1,613 research outputs found
The intermediate neutron capture process: IV. Impact of nuclear model and parameter uncertainties
We investigate both the systematic and statistical uncertainties associated
with theoretical nuclear reaction rates of relevance during the i-process and
explore their impact on the i-process elemental production, and subsequently on
the surface enrichment, for a low-mass low-metallicity star during the early
AGB phase. We use the TALYS reaction code (Koning et al. 2023) to estimate both
the model and parameter uncertainties affecting the photon strength function
and the nuclear level densities, hence the radiative neutron capture rates. The
STAREVOL code (Siess et al. 2006) is used to determine the impact of nuclear
uncertainties on the i-process nucleosynthesis in a 1 [Fe/H] = -
2.5 model star during the proton ingestion event in the early AGB phase. A
large nuclear network of 1160 species coherently coupled to the transport
processes is solved to follow the i-process nucleosynthesis. We find that the
non-correlated parameter uncertainties lead the surface abundances
uncertainties of element with to range between 0.5 and 1.0 dex, with
odd- elements displaying higher uncertainties. The correlated model
uncertainties are of the same order of magnitude, and both model and parameter
uncertainties have an important impact on potential observable tracers such as
Eu and La. Both the correlated model and uncorrelated parameter uncertainties
need to be estimated coherently before being propagated to astrophysical
observables through multi-zone stellar evolution models. Many reactions are
found to affect the i-process predictions and will require improved nuclear
models guided by experimental constraints. Priority should be given to the
reactions influencing the observable tracers.Comment: Accepted: October 11, 2023 \\ 14 Pages, 14 Figures, 2 Table
The intermediate neutron capture process. V. The i-process in AGB stars with overshoot
The intermediate neutron capture process (i-process) can develop during
proton ingestion events (PIE), potentially during the early stages of low-mass
low-metallicity asymptotic giant branch (AGB) stars. We examine the impact of
overshoot mixing on the triggering and development of i-process nucleosynthesis
in AGB stars of various initial masses and metallicities. We computed AGB
stellar models, with initial masses of 1, 2, 3, and 4 M and
metallicities in the [Fe/H] range, using the stellar
evolution code STAREVOL with a network of 1160 nuclei coupled to the transport
equations. We considered different overshooting profiles below and above the
thermal pulses, and below the convective envelope. The occurrence of PIEs is
found to be primarily governed by the amount of overshooting at the top of
pulse () and to increase with rising . For 0, 0.02, 0.04, and 0.1, we find that 0 %, 6 %, 24 %, and 86 % of our 21
AGB models with [Fe/H] experience a PIE, respectively. We also find
that PIEs leave a C-pocket at the bottom of the pulse that can give rise
to an additional radiative s-process nucleosynthesis, and ultimately produce a
noticeable mixed i+s chemical signature at the surface. Finally, the chemical
abundance patterns of 22 observed r/s-stars candidates with [Fe/H]
are found to be in reasonable agreement with our AGB model predictions. The
binary status of the dwarfs/giants being unclear, we suggest that these stars
have acquired their chemical pattern either from the mass transfer of a
now-extinct AGB companion or from an early generation AGB star that polluted
the natal cloud. Stricter constraints from multi-dimensional hydrodynamical
models on overshoot coefficients could deliver new insights into the
contribution of AGB stars to heavy elements in the Universe.Comment: 21 pages, 15 figures, accepted in A&
Model Predictive Path Integral Control Framework for Partially Observable Navigation: A Quadrotor Case Study
Recently, Model Predictive Path Integral (MPPI) control algorithm has been
extensively applied to autonomous navigation tasks, where the cost map is
mostly assumed to be known and the 2D navigation tasks are only performed. In
this paper, we propose a generic MPPI control framework that can be used for 2D
or 3D autonomous navigation tasks in either fully or partially observable
environments, which are the most prevalent in robotics applications. This
framework exploits directly the 3D-voxel grid acquired from an on-board sensing
system for performing collision-free navigation. We test the framework, in
realistic RotorS-based simulation, on goal-oriented quadrotor navigation tasks
in a cluttered environment, for both fully and partially observable scenarios.
