3,640 research outputs found
An Information-Based Neural Approach to Constraint Satisfaction
A novel artificial neural network approach to constraint satisfaction
problems is presented. Based on information-theoretical considerations, it
differs from a conventional mean-field approach in the form of the resulting
free energy. The method, implemented as an annealing algorithm, is numerically
explored on a testbed of K-SAT problems. The performance shows a dramatic
improvement to that of a conventional mean-field approach, and is comparable to
that of a state-of-the-art dedicated heuristic (Gsat+Walk). The real strength
of the method, however, lies in its generality -- with minor modifications it
is applicable to arbitrary types of discrete constraint satisfaction problems.Comment: 13 pages, 3 figures,(to appear in Neural Computation
Extended transition rates and lifetimes in Al I and Al II from systematic multiconfiguration calculations
Multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration
interaction (RCI) calculations were performed for 28 and 78 states in neutral
and singly ionized aluminium, respectively. In Al I, the configurations of
interest are for with to , as well as and
for . In Al II, the studied configurations are, besides the
ground configuration , with to and to , ,
, and . Valence and core-valence electron correlation
effects are systematically accounted for through large configuration state
function (CSF) expansions. Calculated excitation energies are found to be in
excellent agreement with experimental data from the NIST database. Lifetimes
and transition data for radiative electric dipole (E1) transitions are given
and compared with results from previous calculations and available
measurements, for both Al I and Al II. The computed lifetimes of Al I are in
very good agreement with the measured lifetimes in high-precision laser
spectroscopy experiments. The present calculations provide a substantial amount
of updated atomic data, including transition data in the infrared region. This
is particularly important since the new generation of telescopes are designed
for this region. There is a significant improvement in accuracy, in particular
for the more complex system of neutral Al I. The complete tables of transition
data are available
Besov's Type Embedding Theorem for Bilateral Grand Lebesgue Spaces
In this paper we obtain the non-asymptotic norm estimations of Besov's type
between the norms of a functions in different Bilateral Grand Lebesgue spaces
(BGLS). We also give some examples to show the sharpness of these inequalities
Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps
Supermassive black hole binary systems (SMBHB) are standard sirens -- the
gravitational wave analogue of standard candles -- and if discovered by
gravitational wave detectors, they could be used as precise distance
indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB
signals, seriously degrading any distance measurements. Using a weak lensing
map of the SMBHB line of sight, we can estimate its magnification and thereby
remove some uncertainty in its distance, a procedure we call "delensing." We
find that delensing is significantly improved when galaxy shears are combined
with flexion measurements, which reduce small-scale noise in reconstructed
magnification maps. Under a Gaussian approximation, we estimate that delensing
with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce
distance errors by about 30-40% for a SMBHB at z=2. Including an additional
wide shear map from a space survey telescope could reduce distance errors by
50%. Such improvement would make SMBHBs considerably more valuable as
cosmological distance probes or as a fully independent check on existing
probes.Comment: 9 pages, 4 figures, submitted to MNRA
Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system
In this paper we investigate the superspin glass behavior of a concentrated
assembly of interacting maghemite nanoparticles and compare it to that of
canonical atomic spin glass systems. ac versus temperature and frequency
measurements show evidence of a superspin glass transition taking place at low
temperature. In order to fully characterize the superspin glass phase, the
aging behavior of both the thermo-remanent magnetization (TRM) and ac
susceptibility has been investigated. It is shown that the scaling laws obeyed
by superspin glasses and atomic spin glasses are essentially the same, after
subtraction of a superparamagnetic contribution from the superspin glass
response functions. Finally, we discuss a possible origin of this
superparamagnetic contribution in terms of dilute spin glass models
Fluorine in the solar neighborhood - is it all produced in AGB-stars?
The origin of 'cosmic' fluorine is uncertain, but there are three proposed
production sites/mechanisms: AGB stars, nucleosynthesis in Type II
supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of
these production sites has not been established even for the solar
neighborhood, leading to uncertainties in stellar evolution models of these
stars as well as uncertainties in the chemical evolution models of stellar
populations.
We determine the fluorine and oxygen abundances in seven bright, nearby
giants with well-determined stellar parameters. We use the 2.3 m
vibrational-rotational HF line and explore a pure rotational HF line at 12.2
m. The latter has never been used before for an abundance analysis. To be
able to do this we have calculated a line list for pure rotational HF lines. We
find that the abundances derived from the two diagnostics agree.
