Matching Items (209)

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Synthesis and Characterization of Laser Plasma that Produces Pseudocarbyne Using Laser Pulses

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Carbon allotropes are the basis for many exciting advancements in technology. While sp² and sp³ hybridizations are well understood, the sp¹ hybridized carbon has been elusive. However, with recent advances

Carbon allotropes are the basis for many exciting advancements in technology. While sp² and sp³ hybridizations are well understood, the sp¹ hybridized carbon has been elusive. However, with recent advances made using a pulsed laser ablation in liquid technique, sp¹ hybridized carbon allotropes have been created. The fabricated carbon chain is composed of sp¹ and sp³ hybridized bonds, but it also incorporates nanoparticles such as gold or possibly silver to stabilize the chain. The polyyne generated in this process is called pseudocarbyne due to its striking resemblance to the theoretical carbyne. The formation of these carbon chains is yet to be fully understood, but significant progress has been made in determining the temperature of the plasma in which the pseudocarbyne is formed. When a 532 nm pulsed laser with a pulsed energy of 250 mJ and pulse length of 10ns is used to ablate a gold target, a peak temperature of 13400 K is measured. When measured using Laser-Induced Breakdown spectroscopy (LIBS) the average temperature of the neutral carbon plasma over one second was 4590±172 K. This temperature strongly suggests that the current theoretical model used to describe the temperature at which pseudocarbyne generates is accurate.

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  • 2019-05

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Comparative Analysis between Lab and Novel dataSONDE Measurements in Tempe Town Lake

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Tempe Town Lake is the site of fifteen years’ worth of chemical data collection by ASU researchers. In 2018 the dataSONDE, an instrument capable of measuring different water quality parameters

Tempe Town Lake is the site of fifteen years’ worth of chemical data collection by ASU researchers. In 2018 the dataSONDE, an instrument capable of measuring different water quality parameters every thirty minutes for a month at a time was installed in the lake. The SONDE has the potential to completely reduce the need for sampling by hand. Before the SONDE becomes the sole means of gathering data, it is important to verify its accuracy. In this study, the measurements gathered by the SONDE (pH, dissolved oxygen, temperature, conductivity and colored dissolved organic matter) were compared to measurements gathered using the verified methods from the past fifteen years.

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  • 2020-12

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The Focusing of Proteins Using Dielectrophoresis in an Improved Microfluidic Device

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Dielectrophoresis is a separations strategy that has the potential to separate small amounts of different proteins from each other. The forces at play in the channel used for dielectrophoresis are

Dielectrophoresis is a separations strategy that has the potential to separate small amounts of different proteins from each other. The forces at play in the channel used for dielectrophoresis are electroosmotic flow (EOF), electrophoresis (EP), and dielectrophoresis (DEP). EOF is the force exerted on liquid from an applied potential (1). EP is the force exerted on charged particles in a uniform electric field (2). DEP is the force exerted on particles (charged and uncharged) in a non-uniform electric field (3). This experiment was focused on the testing of a new microfluidic device to see if it could improve the focusing of proteins in dielectrophoresis. It was predicted that the addition of a salt bridge would improve focusing by preventing the ions created by the electrolysis of water around the electrodes from interacting with the proteins and causing aggregation, among other problems. Control trials using the old device showed that electrolysis was likely occurring and was the causal agent for poor outcomes. After applying the electric potential for some time a pH front traveled through the channel causing aggregation of proteins and the current in the channel decreased rapidly, even while the voltage was held constant. The resistance in the channels of the control trials also slightly decreased over time, until the pH shift occurred, at which time it increased rapidly. Experimental trials with a new device that included salt bridges eliminated this pH front and had a roughly linear increase of current in the channel with the voltage applied. This device can now be used in future research with protein dielectrophoresis, including in the potential differentiation of different proteins. References: 1) Electroosmosis. Oxford Dictionary of Biochemistry and Molecular Biology. 2. Oxford University Press: Oxford, England. 2006. 2) Electrophoresis. Oxford Dictionary of Biochemistry and Molecular Biology. 2. Oxford University Press: Oxford, England. 2006. 3) Dielectrophoresis. Oxford Dictionary of Biochemistry and Molecular Biology. 2. Oxford University Press: Oxford, England. 2006.

