When electron beams are directed against solid targets (unsupported thin film, bulk or surface film) some particles come back and emerge from the surface. These particles are not reflected without dissipation of energy because of their penetration below the surface and the resulting loss of small amounts of energy by ionizations, electrons excitations, plasmon emissions and so on. In this paper the fractions of electrons backscattered from surface films with various thicknesses deposited on different substrates, calculated by using both an analytical approximation (Multiple Reflection Method) and a numerical approach (Monte Carlo) are presented. The results of the two approaches are compared. The analytical method results are also compared with experimental data concerning surface films and good agreement is found between theory and experiment. The comparison allows us to conclude that the proposed analytical method, keeping in mind the underlying approximations, represents a useful and informative approach.

In this paper we extend the recently developed models that predict the magnetic field produced by thermoelectric currents in anisotropic homogeneous metal media to laminated composite metals. The premise is that thermoelectric anisotropy produced by the layering could be more pronounced and tailored to the specific needs as contrasted with the relatively small inherent crystallographic anisotropy in conventional metals. The effective anisotropic properties of the layered composite are first obtained for both directions along and normal to the layering using mixture theories. The magnetic field produced by directional heating of the composite panel is then calculated using the approach developed in A.H. Nayfeh et al. (J. Appl. Phys. 91, 225 (2002)).

We present a new approach for the realisation of a molecular photo-switch, based on photochrochromic oligothiophene-substituted chromenes. When optically excited, these compounds undergo a structural change passing from a neutral state (closed form) to a strongly polarized one (open form). This photochromic process is accompanied by a deep changes in the electrical characterisation.

We report measurements of photoluminescence from corrugated thin films of a light-emitting polymer. We find that emission into guided modes that would otherwise be trapped in the polymer may Bragg scatter off the corrugation to produce useful, far-field radiation. Analysis of the angle dependence of this far-field emission together with theoretical modeling enables us to establish the nature of the optical modes guided by the structure. We show that the dispersion of the modes supported by corrugated polymer films depends on the depth of modulation of the corrugation and find that if the periodic corrugation is strong enough photonic band gap effects may be induced. We also address the question of whether Bragg-scattering of the guided modes, including surface plasmon polariton modes, may increase the efficiency of the emission. We measure and compare the efficiency with which radiation is produced by planar and corrugated structures, finding the corrugated structures to be up to a factor of 2.6 more efficient. We indicate how our results may be used in the search for ways to improve the efficiency of devices based on light emitting thin films.

Nowadays, the switched reluctance machine are widely used. To determine their performances and to elaborate control strategy, we generally use the linear analytical model. Unhappily, this last is not very accurate. To yield accurate modelling results, we use then numerical models based on either 2D or 3D Finite Element Method. However, this approach is very expensive in terms of computation time and remains suitable to study the behaviour of eventually a whole device. However, it is not, a priori, adapted to elaborate control strategy for electrical machines. This paper deals with a non linear analytical model in terms of variable inductances. The theoretical development of the proposed model is introduced. Then, the model is applied to study the behaviour of a whole controlled switched reluctance machine. The parameters of the structure are identified from a 2D numerical model. They can also be determined from an experimental bench. Then, the results given by the proposed model are compared to those issue from the 2D-FEM approach and from the classical linear analytical model.

A systematic investigation on growth and sensor characteristics of SnO2 thin films of different orientations is reported for the first time. Thin films were grown by pulsed laser (KrF; λ = 248 nm) ablation technique under in-situ conditions. Films deposited at 525 °C on (1102) sapphire were predominantly (101) orientated whereas those deposited on (100) LaAlO3 were highly a-axis orientated. Sensors made of predominantly (101) oriented films exhibited more than two orders magnitude change in resistance even for 100 ppm of H2 in air at 310 °C. The response and retracing times of the sensor were remarkably short respectively 30 and 200 s. Sensors made of a-axis oriented films also exhibited similar sensitivity and response time for the same quantity of both H2 and LPG. However, the retrace time was very long typically about 20 min. Atomic force microscopic (AFM) investigation reveals that the films are highly granular with an average size of about 100–150 nm which is ten times larger than the critical size of 6 nm, a criterion required for high sensitivity. (The Debye length of ${\rm SnO}_2 \cong 3.07$ nm at 293 K and the critical grain size is therefore 2 × Debye length, which is 6 nm.)

