290 research outputs found
Signature of a chemical spread in the open cluster M37
Recent Gaia photometry of the open cluster M37 have disclosed the existence
of an extended main-sequence turn off -- like in Magellanic clusters younger
than about 2 Gyr -- and a main sequence that is broadened in colour beyond what
is expected from the photometric errors, at magnitudes well below the region of
the extended turn off, where neither age differences nor rotation rates (the
candidates to explain the extended turn off phenomenon) are expected to play a
role. Moreover, not even the contribution of unresolved binaries can fully
explain the observed broadening. We investigated the reasons behind this
broadening by making use of synthetic stellar populations and differential
colour-colour diagrams using a combination of Gaia and Sloan filters. From our
analysis we have concluded that the observed colour spread in the Gaia
colour-magnitude diagram can be reproduced by a combination of either a
metallicity spread Delta[Fe/H] ~ 0.15 plus a differential reddening across the
face of the cluster spanning a total range DeltaE (B - V) ~ 0.06, or a spread
of the initial helium mass fraction DeltaY ~ 0.10 plus a smaller range of
reddening DeltaE (B - V) ~ 0.03. High-resolution differential abundance
determinations of a sizeable sample of cluster stars are necessary to confirm
or exclude the presence of a metal abundance spread. Our results raise the
possibility that also individual open clusters, like globular clusters and
massive star clusters, host stars born with different initial chemical
compositions.Comment: 10 pages, 10 figures. Accepted for publication in MNRAS on 2022,
August 31, manuscript ID. MN-22-2637-M
Automatic Abstraction in SMT-Based Unbounded Software Model Checking
Software model checkers based on under-approximations and SMT solvers are
very successful at verifying safety (i.e. reachability) properties. They
combine two key ideas -- (a) "concreteness": a counterexample in an
under-approximation is a counterexample in the original program as well, and
(b) "generalization": a proof of safety of an under-approximation, produced by
an SMT solver, are generalizable to proofs of safety of the original program.
In this paper, we present a combination of "automatic abstraction" with the
under-approximation-driven framework. We explore two iterative approaches for
obtaining and refining abstractions -- "proof based" and "counterexample based"
-- and show how they can be combined into a unified algorithm. To the best of
our knowledge, this is the first application of Proof-Based Abstraction,
primarily used to verify hardware, to Software Verification. We have
implemented a prototype of the framework using Z3, and evaluate it on many
benchmarks from the Software Verification Competition. We show experimentally
that our combination is quite effective on hard instances.Comment: Extended version of a paper in the proceedings of CAV 201
SimpleCAR: An Efficient Bug-Finding Tool Based on Approximate Reachability
We present a new safety hardware model checker SimpleCAR that serves as a reference implementation for evaluating Complementary Approximate Reachability (CAR), a new SAT-based model checking framework inspired by classical reachability analysis. The tool gives a “bottom-line” performance measure for comparing future extensions to the framework. We demonstrate the performance of SimpleCAR on challenging benchmarks from the Hardware Model Checking Competition. Our experiments indicate that SimpleCAR is particularly suited for unsafety checking, or bug-finding; it is able to solve 7 unsafe instances within 1 h that are not solvable by any other state-of-the-art techniques, including BMC and IC3/PDR, within 8 h. We also identify a bug (reports safe instead of unsafe) and 48 counterexample generation errors in the tools compared in our analysis
Molecular basis of autotrophic vs mixotrophic growth in Chlorella sorokiniana
In this work, we investigated the molecular basis of autotrophic vs. mixotrophic growth of Chlorella sorokiniana, one of the most productive microalgae species with high potential to produce biofuels, food and high value compounds. To increase biomass accumulation, photosynthetic microalgae are commonly cultivated in mixotrophic conditions, adding reduced carbon sources to the growth media. In the case of C. sorokiniana, the presence of acetate enhanced biomass, proteins, lipids and starch productivity when compared to autotrophic conditions. Despite decreased chlorophyll content, photosynthetic properties were essentially unaffected while differential gene expression profile revealed transcriptional regulation of several genes mainly involved in control of carbon flux. Interestingly, acetate assimilation caused upregulation of phosphoenolpyruvate carboxylase enzyme, enabling potential recovery of carbon atoms lost by acetate oxidation. The obtained results allowed to associate the increased productivity observed in mixotrophy in C. sorokiniana with a different gene regulation leading to a fine regulation of cell metabolism
HST astrometry of the closest Brown Dwarfs -- II. Improved parameters and constraints on a third body
Located at less than 2pc away, Luhman16AB (WISE.J104915.57-531906.1) is the
closest pair of brown dwarfs and third closest `stellar' system to Earth. An
exoplanet candidate in the Luhman16 binary system was reported in 2017 based on
a weak astrometric signature in the analysis of 12 HST epochs. An additional
epoch collected in 2018 and re-analysis of the data with more advanced methods
further increased the significance level of the candidate, consistent with a
Neptune-mass exoplanet orbiting one of the Luhman16 brown dwarf components. We
report the joint analysis of these previous data together with two new
astrometric HST epochs we obtained to confirm or disprove this astrometric
signature. Our new analysis rules out presence of a planet orbiting one
component of the Luhman16AB system for masses M > 1.5 M_Nep (Neptune masses)
and periods between 400 and 5000 days. However, the presence of third bodies
with masses M < 3 M_Nep and periods between 2 and 400 days (~1.1yrs) can not be
