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Step Length (step + length)
Selected AbstractsDynamic Balance and Stepping Versus Tai Chi Training to Improve Balance and Stepping in At-Risk Older AdultsJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 12 2006Joseph O. Nnodim MD OBJECTIVES: To compare the effect of two 10-week balance training programs, Combined Balance and Step Training (CBST) versus tai chi (TC), on balance and stepping measures. DESIGN: Prospective intervention trial. SETTING: Local senior centers and congregate housing facilities. PARTICIPANTS: Aged 65 and older with at least mild impairment in the ability to perform unipedal stance and tandem walk. INTERVENTION: Participants were allocated to TC (n= 107, mean age 78) or CBST, an intervention focused on improving dynamic balance and stepping (n=106, mean age 78). MEASUREMENTS: At baseline and 10 weeks, participants were tested in their static balance (Unipedal Stance and Tandem Stance (TS)), stepping (Maximum Step Length, Rapid Step Test), and Timed Up and Go (TUG). RESULTS: Performance improved more with CBST than TC, ranging from 5% to 10% for the stepping tests (Maximum Step Length and Rapid Step Test) and 9% for TUG. The improvement in TUG represented an improvement of more than 1 second. Greater improvements were also seen in static balance ability (in TS) with CBST than TC. CONCLUSION: Of the two training programs, in which variants of each program have been proven to reduce falls, CBST results in modest improvements in balance, stepping, and functional mobility versus TC over a 10-week period. Future research should include a prospective comparison of fall rates in response to these two balance training programs. [source] Stepwise fatigue crack propagation in poly(vinyl chloride)JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2004T. E. Berna-Lara The kinetics and mechanism of fatigue crack growth in poly(vinyl chloride) (PVC) compounds of different molecular weight were studied. The fatigue crack propagation rate of all the PVC compounds followed the Paris law: da/dt = Af ,K. Fatigue crack propagation rate, as reflected by the pre-factor Af in the Paris law, was highly dependent on molecular weight of the resin, strain rate, and temperature. A stepwise mechanism of fatigue crack propagation was observed in all the PVC compounds. Steps were formed by discontinuous growth of the crack through a single craze in the shape of a narrow strip. Step length and lifetime were used to characterize fatigue crack propagation. J. Vinyl Addit. Technol. 10:5,10, 2004. © 2004 Society of Plastics Engineers. [source] The influence of age on gait parameters during the transition from a wide to a narrow pathwayPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 2 2008Nataliya Shkuratova Abstract Background and Purpose.,The ability to negotiate pathways of different widths is a prerequisite of daily living. However, only a few studies have investigated changes in gait parameters in response to walking on narrow pathways. The aim of this study is to examine the influence of age on gait adjustments during the transition from a wide to a narrow pathway.,Method.,DESIGN: Two-group repeated measures design. SETTING: Gait Laboratory. PARTICIPANTS: Twenty healthy older participants (mean [M] = 74.3 years, Standard deviation [SD] = 7.2 years); 20 healthy young participants (M = 26.6 years, SD = 6.1 years).,Interventions.,Making the transition from walking on a wide pathway (68,cm) to walking on a narrow pathway (15,cm). MAIN OUTCOME MEASURES: Step length, step time, step width, double support time and base of support. Results.,Healthy older participants were able to make the transition from a wide to a narrow pathway successfully. There was only one significant interaction, between age and base of support (p < 0.003). Older adults decreased their base of support only when negotiating the transition step, while young participants started decreasing their base of support prior to the negotiation of transition step (p < 0.01). Conclusion.,Adjustments to the transition from a wide to a narrow pathway are largely unaffected by normal ageing. Difficulties in making the transition to a narrow pathway during walking should not be attributed to normal age-related changes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Gait characteristics of diabetic patients: a systematic reviewDIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 3 2008L. Allet Abstract Patients with diabetes are at higher risk of experiencing fall-related injuries when walking than healthy controls. The underlying mechanism responsible for this is not yet clear. Thus we intend to summarize diabetic patients' gait characteristics and emphasize those which could be the possible underlying mechanisms for increased fall risk. This systematic review aims, in particular, to: (1) evaluate the quality of existing studies which investigate the gait characteristics of diabetic patients, (2) highlight areas of agreement and contradiction in study results, (3) discuss and emphasize parameters associated with fall risk, and (4) propose new orientations and further domains for research needed for their fall risk prevention. We conducted an electronic search of Pedro, PubMed, Ovid and Cochrane. Two authors independently assessed all abstracts. Quality of the selected articles was scored, and the study results summarized and discussed. We considered 236 abstracts of which 28 entered our full text review. Agreement on data quality between two reviewers was high (kappa: 0.90). Authors investigating gait parameters in a diabetic population evaluated in particular parameters either associated with fall risk (speed, step length or step-time variability) or with ulcers (pressure). There is agreement that diabetic patients walk slower, with greater step variability, and present higher plantar pressure than healthy controls. We concluded that diabetic patients present gait abnormalities, some of which can lead to heightened fall risk. To understand