• Smart Structures and Systems
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• v.14 no.5
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• pp.901-916
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• 2014

Magnetorheological (MR) fluid is one of the field-responsive fluids that is of interest to many researchers due to its high yield stress value, which depends on the magnetic field strength. Similar to electrorheological (ER) fluid, the combination of working modes is one of the techniques to increase the performance of the fluids with limited focus on MR fluids. In this paper, a novel MR testing cell incorporated with valve, shear and squeeze operational modes is designed and constructed in order to investigate the behaviour of MR fluid in combined mode. The magnetic field distribution in the design concept was analyzed using finite element method in order to verify the effective areas of each mode have the acceptable range of flux density. The annular gap of valve and shear were fixed at 1 mm, while the squeeze gap between the parallel circular surfaces was varied up to 20 mm. Three different coil configurations, which were made up from 23 SWG copper wires were set up in the MR cell. The simulation results indicated that the magnetic field distributed in the squeeze gap was the highest among the other gaps with all coils were subjected to a constant applied current of 1 A. Moreover, the magnetic flux densities in all gaps were in a good range of magnitude based on the simulations that validated the proposed design concept. Hence, the 3D model of the MR testing cell was designed using Solidworks for manufacturing processes.

• BMB Reports
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• v.38 no.5
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• pp.624-631
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• 2005

Tuberculosis, caused by Mycobacterium tuberculosis, continues to be one of the main diseases to mankind. It is urgent to discover novel drug targets for appropriate antimicrobial agents against this human pathogen. The shikimate pathway is onsidered as an attractive target for the discovery of novel antibiotics for its essentiality in bacteria and absence in mammalian cells. The Mycobacterium tuberculosis aroE-encoded shikimate dehydrogenase was cloned, expressed and purified. Sequence alignment analysis shows that shikimate dehydrogenase of Mycobacterium tuberculosis exhibit the pattern of G-X-(N/S)-V-(T/S)-X-PX-K, which is highly conserved within the shikimate dehydrogenase family. The recombinant shikimate dehydrogenase spectrum determined by CD spectroscopy showed that the percentages for $\alpha$-helix, $\beta$-sheet, $\beta$-turn, and random coil were 29.2%, 9.3%, 32.7%, and 28.8%, respectively. The enzymatic characterization demonstrates that it appears to be fully active at pH from 9.0 to 12, and temperature $63^{\circ}C$. The apparent Michaelis constant for shikimic acid and $NADP^+$ were calculated to be about $29.5\;{\mu}M$ and $63\;{\mu}M$. The recombinant shikimate dehydrogenase catalyzes the substrate in the presence of $NADP^+$ with an enzyme turnover number of $399\;s^{-1}$. Zymological studies suggest that the cloned shikimate dehydrogenase from M. tuberculosis has a pretty activity, and the work should help in the discovery of enzyme inhibitors and further of possible antimicrobial agents against Mycobacterium tuberculosis.

• Composites Research
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• v.12 no.6
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• pp.22-30
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• 1999

Since the surface diffusion processed $Nb_3Sn$ superconducting tape has the advantage of having large overall critical current density. it is used for the construction of open type MRI superconducting magnets. However one of the disadvantages of this tape is that $Nb_3Sn$ compound often exhibited multiple cracking due to its intrinsic brittleness when subjected to mechanical loading such as bending and winding during the fabrication process for superconducting coil. This will eventually cause the severe degradation of critical current density. Therefore it is important to understand the microscopic deformation behavior of this kind of superconducting tape under the mechanical loading.In this study, acoustic emission(AE) was used to clarify microscopic deformation behavior at room temperature for $Nb_3Sn$ superconducting tape which was strengthened and stabilized with copper. For this purpose, special attention was paid to AE characteristics including AE event, energy, and amplitude distribution which were associated with microscopic mechanism of deformation of $Nb_3Sn$ superconducting tape under tensile load.

• Journal of the Korean Magnetics Society
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• v.25 no.2
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• pp.58-65
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• 2015

This paper deals with the generating characteristic analysis of permanent magnet linear generator (PMLG) with double-sided Halbach magnet array mover and three phases concentrated stator windings by using analytical method. On the basis of a magnetic vector potential and Maxwell's equations, governing equations are obtained, and magnetization modeling for Halbach magnet array is performed analytically by using the Fourier series. And then, we obtain electrical parameters such as back-EMF constant, resistance, and coil inductance based on magnetic field calculations. Finally, analytical results for generating performance are confirmed by comparing with finite element analysis results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.10
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• pp.387-393
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• 2016

