Metallurgical aspects of corrosion resistance of aluminium alloys

Aluminium is the second most often used metal after steel. In this paper, the most current uses of aluminium alloys are first summarised. Then, their different corrosion modes, i.e. pitting, crevice, filiform, galvanic and structural corrosion (including inter‐granular, exfoliation and stress corrosion cracking) are reviewed, with particular attention paid to metallurgical factors controlling the corrosion process. For each mode, some instances of possible in‐service failure are given, followed by the discussion of the involved mechanisms and the presentation of appropriate solutions to prevent corrosion. Last, passivity and polarisation behaviour are discussed with reference to stainless steels.     

Nanostructured silica templated by double hydrophilic block copolymers with a comb-like architecture

An original way to synthesize nanostructured materials is to use new structuring agents constituted of double hydrophilic block copolymers (DHBC). The originality of these structuring agents is multiple: in water, the hydrosoluble DHBC copolymers can become amphiphilic and form micelles in specific conditions, i.e. after addition of other molecules or after a change of a physicochemical parameter (pH), which selectively makes one of the blocks insoluble in water. The addition of a silica precursor to a micelle suspension can lead to the formation of hybrid mesostructured materials, precursors for mesoporous silica. The micellization process may be reversible and the micelles can then be removed from the silica materials in an aqueous solution at room temperature after application of a dissociation stimulus, leading to the mesoporous materials. A new original DHBC is used here for silica structuring: instead of a classical linear diblock copolymer, it is a diblock copolymer with a linear polyacid block (PAA) and a poly(ethylene oxide) based neutral block (PAMPEO) with a comb-type architecture. It is synthesized by controlled radical polymerization (RAFT method) which permits a control of the block lengths. It is shown here that these new DHBC polymers can form polyion complex micelles by complexation with a natural polyamine and that the micellization is reversible as a function of the pH. It is also shown that the new pH sensitive micelles can act as structuring agents in the preparation of mesoporous silica materials.     

A statistical analysis of void size distribution in a simulated narrowly graded packing of spheres

The void microstructure of a simulated packing of polydisperse spheres has been investigated by means of a radical Delaunay tessellation. We have focused on creating sphere packings by mimicking processes involved in the construction of embankment dams: the polydisperse spheres are collectively released under gravity and denser states are mainly obtained by means of shearing cycles. This study has been performed on a narrowly graded material for four porosities ranging from 0.42 to 0.36. The void structure is quantified in terms of probability density functions of pore and constriction sizes, cumulative distributions and connectivity functions. We emphasize the implications of the sample construction technique on the geometric packing arrangements, among them a well disordered medium where tetrahedra remain the most represented unit void structure. We point out that when porosity decreases, void distributions become narrower but the initial structure is never destroyed. Nevertheless, the densification modifies significantly the computed mean void quantities. In this study, usual geometric arrangements obtained for very dense materials are not encountered.     

Influence of BaTiO3 additive and electrode material onspace-charge formation in polyethylene. Evidence from thermal stepspace-charge measurements

The effects of 5% wt BaTiO₃ additive and of electrode material on space charge formation and electric field distribution in low density polyethylene (LDPE) were investigated using a thermal step technique. Space charge was formed at an average dc field of ~28 kV/mm and at 50°C. Results indicate that the addition of BaTiO₃ to LDPE has considerably reduced the remanent space charge and electric field and changed their distribution patterns in the doped material when compared with the plain material. It is also shown that the remanent space charge and electric field in plain LDPE are strongly dependent on the type of electrode material     

Serotoninergic control of the activity and expression of glial GABA transporters in the rat cerebellum

OBJECTIVE: The purpose of the study was to compare staff versus patient perceptions of the causes and emotional impact of verbal and physical aggression on a psychiatric inpatient unit, and the corrective measures each group would endorse. METHODS: Fifty-four patients and 32 nursing staff members responded to similar questions about physical and verbal aggression. They also reported their emotional responses to aggression and steps they would endorse to reduce aggression at the medical center. Data was analyzed by chi-square tests for proportion comparisons between groups. RESULTS: "Verbal Abuse" was viewed an important contributor to physical aggression. Staff stressed patient substance abuse and violent lifestyles. Patients focused on the use of involuntary procedures and cultural differences between patients and staff. CONCLUSIONS: Patients endorsed more restrictive safety measures as long as the measures such as metal detectors and searches were applied to staff and visitors, as well as patients. Patients requested more input into decision-making processes through patient-staff workgroups.     

Polyalphaolefins — base fluids for modern heavy duty diesel oils

A combination of environmental legislation and a need for improved economics currently presents both OEMs and fleet owners with a conflicting set of performance and operational requirements. These include lower emission and paniculate levels, fuel economy, longer drain/service intervals, and enhanced engine durability. Improved engine lubricants will play a crucial role in achieving these goals. The impact of base-fluid composition and viscosity grade on emission/paniculate levels and fuel economy of a Euro II engine has been investigated. Polyalphaolefin-based lubricants appear as an encouraging solution, as shown by our results centred on an SAE 5W40 grade.     

Digital stochastic realization of complex analog controllers

Stochastic logic is based on digital processing of a random pulse stream, where the information is codified as the probability of a high level in a finite sequence. This binary pulse sequence can be digitally processed exploiting the similarity between Boolean algebra and statistical algebra. Given a random pulse sequence, any Boolean operation among individual pulses will correspond to an algebraic expression among the variables represented by their respective average pulse rates. Subsequently, this pulse stream can be digitally processed to perform analog operations. In this paper, we propose a stochastic approach to the digital implementation of complex controllers using programmable devices as an alternative to traditional digital signal processors. As an example, a practical realization of nonlinear dissipative controllers for a series resonant converter is presented.