Internal friction and its thermal evolution on 304 L stainless steel films

Internal friction has been measured between 300 and 760K on 304 L stainless steel (SS) using a vibrating reed device. The 0.6 µm thick samples were deposited with ion beam sputtering technique on (100) silicon substrate. It has been shown that the damping level is considerably reduced by annealing between 500 and 760K. The calculated activation energy and the reaction order, using the Johnson-Mehl-Avrami (J-M-H) kinetic enable us to assume that the observed mechanism is closely related to microstructural rearrangements located at grain boundaries.Internal friction has been measured between 300 and 760K on 304 L stainless steel (SS) using a vibrating reed device. The 0.6 µm thick samples were deposited with ion beam sputtering technique on (100) silicon substrate. It has been shown that the damping level is considerably reduced by annealing between 500 and 760K. The calculated activation energy and the reaction order, using the Johnson-Mehl-Avrami (J-M-H) kinetic enable us to assume that the observed mechanism is closely related to microstructural rearrangements located at grain boundaries

Study of Optical Response of Gold Nanoclusters Deposited on Polymer Substrates: Influence of in Situ Mechanical Deformation

Nanomaterials are the building blocks of today’s nanoscience and nanotechnology. Due to the distinct features of the nanomaterials, their utilization in the application sectors has increased. The field of metal nanocluster has been studied with increasing interest in the past few years. In this context, we study the influence of mechanical deformation on the optical transmittance of gold nanoclusters deposited on polymer substrate the polyurethane Clear Flex® 50 during in situ tensile test

Warm inflation model building

We review the main aspects of the warm inflation scenario, focusing on the inflationary dynamics and the predictions related to the primordial spectrum of perturbations, to be compared with the recent cosmological observations. We study in detail three different classes of inflationary models, chaotic, hybrid models and hilltop models, and discuss their embedding into supersymmetric models and the consequences for model building of the warm inflationary dynamics based on first principles calculations. Due to the extra friction term introduced in the inflaton background evolution generated by the dissipative dynamics, inflation can take place generically for smaller values of the field, and larger values of couplings and masses. When the dissipative dynamics dominates over the expansion, in the so-called strong dissipative regime, inflation proceeds with sub-planckian inflaton values. Models can be naturally embedded into a supergravity framework, with sugra corrections suppressed by the Planck mass now under control, for a larger class of K\"ahler potentials. In particular, this provides a simpler solution to the "eta" problem in supersymmetric hybrid inflation, without restricting the K\"ahler potentials compatible with inflation. For chaotic models dissipation leads to a smaller prediction for the tensor-to-scalar ratio and a less tilted spectrum when compared to the cold inflation scenario. We find in particular that a small component of dissipation renders the quartic model now consistent with the current CMB data.Comment: 22 pages, 5 figure

Southern Europeans in France: Invisible Migrants?

France fared relatively well at the start of the current economic crisis, but has experienced low economic growth and high unemployment rates in the recent years. As a result it has been a less popular destination with Southern Europeans and EU migrants in general in search of economic opportunities. Although their numbers have increased and represent a growing proportion of recent flows to France, they remain low compared to numbers observed in Germany and the UK. Despite this statistical reality, EU mobility and more generally the role of the EU in economic and social policy have been at the forefront of debates in France since the start of the 2000s, thus well before the start of the crisis. These debates have focused on two populations – the Roma and posted workers – with both groups being portrayed as threats to the French welfare state. Although posted workers are not migrants, according to official EU definitions, their characteristics and experiences are similar to other groups of temporary migrant workers. Southern Europeans account for an increasing number of posted workers, and although they have not been the primary nationalities targeted in discussions concerning this issue, the debates and policy changes introduced in the recent years concern them as well. Moreover, we argue that the focusing of political debates on other populations in France has contributed to the relative invisibility of Southern European immigrants in this country

Primordial Black Holes: sirens of the early Universe

Primordial Black Holes (PBHs) are, typically light, black holes which can form in the early Universe. There are a number of formation mechanisms, including the collapse of large density perturbations, cosmic string loops and bubble collisions. The number of PBHs formed is tightly constrained by the consequences of their evaporation and their lensing and dynamical effects. Therefore PBHs are a powerful probe of the physics of the early Universe, in particular models of inflation. They are also a potential cold dark matter candidate.Comment: 21 pages. To be published in "Quantum Aspects of Black Holes", ed. X. Calmet (Springer, 2014

Kinetics of the initial stages of film formation during low pressure chemical vapour deposition of polysilicon by pyrolysis of silane

A kinetic model for description of the process of silicon film formation on silica by thermal decomposition of silane at reduced pressure has been proposed. The model is based on the concept of kinetic interdependence between heterogeneous catalytic chemical reaction and fundamental structure forming phenomena - nucleation and nuclei growth. A number of experimental data for deposition rates and polysilicon grains sizes have been mathematically processed in order to derive kinetic equations for the rates of nucleation and nuclei growth as functions of reactor operating conditions (pressure and temperature) as well as process duration. Furthermore, based on both the good correspondence achieved between the experimental results and the model, and the deductions of thermodynamic theory of nucleation, the kinetic equations derived were analysed in regard to the general description of silicon film structure evolution. The analysis of the model, by confïrming the general trends established between the arrival and the surface diffusion rates of silicon adspecies, contributes to clarify the mechanism of the initial stages of film microstructure formation. The results obtained show that kinetics of structure evolution can be successfully described by developing the existing CVD phenomenological kinetic models further to an atomistic level

Structure and related corrosion behaviour in 1M H2SO4 of b.c.c. 304L films prepared by ion beam sputtering

The corrosion behaviour in a non-deaered 1M H2SO4 solution of 304L stainless steel (SS) in bulk and thin film state was investigated. In the first step, we elaborated based cubic-centred 304L stainless steel thin films onto Si and f.c.c. 304L SS bulk substrates by using a sputter deposition method. Then, the structure and residual macrostress state of the films were studied by X-ray diffraction. It was found that films are in a highly compressive state ( 3 GPa). Finally, corrosion tests revealed an improvement in corrosion resistance of the films with respect to the bulk 304L stainless steel