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Articles 31 - 54 of 54
Full-Text Articles in Physical Sciences and Mathematics
Rhythmogenic And Premotor Functions Of Dbx1 Interneurons In The Pre-Bötzinger Complex And Reticular Formation: Modeling And Simulation Studies, Hanbing Song
Dissertations, Theses, and Masters Projects
Breathing in mammals depends on rhythms that originate from the preBötzinger complex (preBötC) of the ventral medulla and a network of brainstem and spinal premotor neurons. The rhythm-generating core of the preBötC, as well as some premotor circuits, consists of interneurons derived from Dbx1-expressing precursors but the structure and function of these networks remain incompletely understood. We previously developed a cell-specific detection and laser ablation system to interrogate respiratory network structure and function in a slice model of breathing that retains the preBötC, premotor circuits, and the respiratory related hypoglossal (XII) motor nucleus such that in spontaneously rhythmic slices, cumulative …
Resolution Limits Of Time-Of-Flight Mass Spectrometry With Pulsed Source, Guangzhi Qu
Resolution Limits Of Time-Of-Flight Mass Spectrometry With Pulsed Source, Guangzhi Qu
Dissertations, Theses, and Masters Projects
Matrix Assisted Laser Desorption/Ionization (MALDI) is a time-of-flight mass spectrometry commonly used to detect a wide mass range of biomarkers. However, MALDI requires a high laser pulse energy to create ions with a mass higher than 50,000 Daltons. That high laser energy increases the net ion production but it also degrades the instrument's mass resolution. This project uses a Room Temperature Ionization Liquid (RTIL) as a liquid matrix with a self healing surface instead of a standard crystal matrix to increase shot to shot reproducibility, enabling a systematic study of the origin of the resolution degradation. This study shows that …
Modeling Phytoplankton Community Response To Nutrient Loading And Climate Change In A Shallow Temperate Estuary, Sara Aimee Blachman
Modeling Phytoplankton Community Response To Nutrient Loading And Climate Change In A Shallow Temperate Estuary, Sara Aimee Blachman
Dissertations, Theses, and Masters Projects
Phytoplankton account for at least half of all primary production in estuarine waters and are at the center of biogeochemical cycles and material budgets. Environmental managers use water column chlorophyll-a (chl-a) concentrations as a basic water quality indictor, as the problems of eutrophication and hypoxia are intrinsically linked to excessive phytoplankton growth. Evidence suggests that the distribution and frequency of harmful algal blooms may be increasing worldwide. For the most part, phytoplankton communities follow a standard seasonal pattern, with specific groups dominating the assemblage during the time of year when environmental conditions correspond to their requisites for growth. However, climate …
Dye-Sensitized Tio2 Modified With Iron Polypyridyl Catalyst For Photocatalytic Hydrogen Evolution, Wanji Zhang
Dye-Sensitized Tio2 Modified With Iron Polypyridyl Catalyst For Photocatalytic Hydrogen Evolution, Wanji Zhang
Dissertations, Theses, and Masters Projects
Artificial Photosynthesis (AP) focuses on finding a way to harness solar energy to generate a chemical fuel. TiO2 semiconductors are of interest to AP research due to its relatively low cost and widespread use as an efficient charge-separating support. This research focuses on the development of a device for photocatalytic hydrogen generation. Our approach utilizes the immobilization of iron polypyridyl catalysts and ruthenium chromophores on TiO2 through stable phosphonic acid anchoring groups.
