Showing papers by "Korea University published in 2011"

Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials

Abstract: If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.

Determination of jet energy calibration and transverse momentum resolution in CMS

Abstract: Measurements of the jet energy calibration and transverse momentum resolution in CMS are presented, performed with a data sample collected in proton-proton collisions at a centre-of-mass energy of 7TeV, corresponding to an integrated luminosity of 36pb−1. The transverse momentum balance in dijet and γ/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transverse momentum resolution. The results are presented for three different methods to reconstruct jets: a calorimeter-based approach, the ``Jet-Plus-Track'' approach, which improves the measurement of calorimeter jets by exploiting the associated tracks, and the ``Particle Flow'' approach, which attempts to reconstruct individually each particle in the event, prior to the jet clustering, based on information from all relevant subdetectors

Recent progress in fluorescent and colorimetric chemosensors for detection of precious metal ions (silver, gold and platinum ions)

Abstract: Due to the wide range of applications and biological significance, the development of optical probes for silver, gold and platinum ions has been an active research area in the past few years. This tutorial review focuses on the recent contributions concerning the fluorescent or colorimetric sensors for these metal ions, and is organized according to their structural classifications (for Ag+ detection) and unique mechanisms between the sensors and metal ions (for Au3+ and Pt2+ detection).

High-performance supercapacitors based on poly(ionic liquid)-modified graphene electrodes.

Abstract: We report a high-performance supercapacitor incorporating a poly(ionic liquid)-modified reduced graphene oxide (PIL:RG-O) electrode and an ionic liquid (IL) electrolyte (specifically, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide or EMIM-NTf2). PIL:RG-O provides enhanced compatibility with the IL electrolyte, thereby increasing the effective electrode surface area accessible to electrolyte ions. The supercapacitor assembled with PIL:RG-O electrode and EMIM-NTf2 electrolyte showed a stable electrochemical response up to 3.5 V operating voltage and was capable of yielding a maximum energy density of 6.5 W·h/kg with a power density of 2.4 kW/kg. These results demonstrate the potential of the PIL:RG-O material as an electrode in high-performance supercapacitors.

A Meta-analysis of the Effectiveness of Intervention Programs Designed to Support Autonomy

Abstract: The twofold purpose of the present study was, first, to determine whether training intervention programs designed to help people support the autonomy of others are effective and, second, to identify the set of conditions that allowed these interventions to be most effective. A meta-analysis of the findings from 19 studies with 20 effect sizes showed that the training programs were, overall, effective with a weighted effect size of 0.63. Moderator analyses of the overall effect size showed that the relatively more effective intervention programs were structured in ways that trained multiple elements of autonomy support and were presented in relatively brief (1–3 h) sessions in a laboratory training setting that focused on skill-based activities and utilized multiple types of media to deliver its content. Furthermore, relatively effective intervention programs were offered to teachers (rather than to other professionals), trainees (rather than to experienced professionals), and individuals with an autonomy (rather than a control) causality orientation. Though the small number of included studies warrants caution, results generally affirmed the effectiveness of autonomy-supportive training programs and identified the conditions under which future programs can be designed to be highly effective.

Observation and studies of jet quenching in PbPb collisions at √sNN=2.76 TeV

Abstract: Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

Randomized trial of stents versus bypass surgery for left main coronary artery disease.

Abstract: Background Percutaneous coronary intervention (PCI) is increasingly used to treat unprotected left main coronary artery stenosis, although coronary-artery bypass grafting (CABG) has been considered to be the treatment of choice. Methods We randomly assigned patients with unprotected left main coronary artery stenosis to undergo CABG (300 patients) or PCI with sirolimus-eluting stents (300 patients). Using a wide margin for noninferiority, we compared the groups with respect to the primary composite end point of major adverse cardiac or cerebrovascular events (death from any cause, myocardial infarction, stroke, or ischemia-driven target-vessel revascularization) at 1 year. Event rates at 2 years were also compared between the two groups. Results The primary end point occurred in 26 patients assigned to PCI as compared with 20 patients assigned to CABG (cumulative event rate, 8.7% vs. 6.7%; absolute risk difference, 2.0 percentage points; 95% confidence interval [CI], −1.6 to 5.6; P=0.01 for noninferiority...

