Physical Sciences and Mathematics Commons^™

Persistence And Extinction Dynamics In Reaction-Diffusion-Advection Stream Population Model With Allee Effect Growth, Yan Wang

Dissertations, Theses, and Masters Projects

The question how aquatic populations persist in rivers when individuals are constantly lost due to downstream drift has been termed the ``drift paradox." Reaction-diffusion-advection models have been used to describe the spatial-temporal dynamics of stream population and they provide some qualitative explanations to the paradox. Here random undirected movement of individuals in the environment is described by passive diffusion, and an advective term is used to describe the directed movement in a river caused by the flow. In this work, the effect of spatially varying Allee effect growth rate on the dynamics of reaction-diffusion-advection models for the stream population is …

Electronic Properties Of Two-Dimensional Van Der Waals Systems, Yohanes Satrio Gani

Dissertations, Theses, and Masters Projects

In this dissertation we study the electronic structure of van der Waals systems. A van der Waals systems is a heterostructure in which the different constituents are held together by van der Waals forces. We study two different types of van der Waals systems: van der Waals systems formed by graphene and a monolayer of NbSe2, van der Waals systems obtained by placing graphene nanoribbons on a two-dimensional crystal. For the first type of systems we build a continuous low-energy effective model that takes into account the presence of a twist angle between graphene and NbSe2, and of spin-orbit coupling …

Optimization Approaches For Open-Locating Dominating Sets, Daniel Blair Sweigart

Dissertations, Theses, and Masters Projects

An Open Locating-Dominating Set (OLD set) is a subset of vertices in a graph such that every vertex in the graph has a neighbor in the OLD set and every vertex has a unique set of neighbors in the OLD set. This can also represent where sensors, capable of detecting an event occurrence at an adjacent vertex, could be placed such that one could always identify the location of an event by the specific vertices that indicated an event occurred in their neighborhood. By the open neighborhood construct, which differentiates OLD sets from identifying codes, a vertex is not able …

Investigation Of Pattern Formation In Marine Environments Through Mathematical Modeling And Analysis Of Remotely Sensed Data, Sofya Zaytseva

Dissertations, Theses, and Masters Projects

Pattern formation in ecological systems refers to a nonuniform distribution of animal and plant species across a landscape. Pattern formation can be observed in many aquatic and terrestrial systems and can provide important insights into their dynamics and ability to cope with environmental changes. In this dissertation, we focus on pattern formation in tidal marshes and oyster reefs, two important habitats that provide a number of essential ecosystem services. Both of these systems have also experienced dramatic losses, prompting much research to investigate their dynamics as and viable restoration and management strategies. The first part of this dissertation focuses on …

Applying The Concept Of Thresholds In Ecotoxicology With Focus On The Joint Effects Of Habitat Fragmentation And Contamination, Marcos Krull

Dissertations, Theses, and Masters Projects

A threshold can be defined as the point where small changes in an environmental driver produce an abrupt change within a biological system. These changes can occur at different levels of organization, from organisms to ecosystems. Although thresholds seem to be receiving more attention by ecotoxicologist, not much is known about how contaminants cause or affect thresholds at the landscape level, such as habitat fragmentation thresholds. Habitat fragmentation thresholds can occur due to rapid changes in the landscape structure after a certain amount of habitat is lost, which can cause abrupt effects on the movement of organisms, population abundance and …

King And Queen County, Virginia Shoreline Inventory Data 2019, Marcia Berman, Karinna Nunez, Sharon Killeen, Tamia Rudnicky, Julie Bradshaw, Jessica Hendricks, Carl Hershner, Evan Hill

Data

The 2019 Inventory for King and Queen County was generated using on-screen, digitizing techniques in ArcGIS® -ArcMap v10.4.1 while viewing conditions observed in 2017 imagery from the Virginia Base Mapping Program (VBMP), Google Earth, and Bing high resolution oblique imagery. Five GIS shapefiles are developed. The first describes land use and bank conditions (kq_lubc_2019). The second portrays the presence of beaches (kq_beach_2019). The third reports shoreline structures that are described as arcs or lines (e.g. riprap) (kq_sstru_2019). The fourth shapefile includes all structures that are represented as points (e.g. piers) (kq_astru_2019). The Tidal Marsh Inventory is included as the fifth …

The Problem Of Failing Septic Systems, Center For Coastal Resources Management, Virginia Institute Of Marine Science.

