• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.499-504
• /
• 2001

A validation of a 3D CFD model for predicting local subcooling of moderator in the vicinity of calandria tubes in a CANDU reactor is performed. The small scale moderator experiments performed at Sheridan Park Experimental Laboratory(SPEL) in Ontario, Canada[1] is used for the validation. Also a comparison is made between previous CFD analyses based on 2DMOTH and PHOENICS, and the current model analysis for the same SPEL experiment. For the current model, a set of grid structures for the same geometry as the experimental test section is generated and the momentum, heat and continuity equations are solved by CFX-4.3, a CFD code developed by AEA technology. The matrix of calandria tubes is simplified by the porous media approach. The standard $k-\varepsilon$ turbulence model associated with logarithmic wall treatment and SIMPLEC algorithm on the body fitted grid are used and buoyancy effects are accounted for by the Boussinesq approximation. For the test conditions simulated in this study, the flow pattern identified is a buoyancy-dominated flow, which is generated by the interaction between the dominant buoyancy force by heating and inertial momentum forces by the inlet jets. As a result, the current CFD moderator analysis model predicts the moderator temperature reasonably, and the maximum error against the experimental data is kept at less than $2.0^{\circ}C$ over the whole domain. The simulated velocity field matches with the visualization of SPEL experiments quite well.

• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.471-473
• /
• 2002

Public concerns associated with the electromagnetic field (EMF) exposures from mobile phones on human body are increased. Although studies on the effects of the EMF exposures on human have been carried out for a long time, it is not proved yet whether the EMF effect is harmful or not. Based on the scientific results by experts, EMF exposure limits have been regulated as a precautionary approach on the assumption that the EMF effect may be harmful. It is well known that absorbed EMF can be transformed into heat within biological tissues and that thermal effects are related with the specific absorption rate (SAR) distribution. However, the relative magnitude and distribution of the energies are not well defined. Although there is comprehensive information of the thermal effects, most of them come from animal and in vitro studies. Considerable efforts have been made to analyze the EMF absorption model while the actual temperature in the human body has been rarely measured. Temperature changes on the face of a healthy male volunteer were studied. A digital mobile phone of 1.8GHz was used. A digital infrared imaging system (IRIS-5000, Medicore, Seoul, Korea) was applied to take infrared pictures of the face every minute while the volunteer talked over the mobile phone for 20 minutes. The specification of the imaging system was as follows: Temperature resolution = 0.1$^{\circ}C$; Range of temperature measurement = 17～40$^{\circ}C$; Pixel size = 0.9mm ${\times}$ 0.9mm; Frame time = 2.6s; Active temperature of detector = 77$^{\circ}$K. The result showed that temperature of the ear region was increased during the phone call and the region of the temperature increase on the face was expanded as the phone call time increased. Further study is necessary to investigate the temperature rise analytically and quantitatively.

• 한국화재소방학회논문지
• /
• 제30권6호
• /
• pp.118-123
• /
• 2016

건물에서 화재가 발생했을 때 재실자의 안전한 대피를 위하여 발생되는 연기를 제어하는 것이 중요하다. 화재 연기를 배출하기 위해 설치해야 하는 배연창은 자연배연설비로, 이와 관련한 내용은 건축 관련법에 규정하고 있다. 그러나 현재법 규정에서 배연창에 대해 최소 기준만 제시하고 있고, 그 내용이 구체적이지 않아 건물에 적용할 때 다수의 문제점이 발생하고 있다. 배연창의 설치대상, 설치위치, 유효면적, 제어 및 유지관리 등 여러 부분에서 발생하는 문제들에 대한 개선이 필요하다. 본 연구에서는 국내 외 배연창 관련 기준과 선행연구 조사, 현장조사를 통해 현 제도의 문제점을 파악하고 이에 대한 개선방안을 제시하고자 한다.

• 한국자원식물학회지
• /
• 제10권2호
• /
• pp.135-139
• /
• 1997

식방풍 1호는 1990년에서 1995년까지 6개년간 전국에서 수집한 11개 식방풍재래종 중 영덕종 등 4계통을 순계분리한 후 생산력 검정시험에 공시한 다음 그 중 생육특성이 우수한 영덕종과 봉화종에 대해 지역적응시험 및 농가실증시험을 실시한 결과 영덕종이 다수성 순계임이 확인되어 1995년도에 농촌진흥청 우량종자선정 심의회에서 우량품종으로 결정되어 식방풍 1호로 명명되었기에 육성 과정에서 나타난 주유특성과 수량성을 요약하면 다음과 같다. 1. 식방풍 1호는 봉화식방풍과 초장은 비슷하고 주근장은 짧았으나 엽수가 많고 경자과 근두직경은 굵었고 종실량도 증수되었다. 2. 식방풍 1호는 근피색이 황갈색이고 근 형태는 식립원추형으로서 양질의 생약 재 생산에 유리한 품종이었다. 3. 식방풍 1호는 근중 엑스함량과 회분 및 산불용성 회분 함량으로 보아 대한 약전 규격집에 규정된 함량치에 적합하여 생약으로 이용시 유효성을 갖추었다. 4. 식방풍 1호는 토양선층에 비교적 강한 편이었고 내병성, 내습성, 내서성 및 내도복성도 강한 특성을 나타내었다. 5. 식방풍 1호의 건근수량은 생산력 검정시험, 지역적응시험 및 농가실증시험 결과 모두 봉화 식방풍보다 ha당 $10\sim28%$ 증수되었다.

• 한국지구물리탐사학회:학술대회논문집
• /
• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
• /
• pp.244-251
• /
• 2003

A two-dimensional BEM code, $FRACOD^{2D}$, was applied to simulate fracture initiation and propagation processes in a rock pillar during an in situ heater test of a rock pillar planned at the $\"{A}sp\"{o}$ Underground Rock laboratory of SKB, in Southern Sweden. To take the advantage of conventional BEM for simulating fracturing processes, but without efforts for domain integral transformation, a hybrid approach is developed to simulate the fracturing processes in rock pillar under coupled thermo-mechanical loading. The code FRACOD was used for simulating the fracture initiation and propagation processes with its boundary tractions reflecting the effects of the initial and redistributed thermomechanical stresses in the domain of interest at multiple excavation and heating steps were produced by a special algorithm of stress inversion, based on resultant thermo-mechanical stress fields at each excavation and heat loading step by a FEM code without considering fracturing processes. This hybrid approach can take the advantages of both types of numerical methods and avoids their shortcomings for fracturing process simulation and domain effects, respectively. In this paper, we present the hybrid approach for the stress, displacements, and fracturing processes at sequential excavation and heating steps of the in situ heater test as a predictive modelling, the formulation of the fracturing models and the predictive results. Two sections of borehole depth, 0.5 m and 1.5 m below the tunnel floor are considered. The pillar area is modelled with the FRACOD and the stress field produced by excavation and heating is transferred with corresponding boundary stresses. From the modelling results, the degree of fracturing and damage are evaluated for 120 days of heating. Dominated shear fracturing in the vicinity of the central pillar was observed from the models at both sections, but spalled area appears to be limited. Based on the modelling results, a sensitivity study for the effect of pre-existing fractures in the vicinity of the holes is also conducted, and the initiation and evolution of EDZ around the deposition holes are investigated using this particular numerical technique.

• Journal of Welding and Joining
• /
• 제29권1호
• /
• pp.80-84
• /
• 2011

The weight reduction of the transportations has become an important technical subject Al and Al alloys, especially Al 5052 alloys have been being applied as door materials for automobile. One of the most widely known car weight-reduction methods is to use light and corrosion-resistant aluminum alloys. However, because of high electrical and thermal conductivity and a low melting point, it is difficult to obtain good weld quality when working with the aluminum alloys. Also, Pulse MIG welding is the typical aluminum welding process, but it is difficult to apply to the thin plate, because of melt-through and humping-bead. In order to enhance weld quality, welding parameters should be considered in optimizing the welding process. In this experiment, Al 5052 sheets were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) pulse process. The proper welding conditions such as welding current, welding speed, torch angle $50^{\circ}$ and gap 0~1mm are determined by tensile test and bead shape. Through this study, range of welding current are confirmed from 100A to 120A. And, the range of welding speed is confirmed from 1.2m/min to 1.5m/min.

• 한국세라믹학회지
• /
• 제56권4호
• /
• pp.360-364
• /
• 2019

PZT suspensions for photo-curable 3D printing were fabricated and their characteristics were evaluated. After mixing the PZT, photopolymer, photo-initiator, and dispersant for 10 min by using a high-shear mixer, the viscosity characteristics were investigated based on the powder content. To determine an appropriate dispersant content, the dispersant was mixed at 1, 3, and 5 wt% of the powder and a precipitation test was conducted for two hours. Consequently, it was confirmed that the dispersibility was excellent at 3 wt%. Through thermogravimetric analysis, it was confirmed that weight reduction occurred in the photopolymer between 120? and 500?, thereby providing a debinding heat treatment profile. The fabricated suspensions were cured using UV light, and the polymer was removed through debinding. Subsequently, the density and surface characteristics were analyzed by using the Archimedes method and field-emission scanning electron microscopy. Consequently, compared with the theoretical density, an excellent characteristic of 97% was shown at a powder content of 87 wt%. Through X-ray diffraction analysis, it was confirmed that the crystallizability improved as the solid content increased. At the mixing ratio of 87 wt% powder and 13 wt% photo-curable resin, the viscosity was 3,100 cps, confirming an appropriate viscosity characteristic as a stereolithography suspension for 3D printing.

