Design and comparative analysis of single and multi-stack axial flux permanent magnet synchronous generator

Syed, Qurban Ali Shah 한양대학교 대학원 2012 국내석사

Design and Comparative Analysis of Single and Multi-stack Axial Flux Permanent Magnet Synchronous Generator Syed Qurban Ali Shah Advisor: Prof. Byung-il Kwon Department of Electronics, Electrical, Control and Instrumentation Engineering Graduate School of Engineering Hanyang University South Korea This paper attempts to design a direct-driven axial flux permanent magnet synchronous generator (AFPMSG) with better design accuracy considering magnetic flux leakages and fringing effect, using D²L design process. Design results of conventional and improved design process are analyzed and compared using 3-D finite element method (FEM). Improved design process shows better accuracy results than the conventional one. Improved design process is utilized to design single and multi-stack AFPMSG topologies. FEM structural analysis is utilized to decrease the intermediate rotor yoke thickness as to improve the output power to weight and output power to volume ratio of three-stack AFPMSG. Finally, characteristics of both single-stack and best model of three-stack AFPMSG topologies are analyzed and compared using 3-D FEM. Although single-stack AFPMSG has less weight and volume and higher power density, its output power depends on its outer rotor diameter. Whereas, three-stack AFPMSG has smaller outer rotor diameter and lower rotor inertia, but it is more costly due to its higher weight and volume and lower power density.

Energy Recycling Techniques for Ultra-Low Power Dynamic Voltage Scaler Circuits

Syed Asmat Ali Shah 충북대학교 전자공학전공 2020 국내박사

A study regarding turning solid waste into resource for environment and creation of jobs in islamabad

Shah, Syed Zia Hussain 서울시립대학교 국제도시과학대학원 2018 국내석사

Solid waste management is one of the significant and common challenge and issue in urban areas throughout the world, especially most populated cities and towns. Inadequate collection and disposal of wastes created serious sanitation and environmental problems and directly inflict to human health and life. Solid waste management in Pakistan also is a grave concern due to various challenges including administrative and lack of education and awareness. In Pakistan, the management of solid waste is serious concern particularly in major cities of the country including Islamabad. The waste accumulates from common areas and then converting into trash using burning methods. This process leads to hazardous toxins which is one of the serious threats for human and environmental health. The root cause of solid waste management in Pakistan is lack of public awareness, improper waste management planning, lack of urban planning and public involvement. This study proposed a conceptual model to evaluate the current household participation, current situation and challenges to adopt solid waste management in four zones of Islamabad and proposed a pilot project to convert waste into resource and create new job opportunities in Islamabad. This research objective will achieve through quantitative research method and pilot project. The results indicated that household and other stakeholder participation through incentive projects is necessary to handle the current situation of waste. 전 세계적으로 고형 폐기물 관리는 도시(특히 인구가 많은 도시)의 중요하고 보편적인 과제이자 현안 중 하나이다. 부적절한 폐기물 수거 및 폐기는 심각한 위생 및 환경 문제를 야기하고 인간의 보건과 생활에도 직접적인 피해를 입힌다. 파키스탄의 고형 폐기물 관리 또한 행정 및 인식 제고 교육의 부재로 인해 심각한 상황에 처해 있다. 파키스탄의 경우 고형 폐기물 관리 문제가 이슬라마바드를 포함한 대도시에서 특히 심각한 실정이다. 폐기물은 공용 장소에서 수거한 다음 소각을 통해 재로 변환한다. 이 공정은 인간의 건강과 환경에 대한 심각한 위협 중 하나인 유해 독성 물질 생성으로 이어진다. 파키스탄 내 고형 폐기물의 부적절한 관리의 근원은 국민들의 인식 부족, 부적절한 폐기물 관리 계획, 도시 계획 및 시민 참여 부재이다. 본 연구에서는 이슬라마바드 내 4개 구역에 고형 폐기물 관리를 채택하기 위한 가구 참여도, 현황 및 해결 과제 평가의 개념 모델을 제시하고 폐기물을 자원으로 변환하고 이슬라마바드에 새로운 고용 기회를 창출하는 시범 프로젝트를 제안하고 있다. 본 연구의 목적은 정량적 연구 방법론과 시범 프로젝트를 통해 상기 목표를 달성하는 것이다. 연구 결과 현재의 폐기물 관리 문제를 해결하기 위해서는 인센티브를 통한 가구 및 기타 이해 당사자들의 참여 유도가 필요한 것으로 나타났다.

Enhancement of the User Experiences in the 360° Multimedia Entertainment and Air Traffic Management using Extended Reality

Shah, Syed Hammad Hussain 세종대학교 대학원 2020 국내석사

In recent period of time, substantial advancements have been seen in the display technologies and human-computer interaction (HCI). Computer-generated 3D simulated immersive environments, such as Virtual Reality (VR), Augmented Reality (AR) and Mixed Reality (MR), have revolutionized the ways of interaction and humans’ experiences with the computers. Nowadays, such immersive environments are gaining popularity. Ease of access to the latest Head Mounted Displays (HMDs), such as Oculus VR Gear and HoloLens, plays a vital role in this respect. These HMDs are shaping users’ experiences in various fields of life, such as entertainment, workflows, education and health. Due to advancements in VR technology, demands for VR applications, such as 360° movies and virtual tours, are also increasing. This work proposes the novel methodologies in VR and MR, for enhancing user experiences in different fields of life. Firstly, it targets the field of multimedia and entertainment. An application has been developed for generating and transferring of multiple interesting experiences of 360° movies in VR. Secondly, it provides 4D holographic MR simulator for air traffic controllers, to enhance their interaction and experience with air traffic control system. This work presents the detail user studies for testing and investigation of the impact of the proposed methodologies in the enhancement of the users’ experiences through latest HMDs. 최근 디스플레이 기술과 인간-컴퓨터 상호작용 (Human-Computer Interaction, HCI) 기술이 굉장히 많이 발전하였다. 이러한 발전에 힘입어 가상현실 (Virtual Reality, VR), 증강현실 (Augmented Reality, AR) 및 혼합현실 (Mixed Reality, MR)과 같은 3D 시뮬레이션 몰입형 가상환경 기술은 인간과 컴퓨터 사이의 상호작용 방식과 인간의 경험 (Human Experience, HX)에 혁신을 일으켰다. 오늘날 이러한 몰입형 가상환경을 이용한 콘텐츠들이 인기를 얻고 있다. 이는 오큘러스 VR 기어(Oculus VR Gear)와 홀로렌즈 (HoloLens) 같은 최신 HMD (Head Mounted Displays) 기기들을 전보다 더 쉽게 접할 수 있기 때문에 가능해졌다. HMD는 엔터테인먼트, 워크플로 (Workflow), 교육 및 의료 서비스 등 다양한 삶의 분야에서 사용자 경험 (User Experience, UX)을 형성해주고 있다. 가상현실 기술의 발전으로 인해 360° 영화와 가상 투어 같은 VR 콘텐츠에 대한 수요도 증가하고 있다. 이 연구는 다양한 분야의 사용자 경험을 발전시키기 위한 VR 및 MR의 새로운 방법론을 제안한다. 첫째, 본 연구는 멀티미디어 및 엔터테인먼트 분야를 대상으로 한다. 360° 영화의 다양하고 흥미로운 경험을 만들고 전달해주는 응용 프로그램을 제공한다. 둘째, 항공 교통 관제사와의 상호작용 및 사용자 경험을 발전시키기 위해 4D 홀로그램 MR 시뮬레이터를 제공한다. 이 작업에서는 최신 HMD 기기를 통해 사용자 경험을 향상시키는데 제안된 방법의 효과를 테스트하기 위한 사용자 경험 연구에 대해 설명한다.

