• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.1003-1013
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• 2006

There is a serious problem in an 802.11g VoWLAN (Voice over Wireless LAN) terminal that talk time is less than 30% compared with an 802.11b terminal. It is almost impossible to achieve talk time level of the 802.11b MAC transmission method because IEEE 802.11g uses OFDM modulation, which is a kind of multi-carrier method and OFDM transmission speed is 54 Mbps faster than normal modulation. In this paper, a new concept of a Holdover time as a power saving method during a call with 802.11g terminal is suggested for the first time. Increase in the number of engaged terminals as a result of holdover time causes to QoS problem because of the increase in the number of back-off and then contention window. In this paper, to solve the QoS problem, a new approach is suggested such that when in down lint the sequence number of 802.11 G.711 is analyzed in the MAC of the terminal and then the Hold over time depending on loss rate is changed. Also, consumption of an electric current of 802.11b/g and MAC parameter's performance due to busy traffic caused by increase in the number of terminal are analyzed and then real data using VQT and Airopeek are analyzed.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.2
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• pp.45-50
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• 2004

The field utilization factor (equation omitted) (the mean electric field / the maximum electric field) of standard sphere gaps was calculated by the charge simulation method, taking into account the ground plane and shanks. n changes mainly with g/r and slightly with 1$_1$, 1$_2$ and 1, where D=2r is the sphere diameter, g is the gap length, 1$_1$ and 1$_2$, respectively, are the lengths of the upper and lower shank, and t is the shank diameter. Generally, (equation omitted) increases as 1$_1$,1$_2$ and t each becomes larger. IEC standard 60052(2002) limits t$\leq$0.2D 1$_1$$\geq$1D and prescribes A=1$_2$＋D＋g where A is the height of the spark point on the upper sphere. Therefore, (equation omitted) is the largest when A=9D and the smallest when A=3D. The simple equation of a straight line, (equation omitted)=1- (g/3r), can generally be used as a representative value of (equation omitted) for a wide variety of sphere diameters that are permitted by the IEC standard. The maximum electric field E$_{m}$ at sparkover of standard air gaps has also been calculated by the relation E$_{m}$=V/(equation omitted)g). E$_{m}$ describes a U-curve for g/r, up to the sphere diameter of 1 m. Moreover, for 1.5-m and 2-m diameters and especially .for negative polarity, sparkover voltages have been calculated by integration of the ionization index.index.

• Journal of Hydrogen and New Energy
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• v.26 no.6
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• pp.524-531
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• 2015

To improve the electrochemical and mechanical characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The SPEEK organic-inorganic blended composite membranes were prepared by sol-gel casting method. It was loaded with the highly dispersed ceria and cesium-substituted molybdosilicic acid (Cs-MoSiA) and 1,4-diiodobutane which was cross-linking agent contents of $10{\mu}L$. Cs-MoSiA was added to increase proton conductivity. Ceria ($CeO_2$) was used as a free radical scavenger which degrade the membrane in polymer electrolyte membrane water elctrolysis (PEMWE). In conclusion, CL-SPEEK/Cs-MoSiA/Ceria 1% composite membrane showed high proton conductivity 0.2104 S/cm at $25^{\circ}C$ which was better than Nafion 117 membrane.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.2 s.314
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• pp.55-62
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• 2007

This paper proposes method to get exquisite third dimension data removing included noise by error that occur in third dimension reconstruction through camera auto-calibration. Though reconstructing third dimension data by previous noise removing method, mesh that area is wide is happened problem by noise. Because mesh's area is important, the proposed algorithm need preprocessing that remove unnecessary triangle meshes of acquired third dimension data. The research analyzes the characteristics of noise using the area information of 3-dimensional meshes, separates a peek noise and a Gauss noise by its characteristics and removes the noise effectively. We give a quantitative evaluation of the proposed preprocessing filter and compare with the mesh smoothing procedures. We demonstrate that our effective preprocessing filter outperform the mesh smoothing procedures in terms of accuracy and resistance to over-smoothing.

