• Journal of the Korean Geographical Society
• /
• v.51 no.1
• /
• pp.23-40
• /
• 2016

In this study, long-term changes in means and extreme events of precipitation during summer rainy period called Changma (late June~early September) are examined based on rainfall data observed by Chukwooki during Joseon Dynasty (1777~1907) and by modern rain-gauge onward (1908~2015) in Seoul, Korea. Also, characterizations of the relevant changes in synoptic climate fields in East Asia are made by the examination of the NCEP-NCAR reanalysis I data. Analyses of 239-year time series of precipitation data demonstrate that the total precipitation as well as their inter-annual variability during the entire Changma period (late June~early September) has increased in the late 20th century and onward. Notably, since the early 1990s the means and extreme events during the summer Changma period (late June~mid-July) and Changma break period (late July~early August) has significantly increased, resulting in less clear demarcations of sub-Changma periods. In this regard, comparisons of synoptic climate fields before and after the early 1990s reveal that in recent decades the subtropical high pressure has expanded in the warmer Pacific as the advection of high-latitude air masses toward East Asia was enhanced due to more active northerly wind vector around the high pressure departure core over Mongolia. Consequently, it is suggested that the enhancement of rising motions due to more active confluence of the two different air masses along the northwestern borders of the Pacific might lead to the increases of the means and extreme events of Changma precipitation in Seoul in recent decades.

• Korean Chemical Engineering Research
• /
• v.52 no.3
• /
• pp.328-334
• /
• 2014

This study examined the effect of concentration polarization on permeate flux in forward osmosis (FO) membrane process for saline and sucrose solution. The reduction in permeate flux during the FO membrane process is largely due to the formation of concentration polarization on membrane surfaces. The flux reduction due to internal concentration polarization formed on the porous support layer was larger than that due to the external concentration polarization on the active membrane surface. Water permeate flux through the FO membrane increased nonlinearly with the increase in osmotic pressure. The water permeability coefficient was $1.8081{\times}10^{-7}m/s{\cdot}atm$ for draw solution on active layer (DS-AL) mode and $1.0957{\times}10^{-7}m/s{\cdot}atm$ for draw solution on support layer (DS-SL) mode in NaCl solution system. The corresponding membrane resistance was $5.5306{\times}10^6$ and $9.1266{\times}10^6s{\cdot}atm/m$, respectively. With respect to the sucrose solution, the permeate flux for DS-AL mode was 1.33~1.90 times higher than that for DS-SL mode. The corresponding variation in the permeation flux (J) due to osmotic pressure (${\pi}$) would be expressed as $J=-0.0177+0.4506{\pi}-0.0032{\pi}^2$ for the forward and $J=0.0948+0.3292{\pi}-0.0037{\pi}^2$ for the latter.

• The korean journal of orthodontics
• /
• v.30 no.6 s.83
• /
• pp.723-730
• /
• 2000

Orthodontic tooth movement requires remodelling of periodontal tissues, especially alveolar bone. Fluoride is known to be a potent inhibitor of osteoclastic bone resorption. The purpose of this study was to examine the effects of a consumption of fluoride on osteoclast numbers appearing on the pressure side of alveolar bones at experimental tooth movement. 40 male rats were exposed to 0, 10, 25 mg/kg/day of sodium fluoride(NaF) in their drinking water for up to 60 days. Orthodontic appliance were activated to mesially tip maxillary first molar with 50-70g. The rats were sacrificed at 1, 2, 4 days after initial activation. The number of osteoclast was counted in a $450\times700\;{\mu}m^2$ area interradicular septum on the pressure side of the maxillary first molar. The results were as fellows, 1. There was significantly different osteoclast number between control group and 25 mg/kg/day group at all measured time. (p<0.05) 2. There was significantly different active bone-resorption area between control group and 25 mg/kg/day group except at 96 hours post activation. (p<0.05) 3. There was slight reduction of active bone- resorption area in control group from 48 hours to 96 hours but in both 10 mg/kg/day group and 25 mg/kg/day group a slight increase was observed from 48 hours to 96 hours.

