• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.38-42
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• 2015

Polydimethylsiloxane (PDMS) is a widely used material for replicating micro-structures because of its transparency, deformability, and easy fabrication. At the nanoscale, however, it is hard to fill a nanohole template with uncured PDMS. This paper introduces several simple methods by changing the surface energy of a nanohole template and PDMS elastomer for replicating 100nm-scale structures. In the case of template, pristine anodic aluminum oxide (AAO), hydrophobically treated AAO, and hydrophillically treated AAO are used. For the surface energy change of the PDMS elastomer, a hydrophilic additive and dilution solvent are added in the PDMS prepolymer. During the molding process, a simple casting method is used for all combinations of the treated template and modified PDMS. The nanostructured PDMS surface was investigated with a scanning electron microscope after the molding process for verification.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.32.1-32.1
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• 2010

본 연구에서는 질화물계 발광 다이오드의 광추출효율을 향상시키기 위해서 Bi-layer나노 임프린트 리소그래피와 Lift-off 공정을 이용하여 ITO투명전극 층 상부에 TiO2 나노 패턴을 형성하였다. 발광 다이오드의 투명전극 층 상부에 UV 나노 임프린트 리소그래피를 이용하여 주기적인 폴리머 패턴을 형성한 후 폴리머 패턴 상부에 RF magnetron Sputtering 공법을 이용하여 TiO2를 증착하고 Lift-off 공정을 이용하여 TiO2 나노 패턴을 제작하였다. 그 결과를 주사전사 현미경(SEM)으로 확인한 결과 임프린트 스탬프와 동일한 나노 패턴이 질화물 계 발광다이오드 투명 전극층 표면에 주기적으로 형성되었다. TiO2 나노 패턴 형성을 통한 광추출 효율의 향상 효과를 확인하기 위해 Electroluminescence (EL) 측정한 결과 TiO2 나노 패턴이 형성된 발광다이오드 소자의 EL 강도가 나노 패턴이 없는 발광다이오드와 비교하여 12% 정도 향상 되었음을 보였고, 이는 고 굴절율 나노 패턴이 활성층에서 발생된 빛의 산란 효과를 유도하여 빛의 내부 전반사를 감소시킨 결과로 해석된다. 또한 소자의 전기적 특성평가를 위한 I-V 측정결과, TiO2 나노 패턴이 형성된 발광 다이오드의 전기적 성질이 저하되지 않았음을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.868-877
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• 2006

Sensor network applications need synchronized time to the highest degree such as object tracking, consistent state updates, duplicate detection, and temporal order delivery. In addition, reliability issues and fault tolerance in sophisticated sensor networks have become a critical area of research today. In this paper, we proposed a fault tolerant clock management scheme in sensor networks considering two cases of fault model such as network faults and clock faults. The proposed scheme restricts the propagation of synchronization error when there are clock faults of nodes such as rapid fluctuation, severe changes in drift rate, and so on. In addition, it handles topology changes. Simulation results show that the proposed method has about $1.5{\sim}2.0$ times better performance than TPSN in the presence of faults.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06c
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• pp.179-183
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• 2008

연속적이고 무한히 발생되는 데이터 스트림을 관리하는 데이터 스트림 관리시스템(DSMS)은 연속질의를 이용하여 스트림을 처리한다. 연속질의는 질의 별로 독립적인 큐를 유지하기 때문에 질의 개수가 증가함에 따라서 메모리 비용이 증가되며, 잦은 메모리 할당으로 인한 시스템의 성능 저하를 갖는다. 이러한 문제점을 해결하기 위한 기존의 연구로 메모리 풀을 이용한 메모리 관리 기법이 있다. 하지만 페이지의 크기가 고정되어 있기 때문에 각 질의마다 필요로 하는 데이터 스트림의 최적의 크기에 적합하게 할당되지 못하여 메모리를 낭비하는 문제점이 있다. 본 논문에서는 이러한 문제를 해결하기 위해 연속질의 처리를 위한 큐 메모리 관리 기법을 제안한다. 제안기법은 큐 관리 테이블에서 관리하는 각각의 큐 메모리들을 타임스탬프를 가지고 일정한 기간을 주기로 큐 메모리의 사용량을 분석한다. 분석된 큐 메모리들은 이전의 큐 메모리의 사용량과 현재 사용된 큐 메모리의 사용량을 비교함으로써 상한 값과 하한 값을 구함으로써 현재 큐 메모리에서 가지고 있는 사용량을 추가할 것인지, 줄일 것인지를 판단하여, 메모리의 사용량을 최적화 함으로써 시스템의 메모리 가용성을 향상한다. 제안 기법은 성능평가를 통해 메모리의 가용성이 기존의 방식에 비하여 향상된 성능을 보인다.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.4 s.193
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• pp.153-158
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• 2007

