Search

This study aimed to understand why and how community college practitioners act for institutional change in support of undocumented students--drawing on concepts from the tempered radicals framework. I used qualitative inquiry and exploratory interviews to understand how community college practitioners make meaning of the changes they have been involved in or have observed on campus for undocumented students. I conducted interviews with 27 participants across 16 community college institutions who were involved in supporting undocumented students. The interviews explored the nature and timeline of institutional support, how and why the practitioners began supporting undocumented students, perceptions of institutional culture, the process by which support for undocumented students was adopted and institutionalized, and the role of practitioners and allies in that change. The findings illustrate how tempered radicals were motivated to act when their social, personal, and professional identities highlighted a misalignment between their and the institution's equity values. When practitioners had the opportunity to act in support of undocumented students, it was usually on their own or within organizational norms, contributing to continuous and fragmented change. However, episodic events also provided windows of opportunity or could present significant challenges for change. This dissertation suggests seven major components of the context for action that can show adverse or favorable contexts for change in support of undocumented students; two notable components are discourses around "serving all students" and who was deemed responsible for serving undocumented students. Adverse contexts for change were reproduced by tempered resistance, inconspicuous actions that practitioners took (or did not take) that effectively resulted in sustaining the status quo inequitable practices for undocumented students. Ultimately, this study adds to the literature on how organizational norms of community colleges can shape individual practitioner's actions, which, in exchange, provide opportunities and constraints for future change for undocumented students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Every citizen has the right to be equipped with scientific literacy to understand and make informed decisions within the discipline of science. Educators can utilize core science teaching practices (CSTPs) to develop scientific literacy. In response, this study identified the CSTPs utilized by preservice elementary teachers (PSETs) to develop scientific literacy during their spring 2022 student teaching semester. Furthermore, this study identified contextual constructs that led to the utilization of the CSTPs to develop scientific literacy. The study used a qualitative exploratory case study using semi-structured interviews as the primary data. Surveys and artifacts were used as supporting secondary data. The identification of CSTPs and their contextual constructs were conducted using inductive content analysis. Afterward, the identified CSTPs and their contextual constructs were deconstructed, interpreted, and synthesized through the critical theoretical framework of disciplinary literacy. Relationships, time, school structure, and community were contextual constructs that enabled and disabled PSETs' utilization of CSTPs to develop scientific literacy. The contextual constructs are represented using the Framework to Develop Scientific Literacy (FDSL). The FDSL contain contextual constructs that enabled PSETs to utilize CSTPs through the sharing of power between the PSET and their cooperating teacher, school district, community, or teacher education programs. In contrast, contextual constructs that disabled PSETs include denying of power that negatively impacted the utilization of CSTPs to develop scientific literacy. The findings of the study call for teacher education programs to include contextual constructs as elements that impact PSETs' student teaching experiences to navigate power dynamics in authentic school settings. By identifying and using constructs as represented in the FDSL, teacher education programs can support PSETs' utilization of CSTPs to develop scientific literacy. In addition, this study calls for a reframing of power relationships between teacher education programs and their partnering school districts. By revealing the complex contextual nature of the PSETs' student teaching experiences, this study seeks to initiate discussion on how teacher education programs can support the practice of PSETs as they educate the next generation of scientifically literate citizens. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Leveraging big data for student data analytics is increasingly integrated throughout university operations from admissions to advising to teaching and learning. Though the possibilities are exciting to consider, they are not without risks to student autonomy, privacy, equity, and educational value. There has been little research showing how universities address such ethical issues in their student data policies and procedures to date though privacy and security policies are abundant. Though privacy and security policies that students sign cover institutions legally, there is more that can be done to support the ethical use of student data analytics at higher education institutions. This exploratory study addressed why it is important to support the four values of autonomy, privacy, equity, and educational value within university student data analytics policies and procedures. A rationale for focusing on these values was discussed through the lens of Paulo Freire's "Pedagogy of the Oppressed". A comparative case analysis of data analytics policies and procedures at two large, public universities provided insight into what they emphasized and where risks to student autonomy, privacy, equity, and educational value existed. This study concluded with recommendations of how institutional leadership can use proposed principles of ethical student data analytics to evaluate their own policies and procedures and amend risks that are uncovered through analysis. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Researchers have shown that principals are second only to teachers in their impact on student learning. The problem studied was principals' abilities to balance their responsibilities as operational managers while placing primary focus on instructional leadership. The purpose of this qualitative study was to explore the processes established by school principals to balance the expectation of managing their buildings while being instructional leaders and how their sense of self-efficacy influenced their ability to establish and adhere to those processes and structures. The theories of complexity self-efficacy guided this study. Data were collected using structured and semistructured interviews with six elementary and middle school principals from one district in a MidAtlantic U.S. state. A combination of in vivo and value coding was used to support thematic analysis. Themes included shared vision/responsibility, setting priorities, shared leadership, continued professional learning, and organizational procedure. Results indicate that principals need a stable sense of self-efficacy to be the conduit through which continuous adaptation of processes and structures necessary to accommodate the needs of a complex organization like a school. Key findings indicated that principals need to establish structures that ensure they are not the only instructional leader within their schools and they need to develop processes that ensure they are not the only managers within their schools. Recommendations include a system of continuous authentic feedback for school leaders through supervisors or a principal mentorship program. The findings of this study inform social change by identifying the ways in which principals meet the expectation of maintaining priority focus on instructional leadership while being efficient organizational managers of their schools. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Precision medicine refers to the delivering of customized treatment to patients based on their individual characteristics, and aims to reduce adverse events, improve diagnostic methods, and enhance the efficacy of therapies. Among efforts to achieve the goals of precision medicine, researchers have used observational data for developing predictive modeling to best predict health outcomes according to patients' variables. Although numerous predictive models have been reported in the literature, not all models present high prediction power, and as the result, not all models may reach clinical settings to help healthcare professionals make clinical decisions at the point-of-care. The lack of generalizability stems from the fact that no comprehensive medical data repository exists that has the information of all patients in the target population. Even if the patients' records were available from other sources, the datasets may need further processing prior to data analysis due to differences in the structure of databases and the coding systems used to record concepts. This project intends to fill the gap by introducing an interoperable solution that receives patient electronic health records via Health Level Seven (HL7) messaging standard from other data sources, transforms the records to observational medical outcomes partnership (OMOP) common data model (CDM) for population health research, and applies predictive models on patient data to make predictions about health outcomes. This project comprises of three studies. The first study introduces CCD-TO-OMOP parser, and evaluates OMOP CDM to accommodate patient data transferred by HL7 consolidated continuity of care documents (CCDs). The second study explores how to adopt predictive model markup language (PMML) for standardizing dissemination of OMOP-based predictive models. Finally, the third study introduces Personalized Health Risk Scoring Tool (PHRST), a pilot, interoperable OMOP-based model scoring tool that processes the embedded models and generates risk scores in a real-time manner. The final product addresses objectives of precision medicine, and has the potentials to not only be employed at the point-of-care to deliver individualized treatment to patients, but also can contribute to health outcome research by easing collecting clinical outcomes across diverse medical centers independent of system specifications. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Higher education appears to be changing in Saudi Arabia, which has made considerable progress in the adoption of more student-centered learning approaches as a reaction to the global pedagogical shift. Saudi Arabia has prioritized instructional technology integration in its educational system. The proliferation and popularity of mobile handheld devices, particularly among young students, will significantly make the future of Mobile learning, or M-learning in higher education bright and promising. However, M-learning in higher education is still in its embryonic stage of implementation, especially in developing countries such as Saudi Arabia; therefore, an in-depth study of each aspect of this issue is necessary. To ensure the success of M-learning in higher education, it is crucial to examine the students' intention to use M-learning as the first step in the process of implementing it into higher education. A quantitative, non-experimental survey research design and descriptive research were conducted on the determinants--performance expectancy, effort expectancy, and social influence--that predict undergraduate Saudi students' intention at King Khalid University (KKU) to use M-learning, based on the Unified Theory of Acceptance and Use of Technology (UTAUT) (Venkatesh et al., 2003) as the framework. Data were collected by means of a self-administered online questionnaire. The hypothesized model was validated empirically using data collected from 1,207 undergraduate students at KKU, Saudi Arabia. A multiple linear regression was administered to test the proposed hypothesis. The proposed