Evolution of magnetic fields from the 3+1 dimensional self-similar and Gubser flows in ideal relativistic magnetohydrodynamics

Motivated by the recently found realization of the $1+1$ dimensional Bjorken flow in ideal and nonideal relativistic magnetohydrodynamics (MHD), we use appropriate symmetry arguments, and determine the evolution of magnetic fields arising from the $3+1$ dimensional self-similar and Gubser flows in an infinitely conductive relativistic fluid (ideal MHD). In the case of the $3+1$ dimensional self-similar flow, we arrive at a family of solutions, that are related through a differential equation arising from the corresponding Euler equation. To find the magnetic field evolution from the Gubser flow, we solve the MHD equations of a stationary fluid in a conformally flat $dS^{3}\times E^{1}$ spacetime. The results are then Weyl transformed back into the Minkowski spacetime. In this case, the temporal evolution of the resulting magnetic field is shown to exhibit a transition between an early time $1/t$ decay to a $1/t^{3}$ decay at a late time. Here, $t$ is the time coordinate. Transverse and longitudinal components of the magnetic fields arising from these flows are also found. The latter turns out to be sensitive to the transverse size of the fluid. In contrast to the result arising from the Gubser flow, the radial domain of validity of the magnetic field arising from the self-similar flow is highly restricted. A comparison of the results suggests that the (conformal) Gubser MHD may give a more appropriate qualitative picture of the magnetic field decay in the plasma of quarks and gluons created in heavy ion collisions.Comment: 26 pages, 10 figure

Evolution of magnetic fields in a transversely expanding highly conductive fluid

Due to the absence of a transverse expansion with respect to the beam direction, the Bjorken flow is unable to describe certain observables in heavy ion collisions. This caveat has motivated the introduction of analytical relativistic hydrodynamics (RH) solutions with transverse expansion, in particular, the 3+1 self-similar (SSF) and Gubser flows. Inspired by recent generalizations of the Bjorken flow to the relativistic magnetohydrodynamics (RMHD), we present a procedure for a generalization of RH solutions to RMHD. Our method is mainly based on symmetry arguments. Using this method, we find the relation between RH degrees of freedom and the magnetic field evolution in the ideal limit for an infinitely conductive fluid, and determine the proper time dependence of the magnetic field in aforementioned flows. In the case of SSF, a family of solutions are found that are related through a certain differential equation. To find the magnetic field evolution in the Gubser flow, we solve RMHD equations for a stationary fluid in a conformally flat $dS^3\times E^1$ spacetime. The result is then Weyl transformed back into the Minkowski spacetime. In this case, the temporal evolution of the magnetic field exhibits a transmission between $1/t$ to $1/t^3$ near the center of the collision. The longitudinal component of the magnetic field is found to be sensitive to the transverse size of the fluid. We also find the radial evolution of the magnetic field for both flows. The radial domain of validity in the case of SSF is highly restricted, in contrast to the Gubser flow. A comparison of the results suggests that the Gubser RMHD may give a more appropriate qualitative picture of the magnetic field decay in the quark-gluon plasma (QGP).Comment: 8 pages, 1 figures, XIII Quark Confinement and the Hadron Spectrum - Confinement2018, 31 July - 6 August 2018, Maynooth University, Irelan

Spatial variation of symbiotic dinoflagellates on coral reefs of the northern Persian Gulf

Density, mitotic index, Chlorophyll-a content and cell size of symbiotic dinoflagellates of dominant reef-building corals were measured at two different depths in Kish Island and from one depth of Larak Island in the Persian Gulf. The higher densities of symbionts were found in shallow waters of Kish Island. However, ANOVA analyses of the mitotic index yielded mixed results. The cell sizes of symbionts did not significantly differ among depths, except for Porites corals at one site in Kish Island which displayed the larger cells in deeper water. The comparison of symbiont attributes between islands exhibited intraspecific variability. Density of zooxanthellae was only different in Porites and Favia corals between islands. Chlorophyll-a density (cm-2) was significantly different between islands in all species, with higher values for Kish corals. Chlorophyll a cell-1 was only significantly different in Porites and Platygyra corals, with higher values for Larak Island. The symbiont cell sizes usually exhibited no variability, except for Porites corals with larger sizes in Kish Island

Effect of Gliricidia sepium leaves and molases inclusion on aerobic stability, value and digestibility of Napier grass silage

Most tropical roughage feeds are generally deficient in nitrogen, energy or some minerals and vitamins. A study was conducted to evaluate the effect of adding Gliricidia (Gliricidia sepium) leaves and molasses to Napier grass (Pennisetum purpureum) silage. Silage were prepared from Napier grass and mixed with Gliricidia and molasses. There were four treatments involved which were NG, containing Napier grass only which was the experiment control, GS containing Napier grass mixed with 5% Gliricidia leaves, ML containing the Napier grass mixed with 5% molasses, and MG containing Napier grass mixed with 5% molasses and 5% Gliricidia leaves. The treatments were analyzed for aerobic stability, dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), and digestibility. There were no significant differences in aerobic stability of silage between treatments, and the treatments with Gliricidia were higher in crude protein (p<0.05) and had better digestibility (p<0.05) when compared to the control. In conclusion, Gliricidia leaves as additives to Napier grass silage can improve its nutritive value and quality

