Sang Hyun Ahn

Korea Institute of Science and Technology, Sŏul, Seoul, South Korea

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Publications (23)40.67 Total impact

  • International Journal of Hydrogen Energy 01/2014; 39(8):3681–3689. · 3.55 Impact Factor
  • Applied Catalysis B: Environmental. 01/2014; s 154–155:197–205.
  • Chemical Engineering Journal. 01/2014; 247:9–15.
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    ABSTRACT: There is a growing concern about the therapeutic equivalence of the generic tacrolimus formulation (GEN Tacrolimus) to the reference tacrolimus (REF Tacrolimus) in solid organ transplantation. A prospective, randomized study of 126 de novo renal transplant patients was conducted to compare the efficacy, safety and pharmacokinetic (PK) profiles between GEN tacrolimus (n = 63) and REF tacrolimus (n = 63). The PK of tacrolimus was evaluated on Day 10 and 6 months under steady-state condition. Crossover study was carried out in 66 patients at 6 months. On Day 10, 117 patients completed PK profiles (54 GEN tacrolimus and 63 REF tacrolimus) and GEN tacrolimus showed comparable C0 (9.8 ± 2.5 versus 9.7 ± 3.0 ng/mL, P = 0.80) but significantly higher dose-normalized Cmax (309.1 ± 191.9 versus 192.5 ± 95.2 ng/mL/mg/kg, P < 0.001). The dose-normalized AUC0-12 tended to be higher in the GEN tacrolimus than in the REF tacrolimus group (1513.4 ± 935.4 versus 1262.5 ± 593.5 ng.h/mL/mg/kg, P = 0.084). Because of this early and high Cmax with a rapid decline in GEN tacrolimus concentration, the trough concentration was maintained lower than that of REF tacrolimus. At 6 months, GEN tacrolimus showed equivalent dose-normalized AUC0-12 (1882.2 ± 935.6 versus 1718.1 ± 946.3 ng.h/mL/mg/kg, P = 0.429) but still higher dose-normalized Cmax (346.3 ± 184.4 versus 273.2 ± 148.9 ng/mL/mg/kg, P = 0.056), despite a reduced trough concentration (5.7 ± 1.6 versus 6.9 ± 2.2 ng/mL, P = 0.004). PK profiles evaluated at 9 months showed that generic substitution also resulted in an 'early and high Cmax'. Efficacy and safety data were comparable over the 9-month study period. Therapeutic equivalence and the PK of GEN tacrolimus should be evaluated in patients undergoing de novo renal transplantation.
    Nephrology Dialysis Transplantation 09/2013; · 3.37 Impact Factor
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    ABSTRACT: We have investigated the release of active sites blocked by bubbles attached on the surface of catalysts during the oxygen evolution reaction (OER) in alkaline water electrolysis, via the modulation of the wetting properties of the four different morphologies of a nickel catalyst.
    Chemical Communications 09/2013; · 6.38 Impact Factor
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    ABSTRACT: In this work, the degradation of poly(ethylene glycol-propylene glycol) copolymer (PEG-PPG) and its effect on the electrodeposition of Cu were investigated. PEG-PPG became fragmented during the electrodeposition with changing its terminal groups from hydroxyl to aldehyde, formic ester, and ketone. The aged solution showed a higher saturation current density than the fresh solution in chronoamperometry (CA) measurements, resulting from an easier desorption of the cleaved PEG-PPG from the copper surface through the competition with bis-(3-sulfopropyl)-disulfide (SPS). Furthermore, the electrical resistivity of Cu films deposited from the aged solution increased due to a decrease in the grain sizes.
    Journal of Electroanalytical Chemistry. 01/2013;
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    ABSTRACT: Different shapes of various nickel structures, including dendrite, particle and film are fabricated by electrodeposition under various conditions. The shape of nickel structures is definitely dependent on the deposition potential, leading to different electrochemical surface area and edge facets. The nickel particle which has a polycrystalline center and edge is obtained at high negative potential. On the other hand, the nickel dendrite deposited by relatively low negative potential exhibits large electrochemical surface area and a particularly active facet for hydrogen evolution reaction (HER) in alkaline water electrolysis. In fact the nickel dendrite shows the highest catalytic activity and stability for HER among the various nickel structures.
    Journal of Materials Chemistry 07/2012; 22(30):15153-15159. · 5.97 Impact Factor
