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Jupiter’s atmosphere is one of the most turbulent places in the solar system. Whereas observations of lightning and thunderstorms point to moist convection as a small-scale energy source for Jupiter’s large-scale vortices and zonal jets, this has never been demonstrated due to the coarse resolution of pre-Juno measurements. The Juno spacecraft discovered that Jovian high latitudes host a cluster of large cyclones with diameter of around 5,000 km, each associated with intermediate- (roughly between 500 and 1,600 km) and smaller-scale vortices and filaments of around 100 km. Here, we analyse infrared images from Juno with a high resolution of 10 km. We unveil a dynamical regime associated with a significant energy source of convective origin that peaks at 100 km scales and in which energy gets subsequently transferred upscale to the large circumpolar and polar cyclones. Although this energy route has never been observed on another planet, it is surprisingly consistent with idealized studies of rapidly rotating Rayleigh–Bénard convection, lending theoretical support to our analyses. This energy route is expected to enhance the heat transfer from Jupiter’s hot interior to its troposphere and may also be relevant to the Earth’s atmosphere, helping us better understand the dynamics of our own planet.

The Stokes velocity u S , defined approximately by Stokes (1847, Trans. Camb. Philos. Soc. , 8 , 441–455.), and exactly via the Generalized Lagrangian Mean, is divergent even in an incompressible fluid. We show that the Stokes velocity can be naturally decomposed into a solenoidal component, u sol S , and a remainder that is small for waves with slowly varying amplitudes. We further show that u sol S arises as the sole Stokes velocity when the Lagrangian mean flow is suitably redefined to ensure its exact incompressibility. The construction is an application of Soward & Roberts’s glm theory (2010, J. Fluid Mech. , 661 , 45–72. ( doi:10.1017/S0022112010002867 )) which we specialize to surface gravity waves and implement effectively using a Lie series expansion. We further show that the corresponding Lagrangian-mean momentum equation is formally identical to the Craik–Leibovich (CL) equation with u sol S replacing u S , and we discuss the form of the Stokes pumping associated with both u S and u sol S . This article is part of the theme issue ‘Mathematical problems in physical fluid dynamics (part 1)’.

Vortex crystals are quasiregular arrays of like-signed vortices in solid-body rotation embedded within a uniform background of weaker vorticity. Vortex crystals are observed at the poles of Jupiter and in laboratory experiments with magnetized electron plasmas in axisymmetric geometries. We show that vortex crystals form from the free evolution of randomly excited two-dimensional turbulence on an idealized polar cap. Once formed, the crystals are long lived and survive until the end of the simulations (300 crystal-rotation periods). We identify a fundamental length scale, L γ = ( U / γ ) 1 / 3 , characterizing the size of the crystal in terms of the mean-square velocity U of the fluid and the polar parameter γ = f p / a p 2 , with f p the Coriolis parameter at the pole and a p the polar radius of the planet.

Background worries about falling are common in older people. It has been suggested that these worries can reduce balance safety by acting as a distracting dual-task. However, it is also possible that worries may serve a protective purpose. The present work adopted a qualitative approach to conduct an in-depth exploration of older people’s experiences of worries about falling. Methods semi-structured interviews were conducted with 17 community-dwelling older people (mean age = 79 years; males = 5/17) who reported experiencing worries about falling. Reflexive thematic analysis was used to analyse the data. Results experiencing a fall—or otherwise recognising one’s balance limitations—brought the physical realities of participants’ ageing bodies to the forefront of their awareness. This led to the recognition of their susceptibility for an injurious fall, which triggered worries about falling in situations that threatened their balance. When preventing the subject of their worries (i.e. an injurious fall) was perceived to be within the individual’s locus of control, worries led to protective adaptations to behaviour. In contrast, when the subject of their worries was perceived to be outside their control, worries triggered feelings of panic—leading to unhelpful changes in behaviour. Conclusion these findings provide novel insight into the development and consequences of worries about falling in older people. They highlight the importance of considering an individual’s perception of control before deciding to clinically intervene to reduce worries about falling.

Virtual reality (VR) is a promising and cost-effective tool that has the potential to reduce the prevalence of falls and locomotor impairments in older adults. However, we believe that existing VR-based approaches to prevent falls do not mimic the full breadth of perceptual, cognitive, and motor demands that older adults encounter in daily life. Researchers have not yet fully leveraged VR to address affective factors related to fall risk, and how stressors such as anxiety influence older adult balance and real-world falls. In this perspective paper, we propose developing VR-based tools that replicate the affective demands of real-world falls (eg, crossing the street) to enhance fall prevention diagnostics and interventions by capturing the underlying processes that influence everyday mobility. An effort to replicate realistic scenarios that precipitate falls in VR environments will inform evidence-based diagnostics and individualize interventions in a way that could reduce falls in older adults in daily life.

