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We model compact objects of known stellar mass and radius made of isotropic matter within Einstein's gravity. The interior solution describing hydrostatic equilibrium we are using throughout the manuscript corresponds to the Tolman IV exact analytic solution obtained a long time ago. The three free parameters of the solutions are determined by imposing the matching conditions for objects of known stellar mass and radius. Finally, using well established criteria, it is shown that, contrary to the Kohler Chao solution, the Tolman IV solution is compatible with all requirements for well-behaved and realistic solutions, except for the relativistic adiabatic index that diverges at the surface of stars. The divergence of the index Γ may be resolved, including a thin crust assuming a polytropic equation of state, which is precisely the case seen in studies of neutron stars. To the best of our knowledge, we model here for the first time the recently discovered massive pulsar PSR J0740+6620 and the strangely light HESS compact object via the Tolman IV solution. The present work may be of interest to model builders as well as a useful reference for future research. [ABSTRACT FROM AUTHOR]

We present a new extended parametric equation-of-state model for thermodynamic properties and the correlation length for a simple fluid near its liquid–gas critical point. The model involves 16 universal parameters to perfectly match 10 leading universal amplitudes of the asymptotic Ising-like limit of the critical-to-classical crossover functions calculated by Garrabos and Bervillier [Phys. Rev. E 74,021113 (2006)] from the massive renormalization scheme. The universal values of 8 Ising-like amplitude combinations are then matched exactly. The closure of the construction of parameters is determined after a careful analysis of the intrinsic limitation of parametric equations to describe the universal features at the first order of the confluent corrections-to-scaling. In the asymptotic mean-field limit, the crossover master model also reproduces the mean-field amplitude combinations except for the susceptibility case. The new model is compared with the crossover parametric model previously developed by Agayan et. al [Phys. Rev. E 64, 02615 (2001)]. The residuals from comparison with the mean crossover functions of Garrabos and Bervillier are reported to define the application range of the crossover master model to any simple fluid for which the generalized critical coordinates of the liquid–gas critical point are known. [ABSTRACT FROM AUTHOR]

A modified thermochemical energy term and y-law extension are incorporated into the JWL equation of state for predicting PBXN-111 detonation behavior under self- and externally supported conditions. The modifications resolve previous speculations regarding the causes affecting non-scalability of the reaction zone and detonation velocity with respect to explosive diameter, and a problem encountered to quantify increased detonation power gain by circumferential initiation. The modifications accurately consider "static effects" of size and the additional hydro-dynamic compression resulting from a consecutive 2-step shock jump during convergent front collapse, leading to an elevated von Neumann spike and Chapman-Jouguet state between which physical and chemical transformations take place affecting shock regeneration and detonation power release. Necessary modifications to the CYLEX test are recommended to ensure that wall expansions are measured under steady-state conditions. [ABSTRACT FROM AUTHOR]

The superdense hexagonal phosphides BP and AlP, whose structures are formed by distorted tetrahedra and characterized by quartz-derived (qtz) topology, were predicted from crystal chemistry and first principles as potential high-pressure phases. From full geometry structure relaxations and ground state energy calculations based on quantum density functional theory (DFT), qtz BP and AlP were found to be less cohesive than the corresponding cubic zinc-blende (zb) phases with diamond-like (dia) topology, but were confirmed to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, qtz phases were found to be energetically favorable at small volumes (high pressures), with zb-to-qtz transition pressures of 144 GPa for BP and 28 GPa for AlP. According to the electronic band structures and the site projected density of states, both phosphides exhibit larger band gaps of the zinc-blende phases compared to the qtz phases; the smaller values for the latter result from the smaller volumes per formula unit, leading to increased covalence. [ABSTRACT FROM AUTHOR]

We model compact objects of known stellar mass and radius made of isotropic matter within Einstein’s gravity. The interior solution describing hydrostatic equilibrium we are using throughout the manuscript corresponds to the Tolman IV exact analytic solution obtained a long time ago. The three free parameters of the solutions are determined by imposing the matching conditions for objects of known stellar mass and radius. Finally, using well established criteria, it is shown that, contrary to the Kohler Chao solution, the Tolman IV solution is compatible with all requirements for well-behaved and realistic solutions, except for the relativistic adiabatic index that diverges at the surface of stars. The divergence of the index Γ may be resolved, including a thin crust assuming a polytropic equation of state, which is precisely the case seen in studies of neutron stars. To the best of our knowledge, we model here for the first time the recently discovered massive pulsar PSR J0740+6620 and the strangely light HESS compact object via the Tolman IV solution. The present work may be of interest to model builders as well as a useful reference for future research.

