• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.385-386
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• 2006

For attaining optimum fatigue resistance of PM steels, high density levels are necessary. In this work, sintered steels Fe-1.5%Mo-0.6%C and Fe-1.5%Cr-0.2%Mo-0.6%C were produced with density levels of 7.1 to $7.6\;g.cm^{-3}$. Ultrasonic fatigue testing with 20 kHz was performed in push-pull mode up to 10E9 cycles. It was shown that the fatigue endurance strength is strongly improved by higher density levels, but also higher sintering temperatures are beneficial. The Cr-Mo steels proved to be superior to the plain Mo alloyed, due to a more favourable as-sintered matrix microstructure.

• Fire Science and Engineering
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• v.23 no.4
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• pp.7-12
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• 2009

As the concrete strength increases the degree of damage caused by the spalling becomes more serious because of the permeability. It is reported that the polypropylene (PP) fiber has an important role in protecting concrete from spalling. However, the excessive usage of PP fiber would not useful in spalling control and would decrease the workability of ultra high strength concrete. The high-temperature behaviors of high-strength reinforced concrete columns with various dosage of PP fibers and three types of fire endurance fibers were observed this study. In results, the ratio of unstressed residual strength of columns, in case of concrete strength 60MPa, increases as the dosage of PP fiber increases from 0% to 0.2%, however, the effect of fiber dosage on residual strength of column barely changes above 0.2% and in case of concrete strength 120MPa, PVA fiber is the most suitable fire endurance fiber in accounting fire endurance performance and workability.

• Korean Journal of Exercise Nutrition
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• v.25 no.3
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• pp.16-22
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• 2021

[Purpose] Exercise-associated hyponatremia (EAH) is a well-known condition among endurance athletes at low altitudes. The incidence of EAH during ultramarathons at high altitudes warrants further investigation. This prospective observational study was conducted on the participants of the Leadville Trail 100 run, a 161-km race held at a high altitude (2,800 m-3,840 m). [Methods] Venous blood samples were collected before and immediately after the race. The participants completed an electronic survey after the race. Our main outcome measure was the post-race serum sodium ([Na⁺]) level. [Results] Of the 672 athletes who started the race, 351 (52%) successfully completed the event within the 30-hour cut-off. Post-race blood samples were collected from 84 runners (66 finishers). Both pre- and post-race blood samples were collected from 37 participants. Twenty percent of the post-race participants had EAH. Only one post-race participant had a [Na⁺] level of <130 mmol/L. All participants with EAH were asymptomatic. One participant had an abnormal pre-race [Na⁺] level (134 mmol/L). Female participants had a significantly higher rate of EAH than male participants (40% vs. 16%; p=0.039). Age, body mass index, weight changes, race completion status, nonsteroidal anti-inflammatory drug use, and urine specific gravity were not associated with the development of EAH. Lower postrace [Na⁺] levels were associated with higher serum creatine kinase values (R²=0.1, p<0.005). [Conclusion] High altitude (3,840 m peak) does not appear to enhance the incidence of EAH after an ultramarathon footrace. This suggests that ambient temperature (low temperatures reduce risk), sex (female predilection), endurance running, and overhydration are more prominent risk factors for EAH than high altitude.

• Journal of Korean Physical Therapy Science
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• v.30 no.3
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• pp.72-83
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• 2023

Background: Normal-weight obese women have a normal weight with relatively low muscle mass resulting from high body fat. We aimed to investigate the effects of core exercise on body composition, abdominal muscle thickness, trunk muscular endurance, and psychological factors in normal-weight obese women. Design: One group pre-, mid-, and post-test design. Methods: A total of 20 normal-weight obese women were recruited voluntarily. Core exercises were performed for 30 minutes, three times a week for 4 weeks. InBody measurements, ultrasound imaging, and clinical tests were used to assess body composition, abdominal muscle thickness, trunk and core muscular endurance, and psychological condition(satisfaction with appearance and self-esteem). The dependent variables were measured three times: before the intervention (pre-test), 2 weeks after the intervention (mid-test), and 4 weeks after intervention (post-test). One-way repeated measures ANOVA and Friedman test were used for statistical analysis. Results: Although there was no change in the body composition (p>0.05), thickness of the transversus abdominis and internal and external oblique muscles, endurance of the trunk flexors and extensors and core muscles, and psychological condition showed significant differences after the intervention (p<0.05). Conclusion: Our findings will help develop exercise programs for normal-weight obese individuals that utilize the beneficial effect of core exercises.