Fast-moving synoptic-scale atmospheric disturbances produce large-scale near-inertial waves in the ocean mixed layer. In this paper, we analyze the distortion of such waves by smaller-scale barotropic eddies, with a focus on the evolution of the horizontal wavevector k under the effects of straining and refraction. The model is initialized with a horizontally uniform (k = 0) surface-confined near-inertial wave, which then evolves according to the phase-averaged model of Young and Ben Jelloul. A steady barotropic vortex dipole is first considered. Shear bands appear in the jet region as wave energy propagates downward and toward the anticyclone. When measured at a fixed location, both horizontal and vertical wavenumbers grow linearly with the time t elapsed since generation such that their ratio, the slope of wave bands, is time independent. Analogy with passive scalar dynamics suggests that straining should result in the exponential growth of |k|. Here instead, straining is ineffective, not only at the jet center, but also in its confluent and diffluent regions. Low modes rapidly escape below the anticyclonic core such that weakly dispersive high modes dominate in the surface layer. In the weakly dispersive limit, k = −t∇ζ(x, y, t)/2 provided that (i) the eddy vertical vorticity ζ evolves according to the barotropic quasigeostrophic equation and (ii) k = 0 initially. In steady flows, straining is ineffective because k is always perpendicular to the flow. In unsteady flows, straining modifies the vorticity gradient and hence k, and may account for significant wave–eddy energy transfers.

Since 2017 the Juno spacecraft has observed a cyclone at the north pole of Jupiter surrounded by eight smaller cyclones arranged in a polygonal pattern. It is not clear why this configuration is so stable or how it is maintained. Here we use a time series of images obtained by the JIRAM mapping spectrometer on Juno to track the winds and measure the vorticity and horizontal divergence within and around the polar cyclone and two of the circumpolar ones. We find an anticyclonic ring between the polar cyclone and the surrounding cyclones, supporting the theory that such shielding is needed for the stability of the polygonal pattern. However, even at the smallest spatial scale (180 km) we do not find the expected signature of convection—a spatial correlation between divergence and anticyclonic vorticity—in contrast with a previous study using additional assumptions about the dynamics, which shows the correlation at scales from 20 to 200 km. We suggest that a smaller size, relative to atmospheric thickness, of Jupiter’s convective storms compared with Earth’s, can reconcile the two studies.

Copyright © 2021 The Authors. Freezing of gait (FOG) can severely compromise daily functioning in people with Parkinson’s disease. Inability to initiate a step from FOG is likely underpinned, at least in part, by a deficient preparatory weight-shift. Conscious attempts to weight-shift in preparation to step can improve success of initiating forward steps following FOG. However, FOG often occurs during turning, where weight-shifting is more complex and risk of falling is higher. We explored the effectiveness of a dance-based (‘cha-cha’) weight-shifting strategy to re-initiate stepping following FOG during turning. Results suggest that this simple movement strategy can enhance turning steps following FOG, without compromising safety. Parkinson's UK project grant (K-1604).

Anxiogenic settings lead to reduced postural sway while standing, but anxiety-related balance may be influenced by the location of postural threat in the environment. We predicted that the direction of threat would elicit a parallel controlled manifold relative to the standing surface, and an orthogonal uncontrolled manifold during standing. Altogether, 14 healthy participants (8 women, mean age = 27.5 years, SD = 8.2) wore a virtual reality (VR) headset and stood on a matched real-world walkway (2 m × 40 cm × 2 cm) for 30 s at ground level and simulated heights (elevated 15 m) in two positions: (1) parallel to walkway, lateral threat; and (2) perpendicular to walkway, anteroposterior threat. Inertial sensors measured postural sway acceleration (e.g., 95% ellipse, root mean square (RMS) of acceleration), and a wrist-worn monitor measured heart rate coefficient of variation (HR CV). Fully factorial linear-mixed effect regressions (LMER) determined the effects of height and position. HR CV moderately increased from low to high height (p = 0.050, g = 0.397). The Height × Position interaction approached significance for sway area (95% ellipse; β = - 0.018, p = 0.062) and was significant for RMS (β = - 0.022, p = 0.007). Post-hoc analyses revealed that sagittal plane sway accelerations and RMS increased from low to high elevation in parallel standing, but were limited when facing the threat during perpendicular standing. Postural response to threat varies depending on the direction of threat, suggesting that the control strategies used during standing are sensitive to the direction of threat.

BackgroundThis study evaluated the effect of attentional focus instructions on movement efficiency during a level-ground walking task in older adults with and without a history of falls.MethodsOne hundred and thirty-four community-dwelling older adults were categorised into older fallers (OF) (n = 37) and older non-fallers (ONF) (n = 97). Each participant was instructed to walk at a self-selected pace along a 6 m walkway under three attentional focus conditions (i.e. internal, goal-directed and control) for a total of nine trials. Average muscle activity indices of lower limb co-contractions were measured using surface electromyography.ResultsBoth shank and thigh muscle co-contractions were higher in OF than in ONF in all three conditions. OF also demonstrated higher shank muscle co-contraction under the internal relative to the goal-directed condition, with no such change observed in ONF.ConclusionDespite no significant between-group differences in functional balance and balance confidence, relative walking inefficiencies were observed in OF compared with ONF. This finding demonstrates the debilitating consequences of falling that can occur with relative independence from various physiological or psychological factors that are commonly associated with falling and used to rationalise behavioural change. We also provide evidence that OF are more susceptible to conditions that provoke them to allocate attention internally. Therefore, in clinical contexts (e.g. gait rehabilitation), verbal instructions that refer to body movements (internal focus) might serve to compromise movement efficiency in older adults with a history of falls. Such changes will, theoretically, lessen the ability to react efficiently to changing environments experienced in daily life.

