• Applied Chemistry for Engineering
• /
• v.21 no.5
• /
• pp.537-541
• /
• 2010

Pt-Sn with various ratios was supported on carbon black after pretreatment in an acidic solution by a reduction method. The Pt/Sn ratio was controlled by varying the concentration of each component in the solution, and the influence of the composition on the electrocatalytic activities was investigated. The crystallinity of the synthesized materials was investigated by XRD (X-ray Diffraction), and the oxidation states of both the platinum and tin were determined by XPS (X-ray Photoelectron Spectroscopy). SEM (Scanning Electron Microscopy)-EDS (Energy Dispersive Spectroscopy) was utilized to examine the morphology and composition of the synthesized electrode, and the particle size of the Pt-Sn was analyzed by TEM (Transmission Electron Microscopy). The electrocatalytic activity for oxygen reduction was evaluated in a 0.5 M $H_2SO_4$ solution using a rotating disk electrode system. The activity and stability were found to be strongly dependent on the electrode composition (Pt/Sn ratio). The catalytic activity and stability for methanol oxidation were also measured using cyclic voltammetry (CV) in a mixture of 0.5 M $H_2SO_4$ and 0.5 M $CH_3OH$ aqueous solution. The addition of proper amount of Sn was found to significantly improve both catalytic activity and stability for methanol oxidation.

• Proceedings of the Korean Society of Dyers and Finishers Conference
• /
• 2009.11a
• /
• pp.21-22
• /
• 2009

최근, 헵타메틴 시아닌색소(heptamethinecyanine)는 그 적용 범위가 넓기 때문에 많은 연구자들의 관심을 받고 있다. 특히, photo-sensitizers, dye lasers, optical recordings와 storage media 등 다양한 분야에 적용이 가능하다. 헵타메틴 시아닌색소의 주된 특징은 polymethine 사슬에 연결된 cyclohexene 고리에 의하여 근적외선 부근에서 흡수가 이뤄진다는 것이다. 근적외선 색소의 흡수 특성을 HOMO와 LUMO 에너지 전위를 사용하여, 수치화 함으로써 분자간, 분자내 상호작용을 분석 할 수 있다. 따라서, 본 실험은 헵타메틴 시아닌 색소의 치환체에 따른 전기화학적 특성을 순환 전압-전류법(Cyclic voltammetry)과 분자 모델링을 통하여 HOMO와 LUMO의 에너지 준위를 구하고, 치환체 효과가 헵타메틴 시아닌색소에 미치는 전기화학적 특성을 UV-Vis와 계산으로부터 얻어진 에너지준위를 분석하고자 한다. 본 실험에 사용된 Uv-Vis 스펙트럼 측정은 Agilent 8453 UV-Vis spectrophotometer를 사용하였고, 전기화학적 분석 방법인 순환 전압-전류법은 Versa STAT 3 (Princeton allied research in USA)를 사용하였다. 순환전압-전류법의 측정은 Acetonitrile 용액에 $TBAPF_6$ (Tetrabutylammonium hexafluorophosphate)를 전해질로 하고, Ag/$Ag^+$을 기준전극으로 사용하여 주사 속도를 50mV/s로 하여 측정 하였다. 치환체에 의한 영향을 알아보기 위하여 분자구조 최적화 모델링을 사용하였다. 3차원 분자입체 특성 및 에너지 준위 상태는 Materials studio 4.2를 사용하여 특성을 예측 하였다. 본 연구에서는, 헵타메틴 시아닌 색소의 기본 골격에 각기 다른 치환체를 치환 시켜 치환체에 의한 영향을 전기화학적인 방법인 순환 전압-전류법(Cyclic voltammetry)와 분자 모델링 방법을 사용하여, HOMO와 LUMO에너지 준위 값을 구함으로써 치환체에 의한 영향을 알아보았다. 치환체로는 Dye 1과 Dye 2로 치환된 헵타메틴 시아닌 색소를 사용하였다. 이렇게 얻어진 HOMO/LUMO 에너지 준위 값으로부터 이온화 에너지($I_p$)와 전자 친화도($E_a$) 또한 구할 수 있는데, $I_p$와 $E_a$는 분자 오비탈과 전자전이에 관련된 값들이고, 이는 계산을 통하여 얻을 수 있다. 순환 전압-전류법의 계산 방법은 봉우리 전위(peak postential)와 (onset potential)방법이 있는데, 이 계산을 통한 전위 값들이 봉우리 전위 계산 방법이 onset potential 방법에 비하여 작은 전위 값으로 나타난다. 하지만 이 두 가지 방법 모두 현재 순환 전압-전류법을 사용하여 HOMO/LUMO 에너지 준위를 측정하는 방법에 쓰이고 있으며, 어떠한 계산 방법이 더 정확하다고는 말 할 수 없지만, 본 실험 결과를 통하여 비교 분석한 결과 onset potential 계산 방법이 봉우리 전위 계산 방법에 비하여 정확하다고 판단된다. Dye 1과 Dye 2를 순환 전압-전류법으로 측정한 결과 각기 다른 전위를 나타내고 이것을 계산을 통하여 정량화하면 Dye 2가 Dye 1에 비하여 높은 전위 값을 갖음을 알 수 있는데, 이것은 ethyl 에 비하여 surful 원자의 전자공여성이 더 크다고 할 수 있다.

