Contribution To Dissipation Research Articles

Contribution of energy dissipation to dynamic fracture resistance of the turtle carapace

The turtle carapace is a biological armor possessing superior damage tolerance. In spite of efforts to characterize the mechanical properties of such biological armor, the protection mechanisms associated with the multilayered structure of turtle carapace are largely unknown. In this study, we carry out the calculations of energy dissipation in dynamic fracture of the turtle carapace. The plastic deformation of keratin-collagen bi-layer, keratin-collagen interfacial debonding, collagen-bone interfacial debonding and crack growth in the boney layer are accounted for in the analyses. It is found that the interfacial debonding and plastic deformation of the keratin-collagen bi-layer contribute equally to toughening of the carapace at low impact velocity, while plastic energy dissipation dominates in the case of high impact velocity. As the impact velocity is increased, energy dissipation in the turtle carapace decreases at first and then increases. We reveal that the low energy dissipation of carapace at intermediate level of impact velocity is attributed to small plastic zones in the keratin-collagen bi-layer. Furthermore, we have identified the role of the waviness of the keratin-collagen and collagen-bone interfaces. The presence of wavy interfaces enhances plastic energy dissipation of the keratin-collagen bi-layer and promotes interfacial debonding, thereby suppressing crack propagation in the boney layer. The findings provide mechanistic explanations for incorporation of wavy interfaces in the multilayered structure of turtle carapace.

On the Kelvin–Voigt model in anisotropic viscoelasticity

We propose an anisotropic and nonlinear generalization of the Kelvin–Voigt viscoelastic model obtained considering the additive splitting of the Cauchy stress tensor in an elastic and a dissipative part. The former one corresponds to a fiber-reinforced hyperelastic material while the dissipative effect is described by the most general linear transverse-isotropic tensorial function of symmetric part of the velocity gradient. In a such a way we characterize the dissipative contribution via three viscoelastic moduli. We then show, by a detailed analysis of the simple shear quasistatic motion and the corresponding creep phenomena, that this motion may be used to determine experimentally the viscoelastic parameters.

Revisiting the matching of black hole tidal responses: A systematic study of relativistic and logarithmic corrections

The worldline effective field theory (EFT) gives a gauge-invariant definition of black hole conservative tidal responses (Love numbers), dissipation numbers, and their spin-0 and spin-1 analogs. In the first part of this paper we show how the EFT allows us to circumvent the source/response ambiguity without having to use the analytic continuation prescription. The source/response ambiguity appears if relativistic corrections to external sources overlap with the response. However, these corrections can be clearly identified and isolated using the EFT. We illustrate that by explicitly computing static one-point functions of various external fields perturbing the four-dimensional Schwarzschild geometry. Upon resumming all relevant Feynman diagrams, we find that the relativistic terms that may mimic the response actually vanish for static black holes. Thus, the extraction of Love numbers from matching the EFT and general relativity (GR) calculations is completely unambiguous, and it confirms previous results that the Love numbers vanish identically for all types of perturbations. We also study in detail another type of fine-tuning in the EFT, the absence of Love numbers' running. We show that logarithmic corrections to Love numbers do stem from individual loop diagrams in generic gauges, but cancel after all diagrams are summed over. In the particular cases of spin-0 and spin-2 fields the logarithms are completely absent if one uses the Kaluza-Klein metric decomposition. In the second part of the paper we compute frequency-dependent dissipative response contributions to the one-point functions using the Schwinger-Keldysh formalism. We extract black hole dissipation numbers by comparing the one-point functions in the EFT and GR. Our results are in perfect agreement with those obtained from a manifestly gauge-invariant matching of absorption cross sections.

