Free Contraction Research Articles

Development of enhanced force models to analyze the nonlinear hysteresis response of miniaturized pneumatic artificial muscles

Miniaturized pneumatic artificial muscles (MPAMs), designed to replicate natural muscle actuation, offer unique attributes such as a high power-to-weight ratio, flexibility, easy integration, and compactness, making them favourable for many applications. The present paper aims at the development of an accurate semi-analytical force model considering the effect of the bladder material and friction terms to predict the nonlinear force-deformation response of MPAMs during contraction and expansion cycles. Existing force models for MPAMs exhibit limitations to accurately capturing the force-deformation behaviours due to several simplification factors. This study enhances these models by integrating correction terms to accurately address the nonlinearity and frictional effects exhibited by MPAMs. An analysis of the hysteresis loops resulting from the cyclic loading and unloading of MPAMs under specific pressures is undertaken to compare different methodologies in order to determine the most accurate correction terms. To investigate the nonlinear behaviour of MPAMs, the stress-strain relationship of the bladder material and results from force-deformation experimental tests on the entire actuator are considered and for the effect of friction term, theoretical and empirical approaches are investigated. Results suggest that the theoretical force model based on analytical and empirical friction forces, respectively, slightly overestimates and underestimates the force experienced by MPAMs during contraction while slightly underestimate and overestimates during expansion, respectively. A comparative analysis between MPAMs featuring Ecoflex-50 silicone and Ecoflex30 + PDMS mixture as bladder materials has also been conducted to further investigate the effect of bladder materials on their force and contraction outputs under inlet pressures ranging from 0 kPa to 300 kPa. It is shown that the MPAM feauting Ecoflex-50 bladder, exhibits lower dead-band pressure and an overall reduced blocked force in comparison to MPAM with bladder made of Ecoflex30 + PDMS while exhibiting a substantially enhanced free contraction capacity.

Linear contraction of sand casting Mg–9Gd–3Y–0.5Zr alloy

The effect of geometric characteristics of castings on the linear contraction of sand casting Mg–9Gd–3Y– 0.5Zr alloy (VW93) was studied. The dimensions of free and restrained structure castings were precisely extracted by a 3D scanner and then used for the calculation of the contraction coefficient. The ratio of sand core volume to enveloping volume of casting (γ), was introduced to quantify the degree of constraint caused by sand cores. According to the statistical distribution of free contraction coefficients and the evolution of restrained contraction coefficients against γ, it is indicated that the free contraction coefficient of VW93 alloy equals 1.96%, and the restrained contraction coefficient declines linearly with the increasing γ, which supplies support on predicting the contraction of VW93 alloy through the geometric characteristic of castings.

Fetal echocardiography changes of the right ventricle of well-controlled gestational diabetes mellitus

BackgroundThere is few evidence of right ventricular (RV) function in fetuses with gestational diabetes mellitus (GDM). Therefore, the aim of this study was to assess the RV function of fetuses using routine and two-dimensional speckle-tracking echocardiography (2D STE) to determine the effects of well-controlled GDM in the third trimester.MethodsWe used a Philips Epiq7C ultrasound instrument to obtain RV data sets from 63 subjects from July 2019 to February 2022. We compared the free wall thickness (FWT), fractional area change (FAC), Tei index (TEI), tricuspid annular plane systolic excursion (TAPSE) and free wall longitudinal strain(FWLS)of the RV in mothers with well-controlled GDM and normal gestational age-matched fetuses.Results63 third trimester fetuses (32 GDM; 31 healthy controls) met the enrolment criteria. Significant differences in fetal RV were detected between the GDM and control groups for the FAC (36.35 ± 6.19 vs. 41.59 ± 9.11; P = 0.008) and the FWLS (-18.28 ± 4.23 vs. -20.98 ± 5.49; P = 0.021). There was a significant difference among the segmental strains of the base, middle and apex of the RV free wall in the healthy controls (P = 0.003), but in the GDM group, there was no statistical difference (p = 0.076). RV FWLS had a strong correlation with FAC (r = 0.467; P = 0.0002).ConclusionsIn well-controlled GDM, there was measurable fetal RV hypertrophy and significant systolic function decline, indicating the presence of ventricular remodeling and dysfunction. 2D-STE can evaluate the RV free wall contraction in a more comprehensive way.

