• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.381-381
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• 2010

$(ZrO_2)_{0.66}(HfO_2)_{0.34}$ thin films as gate dielectrics have been proposed to overcome the problems of tunneling current and degradation mobility inachieving a thin equivalent oxide thickness. An extremely thin $SiO_2$ layer is used in order to separate the carrier in MOSFET channel from the dielectric field fluctuation caused by phonons in the dielectric which decreases the carrier mobility. The electronic and optical properties influenced the device performance to a great extent. $(ZrO_2)_{0.66}(HfO_2)_{0.34}$ dielectric films on p-Si (100) were grown by atomic layer deposition method, for which the conduction band offsets, valence band offsets and band gapswere obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence and conduction band offset values for $(ZrO_2)_{0.66}(HfO_2)_{0.34}$ dielectric thin film, grown on Si substrate were about 5.34, 2.35 and 1.87 eV respectively. This band alignment was similar to that of $ZrO_2$. In addition, The dielectric function (k, $\omega$), index of refraction n and the extinction coefficient k for the $(ZrO_2)_{0.66}(HfO_2)_{0.34}$ thin films were obtained from a quantitative analysis of REELS data by comparison to detailed dielectric response model calculations using the QUEELS-$\varepsilon$(k, $\omega$)-REELS software package. These optical properties are similar with $ZrO_2$ dielectric thin films.

• Transactions on Electrical and Electronic Materials
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• v.11 no.5
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• pp.206-211
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• 2010

Piezoelectric energy harvesting uses piezoelectric, which is able to convert unused mechanical vibration energy to electrical energy, such as with motor and machinery. The piezoelectric energy harvester was constructed with a cantilever made of lead zirconate titanate with a metal plate. The primary material was soft lead zirconium titanate (PZT-5H) due to the large strain availability, acceptable mechanical strength and high piezoelectric constant. This technique's drawback is that the energy efficiency is lower than the other energy harvesting methods, but this study increases the output electric power efficiency by analyzing a finite element method for the structure of the piezoelectric energy harvester. We manufactured two cantilever types as follows: the L-60 and L-33 bimorph piezoelectric energy harvesters. Their resulting energy harvesters were able to obtain high voltage values as follows: 27.4 mV and 40.6 mV. Moreover, these results have a similar band of resonance frequency it comparison to the simulation. Consequently, this study was confirmed with validity. The output electric powers of the L-60 and L-33 types have 3.1 mW/s and 5.8 mW/s with 47 Hz and 148 Hz of resonance frequency and then, the load resistivities were $100k\Omega$ and $10k\Omega$, respectively.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.3
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• pp.33-44
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• 1999

An energy balance procedure is developed to incorporate the effects of earthquake duration which involves the effect of cyclic loading and the corresponding cumulative plastic deformation. Particular emphasis is given to the flexural failure of non-seismically designed columns of reinforced concrete frames. For this, conceptual strength deterioration models for columns, governed by concrete, anchorage failure and longitudinal steel fracture due to low-cycle fatigue, are proposed. It is evident that the energy-based method has good agreement with the experimental data and is able to predict the failure mode.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.199-204
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• 1998

To analysis the failure character of Low-Heat concrete which is used to prevent the thermal crack caused by hydration heat, static loading test was performed by this test method, "Determination of the Fracture Energy of Motar and Concrete by Means of Three-Point Band Tests on Notched Beam" (suggested by RILEM 50-FMC Committe). This study compared and analysised the fracture energy of Mode I (opening mode), the most general pattern in the view of water-cemente ratio(W/C), compressive strength and age of Ordinary Portland Concrete and Low-Heat Concrete under the same mixture. The test results show that the case of Ordinary Portland Concrete and Low-Heat Concrete, low Water-Cemente ratio(W/C) cause the increase of fracture energy, and high failure-strength decrease failure-deflection, and the fracture energy of Low-Heat Concrete is similar to Ordinary Portland Concrete as the age increase. increase.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.14-22
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• 1995

We treat the vibrations of circular beam and make use of the method employed by J.T.Tielking, which is based on the principle of Hamilton. The Hamilton's principle requires the determinations of the potential and the kinetic energy of the model as well as done by internal pressure forces. Thje potential energy is composed of a part due to elastic deformations of the beam and a part due to radial and tangential displacements of the tread band with respect to the wheel rim. The equations of motion for such a model are derived by reference to conventional energy method. The accuracy of the expressions is demonstrated by comparison of calculated and experimental natural frequencies for circular beam. The circular beam experiences a harmonic, radial excitat- ion acting at a fixed point on the beam. Modal parameters varying the inflation pressure and load are determined experimentally by using the transfer function method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1199-1205
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• 2008

The vehicle design engineers have studied the method of applying damping materials to the vehicle bodies by computer simulations and experimental methods in order to improve the vibration and noise characteristics of the vehicles. The unconstrained layer damping, being concerned with this study, has two layers(base layer and damping layer) and proyides vibration control of the base layer through extensional damping. Generally this kind of surface damping method is effectively used in reducing structural vibration at frequencies beyond 150Hz. The most important thing is how to apply damping treatment with respect to location and size of the damping material. To solve these problems, the current experimental methods have technical limits which are cumbersome, time consuming, and expensive. This Paper proposes a method based on finite element method and it employes averaged ESE(element strain energy) percent of total of dash panel assembly for 1/1 octave band frequency range by MSC/NASTRAN. The regions of high ESE percent of total are selected as proposed location of damping treatment. The effect of damping treatment is analyzed by comparing the frequency response function of the SPCC bare Panel and the damping treated panels.

