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Articles de revues sur le sujet « Medium gravity »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 10 mars 2023

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1

Cembranos, José A. R., Mario Coma Díaz et Prado Martín-Moruno. « Modified gravity as a diagravitational medium ». Physics Letters B 788 (janvier 2019) : 336–40. http://dx.doi.org/10.1016/j.physletb.2018.10.068.

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LYLE, SARAH, HERBERT E. HUPPERT, MARK HALLWORTH, MIKE BICKLE et ANDY CHADWICK. « Axisymmetric gravity currents in a porous medium ». Journal of Fluid Mechanics 543, n^o -1 (7 novembre 2005) : 293. http://dx.doi.org/10.1017/s0022112005006713.

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Dolgunin, V. N., V. Ya Borshchev et P. A. Ivanov. « Rapid Gravity Flow of a Granular Medium ». Theoretical Foundations of Chemical Engineering 39, n^o 5 (septembre 2005) : 548–54. http://dx.doi.org/10.1007/s11236-005-0115-3.

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Fakir, Redouane. « The Interstellar Medium as a Gravity Wave Detector ». International Journal of Modern Physics D 06, n^o 01 (février 1997) : 49–56. http://dx.doi.org/10.1142/s0218271897000042.

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An observer, situated several thousand light-years away from a radio pulsar, finds himself embedded in the diffraction pattern resulting from the propagation of the radio waves through the irregular interstellar medium. The gravity waves produced by an intervening binary star cause the diffraction pattern to be displaced laterally in a manner familiar from refractive interstellar scintillation, except that this gravity wave effect is not dispersive. This periodic displacement can reach a few hundred kilometers. Thus, there seems to be a possibility that the exceedingly faint gravity waves can manifest themselves macroscopically.

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WOODS, ANDREW W. « Vaporizing gravity currents in a superheated porous medium ». Journal of Fluid Mechanics 377 (25 décembre 1998) : 151–68. http://dx.doi.org/10.1017/s0022112098003012.

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We analyse the motion of a current of water migrating under gravity into a hot vapour-saturated porous rock accounting for the vaporization which occurs as the water invades the hot rock. We present a series of similarity solutions to describe the rate of advance of both planar and axisymmetric currents when the total mass of water injected after time t is proportional to tγ. Three distinct cases arise. When γ>1/2 (planar) or γ>1 (axisymmetric), the depth of the current increases at all points from the source, and therefore vaporization occurs at all points on its surface. This case is described by a simple extension of the well-known similarity solutions for non-vaporizing currents. When 0<γ<1/2 (planar) or 0<γ<1 (axisymmetric), there is a region near the source where the depth of the current decreases. The depth only increases at the more distant points. Vaporization therefore only occurs in the leading part of the current where it is advancing into the superheated rock. In this case, we develop modified similarity solutions which account for the vaporization in the distal part of the current. The third case involves the finite release of fluid. Owing to the vaporization, the mass of the current decreases with time. Since there is no injection, the rate of advance of the current can no longer be found by comparing the exponents of time in the local and global equations for mass conservation. Instead, the motion is described by a class of similarity solutions of the second kind, analogous to those described by Barenblatt (1997), in which the total mass of the current is proportional tγ, where γ is a function of the mass fraction which vaporizes, [Fscr ], such that γ→0 as [Fscr ]→0 and γ→−1 as [Fscr ]→1. The model is extended to include the effects of capillary retention of fluid in the pore spaces and we discuss the relevance of our results to the process of liquid reinjection in the geothermal power industry.

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Ryazhskikh, V. I., et Yu V. Chernukhin. « Steady-state gravity flow of a granular medium ». Theoretical Foundations of Chemical Engineering 34, n^o 5 (septembre 2000) : 500–501. http://dx.doi.org/10.1007/bf02827396.

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Kuipers, M., et A. A. F. van de Ven. « Rayleight-gravity waves in a heavy elastic medium ». Acta Mechanica 81, n^o 3-4 (septembre 1990) : 181–90. http://dx.doi.org/10.1007/bf01176985.

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Sennerby-Forsse, Lisbeth. « Clonal variation of wood specific gravity, moisture content, and stem bark percentage in 1-year-old shoots of 20 fast-growing Salix clones ». Canadian Journal of Forest Research 15, n^o 3 (1 juin 1985) : 531–34. http://dx.doi.org/10.1139/x85-087.

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Specific gravity, moisture content of the wood, and stem bark percentages in 1-year-old shoots of 20 Salix (L.) clones originating from natural and artificial stands in Sweden were measured for 3 years. Clones were classified into three groups with high, medium, and low specific gravity. Ranking stability for specific gravity was high. Moisture content and bark percentage fluctuated considerably from one year to another but showed a slight increase from the high to the medium and low specific gravity groups.

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Zhu, Yiqing, et F. Benjamin Zhan. « Medium-Term Earthquake Forecast Using Gravity Monitoring Data : Evidence from the Yutian and Wenchuan Earthquakes in China ». International Journal of Geophysics 2012 (2012) : 1–6. http://dx.doi.org/10.1155/2012/307517.

