• Bulletin of the Korean Chemical Society
• /
• v.24 no.3
• /
• pp.389-392
• /
• 2003

• Journal of Electrical Engineering and Technology
• /
• v.9 no.1
• /
• pp.273-279
• /
• 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 the Korean Ceramic Society
• /
• v.13 no.4
• /
• pp.5-8
• /
• 1976

Both oriented and non-oriented ferroxplana $Co_{1-x}Zn_xZ(Ba_3Co_{2(1-x)}Zn_{2x} Fe_{24}O_{41})$ with x=0.00, 0.45 were prepared by conventional ceramic method. The magnetostrictions of thus prepared specimens were measured by use of the three terminal capacitor device at room temperature. The magnitude of measured values was approximately five times greater than that of ZnY ferroxplana. The easy-magnetization plane at room temperature of both CoZ and Co0.55 $Zn_{0.45}$Z was their basal plane. The magentostrictions in the basal plane and the other planes showed saturated values at magnetic field intensity of about 2Koe and 4Koe, respectively. The magnetostriction constants $K_1, \; K_2, \;K_3\; and\; K_4$ for CoZ were -2.4, -10.5, -5.9 and -45.2$\times10^{-6}$ , while those for $Co_{0.55}Zn_{0.45}Z$ were +0.1, -1.2, -6.3 and -39.0$\times$10^{-6}, , respectively.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1293_1294
• /
• 2009

The sintering and high frequency electro-magnetic properties of Ba-hexagonal ferrite were investigated. All samples of the Ba-hexagonal ferrite were prepared by the conventional mixed oxide method and sintered at $1150^{\circ}C$~$1400^{\circ}C$. From the X-ray diffraction patterns of sintered Ba-hexagonal ferrite, the $Ba_3Co_2Fe_{24}O_{41}$ phase was represented as main phase in the almost sintering conditions. The bulk densities with sintering temperature and decreased at $1400^{\circ}C$. The permittivity ($\varepsilon$') and loss tangent of permittivity ($\varepsilon$"/$\varepsilon$') of $Ba_3Co_2Fe_{24}O_{41}$ ceramics increased and decreased with sintering temperature, respectively. The permeability of $Ba_3Co_2Fe_{24}O_{41}$ ceramics decreased with sinteirng temperature. The loss tangent of permeability was not changed compared each other with sintering temperature. The bulk density of $Ba_3Co_2Fe_{24}O_{41}$ ceramics sintered at $1300^{\circ}C$ was 4.79 g/$cm^3$. The permittivity, loss tangent of permittivity and permeability, loss tangent of permeability were 19.896, 0.1718 and 14.218, 0.2046 at 210 MHz, respectively.

• Applied Biological Chemistry
• /
• v.39 no.6
• /
• pp.517-520
• /
• 1996

To identify the volatiles of Platycodon roots, the three-year-old and the 24-year-old Platycodon roots cultivated in a local farm were extracted with ethyl ether by SDE method. 54.71mg% and 80.01mg% of volatile components were collected in the three-year-old and in 24-year-old Platycodon roots, respectively. As a result of GC/MS(TIC) analysis, 24 and 28 compounds were identified, respectively; The amounts of volatile components such as hexanol, trans-2-hexenol and nonanal in 24-year-old roots were detected above ten times than those in 3-year-old roots. The Volatiles of 24-year-old roots were fractionated by SCC and identified by GC/MS to be 10 hydrocarbons, 8 alcohols, 10 aldehydes, 5 esters, 6 acids and 1 unknown compound as the major components. The species and total amounts of volatile component in 24-year-old Platycodon roots were considered to be higher than those in 3-year-old Platycodon roots. *Abbreviations 1. Platycodon : platycodon grandiflorus (jacquin) A. De Candolle. 2. SDE : Simultaneous Distillation Extraction 3. SCC : Silicagel Column Chromatography 4. GC : gas chromatography 5. GC/MS : Gas Chromatography-Mass Spectrometer 6. TIC : Total Ion Chromatogoraphy

• Journal of the Korean Magnetics Society
• /
• v.19 no.1
• /
• pp.12-16
• /
• 2009

Z-type barium ferrite [($Ba_{3}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$, $Ba_{3+{\delta}}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$ ${\delta}$ = 3, 5, 7, 13 wt%. $Ba_{3}Co_{0.8}Zn_{1.2}Fe_{24+{\delta}}O_{41}$ ${\delta}$ = 5, 7, 10 wt% )] were synthesized using co-precipitation method. The microstructure and magnetic properties of synthesized particles were investigated. In all prepared particles M-type Ba ferrite is identified with Z-type Ba ferrite together. It is found that particles having 7 wt% for Ba and 5 wt% for Fe excess addition revealed high saturation magnetization, respectively. All synthesized particles showed relatively high coercivity for device application. This result may be attributed to the contribution of M-type Ba ferrite. Ba and Fe excess addition was not affected to the structural change of CoZnZ Ba ferrite. The certain amount of excess additions of Ba and Fe and the 2 step heat-treatment may be beneficial to the improvement of soft magnetic properties of Z-type barium hexa-ferrite

