Study of material activation in nanosatellites for gamma-ray astrophysics

For satellite gamma astrophysics, new missions have been proposed to investigate the Compton regime. The predecessors demonstrated as material activation is an important problem at these energies, because of the irradiation received from cosmic rays. We have quantified the material activation in a nanosatellite Compton in LEO with some Monte Carlo simulations. In this work we focused on primary protons, estimating the produced radioisotopes and in particular those that give gamma rays in out energetic range.ope

Features of narrative language in fluent aphasia

Fluent aphasia is a disorder affecting linguistic processing in persons who suffered a brain damage. It is a syndrome gathering several typologies of aphasia and is less severe than a non-fluent aphasia. Indeed, patients suffering from fluent aphasia experience minor difficulties: normally, they are still able to produce complete and informative sentences. However, they are often affected at semantic level, therefore they face impairments in lexical retrieval. Interestingly, these difficulties affecting the microlinguistic dimension of language, may also lead to impairments at macrolinguistic level. For instance, in a group of patients with anomic aphasia, the lexical impairment was related to a significative higher percentage of global coherence errors with respect to healthy controls (Andreetta et al., 2012). The aim of the present study is investigating the linguistic skills of a group of individuals with fluent aphasia. The assessment is focused on narrative discourse since evidence showed that spontaneous discourse can provide more information than classical standardized tests for aphasia. In particular, I used a multi-level approach gathering quantitative and functional measures of narrative analysis (Marini et al., 2011). Forty individuals participated in the study. They were divided into two groups: twenty persons with fluent aphasia made up the experimental group, and twenty healthy individuals made up the control group. The group of persons with fluent aphasia produced narratives with a comparable number of words but with a lowered speech rate, a reduced mean length of utterances and a higher percentage of both phonological and semantic errors with respect to healthy controls. Also the percentage of complete sentences was reduced in persons with aphasia. At macrolinguistic level persons with aphasia significantly produced more errors of cohesion and of both local and global coherence. Furthermore, a significative difference was found also for thematic informativeness. A further analysis investigated the grammatical skills and the errors of global coherence committed by persons with aphasia. A bivariate correlational analysis showed a strong correlation between the percentage of words and the percentage of tangential utterances, and between the production of semantic paraphasias and filler utterances. These correlations suggest that semantic processing is related to the macrolinguistic level. Indeed, the first result indicates that the comparable number of words produced by the two groups isn\u2019t comparable from the informative point of view; the second result indicates that the difficulty in lexical retrieval influences the production of both semantic errors and lexical fillers. Lexical fillers in particular are a strategy to cope with their difficulty. Another bivariate correlation analysis was used to observe the clinical implications of the multi-level approach. These analyses were based on the potential interrelations between narrative measures and subtests of the Aachener Aphasie Test. Several measures significantly correlate, indicating that the multi-level approach is a valid instrument for the clinical practice as it provides complete information of the linguistic impairments in persons with aphasia. This thesis also constitutes the Italian contribution of an international multimedia database for aphasia: AphasiaBank. AphasiaBank is an American project which aims at collecting data about the spontaneous speech in persons with aphasia. Spontaneous speech is elicited through interviews between researchers and persons with aphasia. The project aims at collecting data in several languages. Ten of the persons with aphasia participating in this study were videorecorded during test sessions and transcriptions were also made according to AphasiaBank instructions. Their performance then, will be soon at disposal in the official website of the project (http://talkbank.org/AphasiaBank/)

Measuring the elemental composition of asteroids with a Compton telescope

Element composition of Solar system objects can be studied with remote spectroscopy. We evaluate gamma-ray spectroscopy in the Compton regime to analyse the surface composition of an asteroid. We simulate one month of observation of a near-Earth asteroid from an orbiting satellite. We analyse characteristic lines coming from the Fe and Si to evalutate elemental abundances in the target. We compare the performances of three different instruments: a Compton tracking camera, a Compton non-tracking camera and a simple scintillator system. All the three detectors reveal the presence of Fe and Si, but with different sensitivity. Rare precious metals in the Pt family, instead, cannot be detected by our instruments