• Korean Chemical Engineering Research
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• v.53 no.4
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• pp.509-516
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• 2015

We investigated the reduction leaching process of manganese dioxide ore using black locust as reductant in sulfuric acid solution. The effect of parameters on the leaching efficiency of manganese was the primary focus. Experimental results indicate that manganese leaching efficiency of 97.57% was achieved under the optimal conditions: weight ratio of black locust to manganese dioxide ore (WT) of 4:10, ore particle size of $63{\mu}m$, $1.7mol{\cdot}L^{-1}\;H_2SO_4$, liquid to solid ratio (L/S) of 5:1, leaching time of 8 h, leaching temperature of 368 K and agitation rate of $400r{\cdot}min^{-1}$. The leaching rate of manganese, based on the shrinking core model, was found to be controlled by inner diffusion through the ash/inert layer composed of associated minerals. The activation energy of reductive leaching is $17.81kJ{\cdot}mol^{-1}$. To conclude the reaction mechanism, XRD analysis of leached ore residue indicates manganese compounds disappear; FTIR characterization of leached residue of black locust sawdust shows hemicellulose and cellulose disappear after the leaching process.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.115.2-115.2
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• 2012

In this study we have used the data of various instruments onboard the THEMIS spacecraft to study the characteristics of the outer radiation belt during the ascending phase of solar cycle 24. The most astonishing result is that we discovered four long-term (a month or so) periods during which the belt has nearly disappeared. The first disappearance started late 2008, followed by reappearance in ~a month, and three more similar events repeated until early 2010 when the belt has reappeared. This is well revealed at 719 keV electrons, which is the currently available uppermost energy channel from the THEMIS SST observation, but also seen at even lower energies. Overall consistent features were confirmed using the NOAA-POES observations. The vanished belt periods are associated with extremely weak solar wind conditions, low geomagnetic disturbances (in terms of Kp and AE/AL), greatly suppressed wave (ULF and chorus) activities, greatly reduced storm and substorm activities (little source particle supply), and expanded plasmapause locations. The direct observations of such events shed light on the fundamental question of the origin of the radiation belt, which is the main focus of our presentation.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.101.2-101.2
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• 2012

Shocks are ubiquitous in astrophysical plasmas: bow shocks are formed by the interaction of solar wind with planetary magnetic fields, and supernova explosions and jets produce shocks in interstellar and intergalactic spaces. The global morphologies of these shocks are usually described by a set of magnetohydrodynamic (MHD) equations which tacitly assumes local thermal equilibrium, and the resulting Rankine-Hugoniot shock jump conditions are applied to obtain the relationship between the upstream and downstream physical quantities. While thermal equilibrium can be achieved easily in collisional fluids, it is generally believed that collisions are infrequent in astrophysical settings. In fact, shock widths are much smaller than collisional mean free paths and a variety of kinetic phenomena are seen at the shock fronts according to in situ observations of planetary shocks. Hence, both the MHD and kinetic equations have been adopted in theoretical and numerical studies to describe different aspects of the physical phenomena associated with astrophysical shocks. In this paper, we present the results of 3D relativistic particle-in-cell (PIC) simulations for ion-electron plasmas, with focus on the shock structures: when a jet propagates into an unmagnetized ambient plasma, a shock forms in the nonlinear stage of the Weibel instability. As the shock shows the structures that resemble those predicted in MHD systems, we compare the results with those predicted in the MHD shocks. We also discuss the thermalization processes of the upstream flows based on the time evolutions of the phase space and the velocity distribution, as well as the wave spectra analyses.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.279-285
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• 2016

The space radiation dose over air routes including polar routes should be carefully considered, especially when space weather shows sudden disturbances such as coronal mass ejections (CMEs), flares, and accompanying solar energetic particle events. We recently established a heliocentric potential (HCP) prediction model for real-time operation of the CARI-6 and CARI-6M programs. Specifically, the HCP value is used as a critical input value in the CARI-6/6M programs, which estimate the aviation route dose based on the effective dose rate. The CARI-6/6M approach is the most widely used technique, and the programs can be obtained from the U.S. Federal Aviation Administration (FAA). However, HCP values are given at a one month delay on the FAA official webpage, which makes it difficult to obtain real-time information on the aviation route dose. In order to overcome this critical limitation regarding the time delay for space weather customers, we developed a HCP prediction model based on sunspot number variations (Hwang et al. 2015). In this paper, we focus on improvements to our HCP prediction model and update it with neutron monitoring data. We found that the most accurate method to derive the HCP value involves (1) real-time daily sunspot assessments, (2) predictions of the daily HCP by our prediction algorithm, and (3) calculations of the resultant daily effective dose rate. Additionally, we also derived the HCP prediction algorithm in this paper by using ground neutron counts. With the compensation stemming from the use of ground neutron count data, the newly developed HCP prediction model was improved.

