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Littérature scientifique sur le sujet « Galactic proton »

Auteur : Grafiati

Publié le 1 avril 2023

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Articles de revues sur le sujet "Galactic proton"

Sikora, Marek, Bronisław Rudak et Mitchell Begelman. « Relativistic Neutrons in Active Galactic Nuclei ». Symposium - International Astronomical Union 134 (1989) : 215–16. http://dx.doi.org/10.1017/s0074180900140902.

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A substantial fraction of the radiation from an active galactic nucleus (AGN) is apparently nonthermal in origin, and is probably produced by ultrarelativistic electrons. How much energy goes into relativistic protons is uncertain, but it is likely to be comparable to the electron energy or larger. Indeed, several authors (Sikora et al. 1987; Kazanas and Ellison 1986; Zdziarski 1986) have shown that proton-photon and proton-proton collisions can be efficient sources of relativistic pairs in the central engine of an AGN. Thus it is not necessary for electrons to be accelerated directly in AGNs, provided that protons are accelerated with high enough efficiency.

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Fiandrini, E., B. Bertucci, N. Tomassetti et B. Khiali. « New solar modulation modeling of the galactic proton flux measured by the AMS02 and PAMELA experiments ». EPJ Web of Conferences 209 (2019) : 01032. http://dx.doi.org/10.1051/epjconf/201920901032.

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A thorough understanding of solar effects on the galactic cosmic rays is relevant both to infer the local interstellar spectrum characteristics and to investigate the dynamics of charged particles in the heliosphere. We present a newly developed numerical modulation model to study the transport of galactic protons in the heliosphere. The model was applied to the 27-day averaged galactic proton flux recently released by the PAMELA and AMS02 experiments, covering an extended time period from mid-2006 to mid-2017.

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Jansen, F., K. P. Wenzel, D. O' Sullivan et A. Thompson. « The Bulge of the Milky Way and cosmic rays ». Symposium - International Astronomical Union 153 (1993) : 283–84. http://dx.doi.org/10.1017/s0074180900123265.

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The propagation of cosmic ray protons and anti–protons from the inner Galaxy via the galactic halo to the Sun supplies a good agreement with the observed cosmic ray gradient and is in the order of the measured anti-proton flux. Ultra heavy cosmic ray nuclei may have the same origin.

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Buchvarova, M., et P. Velinov. « Cosmic ray spectra in planetary atmospheres ». Proceedings of the International Astronomical Union 4, S257 (septembre 2008) : 471–73. http://dx.doi.org/10.1017/s1743921309029718.

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AbstractOur model generalizes the differential D(E) and integral D(>E) spectra of cosmic rays (CR) during the 11-year solar cycle. The empirical model takes into account galactic (GCR) and anomalous cosmic rays (ACR) heliospheric modulation by four coefficients. The calculated integral spectra in the outer planets are on the basis of mean gradients: for GCR – 3%/AU and 7%/AU for anomalous protons. The obtained integral proton spectra are compared with experimental data, the CRÈME96 model for the Earth and theoretical results of 2D stochastic model. The proposed analytical model gives practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component.

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Abdollahi, S., F. Acero, M. Ackermann, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri et al. « Search for New Cosmic-Ray Acceleration Sites within the 4FGL Catalog Galactic Plane Sources ». Astrophysical Journal 933, n^o 2 (1 juillet 2022) : 204. http://dx.doi.org/10.3847/1538-4357/ac704f.

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Abstract Cosmic rays are mostly composed of protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma-rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum, with a low-energy break around 200 MeV, was detected in the gamma-ray spectra of four supernova remnants (SNRs), IC 443, W44, W49B, and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs. Here, we present a comprehensive search for low-energy spectral breaks among 311 4FGL catalog sources located within 5° from the Galactic plane. Using 8 yr of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV, we find and present the spectral characteristics of 56 sources with a spectral break confirmed by a thorough study of systematic uncertainty. Our population of sources includes 13 SNRs for which the proton–proton interaction is enhanced by the dense target material; the high-mass gamma-ray binary LS I+61 303; the colliding wind binary η Carinae; and the Cygnus star-forming region. This analysis better constrains the origin of the gamma-ray emission and enlarges our view to potential new cosmic-ray acceleration sites.

