Forbidden directions for TM waves in anisotropic conducting media

We investigate the wave propagation properties of nonuniform plane waves in an (unbounded homogeneous) anisotropic conducting material. Such waves (for which amplitudes vary across surfaces of constant phase) characterize the refracted field in an imperfect dielectric, like the earth when a uniform electromagnetic plane wave is incident from the air. The results, presented in terms of polar diagrams of the attenuation, slowness, energy velocity, and quality factor predict the existence of “stopbands” beyond a given degree of nonuniformity (i.e., combinations of propagation and attenuation directions where there is no wave propagation). This is a peculiar, effect due to the joint presence of anisotropy and conductivity that may have application in the design of synthetic materials acting as absorbers of electromagnetic radiation     

Effect of supply voltage frequency on testing of insulation system

This paper deals with the effect of supply frequency on partial discharge phenomena. Results of measurements performed on artificial and practical test objects are compared with computer simulations based on physical models. This comparative analysis points out and explains the differences in partial discharge phenomena observed in tests performed at different frequencies (from 0.1 to 300 Hz). The consequences associated to the use of different supply frequencies in practical applications are, eventually, outlined.     

Application of the Kalman filter for electrical endurancecharacterization of insulating materials and systems

The Kalman filter algorithm is applied to the results of accelerated life tests performed on insulating materials and systems carried out for electrical endurance characterization purposes. It consists of a recursive procedure that applies to the failure-time percentiles obtained from life tests, on the basis of the inverse power or the exponential models, and provides estimates of the endurance indices which give particular weight to the results of the life tests performed at the lowest test stresses. This allows more meaningful endurance characterization and accurate life prediction. This paper provides the algorithms for Kalman filter applications, giving emphasis to error estimation, as well as the method for calculation of confidence limits of life-line parameters and predicted failure times. The proposed Kalman filter procedure is applied to the experimental results of accelerated life tests relevant to different insulating materials and systems     

Chip-level differential encoding/detection of spread-spectrumsignals for CDMA radio transmission over fading channels

This paper is concerned with the design and performance evaluation of a direct-sequence spread-spectrum transmission and signal-detection technique for application to code-division multiple-access mobile radio networks. Unlike the conventional differential encoding/detection of data symbols, such a technique envisages differential encoding/detection of the spreading code chips to counteract the fast time-selective fading encountered in mobile radio transmissions. Binary PSK modulation on a Rician frequency-flat-fading channel is assumed, with Gaussian and Rayleigh channels as particular cases. The bit-error rate performance of the receiver is analytically evaluated as a function of the relevant system parameters, and the impact on the receiver performance of a carrier frequency offset is also investigated     

Comparison of three restriction endonucleases in IS1245-based RFLP typing of Mycobacterium avium

IS1245-based restriction fragment length polymorphism (RFLP) analysis has been proposed recently for molecular typing of Mycobacterium avium isolates. As there is no standardised method with respect to the optimal restriction enzyme, three restriction endonucleases were tested for analysis of 17 human isolates. The restriction endonucleases, selected on the basis of the physical maps of IS1245 and of the highly homologous IS1311, were BsaAI, that cleaves IS1245, PvuII, that cleaves IS1311, and NruI, that cleaves both IS1245 and IS1311. All the restriction endonucleases yielded polymorphic and complex RFLP patterns. However, BsaAI- and NruI-generated bands were more evenly distributed and easier to detect than PvuII-generated bands, most of which clustered in a narrow zone of the fingerprint. In some cases, DNA digestion with BsaAI or NruI yielded probe-specific restriction fragments of molecular size lower than expected. Moreover, digestion with NruI, which was expected to generate the highest numbers of bands in all the isolates, yielded fewer bands than were obtained with BsaAI or PvuII in 14 and 5 isolates, respectively. These findings might suggest the existence of unidentified IS1245-related insertion element(s) in M. avium isolates. Computer analysis of the IS1245-based RFLP patterns of M. avium isolates showed that the restriction endonucleases were capable, although with minor differences, of defining distinct banding patterns and clusters of identical or highly related isolates, thus confirming IS1245-based RFLP analysis as a useful technique for epidemiological studies.     

Capacitance DNA bio-chips improved by new probe immobilization strategies

Label-free DNA detection plays a crucial role in developing point-of-care biochips. Capacitance detection is a promising technology for label-free detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To address these problems, mercapto-hexanol or similar alkanethiols are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, florescence microscopy, and capacitance measurements are used to investigate new lipoate and ethylene-glycol molecules. The new surfaces offer further improvements in terms of diminished detection errors. Film structures are investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.     

The effects of heat treatment and implantation of aluminium on the oxidation resistance of FeCrAlY alloys

The oxidation resistance of FeCrAlY alloys is known to be due to the rapid formation of a protective film containing α-Al₂O₃. The near-surface concentration of Al has been increased by ion implantation, and for a dose of 10¹⁷ Al⁺ ions cm^?2 (equivalent to 4.5 μ cm^?3 the parabolic oxidation rate constant has been reduced by a factor of 140 in tests at 1100°C. Heat treatment prior to oxidation also proved beneficial for reasons which are discussed. These relate to the diffusivity of Cr and other spinel-forming elements within the metal. Analysis of Al⁺-implanted steels after oxidation, using ESCA and EDS techniques, confirmed the high concentration of Al₂O₃ within the oxide, and SEM examination showed that the scale is much more compact than in the unimplanted case. Suggestions are made for enhancing still further the efficacy of Al⁺ implantation as a means of improving oxidation resistance and for optimizing the synergistic effect of yttrium and aluminium.     

Pressure drop during air flow in aluminum foams

This paper aims at investigating experimentally the pressure drop during air flow in six different aluminum open-cell foam samples with different number of pores per inch (PPI) and different porosity under a wide range of air mass flow rate. Three imposed heat fluxes are considered for each foam sample. The collected pressure drop data are analysed with reference to models available in the literature. A new simple pressure drop model, based on present data, has then been developed. The consistency of the proposed model is finally checked by comparison to data available in the literature from different laboratories.