• Proceedings of the Korea Multimedia Society Conference
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• 2002.11b
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• pp.553-556
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• 2002

최근 초고속 통신망의 하부 가입자망으로 HFC-CATV에 관한 연구가 활발하게 이루어지고 있다. 특히, HFC-CATV 망은 양방향 멀티미디어 서비스를 제공할 수 있는 것이 특징이다. 따라서 본 논문에서는 HFC-CATV 망을 이용하여 다양한 멀티미디어 트래픽의 QoS를 만족시키기 위한 매체접근제어 프로토콜 중 우선순위 큐(Priority Queue)와 마이크로슬롯을 이용한 MAC 프로토콜을 제안한다. 제안한 알고리즘의 우수성을 입증하기 위해 기존 표준안에서 제안한 알고리즘과 비교 시뮬레이션을 통해 성능분석을 하였다.

• Journal of the Korean Professional Engineers Association
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• v.34 no.2
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• pp.23-27
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• 2001

Until 1996, CFC refrigerants haven't been used because it destroyed ozone that affecting In ecosystem. And HCFC will prohibit until 2020. In Europe, they attempt to move up its fulfillment. Until now the change have completed CFC into HFC134a and is considerated HCFC into HFC410A and HFC407C. But HFC41 OA has high condenser temperature and HFC407C is non-azeotropic refrigerant mixture and gliding temperature phenomenon. New refrigerant ell POE, PVE, PAG was also developed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.234-248
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• 1995

A super-heat pump system composed of a suction line heat exchanger, low and high stage economizers, and a screw compressor is simulated to examine the energy performance and design options. CFC12, HCFC22, HFC134a, HCFC22/HCFC142b, HFC32/HFC134a, and HFC125/HFC134a are used as working fluids for comparison. The results indicate that the proposed system charged with appropriate mixtures is up to 33.4% more energy efficient than the normal system with CFC12. The performance of the super-heat pump system charged with mixtures was influenced by such factors as the temperature matching, heat source temperature difference, low stage economizer, and high stage economizer. The fluids with a larger liquid specific heat such as HFC134a would have more benefits when a suction line heat exchanger is installed. 40%HCFC22/60%HCFC142b mixture seems to be a good candidate to replace CFC12. On the other hand, 25%HFC32/75% HFC134a would be a good long term candidate to replace HCFC22.

• Resources Recycling
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• v.21 no.4
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• pp.69-75
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• 2012

Destruction of HFC-134a from ELV (End of Life Vehicle) were determined in a gasification-melting demonstration system of municipal solid waste (100ton/day). The injection system has been developed for the uniform injection of HFC-134a to the gasification-melting system. The destruction characteristics of HFC-134a and analysis of exhaust gases have been performed. The destruction efficiency was 99.995% for HFC-134a feeding of 3 kg/hr and the exhaust gases such as CO, SOx, NOx, HCl and HF satisfied the environmental standards.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.6
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• pp.321-327
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• 2015

This study presents an HFC152a refrigerant air conditioner as an alternative to HFC134a, which is currently used in mobile air conditioning systems. Cool-down performance tests of an HFC152a air conditioning system were conducted and compared to a baseline HFC134a air conditioner. The experimental set-up consisted of a belt-driven compressor, a sub-cooled type condenser, an evaporator, and a block-type thermal expansion valve (TXV). A drop-in test was carried out on the mobile air conditioning system under various vehicle running speeds in a climate-controlled wind tunnel (CWT). Additionally, to optimize the HFC152a air conditioning system, the effects of the TXVs on the performance were studied. The results show that compared to the HFC134a air conditioning system, the refrigerant charge quantity was reduced by approximately 20%, the discharge pressure was reduced by about 350~430 kPa, and the air discharge temperature at vehicle running conditions was $0.5{\sim}1.5^{\circ}C$ lower. In addition, good compressor durability was expected due to the lower compression ratio.

• Journal of Energy Engineering
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• v.18 no.3
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• pp.203-211
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• 2009

Vapor pressure of HFC-404a and polyol ester system were measured at 56 points from 263.15 to 323.15 K and from 0 to 90 mass %polyol ester. It was found that below 273.15 K, the effect of the polyol ester on the vapor pressure was negligible up to 30 mass % polyol ester. The vapor pressure of the system significantly decreased as the mass fraction of polyol ester increased over 50 percent. Raoult's model and Flory-Huggins model were tested for data reduction. Empirical vapor pressure equations were obtained in terms of temperature and mass fraction of polyol ester.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1252-1260
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• 1999

The HFC network has a architecture of a star topology in fiber optic trunks, and tree and branch topology is used in the part of coaxial cable. It is well known that the HFC upstream channel is noisy. Ingress, common mode distortion and impulse noise exist in the upstream channel. In order to provide Quality of Service(QoS) to users with real-time data such as voice, video and interactive services, the evolving IEEE 802.14 standard for HFC networks must include an effective priority scheme. The scheme separates and resolves collisions between stations in a priority order. It is important to simulate protocols under a practical environment. The proposed algorithm in this paper is simulated with the assumption that the collision detector made certain mistake due to noises. Simulation results show that the proposed algorithm is more efficient than existing tree-based algorithm under practical environment.

