Demand Determinant for Urban Freight Consolidation Center : A Case of Korea

Mohammad Khaled Afzal 인하대학교 물류전문대학원 2013 국내박사

Abstract Demand Determinants for Urban Freight Consolidation Center: A Case of Korea Mohammad Khaled Afzal Graduate School of Logistics, Inha University, Korea Advisor: Professor Yong Jin Kim Urban freight consolidation center (UFCC) becomes popular to the academician and policy makers due to its ability to improve economic, environmental and social conditions of urban logistics system. But the failure of many UFCCs in Europe provokes its sustainability analysis. Inflated estimation of demand in feasibility studies was one of the key reasons for these failures. Proper identification of customers for demand estimation is crucial for a sustainable UFCC. In order to help estimating potential demand for UFCC in Korea, this research identified the Korean transport company’s characteristics and their goods that are most feasible for UFCC. The basic framework of this research is to connect freight transport company’s operational characteristics with their responses for using UFCC. Since the company’s operational characteristics are mostly categorical or dichotomous and responses regarding future demand are hard to verify quantitatively, the key methodologies chosen for this analysis are Spearman rank order correlation and ordered logistic regression model. At this stage, a localized survey form was sent to the identified freight transport companies through E-mail. However it became difficult to get enough responses required for valid analysis. Therefore, respondents were interviewed personally by visiting to the cargo terminal and transport companies’ offices and thus valid numbers of responses were obtained. Primary survey data from the transport companies are analyzed by SPSS version 17. Four characteristics from three operational dimensions of transport companies were found significantly correlated (at 95% confidence level) with demand responses. Among these characteristics, number of employees and yearly revenue attributes are positively related with demand for UFCC. And vehicle’s (cargo) capacity and the attribute of “key suppliers as vendor, cooperatives, or other transport companies” are negatively related with the demand for UFCC. After relaxing confidence level to 15%, we have found revenues from cargo and container vehicle operations, vehicle ownership style, food and beverage freight, and the attribute of key suppliers being distribution companies are also correlated with demand for UFCC. Except cargo vehicle’s revenue attribute, all other new attributes were positively related with the demand for UFCC. The next task was to compare between the predictors so that we can find the most reliable measure for classification. The ordered logistic regression identified only two characteristics that are significant at 5% level of confidence. These are companies’ yearly revenue and the capacity of cargo vehicles. The significant beta parameter for the revenue at lower level category (Yearly 50B won or less) is negative which means that small revenue earning companies are less likely to opt for UFCC compared to higher revenue earning companies. On the contrary, the