Transcript Maxwellian models - University of Texas at Austin

Generalizations to Boltzmann-Maxwell
Interaction Dynamics
Irene M. Gamba
Department of Mathematics and ICES
The University of Texas at Austin
IAS, February 2009
A general form statistical transport : The Boltzmann Transport Equation (BTE) with
external heating sources: important examples from mathematical physics and social sciences:
The term
models external heating sources:
Space homogeneous examples:
•background thermostat (linear collisions),
•thermal bath (diffusion)
•shear flow (friction),
•dynamically scaled long time limits (self-similar
solutions).
Inelastic Collision
γ=0 Maxwell molecules
γ=1 hard spheres
u’= (1-β) u + β |u| σ , with σ the direction of elastic post-collisional relative velocity
Molecular models of Maxwell type as originally studied:
so
is also a probability distribution function in v.
We work in the space of Characteristic functions associated to Probabilities:
The Fourier transformed problem:
Γ
Bobylev operator
characterized by
One may think of this model as the generalization original Kac (’59) probabilistic interpretation of rules of dynamics on
each time step Δt=2/M of M particles associated to system of vectors randomly interchanging velocities pairwise while
preserving momentum and local energy.
Bobylev, ’75-80, for the elastic, energy conservative case.
Drawing from Kac’s models and Mc Kean work in the 60’s
Carlen, Carvalho, Gabetta, Toscani, 80-90’s
For inelastic interactions: Bobylev,Carrillo, I.M.G. 00
Bobylev, Cercignani,Toscani, 03, Bobylev, Cercignani, I.M.G’06, for general non-conservative problem
1
Accounts for the integrability of the function b(1-2s)(s-s2)(3-N)/2
In general we can see that
1. For more general systems multiplicatively interactive stochastic processes
the lack of entropy functional does not impairs the understanding and
realization of global existence (in the sense of positive Borel measures), long
time behavior from spectral analysis and self-similar asymptotics.
2. “power tail formation for high energy tails” of self similar states is due to
lack of total energy conservation, independent of the process being
micro-reversible (elastic) or micro-irreversible (inelastic).
It is also possible to see Self-similar solutions may be singular at zero.
3. The long time asymptotic dynamics and decay rates are fully described by
the continuum spectrum associated to the linearization about
singular measures.
Existence,
(Bobylev, Cercignani, I.M.G.;. 06-08)
θ
with 0 < p < 1 infinity energy,
or p ≥ 1
finite energy
(for initial data with finite energy)
Relates to the work of Toscani, Gabetta,Wennberg, Villani,Carlen, Carvallo,…..
-I
Boltzmann Spectrum
Stability estimate for a
weighted pointwise distance
for finite or infinite
initial energy
Theorem: appearance of stable law
(Kintchine type of CLT)
Study of the spectral function μ(p)
μ(p)
associated to the linearized collision operator
For any initial state φ(x) = 1 – xp + x(p+Є) , p ≤ 1.
Decay rates in Fourier space: (p+Є)[ μ(p) - μ(p +Є) ]
For finite (p=1) or infinite (p<1) initial energy.
For μ(1) = μ(s*) , s* >p0 >1
For p0 >1 and 0<p< (p +Є) < p0
Power tails
CLT to a stable law
Self similar asymptotics for:
1
p0
s*
p
μ(s*) =μ(1)
μ(po)
Finite (p=1) or infinite (p<1) initial energy
For p0< 1 and p=1
No self-similar asymptotics with finite energy
ms> 0 for all s>1.
)
An example for multiplicatively interacting stochastic process (Bobylev, Cercignani, I.M.G’08):
Phase variable: goods (monies or wealth)
particles: n- indistinguishable players
•
A realistic assumption is that a scaling transformation of the phase variable (such as a change of
goods interchange) does not influence a behavior of player.