In this paper, we aim to explore novel machine learning (ML) techniques to facilitate and accelerate the construction of universal equation-Of-State (EOS) models with a high accuracy while ensuring important thermodynamic consistency. When applying ML to fit a universal EOS model, there are two key requirements: (1) a high prediction accuracy to ensure precise estimation of relevant physics properties and (2) physical interpretability to support important physics-related downstream applications. We first identify a set of fundamental challenges from the accuracy perspective, including an extremely wide range of input/output space and highly sparse training data. We demonstrate that while a neural network (NN) model may fit the EOS data well, the black-box nature makes it difficult to provide physically interpretable results, leading to weak accountability of prediction results outside the training range and lack of guarantee to meet important thermodynamic consistency constraints. To this end, we propose a principled deep regression model that can be trained following a meta-learning style to predict the desired quantities with a high accuracy using scarce training data. We further introduce a uniquely designed kernel-based regularizer for accurate uncertainty quantification. An ensemble technique is leveraged to battle model overfitting with improved prediction stability. Auto-differentiation is conducted to verify that necessary thermodynamic consistency conditions are maintained. Our evaluation results show an excellent fit of the EOS table and the predicted values are ready to use for important physics-related tasks.

We present results from earthbound experiments on the equation of state of strongly interacting matter, which are relevant for neutron start and gravitational wave studies. [ABSTRACT FROM AUTHOR]

We calculated the electron-ion energy relaxation times in warm dense aluminum and gold. Our calculations span a wide temperature range from a thousand to a million kelvins for both dense aluminum and gold. To determine the temporal evolution of electron and ion temperatures, we employed the two-temperature model with the SESAME equation-of-state tables, and well-known electron-ion coupling factors. Our calculations indicate that the relaxation times for warm dense aluminum were within 5 ps, whereas they were within 20 ps for warm dense gold. The maximum relaxation times were observed at initial electron temperatures of approximately 30,000 K for both aluminum and gold. Our calculated relaxation times using the SESAME database agree very well with the existing theories both in the cold-solid and hot-plasma limits. Furthermore, we found that the melting times calculated using the Lindemann criterion were in good agreement with the melting times for gold from measurements in recent literature. [ABSTRACT FROM AUTHOR]

This paper focuses on the modeling of hydrogen (H2) storage in subsurface formations, particularly focusing on the equilibrium between H2 and brine and its implications for hydrogen transport properties in black-oil reservoir simulations. Initially, we evaluate and calibrate various equations of state (EoS) for H2-water and H2-brine mixtures. Our analysis ranges from the molecular-level Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation to a more explicit version of the Redlich–Kwong cubic EoS, and concludes with an empirical Henry–Setschenow (HS) model. These models are compared in terms of their ability to predict mutual solubilities with validation against experimental data. This study compares the strengths and limitations of each thermodynamic model, highlighting their overall good predictability across various temperatures, pressures, and salinity levels with a relatively moderate number of adjustable parameters. Subsequently, we apply these thermodynamic models to generate Pressure–Volume–Temperature (PVT) phase equilibrium data for use in black-oil simulations, focusing on the behavior of H2 in saline aquifers. Our investigation examines the effects of salt concentration, H2 solubility, molecular diffusion, and the impact of cycling frequency, injection and withdrawal rates on the storage and recoverability process. We present three numerical examples to illustrate these concepts: a 2D aquifer model, a modified benchmark originally designed for simulating the conversion of natural gas to hydrogen storage, and a 3D anticlinal dome-shaped aquifer model. These examples cover a range of complexities, such as heterogeneous permeability, porosity variations, and diverse rock types with specific entry pressures, providing a comprehensive overview of the factors influencing H2 storage in subsurface formations. • Comparison of EoS (PC-SAFT, RK-EoS, HS) for H 2 -water and H 2 -brine mixtures. • Validation of thermodynamic models against experimental data for various conditions. • Generation of PVT phase equilibrium data for H 2 in saline aquifers. • Numerical examples showing hydrogen storage in heterogeneous and diverse rock types. • Impact of salt concentration, H 2 solubility, diffusion, and cycling on storage. [ABSTRACT FROM AUTHOR]