its' underlying mechanisms, and to promote efficient prevention, further studies should analyse gait under ,real-life' conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by EinsteinHYDROLOGICAL PROCESSES, Issue 3 2001H. M. Habersack Abstract Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio-tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain-diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain-diameters and 6·1 m or 120 grain-diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. [source] Displacement-controlled method and its applications to material non-linearityINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2005H. Zheng Abstract For the analysis of non-linear problems, the displacement-controlled method (DCM) has a more extensive application scope and more powerful abilities than the load-controlled method (LCM). However, difficulties of the DCM's procedure not amenable to most finite element implementations of the conventional LCM have restricted its applications in geomechanics. By means of Sherman,Morrison's theorem, the solution of DCM is improved. The improved procedure is characterized by high efficiency, good numerical stability and a programme structure similar to LCM. Two aspects of applications of DCM are illustrated. The first application is to compute the response of a structure under a given load level like the conventional finite element analysis. The second application is to trace the equilibrium path of a structure under a given load distribution type. A simple but effective algorithm is presented for automatically adjusting the step length in tracing the equilibrium path. Examples illustrate that the proposed procedures are suited for modelling complicated non-linear problems in geomechanics. Copyright © 2005 John Wiley & Sons, Ltd. [source] Mechanisms and kinetics for preparing carbohydrazide by reacting dimethyl carbonate with hydrazine: A theoretical studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008Jianguo Zhang Abstract The mechanism and kinetic modeling for preparing carbohydrazide from dimethyl carbonate and hydrazine has been declared. The geometries of all the stationary points (reactants, intermediates, transition states, and products) are optimized by using the B3LYP method with the cc-pVDZ basis set, and the harmonic vibrational frequencies as well as infrared intensities are predicted with the same method. The minimum-energy paths are obtained by using the intrinsic reaction coordinate (IRC) theory at the B3LYP/cc-pVDZ level of theory with the step length 0.02 (amu)1/2·bohr. The rate constants are evaluated by using the TST, TST/Eckart, and RRKM (T)/Eckart methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Minimizing errors in identifying Lévy flight behaviour of organismsJOURNAL OF ANIMAL ECOLOGY, Issue 2 2007DAVID W. SIMS Summary 1Lévy flights are specialized random walks with fundamental properties such as superdiffusivity and scale invariance that have recently been applied in optimal foraging theory. Lévy flights have movement lengths chosen from a probability distribution with a power-law tail, which theoretically increases the chances of a forager encountering new prey patches and may represent an optimal solution for foraging across complex, natural habitats. 2An increasing number of studies are detecting Lévy behaviour in diverse organisms such as microbes, insects, birds, and mammals including humans. A principal method for detecting Lévy flight is whether the exponent (µ) of the power-law distribution of movement lengths falls within the range 1 < µ , 3. The exponent can be determined from the histogram of frequency vs. movement (step) lengths, but different plotting methods have been used to derive the Lévy exponent across different studies. 3Here we investigate using simulations how different plotting methods influence the µ-value and show that the power-law plotting method based on 2k (logarithmic) binning with normalization prior to log transformation of both axes yields low error (1·4%) in identifying Lévy flights. Furthermore, increasing sample size reduced variation about the recovered values of µ, for example by 83% as sample number increased from n = 50 up to 5000. 4Simple log transformation of the axes of the histogram of frequency vs. step length underestimated µ by c.40%, whereas two other methods, 2k (logarithmic) binning without normalization and calculation of a cumulative distribution function for the data, both estimate the regression slope as 1 , µ. Correction of the slope therefore yields an accurate Lévy exponent with estimation errors of 1·4 and 4·5%, respectively. 5Empirical reanalysis of data in published studies indicates that simple log transformation results in significant errors in estimating µ, which in turn affects reliability of the biological interpretation. The potential for detecting Lévy flight motion when it is not present is minimized by the approach described. We also show that using a large number of steps in movement analysis such as this will also increase the accuracy with which optimal Lévy flight behaviour can be detected. [source] Critical flux determination by flux-steppingAICHE JOURNAL, Issue 7 2010Søren Prip Beier Abstract In membrane filtration related scientific literature, often step-by-step determined critical fluxes are reported. Using a dynamic microfiltration device, it is shown that critical fluxes determined from two different flux-stepping methods are dependent upon operational parameters such as step length, step height, and flux start level. Filtrating 8 kg/m3 yeast cell suspensions by a vibrating 0.45 × 10,6 m pore size microfiltration hollow fiber module, critical fluxes from 5.6 × 10,6 to 1.2 × 10,5 m/s have been measured using various step lengths from 300 to 1200 seconds. Thus, such values are more or less useless in itself as critical flux predictors, and constant flux verification experiments have to be conducted to check if the determined critical fluxes can predict sustainable flux regimes. However, it is shown that using the step-by-step predicted critical fluxes as start guesses, in our case, in constant flux verification experiments for 5 and 1/2 hours, a sustainable flux was identifiable. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Scale sensitivity of synthetic long-term vegetation time series derived through overlay of short-term field recordsJOURNAL OF VEGETATION SCIENCE, Issue 4 2007Otto Wildi Abstract Questions: Is change in cover of dominant species driving the velocity of succession or is it species turnover (1)? Is the length of the time-step chosen in sampling affecting our recognition of the long-term rate of change (2)1 Location: 74 permanent plots located in the Swiss National Park, SE Switzerland, ca. 1900 m a.s.l. Methods: We superimpose several time-series from permanent plots to one single series solely based on compositional dissimilarity. As shown earlier (Wildi & Schütz 2000) this results in a synthetic series covering about 400 to 650 yr length. Continuous power transformation of cover-percentage scores is used to test if the dominance or the presence-absence of species is governing secondary succession from pasture to forest. The effect of time step length is tested by sub-samples of the time series. Results: Altering the weight of presence-absence versus dominance of species affects the emerging time frame, while altering time step length is uncritical. Where species turnover is fast, different performance scales yield similar results. When cover change in dominant species prevails, the solutions vary considerably. Ordinations reveal that the synthetic time series seek for shortest paths of the temporal pattern whereas in the real system longer lasting alternatives exist. Conclusions: Superimposing time series differs from the classical space-for-time substitution approach. It is a computation-based method to investigate temporal patterns of hundreds of years fitting between direct monitoring (usually limited to decades) and the analysis of proxy-data (for time spans of thousands of years and more). [source] Wearable Data Collection System for Online Gait Stability AnalysisNEUROMODULATION, Issue 3 2004Tomaz Karcnik DSc Abstract We had shown in our previous research that the stability assessment and control are essential for generation of faster and more energy efficient functional electrical stimulation (FES) and/or crutch-assisted gait. The objective of our recent research work has been to design a wearable and portable system for gait stability analysis with online capabilities that is also applicable to crutch-assisted gait modes. The developed wearable stability assessment system for as yet only biped gait consists of foot switches and goniometers attached to the leg joints. The instantaneous static and dynamic stability is, within the wearable system, assessed from the trajectory of the estimated body center of gravity (COGHAT) and the supporting area shape/size as derived from step length and foot-floor contact state. We used motion analysis system data as reference for testing the wearable system accuracy. The wearable system was tested on five healthy subjects and one above-knee amputee. It proved to be reasonably accurate if compared to the classical, motion analysis system based method. However, additional work is required to port the system to the FES assisted and/or crutch assisted gait. [source] Scale-dependence of movement rates in stream invertebratesOIKOS, Issue 1 2004Göran Englund We used analytical models and random walk simulations in a one-dimensional habitat to study the scale-dependence of migration rates in stream invertebrates. Our models predict that per capita migration rate is inversely proportional to patch length when patches are large compared to the scale of movements. When patches are small the scale-dependence is weaker and primarily determined by the length of individual movements (steps) relative to patch size. Laboratory experiments using isopods (Asellus aquaticus L.) and mayfly nymphs (Baetis sp.) confirmed that the strength of the scale-dependence decreased with increasing step length. For the case when step length distributions follow an exponential probability distribution, which is often the case for stream organisms, we provide a simple model that allows the scale-dependence to be predicted from the mean step length. We fitted this model to published field data on drift densities at different downstream distances from a net that blocks the drift from upstream areas. Agreement between model and data was excellent in most cases. We then used already published data on the length of induced drift movements to predict the scale-dependence that was observed in block experiments performed in the same system. Predicted and observed scale-dependence showed very close agreement. We conclude that our models and published data on drift distances can be used to calculate the expected scale-dependence of per capita emigration rates for a large number of taxa under a wide range of environmental conditions. [source] Mobility on discharge from an aged care unitPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 2 2007Edward Gorgon Abstract Background and Purpose.,Independent mobility is a crucial element of independent living and quality of life. However, little is known about the mobility of older people around the time of discharge from inpatient rehabilitation. The present study aimed to describe mobility on discharge from an aged care rehabilitation unit. Method.,The study utilized a descriptive, cross-sectional design. Ninety-five patients (mean age 81 (±8) years; 60% female) with diverse chronic conditions (median 5) who were able to walk at least 10,m without weight-bearing restrictions were recruited from the aged care rehabilitation wards. Scores on the Barthel Index were obtained on admission and discharge to provide information about their overall level of function. Within the last week of rehabilitation stay, scores on the mobility and locomotion subsections of the Functional