Diseño de estructura porosa irregular bioinspirada aplicada a productos de movilidad inteligente

La estructura de los materiales es una parte crucial del diseño de cualquier producto en el que se pretenda disipar las cargas y aligerar el material. Dado que algunas estructuras actuales son cada vez más complejas en cuanto a geometría y estructura interna, resulta imposible optar por los métodos tradicionales para fabricarlas. En este sentido, la fabricación aditiva permite crear estructuras complejas con geometrías intrincadas. Mientras los fabricantes buscan optimizar las propiedades de los materiales y su rendimiento en diversas condiciones de estrés, la ingeniería bioinspirada se fija en la naturaleza para resolver los retos más complejos del ser humano. Al imitar los patrones y las formas de la naturaleza, podemos optimizar la resistencia a la fractura, la absorción de energía y la tenacidad de los materiales. En este trabajo, empleamos patrones de teselación de Voronoi y software de diseño asistido por ordenador para diseñar un algoritmo para la creación de estructuras porosas irregulares, similares a las que se encuentran en la naturaleza (por ejemplo, el hueso trabecular). Este algoritmo es escalable y aplicable a cualquier producto que necesite cumplir con requisitos de ligereza y propiedades mecánicas sobresalientes. En este caso, los autores realizan ensayos de compresión estática para determinar las propiedades mecánicas. Los resultados indican que las propiedades mecánicas dependen directamente de las características microestructurales de la propia estructura porosa. Además, el área superficial y la porosidad son los principales parámetros a controlar. Por último, el algoritmo tiene una amplia gama de aplicaciones de ingeniería en las industrias de la automoción y aeroespacial

Spin rotation for ballistic electron transmission induced by spin-orbit interaction

We study spin dependent electron transmission through one- and two-dimensional curved waveguides and quantum dots with account of spin-orbit interaction. We prove that for a transmission through arbitrary structure there is no spin polarization provided that electron transmits in isolated energy subband and only two leads are attached to the structure. In particular there is no spin polarization in the one-dimensional wire for which spin dependent solution is found analytically. The solution demonstrates spin evolution as dependent on a length of wire. Numerical solution for transmission of electrons through the two-dimensional curved waveguides coincides with the solution for the one-dimensional wire if the energy of electron is within the first energy subband. In the vicinity of edges of the energy subbands there are sharp anomalies of spin flipping.Comment: 9 oages, 7 figure

Use of Silver Nanoparticles as Tougheners of Alumina Ceramics

In this work, alumina/silver composites were produced through powder techniques, which involve the combination of high energy mechanical milling combined with sintering in the presence of a liquid phase and with the idea of having ceramics with good toughness values. From mechanical characterizations, it was found that increases of the silver content in the alumina origins decrease the elastic’s modulus and flexural strength of the final composite. The fracture toughness of alumina increases from 4.2 MPam−0.5 for monolithic alumina to 10 MPam−0.5 for alumina with 2 wt% silver additions. It was determined that the reinforcement mechanism of these materials is due to the deflection of cracks owing to metallic bridges formed by the silver used as toughener material

Securing the legacy of TESS through the care and maintenance of TESS planet ephemerides

Much of the science from the exoplanets detected by the TESS mission relies on precisely predicted transit times that are needed for many follow-up characterization studies. We investigate ephemeris deterioration for simulated TESS planets and find that the ephemerides of 81% of those will have expired (i.e. 1$\sigma$ mid-transit time uncertainties greater than 30 minutes) one year after their TESS observations. We verify these results using a sample of TESS planet candidates as well. In particular, of the simulated planets that would be recommended as JWST targets by Kempton et al. (2018), $\sim$80% will have mid-transit time uncertainties $>$ 30 minutes by the earliest time JWST would observe them. This rapid deterioration is driven primarily by the relatively short time baseline of TESS observations. We describe strategies for maintaining TESS ephemerides fresh through follow-up transit observations. We find that the longer the baseline between the TESS and the follow-up observations, the longer the ephemerides stay fresh, and that 51% of simulated primary mission TESS planets will require space-based observations. The recently-approved extension to the TESS mission will rescue the ephemerides of most (though not all) primary mission planets, but the benefits of these new observations can only be reaped two years after the primary mission observations. Moreover, the ephemerides of most primary mission TESS planets (as well as those newly discovered during the extended mission) will again have expired by the time future facilities such as the ELTs, Ariel and the possible LUVOIR/OST missions come online, unless maintenance follow-up observations are obtained.Comment: 16 pages, 10 figures, accepted to AJ; main changes are cross-checking results against the sample of real TOIs, and addressing the impact of the TESS extended missio

