• Animal cells and systems
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• 제2권3호
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• pp.333-339
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• 1998

Litter decomposition is a key process in energy flow and nutrient cycling in the freshwater littoral zone, and is regulated by physicochemical properties of litters. Using a litterbag method, we compared the decomposition rates of 16 different litter types from 10 plant species of the emergent macrophytes for one year in the littoral zone of the Paltangho Reservoir, Korea. The regression analysis fitted to the various decomposition models showed that mass loss of the litters with time best fitted an asymptotic function. The litters of the emergent macrophytes were composed of two compartments, labile and refractory. The macrophytic litters showed a great variety in decomposition dynamics depending on sources of litters. The labile compartment of the initial litter mass was in a wide range between 18% and 99%, and their decomposition rates varied from 0.0037 to 0.0131 day-1. The decomposition processes of the emergent macrophytes were determined by the relative amounts of the labile and refractory compartments and by the decomposition rate of the habile one in the littoral zone.

• 한국안전학회지
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• 제14권1호
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• pp.3-9
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• 1999

The vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream without any chemical reactions. Recently, vortex tube is widely used to local cooler of industrial equipments and air supply system. In this study, the insulation effect of surface on the efficiency of vortex tube was performed experimentally. The experiment is carried out for nozzle area ratio of 0.194, diameter ratio of cold end orifice of 0.6 and input pressure ranging from 0.2Mpa to 0.5Mpa. The purpose of this study is focused on the effect of surface insulation of vortex tube with the variation of cold air mass flow ratio. The results indicate that the temperature difference of cold and hot air are higher about 12% and 30% than that of not insulated vortex tube respectively. Furthermore, for the insulated vortex tube, the similarity relation for the prediction of cold end temperature as the function of cold air mass flow ratio and input pressure is obtained.

• Structural Engineering and Mechanics
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• 제32권6호
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• pp.741-754
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• 2009

Excessive cable vibrations are detrimental to cable-stayed bridges. Increasing the system damping of cables is a key solution to resolve this severe problem. Equations representing the dynamic characteristics of an inclined cable with a Deck-Anchored Damper (DAD) or with a Clipped Tuned Mass Dampers (CTMD) are reviewed. A theoretical comparison on the performance of cable vibration reduction between the cable-DAD system and the cable-CTMD systems is thoroughly discussed. Optimal system modal damping for the free vibration and transfer functions for the forced vibration for the two cabledamper systems are addressed and compared in detail. Design examples for these two different dampers are also provided.

• 한국기계가공학회지
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• 제9권5호
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• pp.83-89
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• 2010

In this paper, the dynamic response of a CNC 5 Axles machining center was analyzed and then controlled passively by using the dynamic absorber. For the simplification of the theoretical approach, the CNC 5 Axles machining center was modeled as a flexible beam(Bed) having a point mass(Column), two discrete systems(a Table-set and a dynamic absorber). Specifically by using the dynamic absorber, the dynamic response of a Table-set which be caused by the vibration of a flexible beam, was reduced down to the infinitesimal level. The optimal design factors of the dynamic absorber were obtained from the minimization of the cost function. It was found that the natural frequencies of a UT-380 machining center be varied due to the movement of the Table-set. In view of the dynamic response of a Table-set, the larger spring stiffness and mass of the dynamic absorber were found to give the greater reduction.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 봄 학술발표회 논문집
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• pp.139-146
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• 1997

The main purpose of this paper is to investigate the near-optimal parameters of continuous beam subject to a moving load. The computer-aided optimization technique is used to obtain the near-optimal parameters. The computer program is developed to obtain the natural frequency parameters and the forced vibration responses to a transit point load for the continuous beam with variable support spacing, mass and stiffness. The optimization function to describe the design efficiency is defined as a linear combination of four dimensionless span characteristics: the maximum dynamic stress; the stress difference between span segments; the rms deflection under the transit point load; and the total span mass. Studies of three span beams show that the beam with near-optimal parameters can improve design efficiency by 12 to 24 percent when compared to a reference configuration beams of the same total span length.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.167-173
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• 2003

For the measurement of mass flow rate at a wide range of operation conditions, it is required that the critical nozzle gas different diameters, since the mass flow rate through the critical nozzle depends on the nozzle supply conditions and the nozzle throat diameter. In the present study, both computational and experimental investigations are performed to explore the variable critical nozzle. Computational work using the 2-dimensional, axisymmetric, compressible Navier-Stokes equations are carried out to simulate the gas flow through variable critical nozzle. In experimnet, a cylinder with several different diameters is inserted into the critical nozzle to vary the nozzle throat diameter. Computational results are compared with the experimented ones. The computed results are in close agreement with experiment. It is found that the displacement and momentum thickness of variable critical nozzle are given as a function of Reynolds numbers. The discharge coefficient of the variable critical nozzle is predicted using an empirical equation.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.697-703
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• 2003

For a single stage two cylinder rotary compressor, an analytical study has been made on the discharge gas pulsation. Discharge system of the twin rotary compressor consists of lower and upper mufflers and connecting passage holes between them, and cavities on both sides of the motor and passages between them. Acoustic modeling for the discharge system by transfer matrix method gives acoustic impedances at discharge valves so that gas pulsation at the valve sections can be obtained from discharge mass velocity. Since the mass velocity and the pressure pulsation at the valves are affected by each other, iteration should be made for convergence. Gas pulsations at other sections can also be calculated by using transfer matrix.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권3호
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• pp.108-113
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• 2004

This paper presents methods to improve performance of the power supply system in a NASA deep space explorer. In the Stirling engine driven reciprocating Brushless DC (BLDC) generator, the accurate position information of the prime mover is important to diagnose the performance of the engine and prevent distortion of the output power. Since sensors to detect the position are fragile and unreliable, and conventional sensorless techniques have drawbacks in the low speed region, a novel sensorless position detection technique for the prime mover has been proposed and verified. Another major issue of the generator for the spacecraft is power density maximization. The mass of the power system is important to the mass of the satellite. Therefore, the components of the spacecraft should be lightweight. Conventional rectification methods cannot achieve the maximum power possible due to non-optimal current waveforms. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation work.

• International Journal of Contents
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• 제9권3호
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• pp.55-61
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• 2013

The Korean films in the 1980s played an important role in impeding the interaction between the media and the audience. In terms of two mechanisms of money and power, the Korean films lost the function of publicity and were forced to disregard positive aspects of culture as a way of understanding society. As a mass medium, the film did not give people the space for critical thought and discussion on social reality. This study tries to discuss how Korean movies in the 1980s functioned as a bulwark of critical debate provided by the interaction between cultural texts and audiences through the notion of the public sphere. For Habermas, the public sphere provides a basis for critical analysis in order to reveal the relationship between media and economic and administrative power in a modern society.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.219-222
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• 2015

The kinetic analysis of energetic materials using Differential Scanning Calorimetry (DSC) is proposed. Friedman Isoconversional method is applied to DSC experiment data and AKTS software is used for analysis. The frequency factor and activation energy are extracted as a function of product mass fraction. The extracted kinetic scheme does not assume multiple chemical steps to describe the response of energetic materials; instead, multiple set of Arrhenius factors are used in describing a single global step. The proposed kinetic scheme has considerable advantage over the standard method based on One-Dimenaionl Time to Explosion (ODTX). Reaction rate and product mass fraction simulation are conducted to validate extracted kinetic scheme. Also a slow cook-off simulation is implemented for validating the applicability of the extracted kinetics scheme to a practical thermal experiment.