Transition metal chalcogenides (TMCs) as bifunctional electrodes for water splitting

Afzal, Rana Arslan 세종대학교 대학원 2019 국내석사

The modern world confronts energy crises and climate changes using carbon-based energy sources such as oil, coal, and natural gas. It is essential to switch from traditional energy sources (fossil fuels) to environmentally friendly and renewable ones to overcome those global issues. Hydrogen (H2) has considered being the most promising future renewable energy source due to the negligible pollutants and high mass-specific energy density (283 kJ/mol). Hydrogen can be produced by the electrolysis reaction of ‘water’ in the water-splitting cell. However, the slow kinetics of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the water-splitting cell, decreases the cell efficiency. Now, precious metal-based catalysts such as IrO2 and Pt/C are used for OER and HER, respectively. However, high cost, low abundance, and limited durability of noble materials restrict their application for the large-scale commercialization. Hence, it needs to develop readily available and inexpensive materials, which can simultaneously catalyze both OER and HER in the single device, with outstanding electrochemical activity and durability. According to our best comprehension, limited studies have been done on transition metals sulfides, selenides, and tellurides for the application of bifunction catalysis of water splitting. We investigate the bifunctional behavior (OER and HER) of transition metal chalcogenides using a binder-free approach to develop the water splitting cell. Herein, firstly we report successful preparation of cobalt sulfide on nickel foam (Co3S4/NiF) using the facile hydrothermal method. Cobalt oxide on NiF (Co3O4/NiF) is also synthesized with the same method and compares with the catalytic behaviors of Co3S4/NiF. In addition, iron and nickel sulfides on nickel foam are also synthesized and analyzed their OER and HER properties. Among these, Co3S4/NiF showed the best OER and HER performances. To further enhance the performance of Co3S4/NiF, the synthesis conditions such as temperature (150℃, 200℃, and 250℃) and growth time (3 h, 6 h, 12 h, 24 h, and 48 h) in the hydrothermal method are optimized. The synthesized cobalt sulfide hierarchical nanosheet arrays on nickel foam (Co3S4 HNSA/NiF) at 150℃ and 24 h show the best bifunctional (OER and HER) performances with excellent durability under alkaline (1M KOH) circumstances. As an instance, Co3S4/NiF (150℃ - 24 h) shows the lowest overpotentials of 250 and 230 mV at the current density of 10 mA/cm2 for OER and -10 mA/cm2 for HER, in 1 M KOH electrolyte. The OER and HER Tafel slopes of Co3S4/NiF are 68 and 115 mV/dec respectively. Co3S4/NiF (150℃ – 24 h) has the mass activity of 325 and 50 mA/mg at 1.6 V (OER) and -0.3 V (HER), respectively, and their corresponding Tafel slopes are 67 and 123 mV/dec, respectively. In particular, Co3S4/NiF shows remarkably superior activities for OER and HER, compared to those of the previously reported materials. Moreover, Co3S4/NiF (150℃ – 24 h) shows a high stability for OER and HER in 1 M KOH over continuous 12 h of operation. Electrochemical impedance spectroscopy (EIS) and electrochemical surface area (ECSA) of catalysts with roughness factor (RF) are also analyzed to investigate the conductivity and number of active sites. Cobalt selenide (CoSe2) and telluride (CoTe2) are also synthesized with the same method and show the similar activity of Co3S4/NiF.