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Gravity changes derived from regional gravity monitoring data in China from 1998 to 2005 exhibited noticeable variations before the occurrence of two large earthquakes in 2008 in China—the 2008 Yutian (Xinjiang)Ms=7.3earthquake and the 2008 Wenchuan (Sichuan)Ms=8.0earthquake. Based on these gravity variations, a group of researchers at the Second Crust Monitoring and Application Center of China Earthquake Administration made a suggestion in December of 2006 that the possibility for the Yutian (Xinjiang) and Wenchuan (Sichuan) areas to experience a large earthquake in either 2007 or 2008 was high. We review the gravity monitoring data and methods upon which the researchers reached these medium-term earthquake forecasts. Experience related to the medium-term forecasts of the Yutian and Wenchuan earthquakes suggests that gravity changes derived from regional gravity monitoring data could potentially be a useful medium-term precursor of large earthquakes, but significant additional research is needed to validate and evaluate this hypothesis.

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Bhadauria, Beer S., Atul K. Srivastava, Nirmal C. Sacheti et Pallath Chandran. « Gravity Modulation of Thermal Instability in a Viscoelastic Fluid Saturated Anisotropic Porous Medium ». Zeitschrift für Naturforschung A 67, n^o 1-2 (1 février 2012) : 1–9. http://dx.doi.org/10.5560/zna.2011-0045.

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The present paper deals with a thermal instability problem in a viscoelastic fluid saturating an anisotropic porous medium under gravity modulation. To find the gravity modulation effect, the gravity field is considered in two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity field, which can be realized by shaking the fluid, has been represented by a sinusoidal function. Using Hill’s equation and the Floquet theory, the convective threshold has been obtained. It is found that gravity modulation can significantly affect the stability limits of the system. Further, we find that there is a competition between the synchronous and subharmonic modes of convection at the onset of instability. Effects of various parameters on the onset of instability have also been discussed.

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Aketi, Veera AK, TR Vakamalla, M. Narasimha, GE Sreedhar, R. Shivakumar et RajanKumar. « Computational Fluid Dynamic study on the effect of near gravity material on dense medium cyclone treating coal using Discrete Phase Model and Algebraic Slip mixture multiphase model ». Journal of Computational Multiphase Flows 9, n^o 2 (9 décembre 2016) : 58–70. http://dx.doi.org/10.1177/1757482x16677755.

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In this paper, the effect of near gravity material at desired separation density during the coal washing is studied. It is believed that the Dense Medium Separation of coal particles in the presence of high percentage of near gravity material, results in a significant misplacement of coal particles to wrong products. However the performance of dense medium cyclone does not merely depend on the total amount of near gravity materials but also on their distribution as well as on their quality. This paper deals with numerical simulation of magnetite medium segregation and coal partitioning handled in a 350 mm dense medium cyclone. Volume of Fluid coupled with Reynolds Stress Model is used to resolve the two-phase air-core and turbulence. Algebraic Slip mixture multiphase model with the granular options are considered to predict magnetite medium segregation. Medium segregation results are validated against Gamma Ray Tomography measurements. Further, Discrete Phase Model is used to track the coal particles. Residence Time Distribution of different size and density coal particles are also estimated using Discrete Phase Model. Additionally, Algebraic Slip mixture model is also utilised to simulate magnetite and coal particle segregation at different near gravity material proportions. Discrepancies in the coal particle behaviour at different near gravity material content are explained using locus of zero vertical velocities, mixture density, coal volume fractions.

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Biswas, P. K., P. R. Sengupta et Lokenath Debnath. « Axisymmetric Lamb's problem in a semi-infinite micropolar viscoelastic medium ». International Journal of Mathematics and Mathematical Sciences 19, n^o 4 (1996) : 815–20. http://dx.doi.org/10.1155/s0161171296001135.

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A study is made of the axisymmetric problem of wave propagation under the influence of gravity in a micropolar viscoelastic semi-infinite medium when a time varying axisymmetric loading is applied on the surface of the medium. Special attention is given to the effects of gravity which induces a kind of initial stress of a hydrostatic nature on the wave propagation.

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Elhag, S. H., et F. S. Bayones. « Effect of Rotation, Gravity, Primary Stress and Magnetic Field on Shear Waves Spreading in an Anisotropic Incompressible Sandy Elastic Medium ». Journal of Computational and Theoretical Nanoscience 16, n^o 11 (1 novembre 2019) : 4443–54. http://dx.doi.org/10.1166/jctn.2019.8610.

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In this paper, we investigated the spreading of shear wave in an anisotropic non-homogeneous elastic medium under effect of dry sand, rotation, gravity, primary stress, and magnetic field. We have reached equation of variation of shear wave velocity c1 in an anisotropic incompressible medium according to sand, rotation, gravity, primary stress, and magnetic field, then we used graphs to illustrate to show the effect of direction of spreading of shear wave. The results indicate that the effect of dry sand, rotation, gravity, primary stress, and magnetic field on the spreading of shear wave in an anisotropic inhomogeneous elastic medium are very pronounced. The results have been obtained are discussed and presented visually, the results demonstrate that the effect of sand, gravity field, primary stress, magnetic field, anisotropy and rotation are noticeable.

