1,348,761 research outputs found
Recommended from our members
White-headed Vultures Trigonoceps occipitalis show visual field characteristics of hunting raptors
The visual fields of Aegypiinae vultures have been shown to be adapted primarily to meet two key perceptual challenges of their obligate carrion-feeding behaviour: scanning the ground and preventing the sun’s image falling upon the retina. However, field observations have shown that foraging White-headed Vultures (Trigonoceps occipitalis) are not exclusively carrion-feeders; they are also facultative predators of live prey. Such feeding is likely to present perceptual challenges that are additional to those posed by carrion-feeding. Binocularity is the key component of all visual fields and in birds it is thought to function primarily in the accurate placement and time of contact of the talons and bill, especially in the location and seizure of food items. We determined visual fields in White-headed Vultures and two species of carrion-eating Gyps vultures, and show that the visual field of White-headed Vultures have more similarities with those of predatory raptors (e.g. Accipitrid hawks), compared with the taxonomically more closely related Gyps vultures. We found that maximum binocular field width in White-headed vultures (30°) is significantly wider than Gyps vultures (20°). The broader binocular fields in White-headed Vultures probably facilitate accurate placement and timing of the talons when capturing evasive live prey
Model-based learning of local image features for unsupervised texture segmentation
Features that capture well the textural patterns of a certain class of images
are crucial for the performance of texture segmentation methods. The manual
selection of features or designing new ones can be a tedious task. Therefore,
it is desirable to automatically adapt the features to a certain image or class
of images. Typically, this requires a large set of training images with similar
textures and ground truth segmentation. In this work, we propose a framework to
learn features for texture segmentation when no such training data is
available. The cost function for our learning process is constructed to match a
commonly used segmentation model, the piecewise constant Mumford-Shah model.
This means that the features are learned such that they provide an
approximately piecewise constant feature image with a small jump set. Based on
this idea, we develop a two-stage algorithm which first learns suitable
convolutional features and then performs a segmentation. We note that the
features can be learned from a small set of images, from a single image, or
even from image patches. The proposed method achieves a competitive rank in the
Prague texture segmentation benchmark, and it is effective for segmenting
histological images
Soiling and other optical losses in solar-tracking PV plants in Navarra
Field data of soiling energy losses on PV plants are scarce. Furthermore, since dirt type and accumulation vary with the location characteristics (climate, surroundings, etc.), the available data on optical losses are, necessarily, site dependent. This paper presents field measurements of dirt energy losses (dust) and irradiance incidence angle losses along 2005 on a solar-tracking PV plant located south of Navarre (Spain). The paper proposes a method to calculate these losses based on the difference between irradiance measured by calibrated cells on several trackers of the PV plant and irradiance calculated from measurements by two pyranometers (one of them incorporating a shadow ring) regularly cleaned. The equivalent optical energy losses of an installation incorporating fixed horizontal modules at the same location have been calculated as well. The effect of dirt on both types of installations will accordingly be compared
On the representation of polyhedra by polynomial inequalities
A beautiful result of Br\"ocker and Scheiderer on the stability index of
basic closed semi-algebraic sets implies, as a very special case, that every
-dimensional polyhedron admits a representation as the set of solutions of
at most polynomial inequalities. Even in this polyhedral case,
however, no constructive proof is known, even if the quadratic upper bound is
replaced by any bound depending only on the dimension.
Here we give, for simple polytopes, an explicit construction of polynomials
describing such a polytope. The number of used polynomials is exponential in
the dimension, but in the 2- and 3-dimensional case we get the expected number
.Comment: 19 pages, 4 figures; revised version with minor changes proposed by
the referee
The heat of atomization of sulfur trioxide, SO - a benchmark for computational thermochemistry
Calibration ab initio (direct coupled cluster) calculations including basis
set extrapolation, relativistic effects, inner-shell correlation, and an
anharmonic zero-point energy, predict the total atomization energy at 0 K of
SO to be 335.96 (observed 335.920.19) kcal/mol. Inner polarization
functions make very large (40 kcal/mol with , 10 kcal/mol with
basis sets) contributions to the SCF part of the binding energy. The molecule
presents an unusual hurdle for less computationally intensive theoretical
thermochemistry methods and is proposed as a benchmark for them. A slight
modification of Weizmann-1 (W1) theory is proposed that appears to
significantly improve performance for second-row compounds.Comment: Chem. Phys. Lett., in pres
- …