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UnGyu Han,Jinho Ahn 보안공학연구지원센터 2015 International Journal of Software Engineering and Vol.9 No.2
Typically, the previous load balancing methods for Flume which completely depends on the user-specified threshold does not adaptively deal with the performance change of the entire log processing system at runtime. Furthermore, their task-transferring algorithm aggravates the performance degradation of the overloaded node because the excessive data transfer to another node should be done on the overloaded node. In this paper, we propose a new load balancing method for Apache Flume by automatically and dynamically modifying threshold of node load status in accordance with the runtime performance of the system. This feature can be realized by monitoring both the increasing rate of incoming log information in the queue of each collector agent and its occupancy rate at the request of the overloaded or under-loaded collection node in a decentralized manner. The proposed method considerably alleviates the additional overhead incurred by the task migration and makes the load of the entire system as fair as possible by selecting the optimal task migration destination depending on the current load-state values of collector agents unlike the previous round-robin and random ones.
Han, Hyungkyu,Sudhagar, P.,Song, Taeseup,Jeon, Yeryung,Mora-Seró,, Ivá,n,Fabregat-Santiago, Francisco,Bisquert, Juan,Kang, Yong Soo,Paik, Ungyu The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.27
<P>Facile synthesis of TiO<SUB>2</SUB> nanotube branched (length ∼0.5 μm) thin hollow-nanofibers is reported. The hierarchical three dimensional photoanodes (H-TiO<SUB>2</SUB>-NFs) (only ∼1 μm thick) demonstrate their excellent candidature as photoanodes in QD-sensitized solar cells, exhibiting ∼3-fold higher energy conversion efficiency (<I>η</I> = 2.8%, <I>J</I><SUB>sc</SUB> = 8.8 mA cm<SUP>−2</SUP>) than that of the directly grown nanotube arrays on a transparent conducting oxide (TCO) substrate (<I>η</I> = 0.9%, <I>J</I><SUB>sc</SUB> = 2.5 mA cm<SUP>−2</SUP>).</P> <P>Graphic Abstract</P><P>Facile synthesis of TiO<SUB>2</SUB> nanotube branched (length ∼0.5 μm) thin hollow-nanofibers is reported. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc40439k'> </P>
Han, Hyungkyu,Song, Taeseup,Bae, Jae-Young,Nazar, Linda F.,Kim, Hansu,Paik, Ungyu Royal Society of Chemistry 2011 ENERGY AND ENVIRONMENTAL SCIENCE Vol.4 No.11
<P>TiO<SUB>2</SUB> nanofibers, TiO<SUB>2</SUB> hollow nanofibers, and nitridated TiO<SUB>2</SUB> hollow nanofibers were synthesized using a simple electrospinning method and subsequent nitridation treatment. The nitridated TiO<SUB>2</SUB> hollow nanofibers showed twice higher rate capability compared to that of pristine TiO<SUB>2</SUB> nanofibers at 5 C. This improvement is mainly attributed to shorter lithium ion diffusion length and high electronic conductivity along the surface of nitridated hollow nanofibers.</P> <P>Graphic Abstract</P><P>Excellent rate performance of TiO<SUB>2</SUB> based lithium ion batteries was achieved by balanced electrode design in both morphology and composition. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1ee02333k'> </P>
Han, Hyungkyu,Park, Hyunjung,Kil, Ki Chun,Jeon, Yeryung,Ko, Youngsan,Lee, Changju,Kim, Minjae,Cho, Chae-Woong,Kim, Kijun,Paik, Ungyu,Song, Taeseup Elsevier 2015 ELECTROCHIMICA ACTA Vol.166 No.-
<P><B>Abstract</B></P> <P>As the density of graphite anode is increasing, the pore size and volume in the graphite anode is reduced, which results in a decrease in the electrolyte permeability of electrode. The electrochemical degradation of high density graphite anode due to the low permeability is a major obstacle to its use as anode for lithium ion batteries. In this study, we report on high density graphite anode with the carbon additive added that provides micron size pore structure of the high density graphite anode, which results in an increase in the rate capability. The high density graphite anode with carbon additive exhibited 32.4% higher rate capability at 1C compared to the high density graphite anode without carbon additive. This improvement is mainly attributed to the increased micron-size pores, which enhances the kinetic associated with lithium by improved electrolyte permeation and increased interface between the electrolyte and active material.</P>
Han, Hyungkyu,Song, Taeseup,Lee, Eung-Kwan,Devadoss, Anitha,Jeon, Yeryung,Ha, Jaehwan,Chung, Yong-Chae,Choi, Young-Min,Jung, Yeon-Gil,Paik, Ungyu American Chemical Society 2012 ACS NANO Vol.6 No.9
<P>Titanium dioxide (TiO(2)) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO(2)-based electrode. The vertically aligned TiO(2) nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO(2) nanotubes electrodes were prepared for this study. The vertically aligned TiO(2) nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO(2) nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system.</P>
Gold nanoparticle-composite nanofibers for enzymatic electrochemical sensing of hydrogen peroxide
Devadoss, Anitha,Han, Hyungkyu,Song, Taeseup,Kim, Young-Pil,Paik, Ungyu The Royal Society of Chemistry 2013 The Analyst Vol.138 No.17
