Quantifying the local mechanical properties of twisted double bilayer graphene.

Nanomechanical measurements of minimally twisted van der Waals materials remained elusive despite their fundamental importance for device realisation. Here, we use Ultrasonic Force Microscopy (UFM) to locally quantify the variation of out-of-plane Young's modulus in minimally twisted double bilayer graphene (TDBG). We reveal a softening of the Young's modulus by 7% and 17% along single and double domain walls, respectively. Our experimental results are confirmed by force-field relaxation models. This study highlights the strong tunability of nanomechanical properties in engineered twisted materials, and paves the way for future applications of designer 2D nanomechanical systems.

Quantum Advantage in a Molecular Spintronic Engine that Harvests Thermal Fluctuation Energy.

Recent theory and experiments have showcased how to harness quantum mechanics to assemble heat/information engines with efficiencies that surpass the classical Carnot limit. So far, this has required atomic engines that are driven by cumbersome external electromagnetic sources. Here, using molecular spintronics, an implementation that is both electronic and autonomous is proposed. The spintronic quantum engine heuristically deploys several known quantum assets by having a chain of spin qubits formed by the paramagnetic Co center of phthalocyanine (Pc) molecules electronically interact with electron-spin-selecting Fe/C60 interfaces. Density functional calculations reveal that transport fluctuations across the interface can stabilize spin coherence on the Co paramagnetic centers, which host spin flip processes. Across vertical molecular nanodevices, enduring dc current generation, output power above room temperature, two quantum thermodynamical signatures of the engine's processes, and a record 89% spin polarization of current across the Fe/C60 interface are measured. It is crucially this electron spin selection that forces, through demonic feedback and control, charge current to flow against the built-in potential barrier. Further research into spintronic quantum engines, insight into the quantum information processes within spintronic technologies, and retooling the spintronic-based information technology chain, can help accelerate the transition to clean energy.

Perceptual distortion in virtual reality and its impact on dynamic postural control.

BACKGROUND: Voluntary movement such as lifting a foot in preparation to stepping acts as a self-initiated perturbation that disturbs postural equilibrium. To maintain and restore equilibrium, humans utilize early, anticipatory, and compensatory postural adjustments. Despite technological progress in accessible virtual reality (VR) devices, little is known on the usage of VR in control and maintenance of balance while standing. RESEARCH QUESTION: How does VR modulate early, anticipatory, and compensatory postural adjustments during a dynamic task of leg lifting while avoiding an obstacle? METHODS: First, the postural adjustments in a single-leg obstacle avoidance were compared between real and VR settings, where a statistical reanalysis was performed with data subsets that minimize the difference of foot elevation speed. Second, the effect of simple foot elevation was examined to identify the fundamental nature of leg lifting motion as a self-initiated perturbation. Lastly, perceptual distortion in VR was assessed by evaluating how the spatial scale of the virtual scene used in the single-leg obstacle avoidance experiment was recognized by participants. RESULTS: The VR setting reduced the activities of lower leg muscles on the supporting side not only in the compensatory phase but also in the preparatory early and anticipatory phases. On the other hand, simple foot elevation resulted in a significant increase of muscle activities with lifting height only found in the compensatory phase. Furthermore, it is suggested that the VR induced perceptual distortion in estimating the sizes of the virtual objects. SIGNIFICANCE: The findings provide more definitive evidence that VR presentation modulates the components of postural adjustments for maintaining upright stance while being perturbed. One of the potential psychophysical factors is perceptual distortion in VR, and this provides critical information for further development of VR based training system.

Accessing nanoscopic polarization reversal processes in an organic ferroelectric thin film.

Towards eliminating toxic substances from electronic devices, Croconic Acid (CA) has great potential as a sublimable organic ferroelectric material. While studies on CA thin films are just beginning to emerge, its capability to be integrated in nanodevices remains unexplored. We demonstrate at the laterally nanoscopic scale robust ferroelectric switching of a stable enduring polarization at room temperature in CA thin films, without leakage. The challenging ferroelectric characterization at the nanoscale is performed using a unique combination of piezoresponse force microscopy, polarization switching current spectroscopy and concurrent strain response. This helps rationalize the otherwise asymmetric polarization-voltage hysteresis due to background noise limited undetectable switching currents, which are statistically averaged in macrojunctions but become prevalent at the nanoscale. Apart from successfully estimating the nanoscopic polarization in CA thin films, we show that CA is a promising lead-free organic ferroelectric towards nanoscale device integration. Our results, being valid irrespective of the ferroelectrics' nature; organic or inorganic, pave the way for fundamental understandings and technological applications of nanoscopic polarization reversal mechanisms.

