The behavior of a coil with ferrite core applied with an ac current and under a magnetic field has been investigated. The field-induced changes of both inductance and impedance have been observed. Based on this, a device for electric current monitoring with the coil has been developed. The result has shown that such a device is very sensitive and high efficiency, and convenient to use in the field of power transmission and management.

Multiwalled carbon nanotubes (MWCNTs) were synthesised by chemical vapour deposition (CVD) in a C2H6+H2 atmosphere over 20%Fe/SiO2 catalysts. The influence of synthesis temperature, flow-rate and flow ratio of the reactant gases, the amount of catalyst employed and the catalyst reduction temperature on the abundance and crystalline perfection of product was analysed by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The changes in yield and crystalline perfection, as monitored by Raman G' band relative intensity, were correlated with the variations of synthesis temperature, the diverse catalyst surface area and H2/C supply ratio attained by varying growth conditions. In the range examined, the lowering of catalyst reduction-temperature turns out to be beneficial for both yield and crystalline perfection of the MWCNTs. All the other growth parameters produce opposite effects so the best compromise has to be sought.

We report for the first time, to the best of our knowledge, an inexpensive fabrication procedure for obtaining perfectly coupled PbS quantum dots. Evidence of quantum dot pairing (each, 10–12 nm) was confirmed by transmission electron microscopy, and the stability with aging was checked by dark-current measurements. The method of encapsulating PbS quantum dots in a nontoxic cis-trans polymer is simple, convenient and attractive for reproducible reasons. Such coupled quantum dots are promising to act as qubits which are vital in quantum computers and qubit architecture.

This paper presents a set of shape parameters giving an estimation of features for 3D objects, in particular bounded surfaces such as molecular island of self-assembled carbon chains on silicon, in order to classify them. These features are quantified both in 2D and 3D and concern an evaluation of the circularity degree or the fractal degree of the object boundary in 2D and a study of peak dispersion and height variations in 3D. The originality of this approach mainly lies in the way of estimating the isotropic and fractal degrees from the boundary of the surface and in the combination of different data, such as height or distance to the edges, for peak characterization. An application to small molecular islands of carbon, studied in nano-elec-tronics, is also presented, in order to illustrate the purpose and the efficiency of the previous shape parameters. This application also includes a new method of adaptive filtering, processed from distance maps.

In the present study, nano-ferrite of composition Mn0.4Zn0.6In0.5Al0.1Fe1.4O4 has been synthesized by co-precipitation method. Decomposition of residue at a temperature as low as 200 °C, gives the ferrite powder. The ferrite has been, finally, sintered at 500 °C. The structural studies have been made by using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), which confirms the formation of single spinel phase and nanostructure. The dc resistivity is studied as a function of temperature and values are found more than twice than those for the samples prepared by the other chemical methods ... It is found that the resistivity decreases with an increase in temperature. The initial permeability value is found to be higher as compared to the other chemical routes. The initial permeability value is found to increase with an increase in temperature. At a certain temperature called Curie temperature, it attains a maximum value, after which the initial permeability decreases sharply. Even at nanolevel, appreciable value of initial permeability is obtained and low magnetic losses make these ferrites especially suitable for high frequency applications. The particle size is calculated using Scherrer's equation for Lorentzian peak, which comes out between 55 nm–69 nm. Possible mechanisms contributing to these processes have been discussed.

Based on numerical simulation technology, the influence of arc currents and axial magnetic fields (AMFs) strength on high current vacuum arc (HCVA) characteristics is studied and analyzed. Simulation results show that electron temperature, ion number density, axial current density, plasma potential, plasma pressure and heat flux density to anode in HCVA are all increased with the increase of arc currents. For very high current vacuum arc, current constriction near cathode side can be more significant than that of anode side. The increase of AMF strength can decrease the above parameters, and will control HCVA more efficiently. The simulation results of HCVA under different arc currents are also verified by experiments.

