• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1782-1798
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• 2004

A numerical study of a natural convection in a rectangular cavity with the low-Reynolds-number differential stress and flux model is presented. The primary emphasis of the study is placed on the investigation of the accuracy and numerical stability of the low-Reynolds-number differential stress and flux model for a natural convection problem. The turbulence model considered in the study is that developed by Peeters and Henkes (1992) and further refined by Dol and Hanjalic (2001), and this model is applied to the prediction of a natural convection in a rectangular cavity together with the two-layer model, the shear stress transport model and the time-scale bound ν$^2$- f model, all with an algebraic heat flux model. The computed results are compared with the experimental data commonly used for the validation of the turbulence models. It is shown that the low-Reynolds-number differential stress and flux model predicts well the mean velocity and temperature, the vertical velocity fluctuation, the Reynolds shear stress, the horizontal turbulent heat flux, the local Nusselt number and the wall shear stress, but slightly under-predicts the vertical turbulent heat flux. The performance of the ν$^2$- f model is comparable to that of the low-Reynolds-number differential stress and flux model except for the over-prediction of the horizontal turbulent heat flux. The two-layer model predicts poorly the mean vertical velocity component and under-predicts the wall shear stress and the local Nusselt number. The shear stress transport model predicts well the mean velocity, but the general performance of the shear stress transport model is nearly the same as that of the two-layer model, under-predicting the local Nusselt number and the turbulent quantities.

• Journal of Elementary Mathematics Education in Korea
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• v.18 no.1
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• pp.105-122
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• 2014

In this paper, fraction division algorithms in Korean elementary mathematics textbooks are analyzed as a part of the groundwork to improve teaching methods for fraction division algorithms. There are seemingly six fraction division algorithms in ${\ll}Math\;5-2{\gg}$, ${\ll}Math\;6-1{\gg}$ textbooks according to the 2006 curriculum. Four of them are standard algorithms which show the multiplication by the reciprocal of the divisors modally. Two non-standard algorithms are independent algorithms, and they have weakness in that the integration to the algorithms 8 is not easy. There is a need to reconsider the introduction of the algorithm 4 in that it is difficult to think algorithm 4 is more efficient than algorithm 3. Because (natural number)${\div}$(natural number)=(natural number)${\times}$(the reciprocal of a natural number) is dealt with in algorithm 2, it can be considered to change algorithm 7 to algorithm 2 alike. In textbooks, by converting fraction division expressions into fraction multiplication expressions through indirect methods, the principles of calculation which guarantee the algorithms are explained. Method of using the transitivity, method of using the models such as number bars or rectangles, method of using the equivalence are those. Direct conversion from fraction division expression to fraction multiplication expression by handling the expression is possible, too, but this is beyond the scope of the curriculum. In textbook, when dealing with (natural number)${\div}$(proper fraction) and converting natural numbers to improper fractions, converting natural numbers to proper fractions is used, but it has been never treated officially.

• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.715-720
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• 2004

Amineterminated, ethylenediamine core polyamidoamine starburst dendrimers of generation 2 (G2), generation 4 (G4) and generation 6 (G6) have been successfully surface-modified via an amide coupling reaction with 4-ethyl, 4'-(3-propionic) bipyridinium cation and the electrochemical behavior of the resulting dendrimers were investigated in aqueous potassium chloride electrolyte solutions. The 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide-mediated reaction resulted in 25-39% end-group functionalization. The water-soluble 4-ethyl, 4'-(3-propylamide) bipyridinium dibromide dendrimers (G2-V2+, G4-V2+ and G6-V2+) were characterized by $^1H$ NMR and UV-Vis spectroscopic methods. The cyclic voltammetric and chronoamperometric experiments were performed to determine the diffusion coefficient and the number of electrons transferred in the process of the first reduction of the viologen-functionalized dendrimers. Adsorption of viologen-functionalized dendrimers at electrode surface was evidenced in the voltammograms. Experimentally determined diffusion coefficients were in good agreement with the values expected from the Stokes-Einstein relation, while the number of electrons transferred concurred with the extent of functionalization determined by $^1H$ NMR and UV-Vis spectra.

• East Asian mathematical journal
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• v.38 no.4
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• pp.379-396
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• 2022

In this paper, we investigate distribution strategies in the Egyptian fraction, and through this, we examine the distribution strategies of (fraction)÷(fraction) and then provide some educational implications. The (natural number)÷(natural number) of the sharing situation has the meaning of 'share' per unit, which can be seen as a situation where the unit ratio is determined. These concepts can also naturally be extended to the case of (fraction)÷(fraction) by some problem posing situations. That is to say, the case of (fraction)÷(fraction) can be deduced the case (natural number)÷(natural number) by the re-statement of the problem.