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    ABSTRACT: The goal of this study was to identify the clinical significance of the low-frequency air-bone gap (LFABG) that often develops after endolymphatic sac surgery. Prospective study. Sixteen patients who had been diagnosed with definite Ménière disease and underwent endolymphatic sac surgery were studied. The surgical outcome was evaluated based on the 1995 guidelines of the American Academy of Otolaryngology-Head and Neck Surgery. The number of patients who developed LFABGs (a mean air-bone gap >10 dB HL at 250, 500, and 1,000 Hz) after surgery was determined, and the significance of the LFABGs was evaluated by analyzing their relation with the surgical outcome. The vertigo spells of nine patients were completely controlled (class A). The number of vertigo spells was reduced by 60% to 99% in 6 patients (class B) and by 20% to 59% in 1 patient (class C). Postoperative LFABGs were observed in 13 patients. The mean LFABG of the patients in class A was significantly larger than that of the patients in classes B and C (25.0 ± 7.6 dB nHL in class A vs. 10.0. ± 7.5 dB nHL in class B and C; P = .005). Based on the data of the current study, we conjectured that the correlation of large LFABGs with excellent vertigo control in this study may be due to a third window phenomenon related to bony decompression of the endolymphatic sac and duct, and may serve as a favorable prognostic marker.
    The Laryngoscope 04/2012; 122(8):1838-43. · 1.98 Impact Factor
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    ABSTRACT: CoRuPt and CoPtRu catalysts were prepared on carbon paper (CP) using various electrochemical processes including Sn sensitization, Pd activation, Co electrodeposition and galvanic displacement. The Sn–Pd process is a surface treatment that guarantees a larger number of nucleation sites on CP for subsequent Co electrodeposition by modifying the surface to be more hydrophilic. Co particles were deposited on Sn-Pd-treated CP (SCP) by controlling deposition potential and time. Then, Pt and Ru galvanic displacements were performed on the Co particles to form CoRuPt/SCP and CoPtRu/SCP catalysts. Electrochemical measurements confirmed that the CoRuPt/SCP – 1 catalyst with a 1.02 Pt/Ru surface molar ratio showed a peak potential of 741 mV (vs. NHE) for methanol oxidation and 637 mV for carbon monoxide stripping. These values were 80 and 8 mV lower, respectively, than those of a PtRu/C commercial catalyst.
    Fuel and Energy Abstracts 01/2012;
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    ABSTRACT: The design of a flow field channel of a polymer electrolyte membrane fuel cell (PEMFC) was investigated by computational fluid dynamic (CFD) simulation and in-situ three-channel impedance spectroscopy. To investigate the efficiency of the in-situ three-channel impedance spectroscopy method, it was adopted with a heterogeneous stack, which was composed according to three different types of flow field design. The in-situ three-channel method proved its validity by showing corresponding result with that obtained from the experiments and CFD simulation at the same experimental condition. This study demonstrates that a heterogeneous stack and in-situ three-channel impedance spectroscopy are powerful tools for predicting and analyzing the performance of a fuel cell stack.
    International Journal of Hydrogen Energy 08/2011; 36(16):9799–9804. · 3.55 Impact Factor
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    ABSTRACT: Spontaneous isolated dissection of the superior mesenteric artery (SIDSMA) is extremely rare. Various treatment options are currently available, including conservative management, anticoagulation, endovascular stenting, and surgical repair. Herein, we present our experience in the treatment of symptomatic SIDSMA. A retrospective study was conducted on 14 consecutive patients with symptomatic SIDSMA between January 2000 and January 2010. All patients had acute onset abdominal pain. The decision to intervene was based on patient symptoms and signs, as well as the morphologic characteristics of superior mesenteric artery (SMA) dissection on computed tomography (CT) angiography. Endovascular stenting (ES) was indicated in patients with severe compression of the true lumen or dissecting aneurysm likely to rupture. Self-expandable stents were placed via a right common femoral approach. None of the patients underwent anticoagulation, and patients who underwent ES were maintained on antiplatelet therapy for 3 months postoperatively. The median age of the study subjects was 59 years (range, 50-75 years). The median follow-up time was 27.5 months (range, 2-64 months). Treatment included conservative management without the use of anticoagulation in seven patients, ES in six, and necrotic bowel resection in one. Four patients with severe compression of the true lumen or large dissecting aneurysm underwent ES as a primary treatment. ES was additionally performed in two patients in whom initial conservative treatment failed (increasing dissecting aneurysm at 7-day follow-up CT scan in one and a reappearance of abdominal pain after resuming diet in the other). The median fasting time was significantly shorter in patients with primary ES (2.5 days) than in those managed conservatively (8.0 days). No complications associated with the SIDSMA or ES were developed. The patency of stents was demonstrated on follow-up CT scans up to 60 months (range, 1-60 months). Conservative management without anticoagulation can be applied successfully to the patients with symptomatic SIDSMA. Primary endovascular stenting is indicated if patients have suspected bowel ischemia, compression of the true lumen of the SMA >80%, or SMA aneurysm of >2.0 cm in diameter on initial CT scan. Endovascular stenting can also be provided to the patients in whom initial conservative treatment failed, as a rescue therapy.