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RUITH, MICHAEL, et ECKART MEIBURG. « Miscible rectilinear displacements with gravity override. Part 1. Homogeneous porous medium ». Journal of Fluid Mechanics 420 (10 octobre 2000) : 225–57. http://dx.doi.org/10.1017/s0022112000001543.

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Rectilinear homogeneous miscible displacements with gravity override are analysed by means of direct numerical simulations on the basis of the vorticity–streamfunction formulation of the governing equations. The vorticity-based point of view offers the advantage of clearly attributing the dominant flow characteristics to the effects of viscosity contrast, density difference, impermeable boundary conditions, or interactions among the above. Basic considerations regarding the vorticity field show that in an integral sense the coupling between viscosity and gravity vorticity is predominantly one way in nature, in that the gravity vorticity can amplify the viscous vorticity, but not vice versa. In particular, the vorticity point of view provides an explanation for the formation of the gravity tongue in terms of a focusing mechanism, which results from the combined action of the unfavourable viscosity gradient and the potential flow field generated by the interaction of the gravitational vorticity with the horizontal boundaries. This potential velocity field locally enhances the uniform global displacement velocity near the upper boundary, and thereby amplifies the viscous fingering instability along this section of the interface. In some parameter ranges, the gravity tongue exhibits interesting interactions with the viscous fingers next to it, such as pinching and partial merging. The influence of the Péclet number, the viscosity and density contrasts, and the aspect ratio on the dynamic evolution of the displacement is investigated quantitatively.

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Othman, Mohamed I. A., et Montaser Fekry. « Effect of rotation and gravity on generalized thermo-viscoelastic medium with voids ». Multidiscipline Modeling in Materials and Structures 14, n^o 2 (4 juin 2018) : 322–38. http://dx.doi.org/10.1108/mmms-08-2017-0082.

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PurposeThe purpose of this paper is to study the effect of rotation and gravity on a homogeneous, isotropic, and generalized thermo-viscoelastic material with voids. The problem is studied in the context of the coupled theory, Lord-Shulman theory with one relaxation time, and Green-Lindsay theory with two relaxation times.Design/methodology/approachThe analytical method used was the normal mode analysis technique.FindingsNumerical results for the physical quantities were analyzed and presented graphically. The graphical results indicated that the effects of rotation and gravity were observable physical effects on the thermo-viscoelastic material with voids. Comparisons were made between the results obtained in the absence and presence of rotation and gravity.Originality/valueIn the present work, the authors investigated the effect of rotation and gravity on thermo-viscoelastic medium with voids. Comparisons were also made between the three theories in the absence and the presence of rotation and gravity. Such problems are very important in many dynamical systems.

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Senin, Nor Halawati, Nor Fadzillah Mohd Mokhtar et Mohamad Hasan Abdul Sathar. « Ferroconvection in an Anisotropic Porous Medium with Variable Gravity ». Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 71, n^o 2 (27 mai 2020) : 56–68. http://dx.doi.org/10.37934/arfmts.71.2.5668.

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Lingevitch, Joseph F., Michael D. Collins et William L. Siegmann. « Modeling internal gravity waves in a range‐dependent medium ». Journal of the Acoustical Society of America 100, n^o 4 (octobre 1996) : 2614. http://dx.doi.org/10.1121/1.417665.

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18

PRITCHARD, DAVID. « Gravity currents over fractured substrates in a porous medium ». Journal of Fluid Mechanics 584 (25 juillet 2007) : 415–31. http://dx.doi.org/10.1017/s0022112007006623.

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We consider the behaviour of a gravity current in a porous medium when the horizontal surface along which it spreads is punctuated either by narrow fractures or by permeable regions of limited extent. We derive steady-state solutions for the current, and show that these form part of a long-time asymptotic description which may also include a self-similar ‘leakage current’ propagating beyond the fractured region with a length proportional to t1/2. We discuss the conditions under which a current can be completely trapped by a permeable region or a series of fractures.

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SPANNUTH, MELISSA J., JEROME A. NEUFELD, J. S. WETTLAUFER et M. GRAE WORSTER. « Axisymmetric viscous gravity currents flowing over a porous medium ». Journal of Fluid Mechanics 622 (10 mars 2009) : 135–44. http://dx.doi.org/10.1017/s0022112008005223.

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We study the axisymmetric propagation of a viscous gravity current over a deep porous medium into which it also drains. A model for the propagation and drainage of the current is developed and solved numerically in the case of constant input from a point source. In this case, a steady state is possible in which drainage balances the input, and we present analytical expressions for the resulting steady profile and radial extent. We demonstrate good agreement between our experiments, which use a bed of vertically aligned tubes as the porous medium, and the theoretically predicted evolution and steady state. However, analogous experiments using glass beads as the porous medium exhibit a variety of unexpected behaviours, including overshoot of the steady-state radius and subsequent retreat, thus highlighting the importance of the porous medium geometry and permeability structure in these systems.

