6,796 research outputs found
Variation of Hilbert Coefficients
For a Noetherian local ring (\RR, \m), the first two Hilbert coefficients,
and , of the -adic filtration of an \m-primary ideal are
known to code for properties of \RR, of the blowup of \spec(\RR) along
, and even of their normalizations. We give estimations for these
coefficients when is enlarged (in the case of in the same integral
closure class) for general Noetherian local rings
Variation of the first Hilbert coefficients of parameters with a common integral closure
A problem posed by Wolmer V. Vasconcelos on the variation of the first
Hilbert coefficients of parameter ideals with a common integral closure in a
local ring is studied. Affirmative answers are given and counterexamples are
explored as well
Abundances of Stars with Planets: Trends with Condensation Temperature
Precise abundances of 18 elements have been derived for ten stars known to
host giant planets from high signal-to-noise ratio, high-resolution echelle
spectroscopy. Internal uncertainties in the derived abundances are typically
<=0.05 dex. The stars in our sample have all been previously shown to have
abundances that correlate with the condensation temperature (T_c) of the
elements in the sense of increasing abundances with increasing T_c; these
trends have been interpreted as evidence that the stars may have accreted
H-depleted planetary material. Our newly derived abundances also correlate
positively with T_c, although slopes of linear least-square fits to the
[m/H]-T_c relations for all but two stars are smaller here than in previous
studies. When considering the refractory elements (T_c > 900 K) only, which may
be more sensitive to planet formation processes, the sample can be separated
into a group with positive slopes (four stars) and a group with flat or
negative slopes (six stars). The four stars with positive slopes have very
close-in giant planets (three at 0.05 AU) and slopes that fall above the
general Galactic chemical evolution trend. We suggest that these stars have
accreted refractory-rich planet material but not to the extent that would
increase significantly the overall stellar metallicity. The flat or negative
slopes of the remaining six stars are consistent with recent suggestions of a
planet formation signature, although we show that the trends may be the result
of Galactic chemical evolution.Comment: 64 pages (single column), 5 figures, 10 tables. Accepted by Ap
Metallicities of Planet Hosting Stars: A Sample of Giants and Subgiants
This work presents a homogeneous derivation of atmospheric parameters and
iron abundances for a sample of giant and subgiant stars which host giant
planets, as well as a control sample of subgiant stars not known to host giant
planets. The analysis is done using the same technique as for our previous
analysis of a large sample of planet-hosting and control sample dwarf stars. A
comparison between the distributions of [Fe/H] in planet-hosting main-sequence
stars, subgiants, and giants within these samples finds that the main-sequence
stars and subgiants have the same mean metallicity of \simeq +0.11
dex, while the giant sample is typically more metal poor, having an average
metallicity of = -0.06 dex. The fact that the subgiants have the same
average metallicities as the dwarfs indicates that significant accretion of
solid metal-rich material onto the planet-hosting stars has not taken place, as
such material would be diluted in the evolution from dwarf to subgiant. The
lower metallicity found for the planet-hosting giant stars in comparison with
the planet-hosting dwarfs and subgiants is interpreted as being related to the
underlying stellar mass, with giants having larger masses and thus, on average
larger-mass protoplanetary disks. In core accretion models of planet formation,
larger disk masses can contain the critical amount of metals necessary to form
giant planets even at lower metallicities.Comment: 38 pages, 7 figures, 4 tables, accepted for publication in Ap
MORPH: A Reference Architecture for Configuration and Behaviour Self-Adaptation
An architectural approach to self-adaptive systems involves runtime change of
system configuration (i.e., the system's components, their bindings and
operational parameters) and behaviour update (i.e., component orchestration).
Thus, dynamic reconfiguration and discrete event control theory are at the
heart of architectural adaptation. Although controlling configuration and
behaviour at runtime has been discussed and applied to architectural
adaptation, architectures for self-adaptive systems often compound these two
aspects reducing the potential for adaptability. In this paper we propose a
reference architecture that allows for coordinated yet transparent and
independent adaptation of system configuration and behaviour
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