• Korean Journal of Materials Research
• /
• v.23 no.3
• /
• pp.161-167
• /
• 2013

The ZnO thin films were grown on GaN template substrates by RF magnetron sputtering at different RF powers and n-ZnO/p-GaN heterojunction LEDs were fabricated to investigate the effect of the RF power on the characteristics of the n-ZnO/p-GaN LEDs. For the growth of the ZnO thin films, the substrate temperature was kept constant at $200^{\circ}C$ and the RF power was varied within the range of 200 to 500W at different growth times to deposit films of 100 nm thick. The electrical, optical and structural properties of ZnO thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and by assessing the Hall effect. The characteristics of the n-ZnO/p-GaN LEDs were evaluated by current-voltage (I-V) and electroluminescence (EL) measurements. ZnO thin films were grown with a preferred c-axis orientation along the (0002) plane. The XRD peaks shifted to low angles and the surface roughness became non-uniform with an increase in the RF power. Also, the PL emission peak was red-shifted. The carrier density and the mobility decreased with the RF power. For the n-ZnO/p-GaN LED, the forward current at 20 V decreased and the threshold voltage increased with the RF power. The EL emission peak was observed at approximately 435 nm and the luminescence intensity decreased. Consequently, the crystallinity of the ZnO thin films grown with RF sputtering powers were improved. However, excess Zn affected the structural, electrical and optical properties of the ZnO thin films when the optimal RF power was exceeded. This excess RF power will degrade the characteristics of light emitting devices.

• Korean Journal of Optics and Photonics
• /
• v.10 no.2
• /
• pp.152-156
• /
• 1999

We have developed the pulse-width variable Quenched Dye Laser (QDL). QDL consisted of the dye cell of 5 mm length containing a $2.5{\times}10^{-3}$[mol/l] solution of Rhodamine 6G and the cylindrical lens focal length of 150 mm and quenching mirror. QDL system was pumped by s XeCl excimer laser with 150 mJ pulse energy in a 20 ns pulse at 1 Hz repetition rate. Pulse-width of QDL was measured by a noncollinear intensity autocorrelator. The focused thckness was measured by changing the position of the focusing cylindrical lens. Pulse-width of QDL as a function of the focused thickness (273.0${\mu}{\textrm}{m}$~845.0${\mu}{\textrm}{m}$) varied continuously from 86 ps to 201 ps.

• Journal of Species Research
• /
• v.2 no.2
• /
• pp.159-166
• /
• 2013

Typical of large, oligotrophic lakes, Lake H$\ddot{o}$vsg$\ddot{o}$l, Mongolia, exhibits complex morphometry which should support a spatially heterogeneous community of benthic macroinvertrates. The lake also exhibits a broad range of land uses. Based on the variation in land use and complex physical habitat of the lake (e.g. substrate variation and presence of affluent streams in bays), we asked two questions. First, does density of total benthic macroinvertebrates vary between different bays in Lake H$\ddot{o}$vsg$\ddot{o}$l? Second, does density of individual benthic taxa vary by bay? Samples collected in 1997, the last year for benthic sampling of the lake, were designed to test for variation in macroinvertebrate density between bays and can now be used to establish baseline variation in density for future studies. A total of 56 Ponar grab samples were analyzed from six bays in Lake H$\ddot{o}$vsg$\ddot{o}$l. Results of a general linear model analysis of variance showed that total density of macroinvertebrates varied only slightly between bays of the lake, but that most individual taxa showed significant variation between bays. Variation in density for most taxa was linked to substrate composition rather than other geographic or physical variables in the lake. Recent increases in grazing intensity and ecotourism along the shores should be managed to reduce the nutrient load into the lake to avoid impairment of the benthic biota of this unique, ancient ecosystem.