Recently nano imprint lithography to fabricate photonic crystal on polymer is preferred because of its simplicity and short process time and ease of precise manufacturing. But, the technique requires the precise mold as an imprinting tool for good replication. These molds are made of the silicon, nickel and quartz. But this is not desirable due to complex fabrication process, high cost. So, we describe a simple, precise and low cost method of fabricating PDMS stamp to make the photonic crystals. In order to fabricate the PDMS mold, we make the original pattern with designed hole array by finding the optimal electron beam writing condition. And then, we have tried to fabricate PDMS mold by the replica molding with ultrasonic vibration and pressure system. We have used the cleaning process to solve the detaching problem on the interface. Using these methods, we acquired the PDMS mold for photonic crystals with characteristics of a good replication. And the accuracy of replication shows below 1% in 440nm at diameter and in 610nm at lattice constant by dimensional analysis by SEM and AFM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7A
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• pp.1036-1045
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• 1999

In this paper, we proposed a causal ordering algorithms which is efficiently applicable to overlapped process group environments where one process may belong to several process groups. The ones is proposed to choose with topology of the network. We proposed receiver select algorithm in broadcast network, sender select algorithm in point-to-point network. Each algorithms removes unnecessary vector timestampes to reduce the message overhead required for the causual ordering. And, compressed vector timestamps using the locally maintained vector timestamp information of other processes and other groups to minimize the message overhead. Also, we logically proved the proposed causal ordering method, and compared the performance of the proposed algorithm with ones of other existing algorithms by computer simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.467-469
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• 2016

Car smart key system is a technology that allows you to turn activate / deactivate the auto lock through the contact form of electronic keys on the remote control and turn on the ignition by pressing the button. Smart key system is regarded as one of the essential options of the car as it is increasingly convenient to user, but there is no response yet for an attack to this situation. Therefore, in this paper, through an analysis of the amplification attack of a smart key we propose a way to stop the amplification attack and stop the car seized in case the car door opened due to the amplification attack.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.331-338
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• 2006

Most fair packet schedulers supporting quality-of-services of real-time multimedia applications are based on the finish time design scheme in which the expected transmission finish time of each packet is used as its timestamp. This scheme can adjust the latency of a flow with raising the flow's scheduling rate but it may suffer from severe bandwidth loss due to the coupled rate and delay allocation. This paper first introduces the concept of delay resource, and then proposes a scheduling method to improve the bandwidth utilization in which delay resource being lost due to the coupled allocation is transformed into bandwidth one. The performance evaluation shows that the proposed method gives higher bandwidth utilization by up to 50%.

• The Transactions of the Korea Information Processing Society
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• v.6 no.5
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• pp.1143-1152
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• 1999

A Mobile computing environment is a new paradigm which provides users with the access to information irrespective of users' location. A transaction scheduling method for the mobile computing environment must be designed so that database consistency is maintained with considering the limited performance of mobile hosts and the narrow bandwidth of a wireless network. The scheduling method using a lock has some problems: the high message overhead between a server and a mobile host for maintaining a lock and the high abort ratio of the mobile transactions owing to violating the serializability when a mobile host uses a cache. So, in this paper, we propose an efficient transaction management method using timestamp to resolve these problems. The proposed method is used in the environment under which a mobile host uses a cache having two versions for each cached data item and a server maintains several versions for each data item. So, even though a mobile transaction is executed during several broadcasting interval, can be committed. As a result, the proposed method can improve the commit ratio of the mobile transactions by maintaining multiversion for each data item and does not require the additional message exchange to schedule transactions by using timestamp.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.6
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• pp.153-159
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• 2004

In this study, a new process to pattern directly on a thin metal layer using improved nano replication printing (nRP) process is suggested to evaluate the possibilities of fabricating a stamp for nano-imprinting. In the nRP process, any figure can be replicated from a bitmap figure file in the range of several micrometers with nano-scaled details. In the process, liquid-state resins are polymerized by two-photon absorption which is induced by femto-second laser. A thin gold layer was sputtered on a glass plate and then, designed patterns or figures were developed on the gold layer by newly developed top-down building approach. Generally, stamps fur nano-imprinting have been fabricated by using the costly electron-beam lithography process combined with a reactive ion-etching process. Through this study, the effectiveness of the improved nRP process is evaluated to make a stamp with the resolution of around 200nm with reduced cost.