• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1169-1175
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• 1994

Five Al2O3/SiC/metal composites with four different particle sizes of green SiC abrasive grains are grown by the directed oxidation of an commercially available Al-alloy. Oxidation was conducted in air at 100$0^{\circ}C$, 96 hours long. Slip casted SiC-fillers were placed on the alloy or SiC powder deposited up to the required layer thickness. Their microstructures are described and measurements of density, elastic constants, frexural strength, fracture toughness and work of fracture are reported. The results are compared with those of commercial dense sintered Al2O3. The properties of produced materials have a strong relationship to not only the properties of Al2O3, SiC, Al and Si but also to the phase share and phase distribution. The composite materials are dense (0.5% porosity), tough (KIC = 3.4~6.4 MPa{{{{ SQRT { m} }}), strong ({{{{ sigma }}B = 170~345 MPa) and reasonably shrinkage free producible. The reinforcements is attained mainly through the plastic deformation of ductile metal phase.

• Journal of the Semiconductor & Display Technology
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• v.10 no.1
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• pp.17-22
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• 2011

LEDs(Light Emitting Diodes) are becoming widely used and increasingly in demand. Quality inspection of the LEDs has become more important. Two-dimensional inspection systems are limited in inspection capability, so threedimensional(3-D) inspection systems are needed. In this paper, a cost-effective and simple 3-D measurement system of LED packages using phase measuring profilometry(PMP) is proposed. The proposed system uses a pico projector to project sinusoidal fringe patterns and to shift phases instead of piezocrystal. It was evaluated using extremely accurate gauge blocks, yielding excellent repeatability of about 12 um(3-sigma). 3-D measurements of various LED packages were performed to demonstrate the applicability and efficiency of the proposed system.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.388-390
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• 2006

This paper presents a hybrid SoC design for phase detection of single tone signal. The designed hybrid SoC is composed of three functional blocks, i.e., an analog to digital converter module, a phase detection module and a controller module. A design of the controller module is based on a 16-bit RISC architecture. An I/O interface and an LCD control interface for transmission and display of phase measurement values are included in the design of the controller module. A design of the phase detector is based on a recursive sliding-DFT. The recursive architecture effectively reduces the gate numbers required in the implementation of the module. The ADC module includes a single-bit second-order sigma-delta modulator and a digital decimation filter. The decimation filter is designed to give 98dB of SNR for the ADC. The effective resolution of the ADC is enhanced to 98dB of SNR by the incorporation of a pre FIR filter, a 2-stage cascaded integrator- comb(CIC) filter and a 30-tab FIR filter in the decimation. The hybrid SoC is verified in FPGA and implemented in 0.35 CMOS Technology.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.6
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• pp.60-67
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• 2008

A low-power 2.4GHz fractional-N frequency synthesizer has been designed for 2.4GHz ISM band applications such as Bluetooth, Zigbee, and WLAN. To achieve low-power characteristic, the design has been focused on the power optimization of power-hungry blocks such as VCO, prescaler, and ${\Sigma}-{\Delta}$ modulator. An NP-core type VCO is adopted to optimize both phase noise and power consumption. Dynamic D-F/Fs with no static DC current are employed in designing the low-power prescaler circuit. The ${\Sigma}-{\Delta}$ modulator is designed using a modulus mapping circuit for reducing hardware complexity and power consumption. The designed frequency synthesizer which was fabricated using a $0.18{\mu}m$ CMOS process consumes 7.9mA from a single 1.8V supply voltage. The experimental results show that a phase noise of -118dBc/Hz at 1MHz offset, the reference spur of -70dBc at 25MHz offset, and the channel switching time of $15{\mu}s$ over 25MHz transition have been achieved. The designed chip occupies an area of $1.16mm^2$ including pads where the core area is only $0.64mm^2$.

• Journal of the Korean Institute of Telematics and Electronics
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• v.12 no.2
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• pp.18-23
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• 1975

The dc conductivity, ac conductivity and switching effect of As.Te-Si.Ge have beon investigated. The dc conductivity ranged from $3{\times}10^{-7}{\Omega}^{-1}cm^{-1}$ to $1.5{\times}10^{-8}{\Omega}^{-1}cm^{-1}$ at room temperature and was found to be expressed by ${\sigma}$ = ${\sigma}_0$exp(-${\Delta}$E/kT) below the phase transition temperature Tg. The ac conductivity was much higher than dc conductivity and this result is consistent to experimental formula ${\sigma}$(w)=${\sigma}_0+Aw^n$. In the temperature range of 298$^{\circ}K$ ~ $473^{\circ}K$ the ac conductivity was independent of temperature at 200KHs. At lower frequencies the ac conductivity increased strong1y with temperature. Also, it has been found that all samples showed a threshold switching, but not a memory switching.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.111-116
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• 2000

Fracture mode and carbide reactions of cast alloy 738LC during thermal exposure and creep at 816$^{\circ}C$/440MPa and 982$^{\circ}C$/152MPa were investigated. Crystallographic transgranular failure was observed in the specimen crept at 816$^{\circ}C$ due to shearing on the slip plane. Because selective oxidation at the grainboundaries which was exposed at the surface leads reduction in surface energy, however, early initiation of crack at the grainboundaries and intergranular failure were observed in the specimen crept at 982$^{\circ}C$/152MPa. As a result of decomposition of MC carbide at the tested temperatures, M(sub)23C(sub)6 carbide precipitated either on the grainboundaries or on the deformation band. The applied stress enhanced decomposition of MC. $\sigma$phase nucleated from Cr(sub)23C(sub)6 then grew to the ${\gamma}$+${\gamma}$\\` matrix. Precipitation of $\sigma$was accelerated by increasing temperature and applied stress.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.87-98
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• 2007

