•One in four pregnant women falls at least once during her pregnancy.•The pregnancy-induced weight gain results in a shift in segmental centers of mass.•We built a musculoskeletal model of the ...pregnant women.•The model includes changes in the thorax, pelvis, thighs, and legs weights.•Gait simulation results show a large impact on the lumbar moment.
One in four pregnant women falls at least once during her pregnancy. During pregnancy, the body undergoes tremendous vascular, hormonal, physiological, and psychological changes to accommodate the growing fetus. The pregnancy-induced mass gain of 10 to 25 kg is not evenly distributed and results in a large change in mass distribution and shift in segmental centers of mass. To accurately understand how the change in mass distribution leads to an increase in fall events, a musculoskeletal model of the pregnant body is necessary. Generic musculoskeletal models cannot accurately represent the morphology of pregnant women and the study of postural stability of pregnant women is limited by the lack of adapted musculoskeletal models.
Could a model reflecting the change in segmental inertia during pregnancy explain the pregnancy-related risk of falling?
We built a musculoskeletal model of the pregnant women, combining literature anthropomorphic measurements with generic models. We optimized the dimensions of the anthropomorphic model shapes to fit the average measurements of 25 pregnant women. The mass, center of mass, and inertia of each segment are then computed throughout pregnancy. Finally, the stance phase of a gait cycle was modeled using the pregnancy-specific and the generic models. The ankle, knee, hip and lumbar joint moments during gait were compared between the two models.
The built musculoskeletal model of the pregnant woman includes changes in mass and geometry of the thorax, pelvis, thighs, and legs. The model reproduces the change in lumbar curvature during pregnancy. Gait simulation results show a limited impact of pregnancy on the ankle, knee, and hip moment, but a large impact on the lumbar moment.
Such a musculoskeletal model will help elucidate the mechanisms leading to falls or low back pain during pregnancy.
The goal of this study was to explore the rate-dependent behavior of the stretch-induced polydomain-monodomain (PM) transition of a liquid crystal elastomer (LCE). The main-chain LCE was synthesized ...and then cross-linked in the nematic polydomain state. The PM transition caused a soft-elastic behavior, which was measured using uniaxial tensile tests at multiple strain rates and temperatures. The main finding was that we were able to apply the temperature-dependent shift factor determined for the small strain behavior and in the frequency domain to create master curves for the large-strain response in the strain rate domain. The soft elasticity phenomenon was absent from the stress-strain curve at equilibrium. The results also suggest that the relaxation mechanisms of the network, and not of the mesogen orientation, dominate the rate-dependent behavior. Finally, we observed a relatively slow recovery behavior, suggesting the presence of an additional slow relaxation mechanism.
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•Master curves of small and large strain behavior are built using one shift factor.•Master curves show the rate-dependence of the soft elasticity, absent at equilibrium.•The relaxation of the polymer network controls the rate-dependent soft elasticity.
A stable quiet stance is achieved by controlling the relative position of the center of pressure and the vertical projection of the center of mass. The best postural performances include efficient ...strategies to mitigate external perturbations. Footwear impacts postural stability and strategy by affecting cutaneous proprioception and ankle proprioception in the case of heeled shoes. The purpose of this study was to quantify the effects of four common footwear conditions, i.e. barefoot, sports, flats, and heels, on postural stability and strategy during quiet standing of healthy young women. Postural stability and strategy were assessed overall and in the antero-posterior and medio-lateral directions using five parameters: total sway, average center of pressure (COP) velocity, α value computed using detrended fluctuation analysis, hip over ankle ranges of motion, and power of the COP time series. Significant differences with barefoot were consistently found when wearing heels, namely a decrease in postural sway and average COP velocity. Results seemed counter-intuitive as they indicate an apparent increase in postural stability when wearing heels. A deeper analysis revealed a more complex scheme. A potential tightening of the motion when wearing heels, combined with an increase of the neutral plantarflexion angle, shifts the postural strategy towards a predominant hip strategy. Finally, proprioception did not play a key role. This study highlighted the complexity of the multifactorial interactions between footwear characteristics and postural strategies. Additional work is needed to develop footwear that will enhance postural stability of populations at risk, such as pregnant women or the elderly.
