Step Motion Research Articles

Timing and correction of stepping movements with a virtual reality avatar.

Research into the ability to coordinate one’s movements with external cues has focussed on the use of simple rhythmic, auditory and visual stimuli, or interpersonal coordination with another person. Coordinating movements with a virtual avatar has not been explored, in the context of responses to temporal cues. To determine whether cueing of movements using a virtual avatar is effective, people’s ability to accurately coordinate with the stimuli needs to be investigated. Here we focus on temporal cues, as we know from timing studies that visual cues can be difficult to follow in the timing context. Real stepping movements were mapped onto an avatar using motion capture data. Healthy participants were then motion captured whilst stepping in time with the avatar’s movements, as viewed through a virtual reality headset. The timing of one of the avatar step cycles was accelerated or decelerated by 15% to create a temporal perturbation, for which participants would need to correct to, in order to remain in time. Step onset times of participants relative to the corresponding step-onsets of the avatar were used to measure the timing errors (asynchronies) between them. Participants completed either a visual-only condition, or auditory-visual with footstep sounds included, at two stepping tempo conditions (Fast: 400ms interval, Slow: 800ms interval). Participants’ asynchronies exhibited slow drift in the Visual-Only condition, but became stable in the Auditory-Visual condition. Moreover, we observed a clear corrective response to the phase perturbation in both the fast and slow tempo auditory-visual conditions. We conclude that an avatar’s movements can be used to influence a person’s own motion, but should include relevant auditory cues congruent with the movement to ensure a suitable level of entrainment is achieved. This approach has applications in physiotherapy, where virtual avatars present an opportunity to provide the guidance to assist patients in adhering to prescribed exercises.

A Landscape-Based View on the Stepping Movement of Myosin VI

Myosin VI walks towards the minus end of the actin filament with a large and variable step size of about 25-36 nm, which cannot be fully accounted for with the lever-arm-like conformational changes within the two heads. So far, two competing models have been put forward to explain this large step size. Spudich's model (Spink et al., Nat. Struct. Mol. Biol. 15, 591 (2008)) assumes that two myosin VI monomers associate at distal tail, forming a myosin dimer, which makes two full-length Single Alpha Helix (SAH) domains serve as long legs in the dimer. In contrast, the Houdusse-Sweeney model (Mukherjea et al., Mol. Cell 35, 305 (2009)) assumes that the association occurs in the middle of the SAH domain and that the three-helix bundle unfolds to ensure the large step size. Each of these models has experimental grounds, but their consistency with the large and variable step size has not been examined quantitatively. Using a same computational method as we have used for myosin II (Nie et al., PLoS Comput. Biol. 10, e1003552 (2014)), we have theoretically characterized the free energy landscape experienced by the leading head to compare the two proposed models of myosin VI. Our results showed that the leading head is pulled toward the minus end of the actin filament according to the energy bias in the actin-myosin interactions, leading to the variable step size of movement in both two models. However, the large stepping size is realized only in the Spudich model, because in the Houdusse-Sweeney model, unfolding of the three-helix bundle gives rise to the entropic force to shorten the distance between two heads. The stiffness of the SAH domain is a key factor for giving strong free energy bias toward longer stepping distance.

On some peculiarities of the contemporary world system

In the article a number of the peculiarities of the contemporary world system are analyzed. The main context of the development of this system is step by step movement towards multipolar one. The author proves inability of the USA to establish unipolar world order, studies the certain rising structures in the world financial system, polemizes with an authoritative Russian expert of the prowestern thinking orientation, who denies movement towards multipolar world structure on the basis of his theoretical judgments. The last 2019 summits of the BRICS’ community and NATO alliance are also compared, while the Western military block is in certain disarray. The US renunciation of the 1987 Intermediate-Range Nuclear Forces Treaty (IRNFT) and Washington’s refusal to prolong the START III are estimated as new steps to degrade global arms control regime. At the same time BRICS is converting more and more into a stabilizing force of the modern world.

In Situ Variable-Temperature Scanning Tunneling Microscopy Studies of Graphene Growth Using Benzene on Pd(111).

