Dynamic Elasticity Research Articles

Stoneley wave at the interface of elastic-nematic elastomer half spaces

In this paper the Stoneley wave propagation along the interface of the elastic-nematic elastomer half spaces is investigated. Firstly, the characteristic equation of the Stoneley wave along the interface is obtained. Then the influence of the distinct parameters of nematic elastomers on the propagation characteristic of the Stoneley wave are discussed in detail. The particle traces of the Stoneley wave in both sides are plotted, and the propagation characteristic of the waves across the interface of anisotropic viscoelastic-isotropic elastic half spaces are clarified. The results show that the Stoneley wave displays particular properties that are different from those at the liquid-solid or (visco)elastic-(visco)elastic solid interfaces, which is related to the dynamic soft elasticity of the nematic elastomer. There exists a trigger frequency above which the Stoneley wave starts to form. This work provides a potential strategy for the intelligent tuning of interface waves based on nematic elastomers.

Simulation of generally shaped 3D elastic body dynamics with large motion using transfer matrix method incorporating model order reduction

Simulation of generally shaped 3D elastic body dynamics with large motion using transfer matrix method incorporating model order reduction

Research on Rigid–Elastic Coupling Flight Dynamics of Hybrid Wing Body Based on a Multidiscipline Co-Simulation

Due to the special aerodynamic layout and mass distribution, the natural frequency differences between the hybrid wing body (HWB)’s rigid-body motion modes and the fuselage structure elastic modes are smaller compared to conventional aircraft, resulting in the disappearance of the decoupling relationship between the HWB’s rigid-body motion and the elastic motion of the airframe structure. For the above reason, the traditional analysis approach based on the rigid-body assumption is no longer applicable when analyzing the flight dynamics of an HWB aircraft, and a shift must be made to an analysis method that takes into account aeroelastic effects. Therefore, in this paper, a time-domain co-simulation program combining the computational fluid dynamics (CFD) method with computational structure dynamics (CSD) and rigid-body dynamics (RBD) is developed to investigate the effect of a rigid–elastic coupling effect on the flight dynamics of the HWB and this co-simulation method is more advantageous in the calculation of unsteady aerodynamics compared to existing methods of rigid–elastic coupling dynamics analysis. By means of the co-simulation technology, this paper completed a series of simulations, based on which the influence of rigid–elastic coupling effect on the short-period dynamic characteristics of aircraft was studied.

Demulsification of oily wastewater driven by an amine functionalized cellulose derived from waste cotton textiles

An ANPC demulsifier for oily wastewater (OW) was obtained through amine functionalization of regenerated cellulose derived from waste cotton textiles by a hydrothermal process. ANPC was systematically analyzed through morphology, composition, chemical properties, and interfacial properties. The results showed that ANPC had good interfacial activity and a strong ability to reduce the interfacial tension. The bottle test displayed that the light transmittance of separated water (LT) could reach 92.5% and the corresponding oil removal rate (ORR) was 99.4% when the ANPC dosage was 125 mg/L at room temperature. Importantly, ANPC could be adopted at a wide pH range and high salinity. Also, the possible demulsification mechanism was explored by wettability, interfacial activity, interfacial film self-assembly, dynamic interfacial tension, Zeta potential, elasticity modulus and micrographs. This study provides a biological derived demulsifier with low cost and high efficiency.

Dynamic Arterial Elastance to Predict Mean Arterial Pressure Decrease after Reduction of Vasopressor in Septic Shock Patients.

After fluid status optimization, norepinephrine infusion represents the cornerstone of septic shock treatment. De-escalation of vasopressors should be considered with caution, as hypotension increases the risk of mortality. In this prospective observational study including 42 patients, we assess the role of dynamic elastance (EaDyn), i.e., the ratio between pulse pressure variation and stroke volume variation, which can be measured noninvasively by the MostCare monitoring system, to predict a mean arterial pressure (MAP) drop > 10% 30 min after norepinephrine reduction. Patients were divided into responders (MAP falling > 10%) and non-responders (MAP falling < 10%). The receiver-operating-characteristic curve identified an area under the curve of the EaDyn value to predict a MAP decrease > 10% of 0.84. An EaDyn cut-off of 0.84 predicted a MAP drop > 10% with a sensitivity of 0.71 and a specificity of 0.89. In a multivariate logistic regression, EaDyn was significantly and independently associated with MAP decrease (OR 0.001, 95% confidence interval 0.00001-0.081, p < 0.001). The nomogram model for the probability of MAP decrease > 10% showed a C-index of 0.90. In conclusion, in a septic shock cohort, EaDyn correlates well with the risk of decrease of MAP > 10% after norepinephrine reduction.

