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- 저자 : Chow, Seinen (검색결과 260 건)
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ATRIUM SMOKE FILLING PROCESS BY COMPUTATIONAL FLUID DYNAMICS
Chow,W,K,Yin,R 한국화재소방학회 1997 한국화재소방학회 학술대회 논문집 Vol.1997 No.-
Atrium buildings are commonly found in Hong Kong since 1980. Those spaces are usually crowded with people and so fire protection systems have to be installed for providing a safe environment. Smoke control system was identified to be important but no clear design guidelines are available because the smoke filling process was not well-understood. In this paper., Computational Fluid Dynamics(CFD) or fire field model is applied to study the smoke filling pattern in atrium. Two common cases on smoke spreading out from a shop adjacent to the atrium; and with a fire located at the atrium floor itself were considered. Simulations with a modified form of the CFD package TEAM were performed. Application of the predicted results Is illustrated.
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Lam, Ian P Y,Lee, Leo T O,Choi, Hueng-Sik,Alpini, Gianfranco,Chow, Billy K C American Physiological Society 2009 American journal of physiology, Gastrointestinal a Vol.297 No.1
<P>Small heterodimer partner (SHP) is an orphan nuclear receptor in which gene expression can be upregulated by bile acids. It regulates its target genes by repressing the transcriptional activities of other nuclear receptors including NeuroD, which has been shown to regulate secretin gene expression. Here, we evaluated the regulation on duodenal secretin gene expression by SHP and selected bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA). In vitro treatment of CDCA or fexaramine elevated the SHP transcript level and occupancy on secretin promoter. The increase in the SHP level, induced by bile acid treatment or overexpression, reduced secretin gene expression, whereas this gene inhibitory effect was reversed by silencing of endogenous SHP. In in vivo studies, double-immunofluorescence staining demonstrated the coexpression of secretin and SHP in mouse duodenum. Feeding mice with 1% CA-enriched rodent chow resulted in upregulation of SHP and a concomitant decrease in secretin transcript and protein levels in duodenum compared with the control group fed with normal chow. A diet enriched with 5% cholestyramine led to a decrease in SHP level and a corresponding increase in secretin expression. Overall, this study showed that bile acids via SHP inhibit duodenal secretin gene expression. Because secretin is a key hormone that stimulates bile flow in cholangiocytes, this pathway thus provides a novel means to modulate secretin-stimulated choleresis in response to intraduodenal bile acids.</P>
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Cho, W.,An, K.-S.,Chung, T.-M.,Kim, C. G.,So, B.-S.,You, Y.-H.,Hwang, J.-H.,Jung, D.,Kim, Y. WILEY-VCH Verlag 2006 Chemical vapor deposition Vol.12 No.11
<P>A new alkoxide precursor, Hf(mp)<SUB>4</SUB> [mp = 3-methyl-3-pentoxide, OC(CH<SUB>3</SUB>)(C<SUB>2</SUB>H<SUB>5</SUB>)<SUB>2</SUB>] has been employed in the atomic layer deposition (ALD) of HfO<SUB>2</SUB> thin films using water (H<SUB>2</SUB>O) as the oxygen source. The self-limiting ALD process via alternate surface reactions of Hf(mp)<SUB>4</SUB> and H<SUB>2</SUB>O is confirmed from thickness measurements of the HfO<SUB>2</SUB> films grown with varied Hf(mp)<SUB>4</SUB> supply time and number of Hf(mp)<SUB>4</SUB>/H<SUB>2</SUB>O ALD cycles. The ALD temperature window for this precursor is found to be between 250 and 350 °C. Under optimal reaction conditions, the growth rate of the HfO<SUB>2</SUB> films is ∼0.9 Å per cycle. Amorphous films can be obtained across the entire temperature range with atomically flat and uniform surfaces. X-ray photoelectron spectroscopy (XPS) and depth-profiling Auger electron spectroscopy (AES) indicate that the films are stoichiometric with negligible amounts (less than 2 %) of carbon impurities.</P> <B>Graphic Abstract</B> <P>The new precursor hafnium 3-methyl-3-pentoxide is shown to have excellent ALD behavior when used with water as the oxygen source. It is a liquid, volatile at moderately elevated temperatures, and shows a relatively low ALD temperature window, 250–350 °C, and minimal carbon incorporation in the HfO<SUB>2</SUB> films deposited. The growth rate of the HfO<SUB>2</SUB> films was found to be ca. 0.9 Å/cycle under optimal reaction conditions.</P>
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A GHz-Level RSFQ Clock Distribution Technique with Bias Current Control in JTLs
Cho W.,Lim J.H.,Moon G. The Korean Society of Superconductivity and Cryoge 2006 한국초전도저온공학회논문지 Vol.8 No.2
A novel clock distribution technique for pipelined-RSFQ logics using variable Bias Currents of JTLs as delay-medium is newly proposed. RSFQ logics consist of several logic gates or blocks connected in a pipeline structure. And each block has variable delay difference. In the structure, this clock distribution method generates a set of clock signals for each logic blocks with suitable corresponding delays. These delays, in the order of few to tens of pS, can be adjusted through controlling bias current of JTL of delay medium. While delays with resistor value and JJ size are fixed at fabrication stage, delay through bias current can be controlled externally, and thus, is heavily investigated for its range as well as correct operation within current margin. Possible ways of a standard delay library with modular structure are sought for further modularizing Pipelined-RSFQ applications. Simulations and verifications are done through WRSpice with Hypres 3-um process parameters.
