1,142 research outputs found
Hubble-Lema\^itre fragmentation and the path to equilibrium of merger-driven cluster formation
This paper discusses a new method to generate self-coherent initial
conditions for young substructured stellar cluster. The expansion of a uniform
system allows stellar sub-structures (clumps) to grow from fragmentation modes
by adiabatic cooling. We treat the system mass elements as stars, chosen
according to a Salpeter mass function, and the time-evolution is performed with
a collisional N-body integrator. This procedure allows to create a
fully-coherent relation between the clumps' spatial distribution and the
underlying velocity field. The cooling is driven by the gravitational field, as
in a cosmological Hubble-Lema\^itre flow. The fragmented configuration has a
`fractal'-like geometry but with a self-grown velocity field and mass profile.
We compare the characteristics of the stellar population in clumps with that
obtained from hydrodynamical simulations and find a remarkable correspondence
between the two in terms of the stellar content and the degree of spatial
mass-segregation. In the fragmented configuration, the IMF power index is ~0.3
lower in clumps in comparison to the field stellar population, in agreement
with observations in the Milky Way. We follow in time the dynamical evolution
of fully fragmented and sub-virial configurations, and find a soft collapse,
leading rapidly to equilibrium (timescale of 1 Myr for a ~ 10^4 Msun system).
The low-concentration equilibrium implies that the dynamical evolution
including massive stars is less likely to induce direct collisions and the
formation of exotic objects. Low-mass stars already ejected from merging clumps
are depleted in the end-result stellar clusters, which harbour a top-heavy
stellar mass function.Comment: 22 pages, accepted for publication in MNRA
A search for passive protoplanetary disks in the Taurus-Auriga star-forming region
We conducted a 12-month monitoring campaign of 33 T Tauri stars (TTS) in
Taurus. Our goal was to monitor objects that possess a disk but have a weak
Halpha line, a common accretion tracer for young stars, to determine whether
they host a passive circumstellar disk. We used medium-resolution optical
spectroscopy to assess the objects' accretion status and to measure the Halpha
line. We found no convincing example of passive disks; only transition disk and
debris disk systems in our sample are non-accreting. Among accretors, we find
no example of flickering accretion, leading to an upper limit of 2.2% on the
duty cycle of accretion gaps assuming that all accreting TTS experience such
events. Combining literature results with our observations, we find that the
reliability of traditional Halpha-based criteria to test for accretion is high
but imperfect, particularly for low-mass TTS. We find a significant correlation
between stellar mass and the full width at 10 per cent of the peak (W10%) of
the Halpha line that does not seem to be related to variations in free-fall
velocity. Finally, our data reveal a positive correlation between the Halpha
equivalent width and its W10%, indicative of a systematic modulation in the
line profile whereby the high-velocity wings of the line are proportionally
more enhanced than its core when the line luminosity increases. We argue that
this supports the hypothesis that the mass accretion rate on the central star
is correlated with the Halpha W10% through a common physical mechanism.Comment: accepted for publication in MNRAS; 26 pages, 9 figures, 3 table
Cosmic-ray electron transport in the galaxy M 51
Context. Indirect observations of the cosmic-ray electron (CRE) distribution
via synchrotron emission is crucial for deepening the understanding of the CRE
transport in the interstellar medium, and in investigating the role of galactic
outflows.
Aims. In this paper, we quantify the contribution of diffusion- and
advection-dominated transport of CREs in the galaxy M51 considering relevant
energy loss processes.
Methods. We used recent measurement from M 51 that allow for the derivation
of the diffusion coefficient, the star formation rate, and the magnetic field
strength. With this input, we solved the 3D transport equation numerically
including the spatial dependence as provided by the measurements, using the
open-source transport framework CRPropa (v3.1). We included 3D transport
(diffusion and advection), and the relevant loss processes.
Results. We find that the data can be described well with the parameters from
recent measurements. For the best fit, it is required that the wind velocity,
following from the observed star formation rate, must be decreased by a factor
of 5. We find a model in which the inner galaxy is dominated by advective
escape and the outer galaxy is composed by both diffusion and advection.
