Publications

Background Whole-body movement initiation with change of base of support is a common paradigm used to assess balance-movement coordination. During clinical evaluation, two transitions are commonly used: gait or step initiation. During their respective anticipatory periods, two mechanisms regulate the whole-body centre of mass acceleration: a shift in the centre of pressure (CoP); and modulation of internal whole-body angular momentum (HM). These transitions have different final states, and we do not know whether the two mechanisms are used similarly during the anticipatory period. Research question Is the final state already taken into account during the anticipatory period of a whole-body movement initiation? Methods We compared the time evolution of the CoP and HM in the sagittal plane during the anticipatory period of both gait and step initiation in 13 young, healthy participants. Results During gait initiation, we observed a larger backward CoP shift (31–56 % and 75–100 % of the anticipatory period), a larger forward-directed HM (45–68 %), and a lower backward-directed HM (84–100 %) compared to step initiation. Significance Our results show that mechanical instability is larger during gait initiation, while HM modulation is larger during step initiation. These findings suggest that the final state of a transition is taken into account during the anticipatory period. Based on our results, we suggest future research should use gait and step initiation to evaluate the generation of mechanical instability, and the use of free segments, respectively, in populations with balance deficits.

With regard to the large amount produced from this type of slag in flash lead smelting furnace of Ghaniabad plant and considerable lead content of the slag, the recovery of lead is of prime importance. This research work was under taken to study the lead recovery from the mentioned slag using a hydrometallurgical process. Solving in water is done on slag for 30 minutes. XRD analysis showed that PbS is the main mineral in the slag and the difference between washed and unwashed samples is lack of Na2O in washed one so that before washing this compound existed. The slag sample was first crushed and washed in distilled water. The residue was classified into different sizes. The slag powder was then leached in Hydrochloric acid under different conditions to evaluate the effect of such parameters as pH, temperature and slag particle size on the dissolution rate of lead. It was depicted that the most critical parameter affecting the leaching rate is pH whereby the decrease of down to negative number the leaching rate increased pH significantly. Finally kinetic study of slag leaching showed that the diffusion of in the solid particle controlled the lead leaches process. This was confirmed by calculation of activation energy where was obtained as 9.47 kJ mol−1 calculated.

The effects of fibre concentration on the mechanical response of welded glass-fibre-reinforced polypropylene (GF-PP) were studied in-depth. Experimental observations during tensile tests of unwelded and welded GF-PP have shown a weld ratio reduction – ratio between the strength of the welded material and that of the bulk material – as high as 60%. For all conditions studied, no significant change in the polymer matrix was observed. Increasing the fibre content on the welded material was additionally associated with a decrease in the stress at break and the strain at the maximum stress, respectively 68 and 84% for 50 wt% GF-PP. The DIC technique was used to retrieve the local response in the welded zone, showing local strain as high as 19.5 times the macroscopic strain. Using X-ray microtomography, the strain magnification could be explained by the significant increase of the fibre density at the welded zone. It was also shown that at least 2/3 of the fibres were orientated within the weld plane limiting the transverse strain, favouring void nucleation and embrittlement of the material. As a consequence, the rupture can be explained by the amplification of the strain linked with the fibre concentration and orientation of the welded material.