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  • 2016-05

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Exploration of Enzymatic Efficiency in Double-Stranded DNA by Uracil-DNA Glycosylase and Optimization of Glycosylation Reaction of DNA Precursor

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The two chapters of this thesis focus on different aspects of DNA and the properties of nucleic acids as the whole. Chapter 1 focuses on the structure of DNA and

The two chapters of this thesis focus on different aspects of DNA and the properties of nucleic acids as the whole. Chapter 1 focuses on the structure of DNA and its relationship to enzymatic efficiency. Chapter 2 centers itself on threose nucleic acid and optimization of a step in the path to its synthesis. While Chapter 1 discusses DNA and Uracil-DNA Glycosylase with regards to the base excision repair pathway, Chapter 2 focuses on chemical synthesis of an intermediate in the pathway to the synthesis of TNA, an analogous structure with a different saccharide in the sugar-phosphate backbone.
Chapter 1 covers the research under Dr. Levitus. Four oligonucleotides were reacted for zero, five, and thirty minutes with uracil-DNA glycosylase and subsequent addition of piperidine. These oligonucleotides were chosen based on their torsional rigidities as predicted by past research and predictions. The objective was to better understand the relationship between the sequence of DNA surrounding the incorrect base and the enzyme’s ability to remove said base in order to prepare the DNA for the next step of the base excision repair pathway. The first pair of oligonucleotides showed no statistically significant difference in enzymatic efficiency with p values of 0.24 and 0.42, while the second pair had a p value of 0.01 at the five-minute reaction. The second pair is currently being researched at different reaction times to determine at what point the enzyme seems to equilibrate and react semi-equally with all sequences of DNA.
Chapter 2 covers the research conducted under Dr. Chaput. Along the TNA synthesis pathway, the nitrogenous base must be added to the threofuranose sugar. The objective was to optimize the original protocol of Vorbrüggen glycosylation and determine if there were better conditions for the synthesis of the preferred regioisomer. This research showed that toluene and ortho-xylene were more preferable as solvents than the original anhydrous acetonitrile, as the amount of preferred isomer product far outweighed the amount of side product formed, as well as improving total yield overall. The anhydrous acetonitrile reaction had a final yield of 60.61% while the ortho-xylene system had a final yield of 94.66%, an increase of approximately 32%. The crude ratio of preferred isomer to side product was also improved, as it went from 18% undesired in anhydrous acetonitrile to 4% undesired in ortho-xylene, both values normalized to the preferred regioisomer.

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  • 2016-05

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Reduction of Carbon Dioxide with Cobalt and Iron Porphyrins

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The free-base tetra-tolyl-porphyrin and the corresponding cobalt and iron porphyrin complexes were synthesized and characterized to show that this class of compound can be promising, tunable catalysts for carbon dioxide

The free-base tetra-tolyl-porphyrin and the corresponding cobalt and iron porphyrin complexes were synthesized and characterized to show that this class of compound can be promising, tunable catalysts for carbon dioxide reduction. During cyclic voltammetry experiments, the iron porphyrin showed an on-set of ‘catalytic current’ at an earlier potential than the cobalt porphyrin’s in organic solutions gassed with carbon dioxide. The cobalt porphyrin yielded larger catalytic currents, but at the same potential as the electrode. This difference, along with the significant changes in the porphyrin’s electronic, optical and redox properties, showed that its capabilities for carbon dioxide reduction can be controlled by metal ions, allotting it unique opportunities for applications in solar fuels catalysis and photochemical reactions.

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  • 2016-05

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Dating Deep-Sea Pelagic Clays with Osmium Isotopes to Reconstruct Sources of Iron to the South Pacific Gyre over 90 Million Years

