Doctoral Dissertations

Permanent URI for this collection

https://hdl.handle.net/20.500.12090/275

Browse

Now showing 1 - 20 of 65

Microelectrode electrode array studies of spinal motor neurons
Tharaneetharan, Arumugarajah
Co-cultures are a traditional method for studying the cellular properties of cell to cell interactions among different cell types. How network properties in these multicellular synthetic systems vary from monocultures are of particular interest. Understanding the changes in the functional output of these in vitro spiking neural networks can provide new insights into in vivo systems and how to develop biological system models that better reflect physiological conditions - something of paramount importance to the progress of synthetic biology. Culture models of spinal motor neurons have been customarily studied as a monoculture, and the overwhelming consensus is that in culture they are different in nature from their in vivo counterparts. I studied the electrophysiological properties of spinal ventral horn networks cocultured with myocytes or astrocytes using a 64 channel microelectrode array system to record extracellular voltage measurements. When compared over a period of 40 days, significant differences were found between coculture types in metrics of spiking, bursting, and network bursting. Myocyte cocultures, when compared with simple ventral horn cultures, showed significant decreases in spikes, spike amplitudes, spike energy, number of units in network burst, and an increase in interspike interval. Astrocyte cocultures, when compared with simple ventral horn cultures showed decreases in sorted units, burst duration, mean interspike interval, and network burst duration but increases in spikes, energy of spikes, bursts, spikes per burst, network bursts, and number of units per network burst. This suggests that traditional culturing techniques involving a uniform cell type might not be the best way to functionally model in vivo neural networks. Concerning an in vitro model system for lower motor neurons, the most accurate model would most likely be a combination of spinal motor neurons cultured with myocytes as well as increased levels of astrocytes. A synthetic ecosystem of various cell types is beneficial to replicating cell behavior in vitro, thus is a necessary refinement to the commonly used technique of cell culture. With a more physiological model system, hypotheses about interacting systems can be better addressed and the outcomes will have greater relevancy.
Numerical determination of scattering and bound states via self-consistent field theory
Tyler, Micah Danielle
Interpretation of atomic spectra and the applications of atomic spectroscopy to current problems in astrophysics, laser physics, and thermonuclear plasma require a precise knowledge of atomic structure and dynamics. The collisional excitation and ionization of atomic targets by electron impact is distinct in that one or more electrons are in the continua, which makes the theory complicated and also drastically disturbs the system for probing and detection. Analysis of interacting atomic systems is complex and many approximate methods have been developed in the past. The most prominent of these methods is the Hartree-Fock procedure and its relativistic and multiconfiguration extensions. This self-consistent-field (SCF) approach has been limited to treating only fully bound, negative energy states whose corresponding wave functions are square-integrable. Recently, the SCF extension to scattering in which continuum (positive-energy) states are involved, has been formulated. The non-integrability of the continuum functions can be overcome by an amputation procedure that retains all of the physical essentials of the scattering system. It is extended here to the electron-hydrogenic scattering system in the zero angular momentum coupling models. In this project, the focus is on devising a numerical algorithm for solving such systems of integro-differential equations stemming from the SCF theory. The method is compared with results obtained by several other approaches. It is shown that the newly devised numerical approach converges as the amputated continuum functions provide an effective projection of the scattering function.
A Study on the Numerical and Analytical Solutions of Complex-Variable Partial Differential Equations
Moore, Matthew Neil
In this work, we consider the analogue of a real-variable partial differential equation. In comparison to what has already been thoroughly investigated, recall the non-linear Schrodinger equation (NLSE). The NLSE, which is used in determining the wave equation for quantum particles, is a real-variable PDE with complex coefficients. Instead, we consider equations where both the function $\omega$ and its independent variable $z$ belong to the complex plane. We approach the complex problem by an intuitive approach of treating a one-complex variable differential equation as a two-real variable partial differential equation by analyzing the real and imaginary parts of both $\omega$ and $z$. We investigate thoroughly the first-order complex PDE case and prove the existence and uniqueness theorem for these types of equations. We also investigate the analytical solutions by considering the complex-variable Laplace transform, which can be thought of in parallel as a two-variable Laplace transform with in $\mathbb{R}^2$. Upon completion of the first-order case, we consider the higher order complex-variable PDE. We discuss both the direct way of solving higher-order equations via systems of real-variable PDE’s and also via first-order systems of complex-variable PDE’s, in which we implement the methods of the previous topics. As a direct consequence of the higher-order differential equation solution method, we also discuss an alternative method of evaluating complex contour integrals via a real-variable partial differential equation evaluation. To conclude, we consider the time-dependent complex variable PDE analogues of the advection and wave equations, we briefly discuss multi-complex variable PDE’s and methods that we plan to investigate in the near future.
