Direct Acceleration Research Articles

Laser wakefield and direct laser acceleration of electron by chirped laser pulses

Chirped laser pulses are investigated theoretically for laser wakefield (LW) and direct laser (DL) acceleration of electrons in the plasma-bubble regime. Chirping of laser pulse with a suitable frequency allows a better trapping of electron in bubble regime which enforces a strong betatron resonance inside the plasma bubble. Linear and non-linear effects of frequency chirp determine electron acceleration, de-phasing, beam quality in terms of energy spread and high energy from the direct laser field and its plasma wake in bubble regime. Gaussian chirped laser pulse exhibit high energy to the electrons compared with linear and other non-linear chirped pulses in plasma-bubble regime. The investigation with chirped laser pulse opens new dimension to hybrid LW-DL acceleration mechanism in bubble regime.

Early Maize (Zea mays) in the North American Central Plains: The Microbotanical Evidence

Artifacts, including ceramics, ground stone, and soil samples, as well as dental calculus, recovered from sites in the eastern North American central Plains were submitted to multiple laboratories for analysis of microbotanical remains. Direct accelerator mass spectrometer (AMS) dates of 361–197 cal BC provide evidence for the earliest use of maize (Zea maysssp.mays) in this region. Squash (Cucurbitasp.), wild rice (cf.Zizaniaspp.), and palm (Arecaceae sp.) microremains were also found. This research adds to the growing evidence of the importance of microbotanical analysis in documenting plant use and in the identification of early maize. The combined data on early maize from the eastern Plains adds to our understanding of the timing and dispersal of this crop out of the American Southwest. Alternative explanations for the adoption and early use of maize by eastern central Plains communities include its value as a secondary resource, as an addition to an existing farming strategy, or as a component of Middle Woodland rituals.

Analysis of flame propagation mechanisms during light-round in an annular spray flame combustor: the impact of wall heat transfer and two-phase flow

Ignition in annular multi-burner combustors is marked by a succession of four phases, ending with a characteristic flame expansion from burner to burner, often referred to as light-round. During this last phase, flame propagation is prone to substantial change depending on the boundary and operating conditions. With realistic aero-engine conditions in mind, wall heat transfers can be enhanced during ignition in cold wall conditions, which aid an understanding of the main governing mechanisms of flame propagation. From a modeling perspective, several works have outlined the need for detailed descriptions of the liquid phase, turbulent combustion and wall heat transfer, which are all included in the present work for the first time. Large-Eddy Simulations of light-round are performed in the annular MICCA-Spray combustor with cold walls, Lagrangian particle tracking, a dynamic closure for the sub-grid scale flame surface wrinkling as well as a custom tabulated wall model. The predicted light-round duration from the simulation is found to be in good agreement with experimental data. It is shown that the volumetric expansion of burnt gases induces a flow acceleration in azimuthal direction which constitutes the main driving mechanism of flame propagation. Droplet accumulations in the wake of swirling jets are generated ahead of the propagating flame fronts, which in turn cause a characteristic sawtooth propagation mode of the leading point. A cooling effect of the combustor walls on burnt gases is particularly pronounced downstream, diminishing the resulting flame propagation speed. The main governing mechanisms are investigated by means of a mathematical model for the absolute turbulent flame speed to quantify their relative impact on flame propagation. Finally, a priori estimations are provided for the flame propagation speed based on different models and boundary conditions, which are directly plugged into the model.

Differences in Peak Impact Accelerations Among Foot Strike Patterns in Recreational Runners.

