1,071 research outputs found
The interior structure of Jupiter (Consequences of Pioneer 10 data)
Models of the Jovian interiors based on theoretical equations of state of hydrogen and helium supported by a few experimental points and on observed parameters such as oblateness, gravitational coefficients, heat emission, magnetic fields, are discussed. The models fall into three categories: (1) those that assume a uniform and rather low H2/He ratio throughout the planet; (2) those in which this ratio is solar and thus higher; and (3) those that take into account the lack of complete miscibility of the two elements in the condensed state. It appears now also that within the limits of error the planet is in a hydrostatic equilibrium. The large heat emission and the need for an efficient source of internal heat are confirmed, but the results do not indicate which one of the various possible mechanisms is favored, although new evolutionary models suggest that the primordial heat may be insufficient. A new red spot has been discovered. Finally, the presence of a highly eccentric and inclined magnetic field poses new problems related to the pattern of internal convection and to the possibility of a north-south asymmetry of the interior. Further analysis of the available data may throw additional light on these questions
The interior structure of Jupiter (consequences of Pioneer 10 data)
Models of the Jovian interiors are based on theoretical equations of state of hydrogen and helium supported by a few experimental points and an observed parameter such as oblateness, gravitational coefficients, heat emission, and magnetic fields. The models fall into three categories: (1) those which assume a uniform and rather low H2/He ratio throughout the planet, (2) those in which this ratio is solar and thus higher and (3) those which take into account the lack of complete miscibility of the two elements in the condensed state. Recent values of the observed parameters obtained by Pioneer 10 permit improvements of the first two models but also pose new questions. In the first category of models the new data indicate that the amount of hydrogen has to be increased, while in the solar models which have a heavy core (made of SiO2, MgO, Fe and Ni), the abundance of hydrogen has to be decreased, both changes pointing in the direction of incomplete miscibility present in the third category of models
Gravitational and phase change sources of energy in Jupiter
Gravitational and phase change sources of energy in Jupite
Mesoscopic Model for Diffusion-Influenced Reaction Dynamics
A hybrid mesoscopic multi-particle collision model is used to study
diffusion-influenced reaction kinetics. The mesoscopic particle dynamics
conserves mass, momentum and energy so that hydrodynamic effects are fully
taken into account. Reactive and non-reactive interactions with catalytic
solute particles are described by full molecular dynamics. Results are
presented for large-scale, three-dimensional simulations to study the influence
of diffusion on the rate constants of the A+CB+C reaction. In the limit of
a dilute solution of catalytic C particles, the simulation results are compared
with diffusion equation approaches for both the irreversible and reversible
reaction cases. Simulation results for systems where the volume fraction of
catalytic spheres is high are also presented, and collective interactions among
reactions on catalytic spheres that introduce volume fraction dependence in the
rate constants are studied.Comment: 9 pages, 5 figure
Survival probability of a diffusing test particle in a system of coagulating and annihilating random walkers
We calculate the survival probability of a diffusing test particle in an
environment of diffusing particles that undergo coagulation at rate lambda_c
and annihilation at rate lambda_a. The test particle dies at rate lambda' on
coming into contact with the other particles. The survival probability decays
algebraically with time as t^{-theta}. The exponent theta in d<2 is calculated
using the perturbative renormalization group formalism as an expansion in
epsilon=2-d. It is shown to be universal, independent of lambda', and to depend
only on delta, the ratio of the diffusion constant of test particles to that of
the other particles, and on the ratio lambda_a/lambda_c. In two dimensions we
calculate the logarithmic corrections to the power law decay of the survival
probability. Surprisingly, the log corrections are non-universal. The one loop
answer for theta in one dimension obtained by setting epsilon=1 is compared
with existing exact solutions for special values of delta and
lambda_a/lambda_c. The analytical results for the logarithmic corrections are
verified by Monte Carlo simulations.Comment: 8 pages, 8 figure
The Equilibrium Distribution of Gas Molecules Adsorbed on an Active Surface
We evaluate the exact equilibrium distribution of gas molecules adsorbed on
an active surface with an infinite number of attachment sites. Our result is a
Poisson distribution having mean , with the
mean gas density, the sticking probability, the evaporation
probability in a time interval , and Smoluchowski's exit probability
in time interval for the surface in question. We then solve for the case
of a finite number of attachment sites using the mean field approximation,
recovering in this case the Langmuir isotherm.Comment: 14 pages done in late
Diffusion, Fragmentation and Coagulation Processes: Analytical and Numerical Results
We formulate dynamical rate equations for physical processes driven by a
combination of diffusive growth, size fragmentation and fragment coagulation.
Initially, we consider processes where coagulation is absent. In this case we
solve the rate equation exactly leading to size distributions of Bessel type
which fall off as for large -values. Moreover, we provide
explicit formulas for the expansion coefficients in terms of Airy functions.
Introducing the coagulation term, the full non-linear model is mapped exactly
onto a Riccati equation that enables us to derive various asymptotic solutions
for the distribution function. In particular, we find a standard exponential
decay, , for large , and observe a crossover from the Bessel
function for intermediate values of . These findings are checked by
numerical simulations and we find perfect agreement between the theoretical
predictions and numerical results.Comment: (28 pages, 6 figures, v2+v3 minor corrections
A Note on the Smoluchowski-Kramers Approximation for the Langevin Equation with Reflection
According to the Smoluchowski-Kramers approximation, the solution of the
equation
converges to the solution of the equation
as {\mu}->0. We consider here
a similar result for the Langevin process with elastic reflection on the
boundary.Comment: 14 pages, 2 figure
Motion by Stopping: Rectifying Brownian Motion of Non-spherical Particles
We show that Brownian motion is spatially not symmetric for mesoscopic
particles embedded in a fluid if the particle is not in thermal equilibrium and
its shape is not spherical. In view of applications on molecular motors in
biological cells, we sustain non-equilibrium by stopping a non-spherical
particle at periodic sites along a filament. Molecular dynamics simulations in
a Lennard-Jones fluid demonstrate that directed motion is possible without a
ratchet potential or temperature gradients if the asymmetric non-equilibrium
relaxation process is hindered by external stopping. Analytic calculations in
the ideal gas limit show that motion even against a fluid drift is possible and
that the direction of motion can be controlled by the shape of the particle,
which is completely characterized by tensorial Minkowski functionals.Comment: 11 pages, 5 figure
Validity of the Law of Mass Action in Three-Dimensional Coagulation Processes
Diffusion-limited reactions are studied in detail on the classical coalescing process. We demonstrate how, with the aid of a recent renormalization group approach, fluctuations can be integrated systematically. We thereby obtain an exact relation between the microscopic physics (lattice structure and particle shape and size) and the macroscopic decay rate in the law of mass action. Moreover, we find a strong violation of the law of mass action. The corresponding term in the kinetic equations originates in longwavelength fluctuations and is a universal function of the macroscopic decay rate
- …