(A) study on the refrigerant distribution in a two-row and six-pass micro-channel evaporator

Shah, Yousaf Incheon National University 2018 국내석사

Air Conditioning, whether it is a residential building, Commercial building or in Automotive Sector, It needs a great care of investigation to be carried out by researcher for the better performance and highest efficiency. Although there are many factors to be investigated for the better performance of Air-conditioning system, in this particular study we carried out experiments on the flow distribution of refrigerant effected by the geometrical parameters and Orientations of header assembly. Refrigerant flow distribution was experimentally investigated for multi-row and multi-pass configuration of microchannel heat exchanger to provide essential research data for designing the energy efficient evaporator. Experiments were carried out by different orientation of headers i.e. (Top row crossing header and bottom row crossing header) and operating conditions by varying mass flux from 70 kg/hr to 120kg/hr and quality was maintained 0.2 at inlet of header. Additional heaters were used to maintain the superheated condition of 5°C at Micro-Channels. High speed camera was used for the flow visualization at both headers for each case respectively.

Preparation of MIP composite membrane for effective separation of phenylalanine racemate solution : 패닐알라닌 라세믹 용액의 효과적 분해를 위한 분자각인 고분자 복합 막 제조

Shah, Nasrullah 경북대학교 대학원 2011 국내박사

L-Phe and D-Phe imprinted P(MAA-co-EGDMA) submicron/nanoscale beads (LIBs and DIBs) were prepared by modified suspension polymerization. The percentages of template removal from LIBs and DIBs were 95.5% and 92.5% respectively. Adsorption equilibrium time was determined as 6 h.The adsorption capacity of the prepared submicron/nanoscale beads increased continuously with increase in concentration of racemate solution. The adsorption capacity of beads increased continuously with increase in concentration of racemate solution. Maximum adsorption selectivity was obtained at 100 mg L-1 of Phenylalanine racemate solution. The trend of adsorption capacity and selectivity at different pH was pH 2 ≥ 6 > 4. LIBs prepared for the first time by modified suspension polymerization showed the highest adsorption capacity 0.35 mg/g and selectivity 1.62 at STP. LIBs and DIBs maintained their higher adsorption capacity and selectivity up to 5 successive batches. The trend of adsorption capacity and selectivity was LIBs ≥ DIBs > non-imprinted beads (NIBs). FE-SEM analysis showed that the presence of template had caused greater effect on the beads sizes. The size of LIBs and DIBs was slightly larger (100nm~1.5µm) than NIBs (100nm~800nm). Similarly, FT-IR study revealed higher number of binding sites in LIBs than that of DIBs and NIBs. 13C CP-MAS NMR spectroscopy was used to evaluate the basic structure of the prepared beads. It also helped in correlated the beads sizes with the extent of polymerization. This whole study revealed that the newly prepared Phe imprinted submicron/nanoscale beads showed higher adsorption capacity and selectivity compared to the previously reported Phe imprinted microbeads. D-Phe and L-Phe imprinted P(AA-co-AN) membranes (DIM and LIM) were prepared by phase inversion method. The average thickness of DIMs, LIMs and non-imprinted P(AA-co-AN) membrane (NIM) was in the range of 40 µm - 50 µm. A total of 83.75% and 84.29% of template was removed during complete washing of DIMs and LIMs respectively. The trend of improved physical properties, adsorption capacity and selectivity was LIM ≥ DIMs > NIMs. FT-IR analysis supported the higher number of binding sites in LIMs compared to DIMs and NIMs. Four types of composite membranes i.e, composite membrane composed of LIBs and LIM (CMLIBLIM), composite membrane composed of DIBs and DIM (CMDIBDIM), composite membrane composed of LIBs and DIM (CMLIBDIM) and composite membrane composed of DIBs and LIM (CMDIBLIM) were prepared for chiral resolution of Phe racemate solution. These composite membranes were prepared by phase inversion technique, after a uniform dispersion of 3 % (w/w) of the prepared submicron/nanoscale beads into Phe incorporated P(AN-co-AA) solution using a simple physico-mechanical process (vertexing and sonication). In all types of composite membranes the extraction of template (73% – 75%) during coagulation step and after complete washing (88% - 90%) was higher compared to Phe imprinted membranes (control membranes). The average thickness of the resultant Phe imprinted composite membranes was 70 µm ~ 80 µm. The higher thickness, large surface area and large number of ionic sites in the composite membranes caused improvement in physical properties of the composite membranes compared to control. The maximum percent swelling ratio (387% - 426%) and water holding capacity (0.16 g/g - 0.17 g/g) of Phe imprinted composite membranes were higher than that of control membranes. The wet weight decrease rate was 1.5 to 2 times lower than that of control membranes. FE-SEM analyses clarified that all types of composite membranes were composed of three portions i.e. upper and lower dense layers and a middle broad layer. The thickness of the two cover layers was in the range of 6 µm ~7 µm. The average size of the nano-pores observed in the prepared composite membranes was in the range of 6 nm ~16 nm. The structure characterization of