Fabrication of SERS and Fluorescence Sensors Useful in Detection of R6G and Ionic Phosphate Respectively
Bhandari, Anjuli
This dissertation focuses on organically synthesized sensors. A variety of projects were worked on to find the best method of a selective and sensitive sensor. Findings presented in this dissertation will cover a fluorescence based sensor used to detect ions as well as a Surface Enhanced Raman Spectroscopy (SERS) active sensor that can achieve low Rhodamine 6G (R6G) quantification. Fluorescent probes are of vast research interest due to the ease of fabrication, high sensitivity, selectivity, and application in both in vivo/in vitro studies. Coumarin compounds are innately fluorescent and are ultimately suitable as fluorescent probes. By altering the mechanism used as well as the probe compound, the target analyte can vary. Work performed in this dissertation synthesized a variation of Coumarin that was suitable in phosphate and sulfate detection methods. When in solution, the chemodosimeter proved to be selective in distinguishing between four ions out of the eleven tested. Beyond detection, the sensor was capable of quantification of these ions when in solution. Raman SERS substrates are another type of sensor that can prove incredibly useful by increasing the intensity in a given spectrum. Using a metallic nanoparticle material, the localized surface plasmon resonance helps achieve an amplified signal. A novel SERS substrate was fabricated utilizing both silver nanostars and mesoporous silica nanoparticles that was suitable in R6G detection. Using this sensor, R6G was capable of being quantified down to 100 pM. Findings presented in the work below were achieved using prior research and new concepts. Both sensors described proved to be reproducible and stable materials. This dissertation will go into detail of the fabrication and utilization of these sensor based materials and applications of testing methods.
Wavefront Shaping via a Learning Algorithm Guided, Adaptive Optics Device for Focal Volume Control
Burton, Harry
ABSTRACT The topic of this dissertation is the development of a learning algorithm for the shaping of a lasers three-dimensional focal intensity distribution, specifically for the interest of generating non-diffracting beams. These beams have garnered growing interest in fields such as microscopy and laser physics. The learning algorithm developed is based on a genetic algorithm (GA) approach. The goal of the algorithm is to find the necessary bi-dimensional phase (or wavefront) to apply to a Spatial Light Modulator (SLM) in order to optimize the laser spatial profile; which is measured by a Charged Coupling Device (CCD) camera. Two versions of the GA were developed, validated and used, the first one performing wavefront correction (or focal spot optimization), and the second one focal volume optimization. The first version of GA is called single-plane GA, as it uses the signal of the CCD camera in one single transverse plane. This approach is similar to what is standard in wavefront correction schemes that are not using - for optimization - the direct measurement of the laser wavefront, but instead a signal generated by the laser that is dependent on the wavefront aberrations (or shape). An experimental setup is described, and wavefront optimization experiments validate the use of the single-plane GA as a way of correcting aberrations purposely induced on a Gaussian beam laser. The feedback signal, which can be maximized or minimized, is the spatial profile maximum intensity or its beam width. As the single-plane GA uses the spatial profile, measured in one transverse plane, it is unable to optimize the lasers focal distribution in a predictable way. An extension of the method, called multi-plane GA, is later proposed. This novel approach to beam shaping uses, as feedback for algorithm optimization, the spatial profiles measured in multiple transverse planes. Recording multiple transverse planes at different longitudinal positions is achieved using the SLM, which applies a defocus term without physical translation of the CCD camera. This multiple recording capability requires a proper defocus calibration of the SLM, which was performed and validated via measurement of a non-aberrated Gaussian beam, as well as a SLM-generated astigmatic Gaussian beam, with comparisons taking the 3D recording of the focal distribution using manual translation of the CCD camera. Different fitness methods using multiple transverse planes were developed and their implications and limits tested. The balance between the algorithm convergence speed, the degrees of freedom of the 2D phases induced by the SLM, the size of the algorithm search space, and ability of the GA to perform a given focal volume shaping goal, are discussed. Using the minimization of energy, size or similitude between spatial profiles in the five planes, convergence of the multi-plane GA towards a non-diffracting Bessel beam and Airy beam was demonstrated. Compared to the initial starting corrected Gaussian beam, the multi-plane GA was able to increase the laser depth of field up to 32 times for the Bessel beam, and up to 7 times for the Airy beam.
