5,434 research outputs found
Study on RDT and Computational models of pressure strain correlation in turbulent homogeneous shear flows
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2010.2, [ 76 p. ]Rapid distortion 이론은 큰 평균 속도 구배장에서 어떻게 난류 에디가 발전하는지, 레이놀즈 응력, 에너지 스펙트럼이 어떻게 변하는 지를 해석할 수 있는 선형해석방식이다. 본 연구의 목표는 크게 두 가지로 나뉠 수 있다. 우선 다양한 난류전단 유동장에 대해 WKB형 RDT를 수치 해석하여 이전의 연구결과와 비교하는 것이 일차 목표이며, RDT이론을 자세하게 언급한 책의 부재로 RDT이론을 최대한 자세하게 풀어쓰는 것을 일차의 부수적 목표로 하였다. 그리고 다른 하나는 레이놀즈응력방정식 모델에서 압력-변형률 상관관계 모형에서 저율항 모델과 고율항 모델을 동시에 사용하였을 때 어떠한 결과가 나타나는 가를 알아보고, 이 복합 모델을 사용하였을 때 Rapid distortion limit에서 앞서 언급된 수치해석 결과와 비교하는 것이 목표하다. 저율항 모델은 다양한 유동에서 가장 성능이 좋은 Chung & Kim 모델을 사용하였으며 고율항 모델은 Launder등에 의한 준 등방 모델 (LRR-QI)과 Jones & Musonge에 의한 JM모델, Speziale, Sarkar, Gatski에 의한 SSG 모델, 그리고 FLT모델과, HP모델이 사용하였다.한국과학기술원 : 기계공학전공
Design Optimisation of Electromagnetic Devices Using Continuum Design Sensitivity Analysis Combined with Commercial EM Software
No full textThis paper deals with two kinds of optimisation problems, relevant to the optimised source distribution and the shape optimum design, using Continuum Design Sensitivity Analysis (CDSA) in combination with standard electromagnetic (EM) software. Fast convergence and compatibility with existing EM software are the distinctive features of the proposed implementation. In order to verify the advantages and also to facilitate understanding of the method itself, two design optimisation problems have been tested: one is an MRI design problem related to finding an optimal permanent magnet distribution and the other is a pole shape design problem of a BLDC motor for reducing cogging torque, using both 2D and 3D models
고유전 절연막을 이용한 기반의 박막 트랜지스터의 저전압 구동 특성 연구
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2009.2, [ xv, 133 p. ]Mechanically flexible, optically transparent, light, and low cost thin film transistors (TFTs) on polymer substrate are intensively interested for flexible and transparent display at future ubiquitous era. Until now organic thin film transistors (OTFTs) satisfied the requirements and they were studied for applications like active matrix OLED or LCD display, sensor devices, and radio frequency identification (RFID) tags. However, the operation voltage of OTFTs is large because of low capacitance of organic dielectrics. For low voltage operation devices suitable at portable and battery-powered electronic devices, high capacitance gate dielectrics are necessary. They can be obtained by using very thin film or using high-k dielectrics. Very thin gate dielectrics can lead to significant manufacturing problems such as poor leakage characteristics and pinholes come from rough surface of polymer thin film. I had an effort to use high-k oxides (BST) to reduce the operation voltage of TFTs. However, because BST films had poor leakage characteristics despite high dielectric constant, I added excess MgO having good leakage characteristics. In Chap. 3, four kinds of dielectrics BST, , , and thin films were fabricated at room temperature using pulsed laser deposition (PLD) at room temperature for feasibility test. As increasing MgO contents the leakage characteristics got better while the dielectric constants were decreased. After confirmed the possibility of MgO-BST to gate insulator of TFTs, I used sputtering method for large area application. I demonstrated the reason of reducing dielectric constant of the MgO-mixed BST thin film can be explained as the sum of each individual thin film (MgO and BST) using a series connection capacitance model, and the MgO plays a significant role in reducing the leakage current density of the thin film forming potential barrier.
