• Development and Reproduction
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• v.24 no.2
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• pp.79-88
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• 2020

This study was carried out to obtain information on the developmental biology and the management of biological resources of the abalone Haliotis gigantea in Korea. The sex ratio (female:male) in the present study was 1:1.7 and the proportion of females was 36.6% (n=106/290). Their gonadal structures displayed definitive seasonal changes which were similar in pattern to the changes in the gonad index (GI). The GI showed a pattern of definitive seasonal changes in both males and females it was high in the fall and low in the spring. The reproductive cycle could be categorized into the following six stages: inactive, early active, late active, ripe, spent, and degenerative stage. Based on the monthly changes in GI and stages of gonadal development, October to November was determined to be the main spawning period for H. gigantea on Jeju Island, Korea.

• Food Science and Biotechnology
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• v.14 no.1
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• pp.143-146
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• 2005

Although many studies have been performed to elucidate the molecular consequences of ultraviolet irradiation, little is known about the effect of natural products. Ultraviolet irradiation is widely considered to be an environmental stress. Here we investigated the effect of 2',4',7-trihydroxyisoflavone on the regulation of MMP-1 and type 1 procollagen in Ultraviolet irradiation of cultured human dermal fibroblasts. Phytochemical investigation of the whole plants of Viola hondoensis led to the isolation of five flavonoids. The structures of these compounds were identified 2',4',5,7-tetrahydroxyisoflavone (1), 2',4',7-trihydroxyisoflavone (2), 4',7-dihydroxyflavone (3), isoorientin (4), and isovitexin (5) using spectroscopic analysis. Among these, 2',4',7-trihydroxyisoflavone reduced the expression of MMP-1 at the protein levels in a dose-dependent manner by ultraviolet irradiation. Taken together, our results suggest that 2',4',7-trihydroxyisoflavone an important role in the reduction of MMP-1 induction by ultraviolet irradiation.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.281-283
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• 2001

As a companion to an adiabatic version developed by Ryu and his coworkers, we have built an isothermal magnetohydrodynamic code for astrophysical flows. It is suited for the dynamical simulations of flows where cooling timescale is much shorter than dynamical timescale, as well as for turbulence and dynamo simulations in which detailed energetics are unimportant. Since a simple isothermal equation of state substitutes the energy conservation equation, the numerical schemes for isothermal flows are simpler (no contact discontinuity) than those for adiabatic flows and the resulting code is faster. Tests for shock tubes and Alfven wave decay have shown that our isothermal code has not only a good shock capturing ability, but also numerical dissipation smaller than its adiabatic analogue. As a real astrophysical application of the code, we have simulated the nonlinear three-dimensional evolution of the Parker instability. A factor of two enhancement in vertical column density has been achieved at most, and the main structures formed are sheet-like and aligned with the mean field direction. We conclude that the Parker instability alone is not a viable formation mechanism of the giant molecular clouds.

• Journal of Information Display
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• v.3 no.2
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• pp.6-12
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• 2002

In order to achieve white emission from organic light emitting devices (OLEDs), five distinct structures were fabricated and tested. The white emission was obtained using two different color-emitting materials (yellow from rubrene-doped $Alq_3$ and blue from DPVBi) with or without a carrier-blocking layer. For enhancing the red emission, two types of devices with three-color emitting materials were fabricated. The white emission, close to the CIE coordinate of (0.3,0.3), was achieved by using two blocking layers as well that as without a blocking layer. This paper covers the subject of controlling the location of exciton recombination zone. It has been found that there is a trade-off in that the devices with three color emitting layers do not show as much luminescence efficiency compared to those with two color emitting layers, but rather, show distinct red emission in the resultant emission spectra. The highest power efficiency was measured to be 1.15lm/W at 2,000 $cd/m^2$ for a structure with two color-emitting layers.

• Smart Structures and Systems
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• v.2 no.3
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• pp.225-235
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• 2006

With the discovery in plants of the proteinaceous forisome crystalloid (Knoblauch, et al. 2003), a novel, non-living, ATP-independent biological material became available to the designer of smart materials for advanced actuating and sensing. The in vitro studies of Knoblauch, et al. show that forisomes (2-4 micron wide and 10-40 micron long) can be repeatedly stimulated to contract and expand anisotropically by shifting either the ambient pH or the ambient calcium ion concentration. Because of their unique abilities to develop and reverse strains greater than 20% in time periods less than one second, forisomes have the potential to outperform current smart materials as advanced, biomimetic, multi-functional, smart sensors or actuators. Probing forisome material properties is an immediate need to lay the foundation for synthesizing forisomebased smart materials for health monitoring of structural integrity in civil infrastructure and for aerospace hardware. Microfluidics is a growing, vibrant technology with increasingly diverse applications. Here, we use microfluidics to study the surface interaction between forisome and substrate and the conformational dynamics of forisomes within a confined geometry to lay the foundation for forisome-based smart materials synthesis in controlled and repeatable environment.

