Formation of spiral waves in cylindrical containers under orbital excitation

The lowest swirling wave mode arising in upright circular cylinders as a response to circular orbital excitation has been widely studied in the last decade, largely due to its high practical relevance for orbitally shaken bioreactors. Our recent theoretical study (Horstmann et al., J. Fluid Mech., vol. 891, 2020, A22) revealed a damping-induced symmetry breaking mechanism that can cause spiral wave structures manifested in the so far widely disregarded higher rotating wave modes. Building on this work, we develop a linear criterion describing the degree of spiralisation and classify different spiral regimes as a function of the most relevant dimensionless groups. The analysis suggests that high Bond numbers and shallow liquid layers favour the formation of coherent spiral waves. This result paved the way to find the predicted wave structures in our interfacial sloshing experiment. We present two sets of experiments, with different characteristic damping rates, verifying the formation of both coherent and overdamped spiral waves in conformity with the theoretical predictions.

Spectrum of the $$uudc \bar{c}$$ hidden charm pentaquark with an SU(4) flavor-spin hyperfine interaction

We study a few of the lowest states of the pentaquark $$uudc\overline{c}$$uudcc¯, of positive and negative parity, in a constituent quark model with an SU(4) flavor-spin hyperfine interaction. For positive parity we introduce space wave functions of appropriate permutation symmetry with one unit of orbital angular momentum in the internal motion of the four-quark subsystem or an orbital excitation between the antiquark and the four quark subsystem which remains in the ground state. We show that the lowest positive parity states $$1/2^+, 3/2^+$$1/2+,3/2+ are provided by the first alternative and are located below the $$1/2^-$$1/2- and the $$1/2^+$$1/2+ states with all quarks in the ground state. We compare our results with the LHCb three narrow pentaquark structures reported in 2019.