The ability to increase the base of support and recover stability is limited in its generalisation for different balance perturbation tasks

Abstract Background The assessment of stability recovery performance following perturbations contributes to the determination of fall resisting skills. This study investigated the association between stability recovery performances in two perturbation tasks (lean-and-release versus tripping). Methods Healthy adults (12 young: 24 ± 3 years; 21 middle-aged: 53 ± 5 years; 11 old: 72 ± 5 years) were suddenly released from a forward-inclined position attempting to recover stability with a single step. In a second task, all participants experienced a mechanically induced trip during treadmill walking. To assess dynamic stability performance, the antero-posterior margin of stability (MoS), the base of support (BoS), and the rate of increase in BoS were determined at each foot touchdown (TD) for both tasks. Results Only weak to moderate correlations in dynamic stability performance parameters were found between the two tasks (0.568 > r > 0.305, 0.001 < p < 0.04). A separation of participants according to the number of steps required to regain stability in the lean-and-release task revealed that multiple- (more than one step) compared to single-steppers showed a significantly lower MoS at TD (p = 0.003; g = 1.151), lower BoS at TD (p = 0.019; g = 0.888) and lower rate of increase in BoS until TD (p = 0.002; g = 1.212) after release. Despite these profound subgroup differences in the lean-and-release task, no differences between multiple- and single-steppers were observed in the stability recovery performance during tripping. Conclusion The results provide evidence that the ability to effectively control dynamic stability following a sudden balance disturbance in adults across a wide age range is limited in its generalisation for different perturbation tasks.

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Validating Determinants for an Alternate Foot Placement Selection Algorithm During Human Locomotion in Cluttered Terrain

Journal of Neurophysiology ◽

10.1152/jn.00044.2006 ◽

2007 ◽

Vol 98 (4) ◽

pp. 1928-1940 ◽

Cited By ~ 35

Author(s):

Renato Moraes ◽

Fran Allard ◽

Aftab E. Patla

Keyword(s):

Dynamic Stability ◽

Center Of Mass ◽

Frontal Plane ◽

Human Locomotion ◽

The Body ◽

Selection Algorithm ◽

Foot Placement ◽

Double Support ◽

One Step ◽

Base Of Support

The goal of this study was to validate dynamic stability and forward progression determinants for the alternate foot placement selection algorithm. Participants were asked to walk on level ground and avoid stepping, when present, on a virtual white planar obstacle. They had a one-step duration to select an alternate foot placement, with the task performed under two conditions: free (participants chose the alternate foot placement that was appropriate) and forced (a green arrow projected over the white planar obstacle cued the alternate foot placement). To validate the dynamic stability determinant, the distance between the extrapolated center of mass (COM) position, which incorporates the dynamics of the body, and the limits of the base of support was calculated in both anteroposterior (AP) and mediolateral (ML) directions in the double support phase. To address the second determinant, COM deviation from straight ahead was measured between adaptive and subsequent steps. The results of this study showed that long and lateral choices were dominant in the free condition, and these adjustments did not compromise stability in both adaptive and subsequent steps compared with the short and medial adjustments, which were infrequent and adversely affected stability. Therefore stability is critical when selecting an alternate foot placement in a cluttered terrain. In addition, changes in the plane of progression resulted in small deviations of COM from the endpoint goal. Forward progression of COM was maintained even for foot placement changes in the frontal plane, validating this determinant as part of the selection algorithm.

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Dynamic and static stability in hexapedal runners.

Journal of Experimental Biology ◽

10.1242/jeb.197.1.251 ◽

1994 ◽

Vol 197 (1) ◽

pp. 251-269 ◽

Cited By ~ 3

Author(s):

L H Ting ◽

R Blickhan ◽

R J Full

Keyword(s):

