From the Hofstadter to the Fibonacci butterfly

We show that the electronic spectrum of a tight-binding Hamiltonian defined in a quasiperiodic chain with an on-site potential given by a Fibonacci sequence, can be obtained as a superposition of Harper potentials. The electronic spectrum of the Harper equation is a fractal set, known as Hofstadter butterfly. Here we show that is possible to construct a similar butterfly for the Fibonacci potential just by adding harmonics to the Harper potential. As a result, the equations in reciprocal space for the Fibonacci case have the form of a chain with a long range interaction between Fourier components. Then we explore the transformation between both spectra, and specifically the origin of energy gaps due to the analytical calculation of the components in reciprocal space of the potentials. We also calculate some localization properties by finding the correlator of each potential.Comment: 7 pages, 4 figure

Assessing the reliability and validity of agility testing in team sports: a systematic review

The aims of this systematic review were to: 1) examine the reliability of the reactive agility tests and, 2) analyse the discriminatory validity of the agility tests. A literature search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We explored PubMed, SPORTDiscus and Cochrane Plus databases looking for articles about agility in team sports. After filtering for article relevance, only 42 studies met the inclusion criteria; 37 of which assessed the reliability of agility tests and 22 assessing their validity. Reliability showed a high ICC in almost all studies (range 0.79-0.99) with the exception of two studies. In addition, other studies also assessed the reliability of decision time (ICC=0.95), movement time (ICC=0.92) and decision accuracy (ICC=0.74-0.93), all of which exhibited acceptable reliability. Furthermore, these data show high discriminatory validity, with higher performance players being faster than lower performance level players (mean = 6.4%, range = 2.1-25.3%), with a faster decision time (mean = 23.2%, range = 10.2-48.0%) with the exception of one study, and better decision accuracy (mean = 9.3%, range = 2.5-21.0%). Thus, it can be concluded that reactive agility tests show good reliability and discriminatory validity. However, most agility tests occur in simple contexts whereby only two possible responses are possible. Therefore, future research should consider creating more specific and complex environments which challenge the cognitive process of high-level athletes

Predicting volleyball serve-reception at group level

In a group-serve-reception task, how does serve-reception become effective? We addressed "who" receives/passes the ball, what task-related variables predict action mode selection and whether the action mode selected was associated with reception efficacy. In 182 serve-receptions we tracked the ball and the receivers' heads with two video-cameras to generate 3D world-coordinates reconstructions. We defined receivers' reception-areas based on Voronoi diagrams (VD). Our analyses of the data showed that this approach was accurate in describing "who" receives the serve in 95.05% of the times. To predict action mode selection, we used variables related to: serve kinematics, receiver's movement and on-court positioning, the relation between receiver and his closest partner, and interactions between receiver-ball and receiver-target. Serve's higher initial velocities together with higher maximum height, as well as smaller longitudinal distances between receiver and target increased the chances for the use of the overhand pass. Conversely, decreasing alignment of the receiver with the ball and the target increased the chances of using the underhand-lateral pass. Finally, the use of the underhand-lateral pass was associated with lower quality receptions. Behavioural variability's relevance for serve-reception training is discussed

Cambios en la arquitectura muscular y en la velocidad de ejecución de sentadillas en VersaPulley en condiciones estables e inestables en jugadores junior de baloncesto de élite durante una temporada

Los objetivos del presente estudio fueron: a) monitorizar y comparar la velocidadpico de ejecución de sentadillas con VersaPulley (VP) en condiciones estables (CE) y condiciones inestables (CI) en jugadores junior de baloncesto de élite durante una temporada y b) evaluar los cambios en la arquitectura muscular (AM). Siete jugadores junior de baloncesto realizaron el entrenamiento técnico-táctico y de acondicionamiento físico de la temporada (16 horas semanales) incluyendo entrenamiento de fuerza mediante sentadillas con VP en CE y CI. Durante la temporada se evaluó la velocidadpico de ejecución de las sentadillas mediante el sistema T-FORCE. Además, cada 3 meses se valoró la AM del vasto lateral mediante ultrasonidos. Los resultados no mostraron diferencias significativas en la velocidad pico al realizar sentadillas entre ambas condiciones en ningún momento de la temporada, aumentando un 17% en CE y un 23% en CI (p<0,01). El grosor muscular (p= 0,009) y el ángulo de peneación (p<0,05) aumentaron mientras que la longitud de los fascículos no experimentó cambios significativos. El entrenamiento regular de baloncesto y el entrenamiento de fuerza incluyendo sentadillas con VP en CE y CI generaron niveles similares de velocidadpico en ambas condiciones en jugadores de baloncesto júnior de élite. La velocidadpico aumentó tanto en CE como en CI durante la temporada. Además, se produjeron cambios en la AM

Design of the traction battery for a Formula SAE racing car

This paper describes the design of the traction battery for the new electric Formula SAE vehicle of the University of Pisa. A model based design methodology extended to the mechanical, electrical and thermal domains was applied to find the best trade-off between the battery weight and the maximum power available at the wheel. The designed battery configuration was validated by means of electrical and thermal simulations

MoS2 Nanosheets Uniformly Anchored on NiMoO4 Nanorods, a Highly Active Hierarchical Nanostructure Catalyst for Oxygen Evolution Reaction and Pseudo-Capacitors

Hierarchical nanostructures have attracted considerable research attention due to their applications in the catalysis field. Herein, we design a versatile hierarchical nanostructure composed of NiMoO4 nanorods surrounded by active MoS2 nanosheets on an interconnected nickel foam substrate. The as-prepared nanostructure exhibits excellent oxygen evolution reaction per-formance, producing a current density of 10 mA cm−2 at an overpotential of 90 mV, in comparison with 220 mV necessary to reach a similar current den-sity for NiMoO4. This behavior originates from the structural/morphological properties of the MoS2 nanosheets, which present numerous surface-active sites and allow good contact with the electrolyte. Besides, the structures can effectively store charges, due to their unique branched network providing accessible active surface area, which facilitates intermediates adsorptions. Particularly, NiMoO4/MoS2 shows a charge capacity of 358 mAhg−1 at a current of 0.5 A g−1 (230 mAhg−1 for NiMoO4), thus suggesting promising applications for charge-storing devices

Implementation of the fast charging concept for electric local public transport: The case-study of a minibus

This paper shows an effective implementation of the fast charging concept in the electric local public transport context. An electric minibus powered with a lead-acid battery is considered as a case-study. Its traction battery is redesigned using 12 V standard lithium-iron-phosphate modules to benefit from the higher performance of the lithium battery technology compared to the lead-acid one. The minibus can achieve a continuous operation characterised by 20 min of traveling alternated with 10 min of standstill for fast recharging of the battery. Experiments performed on a single module of the battery show that the load profile is sustained without appreciable issues both in temperature and life degradation of the lithium cells