Magnetization pinning in modulated nanowires: from topological protection to the "corkscrew" mechanism

Diameter-modulated nanowires offer an important paradigm to design the magnetization response of 3D magnetic nanostructures by engineering the domain wall pinning. With the aim to understand its nature and to control the process, we analyze the magnetization response in FeCo modulated polycrystalline two-segment nanowires varying the minor diameter. Our modelling indicates a very complex behavior with a strong dependence on the disorder distribution and an important role of topologically non-trivial magnetization structures. We demonstrate that modulated nanowires with a small diameter difference are characterized by an increased coercive field in comparison to the straight ones which is explained by a formation of topologically protected walls formed by two 3D skyrmions with opposite chiralities. For a large diameter difference we report the occurrence of a novel pinning type called here the "corkscrew": the magnetization of the large diameter segment forms a skyrmion tube with a core position in a helical modulation along the nanowire. This structure is pinned at the constriction and in order to penetrate the narrow segments the vortex/skyrmion core size should be reduced

Semiempirical Modeling of Reset Transitions in Unipolar Resistive-Switching based Memristors

We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-phi), they can be described by a simple model containing only three parameters: the charge (Qrst) and the flux (rst) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q-phi plots. There is a strong correlation between these three parameters, the origin of which is still under study

Clima organizacional y liderazgo transformacional en los trabajadores del Estadio Nacional - Lima, 2016

La presente investigación, tiene como objetivo establecer la relación entre el clima organizacional y el liderazgo transformacional en los trabajadores del Estadio Nacional de Lima. Las variables investigadas fueron el clima organizacional y el liderazgo transformacional y sus dimensiones: identidad institucional, relaciones interpersonales y dinámica institucional. El tipo de investigación es básica de nivel descriptivo-correlacional y de diseño no experimental de corte transversal. Se trabajó con una población de 100 trabajadores, empleándose las escalas de liderazgo transformacional de Bass (1985), y de clima organizacional de Berrocal (2007), ambos instrumentos tienen validez y confiabilidad. La conclusión a la que se llegó con este estudio luego del análisis e interpretación de los resultados es que existe la relación entre las variables Clima Organizacional y Liderazgo Transformacional obteniendo un Rho de Spearman igual a 0,894, señalando que existe una relación positiva con un nivel de correlación alta. Así mismo el nivel de significancia fue de ρ = 0,00 (ρ < 0,01), lo que indica una relación significativa entre el clima organizacional y el liderazgo transformacional en los trabajadores del estadio nacional, Lima 2016, por lo que se acepta la hipótesis general alternativa

Micromagnetic modelling of magnetic domain walls and domains in cylindrical nanowires

Magnetic cylindrical nanowires are very fascinating objects where the curved geometry allows many novel magnetic effects and a variety of non-trivial magnetic structures. Micromagnetic modelling plays an important role in revealing the magnetization distribution in magnetic nanowires, often not accessible by imaging methods with sufficient details. Here we review the magnetic properties of the shape anisotropy-dominated nanowires and the nanowires with competing shape and magnetocrystalline anisotropies, as revealed by micromagnetic modelling. We discuss the variety of magnetic walls and magnetic domains reported by micromagnetic simulations in cylindrical nanowires. The most known domain walls types are the transverse and vortex (Bloch point) domain walls and the transition between them is materials and nanowire diameter dependent. Importantly, the field or current-driven domain walls in cylindrical nanowires can achieve very high velocities. In recent simulations of nanowires with larger diameter the skyrmion tubes are also reported. In nanowires with large saturation magnetization the core of these tubes may form a helicoidal ('corkscrew') structure. The topology of the skyrmion tubes play an important role in the pinning mechanism, discussed here on the example of FeCo modulated nanowires. Other discussed examples include the influence of antinotches ('bamboo' nanowires) on the remanent magnetization configurations for hcp Co and FeCo nanowires and Co-Ni multisegmented nanowires.Comment: 24 pages, 17 figures, 1 tabl

Analysis of the Influence of Power System Diversion on the Optimal Supply Strategy of Renewable Power Plants

This paper presents an analysis of the influence of power system deviation prediction on the bidding strategy of renewable generation units in spot markets. The optimal bid that a renewable generator makes is subject to the best possible forecast at the time it submits the energy bid to the spot market, which is usually between 12–36 hours in advance of the time of delivery. With these lead times, renewable generators have to assume a significant volume risk in relation to the difference that may occur between the energy finally delivered and the energy previously committed for their participation in the market, since deviations from the committed energy will be valued at the deviations price. In this sense, the analysis carried out in this work shows that the prices of deviations are highly influenced by the energy needs to be raised or lowered by the system at the time of delivery. In other words, in the event that the deviation of the renewable generator goes against the system, the generator will generally have a higher penalty, having to assume the cost of the energy deviation at a price higher than the spot market price. On the other hand, if the plant’s deviation benefits the system, the penalty will be significantly lower (and sometimes even zero). The proposed analysis methodology develops the formulation of the expected benefit of the plant obtained through its participation in the spot market and subsequent settlement of the deviations. This formulation includes the modeling of the effect of the system deviation on the plant’s profits, which allows to satisfactorily identify the influence of the prediction of this variable on the optimal offer strategy. This methodology has been tested for the case of a wind farm operating in the Spanish market. For this purpose, real data of forecasts and final production of the wind farm have been used, as well as real data of the spot market, prices of the balancing service and real deviation of the system, which has allowed to verify in totally realistic conditions the importance of the prediction of the direction of deviation of the system in the optimal bidding. In this way, it will be possible to establish new optimal bidding strategies that focus efforts on advanced prediction techniques for this variable, which will result in greater benefits for wind power plants for their participation in the energy markets.