• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.5
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• pp.2741-2761
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• 2017

With the purpose of copyright protection for digital video, a novel H.264/AVC watermarking algorithm based on JND model is proposed. Firstly, according to the characteristics of human visual system, a new and more accurate JND model is proposed to determine watermark embedding strength by considering the luminance masking, contrast masking and spatial frequency sensitivity function. Secondly, a new embedding strategy for H.264/AVC watermarking is proposed based on an analysis on the drift error of energy distribution. We argue that more robustness can be achieved if watermarks are embedded in middle and high components of $4{\times}4$ integer DCT since these components are more stable than dc and low components when drift error occurs. Finally, according to different characteristics of middle and high components, the watermarks are embedded using different algorithms, respectively. Experimental results demonstrate that the proposed watermarking algorithm not only meets the imperceptibility and robustness requirements, but also has a high embedding capacity.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.11
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• pp.635-644
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• 2002

Many generating units can be in parallel connection to one battery and inverter. However, one of the biggest problems we encountered is that wind speed is fluctuated sharply in accordance with the unstable weather conditions. To solve this problem, we need energy storage equipment such as storage lead-acid battery. We design a system and analyze its modeling so that it supplies a stable power to the load through DC-AC inverter part. In this paper, we applied dual step-up/down buck-boost converter and dual high-frequency half-bridge converter to the proposed system. These converters are used to store energy in the battery regardless of the change of the wind speed. The operation process of two proposed types of converters for high-power battery charging is discussed along with simulation and experimental result. We design a charging circuit which is applicable in the actual wind power generation system for 30kw and confirm the circuit's validity.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.606-608
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• 1997

In this paper, Neuro-Fuzzy Controller(NFC), a fuzzy system realized using a neural network, is to adopt for the multivariable system. In the multivariable system, the interactive effects between the variables should be taken into account. A simple compensator, using the steady-state information can be obtained for open-loop stable systems, is presented to cope with this problem. However, it should be supposed that the plant is unknown to the control system designer, but an estimate of the DC gain has been obtained by carrying out experiments on the plant. Also, if the variables are not combinated completely, it is difficult to design the controller. Therefore, we design a neuro-fuzzy controller which controls a multivariable system with only input output informations, and compare its performance with that of a PI controller. In the proposed controller, the construction of the membership functions and rule base, which is highly heuristic, can be achieved using a training process. This allows the combination of knowledge of human experts and evidence from input-output data.

• Journal of the Korean Solar Energy Society
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• v.28 no.1
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• pp.33-42
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• 2008

Zr-O ($Zr-ZrO_2$) cermets solar selective coatings with a double cermets layer film structure were prepared using a DC (direct current) magnetron sputtering method. The typical film structure from surface to bottom substrate were an $Al_2O_3$ anti-reflection layer on a double Zr-O cermets layer on an Al metal infrared reflection layer. Optical properties of optimized Zr-O cermets solar selective coating had an absorptance of ${\alpha}\;=\;0.95$ and thermal omittance of ${\epsilon}\;=\;0.10\;(100^{\circ}C)$. The absorbing layer of Zr-O cermets coatings on glass and silicon substrate was identified as being amorphous by using XRD. AFM showed that ZF-O cermets layers were very smooth and their surface roughness were approximately $0.1{\sim}0.2 nm$. The chemical analysis of the cermets coatings were determined by using XPS. Chemical shift of photoelectron binding energy was occurred due to the change of Zr-O cermets coating structure deposited with increase in oxygen flow rate. The result of thermal stability test showed that the Zr-O cermets solar selective coating was stable for use at temperature below $350^{\circ}C$.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1612-1614
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• 1994

Modulators Installed in PLS(Pohang Light Source) Linac are composed of a DC high voltage section, a charging section and a discharging section. PFN is charged by a resonant charging mechanism, and discharged by a switching device through the primary of the pulse transformer connected to a load. Charged PFN voltage must be well regulated to obtain stable output pulse voltage at the load. For this purpose, DCHV is controlled by a SCR controller with feedback signal, and PFN voltage is regulated by a De-Q'ing circuit. The full power operation test shows the pulse voltage regulation within ${\pm}0.13%$ with SCR feedback control alone, and within ${\pm}0.08%$ together with De-Q'ing. This paper describes the design concept and operational characteristics of the De-Q'ing circuit.