Reactive Oxygen Species in Plants: Their Generation, Signal Transduction, and Scavenging Mechanisms

Abstract: Reactive oxygen species (ROS) are a by-product of normal cell metabolism in plants; however, under stress conditions, the balance between production and elimination is disturbed. ROS rapidly inactivate enzymes, damage vital cellular organelles in plants, and destroy membranes by inducing the degradation of pigments, proteins, lipids and nucleic acids which ultimately results in cell death. In addition to degrading macromolecules, ROS act as a diffusible signal in signal transduction pathways and also as a secondary messenger in various developmental pathways in plants. Plants possess a complex battery of enzymatic and non-enzymatic antioxidative defense systems that can protect cells from oxidative damage and scavenge harmful ROS that are produced in excess of those normally required for various metabolic reactions. The mechanism by which ROS is generated in aerobic organisms is poorly understood. This review paper describes the generation, origin, and role of ROS in signal transduction and cell death, and the removal of ROS by antioxidative defense systems in plants during various developmental pathways.

Regulation of Reactive Oxygen Species Generation in Cell Signaling

Abstract: Reactive oxygen species (ROS) including superoxide anion and hydrogen peroxide (H2O2) are thought to be byproducts of aerobic respiration with damaging effects on DNA, protein, and lipid. A growing body of evidence indicates, however, that ROS are involved in the maintenance of redox homeostasis and various cellular signaling pathways. ROS are generated from diverse sources including mitochondrial respiratory chain, enzymatic activation of cytochrome p450, and NADPH oxidases further suggesting involvement in a complex array of cellular processes. This review summarizes the production and function of ROS. In particular, how cytosolic and membrane proteins regulate ROS generation for intracellular redox signaling will be detailed.

Ephaptic coupling of cortical neurons

Abstract: The electrochemical processes that underlie neural function manifest themselves in ceaseless spatiotemporal field fluctuations. However, extracellular fields feed back onto the electric potential across the neuronal membrane via ephaptic coupling, independent of synapses. The extent to which such ephaptic coupling alters the functioning of neurons under physiological conditions remains unclear. To address this question, we stimulated and recorded from rat cortical pyramidal neurons in slices with a 12-electrode setup. We found that extracellular fields induced ephaptically mediated changes in the somatic membrane potential that were less than 0.5 mV under subthreshold conditions. Despite their small size, these fields could strongly entrain action potentials, particularly for slow (<8 Hz) fluctuations of the extracellular field. Finally, we simultaneously measured from up to four patched neurons located proximally to each other. Our findings indicate that endogenous brain activity can causally affect neural function through field effects under physiological conditions.

A multifunctional core–shell nanoparticle for dendritic cell-based cancer immunotherapy

Abstract: Iron oxide and zinc oxide core–shell nanoparticles can deliver antigens into dendritic cells and also act as an imaging agent for cancer immunotherapy.

Convertible organic nanoparticles for near-infrared photothermal ablation of cancer cells.

Abstract: Well-designed photothermal nanomaterials have attractedthe interest of many scientists pursuing a better means toaccurately diagnose cancer and assess the efficacy of treat-ment, because these materials enable therapies in which thetumor region is pin-pointed with a laser-guided light sourcewithout surgical intervention.

Ultrasonography and the Ultrasound-Based Management of Thyroid Nodules: Consensus Statement and Recommendations

Abstract: The detection of thyroid nodules has become more common with the widespread use of ultrasonography (US). US is the mainstay for detecting and making the differential diagnosis of thyroid nodules as well as for providing guidance for a biopsy. The Task Force on Thyroid Nodules of the Korean Society of Thyroid Radiology has developed recommendations for the US diagnosis and US-based management of thyroid nodules. The review and recommendations in this report have been based on a comprehensive analysis of the current literature, the results of multicenter studies and from the consensus of experts.

Candida albicans , a major human fungal pathogen

Abstract: Candida albicans is the most common human fungal pathogen (Beck-Sague and Jarvis, 1993). It is normally a harmless commensal organism. However, it is a opportunistic pathogen for some immunologically weak and immunocompromised people. It is responsible for painful mucosal infections such as the vaginitis in women and oral-pharangeal thrush in AIDS patients. In certain groups of vulnerable patients it causes severe, life-threatening bloodstream infections and it causes severe, life-threatening bloodstream infections and subsequent infections in the internal organs. There are various fascinating features of the C. albicans life cycle and biology that have made the pathogen the subject of extensive research, including its ability to grow in unicellular yeast, psudohyphal, and hyphal forms (Fig. 1A); its ability to switch between different but stable phenotypic states, and the way that it retains the ability to mate but apparently loses the ability to go through meiosis to complete the sexual cycle. This research has been greatly facilitated by the derivation of the complete C. albicans genome sequence (Braun et al., 2005), the development of a variety of molecular tools for gene manipulation, and a store of underpinning knowledge of cell biology borrowed from the distantly related model yeast Saccharomyces cerevisiae (Berman and Sudbery, 2002; Noble and Johnson, 2007). This review will provide a brief overview of the importance of C. albicans as a public health issue, the experimental tools developed to study its fascinating biology, and some examples of how these have been applied.

