371 research outputs found
Orbital Decay of the PSR J0045-7319/B Star Binary System: Age of Radio Pulsar and Initial Spin of Neutron Star
Recent timing observations of PSR J0045-7319 reveal that the neutron star/B
star binary orbit is decaying on a time scale of |\Porb/\dot\Porb|=0.5 Myr,
shorter than the characteristic age ( Myr) of the pulsar (Kaspi et
al.~1996a). We study mechanisms for the orbital decay. The standard weak
friction theory based on static tide requires far too short a viscous time to
explain the observed \dot\Porb. We show that dynamical tidal excitation of
g-modes in the B star can be responsible for the orbital decay. However, to
explain the observed short decay timescale, the B star must have some
significant retrograde rotation with respect to the orbit --- The retrograde
rotation brings lower-order g-modes, which couple much more strongly to the
tidal potential, into closer ``resonances'' with the orbital motion, thus
significantly enhancing the dynamical tide. A much less likely possibility is
that the g-mode damping time is much shorter than the ordinary radiative
damping time. The observed orbital decay timescale combined with a generic
orbital evolution model based on dynamical tide can be used as a ``timer'',
giving an upper limit of Myr for the age of the binary system since the
neutron star formation. Thus the characteristic age of the pulsar is not a good
age indicator. Assuming standard magnetic dipole braking for the pulsar and no
significant magnetic field decay on a timescale \lo 1 Myr, the upper limit
for the age implies that the initial spin of the neutron star at birth was
close to its current value.Comment: AASTeX, 9 pages, 3 ps figures. ApJ Letters, in pres
Sleptsov Nets are Turing-complete
The present paper proves that a Sleptsov net (SN) is Turing-complete, that
considerably improves, with a brief construct, the previous result that a
strong SN is Turing-complete. Remind that, unlike Petri nets, an SN always
fires enabled transitions at their maximal firing multiplicity, as a single
step, leaving for a nondeterministic choice of which fireable transitions to
fire. A strong SN restricts nondeterministic choice to firing only the
transitions having the highest firing multiplicity.Comment: Sleptsov Net Computing Resolves Modern Supercomputing Problems,
https://technews.acm.org/archives.cfm?fo=2023-04-apr/apr-21-2023.htm
Testing real-time systems using TINA
The paper presents a technique for model-based black-box conformance testing of real-time systems using the Time Petri Net Analyzer TINA. Such test suites are derived from a prioritized time Petri net composed of two concurrent sub-nets specifying respectively the expected behaviour of the system under test and its environment.We describe how the toolbox TINA has been extended to support automatic generation of time-optimal test suites. The result is optimal in the sense that the set of test cases in the test suite have the shortest possible accumulated time to be executed. Input/output conformance serves as the notion of implementation correctness, essentially timed trace inclusion taking environment assumptions into account. Test cases selection is based either on using manually formulated test purposes or automatically from various coverage criteria specifying structural criteria of the model to be fulfilled by the test suite. We discuss how test purposes and coverage criterion are specified in the linear temporal logic SE-LTL, derive test sequences, and assign verdicts
A Generic Tool for Tracing Executions Back to a DSML's Operational Semantics
International audienceThe increasing complexity of software development requires rigorously defined domain specific modeling languages (DSML). Model-driven engineering (\mde) allows users to define a DSML's syntax in terms of metamodels. The behaviour of a language can also be described, either operationally, or via transformations to other languages (e.g., by code generation). If the first approach requires to redefine analysis tools for each DSML (simulator, model-checker...), the second approach allows to reuse existing tools in the targeted language. However, the second approach (also called translational semantics) imply that the results (e.g., a program crash log, or a counterexample returned by a model checker) may not be straightforward to interpret by the users of a DSML. We propose in this paper a generic tool for formally tracing such analysis/execution results back to the original DSML's syntax and operational semantics, and we illustrate it on xSPEM, a timed process modeling language
Interzone short wave radiative couplings through windows and large openings : proposal of a simplified model
International audienceA simplified model of indoor short wave radiation couplings adapted to multi-zone simulations is proposed, thanks to a simplifying hypothesis and to the introduction of an indoor short wave exchange matrix. The specific properties of this matrix appear useful to quantify the thermal radiation exchanges between the zones separated by windows or large openings. Integrated in CODYRUN software, this module is detailed and compared to experimental measurements carried out on a real scale tropical buildin
Algorithms for zero-dimensional ideals using linear recurrent sequences
Inspired by Faug\`ere and Mou's sparse FGLM algorithm, we show how using
linear recurrent multi-dimensional sequences can allow one to perform
operations such as the primary decomposition of an ideal, by computing the
annihilator of one or several such sequences.Comment: LNCS, Computer Algebra in Scientific Computing CASC 201
Proper orthogonal decomposition of solar photospheric motions
The spatio-temporal dynamics of the solar photosphere is studied by
performing a Proper Orthogonal Decomposition (POD) of line of sight velocity
fields computed from high resolution data coming from the MDI/SOHO instrument.