significant beta value for light capacity cargo vehicle (Below 8.5ton) is positive which indicates that the light capacity cargo vehicles are more likely to choose UFCC compared to heavy capacity cargo vehicles. Therefore, after descriptive, correlation, and regression analysis, this thesis finally recommends that, for estimating demand for UFCC, significant focus should be given on those transport companies who generate larger revenue but uses mainly light (small and medium) capacitated cargo vehicles. Other moderately potential user/ customers may be food and beverage transporters, transporters of distribution companies’ goods, container vehicles, and long contracted & self-owned vehicles. Besides, the companies dealing with container and express parcel deliveries and making mostly home deliveries could be also good prospect for UFCC. Key words: Urban, Freight, Consolidation, UFCC, Demand, Transport Companies, Logistics Characteristics, Preferences, Korea, Rank Order Correlation, Logistic Regression 국문요약 Demand Determinants for Urban Freight Consolidation Center: A Case of Korea 도시공동물류센테의 수요 결정요인 : 한국사례를 중심으로 아브잘 모하매드 갈래드 인하대학교 물류전문대학원 지도교수 김용진 도시 공동 물류 센터 (UFCC: Urban Freight Consolidation Center)는 도시물류시스템의 경제, 환경, 사회 상황을 지속적으로 개선시킬 수 있다는 기대를 받고 있어서 학술적뿐만 아니라 정치적으로도 많은 사람들의 주목을 받아왔다. 그러나 유럽의 각국에서 시도되었던 도시공동물류센터의 실패는 지속가능성에 대한 의구심을 품게 하여 이에 대한 분석의 필요성을 제기하였다. 타당성 분석 시 과도한 수요추정은 이러한 도시공동물류센터 실패의 주요 원인이다. 지속가능한 도시공동물류센터의 건립 및 운영을 위해서는 수요자에 대한 정확한 규정이 무엇보다도 중요하다. 본 연구는 한국에서 UFCC를 위한 잠재적 수요 추정을 위해서 UFCC에 가장 적합한 운송회사의 특성과 화물품목을 추정하였다. 본 논문은 기본적으로 UFCC 이용하고자 하는 의도를 가진 화물운송회사의 운영 특성을 파악하는 것이다. 이를 위하여 화물운송회사 명단을 파악하여 이를 대상으로 이메일 등을 통한 설문조사를 실시하였다. 그러나, 회사 운영에 대한 자료를 요구하고 있어서 설문조사 분석을 위한 유효한 숫자의 응답을 확보하는 것이 어려워서 화물터미널 등을 직접 방문하여 면접조사를 통하여 유효한 응답수를 확보하였다. 운송회사의 운영 특성은 대부분 범주적이거나 이분법적이며 현재 구현되지 않고 있는 도시공동물류센터 서비스에 대한 미래 수요를 정량적으로 확인하기 어렵기 때문에 이 분석을 위해 선택한 주요 방법론은 Spearman rank order Correlation과 순서형 로지스틱 회귀분석 모델이다. 운송회사의 기본 조사 데이터는 SPSS 17버전으로 분석하였다. 95% 신뢰도 수준에서 운송회사의 세 개의 운영 측면으로부터 네 가지 특성이 수요 응답과 유의하게 상관되었다. 이러한 특성 중, 직원 수, 연간 수익 특징이 UFCC에 대한 수요와 양의 상관관계가 있었다. 그리고 화물차의 적재 용량과 “판매자, 조합, 혹은 다른 운송회사와 같은 주요 공급업자”의 속성은 UFCC에 대한 수요와 음의 상관관계가 있었다. 신뢰수준을 15%으로 완화 시 화물 및 컨테이너 화물차 운영, 화물차 소유 형태, 식품 및 음료화물의 수익, 유통회사의 주요 공급업자의 특징이 UFCC에 대한 수요와 또한 상관됨을 알 수 있었다. 화물차의 수익 특징을 제외하고 다른 모든 새로운 특징은 UFCC에 대한 수요와 양의 상관관계가 있었다. 다음 과정은 분류를 위한 가장 신뢰할 수 있는 수단을 찾기 위해 특성을 비교하는 것이다. 순서형 로지스틱 회귀분석에서 5% 신뢰수준에서 유의한 단 2개의 특성, 운송회사의 연간 매출과 화물차의 적재용량을 확인하였다. 연간 500억 이하의 매출에 대한 유의한 베타 파라미터가 음이라는 것은 낮은 수익을 얻는 회사가 높은 수익을 얻는 회사보다 UFCC를 선택할 가능성이 낮다는 것을 의미한다. 반대로 소형 화물차(8.5톤 이하)에 대한 유의한 베타값이 양이라는 것은 소형 화물차를 소유한 회사가 대형 화물차를 소유한 회사에 비해 UFCC를 선택할 가능성이 더 높다는 것을 나타낸다. 따라서 본 논문은 설문조사 자료에 대한 기술적 분석, 순위순서 상관분석, 순서-순위 상관관계, 순서형 로지스틱스 회귀분석의 결과로 UFCC에 대한 수요 확보를 위해 매출액이 크고 주로 소형 화물차(소형/중형 포함)를 사용하는 운송회사에 초점을 맞출 것을 제안한다. 또한 UFCC의 잠재적 수요 운송회사 특성으로서 식품과 음료 운송업자, 유통회사의 상품 운송업자, 컨테이너 운송업자, 장기 고용 혹은 자차소유 업자들이다. 그리고 컨테이너, 익스프레스 소포 배달, 가정 배달을 취급하는 회사 또한 UFCC의 좋은 고객이 될 수 있을 것이다. 주제어 도시, 화물, 공동, 도시공동물류센터(UFCC), 수요, 운송회사, 물류 특성, 선호, 한국, 순위-순서 상관관계, 순서 로지스틱 회귀분석

Protein-Ligand Interactions Determined by Fluorescence Spectroscopy Chonnam National University Medical School Afzal Rana Aqeel : Protein-Ligand Interactions Determined by Fluorescence Spectroscopy