IntroductionRunning-related injuries (RRIs) occur from a combination of training load errors and aberrant biomechanics. Impact loading, measured by peak acceleration, is an important measure of running biomechanics that is related to RRI. Foot strike patterns may moderate the magnitude of impact load in runners. The effect of foot strike pattern on peak acceleration has been measured using tibia-mounted inertial measurement units (IMUs), but not commercially available insole-embedded IMUs. The aim of this study was to compare the peak acceleration signal associated with rearfoot (RFS), midfoot (MFS), and forefoot (FFS) strike patterns when measured with an insole-embedded IMU.Materials and MethodsHealthy runners ran on a treadmill for 1 min at three different speeds with their habitual foot strike pattern. An insole-embedded IMU was placed inside standardized neutral cushioned shoes to measure the peak resultant, vertical, and anteroposterior accelerations at impact. The Foot strike pattern was determined by two experienced observers and evaluated using high-speed video. Linear effect mixed-effect models were used to quantify the relationship between foot strike pattern and peak resultant, vertical, and anteroposterior acceleration.ResultsA total of 81% of the 187 participants exhibited an RFS pattern. An RFS pattern was associated with a higher peak resultant (0.29 SDs; p = 0.029) and vertical (1.19 SD; p < 0.001) acceleration when compared with an FFS running pattern, when controlling for speed and limb, respectively. However, an MFS was associated with the highest peak accelerations in the resultant direction (0.91 SD vs. FFS; p = 0.002 and 0.17 SD vs. RFS; p = 0.091). An FFS pattern was associated with the lowest peak accelerations in both the resultant and vertical directions. An RFS was also associated with a significantly greater peak acceleration in the anteroposterior direction (0.28 SD; p = 0.033) than an FFS pattern, while there was no difference between MFS and FFS patterns.ConclusionOur findings indicate that runners should be grouped by RFS, MFS, and FFS when comparing peak acceleration, rather than the common practice of grouping MFS and FFS together as non-RFS runners. Future studies should aim to determine the risk of RRI associated with peak accelerations from an insole-embedded IMU to understand whether the small observed differences in this study are clinically meaningful.

Fast reconstruction of centre of mass and foot kinematics during a single-legged horizontal jump: A point-cloud processing approach

Horizontal jumps are discrete, fast, over-ground movements requiring coordination of the centre of mass (CoM) and base of support and are routinely assessed in sports settings. There is currently no biomechanics-based system to aid in their quick and objective large-scale assessment. We describe a practical system combining a single low-cost depth-sensing camera and point-cloud processing (PCP) to capture whole-body CoM and foot kinematics. Fourteen participants performed 10 single-leg horizontal jumps for distance. Foot displacement, CoM displacement, CoM peak velocity and CoM peak acceleration in the anterior-posterior direction of movement were compared with a reference 15-segment criterion model, captured concurrently using a nine-camera motion capture system (Vicon Motion Systems, UK). Between-system Pearson’s correlations were very-large to near-perfect (n = 140; foot displacement = 0.99, CoM displacement = 0.98, CoM peak velocity = 0.97, CoM peak acceleration = 0.79), with mean biases being trivial–small (-0.07 cm [0.12%], 3.8 cm [3.5%], 0.03 m·s−1 [1.6%], 0.42 m·s−2 [7%], respectively) and typical errors being trivial–small for displacement (foot: 0.92 cm [0.8%]; CoM: 3.8 cm [3.4%]) and CoM peak velocity (0.07 m·s−1 [4.3%]), and large for CoM peak acceleration (0.72 m·s−2 [15%]). Limits of agreement were −1.9 to 2.0 cm for foot displacement, −11.3 to 3.6 cm for CoM displacement, −0.17 to 0.12 m·s−1 for CoM peak velocity and −2.28 to 1.43 m·s−2 for CoM peak acceleration. The practical system captured CoM and foot kinematics during horizontal jumps with acceptable precision. Further work to improve estimates of CoM accelerations and different populations are warranted.

Array Signal Processing on Distributed Acoustic Sensing Data: Directivity Effects in Slowness Space

AbstractDistributed Acoustic Sensing (DAS) involves the transmission of laser pulses along a fiber‐optic cable. These pulses are backscattered at fiber inhomogeneities and again detected by the same interrogator unit that emits the pulses. Elastic deformation along the fiber causes phase shifts in the backscattered laser pulses which are converted to spatially averaged strain measurements, typically at regular fiber intervals. DAS systems provide the potential to employ array processing algorithms. However, there are certain differences between DAS and conventional sensors. While seismic sensors typically record the directional particle displacement, velocity, or acceleration, the DAS axial strain is inherently proportional to the spatial gradient of the axial cable displacement. DAS is therefore insensitive to broadside displacement, for example, broadside P‐waves. In classical delay‐and‐sum beamforming, the array response function is the far‐field response on a horizontal slowness (or wavenumber) grid. However, for geometrically non‐linear DAS layouts, the angle between wavefront and cable varies, requiring the analysis of a steered response that varies with the direction of arrival. This contrasts with the traditional array response function which is given in terms of slowness difference between arrival and steering. This paper provides a framework for DAS steered response estimation accounting also for cable directivity and gauge‐length averaging – hereby demonstrating the applicability of DAS in array seismology and to assess DAS design aspects. It bridges a gap between DAS and array theory frameworks and communities, facilitating increased employment of DAS as a seismic array, while providing building blocks for the development of DAS array design tools.

