• Korean Journal of Environmental Biology
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• v.34 no.4
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• pp.281-291
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• 2016

Bloom of small centric diatom Stephanodiscus is quite occasional in winter season in temperate freshwater ecosystems. It often leads to degradation of water quality and affects the quality of supplied drinking water. In a previous study, we have found that naphthoquinone (NQ) 4-6 derivate is an effective tool for efficient mitigation of natural S. hantzschii blooms. In the present research, polylactide (PLA) and agar foam were used as immobilized agent for NQ 4-6 to improve the efficiency of NQ 4-6 compound releasing process for its application under various field conditions. Mesocosm experiments at 10 ton scale suggested that the abundance of S. hantzschii was continuously increased in the control and upon treatment of the mesocosm with immobilized NQ 4-6 from PLA and agar foam. Their algicidal activities were 78.8% and 77.1%, respectively, on S. hantzschii after 10 days. In the mesocosm experiments, the dynamics of biotic (bacteria, HNFs, ciliates, zooplankton) and abiotic (water temperature, dissolved oxygen, pH, conductivity, nutrients) factors remained unaffected. They exhibited similar trends in the control and treatment groups. Therefore, the immobilized NQ 4-6 from PLA and agar foam has potential to be used as an alternative algicidal substance to effectively mitigate natural S. hantzschii blooms under various field conditions. In addition, it not only can be used to control S. hantzschii, but also is an effective technique. The immobilized NQ 4-6 showed stable controlled release in desired system.

• Journal of Sensor Science and Technology
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• v.13 no.2
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• pp.96-100
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• 2004

Optical fiber sensors have been used to detect small amounts of chemical species. In this work, a new thin polymer-clad fiber sensor is developed. Polyaniline is chemically synthesized and thin clad layers of the polymer are easily deposited on optical fiber by dip-coating technique. The optical property of polyaniline as a sensing material is analyzed by UV-Vis-NIR. The light source is stabilized He-Ne laser at 635 nm wavelength with 1 mW power. The light power transmitted through the optical fiber is measured with a spectrophotometer. By selecting a fixed incident angle, variation of transmitted light intensity through the optical fiber can be detected as gas molecules absorbed in the polyaniline clad layer. Among the various gases, the fabricated optical fiber sensor shows good sensitivity to $NH_{3}$ gas. The optical fiber sensors was shown more improved properties than polymer based sensors which measure conductivity changes.

• Journal of Powder Materials
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• v.17 no.4
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• pp.319-325
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• 2010

Electrical discharge machining (EDM) is an attractive machining technique but it requires electrically conductive ceramic materials. In this study, Alumina matrix composites reinforced with CNTs were fabricated through CNT purification, mixing, compaction and spark plasma sintering (SPS) processes. $Al_2O_3$ nanocomposites with the different CNT concentrations were synthesized. The mechanical and electrical characteristics of $Al_2O_3$/CNTs composites were examined in order to apply the materials to the EDM process. In addition, micro-EDM using wire electrical discharge grinding (WEDG) was conducted under the various EDM parameters to investigate the machining characteristics of machined hole by Field Emission Scanning Electron Microscope (FE-SEM). The results show that $Al_2O_3$/CNTs 10%Vol. was more suitable than the other materials because high conductivity and large discharge energy caused violent sparks resulting in bad machining accuracy and surface quality.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.11
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• pp.4662-4679
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• 2015

Currently, the leakage of internal information has emerged as one of the most significant security concerns in enterprise computing environments. Especially, damage due to internal information leakage by insiders is more serious than that by outsiders because insiders have considerable knowledge of the system's identification and password (ID&P/W), the security system, and the main location of sensitive data. Therefore, many security companies are developing internal data leakage prevention techniques such as data leakage protection (DLP), digital right management (DRM), and system access control, etc. However, these techniques cannot effectively block the leakage of internal information by insiders who have a legitimate access authorization. The security system does not easily detect cases which a legitimate insider changes, deletes, and leaks data stored on the server. Therefore, we focused on the insider as the detection target to address this security weakness. In other words, we switched the detection target from objects (internal information) to subjects (insiders). We concentrated on biometrics signals change when an insider conducts abnormal behavior. When insiders attempt to leak internal information, they appear to display abnormal emotional conditions due to tension, agitation, and anxiety, etc. These conditions can be detected by the changes of biometrics signals such as pulse, temperature, and skin conductivity, etc. We carried out experiments in two ways in order to verify the effectiveness of the emotional recognition technology based on biometrics signals. We analyzed the possibility of internal information leakage detection using an emotional recognition technology based on biometrics signals through experiments.

• Water for future
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• v.22 no.1
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• pp.81-90
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• 1989

A numerical simulation technique of three-dimensional finite difference model is developed to study the groundwater flow system in Dejima, an upland area which faces Kasumigaura Lake. For general perspectives of the groundwater flow system, a steady state three-dimensinal model is simulated. For the sedimentary mud formations which are found in the representative formation, three situations where the horizontal permeability is equal to 10 times and 100 times of the vertical one. The finite difference grid used in the simulation has 60$\times$50$\times$30=90,000 nodes. A converged solution with a tolerance of 0.001 meter of hydraulic head is set. Having determined the flow net by using a steady state three-dimensional model, the results for the three cases of hydraulic conductivity are compared with the results of the tracer methods (Bae and Kayane, 1987). With the aid of four representative vertical cross-sections, groundwater flow systems in the study area are assumed. The results of these are reasonally good comparable with the results of the basin yield and thd recharge-discharge distribution 8.

