Equation Of State Model Research Articles

Maximum mass of charged strange quark star in presence of strange quark mass (m s )

In this manuscript, we present an approach to calculate maximum mass of strange quark star having net charge inside. For this purpose we took the modified MIT bag model equation of state in presence of non-zero strange quark mass (m s ). The general solution of Einstein field equations in presence of charge is obtained by considering a specific form of the g rr component of the line element according to Vaidya & Tikekar. Such metric ansatz describes a homogeneous fluid distribution which has a departure from the spherical geometry determined by the two parameters: spheroidal (λ) and curvature (R). In this approach, we find that maximum mass as well as radius both decreases with the increase of strange quark mass (m s ). Also maximum mass increases with charge and obtained from our model is as high as 4.383 M ⊙ for maximum allowed value of charge with m s = 0. The stability is also studied in this model and note that our model is stable for the constraint value of parameters.

Charged anisotropic tolman IV solution in matter-geometry coupled theory

This paper discusses the interior distribution of several anisotropic star models coupled with an electromagnetic field in the context of gravity, where . In this regard, a standard model of this modified gravity is taken as , where ν 3 symbolizes an arbitrary coupling constant. We assume a charged spherically symmetric metric that represents the interior geometry of compact quark stars and develop the corresponding modified field equations. These equations are then solved with the help of metric potentials of Tolman IV spacetime and a linear bag model equation of state. We consider the experimental data (i.e. radii and masses) of different quark models such as SMC X-4, SAX J 1808.4-3658, Her X-I and 4U 1820-30 to analyze how the charge and modified corrections affect their physical characteristics. The viability and stability of the resulting model is also checked for the considered star candidates with two different values of ν 3. We conclude that only two models, Her X-I and 4U 1820-30 show stable behavior in this modified framework for both values of the coupling constant.

COSMO-RS and LSER models of solution thermodynamics: Towards a COSMO-LSER equation of state model of fluids

The present work examines the formulation of a statistical thermodynamic framework for the direct interconnection of the quantum-mechanics based COSMO-RS (Conductor Screening Model for Realistic Solvation) model with Abraham’s LSER (Linear Solvation Energy Relationship) model and LSER molecular descriptors. The focus is on the hydrogen-bonding (HB) contribution to solvation enthalpy. An extensive comparison is made between COSMO-RS predictions of the HB contribution to solvation enthalpy of a variety of solute – solvent systems and the corresponding LSER predictions. A rather good agreement is observed in most of the studied systems. The cases of large discrepancies are also compared with corresponding equation-of-state calculations. The perspectives for a combination of COSMO-RS, LSER and equation-of-state approaches, which would lead to the development of a COSMO-LSER equation-of-state framework are critically discussed.

Study of charged celestial objects in modified gravity

In this paper, we assess different charged self-gravitating stellar models possessing anisotropic matter source in the background of f(G,T) gravity. For this purpose, we choose a well-known model of this gravity, i.e., f(G,T)=G2+ϱT, where ϱ stands for the coupling constant. The modified field equations are developed using MIT bag model equation of state, and their solution is found with the help of Tolman IV ansatz which contains three unknown constants. This solution is further exploited to examine the graphical behavior of Her X-I, PSR J1614-2230, 4U1820-30 and LMC X-4 celestial objects. We assume two different values of charge to figure out the pressure constituents, energy density, anisotropy and energy constraints graphically. We also discuss compactness, mass and redshift parameters. Finally, we explore stability of the considered stars through two different methods. It is concluded that all the star candidates are viable as well as stable for Q=0.1. For the larger charge, the viable behavior is also observed for all stars but PSR J1614-2230 shows unstable trend.