Fruit Extract of Oil Palm (<i>Elaeis Guineensis</i> (Jacq.)) Inhibits Uterine Contractility in <i>Ex-Vivo</i> Mouse Models

Background: Different parts of Elaeis guineensis (EG) plants are used ethno-medicinally for treating numerous illnesses including abdominal contraction.
 Objectives: Thus, this study evaluated the inhibitory potential of the fruit-extract of EG on the uterine contractility in ex-vivo mouse models.
 Material and Methods: The effect of EG extract on spontaneous uterine contractions, oxytocin (OT)-induced uterine contractions, high potassium chloride induced uterine contractions and oxytocin-induced calcium free contraction were evaluated in adult non-pregnant female albino mice.
 Results: EG in a concentration dependent mode diminished spontaneous uterine contractions, while amplitude and frequency of contractions were inhibited significantly, but the frequency of contraction was at the highest concentration of EG. EG also produced a significant inhibition of the frequency of OT-induced contraction in calciumfree media.
 Conclusion: The aqueous fruit extracts of EG inhibited uterine contraction in the uterus through inhibition of intracellular calcium stores.

A novel design idea of high-stability silicon anodes for lithium-ion batteries: Building in-situ “high-speed channels” while reserving space

As one of the most promising anode materials for high-performance lithium-ion batteries, the commercial application of Si faces many dilemmas. In this paper, a facile method is developed to substantially improve the cycling stability of Si-based anodes. Firstly, based on the Kirkendall effect, the Si nanoparticle was transformed into multi-Si-void@SiO2 by heat-treatment. Then, the acid precipitation process was used to coat the lignin on the surface of the multi-Si-void@SiO2 structure via the hydrogen-bond interaction, and after in-situ carbonization, multi-Si-void@SiO2@lignin-based carbon composite was formed. The optimum electrode material maintained the specific capacity of 759 mA h g−1 after 1300 cycles at the current density of 1.0 A/g. The great electrochemical performance is attributed to the four components of voids, Si, SiO2 and lignin-based carbon (LC) performing their duties and synergistically, making the electrode exhibit excellent cycle stability. After long-term charge/discharge process, SiO2 layer is fully activated to construct Li4SiO4 and Li2O “high-speed channels”, providing a “bridge” for Si to connect with the outside. And the reserved space inside the structure is conducive to the free expansion and contraction of Si. Meanwhile, lignin, as a cheap and renewable carbon source, greatly reduces the cost of material preparation. Consequently, the multi-Si-void@SiO2@LC composite presented here provides a feasible strategy for the large-scale development of highly stable Si-based anodes.

Blackbody thermodynamics in the presence of Casimir’s effect

This paper is a study of the electromagnetic radiation at temperature T in a rectangular slab whose walls are made of a perfect conductor. The two large parallel walls of area A are apart by a distance . We take T, A, and d as thermodynamic parameters, obtaining the free energy from a procedure that involves the integration over the slab of the ensemble average of the stress–energy–momentum tensor calculated long ago by Brown and Maclay. Both thermodynamic regimes and are fully addressed. We show that certain thermodynamic quantities that are notoriously ill defined (or trivial) in ordinary blackbody thermodynamics are now well defined (or nontrivial) due to the presence of boundary conditions at the walls of the slab (‘Casimir’s effect’). The relationships among such quantities are fully explored and it is speculated that they may be experimentally checked. Stability is addressed, showing that electromagnetic radiation in the slab is thermally stable; but mechanically unstable. We investigate thermodynamic processes where temperature, internal energy, entropy and enthalpy are each taken to be constant, revealing rather atypical behaviors. For example, in sharp contrast with what one would expect from a gas, when , ‘free expansion’ gives place to ‘free contraction’ in accordance with the second law of thermodynamics. As a check of consistency of the formulae we remark that various Carnot cycles have been examined and verified that they correctly lead to Carnot’s efficiency.

