• 소성∙가공
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• 제23권8호
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• pp.489-494
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• 2014

Micro forming is an appropriate process to manufacture very small metal parts which can be employed in the field of electronic devices or electrically controlled mechanical systems. The purpose of the current study was to investigate the influences of both blankholding force and blank diameter for the deep drawing of very small cups. It is essential to control the blankholding force because improper force can result in defects such as wrinkles in the flange or cracks in the corner of the drawn cups. In the current study blankholding force was controlled by springs connected to the blankholder of a press die. Exchangeable bushing dies with various die-corner radii were also used. To obtain the limit drawing ratio for each working condition several sizes of circular specimens were prepared using blanking tools. Beryllium copper(C1720) alloy sheet of $50{\mu}m$ thickness was chosen for the experiments. The maximum limit drawing ratio of 2.1 was achieved experimentally for the conditions of the blankholder force(BHF)=5.3kgf and Rd=0.3mm. Both thickness and hardness along the central section of drawn cups were measured and compared for different drawing conditions. It was found that the deviation of measured data in the thickness and hardness distribution increases with increasing blankholder force and blank diameter.

• 반도체디스플레이기술학회지
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• 제8권4호
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• pp.15-19
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• 2009

A high efficient organic red light emitting device with structure of DNTPD/TAPC/$Bebq_2$ :[$(pq)_2Ir(acac)$, SFC-411]/SFC-137 was fabricated on the plastic substrate, which can be applied in the fields of flexible display and illumination. In the device structure, N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolylamino)-phenyl]-biphenyl-4,4'-diamine[DNTPD] as a hole injection layer and 1,1-bis-(di-4-tolylaminophenyl) cyclohexane [TAPC] as a hole transport were used. Bis(10-hydroxybenzo[h]quinolinato) beryllium complex [$Bebq_2$] was used as a light emitting host material. The host material, $Bebq_2$ was doubly doped with volume ratio of 7% iridium(III)bis-(2-phenylquinoline)acetylacetonate[$(pq)_2$Ir(acac)] and 3% SFC-411[red phosphor dye coded by the proprietary company]. And then, SFC-137 was used as an electron transport layer. The luminous intensity and current efficiency of the fabricated device were $22,780\;cd/m^2$ at 9V and 17.3 cd/A under $10,000\;cd/m^2$, respectively. The maximum current efficiency of the device was 22.4cd/A under $580\;cd/m^2$.

• 한국산업보건학회지
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• 제28권2호
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• pp.230-239
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• 2018

Objective: The purpose of this study is to identify the kinds and exposure levels of health hazards in the metalworking process in relation to acute poisoning accidents caused by methanol in 2016. Methods: The number of industries, workplaces, exposed workers, regional distribution, and exposure level of health hazards in metalworking process were investigated based on employee exposure assessment database provided by KOSHA (the Korea Occupational Safety and Health Agency), which was collected from workplace hazard evaluation programs in Korea. Exposure metrics for methanol were assessed by RCR (risk characterization ratio). Results: The numbers of processes, workplaces, and exposed workers of metalworking, which include CNC (computer numerical control) were 25, 14,405, and 169,102 respectively. The numbers of samples of chemical hazards including methanol were 91,325, and it was found that workers in metalworking were exposed to 249 kinds of chemical hazards. There were 16 kinds of special controlled substances including beryllium. It is estimated that the number of workplaces involving CNC process was 2,537, and the number of exposed workers was 27,976. In CNC process, the total number of workplaces handling methanol was 36, and 298 workers were estimated to be exposed. There was no exceeded that surpassed the OEL and 49% of samples were below the limit of detection. Methanol exposure concentrations in Gyeonggido Province were statistically significantly higher than in other areas (p <0.0001). Conclusions: In the metalworking process including CNC, there is exposure to a wide variety of health hazards. There was no sample exceeding the OEL for methanol. Therefore, it is necessary to recognize the limits of the employee exposure assessment system and urgently improve measures to prevent the occurrence of events like methanol poisoning.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1964-1969
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• 2019