Dynamics of water evaporation from porous asphalt

The dynamics of water evaporation from porous asphalt mixture, with porosity ranging from 15% to 12 29%, have been investigated in this article. In order to test the same samples under different conditions, the pore structure of asphalt was quantified using X-ray Computed Tomography (CT) scans and 3D printed in transparent resin blocks. 3D printed transparent resin samples were tested under controlled laboratory conditions to understand the effect of pore space topology on the water retention and drying dynamics. The macroporosity, pore size distribution, air void tortuosity, water conductivity, and water retention curves of the 3D printed porous asphalt samples were quantified by means of image analysis. Moreover, a model was developed and tested experimentally to estimate the evaporation rates from porous asphalt materials under a wide range of porosities. Within the range of asphalt mixtures studied in the present work, the evaporation rate is related predominantly to the porosity, pore size distribution and tortuosity. It was found that the period over which water evaporation occurs at the surface is relatively short during drying of porous asphalt materials due to their relatively large pores weakening the capillary forces. This results in significantly shortening the so-called stage-1 evaporation (when the drying rate is controlled by liquid vaporisation at the surface) and early onset of the transition period (when both surface water evaporation and vapour diffusion inside porous asphalt play a comparable role in supplying the 26 evaporative demand). The transition period is followed by the stage-2 evaporation when the process is limited by the vapour diffusion inside the porous asphalt. Our results illustrate that the beginning of the stage-2 evaporation depends on the porosity and tortuosity of the porous asphalt material among other parameters. Our results and analysis provide new insights into the dynamics of water evaporation from asphalt materials

Nyquist method for Wigner-Poisson quantum plasmas

By means of the Nyquist method, we investigate the linear stability of electrostatic waves in homogeneous equilibria of quantum plasmas described by the Wigner-Poisson system. We show that, unlike the classical Vlasov-Poisson system, the Wigner-Poisson case does not necessarily possess a Penrose functional determining its linear stability properties. The Nyquist method is then applied to a two-stream distribution, for which we obtain an exact, necessary and sufficient condition for linear stability, as well as to a bump-in-tail equilibrium.Comment: 6 figure

Foam front propagation in anisotropic oil reservoirs

The pressure-driven growth model is considered, describing the motion of a foam front through an oil reservoir during foam improved oil recovery, foam being formed as gas advances into an initially liquid-filled reservoir. In the model, the foam front is represented by a set of so called ‘material points’ that track the advance of gas into the liquid-filled region. According to the model, the shape of the foam front is prone to develop concave sharply-curved concavities, where the orientation of the front changes rapidly over a small spatial distance: these are referred to as 'concave corners'. These concave corners need to be propagated differently from the material points on the foam front itself. Typically the corner must move faster than those material points, otherwise spurious numerical artifacts develop in the comp uted shape of the front. A propagation rule or ‘speed up’ rule is derived for the concave corners, which is shown to be sensitive to the level of anisotropy in the permeability of the reservoir and also sensitive to the orientation of the corners themselves. In particular if a corner in an anisotropic reservoir were to be propagated according to an isotropic speed up rule, this might not be sufficient to suppress spurious numerical artifacts, at least for certain orientations of the corner. On the other hand, systems that are both heterogeneous and anisotropic tend to be well behaved numerically, regard less of whether one uses the isotropic or anisotropic speed up rule for corners. This comes about be cause, in the heterogeneous and anisotropic case, the orientation of the corner is such that the 'correct' anisotropic speed is just very slightly less than the ‘incorrect’ isotropic one. The anisotropic rule does however manage to keep the corner very slightly sharper than the isotropic rule does

Dynamics of water evaporation from porous asphalt

The dynamics of water evaporation from porous asphalt mixture, with porosity ranging from 15% to 29%, have been investigated in this article. In order to test the same samples under different conditions, the pore structure of asphalt was quantified using X-ray Computed Tomography (CT) scans and 3D printed in transparent resin blocks. 3D printed transparent resin samples were tested under controlled laboratory conditions to understand the effect of pore space topology on the water retention and drying dynamics. The macroporosity, pore size distribution, air void tortuosity, water conductivity, and water retention curves of the 3D printed porous asphalt samples were quantified by means of image analysis. Moreover, a model was developed and tested experimentally to estimate the evaporation rates from porous asphalt materials under a wide range of porosities. Within the range of asphalt mixtures studied in the present work, the evaporation rate is related predominantly to the porosity, pore size distribution and tortuosity. It was found that the period over which water evaporation occurs at the surface is relatively short during drying of porous asphalt materials due to their relatively large pores weakening the capillary forces. This results in significantly shortening the so-called stage-1 evaporation (when the drying rate is controlled by liquid vaporisation at the surface) and early onset of the transition period (when both surface water evaporation and vapour diffusion inside porous asphalt play a comparable role in supplying the evaporative demand). The transition period is followed by the stage-2 evaporation when the process is limited by the vapour diffusion inside the porous asphalt. Our results illustrate that the beginning of the stage-2 evaporation depends on the porosity and tortuosity of the porous asphalt material among other parameters. Our results and analysis provide new insights into the dynamics of water evaporation from asphalt materials