• KSBB Journal
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• 제20권6호
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• pp.393-400
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• 2005

수소를 생산하는 미생물은 크게 광합성 세균(photosynthetic bacteria), 혐기성세균(non-photosynthetic anaerobic bacteria), 조류(algae) 등으로 구분되고, 이들의 수소 생성 기작, 사용가능기질 및 수소 발생량은 상당한 차이가 있다. 광합성세균은 Rhodospirillaceae, Chromatiaceae 및 Chlorobiaceae로 구분되며, 이는 각각 홍색비유황세균(purple non-sulfur bacteria), 홍색유황세균(purple sulfur bacteria), 녹색유황세균(green sulfur bacteria)으로 통칭된다. 혐기성 세균은 절대 또는 통성혐기세균중 일부가 수소생산에 관여하며, 조류는 녹조류(green algae)와 남조류(blue-green algae, cyanobacteria)가 알려져 있다. 생물학적 수소생산 기술은 (1) 녹조류(green algae)가 광합성 메카니즘에 의해 수소를 생산하는 직접 물 분해 수소생산(direct bio-photolysis) (2) 광합성 작용에 의해 물을 분해하여 산소를 발생하고, 동시에 공기 중 이산화탄소를 고정하여 고분자 저장물질로 균체 내에 저장한 후 혐기 발효 또는 광합성 발효에 의해 수소를 발생하는 간접 물 분해 수소생산(indirect bio-photolysis or two stage photolysis) (3) 빛이 존재하는 혐기상태 배양 조건에서 홍색 세균에 의한 광합성 발효(photo-fermentation) 또는 (4) 광이 존재하지 않는 조건에서 혐기 미생물에 의해 수소와 유기산을 내는 혐기 발효(dark anaerobic fermentation) (5) 균체 외(in virro) 수소 발생 (6) 일산화탄소 가스 전환 반응(microbial gas shift reaction)에 의한 수소 생산 기술로 구분할 수 있다. 물로부터 생물학적 기술에 의한 수소생산은 공기 중의 이산화탄소를 고정하고, 수소와 산소를 발생하는 원천기술로써 오래 전부터 미국, 유럽에서 태양에너지를 이용하는 광합성 미생물의 분리, 개선 및 반응기에 관한 연구가 축적되어 왔으며, 유기물 즉 바이오매스로부터 혐기 및 광합성 발효를 연속적으로 적용하는 기술은 비교적 최근에 일본을 비롯한 유기성 폐기물이 많은 국가에서 수소에너지 생산과 유기성 폐기물 처리라는 두 가지 목적에 부합하는 연구로써 활발히 진행되고 있다. 유기성 폐기물이나 폐수와 같은 수분함량이 높은 바이오매스는 대부분이 매립처리 되는 실정이지만 높은 수분 함량 때문에 매립 시 발생하는 침출수는 환경오염의 주범으로 가까운 장래에는 매립도 금지될 전망이다. 이와 같은 수소에너지 생산기술과 이용시스템 개발은 화석연료 사용을 최소화 할 수 있으며, 국내에서 다량 발생하는 유기성 폐기물을 이용한 에너지 생산으로 자원 강대국 입지에 설 수 있다. 미생물에 의한 수소생산 기술은 청정에너지 생산과 아울러, 동시에 산소 발생, 공기 중 이산화탄소 고정, 식품공장 폐수 및 음식쓰레기와 같은 유기성 폐기물 처리 등 환경에 이로운 방향으로 진행될 뿐만 아니라, 미생물 자체가 갖는 생물 산업성도 높아서 비타민류, 천연색소, 피부암 치료제등의 고부가가치 의약품 생산도 활성화할 수 있다.

