UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item AIR POLLUTION EMISSIONS FROM HIGHWAY VEHICLES: QUANTIFYING IMPACTS OF HUMIDITY, AMBIENT TEMPERATURE, AND COVID-19–RELATED TRAVEL RESTRICTIONS(2022) Hall-Quinlan, Dolly; Dickerson, Russell R; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Air pollution adversely affects human health and climate at both local and regional scales. With vehicles representing the dominant source of several important air pollutants, more work is needed to improve our understanding of the factors impacting vehicular emissions to further reduce pollution levels. In this dissertation, I use ambient, near-road (NR) observations of nitrogen oxides (NOx), carbon monoxide (CO), black carbon (BC), carbon dioxide (CO2), and traffic to characterize vehicular emissions and the influence of weather and traffic patterns. The first part focuses on how vehicular emissions respond to ambient temperature. The second part investigates traffic pattern changes resulting from COVID-19 travel restrictions and the effects on mobile emissions.Chapter 2 discusses the temperature and specific humidity sensitivity of vehicular NOx, CO, and CO2 emissions. Using NR (along Interstate 95) observations during the cold season, I calculated hourly ΔCO/ΔNOx, ΔCO2/ΔNOx, and ΔCO2/ΔCO ratios to infer emissions ratios from vehicular exhaust. Chapter 3 builds on this work by extending the temperature analysis to BC emissions using ∆BC/∆CO and ∆BC/∆CO2. Results show a factor of two decrease in NOx (−5°C to 25°C) and a ~50% increase in BC emissions (−5°C to 20°C). Combined with traffic observations, we trace this effect to diesel-powered trucks. The observed trends are then used to evaluate the temperature sensitivity in modeled mobile emissions. Important public policy decisions regarding air quality often depend on models that generate accurate emissions estimates from various sectors, including mobile sources. The US EPA estimates vehicular emissions for air quality models using the MOtor Vehicle Emissions Simulator (MOVES). Our analysis shows that MOVES underestimates the temperature effect in NOx emissions and does not adjust BC emissions, indicating that more work is needed to improve the temperature sensitivity in the model. Chapter 4 examines the impact of changing traffic patterns on I-95 in April 2020 on mobile emissions revealing ~60% fewer on-road cars and ~10% fewer trucks, resulting in faster highway speeds and less stop-and-go traffic. Coupled with an analysis of emission ratios, the results of this study suggest a significant decrease in BC emissions from diesel-powered trucks attributable to improved traffic flow.Item Energy Harvesting Communication Networks with System Costs(2017) Arafa, Ahmed; Ulukus, Sennur; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on characterizing optimal energy management policies for energy harvesting communication networks with system costs. The system costs that we consider are the cost of circuitry to be on (processing cost) at the transmitters, cost of decoding at the receivers, cost of moving to harvest more energy in mobile energy harvesting nodes, and the cost of collecting measurements (sampling cost) from physical phenomena. We first consider receiver decoding costs in networks where receivers, in addition to transmitters, rely on energy harvested from nature to communicate. Energy harvested at the receivers is used to decode their intended messages, and is modeled as a convex increasing function of the incoming rate. With the goal of maximizing throughput by a given deadline, we study single-user and multi-user settings, and show that decoding costs at the receivers can be represented as generalized data arrivals at the transmitters. This introduces a further coupling between the transmitters and receivers of the network and allows us to characterize optimal policies by moving all constraints to the transmitter side. Next, we study the decoding cost effect on energy harvesting cooperative multiple access channels, where users employ data cooperation to increase their achievable rates. Data cooperation requires each user to decode the other user's data before forwarding it to the destination, which uses up some of the harvested energy. With the presence of decoding costs, we show that data cooperation may not be always helpful; if the decoding costs are relatively high, then sending directly to the receiver without data cooperation between the users achieves higher throughput. When cooperation is helpful, we determine the optimum allocation of available energy between decoding cooperative partner's data and forwarding it to the destination. We then study the impact of adding processing costs, on top of decoding costs, in energy harvesting two-way channels. Processing costs are the amounts of energy spent for circuitry operation, and are incurred whenever a user is communicating. We show that due to processing costs, transmission may become bursty, where users communicate through only a portion of the time. We develop an optimal scheme that maximizes the sum throughput by a given deadline under both decoding and processing costs. Next, we focus on online policies. We consider a single-user energy harvesting channel where the transmitter is equipped with a finite-sized battery, and the goal is to maximize the long term average utility, for general concave increasing utility functions. We show that fixed fraction policies are near optimal; they achieve a long term average utility that lies within constant multiplicative and additive gaps from the optimal solution for all battery sizes and all independent and identically distributed energy arrival patterns. We then consider a specific scenario of a utility function that measures the distortion of Gaussian samples communicated over a Gaussian channel. We formulate two problems: one with, and the other without sampling costs, and design near optimal fixed fraction policies for the two problems. Then, we consider another aspect of costs in energy harvesting single-user channels, that is, the energy spent in physical movement in search of better energy harvesting locations. Since movement has a cost, there exists a tradeoff between staying at the same location and moving to a new one. Staying at the same location allows the transmitter to use all its available energy in transmission, while moving to a new one may let the transmitter harvest higher amounts of energy and achieve higher rates at the expense of a cost incurred through the relocation process. We characterize this tradeoff optimally under both offline and online settings. Next, we consider different performance metrics, other than throughput, in energy harvesting communication networks. First, we study the issue of delay in single-user and broadcast energy harvesting channels. We define the delay per data unit as the time elapsed from the unit's arrival at the transmitter to its departure. With a pre-specified amount of data to be delivered, we characterize delay minimal energy management policies. We show that the structure of the optimal policy is different from throughput-optimal policies; to minimize the average delay, earlier arriving data units are transmitted using higher powers than later arriving ones, and the transmit power may reach zero, leading to communication gaps, in between energy or data arrival instances. Finally, we conclude this dissertation by considering the metric of the age of information in energy harvesting two-hop networks, where a transmitter is communicating with a receiver through a relay. Different from delay, the age of information is defined as the time elapsed since the latest data unit has reached the destination. We show that age minimal policies are such that the transmitter sends message updates to the relay just in time as the relay is ready to forward them to the receiver.Item Implementation, Evaluation, and Applications of Mobile Mesh Networks for Platforms in Motion(2009) Napora, Jared Stanislaus; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis explores the selection, implementation, and evaluation of two mobile mesh networks, each involving a different distributed computing problem. In the forthcoming discussion, it will become apparent how system constraints affect the optimal choice of mesh networking design and implementation in these cases. The first problem explores the design and implementation of a distributed computing mesh network that will allow a collection of autonomous land vehicles to gather, process, and exchange information in an unknown environment. This network was established by adapting standard commercial 802.11 routers and by providing a software framework that handles all communication between wireless nodes. The second problem involves the design of a network for tracking and monitoring personnel. This network was implemented utilizing ZigBee modules due to power and custom implementation constraints. Both networks were tested with respect to their specific design constraints and they lay the foundation for additional application development and research.