Case analysis of sexual violence programs on college campuses
Johnson, Sherri Lee Niblett
ABSTRACT President Obama created a White House Task Force in January 2014 that revealed many colleges were not complying with several federal mandates regarding safety of students/employees when reporting sexual assaults on campus. This doctoral comparative case study analysis looked at the statistics of sexual violence on college campuses, the mandates given to colleges to immediately comply with, and the best practices many colleges are striving to find. Three cases were examined, contrasted, compared, and analyzed, along with literature that’s emerging daily to find best practices for a community college in Delaware. The study was able to find best practices regarding local programs, prevention and awareness that includes bystander intervention, reporting and investigating methods, confidentiality, climate surveys, and the allocation of resources to better protect students and employees from violence on college campuses. The study looked at the theoretical framework of the three waves of feminism, social learning theory, and differential association theory of deviance, to look at the culture of rape and how this could be used to change the campus climate to a less hostile environment for men, gay, lesbian, women, transgender and non-conforming, races, ethnicities, those with disabilities, and those with any other differences collectively. This study also used transformational and educational leadership practices to develop collaborative models toward future research and community college, university, state-level, and national-level campus and community collaboration.
Dual Grid Finite-Difference Time-Domain Method for Maxwell Equations in Complex Media
Cornelius, Jason Michael
In recent years, the study of electromagnetic waves and their propagation through non-traditional material, such as nonlinear and magneto-electrically coupled materials, has become one of the more interesting topics in electromagnetics. Nonlinear materials exhibit phenomena not present in traditional media such as high harmonic generation and self-focusing. Both these properties are desirable in the field of optics, especially in the growing field of nanophotonics. Because of the interesting nature of these materials, simulation is desired. While there are FDTD based methods for the simulation of these types of materials, they tend to be unstable or computationally intensive from a run-time perspective. In this dissertation, we propose a Dual Grid FDTD method to address these issues. The Dual grid method is capable of stably simulating nonlinear dispersive materials as well as magneto-electric materials. In this work we verify that this is the case and also show, that from a run-time standpoint this method is more time-efficient than preexisting methods.
Exploring the Impact of Educating Nursing Students in Higher Education on Trauma and Trauma Informed Care
Zeitler, Meredith
ABSTRACT According to Felitti, et al, (1998) more than half of the population had one exposure to an adverse childhood experience. Knowing this, the healthcare system must be prepared to care for these individuals. Unfortunately, unless nurses are being trained in their institutions they are not receiving TIC education in theory undergraduate studies. This raises the question of how are they expected to care for these patients if they do not know the correlation trauma has on their physical, emotional and cognitive health. The purpose of this research study was to ascertain the impact of a trauma and trauma-informed care education session on nursing students who were currently enrolled in a mental health nursing course. This quantitative, quasi-experimental research study was completed by implementing a pre-survey, followed by an education session which was given by the researcher, and then a post-survey was administered. The researcher conducted a paired t-test to analyze the data from both surveys to determine the statistical significance. The research question revealed a significant finding. The mean score of the pre-survey and the post-survey displayed an increase in knowledge of all the topics included in the survey. The findings also supported the fact that even though the nursing students were knowledgeable, the education session reinforced and expanded their knowledge. The p-value or significance of all the survey questions were .001. which indicates the null hypothesis is rejected and the alternative hypothesis is true. In conclusion, even though nursing students perceive they are knowledgeable of trauma and trauma-informed care the post-survey results revealed an increase in knowledge for each individual survey question.
