• Bulletin of the Korean Chemical Society
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• 제29권8호
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• pp.1554-1560
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• 2008

The probe diffusion and friction constants of methyl yellow (MY) in liquid n-alkanes of increasing chain length were calculated by equilibrium molecular dynamics (MD) simulations at temperatures of 318, 418, 518 and 618 K. Lennard-Jones particles with masses of 225 and 114 g/mol are modeled for MY. We observed that the diffusion constant of the probe molecule follows a power law dependence on the molecular weight of nalkanes, DMY${\sim}M^{-\gamma}$ well. As the molecular weight of n-alkanes increases, the exponent $\gamma$ shows sharp transitions near n-dotriacontane ($C_{32}$) for the large probe molecule (MY2) at low temperatures of 318 and 418 K. For the small probe molecule (MY1) $D_{MY1}$ in $C_{12}$ to C80 at all the temperatures are always larger than Dself of n-alkanes and longer chain n-alkanes offer a reduced friction relative to the shorter chain n-alkanes, but this reduction in the microscopic friction for MY1 is not large enough to cause a transition in the power law exponent in the log-log plot of DMY1 vs M of n-alkane. For the large probe molecule (MY2) at high temperatures, the situation is very similar to that for MY1. At low temperatures and at low molecular weights of n-alkanes, $D_{MY2}$ are smaller than $D_{self}$ of n-alkanes due to the relatively large molecular size of MY2, and MY2 experiences the full shear viscosity of the medium. As the molecular weight of n-alkane increases, $D_{self}$ of n-alkanes decreases much faster than $D_{MY2}$ and at the higher molecular weights of n-alkane, MY2 diffuses faster than the solvent fluctuations. Therefore there is a large reduction of friction in longer chains compared to the shorter chains, which enhances the diffusion of MY2. The calculated friction constants of MY1 and MY2 in liquid n-alkanes supported these observations. We deem that this is the origin of the so-called“solventoligomer”transition.

• 한국세라믹학회지
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• 제52권4호
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• pp.279-283
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• 2015

Ni (100 nm thick) was deposited onto synthesized diamonds to fabricate etched diamonds. Next, those diamonds were annealed at varying temperatures ($400{\sim}1200^{\circ}C$) for 30 minutes and then immersed in 30 wt% $HNO_3$ to remove the Ni layers. The etched properties of the diamonds were examined with FE-SEM, micro-Raman, and VSM. The FE-SEM results showed that the Ni agglomerated at a low annealing temperature (${\sim}400^{\circ}C$), and self-aligned hemisphere dots formed at an annealing temperature of $800^{\circ}C$. Those dots became smaller with a bimodal distribution as the annealing temperature increased. After stripping the Ni layers, etch pits and trigons formed with annealing temperatures above $400^{\circ}C$ on the surface of the diamonds. However, surface graphite layers existed above $1000^{\circ}C$. The B-H loop results showed that the coercivity of the samples increased to 320 Oe (from 37 Oe) when the annealing temperature increased to $600^{\circ}C$ and then, decreased to 150 Oe with elevated annealing temperatures. This result indicates that the coercivity was affected by magnetic domain pinning at temperatures below $600^{\circ}C$ and single domain behavior at elevated temperatures above $800^{\circ}C$ consistent with the microstructure results. Thus, the results of this study show that the surface of diamonds can be etched.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1491-1494
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• 2014

High-crystallinity poly(3-hexylthiophene) (P3HT) thin films were prepared by aging the precursor solutions, prepared using a good solvent, chloroform, at low temperatures prior to spin-casting. Lower solution temperatures significantly improved the molecular ordering in the spin-cast P3HT films and, therefore, the electrical properties of field-effect transistors prepared using these films. Solution cooling enhanced the electrical properties by shifting the P3HT configuration equilibrium away from random coils and toward more ordered aggregates. At room temperature, the P3HT molecules were completely solvated in chloroform and adopted a random coil conformation. Upon cooling, however, the chloroform poorly solvated the P3HT molecules, favoring the formation of ordered P3HT aggregates, which then yielded more highly crystalline molecular ordering in the P3HT thin films produced from the solution.

• 자원환경지질
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• 제21권4호
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• pp.381-387
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• 1988

Maewol Feldspar Mine produces feldspar ore from pegmatites. K-Rb Age of muscovite is 137.7Ma. Fluid inclusions in quartz crystal of the pegmatite show bimodal distribution of homogenization temperatures. The high homogenization temperatures range from 290 to $302^{\circ}C$ while low homogenization temperatures range from 157 to $195^{\circ}C$. Three phases liquid $CO_2$ bearing inclusions indicate $CO_2$ gases were abundantly mixed with granitic melt until the pegmatic magma melt cooled to $290^{\circ}C$. Low density of the magmatic melt relative to the same volume of granitic magma is due to mixture of volatiles(mainly $CO_2$ gases) with the melt and larger space and slow cooling allowed to grow crystals of the pegmatic magma.