Using a combination of in situ ultrahigh-vacuum variable-temperature scanning tunneling microscopy, ex situ Raman spectroscopy, and scanning electron microscopy, we investigated the growth of graphene using benzene on Pd(111) at temperatures up to 1100 K. Benzene adsorbs readily on Pd(111) at room temperature and forms an ordered superstructure upon annealing at 473 K. Exposure to benzene at 673 K enhances Pd step motion and yields primarily amorphous carbon upon cooling to room temperature. Monolayer graphene domains, 10-30 nm in size, appear during annealing this sample at 873 K. Dosing benzene at 1100 K results in graphene domains with varying degrees of crystallinity, while post-deposition annealing at 1100 K for 1200 s yields monolayer graphene domains larger than 150 × 150 nm2. Our results, which indicate that graphene growth on Pd(111) using benzene requires deposition/annealing temperatures higher than 673 K, are in striking contrast with the reported growth of graphene using benzene at temperatures as low as 373 K on relatively inert Cu surfaces.

Novel sweep-type triboelectric nanogenerator utilizing single freewheel for random triggering motion energy harvesting and driver habits monitoring

Traffic safety has always been a social concern, and driver habits directly affect traffic safety. Therefore it is significant to monitor driver habits. The pedal is the core operating device in the process of driving, so increasingly importance has been attached to the step movement of driver. The triboelectric nanogenerators (TENGs) performs well in harvesting the energy of random triggering motion and reflecting the characteristics of random triggering motion. This reports a novel sweep-type triboelectric nanogenerator (ST-TENG), which consists of a push rod, shells, two flywheels and a single freewheel. ST-TENG can harvest the energy of random triggering motion and monitor driver habits. Experiments show that the ST-TENG can generate the open-circuit voltage is 400 V and the short-circuit current is 15 μA, and it is found that ST-TENG data could be exploited to reflect road conditions and driver habits. And ST-TENG has the potential to popularize intelligent driving systems.

Growth of Faceted Pores in a Crystal by the Burton–Cabrera–Frank Mechanism

The growth of a faceted pore in a crystal by the Burton–Cabrera–Frank mechanism under action of a mechanical tensile load is considered. The growth is determined by the diffusion of vacancies existing in a crystal to the terraces and steps on the pore surface. The expressions for the speed of movement of a single step and a group of parallel steps, and also for the dependence of the normal growth rate of a pore by the spiral mechanism under action of applied load have been found. It is shown that, in a certain range of low tensile loads, the rate has a quadratic dependence on the load, while the dependence is linear at high loads. The influence of impurities on the crystal fracture by the pore growth mechanism under consideration is discussed.

Grain growth in Nio–MgO and its dependence on faceting and the equilibrium crystal shape

The impact of faceting on grain growth was approached by model experiments in NiO–MgO. Grain growth rates were found to be 10 times higher in NiO compared to MgO. As the self-diffusion acoefficients differ by a factor of 250, grain growth in NiO is unexpectedly slow compared to MgO. Recently, the movement of steps was identified as the atomic mechanism of grain boundary migration. According to the equilibrium crystal shape, grain boundaries in NiO are more faceted. The faceted grain boundaries of NiO have fewer steps at the grain boundaries resulting in a relatively lower mobility.

A Novel Parallel Precision Stage with Large Working Range Based on Structural Parameters of Flexible Hinges

In order to solve the inherent contradiction of high precision and large working range in the traditional parallel positioning stage, a novel parallel precision stage with large working range based on optimized flexible hinge was studied. Firstly, a new structure parameter Ps was proposed, and its influence on the rotation stiffness was analyzed by comparing the commonly used flexible hinges. The factors that could enlarge the rotation ability were summarized, and the cylindrical flexible hinge with large working range was optimized. Then the cylindrical flexible hinge was used to constructed a novel parallel precision positioning stage, which could realize both of high resolution and large working range by taking use of the step and continuous motion of the piezoelectric actuators. The experiment results show that the resolution of translation is 0.09 μm, and the rotation resolution are 0.8 μrad, 0.9 μrad and 1.0 μrad, respectively. While the working range of the parallel stage could achieve 120 mm for translation, and 6.18°, 6.74° and 6.58°, respectively for each axis of rotation. All of the basic research contents is helpful for further study of the control laws of the compliant parallel mechanism.

