Effects of synthetic turf and shockpads on impact attenuation related biomechanics during drop landing

Synthetic turf has been widely utilized in sports since 1964. Discrepancies, however, in injury incidence on synthetic turf and natural grass have been reported throughout studies. Adding a shock pad under synthetic turf carpet is claimed to aid in energy absorption and decrease impact loading. Although some studies have conducted materials tests and compared mechanical characteristics of synthetic turf with different shock pads, no studies have examined biomechanical characteristics of impact related human movements on an infilled synthetic turf system with different underlying shock pads. The purpose of this research was to investigate effects of an infilled synthetic turf with three shock pads of different energy absorption characteristics on impact attenuation related biomechanics of lower extremity during drop landing. Wearing running shoes, twelve active and healthy recreational male athletes performed five trials of drop landing from 60 cm with a controlled landing style (maximum knee flexion) on five surface conditions: a regular surface (force platform), an infilled synthetic turf, turf plus foam shock pad, turf plus a lower density shock pad, and turf plus a high density shock pad. A motion analysis system and force platform were utilized to collect kinematic and kinetic data. Furthermore, a mechanical test was conducted based on ASTM F355 standard. The turf plus shock pad systems resulted in lower 1st vertical peak ground reaction force (GRF) and its loading rates compared to synthetic turf without a shock pad. However, no differences in 2nd vertical GRF and joint kinematics and kinetics across surfaces were found. These results suggest that landing from 60 cm may cause a plateau effect in energy attenuation for the examined turf and turf plus shock pad systems. Future studies may be needed to explore the shock attenuation capacities of landing surfaces in landing activities from a lower height (\u3c 60 cm)

Liquid-core low-refractive-index-contrast Bragg fiber sensor

We propose and experimentally demonstrate a low-refractive-index-contrast hollow-core Bragg fiber sensor for liquid analyte refractive index detection. The sensor operates using a resonant sensing principle- when the refractive index of a liquid analyte in the fiber core changes, the resonant confinement of the fiber guided mode will also change, leading to both the spectral shifts and intensity changes in fiber transmission. As a demonstration, we characterize the Bragg fiber sensor using a set of NaCl solutions with different concentrations. Strong spectral shifts are obtained with the sensor experimental sensitivity found to be ~1400nm/RIU (refractive index unit). Besides, using theoretical modeling we show that low-refractive-index-contrast Bragg fibers are more suitable for liquid-analyte sensing applications than their high-refractive-index-contrast counterparts.Comment: 3 pages, 4 figure

Robust Intrinsic Ferromagnetism and Half Semiconductivity in Stable Two-Dimensional Single-Layer Chromium Trihalides

Two-dimensional (2D) intrinsic ferromagnetic (FM) semiconductors are crucial to develop low-dimensional spintronic devices. Using density functional theory, we show that single-layer chromium trihalides (SLCTs) (CrX$_3$,X=F, Cl, Br and I) constitute a series of stable 2D intrinsic FM semiconductors. A free-standing SLCT can be easily exfoliated from the bulk crystal, due to a low cleavage energy and a high in-plane stiffness. Electronic structure calculations using the HSE06 functional indicate that both bulk and single-layer CrX$_3$ are half semiconductors with indirect gaps and their valence bands and conduction bands are fully spin-polarized in the same spin direction. The energy gaps and absorption edges of CrBr$_3$ and CrI$_3$ are found to be in the visible frequency range, which implies possible opt-electronic applications. Furthermore, SLCTs are found to possess a large magnetic moment of 3$\mu_B$ per formula unit and a sizable magnetic anisotropy energy. The magnetic exchange constants of SLCTs are then extracted using the Heisenberg spin Hamiltonian and the microscopic origins of the various exchange interactions are analyzed. A competition between a near 90$^\circ$ FM superexchange and a direct antiferromagnetic (AFM) exchange results in a FM nearest-neighbour exchange interaction. The next and third nearest-neighbour exchange interactions are found to be FM and AFM respectively and this can be understood by the angle-dependent extended Cr-X-X-Cr superexchange interaction. Moreover, the Curie temperatures of SLCTs are also predicted using Monte Carlo simulations and the values can further increase by applying a biaxial tensile strain. The unique combination of robust intrinsic ferromagnetism, half semiconductivity and large magnetic anisotropy energies renders the SLCTs as promising candidates for next-generation semiconductor spintronic applications.Comment: 12 pages, 14 figures. published in J. Mater. Chem.

All-solid flexible fiber-shaped lithium ion batteries

We propose fabrication of the fiber-shaped lithium ion batteries assembled by twisting a cathode filament together with an anode filament. The cathode filament is fabricated by depositing a LiFePO4 (LFP)-composite layer onto a steel-filled polyester conductive thread (SPCT). As anode filaments, we propose several scenarios including a Li4Ti5O12 (LTO)-composite coated SPCT (dip-and-dry deposition), a tin-coated SPCT (PVD deposition) as well as a bare tin wire. An electrolyte composite layer consisting of LiPF6 and polyethylene oxide (PEO) is then deposited onto both the anode and cathode filament before the battery assembly. By twisting the cathode filament and anode filament together using a customized jig, the batteries are then assembled. The open-circuit voltage is found to be ~ 2.3 V for the battery using the LTO@SPCT anode, and ~3.3 V for the battery using the tin@SPCT anode and the tin wire anode. Charge-discharge tests are carried out at different C rates for each battery sample. Experimental results suggest that the LIBs using the LTO@SPCT anode, the tin@SPCT anode and the bare tin wire anode could achieve a specific capacity of ~64, ~67, and ~96 mAh/g, respectively, when charge-discharged at 0.5-C rate. The battery could retain well its capacity after 80 charge-discharge cycles. During operation of all the batteries reported in this paper, their coulombic efficiency remained above 80%. Among the advantages of the proposed LIB are light weight, ease of fabrication, high specific capacitance, high energy density, and good durability. Finally, employing cheap and commercially-available steel-filled polyester threads as a base material in our batteries, makes them potentially suitable for integration into wearables using various standard textile manufacturing techniques