• Journal of Microbiology and Biotechnology
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• 제22권11호
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• pp.1471-1477
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• 2012

Carotenoids produced by non-photosynthetic bacteria protect organisms against lethal photodynamic reactions and scavenge oxygenic radicals. However, the carotenoid produced by Gordonia alkanivorans SKF120101 is coupled to reducing power generation. SKF120101 selectively produces carotenoid under light conditions. The growth yield of SKF120101 cultivated under light conditions was higher than that under dark condition. In the cyclic voltammetry, both upper and lower voltammograms for neutral red (NR) immobilized in intact cells of SKF120101 were not shifted in the condition without external redox sources but were commonly shifted downward by glucose addition and light. Electric current generation in a biofuel cell system (BFCS) catalyzed by harvested cells of SKF120101 was higher under light than dark condition. The ratio of electricity generation to glucose consumption by SKF120101 cultivated in BFCS was higher under light than dark condition. The carotenoid produced by SKF120101 catalyzes production of reducing power from light energy, first evaluated by the electrochemical technique used in this research.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.618-625
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• 2021

In this paper, the single-photon avalanche diodes (SPADs) featuring three different p-well implantation doses (∅_p-well) of 5.0 × 10¹², 4.0 × 10¹², and 3.0 × 10¹² atoms/cm² under the identical device layouts were fabricated and characterized to evaluate the effects of field enhanced mechanisms on primary dark pulses due to the maximum electric field. From the I-V curves, the breakdown voltages were found as 23.2 V, 40.5 V, and 63.1 V with decreasing ∅_p-well, respectively. By measuring DCRs as a function of temperature, we found a reduction of approximately 8% in the maximum electric field lead to a nearly 72% decrease in the DCR at V_ex = 5 V and T = 25 ℃. Also, the activation energy increased from 0.43 eV to 0.50 eV, as decreasing the maximum electric field. Finally, we discuss the importance of electric field engineering in reducing the field-enhanced mechanisms contributing to the DCR in SPADs and the benefits on the SPADs related to different types of radiation detection applications.

• 태양에너지
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• 제11권2호
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• pp.70-76
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• 1991

본 실험에서는 태양광의 photon energy를 활용한 물분해 수소제조 연구를 위하여 일차적으로 $TiO_2$ 광전극의 제조와 함께 전기화학적 특성관찰의 기초실험을 수행하였다. $TiO_2$ anatase 분말을 원형으로 molding 한 후 $1250^{\circ}C$에서 sintering하여 n형 반도체 전극을 제조하였으며, titanium plate를 직접 funace내에서 $800^{\circ}C$의 공기 및 산소 분위기 속에서 각각 산화막을 생성시켰다. 각 전극들의 XRD pattern을 관찰한 결과 rutile $TiO_2$ 성질의 표면구조를 지니고 있었으며, 표면상태를 광학 현미경으로 관찰하였다. 선택된 $TiO_2$ 전극의 전기적 특성을 조사하기 위하여 두가지 농도의 NaOH electrolyser내에서, dark상태 그리고 Xenon lamp를 활용한 illuminated상태에 대하여 각각의 I-E 특성을 Potentiostat을 이동하여 관찰분석하였다.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.175-180
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• 2012

White dwarf stars have played important roles in rather diverse areas of astrophysics. This paper outlines how these stellar remnants, especially those in widely separated "fragile" binaries, have provided unique leverage on difficult astrophysical problems such as the ages of stars, the structure and evolution of the Galaxy, the nature of dark matter and even the discovery of dark energy.

• Mycobiology
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• 제39권1호
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• pp.1-6
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• 2011

Isolates of Ophiocordyceps heteropoda (Kobayasi) collected from Mt. Halla on Jeju-do, Korea were tested for mycelial growth on different agar media and in the presence of different carbon and nitrogen sources. Similarly, isolates were also incubated at different temperatures as well as under continuous light and dark conditions. Growth was better on Hamada agar, basal medium, and malt-yeast agar, but poor on Czapek-Dox agar. Different carbon sources such as dextrin, saccharose, starch, lactose, maltose, fructose, and dextrose resulted in better growth. Complex organic nitrogen sources such as yeast extract and peptone revealed the most effective growth. Mycelial growth was best at $25^{\circ}C$. The growth rate was faster in the dark than the light, but mycelial density was less compact in the dark.

