Academic literature on the topic 'Cosmic-ray diffusion'
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Journal articles on the topic "Cosmic-ray diffusion"
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Duffy, Peter. "Bohm Diffusion and Cosmic-Ray-Modified Shocks." International Astronomical Union Colloquium 142 (1994): 981–83. http://dx.doi.org/10.1017/s0252921100078428.
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AbstractA numerical solution to the problem of self-consistent diffusive shock acceleration is presented. The cosmic rays are scattered, accelerated and exert a back-reaction on the gas through their interaction with turbulence frozen into the local fluid frame. Using a grid with a hierarchical spacetime structure the physically interesting limit of Bohm diffusion (к ∝ pv), which introduces a wide range of diffusion lengthscales and acceleration timescales, can be studied. Some implications for modified shocks and particle acceleration are presented.Subject headings: acceleration of particles — cosmic rays — diffusion — shock waves
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Zhang, Yiran, Siming Liu, and Dejin Wu. "Cosmic-Ray Convection–Diffusion Anisotropy." Astrophysical Journal 938, no. 2 (October 1, 2022): 106. http://dx.doi.org/10.3847/1538-4357/ac8f28.
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Abstract Under nonuniform convection, the distribution of diffusive particles can exhibit dipole and quadrupole anisotropy induced by the fluid inertial and shear force, respectively. These convection-related anisotropies, unlike the Compton–Getting effect, typically increase with the cosmic-ray (CR) energy, and are thus candidate contributors for the CR anisotropy. In consideration of the inertial effect, CR observational data can be used to set an upper limit on the average acceleration of the local interstellar medium in the equatorial plane to be on the order of 100 μm s−2. Using Oort constants, the quadrupole anisotropy above 200 TeV may be modeled with the shear effect arising from the Galactic differential rotation.
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Reichherzer, P., J. Becker Tjus, E. G. Zweibel, L. Merten, and M. J. Pueschel. "Turbulence-level dependence of cosmic ray parallel diffusion." Monthly Notices of the Royal Astronomical Society 498, no. 4 (August 21, 2020): 5051–64. http://dx.doi.org/10.1093/mnras/staa2533.
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ABSTRACT Understanding the transport of energetic cosmic rays belongs to the most challenging topics in astrophysics. Diffusion due to scattering by electromagnetic fluctuations is a key process in cosmic ray transport. The transition from a ballistic to a diffusive-propagation regime is presented in direct numerical calculations of diffusion coefficients for homogeneous magnetic field lines subject to turbulent perturbations. Simulation results are compared with theoretical derivations of the parallel diffusion coefficient’s dependences on the energy and the fluctuation amplitudes in the limit of weak turbulence. The present study shows that the widely used extrapolation of the energy scaling for the parallel diffusion coefficient to high turbulence levels predicted by quasi-linear theory does not provide a universally accurate description in the resonant-scattering regime. It is highlighted here that the numerically calculated diffusion coefficients can be polluted for low energies due to missing resonant interaction possibilities of the particles with the turbulence. Five reduced-rigidity regimes are established, which are separated by analytical boundaries derived in this work. Consequently, a proper description of cosmic ray propagation can only be achieved by using a turbulence-level-dependent diffusion coefficient and can contribute to solving the Galactic cosmic ray gradient problem.
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Schlickeiser, Reinhard. "Cosmic-Ray Transport and Acceleration." International Astronomical Union Colloquium 142 (1994): 926–36. http://dx.doi.org/10.1017/s0252921100078337.
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AbstractWe review the transport and acceleration of cosmic rays concentrating on the origin of galactic cosmic rays. Quasi-linear theory for the acceleration rates and propagation parameters of charged test particles combined with the plasma wave viewpoint of modeling weak cosmic electromagnetic turbulence provides a qualitatively and quantitatively correct description of key observations. Incorporating finite frequency effects, dispersion, and damping of the plasma waves are essential in overcoming classical discrepancies with observations as the Kfit - Kql discrepancy of solar particle events. We show that the diffusion-convection transport equation in its general form contains spatial convection and diffusion terms as well as momentum convection and diffusion terms. In particular, the latter momentum diffusion term plays a decisive role in the acceleration of cosmic rays at super-Alfvénic supernova shock fronts, and in the acceleration of ultra-high-energy cosmic rays by distributed acceleration in our own galaxy.Subject headings: acceleration of particles — convection — cosmic rays — diffusion — shock waves
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Commerçon, Benoît, Alexandre Marcowith, and Yohan Dubois. "Cosmic-ray propagation in the bi-stable interstellar medium." Astronomy & Astrophysics 622 (February 2019): A143. http://dx.doi.org/10.1051/0004-6361/201833809.
