• Journal of Dental Rehabilitation and Applied Science
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• v.21 no.2
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• pp.143-151
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• 2005

The purpose of this study was to evaluate the most effective method for repairing the exfoliated resin teeth. The specimens were divided into five groups according to repair method and presence of retention holes. The groups were as follows Group1 : Control group Group2 : Sprinkle method with no retention holes Group3 : Sprinkle method with retention holes Group4 : Flask method with no retention holes Group5 : Flask method with retention holes The results were as follows. 1. According to shear bond strength, the value decreased in the order of group1, group5, group3, group2, group4 and there were significant difference between, each group except between group1 and groups5, group2 and group3, group2 and group4(p < 0.05). 2. According to observations of the exfoliation surface, group2 and 4 showed more failure in the denture base resin and repair resin interface, but in group1, 3 and 5 there were more mixed failures. From the results above, there were no significant difference between repair methods without retention holes. But when comparing groups with retention holes, the flask method showed significantly improved results compared to the sprinkle method. Especially, group5 showed similar results as the control group.

• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.326-333
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• 2006

In this study, the vibration waveform of the single hole which is not interfered from the different blasting holes is separated, the each dominant frequency which is determinated through the Fast Fourier Transform(FFT) is measured. Also the separation waveform executed a superposition modeling which changes to delay time from 1ms to 80 ms in 1ms interval and controls the number of blasting holes from 2 holes to 15 holes in order to investigate the effect of PPV according to the duration time of the vibration and the number of blasting holes. As a result of analysis, the longer the duration time of the vibration, the longer the delay time which is not interfered from the different blasting holes and the effect regarding the number of blasting holes from inside identical delay time did not appear a lot.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.196-202
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• 2012

An industrial safety helmet primarily intended to protect the wearer's head. It is to prevent or reduce the danger due to flying or dropping objects, falling and prevent the danger due to an electric shock given to the head. However, thermal discomfort of the head is one of the main complaints in the case of wearing safety helmet. Ventilation holes are not allowed in safety helmets on domestic regulations except for industrial safety helmets which are to protect wearer's head against flying or dropping objects. This paper is to produce the need for enlargement of allowing on ventilation holes' regulation to class B. This study reviewed foreign standards' regulations on ventilation holes of safety helmets. Some standards recommend that ventilation may be improved when fresh air is able to enter the helmet around its lower edge and to exit via holes in the helmet located in the upper one third of the helmet. And in the experiments, relationships of ventilation holes and the temperature over the head are analyzed. The experimental results show that the cooling effect of ventilation holes in the upper one third of the helmet is meaningful.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1606-1615
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• 2001

The present study has been conducted to investigate heat/mass transfer characteristics on a target plate fur arrays of circular impingement jets with and without effusion holes. A naphthalene sublimation method is employed to determine local heat/mass transfer coefficients on the target plate. The effusion holes are located at the center of four injection holes in the injection plate where the spent air is discharged through the effusion hole after impingement on the target plate. For the array jet impingement without effusion holes, the array jets are injected into the crossflow formed by upstream spent air because the impinged jets must flow to the open exit. For small gap distances, heat/mass transfer coefficients without effusion holes are very non-uniform due to crossflow effects and re-entrainments of spent air. However, uniform distributions and enhanced values of heat/mass transfer coefficients are obtained by installing the effusion holes. For large gap distances, the crossflow has little influence on heat/mass transfer characteristics on the target palate due to the large cross-sectional open area between the injection and target plates. Therefore, the distributions and levels of heat/mass transfer coefficients are almost the same for both cases.

• Journal of Magnetics
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• v.16 no.2
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• pp.181-185
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• 2011

To improve trapped field characteristics of a high temperature superconducting (HTS) bulk, a technique to implement artificial holes has been studied. The artificial holes, filled up with epoxy or metal, may provide better cooling channel and enhance mechanical strength of the HTS bulk. Although many useful researches based on experiments have been reported, a numerical approach is still limited because of several reasons that include: 1) highly non-linear electromagnetic properties of HTS; and 2) difficulty in modeling of randomly scattered "small" artificial holes. In this paper, a 2-D finite element method with iteration is adopted to analyze trapped field characteristics of HTS bulk with artificial holes. The validity of the calculation is verified by comparison between measurement and calculation of a trapped field in a $40{\times}40\;mm$ square and 3.1 mm thick HTS bulk having 16 artificial holes with diameter of 0.7 mm. The effects of sizes and array patterns of artificial holes on distribution of trapped field within HTS bulk are numerically investigated using suggested method.