Reports

Rivers & Coast is a periodic publication of the Center for Coastal Resources Management, Virginia Institute of Marine Science. The goal of Rivers & Coast is to keep readers well informed of current scientific understanding behind key environmental issues related to watershed rivers and coastal ecosystems of the Chesapeake Bay.

Improving Wifi Sensing And Networking With Channel State Information, Yongsen Ma

Dissertations, Theses, and Masters Projects

In recent years, WiFi has a very rapid growth due to its high throughput, high efficiency, and low costs. Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency-Division Multiplexing (OFDM) are two key technologies for providing high throughput and efficiency for WiFi systems. MIMO-OFDM provides Channel State Information (CSI) which represents the amplitude attenuation and phase shift of each transmit-receiver antenna pair of each carrier frequency. CSI helps WiFi achieve high throughput to meet the growing demands of wireless data traffic. CSI captures how wireless signals travel through the surrounding environment, so it can also be used for wireless sensing purposes. This dissertation …

Discrete Co2-System Measurements In The Chesapeake Bay Mainstem Between 2016 And 2018, Elizabeth H. Shadwick, Olivia A. De Meo, Jaclyn R. Friedman

Data

These are discrete observations of total dissolved inorganic carbon (DIC) and alkalinity (TA), and associated computed CO₂-system parameters, from samples collected throughout the Chesapeake Bay mainstem between 2016 and 2018. Samples were collected on board the R/V Kerhin in Maryland and the R/V Fay Slover in Virginia at a subset of fixed stations in collaboration with the Chesapeake Bay Water Quality Monitoring Program. Samples were analyzed following standard procedures at the Virginia Institute of Marine Science. The DIC and TA data were then used to compute the remaining CO₂-system parameters (pH, CO₂ partial pressure (pCO …

Virginia Non-Tidal Wetland Condition Assessment 2016, Tamia Rudnicky, Kirk J. Havens, Michelle Henicheck, Dave Davis, Kory Angstadt, David Stanhope

Data

This data set is a GIS-based landscape (Level one) assessment of the water quality and habitat benefits of non-tidal wetlands from the National Wetlands Inventory (NWI) in Virginia utilizing the 2016 National Land Cover Dataset (NLCD) and 2016 Tiger/Line roads. The model assessment uses remote sensing and GIS technology to characterize land use patterns and features around wetlands such as surrounding land cover and density of roads as well as individual wetland characteristics such as wetland size and type to determine the wetlands overall condition as related to habitat and water quality functions. The water quality analysis determines the percentages …

Gis Data: King William County Tidal Marsh Inventory, Marcia Berman, Karinna Nunez, Sharon Killeen, Tamia Rudnicky, Julie G. Bradshaw, Carl Hershner, Evan Hill

Data

The Virginia Institute of Marine Science published the first Tidal marsh Inventories using data collected in the early 1970's. Using high resolution color infra-red imagery from 2009 a new Tidal Marsh Inventory has been developed for the York River Watershed in 2010. Marsh boundaries were generated using heads-up digitizing techniques at a scale of 1:1,000. Each marsh polygon was classified by morphologic type: fringe, extensive, embayed, or marsh island. Marshes were ground-truthed in the field where a community type index was assigned to each marsh based on plant community make-up. Each marsh was also coded with a marsh number which …

Human Dimensions Of A Participatory, Collaborative Modeling Process - Oysterfutures, Taylor Dawn Goelz

Dissertations, Theses, and Masters Projects

Participatory, collaborative modeling processes represent a unique decision-making technique within natural resources management that allows for the combination of stakeholder involvement with the analytical and predictive power of scientific models. The continued use of participatory modeling within decision-making processes depends in part upon the willingness of stakeholders to participate. Continued participation of stakeholders is key to the persistence and overall success of these processes, and yet limited information exists concerning the impacts of these processes on participants. The consideration of human dimensions advances our understanding of the design and function of participatory modeling processes, including their ability to create consensus …

