• Carbon letters
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• 제21권
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• pp.8-15
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• 2017

The thermoelectric Seebeck and Peltier effects of a single walled carbon nanotube (SWCNT) quantum dot nanodevice are investigated, taking into consideration a certain value of applied tensile strain and induced ac-field with frequency in the terahertz (THz) range. This device is modeled as a SWCNT quantum dot connected to metallic leads. These two metallic leads operate as a source and a drain. In this three-terminal device, the conducting substance is the gate electrode. Another metallic gate is used to govern the electrostatics and the switching of the carbon nanotube channel. The substances at the carbon nanotube quantum dot/metal contact are controlled by the back gate. Results show that both the Seebeck and Peltier coefficients have random oscillation as a function of gate voltage in the Coulomb blockade regime for all types of SWCNT quantum dots. Also, the values of both the Seebeck and Peltier coefficients are enhanced, mainly due to the induced tensile strain. Results show that the three types of SWCNT quantum dot are good thermoelectric nanodevices for energy harvesting (Seebeck effect) and good coolers for nanoelectronic devices (Peltier effect).

• Journal of Power Electronics
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• 제9권1호
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• pp.51-60
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• 2009

Hybrid Electric Vehicles (HEVs) utilize electric power as well as a mechanical engine for propulsion; therefore the performance of HEV s can be directly influenced by the characteristics of the Energy Storage System (ESS). The ESS for HEVs generally requires high power performance, long cycle life and reliability, as well as cost effectiveness. So the Hybrid Energy Storage System (HESS), which combines different kinds of storage devices, has been considered to fulfill both performance and cost requirements. To improve operating efficiency, cycle life, and cold cranking of the HESS, an advanced dynamic control regime with which pertinent storage devices in the HESS can be selectively operated based on their status was presented. Verification tests were performed to confirm the degree of improvement in energy efficiency. In this paper, an advanced HESS with improved an Battery Management System (BMS), which has optimal switching control function based on the estimated State of Charge (SOC), has been developed and verified.

• The Journal of Asian Finance, Economics and Business
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• 제8권9호
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• pp.1-9
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• 2021

This study aimed to investigate the existence of the Feldstein-Horioka (1980) puzzle in international macroeconomics by applying the conditional Autoregressive Distributed Lag (ARDL) model to examine the long-run relationship between national savings and investments in Thailand and China. The input of this study relied on annual national savings and investments as a fraction of GDP during 1980-2019 which was collected from China National Bureau of Statistics (NBS) and Thailand National Economic and Social Development Council (NESDC). Hypothetically, Augmented Dickey-Fuller (ADF) and Phillips-Perron (PP) unit root tests were applied to test the stationary properties and to investigate the integration level of selected time series. The empirical results, confirmed by cumulative sum (CUSUM) and cumulative sum square (CUSUMSQ), maintained no serial correlation and structural break problems. The finding of this study suggested that the Feldstein-Horioka puzzle in Thailand did not exist significantly. Thailand's national savings and investments nexus was independent, following the classic economic idea that financial liberalization, or perfect capital mobility, allowed national savings and investments to flow freely to countries with better interest rates. Whereas, a strong significant correlation was found in the case of China during the fixed exchange rate regime switching in 1994 and post WTO participation after 2001-2019.

• 경영과정보연구
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• 제35권3호
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• pp.1-22
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• 2016

본 연구는 MS-VAR 모형을 이용하여 1971년 1분기부터 2016년 1분기까지 분기별 실질 GDP의 국제적 동조화 및 구조적 변화를 조사하고자 하였다. 본 연구의 주요 결과는 다음과 같다. 첫째, 본 연구에서 실질 GDP에서 모형 또는 개별 시계열에서 발생되는 경기변동현상은 마코프 국면전환 분석으로 파악되었다. 또한 본 연구에서 국가별 실질 GDP를 이용한 MS-VAR 모형의 동조성과 비대칭성을 현저하게 보여 주었다. 둘째, 본 연구에서 부분적으로 차이가 있을지라도 MS-VAR 모형에서 글로벌 오일쇼크위기가 끝나는 1988년 2분기와 글로벌 금융위기가 시작된 2007년 3분기 등에서 경기수축국면(불경기)이 나타나는 구조적 변화가 현저하게 존재하였다. 1988년 2분기 전의 경우 독일과 일본의 상관관계가 가장 높았고 다음으로 미국과 일본, 미국과 독일, 한국과 미국 등의 순으로 높았으며, 이후에는 미국과 독일간의 상관관계가 가장 높았고 미국과 캐나다, 독일과 캐나다, 한국과 일본 등의 순으로 높았다. 셋째, 경기확장과 경기수축국면은 동시적으로 국가간에 대규모로 구조적 변화를 발생시켰다. 1973년과 1974년의 1차의 글로벌 오일쇼크 이후에 동시에 발생한 2차의 전세계 오일쇼크가 대규모의 국제적 실질 GDP의 동조화를 일으킨 주요 원인이었다. 또한 이용되는 G7 국가들이 1997년부터 1999년까지의 아시아의 외환위기 동안에 한국과 관련된 동조화가 미약하게 나타났을지라도 글로벌 금융위기기간인 2007년 말에는 한국과 G7 국가간에 현저한 동조화를 나타내었다. 넷째, 실질 GDP를 이용한 국면전환과 더불어 1973년 이후는 국가별로 발생하는 고유의 충격으로 인해 동시적 상관관계가 높게 나타나는 특징을 보여 주었다. 이러한 결론은 이용가능한 많은 이론적 및 실증적 증거와 일치하였으며, 과거 30년의 거시경제적 변동은 주로 전세계적인 충격에 의해 발생되었다는 것을 확인하였다. 글로벌 경기변동은 대규모의 비대칭적 충격이 일반적 변동으로 인하여 일시적으로 상쇄될 수 있다는 가능성을 배제하지 못할 지라도, 본 연구의 결과는 국가별 고유의 충격으로 인한 주요 국제적 동조화 및 구조적 변화를 보여 주었다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1649-1660
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• 1996