• Food Science and Preservation
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• v.24 no.5
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• pp.666-672
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• 2017

The purpose of this study was to examine the effects of long-term endurance exercise and salvia miltiorrhiza vinegar on body composition and insulin resistance of high-fat diet (30% carbohydrate, 50% fat and 20% protein) induced obese rats. After 8 weeks of high fat diet (50% of total calories), rats were divided into 4 groups (sedentary group, n=10; exercise group, n=10; Salvia miltiorrhiza vinegar group, n=10; exercise+Salvia miltiorrhiza vinegar group, n=10) for 8 weeks. Body weight, body composition, diet intake volume, oral glucose tolerance test, plasma total cholesterol were measured. The results showed that Salvia miltiorrhiza vinegar plus endurance exercise training for 8 weeks significantly improved body weight control, visceral fat weight, and insulin resistance. However, only Salvia miltiorrhiza vinegar treatment did not significantly improve body composition and insulin resistance. In addition, there was no additive by the combination of Salvia miltiorrhiza vinegar and endurance exercise in insulin, body fat, and total cholesterol. The reduction of body fat, glucose, insulin and cholesterol by combination was resulted from the exercise. These results suggest that Salvia miltiorrhiza vinegar has slight effect on anti-hyperglycemia and anti-obesity.

• Journal of the Korean Applied Science and Technology
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• v.5 no.2
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• pp.39-54
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• 1988

The effects of exercise and selenium added high fat diet on edurance and serum lipid components were studied in rats. A total of 72 male Sprague-Dawley ($150{\pm}35g$, body weight) were divided into trained group and untrained group and were bred for 7 weeks. Each group had 6 different dietary subgroups; namely, basal diet, 20％ shortening and 20％ soybean oil subgroup and selenium (0.01mg％) added each subgroups. Exercises of 8-min treadmill running and 10-min swimming were given to the trained group every other day during the experimental period while only treadmill running was given to the untrained group during the last week. The amounts of food intake, changes in body weight and endurance were determined once a week and serum lipid components were measured before and after experimental period. Following are the results obtained : 1) The untrained group took a slightly larger amount of food than that in the trained group. The food efficiency is, however, higher in the trained group. Body weight increased more in untrained group, while high fat diet resulted in greater increment in body weight than that in normal diet groups. 2) The trained group showed remarkably longer endurance than the untrained group and selenium added high fat diet enhanced the effect. 3) The trained group showed lower blood level of T-chol., TG and TG/PL than the untrained group. All the other blood values of HDL-chol., PL, MDL-chol./T-chol., HDL/LDL and A/G ratio were higher in trained group. 4) Soybean oil added dietary groups exibited lower blood levels of T-chol., TG, TG/PL and A/G than those in shortening added dietary groups. On the contrary, the former groups showed higher blood HDL-chol., PL., HDL, HDL-chol. and HDL/LDL ratio than those of soybean oil added dietary groups. 5) $LDH_5$ was the most abundant one among serum LDH isozymes. The electrophoretic pattern of serum LDH isozymes was not changed by exercise training and selenium added high fat diet. 6) Exercise training lowered blood GOT and TBA. These effects were enhanced by soybean oil added diets. From the above results it was concluded that a regular and long term exercise training as well as a small amount of selenium added high fat diet result in reduction of body weight and TBA and improve dietary efficiency and physical endurance in rats.

• Tribology and Lubricants
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• v.27 no.1
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• pp.25-33
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• 2011

Rolling contact ball bearings are utilized almost exclusively for liquid propellant rocket engine turbopump. Turbopump ball bearings are required to endure high speed and high load for a poor lubricated condition in cryogenic environment. To evaluate bearing heat generation performance, friction torque is investigated as a function of rotation speed, bearing load and cooling flow rate through an experimental study using water coolants. Radial and axial loads are simultaneously applied to the test bearing by gas pressurized cylinder rod. Endurance performance of bearing has been also verified under the bearing required load for operating condition during total accumulated test time 2,100 sec.

• Journal of the Korean Society for Railway
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• v.14 no.5
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• pp.391-397
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• 2011

In this paper, the pressure endurance test of passenger train's glass window which was developed for next high speed train was studied. At first, pressure test equipment which will be able to generate the maximum pressure same as crossing case between two trainsets in the tunnel was developed. Afterwards the pressure test and evaluation that are based on NFF31-314 were carried out and studied.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.57-60
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• 2005

This study discusses spalling and fire enduring performance of high performance concrete (HPC) RC column subjected to loading under heating for 3 hours. According to the test, both the plain concrete and the concrete attached with fire enduring PC panel exceed allowable temperature after 60 minutes due to the exposure of steel bar and falling off of concrete resulting from severe spalling failure. It leads to buckling of main bar and at the same time, occurrence of collapse of plain HPC column member is observed after 2 hours and 1 hour 40 minutes's exposure to fire, respectively. On the other hand, HPC applying both PP fiber of 0.1$\%$ by mass of concrete and PP fiber+lateral confinement by metal lath maintains their original cross section, which is satisfied with the 3 hours fire endurance criteria, by discharging internal vapour pressure and enhanced lateral confinement force.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.481-484
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• 2006

This study investigates the engineering and fire endurance properties of ultra high strength concrete. The mixture proportions with water to binder ratios (W/B) of 0.15 and 0.25 consist of various adding ratios, such as 0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 percent respectively, of polypropylene (PP) fiber. As for the parameters of specimens, fluidity, compressive strength and unloading fire test were carried out. Test showed that an increase of fiber contents had the favorable properties in fire endurance performance; specimens in W/B 15% required 0.3vol% of PP fiber and specimens in W/B 25% needed only 0.1vol% to prevent spalling.