• Journal of Sensor Science and Technology
• /
• v.6 no.6
• /
• pp.500-507
• /
• 1997

For fine control of operating temperature of shape memory alloy, we investigated the effect of thermal teratment of shape memory alloy with the impurity kind. The martensitic transformation temperature in a Cu-17.25Zn-15Al and Cu-17.25Zn-15Al-1Ag/Fe was measured using electrical resistivity as a function of quenching temperature. Order-disorder phase transition temperatures in parent phase were measured and kind of transition were distinguised by DSC(differential scanning calorimeter) with heating rate variation. And structual changes were studied with XRD. For the Cu-17.25Zn-15Al shape memory alloy, the order-disorder phase transition temperature, $T_{B2}$ and $T_{L21}$ was 809K and 610K and for the Cu-17.25Zn-15Al-1Ag and Cu-17.25Zn-15Al-1Fe specimen $T_{B2}$ and $T_{L21}$ was 794K and 610K, and 803K and 613K, respectively. In all the specimens, quenching from near $T_{B2}$ leads to an increase in martensitic temperature, whereas quenching from near $T_{L21}$ leads to an decrease in martensitic temperature.

• Journal of the Korean Geosynthetics Society
• /
• v.12 no.1
• /
• pp.39-50
• /
• 2013

This study aims at investigating the behavior of the ground water level when installing upward soil nails that drain water as well. To do this, a series of down-scaled model tests were conducted. A model slope with weathered soils was prepared and then an artificial rain was scattered on the slope. The relative densities of soil specimen were 60%, 75%, and 90%, and the rainfall intensities 50mm/hr, 75mm/hr, 100mm/hr, and 125mm/hr, respectively. The experimental parameters, such as the ground water level, ratio of soil runoff, and failure mode of the slope were measured and analyzed. As the results, It may be concluded that the ground water level in the slope supported by drainable upward soil nails increases very gradually while the unsupported soil changes dramatically. In addition, the ground water level becomes constant and no failure occurs as time goes by. In case of the relative density of 75%, the runoff ratio seemed to increase up to about 8~15% after reinforcement.

• Journal of Conservation Science
• /
• v.28 no.1
• /
• pp.29-37
• /
• 2012

This study discusses a mercury amalgam gilding technique and examines how the color, surface and section of the gilt layer changes as the condition of heat treatment with mercury amalgam gilt object is changed. Some previous studies have mentioned reasons for various colors on gilt bronze artifacts depending on gilding manufacture and environment. However, reason for reddish color with gold on the artifacts' surface brought on high temperature corrosion has yet to be discussed and analyzed. A methodology was found in representing the mercury amalgam gilding technique and heat treatment test. According to the result of the heat treatment test, in the conditions of higher temperature and longer time, the oxidized layer on the gilt layer was distributed more widely and in the part when the oxide layer was eliminated, the gilt layer with a reddish color was observed. Moreover, in the surface observation of the specimen on which yellow and reddish colors were agitated, the changing aspects of its surface condition differed by colors. When investigated the section, it was observed that the void density and size became larger. After a test, the surface components changed; the temperature of heat treatment increased, component ratio of Hg and Au decreased gradually but component ratio of Cu increased. In regard to the gilt layer, as the time was longer and the temperature became higher for the heat treatment, the component ratio of Au and Cu by layers tended to change in inverse proportion. It is concluded that gilding techniques and the burial environment can make a difference in the surface color of the gilt layer on the gilt bronze artifacts, the high temperature corrosion that occurs by heat after they are manufactured is also one of the factors that affects their surface color.

• Restorative Dentistry and Endodontics
• /
• v.31 no.6
• /
• pp.470-476
• /
• 2006

The objective of this in situ study was to evaluate the effects of whitening strip (Claren, LG Household & Health Care Ltd, 2.6% hydrogen peroxide) and gel (Opalescence, Ultradent, 10% carbamide peroxide) on microhardness of enamel in comparison with untreated control. Extracted twenty human upper incisors were disinfected, cleaned, and labial side of each incisor sectioned into 3 fragments by 2 ${\times}$ 2 mm size. After sectioning, labial sides of fragments were flattened and fixed to orthodontic bracket using flowable composite resin. Specimens prepared from each tooth were attached to the labial side of upper incisors of twenty volunteers one by one and treated by three different methods: (1) untreated control (2) treated with whitening strip for 14 days (3) treated with whitening gel for 14 days. Microhardness (Microhardness tester, Zwick) of each specimen was measured at the baseline of pre-treatment, immediate after bleaching treatment, 14 days after bleaching treatment and Knoop Hardness Number was determined. Microhardness changes of experimental groups were compared. The results show that tooth whitening strip and gel used in this study does not effect the microhardness of enamel during bleaching procedure.