• Journal of the Korean institute of surface engineering
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• v.37 no.3
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• pp.152-157
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• 2004

Ti-Al-N ($Ti_{75}$ $Al_{25}$ N) and Ti-Al-Si-N ($Ti_{69}$ $Al_{23}$ $Si_{8}$N) coatings synthesized by a DC magnetron sputtering technique were studied comparatively with respect to phase characterization and high-temperature oxidation behavior. $Ti_{69}$ $Al_{23}$ $Si_{ 8}$N coating had a nanocomposite microstructure consisting of nanosized(Ti,Al,Si)N crystallites and amorphous $Si_3$$N_4$, with smooth surface morphology. Ti-Al-N coating of which surface $Al_2$$O_3$ layer formed during oxidation suppressed further oxidation. It was sufficiently stable against oxidation up to about $700^{\circ}C$. Ti-Al-Si-N coating showed better oxidation resistance because both surface Ab03 and near-surface $SiO_2$ layers suppressed further oxidation. XRD, GDOES, XPS, and scratch tests were performed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.2
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• pp.81-84
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• 2014

The bipolar resistive switching characteristics of resistive random access memory (ReRAM) based on $HfO_2$ thin films have been demonstrated by using Ag/$HfO_2$/Pt structured ReRAM device. MIcrowave irradiation (MWI) treatment at low temperature was employed in device fabrication with $HfO_2$ thin films as a transition layer. Compared to the as-deposited Ag/$HfO_2$/Pt device, highly improved uniformity characteristics of resistance values and operating voltages were obtained from the MWI treatment Ag/$HfO_2$/Pt ReRAM device. In addition, a stable DC endurance (> 100 cycles) and a high data retention (> $10^4$ sec) were achieved.

• Journal of the Korean Solar Energy Society
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• v.30 no.6
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• pp.22-27
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• 2010

In photovoltaic system, the specifications of solar array is changed as open circuit voltage and short circuit current because of cell temperature and solar radiation. A boost converter of this system connects between output of photovoltaic system and DC link capacitor of grid connected inverter as controlling duty ratio. Therefore to supply stable voltage to the grid, a boost converter is need to keep certain voltage output. Considering the capacitance and the resistance of boost converter, this paper designed proper digital controller.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.225-231
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• 2013

Low voltage ride through capability augmentation of a hybrid micro-grid system is presented in this paper which reflects enhanced reliability in the system. The control scheme involves parallel connected multiple ac-dc bidirectional converters. When the micro-grid system is subjected to a severe voltage dip by any transient fault single power converter may not be able to provide necessary reactive power to overcome the severe voltage dip. This paper discusses the control strategy of additional power converter connected in parallel with main converter to support extra reactive power to withstand the severe voltage dip. During transient fault, when the terminal voltage crosses 90% of its pre-fault value, additional converter comes into operation. With the help of additional power converter, the micro-grid system withstands the severe voltage fulfilling the grid code requirements. This multiple converter scheme provides the micro-grid system the capability of low voltage ride through which makes the system more reliable and stable.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.611-616
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• 2004

In this study, microfabrication of a micro-arcjet nozzle with Fifth-harmonic generation Nd：YAG pulses (wavelength 213 nm) and its thrust performance tests were conducted. A micro-arcjet nozzle was machined in a 1.2 mm thick quartz plate. Sizes of the nozzle were 0.44 mm in width of the nozzle exit and constrictor diameter of 0.1 mm. For an anode, a thin film of Au (~100 nm thick) was deposited by DC discharge PVD in vacuum on divergent part of the nozzle. As for a cathode, an Au film was also coated on inner wall surface. In operational tests, a stable discharge was observed for mass flow of 1.0mg/sec, discharge current of 6 ㎃, discharge voltage of 600 V, or 3.6 W input power (specific power of 3.6 MW/kg). In this case, plenum pressure of the discharge chamber was 80 ㎪. With 3.6 W input power, thrust obtained was 1.4 mN giving specific impulse of 138 sec with thrust efficiency of 24 %.