• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.183-184
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• 2006

The simulation on the mechanism of terahertz NSOM(near-field scanning optical microscopy) have been investigated. Based on experimental results, we have demonstrated the antenna effects on the coupling between a metal tip and substrate for an emission-type terahertz NSOM. It has been found that the lateral resolution can be estimated by a simplified model using an infinitesimal dipole in the substrate.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.151-154
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• 1996

We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform ($B_u$), random ($B_r$), and total ($B_t$) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of $B_t$ is 4.2$\mu$G and we adopt $B_u\~$2.2 and $B_r\~3.6{\mu}G$. $B_t$ is higher in spiral arms, reaching $\~5.9{\mu}G$. $B_t$ is higher for smaller $R_{Gal}$, reaching $\~8.0{\mu}G$ for $R_{Gal}$ = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.

• Current Optics and Photonics
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• v.2 no.6
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• pp.508-513
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• 2018

We report the development of a theoretical model describing the strong field tunneling of electrons in an extremely small nanogap (having a width of a few nanometers) that is driven by terahertz-pulse irradiation, by modifying a conventional semiclassical model that is widely applied for near-infrared wavelengths. We demonstrate the effects of carrier-envelope phase difference and strength of the incident THz field on the tunneling current across the nanogap. Additionally, we show that the dc bias also contributes to the generation of tunneling current, but the nature of the contribution is completely different for different carrier-envelope phases.

• Journal of Ceramic Processing Research
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• v.20 no.1
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• pp.80-83
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• 2019

The Mn4+-activated Li2ZnSn2O6 (LZSO:Mn4+) red phosphors were synthesized by the solid-state reaction at temperatures of 1100-1400 ℃ in air. The synthesized LZSO:Mn4+ phosphors were confirmed to have a single hexagonal LZSO phase without the presence of any secondary phase formed by the Mn4+ addition. With near UV and blue excitation, the LZSO:Mn4+ phosphors exhibited a double band deep-red emission peaked at ~658 nm and ~673 nm due to the 2E → 4A2 transition of Mn4+ ion. PL emission intensity showed a strong dependence on the Mn4+ doping concentration and the 0.3 mol% Mn4+-doped LZSO phosphor produced the strongest PL emission intensity. Photoluminescence emission intensity was also found to be dependent on the calcination temperature and the optimal calcination temperature for the LZSO:Mn4+ phosphors was determined to be 1200 ℃. Dynamic light scattering (DLS) and field-effect scanning electron microscopy (FE-SEM) analysis revealed that the 0.3 mol% Mn4+-doped LZSO phosphor particles have an irregularly round shape and an average particle size of ~1.46 ㎛.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.93.1-93.1
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• 2014

The reflection nebula NGC 7023 is a typical example of a photodissociation region (PDR), which consists of high density molecular gas that is exposed to an intense UV radiation field. The source of the UV photons in NGC 7023 is the young pre-main-sequence Be star HD 200755. We present our near-infrared high-resolution (R ~ 40,000) spectrum of NGC 7023, covering a region of $1{\times}15$ arcseconds, observed during the commissioning runs of IGRINS (Immersion GRating near-INfrared Spectrometer). The spectrum shows many strong narrow emission lines that arise from the molecular rovibrational transitions of H2. From the intensity ratios between these H2 lines, we investigate physical conditions within the PDR such as the temperature, density, and pressure. The high spectral resolution of IGRINS allows us to resolve the velocity field of the PDR. In addition, we compare the IGRINS spectrum to Cloudy PDR model.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.291-298
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• 2016

