Publications

Background: Adults with spinal deformity (ASD) are known to have spinal malalignment, which can impact their quality of life and their autonomy in daily life activities. Among these tasks, ascending and descending stairs is a common activity of daily life that might be affected. Research question: What are the main kinematic alterations in ASD during stair ascent and descent? Methods: 112 primary ASD patients and 34 controls filled HRQoL questionnaires and underwent biplanar X-from which spino-pelvic radiographic parameters were calculated. Patients were divided into 3 groups: 44 with sagittal malalignment (ASD-Sag: PT > 25°, SVA>5 cm or PI-LL>10°), 42 with isolated thoracic hyperkyphosis (ASD-HyperTK: TK > 60°), 26 with isolated frontal spine deformity (ASD-Front: Cobb>20°). All participants underwent 3D motion analysis of the whole body while ascending and descending a stair step from which kinematic waveforms were extracted. Results: During stair ascent, ASD-Sag exhibited an increased thorax flexion (20 vs 5°), a decreased lumbar lordosis L1L3-L3L5 (7 vs 14°), and an increased ROM of lumbo-pelvic joint (15 vs 10°, all p < 0.05), compared to controls. Similar compensations were shown while descending the stairstep. ASD-HyperTK had similar kinematic limitations as ASD-Sag but to a lesser extent. ASD-Front had normal kinematic patterns. PCS-SF36 correlated to thorax flexion (r = -0.45) and ODI was correlated to pelvic tilt ROM (r = 0.46). Discussion and conclusion: ASD subjects with sagittal malalignment tend to ascend and descend stairs with increased thorax flexion, making them more prone to falls. Compensation mechanisms occur at the head and lumbo-pelvic levels to maintain balance and avoid falling forward.

Background: Adult spinal deformity (ASD) is associated with muscles' degeneration that affects postural control and outcomes of an eventual corrective surgery. Evaluation of ASD is usually based on static radiographs and more recently on functional assessment. However, there has been limited exploration of muscle strength weakness in ASD. The aim was to investigate the relationship between trunk muscles' strength in ASD and its relationship with radiographic and kinematic alterations and quality-of-life decline. Methods: 28 ASD and 18 asymptomatic subjects underwent biplanar radiographs with 3D calculation of spino-pelvic and global postural parameters. 3D movement analysis of gait, sitting to standing and stair ascent, was studied allowing the calculation of head, trunk and lower limbs 3D kinematics. Participants filled out health related quality of life questionnaires. A single operator measured 4 times the strength of the trunk muscles, using a hand-held dynamometer, to assess measurements' reliability. ASD population was divided into two groups based on the strength of trunk extensors: ASD-weak extensors (N = 11 patients having trunk extensors strength<mean-1SD in controls) and ASD-normal extensors (N = 17). Radiographic, kinematic, and quality of life scores were compared between groups. Results: Measurements of muscle strengths using the hand-held dynamometer were reliable (ICC>0.94). On standing radiographs, the ASD-weak extensors group showed an increased positive sagittal malalignment compared to the other groups (SVA=61 mm vs ASD-normal extensors: 18 mm, controls: -4 mm, p < 0.001). This sagittal malalignment remained during movement (kinematic-SVA=223 mm vs ASD-normal extensors:178 mm, controls:138 mm, p < 0.001). Muscle strength weakness was correlated to the decline of quality-of-life scores (PCS-SF36: r = 0.48, VAS for pain: ρ=-0.39). Conclusions: This study showed that weak trunk extensors are associated with sagittal malalignment in static position, kinematic limitations during daily life activities and reduced quality of life scores. Future studies will investigate the effect of muscle strengthening on both static and dynamic alignment in ASD and their quality of life.

Embodied representations are known to impact user behavior in Virtual Reality (VR) through stereotypes associated with their appearance, a phenomenon known as the Proteus effect, or through perceived affordances. This latter concept refers to the interaction possibilities suggested by the environment, as perceived from the capabilities of the user's avatar. VR offers the unique potential of allowing non-anthropomorphic embodiment, enabling new interaction modalities. In this context, we propose to explore the possibilities offered by wildlife inspired avatars. We designed a chimeric avatar providing new interaction possibilities and developed an experiment to assess the effect of embodying a giant crab claw compared to a regular hand on participants' sense of embodiment and behavior when interacting in the virtual environment. This study is a work in progress and will inform designers about the potential of biomimetic avatars to shape user behaviors while supporting embodiment in VR.

The way users interact with Virtual Reality (VR) environments plays a crucial role in shaping their experience when embodying an avatar. How avatars are perceived by users significantly influences their behavior based on stereotypes, a phenomenon known as the Proteus effect. The psychological concept of affordances may also appear relevant when it comes to interact through avatars and is yet underexplored. Indeed, understanding how virtual representations suggest possibilities for action has attracted considerable attention in the human-computer interaction community, but only few studies clearly address the use of affordances. Of particular interest is the fact aesthetic features of avatars may signify false affordances, conflicting with users' expectations and impacting perceived plausibility of the depicted situations. Recent models of congruence and plausibility suggest altering the latter may result in unexpected consequences on other qualia like presence and embodiment. The proposed research initially aimed at exploring the operationalization of affordances as a tool to investigate the impact of congruence and plausibility manipulations on the sense of embodiment. In spite of a long and careful endeavor materialized by a preliminary assessment and two user studies, it appears our participants were primed by other internal processes that took precedence over the perception of the affordances we selected. However, we unexpectedly manipulated the internal congruence following repeated exposures (mixed design), causing a rupture in plausibility and significantly lowering scores of embodiment and task performance. The present research then constitutes a direct proof of a relationship between a break in plausibility and a break in embodiment

