Isothermal Fluctuations Research Articles

Magnetospheric Multiscale measurements of turbulent electric fields in earth's magnetosheath: How do plasma conditions influence the balance of terms in generalized Ohm's law?

Turbulence is ubiquitous within space plasmas, where it is associated with numerous nonlinear interactions. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose the electric field (E) dynamics into contributions from different linear and nonlinear processes via direct measurements of the terms in generalized Ohm's law. Using high-resolution multipoint measurements, we compute the magnetohydrodynamic (EMHD), Hall (EHall), electron pressure (EPe), and electron inertia (Einertia) terms for 60 turbulent magnetosheath intervals, to uncover the varying contributions to the dynamics as a function of scale for different plasma conditions. We identify key spectral characteristics of the Ohm's law terms: the Hall scale, kHall, where EHall becomes dominant over EMHD; the relative amplitude of EPe to EHall, which is constant in the sub-ion range; and the relative scaling of the nonlinear and linear components of EMHD and of EHall, which are independent of scale. We find expressions for the characteristics as a function of plasma conditions. The underlying relationship between turbulent fluctuation amplitudes and ambient plasma conditions is discussed. Depending on the interval, we observe that EMHD and EHall can be dominated by either nonlinear or linear dynamics. We find that EPe is dominated by its linear contributions, with a tendency for electron temperature fluctuations to dominate at small scales. The findings are not consistent with existing linear kinetic Alfvén wave theory for isothermal fluctuations. Our work shows how contributions to turbulent dynamics change in different plasma conditions, which may provide insight into other turbulent plasma environments.

A Thermostat‐Consistent Fully Coupled Molecular Dynamics—Generalized Fluctuating Hydrodynamics Model

AbstractThe previously developed multiscale method for concurrently coupling atomistic and continuum hydrodynamic representations of the same chemical substance is extended to consistently incorporate the Langevin‐type thermostat equations in the model. This allows not only to preserve the mass and momentum conservation laws based on the two‐phase flow analogy modeling framework but also to capture the correct local fluctuations and temperature in the pure atomistic region of the hybrid model. Numerical results for the test problem of equilibrium isothermal fluctuations of SPC/E water are presented. Advantages of using local thermostat equations adjusted for the multiresolution model for accurately capturing of the local water density in the atomistic part of the hybrid simulation domain are discussed. Comparisons with the reference pure all‐atom molecular dynamics simulations in GROMACS show that the suggested hybrid models are by a factor of 5–20 faster depending on the simulation domain size.

Prediction of high pressure properties of complex mixtures without knowledge of their composition as a problem of thermodynamic linear analysis

We propose a mathematical framework, which argues the possibility to predict thermodynamic properties of molecular liquids and their mixtures at elevated pressures using their properties measured at ambient conditions only by considering such procedure as a modified analogue to the linear analysis procedure known from the theory of dynamical system when time is replaced by one of PVT quantities. This approach reveals reasons, why so-called isothermal Fluctuation Theory-based Equation of State has universal effectiveness for different classes of liquid. Further, we generalize this line of reasoning on the case of the speed of sound and other thermodynamic quantities, which can be derived from such data via the acoustic route. This approach is illustrated among others by example of SRS diesel calibrating liquid, for which new original set of experimental data for a wide range of temperatures and pressures is reported.

Gas Perturbations in the Cool Cores of Galaxy Clusters: Effective Equation of State, Velocity Power Spectra, and Turbulent Heating

Abstract We present the statistical analysis of X-ray surface brightness and gas density fluctuations in the cool cores of 10 nearby, X-ray-bright galaxy clusters that have deep Chandra observations and show observational indications of radio-mechanical active galactic nucleus (AGN) feedback. Within the central parts of the cool cores, the total variance of fluctuations is dominated by isobaric and/or isothermal fluctuations on spatial scales ∼10–60 kpc, which are likely associated with slow gas motions and bubbles of relativistic plasma. Adiabatic fluctuations, associated with weak shocks and/or sonic turbulence, constitute less than 10% of the total variance in all clusters. The typical amplitude of density fluctuations is small, ∼10% or less on scales of ∼10–15 kpc. The observed subdominant contribution of adiabatic fluctuations and the small amplitude of density fluctuations support a model of gentle AGN feedback. The measured one-component velocities of gas motions are typically below 100–150 km s−1 on scales <50 kpc and can be up to ∼300 km s−1 on ∼100 kpc scales. The nonthermal energy is <12% of the thermal energy. Regardless of the source that drives these motions, the dissipation of the energy in such motions provides heat that is sufficient to balance radiative cooling on average, albeit with significant uncertainties. The results presented here support previous conclusions based on the analysis of the Virgo and Perseus Clusters and agree with the Hitomi measurements. With next-generation observatories like Athena and Lynx, these techniques will be yet more powerful.