Solubility modeling of hydrogen sulfide in aqueous sodium salt solutions

Accurate solubility prediction of hydrogen sulfide in aqueous electrolyte solutions is critical for gas exploitation and geological storage. However, there is a lack of electrolyte Equation of State model that can accurately calculate the solubilities of hydrogen sulfide in aqueous electrolyte solutions over wide ranges of temperature, pressure, and salt molality. This work presents a modeling study on the solubilities of hydrogen sulfide in pure water and several aqueous sodium salt solutions. The thermodynamic framework used in this work is an electrolyte version of Cubic-Plus-Association Equation of State. The model’s temperature-dependent ion-gas binary interaction parameters are obtained by regressing the experimental solubilities in the aqueous electrolyte solutions. The modeling results show that the electrolyte Cubic-Plus-Association Equation of State can satisfactorily correlate the solubilities of hydrogen sulfide in aqueous electrolyte solutions over wide ranges of temperature, pressure, and salt molality. For the typical water–sodium chloride–hydrogen sulfide system, the model can satisfactorily correlate the gas solubilities with the mean relative deviation being 6.2%, with the temperature up to 593.95 K, pressure up to 32.30 MPa, and salt molality up to 6.0 mol⋅kg−1 water. Moreover, the salting-out effects and model adaptability are analyzed and discussed.

Relativistic structure of charged quark stars in energy–momentum squared gravity

Within the context of energy–momentum squared gravity (EMSG), where non-linear matter contributions appear in the gravitational action, we derive the modified TOV equations describing the hydrostatic equilibrium of charged compact stars. We adopt two different choices for the matter Lagrangian density (Lm=p versus Lm=−ρ) and investigate the impact of each one on stellar structure. Furthermore, considering a charge profile where the electric charge density ρch is proportional to the standard energy density ρ, we solve numerically the stellar structure equations in order to obtain the mass–radius diagrams for the MIT bag model equation of state (EoS). For Lm=p and given a specific value of β (including the uncharged case when β=0), the maximum-mass values increase (decrease) substantially as the gravity model parameter α becomes more negative (positive). However, for uncharged configurations and considering Lm=−ρ, our numerical results reveal that when we increase α (from a negative value) the maximum mass first increases and after reaching a maximum value it starts to decrease. Remarkably, this makes it a less trivial behavior than that caused by the first choice when we take into account the presence of electric charge (β≠0).

Comparisons of equation of state models for electrolytes: e-CPA and e-PPC-SAFT

Comparisons of equation of state models for electrolytes: e-CPA and e-PPC-SAFT

Hugoniot properties of porous stainless steel: Insights from molecular dynamics simulations

We present a systematic study of Hugoniot properties of porous 316L stainless steel using both a simple interpolation scheme and direct shock simulations in order to probe pore collapse kinetics as well as final thermodynamic states. Both methods indicate that equilibrated Hugoniot properties depend on pore density only and not on the pore distribution or size. We then create a simple porous equation of state model that is shown to be accurate for a range of validation data. This allows us to extend our simulations to make direct comparison to experimental data that have generally significantly larger system sizes and durations. In addition, our direct shock simulations indicate that the relaxation time after hotspot formation is system size dependent and can reach nanosecond timescales for the largest pores investigated in our study, thereby possibly having a measurable effect on fast dynamic loading experiments

Physical characteristics and maximum allowable mass of hybrid star in the context of f(Q) gravity

In this study, we explore several new characteristics of a static anisotropic hybrid star with strange quark matter (SQM) and ordinary baryonic matter (OBM) distribution. Here, we use the MIT bag model equation of state to connect the density and pressure of SQM inside stars, whereas the linear equation of state p_r =alpha rho -beta connects the radial pressure and matter density caused by baryonic matter. The stellar model was developed under a background of f(Q) gravity using the quadratic form of f(Q). We utilized the Tolman–Kuchowicz ansatz (Tolman in Phys. Rev. 55:364–373, 1939; Kuchowicz in Acta Phys Pol 33: 541, 1968) to find the solutions to the field equations under modified gravity. We have matched the interior solution to the external Schwarzschild spacetime in order to acquire the numerical values of the model parameters. We have selected the star Her X-1 to develop various profiles of the model parameters. Several significant physical characteristics have been examined analytically and graphically, including matter densities, tangential and radial pressures, energy conditions, anisotropy factor, redshirt, compactness, etc. The main finding is that there is no core singularity present in the formations of the star under investigation. The nature of mass and the bag constant B_g have been studied in details through equi-mass and equi-B_g contour. The maximum allowable mass and the corresponding radius have been obtained via M-R plots.

