Proposition and verification of an energy saving secondary control swing for hydraulic excavator

Puja, Chowdhury 울산대학교 대학원 2016 국내석사

Energy efficiency has become a major research issue in all fields of engineering. Consuming rate of energy and pollution is more and more serious nowadays, so research on energy saving of hydraulic excavators has great interpretation because of their large application quantities, high energy consumption and bad exhaust. The rotating movement of excavator is called swing or slew and is driven hydraulically. In the swing braking time the remaining fluid will save as energy by a simple accumulator. This remaining save energy will use in the system from accumulator. Proposed swing system have some dissimilarities from the conventional swing system. The proposed system is considered as secondary by using two combination of transformer (motor & pump combination). The effect of accumulator capacity in the save energy is basically discussed. With different motor and pump parameter, comparison result of the proposed Secondary swing system and conventional system is also discussed. Furthermore, simulates variable inertia and show the effect of variable moment of inertia in different simulation result .Different simulation result with different parameter will show the change of proposed secondary swing systems different criteria. The proposed system will be developed in AMESim software. Depends on some specific parts parameter variation, the proposed system will be more efficient in saving energy.

Wave Energy Harvesting with Enhanced Oscillating Water Column Technology

Olly Roy Chowdhury 순천대학교 대학원 2015 국내박사

The growing consumption of energy is fueled by an increasing population together with its improving living standard and it is consecutively diminishing the resources like oil, coal and natural gas. There is no doubt that renewable energy is the only option left for facing the future energy crisis. The most plentiful solar energy has the drawback that solar cells are very expensive to till date and it is land based mainly which adds cost and reduces efficiency. As a solution to this problem, this study focuses on other renewable source like ocean energy, which is abundant. Oscillating water column technology is frequently used for harvesting ocean or wave energy. But this suffers from performance disruption due to rough ocean weather. As renewable energy is all about using natural resources, and nature is unpredictable totally, so extracting maximum power from any system, in any irregular natural condition is very important otherwise the system will be derailed from its goal of perfection. In light with this, we invented two new wave energy harvester devices for conversion of hydro power into electricity: Closed type OWC and Double Chambered Backward Bend Duct Buoy. This thesis is centered on the modeling, numerical analysis and application of these devices and also a new, improved, adaptive step size maximum power point tracking (MPPT) algorithm is proposed here to extract power at the maximum level of system’s limit. The proposed WECs are ecofriendly, land saving, simple in structure and require less maintenance through their lifetime, thereby being cost effective in many ways. These two devices are expected to be more efficient as compared to other traditional WECs, avoiding the common environmental hurdles that would hamper the normal power extracting activities of the existing OWC or BBDB type WECs. The structural betterments performed in these devices and the upgradation done beyond the traditional MPPT algorithm, are anticipated to work thus. Analysis has been done to study the effect of different scenarios like device sizing parameters, chamber ratios and environmental parameters like wave height and wave period, on the power output of the converter. Result study through MATLAB simulation showed some interesting findings about device sizing and environmental factors which will help in further development and installation of the system. New adaptive step size MPPT algorithm stated here uses least measuring equipment but is faster than other complex algorithms and can be applied in air driven turbine based WECs like OWC or BBDB as well as in standalone wind turbines. The study can have important impact in designing, application and implementation of OWC based wave energy converters as well as extracting power at maximum power point from these. Key Words:Ocean Energy Harvesting, Wave Energy Converter, Closed OWC, Double Chambered BBDB, Adaptive Step Size MPPT Algorithm.

한국인의 thromboxane A2 synthase (CYP5A1) 유전자 변이발견과 기능적 연구 : Genetic Findings and Functional Studies of Thromboxane A2 Synthase (CYP5A1) Polymorphisms in a Korean Population