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Fang, Jun, Qi Xia, Shiting Tian, Liancheng Zhou et Huan Yu. « Kinetic simulation of electron, proton and helium acceleration in a non-relativistic quasi-parallel shock ». Monthly Notices of the Royal Astronomical Society 512, n^o 4 (14 avril 2022) : 5418–22. http://dx.doi.org/10.1093/mnras/stac886.

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ABSTRACT In addition to accelerating electrons and protons, non-relativistic quasi-parallel shocks are expected to possess the ability to accelerate heavy ions. The shocks in supernova remnants are generally supposed to be accelerators of Galactic cosmic rays, which consist of many species of particles. We investigate the diffusive shock acceleration of electrons, protons and helium ions in a non-relativistic quasi-parallel shock through a 1D particle-in-cell simulation with a helium-to-proton number density ratio of 0.1, which is relevant for Galactic cosmic rays. The simulation indicates that waves can be excited by the flow of energetic protons and helium ions upstream of a non-relativistic quasi-parallel shock with a sonic Mach number of 14 and an Alfvén Mach number of 19.5 in the shock rest frame, and that the charged particles are scattered by the self-generated waves and accelerated gradually. Moreover, the spectra of the charged particles downstream of the shock are thermal with a non-thermal tail, and the acceleration is efficient, with about $7{{\ \rm per\ cent}}$ and $5.4{{\ \rm per\ cent}}$ of the bulk kinetic energy transferred into the non-thermal protons and helium ions, respectively, in the near downstream region by the end of the simulation.

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Casolino, Marco, N. De Simone et V. Formato. « PAMELA recent results on galactic proton and helium ». Nuclear Physics B - Proceedings Supplements 212-213 (mars 2011) : 362–67. http://dx.doi.org/10.1016/j.nuclphysbps.2011.03.049.

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Khokhlov, Dmitri L. « Planck Neutrinos as Ultra High Energy Cosmic Rays ». Open Astronomy 29, n^o 1 (24 juin 2020) : 40–46. http://dx.doi.org/10.1515/astro-2020-0005.

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AbstractThe studied conjecture is that ultra high energy cosmic rays (UHECRs) are hypothetical Planck neutrinos arising in the decay of the protons falling onto the gravastar. The proton is assumed to decay at the Planck scale into positron and four Planck neutrinos. The supermassive black holes inside active galactic nuclei, while interpreted as gravastars, are considered as UHECR sources. The scattering of the Planck neutrinos by the proton at the Planck scale is considered. The Planck neutrinos contribution to the CR events may explain the CR spectrum from 5 × 1018 eV to 1020 eV. The muon number in the Planck neutrinos-initiated shower is estimated to be larger by a factor of 3/2 in comparison with the standard model that is consistent with the observational data.

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Werhahn, Maria, Christoph Pfrommer, Philipp Girichidis, Ewald Puchwein et Rüdiger Pakmor. « Cosmic rays and non-thermal emission in simulated galaxies − I. Electron and proton spectra compared to Voyager-1 data ». Monthly Notices of the Royal Astronomical Society 505, n^o 3 (10 mai 2021) : 3273–94. http://dx.doi.org/10.1093/mnras/stab1324.

