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Intervention to improve the balance ability of individuals with impaired balance is needed to prevent falls. While sub-threshold mechanical noise applied to foot soles has been shown to improve balance not only for balance-impaired but also healthy individuals, how calf muscle activity is changed to enhance motor control to achieve improvement has not been explored. To address this issue, we study the calf muscle activity of healthy young adults standing on firm and compliant surfaces, with and without noise applied to their feet. The compliant surface experiment simulates balance impairment. Center of pressure (COP) data was used to assess balance changes, surface electromyography (EMG) recorded muscle activity, and COP-EMG correlations measured muscle contribution to postural control. The Wilcoxon signed-rank test was used to compare the data between the control and noise conditions. On both surfaces, the applied noise enhanced motor control efficiency of all three calf muscle groups studied - the tibialis anterior (TA), lateral gastrocnemius lateralis (LG), and medial gastrocnemius (MG). Noise also increased the contribution of the LG muscle group to postural control in the anteroposterior direction. Our finding suggests that, for balance-impaired individuals with weak calf muscles, higher-frequency noise should be used - this will increase motor control efficiency, i.e., increase posture correction frequency with concomitant reduction in calf muscle contractions, which is well-suited to the weak muscles.

Based on the true stress–strain data obtained from dynamic compression experiments using split Hopkinson pressure bar, constitutive models including the Johnson–Cook model, modified Johnson–Cook model, Mechanical Threshold Stress model, and modified Arrhenius-type constitutive model are developed to describe the plastic flow behavior of GCr15 steel over a temperature range of 298 to 873 K and strain rates from 460 to 3940 s −1 . The material parameters for the models are optimized using the Grey Wolf Optimizer, and the predictive performance is evaluated based on the correlation coefficient and average absolute relative error. Furthermore, the micromorphology of the specimen after impact is observed using a scanning electron microscope. The results indicate that all four constitutive models effectively reflect the plastic flow behavior of GCr15 steel. The modified Johnson–Cook model is more effective and accurate than the Johnson–Cook model, Mechanical Threshold Stress model, and modified Arrhenius-type constitutive model for predicting the dynamic compression behavior of GCr15 steel, with a correlation coefficient of 0.9711, an average absolute relative error of 2.6501% and a mean relative error of −0.2899%.

The ever-increasing relationship between energy consumption and economic growth continues to reinforce functional power generation infrastructure as the centerpiece of development. However, downtimes from in-service failure of power plant components, such as turbine blades, portend dire consequences in the form of huge financial and safety concerns. This challenge is now being progressively overcome through intensive research in the development of laser shock peening (LSP) models, which simulate the induction of compressive layers around and beneath the surface of the blades. This paper presents an alternate experimentally validated computational modelling approach of the LSP process, grounded on a physics-based plasticity model which describes a mechanical threshold for compressive residual stress induction irrespective of increasing laser shock intensities. This is a phenomenon which hitherto has previously been overlooked by many researches. The results of this work show considerable promise when compared to experimental results.

The Mechanical Threshold Stress (MTS) model provides excellent predictive capabilities for the material constitutive response for a wide range of temperatures and strain rates. However, the MTS model fails to capture the rapidly increasing yield stress at high strain rate behavior as the deformation controlling mechanism transitions from thermal activation to drag mechanisms, only capturing the linear behavior. Further, the model typically over predicts the flow stress behavior at yield and post yield due to its use of a constant work hardening rate parameter derived from the stress–strain response at constant saturation stress. An alternative approach to fitting portions of the MTS model is investigated and mathematical models are developed to address these issues. The results show that with appropriate experimental data, the mechanical threshold stress and work hardening rate parameters within the MTS model can quite easily and accurately be modified to extend applicability to high strain rate behavior and more accurately model the initial flow stress behavior at early work hardening rates without modification of the functions core to the MTS model itself.