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Bayones, Fatimah S., et Nahed S. Hussien. « Fibre-Reinforced Generalized Thermoelastic Medium Subjected to Gravity Field ». Journal of Modern Physics 06, n^o 08 (2015) : 1113–34. http://dx.doi.org/10.4236/jmp.2015.68116.

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Schiller, S., G. M. Tino, P. Gill, C. Salomon, U. Sterr, E. Peik, A. Nevsky et al. « Einstein Gravity Explorer–a medium-class fundamental physics mission ». Experimental Astronomy 23, n^o 2 (29 novembre 2008) : 573–610. http://dx.doi.org/10.1007/s10686-008-9126-5.

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Füglistaler, A., et D. Pfenniger. « Solid H2 in the interstellar medium ». Astronomy & ; Astrophysics 613 (mai 2018) : A64. http://dx.doi.org/10.1051/0004-6361/201731739.

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Context. Condensation of H2 in the interstellar medium (ISM) has long been seen as a possibility, either by deposition on dust grains or thanks to a phase transition combined with self-gravity. H2 condensation might explain the observed low efficiency of star formation and might help to hide baryons in spiral galaxies. Aims. Our aim is to quantify the solid fraction of H2 in the ISM due to a phase transition including self-gravity for different densities and temperatures in order to use the results in more complex simulations of the ISM as subgrid physics. Methods. We used molecular dynamics simulations of fluids at different temperatures and densities to study the formation of solids. Once the simulations reached a steady state, we calculated the solid mass fraction, energy increase, and timescales. By determining the power laws measured over several orders of magnitude, we extrapolated to lower densities the higher density fluids that can be simulated with current computers. Results. The solid fraction and energy increase of fluids in a phase transition are above 0.1 and do not follow a power law. Fluids out of a phase transition are still forming a small amount of solids due to chance encounters of molecules. The solid mass fraction and energy increase of these fluids are linearly dependent on density and can easily be extrapolated. The timescale is below one second, the condensation can be considered instantaneous. Conclusions. The presence of solid H2 grains has important dynamic implications on the ISM as they may be the building blocks for larger solid bodies when gravity is included. We provide the solid mass fraction, energy increase, and timescales for high density fluids and extrapolation laws for lower densities.

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Aggarwal, A. K., et D. Dixit. « Effect of Suspended Particles on Thermosolutal Convection of Rivlin-Ericksen Fluid in Porous Medium with Variable Gravity ». International Journal of Applied Mechanics and Engineering 23, n^o 3 (1 août 2018) : 813–20. http://dx.doi.org/10.2478/ijame-2018-0045.

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Abstract The thermosolutal stability of a layer of the Rivlin-Ericksen fluid in a porous medium is considered under varying gravity conditions. It is found that for stationary convection, medium permeability and suspended particles have a destabilizing/stabilizing effect when gravity increases/decreases. The stable solute gradient has a stabilizing effect on the system.

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Gupta, Asit Kumar, et Pulak Patra. « Influence of gravity on torsional surface waves in a dissipative medium ». Geofísica Internacional 60, n^o 1 (1 janvier 2021) : 1–13. http://dx.doi.org/10.22201/igeof.00167169p.2021.60.1.1916.

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The present paper deals with the possibilities of propagation of torsional surface waves in a viscoelastic medium under gravity field. During the study it will observe that the increase in gravity parameter will increase the velocity of the wave, the increase in viscoelastic parameter, decrease the velocity of the wave until the product of angular frequency and viscoelastic parameter is less than unity. It also notes that as the velocity increases, the curve becomes asymptotic in nature when the period of oscillation increases. In fact the maximum damping in velocity has been identified at this cut off point which may be considered as the point where a viscoelastic material becomes a viscous medium.The absorption coefficients have also been calculated for different values of the viscoelastic parameter and gravity field.

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Philatov, Vladimir, Lubov Boltnova et Ksenya Vandysheva. « Generalization of study experience of Ural ore deposits by method of tectonophysical analysis gravitational field ». E3S Web of Conferences 177 (2020) : 02001. http://dx.doi.org/10.1051/e3sconf/202017702001.

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Gravity is important in the history of Earth 's formation and evolution. Gravitational accretion, gravitational differentiation of Earth matter by density. Gravitational accretion, gravity differentiation of the Earth 's substance in density, its movement and other processes deform the Earth 's crust, contribute to the formation in it of different scale, shape and metallogenical specialization of plicative and disjunctive structures, with which genetically and spatially related deposits of different minerals. The link between gravity and deformation of the geological medium is its density inhomogeneities. Their role is twofold: they are either formed by gravity stresses or are themselves sources of stress and strain. The method of studying the deformation of the geological medium by gravity is called tectonophysical analysis of the gravitational field. Its physical basis is two fundamental laws: the law of world gravity and the law on proportional dependence between stress and deformation. This method solves two problems.