A series of dilatometer test, field vane test, and $CK_0U$ triaxial test were performed for clayey soils of Busan new port site to develop the relationships between undrained shear strength and the DMT results. Normalized undrained shear strength is turned out to be $S_{u(CKU)}/{\sigma}'_v=0.30{\sim}0.35\;for\;CK_0U$ triaxial test and ${\mu}S_{u(VST)}/{\sigma}'_v=0.20{\sim}0.22$ for vane shear test. By comparing the undrained shear strength estimated from DMT indices with the results measured by in-situ vane test or $CK_0U$ triaxial test, two methods to predict the undrained shear strength from DMT results are suggested. One is based on the relationship between $S_u/{\sigma}'_v$ and horizontal stress index (KD) while another method comes from $N_c-I_D$ and $N_c-E_D$ correlation. It was observed that the method based on $N_c-I_D\;or\;N_c-E_D$ relation shows slightly better accuracy than the one based on $K_D$ although all of the methods suggested in this study provided comparable values of predicted undrained shear strength. Since the definitions of $I_D\;and\;E_D$ contain $p_1-p_0$, in which soil condition is reflected, it is believed that the prediction method using $N_c$ is capable of taking a material type into consideration.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.26-30
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• 2015

Hastelloy X in this study was applied in jet engine F-15 air fighter as shroud to isolate the engine from outer skin. After 15 years operation at elevated temperature the mechanical properties decreased gradually due to the precipitation of continues second phases in the grain boundaries and precipitated inside the grain. The crack happened at the edge of the shroud due to the thermal and mechanical stress from jet engine. Selective TEM analysis found that the grain boundaries consist of $M_{23}C_6$ carbide, $M_6$ Ccarbide and small percentage of sigma(${\sigma}$) phase. Furthermore, it was confirmed the nano size of ${\sigma}$ and miu (${\mu}$) phase inside the grain. In this study, it was investigated the microstructure of the degraded shroud component and HAZ of repair welded shroud. In the HAZ, it was observed the dissolution of the $M_{23}C_6$ carbides and smaller precipitates, the migration of the undissolved larger $M_{23}C_6$ carbide and $M_6$ Ccarbide. It is also observed the liquation due to the simply melt of the segregated precipitates in the grain boundaries. Interestingly, the segregated second phases which simply melt in the grain boundaries more easily happened at higher heat input welding condition. High temperature tensile test was done at $300^{\circ}C$, $700^{\circ}C$ and $900^{\circ}C$. It was obtained that the toughness of welded sample is lower compare to the non-welded sample. The solution heat treatment at $1170^{\circ}C$ for 5 minutes was suggested to obtain a better mechanical properties of the shroud. The high cycle fatigue number of the repair welded shroud shows a much lower compare to the shroud. In addition, the high cycle fatigue number at room temperature after solution heat treatment was almost double compare to the before solution heat treatment under 420-500MPa stress amplitude. However, the high cycle fatigue number of repaired welded sample was shown a much lower compare to the non- welded shroud and solution treated shroud. One of the main reasons to decrease the tensile strength and the high cycle fatigue properties of the repair welded shroud is the formation of the liquid phase in HAZ.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.11
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• pp.2444-2450
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• 2011

In this paper, we propose the low fractional spur phase-locked loop(PLL) with multiple phase-frequency detector(PFD). The fractional spurs are suppressed by using a new PFD. The new PFD architecture with two different edge detection methods is used to suppress the fractional spur by limiting a maximum width of the output signals of PFD. The proposed PLL was simulated by HSPICE using a 0.35m CMOS parameters. The simulation results show that the proposed PLL is able to suppress fractional spurs with fast locking.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.499-504
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• 2012

Characteristics of overall heat transfer were investigated in a three-phase slurry bubble column with relatively low surface tension media, which has been frequently encountered in the fields of industry. The heat transfer phenomena was examined in the system which was composed of a coaxial vertical heater and a proper of bubble column. The heat transfer coefficient was estimated from the measured mean value of temperature difference between the heater surface and the column proper at the steady state condition. Effects of gas velocity ($U_G$), solid fraction in the slurry phase ($C_S$) and surface tension (${\sigma}_L$) of continuous liquid media on the overall heat transfer coefficient (h) in the bubble column were determined. The mean value of temperature difference was estimated from the data of temperature difference fluctuations with a variation of time. The amplitude and mean value of temperature difference fluctuations with respect to the elasped time appeared to decrease with decreasing the surface tension of liquid phase. The overall heat transfer coefficient between the immersed heated and the bubble column increased with an increase in the gas velocity or solid fraction in the slurry phase, but it decreased with an increase in the surface tension of continuous liquid media. The overall heat coefficient in the slurry bubble column with relatively low surface tension media was well correlated in term of operating variables and dimensionless groups within this experimental conditions.