Improving the Orbits of the BDS-2 IGSO and MEO Satellites with Compensating Thermal Radiation Pressure Parameters

The orbit accuracy of the navigation satellites relies on the accurate knowledge of the forces on the spacecraft, in particular the non-conservative perturbations. This study focuses on the Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites of the regional Chinese BeiDou Navigation Satellite System (BDS-2), for which apparent deficiencies of non-conservative models are identified and evidenced in the Satellite Laser Ranging (SLR) residuals. The orbit errors derived from the empirical 5-parameter Extended CODE Orbit Model (ECOM) as well as a semi-analytical adjustable box-wing model show prominent dependency on the Sun elongation angle, even in the yaw-steering attitude mode. Hence, a periodic acceleration in the normal direction of the +X surface, presumably generated by the mismodeled thermal radiation pressure, is introduced. The SLR validations reveal that the Sun elongation angle-dependent systematic errors were significantly reduced, and the orbit accuracy was improved by 10–30% to approximately 4.5 cm and 3.0 cm for the BDS-2 IGSO and MEO satellites, respectively.

Identification of Gait Unbalance and Fallers Among Subjects with Cerebellar Ataxia by a Set of Trunk Acceleration-Derived Indices of Gait.

This study aimed to assess the ability of 25 gait indices to characterize gait instability and recurrent fallers among persons with primary degenerative cerebellar ataxia (pwCA), regardless of gait speed, and investigate their correlation with clinical and kinematic variables. Trunk acceleration patterns were acquired during the gait of 34 pwCA, and 34 age- and speed-matched healthy subjects (HSmatched) using an inertial measurement unit. We calculated harmonic ratios (HR), percent recurrence, percent determinism, step length coefficient of variation, short-time largest Lyapunov exponent (sLLE), normalized jerk score, log-dimensionless jerk (LDLJ-A), root mean square (RMS), and root mean square ratio of accelerations (RMSR) in each spatial direction for each participant. Unpaired t-tests or Mann-Whitney tests were performed to identify significant differences between the pwCA and HSmatched groups. Receiver operating characteristics were plotted to assess the ability to characterize gait alterations in pwCA and fallers. Optimal cutoff points were identified, and post-test probabilities were calculated. The HRs showed to characterize gait instability and pwCA fallers with high probabilities. They were correlated with disease severity and stance, swing, and double support duration, regardless of gait speed. sLLEs, RMSs, RMSRs, and LDLJ-A were slightly able to characterize the gait of pwCA but failed to characterize fallers.

Study on the test load for the structural test of the flight-load condition of the external fuel tank for fixed-wing aircraft

In this study, for the purpose of conducting the structural tests for the verification of structural soundness of the flight-load conditions of the external fuel tank for the fixed-wing aircraft, the flight load acting on the external fuel tank was converted to test load and the suitability of the converted loads was verified. The loads imposed on the external fuel tank were expressed as the combination of the inertial load (based on the acceleration in the translational direction) and the tangential direction inertial load (based on the angular acceleration of the moment). To calculate the test load, the transfer function table was generated by calculating the shear load and moment based on the unit load. For this purpose, a transfer function table was established by dividing the external fuel tank into a few sections and calculating the shear load and moment generated by the unit shear load and unit moment in each section. In addition, the test load for each section was calculated by computing the established transfer function table and flight-load conditions. However, in actual structural tests, it is often not possible to impose a load in the same position as the point at which the shear load and moment are calculated. For this reason, the actual test-load positions had to be determined and the calculated test loads were redistributed to those positions. Then, the final test load plan was established by applying a whiffle tree to increase the efficiency of the test while also making it easier to apply the actuators. Finally, the suitability of the established test load plan was confirmed by comparison with the flight-load conditions.

Numerical simulation on heat transfer of supercritical carbon dioxide in helical coiled channels under one-side heating

The flow and heat transfer characteristics of supercritical CO2 heated in helical coiled channel under one-side condition are conducted in this work. The numerical results are compared with the experimental data under different conditions and results show good consistency.The effects of pressure, mass flux, heat flux, gravity level, flow direction, buoyant force, and flow thermal acceleration on temperature and heat transfer coefficient are analyzed. Results show that appropriate matching of the heat flux and mass flux generates high heat transfer coefficient with CO2 fluid staying near pseudo-critical state until the outlet of the channel. Semicircular heating mode reinforces the centrifugal effect and creates crescent-shaped flow pattern with large velocity gradient. The flow instability in both radial and longitude direction induced by the large velocity gradient is quantified by the turbulent kinetic energy and contributes to the heat transfer enhancement.