• Cross-Cultural Studies
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• v.46
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• pp.143-171
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• 2017

In this paper, we present a morphosyntactic and semantic study of the concessive conjunctive phrase [todavía que] in the Andean and River Plate areas of Latin America. Real Academia $Espa{\tilde{n}}ola$(2009) describes that the adverb todavía occurs in a variety of focus-sensitive environments and specially, in the Andean and River Plate areas, the phrase [todavía que] participates in the concessive constructions and triggers an additive interpretation. It is well known that the Quechuan suffix '-raq' and the Aymaran suffix '-raki' have the meaning of todavía which is characterized as a additive particle. Due to the absence of the paratactic relationship between the mentioned Spanish adverb and those indigenous suffixes, the adverb todavía in [todavía que] is used as a additive focalizer. We assume that these morphosyntactic and semantic properties are derived from the language contact of Quechua-Spanish and Aymara Spanish. Based on this assumption, we will further assume that the etymological peculiarity of todavía as a universal quantifier is closely related to the reading of [todavía que] as a Scalar Additive Concessive Conjunctive Phrase.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.287-295
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• 2023

Iron nanoparticles (Fe-NPs) were synthesized employing Lagenaria siceraria (LS) leaf aqueous extract as a reducing and capping medium to remove methylene blue (MB) dye and have antibacterial properties against G-negative (Escherichia coli) and G-positive bacteria (Staphylococcus aureus). The formation of LS-Fe-NPs (Lagenaria-siceraria-iron-nanoparticles) was confirmed by a change in color from pale yellow to dark brown. Characterization techniques, such as particle size analysis (PSA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), were employed to prove nano spherical particles of size range between 80-100 nm. Phytochemicals and the presence of iron in LS-Fe-NPs nanoparticles were proved by UV-visible spectrophotometry. Further, Fourier transform infrared spectroscopy (FTIR) analysis results confirmed the existence of bioactive molecules in the plants. The magnetic property was analyzed using a vibrating sample magnetometer (VSM), which displayed that the synthesized nanoparticles were superparamagnetic and exhibiting a saturation magnetization of 12.5 emu/g. Synthesized magnetic nanoparticles were used in methylene blue (MB) dye removal through adsorption. About 83% of 100 mg/L MB dye was removed within 120 min at pH 6 with a maximum adsorption capacity of 246.8 mg/g. Antibacterial efficacy of LS-Fe-NPs was screened against G-negative (Escherichia coli) and G-positive bacteria (Staphylococcus aureus), respectively, and found that LS-Fe-NPs were effective against Staphylococcus aureus.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.441-441
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• 2009

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple fabrication process and low coats. The cells use a porous nanocrystalline TiO2 matrix coated with a sensitizer dye that acts as the light-harvesting element. The photo-exited dye injects electrons into the $TiO_2$ particles, and the oxide dye reacts with I- in the electrolyte in regenerative cycle that is completed by the reduction of $I_3^-$ at a platinum-coated counter electrode. Since $TiO_2$ porous film plays a key role in the enhancement of photoelectric conversion efficiency of DSSC, many scientists focus their researches on it. Especially, a high light-to-electricity conversion efficiency results from particle size and crystallographic phase, film porosity, surface structure, charge and surface area to volume ratio of porous $TiO_2$ electrodes, on which the dye can be sufficiently adsorbed. Effective treatment of the photoanode is important to improve DSSC performance. In this paper, to obtain properties of surface and dispersion as nitric acid treated $TiO_2$ photoelectrode was investigate. The photovoltaic characteristics of DSSCs based the electrode fabricated by nitric acid pre-treatment $TiO_2$ materials gave better performances on both of short circuit current density and open circuit voltage. We compare dispersion of $TiO_2$ nanoparticles before and after nitric acid treatment and measured Ti oxidized state from XPS. Low charge transfer resistance was obtained in nitric acid treated sample than that of untreated sample. The dye-sensitized solar cell based on the nitric acid treatment had open-circuit voltage of 0.71 V, a short-circuit current of 15.2 mAcm-2 and an energy conversion efficiency of 6.6 % under light intensity of $100\;mWcm^{-2}$. About 14 % increases in efficiency obtained when the $TiO_2$ electrode was treated by nitric acid.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.37 no.1
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• pp.1-21
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• 2011

