Gilberto Corso

Evidence of a nanomechanical resonator being driven into chaotic response via the Ruelle–Takens route

Nanomechanical resonators, of importance for signal filtering and transduction, are investigated within the limit of extreme nonlinear excitation. The Ruelle–Takens route establishes the transition of a system into chaos with n frequencies present. By providing a set of three sources, this transition from linear to nonlinear and finally to chaotic response can be traced, and it is found in our experiment. Knowledge of potentially chaotic behavior of nanomechanical systems is crucial for their application. Our resonator system has an overall length of 4 μm and a cross section of about 100 nm×300 nm with natural frequencies of ∼50 MHz.

Omnivory by Planktivores Stabilizes Plankton Dynamics, but May Either Promote or Reduce Algal Biomass

Classical models of phytoplankton–zooplankton interaction show that with nutrient enrichment such systems may abruptly shift from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton. Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking or strong reduction of such fish is best.

Families and clustering in a natural numbers network.

We develop a network in which the natural numbers are the vertices. The decomposition of natural numbers by prime numbers is used to establish the connections. We perform data collapse and show that the degree distribution of these networks scales linearly with the number of vertices. We explore the families of vertices in connection with prime numbers decomposition. We compare the average distance of the network and the clustering coefficient with the distance and clustering coefficient of the corresponding random graph. In case we set connections among vertices each time the numbers share a common prime number the network has properties similar to a random graph. If the criterion for establishing links becomes more selective, only prime numbers greater than p(l) are used to establish links, where the network has high clustering coefficient.

Seismic ground roll time–frequency filtering using the gaussian wavelet transform

Seismic signal processing is an important task in geophysics sounding and represents a permanent challenge in petroleum exploration. Although seismograms could in principle give us a picture of a geological structure, they are very contaminated by spurious signals (having the ground roll as the main component). This fact demands a big effort in developing new filtering methodologies. Using the Gaussian wavelet transform, a filtering method for ground roll removal is developed. The filter allows a local extraction of the ground roll, it is adaptative to trace and it has an attenuation factor that keeps the average frequency spectrum. This method is tested for a land-based seismic signal leading to promising results.

The small-world of economy: a speculative proposal

Using the small-world approach we suggest a network model for the economy. Our basic assumption is that the economic agents prefer to make business with the big business. This assumption makes the preferential attachment the main mechanism for the evolution of the economic network. We hypothesize that the connectivity of the economic network should reflect the wealth distribution of the society which is considered to be an exponential truncated power law. The objective of this paper is to model qualitatively the wealth distribution of a society using concepts based on evolving network. Several alternatives of evolving networks are discussed in an economic context.

Application of data envelopment analysis in the performance evaluation of electricity distribution: a review

The objective of this paper is to review the application of data envelopment analysis to performance evaluation of electricity distribution. After introducing the basic concepts and models of data envelopment analysis, work on its application in electricity distribution is discussed via a number of case studies. Suggestions for further research are presented, with a view to enhancing the use of data envelopment analysis in electrical energy distribution.

Charge transport in fibrous/not fibrous α3-helical and (5Q,7Q)α3 variant peptides

Although differing only by the Ala→Gln substitution at the fifth or seventh position of the α3-peptide amino acid sequence (Leu-Glu-Thr-Leu-Ala-Lys-Ala)3, the 5Qα3 variant forms fibrous assemblies more attenuated than those of the α3-peptide, while the 7Qα3 variant does not form fibrils. A tight-binding transport modeling was performed to obtain their current-voltage patterns, with hopping energies of the dipeptides calculated within the density functional theory framework. Beyond the semiconductor character, we obtain that the current pattern can be used to distinguish them, suggesting that it can be useful for the development of devices as diagnostics tools for amyloidosislike diseases.

Anisotropy and percolation threshold in a multifractal support

Recently a multifractal object, Qmf, was proposed to allow the study of percolation properties in a multifractal support. The area and the number of neighbors of the blocks of Qmf show a non-trivial behavior. The value of the probability of occupation at the percolation threshold, pc, is a function of r, a parameter of Qmf which is related to its anisotropy. We investigate the relation between pc and the average number of neighbors of the blocks as well as the anisotropy of Qmf.

Modeling Habitat Split: Landscape and Life History Traits Determine Amphibian Extinction Thresholds

Habitat split is a major force behind the worldwide decline of amphibian populations, causing community change in richness and species composition. In fragmented landscapes, natural remnants, the terrestrial habitat of the adults, are frequently separated from streams, the aquatic habitat of the larvae. An important question is how this landscape configuration affects population levels and if it can drive species to extinction locally. Here, we put forward the first theoretical model on habitat split which is particularly concerned on how split distance – the distance between the two required habitats – affects population size and persistence in isolated fragments. Our diffusive model shows that habitat split alone is able to generate extinction thresholds. Fragments occurring between the aquatic habitat and a given critical split distance are expected to hold viable populations, while fragments located farther away are expected to be unoccupied. Species with higher reproductive success and higher diffusion rate of post-metamorphic youngs are expected to have farther critical split distances. Furthermore, the model indicates that negative effects of habitat split are poorly compensated by positive effects of fragment size. The habitat split model improves our understanding about spatially structured populations and has relevant implications for landscape design for conservation. It puts on a firm theoretical basis the relation between habitat split and the decline of amphibian populations.

Universal temporal characteristics and vanishing of multifractality in Barkhausen avalanches

Barkhausen effect in ferromagnetic materials provides an excellent area for investigating scaling phenomena found in disordered systems exhibiting crackling noise. The critical dynamics is characterized by random pulses or avalanches with scale-invariant properties, power-law distributions, and universal features. However, the traditional Barkhausen avalanches statistics may not be sufficient to fully characterize the complex temporal correlation of the magnetic domain walls dynamics. Here we focus on the multifractal scenario to quantify the temporal scaling characteristics of Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films with thicknesses from 50 to 1000 nm. We show that the multifractal properties are dependent on film thickness, although they seem to be insensitive to the structural character of the materials. Moreover, we observe for the first time the vanishing of the multifractality in the domain walls dynamics. As the thickness is reduced, the multifractal behavior gives place to a monofractal one over the entire range of time scales. This reorganization in the temporal scaling characteristics of Barkhausen avalanches is understood as a universal restructuring associated to the dimensional crossover, from three- to two-dimensional magnetization dynamics.Barkhausen effect in ferromagnetic materials provides an excellent area for investigating scaling phenomena found in disordered systems exhibiting crackling noise. The critical dynamics is characterized by random pulses or avalanches with scale-invariant properties, power-law distributions, and universal features. However, the traditional Barkhausen avalanches statistics may not be sufficient to fully characterize the complex temporal correlation of the magnetic domain walls dynamics. Here we go beyond power laws and focus on the multifractal scenario to quantify the temporal scaling characteristics of Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films with thicknesses from