• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.357-362
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• 2003

The pathway producing imide ring closure during the thermal imidization of poly(amic acid) (PAA) was investigated in detail using a new analytical method, two-dimensional (2D) Raman correlation spectroscopy. The signs of the cross peaks in synchronous spectra provided evidence of the thermal imidization of PAA into PI as the heating temperature increased. The signs of the cross peaks in asynchronous spectra suggested that the imide-related modes changed prior to the amide or carboxylic mode, which indicates that cyclization occurred before the amide proton was abstracted.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.98-104
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• 2002

A study on microstructures of welds for Zircaloy-4 sheath end closure by the resistance upset welding methods was carried out. Two upset welding process variations such as magnetic farce and multi-impulse resistance welding were used. Grain size and microhardness across welds were analysed in terms of welding parameters. Magnetic farce resistance weld with one cycle of unbalanced mode has smaller upset length and $\alpha-grain$ size in heat affected zone than those of multi-impulse resistance weld because of lower heat input and shorter welding time. Heat affected zone formed by two upset resistance welding variations revealed fine Widmanstatten structure or martensitic ${\alpha}'$ structure due to the high heating rate and foster cooling rate. Magnetic force resistance welds showed recrystallized grains before grain growth, whereas multi-impulse resistance welds showed full grain growth.

• Elastomers and Composites
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• v.53 no.2
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• pp.52-56
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• 2018

The present study examines the transformation of dynamic DSC data into the equivalent isothermal data for the formation kinetics of a polyurethane elastomer. The reaction of 2'-dichloro-4,4'-methylenedianiline (MOCA) with a PTMG/TDI-based isocyanate prepolymer was evaluated. DSC measurement was performed in the dynamic scanning mode with several different heating rates to obtain the reaction thermograms. Then, the data was transformed into the isothermal data through a procedure based on Ozawa analysis. The main feature of this procedure was the transformation of $({\alpha}-T)_{\beta}$ curves from dynamic DSC into $({\alpha}-t)_T$ curves using the isoconversional $(t-T)_{\alpha}$ diagram. Validity was discussed for the relationship between the dynamic DSC data and the transformed isothermal results.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.1
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• pp.29-39
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• 2000

A series of tests were performed to verify the transient characteristics of heat pump in heating and cooling mode when operating speed was varied over the 30 to 102Hz. One of the major issues that has not been addressed so far is transient characteristics during speed modulation. The model for cycle simulation has been developed to predict the cycle performance under conditions of decreasing drive frequency and the results of the theoretical study were compared with the results of the experimental study. The simulated results were in good agreement with the experimental result within 10%. The transient cycle migration of the liquid state refrigerant causes significant dynamic change in system. Thus, the migration of refrigerant was the most important factor whenever do experimental results analysis or develop simulation model.

• Macromolecular Research
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• v.16 no.6
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• pp.544-548
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• 2008

An HPLC column with a self-contained temperature control device was constructed for preparative temperature programmed interaction chromatography. Two Peltier plates were attached to a large bore column ($120{\times}22\;mm$ i.d.) and the column temperature was controlled by PID mode feed back control. At a flow rate of 1.5 mL/min, the column temperature could be increased and decreased at a rate as high as $50^{\circ}C/min$ and $10^{\circ}C/min$, respectively, which is much faster than using a column jacket and bath/circulator. The rapid heating and cooling rates allows a high repetition rate of chromatographic fractionation. The performance of the temperature controllable column was demonstrated successfully by the fractionation of homo-polymer precursors from diblock copolymers.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.905-913
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• 2006

The instability curve of a Rijke tube system was obtained accurately by following different paths of heat power and flow-rate for three regions and by defining its locus from the criterion based on the measured sound pressure levels. The unstable limits in the region of flow-rate lower than that at the minimal power are compared with previous data. To observe the effect of turbulence on the unstable limits, inflow turbulence was introduced by placing a bundle of circular cylinders upstream of the heating part ($50). The large-amplitude inflow fluctuation may delay the transition of the chamber acoustic mode to the unstable Bone even at a sufficient power.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.345-346
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• 2010

The HVAC(Heating Ventilation and Air Conditioning) system is only controlled by turn on/turn off operations against to AC 380V input. Therefore, the efficiency of the system is reduced and noise occurs. Also, the blower is shut down at the AC power failure. In this paper, the inverter system with UPS function for the A/C(Air Conditioning) blower is proposed. Proposed inverter system which is powered from the AC and DC voltage can control speed, operation mode, and soft-start time using CAN communication. In case of the CAN communication failure, RS-232 communication could be used to control the hardware directly by the engineer that can solve existing problems. To verify the validity of proposed inverter system, simulations and experiments are carried out.

• Journal of Power Electronics
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• v.17 no.4
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• pp.860-873
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• 2017

The present article reports an analysis and investigation of a direct AC-AC quasi-resonant converter. A bidirectional power device, whose switching frequency is lower than the frequency of the current passing through the load, is used for its realization. The zero voltage switching mode is described when zero voltage on the power device is available by measuring it with the control system. The continuous current in the resonant inductance by switching the power device at zero voltage is considered, and it is characterized by two sub-modes. A mathematical analysis of the processes has been made and comparative results from the computer simulation and experimental study have been brought. The converter can be used in a wide areas of power electronics: induction heating, wireless power transfer, AC-DC converters, etc.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.618-622
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• 1995

We studied the effects of Pt and Cr addition in a new Co-Cr-P-Pt alloy system with the coercivity higher than 2000 Oe even when they were deposited without substrate heating and bias voltage. The coercivity of the films increased from 1000 to 2000 Oe or higher by addition of 12 at.%Pt. The variation of the anisotropy field with increasing Pt content was similar to that of the coercivity. This indicate that the increase of the coercivity might be associated with increase of the anisotropy field with Pt addition. With the addition of Cr, the coercivity of the films increased up to 8 at.%Cr and the coercive squareness of the films decreased. The angular variation of coercivity deviated at a lower angle from domain wall motion mode as the Cr content increases. From these result, it is believed that the grain isolation of the films is enhanced with the addition of Cr.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.17 no.3
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• pp.21-29
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• 2021

In this study, the current regulation of the water source energy, one of the renewable energy, was analyzed, and the improvement plan for the high efficient data center cooling system was suggested. In the improvement plan, the design and construction guidelines of the water source energy system permit to adopt the cooling and heating system with or without heat pump. In addition, it should also include the system operated in the cooling mode only all year-round. The domestic test standards to consider the water source operating conditions should be developed. Especially, it is highly recommended that the test standards to include the system with forced cooling and free cooling modes related with the enhanced data center cooling system adopting the water source energy.