• Journal of ILASS-Korea
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• v.25 no.2
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• pp.81-88
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• 2020

Electrospray is used in various industries because it can produce continuous and uniform droplets. However, it is difficult to find optimal spraying condition due to lack of data in various conditions. In this study, various conditions were divided into electric parameters and fluid property. The electric parameters set Nozzle to Substrate(NTS), nozzle diameters and the fluid property set viscosity and conductivity as conditions. In this study, it observes spray patterns, Sauter Mean Diameter(SMD) according to conditions. As a result, fluid properties had a greater effect on the cone-Jet mode than on the nozzle diameter, NTS, and flowrate. All of solutions have Stable cone-jet mode at voltage of 8.5 kV, NTS of 20 mm and nozzle diameter of 0.2 mm. SMD has 27% different depending on viscosity and conductivity. The increased flowrate and viscosity are rising break-up length and thickening jet also jet is thinned by increased conductivity. Experiments have confirmed that the jet is thickened by increased flowrate and viscosity, and that the jet is thinned by conductivity.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.283-289
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• 2009

In level set method, material properties are made to change smoothly across an interface of two materials with different properties by introducing an interpolation or smoothing scheme. So far, the weighted arithmetic mean (WAM) method has been exclusively adopted in level set method, without complete assessment for its validity. We showed here that the weighted harmonic mean (WHM) method for rate constants of various rate processes, including viscosity, thermal conductivity, electrical conductivity, and permittivity, gives much more accurate results than the WAM method. The selection of interpolation scheme is particularly important in multi-phase electrohydrodynamic problems in which driving force for fluid flow is electrical force exerted on the phase interface. Our analysis also showed that WHM method for both electrical conductivity and permittivity gives not only more accurate, but also more physically realistic distribution of electrical force at the interface. Our arguments are confirmed by numerical simulations of drop deformation under DC electric field.

• Journal of Astronomy and Space Sciences
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• v.25 no.2
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• pp.129-138
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• 2008

This study attempts to show how the geomagnetic indices, AU, AL and Dst, respond to the interplanetary parameters, more specifically, the solar wind electric field VBz during southward interplanetary magnetic field (IMF) period. The AU index does not seem to respond linearly to the variation of southward IMF. Only a noticeable correlation between the AU and VBz is shown during summer, when the ionospheric conductivity associated with the solar EUV radiation is high. It is highly likely that the effect of electric field on the eastward electrojet intensification is only noticeable whenever the ionospheric conductivity is significantly enhanced during summer. Thus, one should be very cautious in employing the AU as a convection index during other seasons. The AL index shows a significantly high correlation with VBz regardless of season. Considering that the auroral electrojet is the combined result of electric field and ionospheric conductivity, the intensification of these two quantities seems to occur concurrently during southward IMF period. This suggests that the AL index behaves more like a convection index rather than a substorm index as far as hourly mean AL index is concerned. Contrary to the AU index, the AL index does not register the maximum value during summer for a given level of VBz. It has something to do with the findings that discrete auroras are suppressed in sunlight hemisphere (Newell et al. 1996), thus reducing the ionospheric conductivity during summer. As expected, the Dst index tends to become more negative as VBz gets intensified. However, the Dst index (nT) is less than or equal to 15VBz(mV/m) + 50(Bz < 0). It indicates that VBz determines the lower limit of the storm size, while another factor(s), possibly substorm, seems to get further involved in intensifying storms. Although it has not been examined in this study, the duration of southward IMF would also be a factor to be considered in determining the size of a storm.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.3
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• pp.323-332
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• 1996