Turbulent Wagner problem with transition

Wagner problem is originally concerned with inviscid flow and unsteady force due to a small step motion, or attaining of a small angle of attack, of an airfoil in an initially uniform flow and has been studied recently for inviscid flow with large amplitude step motion. Here we propose to consider turbulent Wagner problem for a plate that is initially covered with a mixed laminar-boundary layer on both sides and is set into step motion of small or large amplitude and in direction normal to the plate. The evolution of skin friction and transition region in time are examined numerically. It is found that transition region unexpectedly changes direction of movement for small amplitude of step motion while global transition or laminarization exists for large amplitude step motion. The significance of this study is twofold. First, the present study treated a new and interesting problem since it combines two problems of fundamental interests, one is Wagner problem and the other is boundary layer transition. Second, the present study appears to show that the pressure gradient normal to the airfoil and caused by discontinuous step motion may have subtle influence on transition and the mechanism of this influence deserves further studies.

CAPTURING REAL-WORLD LOSSES OF BALANCE AND RECOVERY RESPONSES IN OLDER ADULTS AT RISK FOR FALLS

Losses of balance (LOBs) such as trips can lead to falls in older adults; what actually happens during real-world LOBs is unclear. With 4 wearable inertial measurement units (IMUs), we recorded feet, trunk and wrist movements over 2 weeks. Using a wrist voice recorder to report the LOBs, we applied our IMU processing algorithms and reconstructed the full body LOB and recovery motions. We recruited 7 at-risk older adults (M=76 yrs) who reported 114 LOBs of which we reconstructed over 90%. Using a rating system, 52% of the LOBs involved a significant trip, stumble, recovery step, and/or large trunk motion. 25% involved double or stutter steps and smaller trunk motions. The other 23% had less striking associated motions. These data suggest that most, but not all, self-reported real world LOBs involve substantial postural destabilization and near falls. Analyses of the voice-recorded context under which the LOBs occurred are ongoing.

A Method for Numerical Simulation of Haline Convective Flows in Porous Media as Applied to Geology

A numerical code for simulating haline convective flows in porous media based on the finite difference method on a staggered nonuniform grid is developed. The mathematical model includes the equations of continuity, Darcy, and transport of contaminants with variable properties of the solid and fluid phases. The convective term in the convection–diffusion equation is approximated using the QUICK scheme. The code is tested using the problem of the concentration step motion as an example. A numerical solution of the onset and development of haline convection in a semi-infinite porous (homogeneous or inhomogeneous) domain with a contaminant source on the upper boundary is obtained.

Characterization of rotary magnetic micromotor supported on single droplet

Micromotors are key devices for various micromanipulation systems for potential scientific and industrial applications. In this study, a magnetic micromotor consisting of an 800 µm-diameter plate supported by a single droplet on a hydrophobic substrate is constructed. It is actuated by external uniform magnetic fields generated by three-dimensional electromagnetic coils. Due to the submillimeter-scale size of the top plate, the capillary force from the droplet makes it capable of working in horizontal and tilting orientations. The single droplet, also called liquid bearing, lubricates the micromotor well and improves its flexible workability. The micromotor can rotate at a speed of more than 1000 rpm in a rotating magnetic field. Besides, step motion with a stepping angle of less than 4° can be easily achieved. It is found that reducing the thickness of the liquid bearing could promote the stiffness and anti-interference capability of the micromotor. Due to its simple structure, the micromotor can be easily further miniaturized. The microscale size and flexible working performance make it suitable for wide micropositioning and micromanipulation tasks.

User-defined microstructures array fabricated by DMD based multistep lithography with dose modulation.

