• 천문학회보
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• 제42권2호
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• pp.72.1-72.1
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• 2017

Energetic ionized gas outflows driven by active galactic nuclei (AGN) have been studied as a key phenomenon related to AGN feedback. To probe the kinematics of the gas in the narrow line region, [O III] ${\lambda}5007$ has been utilized in a number of studies, showing non-virial kinematic properties due to AGN outflows. We statistically investigate whether the $H{\alpha}$ emission line is influenced by AGN driven outflows, by measuring the kinematic properties based on the $H{\alpha}$ line profile, and by comparing them with those of [O III]. Using the spatially integrated spectra of ~37,000 Type 2 AGNs at z < 0.3 selected from the SDSS DR7, we find a non-linear correlation between $H{\alpha}$ velocity dispersion and stellar velocity dispersion, which reveals the presence of the non-gravitational component, especially for AGNs with a wing component in $H{\alpha}$. The large $H{\alpha}$ velocity dispersion and velocity shift of luminous AGNs are clear evidence of AGN outflow impacts on $H{\alpha}$ emitting gas, while relatively smaller kinematic properties compared to those of [O III] imply that the observed outflow effect on the $H{\alpha}$ line is weaker than the case of [O III].

• 천문학회보
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• 제36권2호
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• pp.108.2-108.2
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• 2011

We investigate decaying magnetohydrodynamic (MHD) turbulence by including the effects of expansion and collapse of the background medium. The problem has two time scales, the eddy turn-over time($t_{eddy}$) and the expansion/collapse time scale(${\tau}_H$). The turbulence is expected to behave differently in two regimes of $t_{eddy}$ < ${\tau}_H$ and $t_{eddy}$ > ${\tau}_H$. For instance, for $t_{eddy}$ < ${\tau}_H$, the turbulence would decay more or less as in a static medium. On the other hand, for $t_{eddy}$ > ${\tau}_H$, the effects of expansion and collapse would be dominant. We examine the properties of turbulence in the regimes of $t_{eddy}$ < ${\tau}_H$ and $t_{eddy}$ > ${\tau}_H$. Based on it, we derive a scaling for the time evolution of flow velocity and magnetic field.

• 한국환경과학회지
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• 제30권1호
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• pp.57-67
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• 2021

Photocatalytic green energy H2 production utilizing inexhaustible solar energy has been considered as a potential solution to problems of energy scarcity and environmental contamination. However, the design of a cost-effective photocatalyst using simple synthesis methodology is still a grand challenge. Herein, a low-cost transition metal, Cu-loaded one-dimensional TiO2 nanorods (Cu/TNR) were fabricated using an easy-to-use synthesis methodology for significant H2 production under simulated solar light. X-ray photoelectron spectral studies and electron microscopy measurements provide evidence to support the successful formation of the Cu/TNR catalyst under our experimental conditions. UV-vis DRS studies further demonstrate that introducing Cu on the surface of TNR substantially increases light absorption in the visible range. Notably, the Cu/TNR catalyst with optimum Cu content, achieved a remarkable H2 production with a yield of 39,239 µmol/g after 3 h of solar light illumination, representing 7.4- and 27.7-fold enhancements against TNR and commercial P25, respectively. The notably improved H2 evolution activity of the target Cu/TNR catalyst was primarily attributed to its excellent separation and efficiently hampered recombination of photoexcited electron-hole pairs. The Cu/TNR catalyst is, therefore, a potential candidate for photocatalytic green energy applications.

• Journal of Photoscience
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• 제8권1호
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• pp.1-7
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• 2001

The deteriorative effect of ultraviolet-B(UV-B) radiation on photosynthesis was assessed by the simultaneous measurement of O$_2$ evolution and chlorophyll(Chl) fluorescence in green pepper. UV-B was given at the intensity of 1 W$.$m$\^$-2/, a dosage often encountered in urban area of Seoul in Korea, to detached leaves. Both Pmax and quantum yield of O$_2$ evolution was rapidly decreased, in a parallel phase, with increasing time of UV-B treatment. Chl fluorescence parameters were also significantly affected. Fo was increased while both Fm and Fv were decreased. Photochemical efficiency of PSII(Fv/Fm) was also declined, although to a lesser extent than Pmax. Both qP and NPQ were decreased similarly with increasing time of UV-B treatment. However, PS I remained stable. The addition of lincomycin prior to UV-B treatment accelerated the decline in Fv/Fm to some extent, suggesting that D1 protein turnover may play a role in overcoming the harmful effect of UV-B. The amount of photosynthetic pigments was less affected than photosynthetic response in showing decline in Chl a and carotenoids after 24 h-treatment. Presumptive flavonoid contents, measured by changes in absorbance at 270 nm , 300 nm and 330nm, were all increased by roughly 50% after 8 h-treatment. Among antioxidant enzymes, activities of catalase and peroxidase were steadily increased until 12h of UV-B treatment whereas ascorbate perxidase, dehydroascorvate reductase and glutathione reductase did not show any significant change. The results indicate that deteriorative effect of UV-B on photosynthesis precedes the protection exerted by pigment synthesis and antioxidant enzymes.