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Context. Cosmic rays propagate through the galactic scales down to the smaller scales at which stars form. Cosmic rays are close to energy equipartition with the other components of the interstellar medium and can provide a support against gravity if pressure gradients develop. Aims. We study the propagation of cosmic rays within the turbulent and magnetised bi-stable interstellar gas. The conditions necessary for cosmic-ray trapping and cosmic-ray pressure gradient development are investigated. Methods. We derived an analytical value of the critical diffusion coefficient for cosmic-ray trapping within a turbulent medium, which follows the observed scaling relations. We then presented a numerical study using 3D simulations of the evolution of a mixture of interstellar gas and cosmic rays, in which turbulence is driven at varying scales by stochastic forcing within a box of 40 pc. We explored a large parameter space in which the cosmic-ray diffusion coefficient, the magnetisation, the driving scale, and the amplitude of the turbulence forcing, as well as the initial cosmic-ray energy density, vary. Results. We identify a clear transition in the interstellar dynamics for cosmic-ray diffusion coefficients below a critical value deduced from observed scaling relations. This critical diffusion depends on the characteristic length scale L of Dcrit ≃ 3.1 × 1023 cm2 s−1(L/1 pc)q+1, where the exponent q relates the turbulent velocity dispersion σ to the length scale as σ ~ Lq. Hence, in our simulations this transition occurs around Dcrit ≃ 1024–1025 cm2 s−1. The transition is recovered in all cases of our parameter study and is in very good agreement with our simple analytical estimate. In the trapped cosmic-ray regime, the induced cosmic-ray pressure gradients can modify the gas flow and provide a support against the thermal instability development. We discuss possible mechanisms that can significantly reduce the cosmic-ray diffusion coefficients within the interstellar medium. Conclusions. Cosmic-ray pressure gradients can develop and modify the evolution of thermally bi-stable gas for diffusion coefficients D0 ≤ 1025 cm2 s−1 or in regions where the cosmic-ray pressure exceeds the thermal one by more than a factor of ten. This study provides the basis for further works including more realistic cosmic-ray diffusion coefficients, as well as local cosmic-ray sources.
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Armillotta, Lucia, Eve C. Ostriker, and Yan-Fei Jiang. "Cosmic-Ray Transport in Simulations of Star-forming Galactic Disks." Astrophysical Journal 922, no. 1 (November 1, 2021): 11. http://dx.doi.org/10.3847/1538-4357/ac1db2.
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Abstract Cosmic-ray transport on galactic scales depends on the detailed properties of the magnetized, multiphase interstellar medium (ISM). In this work, we postprocess a high-resolution TIGRESS magnetohydrodynamic simulation modeling a local galactic disk patch with a two-moment fluid algorithm for cosmic-ray transport. We consider a variety of prescriptions for the cosmic rays, from a simple, purely diffusive formalism with constant scattering coefficient, to a physically motivated model in which the scattering coefficient is set by the critical balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We separately focus on cosmic rays with kinetic energies of ∼1 GeV (high-energy) and ∼30 MeV (low energy), respectively important for ISM dynamics and chemistry. We find that simultaneously accounting for advection, streaming, and diffusion of cosmic rays is crucial for properly modeling their transport. Advection dominates in the high-velocity, low-density hot phase, while diffusion and streaming are more important in higher-density, cooler phases. Our physically motivated model shows that there is no single diffusivity for cosmic-ray transport: the scattering coefficient varies by four or more orders of magnitude, maximal at density n H ∼ 0.01 cm−3. The ion-neutral damping of Alfvén waves results in strong diffusion and nearly uniform cosmic-ray pressure within most of the mass of the ISM. However, cosmic rays are trapped near the disk midplane by the higher scattering rate in the surrounding lower-density, higher-ionization gas. The transport of high-energy cosmic rays differs from that of low-energy cosmic rays, with less effective diffusion and greater energy losses for the latter.
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Maiti, Snehanshu, Kirit Makwana, Heshou Zhang, and Huirong Yan. "Cosmic-ray Transport in Magnetohydrodynamic Turbulence." Astrophysical Journal 926, no. 1 (February 1, 2022): 94. http://dx.doi.org/10.3847/1538-4357/ac46c8.
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Abstract This paper studies cosmic-ray (CR) transport in magnetohydrodynamic (MHD) turbulence. CR transport is strongly dependent on the properties of the magnetic turbulence. We perform test particle simulations to study the interactions of CR with both total MHD turbulence and decomposed MHD modes. The spatial diffusion coefficients and the pitch angle scattering diffusion coefficients are calculated from the test particle trajectories in turbulence. Our results confirm that the fast modes dominate the CR propagation, whereas Alfvén and slow modes are much less efficient and have shown similar pitch-angle scattering rates. We investigate the cross field transport on large and small scales. On large/global scales, normal diffusion is observed and the diffusion coefficient is suppressed by M A ζ compared to the parallel diffusion coefficients, with ζ closer to 4 in Alfvén modes than that in total turbulence, as theoretically expected. For the CR transport on scales smaller than the turbulence injection scale, both the local and global magnetic reference frames are adopted. Superdiffusion is observed on such small scales in all the cases. Particularly, CR transport in Alfvén modes show clear Richardson diffusion in the local reference frame. The diffusion transitions smoothly from the Richardson’s one with index 1.5 to normal diffusion as the particle mean free path decreases from λ ∥ ≫ L to λ ∥ ≪ L, where L is the injection/coherence length of turbulence. Our results have broad applications to CRs in various astrophysical environments.