An Examination of Nurse Educators’ Experiences with Clinically Failing Students
Maloney, Jeanmarie Carney
ABSTRACT This research describes the experience of nursing educators who have assigned an earned falling clinical grade to nursing students. The fundamental activity of the nursing educator in the clinical setting is clinical teaching or clinical instruction. The nursing educator guides, encourages, facilitates learning, and ultimately evaluates a nursing student’s clinical performance. Clinical evaluations are one of the most challenging aspects of being a clinical nursing educator. Using a case study construct guided by the Self Determination Theory, seven nursing educators were interviewed to examine their personal experiences that surrounded the process. Three questions drove the research: 1. What is the lived experience of nursing educators who have administered an earned clinical failing grade to a nursing student(s) in an associate degree nursing program? 2. What motivated these nurse educators to assign a deserved failing clinical grade? 3. What is the personal impact on the nursing faculty when they experience a clinically failing student? The data was entered into the Atlas Ti8 software and three major themes were identified: the role of nursing educators, criteria used in clinical grading and challenges faced in grading students. One anticipated theme that did not emerge was that of assigning blame on previous educators. This research did reinforce and identify the need for support and guidance when assigning an earned failing clinical grade.
Unauthorized Disclosures of Sensitive and Classified Information: A Meta-Synthesis of Leadership Support, Security Policy, and Security Education, Training and Awareness within the Federal Government Information Security Culture
Simpson, Calvin
This meta-synthesis study examined federal government information security culture through the factors of leadership support, security policy, and security education, training, and awareness (SETA). The occurrence of unauthorized disclosures is a continuing and increasing problem within the federal government, and end-users are identified as the weakest link. The federal government not only remains unsuccessful in its efforts to prevent unauthorized disclosures in previous years, it acknowledges this threat will persist in the future. Selection of studies used in support of this meta-synthesis consisted of two subject matter experts who served as raters that determined inter-rater agreement. Inter-rater reliability was achieved using the Cohen’s Kappa equation while ATLAS.ti 8 supported the semantic coding process. Semantic coding of the 13 studies used in this research resulted in the identification of 4 networks consisting of 36 total nodes (5 - information security culture, 13 - leadership support, 7 - security policy, and 10 - SETA). There was a total of 398 total sub-nodes selected across selected studies. The findings indicate that the greatest positive influences on information security culture and end-user threat-response behaviors were leadership support and SETA. However, these influences are offset by employee behavioral conflicts, inconsistent leadership involvement, varying degrees of policy awareness and non-compliance, and ineffective training. An emphasis on teamwork was noted at all levels across the federal government. There was an overwhelming consensus for tighter controls to protect information. In the area of policy, there is an admitted lack of awareness for the policies, consequences, and penalties associated with security violations. To prevent the occurrence of future security incidents, a better understanding of information security culture within the federal government is needed to assist in further refining and implementing organizational information security programs. This study separates itself from other studies by presenting a new research model supported by a theoretical framework.
A Comparative Case Study Analysis of The Teachers’ Perceptions Causing the Overrepresentation of African American Males in Special Education
Allen, Tara
This comparative case study analyzes the overrepresentation of African American males in special education. The overrepresentation of African American children and youth in special education programs for students with learning disabilities, severe emotional or behavioral disabilities, and mental disabilities has remained a persistent reality, even after nearly 50 years of discovery and research. The disproportionality of African American students is one of the most critical problems in the field of special education within the United States (Skiba, 2006). African American males have historically been overrepresented in all categories of special education (Harry and Anderson, 1994). Twice as many African American male students in the United States are receiving services for Emotional Disturbance as their Caucasian counterparts. The Individuals with Disabilities Education Act (2004) (IDEA) established the legal guidelines for the protection of students with disabilities. The literature has identified a variety of theories to answer why African American males continue to be overrepresented in special education. The review of literature presents the history of this issue, the history of IDEA, and shows how legislation has fallen short in decreasing the overrepresentation of African American males in special education. The examination of overrepresentation of African American males in special education and the factors that may contribute to this disproportionality frame this case study. This case study analysis explores the factors that influence the overrepresentation of African American males in special education programs. This comparative case study analysis will answer the following research questions: Question 1 What factors contribute to the overrepresentation of African American male students in special education? Question 2 What is the association in teachers’ roles, perceptions, and demographics with the overrepresentation of African American males in special education programs? The researcher has dissected several reasons and factors that have caused this disproportionality, such as socio-economic status of the student, student demographic, teacher’ perceptions of African American males, lack of cultural responsiveness training for teachers, teacher demographics, and the teacher’s role in the referral process of special education.
