• Journal of Preventive Medicine and Public Health
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• v.40 no.1
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• pp.59-63
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• 2007

Objectives : Nitrogen dioxide $(NO_2)$ has been inconsistently associated with gradual decreases in lung function. Here, we studied the effects of $NO_2$ exposure in asthmatics by examining the association between changes in lung function and concentrations of $NO_2$ which were personally measured. Methods : Peak expiratory flow (PEF) and daily personal exposures to $NO_2$ were recorded on 28 patients with asthma (confirmed by methacholine provocation test) over 4 weeks. We used generalized estimating equations to assess the relationship between personal $NO_2$ exposure and PEF, adjusting for potential confounders such as age, gender, outdoor particulate matter, temperature, humidity, and exposure to environmental tobacco smoke. Results : The personal $NO_2$ exposures were higher than the corresponding ambient levels. The mean personal: ambient ratio for $NO_2$ was 1.48. The personal $NO_2$ exposures were not associated with the morning PEF, evening PEF, or the diurnal PEF variability. However, environmental tobacco smoke was negatively associated with both the morning and evening PEF. Conclusions : Among the asthmatic adults who participated in this study, we found no apparent impact of personal $NO_2$ exposures on the peak expiratory flow.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.955-962
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• 2015

The Vickers test can be used for all types of materials, and it has one of the widest scales among hardness tests. The hardness may be considered as a probability variable when evaluating the mechanical properties of materials. In this study, we investigate the statistical properties of the bending strength and Vickers hardness in $ZrO_2$ monolithic and $ZrO_2/SiC$ composites depending on the amount of $TiO_2$ additives. The bending strength and Vickers hardness were found to agree well with the Weibull probability distribution. We evaluate the scale parameter and shape parameter in as-received $ZrO_2$ and $ZrO_2/SiC/TiO_2$ ceramics, as well as their heat treated ceramics. We also evaluate the parameters in accordance with the increase in in the indentation load.

• Applied Chemistry for Engineering
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• v.18 no.2
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• pp.142-147
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• 2007

In this study, mesoporous tin oxide was synthesized by sol-gel method using $C_{16}TMABr$ surfactant as a template in a basic condition. The optimum conditions for the synthesis of mesoporous $SnO_2$ were investigated and the obtained samples were characterized by XRD, nitrogen adsorption and TEM analysis. A mesoporous and nanostructured $SnO_2$ gas sensor with Au electrode and Pt heater has been fabricated on alumina substrate as one unit via a screen printing process. Sensing abilities of fabricated sensors were examined for CO and $CH_4$ gases, respectively, at $350^{\circ}C$ in the concentration range of 1~10,000 ppm. Influence of loading amount of palladium impregnated on $SnO_2$ was also tested in detection of those gases. High sensitivity to detecting gases and the fast response speed with stability were obtained with the mesoporous tin oxide sensor as compared to a non-porous one under the same detection conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.5
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• pp.411-420
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• 2009

This study presents an extended finite difference method based on moving least squares(MLS) method for solving potential problems with interfacial boundary. The approximation constructed from the MLS Taylor polynomial is modified by inserting of wedge functions for the interface modeling. Governing equations are node-wisely discretized without involving element or grid; immersion of interfacial condition into the approximation circumvents numerical difficulties owing to geometrical modeling of interface. Interface modeling introduces no additional unknowns in the system of equations but makes the system overdetermined. So, the numbers of unknowns and equations are equalized by the symmetrization of the stiffness matrix. Increase in computational effort is the trade-off for ease of interface modeling. Numerical results clearly show that the developed numerical scheme sharply describes the wedge behavior as well as jumps and efficiently and accurately solves potential problems with interface.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.8
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• pp.97-105
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• 2015

Content-adaptive steganography methods embed secret messages in hard-to-model regions of covers such as complicated texture or noisy area. Content-adaptive steganalysis methods often need high dimensional features to capture more subtle relationships of local dependencies among adjacent pixels. However, these methods require many computational complexity and depend on the location of hidden message and the exploited distortion metrics. In this paper, we propose an improved steganalysis method for content-adaptive steganography to enhance detection rate with small number features. We first show that the features form the difference between DCT coefficients are useful for analyzing the content-adaptive steganography methods, and present feature extraction mehtod using first-order Markov probability for the the difference between DCT coefficients. The extracted features are used as input of ensemble classifier. Experimental results show that the proposed method outperforms previous schemes in terms of detection rates and accuracy in spite of a small number features in various content-adaptive stego images.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2403-2408
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• 2015

