ON THE INFLUENCE OF CHANNEL TORTUOSITY ON ELECTRIC FIELDS GENERATED BY LIGHTNING RETURN STROKES AT CLOSE DISTANCE

In this paper the results of the estimated electric field associated with tortuous lightning paths at close distance (50 m to 500 m) are shown. Such results are compared with experimental data available in the literature and are illustrated along with a quantitative analysis of the field waveforms and their frequency spectra. The limits of the usual straight-vertical channel assumption and the influence of tortuosity at different azimuth and distances from the lightning channel base are also highlighted

Dynamic Boost Based DMPPT Emulator

The Distributed Maximum Power Point Tracking (DMPPT) approach is a promising solution to improve the energetic performance of mismatched PhotoVoltaic (PV) systems. However, there are still several factors that can reduce DMPPT energy efficiency, including atmospheric conditions, the efficiency of the power stage, constraints imposed by the topology, the finite rating of silicon devices, and the nonoptimal value of string voltage. In order to fully explore the advantages offered by the above solution, the implementation of a Boost based DMPPT emulator is of primary concern, especially if it behaves as a controlled voltage or current source. The repeatability of experimental tests, the tighter control of climatic conditions, the closing of the gap between the physical dimensions of a PV array and the space available in a university lab, the simplicity with which new algorithms can be tested, and the low maintenance costs are just some of the benefits offered by an emulator. This paper describes the realization and use of a Boost based Distributed Maximum Power Point Tracking (DMPPT) emulator and shows its high flexibility and potential. The device is able to emulate the output current vs. voltage (I-V) characteristics of many commercial PhotoVoltaic (PV) modules with a dedicated Boost DC/DC converter. The flexibility is guaranteed by the ability to reproduce both I = f (V) and V = g(I) characteristics at different values of not only the irradiance levels but also the maximum allowed voltage across the switching devices. The system design is based on a commercial power supply controlled by a low-cost Arduino board by Arduino (Strambino, Torino, Italy). Data acquisition is performed through a lowcost current and voltage sensor by using a multichannel board by National Instruments. Experimental results confirm the capability of the proposed device to accurately emulate the output I-V characteristic of Boost based DMPPT systems obtained by varying the atmospheric conditions, the rating of silicon devices, and the electrical topology

Assessment of induced voltages in common and differential‐mode for a PV module due to nearby lightning strikes

n/

Dielectric behavior of biopolymer based composites containing multi wall carbon nanotubes: Effect of filler content and aspect ratio

Multi wall carbon nanotubes (MWCNTs) with different aspect ratios (30, 105 and 667) were included in a commercial fully biodegradable blend using melt mixing. Samples of composite systems prepared by hot molding and containing up to 1.2 vol% of MWCNTs were studied by means of DC electrical resistivity and dielectric spectroscopy in order to enhance effect of filler content and aspect ratio on their dielectric behavior. Raman spectroscopic investigations and morphological observations were also performed in order to correlate dielectric behavior with surface carbon nanotubes features and to check the actual level of dispersion of carbon nanotubes under the applied processing conditions. Results emphasized that the carbon nanotubes aspect ratio and their surface regularity determine the electrical properties of composites because they strongly influence percolation thresholds, dielectric permittivity and dissipation factor of produced materials. A satisfying dispersion of the filler seems to be achieved under the employed processing conditions. These preliminary results demonstrates possible applications of this type of biobased systems in many applications going from stress control to devices for high storage energy

Chromosomal plasticity and evolutionary potential in the malaria vector Anopheles gambiae sensu stricto: insights from three decades of rare paracentric inversions

Background: In the Anopheles gambiae complex, paracentric chromosomal inversions are nonrandomly distributed along the complement: 18/31 (58%) of common polymorphic inversions are on chromosome arm 2R, which represents only ~30% of the complement. Moreover, in An.gambiae sensu stricto, 6/7 common polymorphic inversions occur on 2R. Most of these inversions are considered markers of ecological adaptation that increase the fitness of the carriers of alternative karyotypes in contrasting habitats. However, little is known about the evolutionary forces responsible for their origin and subsequent establishment in field populations. Results: Here, we present data on 82 previously undescribed rare chromosomal inversions (RCIs) recorded during extensive field sampling in 16 African countries over a 30 year period, which may shed light on the dynamics of chromosomal plasticity in An. gambiae. We analyzed breakpoint distribution, length, and geographic distribution of RCIs, and compared these measures to those of the common inversions. We found that RCIs, like common inversions, are disproportionately clustered on 2R, which may indicate that this arm is especially prone to breakages. However, contrasting patterns were observed between the geographic distribution of common inversions and RCIs. RCIs were equally frequent across biomes and on both sides of the Great Rift Valley (GRV), whereas common inversions predominated in arid ecological settings and west of the GRV. Moreover, the distribution of RCI lengths followed a random pattern while common inversions were significantly less frequent at shorter lengths. Conclusion: Because 17/82 (21%) RCIs were found repeatedly at very low frequencies – at the same sampling location in different years and/or in different sampling locations – we suggest that BMC Evolutionary Biology 2008, 8:309 http://www.biomedcentral.com/1471-2148/8/309 RCIs are subject mainly to drift under unperturbed ecological conditions. Nevertheless, RCIs may represent an important reservoir of genetic variation for An. gambiae in response to environmental changes, further testifying to the considerable evolutionary potential hidden within this pan-African malaria vector

Archimedes: a feasibility study of an experiment to weigh the electromagnetic vacuum

Archimedes is a feasibility study of a future experiment to ascertain the interaction of vacuum fluctuations with gravity. The experiment should measure the force that the earth's gravitational field exerts on a Casimir cavity by using a small force detector. Here we analyse the main parameters of the experiment and we present its conceptual scheme, which overcomes in principle the most critical problems.Comment: 3 pages, MG14 Conferenc