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- 저자 : Ohh, Myung-Hee (검색결과 252 건)
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Prediction of dominant intraseasonal modes in the East Asian-western North Pacific summer monsoon
Oh, H.,Ha, K. J. Springer Science + Business Media 2016 Climate dynamics Vol.47 No.7
<P>Intraseasonal monsoon prediction is the most imperative task, but there remains an enduring challenge in climate science. The present study aims to provide a physical understanding of the sources for prediction of dominant intraseasonal modes in the East Asian-western North Pacific summer monsoon (EA-WNPSM): pre-Meiyu&Baiu, Changma&Meiyu, WNPSM, and monsoon gyre modes classified by the self-organizing map analysis. Here, we use stepwise regression to determine the predictors for the four modes in the EA-WNPSM. The selected predictors are based on the persistent and tendency signals of the sea surface temperature (SST)/2m air temperature and sea level pressure fields, which reflect the asymmetric response to the El Nio Southern Oscillation (ENSO) and the ocean and land surface anomalous conditions. For the pre-Meiyu&Baiu mode, the SST cooling tendency over the western North Pacific (WNP), which persists into summer, is the distinguishing contributor that results in strong baroclinic instability. A major precursor for the Changma&Meiyu mode is related to the WNP subtropical high, induced by the persistent SST difference between the Indian Ocean and the western Pacific. The WNPSM mode is mostly affected by the Pacific-Japan pattern, and monsoon gyre mode is primarily associated with a persistent SST cooling over the tropical Indian Ocean by the preceding ENSO signal. This study carries important implications for prediction by establishing valuable precursors of the four modes including nonlinear characteristics.</P>
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Oh, H.,Kim, J.,Son, H.,Youn, B. D.,Jung, B. C. Springer Science + Business Media 2016 Structural and multidisciplinary optimization Vol.54 No.6
<P>In recent years, virtual testing has played an increasingly important role in the design and evaluation of engineered products. However, it is challenging to build the highly accurate computational models for virtual testing. Blind and recognized uncertainties are often unintentionally incorporated. These uncertainties consequently decrease the predictive capability of the models. To this end, this paper proposes a systematic approach for model refinement that minimizes the impact of unrecognized blind and recognized epistemic uncertainties in computational modeling. The approach consists of three steps: model invalidity analysis (MIA), development of an invalidity reasoning tree (IRT), and invalidity sensitivity analysis (ISA). First, in the MIA, possible causes that lead to discrepancies between the experimental and simulation responses are identified through brainstorming. Next, the IRT is built using the affinity diagram. It sequentially lists and screens potential candidate issues for model refinement at the stages of conceptual, mathematical, and computational modeling. Finally, the ISA quantifies the effect of incorporating updates in the model to address potential candidate issues with the goal of reducing the impact of the blind and recognized uncertainties. The most critical candidates are determined by using a weighted decision matrix. To demonstrate the effectiveness of the proposed approach, a case study examining a smartphone liquid crystal display fracture is presented.</P>
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Access-based abstract memory localization in static analysis
Oh, H.,Yi, K. North-Holland Pub. Co 2013 Science of computer programming Vol.78 No.9
On-the-fly localization of abstract memory states is vital for economical abstract interpretation of imperative programs. Such localization is sometimes called ''abstract garbage collection'' or ''framing''. In this article we present a new memory localization technique that is more effective than the conventional reachability-based approach. Our technique is based on a key observation that collecting the reachable memory parts is too conservative and the accessed parts are usually tiny subsets of the reachable part. Our technique first estimates, by an efficient pre-analysis, which parts of input states will be accessed during the analysis of each code block. Then the main analysis uses the access-set results to trim the memory entries before analyzing code blocks. In experiments with an industrial-strength global C static analyzer, the technique is applied right before analyzing each procedure's body and reduces the average analysis time and memory by 92.1% and 71.2%, respectively, without sacrificing the analysis precision. In addition, we present three extensions of access-based localization: (1) we generalize the idea and apply the localization more frequently such as at loop bodies and basic blocks as well as procedure bodies, additionally reducing analysis time by an average of 31.8%; (2) we present a technique to mitigate a performance problem of localization in handling recursive procedures, and show that this extension improves the average analysis time by 42%; (3) we show how to incorporate the access-based localization into relational numeric analyses.