Zooplankton Community Composition And Grazing In The Amazon River Plume And Western Tropical North Atlantic Ocean, Brandon J. Conroy
Zooplankton Community Composition And Grazing In The Amazon River Plume And Western Tropical North Atlantic Ocean, Brandon J. Conroy
Dissertations, Theses, and Masters Projects
Large river plumes and frontal zones are important physical features influencing plankton distribution in the marine environment. In the western tropical North Atlantic Ocean (WTNA) the Amazon River plume may extend over an area reaching 1.5 x 106 km2. The freshwater plume creates a low-density lens in the surface 25m and supplies silicon and phosphorus to the WTNA. These physical and chemical gradients create an ideal environment for large-scale blooms of diatom diazotroph associations (DDAs), a symbiotic relationship between nitrogen-fixing cyanobacteria and chain-forming diatoms. While the physical and chemical properties of the plume with regard to influences on phytoplankton have …
Influence Of Perkinsus Marinus Infection And Oyster Health On Levels Of Human-Pathogenic Vibrios In Oysters, Lydia M. Bienlien
Influence Of Perkinsus Marinus Infection And Oyster Health On Levels Of Human-Pathogenic Vibrios In Oysters, Lydia M. Bienlien
Dissertations, Theses, and Masters Projects
The eastern oyster Crassostrea virginica is an ecologically and commercially important species whose natural populations have been devastated by overharvesting, habitat destruction, and disease, but the rapid growth of oyster aquaculture has shown potential to restore the economic significance of this species. A key threat to the growth and sustainability of oyster aquaculture is the association of human-pathogenic Vibrio bacteria with product marketed for raw consumption. Two Vibrio species, Vibrio vulnificus and Vibrio parahaemolyticus, are the causes of the highest rates of seafood consumption-related mortality and gastrointestinal illness, respectively. Identification of the factors influencing V. vulnificus and V. parahaemolyticus prevalence …
A Precision Measurement Of The Weak Charge Of Proton At Low Q^2: Kinematics And Tracking, Siyuan Yang
A Precision Measurement Of The Weak Charge Of Proton At Low Q^2: Kinematics And Tracking, Siyuan Yang
Dissertations, Theses, and Masters Projects
The Standard Model of particle physics represents our present best understanding of the elementary particles and three of the four fundamental forces. One of the most important and challenging tasks of modern particle physics is to test, and perhaps, to find the evidence for new physics not contained in the Standard Model. One such test, the $Q_{weak}$ experiment, was conducted at JLab in Newport News, VA, from 2010 to 2012. The goal of the experiment is to measure the value of the weak charge of proton, $Q_{weak}$ to a 4\% precision, which, if it confirms the Standard Model prediction, will …
Chesapeake Coastal Community Flood Vulnerability--Prediction And Verification, Alexander D. Renaud
Chesapeake Coastal Community Flood Vulnerability--Prediction And Verification, Alexander D. Renaud
Dissertations, Theses, and Masters Projects
Fast moving hurricanes and stationary nor’easters have resulted in significant flood damage in Chesapeake tidewater communities. The Chesapeake Bay region is one of A m erica’s most vulnerable regions with respect to sea-level rise, which will only increase storm surge impacts over upcoming decades. While the general trends are well documented, there is limited information relevant to specific communities’ relative flood risk and response. The dearth o f data is especially troublesome given the lengthy period o f time generally needed for communities to plan and implement adaptive action. This study contributes to the regional understanding of flood and sea-level …
On Shelf-Slope Water Mass Exchanges Near Washington Canyon And Norfolk Canyon In The Mid-Atlantic Bight, Haixing Wang
On Shelf-Slope Water Mass Exchanges Near Washington Canyon And Norfolk Canyon In The Mid-Atlantic Bight, Haixing Wang
Dissertations, Theses, and Masters Projects
The physical exchanges between shelf and slope water masses are important drivers of biological productivity in the shelfbreak region of the Mid-Atlantic Bight (MAB). Based on two ocean glider surveys that were conducted in Autumn 2013, and concurrent wind and satellite based sea surface height observations, this study investigates the dynamic mechanisms of wind, surface height variation, water column hydrographic structure, and canyon topography in driving shelf-slope water mass exchanges across the shelfbreak near Norfolk Canyon and Washington Canyon in the MAB. Over the outer shelf, sea surface height variation and wind are important drivers of cross-shelfbreak transport through geostrophic …
Understanding Security Threats In Cloud, Zhang Xu
Understanding Security Threats In Cloud, Zhang Xu
Dissertations, Theses, and Masters Projects
As cloud computing has become a trend in the computing world, understanding its security concerns becomes essential for improving service quality and expanding business scale. This dissertation studies the security issues in a public cloud from three aspects. First, we investigate a new threat called power attack in the cloud. Second, we perform a systematical measurement on the public cloud to understand how cloud vendors react to existing security threats. Finally, we propose a novel technique to perform data reduction on audit data to improve system capacity, and hence helping to enhance security in cloud. In the power attack, we …
Gas-Phase Thermochemical Properties Of Proline-Containing Dipeptides And Fluorinated Alcohols Using The Extended Kinetic Method, Kathy Tang Huynh
Gas-Phase Thermochemical Properties Of Proline-Containing Dipeptides And Fluorinated Alcohols Using The Extended Kinetic Method, Kathy Tang Huynh
Dissertations, Theses, and Masters Projects
No abstract provided.
