• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권1호
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• pp.185-201
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• 2023

Grant-free random access (GFRA) can reduce the access delay and signaling cost, and satisfy the short transmission packet and strict delay constraints requirement in internet of things (IoT). IoT is a major trend in the future, which is characterized by the variety of applications and devices. However, most existing studies on GFRA only consider a single type of device and omit the effect of access delay. In this paper, we study GFRA in multicell massive multipleinput multiple-output (MIMO) systems where different types of devices with various configurations and requirements co-exist. By introducing the backoff mechanism, each device is randomly activated according to the backoff parameter, and active devices randomly select an orthogonal pilot sequence from a predefined pilot pool. An analytical approximation of the average spectral efficiency for each type of device is derived. Based on it, we obtain the optimal backoff parameter for each type of devices under their delay constraints. It is found that the optimal backoff parameters are closely related to the device number and delay constraint. In general, devices that have larger quantity should have more backoff time before they are allowed to access. However, as the delay constraint become stricter, the required backoff time reduces gradually, and the device with larger quantity may have less backoff time than that with smaller quantity when its delay constraint is extremely strict. When the pilot length is short, the effect of delay constraints mentioned above works more obviously.

• Journal of Electrical Engineering and Technology
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• 제5권2호
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• pp.179-190
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• 2010

This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non.linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.

• Nuclear Engineering and Technology
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• 제17권3호
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• pp.185-192
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• 1985

가압경수로에서 나오는 사용후 핵연료의 fissile 양은 CANDU형 원자로에 쓰는 천연우라늄의 농축도 보다 높다. 따라서 핵연료 활용을 다양화하고 점차 누적되고 있는 가압경수로의 사용후 핵 연료의 저장문제를 부분적으로나마 해결하기 위하여, 가압경수로의 사용후 책 연료를 CANDU 형 원자로에 사용하는 방안을 검토 하였다. 가압경수로에서 나온 사용후 핵 연료에서 가공되는 혼합핵연료(Mixed Oxide Fuel)를 CANDU형 원자로에 장전하였을 경우, WIMS/D 코드를 이용하여 핵적특성을 분석하였다. 그리고 본 분석에서는 현 CANDU형 원자로의 반응도 조절장치를 변경시키지 않고 혼합핵 연료를 CANDU형 원자로에 사용할 수있는 방안만 조사하였다.

• Journal of Information Display
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• 제12권4호
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• pp.223-227
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• 2011

Electrophosphorescent devices with ionomer-type hole transport layers were investigated. On top of the 3,4-ethylenedioxy thiophene:poly(4-styrene sulfonate) [PEDOT:PSS] structures, fluoropolymer interfacial layers (FPIs) with different side chain lengths were introduced. Both for the PEDOT:PSS/FPI (layered) and PEDOT:PSS (mixed) structures with soluble phosphorescent emitters, the short-side-chain FPIs showed higher efficiency. The difference in the electrical properties of the two FPIs for bipolar (light-emitting) devices was not clear, but the hole-only device clearly showed the favored hole injection at the PEDOT:PSS/FPI structure with a shorter side chain, a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.487-487
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• 2009

One of the critical consumables in chemical mechanical polishing (CMP) is a specialized solution or slurry, which typically contains both abrasives and chemicals acting together to planarize films. In single abrasive slurry (SAS), the solid phase consists of only one type of abrasive particle. On the other hand, mixed abrasive slurry (MAS) consists of a mixture of at least two types of abrasive particles. In this paper, we have studied the CMP characteristics of mixed abrasive slurry (MAS) retreated by adding of $CeO_2$ abrasives within 1:10 diluted silica slurry (DSS). The slurry designed for optimal performance should produce reasonable removal rates, acceptable polishing selectivity with respect to the underlying layer, low surface defects after polishing, and good slurry stability. The modified abrasives in MAS are evaluated with respect to their particle size distribution, surface morphology, and CMP performances such as removal rate and non-uniformity. As an experimental result, we obtained the comparable slurry characteristics compared with original silica slurry in the viewpoint of high removal rate and low non-uniformity.

