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Search Results: 1 - 10 of 401393 matches for " M. Gervasi "
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A Giuffrida,F Giarratana,E. Gervasi,M Bucca
Italian Journal of Food Safety , 2010, DOI: 10.4081/ijfs.2010.7.36
Abstract: A challenge test for Aeromonas hydrophila in salted swordfish samples was carried out. Particularly, 24 samples (250g) were experimentally contaminated, salted and stored at two different temperature regimes (fluctuating – F group - and non fluctuating – NF group – regime). The count of A. hydrophila, Enterobacteria and Lactic acid bacteria (LAB) as well as the determination of pH and aw were performed at 0, 19 43, 163, 187, 230, 320 and 368 hours whereas the temperature was monitored continuously by using 6 data-loggers. In both group, the mean concentrations of A. hydrophila did not exceed Log 3 cfu/g and decreased below the mean value of Log 1 cfu/g after 368 hours. However in the F group the A. hydrophila growth was slower and the decrease appeared slightly higher than NF group and this suggests the temperature fluctuations induces a more pronounced behaviour variability of A. hydrophila under stressing conditions.
Sunyaev Zel`dovich effect studies with MASTER
A. Tartari,G. Boella,M. Candotti,M. Gervasi,V. Natale,A. Passerini,G. Sironi,M. Zannoni
Physics , 2003,
Abstract: Our three frequencies radiometer MASTER which allows low noise observations in three frequency intervals around 90, 220 and 345 GHz is being completed. We discuss the possibility of exploiting the MASTER`s charachteristics for studies of the Sunyaev Zel`dovich effect from the Antarctic Plateau and propose an observational program from Dome C
A dual output polarimeter devoted to the study of the Cosmic Microwave Background
M. Gervasi,G. Boella,F. Cavaliere,G. Grossetti,A. Passerini,G. Sironi,A. Tartari,M. Zannoni
Physics , 2003, DOI: 10.1117/12.458871
Abstract: We have developed a correlation radiometer at 33 GHz devoted to the search for residual polarization of the Cosmic Microwave Background (CMB). The two instruments`s outputs are linear combination of two Stokes Parameters (Q and U or U and V). The instrument is therefore directly sensitive to the polarized component of the radiation (respectively linear and circular). The radiometer has a beam-width oif 7 or 14 deg, but it can be coupled to a telescope increasing the resolution. The expected CMB polarization is at most a part per milion. The polarimeter has been designed to be sensitive to this faint signal, and it has been optimized to improve its long term stability, observing from the ground. In this contribution the performances of the instrument are presented, together with the preliminary test and observations.
Search for distortions in the spectrum of the Cosmic Microwave Radiation
G. Sironi,E. Battistelli,G. Boella,F. Cavaliere,M. Gervasi,A. Passerini,A. Tartari,M. Zannoni
Physics , 2003,
Abstract: We present preliminary results of TRIS, an experiment dedicated to the search of deviations from a pure planckian distribution in the spectrum of the Cosmic Microwave Background at frequencies close to 1 GHz
NIEL Dose Dependence for Solar Cells Irradiated with Electrons and Protons
C. Baur,M. Gervasi,P. Nieminen,S. Pensotti,P. G. Rancoita,M. Tacconi
Physics , 2013,
Abstract: The investigation of solar cells degradation and the prediction of its end-of-life performance is of primary importance in the preparation of a space mission. In the present work, we investigate the reduction of solar-cells' maximum power resulting from irradiations with electrons and protons. Both GaAs single junction and GaInP/GaAs/Ge triple junction solar cells were studied. The results obtained indicate how i) the dominant radiation damaging mechanism is due to atomic displacements, ii) the relative maximum power degradation is almost independent of the type of incoming particle, i.e., iii) to a first approximation, the fitted semi-empirical function expressing the decrease of maximum power depends only on the absorbed NIEL dose, and iv) the actual displacement threshold energy value (Ed=21 eV) accounts for annealing treatments, mostly due to self-annealing induced effects. Thus, for a given type of solar cell, a unique maximum power degradation curve can be determined as a function of the absorbed NIEL dose. The latter expression allows one to predict the performance of those solar cells in space radiation environment.
