• Molecules and Cells
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• v.20 no.1
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• pp.1-16
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• 2005

The peptidyl transferase center (PTC) is located in a protein free environment, thus confirming that the ribosome is a ribozyme. This arched void has dimensions suitable for accommodating the 3'ends of the A-and the P-site tRNAs, and is situated within a universal sizable symmetry-related region that connects all ribosomal functional centers involved in amino-acid polymerization. The linkage between the elaborate PTC architecture and the A-site tRNA position revealed that the A-to P-site passage of the tRNA 3'end is performed by a rotatory motion, which leads to stereochemistry suitable for peptide bond formation and for substrate mediated catalysis, thus suggesting that the PTC evolved by genefusion. Adjacent to the PTC is the entrance of the protein exit tunnel, shown to play active roles in sequence-specific gating of nascent chains and in responding to cellular signals. This tunnel also provides a site that may be exploited for local co-translational folding and seems to assist in nascent chain trafficking into the hydrophobic space formed by the first bacterial chaperone, the trigger factor. Many antibiotics target ribosomes. Although the ribosome is highly conserved, subtle sequence and/or conformational variations enable drug selectivity, thus facilitating clinical usage. Comparisons of high-resolution structures of complexes of antibiotics bound to ribosomes from eubacteria resembling pathogens, to an archaeon that shares properties with eukaryotes and to its mutant that allows antibiotics binding, demonstrated the unambiguous difference between mere binding and therapeutical effectiveness. The observed variability in antibiotics inhibitory modes, accompanied by the elucidation of the structural basis to antibiotics mechanism justifies expectations for structural based improved properties of existing compounds as well as for the development of novel drugs.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.444-453
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• 2014

A throttleable rocket engine enables operational possibilities such as the docking of spacecraft, maneuvering in a certain orbit and landing on a planet's surface, altitude control, and entrance to atmosphere-less planets. Thus, throttling methods have long been researched. However, dual-manifold injectors, which represent one throttling method, have been investigated less than others. In this study, dual-manifold and single-manifold injectors were compared to determine the characteristics of dual-manifold injectors. Also, the effects of gas injection were investigated with various F/O ratios. To investigate the characteristics, mass flow rate, spray pattern, spray angle, and droplet size were measured. The spray angle and droplet size were captured by indirect photography. About 30 images were taken to assess the spray patterns and spray angle. Also, 700 images were analyzed to understand the droplet distribution and targeting area, moving to the right from the centerline with 1.11-cm intervals. The droplet size was obtained from an image processing procedure. From the results, the spray angle showed two transition regions, due to swirl momentum in the swirl chamber regardless of the F/O ratio. The droplet size showed similar trends in both dual-manifold and single-manifold injectors except in the low mass flow rate region. In the case of the dual- manifold injector, the spray cone was not fully developed in the low mass flow rate region due to low angular momentum in the swirl chamber.

• The Journal of Engineering Geology
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• v.20 no.2
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• pp.147-153
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• 2010

Cut-off wall with a low permeability can be constructed to prevent groundwater seepage in spillway tunnel areas. Three spillway tunnels are constructed in Im-ha multipurpose dam region and three types of cut-off walls with a variety of directions and scales are designed. As a result of MODFLOW modeling to assess the effect of cut-off wall for three types, groundwater inflows to the tunnels range from 64.26 $m^3/day$ to 65.49 $m^3/day$ and also they through a cut-off wall section from a reservoir do from 44.08 $m^3/day$ to 45.31 $m^3/day$ and it does not show any significant difference among them. Therefore, a construction process and an environmental conservation rather than the effectiveness of cut-off wall need to be considered to select the best cut-off wall in this region.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.22-29
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• 2001

The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.5
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• pp.263-268
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• 2015

In this study, the performance of an ejector in the refrigeration cycle was experimentally studied using R600a. The performance of the ejector is analyzed according to the inlet pressure and nozzle position. The increase in the primary nozzle pressure decreased the pressure difference across the ejector. In the low entrainment region, the increased suction flow pressure led to an increase in the pressure difference. In the high entrainment region, the pressure difference was inversely proportional to the suction pressure. The effects of nozzle position ($L_n$) were also analyzed and for $L_n<0$, the decreased suction chamber volume led to a large pressure drop with the small increase in the suction mass flow rate. For $L_n>0$, the increased $L_n$ disturbed the primary nozzle flow and thus an increase in the primary nozzle flow increased the pressure lifting effect. In contrast, the increased suction mass flow rate decreased the pressure difference. When the nozzle outlet was located at the mixing part entrance ($L_n=0$), the ejector showed the highest pressure lifting effect.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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• pp.15-29
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• 1998

