Sudden Perturbation Research Articles

Fast Transactive Control for Frequency Regulation in Smart Grids with Demand Response and Energy Storage

This paper proposes a framework for controlling grid frequency by engaging the generation-side and demand-side resources simultaneously, via a fast transactive control approach. First, we use a proportional frequency-price relation to build and analyze a transactive frequency droop controller for a single-area power grid. Then, we develop a transactive demand response system by incorporating a large population of thermostatically controlled air conditioning loads. A proportional-integral controller is used to adjust the setpoint temperature of the air conditioners based on price variations. A battery storage system is then developed and augmented to the system to capture the energy arbitrage effects. A nonlinear price-responsive battery management system is developed to enable effective charging and discharging operations within the battery’s state-of-charge and power constraints. Simulation results indicate that the proposed transactive control system improves the steady-state and transient response of the grid to sudden perturbations in the supply and demand equilibrium. To decouple frequency from price during daily operation and maintain frequency near the nominal value, we propose adding a feedforward price broadcast signal to the control loop based on the net demand measurement. Through various simulations, we conclude that a combination of feedback transactive controller with feedforward price broadcast scheme provides an effective solution for the simultaneous generation-side and demand-side energy management and frequency control in smart power grids.

Age-Related Differences in Arm and Trunk Responses to First and Repeated Exposure to Laterally Induced Imbalances.

The objective of this study was to examine age-related differences in arm and trunk responses during first and repeated step induced balance perturbations. Young and older adults received 10 trials of unpredictable lateral platform translations. Outcomes included maximum arm and trunk displacement within 1 s of perturbation and at first foot lift off (FFLO), arm and neck muscle activity as recorded using electromyography (EMG), initial step type, balance confidence, and percentage of harness-assisted trials. Compared to young adults, older adults demonstrated greater arm and trunk angular displacements during the first trial, which were present at FFLO and negatively associated with balance confidence. Unlike young adults, recovery steps in older adults were directed towards the fall with a narrowed base of support. Over repeated trials, rapid habituation of first-trial responses of bilateral arm and trunk displacement and EMG amplitude was demonstrated in young adults, but was absent or limited in older adults. Older adults also relied more on harness assistance during balance recovery. Exaggerated arm and trunk responses to sudden lateral balance perturbations in older adults appear to influence step type and balance recovery. Associations of these persistently amplified movements with an increased reliance on harness assistance suggest that training to reduce these deficits could have positive effects in older adults with and without neurological disorders.

Local knee heating increases spinal and supraspinal excitability and enhances plantar flexion and dorsiflexion torque production of the ankle in older adults.

Aging is associated with progressive loss of active muscle mass and consequent decreases in resting metabolic rate and body temperature, and slowing of nerve conduction velocities and muscle contractility. These effectors compromise the ability of the elderly to maintain an upright posture during sudden balance perturbation, increase the risk of falls, and lead to self-imposed reduction in physical activity. Short-term superficial acute heating can modulate the neural drive transmission to exercising muscles without any marked change in deep-muscle temperature. To determine whether the short-term (5min) application of local passive knee-surface heating (next-to-skin temperature, ~ 44°C) in healthy older subjects of both sexes (64-74years; eight men/eight women) enhances reflex excitability, we compared the voluntarily and electrically induced ankle muscle torque production and contractile properties with those of healthy younger subjects of both sexes (21-35years, 10 men/10 women). The application of local heating (vs. control) increased the maximal Hoffman reflex (Hmax), the maximal volitional wave (Vsup) amplitude, and the Hmax/Mmax amplitude ratio, and decreased Vsup latency only in older adults. In the older adults (vs. younger adults), the application of local heating (vs. control trial) was accompanied by a significant increase in maximal voluntary peak torque, rate of torque development, and isokinetic peak torque of plantar flexion/dorsiflexion muscle contraction. The spinal and supraspinal reflex excitability of older adults increased during local knee-heating application. The improved motor drive transmission observed in older adults was accompanied by increased voluntarily induced torque production of the ankle muscles during isometric/isokinetic contractions.

Auditory-Motor Perturbations of Voice Fundamental Frequency: Feedback Delay and Amplification.

