1,721,030 research outputs found
Nuove tecnologie per il restauro dei monumenti
No full textL’impiego delle fibre sintetiche, invece che l’acciaio, nel consolidamento delle murature storiche si pone sempre più all’attenzione delle Soprintendenze e degli studiosi del restauro strutturale; in collaborazione con la Soprintendenza dei Beni Ambientali e Architettonici delle Marche- Soprintendente Arch. M. L. Polichetti) si sviluppa una serie di prove sperimentali su muri rinforzati con fibre sintetiche applicate con diverse tecniche, posti a confronto tra loro e con muri privi di rinforzi. Si studiano oltre ai problemi tecnici del loro inserimento, i benefici a rottura per effetto di azioni orizzontali e la loro durabilità. Si presentano i risultati e le conclusioni sui primi elementi sottoposti a prova fino al collasso
Transport and magnetic properties of Bi(Pb)2212 superconducting ceramics doped by low rate of potassium
No full textSamples of Bi1.5Pb0.5(Sr1.8-xKx)CaCu2O8+d and Bi1.5Pb0.5Sr1.8CaCu2O8+dKx have been prepared from powders of carbonates and primary oxides using the solid state reaction method and compared in this study. In the first case, potassium (K) is substituted in the strontium (Sr) site. In the second one, K is added. A part of the paper is devoted to discuss the results obtained by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) observations of (Bi,Pb)2Sr1.8CaCu2O8+d samples doped by potassium to provide additional microstructural information related to the doping method. These analyses are supplemented by resistivity and magnetic measurements. Results show how the rate of doping by potassium affects transport and magnetic properties of Bi(Pb)2212 phase. The critical current density (Jc) is improved using the two methods and it reaches a double value by the addition of K as compared to the undoped sample
Complex AC Magnetic Susceptibility as a Tool for Exploring Nonlinear Magnetic Phenomena and Pinning Properties in Superconductors
No full textThe versatile AC magnetic susceptibility technique offers a detailed insight into the complex electrodynamic phenomena in superconductors. In the present study, we outline the key effects related to the temperature, AC field amplitude and frequency variations of the fundamental and harmonic components for an investigation of the vortex dynamics in a flux-grown FeSe crystal. By means of higher harmonic (nonlinear) analysis, we have explored certain atypical, asymmetric features in the AC magnetic response. These effects were identified through the detection of an even (second) harmonic and an unusual temperature shift in the odd (third) harmonic, possibly due to the complex interactions related to the composite superconducting/magnetic morphology of the crystal. Using the high-frequency sensitivity of the third harmonic, the basic functional dependencies of the pinning activation energy, as the main mixed state parameter, were determined with the implementation of the Kim–Anderson Arrhenius relation in the framework of the collective creep theory
Study of magnetic interactions in a sample of Fe3O4 magnetic nanoparticles in DC and AC fields
No full textThe study conducted on a sample of Fe3O4 nanoparticles coated with oleic acid has been performed by using DC and AC field techniques useful to determine the presence of a mixed state of interactions within the same sample, confirmed by the qualitative comparison between the results of the two techniques. In particular, a thorough study of the AC response of the sample, in presence of an overlapping DC field, allowed to determine the types of interactions observed by the DC analysis
Fabrication of novel hybrid materials based on iron-aluminum modified hemp fibers: Comparison between two proposed methodologies
No full textThis paper reports the fabrication of novel hybrid and structured materials by using hemp fibers as organic support. Two in-situ methodologies were proposed and applied to modify the surface of hemp fibers in order to improve their physical properties and to confer a magnetic behavior: i) coprecipitation of Fe/Al layered double hydroxides through urea method (MHF@LDH Fe/Al) and ii) deposition of Fe3O4 particles onto AlOOH modified hemp fibers in ammonia solution (MHF@AlOOH-FePs). The obtained hybrid materials have been widely characterized in terms of spectroscopic, morphological, thermal and barrier properties. Finally, a further investigation concerned the evaluation of surface charge and the estimation of magnetic properties showing a ferromagnetic behavior (Curie Temperature Tc > 300 K) for both samples with a coercive field of Hc ≈± 40 Oe for MHF@LDH Fe/Al and Hc ≈ ± 10 Oe for MHF@AlOOH-FePs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Study of the Coercivity Field in a Sample of NiFe2O4-OA Nanoparticles at Different Temperatures: Comparing the Different Processes to Evaluate TB by DC Measurements*
No full textA sample of nickel ferrite (NiFe_2 O_4 ) magnetic nanoparticles covered with oleic acid (OA) has been analyzed in DC magnetic fields. The most commonly used methods to extract the blocking temperature (TB) have been compared in a study of the coercive field as a function of temperature. The temperature corresponding to a zero coercive field has been considered to be the best candidate for TB. In addition, several information about the anisotropy of the sample has been deduced from the temperature behavior of the coercive field
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Demagnetization harmonic effects on the magnetization of granular systems on a macroscopic scale: The superconducting case
No full textA model has been developed to determine the effective ac magnetic response of magnetic systems, taking into account the demagnetization effects arising from the sample geometry which determine the out-of-phase components of the applied fundamental frequency and higher harmonic components. Indeed, demagnetization fields and their intermodulation can significantly affect the ac magnetic response. This approach provides a system of self-consistent linear equations relating the magnetic response to the external magnetic field by means of nonlinear magnetic susceptibility. The model is extended to the magnetic response of granular systems in terms of the contributions of the individual grains and of the whole sample in the presence of demagnetization effects of the whole sample and of the grains on a macroscopic scale. In particular, our model is applied to a granular superconducting system. The comparison between the performed numerical simulations and the experimental data shows that the demagnetization fields of the single grains and of the whole sample, and their intermodulation, are relevant if magnetic measurements are used to extract detailed information about the analyzed material
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