• Nutrition Research and Practice
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• v.12 no.4
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• pp.298-306
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• 2018

BACKGROUND/OBJECTIVES: Obesity is a global health problem of significant importance which increases mortality. In place of anti-obesity drugs, natural products are being developed as alternative therapeutic materials. In this study, we investigated the effect of Brassica juncea L. leaf extract (BLE) on fat deposition and lipid profiles in high-fat, high-cholesterol diet (HFC)-induced obese rats. MATERIALS/METHODS: Male Sprague-Dawley rats were divided into four groups (n = 8 per group) according to diet: normal diet group (ND), high-fat/high-cholesterol diet group (HFC), HFC with 3% BLE diet group (HFC-A1), and HFC with 5% BLE diet group (HFC-A2). Each group was fed for 6 weeks. Rat body and adipose tissue weights, serum biochemical parameters, and tissue lipid contents were determined. The expression levels of mRNA and proteins involved in lipid and cholesterol metabolism were determined by reverse transcription polymerase chain reaction and western blot analysis, respectively. RESULTS: The HFC-A2 group showed significantly lower body weight gain and food efficiency ratio than the HFC group. BLE supplementation caused mesenteric, epididymal, and total adipose tissue weights to decrease. The serum levels of triglyceride, total cholesterol, and low-density lipoprotein cholesterol were significantly reduced, and high-density lipoprotein cholesterol was significantly increased in rats fed BLE. These results were related to lower glucose-6-phosphate dehydrogenase, acetyl-coA carboxylase, and fatty acid synthase mRNA expression, and to higher expression of the cholesterol $7{\alpha}$-hydroxylase and low density lipoprotein-receptor, as well as increased protein levels of peroxisome proliferator-activated receptor ${\alpha}$. Histological analysis of the liver revealed decreased lipid droplets in HFC rats treated with BLE. CONCLUSIONS: Supplementation of HFC with 3% or 5% BLE inhibited body fat accumulation, improved lipid profiles, and modulated lipogenesis- and cholesterol metabolism-related gene and protein expression.

• Food Science of Animal Resources
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• v.33 no.6
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• pp.701-707
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• 2013

The present study was carried out to investigate the antiobesity and hypocholesterolemic effects of Bifidobacteria animalis DY-64 (B. animalis DY-64), a lactic acid bacterium isolated from the human intestine, in rats fed a high-fat/high-cholesterol diet for 4 weeks. Forty male Sprague-Dawley rats were divided into four groups and fed either a normal (N) or high-fat/high-cholesterol (HFC) diet without or with oral administration of B. animalis DY-64 (N-BA, HFC-BA). The gain in body weight, and liver and adipose tissue weights of the HFC group were heavier than that of the HFC-BA group. Serum total cholesterol (TC), LDL-cholesterol, and leptin levels of the HFC group, which were significantly elevated compared to those of the N group, dropped by 19, 18, 21, and 13% in the HFC-BA group, respectively, whereas the serum HDL-cholesterol level markedly increased. However, serum TG, LDL-cholesterol, HDL-cholesterol, and leptin levels were not significantly different among the N groups (N, N-BA) with or without B. animalis DY-64 administration. TC and TG levels of the liver as well as the TG level of the adipose tissue were significantly reduced in the HFC-BA group. In addition, HR-LPL activity in adipose tissue was also lower in the HFC-BA group than in the HFC group. These results suggest that B. animalis DY-64 isolated from the human intestine exerts hypocholesterolemic effects by reducing serum and liver cholesterol levels and plays a role in the prevention of obesity induced by HFC diet.

• Fire Science and Engineering
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• v.16 no.3
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• pp.26-31
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• 2002

Bromotrifluoromethane(halon-1301) and bromochlorodifluoromethane(halon-1211) have been widely used as a clean fire extinguishing agents due to their outstanding properties. However, production and use of halon are currently being phased out under an international agreements Montreal Protocol because of global environmental concerns and HFCs have been considered as promising alter-natives for the replacement of halon since their ozone depletion potentials are low. The vapor-liquid equilibrium data are required as important basic information in evaluating the solubility of clean fire extinguishing agents and determining their optimal compositions. In this work, we chose HFCs such as HFC-22 HFC-125, and HFC-l34a for gaseous fire extinguishing agents and nitrogen as a pressurization gas for a proper jet velocity of these agents. Phase equilibria for binary mixtures of nitrogen/HFC-22, nitrogen/HFC-125, and nitrogen/HFC-l34a were measured in the temperature range from 283.15K to 303.15K. For equilibrium measurement, we used a circulation type apparatus in which both vapor and liquid phases were continuously recirculated. The experimental data were relatively well correlated with the Peng-Robinson equation of state with Wong-Sandier mixing rules.