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2-D Material Sensors on the Electronic Nose for the Sensitive Detection of VOCs
Get PDFChapter 1
When coated with a polymer surface layer and suspended on 3-D textured glass electrodes, the hybrid combination of polymer and graphene yields sensitive chemiresistive vapor sensors. The expansion and contraction of the polymer layer when it absorbs/reacts with the VOCs, is proposed to produce tremendous train on the suspended graphene. Hence, when VOCs permeates into the polymer layer, sizable electrical resistive changes as folds and creases is induced in the graphene due to its high gauge factor. The hybrid suspended polymer/Gr sensor exhibits substantial responses to polar organic vapors, especially pyridine, while also exhibiting reversibility and the potential future tunability in the types of polymers used as the reactive surface layer.
Chapter 2
Various polar and non-polar functional groups were covalently bonded onto MoS2 yielding incredibly sensitive chemiresistive vapor sensors. The VOCs' interaction to the functional end groups produced tremendous signal, while also exhibiting reproducibility and reversibility. Future work will further standardize the sensors while also exploring tunability in the types of groups used.
Chapter 3
This chapter reflects the very start of my PhD research, and one of the important lessons to learn about the electronic nose. It is an example that I wish my predecessors taught me (all had graduated by the time I began my research) that I hope to pass onto future nose users. It is just one example of many projects that had similar end result. Many key lessons can be learned for future nose users. Readers can choose to skip reading this.</p
Sulfur Cycling in the Water Columns of Lakes and Oceans
Get PDFSulfur is a critical bioelement central to many of Earth’s biogeochemical cycles. Studies of sulfur have overwhelmingly focused on sediments, where transformations between organic and inorganic sulfur phases drive short-term biological reactions and long-term climate cycles. However, sulfur cycling in the water column is just as dynamic and exerts similar controls over biogeochemical cycles in lakes and oceans – although the exact dynamics are only beginning to be understood. This thesis provides new understanding of sulfur cycling in aquatic environments through three chapters that span laboratory developments and field observations. Chapter 1 presents a time-series in enigmatic Mono Lake, CA, where the temporal dynamics of sulfur cycling microbes was investigated. This study, published in Geobiology, highlights the dependency of sulfate reduction and oxidation on lake chemistry and the need for studies to move beyond “snapshots” of microbial diversity. Chapter 2, published in Rapid Communications in Mass Spectrometry, presents development of a highly sensitive (1-10 µg S) mass spectrometry technique that allows, for the first time, sulfur isotope measurements of amino acids. These new measurements permitted discovery of new connections between metabolism and sulfur isotope signatures. Chapter 3 further applies these novel methods, making the first sulfur isotope measurements of marine dissolved organic matter. The data indicated that marine organic sulfur is entirely produced by phytoplankton and implied that heterotrophic bacteria rapidly and efficiently recycle reduced sulfur compounds, even in the water column. Taken together, these three chapters significantly advanced available tools for studying sulfur in the environment and expanded our understanding of modern aquatic sulfur cycling. The final chapter represents a departure from oceans, lakes, mass spectrometry, and sulfur. Here, I evaluate the success and impacts of my outreach project, the popular Women Doing Science Instagram, in portraying diverse, international women scientists, noting the powerful potential for social media to bolster STEM identity for graduate students.</p
Fairness, Morality, and Pursuing an Ideal System of Distributive Justice
No full text[Introduction] In the pursuit of an ideal society, an important factor to consider is what system of distributive justice to establish. Given a group of people and some measure of well-being – for example, wealth, income, or respect – systems of distributive justice attempt to answer the question “Who should get what?”