QoE Estimation & Management in Video Streaming Networks

Arslan, Usman Muhammad 금오공과대학교 2018 국내박사

Recent surge in the usage of multimedia services has highlighted the need for continuous monitoring and management of multimedia networks based on the users’ quality of experience (QoE). Multimedia services are no longer limited to entertainment, as usage of medical multimedia services, such as telemedicine, are becoming common day by day. With these overwhelming trends, the network operators employ mechanisms that can help in continuous monitoring and efficient resource management of entertainment and medical multimedia services. A major chunk of the content being delivered through multimedia networks belongs to video related services. The perceptual quality of a transmitted video stream can be degraded due to compression and its transmission over an error-prone channel. There are two ways to estimate the perceptual quality of streamed videos, either by human observers (subjective tests) or through an objective video quality metric (VQM). Most of the objective VQMs estimate the quality of delivered videos by using a full or reduced-reference of the source videos. But, recently researchers have been focusing on blind estimation of perceptual quality, where no reference is required from the source videos at the receiver end of the multimedia networks. No reference and reduced reference methods are preferable as they are much practical for real-time implementation. A modern video transmission system consists of three main stages, video encoding, channel through which video is transmitted and video decoding. The video encoder encodes the video at a certain bitrate, according to the network conditions such as bandwidth etc. The encoding process usually leads to compression of the source video, which can result in degradation of its perceptual quality. Bandwidth is one of the most precious resources in a network and network operators make sure to efficiently utilize without compromising the QoE of end users. Recent inclusion of state-of-the-art video encoder known as High Efficiency Video Coder (HEVC) has made it possible that without heavily compressing the video, 50% of bandwidth can be saved, compared to preceding video encoders. Through researches are being conducted to evaluate the performance of HEVC for different types of multimedia content. In the second stage of video transmission, i.e. the channel through which video is transmitted, packet losses and delays can take place which also result in degradation of the perceptual quality of streamed videos. The effects that packet losses and delays produce on the end users is always negative and is highly undesirable by the network operators. For a network operator to prepare remedies for these kind of network impairments, objective estimation of quality of delivered videos is very important. Furthermore, as mentioned earlier, usage of medical multimedia services is on the rise, and as medical videos contain sensitive information so seamless delivery of these videos is of utmost importance. Medical multimedia content needs to be protected from any unwanted compression and transmission impairments, so for this purpose research is continuously being conducted for quality estimation of transmitted medical videos. Additionally, researchers are focusing on non-conventional methods for saving network resources without compromising the perceptual quality of streamed videos. These methods include lossless compression techniques and various heuristic approaches for efficient management of network resources. For this purpose, in this doctoral thesis, following works have been performed which are based on papers in reputed peer reviewed journals and conferences. This doctoral thesis begins with a review of recent state-of-the-art approaches proposed in the field of video quality assessment (VQA), encompassing both entertainment and medical multimedia content, and efficient resource management in multimedia networks. This is followed by the chapter which presents novel no-reference VQMs (NR-VQMs) that estimate the packet loss and delay impairments in a video stream transmitted over a multimedia network. This chapter mainly focuses on perceptual quality estimation of entertainment multimedia content. It also includes the subsequent subjective experiments conducted for these studies. The impairments in the video streams due to packet losses and delays are estimated by efficiently detecting dropped/skipped/frozen video frames in the received videos. These methods are pixel based methods and they rely on several temporal features that are estimated and modelled into mathematical models. The presented studies on subjective experiments