• 한국진공학회지
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• 제6권S1호
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• pp.59-65
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• 1997

Efficient Si(100) etching by thermal H atoms at low substrate temperatures has been achieved. Gas-phase etching product $SiH_4$(g) upon H atom bombardment resulting from direct abstraction of $SiH_3$(a) by impinging H atoms was detected with a quadrupole mass spectrometer over the substrate temperature range of 105-408 K Facile depletion of all surface silyl ($SiH_3$) groups the dissociative adsorption product of disilane ($Si_2H_6$) at 105K from Si(100)2$\times$1 by D atoms and continuous regeneration and removal of $SiD_3$(a) were all consumed. These results provide direct evidence for efficient silicon surface etching by thermal hydrogen bombardment at cryogenic temperatures as low as 105K We attribute the high etching efficiency to the formation and stability of $SiH_3$(a) on Si(100) at lowered surface temperatures allowing the $SiH_3$(a) abstraction reaction by additional H atom to produce $SiH_4$((g).

• 한국세라믹학회지
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• 제52권6호
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• pp.527-530
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• 2015

The electrical properties of nanostructured Gd-doped $CeO_2$ (n-GDC) as a function of temperature and water partial-pressure were investigated using ac and dc measurements. For n-GDC, protonic conductivity prevails under wet condition and at low temperatures (< $200^{\circ}C$), while oxygen ionic conductivity occurs at high temperatures (> $200^{\circ}C$) under both dry and wet conditions. The grain boundaries in n-GDC were highly selective, being conductive for protonic transport but resistive for oxygen ionic transport. The protonic conductivity reaches about $4{\times}10^{-7}S/cm$ at room temperature (RT).

• The Korean Journal of Ceramics
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• 제5권1호
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• pp.50-54
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• 1999

$(Pb_xLa_{1-x}) (Zr_yTi_{1-y})O_3$ (PLZT) thin films with electrooptic effect are promising for the optical application such as display or light shutter. However, it is difficult to use inexpensive and transparent glass substrates because the conventional process for preparation of PLZT requires temperatures above $600^{\circ}C$. In order to deposit a perovskite PLZT thin films at low processing temperatures through alkoxide route, we have offered several seeding processes which reduce the activation energy for crystallization. In this study, we optimized the stacking structure of multilayered PLZT for obtaining single phase perovskite at lower temperatures. As a result, ferroelectric PLZT thin films with different compositions were successfully prepared at a temperature as low at $500^{\circ}C$.

• 한국생산제조학회지
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• 제25권3호
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• pp.224-229
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• 2016

Recently, polymeric micro-fluidic biochips with numerous micro patterns on the surface were fabricated by injection molding for realizing low-cost mass production of devices. To evaluate the effects of process parameters on large-scale micro-structure replication, a $50{\times}50mm^2$ tool insert with surface structures having a patterns of trapezoidal shapes (height: $30{\mu}m$) was employed. During injection molding, PMMA was used; packing phase parameters and mold temperature were investigated. The replicated surface textures were quantitatively characterized by confocal laser microscopy with 10-nm resolution. The degree of replication at low mold temperatures was found to be higher than that at high mold temperature at the beginning of the packing stage. Thereafter, the degree of replication increased to a greater extent at higher mold temperatures; application of higher mold temperatures improved the degree of replication.

• 한국초전도ㆍ저온공학회논문지
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• 제17권1호
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• pp.25-27
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• 2015

The experimental investigation of resistance and thermal impacts stability of coated conductor joints has been carried out. We measured resistances of solder layers with the thicknesses ca. 10, 20, 30 and $40{\mu}m$ and additionally studied their stability against thermal impacts. The obtained results show a high quality of this joints and their applicability, e.g., for design of current leads in various superconductive energy applications.

• International Journal of Advanced Culture Technology
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• 제7권4호
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• pp.260-267
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• 2019

Harvested de-astringent persimmon 'Fuyu' were treated with various lighting sources under low (3℃) and high (22℃) temperatures. The weight loss rate of fruits was lower in those with Red LED than Fluorescence and Blue LED under both temperature conditions. Hardness and soluble solid content of fruits were higher in those with 3℃ / Blue LED or mixed LED (Blue+Red LEDs). Beta-carotene and lycopene content of fruit peel were higher in those with 3℃ than 22℃ and with Red LED or light sources with mixed red wavelength under both temperatures. When the fruits treated with light and temperature were stored for 4 days under 3℃ / dark condition, the hardness of the fruits did not significant difference among the treatments. Taken together all the results, it would be best to treat it light sources mixed red wavelength under 3℃.