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BOLSTER, DIOGO, ALICE HANG et P. F. LINDEN. « The front speed of intrusions into a continuously stratified medium ». Journal of Fluid Mechanics 594 (14 décembre 2007) : 369–77. http://dx.doi.org/10.1017/s0022112007008993.

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This paper examines intrusive Boussinesq gravity currents, propagating into a continuously stratified fluid. We develop a model, based on energy arguments, to predict the front speed of such an intrusive gravity current from a lock release. We find that the depth at which the intrusion occurs, which corresponds to the level of neutral buoyancy (i.e. the depth where the intrusion density equals the stratified fluid density), affects the front speed. The maximum speeds occur when the intrusion travels along the top and bottom boundaries and the minimum speed occurs at mid-depth. Experiments and numerical simulations were conducted to compare to the theoretically predicted values, and good agreement was found.

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Dolgunin, V. N., O. O. Ivanov et S. A. Akopyan. « Quasithermal Effects During Rapid Gravity Flow of a Granular Medium ». Advanced Materials & ; Technologies, n^o 3(19) (2020) : 047–55. http://dx.doi.org/10.17277/amt.2020.03.pp.047-055.

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The investigation results of granular temperature during rapid gravity flow of granular medium on a rough chute are discussed. The granular temperature is determined as the kinetic energy of several forms of mutual displacements of particles. The influence of the chute angle on the value ratio of different components of granular temperature is analyzed. The components of granular temperature induced by fluctuation, shear and transversal mutual displacements of particles were taken into account.

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Barsky, E. M. « Medium Motion Modes and Universal Curves for Gravity Separation Processes ». Refractories and Industrial Ceramics 62, n^o 1 (mai 2021) : 11–14. http://dx.doi.org/10.1007/s11148-021-00553-0.

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Bulatov, V. V., et Yu V. Vladimirov. « Asymptotical analysis of internal gravity wave dynamics in stratified medium ». Applied Mathematical Sciences 8 (2014) : 217–40. http://dx.doi.org/10.12988/ams.2014.311637.

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VELLA, DOMINIC, et HERBERT E. HUPPERT. « Gravity currents in a porous medium at an inclined plane ». Journal of Fluid Mechanics 555 (mai 2006) : 353. http://dx.doi.org/10.1017/s0022112006009578.

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Fan, Tianguang, et Jill S. Buckley. « Rapid and Accurate SARA Analysis of Medium Gravity Crude Oils ». Energy & ; Fuels 16, n^o 6 (novembre 2002) : 1571–75. http://dx.doi.org/10.1021/ef0201228.

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Kaladze, T. D., L. V. Tsamalashvili et D. T. Kaladze. « Electromagnetic internal gravity waves in an ideally conducting incompressible medium ». Journal of Atmospheric and Solar-Terrestrial Physics 182 (janvier 2019) : 177–80. http://dx.doi.org/10.1016/j.jastp.2018.11.011.

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Hueckstaedt, R. M., J. H. Hunter et R. V. E. Lovelace. « Self-gravity driven instabilities of interfaces in the interstellar medium ». Monthly Notices of the Royal Astronomical Society 369, n^o 3 (1 juillet 2006) : 1143–51. http://dx.doi.org/10.1111/j.1365-2966.2006.10348.x.

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Othman, Mohamed I. A., et Ethar A. A. Ahmed. « Effect of gravity field on piezothermoelastic medium with three theories ». Journal of Thermal Stresses 39, n^o 4 (28 mars 2016) : 474–86. http://dx.doi.org/10.1080/01495739.2016.1152136.

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35

Qinghe, Zhang, Wu Yongsheng et Zhao Zidan. « Linear theory of gravity waves on a Voigt viscoelastic medium ». Acta Mechanica Sinica 16, n^o 4 (novembre 2000) : 301–8. http://dx.doi.org/10.1007/bf02487683.

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Gouyet, J. F., M. Rosso, E. Clément, C. Baudet et J. P. Hulin. « Invasion of a porous medium under gravity : A quantitative analysis ». Physica A : Statistical Mechanics and its Applications 157, n^o 1 (mai 1989) : 497–98. http://dx.doi.org/10.1016/0378-4371(89)90349-x.

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Chand, R., G. C. Rana et S. Kumar. « Variable Gravity Effects on Thermal Instability of Nanofluid in Anisotropic Porous Medium ». International Journal of Applied Mechanics and Engineering 18, n^o 3 (1 août 2013) : 631–42. http://dx.doi.org/10.2478/ijame-2013-0038.

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Abstract In this paper, we study the effects of variable gravity on thermal instability in a horizontal layer of a nanofluid in an anisotropic porous medium. Darcy model been used for the porous medium. Also, it incorporates the effect of Brownian motion along with thermophoresis. The normal mode technique is used to find the confinement between two free boundaries. The expression of the Rayleigh number has been derived, and the effects of variable gravity and anisotropic parameters on the Rayleigh number have been presented graphically

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GOLDING, MADELEINE J., et HERBERT E. HUPPERT. « The effect of confining impermeable boundaries on gravity currents in a porous medium ». Journal of Fluid Mechanics 649 (13 avril 2010) : 1–17. http://dx.doi.org/10.1017/s0022112009993223.

