Electroosmotic flow in nanoporous membranes in the region of electric double layer overlap

This study investigates electroosmotic flow (EOF) with sodium tetraborate buffer in nanoporous anodized alumina membranes. Membranes with pore diameters ranging from 8 to 100 nm have been fabricated with narrow pore size distributions to systematically investigate the effect of pore diameter on the electroosmosis (EO) pumping down to the electric double layer overlap region. EOF was observed in membranes with pore diameters in and below this region, along with evidence of concentration polarization (CP), which resulted in a significant reduction in flux. The initial flux, though, could be fully recovered by temporarily reversing the flow and dislodging the accumulated ion layer from the feed side of the membrane. Stable pumping for up to 2 h was obtained before any flux reduction caused by CP was observed.     

Flash spark plasma sintering of 3YSZ

Flash SPS (FSPS) consolidation of 3YSZ cold pressed pellets was investigated. The results show that FSPS allows ultra-rapid consolidation of 3YSZ samples in 30–90 s under an applied electric field. The DC field induces electrochemical blackening. The partial reduction process starts from the cathode (-) and propagates toward the anode (+). This phenomenon, not previously discussed in FSPS literature, induces the development of internal temperature gradients resulting in a polarity dependent grain size/densification.     

Vortex Molecules in Bose-Einstein Condensates

Stable vortex dimers are known to exist in coherently coupled two component Bose-Einstein condensates (BECs). We construct stable vortex trimers in three component BECs and find that the shape can be controlled by changing the internal coherent (Rabi) couplings. Stable vortex N-omers are also constructed in coherently coupled N-component BECs. We classify all possible N-omers in terms of the mathematical graph theory. Next, we study effects of the Rabi coupling in vortex lattices in two-component BECs. We find how the vortex lattices without the Rabi coupling known before are connected to the Abrikosov lattice of integer vortices with increasing the Rabi coupling. In this process, vortex dimers change their partners in various ways at large couplings. We then find that the Abrikosov lattices are robust in three-component BECs.     

Simulated moving bed technology applied to coal gasification

An alternative technology to conventional coal gasification is discussed in order to improve the performances of the existing processes. The concept of simulated moving bed (SMB) is applied to coal gasification: a number of fixed-bed reactors are connected in series and a suitable switching policy is applied so that each fixed-bed is cyclically operated both as a combustion and a gasification reactor.     

Impact behaviour of A356 alloy for low-pressure die casting automotive wheels

Instrumented impact strength tests have been carried out on KV sub-size Charpy samples drawn from A356 aluminium alloy 17-in. wheels, produced by a low-pressure die casting. The wheels show different geometry and thermal treatment. In this paper, the effects of microstructure and defects on the impact properties are studied. The results indicate that the impact energy is lower in as-cast wheel than in T6 heat-treated wheels. A finer microstructure always corresponds to higher impact strength, while a direct correlation between the resistance to crack propagation values and secondary dendrite arm spacing (SDAS) exists. Casting defects, revealed by means of X-ray and density measurements techniques, become critical when concentrated around the V-notch, where they reduce the load bearing area of Charpy specimens. The fracture profile and surface of Charpy specimens have been investigated revealing how the crack crosses the interdendritic eutectic region where a significant fraction of cracked eutectic silicon and intermetallic particles is found.Numerical simulations have been performed to study the filling and solidification behaviour of the alloy of the wheels analysed, in order to predict the final microstructure and shrinkage formation. Solidification times, estimated by means of SDAS measurements and calculated with a numerical simulation approach, show a good correspondence. Critical areas, as concern hot spots and shrinkage porosities, are generally revealed in the zone of the wheels between the spoke and the rim, as well as in the rim area.     

Multidisciplinary Design Optimization Framework for the Pre Design Stage

Presented is a novel framework for performing flexible computational design studies at preliminary design stage. It incorporates a workflow management device (WMD) and a number of advanced numerical treatments, including multi-objective optimization, sensitivity analysis and uncertainty management with emphasis on design robustness. The WMD enables the designer to build, understand, manipulate and share complex processes and studies. Results obtained after applying the WMD on various test cases, showed a significant reduction of the iterations required for the convergence of the computational system. The tests results also demonstrated the capabilities of the advanced treatments as follows:

The novel procedure for global multi-objective optimization has the unique ability to generate well-distributed Pareto points on both local and global Pareto fronts simultaneously.

The global sensitivity analysis procedure is able to identify input variables whose range of variation does not have significant effect on the objectives and constraints. It was demonstrated that fixing such variables can greatly reduce the computational time while retaining a satisfactory quality of the resulting Pareto front.

The novel derivative-free method for uncertainty propagation, which was proposed for enabling multi-objective robust optimization, delivers a higher accuracy compared to the one based on function linearization, without altering significantly the cost of the single optimization step.

The work demonstrated for the first time that such capabilities can be used in a coordinated way to enhance the efficiency of the computational process and the effectiveness of the decision making at preliminary design stage.