• Korean Journal of Materials Research
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• v.2 no.5
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• pp.360-365
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• 1992

Ga-doped polycrystalline ZnO films on glass substrates were prepared by sputtering the targets, which had been prepared by sintering discs consisting of ZnO powder and various amounts of G$a_2O_3$, to investigate the effects of gallium doping and sputtering conditions on electrical properties. Optimizing the RF power density, argon gas pressure and gallium content, transparent Ga-doped ZnO films with resistivity less than 1$0^{-3}$ohm-cm are obtained. Electron concentration of undoped and Ga-doped ZnO films are order of $10^{18}$, $10^{21}$/c$m^2$respectively. After heat treatment in air and $N_2atmosphere, $ the resistivity of Ga-doped ZnO films increases by about two orders of magnitude. The optical transmission is above 80% in the visible range and the optical band widens as the Ga content increases.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.592-595
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• 2011

It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.

• Biomolecules & Therapeutics
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• v.25 no.2
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• pp.105-111
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• 2017

It has been known that RA, one of major constituents of Perilla frutescens which has been used as a traditional folk remedy for sedation in oriental countries, shows the anxiolytic-like and sedative effects. This study was performed to know whether RA may enhance pentobarbital-induced sleep through ${\gamma}-aminobutyric$ acid $(GABA)_A-ergic$ systems in rodents. RA (0.5, 1.0 and 2.0 mg/kg, p.o.) reduced the locomotor activity in mice. RA decreased sleep latency and increased the total sleep time in pentobarbital (42 mg/kg, i.p.)-induced sleeping mice. RA also increased sleeping time and number of falling sleep mice after treatment with sub-hypnotic pentobarbital (28 mg/kg, i.p.). In electroencephalogram (EEG) recording, RA (2.0 mg/kg) not only decreased the counts of sleep/wake cycles and REM sleep, but also increased the total and NREM sleep in rats. The power density of NREM sleep showed the increase in ${\delta}-waves$ and the decrease in ${\alpha}-waves$. On the other hand, RA (0.1, 1.0 and $10{\mu}g/ml$) increased intracellular $Cl^-$ influx in the primary cultured hypothalamic cells of rats. RA (p.o.) increased the protein expression of glutamic acid decarboxylase ($GAD_{65/67}$) and $GABA_A$ receptors subunits except ${\beta}1$ subunit. In conclusion, RA augmented pentobarbital-induced sleeping behaviors through $GABA_A-ergic$ transmission. Thus, it is suggested that RA may be useful for the treatment of insomnia.

• Journal of the Korean Society for Precision Engineering
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• v.1 no.3
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• pp.85-94
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• 1984

The WILDHABER-NOVIKOV gear, one of the circular arc gears, has the large contact area between the convex and concave profiled mating teeth, moves from one end of the tooth to the other axially making a face contact. Hence it provides a large load capacity than the Involute gear and still satisfying the law of gearing. In order to analyze the gear stress, a photoelastic investigation was carried out. Photo elastic model of the WILDHABER-NOVIKOV gears were made of Araldite CT200 in this investigation. For both the many teeth gear and the few teeth gear segments, External gears of all addendum type WILDHABER-NOVIKOV gear and the involute gear were tested. Included were the models with various profile raddi at the same pressure angle 20 .deg. and module 13.5. The flank stresses and fillet stresses of these gears were observed in each case and compared with those of gears. From this investigation, the following results were obtained. A. In the case of having many teeth gear: As the profile radius is increased, the fillet stresses of the WILDHABER-NOVIKOV gear become the same or less than that of the INVOLUTE gea, and the flank stress becomes smaller than that of the INVOLUTE gear. Therefore the better design condition is satisfied with a large profile radius. B. IN the case of having a few teeth gear: As the profile radius is increased the flank stress of WILDHABER-NOVIKOV gear becomes smaller than that of the INVOLUTE gear, but the fillet stresses become larger than that of the INVOLUTE gear. Therefore the larger design condition is satisfied with small profile radius.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4883-4901
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• 2016

Energy efficiency in Wireless Sensor Networks (WSNs) is very appealing research area due to serious constrains on resources like storage, processing, and communication power of the sensor nodes. Due to limited capabilities of sensing nodes, such networks are composed of a large number of nodes. The higher number of nodes increases the overall performance in data collection from environment and transmission of packets among nodes. In such networks the nodes sense data and ultimately forward the information to a Base Station (BS). The main issues in WSNs revolve around energy consumption and delay in relaying of data. A lot of research work has been published in this area of achieving energy efficiency in the network. Various techniques have been proposed to divide such networks; like grid division of network, group based division, clustering, making logical layers of network, variable size clusters or groups and so on. In this paper a new technique of group based WSNs is proposed by using some features from recent published protocols i.e. "Energy-Efficient Multi-level and Distance Aware Clustering (EEMDC)" and "Energy-Efficient Multi-level and Distance Aware Clustering (EEUC)". The proposed work is not only energy-efficient but also minimizes the delay in relaying of data from the sensor nodes to BS. Simulation results show, that it outperforms LEACH protocol by 38%, EEMDC by 10% and EEUC by 13%.

