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Pohang, South Korea

Pohang University of Science and Technology or POSTECH is a private university located in Pohang, South Korea dedicated to research and education in science and technology. In 2012 and 2013, the Times Higher Education ranked POSTECH 1st in its "100 Under 50 Young Universities" rankings. Wikipedia.

Kinaci A.,Texas A&M University | Sevincli H.,Leibniz Institute of Polymer Research | Cuniberti G.,Leibniz Institute of Polymer Research | Cuniberti G.,Pohang University of Science and Technology
ACS Nano | Year: 2011

The influence of the structural detail and defects on the thermal and electronic transport properties of graphene nanoribbons (GNRs) is explored by molecular dynamics and nonequilibrium Green's function methods. A variety of randomly oriented and distributed defects, single and double vacancies, Stone-Wales defects, as well as two types of edge form (armchair and zigzag) and different edge roughnesses are studied for model systems similar in sizes to experiments (>100 nm long and >15 nm wide). We observe substantial reduction in thermal conductivity due to all forms of defects, whereas electrical conductance reveals a peculiar defect-type-dependent response. We find that a 0.1% single vacancy concentration and a 0.23% double vacancy or Stone-Wales concentration lead to a drastic reduction in thermal conductivity of GNRs, namely, an 80% reduction from the pristine one of the same width. Edge roughness with an rms value of 7.28 Å leads to a similar reduction in thermal conductivity. Randomly distributed bulk vacancies are also found to strongly suppress the ballistic nature of electrons and reduce the conductance by 2 orders of magnitude. However, we have identified that defects close to the edges and relatively small values of edge roughness preserve the quasi-ballistic nature of electronic transport. This presents a route of independently controlling electrical and thermal transport by judicious engineering of the defect distribution; we discuss the implications of this for thermoelectric performance. © 2011 American Chemical Society.

Soare S.C.,Technical University of Cluj Napoca | Barlat F.,Pohang University of Science and Technology
European Journal of Mechanics, A/Solids | Year: 2011

As shown recently in (Soare and Barlat, 2010. Convex polynomial yield functions. J. Mech., Phys. Solids, 58, 1804-1818), the principal values based yield function Yld2004, proposed in (Barlat et al., 2005. Linear transformation based anisotropic yield function. Int. J. Plast., 21, 1009-1039), is polynomial for integer exponents. Based on this observation, a new algorithm is proposed for implementing symmetric yield functions formulated in terms of principal values. The algorithm is tested here by simulating with a commercial FE code the cylindrical deep drawing of two aluminum sheets. It is found that the classical description of the in-plane directional properties of the sheet (uniaxial r-values and yield stresses), even if modeled correctly by the yield function, is not sufficient for a unique characterization of the predicted earing profile. For certain combinations of the directional properties the r-value in biaxial stressing has to be considered for a correct calibration of the material model. This in turn requires a finer detail in yield surface modeling and, to achieve it, an ad-hoc extension of Yld2004 is constructed. In combination with the proposed implementation algorithm, the extension is shown to be a useful research tool, having some interesting modeling capabilities and satisfactory FE runtime. © 2011 Elsevier Masson SAS. All rights reserved.

Au A.K.,University of Washington | Lee W.,University of Washington | Lee W.,Pohang University of Science and Technology | Folch A.,University of Washington
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2014

The vast majority of microfluidic devices are developed in PDMS by molding ("soft lithography") because PDMS is an inexpensive material, has physicochemical properties that are well suited for biomedical and physical sciences applications, and design cycle lengths are generally adequate for prototype development. However, PDMS molding is tediously slow and thus cannot provide the high- or medium-volume production required for the commercialization of devices. While high-throughput plastic molding techniques (e.g. injection molding) exist, the exorbitant cost of the molds and/or the equipment can be a serious obstacle for device commercialization, especially for small startups. High-volume production is not required to reach niche markets such as clinical trials, biomedical research supplies, customized research equipment, and classroom projects. Crucially, both PDMS and plastic molding are layer-by-layer techniques where each layer is produced as a result of physicochemical processes not specified in the initial photomask(s) and where the final device requires assembly by bonding, all resulting in a cost that is very hard to predict at the start of the project. By contrast, stereolithography (SL) is an automated fabrication technique that allows for the production of quasi-arbitrary 3D shapes in a single polymeric material at medium-volume throughputs (ranging from a single part to hundreds of parts). Importantly, SL devices can be designed between several groups using CAD tools, conveniently ordered by mail, and their cost precisely predicted via a web interface. Here we evaluate the resolution of an SL mail-order service and the main causes of resolution loss; the optical clarity of the devices and how to address the lack of clarity for imaging in the channels; and the future role that SL could play in the commercialization of microfluidic devices. This journal is © The Royal Society of Chemistry.

Hwang M.-R.,Kyungnam University | Park D.,Kyungnam University | Jung E.,Pohang University of Science and Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

Tripartite entanglement is examined when one of the three parties moves with a uniform acceleration with respect to other parties. As the Unruh effect indicates, tripartite entanglement exhibits a decreasing behavior with increasing acceleration. Unlike bipartite entanglement, however, tripartite entanglement does not completely vanish in the infinite acceleration limit. If the three parties, for example, share the Greenberger-Horne-Zeilinger or W state initially, the corresponding π-tangle, one of the measures of tripartite entanglement, is shown to be π/6∼0.524 or 0.176 in this limit, respectively. This fact indicates that tripartite quantum-information processing may be possible even if one of the parties approaches the Rindler horizon. The physical implications of this striking result are discussed in the context of black-hole physics. © 2011 American Physical Society.

Zare R.N.,Stanford University | Kim S.,Pohang University of Science and Technology
Annual Review of Biomedical Engineering | Year: 2010

Microfluidics, the study and control of the fluidic behavior in microstructures, has emerged as an important enabling tool for single-cell chemical analysis. The complex procedures for chemical cytometry experiments can be integrated into a single microfabricated device. The capability of handling a volume of liquid as small as picoliters can be utilized to manipulate cells, perform controlled cell lysis and chemical reactions, and efficiently minimize sample dilution after lysis. The separation modalities such as chromatography and electrophoresis within microchannels are incorporated to analyze various types of intracellular components quantitatively. The microfluidic approach offers a rapid, accurate, and cost-effective tool for single-cell biology. We present an overview of the recent developments in microfluidic technology for chemical-content analysis of individual cells. © 2010 by Annual Reviews. All rights reserved.

Ponomareva V.G.,RAS Institute of Solid State Chemistry and Mechanochemistry | Kovalenko K.A.,RAS Nikolaev Institute of Inorganic Chemistry | Chupakhin A.P.,Novosibirsk State University | Dybtsev D.N.,Pohang University of Science and Technology | And 2 more authors.
Journal of the American Chemical Society | Year: 2012

The extensive implementation of hydrogen-powered technology today is limited by a number of fundamental problems related to materials research. Fuel-cell hydrogen conversion technology requires proton-conducting materials with high conductivity at intermediate temperatures up to 120 °C. The development of such materials remains challenging because the proton transport of many promising candidates is based on extended microstructures of water molecules, which deteriorate at temperatures above the boiling point. Here we show the impregnation of the mesoporous metal-organic framework (MOF) MIL-101 by nonvolatile acids H 2SO 4 and H 3PO 4. Such a simple approach affords solid materials with potent proton-conducting properties at moderate temperatures, which is critically important for the proper function of on-board automobile fuel cells. The proton conductivities of the H 2SO 4@MIL-101 and H 3PO 4@MIL-101 at T = 150 °C and low humidity outperform those of any other MOF-based materials and could be compared with the best proton conductors, such as Nafion. © 2012 American Chemical Society.

Kim M.,Pohang University of Science and Technology
Nature Physics | Year: 2016

Ever since the discovery of graphene, valley symmetry and its control in the material have been a focus of continued studies in relation to valleytronics. Carrier-guiding quasi-one-dimensional (1D) graphene nanoribbons (GNRs) with quantized energy subbands preserving the intrinsic Dirac nature have provided an ideal system to that end. Here, by guiding carriers through dual-gate operation in high-mobility monolayer graphene, we report the realization of quantized conductance in steps of 4e2/h in zero magnetic field, which arises from the full symmetry conservation of quasi-1D ballistic GNRs with effective zigzag-edge conduction. A tight-binding model calculation confirms conductance quantization corresponding to zigzag-edge conduction even for arbitrary GNR orientation. Valley-symmetry conservation is further confirmed by intrinsic conductance interference with a preserved Berry phase of π in a graphene-based Aharonov–Bohm (AB) ring prepared by similar dual gating. This top-down approach for gate-defined carrier guiding in ballistic graphene is of particular relevance in the efforts towards efficient and promising valleytronic applications. © 2016 Nature Publishing Group

Kim G.,Ulsan National Institute of Science and Technology | Kang S.-J.,Dongguk University | Dutta G.K.,Ulsan National Institute of Science and Technology | Han Y.-K.,Dongguk University | And 3 more authors.
Journal of the American Chemical Society | Year: 2014

By considering the qualitative benefits associated with solution rheology and mechanical properties of polymer semiconductors, it is expected that polymer-based electronic devices will soon enter our daily lives as indispensable elements in a myriad of flexible and ultra low-cost flat panel displays. Despite more than a decade of research focused on designing and synthesizing state-of-the-art polymer semiconductors for improving charge transport characteristics, the current mobility values are still not sufficient for many practical applications. The confident mobility in excess of ∼10 cm2/V·s is the most important requirement for enabling the realization of the aforementioned near-future products. We report on an easily attainable donor-acceptor (D-A) polymer semiconductor: poly(thienoisoindigo-alt- naphthalene) (PTIIG-Np). An unprecedented mobility of 14.4 cm 2/V·s, by using PTIIG-Np with a high-k gate dielectric poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)), is achieved from a simple coating processing, which is of a magnitude that is very difficult to obtain with conventional TFTs by means of molecular engineering. This work, therefore, represents a major step toward truly viable plastic electronics. © 2014 American Chemical Society.

Hazra D.K.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Pohang University of Science and Technology
Journal of Cosmology and Astroparticle Physics | Year: 2014

We confront the concordance (standard) model of cosmology, the spatially flat ΛCDM Universe with power-law form of the primordial spectrum with Planck CMB angular power spectrum data searching for possible smooth deviations beyond the flexibility of the standard model. The departure from the concordance cosmology is modeled in the context of Crossing statistic and statistical significance of this deviation is used as a measure to test the consistency of the standard model to the Planck data. Derived Crossing functions suggest the presence of some broad features in angular spectrum beyond the expectations of the concordance model. Our results indicate that the concordance model of cosmology is consistent to the Planck data only at 2 to 3σ confidence level if we allow smooth deviations from the angular power spectrum given by the concordance model. This might be due to random fluctuations or may hint towards smooth features in the primordial spectrum or departure from another aspect of the standard model. Best fit Crossing functions indicate that there are lack of power in the data at both low-ℓ and high-ℓ with respect to the concordance model. This hints that we may need some modifications in the foreground modeling to resolve the significant inconsistency at high-ℓ. However, presence of some systematics at high-ℓ might be another reason for the deviation we found in our analysis. © 2014 IOP Publishing Ltd and Sissa Medialab srl.

Lee Y.K.,Kongju National University | Kim Y.H.,Chonnam National University | Heo J.,Pohang University of Science and Technology | Im W.B.,Chonnam National University | Chung W.J.,Kongju National University
Optics Letters | Year: 2014

Phosphor-in-glass (PiG) color converters for LED applications were fabricated with a mixture of phosphors, Y3Al5O 12:Ce3+ (yellow) and CaAlSiN3:Eu2+ (red). The low sintering temperature (550°C) of SiO2-Na 2O-RO (R = Ba, Zn) glass powder enabled the inclusion of CaAlSiN 3:Eu2+ (red) phosphor which cannot be embedded with conventional glass powders for PiGs. By simply varying the mixing ratio of glass to phosphors as well as the ratio of yellow to red phosphors, the facile control of the CIE chromaticity coordinates and correlated color temperature of the LED following the Planckian locus has been achieved. Phosphors were well distributed within the glass matrix without noticeable reactions, preserving the enhanced thermal quenching property of the PiG compared to those with silicone resins, for LEDs. © 2014 Optical Society of America.

Hong D.K.,Pusan National University | Hong D.K.,Pohang University of Science and Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We consider fermionic dense matter under a magnetic field, where fermions couple minimally to gauge fields, and calculate anomalous currents at one loop. We find anomalous currents are spontaneously generated along the magnetic field but fermions only in the lowest Landau level contribute to anomalous currents. We then show that there are no more corrections to the anomalous currents from two or higher loops. © 2011 Elsevier B.V.

Hwang H.J.,Pohang University of Science and Technology | Velazquez J.J.L.,Complutense University of Madrid
Archive for Rational Mechanics and Analysis | Year: 2010

In this paper we prove global existence for solutions of the Vlasov-Poisson system in convex bounded domains with specular boundary conditions and with a prescribed outward electrical field at the boundary. © Springer-Verlag 2009.

Gong J.-O.,Asia Pacific Center for Theoretical Physics | Gong J.-O.,Pohang University of Science and Technology
Journal of Cosmology and Astroparticle Physics | Year: 2014

We examine the possibility of positive spectral index of the power spectrum of the primordial tensor perturbation produced during inflation in the light of the detection of the B-mode polarization by the BICEP2 collaboration. We find a blue tilt is in general possible when the slow-roll parameter decays rapidly. We present two known examples in which a positive spectral index for the tensor power spectrum can be obtained. We also briefly discuss other consistency tests for further studies on inflationary dynamics. © 2014 IOP Publishing Ltd and Sissa Medialab srl .

Kim K.-S.,Pohang University of Science and Technology | Pepin C.,CEA Saclay Nuclear Research Center | Pepin C.,Federal University of Rio Grande do Norte
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We present a series of arguments showing that the Seebeck coefficient can be used as a decisive experiment to characterize the nature of the quantum-critical point (QCP) in heavy fermion compounds. Being reactive almost exclusively to the presence of delocalized entropic carriers, the Seebeck coefficient shows a drastic collapse at the Kondo breakdown QCP, as the reconstruction of the Fermi surface takes place. In contrast, around a spin-density-wave QCP, the Seebeck coefficient is broadly symmetric. We discuss the possibility of a change of sign at the QCP, the characteristic variation in | S/T | with temperature and external parameter, as well as the capacity of the Seebeck coefficient to distinguish between localized and itinerant antiferromagnetism. Suggestions of experiments are given in the case of four nonconventional compounds: YbRh2 Si2, Ce (Mn) In 5, CeCu6-x Aux, and URu2 Si 2. © 2010 The American Physical Society.

Ghosh S.,Pohang University of Science and Technology
Materials Chemistry and Physics | Year: 2010

Nb alloyed ferritic stainless steel is an attractive material to be used in automobile exhaust systems. Recently, in some published experimental work it was reported that coarsening rate of Laves phase (Fe2Nb) can be higher than NbC in Nb alloyed ferritic stainless steels during aging at 700 °C. This observation was attributed to the fact that NbC has a more coherent interface with ferrite than has Laves phase. We explore this conclusion and find that the real reason for the smaller coarsening rate of NbC is the incredibly low solubility of carbon in ferrite. © 2010 Elsevier B.V. All rights reserved.

Oh J.K.,Concordia University at Montreal | Park J.M.,Pohang University of Science and Technology
Progress in Polymer Science (Oxford) | Year: 2011

Recent advances in the development and biological applications of polymeric nanomaterials embedded with superparamagnetic iron oxide nanoparticles (SIONPs) are summarized. Novel SIONP-polymer hybrid nanoparticles are prepared by various methods, including direct modification with polymers, surface-initiated controlled polymerization, inorganic silica/polymer hybridization, self-assembly, self-association, and various heterogeneous polymerization methods. They have potential for various biomedical applications, including magnetic resonance imaging (MRI) contrast enhancement, targeted drug delivery, hyperthermia, biological separation, protein immobilization, and biosensors. © 2010 Elsevier Ltd All rights reserved.

Purich A.,CSIRO | Cowan T.,CSIRO | Min S.-K.,Pohang University of Science and Technology | Cai W.,CSIRO
Journal of Climate | Year: 2013

In recent decades, Southern Hemisphere midlatitude regions such as southern Africa, southeastern Australia, and southern Chile have experienced a reduction in austral autumn precipitation; the cause of which is poorly understood. This study focuses on the ability of global climate models that form part of the Coupled Model Intercomparison Project phase 5 to simulate these trends, their relationship with extratropical and subtropical processes, and implications for future precipitation changes. Models underestimate both the historical autumn poleward expansion of the subtropical dry zone and the positive southern annular mode (SAM) trend. The multimodel ensemble (MME) is also unable to capture the spatial pattern of observed precipitation trends across semiarid midlatitude regions. However, in temperate regions that are located farther poleward such as southern Chile, the MME simulates observed precipitation declines. The MME shows a strong consensus in twenty-first-century declines in autumn precipitation across southern Chile in both the medium-low and high representative concentration pathway (RCP) scenarios and across southern Africa in the high RCP scenario, but little change across southeastern Australia. Projecting a strong positive SAM trend and continued subtropical dry-zone expansion, the models converge on large SAM and dry-zoneexpansion-induced precipitation declines across southern midlatitudes. In these regions, the strength of future precipitation trends is proportional to the strength of modeled trends in these phenomena, suggesting that unabated greenhouse gas-induced climate change will have a large impact on austral autumn precipitation in such midlatitude regions.

Ghosh S.,Pohang University of Science and Technology
Scripta Materialia | Year: 2010

Refining cementite with Si and Mn is of technological interest due to the low cost and recyclability. Recently, some experimental data were published which permit a discussion of the operative mechanism. A kinetic study led by simulation indicates that enrichment of ferrite with Si is time consuming; dissolution of Mn from cementite is the key to the slow coarsening rate of the carbide when Si is substituted by Mn in Fe-0.6C wt.% steels during tempering. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hoang A.T.,Pohang University of Science and Technology | Hoang A.T.,Institute of Physics
Journal of Physics Condensed Matter | Year: 2010

We study electronic phase transitions in the half-filled ionic Hubbard model with an on-site Coulomb repulsion U and an ionic energy Δ by using the coherent potential approximation. For a fixed and finite Δ two transitions from the band insulator via a metallic state to a Mott insulator are found with increasing U. The values of the critical correlation-driven metal-insulator transitions Uc1(Δ) and Uc2(Δ) are estimated. Our results are in reasonable agreement with the ones obtained by single-site dynamical mean-field theory and determinant quantum Monte Carlo simulation. © 2010 IOP Publishing Ltd.

Kim K.-S.,Pohang University of Science and Technology | Pepin C.,CEA Saclay Nuclear Research Center
Journal of Physics Condensed Matter | Year: 2010

We develop the quantum Boltzmann equation approach for the Kondo breakdown quantum critical point, involved with two bands for conduction electrons and localized fermions. Particularly, the role of vertex corrections in transport is addressed, crucial for non-Fermi liquid transport with temperature linear dependence. Only one band of spinons may be considered for scattering with gauge fluctuations, and their associated vertex corrections are introduced in the usual way, where the divergence of self-energy corrections is cancelled by that of vertex corrections, giving rise to a physically meaningful result in the gauge invariant expression for conductivity. On the other hand, two bands should be taken into account for scattering with hybridization excitations, giving rise to coupled quantum Boltzmann equations. We find that vertex corrections associated with hybridization fluctuations turn out to be irrelevant due to the heavy mass of spinons in the so called decoupling limit, consistent with the diagrammatic approach showing non-Fermi liquid transport. © 2009 IOP Publishing Ltd.

Han B.,Pohang University of Science and Technology | Davis L.S.,University of Maryland University College
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

Background modeling and subtraction is a natural technique for object detection in videos captured by a static camera, and also a critical preprocessing step in various high-level computer vision applications. However, there have not been many studies concerning useful features and binary segmentation algorithms for this problem. We propose a pixelwise background modeling and subtraction technique using multiple features, where generative and discriminative techniques are combined for classification. In our algorithm, color, gradient, and Haar-like features are integrated to handle spatio-temporal variations for each pixel. A pixelwise generative background model is obtained for each feature efficiently and effectively by Kernel Density Approximation (KDA). Background subtraction is performed in a discriminative manner using a Support Vector Machine (SVM) over background likelihood vectors for a set of features. The proposed algorithm is robust to shadow, illumination changes, spatial variations of background. We compare the performance of the algorithm with other density-based methods using several different feature combinations and modeling techniques, both quantitatively and qualitatively. © 2012 IEEE.

Wenk P.,Jacobs University Bremen | Kettemann S.,Jacobs University Bremen | Kettemann S.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The quantum correction to the conductivity in disordered quantum wires with linear Rashba spin-orbit coupling is obtained. For quantum wires with spin-conserving boundary conditions, we find a crossover from weak antilocalization to weak localization as the wire width W is reduced using exact diagonalization of the Cooperon equation. This crossover is due to the dimensional dependence of the spin relaxation rate of conduction electrons, which becomes diminished, when the wire width W is smaller than the bulk spin precession length LSO. We thus confirm previous results for small wire width, W/ Lso≲1 [S. Kettemann, Phys. Rev. Lett.98, 176808 (2007)] where only the transverse 0 modes of the Cooperon equation had been taken into account. We find that spin helix solutions become stable for arbitrary ratios of linear Rashba and Dresselhaus coupling in narrow wires. For wider wires, the spin relaxation rate is found to be not monotonous as function of wire width W: it becomes first enhanced for W on the order of the bulk spin precession length LSO before it becomes diminished for smaller wire widths. In addition, we find that the spin relaxation is smallest at the edge of the wire for wide wires. The effect of the Zeeman coupling to the magnetic field perpendicular to the 2D electron system (2DES) is studied and found to result in a modification of the magnetoconductivity: it shifts the crossover from weak antilocalization to weak localization to larger wire widths Wc. When the transverse confinement potential of the quantum wire is smooth, the boundary conditions become rather adiabatic. Then, the spin relaxation rate is found to be enhanced as the wire width W is reduced. We find that only a spin-polarized state retains a finite spin relaxation rate in such narrow wires. Thus, we conclude that the injection of polarized spins into nonmagnetic quantum wires should be favorable in wires with smooth confinement potential. Finally, in wires with tubular shape, corresponding to transverse periodic boundary conditions, we find no reduction of the spin relaxation rate. © 2010 The American Physical Society.

Jeon T.H.,Kyungpook National University | Choi W.,Pohang University of Science and Technology | Park H.,Kyungpook National University
Physical Chemistry Chemical Physics | Year: 2011

BiVO4 semiconductor electrodes were coupled with cobalt-phosphate complexes (CoPi) to enhance the photoelectrochemical (PEC) performance for water oxidation reaction. CoPi was deposited on a 550 nm-thick BiVO4 film via electrodeposition (ED) and photodeposition (PD) methods for comparison of their effects. The CoPi on BiVO4 exhibited Co:P atomic ratios of approximately 1:7 for the electrodeposited sample and approximately 1:18 for the photodeposited sample, and Co2+ and Co3+ co-existed in both samples. Optimized CoPi ED resulted in a CoPi overlayer of approximately 850 nm thick, which showed an electrochromic-like behavior that was likely due to limited access of phosphate into BiVO 4 across the CoPi layer. Optimized CoPi PD, however, had very thin and rather uniform CoPi dispersion and did not show electrochromic-like behavior. Despite the lesser amount of CoPi, the PEC performance of BiVO 4/CoPi (PD) was comparable to that of BiVO4/CoPi (ED). Real-time measurements of the headspace molecular oxygen that evolved from water oxidation indicated that CoPi enhances O2 production and photocurrent generation at BiVO4 by a factor of around 15 and a maximum of 20, respectively, at 0.576 VSCE (equivalent to 1.23 V RHE) under air mass 1.5 irradiation (400 mW cm-2). Prolonged irradiation of BiVO4/CoPi (ED) resulted in a reduced Co:P ratio to 1:1.77 without changing the mixed valency of Co(ii/iii). This finding indicates that incorporation of phosphate into the CoPi was kinetically slower than water oxidation. The primary role of CoPi has been suggested as a hole-conducting electrocatalyst making the photogenerated electrons more mobile and, consequently, increasing conductivity and boosting the PEC water oxidation performance of BiVO4. © 2011 the Owner Societies.

Kang Y.-B.,Pohang University of Science and Technology
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2015

In the context of a boundary phase model, surface tension (σ) of a solution can be regarded as a system property of an equilibrium between a bulk phase and a surface phase. In the present article, a geometric relationship is shown among molar Gibbs energy of the bulk phase (g), that of the surface phase (gs), and corresponding surface tension of the system. The geometric relationship is based on a phase equilibrium between the bulk phase and the surface phase, under a constraint: constant surface area (A). The relationship is consistent with the proposal of Butler, Proc. R. Soc. Lond. A: Math. Phys. Eng. Sci., 135 (1932) 348 [1], and is mathematically equivalent to the Constrained Gibbs Energy Minimization (CGEM) for the surface tension calculation by Pajarre et al., Calphad 30 (2006) 196 [7]. The geometric relationship can be simply utilized by available CALPHAD type code, in order to calculate surface tension of a solution composed of any number of components. Role of various properties (surface tension (σi°) and molar surface area (Ai°) of pure components, excess Gibbs energy of the bulk phase and that of the surface phase) in the surface tension and surface concentration is examined using the CGEM. © 2015 Elsevier B.V. All rights reserved.

Wagoner R.H.,Ohio State University | Lim H.,Sandia National Laboratories | Lee M.-G.,Pohang University of Science and Technology
International Journal of Plasticity | Year: 2013

For purposes of this review, springback is the elastically driven change of shape of a metal sheet during unloading and following forming. Scientific advances related to this topic have accelerated dramatically over roughly the last decade, since the publication of two reviews in the 2004-2006 timeframe (Wagoner, 2004; Wagoner et al., 2006). The current review focuses on the period following those publications, and on work in the first author's laboratory. Much of this recent work can be categorized into five main topics. (1) Plastic constitutive equations (2) Variable Young's modulus (3) Through-thickness integration of stress (4) Magnesium (5) Advanced high strength steels (AHSS) The first two subjects are related to accurate material representation, the third to numerical procedures, and the last two to particular classes of sheet materials. The principal contributions in these areas were summarized and put into context. © 2012 Elsevier Ltd. All rights reserved.

