463 research outputs found
Galactic consequences of clustered star formation
If all stars form in clusters and both the stars and the clusters follow a
power law distribution which favours the creation of low mass objects, then the
numerous low mass clusters will be deficient in high mass stars. Therefore, the
mass function of stars, integrated over the whole galaxy (the Integrated
Galactic Initial Mass Function, IGIMF) will be steeper at the high mass end
than the underlying IMF of the stars. We show how the steepness of the IGIMF
depends on the sampling method and on the assumptions made for the star cluster
mass function. We also investigate the O-star content, integrated photometry
and chemical enrichment of galaxies that result from several IGIMFs, as
compared to more standard IMFs.Comment: 4 pages, 2 figures, to appear in online version of Proceedings of IAU
S266, a two page version will appear in the Proceedings of IAU S26
A Toolkit for uncertainty reasoning and representation using fuzzy set theory in PROLOG expert systems
This thesis examines the issue of uncertainty reasoning and representation in expert systems. Uncertainty and expert systems are defined. The value of uncertainty in expert systems as an approximation of human reasoning is stressed. Five alternative methods of dealing with uncertainty are explored. These include Bayesian probabilities, Mycin confirmation theory, fuzzy set theory, Dempster-Shafer\u27s theory of evidence and a theory of endorsements. A toolkit to apply uncertainty processing in PROLOG expert systems is developed using fuzzy set theory as the basis for uncertainty reasoning and representation. The concepts of fuzzy logic and approximate reasoning are utilized in the implementation. The toolkit is written in C-PROLOG for the PYRAMID UNIX system at the Rochester Institute of Technology
Using Computational Approaches in Visual Identity Design: A Visual Identity for the Design and Multimedia Courses of Faculty of Sciences and Technology of University of Coimbra
Computational approaches are beginning to be used to design dynamic visual
identities fuelled by data and generative processes. In this work, we explore
these computational approaches in order to generate a visual identity that
creates bespoke letterings and images. We achieve this developing a generative
design system that automatically assembles black and white visual modules. This
system generates designs performing two main methods: (i) Assisted generation;
and (ii) Automatic generation. Assisted generation method produces outputs
wherein the placement of modules is determined by a configuration file previous
defined. On the other hand, the Automatic generation method produces outputs
wherein the modules are assembled to depict an input image. This system speeds
up the process of design and deployment of one visual identity design as well
as it generates outputs visual coherent among them. In this paper, we
compressively describe this system and its achievements.Comment: Paper presented in 10th Typography Meeting "Borders", 22--23 Oct.
2019, Matosinhos, Portuga
Serotonin immunoreactive interneurons in the brain of the Remipedia: new insights into the phylogenetic affinities of an enigmatic crustacean taxon
BACKGROUND: Remipedia, a group of homonomously segmented, cave-dwelling, eyeless arthropods have been regarded as basal crustaceans in most early morphological and taxonomic studies. However, molecular sequence information together with the discovery of a highly differentiated brain led to a reconsideration of their phylogenetic position. Various conflicting hypotheses have been proposed including the claim for a basal position of Remipedia up to a close relationship with Malacostraca or Hexapoda. To provide new morphological characters that may allow phylogenetic insights, we have analyzed the architecture of the remipede brain in more detail using immunocytochemistry (serotonin, acetylated α-tubulin, synapsin) combined with confocal laser-scanning microscopy and image reconstruction techniques. This approach allows for a comprehensive neuroanatomical comparison with other crustacean and hexapod taxa. RESULTS: The dominant structures of the brain are the deutocerebral olfactory neuropils, which are linked by the olfactory globular tracts to the protocerebral hemiellipsoid bodies. The olfactory globular tracts form a characteristic chiasm in the center of the brain. In Speleonectes tulumensis, each brain hemisphere contains about 120 serotonin immunoreactive neurons, which are distributed in distinct cell groups supplying fine, profusely branching neurites to 16 neuropilar domains. The olfactory neuropil comprises more than 300 spherical olfactory glomeruli arranged in sublobes. Eight serotonin immunoreactive neurons homogeneously innervate the olfactory glomeruli. In the protocerebrum, serotonin immunoreactivity revealed