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[en] In order to develop and design a good transmutation system, it is necessary first to select the best available coolant material for a reactor coolant system. Choosing the best coolant material may not be easy since there are several criteria associated with thermal performance, safety problem, cost problem, neutronic aspects. etc. The best option should be chosen based on the maximization of our needs in this situation. It is a challenging task. Decision theory can be employed to solve this type of problem. This report presents the feasibility study for evaluating the best coolant material in transmutation reactors based on the multi=attribute utility theory. The main problem presented here is how to logically evaluate candidate coolant materials under multiple criteria such as thermal performance, safety problem, cost problem, cost problem, neutronic aspects, etc. Since the current problem involves multiple criteria or attributes, first of all, the multi-attribute utility theory (MAUT) such as SMART and AHP has been extensively reviewed. Then, many candidate coolant material for transmutation reactors have been identified. The next step is to construct a value tree that express to reflect the relative importance of the attributes for overall evaluation. Finally, given these assignments, the final goal were obtained by manipulating these ranks through the value tree. The proposed approach is intended to help people be rational and logical in making decisions such complex tasks. (author). 8 refs., 7 tabs., 22 figs
[en] The influence of vacuum pressure (VP) on the field emission (FE) properties of ZnO nanowires (ZNWs) were investigated by using in-situ measurements of the emission current and the VP. The FE of ZNWs showed a stable and rapid response to variations in the high-vacuum pressure range from ∼10-6 to 10-3 Torr at room temperature, showing a straight line plot of log(l) versus log(1/p). From Fowler-Nordheim plots obtained from the current-voltage curves for various values of the VP, a systematic change in the work function was confirmed. The FE dependence on the VP could be attributed to a scalable change in the work function induced by adsorbed molecules and by oxygen vacancies. The ZNWs could represent an alternative mechanism for fingerprinting a variable VP.
[en] The effect of gaseous O2, N2, and air on the field emission (FE) properties of ZnO nanowires (ZNWs) was investigated. The ZNWs showed a reversible dependence of the FE, with a rapid response on variations in vacuum pressure (VP). The FE properties of ZNWs were fully recovered after evacuation to the initial VP, even after an abrupt current drop, induced by the presence of all gases tested, under a severe vacuum condition of ∼ 2 X 10-4 Torr. A steady-state emission current with no detectable current degradation was obtained at each VP over an approximately a 4-hr period. The present findings suggest that ZNWs are promising candidates for use as robust field emitters. However, the dependence of the FE current on the VP might also be useful in further applications. A possible mechanism, based on a change in work function due to adsorbed molecules, for the reversible response of the FE from ZNWs is discussed.
[en] CdSe0.02S0.98 quantum dots (QDs), LaF3:Ce3+/CdSe0.02S0.98 nanocomposites (NCs), and CsPbI3 QDs were prepared to compare the properties of photoluminescence (PL) and X-ray excited luminescence (XEL) in these materials. CdSe0.02S0.98 QDs have an intense PL peak but negligible XEL. The LaF3:Ce3+/CdSe0.02S0.98 NCs have a single XEL peak and a corresponding PL peak. The XEL peak in LaF3:Ce3+/CdSe0.02S0.98 NCs originates from a resonance energy transition from LaF3:Ce3+ nanocrystals to CdSe0.02S0.98 QDs. The CsPbI3 QDs, which contain the heavy element Pb (atomic number Z = 82), exhibited a higher XEL than the CdSe0.02S0.98 QDs and the LaF3:Ce3+/CdSe0.02S0.98 NCs.
[en] Kim et al. described and compared other methods of measuring stress triaxiality using the displacements near the side necking, proved the validities of these models and explored the effect of location where the displacements are measured using three-dimensional finite element analysis for a standard CT specimen with 20% side-grooves. In this paper, the applicability of these models to various specimen and materials are examined in detail. To consider the effects of side groove, thickness of specimen, crack length, specimen geometry and strain hardening exponents, three-dimensional finite element simulation has been performed for various specimen geometries. For a case without a side groove, in the whole the difference between the stress triaxilaity analytically evaluated and directly determined is similar. For a case with a 20% side groove the stress triaxiality is measured at the area where θ is smaller than 60 .deg., which excludes a side grooved area
[en] In addition to the intrinsic blue emission band near 430 nm for an ideal PbWO4 scheelite structure, the presence of three extra emission bands peaking near blue-green and green-red colors was clearly identified for thermally synthesized bulk crystals with the help of a reliable fitting process applicable for microscopic analysis of recorded PL spectra. The origin, nature, and electro-optical behaviors of the extra emission bands are strongly related to the structural change from an ideal scheelite to modified ones, so now we can more closely track down the nature and the relevant behaviors, which are still in dispute, of the apparent colors of the PbWO4 scintillating medium by constructing structural models and by considering the energy transfer mechanism between the color centers
[en] A plastic zone size is regarded as a measure of material resistance, and also it determines the fracture behavior. The importance of estimating or measuring the plastic zone size cannot be too emphasized. In this article, SDSP(Stereo Digital Speckle Photography) is examined as a new techniques to measure the plastic zone developed in a ductile metal. This technique is simple, vibration free and non-contact, and measures simultaneously in-plane displacements as well as out-of plane displacements like the side necking. Experimental results for a CT specimen are presented to demonstrate the accuracy in comparison with those obtained by recrystallization technique and finite element analysis
[en] Highly regular arrays of freestanding single carbon nanotubes (CNTs) were grown by using dc plasma-enhanced chemical vapor deposition (PECVD) on regular arrays of nickel dots prepared by conventional photolithography and a lateral wet-etch process. The size of the Ni dot was controlled by changing the wet-etch duration to obtain the optimum size for single CNT growth. A direct correlation between the vertical alignment of a single CNT and the location of the catalyst metal was a major factor in the growth of CNTs on the confined size of the catalyst. With this method, well-separated and well-defined regular arrays of freestanding CNTs can be scaled up at lower cost than they can for electron-beam lithography.
[en] The field-emission properties of transparent tungsten oxide nano-urchin (NU) films deposited on conducting glass substrates were examined. The novel crystalline tungsten oxide NUs consisted of nanowires added to a spherical shell. The WO2.72 NUs showed better field-emission properties than the WO3 NUs with a low turn-on field of approximately 5.8 V/μm and a current density as high as 1.3 mA/cm2 at 7.2 V/mm. The WOx NUs films could be used in FE applications using a large-area glass substrate without the need for a catalyst and a mechanical rubbing or lift-up process. These results have implications for the enhancement of FE properties by further tuning the WOx phases. (orig.)
[en] Following the Fukushima accident, the Korean government set up a response led by a Prime Ministerial Task Force to precisely assess the safety of operating nuclear power plants (NPPs) against such an event in Japan in March 11th, 2011. KINS organized a targeted Special Safety Inspection (SSI), and a team composed of 37 KINS staffs and 36 external experts stemming from various different organizations was brought together to undertake the mission. The assumed scenario which was investigated mirrored the Fukushima accident. Accordingly, areas for improvement were promptly identified. This paper describes the findings of the SSI and their technical backgrounds, especially on the severe accident countermeasures of operating NPPs