Rare earths: jewels for functional materials of the future

Abstract: In recent decades, rare earths have become vital to a wealth of advanced materials and technologies including catalysts, alloys, magnets, optics and lasers, rechargeable hydride batteries, electronics, economical lighting, wind- and solar-energy conversion, bio-analyses and imaging. In this perspective article we give a broad overview of rare earth resources and uses first and then of selected applications in dedicated fields such as telecommunications, lasers, photovoltaics (solar-energy conversion), lighting (fluorescent lamps and OLEDs), luminescent probes for bio-analyses and bio-imaging, as well as magnetism and magnetic refrigeration.

Digitally tunable physicochemical coding of material composition and topography in continuous microfibres

Abstract: Heterotypic functional materials with compositional and topographical properties that vary spatiotemporally on the micro- or nanoscale are common in nature. However, fabricating such complex materials in the laboratory remains challenging. Here we describe a method to continuously create microfibres with tunable morphological, structural and chemical features using a microfluidic system consisting of a digital, programmable flow control that mimics the silk-spinning process of spiders. With this method we fabricated hydrogel microfibres coded with varying chemical composition and topography along the fibre, including gas micro-bubbles as well as nanoporous spindle-knots and joints that enabled directional water collection. We also explored the potential use of the coded microfibres for tissue engineering applications by creating multifunctional microfibres with a spatially controlled co-culture of encapsulated cells.

In vivo targeted delivery of nanoparticles for theranosis

Abstract: Therapy and diagnosis are two major categories in the clinical treatment of disease. Recently, the word “theranosis” has been created, combining the words to describe the implementation of these two distinct pursuits simultaneously. For successful theranosis, the efficient delivery of imaging agents and drugs is critical to provide sufficient imaging signal or drug concentration in the targeted disease site. To achieve this purpose, biomedical researchers have developed various nanoparticles composed of organic or inorganic materials. However, the targeted delivery of these nanoparticles in animal models and patients remains a difficult hurdle for many researchers, even if they show useful properties in cell culture condition.In this Account, we review our strategies for developing theranostic nanoparticles to accomplish in vivo targeted delivery of imaging agents and drugs. By applying these rational strategies, we achieved fine multimodal imaging and successful therapy. Our first strategy involves physi...

Frequencies of BRAF and NRAS mutations are different in histological types and sites of origin of cutaneous melanoma: a meta-analysis.

Abstract: Summary Background There have been conflicting data regarding the prevalence and clinicopathological characteristics of BRAF and NRAS mutations in primary cutaneous melanoma. Objectives To solve this controversy, this study used a meta-analysis to evaluate the frequencies of BRAF and NRAS mutations, and the relationship between these mutations and clinicopathological parameters of cutaneous melanoma. Methods Data from studies published between 1989 and 2010 were combined. The BRAF and NRAS mutations were reported in 36 and 31 studies involving 2521 and 1972 patients, respectively. The effect sizes of outcome parameters were calculated by odds ratios (OR). Results BRAF and NRAS mutations were reported in 41% and 18% of cutaneous melanomas, respectively. The mutations were associated with histological subtype and tumour site, but not with age and sex. The BRAF mutation was frequently detected in patients with superficial spreading melanoma (OR = 2·021; P < 0·001) and in melanomas arising in nonchronic sun-damaged skin (OR = 2·043; P = 0·001). In contrast, the NRAS mutation was frequently evident in patients with nodular melanoma (OR = 1·894; P < 0·001) and in melanomas arising in chronic sun-damaged skin (OR = 1·887; P = 0·018). Conclusions This pooled analysis shows that the incidences of BRAF and NRAS mutations in cutaneous melanomas differ according to histological type and tumour location based on the degree of sun exposure.

Rapid induction and long-term self-renewal of primitive neural precursors from human embryonic stem cells by small molecule inhibitors

Abstract: Human embryonic stem cells (hESCs) hold enormous promise for regenerative medicine. Typically, hESC-based applications would require their in vitro differentiation into a desirable homogenous cell population. A major challenge of the current hESC differentiation paradigm is the inability to effectively capture and, in the long-term, stably expand primitive lineage-specific stem/precursor cells that retain broad differentiation potential and, more importantly, developmental stage-specific differentiation propensity. Here, we report synergistic inhibition of glycogen synthase kinase 3 (GSK3), transforming growth factor β (TGF-β), and Notch signaling pathways by small molecules can efficiently convert monolayer cultured hESCs into homogenous primitive neuroepithelium within 1 wk under chemically defined condition. These primitive neuroepithelia can stably self-renew in the presence of leukemia inhibitory factor, GSK3 inhibitor (CHIR99021), and TGF-β receptor inhibitor (SB431542); retain high neurogenic potential and responsiveness to instructive neural patterning cues toward midbrain and hindbrain neuronal subtypes; and exhibit in vivo integration. Our work uniformly captures and maintains primitive neural stem cells from hESCs.