The objective of this paper is to explore the possibility to use composites polyester/titanates (M2+Ti4+O$_3^{2-}$ with M = Ba2+, Sr2+, Ca2+, Mg2+) to get a miniature high- frequency components, and the proposal of signal processing allowing to minimize the different errors particular to the temporal spectroscopy in matched line for two spaces (time, frequency), and the establishment of an expression that determines directly the permittivity without having to make the inverse resolution transcendent equations related to the propagation. Analysis of results obtained by this signal processing, confirms the validity of Bottreau's modeling law, in low frequency according to the volume fraction and the spectral viewpoint, which allows to anticipate the composition of materials to be used to reply to electromagnetic predefined characteristics.

This paper presents some results from experiments carried out on a flyback converter whose transformer has been built with a new stress-annealed nanocrystalline (iron-based) material developed by our laboratory team. This original process has provided a low value of relative permeability (around 200) at a high induction level, thereby making it possible to store large amounts of energy. A flyback transformer without air-gap was thus tested in order to evaluate the performance of this material, with highly satisfactory results being obtained. Because of the material's low magnetic losses at a high induction level and high-frequency switching (up to 25 kHz), low transformer losses along with a low temperature rise were observed. A figure of merit is proposed in order to situate our material performances among others.

A new mixed acid sulphate K0.9Rb0.1HSO4 was synthesized at room temperature. It has been firstly characterised by X-ray diffraction (XRD) and vibrational spectroscopy investigations. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by differential scanning calorimetry (DSC), (XRD), electrical conductivity measurements, and impedance spectroscopy were carried out. The XRD results on single crystals showed that at room temperature, K0.9Rb0.1HSO4 has an orthorhombic symmetry with space group Pbca. The unit cell parameters are: a = 8.39(6) Å; b = 9.79(8) Å and c = 18.98(5) Å. The Raman and infrared spectra at room temperature were also investigated. The structural similarity with KHSO${_4}$ has been confirmed. The thermal studies showed that K0.9Rb0.1HSO4 undergoes two structural phase transitions at about 400 K and 435 K. A partial substitution of K+ by Rb+ increases the conductivity even at room temperature. The transition at 435 K leads to a super-ionic conductor state at high temperatures related with rotational motions of HSO4− ions.

The crystallization processes of Zr70Cu20Rh10 and Zr70Cu27.5Rh2.5 metallic glasses were studied. The initial precipitates are the mixture of an icosahedral quasicrystalline phase (I phase) and a face centered cubic Zr2Rh phase (fcc-Zr2Rh) for Zr70Cu20Rh10 alloy and that for the Zr70Cu27.5Rh2.5 alloy is a single I phase. Under optimum annealing conditions, the largest I phase particle size is 40 nm and 80 nm for Zr70Cu20Rh10 and Zr70Cu27.5Rh2.5, respectively. To explain these results, it is assumed that icosahedral atomic cluster exists in the metallic glasses, which serves as the seeds for the precipitation of metastable I and FCC-Zr2Rh phases. Further, it is suggested that the number density of icosahedral atomic cluster and the ease of fcc-Zr2Rh phase formation depend on the Rh concentration, which explain the above-mentioned dependence of the I phase particle size on Rh concentration.

In this paper a method is proposed in order to obtain an interval of possible values for the surface power density brought to the electrodes by an electric arc of short duration and short electrode gap. Two examples of results (for a copper anode and a copper cathode) are presented in the case of an electric arc in air at atmospheric pressure.

Thermally stimulated current measurements have been performed on polycrystalline layers of lead iodide grown from solution. Several TSC peaks or bands have been observed at temperatures of 100 K, 195–220 K, 230–240 K and 270–300 K. Comparison with PbI2 single crystal shows that the polycrystalline structure of the material introduces additional defects. In contrast the defect currently found in single crystal and attributed to the lead vacancy has not been clearly evidenced in the polycrystalline layers. The position and relative intensity of the peaks can be modified by Ag doping and thermal annealing. On the other hand, only small differences resulting from the anisotropy of the material have been observed depending on the orientation of the electric field with regards to the grains orientation.