ON THE NATURE OF X-RAY SURFACE BRIGHTNESS FLUCTUATIONS IN M87

ABSTRACT X-ray images of galaxy clusters and gas-rich elliptical galaxies show a wealth of small-scale features that reflect fluctuations in density and/or temperature of the intracluster medium. In this paper we study these fluctuations in M87/Virgo to establish whether sound waves/shocks, bubbles, or uplifted cold gas dominate the structure. We exploit the strong dependence of the emissivity on density and temperature in different energy bands to distinguish between these processes. Using simulations we demonstrate that our analysis recovers the leading type of fluctuation even in the presence of projection effects and temperature gradients. We confirm the isobaric nature of cool filaments of gas entrained by buoyantly rising bubbles, extending to 7′ to the east and southwest, and the adiabatic nature of the weak shocks at 40″ and 3′ from the center. For features of ∼5–10 kpc, we show that the central 4′ × 4′ region is dominated by cool structures in pressure equilibrium with the ambient hotter gas while up to 30% of the variance in this region can be ascribed to adiabatic fluctuations. The remaining part of the central 14′ × 14′ region, excluding the arms and shocks described above, is dominated by apparently isothermal fluctuations (bubbles) with a possible admixture (at the level of ∼30%) of adiabatic (sound waves) and by isobaric structures. Larger features, of about 30 kpc, show a stronger contribution from isobaric fluctuations. The results broadly agree with a model based on feedback from an active galactic nucleus mediated by bubbles of relativistic plasma.

Steering of a grain boundary with strain, electromagnetic field, and stochastic boundary excitation

In a previous work [Lusk et al., J. Appl. Phys. 99, 023505 (2006)], grain boundary and triple junction motion control using a laser spot was simulated within a noninertial, two-dimensional setting. That work focused on the physical process by which these defect structures could be induced to move. The present work seeks to begin the development of a control theory for such steering operations. To this end, a model system is introduced wherein the control of grain boundaries is abstracted into a piecewise homogeneous chain of harmonic oscillators. The interface demarcates regions of differing elastic stiffness and accretes via isothermal fluctuation theory. Energy is controlled via Langevin excitation and viscous damping applied to a single boundary mass. Steering of the grain boundary is achieved via applied strain and body forces. A closed-form relationship is established which allows the time-dependent probability distribution of the interface position to be expressed in terms of temperature, strain, body force, number of masses, and one dimensionless ratio. This analytical result is used to validate the predictions of molecular dynamics and dissipative particle dynamics (DPD) simulations. The DPD simulator is then treated as a physical experiment, and interface control via both constant and time-varying actuation is explored, with time-varying trajectories calculated using the analytic expression for interface position distribution.

Nonequilibrium statistical mechanics of chemically reactive fluids

A formula is derived which expresses the rate of a chemical reaction (or relaxation process) as the convolution of a correlation integral and the isothermal fluctuation from equilibrium of the affinity of the reaction. Two examples are provided of the dynamic variables (reaction densities) that appear in this correlation integral. The first of these is the model of simple reactive spheres. The second incorporates mechanisms by which two colliding atoms can be transformed into a bound dimer and, conversely, by which dimer dissociation can occur.

Isobaric–isothermal fluctuation theorem

The fluctuation theorem (FT) gives an analytical expression for the probability that in a finite nonequilibrium system observed for a finite time, the Second Law of Thermodynamics is violated. Since FT deals with fluctuations, the precise form of the theorem is dependent on the particular statistical mechanical ensemble. In the present paper we describe the application of the FT to the isothermal–isobaric ensemble.

Can non-linear structure form at the era of decoupling?

