Pressure dependence of the dielectric loss in semi-conducting polypyrrole aged at room temperature

The effect of physical aging of semi-conducting polypyrrole at ambient temperature for 2 years duration on the dielectric loss at various pressures is investigated. Changes of the dielectric loss spectra and the modification of the values of the activation volume for relaxation are interpreted through the division of chain clusters into smaller components and the reduction of the size of the conductive grains.     

Towards a detection of grassland cutting practices with dual polarimetric TerraSAR-X data

In this study, polarimetric synthetic aperture radar (SAR) parameters are analysed and compared with in situ measurements in order to develop a methodology for detecting cutting practices within grassland areas. The grasslands were monitored with TerraSAR-X radar imaging in dual polarization HH/VV mode and are located near the banks of the Kasari River, close to the Baltic Sea coast of Estonia. The parameters analysed include HH, VV, HH + VV, and HH – VV backscatter, HH/VV polarimetric coherence magnitude and phase, T₁₂ polarimetric coherence magnitude and phase, and also dual polarimetric entropy, alpha, and alpha dominant parameters. Using these parameters derived from the dual polarimetric TerraSAR-X data set, it was virtually impossible to distinguish tall grass (height >30 cm) from short grass (height <30 cm). On the other hand, it proved feasible to detect areas where grass had been cut and left on the ground. Several parameters showed specific behaviour for the state of grassland and the most notable change was found in the dual polarimetric dominant scattering alpha angle. This angle changed from 10° to 25° after tall grass had been cut and left on the ground. This behaviour of the dominant scattering alpha angle can effectively be described using a particle scattering model for vegetation backscattering.     

Stress redistributions in adhesively bonded double-lap joints, with elastic–perfectly plastic adhesive behavior, subjected to axial lap-shear cyclic loading

A shear-lag model is developed in order to evaluate stress redistributions in double-lap joints under axial (tensile) lap-shear cyclic loading. The adherend materials exhibit linear elastic behavior, whereas the material of the adhesive layer satisfies the elastic–perfectly plastic shear stress–strain constitutive relation. The reference state (from which the stresses are redistributed) is based on the standard elastic–perfectly plastic shear-lag analysis for double-lap joints. The main conclusion of the current analysis is that, during unloading, shear stresses of opposite sign may develop in the plastic zones of the adhesive layer, at the ends of the overlap, without reversing the direction of the applied load. A simple model for evaluating the variation of the maximum peel stress in the adhesive layer, based on the variation of the peak shear stress, demonstrates that the sign of peel stresses may alternate, as well. Under cyclic (fatigue) loading, the range of the peak stresses in the adhesive layer is the basic parameter for the evaluation of the variation of the energy release rate and the associated crack growth rate in the overlap. In this framework, the current simplified analysis may provide a reference model for comparisons with experimental data or with results which are based on more complex numerical models. The current model can be readily extended to cover the cases of development of plastic zones in the adhesive layer with shear stresses and plastic strains of opposite sign (during unloading or during load direction change).     

Smart Antennas with Two-Dimensional Array Configurations for Performance Enhancement of a Joint Detection CDMA Mobile Radio System

Smart antennas for base stations of cellular mobile radio systems offer the potential of system performance enhancement by taking advantage of the directionally inhomogeneous signal reception at the receiver. In this paper, two-dimensional array configurations employed at the uplink receiver of a joint detection CDMA (JD-CDMA) mobile radio system are investigated. This smart antenna concept can be split up into a novel channel estimator and data detector which incorporate explicitely the information of the direction-of-arrival (DOA) of signals emerging from users assigned to the considered base station. Proceeding from channel models that model the directional inhomogeneity of the mobile radio channel with single DOAs, the link level performance of a JD-CDMA mobile radio system using this smart antenna concept is evaluated for the rural propagation environment. The performance evaluation is based on Monte Carlo simulations of data transmission and average bit error rates versus the average signal to noise ratio per net information bit are presented for different array configurations. Although these results should be considered as upper bounds for the link level performance, they reveal the advantages of implementing two-dimensional array configurations at the uplink receiver of a JD-CDMA mobile radio system.     