• Membrane Journal
• /
• v.31 no.1
• /
• pp.16-34
• /
• 2021

Water supplies are decreasing in comparison to increasing clean water demands. Using nanofiltration is one of the most effective and economical methods to meet the need for clean water. Common methods for desalination are reverse osmosis and nanofiltration. However, pristine membranes lack the essential features which are, stability, economic efficiency, antibacterial and antifouling performances. To enhance the properties of the pristine membranes, graphene oxide (GO) is a promising and widely researched material for thin film composites (TFC) membrane due to their characteristics that help improve the hydrophilicity and anti-fouling properties. Modification of the membrane can be done on different layers. The thin film composite membranes are composed of three different layers, the top filtering active thin polyamide (PA) layer, supporting porous layer, and supporting fabric. Forward osmosis (FO) process is yet another energy efficient desalination process, but its efficiency is affected due to biofouling. Incorporation of GO enhance antibacterial properties leading to reduction of biofilm formation on the membrane surface. Pressure retarded osmosis (PRO) is an excellent process to generate clean energy from sea water and the biofouling of membrane is reduced by introduction of GO into the active layer of the TFC membrane. Different modifications on the membranes are being researched, each modification with its own advantages and disadvantages. In this review, modifications of nanofiltration membranes and their composites, characterization, and performances are discussed.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.49 no.2
• /
• pp.127-139
• /
• 2023

In this study, minoxidil, which is well known as a pharmaceutical raw material, and diaminopyrimidine oxide (DAO), which is a cosmetic raw material, were used as active ingredients to evaluate the physical properties of niosomes and compare the skin penetrations of artificial skin. To prepare niosomes of the size of nanoparticles, a high pressure homogenization method was used, and physical properties were evaluated with a zetasizer. The particle size of the noisome including the active ingredient was measured to be 99 to 123 nm according to HLB, and the zeta potential was measured in the range of -60 to -81 mV. Through DSC (differential scanning colorimetry), it was confirmed that minoxidil, a crystalline component, was uniformly dissolved in an amorphous state in niosomes. In order to confirm and compare skin penetration, it was measured by the in vitro Franz diffusion cell method, and the niosome formulation showed 3.4 times higher penetration for minoxidil and 11.1 times higher penetration for DAO than the control gel formulation. In addition, when comparing the skin penetration of minoxidil niosome and DAO niosome, a similar trend was shown, and the penetration amount of DAO was relatively high. The shapes of the niosome formulations with different HLB values were observed using Cryo-TEM, and it was confirmed that vesicles were formed in all of them and that they were intermediate between SUV (small unilamella vesicle) and LUV (large unilamella vesicle). Through this study, minoxidil, an effective drug for hair loss, and DAO, a cosmetic raw material, can be effectively delivered to the skin by encapsulating them in a noisome formulation.

• Korean Chemical Engineering Research
• /
• v.45 no.2
• /
• pp.183-189
• /
• 2007

We have investigated the oxidation of gas phase elemental mercury using dielectric barrier discharge (DBD). In the DBD process, active species such as $O_3$, OH, O and $HO_2$ are generated by collisions between electrons and gas molecules. Search active species convert elemental mercury into mercury oxide which is deposited into the wall of DBD reactor because of its low vapor pressure. The oxidation efficiency of elemental mercury has been decreased from 60 to 30% by increasing the initial concentration of the elemental mercury from 72 to $655{\mu}g/Nm^3$. The gas retention time at the DBD reactor has showed the little effect on the oxidation efficiency. The more oxygen concentration has induced the more oxidation of elemental mercury, whereas there has been no appreciable oxidation within pure $N_2$ discharge. It has indicated that oxygen atom and ozone, generated in air condition determine the oxidation of elemental mercury.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.4
• /
• pp.44-52
• /
• 2003

