Search

The objective of this work was the development of a three-phase, six pole stepper motor with stator and rotor core built from Fe50%Ni alloy via powder metallurgy. The study involves analysis of the magnetic, electrical and mechanical properties, besides motor design and software simulation using finite elements. The Fe50%Ni alloy showed as result an electrical resistivity of 0.37 %%˙m, relative permeability of 946 and maximum induction of 0.93 T. In the computational simulation, with the application of 1 A current per phase, the required voltage was 2.88 V, which resulted in a power of 2.88 W. In this condition the stepper motor generates a torque of 6.81.10- 4 Nm with an air gap induction of 0.55 T. [ABSTRACT FROM AUTHOR]

This paper studies the global dynamics of piecewise smooth differential equations defined in the two-dimensional torus and sphere in the case when the switching manifold breaks the manifold into two connected components. Over the switching manifold, we consider the Filippov's convention for discontinuous differential equations. The study of piecewise smooth dynamical systems over torus and sphere is common for maps and up to where we know this is the first characterization for piecewise smooth flows arising from solutions of differential equations. We provide conditions under generic families of piecewise smooth equations to get periodic and dense trajectories. Considering these generic families of piecewise differential equations, we prove that a non-deterministic chaotic behaviour appears. Global bifurcations are also classified. [ABSTRACT FROM AUTHOR]

This work aims to present the study of synchronous electrical machines with permanent magnets for use in wind turbines, where the rotor, usually built from laminated sheets of low carbon steel and FeSi, will be replaced by sintered alloys obtained from Powder Metallurgy. Thus, in this work, studies will be conducted in order to verify the feasibility of using pure iron and some sintered alloys, such as FeSi and FeNi, to construct the referred rotor. These materials will be characterized in terms of their physical properties as well as simulations of the machine will be carried out in three different topologies of the rotors. Two machines have the magnets bonded to the surface of the rotors, with two different configurations, namely straight poles and poles protruding, and the third one has the magnets inserted inside the rotor core. The simulations results of different topologies pointed out that for machines with rolled sheet, the best-sintered alloy in order to replace the rotor core would be Fe-2%P. The worst case would be the machine with magnets embedded having the other two similar torque results. [ABSTRACT FROM AUTHOR]

The purposes of this paper were to study the thermal treatment of Fe-Si sheet, as well as the sheet cutting concerning the topology of a mini stepper motor and mini motor simulation using finite element software. The research consisted of the execution of an "Inductive Reheating" thermal treatment of Iron Silicon sheets, NM71-2000/35F 420M with GNO (Grain Non Oriented), and 0.35mm width. The new technique has the benefit of minimizing magnetic losses produced by the cut on the edge of electric sheets. To carry out the process, the system includes a furnace, an induction coil, and a power supply that, when activated in a controlled way, causes relevant changes to the crystalline structure of the material. Related to the cut of the sheets, the topology of a three phase mini stepper motor was considered. The sheets were initially cut using the geometry of the rotor and stator cores. Firstly, a die cutting process was used and later a wire electroerosion cutting process was employed, which provided parts with excellent finishing. Finally, the mini motor was simulated using the finite element software FEMM 4.2 in order to analyze the airgap flow and torque development of the axis end, in comparison to a solid block of the same material (Fe-Si). [ABSTRACT FROM AUTHOR]

This study assessed the effect of acute continuous and intermittent physical activity (PA) on children's executive function (EF). Twenty-four participants (14 boys M = 10.32 ± 0.48 years), using a within-subjects design, performed a continuous (70% HRmax) and an intermittent (≥85%HRmax; 12 bouts: 30 s work, 45 s rest) PA bout of cycling, both lasting 15 min. Executive function was assessed using the Stroop task, Digit Span and Corsi Blocks tests and these were administered before and 1 min and 30 min post PA. Comparing both conditions, performance at the Stroop task (i.e., reaction time) improved in the continuous condition after 1 min and after 30 min (congruent stimuli) (mean diff = 126 ms ± 59; p = 0.047 and mean diff = 89 ms ± 38; p = 0.031, respectively). The intermittent condition improved at 30 min post (congruent and incongruent) (mean diff = 116 ms ± 46; p = 0.021 and mean diff = 111 ms ± 49; p = 0.039, respectively) showing a delayed benefit from the PA bout and greater improvements compared to the continuous condition. Verbal memory was improved for the continuous condition 1 min post only and no effects on visual memory were observed for both experimental conditions. The results demonstrated that both acute PA bouts might be a time-efficient approach for enhancing EF, with intermittent PA having a delayed and greater benefit., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)