Availability of data and materials: All analysed data are available via Open Science Framework (https://osf.io/pe52a/). The materials used in the study are available via the same Open Science Framework repository, otherwise they are widely available. Data analysis scripts are available via the same Open Science Framework repository (https://osf.io/pe52a/) Copyright © 2021 The Authors. The ‘two-system’ view of fear builds on traditional conceptualisations of emotion; proposing that the mechanism(s) responsible for behavioural and physiological responses to threat may be distinct from that underpinning the (conscious) emotional experience itself. We empirically tested this notion within a novel, applied context of social and economic importance: fear of falling in older adults. Older adults stood on the edge of a raised platform and were stratified based on whether they reported fear in response to this postural threat. Irrespective of whether participants reported fear, we observed behaviours indicative of postural ‘stiffening’ during the threat condition. Self-reports indicated that participants cognitively monitored these changes in balance, and fear of falling was experienced in those who interpreted these behaviours to imply that harm was likely to occur. Fearful participants exhibited additional changes in balance (increased movement complexity and altered utilisation of sensory feedback) – behaviours likely influenced by attempts to consciously control balance. Taken together, these findings provide novel insight into the systems that regulate behavioural and emotional responses to postural threats. The novel conceptual framework developed from these findings helps identify specific mechanisms that might be targeted for clinical intervention. Economic and Social Research Council SWDTP Postdoctoral Fellowship (Grant Number: ES/V010131/1).

This chapter will describe how eye tracking outcomes can be used to evaluate psychological processes, particularly in applied contexts (e.g., clinical anxiety disorders, elite motor performance and rehabilitation settings). Our discussion will focus primarily on the influence of emotion on two key aspects of attentional processing related to Attentional Control Theory: i) attentional bias for threatening stimuli, and ii) processing (in)efficiency. We present key metrics than can be used to infer these processes and describe that previous management of outcome measures can be allocated into two categories: transferred and retrofitted. This content is primarily aimed at readers thinking about using eye-tracking in the context of psychological research and practice; to help them design their task(s) and select appropriate outcome measures in order to avoid potential confounds.

Inertia-gravity waves in the atmosphere and ocean are transported and refracted by geostrophic turbulent currents. Provided that the wave group velocity is much greater than the speed of geostrophic turbulent currents, kinetic theory can be used to obtain a comprehensive statistical description of the resulting interaction (Savva et al., J. Fluid Mech., vol. 916, 2021, A6). The leading-order process is scattering of wave energy along a surface of constant frequency, is the horizontal wavenumber.

From its unique pole-to-pole orbit, the Juno spacecraft discovered cyclones arranged in polygonal patterns around the poles of Jupiter. In a related modeling study the stability of the pattern depends on shielding -- a ring of anticyclonic vorticity surrounding each cyclone. Without shielding the vortices merge. Here we present high-resolution measurements obtained by tracking clouds in sequences of infrared images. There is vorticity of both signs at 200-km scales. The standard deviation is 0.32 times the vorticity of a large cyclone, whose relative vorticity is 0.46 times the planetary vorticity. Shielding exists at large scales, and it has the magnitude and distance from the vortex center predicted in the model. There is horizontal divergence of both signs at 200-km scales, with standard deviation 0.64 times the vorticity standard deviation. We propose that these intense structures are convection and that convection is the principal energy source for the large vortices.

Background/Study Context: Adjustments of posture in response to balance challenges may lead to subsequent increases in conscious posture processing. If cognitive resources are stretched by conscious processing of postural responses fewer resources will be available to attend to environmental trip or fall hazards. The objective of the study was to explore brain activity related to conscious processing of posture as a function of movement specific reinvestment and fear of falling. Method: Forty-three older adults (M = 71.4, SD = 4.1) stood with a wide or narrow stance on a force-plate while neural coherence between verbal-analytical (T3) and motor planning (Fz) regions of the brain was assessed using electroencephalography. The propensity for movement specific reinvestment was assessed using the Chinese version Movement Specific Reinvestment Scale (MSRS-C) and fear of falling was assessed using the Chinese version Fall Efficacy Scale International (FES-I[CH]). Results: Scores from the MSRS-C were negatively correlated with changes in T3-Fz coherence that occurred when participants shifted from wide to narrow stance. Together, MSRS-C and FES-I(CH) uniquely predicted the percentage change in T3-Fz coherence between the two stance conditions. Conclusion: Presented with two postural tasks of different complexities, participants with a lower propensity for conscious control of their movements (movement specific reinvestment) exhibited larger changes in real-time brain activity (neural coherence) associated with conscious postural processing.

The YBJ equation (Young & Ben Jelloul, J. Marine Res., vol. 55, 1997, pp. 735–766) provides a phase-averaged description of the propagation of near-inertial waves (NIWs) through a geostrophic flow. YBJ is obtained via an asymptotic expansion based on the limit $\mathit{Bu}\rightarrow 0$, where $\mathit{Bu}$ is the Burger number of the NIWs. Here we develop an improved version, the YBJ+ equation. In common with an earlier improvement proposed by Thomas, Smith & Bühler (J. Fluid Mech., vol. 817, 2017, pp. 406–438), YBJ+ has a dispersion relation that is second-order accurate in $\mathit{Bu}$. (YBJ is first-order accurate.) Thus both improvements have the same formal justification. But the dispersion relation of YBJ+ is a Padé approximant to the exact dispersion relation and with $\mathit{Bu}$ of order unity this is significantly more accurate than the power-series approximation of Thomas et al. (2017). Moreover, in the limit of high horizontal wavenumber $k\rightarrow \infty$, the wave frequency of YBJ+ asymptotes to twice the inertial frequency $2f$. This enables solution of YBJ+ with explicit time-stepping schemes using a time step determined by stable integration of oscillations with frequency $2f$. Other phase-averaged equations have dispersion relations with frequency increasing as $k^{2}$ (YBJ) or $k^{4}$ (Thomas et al. 2017): in these cases stable integration with an explicit scheme becomes impractical with increasing horizontal resolution. The YBJ+ equation is tested by comparing its numerical solutions with those of the Boussinesq and YBJ equations. In virtually all cases, YBJ+ is more accurate than YBJ. The error, however, does not go rapidly to zero as the Burger number characterizing the initial condition is reduced: advection and refraction by geostrophic eddies reduces in the initial length scale of NIWs so that $\mathit{Bu}$ increases with time. This increase, if unchecked, would destroy the approximation. We show, however, that dispersion limits the damage by confining most of the wave energy to low $\mathit{Bu}$. In other words, advection and refraction by geostrophic flows does not result in a strong transfer of initially near-inertial energy out of the near-inertial frequency band.