Description

Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the

Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the development of modern marine ecosystems and perhaps even contributed to past changes in Earth’s climate. Three sources of Fe—wind-blown dust, hydrothermal activity, and sediment dissolution—carry distinct Fe isotopic fingerprints, and can therefore be used to track Fe source variability through time. However, establishing the timing of this source variability through Earth’s history remains challenging because the major depocenters for dissolved Fe in the ocean lack well-established chronologies. This is due to the fact that they are difficult to date with traditional techniques such as biostratigraphy and radiometric dating. Here, I develop age models for sediments collected from the International Drilling Program Expedition 329 by measuring the Os (osmium) isotopic composition of the hydrogenous portion of the clays. These extractions enable dating of the clays by aligning the Os isotope patterns observed in the clays to those in a reference curve with absolute age constraints through the Cenozoic. Our preliminary data enable future development of chronologies for three sediment cores from the high-latitude South Pacific and Southern Oceans, and demonstrate a wider utility of this method to establish age constraints on pelagic sediments worldwide. Moreover, the preliminary Os isotopic data provides a critical first step needed to examine the changes in Fe (iron) sources and cycling on millions of years timescales. Fe isotopic analysis was conducted at the same sites in the South Pacific and demonstrates that there are significant changes in the sources of Fe to the Southern Ocean over the last 90 Ma. These results lay the groundwork for the exploration of basin-scale sources to Fe source changes, which will have implications for understanding how biological productivity relates to Fe source variability over geological timescales.

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  • 2018-05

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Tecolote Cinder Cone Ballistics: Volcanic Bomb Formation and Dynamics

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Cinder cones are common volcanic structures that occur in fields, and on the flanks of shield volcanoes, stratovolcanoes, and calderas. Because they are common structures, they have a significant possibility

Cinder cones are common volcanic structures that occur in fields, and on the flanks of shield volcanoes, stratovolcanoes, and calderas. Because they are common structures, they have a significant possibility of impacting humans and human environments. As such, there is a need to analyze cinder cones to get a better understanding of their eruptions and associated hazards. I will approach this analysis by focusing on volcanic bombs and ballistics, which are large clots of lava that are launched from the volcanic vent, follow ballistic trajectories, and can travel meters to a few kilometers from their source (e.g. Fagents and Wilson 1993; Waitt et al. 1995).
Tecolote Volcano in the Pinacate Volcanic Field in Mexico contains multiple vents within a horseshoe-shaped crater that have all produced various ejecta (Zawacki et al. 2019). The objectives of this research are to map ballistic distribution to understand the relationship between the source vent or vents and the bombs and ballistics that litter the region around Tecolote, and interpret the eruption conditions that ejected those bombs by using their distributions, morphologies, and fine-scale textures.
The findings of this work are that these bombs are apparently from the last stages of the eruption, succeeding the final lava flows. The interiors and exteriors of the bombs display different cooling rates which can are indicated by the fabric found within. Using this, certain characteristics of the bombs during eruption were extrapolated. The ‘cow pie’ bombs were determined to be the least viscous or contained a higher gas content at the time of eruption. Whereas the ribbon/rope bombs were determined to be the most viscous or contained a lesser gas content. Looking at the Southern Bomb Field site, it is dominated by large bombs that were during flight were molded into aerodynamic shapes. The Eastern Rim site is dominated by smaller bombs that appeared to be more liquid during the eruption. This difference in the two sites is a probable indication of at least two different eruptive events of different degrees of explosivity. Overall, aerodynamic bombs are more common and extend to greater distances from the presumed vent (up to 800 m), while very fluidal bombs are uncommon beyond 500 meters. Fluidal bombs (‘cow pie’, ‘ribbon’, ‘rope/spindle’) show a clear trend in decreasing size with distance from vent, whereas the size-distance trend is less dramatic for the aerodynamic bombs.

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  • 2020-05

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Exploring Synthesis Strategies Towards Spherical Cr2GaC

Description

MAX phases are layered hexagonal early transition metal carbides, sometimes nitrides, where M is an early transition metal, A is an A group element, most prominently groups 13 or 14,

