• Journal of computational fluids engineering
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• v.10 no.2
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• pp.21-29
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• 2005

In this paper, we present the theoretical and numerical results of scavenge characteristics in a small subchamber of an HCCI(Homogeneous Charge Compression Ignition) engine. Two theoretical models are proposed in prediction of the scavenge time and the efficiency; one is the non-mixing model in which the input gas(CH4) and the existing gas(air) do not mix at all, and the other is the fully-mixed model in which the two gases are assumed to mix completely before ejection. Focus is also given to the effect on the scavenge performance of the size of the chamber outlet.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.335-340
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• 2000

A 3 valve-type pulse tube refrigerator optains its cooling effect from pressure drop by releasing the part of the charged gas through hot end nozzle. The objective of this study is to analyze the performance and to find an optimal expansion pressure of the 3 valve-type pulse tube refrigerator. It is assumed that gas lumps are not mixed and periodically repeat the adiabatic compression and expansion processes. And the nodal model is applied for the analysis of the regenerator. As the result of analysis, the optimum pressure at the end of expansion process was about 80-90% of the maximum pressure.

• Management Science and Financial Engineering
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• v.19 no.2
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• pp.1-11
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• 2013

An interesting puzzle in business practices is that although many researchers emphasize the benefits of a revenue-sharing contract, a wholesale contract has remained to be the most common contractual form. By introducing the concept of unobservable efforts, we examine the contractual efficiency of a wholesale contract and a revenue-sharing contract. The multi-task agency model and experimental design approach are used to analyze the relationship between the contractual efficiency and parameters. A major finding of our study is that a wholesale contract coordinates unobservable efforts, while it fails to coordinate the order quantity decision. Because unobservable efforts have mixed effects on the contractual efficiency, the superiority of contract type depends on parameters. This finding implies that a wholesale contract can be a competitive contract, especially when unobservable efforts are heavily involved. Our conclusion is that the current popularity of a wholesale contract is manager's rational response to complex supply chain environments rather than irrational behaviors.

• International Journal of Highway Engineering
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• v.14 no.3
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• pp.25-32
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• 2012

The thickness of anti-freezing layer has been empirically determined using the frost depth obtained from the freezing index and has not been generally considered as a structural layer in pavement design procedure. In fact, the anti-freezing layer makes a role in structural layer and enables to reduce the total thickness of pavement system. The objective of this study is to develop the statistical regression model for evaluating the structural capacity of anti-freezing layer using Falling Weight Deflectormeter(FWD) test data in asphalt pavements. The FWD testing was conducted at the embankment, cutting, and boundary area of various test sections to estimate the structural capacity of anti-freezing layer in different foundation condition. It is observed from this testing that the center deflections of pavement structure with anti-freezing layer are smaller than those without anti-freezing layer ranging from 0.4 to 82.6%. To determine the variables of statistical model, the correlation study has been conducted between various FWD deflection indexes and the anti-freezing layer thickness. It is found that the ${\Delta}BDI$(%)(${\Delta}Basin$ Damage Index(%)) is highly correlated with anti-freezing layer thickness. The ${\Delta}BDI$(%) model were developed for evaluating structural capacity of anti-freezing layer using linear mixed-effect models.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.95-96
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• 2002

The operation of proceeding bearing in the conditions of misaligned axis of proceeding and bush leads to the load concentration on the bearing edges causing further mixed lubrication conditions, unstable operation and intensive wear of mating parts. For the design process of proceeding bearing the knowledge of static characteristics determined from the oil film pressure and temperature distribution is very important. For the 3-lobe proceeding bearing, the pressure, temperature and viscosity fields, load capacity, minimum oil film thickness, power loss, oil flow and maximum oil film temperature have been determined by iterative solution of the Reynolds', energy and viscosity equations. The paper introduces the results of theoretical investigations of static characteristics of 3-lobe proceeding bearing operating at misaligned axis of proceeding and bush. An effect of misalignment ratio, length to diameter ratio of the proceeding bearing, the lobe clearance ratio on the static characteristics was investigated. Laminar, adiabatic model of oil film for the solution of Reynolds, energy and viscosity equations was applied.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.4
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• pp.56-63
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• 1997

