Results 1 - 10 of 35
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[en] The reliability of a magnetic tunnel junction (MTJ) with an MgO tunnel barrier was evaluated. In particular, various voltage tests were used to investigate the effects of the barrier thickness and the temperature on the resistance drift. We compared the resistance change during a constant voltage stress (CVS) test and confirmed a trap/detrap phenomenon during the interval stress for different barrier thicknesses and temperatures. The resistance drift representing degradation and the time to breakdown (TBD) representing the breakdown characteristic were better for a thicker barrier and lower temperature, but were worse for a thinner barrier and a higher temperature. The results suggest that breakdown and degradation due to trap generation strongly depend on both the barrier thickness and the temperature. Furthermore, as the TBD varies at steady rates with changing barrier thickness, temperature, and electric field, we assume that a MTJ with an adnormal thin layer of MgO can be screened effectively based on the predicted TBD. As a result, the barrier thickness and the temperature are very important in determining the reliability of a MTJ, and this study is expected to be helpful in understanding the degradation and the breakdown of a MTJ.
[en] This study was designed to predict work hardening exponent of materials from AFM (atomic force microscope) observations of residual indentation impression in sharp indentations. FE simulations of nano-indentation were performed to 140 combinations to each parameter (elastic modulus E, yield stress σ y , work hardening exponent n, and Poisson's ratio ν) expressing elastic-plastic behaviors of universal engineering metals. Using the results from FE simulations and dimensional analysis, dimensionless functions were established to correlate residual indentation profiles with the work hardening exponent. This function was examined with nano-indentation, tensile test, and AFM observations after indentation for two materials (Al6061-T6 and copper)
[en] The aim of this study was to survey the radon concentrations at 21 elementary schools in Gyeongju, Republic of Korea, to identify those schools with high radon concentrations. Considering their geological characteristics and the preliminary survey results, three schools were finally placed under close scrutiny. For these three schools, continuous measurements over 48 h were taken at the principal's and administration office. The radon concentrations at one school, Naenam, exceeded the action level (148 Bq/m3) established by the U.S. EPA, while those at the other two schools were below that level. - Highlights: • Preliminary measurements of the indoor radon concentrations were performed at the auditoriums in 23 elementary schools in Gyeongju. • Considering the geological characteristics and preliminary survey results, three elementary schools were screened for closer scrutiny. • For the three schools, continuous measurements were made at their principal's and administration offices over 48-h period. • The scrutiny revealed one elementary school of high radon concentration much higher than the U.S. EPA action level
[en] The most important point of decommissioning nuclear facilities and nuclear power plants is to spend less money and do this process safely. In order to perform a better decommissioning nuclear facilities and nuclear power plants, a data base of radioactive waste from decontamination and decommissioning of nuclear facilities should be constructed. This data base is described herein, from the radioactive nuclide to the shape of component of nuclear facilities, and representative results of the status and analysis are presented. With the increase in number of nuclear facilities at the end of their useful life, the demand of decommissioning technologies will continue to grow for years to come. This analysis of medium-and large-sized radioactive metal wastes and 3D visualization technology of the radioactive metal wastes using the 3D-SCAN are planned to be used for constructing data bases. The data bases are expected to be used on development of the basic technologies for decommissioning nuclear facilities 4 session
[en] Hydrogen isotope gases needed for the daily operation of the tokamak of nuclear fusion plants are safely stored in and supplied from beds. Metal tritides are currently proposed for the safe and high density storage and delivery of tritium gas during the operation of fusion machines. Different metal tritides show various storage and delivery properties. Among the many metal tritides, uranium and zirconium cobalt have been suggested as two of the most applicable tritium storage materials. A small-scale bed was fabricated to compare the properties of tritium recovery and the delivery of materials. It should be equipped with a heat control. Thus, in this study, we have performed thermal control tests (heating, cooling, and thermal insulation) of the small-scale bed
