Vortices and dynamics in trapped Bose-Einstein condensates

I review the basic physics of ultracold dilute trapped atomic gases, with emphasis on Bose-Einstein condensation and quantized vortices. The hydrodynamic form of the Gross-Pitaevskii equation (a nonlinear Schr{\"o}dinger equation) illuminates the role of the density and the quantum-mechanical phase. One unique feature of these experimental systems is the opportunity to study the dynamics of vortices in real time, in contrast to typical experiments on superfluid $^4$He. I discuss three specific examples (precession of single vortices, motion of vortex dipoles, and Tkachenko oscillations of a vortex array). Other unusual features include the study of quantum turbulence and the behavior for rapid rotation, when the vortices form dense regular arrays. Ultimately, the system is predicted to make a quantum phase transition to various highly correlated many-body states (analogous to bosonic quantum Hall states) that are not superfluid and do not have condensate wave functions. At present, this transition remains elusive. Conceivably, laser-induced synthetic vector potentials can serve to reach this intriguing phase transition.Comment: Accepted for publication in Journal of Low Temperature Physics, conference proceedings: Symposia on Superfluids under Rotation (Lammi, Finland, April 2010

Quasi-periodic x-ray eruptions years after a nearby tidal disruption event

Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei of galaxies, repeating on timescales of hours to weeks. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs) undergoing instabilities or interacting with a stellar object in a close orbit. It has been suggested that this disk could be created when the SMBH disrupts a passing star implying that many QPEs should be preceded by observable tidal disruption events (TDEs). Two known QPE sources show long-term decays in quiescent luminosity consistent with TDEs and two observed TDEs have exhibited X-ray flares consistent with individual eruptions . TDEs and QPEs also occur preferentially in similar galaxies. However, no confirmed repeating QPEs have been associated with a spectroscopically confirmed TDE or an optical TDE observed at peak brightness. Here we report the detection of nine X-ray QPEs with a mean recurrence time of approximately 48 h from AT2019qiz, a nearby and extensively studied optically selected TDE16. We detect and model the X-ray, ultraviolet (UV) and optical emission from the accretion disk and show that an orbiting body colliding with this disk provides a plausible explanation for the QPEs

Bias and measurement errors in radioactivity data from four European radiation research laboratories

Four radiation research laboratories participated in an interlaboratory comparison exercise to assess precision in the measurement of radionuclide concentrations. Each laboratory was required to report results for 137Cs, 134Cs and 40K in accordance with their usual procedures. A normal probability plot of the pooled data showed ten of the 161 readings to be obvious outliers and seven of these were attributed to one of the laboratories. One laboratory consistently overestimated relative to the global mean, another laboratory consistently underestimated while the other two showed positive and negative bias dependent on isotope. Both bias and measurement errors were found to increase in the order 137Cs, 134Cs, 40K. A need for greater standardization of analytical techniques was identified

Bias and measurement errors in radioactivity data from 4 European radiation research laboratories

Four radiation research laboratories participated in an interlaboratory comparison exercise to assess precision in the measurement of radionuclide concentrations. Each laboratory was required to report results for 137Cs, 134Cs and 40K in accordance with their usual procedures. A normal probability plot of the pooled data showed ten of the 161 readings to be obvious outliers and seven of these were attributed to one of the laboratories. One laboratory consistently overestimated relative to the global mean, another laboratory consistently underestimated while the other two showed positive and negative bias dependent on isotope. Both bias and measurement errors were found to increase in the order 137Cs, 134Cs, 40K. A need for greater standardization of analytical techniques was identified