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Balaram, N.,Reddy, M. Siva Pratap,Reddy, V. Rajagopal,Park, Chinho Elsevier 2016 THIN SOLID FILMS - Vol.619 No.-
<P><B>Abstract</B></P> <P>The structural, chemical, electrical and carrier transport properties of high-k ZrO<SUB>2</SUB> on n-type InP with Au electrode have been studied by <U>X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS)</U>, current-voltage (IV) and capacitance-voltage (CV) techniques at room temperature. Results show that the high barrier height is achieved for the Au/ZrO<SUB>2</SUB>/n-InP metal-insulator-semiconductor (MIS) diode as compared to the Au/n-InP metal-semiconductor (MS) diode. Using Cheung's functions, the barrier height, ideality factor and series resistance are estimated for the MS and MIS diodes. The barrier heights are determined by IV, Cheung's and surface potential-forward voltage plot for both the MS and MIS diodes which are found to be in good agreement with each other. Results indicate that the interface state density of Au/ZrO<SUB>2</SUB>/n-InP MIS diode is lower than that of Au/n-InP MS diode. This may be attributed to the fact that the introduction of the high-k ZrO<SUB>2</SUB> interlayer led to reduction of the interface state density in the Au/n-InP MS diode. Results indicate that the Poole-Frenkel emission is the dominant conduction mechanism in the lower bias region while Schottky emission is dominant in the higher bias region for both the Au/n-InP MS and Au/ZrO<SUB>2</SUB>/n-InP MIS diodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of high-k ZrO<SUB>2</SUB> interlayer on electrical properties of Au/n-InP MS diode has been studied. </LI> <LI> High barrier height is obtained for Au/ZrO<SUB>2</SUB>/n-InP MIS diode compared to the MS diode. </LI> <LI> Interface state density of Au/ZrO<SUB>2</SUB>/n-InP MIS diode is lower than that of Au/n-InP MS diode. </LI> <LI> Transport properties of Au/n-InP MS and Au/ZrO<SUB>2</SUB>/n-InP MIS diodes have been investigated. </LI> </UL> </P>
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Park, KS,Poburko, D,Wollheim, CB,Demaurex, N Wiley (Blackwell Publishing) 2009 British journal of pharmacology Vol.156 No.8
<P>BACKGROUND AND PURPOSE: Amiloride derivatives are blockers of the Na(+)/H(+) exchanger (NHE) and at micromolar concentrations have protective effects on cardiac and brain ischaemia/reperfusion injury but at higher concentrations also induce apoptosis. Here, we aimed to elucidate the mechanism related to this cytotoxic action. EXPERIMENTAL APPROACH: We quantified the expression of genes associated with endoplasmic reticulum (ER) stress and measured changes in luminal ER Ca(2+) concentration ([Ca(2+)](ER)) with a 'cameleon' indicator, D1ER. KEY RESULTS: Amiloride derivatives induced apoptosis in vascular endothelial cells, an effect that increased at alkaline extracellular pH. The potency order for cytotoxicity was 5-(N,N-hexamethylene)-amiloride (HMA) > 5-(N-methyl-N-isobutyl) amiloride > 5-(N-ethyl-N-isopropyl) amiloride (EIPA) >> amiloride. HMA dose-dependently increased the transcription of the ER stress genes GADD153 and GADD34 and rapidly depleted [Ca(2+)](ER), mimicking the effects of the sarco/endoplasmic reticulum ATPase (SERCA) inhibitor thapsigargin. The NHE1-specific inhibitor HOE 694 inhibited NHE activity by 87% but did not alter [Ca(2+)](ER). The decrease in [Ca(2+)](ER) evoked by amiloride derivatives was also observed in HeLa cells and was mirrored by an increase in cytosolic Ca(2+) concentration. CONCLUSIONS AND IMPLICATIONS: Amiloride derivatives disrupt ER and cytosolic Ca(2+) homeostasis by a mechanism unrelated to NHE inhibition, most likely by interfering with the activity of SERCA. We propose that ER Ca(2+) depletion and subsequent ER stress provide a rationale framework for the apoptotic effects of amiloride derivatives.</P>
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Park, N. W.,Ahn, J. Y.,Park, T. H.,Lee, J. H.,Lee, W. Y.,Cho, K.,Yoon, Y. G.,Choi, C. J.,Park, J. S.,Lee, S. K. Royal Society of Chemistry 2017 Nanoscale Vol.9 No.21
