• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.14 no.1
• /
• pp.12-16
• /
• 2004

In this study, we have investigated the development of the crystal growth stability and reproducibility for large and high-quality DAST. DAST crystal were grown from a saturated methanol solution by a slow cooling method and DAST was synthesized by the condensation of 4-methyl-n-methyl pyridinum tosylate, which was prepared from 4-pocoline and methyl toluenesulponate and 4-N-dimethyl amino-bezaldehyde in the presence of piperidine. We had synthesized DAST crystals in dry Argon atmosphere in order to avoid the formation of hydride organge co-crystals, DAST$.$$H_2O$. Since DAST molecules crystallize in a humid atmosphere, crystal structure become centrosymmetric, and then second order NLO (nonlinear optical) properties would be disappeared. We fixed the growth orientation of DAST crystal (001) surface. The crystal growth was proceeded at a cooling rate of $H_2O$/day and the cooling period is for 4 days. The dimensions of seed crystal was $2.5\times 3.6\times0.4\textrm{mm}^3$ and we have obtained a DAST crystal with the dimension of $10\times 10.5\times3.0\textrm{mm}^3$. The color of grown DAST crystal is red and it's surface appears to be metallic green.

• Journal of Korean Elementary Science Education
• /
• v.17 no.1
• /
• pp.1-10
• /
• 1998

A number of studies have shown that students have a stereotyped image of a scientist, and this image is often a rather negative. Earlier work on images of the scientist revealed to be consistent across the various social classes and across countries. This study aimed to examine a Korean students' stereotyped images of scientist, compare it with earlier work, and also find out whether students have other ideas about scientist, apart from the stereotyped image. To these purposes, modified DAST and individual interviews were carried out with 217 students and 53 students, respectively. The results are as follows : 1. Most of the students portrayed the scientist as a neat and young man with well-featured face, which was different from earlier studies. 2. Year 3 boys described the scientist as a mu, but year 3 girls as a woman. 3. Most of the students gave positive answers which were at variance with the streotyped image. 4. An interview asking only one question was a complement to DAST. It was concluded that students have private perceptions of scientists and their work, as well as a stereotyped image.

• Archives of Pharmacal Research
• /
• v.9 no.4
• /
• pp.237-242
• /
• 1986

The Synthesis of E, E, E-12-fluorofarnesol and E, Z-6-fluorofarnesol which are key intermediates for the study of biosynthesis of some sesquiterpenes, is described. E, E-Farnesyl acetate is treated with selenium dioxide to give E, E, E-12-hydroxy farnesyl acetate, whih is transformed by DAST into E, E, E-12-hydroxy farnesyl acetate, which is transformed by DAST into E, E, E,-12-fluorofarnesylacetate. The latter compound is hydrolyzed to E, E, E,-12-fluorofarnesol. The reformatsky reaction of 6-methyl-5-hepten-2-one with ethyl bromofluoroacetate affords ethyl 2-fluoro-3-hydroxy-3, 7 dimethyl-6-octanoate. This ester is acetylated and eliminated to give ethyl (Z)-2-fluoro-3, 7-dimethylocta-2, 6-dienoate, which is transformed to allyl bromide via allylic alcohol. The allyl bromide is treated with dianion of methyl acetate to give-keto ester. The $\beta$-keto ester is converted to diethyl phosphoryloxy compound. The conjugate addition of lithium dimethylcuprate to the latter compound gives fluoro ester, which is treated with DIBAL to afford E, Z-6-fluorofarnesol.

• Archives of Pharmacal Research
• /
• v.21 no.3
• /
• pp.338-343
• /
• 1998

$2^1$-Fluorohexopyranosyl nucleosides 1a and 1b which contained a bioisosteric double bond and a fluorine were synthesized in 12 steps, starting from D-galactose. During diethylaminosulfur trifluoride (DAST) fluorination, retention of stereochemistry was observed through the participation of methoxy or chloro group at the 6-posiition of the purine base. The final nucleosides 1a and 1b were found to be inactive against HIV-1 and HSV-1,2.