• Restorative Dentistry and Endodontics
• /
• v.12 no.1
• /
• pp.39-49
• /
• 1986

The purpose of this study was to observe characteristic properties through the polarization curves and SEM images from 4 different types of amalgam obtained by using the potentiostats (Princeton EG & G) & SEM (Jeol/35), and to investigate the degree of corrosion on the oxidation peak of the each phase of amalgam. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by means of the mechanical amalgamator (Shofu Co.), the triturated mass was inserted into the cylindrical metal mold which was 12mm in diameter and 10.0mm in height and was condensed by using routine manner. The specimen was removed from the mold and stored at room temperature for about 24 hours. The standard surface preparation was routinely carried out. Anodic polarization measurement was employed to confirm the corrosion behaviour of the amalgams in a 0.9% saline solution (P.H: 6.8-7.0) at $37^{\circ}C$. The initial rest potential (corrosion potential) was determined after 30 minutes of immersion of specimen in electrolyte, and the potential scan was begun at the point of 100mV cathodic from the corrosion potential. The scan rate was 0.17mV/sec. in the study to observe the degree of corrosion of each phase. SEI and EPMA images on the determined oxidation peaks of each amalgam were observed. The results were as follows: 1. In the four anodic polarization curves, low copper amalgams have three oxidation peaks and high copper amalgams have two oxidation peaks, -270mV, +26mV and +179mV(SEC) in the low copper lathe cut, and -300mV, +39mV and +163mV(SEC) in the low copper spherical. -4mV and +154mV(SEC) in the Dispersalloy, and +17mV and +180mV(SEC) in the Tytin as high copper amalgams. 2. ${\gamma}_2$ phase in the low copper amalgam and ${\eta}$ phase in the high copper amalgam were the most corrodible phases and Ag-Cu eutectic in high copper amalgam was the most slowly corroded phase. 3. Low copper amalgam was more susceptible in corrosion than high copper amalgam.

• Applied Chemistry for Engineering
• /
• v.22 no.5
• /
• pp.479-485
• /
• 2011

Pt-Bi/C catalysts supported on carbon black with various Pt/Bi ratios were synthesized by a reduction method. Chloroplatinic acid hydrate ($H_2PtCl_6{\cdot}xH_2O$) and bismuth (III) nitrate pentahydrate ($Bi(NO_3)_3{\cdot}5H_2O$) were used as precursors for Pt and Bi, respectively. Before loading metal on carbon, heat treatment and pretreatment of carbon black in an acidic solution was conducted to enhance the degree of dispersion. The physical property of the synthesized catalysts was investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The XRD pattern of untreated Pt-Bi/C catalyst showed BiPt and $Bi_2Pt$ peaks in addition to Pt peaks. These results imply that Bi atoms were incorporated into the Pt crystal lattice by Pt-Bi alloy formation. The catalytic activity for methanol oxidation was measured using cyclic voltammetry in a mixture of 0.5 M $H_2SO_4$ and 0.5 M $CH_3OH$ aqueous solution. The addition of proper amount of Bi was found to significantly improve catalytic activity for methanol oxidation. The catalytic activity for methanol oxidation was closely related to the stability between electrode and electrolyte. In order to investigate the stability of catalysts, chronoamperometry analysis was carried out in the same solution at 0.6 V.