Operating policies for wind-pumped storage hybrid power stations in island grids

Pumped storage is today viewed as the most suitable storage technology for achieving high wind penetration levels in multi-megawatt-sized autonomous island grids, where the technical constraints introduced by the conventional generating units impose limitations on the output of wind farms. In this study, an operating policy is proposed for hybrid wind-hydro power stations (HPSs) in island grids, to increase wind penetration levels, while at the same time minimising the impact on the conventional generation system and ensuring the viability of the HPS investment. The proposed operating strategy is applied to three different autonomous island systems using a dedicated logistic model, to evaluate the effect of the HPS on the overall operation and economics of the island systems and to assess the feasibility of HPS investments.     

Estimating slope failure potential in an earthquake prone area: a case study at Skolis Mountain, NW Peloponnesus, Greece

One of the most important issues in the evaluation of geological hazards is the delineation of landslide prone areas and the estimation of the slope failure potential. In this study, the GIS-based Newmark’s displacement method was applied for the first time in Greece, in order to compute the permanent displacement values and evaluate the slope failure potential in the area of the Skolis mountain in NW Peloponnesus, Greece. The resulting maps were validated using the distribution of secondary effects triggered by the 8 June 2008 earthquake. The study indicated that as the source areas of the rock falls were delineated by the Newmark displacement method, this may be a useful approach to predict earthquake-induced slope failures when the seismic potential of an area has been previously evaluated.     

Electrical conductivity and TSDC study of the thermal aging in conductive polypyrrole/polyaniline blends

The thermal aging of conducting polypyrrole/polyaniline (PPy/PA) blends heated at 70°C for up to about 600 hours was studied by d.c. conductivity measurements and by thermally stimulated depolarization current (TSDC) spectroscopy in the temperature range from 80 to 300 K. The composition of the samples varied from pure polypyrrole to pure polyaniline with the PA content increasing in steps of 10%. Although the = (T) curves seem smooth, the corresponding /T = f(T) curves exhibit systematically ascattering of points in the temperature ranges from 100 to 140 K and from 225 to 320 K approximately for all the samples before and after the heat treatment. TSDC measurements with the MISIM (metal-insulator-sample-insulator-metal) configuration, show a low temperature peak at 100–120 K and a high temperature peak at 280–300 K. The first disappears when the polypyrrole content exceeds 70% and for all the samples after heat treatment, although the high-temperature peak persists. The explanation given to this correspondence between d.c. conductivity and TSDC signals is based on the destruction of conformons and the mobility change of the polymer chains with rising temperature.     

Polarimetric and interferometric characterization of coherent scatterers in urban areas

In this paper the concept of point-like coherent scatterers (CSs) in urban areas is introduced. The detection of CSs in single and quad-polarized images is addressed and applied on polarimetric and interferometric high-resolution airborne SAR data at L-band. For the detection of CSs two different approaches are proposed and their individual performance is analyzed. The properties of the detected CSs and their polarimetric and interferometric characteristics are assessed. The role of polarimetry on the detection of the CSs is evaluated and the potential of extracting the orientation and dielectric properties of individual CSs is finally addressed.     

Canted antiferromagnetic structure of HoPtGe2

Neutron powder diffraction has been performed on orthorhombic HoPtGe₂ crystallizing in space group Immm. Lattice constants are a=4.321(3) Å, b=16.344(3) Å, and c=8.731(5) Å. Refined atomic positional parameters are given. A magnetic phase transition from paramagnetism into a canted antiferromagnetic structure occurs at the Néel temperature T_N=8.5 K. The ordered moments at Ho sites 4i and 4h are 8.1 μ_B and 4.0 μ_B at 4.2 K, respectively; the moments are aligned within the ab and bc plane, respectively.