[en] Deuterium and tritium fuels are used for thermonuclear reactors. The measurement of tritium inventory is required because the tritium inventory in each bed frequently changes according to the operation scenario of the thermonuclear reactors. One gram of tritium emits about 0.324watt of decay heat. Performance tests of simulated tritium decay heat measurement on a hydrogen storage bed are required to measure the tritium inventory of a storage and delivery vessel in the thermonuclear reactors. In this study, a hydrogen storage bed was designed and fabricated. The performance tests of a simulated decay heat measurement of tritium were carried out. The experimental powers of the simulated heaters were compared with the calculated values of tritium decay heat
[en] A nuclear fusion fuel cycle plant is composed of various subsystems such as a hydrogen isotope storage and delivery system. A metal hydride bed is used for storing hydrogen isotopes. The in-bed calorimetry of a metal hydride bed is important. Helium temperature is the major parameter of the in-bed calorimetry. The optimal helium flow condition determines the performance of the in-bed calorimetry. In the present study, the helium inlet temperature variation was measured for evaluation of heater. A flow rate of 15 liter/min and an initial temperature of 303 K, 313 K and 323 K are experimental conditions
[en] Radon is a naturally occurring radioactive gas that is a well known cause of lung cancer through inhalation. Nevertheless, stomach cancer can also occur if radon-containing water is ingested. This study measured the radon concentration in groundwater for drinking or other domestic uses in the central region of Gyeongju, Korea. The groundwater samples were taken from 11 points chosen from the 11 administrative districts in the central region of Gyeongju by selecting a point per district considering the demographic distribution including the number of tourists who visit the ancient ruins and archaeological sites. The mean radon concentrations in the groundwater samples ranged from 14.38 to 9050.73 Bq.m-3, which were below the recommendations by the U.S. EPA and WHO. (authors)
[en] The annealing temperature dependence of the capacitance-voltage (C-V) characteristic has been studied in a metal-oxide semiconductor structure containing FePt nano-dots. Several in-situ annealing temperatures from 400 to ∼700 .deg. C in a high vacuum ambience (under 1 x 10-5 Pa) were evaluated in view of the cell's characteristics and its reliability. Here, we demonstrate that the annealing temperature is significant for memory performance in an alloy metal nano-dot structure. A higher in-situ temperature provides better retention and a more reliable memory window. In the sample with an in-situ annealing condition of 700 .deg. C for 30 min, a memory window of 9.2 V at the initial stage was obtained, and a memory window of 6.2 V after 10 years was estimated, which is reliable for a non-volatile memory. From these results, the annealing condition for an alloy metal nano-dot memory is one of the critical parameters for the memory characteristics, and should be optimized for better memory performance.
[en] The batch assay has been conventionally used for radioimmunoassay (RIA) because of its technical robustness and practical convenience. However, it has limitations in terms of the relative lag of report time due to the necessity of multiple assays in a small number of samples compared with the random assay technique. In this study, we aimed to verify whether the random assay technique can be applied in RIA and is feasible in daily practice. The coefficients of variation (CVs) of eight standard curves within a single kit were calculated in a CA-125 immunoradiometric assay (IRMA) for the reference of the practically ideal CV of the CA-125 kit. Ten standard curves of 10 kits from 2 prospectively collected lots (pLot) and 85 standard curves of 85 kits from 3 retrospectively collected lots (Lot) were obtained. Additionally, the raw measurement data of both 170 control references and 1123 patients' sera were collected retrospectively between December 2015 and January 2016. A standard curve of the first kit of each lot was used as a master standard curve for a random assay. The CVs of inter-kits were analyzed in each lot, respectively. All raw measurements were normalized by decay and radioactivity. The CA-125 values from control samples and patients' sera were compared using the original batch assay and random assay. In standard curve analysis, the CVs of inter-kits in pLots and Lots were comparable to those within a single kit. The CVs from the random assay with normalization were similar to those from the batch assay in the control samples (CVs % of low/high concentration; Lot1 2.71/1.91, Lot2 2.35/1.83, Lot3 2.83/2.08 vs. Lot1 2.05/1.21, Lot2 1.66/1.48, Lot3 2.41/2.14). The ICCs between the batch assay and random assay using patients' sera were satisfactory (Lot1 1.00, Lot2 0.999, Lot3 1.00). The random assay technique could be successfully applied to the conventional CA-125 IRMA kits. The random assay showed strong agreement with the batch assay. The random assay procedure could increase the flexibility and decrease the turnaround time of the radioimmunoassay technique