3,935 research outputs found
La pertinencia de la historia en la enseñanza de ciencias : argumentos y contraargumentos
Adding up to the debate about the possibility of a historical view in science teaching, the present article frames some responses to the criticisms that, on the basis of the need of simplification and reconstruction of history, object its intrusion in science education. In that sense, the essentially constructive character of history and, particularly, of history of science is appointed, where the epistemological position of the historian acquires special relevance. The multiplicity of historical stories is a constituent characteristic of history and, thus, it does not represent an obstacle in sciences teaching
AUTOMATED MORPHOLOGICAL CLASSIFICATION OF APM GALAXIES BY SUPERVISED ARTIFICIAL NEURAL NETWORKS
We train Artificial Neural Networks to classify galaxies based solely on the
morphology of the galaxy images as they appear on blue survey plates. The
images are reduced and morphological features such as bulge size and the number
of arms are extracted, all in a fully automated manner. The galaxy sample was
first classified by 6 independent experts. We use several definitions for the
mean type of each galaxy, based on those classifications. We then train and
test the network on these features. We find that the rms error of the network
classifications, as compared with the mean types of the expert classifications,
is 1.8 Revised Hubble Types. This is comparable to the overall rms dispersion
between the experts. This result is robust and almost completely independent of
the network architecture used.Comment: The full paper contains 25 pages, and includes 22 figures. It is
available at ftp://ftp.ast.cam.ac.uk/pub/hn/apm2.ps . The table in the
appendix is available on request from [email protected]. Mon. Not. R. Astr.
Soc., in pres
Interior penalty discontinuous Galerkin FEM for the -Laplacian
In this paper we construct an "Interior Penalty" Discontinuous Galerkin
method to approximate the minimizer of a variational problem related to the
Laplacian. The function is log H\"{o}lder
continuous and . We prove that the minimizers of the
discrete functional converge to the solution. We also make some numerical
experiments in dimension one to compare this method with the Conforming
Galerkin Method, in the case where is close to one. This example is
motivated by its applications to image processing.Comment: 26 pages, 2 figure
Morphological Classification of galaxies by Artificial Neural Networks
We explore a method for automatic morphological classification of galaxies by an Artificial Neural Network algorithm. The method is illustrated using 13 galaxy parameters measured by machine (ESO-LV), and classified into five types (E, S0, Sa + Sb, Sc + Sd and Irr). A simple Backpropagation algorithm allows us to train a network on a subset of the catalogue according to human classification, and then to predict, using the measured parameters, the classification for the rest of the catalogue. We show that the neural network behaves in our problem as a Bayesian classifier, i.e. it assigns the a posteriori probability for each of the five classes considered. The network highest probability choice agrees with the catalogue classification for 64 percent of the galaxies. If either the first or the second highest probability choice of the network is considered, the success rate is 90 per cent. The technique allows uniform and more objective classification of very large extragalactic data sets
The Spitzer mid-infrared AGN survey. II-the demographics and cosmic evolution of the AGN population
We present luminosity functions derived from a spectroscopic survey of AGN
selected from Spitzer Space Telescope imaging surveys. Selection in the
mid-infrared is significantly less affected by dust obscuration. We can thus
compare the luminosity functions of the obscured and unobscured AGN in a more
reliable fashion than by using optical or X-ray data alone. We find that the
AGN luminosity function can be well described by a broken power-law model in
which the break luminosity decreases with redshift. At high redshifts
(), we find significantly more AGN at a given bolometric luminosity than
found by either optical quasar surveys or hard X-ray surveys. The fraction of
obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at
high redshifts, appears to remain at \% even at bolometric
luminosities . The data support a picture in which the
obscured and unobscured populations evolve differently, with some evidence that
high luminosity obscured quasars peak in space density at a higher redshift
than their unobscured counterparts. The amount of accretion energy in the
Universe estimated from this work suggests that AGN contribute about 12\% to
the total radiation intensity of the Universe, and a high radiative accretion
efficiency is required to match current
estimates of the local mass density in black holes.Comment: 14 pages, accepted by Ap
Strategies for improving peptide stability and delivery
Peptides play an important role in many fields, including immunology, medical diagnostics, and drug discovery, due to their high specificity and positive safety profile. However, for their delivery as active pharmaceutical ingredients, delivery vectors, or diagnostic imaging molecules, they suffer from two serious shortcomings: their poor metabolic stability and short half-life. Major research efforts are being invested to tackle those drawbacks, where structural modifications and novel delivery tactics have been developed to boost their ability to reach their targets as fully functional species. The benefit of selected technologies for enhancing the resistance of peptides against enzymatic degradation pathways and maximizing their therapeutic impact are also reviewed. Special note of cell-penetrating peptides as delivery vectors, as well as stapled modified peptides, which have demonstrated superior stability from their parent peptides, are reported
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