• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.793-799
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• 2005

A composite cathode of LSCF$(La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3)\;and\;GDC\; (Gd_2O_3-doped\;CeO_2:Ce_{0.9}Gd_{0.1}O_{1.95_})$ was characterized in terms of an electrode response, using a point contact in an Yttria-Stabilized Zirconia (YSZ) electrolyte incorporated into AC two-point impedance spectroscopy. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point contact on the planar LSCF/GDC electrode. The point contact interface increases the bulk resistance allowing the estimation of the point contact geometry and resolving the electrode-related responses. The resultant impedance spectra are analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The bulk responses can be resolved from the electrode-related portions in terms of spreading resistance. The electrode-related polarizations are measured in terms of temperature and oxygen partial pressure. The modified impedance spectroscopy is discussed in terms of methodology and analytical aspects, toward resolving the electrode-polarization issues in solid oxide fuel cells.

• Ceramist
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• v.22 no.4
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• pp.350-356
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• 2019

Recently, transition metal dichalcogenide (TMDC) monolayers have been the subject of research exploring the physical phenomenon generated by low dimensionality and high symmetry. One of the keys to understanding new physical observations is the electronic band structure of 2D TMDCs. Angle-resolved photoelectron spectroscopy (ARPES) is, to this point, the best technique for obtaining information on the electronic structure of 2D TMDCs. However, through ARPES research, obtaining the long-range well-ordered single crystal samples always proves a challenging and obstacle presenting issue, which has been limiting towards measuring the electronic band structures of samples. This is particularly true in general 2D TMDCs cases. Here, we introduce the approach, with a mathematical framework, to overcome such ARPES limitations by employing the high level of symmetry of 2D TMDCs. Their high symmetry enables measurement of the clear and sharp electronic band dispersion, which is dominated by the band dispersion of single-crystal TMDCs along the two high symmetry directions Γ-K and Γ-M. In addition, we present two important studies and observations for the direct measuring of the exciton binding energy and charge transfer of 2D TMDCs, both being established by the above novel approach.

• Journal of the Korean Ceramic Society
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• v.50 no.2
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• pp.163-167
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• 2013

A modified two-point impedance spectroscopy technique exploits the geometric constriction between an electrolyte and a cathode with an emphasis on semispherical-shaped electrolytes. The spatial limitation in the electrolyte/electrode interface leads to local amplification of the electrochemical reaction occurring in the corresponding electrolyte/electrode region. The modified impedance spectroscopy was applied to electrical monitoring of a YSZ ($Y_2O_3$-stabilized $ZrO_2$)/SSC ($Sm_{0.5}Sr_{0.5}CoO_3$) system. The resolved bulk and interfacial component was numerically analyzed in combination with an equivalent circuit model. The effectiveness of the "spreading resistance" concept is validated by analysis of the electrode polarization in the cathode materials of solid oxide fuel cells.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.482-486
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• 1999

Ultrafast carrier dynamics of LT-GaAs semiconductors was investigated by using time-resolved photoreflectance spectroscopy. We can see that decay dynamics of photoreflectance generated by carriers depends strongly on the excitation wavelength due to the structure distortion of LT-GaAs semiconductors. Ultrafast trapping of excited carriers into deep trap states gives rise to transient photoreflectance decays with a lifetime shorter than 1 ps. Also, the long-lived photoreflectance is attributed to the carriers trapped deeply at point defects. fects.

• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.40-46
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• 2012

Purpose : To investigate the feasibility of in vivo proton magnetic resonance spectroscopy (MRS) for evaluation of lung cancer. Materials and Methods: This prospective study was approved by the institutional review board of our hospital and informed consent was obtained in all patients. Ten patients (7 men, 3 women; mean age, 64.4) with pathologicallyproven lung cancer (mean, 56.8 mm; range, 44-77 mm) were enrolled to 1.5 T MRS using a single-voxel respiration-triggered point-resolved spectroscopic sequence. Technical success rate and the reason of technical failure, if any, were investigated. Results: Out of 10 lung cancers, analyzable MRS spectra were obtained in 8 tumors (technical success rate, 80%). Two MRS datasets were not able to be analyzed due to serious baseline distortion. Choline and lipid signals were detected as major metabolites in analyzable MRS spectra. Conclusion: In vivo proton MRS method using a single-voxel respiration-triggered point-resolved spectroscopic sequence is feasible in obtaining the MR spectra of lung cancer because these spectra were analyzable and high success rate was shown in our study although there was the limitation of small patient group.