• 대한치과기공학회지
• /
• 제22권1호
• /
• pp.113-128
• /
• 2000

The purpose of this study was to serve as a basis for the development of dental technology and for creating a condition that dental technicians could work with pride and right values, by examining what problems there were in their health care, what they thought about them, and how the problems could be solved, The findings of this study were as below: 1. The most serious and harmful element in dental technology workshop was a dust(57.5%) and a noise(33.3%). 2. Approximately 99.0% of the dental technicians investigated made a complain of air pollution caused by noise. Their opinion on a possible measure to remove noise air pollution was that the noise-generating machine should be replaced(64.1%) or that it should be isolated(28.8%). 3. 76.0% complained air pollution cause by dust deteriorates their working efficiency. As a way to eliminate it, they suggested a dust chamber(35.3%) or an air cleaner(27.5%) should be installde. 4. About 80% made a complain of gas air pollution. The most common related symptom was a headache(56.9%). They thought that gas-generating machine should be isolated(39.9%) or that an air purifier should be prepared(33.3%). 5. The largest impact of heat and light on their body was weakening their eyesight(56.9%). 47.1% got burn once though four times, and 34.3% did five times or more. The way to prevent them was to install an automatic casting machine(66.0%) or use protective glasses(28.1%). 6. Approximately 47.7% were considering a change of occupation, and the most common reason was heavy work(23.5%), followed by poor prospect(21.6%) and working environment(19.0%) in the order named. 7. 88.9% responded they were likely to have an occupational disease. Their idea about the proper frequency of regular health examination was once a year(53.6%), or once per every six months(41.8%). 8. The field they were most interested in was health care(39.2%), followed by academic research activities(31.4%). This fact indicated it's most urgently required to improve their working environment.

• 대한치과기공학회지
• /
• 제22권1호
• /
• pp.145-152
• /
• 2000

In order to select an effective antibiotic substance against oral resident bacteria, we were isolated from soil and texonomically analyzed. Seven hundred and eighteen strains were isolated on humic acid- vitamin agar(HV agar) and 220 strains were on methanol medium from three each paddy forest, field and riverside soil samples. So, during the screening of antibiotics from soil, we isolated microorganisms showing powerful antagonistic activity against oral resident bacteria. Microorganism was tested against 25 strains of bacteria, yeast and fungi. Among them, No. 248 strain exhibited the most strongly growth inhibition. So, the taxonomical analysis the isolated strain was found to be unknown Actinomyces sp. and was named No 248. A production of the antibiotics from No. 248 begins at the early exponential phase developed at the 72th hour under the optinum conditions. The property of No. 248 antimicrobial compound was very stable under acid(pH 3.0) and alkali(pH 10.0) treatment, but it was instable in heat treatment at $120^{\circ}C$. For the improvement of antibiotic activity, two mutants were isolated from strain No. 248 by the treatment of mutagenic agents, NTG and hydroxylamine. As a result, the mutant strains excreted the potent antibiotics to inhibit the growth of Candida albicans.

• 대한소아치과학회지
• /
• 제23권3호
• /
• pp.631-639
• /
• 1996

Electrosurgical technique have been used in dentistry as an aid to soft tissue management for nearly 60 years. However, it was not until the late 1960s that the principles of electrosurgery were understood and improved equipment became available. Electrosurgery is a surgical procedure performed on soft tissue utilizing controlled high frequency electricaI(radio-frequency) currents in the range of 1,500,000 to 7,500,000 cyclesper second. The radio-frequency energy used in electrosurgery is able to cut and coagulate tissue because it focuses the energy at the small, active electrode. Advantages of electrosurgery for soft-tissue management during dental procedures include improved hemostasis, ease of tissue modification, improved visibility and so on, but adverse healing responses-including necrosis of soft tissue and sequestration of alveolar bone-have been reported. The present report provides examples of treatment of soft tissue and pulp tissue of primary teeth by electrosurgery. The results are as follows; 1. Electrosurgical techniques can be used for various procedures in pedodontics. 2. Electrosurgical procedures provide improved hemostasis and visibility in the operating field, which enable to remove, reshape, and contour soft tissues easily. 3. In pulpotomy technique, it was difficult to expect the variable pulpal response based on the degree of heat accumulation and the conditions of pulp tissues. Therefore, electrosurgical pulpotomy could not be considered as a method superior to formocresol pulpotomy. 4. A greater degree of dexterity and experiences in manipulation of the electrode is required compared with the conventional scalpel surgery.