• Journal of the Korea institute for structural maintenance and inspection
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• 제7권1호
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• pp.165-172
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• 2003

The fatigue problem of Prestressed Concrete(PSC) bridges are more serious than the other type of concrete bridges, because the cross sectional area and self weight of PSC bridges are smaller. The endurance of strengthening methods for PSC bridges are tested in this study. Glass fiber sheeting and external post-tensioning methods were applied. 1/5 scale PSC beams were made for fatigue test, same as static test. The range of repeated load is from 10% to 80% of yielding load with sine curve. The experimental results show that the failure cycle of strengthened members are increased compare to non-strengthened members. The members strengthened with glass fiber show better enhancement in fatigue problem than the members strengthened with external post-tensioning method, though the adhesion of glass fiber and concrete is failed, as increase of crack. With these experimental results, it can be said that the strengthening methods used in this study are efficient at extending the life time of aged PSC bridges.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제16권1호
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• pp.5-10
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• 2003

In this study, a new programming method to minimize the generation of Si-SiO$_2$interface traps of SONOS nonvolatile memory device as a function of number of porgram/erase cycles was proposed. In the proposed programming method, power supply voltage is applied to the gate. forward biased program voltage is applied to the source and the drain, while the substrate is left open, so that the program is achieved by Modified Fowler-Nordheim(MFN) tunneling of electron through the tunnel oxide over source and drain region. For the channel erase, erase voltage is applied to the gate, power supply voltage is applied to the substrate, and the source and dram are left open. Also, the asymmetric mode in which the program voltage is higher than the erase voltage, is more efficient than symmetric mode in order to minimize the degradation characteristics or SONOS devices because electrical stress applied to the Si-SiO$_2$interface is reduced due to short program time.

• Journal of Oral Medicine and Pain
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• 제17권1호
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• pp.41-50
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• 1992

The authors performed a experimental study to evaluate the effects of masticatory muscle fatigue on tooth contact and masticatory muscle activity in 26 normal healthy women. The experimental masticatory muscle fatigue was induced by unilateral biting of 5kg force on mandibular first molar. The results were as follows : 1. The initial symptom related to muscle fatigue pain appeared in 85.19 seconds of isometric contraction and the endurance time of isometric contraction was 203.15 seconds. 2. The pain occurred more frequently in masseter region than in temporal region. In masseter pain the incidence was almost equal between both sides, whereas the temporal pain was more in contralateral side. 3. The spontaneity and the symmetry of tooth contact during maximum clenching were reduced after isometric unilateral biting. 4. After induction of experimental muscle fatigue, the EMG activities of masseter muscles of both sides and ipsilateral temporal muscle showed the tendency of decreasing activities. 5. The asymmetry indicies of masseter and temporal muscles were reduced after isometric bilateral biting.

• The KSFM Journal of Fluid Machinery
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• 제7권1호
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• pp.30-35
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. Many experiments should be safely performed to activate the utilization of the HANARO. HANARO flow simulation facility is being developed for the endurance test of reactivity control units for extended life time and the verification of structural integrity of those experimental equipments prior to loading in the HANARO. This facility is composed of three major parts; a half-core structure assembly, a flow circulation system and a support system. The flow circulation system is composed of a circulation pump, a core flow piping, a core bypass flow piping and instruments. The system is to be filled with de-mineralized water and the flow should be met the design requirements to simulate a similar flow characteristics in the core channel of the half-core structure assembly to the HANARO. This paper, therefore, presents an analytical analysis to study the flow behavior of the system. Computational flow analysis has been performed for the verification of system pressure variation through the three-dimensional analysis program with the standard $k-{\epsilon}$ turbulence model and for the verification of the structural piping integrity through the finite element method. According to the analysis results, it could be said that the design requirements and the structural piping integrity of the flow circulation system are satisfied.

• Corrosion Science and Technology
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• 제10권4호
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• pp.136-142
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• 2011

Al alloys have been used widely for commercial and military ships in most ocean countries since mid-1950s, and the value as light metal with high mechanical strength has been proven. As the safety and fuel efficiency of Al ships have improved, she can carry more freight, sail faster and travel longer distances. Furthermore, in the shipbuilding industry, Al alloys are applied as structural materials for ships to various areas including the deck of luxurious cruises, battleships and leisure ships. In addition, Al alloys are being spotlighted as environmental-friendly material as they can be recycled even after end of lifespan. However, Al alloys for ships must be carefully selected after considering corrosion resistance, endurance, strength, and weldability in sea water environment. Al alloys to satisfy these conditions are used widely include 5000 series Al-Mg alloy and 6000 series Al-Mg-Si alloy. Thus, this study selected and evaluated the cavitation characteristics of the 5000 series Al alloys that are used in hulls that directly contact seawater and the 6000 Al alloys that are used in the upper structures of ships. Results of cavitation test with time, weightloss and cavitation rate of 5456-H116 showed the smallest damage among 5052-O, 5456-H116 and 6061-T6.

