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Lee, Youngbin,Lee, Jinhwan,Bark, Hunyoung,Oh, Il-Kwon,Ryu, Gyeong Hee,Lee, Zonghoon,Kim, Hyungjun,Cho, Jeong Ho,Ahn, Jong-Hyun,Lee, Changgu The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.5
We describe a method for synthesizing large-area and uniform molybdenum disulfide films, with control over the layer number, on insulating substrates using a gas phase sulfuric precursor (H2S) and a molybdenum metal source. The metal layer thickness was varied to effectively control the number of layers (2 to 12) present in the synthesized film. The films were grown on wafer-scale Si/SiO2 or quartz substrates and displayed excellent uniformity and a high crystallinity over the entire area. Thin film transistors were prepared using these materials, and the performances of the devices were tested. The devices displayed an on/off current ratio of 10(5), a mobility of 0.12 cm(2) V (1) s (1) (mean mobility value of 0.07 cm(2) V-1 s(-1)), and reliable operation.
Real-time detection of chlorine gas using Ni/Si shell/core nanowires
Lee, Dong-Jin,Heo, Kwang,Lee, Hyungwoo,Jin, Joon-Hyung,Chang, Hochan,Park, Minjun,Lee, Han-Bo-Ram,Kim, Hyungjun,Lee, Byung Yang Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>We demonstrate the selective adsorption of Ni/Si shell/core nanowires (Ni-Si NWs) with a Ni outer shell and a Si inner core on molecularly patterned substrates and their application to sensors for the detection of chlorine gas, a toxic halogen gas. The molecularly patterned substrates consisted of polar SiO<SUB>2</SUB> regions and nonpolar regions of self-assembled monolayers of octadecyltrichlorosilane (OTS). The NWs showed selective adsorption on the polar SiO<SUB>2</SUB> regions, avoiding assembly on the nonpolar OTS regions. Utilizing these assembled Ni-Si NWs, we demonstrate a sensor for the detection of chlorine gas. The utilization of Ni-Si NWs resulted in a much larger sensor response of approximately 23% to 5 ppm of chlorine gas compared to bare Ni NWs, due to the increased surface-to-volume ratio of the Ni-Si shell/core structure. We expect that our sensor will be utilized in the future for the real-time detection of halogen gases including chlorine with high sensitivity and fast response.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-015-0729-2) contains supplementary material, which is available to authorized users.</P>
Optimal Cell Selection Scheme for Load Balancing in Heterogeneous Radio Access Networks
HyungJune Lee(이형준) 한국통신학회 2012 韓國通信學會論文誌 Vol.37 No.12B
스마트폰의 급격한 보급에 따른 무선 접속망의 과부하 문제가 네트워크에서 중요한 문제로 부각되고 있다. 이 논문에서는 매크로 셀, 펨토 셀, 와이파이 접속망으로 다양하게 구성되어 있는 현재 이종 네트워크에서 접속망 과부하 문제를 해결하기 위한 최적의 셀 선정 기법과 리소스 할당 기법을 제안한다. 주어진 현재 서비스 부하 상태에서 네트워크가 동시에 추가 수용할 수 있는 사용자 수를 최대화할 수 있는 사용자-셀 간의 선정 기법을 제공한다. 이를 위해 이종 무선 접속망에서의 셀 선정 문제를 이진 정수계획 모형으로 최적화 문제를 수립하고, 이를 최적화 해법 도구를 이용하여 접속망 과부하를 억제할 수 있는 최적의 셀 선정 기법을 도출한다. 네트워크 레벨 시뮬레이션을 통해 이 논문에서 제안된 기법이 현재 무선 접속망에서 주로 사용되고 있는 국소적 셀 선정기법에 비해, 과부하가 걸린 무선 접속망에서 주어진 여러 셀들을 최대한 균등하게 효율적으로 활용함으로써 현저하게 네트워크 접속 장애율을 감소시킬 수 있음을 보인다. 또한 논문에서 사용된 이진 정수계획 모형의 최적화 문제를 푸는 데 소요되는 계산 복잡도에 대한 실험을 통해 제안된 알고리즘의 실용 가능성에 대해서 검증한다. We propose a cell selection and resource allocation scheme that assigns users to nearby accessible cells in heterogeneous wireless networks consisting of macrocell, femtocells, and Wi-Fi access points, under overload situation. Given the current power level of all accessible cells nearby users, the proposed scheme finds all possible cell assignment mappings of which user should connect to which cell to maximize the number of users that the network can accommodate at the same time. We formulate the cell selection problem with heterogeneous cells into an optimization problem of binary integer programming, and compute the optimal solution. We evaluate the proposed algorithm in terms of network access failure compared to a local ad-hoc based cell selection scheme used in practical systems using network level simulations. We demonstrate that our cell selection algorithm dramatically reduces network access failure in overload situation by fully leveraging network resources evenly across heterogeneous networks. We also validate the practical feasibility in terms of computational complexity of our binary integer program by measuring the computation time with respect to the number of users.