Direct nonlinear acceleration

Optimization acceleration techniques such as momentum play a key role in state-of-the-art machine learning algorithms. Recently, generic vector sequence extrapolation techniques, such as regularized nonlinear acceleration (RNA) of Scieur et al. [22] , were proposed and shown to accelerate fixed point iterations. In contrast to RNA which computes extrapolation coefficients by (approximately) setting the gradient of the objective function to zero at the extrapolated point, we propose a more direct approach, which we call direct nonlinear acceleration (DNA) . In DNA, we aim to minimize (an approximation of) the function value at the extrapolated point instead. We adopt a regularized approach with regularizers designed to prevent the model from entering a region in which the functional approximation is less precise. While the computational cost of DNA is comparable to that of RNA, our direct approach significantly outperforms RNA on both synthetic and real-world datasets. While the focus of this paper is on convex problems, we obtain very encouraging results in accelerating the training of neural networks.

Dynamic simulation analysis of effects of braking by sliding friction against rail on dynamic characteristics of operator cabin of gantry cranes

In this paper, the effects of the operation of braking devices by sliding friction against rails (rail brake) on the dynamic characteristics of operator cabins of gantry cranes after runaway caused by unexpected wind gust were analyzed. The operating characteristics of the rail brakes were defined by the increase ratio of the pressing load of the brake shoe, dPB/dt, the maximum value of the pressing load, PBmax, and the timing that the operation starts. Under the analysis conditions of this paper, in the case where dPB/dt is large, the maximum acceleration in the runaway direction of the operator cabin became large when the rail brakes started to operate. In the case where PBmax is large, the maximum acceleration amplitude of the residual vibration of the operator cabin became large after the runaway of the crane ended. It is advisable to decrease the maximum value and maximum amplitude of the acceleration of the operator cabin by adjusting appropriately dPB/dt and PBmax from a viewpoint of discomfort reduction of the operators.

Review of research solid mechanics laboratory for 2020–2022

The article presents an overview of the research of the Laboratory of Solid Mechanics IMech UFRS RAS for 2020-2022. All studies were published as articles (there are two exceptions in the list of references, registered in the Register of Computer Programs) in well-known domestic and (or) foreign scientific journals on mechanics. During the three years under consideration, a number of new problems of aerohydroelasticity were solved and important results were obtained on the dynamic behavior of thin-walled structural elements interacting with external and internal continuous media. In particular, the linear bending of a cantilever rod loaded with all-round pressure and longitudinal force is considered in static and dynamic formulations. The areas of attraction of the deflection to the upper and lower equilibrium positions of a two-support pipe during its spatial bending-rotational vibrations are determined. The interaction of forced and parametric vibrations of the pipeline has been studied. The influence of the internal and external added masses of continuous media on the frequency of natural vibrations of a pipe moving with acceleration in the transverse direction is studied. The eigenfrequencies of bending vibrations of a micro- and nanometer-sized rod clamped at the ends are calculated. From the solution of the inverse problem for the changed values of natural frequencies, the coordinate and magnitude of the added mass are found. Linear oscillations of micro- and nanostrings are also considered when the pressure in a gaseous medium changes, taking into account surface effects. Using a model of molecular dynamics with a reduced number of degrees of freedom, the eigenfrequencies of bending vibrations of carbon nanotubes (CNTs) of different diameters are calculated under conditions of a plane-deformed state. In addition, part of the work was devoted to the study of the phenomenon of the ascent of an underwater gas pipeline and the determination of its buoyancy parameters. The scientific articles presented in this review are arranged in chronological order. For all articles, their summary is given and the main conclusions are formulated.

External match load and the influence of contextual factors in elite futsal.

