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Bok H.H.,Pohang University of Science and Technology | Bok H.H.,POSCO | Choi J.W.,POSCO | Suh D.W.,Pohang University of Science and Technology | And 2 more authors.
International Journal of Plasticity | Year: 2015

Abstract Elastically driven shape change, or springback, in a press-hardened U-channel part made from a tailor-welded blank (TWB) was simulated using a fully coupled thermo-mechanical-metallurgical finite element (FE) method. The TWB consists of boron steel and high-strength low-alloy steel, which have significantly different hardenabilities. A combined implicit-explicit three-step simulation consisting of air cooling, forming and die quenching, and springback was used for computational efficiency. All the required material models such as the modified phase-transformation kinetics and phase-transformation-related stress-update scheme were implemented in the FE software ABAQUS with the user-defined subroutines UMAT, VUMAT, and HETVAL. The developed FE procedure, including the material models, satisfactorily predicted the experimentally measured shape changes of the TWB part. Here we present an in-depth analysis of the residual stress development during forming and die quenching using different material modeling schemes. It should be noted that the stress evolution of the two materials with high and low hardenabilities were significantly different depending on the phase transformation kinetics during forming and quenching. Moreover, in order to enhance the prediction capability of the press-hardening simulations, it was essential to include the phase-transformation-related strains in the material model. © 2014 Elsevier Ltd.

Li Y.-X.,Korea UniversitySeoul | Lim S.-T.,Korea UniversitySeoul
Carbohydrate Polymers | Year: 2016

Aqueous dispersions prepared with OSA-modified high amylose starch were investigated in comparison with native high amylose starch and beta-cyclodextrin using alpha-lipoic acid as a model substance. Alpha-lipoic acid (ALA), a lipophilic antioxidant essential for energy metabolism in human, was dispersed in gelatinized starch solutions (1.0% w/v) at different temperatures (50-90 °C) and times (3-12 h). High amylose starch modified with 3% OSA (dry starch base) was most favored in maximizing the dispersibility of ALA (84% recovery) under mild heating (70 °C for 3 h). The optimally prepared dispersion was milky white and contained particles with a narrow size distribution (200-300 nm). The precipitate isolated from the dispersion contained crystalline V-complexes of ALA and amylose while the supernatant contained free ALA accounting for 1/3 of total ALA, indicating OSA-modified high amylose starch stabilized ALA either by complexing with amylose or by retarding aggregation of ALA. © 2015 Elsevier Ltd. All rights reserved.

Lee H.-J.,Korea UniversitySeoul | Kim S.-H.,Korea UniversitySeoul | Lee J.-C.,Korea UniversitySeoul
Scripta Materialia | Year: 2016

Despite its excellent strengthening abilities, incorporation of C into most non-ferrous metals is limited by its solubility. In this study, C diffusion in pure Ti powders was promoted in a quantifiable amount using a combined technique of spark plasma sintering and powder metallurgy to synthesize a bulk Ti alloy. The sintered Ti was free from elements toxic to the human body and showed excellent strength, ductility, and wear resistance, which well exceeded those of the commercial Ti-6Al-4V alloy counterpart. Here, we report on the physics underlying the alloy design, its synthesis, resultant properties, and possible applications. © 2015 Elsevier B.V.

Cho Y.-H.,Korea UniversitySeoul | Yoo S.-D.,Korea UniversitySeoul
Frontiers in Plant Science | Year: 2015

The signaling of the plant hormone ethylene has been studied genetically, resulting in the identification of signaling components from membrane receptors to nuclear effectors. Among constituents of the hormone signaling pathway, functional links involving a putative mitogen-activated protein kinase kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) and a membrane transporter-like protein ETHYLENE INSENSITIVE2 (EIN2) have been missing for a long time. We now learn that EIN2 is cleaved and its C-terminal end moves to the nucleus upon ethylene perception at the membrane receptors, and then the C-terminal end of EIN2 in the nucleus supports EIN3-dependent ethylene-response gene expression. CTR1 kinase activity negatively controls the EIN2 cleavage process through direct phosphorylation. Despite the novel connection of CTR1 with EIN2 that explains a large portion of the missing links in ethylene signaling, our understanding still remains far from its completion. This focused review will summarize recent advances in the EIN3-dependent ethylene signaling mechanisms including CTR1-EIN2 functions with respect to EIN3 regulation and ethylene responses. This will also present several emerging issues that need to be addressed for the comprehensive understanding of signaling pathways of the invaluable plant hormone ethylene. © 2015 Cho and Yoo.

