• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.450-459
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• 2009

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume ($14.2\;mm^3$) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at $25{\pm}0.5^{\circ}C$. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test ($\alpha$ = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for $1{\sim}2$ seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G" increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.424-429
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• 2009

This study aimed to assess the influence of different cross-sectional area on the cyclic fatigue fracture of Ni-Ti rotary files using a fatigue tester incorporating cyclical axial movement. Six brands of Ni-Ti rotary files (ISO 30 size with. 04 taper) of 10 each were tested: Alpha system (KOMET), HeroShaper (MicroMega), K3 (SybronEndo), Mtwo (VDW), NRT (Mani), and ProFile (Dentsply). A fatigue-tester (Denbotix) was designed to allow cyclic tension and compressive stress on the tip of the instrument. Each file was mounted on a torque controlled motor (Aseptico) using a 1:20 reduction contra-angle and was rotated at 300 rpm with a continuous, 6 mm axial oscillating motion inside an artificial steel canal. The canal had a $60^{\circ}$ angle and a 5 mm radius of curvature. Instrument fracture was visually detected and the time until fracture was recorded by a digital stop watch. The data were analyzed statistically. Fractographic analysis of all fractured surfaces was performed to determine the fracture modes using a scanning electron microscope. Cross-sectional area at 3 mm from the tip of 3 unused Ni-Ti instruments for each group was calculated using Image-Pro Plus (Imagej 1.34n, NIH). Results showed that NRT and ProFile had significantly longer time to fracture compared to the other groups (p < .05). The cross-sectional area was not significantly associated with fatigue resistance. Fractographycally, all fractured surfaces demonstrated a combination of ductile and brittle fracture. In conclusion, there was no significant relationship between fatigue resistance and the cross-sectional area of Ni-Ti instruments under experimental conditions.

• Restorative Dentistry and Endodontics
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• v.35 no.2
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• pp.88-95
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• 2010

The purpose of this study was to compare the root canal shaping ability of 4 rotary NiTi instruments in simulated root canals. For the preparation of thirty two curved root canals, Mtwo instruments using "single length"technique, and Profile, ProTaper Universal, and K3 using crown-down technique (N = 8) were used. All canal samples were prepared by reaching an apical canal size of #30. Pre- and post-instrumentation digital images were recorded and an assessment of canal shape was determined using a computer image analysis program SigmaScan Pro (Systat Software Inc., San Jose, CA, USA). The changes of the dimension of inner walls of canals, (2) the changes of the dimension of outer walls of canals, and (3) the centering ratio were measured at 7 measuring points, and then data were statistically analyzed using one-way ANOVA and Duncan's test. The results were as below; 1. The root canal shaping ability of Profile was significantly faster than that of other rotary NiTi instruments (p < 0.05). 2. The deformation and fracture of all instruments used for this study were not experienced. 3. In the degree of changes of the dimension of inner walls of canals, Profile demonstrated the lowest changes of the dimension of inner walls of canals except at the measuring points of the 1 and 2 mm (p < 0.05). However, the ProTaper Universal showed the highest changes of the dimension of inner walls of canals at all measuring points (p < 0.05). 4. In the degree of changes of the dimension of outer walls of canals, Mtwo demonstrated the lowest changse of the dimension of outer walls of canals except at the measuring point of the 1 mm (p < 0.05). However, Profile exhibited the highest changes of the dimension of outer walls of canals at the measuring points of 3 and 4 mm and ProTaper Universal and K3 showed the largest changes of the dimension of outer walls of canals at the measuring points of 1, 2, 6, and 7 mm (p < 0.05). 5. In degree of centering ratio, Profile demonstrated the least centering ratio comparing with the centering ratio shown by other NiTi instruments at the measuring points of 1, 4, 5, and 6 mm. Results suggest that in the coronal part of canal preparation, active cutting files such as ProTaper Universal may efficiently flare the canal orifice and form a better taper, and in the apical part of the canal, files which have a better centering ability such as Profile may maintain the original canal curvature and reduce the shaping time.