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The effect of confining boundaries on gravity currents in porous media is investigated theoretically and experimentally. Similarity solutions are derived for currents when the volume increases as tα in horizontal channels of uniform cross-section with boundary height b satisfying b ~ a|y/a|n, where y is the cross-channel coordinate and a is a length scale of the channel width. Experiments were carried out in V-shaped and semicircular channels for the case of gravity currents with constant volume (α=0) and constant flux (α=1). These showed generally good agreement with the theory.Typically, we find that the propagation of the current is well described by L ~ tc for some scalar c. We study the dependence of c on the time exponent of the volume of fluid in the current, α, and the geometry of the channel, parameterized by n. For all channel shapes, there exists a critical value of α, αc = 1/2, above which increasing n causes an increase in c and below which increasing n causes a decrease in c, where increasing n corresponds to opening up the channel boundary to the horizontal. The current height increases or decreases with respect to time depending on whether α is greater or less than αc. It is this fact, along with global mass conservation, which explains why varying the channel shape n affects the propagation rate c in different ways depending on α.We also consider channels inclined at an angle θ to the horizontal. When the slope of the channel is much greater than the slope of the free surface of the current, the component of gravity parallel to the slope dominates, causing the current to move with a constant velocity, Vf say, regardless of channel shape n and flux parameter α, in agreement with results for a two-dimensional gravity current obtained by Huppert & Woods (1995) and some initially axisymmetric gravity currents presented by Vella & Huppert (2006). If the effect of the component of gravity perpendicular to the channel may not be neglected, i.e. if the slopes of the channel and free surface of the current are comparable, we find that, in a frame moving with speed Vf, the form of the governing equation for the height of a current in an equivalent horizontal channel is recovered. We calculate that the height of a constant flux gravity current down an inclined channel will tend to a fixed depth, which is determined by the channel shape, n, and the physical properties of the fluid and rock. Experimental and numerical results for inclined V-shaped channels agree very well with this theory.

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Agullo, Ivan, Adrian del Rio et Jose Navarro-Salas. « Gravity and handedness of photons ». International Journal of Modern Physics D 26, n^o 12 (octobre 2017) : 1742001. http://dx.doi.org/10.1142/s0218271817420019.

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Vacuum fluctuations of quantum fields are altered in the presence of a strong gravitational background, with important physical consequences. We argue that a nontrivial spacetime geometry can act as an optically active medium for quantum electromagnetic radiation, in such a way that the state of polarization of radiation changes in time, even in the absence of electromagnetic sources. This is a quantum effect, and is a consequence of an anomaly related to the classical invariance under electric-magnetic duality rotations in Maxwell theory.

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Ahmed, S. M. « Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of gravity ». International Journal of Mathematics and Mathematical Sciences 2005, n^o 19 (2005) : 3145–55. http://dx.doi.org/10.1155/ijmms.2005.3145.

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The aim of this paper is to investigate the Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of a gravity field. The frequency equation obtained, in the form of a sixth-order determinantal expression, is in agreement with the corresponding result when both media are elastic. The frequency equation when the gravity field is neglected has been deduced as a particular case.

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MOSS, ADAM, et DOUGLAS SCOTT. « GRAVITY HEATS THE UNIVERSE ». International Journal of Modern Physics D 18, n^o 14 (31 décembre 2009) : 2201–7. http://dx.doi.org/10.1142/s021827180901603x.

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Structures in the Universe grew through gravitational instability from very smooth initial conditions. Energy conservation requires that the growing negative potential energy of these structures be balanced by an increase in kinetic energy. A fraction of this is converted into heat in the collisional gas of the intergalactic medium. Using a toy model of gravitational heating, we attempt to link the growth of structure in the Universe with the average temperature of this gas. We find that the gas is rapidly heated from collapsing structures at around z ~ 10, reaching a temperature > 106 K today, depending on some assumptions of our simplified model. Before that there was a cold era from z ~ 100 to ~10 in which the matter temperature was below that of the cosmic microwave background.

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Sethi, Munish, Manisha Gupta, Kishan Chand Gupta, Mahinder Singh Saroa et Deepak Gupta. « Surface waves in fibre-reinforced anisotropic solid elastic media under the influence of gravity ». Journal of the Mechanical Behaviour of Materials 20, n^o 4-6 (1 juin 2012) : 81–85. http://dx.doi.org/10.1515/jmbm.2011.017.

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AbstractThe aim of the present article is to investigate the surface waves in anisotropic, elastic solid medium under the influence of gravity. The theory of generalised surface waves has first been developed and then used to investigate particular cases of waves, viz., Stoneley, Rayleigh, and Love. The wave velocity equations have been obtained for different cases and are in well agreement with the corresponding classical result, when the effect of gravity, viscosity, and fibre-reinforced parameters of the material medium are ignored.