Background Older adults deemed to be at a high risk of falling will often display visual search behaviors likely to impair movement planning when negotiating environmental hazards. It has been proposed that these behaviors may be underpinned by fall-related anxiety. Thus, the aim of this study was to explore the effects of fall-related anxiety on visual search and stepping behaviors during adaptive gait. Methods Forty-four community-dwelling older adults (mean age = 74.61; standard deviation = 6.83) walked along a path and stepped into two raised targets. All participants completed walks at ground level, whereas participants deemed to be at a low risk of falling (n = 24) also completed walks under conditions designed to induce fall-related anxiety (walkway elevated 0.6 m). Participants’ movement kinematics and gaze behavior were measured. Results During ground trials, “high-risk” participants visually prioritized the immediate walkway areas 1–2 steps ahead, at the expense of previewing future stepping constraints. This reduced planning appeared to negatively affect safety, with greater stepping errors observed for future constraints. When completing walks on the elevated walkway, “low-risk” participants similarly prioritized immediate walkway areas, at the expense of planning future stepping actions. These behaviors were associated with greater attention directed toward consciously processing walking movements. Conclusions These findings provide evidence of a link between heightened fall-related anxiety and “high-risk” visual search behaviors associated with greater stepping errors. This information enhances our understanding of why high-risk older adults are less able to safely navigate environmental constraints.

Objectives Threats to balance, and subsequent increases in fall-related anxiety, can disrupt attentional processing during gait in older adults, leading to behavioral adaptations which may increase fall risk. However, limited research has investigated what changes in attention occur to contribute to these disruptions. The aim of this research was to describe changes in attention that occur during gait when older adults’ balance is threatened, while exploring how previous fall history and trait movement reinvestment (conscious monitoring and control of movement) also influence attention. Methods Forty older adults reported where they focus their attention when walking during two scenarios: (1) when they are relaxed and there is little risk of falling, and; (2) when their balance is threatened and they are anxious of falling. Results During the high-threat condition, participants reported greater attention towards movement processes, threats to balance, worries/disturbing thoughts and self-regulatory strategies, with less attention directed towards task-irrelevant thoughts. However, fall history influenced attentional focus, with fallers directing greater attention towards worries/disturbing thoughts. Contrary to predictions, trait movement reinvestment was not associated with attention directed towards movement processes. Discussion As processing worries/disturbing thoughts will likely reduce attentional resources available for effective postural control, we highlight this as one potential area to target interventions aimed at reducing the likelihood of repeated falling.

Objectives: We aimed to address whether increased task difficulty is sufficient to induce heightened conscious control and influence gait performance in older adults through the manipulations of either task difficulty or attentional focus. Method: Fifty older adults, split into high- (HR) and low-reinvestor (LR) groups, performed a walking task on a 7.4 m straight walkway in two conditions: firm level-ground surface (GW) and foam surface (FW). They subsequently performed the same walking task under two attentional focus conditions: Internal focus (IF) and External focus (EF). Electroencephalography (EEG) T3-Fz and T4-Fz coherences were used to indicate real-time conscious motor control and visual-spatial control, respectively. Results: We observed significantly higher T3-Fz and T4-Fz coherences under FW compared to GW. HR reduced their gait speed at a greater extent than LR under FW. Significantly lower T3-Fz coherence and faster gait were demonstrated under EF compared to IF. LR walked slower under IF compared to Baseline while gait speed of HR did not differ. Discussion: Visual-spatial and conscious movement processing increase as a function of task difficulty during gait. Our findings also advocate the use of external focus instructions in clinical settings, with the potential to reduce conscious control and promote movement automaticity, even in relatively complex gait tasks.

Freezing of gait (FoG) is typically a symptom of advanced Parkinson's disease (PD) that negatively influences the quality of life and is often resistant to pharmacological interventions. Novel treatment options that make use of auditory or sensory cues might be optimized by prediction of freezing events. These predictions might help to trigger external sensory cues—shown to improve walking performance—when behavior is changed in a manner indicative of an impending freeze (i.e., when the user needs it the most), rather than delivering cue information continuously. A data-driven approach is proposed for predicting freezing events using Random Forrest (RF), Neural Network (NN), and Naive Bayes (NB) classifiers. Vertical forces, sampled at 100 Hz from a force platform were collected from 9 PD subjects as they stepped in place until they at least had one freezing episode or for 90 s. The F1 scores of RF/NN/NB algorithms were computed for different IL (input to the machine learning algorithm), and GL (how early the freezing event is predicted). A significant negative correlation between the F1 scores and GL, highlighting the difficulty of early detection is found. The IL that maximized the F1 score is approximately equal to 1.13 s. This indicates that the physiological (and therefore neurological) changes leading to freezing take effect at-least one step before the freezing incident. Our algorithm has the potential to support the development of devices to detect and then potentially prevent freezing events in people with Parkinson's which might occur if left uncorrected.

