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      • Enhancement and polarization manipulation of photonic spin hall effect with waveguided-SPR method

        Monu Nath Baitha Graduate School, Yonsei University 2023 국내박사

        RANK : 247358

        광자 스핀 홀 효과(Photonic spin Hall effect, PSHE)는 plane-polarized wave가 광 표면에서 반사와 굴절 이후 right and left-handed circularly-polarized wave로 분리되는 현상이다. 광자 스핀 홀 효과는 전자의 홀 효과와 매우 유사하며, 다양한 모델과 구조내에서 연구되어 왔지만 아직까지 그 수치가 작고 편광에 의존적이어서 현실적으로 적용하기 어렵다. 플라즈모닉 시스템에서 스핀 홀 효과의 증폭은 가능했으나, 수평 편광이라는 조건에 한정되어 있었다. 광자 스핀 홀 효과를 더 증폭시키고 편광 의존성을 제어하기 위해 새로운 도파로-표면 플라즈몬 공명 (Waveguided surface plasmon resonance, WG-SPR) 방법을 채택하였다. 본 논문에서의 사용한 구조는 금속층 위의 얇은 유리층으로 구성되어 있으며, 수직 및 수평 편광 모두 적용이 가능하다. 입사광의 편광 상태는 광자 스핀 홀 효과에 상당한 영향을 미친다. 본 논문은 도파로-표면 플라즈몬 공명을 이용한 거대 광자 스핀 홀 효과를 이론적으로 분석하였으며, 그 수치를 밀리미터 수준까지 향상시켰다. 이 연구는 플라즈몬 공명 기반 모델을 사용하여 빛의 수직 및 수평 편광 모두에 대해 거대 광자 스핀 홀 효과를 관찰한 첫 번째 연구이다. 또한, 도파관의 층 두께를 조정함으로써 편광을 능동적으로 조작할 수 있으며, 이러한 효과는 광 스핀을 주로 이용하는 수직 및 수평 편광 기반의 양자 광학 장치 및 센서에 적용할 수 있다. 더 나아가, 편광의 전환이 가능한 스핀 광자 홀 효과를 얻기 위해 새로운 방법을 제안하였다. 결과적으로 구조의 물리적인 변화없이 광자 스핀 홀 효과를 관찰 할 수 있다. 이 연구는 광자 스핀 홀 효과를 향상시키는 입사 공명 각도만 변경하여 편광 모드를 능동적으로 제어하는 데 매우 적합하며, 이러한 효과는 스위치, 빔 스플리터, 필터 등의 광 편광 기반 장치에 적용할 수 있다. 또한, 모든 입사각에 대해 편광 독립적인 광자 스핀 홀 효과를 관찰 할 수 있는 연구를 진행하였다. 모든 입사각, 모든 평면 편광 입사파에 대해 수직 편광 광자 스핀 홀 효과와 수평 편광 광자 스핀 홀 효과가 같음을 보였다 (δ_±^H=δ_±^V). 이 연구는 모든 입사각에 대해 광자 스핀 홀 효과의 편광 의존성을 없애기 위해 빛의 스핀-궤도 결합을 조작한 첫 번째 연구이다. 이 연구의 결과는 편광 독립적인 양자 장치 및 센서에 적용할 수 있다. The photonic spin Hall effect (PSHE) explains the separation of right- and left-handed circularly-polarized waves after reflection and refraction of a plane-polarized wave from an optical interface. It is a direct analogy to the electronic Hall effect. To date, PSHE has been explored for many different models and structures, but still, its small value and polarization dependency limits the practical application. In plasmonic systems, the enhanced spin Hall effect (SHE) was previously possible but only for horizontal polarization. To further enhance the PSHE and control the polarization dependency, the novel waveguided surface plasmon resonance (WG-SPR) method has been adopted. The proposed structure comprises a thin glass layer over a metal layer that produces a hybrid mode of transverse magnetic and a regular waveguiding transverse electric mode. The polarization state of the incident light has a substantial impact on the photonic spin Hall effect (PSHE). This thesis reports a theoretical analysis of the giant photonic spin Hall effect (G-PSHE) using WG-SPR. An enhancement of millimeter-scale (more than 2 mm to submillimeter) is achieved. To the best of our knowledge, this is the first study to achieve G-PSHE for both vertical and horizontal polarization modes of light with the SPR-based model. Other findings also indicate the manipulation of active polarization mode by only tuning the wave-guiding layer thickness. This study enables the scope for potential applications of both H- and V-polarized based quantum optical devices and sensors, where light spin plays a pivotal role. Further, a novel method has been proposed to get the polarization-switchable PSHE. Outcomes offer the opportunity of eliminating any physical alteration of the given structure to govern the desired results. This research is highly suited to controlling the active polarization mode of enhanced PSHE by only altering the incident resonance angle. It will be a simple alternative for modern light polarization (spin) based devices such as switches, beam splitters, filters, etc. Furthermore, another study revealed an opportunity to polarization-independent photonic spin Hall effect (PSHE), for all incident angles. This work demonstrates that the horizontal (H) and vertical (V) polarized PSHE will remain the same; (�±ு = �±௏) for any plane-polarized incident wave at any incident angle. This is the first study where the Spin-Orbit coupling of light has been manipulated to vanish the polarization dependency of PSHE for all incident angles. The results of this study pave the way for feasible future applications of new polarization-independent quantum devices and sensors.

