Flavescence dorée (FD) is a disease of grapevine transmitted by an insect vector, Scaphoideus titanus Ball. At present, no prophylaxis exists, so mandatory control procedures (e.g. removal of infected plants, and insecticidal sprays to avoid transmission) are in place in Italy and other European countries. We propose a model of the epidemiology of FD by taking into account the different aspects involved into the transmis- sion process (acquisition of the disease, latency and expression of symptoms, recovery rate, removal and replacement of infected plants, insecticidal treatments, and the effect of hotbeds). The model was con- structed as a system of first order nonlinear ODEs in four compartment variables. A bifurcation analysis shows that, in the absence of hotbeds, the state of healthy vineyard is stable, if removal and replacement of infected plants is implemented. In the presence of hotbeds, depending on the grapevine density, we find either a single family of equilibria in which the health of the vineyard gradually deteriorates for pro- gressively more severe hotbeds, or multiple equilibria that give rise to sudden transitions from a nearly healthy vineyard to a highly deteriorated one when the severity of the hotbeds crosses a critical value. These results show the long-term risks in planting new vineyards in environmental situations where strong hotbeds of FD are present or may arise in the surroundings.

Fingering convection is a convective instability that occurs in fluids where two buoyancy-changing scalars with different diffusivities have a competing effect on density. The peculiarity of this form of convection is that, although the transport of each individual scalar occurs down-gradient, the net density transport is up-gradient. In a suitable range of non-dimensional parameters, solutions characterized by constant vertical gradients of the horizontally averaged fields may undergo a further instability, which results in the alter- nation of layers where density is roughly homogeneous with layers where there are steep vertical density gradients, a pattern known as “doubly-diffusive staircases”. This instability has been interpreted in terms of an effective negative diffusivity, but simplistic parameteri- zations based on this idea, obviously, lead to ill-posed equations. Here we propose a math- ematical model that describes the dynamics of the horizontally-averaged scalar fields and the staircase-forming instability. The model allows for unstable constant-gradient solutions, but it is free from the ultraviolet catastrophe that characterizes diffusive processes with a negative diffusivity.

We discuss a simplified mathematical model for alpine lake ecosystems, describing the summer (i.e. ice-free period) dynamics of phosphorus, phytoplankton, three zooplankton compartments and fish abundance. Model output is compared with measurements of total phosphorus, chlorophyll-a and zooplankton biomass recorded in twelve high-altitude mountain lakes in the Gran Paradiso National Park (northwestern Italy) during the summer season from 2006 to 2009. Model results are consistent with measured data, indicating the appropriateness of this modeling approach for quantitatively studying mountain lake ecosystems and their response to environmental changes. The comparison between the results obtained for lakes without fish and those where the allochthonous brook trout (Salvelinus fontinalis) was introduced clearly indicates the strong impact of fish stocking in alpine lakes.

Individual resource ingestion rates depend on both individual body size and resource supply. A component of the latter, namely resource availability, is also body-size dependent. This raises the question of the adequacy of simple scaling laws to describe the body-size dependency of resource ingestion. Here we propose a model which integrates resource ingestion drivers by merging a scaling law for feeding metabolism and Holling’s functional responses into a single mathematical framework. At any fixed level of resource supply, the model predicts a log-log concave-down relationship between resource ingestion rates and body size, rather than a simple scaling law. Deviations from the latter are accounted for by the body size dependency of resource limitations. Experimental and literature data describing patterns of perceived resource availability and individual intake rates under limiting conditions with increasing individual body size are used to validate the model’s assumptions nd predictions. The model incorporates and extends well-established theoretical approaches and is intended as a step towards the integration of metabolic theory with behavioral ecology and population dynamics.

Che Alan Turing sia stato il genio che ideò la “macchina di Turing” cioè l’astrazione matematica che, realizzata in pratica, si concretizza nei moderni calcolatori, è noto a tutti. Molti sono anche al corrente che egli fu determinante, durante la seconda guerra mondiale, nel decifrare il codice militare tedesco “enigma”, dando agli alleati un vantaggio strategico determinante. Tuttavia, non molti sanno che Turing è uno dei fondatori della biologia matematica e che pose le basi teoriche per la comprensione della morfogenesi, cioè di quella disciplina che studia come si formano, durante la crescita, le strutture anatomiche degli esseri viventi.