Anticyclonic vortices focus and trap near-inertial waves so that near-inertial energy levels are elevated within the vortex core. Some aspects of this process, including the nonlinear modification of the vortex by the wave, are explained by the existence of trapped near-inertial eigenmodes. These vortex eigenmodes are easily excited by an initialwave with horizontal scale much larger than that of the vortex radius. We study this process using a wave-averaged model of near-inertial dynamics and compare its theoretical predictions with numerical solutions of the three-dimensional Boussinesq equations. In the linear approximation, the model predicts the eigenmode frequencies and spatial structures, and a near-inertial wave energy signature that is characterized by an approximately time-periodic, azimuthally invariant pattern. The wave-averaged model represents the nonlinear feedback of the waves on the vortex via a wave-induced contribution to the potential vorticity that is proportional to the Laplacian of the kinetic energy density of the waves. When this is taken into account, the modal frequency is predicted to increase linearly with the energy of the initial excitation. Both linear and nonlinear predictions agree convincingly with the Boussinesq results.

Objectives This study examined if people with Parkinson’s and freezing of gait pathology (FoG) could be trained to increase preparatory weight-shift amplitude, and facilitate step initiation during FoG. Methods Thirty-five people with Parkinson’s and FoG attempted to initiate forward walking from a stationary position caused by a freeze (n = 17, FoG-F) or voluntarily stop (n = 18, FoG-NF) in a Baseline condition and two conditions where an increased weight-shift amplitude was trained via: (i) explicit verbal instruction, and (ii) implicit movement analogies. Results At Baseline, weight-shift amplitudes were smaller during: (i) unsuccessful, compared to successful step initiations (FoG-F group), and (ii) successful step initiations in the FoG-F group compared to FoG-NF. Both Verbal and Analogy training resulted in significant increases in weight-shift amplitude in both groups, and a corresponding pronounced reduction in unsuccessful attempts to initiate stepping (FoG-F group). Conclusions Hypometric preparatory weight-shifting is associated with failure to initiate forward stepping in people with Parkinson’s and FoG. However, impaired weight-shift characteristics are modifiable through conscious strategies. This current study provides a novel and critical evaluation of preparatory weight-shift amplitudes during FoG events. The intervention described represents an attractive ‘rescue’ strategy and should be further scrutinised regarding limitations posed by physical and cognitive deficits.

Introduction: Changes in visual attention have been argued to influence freezing of gait (FOG) in people with Parkinson's Disease (PD). However, the specific visual search patterns of people with FOG pathology (PD + FOG) and potential underlying mechanisms are not well understood. The current study explored visual search behavior in PD + FOG while walking on a pathway featuring environmental features known to exacerbate FOG (e.g., narrow doorway and tripping hazards). Potential underpinning attentional mechanisms were also assessed, such as conscious movement processing. Methods: Visual search behavior of twelve people with PD + FOG tested in ON-state (Mage = 74.3) and twelve age-matched healthy controls (Mage = 72.5) were analyzed during a complex walking task. The task required participants to step over an obstacle and navigate through a narrow doorway, surrounded by clutter. Results: People with PD + FOG more frequently directed visual attention to ongoing and imminent steps compared to healthy controls (Mdn = 26% vs Mdn = 14%, respectively; p = 0.042). Self-reported conscious movement processing was also significantly higher in people with PD + FOG. The one participant who froze during the walking task fixated the future trip hazard (obstacle, approximately 6 steps ahead) almost exclusively during freezing trials (i.e., 60-100% of the trial). In contrast, during ‘non-freeze’ trials, this participant increased the duration of fixations towards ongoing and imminent steps. Conclusion: Results suggest that people with PD + FOG strongly monitor/control ongoing and immediately upcoming stepping movements. However, prolonged fixations towards threats to future movements might prevent people with PD + FOG from processing the visual information needed to do this, thereby provoke freezing episodes.

Background. Recent decades have seen increased interest in how anxiety–and associated changes in conscious movement processing (CMP)–can influence the control of balance and gait, particularly in older adults. However, the most prevalent scale used to measure CMP during gait (the Movement-Specific Reinvestment Scale (MSRS)) is generic (i.e., non-gait specific) and potentially lacks sensitivity in this context.\ud \ud \ud Methods. In a preliminary study, we first sought to evaluate if MSRS scores associated with the number of CMP-related thoughts self-reported by older adults while walking. The next aim was to develop and validate a new questionnaire (the Gait-Specific Attentional Profile, G-SAP) capable of measuring gait-specific CMP, in addition to other attentional processes purported to influence gait. This scale was validated using responses from 117 (exploratory) and 107 (confirmatory factor analysis) older adults, resulting in an 11-item scale with four sub-scales: CMP, anxiety, fall-related ruminations, and processing inefficiencies. Finally, in a separate cohort of 53 older adults, we evaluated associations between scores from both the GSAP CMP subscale and the MSRS, and gait outcomes measured using a GAITRite walkway in addition to participants’ fall-history.\ud \ud \ud Results. MSRS scores were not associated with self-reported thoughts categorised as representing CMP. In regression analyses that controlled for functional balance, unlike the MSRS, the G-SAP subscale of CMP significantly predicted several gait characteristics including velocity (p=.033), step length (p=.032), and double-limb support (p=.015).\ud \ud \ud Significance. The G-SAP provides gait-specific measures of four psychological factors implicated in mediating the control of balance and gait. In particular, unlike the MSRS, the G-SAP subscale of CMP appears sensitive to relevant attentional processes known to influence gait performance. We suggest that the G-SAP offers an opportunity for the research community to further develop understanding of psychological factors impacting gait performance across a range of applied clinical contexts.

