9 research outputs found
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
Aspectos reprodutivos e dieta alimentar dos ninhegos de Rhinoptynx clamator (Aves: Strigidae) no campus Marco Zero da Universidade Federal do AmapĂĄ, MacapĂĄ-AP Nesting and diet of Rhinoptynx clamator (Aves: Strigidae) from Campus Marco Zero da Universidade Federal do AmapĂĄ, MacapĂĄ-AP
Este trabalho tem como objetivo relatar os aspectos comportamentais de nidificação, alimentação e desenvolvimento dos ninhegos de Rhinoptynx clamator (Strigidae) em um fragmento florestal no Campus Marco Zero da Universidade Federal do AmapĂĄ. Apenas um ninho foi encontrado, no solo e na base de um tucumĂŁ Astrocaryum oleatum. TrĂȘs ovos brancos com manchas marrons foram observados, cuja medida foi de 41 x 35 mm em mĂ©dia. A incubação durou 28 dias e foi efetuada pela fĂȘmea, e o Ășltimo filhote a nascer viveu apenas dois dias. Os filhotes sobreviventes foram medidos durante o seu desenvolvimento. Durante a estação reprodutiva foram coletadas algumas pelotas de regurgitação, sendo encontrados trĂȘs tipos de vertebrados: Rattus sp., Micoureus cf. regina e Columbina talpacoti.<br>We report nesting behavior, feeding and development of nestling of Rhinoptynx clamator (Strigidae) in a forest fragment on Campus Marco Zero of Universidade Federal do AmapĂĄ. The nest was located on the ground, close to a palm Astrocaryum oleatum and three eggs were observed. These eggs were white whit brown spots and measured 41 x 35 mm in average. Incubation was made by female and lasted 28 days and the last owlet died two days after born. The remaining birds were measured during its development. Feeding items includes Rattus sp., Micoureus cf. regina and Columbina talpacoti