Cosmic-ray acceleration in young protostars

The main signature of the interaction between cosmic rays and molecular clouds is the high ionisation degree. This decreases towards the densest parts of a cloud, where star formation is expected, because of energy losses and magnetic effects. However recent observations hint to high levels of ionisation in protostellar systems, therefore leading to an apparent contradiction that could be explained by the presence of energetic particles accelerated within young protostars. Our modelling consists of a set of conditions that has to be satisfied in order to have an efficient particle acceleration through the diffusive shock acceleration mechanism. We find that jet shocks can be strong accelerators of protons which can be boosted up to relativistic energies. Another possibly efficient acceleration site is located at protostellar surfaces, where shocks caused by impacting material during the collapse phase are strong enough to accelerate protons. Our results demonstrate the possibility of accelerating particles during the early phase of a proto-Solar-like system and can be used as an argument to support available observations. The existence of an internal source of energetic particles can have a strong and unforeseen impact on the star and planet formation process as well as on the formation of pre-biotic molecules.Comment: Accepted by Astronomy and Astrophysic

Protostars: Forges of cosmic rays?

Galactic cosmic rays (CR) are particles presumably accelerated in supernova remnant shocks that propagate in the interstellar medium up to the densest parts of molecular clouds, losing energy and their ionisation efficiency because of the presence of magnetic fields and collisions with molecular hydrogen. Recent observations hint at high levels of ionisation and at the presence of synchrotron emission in protostellar systems, which leads to an apparent contradiction. We want to explain the origin of these CRs accelerated within young protostars as suggested by observations. Our modelling consists of a set of conditions that has to be satisfied in order to have an efficient CR acceleration through diffusive shock acceleration. We analyse three main acceleration sites, then we follow the propagation of these particles through the protostellar system up to the hot spot region. We find that jet shocks can be strong accelerators of CR protons, which can be boosted up to relativistic energies. Other promising acceleration sites are protostellar surfaces, where shocks caused by impacting material during the collapse phase are strong enough to accelerate CR protons. In contrast, accretion flow shocks are too weak to efficiently accelerate CRs. Though CR electrons are weakly accelerated, they can gain a strong boost to relativistic energies through re-acceleration in successive shocks. We suggest a mechanism able to accelerate both CR protons and electrons through the diffusive shock acceleration mechanism, which can be used to explain the high ionisation rate and the synchrotron emission observed towards protostellar sources. The existence of an internal source of energetic particles can have a strong and unforeseen impact on the ionisation of the protostellar disc, on the star and planet formation processes, and on the formation of pre-biotic molecules.Comment: 22 pages, 15 figures, accepted by Astronomy and Astrophysic

A Chalcidoid Egg-parasite of an Australian Buprestid

In the course of a study of the biology of the Buprestid, Prospheres aurantiopictus, Cast., in Australia, Mr. A. R. Brimblecombe has obtained from the eggs an interesting small Chalcid belonging to the family Encyrtidae. Several Encyrtid parasites of insect eggs are already known. In Australia Ovidencyrtus pallidipes, Girault, parasitises Reduviid eggs, Tetracnemella megymeni, Dodd, and T. hyalinipennis, Dodd, Pentatomid eggs, and Cheiloneurus viridiscutum, Girault, has been bred from those of cockroaches. In Hawaii the genera Ectopiognatha, Perkins, and Fulgoridicida, Perkins, are found parasitising the eggs of Homoptera. In addition Leefmansia bicolor, Waterston, has been bred from the eggs of the Orthopteron, Sexava sp., in Amboina and Leurocerus ovivorus, Crawford, from the moth, Amathusia phidippus, L., in Java. But most of the Encyrtid egg parasites belong to the genus Ooencyrtus, Ashmead, and it is among them that is placed the only other species known to breed in the eggs of a Coleopteron, Ooencyrtus batocerae, Ferrière, from Malaya. Another species, Tyndarichus rudnevi, Nowicky, is said to have been obtained from the eggs of Cerambyx cerdo, L., in Russia, but as the species of Tyndarichus are generally considered to be hyperparasites, the real parasite of this European Longicorn is still uncertai

