• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1110-1111
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• 2006

[ $Ti_3SiC_2$ ] was coated with $Al_2O_3$, MgO and $SiO_2$ respectively by sol-gel method and cured at 900 and $1200^{\circ}C$. The coated oxides did not react with $Ti_3SiC_2$ at $900^{\circ}C$ but reacted with it to form $TiC_x$ at $1200^{\circ}C$. The specimen coated with $SiO_2$ at $900^{\circ}C$ formed a dense protecting layer and showed the best oxidation resistance at $800^{\circ}C$ in air. However, the dense protecting layers did not form in $Al_2O_3$ and MgO coated specimens cured even at $900^{\circ}C$. MgO coated specimen showed the worst improvement in the oxidation resistance because the reactivity of MgO with $Ti_3SiC_2$ was highest. On the other hand, the electrical conductivities were measured in MgO and $Al_2O_3$ coated specimens to have TiCx but could not be measured in the $SiO_2$ coated ones because of the nonconductive dense protected layers.

• Journal of Powder Materials
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• v.12 no.1
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• pp.17-23
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• 2005

Dense $WSi_2$-20vol.%SiC composite was synthesized by high-frequency induction-heated combustion synthesis(HFIHCS) method within 2 minutes in one step from elemental powder mixture of W, Si and C. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense $WSi_2$-20vol.%SiC with relative density of up to 97% was produced under simultaneous application of 60MPa pressure and the induced current. The average grain size of $WSi_2$ was about $5.2{\mu}m$. The hardness and fracture toughness values obtained were 1700kg/$mm^2$ and $4.4MPa{\cdot}m^{1/2}$, respectively.

• Journal of the Korean institute of surface engineering
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• v.39 no.6
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• pp.255-262
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• 2006

Pd-Cu alloy membrane for hydrogen separation was fabricated by sputtering and Cu reflow process. At first, the Pd and Cu was continuously deposited by sputtering method on oxidized Si support, the Cu reflow process was followed. Microstructure of the surface and permeability of the membrane was investigated depending on various reflow temperature, time, Pd/cu composition and supports. With respect to our result, Pd-Cu thin film (90 wt.% Pd/10 wt.% Cu) deposited by sputtering process with thickness of $2{\mu}m$ was heat-treated for Cu reflow The voids of the membrane surface were completely filled and the dense crystal surface was formed by Cu reflow behavior at $700^{\circ}C$ for 1 hour. Cu reflow process, which is adopted for our work, could be applied to fabrication of dense Pd-alloy membrane for hydrogen separation regardless of supports. Ceramic or metal support could be easily used for the membrane fabricated by reflow process. The Cu reflow process must result in void-free surface and dense crystalline of Pd-alloy membrane, which is responsible for improved selectivity oi the membrane.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.62.1-62.1
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• 2014

We present preliminary results on the chemical differentiation of two dense gas tracers CS and $N_2H^+$ in five 'evolved' starless cores, L1544, L1552, L1689B, L694-2 and L1197, using our mapping observations in $C^{34}S$(J=2-1) and $N_2H^+$(J=1-0) with Nobeyama 45-m telescope. We compared the intensity maps of two molecular lines with 850 ${\mu}m$ continuum data which precisely trace the density distribution of the dense cores, finding that all of our targets show the central depletion holes in CS distribution, but the similar distribution in $N_2H^+$ to the one in dust continuum. Our data confirm the claim that CS molecule generally deplete out in the central region in starless cores, while $N_2H^+$ keep abundant as they get evolved. The detailed quantitative analysis on CS depletion in the dense cores, for example, the size of CS depletion area and radial (or gas density) dependence of CS depletion, is underway and will be presented in the meeting.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.370-382
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• 2013

Distributed massive MIMO systems, which have high bandwidth efficiency and can accommodate a tremendous amount of traffic using algorithms such as zero-forcing beam forming (ZFBF), may be deployed in large public venues with the antennas mounted under-floor. In this case the channel gain matrix H can be modeled as a multi-banded matrix, in which off-diagonal entries decay both exponentially due to heavy human penetration loss and polynomially due to free space propagation loss. To enable practical implementation of such systems, we present a multi-banded matrix inversion algorithm that substantially reduces the complexity of ZFBF by keeping the most significant entries in H and the precoding matrix W. We introduce a parameter p to control the sparsity of H and W and thus achieve the tradeoff between the computational complexity and the system throughput. The proposed algorithm includes dense and sparse precoding versions, providing quadratic and linear complexity, respectively, relative to the number of antennas. We present analysis and numerical evaluations to show that the signal-to-interference ratio (SIR) increases linearly with p in dense precoding. In sparse precoding, we demonstrate the necessity of using directional antennas by both analysis and simulations. When the directional antenna gain increases, the resulting SIR increment in sparse precoding increases linearly with p, while the SIR of dense precoding is much less sensitive to changes in p.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.441-450
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• 2015

