This paper focuses on the modelling of a SiC-JFET. The novelty aspect is the dependence on temperature. An accurate model has been used in a previous work and an identification procedure for the main model parameters has been demonstrated. Readers have asked for a more advanced SiC JFET temperature-dependent model. A limitation of the current model versus temperature is verified and explained in order to introduce the necessity of a new temperature dependence model. A more advanced model is then considered and a comparative study between experiment and simulation of the device is established. The characteristics of three SiC JFETs devices are considered from experimental and simulation point-of-view. Simulations results clearly replicate the experimental data at different temperatures and a new validity approach, namely validity maps, is proposed. Validity domains are discussed.

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.

The present paper reports the preparation of (Se80Te20)100-xAgx (0 ≤x≤ 4) chalcogenide glasses in bulk by using melt quenching technique. DSC runs of these samples have been taken at four different heating rates (5, 10, 15, 20 K/min). The variation in crystallization temperature Tc with Ag concentration at different heating rates has been studied. A strong co-relation between the pre-exponential factor K0 of rate constant K of crystallization and activation energy of crystallization Ec has been observed. The variation of rate constant K with composition and the dependence of Ec with Ag concentration have been studied.

It has been observed in many cases that the effective dielectric constant of some general composite media can reach as high as thousands at low frequency side. In this paper, a numerical method is used to simulate this phenomenon and study the parameters which could affect the dielectric spectrum. In order to obtain the effective dielectric constant and conductivity of the composite and understand the dominant factors of large dielectric enhancement of low frequency side, a three-dimensional finite difference method (3D-FDM) is used to simulate general mixtures and mixtures with membrane structure. A special FDM grid is introduced to handle the membrane that coats the inclusions of the composite medium. We analyze the influence of the membrane thickness, membrane conductivity, inclusion insertion ratio, and inclusion shape on the effective dielectric constant and conductivity of the composite. The results show that: (1) the low-conductivity membrane may be the cause of the dielectric enhancement of low frequency side; (2) the membrane thickness, membrane conductivity, and inclusion insertion ratio can affect the dielectric enhancement level significantly; and (3) the physics of the dielectric enhancement is probably related to the frequency dependence of the effective plate separation of the capacitor model.

Gallium arsenide (GaAs) thin films have been deposited on ITO-coated glass substrates from acid aqueous solution by electrodeposition technique. The structure and the morphology of the samples were analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM). The optical characteristics were investigated at room temperature using a UV-Vis spectrometer. At lower deposition time, the XRD patterns exhibit a mixture of both cubic and orthorhombic GaAs phases. With further increase of the film thickness, only orthorhombic structure was observed with a preferred (100) orientation. By applying the Debye-Scherrer method, the estimated crystallite size for the (200) orientation ranged from 30 to 50 nm, whereas for the (022) orientation was found to be 13–22 nm. From the AFM measurements, the rms surface roughness ranged between 11.4 and 18.4 nm. The analysis of the optical absorption data of the annealed GaAs film deposited at different times revealed direct band gap energy in the range of 1.60–1.85 eV. The large blueshifts observed in this study can be fully explained by the Burstein-Moss effect.

In this work, we demonstrated a simple route to pattern nanostructures on the 3-aminopropyltriethoxysilane (APTES) film adsorbed on mica using nanolithography technology. Various nanopatterns (linear, foursquare and triangular) could be achieved by controlling and designing the scanning direction of AFM tip. Also, it was found that the adsorbed APTES film could be induced to rearrange into a bilayer structure. The parameters for the formation of nanostructures were investigated by contact mode atomic force microscopy (AFM). The results indicated that the height of the nanopatterns built on the adsorbed film increased with the decrease of the depth of a tip pushed in. The driving force for the formation of nanopatterns is the combination of the capillarity and inducement action of a tip to APTES molecules. The results presented in this work will improve our understanding to the formation process of short-chain alkoxysilane molecular bilayer and multilayer on mica in a position-selective way.