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Y. H., Gangadharaiah, Suma S. P et Ananda K. « VARIABLE GRAVITY FIELD AND THROUGHFLOW EFFECTS ON PENETRATIVE CONVECTION IN A POROUS LAYER ». INTERNATIONAL JOURNAL OF COMPUTERS & ; TECHNOLOGY 5, n^o 3 (30 mai 2013) : 172–91. http://dx.doi.org/10.24297/ijct.v5i3.3519.

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The effect of vertical throughflow and variable gravity field on the onset of penetrative convection simulated via internal heating in a porous medium is studied. Flow in the porous medium is governed by Forchheimer-extended Darcy equation. The boundaries are considered to be rigid, however permeable, and insulated to temperature perturbations. The eigen value problem is solved using a regular perturbation technique with wave number as a perturbation parameter. The variable gravity parameter, the direction of throughflow and the presence of volumetric internal heat source in a porous layer play a decisive role on the stability characteristics of the system. In addition, the influence of Prandtl number arising due to throughflow is also emphasized on the stability of the system. It is observed that both stabilizing and destabilizing factors can be enhanced due to the simultaneous presence of a volumetric source, gravity field and vertical throughflow so that a more precise control (suppress or augment) of thermal convective instability in a layer of porous medium is possible.

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Dolgunin, Viktor N., Oleg O. Ivanov et Sergey A. Akopyan. « Transversal mass transfer and shear stress formation during rapid gravity flow of a granular medium ». Image Journal of Advanced Materials and Technologies 6, n^o 3 (2021) : 204–15. http://dx.doi.org/10.17277/jamt.2021.03.pp.204-215.

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The micro structural models for shear stress generation during rapid gravity flow of granular materials on a rough chute are discussed. The mechanism of the shear stress formation, taking into account the tangential impulse formed under transversal mass transfer of particles, is suggested. The analogy between granular media during rapid shear deformation and dense gases is used to develop the suggested mechanism on the basis of kinetic theory. The total shear stress is determined as the sum of the stress components induced by collisions, transversal mass transfer and contact interactions of uniform cohesionless inelastic spherical particles. The mathematical models describing the components of shear kinetic stresses are developed as the functions of particle properties, structural and kinematical gravity flow characteristics. The equations of impulse and energy conservation in the course of rapid gravity flow of uniform cohesionless particles are formulated. A variant of the formulation of boundary conditions at the flow bottom is proposed for mathematical modeling of the dynamics of rapid gravity flows of granular materials on a rough chute. The variant assumes the displacement of the area with the most intense shear rate inside the flow and into its layers adjacent to the rough chute surface.

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GOLDING, MADELEINE J., JEROME A. NEUFELD, MARC A. HESSE et HERBERT E. HUPPERT. « Two-phase gravity currents in porous media ». Journal of Fluid Mechanics 678 (26 avril 2011) : 248–70. http://dx.doi.org/10.1017/jfm.2011.110.

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We develop a model describing the buoyancy-driven propagation of two-phase gravity currents, motivated by problems in groundwater hydrology and geological storage of carbon dioxide (CO2). In these settings, fluid invades a porous medium saturated with an immiscible second fluid of different density and viscosity. The action of capillary forces in the porous medium results in spatial variations of the saturation of the two fluids. Here, we consider the propagation of fluid in a semi-infinite porous medium across a horizontal, impermeable boundary. In such systems, once the aspect ratio is large, fluid flow is mainly horizontal and the local saturation is determined by the vertical balance between capillary and gravitational forces. Gradients in the hydrostatic pressure along the current drive fluid flow in proportion to the saturation-dependent relative permeabilities, thus determining the shape and dynamics of two-phase currents. The resulting two-phase gravity current model is attractive because the formalism captures the essential macroscopic physics of multiphase flow in porous media. Residual trapping of CO2 by capillary forces is one of the key mechanisms that can permanently immobilize CO2 in the societally important example of geological CO2 sequestration. The magnitude of residual trapping is set by the areal extent and saturation distribution within the current, both of which are predicted by the two-phase gravity current model. Hence the magnitude of residual trapping during the post-injection buoyant rise of CO2 can be estimated quantitatively. We show that residual trapping increases in the presence of a capillary fringe, despite the decrease in average saturation.

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Sethi, M., K. C. Gupta et D. Gupta And Manisha. « Surface Waves in Fibre-Reinforced Anisotropic Solid Elastic Media under the Influence of Gravity ». International Journal of Applied Mechanics and Engineering 18, n^o 1 (1 mars 2013) : 177–88. http://dx.doi.org/10.2478/ijame-2013-0012.

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The aim of the present paper is to investigate surface waves in an anisotropic, elastic solid medium under the influence of gravity. First, a theory of generalised surface waves was developed and then it was employed to investigate particular cases of waves, viz., Stoneley and Rayleigh, Love type. The wave velocity equations were obtained for different cases and they are in well agreement with the corresponding classical result, when the effect of gravity, viscosity as well as parameters for fibre-reinforcement of the material medium are ignored.