Nowadays, many WLAN access points (APs) are deployed in hotspot areas such as shopping malls and stations. As the number of WLAN APs deployed increases, how to manage densely deployed APs in an efficient manner becomes one of the most important issues in WLANs. In this environment, uncoordinated multicast services can lead to frequent collisions due to simultaneous transmissions among APs. In this paper, we propose a multicast scheduling algorithm that can exploit simultaneous transmissions in multiple sectors and avoid redundant transmissions in dense networks. Simulation results demonstrate that the proposed scheme can reduce the multicast transmission latency compared to comparison scheduling schemes.

• Journal of the Society of Disaster Information
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• v.7 no.1
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• pp.32-42
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• 2011

Many researches have been conducted to evaluate the performance of modified asphalt concrete mixtures. The research was conducted to estimate the laboratory mechanical characteristics of Elvaloy-modified asphalt concrete mixture. To achieve its intended objective, indirect tensile test and resilient modulus test were performed. The rest results revealed that indirect tensile strengths and resilient moduli of the Elvaloy-modified asphalt concrete mixture were higher than those of the conventional dense-graded. As a result, within the limits of the tests conducted in this research, it is predicted that the performance and stability of the Elvaloy-modified asphalt concrete mixture are better than that of the conventional dense-graded one.

• Tribology and Lubricants
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• v.25 no.1
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• pp.7-12
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• 2009

Coating brittle intermetallic compounds on metal can enlarge the range of their use. It is found that intermetallic compound coating layers made by only combustion synthesis in an electric furnace have porous multi-phase structures containing several intermediate phases, even though the coating layers show good wear resistance. In this study, dense $Ni_{3}Al$ single phase layer corresponding to the initial composition of the mixed powder is coated on two different ferrous materials by the diffusing treatment after combustion synthesis. After- ward, sliding wear behaviors of the coating layer are evaluated in comparison with that of the coating layer with porous multi-phase structure made by only combustion synthesis. As a result, the wear properties of the coating layer composed of dense $Ni_{3}Al$ single phase are considerably improved at the range of low sliding speed com- pared with that of the coating layer with porous multi-phase structure, particularly in the running-in wear region. This is attributed to the fact that wear of the coating layer is progressed by shearing as a sequence of adhesion, not by occurring of pitting on the worn surface due to having dense structure without pores.

• Korean Journal of Veterinary Research
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• v.36 no.4
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• pp.763-771
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• 1996

Ultrastructures of hypophyseal gonadotropes were studied in the hypophysis of the Korean native goat by electron microscopic immunohistochemistry with antisera to follicle stimulating hormone(FSH) and luteinizing hormone(LH). 1. Gonadotropes in the adenohypophysis were observed in the pars distalis and the pars tuberalis, but not in the pars intermedia. 2. FSH cells were round or oval in shape, and contained two types of round secretory granules, i.e., small and large granules. Small secretory granules were electron-dense and 180-275nm in diameter. Large secretory granules were less electron-dense than small granules and 485-555nm in diameter. 3. LH cells were round or oval in shape and also contained two types of secretory granules, the size of which were smaller than that of FSH cells. Small secretory granules were electron-dense and 160-230nm in size. The size of large secretory granules were 315-415nm with moderate electron densities.

• Journal of the Korean institute of surface engineering
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• v.31 no.5
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• pp.237-244
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• 1998

In this stydy, submicron shallow trenches applied to STI(shallow tench isolation) were etched using inductively coupled $CI_2$/HBr and $CI_2/N_2$plasmas and the physical and electrical defects remaining on the etched silicon trench surfaces and the effects of various annealing and oxidation on the removal of the defects were studied. Using high resolution electron microscopy(HRTEM), Physical defects were investigated on the silicon trench surfaces etched in both 90%$CI_2$/ 10%$N_2$ and 50%$CI_2$/50%HBr. Among the areas in the tench such as trench bottom, bottom edge, and sidewall, the most dense defects were found near the trench bottom edge, and the least dense defects were found near the trench bottom edge, and least dense defects compared to that etched with ment as well as hydrogen permeation. Thermal oxidation of 200$\AA$ atthe temperature up to $1100^{\circ}C$apprars not to remove the defects formed on the etched silicon trenches for both of the etch conditions. To remove the physicall defects, an annealing treatment at the temperature high than $1000^{\circ}C$ in N for30minutes was required. Electrical defects measured using a capacitance-voltage technique showed the reduction of the defects with increasing annealing temperature, and the trends were similar to the results on the physical defects obtained using transmission electron microscopy.