• Bulletin of the Korean Chemical Society
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• v.27 no.4
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• pp.519-523
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• 2006

Poly(dimethyl siloxane) (PDMS) has been employed as a microchip material for DNA separation in microfluidic condition. Different sieving molecules such as cellulose derivatives having glucose building block (methyl cellulose (MC), hydroxyethyl cellulose (HEC), and hydroxypropyl methyl cellulose (HPMC)) and polyethylene oxide (PEO) having linear (ring-opened ethylene oxide) unit were used and their performance was compared in terms of separation efficiency and resolution. In general, PEO showed better separation performance than cellulose derivatives probably due to the nature of linear shape polymer conformation. It was possible to perform at least 15 consecutive running with 1.2% PEO at the electric field strength around 200 V/cm. Fast analysis of the standard $\Phi$X 174 RF DNA/Hae III (less than 130s) was obtained with the number of the theoretical plate around 250,000/m. Our PMDS microchip was applied to the measurement of CAG repeat number, which is related to male infertile disease.

• Journal of Crop Science and Biotechnology
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• v.11 no.3
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• pp.193-198
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• 2008

To develop a natural re-seeding technology, the optimum soil incorporation time of Chinese milk vetch(CMV) plant residues, seed persistence in soil, biomass production and subsequent rice yield were determined from 2005 to 2007 in rice with CMV green manure in southern Korea. Generally, insufficient seedling stand was regenerated with CMV incorporation to the soil at 20 and 25 days after flowering(DAF), while high regeneration of greater than 400 seedlings per $m^2$ was observed at 35 and 40 DAF. High re-seeding stand of CMV incorporated at 35 DAF or later was related with high seed viability and heavy seed weight. Appreciable number of CMV seeds remained 4 month after burial in soil and a good number of CMV seedlings regenerated from this seed bank at rice harvest time in the fall. Based on the relationships among re-seeding number of CMV plants, seed weight and seed viability, CMV plants should be incorporated into the soil 35 DAF(May 30) or later when CMV seeds were sufficiently matured. The natural re-seeding stand for the 3-year trials was stable ranging from 437 to 700 plants per $m^2$ and the biomass production was sufficient to supply nitrogen for rice growth. The use of re-seeding CMV plant can produce similar rice yield like that of rice without CMV green manure.

• Journal of Embryo Transfer
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• v.30 no.4
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• pp.283-287
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• 2015

The aim of the present study was to investigate the ovulation rate and its relationship to fertilization ability in Landrace, Durock and Crossbred pigs. Gilts were natural mated at a body weight of at least 120 kg under the same hormone treatment. Embryos were surgically collected 1 day after natural mating (Day 0). Embryos derived from in vivo-fertilized oocytes were cultured in medium PZM-3. The ovaries were examined and the pathological findings were recorded. The number of corpus hemorrhagicum was counted, and was assumed to equal the ovulation rate. There was no difference in the number of corpus hemorrhagicum (20.4, 28.8 and 23.2) and ovulation (13.5, 26.8 and 17.2) in the Landrace, Durock and Crossbred pigs. The two pronucleus formation was 76.0, 80.0 and 86.9%. The Day-7 embryos had blastocyst rates of 68.0, 75.0 and 73.9%. There was no difference in the number of total cells and apoptotic cells. In the future, more studies require determining relationships between ovulation and fertilization rate in different species of pigs.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.25-34
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• 2013

A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.

• The Journal of Natural Sciences
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• v.14 no.1
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• pp.1-6
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• 2004

In this paper, we calculate the Nielsen numbers of periods for maps on the Klein bottle.

• International Journal of Industrial Entomology and Biomaterials
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• v.35 no.2
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• pp.100-105
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• 2017

Under natural conditions, black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), colonizes in warm temperate regions, and is active in Korea from May through October. Information on black soldier fly rearing, which is affected by seasonal factors in Korea, is limited. Oviposition by black soldier flies is dependent on light intensity and wavelength. Therefore, continuous mass rearing of this fly requires determination of optimal artificial conditions of illumination. In this study, we compared the number of eggs laid under an artificial light source (750 watt HPL lamp) versus nature sunlight. Our results showed that compared to oviposition under natural sunlight, the use of one or two lamps for 7 hours, resulted in only 43 and 76%, of the total number of eggs laid under natural sunlight, respectively. We also investigated the hatchability of oviposited eggs under artificial illumination and under natural sunlight. The hatching rate under the former was much significantly lower than under the latter. Further detailed research is required to develop methods for successful mass rearing of black soldier fly throughout the year by means of an indoor system.