Effect of Cultural Congruence and Leadership Practices on the Academic Achievement of African American Students Post-Enactment of Brown V. Board of Education in the State of Delaware
Sudler, Candra Nichelle
Since Brown v. The Board of Education (1954), the demographics of the United States pre-kindergarten through grade 12 (K–12) public schools are dramatically changing as student populations are becoming more diverse. Even though, years have passed since the lawful end of racial segregation in American school systems, many factors still plague our student academic achievement. This comparative case study analyzed how school integration, and the cultural congruence of teachers of African American students pre- and post-enactment of Brown v. The Board of Education affects student achievement. This case study analyzed, compared and contrasted the selected case studies i.e. The Relationship between Socio-Economic Status and the Academic Achievement of Culturally Diverse Students (Ford, 2013), African American Students’ Experiences, Achievement and Outcomes; Examined Through the Lenses of Teacher Expectations, Racial Congruence and Stereotype Threat (Postell, 2011), and A Study of the Relationship of Student-Teacher Racial Congruence and Student Achievement (Strange, 2011) to find out how this landmark case has effected minority students in the United States, particularly in the state of Delaware. Student-teacher relationships appeared to be a common thread among the four themes that emerged from the analysis. Conversely, when no student-teacher relationship formed, stereotype threat was activated, making it difficult for the participant to succeed. The observations of the analysis of the three case studies established that the use of a strategic approach, including evidence-based practices, is vital to sustaining effective culturally responsive instructional strategies and pedagogy for increasing academic achievement of minority students.
The Relationship Between Student Engagement and Alumni Giving at Higher Education Institutions: A Comparative Case Study Analysis
Shockley, Charity
This qualitative comparative case study analysis explored the relationship between undergraduate student engagement and alumni donations to their alma mater. The independent research categories are undergraduate co-curricular engagement and athletics engagement as related to the dependent research category, alumni giving. The research data were three quantitative case studies with settings at private higher education institutions in the South and Midwest; data were analyzed utilizing the Atlas.ti 8 qualitative data analysis software program. The findings of this study indicated that regarding the relationship between undergraduate co-curricular engagement and alumni giving, the results are inconclusive. Findings regarding the relationship between undergraduate athletics engagement and alumni giving indicate either a negative relationship or no significant relationship between the two research categories. However, there is a positive relationship between student engagement and alumni giving when the undergraduates were involved in more than one category of student engagement.
Mixed method study of the impact of calculator usage on 8th and 12th grade students’ fundamental mathematical skills and teachers’ perceptions on using a calculator in learning mathematics
Woodard, Faith Eleanore
Calculator usage in the United States is prevalent in secondary education classrooms. There has been a decline in mathematics achievement in national and international assessments for U.S. students. The U.S. historically introduces the calculator in mathematics classrooms earlier than several other countries, including: Singapore, Ireland, South Korea, Czech Republic, Austria and the Netherlands. This mixed methods study researches the potential impact of early calculator usage and fundamental mathematics skills in two ways: 1) a quantitative proctored mathematics assessment administered to middle and high school students, without access to calculators 2) qualitative semi-structured interviews from teachers to determine perceptions on student fundamental mathematics skills. Both the qualitative and the quantitative strands analyze the observations and insights on calculator usage in the classroom to determine student fundamental mathematics skills (FMS). The hypothesis for the study presumes there is no significant difference between 8th and 12th graders’ scores on a fundamental mathematics skills assessment (FMSA), when assessed without the use of a calculator. However, this study shows that there is indeed a statistically significant difference between the two groups; the middle school 8th grade students had higher scores than the 12th graders on the (FMSA), as assessed without a calculator. Moreover, students believe they need calculators and teachers permit calculator usage, often without restriction (including exams), although teachers acknowledge limited FMS of students, without a calculator. Teachers believe that FMS should be attained before 8th grade. Without a firm foundation in the mastery of basic skills, it is difficult for students to move to higher levels of mathematics understanding. As a result, future research efforts will look at the elementary school level to see how far the early calculator usage extends and encompass comparison between elementary and middle
Transformation Optics Based Finite-Difference Time-Domain Simulation of Superscattering
Strong, Andre Jamaal
In this dissertation we study the Transformation Optics Finite Difference Time-Domain (TO-FDTD) method. We show how applying a coordinate transformation can be employed to map an irregular mesh to a cartesian mesh. We apply the anisotropic FDTD method to solve the transformed Maxwell's equation in the new transformed grid. To validate our claim we model the local field near the metallic nanoparticles and superscattering. The TO method achieves the same level of accuracy or more with half the grid size mesh as the standard FDTD, and the computational cost is reduced compared to the standard FDTD method.
