428 research outputs found
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An optimal control approach to scheduling and production in a process using decaying catalysts
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Real-time feasibility of nonlinear model predictive control for semi-batch reactors subject to uncertainty and disturbances
This paper presents two nonlinear model predictive control based methods for solving closed-loop stochastic dynamic optimisation problems, ensuring both robustness and feasibility with respect to state output constraints. The first one is a new deterministic approach, using the wait-and-see strategy. The key idea is to specifically anticipate violation of output hard-constraints, which are strongly affected by instantaneous disturbances, by backing off of their bounds along the moving horizon. The second method is a stochastic approach to solve nonlinear chance-constrained dynamic optimisation problems under uncertainties. The key aspect is the explicit consideration of the stochastic properties of both exogenous and endogenous uncertainties in the problem formulation (here-and-now strategy). The approach considers a nonlinear relation between uncertain inputs and the constrained state outputs. The performance of the proposed methodologies is assessed via an application to a semi-batch reactor under safety constraints, involving strongly exothermic reactions
An XMM-Newton view of Planetary Nebulae in the Small Magellanic Cloud. The X-ray luminous central star of SMP SMC 22
During an X-ray survey of the Small Magellanic Cloud, carried out with the
XMM-Newton satellite, we detected significant soft X-ray emission from the
central star of the high-excitation planetary nebula SMP SMC 22. Its very soft
spectrum is well fit with a non local thermodynamical equilibrium model
atmosphere composed of H, He, C, N, and O, with abundances equal to those
inferred from studies of its nebular lines. The derived effective temperature
of 1.5x10^5 K is in good agreement with that found from the optical/UV data.
The unabsorbed flux in the 0.1-0.5 keV range is about 3x10^{-11} erg cm^-2
s^-1, corresponding to a luminosity of 1.2x10^37 erg/s at the distance of 60
kpc. We also searched for X-ray emission from a large number of SMC planetary
nebulae, confirming the previous detection of SMP SMC 25 with a luminosity of
(0.2-6)x10^35 erg/s (0.1-1 keV). For the remaining objects that were not
detected, we derived flux upper limits corresponding to luminosity values from
several tens to hundreds times smaller than that of SMP SMC 22. The
exceptionally high X-ray luminosity of SMP SMC 22 is probably due to the high
mass of its central star, quickly evolving toward the white dwarf's cooling
branch, and to a small intrinsic absorption in the nebula itself.Comment: Accepted for publication on Astronomy and Astrophysic
Post-AGB Stars in Globular Clusters and Galactic Halos
We discuss three aspects of post-AGB (PAGB) stars in old populations. (1) HST
photometry of the nucleus of the planetary nebula (PN) K 648 in the globular
cluster (GC) M15 implies a mass of 0.60 Msun, in contrast to the mean masses of
white dwarfs in GCs of ~0.5 Msun. This suggests that K 648 is descended from a
merged binary, and we infer that single Pop II stars do not produce visible
PNe. (2) Yellow PAGB stars are the visually brightest stars in old populations
(Mv ~ -3.3) and are easily recognizable because of their large Balmer jumps;
thus they show great promise as a Pop II standard candle. Two yellow PAGB stars
in the GC NGC 5986 have the same V magnitudes to within +/-0.05 mag, supporting
an expected narrow luminosity function. (3) Using CCD photometry and a u filter
lying below the Balmer jump, we have detected yellow PAGB stars in the halo of
M31 and in its dwarf elliptical companion NGC 205. With the Milky Way zero
point, we reproduce the Cepheid distance to M31, and find that NGC 205 is ~100
kpc further away than M31. The star counts imply a yellow PAGB lifetime of
about 25,000 yr, and their luminosities imply masses near 0.53 Msun.Comment: 6 pages, 2 figures. To appear in proceedings of Torun, Poland,
workshop on "Post-AGB Objects (Proto-Planetary Nebulae) as a Phase of Stellar
Evolution," ed. S.K. Gorn
Spectroscopic investigation of unstudied southern PNe
We present a spectroscopic investigation of two hitherto unstudied galactic
planetary nebulae (MeWe 1-10 and MeWe 1-11) and one candidate object (MeWe
2-5). The candidate object clearly has been identified as a bipolar hourglass
shaped PN. The galactic foreground extinction was derived and using
photoionization models with CLOUDY the two round objects were classified as
highly evolved nebulae.Comment: LaTeX, 5 pages with 6 figures, accepted in Astron. & Astrophy
Striving towards Near Real-Time Data Integration for Data Warehouses
Abstract. The amount of information available to large-scale enterprises is growing rapidly. While operational systems are designed to meet well-specified (short) response time requirements, the focus of data warehouses is generally the strategic analysis of business data integrated from heterogeneous source systems. The decision making process in traditional data warehouse environments is often delayed because data cannot be propagated from the source system to the data warehouse in time. A real-time data warehouse aims at decreasing the time it takes to make business decisions and tries to attain zero latency between the cause and effect of a business decision. In this paper we present an architecture of an ETL environment for real-time data warehouses, which supports a continual near real-time data propagation. The architecture takes full advantage of existing J2EE (Java 2 Platform, Enterprise Edition) technology and enables the implementation of a distributed, scalable, near real-time ETL environment. Instead of using vendor proprietary ETL (extraction, transformation, loading) solutions, which are often hard to scale and often do not support an optimization of allocated time frames for data extracts, we propose in our approach ETLets (spoken “et-lets”) and Enterprise Java Beans (EJB) for the ETL processing tasks. 1
Chemical evolution of the Small Magellanic Cloud based on planetary nebulae
We investigate the chemical evolution of the Small Magellanic Cloud (SMC)
based on abundance data of planetary nebulae (PNe). The main goal is to