• Journal of Korean Neurosurgical Society
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• v.41 no.2
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• pp.105-110
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• 2007

Objective : This purpose of this study was to determine the clinical efficiency and applicability, and to analyze the radiologic findings of the anterior cervical approach using two synthetic cages for interbody fusion. Methods : A total of 41 patients with cervical diseases underwent anterior discectomy and interbody fusion with the PEEK $Solis^{TM}$ cage in 21 patients and the carbon composite $Osta-Pek^{TM}$ cage in 20 patients. Outcome assessment was done using Odom's criteria. Radiological assessment was performed with respect to subsidence, bony fusion and lordosis. The mean follow-up period was 13 months. Results : There were 34 [92.9%] successful cases. The average height of the disc space 12 months after surgery compared the height just after surgery was decreased over 3mm in 4 cases, indicating severe subsidence. The use of these synthetic cages have provided the increase in postoperative cervical lordosis. Conclusion : There were no significant differences between the $Solis^{TM}$ and $Osta-Pek^{TM}$ cages on clinical and radiologic outcomes. Both $Solis^{TM}$ and $Osta-Pek^{TM}$ cages showed low subsidences and complications associated with hardware with good clinical outcomes, high fusion rates, restored disc heights, and restored cervical lordosis.

• Journal of Hydrogen and New Energy
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• v.25 no.6
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• pp.561-569
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• 2014

Ceria ($CeO_2$) was used to increase the durability of the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance. The sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK) to improve electrochemical characteristics. After sulfonation reaction, the organic-inorganic blended composite membranes were prepared by means of sol-gel casting method with loading the highly dispersed $CeO_2$ and Cs-substituted molybdophosphoric acid (Cs-MoPA) with cross-linking agent (tetrapropyl orthosilicate). Consequently, the composite membrane CL-SPEEK/Silane 4wt%/Cs-MoPA/Ceria(1%) showed the improved characteristics such as 82% of water content, 0.11136 S/cm of proton conductivity at $80^{\circ}C$, 55.50 MPa of tensile strength and 4.37% of breeding out of MoPA.

• Journal of Hydrogen and New Energy
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• v.26 no.3
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• pp.212-220
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• 2015

The engineering plastic of sulfonated polyether ether ketone (SPEEK) as a polymer matrix has been developed in this lab to replace Nafion, solid polymer electrolytes of perfluorosulfonic acid membrane which has several flaws such as high cost, and limited operational temperature above $80^{\circ}C$. The SPEEK was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstosilicic acid (Cs-TSiA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TSiA/ceria 1% membrane showed the optimum results such as 0.1882 S/cm of proton conductivity at $80^{\circ}C$, and 99.61 MPa of tensile strength which were better than Nafion 117 membrane.

• Journal of Hydrogen and New Energy
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• v.25 no.2
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• pp.151-160
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• 2014

CL-SPEEK/Cs-TPA/$CeO_2$ composite membrane was prepared for polymer electrolyte membrane water electrolysis (PEMWE). In order to improve the electrochemical, mechanical, durabilities and electrocatalytic characteristics, engineering plastic of polyether ether ketone (PEEK) as polymer matrix was sulfonated and the organic-inorganic blend composite membranes was prepared by loading cesium-substituted tungstophosphoric acid (Cs-TPA) by titration method with cross-linking agent contents of 0.01mL. Ceria ($CeO_2$) was used to scavenge free radicals which attack the membrane in the PEMWE circumstance and to increase the duration of the membrane. CL-SPEEK/$Cs_{(1)}$-TPA/CeriaIn conclusion, 1% membrane showed the optimum results such as 0.119 S/cm at $80^{\circ}C$ of proton conductivity and 62MPa of tensile strength.

• Journal of Hydrogen and New Energy
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• v.25 no.1
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• pp.1-10
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• 2014

Ceria ($CeO_2$) was used to scavenge free radicals which attack the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance and to increase the duration of the membrane. In order to improve the electrochemical, mechanical and electrocatalytic characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK) and the organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted phophomolybdic acid(Cs-MoPA) with cross-linking agent contents of 0.01mL. In conclusion, CL-SPEEK/$Cs_{(2.5)}$-MoPA/ceria(1%) membrane showed the optimum results such as 0.1095S/cm of proton conductivity at $80^{\circ}C$, 2.906meq./g-dry-membrane of ion exchange capacity and mechanical characteristics, and 49.73MPa of tensile strength which were better than Nafion 117 membrane.

• Journal of Hydrogen and New Energy
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• v.23 no.5
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• pp.437-447
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• 2012

Ceria ($CeO_2$) was used to scavenge free radicals which attack the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance and to increase the duration of the membrane. In order to improve the electrochemical, mechanical and electrocatalytic characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK) and the organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstophosphoric acid (Cs-TPA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TPA/ceria (1%) membrane showed the optimum results such as 0.130 S/cm of proton conductivity at $80^{\circ}C$, 2.324 meq./g-dry-membrane of ion exchange capacity and mechanical characteristics, and 65.03 MPa of tensile strength which were better than Nafion 117 membrane.