Quantifying external load during futsal competition can provide objective data for the management of the athlete’s performance and late-stage rehabilitation. This study aimed to report the match external load collected via wearable technology according to time periods (i.e., halves) and contextual factors (i.e., team’s ranking, match result, and location) in elite futsal. Nine professional male players used a GPS-accelerometer unit during all games of the 2019–2020 season. Player load (PL), PL·min-1, high-intensity acceleration (ACCHI), deceleration (DECHI), explosive movements (EXPL-MOV), and change of direction (CODHI) data were collected. On average, players displayed values of: total PL 3868 ± 594 a.u; PL·min-1: 10.8 ± 0.8 a.u; number of ACCHI: 73.3 ± 13.8, DECHI: 68.6 ± 18.8, EXPL-MOV: 1165 ± 188 and CODHI: 173 ± 29.1. A moderate and significant decrease was found in the 2nd half for total PL (p = 0.03; ES = 0.52), PL·min-1 (p = 0.001; ES = 1.16), DECHI (p = 0.001; ES = 0.83), and EXPL-MOV (p = 0.017; ES = 0.58) compared to the 1st half. Small and nonsignificant differences were found between contextual factors. In summary, this study indicates that futsal players are exposed to high-intensity mechanical external loads, and perform a great number of ACCHI, DECHI, EXPL-MOV and CODHI, without being influenced by the team ranking, result and match location. Coaches and sports scientists are advised to implement speed-power, DEC, and COD activities in the training sessions, and may use these reference values to design specific training and return-to-play plans.

Automated Feature Selection: A Reinforcement Learning Perspective

Feature selection is a critical step in machine learning that selects the most important features for a subsequent prediction task. Effective feature selection can help to reduce dimensionality, improve prediction accuracy, and increase result comprehensibility. It is traditionally challenging to find the optimal feature subset from the feature subset space as the space could be very large. While much effort has been made on feature selection, reinforcement learning can provide a new perspective towards a more globally-optimal searching strategy. In the preliminary work, we propose a multi-agent reinforcement learning framework for the feature selection problem. Specifically, we first reformulate feature selection with a reinforcement learning framework by regarding each feature as an agent. Besides, we obtain the state of the environment in three ways, i.e., statistic description, autoencoder, and graph convolutional network (GCN), in order to derive a fixed-length state representation as the input of reinforcement learning. In addition, we study how the coordination among feature agents can be improved by a more effective reward scheme. Also, we provide a GMM-based generative rectified sampling strategy to accelerate the convergence of multi-agent reinforcement learning. Our method searches the feature subset space more globally and can be easily adapted to real-time scenarios due to the nature of reinforcement learning. In the extended version, we further accelerate the framework from two aspects. From the sampling aspect, we show the indirect acceleration by proposing a rank-based softmax sampling strategy. From the exploration aspect, we show the direct acceleration by proposing an interactive reinforcement learning (IRL)-based exploration strategy. Extensive experimental results show the significant improvement of the proposed method over conventional approaches.

Seismic response of horizontally curved bridges in combination with skewed abutments

A bridge having in-plan curvature in combination with the skewed abutments is termed as skew-curved bridge. Present study explores upon the seismic response of a three-span continuous RC skew-curved concrete box-girder bridges under free and forced vibrations for which 3-D models of the bridge with varying configurations are generated in the CSiBridge. The curvature angle for the parametric study has been varied as 0°,30°,60° and 90° in combination with skew angles of 0°,15°,30°,45° and 60°. Modal analysis and response spectrum analysis for all the bridge models has been performed. Modal response of the various bridge configurations has been presented in graphical form in order to have knowledge of the mode shapes, time periods and fundamental frequencies of the bridges. Based on guidelines of AASHTO 2007 response spectrum analysis has been performed considering 0.3 g acceleration in longitudinal and transverse direction and an acceleration of 0.2 g in vertical direction. In-plane bending moments, longitudinal torsion and out-of-plane bending moments are monitored for all skew curved bridges under longitudinal, transverse and vertical excitations and it is observed that especially in-plane moments in longitudinal and transverse direction are significantly affected by inclusion of skewness and curvature in bridges.

Modernization of the construction of the crane traveling wheel

The article discusses the modernization of the running wheel due to the introduction of an elastic element. The structure, which consists of three layers, the outer ones of which consist of strong steel material, and the middle layer consists of low-strength lightweight aggregate, which can significantly reduce dynamic forces, vibrations and shocks, which increases the reliability of cargo transportation. Calculations have shown that the stress state of a wheel with an elastic insert is less than that of an old-design travel wheel. The decrease in force and elastic factors in the travel wheel, which has an elastic insert, is explained by the fact that the use of an elastic ring leads to an increase in the bending stiffness of the outer ring of the shell. The obtained solution to the problem of the strength of a three-layer structure makes it possible to determine the stresses in the shell depending not only on its geometric parameters, but also on the shear modulus of the filler, which improves the reliability of the design and operation of such structures. Theoretical studies of the stress state of a three-layer cylindrical structure, taking into account the shear energy of the filler, makes it possible to assess the strength of such a structure and give certain recommendations for its use. Experimental studies that were carried out on an operating overhead crane fully confirmed a very significant reduction in oscillatory processes in travel wheels. The level of vibration acceleration in the vertical direction on the modernized drive wheel is almost 3 times less than the level of vibration acceleration on the drive wheel at idle speed of a conventional design.