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ZIRAKASHVILI, VLADIMIR N. "COSMIC RAY ANISOTROPY PROBLEM." International Journal of Modern Physics A 20, no. 29 (November 20, 2005): 6858–60. http://dx.doi.org/10.1142/s0217751x05030314.
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The anisotropy of cosmic rays, produced by Galactic supernovae is calculated. It is a factor 100 ÷ 1000 larger than the observed value at 1 PeV. It is shown that this contradiction can be explained if a cosmic ray diffusion coefficient is small in the local vicinity of the Sun.
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Chan, T. K., D. Kereš, P. F. Hopkins, E. Quataert, K.-Y. Su, C. C. Hayward, and C.-A. Faucher-Giguère. "Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV γ-ray emission." Monthly Notices of the Royal Astronomical Society 488, no. 3 (July 10, 2019): 3716–44. http://dx.doi.org/10.1093/mnras/stz1895.
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ABSTRACT We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub-L⋆ starburst, and L⋆ galaxies with different propagation models, including advection, isotropic, and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two-moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L⋆ galaxies with constant isotropic diffusion coefficient $\kappa \sim 3\times 10^{29}\, {\rm cm^{2}\, s^{-1}}$. Advection-only and streaming-only models produce order of magnitude too large γ-ray luminosities in dwarf and L⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are ‘trapped’ in the star-forming disc have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ that match the γ-ray observations, CRs form extended haloes with scale heights of several kpc to several tens of kpc.
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Exarhos, G., and X. Moussas. "On the heliolatitudinal variation of the galactic cosmic-ray intensity. Comparison with Ulysses measurements." Annales Geophysicae 21, no. 6 (June 30, 2003): 1341–45. http://dx.doi.org/10.5194/angeo-21-1341-2003.
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Abstract. We study the dependence of cosmic rays with heliolatitude using a simple method and compare the results with the actual data from Ulysses and IMP spacecraft. We reproduce the galactic cosmic-ray heliographic latitudinal intensity variations, applying a semi-empirical, 2-D diffusion-convection model for the cosmic-ray transport in the interplanetary space. This model is a modification of our previous 1-D model (Exarhos and Moussas, 2001) and includes not only the radial diffusion of the cosmic-ray particles but also the latitudinal diffusion. Dividing the interplanetary region into "spherical magnetic sectors" (a small heliolatitudinal extension of a spherical magnetized solar wind plasma shell) that travel into the interplanetary space at the solar wind velocity, we calculate the cosmic-ray intensity for different heliographic latitudes as a series of successive intensity drops that all these "spherical magnetic sectors" between the Sun and the heliospheric termination shock cause the unmodulated galactic cosmic-ray intensity. Our results are compared with the Ulysses cosmic-ray measurements obtained during the first pole-to-pole passage from mid-1994 to mid-1995.Key words. Interplanetary physics (cosmic rays; interplanetray magnetic fields; solar wind plasma)
Dissertations / Theses on the topic "Cosmic-ray diffusion"
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Cea, del Pozo Elsa de. "Some observational and theoretical aspects of cosmic-ray diffusion." Doctoral thesis, Universitat Autònoma de Barcelona, 2011. http://hdl.handle.net/10803/51003.
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La Tesis contiene ciertos estudios relacionados con la difusión de rayos cósmicos. Está dividida en dos partes, una describe los modelos sobre la fenomenología de difusión de rayos cósmicos, y otra presenta las observaciones realizadas usando el experimento MAGIC y simulaciones del futuro Array de Telescopios Cherenkov (CTA, por sus siglas en inglés).
En la primera parte, se introduce la teoría general más aceptada sobre la difusión de rayos cósmicos. Se cree que los remanentes de supernova (SNR) son uno de los escenarios más probables de aceleración de rayos cósmicos, tanto en procesos leptónicos como hadrónicos. El mecanismo de aceleración de partículas en cada SNR se asume que es aceleración por choque difuso (diffusive shock acceleration). Para obtener confirmación observacional de la aceleración de protones y otros núcleos, y distinguirlos de la emisión leptónica, se deben aislar los efectos de los múltiples mensajeros producidos por partículas secundarias. Partiendo de ahí, se desarrolla un modelo sobre los alrededores del SNR IC443 que explica la fenomenología de alta energía: los rayos cósmicos escapan del remanente, los más energéticos alcanzan antes la nube molecular situada delante de la misma y los menos energéticos aún permanecen confinados a los restos del SNR. Los resultados contrastados con las últimas observaciones obtenidas de la fuente explican su aparente desplazamiento cuando se observa a alta y a muy alta energía.
También se presenta un modelo multi-frecuencia y multi-mensajero (fotones de todo el espectro electromagnético y neutrinos) de la emisión difusa de la galaxia con un estallido de formación estelar M82. Las predicciones para rayos gamma se comparan con (y explican satisfactoriamente) las posteriores detecciones en el rango energético comprendido entre los giga- y los tera-electronvoltios de las galaxias M82 y NGC 253, realizadas por el satélite Fermi y los experimentos en tierra H.E.S.S. y VERITAS.