Our derived abundances are well reproduced by chemical evolution models only
including fluorine production in AGB-stars and therefore we draw the conclusion
that this might be the main production site of fluorine in the solar
neighborhood. Furthermore, we highlight the advantages of using the 12 m
HF lines to determine the possible contribution of the -process to the
fluorine budget at low metallicities where the difference between models
including and excluding this process is dramatic
Kinds of Learning and the Likelihood of Future True Beliefs: Reply to Jäger on Reliabilism and the Value Problem
We reply to Christoph Jager's criticism of the conditional probability solution (CPS) to the value problem for reliabilism due to Goldman and Olsson (2009). We argue that while Jager raises some legitimate concerns about the compatibility of CPS with externalist epistemology, his objections do not in the end reduce the plausibility of that solution
Constraining dark matter halo properties using lensed SNLS supernovae
This paper exploits the gravitational magnification of SNe Ia to measure
properties of dark matter haloes. The magnification of individual SNe Ia can be
computed using observed properties of foreground galaxies and dark matter halo
models. We model the dark matter haloes of the galaxies as truncated singular
isothermal spheres with velocity dispersion and truncation radius obeying
luminosity dependent scaling laws. A homogeneously selected sample of 175 SNe
Ia from the first 3-years of the Supernova Legacy Survey (SNLS) in the redshift
range 0.2 < z < 1 is used to constrain models of the dark matter haloes
associated with foreground galaxies. The best-fitting velocity dispersion
scaling law agrees well with galaxy-galaxy lensing measurements. We further
find that the normalisation of the velocity dispersion of passive and star
forming galaxies are consistent with empirical Faber-Jackson and Tully-Fisher
relations, respectively. If we make no assumption on the normalisation of these
relations, we find that the data prefer gravitational lensing at the 92 per
cent confidence level. Using recent models of dust extinction we deduce that
the impact of this effect on our results is very small. We also investigate the
brightness scatter of SNe Ia due to gravitational lensing. The gravitational
lensing scatter is approximately proportional to the SN Ia redshift. We find
the constant of proportionality to be B = 0.055 +0.039 -0.041 mag (B < 0.12 mag
at the 95 per cent confidence level). If this model is correct, the
contribution from lensing to the intrinsic brightness scatter of SNe Ia is
small for the SNLS sample.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Supernova cosmology: legacy and future
The discovery of dark energy by the first generation of high-redshift
supernova surveys has generated enormous interest beyond cosmology and has
dramatic implications for fundamental physics. Distance measurements using
supernova explosions are the most direct probes of the expansion history of the
Universe, making them extremely useful tools to study the cosmic fabric and the
properties of gravity at the largest scales. The past decade has seen the
confirmation of the original results. Type Ia supernovae are among the leading
techniques to obtain high-precision measurements of the dark energy equation of
state parameter, and in the near future, its time dependence. The success of
these efforts depends on our ability to understand a large number of effects,
mostly of astrophysical nature, influencing the observed flux at Earth. The
frontier now lies in understanding if the observed phenomenon is due to vacuum
energy, albeit its unnatural density, or some exotic new physics. Future
surveys will address the systematic effects with improved calibration
procedures and provide thousands of supernovae for detailed studies.Comment: Invited review, Annual Review of Nuclear and Particle Science
(submitted version
Reducing the gravitational lensing scatter of Type Ia supernovae without introducing any extra bias
Magnification and de-magnification due to gravitational lensing will
contribute to the brightness scatter of Type Ia supernovae (SNe Ia). The
purpose of this paper is to investigate the possibility to decrease this
scatter by correcting individual SNe Ia using observations of galaxies in the
foreground, without introducing any extra bias. We simulate a large number of
SN Ia lines of sight populated by galaxies. For each line of sight the true
magnification factor and an estimate thereof are calculated. The estimated
magnification factor corresponds to what an observer would infer from a survey
like SNLS. Using the simulated data we investigate the possibility to estimate
the magnification of individual supernovae with enough precision to be able to
correct their brightness for gravitational lensing with negligible bias. Our
simulations show that the bias arising from gravitational lensing corrections
of individual SNe Ia is negligible for current and next generation surveys and
that the scatter from lensing can be reduced by approximately a factor 2. The
total scatter in the SN Ia magnitudes could be reduced by 4% for an intrinsic
dispersion of 0.13 mag. For an intrinsic dispersion of 0.09 mag, which might
not be to unrealistic for future surveys, the total scatter could be reduced by
6%. This will reduce the errors on cosmological parameters derived from
supernova data by 4-8%. The prospect of correcting for lensing is thus very
good.Comment: 7 pages, 7 figures, accepted by A&
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