Dynamic spectrum access (DSA) is a promising approach to alleviate spectrum scarcity and improve spectrum utilization. Our work aims to enhance the utilization of the available white spaces in the licensed spectrum by enabling cooperative communication in the secondary networks. We investigate the ability of a two-hop cooperative transmission to reduce the effect of primary user interruption on secondary transmissions. We analyze the performance of a cooperative secondary transmission by modeling the interaction between primary user and secondary user transmissions using a discrete time Markov chain (DTMC). The analysis shows a significant enhancement in the secondary transmission efficiency and throughput when cooperative transmission is utilized compared to that of direct transmission, especially at high levels of primary user activity. We extend our study to model secondary cooperative transmission in realistic scenarios. We evaluate the throughput performance enhancement in the secondary infrastructure network analytical and by simulation. A simple scenario is modeled analytically by a DTMC that captures the probability of finding intermediate relays according to nodes' density and by discrete event simulation where both results confined each other. We introduce a dedicated cooperative and cognitive Media Access Control (MAC) protocol named CO2MAC to facilitate secondary users transmissions in infrastructure-based secondary networks. The proposed MAC enables utilizing cooperative Multi-Input-Multi-Output (MIMO) transmission techniques to further enhance the throughput performance. By using the proposed MAC, we quantify the enhancement in the throughput of secondary infrastructure networks via simulation for complex scenarios. The results show an enhancement in cooperative transmission throughput compared to that of direct transmission, especially at crowded spectrum due to the ability of cooperative transmissions to reduce the negative effect of primary user interruptions by buffering the data at intermediate relays. Also, the cooperative throughput performance enhances compared to that of direct transmission as the nodes' density increases due to the increase in the probability of finding intermediate relays. After that, we answer two questions. The first question is about the way a secondary user pays the cooperation price to its relay and what are the conditions under which the cooperation is beneficial for both of them. The second question is about how to pair the cooperating nodes and allocate channels in an infrastructure based secondary network. To answer the first question, we model the cooperation between the secondary user and its relay as a resource exchange process, where the secondary user vacates part of its dedicated free spectrum access time to the relay as a price for the energy consumed by the relay in forwarding the secondary user's packets. We define a suitable utility function that combines the throughput and the energy then we apply axiomatic bargaining solutions, namely Nash bargaining solution (NBS) and egalitarian bargaining solution (EBS) to find the new free spectrum access shares for the secondary user and the relay based on the defined utility in the cooperation mode. We show that under certain conditions, the cooperation is beneficial for both the secondary user and the relay where both achieve a higher utility and throughput compared to the non-cooperative mode. Finally, based on the bargaining based shares of the cooperating nodes, the node pairing and channel allocation are optimized for different objectives, namely maximizing the total network throughput or minimizing the maximum unsatisfied demand. Our bargaining based framework shows a comparable performance with the case when the nodes' free spectrum access time shares are jointly optimized with the pairing and allocation process, at the same time, our cooperation framework provides an incentive reward for the secondary users and the relays to involve in cooperation by giving every node a share of the free spectrum that proportional to its utility. We also study the case of using multiple secondary access points which gives more flexibility in node pairing and channel allocation and achieves a better performance in terms of the two defined objectives. / Ph. D.

no abstract provided by author / Master of Science

Virginia Cooperative Extension's Family Nutrition Program (FNP), which includes EFNEP and SNAP-Ed, works to help limited-resource families across the state make informed food-choices. Virginia Cooperative Extension (VCE) lacks open-access physical activity resources representing individuals with varying weights, races, and ethnicities. In 2015, an integrated research-practice partnership was initiated for the development of an evidence-based physical activity resource for peer educators employed by FNP to use. The video suite, Move More, Virginia!, was created as open-access and includes demographically diverse individuals, representative of FNP clients. Study I determined client perceptions of physical activity and preferences for new resources. Study II identified FNP peer educators' perceptions of physical activity, their resource needs, and intent to use Move More, Virginia! resources. Both studies involved quantitative and qualitative data through surveys and focus groups. Formative data collected in Study I revealed the prominent themes related to clients (n=12) were physical activity facilitators (n= 100 meaning units (MU)) and physical activity barriers (n=77 MU). In Study II, peer educator responses(n=15) led to the emergence of four themes related to physical activity itself: barriers to incorporating physical activity within FNP (n=189 MU), physical activity facilitators (n=106), current delivery of physical activity (n=102 MU), and physical activity barriers (n= 16 MU). When prompted to share video specific feedback, the top theme was positive video feedback (n = 115 MU). Identified themes and subthemes provide deeper understanding of the organizational culture within FNP as thoughts, perceptions, and barriers to incorporating physical activity into FNP curriculum are highlighted. / Master of Science