En la segunda parte de la Tesis, se describe la técnica de detección de rayos gamma desde tierra a través de la radiación Cherenkov. Esta técnica es explotada, entre otros, por el experimento MAGIC. Algunas de las observaciones realizadas por la estudiante con este telescopio se presentan como parte de esta Tesis. En primer lugar, se muestran los límites superiores (upper limits) al flujo de rayos gamma obtenidos con MAGIC-I sobre dos fuentes detectadas por el experimento Milagro y que se corresponden con dos fuentes brillantes del satélite Fermi en la región del SNR G65.1+0.6. Se cree que puedan tratarse de dos púlsares que inyectan energía y partículas en la nebulosa pulsada que las rodea. También se presentan resultados preliminares de observaciones en estéreo (con los dos telescopios MAGIC) del SNR IC443. El número de horas obtenido resulta insuficiente para completar el estudio morfológico dependiente de la energía para el que se enfocaba la obtención de estos datos, pero nuevas observaciones están previstas para el futuro.
Finalmente, se introducen por primera vez algunas simulaciones realizadas con el futuro CTA y ciertos estudios espectrales sobre particulares casos científicos. En concreto, dichos estudios se centraron en los objetos ya discutidos en el resto de la Tesis, como el SNR IC443, las galaxias con estallido de formación estelar M82 y NGC 253, y nubes moleculares iluminadas por rayos cósmicos escapados de SNRs cercanos. El observatorio CTA representa el futuro de las observaciones de rayos gamma desde tierra, y prevé que se unan las colaboraciones de todas las instalaciones de telescopios actuales. El rango de energías se verá ampliado, la sensibilidad aumentará un orden de magnitud y la resolución angular se mejorará respecto a los experimentos existentes hoy en día. Esta Tesis representa, pues, sólo el principio de lo que queda por venir.This Thesis deals with certain aspects on cosmic-ray diffusion. It is divided in two parts, one describes phenomenological models of cosmic-ray diffusion, and the other presents observations taken with the MAGIC experiments and simulations of the future Cherenkov Telescope Array (CTA). In the first part, the generally accepted theory for cosmic-ray diffusion is introduced. Supernova remnants (SNRs) are believed to be the more likely scenarios of cosmic-ray acceleration, considering both hadronic and leptonic processes. The mechanism for particle acceleration in each SNR is assumed to be diffusive shock acceleration (DSA). To obtain the observational confirmation of proton and nuclei acceleration, and distinguish it from leptonic emission, the effects of multiple messengers produced by secondary particles must be isolated. Following this, a model for the neighborhood of the SNR IC443 is developed, explaining the high energy phenomenology: cosmic rays escape from the remnant, the most energetic ones reach first the molecular cloud located in front of it and the least energetic ones still remain confined on the shell of the SNR. The results are confronted with the latest observations that are obtained from this source. The apparent displacement between high and very high energy detected sources is explained thanks to this model. Moreover, a multi-frequency and multi-messenger model (i.e., photons from the whole electromagnetic spectrum and neutrinos) for the diffuse emission coming from the starburst galaxy M82 is presented. The gamma-ray predictions are compared to the posterior detections in the energy range between the giga- and the tera-electronvolts of the starburst galaxies M82 and NGC 253, observed by the satellite Fermi and the ground-based experiments H.E.S.S. and VERITAS. The model explains rather satisfactorily these detections at high and very high energy. In the second part of the Thesis, the technique for the gamma-ray detection at ground level through Cherenkov radiation is described. This Cherenkov technique is used in the MAGIC experiment, among others. Some of the observations taken by the student with this telescope facility are presented as part of this Thesis. First, the upper limits to the gamma-ray flux coming from two sources in the region of the SNR G65.1+0.6 when observed with MAGIC-I are shown. These two sources were previously detected by the Milagro experiment and are associated with two bright sources in the Fermi catalog. One of the possible explanations is that these sources are two pulsars powering the pulsar wind nebula that surrounds them. Furthermore, preliminar results of the stereo observations (using the two MAGIC telescopes) of the SNR IC443 are presented. The goal for these observations is performing an energy-dependent morphological study. So far, the obtained number of hours is not enough, although new observations are planned for the near future. Finally, some simulations for the future CTA are presented for the first time, together with several spectral studies regarding interesting scientific cases. In particular, those studies are focused on objects that have been already mentioned in this Thesis, like the SNR IC443 and the starburst galaxies M82 and NGC 253, and also on molecular clouds that are illuminated by cosmic rays which escaped from nearby SNRs. The CTA observatory represents the future of the ground-based gamma-ray observations, and it is likely to include every collaboration from the existing telescope facilities nowadays. The energy range will be widened, the sensitivity will be one order of magnitude improved and the angular resolution will be enhanced respect to the existing experiments up to now. Thus, the present Thesis is just the tip of the iceberg of what is yet to come.
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KO, CHUNG-MING. "COSMIC-RAY MODIFIED STELLAR WINDS (ACCELERATION, MODULATION, DIFFUSION, TRANSONIC SOLUTION)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183980.
