The Experts below are selected from a list of 33516 Experts worldwide ranked by ideXlab platform
L.h.v. Van Der Woude - One of the best experts on this subject based on the ideXlab platform.
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The role of Tread fixations in the visual control of stair walking
Gait & posture, 2011Co-Authors: A.r. Den Otter, Mark Hoogwerf, L.h.v. Van Der WoudeAbstract:Abstract Although it is likely that foveal information on Treads provides important sensory cues for stair walking, it is unclear how gaze stabilization on Treads contribute to gait control on stairs. The aim of this study was to determine the extent to which (i) stair walking depends on foveal information on stepped Treads, (ii) fixated Treads correspond to future foot landing locations, and (iii) the distance looked ahead varies with stepping distance. Gaze and foot position was monitored from six healthy young adults when they ascended and descended a 10 Tread long staircase, taking the stairs one or two Treads at a time. The results showed that 55–68% of the total fixation time was aimed at Treads, and that Tread edges were fixated more intensively during stair descent (69% of the total time spent fixating Treads) than during stair ascent (48%). A substantial 28–34% of the stepped Treads was never fixated and, when the staircase was taken two Treads a time, approximately 35% of the fixated Treads was never stepped on. Subjects fixated 3.5–4.5 Treads ahead in both stepping conditions, but when the staircase was taken 2 Treads a time, stepped Treads were fixated shorter ahead (2.7–2.9 Treads) than Treads that were not stepped (3.4–4.1 Treads). These results provide new insights into the visual control of stair walking, and suggest that the stabilization of gaze on Treads is not used solely to guide foot placement, but may serve other purposes as well, e.g., to facilitate postural control on the staircase.
Julie A Chilton - One of the best experts on this subject based on the ideXlab platform.
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Tread Softly.
Journal of the American Academy of Child and Adolescent Psychiatry, 2018Co-Authors: Julie A ChiltonAbstract:Had I the heaven's embroidered cloths, Enwrought with golden and silver light, The blue and the dim and the dark cloths Of night and light and the half-light; I would spread the cloths under your feet: But I, being poor, have only my dreams; I have spread my dreams under your feet; Tread softly because you Tread on my dreams. -W.B. Yeats In Caroline Elton's Also Human: The Inner Lives of Doctors, she references The Cloths of Heaven to evidence her awareness of the responsibility she carries when lecturing hopeful future doctors on the tougher side of medicine. As an occupational psychologist whose specialty is physicians and trainees with career difficulties, she knows the wisdom she shares can be deflating. Elton recounts trying to heed the last line of Yeats' poem- "Tread softly because you Tread on my dreams"-before speaking to medical school applicants at a talk organized by the British Medical Journal.
A.r. Den Otter - One of the best experts on this subject based on the ideXlab platform.
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The role of Tread fixations in the visual control of stair walking
Gait & posture, 2011Co-Authors: A.r. Den Otter, Mark Hoogwerf, L.h.v. Van Der WoudeAbstract:Abstract Although it is likely that foveal information on Treads provides important sensory cues for stair walking, it is unclear how gaze stabilization on Treads contribute to gait control on stairs. The aim of this study was to determine the extent to which (i) stair walking depends on foveal information on stepped Treads, (ii) fixated Treads correspond to future foot landing locations, and (iii) the distance looked ahead varies with stepping distance. Gaze and foot position was monitored from six healthy young adults when they ascended and descended a 10 Tread long staircase, taking the stairs one or two Treads at a time. The results showed that 55–68% of the total fixation time was aimed at Treads, and that Tread edges were fixated more intensively during stair descent (69% of the total time spent fixating Treads) than during stair ascent (48%). A substantial 28–34% of the stepped Treads was never fixated and, when the staircase was taken two Treads a time, approximately 35% of the fixated Treads was never stepped on. Subjects fixated 3.5–4.5 Treads ahead in both stepping conditions, but when the staircase was taken 2 Treads a time, stepped Treads were fixated shorter ahead (2.7–2.9 Treads) than Treads that were not stepped (3.4–4.1 Treads). These results provide new insights into the visual control of stair walking, and suggest that the stabilization of gaze on Treads is not used solely to guide foot placement, but may serve other purposes as well, e.g., to facilitate postural control on the staircase.
Mark Hoogwerf - One of the best experts on this subject based on the ideXlab platform.
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The role of Tread fixations in the visual control of stair walking
Gait & posture, 2011Co-Authors: A.r. Den Otter, Mark Hoogwerf, L.h.v. Van Der WoudeAbstract:Abstract Although it is likely that foveal information on Treads provides important sensory cues for stair walking, it is unclear how gaze stabilization on Treads contribute to gait control on stairs. The aim of this study was to determine the extent to which (i) stair walking depends on foveal information on stepped Treads, (ii) fixated Treads correspond to future foot landing locations, and (iii) the distance looked ahead varies with stepping distance. Gaze and foot position was monitored from six healthy young adults when they ascended and descended a 10 Tread long staircase, taking the stairs one or two Treads at a time. The results showed that 55–68% of the total fixation time was aimed at Treads, and that Tread edges were fixated more intensively during stair descent (69% of the total time spent fixating Treads) than during stair ascent (48%). A substantial 28–34% of the stepped Treads was never fixated and, when the staircase was taken two Treads a time, approximately 35% of the fixated Treads was never stepped on. Subjects fixated 3.5–4.5 Treads ahead in both stepping conditions, but when the staircase was taken 2 Treads a time, stepped Treads were fixated shorter ahead (2.7–2.9 Treads) than Treads that were not stepped (3.4–4.1 Treads). These results provide new insights into the visual control of stair walking, and suggest that the stabilization of gaze on Treads is not used solely to guide foot placement, but may serve other purposes as well, e.g., to facilitate postural control on the staircase.
