• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.4
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• pp.371-382
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• 2022

Carbonates are inorganic ligands that are abundant in natural groundwater. They strongly influence radionuclide mobility by forming strong complexes, thereby increasing solubility and reducing soil absorption rates. We characterized the spectroscopic properties of Am(III)-carbonate species using UV-Vis absorption and time-resolved laser-induced fluorescence spectroscopy. The deconvoluted absorption spectra of aqueous Am(CO₃)₂^- and Am(CO₃)₃^3- species were identified at red-shifted positions with lower molar absorption coefficients compared to the absorption spectrum of aqua Am³⁺. The luminescence spectrum of Am(CO₃)₃^3- was red-shifted from 688 nm for Am³⁺ to 695 nm with enhanced intensity and an extended lifetime. Colloidal Am(III)-carbonate compounds exhibited absorption at approximately 506 nm but had non-luminescent properties. Slow formation of colloidal particles was monitored based on the absorption spectral changes over the sample aging time. The experimental results showed that the solubility of Am(III) in carbonate solutions was higher than the predicted values from the thermodynamic constants in OECD-NEA reviews. These results emphasize the importance of kinetic parameters as well as thermodynamic constants to predict radionuclide migration. The identified spectroscopic properties of Am(III)-carbonate species enable monitoring time-dependent species evolution in addition to determining the thermodynamics of Am(III) in carbonate systems.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.15-20
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• 2007

Low temperature processed ZnO-TFTs on glass below $270^{\circ}C$ for plastic substrate applications were fabricated and their electrical properties were investigated. Films in ZnO-TFTs with bottom gate configuration were made by RF magnetron sputtering system except for $SiO_2$ gate oxide deposited by ICP-CVD. ZnO channel films were grown on glass with various Ar and $O_2$ flow ratios. All of the fabricated ZnO-TFTs showed perfectly the enhancement mode operation, a high optical transmittance of above 80% in visible ranges of the spectrum. In the ZnO-TFTs with pure Ar process, the field effect mobility, threshold voltage, and on/off ratio were measured to be $1.2\;cm^2/Vs$, 8.5 V, and $5{\times}10^5$, respectively. These characteristic values are much higher than those of the ZnO-TFTs of which ZnO channel layers were processed with additional $O_2$ gas. In addition, ZnO-TFT with pure Af process showed smaller swing voltage of 1.86v/decade compared to those with $Ar+O_2$ process.

• Nuclear Engineering and Technology
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• v.43 no.6
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• pp.567-572
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• 2011

A sensitivity analysis of the methods used to evaluate the transport properties of a CdZnTe detector was performed using two different radiations (${\alpha}$ particle and gamma-ray) emitted from an $^{241}Am$ source. The mobility-lifetime products of the electron-hole pair in a planar CZT detector ($5{\times}5{\times}2\;mm^3$) were determined by fitting the peak position as a function of biased voltage data to the Hecht equation. To verify the accuracy of these products derived from ${\alpha}$ particles and low-energy gamma-rays, an energy spectrum considering the transport property of the CZT detector was simulated through a combination of the deposited energy and the charge collection efficiency at a specific position. It was found that the shaping time of the amplifier module significantly affects the determination of the (${\mu}{\tau}$) products; the ${\alpha}$ particle method was stabilized with an increase in the shaping time and was less sensitive to this change compared to when the gamma-ray method was used. In the case of the simulated energy spectrum with transport properties evaluated by the ${\alpha}$ particle method, the peak position and tail were slightly different from the measured result, whereas the energy spectrum derived from the low-energy gamma-ray was in good agreement with the experimental results. From these results, it was confirmed that low-energy gamma-rays are more useful when seeking to obtain the transport properties of carriers than ${\alpha}$ particles because the methods that use gamma-rays are less influenced by the surface condition of the CZT detector. Furthermore, the analysis system employed in this study, which was configured by a combination of Monte Carlo simulation and the Hecht model, is expected to be highly applicable to the study of the characteristics of CZT detectors.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.589-592
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• 2000

무선 LAN은 유선 LAN을 대체하기 보다는 기간망과 이동(Mobile) 사용자간의 수십 미터 이내의 종단 연결점을 제공한다는 개념으로 구성되며, 이동성(Mobility)과 확장성(Scalability)을 발휘할 수 있다는 장점으로 많은 응용 분야에서 각광을 받고 있다. 초광대역 시간 도약(ultra wideband time hopping; UWB/TH) 임펄스 무선기술은 기존 시스템의 정상적인 동작에 거의 영향을 미치지 않기 때문에 별도의 주파수 할당이 필요치 않는 새로운 기술이다. 본 논문에서는 IEEE 802.11의 무선 LAN의 프로토콜을 기적으로 사용하고 전송 방식을 직접수열 확산 스펙트럼 방식을 사용하는 기존의 방법과 임펄스 라디오 방식을 사용하는 경우를 비교하였다.