excluded. Our measurements make significant improvements to the
characterization of this sub-stellar binary, including its mass-ratio
0.8305+/-0.0006, individual component masses 35.4+/-0.2 M_Jup and 29.4+/-0.2
M_Jup (Jupiter masses), and parallax distance 1.9960pc +/- 50AU. Comparison of
the masses and luminosities of Luhman16AB to several evolutionary models shows
persistent discrepancies in the ages of the two components, but strengthens the
case that this system is a member of the 510+/-95 Myr Oceanus Moving Group.Comment: 17 pages, 8+A1 figures. Accepted for publication on Astronomische
Nachrichten on 10th January 2024 available
https://onlinelibrary.wiley.com/doi/10.1002/asna.20230158 on-line
supplementary material and animations
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/Luh16AB_II
Intersection and Rotation of Assumption Literals Boosts Bug-Finding
SAT-based techniques comprise the state-of-the-art in functional verification of safety-critical hardware and software, including IC3/PDR-based model checking and Bounded Model Checking (BMC). BMC is the incontrovertible best method for unsafety checking, aka bug-finding. Complementary Approximate Reachability (CAR) and IC3/PDR complement BMC for bug-finding by detecting different sets of bugs. To boost the efficiency of formal verification, we introduce heuristics involving intersection and rotation of the assumption literals used in the SAT encodings of these techniques. The heuristics generate smaller unsat cores and diverse satisfying assignments that help in faster convergence of these techniques, and have negligible runtime overhead. We detail these heuristics, incorporate them in CAR, and perform an extensive experimental evaluation of their performance, showing a 25% boost in bug-finding efficiency of CAR.We contribute a detailed analysis of the effectiveness of these heuristics: their influence on SAT-based bug-finding enables detection of different bugs from BMCbased checking. We find the new heuristics are applicable to IC3/PDR-based algorithms as well, and contribute a modified clause generalization procedure
Cyclic nucleotide-dependent relaxation in human umbilical vessels
Umbilical vessels have a low sensitivity to dilate, and this property is speculated to have physiological implications. We aimed to investigate the different relaxing responses of human umbilical arteries (HUAs) and veins (HUVs) to agonists acting through the cAMP and cGMP pathways. Vascular rings were suspended in organ baths for isometric force measurement. Following precontraction with the thromboxane prostanoid (TP) receptor agonist U44069, concentration-response curves to the nitric oxide (NO) donor sodium nitroprusside (SNP), the soluble guanylate cyclase (sGC) stimulator BAY 41-2272, the adenylate cyclase (AC) activator forskolin, the \u3b2-adrenergic receptor agonists isoproterenol (ADRB1), salmeterol (ADRB2), and BRL37344 (ADRB3), and the phosphodiesterase (PDE) inhibitors milrinone (PDE3), rolipram (PDE4), and sildenafil (PDE5) were performed. None of the tested drugs induced a relaxation higher than 30% of the U44069-induced tone. Rings from HUAs and HUVs showed a similar relaxation to forskolin, SNP, PDE inhibitors, and ADRB agonists. BAY 41-2272 was significantly more efficient in relaxing veins than arteries. ADRB agonists evoked weak relaxations (< 20%), which were impaired in endothelium-removed vessels or in the presence of the NO synthase inhibitor L-NAME, sGC inhibitor ODQ. PKA and PKG inhibitors impaired ADBR1-mediated relaxation but did not affect ADRB2-mediated relaxation. ADRB3-mediated relaxation was impaired by PKG inhibition in HUAs and by PKA inhibition in HUVs. Although HUA and HUV rings were relaxed by BRL37344, immunohistochemistry and RT-qPCR analysis showed that, compared to ADRB1 and ADRB2, ADRB3 receptors are weakly or not expressed in umbilical vessels. In conclusion, our study confirmed the low relaxing capacity of HUAs and HUVs from term infants. ADRB-induced relaxation is partially mediated by endothelium-derived NO pathway in human umbilical vessels
A Simplex-Based Extension of Fourier-Motzkin for Solving Linear Integer Arithmetic
International audienceThis paper describes a novel decision procedure for quantifier-free linear integer arithmetic. Standard techniques usually relax the initial problem to the rational domain and then proceed either by projection (e.g. Omega-Test) or by branching/cutting methods (branch-and-bound, branch-and-cut, Gomory cuts). Our approach tries to bridge the gap between the two techniques: it interleaves an exhaustive search for a model with bounds inference. These bounds are computed provided an oracle capable of finding constant positive linear combinations of affine forms. We also show how to design an efficient oracle based on the Simplex procedure. Our algorithm is proved sound, complete, and terminating and is implemented in the Alt-Ergo theorem prover. Experimental results are promising and show that our approach is competitive with state-of-the-art SMT solvers
Quantifier-Free Interpolation of a Theory of Arrays
The use of interpolants in model checking is becoming an enabling technology
to allow fast and robust verification of hardware and software. The application
of encodings based on the theory of arrays, however, is limited by the
impossibility of deriving quantifier- free interpolants in general. In this
paper, we show that it is possible to obtain quantifier-free interpolants for a
Skolemized version of the extensional theory of arrays. We prove this in two
ways: (1) non-constructively, by using the model theoretic notion of
amalgamation, which is known to be equivalent to admit quantifier-free
interpolation for universal theories; and (2) constructively, by designing an
interpolating procedure, based on solving equations between array updates.
(Interestingly, rewriting techniques are used in the key steps of the solver
and its proof of correctness.) To the best of our knowledge, this is the first
successful attempt of computing quantifier- free interpolants for a variant of
the theory of arrays with extensionality
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