• Macromolecular Research
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• v.11 no.2
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• pp.104-109
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• 2003

A microcellular, which combines a rubber with the conventional formulation of styrene/divinylbenzene/sorbitan monooleate/water system, was prepared using high internal phase emulsion (HIPE) polymerization. Although the open microcellular foam with low density from the conventional HIPE polymerization shows highly porous characteristics with fine, regular and isotropic structure, the one having much smaller cell size is desirable for various applications. In this study, a polybutadiene was introduced to reduce the cell size with comparable properties. Major interests were focused on the effects of rubber concentration and agitation speed on the cell sizes and compression properties. Scanning electron microscopy was used to observe the microcellular morphology and compression tests were conducted to evaluate the stress-strain behaviors. It was found that the cell size decreased as rubber concentration increased, reflecting a competition between the higher viscosity of continuous phase and the lower viscosity ratio of dispersed to continuous phases due to the addition of high molecular weight rubber into the oil phase of emulsion. A correlation for the average cell size depending on agitation speed was attempted and the result was quite satisfactory.

• Polymer(Korea)
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• v.28 no.6
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• pp.509-518
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• 2004

Microdomain structures and crystallization behavior of the binary blends consisting of an asymmetric block copolymer and a homopolymer were investigated using small-angle X-ray scattering (SAXS), optical micro scope (OM) and differential scanning calorimetry (DSC). Poly(methyl methacrylate)-block-polystyrene block copolymer (PMMA-b-PS) (weight fraction of PMMA =0.53) was mixed with low molecular weight poly(vinylidene fluoride) (PVDF). As the PVDF concentration was increased, the morphological change from a lamellar to a cylindrical structure occurred. The crystallization of PVDF significantly disturbed the orientation of the pre-existing microdomain structure, resulting in a poorly ordered morphology. In the blends, PVDF exhibited unique crystallization behavior due to the PMMA block which is preferentially miscible to PVDF and the space constraint imposed by the microdomains.

• Elastomers and Composites
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• v.43 no.2
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• pp.72-81
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• 2008

Nowadays, modifying asphalt to improve the resistancy of plastic deformation or rutting on roads has been drawing attention. In this study, asphalts were modified with modifying agents and ground rubber from waste tire (GRT), and the effects of modifier and GRT on the properties of asphalt were analyzed. The Marshall stability of modified asphalt was increased by 98% and the tensile strength increased by 43% compared to straight asphalt. GRT played an important role in enhancing these properties. Viscosity tests, penetration tests and TMA analysis showed the deformation resistancy of modified asphalt. IR and GPC tests indicated that asphalt and modifier have similar chemical structures to each other, and chemical bonding between asphalt and modifier have occurred so that the molecular size lengthened.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2345-2350
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• 2009

As part of an effort to discover bioactive natural products from marine sources, we investigated the bioactive secondary metabolites from two marine isolates of the fungi, Trichoderma viride and Rhizopus stolonifer. Three cyclopentenones, myrothenones A (1) and B (2) and trichodenone A (3), were isolated from T. viride and two cyclopentenones, 2-bromomyrothenone B (4) and botrytinone (5), were isolated from R. stolonifer. The molecular structures and absolute stereochemistries of the cyclopentenones were determined from chemical and physicochemical evidence, including quantum chemistry calculations, X-ray analysis, and the circular dichroism (CD) exciton chirality method. Myrothenone A (1) displays tyrosinase inhibitory activity, with an I$C_{50}$ value of 6.6 ${\mu}M$, and is therefore more active than the positive control, kojic acid.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1363-1370
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• 2007

The geometrical structures of pyridazin-3-one derivatives (4,5-dihalopyridazin-3-one and 4-halo-5- alkoxypyridazin-3-one) with various functional and substituent groups were fully optimized using the ab initio Hartree-Fock (HF) and second order Moller-Plesset perturbation (MP2) methods. At the N2-, C4-, and C5- positions on the pyridazin-3-one rings, the structural and electronic features pertaining to the variations of the functional and substituent groups were analyzed, respectively. The trends in the variation of the bond lengths, atomic charges, and energetics (relative energy, binding energy) of the derivatives induced by changing the electron donating functional groups (X1 = OMe, OEt) to electron withdrawing groups (X1 = Cl, NO2) were examined. The variations of the bond lengths, atomic charges, and binding energies with the electron withdrawing strength of the substituent groups (Y = Me → F) were also investigated.