A structural analysis of self-gravitating anisotropic stars via equation of state in modified teleparallel gravity

This work aims to explore spherically symmetric anisotropic solutions describing compact stellar objects in the extended teleparallel theory of gravity with matter coupling. For this purpose, we use the Adler Finch Skea geometry for both the off-diagonal and diagonal tetrads. We explore the complete matching of the tetrad fields for two different choices of the function f(T,T), i.e., linear and nonlinear models. We obtain complete solutions to the stellar models by taking the strange quark matter distribution after defining the MIT bag model equation of state, pr=13(ρ−4BG). By using the proper choice of the tetrad forms, we incorporate the generic model f(T,T)=αTn(r)+βT(r), which can be treated as linear and nonlinear models depending upon the value of parameter n. After obtaining the field equations, we investigate different physical parameters showing the stability and physical acceptability of the stellar models by using the observational data like mass and radius of PSRJ1416−2230, 4U1608−52, CenX−3, EXO1785−248, and SMCX−1 models.

Fluid pulsation modes and tidal deformability of anisotropic strange stars in light of the GW170817 event

The effects of anisotropy on the fluid pulsation modes when adopting the so-called Cowling approximation and the tidal deformability of strange-quark stars are investigated by numerically integrating the hydrostatic equilibrium, nonradial oscillation, and tidal deformability equations, all of which are modified from their standard form to include the anisotropic effects. The fluid matter inside compact stars is described by the MIT bag model equation of state. For the anisotropy profile, we consider a local anisotropy that is both regular at the center and null at the star's surface. We find that the effect of anisotropy is reflected in the fluid pulsation modes and tidal deformability. Finally, we analyze the correlation between the tidal deformability of the GW170817 event and anisotropy.

Numerical modeling and verification of reactive projectile impacting plate

The penetration of reactive projectile into target is an extremely complex thermomechanical coupling process, and most of the researches reveal this coupling mechanism by means of experiments. In this paper, based on the finite element simulation software ANSYS/LS-DYNA, using IGNITION_ANG_GROWTH state equation and Null constitutive model, the process of reactive projectile penetrating target is numerically modeled, and the numerical simulation model is verified by ballistic impact test. The test results are in good agreement with the simulation results. Further, according to this numerical simulation model, the ballistic limit of reactive projectile penetrating target is studied. The results show that the IGNITION_ANG_GROWTH state equation and Null Constitutive model can be used to calculate the mechanical and chemical coupling responses of the reactive projectile in the process of penetration plate effectively based on the SPH algorithm. This provides a new method to study the reactive projectile penetration-explosion coupling process.

Quark matter supported wormhole in third order Lovelock gravity

It is generally believed that wormholes are supported by exotic matter violating Null Energy Condition (NEC). However, various studies of wormhole geometries under Lovelock theories of gravity have reported existence of wormhole supported by matter satisfying NEC. Being inspired by these results, we explore the possibility of the existence of wormhole supported by normal quark matter in third order Lovelock gravity theory. Well known MIT Bag Model Equation of state is chosen for describing the quark matter. Taking physically acceptable approximations, we solve the field equations for shape function which satisfies flare out condition. The residual of the approximate solution is studied for accuracy and found to be acceptable.

Discussion on Operational Stability of Governor Turbine Hydraulic System Considering Effect of Power System

Hydropower has grown to play an important role in power systems including increasing clean and low-carbon energies, and the effect of electric loads should be basically evaluated for the reliable operation of these systems. For the hydraulic–mechanical–electrical system of the hydropower station, the state equation model for stability evaluation was derived with typical electric load models and elastic models for pipe flow, and after experimental confirmation with a built single-unit setup for a system, the effects of different electrical loads and pipe flow models on typical hydropower systems stability were investigated in detail. The results indicate that for the built single-unit system with different load characteristics, the numerical results were basically consistent with experimental research, and the unit’s regulation performance for the dynamic load was superior to that of the static load. Evident differences existed in the effects of different electric loads on the operational stability, mainly depending on the pipe length and the corresponding models, and an optimum-order elastic model of pipe flow was preferred to reveal the dynamic interactions between different systems. Furthermore, for a typical two-unit system, the potential coupling resonance hydraulic–mechanical–electrical system is pointed out with the preferred-order elastic model of pipe flow.