Purpose Gradual and sudden perturbations of vocal fundamental frequency (f o), also known as adaptive and reflexive f o perturbations, are techniques to study the influence of auditory feedback on voice f o control mechanisms. Previous vocal f o perturbations have incorporated varied setup-specific feedback delays and amplifications. Here, we investigated the effects of feedback delays (10-100 ms) and amplifications on both adaptive and reflexive f o perturbation paradigms, encapsulating the variability in equipment-specific delays (3-45 ms) and amplifications utilized in previous experiments. Method Responses to adaptive and reflexive f o perturbations were recorded in 24 typical speakers for four delay conditions (10, 40, 70, and 100 ms) or three amplification conditions (-10, +5, and +10 dB relative to microphone) in a counterbalanced order. Repeated-measures analyses of variance were carried out on the magnitude of f o responses to determine the effect of feedback condition. Results There was a statistically significant effect of the level of auditory feedback amplification on the response magnitude during adaptive f o perturbations, driven by the difference between +10- and -10-dB amplification conditions (hold phase difference: M = 38.3 cents, SD = 51.2 cents; after-effect phase: M = 66.1 cents, SD = 84.6 cents). No other statistically significant effects of condition were found for either paradigm. Conclusions Experimental equipment delays below 100 ms in behavioral paradigms do not affect the results of f o perturbation paradigms. As there is no statistically significant difference between the response magnitudes elicited by +5- and +10-dB auditory amplification conditions, this study is a confirmation that an auditory feedback amplification of +5 dB relative to microphone is sufficient to elicit robust compensatory responses for f o perturbation paradigms.

Ultrafast Quantum Relaxation Dynamics of Magnetically Ordered Systems with Spin Crossover in an Excited State under a Sudden Perturbation

A theoretical model based on the relaxation equation for the density matrix has been proposed to describe the ultrafast time dynamics of magnetically ordered systems with spin crossover in an excited state under a sudden perturbation. Oscillations of the magnetization, the population of the high-spin state, and the generation of local vibrons at a transition of the system from the light-excited Franck-Condon low-spin state to the highspin ground state.

Brace yourself: How abdominal bracing affects intersegmental lumbar spine kinematics in response to sudden loading

Abdominal bracing is a voluntary method of increasing spine stiffness to restrict spine displacement. Previous investigations of abdominal bracing have measured effects on whole lumbar motion; however, how this effect is distributed across the lumbar spine is unknown. Therefore, this study was designed to test the influence of abdominal bracing on spine intersegmental (T9/T10 to L5/S1) flexion, measured via skin surface markers, in response to sudden loading perturbations applied through the hands in 16 young healthy participants. Abdominal and back muscle activation responses were also measured. The results demonstrated that abdominal bracing significantly reduced sagittal plane motion at intersegmental levels T12/L1 to L4/L5, by 45% (0.74 degrees) at L4/L5 to 94% (0.71 degrees) at L1/L2 compared to control. L5/S1 experienced a 50% (0.36 degrees) reduction, but this was not statistically significant. Additionally, abdominal bracing resulted in greater baseline activation of all abdominal and back muscles, but did not affect onset times or response magnitudes of any of the back muscles acting counter to the perturbation. Therefore, the elevated baseline activation of trunk musculature during an abdominal brace serves to restrict flexion motion at the majority of the intersegmental lumbar spine (T12/L1 to L4/5) in response to sudden trunk flexion perturbations.

Effect Of Kinesio Taping On Postural Control In Individuals With Chronic Ankle Instability

