• Advances in nano research
• /
• v.8 no.4
• /
• pp.307-322
• /
• 2020

In this article, free vibration of double-walled carbon nanotubes (DWNT) based on nonlocal Kelvin's model have been investigated. For this purpose, a nonlocal Kelvin's model is established to observe the small scale effect. The wave propagation is employed to frame the governing equations as eigenvalue system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. The new set of inner and outer tubes radii investigated in detail against aspect ratio. The influence of boundary conditions via nonlocal parameter is shown graphically. Due to small scale effect fundamental frequency ratio decreases as length to diameter ratio increases. Small scale effect becomes negligible on all end supports for the higher values of aspect ratio. With the smaller inner tube radius double-walled CNT behaves more sensitive towards nonlocal parameter. The results generated furnish the evidence regarding applicability of nonlocal model and also verified by earlier published literature.

• Nuclear Engineering and Technology
• /
• v.22 no.4
• /
• pp.410-415
• /
• 1990

Prompt fission neutron energy spectrum as a function of energies of neutron inducing fission has been calculated en the basis of the Madland-Nix(MN) model. The resultant spectra have been weighted to excitation functions of $^{27}$ Al(n, $\alpha$), $^{32}$ S(n, p) and $^{115}$ In(n, n') threshold reactions in order to get the average cross sections and then spectral indices which are defined as the average cross section ratio for two selective threshold reactions among the above three. It is appeared that spectral indices together with the neutron spectra are varying with energies of neutron inducing fission. This may indicate that the prompt fission neutron energy spectrum can be determined by measuring experimentally the spectral index.

• The Korean Journal of Pharmacology
• /
• v.29 no.1
• /
• pp.157-163
• /
• 1993

Intramolecular excimer formation with the fluorescent probe 1,3-di(1-pyrenyl)propane (Py-3-Py) was used to investigate the effects of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol and 1-decanol on the lateral diffusion of synaptosomal plasma membrane vesicles isolated from bovine cerebral cortex (SPMV). The n-alkanols increased the excimer to monomer fluorescence intensity ratio (I'/I) of Py-3-Py in the SPMV. In a dose-dependent manner, n-alkanols increased lateral diffusion of hydrocarbon region of bulk (inner+outer monolayers) SPMV lipid bilayers, and the potencies of n-alkanols up to l-nonanol increased with carbon chain length. It appears that the potencies in bilayer fluidization due to the lateral diffusion increase by 1 order of magnitude as the carbon chain length increases by two carbon atoms. The cut-off phenomenon was reached at 1-decanol, where further increase in hydrocarbon length resulted in a decrease in pharmacological activity.

• Composites Research
• /
• v.22 no.5
• /
• pp.15-23
• /
• 2009

The lubricant tribological characteristics of $Al_2O_3$ fiber and SiC particle hybrid metal matrix composites (MMCs) fabricated by squeeze casting method was investigated using a pin-on-disk wear tester. The wear tests of the MMCs were performed according to fiber/particle hybrid ratio in the planar-random (PR) and normal (N) orientations sliding against a counter steel disk at a fixed speed and $25\;kg_f$ loading under different sliding distances and temperatures. The test results showed that the wear behavior of MMCs varied with fiber orientation and hybrid ratio. At room temperature, the lubricant wear behavior of F20P0 unhybrid PR-MMCs was superior to that of N-MMCs while the hybrid composites exhibited the reverse lubricant wear behavior. It was also revealed that the wear resistance of PR-MMCs was superior to that of the N-MMCs due to the joint action of reinforcements and lubricant film between the friction surfaces at an elevated temperature of $100^{\circ}C$ for both fiber only and hybrid cases. In case of $150^{\circ}C$, although the trend of weight loss was similar to that of others, the wear resistance of PR-MMCs was better than that of N-MMCs for hybrid MMCs.

• The Korean Journal of Malacology
• /
• v.32 no.3
• /
• pp.149-155
• /
• 2016

To assess the effects of environmental factors on the sustainability of cultured ark shell Scapharca broughtonii production, we investigated the habitat characteristics of shellfish-farming bays (Gangjin Bay, Yeoja Bay, Keoje Bay and Deukryang Bay). We measured the physiochemical parameters (temperature, salinity, dissolved oxygen, nutrients, chemical oxygen demand and Chlorophyll a) and the geochemical characteristics (chemical oxygen demand, ignition loss, C/N ratio and C/S ratio). Surface sediments were collected from several shellfish-farming bays to examine the geochemical characteristics of both the benthic environment and heavy metal pollution. The grain sizes for Gangjin Bay, Yeoja Bay and Keoje Bay were similar, at the ratio of silt and clay in comparison with Deukryang bay of it. The C/N ratio was more than 5.9, reflecting the range arising from the mix of marine organisms and organic matter. The C/S ratio (more than 4.2) showed that the survey area had anoxic or sub-anoxic bottom conditions. The index of accumulation rate (Igeo) of the metals showed that those research areas can be classified as heavily polluted, heavily to moderately polluted, or more or less unpolluted, respectively. We suggested that the growth of ark shell Scapharca broughtonii in the shellfish-farming bay was effected by the various environmental conditions.

• Korean Journal of Medicinal Crop Science
• /
• v.3 no.1
• /
• pp.61-65
• /
• 1995

Karyotype analysis was carried out in four lines of Bupleurum falcatum L. cultivated in Korea and SDS-PAGE was applied to determine the seed protein profiles among the lines. Chromosomes were classified into two groups, large and small ones. Two kinds of karyotype, 2n=20 and 2n=26, were identified. Chromosome 1 of 2n=20 were all submedian, while that of 2n=26 were median. Chromosomes 2, 3 and 5 of 2n=20 showed polymorphism in size and arm-ratio. Chromosome 2 was submedian, while others were median in the line of 2n=26. Karyotypcs of cultivars native of Korea were similiar each other, while those introduced from Japan showed different patterns. In SDS PAGE gels, qualitative difference s in high molecular weight proteins, more than 45KD, were detected among the lines. The numbers of specific band were three in lines of 2n=20 and two in 2n=26.