<P>Recently, significant progress has been made in increasing the figure-of-merit (ZT) of various nanostructured materials, including thin-film and quantum dot superlattice structures. Studies have focused on the size reduction and control of the surface or interface of nanostructured materials since these approaches enhance the thermopower and phonon scattering in quantum and superlattice structures. Currently, bismuth-tellurium-based semiconductor materials are widely employed for thermoelectric (TE) devices such as TE energy generators and coolers, in addition to other sensors, for use at temperatures under 400 K. However, new and promising TE materials with enhanced TE performance, including doped zinc oxide (ZnO) multilayer or superlattice thin films, are also required for designing solid-state TE power generating devices with the maximum output power density and for investigating the physics of in-plane TE generators. Herein, we report the growth of Al2O3/ZnO (AO/ZnO) superlattice thin films, which were prepared by atomic layer deposition (ALD), and the evaluation of their electrical and TE properties. All the in-plane TE properties, including the Seebeck coefficient (S), electrical conductivity (sigma), and thermal conductivity (kappa), of the AO/ZnO superlattice (with a 0.82 nm-thick AO layer) and AO/ZnO films (with a 0.13 nm-thick AO layer) were evaluated in the temperature range 40-300 K, and the measured S, s, and. were -62.4 and -17.5 mu V K-1, 113 and 847 (Omega cm)(-1), and 0.96 and 1.04 W m(-1) K-1, respectively, at 300 K. Consequently, the in-plane TE ZT factor of AO/ZnO superlattice films was found to be similar to 0.014, which is approximately two times more than that of AO/ZnO films (ZT of similar to 0.007) at 300 K. Furthermore, the electrical power generation efficiency of the TE energy generator consisting of four couples of n-AO/ZnO superlattice films and p-Bi0.5Sb1.5Te3 (p-BST) thin-film legs on the substrate was demonstrated. Surprisingly, the output power of the 100 nm-thick n-AO/ZnO superlattice film/p-BST TE energy generator was determined to be similar to 1.0 nW at a temperature difference of 80 K, corresponding to a significant improvement of similar to 130% and similar to 220% compared to the 100 nm-thick AO/ZnO film/p-BST and n-BT/p-BST film generators, respectively, owing to the enhancement of the TE properties, including the power factor of the superlattice film.</P>
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Park, J.,Wi, J.,Joung, B.,Lee, M.H.,Kim, Y.H.,Hwang, C.,Pak, H.N. Elsevier/North-Holland Biomedical Press 2013 INTERNATIONAL JOURNAL OF CARDIOLOGY Vol.167 No.3
Background: Some outflow tract ventricular tachycardias (VTs) are known to be successfully ablated from the aortic cusp (AC). However, radiofrequency catheter ablation (RFCA) at the AC for the treatment of supraventricular tachyarrhythmia (SVT) has limited experience. Methods: We performed RFCA at the AC in 19 patients (male 64.7%, 46.9+/-21.9years old) with mid- to anteroseptal SVTs (12 atrial tachycardias [AT], 7 atrioventricular reciprocating tachycardia [AVRT]), and analyzed the prevalence, electrophysiologic findings, clinical outcome, and compilation risk. Results: 1. Among 113 patients with AT, 13 patients had mid- to anteroseptal AT and 12 patients (8.8%, 53.4+/-19.8years old, 58.3% female) underwent successful ablation from the non-coronary cusp (NCC; n=10), right CC (RCC; n=1) or left CC (LCC; n=1) without complication (3.1+/-2.3 times RF delivery, 6.15+/-3.08s for termination). During 19.7+/-9.8months of follow-up, AT recurred in a patient with multiple foci. 2. Among 580 patients with AVRT, 27 patients had a mid- to anteroseptal bypass tract (4.7%), and 7 of them (1.1%, 2 pre-excitation syndrome, 5 concealed bypass tract) were successfully ablated at the NCC (n=2) or RCC (n=5) (7.0+/-7.1 times RF delivery, 9.1+/-4.4s for termination). Among 5 patients with AVRT successfully ablated at the RCC, one patient developed complete heart block 48h after procedure, and 2 patients recurred AVRT or delta-wave in ECG during 13.9+/-11.7month follow-up. Conclusion: Catheter ablation within the AC is an effective procedure to eliminate mid- to anteroseptal SVTs. However, RFCA on RCC requires a caution for heart block in our limited experience.