The superdense hexagonal phosphides BP and AlP, whose structures are formed by distorted tetrahedra and characterized by quartz-derived (qtz) topology, were predicted from crystal chemistry and first principles as potential high-pressure phases. From full geometry structure relaxations and ground state energy calculations based on quantum density functional theory (DFT), qtz BP and AlP were found to be less cohesive than the corresponding cubic zinc-blende (zb) phases with diamond-like (dia) topology, but were confirmed to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, qtz phases were found to be energetically favorable at small volumes (high pressures), with zb-to-qtz transition pressures of 144 GPa for BP and 28 GPa for AlP. According to the electronic band structures and the site projected density of states, both phosphides exhibit larger band gaps of the zinc-blende phases compared to the qtz phases; the smaller values for the latter result from the smaller volumes per formula unit, leading to increased covalence.

Horizontal wells are often drilled and hydraulically fractured in tight reservoirs to produce hydrocarbons or heat. Different fracturing fluids such as slick water, gas, foam, gel, or a combination can be used with slick water being the most common fracturing fluid. In this paper, we study the impacts of different fracturing fluids on fractured well productivity using an in-house integrated hydraulic fracturing and reservoir simulator with an equation-of-state compositional model. We analyzed the fracture geometry, stress interference, proppant placement, and the subsequent well productivity using different fracturing fluids. The results clearly show that different fracturing fluids result in very different fracture shape, sand distribution, and water and hydrocarbon production. By conducting fracturing and production simulations in one simulator, we ensure that no physics and data loss occurs due to data migration between two different software packages for hydraulic fracturing and reservoir simulation. To the best of the authors' knowledge, this is the first time that a single integrated equation-of-state compositional hydraulic fracturing and reservoir simulator has been presented and applied for well lifecycle simulation. [ABSTRACT FROM AUTHOR]

• X-ray phase contrast imaging and velocimetry were used to measure shock states of a carbon foam. • Dynamic X-ray phase contrast imaging reduced errors of the measured states. • The foam exhibits anomalous compression arising from shock heating. Porous polymer foams are found in numerous applications where they may be subjected to dynamic compression. The shockwave properties of polymer foams have several features that make shock Hugoniot measurements and interpretation challenging. Here, we present a comparison of dynamic X-ray phase contrast imaging and traditional optical velocimetry approaches to measuring the shocked states for a low-density carbon foam. Overall, dynamic X-ray phase contrast imaging was found to reduce errors associated with the measured Hugoniot states. The foam exhibits anomalous compression as expected due to its high initial porosity arising from shock heating. [ABSTRACT FROM AUTHOR]

We study the expansion behaviors of a Fermionic superfluid in a cigar-shaped optical dipole trap for the whole BEC-BCS crossover and various temperatures. At low temperature (0.06(1) T F ), the atom cloud undergoes an anisotropic hydrodynamic expansion over 30 ms, which behaves like oscillation in the horizontal plane. By analyzing the expansion dynamics according to the superfluid hydrodynamic equation, the effective polytropic index γ ¯ of Equation-of-State (EoS) of Fermionic superfluid is extracted. The γ ¯ values show a non-monotonic behavior over the BEC-BCS crossover, and have a good agreement with the theoretical results in the unitarity and BEC side. The normalized quasi-frequencies of the oscillatory expansion are measured, which drop significantly from the BEC side to the BCS side and reach a minimum value of 1.73 around 1 / k F a = - 0.25. Our work improves the understanding of the dynamic properties of strongly interacting Fermi gas. [ABSTRACT FROM AUTHOR]

We propose to extend the commonly known flow analysis in the transverse p x - p y plane to novel flow coefficients based on the angular distribution in the p x - p z and p y - p z planes. The new flow coefficients, called u n and w n (in addition to v n), turn out to be also highly sensitive to the nuclear Equation-of-State and can be used to explore the EoS in more detail than is possible using only v n. As an example to quantify the effect of the EoS, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to investigate 20-30% central Au+Au collisions at E = lab 1.23 A GeV. [ABSTRACT FROM AUTHOR]