Kamrul Hasan Chowdhury 인제대학교 대학원 2012 국내석사

ABSTRACT Genetic Findings and Functional Studies of Thromboxane A2 Synthase (CYP5A1) Polymorphisms in a Korean Population Md. Kamrul Hasan Chowdhury (Advisor: Professor Jae-Gook Shin, MD, PhD) Department of Medicine, Graduate School Inje University Thromboxane A2 synthase, a cytochrome P450 enzyme CYP5A1, catalyzes the conversion of prostaglandin H2 to thromboxane A2 (TXA2), which has potent biological activities as a mediator of platelet aggregation, vasoconstriction and bronchoconstriction. TXA2 has been implicated in the patho-physiological process of a variety of diseases, such as atherosclerosis, myocardial infarction, stroke and asthma. On the basis of the hypothesis that variations of the CYP5A1 gene may play an important role in blood hemostasis and cardiovascular related diseases, we screened for genetic variations in CYP5A1 gene in a healthy Korean population. We analyzed genomic DNAs from 50 Korean subjects, for identification of genetic mutations in the promoter region, the protein coding sequences and the non-coding region of the CYP5A1gene. Twenty-five single nucleotide polymorphisms have been identified; seven in exon, thirteen in intron and five in 5’-untranslated region (UTR) in the CYP5A1 gene. Six amino acid coding variants include Leu71Phe, Val295Met, Glu388Lys, Ala428Thr, Pro512Leu and Arg534His. Among them Leu71Phe (2%) and Arg534His (1%) are newly identified variants in the present study. All of coding variants could be expected to alter protein structure and function. All of twenty-five variants were used to characterize linkage disequilibrium (LD) and haplotype diversity at the CYP5A1 locus, which resulted in one LD block with selected haplotype structures. Ethnic different frequencies of CYP5A1 variants and haplotype structures were found. This is the first report of CYP5A1 genetic variants identified in Korean population. Discovery and functional characterization of the CYP5A1 variants in Koreans would be useful information in understanding blood hemostasis and its related pathophysiology in clinical settings. Keywords: Thromboxane synthase, thromboxane A2; Cytochrome P450 5A1; Single nucleotide polymorphism (SNP), Genetic polymorphism; Pharmacogenetics; Functional genetics; Platelet activation; thromboxane synthase (CYP5A1); Mutation detection; Cardiovascular diseases. 국문초록 한국인의 thromboxane A2 synthase (CYP5A1) 유전자 변이발견과 기능적 연구 Md. Kamrul Hasan Chowdhury (약리학전공) (지도 교수: 신재국) 의학과 인제 대학교 대학원 트롬보산 A2 합성효소 (Thromboxane A2 synthase, CYP5A1)는 프로스타글란딘 H2를 트롬보산 A2 (TXA2)로의 전환을 촉매한다. TXA2는 혈소판 응집, 혈관수축 을 나타내는 활성을 나타내며 동맥 경화증, 심근경색, 뇌졸중과 천식과 같은 다양한 질병의 병리생리적 과정에 연관되어있다. CYP5A1 유전자 변이체들은 TXA2 합성에 영향을 미치기 때문에 심혈관 관련 질병에서 주요한 역할을 나타낼 수 있다는 가설을 근거로 하여, 본 연구에서는 한국인 에서 CYP5A1 유전자 변이발굴 분석 하였다. CYP5A1 유전자의 프로모터 영역, 단백질 암호화 서열과 인트론영역에서의 변이체 발굴을하기 위하여 50명의 표준 한국인으로부터 genomic DNA를 분리하여 직접적인 DNA sequencing을 통하여 CYP5A1 변이체를 발굴하였다. 그 결과 CYP5A1 유전자에서 엑손에서 7개, 인트론에서 13개 그리고 프로모터에서 5개로 총 25개의 단일염기 다형성 (single nucleotide polymorphism)들을 동정하였다. 이들중 6개의 아미노산 coding 변형체들은 Leu71Phe, Val295Met, Glu388Lys, Ala428Thr, Pro512Leu와 Arg534His로 확인 되었다. 이들 단백질 변이체들은 CYP5A1 단백질구조와 활성에 영향을 미칠것으로 예상되고 있으며 한국인에서 처음으로 발굴된 단백질 변이체는 Leu71Phe (2%) 와 Arg534His (1%) 가 포함된다. 발굴된 변이체를 이용하여 연관불균형 (linkage disequilibrium, LD)과 haplotype 다양성을 분석하여 LD block과 주요 한국인 Haplotype 분포도를 확인하였다. 본 연구는 처음으로 한국인에서 CYP5A1 유전자의 유전적 변이체를 발굴 분석한 보고이며 한국인의 CYP5A1 변이체의 발견과 기능연구는 혈소판 및 심혈관 관련 질병의 예방과 치료에 도움을 주는 중요한 자료가 될 것으로 사료된다. 색인단어: Thromboxane synthase, thromboxane A2, Cytochrome P450 5A1, Single nucleotide polymorphism, Pharmacogenetics, Functional genetics, Platelet activation.

Role of corporate governance on the performance of microfinance institutions(MFIs): : A case study on selected MFIs of Bangladesh

CHOWDHURY Monir Hoss Ajou University, Graduate School of International 2013 국내석사

This research explores and explains the relationship between corporate governance and performance of Microfinance Institutes (MFIs) in Bangladesh utilizing an in-depth qualitative case study. Rapid growth in the microfinance industry and MFIs’ transformation into regulated entities capturing savings and deposits demands clear articulation of effective corporate governance. Notwithstanding its significance, there is a paucity of scholarly work on this issue, the existing ones not being able to take MFIs specific issues into account and dig deeper into the issue to facilitate the understanding of the intricacy of the mechanism. Thus, till there exists vacuum in the area of in-depth analysis of MFIs governance mechanism and performance. This is essential because unlike general financial institutions created with a single objective of making profits, MFIs often have diversified functions, microcredit operations being one of those functions. Moreover, the source of financing also influences the governance mechanism of MFI. Taking all these issues together, this research focuses on more nuanced in-depth analysis of selected number of MFIs. This thesis takes four of the leading microfinance institutions of Bangladesh and their respective governance mechanism along with their performances as the unit of analysis. The country still leads the global microfinance industry both in terms of its sheer size and productivity. This research found evidences that, although the MFIs industry in Bangladesh has commendable success, and the selected MFIs are indeed performing very well so far the MFIs dual mission are concerned, still there is ample scope for improving the corporate governance practices, and institutionalizing those norms owing to the fact that most of the MFIs have increased focus on sustainability. It was also evident that, even for very large and seemingly well established MFI like Grameen Bank, governance crisis may pose significant threat. The regulatory authority does not have enough teeth to have efficient mechanism for supervision. The MFIs suffer from “founder syndrome” which should be neutralized by adopting appropriate succession plan. As many NGO-MFIs are undergoing transition, while large MFIs are venturing increasingly on profitable projects, the financial restructuring should be done very carefully, so that the double bottom line can be maintained.

Confined rapid thermolysis/FTIR/ToF studies of energetic ionic liquids

Chowdhury, Arindrajit The Pennsylvania State University 2010 해외박사(DDOD)

Current research is focused on the identification of the initiation and secondary reactions occurring during the thermal decomposition of energetic ionic liquids (EILs). The synergistic diagnostic tools, rapidscan Fourier transform infrared (FTIR) spectroscopy and time-of-flight mass spectrometry (ToFMS), were utilized in conjunction with confined rapid thermolysis. The thermal decomposition involved submilligram quantities of each compound subjected to heating rates of 2,000K/s and temperatures to 435°C in an ambient inert gas at one atm. The objective of this research is to gain a thorough understanding of the reaction pathways and their corresponding rate parameters that govern the pre-ignition thermal decomposition of EILs. Although particular focus is laid on isolation of the initial reaction pathways, a detailed understanding of the effects of ring structure and the type and location of substituent groups on the secondary reactions are also of interest. The imidazolium salts comprised of 1-ethyl-3-methyl-imidazolium as the cation, and NO3-, Cl-, and Br- as the anions, and are found to be thermally most stable among the three families of salts. Examination of the evolution of gas-phase species reveal that the most probable sites for nucleophilic transfer and subsequent secondary reactions are primarily the methyl group and secondarily the ethyl group. The triazolium family is formed by pairing the 4-amino-1,2,4-triazolium cation with chloride (4ATCl), and nitrate (4ATN) anions, and rank second in thermal stability. Whereas a proton transfer from the N1 position primarily initiates decomposition in 4ATCl, the amino group is found to primarily participate in the initiation reaction in case of 4ATN. The substituted triazolium salts formed by pairing the 1-methyl-4-amino-1,2,4-triazolium and 1-methyl-4-amino-1,2,3-triazolium cations with iodide and nitrate salts are also found to initiate decomposition through the amino group. The compounds studied from the tetrazolium family are 2-amino-4,5-dimethyl-tetrazolium iodide (2AdMTZI) and nitrate (2AdMTZN), and 1-amino-4,5-dimethyl-tetrazolium iodide (1AdMTZI) and nitrate (1AdMTZN). The major decomposition pathway involves a nucleophilic transfer to the anion leading to the formation of methyl iodide and methyl nitrate, from 2AdMTZI and 2AdMTZN, respectively. Unlike the 2AdMTZ salts, the 1AdMTZ salts are found to initiate decomposition through three major pathways---formation of the corresponding methylated anion and 1-amino-5-methyl-tetrazole, formation of ammonia by the amino group, and expulsion of nitrogen from the tetrazole cation itself. The Arrhenius-type reaction rate parameters for the initiation reactions governing the thermal decomposition of several EILs are obtained by an evolutionary genetic algorithm that compares the difference between the experimental and simulated species evolution profiles from the decomposition process. The processes governing the decomposition of these energetic compounds are found to be autocatalytic in nature, and the autocatalytic agents are the strong acids generated by the initial decomposition step. Additionally, the pre-ignition condensed phase chemistry during the hypergolic reaction between 1-ethyl-3-methyl-imidazolium dicyanamide and nitric acid is analyzed by a modified confined rapid thermolysis setup under isothermal conditions.