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Tunable synthesis of hierarchical mesoporous silica via porogen-carrying organosilicates
Cho, W.,Lee, H.I.,Shim, B.S.,Cha, B.J.,Kim, J.M.,Char, K. Elsevier 2017 Microporous and mesoporous materials Vol.239 No.-
We describe the synthesis and characterization of hierarchically porous organic-inorganic hybrid silica with periodic 2-D hexagonal order and tunable location of secondary nanopores through co-condensation of tetraethylorthosilicate (TEOS) and a new type of amphiphilic organosilicate precursors. Our amphiphilic organosilicates offer unique tunability of secondary micropores by carefully controlled bond molecular structure and number of bonds between hydrophobic adamantylphenols pore-generating moieties and siloxane precursors. Small angle X-ray scattering (SAXS) and microscopy results show a good structural order of the organic-inorganic hybrid silica. In addition, <SUP>29</SUP>Si CP-MAS NMR spectra confirm the successful incorporation of organosilicate precursors into a silica framework. The primary cylindrical mesopores (~6.4 nm) were originated from the cooperative self-assembly of Pluronic P123 triblock copolymer templates while smaller meso-/micropores were derived from adamantylphenols groups. We have previously demonstrated that adam-graft SQ had an affinity for hydrophobic PO core blocks to be located close to PO segment, which resulted in small pores next to primary mesopores and the resultant increment of mesopore size as well as wrinkled silica walls. On the contrary, the secondary small pores were mainly generated within a silica network while the size of the primary mesopores unaffected with the addition of adam-bridge SQ due to its selective incorporation into a silica framework. Moreover, the organic-inorganic hybrid silica prepared with adam-bridge SQ showed higher thermal stability than that of adam-graft SQ and SBA-15 type mesoporous silica. It is attributed to more Si?O?Si bonds formed from the bridged structure as well as enhanced hydrogen-bonding interaction between adam-bridge SQ hybrid silica and P123 templates.
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Cho, W.,Kim, Y.,Jeoung, D.I.,Kim, Y.M.,Choe, J. Pergamon Press 2011 Molecular immunology Vol.48 No.6
Originally discovered as a B cell growth and differentiation factor, IL-4 displays a variety of functions in many different cell types. Germinal center T cells are abundant producers of IL-4. In a recent report, we demonstrated that IL-4 inhibits prostaglandins (PGs) production in follicular dendritic cell (FDC)-like cells, HK. To understand the inhibitory mechanisms of IL-4, its effects on the biosynthesis of enzymes in charge of PG production were assessed in this study. Although IL-4 did not affect COX-1 expression, it specifically inhibited LPS-induced COX-2 biosynthesis at mRNA and protein levels. Protein expression of mPGES-1, a downstream enzyme of COX-2, was also markedly diminished by IL-4 but not by IL-10, maximizing the inhibitory activity. Next, we attempted to identify the early signaling molecules that led to this inhibition of COX-2 expression. Although IL-4 induced tyrosine phosphorylation of JAK1 and TYK2, RNA interference experiments revealed that only JAK1 was responsible for the IL-4-stimulated STAT6 phosphorylation. Knocking down JAK1 and STAT6 ablated the inhibitory effect of IL-4 on COX-2 expression and significantly reduced production of PGE<SUB>2</SUB> and prostacyclin. Similar results were obtained with IL-13. Pharmacologic inhibitors of ERK and p38 mitogen-activated protein kinases inhibited the COX-2 upregulation. However, IL-4 did not affect LPS-induced phosphorylation of ERK and p38. These results stress the essential roles of JAK1 and STAT6 in the early signaling pathway of IL-4 and IL-13 leading to suppression of COX-2 expression and repression of PG production by HK cells. Our results suggest that T cells via IL-4 play a regulatory role in PG generation in FDC. IL-4 therapeutics may be applied to immune disorders where normal and ectopic expression of germinal center reactions needs to be regulated.
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Tertiary amines: A new class of highly efficient organocatalysts for CO<sub>2</sub> fixations
Cho, W.,Shin, M.S.,Hwang, S.,Kim, H.,Kim, M.,Kim, J.G.,Kim, Y. Korean Society of Industrial and Engineering Chemi 2016 Journal of industrial and engineering chemistry Vol.44 No.-
<P>To realize a true green CO2 utilization process, the development of a catalytic system having no toxic components is essential. Herein, tertiary amines without any metal or halide additives are introduced as simple and green organocatalysts to activate CO2 and insert into epoxides, producing synthetically important cyclic carbonates. Among those amines, diamine such as N,N,N',N'-tetraethylethylenediamine exhibited a moderate to excellent efficiency. This new class of organocatalyst which does not have any toxic metals and halides is easy to handle and only requires as low as a 0.1 mol% loading. Additional favorable features include solvent free conditions and broad substrate scopes. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.</P>
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A basis of spatial big data analysis with map-matching system
Springer Science + Business Media 2017 Cluster computing Vol.20 No.3
<P>The data collection of vehicle trajectories becomes the basis of big data analysis and prediction for a variety of purposes, such as vehicle navigation and movement analysis. A digital tachograph (DTG) is pre-installed on most commercial vehicles in South Korea and is highly valuable for analyzing eco-driving metrics such as safe driving and fuel consumption estimates. In order to properly analyze a large amount of GPS location information, it is necessary to find the exact match of the location data in space to the link in the digital road network data. We previously discovered the road information of the GPS coordinates using the commonly utilized map-matching technique. However, such a navigation map-matching technique requires a lot of supplementary corrections in order to rapidly and accurately navigate a large amount of data. In this study, we applied enhanced map-matching logics with Geohash as spatial index, long link vertex division, speed filtering, azimuth filtering, and map-matching weight logics. Also, we established and implemented a distributed analysis environment for the big data map-matching with HBase (a Hadoop-based NoSQL DB). This paper shows a spatial analysis system using the map-matching logics on the Hadoop MapReduce mechanism, which improved its performance.</P>
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