Internal stress control in epoxy resins and their composites by material and process tailoring

The development of internal stress during cure of epoxy and hyperbranched polymer-modified epoxy resins was characterized, taking into account the evolving viscoelastic properties, the volumetric shrinkage due to the chemical reaction, and the thermal expansion. A criterion for void formation during cure in a constrained mold was proposed, providing guidelines for the construction of a process window for manufacturing of void-free composites. It was shown that the internal stress development in epoxy resins during cure is strongly influenced by the presence of hyperbranched polymer modifiers. The role of these modifiers was illustrated for the case of autoclave processing of glass fiber/epoxy composites. This study showed that higher fiber volume fractions could be used with hyperbranched polymer-modified resins than with unmodified resins, for producing void-free laminates. It also appeared that by suitable tailoring of the process cycle, a fully stress-free laminate could be obtained after cure, using the modified resin.     

Business cycle and corporate failure in France: Is there a link?

The aim of this paper is to extract cyclical factors from companies’ data possibly used in the construction of the scores by the Bank de France and from these scores themselves. The constraints are those of a database including a large number of variables and companies but over a relatively short period. The method chosen is the “principal components method” adapted by Bai and Ng (2000, 2001) in the context of large N and limited T. Later, these factors may be used to take into account the business cycle in the application of scores. An erratum to this article can be found at     

Frequency stability characterization from the filtered signal of aprecision oscillator in the presence of additive noise

The authors present a generalized theory to express the frequency stability characterization of a precision oscillator when its signal, perturbed by additive noise, is filtered. The general expressions for the power spectral density of the amplitude and phase fluctuations of the filtered signal are calculated as functions of the oscillator amplitude and phase fluctuations, the additive noise, and the filter characteristics. The results obtained for the phase fluctuations of the filtered signal are used to characterize the frequency stability of the oscillator. The contribution of white additive noise to the generalized Allan variance is expressed in terms of a parameter, the equivalent bandwidth. The contributions of other types of noise are also calculated. For the first-order low-pass filter, the contributions of all types of additive, amplitude, phase, and frequency noise are given. Experimental results show excellent agreement with the theoretical predictions     

KSR stimulates Raf-1 activity in a kinase-independent manner

Kinase suppressor of Ras (KSR) is an evolutionarily conserved component of Ras-dependent signaling pathways. Here, we find that murine KSR (mKSR1) translocates from the cytoplasm to the plasma membrane in the presence of activated Ras. At the membrane, mKSR1 modulates Ras signaling by enhancing Raf-1 activity in a kinase-independent manner. The activation of Raf-1 is mediated by the mKSR1 cysteine-rich CA3 domain and involves a detergent labile cofactor that is not ceramide. These findings reveal another point of regulation for Ras-mediated signal transduction and further define a noncatalytic role for mKSR1 in the multistep process of Raf-1 activation.     

Coordinated Maneuvering of Automated Vehicles in Platoons

To eventually have automated vehicles operate in platoons, it is necessary to study what information each vehicle must have and to whom it must communicate for safe and efficient maneuvering in all possible conditions. This paper formulates the problem in terms of sensing and communicated information. By emulating platoons using a group of mobile robots, the authors demonstrate the feasibility of maneuvers (such as entering, exiting, and recuperating from an accident) using different distributed coordination strategies. The coordination strategies studied range from no communication to unidirectional or bidirectional exchanges between vehicles and to fully centralized decision by the leading vehicle. One particularity of this paper is that instead of assuming that the platoon leader or all vehicles globally monitor what is going on, only the vehicles involved in a particular maneuver are concerned, distributing decisions locally among the platoon. This paper reports experimental trials using robots having limited and directional perception of other things, using vision and obstacle avoidance sensing. Results confirm the feasibility of the coordination strategies in different conditions and various uses of communicated information to compensate for sensing limitations     

L'oxyde de vanadium amorphe hydrate

Hydrated amorphous vanadium pentoxide obtained by quenching of molten V₂O₅ in water is compared to amorphous V₂O₅ previously obtained by splat cooling. The first one contains some strongly bonded water which prevents crystallisation up to 300°C. Short range order around V⁴⁺ ions seems to be the same in both samples and in orthorhombic V₂O₅. Disorder in the amorphous phases leads to a localization of the charge carriers, the electron mobility being about ten times smaller than in the crystalline oxide.     

Development of a chitosan-based biofoam: application to the processing of a porous ceramic material

Developing biofoams constitutes a challenging issue for several applications. The present study focuses on the development of a chitosan-based biofoam. Solutions of chitosan in acetic acid were dried under vacuum to generate foams with high-order structures. Chitosan concentration influenced significantly the morphology of developed porosity and the organization of pores in the material. Physico-chemical characterizations were performed to investigate the effects of chitosan concentration on density and thermal conductivity of foams. Even if chitosan-based biofoams exhibit interesting insulating properties (typically around 0.06 W·m(-1)·K(-1)), it has been shown that their durabilities are limited when submitted to a wet media. So, a way of application consists to elaborate a ceramic material with open porosity from a slurry prepared with an organic solvent infiltrating the porous network of the foam.     

In situ inorganic foams prepared from various clays at low temperature

Geopolymers are amorphous three-dimensional aluminosilicate binder materials that may be synthesized at room or slightly higher temperature by alkaline activation of aluminosilicates obtained from industrial wastes, calcined clays, natural minerals or mixtures of two or more of these materials. Among the different families of geopolymers, those based on potassium show modified thermal and mechanical properties due to the larger size of the potassium ion compared to sodium. This work deals with the preparation of geopolymer foams based on potassium silicate, industrial waste and various types of clays (kaolin, metakaolin, illite or montmorillonite). The influence of the clays used is assessed in terms of clay reactivity using structural data determined by FTIR spectroscopy, thermal analysis, XRD, and SEM characterizations.In situ geopolymer foam was obtained from all of the clays but its characteristics depended on the nature of the clays, including their structural alteration and chemistry. The extent of destruction of the clay structure was partial for kaolinite but was greater for illite, followed by montmorillonite. These inorganic foams have a potential use in housing construction, since they display thermal insulating properties.