Another problem of OTF...한국과학기술원 : 신소재공학과
Preparation and characterization of Ag added thin film by RF magnetron sputtering
No full text학위논문(석사) - 한국과학기술원 : 신소재공학과, 2005.2, [ iv, 83 p. ]본 연구에서는 단일 타겟을 이용하여 RF magnetron sputtering법으로 증착하였으며, 균일하고 밀도 높은 박막을 얻기 위한 조건을 잡기위해 다양한 RF Power 와 Ar 압력 조건을 변수로 하여 실험을 하였다. 이렇게 증착된 박막의 미세구조와 전기적 특성을 비교하였다. 비정질로 증착 된 박막의 결정화를 조사하기 위하여 여러 온도에서 RTA 로 열처리를 한 뒤 XRD 분석을 하였다. Four point probe 로 각 어닐링 온도에 따른 비저항을 비교하였고, SEM 분석을 통해 미세구조 관찰과 두께를 측정하였으며 열처리 전ㆍ후의 두께 변화 및 밀도 변화를 측정하기 위해 XRR을 이용하였다. 위의 방법으로 최적의 박막의 증착 조건을 잡은 뒤, co-sputtering 법으로 에 소량의 Ag을 도핑하여 증착된 박막의 결정성과 전기적 특성을 평가하였다.한국과학기술원 : 신소재공학과
Robust optimization utilizing the second-order design sensitivity information
No full textThis paper presents an effective methodology for robust optimization of electromagnetic devices. To achieve the goal, the method improves the robustness of the minimum of the objective function chosen as a design solution by minimizing the second-order sensitivity information, called a gradient index (GI) and defined by a function of gradients of performance functions with respect to uncertain variables. The constraint feasibility is also enhanced by adding a GI corresponding to the constraint value. The distinctive feature of the method is that it requires neither statistical information on design variables nor calculation of the performance reliability during the robust optimization process. The validity of the proposed method is tested with the TEAM Workshop Problem 2
Targeting tyrosine kinases for treatment of ocular tumors
No full textUveal melanoma is the most common intraocular primary malignant tumor in adults, and retinoblastoma is the one in children. Current mainstay treatment options include chemotherapy using conventional drugs and enucleation, the total removal of the eyeball. Targeted therapies based on profound understanding of molecular mechanisms of ocular tumors may increase the possibility of preserving the eyeball and the vision. Tyrosine kinases, which modulate signaling pathways regarding various cellular functions including proliferation, differentiation, and attachment, are one of the attractive targets for targeted therapies against uveal melanoma and retinoblastoma. In this review, the roles of both types of tyrosine kinases, receptor tyrosine kinases and non-receptor tyrosine kinases, were summarized in relation with ocular tumors. Although the conventional treatment options for uveal melanoma and retinoblastoma are radiotherapy and chemotherapy, respectively, specific tyrosine kinase inhibitors will enhance our armamentarium against them by controlling cancer-associated signaling pathways related to tyrosine kinases. This review can be a stepping stone for widening treatment options and realizing targeted therapies against uveal melanoma and retinoblastoma.N
Toward the Clinical Application of Therapeutic Angiogenesis Against Pediatric Ischemic Retinopathy
No full textTherapeutic angiogenesis refers to strategies of inducing angiogenesis to treat diseases involving ischemic conditions. Historically, most attempts and achievements have been related to coronary and peripheral artery diseases. In this review, we propose the clinical application of therapeutic angiogenesis for the treatment of pediatric ischemic retinopathy, including retinopathy of prematurity, familial exudative retinopathy, and NDP-related retinopathy. These diseases are all characterized by the reduction of physiological angiogenesis and the following induction of pathological angiogenesis. Therapeutic angiogenesis, which supplements insufficient physiological angiogenesis, may be a therapeutic approach for ischemic conditions. Various molecules and modalities can be utilized to apply therapeutic angiogenesis for the treatment of ischemic retinopathy, as in coronary and peripheral artery diseases. Experiences with cardiovascular diseases provide a useful reference for the further clinical application of therapeutic angiogenesis in pediatric ischemic retinopathy. Recombinant proteins and gene therapy are powerful tools to deliver angiogenic factors to retinal tissues directly. Furthermore, endothelial progenitor or bone marrow-derived cells can be injected into the vitreous cavity of the eye for therapeutic angiogenesis. Intraocular injections are highly promising for the delivery of therapeutics for therapeutic angiogenesis. We expect that therapeutic angiogenesis will be a breakthrough in the treatment of pediatric ischemic retinopathy.Y
