• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.1
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• pp.170-178
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• 2000

Most of manufacturers try to produce the most efficient filter for respirators with the lowest breathing resistance. Filter performance depends on low penetration, i.e., high efficiency (%), and low pressure drop ($mmH_2O$). This study was performed to evaluate performance of respirator filters by quality factor ($q_F$) and suggest the direction for improvement of respirator filters of good quality in Korea. Two mechanical filters, S and K made in Korea, three filtering facepieces, S made in China, C made in Korea and M made in USA, which were widely used in the workplace, were selected and tested efficiency and pressure drop in accordance with flow rate, using with Automated Filter Tester Model 8110 (TSI, USA). The best quality factor within the same respirator filter categories was $0.0672cm^{-1}\;H_2O$ for mechanical filter S, $0.0698cm^{-1}\;H_2O$ for filtering facepiece M at flow rate of 32Lpm. Mechanical filter S would be the best suitable during heavy work since qulity factors decrease less sharply than any others as increased flow rates. It was necessary for mechanical filter S to lower pressure drop without increasing efficiency, but mechanical filter K should be increased efficiency and decreased pressure drop. While filtering facepiece M had the best quality performance of three ones, Sand C should get much higher efficiency and lower pressure for better performance.

• Resources Recycling
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• v.16 no.3 s.77
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• pp.44-49
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• 2007

In the present work, the high temperature oxygen pressure leaching behavior of chalcopyrite was studied in sulfuric acid solution. The influence of leaching time, temperature and oxygen partial pressure on leaching process were examined. Leaching rate of copper increased significantly with increasing leaching temperature. Copper recovery reached 87.1% within 2 hours at $200^{\circ}C$ and 10 atm oxygen pressure, while most of the solubilized iron readily re-precipitates as hematite($Fe_2O_3$). It was confirmed that e main leach reaction of chalcopyrite occurred through oxidation with oxygen under oxygen pressure and high temperature(above $150^{\circ}C$). Because sulfur was oxidized entirely to sulfate, passivating elemental sulfur layer was not formed.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.120-124
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• 2011

Silicon heterojunction solar cells have been studied by many research groups. In this work, silicon heterojunction solar cells having a simple structure of Ag/ZnO:Al/n type a-Si:H/p type c-Si/Al were fabricated. Samples were fabricated to investigate the effect of transparent conductive oxide growth conditions on the interface between ZnO:Al layer and a-Si:H layer. One sample was deposited by ZnO:Al at low working pressure. The other sample was deposited by ZnO:Al at alternating high working pressure and low working pressure. Electrical properties and chemical properties were investigated by light I-V characteristics and AES method, respectively. The light I-V characteristics showed better efficiency on sample deposited by ZnO:Al by alternating high working pressure and low working pressure. Atomic concentrations and relative oxidation states of Si, O, and Zn were analyzed by AES method. For poor efficiency samples, Si was diffused into ZnO:Al layer and O was diffused at the interface of ZnO:Al and Si. Differentiated O KLL spectra, Zn LMM spectra, and Si KLL spectra were used for interface reaction and oxidation state. According to AES spectra, sample deposited by high working pressure was effective at reducing the interface reaction and the Si diffusion. Consequently, the efficiency was improved by suppressing the SiOx formation at the interface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.653-661
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• 2020

This study derives numerically the shell Knockdown factors for the isogrid-stiffened cylinders of space launch vehicles when the axially compressive force and internal pressure are applied simultaneously. A commercial nonlinear finite element analysis software, ABAQUS, is used for the present work. Nonlinear postbuckling analyses are conducted to calculate the global buckling loads of a cylinder without and with the internal pressure. The shell Knockdown factor is numerically derived using the predicted global buckling loads without and with the geometrically initial imperfection of a cylinder. When the internal pressure of 500 kPa and compressive force are applied to the cylinder, the global buckling load and Knockdown factor increases by 304% and 53%, respectively, as compared to the results without the internal pressure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.1
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• pp.15-20
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• 2006

It is well-known that the corrosive behavior of PMC (polymer matrix composite) structure is much better than the metal structure in the marine environment. The understanding of fracture behavior of PMC in the deep-sea environment is essential to expand its use in the marine industry. For a present study, fracture tests have been performed under low different pressure levels such as 0.1 MPa, 100 MPa, 200 MPa, and 270 MPa using the seawater-absorbed carbon/epoxy composite samples. Fracture toughness was determined from the work factor approach as a function of hydrostatic pressure. It was found that fracture behavior was a linear elastic far all pressure levels. The fracture toughness increased with increasing pressure.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.46-51
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• 2012

