Radial Pressure Research Articles

Physical properties and maximum allowable mass-radius relation of complexity-free compact stellar objects within modified gravity formalism* *The authors MKJ and SKM acknowledge that this work is carried out under TRC Project (BFP/RGP/CBS/22/014). This study is also supported via funding from Prince Sattam bin Abdulaziz University project number (PSAU/2024/R/1445). The authors are thankful to the Deanship of Graduate Studies and Scientific

This paper investigates the physical properties and predicted radii of compact stars generated by the Tolman-IV complexity-free model within the background of modified gravity theory, particularly the -gravity theory, under complexity formalism for a spherically symmetric spacetime proposed by L. Herrera [Phys Rev D 97: 044010, 2018]. By solving the resulting set of differential equations, we obtain the explicit forms of the energy-momentum (EM) tensor components, including the density, radial pressure, and tangential pressure. The influence of the parameter χ on various physical properties of the star is thoroughly investigated. The model undergoes a series of rigorous tests to determine its physical relevance. The findings indicate that the model exhibits regularity, stability, and a surface with vanishing pressure. The boundary of this surface is determined by carefully selecting the parameter space. The complexity method employed in gravity offers an interesting approach for developing astrophysical models that are consistent with observable events as demonstrated by recent experiments. In this regard, we use observational data from the GW190814 event, detected by the LIGO and Virgo observatories, to investigate the validity of the Tolman-IV model in gravity. The analysis includes comparing the model's predictions with the observed characteristics of the compact object involved in the merger. In addition, data from two-millisecond pulsars, PSR J1614-2230 and PSR J0952-0607, are incorporated to further constrain the theoretical theories. However, we present a diagram depicting the relationship between the total mass and radius of the compact object candidates for different values of χ.

Axisymmetric Compression of a Circular Particle Raft Driven by the Diffusion of Surfactant.

Particle rafts are a new kind of soft matter formed by self-organization on the interface, which possesses mechanical properties between fluid and solid, and they have been widely used in many industrial fields. In the present study, the compression experiment of a circular particle raft is first performed, where an SDS (sodium dodecyl sulfate)-coated metal ring is placed around its periphery. When the surfactant diffuses, the particle raft shrinks, and its shrinkage ratio increases with the increase in the surfactant concentration, where the experimental results are consistent with the numerical simulation. Next, the relationship between the initial surface tension difference of SDS and the radius shrinkage of the particle raft is obtained by dimensional analysis. In what follows, the diffusion model is built to quantify the diffusion process of SDS at the liquid-gas interface, and then the analytical concentration solution of the concentration of SDS at the periphery of particle raft is given. The particle raft is viewed as an elastic circular plate under the action of the radial pressure, which originates from the surface tension difference, which has been verified by the experimental result. These explorations cast a new light on how to apply loads to measure mechanical properties of soft matter, which also provide some inspirations on the design of microsensors and microfluidics.

Realistic compact objects in the f(R, T) gravity in the background of polytropic and barotropic gas models

The f(R, T) gravity in the background of the polytropic and barotropic fluid has been investigated in this work. We have selected the TOV equation to determine the internal spacetime of a spherically symmetric galactic object. With the use of the Einstein equation, we have selected KB-spacetime to calculate the mass, compactness, and surface redshift of a spherically symmetric body. Explicit conditions for model parameters have been constructed for the boundary conditions of the interior and exterior spacetime, and the Schwarzschild solution has been employed in the modified f(R, T) gravity theory to evaluate different matching criteria. An increasing pattern in compactness with respect to the different radii is evident in the graphical representation of the compactness evolution for each of the individual star models. After selecting a non-vacuum field equation for higher order curvature, we reformulated f(R, T) for R and T. As a result, the tangential pressure, radial pressure, and matter density have all been calculated. According to the study, as the radius goes to infinity, the tangential and radial pressures display asymptotic flatness and converge to zero. Polytropic and barotropic gas EoS have been adopted since the star model confronts the presence of an isotropic fluid backdrop. It has been noted that in a polytropic background, density and pressure increase with distance from the star’s core, but in a barotropic background, the pressure exhibits an ascending pattern as a function of radius.