Utilization of wearable technology to assess gait and mobility post-stroke: a systematic review.

BACKGROUND: Extremity weakness, fatigue, and postural instability often contribute to mobility deficits in persons after stroke. Wearable technologies are increasingly being utilized to track many health-related parameters across different patient populations. The purpose of this systematic review was to identify how wearable technologies have been used over the past decade to assess gait and mobility in persons with stroke. METHODS: We performed a systematic search of Ovid MEDLINE, CINAHL, and Cochrane databases using select keywords. We identified a total of 354 articles, and 13 met inclusion/exclusion criteria. Included studies were quality assessed and data extracted included participant demographics, type of wearable technology utilized, gait parameters assessed, and reliability and validity metrics. RESULTS: The majority of studies were performed in either hospital-based or inpatient settings. Accelerometers, activity monitors, and pressure sensors were the most commonly used wearable technologies to assess gait and mobility post-stroke. Among these devices, spatiotemporal parameters of gait that were most widely assessed were gait speed and cadence, and the most common mobility measures included step count and duration of activity. Only 4 studies reported on wearable technology validity and reliability metrics, with mixed results. CONCLUSION: The use of various wearable technologies has enabled researchers and clinicians to monitor patients' activity in a multitude of settings post-stroke. Using data from wearables may provide clinicians with insights into their patients' lived-experiences and enrich their evaluations and plans of care. However, more studies are needed to examine the impact of stroke on community mobility and to improve the accuracy of these devices for gait and mobility assessments amongst persons with altered gait post-stroke.

Long-term impact of mild traumatic brain injury on postural stability and executive function.

OBJECTIVE: A substantial number of individuals present with prolonged symptoms after a mild traumatic brain injury (mTBI) or concussion. This has warranted the development of assessment tools that can reliably detect prolonged symptoms after an mTBI. At present, a gold standard diagnostic tool for accurately identifying such prolonged symptoms is not available. The purpose of this study is to utilize specific measures of standing balance, cognitive function, and bimanual coordination to examine persisting long-term deficits in individuals with mTBI. METHODS: A total of 18 (medically diagnosed with an mTBI within the last year) and 14 (healthy age-matched controls) individuals participated in the study. Assessment tools included NIH Toolbox Cognition Battery (NIHTB-CB), TEMPA, and Purdue pegboard (bimanual coordination) and standing balance on a force platform. RESULTS: Individuals with mTBI demonstrated lower scores in all measures of cognition with statistically significant difference (p = 0.03) in executive function. The clinical tests of bimanual coordination did not show any statistically significant differences between groups. Postural stability was significantly reduced (p = 0.039) in the mTBI group. CONCLUSION: Our results show long-term performance deficits (cognition and postural stability) that persist in individuals with mTBI. In addition, to the best of our knowledge, this is the first study to identify cognitive deficits in individuals with mTBI by utilizing NIHTB-CB. Knowledge gained from this study might affect decisions of return-to-play or return-to-learn in individuals with a history of mTBI(s).

Upright balance control strategies during pregnancy.

BACKGROUND: Morphological and physiological changes during pregnancy are considered to interfere with the mechanisms of postural control and potentially increase the risk of falling. A clear understanding of these mechanisms is important to improve pre-natal care and reduce the fall risk in this population. OBJECTIVES: This study focused on investigating how pregnancy affects postural control in each trimester of pregnancy by analyzing pelvic inclination and body sway behavior. Our main hypothesis was that balance control and posture would change during pregnancy. More specifically, pregnancy would increase sway amplitude, anterior pelvic tilt, and body sway regularity in time. STUDY DESIGN: Forty women formed four groups: non-pregnant women (NP) and women at their first, second, and third trimester of pregnancy (P1, P2, and P3, respectively). All participants performed (1) postural evaluation of the pelvic inclination using a digital system of postural analysis and (2) instrumented posturography using a force platform to collect the coordinates of the body's center of pressure (COP) during quiet bipedal stance for 120 s. Kruskal-Wallis H test and post-hoc Mann-Whitney U tests were used to investigate the effects of pregnancy (NP, P1, P2, and P3) on pelvic inclination angle and postural indices computed from the COP signals. RESULTS: Results revealed significant larger body sway accompanied by a more regular medial-lateral pattern of oscillation and a more synchronized anterior-posterior and medial-lateral sway already at the first trimester of pregnancy. The averaged COP migrated posteriorly at third trimester of pregnancy and the anterior pelvic tilt increased at second and third trimesters. CONCLUSIONS: Our results indicate the existence of changes in posture and balance metrics even at early stages of pregnancy. We suggest the use of posturography as one of screening tools for postural instability and fall risk during pregnancy.