The Mediterranean region is one of the hot spots of climate change. This study aims at understanding what are the conditions sustaining tree diversity in Mediterranean wet forests under future scenarios of altered hydrological regimes. The core of the work is a quantitative, dynamic model describing the coexistence of different Mediterranean tree species, typical of arid or semi-arid wetlands. Two kind of species, i.e. Hygrophilous (drought sensitive, flood resistant) and Non-hygrophilous (drought resistant, flood sensitive), are broadly defined according to the distinct adaptive strategies of trees against water stress of summer drought and winter flooding. We argue that at intermediate levels of water supply the dual role of water (resource and stress) results in the coexistence of the two kind of species. A bifurcation analysis allows us to assess the effects of climate change on the coexistence of the two species in order to highlight the impacts of predicted climate scenarios on tree diversity. Specifically, the model has been applied to Mediterranean coastal swamp forests of Central Italy located at Castelporziano Estate and Circeo National Park. Our results show that there are distinct rainfall thresholds beyond which stable coexistence becomes impossible. Regional climatic projections show that the lower rainfall threshold may be approached or crossed during the XXI century, calling for an urgent adaptation and mitigation response to prevent biodiversity losses.

The Equatorial Undercurrent (EUC) is the major source of iron to the equatorial Pacific and it is sensitive to climatic changes as other components of the tropical Pacific. This work proposes a methodology based on a Lagrangian approach aimed at understanding the changes in the transport of iron rich waters to the EUC in a future climate change scenario, using climate model data from an Earth system model. A selected set of regions from the northern and southern extra-equatorial Pacific has been chosen. These regions are characterized by the presence of iron sources from continental shelf processes like the Papua New Guinea region and atmospheric deposition like the northern subtropical gyre. The trajectories that reach the EUC during the 20th and the 21st century departing from these areas have been analyzed using a set of statistics designed to determine variations in the amount of transport and in the travel times of the water masses. The transport of waters to the EUC from the north Pacific subtropical gyre and from the Bismarck Sea is projected to increase during the 21st century. The increase is particularly significant for water masses from the northern subtropical gyre, with travel times lower than 10 years in the second half of the 21st century. This increased interaction between the extra-tropics and the EUC may bring additional iron-rich waters in the high-nutrient low-chlorophyll region of the equatorial Pacific compatibly with the significant increase of the simulated net primary production found in the biogeochemical model, thus partly offsetting the anticipated decrease of production implied by the surface warming.

We report on high-resolution, three-dimensional, high-Rayleigh number and low density ratio numerical simulations of fingering convection. We observe a previously unreported phenomenon of self-organization of fingers, that cluster together to form larger-scale coherent structures. The flow ultimately forms density staircases alternating well mixed regions with fingering convective zones. We give evidence that the mechanical mixing induced by the clusters forms the staircases with a mechanism analogous to staircase formation in a stably-stratified, non-convective, stirred fluid.

Biovolume is commonly used as a size descriptor in the study of phytoplankton ecology. Usually, biovolume is not measured directly but is obtained from a standardized set of geometric models based on linear dimensions measured by light microscopy. This commonly used method allows visualization and measurement in two dimensions (2D) yielding no information at all on the third dimension of phytoplankton cells. Inaccurate biovolume assessment resulting from geometric approximation leads to erroneous interpretation of eco-physiological processes and morpho-functional traits. Here, we use confocal microscopy coupled with an image analysis system (NIS Elements AR software, Nikon) to determine directly shape and biovolume by means a 3D reconstruction of Coscinodiscus cf. granii specimens. We evaluate the accuracy of current methods by comparing the results obtained using geometric models with direct biovolume and shape. We find that calculation of biovolume by approximation to geometric models (cylindrical and complex shapes) leads to a significant overestimation with respect to direct volume. We also propose a data-driven formula for calculating the biovolume of Coscinodiscus cf. granii specimens based on diameter or other linear measurements.

