• 한국정밀공학회지
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• 제8권2호
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• pp.27-35
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• 1991

We propose the crack growth rate equation which applied over three regions (threshold region, stable region, unstable region) of fatigue crack propagation. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R=0.05, R=0.2 and R=0.4. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. The fatigue crack growth rate equation is given by $da/dN={\beta} (1-R)^{\delta}\({\DELTA}K-{\DELTA}K_t)^{\alpha} / (K_{cf}-K_{max})$${\alpha}, {\beta}$ , and ${\delta}$ are constants, and ${\Delta}K_t$ is stress intensity factor range at low ${\Delta}K$ region. The constants are obtained from nonlinear least square method. $K_{ef}$is critical fatigue stress intensity factor. The relation between half crack length and number of cycles obtained by integrating the crack growth rate equation is in agreement with the experimental data. It is also experimented with constant maximum stress and decreasing stress ratios, and the fatigue growth rate of each material is in accord with the proposed equation.

• KSTLE International Journal
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• 제1권2호
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• pp.101-106
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• 2000

Variable displacement axial piston pumps are widely used for raising the energy level of the fluid in hydraulic systems. And the regulator is the device which regulates the discharge flow of the piston pump by controlling the swivel angle. The regulator receives the hydraulic pilot pressure and controls the pump output flow depending on the machine load and engine speed. This work deals with constant power control (horsepower control) in the design of a regulator by using a bent-axis type piston pump. In order to effectively use engine power, we must keep the horsepower from the engine to the pump constant. Therefore the regulator operates the constant power control. As a result, optimum power usage is obtained by accurately following the power hyperbola. This study focused on developing a simulation model of a regulator. First, the governing equations of the regulator are derived, and analysis is performed by computer simulation, which can identify significant parameters of regulator. As a result, the variation of the swivel angle, flow rate, hyperbolic curve, inner leakage and responsibility are simulated, and significant parameters of a regulator are identified.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.764-767
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• 2004

This study was to measure the minuteness structure, dielectric properties of (0.3-x)PMN - XPSS-0.7PZT+0.5wt%NiO+0.5wt%$MnO_2$(x=0.05, 0.10, 0.15, 0.20, 0.25)ceramics according to sintering temperature and PSS moi percentage after manufacturing the specimens with a general method. the results of this study were gotten such as follows. The crystal structure of ceramic has the rombohedral structure in XRD. it appeared that addition of Ni, Mn additive was helpful to the formation of stable structure. Dielectric constant at $20^{\circ}C$ showed its maximum value 890.001 in specimens sintered at $1000^{\circ}C$, x=0.15mol. and dielectric loss showed its minimum value 6.95[%] in specimens sintered at $1000^{\circ}$, x=0.05mol. The variation rate of dielectric constant according to the change of frequency was decreased by increasing frequency, The variation rate of dielectric constant according to the change of temperature was increased by increasing temperature.

• 한국환경과학회지
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• 제2권4호
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• pp.331-336
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• 1993

A mathematical model for organic removal efficiency was investigated in a fluidized bed biofilm reactor by changing the feed flow rate, the residence time and the recycle flow rate. In batch experiment, organic removal could be assumed as first order and an intrinsic first order rate constant(k1) was found $6.4{\times}^{-6}cm^3/mg{\cdot}sec$ at influent COD range of 3040 - 6620 mg/L. In continuous experiment, at the condition of the influent COD, 3040 mg/L, the superficial upflow velocity, 0.47 cm/sec, the biofilm thickness 336 ${\mu}m$ and the biofilm dry density 0.091 g/mL, the calculated COD removal efficiency from the mathematical model gave 60% which was very close to the observed value of 66 %. As the feed flow rate was increased, the COD removal efficiency was sharply decreased and at constant feed flow rate, the COD removal efficiency was decreased also as the residence time being decreased.

• 한국생산제조학회지
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• 제8권1호
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• pp.119-125
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• 1999

The distribution of fatigue crack growth rate is subjected to the measuring interval and calculated method of growth rate. In this paper, in order to establish the method of determining the distribution of fatigue crack growth rate, which ignores those influences, a series of fatigue crack growth experiments and measuring intervals of crack length calculated reasonable are presented. The main conclusions obtained are summarized as follows: 1) As a result of the ΔP constant test and ΔK constant test, it is thought that an approximate measuring interval of 0.3~0.7mm is reasonable, which allows for few errors and is little subjected to the calculated method of crack growth rate. 2) After generally comparing the error estimation by using the experimental data of CCT specimen with the error rating of the CT specimens, it is possible that the fatigue test has few errors within the measuring interval, ξ(Δa/W)=0.0067~0.017, regardless of the dimension of specimen geometry.

• Animal Systematics, Evolution and Diversity
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• 제30권1호
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• pp.39-43
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• 2014

In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR), one-continuous-shift (OCS) and multiple-discrete- shifts (MDS) situations. The OCS diversification model was rejected by ${\gamma}$ statistic (${\gamma}=-5.556$, p<0.001), implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using "laser" package under R environment. Moreover, MDS models, implemented using another R package "MEDUSA", indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using "MEDUSA" package in which any arbitrary numbers of shifts are allowed to model.

