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The counter-rotating mechanism makes a substantial contribution to balance-movement coordination during the anticipatory period of gait initiation
No full textInternational audienceMaintaining balance during gait initiation is essential for mobility and functional independence. The transition from a postural state to steady-state gait relies on two mechanisms to accelerate the whole-body centre of mass (WBCoM): moving centre of pressure (CoP); and counter-rotating segments to modulate internal whole-body angular momentum (HM). While the moving CoP mechanism is well-understood and known to generate mechanical instability, the role of the counter-rotating mechanism is less clear. Therefore, the present study quantified the contribution of the counter-rotating mechanism and explored its coordination with the moving CoP mechanism during the anticipatory period of gait initiation. Based on a sample of 13 healthy participants, we computed the time evolution of CoP, HM, the coefficient of cancellation (i.e., the extend to which segmental angular momenta counterbalance each other), and the relative contribution of each mechanism to WBCoM acceleration. We tested whether the contribution of the counter-rotating mechanism was significantly different from zero using a Statistical Parametric Mapping t-test. In the frontal plane, the counter-rotating mechanism did not appear to play a substantial role. However, in the sagittal plane, we found that: (1) the period of mechanical instability was longer than the period that have been identified based on the moving CoP mechanism alone; (2) rotational instability was reduced in anticipation of unipedal support; and (3) the counter-rotating mechanism significantly contributed to WBCoM forward acceleration. Overall, our findings emphasise the critical role of the counter-rotating mechanism in the sagittal plane for balance-movement coordination. Considering the counter-rotating mechanism appears important for understanding, assessing, and developing interventions for individuals with balance impairments
Mechanical instability lasts longer than the backward centre of pressure shift during gait initiation
No full textInternational audienceIntroduction: Ensuring balance is vital for everyday movement. During gait initiation, a common paradigm to assess balance-movement coordination in humans, mechanical instability must be generated during the anticipatory period to initiate movement. A first phase of the anticipatory period contributing to generate mechanical instability was described, with a backward centre of pressure (CoP) shift, accelerating the whole-body centre of mass (WBCoM) forward [1]. However, this analysis does not consider the rotational contribution of the free segments. The internal whole-body angular momentum (HM) around the mediolateral axis also exhibited a first phase where HM is directed forward, followed by a second one where some segments rotated in the opposite direction to limit the mechanical instability and the increase in HM magnitude, interpreted as a stabilising mechanism [2]. The current study aims to determine whether the forward directed HM only corresponds to the mechanical instability generated by the backward CoP shift, or whether the mechanical instability lasts longer than the backward CoP shift.Methods: Thirteen healthy participants (23.5 ± 4.2 years, 1.72 ± 0.1 m, 65.5 ± 8.8 kg) performed three gait initiation trials. Participants were asked to voluntarily initiate gait and walk for five meters from a hip-width upright standing posture. Ground reaction forces and moments were recorded by four force plates (Sensix) at 2000 Hz, lowpass filtered at 20 Hz and used to compute the CoP. The trajectories of 54 markers placed on anatomical landmarks were recorded with 15 infrared cameras (Vicon) at 200 Hz, lowpass filtered at 10 Hz. HM was computed as the sum of the segment angular momenta transferred to the WBCoM based on a 13 segments whole-body model. The coefficient of cancellation, defined as the amount of segment angular momentum compensating each other divided by the total magnitude of HM was then computed [3]. The duration of the mechanical instability phase was computed using the CoP and HM methods. For both methods, the phase began when the WBCoM acceleration was larger than the mean +3 standard deviations measured during quiet standing. The instability phase ended when the CoP was the most backward and toward the swing limb [1], and when the time derivative of HM became positive (i.e., when some segments started to rotate in the opposite direction), respectively. We compared the phase durations computed by each method using a paired-sample t-test.Results: The duration of the mechanical instability phase based on the CoP was significantly shorter than the one based on HM (260 ± 73 vs. 368 ±101 ms, p<0.001).