Isotropic Pressure Research Articles

Continuum description of confluent tissues with spatial heterogeneous activity.

A continuum description is built to characterize the stationary and transient deformations of confluent tissues subject to heterogeneous activities. By defining a coarse-grained texture matrix field to represent the shape and size of cells, we derive the coarse-grained stress tensor for the vertex model. Activity in the tissue takes the form of inhomogeneous apical contractions, which can be modeled as reductions of the vertex model reference areas or perimeters representing activity in the medial and perimeter regions of the cells, respectively. For medial activity, the extra stress is just an isotropic pressure, while for perimeter activity, it also has a deviatoric component, which is aligned with the texture matrix. The predictions of the continuum description are compared with the average spatiotemporal deformations obtained in simulations of the vertex model subject to localized apical contractions, showing an excellent agreement, even if the active patch is as small as one cell. The fluctuations around the average are more prominent when the activity is in the medial region due to the lack of negative active shape feedback, which, coupled with the confluent property, increases cellular shape and size variations.

Anisotropic pressure effects on nanoconfined water within narrow graphene slit pores.

There is an increasing interest toward disclosing and explaining confinement effects on liquids, such as water or aqueous solutions, in slit pore setups. Particularly puzzling are the changes of physical and chemical properties in the nanoconfinement regime where no bulk-like water phase exists between the two interfacial water layers such that the density profile across the slit pore becomes highly stratified, ultimately leading to bilayer and monolayer water. These changes must be quantified with respect to some meaningful reference state of water, the most natural one being bulk water at the same pressure and temperature conditions. However, bulk water is a homogeneous liquid with isotropic properties, whereas water confined in slit pores is inhomogeneous, implying anisotropic properties as described by the perpendicular and parallel components of the respective tensors. In the case of pressure, the inhomogeneous nature of the setup results in a well-defined difference between the perpendicular and parallel pressure tensor components that is uniquely determined by the interfacial tension being a thermodynamic property. For bilayer water constrained in graphene slit pores that are only about 1 nm wide, we demonstrate that there exists a thermodynamic point where the pressure tensor of the inhomogeneous fluid, nanoconfined water, is effectively isotopic and the pressure is thus scalar as in the homogeneous fluid, bulk water. This specific point of vanishing effective interfacial tension is proposed to serve as a well-defined reference state to compare the properties of nanoconfined liquids to those of the corresponding bulk liquid at the same (isotropic) pressure and temperature conditions. In future work, this idea could be applied to assess confinement effects on chemical reactivity in aqueous solutions as well as to other nanoconfined liquids in other pores such as layered minerals.

Defect Wormhole: A Traversable Wormhole Without Exotic Matter

We present a traversable-wormhole solution of the gravitational field equation of General Relativity without need of exotic matter (exotic matter can, for example, have negative energy density and vanishing isotropic pressure). Instead of exotic matter, the solution relies on a 3-dimensional "spacetime defect" characterized by a locally vanishing metric determinant.

Accelerating scenarios of massive universe in [formula omitted]-gravity

In this study, we have investigated accelerating scenarios of massive universe in a generalized f(R,Lm)-gravity with observational constrained, where R is Ricci scalar curvature and Lm is matter Lagrangian for perfect fluid. We have obtained the field equations using a flat Friedman–Lamatre–Robertson–Walker (FLRW) space–time metric with matter Lagrangian Lm=−p and f(R,Lm)=R2+αLmn−β where α, β&n are positive model parameters. We have solved field equations with constant equation of state (EoS) parameter ω defined by p=ωρ, where p is the isotropic pressure and ρ is the energy density of the perfect fluid. We have derived the Hubble parameter in terms of energy parameters Ωm0 and Ωβ0 and obtained the best fit curve of Hubble parameter with 46 H0 datasets over 0≤z≤2.36 for the best fit present values of Ωm0,Ωβ0,ω,n. We have discussed the result with recent cosmological observations and we have found a transition redshift zt=1.4129 with age of the present universe t0=14.2689 Gyrs. The present universe is found in accelerating phase with q0=−0.3891 and H0=64.75±5.334 Km/s/Mpc. Also, we have analyzed Om diagnostic parameter for our f(R,Lm)-gravity model.