Insectes et épidémies

Les terribles années de guerre que nous venons de traverser, avec tous les maux qu'elles ont amené, ont mis en lumière plus que jamais le rôle important des insectes dans la transmission des maladie

Stochastic and deterministic models for age-structured populations with genetically variable traits

Understanding how stochastic and non-linear deterministic processes interact is a major challenge in population dynamics theory. After a short review, we introduce a stochastic individual-centered particle model to describe the evolution in continuous time of a population with (continuous) age and trait structures. The individuals reproduce asexually, age, interact and die. The 'trait' is an individual heritable property (d-dimensional vector) that may influence birth and death rates and interactions between individuals, and vary by mutation. In a large population limit, the random process converges to the solution of a Gurtin-McCamy type PDE. We show that the random model has a long time behavior that differs from its deterministic limit. However, the results on the limiting PDE and large deviation techniques \textit{\`a la} Freidlin-Wentzell provide estimates of the extinction time and a better understanding of the long time behavior of the stochastic process. This has applications to the theory of adaptive dynamics used in evolutionary biology. We present simulations for two biological problems involving life-history trait evolution when body size is plastic and individual growth is taken into account.Comment: This work is a proceeding of the CANUM 2008 conferenc

On the vertical equilibrium of the local Galactic disk and the search for disk dark matter

Estimates of the dynamical surface mass density at the solar Galactocentric distance are commonly derived assuming that the disk is in vertical equilibrium with the Galactic potential. This assumption has recently been called into question, based on the claim that the ratio between the kinetic and the gravitational energy in such solutions is a factor of 3 larger than required if Virial equilibrium is to hold. Here we show that this ratio between energies was overerestimated and that the disk solutions are likely to be in Virial equilibrium after all. We additionally demonstrate, using one-dimensional numerical simulations, that the disks are indeed in equilibrium. Hence, given the uncertainties, we find no reason to cast doubt on the steady-state solutions which are traditionally used to measure the matter density of the disk.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter

Stuck in the middle with you: the political position of teachers during the Algerian War of Independence

Teachers stand out amongst civil servants by virtue of their embedded position within governed communities, their moral authority within those communities, and the relative autonomy of their work. This paper investigates the political position of teachers in Algeria during the War of Independence from France (1954-62). Although teachers were agents of the French state, and active in facilitating French governance in Algeria, they were regarded with deep suspicion by the French security services, and subjected to a sustained surveillance and repression campaign from the very first months of the war. Teachers were caught in a no-man’s land between the French State, which employed them, and the nascent Algerian nation, whose children they cared for in the classroom. Based on oral history interviews with former teachers, the study of recently declassified public archives in France and Algeria, and a critical engagement with educational research on teachers working in disenfranchised communities, this paper investigates the difficult, and often dangerous, position teachers found themselves in as a result of the war. We examine the routine military incursions into schools by the French army, arrests and assaults of teachers, and how teachers sought to balance their duties of service to education with their political resistance to colonialism. However, we also recognise the heterogeneity of the teaching corps, and the relevance of this factor regarding relations between teachers and members of the armed forces. The data collected for this study indicates strong disparities in the campaign against teachers, depending on region, the teacher’s ethnicity, and on the type of school they worked in. Finally, we use this research as a case study to discuss the tensions which can arise between the right and the left hands of state within a situation of armed conflict

The Stac Fada “impact ejecta” layer: not what it seems

The Stac Fada Member (SFM) forms part of the Stoer Group of the Torridonian of NW Scotland. The SFM is unique in the Torridonian, being characterized by the presence of greenish altered glass clasts. Its origin has been debated for decades with several hypotheses being proposed but all invoking some connection with volcanic activity in the region. More recently, Amor et al. suggested that the SFM represents “a chord section through the continuous ejecta blanket surrounding an impact crater”. Here, we confirm the presence of shocked material within the SFM and then discuss its origin