• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.991-998
• /
• 1989

This investigation was carried out for the purpose of studying the turbulent flow and mixing characteristics after collision of two jets depending upon the cross angle variations. For effectuating this experimental study, a subsonic wind tunnel and a constant temperature type two channel hot-wire anemometer system have been utilized. The jets issuing from two nozzles have same Reynolds numbers and their cross angle was variable. After collision of two jets, the cross section of the mixing flow, mean and fluctuating velocities and Reynolds stresses have been measured, and analyzed comparing them with semi-empirical equations. It was found that the nondirectional contour of the cross section agreed well with an elliptic formula and the mean velocities along the centerline had a good similarity independent of cross angle variations. The distributions of U over bar-components measured in the Y direction have a good similarity and agree well with semi-empirical equations of Hinze and Gortler. The Reynolds stresses of u'v' over bar on the Y axis show a similar distributions and their agreement with the theoretical curve is remarkable but those of u'w' over bar measured along the Z axis are randomly scattered.

• Applied Chemistry for Engineering
• /
• v.4 no.4
• /
• pp.672-682
• /
• 1993

2, 4-Heptadione(abbreviated to 24HTD) was synthesized from methylpropyl ketone and ethyl acetate with sodium amide, and the equilibrium and the kinetic characteristics of copper extraction by 24HTD-chloroform were investigated. Equilibrium constants such as the dissociation constant and the distribution coefficient of 24HTD and the stability constant of the 24HTD-Cu chelate were evaluated from the spectrophotometry, and the overall equilibrium constant of the extraction was also determined. The extracted species of the 24HTD-Cu chelate was found to be $CuR_2$ and the initial rate of the extraction of coupper by 24HTD in chloroform was expressed by $R_0=k[\bar{HR}]([Cu^{2+}]/[H^+])^{0.5}$.

• Korean Journal of Materials Research
• /
• v.28 no.4
• /
• pp.208-213
• /
• 2018

Epitaxial ($11{\bar{2}}0$) a-plane GaN films were grown on a ($1{\bar{1}}02$) R-plane sapphire substrate with photoresist (PR) masks using metal organic chemical vapor deposition (MOCVD). The PR mask with striped patterns was prepared using an ex-situ lithography process, whereas carbonization and heat treatment of the PR mask were carried out using an in-situ MOCVD. The heat treatment of the PR mask was continuously conducted in ambient $H_2/NH_3$ mixture gas at $1140^{\circ}C$ after carbonization by the pyrolysis in ambient $H_2$ at $1100^{\circ}C$. As the time of the heat treatment progressed, the striped patterns of the carbonized PR mask shrank. The heat treatment of the carbonized PR mask facilitated epitaxial lateral overgrowth (ELO) of a-plane GaN films without carbon contamination on the R-plane sapphire substrate. Thhe surface morphology of a-plane GaN films was investigated by scanning electron microscopy and atomic force microscopy. The structural characteristics of a-plane GaN films on an R-plane sapphire substrate were evaluated by ${\omega}-2{\theta}$ high-resolution X-ray diffraction. The a-plane GaN films were characterized by X-ray photoelectron spectroscopy (XPS) to determine carbon contamination from carbonized PR masks in the GaN film bulk. After $Ar^+$ ion etching, XPS spectra indicated that carbon contamination exists only in the surface region. Finally, the heat treatment of carbonized PR masks was used to grow high-quality a-plane GaN films without carbon contamination. This approach showed the promising potential of the ELO process by using a PR mask.

• Korean Journal of Digital Imaging in Medicine
• /
• v.10 no.2
• /
• pp.23-31
• /
• 2008

Computed radiography(CR) has been widely used in the field of diagnostic radiography since digital X-ray image was introduced. The imaging performance of CR system was studied by analyzing the digital image data of the CR images which are the outcomes of the whole imaging system composed of image plate(IP), laser digitizer, analoge-digital convertor, and a given image processing unit. In this study, we used a conventional CR system made by Agfa. From the flat field image of 150$\times$150 image pixels, signal-to-noise ratio(SNR) was calculated. SNR of the CR image increases in proportion to logarithm value of the X-ray exposure irradiated on the IP. SNR is less than about 6 at the exposure below 0.2mR and is more than 10 at the exposure above 0.54mR. In our study, most of images obtained by the smaller exposures less than 2.0mR can not be readable. In general, the minimum value of the SNR ranges from 3 to 5. We obtained modulation transfer function(MTF) by analyzing the bar pattern image which was made under conditions as follows: X-ray tube potential was 55kVp, the IP exposure was 0.54 mR, and the distance between X-ray source to IP was 2m, where bar pattern was located on the IP. MTF is 23% at 2.5lp/mm spatial frequency. Provided that the MTF of noise equivalent modulation is 10%, the CR system has the limiting spatial resolution of 3.2lp/mm. If the image sharpness is evaluated by the spatial frequency where MTF is 50%. the corresponding spatial frequency is 0.5$\sim$0.75lp/mm. MTFA(Modulation Transfer Function Area) is 1.0lp/mm. Compared with the Fuji CR whose MTFA is 1.1lp/mm, Agfa CR in this study shows almost same MTFA performance.