composite membranes was done by FT-IR study. In case of composite membranes the shifting of OH peaks to lower wave numbers indicated the interaction of incorporated beads with the composite membranes matrix. FT-IR inferred that the Phe imprinted submicron/nanoscale beads maintained the active functional groups after incorporation in the Phe imprinted composite membranes matrix. Assemblies of the prepared composite membranes were employed separately in ultrafiltration for chiral separation of D,L-Phe racemate solution. CMLIBLIM and CMDIBDIM followed the selective adsorption phenomenon. CMDIBDIM and CMLIBLIM showed 1.35 - 1.50 times higher adsorption capacity and 1.5 times higher adsorption selectivity compared to the control membranes. The selective rejection by MIP composite membranes was reported for the first time. Percent rejection of Phe imprinted composite membranes was lower compared to control membranes. The permselectivity value of these composite membranes was less than 1 (~0.43). CMLIBDIM and CMDIBLIM followed the facilitated permeation mechanism. These membranes showed 1.5 - 1.6 times higher separation factor (permselectivity) than that of control membranes. Adsorption capacity of CMLIBDIM and CMDIBLIM was 1.35 - 1.45 times higher than that of control membranes while it was much higher than that of Phe imprinted beads. CMLIBDIM and CMDIBLIM also showed a selective but lower rejection of the enantiomers compared to control membranes. The adsorption capacity and separation factor of these newly prepared composite membranes are higher compared to previously reported MIP composite membranes used for enantioseparations. The selective rejection phenomenon by the MIP composite membranes was observed for the first time. It was concluded that these composite systems, where two different MIP formats i.e., Phe imprinted submicron/nanoscale beads and Phe imprinted membranes were combined and both were functionally active, will be useful in future for several industrial and biomedical applications. The enhanced adsorption ability and improved separation properties of these newly developed composite MIP membranes, provide a good basis for use in the practical applications such as in the faster and effective resolution of enantiomers, in the pre-concentration processes as well as in blood filtration, drug delivery, food processing and in scaffold preparation etc. L-Phe 과 D-Phe 각인 P(MAA-co-EGDMA) 초미세/나노 beads (LIBs and DIBs) 가 개량된 고분자 합성법에 의하여 제조 되었다. LIBs와 DIBs로 부터의 template 제거률은 각 95.5%와 92.5%이다. 흡착 평형 시간은 6 h시간으로 측정 되었다. bead의 흡착률(adsorption capacity)은 라세믹 용액(racemate solution)의 농도가 높아짐에따라 지속적으로 높아졌다. 최대 흡착도(adsorption selectivity)는 100 mg L-1 의 phenyalanine 라세믹 용액에서 얻을 수 있었다. 다양한 경향성의 흡착률과 다양한 pH (pH 2≧6>4)에서의 흡착도를 얻을 수 잇었다. 초기 LIBs는 서스펜션(suspension) 중합으로 제작되었고 STP에서 가장 높은 흡착률은 0.35 mg/g 과 흡착도 1.62으로 측정 되었다. LIBs와 DIBs는 5 batch까지 높은 흡착률과 흡착도를 보였다. 흡착률과 흡착도의 크기는 LIBs ≧ DIBs > non imprinted beads (NIBs) 순으로 나타났다. FE-SEM 분석을 통하여 template의 존재가 beads의 크기에 큰 영향을 미침을 확인하였다. LIBs 와 DIBs의 크기는 (100nm ~ 1.5µm) NIBs (100nm~800nm) 보다 약간 큰 것으로 관찰 되었다. 유사하게 FT-IR 분석에서는 LIBs가 DIBs와 NIBs보다 더 많은 결합부위를 가지는 것으로 분석되었다. 13C CP-MAS NMR 분광분석를 통해 beads의 기본 구조를 알고자 하였다. 이러한 일련의 연구를 통하여 새롭게 제작한 Phe 각인 미세/나노 고분자 beads가 Phe imprinted microbeads보다 더 높은 흡착률과 흡착도를 보임을 알 수 있었다. D-Phe 와 L-Phe 각인 P(AA-co-AN) 막 (DIM 과 LIM) 은 상 전환 법으로 제조 되었다. DIMs, LIMs 그리고 non-imprinted P(AA-co-AN) 막 (NIM) 의 평균 두께는 40µm - 50µm 였다. 각 83.75% 와 84.29% 의 template이 DIMs와 LIMs의 완전 세척 공정에서 씻겨 나갔다. 물리적 성질과 흡착률 그리고 흡착도는 LIBs ≧ DiBs > non imprinted beads (NIBs) 순으로 나타났다. 이 결과는 FT-IR 분석에서 LIM이 DIMs와 NIMs보다 많은 결합 부위를 가진다는 사실을 뒷받침 해준다. 네 종류의 합성 막 [DIBs와 DIM (CMDIBDIM), LIBs 와 LIM (CMLIBLIM), LIBs와 DIM (CMLIBDIM), DIBs와 LIM (CMDIBLIM)] 이 chiral resolution Phe 라세믹 용액의 처리에 사용되었다. 이 네가지 종류의 막은 상 전환 법으로 제조되었고 3 % 의 미세/나노 beads를 pHe incorporated P(AN-co-AA) 용액을 사용하여 확산시켜 제조 하였으며 간단한 기계-물리적 공정 (vortexing and sonication)방법을 사용하였다. 모든 종류의 합성 막에서 template의 추출(73% ~ 75%)은 응고과정에에서 일어났고 완전 세척 (88% ~ 90%)은 Phe 각인 막(비교군)에서 더 높았다. 평균 두께는 Phe 각인 중합막이 70~80㎛로 나타났다. 중합 막에서의 더 넓은 두께, 큰 표면적, 더 많은 량의 이온결합이 비교군 보다 더 향상된 물리적 성질을 띄게 한 것으로 판단 되었다. Phe imprinted composite막의 최대 팽윤(swelling) 률과 (387% ~ 476%)와 용수량 (0.16 g/g ~ 0.17 g/g)역시 비교군 보다 컸다. 수분 감소량은 비교군 보다 1.5~2배 가량 늦었다. FE-SEM 분석을 통하여 모든 종류의 중합막이 세가지 부분으로 구성되어 있음을—아래 위의 얇고 밀집된 층과 가운데 부분에 넓게 퍼진 막으로 구성되었다. 두 장의 덮게 막은 6~7 ㎛ 이다확인 할 수 있었다. 중학 막에서 관찰된 nano-기공은 6 nm ~ 16 nm 범위였다. 중합막의 구조 분석은 FT-IR을 통하여 이루어 졌다. 중합막의 경우에서 OH peak의 더 낮은 파장으로의 이동이 의미하는 바는 bead와 중합 막간의 상호작용에 의한 결과로 설명 할 수 있다. FT-IR 분석을 통하여 미세/나노 beads가 Phe 각인 미세/나노 막 상태에서도 작용기가 제 역할을 할 수 있음을 확인 할 수 있었다. 중합 막의 분류는 D,L-Phe 라세믹 용액의 ultrafilteration chiral 분리과정에서 개별적으로 이루어 졌다. CMLIBLIM과 CMDIBIM은 선택적 흡착 현상을 보였다. CMDIBDIM과 DMLIBLIM은 비교군 보다 1.35~1.50배 높은 흡착률과 1.5배 높은 흡착도를 보였다. MIP 중합 막에서 선택적 rejection 현상이 처음으로 연구 되었다. Phe 각인 중합막의 rejection 현상이 비교군 보다 낮았다. Perm selectivity 값은 모든 중합막에서 1 이하(~0.43)으로 측정되었다. CMLIBDIM 과 CMDIBLIM은 중계 삼투 기작을 따른다. 이러한 막들은 비교군 보다 1.5~1.6배 가량 높은 값을 가진다. CMLIBDIM 과 CMDIBLIM의 흡착도는 비교군보다 1.35 ~ 1.45배 높으며 Phe 각인 beads 보다는 훨씬 크다. CMLIBDIM 과 CMDIBLIM은 좋은 흡착도를 보이지만 구조 이성질체의 rejection은 비교군 보다 낮았다. 이러한 중합 막은 흡착률과 분리정도는 기존의 MIP 중합 막보다 높았다. 선택적 rejection 현상은 학계에서 처음으로 보고되었다. 본 연구를 통하여 Phe 각인 미세/나노 beads 와 Phe 각인 막이 결합되었으며 두 가지 모두 제 기능을 잃지 않았다. 이러한 결과를 통하여 미래 많은 산업, 의료 분양에의 적용이 가능할 것이라 예상된다. 본 연구를 통한 MIP 중합막의 흡착률과 분리 정도의 향상은 더 빠르고 효과적인 구조 이성질체 분리의 기반을 공고히 하였고, 앞으로의 연구를 통해 혈액 여과, 약물 투입, 식품제조 등의 기술 적용방법 모색의 필요성이 있다.