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A two fluid hydrodynamical model describing the modification of a stellar wind flow due to its interaction with galactic cosmic-rays is investigated. The two fluids consist of the thermal stellar wind gas and the galactic cosmic-rays. A polytropic one fluid model is used to describe the stellar wind gas, and the cosmic-rays modify the wind via their pressure gradient. The cosmic-rays are considered to be a hot low density gas of negligible mass flux, but with a significant pressure and energy flux compared to the thermal gas. The equations used are essentially those employed in two fluid hydrodynamical models of cosmic-ray shock acceleration by the first order Fermi mechanism, but suitably modified to apply in a spherical geometry and including the effects of gravity on the flow. The stellar wind consists of a transonic flow with a termination shock, and subsonic flow outside the shock. The model shows the deceleration of the wind upstream of the shock by the positive galactic cosmic-ray pressure gradient. The dissertation first discusses the fluid polytropic stellar winds and how to insert shocks in the flow. The hydrodynamical equations governing cosmic-ray modified winds are then introduced followed by a discussion of the physics of the interaction between the thermal stellar wind and the cosmic-rays. A description of the singularities of the equations is also presented. The system of equations is first solved by a finite difference method in the test particle approximation in which the cosmic-rays do not modify the flow, with appropriate boundary conditions applied at infinity, at the wind termination shock, and at the star. A perturbation scheme to determine the modification of the wind by the cosmic-rays is then developed. This scheme applies when the modification of the wind by the cosmic-rays is sufficiently small. Finally a numerical iteration is employed to exactly solve the equations. This latter method has the advantage that it can be applied when there is a considerable modification of the wind by the cosmic-rays.
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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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Engelbrecht, Nicholas Eugéne. "On the heliospheric diffusion tensor and its effect on 26-day recurrent cosmic-ray variations / N.E. Engelbrecht." Thesis, North-West University, 2008. http://hdl.handle.net/10394/2052.
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Nkosi, Godfrey Sibusiso. "A study of cosmic ray anisotropies in the heliosphere / Godfrey Sibusiso Nkosi." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1627.
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Engelbrecht, Nicholas Eugéne. "On the development and applications of a three-dimensional ab initio cosmic-ray modulation model / Nicholas Eugéne Engelbrecht." Thesis, North-West University, 2012. http://hdl.handle.net/10394/8735.
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A proper understanding of the effects of turbulence on the diffusion and drift of cosmic-rays in
the heliosphere is imperative for a better understanding of cosmic-ray modulation. This study
presents an ab initio model for cosmic-ray modulation, incorporating for the first time the results
yielded by a two-component turbulence transport model. The latter model is solved for
solar minimum heliospheric conditions, utilizing boundary values chosen in such a way that
the results of this model are in fair to good agreement with spacecraft observations of turbulence
quantities, not only in the ecliptic plane, but also along the out-of-ecliptic trajectory of the
Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence
energy spectra, which in turn are used as inputs for parallel mean free paths based on those
derived from quasi-linear theory, and perpendicularmean free paths from extended nonlinear
guiding center theory. The modelled 2D spectrum is chosen based on physical considerations,
with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently
exist no models or observations for this quantity, and it is the only free parameter in this
study. The use of such a spectrum yields a non-divergent 2D ultrascale, which is used as an
input for the reduction terms proposed to model the effects of turbulence on cosmic-ray drifts.
The resulting diffusion and drift coefficients are applied to the study of galactic cosmic-ray
protons, electrons, antiprotons, and positrons using a three-dimensional, steady-state numerical
cosmic-ray modulation code. The magnitude and spatial dependence of the 2D outerscale
is demonstrated to have a significant effect on computed cosmic-ray intensities. A form for the
2D outerscale was found that resulted in computed cosmic-ray intensities, for all species considered,
in reasonable agreement with multiple spacecraft observations. Computed galactic
electron intensities are shown to be particularly sensitive to choices of parameters pertaining
to the dissipation range of the slab turbulence spectrum, and certain models for the onset
wavenumber of the dissipation range could be eliminated in this study.Thesis (PhD (Physics))--North-West University, Potchefstroom Campus, 2013
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Giesen, Gaelle. "Dark Matter Indirect Detection with charged cosmic rays." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112160/document.