Chronic ankle instability (CAI), which is characterized by deficient postural control, may be improved through Kinesio Taping (KT) intervention. However, the effect of KT on postural control in individuals with CAI is controversial. PURPOSE: This study aimed to investigate the acute effect of KT on postural control through computerized dynamic posturography (CDP) and perceived sensation in individuals with CAI. METHODS: A total of 35 male adults with CAI participated in the study. Each participant received four random ankle taping, including KT, athletic taping (AT), sham taping (ST), and no taping (NT). Subsequently, a series of postural stability measurements was performed using CDP. The tests included sensory organization test (SOT), unilateral stance (US) test, limit of stability (LOS) test, motor control test, and adaption test (ADT). In addition, perception stability and comfort were measured through visual analogue scaling. One-way repeated measures analysis of variance was conducted to determine difference on postural control among KT, AT, ST, and NT. RESULTS: No significant difference was observed for parameters in SOT, US test, and LOS test among four taping. In the motor control test, the amplitude scaling scores of KT were 35.87% lower than NT (p<. 001) in forward-small slip and 21.58% lower than ST (p=.035) in backward-large slip. In ADT, sway energy scores were 7.59% greater in ST than this in AT (p=.028). For perception stability, KT was performed better than ST (p<.001) and NT (p<.001), and AT was performed better than ST (p=.001) and NT (p<.001). For perception comfort, KT was performed better than AT (p=.001) and NT (p=.031). CONCLUSIONS: KT and AT could not facilitate postural control for CAI individuals during static and voluntary measurements. However, they could provide effective support to cope with sudden perturbation. In addition, KT improved perception stability and comfort, whereas AT improved perception stability but provided the least comfort.

Experimental Determination of the Conditions Associated With “Zebra Stripe” Pattern Generation in the Earth's Inner Radiation Belt and Slot Region

AbstractThe “zebra stripes” are peaks and valleys commonly present in the spectrograms of energetic particles trapped in the Earth's inner belt and slot region. Several theories have been proposed over the years to explain their generation, structure, and evolution. Yet, the plausibility of various theories has not been tested due to a historical lack of ground truth, including in situ electric field measurements. In this work, we leverage the new visibility offered by the database of Van Allen Probes electric drift measurements to reveal the conditions associated with the generation of zebra stripe patterns. Energetic electron fluxes by the Radiation Belt Storm Probes Ion Composition Experiment between 1 January 2013 and 31 December 2015 are systematically analyzed to determine 370 start times associated with the generation of zebra stripes. Statistical analyses of these events reveal that the zebra stripes are usually created during substorm onset, a time at which prompt penetration electric fields are present in the plasmasphere. All the pieces of experimental evidence collected are consistent with a scenario in which the prompt penetration electric field associated with substorm onset leads to a sudden perturbation of the trapped particle drift motion. Subsequent drift echoes constitute the zebra stripes. This study exemplifies how the analysis of trapped particle dynamics in the inner belt and slot region provides complementary information on the dynamics of plasmaspheric electric fields. It is the first time that the signature of prompt penetration electric fields is detected in near‐equatorial electric field measurements below L = 3.

Introducing a drift and diffusion framework for childhood growth research

Background: Growth trajectories are highly variable between children, making epidemiological analyses challenging both to the identification of malnutrition interventions at the population level and also risk assessment at individual level. We introduce stochastic differential equation (SDE) models into child growth research. SDEs describe flexible dynamic processes comprising: drift - gradual smooth changes – such as physiology or gut microbiome, and diffusion - sudden perturbations, such as illness or infection. Methods: We present a case study applying SDE models to child growth trajectory data from the Haydom, Tanzania and Venda, South Africa sites within the MAL-ED cohort. These data comprise n=460 children aged 0-24 months. A comparison with classical curve fitting (linear mixed models) is also presented. Results: The SDE models offered a wide range of new flexible shapes and parameterizations compared to classical additive models, with performance as good or better than standard approaches. The predictions from the SDE models suggest distinct longitudinal clusters that form distinct ‘streams’ hidden by the large between-child variability. Conclusions: Using SDE models to predict future growth trajectories revealed new insights in the observed data, where trajectories appear to cluster together in bands, which may have a future risk assessment application. SDEs offer an attractive approach for child growth modelling and potentially offer new insights.

On a population model with Allee effects and environmental perturbations

The present study takes advantage of the white noise and the Levy noise to portray the small and sudden environmental perturbations respectively, and puts forward a stochastic population model with Allee effects and Levy jumps. First, it is confirmed that the model possesses a unique, global and positive solution. Then, permanence and extinction of the species are examined. Afterwards, the trajectory of population abundance is tested. The findings uncover that both the white noise and the Levy noise have significant functions on the rate of population change. Finally, the theoretical findings are applied to dissect the rate of population change of the African hunting dog Lycaon pictus.