Liquid crystal elastomers (LCEs) are smart elastomers capable of a reversible shape change triggered by a stimulus such as heat or light. This change in shape is programmed into the material by ...orienting the mesogen molecules, often through the post-manufacturing alignment of the polymer chains by mechanical stretching. This method limits the possible orientations and necessitates a second curing step to lock the orientation in the structure. Direct ink writing allows for the curing of LCEs directly in an oriented state and for a fine control of the local orientation of the mesogens. The process parameters dictate the actuation and mechanical properties of the 4D-printed object, where time is the fourth dimension. We present in this paper a study of the influence of the printing speed and raster angle on the actuation strain and mechanical properties of the resulting LCE. Complex shape changes can be programmed into specimens that combine variations in printing angles and speeds. We printed two dimensional specimens actuating into helicoids and hinges. Results show the expected influence of printing speed on the level of orientation of the mesogens and on the actuation strain; that is faster printing equals more orientation and actuation strain. The change in raster angle demonstrates the immediate impact of incompatible strains in the structure, as the flat specimen (i.e. a printed rectangle of a couple of layers thick) actuates in a controlled 3D configuration. Finally, the hinge and helicoid specimens show the versatility of 4D-printed LCE systems, where the folding angle of the hinge or the pitch of the helicoid can be programmed through basic geometry, angle, and speed control at the printing stage. This transformative step in the preparation of LCE actuators opens the door to precise customization exploiting the mobility of mesogens on the polymer chains during printing and the flexibility of the direct ink writing process.
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•Direct ink writing simultaneously orients and cures the liquid crystal elastomer.•We study the influence of printing speed and raster angle on actuation and mechanical properties.•Faster printing improves orientation and actuation strain.•Incompatible strains lead flat specimens to actuate in a controlled 3D configuration.•Hinge folding angle or helicoid pitch can be programmed through geometry, angle, and speed.
Liquid crystal elastomers (LCEs) are a class of smart elastomers exhibiting unusual mechanical behavior, including large energy dissipation and soft elasticity under uniaxial tensile loading. LCEs ...are composed of liquid crystal molecules, called mesogens, linked by a network of polymer chains. During deformation, the mesogens orient in the direction of the loading, leading to soft elasticity, which is an increase in strain at constant stress. The combination of mesogen rotation and intrinsic polymer viscoelasticity leads to a nonlinear viscoelastic soft elastic behavior. The aim of this paper is to investigate the coupling between the viscoelastic mechanisms and soft elasticity in main chain LCEs. We propose a rheological model in which the mesogen rotation during deformation is represented by a reversible slider while viscoelastic relaxation mechanisms are modeled as series of Maxwell elements coupled or decoupled with mesogen rotation. Fitting this model to experimental data demonstrate that the coupling between polymer chain viscoelasticity and mesogen rotation is partial, i.e. the long-time relaxation mechanisms are coupled and the short-time relaxation mechanisms are decoupled from mesogen rotation. Furthermore, we show that the viscosity of mesogen rotation is not necessary to properly predict the elastic modulus during the soft elasticity but it is needed to properly predict the initiation of the phenomenon.
L’hépatite auto-immune (HAI) de type 2 est une forme rare et sévère, d’apparition rapidement progressive de l’hépatite auto-immune de l’adulte. La phytothérapie sur des lésions hépatiques ...pré-existantes peut mettre en jeu le pronostic vital par hépatite fulminante. Nous vous rapportons un cas de plante de la famille des Rhamnacées, connu pour son effet hépatotoxique, le Nerprun alaterne.