For image data the discrete cosine transform (DCT) has comparable energy compaction capability to Karhunen-Loeve transform (KLT) which is optimal. Hence DCT has been widely accepted in various image and video compression standard such as JPEG, MPEG-2, and MPEG-4. Recently some approximate DCT's have been reported, which can be computed much faster than the original DCT because their coefficients are either zero or the power of 2. Although the level of energy compaction is slightly degraded, the approximate DCT's can be utilized in real time implementation of image or visual compression applications. In this paper, an approximate 8-point DCT which contains 17 non-zero power-of-2 coefficients and high energy compaction capability comparable to DCT is proposed. Transform coding experiments with several images show that the proposed transform outperforms the published works.

• Resources Recycling
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• v.27 no.3
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• pp.86-92
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• 2018

The amount of construction waste generated is steadily increasing every year, and the Law for Promotion of Recycling is enacted. However, it is difficult to use it as a recycled aggregate for concrete, which is presented in the quality standard of recycled aggregate with high water uptake and low density due to low separation of aggregate between concrete and cement paste. Therefore, in this study, a multi-stage impact crusher was used to remove mortar, which is essential for improving the quality of recycled aggregate. In analyzing the characteristics of the equipment, the spectrum of energy generated in each part between the particle and the equipment was calculated by using DEM. In order to generate an effective separation phenomenon, it was confirmed that the operation condition of 900 RPM was appropriate based on the ratio of the number of collisions (L/H) of the low energy group (L) to the number of collisions of the high energy group (H).

• KIPS Transactions on Software and Data Engineering
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• v.9 no.2
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• pp.39-44
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• 2020

In this paper, we show a modified Diffie-Hellman key exchange protocol that can exchange keys by exposing only minimal information using pre-computable session key pairs. The discrete logarithm problem, which provides the safety of existing Diffie-Hellman and Diffie-Hellman based techniques, is modified to prevent exposure of primitive root. We prove the algorithm's operation by applying the actual value to the proposed scheme and compare the execution time and safety with the existing algorithm, shown that the security of the algorithm is improved more than the product of the time complexity of the two base algorithms while maintaining the computation amount at the time of key exchange. Based on the proposed algorithm, it is expected to provide a key exchange environment with improved security.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.3
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• pp.691-698
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• 2015

In the area of high traffic volume, such as expressway across large cities, the amount of nitrogen oxides (NOx) emitted into the atmosphere as air pollution can be significant since NOx gases are the major cause of smog and acid rain. Recently, the importance of NOx removal has arisen in the world. Titanium dioxide ($TiO_2$), that is one of photocatalytic reaction material, is very efficient for removing NOx. Therefore, application of $TiO_2$ concrete is a good alternative in order to remove NOx which is a main cause of air pollution. This experimental study aimed to evaluate the long-term performance of $TiO_2$ concrete such as NOx removal efficiency due to performance period and environmental resistance for application of road structures. It was found that the $TiO_2$ is reasonable applicable on the road structure because $TiO_2$ concrete has a long-term performance.

• Analytical Science and Technology
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• v.16 no.6
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• pp.431-437
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• 2003

Metalization yield of uranium oxide to uranium metal from lithium reduction process of spent pressurized water reactor (PWR) fuels was measured using thermogravimetric analyzer. A reduced metal produced in the process was divided into a solid and a powder part, and each metalization yield was measured. Metalization yield of the solid part was 90.7~95.9 wt%, and the powder being 77.8~71.5 wt% individually. Oxidation behaviour of the quartemary alloy was investigated to take data on the thermal oxidation stability necessary for the study on dry storage of the reduced metal. At $600{\sim}700^{\circ}C$, weight increments of alloy of Mo, Ru, Rh and Pd was 0.40~0.55 wt%. Phase change on the surface of the alloy was started at $750^{\circ}C$. In particular, Mo was rapidly oxidized and then the alloy lost 0.76~25.22 wt% in weight.