investigate the time evolution of the oxygen abundance in this galaxy by
deriving an age-metallicity relation. Such a relation is of fundamental
importance as an observational constraint of chemical evolution models of the
SMC. We have used high quality PNe data in order to derive the properties of
the progenitor stars, so that the stellar ages could be estimated. We collected
a large number of measured spectral fluxes for each nebula, and derived
accurate physical parameters and nebular abundances. New spectral data for a
sample of SMC PNe obtained between 1999 and 2002 are also presented. These data
are used together with data available in the literature to improve the accuracy
of the fluxes for each spectral line. We obtained accurate chemical abundances
for PNe in the Small Magellanic Cloud, which can be useful as tools in the
study of the chemical evolution of this galaxy and of Local Group galaxies. We
present the resulting oxygen versus age diagram and a similar relation
involving the [Fe/H] metallicity based on a correlation with stellar data. We
discuss the implications of the derived age-metallicity relation for the SMC
formation, in particular by suggesting a star formation burst in the last 2-3
Gyr.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Potential impact of a nonavalent HPV vaccine on HPV related low-and high-grade cervical intraepithelial lesions: A referral hospital-based study in Sicily
While bivalent and quadrivalent HPV vaccines have been used for about 10 years, a nonavalent vaccine against HPV types 6/11/16/18/31/33/45/52 and 58 has been recently approved by FDA and EMA and is now commercially available. The objective of our study was to evaluate the potential impact of the nonavalent vaccine on HPV infection and related low- and high-grade squamous intraepithelial lesions (LSIL, HSIL), compared to the impact of the quadrivalent vaccine, in a female population living in Sicily (Italy). Low estimates of HPV vaccine impact were calculated as prevalence of HPV 6/11/16/18/31/33/45/52 and 58 genotypes, alone or in association, but excluding presence of other HPV types; high estimates were calculated as prevalence of HPV 6/11/16/18/31/33/45/52 and 58 genotypes alone or in association, in the presence of other HPV types. The nonavalent HPV vaccine showed increased impact, compared to the quadrivalent vaccine. Estimates of potential impact varied from 30.9% (low estimate) to 53.3% (high estimate) for LSIL, and from 56.9% to 81,0% for HSIL. The proportion of additional cases potentially prevented by the nonavalent vaccine was 14.4%\u201323.8% for LSIL, and 19.0%\u201332.8% for HSIL. The benefit of the nonavalent vaccine compared to the quadrivalent vaccine was more than 80% for both low and high impact estimates for LSIL and more than 50% for both low and high impact estimates for HSIL. The present study confirms that the switch from a first generation HPV vaccines to a nonavalent vaccine would increase the prevention of cervical HSIL in up to 90% of cases
Evolution of Planetary Nebulae I. An improved synthetic model
We present a new synthetic model to follow the evolution of a planetary
nebula (PN) and its central star, starting from the onset of AGB phase up to
the white dwarf cooling sequence. The model suitably combines various
analytical prescriptions to account for different (but inter-related) aspects
of planetary nebulae, such as: the dynamical evolution of the primary shell and
surrounding ejecta, the photoionisation of H and He by the central star, the
nebular emission of a few relevant optical lines (e.g. Hbeta; HeII4686;
[OIII]5007). Predictions of the synthetic model are tested by comparison with
both findings of hydrodynamical calculations, and observations of Galactic PNe.
The sensitiveness of the results to the models parameters (e.g. transition
time, mass of the central star, H-/He-burning tracks, etc.) is also discussed.
We briefly illustrate the systematic differences that are expected in the
luminosities and lifetimes of PNe with either H- or He-burning central stars,
which result in different ``detection probabilities'' across the H-R diagram,
in both Hbeta and [OIII]5007 lines. Adopting reasonable values of the model
parameters, we are able to reproduce, in a satisfactory way, many general
properties of PNe, like the ionised mass--nebular radius relationship, the
trends of a few main nebular line ratios, and the observed ranges of nebular
shell thicknesses, electron densities, and expansion velocities. The models
naturally predict also the possible transitions from optically-thick to
optically-thin configurations (and vice versa). In this context, the origin of
the Zanstra discrepancy is also analysed. (abridged)Comment: 28 pages, 23 postscript figures, to appear in A&
Period-luminosity relations of pulsating M giants in the solar neighbourhood and the Magellanic Clouds
We analyse the results of a 5.5-yr photometric campaign that monitored 247
southern, semi-regular variables with relatively precise Hipparcos parallaxes
to demonstrate an unambiguous detection of Red Giant Branch (RGB) pulsations in
the solar neighbourhood. We show that Sequence A' contains a mixture of AGB and
RGB stars, as indicated by a temperature related shift at the TRGB. Large
Magellanic Cloud (LMC) and Galactic sequences are compared in several ways to
show that the P-L sequence zero-points have a negligible metallicity
dependence. We describe a new method to determine absolute magnitudes from
pulsation periods and calibrate the LMC distance modulus using Hipparcos
parallaxes to find \mu (LMC) = 18.54 +- 0.03 mag. Several sources of systematic
error are discussed to explain discrepancies between the MACHO and OGLE
sequences in the LMC. We derive a relative distance modulus of the Small
Magellanic Cloud (SMC) relative to the LMC of \Delta \mu = 0.41 +- 0.02 mag. A
comparison of other pulsation properties, including period-amplitude and
luminosity-amplitude relations, confirms that RGB pulsation properties are
consistent and universal, indicating that the RGB sequences are suitable as
high-precision distance indicators. The M giants with the shortest periods
bridge the gap between G and K giant solar-like oscillations and M-giant
pulsation, revealing a smooth continuity as we ascend the giant branch.Comment: 12 pages, 17 figures, 1 table. Accepted for publication in MNRA
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