Presence Of Gravity Research Articles

Thin-wall vacuum decay in the presence of a compact dimension

We study the problem of false vacuum decay in arbitrary dimensions, in the presence of gravity, and compute the transition probability within the thin-wall approximation, generalising the results of Coleman and de Luccia. In the particular case of one compact dimension, we present explicit formulae for the Euclidean Bounce configuration that drives the transition from a de Sitter to Minkowski or from a Minkowski to anti-de Sitter vacua.

An existence theorem for generalized Abelian Higgs equations and its application

In this note, we construct self-dual vortices and cosmic strings from the generalized Abelian Higgs theory in which the Higgs potential is a polynomial whose degree depends on the number m . When | m | > 0 , we obtain sharp existence theorems for vortices and strings corresponding to the absence and presence of gravity, respectively, over the whole plane. In the absence of gravity, we prove the existence of vortices by using a monotone iteration method. When gravity is taken into account, a regularization method and a fixed-point theorem are used to show that multiple string solutions exist under a sufficient condition imposed only on the total number of strings. In addition, a series of properties with respect to vortices and strings have also been established.

Waves and strings in an interacting conformal chiral 2-form theory in six dimensions

In six dimensions there exists a unique one-parameter family of nonlinear conformal electrodynamics for a chiral 2-form gauge field that includes (in a free-field limit) the linear chiral 2-form theory and is related, by dimensional reduction, to the four-dimensional ModMax electrodynamics. In this work, we present the first exact solutions of this theory in presence of gravity. In particular, we will consider plane wave, Robinson-Trautman, and self-dual dyonic string configurations, generalizing well-known solutions of this type in six-dimensional supergravities with linear chiral 2-form multiplets. Published by the American Physical Society 2024

Local versus Global Time in Early Relativity Theory.

In his groundbreaking 1905 paper on special relativity, Einstein distinguished between local and global time in inertial systems, introducing his famous definition of distant simultaneity to give physical content to the notion of global time. Over the following decade, Einstein attempted to generalize this analysis of relativistic time to include accelerated frames of reference, which, according to the principle of equivalence, should also account for time in the presence of gravity. Characteristically, Einstein's methodology during this period focused on simple, intuitively accessible physical situations, exhibiting a high degree of symmetry. However, in the final general theory of relativity, the a priori existence of such global symmetries cannot be assumed. Despite this, Einstein repeated some of his early reasoning patterns even in his 1916 review paper on general relativity and in later writings. Modern commentators have criticized these arguments as confused, invalid, and inconsistent. Here, we defend Einstein in the specific context of his use of global time and his derivations of the gravitational redshift formula. We argue that a detailed examination of Einstein's early work clarifies his later reasoning and demonstrates its consistency and validity.

Reducing energy consumption and enhancing trapping and capacity of CO2 sequestration: The effects of pore heterogeneity and fluid properties

Sequestrating the CO2 into deep geological formations is a profound approach to reduce green-house gas and thus mitigate climate change. In this context, ceiling the energy consumption, enhancing the CO2 trapping to facilitate further dissolution and mineralization, and expanding the CO2 sequestration capacity have gained extensive interests. Here, we explore the roles of pore heterogeneity and fluid properties in optimizing energy consumption and maximizing CO2 sequestration effectiveness by computational modeling. We validate the modeling results through microfluidic experiments. We discover that placing the low Pore-Throat-Ratio layer at the middle fosters 7 % reductions of energy consumptions per pore volume, and a Ca<4.0 × 10−5 saves 8 % energy consumption per kgCO2. The High-Median-Low heterogeneous pores optimally perform not only in residual CO2 generation (22%PV) and conservation (7%PV) but also in CO2 sequestration capacity (67%PV). Regarding fluid properties, the enlarged hydrophilicity and viscosity ratio with reduced density difference and interfacial tension increase the residual CO2 and energy consumption while suppress the sequestration capacity. The presence of gravity especially when Bo > 6 × 10−5 promotes the residual CO2 generation and conservation yet burdens the energy consumptions. This work bridges the gap between energy consumption and CO2 sequestration effectiveness by uncovering the significant roles of pore heterogeneity and fluid properties.