Double-Step Paradigm in Microgravity: Preservation of Sensorimotor Flexibility in Altered Gravitational Force Field.

The way we can correct our ongoing movements to sudden and unforeseen perturbations is key to our ability to rapidly adjust our behavior to novel environmental demands. Referred to as sensorimotor flexibility, this ability can be assessed by the double-step paradigm in which participants must correct their ongoing arm movements to reach targets that unexpectedly change location (i.e., target jump). While this type of corrections has been demonstrated in normogravity in the extent of reasonable spatiotemporal constraints underpinning the target jumps, less is known about sensorimotor flexibility in altered gravitational force fields. We thus aimed to assess sensorimotor flexibility by comparing online arm pointing corrections observed during microgravity episodes of parabolic flights with normogravity standards. Seven participants were asked to point as fast and as accurately as possible toward one of two visual targets with their right index finger. The targets were aligned vertically in the mid-sagittal plane and were separated by 10 cm. In 20% of the trials, the initially illuminated lower target was switched off at movement onset while the upper target was concomitantly switched on prompting participants to change the trajectory of their ongoing movements. Results showed that, both in normogravity and microgravity, participants successfully performed the pointing task including when the target jumped unexpectedly (i.e., comparable success rate). Most importantly, no significant difference was found in target jump trials regarding arm kinematics between both gravitational environments, neither in terms of peak velocity, relative deceleration duration, peak acceleration or time to peak acceleration. Using inverse dynamics based on experimental and anthropometrical data, we demonstrated that the shoulder torques for accelerating and decelerating the vertical arm movements substantially differed between microgravity and normogravity. Our data therefore highlight the capacity of the central nervous system to perform very fast neuromuscular adjustments that are adapted to the gravitational constraints. We discuss our findings by considering the contribution of feedforward and feedback mechanisms in the online control of arm pointing movements.

Acute Effect of Kinesiology Taping on Postural Stability in Individuals With Unilateral Chronic Ankle Instability.

BackgroundChronic ankle instability (CAI), which is characterized by deficient postural control, could be improved through kinesiology taping (KT). However, the effect of KT on postural control in CAI individuals is controversial. Therefore, this study aimed to investigate the acute effect of KT on postural control through computerized dynamic posturography (CDP) and self-perceived sensation in CAI individuals.MethodsParticipants with CAI received four different ankle treatments randomly, including KT, athletic taping (AT), sham taping (ST), and no taping (NT). A series of postural stability measurements was performed using CDP subsequently. The measurements included sensory organization test (SOT), unilateral stance (US), limit of stability (LOS), motor control test (MCT), and adaption test (ADT). In addition, self-perceived sensation was measured through visual analog scaling. Repeated measures analysis of variance was conducted to determine whether the difference among KT, AT, ST, and NT was significant; Bonferroni test was used for post hoc analysis.ResultsNo significant difference was observed for parameters in SOT, US, and LOS in four different taping treatments. In MCT, the amplitude scaling scores of KT were 35.87% significantly lower than that of NT [p < 0.001, 95% confidence interval (CI) = 0.548–1.795] in forward-small slip and 21.58% significantly lower than that of ST (p = 0.035, 95% CI = 0.089–3.683) in backward-large slip. In ADT, sway energy scores were 7.59% significantly greater in ST than in AT (p = 0.028, 95% CI = −8.343 to −0.320). For perceived stability, KT was significantly greater than ST (p < 0.001, 95% CI = 0.552–1.899) and NT (p < 0.001, 95% CI = 0.797–2.534), and AT was significantly greater than ST (p = 0.001, 95% CI = 0.423–2.246) and NT (p < 0.001, 95% CI = 0.696–2.852). For perceived comfort, KT was significantly greater than AT (p = 0.001, 95% CI = 0.666–3.196) and NT (p = 0.031, 95% CI = 0.074–2.332), and ST was significantly greater than AT (p = 0.007, 95% CI = 0.349–2.931).ConclusionKT and AT have limited effect to facilitate postural control for CAI individuals during SOT, US, and LOS. However, KT and AT could provide effective support to cope with sudden perturbation in MCT and ADT. Moreover, KT provided excellent perceived stability and comfort, whereas AT provided excellent perceived stability but least comfort.