• Korean Journal of Heritage: History & Science
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• v.53 no.2
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• pp.64-87
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• 2020

Copper trihydroxychloride (atacamite, botallackite, paratacamite, etc.), the first green pigment used in Mogao Grotto's mural paintings of China, has been known as "copper green", "green salt", and "salt green", etc. and has been used as an important green pigment with malachite. At first, the natural mineral atacamite was employed, but after the Five Dynasties (907~960 CE), synthetic copper trihydroxychloride was primarily used. In Chinese literature, copper green, green salt, and salt green are recorded as being made via reaction with copper powder, Gwangmyeongyeom (natural sodium chloride), and Yosa (natural ammonium chloride), and the prepared material was analyzed to be copper trihydroxychloride. Copper trihydroxychloride pigment was not found in paintings prior to the Joseon Dynasty (1392~1910 CE) in Korea. In analysis of the green pigments used in paintings and the architectural paintworks in the Joseon Dynasty, copper trihydroxychloride was also shown to have been used as an important green pigment with malachite (Seokrok). In particular, the proportion of copper trihydroxychloride use was high in Buddhist paintings, shamanic paintings, and dancheongs (decorative coloring on wooden buildings). Some of these turned out to be synthetic copper trihydroxychloride, but it is unclear whether the rest of them are synthetic or natural pigments due to a lack of analyzed data. From literature and painting analyses, the pigment name of copper trihydroxychloride in the Joseon Dynasty turns out to be Hayeob, a dark green pigment. It is believed to have first been prepared by learning from China in the early Joseon period (early 15^th century) and its use continued until the late 19^th century with imported Chinese pigment. Round or oval particles with a dark core of copper trihydroxychloride which were used in Chinese literature were similar to the synthetic copper trihydroxychloride pigments used in the Joseon Dynasty and Chinese paintings. Therefore, the synthetic copper trihydroxychloride pigments of Korea and China are believed to have been prepared in a similar way.

• Journal of Chest Surgery
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• v.42 no.6
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• pp.738-743
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• 2009

Background: There is no standardized tool and parameter that can accurately assess the sympathetic function before and after performing sympathectomy in patients with primary palmar hyperhidrosis. We examined the effective-ness of the sympathetic skin response (SSR) study for documenting the change of sympathetic denervation before and after performing selective thoracic sympathicotomy. Material and Method: We prospectively investigated the SSR from 12 healthy subjects who were diagnosed with primary hyperhidrosis. Each SSR was recorded on the right palm or sole with electrical stimuli applied to the skin at the left wrist and foot and vice versa for the controlateral side. This test was performed before, 2 weeks and 1 year after selective thoracic sympathicotomy. The data was corrected for the onset latency and the amplitude of the SSR (n=24). Result: The mean age of the 12 patients was $24.6{\pm}0.4$ years (range: 19~36) and the gender ratio was 1 : 0.7. The mean values of the preoperative, postoperative 2 weeks and postoperative 1 year onset latency and amplitude of the palmar side (n=24) were $1.46{\pm}0.24$ msec and $6,043{\pm}2,339{\mu}V$, $1.63{\pm}0.42$ msec and $823{\pm}638{\mu}V$, and $1.44{\pm}0.39$ msec and $2,412{\pm}1,546{\mu}V$, respectively. The mean values of the plantar side (n=38) were $1.83{\pm}0.42$ msec and $2,816{\pm}1,694{\mu}V$, $2.16{\pm}0.39$ msec and $1,445{\pm}1,281{\mu}V$ and $1.95{\pm}0.25$ msec and $1,622{\pm}865{\mu}V$, respectively. Among the documented parameters, only the palmar amplitude (p=0.002) showed statistical significance in recording the change of the sympathetic system within the same individual for the pre and postoperative period. Conclusion: The SSR amplitude ratio may be a useful parameter for documenting the efficacy of sympathetic denervation after selective sympathicotomy.