We give a detailed analytical and numerical description of the global dynamics of 4+1 points interacting through the singular logarithmic potential and subject to the following symmetry constraint: at each instant 4 of them form an orbit of the Klein group D 2 of order 4. The main device in order to achieve our results is to use a McGehee-like transformation introduced in (Paparella and Portaluri in Global dynamics of the dihedral singular logarithmic potential and nearly parallel vortex filaments, 2011) for a problem analogous to the present one. After performing this transformation in order to regularize the total collision, we study the rest-points of the flow, the invariant (stable and unstable) manifolds and we derive some interesting information about the global dynamics.

We give a detailed analytical description of the global dynamics of N points interacting through the singular logarithmic potential and subject to the following symmetry constraint: at each instant they form an orbit of the dihedral group Dl of order 2l. The main device in order to achieve our results is a technique very popular in Celestial Mechanics, usually referred to as McGehee transformation. After performing this change of coordinates that regularizes the total collision, we study the rest-points of the flow, the invariant manifolds and, with the help of a computer algebra system, we derive inter- esting information about the global dynamics for l = 2. We observe that our problem is equivalent to studying the geometry of stationary configurations of nearly-parallel vortex filaments in three dimensions in the LIA approximation.

Il 6 aprile 2009 la città dell’Aquila subì un devastante terremoto. Il 22 ottobre 2012 il Tribunale dell’Aquila ha condannato i componenti della Commissione Grandi Rischi a sei anni di reclusione per aver mancato ai loro doveri di valutazione, previsione e prevenzione del rischio perché fornirono “al Dipartimento Nazionale della Protezione Civile, all’assessore alla Protezione Civile della Regione Abruzzo, al sindaco di L’Aquila ed alla cittadinanza aquilana informazioni incomplete, imprecise e contraddittorie sulla natura, sulle cause, sulla pericolosità e sui futuri sviluppi dell’attività sismica”

Il dibattito riguardo ai cambiamenti climatici furoreggia sui mezzi di comunicazione di massa. All’indomani di alluvioni, periodi di siccità, tempeste di neve o ondate di calore c’è chi paventa i cambiamenti climatici. Ma questo genere di disastri è sempre esistito, e nessuno di essi, preso singolarmente, può dare informazioni riguardo al clima. Esiste dunque un evento che, se si verificasse, sarebbe da solo la prova inconfutabile che il nostro pianeta sta per entrare in un nuovo regime climatico? Un simile evento esiste, ed il fatto che verosimilmente si verificherà entro qualche decennio non è una buona notizia.

Confocal laser scanner microscopy coupled with an image analysis system was used to directly determine the shape and calculate the biovolume of phytoplankton organisms by constructing 3D models of cells. The study was performed on Biceratium furca (Ehrenberg) Vanhoeffen, which is one of the most complex-shaped phytoplankton. Traditionally, biovolume is obtained from a standardized set of geometric models based on linear dimensions measured by light microscopy. However, especially in the case of complex-shaped cells, biovolume is affected by very large errors associated with the numerous manual measurements that this entails. We evaluate the accuracy of these traditional methods by comparing the results obtained using geometric models with direct biovolume measurement by image analysis. Our results show cell biovolume measurement based on decomposition into simple geometrical shapes can be highly inaccurate. Although we assume that the most accurate cell shape is obtained by 3D direct biovolume measurement, which is based on voxel counting, the intrinsic uncertainty of this method is explored and assessed. Finally, we implement a data-driven formula-based approach to the calculation of biovolume of this complex-shaped organism. On one hand, the model is obtained from 3D direct calculation. On the other hand, it is based on just two linear dimensions which can easily be measured by hand. This approach has already been used for investigating the complexities of morphology and for determining the 3D structure of cells. It could also represent a novel way to generalize scaling laws for biovolume calculation.

We examine the statistics of active scalar fluctuations in high-Rayleigh number fingering convection with high-resolution three-dimensional numerical experiments. The one-point distribution of buoyancy fluctuations is found to present significantly non-Gaussian tails. A modified theory based on an original approach by Yakhot (1989) is used to model the active scalar distributions as a function of the conditional expectation values of scalar dissipation and fluxes in the flow. Simple models for these two quantities highlight the role of blob-like coherent structures for scalar statistics in fingering convection.

We discuss an analytical theory for the statistics of buoyancy fluctuations in high Rayleigh number fingering convection. We propose an idealized model that suggests the shape, depending on just three free parameters, of an otherwise unknown function that appears in the theory. The theoretical results are compared with data obtained from numerical simulations of the Boussinesq equations for double-diffusion.