Kittlaus E.A.,Yale University | Shin H.,Yale University | Shin H.,Pohang University of Science and Technology | Rakich P.T.,Yale University
Nature Photonics | Year: 2016

Both Kerr and Raman nonlinearities are radically enhanced by tight optical-mode confinement in nanoscale silicon waveguides. Counterintuitively, Brillouin nonlinearities - originating from coupling between photons and acoustic phonons - are exceedingly weak in these same nonlinear waveguides. Strong Brillouin interactions have only recently been realized in a new class of optomechanical structures that control the interaction between guided photons and phonons. Despite these major advances, appreciable Brillouin-based optical amplification has yet to be observed in silicon. Using a membrane-suspended waveguide, we report large Brillouin amplification in silicon for the first time, reaching levels greater than 5dB for modest pump powers, and demonstrate a record low (5mW) threshold for net amplification. This work represents an important step towards the realization of high-performance Brillouin lasers and amplifiers in silicon. © 2016 Macmillan Publishers Limited. All rights reserved.

Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Huang Q.-G.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We study the standard model Higgs field as a source for the primordial curvature perturbation, particularly in the curvaton and modulated reheating scenario. We conclude that the Higgs cannot play as a curvaton due to the small energy density when it decays, however the modulated reheating by Higgs can be a viable scenario. In the latter case, the non-Gaussianity is inevitably generated and strongly constrains the type of potential of inflaton field and the Higgs-dependent interaction term. For the quadratic potential of the inflaton field with decay rate which nonlinearly depends on the Higgs vacuum expectation value, the contribution of the Higgs field to the primordial curvature perturbation must be less than 8%. © 2013 American Physical Society.

Xu X.-Q.,Sungkyunkwan University | Han J.H.,Sungkyunkwan University | Han J.H.,Pohang University of Science and Technology
Physical Review Letters | Year: 2012

Hydrodynamic theory of the spinor BEC condensate with Rashba spin-orbit coupling is presented. A close mathematical analogy of the Rashba-Bose-Einstein condensate model to the recently developed theory of chiral magnetism is found. Hydrodynamic equations for mass density, superfluid velocity, and the local magnetization are derived. The mass current is shown to contain an extra term proportional to the magnetization direction, as a result of the Rashba coupling. Elementary excitations around the two known ground states of the Rashba-Bose-Einstein condensate Hamiltonian, the plane-wave, and the stripe states, are worked out in the hydrodynamic framework, highlighting the cross coupling of spin and superflow velocity excitations due to the Rashba term. © 2012 American Physical Society.

Li Y.,Urbana University | Park T.,Urbana University | Park T.,Pohang University of Science and Technology | Quansah J.K.,Urbana University | Zimmerman S.C.,Urbana University
Journal of the American Chemical Society | Year: 2011

A redox-responsive quadruple hydrogen-bonding module (eDAN) has been developed. The strong binding between the reduced form and its partner (DeUG) can be significantly decreased upon oxidation but restored upon subsequent reduction. This on-off switch was successfully applied to provide reversible control of macroscopic supramolecular polymer networks. © 2011 American Chemical Society.

Ahn J.-H.,Sungkyunkwan University | Je J.H.,Pohang University of Science and Technology
Journal of Physics D: Applied Physics | Year: 2012

Stretchable electronics, i.e. elastic electronics that can be bent and stretched, is a new, emerging class of electronics, based on building electronic circuits or devices on stretchable substrates. The potential applications range from fully conformable, stretchable, skin sensors for robotic devices, wearable electronic devices, to flesh-like biodevices. One of the challenges in the development of stretchable electronics is to retain full functionality under high external strains in stretching. In this paper, we review a few approaches recently developed for stretchable electronics and highlight recent research efforts on multi-directional writing for stretchable, three-dimensional structures. © 2012 IOP Publishing Ltd.

Kim K.,Pohang University of Science and Technology
IET Communications | Year: 2014

The sensing field on three-dimensional (3D) terrains that is supposed to be fully covered by deployed nodes may not be covered because of random aerial deployment. Non-uniform coverage has a negative impact upon that their lifetime and performance get short and worse, respectively. Mobile sensor networks (MSNs) are introduced to improve a coverage problem from sensor malfunction by an obstacle or the terrestrial environment. Providing coverage in a mountainous terrain has become critical issues in MSNs. This work proposes a 3D coverage method that can consider a physical feature, such as slope, in a mountainous terrain, that is, a 3D spiral model that allows mobile sensors to move freely in spiral lines devised using the height and radius of a concaved terrain. In the proposed model, the reasonable number of sensors to be deployed and the designated sensing points achieve full coverage. This paper focuses on full coverage for which the spiral model challenges the reasonability in the number of sensors. The experimental results show that the proposed method provides improved performance in terms of coverage ratios and expected coverage time; in addition, this has higher accuracy in lower power cost and better expansibility. © The Institution of Engineering and Technology.

Hwang H.S.,Pohang University of Science and Technology
Methods in molecular biology (Clifton, N.J.) | Year: 2013

Among the molecular diagnostic methods for bacteria-induced diseases, capillary electrophoresis-based single-strand conformation polymorphism (CE-SSCP) combined with 16S rRNA gene-specific PCR has enormous potential because it can separate sequence variants using a simple procedure. However, conventional CE-SSCP systems have limited resolution and cannot separate most 16S rRNA gene-specific markers into separate peaks. A high-resolution CE-SSCP system that uses a poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) triblock copolymer matrix was recently developed and shown to effectively separate highly similar PCR products. In this report, a protocol for the detection of 12 pathogenic bacteria is provided. Pathogen markers were amplified by PCR using universal primers and separated by CE-SSCP; each marker peak was well separated at baseline and showed a characteristic mobility, allowing the easy identification of the pathogens.

Kim J.K.,Sungkyunkwan University | Shin K.,Sungkyunkwan University | Cho S.M.,Sungkyunkwan University | Lee T.-W.,Pohang University of Science and Technology | Park J.H.,Sungkyunkwan University
Energy and Environmental Science | Year: 2011

Tungsten trioxide (WO3) films with a mesoporous morphology, high transparency, and monoclinic phase crystallinity were prepared using polyethyleneglycol (PEG) as a surfactant and their photoelectrochemical properties were measured. By controlling the weight ratio of the tungsten precursor to PEG, a sphere-like WO3 nanoparticle film with high transparency can be synthesized. The photocurrent responses of the films under 1 sun solar light illumination were measured. Due to the high transparency of the WO3 photoanode, it is possible to fabricate a tandem cell composed of a WO3/Pt bipolar electrode connected with a dye-sensitized solar cell. Unassisted water splitting from the tandem cell was demonstrated but the maximum current density was exhibited at around +0.4 V (vs. Pt). © 2011 The Royal Society of Chemistry.

Jhi S.-H.,Pohang University of Science and Technology | Ihm J.,Seoul National University
MRS Bulletin | Year: 2011

Hydrogen is considered by some to be a promising non-CO2- emitting energy carrier for the future. However, to realize a hydrogen economy, there are several technological barriers to overcome. Currently, safe and efficient storage of hydrogen is a bottleneck in the practical usage of hydrogen for fuels. In this article, we present a review on the first-principles computational approach in designing hydrogen storage materials with an emphasis on molecular hydrogen storage in nanostructured materials. Given the limitation of pristine nanostructures for room-temperature hydrogen storage, the strategy of decorating the backbone structure of the nanostructure with transition metal atoms in order to enhance the hydrogen adsorption energy is addressed, and the interplay between the Coulomb interactions and the so-called Kubas interaction (nondissociative weak chemisorption via electron donation and back-donation channels) has been studied. The influence of electron spin on the hydrogen binding energy, problems of metal clustering and oxidation, and the structural instability that may arise during hydrogen sorption are also discussed. We address the limitations and challenges in the development of high-capacity hydrogen storage materials and provide perspectives for how computational materials design can help cope with those problems. © 2011 Materials Research Society.

Lim J.,Pohang University of Science and Technology
Journal of Electrical Engineering and Technology | Year: 2013

In this paper, we propose and assess the performance of "H infinity filter (H∞, HIF)" and "cost reference particle filter (CRPF)" in the problem of tracking a target based on the measurements of the range and the bearing of the target. HIF and CRPF have the common advantageous feature that we do not need to know the noise statistics of the problem in their applications. The performance of the extended Kalman filter (EKF) is also compared with that of the proposed filters, but the noise information is perfectly known for the applications of the EKF. Simulation results show that CRPF outperforms HIF, and is more robust because the tracking of HIF diverges sometimes, particularly when the target track is highly nonlinear. Interestingly, when the tracking of HIF diverges, the tracking of the EKF also tends to deviate significantly from the true track for the same target track. Therefore, CRPF is very effective and appropriate approach to the problems of highly nonlinear model, especially when the noise statistics are unknown. Nonetheless, HIF also can be applied to the problem of timevarying state estimation as the EKF, particularly for the case when the noise statistcs are unknown. This paper provides a good example of how to apply CRPF and HIF to the estimation of dynamically varying and nonlinearly modeled states with unknown noise statistics.

Lim J.,Pohang University of Science and Technology
IEEE Wireless Communications | Year: 2015

Currently, LEDs are popularly employed in our daily life due to various advantages. LEDs can also be employed for wireless data communications (i.e., VLC). Based on these LED-VLC systems, we can obtain high-performance positioning systems beyond the performance of RF communications or global positioning systems. In this article, we present a brief overview of positioning approaches in VLC systems, and also propose a maximum likelihood approach for the positioning system. Currently, the main technologies employ triangulations or image sensors for positioning a receiver in VLC systems. The least squares method is popularly employed for triangulation approaches in various ways, and we enhance the positioning performance by employing an iterative maximum likelihood approach by adopting the least square solution as an initial guess. We show the optimality of the proposed approach based on sufficient SNR. © 2002-2012 IEEE.

Hyun K.D.,Grand Valley State University | Kim J.,Pohang University of Science and Technology
Computers in Human Behavior | Year: 2015

This study investigates whether three different types of news activities (i.e., news reception, news following, and news dissemination) and political conversation via social media have differential and interactive relationships on political participation. Analyses of survey data of social media users revealed that political conversation via social media was positively associated with political participation. Moreover, political conversation moderated the relationships among the three types of news activities and participation. Effects of news activities on political participation increased with the frequency with which people talked about politics on social media. © 2014 Elsevier Ltd. All rights reserved.

Ikeda H.,Kyoto University | Suzuki M.-T.,Japan Atomic Energy Agency | Arita R.,University of Tokyo | Takimoto T.,Pohang University of Science and Technology | And 2 more authors.
Nature Physics | Year: 2012

Exotic electronic states resulting from entangled spin and orbital degrees of freedom are hallmarks of strongly correlated f-electron systems. A spectacular example is the so-called hidden-order (HO) phase transition in the heavy-electron metal URu 2Si 2, which is characterized by the huge amount of entropy lost at T HO =17.5K (refs 2,3). However, no evidence of magnetic/structural phase transition has been found below T HO so far. The origin of the HO phase transition has been a long-standing mystery in condensed-matter physics. Here, on the basis of a first-principles theoretical approach, we examine the complete set of multipole correlations allowed in this material. The results uncover that the HO parameter is a rank-5 multipole (dotriacontapole) order with nematic E - symmetry, which exhibits staggered pseudospin moments along the [110] direction. This naturally provides comprehensive explanations of all key features in the HO phase including anisotropic magnetic excitations, the nearly degenerate antiferromagnetic-ordered state and spontaneous rotational-symmetry breaking. © 2012 Macmillan Publishers Limited. All rights reserved.

Kim C.S.,Hanyang University | Choi S.H.,Pohang University of Science and Technology | Bang J.H.,Hanyang University
ACS Applied Materials and Interfaces | Year: 2014

Despite recent significant strides in understanding various processes in quantum dot-sensitized solar cells (QDSSCs), little is known about the intrinsic electrocatalytic properties of copper sulfides that are the most commonly employed electrocatalysts for the counter electrode of QDSSCs. Given that the physical properties of copper sulfides are governed by their stoichiometry, the electrocatalytic activity of copper sulfides toward polysulfide reduction may also be dictated by their compositions. Using a new, simple approach to prepare robust copper sulfide films based on chemical bath deposition (CBD), we were able to delicately control the compositions of copper sulfides, which allowed us to perform a systematic investigation to gain new insight into copper sulfide-based electrocatalysts. The electrocatalytic activity is indeed dependent on the compositions of copper sulfides: Cu-deficient films (CuS and Cu1.12S) are superior to Cu-rich films (Cu1.75S and Cu1.8S) in their electrocatalytic activity. In addition, the stability of the Cu-deficient electrocatalysts is substantially better than that of the Cu-rich counterparts. © 2014 American Chemical Society.

Lee J.K.,Hoseo University | Kim M.-J.,Pohang University of Science and Technology
Journal of Molecular Catalysis B: Enzymatic | Year: 2011

The room temperature solid-phase ionic liquid (RTSPIL) co-lyophilized enzyme exhibited markedly enhanced activity in organic solvent. The enzyme co-lyophilized with a dodecyl-imidazolium salt was 660-fold more active compared to its RTSPIL-free counterpart. The activity enhancement by RTSPILs was mainly attributable to the reduced particle sizes and improved dispersion of enzymes suspended in organic solvent. Also, the RTSPIL co-lyophilized enzyme displayed significantly enhanced enantioselectivity. Its enantioselectivity was 2.5-fold higher than that of its RTSPIL-free counterpart. © 2010 Elsevier B.V. All rights reserved.

Reunchan P.,Asia Pacific Center for Theoretical Physics | Jhi S.-H.,Pohang University of Science and Technology
Applied Physics Letters | Year: 2011

First-principles calculations are carried out to study the role of various metal atoms on porous graphene for molecular hydrogen (H2) adsorption. The binding sites of each metal atom on porous graphene are investigated and the binding energies are determined. It is shown that H 2 exhibits different adsorption characteristics onto alkaline, alkaline-earth, or transition metals in porous graphene. In particular, Ca-decorated porous graphene is investigated and found to be feasible for high-capacity hydrogen storage. Our results provide a general picture on the interactions of H2 with porous graphene decorated with various metals. © 2011 American Institute of Physics.

Lee J.,Carnegie Mellon University | You D.,Carnegie Mellon University | You D.,Pohang University of Science and Technology
Journal of Computational Physics | Year: 2013

A fully-implicit ghost-cell immersed boundary method for simulations of flow over complex moving bodies on a Cartesian grid is presented. The present immersed boundary method is highly capable of controlling the generation of spurious force oscillations on the surface of a moving body, thereby producing an accurate and stable solution. Spurious force oscillations on the surface of an immersed moving body are reduced by alleviating spatial and temporal discontinuities in the pressure and velocity fields across non-grid conforming immersed boundaries. A sharp-interface ghost-cell immersed-boundary method is coupled with a mass source and sink algorithm to improve the conservation of mass across non-grid conforming immersed boundaries. To facilitate the control for the temporal discontinuity in the flow field due to a motion of an immersed body, a fully-implicit time-integration scheme is employed. A novel backward time-integration scheme is developed to effectively treat multiple layers of fresh cells generated by a motion of an immersed body at a high CFL number condition. The present backward time-integration scheme allows to impose more accurate and stable velocity vectors on fresh cells than those interpolated. The effectiveness of the present fully-implicit ghost-cell immersed boundary method coupled with a mass source and sink algorithm for reducing spurious force oscillations during simulations of moving body problems is demonstrated in a number of test cases.©2012 Elsevier Inc.

Bhadeshia H.K.D.H.,Pohang University of Science and Technology | Bhadeshia H.K.D.H.,University of Cambridge
Scripta Materialia | Year: 2014

The creation and use of computational models is seminal to the design of steels and associated processes, and many such models have now become of generic value. We illustrate here a few examples that explain the vitality of the subject and how the methodology is leading to benefits for commerce and academia alike. There are some breathtaking developments, which are critically assessed. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sahni V.,Inter-University Center for Astronomy and Astrophysics | Shafieloo A.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Pohang University of Science and Technology | Starobinsky A.A.,Kazan Federal University
Astrophysical Journal Letters | Year: 2014

Baryon acoustic oscillations (BAOs) allow us to determine the expansion history of the universe, thereby shedding light on the nature of dark energy. Recent observations of BAOs in the Sloan Digital Sky Survey (SDSS) DR9 and DR11 have provided us with statistically independent measurements of H(z) at redshifts of 0.57 and 2.34, respectively. We show that these measurements can be used to test the cosmological constant hypothesis in a model-independent manner by means of an improved version of the Om diagnostic. Our results indicate that the SDSS DR11 measurement of H(z) = 222 ± 7 km s-1Mpc-1at z = 2.34, when taken in tandem with measurements of H(z) at lower redshifts, imply considerable tension with the standard ΛCDM model. Our estimation of the new diagnostic Omh 2from SDSS DR9 and DR11 data, namely, Omh 20.122 ± 0.01, which is equivalent to Ω0m h 2for the spatially flat ΛCDM model, is in tension with the value Ω0m h 2= 0.1426 ± 0.0025 determined for ΛCDM from Planck+WP. This tension is alleviated in models in which the cosmological constant was dynamically screened (compensated) in the past. Such evolving dark energy models display a pole in the effective equation of state of dark energy at high redshifts, which emerges as a smoking gun test for these theories. © 2014. The American Astronomical Society. All rights reserved..

Das S.K.,McGill University | Kang Y.-B.,Pohang University of Science and Technology | Ha T.,Gangneung - Wonju National University | Jung I.-H.,McGill University
Acta Materialia | Year: 2014

Diffusion couple experiments for the Mg-Gd and Mg-Y systems were performed with Mg single crystals to investigate the anisotropic diffusion behavior of Gd and Y in hexagonal close packed (hcp) Mg at temperatures between 703 and 803 K (430 and 530 °C). Diffusion coefficients for both Gd and Y along the basal plane of hcp Mg are approximately three times higher than those along the normal direction of the basal plane. The impurity diffusion coefficients of both Gd and Y in hcp Mg are lower than the self-diffusion of Mg and impurity diffusions of Al and Zn by about one order of magnitude. Growth constants and inter-diffusion coefficients of the intermediate phases for both systems were determined. Accurate thermodynamic modeling of the Mg-Y and Mg-Gd systems were also carried out based on the phase diagram data obtained from the present diffusion couple experiments and available literature data. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Bak A.,Kyungpook National University | Choi W.,Pohang University of Science and Technology | Park H.,Kyungpook National University
Applied Catalysis B: Environmental | Year: 2011

Photoelectrochemical (PEC) water oxidation using hematite (α-Fe2O3) is of great interest in terms of solar fuels and artificial photosynthesis. In this study, Cd-incorporated nanocrystalline hematite films (Cd-Fe2O3) supported on conducting glass have been prepared via co-electrodeposition of aqueous Fe(III) and Cd(II) with varying Cd:Fe atomic ratios (up to 3.2at.%) and optimized for their PEC performances under a simulated solar light (AM 1.5-irradiation). Surface analysis indicates that the Cd co-deposition increases the hematite particle size from ca. 50nm to 70-100nm due to interparticle agglomeration and decreases the overall UV-Vis absorbance of hematite. X-ray photoelectron spectroscopic study also indicates that Cd incorporation shifts the binding energy of oxygen atoms to lower energy direction whereas it does not affect the binding energy of Fe 3d. This suggests that Cd exists mainly as CdO and/or Cd(OH)2 in the hematite surface. When an optimal level of Cd content (∼1at.%) is electrodeposited, the photocurrent of hematite film is significantly enhanced by a factor of ca. four at E=1.23VRHE under AM 1.5-irradiation and the photoactive spectral region is red-shifted. Electrochemical impedance spectroscopic analysis further reveals that the flat band potential of hematite is shifted by ca. -30mV to negative potential direction and the charge transfer resistance (Rct) is significantly reduced by Cd incorporation. Detailed surface analyses, optimization for preparation condition of hematite films, and discussion for PEC behaviors were described. © 2011 Elsevier B.V.

Choi S.,Pohang University of Science and Technology | Kuchenbecker K.J.,University of Pennsylvania
Proceedings of the IEEE | Year: 2013

This paper reviews the technology and applications of vibrotactile display, an effective information transfer modality for the emerging area of haptic media. Our emphasis is on summarizing foundational knowledge in this area and providing implementation guidelines for application designers who do not yet have a background in haptics. Specifically, we explain the relevant human vibrotactile perceptual capabilities, detail the main types of commercial vibrotactile actuators, and describe how to build both monolithic and localized vibrotactile displays. We then identify exemplary vibrotactile display systems in application areas ranging from the presentation of physical object properties to broadcasting vibrotactile media content. © 1963-2012 IEEE.

Meier I.,Ohio State University | Somers D.E.,Ohio State University | Somers D.E.,Pohang University of Science and Technology
Current Opinion in Plant Biology | Year: 2011

The timing and position of molecular components within the cell are clearly important in the context of signal transduction. One challenge in attaining correct cellular positioning is the nuclear envelope, which separates the cell into two fundamentally different compartments. Molecular passaging from one to the other is highly selective due to the required recognition by the nucleocytoplasmic transport machinery. It is becoming increasingly clear that a highly diverse set of mechanisms have developed to allow environmental (biotic and abiotic) and endogenous signals to alter the nucleocytoplasmic partitioning of key molecules. In many cases this occurs by adjusting the access of the regulated species to the canonical import/export machinery. Recent studies are uncovering the sophistication and complexity of the processes that use the canonical transport machinery in the service of a diversity of signaling pathways. © 2011.

Zhou W.,Northwestern University | Zhou W.,Harvard University | Dridi M.,Northwestern University | Suh J.Y.,Northwestern University | And 6 more authors.
Nature Nanotechnology | Year: 2013

Periodic dielectric structures are typically integrated with a planar waveguide to create photonic band-edge modes for feedback in one-dimensional distributed feedback lasers and two-dimensional photonic-crystal lasers. Although photonic band-edge lasers are widely used in optics and biological applications, drawbacks include low modulation speeds and diffraction-limited mode confinement. In contrast, plasmonic nanolasers can support ultrafast dynamics and ultrasmall mode volumes. However, because of the large momentum mismatch between their nanolocalized lasing fields and free-space light, they suffer from large radiative losses and lack beam directionality. Here, we report lasing action from band-edge lattice plasmons in arrays of plasmonic nanocavities in a homogeneous dielectric environment. We find that optically pumped, two-dimensional arrays of plasmonic Au or Ag nanoparticles surrounded by an organic gain medium show directional beam emission (divergence angle <1.5and linewidth <1.3 nm) characteristic of lasing action in the far-field, and behave as arrays of nanoscale light sources in the near-field. Using a semi-quantum electromagnetic approach to simulate the active optical responses, we show that lasing is achieved through stimulated energy transfer from the gain to the band-edge lattice plasmons in the deep subwavelength vicinity of the individual nanoparticles. Using femtosecond-transient absorption spectroscopy, we verified that lattice plasmons in plasmonic nanoparticle arrays could reach a 200-fold enhancement of the spontaneous emission rate of the dye because of their large local density of optical states. © 2013 Macmillan Publishers Limited. All rights reserved.

Ahn H.S.,Incheon National University | Kim M.H.,Pohang University of Science and Technology
International Journal of Heat and Mass Transfer | Year: 2013

This study examined saturated water/alumina nanofluid pool boiling on a 10-mm-diameter, upward-facing, plain copper heater under atmospheric pressure. In order to investigate the effect of a nanoparticle coating on the boiling phenomenon near critical heat flux, we compared the boiling characteristics of water boiling before, alumina nanofluid boiling, and water boiling after alumina nanoparticles. The unusual boiling characteristics (bending point in the boiling curve at a high heat flux), CHF enhancement, and gradual increase of wall temperature just after the CHF (instead of the rapid increase of wall temperature) were analyzed based on high-speed visualizations. A thicker macrolayer resulting from the nanoparticle coating is estimated to influence the CHF enhancement, which played a role similar to a porous medium. Thus, we revealed that the nanoparticle coating induced the transition boiling with the nucleate boiling and the partial dry-patch (vapor film in the large vapor mushroom) at a high heat flux as the role of porous medium, which explained the bending point in the boiling curve and the gradual increase of wall temperature. © 2013 Elsevier B.V. All rights reserved.

Lee D.,University of Ulsan | Lee J.,Pohang University of Science and Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2010

Clustering methods utilizing support estimates of a data distribution have recently attracted much attention because of their ability to generate cluster boundaries of arbitrary shape and to deal with outliers efficiently. In this paper, we propose a novel dissimilarity measure based on a dynamical system associated with support estimating functions. Theoretical foundations of the proposed measure are developed and applied to construct a clustering method that can effectively partition the whole data space. Simulation results demonstrate that clustering based on the proposed dissimilarity measure is robust to the choice of kernel parameters and able to control the number of clusters efficiently. © 2006 IEEE.

Jung S.-M.,Pohang University of Science and Technology
ISIJ International | Year: 2014

The effects of molar ratio of C/O and the particle size of char on carbothermic reduction of titanomagnetite (TTM) were investigated from a kinetic viewpoint at 1 100°C employing thermogravimetric analysis (TGA) and quadruple mass spectrometry (QMS). An increase in molar ratio of C/O results in a higher rate of carbon gasification, leading to an increase in final fraction reduction of TTM since excessive amount of char in TTM and char composite shifted the equilibrium in carbothermic reduction of TTM from the wustite/Fe equilibrium to that by the carbon gasification. With decreasing the particle size of char, the carbothermic reduction of TTM was improved by the activation of carbon gasification. © 2014 ISIJ.

Kim J.,Ohio State University | Somers D.E.,Ohio State University | Somers D.E.,Pohang University of Science and Technology
Plant Physiology | Year: 2010

Rapid assessment of the effect of reduced levels of gene products is often a bottleneck in determining how to proceed with an interesting gene candidate. Additionally, gene families with closely related members can confound determination of the role of even a single one of the group. We describe here an in vivo method to rapidly determine gene function using transient expression of artificial microRNAs (amiRNAs) in Arabidopsis (Arabidopsis thaliana) mesophyll protoplasts. We use a luciferasebased reporter of circadian clock activity to optimize and validate this system. Protoplasts transiently cotransfected with promoter-luciferase and gene-specific amiRNA plasmids sustain free-running rhythms of bioluminescence for more than 6 d. Using both amiRNA plasmids available through the Arabidopsis Biological Resource Center, as well as custom design of constructs using the Weigel amiRNA design algorithm, we show that transient knockdown of known clock genes recapitulates the same circadian phenotypes reported in the literature for loss-of-function mutant plants. We additionally show that amiRNA designed to knock down expression of the casein kinase II β-subunit gene family lengthens period, consistent with previous reports of a short period in casein kinase II β-subunit overexpressors. Our results demonstrate that this system can facilitate a much more rapid analysis of gene function by obviating the need to initially establish stably transformed transgenics to assess the phenotype of gene knockdowns. This approach will be useful in a wide range of plant disciplines when an endogenous cell-based phenotype is observable or can be devised, as done here using a luciferase reporter. © 2010 American Society of Plant Biologists.

