1,000 research outputs found
The influence of pulsed redox conditions on soil phosphorus
The effects of eleven pulsed reduction-oxidation cycles (20 and 2 days respectively) on soil phosphorus (P) dynamics are compared for 12 soils having contrasting properties and overfertilised with respect to P. Incubation conditions simulated transient waterlogging of the soil profile and involved repeated sampling and analysis of both the solution and solid phase P forms. An initial increase in P concentration occurred upto and including the fourth full cycle was followed by a sharp decline in concentration for all but one soil. Accompanying changes in the main extractable forms of P, which appeared to be cumulative, could be summarised as a general decline in the organic P fraction and an overall increase in amorphous associated inorganic forms of P. The fact that up to 60% of the total soil P was demonstrated to change its sensitivity for a particular extractant suggests that these operationally defined P forms can experience substantial transformations. There was also a suggestion that certain changes in P forms may not be reversible. While the laboratory conditions represent an extreme situation changes in timing and frequency of intense precipitation events, as predicted in many climate change scenarios, may increase the risk of episodic soil waterlogging. The potential onset of reducing conditions even for periods of less than twenty days will influence soil P dynamics and short-term bioavailable P. Various mechanisms are involved but the robustness of sequential extraction procedures and general soil test methods (e.g. Olsen) for quantifying and reliably distinguishing specific soil P forms/associations are questioned
Complexity aided design: The FuturICT technological innovation paradigm
"In the next century, planet earth will don an electronic skin. It will use the Internet as a scaffold to support and transmit its sensations. This skin is already being stitched together. It consists of millions of embedded electronic measuring devices: thermostats, pressure gauges, pollution detectors, cameras, microphones, glucose sensors, EKGs, electroencephalographs. These will probe and monitor cities and endangered species, the atmosphere, our ships, highways and fleets of trucks, our conversations, our bodies-even our dreams ....What will the earth's new skin permit us to feel? How will we use its surges of sensation? For several years-maybe for a decade-there will be no central nervous system to manage this vast signaling network. Certainly there will be no central intelligence...some qualities of self-awareness will emerge once the Net is sensually enhanced. Sensuality is only one force pushing the Net toward intelligence”. These statements are quoted by an interview by Cherry Murray, Dean of the Harvard School of Engineering and Applied Sciences and Professor of Physics. It is interesting to outline the timeliness and highly predicting power of these statements. In particular, we would like to point to the relevance of the question "What will the earth's new skin permit us to feel?” to the work we are going to discuss in this paper. There are many additional compelling questions, as for example: "How can the electronic earth's skin be made more resilient?”; "How can the earth's electronic skin be improved to better satisfy the need of our society?”;"What can the science of complex systems contribute to this endeavour?” Graphical abstrac
On the Limit Performance of Floating Gossip
In this paper we investigate the limit performance of Floating Gossip, a new,
fully distributed Gossip Learning scheme which relies on Floating Content to
implement location-based probabilistic evolution of machine learning models in
an infrastructure-less manner. We consider dynamic scenarios where continuous
learning is necessary, and we adopt a mean field approach to investigate the
limit performance of Floating Gossip in terms of amount of data that users can
incorporate into their models, as a function of the main system parameters.
Different from existing approaches in which either communication or computing
aspects of Gossip Learning are analyzed and optimized, our approach accounts
for the compound impact of both aspects. We validate our results through
detailed simulations, proving good accuracy. Our model shows that Floating
Gossip can be very effective in implementing continuous training and update of
machine learning models in a cooperative manner, based on opportunistic
exchanges among moving users
Relation between stress heterogeneity and aftershock rate in the rate-and-state model
We estimate the rate of aftershocks triggered by a heterogeneous stress
change, using the rate-and-state model of Dieterich [1994].We show that an
exponential stress distribution Pt(au) ~exp(-tautau_0) gives an Omori law decay
of aftershocks with time ~1/t^p, with an exponent p=1-A sigma_n/tau_0, where A
is a parameter of the rate-and-state friction law, and \sigma_n the normal
stress. Omori exponent p thus decreases if the stress "heterogeneity" tau_0
decreases. We also invert the stress distribution P(tau) from the seismicity
rate R(t), assuming that the stress does not change with time. We apply this
method to a synthetic stress map, using the (modified) scale invariant "k^2"
slip model [Herrero and Bernard, 1994]. We generate synthetic aftershock
catalogs from this stress change.The seismicity rate on the rupture area shows
a huge increase at short times, even if the stress decreases on average.
Aftershocks are clustered in the regions of low slip, but the spatial
distribution is more diffuse than for a simple slip dislocation. Because the
stress field is very heterogeneous, there are many patches of positive stress
changes everywhere on the fault.This stochastic slip model gives a Gaussian
stress distribution, but nevertheless produces an aftershock rate which is very
close to Omori's law, with an effective p<=1, which increases slowly with time.
We obtain a good estimation of the stress distribution for realistic catalogs,
when we constrain the shape of the distribution. However, there are probably
other factors which also affect the temporal decay of aftershocks with time. In
particular, heterogeneity of A\sigma_n can also modify the parameters p and c
of Omori's law. Finally, we show that stress shadows are very difficult to
observe in a heterogeneous stress context.Comment: In press in JG
- …