We study the limitation possibilities of bulk Bi high T c materials. For this we test these materials with a.c. or d.c. currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3–4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current.

Textile cardiovascular prostheses are tubular structures made of polyester filaments. They present particular mechanical properties linked to wavy form of their walls allowing them to stretch under pressure. Pulsatile blood flow was studied in a moving walls vascular prosthesis. First, an image processing device was used to measure prosthesis displacement under air pressure in an free end impregnated textile prosthesis. Then, fluid-structure interaction is simulated with a numerical computation code allowing to couple prosthesis walls motion with blood flow. Navier-Stokes equations governing fluid flow are numerically solved with N3S code based on finite elements method. The numerical process is based on the Arbitrary Lagrangian Eulerian (ALE) formulation allowing moving domains. The obtained results showed a particular distribution of blood flow velocities and shear stress near the graft walls. The flow velocity distribution near a prosthetic surface is strongly influenced by the crimping morphology and deformation. A local flow analysis is imperative to understanding pathologies implying hemodynamic factors and to optimize the prosthesis design.

In the present paper, we report the compensation effect for the crystallization of different binary and ternary systems of some chalcogenide glasses. We have observed Meyer-Neldel rule between the pre-exponential factor K 0 of rate constant K(T) of crystallization and activation energy of crystallization E c in the present case.

A hollow cathode source with a specially designed cusp magnetic field Bz (r,θ) provides clustering environment to thesputtered carbon atoms and ions. Source's distinctive features are itssooting properties that depend upon the two well-defined regions within thedischarge. The cusp field drives both of these regions but in differentmodes – one region ionizes the source gas, introduces the sputtered C fromthe hollow cathode while the other is the collision dominated gyrationalmotion of the C+ ions along Bz (r,θ) contours.Tunability of plasma's discharge characteristics provides the tool toinvestigate clustering in the sooting plasma.

The process of multiwavelengh detection by a single system is possible when considering multilevel structures. Indeed, in a quantum structure with specific profile, levels can be confined in a single band leading to Infrared intersubband transitions which may be responsible of strong enough absorption. In this work we present the theoretical determination of the absorption spectra in a specific GaAs/AlGaAs superlattice containing four confined minibands. For this, we have calculated the electronic states, the dipole matrix elements and the Fermi level's position versus temperature and doping. We analyze the importance of the different transitions absorption peaks and their behavior when varying either the temperature or the free electrons density, both in the parabolic and the non parabolic cases.

Several ways using surface modification are commonly used to enhance thermal stability of polymer matrices. In this study, Continuous-Wave carbon dioxide (CW CO2) laser irradiation and atmospheric pressure non-thermal He plasma treatment on microporous poly(vinyl chlo-ride)/Silica composite have been investigated and compared. On one hand the alternative was based on the efficiency of the thermal energy afforded by CW CO2 laser irradiation and induced photodegradation processes to release HCl and form polyene sequences under well-controlled condition. On the other hand atmospheric plasma treatment involved surface modification by formation of unstable radicals, inducing crosslinking and dehydrochlorination. In both cases a global thermal stabilization of the composite was noticed by partial dehydrochlorination of PVC, even for short exposure time. The main effects observed after laser irradiation were related to the formation of a very dense structure on surface with very low chlorine content and an important chlorine atoms in-depth gradient on the cross section up to 150 μm in thickness; whereas atmospheric He plasma treatment led to a homogeneous decrease of the chlorine in-depth content due to the plasma interpenetration in the porous microstructure. Structural and chemical modifications both on extreme surface and in the thickness have been investigated respectively by Environmental Scanning Electron Microscope (ESEM) coupled with an Energy Dispersive X-ray analysis (EDX) and X-ray Photoelectron Spectroscopy (XPS). Composites thermal stability and investigation on chlorine release have been evaluated by Thermo Gravimetric Analysis (TGA) coupled with Mass Spectrometry (MS).