. In this essay, I will argue that the ideal system of distributive justice must be primarily based on libertarianism, with some added amount of socialism; the former represents the most morally justified system, while the latter represents a more fair system. Fairness and morality seem to be at odds, and while both are necessary to some extent in our society, our system of distributive justice must ultimately be morally justified by the people who will live under it. First, I will introduce four classical theories of distributive justice: meritocracy, egalitarianism, socialism, and libertarianism. Then, we will look at each theory individually, considering how one would best go about constructing such a system, and evaluating the advantages and disadvantages of each. This will allow us to rule out meritocracy and egalitarianism as viable systems, as they are either too vague or reducible to other systems. Next, being left with socialism and libertarianism, we will claim that these two plausible theories are on two sides of a sort of fairness-morality spectrum, and proceed to argue that the two can be consistently mixed. Finally, to decide the ideal libertarianism-socialism mixture, we will consider the emergence of forms of government from the perspective of a citizen, and find that libertarianism is to be preferred, but some socialism is necessary to protect certain fundamental rights
Poetry Pieces
No full text[Introduction]
Savor:
A metal wind chime rings hello
as Mom and I enter Dolce vita,
the new bakery down the
block.</p
Engineering and Delivery of Programmable Protein Circuits as Potential Therapeutic Devices
Get PDFCell-specific targeting of therapeutics is a fundamental challenge in biomedicine. The use of engineered proteins that interact with one another as designed, synthetic circuits represents a promising solution to this challenge. These circuits can be constructed to directly sense endogenous cell signals, act on these signals to classify cellular state, and produce a specific response such as conditional triggering of cell death or targeted expression of a reporter. Synthetic protein circuits can also be delivered in mRNA vectors transiently to avoid permanent gene modification.
We recently showed viral proteases can be engineered to regulate one another in a composable manner, permitting the construction of diverse protein-level circuits (Circuits of Hacked Orthogonal Modular Proteases). CHOMP could perform a wide range of computations including Boolean logic, analogue signal processing, and dynamic signal processing. Using this system we were also able to directly sense key cellular pathways and conditionally respond to trigger apoptosis in cancer-like cells. Further expansion of synthetic protein circuits to include nonlinear signal processing enables new system-level behaviors.
Protein-based circuits are compatible with innovative delivery methods including mRNA encapsulated in lipid-nanoparticle formulations and engineered viruses. As a proof of principle, we were able to develop a controllable, transient RNA-virus delivery system that allowed for targeted delivery to defined cell populations. This paradigm requires control over multiple aspects of the viral delivery system, including (1) production and release of viral particles, (2) target cell entry based on cell-surface proteins, (3) replication within the cell depending on intracellular proteins, and (4) drug-dependent elimination of the virus. Here, we integrate each of these distinct levels of control can into a single system based on the well-characterized negative stranded RNA virus. This RNA-virus platform will enable synthetic protein circuit delivery.
Combining viral engineering and protein circuit construction, the work described here suggests a roadmap towards “smarter” circuit-based therapies that can integrate multiple cues to maximize therapeutic specificity and establishes a role for post-translational circuits as future therapeutic devices.</p
Freeze Casting of Ceramics: Pore Design from Solidification Principles
Get PDFFreeze casting is a porous material processing method which allows the creation of directionally aligned pores by the solidification process. Pores are generated by sublimation of solidified crystals which reject suspending particles or dissolved solutes during freezing. Although freeze-cast ceramics have been identified for applications such as filtration and bioceramics, the lack of understanding of the process often results in a discrepancy between the desired pore structure and the fabricated structures.
Since solidification is the foundation upon which freeze casting is built, this work seeks to understand the solidification process, especially the growth and time evolution of dendrites. To understand the dendritic growth process, two solidification parameters, freezing front velocity and temperature gradient, are independently controlled to investigate the effects of each parameter. Dendritic pore size changes with solidification parameters and shows good agreement with dendrite growth theory. The theory of constitutional supercooling serves as a guide to control pore morphology between dendritic pores and cellular pores. Furthermore, dendrite growth under the effects of the gravitational force is investigated by changing the solidification direction with respect to the gravity direction. Convection changes the degree of constitutional supercooling, and results in different pore sizes as well as pore morphology.