Preliminary results demonstrate that the proposed framework works perfectly,
under partial observability, in 2D and 3D cluttered environments.Comment: The withdrawal reason is that the co-authors do not want to associate
their name to the article on arXi
Development of a TE011 Cavity for Thin-Films Study
Bulk niobium cavities have almost reached their maximum performances. Maximum accelerating gradient field is above 35-40 MV/m for a multi-cells cavity at 1.8 Kelvin and it achieves 25-30 MV/m with high reliability. The question of increasing the accelerating gradient in a significant way is running regarding the huge amount of units required for new projects (16000 units for ILC). A promising solution is to use thin films of new materials deposited on copper or niobium. In order to investigate the behaviour of these materials for the accelerating cavities, we have developed a dedicated setup based on thermometric method and a TE011 cavity. We present here the design study of the setup and the expected sensitivity of the method for the surface measurement of materials properties under RF fields
Very Massive Star Models: I. Impact of Rotation and Metallicity and Comparisons with Observations
In addition to being spectacular objects, Very Massive Stars (VMS) are
suspected to have a tremendous impact on their environment and on the whole
cosmic evolution. The nucleosynthesis both during their advanced stages and
their final explosion may contribute greatly to the overall enrichment of the
Universe. Their resulting supernovae are candidates for the most superluminous
events and their extreme conditions also lead to very important radiative and
mechanical feedback effects, from local to cosmic scale. We explore the impact
of rotation and metallicity on the evolution of very massive stars across
cosmic times. With the recent implementation of an equation of state in the
GENEC stellar evolution code, appropriate for describing the conditions in the
central regions of very massive stars in the advanced phases, we present new
results on VMS evolution from Population III to solar metallicity. Low
metallicity VMS models are highly sensitive to rotation, while the evolution of
higher metallicity models is dominated by mass loss effects. The mass loss
affects strongly their surface velocity evolution, breaking quickly at high
metallicity while reaching the critical velocity for low metallicity models.
The comparison to observed VMS in the LMC shows that the mass loss
prescriptions used for these models are compatible with observed mass loss
rates. In our framework for modelling rotation, our models of VMS need a high
initial velocity to reproduce the observed surface velocities. The surface
enrichment of these VMS is difficult to explain with only one initial
composition, and could suggest multiple populations in the R136 cluster. At a
metallicity typical of R136, only our non- or slowly rotating VMS models may
produce Pair Instability supernovae. The most massive black holes that can be
formed are less massive than about 60 M.Comment: 13 pages, 11 figure
Hyperasymptotic solutions for certain partial differential equations
We present the hyperasymptotic expansions for a certain group of solutions of
the heat equation. We extend this result to a more general case of linear PDEs
with constant coefficients. The generalisation is based on the method of Borel
summability, which allows us to find integral representations of solutions for
such PDEs.Comment: 17 page
Chern-Simons Theory on S^1-Bundles: Abelianisation and q-deformed Yang-Mills Theory
We study Chern-Simons theory on 3-manifolds that are circle-bundles over
2-dimensional surfaces and show that the method of Abelianisation,
previously employed for trivial bundles , can be adapted to
this case. This reduces the non-Abelian theory on to a 2-dimensional
Abelian theory on which we identify with q-deformed Yang-Mills theory,
as anticipated by Vafa et al. We compare and contrast our results with those
obtained by Beasley and Witten using the method of non-Abelian localisation,
and determine the surgery and framing presecription implicit in this path
integral evaluation. We also comment on the extension of these methods to BF
theory and other generalisations.Comment: 37 pages; v2: references adde
Central Mass Concentration and Bar Dissolution in Nearby Spiral Galaxies
We use data from the BIMA Survey of Nearby Galaxies (SONG) to investigate the
relationship between ellipticity and central mass concentration in barred
spirals. Existing simulations predict that bar ellipticity decreases as
inflowing mass driven by the bar accumulates in the central regions, ultimately
destroying the bar. Using the ratio of the bulge mass to the mass within the
bar radius as an estimate of the central mass concentration, we obtain
dynamical mass estimates from SONG CO 1-0 rotation curve data. We find an
inverse correlation between bar ellipticity and central mass concentration,
consistent with simulations of bar dissolution.Comment: 10 pages, 2 figures and 2 tables, accepted for publication in the
Astrophysical Journa
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