1,095 research outputs found
Cenozoic evolution of Neotethys and implications for the causes of plate motions
Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations and new estimates of crustal shortening in Iran define the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia. The new constraints indicate that Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with slowing of Africa-Eurasia motion to <1 cm/yr near 25 Ma, coeval with the opening of the Red Sea. Ocean closure occurred no later than 10 Ma, and could have occurred prior to this time only if a large amount of continental lithosphere was subducted, suggesting that slowing of Africa significantly predated the Arabia-Eurasia collision. These kinematics imply that Africa's disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern Eurasia slowed its motion. The slow, steady rate of northward subduction since 56 Ma contrasts with strongly variable rates of magma production in the Urumieh-Dokhtar arc, implying magma production rate in continental arcs is not linked to subduction rate
Statics and dynamics of a cylindrical droplet under an external body force
We study the rolling and sliding motion of droplets on a corrugated substrate
by Molecular Dynamics simulations. Droplets are driven by an external body
force (gravity) and we investigate the velocity profile and dissipation
mechanisms in the steady state. The cylindrical geometry allows us to consider
a large range of droplet sizes. The velocity of small droplets with a large
contact angle is dominated by the friction at the substrate and the velocity of
the center of mass scales like the square root of the droplet size. For large
droplets or small contact angles, however, viscous dissipation of the flow
inside the volume of the droplet dictates the center of mass velocity that
scales linearly with the size. We derive a simple analytical description
predicting the dependence of the center of mass velocity on droplet size and
the slip length at the substrate. In the limit of vanishing droplet velocity we
quantitatively compare our simulation results to the predictions and good
agreement without adjustable parameters is found.Comment: Submitted to the Journal of Chemical Physic
On the Simple Tensile Deformation of an Incompressible Rubber Matrix Filled with Non-Adherent Rigid Spheres of Uniform Size Distribution
Two striking features revealed in a photograph (cf Figure 1) of a thin film of rubber binder highly filled with glass beads are: a) that the growth of voids around particles increases with increasing strain and b) that the
preferred direction of the void growth seems to be in the direction of the applied macroscopic strain. It is obvious that the local stress field around particles in a deformed composite is not as high as it would be if the binder
did not pull away from the filler particles. On the other hand, because of the high rigidity of the particles relative to the binder, the local stress field in the binder will still be significantly higher than the average macroscopic stress field. It is of interest to define both this stress field and the associated dilatation in terms of a simple model
Renormalized one-loop theory of correlations in polymer blends
The renormalized one-loop theory is a coarse-grained theory of corrections to
the self-consistent field theory (SCFT) of polymer liquids, and to the random
phase approximation (RPA) theory of composition fluctuations. We present
predictions of corrections to the RPA for the structure function and to
the random walk model of single-chain statics in binary homopolymer blends. We
consider an apparent interaction parameter that is defined by
applying the RPA to the small limit of . The predicted deviation of
from its long chain limit is proportional to , where
is chain length. This deviation is positive (i.e., destabilizing) for weakly
non-ideal mixtures, with \chi_{a} N \alt 1, but negative (stabilizing) near
the critical point. The positive correction to for low values of
is a result of the fact that monomers in mixtures of shorter
chains are slightly less strongly shielded from intermolecular contacts. The
depression in near the critical point is a result of long-wavelength
composition fluctuations. The one-loop theory predicts a shift in the critical
temperature of , which is much greater than the predicted
width of the Ginzburg region. Chain dimensions deviate
slightly from those of a random walk even in a one-component melt, and contract
slightly with increasing . Predictions for and single-chain
properties are compared to published lattice Monte Carlo simulations.Comment: submitted to J. Chem. Phy
Ion-ion correlations: an improved one-component plasma correction
Based on a Debye-Hueckel approach to the one-component plasma we propose a
new free energy for incorporating ionic correlations into Poisson-Boltzmann
like theories. Its derivation employs the exclusion of the charged background
in the vicinity of the central ion, thereby yielding a thermodynamically stable