• 천문학회보
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• 제38권2호
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• pp.37.1-37.1
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• 2013

We present our study of analyzing the photometric properties of the globular cluster (GC) system which resides in the extended halo of the central bright Coma cluster galaxy NGC 4874. The core of the Coma cluster of galaxies (Abell 1656) was observed with both the HST Advanced Camera for Surveys (ACS) in the F475W (g475) and F814W (I814) and Wide Field Camera 3 IR Channel (WFC3/IR) in the F160W (H160) filters. The data analysis procedure and GC candidate selection criteria are briefly described. We investigate the interesting "tilt" features in color-magnitude diagrams for this GC system and their link to the nonlinear color-metallicity relation for GCs. The NGC 4874's GC system exhibits a bimodal distribution in the optical g475-I814 color and much more than half the GCs fall in the red side at g475-I814 ~ 1.1. This bimodality is weakened in the optical-IR I814-H160 color; the quantitative analysis on the features of both color distributions using the Gaussian Mixture Modeling code proves the bimodalities are different. Both colors, thus, cannot linearly reflect the bimodality of an underlying metallicity, supporting the suggestion that observed bimodalities in extragalactic GC colors are the metallicity-to-color projection effect.

• Animal Systematics, Evolution and Diversity
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• 제9권2호
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• pp.251-259
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• 1993

서울대학교 관악캠퍼스의 이끼로 덮힌 토양에서 채집된 하모류가 Holosticha multistylata Kahl, 1928와 H. sylvatica Foissner, 1982로 밝혀져서 재기재하였다. 기재는 서식처에서 채집된 표본과 배양된 것을 생체로 관찰하고 protargol로 염색하여 섬모하부구조를 관찰한 자료를 통계처리하여 실시하였다. 이 두 종은 한국에서 처음으로 기록되는 종으로 아래의 식별형질로 구분된다. 다구극모전열하모충은 4개의 전방극모, 3개의 구극모와 3개의 구극모와 3개의 등쪽섬모열을 가지는 반면 삼림전열하무충은 7-8개의 전방극모, 1개의 구극모와 5개의 등쪽섬모열을 가진다.

• Animal Systematics, Evolution and Diversity
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• 제18권1호
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• pp.91-98
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• 2002

바다가시곰벌레속 (Halechiniscus)에 속하는 해양완보류 2종 (H. Jejuensis, H. remanei)을 보고한다. 신종인 제주가시곰벌레 (H. Jejuensis)는 몸통 측돌기의 위치와 모양, 제4다리 기부에 난 유두형의 감각톤기의 모양, 그리고 머리의 전단부가 두 갈래로 갈라져 있지 않은 점에서 본 속의 다른 종들과 뚜렷이 구별된다. 지금까지 바다가시곰벌레속에 기록된 9종에 대한 종검색표를 새롭게 작성하였다.

• 전기화학회지
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• 제6권2호
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• pp.119-129
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• 2003

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic $H_2$ evolution reaction (HER) at the poly-Au and $Rh|0.5M\;H_2SO_4$ aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift $(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1{\geq}{\theta}{\geq}0)$ at the interfaces. The phase-shift profile $({-\phi}\;vs.\;E)$ for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm $({\theta}\;vs.\;E)$ of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M $H_2SO_4$ aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the OPD H are $2.3\times10^{-6}$ and 32.2kJ/mol, respectively. At the poly-Rh|0.5M $H_2SO_4$ aqueous electrolyte interface, K and ${\Delta}G_{ads}$ of the OPD H are $4.1\times10^4\;or\;1.2\times10^{-2}$ and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.

• 분석과학
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• 제18권1호
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• pp.1-4
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• 2005

반응 속도를 조절하기 위하여 유기 첨가제인 아세트산을 사용해 치환된 티타늄 이소프로폭사이드를 합성한 뒤 가수분해 시킨 실리콘(IV)에톡사이드와 반응시켜 $TiO_2-SiO_2$ 분말을 얻었다. 반응 과정 동안의 구조 변화와 특징을 NMR과 FT-IR을 통해서 살펴보았다. 열처리 과정을 거친 분말의 FT-IR 결과로부터 상 분리를 관찰하였다.

• Korea-Australia Rheology Journal
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• 제13권2호
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• pp.89-95
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• 2001

Effects of particulate size and frictional characteristics were examined on the melting behavior of PP(polypropylene) in a twin screw extruder. Powder and pellet types of PP were used and each component was blended with PE(polyethylene) wax and clay, respectively. It was observed that small size particulates, 1.e. powder systems exhibit accelerated melting behavior; and it was also found that the abrasive auditive acts as an effective agent for fast melting of PP powder. Retardation of melting due to the reduced friction was observed in both types of PP, contrary to the result found in a batch mixer. The tendency observed in variation of torque and exit temperature was explained in terms of frictional effect and length of compacted region formed during evolution of melting.