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ABSTRACT Current-day cosmic ray (CR) propagation studies use static Milky Way models and fit parametrized source distributions to data. Instead, we use three-dimensional magnetohydrodynamic (MHD) simulations of isolated galaxies with the moving-mesh code arepo that self-consistently accounts for hydrodynamic effects of CR protons. In post-processing, we calculate their steady-state spectra, taking into account all relevant loss processes. We show that this steady-state assumption is well justified in the disc and generally for regions that emit non-thermal radio and gamma rays. Additionally, we model the spectra of primary electrons, accelerated by supernova remnants, and secondary electrons and positrons produced in hadronic CR proton interactions with the gas. We find that proton spectra above 10 GeV only weakly depend on galactic radius, while they acquire a radial dependence at lower energies due to Coulomb interactions. Radiative losses steepen the spectra of primary CR electrons in the central galactic regions, while diffusive losses dominate in the outskirts. Secondary electrons exhibit a steeper spectrum than primaries because they originate from the transported steeper CR proton spectra. Consistent with Voyager-1 and AMS-02 data, our models (i) show a turnover of proton spectra below GeV energies due to Coulomb interactions so that electrons start to dominate the total particle spectra and (ii) match the shape of the positron fraction up to 10 GeV. We conclude that our steady-state CR modelling in MHD CR galaxy simulations is sufficiently realistic to capture the dominant transport effects shaping their spectra, arguing for a full MHD treatment to accurately model CR transport in the future.

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Mastichiadis, Apostolos, Ioulia Florou, Elina Kefala, Stella S. Boula et Maria Petropoulou. « A roadmap to hadronic supercriticalities : a comprehensive study of the parameter space for high-energy astrophysical sources ». Monthly Notices of the Royal Astronomical Society 495, n^o 2 (11 mai 2020) : 2458–74. http://dx.doi.org/10.1093/mnras/staa1308.

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ABSTRACT Hadronic supercriticalities are radiative instabilities that appear when large amounts of energy are stored in relativistic protons. When the proton energy density exceeds some critical value, a runaway process is initiated resulting in the explosive transfer of the proton energy into electron–positron pairs and radiation. The runaway also leads to an increase of the radiative efficiency, namely the ratio of the photon luminosity to the injected proton luminosity. We perform a comprehensive study of the parameter space by investigating the onset of hadronic supercriticalities for a wide range of source parameters (i.e. magnetic field strengths of 1 G−100 kG and radii of 1011−1016 cm) and maximum proton Lorentz factors (103−109). We show that supercriticalities are possible for the whole range of source parameters related to compact astrophysical sources, like gamma-ray bursts and cores and jets of active galactic nuclei. We also provide an in-depth look at the physical mechanisms of hadronic supercriticalities and show that magnetized relativistic plasmas are excellent examples of non-linear dynamical systems in high-energy astrophysics.

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Thèses sur le sujet "Galactic proton"

Vos, Etienne Eben. « Cosmic ray modulation processes in the heliosphere / Vos E.E ». Thesis, North-West University, 2011. http://hdl.handle.net/10394/7266.

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The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a three–dimensional, steady–state modulation model was used to reproduce a selection of consecutive PAMELA proton and electron spectra from 2006 to 2009. Thiswas done by assuming full drifts and simplified diffusion coefficients, where the rigidity dependence and absolute value of themean free paths for protons and electrons were sequentially adjusted below 3 GV and 300 MV, respectively. Care has been taken in calculating yearly–averaged current–sheet tilt angle and magnetic field values that correspond to the PAMELA spectra. Following this study where the numerical model was used to investigate the individual effects resulting from changes in the tilt angle, diffusion coefficients, and global drifts, it was found that all these modulation processes played significant roles in contributing to the total increase in CR intensities from 2006 to 2009, as was observed by PAMELA. Furthermore, the effect that drifts has on oppositely charged particles was also evident from the difference between the peak–shaped time profiles of protons and the flatter time profiles of electrons, as is expected for an A < 0 polarity cycle. Since protons, which drift into the heliosphere along the heliospheric current–sheet, haven’t yet reached maximum intensity levels by 2008, their intensities increased notably more than electrons toward the end of 2009. The time and energy dependence of the electron to proton ratios were also studied in order to further illustrate and quantify the effect of drifts during this remarkable solar minimum period.
Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

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de, Séréville Nicolas. « Etude de la réaction 18F(p,alpha)15O par réction de transfert pour application à l'émission gamma des novae ». Phd thesis, Université Paris-Diderot - Paris VII, 2003. http://tel.archives-ouvertes.fr/tel-00007988.