Precipitation samples were collected by the wet-only sampling method at Seoul from September 1993 to June 1995. Sample were analysed for the anions $(NO_3^-, NO_2^-, SO_4^{2-}, Cl^-, and F^-)$ and cations $(Na^+, K^+, Ca^{2+}, Mg^{2+}, and NH_4^+)$ in addition to pH and electric conductivity. In order to establish the chemical analysis data of high quality, the assurance checks for analytical data of precipitation were performed by considering the ion balance and by comparing the measured conductivity with the calculated conductivity. As we applied the various assurance checking methods by the ion balance used until recently to a data set measured in this study, the f value expressed as $\Sigma C/\Sigma A$ was found to be not appropriate for the data screening. Also, the scattering plot between cations and anions in each sample was found to show the general tendency of ion balance but was proved to not quantitate the standard of data screening at a data set of samples of various concentration levels. The h value defined as (A-C)/C for C $\geq$ A and (A-C)/A for C < A was used to check the ion balance. However, the standard of data screening by h value must very in response to total ion concentration of samples. In this study, the quality assurance of chemical analysis data was checked by considering both the ion balance of evaluating by h value and the conductivity balance. Further the quality control was achieved by these quality assurance methods. As the result, 67 samples among total 77 were obtained as valid. As the central tendency value for a statistical summary in the analytical parametr of samples, the volume-weighted mean value was found to represent more the general chemistry of precipitation rather than the arithmetic mean. The volume-weighted mean pH was 5.0 and 25% of samples was less than this mean. The concentrations of sufate and nitrate in precipitation were 90.4 ueq/L and 32.4 ueq/L which made up 59% and 21% of all anions. The raion of $SO_4^{2-}/(NO_3^- + NO_2^-)$ in precipitation was 2.7, which indicates that the contributions of $H_2SO_4$ and $HNO_3$ to the acidity of precipitation are 70% and 30%, respectively.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.3
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• pp.1327-1331
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• 2014

Background: Electrical impedance tomography (EIT) is a new non-invasive, mobile screening method which does not use ionizing radiation to the human breast; allows conducting quantitative assessment of the images besides the visual interpretation. The aim of this study was to correlate the quantitative assessment and visual interpretation of breast electrical impedance tomographs and associated factors. Materials and Methods: One hundred and fifty mammography patients above 40 years and undergoing EIT were chosen using convenient sampling. Visual interpretation of the images was carried out by a radiologist with minimum of three years experience using the breast imaging - electrical impedance (BI-EIM) classification for detection of abnormalities. A set of thirty blinded EIT images were reinterpreted to determine the intra-rater reliability using kappa. Quantitative assessment was by comparison of the breast average electric conductivity with the norm and correlations with visual interpretation of the images were determined using Chi-square. One-way ANOVA was used to compare the mean electrical conductivity between groups and t-test was used for comparisons with pre-existing Caucasians statistics. Independent t-tests were applied to compare the mean electrical conductivity of women with factors like exogenous hormone use and family history of breast cancer. Results: The mean electrical conductivity of Malaysian women was significantly lower than that of Caucasians (p<0.05). Quantitative assessment of electrical impedance tomography was significantly related with visual interpretation of images of the breast (p<0.05). Conclusions: Quantitative assessment of electrical impedance tomography images was significantly related with visual interpretation.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.39-46
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• 2006

The fuel cell is one of promising environment-friendly energy sources for the next generation. The bipolar plate is a major component of the PEM fuel cell stack, which takes a large portion of stack cost. In this study, as alternative materials for bipolar plate of PEM fuel cells, graphite composites were fabricated by compression molding. Graphite particles mixed with epoxy resin were used as the main substance to provide electric conductivity To achieve desired electrical properties, specimens made with different mixing ratio, processing pressure and temperature were tested. To increase mechanical strength, one or two layers of woven carbon fabric were added to the graphite and resin composite. Thus, the composite material was consisted of three phases: graphite particles, carbon fabric, and epoxy resin. By increasing mixing ratio of graphite, fabricated pressure and process temperature, the electric conductivity of the composite was improved. The results of tensile test showed that the tensile strength of the two-phase graphite composite was about 4MPa, and that of three-phase composite was increased to 57MPa. As surface properties, contact an91e and surface roughness were tested. Graphite composites showed contact angles higher than $90^{\circ}$, which mean low surface energy. The average surface roughness of the composite specimens was $0.96{\mu}m$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.371-374
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• 2007

A method for metal nano powder imprinting is proposed as a patterning process for conductive tracks that is inexpensive and scalable down to the nanoscale. Conductive tracks with line widths of $0.5{\sim}20{\mu}m$ were fabricated using this method. The processing conditions were optimized to avoid various types of defects, and to increase the degree of sintering and electric conductivity of the imprinted conductive tracks. The mean electric resistivity of the conductive tracks imprinted under optimum conditions was $8.95{\mu}{\Omega}{\cdot}cm$, which is in the range required for practical applications.