•
The game of these n partners is understood as a random linear transformation (n-particle collision)
is a quadratic n x n matrix with non-negative random elements, and must satisfy a condition that
ensures the model does not depend on numeration of identical particles.
Simplest example: a 2-parameter family
The parameters
(a,b) can be fixed or randomly distributed in R+2 with some probability density Bn(a,b).
The corresponding transformation is
Model of M players participating in a N-linear ‘game’ according to the Kac rules (Bobylev, Cercignani,I.M.G.):
Assume hat VM(t), n≥ M undergoes random jumps caused by interactions.
Intervals between two successive jumps have the Poisson distribution with the average ΔtM = θ /M, θ const.
Then we introduce M-particle distribution function F(VM; t) and consider a weak form as in the Kac Master eq:
• Jumps are caused by interactions of 1 ≤ n ≤ N ≤ M particles (the case N =1 is understood as a interaction with
background)
• Relative probabilities of interactions which involve 1; 2; : : : ;N particles are given respectively by non-negative real
numbers β1; β2 ; …. βN such that β1 + β2 + …+ βN = 1 , so it is possible to reduce the hierarchy of the system to
• Taking the Laplace transform of the probability f:
• Taking the test function on the RHS of the equation for f:
• And making the “molecular chaos” assumption (factorization)
In the limit M
∞
Example: For the choice of
rules of random interaction
With θ a random variable with a pdf
So we obtain a model of the class being under discussion where self-similar asymptotics are achivable:
N
,
N
N
Where μ(p) is a curve with a unique minima at p0>1 and approaches + ∞ as p
Also μ’(1) < 0 for
0
and it is possible to find a second root conjugate to μ(1)
So a self-similar attracting state with a power law exists
Another benchmark case: Self-similar asymptotics for a for a slowdown process given by
elastic BTE with a thermostat
Explicit formula in Fourier space
Soft condensed matter
phenomena
Remark: The numerical algorithm is based on the evolution of the continuous spectrum of the solution in
the same spirit of Greengard-Lin’00 spectral calculation of the free space heat kernel, i.e. self-similar of
the heat equation in all space.
Testing: BTE with Thermostat
explicit solution problem of colored particles
Maxwell Molecules model
Rescaling of spectral modes
exponentially by the continuous
spectrum with λ(1)=-2/3
Testing: BTE with Thermostat
Moments calculations:
A.V. Bobylev, C. Cercignani and I. M. Gamba, On the self-similar asymptotics for generalized non-linear
kinetic Maxwell models, ’08 submitted.
A.V. Bobylev and I. M. Gamba, On special solutions for linear Maxwell-Boltzmann models for slow
down processes. In preparation.
A.V. Bobylev, C. Cercignani and I. M. Gamba, Generalized kinetic Maxwell models of granular gases;
Mathematical models of granular matter Series: Lecture Notes in Mathematics Vol.1937, Springer, (2008).
A.V. Bobylev and I. M. Gamba, Boltzmann equations for mixtures of Maxwell gases: exact solutions and power
like tails. J. Stat. Phys. 124, no. 2-4, 497--516. (2006).
A.V. Bobylev, I.M. Gamba and V. Panferov, Moment inequalities and high-energy tails for Boltzmann equations
wiht inelastic interactions, J. Statist. Phys. 116, no. 5-6, 1651-1682.(2004).
A.V. Bobylev, J.A. Carrillo and I.M. Gamba, On some properties of kinetic and hydrodynamic equations
for inelastic interactions, Journal Stat. Phys., vol. 98, no. 3?4, 743?773, (2000).
I.M. Gamba and Sri Harsha Tharkabhushaman, Spectral - Lagrangian based methods applied to computation
of Non - Equilibrium Statistical States. Jour. Computational Physics, (2008).
I.M. Gamba and Sri Harsha Tharkabhushaman, Shock Structure Analysis Using Space Inhomogeneous Boltzmann
Transport Equation, To appear in Jour. Comp Math. 09
And references therein
Thank you very much for your attention