• Proceedings of the KSME Conference
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• 2001.06d
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• pp.605-611
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• 2001

A numerical technique for simulating the aggregation of charged particles was presented with a Brownian dynamic simulation in the free molecular regime. The Langevin equation was used for tracking each particle making up an aggregate. A periodic boundary condition was used for calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered the thermal force and the electrostatic force for the calculation of the particle motion. The morphological shape of aggregates was described in terms of the fractal dimension. The fractal dimension for the uncharged aggregate was $D_{f}=1.761$. The fractal dimension changed slightly for the various amounts of bipolar charge. However, in case of unipolar charge, the fractal dimension decreased from 1.641 to 1.537 with the increase of the average number of charges on the particles from 0.2 to 0.3 in initial states.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.994-995
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• 2008

It is possible to suppress voltage drops, power loading fluctuations and regeneration power lapses for DC railway systems by applying an energy storage system. A electric double layer capacitor (EDLC) of the rapid charge/discharge type has been developed and used in wide ranges. It has a long life, high efficiency and maintenance free/low pollution features as a new energy storage element. In this paper, an efficient charge and discharge control method of a bidirectional DC-DC converter using the supercapacitor is proposed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2329-2335
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• 2011

The Wireless low floor tram uses the energy more effectively than other systems with onboard battery system. But for this the SOC(state of charge) management of the battery system is required. This paper is focused on the SOC management strategy of battery system for propulsion in wireless low floor tram. For minimizing consumption energy, the SOC management strategy that maximizes the regeneration energy is studied. The SOC operating region is divided to overcome the limited life cycle pointed out as a disadvantage of battery system. And the effective energy management strategy of tram is suggested through the charge/discharge of the battery system according to tram status in catenary/catenary-free section.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.6
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• pp.664-670
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• 2015

A four-times-VDD switch that supports high and low voltage mode operations is demonstrated in a generic 65 nm logic process. The proposed switch shows the robust operation for supply voltages ranging from VDD to $4{\times}VDD$. A cascaded voltage switch and a voltage doubler based charge pump generate the intermediate supply voltage levels required for the proposed high voltage switch. All the high voltage circuits developed in this work can be implemented using standard logic transistors without being subject to any voltage overstress.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.2
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• pp.79-99
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• 2010

Pulsed current-voltage (I-V) methods are introduced to evaluate the impact of fast transient charge trapping on the performance of high-k dielectric transistors. Several pulsed I-V measurement configurations and measurement requirements are critically reviewed. Properly configured pulsed I-V measurements are shown to be capable of extracting such device characteristics as trap-free mobility, trap-induced threshold voltage shift (${\Delta}V_t$), as well as effective fast transient trap density. The results demonstrate that the pulsed I-V measurements are an essential technique for evaluating high-$\kappa$ gate dielectric devices.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.35-39
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• 2005

This paper presents a method to reduce hysteresis in multilayer ceramic actuator by connecting the actuator with a capacitor in a series circuit. The change in hysteresis with respect to the capacitor was examined. $0.2Pb(Mg_{1/3}Nb_{2/3})O_3-0.8Pb(Zr_{0.475}Ti_{0.525})O_3$ ceramic material was used as a piezoelectric material for the actuator. Displacement of the actuator was measured in a capacitive gap sensor measuring system. In case of inserting a capacitor in a total circuit, hysteresis became dramatically decreased, and then finally the hysteresis value can be reduced below $0.2\%$. It was found in this present study that reducing the hysteresis in the actuator is dependent upon the characteristics of the capacitor in total circuit and also operating frequency.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.10
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• pp.1499-1504
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• 2013

As oil price and demand for environment friendly vehicle rapidly increase, research on electric car is being widely carried out. Especially, NEV(Neighborhood Electric Vehicle) is a pollution-free vehicle that can be mass-produced which the time of development for related technologies is urgently needed. In this paper the On-Board charger for mid- and large- sized secondary cell is applicable in aerospace and other general industries, and the Off-Board standing charger is expected to be employed in creating charging infrastructure.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.175.1-175.1
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• 2014

Despite growing interest in Ge as a possible alternative to Si, reliable data on Ge surface has been relatively scarce. Using low temperature scanning tunneling microscopy (STM), we investigate band-bending effects of localized charge traps at Ge(001) surface at 78 K. For this investigation, we prepared nearly defect-free Ge(001) surface by keeping the background pressure to < $1{\times}10^{-10}$ mbar during outgassing. Ge(001) surfaces this obtained exhibit a flat-band condition, and deposition of charge traps induce a distinct, sharp boundary between pinned and depinned surface area in the constant current mode STM images. We will show the tip-surface interaction plays an essential role in producing the boundary, and discuss about the conditions that enable the pinning effect.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.890-893
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• 2003

In this paper, we have designed the fractional-N frequency synthesizer for bluetooth system using 0.35-um CMOS technology and 3.3-V single power supply. The designed synthesizer consist of phase-frequency detector (PFD), charge pump, loop filter, voltage controlled oscillator (VCO), frequency divider, and sigma-delta modulator. A dead zone free PFD is used and a modified charge pump having active cascode transistors is used. A Multi-modulus prescaler having CML D flip-flop is used and VCO having a tuning range from 746 MHz to 2.632 GHz at 3.3 V power supply is used. Total power dissipation is 32 mW and phase noise is -118 dBc/Hz at 1 MHz offset.

• Bulletin of the Korean Chemical Society
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• v.28 no.1
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• pp.95-98
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• 2007

Polyethylenimine (PEI) has been widely investigated for delivery of DNA into cells. It was previously reported that there were at least two types of cytotoxicity in PEI-mediated gene delivery, immediate and delayed toxicities. PEI-mediated gene delivery protocols use net cationic complexes with an excess of PEI to maintain equilibrium between the complexed and dissociated forms in solution. In this study, toxicity of free PEI or PEI/ DNA complex was investigated. Human embryonic kidney 293 cells were incubated with free PEI or PEI/DNA complex for 4 hrs. Then, the cells were analyzed at 6, 24, 48, and 96 hrs after the incubation. In MTT assay, the viability of the cells incubated with PEI/DNA complex was continuously decreased with time, while that of the cells incubated with free PEI was not. On the contrary, the expression level of the luciferase gene increased gradually along with time. Release of DNAs from the complexes for transcription produces free PEIs in the cells. This process may proceed slowly due to high charge density of PEI and may be related to delayed toxicity. In addition, apoptotic cells were observed only in the cells incubated with the PEI/DNA complex from 24 hrs after the incubation. The results suggest that PEI/DNA complex contributes to the delayed toxicity by inducing apoptosis and that the delayed toxicity may be related to decomplexation of the complexes in the cells.