Tore V Vernersson - One of the best experts on this subject based on the ideXlab platform.
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Thermal impact on rolling contact fatigue and capacity of railway wheels
2017Co-Authors: Mandeep Singh Walia, Tore V Vernersson, Ali Esmaeili, Kazuyuki Handa, Roger LundénAbstract:Tread braked railway wheels are subjected to complex loading due to combined rolling contact stresses and thermally induced stresses. The main objective of the present study is to find the limits for Tread braking with respect to temperature impact on rolling contact fatigue (RCF) of the wheel Tread. A wheel with an S-shaped web is studied for some different stop braking loads. Using 3D FE simulations, the effects of simultaneous thermal loading from braking and mechanical loading, with traversing wheel-rail rolling contact, are studied. In order to account for the elevated temperatures, the simulations utilise a temperature-dependent elastoplastic material model. The mechanical loads account for frictional rolling contact stress distributions induced by braking, using a novel method that is based on elastoplastic contact simulations. Partial slip is considered and interfacial shear stresses are introduced in the wheel-rail contact area. Evolution of damage in the vicinity of the wheel Tread is studied for various brake loading cases. In order to assess limits for the Tread braking, the calculated damage is compared to previously developed critical damage levels which were based on full-scale brake rig testing. Results are presented for a parametric study with thermomechanical loading based on different load cases. The influence from operational parameters such as axle loads, initial speeds, decelerations and block material is studied. The results show that the temperature has a strong influence on the rolling contact fatigue of the wheel Treads and, hence, also on the thermal capacity of the wheels. The study gives preliminary limits for revenue traffic, described as combinations of Tread temperatures and wheel-rail rolling contact loading, which should be respected to avoid thermal cracking of the wheel Treads.
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wheel Tread damage a numerical study of railway wheel Tread plasticity under thermomechanical loading
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2010Co-Authors: Tore V Vernersson, Håkan Hansson, Sara Caprioli, Elena Kabo, Anders EkbergAbstract:A numerical study is presented where the impact of simultaneous thermal and mechanical loading on a railway wheel Tread, as imposed by braking and rolling contact, is reported. A comparison is made of two-dimensional (2D) and 3D finite-element simulations of the thermomechanical problem featuring a material model that accounts for thermal expansion and plastic deformations. It is found that 2D simulations give unrealistic predictions of plastic deformations. The 3D simulations demonstrate a significant influence of the thermal loading also in cases of rather moderate temperature increases. In particular, the combination of thermal loading and high traction is found to be very detrimental.
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Tread Braking of Railway Wheels - Noise-related Tread Roughness and Dimensioning Wheel Temperatures
2006Co-Authors: Tore V VernerssonAbstract:Block braking is a commonly used braking system for freight wagons and other types of railway vehicles. One or several brake blocks are pressed against the Tread (running surface) of the wheel, which is also in rolling contact with the rail. The kinetic energy of the running train is then transformed into heat, which is partitioned between block(s) and wheel and is conducted from block to block holder and from wheel to rail and also dissipated into the surroundings by convection and radiation. During the last decade, one aspect of block braking has become an environmental issue: the high rolling noise levels generated by trains with block braked wheels. A roughness (corrugation, waviness) develops on the wheel Tread during the sliding contact between block and wheel, and this Tread roughness (out-of-roundness) induces vibrations and noise when the train rolls. The roughness level strongly depends on the properties of the brake block material. Here cast iron blocks generate higher roughness levels than do composite and sinter blocks. In Europe, cast iron is presently the most commonly used brake block material on freight wagons, but composite and sinter materials are now gradually being introduced. In the first part of the present thesis, the thermomechanical interaction between brake block and wheel Tread is studied to search for the mechanisms behind the growth of wheel roughness. The evolution of hot spots, i e areas on the wheel Tread with significantly higher temperature than the rest of the Tread, is believed to be a key phenomenon that can explain the differences between the different block materials. Results from full-scale Tread braking experiments with forged wheels in an inertia dynamometer are reported. A numerical model for studying the thermoelastic contact between brake block and wheel Tread demonstrates the principal phenomena. Also, results from field measurements of wheel roughness are presented. The tendency of cast iron brake blocks to generate high roughness levels on wheel Treads has propelled a general shift away from cast iron to other materials which do not give disturbing roughness levels. However, this change of block material will affect the heat partitioning between wheel and block. Excessive heating of the wheel may cause damage and may result in problems with axial deflection of the wheel rim (change of wheelset gauge). High tensile stresses in the wheel rim after its cooling down can lead to initiation and growth of transverse cracks in the wheel rim. In the second part of the present thesis, a thermal model of railway Tread braking is developed for use in routine calculations of wheel and block temperatures, including the cooling influence from the rail. Brake rig tests have been performed for drag braking at constant brake power for blocks made of cast iron and sinter and composite materials. Results on the influence of block configuration, brake power and brake speed on wheel and block temperatures are reported. Rolling contact heat transfer from wheel to rail is studied in the brake rig using a so-called rail-wheel in contact with the braked wheel, along with results from field tests. The model has been calibrated by using data from the experiments and can be employed to calculate temperatures and the heat partitioning between block, wheel and rail. The rail chill is found to have a considerable influence on the wheel temperature for long brake cycles. The present model can be used to efficiently design Tread braking systems for both freight and passenger trains. It can handle stop braking, drag braking at constant brake power, and also intermediate periods of cooling. The temperature history during a full train route can thus be calculated.