Possible Contribution to Electron and Positron Fluxes from Pulsars and their Nebulae
S Della Torre,M Gervasi,PG Rancoita,D Rozza,A Treves
Physics , 2013,
Abstract: The AMS-02 experiment confirms the excess of positrons in cosmic rays (CRs) for energy above 10 GeV with respect to the secondary production of positrons in the interstellar medium. This is interpreted as evidence of the existence of a primary source of these particles. Possible candidates are dark matter or astrophysical sources. In this work we discuss the possible contribution due to pulsars and their nebulae. Our key assumption is that the primary spectrum of electrons and positrons at the source is the same of the well known photon spectrum observed from gamma-rays telescopes. Using a diffusion model in the Galaxy we propagate the source spectra up to the Solar System. We compare our results with the recent experiments and with the LIS model
On the Contribution of Pulsars to the Positron Fraction in Cosmic Rays
S. Della Torre,M. Gervasi,P. G. Rancoita,D. Rozza,A. Treves
Physics , 2013,
Abstract: Several cosmic ray experiments have measured the positron fraction up to few hundred GeV. Their data have revealed an excess of positrons above 10 GeV that is not consistent with the secondary production of these particles in the interstellar medium. A primary source like dark matter or astrophysical sources (e.g pulsars and their nebulae) were considered to account for such an excess. In this paper we analyse the possibility of a primary positron production due to pulsars. Under the assumption of equal initial spectra at the source for positrons, electrons, and gamma-rays we study the propagation of particle spectra using a diffusion model in the Galaxy. We focused our analysis on the Vela and Crab pulsars and their associated nebulae, which are well observed in gamma-rays. Comparison with experimental data is reported. The propagated positron and electron spectra generated from these sources result in a positron ratio, which is largely inconsistent with the excess observed by PAMELA and AMS
Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X
S. Della Torre,M. Gervasi,P. G. Rancoita,D. Rozza,A. Treves
Physics , 2015,
Abstract: We investigate, in terms of production from pulsars and their nebulae, the cosmic ray positron and electron fluxes above $\sim10$ GeV, observed by the AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from the gamma-ray photon spectrum of the source, generated via synchrotron and inverse Compton processes, we estimated the electron and positron injection spectra. Several features are fixed from observations of Vela-X and unknown parameters are borrowed from the Crab nebula. The particle spectra produced in the pulsar wind nebula are then propagated up to the Solar System, using a diffusion model. Differently from previous works, the omnidirectional intensity excess for electrons and positrons is obtained as a difference between the AMS-02 data and the corresponding local interstellar spectrum. An equal amount of electron and positron excess is observed and we interpreted this excess (above $\sim$100 GeV in the AMS-02 data) as a supply coming from Vela-X. The particle contribution is consistent with models predicting the gamma-ray emission at the source. The input of a few more young pulsars is also allowed, while below $\sim$100 GeV more aged pulsars could be the main contributors.
Models of the electroreduction of passive layers on cobalt
Gervasi, C.A.;
Journal of the Brazilian Chemical Society , 1997, DOI: 10.1590/S0103-50531997000200015
Abstract: potentiostatic current transient techniques were employed to study the electroreduction process of surface layers formed on polycrystalline cobalt in carbonate-bicarbonate ion-containing solutions. the dynamic system analysis performed using parametric identification procedures and non-linear fit routines demonstrated that data obtained under a wide variety of experimental conditions may be interpreted by taking into account the participation of various co(ii)/co(iii)-containing surface species. the influence of the anodizing time at the potential of oxide film formation may be discussed on the basis of the proposed electroreduction models.
Le groupe de travail EPNAC
MOLLE, Pascal ; GERVASI, Claudia
Sciences Eaux & Territoires : la Revue du IRSTEA , 2012,
Abstract: En France, les procédés de traitement des eaux usées des petites et moyennes collectivités sont en constante évolution et leur diversité augmente fortement. Constitué à l'initiative d'Irstea, le groupe de travail EPNAC a pour objectif de mutualiser et de diffuser une information technique et cohérente sur ces procédés auprès des acteurs de l'assainissement.
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