• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.3C
• /
• pp.234-240
• /
• 2002

A power amplifier with AlGaAs/InGaAs/GaAs HBT's has been developed for customer premise equipments of the quasi millimeter-wave frequency-band broadband wireless local loop(BWLL) system. Parameters of the linear and nonlinear equivalent circuits for a common base HBT have been extracted by a fitting method. The amplifier has been designed through the linear and nonlinear circuit simulations and fabricated on a ceramic substrate for a hybrid IC. The amplifier has produced a 25.5-dBm output power with 35% power-added efficiency(PAE) at 24.4 GHz and achieved a 7.5-dB linear power gain at 24.8 GHz. In 24.25 ∼24.75 GHz band, the amplifier has exhibited a saturated output over larger than 22 dBm and PAE higher than 25%.

• Tribology and Lubricants
• /
• v.10 no.3
• /
• pp.18-28
• /
• 1994

Sliding friction between a spherical pin of 8mm in diameter and flat (disk) substrates coated with vacuum-deposited thin film was measured under ultra high vacuum pressure for various materials, various rates of film supply (8~210 nm/min), various sliding velocities (1.5~67.0 mm/s). It was found that the most effective lubrication was obtained when the adhesion between $Si_3N_4$ pin and SUS440C disk was high and that between $Si_3N_4$ pin and $Si_3N_4$ disk was low. When In film was used as a lubricant between $Si_3N_4$ pin and stainless steel disk, the friction coefficient had a value as low as 0.04. In this case, the normal load W and the sliding speed V were expressed as 10N and 24 mm/s for $10^{-6}Pa$. The dependence of $\mu$ on the thickness h of the Ag film, which was used as a lubricant between $Si_3N_4$ pin and SUS440C (Q) disk was expressed as $\mu$=0.12 for W=10N and V=24mm/s when the film was thicker than 100nm. A brief discussion on these relations is presented from the viewpoint of the real contact area.

• Korean Journal of Environmental Biology
• /
• v.32 no.3
• /
• pp.225-233
• /
• 2014

In this study, we investigated the changes in the physiological and histological traits of a sea squirt (Halocynthia roretzi) with the emergence of the soft tunic syndrome induced by the water temperature control (6, 9, 12, 15, 18, 21, 24 and $27^{\circ}C$). It was observed that the induction rate of the soft tunic syndrome was highest at $15^{\circ}C$, but lowest at $24^{\circ}C$. Based on the tunic color condition and contraction strength, the whole process were classified into 4 stages as S0, S1, S2 and S3. Interestingly, there were significant differences in oxygen consumption and filtration rate were observed during S0-S3. The most distinctive aspects were change of blood cell composition at stage S3, whereas multi-vacuole cell ratio was decreased by 1/2 and morula cell ratio expanded about 10 times during S0-S3. Further, change of organ structure started following the syndrome such as degeneration of epithelial cells, microfilaments, increment in hemocytes and damage in muscle fiber have been detected in tunic, siphon, branchial sac, body wall musculature and pyloric gland. Briefly, our study results indicated that the normal physiological functions of the sea squirt can be affected due to the soft tunic syndrome induced by water temperature.

• Korean Journal of Ichthyology
• /
• v.13 no.4
• /
• pp.261-266
• /
• 2001

The ichthyofauna and the structure of fish community were surveyed from June to August in 2000 at four stations of the Wondong marsh, Yangsan city in Kyungnam province. During the study period, 24 species belonging to eight families were collected. Cyprinid fish occupied 62.5% (15 species) and cobitid and centrarchid fish 8.3% (each 2 species). According to relative abundance in the whole marsh, Z. platypus (23.2%) was dominant species and S. gracilis majimae (14.2%) was subdominant species. M. salmoides (9.6%), C. auratus (8.3%), P. herzi (8.3%), M. yaluensis (6.5%), M. anguillicaudatus (4.0%), L. macrochirus (3.4%), P. parva (2.8%), R. ocellatus (2.5%), C. brevicauda (2.5%), C. sinensis (2.5%) and O. platycephala (2.2%) were common species and C. carpio, A. rhombeus, H. labeo, S. variegatus wakiyae, S. chankaensis tsuchigae, Z. temmincki, O. bidens, S. asotus, C. herzi, R. brunneus, C. argus were rare specieswhich occupied less than 2.0% in relative abundance. Six species of S. variegatus wakiyae, S. chankaensis tsuchigae, S. gracilis majimae, M. yaluensis, C. herzi and O. platycephala in observed species were known as endemic species. By analyzing of fish community in the surveyed area, the species diversity and evenness of the fishes were high but dominance was low. And the similarity of the fish species among the sites was mid-grade as more than 0.55 in index.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.3
• /
• pp.274-278
• /
• 2003

