• Journal of Aerospace System Engineering
• /
• v.12 no.4
• /
• pp.106-111
• /
• 2018

Hydrodynamic ram phenomenon could be generated by external threats such as impact and blast in the aircraft. High strain rate deformation caused by the hydrodynamic ram phenomenon is one of the main factors to influence structural survivability. Mechanical properties of composite structure change rapidly under conditions of high strain rate. Therefore, it is necessary to experimentally investigate the influence of strain rates for aircraft structural survivability. In this paper, tensile tests of composite material were conducted for low and high strain rates to investigate the influence of the various strain rates. Tensile modulus increases more compared to tensile strength at high strain rate under hydrodynamic ram condition. Regression analysis was conducted to predict tensile modulus at various strain rates because it is one of the main damaging factors for composite structures under high strain rate conditions. Also, the mechanical properties of composite materials were acquired and analyzed under high strain rate conditions. It is hypothesized that the results from this study would be used for designing aircraft composite structures and evaluation considering structural survivability.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.2209-2219
• /
• 1997

A split hopkinson bar could be used for obtaining the high strain rate material properties of sheet metals for an autobody. In high speed tensile tests of sheet matals, a new design of a tension split Hopkinson bar apparatus is needed. The design of grips and an anvil length are numerically analyzed with ABAQUS/Explicit for the new apparatus of split Hopkinson bars. From the experiments with the new apparatus, the material properties of SPCEN in the high strain rate state have been acquired and compared with quasi-static experimental results. The material properties of SPCEN as well as other sheet metals in an autobody are indispensible for the analysis of crashworthness. Nevertheless the experiment of sheet metal in the high strain rate state has not been done or reported.

• Biomedical Science Letters
• /
• v.25 no.1
• /
• pp.32-39
• /
• 2019

Conventional high-flux hemodialysis (HD) is not as good as normal kidney function. Morbidity and mortality rates of patients receiving HD are still very high. To increase mid-to-large molecule clearance by combining diffusion and convection, on-line hemodiafiltration (HDF) is required. The objective of this study was to compare long-term survival rate of patients treated with on-line HDF to those who received conventional high-flux HD by reviewing data from Chonnam National University Hospital (CNUH). We selected patients who attended the 'CUNH dialysis center' and agreed to participate in the study. Overall, 40 patients with ESRD switched from high flux HD to on-line HDF or started on-line HDF from August 2007 to December 2009. Additionally, a total of 42 patients receiving conventional high-flux HD during the same period were enrolled. We then reviewed long-term survival rate of patients receiving on-line HDF over the next seven years. When we compared survival rates for seven years, the survival rate of the group receiving on-line HDF was 65% (26/40) while that of the group receiving the conventional high-flux HD was 54.8% (23/42). Although the number of patients was small to see survival difference clearly by one specific dialysis modality, there was somewhat difference in survival rate between the two groups. Indicators such as anemia, calcium-phosphate metabolism, nutritional status, treatment adequacy, and hospitalization were also improved in the group receiving HDF. Overall, results of our study showed beneficial effects of on-line HDF on clinical outcomes and survival in chronic HD patients.

• Journal of the Semiconductor & Display Technology
• /
• v.21 no.3
• /
• pp.50-56
• /
• 2022

In order to process a vast amount of data, there is demand for a new system with higher processing speed and lower energy consumption. To prevent 'memory wall' in von Neumann architecture, RRAM, which is a neuromorphic device, has been researched. In this paper, we summarize the features of RRAM and propose the device structure for characteristic improvement. RRAM operates as a synapse device using a change of resistance. In general, the resistance characteristics of RRAM are nonlinear and random. As synapse device, linearity and uniformity improvement of RRAM is important to improve learning recognition rate because high linearity and uniformity characteristics can achieve high recognition rate. There are many method, such as TEL, barrier layer, NC, high oxidation properties, to improve linearity and uniformity. We proposed a new device structure of TiN/Al doped TaO_x/AlO_x/Pt that will achieve high recognition rate. Also, with simulation, we prove that the improved properties show a high learning recognition rate.

• Journal of Fisheries and Marine Sciences Education
• /
• v.4 no.2
• /
• pp.109-120
• /
• 1992

The auther reported the distribution of fisheries high schools and arrangement of curriculum in Japan in the forward report, and describes on the outer apparance and substantiality of education of fisheries high schools in Japan in the present report. 1. The rate of population to the number of fisheries high school shows 2,350 thousands in Japan, compared with 3,250 thousands in Korea. Then the rate in Korea is 1.4 times as high as that in Japan. 2. The rate of pupil to the whole regular instructors for fundamental subjects and for vocational subjects in the fisheries high schools, and also the rate to the instructors for vocational subjects show 10.4 and 16.3 in Japan, compared with 18.2 and 30.2 in Korea. Then the rate in Korea is 1.8 times as high as that in Japan. In addition to the instructors for vocational subjects. trainer and assistants for technical training-are employed in Japan compared with no such instructors or assistants in Korea. Then the rate of pupil to the whole instructing staffs in Korea is 2.4 times as high as that in Japan. 3. 81 percents of training ships in Japan are larger than 400 gross tons, which is extremely higher to that in Korea. The rate of gross tonnage of the ships to the number of trainees shows 6.2 tons in Japan compared with 1.1 tons in Korea. Also such large dimensioned training ships are newly built every other 12 years. the construction cost per 1 gross ton of such ships are said as 2.5 to 3 million yen, which corresponds to 15 to 18 million wons, and is over 3 times as much as that in Korea. 4. The basic education on the marine field is widely diffused in Japan. For an example, swimming pools are prepared not only in fisheries high schools but also in primary schools although it is rate even in fisheries high schools or colleges in Korea. 5. Almost all provinces which locate on the seashore have at least one fisheries high school and the curriculum is arranged to match the needs of local districts, then the management of school is tightly linked to the local government. 6. Entrance system is also flexible and recommended entrance system for successors of fishermen is settled. 7. Re-education of instructors for the new subjects which should be prepared to match the demands of ages are supported by local government in the aspect of time and budget. 8. The special two-year course for advanced seamen' s education is attached to some fisheries high schools and the graduates are qualified to get the third grade marine officer's or engineer's liscence.