Using Hydrodynamic Similarity as a Verification Method for Impact Cratering Simulations in the FLAG Hydrocode

Hydrodynamic codes (hydrocodes) are common tools for modeling hypervelocity impacts to provide insight into the physical phenomenon. Hydrocodes can simulate impacts from micrometer to kilometer spatial scales and reach impact velocities difficult to achieve in experimental settings. However, numerical models are approximations, and demonstrating that a numerical method is capable of providing physical results for these models is essential. In this work, we employ a hydrocode verification technique that leverages hydrodynamic similarity, a mathematical property of the conservation equations of fluid mechanics that form the basis for hydrocode models. Using the FLAG hydrocode, we simulate aluminum (Al) and basalt projectiles and targets at spatial scales spanning 7 orders of magnitude (hundreds of micrometers to kilometers). These materials were chosen because Al-6061 is a common material in spacecraft and satellites and basalt is a useful approximation of rocky astronomical bodies. Our results show that hydrodynamic similarity holds for each material model used and across spatial scales. We show that under certain conditions hydrodynamic similarity can apply in the presence of gravity and that similarity does not hold in the presence of strength models. We conclude that the FLAG hydrocode preserves important mathematical properties of fluid dynamics in hypervelocity impacts of Al-6061 and basalt.

A numerical investigation on the vibration of a two-deck Euler–Bernoulli beam flooded by a potential flow

Abstract This work concerns the structural vibration of a bladeless wind turbine, modelled by a two-deck Euler–Bernoulli beam, due to a surrounding potential flow. The deflection is governed by the Euler–Bernoulli equation which is studied first by a linear theory and then computed numerically by a finite difference method in space with a collocation method over the arc length, and an implicit Euler method in time. The fluid motion in the presence of gravity is governed by the full Euler equations and solved by the time-dependent conformal mapping technique together with a pseudo-spectral method. Numerical experiments of excitation by a moving disturbance on the fluid surface with/without a stochastic noise are carried out. The random process involved in generating the noise on the water surface is driven by a Wiener Process. A Monte Carlo method is used for stochastic computations. The generated surface waves impinge on the beam causing structural vibration which is presented and discussed in detail. By elementary statistical analysis, the structural response subject to the stochastic hydrodynamic disturbance caused by white noise is found to be Gaussian.

Graviton–photon conversions in Euler–Heisenberg nonlinear electrodynamics

We study graviton–photon conversions in an environment of the uniform and constant magnetic field considering Euler–Köckel–Heisenberg-type nonlinear corrections in electrodynamics. We take the transverse-tracefree gauge for gravitons and employ both the field potential and the electric and magnetic (EM) fields for photons. The nonlinear correction causes parity violating (chiral) graviton propagation equations, which depend on the two treatments for photons. Thus, the medium becomes effectively birefringent for two polarizations of gravitational waves similar to the photon birefringence, a characteristic of the nonlinear correction. In the presence of gravity, due to the nontrivial relation between the potential and EM fields, it is important to present the result using the EM fields.

Is the Coleman–de Luccia Action Minimum?: An AdS/CFT Approach

Abstract We use the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to find the least bounce action in an AdS false vacuum state, i.e. the most probable decay process of the metastable AdS vacuum within the Euclidean formalism by Callan and Coleman. It was shown that the O(4) symmetric bounce solution leads to the action minimum in the absence of gravity, but it is nontrivial in the presence of gravity. The AdS/CFT duality is used to evade the difficulties particular to a metastable gravitational system. To this end, we show that the Fubini bounce solution in CFT, corresponding to the Coleman–de Luccia (CdL) bounce in AdS, gives the least action among all finite bounce solutions in a conformal scalar field theory. Thus, we prove that the CdL action is the least action among all possible large and thin-wall configurations under certain conditions.