Oxygenation management during veno-arterial ECMO support for cardiogenic shock: a multicentric retrospective cohort study.

Hyperoxemia is common and associated with poor outcome during veno-arterial extracorporeal membrane oxygenation (VA ECMO) support for cardiogenic shock. However, little is known about practical daily management of oxygenation. Then, we aim to describe sweep gas oxygen fraction (FSO2), postoxygenator oxygen partial pressure (PPOSTO2), inspired oxygen fraction (FIO2), and right radial arterial oxygen partial pressure (PaO2) between day 1 and day 7 of peripheral VA ECMO support. We also aim to evaluate the association between oxygenation parameters and outcome. In this retrospective multicentric study, each participating center had to report data on the last 10 eligible patients for whom the ICU stay was terminated. Patients with extracorporeal cardiopulmonary resuscitation were excluded. Primary endpoint was individual mean FSO2 during the seven first days of ECMO support (FSO2mean (day 1-7)). Between August 2019 and March 2022, 139 patients were enrolled in 14 ECMO centers in France, and one in Switzerland. Among them, the median value for FSO2mean (day 1-7) was 70 [57; 79] % but varied according to center case volume. Compared to high volume centers, centers with less than 30 VA-ECMO runs per year were more likely to maintain FSO2 ≥ 70% (OR 5.04, CI 95% [1.39; 20.4], p = 0.017). Median value for right radial PaO2mean (day 1-7) was 114 [92; 145] mmHg, and decreased from 125 [86; 207] mmHg at day 1, to 97 [81; 133] mmHg at day 3 (p < 0.01). Severe hyperoxemia (i.e. right radial PaO2 ≥ 300 mmHg) occurred in 16 patients (12%). PPOSTO2, a surrogate of the lower body oxygenation, was measured in only 39 patients (28%) among four centers. The median value of PPOSTO2mean (day 1-7) value was 198 [169; 231] mmHg. By multivariate analysis, age (OR 1.07, CI95% [1.03-1.11], p < 0.001), FSO2mean (day 1-3)(OR 1.03 [1.00-1.06], p = 0.039), and right radial PaO2mean (day 1-3) (OR 1.03, CI95% [1.00-1.02], p = 0.023) were associated with in-ICU mortality. In a multicentric cohort of cardiogenic shock supported by VA ECMO, the median value for FSO2mean (day 1-7) was 70 [57; 79] %. PPOSTO2 monitoring was infrequent and revealed significant hyperoxemia. Higher FSO2mean (day 1-3) and right radial PaO2mean (day 1-3) were independently associated with in-ICU mortality.

Thermal Hydraulic Analysis of Turbulent Flow of Superheated Steam Through Multiple Configurations of 3D Angular Piping Bend in Power Plant Installations

Abstract One of the most vulnerable parts in high-pressure and temperature pipeline networks in steam turbine power plant installations is pipe bends, due to intense fluctuation of velocity and pressure of the superheated steam flowing through the piping bend. On the other hand, because of unique chemical and physical properties, the transportation of superheated steam can adversely effect on the integrity of the pipe bends in the piping network. Therefore, the potential risk of pipeline failure becomes more probable at bends. Therefore, to ensure the survivability of the piping network, thorough investigations of the superheated steam flowing through pipe bends are of great significance in better understanding its flow behavior. However, to predict flow behavior at piping bend, intensive research by direct experiment at high temperature and pressure might not be possible to some extent. In that case, computer codes and models can help us analyze flow behavior of superheated steam at pipe bends. The current work is a computational fluid dynamics investigation, where numerical examination is carried out by commercial code ansys fluent for thermal hydraulic analysis of flow behavior of superheated steam through multiple configurations of 3D angular piping bend: 90 deg, 120 deg, and 135 deg. Validation of credibility of the computational approach is done against Sudo et al.'s experiment. With relatively good agreement between the experiment and numerical result using air flowing through 90 deg elbow, single-phase turbulent flow of superheated steam is examined by the application of realizable turbulence model (k–ɛ). The final assessment of the computed results has been done using qualitative and quantitative analyses. The study reveals that unlike the pressure profiles, the radial velocity profiles at the bend exit are noticeably different from those at the bend inlet, since they exhibit more rounded peaks and gentler velocity gradients. The study also shows that the radial pressure and velocity profiles do not display any sign of the existence of a pair of vortices.