The Role of Income and Food Prices in Diet-Related Greenhouse Gas Emissions in China: A Path towards a Sustainable Diet.

China has undergone rapid economic growth and diet transition over the past decades, along with environmental challenges. To help to achieve carbon peaking by 2030, this study investigates the time-variable diet-related greenhouse gas emissions (GHGEs) from 2000 to 2020 and examines the responses of food demands and diet-related GHGEs to an increase in per capita income and animal-based food prices. Based on the Almost Ideal Demand System model, addressing the problem of the endogeneity of food expenditure, we estimate the demand elasticities for six food groups and analyze their changing trends with time. Then, we perform two projections. One is to project the impacts of income growth on food demands and diet-related GHGEs, taking into consideration dynamic income elasticities as per capita income increases; the other is to project the effects of an increase in prices of different animal-based foods on food demands and diet-related GHGEs. Our results reveal that diet-related agricultural GHGEs show a continued increase in the short term, but the increased effect tends to decline gradually. The dominant driver of increased diet-related GHGEs is the increased consumption of beef, mutton, and pork. However, an increase in prices of beef and mutton; pork; and poultry and eggs can reduce diet-related GHGEs, while a decrease in the prices of aquatic products can also deliver a significant decrease in GHGEs. The results imply that policymakers should take an interest in the environmental impacts of diet transition and promote a more sustainable diet structure.

Molecular simulations and NMR reveal how lipid fluctuations affect membrane mechanics

Lipid bilayers form the main matrix of functional cell membranes, and their dynamics underlie a host of physical and biological processes. Here we show that elastic membrane properties and collective molecular dynamics (MD) are related by the mean-square amplitudes (order parameters) and relaxation rates (correlation times) of lipid acyl chain motions. We performed all-atom MD simulations of liquid-crystalline bilayers that allow direct comparison with carbon-hydrogen (CH) bond relaxations measured with NMR spectroscopy. Previous computational and theoretical approaches have assumed isotropic relaxation, which yields inaccurate description of lipid chain dynamics and incorrect data interpretation. Instead, the new framework includes a fixed bilayer normal (director axis) and restricted anisotropic motion of the CH bonds in accord with their segmental order parameters, enabling robust validation of lipid force fields. Simulated spectral densities of thermally excited CH bond fluctuations exhibited well-defined spin-lattice (Zeeman) relaxations analogous to those in NMR measurements. Their frequency signature could be fit to a simple power-law function, indicative of nematic-like collective dynamics. Moreover, calculated relaxation rates scaled as the squared order parameters yielding an apparent κC modulus for bilayer bending. Our results show a strong correlation with κC values obtained from solid-state NMR studies of bilayers without and with cholesterol as validated by neutron spin-echo measurements of membrane elasticity. The simulations uncover a critical role of interleaflet coupling in membrane mechanics and thus provide important insights into molecular sites of emerging elastic properties within lipid bilayers.

Stroke Volume and Arterial Pressure Fluid Responsiveness in Patients With Elevated Stroke Volume Variation Undergoing Major Vascular Surgery: A Prospective Intervention Study

The identification of potential hemodynamic indicators to increase the predictive power of stroke-volume variation (SVV) for mean arterial pressure (MAP) and stroke volume (SV) fluid responsiveness. A prospective intervention study. At a single-center university hospital. Nineteen patients during major vascular surgery with 125 fluid interventions. When SVV ≥13% occurred for >30 seconds, 250 mL of Ringer's lactate were given within 2 minutes. Hemodynamic variables, such as pulse-pressure variation (PPV) and dynamic arterial elastance (Edyn), were measured by pulse power-wave analysis. The outcomes were MAP and SV responsiveness, defined as an increase of at least 10% of MAP and SV within 5 minutes of the fluid intervention. Of the fluid interventions, 48% were MAP-responsive, and 66% were SV-responsive. The addition of PPV and Edyn cut-off values to the SVV cut-off decreased sensitivity from 1-to-0.66 to-0.82, and concomitantly increased specificity from 0-to- 0.65-to-0.93 for the prediction of MAP and SV responsiveness in the authors' study setting. The areas under the receiver operating characteristic curves of PPV and Edyn for the prediction of MAP responsiveness were 0.79 and 0.75, respectively. The areas under the receiver operating characteristic curves for PPV and Edyn to predict SV responsiveness were 0.85 and 0.77, respectively. The PPV and Edyn showed good accuracy for the prediction of MAP and SV responsiveness in patients with elevated SVV during vascular surgery. Either PPV or Edyn may be used in conjunction with SVV to better predict MAP and SV fluid responsiveness in patients undergoing vascular surgery.

