• Structural Engineering and Mechanics
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• v.30 no.2
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• pp.165-176
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• 2008

In this paper, a new iterative method for solving vehicle-bridge interaction problems is proposed. Iterative methods have advantages over the non-iterative methods in that it is not necessary to update the system matrix for a given wheel location, and the method can be applied for a new type of car or bridge with few or no modifications. In the proposed method, the necessity of system matrices update is eliminated using the equivalent interaction force acting on the bridge, which is obtained iteratively. Ballast stiffness is included in the interaction forces and the geometric compatibility at the contact points are used as convergence criteria. The bridge is considered as an elastic Bernoulli-Euler beam with surface irregularity and ballast stiffness. The moving vehicle is modeled as a multi-axle mass-spring-damper system having many degrees of freedom depending on the number of axles. The pitching effect, which is the interaction effect between the rear and front wheels when a vehicle begins to enter or leave the bridge, is also considered in the formulation including extended ground boundaries having surface irregularity and ballast stiffness. The applicability of the proposed method is illustrated in the numerical studies.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• v.3 no.1
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• pp.84-96
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• 1992

The present study was designed to investigate variables associated with mother-child interaction patterns of Attention Deficit Hyperactivity Disorder(ADHD), and also to evaluate short-term effects of stimulant medication on the behaviors of ADHD children and their mothers during interaction. 15 ADHD boys(ages 5${\sim}$10 years) were treated with metylphenidate(0.5mg/kg per day) for 1 month, and their behaviors as well as their mothers for the 10 minute free play and 20 minute task performance period were videotaped through one-way mirror. The childrens attention was also evaluated using the Continuous Performance Task(CPT) and ratings of their hyperactive behaviors were obtained from their mother prior to the treatment. The videotaped interaction were rated according to the Response Class Matrix developed by Mash, Terdal & Anderson(1973). Results indicated that percentage of behavior of the mother and child during interaction was highly correlated with each other, which, in turn, was highly correlated with the symptom severity of the ADHD child. That is the more severe the cognitive and behavioral symptoms of ADHD, the more negative the interaction behavior pattern was. After 4 weeks of stimulant medication the mothers as well as the ADHD children showed a significant decrease in the percentage of negative-aggressive behavior during the task performance period. The results indicated that negative interaction behavior of the mothers was in large part a response to the negative behavior of their ADHD children.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.1
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• pp.214-221
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• 2003

In this study, based on the effect of the interaction of fracture mechanics by graphite and fatigue limit phenomena of the microscopic observation various matrix structure, spheroidal ratio, size of graphite and distribution etc. parameters containd with Ductile Cast Iron. Therefore, in this study, different ferrite-pearlite matrix structure and spheroidal ratio of graphite of 70%, 80% and 90%, GCD40, GCD45-1 and GCD45-2 series and three different ferrite-pearlite matrix structure, GCD 45-3, GCD 50, GCD 60 series, all of which contain more than 90% spheroidal ratio of graphite, were used to obtain the correlation between mean size of spheroidal graphite and fatigue strength. (1) 73% pearlite structure had the highest fatigue limitation while 36% pearlite structure had the lowest fatigue limitation among ferrite-pearlite matrix. the increase in spheroidal ratio with increasing fatigue limitation, 90% had the highest, 14.3% increasing more then 10%, distribution range of fatigue life was small in same stress level. (2) (equation omitted) of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of (equation omitted) may be used as a guideline for the control of inclusion size in the steelmaking processes.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.54-54
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• 2003

We have developed a Cu-based bulk amorphous composite reinforced with a micron-sized crystalline phase, the (Cu60Zr30Ti10)95Ta5 amorphous matrix composite. The composite demonstrates the ultimate strength of 2332 MPa with a dramatically enhanced fracture strain of 15.3 %. Macroscopic observation of the fractured (Cu60Zr30Ti10)95Ta5 amorphous matrix composite showed the development of multiple shear bands along with numerous branching and deflection of shear bands. Microscopic observation on the amorphous matrix of the composite showed that cracks propagate through the residual amorphous matrix located between nanocrystallites, which had formed during deformation. Simulations based on finite element method were conducted to understand the formation mechanisms of multiple shear bands, the initiation site of shear bands, and interaction of shear bands with crystalline particles. Other microscopic fracture mechanism responsible for the enhanced plasticity was discussed.

