• 대한수학회보
• /
• 제48권2호
• /
• pp.397-412
• /
• 2011

In this paper, the equation of the transient Stokes flow of an incompressible viscous fluid is studied. Growth and decay estimates are established associating some appropriate cross sectional line and area integral measures. The method of the proof is based on a first-order differential inequality leading to an alternative of Phragm$\'{e}$n-Lindell$\"{o} $f type in terms of an area measure of the amplitude in question. In the case of decay, we also indicate how to bound the total energy.

• 전기학회논문지
• /
• 제59권6호
• /
• pp.1126-1130
• /
• 2010

Speech production can be viewed as a filtering operation in which a sound source excites a vocal tract filter. The vocal tract is modeled as a chain of cylinders of varying cross-sectional area in linear prediction acoustic tube modeling. In this modeling the most common implementation assumes equal length of tube sections. Therefore, to model complex vocal tract shapes, a large number of tube sections are needed. This paper proposes a new vocal tract model with unfixed sectionlengths, which uses the reduced lattice filter for modeling the vocal tract. This model transforms the lattice filter to reduced structure and the Burg algorithm to modified version. When the conventional and the proposed models are implemented with the same order of linear prediction analysis, the proposed model can produce more accurate results than the conventional one. To implement a system within similar accuracy level, it may be possible to reduce the stages of the lattice filter structure. The proposed model produces the more similar vocal tract shape than the conventional one.

• Journal of Advanced Marine Engineering and Technology
• /
• 제30권2호
• /
• pp.231-238
• /
• 2006

The performance of free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally and the effect of cathode separator structure on the cell performance was investigated. Cathode separators were used for the cell with $18cm^2$ active area. In channel type, the contact resistance is low, and the nature convection. which is strongly affected by the cross-sectional shape of cathode separator channel, is dominant in a cell performance. The maximum power density with $18cm^2$ active area is $105mW/cm^2$ using the 10mm depth and 2mm width channel. A computational analysis was optimum structure of free-breathing channel type PEMFC for robotic application.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 춘계학술대회논문집
• /
• pp.273-280
• /
• 1997

Rotary swaging is a process for reducing the cross-sectional area or changing the shape of bar, tube or wires by repeated radial blows with one or more parirs of opposed dies. The present study is concerned with investigation the effect of process parameters upon product quality(hardness, roughness, precision of dimension). To enhance the product quality, experimental works are carried out for some process parameters such as forming speed, billet shape, lubrication, reduction of area and ratio of t/D. Rod shift formed by RSM25 under cold conditions has good surface quality, hardness and precision of dimension. The recommendable process conditions are suggested for solid and tubular products.

• 펄프종이기술
• /
• 제31권2호
• /
• pp.70-76
• /
• 1999

This study was to measure the potential of nonwoody fibrous material, kenaf. Whole stalk of kenaf, Hibiscus cannabinus was separated by two parts of bast and core portion, and cooked separately by alkaline method. Morphological characteristic was evaluated using confocal laser scanning microscope (CLSM) and fiber quality analyzer(FQA). The strength properties of handsheets, made by different mixing ration between kenaf base and core fibers, were measured. Cross-sectional area of bast fibers was smaller than that of core fibers, but the bast fibers had a thick cell wall and narrow lumen area. Bast fibers were longer in length than core fibers. Core fibers had thin cell walls, broad lumen areas, and short lengths, and they had collapsed shape even in water. These characteristics of core fibers affected strength properties of handsheet positively. When the amount of core fibers increased, the strength properties of handsheet were increased. When the amount of bast fibers increased, the handsheet had rougher surface and higher air permeability.

• 지역연구
• /
• 제11권2호
• /
• pp.1-17
• /
• 1995

Regional production structres are investigated through an estimation of three-input(labor, capital and material) translog cost function. The estimation uses the pooled data in which time series data of 1970-1990 are combined with cross-sectional data corresponding to firm sizes. The empirical finding are the following: (1) the factors are Allen substitutes each otner in general except Pusan and a couple of regionss, and (2) estimates are very small in its absolute value irrespective of the regions. The low elasticity estimates of this study implies that substitytability among the three inputs are very weak in the regional manufacturing production compared to that in the national production. Seoul-Kyungki metropolitan area produces not only the smallest elasticities but relatively stable estimates without much fluctuation between the sub-regions of the area.

• 한국정밀공학회지
• /
• 제15권10호
• /
• pp.113-119
• /
• 1998

Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

• 소성∙가공
• /
• 제1권1호
• /
• pp.52-65
• /
• 1992

In this study a new simplified three-dimensional numerical method and the associated computer program have been developed to simulate the non-axisymmetric extrusion processes. The two-dimensional rigid-plastic finite element method under the generalized plane-strain condition is combined with the slab method. To define the die geometry for a non-axisymmetric extrusion. area mapping technique was used. Streamlined die surface was used to minimize the total extrusion pressure. Extrusion of square, hexagonal and 'T' section from round billet have been simulated and experimented with a model material. The computed results were in good agreement with the experiments in cross-sectional grid distortion. Computational results will be valuable for designing tool geometries and corresponding processes.

• 반도체디스플레이기술학회지
• /
• 제10권4호
• /
• pp.21-23
• /
• 2011

Uniformity of plasma etching processes critically depends on the wafer temperature and its distribution. The wafer temperature is affected by plasma, chucking force, He back side pressure and the surface temperature of ESC(electrostatic chuck). In this work, 3D mathematical modeling is used to investigate the influence of the geometry of coolant path and the temperature distribution of the ESC surface. The model that has the coolant path with less change of the cross-sectional area and the curvature shows low standard deviation of the ESC surface temperature distribution than the model with the coolant path of the larger surface area and more geometric change.

• 한국재료학회지
• /
• 제16권7호
• /
• pp.408-411
• /
• 2006

An effective wet-chemical approach is demonstrated for growing large-area, selectively-patterned, and low-temperature-synthesized ZnO nanorods (ZNRs). The growth of ZNRs was enhanced on a Co layer. The selectivity and density were readily controlled by the control of the temperature when the substrate transfers into aqueous solution. The cross-sectional transmission electron microscopy image shows that single crystalline ZNRs grown along [0001] have good adhesion at interface between ZNRs/substrate. The turn-on field was 4 $V/{\mu}m$ at the emission current density of 1 ${\mu}A/cm^2$. The stable emission was obtained at 0.11 $mA/cm^2$ under 7.2 $V/{\mu}m$ over 10 hr. These results suggest that selectively-patterned ZNRs have the potential for use as field emitters in large-area field emission displays.