1,023 research outputs found
Softening of edges of solids by surface tension
Surface tension tends to minimize the area of interfaces between pieces of
matter in different thermodynamic phases, be they in the solid or the liquid
state. This can be relevant for the macroscopic shape of very soft solids, and
lead to a roughening of initially sharp edges. We calculate this effect for a
neo-Hookean elastic solid, with assumptions corresponding to actual
experiments, namely the case where an initially sharp edge is rounded by the
effect of surface tension felt when the fluid surrounding the soft solid (and
so surface tension) is changed at the solid/liquid boundary. We consider two
opposite limits where the analysis can be carried to the end, the one of a
shallow angle and the one of a very sharp angle. Both cases yield a
discontinuity of curvature in the state with surface tension although the
initial state had a discontinuous slope
Casimir-like force arising from quantum fluctuations in a slow-moving dilute Bose-Einstein condensate
We calculate a force due to zero-temperature quantum fluctuations on a
stationary object in a moving superfluid flow. We model the object by a
localized potential varying only in the flow direction and model the flow by a
three-dimensional weakly interacting Bose-Einstein condensate at zero
temperature. We show that this force exists for any arbitrarily small flow
velocity and discuss the implications for the stability of superfluid flow.Comment: v3: revised discussion of toroidal geometry; replotted figure; minor
editorial changes; quantitative and qualitative conclusions remain unchange
Super-Arrhenius dynamics for sub-critical crack growth in disordered brittle media
Taking into account stress fluctuations due to thermal noise, we study
thermally activated irreversible crack growth in disordered media. The
influence of material disorder on sub-critical growth of a single crack in
two-dimensional brittle elastic material is described through the introduction
of a rupture threshold distribution. We derive analytical predictions for crack
growth velocity and material lifetime in agreement with direct numerical
calculations. It is claimed that crack growth process is inhibited by disorder:
velocity decreases and lifetime increases with disorder. More precisely,
lifetime is shown to follow a super-Arrhenius law, with an effective
temperature theta - theta_d, where theta is related to the thermodynamical
temperature and theta_d to the disorder variance.Comment: Submitted to Europhysics Letter
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