Partitioning Of Hydrophobic Organic Contaminants And Microbial Communities On Microplastics, Kelley Ann Uhlig

Dissertations, Theses, and Masters Projects

Microplastic contamination of aquatic environments has only recently caught the attention of scientists, regulators and the public. Microplastics are typically more recalcitrant than naturally occurring polymers and so have the potential to cause a range of issues, including increased exposure of marine life to chemical contaminants sorbed to or leached from microplastics, negative impacts due to ingestion of microplastics by biota, and the potential to carry and transport pathogenic and invasive species long distances. Bio-based, bio-degradable polymers have begun to gain market share as an alternative to traditional petrochemical-based plastics, but not much is known about their impacts in marine …

Extraction And Parametrization Of Isobaric Trinucleon Elastic Cross Sections And Form Factors, Scott Kevin Barcus

Dissertations, Theses, and Masters Projects

By mining data from Jefferson Lab Hall A experiment E08-014 a new measurement of the 3He elastic cross section at Q^2 ≈ 34 fm^−2 was extracted from a large quasielastic background. This new data point falls approximately halfway between the first and second diffractive minima of the 3He form factors. When combined with recent high Q^2 3He elastic cross section measurements from JLab this new point improves our knowledge of the cross section and form factors at large momentum transfers. The new high Q^2 data motivate a reanalysis of the 3He elastic cross section world data and promise an improved …

Computational Graphics And Statistical Analysis: Mixed Type Random Variables, Confidence Regions, And Golden Quantile Rank Sets, Christopher Weld

Dissertations, Theses, and Masters Projects

This dissertation has three principle areas of research: mixed type random variables, confidence regions, and golden quantile rank sets. While each offers a specific focus, some common themes persist; broadly stated, there are three. First, computational graphics play a critical role. Second, software development facilitates implementation and accessibility. Third, statistical analysis---often attributable to the aforementioned automation---provides valuable insights and applications. Each of the principle research areas are briefly summarized next. Mixed type random variables are a hybrid of continuous and discrete random variables, having components of both continuous probability density and discrete probability mass. This dissertation illustrates the challenges inherent …

Beyond The Standard Model: Flavor Symmetry, Nonperturbative Unification, Quantum Gravity, And Dark Matter, Shikha Chaurasia

Dissertations, Theses, and Masters Projects

Despite the vast success of the Standard Model of particle physics, it is no secret that is also has its shortcomings, thus providing incentive to look beyond the Standard Model for solutions. In this thesis we focus in particular on a model of horizontal flavor symmetry, unification via a universal Landau pole, emergent gravity, and dark matter. First we explain the observed hierarchies in the elementary fermion mass spectrum via a model based on the double tetrahedral group, the smallest discrete subgroup of SU(2), while relaxing previous assumptions of supersymmetry. A sequential symmetry breaking process results in a hierarchy in …

Investigating The Molecular Choreography Of Atmospherically Relevant Molecules: A Dynamics Study, Kenneth Jacob Blackshaw

Dissertations, Theses, and Masters Projects

Investigating and understanding the chemistry of the atmosphere has historically been an important research topic. This importance has only strengthened in the recent decades as technological advancements have drastically increased anthropogenic emissions of hydrocarbons and nitroaromatic compounds. Indeed, we are in an era of unprecedented change of the chemical composition of the troposphere and never before has an in-depth understanding of atmospheric chemical properties been more sought-after. This study seeks to fill that need by probing the molecular dynamics of atmospherically relevant molecules through the use of velocity map imaging (VMI). In particular, we utilize VMI to study the photolysis …

Research On Efficiency And Security For Emerging Distributed Applications, Zijiang Hao