The effects of large-scale fluctuations on small-scale isothermal modes at the epoch of recombination are analysed. We find the following. (a) Albeit the fact that primordial fluctuations were at this epoch still well in the linear regime, a significant non-linear radiation hydrodynamic interaction could have taken place. (b) Short-wavelength isothermal fluctuations are unstable. Their growth rate is an exponential function of the amplitude of the large-scale fluctuations and is therefore very sensitive to the initial conditions. (c) The observed cosmic microwave background radiation (CMBR) fluctuations are of order of the limit above which the effect should be significant. Thus, depending on their exact value, the effect may be negligible or lead to structure formation out of the isothermal fluctuations within the period of recombination. (d) If the cosmological parameters are within the prescribed regime, the effect should be detectable through induced deviations in the Planck spectrum. (e) The sensitivity of the effect to the initial conditions provides a tool to set limits on various cosmological parameters with emphasis on the type and amplitude of the primordial fluctuation spectrum. (f) Under proper conditions, the effect may be responsible for the formation of sub-globular-cluster sized objects at particularly high redshifts. (g) Under certain circumstances, it can also affect horizon-sized large-scale structure.

Large-amplitude isothermal fluctuations and high-density dark-matter clumps.

Large-amplitude isothermal fluctuations in the dark-matter energy density, parametrized by [Phi][equivalent to][delta][rho][sub DM]/[rho][sub DM], are studied within the framework of a spherical collapse model. For [Phi][approx gt]1, a fluctuation collapses in the radiation-dominated epoch and produces a dense dark-matter object. The final density of the virialized object is found to be [rho][sub [ital F]][approx]140[Phi][sup 3]([Phi]+1)[rho][sub eq], where [rho][sub eq] is the matter density at equal matter and radiation energy density. This expression is valid for the entire range of possible values of [Phi], both for [Phi][much gt]1 and [Phi][much lt]1. Some astrophysical consequences of high-density dark-matter clumps are discussed.

Baryon-number fluctuations in a quark-hadron phase transition.

Isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe are obtained by including the quark-gluon interactions up to the order [ital g][sub [ital s]][sup 3] in the perturbative QCD coupling constant in the quark-gluon plasma (QGP) phase and the finite-size volume corrections for the hadrons in the hadron-resonance gas (HRG) and their effects on the primordial nucleosynthesis (PNS) are analyzed. The ratio of the baryon-number densities in the QGP and HRG phases at the critical temperature [ital T][sub [ital c]] is larger than one in the range 150 MeV[lt][ital T][sub [ital c]][lt]260 MeV. However, it is far larger than one even when [ital T][sub [ital c]] is outside this range, thus affecting primordial nucleosynthesis significantly.

Cosmological fluids as time variables in general relativity.

The use of potentials describing perfect fluids illuminates the role of time in general relativity. Using Hamilton-Jacobi methods, one can find solutions for inhomogeneous situations of interest to cosmology without making an explicit time choice until the very end of the calculation. We compute exact general solutions of long-wavelength matter and radiation interacting with gravity. Hamilton-Jacobi methods can describe adiabatic and isothermal fluctuations as well as the scalar, vector, and tensor modes.

Can quark-gluon-plasma formation in relativistic heavy-ion collisions constrain inhomogeneous cosmologies?

The separation distance between droplets of quark-gluon plasma (QGP) in the early Universe and in relativistic heavy-ion collisions is calculated in isothermal fluctuation theory. It is found that experimental information on the size of the QGP from relativistic heavy-ion collisions has the potential possibility of constraining the degrees of the inhomogeneous baryon-number density distribution and the formation of strange-quark matter at the epoch of the cosmic phase transition in quantum chromodynamics.

Link between the effective and true energy parameters of activated processes in polymers

Activation of an elementary process is regarded as a fluctuational disturbance of equilibrium between a small region (activated element) of the system and the rest of it and also between parts of the activated element. The free energy of activation is equated with the work of isothermal fluctuation taking the activated element into the activated state. Relations are obtained linking the energy and volume of activation with the free energy of activation, the fluctuation in volume of the activated element and the isothermal compressibility of the system.

