• Journal of Powder Materials
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• v.18 no.2
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• pp.149-158
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• 2011

Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.

• Bulletin of the Korean Mathematical Society
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• v.53 no.4
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• pp.1071-1085
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• 2016

For $b{\in}L^1_{loc}({\mathbb{R}}^n)$, let ${\mathcal{I}}_{\alpha}$ be the bilinear fractional integral operator, and $[b,{\mathcal{I}}_{\alpha}]_i$ be the commutator of ${\mathcal{I}}_{\alpha}$ with pointwise multiplication b (i = 1, 2). This paper shows that if the commutator $[b,{\mathcal{I}}_{\alpha}]_i$ for i = 1 or 2 is bounded from the product Morrey spaces $L^{p_1,{\lambda}_1}({\mathbb{R}}^n){\times}L^{p_2,{\lambda}_2}({\mathbb{R}}^n)$ to the Morrey space $L^{q,{\lambda}}({\mathbb{R}}^n)$ for some suitable indexes ${\lambda}$, ${\lambda}_1$, ${\lambda}_2$ and $p_1$, $p_2$, q, then $b{\in}BMO({\mathbb{R}}^n)$, as well as that the compactness of $[b,{\mathcal{I}}_{\alpha}]_i$ for i = 1 or 2 from $L^{p_1,{\lambda}_1}({\mathbb{R}}^n){\times}L^{p_2,{\lambda}_2}({\mathbb{R}}^n)$ to $L^{q,{\lambda}}({\mathbb{R}}^n)$ implies that $b{\in}CMO({\mathbb{R}}^n)$ (the closure in $BMO({\mathbb{R}}^n)$of the space of $C^{\infty}({\mathbb{R}}^n)$ functions with compact support). These results together with some previous ones give a new characterization of $BMO({\mathbb{R}}^n)$ functions or $CMO({\mathbb{R}}^n)$ functions in essential ways.

• Publications of The Korean Astronomical Society
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• v.30 no.3
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• pp.811-819
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• 2015

The e-CALLISTO is a network of CALLISTO (Compact Astronomical Low-frequency, Low-cost Instrument for Spectroscopy in Transportable Observatories) spectrometers which detect solar radio bursts 24 hours a day in frequency range 45-870 MHz. The number of channels per spectrum is 200 and the time resolution of whole spectrum is 0.25 second. The Korean e-CALLISTO station was developed by Korea Astronomy and Space Science Institute (KASI) collaborating with Swiss Federal Institute of Technology Zurich (ETH Zurich) since 2007. In this paper, we report replacement of the tracking mount and development of the control program using Visual C++/MFC. The program can make the tracking mount track the Sun and schedule CALLISTO to start and to finish its observation automatically using the Solar Position Algorithm (SPA). Daily tracking errors (RMSE) are 0.0028 degree in azimuthal axis and 0.0019 degree in elevational axis between 2014 January and 2015 July. We expect that the program can save time and labor to make the observations of solar activity for space weather monitoring, and improve CALLISTO data quality due to the stable and precise tracking methods.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.637-642
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• 1994

Using SHS(Self-propagating High-temperature Synthesis) method, the optimum synthetic condition of titanium carbonitride was established by controlling the parameters such as relative density of mixture (Ti+C), nitrogen pressure, additive amounts of titanium hydride(TiH1.924) and protecting heat loss. Under 1 atm nitrogen pressure, nitridation ratio with changing relative density of the sample compacts has a maximum (87.2%) at about 55%, and in the case of enveloping the pellet with a quartz tube, the highest nitridation ratio of 90% was obtained at about 68%. At relative density of 55%, nitridation ratio with the nitrogen pressure has a miximum (87.3%) at 7 atm. As the amounts of additive titanium hydride increased, nitridation ratio decreased at below 7 atm nitrogen pressure and, increased at above this pressure until percent of addition percent reached 15 wt% and decreased abruptly upon futher increases in titanium hydride. In the synthesis of TiCxNy by combustion reaction, heat transfer from combustion zone to preheating zone and nitrogen gas penetration into the compact were found to be important factors affecting the TiCxNy formation. It was difficult to obtain high nitridation ratio when the conbustion temperature was either too high or too low, and it seems that the retention of high temperature after a combustion wave sweeped through the reactant mixture pellet is critical to obtain a satisfactory nitridation ratio.

• Journal of IKEEE
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• v.14 no.3
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• pp.232-235
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• 2010

A 60GHz active phase shifter with 65nm CMOS is presented by replacing passive switches in switched-line type phase shifter with active ones. Active-switch phase shifter is composed of active-switch blocks and passive delay network blocks. The active-switch phase shifter design is compact compare with the conventional vector-sum phase shifter. Active-switch blocks are designed to accomplish required input and output impedances whose requirements are different whether the switch is on or off. And passive delay network blocks are composed of lumped L,C instead of normal microstrip line to reduce the size of the circuit. An 1-bit phase shifter is fabricated by TSMC 65nm CMOS technology and measurement results present -4dB average insertion loss and 120 degree phase shift at 65GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.154-160
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• 2005