• Fibers and Polymers
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• v.6 no.2
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• pp.121-126
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• 2005

Semicrystalline poly(ethylene terephthalate) (cPET)/amorphous poly(ethylene terephthalate) with isophthalic acid (aPET) blends with 100/0, 75/25, 50/50, 25/75, and 0/100 by weight ratios were dissolved in a mixture of trifluoroacetic acid (TFA)/methylene chloride (MC) (50/50, v/v) and electrospun via the electrospinning technique. Solution properties such as solution viscosity, surface tension and electric conductivity were determined. The solution viscosity slightly decreased as aPET content increased, while there was no difference in surface tension with respect to aPET composition. The characteristics of the electro spun cPET/aPET blend nonwovens were investigated in terms of their morphology, pore size and gas permeability. All these measurements were carried out before and after heat treatment for various blend weight ratios. The average diameter of the fibers decreased with increasing aPET composition due to the decrease in viscosity. Also, the morphology of the electrospun cPET/aPET blend nonwovens was changed by heat treatment. The pore size and pore size distribution varied greatly from a few nanometers to a few microns. The gas permeability after heat treatment was lower than that before heat treatment because of the change of the morphology.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1357-1368
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• 1995

Nasigels of composition Na0.75Zr2PSi2O12 and Na3Zr2PSi2O12 have been synthesized by the sol-gel technique using metal alkoxide precursors. The monolithic dry gels of Na0.75Zr2PSi2O12 with no crack have been prepared by the control of the shrinkage rte, but gels of Na3Zr2PSi2O12 were impossible to prepare without cracking. The gels treated up to 80$0^{\circ}C$ led to the formtion of glass but the glasses were converted to the crystalline phases at above this temperature. Crystaline phases precipitated from the Na0.75Zr2PSi2O12 glass were NASICON-like phase, Na2Si2O5, and free Zirconia. Phase that precipitated from the Na3Zr2PSi2O12 was only rhombohedral NASICON. For Na0.75Zr2PSi2O12 gels, framework of PO4 tetrahedra and SiO4(PO4) tetrahedra formed at low temperature but changed to that of SiO4 and SiO4(PO4) tetrahedras as it were crystallized. In the case of Na3Zr2PSi2O12 gel, framework of isolated PO4 and SiO4 tetrahedras formed at low temperature but changed to SiO4(PO4) tetrahedra framework which usually formed in the NASICON crystal after crystallization at high temperature. The gels treated up to 80$0^{\circ}C$ contained the residual water. The ionic conduction was attributed to the motion of proton and Na+ ion at low (up to 150~20$0^{\circ}C$) and high temperatures, respectively. As the temperature of heat treatment increased, ionic conductivity gradaully increased with the extent of precipitation of crystalline phase.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.659-659
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• 2013

Recently, graphene has been intensively studied due to the fascinating physical, chemical and electrical properties. It shows high carrier mobility, high current density, and high thermal conductivity compare with conventional semiconductor materials even it has single atomic thickness. Especially, since graphene has fantastic electrical properties many researchers are believed that graphene will be replacing Si based technology. In order to realize it, we need to prepare the large and uniform graphene. Chemical vapor deposition (CVD) method is the most promising technique for synthesizing large and uniform graphene. Unfortunately, CVD method requires transfer process from metal catalyst. In transfer process, supporting polymer film (Such as poly (methyl methacrylate)) is widely used for protecting graphene. After transfer process, polymer layer is removed by organic solvents. However, it is impossible to remove it completely. These organic residues on graphene surface induce quality degradation of graphene since it disturbs movement of electrons. Thus, in order to get an intrinsic property of graphene completely remove of the organic residues is the most important. Here, we introduce modified wet graphene transfer method without PMMA. First of all, we grow the graphene from Cu foil using CVD method. And then, we deposited several metal films on graphene for transfer layer instead of PMMA. Finally, we fabricate graphene FET devices. Our approaches show low defect density and non-organic residues in comparison with PMMA coated graphene through Raman spectroscopy, SEM and AFM. In addition, clean graphene FET shows intrinsic electrical characteristic and high carrier mobility.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1133-1137
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• 2011

A novel technique for the fabrication of a glass micropipette-based thermal sensor was developed utilizing inexpensive thermocouple materials. Thermal fluctuation with a resolution of ${\pm}0.002$ K was measured using the fabricated thermal probe. The sensors comprise unleaded low-melting point solder alloy (Sn) as a core metal inside a borosilicate glass pipette coated with a thin film of Ni, creating a thermocouple junction at the tip. The sensor was calibrated using a thermally insulated calibration chamber, the temperature of which can be controlled with a precision of ${\pm}0.1$ K and the thermoelectric power (Seebeck coefficient) of the sensor was recorded from 8.46 to $8.86{\mu}V$/K. The sensor we have produced is both cost-effective and reliable for thermal conductivity measurements of micro-electromechanical systems (MEMS) and biological temperature sensing at the micron level.

• Journal of the Korean Electrochemical Society
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• v.20 no.3
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• pp.49-54
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• 2017

We develop a ceramic composite separator prepared by coating $ZrO_2$ nanoparticles with a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer on a polyvinyl alcohol (PVA) mechanical support prepared by electrospinning technique to improve thermal properties. The gurley number of the ceramic composite separator shows much lower value than that of a PE separator even though it possesses the polymeric coating layer with ceramic nanoparticles. In addition, the proposed sample shows higher electrolyte uptake than PE separator, leading to enhancing the ionic conductivity of the proposed sample and, by extension, the rate discharge properties of lithium ion batteries. Thermal stability of the ceramic composite separator is dramatically improved without any degradation in electrochemical performance compared to the performance of conventional PE separators.