• Title/Summary/Keyword: dark energy

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THE NEW HORIZON RUN COSMOLOGICAL N-BODY SIMULATIONS

  • Kim, Ju-Han;Park, Chang-Bom;Rossi, Graziano;Lee, Sang-Min;Gott, J. Richard III
    • Journal of The Korean Astronomical Society
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    • v.44 no.6
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    • pp.217-234
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    • 2011
  • We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using $6000^3$ = 216 billions and $7210^3$ = 374 billion particles, spanning a volume of $(7.200\;h^{-1}Gpc)^3$ and $(10.815\;h^{-1}Gpc)^3$, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to $1.25{\times}10^{11}h^{-1}M_{\odot}$, allowing to resolve galaxy-size halos with mean particle separations of $1.2h^{-1}$Mpc and $1.5h^{-1}$Mpc, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the CDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science - in connection with the new SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the past light cone out to z = 0.7 (8 from the HR2 and 27 from the HR3), to simulate the BOSS geometry. The simulations and mock surveys are already publicly available at http://astro.kias.re.kr/Horizon-Run23/.

Revealing the Powering Mechanism of Lyman Alpha Blob via Polarization

  • Kim, Eunchong;Yang, Yujin;Zabludoff, Ann;Smith, Paul;Jannuzi, Buell;Lee, Myung Gyoon
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.35.4-36
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    • 2018
  • $Ly{\alpha}$ blobs are mysterious, giant (~100 kpc), glowing gas clouds in the distant universe. They occupy the dark matter halos that will evolve into the richest groups and clusters today. The blob's gas may be the proto-intracluster medium and their embedded galaxies are considered as the progenitors of massive cluster galaxies. Yet we do not know why $Ly{\alpha}$ blobs glow. There are evidences of kinematic measurements to exclude shocks and winds from AGN or starbursts as a power source, suggesting that photoionizing radiation or scattering of $Ly{\alpha}$ photons might be responsible. Polarization mapping can discriminate between these photo-ionization and scattering. Previous results of imaging polarimetry for $Ly{\alpha}$ nebulae are roughly consistent with scattering models. However the polarization morphologies in those of previous results are all different, motivating our polarimetric survey of $Ly{\alpha}$ nebulae for the statisticallymeaningful sample. As initial results of our survey, we present the total polarization map of the LABd05 which has the spatial offset between the peak of $Ly{\alpha}$ surface brightness and an obscured AGN. We detect the significant polarization in this target with the radially increasing polarization gradient, suggesting that scattering plays major role within this nebula. The polarization pattern is more aligned with the $Ly{\alpha}$ peak rather than the AGN (the potential energy source), indicating that the $Ly{\alpha}$ photons are originated from the region near the peak of $Ly{\alpha}$ intensity.

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Symbolism and Psychology of Colors in Painting - Focusing on a Color Comparison between Vincent Van Gogh and Gustav Klimt - (회화에 나타난 색채상징성 및 색채심리 - 빈센트 반 고흐와 구스타프 클림트의 그림에 나타난 색채비교를 중심으로 -)

  • Im, Nu-Ry;Oh, In-Young
    • Journal of the Korean Society of Costume
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    • v.60 no.5
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    • pp.19-34
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    • 2010
  • This study aims to examine associationistic psychology and psychological operation associated with each color image, then to study the relation between particular colors used in paintings produced by Gogh and Klimt in different times and these painters' psychology in a bid to explore the meaning and role of psychological operation of colors. The findings of the study indicated that red and blue colors represent mainly negative images, while yellow and orange colors represent mainly positive images and psychologies. Specifically, in the case of Gogh, red expresses anxiety, a negative image, yellow symbolizes passion, a major positive image of emotional liberation, dark and thick green and the green involving blue symbolize negative images, emptiness and despair, and blue represents negative images of internal desire conflicts, and screaming. Also, purple used together with white represents anxiety and depression. In the case of Klimt, red represents negative images of anger toward mother and suppressed energy, yellow, an alternative to gold color, symbolizes the positive image of hope, passion, desire and eroticism, the arrangement of strong gold and orange colors represents a color of psychological healing more than a color of hope. As such, colors used in paintings produced by modern Western painters express the physiological conditions, psychological feeling and emotion in life, at the time when the artists produced such works. It was found that colors are yet another language of expressing emotions, and symbolize the psychologies of the artists, indicating that colors have something to do with the painters' experience and emotional impulses.