Context: Dexmedetomidine (Dex) has been reported to have an anti-inflammatory effect. However, its role on osteoarthritis (OA) has not been explored. Objective: This study investigates the effect of Dex on OA rat model induced by papain. Materials and methods: The OA Wistar rat model was induced by intraluminal injection of 20 mL of papain mixed solution (4% papain 0.2 mL mixed with 0.03 mol L −1 l-cysteine 0.1 mL) into the right knee joint. Two weeks after papain injection, OA rats were treated by intra-articular injection of Dex (5, 10, or 20 μg kg −1 ) into the right knee (once a day, continuously for 4 weeks). Articular cartilage tissue was obtained after Dex treatment was completed. Results: The gait behavior scores (2.83 ± 0.49), PWMT (15.2 ± 1.78) and PTWL (14.81 ± 0.92) in H-DEX group were higher than that of OA group, while Mankin score (5.5 ± 0.81) was decreased (p < 0.05). Compared with the OA group, the IL-1β (153.11 ± 16.05 pg mg −1 ), IL-18 (3.71 ± 0.7 pg mg −1 ), IL-6 (14.15 ± 1.94 pg/mg) and TNF-α (40.45 ± 10.28 pg mg −1 ) levels in H-DEX group were decreased (p < 0.05). MMP-13, NLRP3, and caspase-1 p10 expression in Dex groups were significantly lower than that of OA group (p < 0.05), while collagen II was increased (p < 0.05). p65 in the nucleus of Dex groups was significantly down-regulated than that of OA group (p < 0.05). Discussion and Conclusions: Dex can improve pain symptoms and cartilage tissue damage of OA rats, which may be related to its inhibition of the activation of NF-κB and NLRP3 inflammasome.

The primary aim of this article was to predict the flow stress of Ta–W alloys using the eXtreme Gradient Boosting (XGBoost) machine learning model and to explain the outcome using SHapley Additive exPlanations (SHAP). The article details the effect of temperature, strain rate, and alloying content on the deformation behavior. Though grain size, dislocation density, texture and impurities are also important factors affecting the deformation behavior, these have not been considered in this work. Data and constitutive models from the literature were used to find and compare the predictiveness of the flow stress in Ta–W alloys. XGBoost predicted flow stress with a root mean square error of 12 MPa during training and 40 MPa during testing, while constitutive models such as Johnson–Cook (JC), Zerilli–Armstrong (ZA) and mechanical threshold stress (MTS) models showed a root mean square error of 208, 131 and 149 MPa respectively. The linear correlation between the predicted and experimental flow stress at 10% strain was calculated using the Pearson correlation coefficient and found to be 0.64, 0.93, and 0.70 for JC, ZA and MTS models respectively, while XGBoost showed 0.99 during training and 0.98 during testing. The optimized XGBoost model was validated using five-fold and leave-one-group-out cross-validations. The flow stress at 10% strain was predicted using XGBoost at various temperatures, strain rates, and alloying content. The flow stress was low at temperatures above 1000 K and strain rates below 10 −2 s −1 . From SHAP analysis, it was found that the base flow stress value (at which the SHAP value is zero) was 477 MPa. For temperatures less than 275 K, strain rates greater than 1 s −1 , and alloying content greater than 2.5 wt.% W, the flow stress showed an increase from its base value.

Background and Objectives Somatosensory function is critical for successful aging. Prior studies have shown declines in somatosensory function with age; however, this may be affected by testing site, modality, and biobehavioral factors. While somatosensory function declines are associated with peripheral nervous system degradation, little is known regarding correlates with the central nervous system and brain structure in particular. The objectives of this study were to examine age-related declines in somatosensory function using innocuous and noxious stimuli, across 2 anatomical testing sites, with considerations for affect and cognitive function, and associations between somatosensory function and brain structure in older adults. Research Design and Methods A cross-sectional analysis included 84 “younger” (n = 22, age range: 19–24 years) and “older” (n = 62, age range: 60–94 years) healthy adults who participated in the Neuromodulatory Examination of Pain and Mobility Across the Lifespan study. Participants were assessed on measures of somatosensory function (quantitative sensory testing), at 2 sites (metatarsal and thenar) using standardized procedures, and completed cognitive and psychological function measures and structural magnetic resonance imaging. Results Significant age × test site interaction effects were observed for warmth detection (p = .018, ηp2= 0.10) and heat pain thresholds (p = .014, ηp2= 0.12). Main age effects were observed for mechanical, vibratory, cold, and warmth detection thresholds (ps < .05), with older adults displaying a loss of sensory function. Significant associations between somatosensory function and brain gray matter structure emerged in the right occipital region, the right temporal region, and the left pericallosum. Discussion and Implications Our findings indicate healthy older adults display alterations in sensory responses to innocuous and noxious stimuli compared to younger adults and, furthermore, these alterations are uniquely affected by anatomical site. These findings suggest a nonuniform decline in somatosensation in older adults, which may represent peripheral and central nervous system alterations part of aging processes.