Predictive Data Delivery to Mobile Users Through Mobility Learning in Wireless Sensor Networks
HyungJune Lee,Wicke, Martin,Kusy, Branislav,Gnawali, Omprakash,Guibas, Leonidas IEEE 2015 IEEE Transactions on Vehicular Technology VT Vol.64 No.12
<P>We consider applications, such as indoor navigation, evacuation, or targeted advertising, where mobile users equipped with a smartphone-class device require access to sensor network data measured in their proximity. Specifically, we focus on efficient communication protocols between static sensors and users with changing location. Our main contribution is to predict a set of possible future paths for each user and store data at sensor nodes with which the user is likely to associate. We use historical data of radio connectivity between users and static sensor nodes to predict the future user-node associations and propose a network optimization process, i.e., data stashing, which uses the predictions to minimize network and energy overheads of packet transmissions. We show that data stashing significantly decreases routing cost for delivering data from stationary sensor nodes to multiple mobile users compared with routing protocols where sensor nodes immediately deliver data to the last known association nodes of mobile users. We also show that the scheme provides better load balancing, avoiding collisions and consuming energy resources evenly throughout the network, leading to longer overall network lifetime. Finally, we demonstrate that even limited knowledge of the location of future users can lead to significant improvements in routing performance.</P>
Lee, Soyoung,Lee, Yonghyun,Kim, Hyungjun,Lee, Dong Yun,Jon, Sangyong American Chemical Society 2018 Biomacromolecules Vol.19 No.6
<P>Despite growing interest in targeted cancer therapy with small molecule drug conjugates (SMDCs), the short half-life of these conjugates in blood associated with their small size has limited their efficacy in cancer therapy. In this report, we propose a new approach for improving the antitumor efficacy of SMDCs based on nanoparticle-assisted delivery. Ideally, a nanoparticle-based delivery vehicle would prolong the half-life of an SMDC in blood and then release it in response to stimuli in the tumor microenvironment (TME). In this study, PEGylated bilirubin-based nanoparticles (BRNPs) were chosen as an appropriate delivery carrier because of their ability to release drugs in response to TME-associated reactive oxygen species (ROS) through rapid particle disruption. As a model SMDC, ACUPA-SN38 was synthesized by linking the prostate-specific membrane antigen (PSMA)-targeting ligand, ACUPA, to the chemotherapeutic agent, SN38. ACUPA-SN38 was loaded into BRNPs using a film-formation and rehydration method. The resulting ACUPA-SN38@BRNPs exhibited ROS-mediated particle disruption and rapid release of the SMDC, resulting in greater cytotoxicity toward PSMA-overexpressing prostate cancer cells (LNCaP) than toward ROS-unresponsive ACUPA-SN38@Liposomes. In a pharmacokinetic study, the circulation time of ACUPA-SN38@BRNPs in blood was prolonged by approximately 2-fold compared with that of the SMDC-based micellar nanoparticles. Finally, ACUPA-SN38@BRNPs showed greater antitumor efficacy in a PSMA-overexpressing human prostate xenograft tumor model than SN38@BRNPs or the SMDC alone. Collectively, these findings suggest that BRNPs are a viable delivery carrier option for various cancer-targeting SMDCs that suffer from short circulation half-life and limited therapeutic efficacy.</P> [FIG OMISSION]</BR>
Joint Radio Selection and Relay Scheme through Optimization Model in Multi-Radio Sensor Networks
( Hyungjune Lee ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.12
We present joint radio selection and relay scheme that delivers data from a source to a sink in heterogeneous stationary sensor networks consisting of various radio interfaces. The proposed scheme finds the optimal relay nodes and their corresponding radio interfaces that minimize energy consumption throughout the network while satisfying the end-to-end packet deadline requirement. We formulate the problem of routing through radio interface selection into binary integer programs, and obtain the optimal solution by solving with an optimization solver. We examine a trade-off relationship between energy consumption and packet delay based on network level simulations. We show that given the end-to-end deadline requirement, our routing algorithm finds the most energy-efficient routing path and radio interface across mesh hops. We demonstrate that the proposed routing scheme exploits the given packet delivery time to turn into network benefit of reducing energy consumption compared to routing based on single radio interface.
Formation of Vertically Aligned Cobalt Silicide Nanowire Arrays Through a Solid-State Reaction
Seulah Lee,Jaehong Yoon,Bonwoong Koo,Dong Hoon Shin,Ja Hoon Koo,Cheol Jin Lee,Young-Woon Kim,Hyungjun Kim,Taeyoon Lee IEEE 2013 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.12 No.5
<P>We report for the first time synthesis of high-density arrays of vertically well-aligned cobalt monosilicide (CoSi) nanowires (NWs) in a large area via a solid-state reaction. The vertical arrays of 1-μm-long Si NWs were first grown on a p-type (1 0 0) Si substrate by the aqueous electroless etching (AEE) method, and a 40-nm-thick Co layer was conformally deposited using a thermal atomic layer deposition system as revealed by SEM and transmission electron microscope analyses. The rapid thermal annealing process was carried out at various temperatures ranging from 700 to 1000 °C; the X-ray diffraction analysis confirmed that the polycrystalline CoSi NW arrays were formed at temperatures above 900 °C. The required high driving force for this silicide formation can be attributed to the significant amounts of oxygen-related contaminants at the defect sites of the highly rough surfaces of AEE-grown Si NWs. To demonstrate practical applications, field emitters and Schottky diodes were fabricated using the vertically aligned CoSi NW arrays. The field emission measurements showed a turn-on field of 10.9 V/μm and a field enhancement factor of 328, indicating the feasibility of vertically aligned CoSi NW arrays as promising field emitters. For the Schottky diodes, the measured Schottky barrier height was 0.52 eV and the estimated ideality factor obtained from the I-V characteristic curves was 2.28.</P>