Identification of plastic constitutive parameters at large deformations from three dimensional displacement fields

The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated

Marine invasive species:Establishing pathways, their presence and potential threats in the Galapagos Marine Reserve

Worldwide, marine biological invasions of non-native species have increased significantly in recent years due to a rapid rise in global trade, transport and tourism. Invasions occur when non-native species are transported from one region to another and establish, often resulting in competition displacing native species and changing ecosystems. Historic literature searches were conducted along with dive surveys of the main ports and in sites around the archipelago in order to produce a baseline of which non-native species are present in the Galapagos Marine Reserve at this time. Confounding processes of anthropogenic and natural activities are increasing the potential spread of marine invasive species in the Eastern Tropical Pacific and the Galapagos Marine Reserve. We discuss the potential vectors facilitating marine invasions with the suggestion that marine traffic could be the most influential vector in the transport of marine non-natives to the Galapagos Marine Reserve. The challenge for marine park authorities is to identify those species that are likely to cause negative impacts on native biodiversity and ecosystems before they establish in the Galapagos, and to develop pre-emptive strategies that would likely include prevention as well as risk-based management strategies to remove them or to mitigate their harmful effects

Mapping the Spread of Malaria Drug Resistance

Tim Anderson discusses a new study of molecular variation in alleles at the dihydropteroate synthase locus, which underlies resistance to sulfadoxine, in over 5,000 parasites from 50 locations

Propulsion biomechanics do not differ between athletic and nonathletic manual wheelchair users in their daily wheelchairs

The purpose of this study was to investigate whether athletic and nonathletic manual wheelchair users (MWU) display differences in kinetic and kinematic variables during daily wheelchair propulsion. Thirty-nine manual wheelchair users (athletic n = 25; nonathletic n = 14) propelled their own daily living wheelchair on a roller ergometer at two submaximal speeds for three minutes (1.11 m s−1 and 1.67 m s−1). A 10 camera Vicon motion capture system (Vicon, Motion Systems Ltd. Oxford, United Kingdom) collected three-dimensional kinematics of the upper limbs and thorax at 200 Hz during the final minute of each propulsion trial. Kinetics, kinematics and kinematic variability were compared between athletic and nonathletic groups. Kinematic differences were investigated using statistical parametric mapping. Athletic MWU performed significantly greater physical activity per week compared to nonathletic MWU (920 ± 601 mins vs 380 ± 147 mins, respectively). However, no significant biomechanical differences between athletic and nonathletic MWU were observed during either propulsion speed. During the 1.11 m s−1 trial wheelchair users displayed a stroke frequency of 53 ± 12 pushes/min and a contact angle of 92.5 ± 16.2°. During the 1.67 m s−1 trial the mean stroke frequency was 64 ± 22 pushes/min and contact angle was 85.4 ± 13.6°. Despite the hand being unconstrained during the recovery phase the magnitude of joint kinematic variability was similar across both glenohumeral and scapulothoracic joints during recovery and push phases. To conclude, although athletic MWU participate in more physical activity per week they adopt similar strategies to propel their daily living wheelchair. Investigations of shoulder pain and dailywheelchair propulsion do not need to distinguish between athletic and nonathletic MWU

Managing shoulder pain in manual wheelchair users:a scoping review of conservative treatment interventions

Objective:To review the literature that has explored conservative treatments for the management of shoulder pain in manual wheelchair users.Methods:Five databases were systematically searched in february 2020 for terms related to shoulder pain and manual wheelchair use. Articles were screened and included if they investigated the conservative treatment of shoulder pain in wheelchair users. Participants’ physical characteristics, experimental design and primary and secondary outcome measures were extracted from studies. Studies were grouped according to treatment type to identify gaps in the literature and guide future research.Results:The initial search identified 407 articles, of which 21 studies met the inclusion criteria. Exercise-based treatment interventions were most prevalent (n = 12). A variety of exercise modalities were employed such as strengthening and stretching (n = 7), ergometer training (n = 3), Pilates classes (n = 1) and functional electrical stimulation (n = 1). Only three studies supplemented exercise with an additional treatment type. The Wheelchair Users Shoulder Pain Index was used by 18 studies as the primary measure of shoulder pain. Only seven of these included an objective measure of shoulder function. Participant characteristics varied among studies, and physical activity levels were frequently not reported.Conclusions:Despite the high prevalence of shoulder pain in manual wheelchair users, the number of studies to have explored conservative treatment types is low. Exercise is the most commonly used treatment, which is encouraging as physical inactivity can exacerbate other health conditions. Few studies have adopted interdisciplinary treatment strategies or included objective secondary measures to better understand the mechanisms of pain.<br

Scapular kinematic variability during wheelchair propulsion is associated with shoulder pain in wheelchair users