free energy density, applicable within a local density approximation. This is
an improvement over the existing Debye-Hueckel plus hole theory, which in this
situation suffers from a "structuring catastrophe". For the simple example of a
strongly charged stiff rod surrounded by its counterions we demonstrate that
the Poisson-Boltzmann free energy functional augmented by our new correction
accounts for the correlations present in this system when compared to molecular
dynamics simulations.Comment: 5 pages, 2 figures, revtex styl
Inversion of perturbation series
We investigate the inversion of perturbation series and its resummation, and
prove that it is related to a recently developed parametric perturbation
theory. Results for some illustrative examples show that in some cases series
reversion may improve the accuracy of the results
Free Thermal Convection Driven by Nonlocal Effects
We report and explain a convective phenomenon observed in molecular dynamics
simulations that cannot be classified either as a hydrodynamics instability nor
as a macroscopically forced convection. Two complementary arguments show that
the velocity field by a thermalizing wall is proportional to the ratio between
the heat flux and the pressure. This prediction is quantitatively corroborated
by our simulations.Comment: RevTex, figures is eps, submited for publicatio
Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension
We study the diffusion-limited process in one dimension, with
finite reaction rates. We develop an approximation scheme based on the method
of Inter-Particle Distribution Functions (IPDF), which was formerly used for
the exact solution of the same process with infinite reaction rate. The
approximation becomes exact in the very early time regime (or the
reaction-controlled limit) and in the long time (diffusion-controlled)
asymptotic limit. For the intermediate time regime, we obtain a simple
interpolative behavior between these two limits. We also study the coalescence
process (with finite reaction rates) with the back reaction , and in
the presence of particle input. In each of these cases the system reaches a
non-trivial steady state with a finite concentration of particles. Theoretical
predictions for the concentration time dependence and for the IPDF are compared
to computer simulations. P. A. C. S. Numbers: 82.20.Mj 02.50.+s 05.40.+j
05.70.LnComment: 13 pages (and 4 figures), plain TeX, SISSA-94-0
Lattice Model for water-solute mixtures
A lattice model for the study of mixtures of associating liquids is proposed.
Solvent and solute are modeled by adapting the associating lattice gas (ALG)
model. The nature of interaction solute/solvent is controlled by tuning the
energy interactions between the patches of ALG model. We have studied three set
of parameters, resulting on, hydrophilic, inert and hydrophobic interactions.
Extensive Monte Carlo simulations were carried out and the behavior of pure
components and the excess properties of the mixtures have been studied. The
pure components: water (solvent) and solute, have quite similar phase diagrams,
presenting: gas, low density liquid, and high density liquid phases. In the
case of solute, the regions of coexistence are substantially reduced when
compared with both the water and the standard ALG models. A numerical procedure
has been developed in order to attain series of results at constant pressure
from simulations of the lattice gas model in the grand canonical ensemble. The
excess properties of the mixtures: volume and enthalpy as the function of the
solute fraction have been studied for different interaction parameters of the
model. Our model is able to reproduce qualitatively well the excess volume and
enthalpy for different aqueous solutions. For the hydrophilic case, we show
that the model is able to reproduce the excess volume and enthalpy of mixtures
of small alcohols and amines. The inert case reproduces the behavior of large
alcohols such as, propanol, butanol and pentanol. For last case (hydrophobic),
the excess properties reproduce the behavior of ionic liquids in aqueous
solution.Comment: 28 pages, 13 figure
Phonon Life-times from first principles self consistent lattice dynamics
Phonon lifetime calculations from first principles usually rely on time
consuming molecular dynamics calculations, or density functional perturbation
theory (DFPT) where the zero temperature crystal structure is assumed to be
dynamically stable. Here a new and effective method for calculating phonon
lifetimes from first principles is presented, not limited to crystal structures
stable at 0 K, and potentially much more effective than most corresponding
molecular dynamics calculations. The method is based on the recently developed
self consistent lattice dynamical method and is here tested by calculating the
bcc phase phonon lifetimes of Li, Na, Ti and Zr, as representative examples.Comment: 4 pages, 4 figur
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