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Oh, H.,Kwak, J.S.,Yang, S.,Gong, M.K.,Kim, J.H.,Rhee, J.,Kim, S.K.,Kim, H.E.,Ryu, J.H.,Chun, J.S. Published for the Society by Baillère Tinda 2015 Osteoarthritis and cartilage Vol.23 No.12
Objective: Hypoxia-inducible factor-2α (HIF-2α) transcriptionally upregulates Nampt in articular chondrocytes. NAMPT, which exhibits nicotinamide phosphoribosyltransferase activity, in turn causes osteoarthritis (OA) in mice by stimulating the expression of matrix-degrading enzymes. Here, we sought to elucidate whether HIF-2α activates the NAMPT-NAD<SUP>+</SUP>-SIRT axis in chondrocytes and thereby contributes to the pathogenesis of OA. Methods: Assays of NAD levels, SIRT activity, reporter gene activity, mRNA, and protein levels were conducted in primary cultured mouse articular chondrocytes. Experimental OA in mice was induced by intra-articular (IA) injection of adenovirus expressing HIF-2α (Ad-Epas1) or NAMPT (Ad-Nampt). The functions of SIRT in OA were examined by IA co-injection of SIRT inhibitors or adenovirus expressing individual SIRT isoforms or shRNA targeting specific SIRT isoforms. Results: HIF-2α activated the NAMPT-NAD<SUP>+</SUP>-SIRT axis in chondrocytes by upregulating NAMPT, which stimulated NAD<SUP>+</SUP> synthesis and thereby activated SIRT family members. The activated NAMPT-SIRT pathway, in turn, promoted HIF-2α protein stability by negatively regulating its hydroxylation and 26S proteasome-mediated degradation, resulting in increased HIF-2α transcriptional activity. Among SIRT family members (SIRT1-7), SIRT2 and SIRT4 were positively associated with HIF-2α stability and transcriptional activity in chondrocytes. This reciprocal regulation was required for the expression of catabolic matrix metalloproteinases (MMP3, MMP12, and MMP13) and OA cartilage destruction caused by IA injection of Ad-Epas1 Ad-Nampt. Conclusion: The reciprocal regulation of HIF-2α and the NAMPT-NAD<SUP>+</SUP>-SIRT axis in articular chondrocytes is involved in OA cartilage destruction caused by HIF-2α or NAMPT.
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Limits of translates of divergent geodesics and integral points on one-sheeted hyperboloids
Oh, H.,Shah, N. A. Springer Science + Business Media 2014 Israel journal of mathematics Vol.199 No.2
For any non-uniform lattice Gamma in SL2(R), we describe the limit distribution of orthogonal translates of a divergent geodesic in Gamma\SL2(R). As an application, for a quadratic form Q of signature (2, 1), a lattice Gamma in its isometry group, and v(0) is an element of R-3 with Q(v(0)) > 0, we compute the asymptotic (with a logarithmic error term) of the number of points in a discrete orbit v(0)Gamma of norm at most T, when the stabilizer of v(0) in Gamma is finite. Our result in particular implies that for any non-zero integer d, the smoothed count for the number of integral binary quadratic forms with discriminant d (2) and with coefficients bounded by T is asymptotic to c . T log T + O(T).
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Oh, H.,Park, J.,Min, K.,Lee, E.,Jyoung, J.Y. Applied Science Publishers 2015 APPLIED ENERGY Vol.149 No.-
The proton exchange membrane fuel cell (PEMFC) is one of the up-and-coming power sources for automotive vehicles. To generate a stable performance during driving, the PEMFC needs to achieve an optimized water management under various humidity conditions. Being the path for the two-phase flow of fuel, air, and water, the gas diffusion layer (GDL) is a critical component, which influences water balance. In this study, a pore size gradient structure is introduced in the substrate of a GDL to control the local capillary pressure gradient, which is the driving force of the water flux inside the PEMFC. Through measurements of steady-state performance, transient response, voltage instability and electrochemical impedance spectroscopy, it was found that the pore size gradient structure improves the cell performance regardless of the relative humidity conditions used (50% and 100%). Furthermore, it is possible to hold the water on the membrane for higher ion conductivity and drain it toward the channel to secure gas supply toward the catalyst layer. In addition, it was also confirmed that the structural change enhances the bending stiffness of the GDL.
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Oh, H.,Yoon, G.,Shin, J.-C.,Park, S.-M.,Cho, S.-S.,Cho, J. H.,Lee, M.-H.,Liu, K.,Cho, Y. S.,Chae, J.-I. Spandidos Publications 2016 International journal of oncology Vol.48 No.4
<P>Licochalcone B (Lico B), which belongs to the retrochalcone family, is isolated from the roots of Chinese licorice. Lico B has been reported to have several other useful pharmacological properties, such as anti-inflammatory, antibacterial, antioxidant, antiulcer, anticancer, and anti-metastasis activities. We elucidated the underlying mechanism by which Lico B can induce apoptosis in oral squamous cell carcinoma (OSCC). Our results showed that exposure of OSCC cells (HN22 and HSC4) to Lico B significantly inhibited cell proliferation in a time- and concentration-dependent manner. Lico B caused cell cycle arrest at G1 phase along with downregulation of cyclin D1 and upregulation of p21 and p27 proteins. Lico B also facilitated the diffusion of phospholipid phosphatidylserine (PS) from inner to outer leaflets of the plasma membrane with chromatin condensation, DNA fragmentation, accumulated sub-G1 population in a concentration-dependent manner. Moreover, Lico B promoted the generation of reactive oxygen species (ROS), which, in turn, can induce CHOP, death receptor (DR) 4 and DR5. Lico B treatment induced downregulation of anti-apoptotic proteins (Bid and Bcl-(xl) and Mcl-1), and up-regulation of pro-apoptotic protein (Bax). Lico B also led to the loss of mitochondrial membrane potential (MMP), resulting in cytochrome c release. As can be expected from the above results, the apoptotic protease activating factor-1 (Apaf-1) and survivin were oppositely expressed in favor of apoptotic cell death. This notion was supported by the fact that Lico B activated multi-caspases with cleavage of poly (ADP-ribose) polymerase (PARP) protein. Therefore, it is suggested that Lico B is a promising drug for the treatment of human oral cancer via the induction of apoptotic cell death.</P>
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