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L'émission gamma des novae à, et en dessous, de 511 keV provient essentiellement de l'annihilation des positrons venant de la décroissance beta+ du 18F. L'interprétation de cette émission, à l'aide d'observations par le satellite INTEGRAL par exemple, nécessite une bonne connaissance de la nucléosynthèse du 18F. Dans ce contexte, le taux de la réaction 18F(p,alpha)15O est le moins bien connu à cause de deux résonances correspondant aux niveaux excités Ex = 6.419 et 6.449 MeV dans le 19Ne dont les largeurs protons sont totalement inconnues. Nous avons déterminé ces largeurs protons par le biais d'une réaction de transfert d'un nucléon D(18F,p alpha)15N peuplant les niveaux analogues, dans le 19F, des niveaux d'intérêt astrophysique. Nous avons utilisé un faisceau radioactif de 18F accéléré à 14 MeV au Centre de Recherche du Cyclotron de Louvain--la--Neuve sur une cible de CD2 en cinématique inverse ainsi que le détecteur multi--piste au silicium LEDA. Une analyse en DWBA a permi de déterminer la largeur proton de ces deux résonances et a montré qu'elles ne pouvaient pas être négligées dans le calcul du taux de réaction. Une étude détaillée des incertitudes restantes sur le taux de réaction a été entreprise et particulièrement en ce qui concerne les interférences entre ces résonances et une autre résonance à plus haute énergie dans le 19Ne. Le taux de réaction ainsi établi diffère peu de l'ancien taux nominal mais repose maintenant sur des bases plus solides permettant une meilleure interprétation des futures observations gamma des novae et donc une meilleure contrainte des modèles astrophysiques.

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Livres sur le sujet "Galactic proton"

Center, Langley Research, dir. Multiple-scattering model for inclusive proton production in heavy ion collisions. Hampton, Va : National Aeronautics and Space Administration, Langley Research Center, 1994.

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Mars surface radiation exposure for solar maximum conditions and 1989 solar proton events. [Washington, DC] : National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1993.

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Parameterized spectral distributions for meson production in proton-proton collisions. [Washington, DC] : NASA, 1995.

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Multiple-scattering model for inclusive proton production in heavy ion collisions. Hampton, Va : National Aeronautics and Space Administration, Langley Research Center, 1994.

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Chapitres de livres sur le sujet "Galactic proton"

Smart, D. F., et M. A. Shea. « Predicting and Modeling Solar Flare Generated Proton Fluxes in the Inner Heliosphere ». Dans Biological Effects and Physics of Solar and Galactic Cosmic Radiation Part B, 101–17. Boston, MA : Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-2916-3_6.

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Miller, J. H., D. L. Frasco, M. Ye, C. E. Swenberg, L. S. Myers et A. Rupprecht. « Free-Radical Yields in Proton Irradiation of Oriented DNA : Relationship to Energy Transfer Along DNA Chains ». Dans Biological Effects and Physics of Solar and Galactic Cosmic Radiation, 85–91. Boston, MA : Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-2918-7_8.

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Caimmi, R., E. Andriani et L. Secco. « Acquisition of angular momentum in the proto-galactic phases ». Dans Large Scale Structures of the Universe, 544. Dordrecht : Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2995-1_98.

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Nakasato, Naohito. « Metal Enrichment History of the Proto-Galactic Interstellar Medium ». Dans The Evolution of Galaxies, 257–60. Dordrecht : Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-017-3311-3_50.

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Robertson, James B., William C. Glisson, John O. Archambeau, George B. Coutrakan, Daniel W. Miller, Michael F. Moyers, Jeffrey F. Siebers, James M. Slater et John F. Dicello. « The Relative Biological Effectiveness of Attenuated Protons ». Dans Biological Effects and Physics of Solar and Galactic Cosmic Radiation Part B, 853–58. Boston, MA : Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-2916-3_18.

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Koskinen, Hannu E. J., et Emilia K. J. Kilpua. « Particle Source and Loss Processes ». Dans Astronomy and Astrophysics Library, 159–211. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-82167-8_6.