(A) Secure and Efficient Low-power Bootstrapping and Commissioning Protocol for 6LoWPAN

Chowdhury Md. Aminul Haque 아주대학교 일반대학원 2010 국내석사

This thesis is devoted to define a novel bootstrapping protocol for 6LoWPAN (IPv6 based Lowpower Wireless Personal Area Network). Bootstrapping is the way of associating a new node with a specific network with or without minimum human intervention and gets connected with the desired network. Generally, the gateway or the Personal Area Network (PAN) coordinator of a 6LoWPAN network is multihop away from new sensor nodes. In this thesis, we propose a novel protocol ?gLow-power Bootstrapping and Commissioning Protocol (LBCP)?h for 6LoWPAN which satisfies multihop property of 6LoWPAN. In our protocol we assume three different kinds of sensor nodes called a new device as LBD, an already bootstrapped device as LBA, and the gateway or the PAN coordinator as LBS. An LBA helps an LBD to communicate with the LBS and eventually gets connected with the network. For secure authentication of new sensor nodes we propose to use existing EUI-64 address and ?gjoin key?h which are known by the LBS. We call this method as centralized approach. We also introduce the concept of semidistributed approach where ?gjoin keys?h of new nodes are randomly distributed to agent nodes or LBAs, and LBAs can perform bootstrapping actions without help of the LBS. We propose two novel LBA selection algorithms to select the best LBA in the bootstrapping phase for both centralized and semi-distributed approaches. To prevent denial-of-service (DoS) attack in the bootstrapping phase we provide some roles to LABS and already commissioned devices, and define a blacklisting policy in the LBS. To show the effectiveness of our protocol we simulate our protocol in a discrete event simulator called QualNet. The simulation results show that our protocol is scalable as well as efficient in terms of number of control packets exchanged in the bootstrapping phase and average end-to-end delay between LBD and LBS. We compare LBCP with basic flooding scheme where bootstrapping is performed using only broadcast of request and reply messages. Latter, we discuss about various security attacks in bootstrapping phases and how we can provide solution for those attacks. Finally, we argue that the usage of agent nodes is very useful for secure network bootstrapping of 6LoWPAN.

Efficient Techniques for Utility-Based Pattern Mining

Chowdhury Farhan Ahmed 경희대학교 2010 국내박사

Traditional frequent pattern mining methods consider an equal profit/weight for all items and only binary occurrences (0/1) of the items in transactions. Therefore, utility-based pattern mining is a necessary research issue in data mining in order to consider different utility values of items. Recently, high utility pattern (HUP) mining becomes a challenging utility-based pattern mining problem by considering the non-binary frequency values of items in transactions and different profit values for each item. But, most of the existing HUP mining algorithms suffer in the level-wise candidate generation-and-test problem and generate too many candidate patterns. Moreover, they need several database scans which are directly dependent on the maximum candidate length. In this thesis, we present an efficient tree-based candidate pruning technique to solve these problems in HUP mining. However, many real-life databases are dynamic in nature, i.e., insertions/deletions/modifications operations can be occurred very frequently in those databases. The existing HUP mining algorithms are not suitable for incremental and interactive mining. In this thesis, we propose three efficient tree structures for incremental and interactive HUP mining. To capture the recent change of knowledge in a data stream adaptively, we propose an efficient sliding window-based HUP mining algorithm. This thesis also introduces the concept of applying a dynamic weight for each item and proposes an efficient algorithm to handle it in utility-based pattern mining. Furthermore, this thesis introduces a framework for high utility sequential pattern mining and proposes efficient techniques to mine high utility sequential patterns in sequence databases. Extensive experimental analyses show that our proposed above techniques are very efficient and significantly outperform the existing algorithms.

