• Molecules and Cells
• /
• 제20권1호
• /
• pp.1-16
• /
• 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.

• Korean Chemical Engineering Research
• /
• 제56권6호
• /
• pp.826-831
• /
• 2018

This study presents fabrication of bi-compartmental particles labeled by multiple fluorescence. To compartmentalize fluorescent expression at the particle, two fluorescent dyes with less overlap of the excitation and emission spectra are selected. To ensure the fluorescence stability, the fluorescent dyes contain acrylate functional groups in the molecules so that they can be cross-linked together with monomers constituting the particle. Strong fluorescent expression and compartmentalization were observed at the particle fabricated using the selected fluorescent dyes through confocal microscopy. Furthermore, long-term fluorescence stability was verified by measuring fluorescent expression and intensity for 4 weeks. We anticipate that the bi-compartmental particles labeled by multiple fluorescence can be widely used for multi-target drug delivery system, analysis of 3 dimensional Brownian motion, and investigation of 3 dimensional complex self-assembled morphologies.

• Journal of the Korean Chemical Society
• /
• 제50권4호
• /
• pp.338-345
• /
• 2006

study investigated the effect of an instruction using generating analogy on scientific conceptual understanding, science learning motivation, attitude toward science instruction, and perception of instruction. Two classes of seventh graders at a middle school in Seoul were randomly assigned to the treatment group and the control group, and they were taught about the motion of molecules for 5 class hours. The instruction for treatment group was developed based on the Glynns Teaching-With-Analogy model. Two-way ANCOVA results revealed that the scores of the treatment group were significantly higher than those of the control group in the conception test. However, there was no significant difference between two groups in the science learning motivation test and the test on the attitude toward science instruction. Survey results on the students perception of instruction showed that generating analogy was hard for the greater part of students, and finding appropriate analog was the most difficult work. Educational implications are discussed.

• Particle and aerosol research
• /
• 제9권2호
• /
• pp.103-110
• /
• 2013

The electrostatic precipitator (ESP) has been used for degrading atmospheric pollutants. These devices induce the electrical forces to facilitate the removal of particulate pollutants. The ions travel from the high voltage electrode to the grounded electrode by Coulomb force induced by the electric field when a high voltage is applied between two electrodes. The ions collide with gas molecules and exchange momentum with each other thus inducing fluid motion, electrohydrodynamic (EHD) flow. In this study, for the simulation of electric field and EHD flow in ESPs, an open source EHD solver, "espFoam", has been developed using open source CFD toolbox, OpenFOAM(R) (Open Field Operation and Manipulation). The electric potential distribution and ionic space charge density distribution were obtained with the developed solver, and validated with experimental results in the literature. The comparison results showed good agreement. Turbulence model is also incorporated to simulate turbulent flow; hence the developed solver can analyze laminar and turbulent flow. In distributions of electric potential and space charge, the distributions become distorted and asymmetric as the flow velocity increases. The effect of electrical drift flow was investigated for different flow velocities and the secondary flow in a flow of low velocity is successfully predicted.

• Nuclear Engineering and Technology
• /
• 제11권1호
• /
• pp.1-20
• /
• 1979

Neutron inelastic scattering studies on polycrystalline hydrates, NaBr-2$H_2O$ and BaCl$_2$-2$H_2O$ have been performed to observe librational modes. Assuming all observed peaks are from the $H_2O$ librational origin, the weighted frequency distribution functions are obtained by eliminating the contributions from the higher order processes. All of theoretical frequencies obtained using FG matrix method are dus to highly mixed modes, and therefore the modes identified as significant $H_2O$ librationat modes from their large potential energy distributions are assigned to the observed peaks. The H-bond interactions are estimated using a modified Lippincott Schroeder potential function, and the applicability of the potential function to the H-bond with highly bent or bifurcated configuration is examined on the basis of the shape of $H_2O$ librational potential energies. Some discussions are given on the usefulness of introducing O-H…Y bending terms in addition to the H…Y stretching in similar frequency calculation in order to obtain more information on the nature of H-bond. Also the purity and symmetry properties of the $H_2O$ librational modes are discussed using group theoretical analyses.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• 제37권4호
• /
• pp.443-446
• /
• 2013

An infrared thermography technique can be used to inspect a large area simultaneously and to detect defects such as cracks or delaminations in real time. Infrared thermography is a technique in which visual images are formed from the infrared range from subjects according to their thermal radiation. The molecules of all objects are disturbed by heat, and the molecular motion becomes more active when the temperature rises and less active when the temperature falls. In this study, the applicability and feasibility of ultrasound thermography for detecting defects in an engine block, which is a key component in the automobile industry, were verified. A nondestructive reliability test was conducted to study the defects, after which the results were analyzed.