Transition-layer of core–rim structures and β→α transformation in SiC ceramics

Similar to Si3N4 ceramics, β→α phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties. SiC microstructures are dominated with the core–rim structures by AlN-solution, and by EBSD analysis, α-lamellae were revealed as stacking-faults (SF) and twin-boundaries (TB) in β-grains, co-existing with the core–rim structures as α/β→α’/β’ transformation by sintering. The structural transformation can proceed much further by gas-pressure-sintering than hot-pressing with only RE2O3 agents, while the latter retain a high-density of SF/TB in the metastable β-SiC grains. By high-angle secondary-electron imaging, nanoscale transition-layer (TL) was observed as an inter-phase to fully separate the core and rim, which is created by a transitory equilibrium in the solution–reprecipitation process. The enrichment of AlN or RE in TL demonstrates their segregation to core surface until reaching the super-saturation and before the growth of rims. With higher AlN or RE solution and after sintering, a shear stress can develop from TL contour to drive the expansion of SF/TB in Martensitic transition, especially under an external isotropic pressure. The combinations of β→α transformation, core–rim structures and viscous liquid-phase enable the comprehensive assessment of sintering–microstructure–property–performance relationship of SiC ceramics, as demonstrated for their creep behaviors and fracture toughness.

A STUDY ON MANIFOLD KAEHLERIAIN SPACE

This work delves into the space-time theory of the 4-dimensional Kaehler manifold. Since the isotropic pressure, energy density, and energy momentum tensor all vanish in a perfect fluid Kaehler space-time manifold, we have established that this space-time manifold is an Einstein manifold and studied the Einstein equation with a cosmological constant in it. Finally, we demonstrated that, on a conformally flat, perfectly fluid Kaehler space-time manifold, the velocity vector field is infinitesimally spatially isotropic. Ideal fluid dilution to the point where only Ricci and minimal symmetry hold. We have proven that Kaehler space-time manifolds have either 0 scalar curvature or a connection between the respective rho and alpha vector fields via g(rho,alpha) = 4. To conclude, we have proved that a Kaehler space-time manifold cannot have both perfect fluidity and non-zero scalar curvature (weak Ricci symmetry).

Chemical compaction and fluid segregation in piston cylinder experiments

Fluid segregation is a ubiquitous process in deep-seated rocks, mainly driven by buoyancy and gravitational compaction, which occur in drained systems until permeability decreases and the system become practically undrained. The mechanism and rate of fluid segregation following this stage are poorly constrained, despite the importance of these factors for fluid distribution and the physical and chemical properties in the Earth. To this end, we performed sintering experiments of quartzite, with H2O–CO2 fluids of 1.9%–18.0% added volume fraction using a piston-cylinder apparatus at 900°C under nominally isotropic pressure of 1 GPa. The subsequent chemical redistribution of silica and fluids resulted in capsule-scale fluid segregation (CFS) and the formation of dense quartzite (∼0.3%) within 192 h in pure H2O systems. Comparative experiments showed that dissolution/precipitation was not caused by the temperature gradient. Instead, we considered the fluid pressure difference within the experimental capsule between fluid-rich and fluid-poor domains caused by the different response against small pressure oscillation during experiments. Fluid-rich rock is elastically “soft” (i.e., having larger Skempton's coefficient) compared to fluid-poor rock to increase pore fluid pressure under a compressional stress change. Therefore, more silica dissolves in fluid-rich domains with higher solubility, while it precipitates in fluid-poor domains through diffusive transport, expanding porosity contrast. This chemical compaction in the capsule scale is effective as long as elasticity dominates matrix viscosity because the pressure difference relaxes with time. The calculated relaxation time of quartzite at the experimental condition was comparable to the intervals of the oil pressure addition which produced stress change. A one-dimensional model for porosity evolution showed that time-averaged SiO2 diffusivity during CFS was much larger than the grain boundary diffusivity of tightly sintered quartz aggregates, but was comparable to the diffusivity of SiO2 in aqueous fluid with ∼0.1 vol% fluid fraction. During metamorphism where the fluid pressure difference may be maintained for longer duration, the spontaneous silica cementation may play a role for formation of syn-metamorphic veins and control of the amount of pore fluids transported to deep Earth.