Right ventricular cardiac resynchronization therapy in patients with right ventricular conduction delay and heart failure

Right ventricular cardiac resynchronization therapy in patients with right ventricular conduction delay and heart failure

Two devices to facilitate the perception of pelvic floor muscle contraction in the sitting position in women with urinary incontinence: comparative analysis

ABSTRACT The use of support devices may facilitate the perception of pelvic floor muscle (PFM) contraction, which is difficult to be performed. Therefore, this study aimed to compare the perception of PFM contraction in the sitting position during the use of two different support devices on women with PFM dysfunction. This is a cross-sectional study performed with 37 women with stress or mixed urinary incontinence (UI). All women performed three free PFM contractions sitting on a chair, followed by three contractions using each support device (sand pads and a cylindrical foam, which provide sciatic and perineal support, respectively). Women scored the perception of PFM contraction from 1 to 5, as well as the perception of facilitation of contraction (higher grades show better results) and discomfort (higher grades show more discomfort) when compared with free contraction. The cylindrical foam presented similar results to sand pads for the perception of PFM contraction (2.84±1.61 vs. 3.19±1.43; p=0.34) and facilitation of contraction (3.38±1.34 vs. 3.19±1.54; p=0.61), as well as for their discomfort (1.83±1.23 vs. 1.5±1.16; p=0.20). Of all women, 57% preferred sand pads. Thus, both sand pads (sciatic support) and the cylindrical foam (perineal support) improved the perception of PFM contraction and facilitation of contraction in the sitting position of women with PFM dysfunction when compared with sitting with no device. The two devices presented no difference between them.

Theoretical Control-Centric Modeling for Precision Model-Based Sliding Mode Control of a Hydraulic Artificial Muscle Actuator

Abstract Artificial muscles (AMs) traditionally rely on pneumatic sources of fluid power. The use of hydraulics can increase the power and force to weight and volume ratios of AM actuators. This paper develops a control-centric third-order single-input single-output (SISO) lumped-parameter dynamic model and sliding mode position controller based on Filippov's principle of equivalent dynamics for a braided hydraulic artificial muscle (HAM) actuator. The model predicts the nonlinear behavior of the HAM free contraction and captures the fluid and actuator nonlinear dynamic interactions in addition to the braid deformation. Model simulations are compared to experimental results for quasi-static pressurization, isometric pressurization, and open-loop square wave commands at 0.25, 0.5, and 1 Hz. Experiments of sine wave tracking at 0.25, 0.5, and 1 Hz and continuous square wave tracking at 0.067 Hz are conducted using a sliding mode controller (SMC) derived from the model. The SMC achieves a steady-state error of 6 μm at multiple setpoints within the actuator's 17 mm stroke. Compared to a proportional-integral-derivative (PID) controller, the SMC root-mean-square (RMS) error, mean error, and absolute maximum error are reduced on average by 53%, 61%, and 44%, respectively, demonstrating the benefit of model-based approaches for controlling HAMs.

Thermal Effect of Thin Elastic Plates

Thermal effect refers to the heat released or absorbed by the object in the changing process at a certain temperature. In this process, the stress inside the material will change. Thermal stress refers to the stress produced when the temperature changes, because of the external constraints and the internal constraints between the various parts, so that it can not completely free expansion and contraction.

Atrial Dyssynchrony Measured by Strain Echocardiography as a Marker of Proarrhythmic Remodeling and Oxidative Stress in Cardiac Surgery Patients.

Aging leads to structural and electrophysiological changes that increase the risk of postoperative atrial arrhythmias; however, noninvasive preoperative markers of atrial proarrhythmic conditions are still needed. This study is aimed at assessing whether interatrial dyssynchrony determined using two-dimensional speckle tracking echocardiography relates to proarrhythmic structural and functional remodeling. A cohort of 45 patients in sinus rhythm referred for cardiac surgery was evaluated by echocardiography and surface electrocardiogram the day before the intervention. Transmembrane potential, connexin, and potassium channel distribution, inflammatory, and nitrooxidative markers were measured from right atrial tissue obtained from patients. A difference greater than 40 milliseconds between right and left atrial free wall contraction confirmed the presence of interatrial dyssynchrony in 21 patients. No difference in relation with age, previous diseases, and 2-dimensional echocardiographic findings as well as average values of global longitudinal right and left atrial strain were found between synchronic and dyssynchronic patients. Postoperative atrial fibrillation incidence increased from 8.3% in the synchronic group to 33.3% in the dyssynchronic ones. P wave duration showed no difference between groups. Action potentials from dyssynchronous patients decreased in amplitude, maximal rate of depolarization, and hyperpolarized. Duration at 30% of repolarization increased, being markedly shorter at 90% of repolarization. Only the dyssynchronous group showed early and delayed afterdepolarizations. Atrial tissue of dyssynchronous patients displayed lateralization of connexin 40 and increased connexin 43 expression and accumulation of tumor necrosis factor-α in the intercalated disc. Tumor necrosis factor-α did not colocalize, however, with lateralized connexin 40. Nitroxidative marks and KATP channels increased perivascularly and in myocytes. Our results demonstrate that, as compared to a traditional surface electrocardiogram, the novel noninvasive echocardiographic evaluation of interatrial dyssynchrony provides a better identification of nonaged-related proarrhythmic atrial remodeling with increased susceptibility to postoperative atrial fibrillation.

