Theses and Dissertations from UMD
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Item PUBLIC MOBILITY AND THE IMPACT ON SOCIAL NETWORKS: UNDERSTANDING THE SOCIETAL AND TRANSNATIONAL COMMUNICATION OF MIGRANT NETWORKS FROM A QUALITATIVE APPROACH(2023) Iannacone, Jeannette Isabelle; Sommerfeldt, Erich J; Communication; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In considering the realities of 21st century society, research cannot overlook how livelihoods are becoming increasingly defined by one’s (in)ability for and agency over movement, i.e. mobility, especially on the transnational scale. Simultaneously, the relational turn of public relations scholarship has emphasized a network perspective, examining how a set of relations among social actors—be it people, groups, or organizations—create systems that comprise, maintain, and/or disrupt society (Yang & Taylor, 2015). As such, public relations should be inclusive of the depth of multiple, rich, and mobile relationships in social networks that span national borders. Yet the development of the network perspective in public relations has not been without its limitations, notably the absence of public perspectives, actions, and realities—all of which impact the communicative interactions that produce their social networks. This research thereby incorporates a public perspective through insights from people who migrate to highlight an increasingly important dimension to public formation and relationship dynamics: mobility. In doing so, this dissertation takes an innovative qualitative approach to social network analysis (SNA), which integrates a visual network mapping exercise alongside qualitative interviews and ethnographic observations. Findings captured how the enactment and context of mobility impact migrant network dynamics across the world as well as their subsequent communication behaviors and relational expectations, particularly with U.S. civil society organizations (CSOs). They further depicted an organizational perspective that highlighted three dichotomies to how CSOs perceive and maintain their social networks, and showcased the role of mobility as an underlying context generating distinct actors, ties, and positioning. Findings lastly emphasized entanglements between social and other forms of capital as well as patterns in who is perceived as having versus needing capital.As such, this dissertation proposes the conceptualization of the mobile social network ecology, a concept that integrates social network analysis and the experiences of public mobility by accounting for distinct publics and organizations perceptions. It allows for public relations to better consider the impacts of the enactment and context of mobility on key public relationships, inclusive of the distinct publics of the modern world, the CSOs that seek to serve them, and their linkages to civil societies on a transnational scale. Additionally, in noting the significant ties between migrant publics and migrant-serving CSOs, this dissertation connects the exchanges of (social) capital within a mobile social network ecology to relational power dynamics and differentials, emphasizing their lived, embodied impact as well as introducing a new salient category: spatial capital. All together, these contributions advance public relations in reckoning with the transnational, globalized dimensions of the modern world, showcasing how public mobility shapes and complicates our fundamental societal connections and presenting unique takeaways for the field in scholarship and practice.Item ACCOUNTING FOR STUDENT MOBILITY IN SCHOOL RANKINGS: A COMPARISON OF ESTIMATES FROM VALUE-ADDED AND MULTIPLE MEMBERSHIP MODELS(2023) Cassiday, Kristina; Stapleton, Laura M; Measurement, Statistics and Evaluation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Student mobility exists, but it’s not always taken into account in value-added modeling approaches used to determine school accountability rankings. Multiple membership modeling can account for student mobility in a multilevel framework, but it is more computationally demanding and requires specialized knowledge and software packages that may not be available in state and district departments of education. The purpose of this dissertation was to compare how different multilevel value-added modeling approaches perform at various levels of mobility to be able to provide recommendations to state- and district-administrators about the type of models that would be best suited to their data. To accomplish this task, a simulation study was conducted, manipulating the percentage of mobility in the dataset and the similarity of the sender and receiver schools of mobile students. Traditional gains score and covariate adjustment models were run, along with comparable multiple membership models to determine the extent to which school effect estimates and school accountability rankings were affected and to investigate the conditions under which a multiple membership model would produce a meaningful increase in accuracy to justify its computational demand. Additional comparisons were made on measures of relative bias of the fixed effect coefficients, the random effect variance components, and the relative bias of the standard errors of the fixed effects and random effects variance components. The multiple membership