The purpose of this study was to investigate whether wheelchair propulsion biomechanics differ between individuals with different magnitudes of shoulder pain. Forty (age 36 11 years) manual wheelchair users propelled their own daily living wheelchair at 1.11 m.s(-1) for three minutes on a dual-roller ergometer. Shoulder pain was evaluated using the Performance Corrected Wheelchair User's Shoulder Pain Index (PC-WUSPI). Correlation analyses between spatio-temporal, kinetic and upper limb kinematic variables during wheelchair propulsion and PC-WUSPI scores were assessed. Furthermore, kinematic differences between wheelchair users with no or mild shoulder pain (n = 33) and moderate pain (n = 7) were investigated using statistical parametric mapping. Participant mean PC-WUSPI scores were 20.3 +/- 26.3 points and varied from zero up to 104 points. No significant correlations were observed between kinetic or spatio-temporal parameters of wheelchair propulsion and shoulder pain. However, lower inter-cycle variability of scapular internal/external rotation was associated with greater levels of shoulder pain (r = 0.35, P = 0.03). Wheelchair users with moderate pain displayed significantly lower scapular kinematic variability compared to those with mild or no pain between 17 and 51% of the push phase for internal rotation, between 31-42% and 77-100% of the push phase for downward rotation and between 28-36% and 53-65% of the push phase for posterior tilt. Lower scapular variability displayed by wheelchair users with moderate shoulder pain may reflect a more uniform distribution of repeated subacromial tissue stress imposed by propulsion. This suggests that lower scapular kinematic variability during propulsion may contribute towards the development of chronic shoulder pain. (C) 2020 Elsevier Ltd. All rights reserved

Alterations in shoulder kinematics are associated with shoulder pain during wheelchair propulsion sprints

The study purpose was to examine the biomechanical characteristics of sports wheelchair propulsion and determine biomechanical associations with shoulder pain in wheelchair athletes. Twenty wheelchair court-sport athletes (age: 32 +/- 11 years old) performed one submaximal propulsion trial in their sports-specific wheelchair at 1.67 m/s for 3 min and two 10 s sprints on a dual-roller ergometer. The Performance Corrected Wheelchair User's Shoulder Pain Index (PC-WUSPI) assessed shoulder pain. During the acceleration phase of wheelchair sprinting, participants propelled with significantly longer push times, larger forces, and thorax flexion range of motion (ROM) than both the maximal velocity phase of sprinting and submaximal propulsion. Participants displayed significantly greater peak glenohumeral abduction and scapular internal rotation during the acceleration phase (20 +/- 9 degrees and 45 +/- 7 degrees) and maximal velocity phase (14 +/- 4 degrees and 44 +/- 7 degrees) of sprinting, compared to submaximal propulsion (12 +/- 6 degrees and 39 +/- 8 degrees). Greater shoulder pain severity was associated with larger glenohumeral abduction ROM (r = 0.59, p = 0.007) and scapular internal rotation ROM (r = 0.53, p = 0.017) during the acceleration phase of wheelchair sprinting, but with lower peak glenohumeral flexion (r = -0.49, p = 0.030), peak abduction (r = -0.48, p = 0.034), and abduction ROM (r = -0.44, p = 0.049) during the maximal velocity phase. Biomechanical characteristics of wheelchair sprinting suggest this activity imposes greater mechanical stress than submaximal propulsion. Kinematic associations with shoulder pain during acceleration are in shoulder orientations linked to a reduced subacromial space, potentially increasing tissue stress

The longitudinal relationship between shoulder pain and altered wheelchair propulsion biomechanics of manual wheelchair users

The purpose of this study was to investigate the longitudinal association between within-subject changes in shoulder pain and alterations in wheelchair propulsion biomechanics in manual wheelchair users. Eighteen (age 33 ± 11 years) manual wheelchair users propelled their own daily living wheelchair at 1.11 m.s-1 for three minutes on a dual-roller ergometer during two laboratory visits (T1 and T2) between 4 and 6 months apart. Shoulder pain was assessed using the Performance Corrected Wheelchair User's Shoulder Pain Index (PC-WUSPI). Between visits mean PC-WUSPI scores increased by 5.4 points and varied from - 13.5 to + 20.9 points. Of the eighteen participants, nine (50%) experienced increased shoulder pain, seven (39%) no change in pain, and two (11%) decreased pain. Increasing shoulder pain severity correlated with increased contact angle (r = 0.59, P = 0.010), thorax range of motion (r = 0.60, P = 0.009) and kinetic and kinematic variability. Additionally, increasing shoulder pain was associated with reductions in peak torque (r = -0.56, P = 0.016), peak glenohumeral abduction (r = -0.69, P = 0.002), peak scapular downward rotation (r = -0.68, P = 0.002), and range of motion in glenohumeral flexion/extension and scapular angles. Group comparisons revealed that these biomechanical alterations were exhibited by individuals who experienced increased shoulder pain, whereas, propulsion biomechanics of those with no change/decreased pain remained unaltered. These findings indicate that wheelchair users exhibit a protective short-term wheelchair propulsion biomechanical response to increases in shoulder pain which may temporarily help maintain functional independence