• Journal of Biosystems Engineering
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• 제19권2호
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• pp.112-123
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• 1994

At present, no appropriate drying conditions can be found for the heated-air drying of mushroom in Korea. Usually, mushroom is being dried at the temperature range of 40 to $50^{\circ}C$ until the moisture content reaches 10~13% (wb). However, drying characteristics of the mushroom should be investigated for quality improvement and efficient drying operation of the mushroom. The results of this study may be summarized as follows ; 1. The effect of air temperature on the rate of drying was greater than that of relative humidity for drying of mushroom, and the rate of drying was increased with increase in the air temperature. 2. Drying rate for Shiitake mushroom showed falling-rate period of drying without constant-rate period of drying. Drying rate for Oyster mushroom showed a short constant-rate period at the initial stage of drying process, and followed by falling-rate period of drying. 3. Exponential and App.-Diffusion models were found to describe well the drying process of Shiitake mushroom. Exponential and Thompson models for Oyster mushroom in which Thompson model was the most suitable for Oyster mushroom. 4. The equilibrium moisture content of the mushroom decreased with decrease in the air temperature and increase in the relative humidity. In room condition($20^{\circ}C$, 54% RH), the calculated values of the equilibrium moisture content showed 11.17% for Shiitake mushroom and 13.19% for Oyster mushroom, respectively.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.80-83
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• 2007

In order to characterize the catalytically active sites on carbon black, acetylene chemisorption had been examined recently at 773 and 873 K by using a pulse technique. As the inject ion was repeated at 773 K, the adsorbed amount gradually decreased and eventually the adsorption did not occur any more. At 873 K a constant amount of $C_2H_2$ was consumed repeatedly after several injections. Good linear relationships were obtained between the methane decomposition rate at 1123 or 1173 K and the cumulative acetylene adsorption at 773 K or the constant acetylene consumption at 873 K. Reasonable models for the associative acetylene chemisorption at 773 K and the constant acetylene consumption at 873 K on the armchair face at the edges of graphene layers were proposed. The constant consumpt ion may be explained by the "$C_2H_2$-addition-hydrogen- abstract ion (CAHA)" mechanism.

• Ocean Science Journal
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• 제40권2호
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• pp.79-89
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• 2005

Laboratory radiotracer experiments were conducted to determine assimilation efficiencies (AE) from ingested algal food and oxic sediment particles, uptake rates from the dissolved phase, and the efflux rates of Cd, Cr and Zn in the Asiatic clam Corbicula fluminea. Among three elements, AE from both algal and sediment food was greatest for Cd, followed by Zn and Cr. The AEs of tested elements from algal food (Phaeodactylum tricornutum) were consistently higher than those from sediments at a given salinity and temperature. The influence of salinity (0, 4 and 8 psu) and temperature (5, 13 and $21^{\circ}C$) on the metal AEs was not evident for most tested elements, except Cd AEs from sediment. The rate constant of metal uptake from the dissolved phase $(k_u)$ was greatest for Cd, followed by Zn and Cr in freshwater media. However, in saline water, the $(k_u)$ of Zn were greater than those of Cd. The influx rate of all tested metals increased with temperature. The efflux rate constant was greatest for Cr $(0.02\;d^{-1})$, followed by Zn $(0.010{\sim}0.017\;d^{-1})$ and $Cd\;(0.006\;d^{-1})$. The efflux rate constant for Zn in clam tissues depurated in 0 psu $(0.017\;d^{-1})$ was faster than that in 8 psu $(0.010\;d^{-1})$. Overall results showed that the variation of salinity and temperature in estuarine systems can considerably influence the metal bioaccumulation potential in the estuarine clam C. fluminea. The relatively high Cd accumulation capacity of C. fluminea characterized by the high AE, high dissolved influx rate and low efflux rate, suggested that this clam species can be used as an efficient biomonitor for the Cd contamination in freshwater and estuarine environments.

• 반도체디스플레이기술학회지
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• 제8권3호
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• pp.19-23
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• 2009

We have studied dielectric characteristics of low-k interlayer dielectric materials was fabricated by plasma enhanced chemical vapor deposition (PECVD). BTMSM precursor was introduced with the flow rates from 24 sccm to 32 sccm by 2 sccm step in the constant flow rate of 60 sccm $O_2$. Then, SiOCH thin film deposited at room temperature was annealed at temperature of $400^{\circ}C$ and $500^{\circ}C$ for 30 minutes in vacuum. The vibrational groups of SiOCH thin films were analyzed by FT/IR absorption lines, and the dielectric constant of the low-k SiOCH thin films were obtained by measuring C-V characteristic curves. With the result that FTIR analysis, as BTMSM flow rate increase, relative carbon content of SiOCH thin film increased from 29.5% to 32.2%, and increased by 32.8% in 26 sccm specimen after $500^{\circ}C$ annealing. Dielectric constant was lowest by 2.32 in 26 sccm specimen, and decreased more by 2.05 after $500^{\circ}C$ annealing. Also, leakage current is lowest by $8.7{\times}10^{-9}A/cm^2$ in this specimen. In the result, shift phenomenon of chemical bond appeared in SiOCH thin film that BTMSM flow rate is deposited by 26 sccms, and relative carbon content was highest in this specimen and dielectric constant also was lowest value