Author Correction: Long-term effects of mild traumatic brain injuries to oculomotor tracking performances and reaction times to simple environmental stimuli.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Long-term effects of mild traumatic brain injuries to oculomotor tracking performances and reaction times to simple environmental stimuli.

Understanding the long-term effects of concussive events remains a challenge for the development of modern medical practices and the prevention of recurrent traumas. In this study, we utilized indices of oculomotor performance and the ability to react to simple environmental stimuli to assess the long-term motor effects of traumatic brain injury in its mildest form (mTBI). We performed analysis of eye movement accuracy, investigated the presence of abnormal eye movements, and quantified time to react to simple environmental stimuli on long-term mTBI survivors. Results indicated the presence of impairments to basic neural functions used to explore and respond to environmental demands long after the occurrence of mTBIs. Specifically, the result revealed the presence of abnormal saccadic eye movements while performing horizontal smooth pursuit, diminished accuracy of primary saccadic horizontal eye movement, and a widespread slower reaction to both visual and auditory stimuli. The methodology used in this study indicated to be potentially useful in aiding future investigations of neural circuitry impaired by mTBI and provide indices of recovery in future clinical trials testing mTBI-related clinical interventions.

Proof-of-Concept Testing of a Real-Time mHealth Measure to Estimate Postural Control During Walking: A Potential Application for Mild Traumatic Brain Injuries.

Background: Most individuals with mild traumatic brain injury (mTBI) experience post-injury deficits in postural control. Currently available measures of postural control are lab-based or supervised, which may hinder timely symptom assessment for individuals with mTBI, including Asian populations, who do not seek initial screening post-injury. In this proof-of-concept testing study, we introduce a real-time mobile health (mHealth) system to measure postural control during walking. The proposed mHealth system can be used for home-based symptom assessment and management of mTBI. Methods: In our proposed mHealth system, a smartwatch, a smartphone, and a cloud server communicate to measure, collect, and store body balance data in real time. Specifically, we focus on the rotation vector data that have been reported to be the most effective in terms of differentiating balance control during walking across different participants. Results: Constant motion change in four participants (two females and two males; three healthy participants, and one individual with reduced physical mobility) was collected and analyzed. The results of our data analysis show that, compared to healthy participants, the individual was reduced physical mobility had a wider range of motion between right and left, up and down, and forward and backward while walking. We also found that female participants had narrower ranges of right-to-left and up-and-down motions than their male counterparts. Conclusions: Our results highlight the potential of the proposed real-time mHealth system for home-based symptom assessment and management of mTBI, which may benefit Asian and other nonwhite racial minority groups that appear to be more reluctant to access post-acute rehabilitation services.

Control of vertical posture while elevating one foot to avoid a real or virtual obstacle.

The purpose of this study is to investigate the control of vertical posture during obstacle avoidance in a real versus a virtual reality (VR) environment. Ten healthy participants stood upright and lifted one leg to avoid colliding with a real obstacle sliding on the floor toward a participant and with its virtual image. Virtual obstacles were delivered by a head mounted display (HMD) or a 3D projector. The acceleration of the foot, center of pressure, and electrical activity of the leg and trunk muscles were measured and analyzed during the time intervals typical for early postural adjustments (EPAs), anticipatory postural adjustments (APAs), and compensatory postural adjustments (CPAs). The results showed that the peak acceleration of foot elevation in the HMD condition decreased significantly when compared with that of the real and 3D projector conditions. Reduced activity of the leg and trunk muscles was seen when dealing with virtual obstacles (HMD and 3D projector) as compared with that seen when dealing with real obstacles. These effects were more pronounced during APAs and CPAs. The onsets of muscle activities in the supporting limb were seen during EPAs and APAs. The observed modulation of muscle activity and altered patterns of movement seen while avoiding a virtual obstacle should be considered when designing virtual rehabilitation protocols.

