Comparison of CDMA and FDMA for the MobileStar(sm) system

Spread-spectrum code division multiple access (CDMA) and single channel per carrier frequency division multiple access (FDMA) systems are compared for spectrum efficiency. CDMA is shown to have greater maximum throughput than FDMA for the MobileStar(sm) system which uses digital voice activated carriers and directive circularly polarized satellite antennas

Using rowers’ perceptions of on-water stroke success to evaluate sculling catch efficiency variables via a boat instrumentation system

Aim: An effective catch in sculling is a critical determinant of boat velocity. This study used rowers’ performance-based judgments to compare three measures of catch slip efficiency. Two questions were addressed: (1) would rower-judged Yes strokes be faster than No strokes? and (2) which method of quantifying catch slip best reflected these judgements? Methods: Eight single scullers performed two 10-min blocks of sub maximal on-water rowing at 20 strokes per minute. Every 30 s, rowers reported either Yes or No about the quality of their stroke at the catch. Results: It was found that Yes strokes identified by rowers had, on average, a moderate effect advantage over No strokes with a standardised effect size of 0.43. In addition, a quicker time to positive acceleration best reflected the change in performance; where the standardised mean difference score of 0.57 for time to positive acceleration was larger than the scores of 0.47 for time to PowerLine force, and 0.35 for time to 30% peak pin force catch slip measures. For all eight rowers, Yes strokes corresponded to time to positive acceleration occurring earlier than No strokes. Conclusion: Rower judgements about successful strokes was linked to achieving a quicker time to positive acceleration, and may be of the most value in achieving a higher average boat velocity

Modelling batting expertise from the perspective of high performance coaches

Cricket coaching literature on developing batting expertise has largely focused on the individual, and typically, technical features of batting. Research in cricket batting has addressed developmental factors of expertise (Weissensteiner, et al., 2009) or the perceptual advantage of expert batters (Muller & Abernethy, 2006). Little attention has been paid to the importance of the individual-environment relationship in expert behaviour. In order to address this missing ingredient, one on one, in-depth, semi- structured interviews were undertaken by the primary researcher with eight high performance coaches (e.g., international or state) who were purposely sampled from Cricket Australia or State Cricket associations. Six of these coaches had played international cricket as batsmen, one played state level and one a first grade player. Interviews were transcribed verbatim and coded separately by the first and second author after each interview. The third author then reviewed all codes and provided feedback. Strategies used to enhance validity included; sampling coaches of different high performance levels and retrospective member checking with coaches. Key themes that emerged include expert's superior knowledge of, and attunement to internal (e.g., emotions) and external (e.g. pitch type, field settings) information. This informs their intentions, perceptions and actions to achieve the task goal at any game moment. A skilful batter has time to execute their action and is in ‘rhythm’ with the bowler through attunement to specifying information sources. Experts also adapt to and manipulate the performance environment. Self-evaluative processes, through between-ball routines provide opportunity to reflect, re-evaluate and plan for the next delivery. Examples include; changing stance, forcing field changes or manipulating bowler’s emotions. These results highlight the importance of capturing the experiential knowledge of high performance coaches that cannot be obtained through traditional laboratory based studies. For cricket batting coaches, this work emphasizes the importance of designing learning environments that enable players to better understand their own performance in the context of emergent dynamic game-based constraints

Evaluating a 12-week games-based training program to improve cricket batting skill

Although a constraints-led approach (CLA) to skill acquisition is different from teaching games for understanding (Renshaw et al., 2015), the theoretical underpinnings of CLA can be utilized when designing games-based training approaches. This study examined whether a games-based training design, underpinned by CLA, was more effective at developing cricket batting skill than a more traditional technically focused coaching approach. Sixteen under-15 skilled cricket batters participated in a 12-week intervention study and were randomly allocated to a traditional or experimental training group. The experimental group participated in activities with manipulated rules, equipment, and outcome goals, while the traditional group focused on optimizing technical batting skill processes. Both groups completed two 2-hr sessions per week, bookended by a pre-intervention and post-intervention batting skills test. This test involved facing 18 balls delivered by bowlers, with the number of successful scoring shots, total runs scored, attacking strokes played, and quality of bat–ball contact recorded. An analysis of variance was used to examine between and within-group differences over time. The experimental group (CLA) demonstrated an increased number of successful scoring shots (3.88 vs. 6.63), and increased number of runs scored (11.63 vs. 20.7), and an improvement in the quality of bat–ball contact (1.26 vs. 1.52) after intervention, while there was no change in the number of attacking strokes played (72.37% vs. 74.63%). These numbers were significantly greater than those for the traditional group, which revealed no changes in the number of successful scoring shots played (4.62 vs. 3.75), the number of runs scored (10.25 vs. 10.00), the quality of bat–ball contact (1.26 vs. 1.29), or attacking strokes played (77.78% vs. 78.87%). Skilled U15 players significantly improved facets of their batting using a games-based training approach, while a more traditional training approach did not lead to improvements. Training using a systematic approach to manipulating constraints is suggested to benefit the overall development of a batter

Proximity-to-goal as a constraint on patterns of behaviour in attacker-defender dyads in team games

Abstract The aim of this study was to determine whether spatiotemporal interactions between footballers and the ball in 1 vs. 1 sub-phases are influenced by their proximity to the goal area. Twelve participants (age 15.3 +/- 0.5 years) performed as attackers and defenders in 1 vs. 1 dyads across three field positions: (a) attacking the goal, (b) in midfield, and (c) advancing away from the goal area. In each position, the dribbler was required to move beyond an immediate defender with the ball towards the opposition goal. Interactions of attacker-defender dyads were filmed with player and ball displacement trajectories digitized using manual tracking software. One-way repeated measures analysis of variance was used to examine differences in mean defender-to-ball distance after this value had stabilized. Maximum attacker-to-ball distance was also compared as a function of proximity-to-goal. Significant differences were observed for defender-to-ball distance between locations (a) and (c) at the moment when the defender-to-ball distance had stabilized (a: 1.69 +/- 0.64 m; c: 1.15 +/- 0.59 m; P < 0.05). Findings indicate that proximity-to-goal influenced the performance of players, particularly when attacking or advancing away from goal areas, providing implications for training design in football. In this study, the task constraints of football revealed subtly different player interactions than observed in previous studies of dyadic systems in basketball and rugby union

A systematic study of element mobilisation from gas shales during hydraulic fracturing

The large quantities of wastewater produced throughout the lifetime of a shale gas well can contain heavy metals and other regulated potentially toxic elements. These can be mobilised from the target formation by some of the additives present in the hydraulic fracturing fluids (HFF). High levels of inorganic geogenic chemicals may pose a hazard to the environment through accidental releases such as spills of untreated wastewater. The concentration of mobilised elements and the hazard they pose is uncertain and is likely dependant on the chemical agents used in HFF, groundwater composition and the trace element content of targeted shale gas formation. Laboratory protocols were developed to investigate the release of inorganic contaminants of potential concern (e.g. As, Co, Cu, Pb, Se) from shale gas formations around the world. Powdered rock samples were leached for up to 360 hours at elevated temperature (80°C) and a range of pressures (1-200 bar), with synthetic HFF and synthetic groundwater (SGW). Elemental concentrations released into solution were generally much higher in the HFF leachates than in the SGW treatments, indicating that the chemical additives in the HFF influenced element mobilisation. SEM and EDX images show substantial mineral etching and precipitation of secondary phases on shale chips leached for 360 hours with HFF at 80°C and ~180 bar when compared to the SGW experiment. Time-series data also show evidence of mineral dissolution and subsequent precipitation of new phases, which resulted in sequestration of a number of trace elements that were initially mobilised into the solution. We also observed that the carbonate content of the unreacted shale sample had a strong control on the final pH of the HFF leachates. This study shows that additives can enhance the release of geogenic chemicals, but also that subsequent precipitation within the fracture system could limit ultimate release to surface

A method for transplantation of human HSCs into zebrafish, to replace humanised murine transplantation models

Haematopoietic stem cell (HSC) transplantation is a critical therapy for haematopoietic malignancies and immune disorders. Incomplete or delayed engraftment of HSCs in the host results in increased risk of infection and morbidity. The mechanisms of HSC engraftment are poorly understood and understanding these processes will increase transplantation success on many levels. Current animal models are immunocompromised 'humanised' mice transplanted with human HSCs. Harmful procedures include genetic manipulations and irradiation to ablate the mouse immune system, and opaque mouse tissues make visualisation of the early steps of HSC engraftment impossible. There is a need for new models to offer alternatives to humanised mice in the study of HSC transplantation. Here we described a detailed method for transplantation of human HSCs into zebrafish, before the onset of adaptive immunity. Human HSCs were purified from whole blood by enrichment of the CD34 cell population using a positive magnetic selection and further purified using an anti-CD34 antibody and cell sorting. Sorted CD34 cells were transplanted into the blood stream of 52 hour old zebrafish larvae. Human HSCs home into the zebrafish haematopoietic niche, where they engage with endothelial cells and undergo cell division. Our model offers the opportunities to image in vivo human HSC engraftment in a transparent organism, without the myeloablative strategies used in mice, and provides a unique system to understand the dynamic process of engraftment and replace current murine models. This technique can be applied to current engraftment protocols to validate the viability and efficiency of cryofrozen HSC grafts. This humanised zebrafish model will be instrumental to develop the 3Rs values in stem cell transplantation research and our detailed protocol will increase the chances of uptake of this zebrafish model by the mouse community

The effectiveness of constraint-led training on skill development in interceptive sports: a systematic review (Clark, McEwan and Christie) – a commentary

Clark, McEwan and Christie's systematic review1 offers a timely examination of current literature assessing effects of a constraints-led approach (CLA) to training on ‘technical and cognitive skill in sport’, in comparison to traditional training methods. They concluded that, currently, there is strong evidence to advocate for the effects of training interventions that espouse benefits of constraints-led training on acquiring skill in interceptive actions. Clark, McEwan and Christie reported that 18 studies satisfied their proposed inclusion criteria and, of these studies, 77% provided evidence of the effectiveness of the CLA. Consequently, Clark, McEwan and Christie argued that a ‘the implementation of the constraints-led approach within interceptive sport can be advocated’ (p. 17). This is a revealing insight, which supports their claims that this finding ‘provides the opportunity for researchers to collect more compelling evidence to answer the question: “Does constraint-led training assist with the development of technical skills within interceptive sport?”’. While we endorse their call for more empirical evidence on the effectiveness of a CLA to practice and training design, we qualify it by highlighting some limitations of Clark, McEwan and Christie's systematic review

Specialist role coaching and skill training periodisation: A football goalkeeping case study

© The Author(s) 2020. In sports like association football, professional teams are increasingly devoting resources to the role-based development of individual athletes and sub-groups. By employing ‘specialist coaches’ into athlete-support structures, clubs aim to facilitate individualised athlete training programs to enhance performance preparation as well as skill learning and talent development. Here, we discuss how contemporary pedagogical training approaches, like Nonlinear Pedagogy and the Constraints-Led approach, can enhance effectiveness of specialist role-based athlete development programs to facilitate performance functionality. We argue the need for a model of specialist role-based coaching practice in high performance sports organisations, based on a unified theoretical rationale, such as ecological dynamics. To exemplify the nature of specialist role-based coaching, a case study addresses how Nonlinear Pedagogy and Constraints-Led approach are being used for training professional football goalkeepers in an U23 years age group. Integrating key concepts from ecological dynamics, allied to principles of Nonlinear Pedagogy and the Constraints-Led approach, common skill training principles for specialist role coaches are highlighted. These illustrate the use of the recently introduced ‘Periodization of Skill Training’ framework for specialist role coaching, practically exemplifying a way to harness opportunities for performance enhancement and individualised talent development in the football goalkeeping context