Disorder Effects In Dirac Heterostructures, Martin Alexander Rodriguez-Vega
Disorder Effects In Dirac Heterostructures, Martin Alexander Rodriguez-Vega
Dissertations, Theses, and Masters Projects
In this dissertation, we study theoretically heterostructures based on Dirac mate- rials, i.e. materials, such as graphene in which the electrons behave as massless Dirac fermions at low energies. We first examine how the presence of long-range disorder affects the electronic ground state of a double layer graphene heterostruc- ture formed by two graphene layers separated by a thin dielectric film. We then identify the necessary conditions for the formation of an interlayer exciton conden- sate in such a system. We also comment on the effect of long-range disorder on the broken symmetry ground state induced by electron-electron interactions in …
Molecular And Performance Properties Of Poly(Amides & Imides) And The Use Of Graphene Oxide Nano-Particles For Improvement, John-Andrew Samuel Hocker
Molecular And Performance Properties Of Poly(Amides & Imides) And The Use Of Graphene Oxide Nano-Particles For Improvement, John-Andrew Samuel Hocker
Dissertations, Theses, and Masters Projects
Macroscopic properties of polymers, and in general all types of materials, are innately related to their molecular structure and intermolecular properties. This dissertation offers insight into how the molecular structure, chain properties, and inter-molecular chain interactions within PA11 can be used to explain and predict improved macro level performance properties; and how the addition of graphene oxide nanosheets enhances the performance properties of PA11 and polyimide(ODA-BTDA) through those same intermolecular interactions. Chapter 3 describes the unexpected result that weak small organic acids at low concentrations hydrolyze a polyamide at rates approximately twice that of a water HCl solution of the …
Expanding The Scope Of Terminal Alkynes In Chemical Biology, Johnathan Charles Maza
Expanding The Scope Of Terminal Alkynes In Chemical Biology, Johnathan Charles Maza
Dissertations, Theses, and Masters Projects
The terminal alkyne is one of the most widely used chemical moieties in chemical biology. Thanks to the relative absence of this functional group in biology, it has become a widespread functional handle for a plethora of biorthogonal chemistries. Our group has extended the scope of this functionality by developing a biological variant of the Glaser-Hay coupling, which brings together two terminal alkynes to form a diyne linkage. However, our initial findings revealed that the chemistry is plagued by protein degradation due to a deleterious copper(II) hydroxyl intermediate. Herein we extend the scope of the terimanl alkyne be developing a …
Biogeochemistry Of Redox-Sensitive Elements In The Subterranean Estuary, Alison E. O'Connor
Biogeochemistry Of Redox-Sensitive Elements In The Subterranean Estuary, Alison E. O'Connor
Dissertations, Theses, and Masters Projects
Submarine groundwater discharge (SGD) is any flow of water along the continental margins from the seabed into the coastal ocean, and it represents an important source of nutrients and trace metals to the coastal ocean. The chemical composition of SGD is strongly influenced by biogeochemical reactions that take place within the subterranean estuary (STE), the subsurface mixing zone of fresh and saline waters. Understanding the reactions that take place within the shallow STE is critical to evaluating the composition of SGD, and therefore SGD-driven chemical fluxes. In this dissertation, I seek to determine the biogeochemical processes controlling the behavior of …
Patterns Of Abundance And Community Dynamics In Atlantic Coastal Sharks, Cassidy Peterson
Patterns Of Abundance And Community Dynamics In Atlantic Coastal Sharks, Cassidy Peterson
Dissertations, Theses, and Masters Projects
No abstract provided.
