Fabrication of Cermets via Spark-Plasma Sintering for Nuclear Applications

The development of the optimum processing path for ultrahigh-temperature W-UO₂ cermet fuels is of great importance. While W-UO₂ is the main point of interest, as part of a scoping study, a set of experiments was conducted to determine the suitability of spark-plasma sintering (SPS) for producing W-CeO₂ specimens with CeO₂ serving as a surrogate for UO₂ fuel kernels. The experiments confirmed that SPS takes place via diffusional mass transfer; however, the densification process is rapidly accelerated because of the effects of current densities within the consolidating specimen. The SPS process yielded dense W-CeO₂ specimens with a finer microstructure than other sintering techniques. The specimens were examined using scanning electron microscopy, energy-dispersive spectroscopy, and electron-backscattered diffraction techniques. Also, great care must be taken to ensure that the particles remain spherical in geometry under the influence of a uniaxial stress as applied during SPS, which involves mixing different fuel kernel sizes to reduce the porosity. Particle mixing techniques are shown to be capable of producing consolidated cermets but with a less than desirable microstructure. The work presented herein will help in the development of high performance cores of very high-temperature reactors for terrestrial and space missions in the future.     

Non-destructive ultrasonic evaluation of CFRP–concrete specimens subjected to accelerated aging conditions

The objective of this work is to utilize surface acoustic waves (SAWs) for non-destructive structural health monitoring of concrete specimens externally bonded with carbon fiber-reinforced polymer (CFRP) composites and subjected to accelerated aging conditions. Both experimental testing and signal processing schemes of ultrasonic wave propagation through the CFRP substrate are described. The surface waves are generated and received at the external face of the CFRP using narrow-band transducers with a 110-kHz center frequency. The received signals are filtered and amplified then digitized and processed to extract various parameters in both time and frequency domains including average power (P_Avg), maximum amplitude (V_max), and maximum power–frequency ratio ((P/F)_max). Changes in these parameters due to water-immersion aging at different temperatures were monitored over 12 weeks. Results indicated a marked decrease in measured ultrasonic parameters over time, particularly after the first 2 weeks, indicating a possible debonding or deterioration in the samples. Ultrasonic results showed good agreement with the findings of a parallel destructive study on mode-II fracture loading of CFRP–concrete samples, tested to obtain fracture energy (G_f) and define traction–separation response under temperature and water-immersion aging effects. It was observed that all ultrasonic parameters exhibit good correlations (|r|>0.5, P<0.05) with the fracture energy at all temperatures. Moreover, when the measurements at all temperatures were incorporated and linear relationships between destructive and non-destructive parameters were assumed, correlations of r=0.84, 0.80, and 0.80 were found between G_f and P_Avg, V_max, and (P/F)_max, respectively. This study paves the way for developing a non-destructive testing protocol for structural health monitoring of bridges and concrete structures undergoing repair and rehabilitation with CFRP composites.     

Effect of annealing atmosphere on microstructure,optical and electronic properties of spray-pyrolysed In-doped Zn(O,S) thin films

Spray-pyrolysed zinc oxy-sulphide Zn(O,S) has been doped with varying concentrations of indium (In) to improve its electrical and optical properties for possible application as buffer layer in thin film solar cells. The In-doping in Zn(O,S) is found to change the electron carrier concentration from \(10^{19}\) to \(10^{18}\,\hbox {cm}^{-3}\) and a subsequent annealing in argon atmosphere is found to improve its electrical conductivity. Moreover, annealing in air atmosphere reduces the carrier concentration to a range of \(10^{13}\)–\(10^{15}\,\hbox {cm}^{-3}\) making it useful as a buffer layer. The reduction in degeneracy of In-doped Zn(O,S) is desirable for its application as buffer material, whereas annealing in argon makes it suitable as electron membrane (window layer) in thin film solar cell.     

Observation of phase separation in (Ge2)x(GaAs)1−x alloys grown by molecular beam epitaxy

(Ge₂)_x(GaAs)_1?x alloys with 0 < x < 1 have been grown by molecular beam epitaxy on various Ge and GaAs substrates. The structure of these alloys has been studied using transmission electron microscopy. We observe that in all cases studied, Ge tends to phase-separate from GaAs, with the Ge domain size ranging from 100 to 300 Å.     

