• Journal of Korean Institute of Industrial Engineers
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• v.37 no.2
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• pp.89-95
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• 2011

The distributed coordination function (DCF) and point coordination function (PCF) protocols are the basic MAC protocols for legacy IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g and IEEE 802.11n wireless LANs. When the DCF protocol is used for the various versions of IEEE 802.11 wireless LANs, the MAC performance seriously degrades due to the collisions among the stations (STAs) as more and more STAs attempt to transmit their data frames. On the other hand, the PCF MAC performance becomes poor when many STAs exist in IEEE 802.11 wireless LANs, however, only small number of STAs actually attempt to transmit their data frames. In this paper, we propose the algorithm for improving the MAC performance by selectively using the DCF and PCF protocols according to the state of IEEE 802.11 wireless LANs. Numerical examples are presented to show the MAC performance improvement by the selective use of the DCF and PCF protocols according to the network state.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.387-394
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• 2005

Every MAC (Medium Access Control) sub-layers of IEEE 802.11x, including IEEE 802.11e, defines Connection-based and CF (Contention Free)-based service functions in common. In this paper, a New-CF method is proposed. In the proposed method, conventional Round Robin method, which is used as a polling method by IEEE 802.11x PCF (Point Coordination Function) or IEE 802.11e HCCA, is modified to give weights to channels with heavier traffic load and to provide those weighted channels with more services. Based on NS-2 simulations, it is verified the proposed method shows better throughput in general, particularly under unbalanced traffic load conditions.

• Journal of the Korean Society of Safety
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• v.11 no.1
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• pp.99-107
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• 1996

This survey is to compare the the number of accidents which were occurred in 24 construction companies with the average accident in construction industry. The number of accidents in 24 companiesis is lower than the average accident, then it is classified "save", otherwise it is classified "loss". This survey is conducted to have top management be interested and invest for safety by recognizing that safety management could be profit for the company. The result of this survey is as follows : The total save amount in 1992 is 44,780mi11ion Won and average is 1,870mi11ion Won, with being 11, 200mi11ion Won by reduction amount of deaths and 33,580mi11ion Won by reduction amount of injuries. In 1993 the total is 33,330mi11ion Won and average is 1,390mi11ion Won, and in 1994 the total is 38, 720mi11ion Won and the average is 1,610mi11ion Won. This result is save amount of workmen's compensation insurance with excluding the indirect costs for accidents. The company which ranked the highest save amount is B Construction Company with being 15.1 billion Won and the next is A Construction Company during 3 years. The Company which ranked highest percentage of save amount to sales amount is Q Heavy industry with being 0.359% and the next is B Construction Company during 3 years.pany during 3 years.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.952-956
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• 1998

An automated system was developed for the routine preparation of carbon-11 ($^11C$) labeled radiopharmaceuticals, which consisted of three major parts including [$^11C$]methylation of the precursor with [$^11C$] iodomethane ($[^11C]CH_3I)$, purification of the desired product and formulation of the final $^11C$ labeled radiopharmaceutical. The whole system included seven three-way slider valves, eleven solenoid valves, four pneumatic cylinders, a HPLC (High Performance Liquid Chromatography) system and a rotary evaporator. Using this system, we investigated the radiochemical synthesis of L-[$methyl-^11C$]methionine, which is the most widely used amino acid in tumor PET (Positron Emission Tomography) studies. The overall operation took 3035 min including the production of $[^11C]CH_3I$ (10.5 min) and decay-corrected radiochemical yield was 25%. The automated system we described herein can be widely utilized for the preparation of many $^11C$ labeled radiopharinaceuticals and has been shown to be efficient, reliable and easy to operate.

• The Korean Journal of Nuclear Medicine
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• v.35 no.3
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• pp.185-191
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• 2001

Objectives: Recently, $[methyl-^{11}C]-({\beta}$-Hydroxyethyl)trimethylammonium ($[^{11}C]$choline) Has been discovered to be a very effective tracer in imaging various human tumors using positron omission tomography. Because of the short half-life of C-11, it is very difficult to use in a routine imaging procedure and needs a frequent synthesis of $[^{11}C]$choline. This can be supplemented by the substitution of $[^{11}C]$choline with $[methyl-^{18}F]$fluorocholine. Here, we would like to report ceil uptake and biodistribution of $[^{11}C]$choline and $[^{18}F]$fluorocholine as a basic study. Methods: $[^{11}C]$Choline was prepared by the treatment of $[^{11}C]CH_3I$ with N,N-dimethylaminoethanol and $[^{18}F]$fluorocholine was synthesized from reaction of $CH_2Br[^{18}F]F$ with N,N-dimethylaminoethanol. The radiochemical purity was checked by high performance liquid chromatography (HPLC). The blodistribution of $[^{11}C]$choline and $[^{18}F]$fluorocholine was determined in balb/c mouse at 5 min, 20 min, 40 min and 80 min. The cell uptake was measured using glioma (9L) and colon adenocarcinoma (SW620). Results: The radiochemical purity was more than 98% after purification. In the liver, uptake did not change over time; the uptake was 20%ID/g for $[^{11}C]$choline and 13%ID/g for $[^{18}F]$fluorocholine. In the kidney, radioactivity decreased over time; the uptake was 15%ID/g for $[^{11}C]$choline and 20%ID/g for $[^{18}F]$fluorocholine, 80 min post-injection. The cell uptake of $[^{11}C]$choline was 4.93% for glioma (9L) and 18.69% for colon adenocarcinoma (SW620). For $[^{18}F]$fluorocholine, 1.77% for glioma (9L) and 2.77% for colon adenocarcinoma (SW620). Conclusion: $[^{11}C]$Choline and $[^{18}F]$fluorocholine showed a different cell uptake tendency, depending on cancer cell line.

