Single phase Pb(Fe1/2Ta1/2)O3, ceramics were successfully synthesized from the powders prepared by solid state reaction (sintering temperature: 1100∘C, density: 9.3g/cm3, average grain size: 5.1±1.2mm, space group: Pm3m). Their dielectric properties measured at −150∼50∘C showed the maximum relative dielectric constant of 31000 at −41∘C. 1 kHz, and typical relaxor ferroelectrics characteristics such as diffuse phase transition and dielectric relaxation phenomena. However, the diffuseness of phase transition decreased and the dielectric properties became more normal ferroelectrics as the time of annealing at 1000∘C increased. By using Raman spectroscopy, it was revealed that the Fe3+ and Ta5+ ions in the as-sintered Pb(Fe1/2Ta1/2)O3, are stoichiometrically 1 : 1 ordered within the short-range that can not be probed even by transmission electron microscopy, and this stoichiometric 1 : 1 ordering is enhanced by the annealing. The relaxor ferroelectric characteristics in the as-sintered Pb(Fe1/2Ta1/2)O3, could be correlated with the stoichiometric 1 : 1 short-range ordering of B-site cations, and the decrease of relaxor ferroelectric characteristics in the annealed Pb(Fe1/2Ta1/2)O3 could be correlated with the enhanced stoichiometric 1 : 1 short-range ordering of B-site cations.
Journal of the Korean Society of Food Science and Nutrition
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v.17
no.3
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pp.191-197
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1988
Sorption properties of corn starch(CS) and Soy protein isolates(SPI) in plastic films packaging were investigates for binary system. The mixture were sealed in plastic films of low density polyethylene(LDPE), oriented polypropylene(OPP) and LDPE/OPP coated film and packaging effect on the changes of moisture sorption during storage at 40∘C were studied. The following results were obtained. The water vapor permeability of material films was 32.6g/m2/24hrs(belowg) for 0.02mm LDPE film, 14.01g for 0.04mm LDPE film, 7.30g for 0.02mm OPP film, 3.37g for 0.04mm OPP film and 4.869 for 0.02mm LDPE/0.02 mm OPP confine film at 40\cireC 90%RH, therefore the OPP film was more effective than LDPE film on the resistance of relative humidity. And the OPP film packaging sealed mixture of food samples was also more elective then LDPE film, having same thickness for increase of water vapor permeability during storage at 40\cireC. A general increase in sorption rate was found more in SPI than CS in the packaged mixtures.
In order to examine how climatological condition can influence on urban scale particulate air pollutants, single and cross spectrum analysis have been performed to daily mean concentrations of particulate matters (PM10) in Busan together with the climatological variables over the Asian dust source regions. Single power spectrum analysis of PM10 concentrations in Busan shows that, aside from the typical and well-known periodicities, 3-4 year of peak periodicity of power spectrum density was identified. In cross spectrum analysis, this 3-4 year periodicity is found to have a strong positive correlation with the wind speed and pressure, and negative with the temperature and relative humidity, which is rather consistent with both characteristics of air mass during the Asian dust event whose periodicities have been recorded inter-annually over the Korean urban cities. Over the Asian dust source regions, PM10 vs. precipitation shows no significant periodicity from the time series of precipitation data, but the periodicity of EDI (Effective Drought Index) shows some interannual variabilities ranging from 2 to 4 years over the various source regions, suggesting that, rather than precipitation itself, the EDI could be more closely associated with the occurrence frequency of Asian dust and interannual variability of urban particle concentrations in Korean cities.
When a tracked vehicle travels off-road, shearing action and ground sinkage occur on the soil-track interface and severely affect tractive performance of the tracked vehicle. Especially, the ground sinkage, which is induced by vehicle's weight (hereinafter referred to as static sinkage) and longitudinal forces in the direction of travel producing slip (hereinafter referred to as slip sinkage), develops soil resistance, directly restricting the tractive performance of an off-road tracked vehicle. Thus, to assess the tractive performance of an off-road tracked vehicle, it is imperative to take both of static sinkage and slip sinkage into consideration. In this research, a series of model track experiments was conducted to investigate the slip sinkage which has not been clarified. Experiment results showed that the slip sinkage increased with increasing the slip ratio, but the increasing rate gradually decreased. Also, the slip sinkage was found to increase as relative density of soil decreased and imposed vertical load increased. From the experiment results, the normalized slip sinkage defined as slip sinkage to static sinkage calculated in the identical condition was investigated, and an empirical equation for the slip sinkage was developed in terms of slip ratio, which allows vehicle operators to predict the slip sinkage in a given soil and operating conditions.
