Acceleration statistics in thermally driven superfluid turbulence

New methods of flow visualization near absolute zero have opened the way to directly compare quantum turbulence (in superfluid helium) to classical turbulence (in ordinary fluids such as air or water) and explore analogies and differences. We present results of numerical simulations in which we examine the statistics of the superfluid acceleration in thermal counterflow. We find that, unlike the velocity, the acceleration obeys scaling laws similar to classical turbulence, in agreement with a recent quantum turbulence experiment of La Mantia et al.Comment: 5 pages, 5 figures, to appear in PR

A primer on quantum fluids

This book introduces the theoretical description and properties of quantum fluids. The focus is on gaseous atomic Bose-Einstein condensates and, to a minor extent, superfluid helium, but the underlying concepts are relevant to other forms of quantum fluids such as polariton and photonic condensates. The book is pitched at the level of advanced undergraduates and early postgraduate students, aiming to provide the reader with the knowledge and skills to develop their own research project on quantum fluids. Indeed, the content for this book grew from introductory notes provided to our own research students. It is assumed that the reader has prior knowledge of undergraduate mathematics and/or physics; otherwise, the concepts are introduced from scratch, often with references for directed further reading.Comment: 132 pages. Published as SpringerBriefs in Physics book. Typos corrected in this versio

Transition from Ekman flow to Taylor vortex flow in superfluid helium

By numerically computing the steady axisymmetric flow of helium II confined inside a finite aspect ratio Couette annulus, we determine the transition from Ekman flow to Taylor vortex flow as a function of temperature and aspect ratio.We find that the low-Reynolds number flow is quite different to that of a classical fluid, particularly at lower temperatures.At high aspect ratio our results confirm the existing linear stability theory of the onset of Taylor vortices, which assumes infinitely long cylinders.Comment: 12 pages, 8 figures; submitte

Polarization of superfluid turbulence

We show that normal fluid eddies in turbulent helium II polarize the tangle of quantized vortex lines present in the flow, thus inducing superfluid vorticity patterns similar to the driving normal fluid eddies. We also show that the polarization is effective over the entire inertial range. The results help explain the surprising analogies between classical and superfluid turbulence which have been observed recently.Comment: 3 figure

Hydromagnetic Taylor--Couette flow: wavy modes

We investigate magnetic Taylor--Couette flow in the presence of an imposed axial magnetic field. First we calculate nonlinear steady axisymmetric solutions and determine how their strength depends on the applied magnetic field. Then we perturb these solutions to find the critical Reynolds numbers for the appearance of wavy modes, and the related wavespeeds, at increasing magnetic field strength. We find that values of imposed magnetic field which alter only slightly the transition from circular--Couette flow to Taylor--vortex flow, can shift the transition from Taylor--vortex flow to wavy modes by a substantial amount. The results are compared against onset in the absence of a magnetic field.Comment: 12 pages, 8 figures. To appear in J. Fluid Mech. To appear in J. Fluid Mec

Infection Control in Dentistry and Drug-Resistant Infectious Agents: A Burning Issue. Part 1

Using molecular biological methods and retrospective investigations, some outbreaks in dental settings have been proven to be caused by mainly blood-borne viruses and water-borne bacteria. Nowadays, drug-resistant bacteria seem further hazards taking into account the worldwide overuse of antibiotics in dentistry, the limited awareness on infection prevention guidelines, and the lapses and errors during infection prevention (reported in more detail in Part 2). We chose MRSA and VRE as markers since they are considered prioritized bacteria according antibiotic resistance threats. Antibiotic-resistant bacterial infections inside of dental setting are relevant, and we argue about some hazards in dentistry, including dedicated surgeries. MRSA has a key role for its colonization in patients and dental workers, presence on gloves, resistance (days-months on dry inanimate surfaces), the contamination of different clinical contact surfaces in dental settings, the ability of some strains to produce biofilm, and finally its estimated low infective dose. For better dental patient and healthcare personnel safety, we need evidence-based guidelines to improve education and training initiatives in surgery

Infection Control in Dentistry and Drug-Resistant Infectious Agents: A Burning Issue. Part 1

Using molecular biological methods and retrospective investigations, some outbreaks in dental settings have been proven to be caused by mainly blood-borne viruses and water-borne bacteria. Nowadays, drug-resistant bacteria seem further hazards taking into account the worldwide overuse of antibiotics in dentistry, the limited awareness on infection prevention guidelines, and the lapses and errors during infection prevention (reported in more detail in Part 2). We chose MRSA and VRE as markers since they are considered prioritized bacteria according antibiotic resistance threats. Antibiotic-resistant bacterial infections inside of dental setting are relevant, and we argue about some hazards in dentistry, including dedicated surgeries. MRSA has a key role for its colonization in patients and dental workers, presence on gloves, resistance (days-months on dry inanimate surfaces), the contamination of different clinical contact surfaces in dental settings, the ability of some strains to produce biofilm, and finally its estimated low infective dose. For better dental patient and healthcare personnel safety, we need evidence-based guidelines to improve education and training initiatives in surgery

Ballistic propagation of thermal excitations near a vortex in superfluid He3-B

Andreev scattering of thermal excitations is a powerful tool for studying quantized vortices and turbulence in superfluid He3-B at very low temperatures. We write Hamilton's equations for a quasiparticle in the presence of a vortex line, determine its trajectory, and find under wich conditions it is Andreev reflected. To make contact with experiments, we generalize our results to the Onsager vortex gas, and find values of the intervortex spacing in agreement with less rigorous estimates