1,966 research outputs found
State-dependence of climate sensitivity: attractor constraints and palaeoclimate regimes
Equilibrium climate sensitivity (ECS) is a key predictor of climate change.
However, it is not very well constrained, either by climate models or by
observational data. The reasons for this include strong internal variability
and forcing on many time scales. In practise this means that the 'equilibrium'
will only be relative to fixing the slow feedback processes before comparing
palaeoclimate sensitivity estimates with estimates from model simulations. In
addition, information from the late Pleistocene ice age cycles indicates that
the climate cycles between cold and warm regimes, and the climate sensitivity
varies considerably between regime because of fast feedback processes changing
relative strength and time scales over one cycle.
In this paper we consider climate sensitivity for quite general climate
dynamics. Using a conceptual Earth system model of Gildor and Tziperman (2001)
(with Milankovich forcing and dynamical ocean biogeochemistry) we explore
various ways of quantifying the state-dependence of climate sensitivity from
unperturbed and perturbed model time series. Even without considering any
perturbations, we suggest that climate sensitivity can be usefully thought of
as a distribution that quantifies variability within the 'climate attractor'
and where there is a strong dependence on climate state and more specificially
on the 'climate regime' where fast processes are approximately in equilibrium.
We also consider perturbations by instantaneous doubling of CO and
similarly find a strong dependence on the climate state using our approach.Comment: 32 pages, 10 figure
Extreme sensitivity and climate tipping points
A climate state close to a tipping point will have a degenerate linear
response to perturbations, which can be associated with extreme values of the
equilibrium climate sensitivity (ECS). In this paper we contrast linearized
(`instantaneous') with fully nonlinear geometric (`two-point') notions of ECS,
in both presence and absence of tipping points. For a stochastic energy balance
model of the global mean surface temperature with two stable regimes, we
confirm that tipping events cause the appearance of extremes in both notions of
ECS. Moreover, multiple regimes with different mean sensitivities are visible
in the two-point ECS. We confirm some of our findings in a physics-based
multi-box model of the climate system.Comment: 11 figure
Engineering analysis of ERTS data for southeast Asian agriculture
The present program focuses on rice because of its importance world-wide as a food. Specifically, the focus is on rice fields in the Philippines. Two primary program objectives are: (1) to establish the feasibility of extracting from ERTS imagery the areas where rice is grown, and (2) to determine those measurements on the imagery which enable the assessment of crop condition. Achieving these objectives with procedures which can be cost-effective can lead the way toward yield prediction, irrigation system management, and similar functions which are known to be important needs in Southeast Asia
Response maxima in modulated turbulence
Isotropic and homogeneous turbulence driven by an energy input modulated in
time is studied within a variable range mean-field theory. The response of the
system, observed in the second order moment of the large-scale velocity
difference D(L,t)=>~Re(t)^2$, is calculated for varying
modulation frequencies w and weak modulation amplitudes. For low frequencies
the system follows the modulation of the driving with almost constant
amplitude, whereas for higher driving frequencies the amplitude of the response
decreases on average 1/w. In addition, at certain frequencies the amplitude of
the response either almost vanishes or is strongly enhanced. These frequencies
are connected with the frequency scale of the energy cascade and multiples
thereof.Comment: 11 pages, 6 figure
Elasticity of cross-linked semiflexible biopolymers under tension
Aiming at the mechanical properties of cross-linked biopolymers, we set up
and analyze a model of two weakly bending wormlike chains subjected to a
tensile force, with regularly spaced inter-chain bonds (cross-links)
represented by harmonic springs. Within this model, we compute the
force-extension curve and the differential stiffness exactly and discuss
several limiting cases. Cross-links effectively stiffen the chain pair by
reducing thermal fluctuations transverse to the force and alignment direction.
The extra alignment due to cross-links increases both with growing number and
with growing strength of the cross-links, and is most prominent for small force
f. For large f, the additional, cross-link-induced extension is subdominant
except for the case of linking the chains rigidly and continuously along their
contour. In this combined limit, we recover asymptotically the elasticity of a
weakly bending wormlike chain without constraints, stiffened by a factor four.
The increase in differential stiffness can be as large as 100% for small f or
large numbers of cross-links.Comment: 11 pages, 6 figures, submitted to PR
Complex regulation of the aflatoxin biosynthesis gene cluster of Aspergillus flavus in relation to various combinations of water activity and temperature
A microarray analysis was performed to study the effect of varying combinations of water activity and temperature on the activation of aflatoxin biosynthesis genes in Aspergillus flavus grown on YES medium. Generally A. flavus showed expression of the aflatoxin biosynthetic genes at all parameter combinations tested. Certain combinations of aw and temperature, especially combinations which imposed stress on the fungus resulted in a significant reduction of the growth rate. At these conditions induction of the whole aflatoxin biosynthesis gene cluster occurred, however the produced aflatoxin B1 was low. At all other combinations (25 °C/0.95 and 0.99; 30 °C/0.95 and 0.99; 35 °C/0.95 and 0.99) a reduced basal level of cluster gene expression occurred. At these combinations a high growth rate was obtained as well as high aflatoxin production. When single genes were compared, two groups with different expression profiles in relation to water activity/temperature combinations occurred. These two groups were co-ordinately localized within the aflatoxin gene cluster. The ratio of aflR/aflJ expression was correlated with increased aflatoxin biosynthesis
On the sound of snapping shrimp
Fluid dynamics video: Snapping shrimp produce a snapping sound by an
extremely rapid closure of their snapper claw. Our high speed imaging of the
claw closure has revealed that the sound is generated by the collapse of a
cavitation bubble formed in a fast flowing water jet forced out from the claws
during claw closure. The produced sound originates from the cavitation collapse
of the bubble. At collapse a short flash of light is emitted, just as in single
bubble sonoluminescence. A model based on the Rayleigh-Plesset equation can
quantitatively account for the visual and acoustical observations.Comment: Fluid dynamics vide
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
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