• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.2
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• pp.216-233
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• 2013

Conventional optimization designs of wireless networks mainly focus on spectral efficiency (SE) as a performance metric. However, as diverse media services are emerging, a green wireless network, which not only meets the quality of experience (QoE) requirements for users and also improves energy efficiency (EE), is the most appropriate solution. In this paper, we firstly propose the unit QoE per Watt, which is termed QoE efficiency (QEE), as a user-oriented metric to evaluate EE for wireless networks. We then analyze which is the kind of wireless resource given priority to use under different scenarios to obtain an acceptable QEE. Particularly, power, delay and data-rate related to QoE are separately addressed for several typical services, such as file download, video stream and web browsing services. Next, the fundamental tradeoffs are investigated between QEE and SE for wireless networks. Our analytical results are helpful for network design and optimization to strike a good balance between the users perceived QoE and energy consumption.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.4
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• pp.487-494
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• 2014

This study describes the result on PV system for evaluating the performance of small fishing boats. Photovoltaic system with 200 watts power generation facilities on the 3-ton fishing boat was carried. Load test was performed on the condition that the work lamps lit during night operations. As a result the performance can be used for more than two hours at 60 watt work lamps. The load test was performed on the condition that fishing vessels are on the cruising condition at sea. The solar power systems have been investigated as a power generation efficiency of about 36.55%. Additional tests show that the power generation efficiency is difficult to expect a maximum of 50% or more. Fuel consumption of fishing boats by installing a solar power system is reduced. Also the PV system is useful for the verification of their availability for fishing vessels as well as the satisfaction of the fishermen. The results for the durability of the photovoltaic device is acceptable, including a solar panel, controller and the performance exhibited no breakage in the harsh marine environment or failure so far. The installed PV system was confirmed that the durability with at least 2 years.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.288-294
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• 2011

Simultaneous Ni and C codeposition by electrolysis was investigated with the aim of obtaining better corrosion resistivity and surface conductivity of a metallic bipolar plate for application in fuel cells and redox flow batteries. The carbon content in the Ni-C composite plate fell in a range of 9.2~26.2 at.% as the amount of carbon in the Ni Watt bath and the roughness of the composite were increased. The Ni-C composite with more than 21.6 at.% C content did not show uniformly dispersed carbon. It also displayed micro-sized defects such as cracks and crevices, which result in pitting or crevice corrosion. The corrosion resistance of the Ni-C composite in sulfuric acid is similar with that of pure Ni. Electrochemical test results such as passivation were not satisfactory; however, the Ni-C composite still displayed less than $10^{-4}$ $A/cm^2$ passivation current density. Passivation by an anodizing technique could yield better corrosion resistance in the Ni-C composite, approaching that of pure Ni plating. Surface resistivity of pure Ni after passivation was increased by about 8% compared to pure Ni. On the other hand, the surface resistivity of the Ni-C composite with 13 at.% C content was increased by only 1%. It can be confirmed that the metal plate electrodeposited Ni-C composite can be applied as a bipolar plate for fuel cells and redox flow batteries.

• The Transactions of the Korea Information Processing Society
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• v.3 no.4
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• pp.961-968
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• 1996

In the frame of Koreasat Project, it has been identified the task to implement a pilot satellite network module to provide LAN-to-LAn in ground system for satellite links. The pilot network will support an experiment to verify the performances of the considered applications through a satellite.This paper proposes a satellite-LAN interconnecting architecture making full use of satellite benefits and counteracting satellite demerits. The architectureprovides high quality data transmission and high perfrmance for satellite bit errors by using a connection- oriented satellite protocol which can establish multiple logical links between two nodes. As a protocol conversion method, router-type interconnection was selected to guard against problems. Based on this architecture, a satellite LAN interconnecting system has been designed, which includes a 1.8 meter antenna with a 4 watt transceiver, a satellite modem and the developed satellite network interface. The system can support high speed transmission rates of up to 1.544 Mbs and superior network management as well.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.5 no.2
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• pp.1-9
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• 2007

Purpose: The purpose of this study was to investigate influence of superficial heat and deep heat for lumbo-sacral segment on H-reflex. Methods: Subjects of this research were 12 normal men and women (6 men and 6 women) and they were assigned to superficial heat group (6) and deep heat group (6). Heat treatment was applied between Th12-L2 by placing them at prone posture. superficial heat was applied for 20 min at 30 cm height with infrared lamp. Deep heat was applied for 20 mm at 5 cm height with 100 watt of microwave diathermy. H-reflex used diagnostic electromyography, active electrode was placed at muscle belly of medial gastrocnemius muscle at prone posture and electrical stimulation was given to posterior tibial nerve. Measurement was made before and after experiment and 10 min. and 20 min. after experiment. All data were analyzed with window 12.0 program, comparison of differences among measured items of groups according to repeated measurement was made with repeated measures ANOVA and significance level a was 0.05. Results: M latency at latency analysis showed little changes at two groups. H latency was reduced a little immediately after experiment and recovered to original state, there was significant difference. In analysis of amplitude, Mmax amplitude showed rise a little immediately after.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.1
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• pp.59-68
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• 2009