Shape memory alloys (SMA) are often used in smart structures as active components. Their ability to provide large recovery forces and displacements has been useful in many applications, including devices for artificial muscles, active structural acoustic control, and shape control. Based on the 3-dimensional SMA constitutive equation in this paper, the radial displacement control of externally pressurized circular and semicircular composite cylinders under external pressure with a thin SMA layer bonded on its inner surface or inserted between composite layers in investigated using 3-dimensional finite element analysis. Upon actuation through resistive heating, SMAs start to transform from martensitic into austenitic state, simultaneously recover the prestrain, and thus cause the composite cylinders to go back to their original shapes of the cylinder cross-sections.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.688-688
• /
• 2013

Al-doped ZnO (AZO) thin films have attracted a lot of attention as a cheap transparent conducting oxide (TCO) material that can replace the expensive Sn-doped In2O3. In particular, AZO thin films are widely used as a window layer of chalcogenide-based thin film solar cells such as Cu(In,Ga)Se2 and Cu2ZnSnS4 (CZTS). Mostly important requirements for the window layer material of the thin film solar cells are the high transparency and the low sheet resistance, because they influence the light absorption by the activelayer and the electron collection from the active layer, respectively. In this study, we prepared the AZO thin films by RF magnetron sputtering using a ZnO/Al2O3 (98：2wt%) ceramic target, and the effect of the sputtering condition such as the working pressure, RF power, and the working distance on the optical, electrical, and crystallographic properties of the AZO thin films was investigated. The AZO thin films with optimized properties were used as a window layer of CZTS thin film solar cells. The CZTS active layers were prepared by the electrochemical deposition and the subsequent sulfurization process, which is also one of the cost-effective synthetic approaches. In addition, the solar cell properties of the CZTS thin film solar cells, such as the photocurrent density-voltage (J-V) characteristics and the external quantum efficiency (EQE) were investigated.

• Journal of Hydrogen and New Energy
• /
• v.24 no.2
• /
• pp.160-171
• /
• 2013

$LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ powder for cathode materials in lithium rechargeable batteries was treated by atmospheric plasma containing hydrogen to investigate the relationship between charge/discharge performance and physical/chemical changes of materials. Hydrogen plasma at atmosphere pressure was irradiated on the surface of active materials, and the change for their crystal structure, surface morphology, and chemical composition were observed by XRD, SEM-EDS and titration method, respectively. The crystal structure and surface morphology of $H_2$ plasma-treated powders were not changed but their chemical compositions were slightly varied. For charge/discharge test, $H_2$ plasma affected initial capacity and rate capability of active materials but continuous cycling was not subject to plasma treatment. Therefore, it was observed that $H_2$ plasma treatment affected the surface of materials and caused the change of chemical composition.

• Journal of Biomedical Engineering Research
• /
• v.39 no.1
• /
• pp.36-42
• /
• 2018

The risk of venous thromboembolism (VTE) is known higher in cancer patients and lower incidence in the east country. This study was conducted in order to check the incidence rate of VTE in the Korean high risk patients who are treated in the intensive care unit (ICU), and to verify the correlation of the incidence of VTE and prophylaxis methods. This study was conducted as a retrospective study for 492 cancer patients from April 2011 to December 2014. According to the medical records of subjects, their prophylaxis methods and the incidence of VTE were surveyed and then correlation of them was investigated with statistical methods. 385 patients met the inclusion criteria. VTE occrred in 17 of them (4.4%). The prophylaxis methods are consisted of medical method (136 subjects), mechnical method(33 subjects), and medical & mechnkcal method (124 subjects). VTE occurred in 14 patients (4.8%) from 293 patients (76%) who were given at least one prophylaxis method. From all of 93 patients without prophylaxis, three patients experienced VTE (3.3%). The target patients were high risk in VTE, but the incidence rate of VTE was lower than reported in previous studies. The reason of this is considered that more active prophylaxis intervention was applied to the subjects because of their high risk status. As a result, it is considered that in the high risk patients, it would be effective to apply active and complex prophylaxis intervention for the prevention of VTE.