Dispersion relation and instability for an anisotropic nonuniform flowing plasma

A generalized formula for wave instability is developed for an anisotropic nonuniform plasma with finite flows and temperatures. Six-moment fluid equations are solved to give the analytic expression for wave instability in arbitrarily nonuniform plasmas. The analytic formula explicitly states the dependence of wave instability on the nonuniformities of number density, flow velocity, and anisotropic or isotropic pressure. The accuracy of the formalism is verified by a numerical calculation of implicit dispersion relations in complex Fourier space. The analysis shows that nonuniformity plays a critical role in plasma instability, while the flow velocity and anisotropic pressures determine the growth rate of the instability. The instability diagram and associated instability criterion for anisotropy-driven instability are introduced as applications of the formalism.

Thermal Radiation from Compact Objects in Curved Space-Time

We highlight here the fact that the distantly observed luminosity of a spherically symmetric compact star radiating thermal radiation isotropically is higher by a factor of (1+zb)2 compared to the corresponding flat space-time case, where zb is the surface gravitational redshift of the compact star. In particular, we emphasize that if the thermal radiation is indeed emitted isotropically along the respective normal directions at each point, this factor of increment (1+zb)2 remains unchanged even if the compact object would lie within its photon sphere. Since a canonical neutron star has zb≈0.1, the actual X-ray luminosity from the neutron star surface could be ∼20% higher than what would be interpreted by ignoring the general relativistic effects described here. For a static compact object, supported by only isotropic pressure, compactness is limited by the Buchdahl limit zb<2.0. However, for compact objects supported by anisotropic pressure, zb could be even higher (zb<5.211). In addition, in principle, there could be ultra-compact objects having zb≫1. Accordingly, the general relativistic effects described here might be quite important for studies of thermal radiation from some ultra-compact objects.

A measure of complexity for axial self-gravitating static fluids

One of the feasible potential candidates for illustrating the accelerating expansion of the cosmos can be taken through the notion of modified gravity. Within the context of metric f(R) gravity, the contribution of this work features a better understanding of complexity factors for anisotropic static fluid composition in axially symmetric spacetime. This is a generalization of the work done by Herrera et al (2019, Phys. Rev. D 99, 044 049). We formulate generalized dynamical and field equations for anisotropic sources in our analysis. We will compute three distinct complexity factors (Y TF1, Y TF2, Y TF3) after incorporating structure scalars via orthogonal breakdown of the curvature tensor. The differential equations for the conformal tensor are assessed in terms of these complexity factors for the physical illustration. It is inferred that all these factors vanish for the matter spheroid provided with energy homogeneity and isotropic pressure. Nonetheless, the vanishing of these factors might be observed in different scenarios. This happened because energy inhomogeneity and pressure anisotropy cancel out each other in the description of complexity factors. Certain exact solutions of this nature have been reported and studied. All of the outcomes would reduce to general relativity within usual limits.

Isotropic pressure-induced electronic band structure of BaTiO3, SrTiO3 and CaTiO3 with its impact on structural and optical properties: ab-initio calculation

ABSTRACT The present theoretical study offers a comprehensive investigation under the application of systematic external static isotropic pressure, phase stability, electronic-band structure and their impact on the optical characteristics of BaTiO3, SrTiO3 and CaTiO3. All the computational works were performed by Cambridge Serial Total Energy Package, using generalised gradient approximation and density functional theory, Perdue-Burke-Ernzerhof, along with the ultra-soft pseudo-potential for the frozen core. According to structural properties, there is no phase transformation and the structure of all compounds remains cubic. The band structure is a perfect tool to observe the nature of a material, such as an insulator, semiconductor or metal. When the pressure is applied, the band gap of BaTiO3, SrTiO3 and CaTiO3 increases and retains their indirect nature. The total/partial/elemental density of states has been estimated for the full description of the band structure. To verify the authenticity of BaTiO3, SrTiO3 and CaTiO3, various optical parameters have been reported such as the real dielectric functions, imaginary dielectric functions, absorption, refractive index, extinction coefficient, energy loss function and reflectivity. All discrepancies in structural parameters, band structure and optical properties occurred due to applied pressure, and BaTiO3, SrTiO3, and CaTiO3 are connected .