The safety and efficiency of nuclear reactors largely depend on the monitoring and control of nuclear radiation. Due to the unique nuclear-physical characteristics, Hf is one of the most promising materials for the manufacturing of the control rods and the emitters of neutron detectors. It is proposed to use the Compton neutron detector with the emitter made of Hf in the In-core Instrumentation System (ICIS) for monitoring the neutron field. The main advantages of such a detector in comparison the conventional β-emission sensors are the possibility of reaching of a higher cumulative radiation dose and the absence of signal delays. The response time of the detection is extremely important when a nuclear reactor is operating near its critical operational parameters. Taking Hf as an example, the general principles for calculating the chains of materials transformation under neutron irradiation are reported. The influence of ^179m1Hf on the Hf composition changing dynamics and the process of transmutants' (Ta, W) generation were determined. The effect of these processes on the absorbing properties of Hf, which inevitably predetermine the lifetime of the detector and its ability to generate a signal, is estimated.

• 대한의용생체공학회:의공학회지
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• 제6권1호
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• pp.37-46
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• 1985

Development of a dental Ni-Cr alloy system for porcelain veneering crown and bridge was studied in this research. The principles of alloy design were a) It should not contain toxic beryllium. b) It should have low melting Point. c) It should be easily ground and polished. d) It should possess an adequate strength to resist the deformational force In the mouth. e) It should be bondable Ivith porcelain by chemically. After investigating the effect of minor elements such as boron and rare earth metals on the mechanical properties of the Ni-Cr alloy system, the compromised ideal composition for dental use was determined. The composition was l9.6%, Cr, 5.6% Mo, 3.4% Si, 1, 0% Fe, 0.01% Ti, 0.5-1.0% B, 0.2-0.6% misch metal, balance Ni. To compare the performance of experimental alloy with commercially available alloys, the properties such as strength, melting point, and bond strength were measured. The results Ivere as follows: a) Boron increases the strength of the alloy but reduces the elongation. b) Misch metal increases the strength when the boron content is low, but does not increase the strength when boron content is high. And it reduces the elongation drastically, c) Mechanical strength of the experimental alloy was not superior to commercially available Be containing alloy, but handling performance such as castability, ease of granting and polishing, and cuttability were superior to the Be containing alloy.

• Tuberculosis and Respiratory Diseases
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• 제78권4호
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• pp.445-449
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• 2015

Occupational lung diseases are caused by several toxic substances including heavy metals; however, the exact pathologic mechanisms remain unknown. In the workplace, dental technicians are often exposed to heavy metals such as cobalt, nickel, or beryllium and occasionally develop occupational lung diseases. We described a case of occupational lung disease in a patient who was employed as a dental technician for over a decade. A 31-year-old, non-smoking woman presented with productive cough and shortness of breath of several weeks duration. Chest computed tomography revealed a large number of scattered, bilateral small pulmonary nodules throughout the lung field, and multiple mediastinal lymph nodes enlargement. Percutaneous needle biopsy showed multifocal small granulomas with foreign body type giant cells suggestive of heavy metals inhalation. The patient's condition improved on simple avoidance strategy for several months. This case highlighted the importance of proper workplace safety.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.3026-3034
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• 2021

Multi-target X-ray tube is a new type X-ray source, and can be applied in many fields such as sensitive X-ray fluorescence analysis and medical imaging. In this work, we report an electric field modulation multi-target X-ray tube, which contains four targets (Cr, Ni, Au, Mo) coated on a Beryllium (Be) window. A four-valve electric field deflector was developed to deflect the electron beam to bombard the corresponding targets. Particle dynamics analysis software was employed to simulate the particle tracking of electron beam. The results show that the 30 keV electron beam could get a 6.7 mm displacement on the target plane by 10⁵ V/m electric field. The focus areas are about 2 mm × 5 mm and 4 mm × 2.5 mm after deflection in two directions. Thermal behavior calculated by ANSYS shows that the designed target assembly could withstand a 10 W continuous power. The optimum target thicknesses and emission spectra were obtained by Geant4 when the thickness of Be window was 300 mm and the electron beam incident angle was 0.141 rad. The results indicate that this multi-target X-ray tube could provide different X-ray sources effectively.

