3,976 research outputs found
Remarks on the properties of elliptical galaxies in modified Newtonian dynamics
Two incorrect arguments against MOND in elliptical galaxies could be that the
equivalent circular velocity curves tend to become flat at much larger
accelerations than in spiral galaxies, and that the Newtonian dark matter halos
are more concentrated than in spirals. Here, we compare published scaling
relations for the dark halos of elliptical galaxies to the scaling relations
expected for MONDian phantom halos. We represent the baryonic content of
galaxies by spherical profiles, and their corresponding MONDian phantom halos
by logarithmic halos. We then derive the surface densities, central densities,
and phase space densities and compare them with published scaling relations. We
conclude that it is possible to get flat circular velocity curves at high
acceleration in MOND, and that this happens for baryonic distributions
described by Jaffe profiles in the region where the circular velocity curve is
flat. Moreover, the scaling relations of dark halos of ellipticals are
remarkably similar to the scaling relations of phantom halos of MOND.Comment: Accepted for publication in A and
The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting
We investigate the amount and spatial distribution of interstellar dust in
edge-on spiral galaxies, using detailed radiative transfer modeling of a
homogeneous sample of 12 galaxies selected from the CALIFA survey. Our
automated fitting routine, FitSKIRT, was first validated against artificial
data. This is done by simultaneously reproducing the SDSS -, -, - and
-band observations of a toy model in order to combine the information
present in the different bands. We show that this combined, oligochromatic
fitting, has clear advantages over standard monochromatic fitting especially
regarding constraints on the dust properties. We model all galaxies in our
sample using a three-component model, consisting of a double exponential disc
to describe the stellar and dust discs and using a S\'ersic profile to describe
the central bulge. The full model contains 19 free parameters, and we are able
to constrain all these parameters to a satisfactory level of accuracy without
human intervention or strong boundary conditions. Apart from two galaxies, the
entire sample can be accurately reproduced by our model. We find that the dust
disc is about 75% more extended but only half as high as the stellar disc. The
average face-on optical depth in the V-band is and the spread of
within our sample is quite substantial, which indicates that some spiral
galaxies are relatively opaque even when seen face-on.Comment: 18 pages, 6 figures, 4 tables, Accepted for publication in MNRA
An extremely low gas-to-dust ratio in the dust-lane lenticular galaxy NGC 5485
Date of Acceptance: 21/07/2014Peer reviewe
Preliminary spacecraft design by means of structured-chromosome genetic algorithms
This paper presents a new methodology for complex system design by means of optimisation techniques. Within the Model-based Engineering approach, optimisation algorithms are used to explore optimal solutions of highly coupled and nonlinear systems. In such scenario, the optimal technology has to be identified and its settings have to be optimised. Relying on optimisation strategies for both the challenges brings to complex mixed-variable problem formulations involving continuous, integer and categorical parameters. Furthermore, part of the parameters are required only if certain technologies are adopted, bringing to variable-size formulations that standard optimisers cannot manage. Therefore, the proposed methodology relies on the use of variable-size mixed-variable global optimiser Structured-Chromosome Genetic Algorithm (SCGA). The advantages of this new method are shown by applying it for solving a space system preliminary design. In particular, two variants have been implemented distinguished by two different levels of complexity. To better appreciate the proposed approach, the same problems have been reformulated to be treated by a well known and appreciated optimiser in the field of spacecraft design, Multi– Population Adaptive Inflationary Differential Evolution Algorithm (MP–AIDEA). The final results of the two approaches are compared and commented
Navel Healing and Calf Fitness for Transport
open5noDairy male calves are at risk of welfare compromise as they are usually transported at a very young age. The European Union has set a “completely healed navel” requirement for calf transport; moreover, a minimum age is established for longer journeys. However, this requirement has proven to be prone to misinterpretation. This study aimed to clarify what is meant by “navel healing” and to provide strong elements for reaching a consensus. The navels of 299 dairy calves (55 males, 244 females) aged 0–90 days were examined and scored 1 to 5 according to their healing status. Based on our results, a completely dry and shriveled navel (score 3) would imply a 25.5–38.0% risk of transporting too young calves. Alternatively, the presence of a scab covering the umbilical wound (score 4) would entail a 4.3% risk of transporting calves less than 10 days old and could be considered good practice for transporting calves (except for journeys exceeding 8 h). Conversely, complete navel healing (score 5) guarantees that calves that are too young are not transported; therefore, it should be considered best practice for transporting calves in general and the minimum requirement for transporting calves for journeys exceeding 8 h.openRoccaro, Mariana; Bolcato, Marilena; Masebo, Naod Thomas; Gentile, Arcangelo; Peli, AngeloRoccaro, Mariana; Bolcato, Marilena; Masebo, Naod Thomas; Gentile, Arcangelo; Peli, Angel
High-lift devices topology optimisation using structured-chromosome genetic algorithm
This paper addresses the problem of including the choice of the High-Lift Devices (HLDs) configuration as a decision variable of an automatic optimisation tool. This task requires the coupling of an estimation routine and an optimisation algorithm. For the former, SU2 flow solver has been used. The Structured-Chromosome Genetic Algorithm (SCGA) optimiser has been employed to search for the optimal HLD. SCGA can overcome the limitations dictated by standard fixed-size continuous optimisation algorithms. Indeed, using hierarchical formulations, it can manage configurational decisions that are conventionally the responsibility of expert designers. The search algorithm bases its strategy on revised genetic operators conceived for handling hierarchical search spaces. The presented research not only shows the practicability of delegating to a specialised optimisation algorithm the complete HLD design but is intended to be a proof of concept for the whole field of multidisciplinary design optimisation. Indeed, the aerospace sector as a whole would benefit by reducing human intervention from the decision process
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