Accretion Disk Luminosity for Black Holes Surrounded by Dark Matter with Tangential Pressure

We study the motion of test particles in the gravitational field of a Schwarzschild black hole surrounded by a spherical dark matter cloud with nonzero tangential pressure, and compute the luminosity of the accretion disk. The presence of nonvanishing tangential pressure allows us to mimic the dark matter’s angular momentum, while still considering a static model, which simplifies the mathematical framework. We compare the numerical results of the influence of dark matter on the luminosity of the accretion disks around static supermassive black holes with the previously studied cases of isotropic and anisotropic pressures. We show that the flux and luminosity of the accretion disk in the presence of dark matter are different from the case of a Schwarzschild black hole in a vacuum, and highlight the impact of the presence of tangential pressures.

Theoretical Search for Gravitational Bound States of Tachyons

The mission here is to see if we can find bound states for tachyons in some gravitational environment. That could provide an explanation for the phenomena called Dark Matter. Starting with the standard Schwarzschild metric in General Relativity, which is for a static and spherically symmetric source, it appears unlikely that such localized orbits exist. In this work, the usual assumption of isotropic pressure is replaced by a model that has different pressures in the radial and angular directions. This should be relevant to the study of neutrinos, especially if they are tachyons, in cosmological models. We do find an arrangement that allows bound orbits for tachyons in a galaxy. This is a qualitative breakthrough. Then we go on to estimate the numbers involved and find that we do have a fair quantitative fit to the experimental data on the Galaxy Rotation Curve. Additionally we are led to look in the neighborhood of a Black Hole and there we find novel orbits for tachyons.

Two-dimensional MHD equilibria of diamagnetic bubble in gas-dynamic trap

This article presents a magnetohydrodynamic (MHD) two-dimensional numerical model of diamagnetic bubble equilibria in an axisymmetric open trap. The theoretical model consists of the Grad–Shafranov equilibrium equation and the transport equation obtained within the resistive single-fluid MHDs with isotropic pressure. Found are the numerical solutions corresponding to the diamagnetic confinement mode. In particular, the equilibria of the diamagnetic bubble in the gas-dynamic multimirror trap are calculated. We investigate the effect of magnetic field corrugation on the equilibrium; the corrugation of the vacuum field is shown to lead to a rather moderate corrugation of the bubble boundary if the period of corrugation is sufficiently small. A valuable numerical result is the distribution of the diamagnetic field, which would be useful for optimizing the position of the wall-stabilization plates.

Exploiting the stereoelectronic effects for selective tuning of band edge states of α-SnO: GW quasiparticle calculations

Tuning the electronic structure of materials, and thus their electronic, transport, and optical properties, is of fundamental importance for materials design and optimization. Although alloying is a well-established method for engineering the band gap of semiconductors, strain engineering has emerged as a promising approach to selective tuning of band-edge states. Using a combined density functional theory and $GW$ approach, we show that the highly directional intralayer and interlayer couplings, together with the unusual stereoelectronic effects of the Sn $5s$ lone pair in \ensuremath{\alpha}-SnO, may be exploited to tune, in addition to the band gap, the valence and conduction band-edge states selectively using in-plane and/or out-of-plane strains. Whereas the uniaxial strain along the lattice $c$ direction primarily affects the position of the conduction band edge, the valence band edge is very sensitive to the biaxial $ab$ strain. We also establish a strain electronic phase diagram of \ensuremath{\alpha}-SnO, including the insulator--metal phase transition boundary. It is predicted that a compressive biaxial strain of about 3% or an isotropic pressure of 5 GPa can trigger an insulator--metal transition. The quasiparticle band gap can be widely tuned from 0 to more than 2.0 eV with moderate strains.

Electronic, elastic and optical properties of ZnAl2Te4 semiconductor under isotropic pressures via first-principles calculations

Electronic, elastic and optical properties of ZnAl2Te4 semiconductor under isotropic pressures via first-principles calculations

First-principles calculations to investigate band gap of cubic BaThO3 with systematic isotropic external static pressure and its impact on structural, elastic, mechanical, anisotropic, electronic and optical properties

