39 research outputs found
Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V_2O_3
Magnetic correlations in all four phases of pure and doped vanadium
sesquioxide V_2O_3 have been examined by magnetic thermal neutron scattering.
While the antiferromagnetic insulator can be accounted for by a Heisenberg
localized spin model, the long range order in the antiferromagnetic metal is an
incommensurate spin-density-wave, resulting from a Fermi surface nesting
instability. Spin dynamics in the strongly correlated metal are dominated by
spin fluctuations in the Stoner electron-hole continuum. Furthermore, our
results in metallic V_2O_3 represent an unprecedentedly complete
characterization of the spin fluctuations near a metallic quantum critical
point, and provide quantitative support for the SCR theory for itinerant
antiferromagnets in the small moment limit. Dynamic magnetic correlations for
energy smaller than k_BT in the paramagnetic insulator carry substantial
magnetic spectral weight. However, the correlation length extends only to the
nearest neighbor distance. The phase transition to the antiferromagnetic
insulator introduces a sudden switching of magnetic correlations to a different
spatial periodicity which indicates a sudden change in the underlying spin
Hamiltonian. To describe this phase transition and also the unusual short range
order in the paramagnetic state, it seems necessary to take into account the
orbital degrees of freedom associated with the degenerate d-orbitals at the
Fermi level in V_2O_3.Comment: Postscript file, 24 pages, 26 figures, 2 tables, accepted by Phys.
Rev.
The beagle dog MicroRNA tissue atlas: identifying translatable biomarkers of organ toxicity
Nonlinear analysis of concrete structures using GFEM enrichment strategy with a microplane constitutive model
Experimental and finite element analysis of bond-slip in reinforced concrete
Abstract The modeling of reinforced concrete structures has taken advantage of the increasing progress on Computational Mechanics, in such way that complex phenomena, such as cracking and crushing, creep, reinforcement yielding, steel-concrete bond loss, can be modeled in a reasonable realistic way, using the proper set of numerical and computational resources. Among several options, the ones based on the Finite Element Method (FEM) allow complex analysis simulations of reinforced concrete structures, including the interaction of different nonlinear effects. This paper deals with the nonlinear finite element analysis of the bond-slip between reinforcing steel and concrete, taking into account an experimental study previously performed. The FEM analysis presented uses a combination of resources where the material behavior of concrete is described by the Microplane Constitutive Model, and an embedded reinforcement model is used to represent steel inside the concrete and take into account the effect of bond-slip. The FEM models were created using the INSANE (INteractive Structural ANalysis Environment) computational system, open source software that has a set of FEM tools for nonlinear analysis of reinforced concrete structures. The correlations between numerical-experimentals results and several parameters validate the proposed combination of resources and identifies the significance of various effects on the response
Nonlinear analysis of concrete structures using GFEM enrichment strategy with a microplane constitutive model
<div><p>Abstract One of the most widespread methods to the nonlinear analysis of structures is the Finite Element Method (FEM). However, there are phenomena whose behavior is not satisfactorily simulated by the standard FEM and this fact has quickened the development of new strategies such as the Generalized Finite Element Method (GFEM), understood as a variation of the FEM. In parallel, nonlinear analysis of concrete structures requires the use of constitutive models that represents the nucleation and propagation of cracks. In this paper it is used an anisotropic constitutive model, based on the microplane theory, which is able to represent the behavior of concrete structures, together with the GFEM approach. These resources are incorporated on the INSANE system (INteractive Structural ANalysis Environment), used in the numerical simulations presented here to demonstrate the feasibility of using the GFEM enrichment strategy, in the nonlinear analysis of concrete structures, with validation made from comparisons with experimental results available in the literature.</p></div