models with schools proportionally weighted by time spent were considered better fitting models across all conditions. All multiple membership models were able to better recover the intercept and school-level residual variance better than other models. However, when considering school accountability rankings, the proportion of school quintile shifts was close to equal across the traditional and multiple membership models that were structurally similar to each other. This finding suggests that the use of a multiple membership model is preferable in providing the most accurate parameter and standard error estimates. However, if school accountability rankings are of primary interest, a traditional VAM performs equally as well as a multiple membership model. An empirical data analysis was conducted to demonstrate how to prepare data and properly run these various models and how to interpret the results, along with a discussion of issues to consider when selecting a model. Recommendations are provided on how to select a model, informed by the findings from the simulation portion of the study.Item FROM MÚSICA DE CARRILERA TO CORRIDOS PROHIBIDOS AND NORTEÑA: MOBILITY, MEANING, WAR, AND THE RECONTEXTUALIZATION OF MEXICAN MUSICAL STYLES IN COLOMBIA(2017) Vergara, Patricia; Rios, Fernando; Music; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation analyses the adoption and multiple layers of recontextualization of Mexican musical styles in Colombia since the 1930s, particularly música norteña and corridos, story-songs that narrate current events perceived by listeners to be “the pure truth” about the Colombian conflict involving insurgent guerrillas, paramilitary squads, military officials, and drug traffickers that plagued the country for nearly six decades. The dissertation analyses the processes of music production, circulation, and reception that enabled the rise of a Colombian genre family of Mexican-inspired musical practices that thrives today, in spite of being dismissed by the Colombian culture industries for their supposed lack of artistic value and authenticity. Through a historic and spatial perspective this study examines long-standing rhetorics of class and race difference in Colombia, from the nineteenth-century elite’s conceptions of nation, modernity, and civilization to the project of multiculturalism that currently undergirds Colombia’s peace and nation building efforts. It highlights how these enduring discourses have been implicated in the disenfranchisement of both the participants and the musical practices that are the subject of this study. A boom in the production of corridos in Colombia coincided with the intensification of the conflict throughout the 1990s. Named “corridos prohibidos” (forbidden corridos), the production and distribution of these compositions has since relied on the informal economy, since they continue to be shunned by Colombian mass media channels. The political economy of corridos prohibidos thus provides an apt case study of how contemporary musicians and audiences have forged relationships with musical piracy that they view as a beneficial partnership, differing drastically from the attitudes of the traditional recording music industry and its professionals. This dissertation presents the current practices of corridos prohibidos and Colombian música norteña as vibrant spheres of cultural production from which participants derive a range of meanings and ways to mediate their lived experiences of violence and disenfranchisement, as well as pleasure and respite.Item QUANTIFYING PARTICLE PROPERTIES FROM ION-MOBILITY MEASUREMENTS(2012) Li, Mingdong; Zachariah, Michael R.; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoparticles have received considerable interest due to the wide variety of potential applications in biomedical, optical, and electronic fields. However, our capabilities for quantitatively charactering these materials, for example in number concentration or shape are limited. The objective of this work is to develop experimentally verified theories to quantify particle properties from aerosol based ion-mobility measurement. The use of aerosol tools is predicated on the idea that these methods offer the best chance for quantification, due to a better understanding of the physics of ion transport in the gas phase. Nevertheless this does not preclude us from using these techniques to characterize particles in liquids as will be show in the first part of this work which resolves problems associated with generating an aerosol from colloidal suspensions. In this dissertation I resolve the problem of artificial "droplet induced aggregation" during electrospray which can corrupt the eventual determination of particle size. I develop an experimentally verified statistical based model, to determine and correct this undesired artifact. Furthermore, I have found that this nominally undesired artifact can be used in a beneficial way that allows one to determine the absolute number concentration of nanoparticles in solution, without the need for calibration particles. Mobility is one of the most important and fundamental properties of a particle. However most particle characterization approaches interpret the results of mobility measurement in the context of spherical particle transport. I have undertaken to systematically