Effect of slab stiffness on the geotechnical performance of energy piled-raft foundation under thermo-mechanical loads

Several studies have examined the geotechnical behaviour of energy piles; however, the behaviour of piled-raft foundations containing thermal piles is not fully understood. Because piled-raft foundations are optimally designed to bear mechanical loading from the top structure, the energy piles induce extra stress and bending moments on the raft foundation (slab) from the thermal loads, which may cause structural failure. The present study evaluated the thermo-mechanical behaviour of the energy piled-raft foundations using 3D FEM to simulate the geometrical and mechanical parameters of the pile group with an emphasis on slab stiffness. The interaction between the adjacent piles in a group as well as the bending moment induced through the slab have been evaluated. The results showed that, under thermo-mechanical loads, the stiffness of the slab prevented the free expansion and contraction of the energy pile. Increasing in slab thickness from 0.2 to 0.5 m reduced the energy-pile displacement about 50%. It also was observed that a heating load induced more stress than a cooling load along the longer piles. Cooling mechanical loads caused negative skin friction in the longer piles. It was shown that the equivalent pier method is generally applicable for a group of energy piles.

A mechanical model for McKibben pneumatic artificial muscles based on limiting chain extensibility and 3D application of the network alteration theories

Pneumatic Artificial Muscles (PAMs) mimic the behavior of skeletal muscles by generating contractile force when they are pressurized. Stiffness of these actuators depends on the applied pressure because the inner elastomeric tube exhibits non-linear mechanical behavior which also makes control of the actuator difficult. Therefore, it is crucial to obtain a precise mechanical model for these actuators. In this work, based on the theory of limiting chain extensibility, a new continuum mechanics-based model is developed for elastomeric McKibben PAMs to predict stiffness and output parameters such as free contraction, blocked force, and dead-band pressure during the actuation course. The developed model is consistent with network alternation theories, which allow predicting the softening observed in first cycles of inflation-deflation (Mullins effect). The established relations can predict variations of the actuation force due to the alternation of the material network parameters as a result of Mullins softening. In order to determine the material parameters of the bladder, uniaxial tensile tests have been conducted on a virgin silicon rubber. Cyclic tests have also been conducted on the fabricated PAMs in virgin and completely softened states to obtain their characteristic curves. It is concluded that, fractional evolution laws can be well combined with the developed model to predict the behavior of PAMs during cyclic deformations. It is observed that, even for contractions less than 25%, the maximum principal stretch in a PAM can exceed three which implies that, simple strain energy functions such as NeoHookean and Mooney-Rivlin should not be employed for PAMs. It is also concluded that, the Mullins softening increases the free contraction while makes no remarkable effect on the blocked force.

A publicly available virtual cohort of four-chamber heart meshes for cardiac electro-mechanics simulations.

Computational models of the heart are increasingly being used in the development of devices, patient diagnosis and therapy guidance. While software techniques have been developed for simulating single hearts, there remain significant challenges in simulating cohorts of virtual hearts from multiple patients. To facilitate the development of new simulation and model analysis techniques by groups without direct access to medical data, image analysis techniques and meshing tools, we have created the first publicly available virtual cohort of twenty-four four-chamber hearts. Our cohort was built from heart failure patients, age 67±14 years. We segmented four-chamber heart geometries from end-diastolic (ED) CT images and generated linear tetrahedral meshes with an average edge length of 1.1±0.2mm. Ventricular fibres were added in the ventricles with a rule-based method with an orientation of -60° and 80° at the epicardium and endocardium, respectively. We additionally refined the meshes to an average edge length of 0.39±0.10mm to show that all given meshes can be resampled to achieve an arbitrary desired resolution. We ran simulations for ventricular electrical activation and free mechanical contraction on all 1.1mm-resolution meshes to ensure that our meshes are suitable for electro-mechanical simulations. Simulations for electrical activation resulted in a total activation time of 149±16ms. Free mechanical contractions gave an average left ventricular (LV) and right ventricular (RV) ejection fraction (EF) of 35±1% and 30±2%, respectively, and a LV and RV stroke volume (SV) of 95±28mL and 65±11mL, respectively. By making the cohort publicly available, we hope to facilitate large cohort computational studies and to promote the development of cardiac computational electro-mechanics for clinical applications.