• Applied Chemistry for Engineering
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• v.23 no.6
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• pp.561-566
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• 2012

PtRuW/C catalysts were prepared with the different molar ratios of Pt : Ru : W and their compositions were analyzed by energy dispersive X-ray (EDX). The uniform distribution of particles was observed using transmission electron microscopy (TEM). An average crystalline size of 3.5~5.5 nm was calculated based on x-ray diffraction (XRD) data. The electrochemical properties such as electrochemically active surface areas, current densities, specific activities and poisoning rates, were analyzed via CO stripping, linear sweep voltammetry and chronoamperometry. From the analysis, we observed that ternary alloy catalysts, except $PtRu_2W_2/C$, have higher current densities, specific activities and stabilities than those of commercial binary catalysts. Among all in-house catalysts, Pt5Ru4W/C showed the highest specific activity of $121.05mA{\cdot}m^{-2}$ and the lowest poisoning rate of $0.01%{\cdot}s^{-1}$.

• Korean Journal of Clinical Laboratory Science
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• v.37 no.3
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• pp.220-227
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• 2005

Recently, the use of an electrical apparatus has brought up concerns of health risks from exposure to electromagnetic fields. EMF is composed of electric fields and magnetic fields. Heavy exposure to EMF can occur only in the vicinity of high-voltage overhead transmission lines, close to transformers and underground cables, and also close to large electrical machinery. In this thesis I have investigated the hypothesis of the correlation between occupational exposure to ELF-EMF and the risks of leukemia, anemia, cancer. Therefore, the aim of this study is to investigate whether or not ELF-EMF emitted from electric power stations and transformer substations affect some hematological parameters and tumor markers of electric utility workers. The hematological test results and tumor markers under investigation were similar in the two groups but some of parameters such as RBC, AFP, LDH showed significant difference between the two groups from two sample t-test (p<0.05). The exposure group showed increased LDH level compared to the control group by two sample t-tests. In addition, the abnormal LDH level in the exposure group was observed to be clinically significant by ${\chi}^2$-test. However, the levels of RBC, AFP observed were not clinically significant by ${\chi}^2$-test (p>0.05). These results suggested that ELF-EMF does not affect most blood test parameters except LDH of electric utility workers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.3139-3145
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• 2014

This paper describes the design of a size-reduced ring hybrid coupler for microwave band using an artificial dielectric substrate(ADS). ADS structure adopts the second substrate on which has lots of the metalized via-holes. The effective capacitance and effective dielectric constant per unit length of ADS increases compared to the normal substrate due to the via-holes. This enables the physical length of microstrip transmission line to be reduced by adopting ADS instead of the normal substrate. In order to present an example of size-reduction of microwave wireless circuit by ADS, a size-reduced 3GHz ring hybrid coupler is designed, fabricated and measured in this work. The designed coupler has the smaller size from the normal one by 65% due to the ADS, while no critical degradation from ideal performances is observed. The measured power division ratio at two output ports are -3.05dB and -3.135dB, respectively. In addition, the phase differences are 3o for in-phase division and 176o for out of phase split. The measured performances are so similar to ideal ones, and prove the design of size-reduced ring hybrid coupler using ADS is successful.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.996-1001
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• 2010

In this paper, network selection algorithm for services of mobile IPTV(internet protocol television) and implementation of a hierarchical processing system for reducing overload by terminal with low speed is proposed. This algorithm selects the network according to the following priorities derived from formulas; value that uses remaining bandwidth, network cost, signal strength. If terminal has a low processing power for using selected network and TV service, quality of service declines due to the system overloading. Hence, we implemented system which processes selected network and TV services accomplished by layer divided. Through experiments results, the method of direct user network selection waits for bandwidth assignment. However, on the one hand, that waiting time in exhausted situation will be very long. On the other hand, if we consider the priority plot of used networks, we should select the network with the best state. Therefore, data transmission rate will keep on average and the waiting time will be low.

• Journal of Advanced Navigation Technology
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• v.17 no.6
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• pp.693-699
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• 2013

In this paper, ${\pi}/4$-DQPSK modem according to ITU-R M.1842-1 recommendation Annex1 is investigated and simulated. At first, standardization and technical trend of VHF maritime mobile communication are introduced. The ${\pi}/4$-DQPSK modem defined in the Annex1 should support 28.8Kbps bit transmission rate within 25KHz frequency bandwidth. We describe the system model and simulation process of ${\pi}/4$-DQPSK modem transmitter and receiver design with RRC(Root Raised Cosine) transmitter and receiver filter. Then we suggest various graphical simulation results(time domain signals, constellation, power spectral density according to roll-off factor, eye diagram), and show simulated BER performance of the modem. From the simulation results, it is shown that roll-off factor of RRC filter affects to BER performance according to SNR and the designed simulation model meets the spectrum mask requirement suggested in ITU-R M.1842-1 recommendation.