AFZAL RANA AQEEL 전남대학교 2024 국내박사

Almost all processes that occur in living organisms, such as DNA replication, gene expression and its regulation, and metabolic reactions, involve the interaction of biomolecules. Among these interactions, various methods are used to measure 'strong' interactions with low dissociation constants (KD), but methods for measuring 'weak' interactions with high KD are relatively insufficient. Among the molecules that make up the organism, there are those with high intracellular concentrations in mM ranges, such as glutathione, ATP, and NAD, and the interaction between these molecules and proteins becomes 'strong' enough to fill all binding sites in the protein, even if the KD is 'weak,' as much as 100 μM. Proteins exhibit intrinsic fluorescence by tryptophan and tyrosine residues. In this study, the interaction between proteins and biomolecules was determined by measuring the change in protein intrinsic fluorescence. Malate dehydrogenase (MDH) was used as a model protein to measure the dissociation constant between MDH and biomolecules. MDH of Escherichia coli did not have tryptophan residues but four tyrosine residues. In the present study, each tyrosine residue was converted to tryptophan to make four mutant MDHs, and the fluorescence properties of each mutant MDH were compared. Dissociation constants of substrate and product NADH, oxaloacetate, NAD, malic acid of MDH were determined and compared with enzyme’s kinetic constants. ATP, ADP, and GTP bound to MDH with higher affinity and inhibited enzyme activity noncompetitively. This study proposes a method that can effectively measure the interaction between proteins and ligands without any chemical modification of proteins or ligands. Fumarase C (FumC) is an enzyme that catalyzes the interconversion of fumarate and malate. In the present study, it was found that FumC of E. coli is a novel DNA-binding protein. The oligonucleotides used in DNA-binding studies of CRP (cAMP receptor protein) and HNS (Histone-like nucleoid structuring protein) were used in this study. The dissociation constants between each oligonucleotide and CRP, HNS, SspA, and FumC were measured by fluorescence spectroscopy. FumC seems to have sequence specificity in the