The effects of mild traumatic brain injury on postural control.

PRIMARY OBJECTIVE: The purpose of this study was to investigate the effects of mild traumatic brain injury (mTBI) on multiple postural indices that characterize body sway behaviour. METHODS AND PROCEDURES: The body's centre of pressure (COP) displacement was recorded from 11 individuals with a history of mTBI (29.4 ± 6.7 years old) and 11 healthy controls (26.8 ± 3.7 years old) performing bipedal stance on a force platform for 120 seconds. Spatio-temporal (area, amplitude and mean velocity of the COP displacement) and frequency characteristics (frequency containing 80% of the power spectral density) of the body oscillation, as well as its dynamic characteristics (sample entropy estimate of the COP displacement) were extracted from COP signals. MAIN OUTCOMES AND RESULTS: All postural indices studied were significantly affected by mTBI (p < 0.010). Participants with a history of mTBI presented a larger, slower, and more random body oscillation compared to controls. CONCLUSION: The results suggest that (a) balance deficits can be recognized as an effect of mTBI; (b) balance deficits induced by mTBI are multi-dimensional, affecting all three domains included in this study; and

Role of contralesional hemisphere in paretic arm reaching in patients with severe arm paresis due to stroke: A preliminary report.

Stroke is highly prevalent and a leading cause of serious, long-term disability among American adults. Impaired movement (i.e. paresis) of the stroke-affected arm is a major contributor to post-stroke disability, yet the mechanisms of upper extremity motor recovery are poorly understood, particularly in severely impaired patients who lack hand function. To address this problem, we examined the functional relevance of the contralesional hemisphere in paretic arm motor performance in individuals with severe arm paresis. Twelve individuals with severe stroke-induced arm paresis (Upper Extremity Fugl-Meyer Assessment=17.1 ± 8.5; maximum score=66) participated in the study. Participants performed a reaching response time task with their paretic arm. At varying time intervals following a 'Go' cue, a pair of transcranial magnetic stimulation (TMS) pulses were delivered to contralesional hemisphere primary motor (M1) or dorsal pre-motor cortex (PMd) to momentarily disrupt the pattern of neural firing. Response time components and hand-path characteristics were compared across the 2 sites for trials with and without TMS disruption. There was no significant effect of TMS disruption on overall Response time or Reaction time, but Movement time was significantly longer (i.e. slower) with disruption of the contralesional hemisphere (p=0.015), regardless of which area was stimulated. Peak hand-path velocity and hand-path smoothness were also significantly lower (p=0.005 and p<0.0001, respectively) with TMS disruption of the contralesional hemisphere. The data from this study provide evidence supporting a functionally relevant role of contralesional hemisphere motor areas in paretic arm reaching movements in individuals with severe post-stroke arm impairment.

Support surface related changes in feedforward and feedback control of standing posture.

The aim of the study was to investigate the effect of different support surfaces on feedforward and feedback components of postural control. Nine healthy subjects were exposed to external perturbations applied to their shoulders while standing on a rigid platform, foam, and wobble board with eyes open or closed. Electrical activity of nine trunk and leg muscles and displacements of the center of pressure were recorded and analyzed during the time frames typical of feedforward and feedback postural adjustments. Feedforward control of posture was characterized by earlier activation of anterior muscles when the subjects stood on foam compared to a wobble board or a firm surface. In addition, the magnitude of feedforward muscle activity was the largest when the foam was used. During the feedback control, anterior muscles were activated prior to posterior muscles irrespective of the nature of surface. Moreover, the largest muscle activity was seen when the supporting surface was foam. Maximum CoP displacement occurred when subjects were standing on a rigid surface. Altering support surface affects both feedforward and feedback components of postural control. This information should be taken into consideration in planning rehabilitation interventions geared towards improvement of balance.

Static and dynamic visual cues in feed-forward postural control.