    Journal of vascular surgery: official publication, the Society for Vascular Surgery [and] International Society for Cardiovascular Surgery, North American Chapter 05/2011; 54(2):461-6. · 3.52 Impact Factor
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    ABSTRACT: High over-potential induced by the irreversibility of oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) causes low cell performance. In order to overcome such a problem, many research groups have been studying to enhance the catalytic activity of platinum in fuel cell. In this regard, Ptshell–Pdcore (Pt/Pd/C) nanoparticle was prepared by electrochemical method in this study. The home-made Pd/C was surrounded by Cu as a result of electroless deposition (ELD) which was followed by displacement reaction with Pt. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were applied to identify metallic composition. Transmission electron microscope (TEM) was adopted to image the catalysts. Besides, the catalytic properties were investigated using rotating disk electrode (RDE). The results indicated that the kinetics of electrochemically-prepared Pt/Pd/C catalyst for O2 reduction was superior to conventional Pt/C catalyst and the feasibility of electroless deposition in fabricating electro-catalyst was confirmed through the formation of Cu ad-layer.
    Applied Catalysis B-environmental - APPL CATAL B-ENVIRON. 01/2011; 102(3):608-613.
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    ABSTRACT: Tacrolimus is a major immunosuppressant, which has a narrow therapeutic range and wide interindividual variation. The effects of genetic polymorphisms of cytochrome P450 3A (CYP3A) 5 and Adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1) genes on the achievement of target tacrolimus trough levels and clinical outcomes in renal transplants were evaluated. A total of 62 patients participated in this prospective study. After an initial fixed oral dose (0.08 mg/kg two times per day), tacrolimus doses were adjusted to a target range based on daily measurement of blood trough concentration. Every patient underwent 10-day scheduled biopsy. Both the patients and investigators were blinded for the genetic polymorphisms. Those subjects expressing CYP3A5 (n=29) evidenced significantly lower tacrolimus trough levels between days 1 and 5 after transplantation, when compared with nonexpressers (n=33). Significantly higher overall incidences of early T-cell-mediated rejection (TCR) of at least Banff grade 1 in severity (P=0.017), including clinical rejection within 10 days and subclinical rejection in biopsies at postoperative day 10 were detected in CYP3A5 expressers. The severity of TCR according to Banff '07 classification was associated with CYP3A5 genotypes (P=0.012). Moreover, multivariate analysis identified CYP3A5 expression as an independent risk factor for TCR (odds ratio: 2.79; P=0.043). Significantly lower estimated glomerular filtration rates until 1 month and numerically lower estimated glomerular filtration rates by 12 months were noted in the CYP3A5 expressers. The genetic polymorphisms of the ABCB1 genes exerted no significant effects. We confirmed the significant effects of CYP3A5 polymorphism on the achievement of target tacrolimus trough levels and the development of acute rejection in early period after transplantation and consequent renal allograft function.
    Transplantation 11/2010; 90(12):1394-400. · 3.78 Impact Factor
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    J. Inf. Sci. Eng. 01/2010; 26:833-850.
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    ABSTRACT: The CoPtRu catalyst was prepared with electrochemical methods on carbon paper. The preparation of Co particles on the carbon paper was performed through an electrodeposition process by varying the deposition potential and time. After Co electrodeposition, Pt and Ru galvanic displacements were carried out by controlling displacement time. The bulk and surface composition of the catalysts were analyzed by using inductively coupled plasma (ICP) mass spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. It was proved that the CoPtRu catalyst was successfully synthesized using the electrochemical process. In this study, the electrochemically prepared catalysts showed superior catalytic activity for methanol oxidation and tolerance to CO poisoning compared to a commercial PtRu/C catalyst (E-tek).
    Fuel and Energy Abstracts 01/2010; 35(24):13309-13316.