Lu Q.,University of Alberta | Hwang D.S.,Pohang University of Science and Technology | Liu Y.,University of Alberta | Zeng H.,University of Alberta
Biomaterials | Year: 2012

Protective coating of the byssus of mussels (Mytilus sp.) has been suggested as a new paradigm of medical coating due to its high extensibility and hardness co-existence without their mutual detriment. The only known biomacromolecule in the extensible and tough coating on the byssus is mussel foot protein-1 (mfp-1), which is made up with positively charged residues (~20 mol%) and lack of negatively charged residues. Here, adhesion and molecular interaction mechanisms of Mytilus californianus foot protein-1 (mcfp-1) from California blue mussel were investigated using a surface forces apparatus (SFA) in buffer solutions of different ionic concentrations (0.2-0.7 M) and pHs (3.0-5.5). Strong and reversible cohesion between opposed positively charged mcfp-1 films was measured in 0.1 M sodium acetate buffer with 0.1 M KNO 3. Cohesion of mcfp-1 was gradually reduced with increasing the ionic strength, but was not changed with pH variations. Oxidation of 3,4-dihydroxyphenylalanine (DOPA) residues of mcfp-1, a key residue for adhesive and coating proteins of mussel, didn't change the cohesion strength of mcfp-1 films, but the addition of chemicals with aromatic groups (i.e., aspirin and 4-methylcatechol) increased the cohesion. These results suggest that the cohesion of mcfp-1 films is mainly mediated by cation-π interactions between the positively charged residues and benzene rings of DOPA and other aromatic amino acids (~20 mol% of total amino acids of mcfp-1), and π-π interactions between the phenyl groups in mcfp-1. The adhesion mechanism obtained for the mcfp-1 proteins provides important insight into the design and development of functional biomaterials and coatings mimicking the extensible and robust mussel cuticle coating. © 2011 Elsevier Ltd.

Hazra D.K.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Pohang University of Science and Technology | Souradeep T.,Inter-University Center for Astronomy and Astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Constraints on the main cosmological parameters using cosmic microwave background (CMB) or large scale structure data are usually based on the power-law assumption of the primordial power spectrum (PPS). However, in the absence of a preferred model for the early Universe, this raises a concern that current cosmological parameter estimates are strongly prejudiced by the assumed power-law form of PPS. In this paper, for the first time, we perform cosmological parameter estimation allowing the free form of the primordial spectrum. This is in fact the most general approach to estimate cosmological parameters without assuming any particular form for the primordial spectrum. We use a direct reconstruction of the PPS for any point in the cosmological parameter space using the recently modified Richardson-Lucy algorithm; however, other alternative reconstruction methods could be used for this purpose as well. We use WMAP 9 year data in our analysis considering the CMB lensing effect, and we report, for the first time, that the flat spatial universe with no cosmological constant is ruled out by more than a 4σ confidence limit without assuming any particular form of the primordial spectrum. This would be probably the most robust indication for dark energy using CMB data alone. Our results on the estimated cosmological parameters show that higher values of the baryonic and matter density and a lower value of the Hubble parameter (in comparison to the estimated values by assuming power-law PPS) is preferred by the data. However, the estimated cosmological parameters by assuming a free form of the PPS have an overlap at 1σ confidence level with the estimated values assuming the power-law form of PPS. © 2013 American Physical Society.

Jeong H.Y.,Pohang University of Science and Technology | Han Y.-S.,University of Michigan | Hayes K.,University of Michigan
Environmental Science and Technology | Year: 2010

In this study we investigated the speciation of the solidphase As formed by reacting 2 x 10-4 M As(III) with 1.0 g/L mackinawite and the potential for these sorbed species to be mobilized (released into the aqueous phase) upon exposure to atmospheric oxygen at pH 4.9, 7.1, and 9.1. Before oxygen exposure, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analyses indicated that As(III) was removed from the aqueous phase by forming As(0), AsS, and surface precipitates as thioarsenites at pH 4.9 and As(0) and thioarsenite surface precipitates at pH 7.1 and 9.1. When oxygen was introduced, XAS analysis indicated that As(0) and the surface precipitates were quickly transformed, whereas AsS was persistent. During intermediate oxygen exposure times, dissolved As increased at pH 4.9 and 7.1 due to the rapid oxidation of As(0) and the slow precipitation of iron (oxyhydr)oxides, the oxidation products of mackinawite. This indicates that oxidative mobilization is a potential pathway for arsenic contamination of water at acidic to neutral pH. The mobilized As was eventually resorbed by forming edgesharing and double-corner-sharing surface complexes with iron (oxyhydr)oxides. © 2010 American Chemical Society.

Lim Y.T.,Pohang University of Science and Technology | Son J.Y.,Kyung Hee University | Rhee J.-S.,Kyung Hee University
Ceramics International | Year: 2013

We report a vertical ZnO nanorod array as a highly sensitive hydrogen gas sensor. The vertical ZnO nanorod array on an Nb/Si substrate was fabricated using an anodized aluminum oxide nanotemplate and an atomic layer deposition method. The vertical ZnO nanorod array hydrogen gas sensor exhibited a high sensitivity for hydrogen in a wide concentration range. © 2012 Elsevier Ltd and Techna Group S.r.l.

Soare S.,Technical University of Cluj Napoca | Barlat F.,Pohang University of Science and Technology
Journal of the Mechanics and Physics of Solids | Year: 2010

It is shown that some of the recently proposed orthotropic yield functions obtained through the linear transformation method are homogeneous polynomials. This simple observation has the potential to simplify considerably their implementation into finite element codes. It also leads to a general method for designing convex polynomial yield functions with powerful modeling capabilities. Convex parameterizations are given for the fourth, sixth and eighth order plane stress orthotropic homogeneous polynomials. Illustrations are shown for the modeling of biaxial and directional yielding properties of steel and aluminum alloy sheets. The parametrization method can be easily extended to general, 3D stress states. © 2010 Elsevier Ltd. All rights reserved.

Cho K.-H.,Korea Advanced Institute of Science and Technology | Kim M.-H.,Pohang University of Science and Technology
International Journal of Heat and Mass Transfer | Year: 2012

Here we develop new vascular designs for the volumetric bathing of smart structures under time-varying conditions. The three flow configurations described in this paper are the first, second, and third constructal structures with optimized hydraulic diameters (D 1 and D 2) and non-optimized hydraulic diameter (D) for one system size, 20 × 20. The main objective was to determine the longest permissible time delay so that the maximum temperatures do not exceed the maximum allowable limit. It is the best to cool with the first construct in the optimized constructal configurations when pressure drop number (Be) is lower than 1 × 10 11 and the best structure is the second constructal structure when pressure drop number (Be) is greater than 2 × 10 11, whereas the best structure in the non-optimized constructal configurations is the third construct. It is also shown that the most attractive configurations have larger allowable delay times: in both the optimized and non-optimized constructal structures, the best configuration is the second construct where the pressure drop is fixed at about 1 kPa. © 2012 Elsevier Ltd. All rights reserved.

Das L.K.,University of Calcutta | Park S.-W.,Pohang University of Science and Technology | Cho S.J.,Chosun University | Ghosh A.,University of Calcutta
Dalton Transactions | Year: 2012

Two new trinuclear hetero-metallic copper(ii)-zinc(ii) complexes [(CuL)2Zn(N3)2] (1A and 1B) have been synthesized using [CuL] as a so-called "metalloligand" (where H 2L = N,N′-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Complexes 1A and 1B have the same molecular formula but crystallize in different crystal systems (triclinic for 1A and monoclinic for 1B) with space group P1 for 1A and P21/c for 1B. 1A is an angular trinuclear species, in which two terminal four-coordinate square planar "metalloligand" [CuL] are coordinated to a central Zn(ii) through double phenoxido bridges. The Zn(ii) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal azide ions. In complex 1B, in addition to the double phenoxido bridge, the two terminal Cu(ii) ions are linked to the central Zn(ii) via a μ-l,l azido bridge giving rise to a square pyramidal environment around the Cu(ii) ions and consequently the structure becomes linear. These two species can be considered as "linear-bent" isomers. EPR spectra and ESI mass spectra show that the two isomers are identical in solution. The DFT calculation reveals that the energy of 1A is 7.06 kcal mol-1 higher than that of 1B. The existence of both isomers in the solid state suggests that crystal packing interactions in 1A are more efficient and probably compensate for the difference in energy. © 2012 The Royal Society of Chemistry.

Jung J.-I.,Ulsan National Institute of Science and Technology | Jeong H.Y.,Ulsan National Institute of Science and Technology | Kim M.G.,Pohang University of Science and Technology | Nam G.,Ulsan National Institute of Science and Technology | And 2 more authors.
Advanced Materials | Year: 2015

(Figure Presented) A heat-treatment approach for Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF5582) is introduced as a way of enhancing the electrocatalytic performance of perovskite catalysts. The perovskite made by heat-treatment in oxygen atmosphere loses around 30 nm of spinel layer on the surface relative to the untreated version, and demonstrates enhanced oxygen reduction reaction and oxygen evolution reaction catalytic activities. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

Sasano Y.,Tohoku University | Nagasawa S.,Tohoku University | Yamazaki M.,Tohoku University | Shibuya M.,Tohoku University | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2014

The direct oxidation of unprotected amino alcohols to their corresponding amino carbonyl compounds has often posed serious challenges in organic synthesis and has constrained chemists to adopting an indirect route, such as a protection/deprotection strategy, to attain their goal. Described herein is a highly chemoselective aerobic oxidation of unprotected amino alcohols to their amino carbonyl compounds in which 2-azaadamantane N-oxyl (AZADO)/copper catalysis is used. The catalytic system developed leads to the alcohol-selective oxidation of various unprotected amino alcohols, carrying a primary, secondary, or tertiary amino group, in good to high yield at ambient temperature with exposure to air, thus offering flexibility in the synthesis of nitrogen-containing compounds. Strong as an ox: The highly chemoselective aerobic oxidation of unprotected amino alcohols to their corresponding amino carbonyl compounds has been achieved by using 2-azaadamantane N-oxyl (AZADO)/copper catalysis. This catalytic system oxidizes not only alcohols with tertiary amino groups but also those with secondary and primary amines in good to high yield at ambient temperature in air. bpy=2,2-bipyridyl, DMAP=4-(N,N-dimethylamino)pyridine. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lim S.-R.,University of California at Davis | Park J.M.,Pohang University of Science and Technology
Industrial and Engineering Chemistry Research | Year: 2010

Water network synthesis is to optimize a water supply system by connecting water sources to sinks in order to maximize water reuse. This synthesis has been applied within a factory to reduce freshwater consumption. This study illustrates (i) the synthesis and design of an interfactory and intrafactory water network system for an eco-industrial park (EIPWNS) utilizing more opportunities for water reuse within an industrial park, and (ii) an environmental and economic feasibility study to demonstrate benefits from industrial symbiosis. An EIPWNS is synthesized, designed, and compared to a conventional water system (CWS). The feasibility study using life cycle assessment and life cycle costing shows that the total environmental impacts of the EIPWNS are 7.5% to 16.0% less than those of the CWS, and the life cycle cost of the EIPWNS is 15.6% less. Therefore, the EIPWNS can be employed in remodeling a conventional industrial park to an eco-industrial park. This study provides a good example for disseminating EIPWNSs. © 2010 American Chemical Society.

Gunjakar J.L.,Ewha Womans University | Kim I.Y.,Ewha Womans University | Lee J.M.,Ewha Womans University | Lee N.-S.,Pohang University of Science and Technology | Hwang S.-J.,Ewha Womans University
Energy and Environmental Science | Year: 2013

Highly efficient photocatalysts for visible light-induced O2 generation are synthesized via an electrostatically derived self-assembly of Zn-Cr-LDH 2D nanoplates with graphene 2D nanosheets. In the obtained nanohybrids, the positively charged Zn-Cr-LDH nanoplates are immobilized on the surface of negatively charged graphene nanosheets with the formation of a highly porous stacked structure. A strong electronic coupling of the subnanometer-thick Zn-Cr-LDH nanoplates with reduced graphene oxide (RGO)/graphene oxide (GO) nanosheets gives rise not only to the prominent increase of visible light absorption but also to a remarkable depression of the photoluminescence signal. The self-assembled Zn-Cr-LDH-RGO nanohybrids display an unusually high photocatalytic activity for visible light-induced O 2 generation with a rate of ∼1.20 mmol h-1 g -1, which is far superior to that of the pristine Zn-Cr-LDH material (∼0.67 mmol h-1 g-1). The fact that pristine Zn-Cr-LDH is one of the most effective visible light photocatalysts for O2 production with unusually high quantum efficiency of 61% at λ = 410 nm highlights the excellent functionality of the Zn-Cr-LDH-RGO nanohybrids as visible light active photocatalysts. The Zn-Cr-LDH-RGO nanohybrid shows a higher photocatalytic activity than the Zn-Cr-LDH-GO nanohybrid, providing strong evidence for the superior advantage of the hybridization with RGO. The present findings clearly demonstrate that graphene nanosheets can be used as an effective platform for improving the photocatalytic activity of 2D nanostructured inorganic solids. © 2013 The Royal Society of Chemistry.

Lee Y.K.,Kongju National University | Lee J.S.,Chonnam National University | Heo J.,Pohang University of Science and Technology | Im W.B.,Chonnam National University | Chung W.J.,Kongju National University
Optics Letters | Year: 2012

Phosphor-in-glass (PiG) typed robust color converters were fabricated using Pb-free silicate glasses for high-power white LED applications. SiO 2-B2O3-RO(R = Ba, Zn) glass powder showed good sintering behavior and high visible transparency under the sintering condition of 750 °C for 30 min without noticeable interaction with phosphors. By simply changing the thickness of the PiG plate or mixing ratio of glass to Y3Al5O12:Ce3+ phosphor, CIE chromaticity coordinates of the LED can be easily controlled. Enhanced thermal quenching property of PiG compared to phosphor with conventional silicone resin suggests its prominent feasibility for high-power/high-brightness white LEDs. © 2012 Optical Society of America.

Hazra D.K.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Pohang University of Science and Technology | Smoot G.F.,University Paris Diderot | Smoot G.F.,University of California at Berkeley | Starobinsky A.A.,Russian Academy of Sciences
Physical Review Letters | Year: 2014

Motivated by the idea that inflation occurs at the grand unified theory symmetry breaking scale, in this Letter we construct a new class of large field inflaton potentials where the inflaton starts with a power law potential; after an initial period of relatively fast roll that lasts until after a few e folds inside the horizon it transits to the attractor of the slow roll part of the potential with a lower power. Because of the initial fast roll stages of inflation, we find a suppression in scalar primordial power at large scales and at the same time the choice of the potential can provide us a tensor primordial spectrum with a high amplitude. This suppression in scalar power with a large tensor-to-scalar ratio helps us to reconcile the Planck and BICEP2 data in a single framework. We find that a transition from a cubic to quadratic form of inflaton potential generates an appropriate suppression in the power of the scalar primordial spectrum that provides a significant improvement in fit compared to the power law model when compared with Planck and BICEP2 data together. We calculate the extent of non-Gaussianity, specifically, the bispectrum for the best fit potential, and show that it is consistent with Planck bispectrum constraints. © 2014 American Physical Society.

Jung S.-H.,Korea Advanced Institute of Science and Technology | Yoon D.Y.,Pohang University of Science and Technology | Kang S.-J.L.,Korea Advanced Institute of Science and Technology
Acta Materialia | Year: 2013

During annealing of ultrafine nickel powder compacts, abnormal grain growth (AGG) occurred with the formation of cube-shaped grains. The observed AGG is similar to the late-stage abnormal grain growth (LS-AGG) that is commonly observed in electrodeposited (ED) Ni sheets. The cube shape of the abnormal grains with {1 0 0} facets was identical to that of late-stage abnormal grains in ED Ni. As the temperature increased, the time to the appearance of abnormal grains decreased. After impingement of abnormal grains, little further grain growth occurred, indicating stagnant grain growth behavior. The formation of abnormal grains in the present study, however, cannot be explained by the previously suggested AGG mechanisms, i.e. the S phase wetting mechanism and initial texture mechanism, because no amorphous phase containing S was present and no texture developed in our samples. In contrast, the observed grain growth behavior can be well explained in terms of the coupling effect of the maximum driving force for grain growth and the critical driving force for appreciable migration of faceted boundaries. It is concluded that the AGG in ultrafine-grained Ni occurs via mixed migration mechanisms, i.e. diffusion and interface reaction-controlled, of faceted boundaries with respect to the driving force. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Weng S.,Pohang University of Science and Technology
Mathematical Methods in the Applied Sciences | Year: 2016

In this paper, we first address the space-time decay properties for higher-order derivatives of strong solutions to the Boussinesq system in the usual Sobolev space. The decay rates obtained here are optimal. The proof is based on a parabolic interpolation inequality, bootstrap argument, and some weighted estimates. Secondly, we present a new solution integration formula for the Boussinesq system, which will be employed to establish the existence of strong solutions for small initial data in some scaling invariant function spaces. The smallness conditions are somehow weaker than those presented by Brandolese and Schonbek. We further investigate the asymptotic profiles and decay properties of these strong solutions. © 2016 John Wiley & Sons, Ltd.

Lim Y.-T.,Pohang University of Science and Technology | Son J.Y.,Kyung Hee University
Electronic Materials Letters | Year: 2013

La0. 8Sr0. 2Ga0. 8Mg0. 2O3 (LSGM) and La0. 8Sr0. 2Ga0. 8Mg0. 115Co0. 085O3 (LSGMC) thin films were deposited on single crystalline (001) Al2O3 substrates using a pulsed laser deposition technique. The LSGM and LSGMC thin films exhibited only a single phase, which was verified through x-ray diffraction (XRD) experiments. Scanning electron microscopy (SEM) showed that the grain size of the LSGM film was smaller than that of the LSGMC films. Below 800 K, the ionic conductivity of both the thin films was higher than that of bulk sample. Furthermore, the LSGM thin film showed higher ionic conductivity than the LSGMC thin film at temperatures above 600 K. © 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.

Zhang K.,Sungkyunkwan University | Shi X.,Sungkyunkwan University | Kim J.K.,Sungkyunkwan University | Lee J.S.,Pohang University of Science and Technology | Park J.H.,Sungkyunkwan University
Nanoscale | Year: 2013

A graphene interlayer was successfully inserted into inverse opaline hematite (α-Fe2O3) photoanodes for solar water splitting using the template assisted electrodeposition method. Finding the optimal thermal annealing temperature is crucial for the successful attainment of the inverse opaline hematite nanostructure on a graphene thin film. This is because an appropriate temperature is required to convert pre-deposited Fe 0 into hematite with optimum crystalline structure and to simultaneously remove the soft polystyrene template without thermal degradation of the graphene film on a transparent conductive substrate. Different from the conventional strategies based on graphene-semiconductor systems, this novel mechanism has been proposed whereby the graphene interlayer can act as both an electron transfer layer and an electrolyte blocking barrier, by which it not only reduces the charge recombination at the substrate-electrolyte interface but also helps electron transportation from α-Fe2O3 to the substrate of the photoanode. Therefore, both photocurrent density and incident photon-to-current efficiency (IPCE) have been remarkably improved, which are several times higher than those of the pure inverse opaline hematite photoanode. © 2013 The Royal Society of Chemistry.

Choi S.K.,Kyungpook National University | Choi W.,Pohang University of Science and Technology | Park H.,Kyungpook National University
Physical Chemistry Chemical Physics | Year: 2013

A naturally abundant nickel-borate (Ni-Bi) complex is demonstrated to successfully catalyze the photoelectrochemical (PEC) water oxidation of BiVO4 electrodes at 1.23 VRHE with nearly 100% faradaic efficiency for oxygen evolution. Ni-Bi is electrodeposited (ED) and photodeposited (PD) for varying times on BiVO4 electrodes in the 0.1 M borate electrolyte with 1 mM Ni2+ at pH 9.2. Surprisingly, optimally deposited Ni-Bi films (ED-10 s and PD-30 min) display the same layer thickness of ca. 40 nm. Both Ni-Bi films enhance the photocurrent generation of BiVO4 at 1.23 VRHE by a factor of 3-4 under AM 1.5-light irradiation (100 mW cm-2) along with ca. 250% increase in the incident and absorbed photon-to-current efficiencies. Impedance analysis further reveals that the charge transfer resistance at BiVO4 is markedly decreased by Ni-Bi deposits. The primary role of Ni-Bi has been suggested to be a hole-conductor making photogenerated electrons more mobile and catalyzing a four-hole transfer to water through cyclic changes between the lower and higher Ni oxidation states. However, thick Ni-Bi films (>∼40 nm) significantly reduce the PEC performance of BiVO4 due to the kinetic bottleneck and charge recombination. Under identical PEC conditions (0.1 M, pH 9.2), the borate electrolyte (good proton acceptor) is found to be better than nitrate (poor proton acceptor), indicative of a proton-coupled electron transfer pathway in PEC water oxidation. © 2013 the Owner Societies.

Asgharzadeh H.,University of Tabriz | Kim H.S.,Pohang University of Science and Technology | Simchi A.,Sharif University of Technology
Materials Characterization | Year: 2012

An ultrafine-grained Al6063/Al 2O 3 (0.8vol.%, 25nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (<0.1μm), ultrafine grains (0.1-1μm), and micron-size grains (>1μm) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle grain boundaries rather than nanometric alumina particles. Hot deformation behavior of the material at different temperatures and strain rates was studied by compression test and compared to coarse-grained Al6063 alloy. The activation energy of the hot deformation process for the nanocomposite was determined to be 291kJmol -1, which is about 64% higher than that of the coarse-grained alloy. Detailed microstructural analysis revealed that dynamic recrystallization is responsible for the observed deformation softening in the ultrafine-grained nanocomposite. © 2012 Elsevier Inc.

Cho J.,Rensselaer Polytechnic Institute | Schubert E.F.,Rensselaer Polytechnic Institute | Kim J.K.,Pohang University of Science and Technology
Laser and Photonics Reviews | Year: 2013

Efficiency droop, i.e. the loss of efficiency at high operating current, afflicts nitride-based light-emitting diodes (LEDs). The droop phenomenon is currently the subject of intense research, as it retards the advancement of solid-state lighting which is just starting to supplant fluorescent as well as incandescent lighting. Although the technical community does not yet have consented to a single cause of droop, this article provides a summary of the present state of droop research, reviews currently discussed droop mechanisms, and presents a recently developed theoretical model for the efficiency droop. In the theoretical model, carrier leakage out of the active region caused by the asymmetry of the pn junction, specifically the disparity between electron and hole concentrations and mobilities, is discussed in detail. The model is in agreement with the droop's key behaviors not only for GaInN LEDs but also for AlGaInP LEDs. © 2012 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bhadeshia H.K.D.H.,University of Cambridge | Bhadeshia H.K.D.H.,Pohang University of Science and Technology
Progress in Materials Science | Year: 2012

A casual metallurgist might be forgiven in believing that there are but a few basic types of steels used in the manufacture of some of the most technologically important engineering components, the rolling bearings. First the famous 1C-1.5Cr steel from which the majority of bearings are made. Its structure is apparently well-understood and the focus is on purity in order to avoid inclusions which initiate fatigue during rolling contact. Then there is the M50 steel and its variants, from which bearings which serve at slightly higher temperatures in aeroengines are manufactured, based on secondary-hardened martensite. The casual metallurgist would be wrong; there is a richness in the subject which inspires deep study. There are phenomena which are little understood, apparently incommensurate observations, some significant developments and other areas where convincing conclusions are difficult to reach. The subject seemed ready for a critical assessment; hence, this review. The structure and properties of bearing steels prior to the point of service are first assessed and described in the context of steelmaking, manufacturing and engineering requirements. This is followed by a thorough critique of the damage mechanisms that operate during service and in accelerated tests. © 2011 Elsevier Ltd. All rights reserved.

Yoon H.,Pohang University of Science and Technology
Nature Materials | Year: 2016

Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d1 electronic configuration, and induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)–metal (HxVO2)–insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage. © 2016 Nature Publishing Group

Gong J.-O.,Asia Pacific Center for Theoretical Physics | Gong J.-O.,Pohang University of Science and Technology | Sasaki M.,Kyoto University
Classical and Quantum Gravity | Year: 2013

We study the general relation between the power spectrum and the squeezed limit of the bispectrum of the comoving curvature perturbation produced during single-field slow-roll inflation when the initial state is a general vacuum. Assuming the scale invariance of the power spectrum, we derive a formula for the squeezed limit of the bispectrum, represented by the parameter fNL, which is not slow-roll suppressed and is found to contain a single free parameter for a given amplitude of the power spectrum. Then, we derive the conditions for achieving a scale-invariant fNL and discuss a few examples. © 2013 IOP Publishing Ltd.

Bernasconi L.,Rutherford Appleton Laboratory | Baerends E.J.,VU University Amsterdam | Baerends E.J.,Pohang University of Science and Technology | Baerends E.J.,King Abdulaziz University
Journal of the American Chemical Society | Year: 2013

Solvation effects on chemical reactivity are often rationalized using electrostatic considerations: the reduced stabilization of the transition state results in higher reaction barriers and lower reactivity in solution. We demonstrate that the effect of solvation on the relative energies of the frontier orbitals is equally important and may even reverse the trend expected from purely electrostatic arguments. We consider the H abstraction reaction from methane by quintet [EDTAHn·FeO](n-2)+, (n = 0-4) complexes in the gas phase and in aqueous solution, which we examine using ab initio thermodynamic integration. The variation of the charge of the complex with the protonation of the EDTA ligand reveals that the free energy barrier in gas phase increases with the negative charge, varying from 16 kJ mol -1 for [EDTAH4·FeO]2+ to 57 kJ mol -1 for [EDTAHn·FeO]2-. In aqueous solution, the barrier for the +2 complex (38 kJ mol-1) is higher than in gas phase, as predicted by purely electrostatic arguments. For the negative complexes, however, the barrier is lower than in gas phase (e.g., 45 kJ mol -1 for the -2 complex). We explain this increase in reactivity in terms of a stabilization of the virtual 3σ* orbital of FeO 2+, which acts as the dominant electron acceptor in the H-atom transfer from CH4. This stabilization originates from the dielectric screening caused by the reorientation of the water dipoles in the first solvation shell of the charged solute, which stabilizes the acceptor orbital energy for the -2 complex sufficiently to outweigh the unfavorable electrostatic destabilization of the transition-state relative to the reactants in solution. © 2013 American Chemical Society.