Low iron intake aggravates the adverse effect of prenatal lead exposure on children’s neurodevelopment up to 36 months

SHAH, SURABHI SURESH 이화여자대학교 대학원 2017 국내박사

Background: Threshold of lead concentration affecting children’s development is not still identified. Current lead exposure in developed countries still remains a major public health issue. Lead exposure affects the most, in high risk population like pregnant women and children. The theme of this dissertation is to study the impact of very low prenatal lead exposure on children’s cognitive growth. Nutrients are also known to interact with the harmful action of lead. Another objective was to study the effect of mother’s dietary iron intake on the adverse action of prenatal lead exposure. Also, the susceptible window of prenatal lead exposure affecting children’s growth was explored. Objectives: The aim of this dissertation was to study the effect of very low prenatal lead (<5µg/dL) exposure on cognitive development of children and the role of mother’s dietary iron intake in reducing the adverse effects of prenatal lead. Methods: The eligible study participants were selected from the mother’s and children’s environment health study (MOCEH); a prospective cohort study that studied the effect of various environmental exposures on children’s growth and health. It is a multicentric study involving network of hospitals and community health centers, conducted from the year 2006-2010. Study participants whose blood lead levels and their children whose cognitive measurements were assessed were included in the study (n=965). Linear model analysis was done to evaluate the action of low level lead exposure on children’s cognitive development. Interaction between maternal and cord blood lead levels and mother’s dietary iron intake was assessed on multiplicative scale. Stratified analysis by mother’s dietary iron intake was performed. Linear mixed model was explored to study the long term impact of low prenatal lead exposure on children. Results: Late pregnancy maternal lead levels marginally affected MDI scores in children at 6 months. Less mother’s dietary iron intake further pronounced these adverse effects of late pregnancy lead on children’s MDI score at 6 months (β= -2.53, p <0.05). Late pregnancy maternal lead was found to affect children’s neurodevelopment up to 36 months of age with mothers less dietary iron intake pronouncing the adverse effects of lead. Conclusion: This dissertation shows that even very low level of prenatal lead exposure has detrimental impact on children’s cognitive growth. The susceptible window of prenatal lead exposure affecting the child’s development was found to be late pregnancy. The harmful effect of prenatal lead exposure on postnatal neurodevelopment of children gets aggravated in the condition of mother’s low iron intake. Thus, the current level of lead exposure still continues to be a public health issue, especially in vulnerable population like pregnant mother, fetuses and children. 연구 배경: 납은 잘 알려진 환경 오염 물질이나, 어린이 성장 영향을 예방할 수 있는 납 노출 기준은 여전히 밝혀지지 않고 있다. 국내에서는 유연 휘발유 사용 금지 정책으로 인해, 일반 인구의 납 농도가 감소하였으나, 저농도 납 노출로 인한 공중 보건 문제는 계속되고 있다. 하지만, 적절한 영양소 섭취는 납과 영양소의 상호작용을 통해 납 노출로 인한 건강 문제를 예방할 수 있다. 따라서, 이러한 모든 상황들을 고려하여, 어린이 성장에 영향을 미치는 태내 납 노출의 영향과 태내 납 노출에 특히 취약한 시기 (susceptible period)를 알아야 할 필요가 있다. 연구 목적: 본 논문의 목적은 어린이 인지 발달에 미치는 저농도 납 노출의 영향을 보고, 태내 납 노출의 부정적인 영향을 줄이는 철의 역할에 대해 알아보는 것이다. 연구자료 및 방법: 본 연구는 산모와 영유아 대상의 환경노출에 의한 건강영향연구(Mother’s and children’s environment health study, MOCEH)의 일환으로 진행되었다. MOCEH는 다양한 환경 오염원이 어린이의 성장과 건강에 미치는 영향을 연구하는 전향적 코호트 연구로, 병원 및 지역 보건 센터를 포함하는 다기관 연구이다. 연구대상자들의 혈중 납 농도와 신경행동발달이 측정되었는데, 총 965명 어린이의 인지발달지수 (Mental development index, MDI) 및 동작발달지수 (psychomotor development index, PDI)가 평가였다. 선형모델분석 (Linear model analysis)로 아이들의 인지 발달에 미치는 저농도 납 노출의 영향을 평가하였다. 곱셈교호작용을 통해 납과 철 간의 상호작용을 평가하였다. 어머니의 철 섭취량 중 75퍼센타일 값으로 층화한 분석을 수행하였다. 선형혼합모델을 사용하여 태 내 저농도 납노출이 6개월부터 36개월에 이르는 어린이 인지발달에 미치는 장기 영향을 살펴보았다 결과: 임신부의 임신 후기 혈중 납 농도는 제한적으로 (marginally) 6개월 어린이 MDI 점수에 영향을 주었다. 철분을 적게 섭취하는 산모에서, 임신 후기 납 노출이 6개월 어린이 MDI 점수에 더 명확한 영향을 주었다 (β=-2.53,p<0.05). 임신부의 임신 후기 납 노출은 36개월까지 어린이 인지 발달에 부정적인 영향을 주었으며, 임신부의 철분 섭취가 적을 경우 납 노출의 부정적인 영향이 더 명확하게 나타났다. 결론: 태내 저농도 납 노출은 어린이 인지 발달에 부정적인 영향을 나타내었으며, 임신부의 철분 섭취가 낮을수록 그 영향이 증가되었다. 또한, 아이의 발달에 영향을 미치는 임신부 납 노출의 취약 시기는 임신 후기로 관찰되었다. 결론적으로, 현재의 매우 낮은 수준의 납 노출이 어린이의 신경행동발달에 영향을 미치고 있어, 여전히 공중보건학적 문제가 된다고 하겠다. 영양섭취를 고려한 중재 전략은 더 나은 어린이 발달을 위한 정책으로 활용될 수 있을 것이다.

