852 research outputs found
Measurement of Turbulence in Superfluid 3He-B
The experimental investigation of superfluid turbulence in 3He-B is generally
not possible with the techniques which have been developed for 4He-II. We
describe a new method by which a transient burst of turbulent vortex expansion
can be generated in 3He-B. It is based on the injection of a few vortex loops
into rotating vortex-free flow. The time-dependent evolution of the quantized
vorticity is then monitored with NMR spectroscopy. Using these techniques the
transition between regular (i.e. vortex number conserving) and turbulent vortex
dynamics can be recorded at T ~ 0.6 Tc and a number of other characteristics of
turbulence can be followed down to a temperature of T ~ 0.4 Tc.Comment: 31 pages, 10 figure
Onset of turbulence in superfluid 3He-B and its dependence on vortex injection in applied flow
Vortex dynamics in 3He-B is divided by the temperature dependent damping into
a high-temperature regime, where the number of vortices is conserved, and a
low-temperature regime, where rapid vortex multiplication takes place in a
turbulent burst. We investigate experimentally the hydrodynamic transition
between these two regimes by injecting seed vortex loops into vortex-free
rotating flow. The onset temperature of turbulence is dominated by the roughly
exponential temperature dependence of vortex friction, but its exact value is
found to depend on the injection method.Comment: To be published in the proceedings of the 24th International
Conference on Low Temperature Physics - LT24, in Conference Proceedings of
the American Institute of Physic
Internalization of a polysialic acid-binding Escherichia coli bacteriophage into eukaryotic neuroblastoma cells
Eukaryotic organisms are continuously exposed to bacteriophages, which are efficient gene transfer agents in bacteria. However, bacteriophages are considered not to pass the eukaryotic cell membrane and enter nonphagocytic cells. Here we report the binding and penetration of Escherichia coli PK1A2 bacteriophage into live eukaryotic neuroblastoma cells in vitro. The phage interacts with cell surface polysialic acid, which shares structural similarity with the bacterial phage receptor. Using fluorescence and electron microscopy, we show that phages are internalized via the endolysosomal route and persist inside the human cells up to one day without affecting cell viability. Phage capsid integrity is lost in lysosomes, and the phage DNA is eventually degraded. We did not detect the entry of phage DNA into the nucleus; however, we speculate that this might occur as a rare event, and propose that this potential mechanism could explain prokaryote-eukaryote gene flow.Peer reviewe
Antecedents and Consequences of Outward Emotional Reactions in Table Tennis
The purpose of the present study was to shed light on the behavioral component of emotions by investigating antecedents and consequences of outward emotional reactions during table tennis competitions. With regards to the antecedents of outward emotional reactions, in line with appraisal theories, we considered the importance and the controllability of the situation as two important constructs. Fifteen table tennis matches, involving in total 21 players (7 females) with a mean age of 16.71 (SD = 0.70), were video recorded during the finals of the youth National Championship in Greece. Based on the footage, outward emotional reactions after every point were classified as neutral, positive, or negative. Situational factors in relation to the scoring system, bearing the importance and the controllability of the situation, were formed to assess antecedents of outward emotional reactions. To measure the consequences of outward emotional reactions, the impact on the outcome of the next point was assessed. Generalized linear models with a logit link were computed separately for positive outward emotional reactions after having won a point and negative outward emotional reactions after having lost a point. In general, the results show that while situational factors bearing the importance of the situation could predict positive and negative outward emotional reactions, the effects of situational factors bearing the controllability of the situation were less conclusive. In addition, the results also showed interactive effects between the two constructs for both positive and negative outward emotional reactions. With regard to the consequences of outward emotional reactions, negative and positive outward emotional reactions could not predict the outcome of the next point. To conclude, this study highlights the behavioral component of emotions as a viable alternative to enhance our understanding of the role of emotions in sport
Vortex Multiplication in Applied Flow: the Precursor to Superfluid Turbulence
The dynamics of quantized vortices in rotating He-B is investigated in
the low density (single-vortex) regime as a function of temperature. An abrupt
transition is observed at . Above this temperature the number of
vortex lines remains constant, as they evolve to their equilibrium positions.
Below this temperature the number of vortices increases linearly in time until
the vortex density has grown sufficiently for turbulence to switch on. On the
basis of numerical calculations we suggest a mechanism responsible for vortex
formation at low temperatures and identify the mutual friction parameter which
governs its abrupt temperature dependence.Comment: 5 pages, 4 figures; version submitted to Phys. Rev. Let
System size scaling of topological defect creation in a second-order dynamical quantum phase transition
We investigate the system size scaling of the net defect number created by a
rapid quench in a second-order quantum phase transition from an O(N) symmetric
state to a phase of broken symmetry. Using a controlled mean-field expansion
for large N, we find that the net defect number variance in convex volumina
scales like the surface area of the sample for short-range correlations. This
behaviour follows generally from spatial and internal symmetries. Conversely,
if spatial isotropy is broken, e.g., by a lattice, and in addition long-range
periodic correlations develop in the broken-symmetry phase, we get the rather
counterintuitive result that the scaling strongly depends on the dimension
being even or odd: For even dimensions, the net defect number variance scales
like the surface area squared, with a prefactor oscillating with the system
size, while for odd dimensions, it essentially vanishes.Comment: 20 pages of IOP style, 6 figures; as published in New Journal of
Physic
Classical and quantum regimes of the superfluid turbulence
We argue that turbulence in superfluids is governed by two dimensionless
parameters. One of them is the intrinsic parameter q which characterizes the
friction forces acting on a vortex moving with respect to the heat bath, with
1/q playing the same role as the Reynolds number Re=UR/\nu in classical
hydrodynamics. It marks the transition between the "laminar" and turbulent
regimes of vortex dynamics. The developed turbulence described by Kolmogorov
cascade occurs when Re >> 1 in classical hydrodynamics, and q << 1 in the
superfluid hydrodynamics. Another parameter of the superfluid turbulence is the
superfluid Reynolds number Re_s=UR/\kappa, which contains the circulation
quantum \kappa characterizing quantized vorticity in superfluids. This
parameter may regulate the crossover or transition between two classes of
superfluid turbulence: (i) the classical regime of Kolmogorov cascade where
vortices are locally polarized and the quantization of vorticity is not
important; and (ii) the quantum Vinen turbulence whose properties are
determined by the quantization of vorticity. The phase diagram of the dynamical
vortex states is suggested.Comment: 12 pages, 1 figure, version accepted in JETP Letter
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