Park Y.-S.,Kookmin University | Lee J.-S.,Pohang University of Science and Technology
Advanced Materials | Year: 2015

A fully feasible and versatile way to fabricate highly reliable organic-transistor memory devices is made possible by a novel design of the charge-trappling layer. Gold@silica (core-shell)-structured nano particles are synthesized and used as the charge-trapping layer. Superior electrical reliability is obtained because the silica shell acts as a built-in tunnel potential barrier. (Figure Presented). © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

Hwang I.,Pohang University of Science and Technology | Sheen J.,Massachusetts General Hospital | Sheen J.,Harvard University | Muller B.,University of Zurich
Annual Review of Plant Biology | Year: 2012

Despite long-standing observations on diverse cytokinin actions, the discovery path to cytokinin signaling mechanisms was tortuous. Unyielding to conventional genetic screens, experimental innovations were paramount in unraveling the core cytokinin signaling circuitry, which employs a large repertoire of genes with overlapping and specific functions. The canonical two-component transcription circuitry involves His kinases that perceive cytokinin and initiate signaling, as well as His-to-Asp phosphorelay proteins that transfer phosphoryl groups to response regulators, transcriptional activators, or repressors. Recent advances have revealed the complex physiological functions of cytokinins, including interactions with auxin and other signal transduction pathways. This review begins by outlining the historical path to cytokinin discovery and then elucidates the diverse cytokinin functions and key signaling components. Highlights focus on the integration of cytokinin signaling components into regulatory networks in specific contexts, ranging from molecular, cellular, and developmental regulations in the embryo, root apical meristem, shoot apical meristem, stem and root vasculature, and nodule organogenesis to organismal responses underlying immunity, stress tolerance, and senescence. © 2012 by Annual Reviews. All rights reserved.

Boyman O.,University of Zurich | Krieg C.,University of Zurich | Homann D.,University of Colorado at Denver | Sprent J.,Garvan Institute of Medical Research | Sprent J.,Pohang University of Science and Technology
Cellular and Molecular Life Sciences | Year: 2012

Homeostasis in the immune system encompasses the mechanisms governing maintenance of a functional and diverse pool of lymphocytes, thus guaranteeing immunity to pathogens while remaining selftolerant. Antigen-naïve T cells rely on survival signals through contact with self-peptide-loaded major histocompatibility complex (MHC) molecules plus interleukin (IL)-7. Conversely, antigen-experienced (memory) T cells are typically MHC-independent and they survive and undergo periodic homeostatic proliferation through contact with both IL-7 and IL-15. Also, non-conventional γδ T cells rely on a mix of IL-7 and IL-15 for their homeostasis, whereas natural killer cells are mainly dependent on contact with IL-15. Homeostasis of CD4 + T regulatory cells is different in being chiefly regulated by contact with IL-2. Notably, increased levels of these cytokines cause expansion of responsive lymphocytes, such as found in lymphopenic hosts or following cytokine injection, whereas reduced cytokine levels cause a decline in cell numbers. © 2011 Springer Basel AG.

Cho J.,Pohang University of Science and Technology | Lee J.,Kyung Hee University
Expert Systems with Applications | Year: 2013

As the number of new products developed by new technologies has increased, the importance of the commercialization of new technology products has become crucial to manufactures in the successful delivery of valuable new products and services. This study classified success factors for commercialization of new products and analyzed which factors should be primarily considered. Based on the literature review and Delphi method, we identified four decision areas and further prioritized the sixteen factors under a hierarchy model structured by fuzzy AHP (analytic hierarchy process) approach. The FAHP is conducted by 111 R&D and business experts working at the world's major players in machinery industry; using the priorities of success factors derived by FAHP, we devise an example of commercialization assessment model. The paper drives the assessment initiatives of the new product development in manufactures and provides them with practical implications about the commercialization of new technology product. © 2013 Elsevier Ltd. All rights reserved.

Jung S.-M.,Pohang University of Science and Technology
ISIJ International | Year: 2014

The carbothermic reduction of titanomagnetite (TTM) was investigated from a kinetic viewpoint in the temperature range of 1 000 to 1 150°C employing thermogravimetric analysis (TGA) and quadruple mass spectrometry (QMS). The method of evaluating the fractional reduction in the carbothermic reduction of TTM by TGA was validated. The carbon in char consumed for the reduction of TTM was fully gasified into CO and CO2, which indicates that the TGA can be coupled to QMS from the viewpoint of mass balance of carbon. The carbon gasification reaction was activated when the Fe3O4 in TTM, wustite and Fe coexist at the fractional reduction of 0.21, indicating that Fe-catalyzed nature of Fe was confirmed for the carbon gasification. The activation energy for the reduction in TTM to wustite was evaluated to be 241 kJ/mol and the initial reduction stage is believed to be limited by carbon gasification. In the current study, it was considered that the changeover in reaction mechanism might be carried out from carbon gasification to the reduction in wustite to Fe by CO during the isothermal reduction of TTM with char.

Kim E.-H.,LG Corp | Kwon B.-H.,Pohang University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2010

A zero-voltage- and zero-current-switching full-bridge (FB) converter with secondary resonance is presented and analyzed. The primary side of the converter is composed of FB insulated-gate bipolar transistors, which are driven by phase-shift control. The secondary side is composed of a resonant tank and a half-wave rectifier. Without an auxiliary circuit, zero-voltage switching (for leading-leg switches) and zero-current switching (for lagging-leg switches) are achieved in the entire operating range. To implement the converter without an additional inductor, the leakage inductance of the transformer is utilized as the resonant inductor. Due to its many advantages, including high efficiency, minimum number of devices, and low cost, this converter is attractive for high-voltage and high-power applications. The analysis and design considerations of the converter are presented. A prototype was implemented for an application requiring a 5-kW output power, an input-voltage range varying from 250 to 350 V, and a 350-V output voltage. The experimental results obtained from a prototype verify the analysis. The prototype's efficiency at full load is over 95.5%. © 2006 IEEE.

Hong E.,Agency for Defense Development | Kim H.,Pohang University of Science and Technology | Yang K.,Korea Advanced Institute of Science and Technology | Har D.,Korea Advanced Institute of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2013

Selected mapping (SLM) based schemes effectively reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. However, they require side information (SI) transmission, which incurs a loss in the data throughput in addition to the increased system complexity. This paper presents a blind SLM scheme based on a decision metric obtained from pilot sub-channel responses. A novel SI detection method enabling low complexity data decoding is proposed. The SI is detected by exploiting the high autocorrelation between adjacent pilot sub-channel responses. The SI detection error rate is analytically derived and compared with that obtained by simulations. Simulation results of the data decoding scheme based on the proposed SI detection method show the bit error rate performance comparable to that of the simplified maximum likelihood (ML) data decoding scheme, while the computational complexity is close to that of the embedded SI based decoding scheme. © 2002-2012 IEEE.

Kim S.H.,Pohang University of Science and Technology
IEEE Transactions on Fuzzy Systems | Year: 2010

This study is concerned with the robust stabilization problem for a class of discrete-time Takagi - Sugeno (TS) fuzzy systems with time-varying delays. To improve the conditions for the solvability of the stabilization problem, a nonquadratic LyapunovKrasovskii functional with a triple-summation term is established, and a nonparallel distributed compensation (non-PDC) scheme is adopted along with the matrix-transformation technique. In addition, an appropriate free-weighting-matrix method is proposed to exploit novel slack variables for null sum terms, especially resulting from Σ i(xi+1- xi)T (•) (x i+1 + xi). © 2010 IEEE.

Lim J.,Pohang University of Science and Technology | Hong D.,Sogang University
IEEE Signal Processing Letters | Year: 2013

We propose Gaussian particle filtering (PF) approach for estimating carrier frequency offset (CFO) in OFDM systems. PF is more powerful especially for nonlinear problems where classical approaches (e.g., maximum likelihood estimators) may not show optimal performance. Standard PF undergoes the particle impoverishment (PI) problem resulting from resampling process for this static parameter (i.e., CFO) estimation. Gaussian PF (GPF) avoids the PI problem because resampling process is not needed in the algorithm. We show that GPF outperforms current approaches in this nonlinear estimation problem. © 1994-2012 IEEE.

Bae M.,Pohang University of Science and Technology
Zeitschrift fur Angewandte Mathematik und Physik | Year: 2013

In this paper, we prove stability of contact discontinuities for full Euler system. We fix a flat duct N0 of infinite length in R2 with width W 0 and consider two uniform subsonic flow U l± = (u l±, 0, pl, ρl±) with different horizontal velocity in N0 divided by a flat contact discontinuity Γcd. And, we slightly perturb the boundary of N0 so that the width of the perturbed duct converges to W0+ω for {pipe}ω{pipe} < δ at x = ∞ for some δ >0. Then, we prove that if the asymptotic state at left far field is given by Ul±, and if the perturbation of boundary of N0 and δ is sufficiently small, then there exists unique asymptotic state Ur± with a flat contact discontinuity Γcd* at right far field (x= ∞) and unique weak solution U of the Euler system so that U consists of two subsonic flow with a contact discontinuity in between, and that U converges to Ul± and Ur± at x = -∞ and x = ∞ respectively. For that purpose, we establish piecewise C 1 estimate across a contact discontinuity of a weak solution to Euler system depending on the perturbation of ∂N0 and δ. © 2012 Springer Basel.

Suh J.Y.,Northwestern University | Kim C.H.,Northwestern University | Kim C.H.,Pohang University of Science and Technology | Zhou W.,Northwestern University | And 4 more authors.
Nano Letters | Year: 2012

Plasmonic lasers exploit strong electromagnetic field confinement at dimensions well below the diffraction limit. However, lasing from an electromagnetic hot spot supported by discrete, coupled metal nanoparticles (NPs) has not been explicitly demonstrated to date. We present a new design for a room-temperature nanolaser based on three-dimensional (3D) Au bowtie NPs supported by an organic gain material. The extreme field compression, and thus ultrasmall mode volume, within the bowtie gaps produced laser oscillations at the localized plasmon resonance gap mode of the 3D bowties. Transient absorption measurements confirmed ultrafast resonant energy transfer between photoexcited dye molecules and gap plasmons on the picosecond time scale. These plasmonic nanolasers are anticipated to be readily integrated into Si-based photonic devices, all-optical circuits, and nanoscale biosensors. © 2012 American Chemical Society.

Kim N.J.,Pohang University of Science and Technology
Materials Science and Technology (United Kingdom) | Year: 2014

Increasing global demands for energy conservation and environmental protection have prompted automotive manufactures to develop lightweight automobiles. As the lightest of structural alloys, Mg alloys offer significant potential for weight reduction, but have yet to see significant application in automobiles, particularly in sheet form. The current technical issues preventing the widespread application of Mg sheet alloys in automobiles (cost, mechanical properties and formability, joining, corrosion resistance) are assessed and future research needs to develop viable Mg sheet alloys for these applications are identified. © 2014 Institute of Materials.

Park W.B.,Sunchon National University | Shin N.,Pohang University of Science and Technology | Hong K.-P.,Korea Atomic Energy Research Institute | Pyo M.,Sunchon National University | Sohn K.-S.,Sunchon National University
Advanced Functional Materials | Year: 2012

The combinatorial chemistry (combi-chem) of inorganic functional materials has not yet led to the discovery of commercially interesting materials, in contrast to the many successful discoveries of heterogeneous catalysts leading to commercialization. Novel materials for practical use are likely hidden in the multicompositional search space that contains an infinite number of possible stoichiometries, as well as a large number of well-known materials. To discover new, inorganic luminescent materials (phosphors) from the SrO-CaO-BaO-La 2O 3-Y 2O 3-Si 3N 4-Eu 2O 3 search space, heuristics optimization strategies, such as the non-dominated-sorting genetic algorithm (NSGA) and particle swarm optimization (PSO) are coupled with high-throughput experimentation (HTE) in such a manner that the experimental evaluation of fitness functions for the NSGA and PSO is accomplished by the HTE. The proposed strategy also involves the parameterization of the material novelty to avoid systematically a futile convergence on well-known, already-established materials. Although the process starts with random compositions, we finally converge on a novel, single-phase, yellow-green-emitting luminescent material, La 4-xCa xSi 12O 3+xN 18-x:Eu 2+, that has strong potential for practical use in white light-emitting diodes (WLEDs). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Suh D.-W.,Pohang University of Science and Technology
Materials Science and Technology (United Kingdom) | Year: 2014

Austenitic steels containing large manganese concentrations, that deform by mechanical twinning and dislocation slip, have attractive mechanical properties. They are often known as TWIP steels because the work hardening rate is enhanced by twinning, thus permitting large elongations before the onset of plastic instabilities. However, some such steels suffer from hydrogen-induced fracture. This susceptibility can be relieved by adding aluminium, although the mechanism by which aluminium acts remains a matter of discussion. The various proposed mechanisms and data from the literature are critically assessed, and some indications given on fruitful paths for progress. © 2014 Institute of Materials.

Ha C.-D.,Sungkyunkwan University | Cho J.-K.,Sungkyunkwan University | Lee S.-H.,Pohang University of Science and Technology | Kang H.-S.,Sungkyunkwan University
Medicine and Science in Sports and Exercise | Year: 2013

Purpose: The purpose of this study was to investigate the relationship of serum vitamin D levels with lifestyle factors, including body fatness and physical activity (PA) parameters, and the clustering of metabolic risk factors in the Korean pediatric population. Methods: Serum 25-hydroxyvitamin D levels, accelerometer-based PA, and body fatness and metabolic syndrome parameters were assessed in a sample of children of Korean descent (N = 310). Correlation and multivariate linear regression were used to explore the relationships among serum vitamin D levels, lifestyle factors, and the clustering of metabolic risk factors in the study sample. Results: Serum vitamin D levels were negatively associated with body fatness parameters, including body mass index, percent body fat, and waist circumference, but positively associated with accelerometer-based PA including low, moderate, and vigorous levels. In addition, serum vitamin D levels were inversely related to total cholesterol, triglycerides, fasting glucose, and insulin. A stepwise linear regression model showed that both low serum vitamin D levels and decreased vigorous PA were independent predictors for individual variation in the clustering of metabolic risk factors in this study sample. Conclusion: The results of this study suggest that an increase in vigorous PA and vitamin D intake should be two major targets of public health inventions against the clustering of metabolic risk factors in the Korean pediatric population. © 2012 by the American College of Sports Medicine.

Park D.,Kyungpook National University | Yun Y.-S.,Chonbuk National University | Park J.M.,Pohang University of Science and Technology
Biotechnology and Bioprocess Engineering | Year: 2010

The discovery and further development of biosorption phenomena provide a basis for a whole new technology aimed at the removal of various pollutants or the recovery of valuable resources from aqueous systems. Today, biosorption is one of the main components of environmental and bioresource technology. Since the status of scientific development of a technology can be reflected through analyses of the literatures pertaining to it, in this review, we qualitatively examine almost all aspects of biosorption research. A range of subjects are covered, including the initial history, raw materials, mechanisms, instrumental tools, process factors, modification and immobilization methods, recovery and regeneration, continuous processes, commercial application, and modeling studies of biosorption. Finally, we summarized the important considerations of the current research on biosorption, as well as the suggestions for its future directions. We believe that this review will prove to be useful for scientists and engineers in the performance of their research into biosorption. © KSBB.

Lee J.K.,Hoseo University | Kim M.-J.,Pohang University of Science and Technology
Tetrahedron Letters | Year: 2011

Single-walled carbon nanotubes (SWNTs) are used as supporting materials for palladium (Pd) nanoparticles generated in situ in ionic liquid (IL); Pd nanocatalysts on SWNTs exhibit superior reactivity for hydrogenation of aryl ketones in IL under mild conditions (1 atm of H2 (g) and room temperature) and can be reused above 10 times without any loss of catalytic activity. © 2010 Elsevier Ltd. All rights reserved.

Kamal T.,Kyungpook National University | Shin T.J.,Pohang University of Science and Technology | Park S.-Y.,Kyungpook National University
Macromolecules | Year: 2012

The structural evolution of poly(ε-caprolactone) (PCL) during uniaxial tensile deformation at 25 °C was examined using small- and wide-angle X-ray scatterings (SAXS and WAXS) techniques with simultaneous stress and strain (S-S) curves. A high-energy X-ray beam at the recently upgraded Pohang synchrotron radiation source revealed the complete lamellar deformation behavior of PCL. Slope-based division of the S-S curves indicated three distinct regions of elastic (region I), yielding (region II) and plastic deformations (region III). In region I, which showed elastic deformation, the WAXS patterns were isotropic, whereas the SAXS patterns became oblate due to elongation of the amorphous chains along the draw direction. In region II, which showed yielding deformation, the WAXS patterns showed a slight orientation, whereas the SAXS patterns exhibited a change from oblate to four-point and to six-point patterns due to the simultaneous fragmentation and melting of the chain-folded lamellae (leading to the four-point pattern) and the subsequent formation of chain-extended lamellae (adding another two maxima along the meridian). In region III, the WAXS patterns revealed the development of the orientation of PCL crystals, whereas SAXS patterns exhibited a two-point pattern. The newly formed chain-extended lamellae in regions II and III might produce network junctions that can transfer an applied force to the PCL crystals for increased orientation. The six-point pattern in region II for PCL was not observed or reported in the past during the uniaxial tensile deformation experiment. This might be due to fast acquisition of the X-ray patterns during mechanical drawing using synchrotron radiation. © 2012 American Chemical Society.

Yu H.,Pohang University of Science and Technology
Designs, Codes, and Cryptography | Year: 2012

In this paper, we give infinitely many examples of (non-isomorphic) connected k-regular graphs with smallest eigenvalue in half open interval [-1-√2, -2) and also infinitely many examples of (non-isomorphic) connected k-regular graphs with smallest eigenvalue in half open interval [α 1, -1-√2) where α 1 is the smallest root (≈ -2.4812) of the polynomial x 3 + 2x 2 - 2x - 2. From these results, we determine the largest and second largest limit points of smallest eigenvalues of regular graphs less than -2. Moreover we determine the supremum of the smallest eigenvalue among all connected 3-regular graphs with smallest eigenvalue less than -2 and we give the unique graph with this supremum value as its smallest eigenvalue. © 2011 Springer Science+Business Media, LLC.

Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Chun E.J.,Korea Institute for Advanced Study | Shin C.S.,Asia Pacific Center for Theoretical Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

We discuss asymmetric or symmetric dark matter candidate in the supersymmetric Dirac leptogenesis scenario. By introducing a singlet superfield coupling to right-handed neutrinos, the overabundance problem of dark matter can be evaded and various possibilities for dark matter candidate arise. If the singlino is the lightest supersymmetric particle (LSP), it becomes naturally asymmetric dark matter. On the other hand, the right-handed sneutrino is a symmetric dark matter candidate whose relic density can be determined by the usual thermal freeze-out process. The conventional neutralino or gravitino LSP can be also a dark matter candidate as its non-thermal production from the right-handed sneutrino can be controlled appropriately. In our scenario, the late-decay of heavy supersymmetric particles mainly produces the right-handed sneutrino and neutrino which is harmless to the standard prediction of the Big-Bang Nucleosynthesis. © 2013 Elsevier B.V.

Inokuma Y.,University of Tokyo | Kawano M.,Pohang University of Science and Technology | Fujita M.,University of Tokyo | Fujita M.,Japan Science and Technology Agency
Nature Chemistry | Year: 2011

A variety of host compounds have been used as molecular-scale reaction vessels, protecting guests from their environment or restricting the space available around them, thus favouring particular reactions. Such molecular 'flasks' can endow guest molecules with reactivities that differ from those in bulk solvents. Here, we extend this concept to crystalline molecular flasks, solid-state crystalline networks with pores within which pseudo-solution-state reactions can take place. As the guest molecules can spontaneously align along the walls and channels of the hosts, structural changes in the substrates can be directly observed by in situ X-ray crystallography during reaction. Recently, this has enabled observation of the molecular structures of transient intermediates and other labile species, in the form of sequential structural snapshots of the chemical transformation. Here, we describe the principles, development and applications of crystalline molecular flasks. © 2011 Macmillan Publishers Limited. All rights reserved.

Han B.,Pohang University of Science and Technology | Joo S.-W.,Google | Davis L.S.,University of Maryland University College
International Journal of Computer Vision | Year: 2011

Sensor fusion for object tracking is attractive since the integration of multiple sensors and/or algorithms with different characteristics can improve performance. However, there exist several critical limitations to sensor fusion techniques: (1) the measurement cost increases typically as many times as the number of sensors, (2) it is not straightforward to measure the confidence of each source and give it a proper weight for state estimation, and (3) there is no principled dynamic resource allocation algorithm for better performance and efficiency. We describe a method to fuse information from multiple sensors and estimate the current tracker state by using a mixture of sequential Bayesian filters (e.g.; particle filter)-one filter for each sensor, where each filter makes a different level of contribution to estimate the combined posterior in a reliable manner. In this framework, multiple sensors interact to determine an appropriate sensor for each particle dynamically; each particle is allocated to only one of the sensors for measurement and a different number of particles is assigned to each sensor. The level of the contribution of each sensor changes dynamically based on its prior information and relative measurement confidence. We apply this technique to visual tracking with multiple cameras, and demonstrate its effectiveness through tracking results in videos. © 2010 Springer Science+Business Media, LLC.

Park M.J.,Pohang University of Science and Technology | Balsara N.P.,University of California at Berkeley | Balsara N.P.,Lawrence Berkeley National Laboratory
Macromolecules | Year: 2010

The effect of alignment of proton-conducting domains in hydrated poly(styrenesulfonate-b-methylbutylene) copolymer films on conductivity was studied by impedance spectroscopy. Pressing isotropic samples obtained by casting results in lamellae aligned in the plane of the film. Application of electric fields and flow fields on the isotropic samples results in lamellae aligned perpendicular to the plane of the film. The alignment of lamellae, quantified by a combination of two dimensional small angle X-ray scattering (SAXS), birefringence and transmission electron microscopy (TEM), was much better in the pressed samples than in the field-aligned samples. Conductivity was measured in the plane of the film (σ||) and normal to the plane of the film (σ⊥). Only the pressed sample showed highly anisotropic proton conduction with σ||/ σ⊥ = 75. In this case, the value of σ|| increased by 30% after alignment, relative to that obtained from the as-cast samples. The values of σ||/σ⊥ obtained after electric field and shear field alignment were 1.2 and 1.4, respectively, in spite of partial alignment of the domains, and the increase in σ⊥ after alignment was less than 20%. © 2009 American Chemical Society.

Ahn H.-K.,Pohang University of Science and Technology | Cheong O.,KAIST
Algorithmica (New York) | Year: 2012

Given two compact convex sets P and Q in the plane, we consider the problem of finding a placement P of P that minimizes the convex hull of PQ. We study eight versions of the problem: we consider minimizing either the area or the perimeter of the convex hull; we either allow P and Q to intersect or we restrict their interiors to remain disjoint; and we either allow reorienting P or require its orientation to be fixed. In the case without reorientations, we achieve exact near-linear time algorithms for all versions of the problem. In the case with reorientations, we compute a (1+ε)-approximation in time O(ε -1/2log∈n+ε -3/2log∈ a (1/ε)) if the two sets are convex polygons with n vertices in total, where a 0,1,2 depending on the version of the problem. © 2010 Springer Science+Business Media, LLC.

Oh J.-M.,Pohang University of Science and Technology
European Journal of Combinatorics | Year: 2012

Tǎrnǎuceanu and Bentea [M. Tǎrnǎuceanu, L. Bentea, On the number of fuzzy subgroups of finite abelian groups, Fuzzy Sets and Systems 159 (2008) 1084-1096] gave an explicit formula for the number of chains of subgroups in the lattice of a finite cyclic group by finding its generating function of one variable. Using this result Tǎrnǎuceanu [M. Tǎrnǎuceanu, Fuzzy subgroups of finite cyclic groups and Delannoy numbers, European J. Combin. 30 (2009) 283-287] found an explicit formula for the central Delannoy number. In this note we find a generating function of multi-variables for the number of chains of subgroups in the lattice of subgroups of a finite cyclic group. As results we give simplified formulas for the number of chains of subgroups in the lattice of subgroups of a finite cyclic group and for the central Delannoy numbers compared with the formulas given by Tǎrnǎuceanu and Bentea. © 2011 Elsevier Ltd.

Qin R.S.,Pohang University of Science and Technology
Materials and Manufacturing Processes | Year: 2011

A scheme for integrating grain growth model in phase transition and grain distortion calculation in plastic deformation is proposed, which enables the simulation of microstructure evolution in steel processing when phase transition takes place during rolling. The grain shape deformation is calculated by transforming grid coordinates according to homogeneous deformation matrix. Grain growth in phase transition is computed by phase-field model. Apart from the direct distortion effect of rolling on grain geometry, the change of interface geometry affects the interface propagation due to the anisotropic property of the interface energy. Finally, the method for integration of microstructure simulation with steel crystallography is discussed. © Taylor & Francis Group, LLC.

