InxGa1-xAs ohmic contacts to n-type GaAs prepared by sputter deposition

Thermally stable, low contact resistance InAs/Ni/W contacts were previously prepared by sputter depositing InAs, Ni, and W targets in our laboratory. However, the optimum annealing temperature to provide low contact resistance (R_c) was high, resulting in rough contact surface. In the present experiment, the effects of the In concentrations of In_xGa_1-x As targets on the optimum annealing temperature to prepare low R_cand the surface morphology of the_xGa_1-x/ W contacts were studied. In addition, the electrical properties and the interfacial microstructure were correlated to search the optimum In concentration to provide the minimum R_c, where the interfacial microstructure was analyzed by x-ray diffraction and transmission electron microscopy and the contact resistances (R_cc) were measured by the transmission line method. The optimum annealing temperature to provide minimum R_c was reduced by 150°C by using the In_0.7Ga_0.3As targets instead of the previous targets. The contact resistance of 0.4 Ω-mm was obtained for the In_0.7Ga_0.3As/Ni/W contacts after annealing at temperatures of around 600°C. The R_c values did not deteriorate after annealing at 400°C for 2 h. Also, the surface of this contact was smooth and no evidence of In outdiffusion on the contact surface was seen. Finally, the effect of the In concentrations at the metal/GaAs interfaces on the electrical properties will be discussed.     

Analytical and experimental study of a forced-convection type nocturnal radiator

An analytical model is developed to predict the nocturnal thermal performance of a forced-convection type nonselective radiator: its validity is examined by comparison of the predictions with the results of several outdoor experiments. In the experiments, the Reynolds number of a working fluid, which is water in the present study, is varied, while the inlet fluid temperature is kept constant. The presented model predicts time variations in the exit fluid temperature of the radiator accurately.     

Experiments on the leak path factor of ruthenium volatilized from high-level liquid waste tanks in a reprocessing plant in case of the boiling and drying accident

In case of the boiling and drying accident of a high-level liquid waste (HLLW) tank, a large amount of ruthenium (Ru) will be volatilized. In order to suppress the release of radioactive materials to the environment, the vapor may be led to the neighboring cells in which it will contact with the cell walls to be partially condensed. To understand the behavior of Ru in this situation, we have prepared an experimental apparatus. It consists of a small tank in which 60 mL simulated HLLW is heated to dryness, a 9.6 L stainless steel box which mimics the neighboring cell accepting the vapor from the small tank, and a condenser where the vapor coming out from the box is cooled to collect the condensate. The results show that more than 99% of the volatilized Ru is removed from the vapor in the box if its temperature is below about 120 °C.     

Calibration of Modified Spalart-Allmaras Model Parameters for Linear Compressor Cascade Corner Flow

In this study,Bayesian parameter calibration is applied to Saplart-Allmaras (SA) turbulence model,and the prediction improvement by the calibrated model is demonstrated.The quantity of interest (QOI) is the pitch-wise distribution of Mach number in the corner separation flow region.The 10 model parameters included in the SA model with Rotation-Curvature correction are considered as random variables obeying uniform prior probability distributions.The order of generalized Polynomial Chaos (gPC) used for sensitivity analysis and surrogate model in calibration is incrementally increased during the calibration process.Posterior convergence is obtained at the 3rd order expansion level in this study.At this final level,sensitivity analysis indicates 3 model parameters,cb1,κ and Cr3 are the most influential random variables,and 3-parameter Bayesian calibration is conducted.The likelihood function in the Bayesian theorem is specified in the form of Gaussian distribution,including experimental uncertainty.The combination of prior and likelihood brings the posterior distribution of model parameters,and Maximum A Posterior (MAP) value is selected as a calibrated parameter set.The flow simulation with calibrated parameters shows a significant increase in the accuracy of the Mach number profile in the corner separation region.The increase in accuracy is attributed to enlarged turbulent viscosity due to the parameter modification of the turbulent viscosity source term.The calibrated parameter is also tested in the off-design flow field,not included in the calibration process.The calibrated CFD again shows improved accuracy for corner separation prediction,and the effectiveness of the parameter set outside of the calibration field is demonstrated.     

Comparison of stress intensity factor solutions for cylinders with axial and circumferential cracks

Numerous stress intensity factor solutions have been proposed so far depending on the objects of evaluation including the variations of structures, cracks, and applied loads. In applying the flaw evaluation methodology to components of nuclear power plants, the use of reliable stress intensity factor solutions is essential. In this study, cracked cylinders were focused on as one of the typical configurations in actual plants. Existing stress intensity factor solutions for cracked cylinders were reviewed, and the accuracy of these solutions was investigated thorough the comparison with each other. Specific solutions were then recommended for cylindrical structures. Approximate expressions were newly derived for axially through-wall cracked cylinder subjected to linear stress distribution and for circumferentially through-wall cracked cylinder subjected to bending to realize simple evaluation of stress intensity factor. Considering that the cylindrical structures are often replaced with flat plates in the evaluation of actual components, the propriety of the replacement was also studied.     

Effects of solute elements on hardening and microstructural evolution in neutron-irradiated and thermally-aged reactor pressure vessel model alloys

Nanometer-sized Cu-enriched solute clusters containing Mn, Ni, and Si atoms are considered as the primary embrittling feature in reactor pressure vessel steels. In order to understand the effects of solute atoms Mn, Ni, and Si on hardening and cluster formation, reactor pressure vessel model alloys FeCu, FeCuSi, FeCuNi, and FeCuNiMn were irradiated at 290 °C in a research reactor. Thermal ageing at 450 °C was also carried out to compare with the results in the neutron irradiation. The addition of Mn resulted in larger hardening and higher cluster number density in both thermal ageing and neutron irradiation. In FeCu0.8NiMn alloy, the size distribution of Cu-enriched clusters formed in 62-h thermal ageing (almost peak hardening) was very similar to that formed in the neutron irradiation, indicating they are on a similar growing stage. But the average Ni and Mn composition in clusters formed in neutron irradiation was higher. A good linear relationship between hardening and the square root of cluster volume fraction for both neutron irradiation and thermal ageing data was found.