• Progress in Superconductivity
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• v.7 no.1
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• pp.6-10
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• 2005

We have studied feasibility of single-layer second-order $high-T_c$ SQUID gradiometers in magnetocardiography. We have measured human cardiomagnetic signals using a short-baseline (5.8 mm) single-layer second-order YBCO gradiometer in partially shielded environments. The gradiometer has an overall size of $17.6\;mm{\times}6\;mm$ and contains three parallel-connected pickup coils which are directly coupled to a step-edge junction SQUID. The gradiometer showed an unshielded gradient noise of $0.84\;pT/cm^2/Hz^{1/2}$ at 1 Hz, which corresponds to an equivalent field noise of $280\;fT/Hz^{1/2}$. The balancing factor was $10^3$. Based on the same design rules as the short-baseline devices, we have studied fabrication of 30 mm-long baseline gradiometers. The devices had an overall size of $70.2\;mm{\times}10.6\;mm$ with each pickup coil of $10\;mm{\times}10\;mm$ in outer size. As Josephson elements we made two types of submicron bridges, which are variable thickness bridge (VTB) and constant thickness bridge (CTB), from $3\;{\mu}m-wide$ and 300 nm-thick YBCO lines with a thin layer of Au on top by using a focused ion beam (FIB) patterning method. VTB was 300 nm wide, 200 nm thick, 30 nm long with Au removed and CTB 100 nm wide and 30 nm long. In temperature-dependent critical currents, $I_c(T)$, VTB showed an nonmetallic barrier-type behavior and CTB an SNS behavior. We believe that those characteristics are ascribed to naturally formed grain boundaries crossing the bridges.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.8
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• pp.153-165
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• 1995

The design procedure of a GaAs/AlGaAs semiconductor matrix optical switch is presented for a simplified tree architecture in the viewpoint of optical loss. A low loss, 0.537 dB/cm, pin type substrate is designed by considering the loss due to imputity doping at 1.3 $\mu$m wavelength. The operating voltage and the device length of a reversed ${\Delta}{\beta}$ electro-optic directional coupler(EODC) swith which is a cross-point device of the 4${\times}$4 matrix optical switch and the bending loss of rib waveguide are caculated as functions of waveguide parameters and bending parameters. There is an optimum bending radius for some waveguide parameters. It is recommened that higher optical confinement conditions such as wide waveguide width and higher rib-height should be chosen for structural parameters of a low loss and a process insensitive 4${\times}$4 matris optical switch. A 4${\times}$4 optical matrix switch which has a 3 dB loss and a 12 volt operating voltage is designed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.7-7
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• 2009

Lead telluride (PbTe) is a very promising thermoelectric material due to its narrow band gap (0.31 eV at 300 K), face-centered cubic structure and large average excitonic Bohr radius (46 nm) allowing for strong quantum confinement within a large range of size. In this work, we present the thermoelectric properties of individual single-crystalline PbTe nanowires grown by a vapor transport method. A combination of electron beam lithography and a lift-off process was utilized to fabricate inner micron-scaled Cr (5 nm)/Au (130 nm) electrodes of Rn (resistance of a near electrode), Rf (resistance of a far electrode) and a microheater connecting a PbTe nanowire on the grid of points. A plasma etching system was used to remove an oxide layer from the outer surface of the nanowires before the deposition of inner electrodes. The carrier concentration of the nanowire was estimated to be as high as $3.5{\times}10^{19}\;cm^{-3}$. The Seebeck coefficient of an individual PbTe nanowire with a radius of 68 nm was measured to be $S=-72{\mu}V/K$ at room temperature, which is about three times that of bulk PbTe at the same carrier concentration. Our results suggest that PbTe nanowires can be used for high-efficiency thermoelectric devices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.486-490
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• 2012

$La_{7.33}Bi_2(SiO_4)_6O_2$ specimens were fabricated by standard solid-state synthesis route for solid oxide electrolytes. The calcined powders exhibited uniform particles with a mean particle size of about $28{\mu}m$. The room-temperature structure of $La_{7.33}Bi_2(SiO_4)_6O_2$ specimens was analyzed as hexagonal, space group P63 or P63/m, and the unit cell volume increased with increase a sintering temperature. The specimens sintered at $1,175^{\circ}C$ showed X-ray patterns of homogeneous apatite single phase without the second phase such as $La_2Si_2O_7$ and $La_2SiO_5$. The specimen sintered at $1,175^{\circ}C$ showed the maximum sintered density of 5.49 $g/cm^3$. Increasing the sintering temperature, total conductivities increased, activation energy decreased and the values were $1.98{\times}10^{-5}Scm-1$ and 1.23 eV, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.601-607
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• 2016

