Signs of low frequency dispersions in disordered binary dielectric mixtures (50-50)

Dielectric relaxation in disordered dielectric mixtures are presented by emphasizing the interfacial polarization. The obtained results coincide with and cause confusion with those of the low frequency dispersion behavior. The considered systems are composed of two phases on two-dimensional square and triangular topological networks. We use the finite element method to calculate the effective dielectric permittivities of randomly generated structures. The dielectric relaxation phenomena together with the dielectric permittivity values at constant frequencies are investigated, and significant differences of the square and triangular topologies are observed. The frequency dependent properties of some of the generated structures are examined. We conclude that the topological disorder may lead to the normal or anomalous low frequency dispersion if the electrical properties of the phases are chosen properly, such that for ``slightly'' {\em reciprocal mixture}--when $\sigma_1\gg\sigma_2$, and $\epsilon_1<\epsilon_2$--normal, and while for ``extreme'' {\em reciprocal mixture}--when $\sigma_1\gg\sigma_2$, and $\epsilon_1\ll\epsilon_2$--anomalous low frequency dispersions are obtained. Finally, comparison with experimental data indicates that one can obtain valuable information from simulations when the material properties of the constituents are not available and of importance.Comment: 13 pages, 7 figure

Prompt and delayed emission properties of Gamma-Ray Bursts observed with BeppoSAX

We investigated the spectral evolution in the 2--700 keV energy band of Gamma-Ray Bursts (GRBs) detected by the Gamma-Ray Burst Monitor (GRBM) and localized with the Wide Field Cameras (WFCs) aboard the BeppoSAX satellite before May 1998. Most of them have been followed-up with the Narrow Field Instruments aboard the same satellite. In the light of these results we discuss open issues on the GRB phenomenon. We find that the optically thin synchrotron shock model (SSM) provides an acceptable representation of most of the time-resolved GRB spectra extending down to 2 keV, except in the initial phases of several bursts and during the whole duration of the quite strong GRB970111, where a low-energy photon depletion with respect to the thin SSM spectrum is observed. We find that the X-ray afterglow starts at about 50% of the GRB duration, and that its fluence, as computed from the WFC light curve, is consistent with the decay law found from the afterglow NFI observations. We also investigate the hydrodynamical evolution of the GRB in our sample and their associated afterglow, when it was detected. We find that the photon index of the latest spectrum of the GRB prompt emission is correlated with the index of the afterglow fading law, when available, as expected on the basis of an external shock of a relativistic fireball.Comment: 35 pages, 1 LaTeX file, 20 postscript figures, 1 postscript table, accepted for pubblication in Astrophysical Journal Supplement Series. Corrected error bars in Fig.2/GRB980425/panel B and GRB980425 fluence in Tab.

Amplitude measurements of Faraday waves

A light reflection technique is used to measure quantitatively the surface elevation of Faraday waves. The performed measurements cover a wide parameter range of driving frequencies and sample viscosities. In the capillary wave regime the bifurcation diagrams exhibit a frequency independent scaling proportional to the wavelength. We also provide numerical simulations of the full Navier-Stokes equations, which are in quantitative agreement up to supercritical drive amplitudes of 20%. The validity of an existing perturbation analysis is found to be limited to 2.5% overcriticaly.Comment: 7 figure

Viscoelastic material behaviour of PBT-GF30 under thermo-mechanical cyclic loading

Abstract This paper deals with the simulation of the behaviour of a short glass fibre reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. Thermo-mechanical fatigue (TMF) tests, consisting of thermal cycling with a superimposed constant strain, have been carried out in the temperature ranges of -40 °C to 120 °C and -40 °C to 40 °C, applying different mean strain values. The main goal of the work is to model the stress trend during TMF cycles and assess the performance of a linear viscoelastic material model. A linear viscoelastic model has been implemented in ABAQUS 6.9-1 by means of Prony series, using the UTRS subroutine to model the time-temperature shift. The stress-time trend during TMF tests is discussed, comparing the simulated versus the experimental stress results. In particular, the maximum and minimum values within each cycle are considered, in order to evaluate the performance of the material model. Linear viscoelastic simulations show good agreement between experimental tests and FE analysis, both for plain and notched specimen