The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 10$\^$4/, 2.3 * 10$\^$5/ and 3.8 * 10$\^$5/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Re$\_$d/, = 7.8 * 10$\^$4/, the drag is reduced and the lift is generated to upward direction, however, at Re$\_$d/, =2.3 * 10$\^$5/ and 3.8 * 10$\_$5/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Re$\_$d/ = 7.8 * 10$\^$4/, but are inclined to upward direction at Re$\_$d/ = 2.3 * 10$\^$5/.

• Advances in nano research
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• 제10권5호
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• pp.415-422
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• 2021

Silicene, a 2D allotrope of silicon, is predicted to be a potential material for future transistor that might be compatible with present silicon fabrication technology. Similar to graphene, silicene exhibits the honeycomb lattice structure. Consequently, silicene is a semimetallic material, preventing its application as a field-effect transistor. Therefore, this work proposes the uniform doping bandgap engineering technique to obtain the n-type silicene nanosheet. By applying nearest neighbour tight-binding approach and parabolic band assumption, the analytical modelling equations for band structure, density of states, electrons and holes concentrations, intrinsic electrons velocity, and ideal ballistic current transport characteristics are computed. All simulations are done by using MATLAB. The results show that a bandgap of 0.66 eV has been induced in uniformly doped silicene with phosphorus (PSi₃NW) in the zigzag direction. Moreover, the relationships between intrinsic velocity to different temperatures and carrier concentration are further studied in this paper. The results show that the ballistic carrier velocity of PSi₃NW is independent on temperature within the degenerate regime. In addition, an ideal room temperature subthreshold swing of 60 mV/dec is extracted from ballistic current-voltage transfer characteristics. In conclusion, the PSi₃NW is a potential nanomaterial for future electronics applications, particularly in the digital switching applications.

• Progress in Superconductivity
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• 제4권1호
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• pp.1-9
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• 2002

Transferring single flux quanta across a Josephson junction at an exactly determined rate has made highly precise voltage measurements possible. Making use of self-shunted Nb-based SINIS junctions, programmable fast-switching DC voltage standards with output voltages of up to 10 V were produced. This development is now extended from fundamental DC measurements to the precise determination of AC voltages with arbitrary waveforms. Integrated RSFQ circuits will help to replace expensive semiconductor devices for frequency control and signal coding. Easy-to-handle AC and inexpensive quantum voltmeters of fundamental accuracy would be of interest to industry. In analogy to the development in the flux regime, metallic nanocircuits comprising small-area tunnel junctions and providing the coherent transport of single electrons might play an important role in quantum current metrology. By precise counting of single charges these circuits allow prototypes of quantum standards for electric current and capacitance to be realised. Replacing single electron devices by single Cooper pair circuits, the charge transfer rates and thus the quantum currents could be significantly increased. Recently, the principles of the gate-controlled transfer of individual Cooper pairs in superconducting A1 devices in different electromagnetic environments were demonstrated. The characteristics of these quantum coherent circuits can be improved by replacing the small aluminum tunnel Junctions by niobium junctions. Due to the higher value of the superconducting energy gap ($\Delta_{Nb}$ ＝ $7\Delta_{Al}$), the characteristic energy and the frequency scales for Nb devices are substantially extended as compared to A1 devices. Although the fabrication of small Nb junctions presents a real challenge, the Nb-based metrological devices will be faster and more accurate in operation. Moreover, the Nb-based Cooper pair electrometer could be coupled to an Nb single Cooper pair qubit which can be beneficial for both, the stability of the qubit and its readout with a large signal-to-noise ratio..

• Advances in nano research
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• 제15권6호
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• pp.521-531
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• 2023

Quantum-dot cellular automata (QCA) has shown great potential in the nanoscale regime as a replacement for CMOS technology. This work presents a specific approach to static random-access memory (SRAM) cell based on 2:1 multiplexer, 4-bit SRAM array, and 32-bit SRAM array in QCA. By utilizing the proposed SRAM array, a single-layer 16×32-bit SRAM with the read/write capability is presented using an optimized signal distribution network (SDN) crossover technique. In the present study, an extremely-optimized 2:1 multiplexer is proposed, which is used to implement an extremely-optimized SRAM cell. The results of simulation show the superiority of the proposed 2:1 multiplexer and SRAM cell. This study also provides a more efficient and accurate method for calculating QCA costs. The proposed extremely-optimized SRAM cell and SRAM arrays are advantageous in terms of complexity, delay, area, and QCA cost parameters in comparison with previous designs in QCA, CMOS, and FinFET technologies. Moreover, compared to previous designs in QCA and FinFET technologies, the proposed structure saves total energy consisting of overall energy consumption, switching energy dissipation, and leakage energy dissipation. The energy and structural analyses of the proposed scheme are performed in QCAPro and QCADesigner 2.0.3 tools. According to the simulation results and comparison with previous high-quality studies based on QCA and FinFET design approaches, the proposed SRAM reduces the overall energy consumption by 25%, occupies 33% smaller area, and requires 15% fewer cells. Moreover, the QCA cost is reduced by 35% compared to outstanding designs in the literature.