• 생태와환경
• /
• 제40권4호
• /
• pp.576-580
• /
• 2007

Phytoplankton community dynamics were studied from 2004 to 2006 with two and four weeks interval at mid to lower part of the Nakdong River (Waegwan: RK 194, Goryeong: RK 157, Jukpo: RK 112, Namji: RK 75 and Hanam: RK 63: RK: distance from the Estuarine Barrage), South Korea. Annual averages of water temperature was about $16^{\circ}C$, and dissolved oxygen was ranged between 10.0 and 11.5 mg $L^{-1}$ (percent saturation, 106.5 to 112.8%). Diatoms were dominant group with over 60% of phytoplankton abundance in all study sites (Waegwan: 64%, Goryeong: 69%, Jukpo: 73%, Namji: 79%, and Hanam: 83%). However, the occasional dominances of other groups such as green algae and blue-green algae were observed from March to October. Stephanodiscus hantzschii was dominant species and the relative abundances were highat all study sites (48-72%). The ratio of S. hantzschiiltotal phytoplankton abundance were showed a clear increasing tendency toward the estuarine barrage: i.e. 0.31 at Waegwan, 0.39: Goryeong, 0.50: Jukpo, 0.56: Namji, 0.60: Hanam. The results of this study provide the information that the phytoplankton community structure in a regulated river system is basically affected by the physical properties such as water velocity and retention time, resulting in single species dominance by the stagnancy of river flow.

• Journal of Electrical Engineering and Technology
• /
• 제7권4호
• /
• pp.576-581
• /
• 2012

A 23 W continuous wavelength $CO_2$ laser system exited by a high-frequency LCC resonant converter is adapted to cut a biodegradable rope fabricated with polybutylene succinate. As the biodegradable rope consists of three twisted strands, the thickness changes relative to the position of the laser beam and we thus propose a method to determine exact cutting depth. In order to obtain the parameters related to the rope cutting, the experimental and theoretical cutting depths are compared and analyzed for a range of laser heat sources. The melted thickness and groove width of the cut biodegradable rope are also examined. The proposed theoretical cutting depth depends on the incident power and target velocity ratio. From these experimental results, the biodegradable rope with a diameter of 22 mm can be cut with a heat source of 50 J/cm resulting in a melted thickness of 1.96 mm and a groove width of 0.65 mm. The laser system is shown to be perfect tool for the processing of biodegradable rope without the occurrence of raveling.

• 대한기계학회논문집B
• /
• 제23권8호
• /
• pp.945-956
• /
• 1999

This work reports a set of approximate analytical solutions describing the initial transient process of close-contact melting between a rectangular parallelepiped solid and a flat plate on which either constant temperature or constant heat flux is imposed. Not only relative motion of the solid block tangential to the heating plate, but also the density difference between the solid and liquid phase is incorporated in the model. The thin film approximation reduces the force balance between the solid weight and liquid pressure, and the energy balance at the melting front into a simultaneous ordinary differential equation system. The normalized model equations admit compactly expressed analytical solutions which include the already approved two-dimensional solutions as a subset. In particular, the normalized liquid film thickness is independent of all pertinent parameters, thereby facilitating to define the transition period of close-contact melting. A unique behavior of the solid descending velocity due to the density difference is also resolved by the present solution. A new geometric function which alone represents the three-dimensional effect is introduced, and its properties are clarified. One of the representative results is that heat transfer is at least enhanced at the expense of the increase in friction as the cross-sectional shape deviates from the square under the same contact area.

• 대한기계학회논문집B
• /
• 제20권11호
• /
• pp.3620-3629
• /
• 1996

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability which employs the integral method and the test particle Monte-Carlo method. Also, new approximate method combining the double stage solutions, so called double-approximation, is presented here. The calculated values of transmission probability for the single stage agree quantitatively with the previous known numerical results. For a six-stage pump, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method at dimensionless blade velocity ratio C=0.4, the previous known approximate method overestimates as much as 34% than does the Monte-Carlo method. But, the new approximate method gives more accurate results, whose relative error is 10% compared to the Monte-Carlo method, than does the previous approximate method.

• 대한기계학회논문집B
• /
• 제25권4호
• /
• pp.583-592
• /
• 2001

The combustion characteristics of the hybrid catalytic(catalytic+thermal) combustor with a lean methane-air mixture on platinum catalyst were investigated numerically using a 2-D boundary layer model with detailed homogeneous and heterogeneous chemistries. for the more accurate calculations, the actual surface site density of monolith coated with platinum was decided by the comparison with experimental data. It was found that the homogeneous reactions in the monolith had little effect on the change of temperature profile, methane conversion rate and light off location. However, the radicals such as OH and CO were produced rapidly at exit by homogeneous reactions. The effect of operation conditions such as equivalence ratio, temperature, velocity, pressure and diameter of the monolith channel at the entrance were studied. In thermal combustor, the production of N$_2$O was more dominant than that of NO due to the relative importance of the reaction N$_2$+O(+M)→N$_2$O(+M). Finally the productions of CO and NOx by amount of methane addition were studied.