Lee M.H.,University of Texas at Austin | Kim J.S.,Korea UniversitySeoul | Sessler J.L.,University of Texas at Austin
Chemical Society Reviews | Year: 2015

Quantitative determination of specific analytes is essential for a variety of applications ranging from life sciences to environmental monitoring. Optical sensing allows non-invasive measurements within biological milieus, parallel monitoring of multiple samples, and less invasive imaging. Among the optical sensing methods currently being explored, ratiometric fluorescence sensing has received particular attention as a technique with the potential to provide precise and quantitative analyses. Among its advantages are high sensitivity and inherent reliability, which reflect the self-calibration provided by monitoring two (or more) emissions. A wide variety of ratiometric sensing probes using small fluorescent molecules have been developed for sensing, imaging, and biomedical applications. In this research highlight, we provide an overview of the design principles underlying small fluorescent probes that have been applied to the ratiometric detection of various analytes, including cations, anions, and biomolecules in solution and in biological samples. This highlight is designed to be illustrative, not comprehensive. This journal is © The Royal Society of Chemistry.

Lee M.H.,Sookmyung Womens University | Sessler J.L.,University of Texas at Austin | Kim J.S.,Korea UniversitySeoul
Accounts of Chemical Research | Year: 2015

Conspectus Theranostics, chemical entities designed to combine therapeutic effects and imaging capability within one molecular system, have received considerable attention in recent years. Much of this interest reflects the promise inherent in personalized medicine, including disease-targeted treatments for cancer patients. One important approach to realizing this latter promise involves the development of so-called theranostic conjugates, multicomponent constructs that selectively target cancer cells and deliver cytotoxic agents while producing a readily detectable signal that can be monitored both in vitro and in vivo. This requires the synthesis of relatively complex systems comprising imaging reporters, masked chemotherapeutic drugs, cleavable linkers, and cancer targeting ligands. Ideally, the cleavage process should take place within or near cancer cells and be activated by cellular components that are associated with cancer states or specifically expressed at a higher level in cancer cells. Among the cleavable linkers currently being explored for the construction of such localizing conjugates, disulfide bonds are particularly attractive. This is because disulfide bonds are stable in most blood pools but are efficiently cleaved by cellular thiols, including glutathione (GSH) and thioredoxin (Trx), which are generally found at elevated levels in tumors. When disulfide bonds are linked to fluorophores, changes in emission intensity or shifts in the emission maxima are typically seen upon cleavage as the result of perturbations to internal charge transfer (ICT) processes. In well-designed systems, this allows for facile imaging. In this Account, we summarize our recent studies involving disulfide-based fluorescent drug delivery conjugates, including preliminary tests of their biological utility in vitro and in vivo.To date, a variety of chemotherapeutic agents, such as doxorubicin, gemcitabine, and camptothecin, have been used to create disulfide-based conjugates, as have a number of fluorophores, including naphthalimide, coumarin, BODIPY, rhodol, and Cy7. The resulting theranostic core (drug-disulfide-fluorophore) can be further linked to any of several site-localizing entities, including galactose, folate, biotin, and the RGD (Arg-Gly-Asp) peptide sequence, to create systems with an intrinsic selectivity for cancer cells over normal cells. Site-specific cleavage by endogenous thiols serves to release the cytotoxic drug and produce an easy-to-monitor change in the fluorescence signature of the cell. On the basis of the results summarized in this Account, we propose that disulfide-based cancer-targeting theranostics may have a role to play in advancing drug discovery efforts, as well as improving our understanding of cellular uptake and drug release mechanisms. © 2015 American Chemical Society.