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    ABSTRACT: With the rapidly increasing demand of traffic applications, the need to support seamless multimedia services in the Vehicular Wireless Networks and Vehicular Intelligent Transportation Systems (V-WINET/V-ITS) is growing. Several mobility support protocols such as the Mobile IPv6 (MIPv6) and the fast handover for the MIPv6 (FMIPv6) have been developed to support seamless handover. However, MIPv6 depreciates Quality-of-Service (QoS) especially for multimedia service applications due to the long handover latency and the packet loss problem. FMIPv6 tries to solve these problems of MIPv6 through handover prediction but the high speed and sudden direction change of vehicles make predictions inaccurate. In this paper, we propose a seamless and robust handover scheme that supports multimedia services in V-WINET/V-ITS. Unlike MIPv6 or FMIPv6 where a new Care-of-Address (nCoA) has to be configured every time when a vehicle meets a new AR (nAR), the proposed scheme continuously maintains the original CoA (oCoA) configured at original Access Router (oAR) and reduces the handover delay caused by the Duplicate Address Detection (DAD). While a vehicle maintains its oCoA, the data packet destined to the vehicle is forwarded from the oAR to the nAR, and finally to the vehicle. At the intersection, the vehicle creates a nCoA to limit the packet forwarding hops between the oAR and the nAR. However, our background DAD scheme reduces the DAD delay at the intersection and also reduces the number of Home Agent (HA) binding updates. Through extensive simulations, we show that the proposed scheme significantly reduces the average handover latency by up to 40%.
    Communications and Information Technology, 2009. ISCIT 2009. 9th International Symposium on; 10/2009
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    ABSTRACT: Commercial Cu–ZnO–Al2O3 catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al2O3 catalyst with Pt–Al2O3 catalyst. The Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al2O3 and Cu–ZnO–Al2O3 catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture was used.
    Catalysis Communications 09/2009; 10(15):2018–2022. · 2.92 Impact Factor
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    ABSTRACT: A silicon-based micro-reactor was fabricated using a micro-electromechanical system (MEMS) process and silicon micromachining technology (SMT) to allow preferential CO oxidation (PrOx) to be applied to compact portable devices. To design the micro-PrOx reactor, the effects of channel length, channel width, channel array, and O2 content in the reactant gas on the CO conversion and selectivity for CO were investigated. The single micro-PrOx reactor required an O2 concentration four times higher than the theoretical quantity for a complete conversion of 1% CO into CO2. The optimum operating temperature to obtain high CO conversion, by suppressing the reverse water–gas shift (r-WGS) reaction, depended considerably on the channel lengths of the micro-reactor rather than on the channel widths or the channel arrays. The micro-PrOx reactor showed 99.4% conversion of CO and 44.14% selectivity for CO at 260 °C when operating with 1% CO, 50% H2, 35% CO2, N2 (balance), and 2% O2.
    Chemical Engineering Journal. 01/2009; 146(1):105-111.
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    ABSTRACT: Wild Panax ginseng C.A. Meyer (WG) is a well-known medicinal herb. In this study, the protective effects of a water extract from the root of WG on benzo[alpha]pyrene (BP)-induced hepatotoxicity and the mechanism of these effects were investigated for the first time. The effects of WG on liver toxicities induced by BP were assessed by blood biochemical and histopathological analyses. BP caused severe liver injury in rats, as indicated by elevated plasma ALT, AST and LPO levels. Pretreatment with WG for 4 weeks completely abrogated increases in the ALT, AST and LPO levels when challenged with BP. Reductions in GSH content and GST activity by BP were reversed by WG. These protective effects of WG against BP-induced toxicity were consistent with the results of histopathological examinations. We next examined the effects of WG on the gene expression of the enzymes that metabolize BP in H4IIE cells. CYP1A1 mRNA and protein expression were increased by BP. WG moderately inhibited BP-induced CYP1A1 gene expression. Moreover, GSTA2, GSTA3 and GSTM2 gene expressions were significantly increased by WG through the Nrf2/antioxidant responsive element pathway for enzyme induction. In summary, WG is efficacious in protecting against BP-induced hepatotoxicity as results of metabolic regulations through both the inhibition of metabolic enzyme activation and the enhancement of electrophilic detoxification, implying that WG should be considered a potential chemopreventive agent.
    Journal of Ethnopharmacology 08/2007; 112(3):568-76. · 2.76 Impact Factor
  • Materials Science Forum - MATER SCI FORUM. 01/2000;

Publication Stats

42 Citations
40.67 Total Impact Points

Institutions

  • 2012–2014
    • Korea Institute of Science and Technology
      • Fuel Cell Research Center
      Sŏul, Seoul, South Korea
  • 2009–2013
    • Seoul National University
      • • Department of Chemical and Biological Engineering
      • • School of Computer Science and Engineering
      Sŏul, Seoul, South Korea
  • 2000
    • Chonbuk National University
      • Semiconductor Physics Research Center
      Seoul, Seoul, South Korea