2,620 research outputs found
HBT shape analysis with q-cumulants
Taking up and extending earlier suggestions, we show how two- and
threedimensional shapes of second-order HBT correlations can be described in a
multivariate Edgeworth expansion around gaussian ellipsoids, with expansion
coefficients, identified as the cumulants of pair momentum difference q, acting
as shape parameters. Off-diagonal terms dominate both the character and
magnitude of shapes. Cumulants can be measured directly and so the shape
analysis has no need for fitting.Comment: 8 pages, 6 figures for a total of 29 subfigs, revtex4. Typos
corrected, three missing terms added, minor text change
Self-similar breakup of polymeric threads as described by the Oldroyd-B model
When a drop of fluid containing long, flexible polymers breaks up, it forms
threads of almost constant thickness, whose size decreases exponentially in
time. Using an Oldroyd-B fluid as a model, we show that the thread profile,
rescaled by the thread thickness, converges to a similarity solution. Using the
correspondence between viscoelastic fluids and non-linear elasticity, we derive
similarity equations for the full three-dimensional axisymmetric flow field in
the limit that the viscosity of the solvent fluid can be neglected. A
conservation law balancing pressure and elastic energy permits to calculate the
thread thickness exactly. The explicit form of the velocity and stress fields
can be deduced from a solution of the similarity equations. Results are
validated by detailed comparison with numerical simulations
- …