• KSBB Journal
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• v.23 no.2
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• pp.135-141
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• 2008

SMB (simulated moving bed) chromatography is a very useful utility for the separation of binary system. We simulated the separation of L-arabinose and L-ribose from the mixture by using lab-scale 4(1-1-1-1)-zone SMB chromatography. Preliminary experiments of PIM (pulse input method) were performed to measure adsorption isotherms of L-ribose and L-arabinose in $NH_2$ HPLC column, and experimental and simulated results from ASPEN chromatography were compared. To find the most suitable separation condition in SMB, we carried out a simulation in $m_2-m_3$ plane base on the triangle theory and calculated operating parameters (flow rate of four zone, switching time and feed concentration and so on) using ASPEN chromatography under the conditions of linear isotherms obtained from PIM.

• Journal of Biosystems Engineering
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• v.37 no.2
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• pp.113-121
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• 2012

Purpose: Particle separation in solution is one of important process in a unit operation as well as in an extract preparation for biosensors. Contrary to centrifuge-type of mesh-type filter, using an ultrasonic standing wave make the filtering process continuous and free from maintenance. It is needed to investigate the characteristics of particle movement in the ultrasonic standing wave field. Methods: Through the computer simulation the effects of major design and driving parameters on the alignment characteristics of particles were investigated, and a cylindrical chamber with up-stream flow type was devised using two circular-shape PZTs on both sides of the chamber, one for transmitting ultrasonic wave and the other for just reflecting it. Then, the system performance was experimentally investigated as well. Results: The speed of a particle to reach pressure-node plane increased as the acoustic pressure and size of particle increased. The maximum allowable up-stream flow rate could be calculated as well. As expected, exact numbers of pressure-node planes were well formed at specific locations according to the wavelength of ultrasonic wave. As the driving frequency of PZT got close to its resonance frequency, the bands of particles were observed clearer, which meant the particles were trapped into narrower space. Higher excitation voltages to the PZT produced a greater acoustic force with which to trap particles in the pressure-node planes, so that the particles gathered could move upwards without disturbing their alignments even at a higher inlet flow rate. Conclusions: This research showed the feasibility of particle separation in solution in the continuous way by an ultrasonic standing wave. Further study is needed to develop a device to collect or harvest those separated particles.

• Geomechanics and Engineering
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• v.11 no.2
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• pp.235-252
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• 2016

This paper presents a new numerical solution of the ultimate lateral capacity of rectangular piles in clay. The two-dimensional plane strain finite element was employed to determine the limit load of this problem. A rectangular pile is subjected to purely lateral loading along either its major or minor axes. Complete parametric studies were performed for two dimensionless variables including: (1) the aspect ratios of rectangular piles were studied in the full range from plates to square piles loaded along either their major or minor axes; and (2) the adhesion factors between the soil-pile interface were studied in the complete range from smooth surfaces to rough surfaces. It was found that the dimensionless load factor of rectangular piles showed a highly non-linear function with the aspect ratio of piles and a slightly non-linear function with the adhesion factor at the soil-pile interface. In addition, the dimensionless load factor of rectangular piles loaded along the major axis was significantly higher than that loaded along the minor axis until it converged to the same value at square piles. The solutions of finite element analyses were verified with the finite element limit analysis for selected cases. The empirical equation of the dimensionless load factor of rectangular piles was also proposed based on the data of finite element analysis. Because of the plane strain condition of the top view section, results can be only applied to the full-flow failure mechanism around the pile for the prediction of limiting pressure at the deeper length of a very long pile with full tension interface that does not allow any separation at soil-pile interfaces.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.145-145
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• 2011

Light-emitting diodes (LEDs) based on III-nitrides compound semiconductors have achieved a high performance device available for display and illumination sector. However, the conventional c-plane oriented LED structures are still showing several problems given by the quantum confined Stark effect (QCSE) due to the effects of strong piezoelectric and spontaneous polarizations. The QCSE results in spatial separation of electron and hole wavefunctions in quantum wells, thereby decreasing the internal quantum efficiency and red-shifting the emission wavelength. Due to demands for improvement of device performance, nonpolar structure has been attracting attentions, since the quantum wells grown on nonpolar templates are free from the QCSE. However, current device performance for nonpolar LEDs is still lower than those for conventional LEDs. In this study, we discuss the potential possibilities of nonpolar LEDs for commercialization. In this study, we characterized current-light output power relation of the a-plane InGaN/GaN LEDs structures with the variation of quantum well structures. On-wafer electroluminescence measurements were performed with short pulse (10 us) and low duty factor (1 %) conditions applied for eliminating thermal effects. The well and barrier widths, and indium compositions in quantum well structures were changed to analyze the efficiency droop phenomenon.