The numerical simulation of heavy precipitation event occurred in the central Korean Peninsula on July 26-28, 1996 was performed using the fine mesh model. ARPS (Advanced Regional Prediction System) developed by the CAPS (Center for Analysis and Prediction of Storms). Usually, the heavy rainfalls occurred at late July in the Korean Peninsula were difficult to predict, and showed very strong rainfall intensity. As results, they caused a great loss of life and property. As it usual, this case was unsuccessful to predict the location of rain band and the precipitation intensity with the coarse-mesh model. The same case was, however, simulated well with fine-mesh storm-scale model, ARPS. Moisture band at 850 hPa appeared along the Changma Front in the area of China through central Korea passed Yellow Sea. Also the low-level jet at 700 hPa existed in the Yellow Sea through central Korea and they together offered favorable condition to induce heavy rainfall in that area. The convective activities developed to a meso-scale convective system were observed at near the Yangtze River and moved to the central Korean Peninsula. Furthermore, the intrusion of warm and moist air, origninated from typhoon, into the Asia Continent might result in heavy rainfall formation through redistribution of moisture and heat. In the vertical circulation, the heavy rainfall was formed between the upper- and low-level jets, especially, the entrance region of the upper-level jet above the exit the region of the low-level jet. The low level convergence, the upper level divergence and the strong vertical wind were organized to the very north of the low level jet and concentrated on tens to hundreds km horizontal distance. These result represent the upper- and low-level jets are one of the most important reasons on the formation of heavy precipitation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.48-54
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• 2020

Numerical analysis was carried out to analyze the flow fields and mechanical output of a rotor for various positions and inlet flow rates in a shroud, and it was compared with experimental data. Rotor and seawater current largely affects the flow field characteristics in the shroud system. Especially the mechanical output of the rotor increased with axial position near the center of the cylinder, and it gradually decreased close to the entrance and exit. Also, the rotor output increased with the inlet velocity. Axial and angular momentum of flow along the cylinder region rapidly increased and reached a peak, and then decreased as it passed through the rotor, while there was no significant change in the cylinder region. It is expected that these results can be used as applicable design data for the development of the tidal power generation system.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.847-856
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• 2013

In this study, thermal performance of recuperators with plain and offset strip fins is investigated to enhance the thermal efficiency of a micro gas turbine. Thermal cycle analysis is conducted to determine major design parameters of a single-pass counterflow recuperator. In order to evaluate the performance of the recuperator, the effectiveness and the pressure drop in the recuperators are chosen as the objective function and the design constraint, respectively. The optimized geometries for internal structure of the recuperators with plain and offset strip fins are obtained with varying the fin spacing and height. From the result, the recuperator with offset strip fins has better thermal performance when the fin spacing, s, is smaller than 1.45mm and the thermal performance of the recuperator with plain rectangular fins is higher than that with offset strip fins in the region of $s{\geq}1.45mm$. In addition, it is found that the entrance region effect and the longitudinal wall heat conduction effect should be taken into account for accurately predicting the thermal performance of the recuperators with both plain and offset strip fins.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2767-2773
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• 2021

We used the GEANT4 Monte Carlo MC Toolkit to simulate carbon ion beams incident on water, tissue, and bone, taking into account nuclear fragmentation reactions. Upon increasing the energy of the primary beam, the position of the Bragg-Peak transfers to a location deeper inside the phantom. For different materials, the peak is located at a shallower depth along the beam direction and becomes sharper with increasing electron density NZ. Subsequently, the generated depth dose of the Bragg curve is then benchmarked with experimental data from GSI in Germany. The results exhibit a reasonable correlation with GSI experimental data with an accuracy of between 0.02 and 0.08 cm, thus establishing the basis to adopt MC in heavy-ion treatment planning. The Kolmogorov-Smirnov K-S test further ascertained from a statistical point of view that the simulation data matched the experimentally measured data very well. The two-dimensional isodose contours at the entrance were compared to those around the peak position and in the tail region beyond the peak, showing that bone produces more dose, in comparison to both water and tissue, due to secondary doses. In the water, the results show that the maximum energy deposited per fragment is mainly attributed to secondary carbon ions, followed by secondary boron and beryllium. Furthermore, the number of protons produced is the highest, thus making the maximum contribution to the total dose deposition in the tail region. Finally, the associated spectra of neutrons and photons were analyzed. The mean neutron energy value was found to be 16.29 MeV, and 1.03 MeV for the secondary gamma. However, the neutron dose was found to be negligible as compared to the total dose due to their longer range.

• Journal of the Korean GEO-environmental Society
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• v.20 no.4
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• pp.17-21
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• 2019

In the cold region, the frozen damages in highway tunnels and regular road tunnels have widely been investigated and reported, but the measurement has not been sufficient made. The average temperature in cold region is below the zero, resulting in that the damage due to freezing at the entrance/exit of tunnel is more severe than in the middle of tunnel. In this study, a heating element was developed to prevent the tunnel lining from being frozen by enforcing to increase the temperature of tunnel lining. Then field tests using the developed heating element were performed and it was ensured that the temperature of tunnel lining increased after a certain time.