New banana-shaped achiral compounds, 1,3-phenylene bis [4-{4-(alkenyloxy) phenyliminomethyl}benzoate]s were synthesized by varying the length of alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C $(Sm\;C^*)$ phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and triangular wave method. The presence of vinyl groups at the terminals of linear side wings in the banana-shaped achiral molecules containing Schiff's base mesogen induced a decrease in melting temperature and formation of the switchable $(Sm\;C^*)$ phase in the melt. The smectic phases having the octenyloxy group such as $(CH_2)_6CH=CH_2$ showed ferroelctric switching, and their values of spontaneous polarization on reversal of an applied electric field were 120 nC/cm² (X=H) and 225 nC/ cm² (X=F), respectively. We could obtain ferroelectric phases by controlling the number of carbon atom in alkenyloxy chain of a bent-core molecule.

• Journal of Microbiology
• /
• v.37 no.2
• /
• pp.102-110
• /
• 1999

Genetic determinant for the secondary metabolism was studied in heterologous expression in Streptomyces lividans TK-24 using Streptomyces griseus ATCC 10137 as a donor strain. Chromosomal DNA of S. griseus was ligated into the high-copy number Streptomyces shuttle plasmid, pWHM3, and introduced into S. lividans TK-24. A plasmid clone with 4.3-kb BamHI DNA of S. griseus (pMJJ201) was isolated by detecting for stimulatory effect on actinorhodin production by visual inspection. The 4.3-kb BamHI DNA was cloned into pWHM3 under the control of the strong constitutive ermEp promoter in both directions (pMJJ202); ermEp promoter-mediated transcription for coding sequence reading right to left: pMJJ203; ermEp promoter-mediated transcription for coding sequence reading left to right) and reintroduced into S. lividans TK-24. The production of actinorhodin was markedly stimulated due to introduction of pMJJ202 on regeneration agar. The introduction of pMJJ202 also stimulated production of actinorhodin and undecylproidigiosin in submerged culture employing the actinorhodin production medium. Introduction of pMJJ203 resulted in a marked decrease of production of the two pigments. Nucleotide sequence analysis of the 4.3-kb region revealed three coding sequences: two coding sequences reading left to right, ORF1 and ORF2, one coding sequence reading right to left, ORF3. Therefore, it was suggested that the ORF3 product was responsible for the stimulation of antibiotic production. The C-terminal region of ORF3 product showed a local alignment with Myb-related transcriptional factors, which implicated that the ORF3 product might be a novel DNA-binding protein related to the regulation of secondary metabolism in Streptomyces.

• Transactions of Materials Processing
• /
• v.24 no.1
• /
• pp.44-51
• /
• 2015

The current study seeks to examine the effects of V and C additions on the mechanical and low thermal expansion properties of a high strength invar base alloy. The base alloy (Fe-36%Ni-0.9%Co-2.75%Mo-0.7Cr-0.23Mn-0.17Si-0.3%C, wt.%) contains $Mo_2C$ carbides, which form as the main precipitate. In contrast, alloys with additions of 0.4%V+0.3%C (alloy A) or 0.4%V+0.45%C (alloy B) contain $Mo_2C$+[V, Mo]C carbides. The average thermal expansion coefficients of these high strength invar based alloys were measured in the range of $5.16{\sim}5.43{\mu}m/m{\cdot}^{\circ}C$ for temperatures of $15{\sim}230^{\circ}C$. Moreover, alloy B showed lower thermal expansion coefficient than the other alloys in this temperature range. For the mechanical properties, the [V, Mo]C improved hardness and strengths(Y.S. and T.S.) of the high strength invar base alloy. T.S.(tensile strength) and Y.S.(yield strength) of hot forged alloy B specimen were measured at 844.6MPa and 518.0MPa, respectively. The tensile fractography of alloy B exhibited a ductile transgranular fracture mode and voids were initiated between the [V, Mo]C particles and the matrix. Superior properties of high strength and low thermal expansion coefficient can be obtained by [V, Mo]C precipitation in alloy B with the addition of 0.4%V and 0.45%C.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.1
• /
• pp.48-54
• /
• 2012