The Transactions of the Korean Institute of Electrical Engineers C
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v.55
no.10
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pp.467-474
/
2006
The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the SiC−TiB2 electroconductive ceramic composites was investigated. The SiC−TiB2 electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of 1,750∼1,900[∘C], with an addition of 12[wt%] Al2O3+Y2O3(6:4mixtureofAl2O3andY2O3) as a sintering aid. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 84.92[%], 140[MPa], 4.07[GPa] and 3.13[MPa⋅m1/2] for SiC−TiB2 composites of 1,900[∘C] sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from 25[∘C]to700[∘C]. The electrical resistivity showed the value of 5.51×10−4,2.11×10−3,7.91×10−4and6.91×10−4[Ω⋅cm] for ST1750, ST1800, ST1850 and ST1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of 3.116×10−3,2.717×10−3,2.939×10−3,3.342×10−3/[∘C] for ST1750, ST1800, ST1850 and ST1900 respectively in the temperature ranges from 25[∘C]to700[∘C]. It is assumed that because polycrystallines, such as recrystallized SiC−TiB2 electroconductive ceramic composites, contain of porosity and In Situ YAG(Al5Y3O12) crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to Al2O3+Y2O3 additives widely varies with sintering temperature, electrical resistivity of the SiC−TiB2 electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that β−SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.
Kim, In-Seong;Song, Jae-Seong;Yun, Mun-Su;Park, Jeong-Hu
The Transactions of the Korean Institute of Electrical Engineers C
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v.51
no.8
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pp.340-346
/
2002
Capacitor material utilized in the downsizing passive devices and integration of passive devices requires the physical and electrical properties at given area such as capacitor thickness reduction, relative dielectric constant increase, low leakage current and thermal stability. common capacitor materials, Al2O3, SiO2, Si3N4, SiO2/Si3N4, TaN and et al., used until recently have reached their physical limits in their application to integration of passive devices. Ta2O5 is known to be a good alternative to the existing materials for the capacitor application because of its high dielectric constant (25~35), low leakage current and high breakdown strength. Despite the numerous investigations of Ta2O5 material, there have little been established the clear understanding of the annealing effect on capacitance characteristic and conduction mechanism. This study presents the dielectric properties Ta2O5 MIM capacitor structure Processed by O2 RTA oxidation. X-ray diffraction patterns showed the existence of amorphous phase in 600∘C annealing under the O2 RTA and the formation of preferentially oriented-Ta2O5 in 650, 700∘C annealing and the AES depth profile showed O2 RTA oxidation effect gives rise to the O2 deficientd into the new layer. The leakage current density respectively, at 3~1l×10−2(kV/cm) were 10−3~10−6(A/cm2). In addition, behavior is stable irrespective of applied electric field. the frequency vs capacitance characteristic enhanced stability more then Ta2O5 thin films obtained by O2 reactive sputtering. The capacitance vs voltage measurement that, Vfb(flat-band voltage) was increase dependance on the O2 RTA oxidation temperature.
Since the requirement of the high density integration and thin package technique of semiconductor have been increasing, the main package type of semiconductor will be a chip scale package (CSP). The changes of diffusion coefficient and moisture content ratio of epoxy resin systems according to the change of liquid type epoxy resin and fillers for CSP applications were investigated. The epoxy resins used in this study are RE-304S, RE310S, and HP-4032D, and Kayahard MCD as hardener and 2-methylimidazole as catalyst were used in these epoxy resin systems. The micro-sized and nano-sized spherical type fused silica as filler were used in order to study the moisture absorption properties of these epoxy molding compound (EMC) according to the change of filler size. The temperature of glass transition (Tg) of these EMC was measured using Dynamic Scanning Calorimeter (DSC), and the moisture absorption properties of these EMC according to the change of time were observed at 85∘C and 85% relative humidity condition using a thermo-hygrostat. The diffusion coefficients in these EMC were calculated in terms of modified Crank equation based on Ficks' law. An increase of diffusion coefficient and maximum moisture absorption ratio with Tg in these systems without filler can be observed, which are attributed to the increase of free volume with Tg. In the EMC with filler, the changes of Tg and maximum moisture absorption ratio with the filler content can be hardly observed, however, the diffusion coefficients of these systems with filler content show the outstanding changes according to the filler size. The diffusion via free volume is dominant in the EMC with micro-sized filler; however, the diffusion with the interaction of absorption according the increase of the filler surface area is dominant in the EMC with nano-sized filler.
