• Journal of ILASS-Korea
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• v.7 no.4
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• pp.32-41
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• 2002

The breakup characteristics of liquid sheets formed by like-doublet injector were investigated in the cold-flow and atmospheric ambient pressure condition. The sheet breakup wavelength, which induces the sheet to be broken into ligaments, as well as the sheet breakup length, which is important for the flame location, was measured using a stroboscopic light. The liquid ligaments are formed intermittently after the breakup of sheet, and the wavelength of ligaments has been believed to have a relation to the combustion instability of liquid rocket engine. Therefore, the wavelength of ligaments and the breakup length of ligaments into fine drops were also measured. Since these spray characteristics are affected by the flow characteristics of two liquid jets before they impinge on each other, we focused on the effects of orifice internal flow such as the cavitation phenomenon that occurs inside the sharp-edged orifice. From the experimental results, we found that the liquid jet turbulence delays the sheet breakup and makes shorter wavelengths for both sheets and ligaments. Since the turbulent strength of sharp-edged orifice is stronger than that of round-edged orifice, the shape of orifice entrance results in large differences in the spray characteristics. Using these results, we proposed empirical models on the spray characteristics of the like-doublet injector, and these models are believed to provide some useful and actual data for designing liquid rocket combustors.

• Applied Microscopy
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• v.43 no.2
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• pp.47-53
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• 2013

The trichomes on leaves of three species of Mentha such as M. spicata, M. suaveolens, and M. piperita var were examined by scanning electron microscopy. Simple non-glandular trichomes and peltate glandular trichomes were distinctively occurred on these leaves. In M. spicata, short and sharp non-glandular trichomes were dominantly appeared on adaxial surface, whereas capitate glandular trichomes were commonly localized on abaxial surface. In M. suaveolens, non-glandular trichomes were identified with simple unbranched and branched. Unbranched trichomes which were sharp and pointed in shape occurred on adaxial surface, however, branched and v-shaped trichomes appeared abundantly on abaxial surface. Peltate trichomes consisted of a large eight-celled head. Small capitates trichomes consisted of a cylindrical head with an one-celled uniseriate stalk. In M. piperita var, single non-glandular trichomes and peltate trichomes were present on adaxial surface. Small capitate trichomes consisted of a globose unicellular head with a two- or three-celled uniseriate stalk. Peltate trichomes were distinctly present on abaxial surface, whereas they were not observed on adaxial surface. The trichomes were less dense in this species. Peltate trichomes consisted of a large eight-celled head, with an enlarged secretory cavity, attached to an one-celled short stalk.

• Journal of the korean academy of Pediatric Dentistry
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• v.11 no.1
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• pp.159-167
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• 1984

In this experiments, the fracture loads were measured and analysed by using of Instron universal testing machine (Model 1132). With 80 upper and lower deciduous molars that were free of dental caries. Isthmus of teeth were prepared to 1/3 and 1/4 of intercuspal width, and internal line angles with round and sharp shape, and then amalgam restoration were performed. The results of this study were as follows; 1. Resistance to fracture loads were greater with isthmus of 1/3 intercuspal width than of 1/4 intercuspal width, especially, statistically significant difference on upper and lower second deciduous molars. 2. Resistance to fracture loads were greater with rounded internal line angle than sharp internal line angle. The above results were as follows, the fracture loads had greater resistance on isthmus of 1/3 intercuspal width, and rounded internal line angle, but normal physiological occlusal forces could permit isthmus of 1/4 intercuspal width and rounded internal line angle.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.1
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• pp.53-61
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• 1996

A clear understanding of the surface formation mechanism due to cutting is very important to help produce a good quality surface. Much of the roughness along the length of a bar being cut in a lathe can be explained in terms of macroscopic tool shape and feed rate. However, the roughness along the direction of cutting requires a different explanation. The formation of surface roughness is a problem in flow and fracture of materials in the vicinity of the tool edge. On a microscopic scale the cutting edge is rounded because it is impossible to grind a perfectly sharp cutting edge. Even if a perfectly sharp cutting edge were obtained it would soon become dull as a result of rapid breakdown and wear of the cutting edge. A research project is proposed in which in the main object is to model the surface formation mechanism due to cutting. The tool was assumed to be dull, that is, its edge has a finite radius. In order to study the effect of the radius of cutting edge on the surface formation, tools having different cutting edges were used. For orthogonal cutting experiment, cast iron and glass were chosen as brittle materials. Plowing forces acting in the cutting edge were estimated and its effect on the surface roughness was studied by observing the machined surface using optical microscope.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.1
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• pp.71-78
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• 1990