Abstract BACKGROUND Chronic migraine (CM) is a highly debilitating disease, and many patients remain refractory to medicinal therapy. Given the convergent nature of neuronal networks in the ventral posteromedial nucleus (VPM) and the evidence of sensitization of pain circuitry in this disease, we hypothesize CM rats will have increased VPM neuronal firing, which can be attenuated using occipital nerve stimulation (ONS). OBJECTIVE To determine whether VPM firing frequency differs between CM and sham rats, and whether ONS significantly alters firing rates during the application of mechanical stimuli. METHODS Fourteen male Sprague-Dawley rats were infused with inflammatory media once daily through an epidural cannula for 2 wk to induce a CM state. Sham animals (n = 6) underwent cannula surgery but received no inflammatory media. ONS electrodes were implanted bilaterally and single-unit recordings were performed in the VPM of anesthetized rats during mechanical stimulation of the face and forepaw in the presence and absence of ONS. RESULTS CM rats had significantly higher neuronal firing rates (P < .001) and bursting activity (P < .01) in response to mechanical stimuli when compared to shams. ONS significantly reduced neuronal firing in the VPM of CM rats during the application of 0.8 g (P = .04), 4.0 g (P = .04), and 15.0 g (P = .02) Von Frey filaments. ONS reduced bursting activity in CM rats during the 4.0 and 15 g filaments (P < .05). No significant changes in bursting activity or firing frequency were noted in sham animals during ONS. CONCLUSION We demonstrate that neuronal spike frequencies and bursting activity in the VPM are increased in an animal model of CM compared to shams. Our results suggest that the mechanism of ONS may involve attenuation of neurons in the VPM of CM rats during the application of mechanical stimuli.

BACKGROUND: Intervertebral disc herniation is a common cause of spinal cord injury (SCI) causing paralysis and sensory loss. Little quantitative information is available on the loss and recovery of sensation in dogs with SCI. OBJECTIVES: To determine whether quantitative sensory testing (QST) can be used to establish thermal and mechanical sensory thresholds in chrondrodystrophoid dogs and compare thresholds among normal dogs and dogs with different grades of SCI. ANIMALS: Thirty‐three client‐owned chondrodystrophoid dogs: 15 normal and 18 SCI dogs. METHODS: Thermal testing was performed by placing a hot (49°C) and cold (5°C) probe on the dorsal metatarsus and mechanical thresholds were tested using calibrated forceps to apply force to the lateral digit. Stimuli were applied until acknowledged, and response rate, latency, and force applied to response were recorded. Test‐retest repeatability was determined by calculating intraclass correlation coefficients. Response rates were compared using logistic regression and thresholds were compared using Kaplan–Meier Survival curves. RESULTS: Testing was feasible with moderate repeatability. Thresholds and response rates were significantly different between normal and SCI dogs for all modalities (P < .001). When dogs were grouped by their clinical grade, each grade was significantly different from normal dogs, and cold stimuli differentiated among all grades. CONCLUSION AND CLINICAL IMPORTANCE: Sensory thresholds can be measured reliably in chondrodystrophoid dogs and are altered by SCI. The differences in sensation among neurologic grades indicate that these techniques can be used to further characterize recovery of SCI dogs.

Previous studies showed that deep brain stimulation (DBS) relieves pain symptoms in Parkinson disease (PD) patients when programmed for motor-symptom relief. One factor involved in pain processing is sensory perception of stimuli. With the advent of directional leads, we explore whether directional DBS affects quantitative sensory testing (QST) metrics acutely. PD patients with subthalamic (STN) DBS and directional leads were tested in 5 settings (DBS-OFF, DBS-ON with omnidirectional stimulation, and DBS-ON) for each of three directional segments of contact used for clinical programming. The Unified Parkinson's Disease Rating Scale (UPDRS-III) assessed patient's motor skills at time of study visit at clinical contact and at contact which produced optimal sensory threshold (defined by the greatest tolerance to mechanical stimuli). Correlation analyses were performed between stimulation parameters [amplitude, frequency, pulse width (PW), total electrical energy delivered (TEED)] and outcome metrics. Sensory thresholds were obtained in nine patients. Directional stimulation did not significantly alter patient perceptions of sensory stimulus [cold pain ( = 0.69), warm pain ( = 0.99), Von frey fibers ( = 0.09), pin-prick ( = 0.88), vibration ( = 0.40), pressure ( = 0.98)]. With correlation analysis, increasing PW at the posterior contact increased pin prick and vibration sensitivity ( < 0.001). Additionally, an increase in TEED caused a decrease in sensitivity to warm detection when using the anterior ( = 0.04), lateral ( = 0.02), and medial contacts ( = 0.03), and also caused a decrease in sensitivity to cold detection when using the medial contact ( = 0.03). UPDRS-III remained stable during testing. Motor benefit can be acutely maintained at directional contacts, whereas directional stimulation can modulate thermal and mechanical sensitivity. Further investigation will determine whether these changes are maintained chronically or can be improved with optimized programming.