explore the mobility properties of non-spherical particles. In this dissertation I develop a theory to quantify the effect of orientation on the mobility and the dynamic shape factor of charged axially symmetric particles in an electric field. The experimental results of well-defined doublets of NIST traceable size standard 127nm, 150nm, 200nm and 240nm PSL spheres are shown to be in excellent agreement with the expected values based on my theory. More general new theories of the mobility of nonspherical particles are also proposed and compared with current theories. I also propose a new instrument, a pulsed differential mobility analyzer (PDMA), to obtain shape information by measuring the electrical mobility under different electric fields.Item Electronic Structure of SiC/SiO2 by Density Functional Theory(2012) Salemi, Shahrzad; Goldsman, Neil; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Silicon carbide (SiC) is a promising semiconductor material with desirable properties for many applications. SiC-based electronic devices and circuits are being developed for use in high-temperature, high-power, and high-radiation conditions under which conventional semiconductors cannot function. Additionally, it has the advantage of growing a native oxide, SiO2, by simple thermal oxidation. Despite all desirable properties, SiC-based devices still face major challenges. The main problem of SiC-based devices is the great density of imperfections at the SiC/SiO2 interface, which not only degrades the device performance but also causes reliability problems coming from the extreme operating conditions. The quality of the interface affects the channel mobility of MOSFETs, which is the most critical parameter of devices. In this work a hybrid functional density functional theory framework is employed to model the (0001)4H-SiC/SiO2 abrupt interface. Using this, defect energy levels in the bandgap have been calculated through the total and projected density of states. There is experimental evidence for improvement of the quality of the interface after passivation, However the atomic mechanisms of the improvement are not yet clear., Thus, the impact of various passivations on the potential defects has also been studied. Since the interface of SiC/SiO2 is not perfectly abrupt, several atomic configurations for (0001)4H-SiC/SiO2 transition layers have also been modeled, and their effect on the bandgap, and the near interface trap density has been studied. A DFT-based Monte Carlo carrier transport simulation technique is employed to compute the average velocities, phonon-limited and ionized-impurity-limited mobilities of the most probable transition layer structures. Finally, since low frequency noise calculation is a powerful tool to diagnose quality and reliability of semiconductor devices, a DFT-based method is presented to calculate the current spectral noise density of the (0001)4H-SiC/SiO2 transition layers.Item Understanding Electric Field-Enhanced Transport for the Measurement of Nanoparticles and Their Assembly on Surfaces(2007-11-28) Tsai, De-Hao; R. Zachariah, Michael R; Jackson, Gregory S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this dissertation is to understand the synthesis, characterization, and integration of nanoparticles and nanoparticle-based devices by electric field-enhanced transport of nanoparticles. Chapter 1 describes the factors used for determining particle trajectories and found that electric fields provide the directional electrostatic force to overcome other non-directional influences on particle trajectories. This idea is widely applied in the nanoparticle classification, characterization, and assembly onto substrate surfaces as investigated in the following chapters. Chapter 2 presents a new assembly method to position metal nanoparticles delivered from the gas phase onto surfaces using the electrostatic force generated by biased p-n junction patterned substrates. Aligned deposition patterns of metal nanoparticles were observed, and the patterning selectivity quantified. A simple model accounting for the generated electric field, and the electrostatic, van der Waals, and image forces was used to explain the observed results. Chapter 2.2 describes a data set for particle size resolved deposition, from which a Brownian dynamics model for the process can be evaluated. Brownian motion and fluid convection of nanoparticles, as well as the interactions between the charged nanoparticles and the patterned substrate, including electrostatic force, image force and van der Waals force, are accounted for in the simulation. Using both experiment and simulation the effects of the particle size, electric field intensity, and the convective flow on coverage selectivity have been investigated. Coverage selectivity is most sensitive to electric field, which is controlled by the applied reverse bias voltage across the p-n junction. A non-dimensional analysis of the competition between the electrostatic and diffusion force is found to provide a means to collapse a wide range of process operating conditions and an effective indicator or process performance. Directed assembly of size-selected nanoparticles has been applied in the study of nanoparticle enhanced fluorescence (NEF) bio-sensing devices. Chapter 3 presents results of a systematic examination of