• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.6
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• pp.502-509
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• 2003

This paper describes a detailed experimental investigation of heat transfer in a reciprocating rectangular channel fitted with rib structures with particular reference to the design of a piston for marine propulsive diesel engine. The parametric test matrix involves Reynolds number, reciprocating frequency, and reciprocating radius, respectively in the ranges, 1,000～6,000, 1.7～2.5 Hz, and 7～15 cm with four different rib arrangements. The rib arrangements have considerable influences on the heat transfer in the reciprocating channel due to the modified vortex flow structure. The experimental data confirm that the increases in the heat transfer can be seen in order of Case (b), Case (c), Case (d), and Case (a).

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1892-1894
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• 1996

This paper presents optimal charge arrangement through potential error analysis. In order to decide the number of charges per conductor for a large system, adaptive simulation charge arrangement technique has been proposed. "Grouping" technique which means to divide analysis domain into two groups has been described through field error analysis. By this method, the size of matrix to calculate E field at a calculation point is reduced remarkably. The proposed method is applied to the electric field calculation around the Substation busbars.

• Journal of Magnetics
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• v.6 no.3
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• pp.94-100
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• 2001

Fe-Co-Ni particles with an average size of 45 and 135 nm are characterized in terms of magnetic phase transformation and magnetic properties at room temperature. BCC structure of Fe-Co-Ni spherical particles can be synthesized from Fe-Co-Ni-Al-Cu precursor films by heating at 600-80$0^{\circ}C$ for the phase separation of Fe-Co rich Fe-Co-Ni particles, followed by a post heating at $600^{\circ}C$ for 5 hours. The average size of nanoparticles was directly determined by the thickness of precursor films. Exchange interactive hysteresis was observed for the nano-composite (Fe-Co-Ni)+(Fe-Ni-Al) films resulting from the short exchange interface between ferromagnetic Fe-Co-Ni particles surrounded by almost papramagnetic Ni-Al-Fe matrix. Arraying the isolated Fe-Co-Ni nano-particles in a random arrangement on $Al_2O_3$substrate the particle assembly showed a behavior of dipole interactive ferromagnetic clusters depending on their volume and inter-particle distance.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.6 no.1
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• pp.15-18
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• 1976

The authors has observed the effect of X-ray irradiation on the dentin matrix formation of the albino rat fetuses. The lower abdomen of the pregnant ratswere exposed to X-ray on the 9 1/2th day of gestation, respectively 150, 250 and 350 rads. The fetuses of the right sides of the same pregnant rats which were not exposed to X-ray were as controls. The results were as follows: 1) In the 150 rads irradiated fetuses, predentin formation was identical with control groups, but the arrangement of odontoblasts was distorted, subodontoblastic layer was condesed with pulp cells and blood capillaries were enlarged. 2) In the 250 rads irradiation, dentin matrix was imperfact or osteodentin was occured. Short columnar or cuboidal odontoblasts were presented and pulp cells were dispersed. Blood capillaries were cogested. 3) 350 rads irradiated fetuses showed osteodentin matrix and numerous degenerated odontoblasts. Their dental papilla showed reticular atrophy and enlarged capillary.

• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1241-1260
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• 2015

Any rational approach to define the configuration and size of viscous fluid dampers in a structure should be based on the dynamic properties of the system with the dampers. In this paper we propose an alternative representation of the complex eigenvalues of multi degree of freedom systems with dampers to calculate new equivalent natural frequencies. Analytical expressions for the dynamic properties of a two-story building model with a linear viscous damper in the first floor (i.e. with a non-proportional damping matrix) are derived. The formulas permit to obtain the equivalent damping ratios and equivalent natural frequencies for all the modes as a function of the mass, stiffness and damping coefficient for underdamped and overdamped systems. It is shown that the commonly used formula to define the equivalent natural frequency is not applicable for this type of system and for others where the damping matrix is not proportional to the mass matrix, stiffness matrix or both. Moreover, the new expressions for the equivalent natural frequencies expose a novel phenomenon; the use of viscous fluid dampers can modify the vibration frequencies of the structure. The significance of the new equivalent natural frequencies is expounded by means of a simulated free vibration test. The proposed approach may offer a new perspective to study the effect of viscous dampers on the dynamic properties of a structure.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.26-31
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• 2005

