• ALGAE
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• v.22 no.2
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• pp.95-106
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• 2007

Blooms of Chattonella species are normally during summer in inland seas with high nutrients from the land and inflowing water. These blooms cause mass fish kills worldwide. We isolated a Chattonella strain from the south coast of Korea and identified it as C. antiqua. It is known that the morphological changes of phytoplankton correspond to the diurnal vertical migrations that follow an intrinsic biological clock and a nutrient acquisition mechanism during the day and night. In electron micrographs, C. antiqua clearly showed a radial distribution of lipid bodies in subcellular regions and plastids composed in which thylakoid layers were perpendicular to the surface. A single pyrenoid was present in each plastid and it was found at the end of the plastid towards the center of the cell. Throughout the day, plastids of C. antiqua cells appeared as an expanded net-like recticulum. During the night, however, the plastids changed their shape and contracted toward the cell periphery. The electron density of pyrenoids was increased in cells harvested during the night.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.11-18
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• 2008

Anatomical characteristics of volumetric composition, fiber length, vessel diameter, and crystalline properties of cellulose in kenaf (Hibiscus cannabinus L.) planted in the reclaimed land of Buan-si, Korea were examined to understand the growth characteristics using a light microscopy and an X-ray diffraction method. The samples of kenaf were taken from six positions (3 cm, 35 cm, 70 cm, 105 cm, 280 cm, and 320 cm) of each stem over the growth period (July, August, September, and October) after seeding in the mid-May. In the kenaf stem, phloem constituted 10 to 15 %, xylem 66 to 82%, and pith 7 to 19%. The ray, bast fiber, and remainder comprised 50%, 20%, and 30% of the phloem, respectively. The volume of vessel, ray, and fiber in the xylem was approximately 10, 15, and 75%, respectively. The proportion of cell wall was 30.92% at the base of stem and 46.40% at the top of stem, respectively. The average length of bast fiber and xylem fiber was about 2.8 mm and 0.9 mm, respectively. Radial and tangential diameters of vessel increased with the increase of growth period, while they decreased with increasing the stem height. Relative crystallinity ranged from 70 to 79% in phloem and from 50 to 56% in xylem. Cellulose crystallite width was about 3 nm both in the phloem and xylem. Thus, the volumetric composition and cell dimensions in the phloem and xylem appeared to be varied with the growth period and the stem height.

• Journal of Korea Water Resources Association
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• v.51 no.7
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• pp.555-564
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• 2018

The detention reservoir is a hydraulic structure that constructs a levee on the inland of river and sets up side weir in a section of the levee, and this facility stores a part of the flood volume in case of a flood event over a certain scale. In order to optimize the operation of detention reservoir, it is necessary to review the linkage with existing facilities in the river. In this study, the effect of water level reduction and the flow distribution was analyzed according to the location of the side weir in the detention reservoir considering the run-of-the-river gate. Two radial gates were installed in the experimental channel, and the water level in channel and the overflow of weir were measured by moving the location of the side weir upstream from the gate. As a results of experiment, it was confirmed that the water level reduction is more remarkable as the location of the side weir was closer to the gate, and the effect of flow distribution is not greatly changed. When two or more side weirs were operated, it is confirmed that the sufficient storage space was secured and the water level reduction effect with the location of the side weir is not large. In addition, the water level reduction rate according to the location of the side weir was estimated by empirical formula and it is provided as basic data that can be used in the planning of the detention reservoir.

• Korean Journal of Agricultural and Forest Meteorology
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• v.4 no.4
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• pp.203-212
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• 2002

This study was conducted to remove the urban heat island effects embedded in the interpolated surfaces of daily minimum temperature in the Korean Peninsula. Fifty six standard weather stations are usually used to generate the gridded temperature surface in South Korea. Since most of the weather stations are located in heavily populated and urbanized areas, the observed minimum temperature data are contaminated with the so-called urban heat island effect. Without an appropriate correction, temperature estimates over rural area or forests might deviate significantly from the actual values. We simulated the spatial pattern of population distribution within any single population reporting district (city or country) by allocating the reported population to the "urban" pixels of a land cover map with a 30 by 30 m spacing. By using this "digital population model" (DPM), we can simulate the horizontal diffusion of urban effect, which is not possible with the spatially discontinuous nature of the population statistics fer each city or county. The temperature estimation error from the existing interpolation scheme, which considers both the distance and the altitude effects, was regressed to the DPMs smoothed at 5 different scales, i.e., the radial extent of 0.5, 1.5, 2.5, 3.5 and 5.0 km. Optimum regression models were used in conjunction with the distance-altitude interpolation to predict monthly normals of daily minimum temperature in South Korea far 1971-2000 period. Cross validation showed around 50% reduction in terms of RMSE and MAE over all months compared with those by the conventional method.conventional method.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1409-1416
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• 2010

