1,344 research outputs found
Ocean acidification alters predator behaviour and reduces predation rate
Ocean acidification poses a range of threats to marine invertebrates; however, the emerging and likely widespread effects of rising carbon dioxide (COâ) levels on marine invertebrate behaviour are still little understood. Here, we show that ocean acidification alters and impairs key ecological behaviours of the predatory cone snail Conus marmoreus. Projected near-future seawater COâ levels (975 ”atm) increased activity in this coral reef molluscivore more than threefold (from less than 4 to more than 12 mm minâ»Âč) and decreased the time spent buried to less than one-third when compared with the present-day control conditions (390 ”atm). Despite increasing activity, elevated COâ reduced predation rate during predatorâprey interactions with control-treated humpbacked conch, Gibberulus gibberulus gibbosus; 60% of control predators successfully captured and consumed their prey, compared with only 10% of elevated COâ predators. The alteration of key ecological behaviours of predatory invertebrates by near-future ocean acidification could have potentially far-reaching implications for predatorâprey interactions and trophic dynamics in marine ecosystems. Combined evidence that the behaviours of both species in this predatorâprey relationship are altered by elevated COâ suggests food web interactions and ecosystem structure will become increasingly difficult to predict as ocean acidification advances over coming decades
Fatal encephalitis due to the scuticociliate Uronema nigricans in sea-caged, southern bluefin tuna Thunnus maccoyii
A syndrome characterized by atypical swimming behaviour followed by rapid death was first reported in captive southern bluefin tuna Thunnus maccoyii (Castelnau) in the winter of 1993. The cause of this behaviour was found to be a parasitic encephalitis due to the scuticociliate Uronema nigricans (Mueller). Based on parasitological and histological findings, it is proposed that the parasites initially colonise the olfactory rosettes and then ascend the olfactory nerves to eventually invade the brain. Possible epidemiological factors involved in the pathogenesis of the disease include water temperature (>18 degrees C) and the immune status of the fish
Southern Ocean carbon-wind stress feedback
The Southern Ocean is the largest sink of anthropogenic carbon in the present-day climate. Here, Southern Ocean pCO2pCO2 and its dependence on wind forcing are investigated using an equilibrium mixed layer carbon budget. This budget is used to derive an expression for Southern Ocean pCO2pCO2 sensitivity to wind stress. Southern Ocean pCO2pCO2 is found to vary as the square root of area-mean wind stress, arising from the dominance of vertical mixing over other processes such as lateral Ekman transport. The expression for p\hbox {CO} _ {2} is validated using idealised coarse-resolution ocean numerical experiments. Additionally, we show that increased (decreased) stratification through surface warming reduces (increases) the sensitivity of the Southern Ocean pCO2pCO2 to wind stress. The scaling is then used to estimate the wind-stress induced changes of atmospheric pCO2pCO2 in CMIP5 models using only a handful of parameters. The scaling is further used to model the anthropogenic carbon sink, showing a long-term reversal of the Southern Ocean sink for large wind stress strength
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Analytical and Numerical Demonstration of How the Drude Dispersive Model Satisfies Nernst's Theorem for the Casimir Entropy
In view of the current discussion on the subject, an effort is made to show
very accurately both analytically and numerically how the Drude dispersive
model, assuming the relaxation is nonzero at zero temperature (which is the
case when impurities are present), gives consistent results for the Casimir
free energy at low temperatures. Specifically, we find that the free energy
consists essentially of two terms, one leading term proportional to T^2, and a
next term proportional to T^{5/2}. Both these terms give rise to zero Casimir
entropy as T -> 0, thus in accordance with Nernst's theorem.Comment: 11 pages, 4 figures; minor changes in the discussion. Contribution to
the QFEXT07 proceedings; matches version to be published in J. Phys.
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Palliative care in humanitarian crises: always something to offer
More than 128·6 million people across 33 countries require life-saving humanitarian assistance, 92·8 million of whom are particularly vulnerable. Palliative care, however, has been omitted from efforts to tackle humanitarian crises. Palliative care is, according to WHO, âan approach that improves the quality of life of patients and their families facing the problems associated with life-threatening illness, through the prevention and relief of sufferingâ. We propose holistic palliative care as an integral component of relief strategies
On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration
We report on measurements of forces acting between two conducting surfaces in
a spherical-plane configuration in the 35 nm-1 micrometer separation range. The
measurements are obtained by performing electrostatic calibrations followed by
a residual analysis after subtracting the electrostatic-dependent component. We
find in all runs optimal fitting of the calibrations for exponents smaller than
the one predicted by electrostatics for an ideal sphere-plane geometry. We also
find that the external bias potential necessary to minimize the electrostatic
contribution depends on the sphere-plane distance. In spite of these anomalies,
by implementing a parametrixation-dependent subtraction of the electrostatic
contribution we have found evidence for short-distance attractive forces of
magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss
the relevance of our findings in the more general context of Casimir-Lifshitz
force measurements, with particular regard to the critical issues of the
electrical and geometrical characterization of the involved surfaces.Comment: 22 pages, 15 figure
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