High power RF device performance decreases as operation temperature increases (e.g. decreasing electron mobility affects cut-off frequencies and degrades device reliability). Therefore determination of device temperature is a key issue for device topology optimisation. In this work the temperature variation of AlGaN/GaN high-electron-mobility transistors grown either on silicon or sapphire substrate under bias operation was measured by micro Raman scattering spectroscopy. Temperature measurements up to power dissipation of 16 W for 4 mm development devices were carried out and a peak temperature of 650 K was determined. The difference of thermal resistance for similar devices grown on the two different substrates was assessed. The thermal resistances of different device topologies were compared to optimise the component design.

The mechanism of electrical degradation and breakdown of polymeric insulating films is examined by this paper as a two-stage process. Electron injection by Fowler-Nordheim tunnelling, provides the energy for the creation of the first cavity near to the injection contact (the beginning of the formation of the so-called low-density region) where impact ionisation of molecules and hence electron avalanche, can occur. This stage is assisted by intrinsic tunnelling of electrons through local potential barriers. The second stage, the macroion bond scission and the creation of another macroion and a free radical is a thermofluctuational process which involves the action of the stretching force by the local electric field. From the other hand breakdown initiation starts when an electron following a Poole-Frenkel hopping mechanism, is accelerated in a hole with sufficiently large dimensions. The role of the applied electric field Fa and its relation to the local electric field Fl in both stages is examined. Experiments were executed for measuring the breakdown AC voltage Vb and dielectric strength Fb, with voltage rising rate 3 KV/s, in order to examine their relation with specimen thickness d and hence to derive a steady state breakdown criterion. Measurements of PET films life-time were also taken in order to examine the degradation mechanism and the polymer's lifetime.

Solid bodies obtained by sintering glass microspheres through the first stage of sintering have the useful characteristics of large porosity combined with adequate mechanical strength. Additionally, if the microspheres all have the same diameter, the pore morphology is well defined in terms of shape and has a narrow distribution in size parameters. The two major areas of application of the porous bodies are: A. light weight but mechanically strong objects, and B. filtration of liquids. The fracture strength and the specific liquid permeability of these bodies are expressed as empirical functions of volume porosity (ratio of empty volume to the total volume). Here, we describe the results of our systematic study of the geometrical properties like density, linear contraction and global porosity parameter φ, and the flow parameter, the permeability coefficient as a function of the sintering conditions. Our analysis shows that the existing relations, property versus φ, that claim to describe the behaviour are not adequate for our simple system. We think that the contact area between the adjoining spheres is a better parameter to consistently describe a larger set of the properties. Since, for the initial stage sintering of single diameter spheres, the contact area and the pore size can be expressed as a function of linear contraction, latter is a better universal parameter in terms of which the regular features of the property variations can be expressed.

1.3 $\mu $m room temperature emitting multiple-stacked InAs/GaAs(001) quantum dots (QDs) are grown by molecular beam epitaxy (MBE) and investigated by photoluminescence (PL), polarized photoluminescence (PPL), photoluminescence excitation (PLE), time resolved photoluminescence (TRPL) and atomic force microscopy AFM. The PL measurement shows that two distinct sets of QDs coexist in the sample. The AFM image of the tenth QDs layer not only confirms the bimodal size distribution of the QDs but also shows that the large QDs are elongated along the [1-10] direction. The former structural information has been verified by PPL. Through the excitation density dependent PL and the detection energy dependent PLE we have evidenced two kinds of QDs within the small size dots population: isolated QDs and laterally coupled QDs with vertically coupled large size QDs. The large size dot population is found to possess a long PL decay time confirming that they are electronically coupled. In the meanwhile the PL decay time of the small QDs is found to be similar to that of single layer QDs. These results would help improve understanding some fundamental properties of an interesting structure for optoelectronic applications.

Pulsed laser ablation of metal samples in liquid environments by using a combination of two laser beams has been examined in order to clarify a possibility of the formation of size-selected nanoparticles with controlled dimensions. It has been shown that double-pulse laser ablation technique in transparent liquids can be a good choice for fabrication of stable metal nanoparticles where an efficiency of ablation process can be increased and the wider range of a controllable variation of the mean diameter of the fabricated particles can be achieved.

The pick-up coil of a conventional flux-gate sensor has been replaced by a magnetic tunnel junction. With this respect, the magnetic properties of tunnel junctions have been optimized to be relevant to flux-gate operation i.e. low-coercitive field and reproducibility of the dynamic switchings. Furthermore, the use of an alternative two-dimensional magnetic driving field extends the use of the flux-gate like sensor to make a 2D magnetometer with a single magnetic tunnel junction without any cross sensitivity. A first demonstration is given with sensitivity above 500 V/T and a noise level evaluated to 2 $\rm \mu T/ \sqrt{Hz}$ with an optimized magnetoresistive response.

Measurements of electrostatic force generated in the drift region of a positive unipolar wire-to-plane corona discharge in air are compared with numerical simulations. The generated force does not depend on the ion mobilities, preventing the influence of uncertainty and variation of these parameters. A method is described to simulate the voltage and charge distribution for a wire-to-plane set-up. This method enables the determination of the transition between unipolar and bipolar discharges. In the experimental set-up breakdown electric field of air reduces with increasing discharge current.

The influence of pressure and temperature on continuum emission efficacy in a high pressure argon-mercury plasma for lighting applications are investigated. Extreme high temperature (EHT) lamps are introduced.

This article reports observations of significant synergistic effects between dielectric barrier discharge (DBD) plasmas and Cu-ZSM-5 catalysts for C2H4 selective reduction of NOx at 250 °C in the presence of excess oxygen by using a one-stage plasma-over-catalyst (POC) reactor. With a reactant gas mixture of 530 ppm NO, 650 ppm C2H4, 5.8% O2 in N2, GHSV = 12 000 h-1 and input discharge energy density of 155 J L-1, the pure catalytic, pure plasma-induced (discharges over fused silica pellets) and plasma-catalytic (in the POC reactor) NOx conversion percentages are 39%, 1.5% and 79%, respectively. A moderate plasma enhancement of NOx reduction by C2H4 was also observed in a two-stage plasma-followed-by-catalyst (PFC) reactor consisting of a discharge stage filled by fused silica pellets and a Cu-ZSM-5 catalyst stage.

The aim of this paper is to give a solution to unbalance problem of the input DC voltages of the five-level NPC-VSI used in high voltage and great power applications. For that, a Five-level PWM current rectifier – Five-level NPC VSI – PMSM cascade is presented. In the first part, we develop a knowledge model of the five-level NPC VSI and propose a space vector modulation of this converter using four bipolar carriers. The characteristics of this strategy are studied and the performances of the drive of the PMSM fed by this inverter are presented too. In the first case the input DC voltages of the multilevel inverter are supposed constant and equals. After that, we propose to study a new high voltage cascade five-level PWM current rectifier – Five-level NPC VSI – PMSM. This study shows particularly the problem of the stability of the DC voltages of the inverter and its consequence on the performances of the PMSM speed control. Then, we propose a solution to the problem by employed closed loop regulation using sliding mode. We add a Clamping bridge to stabilise the four DC input voltages of the Five-level NPC VSI. This cascade found applications in great power and high voltage fields as electrical traction.