are performed using laboratory based tests. In the laboratory based experiments, the focus has been on using standardized methods in order to generate datasets that can be used to validate objective methods of VQA. The proceeding chapter encompasses the topic of quality estimation of medical multimedia content, in which we have considered wireless capsule endoscopy videos. We start off by presenting a state-of-the-art comprehensive study for full reference (FR) VQA of medical videos that are compressed via HEVC. Several existing objective FR-VQMs are evaluated for their performance in estimation of diagnostic and perceptual quality of compressed medical videos. Also, in this chapter the performance of HEVC is studied for its suitability in modern medical multimedia networks. This study is followed by a novel technique for detection of bleeding regions in wireless capsule endoscopy videos using a support vector classifier. The classifier is trained using spatial features of WCE video frames that contain bleeding regions. The training and classification features are based on thresholding in HSV color space. Finally, based on these mentioned works related to medical multimedia, we present a novel FR-VQM that covers both aspects of medical video quality i.e. perceptual and diagnostic quality. The VQM is a quality index that estimates the diagnostic quality based on detected bleeding regions in wireless capsule endoscopy videos. Lastly, the following chapter covers the topic of resource management in video streaming networks in which different heuristic approaches are presented that are focused on reducing bandwidth and storage consumption. Firstly, an approach is presented that utilizes the spatio-temporal features of videos to allow compression without compromising the perceptual quality. Further, this chapter includes approaches that follow the basic principle of adaptive streaming and network resources are efficiently utilized based on end user activities. 최근 멀티미디어 서비스 사용의 급증으로 사용자의 QoE를 바탕으로한 멀티미디어 네트워크의 지속적인 모니터링과 관리에 대한 필요성이 강조 표시된 있다. 멀티미디어 서비스는 더 이상 엔터테인먼트에 국한되지 않고, 원격진료와 같은 의료 멀티미디어 서비스로써 점점 더 일상화 되고 있다. 이런 강한 추세와 함께, 네트워크 운영자들은 의료 및 엔터테인먼트 멀티미디어의 지속적인 모니터링과 효과적인 자원 관리를 돕는 알고리즘 채용하고 있다. 멀티미디어 네트워크를 통해 전달되는 주요 데이터는 비디오 서비스와 관련되어 있으며, 전송되는 비디오 스트리밍의 체감 품질은 오류가 발생하기 쉬운 채널을 통과하거나 압축을 통해 저하된다. 비디오 스트리밍의 체감 품질은 사람에 의한 관찰 시험이나 객관적인 비디오 체감 품질 측정항목(VQM)에 의해 평가 된다. 이러한 대부분의 VQM 방식은 비디오 전체를 사용하거나 축소하는 방식으로 평가를 한다. 하지만 최근 연구자들은 멀티미디어의 최종 사용자단에서 원본 비디오의 레퍼런스를 요구하지 않는 블라인드 체감 품질테스트에 집중하고 있다. 실시간 구현에 적합하지 않기에, 원본 이미지의 레퍼런스나 부분적인 레퍼런스 적용 평가 방법은 더 이상 선호되지 않기 때문이다. 현대의 비디오 전송 시스템은 비디오 인코딩, 비디오가 전달되는 채널, 비디오 디코딩, 이렇게 3단계로 구성된다. 비디오 인코더는 대역폭과 같은 네트워크 환경에 따라 특정 비트율에 맞추어 인코딩을 실시하며, 실시된 인코딩 과정은 종종 체감 품질을 저하시키는 결과를 낳는 원본 비디오 압축을 실행한다. 대역폭은 최종 사용자의 QoE 손상 없이 최적화를 진행하는 네트워크와 네트워크 운영자에게 가장 귀중한 자원 중의 하나이다. 최근 잘 알려진 HEVC와 같은 최신 비디오 인코더 기술은 기존 기술과 비교하여 과도한 압축 없이 50%의 대역폭 저장이 가능하게 만들었다. 다른 종류의 멀티미디어 컨텐츠에 대한 HEVC 성능 평가 연구들이 수행되었다. 비디오 전송에 대한 두 번째 단계, 즉 비디오 스트리밍이 전송되는지 채널에서, 발생하는 패킷 손실과 지연은 비디오 스트리밍의 체감 품질 저하를 낳는다. 최종 사용자에게 영향을 끼치는 패킷 손실과 지연은 네트워크 운영자들에게 항상 부적절하다. 이와 같은 네트워크 손상들을 운영자들이 해결하기 위해서, 전송되는 비디오의 객관적인 체감 품질 평가는 매우 중요하다. 더구나, 언급했다시피, 의료 멀티미디어 서비스의 사용은 증가하고 있고, 의료 비디오는 민감한 정보를 포함하고 있기에, 이러한 비디오들은 결점 없이 전송되는 게 중요하다. 의료 멀티미디어 컨텐츠는 원치 않는 어떠한 형태의 압축이나 손상으로부터 보호되야 한다. 그래서 이 연구의 목적은 전송되는 의료 영상의 지속적인 체감 품질 평가 수행이다. 추가적으로, 연구자들은 비디오 스트리밍의 체감 품질 손상 없는 네트워크 보호를 위한 비전통적인 방법에 집중하고 있다. 이 방법들은 효과적인 네트워크 자원 관리를 위한 무손실 압축 기술과 다양한 실험적 접근을 포함한다. 이 목적을 위해, 본 박사 학위 논문의 연구내용들은, 관련 분야에서 저명한 논문지와 학회의 논문들을 바탕으로 수행되었다. 본 박사 학위 논문은 엔터테인먼트 및 의료 멀티미디어와 효율적인 자원 관리를 포함하는VQA 관련 최신 연구들을 바탕으로 접근을 시작한다. 멀티미디어 네트워크에서 비디오 스트리밍의 지연 손실 및 패킷 손실을 평가하는 비참조-VQMs(NR-VQMs)에 대해 제시하는 장이 뒤따르고, 이 장에서는 주로 엔터테인먼트 멀티미디어 컨텐츠의 체감 품질 평가에 집중한다. 또한 본 연구들에 대한 주관적인 후속 시험들도 포함한다. 패킷 손실과 지연에 의한 비디오 스트리밍 손상은 수신한 비디오의 버려지고 무시되거나 멈춰있는 비디오 프레임을 효율적으로 탐지하여 평가된다. 이 방법들은 픽셀 단위의 방법들과 몇몇 수학 모델에 모델링 되고 측정되는 일시적인 특징점에 의존한다. 주관적 실험에 대한 제안된 연구들은 시험을 바탕으로 연구실에서 수행되었다. 실험실 기반의 실험에서, 중점은 VQA의 객관적인 방식을 유효화하기 위해 사용될 수 있는 데이터셋을 생성하기 위한 표준화된 방식의 사용이다. 진행되는 장은 무선 캡슐 의료 내시경 비디오를 포함하는 멀티미디어 컨텐츠의 품질 평가를 포함한다. HEVC를 통해 압축된 의료 비디오의 전체참조(Full reference) VQA에 대한 포괄적인 최신연구를 제시하며 시작한다. 몇몇 존재하는 객관적인 FR-VQM들은 압축된 의료 비디오의 체감 품질과 진단의 평가 안에서 성능이 평가된다. 또한, 본 장에서는 현대 의료 멀티미디어 네트워크에 적합성을 위해 HEVC의 성능이 연구된다. 본 연구는 서포트 벡터 머신(SVM)의 분류기술을 사용하는 무선 캡슐 내시경 비디오에서 출혈 부위의 감지를 위한 최신 기술을 따른다. 이 분류기술은 출혈 부위를 포함하는 WCE 비디오 프레임의 공간 특징을 사용하여 학습된다. 이 학습과 분류를 위한 특징은 HSV 색상 공간의 임계점을 바탕으로 되어있다. 최종적으로, 의료 멀티미디어와 연관되어 언급된 연구들을 바탕으로, 진단 및 체감 품질을 보상하는 최신 FR-VQM 서술한다. VQM는 무선 캡슐 내시경 비디오의 출혈 부위 탐지를 바탕으로 진단 품질을 평가하는 품질 표시 기술이다. 마지막으로, 오는 장은 스토리지 소비와 대역폭 절약에 초점을 둔 경험적인 방법에 대한 비디오 스트리밍 자원관리를 다룬다. 먼저, 체감품질 보장이 없이 압축을 허락하는 비디오의 시공간 특징 접근방법이 제시된다. 또, 이 장은 적응형 스트리밍의 기본법칙과 최종 유저 기반 최적화 네트워크 자원 접근방법을 포함한다.