binding between DNAs, FumC bound relatively higher affinity to oligonucleotides specific for HNS. Mutant that lacks the fumC gene from E. coli was prepared, and differences in gene expression between the wild type and mutant were examined. The expression of over 600 genes was doubled or halved, suggesting that FumC might bind to DNA under physiological conditions, affecting gene expression. It is a novel finding that FumC interacts with DNA, and we expect to be able to observe the regulation of gene expression by FumC in E. coli. The present study shows that fluorescence spectroscopy utilizing intrinsic fluorescence of proteins is useful for determining KD between proteins and DNA. DNA 복제, 유전자 발현 및 그 조절, 대사 반응 등 생체 내에서 일어나는 거의 모든 과정은 생체 구성 분자들의 상호작용을 수반한다. 이러한 상호작용 중에서 해리 상수(dissociation constant)가 작은, ‘강한’ 결합의 측정에는 다양한 방법들이 사용되고 있으나, 해리 상수가 큰, ‘약한’ 결합을 측정하기 위한 방법은 상대적으로 미흡한 실정이다. 생체를 구성하고 있는 분자들 중에는, glutathione, ATP, NAD 등 세포 내 농도가 mM 단위로 높게 존재하는 것들이 있고, 이들 분자들과 단백질 사이의 상호 작용은, 그 해리 상수가 100 µM 정도로 ‘약한’ 결합이라 할지라도, 단백질 내 모든 결합 자리에 이들 분자들이 채워져 있을 정도로 ‘강한’ 결합이 된다. 단백질은 트립토판과 티로신 잔기에 의해 고유 형광을 보이며, 본 연구에서는 단백질 고유 형광의 변화를 측정하여 단백질과 생체 분자들 사이의 상호 작용을 측정했다. 말산 탈수소효소(malate dehydrogenase, MDH)를 모델 단백질로 사용하여, MDH와 생체 분자들 사이의 해리 상수를 측정했다. 대장균에서 유래한 MDH에는 트립토판 잔기는 없고 티로신 잔기 4개만 있다. 본 연구에서는 각각의 티로신 잔기를 트립토판 잔기로 변환하는 돌연변이 MDH를 준비하여, 각 돌연변이 MDH의 형광 특성을 비교했다. MDH에 기질 또는 생성물인 NADH, 옥살로아세트산염, NAD, 말산 등의 해리 상수를 결정하고, 효소 동역학 상수와 비교했다. ATP, ADP, GTP가 MDH와 강하게 결합하고 비경쟁적으로 효소 활성을 억제함을 발견했다. 본 연구는, 단백질이나 리간드의 화학적 변형 없이, 단백질과 리간드 사이의 상호 작용을 효과적으로 측정할 수 있는 방법을 제시한다. Fumarase C (FumC)는 fumarate과 malate의 상호 전환을 촉매하는 효소이다. 본 연구에서는 대장균 유래 FumC가 DNA 결합 단백질임을 새롭게 발견했다. cAMP receptor protein (CRP)와 HNS (DNA-binding protein HNS)의 DNA 결합 연구에 사용된 적 있는 oligonucleotide들을 사용했다. 각 oligonucleotide들과 CRP, HNS, SspA, FumC 사이의 해리 상수를 형광 분석법을 측정했다. FumC가 DNA사이의 결합에는 서열 특이성이 있는 것처럼 보이며, FumC는 HNS에 특이적인 oligonucleotide에 상대적으로 더 강하게 결합했다. 대장균에서 fumC 유전자를 없앤 돌연변이체를 준비하고, 야생체와 돌연변이체 사이의 유전자 발현 차이를 조사했다. 600 여 유전자의 발현이 2 배 증가하거나 절반으로 줄어드는 것으로 관찰했으며, 이는 FumC가 생리적인 조전에서 DNA에 결합하여, 유전자 발현에 영향을 줄 수도 있음을 시사한다. FumC가 DNA와 상호 작용한다는 것은 새로운 발견이며, 대장균뿐만 아니라 여러 생물체에서 FumC에 의한 유전자 발현 조절을 관찰할 수 있을 것으로 기대하고 있다. 본 연구는 단백질과 DNA 사이의 해리 상수 측정에는 단백질의 고유 형광을 활용하는 형광분석법이 유용함을 보여준다.

