• International Journal of Fluid Machinery and Systems
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• v.10 no.2
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• pp.176-188
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• 2017

The nozzle-flapper valves are widely applied as a pilot stage in aerospace and military system. A subject of the analysis presented in this work is to find out a reasonable range of null clearance between the nozzle and flapper. This paper has presented a numerical flow coefficient simulation. In every design point, a parameterized model is created for flow coefficient simulation and cavitation under different conditions with varying gap width and inlet pressure. Moreover, a new test device has been designed to measure the flow coefficient and for visualized cavitation. The numerical simulation and test results both indicate that cavitation intensity gets fierce initially and shrinks finally as the gap width varies from small to large. From the curve, the flow coefficient mostly has experienced three stages: linear throttle section, transition section and saturation section. The appropriate deflection of flapper is recommended to make the gap width drop into the linear throttle section. The flapper-nozzle null clearance is optionally recommended near the range of $D_N/16$. Finally through simulation it is also concluded that the inlet pressure plays a little role in the influence on the flow coefficient.

• Informatization Policy
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• v.26 no.4
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• pp.36-61
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• 2019

While smart devices can have a positive impact on work efficiency and productivity by reducing time-space constraints and enabling rapid processing of tasks, side effects can arise from the imbalances between work and personal life. In recent years, as smart devices are increasingly used in work environments, it is more necessary than ever to understand the related phenomenon, find the cause of negative effects, and search for appropriate solutions. This study has developed and verified a theoretical model that shows how the technical characteristics known as the utility of smart devices are converted into negative results such as work-life conflict. As a result of analyzing the collected data from the employees, our study provides significant implications for the researchers, as well as the practitioners and policy makers, regarding various relationships among IT-enabled work flexibility, after-hours work connectivity and work-life conflict, and the new knowledge about the important role of segmentation supplies from the organization.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.61-68
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• 2021

Experiments of vertically upward steam-water two-phase flow have been carried out in single-side heated narrow rectangular channel with a gap of 3 mm. Flow patterns were identified and classified through visualization directly. Slug flow was only observed at 0.2 MPa but replaced by block-bubble flow at 1.0 MPa. Flow pattern maps at the pressure of 0.2 MPa and 1.0 MPa were plotted and the difference was analyzed. The experimental data has been compared with other flow pattern maps and transition criteria. The results show reasonable agreement with Hosler's, while a wide discrepancy is observed when compared with air-water two-phase experimental data. Current criteria developed based on air-water experiments poorly predict bubble-slug flow transition due to the different formation and growth of bubbles. This work is significant for researches on heat transfer, bubble dynamics and flow instability.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.335-346
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• 2021

Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental aspects. As the solution temperature increased, even though with large fluctuation, the cavitation degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.352-364
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• 2017

A novel 3D mathematical model for water film runback and icing on a rotating surface is established in this work, where both inertial forces caused by the rotation and shear forces due to the air flow are taken into account. The mathematical model of the water film runback and energy conservation of phase transition process is established, with a cyclical average method applied to simulate the unsteady parameters variation at angles of attack. Ice accretion on a conical spinner surface is simulated and the results are compared with the experimental data to validate the presented model. Then Ice accretion on a cowling surface is numerically investigated. Results show that a higher temperature would correspond to a larger runback ice area and thinner ice layer for glaze ice. Rotation would enhance the icing process, while it would not significantly affect the droplet collection efficiency for an axi-symmetric surface. In the case at angle of attack, the effect of rotation on ice shape is appreciable, ice would present a symmetric shape, while in a stationary case the shape is asymmetric.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.537-544
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• 2011

This work was conducted to investigate the oxidation characteristics of methane having the highest ignition temperature among the other hydrocarbon gases using transition metal catalysts. The catalyst used for methane oxidation was manganese oxide having a various oxidation number, such as MnO, $MnO_2$, $Mn_2O_3$, $Mn_3O_4$, $Mn_4O_5$. The manganese oxide(MnxOy) catalyst is impregnated on $TiO_2$, $Al_2O_3$ for methane oxidation. To enhanced both of activity and life time of catalysts, Ni and Co was used as a promoter. In this study, various co-catalysts were synthesized by using excess wet impregnation method. The effect of reaction temperature and space velocity was measured to calculate the activity of catalysts such as, activation energy of $T_{50}$, and $T_{90}$. The life time of bi-metallic manganese mixture, such as Mn-Co and Mn-Ni catalysts, were increased more 10 % than manganese oxide catalyst, but activity of those was decreased slightly.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.11
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• pp.49-54
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• 2001

