• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.485-492
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• 2012

Dense and single phase $BiFeO_3$ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of ${\approx}3{\mu}m$ by conventional sintering process. A relative density of ${\approx}96%$ with average grain size $7.3{\mu}m$ was obtained when the powder compacts were sintered at $850^{\circ}C$ even for a shorter duration of 10 min. In contrast, densification barely occurred at $800^{\circ}C$ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at $850^{\circ}C$ for 12 h showed enhanced electrical properties with leakage current density of $4{\times}10^{-7}A/cm^2$ at 1 kV/cm, remnant polarization $2P_r$ of $8{\mu}C/cm^2$ at 20 kV/cm, and minimal dissipation factor (tan ${\delta}$) of ~0.025 at $10^6$ Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.7
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• pp.1379-1385
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• 2009

We propose a low-power and high-speed client receiver for a mobile display digital interface (MDDI) newly in this paper. The low-power receiver is designed such that bias currents, sink and source currents, are insensitive to variations of power supply, process, temperature, and common-mode input voltage (VCM) and is able to operate at a rate of 450Mbps or above under the conditions of a power supply range of 3.0 to 3.6Vand a temperature range of -40 to 85$^{\circ}$C. And it is confirmed by a simulation result that the current dissipation is less than 500${\mu}$A. A test chip is manufactured with the Magna chip 0.35${\mu}$m CMOS process. When a test was done, the data receiver and data recovery circuits are functioning normally.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.395-406
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• 2020

Many prefabricated concrete frame joints have been proposed, and most of them showed good seismic performance. However, there are still some limitations in the proposed fabricated joints. For example, for prefabricated prestressed concrete joints, prefabricated beams and prefabricated columns are assembled as a whole by the pre-stressed steel bar and steel strand in the beams, which brings some troubles to the construction, and the reinforcement in the core area of the joints is complex, and the mechanical mechanism is not clear. Based on the current research results, a new type of fabricated joint of prestressed concrete beams and confined concrete columns is proposed. To study the seismic performance of the joint, the quasi-static test is carried out. The test results show that the nodes exhibit good ductility and energy dissipation. According to the experimental fitting method and the "fixed point pointing" law, the resilience model of this kind of nodes is established, and compared with the experimental results, the two agree well, which can provides a certain reference for elasto-plastic seismic response analysis of this type of structure. Besides, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.645-650
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• 2003

The microstructure and electrical characteristics of $Pr_{6}$ $O_{11}$ -based ZnO varistor ceramics composed of $ZnO-Pr_{6}$ $O_{ 11}$/$-CoO-Cr_2$$O_3$-$Dy_2$$O_3$-based ceramics were investigated with $Dy_2$$O_3$content in the range of 0.0∼2.0 mol%. As $Dy_2$$O_3$content was increased, the average grain size was decreased in the range of 18.6∼4.7 $\mu\textrm{m}$ and the density of the ceramic was decreased in the range of 5.53∼4.34 g/㎤. While, the varistor voltage was increased in the range of 39.4∼436.6 V/mm and the nonlinear exponent was in the range of 4.5∼66.6 with increasing $Dy_2$$O_3$content. The addition of $Dy_2$$O_3$highly enhanced the nonlinear properties of varistors, compared with the varistor without $Dy_2$$O_3$. In particular, the varistor with $Dy_2$$O_3$ content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 66.6 and the leakage current is 1.2 $\mu\textrm{A}$. The donor concentration and the density of interface states were decreased in the range of $(4.19∼0.33) ${\times}$10^{18}$ //㎤ and $(5.38∼1.74) ${\times}$10^{12}$ $\textrm{cm}^2$, respectively, with increasing $Dy_2$$O_3$content. The minimum dissipation factor of 0.0302 was obtained from 0.5mol% $Dy_2$$O_3$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.4
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• pp.691-698
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• 2008

This paper describes a 3.3V 10 bit CMOS digital-to-analog converter with a divided architecture of a 7 MSB and a 3 LSB, which uses an optimal Thermal-to-Binary Decoding method with monotonicity, glitch energy. The output stage utilizes here implements a return-to-zero circuit to obtain the dynamic performance. Most of D/A converters in decoding circuit is complicated, occupies a large chip area. For these problems, this paper describes a D/A converter using an optimal Thermal-to-Binary Decoding method. the designed D/A converter using the CMOS n-well $0.35{\mu}m$ process0. The experimental data shows that the rise/fall time, settling time, and INL/DNL are 1.90ns/2.0ns, 12.79ns, and a less than ${\pm}2.5/{\pm}0.7\;LSB$, respectively. The power dissipation of the D/A converter with a single power supply of 3.3V is about 250mW.

