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Korea, South Korea

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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