• Journal of the Korean Society of Radiology
• /
• v.17 no.1
• /
• pp.1-9
• /
• 2023

For optimal image quality of computer tomography angiography (CTA), different iodine concentrations and scan parameters were applied to quantitatively evaluate the image quality characteristics of filtered back projection (FBP), hybrid-iterative reconstruction (hybrid-IR), and deep learning reconstruction (DLR). A 320-row-detector CT scanner scanned a phantom with various iodine concentrations (1.2, 2.9, 4.9, 6.9, 10.4, 14.3, 18.4, and 25.9 mg/mL) located at the edge of a cylindrical water phantom with a diameter of 19 cm. Data obtained using each reconstruction technique was analyzed through noise, coefficient of variation (COV), and root mean square error (RMSE). As the iodine concentration increased, the CT number value increased, but the noise change did not show any special characteristics. COV decreased with increasing iodine concentration for FBP, adaptive iterative dose reduction (AIDR) 3D, and advanced intelligent clear-IQ engine (AiCE) at various tube voltages and tube currents. In addition, when the iodine concentration was low, there was a slight difference in COV between the reconstitution techniques, but there was little difference as the iodine concentration increased. AiCE showed the characteristic that RMSE decreased as the iodine concentration increased but rather increased after a specific concentration (4.9 mg/mL). Therefore, the user will have to consider the characteristics of scan parameters such as tube current and tube voltage as well as iodine concentration according to the reconstruction technique for optimal CTA image acquisition.

• The Journal of Engineering Geology
• /
• v.6 no.2
• /
• pp.103-110
• /
• 1996

This study shows the variation of poisson's ratio according to stress for the Cretaceous sandstones and shale in the Euiseoung Subbasin. To make a mechanical experiment, samples prepared with 3.0 cm in diameter and 6.2 cm in length were used in testing stress and strain. Generally poisson's ratio has been considered as one of properties, but contrary to steel, the test result makes sure that poisson's ratio has functional relation to stress. I had used four methods to calculate poisson's ratio, Poisson's ratio shows considerable different results according to the calculating, method but it has similar tendency in an elastic limit. Poisson' s ratio increases rapidly and is distinguished clearly in internal fracture region according to the calculating method. Poisson's ratio of sandstone and shale is different from one another in low and high stress regimes,but it is linearly proportional to the stress in an elastic regimes, that is, ${\nu}_t={\;}{\nu}_0+P_{\sigma}({\nu}_0$:first stage Poisson's ratio, ${\nu}_t$:poisson's ratio, P: poisson's coefficient, $\sigma$:stress). Poisson's ratios of two kinds of rock samples show continuous variation from 0.1 to 0.21 in an elastic regime. The variation of poisson's ratio is much wider in an internal fracture regine. It varies from 0.22 to 0.45 in sandstone, which is out of elastic regime.

• Tribology and Lubricants
• /
• v.30 no.3
• /
• pp.146-155
• /
• 2014

In this study, we conduct fretting corrosion tests on tin-plated brass coupons to investigate the effect of temperature on fretting corrosion for various span amplitudes. We prepare a coupled fretting corrosion specimens using a tin-plated brass coupon with a thickness of $10{\mu}m$. One specimen is a flat coupon and the other specimen is a coupon with a protuberance in 1 mm radius, which is produced using 2 mm diameter steel ball. We conduct fretting corrosion tests at $25^{\circ}C$, $50^{\circ}C$, $75^{\circ}C$, $100^{\circ}C$ by rubbing the coupled coupons together at the contact between the flat and protuberance coupons. We measure electric resistance of the contact during the fretting corrosion test period. There is increase in resistance with fretting cycles. It is found that rate of increase in electric resistance becomes faster with increase in testing temperature. Magnitude of friction coefficient increases with fretting span amplitudes. And, change in friction coefficient becomes desensitized to the increment in span amplitude. Assuming that failure cycle is the cycle with an electric resistance of $0.01{\Omega}$, we find that failure lifetime ($N_f$) decreases with increase in testing temperature. Furthermore, based on the assumption that the damage rate of the connector is inversely related to the failure cycle, we calculate the activation energy for fretting damage to be 13.6 kJ/mole by using the Arrhenius equation. We propose a method to predict failure cycle at different temperatures for span amplitudes below $30{\mu}m$. Friction coefficients generally increase with increase in span amplitude and decrease in testing temperature.

