• Bulletin of the Korean Chemical Society
• /
• v.13 no.3
• /
• pp.306-311
• /
• 1992

The stable structures of pure ethylene and mixed ethylene-ammonia cluster ions are studied using an electron impact ionization time-of-flight mass spectrometer. Investigations on the relative cluster ion distributions of $(C_2H_4)_n(NH_3)_m^+$ under various experimental conditions suggest that $(C_2H_4)_2(NH_3)_3^+$ and $(C_2H_4)_3(NH_3)_2^+$ ions have the enhanced structural stabilities, which give insight into the feasible structure of solvated ions. For the stable configurations of these ionic species, we report an experimental evidence that both $(C_2H4)_2^+(C_2H_4)_3^+$ clusters as the central cations provide three and two hydrogen-bonding sites, respectively, for the surrounding $NH_3$ molecules. This interpretation is based on the structural stability for ethylene clusters and the intracluster ion-molecular rearrangement of the complex ion under the presence of ammonia solvent molecules.

• Bulletin of the Korean Chemical Society
• /
• v.14 no.1
• /
• pp.63-71
• /
• 1993

By use of cluster orbitals, analytic solutions of finite face-centered cubic clusters are obtained. Taking interactions between up to the second nearest neighbors into account, the forms of all the elements of the Hamiltonian matrix are found explicitly within Huckel approximation. By adopting $D_{2k}$ point group to the cluster, the matrix is simplified. We assume that the cluster orbitals can mix together only when their state indices are indentical. It is then possible to calculate various physical properties of face-centered cubic metal clusters and example are shown for palladium clusters. The results show that density of states and projected density of states are similar, qualitatively, with those obtained by extended Huckel calculation.

• Molecules and Cells
• /
• v.25 no.4
• /
• pp.538-544
• /
• 2008

Activity-dependent local translation in the dendrites of brain neurons plays an important role in the synapse-specific provision of proteins necessary for strengthening synaptic connections. In this study we carried out combined fluorescence in situ hybridization (FISH) and immunocytochemistry (IC) and showed that more than half of the eukaryotic elongation factor 1A (eEF1A) mRNA clusters overlapped with or were immediately adjacent to clusters of PSD-95, a postsynaptic marker, in the dendrites of cultured rat hippocampal neurons. Treatment of the neurons with KCl increased the density of the dendritic eEF1A mRNA clusters more than two-fold. FISH combined with IC revealed that the KCl treatment increased the density of eEF1A mRNA clusters that overlapped with or were immediately adjacent to PSD-95 clusters. These results indicate that KCl treatment increases both the density of eEF1A mRNA clusters and their synaptic association in dendrites of cultured neurons.

• Journal of the Korean Chemical Society
• /
• v.51 no.6
• /
• pp.487-498
• /
• 2007

Energy landscape is a theoretical tool used for the study of systems where cooperative processes occur such as liquid, glass, clusters, and protein. Theoretical and experimental researches related to energy landscape are introduced in this review.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.68.3-68.3
• /
• 2019

We present the preliminary results on the formation of star clusters by cloud-cloud collision. For this purpose, we perform sub-parsec scale, radiation-hydrodynamic simulations of giant molecular clouds using a sink particle algorithm. The simulations include photo-ionization, direct radiation pressure, and non-thermal radiation pressure from infrared and Lyman alpha photons. We confirm that radiation feedback from massive stars suppresses accretion onto sink particles. We examine the collision-induced star formation and discuss the possibility on the formation of a globular cluster.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.5
• /
• pp.1529-1532
• /
• 2014

• Proceedings of the Korean Society of Plant Pathology Conference
• /
• 2002.09a
• /
• pp.195-195
• /
• 2002

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.36.1-36.1
• /
• 2016

This is a presentation of the paper published as Kimm et al. 2016, ApJ, 823, 52. We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $Mhalo{\sim}4{\times}107Msun$ at z>10 using cosmological radiation-hydrodynamics simulations. We find that very compact (${\leq}1$ pc) and massive (${\sim}6{\times}105Msun$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient $Ly{\alpha}$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (${\ll}1Myr$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.

• International Journal of Industrial Entomology and Biomaterials
• /
• v.31 no.2
• /
• pp.115-126
• /
• 2015

The tropical climate prevailing in India adversely affects temperate bivoltine silkworm rearing and causes crop loss especially during summer. Identification of high temperature tolerant bivoltine breeds by screening for thermotolerance in the silkworm, Bombyx mori (Lepidoptera: Bombycidae) is an essential prerequisite for the development of thermotolerant bivoltine breeds / hybrids. Therefore, in this study, 20 silkworm breeds were reared at different temperatures (25 ± 1℃,32 ± 1℃, 34 ± 1℃ and 36 ± 1℃) for 6 h every day from 3^rd d of 5^th instar to till spinning. Significant differences (p < 0.01) were found among all the rearing traits over temperature. Based on pupation percentage, SK4C and BHR3 were identified as thermotolerant bivoltine breeds. Hierarchical clustering analysis based on rearing traits at tested temperatures grouped 20 silkworm breeds in four clusters which included one cluster each of susceptible and tolerant, and two clusters of moderately tolerant silkworm breeds. This suggests that clustering based on rearing data at high temperatures by using Euclidean distance can be an effective approach in classifying the silkworm breeds on their thermotolerance capacity. The identified breeds would be used for development of thermo tolerant bivoltine silkworm breeds / hybrids.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.11
• /
• pp.3327-3334
• /
• 2013

Infrared multiphoton dissociation (IRMPD) spectra of various protonated 1,2-diaminoethane-water clusters DAE-$H^+-(H_2O)_n$ (n = 1-6) were measured in the wavelength range of 3000-3800 $cm^{-1}$. The IRMPD spectra of the well separated ionic clusters were simulated by the MP2 method employing various basis sets. Comparison of the IRMPD spectra with the theory indicates that each cluster may exist as several low-lying conformers, and the sum spectra of the various conformers reveal almost one to one correspondence between theory and experiment. Free N-H and O-H stretches are observed in the ranges of 3400-3500 and 3600-3800 $cm^{-1}$, respectively. The $O-H{\cdots}N$ and $N-H{\cdots}O$ stretches are, however, observed in the broad region of 3000-3600 $cm^{-1}$. The theoretical calculations on DAE-$H^+-(H_2O)_n$ (n = 1-4) show gradual decrease of the average binding energy between DAE-$H^+$ and $H_2O$ as the cluster size increases, attaining the lowest value of 55 kJ/mol when n = 4. We found a low energy barrier of 21 kJ/mol to the isomerization converting the lowest energy cluster of DAE-$H^+-(H_2O)_n$ to the second lowest one.