Underwater communications through acoustic modems rise several networking challenges for the Underwater Acoustic Sensor Networks (UASN). In particular, opportunistic routing is a novel but promising technique that can remarkably increase the reliability of the UASN, but its use in this context requires studies on the nature of mobility in UASN. Our goal is to study a real-world mobility dataset obtained from the Argo project. In particular, we observe the mobility of 51 free-drifting floats deployed on the Mediterranean Sea for approximately one year and we analyze some important properties of the underwater network we built. Specifically, we analyze the contact-time, inter-contact time as well density and network degree while varying the connectivity degree of the whole dataset. We then consider three known routing algorithms, namely Epidemic, PROPHET and Direct Delivery, with the goal of measuring their performance in real conditions for USAN. We finally discuss the opportunities arising from the adoption of opportunistic routing in UASN showing that, even in a very sparse and strongly disconnected network, it is still possible to build a limited but working networking framework.

We give a detailed analytical description of the global dynamics of a point mass moving on a sphere under the action of a logarithmic potential. We perform a McGehee-type blow-up in order to cope with the singularity of the potential when the point mass goes through the singularity. In addition we investigate the rest-points of the flow, the invariant (stable and unstable) manifolds and we give a complete dynamical description of the motion.

We consider the problem of a Boussinesq fluid forced by applying both non-uniform temperature and stress at the top surface. On the other boundaries the conditions are thermally insulating and either no-slip or stress-free. The interesting case is when the direction of the steady applied surface stress opposes the sense of the buoyancy driven flow. We obtain two-dimensional numerical solutions showing a regime in which there is an upper cell with thermally indirect circulation (buoyant fluid is pushed downwards by the applied stress and heavy fluid is elevated), and a second deep cell with thermally direct circulation. In this two-cell regime the driving mechanisms are competitive in the sense that neither dominates the flow. A scaling argument shows that this balance requires that surface stress vary as the horizontal Rayleigh number to the three-fifths power.

Tropical deforestation is well known to have serious negative consequences for biodiversity, terrestrial carbon sinks and the balance of atmospheric greenhouse gases. By contrast, selective logging of tropical forests is often regarded as having a lesser impact on the ecosystem particularly in long terms, even though there have been few critical evaluations of the practice, particularly in Africa. We compared field data from 511 plots in the tropical forest of Sierra Leone, Ghana, Cameroon and Gabon. These plots were subject to different forest management practices: no recent logging (primary forests), selective logging (up to 30 years old) and re-grown secondary forests post clear-cutting (at least 20 years ago). Our findings suggest that the vertical structure and plant richness of the selectively logged and secondary forests change in different amplitude from those of primary forests, but stem density and the prevalence of vine and weed species differ greatly. We show that the effects of selective logging are greater than those expected simply from the removal of commercial species, and can persist for decades. Selective logging, unless it is practiced at very low harvest intensities, can significantly reduce the biomass of a tropical forest for many decades, seriously diminishing aboveground carbon storage capacity, and create opportunities for weeds and vines to spread and slow down the ecological succession.

We investigate the motion of homogeneous, spheroidal particles immersed in an incompressible, viscous fluid. We assume the particles to be more dense than the surrounding fluid and small enough that inertia is negligible with respect to viscous forces. We give exact solutions for the motion of the particle’s center of mass for steady, linear flows, either irrotational or without strain. For a weakly strained, two-dimensional, rotational flow we give an asymptotic approximation to the solutions, and we compare it with numerical solutions. In the presence of vorticity we find that the spheroid moves along three-dimensional, non-planar paths. With pure strain the three-dimensionality of the paths is transient. If a two-dimensional rotational flow is perturbed by strain, then the generic path of a spheroid is an open curve, even if all the streamlines of the flow are closed. We conclude by speculating about the significance of these findings for the ecology of phytoplankton.

Concrete component comprising at least one reinforcing element in plastic material of elongated shape having a size greater than the other two, characterized by a length of the reinforcement comparable with the length of the artefact measured in the direction in which the reinforcing element is positioned. The section of the reinforcement is such as to ensure a bending strength sufficient to support its own weight in the process of positioning, and a constant section along the longitudinal direction, so as to allow the manufacturability by extrusion of the reinforcing element.