• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.295-300
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• 2005

In this paper we have designed a two-stage Class I power amplifier operated at 2.4CHz for Class-1 Bluetooth application. The power amplifier employs class-I topology to exploit its soft-switching property for high efficiency. The latch-structured pre-amplifier with amplifiers makes its output signal as sharp as possible for soft switching of the next power amplifier. It improves the overall efficiency of the proposed power amplifier. It shows 65.8$\%$ PAE, 20dB power gain and 20dBm output power.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.119-125
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• 2013

IInsulation material is generally used for preventing heat loss from heat transport fluids, and water absorption severely reduces the insulation property. The purpose of this study is to evaluate the amount of water absorption supplied by the pouring method and spraying method, to investigate the effects of water absorption on the thermal conductivity of an insulation material, and modeling the relation between water absorption and thermal conductivity. E-glass, a kind of glass fiber, and HYPERLITE, mainly composed of pearlite, are selected, to compare hygroscopic and insulation properties. E-glass is found to have much higher water absorptivity, compared to HYPERLITE. The thermal conductivity of the water-absorbed E-glass is increased by more than 150%, compared to that of no absorption, while variation of the thermal conductivity of HYPERLITE with water absorption is insignificant. A three-stage model of water absorption for thermal conductivity is developed, and the modeling results are found to be in good agreement with the experimental data.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.926-931
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• 2000

The microwave dielectric properties and the microstructures as a mole fraction of (1-x)ZnNb$_2$O$_{6}$-xPb$_{5}$Nb$_4$O$_{15}$ ceramics with CuV$_2$O$_{6}$, Sb$_2$O$_3$ and glass(ZNPN ceramics) was investigated. 0.98ZN-0.02PN ceramics containing 1.5 wt% CuV$_2$O$_{6}$ 1.0 wt% Sb$_2$O$_3$ and 1.0 wt% glass had a dielectric constant($\varepsilon$$_{r}$) of 23, Qxf$_{o}$ value of 15000 and TCF(Temperature Coefficient of resonance Frequency) of -25 ppm/$^{\circ}C$ and it is possible to be co-fired with Ag electrode at 90$0^{\circ}C$. As sintered temperature increases over 90$0^{\circ}C$ the grain size of ZNPN ceramics was increasing for growth and it has poor co-fired properties with Ag electrode.e.ctrode.e.e.

• International Journal of Highway Engineering
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• v.17 no.4
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• pp.53-61
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• 2015

PURPOSES : The objective of this study is to evaluate the SDAR (solvent deasphaltene residue), which is obtained from the solvent deasphalting (SDA) process, as a pavement material. METHODS : The physical properties of the SDAR were evaluated based on its chemical composition, and asphalt mixtures with the SDAR were fabricated and used for the evaluation of mechanical properties. Firstly, the chemical composition of SARA (saturate, aromatic, resin and asphaltene) was analyzed using the TLC-FID (thin-layer chromatography-flame ionization detector). Moreover, the basic material properties of the asphalt binder with the SDAR were evaluated by the penetration test, softening point test, ductility test, and PG (performance grade) grade test. The rheological properties of the asphalt binder with the SDAR were evaluated by the dynamic shear modulus ($G^*$) obtained using the time-temperature superposition (TTS) principle. Secondly, the mechanical properties of the asphalt mixtures with the SDAR were evaluated. The compactibility was evaluated using the gyratory compacter. Moreover, the tensile strength ratio (TSR) was used for evaluating the moisture susceptibility of the asphalt mixtures (i.e., susceptibility to pothole damage). The dynamic modulus $E^*$, which is a fundamental property of the asphalt mixture, obtained at different temperatures and loading cycles, was used to evaluate the mechanical properties of the asphalt mixtures. RESULTS AND CONCLUSION : The SDAR shows stiffer and more brittle behavior than the conventional asphalt binder. As the application of the SDAR directly in the field may cause early failures, such as cracks on pavements, it should be applied with modifiers that can favorably modify the brittleness property of the SDAR. Therefore, if appropriate additives are applied on the SDAR, it can be used as a pavement material because of its low cost and strong resistance to rutting.

• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.204-209
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• 2014

The electrodeposition of ZnO nanorods was performed on ITO glass. The optimization of two process parameters (solution temperature and growth time) has been studied in order to control the orientation, morphology, density, and growth rate of ZnO nanorods. The structural and optical properties of ZnO nanorods were systematically investigated by using field-emission scanning electron microscopy, X-ray diffractometer, and photoluminescence. Commonly, the results of the structural property show that hexagonal ZnO nanorods with wurtzite crystal structures have a c-axis orientation, and higher intensity for the ZnO (002) diffraction peaks. Furthermore, the nanorods length increased with increasing both the solution temperature and the growth time. The results of the optical property show a strong UV (3.28 eV) peaks and a weak visible (1.9~2.4 eV) bands, the intensity of UV peaks was increased with increasing both the solution temperature and the growth time. Especially, the UV peak for growth of nanorods at $75^{\circ}C$ blue-shift than different temperatures.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1161-1168
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• 1999