Purpose: The purposes of this paper are to develop a theoretical basis that the beam directions should be considered when the mechanical accuracy of teletherapy machine is evaluated by the star pattern test, to develop methods using asymmetric field in length to simulate beam direction for the case that beam direction does not appear on film. Method: In evaluating mechanical rotational accuracy of the gantry of teletherapy unit by the star pattern test, the direction of radiation beams was considered. A star pattern using some narrow beams was made. Density profiles at 10cm far from estimated gantry axis on the star pattern were measured using an optical densitometer. On each profile, one coordimate of a beam axis was determined. A pair of coordinates on a beam axis form an equation of the axis. Assume that a unit vector equation omitted is with same direction as radiation beam and a vector equation omitted is a vector directing to the beam axis from the estimated gantry axis. Then, a vector product equation omitted × equation omitted is an area vector of which the absolute value is equal to the distance from the estimated gantry axis to the beam axis. The coordinate of gantry axis was obtained by using least-square method for the area vectors relative to the average of whole area vectors. For the axis, the maximum of absolute value of area vectors would be an accuracy of the gantry rotation axis. For the evaluation of mechanical accuracies of collimator and couch axes for which beam direction could not be depicted on a star pattern test film, narrow beams asymmetric in field length was used to simulate beam direction. Result: For a star test pattern to evaluate the mechanical accuracy of rotational axes of a telectherapy machine, the result considering beam direction was different from that ignoring beam direction. For the evaluation of mechanical accuracies of collimator and couch axes by means of a star pattern test, narrow asymmetric beams could simulate beam direction. Conclusion: When a star pattern test is used to evaluate the mechanical accuracy of a teletherapy unit, beam direction must be considered or simulated, and quantitatively evaluated.
Journal of the Korean Association of Geographic Information Studies
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v.15
no.3
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pp.13-22
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2012
The spatial structure analysis using the existing space syntax has a weakness only to apply the road factor. Hence, it is necessary to perform a new spatial structure analysis considering the regional characteristics factor as well as the road factor. The purpose of this study is to propose a modified spatial structure analysis which adopts road and regional characteristics factors using the existing space syntax and GIS and then to apply it to the spatial structure analysis of the urbanized areas in Hapdeok town. For the new analysis, the experts' survey has been conducted to derive the spatial structure factors of the area and their relative weights. Specifically, it drew the road factor as well as the regional characteristics factors such as road, district, land value, and building density. This study shows that the existing spatial structure analysis considering only the road factor does not reflect the actual spatial structure but the modified spatial structure analysis considering the road factor and the regional characteristics factors more accurately analyzes the spatial structure of Hapdeok town. Hapdeok is not an area where road networks were developed along main development axis and its centrality was changed, but an area where road networks were developed by effectiveness and equity and its centrality was changed by downtown decline. The towns like Hapdeok is more suitable for applying the modified spatial structure analysis method considering the regional characteristics factors. Further research is required for selecting characteristics factors and appropriate parameters in the modified spatial structure analysis. Further case studies await in other cities for conducting its verification.
Kim Jaeheon;Cheong Cheolung;Kim SungTae;Lee Soogab
Proceedings of the Acoustical Society of Korea Conference
/
spring
/
pp.469-474
/
2002
In recent years, modularization of engine parts has increased the application of plastic products in air intake systems. Plastic intake manifolds provide many advantages including reduced weight, contracted cost, and lower intake air temperatures. These manifolds, however, have some weakness when compared with customary aluminium intake manifolds, in that they have low sound transmission loss because of their lower material density. This low transmission loss of plastic intake manifolds causes several problems related to flow noise, especially when the throttle is opened quickly. The physical processes, responsible for this flow noise, include turbulent fluid motion and relative motion of the throttle to the airflow. The former is generated by high-speed airflow in the splits between the throttle valve and the inner-surface of the throttle body and surge-tank, which can be categorized into the quadrupole source. The latter induces the unsteady force on the flow, which can be classified into the dipole source. In this paper, the mechanism of noise generation from the turbulence is only investigated as a preliminary study. Stochastic noise source synthesis method is adopted for the analysis of turbulence-induced, i.e. quadrupole noise by throttle at quick opening state. The method consists of three procedures. The first step corresponds to the preliminary time-averaged Navier-Stokes computation with a k−ε turbulence model providing mean flow field characteristics. The second step is the synthesis of time-dependent turbulent velocity field associated with quadrupole noise sources. The final step is devoted to the determination of acoustic source terms associated with turbulent velocity. For the first step, we used market available analysis tools such as STAR-CD, the trade names of fluid analysis tools available on the market. The steady state flows at three open angle of throttle valve, i.e. 20, 35 and 60 degree, are numerically analyzed. Then, time-dependent turbulent velocity fields are produced by using the stochastic model and the flow analysis results. Using this turbulent velocity field, the turbulence-originated noise sources, i.e. the self-noise and shear-noise sources are synthesized. Based on these numerical results, it is found that the origin of the turbulent flow and noise might be attributed to the process of formulation and the interaction of two vortex lines formed in the downstream of the throttle valve. These vortex lines are produced by the non-uniform splits between the throttle valve and inner cylinder surface. Based on the analysis, we present the low-noise design of the inner geometry of throttle body.
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