Dissertations, Theses, and Masters Projects

Distributed computing has never stopped its advancement since the early years of computer systems. In recent years, edge computing has emerged as an extension of cloud computing. The main idea of edge computing is to provide hardware resources in proximity to the end devices, thereby offering low network latency and high network bandwidth. However, as an emerging distributed computing paradigm, edge computing currently lacks effective system support. To this end, this dissertation studies the ways of building system support for edge computing. We first study how to support the existing, non-edge-computing applications in edge computing environments. This research leads to …

Controlling Infectious Disease: Prevention And Intervention Through Multiscale Models, Adrienna N. Bingham

Dissertations, Theses, and Masters Projects

Controlling infectious disease spread and preventing disease onset are ongoing challenges, especially in the presence of newly emerging diseases. While vaccines have successfully eradicated smallpox and reduced occurrence of many diseases, there still exists challenges such as fear of vaccination, the cost and difficulty of transporting vaccines, and the ability of attenuated viruses to evolve, leading to instances such as vaccine derived poliovirus. Antibiotic resistance due to mistreatment of antibiotics and quickly evolving bacteria contributes to the difficulty of eradicating diseases such as tuberculosis. Additionally, bacteria and fungi are able to produce an extracellular matrix in biofilms that protects them …

On Enhancing Security Of Password-Based Authentication, Yue Li

Dissertations, Theses, and Masters Projects

Password has been the dominant authentication scheme for more than 30 years, and it will not be easily replaced in the foreseeable future. However, password authentication has long been plagued by the dilemma between security and usability, mainly due to human memory limitations. For example, a user often chooses an easy-to-guess (weak) password since it is easier to remember. The ever increasing number of online accounts per user even exacerbates this problem. In this dissertation, we present four research projects that focus on the security of password authentication and its ecosystem. First, we observe that personal information plays a very …

Interfacial Forces Of 2d Materials At The Oil–Water Interface, William Winsor Dickinson

Dissertations, Theses, and Masters Projects

Two-dimensional (2D) materials, including graphene and graphene oxide (GO), are a subject of interest for many researchers due to their exceptional properties (strength, conductivity, etc.). These materials, comprised of atomically-thin sheets, may naturally occur stacked together like sheets of paper, but their most interesting properties emerge when separated into individual layers. However, scaling up the processes used to isolate single sheets of some of these materials, particularly graphene, has proven problematic. They can be fiercely resistant to exfoliation, difficult to disperse, and have a worrying propensity to restack. All these problems contribute to the great difficulty these fascinating materials have …

Global Shipping Container Monitoring Using Machine Learning With Multi-Sensor Hubs And Catadioptric Imaging, Victor Esteban Trujillo

Dissertations, Theses, and Masters Projects

We describe a framework for global shipping container monitoring using machine learning with multi-sensor hubs and infrared catadioptric imaging. A wireless mesh radio satellite tag architecture provides connectivity anywhere in the world which is a significant improvement to legacy methods. We discuss the design and testing of a low-cost long-wave infrared catadioptric imaging device and multi-sensor hub combination as an intelligent edge computing system that, when equipped with physics-based machine learning algorithms, can interpret the scene inside a shipping container to make efficient use of expensive communications bandwidth. The histogram of oriented gradients and T-channel (HOG+) feature as introduced for …

One Fish, Two Fish, Red Fish, Whose Fish? Subjects: Life Science, Environmental Science, Marine / Ocean Science, Shelby White

Reports

This activity invites students to assume the role of various stakeholders in fisheries management and actively discuss the influence of economics, ecology and human interactions in decision-making.

Students will demonstrate their argument for/against a certain regulation by participating as a specific stakeholder (i.e. commercial fisher, recreational fisher, scientists/researcher, environmental group, management agency, and citizen). Students will recognize that stakeholders tend to advocate based on their individual needs, often making it difficult for proposed policies to satisfy the needs of all stakeholders and achieve sustainability goals.