• Nuclear Engineering and Technology
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• 제53권8호
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• pp.2767-2773
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• 2021

We used the GEANT4 Monte Carlo MC Toolkit to simulate carbon ion beams incident on water, tissue, and bone, taking into account nuclear fragmentation reactions. Upon increasing the energy of the primary beam, the position of the Bragg-Peak transfers to a location deeper inside the phantom. For different materials, the peak is located at a shallower depth along the beam direction and becomes sharper with increasing electron density NZ. Subsequently, the generated depth dose of the Bragg curve is then benchmarked with experimental data from GSI in Germany. The results exhibit a reasonable correlation with GSI experimental data with an accuracy of between 0.02 and 0.08 cm, thus establishing the basis to adopt MC in heavy-ion treatment planning. The Kolmogorov-Smirnov K-S test further ascertained from a statistical point of view that the simulation data matched the experimentally measured data very well. The two-dimensional isodose contours at the entrance were compared to those around the peak position and in the tail region beyond the peak, showing that bone produces more dose, in comparison to both water and tissue, due to secondary doses. In the water, the results show that the maximum energy deposited per fragment is mainly attributed to secondary carbon ions, followed by secondary boron and beryllium. Furthermore, the number of protons produced is the highest, thus making the maximum contribution to the total dose deposition in the tail region. Finally, the associated spectra of neutrons and photons were analyzed. The mean neutron energy value was found to be 16.29 MeV, and 1.03 MeV for the secondary gamma. However, the neutron dose was found to be negligible as compared to the total dose due to their longer range.

• 한국방사선학회논문지
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• 제15권4호
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• pp.415-427
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• 2021

한국원자력의학원에서는 50 MeV 사이클로트론의 빔 라인을 이용하여 연구자들에게 다양한 빔 조사 서비스를 수행하고 있다. 특히 중성자 빔 서비스는 양성자와 베릴륨의 핵반응을 이용하기 때문에 높은 전류를 사용하므로 조사 시료의 방사화 가능성이 높아진다. 본 연구에서는 연구자들이 선호하는 35 MeV 20 ㎂ 중성자 빔 서비스에 의해 발생 가능한 방사화에 대해 MCNP 6.2와 FISPACT-II 4.0을 이용해 평가했다. 평가결과 철, 구리, 텅스텐 시료는 1시간 이상 조사하는 경우 장반감기 핵종이 생성되는 방사화가 발생하여 자체처분농도를 초과했다. 매일 2시간 사용 조건에서 건축물에 대한 방사화는 발생하지 않았고 조사실 내부 공기의 방사화로 인한 종사자의 내부피폭은 매우 미비했고, 이 공기를 배기하는 경우 배출기준도 만족했다.

• 대한치과기공학회지
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• 제43권4호
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• pp.168-174
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• 2021

Purpose: This study was conducted to investigate alloys spectrophotometrically including yttrium of nickel-chromium (Ni-Cr) alloys, which are used as substitutes for the regulation of beryllium and provide helpful improvements in Ni-Cr alloys. Methods: Four groups of specimens (ZN, ZY, SN and EM) were prepared for analysis. Color parameters were measured with a spectrophotometer, and color difference (∆E^*) was calculated. The t-test and one-way analysis of variance test were used to determine significant difference, and the Tukey test was used to identify where the differences were. To measure the spectroscopic reflectivity, the spectroscopic reflectance was measured and converted into CIE L^*, a^*, b^* color system. Results: The ∆E^* value of each metal ceramic group after opaque firing of Ni-Cr alloy with and without yttrium was <2, and the total group color difference (∆E^*) was below 1 in the dentin ceramic all experimental group. However, the a^* and b^* values of the metal ceramic groups were higher than that in the lithium disilicate all ceramic group, and the chroma was higher than the natural tooth. The brightness of all experimental groups was similar to that of the shade guide sample. Conclusion: Yttrium added to Ni-Cr alloys showed similar CIE L^*, a^*, b^* values to Ni-Cr alloys that did not contain yttrium, indicating that yttrium had no effect on color in metallic ceramic systems.