• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권4호
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• pp.1630-1642
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• 2016

Inter-domain routing is the most critical function of the Internet. The routing system is a logical network relying on the physical infrastructure with geographical characteristics. Nature disasters or disruptive accidents such as earthquakes, cable cuts and power outages could cause regional failures which fail down geographically co-located network nodes and links, therefore, affect the resilience of inter-domain routing system. This paper presents a model for regional failures in inter-domain routing system called REFER for the first time. Based on REFER, the resilience of the inter-domain routing system could be evaluated on a finer level of the Internet, considering different routing policies of intra-domain and inter-domain routing systems. Under this model, we perform simulations on an empirical topology of the Internet with geographical characteristics to simulate a regional failure locating at a city with important IXP (Internet eXchange Point). Results indicate that the Internet is robust under a city-level regional failure. The reachability is almost the same after the failure, and the reroutings occur at the edge of the Internet, hardly affecting the core of inter-domain routing system.

• 한국인터넷방송통신학회논문지
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• 제9권4호
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• pp.87-97
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• 2009

A Mobile Ad hoc Network (MANET) is characterized by multi-hop wireless connectivity, frequently changing network topology with mobile nodes and the efficiency of the dynamic routing protocol plays an important role in the performance of the network. In this paper, the performance of five routing protocols for MANET is compared by using OPNET modeler: AODV, DSR, GRP, OLSR and TORA. The various performance metrics are examined, such as packet delivery ratio, end-to-end delay and routing overhead with varying data traffic, number of nodes and mobility. In our simulation results, OLSR shows the best performance in terms of data delivery ratio in static networks, while AODV has the best performance in mobile networks with moderate data traffic. When comparing proactive protocols (OLSR, GRP) and reactive protocols (AODV, DSR) with varying data traffic in the static networks, proactive protocols consistently presents almost constant overhead while the reactive protocols show a sharp increase to some extent. When comparing each of proactive protocols in static and mobile networks, OLSR is better than GRP in the delivery ratio while overhead is more. As for reactive protocols, DSR outperforms AODV under the moderate data traffic in static networks because it exploits caching aggressively and maintains multiple routes per destination. However, this advantage turns into disadvantage in high mobility networks since the chance of the cached routes becoming stale increases.

• Journal of Power Electronics
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• 제13권3호
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• pp.400-408
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• 2013

This paper presents a discrete state-space controller using state feedback control and feed-forward decoupling to provide a desirable control bandwidth and control stability for dynamic voltage restorers (DVR). The paper initially discusses three typical applications of a DVR. The load-side capacitor DVR topology is preferred because of its better filtering capability. The proposed DVR controller offers almost full controllability because of the multi-feedback of state variables, including one-beat delay feedback. Feed-forward decoupling is usually employed to prevent disturbances of the load current and source voltage. Directly obtaining the feed-forward paths of the load current and source voltage in the discrete domain is a complicated process. Fortunately, the full feed-forward decoupling strategy can be easily applied to the discrete state-space controller by means of continuous transformation. Simulation and experimental results from a digital signal processor-based system are included to support theoretical analysis.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권5호
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• pp.980-997
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• 2013

Nowadays, wireless communication has a great advantage in technology. We use wireless devices almost in all expected life such as: entertainment, working and recently in the healthcare area, where Wireless Body Area Networks (WBANs) become a hot topic for researchers and system designers. Recent work on WBANs focus on related issues to communication protocol, especially ZigBee network is fine tuned to meet particular requirements in healthcare area. For example, some papers present real-time patient monitoring via ZigBee communication given the short distance between body sensors and remote devices, while the other work solve the limited coverage problem of Zigbee by designing mechanisms to relay Zigbee data to other types of wire or wireless infrastructure. However, very few of them investigate the scenarios of ZigBee coexisting or integrated with other networks. In this paper, we present the real-time data transmission from ZigBee end devices to Wide Area Network (WAN), Worldwide interoperation for microwave access network (WiMAX) and Long Term Evolution network (LTE). We provide in detail the ZigBee gateway components. Our simulation is conducted by OPNET, we visualize many topology network scenarios in ZigBee hybrid system. The results in simulation show that ZigBee end devices can successfully transmit data in real-time to other network end devices.

