Cosmic Baryon Kinetics Expressed by Its Velocity Moments over Times after the Matter Recombination

As we are going to show here it is not easily understandable how cosmic gases like H-atoms, after the recombination of cosmic matter, do thermodynamically behave under the ongoing Hubble-like expansion of the universe. The question namely is not easy to answer; how cosmic gas atoms do in fact recognize the expansion of cosmic 3- space. Contemporary mainstream cosmology takes for granted that gas atoms do react polytropically or even adiabatically to cosmic volume changes and thus do get more and more tenuous and colder in accordance with gas- and thermo- dynamics. However, one has to face the fact that cosmic gases at the recombination era are already nearly collisionless over scales of 10 AU, and how gases react to cosmic volume changes under such conditions is not a trivial problem. We derive in this article a kinetic transport equation which describes the evolution of the gas distribution function f(t, v) in cosmic time t and velocity space of v. This partial differential equation does not allow for a solution in form a separation of the two variables t and v, but instead we can find solutions for two moments of f(v, t), i.e. the density n(t) and the pressure P(t). Then we show that using kappa-like functions for the cosmic gas we can derive such functions as function of their velocity moments, i.e. as functions of cosmic time. It means we understand the kinetic evolution of the cosmic gas by understanding the evolution in cosmic time of their moments.

The Thermodynamics of Cosmic Gases in Expanding Universes Based on VlasowTheoretical Grounds

Contemporary cosmology is taking for granted that before the phase of matter recombination matter and radiation were in perfect thermodynamic equilibrium. This would mean that protons in this phase of the universe are described by Maxwell distributions and photons are described by a Planckian black body law. When looking, however, a bit deeper into the kinetic theory of the physical processes close to and just after the recombination phase of electrons and protons, it becomes evident that in a homologously expanding universe proton distribution functions will not maintain their Maxwellian profile and connected with it, that their most relevant velocity moments, i.e. their density and their temperature, vary in an unexpected nonclassical, non-adiabatic manner. As consequence of that, in contrast to the classical view, the entropy of free atoms does change with cosmic time contrary to the standard thermodynamically expectation. We shall also demonstrate here that the realistic behaviour of cosmic gases in this phase and later depends on the specific form of the Hubble expansion of the universe, especially an accelerated expansion phase as is discussed nowadays will strongly influence the thermodynamics of the cosmic gas.

Observations of Cross-Shore Chenier Dynamics in Demak, Indonesia

Cheniers are important for stabilising mud-dominated coastlines. A chenier is a body of wave-reworked, coarse-grained sediment consisting of sand and shells overlying a muddy substrate. In this paper we present and analyse a week of field observations of the dynamics of a single chenier along the coast of Demak, Indonesia. Despite relatively calm hydrodynamics during the one-week observational period, the chenier migrated surprisingly fast in the landward direction. The role of the tide and waves on the cross-shore chenier dynamics is explored using velocity moments as a proxy for the sediment transport. This approach shows that both tide and waves are capable of transporting the sediment of the chenier system. During calm conditions (representative for the south-east monsoon season), the tides generate a landward-directed sediment transport when the chenier crest is high relative to mean sea level. Waves only generate substantial sediment transport (direct, via skewness, and indirect, via stirring) when the chenier is submerged during periods with higher waves. The cross-shore chenier dynamics are very sensitive to the timing of tide and waves: most transport takes place when high water levels coincide with (relatively) high waves.

Generalized anisotropic κ-cookbook: 2D fitting of Ulysses electron data

ABSTRACT Observations in space plasmas reveal particle velocity distributions out of thermal equilibrium, with anisotropies (e.g. parallel drifts and/or different temperatures, T∥ – parallel and T⊥ – perpendicular, with respect to the background magnetic field), and multiple quasi-thermal and suprathermal populations with different properties. The recently introduced (isotropic) κ-cookbook is generalized in this paper to cover all these cases of anisotropic and multicomponent distributions reported by the observations. We derive general analytical expressions for the velocity moments and show that the common (bi-)Maxwellian and (bi-)κ-distributions are obtained as limiting cases of the generalized anisotropic κ-cookbook (or recipes). Based on this generalization, a new two-dimensional fitting procedure is introduced, with an improved level of confidence compared to the 1D fitting methods widely used to quantify the main properties of the observed distributions. The non-linear least-squares fit is applied to electron data sets measured by the Ulysses spacecraft confirming the existence of three different populations, a quasi-thermal core and two suprathermal (halo and strahl) components. In general, the best overall fit is given by the sum of a Maxwellian distribution and two generalized κ-distributions.