• Korean Journal of Optics and Photonics
• /
• v.16 no.1
• /
• pp.63-70
• /
• 2005

We propose a method for evaluating the image quality of color liquid crystal display(LCD) monitors by using the polychromatic modulation transfer function(PMTF), which is calculated from the modulation transfer function(MTF) weighted by the overall color response of the system including the test LCD monitor. We confirm that experimental results using the PMTF agree well with simulated results of the PMTF of a color LCD monitor by using three bar targets with different amplitudes and three elementary colors such as red(R), green(G), and blue(B). As a results, we should choose the PMTF instead of the white color MTF or monochromatic MTF in order to evaluate correctly the image quality of color LCD monitors.

• Journal of Advanced Navigation Technology
• /
• v.26 no.6
• /
• pp.464-473
• /
• 2022

In this paper, about a lightweight design that satisfies the performance of UHF-GPS Antenna used in autonomous underwater vehicle is proposed. Structural analysis, watertight external pressure test and non-destructive testing used in the design process are decided in consideration of structural safety for operating external forces in the underwater environment. First, the material of radome is selected for the performance of the UHF-GPS Antenna for communication with the carrier on the underwater operation in consideration of the 20 bar pressure generated. And the material of radome as PA-GF is selected by conducting electromagnetic field analysis and structural analysis and by considering high strength, rigidity and high dielectric constant. Electromagnetic field analysis and structural analysis by the thickness of radome are additionally performed in order to satisfy the required weight of UHF-GPS antenna. After selecting the final model, its structural safety is verified through watertight external pressure test and non-destructive testing.

• Proceedings of the SAREK Conference
• /
• 2005.11a
• /
• pp.414-420
• /
• 2005

For supporting future demands of lower temperature. environmental friendly low- temperature refrigerants must be studied and developed to replace halocarbon. Ethane. which is one of hydrocarbon compound. is an environmental friendly refrigerant because it has zero ODP and GWP ${\sim}$ 20[per 100yr]. On this study, two-stage cascade refrigeration system was utilized to investigate performance of ethane on the low-stage. By employing R22 at higher stages. energetic performance as well as operating condition of R22/R170 system is compared to R22/R23. At low stage evaporation pressure ranges from 1.10 to 2.74 bar, R22/R170 shows higher COP over R22/R23. Furthermore, at the same range evaporation temperature R22/R170 can reach lower temperature.

• Communications of the Korean Mathematical Society
• /
• v.25 no.3
• /
• pp.349-364
• /
• 2010

P. M. Cohn called a ring R reversible if whenever ab = 0, then ba = 0 for a, $b\;{\in}\;R$. Commutative rings and reduced rings are reversible. In this paper, we extend the reversible condition of a ring as follows: Let R be a ring and $\alpha$ an endomorphism of R, we say that R is right (resp., left) $\alpha$-shifting if whenever $a{\alpha}(b)\;=\;0$ (resp., $\alpha{a)b\;=\;0$) for a, $b\;{\in}\;R$, $b{\alpha}{a)\;=\;0$ (resp., $\alpha(b)a\;=\;0$); and the ring R is called $\alpha$-shifting if it is both left and right $\alpha$-shifting. We investigate characterizations of $\alpha$-shifting rings and their related properties, including the trivial extension, Jordan extension and Dorroh extension. In particular, it is shown that for an automorphism $\alpha$ of a ring R, R is right (resp., left) $\alpha$-shifting if and only if Q(R) is right (resp., left) $\bar{\alpha}$-shifting, whenever there exists the classical right quotient ring Q(R) of R.

• Journal of the Korean Chemical Society
• /
• v.37 no.3
• /
• pp.279-286
• /
• 1993

The effect of pressure on solvation of potassium chloride was studied by the density and viscosity measurements of water-methanol systems and the conductance measurements of KCl in this systems. These were used to calculate the r-function of KCl. It was found that the r-function of KCl which is 0.613 at 25$^{\circ}C$ and 1 bar in water was continuously decreased to the minimum point and enhanced with increasing the composition of methanol. At high pressure, the r-function of KCl was similar to that of normal pressure. But r-function decreased with increasing pressure at the specific component of methanol.

• Bulletin of the Korean Mathematical Society
• /
• v.55 no.6
• /
• pp.1869-1889
• /
• 2018

We are concerned with the following fractional p-Laplacian inclusion: $$(-{\Delta})^s_pu+V(x){\mid}u{\mid}^{p-2}u{\in}{\lambda}[{\underline{f}}(x,u(x)),\;{\bar{f}}(s,u(x))]$$ in ${\mathbb{R}}^N$, where $(-{\Delta})^s_p$ is the fractional p-Laplacian operator, 0 < s < 1 < p < $+{\infty}$, sp < N, and $f:{\mathbb{R}}^N{\times}{\mathbb{R}}{\rightarrow}{\mathbb{R}}$ is measurable with respect to each variable separately. We show that our problem with the discontinuous nonlinearity f admits at least one or two nontrivial weak solutions. In order to do this, the main tool is the Berkovits-Tienari degree theory for weakly upper semicontinuous set-valued operators. In addition, our main assertions continue to hold when $(-{\Delta})^s_pu$ is replaced by any non-local integro-differential operator.