The recent huge technological development of unmanned aerial vehicles (UAVs) can provide breakthrough means of fighting wildland fires. We propose an innovative forest firefighting system based on the use of a swarm of hundreds of UAVs able to generate a continuous flow of extinguishing liquid on the fire front, simulating the effect of rain. Automatic battery replacement and extinguishing liquid refill ensure the continuity of the action. We illustrate the validity of the approach in Mediterranean scrub first computing the critical water flow rate according to the main factors involved in the evolution of a fire, then estimating the number of linear meters of active fire front that can be extinguished depending on the number of drones available and the amount of extinguishing fluid carried. A fire propagation cellular automata model is also employed to study the evolution of the fire. Simulation results suggest that the proposed system can provide the flow of water required to fight low-intensity and limited extent fires or to support current forest firefighting techniques.

Segments are fundamental units in animal development which are made of distinct cell lineages separated by boundaries. Although boundaries show limited plasticity during their formation for sharpening, cell lineages make compartments that become tightly restricted as development goes on. Here, we characterize a unique case of breaking of the segment boundary in late drosophila embryos. During dorsal closure, specific cells from anterior compartments cross the segment boundary and enter the adjacent posterior compartments. This cell mixing behaviour is driven by an anterior-to-posterior reprogramming mechanism involving de novo expression of the homeodomain protein Engrailed. Mixing is accompanied by stereotyped local cell intercalation, converting the segment boundary into a relaxation compartment important for tension-release during morphogenesis. This process of lineage switching and cell remodelling is controlled by JNK signalling. Our results reveal plasticity of segment boundaries during late morphogenesis and a role for JNK-dependent developmental reprogramming in this process. Multicellular organisms are assembled from different cell types, each following a particular fate depending on their history and location. During development, cells are organized into compartments, which are essential for the correct formation of organs. Within the compartments, cells follow two general rules: (i) cells that have acquired a given fate cannot change their differentiation state and (ii) cells from one compartment stay together and never mix with cells from other compartments. In this work, we identified a group of unique cells in Drosophila melanogaster embryos called mixer cells which move from one compartment of the epidermis to another, breaking the compartment boundary rule. Our data show that this unique behaviour depends on the nuclear reprogramming of the mixer cells, which change their fate and acquire the identity of the destination compartment de novo. We show that the shift in identity and compartment mixing are due to the expression of a single gene (Engrailed), under the control of JNK, a signalling pathway that is conserved across species. Interestingly, this process of reprogramming and mixing provides a mechanism of tension relaxation to the tissue during morphogenesis that allows dorsal closure of the Drosophila embryo (an event that resembles wound healing). This work reveals a novel model of cell plasticity that is amenable to genetic study, with potential application in the field of regenerative medicine.

We introduce a new homogenized hyperbolic (multiclass) traffic flow model, which allows us to take into account the behaviors of different type of vehicles (cars, trucks, buses, etc.) and drivers. We discretize the starting Lagrangian system introduced below with a Godunov scheme, and we let the mesh size h in (x,t) go to 0: the typical length (of a vehicle) and time vanish. Therefore, the variables---here (w,a)---which describe the heterogeneity of the reactions of the different car-driver pairs in the traffic, develop large oscillations when $h\rightarrow 0$. These (known) oscillations in (w,a) persist in time, and we describe the homogenized relations between velocity and density. We show that the velocity is the unique solution "à la Kruzkov" of a scalar conservation law, with variable coefficients, discontinuous in x. Finally, we prove that the same macroscopic homogenized model is also the hydrodynamic limit of the corresponding multiclass Follow-the-Leader model.