4,740 research outputs found
Motion of nanodroplets near chemical heterogeneities
We investigate the dynamics of nanoscale droplets in the vicinity of chemical
steps which separate parts of a substrate with different wettabilities. Due to
long-ranged dispersion forces, nanodroplets positioned on one side of the step
perceive the different character of the other side even at some distances from
the step, leading to a dynamic response. The direction of the ensuing motion of
such droplets does not only depend on the difference between the equilibrium
contact angles on these two parts but in particular on the difference between
the corresponding Hamaker constants. Therefore the motion is not necessarily
directed towards the more wettable side and can also be different from that of
droplets which span the step.Comment: 6 pages, 6 figure
Stability of liquid ridges on chemical micro- and nanostripes
We analyze the stability of sessile filaments (ridges) of nonvolatile liquids
versus pearling in the case of externally driven flow along a chemical stripe
within the framework of the thin film approximation. The ridges can be stable
with respect to pearling even if the contact line is not completely pinned. A
generalized stability criterion for moving contact lines is provided. For large
wavelengths and no drive, within perturbation theory, an analytical expression
of the growth rate of pearling instabilities is derived. A numerical analysis
shows that drive further stabilizes the ridge by reducing the growth rate of
unstable perturbations, even though there is no complete stabilization. Hence
the stability criteria established without drive ensure overall stability.Comment: 10 pages, 6 figure
A thin film model for corotational Jeffreys fluids under strong slip
We derive a thin film model for viscoelastic liquids under strong slip which
obey the stress tensor dynamics of corotational Jeffreys fluids.Comment: 3 pages, submitted to Eur. Phys. J.
Continuum mesoscale theory inspired by plasticity
We present a simple mesoscale field theory inspired by rate-independent
plasticity that reflects the symmetry of the deformation process. We
parameterize the plastic deformation by a scalar field which evolves with
loading. The evolution equation for that field has the form of a
Hamilton-Jacobi equation which gives rise to cusp-singularity formation. These
cusps introduce irreversibilities analogous to those seen in plastic
deformation of real materials: we observe a yield stress, work hardening,
reversibility under unloading, and cell boundary formation.Comment: 7 pages, 5 .eps figures. submitted to Europhysics Letter
Probing the Production of Actinides under Different r-process Conditions
Several extremely metal-poor stars are known to have an enhanced thorium abundance. These actinide-boost stars have likely inherited material from an r-process that operated under different conditions than the r-process that is reflected in most other metal-poor stars with no actinide enhancement. In this article, we explore the sensitivity of actinide production in r-process calculations to the hydrodynamical conditions as well as the nuclear physics. We find that the initial electron fraction Y e is the most important factor determining the actinide yields and that the abundance ratios between long-lived actinides and lanthanides like europium can vary for different conditions in our calculations. In our setup, conditions with high entropies systematically lead to lower actinide abundances relative to other r-process elements. Furthermore, actinide-enhanced ejecta can also be distinguished from the "regular" composition in other ways, most notably in the second r-process peak abundances.Peer reviewe
Direct neutron capture cross sections of 62Ni in the s-process energy range
Direct neutron capture on 62Ni is calculated in the DWBA and the cross
sections in the energy range relevant for s-process nucleosynthesis are given.
It is confirmed that the thermal value of the capture cross section contains a
subthreshold resonance contribution. Contrary to previous investigations it is
found that the capture at higher energies is dominated by p-waves, thus leading
to a considerably increased cross section at s-process energies and a modified
energy dependence.Comment: 10 pages, 1 figure, corrected typos in Eq. 6 and subsequent paragrap
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