We consider a unified barotropic dark fluid model with dissipation. Our fluid asymptotes between two power laws and so can interpolate between the dust and dark energy (DE) equations-of-state at early and late times. The dissipative part is a bulk viscous part with constant viscosity coefficient. The model is analyzed using the phase-space methodology which helps to understand the dynamical behavior of the model in a robust manner without reference to the system solution. The parameters of the model are constrained through many observational constraints. The model is tested through many physical and observational tests. We first considered the model independent O m (z) test. Results for O m (z) are plotted against the BAO data for this quantity from different authors, which shows that the model is consistent with the data points for the full redshift range. The χ 2 statistics results in the value of χ 2 red = 0. 3 0 with a p -value of 0. 9 5. The Hubble parameter equation is solved numerically and results are plotted against the recent set of Hubble data. The χ 2 test with the Hubble data resulted in the χ 2 red value of 0. 6 7 2 with a p -value of 0. 9 4. The distance modulus at different values of redshift is calculated numerically and results are compared to the newest set of SNe Ia data, the Pantheon Sample. We obtained a χ 2 red value of 1. 0 4 with a p -value of 0. 1 7. These results show that our model is efficiently consistent with observations. The model expectations for the evolution of the universe are also studied by testing the evolution of the deceleration parameter, the density of the universe, and the effective equation-of-state parameter of the model and of its underlying dark energy candidate. The value of the present day viscosity coefficient of the cosmic fluid, ζ 0 , is estimated. It is found to be 8 × 1 0 6 Pa s. We argue that this model is able to explain the behavior of the universe evolution. [ABSTRACT FROM AUTHOR]

Abstract A novel simple method is presented for the characterization of ionic liquids as regards their thermodynamic behavior in bulk phases and interfaces. For this purpose, a simple consistent thermodynamic framework has been developed which may exploit a variety of experimental information, such as activity coefficients at infinite dilution, volumetric data over a temperature/pressure range, or wetting/contact angle data over a variety of solid surfaces. This experimental information is used in order to determine LSER (Linear Solvation Energy Relationships) type molecular descriptors and surface energies that uniquely characterize each ionic liquid. The interconnection of these descriptors with the more familiar equation-of-state scaling constants is established and explored. The emerging trends in the determined molecular descriptors and the consequences and perspectives are critically discussed. As shown by a variety of examples, the efficiency and versatility of the proposed characterization method are rather promising. Graphical abstract The interconnection of molecular descriptors for ionic liquids. Unlabelled Image Highlights • A novel approach for the efficient characterization of interactions in ionic liquids • New framework interconnecting equation-of-state, LSER, and surface energy descriptors • LSER descriptors of ionic liquids for calculations in bulk phases and interfaces [ABSTRACT FROM AUTHOR]

The formalism of dark energy based on modeling speed of sound as a function of equation-of-state parameter is elaborated. A specific model which allows detailed study of cosmological constant boundary crossing is introduced and analytical solutions for the model dynamics are obtained. It is shown how in specific parameter regimes dark energy can be a transient phenomenon. It is further demonstrated how the model reproduces specific features of recent fits of dark energy w (z) to observational data. [ABSTRACT FROM AUTHOR]

We explore the possibility of formation of Δ baryons (1232 MeV) in neutron star matter in an effective chiral model within the relativistic mean-field framework. With variation in delta-meson couplings, consistent with the constraints imposed on them, the resulting equation-of-state (EoS) is obtained and the neutron star properties are calculated for static and spherical configuration. Within the framework of our model, the critical densities of formation of Δ s and the properties of neutron stars (NS) are found to be very sensitive to the iso-vector coupling compared to the scalar or vector couplings. We revisit the Δ puzzle and look for the possibility of phase transition from nonstrange hadronic matter (including nucleons and Δ s) to deconfined quark matter, based on QCD theories. The resultant hybrid star configurations satisfy the observational constraints on mass from the most massive pulsars PSR J1614-2230 and PSR J0348+0432 in static condition obtained with the general hydrostatic equilibrium based on GTR. Our radius estimates are well within the limits imposed from observational analysis of QLMBXs. The obtained values of R 1. 4 are in agreement with the recent bounds specified from the observation of gravitational wave (GW170817) from binary neutron star merger. The constraint on baryonic mass from the study of binary system PSR J0737-3039 is also satisfied with our hybrid EoS. [ABSTRACT FROM AUTHOR]