[Figure 1: Average and standard deviation of internal whole-body angular momentum (HM, top) and coefficient of cancellation (bottom) during the anticipatory period, ending at foot-off. The black and red vertical lines represent the phase delimitation based on the CoP and HM methods, respectively.]Discussion: Our results suggest that the whole-body continues to rotate forward after the end of the backward CoP shift (after the black vertical line in Figure 1), without any regulation from opposite segment rotation, as indicated by a low coefficient of cancellation until change in the time derivative of HM. This suggests that mechanical instability is not large enough to initiate gait at the end of the backward CoP shift, and that the whole-body must continue to rotate forward before any regulation appears. This phase of mechanical instability would not have been detected by analysing only the CoP. These results being obtained on young healthy participants, future studies should assess if this longer period of mechanical instability is also present in older participants and/or participants with balance deficits.References:1. Crenna et al, Exp Brain Res, 172 :519-532, 20062. Bechet et al, MBJ, 1, 20243. Bennet et al, Hum. Mov. Sci, 29 :114-124 : 201
Towards enhancing chiro-optical and magneto-optical properties of magnetic nanocrystals by surface plasmons
No full textInternational audienceMagneto-optics, a research area that studies the interaction between magnetic fields and light, has recently made remarkable progress due to a better understanding of light-matter interactions at the nanoscale. The integration of magnetic and plasmonic functionalities with nanometric resolution offers exciting opportunities, especially due to the ability of plasmonic phenomena to enhance magneto-optical responses. In this respect, wet-chemistry methods are particularly useful in fine-tuning the magnetic and plasmonic properties of nanocrystals, enabling the creation of a large library of hybrid colloidal systems with enhanced magneto-optical features.This Perspective explores recent advancements in these magnetoplasmonic hybrid nanomaterials and puts special focus on a key area of interest, that is, the nascent field of chiral plasmonics. Metal nanocrystals with intrinsic chiroptical features can lead to a combination of chiral plasmonics and magneto-optics effects when interacting with the magnetic counterpart, paving the way toward the establishment of a systematic and comprehensive roadmap for the pre-design and fabrication of chiral magneto-plasmonic systems. The implications of this progress are profound, offering both fundamental insights and promising technological applications.</p
Mechanical properties of ZrCuAlx thin film metallic glasses and nanolaminates: experiments and first principle calculations
No full textInternational audienceThe synthesis of advanced thin film metallic glasses (TFMGs) with tailored composition and engineered microstructures capable to provide a large combination of mutually exclusive mechanical properties (i.e. high strength and ductility) mitigating the shear band (SB) instability, is an open research topic. Here, I will present recent results involving two (2) strategies to finely to improve the mechanical behaviour of TFMGs including (i) the addition of intrinsically ductile elements (Al) and the (ii) development of fully amorphous nanolaminated structures.Firstly, I will provide a holistic picture about the relationship between atomic structure, mechanical properties, and thermal stability of ZrCuAlx TFMGs varying the Al content from 0 to 12 at.%, carrying out a broad characterization involving experiments and ab initio molecular dynamic simulations (AIMD). I will show that the addition of Al resulted in a change of average interatomic distances by ∼10 pm with the formation of shorter bonds (Al-Zr and Al-Cu), influencing the mechanical response (shear/elastic moduli and hardness) which increases by ∼15% for 12 at.% Al. Moreover, tensile tests on polymer substrate revealed a maximum value for the crack initiation strain of 2.1% for ZrCuAl9, while the strain-to-failure rapidly decreases at higher Al contents. The observed reduction in damage tolerance is correlated to a transition in atomic configuration. Specifically, a maximum in density of full and defective icosahedral cluster population is observed at 9 at.% Al, inducing a more shear-resistant behavior to the material [1].Then, I will discuss the fabrication of ZrCu/ZrCuAl9 nanolaminates with different nanoscale bilayer period (Λ, from 200 down to 50 nm). I will show the combined effect of local chemistry variation and nanointerface density influences the propagation of SBs with enhanced plastic deformation (> 10 %) is observed for Λ = 100 and 200 nm during micropillar compression, but accompanied by a reduction of the yield strength. In contrast, for Λ = 50 nm, deformation is dominated by catastrophic SB events, while the yield strength returns to that of the monolithic films of ∼2–2.5 GPa [2].Overall, I will provide guidelines to the design of compositional and microstructural-tailored TFMGs with tuned mechanical properties with potential for applications.REFERENCES[1] C. Poltronieri … M. Ghidelli, Acta Mater., 258, 119226, (2023).[2] C. Poltronieri,… M. Ghidelli, Scripta Mater., 259, 116571, (2025)