Space agencies are in the process of drawing up carefully thought-out Concepts of Operations (ConOps) for future human missions on the Moon. These are typically assessed and validated through costly and logistically demanding analogue field studies. While interactive simulations in Virtual Reality (VR) offer a comparatively cost-effective alternative, they have faced criticism for lacking the fidelity of real-world deployments. This paper explores the applicability of passive haptic interfaces in bridging the gap between simulated and real-world ConOps assessments. Leveraging passive haptic props (equipment mockup and astronaut gloves), we virtually recreated the Apollo 12 mission procedure and assessed it with experienced astronauts and other space experts. Quantitative and qualitative findings indicate that haptics increased presence and embodiment, thus improving perceived simulation fidelity and validity of user reflections. We conclude by discussing the potential role of passive haptic modalities in facilitating early-stage ConOps assessments for human endeavours on the Moon and beyond.

This paper addresses the controller design for the overhead cranes. To this end, a nonlinear model of the overhead cranes is considered, and a continuous-time sliding-mode controller is designed for such a model, ensuring global robust stability. Subsequently, the deadbeat implementation method is employed to obtain a discrete-time equivalent of the designed controller, which is a crucial step to implement any continuous-time controller on digital processors. Comparative analyses based on numerical simulations show that the developed sliding-mode controller shows several advantages over the forward Euler discretization method, which is widely used in the literature.

The way users interact with Virtual Reality (VR) environments plays a crucial role in shaping their experience of embodying an avatar. The perception of avatars significantly influences users’ behaviour based on stereotypes, a phenomenon known as the Proteus effect. Moreover, understanding how virtual representations suggest possibilities for action (affordances) has attracted considerable attention in the human-computer interaction community. The aesthetic features of avatars may thus signify false affordances, conflicting with users’ expectations and impacting perceived plausibility, presence and embodiment. To explore this topic, this research focuses on the perception of virtual hands, comparing ghost-like and gloved representations by leveraging their affordances. This paper presents a preliminary assessment of avatar-related affordances, and the protocol of the follow-up VR experiment. Our future contribution lies in a documented study on the coherence between user representation, suggested affordances and actual agency, aiming to inform designers and researchers on how it could enhance VR qualia.

The aim of this paper is to implement and compare different fatigue post-processing approaches for fatigue life assessment of complex parts. Inconel 718 is taken as an example, as it can exhibit several factors influencing fatigue life, such as mean stress, stress gradient and scale effects. Tests on different specimen geometries to exacerbate these effects were carried out at 550°C. The range of service operating life is between 103 and 106 cycles. A modelling chain was then set up. A structural calculation was performed using an elasto-visco-plastic behavior law to obtain the mechanical fields at cycle stabilize. These values were finally exploited by applying a post-processing treatment approach to predict the fatigue life of the structure. Two main types of post-processing approach were investigated: standard and probabilistic. The way in which the different factors influencing fatigue life are considered, depending on the approach used, was discussed. Finally, the probabilistic volume approach yields better results, thanks to its ability to consider mean stress, stress gradient and scale effects in the proposed formulation.

This study proposes a novel refined differential quadrature finite element (DQFE) framework for the size-dependent dynamic analysis of thick quadrilateral microplates, incorporating couple-stress effect and two kinematic variables. The proposed methodology addresses inter-element compatibility through fifth-order differential quadrature geometric mapping while achieving geometric adaptability via global-local coordinate transformation. Detailed procedures for assembling element matrices and imposing boundary conditions are provided. Validation through representative quadrilateral plate configurations confirms the efficacy of the proposed framework, with particular success in modeling asymmetric trapezoidal plates through experimental correlation. The enhanced DQFE framework further elucidates fundamental mechanisms governing cyclic quadrilateral microplate dynamics by systematically investigating three critical factors: material length scale parameters (MLSP), thickness-to-length ratios, and boundary constraint configurations. Mode localization characteristics are quantitatively assessed using the mode assurance criterion. The principal conclusions reveal: (1) Superior convergence characteristics of the fifty-degree-of-freedom DQFE formulation compared to conventional lower-order implementations; (2) Emergence of mode-transition phenomena driven by central angle variations; (3) Differential sensitivity of critical mode-transition angles to MLSP variations under contrasting boundary constraint intensities; (4) Characteristic modification of vibration mode contours induced by size-dependent effects.

Fiber-reinforced thermoplastic composites are increasingly valued for their light-weight properties, mechanical performance, and recyclability, yet the recycling process introduces microstructural heterogeneities that degrade their mechanical behavior. To address the challenges from a modeling point of view, this study proposes a Multiscale Thermodynamics-Informed Neural Network (MuTINN) approach to predict the nonlinear, anisotropic response of recycled glass fiber-reinforced polyamide 6 composites, with the primary aim of enabling structural simulations in significantly reduced time compared to traditional FE² approaches. The MuTINN framework integrates thermodynamic principles with artificial neural networks (ANNs) to capture the evolution of internal state variables and Helmholtz free energy, eliminating the need for memory-based networks. Finite element simulations of representative volume elements (RVEs) under diverse loading conditions are utilized to provide off-line data for the MuTINN. The latter accurately predicts stress, strain, and energy quantities, accounting for the anisotropic and heterogeneous nature of recycled materials. While trained using numerical simulations at 0◦ and 90◦ orientation specimens, the proposed framework succesfully predicts the response for specimens with 45◦ orientation with error in the maximum stress level up to 1.6%. The model is implemented into commercial finite element analysis (FEA) software via a Meta-UMAT framework, allowing efficient macroscale simulations. Validation against experimental data and finite element-based periodic homogenization confirms the framework’s accuracy for structural computations.