A multi-physics model has been developed to investigate the effects of cellular level mechanisms on the electro-thermo-mechanical response of hydrated soft tissues with radiofrequency (RF) activation. A micromechanical model generates an equation of state (EOS) that provides the additional pressure arising from evaporation of intra- and extracellular water as well as temperature to the continuum level thermo-mechanical model. A level set method is used to capture the interfacial evolution of tissue damage with the level set evolution equation derived from the second law of thermodynamics, which is consistent with Griffith’s fracture evolution criterion. The discretized equations are solved simultaneously using a Krylov subspace based iterative solver (GMRES) with block preconditioning that effectively deflates the spectrum of the system matrix, resulting in exponential convergence of the Arnoldi iterations. Example problems, including experimental validation, illustrate the computational accuracy and efficiency of the technique. [ABSTRACT FROM AUTHOR]

We study for the first time how a new class of stars could impact an ensemble of pulsars with known masses and spin-periods. These new compact objects are strange stars admixed with condensed dark matter (DM). In this exploratory theoretical work, our goal is to determine how the basic parameters of pulsars are modified for such a new class of compact objects. In particular, we consider three different scenarios that correspond to a DM mass fraction of , and . Within each scenario with fixed parameters, we predict theoretically other properties of the pulsars, such as the radius, the compactness, the moment of inertia, as well as the angular momentum. Our numerical results are summarized in tables and also shown graphically for better visualization, where a comparison between the different scenarios can be made. [ABSTRACT FROM AUTHOR]

Generalized uncertainty relation that carries the imprint of quantum gravity introduces a minimal length scale into the description of space–time. It effectively changes the invariant measure of the phase space through a factor ( 1 + β p 2 ) − 3 so that the equation of state for an electron gas undergoes a significant modification from the ideal case. It has been shown in the literature (Rashidi 2016) that the ideal Chandrasekhar limit ceases to exist when the modified equation of state due to the generalized uncertainty is taken into account. To assess the situation in a more complete fashion, we analyze in detail the mass–radius relation of Newtonian white dwarfs whose hydrostatic equilibria are governed by the equation of state of the degenerate relativistic electron gas subjected to the generalized uncertainty principle. As the constraint of minimal length imposes a severe restriction on the availability of high momentum states, it is speculated that the central Fermi momentum cannot have values arbitrarily higher than p max ∼ β − 1 ∕ 2 . When this restriction is imposed, it is found that the system approaches limiting mass values higher than the Chandrasekhar mass upon decreasing the parameter β to a value given by a legitimate upper bound. Instead, when the more realistic restriction due to inverse β -decay is considered, it is found that the mass and radius approach the values 1.4518 M ⊙ and 601.18 km near the legitimate upper bound for the parameter β . [ABSTRACT FROM AUTHOR]

This paper is devoted to study the compact objects whose pressure and density are related through polytropic equation-of-state (EoS) and MIT bag model (for quark stars) in the background of gravity. We solve the field equations together with the hydrostatic equilibrium equation numerically for the model and discuss physical properties of the resulting solution. It is observed that for both types of stars (polytropic and quark stars), the effects of model parameters and remain the same. We also obtain that the energy conditions are satisfied and stellar configurations are stable for both EoS. [ABSTRACT FROM AUTHOR]

The last decade has seen a continued development of better experimental techniques tomeasure equation-of-state (EOS) for various materials. These improvements of both static and shock-compression approaches have increased the accuracy of the EOS and challenged the complimentary theoretical modeling. The conventional modeling of EOS, at least at pressure and temperature conditions that are not too extreme, is founded on density-functional theory (DFT). Naturally, there is an increased interest in the accuracy of DFT as the measurements are becoming more refined and there is a particular interest in the robustness and validity of DFT at conditions where experimental data are not available. Here, we consider a broad and large set of 64 elemental solids from low atomic number Z up to the very high Z actinide metals. The intent is to compare DFT with experimental zero-temperature isotherms up to 1 Mbar (100 GPa) and draw conclusions regarding the theoretical (DFT) error and quantify a reasonable and defensible approach to define the theoretical uncertainty. We find that in all 64 cases the DFT error at high pressure is smaller than or equal to the DFT error at lower pressures which thus provides an upper bound to the error at high compression. [ABSTRACT FROM AUTHOR]

We study the Starobinsky or model of for neutron stars with the structure equations represented by the coupled differential equations and the polytropic type of the matter equation-of-state (EoS). The junction conditions of gravity are used as the boundary conditions to match the Schwarzchild solution at the surface of the star. Based on these the conditions, we demonstrate that the coupled differential equations can be solved directly. In particular, from the dimensionless EoS with and and the constraint of , we obtain the minimal mass of the NS to be around 1.44 . In addition, if is larger than 5.0, the mass and radius of the NS would be smaller. [ABSTRACT FROM AUTHOR]