Undirected graphical model of adjacency matrix for dynamic elasticity in polyelectrolyte hydrogels

Molecular network plays a critical role in determining dynamic elasticity of soft condensed polymers, e.g., their varied cross-linking densities and end-to-end distances with changed Young's moduli. Although it has been studied for decades, the coupling relationship between vertices and edges of molecular networks is not well understood, mainly because the degree of the crosslinking points and asymmetry molecular networks have not been considered in the previously models. In this study, a graph theory was employed to formulate an undirected graphical model and describe the coupling between vertices and edges in molecular networks, based on which the dynamic elasticity of polyelectrolyte hydrogel was modeled. From the Kirchhoff graph theory and bead-spring model, the coupling relationship between vertices and edges was obtained using end-to-end distance and viscosity parameters. Combining the Watts–Strogatz model and kinetic probability, the coupling between vertices and edges for the polyelectrolyte network was studied. Furthermore, an adjacency matrix with eigenvalue, number of vertices and mean degree was proposed to formulate constitutive relationships including dynamic elasticity and stress-strain, according to rubber elasticity theory and Mooney-Rivlin model, respectively. The linking between the vertices and edges determines the network structure and dynamic elasticity of the polyelectrolyte hydrogel. Based on the graph theory, the vertices and edges are encoded by adjacency matrix, which is proposed to describe the dynamic elasticity of symmetric and asymmetric network structures using the crosslinking density and end-to-end distance. Finally, effectiveness of the undirected graphical model was verified using both finite element analysis and experimental results of polyelectrolyte hydrogels reported in literature.

Cavitation over solid surfaces: microbubble collapse, shock waves, and elastic response

We discuss the interaction of the strongly nonlinear fluid motion induced by the collapse of a vapor microbubble over a planar surface and the elastic dynamics of the underlying solid. The fluid is described using an extension of the Navier-Stokes equations endowed with distributed capillary stresses in the context of a diffuse interface approach. The collapse of the bubble is triggered by overpressure in the liquid and leads to an intense jet that pierces the bubble, changing the bubble topology from spheroidal to toroidal, and impinges the solid wall inducing an intense and strongly localized load. Moreover, at bubble collapse, a compression wave is launched into the liquid surrounding the bubble. By propagating along the solid surface, the compression wave combined with the liquid jet excites the dynamics of the elastic solid, producing a complex system of waves, including, longitudinal, transversal, and Rayleigh waves, propagating in the solid. It is conjectured that the intense deformation of the solid induced by the strongly localized liquid jet may lead to the plastic deformation of the solid producing the surface pitting observed in many applications subject to cavitation-induced material damage.

A unified high-order model for size-dependent vibration of nanobeam based on nonlocal strain/stress gradient elasticity with surface effect

In this work, a unified high-order nanobeam model considering various high-order shear deformation beam theories is established to investigate the vibration response of nanobeam on the basis of two-phase local/nonlocal strain and stress gradient theory, as well as surface elasticity theory. The unified model also includes the Euler-Bernoulli beam model and Timoshenko beam model. Herein, the elastic dynamics governing equations and boundary conditions are derived using Hamilton's principle, and the analytical solutions, such as exact formulas for natural frequencies, are obtained by employing the Navier method for simply supported boundary conditions. The effects of local volume fraction, nonlocal parameter, material length scale parameter, shear deformation and surface energy in stress and strain-driven models are analyzed in detail, respectively. The parametric studies reveal that the two scale parameters (nonlocal parameters and material length characteristic parameters) have opposite effects on the stiffness of the nanobeams in the two driving models, while the surface parameters have the same effect on the stiffness of the two driving models. The influence of the slenderness ratio on the surface effect and scale effect is opposite, meaning that the increase of the slenderness ratio deepens the influence of the surface effect but weakens the influence of the scale effect. There are also differences in the effects of higher-order modes on the two effects. Higher modes lead to more significant scale effects, but the effect of higher modes on surface effects depends on the surface elastic properties of the material. We also find that the introduction of surface elasticity increases the gap between the TBT and other higher-order beams, which indicates the prediction results of the higher-order beam model are more accurate when both surface and nonlocal effects are considered. In addition, it is represented that the surface elasticity makes aluminum nanobeams exhibit a stiffness softening effect, while the effect of surface elasticity on the stiffness of silicon nanobeams is significantly dependent on the slenderness ratio and the number of modes.