• Journal of the Korea Concrete Institute
• /
• v.15 no.2
• /
• pp.314-322
• /
• 2003

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structures, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection was developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect on internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. Using experimental results from the developed device, the coefficient of flow convection was calculated. Finally, a general prediction model was proposed by theoretical procedures. The proposed prediction model is able to estimate the coefficient of flow convection with flow velocity and material properties of pipe. From comparison with experimental results, the coefficient of flow convection by this model was well agreed with those by experimental results.

• Horticultural Science & Technology
• /
• v.32 no.4
• /
• pp.421-426
• /
• 2014

To investigate the optimal size of fruit bearing branches (FBBs) of 'Kawanakajima Hakuto' peach (Prunus persica Batsch) for production of high quality fruits, we evaluated shoot growth and fruit characteristics relative to FBB direction and thickness. FBB diameter, shoot length, fruit weight, and soluble solids content (SSC) averaged 6.9 mm, 32.6 cm, 333.6 g, and $11.2^{\circ}Brix$, respectively. Coefficients of variation of FBB diameter and shoot length were high as 35.8% and 75.3%. The highest frequency values revealed that 76.4% of FBBs had a diameter below 9.0 mm, 70.0% of shoot lengths were less than 40 cm, 24.8% of fruits were 310-340 g, and 66.9% of SSCs were $10.5-12.5^{\circ}Brix$. Shoot length and SSC were significantly affected by FBB diameter without direction, and fruit weight was significantly affected by interaction of FBB diameter and direction. There was a negative correlation ($r^2=0.094^*$) of FBB diameter and fruit weight with upward FBB directions, whereas FBB diameter and fruit weight were positively correlated ($r^2=0.246^{**}$) with downward FBB direction. With thick FBB diameter, shoot length, and SSC were significantly increased, but fruit weight was decreased. Therefore, downward FBBs below 9.0 mm in thickness are suitable for producing high-quality fruits of 'Kawanakajima Hakuto' peach.

• Korean Journal of Plant Resources
• /
• v.20 no.1
• /
• pp.7-11
• /
• 2007

This study was conducted by estimate of leaf characteristics and growth performance among selected 20 families progenies of Hovenia dulcis var. koreana Nakai. Mean seedling height and root-collar diameter in whole progenies showed 61.6cm, 6.98mm, respectively. Mean seedling height of KW 2-5 family was 79.3cm and it was higher than that of other families. JN 2-2 family had highest value, 9.16mm, in mean of root-collar diameter. Growth performances of KW 2-5 and JN 2-2 families showed 57% (in seedling height), 53% (in root-collar diameter) superior to those of lowest marked families. The selection level based on growth performances, which are seedling height over 75.0cm and root-collar diameter over 8.0mm, were applied on whole families, and two families selected (KW 2-5, JN 2-2). The selection effects from selected families was evaluated as 125% compared to the mean of whole families. The coefficient of variation (C.V) appeared wide range, $9.4{\sim}42.4%$, in estimated leaf characteristics. Particularly, C.V of petiole length (PL) and petiole diameter (PD) showed 42.4% and 28.7%, respectively. Their were higher value than other leaf characteristics. Analysis of variance for all leaf characteristics were significantly different among families. Also, there had positive correlation between most leaf characteristics except the correlation between leaf length (LL) and leaf morphological index (LMI, LW/LL). Particularly, the correlation between leaf length and leaf width (LW) showed the highest correlation.

• Journal of Korean Society of Forest Science
• /
• v.4 no.1
• /
• pp.24-25
• /
• 1965

A statistical study was made on the size of sample plot to be used in the preparation of a yield table. This has always been an important problem needing solution in Korea. For this purpose, 3 replications of Korean white pine plantings with block size of $80m{\times}80m$ were established in the Kwangneung Experimental Forest. A location map was prepared of the pines in the blocks and the heights and the breast height diameters measured. Then those blocks were divided into 64, 64, 16, 16, 4, 4, and 1 standed $40m{\times}80m$ and $80m{\times}80m$ each. After these divisions, the average heights, average breast height diameters, standard deviations and coefficient of variations were computed for the plots and averaged according to plot size. As the results of these computations, it was shown that the standard deviation and the coefficient of variation suddenly increased with the beginning of an increase in plot size. However, these indicated an approximately constant value at a certain limit. Although the average value decreases with the initial increase in plot size, it also indicates an approximately constant value at a certain limit. This limit was between $20m{\times}40m$ and $40m{\times}40m$. With the purpose of evaluating these facts, the average height and the average diameter were computed for the number of standing trees in the $10m{\times}10m$ plots. A negative (minus) relationship was found between the number of standing trees and the average value. As a result of above evaluation, it was found that when the size of plot area was small, a larger estimated value, was obtained as well as a smaller standard deviation and coefficient of variation. It is possible, therefore, that an incorrect value might be used in the evalution of data as the stand structure could appear to be uniform when the plot size was small. In general, when the size of plot area is larger than $40m{\times}40m$, the probability of the difficulty occurring mentioned above is estimated to be small.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.11 no.3
• /
• pp.143-150
• /
• 2011