The tight-binding model is used to inquire the uniaxial strain effect on the electronic structure of 2D graphene sheet and quasi-1D armchair graphene nanoribbons. The dependence of Dirac points and gap on the uniaxial strain is investigated. The band edges deviate from the corners of the first Brillouin Zone (BZ) gradually with the strain applied. The gap can be opened only when graphene sheet is highly strained. The threshold of the gap induced by strain along armchair directions distinguishes from that by strain along zigzag direction. A controlled strain can be applied to achieve the semiconductor-metal transition in armchair graphene ribbons.

ZnS and Ni doped ZnS nanoparticles were synthesized through chemical precipitation method using a high-boiling solvent. The nanocrystillanity of the prepared nanostructures is confirmed by X-ray diffraction (XRD). The mean crystal size obtained by full width half maxima (FWHM) analysis is 3.2 nm for ZnS and 4.3 nm for ZnS:Ni. An optical absorption study conducted in UV-vis range 150–800 nm reveals the transparency of these nanocrystals in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 3.92 eV for ZnS and 3.88 eV for ZnS:Ni nanoparticles. The electrical resistivity data reveals semiconducting behaviour to both compositions. Fitting of resistivity data in Mott's variable range hopping model (VRH) shows that nickel (1.5%) doping in ZnS reduces gap parameters from 4.78 to 4.22 eV. Based on this model the carrier density, energy gap and hopping distances are calculated for both pure and Ni modified nanocrystals.

As the product of the wear process, the wear particles record the rich information to reflect the state of the equipment's inner abrasion. Analysis of the wear particles in lubricating or hydraulic oils becomes one important branch of diagnosing the wear states of machine parts. Extracting characteristic parameter is an indispensable means to analyse wear particles. In this paper, a method to extract the characteristic parameters of the wear particle boundary based on chaos theory has been discussed. The concept of boundary wave has been firstly conducted, and then based on the Shannon entropy and the theory of phase reconstruction, the concept and the arithmetic of the singular entropy have been conducted. It has been shown that the boundary wave of the wear particles is characterised as chaos, so the singular entropy can be used to describe the complexity of the boundary of the wear particles. Therefore the singular entropy can be considered as one of the characteristic parameters of the wear particles.

Laser Thomson scattering technique has been used to measure the electron density and the electron temperature in a pulsed single filament micro-discharge. The single filament discharge was created between a needle and a hemispherical electrode surface. The spatial and temporal profiles of the electron density and the electron temperature in the center of the discharge gap have been measured. The absolute values of the electron density and electron temperature were found to decrease with time and away from the discharge axis. These profiles have been measured for the first time.

We compared the hydrogen uptake weight percentages (wt.%) of different carbonized materials, before and after modification, for their application in hydrogen storage at room temperature. The Sievert's method [T.P. Blach, E. Mac, A. Gray, J. Alloys Compd. 446-447, 692 (2007)] was used to measure hydrogen uptake values on: (1) Taiwan bamboo charcoal (TBC), (2) white charcoal (WC), (3) single-walled carbon nanotubes (SWCNTs) bought from CBT Inc. and (4) homemade multi-walled carbon nanotubes (MWCNTs) grown on TBC. Modified samples were coated with a metal catalyst by dipping in KOH solutions of different concentrations and then activated in a high temperature oven (800 °C) under the atmospheric pressure of inert gas. The results showed that unmodified SWCNTs had superior uptake but that Taiwan bamboo charcoal, after modification, showed enhanced uptake comparable to the SWCNTs. Due to TBC's low cost and high mass production rate, they will be the key candidate for future hydrogen storage applications.

Thermo-inductive testing is a new technique used for health inspection on different components of automotive and aeronautic industries. Defect detection is based on the modification of induced eddy current and temperatures due to the presence of defects. The temperature change propagated at the surface of the specimen can then be detected by an infrared camera. In this work, a 3D numerical model of this technique is developed and applied to aeronautic materials. Results obtained are compared with the infrared thermography method to demonstrate the relevance of the new technique.