SMART: A new implementation of Schwarzschild’s Orbit Superposition technique for triaxial galaxies and its application to an N-body merger simulation

We present SMART, a new 3D implementation of the Schwarzschild Method and its application to a triaxial N-body merger simulation. SMART fits full line-of-sight velocity distributions (LOSVDs) to determine the viewing angles, black hole, stellar and dark matter (DM) masses and the stellar orbit distribution of galaxies. Our model uses a 5D orbital starting space to ensure a representative set of stellar trajectories adaptable to the integrals-of-motion space and it is designed to deal with non-parametric stellar and DM densities. SMART’s efficiency is demonstrated by application to a realistic N-body merger simulation including supermassive black holes which we model from five different projections. When providing the true viewing angles, 3D stellar luminosity profile and normalized DM halo, we can (i) reproduce the intrinsic velocity moments and anisotropy profile with a precision of $\sim 1\%$ and (ii) recover the black hole mass, stellar mass-to-light ratio and DM normalization to better than a few percent accuracy. This precision is smaller than the currently discussed differences between initial-stellar-mass functions and scatter in black hole scaling relations. Further tests with toy models suggest that the recovery of the anisotropy in triaxial galaxies is almost unique when the potential is known and full LOSVDs are fitted. We show that orbit models even allow the reconstruction of full intrinsic velocity distributions, which contain more information than the classical anisotropy parameter. Surprisingly, the orbit library for the analysed N-body simulation’s gravitational potential contains orbits with net rotation around the intermediate axis that is stable over some Gyrs.

The κ-cookbook: a novel generalizing approach to unify κ-like distributions for plasma particle modelling

ABSTRACT In the literature different so-called κ-distribution functions are discussed to fit and model the velocity (or energy) distributions of solar wind species, pickup ions, or magnetospheric particles. Here, we introduce a generalized (isotropic) κ-distribution as a ‘cookbook’, which admits as special cases, or ‘recipes’, all the other known versions of κ-models. A detailed analysis of the generalized distribution function is performed, providing general analytical expressions for the velocity moments, Debye length, and entropy, and pointing out a series of general requirements that plasma distribution functions should satisfy. From a contrasting analysis of the recipes found in the literature, we show that all of them lead to almost the same macroscopic parameters with a small standard deviation between them. However, one of these recipes called the regularized κ-distribution provides a functional alternative for macroscopic parametrization without any constraint for the power-law exponent κ.

Higher-Order Velocity Moments, Turbulence Scales and Energy Dissipation Rate around a Boulder in a Rock-Ramp Fish Passage

This experimental study investigated the higher-order velocity moments, turbulence time and length scales, and energy dissipation rates around an intermediately submerged boulder within a wake-interference flow regime in a rock-ramp fish passage. The results show a noticeable variation in the studied parameters in the wake of the boulder, as well as near the bed and boulder crest. The higher-order velocity moments show the presence of infrequent strong ejections downstream of the boulder, which may lead to higher sediment deposition and vertical mixing. The eddy length scales and the volumetric energy dissipation in this experimental model were discussed in relation to fish behavior for both the experimental model and a prototype. Relationships were proposed to roughly estimate integral length scales and energy dissipation rates around the boulder over the flow depth. The findings of this study may improve the design of rock-ramp fish passages considering the effects of turbulence on fish swimming performance and sediment transport.

Efficient solution of the anisotropic spherically aligned axisymmetric Jeans equations of stellar hydrodynamics for galactic dynamics

ABSTRACT I present a flexible solution for the axisymmetric Jeans equations of stellar hydrodynamics under the assumption of an anisotropic (three-integral) velocity ellipsoid aligned with the spherical polar coordinate system. I describe and test a robust and efficient algorithm for its numerical computation. I outline the evaluation of the intrinsic velocity moments and the projection of all first and second velocity moments, including both the line-of-sight velocities and the proper motions. This spherically aligned Jeans anisotropic modelling (JAMsph) method can describe in detail the photometry and kinematics of real galaxies. It allows for a spatially varying anisotropy, or stellar mass-to-light ratio gradients, as well as for the inclusion of general dark matter distributions and supermassive black holes. The JAMsph method complements my previously derived cylindrically aligned JAMcyl and spherical Jeans solutions, which I also summarize in this paper. Comparisons between results obtained with either JAMsph or JAMcyl can be used to assess the robustness of inferred dynamical quantities. As an illustration, I modelled the ATLAS3D sample of 260 early-type galaxies with high-quality integral-field spectroscopy, using both methods. I found that they provide statistically indistinguishable total density logarithmic slopes. This may explain the previously reported success of the JAM method in recovering density profiles of real or simulated galaxies. A reference software implementation of JAMsph is included in the publicly available jam software package.

Suprathermal plasma distribution functions with relativistic cut-offs

ABSTRACT In typical plasma physics scenarios, when treated on kinetic levels, distribution functions with suprathermal wings are obtained. This raises the question of how the associated typical velocity moments, which are needed to arrive at magnetohydrodynamic plasma descriptions, may appear. It has become evident that the higher velocity moments in particular, for example the pressure or heat transport, which are constructed as integrations of the distribution function, contain unphysical contributions from particles with velocities greater than the velocity of light. In what follows, we discuss two possibilities to overcome this problem. One is to calculate a maximal, physically permitted, upper velocity, which can be realized in view of the underlying energization processes, and to stop the integration there. The other is to modify the distribution function relativistically so that no particles with superluminal (v ≥ c) velocities appear. On the basis of a typical collision-free plasma scenario, like the plasma in the heliosheath, we obtain the corresponding expressions for electron and proton pressures and can show that in both cases the pressures are reduced compared with their classical values; however, electrons experience a stronger reduction than protons. When calculating pressure ratios, it turns out that these are of the same order of magnitude regardless of which of the two methods is used. The electron, as the low-mass particle, undergoes the more pronounced pressure reduction. It may turn out that electrons and protons constitute about equal pressures in the heliosheath, implying that no pressure deficit need be claimed here.