Individual Variation in Glucocorticoid Plasticity: Considerations and Future Directions

The hypothalamic-pituitary-adrenal (HPA) axis regulates the secretion of glucocorticoids, hormones with diverse roles ranging from regulating daily metabolic demand to coping with sudden perturbations. As a result, glucocorticoids are thought to help vertebrates track their changing environments and coordinate plasticity in diverse phenotypes. While this endocrine system is highly plastic-where one individual can produce multiple phenotypes across varying environmental conditions-little is understood about the degree to which individuals, populations, or species differ in circulating glucocorticoid plasticity. Empirical research quantifying individual variation in glucocorticoid plasticity has increased in recent years, though the multiple complex roles of the HPA-axis make it challenging to generalize the extent to which individual variation in plasticity exists. I provide an overview of current findings on variation in glucocorticoids plasticity, and outline multiple types of glucocorticoid plasticity researchers should consider in future work to advance our understanding of the causes and consequences of individual variation in glucocorticoid plasticity.

Immediate effect of kinesiology tape on ankle stability

BackgroundLateral ankle sprain is one of the most common musculoskeletal injuries, particularly among the sporting population. Due to such prevalence, many interventions have been tried to prevent initial, or further,...

Sudden gait perturbations elicit sex-specific neuromuscular trunk responses in persons with low back pain

Persons with low back pain (LBP) exhibit delayed trunk muscle onset and increased co-contractions as a response to quasi-static and dynamic sudden trunk loading in comparison to back-healthy controls. Although LBP is more prevalent in females, sex-specific responses have not been well documented. Therefore, the purpose was to explore sex-specific neuromuscular differences, to gait perturbation, in LBP patients.Twenty-nine LBP patients (12m/17f;31 ± 10yrs; 174 ± 12 cm; 71 ± 16 kg) walked on a split-belt treadmill at 1 m/s, while 15 right-sided random perturbations (treadmill-belt decelerating, 40 m/s2, 50 ms duration; 200 ms after heel contact) were applied. Muscle activity was assessed using a 12-lead surface EMG (6 back/6 abdominal muscles; 4000 Hz). EMG-RMS [%] (0–200 ms after perturbation) was calculated and normalized to RMS of unperturbed gait for each muscle. Furthermore, muscle onsets (ms) were determined. Two-way ANOVA (factors: sex/muscle) was applied to account for sex differences in main outcomes.EMG-RMS (amplitudes; mean) ranged from 356% to 901% in males and 349% to 694% in females representing a significant interaction effect (sex * muscle: p = 0.017). Post-hoc analysis revealed significant differences for EMG-RMS analysis of rectus abdominis left (p = 0.043; f > m) as well as obliques externus right/left (p = 0.018/p = 0.005; f < m). In the time domain, females showed overall, shorter (mean: 90 ± 16 ms) response times compared to males (mean: 98 ± 22 ms, sex effect: p < 0.0001).In this LBP population, abdominal muscle activation discriminated females from males. Specifically, females had higher activity of the rectus abdominis muscles and lower activation of the externus oblique muscles. These different activation strategies might be relevant to the development of sex-specific intervention strategies.

Scattering of Attosecond Electromagnetic Field Pulses by Atomic and Molecular Anions Including the Magnetic Field Component

Scattering of an attosecond electromagnetic field pulse by atomic and molecular anions is considered in the sudden perturbation approximation. In the interaction with anions, the effect of the magnetic field of the incident pulse is considered. The inclusion of the magnetic component of the ultrashort pulse leads to new results in the scattering spectra for atomic and molecular anions. Analytic dependences of the partial spectrum on frequency are obtained. It is shown that during scattering, the second harmonic is generated, which makes it possible to determine the type of anions and the spatial orientation of molecular anions.

