• Nuclear Engineering and Technology
• /
• v.41 no.6
• /
• pp.753-764
• /
• 2009

JAEA started the LSTF experiments in 1985 for the fourth stage of the ROSA Program (ROSA-IV) for the LWR thermal-hydraulic safety research to identify and investigate the thermal-hydraulic phenomena and to confirm the effectiveness of ECCS during small-break LOCAs and operational transients. The LSTF experiments are underway for the ROSA-V Program and the OECD/NEA ROSA Project that intends to resolve issues in thermal-hydraulic analyses relevant to LWR safety. Six types of the LSTF experiments have been done for both the system integral and separate-effect experiments among international members from 14 countries. Results of four experiments for the ROSA Project are briefly presented with analysis by a best-estimate (BE) code and a computational fluid dynamics (CFD) code to illustrate the capability of the LSTF and codes to simulate the thermal-hydraulic phenomena that may appear during SBLOCAs and transients. The thermal-hydraulic phenomena dealt with are coolant mixing and temperature stratification, water hammer up to high system pressure, natural circulation under high core power condition, and non-condensable gas effect during asymmetric SG depressurization as an AM action.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.4
• /
• pp.1187-1194
• /
• 2011

The hydrogen abstraction reaction of $CF_3CH_2CHO$ + OH has been studied theoretically by dual-level direct dynamics method. Two stable conformers, trans- and cis-$CF_3CH_2CHO$, have been located, and there are four distinct OH hydrogen-abstraction channels from t-$CF_3CH_2CHO$ and two channels from c-$CF_3CH_2CHO$. The required potential energy surface information for the kinetic calculation was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. The rate constants, which were calculated using improved canonical transitionstate theory with small-curvature tunneling correction (ICVT/SCT) were fitted by a four-parameter Arrhenius equation. It is shown that the reaction proceeds predominantly via the H-abstraction from the -CHO group over the temperature range 200-2000 K. The calculated rate constants were in good agreement with the experimental data between 263 and 358 K.

• Journal of Microbiology and Biotechnology
• /
• v.30 no.9
• /
• pp.1436-1442
• /
• 2020

Amylosucrase (ASase, E.C. 2.4.1.4) is capable of efficient glucose transfer from sucrose, acting as the sole donor molecule, to various functional acceptor compounds, such as polyphenols and flavonoids. An ASase variant from Deinococcus geothermalis, in which the 226^th alanine is replaced with asparagine (DgAS-A226N), shows increased polymerization activity due to changes in the flexibility of the loop near the active site. In this study, we further investigated how the mutation modulates the enzymatic activity of DgAS using molecular dynamics and docking simulations to evaluate interactions between the enzyme and phenolic compounds. The computational analysis revealed that the A226N mutation could induce and stabilize structural changes near the substrate-binding site to increase glucose transfer efficiency to phenolic compounds. Kinetic parameters of DgAS-A226N and WT DgAS were determined with sucrose and 4-methylumbelliferone (MU) as donor and acceptor molecules, respectively. The k_cat/K_m value of DgAS-A226N with MU (6.352 mM^-1min^-1) was significantly higher than that of DgAS (5.296 mM^-1min^-1). The enzymatic activity was tested with a small phenolic compound, hydroquinone, and there was a 1.4-fold increase in α-arbutin production. From the results of the study, it was concluded that DgAS-A226N has improved acceptor specificity toward small phenolic compounds by way of stabilizing the active conformation of these compounds.

• Korean Journal of Mineralogy and Petrology
• /
• v.33 no.1
• /
• pp.19-28
• /
• 2020

Ranciéte is a hexagonal phyllomanganate mineral containing random Mn(IV) vacancies with hydrated Ca²⁺ cations charged balanced as interlayer cations. Its Mn²⁺ analogue is called takanelite, and ranciéite and takanelite are regarded as end-members of a solid solution series of (Ca²⁺,Mn²⁺)Mn₄O₉·nH₂O. Because the minerals are found as very small particles associated with other minerals, the crystal structures of the solid solution series have yet to be defined. In this research, we conducted classical molecular dynamics (MD) simulations of ranciéite and takanelite by varying the Mn²⁺/Ca²⁺ interlayer cation ratio to find relations between the interlayer cations and mineral structures. MD simulation results of chalcophanite group minerals are compared with experimental results to verify our method applied. Then, lattice parameters of ranciéite and takanelite models are presented along with detailed interlayer structures as to the distribution and coordination of cations and water molecules. This study shows the potentials of MD simulations in entangling complicated phyllomanganates structures.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.7
• /
• pp.2238-2246
• /
• 2012

Molecular dynamics simulations have been performed to investigate hydrogen bonding characteristics of hydroxyl groups in glucose aqueous solutions with different concentrations. The hydrogen bonding abilities and strength of different O and H atom types have been calculated and compared. The acceptor/donor efficiencies have been predicted and it has been found that: (1) O2-HO2 and O3-HO3 are more efficient intramolecular hydrogen bonding acceptors than donors; (2) O1-HO1, O4-HO4 and O6-HO6 are more efficient intramolecular hydrogen bonding donors than acceptors; (5) O1-HO1 and O6-HO6 are more efficient intermolecular hydrogen bonding acceptors than donors while hydroxyl groups O2-HO2 and O4-HO4 are more efficient intermolecular hydrogen bonding donors than acceptors. The hydrogen bonding abilities of hydroxyl groups revealed that: (1) the hydrogen bonding ability of OH2-$H_w$ is larger than that of hydroxyl groups in glucose; (2) among the hydroxyl groups in glucose, the hydrogen bonding ability of O6-HO6 is the largest and the hydrogen bonding ability of O4-HO4 is the smallest; (3) the intermolecular hydrogen bonding ability of O6-HO6 is the largest; (4) the order for intramolecular hydrogen bonding abilities (from large to small) is O2-HO2, O1-HO1, O3-HO3, O6-HO6 and O4-HO4.