Dynamic Stability ◽

Center Of Pressure ◽

Center Of Mass ◽

Stability Margin ◽

Static Stability ◽

Double Support ◽

Wide Range ◽

One Step ◽

Energy And Momentum ◽

Base Of Support

Stability is fundamental to the performance of terrestrial locomotion. Running cockroaches met the criteria for static stability over a wide range of speeds, yet several locomotor variables changed in a way that revealed an increase in the importance of dynamic stability as speed increased. Duty factors (the fraction of time that a leg spends on the ground relative to the stride period) decreased to 0.5 and below with an increase in speed. The duration of double support (i.e. when both tripods, or all six legs, were on the ground) decreased significantly with an increase in speed. All legs had similar touch-down phases in the tripod, but the shortest leg, the front one, lifted off before the middle and the rear leg, so that only two legs of the tripod were in contact with the ground at the highest speeds. Per cent stability margin (the shortest distance from the center of gravity to the boundaries of support, normalized to the maximum possible stability margin) decreased with increasing speed from 60% at 10 cms-1 to values less than zero at speeds faster than 50 cms-1, indicating instances of static instability at fast speeds. The center of mass moved rearward or posteriorly with respect to the base of support as speed increased. Moments about the center of mass, as shown by the center of pressure (the equivalent of a single 'effective' leg), were variable, but were balanced by opposing moments over a stride. Thus, hexapods can exploit the advantages of both static and dynamic stability. Static or quasi-static assumptions alone were insufficient to explain straight-ahead, constant-speed locomotion and may hinder discovery of behaviors that are dynamic, where kinetic energy and momentum can act as a bridge from one step to the next.

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Influence of high temperature on the stability performance of high density polyethylene and crumb rubber powder modified HMA mixture

Journal of Structural Fire Engineering ◽

10.1108/jsfe-12-2016-0021 ◽

2018 ◽

Vol 9 (1) ◽

pp. 19-27

Author(s):

Hussein Adam Abdalla Gibreil ◽

Cheng Pei Feng

Keyword(s):

High Temperature ◽

Dynamic Stability ◽

High Density Polyethylene ◽

Asphalt Pavement ◽

Crumb Rubber ◽

Water Stability ◽

Content Type ◽

Stability Performance ◽

The Stability ◽

Marshall Stability

Purpose In high-temperature regions (tropical regions) temperatures rises in summer, which affects the performance of asphalt pavement. Therefore, we must consider the conditions of asphalt pavement, especially in these regions. This study aims to investigate the influence of high temperature on the stability performance of high-density polyethylene (HDPE) and crumb rubber powder (CRP) modified hot mix asphalt (HMA) using Marshall design parameters and rutting test. Design/methodology/approach In this study, three HMA mixtures with 4 per cent HDPE and 15 per cent CRP, 5 per cent HDPE and 10 per cent CRP, and 6 per cent HDPE and 5 per cent CRP concentrations were used for the Marshall stability test and dynamic stability (rutting test) at 60-75°C, and water stability test at 60°C. Findings The results showed that when test temperature was increased from 60°C to 75°C, the Marshall stability and dynamic stability of three HDPE- and CRP-modified HMA mixtures decreased, and these three HDPE- and CRP-modified HMA mixtures have a good moisture damage resistance. Of the three HMA mixtures with different HDPE and CRP concentrations, HMA mixtures with 5 per cent HDPE and 10 per cent CRP concentration exhibit optimal Marshall stability, dynamic stability and water stability. Originality/value This study showed the effects of high-temperatures changes on the stability performance of HDPE- and CRP-modified HMA mixtures.

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One-Step Production of Immobilized α-Amylase in Recombinant Escherichia coli

Applied and Environmental Microbiology ◽

10.1128/aem.02782-08 ◽

2009 ◽

Vol 75 (7) ◽

pp. 2012-2016 ◽

Cited By ~ 37

Author(s):

Indira A. Rasiah ◽

Bernd H. A. Rehm

Keyword(s):

Escherichia Coli ◽

Structural Integrity ◽

Amylase Activity ◽

Signal Sequence ◽

Cost Effective ◽

Single Step ◽

Enzyme Analysis ◽

Fusion Partner ◽

One Step ◽

The Stability

ABSTRACT Industrial enzymes are often immobilized via chemical cross-linking onto solid supports to enhance stability and facilitate repeated use in bioreactors. For starch-degrading enzymes, immobilization usually places constraints on enzymatic conversion due to the limited diffusion of the macromolecular substrate through available supports. This study describes the one-step immobilization of a highly thermostable α-amylase (BLA) from Bacillus licheniformis and its functional display on the surface of polyester beads inside engineered Escherichia coli. An optimized BLA variant (Termamyl) was N-terminally fused to the polyester granule-forming enzyme PhaC of Cupriavidus necator. The fusion protein lacking the signal sequence mediated formation of stable polyester beads exhibiting α-amylase activity. The α-amylase beads were assessed with respect to α-amylase activity, which was demonstrated qualitatively and quantitatively. The immobilized α-amylase showed Michaelis-Menten enzyme kinetics exerting a V max of about 506 mU/mg of bead protein with a Km of about 5 μM, consistent with that of free α-amylase. The stability of the enzyme at 85°C and the capacity for repeated usage in a starch liquefaction process were also demonstrated. In addition, structural integrity and functionality of the beads at extremes of pH and temperature, demonstrating their suitability for industrial use, were confirmed by electron microscopy and protein/enzyme analysis. This study proposes a novel, cost-effective method for the production of immobilized α-amylase in a single step by using the polyester granules forming protein PhaC as a fusion partner in engineered E. coli.