Realization of spin field-effect transistors consisting of van der Waals 2-dimensional materials

Afzal, Amir Muhammad 세종대학교 대학원 2019 국내박사

그래핀은 스핀트로닉스 첨단소자의 개발에 주요한 역할을 할 수 있는 소재이다. 그러나 그래핀의 스핀-궤도 상호작용이 작기 때문에 스핀홀 효과, 스핀 전계효과 트랜지스터 (FET), 의미있는 위상상태가 발현되기는 어렵다. 그래핀의 독특한 에너지 밴드 구조는 그래핀의 위상적인 구조에 기인한 것인데 스핀-궤도 상호작용을 증가시켜 밴드 구조를 변형시키려는 시도가 최근 계속되고 있다. 이차원 전이금속 칼코겐화합물을 그래핀에 접합시키면 그래핀의 전기적 특성을 변화시켜 스핀트로닉스에 활용될 수 있는 특성이 나타날 수 있다. 전이금속 칼코겐화합물은 강한 스핀-궤도 상호작용을 가지므로 이차원에서 스핀수송 특성을 연구하는 분야에 적용될 수 있고, 반데르발스 이종접합을 연구하는 분야 등 새로운 연구분야에 적용될 수 있다. 이 논문은 그래핀에서 스핀-궤도 상호작용과 스핀 세차운동을 전기적인 방법으로 제어할 수 있음을 보여주고, 나아가 스핀 FET 개발에 대한 연구를 보여준다. 특히, 다층 WS2 반도체와 2층 그래핀 사이의 접합면에서 상호작용은 고급 스핀소자를 구현하는데 필요한 흥미로운 특성을 만들어낸다. 논문의 첫번째 부분은 얇은 WS2 층으로 이루어진 박막들 사이에 2층 그래핀을 끼어 있는 구조에서 그래핀의 스핀-궤도 상호작용의 변화에 대해 연구한 것이다. 우리는 상, 하층 게이트로 이루어진 이중 게이트 소자를 제작하여 게이트 전압에 가하여 그래핀의 스핀-궤도 상호작용을 조절하였다. 얇은 WS2 층으로 이루어진 박막들 사이에 2층 그래핀의 스핀-궤도 상호작용은 일반 그래핀과 비교하여 아주 크게 증가하였으며 저온에서 weak antilocalization 현상을 관찰할 수 있었다. Weak antilocalization 현상을 분석하여 스핀 이완시간이 일반적인 그래핀보다 10배 감소한 것을 발견하였다. 이러한 발견들을 확인하기 위하여 Shubnikov-de Haas 진동 현상을 실험적으로 살펴보았으며 우리가 만든 구조에서 zero-field spin-splitting을 확인하였다. 두 가지 다른 방법(weak antilocalization, Shubnikov-de Haas 진동 현상)으로 측정한 스핀-궤도 상호작용의 크기는 매우 유사한 값으로 나타났으며 게이트 전압에 대한 의존성도 비슷하게 관찰되었다. WS2 층에 끼어 있는 2층 그래핀은 스핀-궤도 상호작용이 전기장으로 제어할 수 있으므로 스핀트로닉스 응용소자로서 혁신적인 시스템이 될 수 있음을 보여준다. 논문의 두번째 부분에서는 2층 그래핀 위에 WS2 층을 형성하여 스핀 FET를 제작한 것을 보여준다. 게이트 전압으로써 Rashba type 스핀-궤도 상호작용을 제어하여 스핀 세차운동을 조절하여 스핀 FET 작동을 보여주었다. 스핀-궤도 상호작용의 크기가 게이트 전압에 의존하여 변하는 것을 Hanle 신호를 측정하여 실험적으로 확인하였다. 아울러, 스핀 FET가 상온에서 작동하는 것으로 보여 주었다. 논문의 세번째 부분에서는 단층 그래핀 위에 Pb/Au (1 nm/10 nm) 층을 증착하여 스핀-궤도 상호작용의 크기가 변화되는 것을 관찰하였다. 이러한 시스템에서 스핀-궤도 상호작용의 크기가 80 meV로 증가되었으며, 매우 큰 스핀홀 효과를 불러일으키는 것을 non-local 신호 측정으로 확인하였다. 게이트 전압에 의존하는 weak localization 효과를 관찰하였고, 스핀-궤도 상호작용의 크기와 스핀 이완시간을 구해낼 수 있었다. 상온에서 관찰된 스핀홀효과는 스핀응용소자 개발에 새로운 전형을 제시해 줄 수 있으리라 생각한다. 게이트 전압에 의한 스핀-궤도 상호작용의 제어는 스핀 전류, 스핀 세차운동, 전자의 스핀 자유도를 조절할 수 있으므로 새로운 소자 응용의 장을 열 수 있으리라 기대한다. Graphene has an enormous potential in the development of advanced spintronic devices. It is a promising material with intrinsically small spin-orbital interaction (SOI), making the realization of some interesting and practically impossible phenomena such as the spin Hall effect (SHE), spin field effect transistor and non-trivial topological states. The electronic band structure of graphene is owing to interesting topological characteristics and strength to stimulate a systematic method to improve SOI extrinsically. The interfacial interactions of graphene sheet with semiconducting transition metal dichalcogenides (TMDs) cultivate the electronics and spintronics properties drastically, making it an intriguing candidate for spintronic applications. Transition metal dichalcogenide materials are studied to investigate such unexplored research avenues as spin transport behavior in 2-dimensional materials due to their strong spin-orbital interaction (SOI) and the proximity effect in van der Waals (vdW) heterostructures. This thesis demonstrates the realization of a spin field effect transistor (spin-FET) by successfully controling the spin-orbital interaction and spin precession angle in graphene through electrical means. Specifically, the interfacial interactions between the bilayer graphene (BLG) and multilayer tungsten disulfide (ML-WS2) give rise to fascinating properties for the realization of advanced spintronic devices. In the first portion, we designed a bilayer graphene (BLG) encapsulated by thin layers of tungsten disulfide (WS2) to explore the interface-induced spin-orbit interaction. We successfully fabricated a dual-gated device, where the strength of spin-orbital interaction is tuned by gate voltages. The strength of such induced spin-orbital interaction in the graphene is intensely elevated, which leads to a robust weak antilocalization effect at low temperature. The quantitative analysis of the weak antilocalization effect exhibits that the spin relaxation time (τ_so ) is 10 times smaller in magnitude than in graphene on traditional substrates. To support these outcomes, we also studied Shubnikov-de Haas oscillations, which