• Asia pacific journal of information systems
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• v.24 no.4
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• pp.559-575
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• 2014

Individual investors are increasingly flocking to message boards to seek, clarify, and exchange information. Businesses like Seekingalpha.com and business magazines like Fortune are evaluating, synthesizing, and reporting the comments made on message boards or blogs. In March of 2012, Yahoo! Finance Message Boards recorded 45 million unique visitors per month followed by AOL Money and Finance (19.8 million), and Google Finance (1.6 million) [McIntyre, 2012]. Previous studies in the finance literature suggest that online communities often provide more accurate information than analyst forecasts [Bagnoli et al., 1999; Clarkson et al., 2006]. Some studies empirically show that the volume of posts in online communities have a positive relationship with market activities (e.g., trading volumes) [Antweiler and Frank, 2004; Bagnoli et al., 1999; Das and Chen, 2007; Tumarkin and Whitelaw, 2001]. The findings indicate that information in online communities does impact investors' investment decisions and trading behaviors. However, research explicating the correlation between information on online communities and stock market activities (e.g., trading volume) is still evolving. Thus, it is important to ask whether a volume of posts on online communities influences trading volumes and whether trading volumes also influence these communities. Online stock message boards offer two different types of information, which can be explained using an economic and a psychological perspective. From a purely economic perspective, one would expect that stock message boards would have a beneficial effect, since they provide timely information at a much lower cost [Bagnoli et al., 1999; Clarkson et al., 2006; Birchler and Butler, 2007]. This indicates that information in stock message boards may provide valuable information investors can use to predict stock market activities and thus may use to make better investment decisions. On the other hand, psychological studies have shown that stock message boards may not necessarily make investors more informed. The related literature argues that confirmation bias causes investors to seek other investors with the same opinions on these stock message boards [Chen and Gu, 2009; Park et al., 2013]. For example, investors may want to share their painful investment experiences with others on stock message boards and are relieved to find they are not alone. In this case, the information on these stock message boards mainly reflects past experience or past information and not valuable and predictable information for market activities. This study thus investigates the two roles of stock message boards-providing valuable information to make future investment decisions or sharing past experiences that reflect mainly investors' painful or boastful stories. If stock message boards do provide valuable information for stock investment decisions, then investors will use this information and thereby influence stock market activities (e.g., trading volume). On the contrary, if investors made investment decisions and visit stock message boards later, they will mainly share their past experiences with others. In this case, past activities in the stock market will influence the stock message boards. These arguments indicate that there is a correlation between information posted on stock message boards and stock market activities. The previous literature has examined the impact of stock sentiments or the number of posts on stock market activities (e.g., trading volume, volatility, stock prices). However, the studies related to stock sentiments found it difficult to obtain significant results. It is not easy to identify useful information among the millions of posts, many of which can be just noise. As a result, the overall sentiments of stock message boards often carry little information for future stock movements [Das and Chen, 2001; Antweiler and Frank, 2004]. This study notes that as a dependent variable, trading volume is more reliable for capturing the effect of stock message board activities. The finance literature argues that trading volume is an indicator of stock price movements [Das et al., 2005; Das and Chen, 2007]. In this regard, this study investigates the correlation between a number of posts (information on stock message boards) and trading volume (stock market activity). We collected about 100,000 messages of 40 companies at KOSPI (Korea Composite Stock Price Index) from Paxnet, the most popular Korean online stock message board. The messages we collected were divided into in-trading and after-trading hours to examine the correlation between the numbers of posts and trading volumes in detail. Also we collected the volume of the stock of the 40 companies. The vector regression analysis and the granger causality test, 3SLS analysis were performed on our panel data sets. We found that the number of posts on online stock message boards is positively related to prior stock trade volume. Also, we found that the impact of the number of posts on stock trading volumes is not statistically significant. Also, we empirically showed the correlation between stock trading volumes and the number of posts on stock message boards. The results of this study contribute to the IS and finance literature in that we identified online stock message board's two roles. Also, this study suggests that stock trading managers should carefully monitor information on stock message boards to understand stock market activities in advance.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.11 no.3
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• pp.190-197
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• 2001