model was supported and explained up to 52% of the variance in behavioral intention to use M-learning. The results indicate that performance expectancy, effort expectancy, and social influence were all statistically significant predictors of behavioral intention to use M-learning. Despite the great potential of mobile handheld devices to provide students and institutions with many benefits, such as study aids, accessibility to information, and universal communication, students may be constrained by limited or no internet connectivity, limited screen size, short battery life, and low memory, all of which may dampen student interest in using M-learning. Therefore, these obstacles need to be solved for the betterment of M-learning. This study contributes to the literature on M-learning by identifying determinants that predict student's behavioral intention to adopt and use M-learning and also confirms further Venkatesh et al.'s (2003) UTAUT model as a valid model in studying technology acceptance and use. Based on the results of this study, recommendations were made for instructional practice and future research to implement M-learning for academic purposes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Challenging the current discordance in orientation between student assessment models and teacher/school value-added models, this study aims to present the educator performance function (EPERF)-based teacher effect estimation method which utilizes the nature of student criterion-referenced assessment, to evaluate its feasibility and usefulness by comparison with the currently prevailing methods--the education production function (EPROF)-based value-added model. Specifically, this study (1) investigated how different the teacher effect estimates of the EPERF-based method are from those of the EPROF-based method, (2) examined whether the model fit of the EPERF is acceptable, and (3) simulated whether the EPERF-based method is robust to the locations of cut-scores and number of performance levels. A northern state's student-teacher linked data set was used, and the student challenge index, which is defined as the degree of difficulty that teachers face in teaching a student to attain a desired/higher performance standard, was constructed as a summary quantity of individual students' characteristics. The main findings from comparison between the two different teacher effect estimates--the educator performance level (EPL) from the EPERF-based method, and the value-added measure (VAM) from the EPROF-based method--were as follows: First, rank correlations between the two estimates were above 0.82 for mathematics. In particular, the EPL from the polytomous EPERF were very close to the VAM estimates in terms of ranking teachers, showing above 0.8 rank correlations. Second, in consistent and considerable ways, the relationship of the teacher effect estimates to student and teacher characteristics did not differ between the EPL and VAM estimates. Third, intra-teacher rank correlations across different subjects and different grade levels were also similar between the EPL and VAM. These observations implied that the teacher ranking information resulting from the EPERF-based methods did not differ noticeably from the results of the EPROF-based method. The EPERF-based methods, however, produced several useful areas of information for understanding how average or individual teachers perform with their students. For the second question, the EPERF showed a reasonable model fit in mathematics but not in reading. The conditional independence assumption of student success was violated. The amount of conditional dependency within each teacher was reasonable, and tended to be larger than in the EPROF-based models. Regarding the third question, it was found that, as a result of real-data simulations, the EPL based on the polytomous performance levels was quite robust to the location of cut-scores, and the number of performance levels also did not substantially change the teachers' ranking. These mixed results of model-fit and the robustness of the estimates bring into question on whether the EPL estimates change when student challenge index indicators are added, or when more generalized EPERF models are applied. This study appraised a part of the validity evidence of using the EPERF-based method, including if the method is executable and if the estimated teacher effects are trustworthy, along with the comparison with the EPROF-based method. Implications of applying the EPERF-based teacher effect estimation and future directions for expanding the method are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

The concurrent deployment of high-quality wireless networks and large-scale cloud services offers the promise of secure ubiquitous access to seemingly limitless amount of content. However, as users' expectations have grown more demanding, the performance and connectivity failures endemic to the existing networking infrastructure have become more apparent. These problems are in general exacerbated by user mobility. The work presented in this dissertation demonstrates that performance of services for mobile users is significantly affected by environmental factors that are hard to characterize ahead of deployment. This work includes development and evaluation of large-scale mobile experimentation infrastructures (DOME, GENI) that facilitate longitudinal studies of today's technologically diverse mobile environment over a period of four years. Based on the insights gained from these studies, a mechanism called Spider is presented that provides for efficiently utilizing Wi-Fi deployments in highly mobile scenarios to achieve higher throughput and improved connectivity. This work presents the first in-depth analysis of the performance of attempting concurrent AP connections from highly mobile clients. Spider provides a 400% improvement in throughput and 54% improvement in connectivity over stock Wi-Fi implementations. The last part of this dissertation demonstrates there are predictable differences among performances of a cellular