A ground source heat pump system maintains a constant efficiency due to its stable heat source and radiant heat temperature which provide a more effective thermal performance than that of the air source heat pump system. As an eco-friendly renewable energy source, it can reduce electric power and carbon dioxide. In this study, we analyzed one year of data from a web based remote monitoring system to estimate the thermal performance of GSHP with the capacity of 3RT, which is installed in a low energy house located in Daejeon, Korea. This GSHP system is a hybrid system connected to a solar hot water system. Cold and hot water stored in a buffer tank is supplied to six ceiling cassette type fan coil units and a floor panel heating system installed in each room. The results are as follows. First, the GSHP system was operated for ten minutes intermittently in summer in order to decrease the heat load caused by super-insulation. Second, the energy consumption in winter where the system was operated throughout the entire day was 7.5 times higher than that in summer. Moreover, the annual COP of the heating and cooling system was 4.1 in summer and 4.2 in winter, showing little difference. Third, the outlet temperature of the ground heat exchanger in winter decreased from $13^{\circ}C$ in November to $9^{\circ}C$ in February, while that in summer increased from $14^{\circ}C$ to $17^{\circ}C$ showing that the temperature change in winter is greater than that in summer.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.1
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• pp.41-46
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• 2017

Magnetically levitated (Maglev) vehicles maintain a constant air gap between guideway and car bogie, and thereby achieves non-contact riding. Since the straightness and the flatness of the guideway directly affect the stability of levitation as well as the ride comfort, it is necessary to monitor the status of the guideway and to alert the train operators to any abnormal conditions. In order to develop a signal processing algorithm that extracts guideway irregularities from sensor data, virtual testing using a simulation model would be convenient for analyzing the exact effects of any input as long as the model describes the actual system accurately. Simulation model can also be used as an estimation model. In this paper, we develop a state-space dynamic model of a maglev vehicle system, running on the guideway that contains jumps. This model contains not only the dynamics of the vehicle, but also the descriptions of the power amplifier, the anti-aliasing filter and the sampling delay. A test rig is built for the validation of the model. The test rig consists of a small-scale maglev vehicle, tracks with artificial jumps, and various sensors measuring displacements, accelerations, and coil currents. The experimental data matches well with those from the simulation model, indicating the validity of the model.

• 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.

• Microbiology and Biotechnology Letters
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• v.9 no.3
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• pp.165-171
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• 1981

The penicillin amidase from Escherichia coli (ATCC 9637) was immobilized by entrappment in gelatin and DEAE-cellulose mixture cross-linked with glutaraldehyde, and the kinetics in a differential column reactor was studied. The optimal operating condition of a differential reactor was reasonably met when the enzyme loading was 1g, and 30 mM substrate solution in 0.1 M phosphate buffer (pH 8.0) was fed at flow rate 4$m\ell$/min and 4$0^{\circ}C$. The optimal pH and temperature were found to be 8.0 and 55$^{\circ}C$, respectively. The Michaelis-Menten constant was 4.8 mM while the maximum velocity was 308 units/g of the immobilized enzyme under the condition of the differential reactor. The effect of substrate inhibition disappeared in the immobilized enzyme preparation. The differential reactor was proved to be good for studying the true kinetics since the pH drop and the external diffusional resistance could be eliminated.

• Journal of the Korean Magnetics Society
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• v.11 no.1
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• pp.38-44
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• 2001

The magnetic field standard below 1 mT with the resolution of 0.26 nT has been established. Earth magnetic field (EMF) is compensated automatically down to 0.1 nT/10 min. by a closed feedback system with Cs optical pumping magnetometer and 3-axis Helmholtz coils in nonmagnetic facilities. A multi-layer precision solenoid with the optimized single-current method generates the uniform magnetic field better than 1.0$\times$10$\^$-7/ within $\pm$ 1 cm region at its center. The coil constant of solenoid determined from Helium optical pumping magnetometer is 1.231 058 9 mT/A, and temperature coefficient is 0.38 nT/$\^{C}$. This standard system is used for calibration of low field magnetometers and testing relates to low field.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.201-206
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• 2004

The AC-DC magnetic field standard systems were constructed for the calibration of magnetometers for low magnetic field and the tests for low magnetic field characteristics of sensors and materials. In the range of 1 mT, the expanded uncertainty of dc is 8${\times}$10$\^$-6/, ac uncertainties are 0.16% in 0.1～1 kHz, 0.26% in 1～5 kHz, and 0.44% in 5～20 kHz. We have been participated in international key comparison(KC) to achieve the equality and the mutual agreement between standard institutes for the results of calibrations and tests. KRISS participating in ac-dc magnetic flux density of KC got equal level of uncertainty results compare with the advanced nations. It confirm that measurement ability of magnetic flux density is high level in the world.