Li Y.,Xi'an Jiaotong University | Kim J.,Korea UniversitySeoul
Pattern Recognition | Year: 2015

We describe a fast and efficient numerical algorithm for the process of three-dimensional narrow volume reconstruction from scattered data in three dimensions. The present study is an extension of previous research [Li et al., Surface embedding narrow volume reconstruction from unorganized points, Comput. Vis. Image Underst. 121 (2014) 100-107]. In the previous work, we modified the original Allen-Cahn equation by multiplying a control function to restrict the evolution within a narrow band around the given surface data set. The key idea of the present work is to perform the computations only on a narrow band around the given surface data set. In this way, we can significantly reduce the storage memory and CPU time. The proposed numerical method, based on operator splitting techniques, can employ a large time step size and exhibits unconditional stability. We perform a number of numerical experiments in order to demonstrate the efficiency of this method. © 2015 Elsevier Ltd.

Paik J.H.,Korea UniversitySeoul | Lee D.H.,Korea UniversitySeoul
Computer Communications | Year: 2015

Web real-time communication (WebRTC) provides browser-to-browser communications without installing any plug-in. In WebRTC, peers have to prepare their communication session through a signaling protocol which coordinates peers and exchanges Session Description Protocol (SDP) message between two peers. The problem is that the most well known signaling method cannot provide the scalability because the method relies on only single server. To overcome the problem, this paper presents a scalable WebRTC signaling protocol. The main idea is that each peer forms a peer-to-peer topology by structuring relevant WebRTC connections with each other and then sends signals across those connections. The central server needs to handle only a few connection establishments for newly joining peers. The rest of the signaling process can be performed by peers. We define and justify such a protocol including a bootstrap method, a stabilization scheme, and peer lookup. The procedures are designed to be suitable for WebRTC connections and to be resilient against the churn condition. Furthermore, we implement the proposed protocol in pure JavaScript to show that it is realizable. The performance of the implementation is practical, with signaling latency averaging 0.5 s when the number of peers is 1000. Each peer still correctly locates the other peers even when the network is very congested. © 2015 Elsevier B.V.

Woo K.Y.,Korea UniversitySeoul | Kim K.H.,Korea UniversitySeoul | Kim T.G.,Korea UniversitySeoul
IEEE Photonics Technology Letters | Year: 2016

We fabricated Ga2O3-based transparent conductive electrodes (TCEs) for use in near-ultraviolet (NUV) lightemitting diodes (LEDs) by embedding metal layers into Ga2O3. We employ Ni and Ag layers to improve current injection and spreading properties. Our fabricated Ni/Ga2O3/Ag/Ga2O3 multilayer (annealed at 600 °C, 1 min) deposited on an NUV LED wafer exhibits 83% transmittance at 385 nm with a specific contact resistance of 8 × 10-3 Ω • cm2. An NUV LED fabricated with a Ni/Ga2O3/Ag/Ga2O3 TCE exhibits a 17% increase in light output power at 150 mA and a 3.2% decrease in forward voltage at 20 mA over those of an indium tin oxide NUV LED. © 2015 IEEE.

Park G.D.,Korea UniversitySeoul | Cho J.S.,Korea UniversitySeoul | Kang Y.C.,Korea UniversitySeoul
ACS Applied Materials and Interfaces | Year: 2015

Multicomponent metal oxide hollow-nanosphere decorated reduced graphene oxide (rGO) composite powders are prepared by spray pyrolysis with nanoscale Kirkendall diffusion. The double-layer NiFe2O4@NiO-hollow-nanosphere decorated rGO composite powders are prepared using the first target material. The NiFe-alloy-nanopowder decorated rGO powders are prepared as an intermediate product by post-treatment under the reducing atmosphere of the NiFe2O4/NiO-decorated rGO composite powders obtained by spray pyrolysis. The different diffusion rates of Ni (83 pm for Ni2+) and Fe (76 pm for Fe2+, 65 pm for Fe3+) cations with different radii during nanoscale Kirkendall diffusion result in multiphase and double-layer NiFe2O4@NiO hollow nanospheres. The mean size of the hollow NiFe2O4@NiO nanospheres decorated uniformly within crumpled rGO is 14 nm. The first discharge capacities of the nanosphere-decorated rGO composite powders with filled NiFe2O4/NiO and hollow NiFe2O4@NiO at a current density of 1 A g-1 are 1168 and 1319 mA h g-1, respectively. Their discharge capacities for the 100th cycle are 597 and 951 mA h g-1, respectively. The discharge capacity of the NiFe2O4@NiO-hollow-nanosphere-decorated rGO composite powders at the high current density of 4 A g-1 for the 400th cycle is 789 mA h g-1. © 2015 American Chemical Society.

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