Application of genome engineering for treatment of retinal diseases
No full textGenome engineering with clustered regularly interspaced short palindromic repeats (CRISPR) system can be used as a tool to correct pathological mutations or modulate gene expression levels associated with pathogenesis of human diseases. Owing to well-established local administration methods including intravitreal and subretinal injection, it is relatively easy to administer therapeutic genome engineering machinery to ocular tissues for treating retinal diseases. In this context, we have investigated the potential of in vivo genome engineering as a therapeutic approach in the form of ribonucleoprotein or CRISPR packaged in viral vectors. Major issues in therapeutic application of genome engineering include specificity and efficacy according to types of CRISPR system. In addition to previous platfoims based on ribonucleoprotein and CRISPR-associated protein 9 derived from Carnpylobacter jejuni, we evaluated the therapeutic effects of a CRISPR RNA-guided endonuclease derived from Lachnospiraceae bacterium ND2006 (LbCpf1) in regulating pathological angiogenesis in an animal model of wet-type age-related macular degeneration. LbCpf1 targeting Vegfa or Hifla effectively disrupted the expression of genes in ocular tissues, resulting in suppression of choroidal neovascularization. It was also notable that there were no significant off-target effects in vivo.Y
Evaluation of groundwater contamination from glass fiber dumping at Gozan-Dong, Incheon, Korea
No full textThe hydrology and chemistry of groundwaters in the Gozan-Dong area were investigated. The study was organized by the Korea Ministry of Environment to investigate possible groundwater contamination from glass fiber dumping. The flow regimes and chemical compositions of the groundwaters were assessed. Groundwaters in the Gozan-Dong area could be divided into two groups based on water chemistry and flow regime. These two groups have a zonal distribution, and were categorized into A and B zones. Zone A covers the areas near the glass fiber dump site and is characterized by partially confined aquifer condition and groundwaters of locally isolated hydrochemistry with no seasonal variation while zone B covers the other areas with unconfined aquifer condition and seasonally variable hydrochemistry. The groundwater flow regime suggested that the possible area of contamination from glass fiber dumping lay within the A zone. Identifications of, and quantification of fibers in the groundwater were carried out in accord with World Health Organization (WHO) specifications. While many fibers, in concentrations of the order of 10(3)-10(5) fibers per liter of groundwater, were detected, analysis of their chemical composition did not produce any evidence that they were of glass fiber origin. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.N
A New Fine Doppler Frequency Estimator Based on Two-Sample FFT for Pulse Doppler Radar
No full textWe propose a new fine Doppler frequency estimator using two fast Fourier transform (FFT) samples for pulse Doppler radar that offers highly sensitive detection and a high resolution of velocity. The procedure of fine Doppler frequency estimation is completed through coarse frequency estimation (CFE) and fine frequency estimation (FFE) steps. During the CFE step, the integer part of the Doppler frequency is obtained by processing the FFT, after which, during the FFE step, the fractional part is estimated using the relationship between the FFT peak and its nearest resultant value. Our simulation results show that the proposed estimator has better accuracy than Candan's estimator in terms of bias. The root mean square error (RMSE) of the proposed estimator has more than 1.4 time better accuracy than Candan's estimator under a 1,024-point FFT and a signal-to-noise ratio (SNR) of 10 dB. In addition, when the FFT size is increased from 512 to 2,048, the RMSE characteristics of the proposed estimator improve by more than two-fold.FALS
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