A generalized static spherically symmetric anisotropic compact stellar model

We report here a new exact solution of the Einstein field equations that describes a static spherically symmetric, anisotropic compact stellar fluid sphere. A generalized metric form corresponding to the grr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g_{rr}$$\\end{document} component and a specific anisotropic profile generates the model. The new class of generalized solutions reduces to Finch-Skea, Vaidya Tikekar and Schwarzschild interior solutions for specific cho-ices of the model parameters. The model parameters have been determined from the continuity of the interior and exterior metrics at the surface of the star and setting the radial pressure at the boundary to zero. Recent observed measurements from some pulsars as sources have been utilized to validate our model.

Stability of a realistic astrophysical pulsar and its mass–radius relation in higher-order curvature gravity

The objective of this research is to explore compact celestial objects while considering the framework of an extended gravitational theory known as R+f(G) gravity. The notations R and G denote the Ricci scalar and the Gauss–Bonnet invariant, respectively. Radio pulsars, which are neutron stars with masses greater than 1.8 times that of the Sun (M⊙), provide exceptional opportunities for delving into fundamental physics in extraordinary environments unparalleled in the observable universe and surpassing the capabilities of experiments conducted on Earth. Through the utilization of both the linear and quadratic expressions of the function f(G)=α1G2, where α1 (with dimensional units of [length6]) are incorporated, we have achieved an accurate analytical solution for anisotropic perfect-fluid spheres in a state of hydrostatic equilibrium. By integrating the dimensional parameters α1 and the compactness factor, defined as C=2GMRc2, we showcase our capacity to encompass and depict all physical characteristics within the stellar structure. We illustrate that the model is capable of producing a stable arrangement for the pulsar PSR J0740+6620, encompassing its geometric and physical properties. We illustrate that by utilizing the quadratic form of G in the R+f(G) framework, the Krori-Barua ansatz establishes semi-analytical relationships between radial pressure (pr), tangential pressure (pt), and density (ρ). Remarkably, in the context of the positive/negative α1 quadratic R+f(G) gravity framework, the maximum compactness is inherently restricted to values fail below the Buchdahl limit when the surface density exceeds 4×1014 g/cm3. This differs from General Relativity (GR) in which the compactness is unlikely to approach the black hole limit. The model predicts a core density that is multiple times greater than the saturation nuclear density, represented as ρnuc=4×1014 g/cm3, and a surface density ρs that surpasses the nuclear saturation density. We offer the mass–radius diagram associated with the boundary density we have determined, and this diagram has been shown to be consistent with other observational discoveries.

Modelling Einstein cluster using Einasto profile

We demonstrate a general relativistic approach to model dark matter halos using the Einstein cluster, with the matter stress-energy generated by collisionless particles moving on circular geodesics in all possible angular directions and orbital radii. Such matter, as is known, allows an anisotropic pressure profile with non-zero tangential but zero radial pressure. We use the Einasto density profile for the Einstein cluster. Analytical studies on its properties (metric functions) and stability issues are investigated. Further, to establish this model (with the Einasto profile) as one for a dark matter halo,we use the SPARC galactic rotation curve data and estimate the best-fit values for the model parameters. General relativistic features (beyond the Keplerian velocities) such as the tangential pressure profile, are quantitatively explored. Thus, Einstein clusters with the Einasto profile, which tally well with observations, may be considered as a viable model for dark matter halos.

Numerical Solution of Micropolar Fluid for Jenkins Model with Micro-Rotation between Two Rotating Disks

The flow of a steady, axi-symmetric, incompressible micropolar fluid between two infinite rotating disks is described for Jenkins Model. The governing equations are reduced to non-linear ordinary differential equations and are solved numerically through the shooting technique. The graphs are plotted and the impact of the material constant is analysed on the velocity, micro-rotation velocity profiles and pressure. The results reveal that the material constant has a significant effect on radial velocity, axial velocity and pressure.