On-demand fuzzy clustering and ant-colony optimisation based mobile data collection in wireless sensor network

Wireless Networks - In a wireless sensor network (WSN), sensor nodes collect data from the environment and transfer this data to an end user through multi-hop communication. This results in high...     

Bioconjugated PLGA-4-arm-PEG branched polymeric nanoparticles as novel tumor targeting carriers

In this study, we have developed a novel carrier, micelle-type bioconjugated PLGA-4-arm-PEG branched polymeric nanoparticles (NPs), for the detection and treatment of pancreatic cancer. These NPs contained 4-arm-PEG as corona, and PLGA as core, the particle surface was conjugated with cyclo(arginine-glycine-aspartate) (cRGD) as ligand for in vivo tumor targeting. The hydrodynamic size of the NPs was determined to be 150-180 nm and the critical micellar concentration (CMC) was estimated to be 10.5 mg l( - 1). Our in vitro study shows that these NPs by themselves had negligible cytotoxicity to human pancreatic cancer (Panc-1) and human glioblastoma (U87) cell lines. Near infrared (NIR) microscopy and flow cytometry demonstrated that the cRGD conjugated PLGA-4-arm-PEG polymeric NPs were taken up more efficiently by U87MG glioma cells, over-expressing the α(v)β(3) integrin, when compared with the non-targeted NPs. Whole body imaging showed that the cRGD conjugated PLGA-4-arm-PEG branched polymeric NPs had the highest accumulation in the pancreatic tumor site of mice at 48 h post-injection. Physical, hematological, and pathological assays indicated low in vivo toxicity of this NP formulation. These studies on the ability of these bioconjugated PLGA-4-arm-PEG polymeric NPs suggest that the prepared polymeric NPs may serve as a promising platform for detection and targeted drug delivery for pancreatic cancer.     

Synthesis of beta-cyclodextrin-modified water-dispersible Ag-TiO2 core-shell nanoparticles and their photocatalytic activity

The beta-cyclodextrin-modified Ag-TiO2 core-shell nanoparticles were prepared by sodium borohydrate reduction of AgNO3 and the subsequent hydrolysis of the tetraisopropyl orthotitanate in an aqueous medium. Inversely in the preparation of beta-cyclodextrin-modified TiO2-Ag core-shell nanoparticles, first hydrolysis and then following reduction were carried out. The synthesized spherical core-shell nanoparticles were highly water-dispersible and had an average diameter in the range of 9 to 12 nm. A significant shifting of surface plasmon band was observed for the synthesized Ag-TiO2 and TiO2-Ag core-shell nanoparticles. On a model reaction, namely, the photodegradation of phenol by the UV light irradiation, the photocatalytic property of TiO2 nanoparticles was enhanced, when the Ag nanoparticle was embedded in the core of TiO2 nanoparticles but TiO2 nanoparticles coated by Ag shell decreased the photocatalytic property of TiO2 nanoparticles. The mechanism is ascribed to the surface plasmon characteristics of Ag in the core of the TiO2 nanoparticles under the acceleration by host-guest inclusion characteristics.     

Semiconducting properties of the anodic films grown over PbIn alloy electrodes

Semiconducting properties of oxide film grown over PbIn binary alloy electrodes in alkaline medium is elucidated. It has been observed that anodic film formed over Pb0.3 wt%In alloy in the potential range of −0.75 to 1.25 V (vs. Hg/HgO) shows better short circuit photocurrent density (3.2 mA/cm²) than the oxide film over pure Pb electrode (2.2 mA/cm²). The observed photoactivity is correlated with the interfacial parameters of the nonstoichiometric oxide–electrolyte interface using Gartner Butler model. Effect of varying concentration of In dopant in the PbO matrix on the interfacial properties is reported. It is shown that combined effect of space charge width and diffusion length of the minority carriers can describe the observed photoactivity efficiently.