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Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation ou la désintégration de la MN dans le halo de la Voie Lactée. Les efforts expérimentaux actuels se focalisent principalement sur une gamme d'énergie de l'ordre du GeV au TeV, où un signal de WIMP (Weakly Interacting Massive Particles) est attendu. L'analyse des mesures récentes et inédites des rayons cosmiques chargés (antiprotons, électrons et positrons) et leurs émissions secondaires et les améliorations des modèles astrophysiques sont présentées.Les données de PAMELA sur les antiprotons contraignent l'annihilation et la désintégration de la MN de manière similaire (et même légèrement meilleurs) que les contraintes les plus fortes venant des rayons gamma, même dans le cas où les énergies cinétiques inférieures à 10 GeV sont écartées. En choisissant des paramètres astrophysiques différents (modèles de propagation et profils de MN), les contraintes peuvent changer d'un à deux ordres de grandeur. Pour exploiter la totalité de la capacité des antiprotons à contraindre la MN, des effets précédemment négligés sont incorporés et se révèlent être importants dans l'analyse des données inédites de AMS-02 : ajouter les pertes d'énergie, la diffusion dans l'espace des moments et la modulation solaire peut modifier les contraintes, même à de hautes masses. Une mauvaise interprétation des données peut survenir si ces effets ne sont pas pris en compte. Avec les flux de protons et d'hélium exposé par AMS-02, le fond astrophysique et ces incertitudes du ratio antiprotons sur protons sont réévalués et comparés aux données inédites de AMS-02. Aucune indication pour un excès n'est trouvé. Une préférence pour un halo confinant plus large et une dépendance en énergie du coefficient de diffusion plus plate apparaissent. De nouvelles contraintes sur l'annihilation et la désintégration de la MN sont ainsi dérivés.Les émissions secondaires des électrons et des positrons peuvent aussi contraindre l'annihilation et la désintégration de la MN dans le halo galactique : le signal radio dû à la radiation synchrotron des électrons et positrons dans le champs magnétique galactique, les rayons gamma des processus de bremsstrahlung avec le gas galactique et de Compton Inverse avec le champs radiatif interstellaire sont considérés. Différentes configurations de champs magnétique galactique et de modèles de propagation et des cartes de gas et de champs radiatif interstellaire améliorés sont utilisées pour obtenir des outils permettant le calculs des émissions synchrotrons et bremsstrahlung venant de MN de type WIMP. Tous les résultats numériques sont incorporés dans la dernière version du Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID).Une interprétation d'un possible excès dans les données de rayons gamma de Fermi-LAT au centre galactique comme étant dû à l'annihilation de MN en canaux hadronique et leptonique est analysée. Dans une approche de messagers multiples, le calcul des émissions secondaires est amélioré et se révèle être important pour la détermination du spectre pour le canal leptonique. Ensuite, les limites provenant des antiprotons sur l'annihilation en canal hadronique contraignent sévèrement l'interprétation de cet excès comme étant dû à la MN, dans le cas de paramètres de propagation et de modulation solaire standards. Avec un choix plus conservatif de ces paramètres elles s'assouplissent considérablementOverwhelming evidence for the existence of Dark Matter (DM), in the form of an unknownparticle filling the galactic halos, originates from many observations in astrophysics and cosmology: its gravitational effects are apparent on galactic rotations, in galaxy clusters and in shaping the large scale structure of the Universe. On the other hand, a non-gravitational manifestation of its presence is yet to be unveiled. One of the most promising techniques is the one of indirect detection, aimed at identifying excesses in cosmic ray fluxes which could possibly be produced by DM annihilations or decays in the Milky Way halo. The current experimental efforts mainly focus in the GeV to TeV energy range, which is also where signals from WIMPs (Weakly Interacting Massive Particles) are expected. Focussing on charged cosmic rays, in particular antiprotons, electrons and positrons, as well as their secondary emissions, an analysis of current and forseen cosmic ray measurements and improvements on astrophysical models are presented. Antiproton data from PAMELA imposes contraints on annihilating and decaying DM which are similar to (or even slightly stronger than) the most stringent bounds from gamma ray experiments, even when kinetic energies below 10 GeV are discarded. However, choosing different sets of astrophysical parameters, in the form of propagation models and halo profiles, allows the contraints to span over one or two orders of magnitude. In order to exploit fully the power of antiprotons to constrain or discover DM, effects which were previously perceived as subleading turn out to be relevant especially for the analysis of the newly released AMS-02 data. In fact, including energy losses, diffusive reaccelleration and solar modulation can somewhat modify the current bounds, even at large DM masses. A wrong interpretation of the data may arise if they are not taken into account. Finally, using the updated proton and helium fluxes just released by the AMS-02 experiment, the astrophysical antiproton to proton ratio and its uncertainties are reevaluated and compared to the preliminarly reported AMS-02 measurements. No unambiguous evidence for a significant excess with respect to expectations is found. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. New stringed constraints on DM annihilation and decay are derived. Secondary emissions from electrons and positrons can also be used to constrain DM annihilation or decay in the galactic halo. The radio signal due to synchrotron radiation of electrons and positrons on the galactic magnetic field, gamma rays from bremsstrahlung processes on the galactic gas densities and from Inverse Compton scattering processes on the interstellar radiation field are considered. With several magnetic field configurations, propagation scenarios and improved gas density maps and interstellar radiation field, state-of-art tools allowing the computaion of synchrotron and bremssttrahlung radiation for any WIMP DM model are provided. All numerical results for DM are incorporated in the release of the Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID). Finally, the possible GeV gamma-ray excess identified in the Fermi-LAT data from the Galactic Center in terms of DM annihilation, either in hadronic or leptonic channels is studied. In order to test this tantalizing interprestation, a multi-messenger approach is used: first, the computation of secondary emisison from DM with respect to previous works confirms it to be relevant for determining the DM spectrum in leptonic channels. Second, limits from antiprotons severely constrain the DM interpretation of the excess in the hadronic channel, for standard assumptions on the Galactic propagation parameters and solar modulation. However, they considerably relax if more conservative choices are adopted
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Antecki, Thorsten [Verfasser], Reinhard [Gutachter] Schlickeiser, and Horst [Gutachter] Fichtner. "Effects of a finite downstream medium in diffusive cosmic ray acceleration at relativistic shock waves / Thorsten Antecki. Gutachter: Reinhard Schlickeiser ; Horst Fichtner." Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/110905159X/34.