In this paper a steady laminar 2D Poiseuille flow between twoplates with chemical reactions on the upper wall is considered. Thisis a typical configuration in flow chambers (like the BIACORE one), which are used for the determination of the rate constants of reversiblereactions between biological macromolecules. As the chamber thicknessis small compared to its length, simplifications are possible, so,some asymptotic limits of mass conservation equation coupled with thewall chemistry are presented. We obtain a system with a large Péclet number. The small effects of the flow on thechemical reaction, which depend on the combination of the Damköhler and Péclet numbers, are highlighted. The results of these equationsare favorably cross compared with the asymptotic (Lévêque)solution or with the simplified solutions (integral methods) found in the literature. The final result is that, due to the fact that theexchange coefficient is shown to be nearly constant, the simplifiedintegral method is derived in a more rigorous way and its area of useis improved.

In order to investigate the effects and optical properties in the mid-infrared region, thin films of PEDOT:PSS were spin-coated on ITO glasses and ITO/Ag nanoparticles substrates. Scanning Electron Microscopy, SEM, has been applied to investigate the surface morphology and measure the size of nanoparticles. Dielectric and optical coefficients such as refractive index, n, and extinction coefficient, k, were calculated by applying Kramers-Kronig dispersion relations to the experimentally recorded near normal reflection FTIR spectra. Different analyses confirm that Ag nanoparticles are present in the structure of the synthesized thin films. The recorded Raman spectra have shown that the intensity enhancement of Raman peaks of PEDOT:PSS increases due to the plasmon resonance of Ag colloidal silver nanoparticles layer and optical properties investigation has confirmed the electrical conductivity increase in the mid-infrared region.

The local structures and the spin Hamiltonian parameters for the substitutional Nb4+ centers in MO2 (M = Sn, Ti and Ge) crystals are theoretically studied using the perturbation formulas of these parameters for a 4d1 ion in a rhombically compressed octahedron. The above Nb4+ centers are found to experience the Jahn-Teller distortions, characteristic of the relative axial compressions (~ 0.01–0.02 Å) and the non-axial (planar) angular increases (~ 3°). As a result, the ligand octahedra are transformed from original elongation on host tetravalent cation sites to compression in the impurity centers, with additional non-axial distortions smaller than those in the hosts. The influences of the Jahn-Teller distortions and the ligand orbital contributions are also analyzed.

By combining the techniques of dielectric relaxation spectroscopy (DRS), measurement of both ac and dc conductivities, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), we have explored the effect of electrical ageing on poly (methyl methacrylate) (PMMA) films at temperature between 0 °C and 80 °C in the frequency range of 1 Hz–107 Hz. These results are discussed and correlated to FTIR and SEM observations.

The aim of this paper is to provide data on the influence of the geometry of the fins on the acceleration performance of a ram accelerator projectile in the subdetonative mode. The data that are presented in this paper are derived from a non reacting computation performed at the French Research Institute (ISL) with the commercial numerical code TascFlowTM from AEA Technology. This code calculates the pressure and temperature profiles in a non-reactive flow around the ram accelerator projectile. Three types of projectiles were studied with respectively three, four and five fins. Furthermore, different fin geometries were studied. The wall temperature behavior was investigated, in order to explain the high erosion of the projectile that is observed as the projectile comes out of the tube. Moreover, the high temperatures that were derived from the calculation explain the initiation process of the reactive at some point of the projectile, which, in turn, explains the unstart process. These calculations were conducted during ram accelerator operations at ISL and were used to explain some effects observed on the experimental data obtained in both the 30-mm and 90-mm caliber facilities.

Low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we could show that photothermal infrared spectroscopy performed with a pulsed free electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by photothermal beam deflection (PTBD) technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method as compared to conventional FT-IR spectroscopy.

We study the optical behavior of Au-TiO2 thin cermet films, the gold volume fraction of which is varied over the range 10−3 to 8 × 10−2. In this low concentration range, it is mainly governed by the metallic particles size, which very much depends on the deposition substrate temperature and the annealing time and temperature. The samples structure and morphology are characterized by several complementary techniques. Spectrophotometric measurements at quasi-normal incidence have been performed in visible and near infrared regions. Using a short pulse Nd:YAG laser, we also look for nonlinear optical behavior due to the enhancement of the electromagnetic field close to the surface plasmon resonance of the metallic grains.

