• Information and Communications Magazine
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• v.17 no.8
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• pp.83-98
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• 2000

본 논문에서는 cdma2000 1X 및 1XEV HDR의 물리계층 구조와 위의 두 시스템이 TIA/EIA-95 시스템과 비교하여 개선된 점들을 살펴보았다.cdma2000 기술은 무선 인터넷 애플리케이션과 같이 서비스 사업자의 요구에 능동적으로 대처할 수 있는 플랫포옴을 가지고 있으며 그중 하나가 바로 HDR이다. 즉, 기존의 TIA-EIA-95 또는 cdma2000 1X망에 자연스럽게 융화되며, 트래픽이 링크간 비대칭적이고 벌스티한 특성을 가지며 요구되는 지연(delay) 및 QOS가 가변적인 인터넷 패킷 데이터 서비스와 같이 새로운 기능을 추가하는 것이 용이하다. 따라서 cdma2000 1X 와 HDR은 향후 일반화될 IP 서비스를 최적화하는데 있어서도 매우 효율적인 무선접속기술이다.

• Communications of the Korean Mathematical Society
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• v.13 no.4
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• pp.875-888
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• 1998

The use of the zeros of Chebyshev polynomial of the first kind $T_{4n＋4(x}$ ) and second kind $U_{2n＋1}$ (x) for Gauss-Chebyshev quad-rature and collocation of singular integral equations of Cauchy type yields computationally accurate solutions over other combinations of $T_{n}$ /(x) and $U_{m}$(x) as in [8]. We show that the coefficient matrix of the overdetermined system has the generalized inverse. We estimate the residual error using the norm of the generalized inverse.e.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.611-615
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• 2012

In this study non-stoichiometric $(K_{0.5}Na_{0.5})_{0.97}(Nb_{0.96-x}Ta_xSb_{0.04})O_3$ ceramics were prepared by the conventional soild-state teaction method. The effect of Ta-substitution on the dielectric and piezoelectric properties were investigated. X-ray diffraction analysis of all the specimens less than x= 15 mol% indicated orthorhombic phase. Thereafter, the specimens showed orthorhombic phase near to pseudo-cubic. Sinterablity of all the specimens was improved due to secondary products such as KCT and KCN. The ceramics with x= 5 mol% showed the optimum velues of pizoelectric constant($d_{33}$)= 150 pC/N, electromechanical coupling factor (kp)= 0.45, electromechanical quality factor (Qm)= 418.9 and dielectric constant(${\varepsilon}_r$)= 567. Accordingly, These results indicate that the composition ceramics is a promising candidate for lead-free material.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.617-623
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• 2002

In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, $MmNi_{ 4.5}$$Mn_{0.5}$ $Zr_{x}$ (x=0, 0.025, 0.05, 0.1), are prepared by adding the excess Zr in $MmNi_{4.5}$ $Mn_{0.5}$ / alloy for the strong resistance to intrinsic degradation. The hydrogen storage alloys of rare-earth metal such as $LaNi_{5}$ , and $MmNi_{5}$X and $MmNi_{4.5}$ /$_Mn{0.5}$ alloys which substituted La by misch metal properties were characterized as well. The hydrogen storage alloys were produced by melting each metal mixture in arc melting furnace, and the as-cast alloys were heat-treated at $1100^{\circ}C$ for 10 hr. The major elements of misch metal(Mm) were La, Ce, Pr and Nd with some impurities less than 1wt.% determined by ICP-AES. X-ray diffraction indicated that the structure for these samples was a single phase of hexagonal with $CaCu^{5}$ type. As the Zr contents increases, the activation time and the plateau pressure decrease and sloping of the plateau pressure increase. Amount of the 2nd phases increases with increase in Zr contents in $MmNi_{ 4.5}$$Mn_{0.5}$ $Zr_{0.1}$ alloy, This phenomenon indicated that $ZrNi_3$ in this phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage..

• Progress in Medical Physics
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• v.10 no.1
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• pp.55-62
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• 1999

In an effort to study the characteristics of x-rays utilized in radiation therapy, we calculated the energy distribution and the mean energy of x-rays generated from a tungsten target bombarded by 6, 10, and 15 MeV electron beams, using a Monte Carlo technique. The average photon energies calculated as a function of the beam radius lied in 1.4 ∼ 1.6, 2.1 ∼ 2.5 and 2.8 ∼ 3.3 MeV ranges for 4, 10, and 15 MV electron beams, respectively, which turned out to have no strong dependence on the radius. Using the energy distributions of 6,10, and 15 MV x-rays obtained for the target distance of 100 cm, percentage depth doses were determined using Monte Carlo calculations. For the case 10 MV, a comparison was made between our calculation and measurement performed by others. The calculated percentage depth dose appeared somewhat smaller than the measured one except in the surface region. We conclude that this is due to the fact that the beam hardening effect resulting from the flattening filter was not properly allowed for in our Monte Carlo calculations.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.273-279
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• 2014

