• Journal of the Korean Wood Science and Technology
• /
• v.44 no.2
• /
• pp.231-240
• /
• 2016

The change in chemical compositions of leachate and medium density fiberboard (MDF) from a laboratory-scale simulated landfill which constructed in a plastic container containing alternating layers of soil and MDF was investigated to evaluate decomposing of MDF in soil. Four treatments were conducted: 1) MDF in soil, 2) MDF only, 3) cured UF resin in soil, and 4) soil only. Molecular weight (MW) distribution of compounds in leachate from soil only treatment did not change over time. In UF resin in soil treatment, the MW distribution shifted to a lower MW distribution over time, while the peak shifted to the left indicated changing to higher MW distribution in leachate from treatment 1 and 2 contained MDF. Higher percent nitrogen in leachate was observed in MDF containing treatments due to the UF resin in the MDF. The percent carbon slightly increased in MDF only while that greatly decreased in MDF in soil treatment maybe due to bacterial activity. The percent of extractable materials from the MDF decreased greatly on day 35 compare to day 0, and subsequently did not change much on day 77. In contrast, percent holocellulose and lignin did not change much over time. No structural change of the wood fiber in MDF occurs during the study. Water-soluble materials from MDF in soil contributed the change in chemical composition of leachate.

• Journal of Environmental Science International
• /
• v.14 no.6
• /
• pp.525-532
• /
• 2005

Polyelectrolyte titration, which was called colloid titration is based on the stoichiometric reaction between oppositely charged polyelectrolytes, This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulfate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In this work, two methods have been investigated: visual titrimetry based on the color change of a cationic dye (o-toluidine blue, o-Tb) and spectrophotometry based on the absorbance change corresponding to the color change of the same dye. These have been applied to several cationic polyelectrolytes with different charge density and molecular weight. In all cases, the cationic charge was due to quaternary nitrogen groups. In the case of cationic dye, it was shown that the sharpness depends on the charge density of cationic polyelectrolyte. With the polyelectrolytes of lower charge density, the binding to PPVS is weaker and binding of the dye to PPVS can occur before all of the polyelectrolyte charge has been neutralized. However, by carrying out titrations at several polyelectrolyte concentrations, good linear relationships were found, from which reliable charge density values could be derived. Effects of pH and ionic strength were also briefly investigated. For cationic polyelectrolytes (copolymers of acrylamide and dimethylaminoethy] acrylate), there was some loss of charge at higher pH values, probably as a result of hydrolysis. Increasing ionic strength causes a less distinct color change of o-Tb, as a result of weaker electrostatic interactions.

• Bulletin of the Korean Chemical Society
• /
• v.21 no.6
• /
• pp.628-634
• /
• 2000

Crosslink is the most important chemistry in a rubber vulcanizate. Degree and type of crosslinks of the vulcanizate determine its physical properties. Change of crosslink density and deformation of a rubber vulcanizate by thermal aging were studied using natural rubber (NR) vulcanizates with various cure systems (conventional, semi-EV, and EV) and different cure times (under-, optimum-, and overture). All the NR vulcanizates were deformed by the thermal aging at 60-100 $^{\circ}C.$ The higher the aging temperature is, the more degree of the deformation is. The undercured NR vulcanizates after the thermal aging were deformed more than the optimumand overcured ones. The NR vulcanizates with the EV cure system were less deformed than those with the conventional and semi-EV cure systems. The deformation of the NR vulcanizates was found to be due to change of the crosslink density of the vulcanizates. The crosslink densities of all the vulcanizates after the extraction of organic materials were also changed by the thermal ging. The sources to change the crosslink densities of the vulcanizates by the thermal aging were found to be dissociation of the existing sulfur crosslink and the formation of new crosslinks by free sulfur, reaction products of curing agents, and pendent sulfide groups.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.2
• /
• pp.95-100
• /
• 1998

A helical inductively coupled plasma asher, which produces low energy and high density plasma, has been built and investigated for photoresist stripping process. Oxygen ion density in the order of $10^{11}/cm^3$ is measured by Langmuir probe, and higher oxygen radical density is observed by Optical Emission Spectrometer. As RF source power is increased, the plasma density and thus photoresist stripping rate are increased. Independent RF bias power to the wafer stage provides a dc bias to the wafer and an ability to add the ion assisted reaction. At 1 KW of the source power, the coupling mechanism of the RF power to the plasma is changed from the inductive mode to the capacitive one at about 1 Torr. This change causes the plasma density and ashing rate decreases abruptly. The critical pressure of the mode change becomes larger with larger RF power.