(The) Use of the Hundi System for Remittance by Nepali Workers in Korea

Shah, Dhananjay Kumar 경희대학교 국제대학원 2018 국내석사

This research seeks to examine the hundi remittance behavior of Nepalese migrant workers working under the Employment Permit System (EPS) in the Korea-Nepal remittance corridor. It employs a case study based on qualitative techniques using primary data obtained from a hundi questionnaire, focused group discussion and personal interviews. The research draws responses from one hundred respondents out of some 40 000 Nepali workers living and working in Korea. The primary research question is to find out why the EPS Nepali migrant workers prefer hundi to modern banking remittance channels. The most striking finding of this research is the transfer cost as an underlying determinant of hundi remittance behavior of Nepali workers in Korea. Other important factors this research work explores are the customised and cultural convenience of hundi system, speed and time as well as some constraints with formal remittance channels in this bilateral remittance corridor. This research offers policy recommendations for remittance sending and remittance receiving countries as well as to other key stakeholders to discourage informal and illegal money-transmitting businesses like that of the hundi remittance channel and to encourage remittance transfer through formal, legal and official channels. This research leaves room for further research into hundi’s link to money laundering and terrorism financing.

Body-centric wirelessly powered miniaturized biotelemetric and implantable bioelectronic devices

Shah, Syed Ahson Ali 한양대학교 대학원 2022 국내박사

With the advancement in body-centric medical technologies, Wireless implantable medical devices (WIMDs) based remote healthcare monitoring systems are becoming increasing popular. Healthcare solutions to improve the quality of life include the monitoring and telemetry of important physiological signs for diagnosis, therapy, and stimulation of internal human organs. Wireless implantable medical devices (WIMDs) have enabled these solutions as a result of rapid breakthroughs in advanced medical technologies. Biotelemetry is necessary for these applications, as it allows WIMDs to perform the exchange of information by wirelessly transmitting physiological data to the external base station and receiving necessary control commands for therapy, treatment, and stimulation. Due to the lossy nature of human tissues with frequency-dependent dielectric properties, these WIMDs face several challenges including biocompatibility, size miniaturization, patient safety, operation in heterogenous environment, low far-field gains, impedance mismatches, and shorter battery lifetime. The dielectric characteristics (conductivities and dielectric constants) of the human body's different layers (bone, muscle, fat, and skin) vary between the layers as well as from tissue to tissue, which is referred to as heterogeneous in biological research. The dielectric constant of tissues is frequency dependent, ranging from 5.58 to 87, with fat having the lowest dielectric constant and stomach muscle having the highest. The development of WIMDs is hampered by certain constraints due to the lossy nature and heterogeneous behavior of human tissues. The ability of WIMD to communicate with the external device is limited because of the conductive losses in tissues. Moreover, the device contains other electronic components which can cause coupling issues and detune the performance of implantable antenna within the device. For these WIMDs, stable impedance-matched antennas that have sufficient bandwidth to cover the detuning effects are necessary. The biggest problem in designing implantable medical devices is to power them. The most common power source is a primary battery. Batteries, on the other hand, limit the implant's lifespan and size. The use of wireless power transfer (WPT) appears to be a viable answer to this problem. Wireless charging of the WIMDs' batteries is essential for extending their lifespan; unfortunately, a single-band implanted antenna cannot manage both wireless information exchange and wireless power reception at the same time. Furthermore, each function of a multitasking implant has to operate on its own frequency range. To accomplish several activities such as data transfer, energy harvesting, and