Anticipatory postural adjustments (APAs) play an important role in the performance of many activities requiring the maintenance of vertical posture. However, little is known about how variation in the available visual information affects generation of APAs. The purpose of this study was to investigate the role of different visual cues on APAs. Ten healthy young subjects were exposed to external perturbations induced at the shoulder level in standing while the level of visual information about the forthcoming perturbation was varied. The external perturbations were provided by an aluminum pendulum attached to the ceiling. The visual conditions were (1) dynamic cues (full vision and high-frequency strobe light), (2) static cues (low-frequency strobe light) and (3) no cues (eyes open in dark room). Electrical activity of the trunk and leg muscles and center of pressure displacements were recorded and quantified within the time intervals typical for APAs. The results showed that significantly larger APAs were generated in conditions with dynamic visual cues as compared to the conditions with static cues (p < 0.05). Finally, no APAs were observed in the condition where there was complete absence of any visual cues. Principal component analysis further revealed different muscle coupling patterns in the full vision and high-frequency strobe light conditions. These findings suggest the importance of using appropriate visual cues in the generation of APAs.

The effect of decreased visual acuity on control of posture.

OBJECTIVES: The goal of this study was to investigate the effect of visual acuity on the anticipatory (APAs) and compensatory (CPAs) components of postural control. METHODS: Ten individuals participated in the experiments involving perturbations induced by a pendulum while their visual acuity was altered. The different visual acuity conditions were no glasses, blurred vision induced by wearing glasses with positive or negative lenses, and no vision. EMG activity of trunk and leg muscles and ground reaction forces were recorded during the typical anticipatory and compensatory periods. RESULTS: In the no vision condition the subjects did not generate APAs, which resulted in the largest displacements of the center of pressure (COP) after the perturbation (p<0.01). In all other visual conditions APAs were present showing a distal to proximal order of muscle activation. The subjects wearing positive glasses showed earlier and larger anticipatory EMGs than subjects wearing negative glasses or no glasses at all. CONCLUSIONS: The study outcome revealed that changes in visual acuity induced by wearing differently powered eye glasses alter the generation APAs and as a consequence, affect the compensatory components of postural control. SIGNIFICANCE: The observed changes in APAs and CPAs in conditions with blurred vision induced by positive and negative glasses suggest the importance of using glasses with an appropriate power. This outcome should be taken into consideration in balance rehabilitation of individuals wearing glasses.

Postural control in response to an external perturbation: effect of altered proprioceptive information.

The purpose of the study was to investigate the role of altered proprioception on anticipatory (APAs) and compensatory (CPAs) postural adjustments and their interaction. Nine healthy adults were exposed to external perturbations induced at the shoulder level while standing with intact or altered proprioception induced by bilateral Achilles tendon vibration. Visual information was altered (eyes open or closed) in both the conditions. Electrical activity of eight trunk and leg muscles and center of pressure (COP) displacements were recorded and quantified within the time intervals typical for APAs and CPAs. The results showed that when proprioceptive information was altered in eyes-open conditions, anticipatory muscle activity was delayed. Moreover, altered proprioceptive information resulted in smaller magnitudes of compensatory muscle activity as well as smaller COP displacements after the perturbation in both eyes-open and eyes-closed conditions. The outcome of the study provides information on the interaction between APAs and CPAs in the presence of altered proprioception.

Compelled Body Weight Shift Technique to Facilitate Rehabilitation of Individuals with Acute Stroke.

BACKGROUND: The study evaluates the effectiveness of Compelled Body Weight Shift (CBWS) approach in the rehabilitation of individuals with stroke. CBWS involves a forced shift of body weight towards a person's affected side by means of a shoe insert that establishes a lift of the nonaffected lower extremity. METHODS: Eleven patients with acute stroke were randomly assigned to experimental and control groups. The experimental group received a two-week conventional physical therapy combined with CBWS and the control group received only a two-week conventional therapy. Weight bearing, Gait velocity, Berg's Balance, and Fugl-Meyer's Scores were recorded before and after the intervention. RESULTS: Weight bearing on the affected side increased in the experimental group and decreased in the control group. The increase in gait velocity with treatment was significant in both the groups (P < 0.05). However, experimental group (P = 0.01) demonstrated larger improvements in gait velocity compared to the control group (P = 0.002). Berg Balance and Fugl-Meyer scores increased for both the groups. CONCLUSION: The implementation of a two-week intervention with CBWS resulted in the improvement in weight bearing and gait velocity of individuals with acute stroke. The present preliminary study suggests that CBWS technique could be implemented as an adjunct to conventional rehabilitation program for individuals with acute stroke.