This research was made to investigate the change of the image layer and of the vertical and horizontal magnification on the Panelipse radiographic image by the control of profile index. Using the Panelipse, a series of 60 exposures were taken with the steel balls placed in the holes of the plastic model plate, and then evaluated by 4 observers. Two points were assigned for a reading of sharp, one for middling sharp, and zero for unsharp. Each ball image then could be given a total reader score of 0 to 8. The author analyzed the image layer as defined by a sharpness score of 6 or more. The results obtained were as follows: As the profile index was increased, the shape of the image layer was not changed, and the width of the image layer was increased, and the position of the layer shifted away from the rotation center. As the profile index was increased, the ranges of vertical and horizontal magnification was increased, especially the ranges of horizontal magnification was greater than that of vertical magnification.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.647-652
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• 2016

To reduce drag force at supersonic speeds, sharp leading edge is hugely efficient. It is, however, incompatible with leading edge shape to have fine aerodynamic characteristics at subsonic and transonic speeds. It is critical to reduce drag force for enhanced cruise performance and higher efficiency. An air superiority fighter, however, required to have high maneuverability for survivability, and sharp leading edge is not proper. Consequently, variable leading edge is demanded to reduce drag force significantly at supersonic speeds for cruise performance. Leading edge altering system is constructed with rigid material to improve possibility of realization, and minimized movement of its components in altering for reduce effects on flight. It is compared with bi-convex airfoil and NACA 65-006 airfoil, which have comparable maximum thickness. At Mach number 1.7 and zero angle of attack, supersonic mode of designed airfoil indicates approximately 17% higher drag coefficient than the bi-convex airfoil indicates, it is, however, 23% lower than the NACA 65-006 indicates. Also, subsonic mode of the designed airfoil shows fine aerodynamic characteristics in comparison with NACA 65-006 airfoil in subsonic and transonic speed range. In this regard, design of the airfoil achieved the object of this study satisfactorily.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.12
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• pp.145-150
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• 2000

Micro punching is one of general methods to fabricate simple holes such as permanent ink-jet printer nozzles. A thin punch, that is need for micro punching, usually has been obtained by mechanical machining. There are some method to obtain a thin punch from a cylindrical rod, e.g., microgrinding and WEDG (Wire Electro-Discharge Grinding). Inefficiently, only one punch can be obtained from these machining methods. In contrast with these methods, many punches can be fabricated simultaneously by electrochemical process. Electrochemical process has usually aimed to obtain very sharp probe for atomic force microscopy (AFM) or scanning tunneling microscopy (STM), and it has not been considered the whole shape of a probe in spite of good merits. In this paper, an ultrathin punch with a tapered shape and a cylindrical tip is newly fabricated by electrochemical process.

• Restorative Dentistry and Endodontics
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• v.9 no.1
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• pp.115-119
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• 1983

The purpose of this study was to compare the solubility of enamel and dentin to an etchant after fluoride application. Specimens were collected from extracted anterior and bicuspid and each tooth was cut into several pieces. These specimen were allocated in 7 group; 1%, 2%, 3% NaF, 1%, 8%, 20% $SnF_2$, and control group. Five specimens in each group was exposed to pre-determined fluoride solution for 3 minutes, and washed with running water. These specimens were etched by Hipol (commercial label) etchant for 30 seconds. Following are the findings obtained through S.E.M. 1. All specimens with acid etching revealed preferential removal of prism periphery leaving prism core. 2. Specimens treated with 1%, 2% NaF solution showed that the shape of prism tip was thin and sharp like a needle. The case of 3% NaF showed rather round shape at prism end. 3.1% of $SnF_2$ case showed similar findings with the control group but 8% and 20% $SnF_2$ case revealed needle shape at the prism and was less clear than NaF case. Preferential removal of prism periphery was partialy observed and un decalcified area is fused to prism forming reidge. 4. Dentine treated by fluoride compound in low concentration showed the orifice of dentinal tubule was clearly enlarged whereas in high concentration the orifice was not widened.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.663-669
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• 2005

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis as well as experiment. Two kinds of hub-cap, round shape and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depends on the distance between hub-cap and blade leading edge. Flow analysis of the blade passage is peformed by solving the three-dimensional Reynolds-averaged Navier-Stokes equations. numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flowangle. The changed inlet flow angle near the hub invokesa flow separation on the blade surfaces, thus deteriorating the fan efficiency. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

• The Journal of Korea Robotics Society
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• v.17 no.2
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• pp.172-177
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• 2022

In general, detection robots using ultrasonic sensors are equipped with sensors to protrude outward or to contact objects. However, in the case of a screw-propelled robot that detects the inside of a reactor tendon duct, if the ultrasonic sensor protrudes to the outside, resistance due to grease is generated, and thus the propulsion efficiency is reduced. In order to increase the propulsion efficiency, the screw must be sharp, and the sharper the screw, the more difficult it is to apply a high-performance ultrasonic sensor, and the detection efficiency decreases. This paper proposes a screw shape-changing mechanism that can improve both propulsion efficiency and detection efficiency. This mechanism includes an overlapped helical ring (OHR) structure and a magnetic clutch system (MCS), and thus the shape of a screw may be changed to a compact size. As a result, the Screw-propelled robot with this mechanism can reduce the overall length by about 150 mm and change the shape of the screw faster and more accurately than a robot with a linear actuator.