Silicon technology has become a good alternative to copper for the elaboration of efficient cooling devices required in power electronics domain. Owing to its high degree of miniaturization, it is expected to provide suitable microchannels and other inlets holes that were not achievable by copper micromachining. Besides, the use of silicon technology provides a variety of bare materials (silicon dioxide, silicon nitride, silicide, etc.) which may be either insulator or conductive, with a good or bad thermal conductivity. This large choice makes it possible to built up rather complex multilayer devices with mechanical properties good enough in comparison with hybrid copper technology heat sinks. Nevertheless, the use of silicon technology, where the microchannel width may reach few tens of microns, raises fundamental features concerning the fluid displacement within such small sections. More precisely, fundamental fluid mechanics studies have to be conducted out in order to get an accurate description of the fluid boundary layers and to provide basic data on the exchange mechanisms occurring at these surfaces. In this paper, we review the operation principles of both single- and double-phase heat exchange devices elaborated in silicon technology. Forced-convection heat sinks as well as integrated micro heat pipes are analyzed. An analytical approach is adopted to evaluate their total thermal resistances as a function of several geometrical parameters. Numerical simulations are then used in order to assess the accuracy of the analytical approach and to evaluate the impact of the fluidic aspects on the whole performance. The optimum devices are then conceived thanks to an appropriate optimization procedure taken into account the several experimental constraints. Reference values of similar copper devices are reminded and the advantages of the silicon integrated approach are highlighted.

The complementarity between 57Fe Mössbauer spectrometry and classical methods of powder characterizations is pointed out for determining the formula of metal-ferrite composites (Fe$_p^0$Co$_{1-p}^0$)a(CoxFe$_{3-x-t}$$\square_t$O4). It is shown that X-ray diffraction is essential to determine the composition of the metal, while TG measurements in air give an approximate value for the metal ratio. In-field spectrometry is expected as the most suitable tool to determine the Fe sites occupancy, although the complex hyperfine structure might originate some misfits. The composites formulae were therefore determined by selecting the set of refined Mössbauer parameters that were in best agreement with the TG measurements. Magnetic measurements prove the validity of such an approach.

The spatiotemporal relaxation of electrons in spatially one-dimensional plasmas acted upon by electric fields is investigated on the basis of the space- and time-dependent electron Boltzmann equation. The relaxation process is treated using the two-term approximation of an expansion of the electron velocity distribution function in Legendre polynomials. To verify the complex Boltzmann equation approach by a completely independent kinetic method, results for inhomogeneous column-anode plasmas of glow discharges between plane electrodes are compared with corresponding ones obtained by Monte Carlo simulations. The spatiotemporal electron relaxation in argon plasmas, subjected to a space-independent electric field and maintained by a time-independent inflow of electrons at the cathode side of the plasma region, is considered. Starting from steady state at a given electric field, the relaxation process is initiated by a pulse-like change of the electric field strength and is traced until the spatially structured, time-independent state associated to the changed field is reached. The behaviour of the velocity distribution function and macroscopic quantities of the electrons in space and time is analyzed for enlarged and reduced electric field strengths typical of the column region of glow discharges. In particular, the spatiotemporal reformation of plasma structures has been found to progress in two phases, i.e., existing structures in the distribution are driven to merge in wide plasma region first, followed by a formation phase of new spatial structures which are induced by the cathode-sided inflow of electrons. The results for the macroscopic quantities and the isotropic distribution functions obtained by Boltzmann and Monte Carlo calculations agree very well during the spatiotemporal transient process as well as in the new steady state finally reached.

An experimental study of Marangoni flows in horizontal layers of tin based metallic alloys heated from the side is carried out, based on the observation of the motion of tracer particles at the surface associated with a direct measurement of temperatures in the melt. A key feature of the procedure is that the experiments are performed in a high vacuum environment to limit as much as possible the pollution of the liquid vapour interface. In pure tin, depending on the intensity of the driving force measured by the Reynolds-Marangoni number, either viscous or boundary layer flow regimes are found. In addition, the onset of temperature oscillations is found to be consistent with the hydrothermal wave instability mechanism proposed by Smith and Davis. In tin-bismuth alloys, the observed flow directions and velocities are interpreted in terms of a non linear dependence of the surface tension on temperature, and successfully compared with the dependence predicted by interpolating the available experimental surface tension data with the help of a simple thermodynamic model. During the directional solidification of the layer, the concentration gradient in the solute rich boundary layer ahead of the growth front is found to locally modify the flow pattern. For instance, when thermal and solutal driving forces act in the same direction, temperature oscillations are observed at low values of the Reynolds-Marangoni number. As for opposing driving forces, the situation is that a local reversal of the flow direction is observed in correlation with the morphological instability of the growth front.

