2,225 research outputs found
Effect of current corrugations on the stability of the tearing mode
The generation of zonal magnetic fields in laboratory fusion plasmas is
predicted by theoretical and numerical models and was recently observed
experimentally. It is shown that the modification of the current density
gradient associated with such corrugations can significantly affect the
stability of the tearing mode. A simple scaling law is derived that predicts
the impact of small stationary current corrugations on the stability parameter
. The described destabilization mechanism can provide an explanation
for the trigger of the Neoclassical Tearing Mode (NTM) in plasmas without
significant MHD activity.Comment: Accepted to Physics of Plasma
A technical note on the phase transformation in furnace container material after a periodic thermo-chemical treatment
The aim of this work is to investigate the metallurgical changes in the wall of cylindrical containers, fabricated by welding from AISI 310 steel, used in the thermal and chemical treatment of spindle chains for the automotive industry, for an in-service period of over 1000 h. In order to identify the phases originated during this in-service period, several etchants were used in the structural study, together with X-ray diffraction and 57Fe Mössbauer spectroscopy analysis. The metallographic technique demonstrates some limitations in the complete identification of the phases produced in the wall of the containers. The structure of the wall of the containers, after the referred to working period, is composed of an austenitic matrix, whose grain size is about 212 and 238 [mu]m, near the internal and external faces of the wall, respectively. These show numerous precipitates inside the grains and at the grain boundaries. The density of the precipitates decreases from the internal to the external surface. The precipitates are nitrides (Cr, Mo)12 (Fe,Ni)8-x N4-z near the internal surface, and carbides (Cr, Fe, Mo)23C6 on the other zones of the wall.http://www.sciencedirect.com/science/article/B6TGJ-4502Y49-G/1/4e6ae31d16e053b40c961bebbfda1e0
Numerical study of the plastic behaviour in tension of welds in high strength steels
The influence of the mismatch between material properties and constraint on the plastic deformation behaviour of the heat affected zone of welds in high strength steels is investigated in this study, using finite element simulations. An elastoplastic implicit three-dimensional finite element code (EPIM3D) was used in the analysis. The paper presents the mechanical model of the code and the methodology used for the numerical simulation of the tensile test of welded joints. Numerical results of the tensile test of welded samples with different hypothetical widths for the Heat Affected Zone and various material mismatch levels are shown. The analysis concerns the overall strength and ductility of the joint and in relation to the plastic behaviour of the heat affected zone. The influence of the yield stress, tensile strength and constraint on the stress and plastic strain distribution in the soft heat affected zone is also discussed.http://www.sciencedirect.com/science/article/B6TWX-47G3PVT-2/1/f1caf121d3e6678da6f3259e6d795cd
Central factorials under the Kontorovich-Lebedev transform of polynomials
We show that slight modifications of the Kontorovich-Lebedev transform lead
to an automorphism of the vector space of polynomials. This circumstance along
with the Mellin transformation property of the modified Bessel functions
perform the passage of monomials to central factorial polynomials. A special
attention is driven to the polynomial sequences whose KL-transform is the
canonical sequence, which will be fully characterized. Finally, new identities
between the central factorials and the Euler polynomials are found.Comment: also available at http://cmup.fc.up.pt/cmup/ since the 2nd August
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Fertilidade de ovelhas cÃclicas submetidas à sincronização do estro utilizando implantes intravaginais (CIDR) novos ou reutilizados.
Edição dos Resumos XXII Reunião Anual da Sociedade Brasileira de Tecnologia de Embriões, Guarujá, SP, 2008
Formation and Structure of a Current Sheet in Pulsed-Power Driven Magnetic Reconnection Experiments
We describe magnetic reconnection experiments using a new, pulsed-power
driven experimental platform in which the inflows are super-sonic but
sub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,
producing a well-defined reconnection layer that persists over many
hydrodynamic time scales.The layer is diagnosed using a suite of high
resolution laser based diagnostics which provide measurements of the electron
density, reconnecting magnetic field, inflow and outflow velocities and the
electron and ion temperatures.Using these measurements we observe a balance
between the power flow into and out of the layer, and we find that the heating
rates for the electrons and ions are significantly in excess of the classical
predictions. The formation of plasmoids is observed in laser interferometry and
optical self-emission, and the magnetic O-point structure of these plasmoids is
confirmed using magnetic probes.Comment: 14 pages, 12 figures. Accepted for publication in Physics of Plasma
Phylogenomics of pike cichlids (Cichlidae: Crenicichla): the rapid ecological speciation of an incipient species flock
© 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology The rapid rise of phenotypic and ecological diversity in independent lake-dwelling groups of cichlids is emblematic of the East African Great Lakes. In this study, we show that similar ecologically based diversification has occurred in pike cichlids (Crenicichla) throughout the Uruguay River drainage of South America. We collected genomic data from nearly 500 ultraconserved element (UCEs) loci and \u3e260 000 base pairs across 33 species, to obtain a phylogenetic hypothesis for the major species groups and to evaluate the relationships and genetic structure among five closely related, endemic, co-occurring species (the Uruguay River species flock; URSF). Additionally, we evaluated ecological divergence of the URSF based on body and lower pharyngeal jaw (LPJ) shape and gut contents. Across the genus, we recovered novel relationships among the species groups. We found strong support for the monophyly of the URSF; however, relationships among these species remain problematic, likely because of the rapid and recent evolution of this clade. Clustered co-ancestry analysis recovered most species as well delimited genetic groups. The URSF species exhibit species-specific body and LPJ shapes associated with specialized trophic roles. Collectively, our results suggest that the URSF consists of incipient species that arose via ecological speciation associated with the exploration of novel trophic roles
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