4,401 research outputs found
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
Stability of thin liquid films and sessile droplets under confinement
The stability of nonvolatile thin liquid films and of sessile droplets is
strongly affected by finite size effects. We analyze their stability within the
framework of density functional theory using the sharp kink approximation,
i.e., on the basis of an effective interface Hamiltonian. We show that finite
size effects suppress spinodal dewetting of films because it is driven by a
long-wavelength instability. Therefore nonvolatile films are stable if the
substrate area is too small. Similarly, nonvolatile droplets connected to a
wetting film become unstable if the substrate area is too large. This
instability of a nonvolatile sessile droplet turns out to be equivalent to the
instability of a volatile drop which can attain chemical equilibrium with its
vapor.Comment: 14 pages, 13 figure
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
Nucleosynthesis in massive stars revisited
We have performed the first calculations to follow the evolution of all
stable nuclei and their radioactive progenitors in a finely-zoned stellar model
computed from the onset of central hydrogen burning through explosion as a Type
II supernova. Calculations were done for 15, 20, and 25 solar masses Pop I
stars using the most recently available set of experimental and theoretical
nuclear data, revised opacity tables, and taking into account mass loss due to
stellar winds. Here results are presented for one 15 solar masses model.Comment: 4 pages, 1 figure; needs espcrc1.sty; talk at "Nuclei in the Cosmos
2000", Aarhus, Denmark, June 2000; will appear in Nucl. Phys.
Nuclear Aspects of Nucleosynthesis in Massive Stars
Preliminary results of a new set of stellar evolution and nucleosynthesis
calculations for massive stars are presented. These results were obtained with
an extended reaction network up to Bi. The discussion focuses on the importance
of nuclear rates in pre- and post-explosive nucleosynthesis. The need for
further experiments to study specific reactions and nuclear properties (optical
alpha+nucleus potentials) is emphasized.Comment: 6 pages, 2 figures; invited talk, to appear in the Proceedings of the
Int. Conf. "Structure of the Nucleus at the Dawn of the Century", May 2000,
Bologna, Ital
Motion of nanodroplets near edges and wedges
Nanodroplets residing near wedges or edges of solid substrates exhibit a
disjoining pressure induced dynamics. Our nanoscale hydrodynamic calculations
reveal that non-volatile droplets are attracted or repelled from edges or
wedges depending on details of the corresponding laterally varying disjoining
pressure generated, e.g., by a possible surface coating.Comment: 12 pages, 7 figure
Observing Nucleon Decay in Lead Perchlorate
Lead perchlorate, part of the OMNIS supernova neutrino detector, contains two
nuclei, 208Pb and 35Cl, that might be used to study nucleon decay. Both would
produce signatures that will make them especially useful for studying
less-well-studied neutron decay modes, e.g., those in which only neutrinos are
emitted.Comment: 6 pages, 2 figure
Stellar (n,gamma) cross sections of p-process isotopes PartI: 102Pd, 120Te, 130,132Ba,and 156Dy
We have investigated the (n,gamma) cross sections of p-process isotopes with
the activation technique. The measurements were carried out at the Karlsruhe
Van de Graaff accelerator using the 7Li(p,n)7Be source for simulating a
Maxwellian neutron distribution of kT = 25 keV. Stellar cross section
measurements are reported for the light p-process isotopes 102Pd, 120Te,
130,132Ba, and 156Dy. In a following paper the cross sections of 168Yb, 180W,
184Os, 190Pt, and 196Hg will be discussed. The data are extrapolated to
p-process energies by including information from evaluated nuclear data
libraries. The results are compared to standard Hauser-Feshbach models
frequently used in astrophysics.Comment: 13 pages, 4 figure
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