2,5-Bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione-based donor-acceptor alternating copolymer bearing 5,5'-di(thiophen-2-yl)-2,2'-biselenophene exhibiting 1.5 cm2·V(-1)·s(-1) hole mobility in thin-film transistors.

Abstract: A novel diketopyrrolopyrrole-based π-conjugated copolymer P(DPP-alt-DTBSe), 5, and a known copolymer P(DPP-alt-QT), 4, have been synthesized in 80–90% yield using the Stille coupling reaction. The molecular weights of 4 and 5 are 58 781 and 19 271 g/mol, respectively, with polydispersity values of 3.25–3.35. A relatively small band gap of 1.32–1.39 eV and excellent solubility in organic solvents were achieved in the two polymers. Thin-film transistors made of 5 exhibit outstanding performance (e.g., μ > 1.0–1.5 cm2·V–1·s–1, Ion/Ioff > 105–106) with a conventional n-octyltrichlorosilane–SiO2 gate dielectric.

Ratiometric Detection of Mitochondrial Thiols with a Two-Photon Fluorescent Probe

Abstract: We report a ratiometric two-photon probe (SSH-Mito) for mitochondrial thiols. This probe shows a marked blue-to-yellow emission color change in response to RSH, a significant two-photon cross section, good mitochondrial thiol selectivity, low cytotoxicity, and insensitivity to pH over the biologically relevant pH range, allowing the direct visualization of RSH levels in live cells as well as in living tissues at 90–190 μm depth without interference from other biologically relevant species through the use of two-photon microscopy.

Three-dimensional display technologies of recent interest: principles, status, and issues [Invited]

Abstract: Recent trends in three-dimensional (3D) display technologies are very interesting in that both old-fashioned and up-to-date technologies are being actively investigated together. The release of the first commercially successful 3D display product raised new research topics in stereoscopic display. Autostereoscopic display renders a ray field of a 3D image, whereas holography replicates a wave field of it. Many investigations have been conducted on the next candidates for commercial products to resolve existing limitations. Up-to-date see-through 3D display is a concept close to the ultimate goal of presenting seamless virtual images. Although it is still far from practical use, many efforts have been made to resolve issues such as occlusion problems.

Investigating factors that influence social presence and learning outcomes in distance higher education

Abstract: There are many factors that influence distance learning especially in higher education where collaborative and communicative discourse is necessary for pursuing knowledge Social presence, among other factors, is an important concept to be facilitated, developed and sustained in distance higher education as it promotes and supports discourse based learning This study examines the relationship among demographic and other variables, social presence and learning satisfaction Results showed demographic variables, such as gender, online learning experience and work status were not significant factors in terms of influencing on either social presence or learning satisfaction While media integration and instructor's quality teaching were significant predictors of both social presence and learning satisfaction, interactivity among participants was a predictor of social presence but not of learning satisfaction Along with the study findings, some implications were discussed for online learning practitioners in higher education setting

The Effect of Board Structure on Firm Value: A Multiple Identification Strategies Approach Using Korean Data

Abstract: Outside directors and audit committees are widely considered to be central elements of good corporate governance. We use a 1999 Korean law as an exogenous shock to assess how board structure affects firm market value. The law mandates 50% outside directors and an audit committee for large public firms, but not smaller firms. We study how this shock affects firm market value, using event study, difference-in-differences, and instrumental variable methods, within a regression discontinuity approach. The legal shock produces large share price increases for large firms, relative to mid-sized firms; share prices jump in 1999 when the reforms are announced.In a companion paper, Bernard Black, Woochan Kim, Hasung Jang and Kyung-Suh Park, How Corporate Governance Affects Firm Value: Evidence on Channels from Korea (working paper 2011), http://ssrn.com/abstract=844744, we provide evidence on the channels through which governance may affect firm value. For our earlier cross-sectional research on Korean corporate governance, see:Bernard Black, Hasung Jang and Woochan Kim, Does Corporate Governance Affect Firms' Market Values? Evidence from Korea,: 22 Journal of Law, Economics and Organization 366-413 (2006), nearly final version at http://ssrn.com/abstract=311275Bernard Black, Hasung Jang & Woochan Kim, Predicting Firms' Corporate Governance Choices: Evidence from Korea, 12 Journal of Corporate Finance 660-691 (2006), nearly final version at http://ssrn.com/abstract=428662