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AbstractThe main sources of charged particles in the Earth’s inner magnetosphere are the Sun and the Earth’s ionosphere. Furthermore, the Galactic cosmic radiation is an important source of protons in the inner radiation belt, and roughly every 13 years, when the Earth and Jupiter are connected via the interplanetary magnetic field, a small number of electrons originating from the magnetosphere of Jupiter are observed in the near-Earth space. The energies of solar wind and ionospheric plasma particles are much smaller than the particle energies in radiation belts. A major scientific task is to understand the transport and acceleration processes leading to the observed populations up to relativistic energies. Equally important is to understand the losses of the charged particles. The great variability of the outer electron belt is a manifestation of the continuously changing balance between source and loss mechanisms, whereas the inner belt is much more stable.

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Acker, A. « Announcement : The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae ». Dans Planetary and Proto-Planetary Nebulae : From IRAS to ISO, 35–38. Dordrecht : Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3891-5_4.

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Fritze - v. Alvensleben, Uta. « Chemical Evolution of (Proto-) Galactic Disks and Metal Abundances of Damped Lyα Absorbers ». Dans QSO Absorption Lines, 81–84. Berlin, Heidelberg : Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-540-49458-4_14.

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Shea, M. A., et D. F. Smart. « History of Energetic Solar Protons for the Past Three Solar Cycles Including Cycle 22 Update ». Dans Biological Effects and Physics of Solar and Galactic Cosmic Radiation Part B, 37–71. Boston, MA : Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-2916-3_3.

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Rukundo, Wellen. « Solar Proton Activity over the Solar Cycle 24 and Associated Space Radiation Doses ». Dans Solar Wind - Space, Humans and Communications [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.103832.

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The least number of proton events and ground-level enhancements was recorded in the solar cycle 24 which corresponds with the least smoothed sunspot number compared to the last three previous solar cycles. This was attributed to the weak sun’s polar field and decreasing strength of the interplanetary magnetic field at the start of the solar cycle. The majority contribution to background radiation dose within our earth’s atmosphere is galactic cosmic rays and trapped particles in the Van Allen Belts. However, solar proton events cause sudden spikes in radiation doses, and this depends on the fluence and energy spectra of the events. While these doses are least detected in the lower atmosphere, they have significant radiation damage to spacecraft electronic components and astronauts on long space missions and at higher atmospheric altitudes. Therefore, the prediction of such events and estimation of their effective radiation damage is an important consideration for planning long space missions and spacecraft design materials.

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Actes de conférences sur le sujet "Galactic proton"

Ndiitwani, Dzivhuluwani, Donald Ngobeni, O. P. M. ASlam, Driaan Bischoff, Marius Potgieter, Mirko Boezio, Riccardo Munini et Vladimir Mikhailov. « A simulation study of galactic proton modulation from solar minimum to maximum conditions ». Dans 37th International Cosmic Ray Conference. Trieste, Italy : Sissa Medialab, 2021. http://dx.doi.org/10.22323/1.395.1327.

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Urusova, Baidymat I., Mecca S. Kh Bolatchieva et Umar M. Laipanov. « Cosmic rays at ultrahigh energies ». Dans Sustainable and Innovative Development in the Global Digital Age. Dela Press Publishing House, 2022. http://dx.doi.org/10.56199/dpcsebm.iohr6570.

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In this paper, the nature of the origin of cosmic rays is considered. By studying the chemical composition, the intensity of cosmic rays is determined. And when collisions with the nuclei of the interstellar medium, unstable particles appear. The astronomical role of cosmic rays and the probable galactic model of the origin of cosmic rays have been clarified. The results of the chemical composition of cosmic rays are obtained. It is shown that: a) cosmic rays are mostly located in the Galaxy; b) the Virgo supercluster is a metagalactic model in which the main part of the proton-nuclear component forms superclusters; c) the metagalactic model differs from the galactic one in the energy density of cosmic rays. Models of the origin of cosmic rays in the region of energies up to 1017 Ev, the most preferred model is one that assumes an increase in multiplicity. The energy density of cosmic rays is determined. The dependences of the average number of muons on the number of electrons in the shower and the energy spectrum of muons in the shower are found. Depending on where the main sources of cosmic rays are located, the following models of cosmic rays are shown: solar, galactic and metagalactic, and galactic models have several modifications and differ from halo and disk models, since cosmic rays fill a quasi- pherical volume.