Time evolution of dendrites through isothermal coarsening is investigated. During the coarsening of dendrites, they are transformed to cylinder-like crystals, which yield honeycomb-like structures. Moreover, dendrite size changes linearly with the cube root of coarsening time. Both findings are well-established phenomena in alloy solidification. Further comparison with alloy systems are achieved with tomography-based analysis where similar microstructural evolution with alloy system is demonstrated.
Based upon the understanding of underlying solidification principles in freeze casting, three applications are explored. First, the freeze-cast structure is designed to improve shape-memory properties. Processing variables are controlled such that shape-memory porous zirconia can enable martensitic phase transformations and shape deformation without fracture. Other applications utilize unique pore space. Dendritic pores are investigated for size-based filtration to preferentially capture small particles. Flow-through experiments and in-situ observation by confocal microscopy confirm that pores created by secondary dendrites capture small particles. Finally, honeycomb-like structures are filled with functional microgels to create a ceramic/polymer composite as an application for membrane chromatography. The fabricated composite demonstrates advantages such as mechanical stability during the fluid flow.</p
Combining High- and Low-Level Electronic Structure Theories for the Efficient Exploration of Potential Energy Surfaces
Get PDFThe efficient exploration and characterization of potential energy surfaces paves the way for the theoretical elucidation of complex chemical processes. A potential energy surface arises from the application of the Born-Oppenheimer approximation when solving the Schrödinger equation for a molecular system. The extraction of energies and nuclear gradients from the Schrödinger equation is typically cost-prohibitive, which has inspired a plethora of approximations. In this thesis, we present the development of embedding and machine learning methodologies that provide fast and accurate energies and nuclear gradients for different chemical classes by combining high- and low-level electronic structure theories. If a chemical change occurs in a spatially localized region, embedding strategies offer an effective approach for balancing accuracy and computational cost. We first consider embedded mean-field theory (EMFT), which seamlessly combines different mean-field theories for different subsystems to describe the whole molecular system. We analyze the errors in EMFT calculations that occur when subsystems employ different atomic-orbital basis sets. These errors can be alleviated by a Fock-matrix correction scheme or by following general basis set recommendations. Systems exhibiting a more complicated electronic structure require a systematically improvable level of theory for the subsystems, which can be realized by projection-based embedding. Projection-based embedding enables the description of a small part of a molecular system at the level of a correlated wavefunction method while the remainder of the system is described at the mean-field level. We go on to derive and numerically demonstrate the analytical nuclear gradients for projection-based embedding. If description of the entire system at the high level of theory is deemed necessary, molecular-orbital-based machine learning (MOB-ML) calculations offers a framework to predict accurate correlation energies at the cost of obtaining molecular orbitals. We go on to present the derivation, implementation, and numerical demonstration of MOB-ML analytical nuclear gradients. We demonstrate the developed methodologies by exploring potential energy surfaces of organic and transition-metal containing molecules.</p
Investigating Unexpected but Advantageous Integrated Systems for Solar Water Splitting
Get PDFAdvantageous systems are frequently utilized for solar water splitting sometimes are not the most well-understood. Based on fundamental understandings of semiconductor physics, certain combinations of materials should never be advantageous for applications in solar water splitting. (Un)fortunately, these expectations are unrealized. Specifically, we address herein how photogenerated current is able to pass through a-TiO₂ from n-Si as well as the formation of a barrier height from electroless-deposited Pt on p-Si.
Chapter 2 addresses how charge is able to pass through thick layers of atomic layer deposited a-TiO₂ even though the deep valence band of the a-TiO₂ should make the a-TiO₂ act as a blocking layer. It was found that the presence of mid-gap defect states, observable by x-ray photospectroscopy (XPS) valence band spectrum and electron paramagnetic resonance (EPR), in the a-TiO₂ act as a channel for current to pass. The implications of the current traversing through the mid-gap defect states are that global and local changes to the mid-gap defect concentration will strongly affect the amount of current able to pass at all potentials. Thus, the choice of top contacts is limited to metals that have a work-function less than ~5.2 eV else the resistivity would increase.