In this work, we developed a Ka-band hybrid 4-stage power amplifier module using GaAs pHEMTs and waveguide to microstrip transitions. It has high gain and high output power characteristics. We used a 10 mil- thickness duroid substrate to fabricate this power amplifier and waveguide to microstrip transitions. The fabricated waveguide to microstrip transition showed about 1 dB insertion loss(back to back) at 32 40 GHz. The measured results of power amplifier module showed over 1W output power at 36.1 - 37.1 GHz. And it showed 31 dBm output power, 24 dB power gain and 15 % power-added efficiency(PAE) at 36.5 GHz.

• Korean Medical Education Review
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• v.17 no.3
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• pp.97-104
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• 2015

This literature review explores relevant research and evaluation on pedagogy and physical learning spaces. This study also is intended to encourage discussion among stakeholders on the best medical school developments, in light of emerging learning trends relevant to their institutions. The study has revealed that new environments for learning are being designed or reshaped in response to changing pedagogical approaches, to incorporate new information technology, and to accommodate the changing abilities of new generations of learners. Formal teaching spaces for large groups with a 'sage on a stage' are becoming less common than smaller lecture rooms, although classrooms form a large component of universities and will continue to dominate in the future. However, the traditional layout of these spaces is being transformed to incorporate multiple learning modes. Classrooms should be profound places of revelation and discovery. A well-designed space has the ability to elevate discourse, encourage creativity, and promote collaboration. Within the classroom walls, a learning space should be as flexible as possible, not only because different teachers and classes require different configurations, but because in order to fully engage in learning, students need to transition between lectures, group study, presentations, discussions, and individual work time.

• Journal of muscle and joint health
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• v.18 no.2
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• pp.158-168
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• 2011

Purpose: The purpose of this study was to compare musculoskeletal pain, menopausal symptoms and depression by women's menopausal stage. Method: With a survey design, a convenience sample of 203 women between age of 40 to 64 was recruited through a community. Data were collected via a structured study questionnaire from May to July, 2008. Measures included with symptom severity list for menopausal symptoms, Aches and Pains scale, and Beck's Depression Inventory. Results: Thirty-seven percent of women belong to early peri-menopausal stage, 31% to late peri-menopausal stage, and 32% to postmenopausal stage. By group comparison, late peri-menopausal and post menopausal women reported higher scores of depression than early peri-menopausal women. Postmenopausal women had greater scores in two pain subscales (bodily pain and pain that interferes with normal work) and two menopausal symptoms subscales (sleep pattern and sexual behaviors) than early peri-menopausal women. There were moderate levels of positive relationships among study variables at each menopausal stage. Conclusion: Postmenopausal women seem to have greater musculoskeletal pain and menopausal symptoms, and have depression more than did early peri-menopausal women. Tailored nursing strategies are required to reduce these kinds of common symptoms for women with menopausal transition to improve their physical and psychological wellbeing.

• School Mathematics
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• v.2 no.1
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• pp.29-51
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• 2000

In this study, we tried to suggest an example of the analysis on the use of mathematical manipulatives. Taking algebra tiles as an example of mathematical manipulatives, we analysed several effects resulted from the use of algebra tiles. The algebra tiles make it possible to do activities that are needed to introduce and explain the distributive law and factoring. The algebra tiles have a several advantages; First of all, This model is simple. Even though they cannot make algebra easy, this model can play an important role in the transition to a new algebra course. This model provides access to symbol manipulation for students who had previously been frozen out of the course because of their weak number sense. This model provides a geometric interpretation of symbol manipulation, thereby enriching students' understanding, This model supports cooperative learning, and help improve discourse in the algebra class by giving students objects to think with and talk about. On the other hand, The disadvantages of this model are as follows; the model reinforces the misconception that -x is negative, and x is positive; the area model of multiplication is not geometrically sound when minus is involved; only the simplest expressions involving minus can be represented; It is ineffective when be used the learning of already known concept. Mathematics teachers must have a correct understanding about these advantages and disadvantages of manipulatives. Therefore, they have to plan classroom work that be maximized the positive effect of manipulatives and minimized the negative effect of manipulatives.