The motive of this study is to offer a comprehensive evaluation of the structural, elastic, mechanical, anisotropic, electrical and optical characteristics of BaThO3 under the pressure range of 0 GPa–113 GPa. There is no phase transformation and the structure remains cubic but a diminishment in lattice parameters is observed. The material is found to be mechanically stable, inflexible, rigid and has high resistance to shear stress by computing the various elastic and mechanical (bulk modulus, shear modulus and young's modulus) parameters. The Pugh/Frantsevich ratios, Cauchy pressure, Poisson's ratio, and the Kleinman's parameter have proved the ductility, metallic bond nature and high-pressure endurance of the material. Distinctive anisotropy factors are engaged to verify that a compound is anisotropic. When the electronic band structure (BS) is taken into consideration, a change from wide band gap semiconductor (3.174eV) to narrow band gap semiconductor (1.832eV) and eventually metal (0eV) is seen. The total density of states (TDOS), the partial density of states (PDOS) and elemental partial density of states (EPDOS) have all been estimated in order to investigate the electronic BS. To enforce the relevance of this material, the real ε1(ω) and imaginary ε2(ω) dielectric functions, absorption I(ω), refractive index n(ω), extinction coefficient k(ω), loss function L(ω), reflectivity R(ω) and real/imaginary conductivity have all been calculated. The static values of ε1(ω) and n(ω) increase with applied pressure. Since its absorption spectra are present in the UV range, this is the best material to utilize as a UV filter. Additionally, its high refractive index, absorption, reflectivity, and conductivity make it an excellent component in optoelectronic devices.

Manipulation of magnetic configuration by isotropic pressure in NdFeO3

The influence of isotropic physical pressure, applied either during the high-pressure-high-temperature (HPHT) annealing or the measuring processes, on the magnetic properties of NdFeO3 single crystal, has been investigated. In comparison to the complete spin reorientation (SR) in an as-grown NdFeO3 single crystal, the thermomagnetic M(T) and isothermal M(H) curves for a HPHT-annealed sample indicates an incomplete SR transition from a Γ2-rich to a Γ4-rich Γ24 mixed phase. Moreover, the M(T) curves of the as-grown sample under different measuring hydrostatic pressures suggest that the SR transition takes place in the sequence of Γ2→Γ1 +Γ2 +Γ4→Γ1 +Γ4→Γ4, instead of the Γ2→Γ2 +Γ4→Γ4, without applying pressure during the measuring process. Such manipulation of the magnetic configuration reveals that the 3d-4f interaction in the NdFeO3 could be greatly affected by the isotropic pressure. These findings may provide a new perspective and possibility for the tuning of the magnetism and corresponding microscopic interactions.

Magnetic Collapse in Fe3Se4 under High Pressure.

Electronic structure and magnetic properties of FeSe are calculated using the density functional approach. Due to the metallic properties, magnetic moments of the iron atoms in two nonequivalent positions in the unit cell are different from ionic values for Fe and Fe and are equal to and , making the system ferrimagnetic. The total magnetic moment for the unit cell is . Under isotropic compression, the total magnetic moment decreases non-monotonically and correlates with the non-monotonic dependence of the density of states at the Fermi level . For 7% compression, the magnetic order changes from the ferrimagnetic to the ferromagnetic. At 14% compression, the magnetic order disappears and the total magnetic moment becomes zero, leaving the system in a paramagnetic state. This compression corresponds to the pressure of 114 GPa. The magnetic ordering changes faster upon application of an isotropic external pressure due to the sizeable anisotropy of the chemical bondings in FeSe. The ferrimagnetic and paramagnetic states occur under pressures of 5.0 and 8.0 GPa, respectively. The system remains in the metallic state for all values of compression.

A study of almost pseudo 𝒵 symmetric spacetimes with application to f (R) gravity

We prove that an almost pseudo [Formula: see text] symmetric spacetime with Codazzi type of [Formula: see text] tensor is perfect fluid whose velocity vector field [Formula: see text] is parallel. The energy density [Formula: see text] of such perfect fluid spacetime is constant and the state equation is obtained. Also, this spacetime is shown to be a static spacetime. Next, it is shown that such spacetime is a GRW spacetime with Einstein fiber. This kind of spacetime is investigated in f (R) theory of gravity; in this case, we find the forms of the isotropic pressure p and the energy density [Formula: see text] which are constant. Further, some energy conditions are studied in this spacetime. Finally, a concrete example of almost pseudo [Formula: see text] symmetric spacetimes is considered.