• Imaging Science in Dentistry
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• v.40 no.1
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• pp.39-44
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• 2010

Purpose : We want to identify the appearance of the buccolingual root dilaceration teeth in the panoramic views and specify the characteristics of these teeth. Materials and Methods : One thousand-six patients were examined on the basis of both panoramic and CT image criteria. We diagnosed and excluded certain teeth from the samples; both prosthodontic or pathologic lesion appearing teeth and mesiodistally dilacerated ones. We meticulously discerned buccolingually dilacerated teeth in the CT images and total 48 samples were selected. The degree of severity in dilaceration was standardized by 2 types of criteria. The samples were differentiated into 3 groups and again categorized into six types showing from the panoramic views: irregular view on the root apex area, clear blunt on the root tip, stepping on root tip, double lamina dura or double tip, arrow-target shaped root, bull's eye, normal view. Results : The types of teeth selected from total 48 buccolingual root dilaceration samples were mandibular first and second molar, premolars, canines, and lateral incisors. The direction of dilaceration was an even percentage to each buccal and lingual side for most selected teeth, however, that of both canines and lateral incisors were directed in almost a buccal side. In the panoramic views, the root types of the buccolingually dilacerated teeth were irregular view on the root apex area, clear blunt on the root tip, stepping on root tip and normal types were almost always normal view. The more severity in dilareated degree, the more chances of observation in the panoramic views were clear blunt on the root tip and stepping on root tip. Conclusion : As observed in the shape of stepping on root tip or double lamina dura in the panoramic views, there can be much more probability to diagnose as a buccolingually dilacerated root.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.3
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• pp.255-260
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• 2008

STATEMENT OF PROBLEM: Preparation of implant beds with lasers is considered a safe and reliable method, but the accuracy of this technique has not been examined. PURPOSE: The purpose of this study was to evaluate the accuracy and effectiveness of implant bed preparation using an Er,Cr:YSGG laser. MATERIAL AND METHODS: An Er,Cr:YSGG laser was applied to pig rib bone. The laser was employed at a 5.75 W power setting, 30 Hz/sec pulse repetition, and 70 ${\mu}s$ pulse duration with 50 % water and 60% air spray. According to laser tips the groups were divided as follows; Group 1: paralleled - shaped sapphire tip (0.6 mm${\Phi}$), Group 2: paralleled - shaped zirconia tip (0.6 mm${\Phi}$), Group 3: tapered sapphire tip (0.4 mm${\Phi}$). The Er,Cr:YSGG laser tip was separated by 1 mm from the bone and applied for 15 seconds in a non-contact mode. After the application, the bone was sectioned for specimens. Histologic measurements were determined by computerized morphometry. The length of the prepared bone surface was measured and the width of the entrance was measured. The results were analyzed with one-way ANOVA (P<0.05). RESULTS: The prepared length of group 3 was longer than that of group 2. The prepared bone width was larger than the width of the laser tip in every group. Additional bone removal was observed adjacent to the prepared area and displayed an irregular surface. CONCLUSION & DISCUSSION: Different cutting effects were observed according to the laser tip, emphasizing the importance of proper tip selection in the clinical setting. This preliminary study supported the existence of hydrokinetic effects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.377-383
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• 2012

The temperature distribution of an asymmetric trapezoidal fin with various upper lateral surface slopes is investigated by using the two-dimensional analytic method. For this asymmetric fin, convection from the inner fluid to the inner wall, conduction from the inner wall to the fin base and conduction through the fin base are considered simultaneously. The temperature profile with the variation of dimensionless fin length and height coordinates is shown. Also, the temperature variation at the bottom tip of the fin is presented as a function of the fin shape factor. Heat losses through the fin base and from each side are compared for variations in fin length. One of the results shows that temperature at the fin bottom tip decreases linearly as the fin shape factor increases.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.24-37
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• 2021

As one of the development directions of high-performance ships to reduce greenhouse gas emissions, there is research on high-performance propellers. However, in the case of conventional screw propellers, as they have been studied for a long time, there is a limit to improving efficiency only by depending on the conventional design and analysis methods. In this study, we tried to solve the problems using the Coanda effect by spraying a jet on the surface of the hydrofoil. The Coanda hydrofoil consists of a tunnel and jet slit to make jet flow. The computation was performed for each tunnel and slit position, and the efficiency according to the geometry of the hydrofoil was analyzed. In addition, a study on the 3D geometry change was conducted to analyze the performance according to the span direction spraying range and hydrofoil shape. As the height of the slit and the diameter of the tip were lower, when the slit is located in the center of the hydrofoil, the lift force increased and the drag force decreased. The increase rate of lift-to-drag ratio was different according to the shape of the hydrofoil, and the efficiency of the spraying condition of 0.1S-0.5S, which had the least effect on the vortex at the tip of the blade, was high for all 3D hydrofoils. When the geometry of the slit was optimized, and also the shape and spray range of the hydrofoil in 3D was considered, the efficiency of the jet sprayed hydrofoil was increased.

