The study of thermoconvective problems in a laminar external boundary layer flow is theoretically presented for both partial heating and cooling situations after that the fluid/wall system has already reached a first steady heating state. The 4th order Karman-Pohlhausen integral approach is used under the hypothesis that the thermal boundary layer thickness is assumed to be steady during the transient phase. The final mathematical equation for both cooling and heating problems is proposed and exemples of space and time corresponding thermograms are given.

The quenching rate constants of argon atoms in the 4p′[1/2]0−(2p 1), 4p[1/2]0−(2p 5), 4p[3/2]2−(2p 6) and 4p[5/2]2 − (2p 8) states, the upper levels of the 750.4, 751.5, 763.5 and 801.5 nm lines respectively, by H2, CH4, C2H2, C2H4, C2H6, CF4, CHF3 and SF6 have been determined. Argon atoms at room temperature are two-photon excited in the 184–190 nm range, and the decay time of the fluorescence emission is measured in the presence of various reagents. With H2, the collisional quenching rate coefficients of Ar(2p 1), Ar(2p 5), Ar(2p 6) and Ar(2p 8) are 0.27, 4.1, 6.8 and 5.4 × 10−10 cm3s−1, respectively. Therefore, in hydrogen rich plasmas, the 750.4 nm line of argon is the best suited for actinometry measurements. For the other studied molecules, the quenching rates range between 1.6 and 11 × 10−10 cm3s−1. For a correct estimation of the relative density of transient species in plasma by the actinometry technique, it is recommended to consider the collisional quenching of the upper states of the optical emission lines used.

The oxidation at low temperature of fine-grained ferrites containing oxidizable cations such as Cu+, Fe2+, Mn2+, Mo3+, V3+, has led to new mixed-valent cation deficient ferrites with a large number of vacancies. It has been demonstrated by DTG analysis that each cation oxidizes at a specific temperature in close relation with the cation-oxygen distance. The kinetics oxidation of each oxidizable cation has been explained on the basis of a diffusion-induced stress effect when these stresses are generated by the chemical gradient induced during the oxidation process. When fine-grained ferrites contain some Co-cations, it has been revealed that the stresses have a significant influence on the enhancement of the coercivity.

Higher specifications and more narrow tolerances for electrical motor appliances give sense to a renewed interest in the temperature dependence of the demagnetization curve of anisotropic ferrite magnets. Based on physical backgrounds, a first approximation modelling is given for the temperature dependence of a working point, using the room temperature curve and some material and system characteristics. A procedure is derived to give the induced shift of the whole curve at any temperature (−100 to 300 °C). An important characteristic for the application is the field Hki, where irreversible flux losses start. Hence, the critical temperature decrease, at which Hki is reached in the system, is derived.

A numerical integration scheme is presented for integration of the pressure-sensitive yield criterion due to Gurson, suitable for explicit dynamic finite element calculations. This scheme utilizes a sub-increment approach to Mayntain stability for the large strain increments and intense triaxiality that can occur under high strain rate loading. A number of validation problems are presented after which two laboratory-scale high strain experiments are simulated. The integration scheme is shown to be stable and to capture the onset of tensile fracture under high strain rate loading conditions.

The incorporation of silicon from SiH4 in GaAs has been studied on a wide range of growth conditions by atmospheric pressure metalorganic vapor phase epitaxy (AP-MOVPE). The highest free carrier concentration exceeds 1 × 1019 cm−3. Compensation ratios appear to be strongly dependent on the SiH4 partial pressure. The relatively high compensation ratios essentially originate from the amphoteric behaviour of silicon. The temperature dependence of silicon doping has been investigated in the range 650 °C to 765 °C with various silane partial pressures. The activation energy of Si incorporation varies from 0 to 2.2 eV. The dependence of the free electron concentration on the arsine partial pressure (P AsH3 ) leads to the empirical relationship:n = aP AsH3 + $bP_{AsH_3}^{-\frac{4}{3}$ , which describes the relationship between silicon doping concentration and arsine partial pressure.

Samples of a partially crystallized amorphous aluminium-germanium alloy areobserved using high resolution electron microscopy, chemical imaging, and electronenergy loss spectroscopy. Aluminium rich domains with a size 5 to 7 nm are clearlyobserved on plasmon and chemical images using the specific edges of Al and Ge. Thecontrast of the plasmon images is attributed to differences in the intensity of theplasmon peak between the different phases.