Numerical and experimental studies on the thermodynamic characteristics of post-buckling separate plate in the clutch

Considering the influence of the contact and friction for buckling deformation, a comprehensive model is proposed to study the timing-varying thermodynamic characteristics of the clutch. The mathematical model is developed to calculate the contact status of the post-buckling separate plate, which is testified by the finite element method and bench experiments. The post-buckling plate undergoes a five-stage deformation, and the radial contact pressure finally forms ‘M/W′ shape during engagements. With the increasing buckling angle, the plate flattening threshold and pressure decay increase gradually; meanwhile, the radial temperature distribution is sculptured as ‘W′ shape, creating larger thermal stress and thermal bending moment. Thus, the surface morphology is changed by the wear which related to the pressure and thermal distribution.

Gaussian black holes in brane-world model

We present regular black hole solutions in the framework of Brane-world gravity sourced by a Gaussian matter distribution. The black hole metric shares all the common features of regular black holes in the modified General Relativity (GR) with some exciting features. Considering the energy momentum tensor for an isotropic fluid on the brane, the modified Einstein field equation results with an effective energy momentum tensor that describes an anisotropic fluid determined by brane world parameters. Although the effective radial pressure and energy density satisfy the vacuum energy condition, the effective transverse pressure behaves differently. Gaussian black hole (GBH) solutions are obtained from a Gaussian matter distribution. In the paper, a new class of GBH solutions are obtained in the brane-world gravity with effective normal matter in addition to exotic matter distribution. In the brane world gravity, the mass of a GBH depends on the brane tension. The mass of a GBH formed in the brane world is greater than that at low energy (i.e., GR). We study the trajectories of the massive and the massless particles that can be trapped around a GBH for a set of model parameters. The radii of the photon spheres around the GBH and the condition for the stability of the trajectories of the photon spheres are determined. The properties of the GBHs are studied in detail, including their possible observable features.

Fully developed pipeline flow fast simulation model and application to a rod bundle subchannel

For the fully developed pipeline flow, if the radial time-averaged velocity and radial pressure gradient can be ignored, the time-averaged Navier-Stokes equations can be simplified into a diffusion equation. Based on this, the Fully Developed Model (FDM) was proposed. The adiabatic FDM was applied to the simulation of the flow field in a rod bundle subchannel and got results consistent with that from the commercial CFD code. The short time calculation of FDM makes its application in system analysis codes becoming possible.

Physical physiognomies of hybrid Karmarkar stars

Our current study intends to investigate the peculiar features of a Hybrid compact star that is both static and anisotropic, wherein the core consists of strange quark matter, while regular baryonic matter is distributed in its crust. The relationship between the pressure of strange quark matter and density within the stellar interior is described using the simplest form of the phenomenological MIT Bag model equation of state: Pq=13(ρq−4Bg). On the other hand, the radial pressure and matter density resulting from baryonic matter are correlated through a straightforward linear equation of state: Pr=mρ. Apart from that, we also incorporate the Karmarkar condition, which establishes a connection between the two components of the metric potentials, specifically grr and gtt. For one metric potential, we presumptively choose a specific model i.e. eλ=1+a2r2(1+br2)4, and the Karmarkar condition leads to us the second potential. Moreover, the Einstein field equations are solved by using Karmarkar technique, and additional identification of the unknown constants is carried out using some physical constraints. We employ both graphical and analytical techniques to assess the physical plausibility of our suggested framework. More specifically, we focused on seven compact stars as candidates for strange quark stars in this investigation. For this purpose, the existing observational data of the compact objects were compared to theoretical mass–radius estimates. Furthermore, a series of physical tests has been conducted to substantiate the physical feasibility and stability of our proposed model. These experiments encompass both analytical and graphical assessments and involve examining various aspects, such as the dynamic balance of applied forces, compactness factor, energy conditions, surface redshift, and other relevant parameters. In conclusion, our comprehensive analysis reveals that the present system fulfills all the essential physical requirements necessary for a realistic representation of the hybrid compact star. Moreover, the model demonstrates suitability for conducting in-depth investigations pertaining to strange quark stars. The adherence to physical prerequisites and the potential for further exploration make our current model a promising candidate for studying and understanding the intriguing properties of such astrophysical objects.

