decomposition and thus electron-withdrawing ligands tend to stabilize the aluminate transition states. Such molecular-level understandings allow for better design principles for developing new electrolytes with improved stability and performance.
          Cover page: Reductive Decomposition Kinetics and Thermodynamics That Govern the Design of Fluorinated Alkoxyaluminate/Borate Salts for Mg-Ion and Ca-Ion BatteriesCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2015)
          Microbial metabolism involves complex, system-level processes implemented via the orchestration of metabolic reactions, gene regulation, and environmental cues. One canonical example of such processes is acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum, during which cells convert carbon sources to organic acids that are later reassimilated to produce solvents as a strategy for cellular survival. The complexity and systems nature of the process have been largely underappreciated, rendering challenges in understanding and optimizing solvent production. Here, we present a system-level computational framework for ABE fermentation that combines metabolic reactions, gene regulation, and environmental cues. We developed the framework by decomposing the entire system into three modules, building each module separately, and then assembling them back into an integrated system. During the model construction, a bottom-up approach was used to link molecular events at the single-cell level into the events at the population level. The integrated model was able to successfully reproduce ABE fermentations of the WT C. acetobutylicum (ATCC 824), as well as its mutants, using data obtained from our own experiments and from literature. Furthermore, the model confers successful predictions of the fermentations with various network perturbations across metabolic, genetic, and environmental aspects. From foundation to applications, the framework advances our understanding of complex clostridial metabolism and physiology and also facilitates the development of systems engineering strategies for the production of advanced biofuels.
            Cover page: Integrated, systems metabolic picture of acetone-butanol-ethanol fermentation by Clostridium acetobutylicum.
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2016)
            Through coupled experimental analysis and computational techniques, we uncover the origin of anodic stability for a range of nonaqueous zinc electrolytes. By examination of electrochemical, structural, and transport properties of nonaqueous zinc electrolytes with varying concentrations, it is demonstrated that the acetonitrile-Zn(TFSI)2, acetonitrile-Zn(CF3SO3)2, and propylene carbonate-Zn(TFSI)2 electrolytes can not only support highly reversible Zn deposition behavior on a Zn metal anode (≥99% of Coulombic efficiency) but also provide high anodic stability (up to ∼3.8 V vs Zn/Zn(2+)). The predicted anodic stability from DFT calculations is well in accordance with experimental results, and elucidates that the solvents play an important role in anodic stability of most electrolytes. Molecular dynamics (MD) simulations were used to understand the solvation structure (e.g., ion solvation and ionic association) and its effect on dynamics and transport properties (e.g., diffusion coefficient and ionic conductivity) of the electrolytes. The combination of these techniques provides unprecedented insight into the origin of the electrochemical, structural, and transport properties in nonaqueous zinc electrolytes.
              Cover page: Origin of Electrochemical, Structural, and Transport Properties in Nonaqueous Zinc Electrolytes
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2023)
              Out-of-equilibrium electrochemical reaction mechanisms are notoriously difficult to characterize. However, such reactions are critical for a range of technological applications. For instance, in metal-ion batteries, spontaneous electrolyte degradation controls electrode passivation and battery cycle life. Here, to improve our ability to elucidate electrochemical reactivity, we for the first time combine computational chemical reaction network (CRN) analysis based on density functional theory (DFT) and differential electrochemical mass spectroscopy (DEMS) to study gas evolution from a model Mg-ion battery electrolyte─magnesium bistriflimide (Mg(TFSI)2) dissolved in diglyme (G2). Automated CRN analysis allows for the facile interpretation of DEMS data, revealing H2O, C2H4, and CH3OH as major products of G2 decomposition. These findings are further explained by identifying elementary mechanisms using DFT. While TFSI- is reactive at Mg electrodes, we find that it does not meaningfully contribute to gas evolution. The combined theoretical-experimental approach developed here provides a means to effectively predict electrolyte decomposition products and pathways when initially unknown.
                Cover page: Chemical Reaction Networks Explain Gas Evolution Mechanisms in Mg-Ion Batteries
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2021)
                A promising high-voltage spinel oxide cathode material MgCrMnO4 with 18% Mg/Mn inversion was synthesized successfully. A new custom operando battery device was designed to study the cation migration mechanisms of the MgCrMnO4 cathode using 0.1 M Mg(TPFA)2 electrolyte dissolved in triglyme and activated carbon as the anode. For the first time in multivalent batteries, high-quality operando diffraction data enabled the accurate quantification of cation contents in the host structure. Besides the exceptional reversibility of 12% Mg2+ insertion in Mg1-xCrMnO4 (x ≤ 1), a partially reversible insertion of excess Mg2+ during overdischarging was also observed. Moreover, the insertion/extraction reaction was experimentally shown to be accompanied by a series of cation redistributions in the spinel framework, which were further supported by density functional theory calculations. The inverted Mn is believed to be directly involved in the cation migrations, which would cause voltage hysteresis and irreversible structural evolution after overdischarging. Tuning the Mg/Mn inversion rate could provide a direct path to further optimize spinel oxide cathodes for Mg-ion batteries, and more generally, the operando techniques developed in this work should play a key role in understanding the complex mechanisms involved in multivalent ion insertion systems.
                  Cover page: Operando X‑ray Diffraction Studies of the Mg-Ion Migration Mechanisms in Spinel Cathodes for Rechargeable Mg-Ion Batteries
                  • Article
                  • Peer Reviewed
                  LBL Publications (2019)
                  Multimodal microscopy that combines complementary nanoscale imaging techniques is critical for extracting comprehensive chemical, structural, and functional information, particularly for heterogeneous samples. X-ray microscopy can achieve high-resolution imaging of bulk materials with chemical, magnetic, electronic, and bond orientation contrast, while electron microscopy provides atomic-scale spatial resolution with quantitative elemental composition. Here, we combine x-ray ptychography and scanning transmission x-ray spectromicroscopy with three-dimensional energy-dispersive spectroscopy and electron tomography to perform structural and chemical mapping of an Allende meteorite particle with 15-nm spatial resolution. We use textural and quantitative elemental information to infer the mineral composition and discuss potential processes that occurred before or after accretion. We anticipate that correlative x-ray and electron microscopy overcome the limitations of individual imaging modalities and open up a route to future multiscale nondestructive microscopies of complex functional materials and biological systems.
                    Cover page: Multimodal x-ray and electron microscopy of the Allende meteorite
                    • Article
                    • Peer Reviewed
                    UC Santa Cruz Previously Published Works (2020)
                    The use of oxide cathodes in Mg batteries would unlock a potential energy storage system that delivers high-energy density. However, poor kinetics of Mg diffusion in known solid oxide lattices strongly limits reversible intercalation, which motivates the sustained exploration of new candidates. Herein, nanocrystals of a few-layer phyllomanganate, reminiscent of the mineral vernadite, were shown to have considerable electrochemical activity toward Mg intercalation at room temperature, where it delivered ∼190 mAh g-1 at ∼1.9 V (vs Mg/Mg2+) in batteries paired with a Mg metal anode. Multimodal characterization confirmed the notable degree of reversible intercalation by probing the structural, compositional, and redox changes undertaken by the oxide. Distinct levels of Mg activity were also observed while varying the content of small amounts of lattice water and the temperature of the reaction. The results reaffirm the prospects for operational Mg batteries using oxide cathodes in moderate conditions, overcoming current limits of performance of this prospective technology.
                    • 1 supplemental ZIP
                    Cover page: Intercalation of Mg into a Few-Layer Phyllomanganate in Nonaqueous Electrolytes at Room Temperature
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