The Hampton Roads region of southeast Virginia is largely defined by its abundant water resources. These water resources are also a source of unique issues for the region. Specifically, water quality challenges related to the Chesapeake Bay and recurrent flooding are the major concerns. Green infrastructure (GI) has emerged in recent years as an alternative to traditional stormwater conveyance and detention focused systems. GI practices focus on integrating infiltration, evapotranspiration, and other components of the water cycle into more conventional stormwater management systems. These systems provide several positive benefits, including local water quality and quantity control, community revitalization, and various public health benefits. In addition, GI implementation has seen strong levels of support from the Cooperative Extension System, with Extension faculty and staff around the U.S. supporting local municipalities through GI research, promotion, and program development. Despite widespread interest, GI has been slow to be adopted due to various barriers to its implementation. This study sought to identify the major barriers to the implementation of GI practices in Hampton Roads by conducting a needs assessment. Municipal stormwater staff were invited to participate in an online survey aimed at identifying the most significant barriers in the region. At the same time, local staff with Virginia Cooperative Extension (VCE) were interviewed to explore their potential to become involved in promoting GI adoption in Hampton Roads. Survey respondents and interview participants found common ground in identifying costs, funding, and maintenance issues as the most significant barriers to GI implementation in Hampton Roads. In addition, VCE staff were found to be well suited to support widespread GI adoption in the region, having familiarity with the GI concept and access to unique resources in the form of knowledgeable Master Gardener volunteers and connections to Virginia Tech. Recommendations for VCE involvement in promoting GI in Hampton Roads include conducting cost studies, developing and hosting maintenance training programs, and taking advantage of partnerships to identify and obtain funding from diverse sources. By focusing on these widely acknowledged challenges at the regional scale, VCE can support GI implementation throughout all of Hampton Roads. / Master of Science / Hampton Roads is a region with a history and economy tied to its local waters. Today, the region is facing significant challenges related to these waters, including frequent flooding impacts on residents and pollution control needs for the nearby Chesapeake Bay. Green infrastructure (GI), a relatively new approach to managing water in cities, could help local governments address these challenges. Virginia Cooperative Extension (VCE), an organization formed through a partnership between federal and local governments and land grant universities in Virginia, seeks to meet community needs through community outreach and educational programs. As a community-centered organization with a history of advancing environmental education, VCE may also be an important partner for municipalities in Hampton Roads interested in adopting GI practices. To identify the barriers to GI in Hampton Roads and the potential role of VCE in addressing them, a needs assessment of municipalities in the region with stormwater permits was conducted. Based collected documents, surveys of municipal staff, and interviews with VCE personnel, three major barriers to GI adoption were identified. Permitted municipalities in Hampton Roads are uncertain of GI costs, have limited funds to support GI practices, and lack the knowledge and resources needed to maintain GI practices over time. VCE can help municipalities address these challenges using its many resources. Through its connection to Virginia Tech and Virginia State University, VCE can help in developing cost research studies for Hampton Roads. As an educational organization, VCE can also help municipalities win funding for GI projects that they would otherwise not have access to. Finally, local Virginia Tech faculty at the Hampton Roads Agricultural Research and Extension Center and experienced Master Gardener volunteers can work to develop GI maintenance training resources for maintenance staff throughout the region. With its strong background, expert knowledge, and existing connections in the region, VCE can play an important role in addressing the GI adoption challenges in Hampton Roads.