• Investigative Magnetic Resonance Imaging
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• v.19 no.4
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• pp.212-217
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• 2015

Purpose: For a single time-point hyperpolarized $^{13}C$ magnetic resonance spectroscopy imaging (MRSI) of animal models, scan-time window after injecting substrates is critical in terms of signal-to-noise ratio (SNR) of downstream metabolites. Pre-scans of time-resolved magnetic resonance spectroscopy (MRS) can be performed to determine the scan-time window. In this study, based on two-site exchange model, protocol-specific simulation approaches were developed for $^{13}C$ MRSI and the optimal scan-time window was determined to maximize the SNR of downstream metabolites. Materials and Methods: The arterial input function and conversion rate constant from injected substrates (pyruvate) to downstream metabolite (lactate) were precalibrated, based on pre-scans of time-resolved MRS. MRSI was simulated using two-site exchange model with considerations of scan parameters of MRSI. Optimal scan-time window for mapping lactate was chosen from simulated lactate intensity maps. The performance was validated by multiple in vivo experiments of BALB/C nude mice with MDA-MB-231 breast tumor cells. As a comparison, MRSI were performed with other scan-time windows simply chosen from the lactate signal intensities of pre-scan time-resolved MRS. Results: The optimal scan timing for our animal models was determined by simulation, and was found to be 15 s after injection of the pyruvate. Compared to the simple approach, we observed that the lactate peak signal to noise ratio (PSNR) was increased by 230%. Conclusion: Optimal scan timing to measure downstream metabolites using hyperpolarized $^{13}C$ MRSI can be determined by the proposed protocol-specific simulation approaches.

• Journal of radiological science and technology
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• v.39 no.2
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• pp.143-148
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• 2016

The purpose of this study was examined the measurement error factor on AMARES of jMRUI method for magnetic resonance spectroscopy (MRS) quantitative analysis by skilled and unskilled observer method and identified the reason of independent observers. The Point-resolved spectroscopy sequence was used to acquired magnetic resonance spectroscopy data of 10 weeks male Sprague-Dawley rat liver. The methylene protons ($(-CH_{2-})n$) of 1.3 ppm and water proton ($H_2O$) of 4.7 ppm ratio was calculated by LCModel software for using the reference data. The seven unskilled observers were calculated total lipid (methylene/water) using the jMRUI AMARES technique twice every 1 week, and we conducted interclass correlation coefficient (ICC) statistical analysis by SPSS software. The inter-observer reliability (ICC) of Cronbach's alpha value was less than 0.1. The average value of seven observer's total lipid ($0.096{\pm}0.038$) was 50% higher than LCModel reference value. The jMRUI AMARES analysis method is need to minimize the presence of the residual metabolite by identified metabolite MRS profile in order to obtain the same results as the LCModel.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1182-1182
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• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• Journal of Korean Neurosurgical Society
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• v.51 no.5
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• pp.312-315
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• 2012

We report magnetic resonance image (MRI) and magnetic resonance spectroscopy (MRS) findings in a patient of cerebral fat embolism (CFE) occurred in a 26-year-old woman after an autologous fat injection into the face. After initial neurologic symptom onset, MRI and MRS data were obtained two times to investigate repeated CFE. We obtained the MRS data in the two different time intervals and two different echo times to compare the lesions with normal brain parenchyma. The results of MRS data showed that a decrease in N-acetyl-aspartate, an increase in lactate and a very high early peak of free lipids between 0.9 and 1.4 ppm were obtained at the acute infarcted lesion as compared with normal brain parenchyma. In addition, these findings were more clearly detected on short echo time spectrum rather than long spectrum. A close relationship between the clinical manifestations and MRI and MRS findings of the brain can helpful to distinguish CFE with other conditions and to evaluate the cause materials of infarctions rather than conventional MRI or diffusion-weighted imaging.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.302-302
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• 2011

The binary chalcogenide semiconductor Bi2Se3 is at the center of intensive research on a new state of matter known as topological insulators. It has Dirac point in their band structures with robust surface states that are protected against external perturbations by strong spin-orbit coupling with broken inversion symmetry. Such unique band configurations were confirmed by recent angle-resolved photoelectron emission spectroscopy experiments with an unwanted n-type doping effect, showing a Fermi level shift of about 0.3 eV caused by atomic defects such as Se vacancies. Since the number of defects can be reduced using the molecular beam epitaxy (MBE) method. We have prepared the Bi2Se3 film on noble metal Au(111) and semiconductor Si(111) substrates by MBE method. To characterize the film, we have introduced several surface sensitive techniques including x-ray photoemission electron spectroscopy (XPS) and micro Raman spectroscopy. Also, crystallinity of the film has been confirmed by x-ray diffraction (XRD). Using home-built scanning tunneling microscope, we observed the atomic structure of quintuple layered Bi2Se3 film on Au(111).