• Journal of the Korean Geographical Society
• /
• v.43 no.1
• /
• pp.117-133
• /
• 2008

Although development density control has received murk attention in urban planning, there has been little research on empirical methods that can examine local changes in development density. Recently, attempts have been made to develop cellular automata (CA) models that can be applied to urban landuse change. This paper aims to develop an extended landuse change model based on urban CA considering development density. The proposed model not only includes density control component in a model framework, but also directly estimates local density changes in land use. The developed model was applied to the study area, which was a part of central Seoul. The calibration of the model was carried out over the period $1900s\sim2000s$ using parcel-based land use data and related variables The results of the calibrated model have been tested by comparison with actual landuse data, and have demonstrated that the developed model can produce realistic simulations of urban landuse changes. But model output is dependent on the spacio-temporal resolution of input data. Further research is necessary to improve the calibration procedure and methods for evaluating model validity.

• Proceedings of the Korean Statistical Society Conference
• /
• 2003.05a
• /
• pp.287-293
• /
• 2003

In this paper we consider the problem of parameter change based on the cusum test proposed by Lee et al. (2003). The cusum test statistic is constructed utilizing the estimator minimizing density-based divergence measures. It is shown that under regularity conditions, the test statistic has the limiting distribution of the sup of standard Brownian bridge. Simulation results demonstrate that the cusum test is robust when there arc outliers.

• Structural Engineering and Mechanics
• /
• v.86 no.3
• /
• pp.349-359
• /
• 2023

This paper presents a technique for determining the optimal number of elements in stochastic finite element analysis based on reliability analysis. Using the change-of-variable perturbation stochastic finite element approach, the probability density function of the dynamic responses of stochastic structures is explicitly determined. This method combines the perturbation stochastic finite element method with the change-of-variable technique into a united model. To further examine the relationships between the random fields, discretization of the random field parameters, such as the variance function and the scale of fluctuation, is also performed. Accordingly, the reliability index is calculated based on the explicit probability density function of responses with Gaussian or non-Gaussian random fields in any number of elements corresponding to the random field discretization. The numerical examples illustrate the effectiveness of the proposed method for a one-dimensional cantilever reinforced concrete column and a two-dimensional steel plate shear wall. The benefit of this method is that the probability density function of responses can be obtained explicitly without the use simulation techniques. Any type of random variable with any statistical distribution can be incorporated into the calculations, regardless of the restrictions imposed by the type of statistical distribution of random variables. Consequently, this method can be utilized as a suitable guideline for the efficient implementation of stochastic finite element analysis of structures, regardless of the statistical distribution of random variables.

• International Journal of Contents
• /
• v.9 no.2
• /
• pp.66-69
• /
• 2013

In the U.S., performance assessment on the Automatic Exposure Control system (AEC) is managed according to the Mammography Quality Standards Act (MQSA). However, The AEC is not available in the performance assessment conducted in Korea. Also, there is no study made on the performance of the automatic exposure control system for mammography in Korea. For this reason, this study examined the performance of the automatic exposure control system for mammography that was clinically used in the Incheon area. Result showed that the difference of the mean optical density was 0.79 ~ 2.81. This implies that some devices caused unnecessary x-ray exposure to patients. Furthermore, only 61.5% of the entire experimental device was shown to be satisfactory in terms of change in mean optical density. Moreover, in terms of the subject's thickness, change in radiographic density was shown to be severe among lower X-ray tube voltage while there was severe density change in X-ray image depending on X-ray tube voltage among the subjects with more thickness. Therefore, it is suggested to provide performance management on the AEC for mammography.

• Journal of the Korean Applied Science and Technology
• /
• v.34 no.4
• /
• pp.1112-1120
• /
• 2017

Petroleum products are composed of various types of hydrocarbon compounds. Like other types of liquids, they presented the variation of density and volume according to temperature change. The method of measuring the density of petroleum products in a liquid phase is based on experimental data obtained mainly for each fractionally distilled petroleum product. In this study, the density and volume changes of kerosene and automotive diesel according to temperature change were measured and the property of change were analyzed. The conversion values were calculated using the density volume conversion table proposed by international standard ASTM. In addition, we analyzed the differences between the reference values and the measured values for the temperature changes specified in the domestic metering law.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.22 no.1
• /
• pp.128-136
• /
• 1992

This study was undertakened to investigate the change of image characteristics on dental films according to the process of using time of processing solution in automatic processor. Base + fog density, film density and subject contrast were measured with the digital densitometer, the pH of developing and fixing solution were measured with Digital pH / ION Meter. The following results were obtained: 1. Base + fog density was increased with the process of using time of the processing solution and was over the maximum permissible base + fog density 0.25 from the 3rd day. 2. Film density was increased with the process of using time of the processing solution. 3. Subject contrast was decreased with the process of using time of the processing solution. 4. The pH of the developing solution was decreased with the process of using time, the pH of the fixing solution was increased.