The reverse I-V characteristics of In-pWSe2 and Al-pWSe2 Schottky barrier diodes were investigated at room temperature with two different metal thicknesses. A model is presented on the basis of thermionic emission and tunneling to explain the unusually high leakage current observed in these diodes. It has been identified that the major contribution to leakage current is by tunneling mechanism, which significantly affects the reverse I-V characteristics of the Schottky contacts, along with a very small amount of thermionic emission current. We have also extracted various Schottky diode parameters of the two types of diodes fabricated and compared the data. It is found that the diode with 1000 Å metal thickness possesses more tunneling current compared to 500 Å diode.

Growth of thin layers of compound semiconductors such as GaAs and Alx Ga1−x As was obtained by Liquid Phase Epitaxy (LPE) at 838–828 ° C in thickness range of 0.1–4.3 μm which was estimated by Scanning Electron Microscopy (SEM). By Secondary Ion Mass Spectroscopy (SIMS) measurements, type of impurity atoms and their density and uniformity with respect to thickness were measured. In this way we are sure that variation of impurity atoms such as Si, Te, Sn and Ge indicates that epilayers were formed uniformly and it demonstrated that the LPE growth was a suitable way to obtain a good quality of epitaxy layers. Amount of composition parameter x in the compound semiconductor AlxGa1−xAs was measured which varies from 0.13 to 0.4. In-depth profiles of SIMS indicated that Al atom can be replaced by Ga atom in the GaAs crystalline structure.

The effect of sequential deposition of Cu onto a 300 Å-thick film of layered InSe epitaxially grown onto a Si(111) substrate, has been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and photoemission yield spectroscopy (PYS). Cu coverages were from a few hundredth of a monolayer (in terms of InSe atomic surface plane: 1 ML = 7.2 × 1014 at/cm2, that is 0.85 Å of Cu-metal) to 300 ML. The effect of annealings up to 370 °C was also studied. It is shown that Cu has first a non uniform bulk interaction with InSe which looks like an insertion which saturates at 1 ML of Cu per In2Se2 single layer. Then it forms islands which fully mask the surface beyond about 150 ML coverage (130 Å of Cu-metal). Upon annealings beyond 300 °C, the Si substrate behaves as a Cu sink.

Synthesized ZnO nanotubes have finite wall thickness and holy hexagon section. Using density functional theory first we calculated structural and electronic properties of isolated and bundle of these systems. Then same calculations are performed for these systems which encapsulated Fe nanochain or Fe nanowires with different thickness. We found for both cases the bundle is more stable than isolated nanotube. Both pristine of isolated and bundle are semiconductor, in which the bundle energy gap is less than isolated nanotube. All encapsulated systems are spin polarized ferromagnetic with high magnetic moment. In each encapsulated nanotube for lower thickness all ZnO layers are metal but for high thickness the outer layers remained semiconductor.

The present work reports the temperature and frequency dependence of a.c. conductivity in glassy Se70Te30−x Znx (x = 0, 2, 4 and 6) alloys in the temperature range 300–500 K and frequency range 1 kHz. An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of the present samples can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined using this model for all the glassy alloys. The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in terms of lower values of the maximum barrier height for single-polaron hopping.

The numerical solution of partial differential equations requires suitable boundary conditions. Based on a fundamental integral relation for Legendre polynomials, Marshak type boundary conditions are derived that can be applied if an expansion in Legendre polynomials is utilized to solve the spatially inhomogeneous kinetic equation of the electrons in gas discharge plasmas. In particular, it is now possible to relate directly the expansion coefficients of the phase space distribution with macroscopic quantities at the boundaries. That is, a well-defined influx or a reflection of electrons can easily be treated on the microscopic level.