• Journal of Advanced Navigation Technology
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• v.24 no.6
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• pp.587-592
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• 2020

The giant information exchange enabled by the Internet of Things paradigm will likely exploit electrical lines as a ready-to-use infrastructure. The advantage of using the pre-installed infrastructure of wiring networks makes power line communication a competitive technology for broad-band communications. Therefore, there has been a growing interest towards the use of existing power line communication channels as an effective means for transmitting high speed data and Internet service. One of the main noise types affecting power line communication systems is the impulsive noise, and the focus of this work is on the impact of this impulsive noise on the performance of OFDM-QPSK systems. For the performance analysis of impulsive noise, data measured in three environments were used. Through the analysis, it is shown that OFDM-QPSK system outperforms QPSK system for most of the impulsive noise cases. Also, RS-coded OFDM-QPSK system can achieve good BER performance under 3 cases impulsive noise environment.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3855-3863
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• 2022

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO₄-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5-15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where ${\frac{E}{AD}}{\geq}2MeV{\bullet}cm{\bullet}g^{-1}$, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when ${\frac{E}{AD}}<2MeV{\bullet}cm{\bullet}g^{-1}$.

• Journal of the Korean institute of surface engineering
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• v.55 no.2
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• pp.96-101
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• 2022

The effects of the growth temperature on the structural, optical, and morphological properties of BaWO₄:Sm³⁺ phosphor thin films were investigated. The BaWO₄:Sm³⁺ thin films were grown on quartz substrates at several growth temperatures by radio-frequency magnetron sputtering. All the thin films crystallized in a tetragonal structure with a main BaWO₄ (112) diffraction peak. The 830 nm-thick BaWO₄:Sm³⁺ thin films grown at 300 ℃ exhibited numerous polygon-shaped particles. The excitation spectra of BaWO₄:Sm³⁺ thin films consisted of a broad excitation band in the 200-270 nm with a maximum at 236 nm due to the O^2--Sm³⁺ charge transfer and two small bands peaked at 402 and 463 nm, respectively. Under 236 nm excitation, the BaWO₄:Sm³⁺ thin films showed an intense red emission peak at 641 nm due to the ⁴G_5/2→⁶H_9/2 transition of Sm³⁺, indicating that the Sm³⁺ ions occupied sites of non-inversion symmetry in the BaWO₄ host lattice. The highest emission intensity was observed for the thin film grown at 300 ℃, with a 51.8% transmittance and 5.09 eV bandgap. The average optical transmittance in the wavelength range of 500-1100 nm was increased from 53.2% at 200 ℃ to 60.8% after growing at 400 ℃. These results suggest that 300 ℃ is the optimum temperature for growing redemitting BaWO₄:Sm³⁺ thin films.

• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.62-70
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• 2001

The ZnSe sample grown by chemical bath deposition (CBD) method were annealed in Ar gas at $45^{\circ}C$. Using extrapolation method of X-ray diffraction pattern, it was found to have zinc blend structure whose lattice parameter $a_o$ was $5.6687\;{\AA}$. From Hall effect, the mobility was likely to be decreased by impurity scattering at temperature range from 10 K to 150 K and by lattice scattering at temperature range from 150 K to 293 K. The band gap given by the transmission edge changed from $2.700{\underline{5}}\;eV$ at 293 K to $2.873{\underline{9}}\;eV$ at 10 K. Comparing photocurrent peak position with transmission edge, we could find that photocurrent peaks due to excition electrons from valence band, ${\Gamma}_8$ and ${\Gamma}_7$ and to conduction band ${\Gamma}_6$ were observed at photocurrent spectrum. From the photocurrent spectra by illumination of polarized light on the ZnSe thin film, we have found that values of spin orbit coupling splitting ${\Delta}so$ is $0.098{\underline{1}}\;eV$. From the PL spectra at 10K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be $0.061{\underline{2}}\;eV$ and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be $0.017{\underline{2}}\;eV$, $0.031{\underline{0}}\;eV$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.2
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• pp.47-54
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• 2020