Wang H.,Pohang University of Science and Technology | Agoulmine N.,University of Evry Val dEssonne | Ma M.,Nanyang Technological University | Jin Y.,Shanghai University
IEEE Journal on Selected Areas in Communications | Year: 2010

Network lifetime (NL) is a critical metric in the design of energy-constrained wireless sensor networks (WSNs). In this paper, we investigate a joint optimal design of the physical, medium access control (MAC) and routing layers to maximize NL of a multiple-sources and single-sink (MSSS) WSN with energy constraints. The problem of NL maximization (NLM) can be formulated as a mixed integer-convex optimization problem with adoption of time division multiple access (TDMA) technique. When the integer constraints are relaxed to take real values, the problem can be transformed into a convex problem and the solution achieves the upper bounds. We provide an analytical framework for the relaxed NLM problem of a WSN in general planar topology. We first restrict the topologies to the planar networks on a small scale, including triangle and regular quadrangle topologies. In this special case, we employ the Karush-Kuhn-Tucker (KKT) optimality conditions to derive analytical expressions of the globally optimal NL, which take the influence of data rate, link access and routing into account. To handle larger scale planar networks, an iterative algorithm is proposed using the D&C approach. Numerical results illustrate that the proposed algorithm can be extended to the large planar case and its performance is close to globally optimal performance. © 2010 IEEE.

Asgharzadeh H.,Sharif University of Technology | Simchi A.,Sharif University of Technology | Kim H.S.,Pohang University of Science and Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (∼2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains (>100 nm) surrounded by nanostructured grains (<100 nm), revealing the formation of a bimodal grain structure. The grain size distribution was in the range of 20 to 850 nm with an average of 360 and 300 nm for Ar and Ar-5 pct O2 atmospheres, respectively. The amount of oxide particles formed by reactive mechanical alloying under the Ar/O 2 atmosphere was ∼0.8 vol pct, whereas the particles were almost uniformly distributed throughout the aluminum matrix. The UFG materials exhibited significant improvement in the hardness and yield strength with an absence of strain hardening behavior compared with CG material. The fracture surfaces showed a ductile fracture mode for both CG and UFG Al6063, in which the dimple size was related to the grain structure. A mixture of ductile-brittle fracture mode was observed for the UFG alloy containing 0.8 vol pct Al 2O3 particles. The tensile behavior was described based on the formation of nonequilibrium grain boundaries with high internal stress and dislocation-based models. © 2010 The Minerals, Metals & Materials Society and ASM International.

Lee M.-G.,Pohang University of Science and Technology | Kim S.-J.,Korea Institute of Materials Science | Han H.N.,Seoul National University
International Journal of Plasticity | Year: 2010

A new crystal plasticity model incorporating the mechanically induced martensitic transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential martensitic variant based on Kurdjumov-Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between externally applied stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and applied stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the martensitic transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the stress-strain responses, transformed martensitic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel. © 2009 Elsevier Ltd. All rights reserved.

Aretz H.,Hydro Aluminium | Barlat F.,Pohang University of Science and Technology
International Journal of Non-Linear Mechanics | Year: 2013

Two new yield functions for orthotropic sheet metals are proposed. The first one, called Yld2011-18p, provides 18 parameters that may be calibrated to experimental data. The second one, called Yld2011-27p, is a straightforward extension and provides 27 parameters. Both yield functions are unconditionally convex. Their formulations are based on the established concept of multiple linear transformations of the stress deviator. Furthermore, they are able to account for planar as well as for three-dimensional stress states. The proposed yield functions are applied to describe complex plastic anisotropies of different alloys. The ability of accurately predicting earing in cup-drawing is demonstrated by means of a non-linear finite element analysis. © 2012 Elsevier Ltd.

Sung Y.S.,Pohang University of Science and Technology
Applied Physics Letters | Year: 2014

Piezoelectric coefficient (d33) of (Na,K)NbO3 (NKN) is enhanced not only at its morphotropic phase boundary (MPB) composition but also enhanced at its polymorphic phase transition (PPT) temperature between orthorhombic and tetragonal phases (TO-T). Thus, for NKN-based ceramics, even higher d33 could be obtained if both MPB and PPT are simultaneously optimized. This temperature as well as composition dependence of piezoelectric properties of NKN-based ceramics requires a systematic approach that differentiates factors for MPB and PPT. In this paper, the roles of Li and Ta known to affect d33 and TO-T were identified in relation with lattice parameters. © 2014 AIP Publishing LLC.

Lee M.G.,Pohang University of Science and Technology | Lim H.,Ohio State University | Adams B.L.,Brigham Young University | Hirth J.P.,114 E Ramsey Canyon Road | Wagoner R.H.,Ohio State University
International Journal of Plasticity | Year: 2010

Single crystal constitutive equations based on dislocation density (SCCE-D) were developed from Orowan's strengthening equation and simple geometric relationships of the operating slip systems. The flow resistance on a slip plane was computed using the Burger's vector, line direction, and density of the dislocations on all other slip planes, with no adjustable parameters. That is, the latent/self-hardening matrix was determined by the crystallography of the slip systems alone. The multiplication of dislocations on each slip system incorporated standard 3-parameter dislocation density evolution equations applied to each slip system independently; this is the only phenomenological aspect of the SCCE-D model. In contrast, the most widely used single crystal constitutive equations for texture analysis (SCCE-T) feature 4 or more adjustable parameters that are usually back-fit from a polycrystal flow curve. In order to compare the accuracy of the two approaches to reproduce single crystal behavior, tensile tests of single crystals oriented for single slip were simulated using crystal plasticity finite element modeling. Best-fit parameters (3 for SCCE-D, 4 for SCCE-T) were determined using either multiple or single slip stress-strain curves for copper and iron from the literature. Both approaches reproduced the data used for fitting accurately. Tensile tests of copper and iron single crystals oriented to favor the remaining combinations of slip systems were then simulated using each model (i.e. multiple slip cases for equations fit to single slip, and vice versa). In spite of fewer fit parameters, the SCCE-D predicted the flow stresses with a standard deviation of 14 MPa, less than one half that for the SCCE-T conventional equations: 31 MPa. Polycrystalline texture simulations were conducted to compare predictions of the two models. The predicted polycrystal flow curves differed considerably, but the differences in texture evolution were insensitive to the type of constitutive equations. The SCCE-D method provides an improved representation of single-crystal plastic response with fewer adjustable parameters, better accuracy, and better predictivity than the constitutive equations most widely used for texture analysis (SCCE-T).

Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

There might be a light scalar field during inflation which is not responsible for the accelerating inflationary expansion. Then, its quantum fluctuation is stretched during inflation. This scalar field could be a curvaton, if it decays at a late time. In addition, if the inflaton decay rate depends on the light scalar field expectation value by interactions between them, density perturbations could be generated by the quantum fluctuation of the light field when the inflaton decays. This is a modulated reheating mechanism. We study curvature perturbation in models where a light scalar field does not only play a role of curvaton but also induce modulated reheating at the inflaton decay. We calculate the nonlinearity parameters as well as the scalar spectral index and the tensor-to-scalar ratio. We find that there is a parameter region where nonlinearity parameters are also significantly enhanced by the cancellation between the modulated effect and the curvaton contribution. For the simple quadratic potential model of both inflaton and curvaton, both tensor-to-scalar ratio and nonlinearity parameters could be simultaneously large. © 2012 American Physical Society.

Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We show that a Dirac right-handed scalar neutrino can be dark matter (DM) as a weakly interacting massive particle in the neutrinophilic Higgs model. When the additional Higgs fields couple only to the leptonic sector through neutrino Yukawa couplings, the right number of relic density of DM can be obtained from thermal freeze-out of the DM annihilation into charged leptons and neutrinos. At present epoch, this tree-level annihilation into fermions is suppressed by the velocity of DM, and the one-loop annihilation cross section into γγ can be dominant because relevant coupling constants are different. Hence, the recently observed (tentative) gamma-ray line signal in the Fermi-Large Area Telescope can be naturally explained by the annihilation of right-handed sneutrino DM. © 2012 American Physical Society.

Ghosh S.,Pohang University of Science and Technology
Journal of Materials Science | Year: 2010

Tungsten is sometimes used as a solute in the so called 9Cr creep-resistant steels for use in the power generation industry, in part because of its ability to reduce the coarsening rate of M23C6 carbides. The mechanism by which it does so is not fully understood and indeed has been shown to be inconsistent with multicomponent coarsening theory, which predicts an opposite effect. This makes the role of tungsten to the coarsening behaviour of the carbide remain unsolved over decades. The work presented here is an attempt to show that the influence of tungsten can be reconciled with experiments, if kinetic study ignores the presence of Laves phase (Fe2W) in the system. © 2010 Springer Science+Business Media, LLC.

Gwak B.,Sogang University | Lee B.-H.,Sogang University | Lee B.-H.,Asia Pacific Center for Theoretical Physics | Lee B.-H.,Pohang University of Science and Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

We have shown that changes occur in a (2. +. 1)-dimensional charged black hole by adding a charged probe. The particle increases the entropy of the black hole and guarantees the second law of thermodynamics. The first law of thermodynamics is derived from the change in the black hole mass. Using the particle absorption, we test the extremal black hole and find out that the mass of the extremal black hole increases more than the electric charge. Therefore, the outer horizon of the black hole still exists. However, the extremal condition becomes non-extremal. © 2016 The Authors.

Choi K.,Korea Advanced Institute of Science and Technology | Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Shin C.S.,Asia Pacific Center for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Although the standard ΛCDM model describes the cosmic microwave background radiation and the large-scale structure of the Universe with great success, it has some tensions with observations in the effective number of neutrino species (dark radiation) and the number of small-scale structures (overabundance problem). Here we propose a scenario which can relax these tensions by producing both dark matter and dark radiation by late decays of heavy particles. Thanks to the generation mechanism, dark matter is rather warm, so that the small-scale structure problem is resolved. This scenario can be naturally realized in the supersymmetric axion model, in which axions produced by saxion decays provide dark radiation, while axinos from saxion decays form warm dark matter. We identify a parameter region of the supersymmetric axion model satisfying all known cosmological constraints. © 2012 American Physical Society.

Park C.,Asia Pacific Center for Theoretical Physics | Park C.,Pohang University of Science and Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

We investigate meson's spectrum, decay constant and form factor in a nuclear medium through holographic two- and three-point correlation functions. To describe a nuclear medium composed of protons and neutrons, we consider a hard wall model on the thermal charged AdS geometry and show that due to the isospin interaction with a nuclear medium, there exist splittings of the meson's spectrum, decay constant and form factor relying on the isospin charge. In addition, we show that the ρ-meson's form factor describing an interaction with pseudoscalar fluctuation decreases when the nuclear density increases, while the interaction with a longitudinal part of an axial vector meson increases. © 2016 The Author(s)

Kim J.,Max Planck Institute for Iron Research | Estrin Y.,Monash University | De Cooman B.C.,Pohang University of Science and Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

High Mn steels exhibit an exceptional combination of high strength and large ductility owing to their high strain-hardening rate during deformation. The addition of Al is needed to improve the mechanical performance of TWIP steel by means of the control of the stacking fault energy. In this study, a constitutive modeling approach, which can describe the strain-hardening behavior and the effect of Al on the mechanical properties, was used. In order to understand the deformation behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels, a comparative study of the microstructural evolution was conducted by means of transmission electron microscopy and electron backscatter diffraction. The microstructure analysis focused on dislocations, stacking faults, mechanical twins as these are the defects controlling the strain-hardening behavior of TWIP steels. A comparison of the strain-hardening behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels was made in terms of a dislocation density-based constitutive model that goes back to the Kubin-Estrin model. The densities of mobile and forest dislocations are coupled in order to account for the interaction between the two dislocation populations during straining. The model was used to estimate the contribution of dynamic strain aging to the flow stress. As deformation twinning occurred only in a subset of the grains, the grain population was subdivided into twinned grains and twin-free grains. Different constitutive equations were used for the two families of grains. The analysis revealed that (i) the grain size and dynamic recovery effects determine the strain-hardening behavior of the twin-free grains, (ii) the deformation twins, which act as effective barriers to dislocation motion, are the predominant elements of the microstructure that governs the strain hardening of the twinned grains, (iii) the DSA contribution to strain hardening of TWIP steel is only minor. © 2013 The Minerals, Metals & Materials Society and ASM International.

Tchoe Y.,Seoul National University | Han J.H.,Sungkyunkwan University | Han J.H.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Skyrmions, once a hypothesized field-theoretical object believed to describe the nature of elementary particles, became common sightings in recent years among several noncentrosymmetric metallic ferromagnets. For more practical applications of Skyrmionic matter as a carrier of information, thus realizing the prospect of "Skyrmionics," it is necessary to have the means to create and manipulate Skyrmions individually. We show through extensive simulation of the Landau-Lifshitz-Gilbert equation that a circulating current imparted to the metallic chiral ferromagnetic system can create isolated Skyrmionic spin texture without the aid of external magnetic field. © 2012 American Physical Society.

Pavlina E.J.,Pohang University of Science and Technology | Speer J.G.,Colorado School of Mines | Van Tyne C.J.,Colorado School of Mines
Scripta Materialia | Year: 2012

Solubility products for molybdenum carbide and tungsten carbide are absent from the literature despite their importance in secondary hardening steels and in microalloyed steels. Equilibrium solubility products were calculated for MoC, Mo 2C, WC and W 2C in ferrite and austenite. Molybdenum and tungsten carbides exhibit greater solubility than traditional microalloy carbides in iron and their predicted solution behavior is similar to that of other Group VI transition metal carbides. The calculated solubility products are consistent with precipitation behavior during secondary hardening in steels. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Moon H.G.,Pohang University of Science and Technology
Experimental & molecular medicine | Year: 2013

T-helper (Th)17 cell responses are important for the development of neutrophilic inflammatory disease. Recently, we found that acetyl salicylic acid (ASA) inhibited Th17 airway inflammation in an asthma mouse model induced by sensitization with lipopolysaccharide (LPS)-containing allergens. To investigate the mechanism(s) of the inhibitory effect of ASA on the development of Th17 airway inflammation, a neutrophilic asthma mouse model was generated by intranasal sensitization with LPS plus ovalbumin (OVA) and then challenged with OVA alone. Immunologic parameters and airway inflammation were evaluated 6 and 48 h after the last OVA challenge. ASA inhibited the production of interleukin (IL)-17 from lung T cells as well as in vitro Th17 polarization induced by IL-6. Additionally, ASA, but not salicylic acid, suppressed Th17 airway inflammation, which was associated with decreased expression of acetyl-STAT3 (downstream signaling of IL-6) in the lung. Moreover, the production of IL-6 from inflammatory cells, induced by IL-17, was abolished by treatment with ASA, whereas that induced by LPS was not. Altogether, ASA, likely via its acetyl moiety, inhibits Th17 airway inflammation by blockade of IL-6 and IL-17 positive feedback.

Kwon J.-M.,Hanbat National University | Choi W.-Y.,Chonbuk National University | Kwon B.-H.,Pohang University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2011

A single-stage quasi-resonant flyback converter is proposed for a cost-effective plasma display panel (PDP) sustain power module. The proposed converter operates at the boundary of the continuous- and discontinuous- conduction modes to reduce the switching loss of the primary switch. The bulk capacitor voltage can be independent of the output load and maintained within a practical range for the universal line input. By integrating two power conversion stages into one, the proposed converter provides a simple structure and high efficiency for the PDP sustain power module. The operational principle and theoretical analysis are presented. A prototype converter was built and tested for a 32-in PDP, which requires 150-W (180-V/0.83-A) sustain power. The experimental results verify the feasibility of the proposed scheme. © 2010 IEEE.

Carrette F.,Scripps Research Institute | Surh C.D.,Scripps Research Institute | Surh C.D.,Pohang University of Science and Technology
Seminars in Immunology | Year: 2012

After their development in the thymus, mature T cells are maintained in the periphery by two sets of survival signals, namely TCR signals from contact with self-peptide/MHC ligands and the cytokine receptor signals from binding IL-7 and IL-15. These signals cooperate to maximize the utility of finite resources to support a diverse pool of mature T cells. It is becoming increasingly clear that multiple mechanisms exist to regulate expression of IL-7R at the transcriptional and post-translational levels. The interplay between TCR signals and IL-7R signals are also important in regulation of IL-7R expression. This review will focus on regulation of T cell homeostasis by IL-7R signaling, with an emphasis on the cross talk between signals from TCR and IL-7R. © 2012 Elsevier Ltd.

Kwak J.H.,Pohang University of Science and Technology | Kwon Y.S.,Yeungnam University
Journal of Combinatorial Theory. Series B | Year: 2011

A 2-cell embedding of a graph G into a closed (orientable or nonorientable) surface is called regular if its automorphism group acts regularly on the flags - mutually incident vertex-edge-face triples. In this paper, we classify the regular embeddings of complete bipartite graphs Kn,n into nonorientable surfaces. Such a regular embedding of Kn,n exists only when n is of the form n=2p1a1p2a2 pkak where the pi are primes congruent to ±1 mod 8. In this case, up to isomorphism the number of those regular embeddings of Kn,n is 2k. © 2011 Elsevier Inc.

Yan X.,Rensselaer Polytechnic Institute | Poxson D.J.,Rensselaer Polytechnic Institute | Cho J.,Rensselaer Polytechnic Institute | Welser R.E.,Magnolia Solar, Inc. | And 3 more authors.
Advanced Functional Materials | Year: 2013

An optimized four-layer tailored- and low-refractive index anti-reflection (AR) coating on an inverted metamorphic (IMM) triple-junction solar cell device is demonstrated. Due to an excellent refractive index matching with the ambient air by using tailored- and low-refractive index nanoporous SiO2 layers and owing to a multiple-discrete-layer design of the AR coating optimized by a genetic algorithm, such a four-layer AR coating shows excellent broadband and omnidirectional AR characteristics and significantly enhances the omnidirectional photovoltaic performance of IMM solar cell devices. Comparing the photovoltaic performance of an IMM solar cell device with the four-layer AR coating and an IMM solar cell with the conventional SiO2/TiO 2 double layer AR coating, the four-layer AR coating achieves an angle-of-incidence (AOI) averaged short-circuit current density, JSC, enhancement of 34.4%, whereas the conventional double layer AR coating only achieves an AOI-averaged JSC enhancement of 25.3%. The measured reflectance reduction and omnidirectional photovoltaic performance enhancement of the four-layer AR coating are to our knowledge, the largest ever reported in the literature of solar cell devices. A multiple-discrete-layer omnidirectional and broadband anti-reflection (AR) coating is demonstrated on an inverted metamorphic (IMM) triple-junction solar cell device. Due to an excellent refractive index matching with the ambient air and a genetic algorithm optimization of the discrete refractive index profile, the IMM device employing a four-layer AR coating shows better photovoltaic performance at all incident angles (0°-80°) than an IMM device employing a traditional double layer AR coating. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Seo S.-M.,Korea University | Lee H.-W.,Pohang University of Science and Technology | Kohno H.,Osaka University | Lee K.-J.,Korea University
Applied Physics Letters | Year: 2011

A magnetic vortex wall motion driven by propagating spin waves in a nanostrip is investigated by means of micromagnetic simulation. Propagating spin waves can drive a vortex wall into a stream motion in spite of its complex internal spin structure. Compared to the transverse wall, the vortex wall moves faster and its velocity is less sensitive to the spin wave frequency. The amplitude of spin waves changes when passing through the domain wall, closely related to the domain wall velocity. This domain-wall-type-specific study provides important information for developing the theory of the interaction between domain wall and spin waves. © 2011 American Institute of Physics.

Kim J.,Doosan Infracore | Song H.-S.,Hyundai Motor Company | Nam K.,Pohang University of Science and Technology
IEEE Transactions on Power Electronics | Year: 2011

A dual-half-bridge (DHB) converter is integrated with a half-bridge 60-Hz inverter as a converter/inverter system for a small distributed generator. This topology provides an isolation between the power source and the load with a 100-kHz transformer, and therefore, the system volume is small. On the other hand, it reduces the number of switching devices greatly. However, the half-bridge inverter causes severe capacitor-voltage fluctuations. The unbalanced voltage problem can be solved by controlling the converter switching: In addition to the conventional phase-shift control method, an asymmetric charging method is used that charges the upper and lower secondary capacitors differently. This means that the voltage imbalance is corrected by adjusting the switching time of the secondary switches. Furthermore, a decoupling control algorithm can be derived from this approach. The usefulness of this method is then validated by simulation and experimental results. © 2010 IEEE.

Choi Y.S.,Pohang University of Science and Technology
Biofouling | Year: 2011

Mussel adhesive proteins (MAPs) attach to all types of inorganic and organic surfaces, even in wet environments. MAP of type 5 (fp-5), in particular, has been considered as a key adhesive material. However, the low availability of fp-5 has hampered its biochemical characterization and practical applications. Here, soluble recombinant fp-5 is mass-produced in Escherichia coli. Tyrosinase-modified recombinant fp-5 showed ∼1.11 MPa adhesive shear strength, which is the first report of a bulk-scale adhesive force measurement for purified recombinant of natural MAP type. Surface coatings were also performed through simple dip-coating of various objects. In addition, complex coacervate using recombinant fp-5 and hyaluronic acid was prepared as an efficient adhesive formulation, which greatly improved the bulk adhesive strength. Collectively, it is expected that this work will enhance basic understanding of mussel adhesion and that recombinant fp-5 can be successfully used as a realistic bulk-scale bioadhesive and an efficient surface coating material.

Choi Y.S.,Pohang University of Science and Technology
Methods in molecular biology (Clifton, N.J.) | Year: 2011

The technique of selective immobilization of biomolecules in defined positions or areas using a simple procedure is essential for various applications such as biosensors, biochips, biomedical microdevices, and tissue engineering. For the generation of biomolecule microarrays, it is necessary to develop a functional surface retaining protein functionality and cell viability, and an efficient patterning tool having flexibility of size and shape. In this chapter, we have presented the simple tools of protein and cell microarray based on functionalized surface such as a spotting method with improvement of protein functionality, a functionalized silicon-based surface using photolithography, and an orthogonally polyelectrolyte-coated surface based on soft-lithography.

Kim K.-S.,Pohang University of Science and Technology | Jia C.,Martin Luther University of Halle Wittenberg
Physical Review Letters | Year: 2010

We find that the Kondo effect results in a new universality class for an antiferromagnetic (AF) quantum critical point (QCP) in the heavy fermion quantum transition, described by deconfined bosonic spinons with the dynamical exponent z=3. We show that the thermodynamics and transport of the z=3 AF QCP are consistent with the well-known non-Fermi liquid physics such as the divergent Grüneisen ratio with an exponent 2/3 and temperature-linear resistivity. We propose that the hallmark of the Kondo-driven AF QCP is a uniform spin susceptibility that diverges with an exponent 2/3, remarkably consistent with the experimental observations for YbRh2Si2. © 2010 The American Physical Society.

Kim W.-H.,Stanford University | Son J.Y.,Kyung Hee University | Jang H.M.,Pohang University of Science and Technology
ACS Applied Materials and Interfaces | Year: 2014

We report confinement of ferroelectric domain-wall motion at conducting-nanofilament wall in epitaxial BiFeO3 thin film on Nb-doped SrTiO3 substrate. The BiFeO3 film exhibited well-defined ferroelectric response and unipolar resistive switching behavior. We artificially formed conducting-nanofilaments in the BiFeO3 via conducting atomic force microscope techniques. The conducting-nanofilament wall, which does not possess any ferroelectric polarization, is then able to block domain propagation. Consequently, we demonstrate that the domain-wall motion is effectively confined within the conducting-nanofilament wall during polarization switching. This significant new insight potentially gives an opportunity for the artificial manipulation of nanoscale ferroelectric domain. © 2014 American Chemical Society.

Oh-Ishi K.,Japan National Institute of Materials Science | Edalati K.,Kyushu University | Kim H.S.,Pohang University of Science and Technology | Hono K.,Japan National Institute of Materials Science | Horita Z.,Kyushu University
Acta Materialia | Year: 2013

This study reports that solid-state reactions occur by the application of high-pressure torsion (HPT) to the Al-Cu system even at low homologous temperature. A bulk form of disc consisting of two separate half-discs of pure Al and pure Cu are processed by HPT at ambient temperature under a pressure of 6 GPa. X-ray diffraction analysis and high-resolution transmission electron microscopy confirm the formation of different intermetallic phases such as Al2Cu, AlCu and Al4Cu9, as well as the dissolution and supersaturation of Al and Cu in each matrix. It is shown that the diffusion coefficient is enhanced by 1012-1022 times during the HPT processing in comparison with the lattice diffusion and becomes comparable to the surface diffusion. The enhanced diffusion is attributed to the presence of a high density of lattice defects such as vacancies, dislocations and grain boundaries produced by HPT processing. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Lee S.-J.,Pohang University of Science and Technology | Van Tyne C.J.,Colorado School of Mines
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2012

An empirical martensite kinetics model is proposed that both captures the sigmodial transformation behavior for alloy steels and remains computationally efficient. The model improves on the Koistinen and Marburger model and the van Bohemen and Sietsma model with a function that better represents the transformation rate, especially during the early stages. When compared with existing models, the proposed model exhibits better predictions of volume fraction of martensite. The proposed model also predicts various other transformation properties accurately, such as M 900 temperatures and retained austenite. © The Minerals, Metals & Materials Society and ASM International 2011.

Ham Y.-G.,Chonnam National University | Kug J.-S.,Pohang University of Science and Technology
Climate Dynamics | Year: 2014

In this study, the El Nino-Southern Oscillation (ENSO) phase-locking to the boreal winter in CMIP3 and CMIP5 models is examined. It is found that the models that are poor at simulating the winter ENSO peak tend to simulate colder seasonal-mean sea-surface temperature (SST) during the boreal summer and associated shallower thermocline depth over the eastern Pacific. These models tend to amplify zonal advection and thermocline depth feedback during boreal summer. In addition, the colder eastern Pacific SST in the model can reduce the summertime mean local convective activity, which tends to weaken the atmospheric response to the ENSO SST forcing. It is also revealed that these models have more serious climatological biases over the tropical Pacific, implying that a realistic simulation of the climatological fields may help to simulate winter ENSO peak better. The models that are poor at simulating ENSO peak in winter also show excessive anomalous SST warming over the western Pacific during boreal winter of the El Nino events, which leads to strong local convective anomalies. This prevents the southward shift of El Nino-related westerly during boreal winter season. Therefore, equatorial westerly is prevailed over the western Pacific to further development of ENSO-related SST during boreal winter. This bias in the SST anomaly is partly due to the climatological dry biases over the central Pacific, which confines ENSO-related precipitation and westerly responses over the western Pacific. © 2014 Springer-Verlag Berlin Heidelberg.