• Journal of the Korean Magnetic Resonance Society
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• v.18 no.1
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• pp.41-46
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• 2014

In order to obtain information on the structural geometry of $NH_4HSeO_4$ near the phase transition temperature, the spectrum and spin-lattice relaxation time in the rotating frame $T_{1{\rho}}$ for the ammonium and hydrogen-bond protons were investigated through $^1H$ MAS NMR. $T_{1{\rho}}$ for the hydrogen-bond protons abruptly decreased at high temperature and it is associated with the change in the structural geometry in $O-H{\cdots}O$ bonds. This mobility of the hydrogen-bond protons may be the main reason for the high conductivity.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.1909-1915
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• 2004

The hermetic rotary compressor is one of the most important components of an air conditioning system since it has a great effect on both the performance and the noise and vibration of the system. Noise and vibration occurs due to gas pulsation during the compression process and to unbalanced dynamic force. In order to reduce noise and vibration, it is necessary to identify their sources and transmission path and effectively control them. Many approaches have been tried in order to identify the noise transmission path of a compressor. However, identification has proven to be difficult since the characteristics of compressor noise are complicated due to the interaction of the compressor parts and gas pulsation. In this study, the statistical energy analysis has been used to trace the energy flow in the compressor and to identify the transmission paths from the noise source to the exterior sound field.

• Journal of Communications and Networks
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• v.8 no.2
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• pp.175-181
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• 2006

This paper addresses an in-depth analysis of the stratosphere-to-Earth co-channel interference produced by high-altitude platforms (HAPs) and proposes a new methodology for the evaluation of its impact to terrestrial systems in terms of fractional degradation in performance, taking into account parameters such as HAP's mobility, realistic distribution of azimuth and elevation angles of the terrestrial microwave links (TMLs), and gradual high-altitude platform network (HAPN) loading. Simulations performed for different HAPN configurations, prove that the implementation of the methodology proposed, may lead to a more efficient use of the spectrum shared between the two services.

• Interaction and multiscale mechanics
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• v.5 no.4
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• pp.347-368
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• 2012

Measuring the bridge frequencies indirectly from an instrumented test vehicle is a potentially powerful technique for its mobility and economy, compared with the conventional direct technique that requires vibration sensors to be installed on the bridge. However, road surface roughness may pollute the vehicle spectrum and render the bridge frequencies unidentifiable. The objective of this paper is to study such an effect. First, a numerical simulation is conducted using the vehicle-bridge interaction element to demonstrate how the surface roughness affects the vehicle response. Then, an approximate theory in closed form is presented, for physically interpreting the role and range of influence of surface roughness on the identification of bridge frequencies. The latter is then expanded to include the action of an accompanying vehicle. Finally, measures are proposed for reducing the roughness effect, while enhancing the identifiability of bridge frequencies from the passing vehicle response.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.346.2-346.2
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• 2014

To use the GaN based light-emitting diodes (LEDs) as solid state lighting sources, the improvement of light extraction and internal quantum efficiency is essential factors for high brightness LEDs. In this study, we suggested the new materials system of a zinc tin oxide (ZTO) layer formed on blue LED epi-structures to improve the light extraction. ZTO is a representative n-type oxide material consisted of ZnO and SnO system. Moreover, ZTO is one of the promising oxide semiconductor material. Even though ZTO has higher chemical stability than IGZO owing to its SnO2 content this has high mobility and high reliability. After formation of ZTO layer on p-GaN layer by using the spin coating method, structural and optical properties are investigated. The x-ray diffraction (XRD) measurement results show the successful formation of ZTO. The photoluminescence (PL) and absorption spectrum shows that it has 3.6-4.1eV band gap. Finally, the light extraction properties of ZTO/LED chip using electroluminescence (EL) measurement were investigated. The experimental and theoretical analyses were simultaneously conducted.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.72-75
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• 1996

A hydride vapor phase epitaxy (HVPE) method is performed to prepare the GaN thin films on c-plane sapphire substrate. The full-width at half maximum of double crystal X-ray rocking curves from 20$\mu\textrm{m}$-thick GaN was 576 arcsecond. The photoluminescence spectrum measured 10 K shows the hallow bound exciton (I$_2$) line and weak donor-acceptor peak, however, there was not observed deep donor-acceptor pair recombination indicate the GaN crystals prepared in this study are of high purity and high crystalline quality. The GaN layer is n-type conducting with electron mobility of 72 $\textrm{cm}^2$/V$.$sec and with carrier concentration of 6 x 10$\^$18/cm/sup-3/.