Design optimization of longitudinal studies using metaheuristics: Application to lithium pharmacokinetics
No full textInternational audienceLithium is recommended as a first line treatment for patients with bipolar disorder. However, only certain patients show a good response to the drug, and the variability and tolerability of lithium response are poorly understood. Greater precision in the early identification of individuals who are likely to respond well to lithium is a significant unmet clinical need. We create optimal designs to better understand the pharmacokinetic exposition of lithium for patients with and without a genetic covariate. From a Fisher information matrix based method, we find different optimal designs for estimating various parameters in a complicated pharmacokinetics/pharmacodynamics nonlinear mixed effects model with multiple physician specified constraints. Our approach uses flexible state-of-the-art metaheuristics to find various types of efficient designs, including multiple-objective optimal designs that can balance the competitiveness of the objectives and deliver higher efficiencies for more important objectives. Results from this article will be used as part of a broader study to implement efficient designs to better understand the exposition of sustained-release lithium in patients with bipolar disorder
EXISTENCE OF TWO SPONTANEOUS NERVE INFLUX OF DIFFERENT VELOCITIES IN A GIVEN AXON, NUMERICAL EVIDENCE AND SENSITIVITY ANALYSIS
No full textWe prove in this paper, numerically, that there exists at leas two propagation velocities in the original Hodgkin-Huxley system, obtained by a numerical method coming from the analysis of the unstable manifold of the associated ODE. None of the velocities is the one identified by Hodgkin and Huxley. We prove numerically that a sensitivity analysis can be performed on these two velocities and indicate small variations when the constants varies
A polysaccharide-based hydrogel platform for tumor spheroid production and anticancer drug screening
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Risk factors for non-isolation of patients admitted for pulmonary tuberculosis in a high-incidence department: a single-centre retrospective study
No full textInternational audienceBackgroundPulmonary tuberculosis (PTB) is an airborne disease, warranting the identification of suspected cases on admission, and their hospitalization in individual rooms with the implementation of airborne supplementary precautions (ASPs).AimTo identify the frequency of non-isolated PTB and the factors associated with the delay in implementing ASPs in a high-prevalence hospital.MethodsThis retrospective observational study included patients with at least one Mycobacterium tuberculosis-positive specimen. Patient demographic and clinical data, as well as data related to the mode of admission, were collected. Univariate and multi-variate statistical analyses were performed.FindingsDuring the study period, 256 patients were included. Among them, 134 (52.3%) had PTB (75% males, median age 39 years, 70% foreign-born). Among these patients, 46 (34%) were isolated beyond 24 h of admission. The average time to implement ASPs was 4.3 days, and seven patients (5.2%) were not isolated throughout their hospital stay. Multi-variate analysis indicated that three factors were associated with isolation. Previous consultation with a general practitioner was associated with greater likelihood of isolation, whereas admission through the emergency department was not. The presence of so-called ‘cardinal clinical signs’ and a suggestive chest x-ray were also associated with greater likelihood of isolation. Finally, European patients were isolated less frequently than foreign-born patients.ConclusionIn this study, 34% of patients admitted with PTB were not isolated on admission. The likelihood of non-isolation was three times higher in cases admitted via the emergency department, and European patients were isolated less frequently than foreign-born patients. The presence of cardinal signs and prior consultation with a general practitioner were associated with greater likelihood of isolation
OneEncoder: a lightweight framework for efficient multimodal training
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