In this paper we describe how to record on-line filtered diffraction patterns rapidlywith a serial electron energy loss spectrometer. A numerical treatment then yields theRDF for structural identification. Differents treatments ways of improving theaccuracy of the results are proposed and examined in detail.

The electrical conductivity of iron phosphate glasses of different compositions hasbeen reported in the frequency range 100 Hz to 1 MHz and the temperature range25 °C to 400 °C. The measured ac conductivity is nearly independentof temperature but exhibits strong frequency dependence and can be described accordingto the relation σ(ω) = Aωs where the exponent s has beenfound to be less than unity. In the high temperature domain frequency dependence growsweaker at low frequencies but reMayns strongly frequency dependent at high frequencies.The dielectric behaviour is found to be consistent with Debye type dielectricrelaxation. The behaviour of ac conductivity has been divided into two domains, one inwhich ac conductivity remains close to dc conductivity and in the other case where acconductivity is substentially higher than the dc conductivity. Both these cases havebeen discussed in detail.

In the traditional finite difference time domain (FDTD) method, the studied structure is modeled as elementary cells, which sizes have to be small enough to get close to the reality. Then, this discretization is applied to the whole calculation volume, even though some zones do not need such fine discretization. Consequently, this numerical tool requires an important calculation capacity to increase the precision of the grid mesh. For very large dimension structures, computer limitations no longer allow a sufficiently accurate discretization. The aim of this article is to discuss some methods which allow the EM study of large structures containing elements of very unequal size as compared to the wavelengths used, while preserving an acceptable calculation cost. This approach combines finite differences of variable precision and different-sized cells in the same calculation doMayn. It allows a fine discretization of small structures and a rough discretization of the other elements of the EM problem. This spatial subgridding gives a very original possibility of undertaking EM zooms on some specific parts of the calculation doMayn thus allowing a better modelling of the studied structure while preserving good accuracy and an acceptable cost.

Dans cet article nous analysons un modèle mathématique pour les aimants cylindriques sans fer ainsi que la méthodologie de sa mise en point. Nous montrons comment les formules déduites de la loi de Biot et Savart et du modèle en question permettent d'exprimer, sous forme d'intégrales de fonctions analytiques, le champ, le potentiel vecteur et l'énergie magnétique propre. Nous développons la méthode de simulation issue du modèle et nous présentons son algorithme, les résultats d'étude de quelques exemples pratiques d'aimants, et une méthode systématique de traitement de têtes de bobines. Pour valider le modèle proposé, nous utilisons des configurations d'aimants simples dont les expressions du champ magnétique sont parfaitement connues, permettant de comparer les résultats obtenus.

Yb3+–Er3+–codoped phosphate glasses have been studied in the context ofresearch for eye-safe laser source near 1540 nm, wavelength corresponding to the4I13/2→4I15/2 Er3+– transition. Undoped and dopedglasses of the composition La2O3–Li2O–P2O5 have been synthesised.Absorption from both the 2F7/2 Yb3+–ground state and the4I15/2 Er3+–ground state, excited state absorption4I13/2→4I9/2 Er3+–transition, emission spectra,decay time measurements and Raman scattering have been investigated by using laserspectroscopic techniques. The Judd-Ofelt intensity parameters Ωt (t = 2, 4, 6)for Er3+ have been calculated in order to determine the radiative lifetimes, thebranching ratios of the transitions and the line strength of the excited stateabsorption 4I13/2→4I9/2. A thermal conductivitymeasurement has also been realised. In this paper, the Mayn spectroscopic properties of Yb3+–Er3+–codopedLaLiP4O12 will be discussed and compared with otherYb3+–Er3+–codoped phosphate glasses.

Calorimetric studies have been made in glassy Se80−x Te20Sbx where 0 ≤x ≤ 15 with a view to calculate the crystallization kinetic parameters. Multi scantechnique has been used to calculate the activation energy of crystallizationΔE and the order parameter (n). The results indicate that ΔE ishighly composition dependent in these glasses. A discontinuity in ΔE is observedat 10% of Sb which is explained in terms of mechanically optimised structure at aparticular average co-ordination number.

In this work, we study the non–Gaussian dynamic of the magnetic field linesof a plasma confined in a toroidal configuration. We have used the Fourier pathstechnique in order to calculate the kurtosis of the magnetic field lines. We have alsocalculate numerically this quantity. The magnetic field lines are described by thestandard mapping. A comparison between our analytical and numerical calculations hasbeen done.