A plea for a modal realist epistemology

David Lewis’s genuine modal realism postulates the existence of concrete possible worlds that are spatio-temporally discontinuous with the concrete world we inhabit. How, then, can we have modal knowledge? How can we know that there are possible worlds and how can we know the characters of those worlds

On representing the relationship between the mathematical and the empirical

We examine, from the partial structures perspective, two forms of applicability of mathematics: at the “bottom” level, the applicability of theoretical structures to the “appearances”, and at the “top” level, the applicability of mathematical to physical theories. We argue that, to accommodate these two forms of applicability, the partial structures approach needs to be extended to include a notion of “partial homomorphism”. As a case study, we present London’s analysis of the superfluid behavior of liquid helium in terms of Bose-Einstein statistics. This involved both the introduction of group theory at the top level, and some modeling at the “phenomenological” level, and thus provides a nice example of the relationships we are interested in. We conclude with a discussion of the “autonomy” of London’s model

The Scattering Polarization of the Sr I 4607 \AA Line at the Diffraction Limit Resolution of a 1-m Telescope

One of the greatest challenges in solar and stellar physics in coming years will be to observe the Second Solar Spectrum with a spatial resolution significantly better than 1 arcsec. This type of scattering polarization observations would probably allow us to discover hitherto unknown aspects of the Sun's hidden magnetism. Here we report on some theoretical predictions for the photospheric line of Sr I at 4607 \AA, which we have obtained by solving the three-dimensional (3D) radiative transfer problem of scattering line polarization in a realistic hydrodynamical model of the solar photosphere. We have taken into account not only the anisotropy of the radiation field in the 3D medium and the Hanle effect of a tangled magnetic field, but also the symmetry breaking effects caused by the horizontal atmospheric inhomogeneities produced by the solar surface convection. Interestingly, the Q/I and U/I linear polarization signals of the emergent spectral line radiation have sizable values and fluctuations, even at the very center of the solar disk where we meet the forward scattering case. The ensuing small-scale patterns in Q/I and U/I turn out to be sensitive to the assumed magnetic field model, and are of great diagnostic value. We argue that it should be possible to observe them with the help of a 1-m telescope equipped with adaptive optics and a suitable polarimeter.Comment: Accepted for publication in The Astrophysical Journal Letters (12 pages and 2 color figures

Fast Fight Detection

Action recognition has become a hot topic within computer vision. However, the action recognition community has focused mainly on relatively simple actions like clapping, walking, jogging, etc. The detection of specific events with direct practical use such as fights or in general aggressive behavior has been comparatively less studied. Such capability may be extremely useful in some video surveillance scenarios like prisons, psychiatric centers or even embedded in camera phones. As a consequence, there is growing interest in developing violence detection algorithms. Recent work considered the well-known Bag-of-Words framework for the specific problem of fight detection. Under this framework, spatio-temporal features are extracted from the video sequences and used for classification. Despite encouraging results in which high accuracy rates were achieved, the computational cost of extracting such features is prohibitive for practical applications. This work proposes a novel method to detect violence sequences. Features extracted from motion blobs are used to discriminate fight and non-fight sequences. Although the method is outperformed in accuracy by state of the art, it has a significantly faster computation time thus making it amenable for real-time applications

Telenomus remus Nixon egg parasitization of three species of Spodoptera under different temperatures.

Telenomus remus Nixon is a promising biocontrol agent as an egg parasitoid of Spodoptera spp., but the lack of information on the host?parasitoid interactions in this system precludes its applied use in agriculture. Therefore, we studied the parasitism capacity of T. remus on eggs of Spodoptera cosmioides (Walker), Spodoptera eridania (Cramer), and Spodoptera frugiperda (Smith) in a range of temperatures (19, 22, 25, 28, 31, and 34 ± 1°C) under controlled conditions (70 ± 10% RH and 12 h photophase). Egg masses of Spodoptera spp. were offered to a single-mated T. remus female on a daily basis. More than 80% lifetime parasitism on eggs of S. cosmioides, S. frugiperda, and S. eridania was reached from 1 to 5, 1 to 7, and 1 to 9 days, respectively, at temperatures from 19 to 34°C. More than 80% parasitization was obtained at extreme temperatures for all hosts studied. Lifetime parasitization of S. frugiperda, S. cosmioides, and S. eridania was affected by temperature, with the lowest values for S. frugiperda (34°C) and S. cosmioides (19 and 34°C). Parasitization of S. eridania eggs was reduced around 18% at 28 and 31°C, but dropped more severely at 34°C. Parasitoid longevity was reduced as temperature increased. Thus, our data indicated that T. remus might be suitable as a biocontrol agent against S. eridania, S. cosmioides, and S. frugiperda in geographical areas that fit the temperature range studied here, even though T. remus parasitism was reduced at 34°C