give unambiguous confirmation of the zero-field spin-splitting in our heterostructure device. The spin-orbit interaction constants estimated by two different types of measurement (the WAL effect and SdH oscillations), demonstrating close values as a function of gate voltage, supporting the self-consistency of this study’s experimental outcomes. The gate modulation of the spin-orbital interaction in bilayer graphene encapsulated by WS2 nano-flakes establishes an innovative system to explore the manipulation of spin-dependent transport through an electric field. In the second part, a BLG/ML-WS2 vdW heterostructure spin field-effect transistor (FET) is fabricated to demonstrate the gate modulation of Rashba-type SOI and spin precession angle. The gate modulation of Rashba-type SOI and spin precession has been confirmed using the Hanle measurement. The change in spin precession angle agrees well with the local and non-local signals of the BLG/ML-WS2 spin FET. The operation of a spin FET in the absence of a magnetic field at room temperature is successfully demonstrated. Further, we designed a graphene field effect transistor (FET) with lead (Pb) layer intercalated between graphene (Gr) and gold (Au) to stimulate the SOI and studied the effect on the strength of the SOI. The SOI in our system is dramatically elevated to 80 meV, which leads to a giant non-local signal. We observed a strong SHE with non-local signal up to ~ 180 Ω at room temperature without applying any external magnetic field (B) and ferromagnetic contacts. Further, we extract spin key parameter from length and width dependence of nonlocal measurement. To support these findings, we also measured the temperature and gate-dependent weak localization (WL) effect. The quantitative analysis of WL in graphene gives SOI and spin relaxation time. The calculated SOI by two different methods demonstrates close values. The observation of a giant SHE at room temperature is an important step to introducing a new plate form to explore the spin-based concept and applications. The gate control of spin precession at room temperature is an interesting step in the field of spintronics. These outcomes may open a new platform for the manipulation of spin current, precession, and spin degree of freedom of electrons. Furthermore, an innovative ML heterostructure of BLG/ML-WS2 successfully developed as a spin FET to address the challenges of injection, detection, and gate modulation of spin precession angle in spintronics. First of all, the local spin valve (LSV) measurements were conducted at room temperature and 30 K to examine the spin valve behavior in the BLG/ML-WS2 spin FET on SiO2. We observed a distinct and noticeable spin signal and the change in resistance was (∆R=5.85 mΩ) at Vbg = 0 V. We also measured the local signal as a function of Vbg at different temperatures and B = 0 T for each magnetization alignment of the injector and detector. For all magnetization configurations, we observed clear oscillations of the local spin signal as a function of Vbg at room temperature and 30 K. Further, we also made a graphene/Pb/Au heterostructure field effect transistor. For the first time, we used lead (Pb) as an intercalated layer between the graphene and Au and measured SOI in heterostructure device in local and non-local measurement configurations. Intercalation of Pb thin layer between Au and graphene leads to momentous modification of the electronic structure and SOI of graphene. We observed a giant spin Hall effect (R_NL~180 Ω) in the absence of any external magnetic field and with out ferromagnetic leads. To further quantitatively examine the improvement in the magnitude of SOI in graphene with temperature and back gate voltage, we fit our magneto-conductivity data by using the theory of WL. The calculated values of SOI in graphene through non-local configuration and WL analysis give close results, supporting the self-consistency of this study’s experimental results. The effective improvement of SOI in the graphene-based system opens a new gateway to explore new areas of the spin field-effect transport (FET) phenomenon.

