• Explosives and Blasting
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• v.39 no.3
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• pp.1-14
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• 2021

Rockburst is a sudden and violent failure of rock. During the failure process, excess energy is liberated as seismic energy, which in turn causes the surrounding rock mass to vibrate. The level of the ground vibration can reach a magnitude of over 4.5 in the Richter local scale. Thus, a rockburst can cause not only injury to persons, but also damage to both underground workings and surface structures. In this paper the source mechanism of rockburst is analyzed based mainly on the two reports of the Canadian Rockburst Research Program (CRRP). A simplified LS-DYNA modeling is also performed to identify the tensile failure patterns occurring in the remaining rock mass right after blasting in mine stope. The configuration of the simplified model will probably be useful in small-scale laboratory tests for investigating the source mechanism of rockburst.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.891-897
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• 2013

In this study, the compressive deformation behaviors of aluminum alloy under high strain rates were investigated by means of a SHPB test. An acoustic emission (AE) technique was also employed to monitor the signals detected from the deformation during the entire impact by using an AE sensor connected to the specimen with a waveguide in real time. AE signals were analyzed in terms of AE amplitude, AE energy and peak frequency. The impacted specimen surface and side area were observed after the test to identify the particular features in the AE signal corresponding to the specific types of damage mechanisms. As the strain increased, the AE amplitude and AE energy increased whereas the AE peak frequency decreased. It was elucidated that each AE signal was closely associated with the specific damage mechanism in the material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.149-156
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• 2017

Nuclear fuel requires high reliability and safety and therefore contains debris filtering devices to prevent failure-inducing debris from entering it. The debris filtering performance of nuclear fuel is one of the most important factors for fuel integrity. Therefore, the performance must be evaluated and the measurement must be reasonable. In this study, a calculation method of the comprehensive filtering efficiency using the weighted mean was proposed to establish a standard filtering efficiency index. To confirm the suitability of the proposed method, representative debris specimens were selected and the filtering efficiency with the weighted mean was compared with the efficiency of the arithmetic mean. The weighting factor of the weighted mean was introduced to produce a fair evaluation. In addition, the analysis of the debris filtering mechanism was performed according to the size of debris specimens, and the main dimensions of the filtering feature for commercial nuclear fuel.

• Korean Journal of Head & Neck Oncology
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• v.30 no.1
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• pp.10-14
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• 2014

목 적 CO2 가스 삽입 없이 내시경 보조 갑상선 절제술, 특히 액와 절개를 이용하는 경우의 대부분은 기구 사용을 용이하게 하기 위하여 흉부 또는 유륜에 절개를 넣어 시행하는 것이 대부분이다. 본 연구는 후이개 절개를 통하여 추가적 절개 없이 내시경을 이용한 갑상선 절제술 및 중심 임파선 절제술이 가능한지의 여부를 사체연구를 통하여 확인해 보고자 한다. 방 법 사체 이용 해부 및 수술 후이개 내시경 보조 갑상선 절제술이 가능한지의 확인은 수술 시야 및 접근성, 수술 완성도, 그리고 주요 구조물의 보존 여부인 3가지 항목으로 평가하였다. 결 과 수술 시야는 기구를 다루고 수술을 하기에 충분하였으며, 추가 절개 없이 수술을 완성할 수 있었다. 절제된 갑상선 조직의 피막은 손상되지 않았으며, 잔존 갑상선 조직이 없음을 수술 부위를 통하여 확인하여, 수술의 완성도 여부를 평가할 수 있었다. 모든 사체에서 되돌이 후두신경 및 상 또는 하부갑상선의 보존을 확인하였으며, 주변 구조물들의 손상이 없음을 확인하였다. 결 론 로봇이 아닌 후이개 절개를 이용한 내시경 보조 갑상선 절제술은 시행 가능한 접근법 및 수술방법이라 사료된다.

• Journal of Korean Clinical Nursing Research
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• v.18 no.2
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• pp.296-306
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• 2012

Purpose: This study was done to compare the physical injury, emotional response and unplanned self-removal of medical devices in patients with physical restraints and patients not restrained. Methods: Eighty patients admitted to the intensive care unit (ICU) of a university hospital in Seoul participated in this study. Forty patients made up each group and the group not restrained was matched with the restraint group for age and history of smoking and alcohol consumption. Data on occurrence of physical injury, intensity of anxiety, stage of agitation and unplanned self-removal of medical devices were collected by observation and medical chart review using a structured instrument. Statistical processing of collected data was done with the SPSS WIN 17.0 program. Results: The physically restrained group experienced more physical injuries and recorded significantly higher levels of anxiety and agitation than the unrestrained group. However, there were no significant differences between the groups in occurrence of unplanned self-removal of medical devices. Conclusion: Results indicate a need for critical care nurses to carefully monitor physical injuries and emotional responses of physically restrained patients and to develop nursing interventions to prevent adverse effects associated with restraint use. There is also a need to develop patient safety guidelines when using physical restraints.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.300-307
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• 1987