Piezoelectric thick films of soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material (S55) were fabricated using a conventional tape casting method. Ag-Pd electrodes were printed on the piezoelectric film at room temperature and all 5 layered films with a dimension of $12mm{\times}16mm$ were successfully laminated for a multi-layered piezoelectric ceramic actuator. The laminated specimens were co-fired at $1,100^{\circ}C$ for 1 h. A flat layered and dense microstructure was obtained for the $112{\mu}m$ thick piezoelectric actuator after sintering process. Thereafter, a prototype piezoelectric speaker was fabricated using the multi-layered piezoelectric ceramic actuator which can operate as a bimorph. Its SPL (sound pressure level) characteristic was also evaluated for speaker application. Frequency response revealed that the output SPL with a root mean square voltage of 10 V increased gradually to the highest peak of 87.5 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (${\leq}20kHz$) at a distance of 10 cm, implying that the fabricated piezoelectric speaker is potential for speaker applications.

• Particle and aerosol research
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• v.8 no.2
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• pp.89-95
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• 2012

Spherical mesoporous silica particles, of which main pore diameter was 3.8 nm, were successfully prepared by spray pyrolysis from aqueous silicic acid. The effect of precursor concentration, reaction temperature, and the addition of urea and PEG on the particle diameter and pore properties such as pore diameter, total pore volume, and specific surface area were investigated by using FE-SEM, particle size analyzer, and nitrogen absorption-desorption analysis. With an increase of the precursor concentration from 0.2 M to 0.7 M, the average particle diameter, total pore volume, and specific surface area of the porous silica particles increased from 0.56 to $0.96\;{\mu}m$, 0.434 to $0.486\;cm^3/g$, 467.8 to $610.4\;m^2/g$, respectively. Within the temperature range $(600\;^{\circ}C{\sim}800\;^{\circ}C)$, there was no significant difference in the pore diameter, total pore volume, and specific surface area. In addition, the addition of urea as an expansion aid led to slight increases in particle diameter, pore diameter, and specific surface area. However, when the polyethylene glycol (PEG) as an organic template was used, the total pore volume of porous particles increased dramatically.

• Progress in Medical Physics
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• v.27 no.4
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• pp.272-276
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• 2016

To investigate the optimum x-ray tube design for the dental radiology, factors affecting x-ray beam characteristics such as tungsten target thickness and anode angle were evaluated. Another goal of the study was to addresses the anode heel effect and off-axis spectra for different target angles. MCNPX has been utilized to simulate the diagnostic x-ray tube with the aim of predicting optimum target angle and angular distribution of x-ray intensity around the x-ray target. For simulation of x-ray spectra, MCNPX was run in photon and electron using default values for PHYS:P and PHYS:E cards to enable full electron and photon transport. The x-ray tube consists of an evacuated 1 mm alumina envelope containing a tungsten anode embedded in a copper part. The envelope is encased in lead shield with an opening window. MCNPX simulations were run for x-ray tube potentials of 70 kV. A monoenergetic electron source at the distance of 2 cm from the anode surface was considered. The electron beam diameter was 0.3 mm striking on the focal spot. In this work, the optimum thickness of tungsten target was $3{\mu}m$ for the 70 kV electron potential. To determine the angle with the highest photon intensity per initial electron striking on the target, the x-ray intensity per initial electron was calculated for different tungsten target angles. The optimum anode angle based only on x-ray beam flatness was 35 degree. It should be mentioned that there is a considerable trade-off between anode angle which determines the focal spot size and geometric penumbra. The optimized thickness of a target material was calculated to maximize the x-ray intensity produced from a tungsten target materials for a 70 keV electron energy. Our results also showed that the anode angle has an influencing effect on heel effect and beam intensity across the beam.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.6
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• pp.721-730
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• 2017