control signaling, a generic multitasking WIMD requires at least a dual band or wideband antenna. The WIMD must include a power harvesting unit, which contains an antenna, matching network, diode rectifier, and power management circuitry, in order to function as a WPT receiver. The received radio frequency (RF) power is converted to usable direct current (DC) by a rectenna (antenna + rectifier), while the matching circuit adjusts the impedance to enhance the RF-to-DC conversion efficiency. Previous studies, on the other hand, have failed to design such a system. This thesis focuses on a variety of challenges relating to the WIMDs' telemetry and wireless power transfer systems to address the aforementioned problems. Firstly, miniaturized implantable antenna systems for biomedical applications, specifically for scalp implantation has been developed. The proposed designs exhibit dual-band characteristics on the industrial, scientific, and medical bands (i.e., 915 and 2450 MHz). The antenna in the WIMD is integrated with the microelectronic components and a battery, realized as a perfect electric conductor. The proposed implantable antenna has a small volume (8 × 6 × 0.5 = 24 mm$^3$). Moreover, the design complexity is reduced by avoiding the addition of slots and vias in the ground plane. The structure exhibits satisfactory peak gain values of $-$28.5 and $-$22.8 dBi at a lower and higher resonant band, respectively. Furthermore, link budget simulations were conducted to analyze the transmission range for the antenna. It can support the data transmission at a remarkable range, depending upon the bitrate, with a bandwidth of 9.84\% and 8.57\% at 915 and 2450 MHz, respectively. Next, an ultra-small batteryless WIMD for ICP monitoring comprising an off-body power transmitter (Tx) and in-body biotelemetric receiver (Rx) has been developed. The WIMD demonstrates dual-band performance (i.e., 915 and 1900 MHz) for simultaneous power transmission and data telemetry. The implantable antenna has the smallest volume of 6.72 mm$^3$ (5.6 mm $\times$ 6 mm $\times$ 0.2 mm). For improved power transfer efficiency (PTE), the WIMD is powered wirelessly in the radiative near field (1900 MHz). Furthermore, the structure has achieved peak gain values of $-$26.8 and $-$18.8 dBi at 915 and 1900 MHz, respectively, with impedance-matched bandwidths of 9.83 \% and 27.9 \%. The device's wireless power transfer efficiency was also evaluated in terms of distance variations, and a maximum PTE of $-$25.9 dB was attained at 20 mm (0.1267$\lambda$) Tx$-$Rx separation. At 2 dBm input power, the rectifier achieved a maximum power-conversion efficiency of 82 \%. Finally, a deeply implanted stent antenna system for endovascular aneurysm repair (EVAR) has been presented. Previously, the EVAR stent system has only been used to treat abdominal aortic aneurysm (AAA). No study in the literature has conducted research to analyze the antenna characteristics of EVAR stent as it contains metallic component (Stainless Steel 316L) and dielectric layer. In this study, the EVAR stent as an antenna has been analyzed and a first validation of its antenna attributes has been performed. The stent antenna is composed of multiple helical wires connected to form meshed rings incorporating a single feed wire, thereby precluding the random distribution of currents on the stent-struts. In addition to EVAR application, the key features of the proposed stent system are its better antenna characteristics, including an omnidirectional radiation pattern, high gain, and perfect impedance matching. The proposed stent antenna has a wide frequency range of 850 $-$ 950 MHz, which includes ISM bands (i.e., 868 and 915 MHz). Furthermore, at the 868 and 915 MHz bands, the stent has peak gain values of $-$20.75 and $-$19.04 dBi, respectively. The biotelemetry capabilities were assessed using a link budget analysis. For modelling and numerical analysis, electromagnetic computations were performed using the finite-element method and finite-difference time domain to evaluate the properties of dual band implantable antenna, battery-less biotelemetric implantable system, and EVAR stent system. To reduce the simulation time and assess the preliminary results, initial analysis was performed in the homogeneous skin phantom, homogeneous muscle phantom, and homogeneous blood and Aortic vessel