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In this paper the distribution of electrification current flowing across a pipe, for alternating charge near a surface, is presented. A distribution of charge density was arbitrarily assumed compatible to the Stern theory. Assuming that the velocity distribution is parabolic (in laminar regime) or logarithmic (in turbulent regime), the convective current density can be obtained. The distribution of current density shows changes of sign at different distances from the boundary. This may be the reason for the change of total electrification current sign that is often observed during experimental measurements. Index Terms--Streaming electrification, flow electrification, electrostatic charging.

The genesis of the research work presented in this paper constitutes the issue of the effective and efficient recognition of single-source one-time partial discharge forms that can occur in insulation systems of power transformers. The paper presents research results referring to the use of single-direction artificial neural networks for recognizing basic partial discharge forms that can occur in paper-oil insulation impaired by aging processes. The research work results presented show the recognition effectiveness of basic partial discharge forms depending on the descriptor of the analysis of the acoustic emission signal analysis. The detailed cognitive aim was selection of input parameters and an artificial neural network which would be the best, considering recognition effectiveness and processing time, and which could be used as a classifier in an expert diagnostic system making identification of partial discharges measured by using the acoustic method possible. Index Terms--Partial discharge, paper-oil insulation, acoustics emission method, artificial neuron network, power transformer.

The paper presents results the aim of which was determining the most favorable conditions of ECT (Electrostatic Charge Tendency) measurement taking of insulation oils in the spinning disk system. The work proved that a proper selection of the size and roughness of the disk surface makes the measured volume density of charge [q.sub.w] independent of the hydrodynamic conditions in the measuring system on the solid and liquid phase border. Charge [q.sub.w] density meets then the criterion of a material coefficient and can be used for comparing the results obtained from the systems varying in dimensions and hydrodynamic conditions. The changes suggested also ensure a high repeatability and reproducibility of the results obtained. Index Terms--Dielectric liquids, power transformer insulation, transformer oil.

In early February 2001 (during the austral summer), over 900 000 digital images of ice crystals were recorded at the South Pole using two ground-based cloud particle imagers (CPIs). Of these, 721 572 crystals >50 [micro]m were classified into crystal habits. When sorted by number, 30% of the crystals were rosette shaped (mixed-habit rosettes, platelike polycrystals, and rosette shapes with side planes), 45% were diamond dust (columns, thick plates, and plates), and 25% were irregular. When sorted by area, rosette shapes comprised 50%, diamond dust 30% and irregular 20%. By mass, the percentages were 57% rosette shapes, 23% diamond dust, and 20% irregular. Particle size distributions as a function of maximum dimension and equivalent radius are compared with previous studies. Particles are generally found to be slightly larger than previous austral wintertime studies. In 2002, a polar nephelometer (PN) that measures scattering phase function was incorporated with one of the CPIs. Correlated measurements between the two instruments showed that 22[degrees] and 46[degrees] peaks in the phase function were present when diamond dust was recorded by the CPI, but not when rosette shapes were present. Visual observations confirmed the presence of 22[degrees] and 46[degrees] atmospheric halos in some, but not all, of the diamond dust events. No visual halos were observed when rosette shapes were precipitating. Average PN phase functions are presented for diamond dust and rosette shapes. The diamond dust and rosette-shaped ice crystals appear to be very similar in shape to those observed by CPIs in cirrus clouds. Cloud conditions at the South Pole that were associated with various crystal types are discussed, as are some effects of blowing snow.

The subject matter of this paper refers to the application of optical spectral diagnostics to the detection of electromagnetic waves generated by partial discharges. The research work refers to creeping discharges at bakelite/oil interface. The analysis of optical spectrum time changes was performed. The influence of voltage on the changes of the creeping discharge optical spectrum was determined. The spectrum distibutions were determined in the area of creeping discharges. The results obtained at this stage of the research can constitute a source material for people dealing with issues connected with electrical material science and diagnostics of insulation systems. Index Terms--Optical spectroscopy, surface discharges, radiometry, oil insulation.

The subject matter of this paper refers to the improvement of the acoustic emission (AE) method when used for detection, measurement and location of partial discharges (PDs) in oil insulation systems of power appliances. The detailed subject matter refers to the issues connected with the application of modern methods of digital processing of signals obtained during technical high-power measurements. The paper presents the results of measurements and analyses of the AE pulses generated in setups making the modeling of basic PD forms that can occur in oil insulations possible. The research concentrated mainly on the following types of PDs: point-plane, multipoint-plane, multipoint-plane with a layer of pressboard, surface, generated in gas bubbles and on the indeterminate-potential particles moving in oil. In each case, the acoustic pulses generated by PDs in both positive and negative half times of the voltage supplying the spark gaps under study were analyzed. The AE pulses measured were subject to the wavelet analysis. For each of the PD forms the continuous wavelet transform (CWT) was determined and the corresponding time-frequency distributions were drawn. Moreover, for the AE pulses generated by PDs of the surface and multipoint-plane types, the discrete wavelet transform (DWT) was calculated, the runs of the particular details for six frequency levels and the approximation run were presented. In reference to the DWT analysis for the particular details, the probability density functions (PDF) and the autocorrelation functions (ACF) were determined at the particular levels of decomposition. Also columnar diagrams showing the energy value that is transferred at the particular levels of decomposition were presented. Moreover, the energy density spectrum runs determined through a FFT were presented for comparison. The Morlet wavelet was used to determine the CWT, and the symlet wavelet was used to calculate the DWT. Next, the distributions obtained for the particular PD forms underwent a comparative analysis taking into account the voltage polarization. It was observed that different frequency structures occur for the particular PD forms. Also, a different time of coherent structure duration for the particular PD forms was observed. Index Terms--Partial discharges, acoustic emission, continuous wavelet transform, discrete wavelet transform, short time Fourier transform, autocorrelation functions.

Anthropogenic and natural events influence the spatial patterns and temporal succession in soft-bottom macroinvertebrate assemblages. Natural oceanographic cycles are responsible for the shifts observed in benthic assemblages. Different mechanisms are suggested to analyze the localized effect on the stability of infaunal communities.