To develop the bright-vivid red- and yellow-inorganic fluorescent pigments with high luminescence properties, A₃V₅O₁₄ (A = K and Rb) and Cs₂V₄O₁₁ inorganic pigments were synthesized by a water assisted solid state reaction (WASSR) method and a conventional solid state reaction method. Although impurity peaks corresponding to the AVO₃ and AV₃O₈ (A = K, Rb, and Cs) were observed in all samples prepared, the trigonal structure A₃V₅O₁₄ (A = K and Rb) and orthorhombic structure Cs₂V₄O₁₁ were successfully obtained as a main phase. These inorganic pigments showed the broad absorption band (under 550 nm) originated from CT transitions of VO₄ polyhedron, and the strong broad red- and green-emission bands due to ³T₂ → ¹A₁ and ³T₁ → ¹A₁ transitions of the [VO₄]^3- group. The A₃V₅O₁₄ (A = K and Rb) and Cs₂V₄O₁₁ pigments showed a bright-vivid red- and yellow-body color, where the a* values of the A₃V₅O₁₄ (A = K and Rb) were +35.5 and +45.9, respectively, and b* value of Cs₂V₄O₁₁ pigments was +50.3. The L* values of the A₃V₅O₁₄ (A = K and Rb) and Cs₂V₄O₁₁ inorganic pigments were over +45. These results indicate that the A₃V₅O₁₄ (A = K and Rb) and Cs₂V₄O₁₁ inorganic pigments could be an attractive candidate as a bright-vivid red- and yellow inorganic pigments.

• Journal of Plant Biology
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• v.38 no.3
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• pp.305-317
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• 1995

The bryophyte communities on the forest floor of the mixed coniferous, deciduous broad-leaf forest and the evergreen coniferous forest of cool temperate and subalpine zones in Chiri Mountains with the highest peak (Cheonwangbong 1915 m) in south-central part of the Korean Peninsula were investigated from the phytosociology viewpoint. As a result, five bryophyte communities were recognized, considering the species composition of vascular vegetation; A. Sasamorpha borealis-Abies koreana/Dicranum scoparium-Plagiothecium silvaticum community, B. Bosta minor-Abies koreana/Anomodon rugelii-Plagiomnium cuspidatum community, C. Abies koreana/Hylocomiopsis ovicarpa-Entodon rubicundus community, D. Abies koreana-Picea jezoensis/Hylocomiopsis ovicarpa-Thuidium kanedae community, E. Abies koreana-Pieea jezoensis/Hylocomium splendens-Pleurozium sehreberi community. Among these, the communities A, B, C and D were distributed in the mixed coniferous and deciduous broad-leaf forest of lower altitudes (1200 to 1700 m) and characterized by the elements of the cool temperate zone. They were confimled as synusies belonging to the Fraxino-Abietetum koreanae Song 1988. The community E was distributed in higher altitudes (1700 m to near the summit) and characterized by the species group of the holarctic elements, e.g. Hyloeomium splendens, Pleurozium sehreberi, Dieranum majus, etc. limited in subarctic; subalpine and arctic; alpine zones. The community E was confirmed as a synusie of the Abieti koreanae-Piceetum jezoensis Song 1991 belonging the Vaecinio-Pieeetea Br.-BI. 1939. Up to date many investigator have described the coniferous forest distibuted above 1200 m in Chiri mountauns as the forest vegetation of subalpine zone. However, from the results of the present study, the boundary of the mixed forest and the true subalpine coniferous forest was elucidated to be ca. 1700 m phytosociologically. Species richness was highest in the community E, and the other four communities showed a similar species richness. Among the species diversity indices, H' and D were high in the communities Band E, low in the communities A and C, and medium in the community D. The values of J' decreased with the increase in altitudes and the community E showed the lowest value. The result of Bray-Curtis ordination revealed that the diversity analysis and the division of the above two forest zones are justifiable. The taxa of the bryophyte communities were composed of 25 families, 46 genera, 73 species, 1 subspecies and 2 varieties.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.184-184
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• 2012

Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.502-508
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• 2011