We present in this paper a 3D electromagnetic formulation to describe two conductors in electric contact with each other, submitted to the field of a coil in which an AC current is flowing. One of the two conductors is described by the t-ϕ formulation, the other conductor is described by the surface impedance boundary condition. The proposed coupled formulation has been validated with a numerical example with a simple geometry. This coupled formulation has then been applied to a numerical example on which a crack has to be detected. It is composed of a non magnetic tube embedded in a thick steel tube sheet, submitted to the field of a coil.

This paper presents a 3D numerical model of magnetoelectric sensors based on the finite element method. It is obtained using the association of magnetoelastic and piezoelectric behaviour laws. The 3D finite element formulation is evaluated on a bi-layer beam, combining magnetostrictive and piezoelectric materials, submitted to magnetic fields. These results are compared to the ones obtained with a validated 2D finite element model. At last, a cylindrical magnetoelectric sensor, which can not be modelled with a 2D analysis, is evaluated.

This work deals with the eddy current nondestructive testing of carbon fiber reinforced polymer composites (CFRPs), and the development of rapid numerical models for the simulation of the interaction between the electromagnetic field and complex structures. We show qualitatively the possibility of characterizing the CFRPs by using a rotating eddy current sensor. We make use of a numerical model which we have developed in a previous work for eddy current computation in CFRPs. This model is completed in this work to account for the impedance variation of the rotating eddy current sensor, used to determine the anisotropy factor and the fiber orientation in each ply of a layered CFRP plate.

In this paper, we present an alternative method to Sommerfeld integrals for the calculation of a point source radiation in a multilayered background, based on the method of auxiliary sources, also called fictitious sources method. The method lies upon the decomposition of reflected and transmitted fields on a basis of secondary sources, which amplitudes are determined by applying boundary conditions at each multilayer interface, solving an over-determined system of equations. We present a generalization of the classical FSM to open stratified domains, with arbitrary number of layers and arbitrary position of the point source in the multilayer. Two and three dimensional formalisms are proposed, and compared to exact Sommerfeld formulation. Computation time reduction factors as high as 100 are obtained for 2D problems. Moreover, this method enables the study of non-flat interfaces, which is not possible with Sommerfeld approach. This method can be used for example in order to determine radiation efficiency of emitting devices, or it can be integrated in discrete source type electromagnetic methods for calculation of scattering by a complex target.

In this work, an original procedure, based on the finite element method, is presented for the design of a Levitron©, a device made of permanent magnets and relying on stable gyroscopic magnetic levitation, using secondhand components. A perturbation force analysis is performed on finite element models of available magnets in order to derive the locus of stable equilibrium, as well as the top mass, for a given configuration of the magnets. We investigate three methods for the estimation of forces from finite element computations, two of them based on the Virtual Work principle, and one performing numerical integration of the classical expression of forces between magnets. Results are employed to realize a Levitron© in laboratory, and are shown to be in better agreement with experience than those from a simple analytical model available in the literature.

A mainly orthogonal and locally barycentric dual mesh is used to improve the performances of a generalized finite difference method. A criterium is proposed to choose between an orthogonal and a barycentric construction for the dual mesh taking into account stability considerations for an explicit time scheme. The construction of the constitutive matrix is performed using either the microcell or the Galerkin method. The proposed method is shown to considerably reduce the computational cost in the assembly process and the resolution compared to methods using completely barycentric dual meshes.

The modeling and design of eddy currents sensors for non-destructive testing applications, generally, requires numerical methods. Among these methods, the finite element method is one of the most used. Indeed, it presents a great capability to treat a large variety of configurations. However, in the study of eddy current testing problems, the existence of structures that have a geometrical dimension smaller than the others (thin air gaps, coatings...) will lead to difficulties related to the meshing process. The introduction of particular elements such as shell elements allows to simplify the modeling of these problems. In this paper, the shell elements are used in two different 2D axisymmetric formulations, the electric formulation a* and the magnetic formulation t-ϕ in order to simulate the behaviour of the electromagnetic fields. The results obtained with the two formulations are compared with analytical solutions.

A perturbation method for the A-χ geometric formulation to solve eddy-current problems is introduced. The proposed formulation is applied to the feasibility design of a non-destructive evaluation device suitable to detect “long” longitudinal flaws in hot steel bars.