• Food Science of Animal Resources
• /
• v.33 no.2
• /
• pp.181-188
• /
• 2013

The aim of this study was to investigate the quality properties of beef jerky replaced salt with soy sauce, red pepper paste, and soybean paste. The quality properties of beef jerky including final water activity ($a_w$), moisture content, pH, color, shear force, total plate counts, thiobarbituric acid reactive substance (TBARS) values, and sensory evaluations were investigated. The sliced beef samples were marinated in salt (control), soy sauce (T1), red pepper paste (T2), and soybean paste (T3) for 24 h and then dried at $70^{\circ}C$ for 6-8 h. The water activity of finished beef jerky varied from 0.72 to 0.70. The water activity for control and T1 samples decreased more rapidly as drying proceeded up to 6 h. The samples with salt replacement showed a lower pH and lightness than the control (p<0.05). The T1 sample showed a significant decrease in total plate counts after 21 d of storage (p<0.05). The TBARS for all treatments increased with storage days (p<0.05). The TBARS were significantly lower in T2 and T3 samples compared to control and T1 until 21 d of storage (p<0.05). The samples with salt replacement showed a lower intensity of saltiness than the control. Sensory evaluations found that the replaced soy sauce of beef jerky samples had better overall acceptability scores than the other treatment samples. It was concluded that replacing salt with soy sauce can delay lipid oxidation and enhance the sensory acceptance of beef jerkies.

• Microbiology and Biotechnology Letters
• /
• v.24 no.4
• /
• pp.519-524
• /
• 1996

The kinetics of growing microalga, Spirulina platensis was investigated to treat swine wastes with optimum growth conditions. Temperature was varied from 15 to 40$\circ$C at three different light intensities, 6 W/m$^{2}$, 12 W/m$^{2}$ and 24 W/m$^{2}$. The specific growth rate was increased as temperature increased up to 30$\circ$C. The activation energy was estimated as 13.5 kcal/mol by an Arrhenius relationship. 0.24 (1/day) of specific growth rate was obtained from batch cultivation with 30% swine wastes, compared to 0.31 (1/day) from clean culture. It was found that Spirulina platensis was able to reduce 70-93% of PO$_{4}$$^{3-}$ -P, 67-93% of inorganic nitrogen, 80-90% of COD and 37-56% organic nitrogen by adding various concentrations of swine wastes for 12 days of batch cultivation. Rate constants for removing nitrates and phosphates in treating swine wastes were estimated as 0.17 (1/day) and 0.14 (1/day) in the first order reaction, respectively. 1.52 (g/L) of maximum cell density was maintained at 0.20 (1/day) of dilution rate in continuous culture, adding 20% swine wastes for 30 days. The chemical composition of the biomass obtained from the process showed 58.7% of protein, 11.0% of lipid and 15.6% of ash.

• Environmental Engineering Research
• /
• v.18 no.4
• /
• pp.235-239
• /
• 2013

In the present investigation, the efficiency of Chlorella vulgaris (C. vulgaris) was evaluated for the removal of ammonia-nitrogen from wastewater. Eight different wastewater samples were prepared with varied amounts of $NH_4-N$ concentrations from 15.22 to 205.29 mg/L. Experiments were conducted at pH $7.5{\pm}0.3$, temperature $25^{\circ}C{\pm}1^{\circ}C$, light intensity $100{\mu}E/m^2/s$, and dark-light cycles of 8-16 hr continuously for 8 days. From the results, it was found that $NH_4-N$ was completely removed by C. vulgaris, when the initial concentration was between 5.22-25.24 mg/L. However, only 50% removal was obtained when the $NH_4-N$ concentration was 85.52 mg/L, which further decreased to less than 32% when the $NH_4-N$ concentration exceeded 105.43 mg/L. The further influence of nitrogen on chlorophyll was studied by various $NH_4-N$ concentrations. The maximal value of chlorophyll a (Chl a) content was found to be 19.21 mg/L for 65.79 mg/L $NH_4-N$ concentration, and the maximum specific $NH_4-N$ removal rate of 1.79 mg/mg Chl a/day was recorded at an $NH_4-N$ concentration of 85.52 mg/L. These findings demonstrate that C. vulgaris could potentially be employed for the removal of $NH_4-N$ from wastewater.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.347-350
• /
• 1998