A flexible and efficient strategy, digital micromirror devices (DMD) based multistep lithography (DMSL), is proposed to fabricate arrays of user-defined microstructures. Through the combination of dose modulation, flexible pattern generation of DMD, and high-resolution step movement of piezoelectrical stage (PZS), this method enables prototyping a board range of 2D lattices with periodic/nonperiodic spatial distribution and arbitrary shapes and the critical feature size is down to 600 nm. We further explore the use of DMSL to fabricate microlens array by combining with the thermal reflowing process. The square shape and hexagonal shape microlens with customized distribution are realized and characterized. The results indicate that the proposed DMSL can be a significant role in the microfabrication techniques for manufacturing functional microstructures array.

Etching of step-bunched Si(1 1 1) surface by Se molecular beam observed by in situ REM

Using in situ ultrahigh vacuum reflection electron microscopy, we have first visualized the evolution of step-bunched Si(1 1 1) surface during Se beam etching depending on substrate temperature T and terrace size required for survival of etching-induced vacancies. Below T ~ 630 °C, the etching proceeds in layer-by-layer mode via periodic nucleation of small 2D vacancy islands without noticeable motion of steps. However, in 630–830 °C interval, the etching of the 7 × 7 reconstructed Si(1 1 1) step-bunched surface is realized by both step flow and continuous nucleation and growth of 2D vacancy islands on wide terraces, which leads to the excavation of initially flat surface between step bunches. At T > 830 °C, the etching proceeds by step flow with preservation of initial surface morphology. We have found that the Si(1 1 1) surface etching by Se beam is characterized by 2.65 eV activation energy that limits etching kinetics in low-temperature range when the whole Si(1 1 1) surface is converted to disordered impurity-induced Si(1 1 1)“1 × 1”-Se phase.

Early postural adjustments in football players with cerebral palsy

Introduction: The functional limitations associated with Cerebral Palsy (CP) and inactivity are directly related to the deficit in postural control, namely the Early Postural Adjustments (EPAs). On the other hand, same studies showed that the practice of physical exercise can improve stability. Objectives: Thus, the goal of the present study was to evaluate the influence of physical exercise, in this case in a football player, on the EPAs of athletes with CP. Methods: The study included 5 young male adults with CP, aged between 18 and 36 years old, all football players, class 7 and 8.The electromyographic activity was recorded using Delsys Trigno and the ratio of the postural musculature [soleus (SO) and tibialis anterior (TA)] prior to a step motion, as well as the center of pressure displacement amplitude were calculated through the force platforms (Bertec), before and after a 4 month interval of training. The two moments of evaluation were compared using the Wilcoxon test and the Spearman correlation between the CoP amplitude and the muscular activity ratio was calculated.Participants were recruited in a first period in which they had no physical activity at all and in the following 4 months they started training regularly, with a frequency of three times a week for 1h30min, always with the same trainer and in the same physical training space. Results: There was a statistically significant decrease in the anterior CoP amplitude (-4.47cm; p=0.043) after 4 months, with a negative correlation between this amplitude and the ratio of TA / SO (r=-0.90; p=0.037). In the lateral direction, a diminution of amplitude of minimum CoP (-1.49; p=0.893) without statistically significant correlation (r=0.10; p=0.873) was found. Conclusions: Practicing sport, even in pathology, has a significant effect on the improvement of postural oscillation, with an increase in the relationship between muscular activity and postural control.

Subsurface diffusion in crystals and effect of surface permeability on the atomic step motion

A new theoretical approach to characterize the diffusion of both surface and bulk point defects in crystals is presented. In our model, atomic steps are considered as sources and sinks not only for adatoms and advacancies but also for self-interstitials and bulk vacancies, providing a new mechanism for bulk point defect generation and annihilation. It is shown that the creation and annihilation of self-interstitials and vacancies occur at atomic steps and can be described by introducing a diffusive layer of the bulk point defects adsorbed just below the surface. The atomic step rate of advance is studied taking into account finite permeability of the surface for bulk and surface point defects. The surface permeability results in the appearance of the dependence of the total step rate of advance not only on the supersaturation in vapor phase but also on the supersaturation of point defects in the bulk.