Liquid crystal alignment on two dimensional materials

Shehzad, Muhammad Arslan Sejong University 2018 국내박사

액정은 여러 가지 고체 및 액체상을 보유하고 있어 훌륭한 재료 중 하나이다. 이러한 액정 (Liquid Crystal : LC) 은 액체와 같은 물리적 외관을 가지고 있으나 결정과 같은 물리적 특성을 갖는 중간 성질을 나타낸다. 다중 상을 갖는 이들 물질은 일반적으로 메조겐 및 메조 노즈 (mesophase)로서의 상으로 명명된다. 온도, 농도, 치환체 등에 따라 이들 물질은 네마틱, 콜레스테릭, 세미 및 강유전적으로 다양한 유형으로 존재한다. 지금까지 많은 연구가 LC에서 이루어졌지만 대부분 휘발성 디스플레이, 온도 센서 등에 사용되었다. 이러한 물질이 다른 표면과 상호 작용할 때 물리적 및 광학적 특성은 연구할 여지가 많이 남아있다. 이들 액정의 구조적 특성을 살펴보면, 주로 테일 (tail)을 갖는 페닐기로 구성된다. 흥미롭게도, 이들 액정 (LC)의 페닐기는 육각형 2 차원 물질, 즉 그래핀, h-BN 및 다른 전이 금속 칼 코겐화물 (TMD)과 원자 및 구조적 양립성을 나타낸다는 것이 밝혀졌다. 뛰어난 성질 때문에 이 육각형 구조의 물질은 전자 및 광전자 특성을 갖고 있는 것으로 유명하다. 이러한 액정 분자의 호환성은 이러한 물질의 물리적 특성을 향상시키는 새로운 패러다임을 열뿐만 아니라 새로운 전자 및 광전자 응용 분야에 이 시스템을 활용하는데도 도움이 될 것이다. 이 배경을 고려할 때, 현재 연구는 크게 세 부분으로 나뉘어져 있는데, 첫 번째 부분은 부수적인 내용이고 두 번째와 세 번째 부분이 가장 핵심적인 내용이다. (1) 2 차원 재료의 성장 (2) 2 차원 표면의 액정 정렬 (3) 결함 없는 디바이스 및 비 휘발성 디스플레이를 제조하기 위해 이러한 정렬 동작의 활용방안. 첫 번째 부분은 2D 재료의 화학 기상 증착 (CVD) 기반 성장 메커니즘에 중점을 두었습니다. 육각형 표면에 LC 분자의 정렬 특성을 보기 위해 광범위한 연구가 수행되었다. 분자의 고정된 거동은 TMD와 비교하여 육각형 그래핀 및 h-BN 에서 다양함이 발견되었다. 그래핀 (graphene)과 h-BN에서 6 개의 퇴화된 정렬 상태가 발견되었으며, TMD에서는 단지 3 개 뿐이다. 이 고정이 다른 2D 표면에서 대칭이었을 때 LC가 Zig-Zag에 비해 TMD의 안락 의자 가장자리에 정렬하는 것을 선호한다는 것이 입증되었다. 작업의 마지막 부분에서, 이 고정 방식은 결함이 없는 장치를 제조하는데 사용되었고 보다 구체적으로는, MoS2 (Molybdenum dioxide)에 대한 입계 영향을 연구하고 결정립계와 단결정 소자를 비교 하였다. 결정립 경계, 핀홀 등과 같은 결함을 피하는 것이 우리의 새로운 기술을 사용하면 효율적인 장치를 제공 할 수 있다는 것이 입증되었다. h-BN에서 LC 분자의 6 가지 축퇴 정착 상태를 이용하여 새로운 비 휘발성 디스플레이를 제작하여 LC로 정렬 된 입자를 픽셀로 활용했습니다. 심층적인 실험 결과는 h-BN에서 정렬된 LC의 꼬임을 제어하여 한 도메인의 색상을 조정할 수 있음을 보여준다. 전반적으로, Ph.D. 연구 목표가 성공적으로 이루어졌으며, 이 연구는 2D 재료 기반의 효율적인 전자 및 광전자 장치의 발전에 크게 기여했다. 우리는 이 연구가 액정 기반 광학 분야에 혁명을 일으키고 2D 재료에 대한 액정 (LC) 의 상호 작용에 대한 더 나은 이해를 줄 것으로 믿는다. Liquid crystals are one of the magnificent materials as they own multiple solid and liquid phases. These Liquid crystals (LCs) exhibit intermediate nature having physical appearance like liquid but physical characteristics like crystals. These materials having multiple phases are usually named as mesogens and their phases as mesophases. Depending on temperature, concentration, substituents etc they exists in many different types ranging from nematic, cholesteric, sematic and ferroelectric. Until now a lot of work has been done on LCs but mostly they are being used in volatile displays, temperature sensor etc. Studying their physical and optical properties still have plenty of room to work especially when these materials interact with other surfaces. Considering the structural properties of these liquid crystals they are mainly consists of a phenyl group with tail. Interestingly, it was found that the phenyl group of these liquid crystals (LCs) reveal atomic and structural compatibility with hexagonal two dimensional materials i.e. graphene, h-boron nitride and other transition metal chalcogenides (TMDs). These hexagonal materials due to their enormous extraordinary properties are famous for electronics and optoelectronics properties. This compatibility of liquid crystal molecules not only opens a new paradigm to enhance the physical properties of these materials but also help to utilize this system for novel electronic and optoelectronic applications. Considering this background, current work was mainly divided into three parts where first part was minor while 2nd and 3rd were major contribution and distributed as: (i) growth of two dimensional materials (ii) liquid crystal alignment on two dimensional surface (iii) Application of this alignment behavior to fabricate defect free devices and non-volatile display. The first part was focused on the chemical vapor deposition (CVD) based growth mechanism of 2D materials. Extensive study was done to see the alignment characteristics of LC molecules on hexagonal surface. It was found that anchoring behavior of these molecules vary in hexagonal graphene and boron nitride (BN) compared with TMDs. Six degenerate alignment states were found in graphene and h-BN, contrary to this only three on TMDs. It was establish that LC prefer to align on armchair edge of TMD compared to Zig-Zag while this anchoring was symmetric in other 2D surfaces. In last part of the work, this anchoring scheme was utilized to fabricated defect free devices. More specifically, effect of grain boundary was studied on molybdenum dioxide (MoS2) and comparison was done between grain boundary and single crystal device. It was established that avoiding defects like grain boundaries, pinholes etc. using our novel technique could offer efficient devices. Taking advantage of six degenerate anchoring states of LC molecules on h-BN a novel non-volatile display was fabricated where grains with aligned LC were utilized as pixels. In-depth experimental results show that we can tune the color of one domain by controlling the twist of aligned LC on h-BN. Overall, the objectives of Ph.D. research work was successfully achieved, and this work has contributed significantly to the advancement of 2D materials based efficient electronic and optoelectronic devices. We believe this work may revolutionize the field of liquid crystal based optics and give better understanding on interaction of liquid crystals (LCs) on 2D materials.