• Korea-Australia Rheology Journal
• /
• 제14권2호
• /
• pp.63-70
• /
• 2002

Chemical mechanical planarization (CMP) is the polishing process enabled by both chemical and mechanical actions. CMP is used in the fabrication process of the integrated circuits to achieve adequate planarity necessary for stringent photolithography depth of focus requirements. And recently copper is preferred in the metallization process because of its low resistivity. We have studied the effects of chemical reaction on the polishing rate and surface planarity in copper CMP by means of numerical simulation solving Navier-Stokes equation and copper diffusion equation. We have performed pore-scale simulation and integrated the results over all the pores underneath the wafer surface to calculate the macroscopic material removal rate. The mechanical abrasion effect was not included in our study and we concentrated our focus on the transport phenomena occurring in a single pore. We have observed the effects of several parameters such as concentration of chemical additives, relative velocity of the wafer, slurry film thickness or ash)tract ratio of the pore on the copper removal rate and the surface planarity. We observed that when the chemical reaction was rate-limiting step, the results of simulation matched well with the experimental data.

• 천문학회지
• /
• 제34권4호
• /
• pp.329-331
• /
• 2001

We investigate the morphology of Active Galactic Nuclei(AGN) jets. AGN jets propagate over kpc $\~$ Mpc and their beam velocities are close to the speed of light. The reason why many jets propagate over so long a distance and sustain a very collimated structure is not well understood. It is argued that some dimensionless parameters, the density and the pressure ratio of the jet beam and the ambient gas, the Mach number of the beam, and relative speed of the beam compared to the speed of light, are very useful to understand the morphology of jets namely, bow shocks, cocoons, nodes etc. The role of each parameters has been studied by numerical simulations. But more research is necessary to understand it systematically. We have developed 2D relativistic hydrodynamic code to analyze relativistic jets. We pay attention to the propagation velocity which is derived from 1D momentum balance in the frame of the working surface. We show some of our models and discuss the dependence of the morphology of jets on the parameter.

• Structural Engineering and Mechanics
• /
• 제90권6호
• /
• pp.601-610
• /
• 2024

Free vibration of layered conical shell frusta of thickness filled with fluid is investigated. The shell is made up of isotropic or specially orthotropic materials. Three types of thickness variations are considered, namely linear, exponential and sinusoidal along the radial direction of the conical shell structure. The equations of motion of the conical shell frusta are formulated using Love's first approximation theory along with the fluid interaction. Velocity potential and Bernoulli's equations have been applied for the expression of the pressure of the fluid. The fluid is assumed to be incompressible, inviscid and quiescent. The governing equations are modified by applying the separable form to the displacement functions and then it is obtained a system of coupled differential equations in terms of displacement functions. The displacement functions are approximated by cubic and quintics splines along with the boundary conditions to get generalized eigenvalue problem. The generalized eigenvalue problem is solved numerically for frequency parameters and then associated eigenvectors are calculated which are spline coefficients. The vibration of the shells with the effect of fluid is analyzed for finding the frequency parameters against the cone angle, length ratio, relative layer thickness, number of layers, stacking sequence, boundary conditions, linear, exponential and sinusoidal thickness variations and then results are presented in terms of tables and graphs.

• Earthquakes and Structures
• /
• 제26권4호
• /
• pp.285-297
• /
• 2024

Due to the imbalanced vibration of the adjacent buildings, the pounding phenomenon occurs as a result of an insufficient gap between them. Providing enough gap between adjacent structures is the most efficient approach to preventing the pounding effect. This paper calculated the required separation gaps between adjacent buildings, including two, four, eight, twelve and twenty stories steel moment-resisting frames, and investigated their related influencing parameters such as time periods, damping ratios, and the number of bays. The linear and nonlinear dynamic time-history analyses under real seismic event records were conducted to calculate the required separation gaps by obtaining relative displacement and velocity functions of two adjacent frames. The results showed that the required separation gap increased when the time periods of adjacent frames were not the same. The resulting separation gaps values of linear and nonlinear analyses were similar only for two and four stories frames. In other frames, the resulting separation gap values of linear analyses surpassed the corresponding nonlinear analyses. Although increasing the damping ratios in adjacent frames causes a decrease in the required separation gaps, the number of bays had no significant effect on them.

• 방사성폐기물학회지
• /
• 제8권2호
• /
• pp.151-158
• /
• 2010

무에 대한 $I_2$ 증기의 작물체 침적속도와 뿌리 전류계수를 측정하기 위하여 파종 후 29 일에서 53 일 사이에 생육시기별로 작물체를 $I_2$ 증기에 80 분 간 피폭시켰다. 피폭은 오전 중에 투명한 상자 내에서 수행되었다. 침적속도($ms^{-1}$)는 대체로 $1.0{\times}10^{-4}{\sim}2.0{\times}10^{-4}$의 범위로 생육밀도가 높을수록 증가하는 경향이었다. 또한 상대습도가 높을 경우 값이 커진다는 기존 보고와 어느 정도 일치하였다. 본 침적속도는 몇몇 야외 측정치보다 수 십 배 정도 낮았고 이는 주로 피폭상자 내의 낮은 풍속($0.2\;ms^{-1}$ 내외)에 기인하는 것으로 추정되었다. 뿌리 전류계수(작물체 총침적량에 대한 수확시 뿌리 내 함유량의 비)는 다소 보수적으로 계산하여 파종 후 29 일 피폭에서 $1.3{\times}10^{-3}$, 파종 후 53 일 피폭에서는 $5,0{\times}10^{-3}$이었다. 본 실험결과의 이용에 있어서는 기상 조건, 요오드의 물리화학적 형태 등에 유의할 필요가 있다.