Noise-induced hearing loss(NIHL) was the highest rate (43.5%~58.5% from 1996 to 1998) of positive findings through specific medical program in Korea. There were much more NIHL at workers of automobile manufacturing factories than other manufacturing factories. The specific aim of the present study was to determine the noise exposure of automobile press lines, according to their job titles, press line types(auto, semiauto), dosimeter parameters setting. There were a total 11 press lines sampled at a automobile manufacturing company. Among those press lines, 10 press lines were autolines with acoustic enclosure, one semiauto press line was no aucostic enclosure Noise exposure data were sampled for an work shift using noise dosimeter, which recorded both time-weighted average(TWA) and 1-min average. The mean OSHA TWA(Korea TWA with threshold 90) was $80.7dB(A){\pm}4.7dB(A)$ for leader, $82.8dB(A{\pm}4.5dB(A)$ for pallette man, $76.7dB(A){\pm}4.3dB(A)$ for press operators, $76.6dB(A){\pm}5.6dB(A)$ for crane operators, $77.1dB(A){\pm}2.8dB(A)$ for forklift drivers, whereas the mean NIOSH TWA was $88.9dB(A){\pm}1.7dB(A)$ for leader, $89.6dB(A){\pm}2.1dB(A)$ for pallette man, $86.7dB(A){\pm}1.8dB(A)$ for press operators, $88.5dB(A){\pm}2.0dB(A)$ for crane operators, $87.7dB(A){\pm}1.0dB(A)$ for forklift drivers. While L10 for NIOSH TWA samples was 84.8 dB(A) ~ 87.3 dB(A), L10 for OSHA TWA samples was 69.5 dB(A) ~ 77.4 dB(A). L10 means that the TWA for 90% of the samples exceeded L10. Among OSHA TWA(Korea TWA with threshold 90) samples for pallette man, 7.7 % exceeded 90 dB(A), the OSHA permissible exposure level, but OSHA TWA samples for the other job titles didn't. Among NIOSH TWA samples, the samples over 85 dB(A), the NIOSH recommended exposure limit, was 100% (leaders), 83.3 %(operators), 97.4%(palletteman), 100%(forklift drivers), 91.7 %(crane operator). The results of One-way random effects analysis of variance models shows that the difference between job titles was significant by OSHA TWA(p<0.05), but not significant by NIOSH TWA(p>0.05). NIOSH TWA samples were significantly higher than OSHA TWA samples(P<0.05). Regression analysis was used to obtain relationships between OSHA TWA samples and NIOSH TWA samples. In this case the coefficient of determination = 0.90, which shows the high degree association between two methods. Regression equation, NIOSH TWA = 0.552 * OSHA TWA + 42.13 dB(A), shows that if OSHA TWA is known, NIOSH TWA can be predicted by the equation. The mean TWA difference between threshold 80 dBA and 90 dBA was significant(p<0.01). While the TWA noise exposures were 7.7% above the Korea(OSHA) PEL, they were more than 83.3% over NIOSH REL. Automobile workers were exposed to noise level that could be potentially damaging to their hearing. It found that there is approximately 25% excess risk of hearing loss even if a worker is protected to the PEL in according to NIOSH study.

• Journal of Nutrition and Health
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• v.52 no.6
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• pp.559-568
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• 2019