Free surface water waves generated by instability of an exponential shear flow in arbitrary depth

The stability of an exponential current in water to infinitesimal perturbations in the presence of gravity and capillarity is revisited and reformulated using the Weber and Froude numbers. Some new results on the generation of gravity-capillary waves are presented, which supplement the previous works of Morland et al. [“Waves generated by shear layer instabilities,” Proc. Math. Phys. Sci. 433, 441–450 (1991)] and Young and Wolfe [“Generation of surface waves by shear-flow instability,” J. Fluid Mech. 739, 276–307 (2014)] on finite depth. To consider perturbations at much larger scales, special attention is given to the stability of exponential currents only in the presence of gravity. More precisely, the present investigation reveals significant insights into the stability of exponential shear currents under different environmental conditions. Notably, we have identified that the dimensionless growth rate increases with the Froude number, providing a deeper understanding of the interplay between shear layer thickness and surface velocity. Furthermore, our analysis elucidates the dimensional wavelength of the most unstable mode, emphasizing its relevance to the characteristic shear layer thickness. Additionally, within the realm of gravity-capillary instabilities, we have established a sufficient condition for the stability of exponential currents based on the Weber number. Our findings are supported by stability diagrams at finite depth, showing how the size of stable domains correlates with the characteristic thickness of the shear layer. Moreover, we have explored the stability of a thin film of liquid in an exponential shearing flow, further enriching our understanding of the complex dynamics involved in such systems.

Influence of subcooling conditions on pool boiling in microgravity conditions: Single artificial case

A series of boiling experiments on a single artificial nucleation site has been carried out on the International Space Station (ISS) in the framework of the Multiscale Boiling (RUBI) setup installed in space in 2019. The aim of these unique experiments is to understand the bubble nucleation-growth mechanisms involved in heat transfer during boiling under well-controlled operating conditions without being masked/impeded by gravity and natural convection. The bubbles can grow to large sizes that are inaccessible in the presence of gravity. They are observed by a side-view black-and-white camera and by an infrared camera through a transparent heated substrate. In this paper, we present the results of a single-bubble pool-boiling experiment with an emphasis upon the role of the surrounding liquid subcooling, several values of which are investigated. The experimental results are complemented by numerical simulations using a previously developed model. However, the model is slightly modified to account in a simplest way for possible non-condensable residuals, without which we would have a hard time to explain certain observed behaviors.

Temperature statistics of settling particles in homogeneous isotropic turbulence

Heat transfer of settling particles in homogeneous isotropic turbulence is investigated in one-way coupled Eulerian–Lagrangian direct numerical simulations. In the absence of gravity, our observations highlight that there was a correlation between particles concentration and temperature fronts, which are characterized by high-temperature gradients. The particle clustering is mainly influenced by the preferential concentration and the non-local effect, the latter being the memory of their interaction with the flow along their trajectories. Nevertheless, gravity significantly affects the clustering of particles, which further influence the heat transfer of particles with the fluid. We find that the heat transfer of particles is intricately related to particle dynamic inertia and thermal inertia, which can be quantified by the particle Stokes number St and particle thermal Stokes number Stθ, respectively. In this study, we observe that the variance of particle temperature rate of change is independent of Stθ at small thermal inertia but inversely proportional to Stθ2 for large thermal inertia. In the presence of gravity, the variance converges to Stθ−1 for particles with negligible thermal inertia. Our findings reveal that the second-order structure function of the particle temperature, indicating the enhancement of Lagrangian scalar intermittency, adheres to a power-law behavior with limited thermal inertial particles in the dissipation region, denoted as r2. However, as Stθ increases, the power law of the structure function of the particle temperature is disrupted leading to ‘thermal caustics’. The present findings of the heat transfer behavior of settling particles advance the understanding of gravity effect, and are valuable for the modeling of heat transfer in particle-laden turbulent flows.

