• Structural Engineering and Mechanics
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• v.40 no.3
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• pp.393-410
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• 2011

The eight-node 3D solid element is one of the most extensively used elements in computational mechanics. This is due to its simple shape and easy of discretization. However, due to the parasitic shear locking, it should not be used to simulate the behaviour of structural members in bending dominant conditions. Previous researches have indicated that the introduction of incompatible mode into the displacement field of the solid element could significantly reduce the shear locking phenomenon. In this study, an incompatible mode eight-node solid element, which considers both geometric and material nonlinearities, is developed for modelling of structural members at elevated temperatures. An algorithm is developed to extend the state determination procedure at ambient temperature to elevated temperatures overcoming initially converged stress locking when the external load is kept constant. Numerical studies show that this incompatible element is superior in terms of convergence, mesh insensitivity and reducing shear locking. It is also showed that the solid element model developed in this paper can be used to model structural behaviour at both ambient and elevated temperatures.

• Geomechanics and Engineering
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• v.11 no.1
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• pp.41-58
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• 2016

This paper focuses on the deformation behavior of tunnels crossing a weak zone in conventional tunneling. A three-dimensional finite element model was adopted that allows realistic modeling of the tunnel excavation and the support installation. Using the 3D FE model, a parametric study was conducted on a number of tunneling cases with emphasis on the spatial characteristics of the weak zone such as the strike and dip angle, and on the initial stress state. The results of the analyses were thoroughly examined so that the three-dimensional tunnel displacements at the tunnel crown and the sidewalls can be related to the spatial characteristic of the weak zone as well as the initial stress state. The results indicate that the effectiveness of the absolute displacement monitoring data as early warning indicators depends strongly on the spatial characteristics of the weak zone. It is also shown that proper interpretation of the absolute monitoring data can provide not only early warning for a weak zone outside the excavation area but also information on the orientation and the extent of the weak zone. Practical implications of the findings are discussed.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.461-470
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• 2019

This study was carried out to quantify the drought stress in grafted watermelon seedlings non-destructively by using chlorophyll fluorescence (CF) imaging technique rather than the visual judgment. Six-day old watermelon seedlings were grown under uniform irrigation for 3 days, and then given drought stress. Afterward, the sensor for the measurement of water content in plug tray cell unit was used to classify the drought-stress level into nine groups from D1 (53.0%, sufficient moisture state) to D9 (15.7%, extremely dry stress), and the 16 CF parameters were measured. In addition, re-irrigation was performed on the drought stressed seedlings(D5 - D9) to determine the growth and photosynthesis recovery level, which was not confirmed by visual judgment. The kinetic curve patterns of CF in three different drought stressed seedling groups were found to be different for the early detection of drought stress. All the 16 CF parameters decreased continuously with exposure to drought stress and drastically decreased from D5 (32.1%) where the visual judgment was possible. The fluorescence decline ratio (Rfd_Lss) started to decrease from the initial drought stress level (D5 - D6), and the Maximum PSII quantum yield (Fv/Fm) was significantly decreased in the later extreme drought stress range (D7 - D9) by re-irrigation recovery test. Thus, Rfd_Lss and Fv/Fm parameters were finally selected as potent indicators of growth and photosynthesis recovery in the initial and later stages of drought stress. Also, to the differences in the numerical values of the individual chlorophyll fluorescence parameters, the drought stress level was intuitively confirmed through the image. These results indicate that Rfd and Fv/Fm can be considered as potential CF parameters for the detection of low and extremely high drought stress, respectively. Furthermore, Fv/Fm can be considered as the best CF parameters for recovery at re-irrigation.

• Korean Journal of Metals and Materials
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• v.49 no.11
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• pp.853-859
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• 2011

Compressive deformation behavior of Al-10Si-5Fe-1Zr (wt%) alloy preform fabricated by SPS(spark plasma sintering) of gas atomized powder was investigated in the temperature range from 380 to $480^{\circ}C$ and at strain rates from $1.0{\times}10^{-3}$ to $1.0{\times}10^{0}s^{-1}$. Stress-strain curves showed a peak stress (${\sigma}_p$) during initial stage of deformation, followed by a steady state flow at all temperatures and strain rates tested. The (${\sigma}_p$) decreased with both increase in temperature and decrease in strain rate. Nearly full densification was found to occur in the compressively deformed specimens irrespective of test condition. TEM observation revealed a restricted grain growth during steady state flow.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.39-47
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• 1997

Creep rate the elevated temperature is known to be controller by the softening process of microstructure especially in the solid solution alloys such as 125 Cr rotor steel. The change of structure is a decreasing process of the free energy of the state including stress, diffusivity of the material, and tmeperature. This study shows that diffusion coefficient, D of 12% Cr rotor steel at 953K with 74.8 MPa is 1.084~3.140*$10^{15}mm^2sec^1$ compared to $1.658*10^{24}mm^2sec^1$at 963K without stress. During creep, the growth of martensite laths accelerates the diffusion coefficient under stress due to incoherency of interface between carbides and matrix.