It is essential to predict a blasting-induced excavation damage zone (EDZ) beyond the proposed excavation line of a tunnel because the unwanted damage area requires extra support system for tunnel safety. Complicated blasting process which may hinder a proper characterization of the damage zone can be effectively represented by two loading mechanisms. The one is a dynamic impulsive load generating stress waves outwards immediately after detonation. The other is a gas pressure that remains for a relatively long time. Since the gas pressure reopens up the arrested cracks and continues to extend some cracks, it contributes to the final formation of EDZ induced by blasting. This paper presents the simple method to evaluate EDZ induced by gas pressure during blasting in rock. The EDZ is characterized by analyzing crack propagation from the blasthole. To do this, a model of the blasthole with a number of radial cracks of equal length in an infinite elastic plane is considered. In this model, the crack propagation is simulated by using three conditions, the crack propagation criterion, the mass conservation of the gas, and the adiabatic condition. As a result, the stress intensity factor of the crack generally decreases as crack propagates from the blasthole so that the length of the crack is determined. In addition, the effect of rock properties, initial number of cracks, and the adiabatic exponent are investigated.

• Tribology and Lubricants
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• v.34 no.1
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• pp.33-41
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• 2018

This paper describes a new test rig for identification of rotordynamic force coefficients of squeeze film dampers (SFDs) in automotive turbochargers (TCs). Prior studies have mainly concentrated on relatively large-sized SFDs used in aircraft engines, turbocompressors, and turbopumps. The main objective of the current study is to propose a test rig for identification of dynamic force coefficients of small-sized SFDs (a journal diameter of ~11 mm). The current test rig consists of a journal, a SFD cartridge, four support rods, an upper structure, a data acquisition (DAQ) system, and an oil circulation unit. The annular gaps between the journal outer surface and SFD cartridge inner surface create SFD film lands. The damper has two parallel film lands separated by a central groove, having an axial length and depth of 3 mm. Each film land has a length of 4 mm with a $40{\mu}m$ radial clearance. The static load and dynamic impact tests identify the structural characteristics (i.e., stiffness and natural frequency) of the journal and assembled test rig. The measurements show good agreement with predictions. The SFD performance data from this test rig will be used to develop innovative TC rotor systems with improved NVH and reliability characteristics incorporating advanced SFD technology.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2372-2374
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• 2003

With 3-D vision measuring, camera calibration is necessary to calculate parameters accurately. Camera calibration was developed widely in two categories. The first establishes reference points in space, and the second uses a grid type frame and statistical method. But, the former has difficulty to setup reference points and the latter has low accuracy. In this paper we present an algorithm for camera calibration using perspective ratio of the grid type frame with different line widths. It can easily estimate camera calibration parameters such as focal length, scale factor, pose, orientations, and distance. But, radial lens distortion is not modeled. The advantage of this algorithm is that it can estimate the distance of the object. Also, the proposed camera calibration method is possible estimate distance in dynamic environment such as autonomous navigation. To validate proposed method, we set up the experiments with a frame on rotator at a distance of 1,2,3,4[m] from camera and rotate the frame from -60 to 60 degrees. Both computer simulation and real data have been used to test the proposed method and very good results have been obtained. We have investigated the distance error affected by scale factor or different line widths and experimentally found an average scale factor that includes the least distance error with each image. It advances camera calibration one more step from static environments to real world such as autonomous land vehicle use.

• Wind and Structures
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• v.38 no.4
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• pp.261-275
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• 2024

Before performing an experimental study on the downburst-generated wave, it is necessary to examine the scale effects and corresponding corrections or compensations. Analysis of similarity is conducted to conclude the non-dimensional force ratios that account for the dynamic similarity in the interaction of downburst with wave between the prototype and the scale model, along with the corresponding scale factors. The fractional volume of fluid (VOF) method in association with the impinging jet model is employed to explore the characteristics of the downburst-generated wave numerically, and the validity of the proposed scaling method is verified. The study shows that the location of the maximum radial wind velocity in a downburst-wave field is a little higher than that identified in a downburst over the land, which might be attributed to the presence of the wave which changes the roughness of the underlying surface of the downburst. The impinging airflow would generate a concavity in the free surface of the water around the stagnation point of the downburst, with a diameter of about two times the jet diameter (D_jet). The maximum wave height appears at the location of 1.5D_jet from the stagnation point. Reynolds number has an insignificant influence on the scale effects, in accordance with the numerical investigation of the 30 scale models with the Reynolds number varying from 3.85 × 10⁴ to 7.30 × 10⁹. The ratio of the inertial force of air to the gravitational force of water, which is denoted by G, is found to be the most significant factor that would affect the interaction of downburst with wave. For the correction or compensation of the scale effects, fitting curves for the measures of the downburst-wave field (e.g., wind profile, significant wave height), along with the corresponding equations, are presented as a function of the parameter G.