• Microbiology and Biotechnology Letters
• /
• v.39 no.1
• /
• pp.29-36
• /
• 2011

Pseudomonas aeruginosa is an opportunistic pathogen that causes various infections on urinary track, cornea, respiratory track, and burn wound site, and mainly relies on quorum sensing (QS) for its virulence. To control the infectivity of P. aeruginosa, we previously synthesized the structural analogues of a major QS signal, N-3-oxododecanoyl homoserine lactone (3OC12-HSL) to use as a QS inhibitor. Two of them (5b and 5f) had been confirmed to have an inhibitory effect on LasR, a major QS signal receptor of P. aeruginosa in the screening by the recombinant Escherichia coli reporter. To further evaluate these compounds, we tested their efficacy to control the QS and virulence of P. aeruginosa. Unlike the result from E. coli reporter, both 5b and 5f failed to affect the LasR activity in P. aeruginosa, but instead they selectively affected the activity of QscR, another 3OC12-HSL receptor of P. aeruginosa. Interestingly, their effect on QscR was complex and opposite to what we obtained with E. coli system. Both 5b and 5f enhanced the QscR activity at the low concentration range (< 10 ${\mu}m$), but high concentration of 5f (${\approx}$1 mM) strongly inhibited QscR. While 5b and 5f didn't affect the production of proteases, the key virulence factor, they significantly reduced the biofilm formation that is important in mediating chronic infections. Especially, 5f inhibited the initial attachment of P. aeruginosa, rather than the biofilm maturation. Based on our results, we suggest that 5f can be applied for an anti-biofilm agent without increasing virulence of P. aeruginosa.

• Publications of The Korean Astronomical Society
• /
• v.32 no.1
• /
• pp.225-230
• /
• 2017

The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z~1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field ($5.4deg^2$), using ~10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r ~25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star-formation rate density (CSFRD). For example, if they all lie at 1< z <2, the CSFRD will be twice as high at the epoch. We are carrying out deep imaging of the NEP field in 5 broad bands (g, r, i, z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate midIR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.625-628
• /
• 2015

POLARBEAR is a ground-based experiment located in the Atacama desert of northern Chile. The experiment is designed to measure the Cosmic Microwave Background B-mode polarization at several arcminute resolution. The CMB B-mode polarization on degree angular scales is a unique signature of primordial gravitational waves from cosmic inflation and B-mode signal on sub-degree scales is induced by the gravitational lensing from large-scale structure. Science observations began in early 2012 with an array of 1.274 polarization sensitive antenna-couple Transition Edge Sensor (TES) bolometers at 150 GHz. We published the first CMB-only measurement of the B-mode polarization on sub-degree scales induced by gravitational lensing in December 2013 followed by the first measurement of the B-mode power spectrum on those scales in March 2014. In this proceedings, we review the physics of CMB B-modes and then describe the Polarbear experiment, observations, and recent results.

• Korean Journal of Dental Materials
• /
• v.44 no.2
• /
• pp.151-161
• /
• 2017

The purpose of this study was to examine the effect of shade and thickness of resin-nanoceramic CAD-CAM block (RNB) on the microhardness of dual-cured resin cement, as well as to measure the number of photons transmitted through RNBs of different thicknesses and colors. One dual-cured resin cement was used to prepare resin cement specimens. Resin cement specimens were light-cured for 40 seconds through 3 shades (A1, A2, A3 in HT (high translucency) and LT (low translucency) respectively) and four thicknesses (1, 2, 3, 4 mm) of RNB specimens. Vickers microhardness measurements of resin cement specimens were performed using a Vickers hardness tester. The light transmission of RNB specimens was measured using a spectrometer (SpectroPro-500, Acton Research, Acton, MA, U.S.A.), and the translucency parameter was calculated using the CIEL*a*b* system. Data were statistically analyzed by ANOVA and Tukey's test. There was a significant decrease of microhardness of resin cement specimen with an overlay of 4 mm of RNB thickness and A3 shade in comparison to A1 and 1 mm, respectively (p<0.05). The translucency parameter values and light transmission of RNBs tested differed significantly, according to the thicknesses of the specimen (p<0.05). Light transmission is decreased with increase in the thicknesses of RNBs. Shade A1 transmitted more light than darker blocks. A decrease in microhardness of resin cement specimens was observed with increasing thickness and shade (A1 to A3) of RNBs.