Investigating the stability mechanisms of single bulk Nanobubbles: A molecular dynamics perspective

In this study, we investigated the relationship between bubble stability and various parameters, including radial pressure, density, surface tension, charge distribution, and Brownian motion, using molecular dynamics simulations and classical bubble stability theory. Our research sheds light on the contrasting behavior of small and large nanobubbles in water, with larger bubbles demonstrating a prolonged lifespan and lower internal pressure. Specifically, nanobubbles with radii of 14 Å, 18 Å, and 22 Å were found to have pressures of 792 atm, 647 atm, and 518 atm, respectively. Notably, our calculations revealed that smaller bubbles possess a thicker liquid-gas interface compared to the larger bubbles. Additionally, our analysis of gas-liquid interactions and mean squared displacement demonstrated that smaller bubble gas molecules experience stronger liquid forces and exhibit enhanced diffusivity. Importantly, we validated the reliability of classical theories by confirming the consistency between the calculated solubility of nanobubbles using Henry's law and simulation results. Moreover, our findings aligned with the predictions of Young's equation regarding surface tension at the calculated plane, highlighting its applicability in understanding nanobubbles behavior. Notably, we observed that gas density has minimal impact on the surface tension of nanobubbles according to Young's equation. Overall, our research provides valuable insights into the generation of stable nanobubbles for diverse applications.

Flow rate measurements of slug flow by pressure differences of a venturi tube with a swirler

When the elongated bubbles and liquid slugs of slug flow alternately flow through a throttling element, the strong random fluctuations of pressure difference leads to low accuracy of online measurement of gas-liquid flow rates. In this paper, slug flow is converted into an annular flow before entering a venturi tube using a swirler, and the pressure fluctuation amplitude of the gas-liquid two-phase flow is greatly reduced, and the linear correlation between the pressure difference and the gas-liquid flow rates is more significant. The effects of gas-liquid flow rates on the axial pressure difference ΔPs across the swirler, the radial pressure difference ΔPr on a cross-section downstream of the swirler and the axial pressure difference ΔPo of the venturi tube were studied under the condition of 40%–82% gas volume fraction. The square root of the pressure difference increases linearly with the liquid/gas flow rate, and the empirical correlations between the square root of the pressure differences and the gas-liquid flow rates are established. By combining the empirical correlations in pairs, three flow rates measurement models of slug flow based on double pressure differences are established. When ΔPo and ΔPs are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±2% and ±15%, respectively. When ΔPo and ΔPr are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±3% and ±15%, respectively. It provides high-precision, low-cost and non-radioactive two-phase flow measurement technology for oil-gas gathering and transportation.

Finslerian wormhole solution in the framework of modified gravity

Abstract This article investigates the properties of a wormhole model in a specific gravity theory, namely f(Ric, T) = Ric + 2λ T. The wormhole solution is analyzed using an exponential shape function. The study examines various parameters, such as density, radial pressure, transverse pressure, equation-of-state parameters, and energy conditions, within the framework of deformed gravity. The research emphasizes the influence of the parameter λ on energy condition violations and the equilibrium state of the Finslerian wormhole solution. These effects are attributed to anisotropic and hydrostatic forces present in modified gravity. The study demonstrates that the gravity model effectively captures the characteristics of wormholes within the Finslerian space-time. Additionally, the identified features of the wormhole are utilized to visualize its structure by creating a three-dimensional representation of the embedded surface. In summary, this research contributes to understanding wormholes in modified gravity theories, highlighting the importance of the parameter λ in determining their behavior and properties.