The strong continuous fiber reinforced metal matrix composites (MMCs) are recently used in aerospace and transportation applications as an advanced material due to its high strength and light weight. Unidirectional fiber-metal matrix composites have superior mechanical properties along the longitudinal direction. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In order to be able to utilize these MMCs effectively and with safety, it must be determined their elastic plastic behaviors at the interface. In this study, the interfacial stress states of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber volume fractions $(5-60\%)$ were studied numerically. The interlace was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The fiber is modeled as transversely isotropic linear-elastic, and the matrix as isotropic elastic-plastic material. Using proposed model, the effects of the interface region and fiber arrangement in MMCs on the distributions of stress and strain are evaluated. The stress distributions of a thin multi layer interface have much less changes compared with conventional perfect interface. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

• Journal of Applied Reliability
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• v.8 no.4
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• pp.167-179
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• 2008

System risk is the totality of all safety risks to customers, employees, suppliers, and other third parties that arise due to system operations. To assess the risk of major hazards with the potential to cause fatality to the customers and other members of the public, quantitative risk assessment methodologies are used. This paper presents the general principles of risk based management approach to improve the safety of high risk systems such as aviation, railway, and nuclear power plants. For the suitable risk control arrangement, case studies of acceptable risk level, risk rating matrix, and safety management philosophy are presented.

• Journal of Theoretical and Applied Mechanics
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• v.3 no.1
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• pp.45-65
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• 2002

A constitutive model on oorthotropic thermo-elasto-viscoplasticity for fiber-reinforced composite materials Is illustrated, and their thermomechanical responses are predicted with the fully-coupled finite element formulation. The unmixing-mixing scheme can be adopted with the multipartite matrix method as the constitutive model. Basic assumptions based upon the composite micromechanics are postulated, and the strain components of thermal expansion due to temperature change are included In the formulation. Also. more than two sets of mechanical variables, which represent the deformation states of multipartite matrix can be introduced arbitrarily. In particular, the unmixing-mixing scheme can be used with any well-known isotropic viscoplastic theory of the matrix material. The scheme unnecessitates the complex processes for developing an orthotropic viscoplastic theory. The governing equations based on fully-coupled thermomechanics are derived with constitutive arrangement by the unmixing-mixing concept. By considering some auxiliary conditions, the Initial-boundary value problem Is completely set up. As a tool of numerical analyses, the finite element method Is used with isoparametric Interpolation fer the displacement and the temperature fields. The equation of mutton and the energy conservation equation are spatially discretized, and then the time marching techniques such as the Newmark method and the Crank-Nicolson technique are applied. To solve the ultimate nonlinear simultaneous equations, a successive iteration algorithm is constructed with subincrementing technique. As a numerical study, a series of analyses are performed with the main focus on the thermomechanical coupling effect in composite materials. The progress of viscoplastic deformation, the stress-strain relation, and the temperature History are careful1y examined when composite laminates are subjected to repeated cyclic loading.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.8
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• pp.667-677
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• 1990

In this paper, optical inplementation of the Hopfield neural network model for two-dimensinal associative memory is described For the real-time processing of two-dimensional images, the commercial LCTVs are used as a memory mask and an input spatical light modulator. A 4-D memory matrix is realized with a 2-D mask of a matrix arrangement and the inner-products between arbitrary input pattern and memory matrix are carried out by using the multifocus hololens. The output image is then electronically thresholded and fed back to the input of the associative memory system by 2-D CCd camera. From the good experimental results for the high error correction capability, the proposed system can be applied to practical pattern recognition and machine vision systems.

• Journal of the korean academy of Pediatric Dentistry
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• v.3 no.1
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• pp.12-17
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• 1976

The study is about the effect of tetracycline-HCl on the amelogenesis and the dentinogenesis of the albino rats by means of histochemistry and fluorescence microscopy. Females in oestrus were mated overnight and examined the next morning for evidence of copulation. The mothers were intraperitonealy injected with a single dose of tetracycline-HCl from the eighth to tenth day of gestation. The heads of new born rats were fixed in Carnoy's solution and 10% formalin solution. The staining methods were alizarin red S stain, PAS reaction, colloidal iron reaction, Morin's stain and hematoxylin-eosin stain, The results were as follows: 1. By the single injection of tetracycline, the matrix formation of enamel and dentin were disturbed, and the shape and arrangement of ameloblast and odontoblast were distorted. 2. It seemed that, with the higher dose of tetracycline, the positive materials of PAS reaction were increased in the disturbed enamel and dentin matrix, but those of alizarin red S stain and colloidal iron reaction were decreased. 3. The fluorescence intensity in the disturbed enamel and dentin matrix were higher than the other areas and appeared to increase gradually with the higher dose of tetracycline.