In-Situ Analyzing the Influence of Thermoelectromagnetic Convection on the Nucleation Ahead of the Advancing Interface During Directional Solidification

Sn-3wt%Pb alloy was directionally solidified without and with a 0.08T transverse magnetic field(TMF),and real-time recorded by in-situ synchrotron X-ray imaging.Results indicate that TMF shortened the distance from the location of nucleation to the advancing interface,and accelerated the growth rate of the equiaxed crystal,which caused the columnar-to-equiaxed transition(CET)finally.The thermoelectromagnetic convection(TEMC)in front of the interface and around the crystal’s dendritic branch should respond to changes of the distance and the growth rate.     

Degradation rate quantification of solid oxide fuel cell performance with and without Al2TiO5 addition

Degradation rates of electrical current during constant voltage operation of SOFCs with anodes made using NiO precursor powders from two different manufacturers with and without the addition of aluminum titanate (ALT) added by either mechanical mixing or anode infiltration have been quantified using a novel MATLAB algorithm. Because the algorithm has been used to quantify degradation rates for many different SOFC tests, it is thought that the method can be applied to most measured SOFC data to quantify the instantaneous cell degradation rate as a function of time for the entire SOFC performance measurement. Degradation rates determined at different times have been plotted against varying concentrations of ALT addition, facilitating the estimation of optimum ALT concentration for SOFC anodes made with NiO from a specific manufacturer. The algorithm used to determine degradation rates is available upon request to the corresponding author.     

Liquid salt cooled flexible conversion ratio fast reactor: Neutronic design

This paper presents the neutronic design of a liquid salt cooled fast reactor with flexible conversion ratio. The main objective of the design is to accommodate interchangeably within the same reactor core alternative transuranic actinides management strategies ranging from pure burning to self-sustainable breeding. Two, the most limiting, core design options with unity and zero conversion ratios are described. Ternary, NaCl-KCl-MgCl₂ salt was chosen as a coolant after a rigorous screening process, due to a combination of favourable neutronic and heat transport properties. Large positive coolant temperature reactivity coefficient was identified as the most significant design challenge. A wide range of strategies aiming at the reduction of the coolant temperature coefficient to assure self-controllability of the core in the most limiting unprotected accidents were explored. However, none of the strategies resulted in sufficient reduction of the coolant temperature coefficient without significantly compromising the core performance characteristics such as power density or cycle length. Therefore, reactivity control devices known as lithium thermal expansion modules were employed instead. This allowed achieving all the design goals for both zero and unity conversion ratio cores. The neutronic feasibility of both designs was demonstrated through calculation of reactivity control and fuel loading requirements, fluence limits, power peaking factors, and reactivity feedback coefficients.     

Cross-comparison of fast reactor concepts with various coolants

Four fast reactor concepts using lead (LFR), liquid salt, NaCl-KCl-MgCl₂ (LSFR), sodium (SFR), and supercritical CO₂ (GFR) coolants are compared. Since economy of scale and power conversion system compactness are the same by virtue of the consistent 2400 MWt rating and use of the S-CO₂ power conversion system, the achievable plant thermal efficiency, core power density and core specific powers become the dominant factors. The potential to achieve the highest efficiency among the four reactor concepts can be ranked from highest to lowest as follows: (1) GFR, (2) LFR and LSFR, and (3) SFR. Both the lead- and salt-cooled designs achieve about 30% higher power density than the gas-cooled reactor, but attain power density 3 times smaller than that of the sodium-cooled reactor. Fuel cycle costs are favored for the sodium reactor by virtue of its high specific power of 65 kW/kgHM compared to the lead, salt and gas reactor values of 45, 35, and 21 kW/kgHM, respectively. In terms of safety, all concepts can be designed to accommodate the unprotected limiting accidents through passive means in a self-controllable manner. However, it does not seem to be a preferable option for the GFR where the active or semi-passive approach will likely result in a more economic and reliable plant. Lead coolant with its superior neutronic characteristics and the smallest coolant temperature reactivity coefficient is easiest to design for self-controllability, while the LSFR requires special reactivity devices to overcome its large positive coolant temperature coefficient. The GFR required a special core design using BeO diluent and a supercritical CO₂ reflector to achieve negative coolant void worth—one of the conditions necessary for inherent shutdown following large LOCA. Protected accidents need to be given special attention in the LSFR and LFR due to the small margin to freezing of their coolants, and to a lesser extent in the SFR.     

SiC WHISKER-TOUGHENED ALUMINIUM NITRIDE CERAMICS

Aluminium nitride ceramics containing 15-30 w/o of SiC whiskers can be sintered tofull density(by hot pressing at 1800℃)using2-3 w/o of Y_2O_3,additions.The whiskersincrease the toughness and strength of thecomposite,K_(10) increasing from 2.8 to about5.0 and flexural strength increasing by 30-50%.However,the whiskers must be welldispersed and if the dispersion is notsatisfactory,toughness may increase but thestrength decreases.The hot-pressingtemperature can be reduced by up to 100℃ ifY(NO_3)_3 .5H_20 is used as the sinteringadditive instead of Y_2O_3,but some oxidation ofthe AIN occurs during heating.Isopropan-2-01 is a better dispersing agent thancyclohexane,but again some oxidation of theAIN does occur.The best sample prepared during this work contained 20 w/o of SiC whiskers and 2 w/oY_2O_3 added as Y(NO_3)_3. 5H_2O and mixed inisopropanol.This exhibited a mean strength of453MPa(maximum 522MPa,measured bydisc flexure)and a fracture toughness of5.5MPam~(1/2).     

Second harmonic generation in ion-exchanged waveguides of semiconductor microcrystallite-doped glasses

Waveguides written in semiconductor microcrystalline-doped glasses using the ion-exchange method have been optically encoded for second harmonic generation of Nd:YAG radiation.<>     

Prediction of anticoagulation during hemodialysis by population kinetics and an artificial neural network

All systems currently used for routine hemodialysis require heparin administration to prevent blood clotting in the extracorporeal circuit. We tested the hypothesis that population-based statistical techniques can be used to predict heparin concentrations during routine hemodialysis. Two predictive models were developed, one based on nonlinear mixed effects modeling (NONMEM) and the other on a multilayer perceptron neural network. Serial clotting time data were obtained from forty-nine patients and used to develop the models. The models were used to predict the clotting times of 70 patients in a prospective test. We determined that the neural network provided greater precision, had fewer outliers in its predictions, and did not have the model misspecification in bolus administration that the NONMEM predictions demonstrated. A final NONMEM model was developed using all data from 119 patients to identify important covariates for predicting the heparin pharmacodynamic parameters, volume of distribution, and clearance. Both the volume of distribution and clearance increased following the initiation of dialysis and as the patient's baseline clotting time increased. The volume of distribution also increased as the patient's weight increased but was decreased by smoking and diabetes. Population-based statistical techniques may provide a useful alternative to existing methods for prescribing heparin.