• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.12
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• pp.1710-1719
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• 1997

An approximate analytical solution for the initial transient process of close-contact melting occurring between a phase change material kept at its melting temperature and an isothermally heated flat surface is derived. The model is so developed that it can cover both rectangular and circular cross-sectional solid blocks. Normalization of simplified model equations in reference to the steady solution enables the solution to be expressed in a generalized form depending on the liquid-to-solid density ratio only. A selected result shows an excellent agreement with the previously reported numerical data, which justifies the present approach. The solution appears to be capable of describing all the fundamental characteristics of the transient process. In particular, dependence of the solid descending velocity oft the density ratio at the early stage of melting is successfully resolved. The effects of other parameters except the density ratio on the transient behaviors are efficiently represented via the steady solution implied in the normalized result. A simple approximate method for estimating the effect of convection on heat transfer across the liquid film is also proposed.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• v.1 no.1
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• pp.1-8
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• 2020

Recent studies revealed that many animals identify individual humans. In this account, we review previous literatures on individual human recognition by wild or domestic animals and discuss the three hypotheses: "high cognitive abilities" hypothesis, "close human contact" and "pre-exposure to stimuli" hypothesis. The three hypotheses are not mutually exclusive. Close human contact hypothesis is an ultimate explanation for adaptive benefits whereas high cognitive abilities and pre-exposure to stimuli hypothesis are proximate explanations for mechanisms to perform such discriminatory behaviour. We report a case study of two bird species in a human-free habitat. Long-tailed skuas, which are known for having high cognitive abilities, exhibited the human discriminatory abilities whereas ruddy turnstones did not display such abilities toward approaching humans. This suggests that highly intelligent species may have this type of discriminatory ability so that they could learn to identify individual humans quickly by pre-exposure to stimuli, even in a human-free habitat. Here, we discuss that human recognition is more common in species with rapid learning ability and it could develop for a short period of time between an intelligent species and human.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.165-171
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• 2021

To prevent the secondary hospital-acquired infection (cross-infection) from occurring in the general radiographic room in the department of radiology, the microbial measurement was conducted at the points making direct close contact with radiologists and patients. For the case of radiologists, the microbial measurement and incubation were focused on the x-ray tube handle of the radiation generating device, and, for the case of patients, the microbial measurement and incubation were focused on the chin supporting device, chest-contact point, and handle. Once disinfected with Aniosurf, the sterilized media were gathered and identified, and the microorganisms were confirmed. Based on the identification results, it was confirmed that the points making direct close contact with radiologists showed a value of 103 CFU for Proteus mirabilis, Staphylococcus epidermidis, Bacillus spp. and Candida spp., and that the points making direct close contact with patients showed a value of 103~5 CFU for Proteus mirabilis, Enterococcu faecium, Pseudomonas aeruginosa, NTM(Non-Tuberculosis Mycobacteria) and Candida spp.. It was also confirmed that the types and number of microorganisms gathered from the points making direct close contact with patients were greater. Fortunately, most of the involved microorganisms were observed to be on the skin surface and are known to become extinct when disinfected in accordance with the hospital-acquired infection control rules. However, since even minor exposure to such microorganisms may be lethal for patients with reduced immunity, caution must be taken. In particular, since the points making contact with patients showed a high level of microbial measurement, it was thought that it would be necessary for radiologists and personnel having frequent access to strictly disinfect the parts, such as instruments and handles, making frequent contact with patients. The purpose of this study was to announce the importance of safe microbial control in the radiographic inspection room in hospital, and this study is expected to be used as the baseline data for preventing hospital-acquired secondary infection and Nth infectious diseases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.67-74
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• 2000

One of the important application of a contact melting process is a latent thermal energy storage owing to its high heat flux. In some previous works, the split fins have been employed in order to enhance the melting speed. In the present work, the close contact melting was experimentally investigated using an ice as specimen for both split and non-split fins. It was shown that the contact melting by split fins increases the melting rate compared to that of non-split ones.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.404-409
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• 2004