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Kühl, Patrick, Nina Dresing, Jan Gieseler, Bernd Heber et Andreas Klassen. « Galactic Cosmic Ray Spectra During Solar Cycle 23 and 24 - Measurement Capabilities of the Electron Proton Helium Instrument ». Dans The 34th International Cosmic Ray Conference. Trieste, Italy : Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.236.0224.

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Bondarev, Evgeny, Alexander E. Koziukov, Grigory Protopopov, Pavel A. Chubunov, Andrey Repin, Valentina I. Denisova et Alexey V. Tsurgaev. « Variation of proton fluxes of galactic cosmic rays during 2012-2020 according to data from the Russian spacecraft in geostationary orbit ». Dans 37th International Cosmic Ray Conference. Trieste, Italy : Sissa Medialab, 2021. http://dx.doi.org/10.22323/1.395.1308.

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Ivanov, Dmitri. « Search for EeV Protons of Galactic Origin ». Dans The 34th International Cosmic Ray Conference. Trieste, Italy : Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.236.0350.

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FORMATO, V., M. BOEZIO, V. BONVICINI, R. CARBONE, E. MOCCHIUTTI, R. MUNINI, R. SARKAR et al. « Solar modulation of galactic protons and helium with the PAMELA experiment ». Dans International Conference on Advanced Technology and Particle Physics. WORLD SCIENTIFIC, 2014. http://dx.doi.org/10.1142/9789814603164_0028.

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Mathews, Grant J., Lamya Saleh et Timothy Beers. « Early star formation nucleosynthesis and chemical evolution in proto-galactic clouds ». Dans International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX. Trieste, Italy : Sissa Medialab, 2010. http://dx.doi.org/10.22323/1.028.0047.

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Fazio, G. G. « The Space Infrared Telescope Facility (SIRTF) ». Dans Space Optics for Astrophysics and Earth and Planetary Remote Sensing. Washington, D.C. : Optica Publishing Group, 1988. http://dx.doi.org/10.1364/soa.1988.wd1.

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In 1983 the Infrared Astronomical Satellite (IRAS) radically changed our view of the infrared sky. IRAS carried out an all-sky survey in four broad wavelength bands between 8 and 120μm, detecting about 250,000 sources. This survey detected new comets and dust bands in our solar system, discovered protostars and possible proto-planetary disks around near-by stars, generated detailed images of the entire galactic plane, and discovered extremely luminous infrared galaxies. The Space Infrared Telescope Facility (SIRTF) was designed to provide an enormous gain in our ability to explore in greater depth the infrared sky as revealed by IRAS, and to explore some of the most fundamental questions about the origin, evolution, and ultimate fate of the Universe.

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POTGIETER, M. S., E. E. VOS et R. R. NNDANGANENI. « THE FIRST VERY LOCAL INTERSTELLAR SPECTRA FOR GALACTIC PROTONS, HELIUM AND ELECTRONS ». Dans International Conference on Advanced Technology and Particle Physics. WORLD SCIENTIFIC, 2014. http://dx.doi.org/10.1142/9789814603164_0031.

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Heber, B. « Recurrent modulation of galactic cosmic ray electrons and protons : Ulysses COSPIN/KET observations ». Dans Acceleration and transport of energetic particles observed in the heliosphere (ACE-2000 symposium). AIP, 2000. http://dx.doi.org/10.1063/1.1324339.

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Rapports d'organisations sur le sujet "Galactic proton"

Shomer, Ilan, Ruth E. Stark, Victor Gaba et James D. Batteas. Understanding the hardening syndrome of potato (Solanum tuberosum L.) tuber tissue to eliminate textural defects in fresh and fresh-peeled/cut products. United States Department of Agriculture, novembre 2002. http://dx.doi.org/10.32747/2002.7587238.bard.