Concurrent Optimization of Low-Cost Regular Fabrics and Variation-Tolerant Circuit Techniques for Nanoscale SRAM

Arslan, Umut Carnegie Mellon University 2010 해외박사(DDOD)

As CMOS scaling continues, manufacturing costs increase substantially in part due to the challenges of subwavelength lithography. Alternative manufacturing methods that are proposed to enable affordable scaling require extreme layout regularity. Since modern systems are embedding increasing amounts of memory, constructing SRAM circuits efficiently from extremely regular patterns is of utmost importance. Further; robust SRAM design is becoming more challenging due to high random variability in nanoscale processes. Low-cost layout fabrics and variation-tolerant SRAM circuit techniques must be jointly explored to determine the optimal design/manufacturing strategy for affordable scaling. This dissertation proposes a framework to systematically explore the fabric-circuit design space for the SRAM bitcell. The framework integrates performance models for various fabric-circuit solutions with an effective design space exploration strategy. Efficient statistical methods are used to accelerate SRAM parametric failure analysis. The design space of a given fabric-circuit solution, which is reduced due to extreme layout regularity, is exhaustively searched for pareto-optimal designs. The exhaustive exploration is accelerated via subsampling of the design space and highly parallelized design evaluations. The pareto-optimal fronts are used to compare various fabric-circuit solutions. As a demonstration, the framework is used to explore the bitcell design space in a 45nm SOI process. This study considers two low-cost regular fabrics, each with specific regularity constraints for the diffusion layer, and various circuit solutions, including 6T and 8T topologies and a read/write assist technique. The results show that the 6T topologies cannot achieve acceptable parametric yields without using read/write assist. The 8T topology emerges as the optimal circuit solution in case the design cost of assist circuits is not affordable. The assisted 6T cells can be mapped onto the low-cost fabrics more efficiently than the ST cell unless the speed and yield requirements are extremely demanding. Non-gridded diffusion patterning improves cell area and leakage power by 10--25% and 2--16%, respectively, for the considered circuit solutions. The area comparisons demonstrated in this experiment are strongly dependent on the extent of the pushed rules for a gridded design. To validate the area comparisons, prototype 8T bitcells were implemented using the pushed rules that are assumed by the area models. The lithography simulations of cell arrays and silicon measurements confirmed the viability of the pushed rules. The bitcell constructed from non-gridded diffusion patterns is 14% smaller than the bitcell constructed from gridded diffusion patterns, as predicted by the area models. 16 Kb arrays, including all the peripheral logic, were constructed from these bitcells to demonstrate and compare the array efficiency of the low-cost regular fabrics. Both fabrics achieve the same array efficiency of 76% when the decoder and control blocks are excluded. When those blocks are included, the fabric with gridded diffusion attains 58% array efficiency. Silicon measurements demonstrate that two distinctive regularity constraints on the diffusion layer do not lead to any significant difference in array speed and leakage.