Phase-change cooling of lithium-ion battery using parallel mini-channels cold plate with varying flow rate

In this study, a liquid phase-change cooling module with mini-channels cold plate was designed. The temperature properties of a battery monomer with different cooling conditions and varying discharge rates were investigated. The heat dissipation contribution of latent heat transfer to the overall cooling performance of the mini-channels cold plate was analyzed based on the outlet vapor quality. Particularly, a cooling strategy with varying coolant flow rates was proposed and examined at 3C discharge rate. The results illustrated that the designed battery cooling module had an ideal effect on lowering the battery's surface temperature and increasing the battery's temperature uniformity. Compared to the cooling strategy with constant coolant flow rate, the proposed variable flow cooling strategy better matched the dynamic law of battery heat generation and increased the contribution of the latent heat transfer to the battery cooling, thereby efficiently reducing the coolant consumption and the pump power consumption of the BTMS (battery thermal management system) while providing the same or even superior cooling performance. The findings could assist the optimization of the BTMS and be the reference for the application of the varying flow rate cooling strategy in actual engineering.

Understanding Energy Pathways in the Gulf Stream

Abstract The Gulf Stream (GS) is one of the strongest ocean currents on the planet. Eddy-rich resolution models are needed to properly represent the dynamics of the GS; however, kinetic energy (KE) can be in excess in these models if not dissipated efficiently. The question of how and how much energy is dissipated and in particular how it flows through ocean scales thus remains an important and largely unanswered question. Using a high-resolution (∼2 km) ocean model [Coastal and Regional Ocean Community (CROCO)], we characterize the spatial and temporal distribution of turbulent cascades in the GS based on a coarse-grained method. We show that the balanced flow is associated with an inverse cascade while the forward cascade is explained by ageostrophic advection associated with frontogenesis. Downscale fluxes are dominant at scales smaller than about 20 km near the surface and most intense at the GS North Wall. There is also strong seasonal variability in KE flux, with the forward cascade intensifying in winter and the inverse cascade later in spring. The forward cascade, which represents an interior route to dissipation, is compared with both numerical and boundary dissipation processes. The contribution of interior dissipation is an order of magnitude smaller than that of the other energy sinks. We thus evaluate the sensitivity of horizontal momentum advection schemes on energy dissipation and show that the decrease in numerical dissipation in a high-order scheme leads to an increase in dissipation at the boundaries, not in the downscale flux.

Surface stress decomposition in large amplitude oscillatory interfacial dilatation of complex interfaces

HypothesisMultiphase materials are often subjected to large deformations during processing, but the rheological responses of complex interfaces (e.g. stabilized by proteins) in this nonlinear deformation regime are still poorly understood. We expect nonlinearities in the response to be introduce by changes of the interfacial network and surface density of the emulsifier. ExperimentsLarge amplitude oscillatory dilatation (LAOD) experiments were performed on WPI-, pea albumin-, pea globulin- and rapeseed lecithin-stabilized interfaces and analyzed with a general stress decomposition (GSD). With GSD, the stress response was decomposed into the four stress terms (τ1-τ4). Here, τ1 and τ2 represent, the elastic and viscous contribution of the odd Fourier harmonics, and τ3 and τ4 represent the dissipative and recoverable contribution of the even harmonics. FindingsAnalysis of WPI-, pea albumin-, pea globulin- and rapeseed lecithin-stabilized interfaces revealed that higher odd harmonics (k≥3) describe in-plane network responses and that even harmonics describe surface density changes. Analysis of these complex interfaces showed that GSD is a valuable tool for (quantitative) description of interfacial responses in LAOD, providing new insights into the origin of asymmetric nonlinear stress responses.