Unsteady Supersonic Flow for a Plate Undergoing Three-Stage Sinking Motion

A plate sinking in supersonic flow rapidly with pure acceleration was shown recently to have a flow structure and force behavior similar to those caused by a large-amplitude step motion, and this force evolution can be predicted by a nonlinear weighted Duhamel integral integrating a nonlinear solution due to large-amplitude forward step motions. In this paper, this previous study is extended to a more complex case, in which the plate sinks in supersonic flow with acceleration in the first stage and deceleration in the second stage, and stops sinking in the last stage. The flow structures are clarified numerically for each stage, according to whether the sinking is slow or fast compared to the horizontal wave speed, and the force-evolution behavior is displayed and related to the flow structures. It was found that a residual force exists during the motionless stage for fast sinking, due to the historical effect of wave evolution. In addition, although the nonlinear weighted Duhamel method predicts the force well for the first and second stages, it performs less well than a linear force method for the third stage, showing that a force method based on the forward step-motion model should be revised in the future.

Tests of a Noncontact Piezoelectric Motor Modulated by an Electromagnetic Field.

For improving the service life of piezoelectric motors and the performance of noncontact piezoelectric motors, a novel noncontact piezoelectric motor modulated by the electromagnetic field is proposed. This type of piezoelectric motor uses an electromagnetic field to modulate the reciprocating vibrations of a piezoelectric drive mechanism to form the step motion of the rotor. The working principle and structural design of the piezoelectric motor are described in detail. A prototype motor is manufactured and the test system of output characteristics is established. An experiment of the output characteristics was carried out for exploring the driving scheme under different parameters of the drive signals. The results state that the proposed motor has a rotational speed of 0.038 rad/s, step angle of approximately 1°, output torque of 6 [Formula: see text]mm under the drive voltage of 150 V, frequency of 3 Hz, and modulation voltage of 7 V.

Einstein conjecture and resting-time statistics in the bed-load transport of monodispersed particles

Sediment transport in rivers consists, at moderate discharge stage, of individual grains that undergo a series of step movements and rest periods (bed-load). Following a large number of grain trajectories in time and space is difficult and the results are affected by bias due to censorship of the time-spatial window. Therefore, the data sets available for the description of the statistics of resting-times, travel-time and lengths of the steps, are still insufficient. In this paper, an innovative experimental methodology has been designed and applied to get data representing the evolution of a bed surface and to support a robust statistical analysis of sediment transport. The methodology is based on image sequences taken of a flat bed made of well-sorted (mono-dispersed) particles. The acquired data are interpreted analytically through equations that describe the effects of grain entrainment and deposition. We show that grains’ displacement have a mean value independent of bed-load rate under low to moderate transport intensity for a given sediment type and bed-slope. Hence, we provide a strong validation of the seminal conjecture of Einstein in his theoretical statistical description of sediment transport. Finally, we describe the probability density functions of the resting-time for a few values of the sediment discharge.

A novel piezoelectric rotary actuator with a constant contact status between the driving mechanism and rotor

Taking advantage of simple structure and control, stick-slip piezoelectric actuators have been widely employed to realize precision positioning in precision machinery and instrument. However, their output characteristics could be significantly affected by the contact status between the driving mechanism and the mover (or rotor). If the contact status changes in the motion process, strong nonlinearity will appear in the displacement–time curve, deteriorating the performances. To achieve a constant contact status, the gravity of the rotor was used in this paper, and accordingly, a novel stick-slip piezoelectric rotary actuator was developed. The structure design, motion principle, as well as output characteristics of the actuator were addressed and discussed in detail. Experimental results indicated that when the driving frequency was below 350 Hz, stable stepping motions with quite small backward motion could be achieved. By changing the driving frequency, voltage and radius, various stepping rotation angles and speeds were easily obtained. The output characteristics changing with the vertical load were further characterized. Furthermore, by simply changing the direction of the driving waveform, forward and reverse rotation motions showing good linearity with time were achieved in a very large motion range, corresponding to a millimeter scale linear displacement. Comparative experiments with a normal stick-slip actuator further confirmed the validity and advancement of the proposed strategy for keeping a constant contact status, which will be beneficial to the subsequent motion control and mass production.