Educational loan, students’ self-efficacy, attitude towards debt, and their impact on retention and graduation in minority-serving institution
Yankovich, Diana
This study was conducted to address a very critical current national issue: the student loans and its relationship with students’ self-efficacy, attitude toward debt, and retention and graduation rates at a minority serving institution. The findings may guide the leadership decisions toward the best practices for the students’ best academic success, future employment, and career. This research employed a mixed method research design, which involved data collection through a survey. Collected data are the representative sample of the population in several aspects: 1) Gender, 2) Residency (In-State/Out-of-State), 3) Race, 4) Class of the first-time freshmen, 5) Credit hours students are registered for the semester, and 5) student athletes. The collected data was analyzed by t-test, Chi-Square and Fisher’s exact test for the significance, and correlations among the studied variables. Among the other significant correlations, the results show some of the very important findings: (i) The female population is less like to borrow money and agrees more than the male that borrowed money should be repaid as soon as possible; (ii) Out-of-State students have a perception that they will acquire higher debt then the In-State students. This show that they are aware of the higher costs of the Out-of-State tuitions and fees; (iii) The students are aware about the educational debt, they are concerned about its repayment, and this is the first step toward financial self-efficacy. The higher the amount of the perceived debt students believe they will acquire till graduation, the more they are concerned about paying the loan back; (iv) As students matriculate toward the graduation their perception about the amount of debt is higher. Seniors have demonstrated more responsibility toward debt and agree that it is important to live within one’s means; (v) As the amount of perceived loan by the time of graduation increases, the students’ confidence to perform up to the best of his/her potential academically decreases. Findings of the research suggest that academic resources are necessary for the students to help improve their academic progress, which will ultimately improve the institutional retention and graduation rates. Recommendations and suggestion for future research have been made.
Solution-phase synthesis and characterization of fe2ges4 material and photovoltaic devices
Liu, Mimi
Recently, climate change and the energy crisis are warning human race that it is necessary to develop new renewable energy. Solar energy is considered to be one of the cleanest and most abundant energy sources to replace fossil fuels. Solar cells are extensively studied devices that convert sunlight into electricity. However, recent solar cells have been hampered by high cost, use of toxic materials and low conversion efficiency. To further improve the solar cells, a cheap, earth-abundant, and non-toxic material is required. The ternary compound Fe2GeS4 (FGS) has attracted considerable attention because it not only has high absorption coefficient and band gap suitable for photovoltaic applications but also has better sustainability. In addition, the elements contained in FGS are relatively abundant in earth’s crust and are less toxic. In my dissertation work, FGS crystals were prepared using two methods, solution-phase synthesis of FGS precursor, followed by a thermal treatment and one-pot synthesis. In the solution-phase synthesis of FGS precursor, the effects of reaction parameters such as precursors, solvents, reaction times on the chemical and physical properties of the resulting products have been comprehensively investigated. The results show that a stable FGS precursor can be prepared in the mixture of oleylamine (OLA) and 1-Octadecene (ODE), using Fe (III) 2,4-pentanedionate, Ge (Gly)2(H2O)2, elemental sulfur as Fe, Ge and S source, while the reaction time is 15 minutes. Then, the optimization of the annealing conditions for FGS powders has also been studied. Finally, the highly crystalline FGS powders were obtained by a two-step process, solution-phase synthesis of FGS precursors and thermal treatment at 550℃ for 2 hours under sulfur/argon atmosphere. FGS thin films were fabricated by