• Structural Engineering and Mechanics
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• v.71 no.1
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• pp.89-98
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• 2019

In this study, the mechanical bending behaviors of functionally graded porous nanobeams are investigated. Four types of porosity which are, the classical power porosity function, the symmetric with mid-plane cosine function, bottom surface distribution and top surface distribution are proposed in analysis of nanobeam for the first time. A comparison between four types of porosity are illustrated. The effect of nano-scale is described by the differential nonlocal continuum theory of Eringen by adding the length scale into the constitutive equations as a material parameter comprising information about nanoscopic forces and its interactions. The graded material is designated by a power function through the thickness of nanobeam. The beam is simply-supported and is assumed to be thin, and hence, the kinematic assumptions of Euler-Bernoulli beam theory are held. The mathematical model is solved numerically using the finite element method. Numerical results show effects of porosity type, material graduation, and nanoscale parameters on the static deflection of nanobeam.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.325-331
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• 1992

By using the general theoretical framework proposed recently for treating the fluorescence quenching kinetics, we investigate the effect of light pulse intensity on the decay of fluorescence which follows excitation of fluorophors by the light pulse of very short but finite duration. It is seen that conventional theory breaks down when the exciting light pulse has a pulse width comparable to the fluorescent lifetime and its intensity is very high. We also find that even when the light intensity is not too high, conventional theory may fail in either of the following cases: (i) when the quencher concentration is high, (ii) when there is an attractive potential of mean force between the fluorophor and quencher, or (iii) when the energy transfer from the fluorophor to the quencher may also occur at a distance, e.g., via dipole-dipole interaction. The validity of the predictions of the present theory may thus be tested by fluorescence quenching experiments performed under such situations.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.217-231
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• 2023

The bending analysis of sandwich functionally graded (FG) beams under temperature circumstances is performed in this article utilizing Navier's solution-based parabolic shear deformation theory. For the first time, a comparative study has been carried out between the exponential and sigmoidal sandwich FGM beams under thermal conditions. During this investigation, temperature-dependent material characteristics are postulated. Both symmetric and unsymmetric sandwich examples have been studied. The effect of gradation law, gradation coefficient, and thickness scheme on beam behavior has been thoroughly investigated. Three possible temperature combinations at the top and bottom surfaces of the beam are also investigated. Beams with a higher proportion of ceramic to metal are shown to be more resistant to thermal stresses than beams with a higher proportion of metal.

• Current Optics and Photonics
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• v.6 no.4
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• pp.413-419
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• 2022

An oxyfluoride glass ceramic containing Eu²⁺-doped nepheline and LaF₃ crystals was modified, with BaF₂ replacing LaF₃ up to 20 mole percent, and its luminescence change was monitored. With increasing BaF₂ content, the greenish yellow emission centered at 540 nm under 400-nm excitation decreased, and a new afterglow emission from the modified ceramic was observed after removal of the excitation light source. X-ray diffraction (XRD) and transmission electron microscopy with energy dispersive spectroscopy (TEM-EDS) were used to investigate the changes in the crystalline phases within the glass matrix. Time dependent emission intensity was monitored to observe the afterglow, and the possible mechanism for the afterglow due to BaF₂ addition was considered.

• Steel and Composite Structures
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• v.42 no.5
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• pp.649-655
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• 2022

In presented paper, moving load problem of simply supported axially functionally graded (AFG) beam is investigated under temperature rising based on the first shear beam theory. The material properties of beam vary along the axial direction. Material properties of the beam are considered as temperature-dependent. The governing equations of problem are derived by using the Lagrange procedure. In the solution of the problem the Ritz method is used and algebraic polynomials are used with the trivial functions for the Ritz method. In the solution of the moving load problem, the Newmark average acceleration method is used in the time history. In the numerical examples, the effects of material graduation, temperature rising and velocity of moving load on the dynamic responses ofAFG beam are presented and discussed.

• Geomechanics and Engineering
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• v.36 no.1
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• pp.83-97
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• 2024

It is important to make reasonable prediction about the long-term deformation of high rockfill geostructures. However, the deformation is usually underestimated using the rockfill parameters obtained from laboratory tests due to different size effects, which make it necessary to identify parameters from in-situ monitoring data. This paper proposes a novel hybrid back-analysis method with a modified objective function defined for the time-dependent back-analysis problem. The method consists of two stages. In the first stage, an improved weighted average method is proposed to quickly narrow the search region; while in the second stage, an adaptive response surface method is proposed to iteratively search for the satisfactory solution, with a technique that can adaptively consider the translation, contraction or expansion of the exploration region. The accuracy and computational efficiency of the proposed hybrid back-analysis method is demonstrated by back-analyzing the long-term deformation of two high embankments constructed for airport runways, with the rockfills being modeled by a rheological model considering the influence of stress states on the creep behavior.

