Diffusion and drift of cosmic rays in highly turbulent magnetic fields

We determine numerically the parallel, perpendicular, and antisymmetric diffusion coefficients for charged particles propagating in highly turbulent magnetic fields, by means of extensive Monte Carlo simulations. We propose simple expressions, given in terms of a small set of fitting parameters, to account for the diffusion coefficients as functions of magnetic rigidity and turbulence level, and corresponding to different kinds of turbulence spectra. The results obtained satisfy scaling relations, which make them useful for describing the cosmic ray origin and transport in a variety of different astrophysical environments.Instituto de Física La Plat

Rigidity dependent knee and cosmic ray induced high energy neutrino fluxes

Scenarios in which the knee of the cosmic ray spectrum depends on the particle rigidities usually predict that the cosmic ray composition becomes heavier above the knee and have associated a change in the spectral slope of each individual nuclear component which is steeper than the change (Δα≃0.3) observed in the total spectrum. We show that this implies that the very high energy (Eν>1014 eV) diffuse neutrino fluxes produced by cosmic rays hitting the atmosphere or colliding with the interstellar medium in the Galaxy will be significantly suppressed, making their detection harder but also reducing the background for the search of other (more challenging) astrophysical neutrino sources.Facultad de Ciencias Exacta

Cosmic ray photodisintegration and the knee of the spectrum

We explore in some detail the scenario proposed to explain the observed knee of the cosmic ray (CR) spectrum as due to the effects of photodisintegration of the CR nuclei by interactions with optical and soft UV photons in the source region. We show that the photon column densities needed to explain the experimental data are significantly lower than those obtained in previous estimations which neglected multinucleon emission in the photodisintegration process. We also treat more accurately the photodisintegration thresholds, we discuss the effects of photopion production processes and the neutron escape mechanism, identifying the physical processes responsible for the qualitative features of the results. This scenario would require the CR nuclei to traverse column densities of $\sim 5 \times 10^{27}- 2 \times 10^{28}$ eV/cm$^2$ after being accelerated in order to reproduce the observed knee, and predicts that the CR composition should become lighter above $\sim 10^{16}$ eV.Comment: 17 pp. Comments and references added. To appear in Astroparticle Physic

Cosmic ray spectrum and anisotropies from the knee to the second knee

We consider the scenario in which the knee in the cosmic ray spectrum is due to a change in the escape mechanism of cosmic rays from the Galaxy from one dominated by transverse diffusion to one dominated by drifts. We show that this scenario explains not only the changes in spectral slope at the knee and at the second knee, but can also account for the main characteristics of the observed energy-dependent anisotropy amplitude and phase of first harmonic in the energy range between 10¹⁵ and 10¹⁸ eV. This provides a useful handle to distinguish this diffusion/drift model from other scenarios proposed to explain the knee in the spectrum.Facultad de Ciencias Exacta

Cosmic ray drift, the second knee and galactic anisotropies

We show that the second knee in the cosmic ray spectrum (i.e. the steepening occurring at E ≃ 4 × 10¹⁷ eV) could be related to drift effects affecting the heaviest nuclear component, the iron group nuclei, in a scenario in which the knee at 3 × 10¹⁵ eV indicates the onset of drift effects in the lighter proton component. We also study the anisotropies resulting from diffusion and drift currents in the Galaxy, showing their potential relevance to account for the AGASA observations at E ~ 10¹⁸ eV, before the extragalactic component becomes dominant.Facultad de Ciencias Exacta

Las matemáticas, su enseñanza y aprendizaje: concepciones de futuros profesores en formación

Los propósitos del estudio fueron analizar las concepciones que estudiantes de primer año y quinto año de una escuela de formación de profesores de matemáticas manifiestan hacia lo que es la ciencia matemática, la utilidad de la matemática y los procesos de enseñanza y aprendizaje; para ello se adoptó un enfoque metodológico cuantitativo con diseño no experimental del tipo encuesta. El análisis de los datos se realizó a través del programa estadístico PSPP y las técnicas utilizadas fueron principalmente estadístico-descriptivos de tendencia central (media) y dispersión (desviación típica), cálculo de frecuencias, porcentajes y la prueba t para la comparación de medias entre grupos. Los resultados generales dan cuenta de una alta valoración hacia la matemática como ciencia que ayuda en el transcurso de nuestra vida a la solución de problemas cotidianos y su relación con las artes y la música. Así mismo los estudiantes valoran las actividades matemáticas que apelan a la motivación y la conexión con situaciones reales. Se encontraron diferencias significativas en los reactivos asociados al uso de reglas y operaciones en la matemática, en el valor formativo cultural e histórico de la matemática y en aquellas actividades matemáticas que desarrollan ejercicios y destrezas

Turbulent diffusion and drift in galactic magnetic fields and the explanation of the knee in the cosmic ray spectrum

We reconsider the scenario in which the knee in the cosmic ray spectrum is explained as due to a change in the escape mechanism of cosmic rays from the galaxy from one dominated by transverse diffusion to one dominated by drifts. We solve the diffusion equations adopting realistic galactic field models and using diffusion coefficients appropriate for strong turbulence (with a Kolmogorov spectrum of fluctuations) and consistent with the assumed magnetic fields. We show that properly taking into account these effects leads to a natural explanation of the knee in the spectrum, and a transition towards a heavier composition above the knee is predicted.Facultad de Ciencias Exacta

miRNA nanoencapsulation to regulate the programming of the blood-brain barrier permeability by hipoxia.

Central nervous system (CNS)-related diseases are difficult to treat as most therapeutic agents they cannot reach the brain tissue, mainly due to the blood-brain barrier (BBB), arguably the tightest barrier between the human body and cerebral parenchyma, which routinely excludes most xenobiotic therapeutics compounds. The BBB is a multicellular complex that structurally forms the neurovascular unit (NVU) and is organized by neuro-endothelial and glial cells. BBB breakdown and dysfunction from the cerebrovascular cells lead to leakages of systemic components from the blood into the CNS, contributing to neurological deficits. Understanding the molecular mechanisms that regulate BBB permeability and disruption is essential for establishing future therapeutic strategies to restore permeability and improve cerebrovascular health. MicroRNAs (miRNAs), a type of small noncoding RNAs, are emerging as an important regulator of BBB integrity by modulating gene expression by targeting mRNA transcripts. miRNAs is implicated in the development and progression of various illnesses. Conversely, nanoparticle carriers offer unprecedented opportunities for cell-specific controlled delivery of miRNAs for therapeutic purposes. In this sense, we present in this graphical review critical evidence in the regulation of cell junction expression mediated by miRNAs induced by hypoxia and for the use of nanoparticles for the delivery of miRNA-based therapeutics in the treatment of BBB permeability

Diffusion and drift of cosmic rays in highly turbulent magnetic fields

We determine numerically the parallel, perpendicular, and antisymmetric diffusion coefficients for charged particles propagating in highly turbulent magnetic fields, by means of extensive Monte Carlo simulations. We propose simple expressions, given in terms of a small set of fitting parameters, to account for the diffusion coefficients as functions of magnetic rigidity and turbulence level, and corresponding to different kinds of turbulence spectra. The results obtained satisfy scaling relations, which make them useful for describing the cosmic ray origin and transport in a variety of different astrophysical environments.Comment: 17 pages, 7 figure