10,144 research outputs found
The reversibility of sea ice loss in a state-of-the-art climate model
Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere
Preliminary feasibility study of a multi-Phobos encounter experiment during the Viking extended mission
The Viking '75 Mission to Mars is reported which permits a truly unique opportunity to explore the natural satellite, Phobos, from distances measured in tens of kilometers. A preliminary feasibility study has been made which shows that a science mission involving a Phobos close encounter is technically feasible and within the capabilities of the current Viking design. For less than 20 m/s, the Viking Orbiter can provide approximately two 40-day periods of close observation of Phobos, with the first encounter period in January and the second in March, 1977. Multi-pass images of the entire satellite from nearly all aspect angles and with resolution on the order of 10 meters are possible. Close encounters will permit mass determinations to an accuracy of tens of percent. These experiments can be performed in series with the nominal mission; thus, providing complementary scientific information without compromising the original mission and science objectives
Transduction électrochimique de la complexation de cation sur surface
Date du colloque : 12/2013</p
Electrochemical transduction of cation recognition by crown ether nitroxide derivatives : influence of the distance between macrocycle/redox sensor
Date du colloque : 06/2011</p
Transduction électrochimique non covalente sur monocouches auto-assemblées mixtes
Date du colloque : 05/2013</p
Transduction électrochimique de la reconnaissance de cations par des radicaux aminoxyles : influence de la distance éther couronne/sonde redox
Date du colloque : 06/2011</p
Transduction électrochimique de capture de cations par des dérivés aminoxyles.
Date du colloque : 07/2011</p
On a zero speed sensitive cellular automaton
Using an unusual, yet natural invariant measure we show that there exists a
sensitive cellular automaton whose perturbations propagate at asymptotically
null speed for almost all configurations. More specifically, we prove that
Lyapunov Exponents measuring pointwise or average linear speeds of the faster
perturbations are equal to zero. We show that this implies the nullity of the
measurable entropy. The measure m we consider gives the m-expansiveness
property to the automaton. It is constructed with respect to a factor dynamical
system based on simple "counter dynamics". As a counterpart, we prove that in
the case of positively expansive automata, the perturbations move at positive
linear speed over all the configurations
- …