MAX phases are layered hexagonal early transition metal carbides, sometimes nitrides, where M is an early transition metal, A is an A group element, most prominently groups 13 or 14, and X is either carbon or nitrogen.1 They are gaining a lot of attention because of their unusual properties. Particularly, their hardness, chemical stability at room temperature, and high melting points. These properties provide a material that is viable for a wide range of demanding applications.2,3 MAX phases display a combination of both ceramic and metallic characteristics. Furthermore, they also serve as a precursor for two-dimensional MXenes.4,5<br/>Generally, bulk synthesis of MAX phases is done through traditional solid state synthesis techniques. For example, three solid state synthesis techniques include solid state method, hot pressing and arc melting and annealing. During solid state method, the powder precursors are preheated between 350 and 400°C, allowing for decomposition of starting reagents and removal of volatile products leaving only the oxides. At this point the germination phase has completed, and the crystal growth phase begins. Under the effect of a concentration gradient and very high temperatures, cations migrate, forming well-ordered layers. Slow cooling rates are used in order to ensure crystallinity of the product.6 The second method, hot pressing, involves the mixing of powder precursors thoroughly and then cold pressed into a green body – a ceramic body powder pre-sintering. They are then heated under vacuum and often high pressure in order to form the product. Two variants of hot-pressing exits: reactive hot pressing, where the pressure during the reaction will vary throughout the reaction, and isostatic hot pressing, where the pressure is held constant throughout the entire reaction.7 Another solid-state technique is arc melting and annealing. During arc melting, alternating current is applied to the electrode inside an inert reactor, which is arranged as to generate an arc discharge. The heat produced by arcing causes rapid melting of the samples.8 While these methods are most common, they are not always viable due to the specialized equipment required in order to achieve the high temperature and pressure conditions. Furthermore, these specific techniques don’t allow for high control over particle size and morphology. <br/>Because of this, alternative, non-conventional synthesis techniques have been developed involving more readily available tube furnaces and microwaves, which lack the extreme pressures instead opting for ambient conditions.9 Sol-gel techniques have been developed by the group of Christina Birkel, and have successfully produced MAX phases through calcination of homogeneous citric acid-based gel-precursors. Some advantages of using these gel-precursors include shorter diffusion paths, and faster mass transport, thus, resulting in lower reaction temperatures and shorter reaction times. Ultimately, this allows for control over particle morphology and size.10<br/>The focus of this work is to discover optimal synthesis conditions to create spherical Cr2GaC. Spherical MAX phases have been briefly explored in existing literature using polymer-based hollow microsphere templates.10 These polymer microspheres have been used to synthesize spherical metal oxides. This is achieved by heating the metal oxide precursors which adhere to the spheres, then by thermal treatment, the template is then removed.11 <br/>Two different microsphere templates will be explored to study the advantages and disadvantages of different size distributions and surface conditions of the spheres. Furthermore, reaction temperature, reaction time, citric acid equivalents, and gel to microsphere ratio will be altered to determine optimal synthesis parameters for depositing Cr2GaC onto spherical templates. Cr2GaC serves as a model compound because it has been successfully synthesized through sol-gel chemistry in the past.10 This phase will be prepared through non-conventional sol-gel chemistry, with various heating profiles, both furnace and microwave, and will be characterized through X-ray diffraction (XRD), and Rietveld refinement. Further, the morphology and atomic composition will be analyzed through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

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  • 2021-05

Microwave-assisted Sol-gel Synthesis of the MAX Phases Cr2GaC, Cr2GeC, and V2GeC

Description

MAX phases are ternary carbides or nitrides that possess unique material characteristics, often simplified as a mix of metallic and ceramic properties. Many aspects of MAX phases are still being

MAX phases are ternary carbides or nitrides that possess unique material characteristics, often simplified as a mix of metallic and ceramic properties. Many aspects of MAX phases are still being researched, but they have exciting potential applications in high-temperature structural systems, the next generation of nuclear power plants, and concentrated solar power. This project aims to benefit further research into these applications by validating a rapid unconventional synthesis method: microwave-assisted sol-gel synthesis. Three MAX phases (Cr2GaC, Cr2GeC, and V2GeC) were successfully synthesized via this route, which should open the door for more rapid prototyping and ultimately more efficient research.

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  • 2021-05

Grad School: Human Growth Horror - Creative Project Entry of an Action/Adventure Computer Game Designed to Experimentally Demonstrate Viable Engineering Concepts for Educational Purposes

Description

The action/adventure game Grad School: HGH is the final, extended version of a BME Prototyping class project in which the goal was to produce a zombie-themed game that teaches biomedical

The action/adventure game Grad School: HGH is the final, extended version of a BME Prototyping class project in which the goal was to produce a zombie-themed game that teaches biomedical engineering concepts. The gameplay provides fast paced, exciting, and mildly addicting rooms that the player must battle and survive through, followed by an engineering puzzle that must be solved in order to advance to the next room. The objective of this project was to introduce the core concepts of BME to prospective students, rather than attempt to teach an entire BME curriculum. Based on user testing at various phases in the project, we concluded that the gameplay was engaging enough to keep most users' interest through the educational puzzles, and the potential for expanding this project to reach an even greater audience is vast.

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  • 2014-05