2D FDM Simulation of Seismic Waves and Tsunamis Based on Improved Coupling Equations Under Gravity

To understand the characteristics of seismic waves and tsunamis recorded simultaneously by the ocean-bottom observation networks, the coupling between the solid Earth and the ocean has to be modeled in the presence of gravity. However, previous coupled simulations adopted approximate equations that did not fully incorporate the effects of gravity. In this study, we derived correctly linearized governing equations under gravity and compared them with those of previous studies. Numerical experiments were performed for a two-dimensional P-SV wavefield, using the finite difference method (FDM). To validate the accuracy of the calculated tsunamis, we computed the theoretical tsunami dispersion relation using a propagator matrix and compared it with our results and those of previous studies. We found that our proposed method provided more accurate results than those of previous studies, particularly in the short-period band. We also investigated the applicability of the proposed method to distant tsunamis by examining the difference between calculated and theoretical tsunami phase velocities in the long-period band. The proposed formulation provides accurate results that properly incorporate gravity into the simultaneous simulation of seismic waves and tsunamis.

Numerical simulations of bubbly flows in a vertical periodic channel

In this study, numerical simulations of bubbly flows in an infinitely long vertical channel were performed. Generally, the upper and lower boundaries of such channels are simplified as periodic boundary conditions. Unlike horizontal channel flows, the presence of gravity in the streamwise direction complicates the establishment of periodic boundary conditions. Therefore, a specialized treatment is required to prevent fluid acceleration. Here, we developed a novel treatment for the imposition of periodic boundaries and proposed a new microbubble model to consider the surface tension effect of microbubbles. To detect each bubble in the flow field, we implemented a bubble identification algorithm, which facilitates a thorough statistical analysis of bubble number, size, and spatial distribution. Validation tests were conducted, and good agreement was achieved between our results and reference data. We also confirmed that the results obtained with periodic boundaries are consistent with those achieved without them. Finally, we simulated the evolution of rising bubble swarms in a quiescent liquid. The method presented here contributes to the numerical simulations of bubbly flows in industrial systems, including oil-gas transportation, bubble columns, and nuclear reactors.

Constraints on physical computers in holographic spacetimes

Within the setting of the AdS/CFT correspondence, we ask about the power of computers in the presence of gravity. We show that there are computations on nn qubits which cannot be implemented inside of black holes with entropy less than O(2^n)O(2n). To establish our claim, we argue computations happening inside the black hole must be implementable in a programmable quantum processor, so long as the inputs and description of the unitary to be run are not too large. We then prove a bound on quantum processors which shows many unitaries cannot be implemented inside the black hole, and further show some of these have short descriptions and act on small systems. These unitaries with short descriptions must be computationally forbidden from happening inside the black hole.

Absorption cross section in gravity’s rainbow from confluent Heun equation

We investigate the scattering of a massless scalar field by a charged, non-rotating black hole in the presence of gravity’s rainbow. Using the connection coefficients of the confluent Heun equation expressed in terms of the semi-classical confluent conformal blocks and the instanton part of the Nekrasov–Shatashvili free energy, we obtain an asymptotic expansion for the low-energy absorption cross section. Furthermore, we consider the resummation of the instanton contributions to the absorption cross section, which gives the area of the black hole up to a factor of (4/3)2 .