Pennate actuators: force, contraction and stiffness

Hierarchical actuators are comprised of multiple individual actuator elements arranged into a system, resulting in improved and expanded performance. Natural muscle tissue is a complex and multi-level example of hierarchical actuation, with its hierarchy spanning from the micrometer to the centimeter scale. In addition to a hierarchical configuration, muscle tissue exists in varying geometric arrangements. Pennate muscle tissue, denoted by its characteristic fibers extending obliquely away from the muscle tissue line of action, leverages geometric complexity to transform the relationship between fiber inputs and muscle tissue outputs. In this paper, a bioinspired hierarchical pennate actuator is detailed. This work expands on previous pennate actuator studies by deriving constitutive force, contraction, and stiffness models for a general pennate actuator, where the constituent fibers can be constructed from any linear actuator. These models are experimentally validated by studying a pennate actuator with McKibben artificial muscles constituting the actuator fibers. McKibben artificial muscles are used because they have a high force-to-weight ratio and are inexpensive to construct, making them an attractive candidate for hierarchical actuators and mobile robotics. Using the derived constitutive models, general pennate actuator performance is better understood by analyzing the transmission ratio, blocked force, and free contraction. Loaded contractions and stiffness during isotonic and isobaric contractions are also explored. The results allow for informed design decisions and an understanding of the associated tradeoffs when recreating the remarkable properties of pennate musculature. Future work will leverage the results of this paper to create an adaptive pennate actuator that is capable of changing configuration in response to force, contraction and stiffness demands.

Mechanical Effects on Right Ventricular Function From Left Bundle Branch Block and Cardiac Resynchronization Therapy

ObjectivesThe purpose of this study was to investigate how LBBB and CRT modify RV free wall function by direct ventricular interaction. BackgroundRight ventricular (RV) function influences prognosis in patients with left bundle branch block (LBBB) and cardiac resynchronization therapy (CRT). There is, however, limited insight into how LBBB and CRT affect RV function. MethodsIn 24 patients with LBBB with nonischemic cardiomyopathy, RV and left ventricular (LV) strain by speckle-tracking echocardiography was measured before and after CRT. Underlying mechanisms were studied in 16 anesthetized dogs with ultrasonic dimension crystals and micromanometers. ResultsPatients with LBBB demonstrated distinct early systolic shortening in the RV free wall, which coincided with the typical abnormal early systolic septal shortening. In animals, this RV free wall contraction pattern resulted in reduced myocardial work as a large portion of the shortening occurred against low pressure during early systole, coinciding with abnormal leftward septal motion. RV systolic function was maintained by vigorous contraction in the late-activated LV lateral wall, which pushed the septum toward the RV. CRT reduced abnormal septal motion and increased RV free wall work because there was less inefficient shortening against low pressure. ConclusionsLBBB reduces workload on the RV free wall because of abnormal septal motion and delayed activation of the LV lateral wall. Restoring septal and LV function by CRT increases workload in RV free wall and may explain why patients with RV failure respond poorly to CRT. (Contractile Reserve in Dyssynchrony: A Novel Principle to Identify Candidates for Cardiac Resynchronization Therapy [CRID-CRT]; NCT02525185)

Residual Thermal Strain Distribution Measurement of Underfills in Flip Chip Electronic Packages by an Inverse Approach Based on the Sampling Moir\xe9 Method