Seismic stability of vibration-insulated turbine foundations depending on the frequency composition of seismic impact

The seismic resistance of vibration-insulated turbine foundations is a complex and multifaceted problem that includes many aspects. The turbine foundation is a special building structure that unites parts of the turbine and generator unit into a single machine and it is used for static and dynamic loads accommodation. The number of designed and constructed power plants in high seismic level areas is large and steadily growing. In addition, engineers and designers deal with the issue of the frequency composition of the seismic impact influence on the seismic resistance of vibration-insulated turbine foundations. Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismic displacements (deformations of vibration isolators). The results of the calculation experiments proved a significant effect of seismic action frequency composition on the behavior of the vibration-insulated turbine foundations. Calculations of foundations, taking into account earthquakes of the same intensity, but with different values of the prevailing frequencies of the impact, lead to the differing by several times values of the maximum seismic accelerations at the turbine level and seismic displacements.

Testing the effects of body depth on fish maneuverability via robophysical models

Fish show a wide diversity of body shapes which affect many aspects of their biology, including swimming and feeding performance, and defense from predators. Deep laterally compressed bodies are particularly common, and have evolved multiple times in different families. Functional hypotheses that explain these trends include predator defense and increased maneuverability. While there is strong evidence that increasing body depth helps fish avoid gape-limited predators, the evidence that body shape increases a fish’s maneuverability is ambiguous. We used a two-pronged approach to explore the effects of body shape on the control of maneuvers using both live fish and a robotic model that allowed us to independently vary body shape. We captured ventral video of two tetra species (Gymnocorymbus ternetzi and Aphyocharax anisitsi) performing a wide range of maneuvers to confirm that both species of live fish utilize fundamentally similar body deformations to execute a turn, despite their different body depths. Both species use a propagating ‘pulse’ of midline curvature that is qualitatively similar to prior studies and displayed similar trends in the relationships between body kinematics and performance. We then tested the robotic model’s maneuverability, defined as the total heading change and maximum centripetal acceleration generated during a single pulse, at a range of different input kinematics across three body shapes. We found that deepening bodies increase the robot’s ability to change direction and centripetal acceleration, though centripetal acceleration exhibits diminishing returns beyond a certain body depth. By using a robotic model, we were able to isolate the effects of body shape on maneuverability and clarify this confounded relationship. Studying the functional morphology of complex traits such as body shape and their interaction with complex behavior like maneuverability benefits from both the broad view provided by comprehensive comparative studies, and the control of variables enabled by robophysical experiments.

Oh G: The x, y and z of human physiological responses to acceleration.

What is the topic of this review? This review focuses on the main physiological challenges associated with exposure to acceleration in the Gx, Gy and Gz directions and to microgravity. What advances does it highlight? Our current understanding of the physiology of these environments and latest strategies to protect against them are discussed in light of the limited knowledge we have in some of these areas. The desire to go higher, faster and further has taken us to environments where the accelerations placed on our bodies far exceed or are much lower than that attributable to Earth's gravity. While on the ground, racing drivers of the fastest cars are exposed to high degrees of lateral acceleration (Gy) during cornering. In the air, while within the confines of the lower reaches of Earth's atmosphere, fast jet pilots are routinely exposed to high levels of acceleration in the head-foot direction (Gz). During launch and re-entry of suborbital and orbital spacecraft, astronauts and spaceflight participants are exposed to high levels of chest-back acceleration (Gx), whereas once in space the effects of gravity are all but removed (termed microgravity, μG). Each of these environments has profound effects on the homeostatic mechanisms within the body and can have a serious impact, not only for those with underlying pathology but also for healthy individuals. This review provides an overview of the main challenges associated with these environments and our current understanding of the physiological and pathophysiological adaptations to them. Where relevant, protection strategies are discussed, with the implications of our future exposure to these environments also being considered.