• 천문학회보
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• 제44권1호
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• pp.41.1-41.1
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• 2019

We consider dynamical dark energy models based on a minimally coupled scalar field with three different potentials: the inverse power-law, SUGRA and double exponential potentials. For each model, we derived perturbation initial conditions in the early epoch and performed the Markov Chain Monte Carlo (MCMC) analysis to explore the parameter space that is favored by the current cosmological observations like Planck CMB anisotropy, type Ia supernovae, and baryon acoustic oscillation data. The analysis has been done by using the modified CAMB/COSMOMC code in which the dynamical evolution of the scalar field perturbations are fully considered. The MCMC constraints on the cosmological as well as potential parameters are derived. In the talk we will present a progress report.

• 천문학회보
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• 제44권2호
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• pp.54.1-54.1
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• 2019

We use iterative smoothing reconstruction method along with exploring in the parameter space of the light curves of the JLA supernova compilation (Joint Light-curve Analysis) to simultaneously reconstruct the expansion history of the universe as well as putting constrains on the light curve parameters without assuming any cosmological model. Our constraints on the light curve parameters of the JLA from our model-independent analysis seems to be closely in agreement with results assuming ΛCDM cosmology or using Chevallier-Polarski-Linder (CPL) parametrization for the equation of state of dark energy. This implies that there is no hidden significant feature in the data that could be neglected by cosmology model assumption. The reconstructed expansion history of the universe and properties of dark energy seems to be in good agreement with expectations of the standard ΛCDM model. Our results also indicate that the data allows a considerable flexibility for expansion history of the universe.

• 천문학회보
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• 제44권2호
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• pp.59.3-59.3
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• 2019

The last two decades have seen an immense growth in our understanding of the physics of the birth and evolution of our Universe. However there are still many unanswered questions, such as: what is the nature of the dark energy, which drives the acceleration of the expansion of the Universe? Is the acceleration driven by a cosmological constant, some dynamical dark energy, or a modification of the gravitational force law on large scales? The next generation of radio observatories will conduct large area radio continuum and HI intensity mapping surveys, and so will make possible new and complimentary tests of these fundamental questions. In this talk I present the design of these next generation of surveys, current forecasts for the effectiveness of these cosmological probes, and results from precursor experiments.

• Asian-Australasian Journal of Animal Sciences
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• 제27권7호
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• pp.1044-1049
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• 2014

This study was conducted in order to investigate whether the presence of light or different colors of light would influence the energy expenditure and behavior of broiler chickens. Eight 8-week-old broiler chickens were adapted to a respiration chamber (Length, 28.5 cm; Height, 38.5 cm; Width, 44.0 cm) for one week prior to the initiation of the experiment. In experiment 1, energy expenditure and behavior of the chickens were analyzed in the presence or absence of light for four days. Chickens were exposed to 6 cycles of 2 h light/2 h dark period per day. In experiment 2, the broiler chickens that had been used in experiment 1 were used to evaluate the effect of 4 different wavelength light-emitting diodes (LEDs) on the energy expenditure and behavior of broiler chickens. The LEDs used in this study had the following wavelength bands; white (control), red (618 to 635 nm), green (515 to 530 nm) and blue (450 to 470 nm). The chickens were randomly exposed to a 2-h LED light in a random and sequential order per day for 3 days. Oxygen consumption and carbon dioxide production of the chickens were recorded using an open-circuit calorimeter system, and energy expenditure was calculated based on the collected data. The behavior of the chickens was analyzed based on following categories i.e., resting, standing, and pecking, and closed-circuit television was used to record these behavioral postures. The analysis of data from experiment 1 showed that the energy expenditure was higher (p<0.001) in chickens under light condition compared with those under dark condition. The chickens spent more time with pecking during a light period, but they frequently exhibited resting during a dark period. Experiment 2 showed that there was no significant difference in terms of energy expenditure and behavior based on the color of light (white, red, green, and blue) to which the chickens were exposed. In conclusion, the energy expenditure and behavior of broiler chickens were found to be strongly affected by the presence of light. On the other hand, there was no discernible difference in their energy expenditure and behavior of broiler chickens exposed to the different LED lights.