• Analytical Science and Technology
• /
• v.28 no.1
• /
• pp.33-39
• /
• 2015

CdS-QD particles are a nano-sized semiconducting crystal that emits light. Their optical properties show great potential in many areas of applications such as disease-diagnostic reagents, optical technologies, media industries and solar cells. The wavelength of emitting light depends on the particle size and thus the quality control of CdS-QD particle requires accurate determination of the size distribution. In this study, CdS-QD particles were synthesized by a simple ${\gamma}$-ray irradiation method. As a particle stabilizer polyvinyl pyrrolidone (PVP) were added. In order to determine the size and size distribution of the CdS-QD particles, sedimentation field-flow fractionation (SdFFF) was employed. Effects of carious parameters including the the flow rate, external field strength, and field programming conditions were investigated to optimize SdFFF for analysis of CdS-QD particles. The Transmission electron microscopy (TEM) analysis show the primary single particle size was ~4 nm, TEM images indicate that the primarty particles were aggregated to form secondary particles having the mean size of about 159 nm. As the concentration of the stabilizer increases, the particle size tends to decrease. Mean size determined by SdFFF, TEM, and dynamic light scattering (DLS) were 126, 159, and 152 nm, respectively. Results showed SdFFF may become a useful tool for determination of the size and its distribution of various types of inorganic particles.

• Journal of Korean Society of Water and Wastewater
• /
• v.28 no.4
• /
• pp.441-451
• /
• 2014

The flushing is important to maintain good water quality in water main. It is a technique of using water velocity to remove sediments in water distribution system. The variety of water quality problems can occur in a distribution system, so too can a variety of benefits be gained by system flushing. In order to effectively perform the flushing, the contaminants to be removed to set up and it can be solved, it is necessary to ensure the proper flow rate. In this study, the removal of contaminants present in the inner water pipe attached loose deposits such as fine particles of granular activated carbon, sand and iron corrosion product sought to derive flow rates. Thus, the constant observation of using pilot plant scale water distribution plant for the movement of floating characteristics of particles were assessed.

• Applied Chemistry for Engineering
• /
• v.19 no.6
• /
• pp.609-616
• /
• 2008

The present study is concerned with a simple numerical method for estimating the hindered settling velocity of noncolloidal suspensions with bidisperse size distribution of particles. The method is based on an effective-medium theory which uses the conditional ensemble averages for describing the velocity fields or other physical quantities of interest in the suspension system with the particles randomly placed. The effective-medium theory originally developed by Acrivos and Chang[1] for monodisperse suspensions is modified for the bidisperse case. Using the radial distribution functions and stream functions the hindered settling velocity of the suspended particles is calculated numerically. The predictions by the present method are compared with the previous experimental results by Davis and Birdsell[2] and Cheung et al.[3]. It is shown that the estimations by the effective-medium model of the present study reasonably agree with the experimental results.

• Asian-Australasian Journal of Animal Sciences
• /
• v.5 no.1
• /
• pp.55-61
• /
• 1992

To determine the effect of time after feeding on distribution of particle size of digesta in the gastrointestinal tract, 16 sheep given orchardgrass first cut hay were slaughtered at 2, 8, 16 and 24 hours after feeding and digesta in diverse sites of the tract were sieved into four fractions of particle size larger than $1180{\mu}m$, 300-1180, 45-300 and less than 45. Following results were obtained: 1) In the reticulo-rumen, the proportion of particles larger than $1180{\mu}m$ decreased with the time after feeding, while the other particle size fractions did not change with time after feeding. 2) In the post-ruminal alimentary tract, the proportion of particles larger than $1180{\mu}m$ was significantly smaller than that in the reticulo-rumen and distribution of fractions of every particle size stayed consistently at about the same level irrespective of the time after feeding. 3) In the cecum, the fraction of particle size less than $45{\mu}m$ appeared to be selectively retained when the passage rate was considered.

• YAKHAK HOEJI
• /
• v.34 no.3
• /
• pp.206-211
• /
• 1990

Total suspended particles were collected and size-fractionated by an Andersen high-volume air sampler at Chungang University located near the Han River, Seoul, Korea, during the period form March, 1986 to August, 1986 and from March, 1987 to February, 1988. The concentrations and the particle size distributions of anions such as chloride, nitrate and sulfate were determined by ion chromatography. The averages of concentrations were $125.43\;{\mu}g/m^3$ in 1986 and $189.19\;{\mu}g/m^3$ in 1987 for total suspended particles (TSP), $2.12\;{\mu}g/m^3$ in 1986 and $4.14\;{\mu}g/m^3$ in 1987 for chloride, $4.39\;{\mu}g/m^3$ in 1986 and $5.95\;{\mu}g/m^3$ in 1987 for nitrate and $11.98\;{\mu}g/m^3$ in 1986 and $19.29\;{\mu}g/m^3$ in 1987 for sulfate. Size distribution of TSP was found to be generally bimodal. Chloride exhibited a seasonal variation in the distribution; fine particles were predominant in the winter whereas the concentration of coarse ones was almost same through four seasons. Nitrate showed a distribution similar to that of chloride. Such variation was less significant for sulfate. For chloride and nitrate, the relationship between the monthly averaged distribution pattern and air temperature was analyzed in terms of fine fraction (FF). The FF decreased with increasing air temperature.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.1
• /
• pp.47.1-47.1
• /
• 2011