(A) Study on bias, light and humidity induced instabilities of amorphous indium-gallium-zinc oxide thin-film-transistors

Chowdhury, Md Delwar Hossain 경희대학교 대학원 2016 국내박사

Amorphous Indium-Gallium-Zinc-Oxide Thin-Film-Transistors (a-IGZO TFTs) are considered as a most prospective channel materials in TFT families owing to higher field effects mobility>10cm2 /V-s, very low off current, smaller subthreshold swing (~0.2V/decade) and acceptable large area uniformity, which is comparable with conventional a-Si:H and poly crystalline TFTs. It shows very good characteristics with active thickness 5 to 100nm, some cases thinner one shows better performances, which may be impossible with other technology. Amorphous oxide semiconductor (AOS) are very sensitive to hydrogen and oxygen molecule, the carrier concentrations mainly controls by changing the hydrogen and oxygen amounts, substantially controls electron mobility. The most difficulty of AOS based devices are the generation of specific amount of carrier concentration 1015~19 cm-3 to find a good performances TFTs, can be controlled by the Ar/O2 flow rate during sputtered deposition. It assume that hydrogen acts as a donor and oxygen acts as an acceptor in all AOS semiconductor. With 20nm thick a-IGZO devices, it is possible to fabricate high performance etch stopper (ES) and back channel etch (TFTs). In dual gate (additional top gate metal with bottom gate inverted staggered TFT) dual (top and bottom gate are tight together) driving TFT structure, it observed that 20nm a-IGZO film cannot accumulate electrons fully during singe gate sweep measurement. The a-IGZO TFT performances checked many times and recently no significant difference observed both for ES and BCE TFT. Now, important things is the aging effects of a-IGZO TFTs, which will be used for large area flexible and transparent display. The objective of my dissertation is to understand the effects of electrical (positive bias stress/negative bias stress), optical and environmental stability of a-IGZO TFTs. Positive gate bias stress (PBS) in dark shows the positive transfer shift, without any change of mobility, swing and hysteresis. The shift increases with applied gate bias amplitude, stress time and activation temperature. Negative charge (electron) trapping inside gate insulator, a-IGZO/gate insulator interfaces, charge migration by electron trapping and acceptor like defects can be possible reason of PBS. In our investigation, PBS stress and recovery activation is found ~0.95 and 0.97eV, respectively, which completely discard the carrier trapping inside gate insulator with SiO2 & a-IGZO conduction band offset of ~4.27eV. The trapping/migration/acceptor like defects may not in deep level, since PBS induced threshold voltage shows complete recovery at room temperature. We believe the positive transfer shift may be electron trapping at interfaces/ migration of ionized oxygen vacancy (VO +/VO 2+) related positive charges to neutral oxygen vacancy (VO) by capturing electron / electron capture by interstitial oxygen (Oi) atoms which behave as acceptor (Oi - /Oi2-). Optimizing the post fabrication annealing, we are able to improve the gate insulator/aIGZO and passivation/a-IGZO interfaces which gave us a PBS stress free a-IGZO TFTs after 250o C annealing at 100hrs in vacuum. Negative bias stress of a-IGZO TFTs shows a negligible effects in darks. On the other hand, light and negative bias illumination stress (NBIS) show a negative transfer shift which influence to increase the mobility, swing and hysteresis with stress time, negative bias amplitude and temperature. Thickness dependency light and NBIS stress confirmed that donor like defects creation in a-IGZO bulk/hole capturing by oxygen vacancy in IGZO bulk, is the origin of negative transfer shift under stress. Thickness dependent investigation completely discard the hole trapping phenomena inside gate insulator. In disorder a-IGZO semiconductor deficiency of oxygen atom is considered as a donor which named as oxygen vacancy (VO), can capture two electrons as it in neutral states. A-IGZO have an optical bandgap of 3~3.1eV. As subbandgap light (2.4~3eV) or NBIS under sub-bandgap light is applied, the negative transfer shift well explained by the generation of positive charges (VO VO + + e- / VO 2+ + 2e-) inside a-IGZO bulk by photo excitation from oxygen vacancy which are populated as deep level near the valance band, observed by Hard- X-ray photo electron spectroscopy. In case of above bandgap light source (>3eV), the degradation is due to the positive charge formation by capturing the photo excited holes inside oxygen vacancy (VO + 2h+ + 2e-  VO 2+ + 2e- ). Such assumption has given on the basis of various experimental evidence by material science groups discussed inside this dissertation. We found, the activation energy to generate the positive charges (VO + /VO2+) is ~1.06eV and recovery ~1.25eV. Since the degradation of TFT characteristics under NBIS is due to the absorption of light, it is impossible to find a stable device. The only solution is to use the dual gate structure, where top gate metal (Molybdenum) can absorb the expose light from outside and gives a NBIS effects free AOS TFTs for commercially use. Finally, the effects of ambient temperature and humidity on SiO2 and SiO2/SiNx passivated a-IGZO TFTs has been investigated. At room temperature (RT), if the humidity is larger than 40%, cannot protect the external atom diffusion inside aIGZO film. However, SiO2/SiNx double stack passivation easily protect TFT degradation at RT and up to 100% humid conditions. As the temperature is larger than 60o C, the dual stack shows difficulty to protect devices. So need further investigation to find a robust a-IGZO TFTs at harsh ambient (85o C temperature & 85% humidity) before commercially use.

