611 research outputs found
Two-dimensional hydrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic fluid flow through porous media
The behaviour of two dimensional binary and ternary amphiphilic fluids under
flow conditions is investigated using a hydrodynamic lattice gas model. After
the validation of the model in simple cases (Poiseuille flow, Darcy's law for
single component fluids), attention is focussed on the properties of binary
immiscible fluids in porous media. An extension of Darcy's law which explicitly
admits a viscous coupling between the fluids is verified, and evidence of
capillary effects are described. The influence of a third component, namely
surfactant, is studied in the same context. Invasion simulations have also been
performed. The effect of the applied force on the invasion process is reported.
As the forcing level increases, the invasion process becomes faster and the
residual oil saturation decreases. The introduction of surfactant in the
invading phase during imbibition produces new phenomena, including
emulsification and micellisation. At very low fluid forcing levels, this leads
to the production of a low-resistance gel, which then slows down the progress
of the invading fluid. At long times (beyond the water percolation threshold),
the concentration of remaining oil within the porous medium is lowered by the
action of surfactant, thus enhancing oil recovery. On the other hand, the
introduction of surfactant in the invading phase during drainage simulations
slows down the invasion process -- the invading fluid takes a more tortuous
path to invade the porous medium -- and reduces the oil recovery (the residual
oil saturation increases).Comment: 48 pages, 26 figures. Phys. Rev. E (in press
A reduced model for shock and detonation waves. II. The reactive case
We present a mesoscopic model for reactive shock waves, which extends a
previous model proposed in [G. Stoltz, Europhys. Lett. 76 (2006), 849]. A
complex molecule (or a group of molecules) is replaced by a single
mesoparticle, evolving according to some Dissipative Particle Dynamics.
Chemical reactions can be handled in a mean way by considering an additional
variable per particle describing a rate of reaction. The evolution of this rate
is governed by the kinetics of a reversible exothermic reaction. Numerical
results give profiles in qualitative agreement with all-atom studies
A reduced model for shock and detonation waves. I. The inert case
We present a model of mesoparticles, very much in the Dissipative Particle
Dynamics spirit, in which a molecule is replaced by a particle with an internal
thermodynamic degree of freedom (temperature or energy). The model is shown to
give quantitavely accurate results for the simulation of shock waves in a
crystalline polymer, and opens the way to a reduced model of detonation waves
Constant entropy sampling and release waves of shock compressions
We present several equilibrium methods that allow to compute isentropic
processes, either during the compression or the release of the material. These
methods are applied to compute the isentropic release of a shocked monoatomic
liquid at high pressure and temperature. Moreover, equilibrium results of
isentropic release are compared to the direct nonequilibrium simulation of the
same process. We show that due to the viscosity of the liquid but also to
nonequilibrium effects, the release of the system is not strictly isentropic
Current Algebra of Super WZNW Models
We derive the current algebra of supersymmetric principal chiral models with
a Wess-Zumino term. At the critical point one obtains two commuting super
Kac-Moody algebra as expected, but in general there are intertwining fields
connecting both right and left sectors, analogously to the bosonic case.
Moreover, in the present supersymmetric extension we have a quadratic algebra,
rather than an affine Lie algebra, due to the mixing between bosonic and
fermionic fields since the purely fermionic sector displays a Lie algebra as
well.Comment: 13 page
Permutation-type solutions to the Yang-Baxter and other n-simplex equations
We study permutation type solutions to n-simplex equations, that is,
solutions whose R matrix can be written as a product of delta- functions
depending linearly on the indices. With this ansatz the D^{n(n+1)} equations of
the n-simplex equation reduce to an [n(n+1)/2+1]x[n(n+1)/2+1] matrix equation
over Z_D. We have completely analyzed the 2-, 3- and 4-simplex equations in the
generic D case. The solutions show interesting patterns that seem to continue
to still higher simplex equations.Comment: 20 pages, LaTeX2e. to appear in J. Phys. A: Math. Gen. (1997
Classical Poisson structures and r-matrices from constrained flows
We construct the classical Poisson structure and -matrix for some finite
dimensional integrable Hamiltonian systems obtained by constraining the flows
of soliton equations in a certain way. This approach allows one to produce new
kinds of classical, dynamical Yang-Baxter structures. To illustrate the method
we present the -matrices associated with the constrained flows of the
Kaup-Newell, KdV, AKNS, WKI and TG hierarchies, all generated by a
2-dimensional eigenvalue problem. Some of the obtained -matrices depend only
on the spectral parameters, but others depend also on the dynamical variables.
For consistency they have to obey a classical Yang-Baxter-type equation,
possibly with dynamical extra terms.Comment: 16 pages in LaTe
Alleviating the non-ultralocality of coset sigma models through a generalized Faddeev-Reshetikhin procedure
The Faddeev-Reshetikhin procedure corresponds to a removal of the
non-ultralocality of the classical SU(2) principal chiral model. It is realized
by defining another field theory, which has the same Lax pair and equations of
motion but a different Poisson structure and Hamiltonian. Following earlier
work of M. Semenov-Tian-Shansky and A. Sevostyanov, we show how it is possible
to alleviate in a similar way the non-ultralocality of symmetric space sigma
models. The equivalence of the equations of motion holds only at the level of
the Pohlmeyer reduction of these models, which corresponds to symmetric space
sine-Gordon models. This work therefore shows indirectly that symmetric space
sine-Gordon models, defined by a gauged Wess-Zumino-Witten action with an
integrable potential, have a mild non-ultralocality. The first step needed to
construct an integrable discretization of these models is performed by
determining the discrete analogue of the Poisson algebra of their Lax matrices.Comment: 31 pages; v2: minor change
- âŠ