Residual deformation evaluation of underfill (UF) materials in flip chips is crucial to improve the reliability of electronic packages. In this study, we propose to evaluate the residual thermal strain distributions using an inverse method based on the sampling moiré technique. Even if a grid pattern is fabricated on the specimen at room temperature, the residual strain distributions at an arbitrary temperature relative to the specimen formation temperature can be successfully calculated. The residual strain distributions relative to the free contraction state at an arbitrary temperature can also be measured when the coefficient of thermal expansion is available. A thermal chamber for flip chips was designed under a laser scanning microscope. Using the proposed method, the normal, shear and principal internal strain distributions and deformation characteristics of two kinds of UFs in flip chips were investigated relative to 150 °C. The strains of the UF with low glass transition temperature (UF-A) concentrate near the die material, especially at the die corner, while the strain concentration of the underfill with high glass transition temperature (UF-B) mainly occurs at the die corner and the buffer layer. The maximum principal strain of UF-A is greater than that of UF-B around the die corner. The residual maximum principal strain distributions relative to the free contraction state at 25 °C were compared with the simulation results by the finite element method. The residual strain distribution trends from experiments are consistent with those from simulations.

Two-dimensional simulation of mechanical stresses during isothermal drying of Eucalyptus nitens wood

In this work, a two-dimensional mathematical model of the moisture transport and stress–strain phenomena during the conventional drying process of Eucalyptus nitens wood is presented. The model consists of a system of partial differential nonlinear second-order equations, where the moisture transport phenomenon is modeled on the concept of effective diffusion, and the stresses are modeled on the hypothesis of viscoelastic deformation, which is strongly linked to the strains by free contraction and mechano-sorption. The drying was assumed as an isothermal process and without effects of sustained loads over time (creep). Experimental tests were also carried out under constant psychometric conditions at 30/25 (°C/°C) in order to obtain transient distributions of moisture and stress. From these experimental data, the physical parameters of the proposed mathematical model were obtained by optimization in a context of inverse problem. The numerical solution of the model was obtained through the method of control volumes combined with finite elements. The results of transient distribution of moisture and stress correlate well with the experimental data.

Face-centered-cubic to body-centered-cubic phase transformation of Cu nanoplate under [100] tensile loading

ABSTRACTMolecular dynamics simulation was used to stretch Cu nanoplates along its [100] direction at various strain rates and temperatures. Under high strain rate and beyond the elastic limit, the Cu nanoplates underwent an unusual deformation mechanism with expansion along free surface lateral direction and contraction along the other lateral direction, which leaded to the face-centred-cubic phase transforming into unstressed body-centred-cubic phase. Under low strain rate, the deformation of the nanoplate went back to well-known dislocation mechanism. The face-centred-cubic to body-centred-cubic phase transformation mechanism was further discussed in terms of elastic stability theory and free surface stress effect.

In vitro vasoactive effects of dexmedetomidine on isolated human umbilical arteries

We aimed to investigate the vasoactive effects of dexmedetomidine on isolated human umbilical arteries and possible mechanisms involved. Human umbilical artery strips were suspended in Krebs-Henseleit solution and dose-response curves were obtained for cumulative dexmedetomidine before and after incubation with different agents; propranolol, atropine, yohimbine, prazosin, indomethacin, verapamil. Effects of calcium on cumulative dexmedetomidine-induced contractions were also studied. Cumulative dexmedetomidine resulted in dose dependent contraction responses. Incubation with propranolol (Emax: 93.3 ± 3.26 %), atropine (Emax: 92.0 ± 6.54 %), or indomethacin (Emax: 94.25 ± 2.62 %), did not attenuate dexmedetomidine-elicited contractions (p > 0.05). There were significant decreases in the contraction responses of cumulative dexmedetomidine with yohimbine (Emax: 12.1 ± 11.9 %), prazosin (Emax: 28.8 ± 4.6 %) and verapamil (Emax: 11.2 ± 13.6 %) (p < 0.05). In Ca+2 free medium contraction responses to cumulative dexmedetomidine was insignificant (Emax: 5.20 ± 3.42 %). Addition of cumulative calcium to the Ca+2 free medium resulted in concentration dependent increase in contractions (Emax: 64.83 ± 37.7 %) (p < 0.05). Dexmedetomidine induces vasoconstriction in endothelial-free umbilical arteries via both, α1- and α2-adrenergic receptors and also extracellular Ca+2 concentrations play a major role. β-adrenergic receptors, muscarinic cholinergic receptors, and inhibition of cyclooxygenase enzyme are not involved in this vasoconstriction (Fig. 3, Ref. 36).