A rigorous implementation of the Jeans--Landau--Teller approximation

Rigorous bounds on the rate of energy exchanges between vibrational and translational degrees of freedom are established in simple classical models of diatomic molecules. The results are in agreement with an elementary approximation introduced by Landau and Teller. The method is perturbative theory ``beyond all orders'', with diagrammatic techniques (tree expansions) to organize and manipulate terms, and look for compensations, like in recent studies on KAM theorem homoclinic splitting.Comment: 23 pages, postscrip

Mineralogy of the Grès de Thiviers (northern Aquitaine, France)

This paper reports the mineralogical characterisation of the Grès de Thiviers (GT), a unique natural pigment used in the industry of traditional tile ceramics. The only occurrence of this raw material, composed of quartz and goethite, is a small region in the SW of France were it is exploited and exported to the European and Far East markets. GT is mainly used as a bulk red pigment for white stoneware and its stability in firing is a direct consequence of the unique nature. In fact, despite the nature of the raw materials composing the ceramic mixture and their behaviour at high temperature, GT invariably yields a final red colour to the fired ceramic body. The stability stems from the fact that goethite (yellow colour) which later transforms into hematite (red colour) is the cement of quartz grains. Thus, in firing, because of the protective shield formed by the inert quartz grains, the newly-formed hematite crystals do not get in contact with other reacting phases such as the alkaline glass and retain the red colour (Sempio and Gualtieri,2001). The mineralogy of the GT deposits was described in the light of the peculiar genesis and chemical variability. In fact, GT occurrence is closely related to the karstic system permeating the late Cretaceous limestone in this region. According to the different formation environment it was possible to describe the four typical GT textures: laminar, oolitic, dendritic, and homeoblastic. GT samples contain amorphous substance with composition [SiO2+Fe2O 3 or FeO(OH)] which is the colloidal precursor of the crystalline phases quartz and goethite

Behaviour of the natural red pigment "grès de thiviers" in por-celanised gres

This work deals with the characterisation of the Grès de Thiviers (GT), a unique natural red pigment for traditional ceramics. The only occurrence of this raw material, composed of quartz and goethite, is a region in SW of France were it is exploited, enriched and exported all over the world. GT is mainly used as a bulk red pigment for white stoneware and its stability in firing is a direct consequence of its unique mineralogy and texture. In fact, despite of the nature and behaviour in temperature of the raw materials in the ceramic mixture, GT yields a final red colour to the fired ceramic body. The reason of this stability stems from the fact that goethite which transforms into hematite is the cement of quartz grains. In particular we studied the stability of GT in mixtures for porcelanised grès with totally different features (i.e. from highly refractory to poorly refractory). This work is aimed to demonstrate that the application of the mineralogical knowledge in synergy with the use of advanced techniques of material characterisation is capable to give a detailed conclusive picture of the physical-chemical and technological properties of materials of ceramic interest

Numerical investigation on load transfer effects in bogies of urban rail vehicles

Urban rail vehicles can present many types of architecture, definitely different from those of traditional rail vehicles. When dealing with long articulated tramcars, complex coupling effects between the vertical and lateral dynamics may arise. Making reference to a modern tramcar, the coupling phenomena are investigated in detail by means of numerical simulation, considering the dynamic behaviour during the negotiation of curves with or without superelevation

On the Landau--Teller approximation for the energy exchanges with fast degrees of freedom.

We revisit the Landau-Teller heuristic approach to adiabatic invariants and, following Rapp, use it to investigate the energy exchanges between the different degrees of freedom, in simple Hamiltonian systems describing the collision of fast rotating or vibrating molecules with a fixed wall. We critically compare the theoretical results with particularly accurate numerical computations (quite small energy exchanges, namely of one part over 10^{30}, are measured)