network in different geographical locations of a town. Consequently, patterns of data transmission between a server on the Internet and a moving cell phone can reveal the geographic travel path of that phone. While the GPS and location-awareness features on phones explicitly share this information, phone users will likely be surprised to learn that disabling these features does not suffice to prevent a remote server from determining their travel path. We showed that a simple HMM-based classifier can discover and exploit features of the geography surrounding possible travel paths to determine the path a phone took, using only data visible at the remote server on the Internet. Having gathered hundreds of traces over a large geographic area, we showed that the HMM-based technique is able to distinguish mobile phones from stationary phones with up to 94.7% accuracy. Routes taken by each mobile phone could be distinguished with up to 75.9% accuracy using the same technique. This dissertation proposes new tools and techniques for characterization of the impact of the environment on the performance of mobile networks. The concrete set of results and insights gained from this work demonstrates mechanisms for improving connectivity and throughput in highly mobile scenarios while at the same time raising new challenges for maintaining the privacy of mobile users. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

This study aims to explore how collaborative teacher interaction is contingent upon teachers' immediate classroom and school-organizational contexts as well as broader societal and policy environments. Notwithstanding the widely acknowledged connection between teacher collegiality in schools and its beneficial effects, little systematic effort has been made to understand what types of teachers, under what contextual conditions, build and/or sustain collegial relationships with other teachers. In order to understand better a range of multilevel contextual factors associated with collaborative teacher interaction, this study intends to both elaborate and test an uncertainty management perspective as a theoretical framework. In addition, four conventional perspectives--a school climate perspective, a principal instructional leadership perspective, a curriculum policy perspective, and a national culture perspective--are also considered to see if a set of primary hypotheses derived from the uncertainty management perspective is empirically supported even after a range of other plausible hypotheses are simultaneously taken into account. Overall, the main findings from this study support an uncertainty management perspective which understands collegiality as a byproduct of the collective sensemaking of uncertainties, which reduces organizational members' feelings of discomfort with given uncertainties and thus helps them manage those uncertainties without actually removing them completely from given situations. Extensive international and U.S. data analyzed in this study substantiate the central proposition of the uncertainty management perspective that teacher collegiality has to do with teachers' collective effort to deal with various instructional and classroom-contextual uncertainties that they confront in their teaching. This result sheds light on the possibility that lateral collegial relationships among teachers may serve as a source of information processing, sensemaking, and problem-solving, whereby teachers can better manage to go through given situations of uncertainty. This study provides useful implications for educational policy and administration. In particular, given the fact that it is not always either possible or desirable to eliminate the sources of uncertainty in teaching, finding ways to help teachers manage the uncertainty through collaborative interaction with their colleagues is an important task for educational administrators and policy makers. Further, considering the wide variety of possible situations in which teachers confront instructional and classroom-contextual uncertainties, it is important for principals to explore various ways to actively share leadership roles and responsibilities with many teachers, so that individual teachers can become empowered agents to foster and sustain a collegial work environment. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

This dissertation focuses on beginning mathematics teachers from alternative certification programs and their perceptions of what is required to be successful. A mixed-methods research study was completed with several goals in mind: (1) identifying how beginning mathematics teachers define success in the classroom during their earliest years, (2) identifying what important factors, attributes, or experiences helped them achieve this success, and (3) determining where these beginning mathematics teachers learned the necessary attributes, or experiences to become successful in the classroom. A sample of beginning mathematics teachers (n = 28) was selected from an alternative certification program in California for a quantitative survey. A subsample of teachers (n = 7) was then selected to participate further in a qualitative semi-structured interview. The results of the study revealed that beginning teachers defined success in their beginning years by their classroom learning environment, creating and implementing engaging lessons, and a belief in their own ability to grow professionally as educators. Mathematics content knowledge, classroom management, collaboration with colleagues and coaches, reflection, a belief in one's ability to grow professionally as a teacher, a belief in the ability to have a positive impact on students, personality, and previous leadership experiences were several of the factors, attributes, or experiences identified as most important by the participating teachers. The participating teachers also felt that before and after, but not during, their teacher preparation program were the stages of teacher development that best instilled the necessary factors, attributes, or experiences to become successful in a mathematics classroom. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