This study determined the optimal mixing ratio of functional materials to enhance the functionality of batter for fish cutlets. An optimal mixing ratio of the hiziki Hizikia fusiformis, fig fruit Ficus carica L. and pear Pyrus pyrifolia Niitaka extracts (HFP extract) of 3:1:1 was found. The physicochemical properties of the mixture were as follows: total phelonic contents of $1187.29{\pm}41.55mg/L$, 1,1-diphenyl-2-picryhydrazyl (DPPH) radical scavenging activity of $61.50{\pm}2.33%$, ascorbic acid content of $23.68{\pm}0.02g/100g$, ${\beta}-carotene$ content of $51{\pm}3.92{\mu}g/100g$, and sugar content of $12.7{\pm}0.1Brix^{\circ}$. A mixture of the extract, Korean herbal powder, and wheat flour was prepared as the fish cutlet batter. The fish cutlet prepared with the batter had a hardness of $166-202g/cm^2$ and Hunter's color scale values L of $31.14{\pm}2.1$ to $34.62{\pm}1.3$, a of $-4.89{\pm}0.21$ to $-2.26{\pm}0.19$ and b of $-20.65{\pm}2.65$ to $28.93{\pm}3.14$. The FRAP (ferric reducing antioxidant power) and VBN (volatile basic nitrogen) of the fish cutlets were measured to evaluate functionality and determine the optimal mixing ratio for cold storage at $-12^{\circ}C$, $-18^{\circ}C$, and $-24^{\circ}C$. The optimum mixture ratio of extracts /Korean herbal powder/ wheat flour was 1:6:3.

• KCID journal
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• v.14 no.2
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• pp.214-224
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• 2007

This study was carried out to investigate of water quality and irrigation water use possibility of reservoirs near Saemangeum for upland and horticultural fields. Water samples were taken at 6 reservoirs for 5 months from June, 2006 to November, 2006. The water temperature, pH, EC, EC, chlorophyll - a of 6 reservoirs were ranged 8.7-$31.2^circC$, 6.9-9.2, 73.0-637.0$\mu$S/cm, 0.9-443.2mg/$m^3$, respectively. The concentration of DO, BOD, COD, T-N, T-P and SS were ranged 5.7-11.7mg/L, 0.5-8.9mg/L, 2.9-18.0mg/L, 0.07-6.52mg/L, 0.002-0.406mg/L, 0.5-54.0mg/L Also, storage ratio and storage capacity of Mije reservoir, Okgu reservoir, Oknyeo reservoir, Neungje reservoir were decreased between June and April, but those of Oksan reservoir was kept high during irrigation period. Water supply of reservoirs was 4,474,100$m^3$(Oksan), 6,165,900$m^3$(Mije), 13,209,900$m^3$(Okgu), 4,675,600$m^3$(Oknyeo), 7,682,000$m^3$(Neungje), 19,231,000$m^3$(Cheongho) in 2006, respectively. It is resevoirs for upland and horticultural fields that use main irrigation water resources before Saemanguem fresh-water lake development, and use assistance irrigation water resources in emergency after Saemanguem fresh-water lake development. In the meantime, for continuous use of reservoir as irrigation water resource for upland and horticultural fields, we must examine about surplus water capacity, and need investigation about supply possibility of irrigation water, condition of irrigation water, water quality.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.9
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• pp.5371-5374
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• 2013

Objective: Photodynamic therapy (PDT) is an emerging therapeutic procedure suitable for the treatment of cervical cancer. However, the side effects of PDT are severe, including skin ulceration, so we designed an experiment to examine the effects of multiple low-dose photodynamic therapy of 5, 10, 15, 20-tetrakis(1-methylpyridinium-4-yl) porphyrin (Tmpyp4) on tumour growth by utilizing a model in nude mice implanted with Hela cervical cancer cells. Materials and Methods: Female BALB/c nude mice (aged 5-6 weeks, weighing 18-20 g) were used. Hela cervical cancer cells were injected subcutaneously ($1{\times}10^7cells/200{\mu}L$). Ten days after injection, the mice were divided into three groups (n=6), the A group of controls without any treatment, the B group receiving a single-treatment with Tmpyp4 (10 mg/kg, intratumor injection) and irradiation (blue laser, $108J/cm^2$), and the C group given three-treatments with Tmpyp4 (10 mg/kg, intratumor injection) and irradiation at intervals of two days. After starting treatment, tumours were measured every two days, to assess growth. At 2 weeks after the last treatment of C group, tumour tissue and organs were collected from each mouse to evaluate tumor histology and organ damage. Results: Tumour growth in C group was significantly inhibited compared with A and B groups (P<0.05), without any injury to the skin and internal organs. Conclusion: Our novel findings demonstrated that multiple low-dose photodynamic therapy of Tmpyp4 could inhibit cervical cancer growth significantly with no apparent side effects.