Essays in macroeconomics

Arslan, Yavuz University of Rochester 2007 해외박사(DDOD)

This thesis is a collection of three essays in macroeconomics. In Chapter 1, we solve for the housing market equilibrium in the presence of aggregate (interest rate) uncertainty, and examine the behavior of the model in response to fluctuations in interest rates. In addition, households also face idiosyncratic uncertainty resulting from stochastic changes over the lifecycle in tastes (or need) for housing. In this environment, profit maximizing banks offer fixed-rate mortgage (FRM) contracts to home buyers. As seems plausible, each housing market transaction is subject to a fixed cost, which gives rise to S-s policy rules for housing transactions: existing home owners change the size of their houses only if there is a sufficiently large change in the state of the economy (i.e., in interest rates, in their taste for housing, etc.). A plausibly calibrated version of the model is consistent with three empirically documented features of the housing market: (i) highly volatile housing prices and transaction volume, (ii) a strong positive correlation between transaction volume and housing prices, and (iii) a significant negative relationship between interest rates and housing prices, which can rationalize a large part of the recent boom in housing prices in the U.S. and around the world. In Chapter 2, we formulate a two period OLG model to find out the form of the relationship between interest rates and housing prices theoretically. It appears that the distribution of homeownership is also important for housing price dynamics. We show that housing prices in the equilibrium do not always have a negative relation with interest rates. In Chapter 3, we model a mechanism which can generate most of the gender gap in unemployment observed in most of the OECD countries. The main components of the model are moral hazard, labor market institutions, and higher home productivity of women than men. The source of the moral hazard is the imperfect monitoring performed by the government. Higher home productivity of women makes them more likely to reject job offers and stay unemployed which causes higher unemployment level for women. We find that each component has quantitatively large effect on unemployment levels.

Sex determination mechanisms and techniques to control sex differentiation in selected species of sunfishes (Centrarchidae)

Arslan, Tulin Auburn University 2001 해외박사(DDOD)

Control of sexual differentiation through steroid treatments and sex determination mechanisms in three economically important centrarchids, bluegill <italic> Lepomis macrochirus</italic>, black crappie <italic>Pomoxis nigromaculatus </italic>, and largemouth bass <italic>Micropterus salmoides</italic> were studied. Effective timing, duration and mode of administration of steroid treatments were investigated using two synthetic androgens, 17α-methyltestosterone and trenbolone acetate, and a natural estrogen, estradiol-17β. Dietary administration of androgen to bluegill resulted in variable level of masculinization. Immersion method was an effective mode of androgen administration to bluegill to achieve masculinization. Inclusion of a permeation enhancer, dimethyl sulfoxide, to the solutions can increase the masculinization potency of androgens. Unlike androgens, both oral and immersion modes of estrogen administration were effective to induce a high level of feminization in bluegill. Timing of gonadal differentiation in black crappie depends on growth rate, and both size and age were important in the selection of appropriate size black crappie fry for steroid treatments. Dietary administration of androgens to black crappie might give inconsistent results because factors such as feed training or water temperatures might interfere with feed consumption and delivery of steroids. More consistent results were obtained by administering androgens through the rearing water. Feminization in black crappie was achieved through periodic estrogen immersions, but optimum timing, frequency and intensity of estrogen immersions remains unclear. Successful and functional alteration of phenotypic sex in largemouth bass requires initiation of steroid treatments before 40 days of age and 34 mm total length. An estradiol-17β concentration lower than 200 mg/kg diet and probably a 17α-methyltestosterone concentration lower than 60 mg/kg diet should be used to prevent the adverse effects of steroids on gonadal development of largemouth bass. Sex determination mechanisms were studied by comparing the sex ratios of progeny derived from pair spawning of normal (not hormone treated) brooders and backcrossing of hormone treated brooders to normal brooders. Effect of prevailing water temperatures on sex ratios of bluegill were also evaluated by rearing young fry in two different temperature extremes. Sex determination mechanism in largemouth bass has a dual chromosomal basis. Sex determination mechanism of black crappie is predominantly monofactorial and male is the heterogametic sex. Sex determination mechanism of bluegill is polyfactorial, involving multiple autosomal sex modifying genes over the underlying chromosomal system that is yet to be elucidated.