Post-tensioned rocking dissipative timber wall systems: Numerical prediction

Low-damage post-tensioned technologies were born with the aim to obtain structural solutions able to guarantee, in case of seismic events, not only the safeguarding of human life, but also the rapid re-use of the buildings without permanent damage. In this context, structural systems based on rocking dissipative timber walls have been introduced, in which rocking behavior is entrusted to post-tensioned bars, and the dissipative contribution is provided by steel dampers, easily replaceable after an intense seismic event. The paper presents a nonlinear numerical model to predict the response of different configurations of Post-Tensioned (PT)-timber wall systems, particularly useful to support the design phase. More in detail, the geometrical non-linearity due to the rocking behavior of the system and material non-linearities that characterize the dampers are taken explicitly into account. The proposed numerical modelling strategy has been validated on different experimental literature tests performed by non-linear static analyses on both single and double wall systems equipped with different damper configurations. The comparison between numerical and experimental results is performed to demonstrate the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads. Further, parametric analyses have been developed in order to investigate the effect of different parameters, such as wall dimensions, initial post-tensioned force in the bars, number of axial and shear dampers, on the global behaviour of post-tensioned timber systems.

Seismic behavior of steel plate and reinforced concrete composite wall coupled to steel side columns

The steel plate and reinforced concrete (SPRC) composite wall coupled to steel side columns is a new type of coupled system, which consists of a single SPRC composite wall coupled to steel side columns through steel coupling beams at all floors. One 1/4 scaled five-story SPRC composite wall coupled to steel side columns with a plastic coupling ratio (CR) of 0.45 was designed, constructed, and tested under simulated earthquake action. The test results exhibited great seismic performance of the proposed coupled system with the coupling mechanism fully developed. The average displacement ductility coefficient was 3.12. And the average values of the inter-story drift ratio of all stories at the yield, peak load, and ultimate conditions were 1.32%, 2.55%, and 3.70%, respectively, showing good inter-story deformation capacity. The average ultimate plastic shear rotations of steel coupling beams at the 2nd, 3rd, 4th, and 5th floors were 0.0211 rad, 0.0364 rad, 0.0556 rad, and 0.0913 rad, respectively, indicating great energy dissipation contributions of the steel coupling beams. The steel side columns remained elastic under shear forces transmitted from steel coupling beams through hinge joints and provided a stable overturning moment resistance to protect the SPRC wall. The accuracy of the test results was verified against the numerical analysis results. The parametric analyses were conducted to further the understanding on the influences of key design parameters on the seismic performance of the proposed coupled system. The peak lateral load can be enhanced by increasing the axial load or steel plate ratio. In order to obtain good energy dissipation capacity and ductility, a moderate value of 0.15 for the axial load ratio or 6.6% for the steel plate ratio can lead to excellent deformation capacity.

Cyclic model of post-tensioned low damage timber walls with dissipative devices

Post-tensioned rocking dissipative timber wall systems born from the idea to obtain structural solutions able to guarantee, after a seismic event, a rapid re-use of the buildings without permanent damage, as well as to guarantee the safeguarding of human life. In this framework, the rocking of timber walls is entrusted to post-tensioned bars, placed in ad hoc cavities of the panel, while the dissipative contribution is provided by steel dampers, which are sacrificial elements subjected to damage easily replaceable after an intense seismic event. In this context, it can be helpful to have a numerical model in order to support the design phase; indeed, the paper presents a non-linear numerical model of post-tensioned rocking dissipative timber walls able to predict the response of this innovative system. In particular, geometrical and material non-linearities, due to the rocking behavior of the system and to the material that characterize the dampers, are taken explicitly into account. Further, the proposed numerical modelling strategy has been validated on literature experimental campaigns performed on both single and double wall systems, with different damper configurations. The comparison between experimental and numerical cyclic responses are shown in term of global results, i.e. force/displacement curves and post-tension variation of the bars. The comparison demonstrates the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads.