Learning to Ascend Stairs and Ramps: Deep Reinforcement Learning for a Physics-Based Human Musculoskeletal Model.

This paper proposes to use deep reinforcement learning to teach a physics-based human musculoskeletal model to ascend stairs and ramps. The deep reinforcement learning architecture employs the proximal policy optimization algorithm combined with imitation learning and is trained with experimental data of a public dataset. The human model is developed in the open-source simulation software OpenSim, together with two objects (i.e., the stairs and ramp) and the elastic foundation contact dynamics. The model can learn to ascend stairs and ramps with muscle forces comparable to healthy subjects and with a forward dynamics comparable to the experimental training data, achieving an average correlation of 0.82 during stair ascent and of 0.58 during ramp ascent across both the knee and ankle joints.

Cognitive Fuzzy-based Behavioral Learning System for Augmenting the Automated Multi-issue Negotiation in the E-commerce Applications

<p>Evolution of agent-based technology presents behavioral learning and sustainable negotiation challenges in e-commerce applications. In particular, the challenge of designing the negotiation strategy to incorporate sustainability in e-commerce business that can leverage the agent to reach its objectives by increasing the negotiation coordination and cooperation with the opponent agents. Therefore, the proposed research introduces the negotiation strategy sustainable solution using a cognitive fuzzy-based behavioral learning system which can change the preferences of negotiating agents according to human psychological characteristics. It will mimic the attitudes of human risk, patience and regret during the course of bilateral negotiation and also change the preference structures according to the fuzzy logic rules. As a result, the proposed negotiation strategy makes significant improvements on various parameters such as utility value, success rate, total negotiation time, and communication overhead while changing the negotiation rounds from 50 to 500. Since this system leverages the negotiation strategy of the agent by taking appropriate decisions to reach better agreement based on the interest, belief and psychological characteristics of negotiating opponents. Moreover, the usage of negotiation in the cloud-based platform can leverage the e-commerce applications to handle as many requests as possible due to its dynamic elasticity.</p> <p> </p>

Demand elasticities of Bitcoin and Ethereum

In this paper we analyze dynamic demand elasticity for Bitcoin and Ethereum in terms of price, transaction fees, and energy usage. We find that while both BTC and ETH have significantly positive price elasticities, transaction fee elasticity is negative and positive for BTC and ETH respectively, indicating differences in potential uses for these cryptocurrencies. • We analyze the demand elasticity of Bitcoin and Ethereum in terms of price, fees and energy usage. • We find that both have significant positive elasticities on price. • However transaction fee elasticity is negative and positive for Bitcoin and Ethereum.

Clinical relevance of pancreatic fistula in pancreas transplantation: a Comprehensive Complication Index (CCI)-based analysis of postoperative outcomes and predictors of graft survival

Guanidine hydrochloride and urea have different effects on the surface properties of lysozyme solutions due to different interaction mechanisms between the protein and denaturants: an increase in the guanidine hydrochloride concentration leads to noticeable changes in the dynamic surface elasticity, while the main effect of urea consists in a significant drop of the static surface tension.

Matlab-based Study of the Dynamic Performance of Flexible Jointed Robots

In the development and research of industrial robots, due to the defects of traditional mechanical structures in the drive system and sensors, control units and other aspects, so in order to solve these problems and improve the efficiency of flexible work, the author proposes a Matlab based core motion characteristics analysis method, that is mathematical modelling method (GUI) to improve the elastic joint robot dynamics The relationship between performance index evaluation and prediction model parameters. At present, most of the research on elastically articulated robots at home and abroad is focused on the development of one or several functionalised components. In this paper, the kinematic model is developed and its performance characteristics are analysed based on the Matlab c language platform. The kinetic equations are discretized to obtain the velocity and acceleration curves with time for each degree of freedom, so that the non-linear contact angle matrix and the driving torque can be established.