• Research in Community and Public Health Nursing
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• v.26 no.2
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• pp.108-118
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• 2015

Purpose: The purpose of this study was to investigate life stress, social support, and antepartum depression among Southeast Asian immigrant women married to Korean men. Methods: Ninety-three subjects were recruited from local women's clinics and multicultural family support centers in D City. The instruments used were the life stress scale, social support scale, and K-EPDS. All the instruments were translated into their corresponding mother languages (Vietnamese, Cambodian, and Philippine) and notarized. Results: The item mean scores of life stress and social support were 2.65 and 3.17, respectively, on a 5-point Likert scale. The mean score of antepartum depression was 10.16, indicating that they were generally in a depressive state. A positive correlation was observed between life stress and antepartum depression (r=.59, p<.001). Social support was negatively correlated with life stress (r=-.42, p<.001) and antepartum depression (r=-.39, p<.001). The best predictors for antepartum depression were life stress, marital satisfaction, and emotional support, and they explained 43% of the variance. Conclusion: Antepartum depression in Southeast Asian immigrant brides was significantly associated with life stress as well as lack of emotional support. Emotional support may reduce their life stress and antepartum depression.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1999.11a
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• pp.216-221
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• 1999

A mental task combined with noise background is an effective model of laboratory stress for study of psychophysiology of the autonomic nervous system (ANS). The intensity of the background noise significantly affects both a subjective evaluation of experienced stress level during test and the physiological responses associated with mental load in noisy environments. Providing tests of similar difficulties we manipulated the background noise intensity as a main factor influencing a psychophysiological outcome and the analyzed reactivity along withe the noise intensity dimension. The goal of this study was to identify the patterns of ANS responses and the relevant subjective stress scores during performance of word recognition tasks on the background of white noise (WN) of the different intensities (55, 70 and 85 dB). Subjects were 27 college students (19-24 years old). BIOPAC, Grass Neurodata System and AcqKnowlwdge 3.5 software were used to record ECG, PPG, SCL, skin temperature, and respiration. Experimental manipulations were effective in producing subjective and physiological responses usually associated with stress. The results suggested that the following potential autonomic mechanisms might be involved in the mediation of the observed physiological responses: A sympathetic activation with parasympathetic withdrawal during mild 55 and 70dB noise (featured by similar profiles) and simultaneous activation of sympathetic and parasympathetic systems during intense 85dB WN. The parasympathetic activation in this case might be a compensatory effect directed to prevent sympathetic domination and to maintain optimal arousal state for the successful performance on mental stress task. It should be mentioned that obtained results partially support Gellhorn's (1960; 1970) "tuning phenomenon" as a possible mechanism underlying stress response.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• Asian-Australasian Journal of Animal Sciences
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• v.11 no.2
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• pp.139-144
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• 1998

Eighteen lambs were used to determine the effects of zinc (Zn) level and source on Zn status and immune function during both normal conditions and conditions of physiologic stress. Treatments consisted of a basal diet (27.6 mg of Zn/kg), and the basal diet supplemented with 25 mg of Zn/kg, added as either zinc oxide or zinc methionine. The basal diet was a corn-cottonseed hull-isolated soy protein- based diet (14% CP). Lambs were weighed and blood samples taken at 28-d intervals for determination of serum Zn and alkaline phosphatase activity. Weights and serum Zn were similar (p > 0.10) among treatments at all sampling days. To evaluate immune responses and Zn status during conditions of physiologic stress lambs were administered 100 I.U. of adrenocorticotrophin (ACTH) on d 112 and feed was withheld for 48 h. Cortisol levels were elevated (p < .01) 5 h post ACTH injection, but had returned to initial levels after 48 h. Lymphocyte blastogenesis ([$^3H$]-thymidine incorporation) on d 112 (prior to ACTH injection) and 114 was unaffected (p > .10) by dietary treatment. However, blastogenesis in response to pokeweed mitogen was greater (p < .0001), whereas the response to phytohemagglutinin was reduced (p < .01) following ACTH administration and fasting. Antibody response to administration of porcine red blood cells was unaffected (p > .05) by dietary treatment. These results indicate that, given the Zn concentration of the basal diet, there was no enhancement of immune function by supplemental Zn, either before or after lambs were subjected to stress.

• Advances in nano research
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• v.9 no.4
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• pp.295-307
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• 2020

The vibrational characteristics of Multi-Phase Nanocomposite (MPC) reinforced annular/circular plate under initially stresses are presented using the state-space formulation based on three-dimensional elasticity theory (3D-elasticity theory) and Differential Quadrature Method (DQM). The MPC reinforced annular/circular plate is under initial lateral stress and composed of multilayers with Carbon Nanotubes (CNTs) uniformly dispersed in each layer, but its properties change layer-by-layer along the thickness direction. The State-Space based Differential Quadrature Method (SS-DQM) is presented to examine the frequency behavior of the current structure. Halpin-Tsai equations and fiber micromechanics are used in the hierarchy to predict the bulk material properties of the multi-scale composite. A singular point is investigated for modeling the circular plate. The CNTs are supposed to be randomly oriented and uniformly distributed through the matrix of epoxy resin. Afterward, a parametric study is done to present the effects of various types of sandwich circular/annular plates on frequency characteristics of the MPC reinforced annular/circular plate using 3D-elasticity theory.