phantom. Later, these implantable systems were simulated in the heterogenous environment comprising multiple human body tissues, such as Duke Model in Sim4Life and VariPose Man in Remcom. For validation, measurements for dual band implantable antenna were conducted in a saline solution, measurements for battery-less implantable system were conducted in a saline-filled human head phantom, as well as in minced pork, and measurements for EVAR stent system were conducted with a 3D printed AAA placed in a saline-filled American Society for Testing and Materials phantom and in minced pork. Good agreement between simulation and measured results was observed in all cases. 신체 중심 의료 기술의 발전으로 WIMD(Wireless Implantable Medical Device) 기반의 원격 의료 모니터링 시스템이 대중화되고 있다. 삶의 질을 개선하기 위한 의료 솔루션에는 진단, 치료 및 인간 내부 장기의 자극을 위한 중요한 생리적 징후의 모니터링 및 원격 측정이 포함된다. WIMD(Wireless Implantable Medical Device)는 첨단 의료 기술의 급속한 혁신의 결과로 이러한 솔루션을 가능하게 하였다. 생체 원격 측정은 WIMD가 외부 기지국에 무선으로 생리학적 데이터를 전송하고 치료, 치료 및 자극에 필요한 제어 명령을 수신하여 정보 교환을 수행할 수 있도록 하기 때문에 이러한 응용 프로그램에 필요하다. 주파수 의존적 유전 특성을 가진 인간 조직의 손실 특성으로 인해 이러한 WIMD는 생체 적합성, 크기 소형화, 환자 안전, 이기종 환경에서의 작동, 낮은 원거리 이득, 임피던스 불일치 및 짧은 배터리 수명을 비롯한 여러 문제를 가진다. 인체의 여러 층(뼈, 근육, 지방, 피부)의 유전적 특성(전도도 및 유전율)은 각 층뿐만 아니라 조직마다 다르며, 이를 생물학 연구에서는 이질성이라고 부른다. 조직의 유전 상수는 5.58에서 87 사이의 주파수 의존적인 값이며 지방이 유전 상수가 가장 낮고 위 근육이 가장 높다. WIMD의 개발은 손실 특성과 인간 조직의 이질적인 행동으로 인해 특정 제약 조건으로 인한 방해를 받는다. 외부 장치와 통신하는 WIMD의 능력은 조직의 전도성 손실로 인해 제한된다. 또한 장치에는 결합 문제를 일으키고 장치 내 이식 가능한 안테나의 성능을 조정할 수 있는 다른 전자 부품이 포함되어 있으므로 이러한 WIMD의 경우에는 앞서 언급한 디튜닝 효과를 커버할 수 있는 충분한 대역폭을 가진 안정적인 임피던스 매칭 안테나가 필요하다. 이식형 의료 기기를 설계할 때 가장 큰 문제는 전원을 공급하는 것에 관한 것이다. 가장 일반적인 전원은 1차 전지이다. 배터리는 임플란트의 수명과 크기를 제한하는데 WPT(Wireless Power Transfer)의 사용은 이 문제에 대한 실행 가능한 해결책으로 볼 수 있다. WIMD 배터리의 무선 충전은 수명 연장에 필수적이지만, 불행히도 단일 대역 이식 안테나는 무선 정보 교환과 무선 전력 수신을 동시에 관리할 수 없다. 또한, 멀티태스킹 임플란트의 각 기능은 고유한 주파수 범위에서 작동해야 한다. 데이터 전송, 에너지 수확 및 제어 신호와 같은 여러 활동을 수행하기 위해 일반 멀티태스킹 WIMD에는 최소한 이중 대역 또는 광대역 안테나가 필요하다. WIMD는 WPT 수신기로 기능하기 위해 안테나, 정합 네트워크, 다이오드 정류기 및 전력 관리 회로를 포함하는 전력 수확 장치를 포함해야 한다. 수신된 무선 주파수(RF) 전력은 렉테나(안테나 + 정류기)에 의해 사용 가능한 직류(DC)로 변환되고, 매칭 회로는 임피던스를 조정하여 RF-DC 변환 효율을 높일 수 있지만 이전 연구에서는 이러한 시스템을 설계하는데 실패하였다. 본 논문은 앞서 언급한 문제를 해결하기 위해 WIMD의 원격 측정 및 무선 전력 전송 시스템과 관련된 다양한 문제 해결에 중점을 두고 있다. 첫째, 특히 두피 이식을 위한 생물 의학 응용을 위한 소형 이식형 안테나 시스템이 개발되었다. 제안된 설계는 산업, 과학 및 의료 대역 (ISM 대역, 915 및 2450 MHz)에서 이중 대역 특성을 나타낸다. WIMD의 안테나는 마이크로 전자 부품 및 배터리와 통합되어 완벽한 전기 전도체로 구현된다. 제안된 이식 가능한 안테나는 작은 부피(8 $\times$ 6 $\times$ 0.5 = 24 mm$^3$)를 갖는다. 또한 접지면에 슬롯과 비아를 추가하지 않아도 되므로 설계 복잡성이 줄어드는 장점을 가지고 있다. 제안된 안테나는 더 낮은 공진 대역과 더 높은 공진 대역에서 각각 $-$28.5 및 $-$22.8 dBi의 만족스러운 피크 안테나 이득 값을 가진다. 또한 안테나의 전송 범위를 분석하기 위해 링크 버짓 시뮬레이션을 수행하였는데 915 및 2450 MHz에서 각각 9.84\% 및 8.57\%의 대역폭으로 비트 전송률에 따라 상당히 넓은 범위의 데이터 전송을 지원할 수 있었다. 다음으로 인체외 전력송신기(Tx)와 생체원격수신기(Rx)로 구성된 초소형 ICP 모니터링용 무배터리 WIMD를 개발했다. WIMD는 동시 전력 전송 및 데이터 원격 측정을 위한 이중 대역 성능(즉, 915 및 1900 MHz)을 보여준다. 이식 가능한 안테나의 최소 부피는 6.72mm$^3$ (5.6mm $\times$ 6mm $\times$ 0.2mm)이다. 전력 전송 효율(PTE) 개선을 위해 WIMD는 근거리 복사장(1900 MHz)에서 무선으로 전원이 공급된다. 또한, 구조는 9.83\% 및 27.9\%의 임피던스 매칭 대역폭으로 915 및 1900 MHz에서 각각 $-$26.8 및 $-$18.8 dBi의 피크 이득 값을 달성하였다. 장치의 무선 전력 전송 효율도 거리 변화에 따라 평가되었으며, 20mm(0.1267$\lambda$) Tx$-$Rx 이격 거리에서 최대 $-$25.9 dB의 PTE를 달성하였다. 2 dBm 입력 전력에서 정류기는 82\%의 최대 전력 변환 효율을 달성하였다. 마지막으로, 혈관내 동맥류 치료(EVAR)를 위한 스텐트형 안테나 시스템이 제안되었다. 이전에 EVAR 스텐트 시스템은 복부 대동맥류(AAA) 치료에만 사용되었으며 EVAR 스텐트의 금속성분(Stainless Steel 316L)과 유전체층을 활용하여 스텐트 구조가 안테나 특성을 가질 수 있는지 분석한 연구는 소개된 바 없다. 본 연구에서는 안테나로서의 EVAR 스텐트를 최초로 분석하고 안테나 속성에 대한 검증을 수행하였다. 스텐트 안테나는 단일 급전 와이어를 포함하는 메쉬 링을 형성하도록 연결된 여러 나선 와이어로 구성되어 스텐트 스트럿에서 전류의 무작위 분포를 방지한다. EVAR 적용 외에도 제안된 스텐트 시스템의 주요 특징은 무지향성 방사 패턴, 높은 이득 및 완벽한 임피던스 매칭을 포함하여 더 나은 안테나 특성을 가진다는 것이다. 제안하는 스텐트 안테나는 ISM 대역(868, 915 MHz)을 포함하는 850$-$950 MHz의 넓은 주파수 범위를 가지며, 868 및 915 MHz 대역에서 스텐트의 피크 이득 값은 각각 $-$20.75 및 $-$19.04 dBi이다. 생체 원격 측정 기능은 링크 예산 분석을 사용하여 평가되었다. 모델링 및 수치해석을 위해 유한요소법과 유한차분 시간영역을 이용하여 전자기계산을 수행하여 이중대역 이식형 안테나, 무배터리 생체원격 이식형 시스템, EVAR 스텐트 시스템의 특성을 평가하였다. 시뮬레이션 시간을 단축하고 예비 결과를 평가하기 위해 균질한 피부 팬텀, 균질한 근육 팬텀, 균질한 혈액 및 대동맥 혈관 팬텀에서 초기 분석을 수행하였다. 그 후에, 제안된 시스템들은 Sim4Life의 Duke Model 및 Remcom의 VariPose Man과 같은 여러 인체 조직으로 구성된 인체 모델에서 추가적으로 시뮬레이션 분석되었다. 검증을 위해 듀얼 밴드 이식형 안테나의 성능 측정 실험은 식염수에서, 배터리가 없는 이식형 시스템 측정은 식염수를 채운 인간 머리 팬텀과 다진 돼지고기에서, EVAR 스텐트 시스템 측정은 식염수로 채워진 American Society for Testing and Materials (ASTM) 팬텀과 다진 돼지고기에 3D 인쇄된 AAA를 배치함으로서 수행되었다. 측정된 결과는 모두 시뮬레이션으로 수치적으로 분석된 결과와 일치되는 결과를 획득하였다.

