• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.454-462
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• 1998

Mechanisms and conditions for rounding of AUC particles were examined during AUC precipitation. Rounding of AUC particle was possible only by external circulation using pump, not by internal circulation using agitator. The rate of AUC rounding $(dn_p/dt)$ was proporational to operation conditions such as magma density $(M_t:g-U/{\iota}l)$, turn over ratio $(T_o)$ and impeller tip velocity of pump (U); $ dn_p/dt{\propto}M_t{\cdot}T_o{\cdot}U^2$. The validity of this relationship was qualitatively confirmed by comparing the expermental results. Two rounding mechanisms were suggested. One is crack formation mechanism and the other etch-pit formation mechanism on the surface of AUC particle. It was found that the crack formation is more dominant at the initial stage and the etch-pit formation at the final stage of the AUC precipitation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.1-6
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• 2018

Recently nano meter size pattern (sub-micro scale) can be machined mechanically using a diamond tool. Many studies have found a 'size effect' which referred to a specific cutting energy increase with the decrease in the uncut chip thickness at micro scale machining. A new analysis method was suggested in order to observe 'size effect' in nano scale machining and to verify the cause of the 'size effect' in this study. The diamond tool was indented to a vertical depth of 1,000nm depth in order to simplify the stress state and the normal force was measured continuously. The tip rounding was measured quantitatively by AFM. Based on the measurements and theoretical analysis, it was verified that the main cause of the 'size effect' in nano scale machining is geometrically necessary dislocations, one of the intrinsic material characteristics. st before tool failure.

• Journal of Korean Neurosurgical Society
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• v.60 no.2
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• pp.262-268
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• 2017

Objective : Stents are widely used in coil embolization of intracranial aneurysms, but on occasion, a microcatheter must traverse a stented segment of artery (so-called trans-cell technique) to select an aneurysm, or double stenting may necessary. In such situations, microguidewire passage and microcatheter delivery through a tortuous stented parent artery may pose a technical challenge. Described herein is a microguidewire looping technique to facilitate endovascular navigation in these circumstances. Methods : To apply this technique, the microguidewire tip is looped before entering the stented parent artery and then advanced distally past the stented segment, with the loop intact. Rounding of the tip prevents interference from stent struts during passage. A microcatheter is subsequently passed into the stented artery for positioning near the neck of aneurysm, with microguidewire assistance. The aneurysm is then selected, steering the microcatheter tip (via inner microguidewire) into the dome. Results : This technique proved successful during coil embolization of nine saccular intracranial aneurysms (internal carotid artery [ICA], 6; middle cerebral artery, 2; basilar tip, 1), performing eight trans-cell deliveries and one additional stenting. Selective endovascular embolization was enabled in all patients, resulting in excellent clinical and radiologic outcomes, with no morbidity or mortality directly attributable to microguidewire looping. Conclusion : Microguidewire looping is a reasonable alternative if passage through a stented artery is not feasible by traditional means, especially at paraclinoid ICA sites.

• Journal of the korean Society of Automotive Engineers
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• v.6 no.3
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• pp.45-54
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• 1984

Bending strength of an internal gear tooth is discussed as tooth form factor taking into account the actual stress magnitude. Stress analysis was carried out by the finite element method(FEM) for the calculation of tooth form factor of an internal gear. This paper also investigated the influences of number of teeth and addendum modification coefficient of the internal gear and the influences of number of teeth, addendum modification coefficient, pressure angle, radius of rounding of tooth tip, and bottom clearance coefficient of the pinion-shaped cutter on tooth form factor of internal gear. Generalizing the resultant data, a simple formula for the tooth form factor of an internal gear was derived for the calculation of tooth bending strength of an internal gear.

• The Korean Journal of Zoology
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• v.39 no.2
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• pp.173-181
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• 1996

The time-course process by which spermatozoa penetrates through the micropvle apparatus into the egg cytoplasm of rainbow trout, Oncorhvnchus mvkiss, was examined with transmission and scanning electron microscopy. In the unfertilized egg, the ess surface beneath the inner opening of the micropylar canal did not differ distinctly from the rest of the animal pole area. A spermatozoon attached to the micropvle opening 20 seconds after insemination. In the initial stases of penetration, the spermatozoon still within the micropvlar canal attached perpendicularly at its apical tip to the ess surface, then the sperm head was rapidly engulfed by the folded egg surface with its manly microvilli. A large fertilization cone with microvillus-free surface appeared on the esS surface sutra-rounding the penetrating spermatozoon. The head portion of the penetrating spermatozoon was completely wrapped by the ess surface with only the tail portion visible externally 30 seconds after insemination. The fertilization cone displayed the tail portion of the penetrating spermatozoon on the central portion of its surface 60 seconds after insemination. 150 seconds after insemination, breakdown of the cortical granules elevation were initiated at the animal pole, then completed at the vegetable pole area. The spermatozoon disappeared from the outer surface of the ess before the fertilization cone completely retracted 250 seconds after insemination. In result, the block to polvspermv to permit entry of a sin81e sperm is considered to be mechanical by the rnorpholoSical design of the micropvle and fertilization cone.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.64-72
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• 2014

In the past, prism patterns have been linear triangular shapeswith a $90^{\circ}$ angle; however, new micro prism patterns having acute angles or obtuse angles have recently been the subject of demandin the display, lighting and photovoltaic industries. Micro-cutting experiments for micro-prism patterns having $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ angles on an electroplated Ni mold were performed and it was found in this study that the specific cutting resistance increased with a decrease in the tool angles (prism pattern angles). The cause of this variation had been thought to be the increase of the ploughing force due to tip rounding and the friction force due to the edge effect. However, the depth of the cut was large enough that it was possible to neglect these effects. Therefore, this study introduced the concept of representative stress of indentation. The measured stress was varied according to the indentation depth eventhoughthetestedspecimenswereidentical ; the varied stress was termed the representative stress. According to indentation theory, the strain that the Ni mold experienced increased with a decrease in the tool angle. Based on the stress-strain relationship, higher strain means higher stress and higher specific cutting resistance. Therefore, the specific cutting resistance was higher at smaller tool angles that had higher strain and stress.