Fuel cell generators as the distributed generation system with a few hundred watt$\sim$a few hundred kilowatt capacity, can supply the high quality electric power to user as compared with conventional large scale power plants. In this paper, PEMFC(polymer electrolyte membrane fuel cell) generator as micro-source is modelled by using PSIM simulation software and DSP based fuel cell hardware simulator based on the PSIM simulation model is implemented. The relation of fuel cell voltage and current(V-I curve) is linearized by first order function on the ohmic area in voltage-current curve of fuel cell. The implemented system is composed of a PEMFC hardware simulator, an isolated full bridge dc boost converter, and a 60[Hz] voltage source PWM inverter. The voltage-current-power(V-I-P) characteristics of the implemented fuel cell hardware simulator are verified in load variation and transient state and the 60[Hz] output voltage sinusoidal waveform of the PWM inverter is investigated under the resistance load and nonlinear diode load.

• Current Photovoltaic Research
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• v.5 no.2
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• pp.47-54
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• 2017

We report finding ways to improve the long-term reliability of PV module including the heterostructure with the intrinsic thin layer (HIT) solar cell. We point out the stability of the products of Panasonic HIT cell. We account for a brief description of the module manufacturing process to investigate the issues of each process and analyze the causes. We carried out the silicon PV module of the glass to glass type under the damp heat test around 1000 hours. However, it degraded around 7% of PV module power after 300 hours exposure in comparison with the initial status (Initial: 12.7 Watt). We investigated possible cause and solutions for the module performance to develop the long-term reliability.

• Korean Journal of Human Ecology
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• v.14 no.1
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• pp.217-221
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• 2005

In this study, the effect of microwave treatment on physico-chemical properties and microbial changes of beef and pork loin was investigated. Beef and pork were heated in microwave with an adjusted electric output at 500 W and operating frequency 2,450 MHz. The beef and pork samples were treated with microwave for 10 s or 20 s at 50% duty cycle. Drip losses and TBA values of beef and pork samples increased due to the microwave treatment. The samples became darker and more yellowish through microwaves, whereas their redness was unchanged. Microbial content of beef and pork samples declined as the treatment time increased. When pork samples were heated in a microwave oven, organisms were reduced by 2 log cycles in 20 s. It was concluded that a 20 second-long microwave treatment can great1y enhance the microbial safety of the pork sample.

• Korean Journal of Materials Research
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• v.30 no.4
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• pp.169-175
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• 2020

Silicon nitride thin films are deposited by RF (13.57 MHz) magnetron sputtering process using a Si (99.999 %) target and with different ratios of Ar/N₂ sputtering gas mixture. Corning G type glass is used as substrate. The vacuum atmosphere, RF source power, deposit time and temperature of substrate of the sputtering process are maintained consistently at 2 ~ 3 × 10^-3 torr, 30 sccm, 100 watt, 20 min. and room temperature, respectively. Cross sectional views and surface morphology of the deposited thin films are observed by field emission scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscopy. The hardness values are determined by nano-indentation measurement. The thickness of the deposited films is approximately within the range of 88 nm ~ 200 nm. As the amount of N₂ gas in the Ar:N₂ gas mixture increases, the thickness of the films decreases. AFM observation reveals that film deposited at high Ar:N₂ gas ratio and large amount of N₂ gas has a very irregular surface morphology, even though it has a low RMS value. The hardness value of the deposited films made with ratio of Ar:N₂=9:1 display the highest value. The XPS spectrum indicates that the deposited film is assigned to non-stoichiometric silicon nitride and the transmittance of the glass with deposited SiO₂-Si_xN_y thin film is satisfactory at 97 %.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.3
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• pp.485-490
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• 2012

In this paper, driver circuit of LED lights for ships is designed and implemented to replace conventional lights with filament which have short life time due to vibration of ships. The driver of LED module is switching circuit without transformer to reduce volume and cost. As switch circuit controls input 220 VAC with PWM, LED module is reliably driven. Power factor is improved by using valley-fill PFC compensation circuit which is handled to pulse current of switching circuit. Serial-parallel LED circuit is applied to reduce change period of lights of long-term navigation ships. Array of serial-parallel can operate even if some of LEDs is damaged. It is suitable for ships that power consumption and power factor of lights including developed drive circuit have 39Watt and 0.925 respectively.