Energy and exergy analysis of conjugate 3D unsteady heat conduction with solidification of water by turbulent buoyancy-driven freezing of solid food in air

In this work, the influence of the position of salmon in a cooling cavity on heat transfer, freezing rate and local exergy destruction was investigated using mathematical modeling and numerical simulation. The predicted temperature evolution in the food during freezing by turbulent heat convection in air inside a cooling chamber was validated with experimental results. The conjugate turbulent model in three dimensions included the natural heat convection and the unsteady heat diffusion with the phase change of water to ice in the food meat. Three positions of the block of salmon in the freezer were studied: bottom-left, bottom-center, and center of the freezer. The local exergy destruction was calculated to quantify the contribution of viscous dissipation and heat transfer during the salmon freezing process. The unsteady description of air velocity, temperature, and freezing rate were analyzed. The highest cooling rate calculated was for the food at the bottom left, and the lowest when located at the center of the cooling cavity. The exergy destruction analysis determined the useful energy lost during the freezing process.

A Comparison between Statistical Behaviours of Scalar Dissipation Rate between Homogeneous MILD Combustion and Premixed Turbulent Flames

Three-dimensional Direct Numerical Simulations (DNS) data has been utilised to analyse statistical behaviours of the scalar dissipation rate (SDR) and its transport for homogeneous methane-air mixture turbulent Moderate or Intense Low oxygen Dilution (MILD) combustion for different O2 dilution levels and turbulence intensities for different reaction progress variable definitions. Additional DNS has been conducted for turbulent premixed flames and passive scalar mixing for the purpose of comparison with the SDR statistics of the homogeneous mixture MILD combustion with that in conventional premixed combustion and passive scalar mixing. It has been found that the peak mean value of the scalar dissipation rate decreases with decreasing O2 concentration for MILD combustion cases. Moreover, SDR magnitudes increase with increasing turbulence intensity for both MILD and conventional premixed combustion cases. The profiles and mean values of the scalar dissipation rate conditioned upon the reaction progress variable are found to be sensitive to the choice of the reaction progress variable definition. This behaviour arises due to the differences in the distributions of the species mass fractions within the flame. The strain rate contribution and the molecular dissipation term are found to be the leading order contributors in the scalar dissipation rate transport for MILD combustion; whereas, in conventional premixed flames, the terms rising from density variation and reaction rate gradient also play leading roles in addition to the strain rate and molecular dissipation contributions. By contrast, the terms due to density gradient and reaction rate gradient remain negligible in comparison to the leading order contributors in MILD combustion cases due to small density variation because of moderate temperature rise and small reaction rate gradient magnitudes. Furthermore, the qualitative behaviour of the strain rate contribution to the SDR transport in premixed flames is significantly different to that in the case of MILD combustion and passive scalar mixing. The findings of the current analysis indicate that the scalar dissipation rate statistics in MILD combustion show several qualitative similarities to the passive scalar mixing despite major differences with the SDR transport in conventional turbulent premixed flames. This further suggests that the scalar dissipation rate models, which were originally proposed in the context of passive scalar mixing, have the potential to be applicable for MILD combustion but the models for the premixed turbulent combustion may not be applicable for MILD combustion of homogeneous mixtures.

A study of the early life of gasoline particulate filters: Reactive and dissipative acoustic effects

The presence of after-treatment systems (ATS) has some side effects as they modify the wave dynamics, back-pressure and acoustic behavior of the exhaust system, that define the boundary conditions for the main silencing device. Gasoline particulate filters (GPF) have a considerable influence on these traits as their working principle depends on wall-flow monoliths; additionally, particulate filters have an inherent transient behavior due to the loading-regeneration cycles during their operation. In this paper, the steady and unsteady behavior of a typical device containing a three-way catalyst (TWC) and a GPF has been characterized in "new" (prior to any use) and "used" (after regeneration) conditions, with special focus on the role of dissipation. Pressure drop measurements were used in steady flow, whereas an acoustic energy balance was performed in the unsteady case that allows for the identification of the reactive and dissipative contributions. The results obtained for the GPF suggest that after it has been used for a relatively short time it oscillates between a maximum and a minimum loading over load–regeneration cycles burning the soot, never reaching back brand–new cleanness due to accumulation into the substrate pores and only suffering from ash accumulation over very long times. The results were then used to analyze the ability of a standard gas-dynamic code to reproduce the influence of the loading on the reactive and dissipative effects observed, with the main conclusion that by properly tuning the model parameters it is possible to reproduce, at least qualitatively, the trends observed in the experiments. The model can thus be used to provide adequate inlet conditions for the design of the exhaust line.