Persistent Photoconductivity in Hydrogenated Amorphous Carbon Thin Films (수소화된 비정질 탄소 박막에서의 지속광전기전도도)

  • Kang, Sung Soo;Lee, Won Jin;Sung, Duck Yong
    • Journal of Korean Ophthalmic Optics Society
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    • v.1 no.2
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    • pp.49-55
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    • 1996
  • Hydrogenated amorphous carbon(a-C:H) films were fabricated by the low-frequency (60Hz) glow discharge of the mixture of methane and hydrogen, and their electrical properties were investigated. We observed that a-C:H films show the persistent photoconductivity(PPC) by illumination of heat-filtered while light for a few seconds. The PPC was about 10 times larger than the annealed dark conductivity. The samples clearly showed metastable characteristics. With increasing illumination times from 1 to 100 min, the annealing activation energy of the PPC was about 0.39eV. The annealing temperature at which the PPC disappeared increasing from $100^{\circ}C$ to $130^{\circ}C$. Illumination longer than 80 min leads to the formation of ${\pi}$ defects and to the decrease of PPC. From these results, we tentatively propose that the states in the ${\pi}$ band act as deep trap centers generating the metastabilities.

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Effect of Herbicide Paraquat on Electron Donor and Acceptor (제초제 Paraquat의 전자수용 및 방출에 대한 영향)

  • Kim Mi-Lim;Choi Kyung-Ho
    • Journal of Life Science
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    • v.15 no.2 s.69
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    • pp.311-315
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    • 2005
  • When paraquat was added to the bacterial membrane or mitochondrial suspension, the mixture turned dark blue, but the color was disappeared by aeration. The same phenomenon was seen when electrons were supplied to the paraquat. Blue color appeared from near the cathode, and then spreaded to whole transit system. Coloration was accelerated by addition of alkali, but the color was reduced by addition of acid or oxygen. Paraquat exhibited absorption at ultraviolet region by electron transfer at the concentrations as low as 1.0 mM which did not exert difficulty in showing color reaction. Paraquat caused the increase of the optical density at 340 nm by electron transit, and an aspect of that had a strong resemblance to NADH. The acute toxic action of paraquat seemes to depend on inhibition of energy metabolism cased by paraquat action of electron donor and acceptor.

Reset-first Resistance Switching Mechanism of HfO2 Films Based on Redox Reaction with Oxygen Drift-Diffusion

  • Kim, Jong-Gi;Lee, Sung-Hoon;Lee, Kyu-Min;Na, Hee-Do;Kim, Young-Jae;Ko, Dae-Hong;Sohn, Hyun-Chul
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.02a
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    • pp.286-287
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    • 2012
  • Reset-first resistive switching mechanism based on reduction reaction in HfO2-x with oxygen drift-diffusion was studied. we first report that the indirect evidence of local filamentary conductive path formation in bulk HfO2 film with local TiOx region at Ti top electrode formed during forming process and presence of anion-migration at interface between electrode and HfO2 during resistive switching through high resolution transmission electron microscopy (HRTEM), electron disperse x-ray (EDX), and electron energy loss spectroscopy (EELS) mapping. Based on forming process mechanism, we expected that redox reaction from Ti/HfO2 to TiOx/HfO2-x was responsible for an increase of initial current with increasing the post-annealing process. First-reset resistive switching in above $350^{\circ}C$ annealed Ti/HfO2 film was exhibited and the redox phenomenon from Ti/HfO2 to TiOx/HfO2-x was observed with high angle annular dark field (HAADF) - scanning transmission electron microscopy (STEM), EDX and x-ray photoelectron spectroscopy. Therefore, we demonstrated that the migration of oxygen ions at interface region under external electrical bias contributed to bipolar resistive switching behavior.

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In2S3 Co-Sensitized PbS Quantum Dot Solar Cells

  • Basit, Muhammad Abdul;Park, Tae Joo
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2014.11a
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    • pp.273-273
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    • 2014
  • Quantum-dot sensitized solar cells (QDSCs) are an emerging class of solar cells owing to their easy fabrication, low cost and material diversity. Despite of the fact that the maximum conversion efficiency of QDSCs is still far less than that of Dye-Sensitized Solar Cells (>12 %), their unique characteristics like Multiple Exciton Generation (MEG), energy band tune-ability and tendency to incorporate multiple co-sensitizers concurrently has made QDs a suitable alternative to expensive dyes for solar cell application. Lead Sulfide (PbS) Quantum dot sensitized solar cells are theoretically proficient enough to have a photo-current density ($J_{sc}$) of $36mA/cm^2$, but practically there are very few reports on photocurrent enhancement in PbS QDSCs. Recently, $Hg^{2+}$ incorporated PbS quantumdots and Cadmium Sulfide (CdS) co-sensitized PbS solarcells are reported to show an improvement in photo-current density ($J_{sc}$). In this study, we explored the efficacy of $In_2S_3$ as an interfacial layer deposited through SILAR process for PbS QDSCs. $In_2S_3$ was chosen as the interfacial layer in order to avoid the usage of hazardous CdS or Mercury (Hg). Herein, the deposition of $In_2S_3$ interfacial layer on $TiO_2$ prior to PbS QDs exhibited a direct enhancement in the photo-current (Isc). Improved photo-absorption as well as interfacial recombination barrier caused by $In_2S_3$ deposition increased the photo-current density ($J_{sc}$) from $13mA/cm^2$ to $15.5mA/cm^2$ for single cycle of $In_2S_3$ deposition. Increase in the number of cycles of $In_2S_3$ deposition was found to deteriorate the photocurrent, however it increased $V_{oc}$ of the device which reached to an optimum value of 2.25% Photo-conversion Efficiency (PCE) for 2 cycles of $In_2S_3$ deposition. Effect of Heat Treatment, Normalized Current Stability, Open Circuit Voltage Decay and Dark IV Characteristics were further measured to reveal the characteristics of device.