We propose market-based coordinated task allocation mechanisms, which allocate complex tasks that require synchronized and collaborated services of multiple robot agents to robot agents, and an auditing mechanism, which ensures proper behaviors of robot agents by verifying inter-agent activities, for self-interested, fully-distributed, and large-scale multi-robot systems that have multi-agent tasks with real-time constraints in dynamic environments. The studied coordinated task allocation mechanisms include auction mechanisms such as forward auction, reverse auction, forward/reverse auction, and sealed-bid auction with different bidding strategies, which are represented by different utility functions. The coordinated task allocation mechanisms also include 1-to-1 task exchange, which reallocates tasks assigned by auctions in order to adapt to changing environments in real-time. Because the robot agents are self-interested, the agents may try free-riding and cheating, which is to consume resources without providing enough services. Free-riding and cheating attempts may deteriorate the overall performance by discouraging contribution of each robot agent--contribution of honest agents may be not rewarded with enough amount of service consumption. In order to encourage contribution and to ensure the amount contribution is properly accounted, we propose an auditing mechanism with a credit system, which can be combined with the proposed coordinated task allocation mechanisms. We conduct both physical robot experiments and software agent simulations for the coordinated task allocation mechanisms. The experimental results suggest that the proposed mechanisms are scalable and fault-tolerant and work in physical robot systems. We compare the proposed methods to control methods with various performance metrics and the results suggest that the performance can be enhanced by the proposed approaches. We observe and analyze issues such as deadlock, pingpong-bidding, pingpong-swapping, and others. We analyze the auditing mechanism with mathematical analysis and software simulations on the behavior of the mechanism. The results from both analysis and simulations suggest that the auditing mechanism can detect cheating attempts with high probability without excessive communication overheads in various conditions. We also suggest an adaptive mechanism to be included in the auditing mechanism so that each robot or peer can tune the communication overheads and detection probability according to the dynamic environments. The analysis and simulations of the evolutionary game theory on the behaviors of peers or robots suggest that the auditing mechanism can discourage free-riding and cheating attempts effectively without harming the popularity of systems with auditing mechanisms. The analysis shows that a strategy where nodes behave honestly and contribute properly is evolutionarily stable and the simulations show that such a strategy takes the dominance even if the strategy had minor initial population. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

ICT integration into classroom teaching and learning practices depends on teachers' attitude toward ICT and the extent of their training in the technology. Early research suggests that males have more positive attitudes toward ICT and have more knowledge and skills about technology than females. Contemporary research, however, suggests that females have more or less equivalent positive attitudes as they receive more and more knowledge and training about the ICT. The present study used a two way-factorial MANOVA design to examine effect of gender and ICT training on Kuwait public high school teachers' attitudes toward ICT and their use of ICT in their classroom practices. The instrument used to collect the data was a questionnaire prepared by the researcher. In addition to the descriptive and the inferential analyses, the study applied a qualitative analysis to analyze teachers' responses to the open-ended questions. Results indicated that teachers' attitude toward ICT was slightly positive with male teachers' mean attitude was slightly higher than female teachers' and teachers' mean attitude with ICT training was higher than those without training. Teachers were found to use ICT for educational purposes moderately with female teachers used slightly less ICT. In analyzing the interaction between independent variables (gender and ICT training) on dependent variables (teachers' attitudes and ICT use), the findings suggested that training played an important role in affecting the male teachers' attitudes toward ICT, but had even a greater effect on female teachers' ICT use. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

This thesis focuses on the long-term rotational stability of the Earth and terrestrial planets. One important class of perturbation is a reorientation of the solid planet with respect to a rotation pole that remains fixed in an inertial frame. These motions are driven by mass redistribution within or on the surface of the planet (e.g. glaciation, mantle convective flow). Long-term changes in the orientation of the rotation pole are called True Polar Wander (TPW)., Earth and Planetary Sciences