several structures, which, based on their position and connectivity resemble a central complex comprising a central body, a protocerebral bridge, W-, X-, Y-, Z-tracts, and lateral accessory lobes. CONCLUSIONS: The brain of Remipedia shows several plesiomorphic features shared with other Mandibulata, such as deutocerebral olfactory neuropils with a glomerular organization, innervations by serotonin immunoreactive interneurons, and connections to protocerebral neuropils. Also, we provided tentative evidence for W-, X-, Y-, Z-tracts in the remipedian central complex like in the brain of Malacostraca, and Hexapoda. Furthermore, Remipedia display several synapomorphies with Malacostraca supporting a sister group relationship between both taxa. These homologies include a chiasm of the olfactory globular tract, which connects the olfactory neuropils with the lateral protocerebrum and the presence of hemiellipsoid bodies. Even though a growing number of molecular investigations unites Remipedia and Cephalocarida, our neuroanatomical comparison does not provide support for such a sister group relationship
ESSYS* Sharing #UC: An Emotion-driven Audiovisual Installation
We present ESSYS* Sharing #UC, an audiovisual installation artwork that
reflects upon the emotional context related to the university and the city of
Coimbra, based on the data shared about them on Twitter. The installation was
presented in an urban art gallery of C\'irculo de Artes Pl\'asticas de Coimbra
during the summer and autumn of 2021. In the installation space, one may see a
collection of typographic posters displaying the tweets and listening to an
ever-changing ambient sound. The present audiovisuals are created by an
autonomous computational creative approach, which employs a neural classifier
to recognize the emotional context of a tweet and uses this resulting data as
feedstock for the audiovisual generation. The installation's space is designed
to promote an approach and blend between the online and physical perceptions of
the same location. We applied multiple experiments with the proposed approach
to evaluate the capability and performance. Also, we conduct interview-based
evaluation sessions to understand how the installation elements, especially
poster designs, are experienced by people regarding diversity, expressiveness
and possible employment in other commercial and social scenarios.Comment: Paper to be published in 2022 IEEE VIS Arts Program (VISAP 2022). For
the associated supplementary materials, see
https://cdv.dei.uc.pt/essys_sharing_uc
The role of E+A and post-starburst galaxies – II. Spectral energy distributions and comparison with observations
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15036.xIn a previous paper, we have shown that the classical definition of E+A galaxies excludes a significant number of post-starburst galaxies. We suggested that analysing broad-band spectral energy distributions (SEDs) is a more comprehensive method to select and distinguish post-starburst galaxies than the classical definition of measuring equivalent widths of (Hδ) and [O ii] lines. In this paper, we will carefully investigate this new method and evaluate it by comparing our model grid of post-starburst galaxies to observed E+A galaxies from the MORPHS catalogue. In the first part, we investigate the UV-optical-NIR (near-infrared) SEDs of a large variety in terms of progenitor galaxies, burst strengths and time-scales of post-starburst models and compare them to undisturbed spiral, S0 and E galaxies as well as to galaxies in their starburst phase. In the second part, we compare our post-starburst models with the observed E+A galaxies in terms of Lick indices, luminosities and colours. We then use the new method of comparing the model SEDs with SEDs of the observed E+A galaxies. We find that the post-starburst models can be distinguished from undisturbed spiral, S0 and E galaxies and galaxies in their starburst phase on the basis of their SEDs. It is even possible to distinguish most of the different post-starbursts by their SEDs. From the comparison with observations, we find that all observed E+A galaxies from the MORPHS catalogue can be matched by our models. However, only models with short decline time-scales for the star formation rate are possible scenarios for the observed E+A galaxies in agreement with our results from the first paper.Peer reviewe
Galaxy transmutations: The double ringed galaxy ESO 474-G26
Surface photometry and a 21cm HI line spectrum of the giant double-ringed
galaxy ESO 474-G26 are presented. The morphology of this system is unique among
the 30,000 galaxies with >B15. Two almost orthogonal optical rings with
diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc).
The outer one is an equatorial ring, while the inner ring lies in a nearly
polar plane. The rings have blue optical colors typical of late-type spirals.