Using this technique, we are able to identify and characterize the different
dynamical regimes acting in the system. Low frequency oscillations, with
frequencies in the range 20-130 microHz, dominate the most energetic POD modes
(excluding solar rotation), and are characterized by spatial patterns with
typical scales of about 3 Mm. Patterns with larger typical scales of 10 Mm, are
associated to p-modes oscillations at frequencies of about 3000 microHz.Comment: 8 figures in jpg in press on PR
Rotation profiles of solar-like stars with magnetic fields
The aim of this work is to investigate rotation profile of solar-like stars
with magnetic fields. A diffusion coefficient of magnetic angular momentum
transport is deduced. Rotating stellar models with different mass are computed
under the effect of the coefficient. Then rotation profiles are obtained from
the theoretical stellar models. The total angular momentum of solar model with
only hydrodynamic instabilities is about 13 times larger than that of the Sun
at the age of the Sun, and this model can not reproduce quasi-solid rotation in
the radiative region. However, not only can the solar model with magnetic
fields reproduce an almost uniform rotation in the radiative region, but its
total angular momentum is consistent with helioseismic result at the level of 3
at the age of the Sun. The rotation of solar-like stars with magnetic
fields is almost uniform in the radiative region. But there is an obvious
transition region of angular velocity between the convective core and the
radiative region of models with 1.2 - 1.5 , where angular velocity
has a sharp radial change, which is different from the rotation profile of the
Sun and massive stars with magnetic fields. Moreover the changes of the angular
velocity in the transition region increase with the increasing in the age and
mass.Comment: Accepted for publication in ChjA
Multiperiodicity in the newly discovered mid-late Be star V2104 Cygni
We obtained the first long, homogenous time-series of V2104Cyg, consisting of
679 datapoints, with the uvbybeta photometers of Sierra Nevada and San Pedro
Martir Observatories with the aim to detect and subsequently interpret the
intrinsic frequencies of this previously unstudied variable star, which turned
out to be a Be star. We try to figure out its place among the variable B stars
on the upper Main Sequence. In order to obtain additional information on
physical parameters we collected a few spectra with the ELODIE and FIES
instruments. We searched for frequencies in the uvby passbands using 2
different frequency analysis methods and used the S/N>4 criterion to select the
significant periodicities. We obtained an estimate of the physical parameters
of the underlying B star of spectral type between B5 and B7, by correcting for
the presence of a circumstellar disk, using a formalism based on the strenght
of the Halpha line emission. We detected 3 independent frequencies with
amplitudes below 0.01mag, f1 = 4.7126 c/d, f2 = 2.2342 c/d and f3 = 4.671 c/d,
and discovered that V2104Cyg is a Be star. The fast rotation (vsini=290+/-10
km/s, and 27<i<45) hampered the investigation of the associated pulsational
parameters l. Nevertheless, the most plausible explanation for the observed
variability of this mid-late type Be star is a non-radial pulsation model. This
paper is based on observations obtained at the Observatorio Astronomico
Nacional San Pedro Martir (Mexico), Observatorio de Sierra Nevada (Spain),
Observatoire de Haute Provence (France), and on observations made with the
Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Spain.Comment: 7 pages, 4 figures, A&A accepte
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