Dual disorder-driven magnetic dynamics in GdCu2 superantiferromagnetic nanoparticles

The spin dynamics in magnetically disordered GdCu2 nanoparticles, varying the nanoparticle size in the range 53 to 7 nm, has been scrutinized. Dynamic χAC susceptibility measurements have revealed the existence of dissipation at Tg = 18 K, which is associated to the spin freezing transition, for all the ensembles. Besides, the superantiferromagnetic ensembles (〈D〉≥ 24 nm) also showcase a dissipation contribution close to the vicinity of the Néel transition, TN = 40.2 K. This dissipation, which takes the form of two humps located at Td1 = 33.5(5) K and Td2 = 40.0(5) K, is associated to uncompensated antiferromagnetic moments. Time-dependent phenomena (ageing and memory effects) are only evidenced below the spin freezing transition, evidencing that solely this low-temperature disordered phase is driven by the frustration of RKKY exchange interactions. Consequently, GdCu2 nanoparticles display a dual disorder-driven magnetic dynamics, which are the one ascribed to the magnetically frustrated moments located at the nanoparticle surface; and that of uncompensated antiferromagnetic moments located within the nanoparticle core.

Spatiotemporal Evolution of Urban Rain Islands in China under the Conditions of Urbanization and Climate Change

Precipitation is a critical factor affecting regional water cycles, water ecology, and socioeconomic development. Monthly precipitation, water vapor pressure, and temperature datasets from 613 meteorological stations across China were used to analyze the spatiotemporal evolution of urban rain island effects at the national scale during periods of slow (1960–1969) and accelerated (2010–2019) urbanization. The combined effects of artificial water dissipation and heat islands on urban precipitation were a key focus of this study. The results showed that rain island effects (0–31.6 mm/month) were primarily distributed along the southeast coast (dominated by the heat island effect) and northwest inland region (dominated by artificial water dissipation). During winter, the relative contribution of artificial water dissipation was higher in urban areas, and the rain island effect was more apparent than in the summer. Comparisons of precipitation prior to and following large-scale urbanization showed that precipitation and rain island intensity along the southeast coast and northwest inland region increased by 0–28 and 0–28.6 mm/month, respectively. These findings indicate that artificial water dissipation is an important water vapor source for urban precipitation, particularly during winter months.

Coupling between turbulence and solar-like oscillations: A combined Lagrangian PDF/SPH approach

