6,098 research outputs found
On the sound of snapping shrimp
Snapping shrimp produce a snapping sound by an extremely rapid closure of their snapper claw. Source levels reported for Alpheus heterochaelis are as high as 220 dB (peak-to-peak) re. 1 µPa at 1 m distance. The loud snap has been attributed to the mechanical contact made when the snapper claw contracts. The recent ultra-high-speed imaging of the snapper claw closure at 40500 frames per second has revealed that the sound is, in fact, generated by the collapse of a cavitation bubble formed in a fast flowing water jet forced out from between the claws during claw closure. A temporal analysis of the sound recordings and the high-speed images shows that no sound is associated with the claw closure, while a very prominent signal is observed during the collapse of the cavitation bubble. Gallery of Fluid Motion\ud
Award-winning entry 200
Response maxima in time-modulated turbulence: Direct Numerical Simulations
The response of turbulent flow to time-modulated forcing is studied by direct
numerical simulations of the Navier-Stokes equations. The large-scale forcing
is modulated via periodic energy input variations at frequency . The
response is maximal for frequencies in the range of the inverse of the large
eddy turnover time, confirming the mean-field predictions of von der Heydt,
Grossmann and Lohse (Phys. Rev. E 67, 046308 (2003)). In accordance with the
theory the response maximum shows only a small dependence on the Reynolds
number and is also quite insensitive to the particular flow-quantity that is
monitored, e.g., kinetic energy, dissipation-rate, or Taylor-Reynolds number.
At sufficiently high frequencies the amplitude of the kinetic energy response
decreases as . For frequencies beyond the range of maximal response,
a significant change in phase-shift relative to the time-modulated forcing is
observed.Comment: submitted to Europhysics Letters (EPL), 8 pages, 8 Postscript
figures, uses epl.cl
Observation of the Meissner effect with ultracold atoms in bosonic ladders
We report on the observation of the Meissner effect in bosonic flux ladders
of ultracold atoms. Using artificial gauge fields induced by laser-assisted
tunneling, we realize arrays of decoupled ladder systems that are exposed to a
uniform magnetic field. By suddenly decoupling the ladders and projecting into
isolated double wells, we are able to measure the currents on each side of the
ladder. For large coupling strengths along the rungs of the ladder, we find a
saturated maximum chiral current corresponding to a full screening of the
artificial magnetic field. For lower coupling strengths, the chiral current
decreases in good agreement with expectations of a vortex lattice phase. Our
work marks the first realization of a low-dimensional Meissner effect and,
furthermore, it opens the path to exploring interacting particles in low
dimensions exposed to a uniform magnetic field
Heat transfer mechanisms in bubbly Rayleigh-Benard convection
The heat transfer mechanism in Rayleigh-Benard convection in a liquid with a
mean temperature close to its boiling point is studied through numerical
simulations with point-like vapor bubbles, which are allowed to grow or shrink
through evaporation and condensation and which act back on the flow both
thermally and mechanically. It is shown that the effect of the bubbles is
strongly dependent on the ratio of the sensible heat to the latent heat as
embodied in the Jacob number Ja. For very small Ja the bubbles stabilize the
flow by absorbing heat in the warmer regions and releasing it in the colder
regions. With an increase in Ja, the added buoyancy due to the bubble growth
destabilizes the flow with respect to single-phase convection and considerably
increases the Nusselt number.Comment: 11 pages, 14 figure
Scaling and Dissipation in the GOY Shell Model
This is a paper about multi-fractal scaling and dissipation in a shell model
of turbulence, called the GOY model. This set of equations describes a one
dimensional cascade of energy towards higher wave vectors. When the model is
chaotic, the high-wave-vector velocity is a product of roughly independent
multipliers, one for each logarithmic momentum shell. The appropriate tool for
studying the multifractal properties of this model is shown to be the energy
current on each shell rather than the velocity on each shell. Using this
quantity, one can obtain better measurements of the deviations from Kolmogorov
scaling (in the GOY dynamics) than were available up to now. These deviations
are seen to depend upon the details of inertial-range structure of the model
and hence are {\em not} universal. However, once the conserved quantities of
the model are fixed to have the same scaling structure as energy and helicity,
these deviations seem to depend only weakly upon the scale parameter of the
model. We analyze the connection between multifractality in the velocity
distribution and multifractality in the dissipation. Our arguments suggest that
the connection is universal for models of this character, but the model has a
different behavior from that of real turbulence. We also predict the scaling
behavior of time correlations of shell-velocities, of the dissipation,Comment: Revised Versio
Clinical and functional characterisation of a novel TNFRSF1A c.605T > A/V173D cleavage site mutation associated with tumour necrosis factor receptor-associated periodic fever syndrome (TRAPS), cardiovascular complications and excellent response to etanercept treatment.
Objectives: To study the clinical outcome, treatment
response, T-cell subsets and functional consequences of a
novel tumour necrosis factor (TNF) receptor type 1
(TNFRSF1A) mutation affecting the receptor
cleavage site.
Methods: Patients with symptoms suggestive of tumour
necrosis factor receptor-associated periodic syndrome
(TRAPS) and 22 healthy controls (HC) were screened for
mutations in the TNFRSF1A gene. Soluble TNFRSF1A and
inflammatory cytokines were measured by ELISAs.
TNFRSF1A shedding was examined by stimulation of
peripheral blood mononuclear cells (PBMCs) with phorbol
12-myristate 13-acetate followed by flow cytometric
analysis (FACS). Apoptosis of PBMCs was studied by
stimulation with TNFa in the presence of cycloheximide
and annexin V staining. T cell phenotypes were monitored
by FACS.
Results: TNFRSF1A sequencing disclosed a novel V173D/
p.Val202Asp substitution encoded by exon 6 in one
family, the c.194–14G.A splice variant in another and
the R92Q/p.Arg121Gln substitution in two families.
Cardiovascular complications (lethal heart attack and
peripheral arterial thrombosis) developed in two V173D
patients. Subsequent etanercept treatment of the V173D
carriers was highly effective over an 18-month follow-up
period. Serum TNFRSF1A levels did not differ between
TRAPS patients and HC, while TNFRSF1A cleavage from
monocytes was significantly reduced in V173D and R92Q
patients. TNFa-induced apoptosis of PBMCs and T-cell
senescence were comparable between V173D patients
and HC.
Conclusions: The TNFRSF1A V173D cleavage site
mutation may be associated with an increased risk for
cardiovascular complications and shows a strong
response to etanercept. T-cell senescence does not seem
to have a pathogenetic role in affected patients
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