Fear of falling can have a profound influence on anticipatory postural control during dynamic balance tasks (e.g., rise-to-toes and leg-raise tasks), with fearful individuals typically exhibiting postural adjustments of smaller magnitudes prior to movement onset. However, very little is known about how fear of falling influences the generation of anticipatory postural adjustments (APAs) during gait initiation; a task in which producing smaller APAs may compromise stability. Sixteen young adults initiated gait as fast as possible following an auditory cue during two conditions: Baseline (ground level), and Threat (fear of falling induced via a platform raised 1.1 m). While the magnitude and duration of APAs did not change between conditions, participants executed steps of shorter lengths during Threat. As APAs during gait initiation are typically proportionate to the length of the first step, the APAs during Threat are therefore disproportionately large (given the shorter step length). We suggest that such failure to scale the APA to the magnitude of the motor output represents a fear-related ‘overcompensation’, whereby fearful participants sought to ensure that the APA was sufficient for ensuring that their centre of mass was positioned above the support leg prior to gait initiation. During conditions of threat, participants also exhibited greater postural sway prior to initiating gait (i.e., following the auditory cue) and took longer to generate the APA (i.e., impaired reaction). As greater reaction times during voluntary stepping is consistently associated with increased fall-risk, we suggest this as one mechanism through which fear of falling may reduce balance safety. Parkinson’s UK

Background Healthy young adults typically exhibit a progressive ‘top-down’ reorientation of body segments (i.e., head, trunk, then pelvis) during turning. This behaviour is less evident in older adults at risk of falling, who often reduce angular displacement between body segments during turns. The potential functional and psychological contributors to this so-called ‘en-bloc’ turning strategy are not yet understood. Research question Are there associations between concern about falling and variables representing en-bloc turning (i.e., increased coupling between body segments)? Methods Twenty-one older adults were assessed while turning during an adaptive walking task. We collected data from markers forming the head, trunk, and pelvis segments, while gait velocity throughout the turn was calculated from a sternum marker. We correlated several variables with concern about falling alone, as well as while controlling for functional balance ability. Results Correlation analyses revealed that concern about falling was related to en-bloc turning strategies and slower gait velocity throughout the turn, when analysed independently of functional balance. When controlling for balance ability, en-bloc turning strategies between the head and trunk, as well as the head and pelvis, remained significantly associated with concern about falling. Significance Findings offer an insight into the potential role that psychological characteristics may have in determining older adults’ turning behaviour and associated risk of falling.

Exposure to ionizing radiation following environmental contamination (e.g., the Chernobyl and Fukushima nuclear accidents), radiotherapy and diagnostics, occupational roles and space travel has been identified as a possible risk-factor for cognitive dysfunction. The deleterious effects of high doses (≥1.0 Gy) on cognitive functioning are fairly well-understood, while the consequences of low (≤0.1 Gy) and moderate doses (0.1-1.0 Gy) have been receiving more research interest over the past decade. In addition to any impact of actual exposure on cognitive functioning, the persistent psychological stress arising from perceived exposure, particularly following nuclear accidents, may itself impact cognitive functioning. In this review we offer a novel interdisciplinary stance on the cognitive impact of radiation exposure, considering psychological and epidemiological observations of different exposure scenarios such as atomic bombings, nuclear accidents, occupational and medical exposures while accounting for differences in dose, rate of exposure and exposure type. The purpose is to address the question that perceived radiation exposure - even where the actual absorbed dose is 0.0 Gy above background dose - can result in psychological stress, which could in turn lead to cognitive dysfunction. In addition, we highlight the interplay between the mechanisms of perceived exposure (i.e., stress) and actual exposure (i.e., radiation-induced cellular damage), in the generation of radiation-induced cognitive dysfunction. In all, we offer a comprehensive and objective review addressing the potential for cognitive defects in the context of low- and moderate-dose IR exposures.Overall the evidence shows prenatal exposure to low and moderate doses to be detrimental to brain development and subsequent cognitive functioning, however the evidence for adolescent and adult low- and moderate-dose exposure remains uncertain. The persistent psychological stress following accidental exposure to low-doses in adulthood may pose a greater threat to our cognitive functioning. Indeed, the psychological implications for instructed cohorts (e.g., astronauts and radiotherapy patients) is less clear and warrants further investigation. Nonetheless, the psychosocial consequences of low- and moderate-dose exposure must be carefully considered when evaluating radiation effects on cognitive functioning, and to avoid unnecessary harm when planning public health response strategies.