Context. The ever-increasing quality of asteroseismic measurements offers a unique opportunity to use the observed global acoustic modes to infer the physical properties of stellar interiors. In solar-like oscillators, the finite lifetime of the modes allows their amplitudes and linewidths to be estimated, which provide invaluable information on the highly turbulent motions at the top of the convective envelope. But exploiting these observables requires a realistic theoretical framework for the description of the turbulence–oscillation coupling. Aims. The first paper of this series established a linear stochastic wave equation for solar-like p-modes, correctly taking the effect of turbulence thereon into account. In this second paper, we aim at deriving simultaneous expressions for the excitation rate, damping rate, and modal surface effect associated with any given p-mode, as an explicit function of the statistical properties of the turbulent velocity field. Methods. We reduce the stochastic wave equation to complex amplitude equations for the normal oscillating modes of the system. We then derive the equivalent Fokker-Planck equation that governs the evolution of the probability density function jointly associated with the real amplitudes and phases of all the oscillating modes of the system simultaneously. The effect of the finite-memory time of the turbulent fluctuations (comparable to the period of the modes) on the modes themselves is consistently and rigorously accounted for, by means of the simplified amplitude equation formalism. This formalism accounts for mutual linear mode coupling in full, and we then turn to the special single-mode case. This allows us to derive evolution equations for the mean energy and mean phase of each mode, from which the excitation rate, the damping rate, and the modal surface effect naturally arise. Results. The expressions obtained here (1) are written as explicit functions of the statistical properties of turbulence, thus allowing for any prescription thereof to be tested against observations, (2) include the contribution of the turbulent dissipation more realistically, and (3) concern the excitation rate, the damping rate, and the modal surface effect of the modes simultaneously. We show that the expression for the excitation rate of the modes is identical to previous results obtained through a different modelling approach, thus supporting the validity of the formalism presented here. We also recover the fact that the damping rate and modal surface effect correspond to the real and imaginary part of the same single complex quantity. We explicitly separate the different physical contributions to these observables, in particular the turbulent pressure contribution and the joint effect of the pressure-rate-of-strain correlation and the turbulent dissipation. We show that the former dominates for high-frequency modes and the latter for low-frequency modes. To illustrate the usefulness of this formalism, we apply it to a simplified case where we can quantify the relative importance of these two contributions, and in particular the threshold between the two frequency regimes, as a function of the turbulent frequency and the degree of anisotropy of both the Reynolds-stress tensor and the dissipation of turbulent energy. Conclusions. The formalism developed in these first two papers, applied to the case of a simplified Lagrangian stochastic model for proof-of-concept purposes, indeed proves to be viable, relevant, and useful for addressing the issue of turbulence–oscillation coupling in the context of solar-like oscillators. It opens the door to subsequent studies physically more appropriate to the stellar case. It will also allow, once mode coupling is included (i.e. by going beyond the single-mode case), for a realistic description of mode-mode scattering and its influence on mode damping, mode frequency, and the energy distribution across the solar p-mode eigenspectrum.

Turbulence modulation by finite-size particles of different diameters and particle–fluid density ratios in homogeneous isotropic turbulence

In this paper, the influence of particle-fluid density ratio and particle diameter on the turbulence modulation by finite-size particles in forced homogeneous isotropic turbulence is investigated. Results show that the presence of finite-size particles always attenuate the turbulence, and the attenuation is larger for particles with larger density when the particle diameter is fixed. But the attenuation is smaller for particles with larger diameter if the density is fixed, and the weaker attenuation is due to the wake fluctuation when the particle Reynolds number is large enough. The turbulence kinetic energy is attenuated at the large scales and augmented at the small scales. The radial dissipation profiles show that the region affected by the particles with same diameter is identical, but the dissipation near the particle surface is larger if the density is larger due to larger slip velocity and particle Reynolds number. For particles with same density, smaller particles have smaller dissipation near the particle surface but the influence region is larger, and the combined effect leads to the result that the contribution of dissipation in the influence region of smaller particles to the total dissipation is larger. The influence region mainly depends on the particle diameter.

Puncture of a Viscous Liquid Film Due to Droplet Falling

Droplet impact may rupture a liquid film on a non-wettable surface. The formation of a stable dry spot has only been studied in the inviscid case. Here, we examine the break-up of viscous films, and demonstrate the importance and role of the viscous dissipation in both film and droplet. A new model was therefore proposed to predict the necessary droplet energy to create a dry spot. It also showed that the dissipation contribution in film dominates when the ratio of the thicknesses to drop diameter is larger than 7/4.

Fluorescence ratio and photochemical reflectance index as a proxy for photosynthetic quantum efficiency of photosystem II along a phosphorus gradient