Synthesis of $Nd_{2x}Cd_{2-3x}SiO_4$ ($0.01{\leq}x{\leq}0.21$) [S1-S3: x=0.01, 0.11 and 0.21] solid solutions were prepared by solgel method. Powder x-ray diffraction (XRD) results show monoclinic unit cell with space group P21/m. The average crystallite sizes are found to be 20 to 45 nm. The Scanning Electron Microcopy (SEM) images show morphology of the sample is in globular nature. The energy dispersive analysis of x-rays (EDX) and X-ray mapping results confirmed that all the constituent elements of the composites were present and that were distributed in uniformly. The optical absorption band at ~750 nm was due to $^4I_{9/2}{\rightarrow}^4F_{7/2}+^4S_{3/2}$ transition optically active $Nd^{3+}$ ions. Electron Paramagnetic Resonance (EPR) lineshapes of S1-S3 at 10, 40, 77 and 300 K show a broad unresolved isotropic lineshapes were observed due to rapid spin lattice relaxation of $Nd^{3+}$.

• Ocean and Polar Research
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• v.39 no.3
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• pp.181-194
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• 2017

The long-term linear trend of global sea-to-air dimethyl sulfide (DMS) flux was analyzed over a 16-year time span (2000~2015), based on satellite observation data. The emission rates of DMS (i.e. DMS flux) in the global ocean were estimated from sea surface DMS concentrations, which were constructed with chlorophyll a (Chl-a) concentrations and mixed layer depths (MLD), and transfer velocity from sea to air, which was parameterized with sea surface wind (SSW) and sea surface temperature (SST). In general, the DMS flux in the global ocean exhibited a gradual decreasing pattern from 2000 (a total of 12.1 Tg/yr) to 2015 (10.7 Tg/yr). For the latitude band ($10^{\circ}$ interval between $0^{\circ}$ and $60^{\circ}$), the DMS flux at the low latitude of the Northern (NH) and Southern hemisphere (SH) was significantly higher than that at the middle latitude. The seasonal mean DMS flux was highest in winter followed by in summer in both hemispheres. From the long-term analysis with the Mann-Kendall (MK) statistical test, a clear downward trend of DMS flux was predicted to be broad over the global ocean during the study period (NH: $-0.001{\sim}-0.036{\mu}mol/m^2/day\;per\;year$, SH: $-0.011{\sim}-0.051{\mu}mol/m^2/day\;per\;year$). These trend values were statistically significant (p < 0.05) for most of the latitude bands. The magnitude of the downward trend of DMS flux at the low latitude in the NH was somewhat higher than that at the middle latitude during most seasons, and vice versa for the SH. The spatio-temporal characteristics of DMS flux and its long-term trend were likely to be primarily affected not only by the SSW (high positive correlation of r = 0.687) but also in part by the SST (r = 0.685).

• Journal of Life Science
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• v.13 no.1
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• pp.90-98
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• 2003

An allium rhizobacterium Serratia plymuthica AL-1 was previously selected as a biocontrol agent of allium white rot. The chitinase from S. plymuthica AL-1 produced in medium containing colloidal chitin was purified by ammonium sulfate precipitation (40~70%), affinity adsorption, column chromatography on DEAE-sephadex A-50 and sephadex C-200 gel filtration. The enzyme was purified 10.8-fold with a yield of 7.3% from the starting culture broth. The purified chtinase gave a single band on sodium dodecyl sulfate polyacrylamide gel electrophoresis, it's molecular weight was estimated to be 55 kDa. The optimum pH and temperature of the purified enzyme were pH 5.5 and $55^{\circ}C$, respectively and it is stable up to $50^{\circ}C$ and maintains around 90% of its activity for 60min. The enzyme were activated by $Ca^{2+}$, $Mn^{2+}$ and $Mg^{2+}$ and inhibited by $Cu^{2+}$, SDS, $\rho$-CMB, MIA, respectively. The purified chitinase showed broad spectrum of antifungal activities against plant pathogenic fungi Sclerotium cepivoruin, Alternana alternnta, Colletotrichum glceosporioidrs, Phoma sp., Sclerotinia sclerotiorum, Stemphylium solani, Fusarium oxysporium f. sp. niveum but rarely inhibited Phytophthora capsici and Pythium ultimum.. The purified chitinase from S. plymuthica AL-1 caused swelling, lysis, deceleration and degradation of the hyphal tips of S. sczerotiorum causing allium white rot. It suggest that S. prymuthica AL-1 chitinase play an important part in the bifunctional chitinase / lysozyme activity.