Lee J.W.,Gachon University | Cho D.-W.,Pohang University of Science and Technology
Current Pharmaceutical Design | Year: 2015

Many researchers have attempted to use computer-aided design (CAD) and computer-aided manufacturing (CAM) to realize a scaffold that provides a three-dimensional (3D) environment for regeneration of tissues and organs. As a result, several 3D printing technologies, including stereolithography, deposition modeling, inkjet-based printing and selective laser sintering have been developed. Because these 3D printing technologies use computers for design and fabrication, and they can fabricate 3D scaffolds as designed; as a consequence, they can be standardized. Growth of target tissues and organs requires the presence of appropriate growth factors, so fabrication of 3Dscaffold systems that release these biomolecules has been explored. A drug delivery system (DDS) that administrates a pharmaceutical compound to achieve a therapeutic effect in cells, animals and humans is a key technology that delivers biomolecules without side effects caused by excessive doses. 3D printing technologies and DDSs have been assembled successfully, so new possibilities for improved tissue regeneration have been suggested. If the interaction between cells and scaffold system with biomolecules can be understood and controlled, and if an optimal 3D tissue regenerating environment is realized, 3D printing technologies will become an important aspect of tissue engineering research in the near future. © 2015 Bentham Science Publishers.

Dutta S.,Asia Pacific Center for Theoretical Physics | Jho Y.S.,Pohang University of Science and Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

Strong-coupling phenomena, such as like-charge macroion attraction, opposite-charged macroion repulsion, charge renormalization, and charge inversion, are known to be mediated by multivalent counterions. Most theories treat the counterions as point charges and describe the system by a single coupling parameter that measures the strength of the Coulomb interactions. In many biological systems, the counterions are highly charged and have finite sizes and can be well-described by polyelectrolytes. The shapes and orientations of these polymer counterions play a major role in the thermodynamics of these systems. In this work we apply a field-theoretic description in the strong-coupling regime to the polymer counterions in the presence of a fixed charge distribution. We work out the special cases of rodlike polymer counterions confined by one, and two charged walls, respectively. The effects of the geometry of the rodlike counterions and the excluded volume of the walls on the density, pressure, and free energy of the rodlike counterions are discussed. © 2016 American Physical Society.

Garrisi D.,Incheon National University | Garrisi D.,Pohang University of Science and Technology
Advanced Nonlinear Studies | Year: 2012

We show the existence of standing-wave solutions to a coupled non-linear Klein-Gordon equation. Our solutions are obtained as minimizers of the energy under a two-charges constraint. We prove that the ground state is stable and that standing-waves are orbitally stable under a non-degeneracy assumption.

Jung S.-M.,Pohang University of Science and Technology
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2015

Effects of CaO/CaCO3 on the carbothermic reduction of titanomagnetite (TTM) ores were investigated from a kinetic viewpoint in the temperature range of 1273 K to 1423 K (1000 °C to 1150 °C) by employing thermogravimetric analysis (TGA) and quadruple mass spectrometry (QMS). The method of evaluating the reduction progress of TTM and char by TGA was compared with that calculated using the oxygen amount combined with Fe in the reduced TTM. Improved reducibility of TTM by adding CaO was explained by the variation of rates of reduction and gasification which was evaluated using QMS data. The activation energy for the carbothermic reduction of TTM was greatly decreased by adding CaO, which is ascribed to the formation of CaO·SiO2 improving the reducibility of TTM. The activation energy for the carbothermic reduction of TTM containing CaCO3 was further decreased, which is due to the activation of char gasification by CO2 supplied from CaCO3 in addition to the contribution of CaO to the increase of TTM reducibility. It is believed that the admixing of CaO/CaCO3 to TTM would play a predominant role in controlling the reduction rate and the final metallization degree of TTM in direct reduction processes. © 2015, The Minerals, Metals & Materials Society and ASM International.

Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Kyae B.,Pusan National University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

We propose an inflationary model ("natural hybrid model"), which combines the supersymmetric hybrid model and the natural inflation model to achieve the spectral index of 0.96, and the axion decay constant smaller than the Planck scale, f≪MP. By introducing both U(1)R and a shift symmetry and employing the minimal Kähler potential, the eta-problem can be still avoided. The two inflaton fields in this model can admit large non-Gaussianity. © 2011 Elsevier B.V.

Spasova D.S.,Scripps Research Institute | Spasova D.S.,La Jolla Institute for Allergy and Immunology | Surh C.D.,La Jolla Institute for Allergy and Immunology | Surh C.D.,Korea Basic Science Institute | Surh C.D.,Pohang University of Science and Technology
Frontiers in Immunology | Year: 2014

Vertebrates have co-evolved with microorganisms resulting in a symbiotic relationship, which plays an important role in health and disease. Skin and mucosal surfaces are colonized with a diverse population of commensal microbiota, over 1000 species, outnumbering the host cells by 10-fold. In the past 40 years, studies have built on the idea that commensal microbiota is in constant contact with the host immune system and thus influence immune function. Recent studies, focusing on mutualism in the gut, have shown that commensal microbiota seems to play a critical role in the development and homeostasis of the host immune system. In particular, the gut microbiota appears to direct the organization and maturation of lymphoid tissues and acts both locally and systemically to regulate the recruitment, differentiation, and function of innate and adaptive immune cells. While the pace of research in the area of the mucosal-immune interface has certainly intensified over the last 10 years, we are still in the early days of this field. Illuminating the mechanisms of how gut microbes shape host immunity will enhance our understanding of the causes of immune-mediated pathologies and improve the design of next-generation vaccines. This review discusses the recent advances in this field, focusing on the close relationship between the adaptive immune system and commensal microbiota, a constant and abundant source of foreign antigens. © 2014 Spasova and Surh.

Sahlmann H.,Asia Pacific Center for Theoretical Physics | Sahlmann H.,Pohang University of Science and Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

In general relativity, the fields on a black hole horizon are obtained from those in the bulk by pullback and restriction. Similarly, in quantum gravity, the quantized horizon degrees of freedom should result from restricting, or pulling back, the quantized bulk degrees of freedom. This is not yet fully realized in the-otherwise very successful-quantization of isolated horizons in loop quantum gravity. In this work we outline a setting in which the quantum horizon degrees of freedom are simply components of the quantized bulk degrees of freedom. There is no need to quantize them separately. We present evidence that for a horizon of sphere topology, the resulting horizon theory is remarkably similar to what has been found before. © 2011 American Physical Society.

Wen R.,RIKEN | Hong M.,RIKEN | Hong M.,Pohang University of Science and Technology | Byon H.R.,RIKEN
Journal of the American Chemical Society | Year: 2013

Understanding the lithium-oxygen (Li-O2) electrochemical reaction is of importance to improve reaction kinetics, efficiency, and mitigate parasitic reactions, which links to the strategy of enhanced Li-O2 battery performance. Many in situ and ex situ analyses have been reported to address chemical species of reduction intermediate and products, whereas details of the dynamic Li-O2 reaction have not as yet been fully unraveled. For this purpose, visual imaging can provide straightforward evidence, formation and decomposition of products, during the Li-O2 electrochemical reaction. Here, we present real-time and in situ views of the Li-O2 reaction using electrochemical atomic force microscopy (EC-AFM). Details of the reaction process can be observed at nano-/micrometer scale on a highly oriented pyrolytic graphite (HOPG) electrode with lithium ion-containing tetraglyme, representative of the carbon cathode and ether-based electrolyte extensively employed in the Li-O2 battery. Upon oxygen reduction reaction (ORR), rapid growth of nanoplates, having axial diameter of hundreds of nanometers, length of micrometers, and ∼5 nm thickness, at a step edge of HOPG can be observed, which eventually forms a lithium peroxide (Li2O 2) film. This Li2O2 film is decomposed during the oxygen evolution reaction (OER), for which the decomposition potential is related to a thickness. There is no evidence of byproduct analyzed by X-ray photoelectron spectroscopy (XPS) after first reduction and oxidation reaction. However, further cycles provide unintended products such as lithium carbonate (Li2CO3), lithium acetate, and fluorine-related species with irregular morphology due to the degradation of HOPG electrode, tetraglyme, and lithium salt. These observations provide the first visualization of Li-O2 reaction process and morphological information of Li 2O2, which can allow one to build strategies to prepare the optimum conditions for the Li-O2 battery. © 2013 American Chemical Society.

Jung J.-I.,Ulsan National Institute of Science and Technology | Jeong H.Y.,Ulsan National Institute of Science and Technology | Lee J.-S.,Ulsan National Institute of Science and Technology | Kim M.G.,Pohang University of Science and Technology | Cho J.,Ulsan National Institute of Science and Technology
Angewandte Chemie - International Edition | Year: 2014

La0.3(Ba0.5Sr0.5)0.7Co 0.8Fe0.2O3-δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm-scale rhombohedral LaCoO3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A-site cations with La3+ and local stress on Co-site sub-lattice with the cubic perovskite structure. The perovskite La0.3(Ba 0.5Sr0.5)0.7Co0.8Fe 0.2O3-δ (La0.3-5582) is introduced as a bifunctional catalyst to compete with precious-metal-based catalysts. The newly introduced perovskite bears rhombohedral phase LaCoO3-δ particles on the surface of the grains. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim S.Y.,Pohang University of Science and Technology
Nature communications | Year: 2010

Proton exchange fuel cells (PEFCs) have the potential to provide power for a variety of applications ranging from electronic devices to transportation vehicles. A major challenge towards economically viable PEFCs is finding an electrolyte that is both durable and easily passes protons. In this article, we study novel anhydrous proton-conducting membranes, formed by incorporating ionic liquids into synthetic block co-polymer electrolytes, poly(styrenesulphonate-b-methylbutylene) (S(n)MB(m)), as high-temperature PEFCs. The resulting membranes are transparent, flexible and thermally stable up to 180 °C. The increases in the sulphonation level of S(n)MB(m) co-polymers (proton supplier) and the concentration of the ionic liquid (proton mediator) produce an overall increase in conductivity. Morphology effects were studied by X-ray scattering and electron microscopy. Compared with membranes having discrete ionic domains (including Nafion 117), the nanostructured membranes revealed over an order of magnitude increase in conductivity with the highest conductivity of 0.045 S cm(-1) obtained at 165 °C.

Zang S.-L.,Xian Jiaotong University | Lee M.-G.,Pohang University of Science and Technology | Sun L.,General Motors | Kim J.H.,Pusan National University
International Journal of Plasticity | Year: 2014

In this paper, a novel approach is proposed to measure the Bauschinger effect, transient behavior and permanent softening of metallic sheet subjected to reverse loading. The hardening parameters related to the Bauschinger effect, transient behavior and permanent softening are optimized from the springback profiles of three-point bending tests with pre-strained sheets. Taking the dual phase steel sheet DP780 as an example, its Bauschinger effect, transient behavior and permanent softening determined from the new approach are compared with those of the cyclic simple shear method. Finite element simulations are also performed for three-point bending and U-draw/bending of base (as-received) and pre-strained DP780 steel sheets to validate the suggested approach. The results show that the aforementioned hardening behavior determined from the new approach shows good agreements with those of cyclic simple shear tests. Moreover, reasonable springback predictions for three-point bending and U-draw/bending tests are obtained as well. In particular, the proposed approach is quite suitable for the industrial applications because only uni-axial tension and three-point bending tests are required. © 2014 Elsevier B.V. All rights reserved.

Yoon J.,Korea Institute of Intellectual Property | Kim K.,Pohang University of Science and Technology
Scientometrics | Year: 2012

In the competitive business environment, early identification of technological opportunities is crucial for technology strategy formulation and research and development planning. There exist previous studies that identify technological directions or areas from a broad view for technological opportunities, while few studies have researched a way to detect distinctive patents that can act as new technological opportunities at the individual patent level. This paper proposes a method of detecting new technological opportunities by using subject-action-object (SAO)-based semantic patent analysis and outlier detection. SAO structures are syntactically ordered sentences that can be automatically extracted by natural language processing of patent text; they explicitly show the structural relationships among technological components in a patent, and thus encode key findings of inventions and the expertise of inventors. Therefore, the proposed method allows quantification of structural dissimilarities among patents. We use outlier detection to identify unusual or distinctive patents in a given technology area; some of these outlier patents may represent new technological opportunities. The proposed method is illustrated using patents related to organic photovoltaic cells. We expect that this method can be incorporated into the research and development process for early identification of technological opportunities. © 2011 Akadémiai Kiadó, Budapest, Hungary.

Hwang D.S.,Pohang University of Science and Technology | Hwang D.S.,University of California at Santa Barbara | Waite J.H.,University of California at Santa Barbara
Protein Science | Year: 2012

Mussel foot proteins (mfps) mediate fouling by the byssal holdfast and have been extensively investigated as models for versatile polymer-mediated underwater adhesion and coatings. However, insights into the structural properties of mfps have lagged far behind the nanomechanical advances, owing in part to the inability of these proteins to crystallize as well as their limited solubility. Here, solution secondary structures of mfp-1, mfp-2, and mfp-3, localized in the mussel byssal cuticle, adhesive plaque, and plaque-substratum interface, respectively, were investigated using circular dichroism. All three have significant extended coil solution structure, but two, mfp-1 and mfp-2, appear to have punctuated regions of structure separated by unstructured domains. Apart from its punctuated distribution, the structure in mfp-1 resembles other structural proteins such as collagen and plant cell-wall proteins with prominent polyproline II helical structure. As in collagen, PP II structure of mfp-1 is incrementally disrupted by increasing the temperature and by raising pH. However, no recognizable change in mfp-1's PP II structure was evident with the addition with Ca2+ and Fe3+. In contrast, mfp-2 exhibits Ca2 1- and disulfide-stabilized epidermal growth factor-like domains separated by unstructured sequence. Mfp-2 showed calcium-binding ability. Bound calcium in mfp-2 was not removed by chelation at pH 5.5, but it was released upon reduction of disulfide bonds. Mfp-3, in contrast, appears to consist largely of unstructured extended coils. © 2012 The Protein Society.

Burmann F.,Max Planck Institute of Biochemistry | Shin H.-C.,Korea Advanced Institute of Science and Technology | Basquin J.,Max Planck Institute of Biochemistry | Soh Y.-M.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Nature Structural and Molecular Biology | Year: 2013

Eukaryotic structural maintenance of chromosomes (SMC)-kleisin complexes form large, ring-shaped assemblies that promote accurate chromosome segregation. Their asymmetric structural core comprises SMC heterodimers that associate with both ends of a kleisin subunit. However, prokaryotic condensin Smc-ScpAB is composed of symmetric Smc homodimers associated with the kleisin ScpA in a postulated symmetrical manner. Here, we demonstrate that Smc molecules have two distinct binding sites for ScpA. The N terminus of ScpA binds the Smc coiled coil, whereas the C terminus binds the Smc ATPase domain. We show that in Bacillus subtilis cells, an Smc dimer is bridged by a single ScpAB to generate asymmetric tripartite rings analogous to eukaryotic SMC complexes. We define a molecular mechanism that ensures asymmetric assembly, and we conclude that the basic architecture of SMC-kleisin rings evolved before the emergence of eukaryotes. Copyright © 2013 Nature America, Inc.

Loh W.-K.,Gachon University | Yu H.,Pohang University of Science and Technology
Information Sciences | Year: 2015

Graphics processing units (GPUs) have been utilized to improve the processing speed of many conventional data mining algorithms. DBSCAN, a popular clustering algorithm that has been often used in practice, was extended to execute on a GPU. However, existing GPU-based DBSCAN extensions still have impediments in that the distances from all objects need to be repeatedly computed to find the neighbor objects and the objects and intermediate clustering results are stored in costly off-chip memory of the GPU. This paper proposes CudaSCAN, a novel algorithm that improves the efficiency of DBSCAN by making better use of the GPU. CudaSCAN consists of three phases: (1) partitioning the entire dataset into sub-regions of size of an integer multiple of the on-chip shared memory size in the GPU; (2) local clustering within sub-regions in parallel; and (3) merging the local clustering results. CudaSCAN allows an overlap between sub-regions to ensure independent, parallel local clustering in each sub-region, which in turn enables for objects and/or intermediate results to be stored in on-chip shared memory that has an access cost a few hundred times cheaper than that of off-chip global memory. The independence also enables for merging to be parallelized. This paper proves the correctness of CudaSCAN, and according to our extensive experiments, CudaSCAN outperforms CUDA-DClust, a previous GPU-based DBSCAN extension, by up to 163.6 times. © 2015 Elsevier Inc. All rights reserved.

Hazra D.K.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Asia Pacific Center for Theoretical Physics | Shafieloo A.,Pohang University of Science and Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Within the context of the concordance model of cosmology we test the consistency of the angular power spectrum data from WMAP and Planck looking for possible systematics. The best fit concordance model to each observation is used as a mean function along with a Crossing function with an orthogonal basis to fit the data from the other observation searching for any possible deviation. We report that allowing an overall amplitude shift in the observed angular power spectra of the two observations, the best fit mean function from Planck data is consistent with WMAP 9-year data but the best fit mean function generated from WMAP-9 data is not consistent with Planck data at the 3σ level. This is an expected result when there is no clear systematic/tension between two observations and one of them has a considerably higher precision. We conclude that there is no clear tension between Planck and WMAP 9-year angular power spectrum data from a statistical point of view (allowing the overall amplitude shift). Our result highlights the fact that while the angular power spectrum from cosmic microwave background observations is a function of various cosmological parameters, comparing individual parameters might be misleading in the presence of cosmographic degeneracies. Another main result of our analysis is the importance of the overall amplitudes of the observed spectra from Planck and WMAP observations. Fixing the amplitudes at their reported values results in an unresolvable tension between the two observations at more than 3σ level which can be a hint towards a serious systematic. © 2014 American Physical Society.

Krummel M.F.,Pohang University of Science and Technology
Current Topics in Microbiology and Immunology | Year: 2010

The cell-biology of intercellular communication between T cells and their partners has been greatly advanced over the past 10 years. The key morphological and motility features of cell contact-based communication between T cells and APCs can now be seen as a collection of patterns for cell-cell interactions amongst immune cells more generally, each serving to contribute to the outcome of the contact both locally and globally. Here we review the conservation of these patterns, amongst which is the emergent "immunological synapse," and describe a newly defined example, formed between the adjacent activating T cells. We subsequently seek to put these and the pattern more generally into the framework of system-wide behavior of the immune system. We postulate that the patterns are fine-tuned to provide quorum-like decisions by collections of activating and activated cells that interact over time and space. © 2010 Springer-Verlag Berlin Heidelberg.

Sevik C.,Texas A&M University | Sevincli H.,Leibniz Institute of Polymer Research | Cuniberti G.,Leibniz Institute of Polymer Research | Cuniberti G.,Pohang University of Science and Technology | Can T.,Texas A&M University
Nano Letters | Year: 2011

Outstanding thermal transport properties of carbon nanotubes (CNTs) qualify them as possible candidates to be used as thermal management units in electronic devices. However, significant variations in the thermal conductivity (κ) measurements of individual CNTs restrict their utilizations for this purpose. In order to address the possible sources of this large deviation and to propose a route to solve this discrepancy, we systematically investigate the effects of varying concentrations of randomly distributed multiple defects (single and double vacancies, Stone-Wales defects) on the phonon transport properties of armchair and zigzag CNTs with lengths ranging between a few hundred nanometers to several micrometers, using both nonequilibrium molecular dynamics and atomistic Green's function methods. Our results show that, for both armchair and zigzag CNTs, κ converges nearly to the same values with different types of defects, at all lengths considered in this study. On the basis of the detailed mean free path analysis, this behavior is explained with the fact that intermediate and high frequency phonons are filtered out by defect scattering, while low frequency phonons are transmitted quasi-ballistically even for several micrometer long CNTs. Furthermore, an analysis of variances in κ for different defect concentrations indicates that defect scattering at low defect concentrations could be the source of large experimental variances, and by taking advantage of the possibility to create a controlled concentration of defects by electron or ion irradiation, it is possible to standardize κ with minimizing the variance. Our results imply the possibility of phonon engineering in nanostructured graphene based materials by controlling the defect concentration. © 2011 American Chemical Society.

Lee S.,Hanyang University | Song G.-J.,Pohang University of Science and Technology | Kannan K.,New York State Department of Health | Moon H.-B.,Hanyang University
Science of the Total Environment | Year: 2014

Studies on the occurrence of polybrominated diphenyl ethers (PBDEs) and other alternative brominated flame retardants in the environment are scarce. In this study, PBDEs and non-PBDE brominated flame retardants (NBFRs), including decabromodiphenyl ethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), were measured in sludge collected from three types of wastewater treatment plants (WWTPs) in Korea. Total concentrations of PBDEs (∑. PBDE) in sludge ranged from 298 to 48,000 (mean: 3240) ng/g dry weight. Among 10 NBFRs analyzed, DBDPE and BTBPE were the only ones detected in sludge samples. Concentrations of DBDPE and BTBPE ranged from <. LOQ to 3100 (mean: 237) ng/g dry weight and from <. LOQ to 21.0 (mean: 1.57) ng/g dry weight, respectively. Concentrations of PBDEs and DBDPE determined in sludge were higher than those reported in other countries. The highest concentrations of ∑. PBDE and DBDPE were found in sludge samples originated from industrial-WWTPs (I-WWTPs), suggesting that industrial activities are a major source of these contaminants. Non-parametric multidimensional scaling ordination showed that congener profiles of PBDEs in sludge are dependent on the types of WWTPs. Almost all sludge samples contained a low ratio (mean: 0.18) of DBDPE/BDE 209, indicating an on-going contamination by PBDEs in Korea. However, the high ratios (>. 1) of DBDPE/BDE 209 were found in sludge from I-WWTPs, reflecting a shift in the usage pattern of BFRs by the Korean industry. The nationwide annual emission fluxes of ∑. PBDE, DBDPE and BTBPE via WWTPs to the environment were estimated to be 7400, 480, and 3.7. kg/year, respectively. This is the first study on the occurrence of alternative brominated flame retardants in sludge from Korea. © 2013 Elsevier B.V.

Ahn G.,Pohang University of Science and Technology
Journal of biomechanical engineering | Year: 2010

The aim of this study was to maximize oxygen diffusion within a three-dimensional scaffold in order to improve cell viability and proliferation. To evaluate the effect of pore architecture on oxygen diffusion, we designed a regular channel shape with uniform diameter, referred to as cylinder shaped, and a new channel shape with a channel diameter gradient, referred to as cone shaped. A numerical analysis predicted higher oxygen concentration in the cone-shaped channels than in the cylinder-shaped channels, throughout the scaffold. To confirm these numerical results, we examined cell proliferation and viability in 2D constructs and 3D scaffolds. Cell culture experiments revealed that cell proliferation and viability were superior in the constructs and scaffolds with cone-shaped channels.

Chung J.-H.,Ulsan National Institute of Science and Technology | Yang K.,Pohang University of Science and Technology
IEEE Transactions on Information Theory | Year: 2013

Optical orthogonal codes (OOCs) are widely used as spreading codes in optical fiber networks. An (N,w,λa,λ c)-OOC with size L is a family of L{0,1}-sequences with length N, weight w, maximum autocorrelation λa, and maximum cross correlation λc. In this paper, we present two new constructions for OOCs with λa=λc=1 which are asymptotically optimal with respect to the Johnson bound. We first construct an asymptotically optimal left(Mp^{n},M,1,1)-OOC with size (pn-1)/M by using the structure of Zpn, the ring of integers modulo pn, where p is an odd prime with M p-1, and N is a positive integer. We then present another asymptotically optimal (Mp1 pk, M, 1,1)-OOC with size (p1p k-1)/M from a product of k finite fields, where pi is an odd prime and M is a positive integer such that M ,pi-1 for 1≤ i≤k. In particular, it is optimal in the case that k=1 and (M-1)2 > p1-1. © 1963-2012 IEEE.

Kitayama K.,University of Aveiro | Tome C.N.,Los Alamos National Laboratory | Rauch E.F.,Grenoble Institute of Technology | Gracio J.J.,University of Aveiro | And 2 more authors.
International Journal of Plasticity | Year: 2013

Polycrystal aggregates subjected to plastic forming exhibit large changes in the yield stress and extended transients in the flow stress following strain path changes. Since these effects are related to the rearrangement of the dislocation structure induced during previous loading, here we propose a crystallographically-based dislocation hardening model for capturing such behavior. The model is implemented in the polycrystal code VPSC and is applied to simulate strain path changes in low carbon steel. The path changes consist of tension followed by shear at different angles with respect to the preload direction, and forward simple shear followed by reverse shear. The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage. © 2012 Elsevier Ltd.All rights reserved.

Lee J.-S.,Pohang University of Science and Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2013

Nonvolatile memory devices are one of the most important components in modern electronic devices. Many efforts have been made to fabricate high-density, low-cost, nonvolatile solid-state memory devices for use in portable/mobile electronic devices such as laptop computers, tablet devices, smart phones, etc. Among the many available nonvolatile memory devices, flash memory devices are of great interest to the electronics industry owing to their simple device structure, enabling high-density memory applications. Flash memory devices in which nanoparticles or nanocrystals are used as the charge-trapping elements have advantages over conventional flash memory devices because the charge-trapping layer and memory performance of the former can be readily optimized. Active research has recently been conducted to fabricate and characterize self-assembled-nanocrystal-based nonvolatile memory devices. We reviewed various strategies for fabricating nanocrystal-based nonvolatile memory devices and discussed the programmable memory properties and the device reliability characteristics of nanocrystal-based memory devices to possibly apply nanocrystal-based memory devices to those used in portable/ mobile electronic devices. Finally, novel device applications such as printed/flexible/transparent electronic devices were explored based on nanocrystal-based memory devices. © 2013 Elsevier B.V. All rights reserved.

Park S.H.,Korea Institute of Materials Science | Lee J.H.,Pohang University of Science and Technology | Huh Y.-H.,Korea Research Institute of Standards and Science | Hong S.-G.,Korea Research Institute of Standards and Science
Scripta Materialia | Year: 2013

The effect of texture control using {1 0-1 2} twins was capable of being significantly improved by thermal annealing. The removal of the residual tensile stress that developed inside these twins along the c-axis retarded detwinning activity during early deformation by increasing the detwinning stress, and this consequently led to a prolonged and enhanced activity of basal slip in the twinned region, increasing its contribution to the deformation. On the basis of this mechanism, the yield strength and elongation were improved simultaneously. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Choi S.-M.,Korea Institute for Advanced Study | Jhi S.-H.,Pohang University of Science and Technology | Son Y.-W.,Korea Institute for Advanced Study
ACS Nano | Year: 2013

We study the variations of electron-phonon coupling and their spectroscopic consequences in response to the sliding of two layers in bilayer graphene using first-principles calculations and a model Hamiltonian. Our study shows that the long wavelength optical phonon modes change in a sensitive and unusual way depending on the symmetry as well as the parity of sliding atomic structures and that, accordingly, Raman- and infrared-active optical phonon modes behave differently upon the direction and size of the sliding. The renormalization of phonon modes by the interlayer electronic coupling is shown to be crucial to explain their anomalous behavior upon the sliding. Also, we show that the crystal symmetry change due to the sliding affects the polarized Stokes Raman scattering intensity, which can be utilized to detect tiny misalignment of graphene layers using spectroscopic tools. © 2013 American Chemical Society.

