• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.41-50
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• 2007

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.

• Korean Journal of Materials Research
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• v.33 no.5
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• pp.205-213
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• 2023

This paper reports the results of an experimental examination using X-rays to test annealing materials for lapped bearing steel (STB2), to confirm the validity of the weighted averaging analysis method. The distribution behavior for the α_𝜓-sin²𝜓 diagram and the presence or absence of differences in the peak method, half-value breadth method, and centroid method were investigated. When lapping the annealed bearing steel (STB2) material, a residual stress state with a non-directional steep gradient appeared in the surface layer, and it was found that the weighted averaging analysis method was effective. If there is a steep stress gradient, the sin²𝜓 diagram is curved and the diffraction intensity distribution curve becomes asymmetric, resulting in a difference between the peak method, half-value breadth method, and centroid method. This phenomenon was evident when the stress gradient was more than 2~3 kg/mm²/㎛. In this case, if the position of the diffraction line is determined using the centroid method and the weighted averaging analysis method is applied, the stress value on the surface and the stress gradient under the surface can be obtained more accurately. When the stress gradient becomes a problem, since the curvature of the sin²𝜓 diagram appears clearly in the region of sin²𝜓 > 0.5, it is necessary to increase the inclination angle 𝜓 as much as possible. In the case of a lapping layer, a more accurate value can be obtained by considering 𝜎₃ in the weighted averaging analysis method. In an isotropic biaxial residual stress state, the presence or absence of 𝜎₃ can be determined as the presence or absence of strain for sin²𝜓≈0.4.

• The Korean Journal of Pharmacology
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• v.13 no.2
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• pp.1-9
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• 1977

The effects of extracellular calcium concentrations and several concentration of Aconiti tuber butanol fraction, norepinephrine, ouabain on the force of isometric contraction of isolated atrial preparations obtained from rabbits were determined at $11{\sim}14$ different frequencies of contraction. Qualitatively similar results were obtained in all preparations. In most preparations, rested-state contraction was induced at the range of $120{\sim}400$ seconds stimulation interval. Over the range of intervals from 120 to 10 seconds negative inotropic effect of activation (NIEA) was predominant, so the steady-state contractile force progressively declined. At the intervals of 3 seconds, changes in the cumulated negative and positive isotropic effect of activation (PIEA) practically cancelled each other under steady-state conditions. At the interval from 3 seconds to 0.25 seconds, the additional cumulation of PIEA was greater than that of the NIEA. When the intervals between contractions were shorter than 0.25 seconds, the cumulation of the NIEA was again predominant. The positive inotropic effect of cardiac glycoside resulted at least in large part from increase in the rested-state contraction. No significant effect on the PIEA was found. The decay of the NIEA was apparently greatly accelerated in the presence of high concentration of ouabain, but this may also be a reflection of their action on the state determining the strength of the rested-state contraction. In the case of extracellular calcium concentration increment, the similar results with the ouabain treatment were obtained. Norepinephrine produced more powerful inotropic effect at shorter stimulation interval than long. The rested-state contraction and the decay of the NIEA were not significantly altered in the presence of norepinephrine, but cumulated PIEA and the amount of PIEA produced by each contraction were significantly increased. Aconiti tuber butanol fraction showed similar results with that of norepinephrine. The increment of contractile force at various contraction frequency were dose-responsive in the presence of Aconiti tuber butanol fraction. It is suggested that the positive inotropic effect of Aconiti tuber butanol fraction at various contraction frequency may be due to increase of the cumulation of PIEA and the amount of PIEA produced by each beat.