Quantitative Analysis Of Periodic Breathing And Very Long Apnea In Preterm Infants., Mary A. Mohr
Quantitative Analysis Of Periodic Breathing And Very Long Apnea In Preterm Infants., Mary A. Mohr
Dissertations, Theses, and Masters Projects
No abstract provided.
Optical Characterization Of Interface Magnetization In Multifunctional Oxide Heterostructures, Fan Fang
Optical Characterization Of Interface Magnetization In Multifunctional Oxide Heterostructures, Fan Fang
Dissertations, Theses, and Masters Projects
Multifunctional oxides attract much attention recently. The strong correlated electron system involves the notable properties of colossal magnetoresistance, ferroelectric tunneling and spin transport, with the coupling of electron, spin and orbital degrees of freedom. their rich functional behavior is of potential use for nanoelectronics and data storage. Particularly interesting are the mulitferroic materials, which exhibit simultaneously electric and magnetic ordering properties. Understanding the interface coupling mechanism of these two order parameters are critical to future development of high-performance spintronic devices. The goal of this dissertation is to elucidate the interfacial magnetoelectric (ME) coupling with optical characterization method -- magnetization-induced second-harmonic …
Modeling Flocculation And Deflocculation Processes Of Cohesive Sediments, Xiaoteng Shen
Modeling Flocculation And Deflocculation Processes Of Cohesive Sediments, Xiaoteng Shen
Dissertations, Theses, and Masters Projects
The transport and fate of cohesive sediments are responsible for many engineering, environmental, economic and policy issues that relate to, for example, siltation and dredging in navigation channels, water quality, water turbidity, pollutant transports, and biological ecosystem responses. Our current understanding, however, is insufficient to conduct accurate quantitative predictions of these processes. This is because the cohesive particles in natural waters will flocculate, which determines the settling, and thus the deposition behaviors. The simulation of flocculation processes is a primary challenge since the time variation of Floc Size Distribution (FSD) is controlled by a partial differential equation that also contains …
Influence Of Structural Complexity And Location On The Habitat Value Of Restored Oyster Reefs, Melissa Ann Karp
Influence Of Structural Complexity And Location On The Habitat Value Of Restored Oyster Reefs, Melissa Ann Karp
Dissertations, Theses, and Masters Projects
In the Chesapeake Bay, < 1% of the historic oyster population remains, and efforts have been increasing to restore oysters and the services they provide. Building reefs that successfully provide ecosystem services–especially habitat and foraging grounds–may require different restoration techniques than those previously used, and success may depend on reef morphology (complexity), location, and environmental conditions. Salinity and habitat complexity are two important factors that may interact to effect benthic communities and predator-prey interactions on restored reefs. The goals of this project were: (1) Characterize the benthic communities on restored oyster reefs in lower Chesapeake Bay, and (2) examine the effects of structural complexity and salinity on benthic communities and predator-prey interactions. A two-year field survey of restored reefs was carried out in four rivers in lower Chesapeake Bay to characterize faunal communities on restored reefs and to quantify the effect of reef complexity on faunal communities. A laboratory mesocosm experiment was conducted to examine the effect of reef complexity on predator foraging. In total, 61 macrofaunal species were identified among all samples, and restored reefs supported on average, 6,169 org/m2 and 67.88 g-AFDW/m2. There were significant differences in the community composition and diversity among the rivers, and salinity was the environmental factor that best explained the observed differences in species composition across the rivers. Salinity and rugosity (i.e., structural complexity) both positively affected diversity, while salinity negatively affected macrofaunal abundance and biomass. Oyster density and rugosity positively affected macrofaunal biomass, and oyster density positively affected mud crab, polychaete, and mussel densities. In the mesocosm experiment, predator foraging, measured by proportion and number of prey consumed, was significantly reduced in the presence of oyster shell structure. However, predators were able to consume more prey when prey density was increased, even in the presence of oyster shell structure. These results combine to enhance our understanding of the benefits of increased habitat complexity for both prey and predators on restored oyster reefs. Increasing complexity worked to increase the abundance, biomass, and diversity of organisms inhabiting restored reefs, and even though predator consumption was reduced in the presence of structure compared to non-structured habitat, predators were able to consume more prey individuals when prey density was increased. Therefore, increasing the structure of oyster reef habitat may benefit prey species by providing refuge habitat, and benefit predators by providing an increased abundance of available prey items.