Purpose: This study examined the prevalence of food allergies and allergenic factors in a selected sample of children living in Seoul, Korea, along with their dietary habits, environmental factors, and diseases as risk factors for food allergy. The results of this study will provide basic data for addressing food allergies. Methods: We selected 3,004 pre-school and school-age children, aged 0 ~ 12, in the 25 districts of Seoul as the study sample. Structured self-report questionnaires were administered over a two-month period in July-August 2018, and the children's parents recorded the answers on their children's behalf. The research tools in this study included the Korean version of the questionnaire from the International Study of Asthma and Allergies in Childhood (ISAAC). Results: The physician-diagnosed prevalence rate of food allergies was 14.2%, while 20.4% of the children experienced allergic symptoms at least once and 17.4% reported symptoms within the previous 12 months. The children's symptoms included skin problems (88.1%), gastrointestinal issues (19.2%), oral issues (16.7%), respiratory issues (12.7%), and systemic issues (1.3%). The causes of allergies included eggs, peaches, milk, peanuts, and shrimps. The factors influencing the experience of food allergies were the consumption of cereal (aOR, 1.52; 95% CI, 1.09 ~ 2.10; p = 0.013), potatoes (aOR, 1.88; 95% CI, 1.33 ~ 2.65; p < 0.001), and fast food (aOR, 1.73; 95% CI, 1.10 ~ 2.72; p = 0.017). Having food allergy symptoms was associated with a higher risk of experiencing asthma (aOR, 4.22 95% CI, 3.10 ~ 5.76; p < 0.001), allergic rhinitis (aOR, 2.53; 95% CI, 2.03 ~ 3.15; p < 0.001), and atopic dermatitis symptoms (aOR, 3.56; 95% CI, 2.88 ~ 4.40; p < 0.001). Conclusion: Episodes of food allergies warrant examining regular food consumption and placing dietary restrictions through early diagnosis as these episodes may imply the presence of other allergies. Our findings offer basic insights into the patterns, prevalence and symptoms of children's food allergies in Seoul, and our findings will contribute to identifying effective interventions for food allergies.

• Journal of Nutrition and Health
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• v.25 no.2
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• pp.179-186
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• 1992

Dietary intakes of 57 college women were measured by 7-day weight food records(7WR) Nutrient intakes of 7WR were compared with results of using 1-day weighted food records(1WR) and 2-day weighed food records(2WR), 7WR were recorded for 7 consecutive days by subjects and its first two days were chosen to provide 1WR and 2WR Mean nutrient intakes of the group were not significantly different between 1WR or 2WRand 7WR. Within-person variations were found to be greater than between-person variations. The ratio of within- and between-person variability was lowest for the vitamin A and highest for the calcium. Data on 7WR were analyzed to estimate the number of recording days needed to ensure r$\geq$0.9 between observed and turn mean intakes. The 11 to 13 days needed for energy sugar protein and vitamin A and 20 days for calcium The results indicated that the number of days needed varied substantially among individuals for the same nutrient and within individuals for different nutrients.

• Restorative Dentistry and Endodontics
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• v.31 no.3
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• pp.179-185
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• 2006

This study was conducted to evaluate canal configuration after shaping by $ProTaper^{TM}$ with various rotational speed in J-shaped simulated resin canals. Forty simulated root canals were divided into 4 groups, and instrumented using by $ProTaper^{TM}$ at the rotational speed of 250, 300, 350 and 400 rpm. Pre-instrumented and post-instrumented images were taken by a scanner and those were superimposed. Outer canal width, inner canal width, total canal width, and amount of transportation from original axis were measured at 1, 2, 3, 4, 5, 6, 7 and 8 mm from apex. Instrumentation time, instrument deformation and fracture were recorded. Data were analyzed by means of one-way ANOVA followed by Scheffe's test. The results were as follows 1. Regardless of rotational speed, at the $1{\sim}2mm$ from the apex, axis of canal was transported to outer side of a curvature, and at 3~6 mm from the apex, to inner side of a curvature. Amounts of transportation from original axis were not sienifcantly different among experimental groups except at 5 and 6 mm from the apex. 2. Instrumentation time of 350 and 400 rpm was significantly less than that of 250 and 300 rpm (p<0.01). In conclusion the rotational speed of $ProTaper^{TM}$ files in the range of $250{\sim}400rpm$ does not affect the change of canal configuration, and high rotational speed reduces the instrumentation time. However appearance of separation and distortion of Ni-Ti rotary files can occur in high rotational speed.