Operator-based nonlinear free vibration control of a flexible plate with sudden perturbations

In this paper, a new nonlinear vibration control scheme using piezoelectric actuator is proposed for a flexible plate with a free vibration and sudden perturbations. First, the effect of hysteresis nonlinearity from the piezoelectric actuator is considered by Prandtl-Ishlinskii (P-I) hysteresis model. Simultaneously, a dynamic model of the flexible plate with piezoelectric actuator is considered. Then, based on the dynamic model of the flexible plate, operator-based controllers are designed to guarantee the robust stability of the nonlinear control system. In addition, for ensuring the desired vibration control performance of the flexible plate with a free vibration and sudden perturbations, operator-based compensation method is given by the proposed design scheme. In the designed compensator, the desired compensation performances of tracking and of perturbations are obtained by increasing the number of designed n-times feedback loops. Finally, both of numerical simulation and experimental result are shown to verify the effectiveness of the proposed design scheme.

159 Reactive Balance Training for Preventing Falls in Older People

Abstract Appropriately timed and directed balance responses are crucial for avoiding a fall. These responses, including feet-in-place adjustments of the centre of mass, stepping and gait adaptations, may be initiated voluntarily to proactively avoid falling or induced reactively in response to sudden external perturbations to balance. Despite good evidence that poor reactive balance responses contribute to falls and injuries, traditional fall prevention interventions have ignored this skill. Reactive balance (or perturbation) training intervention methods are emerging and show promise for preventing falls in older people, some evidence suggesting a 50% reduction in falls. We recruited 44 older adults into a parallel, blinded randomized controlled trial, comparing 3 sessions of reactive balance training (exposure to trips and slips) to one session of sham training. The primary outcome was falls following laboratory-induced trips and slips (&amp;gt;30% body weight in harness). Relative to the control group, the intervention group experienced fewer total falls (rate ratio [RR]=0.40, 95% confidence interval [CI]=0.22-0.76), slip falls (RR=0.33, 95% CI=0.12-0.90) and trip falls (RR=0.49, 95% CI=0.21-1.12). These results will be discussed in the context of other current evidence for reactive balance training and suggestions made for how such interventions might influence the future of fall prevention.

The effect of various arm and walking conditions on postural dynamic stability when recovering from a trip perturbation

BackgroundAppropriately responding to unexpected perturbations, such as a trip, is critical to sustain balance and avoid falling during walking. Research questionHow do arm motion and walking asymmetry affect postural stability when recovering from a trip perturbation? MethodsFifteen healthy young individuals, who had no experience with treadmill induced perturbations, participated in this study. The Computer-Assisted Rehabilitation Environment system (CAREN-Extended) was used to simulate unexpected perturbations while walking symmetrically and asymmetrically with various arm swings (normal, bound, released). Whole-body angular momentum (WBAM), peak trunk angular velocities, Center of Mass (COM), step width and stance time were analyzed before and when recovering from trip perturbations. ResultsParticipants were able to recover their postural stability within three strides following the sudden anterior-posterior trip perturbation. The perturbation increased peak trunk angular velocity, the COM excursion and WBAM but did not affect stance time and step width. The arm conditions had significant effects on peak trunk angular velocity, WBAM and step width during pre-perturbation. Walking conditions had a significant effect on all variables during pre-perturbation; however, post-perturbation showed significant effects only for peak trunk angular velocity, WBAM, and COM. SignificanceUnexpected perturbation had effects on most of gait variables; nevertheless, participants fully recovered and adapted their gait pattern to sudden perturbations even without using their arms while walking symmetrically and asymmetrically. Arm movements could help young individuals recover after a perturbation but are not essential for perturbations of moderate magnitude. The effect of medial-lateral perturbations on gait still need to be investigated.

Trigeminocardiac reflex and anesthesia

Trigeminocardiac reflex (TCR) is a well-established brain stem reflex that manifests as sudden cardiac perturbations, including bradycardia, arterial hypotension, asystole, apnea, and gastric hypermobility by surgical stimulation. The intense episode of the TCR is life-threatening. It has been widely concerned by anesthesiologists because of the great amount of surgeries could be involved in TCR and the high incidence of TCR. This review summarized the definition, pathological mechanisms, classification, incidences and its correlation with anesthesia, prevention, treatment and prognosis of the TCR so as to provide a reference for anesthesiologists to recognize and manage the TCR in time during general anesthesia. Key words: Trigeminocardiac reflex; Anesthesia