The electrical contact resistance is here estimated using the multiscale microcontact distribution of elastic contact between rough surfaces, simulated from the Archard's model, and the electrical contact conduction theory suggested by Greenwood. These analysis confirms that the electrical contact resistance is converged to a values, larger than would be obtained if the contact spots were widely separated and hence independent. In multiscale process, the base potential is close to the value of the potential difference between the contact surface and the extremity of body, suggesting a possibility to obtain the multiscale electrical contact resistance relations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.942-945
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• 2002

A garter spring, which is a long. special, close-coiled extension spring with its ends joined to form a ring, is used in connection between vacuum circuit breaker and bus bar in switchgear. To carry short-time current and resist welding at the contact surface in the connection, the garter spring must transmits an uniform contact force to the contact surface through the contact chips arranged in the circumference of bus bar. In this paper, the system for measurement of the contact force by the garter spring is developed. Using the developed measurement system, the design of the connection structure including the garter spring is reviewed to obtain the uniform contact forces in all of contact chips.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.242-245
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• 2003

A garter spring, which is a long, special, close-coiled extension spring with its ends joined to form a ring, is used in tulip contactor between vacuum circuit breaker and bus bar in switchgear. To carry short-time current and resist welding at the contact surface in the tulip contactor, the garter spring must transmits an uniform contact force to the contact surface through the contact chips arranged in the circumference of bus bar. In this paper, the system for measurement of the contact force by the garter spring is developed. Using the developed measurement system, the design of the connection structure including the garter spring is reviewed to obtain the uniform contact forces in all of contact chips.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.197-204
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• 1999

The boundary element method was used for studying singularities of an interface crack with contact zones. The iterative procedure is applied to estimate the contact zone size. Because the contact zone size was extremely small in a tension field, a large number of Gaussian points were used for numerical integration of the Kernels. Stress extrapolation method and J-integral were used ofr determining stress intensity factors. When the interface crack was assumed to have opened tips, oscillatory singularities appear near the tips of the interface crack. But the interface crack with contact zone which Comninou suggested had no oscillatory behavior. The contact zone size under shear loading was much larger than that under tensile. The stress intensity factors computed by stress extrapolation method were close to those of Comninou's solution. And the stress intensity factor evaluated by J-integral was similar to that by stress extrapolation method.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.565-571
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• 2011

Because most fatigue cracks in wheel and rail take place by rolling contact of wheel and rail in railroad industry, it is critical to understand the rolling contact phenomena, especially for the three-dimensional situation. This paper presents an approach to steady-state rolling contact problem of three-dimensional contact bodies, with or without tangential force, based on the finite element method. The steady-state conditions are controlled by the applied relative slip and tangential force. The three-dimensional distribution of tangential traction and contact stresses on the contact surface are investigated. Results show that the distribution of tangential traction and contact stresses on the contact surface varies rapidly as a result of the variation of stick-slip region. The tangential traction is very close in form to Carter's distribution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3185-3194
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• 1994

In this study, an impact model and impact response analysis method was suggested for the impacts between arbitrary shaped bodies. Unlike the impacts between geometrically simple structures, there is no rules to analyze the impacts between general elastic structures First of all, it has been attempted to explain the impoot between arbitrary elastic structures as the elastic deformation of a virtual contact spring in the vicinity of contact points. The contact stiffness and the exponent are determined from the Hertz's contact theory and F. E. analysis. In order to evaluate the validities and limitations of the proposed methods, an impact tester and the miniature of container, missile and isolators have been provided and tested experimentally. All the experiments were performed with various impact conditions. The results obtained by the proposed methods were directly compared with the measured values in terms of maximum contract force, contact duration, the shape of contact force and the structure responses. The computed contact force and responses, using this proposed methods, were very close to the measured results, unless any plastic deformations were presented.