Characterization of De Novo Aggregation of Prions and Protein Misfolding Disease Proteins In Yeast

Arslan, Fatih University of Illinois at Chicago 2014 해외박사(DDOD)

Many proteins spontaneously misfold, and escape from protein quality mechanisms in the cell. Accumulation of such proteins may become toxic to the host cell. The toxic conformers of some proteins often interact with other native forms of the same protein and convert them into the toxic state. These proteins can repeatedly cycle this self-sustaining loop, and exacerbate the cellular proteostatis network, resulting in death. Among such proteins, prions and ALS-linked proteins, FUS and TDP-43, are of great interest to understand the mechanism of de novo appearance of protein misfolding diseases. In this study, I have first studied the de novo appearance of a well-established prion in yeast, [PSI+], and showed that [PSI+] aggregates initially appear at a perivacuolar protein deposit site, where they are converted to amyloid by being cross-seeded via other heterologous protein aggregates. Such an interaction causes continued growth of the de novo [PSI +] fibrils, which requires the molecular chaperones. I also showed that the ALS-linked TDP-43, but not FUS protein can propagate as a self-seeding prion in yeast. Like yeast prions, TDP-43 can form self-seeding aggregates, which are cytoplasmically transmissible, and form detergent resistant oligomers. Unlike yeast prions, the TDP-43 prion causes growth inhibition, and does not require the Hsp104 chaperone for maintenance. In contrast to overexpressed TDP-43 or in vitro TDP-43 fibers, stress does not induce the formation of TDP-43 prions, but can partially cure cells of the TDP-43 prion. The study of the aggregation and toxicity of TDP-43 and FUS in yeast revealed that the yeast prion [PIN+] exacerbates FUS toxicity, and TDP-43 and FUS aggregation. I also showed that the level of the Hsp40 chaperone, Sis1 is vitally important to shear/dissolve and partially detoxify FUS and TDP-43 aggregates in yeast as such aggregates titrate the essential Sis1 protein away from the nucleus. This inhibits Sis1's function in UPS-mediated delivery of cytosolic misfolded proteins to the nuclear proteasomes, leading to the accumulation of such proteins in the cytosol, and ultimately death. Taken together, insights gained here help us understand the de novo appearance of prions and prion-like disease protein aggregates, and how they cause toxicity in the cell.

CFD Study on the Air-side Thermal Hydraulic Performance for Micro-Channel Heat Exchanger : MICRO-CHANNEL 열교환기에서의 공기측 열·수력 성능에 대한 CFD 연구

Arslan, Saleem 경북대학교 대학원 2016 국내석사

The air side thermal hydraulic performance of the multi-louvered aluminum fin heat exchangers is investigated. When it comes to the prediction of heat transfer performance, the CFD code is of great essence. A detailed study was performed to analyze the thermal performance of air over a range of Reynolds number i.e. from 30 to 250. Air side heat transfer coefficient as well as other important parameters were calculated and validated over the mentioned broad band of Reynolds numbers. Critical Reynolds number study was performed in order to capture the flow regime change below the Re value of 100, and a correlation for critical Reynolds number was also proposed. Parametric study of the multi-louvered aluminum fin heat exchangers was also performed. For 36 heat exchangers with the Louver angles (19°-31°), Fin pitches (1.0, 1.2, 1.4mm) and Flow depths (16, 20, 24mm), a long series of cases were run for the parametric study. The air-side heat transfer coefficient, pressure drop results for different geometrical configurations were reported in terms of Colburn j factor and Fanning friction factor f, as a function of Reynolds number based on louver pitch. New correlations of j and f factor were also proposed on the basis of the data gathered from the study. (요약) 다중 루버핀(알루미늄) 열교환기의 공기측에서의 열수력 성능을 조사한다. 열전달 성능 예측을 할 때, CFD 코드는 많은 기여를 한다. 레이놀드 수가 30부터 250까지의 넓은 범위에서의 공기의 열성능을 분석하기 위한 상세한 연구가 수행되었다. 공기 측 열전달 계수뿐만 아니라 여러 중요한 매개변수가 계산되었고, 언급된 넓은 영역의 레이놀즈 수에서 검증되었다. 100 이하의 레이놀즈 수에 대한 유동체계의 변화를 관찰하기 위해서 임계 레이놀즈 수에 관한 연구가 수행되었고, 이에 대한 상관관계도 제안되었다. 또한 다중 루버 알루미늄핀 열교환기에 대한 매개변수 연구가 수행되었다. 다양한 루버 각(19° ~ 31°), 핀 피치(1.0, 1.2, 1.4 mm), 그리고 수심(16, 20, 24mm)에서 36 열교환기가 매개변수 연구를 위하여 장기간 연속으로 작동되었다. 루버 피치에 기초한 레이놀즈 수의 요소으로써 콜번 j요소와 패닝의 마찰요소 f의 조건에서 기하학적 구성의 변화를 초래하는 공기측 열전달률과, 압력강하가 보고되었다. 본 연구에서의 새로운 j와 f의 상관관계는 기존의 연구 결과에 기초하여 제안되었다.