Software development teams are often geographically distributed from their customers and end users. This creates significant communication and coordination challenges that impact the effectiveness of requirements engineering. Travel costs, and the local availability of quality technical staff increase the demand for effective distributed software development teams. In this research an empirical study was conducted on the application of groupware to facilitate the requirements phase of the software engineering life cycle. The study considered the impact of the distributed work environment on requirements engineering process quality, as well as the effectiveness of requirements elicitation techniques when used in the distributed setting. Through the examination of the effectiveness of groupware tools, and requirements elicitation techniques, customer participation is found to be paramount for distributed requirements engineering. As requirements negotiation becomes more asynchronous in nature, it appears that customer participation in the elicitation process becomes very important for process effectiveness. Verbal communication barriers negatively effect customer participation. Such barriers cause customers to rely upon mediums such as email and text chat that are very good at reducing social distance, but are less rich in informational content. / Master of Science

The red-cockaded woodpecker (Picoides borealis) is a federally endangered species. As such, populations need to be increased in order to achieve recovery goals outlined by the U.S. Fish and Wildlife Service. My thesis is composed of two chapters that represent opposite sides of this issue. The first chapter investigates whether military training activity negatively affects red-cockaded woodpeckers. Military installations in the southeastern United States contain several of the largest remaining red-cockaded woodpecker populations. Six of the 15 installations harboring these birds are designated primary core populations; thus, population increases on these sites are critical to recovery of the species. However, restrictions on military training activity associated with red-cockaded woodpecker protection are a cause of concern on military installations that sometimes constrains management for population growth. Current restrictions are based on assumptions of potential impacts rather than scientific evidence, so we evaluated two different restriction regimes to test for training activity effects. The second chapter concerns how to induce populations to grow more rapidly through natural processes. As a cooperative breeder, red-cockaded woodpeckers preferentially compete for existing breeding positions and queue in the form of helping or floating to obtain a breeding vacancy, rather than create new territories. I used 20 years of demographic data collected as part of a long-term monitoring study of red-cockaded woodpeckers to investigate mechanisms that stimulate territory creation in this cooperatively breeding species. / Master of Science

The measurement of stress hormone levels in wild free-living animals is becoming an increasingly effective method for examining proximate mechanisms of animal behavior and the physiological impacts of human activities on wildlife. In these studies I measured plasma levels of the stress hormone corticosterone in the endangered red-cockaded woodpecker (Picoides borealis) to determine their role in the reproductive behavior of individuals in this species, and whether they are affected by human disturbance. In chapter one, I provide an introduction to the vertebrate stress response and I describe the natural history of the red-cockaded woodpecker. In chapter two, I compare corticosterone and reproductive hormone levels between breeding males and helper males to examine hormonal mechanisms of reproductive suppression in helper males. No hormonal differences existed between breeding and helper males. However, baseline corticosterone levels were lower in all males living in groups with two or more helper males, suggesting that male helpers reduce the workload of all other group members. In chapter three, I compare corticosterone levels between birds living in clusters subject to two different training restriction regimes on a military installation. Males living in clusters without training restrictions had lower baseline corticosterone than those living in clusters with training restrictions, suggesting that males habituate to chronic disturbance by downregulating baseline corticosterone levels. / Master of Science

Groundwater related courses are offered through several colleges at Virginia Tech. These classes enroll a diverse group of students with varied academic backgrounds and educational levels. Though these classes emphasize different aspects of groundwater resources, they lack a unified approach in instructional materials and learning methodologies for knowledge they do share. The goals of this research are to lessen the impact of variable student backgrounds and to better integrate the courses to improve teaching and learning, through the development of a multi-tiered, interdisciplinary website, Groundwater Interactive (GWI). GWI, as an educational technology, employs a variety of interactive multimedia. The primary educational components of the website include interactive and graphical models and quizzes, and a student-authored primer. An implementation strategy based on experiential and cooperative learning models is developed for application of the GWI tool in the classroom. An assessment methodology to evaluate the effectiveness of these new learning methods and techniques was also developed, but was not implemented as part of this work. / Master of Science

This study concerns the contributions of Major Albert Sobey and his educational leadership during the development of the engineering cooperative education program that became the foundation for the General Motors Institute in Flint, Michigan. This study also examines Albert Sobey's contributions to the emergence of industrial cooperative education in America over the past seventy years.

No description available.