Population Dynamics Of Gelatinous Zooplankton In The Chesapeake Bay And Sargasso Sea, And Effects On Carbon Export, Joshua Paul Stone
Population Dynamics Of Gelatinous Zooplankton In The Chesapeake Bay And Sargasso Sea, And Effects On Carbon Export, Joshua Paul Stone
Dissertations, Theses, and Masters Projects
Gelatinous zooplankton (GZ; cnidarians, ctenophores, and pelagic tunicates) periodically are the dominant members of the zooplankton throughout the majority of the world’s oceans. their unique body plans and life cycles allow them to rapidly take advantage of favorable environmental conditions, which has far-ranging consequences for food web dynamics and biogeochemical cycles. GZ populations have been speculated to respond to anthropogenic changes, but few long-term studies exist to test this hypothesis and even fewer have examined the consequent effects on carbon export. I analyzed two long-term time series in the Chesapeake Bay and one in the Sargasso Sea for annual and …
The Effects Of Drifting Fish Aggregating Devices On Bycatch In The Tropical Tuna Purse Seine Fisheries In The Atlantic And Indian Oceans, Julia Snouck-Hurgronje
The Effects Of Drifting Fish Aggregating Devices On Bycatch In The Tropical Tuna Purse Seine Fisheries In The Atlantic And Indian Oceans, Julia Snouck-Hurgronje
Dissertations, Theses, and Masters Projects
Thousands of floating objects, known as drifting fish aggregating devices (dFADs), are released every year by commercial tropical tuna purse seine vessels in the three equatorial oceans to aggregate tuna and increase catch. The escalation in the number of dFADs deployed over the last three decades has caused changes in fishing effort that are poorly reflected in traditional indices of purse seine effort and catch per unit of effort (CPUE). In addition, concerns have been raised regarding the impacts of such high numbers of dFADs being deployed on both catch and bycatch species. I studied two aspects of dFAD deployments …
Experimental Apparatus For Quantum Pumping With A Bose-Einstein Condensate., Megan K. Ivory
Experimental Apparatus For Quantum Pumping With A Bose-Einstein Condensate., Megan K. Ivory
Dissertations, Theses, and Masters Projects
No abstract provided.
Characterization Of Interfacial Interactions By Functionalized Afm Probes, Laura Rickard Dickinson
Characterization Of Interfacial Interactions By Functionalized Afm Probes, Laura Rickard Dickinson
Dissertations, Theses, and Masters Projects
Interfacial interactions play a crucial role in many complex materials systems, determining many of their properties. However, characterization of these interactions, especially at the micro- to nanometer length scales is experimentally challenging. Consequently, insufficient knowledge of these systems limits technological advances in important applications. In this work, custom functionalized atomic force microscopy (AFM) probes were developed to measure the interaction forces in two important systems: petroleum reservoirs and nanocomposites. Our work seeks a deeper understanding of the specific interactions that occur in these two systems so that modified approaches can be developed to improve them. Petroleum recovery is concerned with …