• Journal of the Korean Chemical Society
• /
• v.45 no.3
• /
• pp.230-235
• /
• 2001

Poly(N-isopropylacrylamide) (PNIPAAm) containing polydimethylsiloxane (PDMS) was synthesized using PDMS as crosslinking agent, and characterized by IR and DSC. It seems that the copolymer has separated phases, PNIPAAm and PDMS. The $T_g$ of PNIPAAm was decreased in accordance with the increase of PDMS-contents. The swelling behavior of polymer in water was examined with the function of temperature and PDMS-contents as well. The equilibrium swelling ratio of polymer in water was decreased with increasing PDMS-contents, but lower critical solution temperature (LCST) was not significantly affected by the incorporated PDMS-contents.

• Journal of Korean Society on Water Environment
• /
• v.35 no.2
• /
• pp.165-180
• /
• 2019

Water quality data of 81 lakes in Korea, 2013 ~ 2017 were analyzed. Most water quality parameters showed left-skewed distribution, while dissolved oxygen showed normal distribution. pH and dissolved oxygen showed a positive correlation with organic matter and nutrients, which appeared to be a nonsense correlation mediated by the algae. The ratio of $BOD_5$ and $COD_{Mn}$ to CBOD was 21 % and 52 % in the freshwater lakes, respectively. TOC concentration appeared to be underestimated by the UV digestion method, when salinity exceeds $700{\mu}S\;cm^{-1}$. In terms of nitrogen/phosphorus ratio, the limiting factor for algal growth seemed to be phosphorus in most of the lakes. Chlorophyll ${\alpha}$ increased acutely with decrease of N/P ratio. However, it seemed to be a nonsense correlation mediated by phosphorus concentration, since the N/P ratio depended on phosphorus. The N/P ratio of brackish lakes was lower than that of the freshwater, at the same concentration of phosphorus. It is worth examining denitrification that occurs, in bottom layer and sediment, during saline stratification. $Chl.{\alpha}$ concentration decreased in the form of a power function with increase of mean depth. The primary reason is that deep lakes are mainly at the less-disturbed upstream. However, it is necessary to investigate the effect of sediment, on water quality in shallow lakes. Light attenuation in the upper layer, was dominated by tripton (non-algal suspended solids) absorption/scattering (average relative contribution of 39 %), followed by CDOM (colored dissolved organic matter) (average 37 %) and $Chl.{\alpha}$ (average 21 %).

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.5 no.1
• /
• pp.1-5
• /
• 2003

This study was carried out to investigate the chemical properties of rainwater in the Suwon area. Rainwater was collected from April to October in 1999 and 2000, and its chemical composition was analyzed. The pH of rainwater in April was higher than that of the months after June. Occurrence frequency of rain above pH 5.6 was 45.1%, which showed the highest ratio from rainwater samples during the investigation periods. Those of pH 5.0∼5.6 and 4.5∼4.9 range were 31.4 and 19.6%, respectively. The major cations in rainwater were $Ca^{2+}$ and N $H_{4}$$^{+}$, and S $O_{4}$$^{2-}$ made up more than 50% of total anion composition. Monthly variation of neutralization capacity of rainwater acidity by $Ca^{2+}$ and N $H_{4}$$^{+}$ decreased during the rainy season. The ratio of non-sea salt sulfate to nitrate (nss-S $O_{4}$$^{2-}$/N $O_{3}$$^{[-10]}$ ) was 2.1, which means anthropogenic S $O_{4}$$^{2-}$ contributed to acidity of rainwater two times more than N $O_{3}$$^{[-10]}$ . .

• Nuclear Engineering and Technology
• /
• v.24 no.1
• /
• pp.98-109
• /
• 1992

In this study uniaxial cyclic loading tests were performed on Cheon-Ho Mt. Limestone specimens to investigate the fatigue failure behavior. The loading rate was kept constantly at 760kg/$\textrm{cm}^2$/sec under cyclic loading. In order to reveal the fatigue behavior for each rock type, the test results were mutually compared with previous studies carried out on Indiana Limes-tone and Seong-Ju Sandstone. Fatigue data is presented in the form of S-N curves, which illustrate the relationship of maximum applied stress(S) to the number of cycles(N) required to produce failure. For the purpose of comparing the S-N curves for each rock type, the test data were formulated up to 10$^4$cycles and the correlation coefficients(R) on Cheon-Ho Mt. Limestone and Seong-Ju Sandstone specimen are 0.886 and 0.983, respectively. All three rock specimens were found to have shorter fatigue life at higher applied stress levels. The fatigue life for each rock type was considered as no less than 81.5, 70 and 74.8%, for Cheon-Ho Mt. Limestone, Indiana Limestone and Seong-Ju Sandstone, respectively. The comparison in static strength for monotonic loaded specimens and specimens which did not fail even after 10$^4$cycles indicated that the increasing rate of strength was about 6.18 and 10.96% , for Cheon-Ho Mt. Limestone and Indiana Limestone, respectively. Poisson's ratio and volumetric strain for Cheon-Ho Mt. Limestone and Seong-ju Sandstone, tended in all the cases to rapidly increase at higher stress levels and with an increase in number of cycles. This increasing trend becomes rapid and obvious just before failure. Also Poisson's ratio and volumetric strain for each stress level were compared and analyzed at the first cycle and the cycle prior to failure.