• Bulletin of the Korean Chemical Society
• /
• v.21 no.2
• /
• pp.274-276
• /
• 2000

• Journal of The Korean Association For Science Education
• /
• v.29 no.8
• /
• pp.934-950
• /
• 2009

This study attempts to identify the relationship between students' images of science and science learning, and their career choices. A total of 163 students (seventh graders) from three different middle schools participated in this study. Students' images of science and science learning were investigated using the Draw-A-Scientist Test (DAST) and the Draw-A-Science-Learner Test (DASLT), respectively. Then, students' drawings were analyzed using the Draw-A-Scientist Test Checklist (DAST-C) and the Draw-A-Science-Learner Test Checklist (DASLT-C). The relationship between each element composing the students' images and their career choices were analyzed. Among several elements constituting the students' image of science, 'expression,' 'lab coat,' 'oddity,' 'knowledge symbol,' 'technology symbol,' 'co-work,' 'danger,' and 'STS' showed significant differences between students who chose a science-related career and students who did not. It was also revealed that the following elements - 'expression,' 'learning type,' 'inquiry symbol,' and 'learning place' - were more significantly associated with a science-related career choice compared to other elements consisting of an image of science learning.

• Journal of Korean Society of Steel Construction
• /
• v.10 no.4 s.37
• /
• pp.677-689
• /
• 1998

In relation to concentrically loaded compression, this research is to describe, analyze, and evaluate the design strength in steel stud. The similarity and difference among load and resistance factor design specification for cold-formed steel structural members (AISI), cold-formed thin gauge members and sheeting (EC3 part 1.3), and German draft (DASt-Richtlinie 016) are introduced, discussed, and systematically evaluated. Especially, the effective width and global instability problems (flexural buckling and torsional flexural buckling) are here implied in this research. The design axial strength by dual standards (AISI and EC3) is calculated and compared using the example.

• Journal of Korean Elementary Science Education
• /
• v.28 no.1
• /
• pp.35-45
• /
• 2009

We analyzed $3^{rd}$ graders' images of scientists and science learning students. We chose $3^{rd}$ graders because this is the time when children first encounter formal science learning opportunities. Draw-A-Scientist-Test (DAST) and the revised Draw-A-Scientist-Test Checklist (DAST-C) were used to analyze students' images of scientists, whereas Drawing-A-Science-Learner- and a checklist were used to analyze students' images of science learning students. We found that $3^{rd}$ graders showed common features of scientists who wore laboratory coats but not wearing glasses, goggles or masks and smiling. While most boys drew a male scientist, about a half of girls drew female scientists. Old and weird looking images of scientists that were typically known in other literatures were not found in this study. Science learning students were not wearing lab coasts, glasses, goggles, nor masks. Most of those students were conducting chemistry related experiments, which seemed to be influenced by the $3^{rd}$ grade's science curriculum. We also found relationships among components of images of scientists and science learning students. Although $3^{rd}$ graders' images of scientists and science learning students showed common features, this typical image was not the same as the previous studies have reported. This implies that the images of scientists and science learning students have not yet fixed by $3^{rd}$ grade. Thus, this seems to be a critical time when children start developing images of scientists. Children's direct experiences in the science classroom along with environmental factors such as media exposures can influence their formation of images of scientists and science learning students.

• Journal of Korean Society of Steel Construction
• /
• v.23 no.5
• /
• pp.581-593
• /
• 2011

The underlying advantages of using thin-walled corrugatedwebs instead of plate girders with stiffeners are the elimination of instability problems associated with buckling of the thin-walled flat plate, and elimination of the need for transverse stiffeners, which alsoresults in economic advantages. This paper focuses on two aspects related to the structural design technique forsinusoidal corrugated web steel beams, and the optimum design of the beams using real-value genetic algorithms. The structural design process and design variables used in this optimization werecomposed with EN 1993-1-5, DASt-R015 standard and Pasternak et al. (2004), and the valid design capacity of shear buckling of the standards were compared. For the optimum structural design, the objective function, presented as the fullweight of the sinusoidal corrugated web beams, and the slenderness, member forces, and maximum deflection of the beam, were considered constraints. Finally, the simple beam under the uniform load was adopted as a numerical example, and the effective probability parameters of the genetic operators were considered to find the global minimum point.

• Journal of Science Education
• /
• v.34 no.2
• /
• pp.327-341
• /
• 2010

The purpose of this study is to obtain science high school students' perceptions of scientists and their work before and after the Green Investigation program with scientists. This study also attempts to determine whether the program affected the participants' perceptions of scientists and their work. A modified DAST was carried out with 64 high school students. Findings revealed that Korean science high school students had normal perceptions of scientists, such as images of 20 to 30 year old males wearing laboratory coats and working alone in research labs with test tubes, flasks, and several machines in the background. After the intervention, students drew fewer typical items representing scientists and had significantly different perceptions of their work places between the pretest (M=1.69, SD=1.14) and posttest (M=1.96, SD=1.24, t=4.43, p<0.001) with the eta squared statistics (.24). These findings reflect the need for continued efforts of developing green investigation programs with scientists for students. Some future studies based on this study are also introduced.