We studied the evolution of the two mass components system with NFW initial density distribution by direct integration of the Fokker-Planck equations. The low mass component is regarded the dark matter particles while the high mass component is assumed to be conglomerates of baryonic matter in order to depict the 'stars'. While the true mass ratio between these two types of particles should be extremely large, our adopted mass ratio is about 1000 beyond which the dynamical evolution and density distribution tend to converge. Since the dynamical evolution is dominated by the dynamical friction, the high mass component slowly moves toward the central part, and eventually undergoes the core collapse. The system reaches the core-collapse at about $7.1{\times}10^{-3}$ $t_{fh}$ in NFW models, where $t_{fh}$is the dynamical friction time at half-mass radius. The distribution of the high mass component is well fitted by the Sersic profiles or modified Hubble profile when the mass segregation is established. From these results, the surface brightness of elliptical galaxies may be explained by the high mass component experiencing dynamical friction by the dark matter particles. In order for the mass segregation to be effective within Hubble time, the mass of the luminous component should be greater than $10^5M_{\bigodot}$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.17 no.1
• /
• pp.31-36
• /
• 2003

This paper describes the quantitative analysis and the pattern recognition of partial discharge signals generated by particles in GIS. Four states of particles were simulated in this paper. Partial discharge signals from each state was measured and the Ф-Q-N distribution of partial discharge signals was displayed and then the Ф-Q, the Ф-Qm, the Ф-N and the Q-N distribution were displayed. Each distribution can be quantitatively represented by statistical parameters and the parameters were used for input data of pattern recognition. As the results, it was found that the forms of each distribution were different according to the particle states. Recognition rate using neural network was about 92〔%〕 and the more input data number, the more accurate results.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.9
• /
• pp.28-34
• /
• 2022

The flow at the top surface of the hopper is of particular industrial interest. Previously, the velocity distribution inside the hopper was predicted using the simple, void and spot models, which are equations for the particle flow field. However, because these equations cannot predict the velocity distribution at the top surface, a new equation has been recently proposed. This study employed the discrete element method with the changed shape of the particles. Based on the results, the shape of the particle had no effect on the discharge angle and shape of the velocity distribution; however, it greatly affected the size of the velocity distribution and bed thickness of the flowing particles. Therefore, in the future, it is necessary to modify the theoretical equation by considering the shape of the particles.

• Journal of Environmental Health Sciences
• /
• v.34 no.2
• /
• pp.131-136
• /
• 2008

The variation of the particle size distribution and density as well as the chemical composition of aerosols is important to evaluate the particles. This study measured and analyzed airborne particles using a scanning mobility particle sizer (SMPS) system and an aerodynamic particle sizer (APS) at the University of Seoul during every season. The highest particle number concentration of airborne particles less than $0.9\;{\mu}m$, occurred in winter, while the highest particle number concentration of airborne particles more than $0.9\;{\mu}m$, occurred in spring. Mass concentration appeared highest at spring. Also, when we compared $\beta$-ray's mass concentration with calculated mass concentration by using the SMPS-APS system during each season, density of the winter is $1.92\;g/cm^3$, spring density is $1.64\;g/cm^3$, fall density is $1.57\;g/cm^3$. We found out that PM10 density was differ every season. However, while the calculated density is whole density for PM10 the density of each diameter was different. In this study the density estimation equation of the QCM cascade impactor measured mass concentration of each diameter.

• Journal of Korean Society for Atmospheric Environment
• /
• v.20 no.3
• /
• pp.411-419
• /
• 2004

Titania particles are widely used as a photocatalyst to treat various contaminants in air and water. Titania particles were formed by vapor-phase oxidation of titanium tetraisopropoxide (TTIP) in a tube furnace between 773 and 1,273 K. The effect of process variables such as furnace temperature, flow rate of carrier air, and flow rate of sheath air on powder size and phase characteristics was investigated using a scanning mobility particle sizer (SMPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The size distribution of synthesized titania particles was characterized with mode diameter and peak concentration. The mode diameter ranging from 20 to 80 nm decreased with increasing flow rates of sheath air and carrier air, and increased with increasing furnace temperature. The peak concentration increased with increasing flow rates of sheath air and carrier air The best synthetic condition for high production rate can be derived from the experimental data set represented by mode diameter and peak concentration. The crystal structure of synthesized titania particles was found to be anatase phase, ensuring high photocatalytic potential.