• Bulletin of the Korean Mathematical Society
• /
• v.54 no.6
• /
• pp.2043-2051
• /
• 2017

Consider a sequence of compactly supported Hamiltonian diffeomorphisms ${\phi}_k$ of an exact symplectic manifold, all of which are "graphical" in the sense that their graphs are identified by a Darboux-Weinstein chart with the image of a one-form. We show by an elementary argument that if the ${\phi}_k$ $C^0$-converge to the identity, then their Calabi invariants converge to zero. This generalizes a result of Oh, in which the ambient manifold was the two-disk and an additional assumption was made on the Hamiltonians generating the ${\phi}_k$. We discuss connections to the open problem of whether the Calabi homomorphism extends to the Hamiltonian homeomorphism group. The proof is based on a relationship between the Calabi invariant of a $C^0$-small Hamiltonian diffeomorphism and the generalized phase function of its graph.

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.1491-1495
• /
• 2004

For the evaluation of the mobile robot performance in complex environments, the experimental approach in an actual physical environment has been commonly taken. In the physical experimental approach, however, it is quite difficult to define the proper environment for the evaluation due to the lack of commonly agreed characteristics of the test environment. Particularly the number of combinations of types and physical parameters of the obstacles that the mobile robot is expected to deal with is practically unlimited. In an effort to simplify and improve the effectiveness of the evaluation process, we propose an evaluation method using decomposed environmental elements, where we evaluated the performance of the robot for a small group of simple and decomposed obstacle components, for examples projection and slope, instead of a large group of complicated random obstacles. The paper describes a set of simple obstacle models and performance parameters that we have chosen for the effective evaluation process. As an alternative to the physical experimental evaluation approach, in this paper, we used a virtual evaluation environment where the robot and the physical test environment has been modeled using a commercial multi-body dynamics analysis packaged called RecurDyn.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.1
• /
• pp.37.2-37.2
• /
• 2011

Our previous study on tiny pores (R < 2") observed by HINODE/Solar Optical Telescope (SOT) revealed that the plasma in the pores at the photosphere is always moving down and the pores are surrounded by the strong downward motions (highly red-shifted) of neighboring granulations. From this study, we speculated that the flow motions above the pore should be related with the motions at the photosphere, since the pore is strong magnetic field region. Meanwhile, SNU and KASI installed Fast Imaging Solar Spectrograph (FISS) in the Cude room of the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory. FISS is a unique system that can do imaging of H-alpha and Ca II 8542 band simultaneously, which is quite suitable for studying of dynamics of chromosphere. To get some clue on the relationship between the photospheric and low-chromospheric motions at the pore region, we took a coordinate observation with NST/FISS and Hinode/SOT for new emerging active region (AR11117) on October 26, 2010. In the observed region, we could find two tiny pores and two small magnetic islands (SMIs), which have similar magnetic flux with the pores but does not look dark. Magnetic flux density and Doppler velocities at the photosphere are estimated by applying the center-of-gravity (COG) method to the HINODE/spectropolarimeter (SP) data. The line-of-sight motions above the photosphere are determined by adopting the bisector method to the wing spectra of Ha and CaII 8542 lines. As results, we found the followings. (1) There are upflow motion on the pores and downflow motion on the SMIs. (2) Towards the CaII 8542 line center, upflow motion decrease and turn to downward motion in pores, while the speed of down flow motion increases in the SMIs. (3) There is oscillating motion above pores and the SMIs, and this motion keep its pattern along the height. (4) As height increase, there is a general tendency of the speed shift to downward on pores and the SMIs. This is more clearly seen on the other regions of stronger magnetic field. In this talk, we will present preliminary understanding of the coupling of pore dynamics between the photosphere and the low-chromosphere.

• Proceedings of the Korean Environmental Sciences Society Conference
• /
• 2000.05a
• /
• pp.251-254
• /
• 2000

In this study, we investigated vertical distribution and seasonal changes of phytophlankton community in the Hae-Dong Reservoir from March 1999 to Feburary 2000. This reservoir is relativly small (surface area, 2.7 $km^2$) and is the source of drinking water supply to the eastern part of Pusan City. Samples were collected at 2 sites (1, 3, and 6 m; site 1, in front of the dam; site 2, inlet). The dominant group was Bacillriophyceae at both sites (over 63%), and other groups exhibited seasonal changes (high cyanobacterial density in summer; green algal communities in winter). Chrysophyceae and Dinophyceae were maintained lower level during the study period. Along the water depth, all classess of phytoplankton did not show distintive vertical distribution at both sites except during the blue-green algal bloom in the middle of July and late September. The phytoplankton community dynamics in the Hoe-Dong Reservoir was strongly affected by the hydrological factors such as concentrated precipitation and short retention time.

• Journal of Labour Economics
• /
• v.23 no.1
• /
• pp.137-165
• /
• 2000

This paper empirically analyzes the behavioral patterns of the labor flows surrounding self-employment. One of the findings is that, while a substantial portion of the labor flows into (and from) the self-employment sector is a movement from (and into) the non-employment, such flows are largely confined to a relatively small group of marginal workers. Still, the share of those marginal workers among the self-employed has declined steadily at least until the outburst of the financial crisis in 1997, evidencing that the job stability has been increased in this sector. On the other hand, the expected duration of self-employment has shown a downward trend up until 1990 but has increased since then. Such a trend reversal is also observed in the proportion of the labor force self-employed, indicating that the former is at least partly responsible for the latter.