In the presence of inertia-gravity waves, the geostrophic and hydrostatic balance that characterises the slow dynamics of rapidly rotating, strongly stratified flows holds in a time-averaged sense and applies to the Lagrangian-mean velocity and buoyancy. We give an elementary derivation of this wave-averaged balance and illustrate its accuracy in numerical solutions of the three-dimensional Boussinesq equations, using a simple configuration in which vertically planar near-inertial waves interact with a barotropic anticylonic vortex. We further use the conservation of the wave-averaged potential vorticity to predict the change in the barotropic vortex induced by the waves.

For the problem of horizontal convection the Nusselt number based on entropy production is bounded from above by indicates that the inequalities used by Siggers et al. (J. Fluid Mech., vol. 517, 2004, pp. 55–70) are surprisingly accurate.

Previous research suggests that reinvestment (i.e. conscious control of movements) is associated with inefficient information processing and compromised movement strategies in older adults during walking. We examined whether reinvestment propensity is associated with conservative gait behaviour in older adults. Trait Reinvestment propensity was measured using the Movement Specific Reinvestment Scale (Chinese version) (MSRS-C). Thirty-eight older adults were categorized into 'Low Reinvestor Group' (LRG) (MSRS-C 27) and another 38 were categorized into 'High Reinvestor Group' (HRG) (MSRS-C 38). There were no significant differences in physical and cognitive abilities between groups. Participants were asked to walk along a 6-m straight level-ground walkway at a self-selected pace under conditions of no instruction (Baseline), instruction related to self-focus on body movements (BI), and instruction related to the external environment (EI). No significant difference was found in gait behaviour between LRG and HRG at Baseline. However, significant changes, indicative of conservative gait patterns, were found in LRG when given instructions that prompted them to consciously control their body movements. No changes were observed in HRG under external-related instructions that are assumed to reduce conscious motor processing and improve motor performance. Our findings contradict previous views on the association between trait reinvestment propensity and compromised motor performance in older adults, which potentially reduces justification for reducing trait reinvestment propensity in older adults. We also suggest that MSRS is insensitive to reflect the degree of conscious control during gait tasks. Our findings also implicate the potential detrimental effect of applying inward-focus-related instructions in healthcare rehabilitation settings.

Background Current evidence suggests that fall-related anxiety can impair attentional processing efficiency during gait in both young and older adults, reducing the cognitive resources available for carrying out concurrent tasks (i.e., holding a conversation whilst walking or planning the safest route for navigation). Research question It has been suggested that fall-related anxiety may impair processing efficiency by directing attention ‘internally’, towards consciously controlling and monitoring movement. The present study aimed to evaluate this interpretation. Methods Fifteen healthy young adults performed a precision stepping task during both single- and dual-task (completing the stepping task while simultaneously performing an arithmetic task), under three conditions: (1) Baseline; (2) Threat (walking on a platform raised 1.1 m above ground), and; (3) Internal focus of attention (cues/instructions to direct attention towards movement processing). Results We observed significantly greater cognitive dual-task costs (i.e., poorer performance on the arithmetic task) during Threat compared to Baseline, with the greatest costs observed in individuals reporting the highest levels of Threat-induced conscious motor processing. Significantly greater cognitive dual-task costs were also observed during the Internal condition, confirming the assumption that consciously attending to movement reduces cognitive resources available for carrying out a secondary task during gait. These results were accompanied with significantly poorer stepping accuracy in dual-task trials during both Threat and Internal. Significance These findings support previous attempts to rationalise attentional processing inefficiencies observed in anxious walkers as being a consequence of an anxiety-induced internal focus of attention.

We study stimulated generation – the transfer of energy from balanced flows to existing internal waves – using an asymptotic model that couples barotropic quasi-geostrophic flow and near-inertial waves with $\text{e}^{\text{i}mz}$ vertical structure, where $m$ is the vertical wavenumber and $z$ is the vertical coordinate. A detailed description of the conservation laws of this vertical-plane-wave model illuminates the mechanism of stimulated generation associated with vertical vorticity and lateral strain. There are two sources of wave potential energy, and corresponding sinks of balanced kinetic energy: the refractive convergence of wave action density into anti-cyclones (and divergence from cyclones); and the enhancement of wave-field gradients by geostrophic straining. We quantify these energy transfers and describe the phenomenology of stimulated generation using numerical solutions of an initially uniform inertial oscillation interacting with mature freely evolving two-dimensional turbulence. In all solutions, stimulated generation co-exists with a transfer of balanced kinetic energy to large scales via vortex merging. Also, geostrophic straining accounts for most of the generation of wave potential energy, representing a sink of 10 %–20 % of the initial balanced kinetic energy. However, refraction is fundamental because it creates the initial eddy-scale lateral gradients in the near-inertial field that are then enhanced by advection. In these quasi-inviscid solutions, wave dispersion is the only mechanism that upsets stimulated generation: with a barotropic balanced flow, lateral straining enhances the wave group velocity, so that waves accelerate and rapidly escape from straining regions. This wave escape prevents wave energy from cascading to dissipative scales.