Sealing of lubricant-air mixture in the high performance machining center is one of most the important characteristics to carry out enhanced lubrication. High speed spindle requires non-contact type of sealing mechanism. Evaluating an optimum seal design to minimize leakage is concerned in the aspect of flow control. Effect of geometry and leakage path are evaluated according to variation of sealing geometry. Velocity, pressure, turbulence intensity of profile is calculated to find more efficient geometry and variables. This offers a methodological way of enhancement seal design for high speed spindle. The working fluid is regarded as two phases that are mixed flow of oil phase and air phase. It is more reasonable to simulate an oil jet or oil mist type high speed spindle lubrication. Turbulence and compressible flow model are used to evaluate a flow characteristic. This paper considers a design effect of sealing capability of non- contact type seals for high speed spindle and analyzes leakage characteristics to minimize a leakage 7 on the same sealing area.

• Electrical & Electronic Materials
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• v.10 no.3
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• pp.255-261
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• 1997

In this study, pore-containing barium titanate ceramics were prepared with different porosities and pore sizes, in order to better understand how porosity and pore size affect electrical breakdown of barium titanate ceramics. A granulated barium titanate powder was mixed with three grades of commercial polymer microspheres up to 11wt%. The electrical breakdown test was performed at two different temperatures of 30.deg. C(below Tc) and 150.deg. C(above Tc) for samples immersed in a silicon oil bath using a 60kV de power supply. Electrical breakdown strength of pore containing barium titanate ceramics with porosity lower than 10% decreased as pore size and porosity increased. However, above the 10% porosity region, electrical breakdown strength decreased as the pore connectivity increased. From the experimental results, an optimum electrical breakdown model is proposed in an attempt to explain the effect of pores.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.349-352
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• 1999

In this paper, we present simplified fault set which is made by analyzing fault relation to design specification in CMOS operational amplifier. The hard fault is easily modeled because an effect of hard fault is out of all design specification. However, the soft fault is not easily modeled because an effect of soft fault on design specification is varied according to position and depth of fault. We simulated hard and soft fault by HSPICE, varying threshold voltage and W/L ratio from 90% increase to 90% decrease. The decrease of test time and the production of high reliability mixed-mode IC are possible by the proposed fault set.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.223-226
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• 2001

Acoustic pressure transmission coefficient and phase velocity are measured as the functions of water porosity and air porosity in sand sediment slabs with water- and air-filled pores. Pores in the sand sediment slab we modeled as the structure of circular cylindrical tube shape filled with water and air. The first kind(fast) wave and second kind (slow) wave, identified by Biot, in the solid and fluid mixed medium are affected by the presence of water and air pores. Acoustic characteristics of such porous medium in water are also theoretically investigated in terms of the modified Biot-Attenborough (MBA) model, which uses the separate treatment of viscosity effect and thermal effect in non-rigid porous medium with water- and air-filed pores. The information on the fast waves introduces new concepts of the generalized tortuosity factor and dynamic shape factor.

• Journal of Preventive Medicine and Public Health
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• v.31 no.3 s.62
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• pp.384-394
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• 1998

In order to investigate the effect of the urinary excretion of sodium and potassium on the change on blood pressure over 3 years, 668 adolescents aged 13 years living in Kangwha area were investigated in a longitudinal follow-up study. Two measurements were taken on each blood pressure (diastolic, systolic) and the average of the two readings was used in the analysis. Sodium and potassium intake were estimated by the determination of those electrolytes in 24hr urine. The mixed model regression analysis was used to identify the effect of urinary sodium and potassium on the change of blood pressure after controlling for BMI of each age. On simple bivariate analysis no relationship was found between urinary sodium excretion and systolic or diastolic blood pressure among both male and female, however, a significant positive association between urinary potassium excretion and systolic blood pressure among male. The results of mixed regression analysis showed that the body mass index (BMI) were more influential that urinary electrolytes among this study subjects. It suggested that risk factors observed from the adults, may not be identical with that of the growing aged population. After control of the BMI and age, significant association between sodium and diastolic BP among male, and association between potassium and systolic BP among female, were found. In summary, the results indicate that growth has been more influential than dietary factor on blood pressure for growing aged population.