<P>Robust composite nanofibers (NFs) are prerequisite for highly efficient electrochemical sensors. We report the electrochemical application of gold nanoparticle (Au NP)-composite Nafion NFs using a facile electrospinning technique. Owing to the uniform distribution and large surface area of the Au NPs in the NFs, the Au NP-composite electrodes gave rise to greatly improved electrochemical properties, compared to AuNP-free composite electrodes. When they were employed as reservoirs for immobilizing horseradish peroxidase (HRP), reliable and sensitive electrochemical detection by the enzyme reaction was achieved. The detection sensitivity for H<SUB>2</SUB>O<SUB>2</SUB> was determined to be as low as 38 nM, which was one order higher than that of previous electrochemical sensors. In addition, there was no change in the enzyme stability over three weeks. In this regard, the developed NP/NF-based electrochemical sensors are anticipated to be very suitable for monitoring other enzyme reactions with high sensitivity and stability.</P> <P>Graphic Abstract</P><P>We demonstrated that gold nanoparticle (Au NP)-composite nanofibers (NFs) with a facile electrospinning technique enabled a sensitive detection of H<SUB>2</SUB>O<SUB>2</SUB>, due to uniform distribution and large surface area of the Au NPs in the NFs. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3an00317e'> </P>
Flash-induced reduced graphene oxide as a Sn anode host for high performance sodium ion batteries
Jeon, Yeryung,Han, Xiaogang,Fu, Kun,Dai, Jiaqi,Kim, Joo Hyun,Hu, Liangbing,Song, Taeseup,Paik, Ungyu The Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.47
<P>Sn is a promising anode material for sodium ion batteries due to its high capacity. However, the fast capacity fading caused by large volume changes limits the employment of Sn anodes. Graphene has been considered as a host for Sn anode materials to improve the cycle performance. However, graphene scaffold preparation with large free spaces is challenging due to the need for a sacrificial template and etching process. Here, we prepared a porous scaffold composed of both reduced graphene oxide and graphene<I>via</I>a camera flash reduction as the host for Sn. The camera flash induces the reduction of the graphene oxide and pores generated by the<I>c</I>-axis popping of the graphene. The mechanical strength of the scaffold is also achieved by adjusting the concentration of graphene which does not react with the flash light. The porosity and mechanical properties of the reduced graphene oxide-graphene scaffold could be controlled by flash irradiation conditions and the mixing ratio between the graphene oxide and graphene. The porous scaffold enables a uniform Sn loading and an improvement in the sodium ion battery performance due to a sufficient free space for accommodating the Sn volume change and mechanical stability.</P>
Dutta, Soumen,Han, HyukSu,Je, Minyeong,Choi, Heechae,Kwon, Jiseok,Park, Keemin,Indra, Arindam,Kim, Kang Min,Paik, Ungyu,Song, Taeseup Elsevier 2020 Nano energy Vol.67 No.-
<P><B>Abstract</B></P> <P>Herein, holey, thin, conductive nickel substituted cobalt molybdenum boride (Ni-CMB) nanosheets have been designed to obtain superior electrochemical HER performance with small overpotential of 69 mV at 10 mA cm<SUP>-2</SUP> current density and lower Tafel slope of 76.3 mV dec<SUP>-1</SUP> in alkaline medium. Incorporation of Ni leads to improved conductivity and favorable hydrogen adsorption on Mo sites, which collectively yield efficient electrocatalytic H<SUB>2</SUB> production from Ni-CMB catalyst. The ultrathin nature (thickness = 5.0 nm) of the designed material expectedly helps to attain high exposure of active sites and facile charge transportation through the nanosheets. Additionally, the decorated mesopores (average size = 3.86 nm) on nanosheets have benefitted towards faster electrolyte diffusion, easy gas escape from catalyst surface to support high electrocatalytic performance. Finally, well-maintained morphology of the sample and evolution of HER active sites in the material have guaranteed long-term, sustainable hydrogen production even at high current densities, which clearly demonstrate its superiority over an expensive electrolyzer (Pt-C) in alkaline water.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nickel-substituted cobalt molybdenum boride (Ni-CMB) nanosheets with controlled chemistry and morphology were successfully synthesized. </LI> <LI> Strategic nickel incorporation is found to be crucial for the improvement of electrical conductivity and adsorption energy boosting electrocatalytic activity. </LI> <LI> Robust nature of the material and sustainable production of hydrogen for long time scale is achieved via structural engineering of Ni-CMB. </LI> <LI> DFT calculations revealed individual roles of elements in Ni-CMB for HER, which can help to understand catalytic reaction mechanism. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Robust, holey nanosheets of nickel substituted cobalt molybdenum boride exhibits tremendous hydrogen evolution activity and long-term durability by utilizing better electrical conductivity on nickel incorporation and easy charge transportation through the mesoporous channel, respectively.</P> <P>[DISPLAY OMISSION]</P>
Liang, Jin,Hu, Han,Park, Hyunjung,Xiao, Chunhui,Ding, Shujiang,Paik, Ungyu,Lou, Xiong Wen (David) The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.6
<P>Bowl-like hybrid structures have been designed and fabricated by anchoring NiO nanosheets on flat carbon hollow particles. When evaluated as an anode material for lithium-ion batteries, these unique NiO/carbon hybrid particles exhibit superior lithium storage properties in terms of high capacity, long term cycling stability and excellent rate capability.</P> <P>Graphic Abstract</P><P>Bowl-like hybrid structures constructed by anchoring NiO nanosheets on flat carbon shells exhibit superior lithium storage properties. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5ee01125f'> </P>