• Journal of applied mathematics & informatics
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• v.42 no.2
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• pp.305-320
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• 2024

We consider a mathematical model which describes the quasistatic contact of electro-viscoelastic rod with an obstacle. We use a modified Kelvin-Voigt viscoelastic constitutive law in which the elasticity operator is nonlinear and locally Lipschitz continuous, taking into account the piezoelectric effect of the material. We model the contact with a general damped response condition. We establish a local existence and uniqueness result of the solution by using arguments of time-dependent nonlinear equations and Schauder's fixed-point theorem and obtain a global existence for small enough data.

• Nanomaterials
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• v.11 no.2
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• pp.494-503
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• 2021

Interface traps between a gate insulator and beta-gallium oxide (β-Ga₂O₃) channel are extensively studied because of the interface trap charge-induced instability and hysteresis. In this work, their effects on mobility degradation at low temperature and hysteresis at high temperature are investigated by characterizing electrical properties of the device in a temperature range of 20-300 K. As acceptor-like traps at the interface are frozen below 230 K, the hysteresis becomes negligible but simultaneously the channel mobility significantly degrades because the inactive neutral traps allow additional collisions of electrons at the interface. This is confirmed by the fact that a gate bias adversely affects the channel mobility. An activation energy of such traps is estimated as 170 meV. The activated trap charges' trapping and de-trapping processes in response to the gate pulse bias reveal that the time constants for the slow and fast processes decrease due to additionally activated traps as the temperature increases.

• Women's Health Nursing
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• v.4 no.3
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• pp.322-331
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• 1998

The postpartum is a period of transition to motherhood where a childless woman transforms into a woman with children. Parents, especially mothers must perform an essential role of implementing instrumental and emotional care behaviors on part of the helpless, dependent, and immature infant. First-time mothers, however, suddenly face the responsibility of round the clock duty without neither parenting training during pregnancy, nor a time to gradually adapt to growing responsibilities after birth, with confusion and frustration as a result. Thus, after providing first-time mothers with childcare education as maternal role preparation, this study will try to examine its effects on childcare behaviors and confidence in maternal role during the early postpartum period. This quasi-experimental study using a nonequivalent control group non-synchronized design, was carried out from March 1995 to May 1996 to verify the effects of a childcare education program with first-time mothers who had vaginal delivery in Ewha University Hospital, Seoul, Korea, and collected data from 60 subjects who consented to the study. The education was given in the early postpartum period(48-72 hours after delivery) and to measure its effects, a posttest was done 4 weeks later with the results analyzed by SPSS shown in the following : 1. The childcare behavior score of the experimental group that had received the newborn care education was higher than the control group(t=3.5, P=.001). 2. The control group and the experimental group which had received the education showed no difference in degree of confidence in maternal role. 3. The higher the childcare behavior score, the higher the degree of confidence in maternal role was among the subjects(r=.56, P=.001). The preceding results are significant in that childcare practices can be promoted by providing child-care education to first-time mothers in the early postpartum period. Thus, this education can be used as a nursing intervention strategy in the early postpartum period.

• Korean Journal of Acupuncture
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• v.22 no.1
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• pp.117-132
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• 2005

Objectives : This study was carried out to determine whether Juglandis Semen herbal acupuncture (JSA) exerts the protective effect against toxic agent-induced live. cell damage. Methods : The cell damage was estimated by measuring lactate dehydrogenase (LDH) release, and lipid peroxidation was estimated by measuring maiondialdehyde (MDA), a product of lipid peroxidation, in rabbit liver slices. Results : When tissues were incubated with 0.5 mM Hg for $10{\sim}120\;min$, LDH release and lipid peroxidation were increased as a function of incubation time, and these effects were significantly prevented by addition of 0.1% JSA. Hg increased LDH release and lipid peroxidation in dose-dependent manner over the range of $0.1{\sim}l\;mM$ concentrations, which were reduced by 0.1% JSA. When tissues were treated with 0.5 mM Hg in the presence of $0.05{\sim}l\;%$ JSA, LDH release and lipid peroxidation induced by Hg were prevented by JSA in a dose-dependent fashion. JSA at 0.5 and 1% prevented completely effects of 0.5 mM Hg. When tissues were treated with 0.5 mM Hg for 60 min, LDH release and lipid peroxidation were increased, which were significantly prevented by addition of 0.1 % JSA. tert-Butyl hydroperoxide (tBHP) increased LDH release and lipid peroxidation, which were significantly reduced by 0.1 % JSA. Such protective effects were similar to those of N,N'-diphenyl-p-phenylenediamine (DPPD), a potent antioxidant. When tissues were treated with 0.5 mM Hg, activities of catalase and glutathione peroxidase were inhibited, and glutathione content was also reduced. Such effects were prevented by JSA, but not by DPPD. JSA prevented Hg-induced morphological changes. Conclusions : These results indicate that JSA exerts the protective effect against liver cell injury induced by toxic agents through antioxidant action, and this effect may be attributed to an increase in activities of endogeous anitoxidant enzymes and GSH content. However, antioxidant effect of JSA is different from that of a well-known potent antioxidant DPPD.