The $[Fe_4S_4]^{2+}$ clusters with 2-, 3-, and 4-pyridinemethanethiolate (S2-Pic, S3-Pic, and S4-Pic, respectively) terminal ligands have been synthesized from the ligand substitution reaction of the $(^nBu_4N)_2[Fe_4S_4Cl_4]$ (I) cluster. The new $(^nBu_4N)_2[Fe_4S_4(SR)_4]$ (R = 2-Pic; II, 3-Pic; III, 4-Pic; IV) clusters were characterized by FTIR and UV-Vis spectroscopy. Cluster II was crystallized in the monoclinic space group C2/c with a = 24.530 (5) $\AA$, b = 24.636(4) $\AA$, c = 21.762(4) $\AA$, ${\beta}=103.253(3)^{\circ}$, and Z = 8. The X-ray structure of II showed two unique 2:2 site-differentiated $[Fe_4S_4]^{2+}$ clusters due to the bidentate-mode coordination by 2-pyridinemethanethiolate ligands. Cluster III was crystallized in the same monoclinic space group C2/c with a = 26.0740(18) $\AA$, b = 23.3195(16) $\AA$, c = 22.3720(15) $\AA$, ${\beta}=100.467(2)^{\circ}$, and Z = 8. The 3-pyridinemethanethiolate ligand of III was coordinated to the $[Fe_4S_4]^{2+}$ core as a terminal mode. Cluster IV with 4-pyridinemethanethiolate ligands was found to have a similar structure to the cluster III. Fully reversible $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ redox waves were observed from all three clusters by cyclic voltammetry measurement. The electrochemical potentials for the $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ transition decreased in the order of II, III and IV, and the reduction potential changes by the ligands were explained based on the structural differences among the complexes. The complex III was reacted with sulfonium salt of $[PhMeSCH_2-p-C_6H_4CN](BF_4)$ in MeCN to test possible radical-involving reaction as a functional model of the [$Fe_4S_4$]-SAM (S-adenosylmethionine) cofactor. However, the isolated reaction products of 3-pyridinemethanethiolate-p-cyanobenzylsulfide and thioanisole suggested that the reaction followed an ionic mechanism and the products formed from the terminal ligand attack to the sulfonium.

• The Korean Journal of Physiology
• /
• v.3 no.1
• /
• pp.45-49
• /
• 1969

The effects of water extracts and powder of Korean ginseng on the division of Saccharomyces cerevisiae were studied. 1. The addition of several doses of water extracts and powder of ginseng to the yeast medium of Moyer and Coghill showed various promoted division of Saccharomyces. 2. The optimal dose of ginseng on tile division of Saccharomyces (0.08% dry ginseng medium solution per $10\;cells/mm^3$) could be recognized. 3. On the culture for 24 hours at $18^{\circ}C$, the cell number of control group was $13.25{\times}10^3\;cells/mm^3$ and that of the optimal dose group of water extracts of ginseng was $23.20{\times}10^3\;cells/mm^3$. On the culture, for 24 hours at $25^{\circ}C$, the cell number of control group was $16.85{\times}10^3\;cells/mm^3$ and that of the optimal dose group was $30.20{\times}10^3\;cells/mm^3$. The increasing rate of cell divison by the ginseng was about twice than that of control group. The optimal dose treatment of ginseng at $18^{\circ}C$ was more effective than control group at $25^{\circ}C$. 4. On the culture for 24 hours at $18^{\circ}C$, the increasing rate of water extracts of ginseng was 75.1%, and the rate of ginseng powder was 7.6%. On the culture for 24 hours at $25^{\circ}C$, the rate of water extracts of ginseng was 79.8%, and the rate of ginseng powder was 57.2%. Therefore water extracts of ginseng was more effective than ginseng powder of same dry weight, and the promoted effect of ginseng powder at $25^{\circ}C$ was more effective than at $18^{\circ}C$.

• Journal of the Korean Magnetic Resonance Society
• /
• v.14 no.1
• /
• pp.1-8
• /
• 2010

Four 5,8-epidioxy sterols were isolated from the marine sponge Plakortis simplex. Their structures were completely determined by an extensive NMR analysis and comparison with NMR data of similar compounds for absolute stereochemistry of the side chain. The compounds were assigned as 5,8-epidioxy- (24S)-ethylcholesta-6,22(E),25-trien-3-ol(1), 5,8-epidioxy-(24S)-methylcholesta- 6,22(E)-dien-3-ol(2), 5,8-epidioxycholesta-6,22(E)-dien-3-ol(3) and 5,8- epidioxycholesta-6-en-3-ol (4).