Injection pressure, an important factor in filling process, should be minimized to enhance injection molding quality. Injection pressure can be controlled by valve gate open timing. In this work, we decided the valve gate open timing to minimize the injection pressure. To solve this design problem, we integrated MAPS-3D (Mold Analysis and Plastic Solution-3Dimension), a commercial injection molding CAE tool, to PIAnO (Process Integration, Automation and Optimization), a commercial PIDO (Process Integration, and Design Optimization) tool using the file parsing method. In order to reduce computational cost, we performed an approximate optimization using meta-models that replaced expensive computer simulations. At first, we carried out DOE (Design of Experiments) using OLHD (Optimal Latin Hypercube Design) available in PIAnO. Then, we built Kriging models using the simulation results at the sampling points. Finally, we used micro GA (Genetic Algorithm) available in PIAnO. Using the proposed design approach, the injection pressure has been reduced by 13.7% compared to the initial one. This design result clearly shows the validity of the proposed design approach.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.9
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• pp.717-722
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• 2012

In this work, we study on the effects of the oxygen pressure on the structural and crystalline of MgZnO thin films. MgZnO thin films were deposited on p-Si (111) substrates by using pulsed laser deposition. The X-ray diffraction analysis and energy-dispersive X-ray results revealed that as the oxygen pressure increased and Mg content in the MgZnO films decreased. Also Crystal structure was changed from cubic rock salt to hexagonal wurtzite. Alpha step and atomic force microscopy results showed that the thickness of the films are about 100 nm, and it has been found that the MgZnO (002) preferred orientation were deposited with increasing the oxygen pressure. Therefore, the effect of the preferred orientation, the crystallization grew in the form of the columnar; Grain size and RMS of the films were increased with increasing oxygen pressure.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.461-467
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• 2012

An experimental study was carried out to measure frictional pressure drop in flow boiling to deionized water in a microchannel having a hydraulic diameter of $500{\mu}m$. Tests were performed in the ranges of heat fluxes from 100 to $400kW/m^2$, vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and $600kg/m^2s$. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. From the experimental results, it is found that the two phase multiplier decreases with an increase in mass flux. Measured data of pressure drop are compared to a few available correlations proposed for macroscale and mini/microscale. The homogeneous model well predicted frictional pressure drop within MAE of 29.4 % for the test conditions considered in this work.

• Journal of the Korean GEO-environmental Society
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• v.11 no.10
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• pp.25-31
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• 2010

Anchor, soil nail, micropile have been widely used for slope reinforcement and foundation. These all methods need grouting work after placing reinforcing member. In domestic case, gravity fill techniques and pressure grouting techniques are mainly used. In contrast the pressure re-injection grouting method is not commonly used because grouting equipment and lack of practical application example is short and the verification of reinforcing effect is difficult. Pressure re-injection grouting is a kind of post grouting which technique increases the radial stresses acting on the grout body and causes irregular surface to be developed around bond length that tends to interlock the grout and the ground. In this study, the field test was performed to evaluate the reinforcing effect with the variation of grouting methods and pullout characteristics of reinforcing member placed by pressure re-injection grouting method. The test results showed that the post-grouting methods were useful to increase the pullout capacity.

• Health Policy and Management
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• v.8 no.2
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• pp.25-57
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• 1998

In order to assess the attractiveness of the hospital industry, the competitive environment of the industry was analyzed. With the employment of Michael Porter's five forces model' the deciding factor was examined and applied to evaluate the intensity of the competitiveness in the hospital industry, and then the structure and attractiveness in hospital industry was assessed. The subject of this study was hospitals that have over 500 beds. Main findings are as follows. 1. Out of 5 factors deciding competitiveness, the pressure from newly opened hospitals and the competition between existing hospitals, were both high in intensity; this makes hospital industry less attractive. The pressure from the substitutes and the pressure from the negotiating power of consumers and suppliers were low; this makes hospital industry more attractive. 2. Overall intensity of competitive pressure pressure for existing hospital industry that have over 500 beds was rather low, consequently the attractiveness of the industry was evaluated quite high. These findings, however, were not solid enough to endorse the attractiveness of the industry. 3. It was understood that future industry would have bigger pressure/ competition so that the attractiveness for the relevant hospital industry would be decreased. This study has its limitations. As the evaluation of competitive factor was not grounded on quantitative data, its objectivity could be questioned. Also, the overall result of each factors could be distorted as it was calculated with same weight against individual factor. This study has its significance in that the specific hospital group was viewed as one industry, and its attractiveness as a potentially profitable industry in which worth investing was estimated, with all factors considered. With this key result, hospitals industustry could work out a plan to enhance the status of hospitals, allowing hospitals to get assistance in making strategic decisions such as mergers, cooperations, and new establishments.