• Journal of The Korean Association For Science Education
• /
• 제22권3호
• /
• pp.508-516
• /
• 2002

This study investigated the influences of group composition in cooperative computer-assisted instruction (CAI) upon students' conceptual understandings, application abilities, learning motivations, and the perceptions of involvement. Seventh graders (N=97) were selected from a co-ed middle school in Seoul, and taught about 'motion of molecules' for 5 class hours. In the two treatment groups with cooperative CAI strategy, homogeneous and heterogeneous small groups were organized by the previous science achievement. Traditional instructions were administered to the comparison group. Two-way ANCOVA results revealed that the scores of the conception test for the treatment groups were significantly higher than those for the comparison group. However, there was no difference between the homogeneous and the heterogeneous groups. The scores of the three groups did not differ significantly in the application test and the learning motivation test. However, the perceptions of involvement for the treatment groups were more positive than those for the comparison group.

• Journal of the Korean Chemical Society
• /
• 제56권3호
• /
• pp.363-370
• /
• 2012

The purpose of the study was to classify scientific models in the seventh grade science textbooks of the 2007 revised science curriculum. The three chapters of 'three states of material', 'motion of molecule', and 'change of state and energy' were investigated. There were two types of the scientific model as 'mode of representation' and 'attribute of representation'. The mode of representation was composed of 'action model', 'analogical model', 'symbolic model', and 'theoretical model' and the attribute of representation was composed of 'static model' and 'dynamic model'. The results showed that the action model and the analogical model were used primarily in mode of representation. The dynamic model were widely used in attribute of representation. Area of matters dealt with conception of molecules and aimed for students to understand the arrangement and movement of molecule microscopically about macroscopic state in a daily life. Tis study could help to recognize the limitations of scientific models on current textbooks and offer more useful information in planning lessons and organizing textbooks for the future.

• Journal of Biomedical Engineering Research
• /
• 제25권6호
• /
• pp.439-445
• /
• 2004

Diffusion tensor image(DTI) exploits the random diffusional motion of water molecules. This method is useful for the characterization of the architecture of tissues. In some tissues, such as muscle or cerebral white matter, cellular arrangement shows a strongly preferred direction of water diffusion, i.e., the diffusion is anisotropic. The degree of anisotropy is often represented using diffusion anisotropy indices (relative anisotropy(RA), fractional anisotropy(FA), volume ratio(VR)). In this study, FA images were obtained using different gradient schemes(N=6, 11, 23, 35. 47). Mean values and the standard deviations of FA were then measured at several anatomic locations for each scheme. The results showed that both mean values and the standard deviations of FA were decreased as the number of gradient directions were increased. Also, the standard error of ADC measurement decreased as the number of diffusion gradient directions increased. In conclusion, different gradient schemes showed a significantly different noise performance and the schem with more gradient directions clearly improved the quality of the FA images. But considering acquisition time of image and standard deviation of FA, 23 gradient directions is clinically optimal.

• Journal of The Korean Association For Science Education
• /
• 제27권7호
• /
• pp.631-638
• /
• 2007

This study investigated the influences of a student-centered analogical instruction using physical analogies upon students' conception and application, retention of conception and application, perceptions of science classroom environment, and perceptions of analogical instruction. Six classes of seventh graders (N=208) at a middle school in Seoul were assigned to the control, the teacher-centered analogy (TCA), and the student-centered analogy (SCA) groups. They were taught about 'three states of matter' and 'motion of molecules' for 8 class hours. Analysis of the results revealed that the scores of the SCA group were significantly higher than those of the other groups in the conception test, retention test of conception and application, and perception test of science classroom environment. The scores of the SCA group in the application test were also higher than those of the other groups, but there was a significant difference only between the control and the SCA groups. The TCA group performed significantly better than the control group only in the test of the retention of application. In addition, the students in the SCA group exhibited more positive perceptions of the analogical instruction than those in the TCA group. Educational implications are discussed.