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Voisin, Fabien. "Environment Studies of Pulsar Wind Nebulae and Their Interactions with the Interstellar Medium." Thesis, 2017. http://hdl.handle.net/2440/119266.
Full textAbstract:
Pulsars, rapidly rotating neutron star born from the core-collapse of massive stars, convert a fraction of their rotational energy to accelerate electrons up to high energies. The generated pulsar wind eventually reaches the termination shock and creates a pulsar wind nebula (PWN). There, the particles’ trajectories become randomized, and they produce radio to X-ray emission via synchrotron radiation; and TeV γ-ray emission from the interaction of high energy electrons with the Cosmic Microwave Background; and the infra-red emission from Galactic dust. Although progress has been made towards the understanding of the structure of the pulsar environment, several issues, such as the composition of the pulsar winds, still need to be addressed. Indeed, no direct evidence of hadronic components have yet been discovered inside the PWN. However, nearby dense molecular clouds could provide sufficient target particles for the potential hadrons from the PWN and its progenitor supernova remnant (SNR) to produce significant TeV emission via proton-proton (p-p) interaction. My work thus first consists of conducting interstellar matter (ISM) studies towards several PWNe using the 22-metre Mopra and the 4-metre Nanten radio telescopes. Among the studied PWNe, I particularly focus on HESS J1825−137 and its plausible association with the nearby unidentified TeV source HESS J1826−130. I have mapped the HESS J1826−130 region with Mopra in the 7 and 12 mm bands which, combined with the Nanten CO(1–0) survey and the GRS ¹³CO(1–0), enable an accurate analysis of the morphological and physical properties of several dense molecular clouds found in the line of sight. Interestingly, I have found a massive molecular cloud adjacent to the PWN HESS J1825−137 and overlapping the HESS J1826−130 TeV emission. From our mass estimates, I suggest that the cosmic-rays originating from the progenitor SNR of the pulsar PSRJ1826−1334 can significantly contribute to the TeV emission. We then attempt to model and predict spectral and morphological properties of the TeV emission from the propagation of high energy CRs and electrons, originating from the progenitor SNR and potentially from the PWN.We find that the resulting spectral shape of the TeV γ-ray emission is very sensitive to the diffusion coefficient of high energy particles inside molecular clouds. I also find that only a ‘slow’ diffusion’ of CRs (diffusion coefficient D(E) ∼ 10²⁶ √E/10GeV cm² s⁻¹) results in a significant contribution of the gamma-ray emission towards HESS J1826−130 at all energies. We finally notice that the contribution from hypothetical CRs escaping the PWN HESS J1825−137 is expected to be overshadowed by the contribution of CRs escaping the progenitor SNR. As one expects the latter’s contribution to decrease as time evolves while the former’s contribution to remain somewhat constant, I thus argue that older PWNe may be more suitable candidates to obtain direct evidence of CRs inside PWNe. Among the studied PWNe, I find that, based on simplistic diffusion studies, the ISM surrounding HESS J1809−193 may be a good laboratory to detect CRs escaping the pulsar PSRJ1809−1917.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2017
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Raath, Jan Louis. "A comparative study of cosmic ray modulation models / Jan Louis Raath." Thesis, 2015. http://hdl.handle.net/10394/15516.
Full textAbstract:
Until recently, numerical modulation models for the solar modulation of cosmic rays have
been based primarily on finite difference approaches; however, models based on the solution
of an appropriate set of stochastic differential equations have become increasingly
popular. This study utilises such a spatially three-dimensional and time-stationary model,
based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful
illustrative capabilities of this model are utilised extensively and in a distinctly comparative
fashion to enable new insights into the processes of modulation. The model is
refined to provide for both the Smith-Bieber (Smith and Bieber, 1991) and Jokipii-Kota
(Jokipii and Kota, 1989) modifcations to the Parker heliospheric magnetic field (Parker,
1958) and the implications for modulation are investigated. During this investigation
it is conclusively illustrated that the Parker field is most conducive to drift dominated
modulation, while the Jokipii-Kota and Smith-Bieber modifcations are seen to induce
successively larger contributions from diffusive processes. A further refinement to the
model is the incorporation of a different profile for the heliospheric current sheet. This
profile is defined by its latitudinal extent given by Kota and Jokipii (1983), as opposed
to the profile given by Jokipii and Thomas (1981). An extensive investigation into current
sheet related matters is launched, illustrating the difference between these current
sheet geometries, the associated drift velocity fields and the effect on modulation. At
high levels of solar activity, such that the current sheet enters deep enough into the polar
regions, the profile of Kota and Jokipii (1983) is found to significantly reduce the effective
inward (outward) drifts of positively (negatively) charged particles during A > 0 polarity
cycles. The analogous effect is true for A < 0 polarity cycles and the overall effect is of
such an extent that the A > 0 and A < 0 solutions are found to coincide at the highest
levels of solar activity to form a closed loop. This is a result that has never before been
achieved without having to scale down the drift coefficient to zero at solar maximum,
as was done by e.g. Ndiitwani et al. (2005). Furthermore, it is found that the drift
velocity fields associated with these two current sheet profiles lead to significant differences
in modulation even at such low levels of solar activity where no difference in the
geometries of these profiles are yet in evidence. The model is finally applied to reproduce
four observed galactic proton spectra, selected from PAMELA measurements (Adriani
et al., 2013) during the atypical solar minimum of 2006 to 2009; a new proton local interstellar
spectrum was employed. The results are found to be in accordance with that
found by other authors and in particular Vos (2011), i.e. the diffusion was required to
consistently increase from 2006 to 2009 and, in addition, the rigidity dependence below ~
3 GV was required to change over this time so that the spectra became increasingly softer.MSc (Space Physics), North-West University, Potchefstroom Campus, 2015
Books on the topic "Cosmic-ray diffusion"
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Shalchi, Andreas. Nonlinear Cosmic Ray Diffusion Theories. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7.