Independence Measure, gait velocity, and time and distance parameters of gait were obtained. Gait variables were measured by use of the GAITRiteTM, an instrumented walkway. Medians and interquartile ranges (IQR) were reported for mobility variables. Results.,Following inpatient rehabilitation, many patients achieved independence in bed or chair transfers (83%), toilet transfers (81%), shower transfers (60%) and level-surface walking (74%). Only 31% achieved independence in stair climbing. Patients walked slowly at a median (IQR) gait velocity of 45.96 (31.51) cm/s and with markedly diminished cadence and step length. Subjects with a low number of chronic conditions generally performed better on mobility measures than those with a high number of chronic conditions. Conclusions.,Although many older people are able to transfer and walk independently around the time of discharge from inpatient rehabilitation their mobility is still often impaired. For example, only 9.5% achieved a walking velocity considered to be adequate for street crossing and few demonstrated the ability to negotiate stairs. This highlights the need for ongoing rehabilitation for many of these older people. The possible cumulative effects of chronic conditions on mobility require further investigation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by EinsteinHYDROLOGICAL PROCESSES, Issue 3 2001H. M. Habersack Abstract Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio-tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain-diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain-diameters and 6·1 m or 120 grain-diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. [source] Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on BorneoJOURNAL OF ANIMAL ECOLOGY, Issue 5 2006KONSTANS WELLS Summary 1Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13 525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features. [source] Critical flux determination by flux-steppingAICHE JOURNAL, Issue 7 2010Søren Prip Beier Abstract In membrane filtration related scientific literature, often step-by-step determined critical fluxes are reported. Using a dynamic microfiltration device, it is shown that critical fluxes determined from two different flux-stepping methods are dependent upon operational parameters such as step length, step height, and flux start level. Filtrating 8 kg/m3 yeast cell suspensions by a vibrating 0.45 × 10,6 m pore size microfiltration hollow fiber module, critical fluxes from 5.6 × 10,6 to 1.2 × 10,5 m/s have been measured using various step lengths from 300 to 1200 seconds. Thus, such values are more or less useless in itself as critical flux predictors, and constant flux verification experiments have to be conducted to check if the determined critical fluxes can predict sustainable flux regimes. However, it is shown that using the step-by-step predicted critical fluxes as start guesses, in our case, in constant flux verification experiments for 5 and 1/2 hours, a sustainable flux was identifiable. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Optimum step-stress for temperature accelerated life testingQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2007Evans Gouno Abstract Step-stress accelerated life testing is a design strategy where the stress is modified several times during the test. In this work we address the problem of designing such a test. We focus on temperature accelerated life testing and we address the problems of setting the step duration and the stress levels. Assuming an Arrhenius model, maximum likelihood estimates of the parameters are computed. Relying on the properties of these estimators we compare different criteria for assessing the optimality of the plans produced. Some tables are presented to illustrate the method. For a fixed number of steps and a set of temperatures, a table of optimal length steps can be computed. For fixed step lengths, sets of temperatures leading to optimal plans are also available. Thus, this work provides useful tools to help engineers make decisions in testing strategy. Copyright © 2007 John Wiley & Sons, Ltd. [source] Not so fast: Speed effects on forelimb kinematics in cercopithecine monkeys and implications for digitigrade postures in primatesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009Biren A. Patel Abstract Terrestrial mammals are characterized by their digitigrade limb postures, which are proposed to increase effective limb length (ELL) to achieve preferred or higher locomotor speeds more efficiently. Accordingly, digitigrade postures are associated with cursorial locomotion. Unlike most medium- to large-sized terrestrial mammals, terrestrial cercopithecine monkeys lack most cursorial adaptations, but still adopt digitigrade hand postures. This study investigates when and why terrestrial cercopithecine monkeys adopt digitigrade hand postures during quadrupedal locomotion. Three cercopithecine species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway at a range of speeds (0.4,3.4 m/s). Three-dimensional forelimb kinematic data were recorded during forelimb support. Hand posture was measured as the angle between the metacarpal segments and the ground (MGA). As predicted, a larger MGA was correlated with a longer ELL. At slower speeds, subjects used digitigrade postures (larger MGA), however, contrary to expectations, all subjects used more palmigrade hand postures (smaller MGA) at faster speeds. Digitigrade postures at slower speeds may lower cost of transport by increasing ELL and step lengths. At higher speeds, palmigrade postures may be better suited to spread out high ground reaction forces across a larger portion of the hand thereby potentially decreasing stresses in hand bones. It is concluded that a digitigrade forelimb posture in primates is not an adaptation for high speed locomotion. Accordingly, digitigrady may have evolved for different reasons in primates compared to other mammalian lineages. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] | |||||||||||||||||||