Sun-induced chlorophyll fluorescence (SIF) is one of the most promising remote-sensing signals to assess spatio-temporal variation in photosynthesis. Yet, it has been shown that the positive linear relationship of SIF and photosynthesis, often reported from satellite and proximal remote sensing, is mainly driven by the amount of absorbed photosynthetic active radiation (APAR). By normalizing SIF by APAR these structural first-order effects can accounted for and SIF is then reflecting physiological regulation of photosynthetic efficiency. However, because of the confounding contribution of non-photochemical energy dissipation, the relationship between SIF and photosynthetic efficiency is non-linear, and therefore additional measurements have to be included to constrain the predictions of photosynthetic efficiency and photosynthetic electron transport.We grew Zea mays at different phosphorus (P) levels to assess if P-induced reduction in quantum efficiency of PSII (ΦPSII), can be estimated by the fluorescence efficiency parameters, APAR normalized fluorescence (Fyield) and the ratio of the two emitted fluorescence peaks (F↑ratio), at leaf level. Results were compared to the photochemical reflectance index (PRI), a well-established index related to the activity of the xanthophyll cycle, a protection mechanism which activates under light-stress conditions. We demonstrate that the relationship between ΦPSII and Fyield is non-monotonic across a P limitation gradient, rendering the prediction of ΦPSII by Fyield alone unfeasible. We show, however, that the pigment corrected PRI (cPRI) and F↑ratio (cF↑ratio) share a strong linear relationship with ΦPSII, thereby enabling the estimation of ΦPSII. We demonstrate that a compensation for reabsorption effects improved the estimation of ΦPSII by Fratio at foliar level. This may allow improved predictions of photosynthetic light use efficiency parameters without the need of measuring green APAR.

First-Order General-Relativistic Viscous Fluid Dynamics

We present the first generalization of Navier-Stokes theory to relativity that satisfies all of the following properties: (a) the system coupled to Einstein’s equations is causal and strongly hyperbolic; (b) equilibrium states are stable; (c) all leading dissipative contributions are present, i.e., shear viscosity, bulk viscosity, and thermal conductivity; (d) nonzero baryon number is included; (e) entropy production is non-negative in the regime of validity of the theory; (f) all of the above hold in the nonlinear regime without any simplifying symmetry assumptions. These properties are accomplished using a generalization of Eckart’s theory containing only the hydrodynamic variables, so that no new extended degrees of freedom are needed as in Müller-Israel-Stewart theories. Property (b), in particular, follows from a more general result that we also establish, namely, sufficient conditions that when added to stability in the fluid’s rest frame imply stability in any reference frame obtained via a Lorentz transformation All of our results are mathematically rigorously established. The framework presented here provides the starting point for systematic investigations of general-relativistic viscous phenomena in neutron star mergers.Received 9 October 2020Revised 18 January 2022Accepted 15 February 2022DOI:https://doi.org/10.1103/PhysRevX.12.021044Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFluids & classical fields in curved spacetimeGeneral relativityGeneral relativity equations & solutionsTechniquesRelativistic hydrodynamicsGravitation, Cosmology & AstrophysicsFluid Dynamics

Regulation of Substrate Dissipation via Tunable Linear Elasticity Controls Cell Activity

AbstractNatural tissues and extracellular matrices (ECMs) are not purely elastic materials but exhibit dissipative properties. Although it has recently emerged as a novel regulator of cellular responses, the contribution of material dissipation to guiding cell‐fate decisions is still in its infancy. Here, a strategy for tuning the dissipation rate of viscoplastic substrates while precisely regulating linear elasticity is reported. Semi‐interpenetrating substrates consisting of a rigid hydrogel network intertwined with a branched biopolymer are described. The release of these weak physical entanglements under loading dissipates the applied stress and leads to the extension of the linear elasticity. These results reveal a crucial link between this material property and cell response in 2D cultures, impacting cell migration mode and speed, vinculin‐dependent focal adhesion geometry and size, F‐actin organization, the transmission of forces, and Yes‐associated protein nuclear translocation. It is shown that cells require joint actomyosin contractility and microtubule tension to probe the substrate and decide whether or not to adhere, revealing a clear correlation between force transmission, substrate dissipation rate, and amount of anchoring points. Overall, these findings introduce linear elasticity as a novel design parameter for assembling tunable dissipative materials to study cell mechanosensing in 2D and possibly also in 3D cultures.