      • DYNAMICS OF HELMINTHIC INFECTIONS IN EPIDEMIC AND EPIZOOTIC SYSTEMS OF BANGLACESH

        TILAK CHANDRA NATH 충북대학교 2022 국내박사

        RANK : 247357

        In view of a growing national and international commitment to control human helminths infection, there is an urgent need to intensify the cases detection from various reservoir hosts and the application of context-based diagnostic methods. The goal of this study was to deepen the understanding of helminthiases, perform a One Health based parasitological screening comprising humans, animals, and environmental samples from same ecological settings and assess feasibility of a diagnostic tool and control intervention in Bangladesh. The dissertation employed a combination of qualitative and quantitative methods including a series of parasitological techniques like copromicroscopy, scanning electron microscopy, experimental sedation, culture and molecular approach. Specimens (stools, soils, and adult helminths) were collected from humans, animals, and environment from the same communities (Dhaka, Chittagong and Chattogram) in Bangladesh. Structured questionnaires and an interventional study were used to collect data. Interviews were conducted among community people and related professionals. The examined host communities harbored diverse types of helminths that were heterogeneously distributed across the hosts. Out of 360 human stool samples, the prevalence of helminths infection was 31.7%. Interventional study showed that integration of new intervention with existing control programs was feasible in the local field settings of the country; however, several barriers like fragmented health delivery system, lack of interdisciplinary communication, and information gaps were dominantly existing. Additionally, this study presents the first human case of Rhabditis sp. infection in Bangladesh; emphasized for careful inspection to diagnose and differentiate the helminths species. Out of 550 fecal samples from animal, 59.6% was found positive for at-least one helminth. This study suggested a new, undescribed nematode, Agriostomum n. sp. (2021) from Black Bangal goat. In captive wild animals, 48.9% of examined fecal samples were found positive for parasitic infections. For the first time, zoonotically important Spirometra decipiens from lion was molecularly characterized in this study. Furthermore, geohelminth contamination was found in 52.5% of examined soil samples. This study also developed a context-based geohelminth diagnostic method and the method found feasible in terms of field applicability and egg recovery rate. And lastly, this study molecularly identified zoonotically important canine hookworms, Ancylstoma caninum from soil that represents a risk to public and animal health. This study assessed the prevalence of helminth infection in humen, animal, wild animal as well as geohelminth contamination, and provides a general overview of host-parasite interactions, diagnostic tools and control strategies of parasitic diseases in Bangladesh. Helminthiases remains dominant among the diverse host range, with a high rate of geohelminth contamination. The need of routine parasitological examination as part of current parasite control programs is highlighted in this study. Armed with this, the study propose One Health approach, integrating human, veterinary, and public health authorities in the development and implementation of parasitic diseases prevention and control strategies.