Microwave Otters are essential device in modem wireless systems. A compact dimension BPF(Band-pass Filter) for IEEE 802.11a WLAN service is realized using LTCC multi-layer process. To extrude 2-stage band-pass equivalent circuit, band-pass and J-inverter transform applied to Chebyshev low-pass prototype filter. Because parallel L-C resonator is complicate and hard to control the inductor characteristics in high frequency, the shorted $\lambda/4$ stripline is selected for the resonator structure. The passive element is located in the different layers connected by conventional via structure and isolated by inner GND. The dimension of fabricated stacked band-pass filter which is composed of six layers, is $2.51\times2.27\times1.02\;mm^3$. The measured filter characteristics show the insertion loss of -2.25 dB, half-power bandwidth of 220 MHz, attenuation at 5.7 GHz of -32.25 dB and group delay of 0.9 ns at 5.25 GHz.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2331-2338
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• 1994

Experimental conditions of the optical shadow methods of caustics for measurement of the stress intensity factor and the J-integral in various materials(polycarbonate, PMMA, Al 5586D) are investigated. The necessary experimental requirements toe determine accurate values of the stress intensity factors and the J-integrals are described. The ratio of $r_o$ (radius of initial curve) to $r_p$ (plastic zone size) is selected as a parameter to verify the experimental limitation of the method of caustics in determination of fracture parameters. In this study, transmission caustics method was used for compact tension specimens made of polycarbonate and PMMA. while reflection caustics method was applied to c-shaped tension specimen made of Al 5586D. The appropriate ranges of $r_o/r_p$ tp determine accurate values of stress intensity factors were found to be 1.5~1.8. Existing experimental results have been obtained mainly by changing $r_p$ with different loads in $r_o/r_p$. However, in this study we could obtain varying $K_{caus}/K_{th}$ over the wide range of $r_o/r_p$ at fixed load conditions with newly designed optical arrangement. Thus, we could find the range in which theoretical and experimental results agree well each other by changing $r_o$ values only. In Al 5586D specimen, experimental caustics were located inside of the plastic zone, and $K_{caus}/K_{th}$ were found to be not unity in this range. It is found that $J_{caus}/J_{th}=1{\;}with{\;}r_o/t{\geq}0.8$ and the experimental plastic zone includes the contours of caustics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.510-519
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• 2001

The tensile and fracture toughness tests have been conducted to investigate the degradations of mechanical properties induced mainly by neutron irradiations in Zr-2.5Nb CANDU pressure tube materials operated in Wolsung Unit-1. the tests were performed at room, 150, 200, 250, 300 $\^{C}$ for the irradiated and unirradiated specimens in hot cell. The specimens were directly machined from the tube retaining original curvature using specially designed electric discharge machine(EDM). From the tensile tests of the irradiated specimens, it was found that tensile strength was increased and total elongation was decreased compared to those of the unirradiated ones. The active voltages in the fracture toughness tests for the irradiated showed the discontinuous abrupt increases caused by crack jumping in lower temperature. In the crack resistance curves we found the stable crack growth in the unirradiated, whereas the unstable and three crack growth stages in the irradiated specimens due to the accumulated irradiation defects. The various fracture characteristic values in the irradiated are remarkably lower than those of the unirradiated. Through the fractography, we found in the irradiated that smaller dimple and shorter fissures than the unirradiated, and that the fractured surface had three regions that were flat, transition and slant/shear area. These can explain the difference in the crack growth characteristic values of the irradiated and the unirradiated ones.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.6
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• pp.799-803
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• 2001

Miniature heat pipe(MHP) with woven-wired wick was used to cool the CPU of a notebook PC. The pipe with circular cross-section was pressed and bent for packaging the MHP into a notebook PC with very limited compact packaging space. A cross-sectional area of the pipe is reduced about 30% as the MHP with 4mm diameter is pressed to 2mm thickness. In the present study a performance test has been performed in order to review varying of operating performance according to pressed thickness variation and heat dissipation capacity of MHP cooling module that is packaged on a notebook PC. New wick type was considered for overcoming low heat transfer limit when MHP is pressed to thin-plate. The limiting thickness or pressing is shown to be within the range of 2mm∼2.5mm through the performance test with varying the pressing thickness. When the wall thickness of 0.4mm is reduced to 0.25mm for minimizing conductive thermal resistance through the wall of heat pipe, heat transfer limit and thermal resistance of MHP were improved about 10%. In the meantime, it is shown that the thermal resistance and heat transfer limit for the MHP with central wick type are higher than those of MHP with existing wick types. The results of performance test for MHP cooling modules with woven-wired wick to cool a notebook PC shows the stability as cooling system since T(sub)j(Temperature of Processor Junction) satisfy a demand condition of 0∼100$\^{C}$ under 11.5W of CPU heat.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1476-1483
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• 2009

In present work, experiments conducted to investigate the heat transfer characteristics and relationship between operating parameters and production of fresh water as output of the system. Plate Heat Exchanger (PHE) applied in vacuum evaporator for product fresh water that system intended to efficiently use low grade heat. PHE have become popular in chemical, power, food and refrigeration industries due to the efficient heat transfer performance, extremely compact design and flexibility of extend or modify to suit changed duty. The heat transfer part contains corrugated plates with 60 degree of chevron angle which verified by many researchers and commonly apply. Fresh water can be produced from saline water under near vacuum pressure by operating ejector. Consequently, evaporating temperature stay around $51-57^{\circ}C$ so it is possible to use any low grade heat source or renewable source. The maximum fresh water produced by freshwater generator with plat heat exchanger applied in the study was designed as 1.0 Ton/day.