Plasmonic waves are waves of mobile charge carriers caused by their collective oscillations. They can be excited in solid-state conducting materials and behave distinctively in different numbers of dimensions. With fabrication technologies available for solid-state materials, one can functionalize the dimensional properties by engineering the boundaries and interfaces of the plasmonic wave medium. For instance, plasmonic waves in two-dimensional (2D) conductors, such as semiconductor heterojunction and graphene, exhibit strong subwavelength confinement – with a wavelength about a factor of 100 below the electromagnetic wavelength at the same frequency. Hence, 2D plasmonic devices can be constructed below the diffraction limit of light. To utilize this ultra-subwavelength confinement is the main motivation of this thesis. This thesis establishes the machinery behind the unique behaviors of 2D plasmons, and compares them to plasmons in higher dimensions, namely plasma oscillations in bulk materials and surface plasmons on conducting-insulating interfaces. The Coulomb restoring force and mobile charge carrier inertia causing the collective oscillations are formulated into a transmission-line model. This formulation is used to engineer ultra-subwavelength plasmonic circuits in gigahertz integrated electronics and terahertz metamaterials. As one of the demonstration platforms, we use GaAs/AlGaAs 2D electron gas. Amongst a variety of devices, the thesis focuses on an on-chip solid-state 2D plasmonic Mach-Zehnder interferometer operating at microwave frequencies. The gated 2D plasmonic waves achieve a velocity of ~c/300 (c: free-space speed of light). Due to this ultra-subwavelength confinement, the resolution of the 2D plasmonic interferometer is two orders of magnitude higher than that of its electromagnetic counterpart at a given frequency. Another material we use, which hosts mobile charge carriers in 2D, is graphene. We fabricate metamaterials in the form of graphene plasmonic crystals in a continuous graphene sheet with periodic structural perturbations. Plasmonic bands in the far-infrared are formed and excited via symmetry-based selection rules, in a manner akin to photonic crystals. The plasmonic bands can be engineered by manipulating the charge carrier concentration, the dimensions of the periodic lattice, the shape of the perturbation and the lattice symmetry. These demonstrations may generate new avenues for a wealth of subwavelength graphene plasmonic devices, such as band gap filters, modulators and switches., Engineering and Applied Sciences - Applied Physics

Plasmonic waves in solid-state are caused by collective oscillation of mobile charges inside or at the surface of conductors. In particular, surface plasmonic waves propagating at the skin of metals have recently attracted interest, as they reduce the wavelength of electromagnetic waves coupled to them by up to ~10 times, allowing one to create miniaturized wave devices at optical frequencies. In contrast, plasmonic waves on two-dimensional (2D) conductors appear at much lower infrared and THz-GHz frequencies, near or in the electronics regime, and can achieve far stronger wavelength reduction factor reaching well above 100. In this thesis, we study the unique machinery of 2D plasmonic waves behind this ultra-subwavelength confinement and explore how it can be used to create various interesting devices. To this end, we first develop a physically intuitive theoretical formulation of 2D plasmonic waves, whose two main components---the Coulomb restoration force and inertia of the collectively oscillating charges---are combined into a transmission-line-like model. We then use this formulation to create various ultra-subwavelength 2D plasmonic devices. For the 2D conductor, we first choose GaAs/AlGaAs heterostructure---a 2D electron gas consisting of massive (m*>0) electrons---demonstrating plasmonic bandgap crystals, interferometers, and negatively refracting metamaterials. We then examine a 2D plasmonic device based on graphene, a 2D electron gas consisting of effectively massless (m*=0) electrons. We theoretically show and experimentally demonstrate that the massless electrons in graphene can surprisingly exhibit a collective mass when subjected to a collective excitation, providing the inertia that is essential for the propagation of 2D plasmonic waves. Lastly, we theoretically investigate the thermal current fluctuation behaviors in massive and massless electron gases. While seemingly unrelated on first sight, we show that the thermal current fluctuation is actually intimately linked to the collective mass of the massive or massless electron gas. Thus, we show that the thermal current fluctuation behaviors can also be described by the same theoretical framework introduced earlier, suggesting a possibility to design new concept devices and experiments based on this linkage., Engineering and Applied Sciences

Conventional nuclear magnetic resonance (NMR) spectrometers—the electronic brain that orchestrates and monitors nuclear spin motions—are bulky, expensive, thus, not scalable. In this thesis, we report on scalable 4-mm2 silicon spectrometer chips that perform a broad range of two-dimensional NMR spectroscopy—e.g., correlation spectroscopy, J-resolved spectroscopy, and heteronuclear quantum coherence spectroscopy—as well as one-dimensional spectroscopy and relaxometry. In this way, they examine a wealth of nuclear spin behaviors and interactions in biological, organic, and pharmaceutical compound molecules, elucidating their structures and dynamics. This semiconductor-based NMR spectroscopy opens up new exciting vistas with two prime advantages. First, with size/cost economy and scalability, the spectrometer chips can be parallelized sharing the same bore of a magnet—whether a large superconducting or small permanent magnet—to greatly simplify multi-channel spectroscopy and vastly increase the spectroscopy throughput, overcoming the intrinsic slowness of NMR spectroscopy; such parallelism may enable the much-desired high-throughput NMR paradigm for drug discovery, metabolomics/metabonomics, and structural biology. We demonstrate the concept of this parallelism by 2-channel heteronuclear quantum coherence NMR experiments, where 2 chips run synchronously in an ultra-compact configuration. Second, the chip spectrometers can complement the recent advance in magnet miniaturization to realize bona fide portable NMR spectroscopy systems. To demonstrate this miniaturization benefit (in addition to the orthogonal benefit of parallelism), we perform all our spectroscopy experiments in a platform combining the spectrometer chips with a compact permanent NdFeB magnet. These demonstrations suggest new dimensions to the technology and applications of NMR spectroscopy enabled by the integrated spectrometers., Engineering and Applied Sciences