Single crystals of semi – organic nonlinear optical (NLO) Tris thiourea zinc cadmium sulphate (TTZCS) have been successfully grown from pH 3.5 solutions by slow cooling method. The thermal behaviour of the TTZCS crystal has been investigated from Thermo gravimetric, differential thermal and differential scanning calorimetric analysis. The micro hardness studies reveal the changes in the mechanical property of the crystals grown at pH 3.5. From Raman spectroscopic analysis, different modes of vibration due to various functional groups present in TTZCS have been observed. The morphologies of the crystals were analysed by Scanning electron microscope (SEM).

This paper concerns the study of contact opening under DC voltage in the case of high intensity currents (a few hundred amperes). The application fields are mainly automotive and aeronautical systems. An experimental device has been designed in order to study the opening of contacts under various conditions. The influence of several parameters on contact opening is studied. These are the following: the opening velocity, the current intensity through the closed contact, the nature of the contact materials (Ag, AgSnO$_{2...})$, the value of the inductance in the electrical circuit... The measured parameters characterizing the opening phase are: the arc duration, the value of the electrode gap when the arc extinguishes, the arc energy.

PbSe films were chemically deposited with a range of controlled microstructures, from nanocrystalline to monocrystalline films. The crystal size in the nanocrystalline films was controlled in a range 7 to 25 nm with a fairly narrow size distribution, which allowed fine-tuning of the PbSe energy gap. The optical properties of the films were investigated using infrared (IR) transmission and IR photoluminescence measurements. The nanocrystalline PbSe films showed single bandgap values in the technologically important near-IR region. Two bandgap values, corresponding to both bulk and confined nanocrystals, were obtained for films with mixed microstructure. Strong blue shifts in both the absorption and emission peaks of the nanocrystalline layers were obtained. The bandgaps of the PbSe films were found to be in good agreement with theoretical calculations. The results point out the potential of these films for nanoscale optical device applications operating in the near-IR range.

The characteristics of transient, optically-induced voltages have been studied in a vicinal cut SrTiO3 single crystal. The effect is induced by pulsed ultraviolet laser irradiation at room temperature, and occurs without an applied bias. The duration of the measured signal agrees with that of the laser pulse. The measured voltage depends weakly on the length and linearly on the width of the irradiated area. Based on the off-diagonal Seebeck effect, the mechanism of such a dependence is proposed.

Infrared to visible upconversion emission bands are observed in Nd3+: LiTeO2 glass at 430, 482, 525, 535, 580, 600, 664 and 766 nm wavelengths due to the 2P1/2$\to$   4I9/2, 2P1/2$\to$   4I11/2, 2P1/2$\to$   4I13/2, 4G7/2$\to$   4I9/2, 2P1/2$\to$   4I15/2, 4G7/2$\to $  4I11/2 & 4G5/2+2G7/2$\to$   4I9/2, 4G7/2$\to$   4I13/2 and 4G7/2$\to$   4I15/2 transitions, respectively. Mechanisms involved in these upconversion emissions are shown to either involve excited state absorption or energy transfer depending upon the concentration of the rare earth ions. The emission bands at 755 and 968 nm are also observed due to the thermally excited phonon absorption, on excitation with 800 nm wavelength. A 90 fold enhancement in the intensity of anti-Stokes emission at 755 nm is observed in this glass when temperature is raised from 298 to 523 K. Fluorescence intensity ratio (FIR) and sensitivity (S) of the two thermally coupled levels viz. 4F3/2 and 4F5/2 are calculated at different temperatures and results show that these levels could act as temperature sensor in tellurite host. Lifetimes of the excited levels 2P1/2, 4G7/2, 4F3/2, 4F5/2 and 4F7/2 involved in the emission process are also determined and their temperature dependence is described.

