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Search Results: 1 - 10 of 189872 matches for " G. Boella "
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Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary Magnetic Field Polar Correction
P. Bobik,G. Boella,M. J. Boschini,C. Consolandi
Advances in Astronomy , 2013, DOI: 10.1155/2013/793072
Abstract:
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
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
Study on Coulomb explosions of ion mixtures
E. Boella,B. Peiretti Paradisi,A. D'Angola,G. Coppa,L. O. Silva
Physics , 2015,
Abstract: The paper presents a theoretical work on the dynamics of Coulomb explosion for spherical nanoplasmas composed by two different ion species. Particular attention has been dedicated to study the energy spectra of the ions with the larger charge-to-mass ratio. The connection between the formation of shock shells and the energy spread of the ions has been the object of a detailed analysis, showing that under particular conditions the width of the asymptotic energy spectrum tends to become very narrow, which leads to a multi-valued ion phase-space. The conditions to generate a quasi mono-energetic ion spectrum have been rigorously demonstrated and verifed by numerical simulations, using a technique that, exploiting the spherical symmetry of the problem, allows one to obtain very accurate and precise results.
Cosmic Ray Modulation studied with HelMod Monte Carlo tool and comparison with Ulysses Fast Scan Data during consecutive Solar Minima
P. Bobik,G. Boella,M. J. Boschini,S. Della Torre,M. Gervasi,D. Grandi,G. La Vacca,K. Kudela,S. Pensotti,P. G. Rancoita,D. Rozza,M. Tacconi
Physics , 2013,
Abstract: The Cosmic Rays propagation was studied in details using the HelMod-2D Monte Carlo code, that includes a general description of the diffusion tensor, and polar magnetic-field. The Numerical Approach used in this work is based on a set of Stochastic Differential Equations fully equivalent to the well know Parker Equation for the transport of Cosmic Rays. In our approach the Diffusion tensor in the frame of the magnetic field turbolence does not depends explicitly by Solar Latitude but varies with time using a diffusion parameter obtained by Neutron Monitors. The parameters of the Model were tuned using data during the solar Cycle 23 and Ulysses latitudinal Fast Scan in 1995. The actual parametrization is able to well reproduce the observed latitudinal gradient of protons and the southward shift of the minimum of latitudinal intensity. The description of the model is also available online at website www.helmod.org. The model was then applied on Pamela/Ulysses proton intensity from 2006 up to 2009. The model during this 4-year continous period agree well with both PAMELA (at 1 AU) and Ulysses data (at various solar distance and solar latitude). The agreement improves when considering the ratio between this data. Studies done also with particles with different charge (e.g. electrons) allow us to explain the presence (or not) of protons and electrons latitudinal gradients observed by Ulysses during the Latitudinal Fast Scan in 1995 and 2007.
Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary Magnetic Field Polar Correction
P. Bobik,G. Boella,M. J. Boschini,C. Consolandi,S. Della Torre,M. Gervasi,D. Grandi,K. Kudela,S. Pensotti,P. G. Rancoita,D. Rozza,M. Tacconi
Advances in Astronomy , 2013, DOI: 10.1155/2013/793072
Abstract: The cosmic rays differential intensity inside the heliosphere, for energy below 30?GeV/nuc, depends on solar activity and interplanetary magnetic field polarity. This variation, termed solar modulation, is described using a 2D (radius and colatitude) Monte Carlo approach for solving the Parker transport equation that includes diffusion, convection, magnetic drift, and adiabatic energy loss. Since the whole transport is strongly related to the interplanetary magnetic field (IMF) structure, a better understanding of his description is needed in order to reproduce the cosmic rays intensity at the Earth, as well as outside the ecliptic plane. In this work an interplanetary magnetic field model including the standard description on ecliptic region and a polar correction is presented. This treatment of the IMF, implemented in the HelMod Monte Carlo code (version 2.0), was used to determine the effects on the differential intensity of Proton at 1 AU and allowed one to investigate how latitudinal gradients of proton intensities, observed in the inner heliosphere with the Ulysses spacecraft during 1995, can be affected by the modification of the IMF in the polar regions. 