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Approximately 35% of Korean railroad bridges are classified as steel plate girder bridges. Their connections in the vicinity of stiffeners and other secondary members toward the main girder can be progressively deteriorated owing to stress concentrations,residual stress, welding defects, and harsh environmental conditions. Most bridges of this type were built in the early 1900s, hence,they suffer from aging and progressive degradation of connection zones, and they require extensive maintenance. In accordance with these efforts, the objective of this study is to address the detailed analysis of thin steel plates with bolt connections in order to simulate a method for detecting damage due to loosening in mechanically fastened zones of steel plate girders. For simplicity, we confine this study to previous laboratory-scale experiments for bolt connection problems using PZT (Lead-Zirconate-Titanate) sensors, and we carry out a comparative study with the aid of stress wave transmission using the finite element method, signal processing using wavelets, and piezoelectricity. We carried out fundamental modal analysis and transient dynamic analysis with 3D piezoelectric elements as a sensor/actuator in an open circuit. The material deviation effect of the piezoelectric patch manufacturing process,poling directional properties, geometrical modeling of bolts (bolt pressure), waveform sensitivity, and phase/group velocity characteristics of generated Lamb waves are discussed in conjunction with time-frequency-scale domain analysis.
Background: Maximizing peak bone mass is advocated as a way to prevent osteoporosis. As a prerequisite to the elaboration of any preventive program aimed at rnaximizing peak bone mass, it is important to determine how the rate of skeletal growth at elinically relevant sites, such as lumbar spine(LS), femoral neck(FN), proceeds in relation to age and pubertal stages in both sexes. The present study was performed to measure bone mineral density(BMD) of Korean children and adolescents and to assess the influence of age, sex, puberty and body size on bone mineral density (BMD) during the period of bone growth. Method: Lumbar spine(LS), femoral neck(FN) BMD were measured in 199 healthy males and fernales 7~23 years of age using dual energy x-ray absorptiometry(DEXA), Tanner staging(TS) was used to assess stage of puberty. Results: Anthropometric measurements generally increased with tanner stage in both sexes. Sex differences were observed. In males, compared to females there were significantly higher in height(TS1, TS3, TS4, TS5), weight(TS1, TS3, TS5), dorsal hand skinfold thickness(TS1, TS5), and lean body mass(TS1, TS3, TS4, TS5): while in females, compared to males there were significantly higher in BMI(TS4), skinfold thickness except dorsal hand and fat %(TS3-TS5), and total fat mass(TS3, TS4)(p$lt;C0.05-p$lt;0.001). BMD increased with age in both sexes(LS BMD, M: r= 0.78, F: r= 0.77, p $lt;0.001) (FN BMD, M: r= 0.76, F: r=0.44, p $lt;0.001). Results of liner regression analyses revealed a significant correlation between age and BMD(LS BMD, M: adjusted R2= 0.60, F: R2= 0.60), (FN BMD M: R2= 0.58, F: R2= 0.19). BMD increased with tanner stage(TS) in both sexes(LS BMD, M: r =0.76, F: r =0.84, p$lt;0.001, FN BMD, M: r= 0.73, F: r= 0.55, p$lt;0.001)(LS RMD, M: TS2-TS3 30%, TS4-TS5 18%, F: TS1-TS2 23%, TS2-TS3 27%, TS4-TS5 11%), (FN BMD, M: TS2-TS3 17%, TS4-TSS 15%, F: TS2-TS3 16%). Results of liner regression analyses revealed a significant correlation between tanner stage and BMD(LS BMD, M: R =0.57, F: R= 0.70), (FN BMD M: R2= 0.53, F: R2=0.30). Sex differences were observed in LS and FN BMD. At the TS3, LS BMD was significantly higher in females than in males(p$lt;0.01), but at the TS1(p $lt;0.05), TS3(p$lt;0.01) and TSS(p$lt;0.01) FN BMD were significantly higher in males than in females, The significant correlations were generaly found between BMD and anthropometric measurements in both sexs, also after being adjusted for age. Particularly lean body mass was highly intercorrelated with BMD in both sexes. Stepwise regression analyses demonstrated lean body mass was the only factor which significantly affected LS and FN BMD in males, accounting for 74% and 70% of the variability respectively. In females, tanner stage, height and hip circum- ference were factors which significantly affected LS BMD, accounting for 70% of the variability: while at the FN BMD, body weight accounted for 50% of the variability. Conclusion: Growth of bone was heterogenerous in terrns of sex, magnitude, and localization. There were sex and puberty differences in BMD at any sites, and several identifiable characteristics among anthropometric variables which appear to exert differential effects on skeletal development. Finally, data presented in this paper are cross-sectional: therefore It remains to be determined whether these same variables contribute to longitudinal skeletal changes associated with growth. (J Kor Soc Endocrinol 11:455~467, 1996)
In notching process, predicting punch replacement period is very important. The retainer made of thick steel plate is one of the importantcomponents of the automatic transmission. The transmission retainer is produced through a shearing process, such as a piercing ornotching process. In this process, very high stress occurs in the punch because of high strength and thickness of steel plate. Therefore,punch life is very short. In this study, the fatigue and wear life of the punch in notching process is predicted using numerical analysis. Anexperiment was conducted to verify the effectiveness of the result of numerical analysis for predicting the punch life. From the experimentthe fatigue failure of the punch and the wear depth in notching process are measured. From the results the wear and fatigue lifepredicted through numerical analysis agree well with the experimental results.