The electronic properties of bilayer graphene

We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energy. We take into account five tight-binding parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure

Pumping in an interacting quantum wire

We study charge and spin pumping in an interacting one-dimensional wire. We show that a spatially periodic potential modulated in space and time acts as a quantum pump inducing a dc-current component at zero bias. The current generated by the pump is strongly affected by the interactions. It has a power law dependence on the frequency or temperature with the exponent determined by the interaction in the wire, while the coupling to the pump affects the amplitudes only. We also show that pure spin-pumping can be achieved, without the presence of a magnetic field.Comment: 13 pages,2 figure

Manufactura y caracterización de aleaciones de alta entropía

High entropy alloys are a new kind of multicomponent alloys, consisting of five or more metallic elements with equiatomic proportions. Despite the large number of alloying elements, HEA can exhibit simple solid solution phases, such as face- and body-centered cubic phases. In this work, the AlxCrCuFeNiTi (x = 0, 0.45, 1, 2.5, 5 mol) alloy was fabricated by mechanical alloying to determine the effect of aluminum on the phase evolution during the process and its impact on the mechanical properties. Grinding of the powders was carried out at 300 rpm during 180 minutes. The powders resulting from milling were pressed at 250 kg/cm2. The pressed samples were sintered at 1,300°C during 1 hour. From results it can be seen that with increasing Al concentration, the alloys undergo a transformation from a single FCC phase to mixture of FCC and BCC phases, as well as the precipitation of FeAl3, Al3Ni, TiAl and Ti3Al intermetallics. The alloy that achieved the highest hardness was the one with the highest Al content. These alloys harden significantly with the addition of Al, due to the BCC phase formation and intermetallic compounds.Las aleaciones de alta entropía son una nueva clase de aleaciones multicomponentes, que consisten en cinco o más elementos metálicos con proporciones equiatómicas. A pesar del gran número de elementos de aleación, las HEA pueden exhibir fases de solución sólida simples, como las fases cúbicas centrada en las caras y centrada en el cuerpo. En este trabajo se fabricó la aleación AlxCrCuFeNiTi (x = 0, 0.45, 1, 2.5, 5 mol) mediante aleado mecánico para determinar el efecto del aluminio en la evolución de fases durante el proceso y su impacto en las propiedades mecánicas. La molienda de los polvos se realizó a 300 rpm durante 180 minutos. Los polvos resultantes de la molienda se prensaron a 250 kg/cm2. Las muestras prensadas se sinterizaron a 1300°C durante 1 hora. De los resultados se tiene que, al aumentar la concentración de aluminio, las aleaciones sufren una transformación de una sola fase FCC a una mezcla de fases FCC y BCC, así como la precipitación de intermetálicos de FeAl3, Al3Ni, TiAl y Ti3Al. La aleación que alcanzó la mayor dureza fue la de mayor contenido de aluminio. Estas aleaciones se endurecen significativamente con la adición de aluminio, debido a la formación de la fase BCC y por la formación de intermetálicos

Investigating the Muscular and Kinematic Responses to Sudden Wrist Perturbations During a Dynamic Tracking Task

Sudden disturbances (perturbations) to the hand and wrist are commonplace in daily activities and workplaces when interacting with tools and the environment. It is important to understand how perturbations influence forearm musculature and task performance when identifying injury mechanisms. The purpose of this work was to evaluate changes in forearm muscle activity and co-contraction caused by wrist perturbations during a dynamic wrist tracking task. Surface electromyography was recorded from eight muscles of the upper-limb. Participants performed trials consisting of 17 repetitions of ±40° of wrist flexion/extension using a robotic device. During trials, participants received radial or ulnar perturbations that were delivered during flexion or extension, and with known or unknown timing. Co-contraction ratios for all muscle pairs showed significantly greater extensor activity across all experimental conditions. Of all antagonistic muscle pairs, the flexor carpi radialis (FCR)-extensor carpi radialis (ECR) muscle pair had the greatest change in co-contraction, producing 1602% greater co-contraction during flexion trials than during extensions trials. Expected perturbations produced greater anticipatory (immediately prior to the perturbation) muscle activity than unexpected, resulting in a 30% decrease in wrist displacement. While improving performance, this increase in anticipatory muscle activity may leave muscles susceptible to early-onset fatigue, which could lead to chronic overuse injuries in the workplace.Brock University Library Open Access Publishing Fun