Manipulation of Magnetic Skyrmions by Superconducting Vortices in Ferromagnet-Superconductor Heterostructures

Dynamics of magnetic skyrmions in hybrid ferromagnetic films harbors novel physical phenomena and holds promise for technological applications. In this work, we discuss the behavior of magnetic skyrmions when coupled to superconducting vortices in a ferromagnet-superconductor heterostructure. We use numerical simulations and analytic arguments to reveal broader possibilities for manipulating the skyrmion-vortex dynamic correlations in the hybrid system, that are not possible in its separated constituents. We explore the thresholds of particular dynamic phases, and quantify the phase diagram as a function of the relevant material parameters, applied current and induced magnetic torques. Finally, we demonstrate the broad and precise tunability of the skyrmion Hall-angle in presence of vortices, with respect to currents applied to either or both the superconductor and the ferromagnet within the heterostructure

Procedure to evaluate multivariate statistical process control using ARIMA-ARCH models

Technological development and production processes require statistical process control in the use of alternative techniques to evaluate a productive process. This paper proposes an alternative procedure for monitoring a multivariate productive process using residuals obtained from the principal component scores modeled by the general class of autoregressive integrated moving average (ARIMA) and the generalized autoregressive conditional heteroskedasticity (GARCH) processes. We seek to obtain and investigate non-correlated and independent residuals by means of X-bar and exponentially weighted moving average (EWMA) charts as a way to capture large and small variations in the productive process. The principal component analysis deals with the correlation among the variables and reduces the dimensions. The ARIMA-GARCH model estimates the mean and volatility of the principal components selected, providing independent residuals that are analyzed using control charts. Thus, a multivariate process can be assessed using univariate techniques, taking into account both the mean and the volatility behavior of the process. Therefore, we present an alternative procedure to evaluate a process with multivariate features to determine the level of volatility persistence in the productive process when an external action occurs

The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model

We investigate the structure of hybrid stars based on two different constructions: one is based on the Gibbs condition for phase coexistence and considers the existence of a mixed phase (MP), and the other is based on the Maxwell construction and no mixed phase is obtained. The hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained are model dependent but not significantly different for both constructions.Comment: 8 pages, 7 figures, 3 table

Constraining relativistic models through heavy ion collisions

Relativistic models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter and finite nuclei properties, these studies taking place at low and moderate temperatures. Nevertheless, all results are model dependent and so far it is unclear whether some of them should be discarded. Moreover, in the regime of hot hadronic matter very few calculations exist using these relativistic models, in particular when applied to particle yields in heavy ion collisions. In the present work we comment on the known constraints that can help the selection of adequate models in this regime and investigate the main differences that arise when the particle production during a Au+Au collision at RHIC is calculated with different models.Comment: 9 pages, 1 figure, 3 table

The influence of the HAZ softening on the mechanical behaviour of welded joints containing cracks in the weld metal

The mechanical behaviour of welds containing cracks was analysed through the numerical simulation of the three-point bending tests of welded specimens. This paper presents the mechanical model and the methodology used for the numerical simulation of the tests. The variation in crack driving force of cracked welds is studied as a function of the strength mismatch in the heat affected zone and of the crack position relative to the weld metal/heat affected zone interface. This analysis was performed with recourse to the numerical calculation of the J integral.http://www.sciencedirect.com/science/article/B6V2R-4B0X38N-6/1/7027467d6e068a7f5c062427de733a1

Numerical simulation of tensile tests of prestrained sheets

The effect of cross section variation on formability of prestrained samples has been investigated using finite element simulations of a standard sheet tensile test. The mechanical model takes into account large elastoplastic strains and rotations that occur during deformation. Hill's orthotropic yield criterion with isotropic hardening describes the anisotropic plastic properties of the sheet. The isotropic hardening is modelled by a modified Swift law that describes the response of prestrained materials in reloading. Two different situations were simulated: reloading in tension of samples with constant cross sectional area and reloading in tension of samples with two zones of slightly different cross sectional areas. The results show that the strain distribution along the tensile axis of a prestrained sample depends on the level of the prestrain and also on the presence and size of geometrical fluctuations in the cross section, which always occur in experimental samples. This dependence is higher for materials with lower work-hardening rates.http://www.sciencedirect.com/science/article/B6TXD-3W6F4W3-D/1/b0ee20cd6d1b35fcfc8bda63d6c9f67

Three-dimensional numerical simulation of Vickers indentation tests

The development of depth sensing indentation equipment has allowed easy and reliable determination of two of the most popular measured mechanical properties of materials: the hardness and the Young's modulus. However, some difficulties emerge in the experimental procedure to calculate accurate values of these properties. This is related to, for example, the tip geometrical imperfections of the diamond pyramidal indenter and the definition of the contact area at the maximum load. Being so, numerical simulation of ultramicrohardness tests can be a helpful tool for better understanding of the influence of these parameters on procedures for determining the hardness and the Young's modulus. For this purpose, specific finite element simulation software, HAFILM, was developed to simulate the ultramicrohardness tests. Different mesh refinements were tested because of the dependence between the values of the mechanical properties and the size of the finite element mesh. Another parameter studied in this work is the value of the friction coefficient between the indenter and the sample in the numerical simulation. In order to obtain numerical results close to reality, a common geometry and size of the imperfection of the tip of Vickers indenter was taken into account for the numerical description of the indenter.http://www.sciencedirect.com/science/article/B6VJS-4FXNRM9-2/1/fc471d8e5a726ca5ef37aaf842f333c