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Synthesis of Polycycles and Oxacycles by Tandem Metathesis of endo–norbornene Derivatives

Synthesis ◽

10.1055/a-1348-4242 ◽

2021 ◽

Author(s):

Sambasivarao Kotha ◽

Sunil Pulletikurti ◽

Ambareen Fatma ◽

gopal dhangar ◽

gonna somu Naidu

Keyword(s):

Natural Products ◽

Metal Complex ◽

Carbonyl Group ◽

Single Step ◽

Time Dependent ◽

Computational Studies ◽

Nmr Studies ◽

Tricyclic Compounds ◽

One Step ◽

Norbornene Derivatives

Here, we have demonstrated that the presence of a carbonyl group at C7 position is preventing the olefin metathesis of endo-norbornene derivatives due to the complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas, computational studies provided that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. Later, these endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of the natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.

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Single Step 2-Port Device De-Embedding Algorithm for Fixture-DUT-Fixture Network Assembly

Electronics ◽

10.3390/electronics10111275 ◽

2021 ◽

Vol 10 (11) ◽

pp. 1275

Author(s):

Simone Scafati ◽

Enza Pellegrino ◽

Francesco de Paulis ◽

Carlo Olivieri ◽

James Drewniak ◽

...

Keyword(s):

Standard Technique ◽

Single Step ◽

Scattering Parameters ◽

Linear Set ◽

S Parameter ◽

Parameter Conversion ◽

Before And After ◽

One Step ◽

Typical Measurement

The de-embedding of measurement fixtures is relevant for an accurate experimental characterization of radio frequency and digital electronic devices. The standard technique consists in removing the effects of the measurement fixtures by the calculation of the transfer scattering parameters (T-parameters) from the available measured (or simulated) global scattering parameters (S-parameters). The standard de-embedding is achieved by a multiple steps process, involving the S-to-T and subsequent T-to-S parameter conversion. In a typical measurement setup, two fixtures are usually placed before and after the device under test (DUT) allowing the connection of the device to the calibrated vector network analyzer coaxial ports. An alternative method is proposed in this paper: it is based on the newly developed multi-network cascading algorithm. The matrices involved in the fixture-DUT-fixture cascading gives rise to a non-linear set of equations that is in one step analytically solved in closed form, obtaining a unique solution. The method is shown to be effective and at least as accurate as the standard multi-step de-embedding one.

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Dynamic Stability Performance of Autonomous Microgrid Involving High Penetration Level of Constant Power Loads

Mathematics ◽

10.3390/math9090922 ◽

2021 ◽

Vol 9 (9) ◽

pp. 922

Author(s):

Mohamed Hassan ◽

Muhammed Worku ◽

Abdelfattah Eladl ◽

Mohammed Abido

Keyword(s):

Dynamic Stability ◽

Power Sharing ◽

Constant Power ◽

Similar Frequency ◽

Stability Performance ◽

High Penetration ◽

Constant Power Loads ◽

The Time Domain ◽

And Control ◽

The Impact

Nowadays, behaving as constant power loads (CPLs), rectifiers and voltage regulators are extensively used in microgrids (MGs). The MG dynamic behavior challenges both stability and control effectiveness in the presence of CPLs. CPLs characteristics such as negative incremental resistance, synchronization, and control loop dynamic with similar frequency range of the inverter disturb severely the MG stability. Additionally, the MG stability problem will be more sophisticated with a high penetration level of CPLs in MGs. The stability analysis becomes more essential especially with high-penetrated CPLs. In this paper, the dynamic stability performance of an MG involving a high penetration level of CPLs is analyzed and investigated. An autonomous MG engaging a number of CPLs and inverter distributed generations (DGs) is modeled and designed using MATLAB. Voltage, current, and power controllers are optimally designed, controlling the inverter DGs output. A power droop controller is implemented to share the output DGs powers. Meanwhile, the current and voltage controllers are employed to control the output voltage and current of all DGs. A phase-locked loop (PLL) is essentially utilized to synchronize the CPLs with the MG. The controller gains of the inverters, CPLs, power sharing control, and PLL are optimally devised using particle swarm optimization (PSO). As a weighted objective function, the error in the DC voltage of the CPL and active power of the DG is minimized in the optimal problem based on the time-domain simulation. Under the presence of high penetrated CPLs, all controllers are coordinately tuned to ensure an enhanced dynamic stability of the MG. The impact of the highly penetrated CPLs on the MG dynamic stability is investigated. To confirm the effectiveness of the proposed technique, different disturbances are applied. The analysis shows that the MG system experiences the instability challenges due to the high penetrated CPLs. The simulation results confirm the effectiveness of the proposed method to improve the MG dynamic stability performance.