A heat exchanger can be modeled as a closed domain containing an incompressible fluid. The moving fluid has a temperature distribution obeying the advection-diffusion equation, with zero temperature boundary conditions at the walls. Starting from a positive initial temperature distribution in the interior, the goal is to flux the heat through the walls as efficiently as possible. Here we consider a distinct but closely related problem, that of the integrated mean exit time of Brownian particles starting inside the domain. Since flows favorable to rapid heat exchange should lower exit times, we minimize a norm of the exit time. This is a time-independent optimization problem that we solve analytically in some limits, and numerically otherwise. We find an (at least locally) optimal velocity field that cools the domain on a mechanical time scale, in the sense that the integrated mean exit time is independent on molecular diffusivity in the limit of large-energy flows., Comment: 16 pages, 5 figures. SIAM LaTeX style with custom margins. Fixed a few typos

Postural control is an adaptive process that can be affected by many aspects of human behavior, including emotional contexts. The main emotional contexts that affect postural control are postural threat and passive viewing of aversive or threatening images, both of which produce a reduction in postural sway. The aim of the present study was to assess whether similar stress-related changes in postural sway can be observed using stress induced by social evaluative threat (SET) while perform-ing arithmetic tasks. Twelve young adults performed an arithmetic and a postural control task separately, concurrently, and concurrently with added time pressure in the arithmetic task. In the final condition, participants were given negative feedback about their performance in the arithmetic task and performed it again while being observed (SET condition). Results showed that stress increased linearly with task demand. Postural sway and reaction times were not affected by the first two conditions; however, when time pressure was introduced, reaction times became faster and sway amplitude increased. Finally, introduc-tion of SET caused the predicted reduction in postural sway and an increase in reaction times relative to the time pressure condition. Our results suggest that stress induced using a combination of arithmetic tasks and social evaluative threat leads to systematic changes in postural control. The paradigm developed in the present study would be very useful in assessing interactions between cognition, stress, and postural control in the context of postural instability and falls in older adults.

Groups of surface gravity waves induce horizontally varying Stokes drift that drives convergence of water ahead of the group and divergence behind. The mass flux divergence associated with spatially variable Stokes drift pumps water downwards in front of the group and upwards in the rear. This ‘Stokes pumping’ creates a deep Eulerian return flow that sets the isopycnals below the wave group in motion and generates a trailing wake of internal gravity waves. We compute the energy flux from surface to internal waves by finding solutions of the wave-averaged Boussinesq equations in two and three dimensions forced by Stokes pumping at the surface. The two-dimensional (2-D) case is distinct from the 3-D case in that the stratification must be very strong, or the surface waves very slow for any internal wave (IW) radiation at all. On the other hand, in three dimensions, IW radiation always occurs, but with a larger energy flux as the stratification and surface wave (SW) amplitude increase or as the SW period is shorter. Specifically, the energy flux from SWs to IWs varies as the fourth power of the SW amplitude and of the buoyancy frequency, and is inversely proportional to the fifth power of the SW period. Using parameters typical of short period swell (e.g. 8 s SW period with 1 m amplitude) we find that the energy flux is small compared to both the total energy in a typical SW group and compared to the total IW energy. Therefore this coupling between SWs and IWs is not a significant sink of energy for the SWs nor a source for IWs. In an extreme case (e.g. 4 m amplitude 20 s period SWs) this coupling is a significant source of energy for IWs with frequency close to the buoyancy frequency.

The fear of falling, or mobility-related anxiety, profoundly affects gait, but is challenging to study without risk to participants.To determine the efficacy of using virtual reality (VR) to manipulate illusions of height and consequently, elevated mobility-related anxiety when turning. Moreover, we examined if mobility-related anxiety effects decline across time in VR environments as participants habituate.Altogether, 10 healthy participants (five women, mean (standard deviation) age = 28.5 (8.5) years) turned at self-selected and fast speeds on a 2.2 m walkway under two simulated environments: (1) ground elevation; and (2) high elevation (15 m above ground). Peak turning velocity was recorded using inertial sensors and participants rated their cognitive (i.e., worry) and somatic (i.e., tension) anxiety, confidence, and mental effort.A significant Height × Speed × Trial interaction (p = 0.013) was detected for peak turning velocity. On average, the virtual height illusion decreased peak turning velocity, especially at fast speeds. At low elevation, participants decreased speed across trials, but not significantly (p = 0.381), but at high elevation, they significantly increased speed across trials (p = 0.001). At self-selected speeds, no effects were revealed (all p 0.188) and only effects for Height were observed for fast speeds (p 0.001). After turning at high elevation, participants reported greater cognitive (p = 0.008) and somatic anxiety (p = 0.007), reduced confidence (p = 0.021), and greater mental effort (p 0.001) compared to the low elevation.VR can safely induce mobility-related anxiety during dynamic motor tasks, and habituation effects from repeated exposure should be carefully considered in experimental designs and analysis.

An idealized storm scenario is examined in which a wind-generated inertial wave interacts with a turbulent baroclinic quasi-geostrophic flow. The flow is initialized by spinning up a Eady model with a realistic stratification profile. The storm is modeled as an initial value problem for a mixed-layer confined, horizontally-uniform inertial oscillation. The primordial inertial oscillation then evolves under the effects of advection, refraction, dispersion and dissipation. Waves feedback onto the flow by modifying its potential vorticity. In the first few days, refraction dominates and wave energy is attracted (repelled) by regions of negative (positive) vorticity. Wave energy is subsequently drained down anticyclonic pipes. This drainage halts as wave energy encounters weakening vorticity. After a week or two, wave energy accumulates at the bottom of negative vorticity features, i.e. along filamentary structures at shallow depths and in larger anticyclones at greater depths. Wave feedback tends to weaken vortices and thus slow down wave penetration. This effect, however, is found to be weak even for vigorous storms., Comment: Sumbitted to the Journal of Physical Oceanography