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.

The Design and Analysis of a Secure Routing Protocol for Mobile Ad Hoc Networks

Afzal, Syed Rehan 아주대학교 정보통신대학원 2008 국내석사

An Ad hoc network is a collection of wireless mobile nodes communicating with each other through a temporarily created infrastructure-less network without any centralized administration. Routing scenario in ad hoc networks is different from infrastructure-based wireless networks; since in ad hoc networks each node acts as a router and is responsible for managing topological information and ensuring correct route learning. Although a number of secure routing protocols have been proposed so far, all of them have certain advantages and disadvantages. Hence, security in ad hoc networks is still a contentious area. In this paper we first explore the security problems and attacks in existing routing protocols and then we present the design and analysis of a new secure on-demand routing protocol, called RSRP which confiscates the problems mentioned in the existing protocols. Moreover, unlike Ariadne, RSRP uses a very efficient broadcast authentication mechanism which does not require any clock synchronization and facilitates instant authentication.

802.16e WiMAX 시스템에서 초기 Ranging Detection 능력 향상과 Time Synchronization 향상을 위한 알고리즘

Afzal, Muhammad Usman 한양대학교 대학원 2008 국내석사

An OFDM system performance highly depends on synchronization between the transmitter and the receiver. When a new SS or MSS is trying to enter a network, it is not synchronized. Initial ranging is proposed for IEEE 802.16e systems for synchronization. In 802.16e OFDMA system code division multiple access (CDMA) codes are used to improve the system efficiency in detecting the new user. A new MSS will transmit one of the predefined CDMA codes, which should be detected at the BS. The BS is not only to detect the new MSS but also to calculate its timing, frequency and power offset. Initial ranging is inherently affected by the channel selectivity and other users' interferences at low SNR. We present an enhanced ranging scheme using modified generalized chirp-like (GCL) sequences that improves ranging detection process using the combine multiple FFT blocks and cope with channel selectivity and other user’s interference at low SNR. Based on the ranging detection timing offset is calculated for synchronization.

Numerical Analysis and Design Optimization of Pressure- and Electroosmotically-Driven Liquid Flow Microchannel Heat sinks : 미세유로열방출기의 압력강하 및 전기삼투에 대한 수치해석 및 최적설계

Afzal Husain 인하대학교 대학원 2010 국내박사

A liquid flow microchannel heat sink (MCHS) has been analyzed and optimized using numerical analysis and surrogate methods for pressure-driven flow (PDF), electroosmotic flow (EOF) and combined flow (PDF+EOF). A silicon-based liquid flow MCHS was studied numerically applying three-dimensional numerical analysis for fluid flow and conjugate heat transfer coupled with surrogate methods and a search algorithm. The various geometric parameters sensitive to MCHS performance were identified to form the design variables which are representative to the MCHS design. The performance of the MCHS was analyzed in terms of overall thermal resistance (this includes conductive thermal resistance, caloric thermal resistance and convective thermal resistance) and pumping power which is required to drive the fluid through MCHS. The electroosmotic flow is developed in an aqueous solution in the presence of surface charge by applying an external electric field along the channel. The MCHS has been studied and characterized for pure PDF, pure EOF and combined flow (PDF+EOF). The effects of Debye layer thickness and zeta potential on the heat and fluid flow characteristics were investigated. The performance of the MCHS was enhanced through the application of EOF which assists the PDF to increase the flow rate. The optimization was first performed for single objective that was overall thermal resistance of the MCHS at constant pumping power and then multi-objective optimization was performed for both thermal resistance and pumping power using evolutionary algorithm. The mathematical model for MCHS was first designed for two design variables and later extended to include three design variables to examine the effect of each design variable. The cooling performance of the MCHS is highly sensitive to surface convection and area subjected to convective heat transfer. Therefore, the surface of the MCHS was roughened through the designed-roughness elements particularly rectangular ribs on the side walls which comprised most of the area subjected to convective heat transfer. In optimization, various surrogate models, viz., response surface approximations (RSA), Kriging (KRG) and radial basis neural network (RBNN), were applied to construct the approximate function for the performance objectives to find out the optimal solutions. The optimal point was searched through the sequential quadratic programming (SQP) for single objective optimization whereas for multi-objective optimization evolutionary algorithm was applied along with surrogate models. It was observed that MCHS can be effectively optimized using surrogate methods and evolutionary algorithms. The performance of the MCHS was significantly improved through the optimization methodology. The effectiveness of various design variables were predicted, and trade-off between the performance-objective functions was found out to achieve a robust and economical design of MCHS.