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Adsorption of sodium dodecyl sulfate on cleaning of an N-polar GaN surface in an alkaline solution
Kim, M.S.,Paluvai, N.R.,Kim, H.T.,Park, J.G. Elsevier 2017 Materials science & engineering. B, Advanced funct Vol.222 No.-
<P>The present study investigated the removal of contaminated particles from a polished N-polar GaN surface using an alkaline cleaning solution along with sodium dodecyl sulfate (SDS) surfactant. The zeta potential, etch rate, and particle removal efficiency (PRE) of N-polar GaN surfaces were reported. A lower etch rate and smoother N-polar GaN surface were obtained when the surface is treated with a diluted NH4OH solution. However, the etch rate and PRE of the N-polar GaN surface increased as a function of the pH of the NH4OH solution. The PRE of the N-polar GaN surface reached to 96% at pH 10 with a high surface roughness of 0.5 nm. SDS was added to the ammonia solutions to control the surface roughness. The N-polar GaN surface reached 100% PRE and surface roughness shown less than 0.4 nm when cleaned in a diluted NH4OH solution with 5 mM SDS surfactant in a megasonic bath. (C) 2017 Elsevier B.V. All rights reserved.</P>
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Park, Sangwook,Hughes, John P.,Slane, Patrick O.,Burrows, David N.,Lee, Jae-Joon,Mori, Koji IOP Publishing 2012 The Astrophysical journal Vol.748 No.2
<P>We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta 'bullet' beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the detected Si-rich ejecta may represent explosive O-burning or incomplete Si-burning products from deep interior of the SN. On the other hand, the observed Si/S abundance ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age of N49, tau(Sed) similar to 4800 yr, with the explosion energy E-0 similar to 1.8 x 10(51) erg. Our blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR 0526-66 indicates that the PL photon index (Gamma similar to 2.5) is identical to that of PSR 1E1048.1-5937, the well-known candidate transition object between anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model implies X-ray emission from a small (R similar to 1 km) hot spot(s) (kT similar to 1 keV) in addition to emission from the neutron star's cooler surface (R similar to 10 km, kT similar to 0.4 keV). There is a considerable discrepancy in the estimated column toward 0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral models would be crucial to test the long-debated physical association between N49 and 0526-66.</P>
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Kim, N. I.,Afzal, R.,Choi, S.,Lee, S.,Ahn, D.,Bhattacharjee, S.,Lee, S. C.,Kim, J.,Park, J. Y. Royal Society of Chemistry 2017 Journal of materials chemistry. A, Materials for e Vol.5 No.25
<P>A-site cation doping in perovskite-based materials with the general ABO(3) formula has a significant effect on the bifunctional oxygen activity (oxygen evolution and reduction reactions) of chemically stable electrocatalysts, enabling the design of highly active, durable, and cost-effective catalysts. In particular, the oxygen activity of double perovskite-structured NdBa0.5Sr0.5Co1.5Fe0.5O5+delta (NBSCF) is 0.973 V, which is much greater than that of previously reported transition metal-based nanostructures. This result is verified by examination of the electronic structure, oxidation state, and electrical properties of the perovskite-based materials using density functional theory (DFT) calculations, the iodometric titration method, X-ray photon spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) analysis. Further improvements of NBSCF for bifunctional oxygen activity are made by incorporating these synergistic hybrid structures with nitrogen doped-reduced graphene-based (N-rGO) nanostructures (NBSCF/N-rGO). The NBSCF/N-rGO has an oxygen electrode activity of 0.766 V, which is superior to that of other previously reported transition metal-based nanostructures and compares favorably to that of precious metal electrocatalysts. Furthermore, strong N-rGO provides considerably greater electrochemical long-term stability and integrity to NBSCF/N-rGO hybrid catalysts under continuous chronopotentiometric and long-term potential sweep testing conditions for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).</P>
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Direct analysis of site-specific N-glycopeptides of serological proteins in dried blood spot samples
Choi, N. Y.,Hwang, H.,Ji, E. S.,Park, G. W.,Lee, J. Y.,Lee, H. K.,Kim, J. Y.,Yoo, J. S. Springer Science + Business Media 2017 Analytical and Bioanalytical Chemistry Vol.409 No.21
<P>Dried blood spot (DBS) samples have a number of advantages, especially with respect to ease of collection, transportation, and storage and to reduce biohazard risk. N-glycosylation is a major post-translational modification of proteins in human blood that is related to a variety of biological functions, including metastasis, cell-cell interactions, inflammation, and immunization. Here, we directly analyzed tryptic N-glycopeptides from glycoproteins in DBS samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS) without centrifugation of blood samples, depletion of major proteins, desalting of tryptic peptides, and enrichment of N-glycopeptides. Using this simple method, we identified a total of 41 site-specific N-glycopeptides from 16 glycoproteins in the DBS samples, from immunoglobulin gamma 1 (IgG-1, 10 mg/mL) down to complement component C7 (50 mu g/mL). Of these, 32 N-glycopeptides from 14 glycoproteins were consistently quantified over 180 days stored at room temperature. The major abundant glycoproteins in the DBS samples were IgG-1 and IgG-2, which contain nine asialo-fucosylated complex types of 16 different N-glycopeptide isoforms. Sialo-non-fucosylated complex types were primarily detected in the other glycoproteins such as alpha-1-acid glycoprotein 1, 2, alpha-1-antitypsin, alpha-2-macroglobulin, haptoglobin, hemopexin, Ig alpha 1, 2 chain C region, kininogen-1, prothrombin, and serotransferrin. We first report the characterization of site-specific N-glycoproteins in DBS samples by LC-MS/MS with minimal sample preparation.</P>
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