Intermittent operation mode is specific to electrostatic precipitators (ESP) used in workshops where the polluting product is produced in a discontinuous way. The rapping system is necessary in order to ensure a continuous and effective operation of a dry electrostatic precipitator, but causes at the same time, a problem of re-entrainment of dust and thus the degradation of filtration efficiency. The objective of this paper is to propose a procedure based on the methodology of experimental designs (Tagushi's Methodology) aiming at optimizing the rapping process; it consists to determine optimal values of rapping, i.e. the moment, the position and the force of rapping. Several “one-factor-at-a-time" experimental designs followed by a Full Factorial design, made it possible to model the process and to analyze interactions between the factors. The experiments were carried out on a laboratory experimental device which simulates an industrial precipitator with intermittent operation.

Photoacoustic imaging is a noninvasive, nonionizing imaging modality that combines the merits of high optical contrast, good ultrasonic resolution and satisfactory imaging depth. These features make it suitable for detecting the pathological changes of subcutaneous vasculature. A setup of photoacoustic imaging system was employed to achieve images of subcutaneous vasculature and subcutaneous tumor-related vascular anomalies in mice in vivo. The networks of subcutaneous vasculature are clearly identified in the photoacoustic images, blood vessels which are invisible to the naked eye under the skin surface and tumor-related abnormal vasculature are also revealed by the photoacoustic system. Moreover, micro blood vessels correlated with the high frequency signals become evident after digital image processing based on high-pass filtering. This work demonstrates that photoacoustic imaging could potentially provide a valuable tool for monitoring the pathological changes of subcutaneous vasculature in early stage.

We measured in function of helium, argon, and oxygen gas pressure, the evolution of the intensities of the fluorescence spectra of YO molecule issuing from a liquid drop of yttrium oxide melted at the focus of a solar furnace. From this evolution and in a simplified approach assuming the independency of the three molecular systems of YO (A2Π1/2-X2Σ+, A2Π3/2-X2Σ+, B2Σ+-X2Σ+) we deduced, through the analysis of Stern-Volmer plots, a mean quenching rate coefficients of this molecule in these states by the above mentioned gases.

Vegetation fires are slightly ionised gaseous medium. Omnipresent alkali metal species in plant's organic structure are the main source of thermally produced electrons in the fires. In the flames, electron-neutral particle collisions dominate other modes of particle interaction. The collision regime absorbs some of the incident energy when the fire is illuminated with electromagnetic waves. The rate of electromagnetic wave absorption in the vegetation fires has implications on the safety of fire-fighters. During wildfire suppression, radio communication blackout at vhf/uhf has been experienced. This may be partly due to thermal ionisation in the fire. In the experiment, the extent of ionisation in vegetation fires is measured using a 2-port vector network analyser. X-band microwaves are caused to propagate combustion zones of eucalyptus bark and guinea grass fires with maximum temperatures of 1114 and 1054 K respectively. Alkali content in the vegetation fuel was different. Measurements show maximum ionisation in flames produced from guinea grass, which had almost twice much potassium as that of eucalyptus bark, to be 2.63 × 1016 m−3 while that produced in eucalyptus bark flame was 1.46 × 1016 m−3.

One important mechanism in the prebreakdown phase is the quantum tunnelling of electrons from the metal cathode to the gas, lowering the breakdown voltage. Considerable departures from the classical Paschen's curve for pd lower than 1.0 Torr cm in microhollow cathodes with D = 200 μm and electrode spacing of 5 μm and 20 μm in air were observed. Fowler-Nordheim approach was employed to characterize the presence of field emission of electrons which modify the classical voltage versus current curve for pressures lower than 40 Torr.

Current source inverters (CSI) associated to rectifiers are used in variable speed drives for the propulsion system onboard ships. The complete structure will generate frequency perturbations in the entire supply system which could become undesirable. In a first part, the modulation theory is applied to the ideal structure of a converter. The designs of the propulsion transformers and of the propulsion motor are considered in order to calculate the injected currents on both sides of the converters. Finally, those results are confronted to experimental ones obtained onboard an electric ship. Those results show a complete validation of the theoretical predictions.