• Earthquakes and Structures
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• v.13 no.2
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• pp.151-164
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• 2017

This article aims to investigate the possible retrofitting of a deficient building with soft story failure mode by connecting it to an adjacent building which is designed based on current code with friction dampers at all floors. Low cost and high performance reliability along with significant energy dissipation pertaining to stable hysteretic loops may be considered in order to choose the proper damper for connecting adjacent buildings. After connecting two neighbouring floors by friction dampers, the sliding forces of dampers at various stories are set in two arrangements: uniform sliding force and then variable sliding force. In order to account for the stochastic nature of the seismic events, incremental dynamic analyses are employed prior and after the installation of the friction dampers at the various floors. Based on these results, fragility curves and mean annual rate of exceedance of serviceability and ultimate limit states are obtained. The results of this study show that the collapse mode of the deficient building can affect the optimum arrangement of sliding forces of friction dampers at Collapse Prevention (CP) performance level. In particular, the Immediate Occupancy (IO) performance level is not tangible to the sliding force arrangement and it depends solely on sliding force value. Generally it can be claimed that this rehabilitation scheme can turn the challenge of pounding two adjacent buildings into the opportunity of dissipating a large amount of the seismic input energy by the friction dampers, thus improving significantly the poor seismic performance of the deficient structure.

• Journal of the Society of Disaster Information
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• v.15 no.1
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• pp.84-97
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• 2019

Purpose: The consolidation settlement of soft ground is dependent on the distribution of pore water pressure which is also affected by hydraulic conductivities (boundary condition) of layers, thickness of clayey soil layer and surcharge. Results: However, the current consolidation analyses are mostly based on Terzaghi's consolidation theory that assumes the initial pore water pressure ratio with depth to be constant. In this study, numerical analysis are carried out to investigate the variation of pore water pressure dissipation with depth and thickness of clayey soil layer, time, surcharge as well as drainage conditions. Conclusion: Comparative study with Terzaghi's consolidation theory is also conducted. The result shows that Terzaghi's consolidation theory should be used with caution unless it is ideally corresponded to the isochrone.

• Tribology and Lubricants
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• v.36 no.6
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• pp.332-341
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• 2020

High-speed turbomachinery implements gas foil bearings (GFBs) due to their distinctive advantages, such as high efficiency, lesser part count, and lower weight. This paper provides the test results of the static structural stiffnesses and loss factors of bump-type foil thrust bearings with increasing preload and bearing deflection. The focus of the current work is to experimentally quantify variability in structural stiffnesses and loss factors among the four test thrust bearings with identical design values and material of the bump and top foil geometries using the same (open-source) fabrication method. A simple test setup, using a rigidly mounted non-rotating shaft and thrust disk, measures the bearing bump deflections with increasing static loads on the test bearing. The inner and outer diameters of the test bearings are 41 mm and 81 mm, respectively. The loss factor, best-representing energy dissipation in the test bearings, is estimated from the area inside the local hysteresis loop of the load versus the bearing deflection curve. The measurements show that structural stiffnesses and loss factors of the test bearings significantly rely on applied preloads and bearing deflections. Local structural stiffnesses of the test bearings increase with applied preloads but decrease with bearing deflections. Changes of loss factors are less sensitive to applied preloads and bearing deflections compared to those of structural stiffnesses. Up to 35% variability in static load structural stiffnesses is found between bearings, while up to 30% variability in loss factors is found between bearings.

• Journal of IKEEE
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• v.26 no.2
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• pp.299-305
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• 2022

Analog-digital converter (ADC) should be one of the most important blocks that convert various physical signals to digital ones for signal processing in the digital signal domain. As most operations of the analog circuit for sensor signal processing have been replaced by digital circuits, high-resolution performance is required for ADC. In addition, low-power must be the critical issue in order to extend the battery time of mobile system. The existing integrating sigma-delta ADCs has a characteristic of high resolution, but due to its low supply voltage condition and advanced technology, circuit error and corresponding resolution degradation of ADC result from the finite gain of the operational amplifier in the integrator. Buffer compensation technique can be applied to minimize gain errors, but there is a disadvantage of additional power dissipation due to the added buffer. In this paper, incremental signal-delta ADC is proposed with buffer switching scheme to minimize current and igh-pass bias circuit to improve the settling time.

• Composites Research
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• v.35 no.6
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• pp.431-438
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• 2022

Efficient heat dissipation in current electronics is crucial to ensure the best performance and lifespan of the devices along with the users' safety. Materials with high thermal conductivity are often used to dissipate the generated heat from the electronics to the surroundings. For this purpose, polymer composites have been attracted much attention as they possess advantages rooted from both polymer matrix and thermally conductive filler. In order to meet the thermal conductivity required by relevant industries, composites with high filler loadings (i.e., >60 vol%) have been fabricated. At such high filler loadings, however, composites lose benefits originated from the polymer matrix. To achieve high thermal conductivity at a relatively low filler loading, therefore, constructing the heat conduction pathway by controlling filler structure within the composites may represent a judicious strategy. To this end, this review introduces several recent approaches to manufacturing heat dissipating materials with high thermal conductivity by manipulating thermally conductive filler structures in polymer composites.