Hexagonal Ba-ferrites are widely suggested as materials for small antennas. In this paper, the sintering behavior and magneto-electric properties of $Ba_3Co_{2-2x}Mn_{2x}Fe_{24}O_{41}$ ($0.1{\leq}x{\leq}0.5$) ceramics were investigated for small antenna application. All samples of $Ba_3Co_{2-2x}Mn_{2x}Fe_{24}O_{41}$ ceramics were prepared by the solid-state reaction method and sintered at $1250^{\circ}C$. From the XRD patterns of the sintered $Ba_3Co_{2-2x}Mn_{2x}Fe_{24}O_{41}$ceramics, the Z-type phases were found to be the main phases. The real part of permittivity and permeability of the $Ba_3Co_{2-2x}Mn_{2x}Fe_{24}O_{41}$ceramics decreased with frequency. On the other hand, loss tangents of permittivity and permeability tended to behave opposite to real part of permittivity and permeability. The real part of permeability was affected by Mn additions. The real part of permittivity, the loss tangent of permittivity and the real part of permeability, the loss tangent of permeability of $Ba_3Co_{0.2}Mn_{0.8}Fe_{24}O_{41}$ ceramics were 19.774, 0.176 and 15.183, 0.073, respectively, at 510 MHz. In order to investigate the effect of magneto-dielectric ceramics on antenna, PIFA (Planar Inverted F Antenna) was simulated with CST (Computer Simulation Technology). The operating frequency of antenna was decreased without considerable change of bandwidth by using the $Ba_3Co_{0.2}Mn_{0.8}Fe_{24}O_{41}$ ceramics as the carrier.

• Journal of Korean Society of Forest Science
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• v.55 no.1
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• pp.47-54
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• 1982

Soft X-ray photography was used to study some characters of seeds, such as fullness, damage by blight and harmful insects and degree of mechanical damages, degree of development of embryos and endosperms, size and position of cotylendons, existence and position of twin seed. Thirty nine species of woody plants (31 angiosperms and 8 gymnosperms)and four species of herbs were examined in this study. The results showed that through the mechanism of the selective sensitivity of seed structure of soft X-ray, seed characters mentioned above could be recognized regardless of size of seeds and thickness of seed coat. We concluded that it is possible to use soft X-ray photography reliably to find out the various characters of seeds.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1123-1128
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• 1999

To investigate the effect of Sn on the recrystallization of Zr-based alloys. Zr-xSn (x=0.5, 0.8, 1.5, 2.0wt.%) alloys were manufactured to be the sheets through the defined manufacturing procedure. The specimens were annealed at $300^{\circ}C$ to $800^{\circ}C$ for 1 hour. The hardness, microstructure and precipitate of the alloys with the annealing temperature were investigated by using micro- knoop hardness tester, optical microscope(O/M) and transmission electron microscope(TEM), respectively. The cold-worked Zr-xSn alloys showed the typical behavior of the recovery. recrystallization, and grain growth. The recrystallization of Zr-xSn alloys occurred between $500^{\circ}C$ and $700^{\circ}C$. As the Sn content increased. the recrystallization temperature of the cold-worked alloys increased but their grain sizes after recrystallization decreased. It is suggested that the recrystallization of the cold- worked Zr alloys be occurred by the subgrain coalescence and growth mechanism.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.215-220
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• 2015

Phase evolution, microstructure, and microwave dielectric properties of $Li_2O$ and $Al_2O_3$ doped $Zn_{1.9}Si_{1.05}O_4$, i.e., $Zn_{1.9-2x}Li_xAl_x-Si_{1.05}O_4$, ceramics (x = 0.02 ~ 0.10) were investigated. The ceramics were densified by $SiO_2$-rich liquid phase composed of the Li-Al-Si-O system, indicating that doped Li and Al contributed to the formation of the liquid. As the secondary phase, ${\beta}$-spodumene solid solution with the composition of $LiAlSi_3O_8$ was precipitated from the liquid during the cooling process. The dense ceramics were obtained for the specimens of $$x{\geq_-}0.06$$ showing the rapid densification above $1000^{\circ}C$, implying that a certain amount of liquid is necessary to densify. The specimen of x = 0.06 sintered at $1050^{\circ}C$ exhibited good microwave dielectric properties; the dielectric constant and the quality factor ($Q{\times}f_0$) were 6.4 and 11,213 GHz, respectively.

• Journal of the Korean Electrochemical Society
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• v.7 no.1
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• pp.1-8
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• 2004

This paper deals with the recent development of high-voltage cathode materials of mono- and di- metal ions substituted spinel $LiMn_2O_4$ for lithium batteries. $LiCu_xMn_{2-x}O_4(0{\leq}x{\leq}0.5)$ shows reversible intercalation/deintercalation in two potential regions, $3.9\~43\;and\;4.8-5.0V$ and stable electrochemical cycling behavior but with low capacity. $LiNi_{0.5}Mn_{1.5}O_4$ obtained by a sol-gel process delivers a capacity of 127mAh $g^{-1}$ on the first cycle and sustains a value of 124 mAh $g^{-1}$ even after the 60th cycle. The $Li_xCr_yMn_{2-y}O_4(0{\leq}x{\leq}0.5)$ solid-solutions exhibit enhanced specific capacity, larger average voltage, and improved cycling behaviors for low Cr content. $LiCr_yMn_{2-y}O_4$ presents a reversible Li deintercalation process at 4.9V, whose capacity is proportional to the Cr content in the range of $0.25{\leq}x{\leq}0.5$ and delivers higher capacities. $LiM_yCr_{0.5-y}Mn_{1.5}O_4(M=Fe\;or\;Al)$ shows that the capacity retention is lowered compared with lithium manganate. The cumulative capacities obtainable with Al-substitutted materials are less than those with Fe-substituted materials. $LiCr_xNi_{0.5-x}Mn_{1.5}O_4(x=0.1)$ delivers a high initial capacity of 1$152mAh\;g^{-1}$ with excellent cycleability.