• Clean Technology
• /
• v.29 no.4
• /
• pp.297-304
• /
• 2023

The rapid advancement of the high-tech electronics industry has led to a significant increase in high-concentration ammonia wastewater. Various methods have been attempted to reliably treat wastewater containing high concentrations of ammonia, but no successful technology has yet been developed and applied. In this study, the removal efficiency and characteristics of ammonia nitrogen was evaluated according to changes in temperature, air loading rate, and liquid loading rate using a closed circulation countercurrent packed tower type demonstration facility for wastewater containing high concentrations of ammonia generated in the high-tech electronics industry. The temperature was varied while maintaining operating conditions of a wastewater flowrate of 20.8 m³ h^-1 and an air flow rate of 18,000 Nm³ h^-1. The results showed that at temperatures of 45,50,55, and 60℃, the removal efficiencies of ammonia nitrogen (NH₃-N) were 87.5%, 93.4%, 96.8%, and 98.7%, respectively. It was observed that temperature had the most significant impact on the removal efficiency of NH₃-N under these conditions. As the air loading rate increases, the removal rate also increases, but the increase in removal efficiency is not significant because droplets from the absorption tower flow into the stripping tower. Even if the liquid loading rate was changed by ±30%, the removal rate did not change significantly. This does not mean that the removal rate was unaffected, but was believed to be due to the relatively high air load rate. Through demonstration research, it was confirmed that ammonia stripping is a reliable technology that can stably treat high-concentration ammonia wastewater generated in the high-tech electronics industry.

• Phonetics and Speech Sciences
• /
• v.5 no.4
• /
• pp.171-184
• /
• 2013

This study investigated the devoicing rate of Japanese high vowels, focusing on regional and generational differences by acoustically analyzing vowels from two large speech databases. The first speech database used in this study was collected between 1986 and 1988 from 41 areas (prefectures) which included 607 participants (299 high school students and 308 their grandparents). The second was taken from a 2006-2007 collection from seven areas as a follow-up investigation to the first database consisting of 463 participants ranging in age from 8-90 year olds. The results revealed there is a generational as well as regional difference in the devoicing rate in almost all areas. Based on those results, a new distribution map reflecting a current devoicing rate of the younger generation was presented. Furthermore, by comparing the two data sets, this study confirmed age difference in the devoicing rate is not age-grading but a sound change in progress. This study discusses the social factors for changes in the devoicing rate of some areas and then applies the devoicing rate of five areas to an S-curve model to predict the future devoicing rate.

• Nuclear Engineering and Technology
• /
• v.33 no.5
• /
• pp.526-538
• /
• 2001

Fatigue tests in air and in room temperature water were performed to obtain comparable data and stable crack measuring conditions. In air environment, fatigue crack growth rate was increased with increasing temperature due to an increase in crack tip oxidation rate. In room temperature water, the fatigue crack growth rate was faster than in air and crack path varied on loading conditions. In simulated light water reactor (LWR) conditions, there was little environmental effect on the fatigue crack growth rate (FCGR) at low dissolved oxygen or at high loading frequency conditions. While the FCGR was enhanced at high oxygen condition, and the enhancement of crack growth rate increased as loading frequency decreased to a critical value. In fractography, environmentally assisted cracks, such as semi-cleavage and secondary intergranular crack, were found near sulfide inclusions only at high dissolved oxygen and low loading frequency condition. The high crack growth rate was related to environmentally assisted crack. These results indicated that environmentally assisted crack could be formed by the Electrochemical effect in specific loading condition.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.9
• /
• pp.1306-1313
• /
• 2004

This paper addresses a theoretical approach to calculate the amount of the stored energy during high strain-rate deformations using atomistic level simulation. The dynamic behavior of materials at high strain-rate deformation are of great interest. At high strain-rates deformations, materials generate heat due to plastic work and the temperature rise can be significant, affecting various properties of the material. It is well known that a small percent of the energy input is stored in the material, and most of input energy is converted into heat. However, microscopic analysis has not been completed without construction of a material model, which can simulate the movement of dislocations and vacancies. A major cause of the temperature rise within materials is traditionally credited to dislocations, vacancies and other defects. In this study, an atomistic material model for FCC such as copper is used to calculate the stored energy.

• Journal of Engineering Education Research
• /
• v.15 no.5
• /
• pp.98-107
• /
• 2012

As the dropout rate of university students is gradually increasing, the studies on exploring the status, characteristics, reasons, and countermeasures of dropout of university students are currently grabbing high attention. This paper analyzes the relationship between the admission types and dropout of university students, mainly focused on engineering students. The analysis shows that the dropout rate of engineering students admitted through the scheduled-time admission procedures is quite higher than that of students admitted through non-scheduled-time admission procedures, the dropout rate of engineering students admitted from the vocational high schools is higher than that of students from the academic high schools, and the dropout rate of engineering students admitted from the liberal art high school tracks is higher than that of students from the natural science high school tracks. From the results, we could find out that student-support programs need to be carefully provided for the engineering university students according to their admission types and underlying backgrounds.