Gravity is a ubiquitous external force that must be considered when producing coordinated movements. Drop-landing is a popular task to study how humans cope with gravity, because anticipatory muscle activations can be released before the estimated ground contact. But the consequences of these anticipatory muscle activations have only been interpreted in terms of stiffening the lower-limbs in preparation for ground contact, without considering potential anticipatory kinematic consequences. The objective of this study is to quantify the kinematic consequences of anticipatory muscle activations in two different landing tasks, to clarify whether anticipatory muscle activations are adapted to cope with gravity, to the dynamic constraints of the movement to perform, or both. Twenty young athletes performed drop-landing and drop-jumping from a 35 cm elevated platform. Sagittal angles and angular velocities of the hip, knee,and ankle joints, and acceleration of the foot were computed, as well as the onset of joint flexions and onset of foot vertical acceleration change. We found the same pattern of anticipatory hip and knee flexion, both starting before ground contact in all participants and in both tasks. We found no anticipatory kinematics for the ankle joint. Consecutive to the hip and knee flexion, the foot accelerated upwards before ground contact. Our results show that anticipatory muscle activations used by humans have systematic and invariant kinematic consequences during the air-time phase to cope with gravity: they initiate the hip and knee joints flexion before ground contact. This strategy likely limits the amount of ground reaction forces developed to oppose the gravity external force, and completes the stiffening role already described in the literature. These two complementary consequences —rotation and stiffening— seem to serve the same purpose of protecting the skeletal system. Since gravity is ubiquitous, these automated movements must be considered in other movements involving landing phases, such as heel strikes during gait.

Non-Schmid (NS) effects in body-centered cubic (BCC) single-phase metals have received special attention in recent years. However, a deep understanding of these effects in the BCC phase of dual-phase (DP) steels has not yet been reached. This study explores the NS effects in ferrite-martensite DP steels, where the ferrite phase has a BCC crystallographic structure and exhibits NS effects. The influences of NS stress components on the mechanical response of DP steels are studied, including stress/strain partitioning, plastic flow, and yield surface. To this end, the mechanical behavior of the two phases is described by dislocation density-based crystal plasticity constitutive models, with the NS effect only incorporated into the ferrite phase modeling. The NS stress contribution is revealed for two types of microstructures commonly observed in DP steels: equiaxed phases with random grain orientations, and elongated phases with preferred grain orientations. Our results show that, in the case of a microstructure with equiaxed phases, the normal NS stress components play significant roles in tension-compression asymmetry. By contrast, in microstructures with elongated phases, a combined influence of crystallographic texture and NS effect is evident. These findings advance our knowledge of the intricate interplay between microstructural features and NS effects and help to elucidate the mechanisms underlying anisotropic-asymmetric plastic behavior of DP steels.

This study investigated the validity of using OpenSim to measure muscle-tendon unit (MTU) length of the bi-articular lower limb muscles in several postures (shortened, lengthened, a combination of shortened and lengthened involving both joints, neutral and standing) using 3D freehand ultrasound (US), and to propose new personalized models. MTU length was measured on 14 participants and 6 bi-articular muscles (semimembranosus SM, semitendinosus ST, biceps femoris BF, rectus femoris RF, gastrocnemius medialis GM and gastrocnemius lateralis GL), considering 5 to 6 postures. MTU length was computed using OpenSim with three different models: OS (the generic OpenSim scaled model), OS + INSER (OS with personalized 3D US MTU insertions), OS + INSER+ PATH (OS with personalized 3D US MTU insertions and path obtained from one posture). Significant differences in MTU length were found between OS and 3D US models for RF, GM and GL (from − 6.3 to 10.9%). Non-significant effects were reported for the hamstrings, notably for the ST (− 1.5%) and BF (− 1.9%), while the SM just crossed the alpha level (− 3.4%, p = 0.049). The OS+ INSER model reduced the magnitude of bias by an average of 4% for RF, GM and GL. The OS + INSER+ PATH model showed the smallest biases in length estimates, which made them negligible and non-significant for all the MTU (i.e. ≤ 2.2%). A 3D US pipeline was developed and validated to estimate the MTU length from a limited number of measurements. This opens up new perspectives for personalizing musculoskeletal models using low-cost user-friendly devices.