• Proceedings of the Plant Resources Society of Korea Conference
• /
• 2018.04a
• /
• pp.45-45
• /
• 2018

We had already reported the successful germination for green pods of purple lady's slipper orchid (Cypripedium macranthos Sw.). The green pod methods is to take immature seeds in green capsules, sterilize the capsule, and take out the sterile seeds. This method, however, needs very critical time of harvest. The critical time of seed harvest changes depending upon the species, condition of the specimen, and climatic influence, and the right time lies between 5 and 12 weeks after fertilization. In this study, the mature seeds were collected after 120-130 days with hand-polination of lady's slipper orchids. Mature seeds are usually dormant and it has to be overcome, either with hormone or storing the seeds near freezing for two or three months to break dormancy. The seeds were first surface sterilized with 70% ethanol and then transferred 1% NaOCl for 10-15 minutes, followed by rinses 3 times with sterilized distilled water. The cypripedium seeds consists of an embryo within a seed coat known as a testa. The testa is water repellent and the seed has a large air space between the embryo and testa so the seed tends to float on water. We had resolved the problems with vacuum pump to soak water into the testa before sterilization. The seeds were placed on liquid or agar solidified germination media. Cultures were incubated at $24{\pm}1^{\circ}C$ in dark. The seeds were germinated in 6-8 weeks in liquid suspension culture (germination percentage over 18%); however, the seeds on agar solidified media took more than 5 months to germinate and the germination percentage less than 5%. The most effective media for liquid culture was 1/4 strength Murashige and Skoog (MS) medium with 50 ml/l coconut water ($4brix^{\circ}$) at pH 5.8.

• Journal of the Korea Concrete Institute
• /
• v.23 no.3
• /
• pp.265-272
• /
• 2011

Even though concrete is the most important material for building structures, its intrinsic gray color degrades urban esthetics. In order to improve this problem, coloring methods of mixing pigment in concrete batch and painting the surface of concrete surface have been tried. However, applications of the coloring methods in construction field are difficult due to high cost and low durability. Recently, acid stain agent is emerging as a new coloring method for concrete. It is able to apply a remarkably thin colored layer on a concrete surface from chemical reaction between acid and alkaline solutions. This study has examined the changes and variations of the surface layer of mortar specimen from chemical reaction of acid stained agents. The colors were changed into natural irregular stains according to aging. After the staining, no shape change was found from visible inspections. Microstructure of the colored surface applied with acid stained agent was much rougher than that of original mortar. When the colored layer was compared to original surface, crystals of hydrate such as $Ca(OH)_2$ and C-S-H gel were observed. Surface hardness was same or slightly higher in the colored layer. The value of pH was reduced by approximately 10%, weight contents of elements such as Ca, Si, and Al were low. In the chemical composition of the colored layer, the non-cement based elements of Mn, Cr, and Cu increased. Also, Fe and alkali elements of K and Na increased.

• Journal of the Korean GEO-environmental Society
• /
• v.13 no.4
• /
• pp.27-36
• /
• 2012

The water in surface of the earth is frozen under freezing point. The freezing phenomenon, which causes the volume change of soils, affects on the behavior of soils and causes the significant damage on the geotechnical structures. The purpose of this study is to investigate the characteristics of elastic waves in sand-silt mixtures using small size freezing cells, which reflect the frozen ground condition due to temperature change. Experiments are carried out in a nylon cell designed to freeze soils from top to bottom. Bender elements and piezo disk elements are used as the shear and compressional wave transducers. Three pairs of bender elements and piezo disk elements are placed on three locations along the depth. The specimen, which is prepared by mixing sand and silt, is frozen in the refrigerator. The temperature of soils changes from $20^{\circ}C$ to $-10^{\circ}C$. The velocities, resonant frequencies and amplitudes of the shear and compressional waves are continuously measured. Experimental results show that the shear and compressional wave velocities and resonant frequencies increase dramatically near the freezing points. The amplitudes of shear and compressional waves show the different tendency. The dominant factors that affect on the shear wave velocity change from the effective stress to the ice bonding due to freezing. This study provides basic information about the characteristics of elastic waves due to the soil freezing.

