Recommendations for measuring tennis racket parameters

Tennis rackets have advanced significantly since the invention of the game in 1874, including innovations in both shape and materials. Advances in these design parameters have implications for racket performance, especially swing speed. This study tested one hundred rackets, spanning brands and eras, using simple, portable instruments in order to pilot protocols and make recommendations for streamlining testing procedures for tennis rackets. A wide range of properties were measured and documented for each racket. We suggest that since Transverse and Lateral Moment of Inertia are well correlated, measuring both is not necessary when processing a large number of rackets. In addition, it is also possible to predict the Transverse Moment of Inertia well from models that use simple dimension and mass measurements, which may be preferable in larger studies. Exploring the use of more complex modelling will allow us to better understand the impact of tennis racket design on performance in the future

Recommendations for estimating the moments of inertia of a tennis racket

Tennis racket properties are of interest to sports engineers and designers as it allows them to evaluate performance, review trends and compare designs. This study explored mathematical models that correlated to the mass moments of inertia of a tennis racket, both about an axis through the butt and about the longitudinal axis, using its dimensions, mass and centre of mass location. The models were tested on 416 rackets, dating from 1874 to 2017. Results showed that moments of inertia about the butt and longitudinal axis can be estimated to within − 4 to 5% and − 11 to 12% of measured values, respectively, using the proposed models on original rackets. When rackets were customised, with 30 g of additional mass, moment of inertia about the butt could be estimated within 6%, but the model for moment of inertia about the longitudinal axis was less accurate (largest error at 25%). A Stepwise Linear Regression model indicated that racket mass and then centre of mass location had the largest effect on moment of inertia about the handle, with head width having the largest effect on moment of inertia about the longitudinal axis

Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v D, of Au and Zn, and put lower bounds on v D of the other metals ranging from 10² to 10⁴ m/s. Knowledge of v D is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10¹⁹ Au/cm³ without cellular breakdown. Values of v D are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D s(T m), and the equilibrium partition coefficient, k e, are shown to simultaneously affect v D. We demonstrate a correlation between v D and the ratio D s(T m)/k e ⁰·⁶⁷, which is exhibited for Group III, IV, and V solutes but not for the transition metals investigated. Nevertheless, comparison with experimental results suggests that D s(T m)/k e ⁰·⁶⁷ might serve as a metric for evaluating the potential to supersaturate Si with transition metals by PLM.Research at Harvard was supported by The U.S. Army Research Office under contracts W911NF-12-1-0196 and W911NF-09-1-0118. M.T.W. and T.B.’s work was supported by the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant No. W911NF-10-1-0442, and the National Science Foundation (NSF) Faculty Early Career Development Program ECCS-1150878 (to T.B.). M.J.S., J.T.S., M.T.W., T.B., and S.G. acknowledge a generous gift from the Chesonis Family Foundation and support in part by the National Science Foundation (NSF) and the Department of Energy (DOE) under NSF CA No. EEC- 1041895. S.C. and J.S.W.’s work was supported by The Australian Research Council. J.M. was supported by a National Research Council Research Associateship

Clean Low-Biomass Procedures and Their Application to Ancient Ice Core Microorganisms

Microorganisms in glacier ice provide tens to hundreds of thousands of years archive for a changing climate and microbial responses to it. Analyzing ancient ice is impeded by technical issues, including limited ice, low biomass, and contamination. While many approaches have been evaluated and advanced to remove contaminants on ice core surfaces, few studies leverage modern sequencing to establish in silico decontamination protocols for glacier ice. Here we sought to apply such “clean” sampling techniques with in silico decontamination approaches used elsewhere to investigate microorganisms archived in ice at ~41 (D41, ~20,000 years) and ~49 m (D49, ~30,000 years) depth in an ice core (GS3) from the summit of the Guliya ice cap in the northwestern Tibetan Plateau. Four “background” controls were established – a co-processed sterile water artificial ice core, two air samples collected from the ice processing laboratories, and a blank, sterile water sample – and used to assess contaminant microbial diversity and abundances. Amplicon sequencing revealed 29 microbial genera in these controls, but quantitative PCR showed that the controls contained about 50–100-times less 16S DNA than the glacial ice samples. As in prior work, we interpreted these low-abundance taxa in controls as “contaminants” and proportionally removed them in silico from the GS3 ice amplicon data. Because of the low biomass in the controls, we also compared prokaryotic 16S DNA amplicons from pre-amplified (by re-conditioning PCR) and standard amplicon sequencing, and found the resulting microbial profiles to be repeatable and nearly identical. Ecologically, the contaminant-controlled ice microbial profiles revealed significantly different microorganisms across the two depths in the GS3 ice core, which is consistent with changing climate, as reported for other glacier ice samples. Many GS3 ice core genera, including Methylobacterium, Sphingomonas, Flavobacterium, Janthinobacterium, Polaromonas, and Rhodobacter, were also abundant in previously studied ice cores, which suggests wide distribution across glacier environments. Together these findings help further establish “clean” procedures for studying low-biomass ice microbial communities and contribute to a baseline understanding of microorganisms archived in glacier ice

Engineering of a Mo/SixNy Diffusion Barrier to Reduce the Formation of MoS2 in Cu2ZnSnS4 Thin Film Solar Cells

The optimisation of the interface between back contact and absorber is one of the main challenges to improve the electrical behaviour and further enhance the efficiencies of Cu2ZnSn(S,Se)4 (CZTS(e)) solar cell devices. In this work, Mo/SixNy thin films with various film thicknesses were introduced as an interfacial layer to explore its influence on opto-electronic properties of the pure sulphide CZTS thin film solar cells. The SixNy was deposited through plasma enhanced chemical vapour deposition (PECVD). The film thickness and stress of the Mo/SixNy films were controlled to improve the adhesion of the CZTS layer and reduce the chances of cracking the deposited films. Energy dispersive X-Ray spectroscopy (EDS) mapping measurements performed directly on the cross-section of Mo/SixNy/CZTS/Mo films indicate that the SixNy intermediate layer can effectively inhibit the formation of a highly resistive MoS2 layer and decomposition of CZTS at the CZTS/Molybdenum (Mo) interface region. A reduced efficiency was obtained with a SixNy modified back contact compared with the devices without this layer. This could be due to the increased recombination and poor hole extraction stemming from the very low valance band maximum of SixNy obtained from ultraviolet photoelectron spectroscopy (UPS) measurements. Temperature dependent current density-voltage (T-JV) and temperature dependent transient photovoltage (T-TPV) measurements were used to uncover insights into the internal recombination dynamics of the charge carriers