Both appear to be rotating around the central galaxy, so that this system can
be considered as a kinematically confirmed polar ring galaxy. Its observational
characteristics are typical of galaxy merger remnants. Although the central
object has a surface brightness distribution typical of elliptical galaxies, it
has a higher surface brightness for its effective radius than ordinary
ellipticals. Possible origins of this galaxy are discussed and numerical
simulations are presented that illustrate the formation of the two rings in the
merging process of two spiral galaxies, in which the observed appearance of ESO
474-G26 appears to be a transient stage.Comment: Accepted for publication in A&
Variations in Integrated Galactic Initial Mass Functions due to Sampling Method and Cluster Mass Function
[abridged] Stars are thought to be formed predominantly in clusters. The
clusters are formed following a cluster initial mass function (CMF) similar to
the stellar initial mass function (IMF). Both the IMF and the CMF favour
low-mass objects. The numerous low-mass clusters will lack high mass stars. If
the integrated galactic initial mass function originates from stars formed in
clusters, the IGIMF could be steeper than the IMF. We investigate how well
constrained this steepening is and how it depends on the choice of sampling
method and CMF. We compare analytic sampling to several implementations of
random sampling of the IMF, and different CMFs. We implement different IGIMFs
into GALEV to obtain colours and metallicities for galaxies. Choosing different
ways of sampling the IMF results in different IGIMFs. Depending on the lower
cluster mass limit and the slope of the cluster mass function, the steepening
varies between very strong and negligible. We find the size of the effect is
continuous as a function of the power-law slope of the CMF, if the CMF extends
to masses smaller than the maximum stellarmass. The number of O-stars detected
by GAIA might help in judging on the importance of the IGIMF effect. The impact
of different IGIMFs on integrated galaxy photometry is small, within the
intrinsic scatter of observed galaxies. Observations of gas fractions and
metallicities could rule out at least the most extreme sampling methods. As we
still do not understand the details of star formation, one sampling method
cannot be favoured over another. Also, the CMF at very low cluster masses is
not well constrained observationally. These uncertainties need to be taken into
account when using an IGIMF, with severe implications for galaxy evolution
models and interpretations of galaxy observations.Comment: Resubmitted to A&A, 14 pages, 9 Figure
Serotonin-immunoreactive neurons in the ventral nerve cord of Remipedia (Crustacea): support for a sister group relationship of Remipedia and Hexapoda?
BACKGROUND: Remipedia were initially seen as a primitive taxon within Pancrustacea based on characters considered ancestral, such as the homonomously segmented trunk. Meanwhile, several morphological and molecular studies proposed a more derived position of Remipedia within Pancrustacea, including a sister group relationship to Hexapoda. Because of these conflicting hypotheses, fresh data are crucial to contribute new insights into euarthropod phylogeny. The architecture of individually identifiable serotonin-immunoreactive neurons has successfully been used for phylogenetic considerations in Euarthropoda. Here, we identified neurons in three species of Remipedia with an antiserum against serotonin and compared our findings to reconstructed ground patterns in other euarthropod taxa. Additionally, we traced neurite connectivity and neuropil outlines using antisera against acetylated α-tubulin and synapsin. RESULTS: The ventral nerve cord of Remipedia displays a typical rope-ladder-like arrangement of separate metameric ganglia linked by paired longitudinally projecting connectives. The peripheral projections comprise an intersegmental nerve, consisting of two branches that fuse shortly after exiting the connectives, and the segmental anterior and posterior nerve. The distribution and morphology of serotonin-immunoreactive interneurons in the trunk segments is highly conserved within the remipede species we analyzed, which allows for the reconstruction of a ground pattern: two posterior and one anterior pair of serotonin-immunoreactive neurons that possess a single contralateral projection. Additionally, three pairs of immunoreactive neurons are found in the medial part of each hemiganglion. In one species (Cryptocorynetes haptodiscus), the anterior pair of immunoreactive neurons is missing. CONCLUSIONS: The anatomy of the remipede ventral nerve cord with its separate metameric ganglia mirrors the external morphology of the animal’s trunk. The rope-ladder-like structure and principal architecture of the segmental ganglia in Remipedia corresponds closely to that of other Euarthropoda. A comparison of the serotonin-immunoreactive cell arrangement of Remipedia to reconstructed ground patterns of major euarthropod taxa supports a homology of the anterior and posterior neurons in Pancrustacea. These neurons in Remipedia possess unbranched projections across the midline, pointing towards similarities to the hexapod pattern. Our findings are in line with a growing number of phylogenetic investigations proposing Remipedia to be a rather derived crustacean lineage that perhaps has close affinities to Hexapoda
RC J0311+0507: A Candidate for Superpowerful Radio Galaxies in the Early Universe at Redshift z=4.514
A strong emission line at 6703A has been detected in the optical spectrum for
the host galaxy (R=23.1) of the radio source RC J0311+0507 (4C+04.11). This
radio galaxy, with a spectral index of 1.31 in the frequency range 365-4850
MHz, is one of the ultrasteep spectrum objects from the deep survey of a sky
strip conducted with RATAN-600 in 1980-1981. We present arguments in favor of
the identification of this line with Ly\alpha at redshift z=4.514. In this
case, the object belongs to the group of extremely distant radio galaxies of
ultrahigh radio luminosity (P_{1400}=1.3 x 10^{29}W Hz^{-1}). Such power can be
provided only by a fairly massive black hole (~10^9M_\sun}) that formed in a
time less than the age of the Universe at the observed z(1.3 Gyr) or had a
primordial origin.Comment: 8 pages, 3 figure
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