• Transactions of The Korea Fluid Power Systems Society
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• 제7권4호
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• pp.9-14
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• 2010

Most power steering systems work by using a hydraulic system to turn the vehicle's wheels. The pressure is usually provided by a hydraulic pump driven by the vehicle's engine. A double-acting hydraulic cylinder applies a force to the steering gear, which in turn applies a torque to the steering axis of the road wheels. The flow to the cylinder is controlled by valves operated by the steering wheel ; the more torque the driver applies to the steering wheel and the shaft it is attached to, the more fluid the valves allow through to the cylinder, and so the more force is applied to steer the wheels in the appropriate direction. Since the pumps employed are of the positive displacement type, the flow rate they deliver is directly proportional to the speed of the engine. And for a long time, the type of hydraulic pump pulley was boss welding type. But recently, monolith type driving pulley is widely used. Therefore in this paper we studied the safety of monolith type driving pulley to the extracting force and endurance by FEM analysis and experiments.

• Journal of Korean Public Health Nursing
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• 제22권1호
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• pp.74-83
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• 2008

Purpose: To identify the effect of walking exercise on the body composition and physical fitness in obese college women. Method: The research design was a nonequivalent control group pretest posttest. Thirty-seven subjects were surveyed using a structured questionnaire, and measured for body composition and physical fitness. Twenty persons in the experimental group among the total sample participated in a 12-week walking program. The data were analyzed by $x^2$-test, and t-test with SPSS 10.1 program. Results: 1) BMI, body fat mass and percentage of body fat in body composition were significantly decreased in the experimental group compared to the control. However, there was no significant difference in skeletal muscle mass between the two groups. 2) Power among physical fitness was significantly increased in the experimental group. However, there was no significant difference in muscular strength (back strength), flexibility (sit and reach), muscular endurance (abdomen curl), power (standing high jump) or agility (trunk reaction time) between the two groups. Conclusion: The above results, confirmed the effectiveness of walking exercise as an effective nursing intervention in order to improve body composition.

• Tuberculosis and Respiratory Diseases
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• 제81권1호
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• pp.13-18
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• 2018

Bronchodilator therapy is central to the management of chronic obstructive pulmonary disease and are recommended as the preferred treatment by the Global Obstructive Lung Disease Initiative (GOLD). Long acting anti-muscarinics (LAMA) and long acting ${\beta}_2$ agonists (LABA) are both more effective than regular short-acting drugs but many patients remain symptomatic despite monotherapy with these drugs. Combination therapy with LAMA and LABA increases the therapeutic benefit while minimizing dose-dependent side effects of long-acting bronchodilator therapy. The TOviTO programme has investigated the benefits of treatment with a combination of tiotropium and olodaterol administered via a single inhaler. Tiotropium+olodaterol $5/5{\mu}g$ significantly improved forced expiratory volume in 1 second ($FEV_1$) area under the curve from 0 to 3 hours, trough $FEV_1$ health status and breathlessness versus the mono-components and placebo. Tiotropium+olodaterol $5/5{\mu}g$ also increased endurance time and reduced dynamic hyperinflation during constant work rate cycle ergometry. On the basis of these and other studies the 2017 GOLD report recommends escalating to dual bronchodilator therapy in patients in groups B and C if they remain symptomatic or continue to have exacerbations and as initial therapy for patients in group D.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2006년도 추계 학술논문 발표대회 논문집
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• pp.13-16
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• 2006

This study investigates filed application in Daebul Free Trade Zone of a flowing method using drying shrinkage-reducing superplasticizer(SRS) and an insulating curing method using double bubble sheets. Test showed that fresh concrete satisfied target slump and air content. A structure adding SRS significantly decreased the total bleeding capacity and accelerated the setting time. As for the crack occurrence, the structure applying the flowing method and double bubble sheets simultaneously exhibited the most favorable crack endurance, while conventional concrete showed more than 1mm size of crack in overall, and a structure applying only the flowing method partially presented micro crack. For the area proportion of crack occurrence, the structure using the double bubble sheets indicated 9.8%, while others applying flowing method was 28%, compared with 100% of conventional one. Standard curing specimens had about $3{\sim}6%$ higher compressive strength than that of specimens cured at adjacent field construction. In addition, using SRS improved about $5{\sim}7MPa$, than that of conventional concrete at 91 days elapse.

• International Journal of Ocean System Engineering
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• 제3권2호
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• pp.61-67
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• 2013

In this study, wave spectrum based fatigue analyses are studied for Turkey's adjacent coastal seas by using Maestro finite element analyzing software. Palmgren-Miner's method is used to obtain the fatigue safe life time. Palmgren-Miner's method was selected for the fatigue analyses because of its good acceptance of data from almost all classification societies such as Germanischer Lloyd, the American Bureau of Shipping, Det Norske Veritas, etc. The maximum stress regions of the structures are obtained by using finite element analyses, and the results are compared with the endurance limit of the W$\ddot{o}$hler diagram of AA5059 H321 aluminum alloy. The wave characteristics table given in this article is used to obtain the number of cycles for each sea condition. By using the wave characteristics table, the wave lengths, wave speeds, and cycles are obtained. This study is performed to estimate the lifetimes of a semi-swath type coast guard boat and/or commercial yacht projects, which are produced by using AA5059 H321 aluminum alloy, under different sea environment conditions. Fatigue examinations are performed for both head seas and oblique seas.