Design of an Anthracite Creep Model Based on Fractional Order Theory: Experiments and Simulations

Fractional order theory was used to characterize the accelerated creep phase of a nonlinear creep model. To accurately describe each stage of the anthracite creep model, the “gyroscope” unit was introduced by combining the Heaviside function and the creep damage definition. The effect of damage on anthracite creep was determined by designing and completing three-axis graded-separation loading creep tests on anthracite. The test curves were combined to classify anthracite into five stages: transient deformation, pseudo-acceleration, deceleration, isothermal, and acceleration creep. Each stage was combined with suitable components to form a combined fractional-order creep model. The one-dimensional equation of the state of the model was extended to three dimensions. The Levenberg–Marquardt optimization algorithm for fitting origin rheological curves was used to complete the fitting of the basic parameters. Finite differences were performed on the model equation of state, and a secondary development of a combined fractional-order creep model (NEG) was completed based on the built-in Burgers model in FLAC3D. A comparison of the numerical simulation results shows that the combined fractional-order creep model is important for accurately predicting the full creep stage of anthracite.

Impact of symmetry energy on sound speed and spinodal decomposition in dense neutron-rich matter

Using a meta model for nuclear Equation of State (EOS) with its parameters constrained by astrophysical observations and terrestrial nuclear experiments, we examine effects of nuclear EOS especially its symmetry energy \esym term on the speed of sound squared $C^2_s(\rho)$ and the critical density $\rho_t$ where $C^2_s(\rho_t)$ vanishes (indicating the onset of spinodal decomposition) in both dense neutron-rich nucleonic matter relevant for relativistic heavy-ion collisions and the cold $n+p+e+\mu$ matter in neutron stars at $\beta$-equilibrium. Unlike in nucleonic matter with fixed values of the isospin asymmetry $\delta$, in neutron stars with a density dependent isospin profile $\delta(\rho)$ determined consistently by the $\beta$ equilibrium and charge neutrality conditions, the $C^2_s(\rho)$ almost always show a peak and then vanishes at $\rho_t$. The latter strongly depends on the high-density behavior of \esym if the skewness parameter $J_0$ characterizing the stiffness of high-density symmetric nuclear matter (SNM) EOS is not too far above its currently known most probable value of about $-190$ MeV inferred from recent Bayesian analyses of neutron star observables. Moreover, in the case of having a super-soft \esym that is decreasing with increasing density above about twice the saturation density of nuclear matter, the $\rho_t$ is significantly lower than the density where the \esym vanishes (indicating the onset of isospin-separation instability and pure neutron matter formation) in neutron star cores.

Derivation and validation of a reference data-based real gas model for hydrogen

Hydrogen plays an important role for the decarbonization of the energy sector. In its gaseous form, it is stored at pressures of up to 1000 bar at which real gas effects become relevant. To capture these effects in numerical simulations, accurate real gas models are required. In this work, new correlation equations for relevant hydrogen properties are developed based on the Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). Within the regarded temperature (150–400 K) and pressure (0.1–1000 bar) range, this approach yields a substantially improved accuracy compared to other data-based correlations. Furthermore, the developed equations are validated in a numerical simulation of a critical flow Venturi nozzle. The results are in much better accordance with experimental data compared to a cubic equation of state model. In addition, the simulation is even slightly faster.

Chalcocite Cu2S solubility in aqueous sulfide and chloride fluids. Thermodynamic properties of copper(I) aqueous species and copper transport in hydrothermal systems