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Aggarwal, A. K., et D. Dixit. « Triple Diffusive Convection of a Non-Newtonian Fluid Under the Combined Effect of Compressibility and Variable Gravity ». International Journal of Applied Mechanics and Engineering 24, n^o 4 (1 novembre 2019) : 1–11. http://dx.doi.org/10.2478/ijame-2019-0046.

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Abstract In this paper, triple diffusive convection in a Rivlin-Ericksen fluid layer, which is permeated with suspended particles in the porous medium under the effect of compressibility and variable gravity, is investigated. Linear stability theory and normal mode analysis have been used to study the problem under consideration. It is observed that, for stationary convection, suspended particles, compressibility and medium permeability have destabilizing/stabilizing effects under certain conditions. The variable gravity parameter destabilizes the system whereas stable solute gradients have a stabilizing effect.

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Xie, Haojun, Aifen Li, Zhaoqin Huang, Bo Gao et Ruigang Peng. « Coupling of two-phase flow in fractured-vuggy reservoir with filling medium ». Open Physics 15, n^o 1 (2 mars 2017) : 12–17. http://dx.doi.org/10.1515/phys-2017-0002.

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AbstractCaves in fractured-vuggy reservoir usually contain lots of filling medium, so the two-phase flow in formations is the coupling of free flow and porous flow, and that usually leads to low oil recovery. Considering geological interpretation results, the physical filled cave models with different filling mediums are designed. Through physical experiment, the displacement mechanism between un-filled areas and the filling medium was studied. Based on the experiment model, we built a mathematical model of laminar two-phase coupling flow considering wettability of the porous media. The free fluid region was modeled using the Navier-Stokes and Cahn-Hilliard equations, and the two-phase flow in porous media used Darcy's theory. Extended BJS conditions were also applied at the coupling interface. The numerical simulation matched the experiment very well, so this numerical model can be used for two-phase flow in fracture-vuggy reservoir. In the simulations, fluid flow between inlet and outlet is free flow, so the pressure difference was relatively low compared with capillary pressure. In the process of water injection, the capillary resistance on the surface of oil-wet filling medium may hinder the oil-water gravity differentiation, leading to no fluid exchange on coupling interface and remaining oil in the filling medium. But for the water-wet filling medium, capillary force on the surface will coordinate with gravity. So it will lead to water imbibition and fluid exchange on the interface, high oil recovery will finally be reached at last.

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Kango, S. K., G. C. Rana et Ramesh Chand. « TRIPLE-DIFFUSIVE CONVECTION IN WALTERS’ (MODEL B’) FLUID WITH VARYING GRAVITY FIELD SATURATING A POROUS MEDIUM ». Studia Geotechnica et Mechanica 35, n^o 3 (1 septembre 2013) : 45–56. http://dx.doi.org/10.2478/sgem-2013-0029.

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Abstract The Triple-Diffusive convection in Walters’ (Model B') fluid with varying gravity field is considered in the presence of uniform vertical magnetic field in porous medium. For the case of stationary convection, the magnetic field, varying gravity field and the stable solute gradients have stabilizing effects whereas the medium permeability has destabilizing (or stabilizing) effect on the system under certain conditions. A linear stability analysis theory and normal mode analysis method have been carried out to study the onset convection. The kinematic viscoelasticity has no effect on the stationary convection. The solute gradients, magnetic field, varying gravity field, porosity and kinematic viscoelasticity introduce oscillatory modes in the system, which were non-existent in their absence. The sufficient conditions for the non-existence of overstability are also obtained. The results are also shown graphically.

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Taylor, M. J., P. D. Pautet, A. F. Medeiros, R. Buriti, J. Fechine, D. C. Fritts, S. L. Vadas, H. Takahashi et F. T. São Sabbas. « Characteristics of mesospheric gravity waves near the magnetic equator, Brazil, during the SpreadFEx campaign ». Annales Geophysicae 27, n^o 2 (2 février 2009) : 461–72. http://dx.doi.org/10.5194/angeo-27-461-2009.

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Abstract. As part of the SpreadFEx campaign, coordinated optical and radio measurements were made from Brazil to investigate the occurrence and properties of equatorial Spread F, and to characterize the regional mesospheric gravity wave field. All-sky image measurements were made from two sites: Brasilia and Cariri located ~10° S of the magnetic equator and separated by ~1500 km. In particular, the observations from Brasilia provided key data in relatively close proximity to expected convective sources of the gravity waves. High-quality image measurements of the mesospheric OH emission and the thermospheric OI (630 nm) emission were made during two consecutive new moon periods (22 September to 9 November 2005) providing extensive data on the occurrence and properties of F-region depletions and regional measurements of the dominant gravity wave characteristics at each site. A total of 120 wave displays were observed, comprising 94 short-period events and 26 medium-scale gravity waves. The characteristics of the small-scale waves agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions for the Brasilia and Cariri datasets. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short-period events, suggesting they originated from the same source regions. Medium-scale waves are generally less susceptible to wind filtering effects and modeling studies utilizing these data have successfully identified localized regions of strong convection, mainly to the west of Brasilia, as their most likely sources (Vadas et al., 2009).

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