INFLUENCE OF TEMPERATURE GRADIENTS AND FLUID VIBRATIONS ON THE THERMOCAPILLARY DROPLET BEHAVIOR IN A ROTATING CYLINDER

In this paper, a computational fluid dynamics (CFD) approach is used to analyze and numerically present the droplet movement in both stagnant and vibrated liquid in a rotating cylinder. The Ansys Fluent commercial software package is used to solve the governing continuum conservation equations for two-phase flow. The volume of fluid (VOF) method is used to track the liquid/liquid interface. The inherent velocity of droplets decreases with increasing Marangoni number, in agreement with previous space onboard experimental findings that have been documented in literature. Complex behaviors of droplets in zero gravity were observed due to small host fluid vibration and rotational motion, which are neglected in the presence of gravity. Therefore, the impact of varying vibration amplitude as well as angular velocity on bubble migration is presented. It has been found that thermocapillary migration slows down with high vibration amplitude (A), when the fluid is vibrating. For a static liquid inside a rotating cylinder, the velocity of thermocapillary droplet migration decreases with the angular velocity increase. Temperature gradient (∇T) increment also increases the droplet's migration speed inside the vibrating fluid and a rotating cylinder of different Marangoni numbers (Ma&lt;sub&gt;T&lt;/sub&gt;). A flow pattern figure that illustrates the actual flow behind each modification is included with every result.

2D Problem of a Nonlocal Thermoelastic Diffusion Solid with Gravity via Three Theories

PurposeThe impact of gravity on nonlocal thermoelastic diffusion solid is discussed in this work.Methods The Green-Naghdi theory (G-N II), the Lord-Shulman theory, and the three-phase-lag model all explore the issue. The governing equations are solved using the normal mode technique to get the analytic forms of the displacements, temperatures, force stress tensors, and mass concentration. Using appropriate boundary conditions, the physical fields are calculated and the numerical computations have been carried out with the help of MATLAB programming.Results In the physical domain, numerical results for the field quantities are provided and graphically displayed in both the absence and presence of gravity and the nonlocal parameter.ConclusionPhysical variables are affected by nonlocal thermoelasticity as well as the gravity field.

High‐pressure high‐temperature fluid displacement by foam injection within a multiblock matrix‐fracture system

AbstractFoam injection has been suggested and demonstrated as a potential gas‐based solution for enhancing oil recovery from underground reservoirs. While the pore‐scale behavior of foam has been investigated for many years, most of those studies were done at room temperature and pressure. A high‐pressure high‐temperature (HPHT) cell was constructed to relax this contributing simplification and evaluate foam behavior under reservoir conditions. The performance of foam injection into a fractured reservoir was investigated experimentally at vertical and horizontal pathways utilizing a 2D microfluidic device. The results showed foam had a higher lamellae density in the fracture network and could direct fluids to the matrix. This was mainly attributed to the created pressure drop in the fractured media dictated by foam self‐tuning ability, which is a higher viscosity in areas with higher conductivity. Generating a viscous crossflow in horizontal tests leads to enhanced recovery relative to gas injection. But the presence of gravity in the vertical tests causes the drainage of the foam film and the segregation of the gas and surfactant solution due to gravity, which ultimately reduces the stability of the foam. Comparing the performance of gas and foam in the vertical injection scenario reveals that foam injection results in a considerably more enhanced oil recovery. The oleic phase had a detrimental impact on foam strength and reduced fluids diversion from fracture to matrix. The sizes of gas bubbles were also larger in the presence of the oleic phase.

Instability of a viscoelastic film with insoluble surfactants on an oscillating plane

The linear instability of viscoelastic film with insoluble surfactants on an oscillating plane for disturbances with arbitrary wavenumbers is investigated. The combined effects of viscoelastic and insoluble surfactants on the instability are described using Floquet theory. For long-wavelength instability, the solution in the limit of long wave perturbations is obtained by the asymptotic expansion method. The results show that the presence of viscoelastic film shifts the stability boundaries to the low-frequency region in the absence of gravity when the imposed frequency is less than 6. The U-shaped neutral curves with separation bandwidth appear in the presence of gravity. The finite-wavelength instability is solved numerically based on the Chebyshev spectral collocation method. Different from the previous results, a new branch point with special structure of a neutral curve is detected for clean-surface film. Results show that the presence of the surfactants will decrease the unstable frequency bandwidth and increase the critical Reynolds number. Both the travelling-wave mode and standing-wave mode are found due to the existence of surface surfactants. For high-frequency oscillation, the viscoelastic parameter may significantly destabilize the flow and the instability is determined by the finite-wavelength mode over a relatively large frequency range.