In this paper, we studied about the radiated emission of EFT(Electrical Fast Transient)/Burst signal, referenced IEC-61000-4-4 of the international EMC standard and its effect on EUT(Equipment Under the Test) when EFT/Burst signal (Conducted noise) induced on a power cable to EUT. Firstly, we set up test sample by the standard and +4 kV standard signal is induced by EFT/Burst signal generator with 1 m length power cable for 1 minute. Consequently, we found not only induced EFT/Burst signal along power line, but also directly radiated emission signal from EFT/Burst signal generator (Radiated emission noise of EFT/Burst). The radiated emission signal of EFT/Burst was 30 dB which is higher than limit of CISPR 22 which is international EMC standard. Moreover, we measured the electric field strength by changing distance from maximum radiated emission point to electric field strength tester. As a result, this electric field strength was 23 V/m which is higher than international EMC standard test level(CISPR 24). Therefore, it was confirmed that the probability of malfunction may be high when radiated emission of EFT/Burst noise exists near the EUT.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.149-154
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• 2007

This study examines the effect of acoustic excitation using forced coaxial air on the flame characteristics of turbulent hydrogen nonpremixed flames. A resonance frequency was selected to acoustically excite the coaxial air jet due to its ability to effectively amplify the acoustic amplitude and reduce flame length and NOx emissions. Acoustic excitation causes the flame length to decrease by 15 % and consequently, a 25 % reduction in EINOx is achieved, compared to a flame without acoustic excitation. Moreover, acoustic excitation induces periodical fluctuation of the coaxial air velocity, thus resulting in slight fluctuation of the fuel velocity. From phase-lock PIV and OH PLIF measurement, the local flow properties at the flame surface were investigated under acoustic forcing. During flame-vortex interaction in the near field region, the entrainment velocity and the flame surface area increased locally near the vortex. This increase in flame surface area and entrainment velocity is believed to be a crucial factor in reducing flame length and NOx emission in coaxial jet flames with acoustic excitation. Local flame extinction occurred frequently when subjected to an excessive strain rate, indicating that intense mass transfer of fuel and air occurs radially inward at the flame surface.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.9
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• pp.957-967
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• 2008

In this paper, we propose the prediction algorithm of radiation emission from the PCB in an enclosure with a rectangular aperture. PCB scanner is used to measure the near field, which is substituted with an equivalent electric dipole source. Green function and Fourier transform are utilized to represent the electromagnetic fields within and outside the enclosure, respectively. The radiation emission is estimated by using the mode matching technique and surface equivalent theorem. The theoretical results are compared with the measurement to check the accuracy of our analysis.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.1
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• pp.71-76
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• 2008

Purpose: A simple and efficient method to prepare nanocrystalline ZnO thin film with pure strong UV emission on soda-lime-silica glass substrates by low-temperature annealing was improved. Methods: Crystal structural, surface morphological, and optical characteristics of nanocrystalline ZnO thin films deposited on soda-lime-silica glass substrates by prefiring final annealing process at 300$^{\circ}C$ were investigated by using X-ray diffraction analysis, field emission-scanning electron microscope, scanning probe microscope, ultraviolet-visible-near infrared spectrophotometer, and photoluminescence. Results: Highly c-axis-oriented ZnO films were obtained by prefiring at 300$^{\circ}C$. A high transmittance in the visible spectra range and clear absorption edge in the ultra violet range of the film was observed. The PL spectrum of ZnO thin film with a deep near band edge emission was observed while the defect-related broad green emission was nearly quenched. Conclusions: Our work will be possibly adopted to cheaply and easily fabricate ZnO-based optoelectronic devices at low temperature, below 300$^{\circ}C$, in the future.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.891-894
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• 2014

The ultrashort electron pulse, laser-emitted from the metal tip apex has been characterized and used as a probing source for a new electron microscope to visualize the morphology of the gold-mesh in the nanometric resolution. As the gap between the tungsten tip and Au-surface is approached within a few nm, the large electromagnetic field enhancement for the incident P-polarized laser pulse with respect to the tip-sample axis is strongly observed. Here, we demonstrate that the time-resolved tip-enhanced electron emission microscope (TEEM) can be implemented on the laboratory table top to give the two-dimensional image, opening lots of challenges and opportunities in the near future.