Madame, A.S., âgée de 26 ans, diabétique type 1 qui présente un tableau d’hépatite aiguë grave suite à la prise d’une plante hépatotoxique « NERPRUN ALATERNE » après apparition d’un ictère cutanéomuqueux franc isolé, sans autres signes de cholestase, d’hépatopathie chronique ou d’hypertension portale. À la biologie, on retrouve un syndrome de cytolyse à 40 XN, légèrement préexistant avant la prise du toxique, des signes d’insuffisance hépatocellulaire (TP et facteur V bas) et un syndrome de cholestase modéré. Le diagnostic d’HAI type 2 est retenu devant un bilan d’auto-immunité en faveur (une hyper IgG à l’EPP, FAN+ et Ac anti-LC 1 fortement positifs) et confirmé par la biopsie hépatique (aspect d’hépatite chronique active avec hépatite sévère d’interface). Un traitement à base de corticoïde, Prednisolone 01mg/kg/j a été initié associé à l’Azathioprine. Nous avons noté une réponse favorable à j 7 de traitement (régression de l’ictère, baisse de la cytolyse à 4 XN et normalisation du TP).
L’effet hépatotoxique du Nerprun Alaterne associé à la gravité de l’hépatite auto-immune de type 2, bien que rare, expose à des lésions hépatiques irréversibles en l’absence de prise en charge précoce et adaptée pouvant nécessiter la transplantation hépatique en urgence.
Roll‐to‐Roll manufacturing aims at scaling ultraviolet‐ and thermally cured nanoimprint lithography (UV‐NIL, T‐NIL) to commercial production speeds and volumes. Winding is the only convenient way of ...storing large quantities of nanoimprinted webs as they await unwinding in sequential R2R processes with distinct transport speeds. At production speeds, the imprinted resin is still chemically evolving when the imprinted web enters the winder, through a phenomenon called dark curing. The viscoelastic resin at various curing stages deforms under the contact pressure due to winding. This study is concerned with the impact of the contact pressure on the imprinted peak heights and potentially the functionality of the nanoimprinted surface. We develop a multiscale numerical model of the winding of the imprinted web. First the evolving properties of the resin through time are characterized, combining the effect of dark curing and viscoelasticity on the time‐dependent properties. Second, a finite element model of the imprinted web uses the resin mechanical properties to determine the effective properties of the imprinted web. Finally, the winding model determines the pressure and resulting strain of the imprints in the wound roll. The surface creep is quantified. This prediction will establish how and how long the imprinted materials should be wound.
In this paper, a novel opto-digital image encryption technique is proposed by introducing a new non-linear preprocessing and using the multiple-parameter discrete fractional Fourier transform ...(MPDFrFT). The non-linear preprocessing is performed digitally on the input image in the spatial domain using a piecewise linear chaotic map (PLCM) coupled with the bitwise exclusive OR (XOR). The resulting image is multiplied by a random phase mask before applying the MPDFrFT to whiten the image. Then, a chaotic permutation is performed on the output of the MPDFrFT using another PLCM different from the one used in the spatial domain. Finally, another MPDFrFT is applied to obtain the encrypted image. The parameters of the PLCMs together with the multiple fractional orders of the MPDFrFTs constitute the secret key for the proposed cryptosystem. Computer simulation results and security analysis are presented to show the robustness of the proposed opto-digital image encryption technique and the great importance of the new non-linear preprocessing introduced to enhance the security of the cryptosystem and overcome the problem of linearity encountered in the existing permutation-based opto-digital image encryption schemes.
•A novel opto-digital image encryption technique is proposed by introducing a new non-linear preprocessing.•This non-linear preprocessing is performed digitally on the input image in the spatial domain using a piecewise linear chaotic map coupled with the bitwise exclusive OR.•The non-linear preprocessing is of great importance to enhance the security of the cryptosystem and overcome the problem of linearity encountered in the existing permutation-based opto-digital image encryption schemes.
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