Expedition Sediments: Mud's Journey Through The Watershed. Subjects: Earth Science / Environmental Science Grades: 9-12, Jessie Turner

Reports

Expedition Sediments is a game-in-a-lesson that allows students to explore the movement of sediments through watersheds by moving around the classroom. This lesson explores how grains of estuarine mud and sand move throughout estuaries and coastal regions, with a focus on processes surrounding a highly populated estuary such as the Chesapeake Bay. By the end of the lesson, students will be able to explain how sediments are transported through an estuary, graph sediment residence times in different locations, and compare the timescales of different sediment transport processes.

Trawling Through The Five Gyres: A Microplastic Research Study. Subjects: Life Science, Earth Science, Marine/Ocean Science - Grade 6, Meredith Seeley

Reports

This activity challenges students to help researchers understand what types of plastics are polluting the oceans!

Teachers will prepare samples of microplastics that were collected in each of the 5 ocean gyres, mimicking plastic concentrations actually found in the oceans! Working as a group, students will count the items of plastic and graph their results. They will share their results with the class to compare their gyre to the other four gyres. Finally, students will understand the link between ocean microplastic pollution, and our use of single-use plastics.

This activity can be completed in 45 minutes in the class. An …

Symbiotic Unicellular Cyanobacteria Fix Nitrogen In The Arctic Ocean, K. Harding, K. A. Turk-Kubo, Rachel E. Sipler, M. M. Mills, D. A. Bronk

VIMS Articles

Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and …

Sediment Transport Model Including Short-Lived Radioisotopes: Model Description And Idealized Test Cases, Justin J. Birchler,, Courtney K. Harris, Christopher R Sherwood, Tara A. Kniskern

VIMS Articles

Geochronologies derived from sediment cores in coastal locations are often used to infer event bed characteristics such as deposit thicknesses and accumulation rates. Such studies commonly use naturally occurring, short-lived radioisotopes, such as Beryllium-7 (Be-7) and Thorium-234 (Th-234), to study depositional and post-depositional processes. These radioisotope activities, however, are not generally represented in sediment transport models that characterize coastal flood and storm deposition with grain size patterns and deposit thicknesses. We modified the Community Sediment Transport Modeling System (CSTMS) to account for reactive tracers and used this capability to represent the behavior of these short-lived radioisotopes on the sediment bed. …

Strong Electron-Boson Coupling In The Iron-Based Superconductor Bafe1.9pt0.1as2 Revealed By Infrared Spectroscopy, Zhen Xing, Shanta Saha, J. Paglione, M. M. Qazilbash

Arts & Sciences Articles

Understanding the formation of Cooper pairs in iron-based superconductors is one of the most important topics in condensed matter physics. In conventional superconductors, the electron-phonon interaction leads to the formation of Cooper pairs. In conventional strong-coupling superconductors like lead (Pb), the features due to electron-phonon interaction are evident in the infrared absorption spectra. Here we investigate the infrared absorption spectra of the iron arsenide superconductor BaFe1.9Pt0.1As2. We find that this superconductor has fully gapped (nodeless) Fermi surfaces, and we observe the strong-coupling electron-boson interaction features in the infrared absorption spectra. Through modeling with the Eliashberg function based on Eliashberg theory, …

Catch The King Tide 2018: All King Tide Data, Jon Derek Loftis

Data

"Catch the King" is a citizen-science GPS data collection effort centered in Hampton Roads, VA, that seeks to interactively map the King Tide's maximum inundation extents. The goal is to validate and improving predictive model accuracy for future forecasting of increasingly pervasive "nuisance" flooding.

Building Capacity For Protection Of Wetland Resources In Virginia - Track One, Virginia Department Of Environmental Quality, Center For Coastal Resources Management - Virginia Institute Of Marine Science

Reports

DEQ continues to make significant progress in the development of a comprehensive nontidal wetland regulatory program; refinement of our permitting/compliance database to track impacts, compliance, and compensation by watershed; and continued refinement of our wetland monitoring and assessment tools for use in management decision-making and integration within our water quality programs. This project focused on development of strategies and extension of outreach to improve understanding and protection of high ecological value aquatic resources such as headwater resources and wetlands that may provide added value in improving impaired waters in Virginia. Project activities specifically addressed three of the priority elements in …