      • Improving Parameter Estimation for Integral Projection Models in Fluctuating Environments

        Nath, Gopal Auburn University ProQuest Dissertations & Theses 2020 해외박사(DDOD)

        RANK : 247343

        The matrix projection model (MPM) is one of the mainstream approaches for population and environmental dynamics in biological and ecological sciences. MPM is very popular in modern biological sciences mainly due to its simplicity and the ease in which results can be explained. The main basis of MPM is a discrete staged transition matrix. MPM then projects the current population into the next census. However, MPM forces continuous trait, such as drought index, length, or mass into discrete staged classes. Easterling proposed the integral projection model (IPM) to avoid this artificial breakpoints of a continuous trait. The application of IPMs is rapidly growing in forest and wildlife ecology and it started attracting statisticians only recently. While IPM has advantages over the MPM, existing IPM estimation techniques are sensitive to outliers or mixing of population traits. We propose a robust fitting approach for IPMs and we analyze how the gain in robustness in the continuous size variable affects the estimation of population growth rate using a simulation study. We demonstrate the benefits of the proposed approach by analyzing the population dynamics of African elephants (Loxodonta africa) in Amboseli National Park, Kenya, where drought is thought to influence the population dynamics. Furthermore, existing IPM fails to generate a fecundity kernel in the situation of incomplete reproduction information. We propose a permutation based model to overcome this situation and demonstrate the applicability using a real life dataset.

      • "Some Rise by Sin, and Some by Virtue Fall": Empirical Articles on Socially Responsible Investing in Financial Markets

        Nath, Saheli Northwestern University ProQuest Dissertations & T 2019 해외박사(DDOD)

        RANK : 247343

        This dissertation project uses both quantitative and qualitative analytical approaches to examine the dynamics of responsible investing in financial markets. The first chapter investigates how the institutionalization of responsible investing as a business strategy affects category claims made by mutual funds. The study finds that as the divestment movement in the late twentieth century became institutionalized in the US financial markets by being incorporated as a business strategy into more mainstream investment vehicles like mutual funds and pension funds, the related terminology, definitions, strategies and practices associated with ethical investing became more diversified and ambiguous due to fuzzy boundaries, duality of virtue inherent in the portfolio targets, and exercise of discretion by portfolio managers. Notwithstanding recent efforts at standardization of metrics measuring portfolio performance on responsible investment, on average socially responsible investment funds differ significantly from conventional funds in terms of ESG-related outcomes. Further, there is still significant heterogeneity among SRI funds themselves. As increased heterogeneity led to greater ambiguity about who belongs to a category, fund managers adopted distinct measures-based, values-based and expertise-based approaches to resolve ambiguity.The second chapter investigates cross-country variation in responsible investing practices using both quantitative and qualitative approaches. The study finds partial support for the claim that pension funds and mutual funds operating in countries where people have more freedom of expression and greater control of corruption will perform better on environmental, social and governance dimensions compared to countries where people have relatively less freedom of expression and less institutional control of corruption. Surprisingly, this article does not find support for the hypothesis that when asset owners and investment managers perceive high regulatory quality and government effectiveness in their country, they will pay greater attention to responsible investment, as measured by the number of organizational employees dedicated specifically to responsible investment. Through a qualitative analysis of the responses explaining employment decisions, the study uncovered that organizations can undertake either an integrative or specialized or hybrid approach to employment, which affects the number of reported staff dedicated to responsible investment.The third chapter uses Hirschman's "exit, voice, and loyalty" framework to review the extant literature and examine exit by ethical funds, barriers to exit, modes and strategies of exit and consequences of exit following a corporate transgression. It employed a case study approach to examine whether socially responsible investment funds that hold equity in a transgressing firm react more negatively to severe ESG violations compared to conventional investment funds. Using the Wells Fargo scandal as our focal point, the results indicated that SRI-status of the mutual fund did not affect the decision to fully or partially "exit" from the fund's equity position in Wells Fargo. Public institutional investors like government agencies that represent the welfare logic of the state were more likely to take up the activist role by imposing discipline on Wells Fargo through sanctions and temporary exit. The study has important implications for the use full or partial exit as a form of shareholder activism to impose discipline on the transgressing firm.

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