Influence of potential decorativeness in Iranian calligraphy on contemporary visual art in Iran

Afzal Tousi, Effatolsadat Hong Ik University 2002 국내박사

Persimmon leaves (Diospyros kaki) extract enhances the viability of human corneal endothelial cells by improving Na + /K +- ATPase activity

Afzal, Ramsha 가톨릭대학교 대학원 2022 국내박사

신채호와 쁘렘짠드 소설의 비교 연구

Khan, Afzal Ahmad 경북대학교 대학원 2011 국내석사

The purpose of this thesis is to examine a comparative analysis of Korean and Indian Literature during the colonial period of both countries from the point of view of anti colonialism and anti imperialism literary works of Korean Writer Shin Chae Ho and Indian Writer Premchand. The relationship between Korea and India has been getting closer day by day and along with this, the research works of both countries scholars are rapidly increasing in the various fields including language, culture and literature. However, the study on the topic of comparative literature of both countries during the colonial period is a very important subject for the discussion. Unfortunately it has been ignored and not yet done properly by both countries Scholars. Moreover, Korea and India suffered patheticly during the colonial period of Japan and British respectively till near the end of second world war. After the end of world war both countries liberated from the colonialization. But unfortunately both countries divided into two parts due to the different ideologies of politicians. Korea divided into South Korea and North Korea on the basis of political ideology. On other hand, India divided into India and Pakistan on the basis of political ideology as well as so called religion. On these similar point of view of both countries, Researcher felt keenly the necessity of a comparative study of both countries anti colonial and patriotic writings during the period of colonialism. In the consideration of above points, Researcher selected two representative nationalist Writers from the both countries respectively for analyzing the subject of both countries pitiful condition of colonial periods, and focused on the national identity of both countries during the colonial period. This comparative study of both Writers literary works and their ideology of anti colonialism will help to the both counties scholars and general people to understand the condition of Japanese colonialization in Korea and British colonialization in India. Also thesis is focusing on the locations of culture of both countries during that period through Shin Chae Ho and Munshi Premchand’s literary writings respectively. Though both Writers does not have any direct influence or relationship with each other, but there are many similarity in their literary works and life. For instance, their anti colonialist ideologies, anti impartialist discourses and both Writers clearly show their purpose to make people realize the patriotism and understand its important. Moreover, both Writers was born in the same year in 1880 and deceased in the same year in 1936. This thesis is consisted into five chapters respectively. First chapter is focusing about the purpose and goal of research, and examined the previous scholars research works on the both Writers Shin Chae Ho and Premchand. Second chapter is focusing on the both Writers important descriptions of the life, both Writers writing activities, realization of colonial eras, and literary ideology respectively. Both Writers were born in the poor families and realized the problems of colonialization in the very early age respectively. Thus, Shin Chae Ho and Premchand started writing activity form the early in 1900s. And their literary writing was filled with full of patriotism. Through this point of view, both Writers tried to express the importancy of patriotism to the whole nation during the colonial period through their countless patriotical literary writings respectively. Third chapter is illuminating a comparative analysis of both Writers six selected novels which reveal the anti colonialism and anti imperialism nature, as well as full of patriotic ardor. Korean Writer Shin Chae Ho’s three well known novels selected for the analysis are “Future Dream of The Earth”, “A tale of the beauty told by 100 year old Monk”, and “Fierce battle of two Dragons”. And Premchand’s selected novels are “Here is my motherland”, “The Shroud”, and “The most precious gem of the world”. Moreover, third chapter is consisted into three parts. First part is focusing how both Writers are expressing their deep emotions to the people of their country during the colonial period through their novels “Future dream of the earth” and “Here is my motherland”. Second part of this chapter is mainly focusing that how imperialism was extorting and looting to the poor people in the colonial countries through Shin Chae Ho’s novel “A tale of the beauty told by 100 year old Monk” and Premchand’s novel “The Shroud”. Third part of this chapter is focusing on the relationship condition of exploited people of two countries’ colonialist Japan and England respectively through Shin Chae Ho’s novel “Fierce battle of two dragons” and Premchand’s novel “The most precious gem of the world”. Fourth chapter is illuminating the patriotic literature and writing technique of both Writers. Though the result of this research clears both Writers novels and other literary works main theme are the patriotism. However their way of expression were technically different form each others. Shin Chae Ho’s selected the allegorical technique, in other hand Premchand used realism technique. Therefore, this research illuminate that both Writers were a great nationalist in their country and devoted their whole life for the nation. In a conclusion, today we need to learn a lot from both Writers ideologies, devotions for the nation through their literary works.