Conclusions. Three-dimensional modelling of cosmic-ray transport in the
face-on galaxy M51 allows for conclusions about the strength of the outflow of
such galaxies by quantifying the need for a wind in the description of the
cosmic-ray signatures. This opens up the possibility of investigating galactic
winds in face-on galaxies in general.Comment: 6 pages, 7 figure
Cosmological constraints on multi-interacting dark matter
The increasingly significant tensions within CDM, combined with the
lack of detection of dark matter (DM) in laboratory experiments, have boosted
interest in non-minimal dark sectors, which are theoretically well-motivated
and inspire new search strategies for DM. Here we consider, for the first time,
the possibility of DM having simultaneous interactions with photons, baryons,
and dark radiation (DR). We have developed a new and efficient version of the
Boltzmann code CLASS that allows for one DM species to have multiple
interaction channels. With this framework we reassess existing cosmological
bounds on the various interaction coefficients in multi-interacting DM
scenarios. We find no clear degeneracies between these different interactions
and show that their cosmological effects are largely additive. We further
investigate the possibility of these models to alleviate the cosmological
tensions, and find that the combination of DM-photon and DM-DR interactions can
at the same time reduce the tension (from to ) and
the tension (from to ). The public release of our
code will pave the way for the study of various rich dark sectors.Comment: 41 pages, 8 figures, 5 tables. Comments are welcom
CMB photons shedding light on dark matter
The annihilation or decay of Dark Matter (DM) particles could affect the
thermal history of the universe and leave an observable signature in Cosmic
Microwave Background (CMB) anisotropies. We update constraints on the
annihilation rate of DM particles in the smooth cosmological background, using
WMAP7 and recent small-scale CMB data. With a systematic analysis based on the
Press-Schechter formalism, we also show that DM annihilation in halos at small
redshift may explain entirely the reionization patterns observed in the CMB,
under reasonable assumptions concerning the concentration and formation
redshift of halos. We find that a mixed reionization model based on DM
annihilation in halos as well as star formation at a redshift z~6.5 could
simultaneously account for CMB observations and satisfy constraints inferred
from the Gunn-Peterson effect. However, these models tend to reheat the
inter-galactic medium (IGM) well above observational bounds: by including a
realistic prior on the IGM temperature at low redshift, we find stronger
cosmological bounds on the annihilation cross-section than with the CMB alone.Comment: 35 pages, 14 figures; version accepted in JCAP after minor revision
Diet pattern and variations of Ocellated Lizard Timon lepidus in a Mediterranean steppe area (Crau plain, France)
The diet of Ocellated Lizard, a reptile considered as vulnerable in Europe, was
studied in a protected area containing one of the most important French populations of the species. It aims
to describe diet composition and its temporal variation but also to identify differences between age classes.
A sample of 221 scats was collected from May to September 2010 in seven different sites of the studied
area (Crau plain, France). From the 4029 items analysed, 156 taxa were identified. The diet is composed by
Coleoptera (26.7 %), Orthoptera (23 %), Hymenoptera (19.3 %) and fruits (17.1 %). Dung beetles represent
only 2.1 % of Coleoptera prey, which is surprising for such a heavily grazed area. The diet composition is different
from one month to another (Ï2 = 943.173, df = 20, p < 0.001) and differences between age classes exist
(V = 572, p < 0.001). Adult lizards eat more fruits than juveniles in August (Ï2 = 80.349, df = 1, p < 0.001). The
prey richness is not different between adults and juveniles (ZÂ = 1.839, p > 0.05). Finally, diet characteristics in
the Crau plain are discussed and compared to other Iberian and French Ocellated Lizard populationsNous avons étudié le régime alimentaire du Lézard ocellé, espÚce considérée comme vulnérable en Europe, sur un espace naturel protégé abritant une des plus importantes populations françaises. Nous proposons de décrire la
composition et les variations saisonniÚres du régime alimentaire dans la Réserve naturelle de Crau, et d'identifier les différences entre les classes d'ùge. Un échantillon de 221 fÚces a été récolté entre mai et septembre 2010 sur sept localités de la zone d'étude. Les 4029 proies et restes