The redox property of oxide materials of the 3rd period transition metals(Cr~Zn), V, Mo, and W was studied with temperature-programmed reduction/temperature-programmed oxidation(TPR/TPO) experiment. The peak temperatures of TPO spectra were equal to or lower than those of TPR spectra. And the peak shapes of TPO spectra were broader than those of TPR ones. The activation energies of TPR/TPO for the oxides of the 3rd period transition metals showed in the range of 33~149 kJ/mol, while for the oxides of V, Mo, and W, they showed relatively higher values. The change of activation energies of TPR/TPO with various metal oxides showed a similar trend to the change of their metal-oxygen bond strengths. The change of activation energies of o-xylene oxidation for various metal oxides was proportional to the difference (${\Delta}E_a$) between the activation energy of TPR and that of TPO. From these results, we concluded that the oxidation of o-xylene over various metal oxide catalysts follows the Mars-van Krevelen mechanism including the surface reduction-oxidation of the metal oxide itself.

• Journal of the Korea society of information convergence
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• v.1 no.1
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• pp.41-46
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• 2008

Contents application from contents development of web technical base and with the operation different environment information of the educational resources integration the importance and necessity of the management central chain e-Learning system will be able to operate are raising its head with base. Is the actual condition which develops the development process where but, the education application currently is not standardized in base. Approaches with an educational domain from the present paper consequently, and defines MDA(Model Driven Architecture) coats e-Learning System. Also uses a studying contents standard metadata and about the contents storage space analyzes and plans the core property which uses MDA automatic tools leads and under developing boil e-Learning System will be able to provide the contents which does in actual professor own necessity.

• Journal of Biosystems Engineering
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• v.33 no.4
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• pp.260-268
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• 2008

Optical diffuse reflectance sensing has potential for rapid and reliable on-site estimation of soil properties. For good results, proper calibration to measured soil properties is required. One issue is whether it is necessary to develop calibrations using samples from the specific area or areas (e.g., field, soil series) in which the sensor will be applied, or whether a general "factory" calibration is sufficient. A further question is if specific calibration is required, how many sample points are needed. In this study, these issues were addressed using data from 42 paddy fields representing 14 distinct soil series accounting for 74% of the total Korean paddy field area. Partial least squares (PLS) regression was used to develop calibrations between soil properties and reflectance spectra. Model evaluation was based on coefficient of determination ($R^2$) root mean square error of prediction (RMSEP), and RPD, the ratio of standard deviation to RMSEP. When sample data from a soil series were included in the calibration stage (full information calibration), RPD values of prediction models were increased by 0.03 to 3.32, compared with results from calibration models not including data from the test soil series (calibration without site-specific information). Higher $R^2$ values were also obtained in most cases. Including some samples from the test soil series (hybrid calibration) generally increased RPD rapidly up to a certain number of sample points. A large portion of the potential improvement could be obtained by adding about 8 to 22 points, depending on the soil properties to be estimated, where the numbers were 10 to 18 for pH, 18-22 for EC, and 8 to 22 for total C. These results provide guidance on sampling and calibration requirements for NIR soil property estimation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3247-3252
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• 2013

The convergence of ICT and cloud computing is treated as a main issue all over the fields including education. This development leads to change from e-learning to u-learning and smart education. Therefore, we need to study in term of the systematic and a long-term viewpoint how smart education environment have an influence on the practical space. And we need a concrete study for smart education space based on property of space. Under these critical mind, this study understands the smart education space in terms of the convergence of computing space and physical space. As a Result, smart education space have major property such as flexibility, communication, polyvalence.

• Advances in biomechanics and applications
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• v.1 no.4
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• pp.253-267
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• 2014

The human head is identified as the body region most frequently involved in life-threatening injuries. Extensive research based on experimental, analytical and numerical methods has sought to quantify the response of the human head to blunt impact in an attempt to explain the likely injury process. Blunt head impact arising from vehicular collisions, sporting injuries, and falls leads to relative motion between the brain and skull and an increase in contact and shear stresses in the meningeal region, thereby leading to traumatic brain injuries. In this paper the properties and material modeling of the subarachnoid space (SAS) as it relates to Traumatic Brain Injuries (TBI) is investigated. This was accomplished using a simplified local model and a validated 3D finite element model. First the material modeling of the trabeculae in the Subarachnoid Space (SAS) was investigated and validated, then the validated material property was used in a 3D head model. In addition, the strain in the brain due to an impact was investigated. From this work it was determined that the material property of the SAS is approximately E = 1150 Pa and that the strain in the brain, and thus the severity of TBI, is proportional to the applied impact velocity and is approximately a quadratic function. This study reveals that the choice of material behavior and properties of the SAS are significant factors in determining the strain in the brain and therefore the understanding of different types of head/brain injuries.