Possible Contribution to Electron and Positron Fluxes from Pulsars and their Nebulae

The AMS-02 experiment confirms the excess of positrons in cosmic rays (CRs) for energy above 10 GeV with respect to the secondary production of positrons in the interstellar medium. This is interpreted as evidence of the existence of a primary source of these particles. Possible candidates are dark matter or astrophysical sources. In this work we discuss the possible contribution due to pulsars and their nebulae. Our key assumption is that the primary spectrum of electrons and positrons at the source is the same of the well known photon spectrum observed from gamma-rays telescopes. Using a diffusion model in the Galaxy we propagate the source spectra up to the Solar System. We compare our results with the recent experiments and with the LIS modelComment: To appear in the Proceedings of the 14th ICATPP Conference, Villa Olmo 23-27 September 201

Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X

We investigate, in terms of production from pulsars and their nebulae, the cosmic ray positron and electron fluxes above $\sim10$ GeV, observed by the AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from the gamma-ray photon spectrum of the source, generated via synchrotron and inverse Compton processes, we estimated the electron and positron injection spectra. Several features are fixed from observations of Vela-X and unknown parameters are borrowed from the Crab nebula. The particle spectra produced in the pulsar wind nebula are then propagated up to the Solar System, using a diffusion model. Differently from previous works, the omnidirectional intensity excess for electrons and positrons is obtained as a difference between the AMS-02 data and the corresponding local interstellar spectrum. An equal amount of electron and positron excess is observed and we interpreted this excess (above $\sim$100 GeV in the AMS-02 data) as a supply coming from Vela-X. The particle contribution is consistent with models predicting the gamma-ray emission at the source. The input of a few more young pulsars is also allowed, while below $\sim$100 GeV more aged pulsars could be the main contributors.Comment: Accepted for publication in Journal of High Energy Astrophysics (2015

NIEL Dose Dependence for Solar Cells Irradiated with Electrons and Protons

The investigation of solar cells degradation and the prediction of its end-of-life performance is of primary importance in the preparation of a space mission. In the present work, we investigate the reduction of solar-cells' maximum power resulting from irradiations with electrons and protons. Both GaAs single junction and GaInP/GaAs/Ge triple junction solar cells were studied. The results obtained indicate how i) the dominant radiation damaging mechanism is due to atomic displacements, ii) the relative maximum power degradation is almost independent of the type of incoming particle, i.e., iii) to a first approximation, the fitted semi-empirical function expressing the decrease of maximum power depends only on the absorbed NIEL dose, and iv) the actual displacement threshold energy value (Ed=21 eV) accounts for annealing treatments, mostly due to self-annealing induced effects. Thus, for a given type of solar cell, a unique maximum power degradation curve can be determined as a function of the absorbed NIEL dose. The latter expression allows one to predict the performance of those solar cells in space radiation environment.Comment: To appear on the Proceedings of the 13th ICATPP Conference on Astroparticle, Particle, Space Physics and Detectors for Physics Applications, Villa Olmo (Como, Italy), 23--27 October, 2013, to be published by World Scientific (Singapore

Optimal-constraint lexicons for requirements specifications

Constrained Natural Languages (CNLs) are becoming an increasingly popular way of writing technical documents such as requirements specifications. This is because CNLs aim to reduce the ambiguity inherent within natural languages, whilst maintaining their readability and expressiveness. The design of existing CNLs appears to be unfocused towards achieving specific quality outcomes, in that the majority of lexical selections have been based upon lexicographer preferences rather than an optimum trade-off between quality factors such as ambiguity, readability, expressiveness, and lexical magnitude. In this paper we introduce the concept of 'replaceability' as a way of identifying the lexical redundancy inherent within a sample of requirements. Our novel and practical approach uses Natural Language Processing (NLP) techniques to enable us to make dynamic trade-offs between quality factors to optimise the resultant CNL. We also challenge the concept of a CNL being a one-dimensional static language, and demonstrate that our optimal-constraint process results in a CNL that can adapt to a changing domain while maintaining its expressiveness. © Springer-Verlag Berlin Heidelberg 2007

Nuclear and Non-Ionizing Energy-Loss for Coulomb Scattered Particles from Low Energy up to Relativistic Regime in Space Radiation Environment

In the space environment, instruments onboard of spacecrafts can be affected by displacement damage due to radiation. The differential scattering cross section for screened nucleus--nucleus interactions - i.e., including the effects due to screened Coulomb nuclear fields -, nuclear stopping powers and non-ionization energy losses are treated from about 50 keV/nucleon up to relativistic energies.Comment: Accepted for publication in the Proceedings of the ICATPP Conference on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo (Como, Italy), 7--8 October, 2010, to be published by World Scientifi

Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction

We implemented a quasi time-dependent 2D stochastic model of solar modulation describing the transport of cosmic rays (CR) in the heliosphere. Our code can modulate the Local Interstellar Spectrum (LIS) of a generic charged particle (light cosmic ions and electrons), calculating the spectrum at 1AU. Several measurements of CR antiparticles have been performed. Here we focused our attention on the CR antiproton component and the antiproton over proton ratio. We show that our model, using the same heliospheric parameters for both particles, fit the observed anti-p/p ratio. We show a good agreement with BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment

Magnetospheric transmission function approach to disentangle primary from secondary cosmic ray fluxes in the penumbra region

[1] The AMS-01 observations (in June 1998, on board the space shuttle orbiter Discovery) have shown the presence of primary (PCR) and secondary (SCR) cosmic rays (most of them protons) at a low Earth orbit (about 400 km altitude). The SCRs are mostly created in interactions with the atmosphere by fast PCRs and can be trapped or become reentrant albedo particles. Some of them seem to be sufficiently energetic to populate the "penumbra region" above the local geomagnetic cutoff rigidity. A backtracking procedure of simulated protons entering the AMS-01 spectrometer has provided the fraction of allowed (and hence forbidden) trajectories of PCRs. Consequently, it has allowed the determination of the so-called transmission function (TF) which is able to describe the properties of the PCR transport from the Earth's magnetopause (i.e., the primary spectrum at 1 AU) to the atmosphere and finally the fluxes of the PCRs in the ten geomagnetic regions for AMS-01 observations. In the penumbra regions, the observed spectra of the AMS-01 geomagnetic regions have been found to be larger than those predicted for the PCRs in the penumbra region by means of the TF, i.e., some SCRs (mainly reentrant albedo protons) are also found to populate the rigidity regions above the local geomagnetic cutoff rigidity. The fraction of the secondary to overall particle flux in the penumbra region increases gradually as the geomagnetic latitude increases