The role of graphene oxide in the strength and vibration characteristics of standard and high-grade cement concrete

This study presents the results of an experimental study of the influence of graphene oxide (GO) on the static and dynamic mechanical characteristics of cement concrete. Four different dosages of GO, 0.05%, 0.10%, 0.15% and 0.20% by weight of cement and two different grades of concrete, standard concrete (M30) and high strength concrete (M60) were studied. The static properties such as compressive strength and chord modulus of elasticity were determined. The impact hammer technique was used to obtain dynamic characteristics such as fundamental natural frequency, damping ratios, and mode shapes of concrete beams under free-free condition. In addition, fundamental resonant frequencies under different modes of vibration were determined. The dynamic elasticity modulus, dynamic shear modulus and dynamic poisons ratio of all concrete mixes were also determined. Experimental results revealed that the compressive strength of the concrete with the incorporation of GO was remarkably enhanced. The highest increase in compressive strength was found at GO dosage of 0.15%, and the improvement at 7 and 28 days was 58.2% and 47.7% for standard concrete and 51.2% and 24.3% for high strength concrete respectively compared to control concrete. The impact hammer test revealed that the maximum increase in fundamental natural frequency was 8.0% and 6.6%, and the maximum decreased damping ratio was 29.1% and 26.3% for standard concrete and high strength concrete respectively when compared to the control concrete. Ultrasonic pulse velocity results indicated that the homogeneity of the concrete with GO addition was significantly improved. SEM and EDX microstructure investigations found that the addition of GO to concrete promoted the development of improved hydration phases leads to the dense microstructure. The findings of this study demonstrated that GO nanomaterial had a potential future as a reinforcing material in cement concrete for improved microstructure, strength, and free vibration characteristics.

The effect of hydrology and crevasse wall contact on calving

Abstract. Calving is one of the main controls on the dynamics of marine ice sheets. We solve a quasi-static linear elastic fracture dynamics problem, forced by a viscous pre-stress describing the stress state in the ice prior to the introduction of a crack, to determine conditions under which an ice shelf can calve for a variety of different surface hydrologies. Extending previous work, we develop a boundary-element-based method for solving the problem, which enables us to ensure that the faces of crevasses are not spuriously allowed to penetrate into each other in the model. We find that a fixed water table below the ice surface can lead to two distinct styles of calving, one of which involves the abrupt unstable growth of a crack across a finite thickness of unbroken ice that is potentially history-dependent, while the other involves the continuous growth of the crack until the full ice thickness has been penetrated, which occurs at a critical combination of extensional stress, water level and ice thickness. We give a relatively simple analytical calving law for the latter case. For a fixed water volume injected into a surface crack, we find that complete crack propagation almost invariably happens at realistic extensional stresses if the initial crack length exceeds a shallow threshold, but we also argue that this process is more likely to correspond to the formation of a localized, moulin-like slot that permits drainage, rather than a calving event. We also revisit the formation of basal cracks and find that, in the model, they invariably propagate across the full ice shelf at stresses that are readily generated near an ice shelf front. This indicates that a more sophisticated coupling of the present model (which has been used in a very similar form by several previous authors) needs modification to incorporate the effect of torques generated by buoyantly modulated shelf flexure in the far field.

DNA Penetration into a Lysozyme Layer at the Surface of Aqueous Solutions.

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer.

Spread and adsorbed layers of protein fibrils at water –air interface

The properties of adsorbed layers of protein fibrils differ significantly from the properties of fibril spread layers on an aqueous subphase. If the dependencies of the dynamic surface elasticity on surface pressure of Lysozyme (LYS) and β-lactoglobulin (BLG) aqueous dispersions proved to be close to the results for native protein solutions, LYS and BLG spread layers on the surface of 0.1 M NaCl solution exhibited the surface elasticity more than two times higher than the values for protein solutions with the same NaCl concentatration, presumably due to lower surface concentrations of hydrolysed peptides in the latter case. The properties of fibril spread and adsorbed layers and also their morphology, unlike the surface properties of protein solutions, depend noticeably on the ionic strength of the aqueous bulk phase. This dependence is stronger in case of LYS layers, which are also more prone to the formation of macroscopic and mesoscopic surface aggregates as compared with BLG layers.