Lehmann T.,TU Dresden | Ryndyk D.A.,TU Dresden | Cuniberti G.,TU Dresden | Cuniberti G.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We investigate the combined influence of structural defects and uniaxial longitudinal strain on the electronic transport properties of armchair graphene nanoribbons using the numerical approach based on the semiempirical tight-binding model, the Landauer formalism, and the recursion method for Green functions. We calculate the conductance of graphene nanoribbons in the quantum coherent regime with different types and concentrations of defects. Further, we apply uniform planar tension to the nonideal graphene ribbons with randomly distributed and oriented single and double vacancies and Stone-Wales defects. Since transport characteristics of graphene nanoribbons are found to be very sensitive to edge termination and aspect ratio, and it has been shown that energy gaps can emerge under critical strain; the interplay of both effects needs to be studied. We show that band gap engineering using strain is still possible for nonideal armchair ribbons with a small defect concentration, as the oscillatory behavior of the gap is preserved. © 2013 American Physical Society.

Wan M.-B.,Asia Pacific Center for Theoretical Physics | Jho Y.,Asia Pacific Center for Theoretical Physics | Jho Y.,Pohang University of Science and Technology
Soft Matter | Year: 2013

Previous work shows that a net directed motion arises from a system of individual particles undergoing run-and-tumble dynamics in the presence of an array of asymmetric barriers. Here, we show that when the individual particle is replaced by a chain of particles linked to each other by spring forces (polymer), the rectification is enhanced. It is found that the rectification increases when the number of particles in each polymer, as well as its length, increases. In addition, the rectification increases when the size of the opening between neighboring funnel tips, lo, decreases. Interestingly, if the conformal entropic difference exceeds the thermal diffusion, a net directed motion is observed even when the run-and-tumble dynamics approaches Brownian motion. Also, when the inelastic collisions between the particles and the barriers are replaced by elastic collisions, a reversed rectification is observed. © 2013 The Royal Society of Chemistry.

Koolen J.H.,Pohang University of Science and Technology | Bang S.,Pusan National University
Journal of Combinatorial Theory. Series B | Year: 2010

A non-complete geometric distance-regular graph is the point graph of a partial linear space in which the set of lines is a set of Delsarte cliques. In this paper, we prove that for a fixed integer m≥2, there are only finitely many non-geometric distance-regular graphs with smallest eigenvalue at least - m, diameter at least three and intersection number c2≥2. © 2010 Elsevier Inc.

Ohara K.,University of Tokyo | Kawano M.,Pohang University of Science and Technology | Inokuma Y.,University of Tokyo | Fujita M.,University of Tokyo
Journal of the American Chemical Society | Year: 2010

(Figure Presented) All-trans retinal efficiently diffused into the pore of a porous coordination network consisting of ZnI2 and an electron-deficient triazine-cored ligand. Enclathrated retinal was isomerized into the 13-cis form and easily replaced with all-trans retinal in solution, thus revealing the catalysis of retinal isomerization by the porous network. © 2010 American Chemical Society.

Joeng J.R.,Pohang University of Science and Technology | Turner S.L.,University of Minnesota
Journal of Counseling Psychology | Year: 2015

This study was an investigation of the relationships between internalized self-criticism and depression and between comparative self-criticism and depression as these relationships are mediated by the fear of self-compassion, fear of compassion from others, self-compassion, and the perception that one is important to others. To examine these relationships, data were gathered via online survey methods from 206 university students at a large public Midwestern university in the United States. The Self-Criticism/Compassion Mediation Model, in which internalized and comparative self-criticism were both modeled to predict depression, was built and tested via structural equation modeling (SEM). In the presence of 4 competing models, this model effectively modeled relationships among the study variables. In the Self-Criticism/Compassion Mediation Model, the fear of self-compassion, and the perception that one is important to others serially mediated the relationship between comparative self-criticism and depression. Additionally, self-compassion partially mediated both the relationship between internalized self-criticism and depression, and the relationship between comparative self-criticism and depression. Implications include the use of the model as a guide to developing evidence-based practice for highly self-critical, depressed clients.

Torres J.,University Pierre and Marie Curie | Nogueira M.,Federal University of Parana | Pujolle G.,University Pierre and Marie Curie | Pujolle G.,Pohang University of Science and Technology
IEEE Communications Surveys and Tutorials | Year: 2013

The Internet as a platform for ubiquitous communication has quickly advanced in the last years. New services have emphasized the limits of the current Internet and motivated the development of the Future Internet. Future communication infrastructures intend to be more distributed and, ideally, more secure, resulting in high complexity. Further, as new technologies emerge, new requirements and security issues are highlighted. These issues reinforce the importance of Identity Management systems for the network infrastructure in the Future Internet, termed Future Network, to provide adequate dynamic services in relation to user's personal data and requirements. Hence, this survey presents the state of the art of Identity Management systems for the Future Network. It highlights the existing architectures, specific devices applied, challenges and future perspectives. © 2013 IEEE.

Kim K.,Pohang University of Science and Technology | Lee J.,Seoul National University
Pattern Recognition | Year: 2014

Sentiment analysis, which detects the subjectivity or polarity of documents, is one of the fundamental tasks in text data analytics. Recently, the number of documents available online and offline is increasing dramatically, and preprocessed text data have more features. This development makes analysis more complex to be analyzed effectively. This paper proposes a novel semi-supervised Laplacian eigenmap (SS-LE). The SS-LE removes redundant features effectively by decreasing detection errors of sentiments. Moreover, it enables visualization of documents in perceptible low dimensional embedded space to provide a useful tool for text analytics. The proposed method is evaluated using multi-domain review data set in sentiment visualization and classification by comparing other dimensionality reduction methods. SS-LE provides a better similarity measure in the visualization result by separating positive and negative documents properly. Sentiment classification models trained over reduced data by SS-LE show higher accuracy. Overall, experimental results suggest that SS-LE has the potential to be used to visualize documents for the ease of analysis and to train a predictive model in sentiment analysis. SS-LE can also be applied to any other partially annotated text data sets. © 2013 Elsevier Ltd.

Choi H.-C.,Multimedia Research Team | Oh S.-Y.,Pohang University of Science and Technology
Pattern Recognition | Year: 2012

Tracking based on gradient descent algorithm using image gradient is one of the popular object tracking method. However, it easily fails to track when illumination changes. Although several illumination invariant features have been proposed, applying the invariant feature to the gradient descent method is not easy because the invariant feature is represented as a non-linear function of image pixel values and its Jacobian cannot be calculated in a closed-form. To make it possible, we introduce the generalized hyperplane approximation technique and apply it to histogram of oriented gradient (HOG) feature, one of the well-known illumination invariant feature. In addition, we achieve partial occlusion invariance using image segments. The hyperplanes are calculated from training segment images obtained by perturbing the motion parameter around the target region. Then, it is used to map the difference in non-linear feature of image onto the increment of alignment parameters. This process is mathematically same to the gradient descent method. The information from each segment is integrated by a simple weighted linear combination with confidence weights of segments. Compared to the previous tracking algorithms, our method shows very fast and stable tracking results in experiments on several practical image sequences. © 2012 Elsevier Ltd. All rights reserved.

Kang Y.-B.,Pohang University of Science and Technology
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2010

Critical evaluations and thermodynamic optimizations of the manganesesulfur binary system and ironmanganesesulfur ternary systems have been carried out over the entire composition range from room temperature to above the liquidus temperature. The Gibbs energies of all available phases have been thermodynamically modeled, and model parameters have been optimized in order to reproduce all available and reliable experimental data simultaneously within experimental error limits. For the liquid phase, the Modified Quasichemical Model (MQM) in the pair approximation is employed in order to properly take into account short-range-ordering in the phase. Thermodynamic model parameters of binary liquid FeS using the MQM and those of binary liquid FeMn using the random-mixing model available in the literature are combined with those of binary liquid Mn-S using the MQM from the present study, in the framework of the MQM, in order to estimate Gibbs energy of ternary liquid Fe-Mn-S. Observed ternary solid solutions: (Mn, Fe)S and Fe1-xS are modeled using simple random-mixing model. © 2010 Elsevier Ltd. All rights reserved.

Kawamichi T.,University of Tokyo | Inokuma Y.,University of Tokyo | Kawano M.,Pohang University of Science and Technology | Fujita M.,University of Tokyo
Angewandte Chemie - International Edition | Year: 2010

(Figure Presented) Pore it on: Huisgen 1,3-dipolarcycloaddition reactions of 2-(azidomethyl)triphenylene and alkynes (see scheme) took place within the pores of a porous coordination network in a single-crystal-tosingle-crystal fashion. Columnar π stacks and nanosized pores in the network complex enforce a particular orientation of the reactants such that the 1,4-substituted isomer of the 1,2,3-triazole product is selectively produced. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Marti-Rujas J.,Italian Institute of Technology | Kawano M.,Pohang University of Science and Technology
Accounts of Chemical Research | Year: 2013

Porous coordination networks are materials that maintain their crystal structure as molecular "guests" enter and exit their pores. They are of great research interest with applications in areas such as catalysis, gas adsorption, proton conductivity, and drug release. As with zeolite preparation, the kinetic states in coordination network preparation play a crucial role in determining the final products. Controlling the kinetic state during self-assembly of coordination networks is a fundamental aspect of developing further functionalization of this class of materials. However, unlike for zeolites, there are few structural studies reporting the kinetic products made during self-assembly of coordination networks. Synthetic routes that produce the necessary selectivity are complex.The structural knowledge obtained from X-ray crystallography has been crucial for developing rational strategies for design of organic-inorganic hybrid networks. However, despite the explosive progress in the solid-state study of coordination networks during the last 15 years, researchers still do not understand many chemical reaction processes because of the difficulties in growing single crystals suitable for X-ray diffraction: Fast precipitation can lead to kinetic (metastable) products, but in microcrystalline form, unsuitable for single crystal X-ray analysis. X-ray powder diffraction (XRPD) routinely is used to check phase purity, crystallinity, and to monitor the stability of frameworks upon guest removal/inclusion under various conditions, but rarely is used for structure elucidation. Recent advances in structure determination of microcrystalline solids from ab initio XRPD have allowed three-dimensional structure determination when single crystals are not available. Thus, ab initio XRPD structure determination is becoming a powerful method for structure determination of microcrystalline solids, including porous coordination networks. Because of the great interest across scientific disciplines in coordination networks, especially porous coordination networks, the ability to determine crystal structures when the crystals are not suitable for single crystal X-ray analysis is of paramount importance.In this Account, we report the potential of kinetic control to synthesize new coordination networks and we describe ab initio XRPD structure determination to characterize these networks' crystal structures. We describe our recent work on selective instant synthesis to yield kinetically controlled porous coordination networks. We demonstrate that instant synthesis can selectively produce metastable networks that are not possible to synthesize by conventional solution chemistry. Using kinetic products, we provide mechanistic insights into thermally induced (573-723 K) (i.e., annealing method) structural transformations in porous coordination networks as well as examples of guest exchange/inclusion reactions. Finally, we describe a memory effect that allows the transfer of structural information from kinetic precursor structures to thermally stable structures through amorphous intermediate phases.We believe that ab initio XRPD structure determination will soon be used to investigate chemical processes that lead intrinsically to microcrystalline solids, which up to now have not been fully understood due to the unavailability of single crystals. For example, only recently have researchers used single-crystal X-ray diffraction to elucidate crystal-to-crystal chemical reactions taking place in the crystalline scaffold of coordination networks. The potential of ab initio X-ray powder diffraction analysis goes beyond single-crystal-to-single-crystal processes, potentially allowing members of this field to study intriguing in situ reactions, such as reactions within pores. © 2012 American Chemical Society.

Stavrositu C.D.,University of Colorado at Colorado Springs | Kim J.,Pohang University of Science and Technology
Computers in Human Behavior | Year: 2014

The present study investigated the role of social media metrics (i.e., number of shares and comments) displayed alongside online news stories in shaping users' perceptions of the content and its influence. In a web-based experiment (N = 144), participants first read a cancer news story that displayed either a high or a low level of social media metrics, then reported their perceived story influence on the self and others, as well as their behavioral intentions. In the low social media metrics condition, the general story influence was perceived to be stronger for others than for the self, indicative of the "third-person effect." This effect, however, was diminished to insignificant levels in the high social media metrics condition. Further, social media metrics had an ultimate indirect effect on behavioral intentions via the third-person effect. Theoretical and practical implications of these findings are provided in the end. © 2014 Elsevier Ltd. All rights reserved.

Jeong H.M.,Korea Advanced Institute of Science and Technology | Lee J.W.,Korea Advanced Institute of Science and Technology | Shin W.H.,Korea Advanced Institute of Science and Technology | Choi Y.J.,Korea Advanced Institute of Science and Technology | And 3 more authors.
Nano Letters | Year: 2011

Although various carbon nanomaterials including activated carbon, carbon nanotubes, and graphene have been successfully demonstrated for high-performance ultracapacitors, their capacitances need to be improved further for wider and more challenging applications. Herein, using nitrogen-doped graphene produced by a simple plasma process, we developed ultracapacitors whose capacitances (∼280 F/gelectrode) are about 4 times larger than those of pristine graphene based counterparts without sacrificing other essential and useful properties for ultracapacitor operations including excellent cycle life (>200000), high power capability, and compatibility with flexible substrates. While we were trying to understand the improved capacitance using scanning photoemission microscopy with a capability of probing local nitrogen - carbon bonding configurations within a single sheet of graphene, we observed interesting microscopic features of N-configurations: N-doped sites even at basal planes, distinctive distributions of N-configurations between edges and basal planes, and their distinctive evolutions with plasma duration. The local N-configuration mappings during plasma treatment, alongside binding energy calculated by density functional theory, revealed that the origin of the improved capacitance is a certain N-configuration at basal planes. © 2011 American Chemical Society.

Kolar M.,Gilead Sciences | Kolar M.,Charles University | Hobza P.,Gilead Sciences | Hobza P.,Palacky University | Hobza P.,Pohang University of Science and Technology
Journal of Chemical Theory and Computation | Year: 2012

Until recently, the description of halogen bonding by standard molecular mechanics has been poor, owing to the lack of the so-called σ hole localized at the halogen. This region of positive electrostatic potential located on top of a halogen atom explains the counterintuitive attraction of halogenated compounds interacting with Lewis bases. In molecular mechanics, the σ hole is modeled by a massless point charge attached to the halogen atom and referred to as an explicit σ hole (ESH). Here, we introduce and compare three methods of ESH construction, which differ in the complexity of the input needed. The molecular mechanical dissociation curves of three model complexes containing bromine are compared with accurate CCSD(T)/CBS data. Furthermore, the performance of the Amber force field enhanced by the ESH on geometry characteristics is tested on the casein kinase 2 protein complex with seven brominated inhibitors. It is shown how various schemes depend on the selection of the ESH parameters and to what extent the energies and geometries are reliable. The charge of 0.2e placed 1.5 Å from the bromine atomic center is suggested as a universal model for the ESH. © 2012 American Chemical Society.

Chatterjee S.,Hanbat National University | Lee M.W.,Pohang University of Science and Technology | Wooa S.H.,Hanbat National University
Bioresource Technology | Year: 2010

The adsorption performance of chitosan (CS) hydrogel beads was investigated after multiwalled carbon nanotubes (MWCNTs) impregnation for the removal of congo red (CR) as an anionic dye. The study of the adsorption capacity of CS/CNT beads as a function of the CNT concentration indicated that 0.01% CNT impregnation was the most useful for enhancing the adsorption capacity. The sulfur (%) in the CS/CNT beads measured by energy dispersive X-ray (EDX) was 2.5 times higher than that of normal CS beads after CR adsorption. Equilibrium adsorption isotherm data of the CS/CNT beads exhibited better fit to the Langmuir isotherm model than to the Freundlich isotherm model, and the heterogeneity factor (n) value of the CS/CNT beads calculated from the Sips isotherm model was close to unity (0.98). The maximum adsorption capacity of CS/CNT beads obtained from the Langmuir model was 450.4 mg g-1. © 2009 Elsevier Ltd.

Lee S.,Pohang University of Science and Technology | An R.,University of Michigan | Hunt A.J.,University of Michigan
Nature Nanotechnology | Year: 2010

Nanofluidic devices make use of molecular-level forces and phenomena to increase their density, speed and accuracy. However, fabrication is challenging, because dissimilar materials need to be integrated in three dimensions with nanoscale precision. Here, we report a three-dimensional nanoscale liquid glass electrode made from monolithic substrates without conductive materials by femtosecond-laser nanomachining. The electrode consists of a nanochannel terminating at a nanoscale glass tip that becomes a conductor in the presence of high electric fields through dielectric breakdown, and returns to being an insulator when this field is removed. This reversibility relies on control of nanoampere breakdown currents and extremely fast heat dissipation at nanoscale volumes. We use the nanoscale liquid glass electrode to fabricate a nano-injector that includes an electrokinetic pump, 4νm across with 0.6νm channels, which is capable of producing well-controlled flow rates below 1fls-1. The electrode can be integrated easily into other nanodevices and fluidic systems, including actuators and sensors. © 2010 Macmillan Publishers Limited. All rights reserved.

Chang B.-Y.,Pohang University of Science and Technology | Park S.-M.,Ulsan National Institute of Science and Technology
Annual Review of Analytical Chemistry | Year: 2010

This review describes recent advances in electrochemical impedance spectroscopy (EIS) with an emphasis on its novel applications to various electrochemistry-related problems. Section 1 discusses the development of new EIS techniques to reduce measurement time. For this purpose, various forms of multisine EIS techniques were first developed via a noise signal synthesized by mixing ac waves of various frequencies, followed by fast Fourier transform of the signal and the resulting current. Subsequently, an entirely new concept was introduced in which true white noise was used as an excitation source, followed by Fourier transform of both excitation and response signals. Section 2 describes novel applications of the newly developed techniques to time-resolved impedance measurements as well as to impedance imaging. Section 3 is devoted to recent applications of EIS techniques, specifically traditional measurements in various fields with a special emphasis on biosensor detections. Copyright © 2010 by Annual Reviews. All rights reserved.

Sung J.,Yonsei University | Choi Y.S.,Yonsei University | Kang S.J.,Yonsei University | Cho S.H.,Yonsei University | And 2 more authors.
Nano Letters | Year: 2011

We developed a high-performance field-induced polymer electroluminescence (FPEL) device consisting of four stacked layers: a top metal electrode/thin solution-processed nanocomposite film of single wall carbon nanotubes (SWNTs) and a fluorescent polymer/insulator/transparent bottom electrode working under an alternating current (AC) electric field. A small amount of SWNTs that were highly dispersed in the fluorescent polymer matrix by a conjugate block copolymer dispersant significantly enhanced EL, and we were able to realize an SWNT-FPEL device with a light emission of approximately 350 cd/m2 at an applied voltage of ±25 V and an AC frequency of 300 kHz. The brightness of the SWNT-FPEL device is much greater than those of other AC-based organic or even inorganic ELs that generally require at least a few hundred volts. Light is emitted from our SWNT-FPEL device because of the sequential injection of field-induced holes and then electron carriers through ambipolar carbon nanotubes under an AC field, followed by exciton formation in the conjugated organic layer. Field-induced bipolar charge injection provides great material design freedom for our devices; the energy level does not have to be aligned between the electrode and the emission layer, and the balance of the carrier injected and transported can be altered in contrast to that in conventional organic light-emitting diodes, leading to an extremely cost-effective and unified device architecture that is applicable to all red-green-blue fluorescent polymers. © 2011 American Chemical Society.

Fishman R.S.,Oak Ridge National Laboratory | Haraldsen J.T.,Los Alamos National Laboratory | Furukawa N.,Aoyama Gakuin University | Miyahara S.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Spectroscopic modes provide the most sensitive probe of the very weak interactions responsible for the properties of the long-wavelength cycloid in the multiferroic phase of BiFeO3 below TN≈640 K. Three of the four modes measured by terahertz (THz) and Raman spectroscopies were recently identified using a simple microscopic model. While a Dzyaloshinskii-Moriya (DM) interaction D along [-1,2,-1] induces a cycloid with wave vector (2π/a)(0.5+δ,0.5,0.5-δ) (δ≈0.0045), easy-axis anisotropy K along the [1,1,1] direction of the electric polarization P induces higher harmonics of the cycloid, which split the Ψ1 modes at 2.49 and 2.67 meV and activate the Φ2 mode at 3.38 meV. However, that model could not explain the observed low-frequency mode at about 2.17 meV. We now demonstrate that an additional DM interaction D′ along [1,1,1] not only produces the observed weak ferromagnetic moment of the high-field phase above 18 T but also activates the spectroscopic matrix elements of the nearly degenerate, low-frequency Ψ0 and Φ1 modes, although their scattering intensities remain extremely weak. Even in the absence of easy-axis anisotropy, D′ produces cycloidal harmonics that split Ψ1 and activate Φ2. However, the observed mode frequencies and selection rules require that both D′ and K are nonzero. This work also resolves an earlier disagreement between spectroscopic and inelastic neutron-scattering measurements. © 2013 American Physical Society.

Kim K.-S.,Asia Pacific Center for Theoretical Physics | Kim K.-S.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Hall coefficient implies the mechanism for reconstruction of a Fermi surface, distinguishing competing scenarios for Mott criticality such as electron fractionalization, dynamical mean-field theory, and metal-insulator transition driven by symmetry breaking. We find that electron fractionalization leaves a signature for the Hall coefficient at Mott criticality in two dimensions, a unique feature differentiated from other theories. We evaluate the Hall coefficient based on the quantum Boltzman equation approach, guaranteeing gauge invariance in both longitudinal and transverse transport coefficients. © 2011 American Physical Society.

Lim T.,Kyonggi University | Lee S.,Kyonggi University | Meyyappan M.,NASA | Meyyappan M.,Pohang University of Science and Technology | Ju S.,Kyonggi University
ACS Nano | Year: 2011

Oxide semiconductors are candidates for chemical sensors, transparent electrodes, and electronic devices. Here, we have investigated metal-to-semiconductor transitions during In 2O 3 nanowire growth with variations in the O 2 gas rate. Photoluminescence and current-voltage characteristics of In 2O 3 nanowire transistors have been used to understand the transition behavior. The proportion of metallic nanowires to semiconducting nanowires significantly changes from 80:20 to 25:75 when the O 2 fraction in argon increases from 0.005% to 0.2%. We believe that excessive oxygen vacancies at low O 2 gas rates increase the conductivity and thereby the number of nanowires with metallic characteristics. With an increase in oxygen flow, the oxygen vacancies in the nanowires are substituted with oxygen and the subsequent reduction in oxygen vacancies increases the number of semiconducting nanowires. The threshold voltage of transistors fabricated with semiconducting nanowires shifts in a positive direction by about +3.3 eV between nanowires grown with 0.005% and 0.2% oxygen. The results here indicate that electrical and optical characteristics of oxide nanowires can be controlled by the amount of oxygen during growth instead of relying on conventional postgrowth high-temperature annealing or other postprocessing techniques. © 2011 American Chemical Society.

Hwang B.,Korea Institute of Materials Science | Suh D.-W.,Pohang University of Science and Technology | Kim S.-J.,Korea Institute of Materials Science
Scripta Materialia | Year: 2011

The hardenability of boron steels was discussed in terms of precipitation behavior and phase stability of M23(C,B)6 borocarbide in accordance with austenitizing temperature. A higher austenitizing temperature reduced the hardenability of Mo-added boron steel by the preferred precipitation of borocarbide because it caused a significant increase in boron concentration segregated to the austenite grain boundary due to grain coarsening and a non-equilibrium segregation mechanism. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Kang S.-J.,Algorithm | Kim Y.H.,Pohang University of Science and Technology
IEEE/OSA Journal of Display Technology | Year: 2011

This paper presents a new method for dynamic backlight dimming that uses multiple histograms for liquid crystal display (LCD) devices. The proposed multi-histogram-based gray-level error control (MGEC) algorithm considers the pixel distribution of an image using multiple histograms, thereby improving the image quality. Additionally, we propose several techniques to reduce the computational cost of the MGEC algorithm. In the experimental results, the average peak signal-to-noise ratio (PSNR) of the proposed method was improved by up to 8.144 dB compared to that of the benchmark method, while the power consumption was reduced substantially. In addition, when we applied the proposed techniques to reduce the computational cost of the MGEC algorithm, the computation time was reduced by up to 95.801% compared to that of the original algorithm. © 2006 IEEE.

Thalmeier P.,Max Planck Institute for Chemical Physics of Solids | Takimoto T.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We discuss the conclusions on the symmetry of hidden order (HO) in URu 2Si2 that may be drawn from recent torque experiments in a rotating magnetic field by Okazaki (to be published). They are very sensitive to changes in the magnetic susceptibility induced by HO. We show that the observed twofold angular torque oscillations give evidence that HO has degenerate E-type (yz, zx) symmetry where both components are realized. The oscillations have the wrong characteristics or are absent for the one-dimensional (1D) nontrivial representations like quadrupolar B 1(x2-y2) and B2(xy) type HO or hexadecapolar A 2[xy(x2-y2)] type HO. Therefore, they may be excluded as candidates for HO. We also predict the field-angular variation of possible field-induced Bragg peaks based on the underlying E-type order parameter and discuss the expected elastic constant anomalies. © 2011 American Physical Society.

Shin S.,University of Michigan | Kaviany M.,University of Michigan | Kaviany M.,Pohang University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Based on the quantum-junction transmission/Green's function formalism and the dynamical matrix/DFT, we find the phonon wave features result in bimodal resonant transmission in the interflake conductance of H or O edge-passivated graphene. The low-frequency resonant transport mode is due to the weak interaction between the flakes, while the high-frequency resonant transport mode depends on the passivated species and brings the temperature dependence. The phonon transport polarized in the transport directions is dominant because of the asymmetric charge distribution of C-O-H-C and this contributes to the conductance. Thermal conductance decreases due to the passivation junctions, and the electronic thermal conductance becomes negligible except for the O-H junction at high temperatures. © 2011 American Physical Society.