• 한국결정성장학회지
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• 제29권3호
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• pp.83-90
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• 2019

본 논문에서는 전력 반도체 소자용 Mg-doped AlN 에피층을 혼합 소스 수소화물 기상 에피택시 방법에 의해 성장하였다. p형 재료로는 Mg을 사용하였다. 소자응용을 위한 기초 기판으로서 역할을 하기 위하여 GaN 에피층이 성장된 기판과 GaN 에피층이 성장되어 패턴이 형성된 사파이어 기판 위에 Mg-doped AlN 에피층을 선택 성장하였다. Mg-doped AlN 에피층의 표면과 결정 구조는 FE-SEM 및 HR-XRD에 의해 조사하였다. XPS 스펙트럼과 라만 스펙트럼 결과로부터 혼합소스 HVPE 방법에 의해 성장된 Mg-doped AlN 에피층은 전력소자 등에 응용이 가능할 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.68-68
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• 2010

Electroluminescence (EL) characteristics of green-emission ZnS:Cu,Cl-based ac-type inorganic powder electroluminescent structures were examined by inserting carbon nanotubes (CNTs) into or next to the dielectric layer. For the top-emission type EL structure, where the luminescent light was emitted from the top of the structure, was fabricated by assembling in order, a top electrode, an emitting layer, a dielectric layer, and a bottom electrode from the top. $BaTiO_3$ powder mixed with CNTs was used as a dielectric layer or CNTs were deposited between the bottom electrode and $BaTiO_3$ dielectric layer in order to improve the role of the dielectric layer in the structure. Luminance of an EL structure with CNTs inclusion was greatly enhanced possibly due to the high dielectric constant in the dielectric layer of $BaTiO_3$/CNTs, which is one of hot research topics utilizing nano-objects for intensifying dielectric constant and reducing dielectric loss at the same time. A variation on the CNTs themselves and their inclusion methods in the dielectric layer has been exhorted, and the underlying mechanism for the role of CNTs in the EL structure will be explained in the poster. In order to extend the flexibility of EL devices, EL devices were fabricated on the paper substrate and their performance was compared other EL devices on the plastic-based substrate.

• 스마트미디어저널
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• 제11권9호
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• pp.81-93
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• 2022

비대면 만남이 일반화 되는 시대에 기존의 사진/영상을 기반으로 한 온라인 만남에서 충족되지 못하는 영역을 확장현실이 빠르게 발전해 나가며 채워가고 있다. 하지만, 가장 보편적으로 확장현실을 경험할 수 있는, 손을 주요 입력도구로 하는 HMD(Head Mount Display)형 혼합현실에서 적용되고 있는 기본 조작들은 표준화 된 체계가 없고 각각의 제조사들에 따라 다른 손동작에 별개로 대응되어 동작하고 있다. 이에 본 연구는 혼합현실에서 수행되는 조작들의 사용성과 효율성을 고려한 체계화된 손동작 매칭체계가 필요하다고 여겨 이를 규명하는 연구를 진행하였다. 먼저, MR환경에서 수행되는 기본적인 조작과 그 속성을 규명하였고, 동시에 손의 구조와 발생할 수 있는 손동작들의 속성들을 규명하였다. 규명한 속성들을 토대로 MR(Mixed Reality)환경에서의 기본조작과 손의 구조/맥락에 따른 미묘한 작동속성을 직관적이고 효율적으로 매칭할 수 있는 체계를 제시하고자 한다.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제16권4호
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• pp.462-466
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• 2010

본 논문은 하드디스크와 NAND 플래시메모리를 동시에 사용하는 저장 시스템 환경에서 전력 소모를 최소화하는 버퍼 캐쉬 관리 기법을 제안한다. 저장장치별 전력 소모율과 입출력 연산 종류(읽기 또는 쓰기) 및 블록의 재참조 가능성(최근성 및 빈도)을 통합적으로 고려하는 버퍼 캐쉬 관리 기법의 설계로 저장 시스템의 전력 소모량을 평균 18.0%, 최대 58.9%까지 줄일 수 있음을 보인다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.368-375
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• 2010

To alleviate NOx emission, a variety of approaches has been applied. In marine diesels, the application of SCR systems has been considered an effective exhaust aftertreatment method for NOx emission control. Most current SCR systems use a various catalyst for the reaction of ammonia with NOx to form nitrogen and water. In theory, it is possible to achieve 100% NOx if the NH3-to-NOx ratio is 1:1. However, the reaction has a limited non-uniformity of the exhaust gas flow and ammonia concentration distribution. Therefore it is necessary to investigate the optimum flow conditions. In order to achieve uniform flow at monolith front face, we are equipped with a various mixed device. In this paper, it is presented that the mixed devices play an important role improvement of flow patterns and particle distributions of NH3 by numerical simulation.