A unified energy formulation for the stability analysis of open and closed thin-walled members in the framework of the generalized beam theory

Generalized beam theory--GBT--is among the most adequate tools for the analysis of thin-walled prismatic elements. It enables the analysis of the distortion of the element cross-section and local buckling of individual walls in a unified manner that incorporates the results from classical bending theory. The basis of this theory was developed in the 1960s by Schardt for first and second order elastic behaviour of thin-walled members.http://www.sciencedirect.com/science/article/B6V59-4CDHH8M-2/1/0dc966f0e6162a1c782229da7969d09

Upper-mantle structure of the Borborema Province, NE Brazil, from P-wave tomography: Implications for rheology and volcanism

We have performed a tomographic study of the upper mantle under the Borborema Province by inverting relative P-wave traveltime residuals (including the PKPdf phase). The events were recorded by more than 50 broad-band and short-period stations deployed across the region, resulting in a total data set of 1912 relative residuals. A multichannel phase cross-correlation technique was utilized to develop the measurements, which were then inverted through an iterative, non-linear inversion scheme based on the subspace inversion method. The Fast Marching Method, a grid-based numerical algorithm that traces an interface evolving over a narrow band of nodes that are updated solving the eikonal equation by finite differences using upwind entropy, was considered to solve the forward problem. Traveltimes from outside of the 3-D model were calculated using a global reference model. The resulting tomographic images reveal structure down to depths of ~600 km, under an area extending approximately 800 km in the EW direction and 900 km in the NS direction. The most important features revealed by the tomographic images include: (i) a relatively fast lithospheric mantle under the southern Borborema Plateau, when compared to the lithospheric mantle north of the Patos Lineament; (ii) a marked, shallow ( < 150 km) low-velocity anomaly under the northeastern most corner of the Borborema Province; and (iii) a low-velocity channel bordering the Borborema Plateau at asthenospheric (250 - 400 km) depths. The lithospheric velocity contrast is interpreted as arising from a colder, stronger lithosphere south of the lineament, while the asthenospheric low-velocity channel is interpreted as resulting from lateral flow from a distant mantle plume (located in SE Brazil). We argue that the rheological contrast validates a stretching model recently proposed to explain the Plateau's elevated topography, and that the postulated lateral flow represents the source of magmas feeding intraplate volcanism in NE Brazil for the past ~80 Ma. © The Author(s) 2018.Data were collected with support of the Instituto Nacional de Ciência e Tecnologia em Estudos Tectônicos (INCT-ET) of the Centro Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grant number 57.3713/2008-01) and the BOrborema Deep Electromagnetic and Seismic experiment (BODES) (CNPq, grant number 400743/2014-0). FLSN acknowledges support from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) through a 4-yr scholarship to complete his PhD at the Universidade Federal do Rio Grande do Norte (UFRN). JJ thanks CNPq for his research fellowship (CNPq, grant number 304421/2015-4). MS acknowledges support by Brazilian Science Without Border Program, grant number 40.2174/2012-7.Peer reviewe