• BMB Reports
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• v.55 no.4
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• pp.192-197
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• 2022

Cell signals for growth factors depend on the mechanical properties of the extracellular matrix (ECM) surrounding the cells. Microtubule acetylation is involved in the transforming growth factor (TGF)-β-induced myofibroblast differentiation in the soft ECM. However, the mechanism of activation of α-tubulin acetyltransferase 1 (α-TAT1), a major α-tubulin acetyltransferase, in the soft ECM is not well defined. Here, we found that casein kinase 2 (CK2) is required for the TGF-β-induced activation of α-TAT1 that promotes microtubule acetylation in the soft matrix. Genetic mutation and pharmacological inhibition of CK2 catalytic activity specifically reduced microtubule acetylation in the cells cultured on a soft matrix rather than those cultured on a stiff matrix. Immunoprecipitation analysis showed that CK2α, a catalytic subunit of CK2, directly bound to the C-terminal domain of α-TAT1, and this interaction was more prominent in the cells cultured on the soft matrix. Moreover, the substitution of alanine with serine, the 236th amino acid located at the C-terminus, which contains the CK2-binding site of α-TAT1, significantly abrogated the TGF-β-induced microtubule acetylation in the soft matrix, indicating that the successful binding of CK2 and the C-terminus of α-TAT1 led to the phosphorylation of serine at the 236th position of amino acids in α-TAT1 and regulation of its catalytic activity. Taken together, our findings provide novel insights into the molecular mechanisms underlying the TGF-β-induced activation of α-TAT1 in a soft matrix.

• Structural Engineering and Mechanics
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• v.67 no.5
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• pp.517-525
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• 2018

In this study, we investigate the vibration of single-walled carbon nanotubes embedded in a polymeric matrix using nonlocal elasticity theories with account arbitrary boundary conditions effects. A Winkler type elastic foundation is employed to model the interaction of nanobeam and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, Winkler modulus parameter, vibration mode and aspect ratio of nanobeam on the vibration frequency are analyzed and discussed. The mechanical properties of carbon nanotubes and polymer matrix are treated and an analytical solution is derived using the governing equations of the nonlocal Euler-Bernoulli beam models. Solutions have been compared with those obtained in the literature and The results obtained show that the non-dimensional natural frequency is significantly affected by the small-scale coefficient, the vibrational mode number and the elastic medium.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.78-83
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• 2001

In this work, the surface of inorganic fillers were modified with some functional groups such as stearic acid, aliphatic long chain, vinylsilane and aminosilane to control the interaction between inorganic fillers and polymer matrix. Ethylene-vinyl acetate copolymers (EVA) with various amount of vinyl-acetate content and copolyether-ester elastomer were used as polymer matrix. The addition of inorganic fillers increases flame retardancy, but results in steep drop of electrical and mechanical properties, which may be caused by the defect in the interface between organic/inorganic hybrid composites. The hybrid composites are found to show better mechanical properties and higher volume resistivities as inorganic fillers are well dispersed and have good adhesion with polymer matrix. Also, the most effective type of functional group coated on fillers depends on the chemical structure of polymer.

• Macromolecular Research
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• v.15 no.4
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• pp.357-362
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• 2007

Polyimide/carbon nanotube (CNT) composite films, for potential use in high performance microelectronics and aerospace applications, were prepared by mixing a polyisoimide (PII) solution and a CNT suspension in NMP, followed by casting, evaporation and thermal imidization. The CNTs were modified by a nitric acid treatment to improve the thermal and electrical properties, as well as to provide good dispersion of the CNTs in a polymer matrix. The formation of functional groups on the modified CNT was confirmed by Raman spectroscopy. Scanning electron microscopy revealed the modified CNTs to be well dispersed in the polyimide matrix, with a uniform diameter of ca. 50 nm. The thermal stability of the films containing the CNTs was improved due to the enhanced interfacial interaction and good dispersion between the polyimide matrix and modified CNTs. In addition, the thermal expansion coefficient of the composites films was slightly decreased, but the dielectric constants increased linearly with increasing CNT content.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.500-504
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• 1997

Perovskite Pb0.7Ba0.3Zn1/3Nb2/3O3 substituted with 0.3 mole fraction for Pb-site in PbZn1/3Nb2/3O3 relaxor and pyrochlore Pb1.83Ba0.29Zn1.71Nb2/3O6.39 were mixed and dielectric characteristics of this composites were investigated. Percolation limit of perovskite phase, which was determined by microstructural observation in the composite as an isolation of perovskite phase from pyrochlore matrix, was 28.9-47.5 vol%. Ferroelectric phase transition below percolation limit depends on a parameter which affects the propagation of lattice vibration between isolated perovskite phase and pyrochlore matrix. Therefore, it is believed that ferroelectric lattice vibration of isolated perovskite phase could be transfered to pyrochlore matrix when the oxygen octahedra are linked in 3-dimension and highly polarizable Pb2+ ions are contained in both phases.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2125-2136
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• 2004

In this paper, a numerical application algorithm for applying the CFAM (Consistent Fluid Added Mass) matrix for a core seismic analysis is developed and applied to the 7-ducts core system to investigate the fluid effects on the dynamic characteristics and the seismic time history responses. To this end, three cases such as the in-air condition, the in-water condition without the fluid coupling terms, and the in-water condition with the fluid coupling terms are considered in this paper. From modal analysis, the core duct assemblies revealed strongly coupled out-of-phase vibration modes unlike the other cases with the fluid coupling terms considered. From the results of the seismic time history analysis, it was also verified that the fluid coupling terms in the CFAM matrix can significantly affect the impact responses and the seismic displacement responses of the ducts.