2,873 research outputs found
ઔદ્યોગિક વિકાસની પર્યાવરણીય અસરોઃ સૌરાષ્ટ્ર પ્રદેશના સિમેન્ટ ઉદ્યોગના સંદર્ભમાં અભ્યાસ
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ARES v2 - new features and improved performance
Aims: We present a new upgraded version of ARES. The new version includes a
series of interesting new features such as automatic radial velocity
correction, a fully automatic continuum determination, and an estimation of the
errors for the equivalent widths. Methods: The automatic correction of the
radial velocity is achieved with a simple cross-correlation function, and the
automatic continuum determination, as well as the estimation of the errors,
relies on a new approach to evaluating the spectral noise at the continuum
level. Results: ARES v2 is totally compatible with its predecessor. We show
that the fully automatic continuum determination is consistent with the
previous methods applied for this task. It also presents a significant
improvement on its performance thanks to the implementation of a parallel
computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage:
www.astro.up.pt/~sousasag/are
Uniqueness of the Fock quantization of a free scalar field on with time dependent mass
We analyze the quantum description of a free scalar field on the circle in
the presence of an explicitly time dependent potential, also interpretable as a
time dependent mass. Classically, the field satisfies a linear wave equation of
the form . We prove that the representation of the
canonical commutation relations corresponding to the particular case of a
massless free field () provides a unitary implementation of the dynamics
for sufficiently general mass terms, . Furthermore, this representation
is uniquely specified, among the class of representations determined by
-invariant complex structures, as the only one allowing a unitary
dynamics. These conclusions can be extended in fact to fields on the two-sphere
possessing axial symmetry. This generalizes a uniqueness result previously
obtained in the context of the quantum field description of the Gowdy
cosmologies, in the case of linear polarization and for any of the possible
topologies of the spatial sections.Comment: 13 pages, typos corrected, version accepted for publication in
Physical Review
Asymptotics of Regulated Field Commutators for Einstein-Rosen Waves
We discuss the asymptotic behavior of regulated field commutators for
linearly polarized, cylindrically symmetric gravitational waves and the
mathematical techniques needed for this analysis. We concentrate our attention
on the effects brought about by the introduction of a physical cut-off in the
study of the microcausality of the model and describe how the different
physically relevant regimes are affected by its presence. Specifically we
discuss how genuine quantum gravity effects can be disentangled from those
originating in the introduction of a regulator.Comment: 9 figures, 19 pages in DIN A4 format. Accepted for publication in
Journal of Mathematical Physic
PowerAqua: fishing the semantic web
The Semantic Web (SW) offers an opportunity to develop novel, sophisticated forms of question answering (QA). Specifically, the availability of distributed semantic markup on a large scale opens the way to QA systems which can make use of such semantic information to provide precise, formally derived answers to questions. At the same time the distributed, heterogeneous, large-scale nature of the semantic information introduces significant challenges. In this paper we describe the design of a QA system, PowerAqua, designed to exploit semantic markup on the web to provide answers to questions posed in natural language. PowerAqua does not assume that the user has any prior information about the semantic resources. The system takes as input a natural language query, translates it into a set of logical queries, which are then answered by consulting and aggregating information derived from multiple heterogeneous semantic sources
Searching for solar siblings among the HARPS data
The search for the solar siblings has been particularly fruitful in the last
few years. Until now, there are four plausible candidates pointed out in the
literature: HIP21158, HIP87382, HIP47399, and HIP92831. In this study we
conduct a search for solar siblings among the HARPS high-resolution FGK dwarfs
sample, which includes precise chemical abundances and kinematics for 1111
stars. Using a new approach based on chemical abundance trends with the
condensation temperature, kinematics, and ages we found one (additional)
potential solar sibling candidate: HIP97507.Comment: 4 pages, 2 figures, 1 table. Accepted in A&
NIR spectroscopy of the Sun and HD20010 - Compiling a new linelist in the NIR
Context: Effective temperature, surface gravity, and metallicity are basic
spectroscopic stellar parameters necessary to characterize a star or a
planetary system. Reliable atmospheric parameters for FGK stars have been
obtained mostly from methods that relay on high resolution and high
signal-to-noise optical spectroscopy. The advent of a new generation of high
resolution near-IR spectrographs opens the possibility of using classic
spectroscopic methods with high resolution and high signal-to-noise in the NIR
spectral window. Aims: We aim to compile a new iron line list in the NIR from a
solar spectrum to derive precise stellar atmospheric parameters, comparable to
the ones already obtained from high resolution optical spectra. The spectral
range covers 10 000 {\AA} to 25 000 {\AA}, which is equivalent to the Y, J, H,
and K bands. Methods: Our spectroscopic analysis is based on the iron
excitation and ionization balance done in LTE. We use a high resolution and
high signal-to-noise ratio spectrum of the Sun from the Kitt Peak telescope as
a starting point to compile the iron line list. The oscillator strengths (log
gf) of the iron lines were calibrated for the Sun. The abundance analysis was
done using the MOOG code after measuring equivalent widths of 357 solar iron
lines. Results: We successfully derived stellar atmospheric parameters for the
Sun. Furthermore, we analysed HD20010, a F8IV star, from which we derived
stellar atmospheric parameters using the same line list as for the Sun. The
spectrum was obtained from the CRIRES- POP database. The results are compatible
with the ones found in the literature, confirming the reliability of our line
list. However, due to the quality of the data we obtain large errors.Comment: 9 pages and 9 figure
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