• The Korean Journal of Zoology
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• v.5 no.2
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• pp.9-12
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• 1962

The present observations on the perforation bored into young bivalve Tapes philippinarum (less than 2 mm in shell length) by boring snails were conducted at Sunjae Island in 1960 and Inchon Harbor inn 1962. 1. Young bivalves of the species which were left with bored in them were found both in Inchon Harbor and Sunjae Island. 2. The location of the holes in the valves of the young bivalve varied widely, while the holes of the adult bivalve were located at relatively definite position in the valves. 3. The author realized that the holes are bored by a species of snails that have radulas, for the inner diameters of the holes were much smaller than the router diameters. 4. The size of the holes in the valves of young bivalve was much smaller than those holes bored in adult valves. The minimum size of the holes was only 7.5microns in diameter. 5. The author considered that the boring snail is Natica severa that is found abundantly in Inchon Harbor and Sunjae Island and that this snail is the only species found in the particular areas and performs the above mentioned behavior. However, the author could not confirm experimentally the snail drilling young bivalve of Tapes philippinarum .

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1424-1428
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• 2004

A new design for deburring tools for intersecting holes is introduced. The tool tip is mounted on a slender cantilever assembled into a circular shank. The tool tip has been design to cover ranges of exit angle and diameter ratio between intersecting holes. The design is an improvement over the previous ones by the authors. Experiments have been performed on AL6061. With the new design, mild exit burrs with exit angles greater than 45$^{\circ}$ are successfully removed. For large burrs with smaller exit angles, however, the deburring could be incomplete.

• Journal for History of Mathematics
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• v.35 no.2
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• pp.59-70
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• 2022

In this paper, we review some aspects of geometry for charged rotating black holes which are formed from the gravitational collapse of a massive spinning star with electric charge. We also introduce the computation of entropy for black holes from loop quantum gravity which is a quantum theory of gravity based on Einstein's theory of general relativity.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.93-104
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• 2004

This paper intended to assess the hydro-structure characteristics of volcanic rocks based on the hydrogeological data obtained from the underground storage cavern during construction. The variation of groundwater levels was periodically measured from the 28 surface monitoring holes(NX size) and the hydraulic pressures and injection rates were daily monitored from the water curtain holes(95 horizontal holes and 63 vertical holes). The hydraulic interference tests were performed in whole water curtain holes. The distribution patterns of hydraulic pressure are closely related to the dip angles of fracture intersected to the water curtain holes. Three domains can be grouped by the distribution of hydraulic pressures in the horizontal water curtain holes. The initial hydraulic pressures measured immediately after drilling of water crutain holes are high in ascending order of the cavern C-2, C-1, and C-3. The priliminary hydrochemical data also indicate that the portions of the deep groundwater composition is relatively great in the cavern C-3 area. Some of the horizontal water curtain holes in the cavern C-3 show a steady higher groundwater pressure with the composition of shallow groundwater indicating the outer boundary as constant hydraulic boundary. The water curtain holes in the cavern C-2 is characterized as low initial hydraulic pressure and less injection rates, suggesting poor hydraulic connectivity to a shallow groundwater system. The results of the study can help to understand a hydraulic compartment concept in a fracture hydro-geology and be utilized during the surface investigation for a groundwater system.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.683-690
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• 2008

When steel fabricators erect structural members in field, temporary tightening of fastener should be useful. However, if bolt holes are not aligned by production error or natural condition, additional effort andpain should be provided to align bolt holes. It lead to longer period than times of construction (a primarily day of construction) and more cost than originally cost. This problem will be overcomed by oversize or slotted holes. Early, AISC and Eurocode have included provision for design process such oversize or slotted holes. But, domestic design method is not refered about oversize and slotted holes. Meanwhile, domestic design method and construction environment are variance with Europe and the United States of America. Therefore, a suitable design method for oversize and slotted holes in domestic real condition is needed. In this study, we evaluated behavior of the joints and decided the friction coefficient on oversize and slotted holes of friction joints with high strength bolts.