The most important Cu reserves, including ores of porphyry deposits, were formed by Cl- and S-bearing hydrothermal fluids transporting and depositing metals within the magmatic-hydrothermal ore systems. In order to determine the state of Cu in the fluids, we measured the solubility of chalcocite Cu2S at 350 and 450 °C, 500 and 1000 bar. The concentration of H2S varied from 0.08 to 0.4 m [mol⋅(kg H2O)−1], NaOH – from 0 to 0.2 m, NaCl + HCl – from 0.01 to 4 m. The solubility of chalcocite can be described by the reactions:0.5 Cu2S(cr) + 0.5 H2S(aq) = CuHS(aq) log K°CuHS = −3.99 ± 0.07 (350 °C/500 bar)−4.61 ± 0.09 (450 °C/500 bar), −4.26 ± 0.11 (450 °C/1000 bar);0.5 Cu2S(cr) + 0.5 H2S(aq) + HS− = Cu(HS)2− log K°Cu(HS)2- = −0.85 ± 0.08 (350 °C/500 bar)−0.65 ± 0.11 (450 °C/1000 bar);0.5 Cu2S(cr) + HCl(aq) = CuCl(aq) + 0.5 H2S(aq) log K°CuCl = −3.11 ± 0.70 (450 °C/1000 bar);0.5 Cu2S(cr) + HCl(aq) + Cl− = CuCl2− + 0.5 H2S(aq) log K°CuCl2- = 0.33 ± 0.19 (450 °C/1000 bar)These results, together with data of Rubtsova et al. (2023) on the coupled solubility of Cu(cr) and Ag in chloride fluids, demonstrated that a simple extended Debye-Hückel equation describe activity coefficients of charged species at any NaCl concentration up to the solubility limit at near- and supercritical PT-parameters; activity coefficients of neutral species can be calculated with Setchenov parameter equal to zero. The Cu2S(cr) solubility in sulfide-chloride-bearing fluids is consistent with the formation of Cu-Cl complexes which implies that mixed Cu-HS-Cl complexes can be neglected. The experimental values pooled with the reliable literature data were fitted to the HKF (Helgeson-Kirkham-Flowers) model equation of state (EoS). The obtained HKF EoS parameters allow to predict thermodynamic properties of CuHS(aq), Cu(HS)2−, and CuCl(aq) from 25 to 700 °C and from Psat. to 2000 bar, and up to 1000 °C/5000 bar for CuCl2−. The AD (Akinfiev and Diamond) EoS parameters were derived for CuCl(aq). The AD EoS can be used to calculate the CuCl(aq) Gibbs free energy in the low-density fluids (ρH2O < 0.35 g⋅cm−3) up to 700 °C. The obtained thermodynamic data imply that CuCl2− predominates in high-density ore-forming fluids (ρH2O > 0.35 g⋅cm−3) of total chloride content >0.1 wt% up to the NaCl saturation limit. The hydrosulfide complexes are the main forms of Cu occurrence in the fluid with concentration of dissolved chlorides <0.1 wt% equilibrated with silicate mineral assemblages (e.g., K-feldspar-muscovite-quartz, pH is near-neutral). However, their concentration in the presence of Cu-bearing sulfides is low (< 0.5 ppm at 500 °C/1500 bar) and decreases with temperature decreasing.

Neural network surrogate models for equations of state

Equation of state (EOS) data provide necessary information for accurate multiphysics modeling, which is necessary for fields such as inertial confinement fusion. Here, we suggest a neural network surrogate model of energy and entropy and use thermodynamic relationships to derive other necessary thermodynamic EOS quantities. We incorporate phase information into the model by training a phase classifier and using phase-specific regression models, which improves the modal prediction accuracy. Our model predicts energy values to 1% relative error and entropy to 3.5% relative error in a log-transformed space. Although sound speed predictions require further improvement, the derived pressure values are accurate within 10% relative error. Our results suggest that neural network models can effectively model EOS for inertial confinement fusion simulation applications.

Phase Behavior and Reversibility Mechanisms of Asphaltene Precipitation for High-Pressure High-Temperature CO2–Oil Systems

Net-zero carbon emission pledges by 2050 are prompting researchers to investigate alternatives to store CO2 safely. Subsurface CO2 storage faces many challenges, especially when the geological space is a depleted oil reservoir. A crucial problem is the newly formed asphaltenes during CO2 injection that could limit or even block the rock-effective zone for gas storage. In this work, a novel pressure–volume–temperature cell and a solid detection system are used to measure the phase behavior, asphaltene onset pressure, and asphaltene precipitation. Results show four different equilibrium phases during the isothermal depressurization processes. Likewise, asphaltene precipitation increases with CO2 fractions and decreases with temperature, reaching its maximum at the bubble point. More importantly, the redissolution of asphaltene particles back into the solution is observed, revealing the formation process reversibility at certain conditions (25 mol % CO2 at 60, 90, and 120 °C; 35 mol % CO2 at 90 and 120 °C). The Peng–Robinson equation of state model is employed to model the fluid phase, while the solid phase equilibrium is modeled with a solid model. A new correlation for the asphaltene molar volume is proposed, which predicts the experimental data with an AARD of 0.7%.