1. Introduction The Solar Modulation, due to the solar activity, affects the Local Interstellar Spectrum (LIS) of Galactic Cosmic Rays (GCR) typically at energies lower than 30?GeV/nucl. This process, described by means of the Parker equation (e.g., see [1, 2] and Chapter 4 of [3]), is originated from the interaction of GCRs with the interplanetary magnetic field (IMF) and its irregularities. The IMF is the magnetic field that is carried outwards during the solar wind expansion. The interplanetary conditions vary as a function of the solar cycle which approximately lasts eleven years. In a solar cycle, when the maximum activity occurs, the IMF reverse his polarity. Thus, similar solar polarity conditions are found almost every 22 years [4]. In the HelMod Monte Carlo code version 1.5 (e.g., see [2]), the “classical” description of IMF, as proposed by Parker [5], was implemented together with the polar corrections of the solar magnetic field suggested subsequently in [6, 7]. This IMF was used inside the HelMod [2] code to investigate the solar modulation observed at Earth and to partially account for GCR latitudinal gradients, that is, those observed with the Ulysses spacecraft [8, 9]. In order to fully account for both the latitudinal gradients and latitudinal position of the proton-intensity minimum observed during the Ulysses fast scan in 1995, the HelMod Code was updated to the version 2.0 to
Proton Modulation in the Heliosphere for Different Solar Conditions and Prediction for AMS-02
P. Bobik,G. Boella,M. J. Boschini,C. Consolandi,S. Della Torre,M. Gervasi,D. Grandi,K. Kudela,E. Memola,S. Pensotti,P. G. Rancoita,M. Tacconi
Physics , 2010,
Abstract: Spectra of Galactic Cosmic Rays (GCRs) measured at the Earth are the combination of several processes: sources production and acceleration, propagation in the interstellar medium and propagation in the heliosphere. Inside the solar cavity the flux of GCRs is reduced due to the solar modulation, the interaction which they have with the interplanetary medium. We realized a 2D stochastic simulation of solar modulation to reproduce CR spectra at the Earth, and evaluated the importance in our results of the Local Interstellar Spectrum (LIS) model and its agreement with data at high energy. We show a good agreement between our model and the data taken by AMS-01 and BESS experiments during periods with different solar activity conditions. Furthermore we made a prediction for the flux which will be measured by AMS-02 experiment.
Systematic Investigation of Solar Modulation of Galactic Protons for Solar Cycle 23 using a Monte Carlo Approach with Particle Drift Effects and Latitudinal Dependence
P. Bobik,G. Boella,M. J. Boschini,C. Consolandi,S. Della Torre,M. Gervasi,D. Grandi,K. Kudela,S. Pensotti,P. G. Rancoita,M. Tacconi
Physics , 2011, DOI: 10.1088/0004-637X/745/2/132
Abstract: A propagation model of galactic cosmic protons through the Heliosphere was implemented using a 2-D Monte Carlo approach to determine the differential intensities of protons during the solar cycle 23. The model includes the effects due to the variation of solar activity during the propagation of cosmic rays from the boundary of the heliopause down to Earth's position. Drift effects are also accounted for. The simulated spectra were found in agreement with those obtained with experimental observations carried out by BESS, AMS and PAMELA collaborations. In addition, the modulated spectrum determined with the present code for the year 1995 exhibits the latitudinal gradient and equatorial southward offset minimum found by Ulysses fast scan in 1995.
An improved upper limit to the CMB circular polarization at large angular scales
R. Mainini,D. Minelli,M. Gervasi,G. Boella,G. Sironi,A. Bau',S. Banfi,A. Passerini,A. De Lucia,F. Cavaliere
Physics , 2013, DOI: 10.1088/1475-7516/2013/08/033
Abstract: Circular polarization of the Cosmic Microwave Background (CMB) offers the possibility of detecting rotations of the universe and magnetic fields in the primeval universe or in distant clusters of galaxies. We used the Milano Polarimeter (MIPOL) installed at the Testa Grigia Observatory, on the italian Alps, to improve the existing upper limits to the CMB circular polarization at large angular scales. We obtain 95% confidence level upper limits to the degree of the CMB circular polarization ranging between 5.0x10^{-4} and 0.7x10^{-4} at angular scales between 8 and 24 deg, improving by one order of magnitude preexisting upper limits at large angular scales. Our results are still far from the nK region where today expectations place the amplitude of the V Stokes parameter used to characterize circular polarization of the CMB but improve the preexisting limit at similar angular scales. Our observations offered also the opportunity of characterizing the atmospheric emission at 33 GHz at the Testa Grigia Observatory.
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