Kim Y.K.,Ajou University | Hwang C.-C.,Pohang University of Science and Technology
Surface Science | Year: 2011

Synchrotron radiation photoemission spectroscopy is employed to study the adsorption of ethanol on the rutile TiO2(110) surface at room temperature (RT). For the present study, well-characterized clean and oxidized rutile TiO2(110) surfaces are reproduced and ethanol is subsequently dosed at RT. We observe that the band-gap state varies in intensity upon ethanol adsorption on TiO2(110) at RT. Especially, the band-gap state is enhanced in intensity when ethanol is dosed on the oxidized TiO2(110) surface. These observations imply that the adsorption of ethanol induces a change in the surface charge associated with defects such as oxygen vacancies and Ti3+ interstitials due to an attractive interaction between ethanol and such defects. Interestingly, pre-dosed ethanol on TiO 2(110) is observed to inhibit the attenuation of the band-gap state during subsequent O2 dose at RT. We interpret the result from a site-blocking effect by the pre-adsorbed ethanol both on oxygen vacancies and Ti4+ sites in inhibiting the interaction between O2 and surface defects on the TiO2(110) surface. © 2011 Elsevier B.V. All rights reserved.

Kang Y.-B.,Pohang University of Science and Technology | Park J.H.,University of Ulsan
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2011

Sulfur dissolution behavior, in terms of sulfide capacity (C S), in ternary silicate slags (molten oxide slags composed of MO - NO - SiO 2, where M and N are Ca, Mn, Fe, and Mg), is discussed based on available experimental data. Composition dependence of the sulfur dissolution, at least in the dilute region of sulfur, may be explained by taking into account the cation- anion first-nearest-neighbor (FNN) interaction (stability of sulfide) and the cation-cation second-nearest-neighbor (SNN) interaction over O anion (oxygen proportions in silicate slags). When the Gibbs energy of a reciprocal reaction MO + NS = MS + NO is positive, the sulfide capacity of slags with virtually no SiO 2 or low SiO 2 concentration decreases as the concentration of MO increases. However, in some slags, as SiO 2 concentration increases, replacing NO by MO at a constant SiO 2 concentration may increase sulfide capacity when the basicity of NO is less than that of MO. This phenomenon is observed as rotation of iso-C S lines in ternary silicate slags, and it is explained by simultaneous consideration of the stability of sulfide and oxygen proportions in the silicate slags. It is suggested that a solution model for the prediction of sulfide capacity should be based on the actual dissolution mechanism of sulfur rather than on the simple empirical correlation. © The Minerals, Metals & Materials Society and ASM International 2011.

Lim T.,Kyonggi University | Kim H.,Kyonggi University | Meyyappan M.,NASA | Meyyappan M.,Pohang University of Science and Technology | Ju S.,Kyonggi University
ACS Nano | Year: 2012

Although oxide nanowires offer advantages for next-generation transparent display applications, they are also one of the most challenging materials for this purpose. Exposure of semiconducting channel areas of oxide nanowire transistors produces an undesirable increase in the photocurrent, which may result in unstable device operation. In this study, we have developed a Zn 2SnO 4 nanowire transistor that operates stably regardless of changes in the external illumination. In particular, after exposure to a light source of 2100 lx, the threshold voltage (V th) showed a negative shift of less than 0.4 V, and the subthreshold slope (SS) changed by ∼0.1 V/dec. ZnO or SnO 2 nanowire transistors, in contrast, showed 1.5-2.0 V negative shift in V th and an SS change of ∼0.3 V/dec under the same conditions. Furthermore, the Zn 2SnO 4 nanowire transistors returned to their initial state immediately after the light source was turned off, unlike those using the other two nanowires. Thus, Zn 2SnO 4 nanowires achieve photostability without the application of a black material or additional processing, minimizing the photocurrent effect for display devices. © 2012 American Chemical Society.

Faraji G.,University of Tehran | Mashhadi M.M.,University of Tehran | Kim H.S.,Pohang University of Science and Technology
Materials Letters | Year: 2011

A severe plastic deformation (SPD) technique based on tubular channel angular pressing (TCAP) is proposed suitable for deforming cylindrical tubes to extremely large strains without changing their dimensions. The tube constrained by inner and outer dies is pressed by a hollow cylindrical punch into a tubular angular channel with three shear zones. This technique was applied to a commercial AZ91 magnesium alloy and a significant grain refinement was achieved even after single cycle TCAP. Microhardness of the tube increased to 78 Hv from an initial value of 51 Hv. This new SPD process is promising for future industrial applications. © 2011 Elsevier B.V. All Rights Reserved.

Kataru R.P.,Korea Advanced Institute of Science and Technology | Kim H.,Korea Advanced Institute of Science and Technology | Jang C.,Korea Advanced Institute of Science and Technology | Choi D.K.,Korea Advanced Institute of Science and Technology | And 6 more authors.
Immunity | Year: 2011

Lymph node lymphatic vessels (LNLVs) serve as a conduit to drain antigens from peripheral tissues to within the lymph nodes. LNLV density is known to be positively regulated by vascular endothelial growth factors secreted by B cells, macrophages, and dendritic cells (DCs). Here, we show that LNLV formation was negatively regulated by T cells. In both steady and inflammatory states, the density of LNLVs was increased in the absence of T cells but decreased when T cells were restored. Interferon-γ secretion by T cells suppressed lymphatic-specific genes in lymphatic endothelial cells and consequently caused marked reduction in LNLV formation. When T cells were depleted, recruitment of antigen-carrying DCs to LNs was augmented, reflecting a compensatory mechanism for antigen presentation to T cells through increased LNLVs. Thus, T cells maintain the homeostatic balance of LNLV density through a negative paracrine action of interferon-γ. © 2011 Elsevier Inc.

Hwang M.-J.,Pohang University of Science and Technology | Choi M.-S.,Korea University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

The nonclassical behavior of a two-level system coupled to a harmonic oscillator is investigated in the ultrastrong coupling regime. We revisit the variational solution of the ground state and find that the existing solutions do not account accurately for nonclassical effects such as squeezing. We suggest a trial wave function and demonstrate that it has an excellent accuracy for the quantum correlation effects as well as for the energy. © 2010 The American Physical Society.

Weon B.M.,Harvard University | Je J.H.,Pohang University of Science and Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

When a coffee drop dries on a solid surface, it leaves a ringlike deposit along the edge and this is known as the "coffee-ring effect." We find a different motion of particles repelling the coffee-ring effect in drying droplets; the motion of particles that is initially toward the edge by the coffee-ring effect is reversed toward the center by a capillary force. The reversal takes place when the capillary force prevails over the outward coffee-ring flow. We discuss the geometric constraints for the capillary force and the reverse motion. Our findings of reversal phenomena would be important in many scenarios of drying colloidal fluids. © 2010 The American Physical Society.

Park C.,Sogang University | Park C.,Asia Pacific Center for Theoretical Physics | Park C.,Pohang University of Science and Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

In a d-dimensional conformal field theory, it has been known that a relevant deformation operator with the conformal dimension, Δ=d+22, generates a logarithmic correction to the entanglement entropy. In the large 't Hooft coupling limit, we can investigate such a logarithmic correction holographically by deforming an AdS space with a massive scalar field dual to the operator with Δ=d+22. There are two sources generating the logarithmic correction. One is the metric deformation and the other is the minimal surface deformation. In this work, we investigate the change of the entanglement entropy caused by the minimal surface deformation and find that the second order minimal surface deformation leads to an additional logarithmic correction. © 2015 American Physical Society.

Chhajed S.,Rensselaer Polytechnic Institute | Lee W.,Rensselaer Polytechnic Institute | Cho J.,Rensselaer Polytechnic Institute | Schubert E.F.,Rensselaer Polytechnic Institute | Kim J.K.,Pohang University of Science and Technology
Applied Physics Letters | Year: 2011

We report on a self-organized nanoscale patterning method by using oblique angle deposition to enhance the light extraction in a GaInN light-emitting diode (LED). The method offers one-step processing with good controllability of the feature size and density of the nanopatterns by varying the deposition angle during oblique angle deposition, eliminating the need for photolithography and annealing. A 5-nm-thick silver (Ag) film, when deposited by using oblique angle deposition, spontaneously forms a nanoscale island-like morphology on the substrate. This method is used to texture p -type GaN with nanoscale features, which results in increased light extraction from a GaInN LED. At 100 mA, the nanotextured LED shows a 46% higher light output than a standard LED with unpatterned (planar) p -type GaN. © 2011 American Institute of Physics.

Ree M.,Pohang University of Science and Technology
Macromolecular Rapid Communications | Year: 2014

For advanced functional polymers such as biopolymers, biomimic polymers, brush polymers, star polymers, dendritic polymers, and block copolymers, information about their surface structures, morphologies, and atomic structures is essential for understanding their properties and investigating their potential applications. Grazing incidence X-ray scattering (GIXS) is established for the last 15 years as the most powerful, versatile, and nondestructive tool for determining these structural details when performed with the aid of an advanced third-generation synchrotron radiation source with high flux, high energy resolution, energy tunability, and small beam size. One particular merit of this technique is that GIXS data can be obtained facilely for material specimens of any size, type, or shape. However, GIXS data analysis requires an understanding of GIXS theory and of refraction and reflection effects, and for any given material specimen, the best methods for extracting the form factor and the structure factor from the data need to be established. GIXS theory is reviewed here from the perspective of practical GIXS measurements and quantitative data analysis. In addition, schemes are discussed for the detailed analysis of GIXS data for the various self-assembled nanostructures of functional homopolymers, brush, star, and dendritic polymers, and block copolymers. Moreover, enhancements to the GIXS technique are discussed that can significantly improve its structure analysis by using the new synchrotron radiation sources such as third-generation X-ray sources with picosecond pulses and partial coherence and fourth-generation X-ray laser sources with femtosecond pulses and full coherence. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yoon J.,Konkuk University | Kim K.,Pohang University of Science and Technology
Expert Systems with Applications | Year: 2012

Patents are an up-to-date and reliable knowledge source of innovative technologies, and therefore patent analysis has been a vital tool for understanding technological trends and formulating technology strategies. One method of patent analysis is citation-based patent analysis. However, one criticism of the citation-based approach is that it may underestimate new patents because they tend to be less cited. This problem gets worse in fast-moving industries where technology life-cycles shorten and innovative technologies are actively patented. As a remedy, this paper proposes a property-function based patent network using an analysis of patent contents. Properties and functions as the innovation concepts of a system can be extracted using grammatical analysis of patent text. First, this paper represents each patent into a matrix codifying properties, functions and their co-occurrences, and then it constructs a patent network by measuring patent similarities. As a result, the proposed network reveals the internal relationships among patents in a given patent set that many new patents. Furthermore, using several analysis indices, this paper suggests a way to identify technological implications from the network such as the technological importance of new patents, the technological capability of applicants with new patents and the pace of technological progress of new patents. The proposed method is illustrated using silicon-based thin film solar cells. We expect that the proposed method can be incorporated into R&D planning processes to assist researchers and R&D policy makers to identify technological implications related to new patents in fast-moving industries. © 2012 Elsevier Ltd. All rights reserved.

Lee M.-G.,Pohang University of Science and Technology | Han C.-S.,University of Wyoming
Computational Mechanics | Year: 2012

Implicit and explicit finite element approaches are frequently applied in real problems. Explicit finite element approaches exhibit several advantages over implicit method for problems which include dynamic effects and instability. Such problems also arise for materials and structures at small length scales and here length scales at the micro and sub-micron scales are considered. At these length scales size effects can be present which are often treated with strain gradient plasticity formulations. Numerical treatments for strain gradient plasticity applying the explicit finite element approach appear however to be absent in the scientific literature. Here such a numerical approach is suggested which is based on patch recovery techniques which have their origin in error indication procedures and adaptive finite element approaches. Along with the proposed explicit finite element procedure for a strain gradient plasticity formulation some numerical examples are discussed to assess the suggested approach. © Springer-Verlag 2011.

Kwak D.-S.,Samsung | Kim K.-J.,Pohang University of Science and Technology
Expert Systems with Applications | Year: 2012

Due to the rapid development of information technologies, abundant data have become readily available. Data mining techniques have been used for process optimization in many manufacturing processes in automotive, LCD, semiconductor, and steel production, among others. However, a large amount of missing values occurs in the data set due to several causes (e.g.; data discarded by gross measurement errors, measurement machine breakdown, routine maintenance, sampling inspection, and sensor failure), which frequently complicate the application of data mining to the data set. This study proposes a new procedure for optimizing processes called missing values-Patient Rule Induction Method (m-PRIM), which handles the missing-values problem systematically and yields considerable process improvement, even if a significant portion of the data set has missing values. A case study in a semiconductor manufacturing process is conducted to illustrate the proposed procedure. © 2011 Elsevier Ltd. All rights reserved.

Lim H.,RIKEN | Lim H.,Pohang University of Science and Technology | Yilmaz E.,RIKEN | Byon H.R.,RIKEN
Journal of Physical Chemistry Letters | Year: 2012

Understanding of electrochemical process in rechargeable Li-O 2 battery has suffered from lack of proper analytical tool, especially related to the identification of chemical species and number of electrons involved in the discharge/recharge process. Here we present a simple and straightforward analytical method for simultaneously attaining chemical and quantified information of Li 2O 2 (discharge product) and byproducts using in situ XRD measurement. By real-time monitoring of solid-state Li 2O 2 peak area, the accurate efficiency of Li 2O 2 formation and the number of electrons can be evaluated during full discharge. Furthermore, by observation of sequential area change of Li 2O 2 peak during recharge, we found nonlinearity of Li 2O 2 decomposition rate for the first time in ether-based electrolyte. © 2012 American Chemical Society.

Agency: Cordis | Branch: FP7 | Program: CP | Phase: FoF.ICT.2010.10.1 | Award Amount: 10.36M | Year: 2010

Todays major challenges for manufacturing companies, operating under productivity pressures, greater product variability and environmental constraints, are clearly identified as global cooperation with multiple supply chain partners, production optimization, and tracking and management of information to meet new requirements like traceability, security, sustainability. These requirements lead to the need for a universal manufacturing information system based on a data exchange standard that allows disparate entities and their associated devices of a manufacturing system to share data seamlessly in a common format. This future digital manufacturing foundation, that represents the brain and knowledge repository of the manufacturing system, will then enable the implementation of the Smart Factory architecture based on a high bandwidth Manufacturing Information Pipeline for data interoperability. The Smart Factory integration towards real-time networking and adaptive capability also envisions:\tOptimizing the numerically controlled (NC) machining systems including programmable logic controllers (PLC) through an embedded Supervisory Control and Data Acquisition (SCADA) system\tSupporting an advanced Manufacturing Execution System (MES) providing not only integrated process automation but also extension of its scope to achieve energy efficiency and sustainability goals as well as waste reduction and e-manufacturing.\tReducing product integration, time-to-market costs and resource diagnosis-maintenance costs through a common control and monitoring platform.\tImplementing homogenous information sources generating data from the whole process, thus achieving information binding and integration from the extended Manufacturing Execution System (MES) to both vertical (innovation) dimension with the Product lifecycle Management (PLM) and horizontal (business) dimension with the Enterprise Resource Planning (ERP)\tUsing STEP and related standards to form an interoperable and scalable solution.The project will deliver:(a) a proof-of-concept Smart Factory based on an open-architecture foundation allowing the demonstration for selected user case study scenarios providing an instantiation of the generic and standards-oriented framework together with(b) a technology exploitation model supported by a living-lab infrastructure covering the complete product-manufacturing lifecycle.

Kang Y.-B.,Pohang University of Science and Technology
Journal of the European Ceramic Society | Year: 2012

A critical evaluation, and thermodynamic optimization of phase equilibrium and thermodynamic properties of the VO-VO 2.5 system are presented. Optimized model parameters for all the oxide phases were obtained so as to reproduce all available and reliable experimental data within experimental error limits. Liquid oxide phase was modeled using the modified quasichemical model in the pair approximation with components representing various valences of vanadium (VO, VO 1.5, VO 2, and VO 2.5) in the liquid oxide. Solid VO and V 2O 3 phases were modeled using simple random mixing models, while all other solid phases were assumed to be stoichiometric compounds. Type of defects in the V 2O 3 solid solution was shown to be extended cluster type defect, based on the available experimental data. Using the presently optimized model parameters, most experimental data has been well reproduced, therefore, the present work can be further extended for the development of thermodynamic database for V oxide containing system. © 2012 Elsevier Ltd.

Lim H.,Ohio State University | Lee M.G.,Pohang University of Science and Technology | Sung J.H.,Korea Institute of Industrial Technology | Kim J.H.,Korea Institute of Materials Science | Wagoner R.H.,Ohio State University
International Journal of Plasticity | Year: 2012

Aluminum alloys are known to undergo time-dependent springback following forming while typical autobody steels of the 1990s do not. This behavior has been attributed to larger residual stresses relative to the yield stress in aluminum and to faster creep rates. In order to determine whether "advanced high strength steels" (AHSS), with high ultimate tensile strength/Young's modulus ratios, also exhibit time dependence, draw-bend springback tests were performed using three dual phase (DP) steels (DP 600, DP 800, and DP 980), a transformation-induced plasticity (TRIP) steel (TRIP 780), and three traditional steels (DQSK, AKDQ, and HSLA). The AHSS alloys showed time-dependent springback at room temperature. Similar to aluminum alloys, the early shape change was proportional to log time for the first few days to weeks, after which the rate of change was lower. The final time-dependent shape change of AHSS was approximately 1/3 of that observed for aluminum alloys under similar conditions. Finite element simulations of the draw-bending, subsequent springback, and post-springback shape change based on creep modeling for DP 600 were in good agreement with the experiments. Effective Young's moduli for tensile unloading were measured and they decreased progressively for unloading from larger pre-strains. Springback simulations showed that Young's moduli affect both initial springback, as well as time-dependent springback significantly. Deformation-induced heating is another complication for AHSS, with springback changing by up to 8% by its influence. © 2011 Elsevier Ltd. All rights reserved.

In this study, the changes in sludge reduction, methane production and microbial community structures in a process involving two-stage thermophilic aerobic digestion (TAD) and mesophilic anaerobic digestion (MAD) under different solid retention times (SRTs) between 10 and 40 days were investigated. The TAD reactor (RTAD) was operated with a 1-day SRT and the MAD reactor (RMAD) was operated at three different SRTs: 39, 19 and 9 days. For a comparison, control MAD (RCONTROL) was operated at three different SRTs of 40, 20 and 10 days. Our results reveal that the sequential TAD-MAD process has about 42% higher methane production rate (MPR) and 15% higher TCOD removal than those of RCONTROL when the SRT decreased from 40 to 20 days. Denaturing gradient gel electrophoresis (DGGE) and real-time PCR results indicate that RMAD maintained a more diverse bacteria and archaea population compared to RCONTROL, due to the application of the biological TAD pre-treatment process. In RTAD, Ureibacillus thermophiles and Bacterium thermus were the major contributors to the increase in soluble organic matter. In contrast, Methanosaeta concilii, a strictly aceticlastic methanogen, showed the highest population during the operation of overall SRTs in RMAD. Interestingly, as the SRT decreased to 20 days, syntrophic VFA oxidizing bacteria, Clostridium ultunense sp., and a hydrogenotrophic methanogen, Methanobacterium beijingense were detected in RMAD and RCONTROL. Meanwhile, the proportion of archaea to total microbe in RMAD and RCONTROL shows highest values of 10.5and 6.5% at 20-d SRT operation, respectively. Collectively, these results demonstrate that the increased COD removal and methane production at different SRTs in RMAD might be attributed to the increased synergism among microbial species by improving the hydrolysis of the rate limiting step in sludge with the help of the biological TAD pre-treatment. © 2013 Elsevier Ltd.

Jeon T.H.,Kyungpook National University | Choi W.,Pohang University of Science and Technology | Park H.,Kyungpook National University
Journal of Physical Chemistry C | Year: 2011

Nanocrystalline hematite particles (α-Fe2O3) were electrodeposited on the TiO2 nanotube (TiNT) arrays that were fabricated via anodization of Ti foils. The short precontact time (1 h) of aqueous ferric ions (Fe3+) on TiNT resulted in formation of hematite particles selectively on the mouth surface of TiNT (hematite@1 h/TiNT), whereas the long precontact time (24 h) resulted in complete filling of the TiNT inside and an even full-covering of the TiNT top surface with the hematite particles (hematite@24 h/TiNT). For comparison, hematite particles were also electrodeposited on TiO2-nanoparticulate films obtained via oxidative annealing of Ti foil resulting in hematite fully covered TiO2 nanoparticles (hematite/TiNP). Photoelectrochemical (PEC) study with AM 1.5 light (UV + Vis) indicated that the PEC activity of TiNT decreased by ca. 40% and almost completely vanished when hematite covered the full surface of TiNT (hematite@ 24 h/TiNT) and loaded on the mouth surface of TiNT (hematite@1 h/TiNT), respectively. The relatively higher PEC activity of hematite@24 h/TiNT was further observed under varying visible light conditions (400 nm < < 500 nm). Hematite/TiNP also has ca. 40%-reduced PEC activity as compared to TiNP under AM 1.5 light, the tendency of which is similar to hematite@24 h/TiNT. Photocatalytic (PC) activities of TiNT and hematite/TiNT for degradation of aqueous phenol under AM 1.5-light were also compared, which indicates that the PC activity of TiNT vanishes almost completely with hematite@1 h/TiNT, whereas it is recovered at a moderate level with hematite@24 h/TiNT. All of these PEC and PC behaviors of TiNT and hematite/TiNT were discussed in terms of hematite-induced charge recombination due to an energy level mismatch between TiO2 and hematite, as well as surface-specific photoactivity of TiNT (i.e., mouth surface vs interwall and/or underlying base layer). Various surface analysis techniques (XRD, XPS, TEM, UV-vis diffuse reflectance) were employed to understand the surface states of TiNT and hematite/TiNT. Finally, more detailed charge transfer mechanism was proposed. © 2011 American Chemical Society.

Park H.,Kyungpook National University | Kim Y.K.,Kyungpook National University | Choi W.,Pohang University of Science and Technology
Journal of Physical Chemistry C | Year: 2011

A facile synthesis of high efficiency semiconductor photocatalyst hybrids is of great importance in making the photocatalytic systems more viable and applicable. This study presents that simply reversing chemical precipitation order of CdS results in significantly different photocatalytic activity in terms of hydrogen production from water under visible light when hybridized with platinized TiO2 particles (Pt-TiO2). It has been found that CdS obtained via dropping an aqueous cadmium cation in aqueous sulfide solution (i.e., Pt-TiO2 suspension with S2-) with equal molar ratios (hereafter CdSR) has a maximum >10-fold greater amount of hydrogen than that obtained by simply reversing the dropping order (i.e., dropping S2- to Pt-TiO2 suspension with Cd 2+; hereafter CdRS). Such a high activity of CdS R, however, is very sensitive to photocatalytic running conditions, in particular, kind and concentration of electron donor (Na2S and/or Na2SO3) which largely changes the hydrogen production ratio (RH) of CdSR to CdRS. Detailed surface analyses indicate that physicochemical properties of CdSR are very different from those of CdRS including larger and red-shifted onset light absorption and altered photoluminescence, S/Cd atomic ratios >1, and hexagonal crystallinity (vs cubic-CdRS), the differences of which were attributed to the primary reasons for higher activity of CdSR. Finally, the photocatalytic hydrogen production mechanism was proposed based on the experimental results. © 2011 American Chemical Society.

Park H.,Pohang University of Science and Technology | Lee J.,Seoul National University
Expert Systems with Applications | Year: 2012

This paper proposes a novel Bayesian kernel model that can forecast the non-negative distribution of target option prices, which are constrained to be positive. The method utilizes a new transform measure that guarantees the non-negativity of option prices, and can be applied to Bayesian kernel models to provide predictive distributions of option prices. Simulations conducted on the model-generated option data and KOSPI 200 index option data show that the proposed method not only provide a predictive distribution of non-negative option prices, but also preserves the probabilistic distribution of large deviations. We also perform a very extensive empirical study on a large-scale time series of option prices to assess the prediction performance of the proposed method. We find that the method outperforms other state of the arts non-parametric methods in prediction accuracy and is statistically different. © 2012 Elsevier Ltd. All rights reserved.

Lee D.-H.,Samsung | Kim K.-J.,Pohang University of Science and Technology
Expert Systems with Applications | Year: 2012

In dual response surface optimization, minimizing weighted mean squared error (WMSE) is a simple yet effective way of obtaining a satisfactory solution. To minimize WMSE, the weights of the squared bias and variance should be determined in advance. Determining the weights in accordance with the decision maker (DM)'s preference structure regarding the tradeoffs between the two responses is critical and difficult. In this study, we develop an interactive weighting method where the DM provides his/her preference information in the form of pairwise comparisons. Our method estimates the weights based on the pairwise comparisons in an interactive manner. The method obtains a satisfactory solution through several pairwise comparisons in the case examples that we tested. © 2011 Elsevier Ltd. All rights reserved.

Chung E.S.,Microsoft | Davis J.D.,Microsoft | Lee J.,Pohang University of Science and Technology
Proceedings - International Symposium on Computer Architecture | Year: 2013

We present LINQits, a flexible hardware template that can be mapped onto programmable logic or ASICs in a heterogeneous system-on-chip for a mobile device or server. Unlike fixed-function accelerators, LINQits accelerates a domain-specific query language called LINQ. LINQits does not provide coverage for all possible applications-however, existing applications (re-)written with LINQ in mind benefit extensively from hardware acceleration. Furthermore, the LIN-Qits framework offers a graceful and transparent migration path from software to hardware. LINQits is prototyped on a 2W heterogeneous SoC called the ZYNQ processor, which combines dual ARM A9 processors with an FPGA on a single die in 28nm silicon technology. Our physical measurements show that LINQits improves energy efficiency by 8.9 to 30.6 times and performance by 10.7 to 38.1 times compared to optimized, multithreaded C programs running on conventional ARM A9 processors. Copyright 2013 ACM.