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Gaggero, Daniele. Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-29949-0.
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service), SpringerLink (Online, ed. Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012.
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Shalchi, Andreas. Nonlinear Cosmic Ray Diffusion Theories. Springer, 2009.
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Shalchi, Andreas. Nonlinear Cosmic Ray Diffusion Theories. Springer Berlin / Heidelberg, 2010.
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Nonlinear Cosmic Ray Diffusion Theories. Springer, 2009.
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Cosmic Ray Diffusion In The Galaxy And Diffuse Gamma Emission. Springer, 2012.
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Gaggero, Daniele. Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission. Springer, 2016.
Find full textBook chapters on the topic "Cosmic-ray diffusion"
1
Shalchi, Andreas. "The General scenario." In Nonlinear Cosmic Ray Diffusion Theories, 1–28. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_1.
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Shalchi, Andreas. "On Astrophysical Turbulence." In Nonlinear Cosmic Ray Diffusion Theories, 29–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_2.
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Shalchi, Andreas. "The Quasilinear Theory." In Nonlinear Cosmic Ray Diffusion Theories, 57–81. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_3.
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Shalchi, Andreas. "The Nonlinear Guiding Center Theory." In Nonlinear Cosmic Ray Diffusion Theories, 83–97. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_4.
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Shalchi, Andreas. "The Weakly Nonlinear Theory." In Nonlinear Cosmic Ray Diffusion Theories, 99–114. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_5.
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Shalchi, Andreas. "The Second-Order QLT." In Nonlinear Cosmic Ray Diffusion Theories, 115–34. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_6.
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Shalchi, Andreas. "The Extended Nonlinear Guiding Center Theory." In Nonlinear Cosmic Ray Diffusion Theories, 135–53. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_7.
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Shalchi, Andreas. "Applications." In Nonlinear Cosmic Ray Diffusion Theories, 155–78. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_8.
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Shalchi, Andreas. "Summary and Outlook." In Nonlinear Cosmic Ray Diffusion Theories, 179–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00309-7_9.
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Gaggero, Daniele. "Cosmic Ray Diffusion in the Galaxy." In Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission, 7–28. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-29949-0_2.
Full textConference papers on the topic "Cosmic-ray diffusion"
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Tautz, Robert. "Cosmic-ray diffusion in magnetized turbulence." In Cosmic Rays and the InterStellar Medium. Trieste, Italy: Sissa Medialab, 2015. http://dx.doi.org/10.22323/1.221.0050.
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Xu, Siyao. "Diffusion of cosmic rays in MHD turbulence." In 37th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2021. http://dx.doi.org/10.22323/1.395.0041.
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Fang, Kun, Xiao-Jun Bi, and Peng-Fei Yin. "Possible origin of the Geminga slow-diffusion halo." In 36th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2019. http://dx.doi.org/10.22323/1.358.0670.
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Giacinti, Gwenael. "Cosmic-Ray Diffusion and Galactic Magnetic Field Models." In 36th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2019. http://dx.doi.org/10.22323/1.358.0075.
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Reimer, Olaf, Ralf Kissmann, Felix Niederwanger, and Andrew W. Strong. "Anisotropic Diffusion in Galactic Cosmic Ray transport using PICARD." In 35th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2017. http://dx.doi.org/10.22323/1.301.0480.
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Brisbois, Chad, and Hao Zhou. "First Galactic Survey of Energy-Dependent Diffusion by HAWC." In 36th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2019. http://dx.doi.org/10.22323/1.358.0640.
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Ilolov, Mamadsho. "Equations of anomalous diffusion of cosmic rays." In The 34th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.236.0510.
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Kollamparambil Paul, Arun Babu, S. K. Gupta, S. R. Dugad, B. Hariharan, Y. Hayashi, P. Jagadeesan, A. Jain, et al. "Diffusion of cosmic rays in heliosphere, observations from GRAPES-3." In 35th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2017. http://dx.doi.org/10.22323/1.301.0011.
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Chirkin, Dmitry, and Martin Rongen. "Light diffusion in birefringent polycrystals and the IceCube ice anisotropy." In 36th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2019. http://dx.doi.org/10.22323/1.358.0854.
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Strauss, Du Toit, and Horst Fichtner. "On the perpendicular diffusion of solar energetic particles." In The 34th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.236.0195.
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