As experimental measurements of thermodynamic properties have improved in accuracy, to five or six figures, over the decades, cubic equations that are widely used for modern thermodynamic fluid property data banks require ever-increasing numbers of terms with more fitted parameters. Functional forms with continuity for Gibbs density surface ρ(p,T) which accommodate a critical-point singularity are fundamentally inappropriate in the vicinity of the critical temperature (Tc) and pressure (pc) and in the supercritical density mid-range between gas- and liquid-like states. A mesophase, confined within percolation transition loci that bound the gas- and liquid-state by third-order discontinuities in derivatives of the Gibbs energy, has been identified. There is no critical-point singularity at Tc on Gibbs density surface and no continuity of gas and liquid. When appropriate functional forms are used for each state separately, we find that the mesophase pressure functions are linear. The negative and positive deviations, for both gas and liquid states, on either side of the mesophase, are accurately represented by three or four-term virial expansions. All gaseous states require only known virial coefficients, and physical constants belonging to the fluid, i.e., Boyle temperature (TB), critical temperature (Tc), critical pressure (pc) and coexisting densities of gas (ρcG) and liquid (ρcL) along the critical isotherm. A notable finding for simple fluids is that for all gaseous states below TB, the contribution of the fourth virial term is negligible within experimental uncertainty. Use may be made of a symmetry between gas and liquid states in the state function rigidity (dp/dρ)T to specify lower-order liquid-state coefficients. Preliminary results for selected isotherms and isochores are presented for the exemplary fluids, CO2, argon, water and SF6, with focus on the supercritical mesophase and critical region. [ABSTRACT FROM AUTHOR]

We present a theoretical analysis of the equation of state (EOS) of metals using a quasi-harmonic Einstein model with a dimensionless cohesive energy versus distance function ( F ( z )) involving the Wigner-Seitz radius and a material-dependent scaling length, as suggested in classical works by Rose, Ferrante, Smith and collaborators. Using this model, and “universal” values for the function and its first and second derivatives at the equilibrium distance ( z =0), three general interrelations between EOS parameters and the cohesive energy are obtained. The first correlation involves the bulk modulus, and the second, the thermal expansion coefficient. In order to test these results an extensive database is developed, which involves available experimental data, and results of current ab initio density-functional-theory calculations using the VASP code. In particular, the 0 K values for volume, bulk modulus, its pressure derivative, and the cohesive energy of 27 elements belonging to the first (Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn), second (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) and third (Hf, Ta, W, Re, Os, Ir, Pt, Au) transition row of the Periodic Table are calculated ab initio and used to test the present results. The third correlation obtained, allows an evaluation of the third derivative of F ( z ) at z =0 for the current elements. With this new information, a discussion is presented of the possibility of finding a “universal” F ( z ) versus z function able to account accurately for the pressure derivative of the bulk modulus of the transition elements. [ABSTRACT FROM AUTHOR]

We study the role played by an equation-of-state during gravitational collapse of a radiating star. Starting from an initially static matter configuration obeying a linear equation-of-state, the star loses hydrostatic equilibrium and undergoes dissipative collapse in the form of a radial heat flux. We show that the equation-of-state parameter plays an important role in determining the temperature profiles of the collapsing body. [ABSTRACT FROM AUTHOR]

A multi-physics model has been developed to investigate the effects of cellular level mechanisms on the thermomechanical response of ultrasonically activated soft tissue. Cellular level cavitation effects have been incorporated in the tissue level continuum model to accurately determine the thermodynamic states such as temperature and pressure. A viscoelastic material model is assumed for the macromechanical response of the tissue. The cavitation model based equation-of-state provides the additional pressure arising from evaporation of intracellular and cellular water by absorbing heat due to structural and viscoelastic heating in the tissue, and temperature to the continuum level thermomechanical model. The thermomechanical response of soft tissue is studied for the operational range of frequencies of oscillations and applied loads for typical ultrasonically activated surgical instruments. The model is shown to capture characteristics of ultrasonically activated soft tissue deformation and temperature evolution. At the cellular level, evaporation of water below the boiling temperature under ambient conditions is indicative of protein denaturation around the temperature threshold for coagulation of tissues. Further, with increasing operating frequency (or loading), the temperature rises faster leading to rapid evaporation of tissue cavity water, which may lead to accelerated protein denaturation and coagulation. [ABSTRACT FROM AUTHOR]