Adaptive Test Cost and Quality Optimization Through An Effective Yet Efficient Delivery of Chip Specific Tests

Arslan, Baris University of California, San Diego 2013 해외박사(DDOD)

The higher levels of integration and process scaling imposes failure behaviors which are challenging to interpret, necessitating the continuous augmentation of fault models and test vectors in the hopes of taming the defect escape rate. The subsequent inflation in the number of test vectors coupled with the constant increase in the size of each test vector continuously boosts test cost. The economics of particularly the competitive consumer marketplace however require a constant vigilance at the test cost while ensuring a satisfactory test quality. While the inclusion of new fault models helps boost test quality, the non-uniform distribution of various defect types and the defect coverage overlaps between fault models imply variable effectiveness of fault models and test vectors, resulting in the inclusion of a large number of ineffective vectors in test flow. A static derivation of test effectiveness however remains problematic in practice as it is well known that defect characteristics are prone to drifts throughout the product lifecycle. Furthermore, the increasing process variation and the integration of hundreds of domains within a chip result in increasingly distinct domains and individualized chip instances with diverse test resource requirements. The conventional test method of a static application of an identical test set to all chips consequently struggles to satisfy the demanding test cost and quality constraints in the face of the evolving defect behaviors and the increasing diversification in test resource requirements. This thesis addresses the simultaneous necessity for satisfactory test quality and low test cost through an adaptive test cost and quality optimization framework. The proposed methodologies not only adaptively assess the effectiveness of fault models and test vectors but also evaluate the variable test resource requirements of the chips and domains based on their distinct characteristics, enabling an effective yet efficient test through the selection of the most effective vectors and a carefully crafted allocation of test resources. The proposed methodologies are tailored for a broad set of application scenarios through the consideration of different defect classes and defect characteristic drift types while incorporating the test data gathering and delivery constraints and overcoming the associated algorithmic challenges.

Bandwidth and Rate Allocation Tradeoffs of Source-Channel Coding, Packetization and Modulation in Unequally Protected Multimedia Communication Systems

Arslan, Suayb S University of California, San Diego 2012 해외박사(DDOD)

A conventional approach to the design of wireless multimedia communications is the layered approach, in which the network layers function independent of each other. This kind of layered approach is inspired partly by Shannon's separation theorem in which the optimization of each block is equivalent to optimization of the overall source-channel coding operation. However, the separation theorem is valid only in a point-to-point communication scenario in the case of asymptotically long block lengths of data and assumes huge amounts of processing power and delay. Therefore, current practical communication systems strive to jointly design building blocks of a multimedia system for better performance. The focus of this dissertation is therefore to present various joint designs for different channel models and systems, although limited by physical constraints such as bandwidth, power and complexity. First, a robust coded scheme for progressive multimedia transmission is considered for an additive white Gaussian noise channel, a Rayleigh fading channel, and a frequency selective channel using in combination different unequal protection methods. We investigate the judicious use of the limited bandwidth through the combination and optimization of a progressive source coder, a rate compatible punctured convolutional code and a hierarchical modulation. Next, we investigate a novel packet formatting scheme for progressive sources using interleavers and various channel codes. The source coder is combined with a concatenated block coding mechanism to produce a robust transmission system for embedded bit streams. The objective is to create embedded codewords such that, for a particular information block, the necessary protection is obtained via multiple channel codings, contrary to the conventional methods which use a single code rate per information block. We show that near--capacity performance can be achieved using the proposed scheme in conjunction with low density parity check codes in a binary symmetric channel scenario. We finally focus on coding strategies for multimedia where the channel state information is missing. A generalized Digital Fountain (DF) code is proposed to provide efficient universal forward error correction solution for lossy packet networks with increased unequal error protection and unequal recovery time properties. We propose a progressive source transmission system using this generalized code design. We apply the generalized DF code to a progressive source and show that it has better unequal protection and recovery time properties than other published results.