This review describes several kinds of emulsification methods for nanoemulsions and the application of nanoemulsions. Nanoemulsion droplet sizes fall typically in the range of 20 ~200 nm and show narrow size distributions. Although most of the publications on either oil-in-water (O/W) or water-in-oil (W/O) nanoemulsions have reported their formation by dispersion or high-energy emulsification methods, an increased interest is observed in the study of nano-emulsion formation by condensation or low-energy emulsification methods based on the phase transitions that take place during the emulsification process. Phase behaviour studies have shown that the size of the droplets is governed by the surfactant phase structure (bicontinuous microemulsion or lamellar) at the inversion point induced by either temperature or composition. Studies on nanoemulsion formation by the phase inversion temperature (PIT) method have shown a relation between minimum droplet size and complete solubilization of the oil in a microemulsion bicontinuous phase independently of whether the initial phase equilibrium is single or multiphase. Due to their small droplet size nanoemulsions possess stability against sedimentation or creaming with Ostwald ripening forming the main mechanism of nanoemulsion breakdown. An application of nanoemulsions is the preparation of nanoparticles using a polymerizable monomer as the disperse phase where nanoemulsion droplets act as nanoreactors, cosmetics and controlled drug delivery. In this review, we mainly focus on the cosmetics.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.2
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• pp.141-151
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• 2013

The nano-surface modification techniques could be classified; internal modifications which enhance surface roughness and porosity in nano level and external modifications as nano particle coating. Nano-modified implant surface has various morphograpies such as nanotube, nanopit, nanonodule and polymorphic structures. Creating surface depends upon preparation method and material, however, there is no standard preparation technique not yet. The nano-modified surfacet is electrochemically stable comparing with the surface modified in micron level. Nano-modified surface has little cytotoxicity, stimulates osteoblast proliferation and differentiation. Moreover, it decreases soft tissue intervention by interrupting the proliferation of fibroblast. Nanostructure has similar size and shape with cells and proteins, consequently leads to good biocompatibility and enhanced osseointegration. However, the actual effect in vivo is limited, due to the distance of effect. Even if nano-modified surface has antibiotic property due to photocatalysis, short duration time makes clinical application questionable. Further investigations should focus on the optimal nano-modified surface, which has many potentials.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.1-6
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• 2002

How is the flow in a rotating impeller. About 35 years have passed since one experimentalist rotating with the impeller. of a huge centrifugal blower made the flow measurements using a hot-wire anemometer (Fowler 1968). Optical measurement methods have great advantages over the intrusive methods especially for the flow measurement in a rotating impeller. One is the optical flow visualization (FV) technique (Senoo, et al., 1968) and the other is the application of laser velocimetry (LV) (Hah and Krain, 1990). Particle image velocimetries (PIVs) combine major features of both FV and LV, and are very attractive due to the feasibility of simultaneous and multi-points measurements (Hayami and Aramaki, 1999). A high-pressure-ratio transonic centrifugal compressor with a low-solidity cascade diffuser was tested in a closed loop with HFC134a gas at 18,000rpm (Hayami, 2000). Two kinds of measurement techniques by image processing were applied to visualize a flow in the compressor. One is a velocity field measurement at the inducer of the impeller using a PIV and the other is a pressure field measurement on the side wall of the cascade diffuser using a pressure sensitive paint (PSP) measurement technique. The PIV was successfully applied for visualization of an unsteady behavior of a shock wave based on the instantaneous velocity field measurement (Hayami, et al., 2002b) as well as a phase-averaged velocity vector field with a shock wave over one blade pitch (Hayami, et al., 2002a. b). A violent change in pressure was successfully visualized using a PSP measurement during a surge condition even though there are still some problems to be overcome (Hayami, et al., 2002c). Both PIV and PSP results are discussed in comparison with those of laser-2-focus (L2F) velocimetry and those of semiconductor pressure sensors. Experimental fluid dynamics (EFDs) are still growing up more and more both in hardware and in software. On the other hand, computational fluid dynamics (CFDs) are very attractive to understand the details of flow. A secondary flow on the side wall of the cascade diffuser was visualized based either steady or unsteady CFD calculations (Bonaiuti, et al.,2002). EFD and CFD methods will be combined to a hybrid method being complementary to each other. Measurement techniques by image processing as well as CFD calculations give a huge amount of data. Then, data mining technique will become more important to understand the flow mechanism both for EFD and CFD.