1,720,969 research outputs found
Analytic Lagrangian tori for the planetary manybody problem
No full textIn 2004 J. Féjoz [Démonstration du ‘théorème d’Arnold’ sur la stabilité du système planétaire
(d’après M. Herman). Ergod. Th. & Dynam. Sys, 24(5):1521-1582, 2004], completing
investigations of M. Herman’s [Démonstration d’un théorème de V.I. Arnold. Séminaire de
Systèmes Dynamiques et manuscripts, Université D. Diderot, Paris 7, 1998], gave a complete
proof of “Arnold’s Theorem” [V.I. Arnol’d. Small Denominators and Problems of Stability of
Motion in Classical and Celestial Mechanics. Usephi Mat. Nauk, 18(6 (114)):91-192, 1963]
on the planetary many–body problem, establishing, in particular, the existence of a positive
measure set of smooth (C1) Lagrangian invariant tori for the planetary many–body problem.
Here, using Rüßmann’s 2001 KAM theory [H. Rüßmann. Invariant Tori in Non-Degenerate
Nearly Integrable Hamiltonian Systems. R. & C. Dynamics, 2(6):119-203, 2001], we prove
the above result in the real–analytic class
Birkhoff Normal form for Gravity Water Waves
No full textWe consider the gravity water waves system with a one-dimensional periodic interface in infinite depth, and present the proof of the rigorous reduction of these equations to their cubic Birkhoff normal form (Berti et al. in Birkhoff normal form and long-time existence for periodic gravity Water Waves. arXiv:1810.11549, 2018). This confirms a conjecture of Zakharov–Dyachenko (Phys Lett A 190:144–148, 1994) based on the formal Birkhoff integrability of the water waves Hamiltonian truncated at degree four. As a consequence, we also obtain a long-time stability result: periodic perturbations of a flat interface that are of size ε in a sufficiently smooth Sobolev space lead to solutions that remain regular and small up to times of order ε- 3
Birkhoff Normal Form and Long Time Existence for Periodic Gravity Water Waves
Full text linkWe consider the gravity water waves system with a periodic one-dimensional interface in infinite depth and give a rigorous proof of a conjecture of Dyachenko-Zakharov [16] concerning the approximate integrability of these equations. More precisely, we prove a rigorous reduction of the water waves equations to its integrable Birkhoff normal form up to order 4. As a consequence, we also obtain a long-time stability result: periodic perturbations of a flat interface that are initially of size ε remain regular and small up to times of order (Formula presented.). This time scale is expected to be optimal. © 2022 The Authors. Communications on Pure and Applied Mathematics published by Wiley Periodicals LLC
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Candidate cases of poecilogony in Neogastropoda: Implications for the systematics of the genus Raphitoma Bellardi, 1847
No full textPoecilogony is the intraspecific variation in developmental mode, with larvae of different types produced by the same individual, population or species. It is very rare among marine invertebrates, and in gastropods has long been described only in a few opisthobranchs. The physiological and regulatory mechanisms underlying larval evolutionary transitions, such as loss of planktotrophy that occurred repeatedly in many caenogastropod lineages, are still largely unknown. We have studied the inter- v. intraspecific variation in larval development in the north-east Atlantic neogastropod genus Raphitoma Bellardi, 1847, starting with an iterative taxonomy approach: 17 morphology-based Preliminary Species Hypotheses were tested against a COI molecular-distance-based method (ABGD), and the retained species hypotheses were eventually inspected for reciprocal monophyly on a multilocus dataset. We subsequently performed an ancestral state reconstruction on an ultrametric tree of the 10 Final Species Hypotheses, time-calibrated by fossils, revealing that the interspecific changes were planktotrophy > lecithotrophy, and all have occurred in the Pleistocene, after 2.5 million years ago. This is suggestive of a major role played by Pleistocene Mediterranean oceanographic conditions-enhanced oligotrophy, unpredictable availability of water column resources-likely to favour loss of planktotrophy. Within this group of species, which has diversified after the Miocene, we identified one pair of sibling species differing in their larval development, Raphitoma cordieri (Payraudeau, 1826) and R. horrida (Monterosato, 1884). However, we also identified two Final Species Hypotheses, each comprising individuals with both larval developmental types. Our working hypothesis is that they correspond to one or two poecilogonous species. If confirmed by other nuclear markers, this would be the first documentation of poecilogony in the Neogastropoda, and the second in the whole Caenogastropoda. Although sibling species with different developmental strategies may offer good models to study some evolutionary aspects, poecilogonous taxa are optimally suited for identifying regulatory and developmental mechanisms underlying evolutionary transitions
Revision of Mediterranean and NE Atlantic Raphitomidae (Gastropoda, Conoidea) 8: The genus Leufroyia Monterosato, 1884
Full text linkThe four recent species of the genus Leufroyia Monterosato, 1884 are revised based on an integrative taxonomy approach: L. leufroyi (Michaud, 1828), L. concinna (Scacchi, 1836), L. erronea Monterosato, 1884 and L. villaria (Pusateri & Giannuzzi-Savelli, 2008)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Maternal hyperphenylalaninemia syndrome: neuropsychological evaluation of four subjects during childhood and adolescence.
No full textAbstract
Maternal hyperphenylalanemia during pregnancy may induce a severe embryopathy characterized by microcephaly, mental retardation, facial dysmorphy and congenital heart defects. Four subjects, two pairs of sibs, with maternal hyperphenylalaninemia syndrome were included in this study and their neuropsychological performances were assessed. Maternal levels of hyperphenylalaninemia were similar in both mothers, one of them had not been diagnosed with the condition until her two children were examined at the ages of 10 and 6 years. A severe cognitive deficit was detected in all 4 subjects, with a typical profile of impaired perceptive abilities, behavioural disturbances, motor difficulties and poor familiar integration
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