• Journal of Radiation Protection and Research
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• v.26 no.2
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• pp.73-78
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• 2001

In order to find the exposure conversion coefficients for 3"X3" NaI spectrum, we measured the exposure rates with the pressurized ion chamber at 29 different areas in the range of $4{\sim}23{\mu}R\;h^{-1}$, and also measured the gamma spectra with 3"X3" and 4"X4" NaI detectors, simultaneously. The exposure conversion coefficient of the total energy method was determined using the linear relation between the measured exposure rate and the gamma spectrum energy. In order to find the exposure conversion coefficients of the energy band method, we applied the exposure conversion coefficients recommended by NCRP to the 4"X4" NaI spectra, and calculated the exposure rates due to $^{40}K,\;^{238}U$, and $^{232}Th$ series respectively. Using the linearly proportional relation between the obtained $^{232}Th$ series exposure rate and peak area of 2614 keV that represents the $^{232}Th$ series, we obtained the exposure conversion coefficients for $^{232}Th$ series. We also determined the conversion coefficients for $^{238}U$ series and $^{40}K$ using a similar method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1105-1116
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• 2008

Cognitive radio is one of the most effective techniques to improve the spectrum utilization efficiency. To implement the cognitive radio, spectrum sensing is considered as the key functionality because only counting on it, can the secondary users identify the spectrum holes and utilize them efficiently without causing interference to primary users. Generally, there are several spectrum sensing methods; the most common and simplest method is energy detection. However, the conventional energy detection has some disadvantages, which are caused by noise, especially, uncertain noise power leads to degradation of energy detector. In this paper, to solve this problem, we proposed sliding window-based energy detection method which can devide the frequency band of primary signal and noise using sliding window to estimate the power of primary user without the noise effect and achieve the better performance. It can calculate the energy of primary user only and can detect the primary signal. The simulation result shows that our proposed method outperforms conventional one.

• Advances in nano research
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• v.13 no.5
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• pp.475-485
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• 2022

Crystalline silicon photovoltaic cells have advantages of zero pollution, large scale and high reliability. A major challenge is that sunlight wavelength with photon energy lower than semiconductor band gap is converted into heat and increase its temperature and reduce its conversion efficiency. Traditional cooling PV method is using water flowing below the modules to cool down PV temperature. In this paper, the idea is proposed to reduce the temperature of the module and improve the energy conversion efficiency of the module through the modulation of the solar spectrum. A spectrally selective nanofilm reflector located directly on the surface of PV is designed, which can reflect sunlight wavelength with low photon energy, and even enhance absorption of sunlight wavelength with high photon energy. The results indicate that nanofilm reflector can reduce spectral reflectivity integral from 9.0% to 6.93% in 400~1100 nm wavelength range, and improve spectral reflectivity integral from 23.1% to 78.34% in long wavelength range. The nanofilm reflector can reduce temperature of PV by 4.51℃ and relatively improved energy conversion efficiency of PV by 1.25% when solar irradiance is 1000 W/m². Furthermore, the nanofilm reflector is insensitive in sunlight's angle and polarization state, and be suitable for high irradiance environment.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2842-2849
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• 2024

The amorphous glasses containing PbO, ZnO, MgO, and B₂O₃ have been fabricated using the melt quenching technique. The structural properties have been analysed using the Fourier-transform infrared (FTIR) and Raman spectroscopy. Derivative of Absorption Spectra Fitting (DASF) method have been used to estimate the band gap energy from the UV-Vis absorption data which decreases from 3.02 eV to 2.66 eV with increasing the concentration of the PbO.The four glass samples 0.284 and 0.826 MeV showed unique variations in terms of gamma attenuation ability. LZMB4 glass sample proved to be the mist effective in terms of shielding of gamma radiation as it requires little distance compared to LZMB3, LZMB2 and LZMB1 to attenuate. RPE revealed a raise with increase in the thickness of the material and reduces as the energy raises. TF is superior in LZMB1 compared to LZMB2, LZMB3 and LZMB4, confirming that, LZMB4 will attenuate better. The Z_Eff of the materials was seen falling as the energy increases, confirming that the linear attenuation coefficient of the glass materials decreases when the energy is increased. The results confirmed that, glass material LZMB4 is the best option especially for gamma radiation shielding applications compared to LZMB3, followed by LZMB2, then LZMB1.