• Journal of Astronomy and Space Sciences
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• v.36 no.4
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• pp.235-248
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• 2019

This paper suggests a relative orbit control strategy for the CubeSat Astronomy by NASA and Yonsei using Virtual Telescope Alignment eXperiment (CANYVAL-X) mission whose main goal is to demonstrate an essential technique, which is an arrangement among two satellites and a specific celestial object, referred to as inertial alignment, for a next-generation virtual space telescope. The inertial alignment system is a relative orbit control system and has requirements for the relative state. Through the proposed orbit control strategy, consisting of separation, proximity keeping, and reconfiguration, the requirements will be satisfied. The separation direction of the two CubeSats with respect to the orbital plane is decided to provide advantageous initial condition to the orbit controller. Proximity keeping is accomplished by differential atmospheric drag control (DADC), which generates acceleration by changing the spacecraft's effective cross section via attitude control rather than consuming propellant. Reconfiguration is performed to meet the requirements after proximity keeping. Numerical simulations show that the requirements can be satisfied by the relative orbit control strategy. Furthermore, through numerical simulations, it is demonstrated that the inertial alignment can be achieved. A beacon signal had been received for several months after the launch; however, we have lost the signal at present.

• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.473-478
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• 2003

Numerical study was made on the flow characteristics around a circular pipeline between parallel walls. The incompressible Navier-Stokes equations were solved by using a third-order upwind differential scheme. When the distance near a wall is small enough, the vortex shedding is almost completely suppressed because of the interaction with the wall boundary layer separation. This study aims to clarify the characteristics of the vortex shedding regime as the body approaches a wall as Reynolds number varies. The feature of separated vorticity dynamics is analyzed at different conditions with particular attention to the interaction between the pipeline wake and the induced separation on the plane walls.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.497-501
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• 2000

Flow over a sphere is controlled experimentally at $Re=10^5$ using electro-magnetic actuators. The electro-magnetic actuator developed in this study is composed of the permanent magnet electro-magnet membrane and slot. Eight actuators are placed inside the sphere at equally spaced intervals on a latitudinal plane and the position of the control slot is 76 from the stagnation point. Each actuator generates a periodic blowing and suction through the slot at variable frequencies of $10{\sim}140Hz$ and variable amplitudes by controlling electric signals applied to the electro-magnet. Drag on the sphere measured using a load cell is significantly reduced with control at the forcing frequencies larger than the natural shedding frequency $({\approx}14Hz\;at\;Re=10^5)$, whereas drag is slightly increased at the forcing frequency of 10Hz. It is shown from pressure measurement that the static pressure in the rear surface of the sphere is significantly increased with control, indicating that the separation is delayed due to control. Flow visualizations also show that the detaching shear layer is more attracted to the sphere center with control, the separation bubble size is significantly reduced, and motion inside the bubble is very weak, as compared to the case of uncontrolled flow.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1121-1127
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• 2000

Among many EMI suppression techniques for radiated emissions from PCB traces, image technique is adapted in this paper. A model for the analysis of the effect of image plane on the radiation of a microstrip trace is presented. After a simulation was carried out by using the FEM(Finite Element Method), field strength was measured with electric probe. The radiated emission levels were measured for various image plane width, separation distances, and their results show that the measured data are very close to those of simulation result. It proves that a proper use of image planes on the PCBs is very effective means of reducing EMI emissions on the PCBs.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5200-5222
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• 2017

The separation of control plane and data plane in Software Defined Network (SDN) makes it flexible to control the network behavior, while also causes some inconveniences to the link failure recovery due to the delay between fail point and the controller. To avoid delay and packet loss, pre-defined backup paths are used to reroute the disrupted flows when failure occurs. However, it may introduce large overhead to build and maintain these backup paths and is hard to dynamically construct backup paths according to the network status so as to avoid congestion during rerouting process. In order to realize congestion aware fast link failure recovery, this paper proposes a novel method which installs multi backup paths for every link via source routing and per-hop-tags and spread flows into different paths at fail point to avoid congestion. We carry out experiments and simulations to evaluate the performance of the method and the results demonstrate that our method can achieve congestion aware fast link failure recovery in SDN with a very low overhead.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.3
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• pp.207-215
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• 2008

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. At the Reynolds number of $2.09{\times}10^5$, heat/mass transfer coefficients are measured for the tip gap height-to-chord ratio, h/c, of 2.0% at turbulence levels of Tu = 0.3 and 14.7%. A tip-surface flow visualization is also performed for h/c = 2.0% at Tu = 0.3%. The results show that there exists a strong flow separation/re-attachment process, which results in severe local thermal load along the pressure-side corner, and a pair of vortices named "tip gap vortices" in this study is identified along the pressure and suction-side tip corners near the leading edge. The loci and subsequent development of the pressure- and suction-side tip gap vortices are discussed in detail. The combustor-level high inlet turbulence, which increases the tip-surface heat/mass transfer, provides more uniform thermal-load distribution.