The present study was investigated on the DNA damage by the peroxidation of polar and non-polar lipid fractionated from mackerel lipid to elucidate the DNA damage mechanism by fish oil peroxidation. The degree of DNA damage by polar lipid peroxidation became greater with the increase of its concentration, and such DNA damage was induced below 100 millieq./kg in POV for 4 days incubation. Among the polar lipid peroxidation products, singlet oxygen $^1O_2$ and superoxide anion ${\cdot}O_2^-$ greatly affected to the DNA damage than hydrogen peroxide $H_2O_2$ and hydroxyl radical ${\cdot}OH$. Non-polar lipid peroxidation also induced the DNA damage with the increase of its concentration, but such effect was lower than the case of total lipid and polar lipid. And, the effects of active crygens on the DNA damage by non-polar lipid peroxidation was the same as in the case of total and polar lipid peroxidation.

• Journal of Chest Surgery
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• v.31 no.5
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• pp.525-530
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• 1998

Thoracoscopic thoracic sympathectomy for primary palmar hyperhidrosis has been known to be effective and to have cosmetic merits compared to conventional open sympathectomy. In spite of its cosmetic advantages over thoracotomy, VATS using 5 mm or 10 mm instruments still has the problem of operative wound as well as pain on trocar sites. Recently, 2 mm thoracoscopic instruments have been used. The purpose of this study was to examine the results of thoracoscopic sympathectomy for palmar hyperhidrosis with 2 mm thoracoscopic instruments. From January 1997 to April 1997, 46 patients underwent bilateral thoracoscopic sympathectomy with 2mm instruments at Seoul National University Hospital. T-2 ganglion was carefully dissected and resected out in all patients. In one patient, the lower third of T-1 ganglion was inadvertently resected together with T-2 ganglion due to poor anatomical localization. In 4 patients who also complained of excessive axillary sweating, T-3 ganglion was resected as well. The instruments were removed without leaving any chest drain after reexpansion of the lung. Trocar sites were approximated with sterile tapes. All patients were relieved of excessive sweating in their upper extremities immediately after the operation. Nine patients(19.6%) showed incomplete reexpansion of the lung, and two of them required needle aspiration. Complications related to the surgical procedures, such as Horner's syndrome, hemothorax, and brachial plexus injury, were not detected in any cases. Most patientsdid not complaine of pain. All patients were discharged from the hospital on the day of operation. Despite a narrow operative viewfield, thoracic sympathectomy with 2 mm thoracoscopic instruments can be performed without increasing any severe complications. We recommend 2 mm instruments for thoracoscopic sympathectomy because they make as the more cosmetic, less painful, and equally effective compared to thoracoscopic sympathectomy using 5 mm or greater instruments.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.401-406
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• 1998

For the applications in optical waveguides and devices, LiNbO_3$ single crystals need to overcome the weakness of optical damage due to the inhomogeneities of laser-induced refractive index. This problem can be solved by doping of Mg in LiNbO_3$ and proton exchange of LiNbO_3$. In this study, to understand the mechanism of optical damage resistance in LiNbO_3$, the changes of lattice defects in LiNbO_3$ caused by MgO doping and acid treatment were observed indirectly by $OH^-$ absorption bands using a FT-IR spectrophotometer. The effect of lattice defects on temperature, heat-treatment and polishing were also investigated. It is shown that MgO doping increases optical damage resistance by generating the defects of $Mg_{Nb}^{2+}$ in the lattice of LiNbO_3$, and that proton exchange by implantation of $H^+$ ion in the hexagonally closest packed oxygen layers on the surface of LiNbO_3$, makes lattice defects, which diffuse into the crystal after heat-treatment above $400^{\circ}C$.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.350-363
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• 1999

The precision cyclic shear test system was established to investigate the mechanical characteristics of rough rock joints under cyclic loading conditions. Laboratory cyclic shear tests were conducted for saw-cut joints and artificial rough rock joints using Hwangdeung granite and Yeosan marble. Surface roughness and aperture characteristics of specimens were examined by measuring surface topography using the laser profilometer. Peak shear strength, phase difference during loading and unloading, and anisotropic shear behavior were investigated throughout the cyclic shear test results. These features and their subsequent variations in each loading cycle are significantly dependent upon the second order asperities and the strength of intact rock. It was observed that degradation of asperities for rough rock joints under cyclic shear loading followed the exponential degradation laws of asperity angle and that the mechanism for asperity degradation would be different depending upon the normal stress level, roughness of joint surface and the loading stage.

• Composites Research
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• v.17 no.4
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• pp.53-60
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• 2004

This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP laminate plates based on considerations of stress wave propagation theory. The absorbed energy of T300 orthotropic composites is higher than that of quasi-isotropic specimen over impact energy 6.8J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of T300 orthotropic composites, which are composed of the same stacking number and orientation became more than that of T700 fiber specimen; however there was no big difference in case of quasi-isotropic specimens. The delamination areas of the impacted specimen were measured with the ultrasonic C-scanner to find correlation between impact energy and delamination area. The fracture surfaces were observed by using the SEM (scanning electron microscope) through a low-velocity impact test in order to confirm the fracture mechanism.