• Bulletin of the Korean Chemical Society
• /
• v.24 no.9
• /
• pp.1284-1288
• /
• 2003

A very short and concise synthetic route for a novel acyclic version of d4T is described. The required quaternary carbon was successfully installed using a [3,3]-sigmatropic rearrangement. The condensation of the mesylates 16-18 with an adenine base under standard nucleophilic substitution conditions ($K_2CO_3$, 18-Crown- 6, DMF) in addition to deblocking afforded the target acyclic nucleosides 22-24. In addition, the antiviral evaluations against various viruses were performed.

• Korean Journal of Food Science and Technology
• /
• v.30 no.4
• /
• pp.871-876
• /
• 1998

'Yeobong' strawberries were stored at $2^{\circ}C$ under controlled atmosphere (CA) containing the combinations of $O_2{\;}(3.8%)$ and $CO_2{\;}(10,{\;}15,{\;}20%)$ and air as control. Atmospheres of $3%{\;}O_2+15%{\;}CO_2$ and $8%{\;}O_2+15%{\;}CO_2$ reduced respiration and ethylene production rates. Fruits kept under CA conditions of 10% and 15% $CO_2$ were harder than those stored under 20% $CO_2$ and air. The CA conditions of 10% or 15% $CO_2$ maintained approximately 80% of vitamin C for 24 days. Redness were increased and then decreased, but the changing trends were not clear among the storage conditions. Anthocyanin contents in $3%{\;}O_2+15%{\;}CO_2$ and $8%{\;}O_2+15%{\;}CO_2$ were slightly increased for 16 days and then decreased thereafter, while anthocyanin content in air was rapidly increased for 8 days. After 16 days of storage, off-flavor were perceived in all CA storage. And strawberries stored in 20% $CO_2$ conditions were unacceptable after 20 days. The 20% $CO_2$ significantly affected off-flavor of strawberries, but there was no significant difference between 10% $CO_2$ and 15% $CO_2$ conditions. Ethanol which is in relation to off-flavor was higher with elevated $CO_2$ levels. Although CA conditions under $3%{\;}O_2+15%{\;}CO_2$ was effective in delaying the quality changes, there was high ethanol content compared to $8%{\;}O_2+15%{\;}CO_2$ condition. Strawberry kept under $8%{\;}O_2+15%{\;}CO_2$ was maintained the shelf-life for 24 days and the condition prolonged more $4{\sim}8$ days and 12 days than the other CA conditions and air, resectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.2
• /
• pp.147-154
• /
• 2012

Recently, many researchers have studied the performance of the transcritical $CO_2$ refrigeration cycle in order to improve the system efficiency. In this study, the length of IHX in the $CO_2$ ejector cycle was varied so as to evaluate the performance improvement. As a result, compressor work and cooling capacity was increased by 3% and 5% as the length of internal heat exchanger was changed from 3 m to 15 m. The best COP was appeared at internal heat exchanger length of 12 m, and it was 3.01. Besides, the length of internal heat exchanger has a big effect to pressure lift ratio and entrainment ratio in the ejector $CO_2$ cycle and it may be changed with operating conditions and system specifications.

• Journal of Korean Society for Atmospheric Environment
• /
• v.24 no.5
• /
• pp.584-593
• /
• 2008

The surface $O_3,\;CO,\;NO_x,\;and\;SO_2$ were measured at Gosan in Jeju Island from May 2004 to April 2005. Over this period, the mean concentrations $({\pm}s.d.)$ of each gas was 40.06 $({\pm}16.01)$ ppbv for $O_3,\;264.92({\pm}115.73)ppbv\;for\;CO,\;1.98({\pm}2.73)ppbv\;for\;SO)_2,\;and\;4.64 ({\pm}3.24) ppbv\;for\;NO_x$. The monthly variations and the diurnal variations of these gases show that the Gosan site is situated in a relatively clean region. However, there were episodic simultaneous peaks in CO and $SO_2$, especially in winter and early spring. Using cluster analysis with air mass back- ward trajectory analysis, we suggest that these episodes are due to the influence of transportation of polluted air mass from polluted regions. In the cluster, which was under the dominant influence of clean maritime air mass, low levels of $O_3,\;CO,\;and\;SO_2$ were observed. The levels of these species were elevated in the other two clusters which had the air mass influenced by polluted continental regions. In addition, ratios of the chemical species such as $CO/NO_x,\;SO_2/NO_x,\;and\;CO/SO_2$ revealed the somewhat different characteristics of emission sources influencing each cluster. The differences in concentration of trace gases among clusters with different origin and transport pathways imply that Gosan is under the effect of pollution transported from other regions.