• Journal of Environmental Science International
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• v.23 no.1
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• pp.69-79
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• 2014

The seasonal variation of pH and ion components in precipitation were investigated from January to December 2009 at Busan, Korea. The precipitation was acidic with a volume-weighted mean pH concentration of 5.32, which ranged from 3.79 to 8.66. The volume-weighted mean conductivity showed 86.77 ${\mu}S/cm$ and indicated higher concentration about 96.69 ${\mu}S/cm$ in summer. The volume-weighted mean equivalent concentration of components followed the order: $K^+$ > $Ca^{2+}$ > $nss-Ca^{2+}$ > $NH_4^+$ > $Mg^{2+}$ > $Na^+$ > $Li^+$ in cations and $Cl^-$ > $SO_4^{2-}$ > $nss-SO_4^{2-}$ > $NO_3^-$ > $NO^{2-}$ > $F^-$ > $Br^-$ in anions. Particularly, concentration of $K^+$ and $Cl^-$ showed 56 and 78 % in cations and anions. The higher concentration in $K^+$, $Na^+$, $Mg^{2+}$ and $Cl^-$ were shown in Busan city as compared to the other cities. The neutralization factors have been found to have higher value for potassium ion in winter compared with different seasons, indicating significant neutralization of acidic components over the region by potassium. Therefore, the precipitation characteristics at Busan had both continental and coastal as consequence of pH, conductivity and ionic analyses.

• Journal of the Korean Applied Science and Technology
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• v.28 no.2
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• pp.225-231
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• 2011

The electrochemical characteristics of electric double layer capacitor(EDLC) were investigated using various carbon materials. The physical properties such as specific surface area and mean pore size of activated carbon were analyzed by BET. The results of the activated carbon used for electrode material showed that the specific surface areas varied from 600 to 1500 $m^2$/g and mean pore sizes from 1.74 to 2.88 nm. A maximum specific capacitance of 0.30 F/$cm^2$ was obtained for the activated carbon with the highest specific surface area and ionic conductivity. Also, it was found that the electrochemical results of the cyclic charge-discharge tests were stable.

• Journal of Korean Society of Forest Science
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• v.102 no.4
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• pp.571-577
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• 2013

This study was carried out to establish the construction guidelines of soil erosion control structures for a restoration of mountain stream with analysis of water quality around constructed soil erosion control structures in mountain streams. Water pH of the Uidong valleys in Bukhansan (Mt.) was similar between the constructed soil erosion control structures of lower stream areas [pH 6.53(6.25~6.82)] and the non-constructed areas of upper stream areas [pH 6.32(5.73~6.90)]. Mean concentration of dissolved oxygen was also similar between the constructed soil erosion control structures of lower steam areas [10.2 mg/L(9.9~10.4 mg/L)] and the non-constructed areas of upper stream areas [10.3 mg/L (9.6~10.6 mg/L)]. Mean electric conductivity was similar between the lower [$63.9{\mu}S/cm$ ($32.6{\sim}120.4{\mu}S/cm$)]a nd the upper stream areas [$62.2{\mu}S/cm$ ($40.3{\sim}89.5{\mu}S/cm$)]. Mean concentration of anions was also similar between the lower [15.94 mg/L (3.43~7.98 mg/L)] and the upper stream areas [14.51 mg/L (2.56~4.29 mg/L)]. Water pH of the Honggei valleys in Sancheong-gun was similar between the lower [pH 6.86(6.50~7.10)] and the upper stream areas [pH 6.89(6.61~7.12)]. Mean concentration of dissolved oxygen was also similar between the lower [11.9 mg/L(11.5~12.3 mg/L)] and the upper stream areas [12.2 mg/L (11.6~12.6 mg/L)]. Mean electric conductivity was similar between the lower [$633.4{\mu}S/cm$ ($31.6{\sim}34.6{\mu}S/cm$)] and the upper stream areas [$32.7{\mu}S/cm$ ($31.4{\sim}34.3{\mu}S/cm$)]. Mean concentration of anion was also similar to both stream areas [1.0 mg/L (0.1~2.2 mg/L)]. Water quality in the Uidong and the Honggei valleys was not significantly different between the constructed soil erosion control structures of lower stream areas and the non-constructed areas of upper stream areas. It will be needed to study the time-series analysis of water quality before and after the construction of soil erosion control structure the restoration of mountain streams because the water quality in mountain streams could be affected during the construction processes of structures.