Tkachenko waves, glitches and precession in neutron star

Here I discuss possible relations between free precession of neutron stars, Tkachenko waves inside them and glitches. I note that the proposed precession period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is consistent with the period of Tkachenko waves for the spin period 8.4s. Based on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al. 2007), I propose a simple model, in which long period precession is powered by Tkachenko waves generated by a glitch. The period of free precession, determined by a NS oblateness, should be equal to the standing Tkachenko wave period for effective energy transfer from the standing wave to the precession motion. A similar scenario can be applicable also in the case of the PSR B1828-11.Comment: 6 pages, no figures, accepted to Ap&S

Scaling of torque in turbulent Taylor-Couette flow with background rotation

We did an experimental study on Taylor-Couette flow in between two coaxial cylinders of length L = 220 mm and radii ri = 110 and ro = 120, respectively, the fluid-filled ’Taylor-Couette gap ’ or TC-gap being h = 10 mm, thus gap ratio η = ri/ro = 0.917, and gap aspect ratio L/h = 22). Both cylinders are rotating independently, with angular frequencies ωi,o, The torque T on the inner cylinder is measured through the axis driving the inner cylinder with a co-rotating torque meter. The system is characterised with parameters as given by Dubrulle et al. [3]: a shear Reynolds number ReS = 2/(1 + η) |ηReo − Rei | and a Rotation number Ro = (1 − η) (Rei + Reo)/(ηReo − Rei), where Rei,o = (ri,oωi,oh/ν) are inner and outer Reynolds number. With this choice, ReS is based on the laminar shear rate S; ReS = h2S/ν. The Rotation number Ro compares mean rotation to mean shear; its sign determines cyclonic (Ro> 0, stabilising) or anti-cyclonic (Ro < 0, destabilising) flow. Two other relevant values are Roi = η − 1 ≃ −0.083 and Roo = (1 − η)/η ≃ 0.091 for the inner and th