Preparation and characterization of conductive polypyrrole/kaolinite composites

Conductive polypyrrole (PPy)/kaolinite clay composites were prepared by in situ chemical polymerization of pyrrole in the presence of kaolinite using FeCl₃ as oxidant. The PPy content and conductivity of the composites reached 32.8% and 8.3×10^?2 S/cm at HCl concentrations of 1.5 M and 0.5 M, respectively. The microhardness of the composites containing different amounts of PPy was higher than that of the PPy and kaolinite components. The highest microhardness observed was 30.17 kg/mm² for the composite containing 9.6% PPy. The electrical resistance of the composites was monitored during heating–cooling cycles over the range 5–120 °C. The change in resistance with temperature was more repeatable for the composite than for PPy. The composites were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The humidity-sensing properties were also examined.     

A new high-performance CMOS fully differential second-generation current conveyor with application example of biquad filter realisation

In this article, a new complementary metal oxide semiconductor (CMOS) high-performance fully differential second-generation current conveyor (FDCCII) implementation is proposed. The presented FDCCII provides high-output impedance at terminals Z+ and Z?, good linearity and excellent output–input current gain accuracy. Also, the proposed FDCCII circuit operates at a supply voltage of ±1.3 V. The applications of the FDCCII to realise voltage-mode multifunction filters are given. Simulations are performed using TSMC CMOS 0.35-μm technology to verify theoretical results.     

Upper bounds for blocking probabilities in large multi‐rate loss networks

In this paper, we consider large loss networks with fixed routing and multirate traffic. We use singlelink formulae and standard results on multidimensional Gaussian distributions to obtain upper bounds for blocking probabilities of new calls under light up to critical loading conditions. This is the loading regime of interest for many practical applications such as admission control in ATM networks. The main advantage of our approach is that the complexity does not scale with the size of the system, making it numerically attractive. Comparison with simulation results show that we get good upper bounds. We conclude by discussing the correlation between links in a network.     

Paraxial approximation effect on a dielectric interface analysis

We are presenting a fast new method of analysing a dielectric interface which is assumed to be cylindrically symmetrical. It is based on a multimode Gaussian beam development. Then two different cases are considered and we show the kind of results we can expect from this process. Finally, we explain in detail the relationships between the paraxial approximation and further justified simplifications which lead to an important calculation time decrease.     

Ordonnancement de paquets équitable par les disciplinesgps etdgps

Providing efficient and flexible quality of service guarantees within interogated services packet networks requires the deployment of advanced scheduling disciplines. This paper concentrates on the class of so-called fair queuing algorithms, firstly reviewing the general principle and its known approximations, then focusing on the service of adaptive applications, shedding light on the need to introduce a new scheduling paradigm, named dgps for decoupled generalized processor sharing; for the latter scheme an approximation technique is introduced and evaluated.     

Investigation of Enhancement Band Using Double Screen Frequency Selective Surfaces with Koch Fractal Geometry at Millimeter Wave Range

Numerical and theoretical investigations are presented for a double screen frequency selective surface (DSFSS) with perfectly conducting Koch fractal patch elements. The work was developed in two steps, in the first step two Koch fractal FSS screens were designed using the commercial software Ansoft Designer^TM. In the second these FSS were cascaded and separated by an air gap layer, forming the so-called DSFSS, to improve the bandwidth behavior. Thereafter, a numerical cascading technique is used to analyze the effect of the air gap on the DSFSS. The results were compared and a good agreement was observed.     

Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C₆₀ as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4 cm²/Vs. Devices with pentacene showed a mobility of 0.16 cm²/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ～0.3 cm²/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels.