The Quantification of Acceleration Events in Elite Team Sport: a Systematic Review

Background Wearable tracking devices are commonly utilised to quantify the external acceleration load of team sport athletes during training and competition. The ability to accelerate is an important attribute for athletes in many team sports. However, there are many different acceleration metrics that exist in team sport research. This review aimed to provide researchers and practitioners with a clear reporting framework on acceleration variables by outlining the different metrics and calculation processes that have been adopted to quantify acceleration loads in team sport research. Methods A systematic review of three electronic databases (CINAHL, MEDLINE, SPORTDiscus), was performed to identify peer-reviewed studies that published external acceleration load in elite team sports during training and/or competition. Articles published between January 2010 and April 2020 were identified using Boolean search phrases in relation to team sports (population), acceleration/deceleration (comparators), and competition and/or training (outcome). The included studies were required to present external acceleration and/or deceleration load (of any magnitude) from able-bodied athletes (mean age ≥ 18 years) via wearable technologies. Results A total of 124 research articles qualified for inclusion. In total, 113/124 studies utilised GPS/GNSS technology to outline the external acceleration load of athletes. Count-based metrics of acceleration were predominant of all metrics in this review (72%). There was a lack of information surrounding the calculation process of acceleration with 13% of studies specifying the filter used in the processing of athlete data, whilst 32% outlined the minimum effort duration (MED). Markers of GPS/GNSS data quality, including horizontal dilution of precision (HDOP) and the average number of satellites connected, were outlined in 24% and 27% of studies respectively. Conclusions Team sport research has predominantly quantified external acceleration load in training and competition with count-based metrics. Despite the influence of data filtering processes and MEDs upon acceleration, this information is largely omitted from team sport research. Future research that outlines acceleration load should present filtering processes, MEDs, HDOP, and the number of connected satellites. For GPS/GNSS systems, satellite planning tools should document evidence of available satellites for data collection to analyse tracking device performance. The development of a consistent acceleration filtering method should be established to promote consistency in the research of external athlete acceleration loads.

Cardiac and behavioural responses to hypoxia and warming in free-swimming gilthead seabream (Sparus aurata)

Gilthead seabream were equipped with intraperitoneal biologging tags to investigate cardiac responses to hypoxia and warming, comparing when fish were either swimming freely in a tank with conspecifics or confined to individual respirometers. After tag implantation under anaesthesia, heart rate (fH) required 60 hours to recover to a stable value in a holding tank. Subsequently, when undisturbed under control conditions (normoxia, 21°C), mean fH was always significantly lower in the tank than respirometers. In progressive hypoxia (100 - 15% oxygen saturation), mean fH in the tank was significantly lower than respirometers at oxygen levels until 40%, with significant bradycardia in both holding conditions below this. Simultaneous logging of tri-axial body acceleration revealed that spontaneous activity, inferred as the variance of external acceleration (VARm), was low and invariant in hypoxia. Warming (21 to 31°C) caused progressive tachycardia with no differences in fH between holding conditions. Mean VARm was, however, significantly higher in the tank during warming, with a positive relationship between VARm and fH across all temperatures. Therefore, spontaneous activity contributed to raising fH of fish in the tank during warming. Mean fH in respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The high fH of confined seabream indicates that respirometry techniques may bias estimates of metabolic traits in some fishes, and that biologging on free-swimming fishes will provide more reliable insight into cardiac and behavioural responses to environmental stressors by fishes in their natural environment.

Development of a novel automated micro-assembly mechanism

In this thesis a novel automated micro assembly mechanism is developed. The assembly mechanism utilizes repulsive-force actuators to flip surface-micromachined 2D structures out-of-plane and assemble them into 3D micro devices. The novel micro assembly mechanism is suitable for wafer-level multi-devices batch assembly without external interference. It can assemble 2D structures not only at the vertical position (perpendicular to the substrate) but also at positions at any angle to the substrate. Two approaches, i.e., graphic method and analytical method, are proposed for designing the micro assembly mechanism. Prototypes are fabricated using the PolyMUMPs surface micromachining technology and tested. The experimental results verify the concept of the novel automated micro assembly mechanism. The strength of the assembled 3D structures in terms of withstanding external acceleration is calculated. The calculated result well matches the experimental result which is about 7g. Using the micro assembly mechanism, 1D and 2D rotation micromirrors are designed for various applications.

Development of a novel automated micro-assembly mechanism

In this thesis a novel automated micro assembly mechanism is developed. The assembly mechanism utilizes repulsive-force actuators to flip surface-micromachined 2D structures out-of-plane and assemble them into 3D micro devices. The novel micro assembly mechanism is suitable for wafer-level multi-devices batch assembly without external interference. It can assemble 2D structures not only at the vertical position (perpendicular to the substrate) but also at positions at any angle to the substrate. Two approaches, i.e., graphic method and analytical method, are proposed for designing the micro assembly mechanism. Prototypes are fabricated using the PolyMUMPs surface micromachining technology and tested. The experimental results verify the concept of the novel automated micro assembly mechanism. The strength of the assembled 3D structures in terms of withstanding external acceleration is calculated. The calculated result well matches the experimental result which is about 7g. Using the micro assembly mechanism, 1D and 2D rotation micromirrors are designed for various applications.

Simulating diverse instabilities of dust in magnetized gas

ABSTRACT Recently, Squire & Hopkins showed that charged dust grains moving through magnetized gas under the influence of a uniform external force (such as radiation pressure or gravity) are subject to a spectrum of instabilities. Qualitatively distinct instability families are associated with different Alfvén or magnetosonic waves and drift or gyro motion. We present a suite of simulations exploring these instabilities, for grains in a homogeneous medium subject to an external acceleration. We vary parameters such as the ratio of Lorentz-to-drag forces on dust, plasma β, size scale, and acceleration. All regimes studied drive turbulent motions and dust-to-gas fluctuations in the saturated state, rapidly amplify magnetic fields into equipartition with velocity fluctuations, and produce instabilities that persist indefinitely (despite random grain motions). Different parameters produce diverse morphologies and qualitatively different features in dust, but the saturated gas state can be broadly characterized as anisotropic magnetosonic or Alfvénic turbulence. Quasi-linear theory can qualitatively predict the gas turbulent properties. Turbulence grows from small to large scales, and larger scale modes usually drive more vigorous gas turbulence, but dust velocity and density fluctuations are more complicated. In many regimes, dust forms structures (clumps, filaments, sheets) that reach extreme overdensities (up to ≫109 times mean), and exhibit substantial substructure even in nearly incompressible gas. These can be even more prominent at lower dust-to-gas ratios. In other regimes, dust self-excites scattering via magnetic fluctuations that isotropize and amplify dust velocities, producing fast, diffusive dust motions.

Robust Inertial Measurement Unit-Based Attitude Determination Kalman Filter for Kinematically Constrained Links

The external acceleration of a fast-moving body induces uncertainty in attitude determination based on inertial measurement unit (IMU) signals and thus, frequently degrades the determination accuracy. Although previous works adopt acceleration-compensating mechanisms to deal with this problem, they cannot completely eliminate the uncertainty as they are, inherently, approaches to an underdetermined problem. This paper presents a novel constraint-augmented Kalman filter (KF) that eliminates the acceleration-induced uncertainty for a robust IMU-based attitude determination when IMU is attached to a constrained link. Particularly, this research deals with an acceleration-level kinematic constraint derived on the basis of a ball joint. Experimental results demonstrate the superiority of the proposed constrained KF over the conventional unconstrained KF: The average accuracy improved by 1.88° with a maximum of 4.18°. More importantly, whereas the accuracy of conventional KF is dependent to some extent on test acceleration conditions, that of the proposed KF is independent of these conditions. Due to the robustness of the proposed KF, it may be applied when accurate attitude estimation is needed regardless of dynamic conditions.

Sub g Threshold Acceleration Sensor Incorporating Latched Bistable Beam

We present a concept and a theoretical feasibility study of a sub g threshold inertial micro sensor, which incorporates a curved bistable beam as a suspension element. For certain range of geometric parameters such a beam can exhibit lathing, namely remain in its switched configuration at zero actuating force. Since the device can be released from its latched state by an external acceleration force, it can therefore serve as a threshold inertial switch. While the snap-through force, associated with the switching from the initial to the buckled state, cannot be reduced without decreasing the frequency of the device, the release value of the acceleration can be tailored to be arbitrarily low. This allows design of a devices with sufficiently high stiffness in the initial and latched configurations, but with a very low release threshold. Our model show that for appropriately chosen parameters, it is possible to design a sub g threshold acceleration micro switch of realistic dimensions.