• Asian-Australasian Journal of Animal Sciences
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• 제19권10호
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• pp.1369-1378
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• 2006

This is the first study in which genetic variability and relationships of a large number of Japanese chicken breeds were revealed along with those of several foreign breeds by using microsatellite DNA polymorphisms. Twenty-eight breeds (34 populations) of native Japanese chickens and seven foreign breeds or varieties were analyzed. The mean number of alleles per locus, the proportion of the polymorphic loci, and the expected average heterozygosity ranged from 1.75 to 4.70, from 0.55 to 1.00, and from 0.21 to 0.67, respectively. Microsatellite alleles being unique to a particular population were detected in some populations. The $D_A$ genetic distance between populations was obtained from allele frequency for every pair of the populations to construct a neighbor-joining tree. According to the phylogenetic tree, excluding a few exceptions, native Japanese chicken breeds and foreign breeds were clearly separated from each other. Furthermore, the tree topology divided native Japanese chickens into four main classes, which was almost in accordance with the classification based on body morphology; that is, (1) Cochin type, (2) Malay type, (3) layer type, and (4) intermediate type between Malay and layer types. This is the first finding for native Japanese chickens.

• 한국자기학회지
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• 제6권4호
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• pp.235-241
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• 1996

수직자기 기록매체를 위해 스퍼터링법으로 Co/Pd 및 Co/Pt 다층막을 형성하였으며 Pd 및 Pt 바닥층의 증착 압력이 다층막의 자화거동 및 보자력에 미치는 영향에 대해 연구하였다. Co/Pd 다층막의 경우 보자력이 바닥층의 증착 압력에 매우 민감하여 바닥층 증착압력만을 조절함으로써 보자력을 크게 증가시킬 수 있었으나 Co/Pt 경우 바닥층의 증착압력 조절에 의한 보자력 증대효과는 미미하였다. 바닥층의 종류 및 증착압력에 따른 다층막의 보자력 변화를 바닥층의 표면 거칠기 및 다층막 증착착시의 계면상태 변화의 측면에서 설명할 수 있었으며 이는 바닥층의 증착압력의 증가에 따른 다층막의 수직이방성 에너지 감소 및 자화반전 기구의 변화와도 연관시킬 수 있었다. 다층막의 Kerr 회전각은 바닥층의 종류 및 증착압력에는 거의 의존하지 않는 것으로 나타났다.

• 전력전자학회논문지
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• 제14권1호
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• pp.8-14
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• 2009

현재 사용하고 있는 LCD(Liquid Crystal Display) Backlight용 램프는 주로 CCFL(Cold Cathod Fluorescent Lamp)과 EEFL(External Electrode Fluorescent Lamp)이 사용되고 있다. 하지만 이 램프는 수은을 사용하여 RoHS(the Restriction of e use of certain Hazardous Substances in electrical and electronic equipment)규제가 점점 강화되면서 사용이 제한되고 있으며, 이에 따라 수은을 사용하지 않는 램프의 제작이 불가피해지고 있다. 또한 LCD TV는 CRT와 PDP와는 다른 LCD만의 Hold-type 특성과 LC(Liquid Crystal)의 응답속도로 인하여 Motion Blur현상이 나타나는 단점이 있다. 본 논문에서는 RoHS 규제를 만족시키는 무수은 면광원 램프를 구동하기 위한 인버터를 제안한다. 제안한 인버터는 포워드 방식을 사용하여 반도체 소자 및 자기 소자의 수를 줄여서 구동회로가 간단하다. 또한 면광원 램프를 세로방향으로 6블록으로 나누어 스캔구동을 하여 Motion Blur현상을 저감 시켰다. 끝으로 실험을 통하여 제안한 인버터의 유용성을 입증하였다.