dip-coating the prepared FGS inks on the substrate and performing the same thermal treatment at 550℃ for 2 hours under sulfur/argon atmosphere. The FGS solution-based solar cell using FGS thin film as the light absorbing layer showed a significant open-circuit voltage (VOC) of 361 mV. When the optimized FGS thin film was incorporated into a well-established dye-sensitized solar cell, the fabricated FGS-catalyzed dye-sensitized solar cell achieved a higher open-circuit voltage (VOC), short-circuit current density (JSC) and conversion efficiency (η). In the one-pot synthesis of FGS NCs, the effects of trioctylphosphine oxide (TOPO) and reaction time on the product have been determined. The results show that the plate-like FGS crystals can be prepared within 5 hours, using FeCl2, Ge(Gly)2(H2O)2, TOPO, and 1-dodecanethiol (1-DDT) as reactants, while OLA acts as the solvent. A high-quality FGS thin film was prepared by dip-coating and thermal treatment at 400 ℃ for 2 hours under sulfur/argon atmosphere. Similar to the solar cells fabricated based on FGS precursor, the photovoltaic devices based on the FGS NCs also exhibited a significant open-circuit voltage.
A Molecular Precursor Solid-State Route to Inorganic Nanoparticles
Hwang, Po-Yu
Iron Pyrite (FeS2) has been the center of development to obtain a high efficiency, low-cost, earth-abundant and environmental-friendly photovoltaic absorber materials in the field of solar research for many decades. Many studies have offered explanations attempting to solve the conundrum, but, between the innate and unsolvable stoichiometric and phase instability challenges and the contradictory conclusions, no effective solution has been made to address pyrite’s failing to reach its theoretical capability. Iron germanium sulfide (Fe2GeS4) has recently emerged as a potential thin-film photovoltaic absorber material to replace its binary predecessor. With the introduction of the third element, germanium (Ge), the new ternary material was theorized to confer better thermal stability while improving with better band-gap and retaining the favorable low-cost of production traits enjoyed by iron pyrite. This work proposes a facile solid-state synthesis route to obtain high-quality, phase pure Fe2GeS4 nanoparticles from molecular precursors undergoing mechanical mixing and a two-hour annealing procedure under a sulfur-rich atmosphere. Analysis of the resulting Fe2GeS4 product has demonstrated good thermal stability under elevated temperatures (up to 500 ˚C), and the elimination of the phase coexistence challenge in comparison to pyrite. A comprehensive phase shift mechanism of iron chalcogenides and a Fe2GeS4 reaction mechanism is proposed to supplement the discussion of pyrite’s phase instability. A facile thin-films fabrication is designed by undergoing further mechanical processing and annealing treatment and is revealed that Fe2GeS4 withstands high temperature in the thin-film device.
Child welfare training: the relationship between perceived transfer of training, retention, and educational supervision of new caseworkers
(Delaware State University, 2008-12) Blakey, Donna L.
In order to meet the challenges that children and families often present, public child welfare organizations need trained, competent, and confident caseworkers. This study examines new caseworker training in a public child welfare organization. New caseworkers who completed preservice training while in a training unit, or in a function based unit, were queried about their perceptions regarding three factors identified in the literature as impacting training transfer; training design, opportunities to use training on the job, and educational supervision. In addition, supervisors who had received new caseworkers were questioned about their best educative supervisory approaches, and their perceptions of the influence of training on the retention of new caseworkers. Following an analysis of the data, it was concluded that there was no statistically significant difference in the perceptions of new caseworkers regarding the training transfer factors, based on their unit assignment while attending pre-service training. Yet, overall, the perceptual indicators were positive for the transfer of training, opportunities to use training, educational supervision, and the impact of training on the retention of new caseworkers.