functionalized gold nanoparticles by electrospray-differential mobility analysis (ES-DMA). Formation of selfassembled monolayers (SAMs) of alkylthiol molecules and singly stranded DNA (ssDNA) on the Au-NP surface was detected from a change in particle mobility, which could be modeled to extract the surface packing density. A gas-phase temperature-programmed desorption (TPD) kinetic study of SAMs on the Au-NP found the data to be consistent with a second order Arrhenius based rate law, yielding an Arrhenius-factor of 1×1011 s-1 and an activation energy ~105 kJ/mol. This study suggests that the ES-DMA can be added to the tool set of characterization methods being employed and developed to study the structure and properties of coated nanoparticles. Chapter 3.2 demonstrates this ES-DMA as a new method to investigate colloidal aggregation and the parameters that govern it. Nanoparticle suspensions were characterized by sampling a Au nanoparticle (Au-NP) colloidal solution via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the mobility distribution, and thus the aggregate distribution. By sampling at various times, the degree of flocculation and the flocculation rate are determined and found to be inversely proportional to the ionic strength and proportional to the residence time. A stability ratio at different ionic strengths, the critical concentration, and surface potential or surface charge density of Au-NPs are obtained from these data. This method should be a generically useful tool to probe the early stages of colloidal aggregation. Study of ES-DMA is extended to include the characterizations of a variety of materials. Biologically interested materials such as viruses and antibodies could also be characterized. These results show ES-DMA provides a general way to characterize the colloidal materials as well as aerosolized particles.Item Managing an Academic Career in Science: What Gender Differences Exist and Why?(2006-06-08) Richards, Gayle Patrice; Landry, Bart; Sociology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Document: MANAGING AN ACADEMIC CAREER IN SCIENCE: WHAT GENDER DIFFERENCES EXIST AND WHY? Gayle Patrice Richards, Doctor of Philosophy, 2006 Directed By: Professor Bart Landry Sociology Department The present study examines the career trajectories of academic scientists during the period from 1993 to 2001 to explore gender differences in mobility. Data from the National Science Foundation's Survey of Doctorate Recipients are used to examine and compare gender differences in the odds of promotion. The effects of age, marital and family status, duration of time to complete doctorate, academic discipline, cumulative number of publications and time in the survey are considered as explanatory variables. Event history analyses are conducted for all scientists, for scientists in four major academic disciplines and for scientists in various academic ranks. While no overall gender differences were observed in the odds of promotion, several important similarities and differences were evident. Expectedly, publications had a significant and positive relationship with advancement for both women and men. The role of parent influenced promotions quite differently for women and men. Contrary to expectations based on prior research, academic women scientists who were mothers advanced at similar rates as women without children. Consistent with expectations based on traditional roles, married men and men with children generally advanced more quickly than single or childless men, respectively. Two surprising patterns emerged among subgroups of women. Marriage was associated with greater odds of advancement for women engineers and motherhood was associated with greater odds of advancement for among assistant professors. Possible explanations for these findings are presented.Item Electronic Properties of Carbon Nanotubes studied in Field-Effect Transistor Geometries(2004-05-12) Dürkop, Tobias; Fuhrer, Michael S; PhysicsDue to their outstanding properties carbon nanotubes have attracted considerable research effort during the last decade. While they serve as an example of a 1-dimensional electron system allowing one to study fundamental quantum effects nanotubes-especially semiconducting nanotubes-are an interesting candidate for next-generation transistor application with the potential to replace silicon-based devices. I have fabricated nanotubes using chemical vapor deposition techniques with various catalysts and gas mixtures. The nanotubes produced with these techniques vary in length from 100 nm to several hundreds of micrometers. While data taken on shorter metallic and semiconducting devices show Coulomb blockade effects, the main part of this work is concerned with measurements that shed light on the intrinsic properties of semiconducting nanotubes. On devices with lengths of more than 300 um I have carried out measurements of the intrinsic hole mobility as well as the device-specific field-effect mobility. The mobility measured on these nanotube devices at room temperature exceeds that of any semiconductor known previously. Another important consideration in nanotube transistor applications are hysteresis effects. I present measurements on the time scales involved in some of these hysteresis effects and a possible application of the hysteresis for memory devices.