Comment on 'Nucleation of 3He-B from the A Phase: A Cosmic-Ray Effect?'

A comment to the article by Leggett, A. J.Peer reviewe

Surface spin waves in 3He-A, a probe for vortex phenomena in narrow gaps

We report measurements on a new collective spin-wave mode trapped by the textural boundary layers of 3 He-A within a stack of thin Mylar plates. The surface mode was seen as a new peak in the cw NMR spectrum measured at H0=284 Oe. Rotation of the sample, with Ω orthogonal to the gaps, increased the spectral weight of the surface mode, indicating an increase in the textural boundary layers caused by a counterflow-induced transition. This phenomenon was used to study vortex creation and persistent currents.Peer reviewe

Continuous Vortices with Broken Symmetry in Rotating Superfluid 3He-A

New NMR measurements are reported on continuous 3He-A vortices in tilted magnetic fields. We introduce a symmetry classification of the continuous vortices with broken axial symmetry. It is found that the discrete internal symmetry may in addition be broken in two inequivalent ways, producing two different continuous vortices. Although NMR may not distinguish between these two vortices, the observed vortex satellite peak is well accounted for by spin waves localized in the soft core of such vortices.Peer reviewe

Persistent-Current Experiments on Superfluid 3He-B and 3He-A

We have investigated persistent flow of superfluid 3He with an ac gyroscope filled with 20-μm powder. In 3He-B, currents circulate undiminished for 48 h at least; this implies a viscosity 12 orders of magnitude lower than in the normal fluid. In 3He-A, the current does not persist. The observed critical velocity in 3He-B at P12 bars there are two regimes in the B phase: For example, at 29.3 bars the ultimate critical velocities are 5.4 and 7.8 mm/s, respectively.Peer reviewe

Detection of elemental sulphur on galena oxidized in acidic solution

Galena (PbS) oxidation on potentiostatically treated specimens in acetate buffer was investigated by atomic force microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), Elemental sulphur was detected as an oxidation product by XPS. To minimize the evaporation of elemental sulphur during the XPS experiments in ultra high vacuum, sample cooling was required before the evacuation was started. Decreasing the pressure to 1 torr for 5 min, before the sample was cooled, removed the elemental sulphur almost completely from the surface, In addition, when an electrochemically oxidized sample was exposed to air at ambient pressure for about 3 h, the relative intensity of the S2p component of elemental sulphur was observed to decrease to about half of the value achieved by instant cooling and measuring, AFM images showed elemental sulphur to be present on galena surface as local accumulations rather than as a uniform layer, The sulphur formation is highly localized, but does not seem to occur preferentially at steps, (C) 1997 Elsevier Science B.V

Magnetic Vortices in Rotating Superfluid 3He-B

Rotating superfluid 3He-B is found to possess a new contribution to the NMR frequency shift, which changes sign on reversal of either the angular velocity of rotation or the magnetic field. For p=29.3 bars this gyromagnetic effect shows a discontinuity in magnitude at the first-order phase-transition temperature T/Tc=0.6, at which a change in the vortex-core structure takes place. These observations support the conclusion that the vortex core possesses a spontaneous intrinsic magnetization.Peer reviewe

Phase Diagram of the First-Order Vortex-Core Transition in Superfluid 3He-B

The phase diagram of quantized vortices in 3He-B has been obtained with two techniques. Our NMR measurements show that magnetization displays a pressure-dependent first-order phase change at TV(P). Our gyroscopic experiments reveal a transition curve TG(P) which marks an abrupt change in the critical velocity. Both curves show a weak magnetic field dependence, run similarly in the (P, T) plane, and seem to mark the same vortex-core transition.Peer reviewe

Do we need MRI quality assurance : experience from a multi-unit imaging center with 14 MRI systems

Volume: 2015 Host publication title: ECR book of abstractsPeer reviewe

Theory and practice in Finnish teacher education : a rhetorical analysis of changing values from the 1960s to the present day

Our aim in this article is to examine the relationship between theory and practice in Finnish teacher education from the 1960s to the present. We identify four different periods to represent this relationship based on our analysis of national committee and evaluation reports. Theory and practice gradually converged, culminating in a research-based agenda that reflects the current situation. This relationship between theory and practice also reflects the ideal teacher of different times and what a teacher's working orientation should be. We use rhetorical analysis and the concept of a 'philosophical pair' introduced by Perelman and Olbrechts-Tyteca to interpret this development.Peer reviewe

Controlled creation of a singular spinor vortex by circumventing the Dirac belt trick

Persistent topological defects and textures are particularly dramatic consequences of superfluidity. Among the most fascinating examples are the singular vortices arising from the rotational symmetry group SO(3), with surprising topological properties illustrated by Dirac’s famous belt trick. Despite considerable interest, controlled preparation and detailed study of vortex lines with complex internal structure in fully three-dimensional spinor systems remains an outstanding experimental challenge. Here, we propose and implement a reproducible and controllable method for creating and detecting a singular SO(3) line vortex from the decay of a non-singular spin texture in a ferromagnetic spin-1 Bose–Einstein condensate. Our experiment explicitly demonstrates the SO(3) character and the unique spinor properties of the defect. Although the vortex is singular, its core fills with atoms in the topologically distinct polar magnetic phase. The resulting stable, coherent topological interface has analogues in systems ranging from condensed matter to cosmology and string theory