The functions of the plasma flow such as electrical conductivity, thermal conduction and chemical reaction can be enhanced by seeding vaporized alkali metal with low ionization potential. In the present study, numerical simulation is conducted for the radio frequency inductively coupled plasma of which functions are enhanced by seeding a small amount of vaporized alkali metal. The effects of seeding, injection flow rate and applied coil frequency on the plasma characteristics are clarified by relating to the flow structure and electromagnetic effect.

The paper presents two large-scale observations of magnetic treatment of industrial water, aimed at investigating changes in the formation of deposits. First, a four-month experiment is described with two identical 25 kW heat exchangers, where in one case the inlet water was treated by a magneto-hydrodynamic method. Deposits recovered from both exchangers were analyzed chemically, by X-ray diffraction, infrared spectroscopy and PIXE. The amount of deposit for untreated water, composed mostly of calcite, increased exponentially with temperature reaching 20 g/m of tube at the warm end of the heat exchanger. The mass of the deposit for magnetically treated water did not depend on temperature and was only ca. 0.5 g/m of tube. It was composed of mainly noncrystalline silica-rich material. Further results were obtained from the practical installation at three blocks of a 1 GW power plant. The soft, amorphous deposit for magnetically treated water had a specific surface area of 80 m2/g and an infrared spectrum similar to that of a silicate hydrogel. Therefore, it appeared that, as a result of the passage through the magnetic device, crystallization of carbonates in water was blocked due to initiation of another, competitive process. This process is the activation of the colloidal silica, which will adsorb calcium, magnesium or other metal ions and then precipitate from the solution as the coagulated agglomerate. The most probable mechanism responsible for silica activation is a Lorentz-force induced deformation of the diffuse layer leading to the increased counterion concentration in the adsorption layer of the negatively charged silica.

The transport of non-equilibrium gases in the flow regime of slightly rarefied gas dynamics within a plane channel bounded by two parallel slabs is addressed. Hydrodynamic derivation of the entrainment of rarefied gases induced by a surface acoustic wave (SAW) along the walls in a confined parallel-plane microchannel is conducted by considering the nonlinear coupling between the interface and the velocity-slip. Both no-slip and slip flow results are obtained with the former ones matched with the previous approach. The critical reflux values associated with the product of the second order pressure-gradient and the Reynolds number decrease as the Knudsen number increases from zero to 0.1. We found when the Reynolds number is larger the surface wave-modulation effect (due to the wave number) to the flow field is significant which represents the strong coupling between the boundary and the flow-inertia term. Meanwhile, the (perturbed) mean flow induced by SAW along the walls of a 2D microchannel is proportional to the square of the wave-amplitude ratio which has been qualitatively confirmed by previous approaches.

This paper is devoted to polystyrene thin film treatment under DC pulsed discharges in nitrogen, oxygen and oxygen-argon mixtures. XPS analysis is used in order to investigate the new chemical bonds generated by the reactive particles colliding the surface from the plasma. The experimental conditions are close to the best running conditions deduced from [16,75,86]. Correlations between microscopic analyses obtained by XPS through the knowledge of the surface chemical composition and macroscopic ones realized by studies of water drop deposited on the films (contact angle measurements) are presented. It is pointed out that the wettability is highly improved when the percentage of oxygen atoms incorporated in polystyrene surface reaches a high value. C − O, C = O and O − C = O are the main chemical bonds and it is found that the oxygen uptake happens during a very short time (about one second for the treatment duration time, i.e. about 10 ms on account of the duty factor value). A high oxygen rate is observed, correlated to the formation of a maximum $\Delta \theta/\theta_i$ plateau value (wettability). Reaction processes in the plasma bulk and on the polystyrene surface are proposed, taking into account the bond energies of polystyrene. As a consequence, the polystyrene treatment is interpreted assuming two steps for the reaction processes: in a first step, chemical bonds are broken by energy transfer from reactive particles to the surface and in a second step, new chemical bonds are generated. In this spirit, the main reactive plasma particles are described and surface reactions are proposed on the polystyrene surface.