Energy loss at manholes, often exceeding friction loss of pipes under surcharged flow, is considered as one of the major causes of inundation in urban area. Therefore, it is important to analyze the head losses at manholes, especially in case of surcharged flow. The stream characteristics were analyzed and head loss coefficients were estimated by using the computational fluid dynamics(CFD) model, FLUENT 6.3, at surcharged square manhole in this study. The CFD model was carefully assessed by comparing simulated results with the experimental ones. The study results indicate that there was good agreement between simulation model and experiment. The CFD model was proved to be capable of estimating the head loss coefficients at surcharged manholes. The head loss coefficients with variation of the ratio of manhole width(B) to inflow pipe diameter(d) and variation of the drop height at surcharged square manhole with a straight-path through were calculated using FLUENT 6.3. As the ratio of B/d increases, head loss coefficient increases. The depth and head loss coefficient at manhole were gradually increased when the drop height was more than 5cm. Therefore, the CFD model(Fluent 6.3) might be used as a tool to simulate the water depth, energy losses, and velocity distribution at surcharged square manhole.

• Korean Journal of Plant Resources
• /
• v.9 no.2
• /
• pp.189-195
• /
• 1996

In order to obtain basic information for breeding varieties of onion which is suitable at the southern part of Korea. 222 early mature variety and 219 late mature variety were grown from sep.1993 to jun. 1994 at experimental field of Muan-Gun area, and yield components and yield of onion plant ware observed. Early mature onion cv. Changnyeongchunghwan-gkeukjoseng and Keumjungjoseng showed higher yield than other early mature variety used in the experiment. It showed relatively long plant height and leaf sheath length and, height of bulb and diameter of bulb and high weight of bulb. Late mature onion cv. Chunjudaego showed higher yield than other late mature variety used in the experiment. It showed relatively long plant height and leaf sheath length and diameter of bulb, and high weight of bulb. Therefore, it was concluded that Changnyeongchunghwangkeukjoseng,Keumjungjoseng and Chunjudaego were the most suitable early and late mature varieties with high yield at the southern part of Korea.

• Journal of Advanced Marine Engineering and Technology
• /
• v.19 no.4
• /
• pp.17-26
• /
• 1995

In general existing air conditioning devices, which are carried out by convection heat transfer, are very popular compared with the radiation type air conditioning devices. But perconal convection tpe air conditioning units are unuseful air conditioning type because it handles amount of surrounded air to meet the temperature and humidity. In this view, this study is intended to develope personal dir conditioning units using a radiation type radiator. Liquid Droplet Radiator(L.P.R.) radiates the energy by means of thermal radiation. Radiative energy from L.P.R. is the infrared rays which heat the objects without lose of energy. It is a desirable heating method for the local area within the large room. In this study, the analysis uses the Monte Carlo methd to predict the temperature distribution in the droplet sheet and the net heat flux from the L.D.R.. And for this study and experiment was carried out to analyse the radiative and convective heat transfer characteristics in the L.D.R.. And the experiment was investigated the effects of inlet temperature, feed rate, optical thickness and droplet diameter on heat transfer characteristics of L.D.R.. The obtained results from the numerical and experimental studies of L.D.R. were as follows ; (1) The heat flux of L.D.R. was effected by extinction coefficient of droplet sheet, optical thickness and droplet temperature, surface area and emissivity of the droplet. And it was increased with the temperature, feed rate and optical thickness, on the other hand decreased with increasing of droplet diameter. (2) The experimental results for heat flux was ecalucted below 20% than that of the numerical solution by Monte Carlo method, but the tendency of the variation shows relatively good agreement.