We studied relation of X-ray diffraction and charge/discharge capacity of LiMn$_2$O$_4$ cathode. LiMn$_2$O$_4$ is prepared by reacting stoichiometric mixture of LiOH.$H_2O$ and MnO$_2$ (mole ratio 1 : 2) and heating at $700^{\circ}C$, 80$0^{\circ}C$ for 24hr, 36hr, 48hr, 60hr and 72hr. Through X-ray diffraction pattern, it is analyzed that crystal structure and lattice parameter and peak ratio so on. We obtained X-ray diffraction pattern that varied lattice parameter and peak intensity by function of calcining temperature and time. Cathode active materials calcined at 80$0^{\circ}C$ for 36hr shown that (111)/(311) Peak ratio at X-ray diffraction pattern was 0.37. It means that crystal structure is formed very well in this temperature and time. In the result of charge/discharge test, cathode active material calcined at 80$0^{\circ}C$ for 36hr displayed excellent charge/discharge properties than that of cathode active materials calcined at other temperature and title. In this study, we certified that spinel structure basied cubic is formed very well at 80$0^{\circ}C$ for 36hr. In this case, (111)/(311) peak ratio at X-ray diffraction is 0.37, and charge/discharge properties is excellent than others.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.5
• /
• pp.60-69
• /
• 2013

An optimum configuration of the hybrid/dual swirl jet combustor for a micro-gas turbine was investigated experimentally. Location of pilot nozzle, angle and direction of swirler vane were varied systematically as main parameters under the conditions of constant thermal load. The results showed that the variation in locations of inner fuel nozzle and pilot burner resulted in significant change in flame shape and swirl intensity due to the changes in recirculating flow pattern and minimum flow area near burner exit, in particular, with the significant reduction of CO emission near lean-flammability limit. In addition, it was observed that the co-swirl configuration produced less CO and NOx emissions compared to the counter-swirl configuration.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.5
• /
• pp.70-79
• /
• 2013

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine (MGT) were numerically investigated. Location of pilot burner, swirl angle and direction were varied as main parameters with the identical thermal load. As a result, the variations in location of pilot nozzle, swirl angle and direction resulted in the significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus the flame stability and emission performance might be significantly changed. With the comparison of experimental results, the case of swirl angle $45^{\circ}$ and co-swirl flow including optimum location of pilot burner were chosen in terms of the flame stability and emissions for the development of hybrid/dual swirl jet combustor.

• Journal of Fisheries and Marine Sciences Education
• /
• v.24 no.1
• /
• pp.18-24
• /
• 2012

This study analyses the effects of various angles in sculling on human body lift and drag by means of computational fluid dynamics, discusses the importance of sculling and provides a basis for the development of future water safety education programmes. Study subjects were based on the mean data collected from males in the age of 20s from a survey on the anthropometric dimensions of the Koreans. Moreover, lift, drag as well as coefficient values, all of which were governed by the angle of the palm, were calculated using 3-dimentional modelling produced by computational fluid dynamics programmes i.e. CFD. Interpretations were performed via general k-${\varepsilon}$ turbulence modelling in order to determine lift, drag and coefficient values. Turbulence intensity was set to one per cent as per the figures from preceding research papers and 3-dimentional simulations were performed for a total of five different angles $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$. The drag and lift values for the differing angles of the hands during sculling movement are as follows. The lift and drag values gradually increased with the increasing angle of the palm, however, the magnitude of increase for drag started to predominate lift from $45^{\circ}$ and lift gradually decreased from $60^{\circ}$. Overall, it is concluded that the optimal efficiency of sculling can be achieved at the angles $15^{\circ}$ and $30^{\circ}$, and it is anticipated that greater safety and informative education can be ensured for Life saving trainees if the results were to be applied to practical settings. However, as the study was conducted using simulation programmes which performed analyses on the collected anthropometric dimension, the obtained results cannot be made universal, which warrants furthers studies involving varied study subjects with actual measurements taken in water.