Chapter 3 focuses on explaining the origin of the barrier height for electroless Pt on p-Si during hydrogen evolution. The work function of Pt should create an ohmic contact which is observed when Pt is e-beam deposited to p-Si. The origin of the barrier height was found to be dependent on the route for charge transfer. Facile redox couples showed that the solution potential of the redox couple controlled the barrier height as charge transferred occurred favorably at the h-terminated surface. While performing hydrogen evolution reaction, the barrier height is formed through the formation of a hydrogen dipole layer that occurs at the interface of the SiOₓ|Pt interface.</p
What Do We Talk About When We Talk About Love? True Love, Passionate Love, and Pining in the Short Fiction of Raymond Carver and Tobias Wolff
Get PDFLove exists in many forms: love between family members, love between friends and significant others, and generally, love of a person for every entity or object in-between. From love between a man and fish, to the love of alcohol, familial or fraternal relationships, and, finally, romantic love, Raymond Carver and Tobias Wolff depict love in its many forms in their short fiction. This thesis specifically explores the portrayal of romantic love in Carver’s story “Beginners” from the collection Beginners and Wolff’s story “Maiden Voyage” from In the Garden of the North American Martyrs. The characters in these stories form a spectrum of love. From the ideal love of Henry and Anna Gates or the modern, simple love, of Nick and Laura in “Beginners,” to the passionless love of Howard and Nora in “Maiden Voyage,” by analyzing the relationships in these stories this thesis concludes that love does exists differently for every marriage. While all relationships can have love in a broad sense, some of these loves are more powerful and lasting than others
Active Flat Optics Wavefront Manipulation for Imaging, Ranging, and Sensing
Get PDFThe emergence and maturity of integrated photonic platforms over the past decade allowed for reliable integration of a large number of photonic components on a single substrate. This ability to process and control coherent light on a chip is a potential pathway for the realization of novel low-cost systems capable of non-conventional functionalities for optical wavefront engineering. In this thesis, integrated active flat optics architectures for generation, manipulation, and reception of optical wavefronts are investigated. In particular, the application of such systems for imaging, ranging, and sensing are studied and multiple photonic systems including a large scale transmitter, a high-sensitivity receiver, and a high-resolution transceiver are demonstrated.
For generation of optical wavefronts, solutions for engineering a radiative optical waveform via emission by an array of nano-photonic antennas are studied and a chip-scale photonic transmitter is implemented. The transmitter forms an optical phased array with a novel architecture in a CMOS compatible silicon photonics process which not only dispenses with the limitations of previously demonstrated systems but also yields a narrower beamwidth leading to a higher resolution. Moreover, an integrated adaptive flat optical receiver architecture that collects samples of the incident light and processes it on-chip with high detection sensitivity is implemented. To detect the optical samples with a high signal to noise ratio, an optoelectronic mixer is proposed and designed that down-converts the optical signals received by each antenna to a radio frequency signal in the electronic domain, provides conversion gain, and rejects interferers. This system allows arbitrary wavefront manipulation of the received signal by adapting itself to new conditions — a capability that does not exist in conventional cameras. Using this system, we realized the first high-sensitivity optical phased array receivers with one-dimensional and two-dimensional apertures and the functionality of the chips as ultra-thin lens-less cameras were demonstrated. To achieve a high-resolution integrated photonic 3D imager with low system complexity, a double spectral sampling method is developed through a special wavefront sampling arrangement on the transmitter and receiver apertures. This transceiver architecture includes a multi-beam transmitter and a high-sensitivity receiver that can distinguish the illuminated points separately and process them simultaneously using a digital signal processor.
Moreover, novel ultra-low power architectures for generation and reception of short RF/microwave pulses are explored. Such systems have a broad range of applications including imaging and ranging. In this study, the capability of generating and receiving orthogonal Hermite pulses of various orders using a capacitor-only time-varying network is demonstrated.</p