• Restorative Dentistry and Endodontics
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• v.27 no.6
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• pp.577-586
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• 2002

The purpose of this in vitro study was to compare the effects of root canal cleanness following two Ni-Ti rotary instruments with different rake angle. Thirty-six sound, extracted human premolars with single root were randomly divided into three groups. The used rotary instruments were HEROShaper (Group 1, Micro-Mega, Besancon, France, n=12) and ProFile (Group 2, Maillefer, Ballaigues, Switzerland, n=12). Control group (n=12) was only extirpated with barbed broach (Mani, Matsutani Seisakusho Co., Japan) Group 1 & 2 teeth were prepared to a #40/.04 taper at the apex followed by 1 mm using crown-down technique. After canal preparation and frequent irrigation with 5.25% sodium hypochlorite, the roots split longitudinally into a bucco-lingual direction. Root halves were cross-sectioned in apical third portion again. All root specimens were processed for SEM investigation and photographed. Separate evaluations by one endodontist were undertaken for smear layer on prepared walls with a five score-index for each using reference photograph in root halves. The penetration depth of smear layer into dentinal tubules was also estimated in the other halves. Following results were obtained: 1. Smear layer was observed on all the prepared walls with two experimental groups except control group. 2. Smear layer characteristics in two experimental groups; 1) HEROShaper group showed snowy, dusty appearance and were shown open dentinal tubuli on the prepared walls of almost specimens, and the thickness of smear layer covering onto dentinal surfaces was within 1-2 ${\mu}m$ in a few specimens. 2) ProFile group showed shiny, burnished appearance and complete root canal wall covered by a homogenous smear layer with no open dentinal tubuli in all specimens. The penetration of smear layer into dentinal tubules was found in all specimens and the thickness was at 2-4 ${\mu}m$ in all specimens. These results demonstrated that a completely clean root canal could not be achieved regardless of positive or negative rake angle, which is in accordance with the majority of previous studies on root canal cleanliness In conclusion, through irrigation with antibacterial solutions or chelating agents is recommended to remove the smear layer on prepared canal wall in spite of Ni-Ti instrumentation.

• Restorative Dentistry and Endodontics
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• v.35 no.4
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• pp.267-272
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• 2010

Screw-in effect is one of the unintended phenomena that occurs during the root canal preparation with nickel-titanium rotary files. The aim of this study was to compare the screw-in effect among various nickel-titanium rotary file systems. Six different nickel-titanium rotary instruments (ISO 20/.06 taper) were used: $K3^{TM}$ (SybronEndo, Glendora, CA, USA), $M_{two}$ (VDW GmbH, Munchen, Germany), NRT with safe-tip and with active tip (Mani Inc., Shioya-gun, Japan), ProFile$^{(R)}$ (Dentsply-Maillefer, Ballaigues, Switzerland) and ProTaper$^{(R)}$ (Dentsply-Maillefer, Ballaigues, Switzerland). For ProTaper$^{(R)}$, S2 was selected because it has size 20. Root canal instrumentations were done in sixty simulated single-curved resin root canals with a rotational speed of 300 rpm and single pecking motion. A special device was designed to measure the force of screw-in effect. A dynamometer of the device recorded the screw-in force during simulated canal preparation and the recorded data was stored in a computer with designed software (LCV-USE-VS, Lorenz Messtechnik GmbH, Alfdorf, Germany). The data were subjected to one-way ANOVA and Tukey's multiple range test for post-hoc test. P value of less than 0.05 was regarded significant. ProTaper$^{(R)}$ produced significantly more screw-in effects than any other instruments in the study (p < 0.001). $K3^{TM}$ produced significantly more screw-in effects than $M_{two}$, and ProFile$^{(R)}$ (p < 0.001). There was no significant difference among $M_{two}$, NRT, and ProFile$^{(R)}$ (p > 0.05), and between NRT with active tip and NRT with safe one neither (p > 0.05). From the result of the present study, it was concluded, therefore, that there seems significant differences of screw-in effect among the tested nickel-titanium rotary instruments. The radial lands and rake angle of nickel-titanium rotary instrument might be the cause of the difference.