végétaux analysés ont permis d'identifier 156 taxons différents. Le régime se compose de ColéoptÚres (26,7 %), d'OrthoptÚres (23 %), d'HyménoptÚres (19,3 %) et de fruits (17,1 %). Les ColéoptÚres coprophages ne représentent que 2,1 % de tous les ColéoptÚres consommés, ce qui est surprenant
pour un site aussi fortement pĂąturĂ©. Il existe une variation saisonniĂšre de la composition (ÏÂČ = 943,173, df = 20, p < 0,001) mais aussi selon la classe d'Ăąge (V = 572, p < 0,001). Les adultes consomment beaucoup plus de fruits au mois d'aoĂ»t que les juvĂ©niles (ÏÂČ = 80,349, df = 1,
p 0,05). Les particularités de la Crau sont discutées et comparées aux autres études existantes dans la péninsule ibérique et en France
Inhibitors of the Cellular Trafficking of Ricin
Throughout the last decade, efforts to identify and develop effective inhibitors of the ricin toxin have focused on targeting its N-glycosidase activity. Alternatively, molecules disrupting intracellular trafficking have been shown to block ricin toxicity. Several research teams have recently developed high-throughput phenotypic screens for small molecules acting on the intracellular targets required for entry of ricin into cells. These screens have identified inhibitory compounds that can protect cells, and sometimes even animals against ricin. We review these newly discovered cellular inhibitors of ricin intoxication, discuss the advantages and drawbacks of chemical-genetics approaches, and address the issues to be resolved so that the therapeutic development of these small-molecule compounds can progress
A cornucopia of diversityâRanunculales as a model lineage
The Ranunculales are a hyperdiverse lineage in many aspects of their phenotype, including growth habit, floral and leaf morphology, reproductive mode, and specialized metabolism. Many Ranunculales species, such as opium poppy and goldenseal, have a high medicinal value. In addition, the order includes a large number of commercially important ornamental plants, such as columbines and larkspurs. The phylogenetic position of the order with respect to monocots and core eudicots and the diversity within this lineage make the Ranunculales an excellent group for studying evolutionary processes by comparative studies. Lately, the phylogeny of Ranunculales was revised, and genetic and genomic resources were developed for many species, allowing comparative analyses at the molecular scale. Here, we review the literature on the resources for genetic manipulation and genome sequencing, the recent phylogeny reconstruction of this order, and its fossil record. Further, we explain their habitat range and delve into the diversity in their floral morphology, focusing on perianth organ identity, floral symmetry, occurrences of spurs and nectaries, sexual and pollination systems, and fruit and dehiscence types. The Ranunculales order offers a wealth of opportunities for scientific exploration across various disciplines and scales, to gain novel insights into plant biology for researchers and plant enthusiasts alike
UMAN â a pluralistic view of uncertainty management
Decisions associated with Radioactive Waste (RW) Management programmes are made in the presence of irreducible and reducible uncertainties. Responsibilities and roles of each actor, the nature of the RW disposal programme and the stage in its implementation influence the preferences of each category of actors in approaching uncertainty management. UMAN (UMAN â Uncertainties Management Multi-Actor Network is a Work Package of the European Radioactive Waste Management Programme â EURAD) carries out a strategic study about the management of uncertainties based on extended exchanges among actors representing Waste Management Organisations, Technical Support Organisations, Research Entities and Civil Society, a review of knowledge generated by past and ongoing R&D projects, and findings of international organisations. UMAN discusses the classification schemes and approaches applied in uncertainty management, and identifies possible actions to be considered in the uncertainty treatment. The relevance for the safety of the uncertainties associated with waste inventory, including spent fuel, near-field, site and geosphere and human aspects, as perceived by each type of actors, and approaches used in their management are explored with the aim to reach either a common understanding on how uncertainties relate to risk and safety and how to deal with them along the programme implementation, or at least arrive at a mutual understanding of each individual view. Finally, uncertainties assessed as highly significant and the associated R&D issues that can be further investigated are being identified
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