Cosmological consequences of the quark-hadron phase transition

A first-order phase transition is likely to have occurred in the early universe at the end of the quark era and the beginning of the hadron era. This phase transition would have created large amplitude isothermal fluctuations in the distribution of baryon number in the universe. These fluctuations have significant impact on the subsequent synthesis of isotopes of hydrogen, helium and lithium out of protons and neutrons. It turns out to be possible that all of the mass in the universe today is baryonic.

Neutron diffusion and nucleosynthesis in the Universe with isothermal fluctuations produced by quark-hadron phase transition.

Nucleosynthesis in the Universe with isothermal baryon-density fluctuations is investigated. It is shown that neutron diffusion during nucleosynthesis plays an important role. Systematic calculations in the wide ranges of parameters suggest that ${\ensuremath{\Omega}}_{B}$=1 is marginally consistent with the light-element abundances (D, $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{7}\mathrm{Li}$) if the Hubble constant is as small as ${H}_{0}$=45 km ${\mathrm{Mpc}}^{\mathrm{\ensuremath{-}}1}$${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ or the mean lifetime of neutrons is shorter than 860 sec. Moreover it is found that the abundances of CNO elements in the low-density and neutron-rich region are very small.

Secondary mineral growth in fractures in the Miravalles geothermal system, Costa Rica

A mineralogical, fluid-chemical, and theoretical study of hydrothermal alteration in veins from drillcore from the Miravalles Geothermal Field, Costa Rica has revealed a complex history of mineral-fluid reaction which may be used to characterise changes in temperature and fluid composition with time. Mineralogical and mineral-chemical data are consistent with hydrothermal alteration in the temperature range 200°–270°C, with deeper portions of the system having undergone temperatures in excess of 300°C. Thermodynamic calculations suggest that the observed alteration assemblage is not in equilibrium with current well fluids, unless estimates of reservoir pH are incorrect. Fe-Al zoning of prehnite and epidote in veins is consistent with rapid, isothermal fluctuations in fluid composition at current reservoir temperatures, and may be due to changes in volatile content of the fluid due to tectonic activity.

Primordial nucleosynthesis in inhomogeneous cosmologies Omega = 1 with baryons

view Abstract Citations (61) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Primordial Nucleosynthesis in Inhomogeneous Cosmologies: Omega = 1 with Baryons Sale, K. E. ; Mathews, G. J. Abstract The authors consider the constraints on Ω from primordial nucleosynthesis in inhomogeneous cosmologies. They find that allowance for isothermal fluctuations significantly weakens the upper bound on the average value of Ω derived from the standard big bang. Under the plausible additional assumption that regions of high baryon density are preferentially absorbed into cold dark matter, the constraints from primordial nucleosynthesis can be satisfied for large values of Ω, including Ω = 1. Publication: The Astrophysical Journal Pub Date: October 1986 DOI: 10.1086/184748 Bibcode: 1986ApJ...309L...1S Keywords: Abundance; Astronomical Models; Baryons; Big Bang Cosmology; Inhomogeneity; Nuclear Fusion; Dark Matter; Density Distribution; Galactic Evolution; Astrophysics; ABUNDANCES; COSMOLOGY; NUCLEOSYNTHESIS full text sources ADS |

"Isothermal" density perturbations in an axion-dominated inflationary universe.

In inflationary models of the Universe which are axion dominated both adiabatic and isothermal density perturbations arise. We point out that the isothermal perturbations can be more important than the adiabatic perturbations and discuss a model for which this is the case. With isothermal perturbations the spectrum of density perturbations when structure formation begins is flatter and we briefly discuss the implications of this fact. That the amplitude of isothermal fluctuations not be too large provides yet another constraint on models of inflation.

Dynamical Evolution of Isothermal Density Perturbations in the Early Universe

Quantitative behaviour of evolution of the initially isothermal perturbations is investigated numerically. It is shown that baryon density contrast decreases slowly in a radiation-dominated epoch, while radiation density perturbation grows in proportion to the scale factor. As a result, contrary to the common understanding, a significant anisotropy on the microwave background is produced. Quantitative results obtained by the numerical analysis make it possible to derive the ratio of the amplitude of baryon irregularities to that of radiation at the time of recombination. Combining it with the observed upper bound on the anisotropy of the cosmic background radiation, we obtain a severe constraint on the amplitude of initially isothermal fluctuations. The resultant constraint casts a serious problem on the theories of galaxy formation based on the isothermal perturbations.