Genetic findings and functional studies of thromboxane A₂ synthase (CYP5A1) polymorphisms in a Korean population

Chowdhury, Md. Kamrul Hasan Inje Univ. 2012 국내석사

Bias and UV induced instabilities in amorphous indium-gallium-zinc-oxide thin-film-transistors

Chowdhury, Delwar Hossain 경희대학교 일반대학원 2011 국내석사

Amorphous Indium-Gallium-Zinc-Oxide Thin-Film-Transistors (a-IGZO TFTs) are considered as a most prospective active channel layer in TFT families owing to higher field effects mobility and uniformity. As a new compound, a lot of obstacle exists to use that material for practical device fabrications because of the unknown properties of free carriers generation and the impact of vacancies on the device performances. Recently, the bias and light induced instabilities of such devices are vastly analyzed. The objective of this dissertation is to provide detail assessment about the origin of device instability for positive bias stress in dark and the UV (Ultraviolet) light stress with negative bias. The effects of positive bias stress on a-IGZO TFTs influence the transfer characteristics to shift positively without any change of mobility, swing and hysteresis. In our investigation, a-IGZO bulk effect is confirmed as the origin of that instability because of the observation of similar activation energy (~ 0.95 eV) for stress and recovery. Interstitial oxygen inside the a-IGZO films is speculated as the acceptor like trap state creator below the midgap, under the influence of positive bias stress. Light and negative stress on a-IGZO TFTs bear on the transfer characteristics to shift negatively with increasing the mobility, swing and hysteresis. Thickness dependency light stress experiment confirmed, a-IGZO bulk effect dominates the origin of light stress instability. Light stress generates the electron-hole pairs and also ionized oxygen vacancies inside the channel. Negative bias stress under light favours the generation of extra oxygen vacancies near the gate insulator/channel interface. Some of those vacancies behave as a stable donor states at room temperature. And some of the photo-generated charged defects are mobile and can drift to wards the insulator/channel interface under the action of the negative vertical field. This can be explained the dependence upon stress of both the negative shift and the hysteresis shifts. The linear increase of sub-threshold swing with negative field under light can be explained with the distribution in energy of the generated defects near the interface. To improve the TFT stabilities, the time dependent annealing at lower temperature also studied in this dissertation. Both optical and electrical stability improvement has found for longer time annealing, sustained the reduction of native point defects by annealing. These experimental data give a lot of assumption to understand the origin of instability of a-IGZO TFTs. But to confirm our assumptions, we need to do more analysis.