LANDSLIDE GEOHAZARD FOR PIPELINES OF NATURAL GAS TRANSPORT

Οι κατολισθήσεις αποτελούν έναν σημαντικό κίνδυνο για τους αγωγούς, επειδή μπορεί να προκαλέσουν εκτός από καταστροφή, μόνιμες παραμορφώσεις και να οδηγήσουν σε διαρροές, περιβαλλοντικά προβλήματα και μεγάλες περιόδους διακοπής της λειτουργίας. Ως εκ τούτου, τα περιστατικά που σχετίζονται με κατολισθήσεις αντιμετωπίζονται ως ένας ιδιαιτέρως σημαντικός κίνδυνος για την λειτουργία του αγωγού. Η παρούσα εργασία επικεντρώνεται κυρίως στην αξιολόγηση της επικινδυνότητας έναντι κατολισθήσεων κατά μήκος ή εγκάρσια ενός αγωγού φυσικού αερίου και στην, κυρίως στο πεδίο, αναγνώριση αυτών των κινδύνων. Το αν η "αναμενόμενη" εκδήλωση κατολίσθησης θα φτάσει την χάραξη του αγωγού και θα τον επηρεάσει, εξαρτάται από το είδος και το μέγεθος της ενδεχόμενης κατολίσθησης, στοιχεία που ελέγχονται προφανώς από τη γεωλογία και τη γεωμορφολογία, ή και την θέση του αγωγού σε σχέση με ενδεχόμενη προυπάρχουσα κατολίσθηση. Η αξιολόγηση της επικινδυνότητας έναντι κατολίσθησης προσδιορίζει σε πρώτη φάση επικίνδυνες περιοχές (hot spots) κατά μήκος της διαδρομής του αγωγού, όπου πρέπει να δοθεί προτεραιότητα είτε σε μέτρα θεραπείας και μείωσης επικινδυνότητας είτε σε αλλαγή χάραξης. Όταν κατολισθήσεις που ενδέχεται να επηρεάσουν την ακεραιότητα του αγωγού δεν είναι δυνατόν να αποφευχθούν, απαιτείται λεπτομερής έρευνα και αξιολόγηση των επί τόπου συνθηκών για την υποστήριξη του σχεδιασμού και της κατασκευής των μέτρων θεραπείας.Landslides represent a significant hazard for pipelines because they can generate permanent ground displacement and tend to result in complete failure or significant leaks, major environmental impacts and long periods of service disruption. Hence, landslide-related incidents are regarded as a significant operational risk. The paper mainly focuses on the assessment of landslide hazard along or across a natural gas pipeline project and on the identification of these hazards, mostly in the field. Whether the “expected” landslide event reaches the Right of Way (RoW) and impacts the pipeline, is influenced by the nature and size of the expected landslide event, controlled by the site geology and geomorphology, the proximity of the existing landslide feature to the pipeline and the position of the pipeline relative to the landslide. Landslide hazard assessment is used to identify “hot spots” along the pipeline route where re-routing or risk reduction measures must be prioritised. When landslides that can threat the pipeline integrity cannot be avoided, more detailed site evaluation is required to support the design and construction of mitigation measures

The Kolumbo submarine volcano of Santorini island is a large pool of bacterial strains with antimicrobial activity

Microbes in hydrothermal vents with their unique secondary metabolism may represent an untapped potential source of new natural products. In this study, samples were collected from the hydrothermal field of Kolumbo submarine volcano in the Aegean Sea, in order to isolate bacteria with antimicrobial activity. Eight hundred and thirty-two aerobic heterotrophic bacteria were isolated and then differentiated through BOX-PCR analysis at the strain level into 230 genomic fingerprints, which were screened against 13 different type strains (pathogenic and nonpathogenic) of Gram-positive, Gram-negative bacteria and fungi. Forty-two out of 176 bioactive-producing genotypes (76 %) exhibited antimicrobial activity against at least four different type strains and were selected for 16S rDNA sequencing and screening for nonribosomal peptide (NRPS) and polyketide (PKS) synthases genes. The isolates were assigned to genus Bacillus and Proteobacteria, and 20 strains harbored either NRPS, PKS type I or both genes. This is the first report on the diversity of culturable mesophilic bacteria associated with antimicrobial activity from Kolumbo area; the extremely high proportion of antimicrobial-producing strains suggested that this unique environment may represent a potential reservoir of novel bioactive compounds

COSEISMIC DEFORMATION AND SEISMIC FAULT OF THE 17 NOVEMBER 2015 M=6.5 EARTHQUAKE, LEFKADA ISLAND

On November 17, 2015 a strong, shallow earthquake, Mw 6.5, occurred on the island of Lefkada along a strike-slip fault with right-lateral sense of slip. The event triggered widespread environmental effects that were mainly reported at the south and western part of the island while moving towards the eastern part, the intensity and severity of these earthquake-induced deformations were decreased. Relocation of seismicity and inversion of geodetic data suggests that the seismic fault runs parallel to the west coast of Lefkada, along the Aegean - Apulia plate boundary. The earthquake measured Mw=6.5 using the PGD relation of Melgar et al (2015, GRL). The fault plane strikes N20±5°E and dips to east with an angle of about 70±5 degrees. Coseismic deformation was measured in the order of tens of centimeters of horizontal motion by continuous GPS stations of NOANET (the NOA GPS network) and by InSAR (Sentinel 1A image pairs). Released interferograms from various groups show a large decorrelation area that extends almost along all the western coast of Lefkada, observation which provides strong support of landsliding. A coseismic slip model was produced from inversion of the ascending InSAR. We have not observed significant vertical motion of the shoreline and this is consistent with the predictions of the model