Background/Objectives: The aim of this study was to evaluate changes in trunk height and variations in spino-pelvic parameters during trunk self-elongation. Two populations were studied: non-athletes and gymnasts, who differ in their engagement with core-strengthening exercises. Methods: EOS biplanar radiographs were taken on 14 non-athletes and 24 gymnasts in both neutral and trunk self-elongation positions. Three-dimensional reconstructions of the pelvis and spine were used to calculate effective trunk height, thoracic and lumbar contributions, and spino-pelvic parameters. Results: Trunk self-elongation resulted in a significant increase in trunk height for both groups (7 mm on average, range: −1 to 14 mm), accompanied by a reduction in thoracic kyphosis for all participants (−10° for non-athletes and −17° for gymnasts, on average) and a reduction in lumbar lordosis in most participants (−5° for non-athletes and −7° for gymnasts, on average). However, some individuals in both groups exhibited an increase in lumbar lordosis, which reduced the contribution of the lumbar region to overall trunk height. Conclusions: Trunk self-elongation instruction effectively increases trunk height, but additional instructions, such as pelvic retroversion, may enhance its effectiveness.

The simulation of the sand gravity casting process is complicated due to its multiscale and multiphysics nature. Although there are many commercial software options available, it remains extremely difficult to accurately predict the filling, solidification, and defects such as oxidation. Smoothed particle hydrodynamics (SPH) is a Lagrangian simulation approach that is particularly well-suited for modeling the gravity casting process. To validate the results of the filling, cooling, and solidification steps of the SPH method, it is interesting to introduce and design a 3D universal experimental test case of the gravity casting process that can be modeled in 2D. This universal test case is developed so that the hydrodynamic filling process can be analyzed in 2D while the cooling and solidification processes can be investigated in 1D. After comparing ProCAST, a commercial 3D mesh-based software, with the 2D SPH method, the results highlight the unique advantages of each approach in analyzing filling step and temperature evolution. The SPH simulations are better at capturing the essential aspects of fluid motion.

Background: Transmission of loads between the prosthetic socket and the residual limb is critical for the comfort and walking ability of people with transfemoral amputation. This transmission is mainly determined by the socket tightening, muscle forces, and socket ischial support. However, numerical investigations of the amputated gait, using modeling approaches such as MusculoSkeletal (MSK) modeling, ignore the weight-bearing role of the ischial support. This simplification may lead to errors in the muscle force estimation. Objective: This study aims to propose a MSK model of the amputated gait that accounts for the interaction between the body and the ischial support for the estimation of the muscle forces of 13 subjects with unilateral transfemoral amputation. Methods: Contrary to previous studies on the amputated gait which ignored the interaction with the ischial support, here, the contact on the ischial support was included in the external loads acting on the pelvis in a MSK model of the amputated gait. Results: Including the ischial support induced an increase in the activity of the main abductor muscles, while adductor muscles' activity was reduced. These results suggest that neglecting the interaction with the ischial support leads to erroneous muscle force distribution considering the gait of people with transfemoral amputation. Although subjects with various bone geometries, particularly femur lengths, were included in the study, similar results were obtained for all subjects. Conclusions: Eventually, the estimation of muscle forces from MSK models could be used in combination with finite element models to provide quantitative data for the design of prosthetic sockets.

Cross-Flow Fans (CFFs) have been widely applied in the automotive and domestic air conditioning industries in recent decades. They are high-pressure coefficient turbomachines compacted diametrically, and thus, the complex interactions of these fans require thorough evaluation. Their innovation has opened up new directions in turbomachinery, and both academic research and industry have seen numerous efforts to develop these types of fans. Despite extensive work, optimizing and improving their performance remains a challenge. Enhancing their efficiency necessitates improvements in structural characteristics, aerodynamic features, and acoustic properties. In this review, we aim to demonstrate the essential aspects of CFFs by introducing their fundamentals and primary characteristics. Furthermore, we delve into a discussion on the acoustic performance of these fans. We also summarize the flow characteristics and different flow-field patterns in CFFs and their impact on aeroacoustic behavior. The main objective of this review paper is to provide an overview of the research in this field, summarizing the critical factors that play a significant role in studying CFFs’ performance.