Study of exponential wormhole metric in f(R) gravity

In this work, we have studied ‘the exponential form’ of space-time metric in some of the viable f(R) gravity models, viz. exponential gravity model, Starobinsky gravity model, Tsujikawa model, and Gogoi-Goswami f(R) gravity model. Here, we have calculated the parameters including energy density, tangential pressure, and radial pressure for these corresponding models of f(R) gravity. Subsequently, we have investigated the energy conditions, viz. null energy condition (NEC), weak energy condition (WEC), strong energy condition (SEC), and dominant energy condition (DEC) for the considered models. We have also explained the suitable stability conditions for these models through related plots. We observed that the exponential wormhole metric obeys all the necessary energy conditions in f(R) gravity without violating any flare-out or stability conditions. Out of four considered viable f(R) gravity models, the exponential, the Tsujikawa, and the Gogoi-Goswami f(R) gravity models are found to be more suitable for the exponential wormhole to exist, although all these models have some constraints on the ranges of the parameters used.

Analysis of vortex characteristics in hump region of reversible pump-turbine based on omega vortex identification method

As the core equipment of pumped storage power stations, reversible pump-turbines will frequently switch between different working modes during operation, and it is easy to appear hump region under pump condition, which will greatly affect the performance of the pumped storage unit. Therefore, in order to explore the causes of the hump region, this paper takes the model reversible pump-turbine as the research object. First, the unit speed–unit flow characteristics are compared with the model test results under different working conditions. Then, based on the omega vortex identification method, the vortex distribution in the flow channel of the unit is analyzed. By analyzing the flow characteristics of the flow components of the unit under different flow rates in the hump region, the internal flow law of the hump region is revealed. It is found that when the flow rate decreases, the rising head cannot offset the head lost by the hydraulic loss, thus forming the hump region, and the unstable flow gradually appears in the guide vane and runner area. There are unstable phenomena, such as flow separation, in the guide vane area. There is a sudden change of radial pressure in the vaneless area between the guide vane and the runner; that is, the unstable vortex almost occupies the whole flow channel due to the change of pressure in this area, resulting in the deterioration of the instability of the unit operation. When the flow rate is large, the radial pressure mutation zone mainly exists between the guide vane cascades, making it easy to form an unstable vortex. The research results can provide a theoretical reference for improving the stability of reversible pump-turbines.

Rotating regular black holes and other compact objects with a Tolman-type potential as a regular interior for the Kerr metric

In this paper, we obtain a new class of stationary axisymmetric spacetimes by using the Gürses–Gürsey metric with an appropriate mass function in order to generate a rotating core of matter that may be smoothly matched to the exterior Kerr metric. The same stationary spacetimes may be obtained by applying a slightly modified version of the Newman–Janis algorithm to a nonrotating spherically symmetric seed metric. The starting spherically symmetric configuration represents a nonisotropic de Sitter-type fluid whose radial pressure [Formula: see text] satisfies an state equation of the form [Formula: see text], where the energy density [Formula: see text] is chosen to be the Tolman-type-VII energy density [R. C. Tolman, Phys. Rev. 55, 364 (1939)]. The resulting rotating metric is then smoothly matched to the exterior Kerr metric, and the main properties of the obtained geometries are investigated. All the solutions considered in this study are regular in the sense they are free of curvature singularities. Depending on the relative values of the total mass m and rotation parameter a, the resulting stationary spacetimes represent different kinds of rotating compact objects such as regular black holes, extremal regular black holes, and regular starlike configurations.

Viscosimetric squeeze flow of suspensions.

The rheology of particle suspensions has been extensively explored in the case of a simple shear flow, but less in other flow configurations which are also important in practice. Here we investigate the behavior of a suspension in a squeeze flow, which we revisit using local pressure measurements to deduce the effective viscosity. The flow is generated by approaching a moving disk to a fixed wall at constant velocity in the low Reynolds number limit. We measure the evolution of the pressure field at the wall and deduce the effective viscosity from the radial pressure drop. After validation of our device using a Newtonian fluid, we measure the effective viscosity of a suspension for different squeezing speeds and volume fractions of particles. We find results in agreement with the Maron-Pierce law, an empirical expression for the viscosity of suspensions that was established for simple shear flows. We prove that this method to determine viscosity remains valid in the limit of large gap width. This makes it possible to study the rheology of suspensions within this limit and therefore suspensions composed of large particles, in contrast to Couette flow cells which require small gaps.