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The project sought to understand factors and mechanisms involved in the hardening of potato tubers. This syndrome inhibits heat softening due to intercellular adhesion (ICA) strengthening, compromising the marketing of industrially processed potatoes, particularly fresh peeled-cut or frozen tubers. However, ICA strengthening occurs under conditions which are inconsistent with the current ideas that relate it to Ca-pectate following pectin methyl esterase (PME) activity or to formation of rhamnogalacturonan (RG)-II-borate. First, it was necessary to induce strengthening of the middle lamellar complex (MLX) and the ICA as a stress response in some plant parenchyma. As normally this syndrome does not occur uniformly enough to study it, we devised an efficient model in which ICA-strengthening is induced consistently under simulated stress by short-chain, linear, mono-carboxylic acid molecules (OAM), at 65 oC [appendix 1 (Shomer&Kaaber, 2006)]. This rapid strengthening was insufficient for allowing the involved agents assembly to be identifiable; but it enabled us to develop an efficient in vitro system on potato tuber parenchyma slices at 25 ºC for 7 days, whereas unified stress was reliably simulated by OAMs in all the tissue cells. Such consistent ICA-strengthening in vitro was found to be induced according to the unique physicochemical features of each OAM as related to its lipophilicity (Ko/w), pKa, protonated proportion, and carbon chain length by the following parameters: OAM dissociation constant (Kdiss), adsorption affinity constant (KA), number of adsorbed OAMs required for ICA response (cooperativity factor) and the water-induced ICA (ICAwater). Notably, ICA-strengthening is accompanied by cell sap leakage, reflecting cell membrane rupture. In vitro, stress simulation by OAMs at pH<pKa facilitated the consistent assembly of ICAstrengthening agents, which we were able to characterize for the first time at the molecular level within purified insoluble cell wall of ICA-strengthened tissue. (a) With solid-state NMR, we established the chemical structure and covalent binding to cell walls of suberin-like agents associated exclusively with ICA strengthening [appendix 3 (Yu et al., 2006)]; (b) Using proteomics, 8 isoforms of cell wall-bound patatin (a soluble vacuolar 42-kDa protein) were identified exclusively in ICA-strengthened tissue; (c) With light/electron microscopy, ultrastructural characterization, histochemistry and immunolabeling, we co-localized patatin and pectin in the primary cell wall and prominently in the MLX; (d) determination of cell wall composition (pectin, neutral sugars, Ca-pectate) yielded similar results in both controls and ICA-strengthened tissue, implicating factors other than PME activity, Ca2+ or borate ions; (e) X-ray powder diffraction experiments revealed that the cellulose crystallinity in the cell wall is masked by pectin and neutral sugars (mainly galactan), whereas heat or enzymatic pectin degradation exposed the crystalline cellulose structure. Thus, we found that exclusively in ICA-strengthened tissue, heat-resistant pectin is evident in the presence of patatin and suberinlike agents, where the cellulose crystallinity was more hidden than in fresh control tissue. Conclusions: Stress response ICA-strengthening is simulated consistently by OAMs at pH< pKa, although PME and formation of Ca-pectate and RG-II-borate are inhibited. By contrast, at pH>pKa and particularly at pH 7, ICA-strengthening is mostly inhibited, although PME activity and formation of Ca-pectate or RG-II-borate are known to be facilitated. We found that upon stress, vacuolar patatin is released with cell sap leakage, allowing the patatin to associate with the pectin in both the primary cell wall and the MLX. The stress response also includes formation of covalently bound suberin-like polyesters within the insoluble cell wall. The experiments validated the hypotheses, thus led to a novel picture of the structural and molecular alterations responsible for the textural behavior of potato tuber. These findings represent a breakthrough towards understanding of the hardening syndrome, laying the groundwork for potato-handling strategies that assure textural quality of industrially processed particularly in fresh peeled cut tubers, ready-to-prepare and frozen preserved products.

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