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The Dependence of Type Ia Supernovae Luminosities on the Morphologies of Host-Galaxies

  • Kim, Young-Lo;Kang, Yi-Jung;Joe, Young-Hoon;Lee, Young-Wook
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.69.2-69.2
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    • 2011
  • The discovery of dark energy from Type Ia supernovae (SN Ia) is based on the implicit assumption that the look-back time evolution of SN Ia luminosity, after light-curve corrections, would be negligible. A strong support for this assumption was the apparent insensitivity of SN Ia distances across the host galaxy morphologies. However, Hicken et al. 2009 (H09) shows a systematic difference in the Hubble residual (HR) of $0.144{\pm}0.070$ mag between the E-S0 and Scd/Sd/Irr galaxies, after light-curve corrections. If true, this indicates that the light-curve fitters used by the SN Ia community can not correct for the population age (and therefore the evolution) effect. In order to confirm this, we have combined nearby SN Ia samples and the first-year SDSS-II SN Survey. The SNANA package was used for analyzing SN Ia light-curve, both for the MLCS2k2 and SALT2 fitters. We find a systematic difference in the HR of $0.10-0.13{\pm}0.030$ mag between E-S0 and Scd/Sd/Irr galaxies, which is in agreement with the result of H09, but now at the 3-5 ${\sigma}$ level. Considering the significant difference in the mean age of stellar population between these morphological types, the difference in the HR reported here suggests that the evolution effect of SN Ia luminosity should be considered in the cosmological application of SN Ia data.

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A Study on the Preparation of Tritium Luminous Compound

  • Kim, Jaerok
    • Nuclear Engineering and Technology
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    • v.4 no.4
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    • pp.331-339
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    • 1972
  • For the syntheses of tritium labelled polystyrene, the basic material for the preparation of tritium luminous compound, various methods of labelling such as Tesla discharge, Wilzbach exposure, gamma irradiation, and U V. irradiation were compared in view of getting high specific activity-product. The obtained polystyrene-T(G) by the method of Tesla discharge and by the method of U. V. irradiation had specific activity of 1~1.2 mCi/mg, and these two methods were the most encouraging. Mixing of 1 part of polystyrene-T(G) with 4 parts of ZnS:Cu phosphor, in weight, appeared to be the most suitable ratio in tile preparation of luminous compound in luminosity point of view. When 30 mg. of obtained luminescent mixture was applied on steel plate by using 1 ml. of the selected binder (i.e., 1g of commercial varnish in 100m1. of benzene) the luminosity maximum was ca. 20 micro Lambert. The prepared luminous compound was confirmed to be practically applicable for mine marker or dark-room light source.

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Analysis on Temperature Dependence of Crystalline Silicon Solar Cells with Different Emitter Types for Desert Environment (사막형 결정질 실리콘 태양전지의 에미터 구조에 따른 온도 별 특성 변화 분석)

  • Nam, Yoon Chung;Kim, Soo Min;Kang, Yoonmook;Lee, Hae-Seok;Kim, Donghwan
    • Current Photovoltaic Research
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    • v.2 no.3
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    • pp.135-139
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    • 2014
  • Different power output of solar cells can be observed at high-temperature regions such as desert areas. In this study, performance dependence on operating temperature of crystalline silicon solar cells with different emitter types was analyzed. Based on the light current-voltage (LIV) measurement, temperature coefficients of short-circuit current density ($J_{SC}$), open-circuit voltage ($V_{OC}$), fill factor (FF) and power conversion efficiency were measured and compared for two groups of crystalline silicon solar cells with different emitter types. One group had homogeneously doped (conventional) emitter and another selectively doped (selective) emitter. Varying the operating temperature from 25 to 40, 60, and $80^{\circ}C$, LIV characteristics of the cells were measured and the properties of saturation current densities ($J_0$) were extracted from dark current-voltage (DIV) curve. From the DIV data, effect of temperature on the performance of the solar cells with different electrical structures for the emitter was analyzed. Increasing the temperature, both emitter structures showed a slight increase in $J_{SC}$ and a rapid degradation of $V_{OC}$. FF and power conversion efficiency also decreased with the increasing temperature. The degrees of $J_{SC}$ increase and $V_{OC}$ degradation for two groups were compared and explained. Also, FF change was explained by series and shunt resistances from the LIV data. It was concluded that the degradation of solar cells shows different values at different temperatures depending on the emitter type of solar cells.