• YAKHAK HOEJI
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• v.26 no.1
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• pp.1-8
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• 1982

Derivation of triterpenoids and then the screening for corticomimetics among them is our primary interest. $C_{11}$-oxo-triterprenoids except glycyrrhetinic acid are rarely found in the plant kingdom. Based on the facts that $C_{3}$ and $C_{11}$-Oxo-group are essential for the corticoid-like-activity through its competitive inhibition on the corticoid-5.betha.-reductase, it was attempted to produce artificial inhibitor on the enzyme by introducing $C_{11}$-oxo group to the triterpenoids of oleanene series such as oleanolic acid and hederagenin. We could obtain the $C_{11}$-oxo-oleanolic acid m.p. $264-6^{\circ}$, uv ${\lambda}max$ 249 and $C_{11}$-oxo-hederagenin amorp. uv ${\lambda}max$ 251 by acetylation, $CrO_{3}$-oxid., and deacetylation. Glycyrrhetinic acid, a natural 11-oxo-compound and the other 11-oxo-derivatives of oleanolic acid and hederagenin were compared in their inhibitory activity on the corticoid-5.betha.-reductase. The inhibitory activity of those compound were decreased in the order of $C_{11}$-oxo-oleanolic acid, $C_{11}$-oxo- hederagenin, glycyrrhetinic acid. This suggests more strong corticomimetic activity of those artificially derived $C_{11}$-oxo-oleanolic acid and $C_{11}$-oxa-hederagenin. Their Ki value were $4.6{\times}10^{-4}M$ and $5.8{\times}10^{-4}M$ respectively.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.485-490
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• 2010

IEEE 802.11n supports two frame aggregation schemes, aggregation for MAC service data unit (A-MSDU) and aggregation for MAC protocol data unit (A-MPDU), to improve throughput at the MAC layer. In this paper, we propose a cooperative frame aggregation (CoFA), which can recover erroneous frames in a cooperative manner based on A-MPDU. Specifically, CoFA receive multiple frames from direct and relay paths, and combined multiple frames jointly. Numerical results show that CoFA outperforms direct transmission and relay transmission over diverse channel conditions.

• Journal of the Korean Chemical Society
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• v.40 no.7
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• pp.519-525
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• 1996

3-Carbomethoxy-1(3H)-isobenzofuranone(9) underwent condensation with ${\alpha}{\beta}-unsaturated$, esters 3a-b to produce the corresponding naphthacene-6,7-diones 11a-b with high yields in one pot procedure. Among the naphthacene-6,7-diones formed, compound 11a without an ethyl group at C-9 position was oxidized to give the naphthacene-5,12-dione 13a, while compound 11b containing the ethyl group was oxidized to give a 3:2 mixture of the naphthacene-5,7,12-trione 12b and naphthacene-5,12-dione 13b under the same experimental conditions.

• Korean Journal of Pharmacognosy
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• v.17 no.2
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• pp.178-183
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• 1986

It was our working hypothesis that introduction of 11-keto groups to 12-oleanene/ursene series of triterpenoids should endow them with corticoid-like activities, since pharmacological actions of glycyrrhetinic acid (GA) are known to be caused by inhibition on $corticoid-{\delta}^4-reductase$. 11-Keto-triterpenoids derived artificially in these studies, such as 11, 19-diketo-18, 19-secoursolic acid methyl ester(I), $11-keto-{\beta}-boswellic$ acid derivatives (IIa-IIc), 11-Keto-presenegenin dimethyl ester (III), II-keto-oleanolic acid derivatives (IVa-IVd) and 11-keto-hederagenin (V) possess the fundamental functions of ${\alpha},\;{\beta}-unsaturated$ ketone on C-11 and hydroxyl group on C-3, as like GA (VI). Additionally, they involve the carboxyl groups on rings A (II, III), D (I, III, IV, V) and E (VI), and the hydroxyl groups on rings A (III, V) and C (III). All the compounds competitively inhibited $corticoid-5{\beta}-reductase$, and the highest inhibitory potency appeared in I. All of them except $3,\;11-diketo-{\beta}-boswellic$ acid methyl ester (IIc) were more effective about five times to twice than GA. On carrageenin-induced edema test, compounds I and IVa-IVd showed anti-inflammatory activities, but III enhanced rather edema. Structure-activity relations were found in the aspects of hydrophilicity of ring A and hydrophobicity of rings C/D. The more they were hydrophilic in ring A and hydrophobic in rings C/D, the more they inhibited the enzyme. And the more they were hydrophobic in rings C/D, the more they exhibited antiiflammatory activities. However, the increased hydrophilicity in ring A resulted in increasing edema, probably due to a nonspecific inhibition on $aldosterone-5{\beta}-reductase$.

• The Korean Journal of Mycology
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• v.13 no.2
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• pp.83-87
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• 1985

The temperature dependency and the stability of enzyme systems for $11{\alpha}-hydroxyla­tion$ of progesterone were investigated using Aspergillus phoenicis. Though A. phoenicis conserves high enzyme activities for lactose hydrolysis even at high temperatures, the bioconversion reaction of progesterone by this strain was found to be very temperature sensitive. The compositions of reaction mediums of inside and outside of cells were analyzed using sonication technique. At early stage of reaction, the concentration of $11{\alpha}-hydroxyprogesterone$ of cell inside was higher than that of outside. But as the reaction proceeded further, the $11{\alpha}-hydroxyprogesterone$ existing inside of cells being converted into another products, its concentration was lower within the cells that in the bulk medium. Even in the reaction mediums containing organic solvents, A. phoenicis was founded to be able to metabolite, so that $11{\alpha}-hydroxyprogesterone$ can be produced continuously from fixed bed reactions packed with immobilized A phoenicis in vivo.