• The KSFM Journal of Fluid Machinery
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• v.15 no.3
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• pp.5-11
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• 2012

This study is to develop a 1kW-class horizontal axis wind turbine(HAWT) rotor blade which will be applicable to relatively low wind speed regions in southwest islands in Korea. Shape design of 1kW-class small wind turbine rotor blade is carried out using a blade profile with relatively high lift to drag ratio by blade element momentum theory(BEMT). Aerodynamic analysis on the newly designed rotor blade is performed with the variation of tip speed ratio. Power coefficient and pressure coefficient of the designed rotor blade are investigated according to tip speed ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.10
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• pp.1039-1045
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• 2007

Ultrasonic machining (USM) is suitable for machining hard, brittle and non-conductive materials such as silicon, glass and ceramics. Usually, when micro holes are machined on glass by USM, roundness of hole entrance is poor and cracks appear around the hole exit. In this paper the machining characteristics were studied for roundness improvement and exit crack prevention. From experiments, the tool bending and the shape of tool tip affect hole roundness. When the tool tip is hemispherical, good roundness of holes was obtained. The feedrate and the rotational speed of the tool affect the exit crack. With the machining conditions of 150 rpm in spindle speed and $0.5\;{\mu}m/s$ in feedrate, micro holes with less than $100\;{\mu}m$ in diameter were machined without an exit crack.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.923-928
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• 2007

The rattle noise originated from the oil-pump system was issued in developing an engine. In this paper, the major concerning factors for rattle noise are analyzed and the NVH developing process is summarized. The main factors are the tip clearance of inner/outer rotor, the clearance between oil pump housing and rotor guide and the rotor mass. Also, the optimization for oil-pump rotor whine noise is performed. The main factors of the rotor whine are the profile of the rotor, the oil pressure and the shape of oil route. This paper will present the design guidelines of the engine oil-pump system.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.566-573
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• 2015

The most important factor for the penetration performance of shaped charge is the liner design. By designing the liner to have properties of both high jet tip velocity and long jet break-up time, the better penetration performance could be acquired. Usually it is very difficult to satisfy above two conditions simultaneously. In this study, the liner with the shape of ogive was developed to have relatively larger jet mass compared to the conventional trumpet liner. The designed shaped charge showed jet properties with high jet tip velocity and long jet break-up time by using ogive liner and wave shaper. A commercially available hydro-dynamic code AUTODYN-2D was used for numerical analysis of jet formation. The flash X-ray test and the static penetration test were conducted to verify the results of numerical analysis.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.1
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• pp.90-94
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• 2005

As the structure of the piezoelectric bimorph cantilever becomes increasingly more complicated, a more accurate and efficient analysis of piezoelectric media is needed. In this paper, the piezoelectric transducer is analyzed by using the three-dimensional finite element method. The validity of the three-dimensional finite element routine is confirmed by comparing the experimental result. The resonance characteristics, such as resonance frequency and anti-resonance frequency, of the piezoelectric cantilever are calculated by the experimentally verified three dimensional finite element method. Subsequently, the characteristics, such as mechanical displacement and impedance, are calculated at the resonance frequency. Besides, to design the piezoelectric bimorph cantilever shape that maximizes displacement at the tip, the ES (Evolution Strategy) algorithm is applied. Finally, optimal design for the fan of the piezoelectric cantilever is fulfilled to obtain maximum displacement at the tip. From these results, the application potentiality of the piezoelectric bimorph cantilever fan is identified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.404-407
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• 2004

Linear ultrasonic motor by bimorph. Transducer for linear ultrasonic motor with symmetric and anti-symmetric modes was studied. The transducer was composed of two piezoelectric ceramic that cross at right angles with each other at tip. In order to exist length vibration mode two piezoelectric ceramics must have 90-degree phase difference with each other. As a result, tip of transducer moves in elliptical motion. Elliptical trajectory of transducer was analyzed by employing the (mite element method(FEM). From the result, the linear ultrasonic motor was measured for characteristics. In this paper, vibration shape of transducer was simulated and the resonant frequency, stabilization frequency and maximum displacement were calculated using the FEA.