Study on angiogenic properties of cancer-associated fibroblasts derived from various molecular subtypes of breast cancer using three-dimensional spheroid assay system

Shah, Sajita 德成女子大學校 大學院 2020 국내박사

Breast cancer is the most prevalent cancer in women. The prognosis and metastasis of breast cancer are very diverse depending on the molecular subtypes. Triple negative breast cancers (TNBC) is characterized by lack of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor2 (HER2). Accumulated evidences indicate that TNBC is extremely aggressive with a poor prognosis, which is associated with high rate of metastasis and relapse, when compared with other molecular subtypes. Angiogenesis, a process of neovascularization, is essential to meet the demands of cancer cells for their growth, mainly for delivering oxygen and nutrients. Newly-formed blood vessels are considered as the direct contributors to the invasive and metastatic features of cancers. It has been suggested that the inhibition of angiogenesis could be effective to treat TNBC. However, several clinical trials investigating the therapeutic benefits of anti-angiogenesis drug targeting vascular endothelial growth factor receptor-A (VEGF-A) and/or its receptors in TNBC patients shows some conflicting results regarding the efficacy of such treatments. This might be because of the lack of adequate in vitro assay systems to identify potential drug candidates, which can effectively modify in vivo angiogenic events or because of the limited understanding of complex intrinsic mechanisms of angiogenesis induced by breast tumor stroma. In the first chapter, as the improvement in currently available 2-dimensional (2D) angiogenesis testing structures, we developed 3-dimensional (3D) co-culture spheroid system by using vascular progenitors: endothelial colony forming cells (ECFCs) and mesenchymal stem cells (MSCs). Blood vessels are formed by two types of vascular cells, namely endothelial cells and pericytes. During angiogenesis, specific cell-cell interactions between these two cell types are needed for functional blood vessels to form. Thus, co-culture of two vascular cells must be engaged to assess angiogenic properties. In 3D in-vitro co-culture spheroid angiogenesis assay, ECFCs+MSCs were seeded to form spheroids. Sprout development from each spheroid was detected by real-time cell recorder for 24 hours. Sprout length and number were higher in ECFC+MSC spheroids compared to ECFC-only spheroids. No sprouts were observed in MSC-only spheroids. Sprout development by ECFC-only spheroids was augmented by treatment with pro-angiogenic factors, vascular endothelial growth factor (VEGF) or combination of VEGF and fibroblast growth factor-2 (FGF-2). Interestingly, there was no additional increase in sprout formation by ECFC+MSC spheroids with VEGF or VEGF+FGF-2 stimulation, signifying that MSCs stimulate sprout formation by ECFCs. Immuno-fluorescent staining technique reveled that MSCs covers ECFCs sprout structure. We verified newly developed ECFC and ECFC+MSC spheroids assay by using vatalanib, VEGF inhibitor. Vatalanib significantly repressed sprout formation in both the spheroids. Of note, the IC50 of vatalanib in ECFC+MSC spheroids was 4.0 ± 0.40 μM at 24 h, which are more associated with the data of previous in vivo studies when compared to IC50 of vatalanib in ECFC spheroids (0.2 ± 0.03 μM). These results proposed that ECFC+MSC spheroids generated physiologically relevant sprout made of two vascular cells, and would be an actual pre-clinical in vitro assay model to assess pro- or anti-angiogenic properties. In the second chapter, we investigated the biological role of cancer-associated fibroblasts (CAFs) in facilitating the angiogenesis in breast cancer. In the stromal section of human breast cancer, fibroblasts are the most predominant cell types and have essential contributions in cancer progression, invasion, and metastasis. Different types of breast cancers can be engaged into separate microenvironmental conditions that may promote different angiogenic potential of CAFs. Indeed, TNBC has been reported to have significant higher microvessel density (MVD) as well as VEGF-A when compared with other types of breast cancers. However, only few researches have focused on targeting CAFs as an anti-angiogenic therapy. Therefore, we studied the angiogenic properties of cancer-associated fibroblasts derived from various molecular subtypes of breast cancer. To overcome the issues related with 2D culture systems and to mimic meticulously the complex angiogenesis process in vivo, 3D assay system using ECFC spheroids was used in the present study. ECFC spheroids were generated using a hanging drop spheroid formation technique. 24 hours-generated spheroids were harvested and mixed with the type1 collagen gel. Spheroids-suspended gels were added into the well, allowed to polymerize, and treated with CM from normal breast fibroblasts (NBFs), non-invasive breast cancer-associated fibroblasts (nCAFs) and invasive breast cancer-associated fibroblasts (iCAFs). The plate was placed in the real-time cell recorder (JuLi Stage, NanoEnTek) for tracking time-dependent sprout formation. The results suggested, for the first time, that iCAFs isolated from human TNBC tissues have more robust angiogenic potential in comparison with nCAFs. This initial result led us to study the specific signaling molecular mechanisms that potentiate iCAFs-mediated angiogenesis. Our results suggested that reduction of TIMP3, tissue inhibitor of metalloproteinase, is responsible for the elevated angiogenic potential in iCAFs, which is acquired by increased expression of pro-angiogenic factors, such as VEGF-A and MMP1, through a disintegrin and metalloproteinase 17 (ADAM17) activation. In conclusion, we developed an advanced 3D co-culture spheroid assay system using two vascular progenitor cells to identify pro- and anti-angiogenic drug candidates. From the study of cross-talk of breast CAFs with ECFCs, we demonstrated that iCAFs isolated from human TNBC tissues have more robust angiogenic potential in comparison with nCAFs and NBFs.