• Elastomers and Composites
• /
• v.46 no.1
• /
• pp.70-77
• /
• 2011

A new piece of test equipment, the slurry wear tester (SWT), was proposed in this study to evaluate the wear behavior of rubber vulcanizate in environmental contact with slurry. Natural rubber (NR) and chloroprene rubber (CR) were chosen as the basic matrices to test the slurry wear. The fluids used to fill the chamber of the SWT were 35% HCl and NaCl solution. The Akron abrasion test was used for comparison with SWT. According to the results of the Akron abrasion test, CR vulcanizate abraded more rapidly than NR vulcanizate under same test condition. It was found that the hysteresis of rubber was key factor contribute to the wear behavior. However, the slurry wear rate of the NR and CR vulcanizates did not change significantly, even with changes in the concentration of acid and the immersion time in both HCl and NaCl solutions; the fluid decreased the friction between the abrasive paper and the specimen. It also reduced the heat generated from repeated deformation and wear debris at the surface of the SWT's abrasion arm. Thus, these phenomena affected the wear behavior of rubber vulcanizate and caused different results in the conventional Akron abrasion test. This outcome could have resulted in an incorrect analysis if the slurry wear behavior of the rubber vulcanizate was estimated by the conventional abrasion tests, which are operated under dry conditions.

• Journal of Periodontal and Implant Science
• /
• v.37 no.4
• /
• pp.839-848
• /
• 2007

Purpose: Various kinds of biodegradable membranes are currently used in dental clinics. And the frequency and the necessity of their usage are increasing due to their numerous advantages. Therefore it is important to understand the difference of various membranes and histological reaction against implanted membranes. Materials and Methods: Biodegradable membranes of $Biogide^{(R)}$, $Resolute^{(R)}$, and $Tutodent^{(R)}$ were cut into small pieces by $1.0{\times}0.5cm$. The membranes were implanted 1.5cm apart from each other under the epithelium on the skull of 18 Sprague Dawley rats. The animals were sacrificed at 3, 7, and 14 days after surgical procedure. The specimens were examined by histological analysis. Results: 1. Early period after implantation of the membranes showed connective tissues surrounding membranes and there were a few inflammatory cells present. 2. In $Biogide^{(R)}$ and $Tutodent^{(R)}$ specimens, inflammatory cells and surrounding tissues were shown to infiltrate from outside with slight density difference inside. In $Resolute^{(R)}$ specimens, membranes were fragmented. Inflammatory cells and connective tissues were also observed inside. 3. In $Resolute^{(R)}$ specimen, giant cells were present which implicates that foreign body reaction has occurred. 4. $Biogide^{(R)}$ had lower integrity than other membranes and is not enough to be used alone in defect area. However, $Resolute^{(R)}$ had superior firmness than others. $Tutodent^{(R)}$ had middle level of integrity. Conclusion: This experimental model enabled to observe early inflammatory reactions and morphological changes of materials and can be used to develop and evaluate the efficacy of biodegradable membranes. Duplication of standardized human oral environment will be required in future experiments.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.248-250
• /
• 2017

The Mar-M-247 alloy is one of the most widely used materials for gas turbine components in aerospace filed and it shows excellent high temperature strength properties. Hot section parts, such as turbine nozzle and blade, are difficult to manufacture because of their complicated shape. So, the joining process usually applies to them. In this study, the high-temperature behavior of Mar-M-247 alloy at liquid diffusion bonding was investigated. Thus, we performed the diffusion bonding at $1,121^{\circ}C$ for 7 minutes, and observed changes in high temperature strength. As a result, the strength of the bonded specimens decreased by about 70% at $649^{\circ}C$, 60% at $825^{\circ}C$, and 45% at $1,000^{\circ}C$ compared to the base metal. As a result of observing the strength change with bonding time, the specimen bonded for 720 minutes showed a similar strength with the base metal at $649^{\circ}C$. Inferring this result, the joint is considered to be the one-body part.