Integrative sparse modeling and classification of biomedical imaging patterns
Zheng, Keni
The analysis and characterization of imaging patterns is a significant research area with several applications to biomedicine (computer-aided diagnosis), remote sensing (urban planning, environmental monitoring), homeland security (face recognition, object recognition, biometrics) social networking, and numerous other domains. In this dissertation we study and develop mathematical methods and algorithms for disease diagnosis and tissue characterization. The central hypothesis is that we can predict the occurrence of diseases with certain level of confidence using supervised learning techniques that we apply to medical imaging datasets that include healthy and diseased subjects that can be used for training. In the first stage of this work we propose to diagnose diseased patterns using texture characteristics that are derived from medical imaging modalities. The texture feature set consists of fractal dimension, local binary patterns, discrete wavelet frames, Gabor filters, discrete Fourier and Cosine Transforms, statistical co-occurrence indices, edge histogram, and Law’s energy maps. Next, we implemented feature selection using correlation-based techniques to reduce the feature dimensionality. In the learning stage we employed bagging methods using fast decision tree learners, Random Forests, Bayes network, or na\"{i}ve Bayes techniques. These techniques are also used for comparisons at the later stages of this work. Next, we develop methods for calculation of sparse representations to classify imaging patterns and we explore the advantages of this technique over traditional texture-based classification. We also introduce integrative sparse classifier systems that utilize structural block decomposition to address difficulties caused by high dimensionality. We propose likelihood functions for classification and decision tuning strategies. These likelihood scores may also be used to determine a type of confidence interval for prediction. The two application domains are osteoporosis diagnosis in radiographs of the calcaneus bone, and breast lesion characterization in mammograms. Both of these applications are very significant for improving public health. Osteoporosis results in deterioration of bone quality and affects the quality of life of aging populations. Timely diagnosis of osteoporosis can effectively predict fracture risk and prevent the disease. Furthermore, breast cancer is one of the leading causes of death among women. Early detection and characterization of breast lesions is important for increasing the life expectancy and quality of health of women. We performed bone osteoporosis classification experiments on the TCB challenge dataset and breast lesion characterization experiments Mammographic Image Analysis Society data set. In TCB there are 87 healthy and 87 osteoporotic subjects in the calcaneus trabecular bone. MIAS includes benign and malignant breast cancer lesions. In both of these two data sets, the scans of healthy and diseased subjects show little or no visual differences, and their density histograms have significant overlap. In the experiments, our method of block-based sparse representation produced the best classification accuracy on these two datasets. We compared the conventional sparse representations classification (SRC) and texture-based methods with our method in a leave-one-out (LOO) cross-validation (CV) framework. The top texture-based classification performances are 67.8% ACC (classification accuracy) and 70.9% AUC (Area Under the Receiver Operating Curve) for bone characterization, and 63.4% ACC and 62.1% AUC for breast lesion characterization. The top performance of our integrative sparse model method by using a decision threshold equal to zero is 100% ACC and AUC for bone characterization by block-based maximum a posteriori sparsity-based (BBMAP-S) decision function, as well as 100% for bone characterization by block-based log likelihood sparsity-based (BBLL-S) decision function, 98.6% ACC and 97.8% AUC for breast lesion characterization by BBMAP-S decision function, and 100% ACC and 100% AUC for breast lesion characterization by BBLL-S decision function for breast lesion characterization. We also used 10-fold and 30-fold cross-validation to evaluate the classification performances of our classification methods. The top rate of accuracy produced by the texture-based method is 66.7% and corresponding AUC is 67.5% for bone characterization using 10-fold cross-validation. Our method using integrative sparse models has obtained the highest ACC for 30-fold cross-validation is 69.33% and 70.2% with BBMAP-S decision function. It also achieved 70.7% ACC and 74.4% AUC with BBLL-S decision function for bone characterization. In 10-fold cross-validation experiments for bone characterization, BBLL-S produced 60.6% ACC and 62.5% AUC. In the breast lesion characterization application, the best performance over all the ROI sizes is 71.2% ACC and 69.8% AUC using texture-based methods and the conventional SRC method reached 55.0% ACC and 51.8% AUC using 10-fold cross-validation. For our system, the top performance is 86.7% ACC and 88.2% AUC for 30-fold experiments and 68.9% ACC and 73.7% AUC for 10-fold experiments. Our results show that ensemble sparse representations of imaging patterns provide very good separation between groups of healthy and diseased subjects in two challenging diagnostic applications.

Browse

Recent Submissions