• 한국정보통신학회논문지
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• 제8권2호
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• pp.239-244
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• 2004

본 논문에서는 LS 밴드에서 동작하는 공액 위상변위기(phase conjugator)용 HEMT 혼합기를 설계 제작하였다. 역지향성 안테나(retrodirective antenna) 시스템의 공액위상변위기로 사용되는 혼합기의 특징은 RF 및 IF 신호의 주파수가 비슷하며, 모두 고주파 신호라는 점이다. 따라서 LO 신호의 주파수는 RF 주파수의 약 2배가 되며, 두 입력신호의 합성 및 임피던스 정합이 쉽지 않게 된다. 본 연구에서는 p-HEMT 소자를 사용하여, LO4.00 GHz, RF 2.01 GHz, IF 1.99 GHz에서 동작하는 게이트 혼합기를 제작하였다. 제작된 혼합기는 -7 dBm의 LO 신호를 인가하였을 때, 변환이득이 12.5 dB이며, 1-dB cmpression point는 -34 dBm으로 측정되었다. 본 연구에서 제작된 혼합기는 single-ended 구조로서, RF 및 IF 주파수가 비슷하므로 RF 누설신호가 관찰되었으며, 평형구조(balanced type)의 혼합기 및 공액 위상변위기의 설계에 직접 적용될 수 있다.

• 한국분말재료학회지
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• 제25권6호
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• pp.475-481
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• 2018

Selective laser melting (SLM), a type of additive manufacturing (AM) technology, leads a global manufacturing trend by enabling the design of geometrically complex products with topology optimization for optimized performance. Using this method, three-dimensional (3D) computer-aided design (CAD) data components can be built up directly in a layer-by-layer fashion using a high-energy laser beam for the selective melting and rapid solidification of thin layers of metallic powders. Although there are considerable expectations that this novel process will overcome many traditional manufacturing process limits, some issues still exist in applying the SLM process to diverse metallic materials, particularly regarding the formation of porosity. This is a major processing-induced phenomenon, and frequently observed in almost all SLM-processed metallic components. In this study, we investigate the mechanical anisotropy of SLM-produced 316L stainless steel based on microstructural factors and highly-oriented porosity. Tensile tests are performed to investigate the microstructure and porosity effects on mechanical anisotropy in terms of both strength and ductility.

• 대한전자공학회논문지SD
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• 제40권9호
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• pp.673-684
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• 2003

디지털 신호에 의해 이득이 조절되는 CMOS VGA의 구조로는 degenerated 차동쌍 구조가 많이 사용되고 있다. 이 구조에서 가변 degeneration 저항을 구현하기 위해 기존해 사용되던 방법으로는 MOSFET 스위치와 함께 저항열 구조를 사용하는 방법과 R-2R ladder 구조를 사용하는 방법이 있다. 그러나 이 방법들을 이용하는 경우에는 degeneration 저항에서의 dc 전압 강하에 의해 저전압 동작이 어려우며, 높은 이득 설정시 대역폭이 크게 제한되기 때문에 고속의 VGA 구현이 어렵다. 따라서, 본 논문에서는 이러한 문제점들을 해결하기 위해 degeneration 저항에서의 dc 전압 강하를 제거한 새로운 가변 degeneration 저항을 제안하였다. 제안된 이득조절 방법을 사용하여, 저전압에서 동작하는 고속의 CMOS VGA를 설계하였다. 0.2㎛ CMOS 공정변수를 사용하여 HSPICE 모의실험을 한 결과, 설계된 VGA는 360MHz의 대역폭과 80dB의 이득조절 범위를 갖는다. 이득오차는 200MHz에서 0.4dB보다 작으며 300MHz에서는 1.4dB보다 작다. 설계된 회로는 2.5V의 전원전압에서 10.8mA의 전류를 소모하며, 칩 면적은 1190㎛×360㎛이다.