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Computational and experimental investigations of one-step conversion of poly(carbonate)s into value-added poly(aryl ether sulfone)s

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1600924113 ◽

2016 ◽

Vol 113 (28) ◽

pp. 7722-7726 ◽

Cited By ~ 29

Author(s):

Gavin O. Jones ◽

Alexander Yuen ◽

Rudy J. Wojtecki ◽

James L. Hedrick ◽

Jeannette M. García

Keyword(s):

High Performance ◽

Density Functional ◽

Value Added ◽

Single Step ◽

Nucleophilic Attack ◽

Experimental Investigations ◽

Aryl Ether ◽

One Step ◽

Poly Carbonate

It is estimated that ∼2.7 million tons poly(carbonate)s (PCs) are produced annually worldwide. In 2008, retailers pulled products from store shelves after reports of bisphenol A (BPA) leaching from baby bottles, reusable drink bottles, and other retail products. Since PCs are not typically recycled, a need for the repurposing of the PC waste has arisen. We report the one-step synthesis of poly(aryl ether sulfone)s (PSUs) from the depolymerization of PCs and in situ polycondensation with bis(aryl fluorides) in the presence of carbonate salts. PSUs are high-performance engineering thermoplastics that are commonly used for reverse osmosis and water purification membranes, medical equipment, as well as high temperature applications. PSUs generated through this cascade approach were isolated in high purity and yield with the expected thermal properties and represent a procedure for direct conversion of one class of polymer to another in a single step. Computational investigations performed with density functional theory predict that the carbonate salt plays two important catalytic roles in this reaction: it decomposes the PCs by nucleophilic attack, and in the subsequent polyether formation process, it promotes the reaction of phenolate dimers formed in situ with the aryl fluorides present. We envision repurposing poly(BPA carbonate) for the production of value-added polymers.

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To What Extent Does Not Wearing Shoes Affect the Local Dynamic Stability of Walking?: Effect Size and Intrasession Repeatability

Journal of Applied Biomechanics ◽

10.1123/jab.2013-0142 ◽

2014 ◽

Vol 30 (2) ◽

pp. 305-309 ◽

Cited By ~ 16

Author(s):

Philippe Terrier ◽

Fabienne Reynard

Keyword(s):

Dynamic Stability ◽

Effect Size ◽

Intraclass Correlation ◽

Clinical Findings ◽

Local Dynamic ◽

Gait Stability ◽

Local Dynamic Stability ◽

Gait Parameters ◽

Absolute Agreement ◽

The Stability

Local dynamic stability (stability) quantifies how a system responds to small perturbations. Several experimental and clinical findings have highlighted the association between gait stability and fall risk. Walking without shoes is known to slightly modify gait parameters. Barefoot walking may cause unusual sensory feedback to individuals accustomed to shod walking, and this may affect stability. The objective was therefore to compare the stability of shod and barefoot walking in healthy individuals and to analyze the intrasession repeatability. Forty participants traversed a 70 m indoor corridor wearing normal shoes in one trial and walking barefoot in a second trial. Trunk accelerations were recorded with a 3D-accelerometer attached to the lower back. The stability was computed using the finite-time maximal Lyapunov exponent method. Absolute agreement between the forward and backward paths was estimated with the intraclass correlation coefficient (ICC). Barefoot walking did not significantly modify the stability as compared with shod walking (average standardized effect size: +0.11). The intrasession repeatability was high (ICC: 0.73–0.81) and slightly higher in barefoot walking condition (ICC: 0.81–0.87). Therefore, it seems that barefoot walking can be used to evaluate stability without introducing a bias as compared with shod walking, and with a sufficient reliability.

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Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.95 ◽

2014 ◽

Vol 745 ◽

pp. 647-681 ◽

Cited By ~ 5

Author(s):

Yee Chee See ◽

Matthias Ihme

Keyword(s):

Transport Properties ◽

Diffusion Flames ◽

Diffusive Transport ◽

Mean Flow ◽

Stability Behaviour ◽

Jet Diffusion Flames ◽

One Step ◽

The Mean ◽

Modelling Assumptions ◽

The Stability

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

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