269 research outputs found

    Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia

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    <p>Abstract</p> <p>Background</p> <p>Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts.</p> <p>Results</p> <p>A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.</p> <p>Conclusion</p> <p>The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.</p

    Effects of geon deletion, scrambling, and movement on picture recognition in pigeons.

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    The Constitutional Prism of Louis-Philippe Pigeon and Jean Beetz

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    Après avoir expliqué ce qu'il entend par notion de constitution (“image of a constitution”, l'auteur examine les écrits judiciaires et doctrinaux des juges Pigeon et Beetz dans le but de voir quelle idée l'un et l'autre se faisaient de ce qu'est une constitution. Ces écrits, selon lui, se fondent sur des conceptions articulées du rôle des textes comme source du droit, du rôle des normes comme prétention de départ de l'analyse constitutionnelle, du rôle scientifique du juriste et, enfin, des positions respectives des différentes règles de droit. L'auteur conclut que cette façon de voir s'inscrit à l'intérieur d'une conception globale du droit dont les tenants et aboutissants n'ont jamais été vraiment étudiés.After introducing the concept of an "image of a constitution", Mr Conklin examines the federalism writings and judgments of Justices Pigeon and Beetz with a view to identifying the bounderies of their respective concepts of a constitution. He argues that their writings presuppose coherent answers to such boundaries as the role of a text as the primary source of law, the posited character of rules, rules as the starting point of constitutional analysis, the scientistic role of a lawyer, and a horizontal / vertical spectrum of posited rules. Mr. Conklin claims that their understanding of law collapses into a more primordial image of law whose boundaries we have for too long left unexamined

    Pigeons discriminate continuous versus discontinuous line segments

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    Three experiments examined various facets of the perception of continuous and discontinuous line segments in pigeons. Pigeons were presented with 2 straight lines that were interrupted by a gap. In some instances, the lines were the same angle and were positioned so that they appeared (to human observers) to form a continuous line. In other instances, the lines were different angles or the same angle but spatially misaligned. The birds were trained to classify each stimulus as continuous or discontinuous using a go/no-go procedure. A series of tests followed in which the birds received novel discontinuous displays made up of familiar line segments, continuous and discontinuous stimuli made up of novel line segments (novel straight lines or curved lines), and familiar displays in which the gap was covered with a gray square. Results from the tests indicated that 2 of the 3 pigeons had learned a continuous-discontinuous categorization and that they appeared to use the relationship between the 2 line segments in discriminating the displays

    Pigeon same-different concept learning with multiple stimulus classes.

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    An Analysis of Newbery Awards: 1922-1947

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    The intent of this project has been to focus on reading the Newbery award winners from 1922-1947 and to analyze and compare the books

    The influence of classical-conditioning procedures on subsequent attention to the conditioned brand.

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    Three experiments are used to investigate the influence of conditioning procedures on attention to a conditioned stimulus. In experiment 1, scenes presented in a sequence that is consistent with prescribed conditioning procedures are shown to encourage attention to the advertised brands in subsequent product displays. Experiment 2 suggests that differential attention to conditioned brands can be attributed to the signaling properties the brand acquires as a consequence of conditioning. Evidence from a third experiment raises the possibility that semantic conditioning may be responsible for the effects observed in experiments 1 and 2. The findings suggest that current prescriptions on the use of conditioning procedures may need to be updated.contingency awareness; orienting response; external validity; consumer research; context; stimulus; recall;
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