Molecular and functional characterization of the Odorant Receptor2 (OR2) in the tiger mosquito Aedes albopictus.

In mosquitoes, olfactory system plays a crucial role in many behaviors, including nectar feeding, host preference selection, searching for the right place to lay eggs. A.albopicus, known also as tiger mosquito, is an anthropophilic species which in the last years, due to a strong ecological plasticity, has spread throughout the world and all over Italy with a high abundance in man-made environments. Although long considered a secondary vector of viruses, the potentiality of its vectorial capacity is very dangerous and may constitute the foundation for a public health alert. Nevertheless, to date, for this mosquito nothing is known at molecular level. Based on the idea that an improved understanding of the olfactory system of mosquitoes may help in developing control methods that interfere with its behavior, recently we have undertaken a study aimed to characterize the A. albopictus Odorant Receptors. During my PhD work, I focused my attention on the identification, cloning and functional characterization of the A. albopictus OR2 ortholog. My data indicate that A. albopictus OR2 (AalOR2) shares a high degree of identity with the other mosquito OR2 orthologs characterized to date, confirming that OR2 is one of the most conserved mosquito ORs; furthermore, AalOR2 is expressed in the olfactory appendages of larvae and adults and its expression increases after a blood meal, as determined by a semi-quantitative RT-PCR. Interestingly, this is the first report of an up-regulation of an OR in response to a blood meal; this increase could suggest a role of AalOR2 in searching oviposition right places. AalOR2, such as the other orthologs, is narrowly tuned to indole, a ubiquitous volatile compound that has been linked to host seeking, and oviposition. The de-orphaning of AalOR2 has been obtained, with same results, through Ca2+ imaging assay in HEK293 cells, and “in vivo” experiments using the Single Sensillum Recording (SSR) in an engineered neuron of the fruitfly Drosophila melanogaster that express AalOR2. Furthermore, by using this technique, I was able to identify also a molecule, (-)Menthone, that produced an inhibitory effect on this Odorant Receptor. In summary, this work led to the cloning and de-orphaning of the first Odorant Receptor in A. albopictus, that may be used as potential molecular target for developing environmentally friendly strategies to control mosquito populations

Towards effective flow simulations in realistic Discrete Fracture Networks

We focus on the simulation of underground flow in fractured media, modeled by means of Discrete Fracture Networks. Focusing on a new recent numerical approach proposed by the authors for tackling the problem avoiding mesh generation problems, we further improve the new family of methods making a step further towards effective simulations of large, multi-scale, heterogeneous networks. Namely, we tackle the imposition of Dirichlet boundary conditions in weak form, in such a way that geometrical complexity of the DFN is not an issue; we effectively solve DFN problems with fracture transmissivities spanning many orders of magnitude and approaching zero; furthermore, we address several numerical issues for improving the numerical solution also in quite challenging networks

A PDE-constrained optimization formulation for discrete fracture network flows

We investigate a new numerical approach for the computation of the 3D flow in a discrete fracture network that does not require a conforming discretization of partial differential equations on complex 3D systems of planar fractures. The discretization within each fracture is performed independently of the discretization of the other fractures and of their intersections. Independent meshing process within each fracture is a very important issue for practical large scale simulations making easier mesh generation. Some numerical simulations are given to show the viability of the method. The resulting approach can be naturally parallelized for dealing with systems with a huge number of fractures

Conforming, non-conforming and non-matching discretization couplings in discrete fracture network simulations

Simulations of fluid flow in naturally fractured rocks have implications for several subsurface applications, including energy storage and extraction, and waste storage. We are interested in flow in discrete fracture networks, which explicitly represent flow in fracture surfaces, but ignore the impact of the surrounding host rock. Fracture networks, generated from observations or stochastic simulations, will contain intersections of arbitrary length, and intersection lines can further cross, forming a highly complex geometry. As the flow exchange between fractures, thus in the network, takes place in these intersections, an adequate representation of the geometry is critical for simulation accuracy. In practice, the intersection dynamics must be handled by a combination of the simulation grid, which may or may not resolve the intersection lines, and the numerical methods applied on the grid. In this work, we review different classes of numerical approaches proposed in recent years, covering both methods that conform to the grid, and non-matching cases. Specific methods considered herein include finite element, mixed and virtual finite elements and control volume methods. We expose our methods to an extensive set of test cases, ranging from artificial geometries designed to test difficult configurations, to a network extruded from a real fracture outcrop. The main outcome is guidances for choice of simulation models and numerical discretization with a trade off on the computational cost and solution accuracy

A three-field based optimization formulation for flow simulations in networks of fractures on non-conforming meshes

A new numerical scheme is proposed for flow computation in complex discrete fracture networks. The method is based on a three-field domain decomposition framework, in which independent variables are introduced at the interfaces generated in the process of decoupling the original problem on the whole network into a set of fracture-local problems. A PDE-constrained formulation is then used to enforce compatibility conditions at the interfaces. The combination of the three-field domain decomposition and of the optimization based coupling strategy results in a novel method which can handle non-conforming meshes, independently built on each geometrical object of the computational domain, and ensures local mass conservation property at fracture intersections, which is of paramount importance for hydro-geological applications. An iterative solver is devised for the method, suitable for parallel implementation on parallel computing architectures

The Mixed Virtual Element Method on curved edges in two dimensions

In this work, we propose an extension of the mixed Virtual Element Method (VEM) for bi-dimensional computational grids with curvilinear edge elements. The approximation by means of rectilinear edges of a domain with curvilinear geometrical feature, such as a portion of domain boundary or an internal interface, may introduce a geometrical error that degrades the expected order of convergence of the scheme. In the present work a suitable VEM approximation space is proposed to consistently handle curvilinear geometrical objects, thus recovering optimal convergence rates. The resulting numerical scheme is presented along with its theoretical analysis and several numerical test cases to validate the proposed approach

Numerical investigation on a block preconditioning strategy to improve the computational efficiency of DFN models

[EN] The simulation of underground flow across intricate fracture networks can be addressed by means of discrete fracture network models. The combination of such models with an optimization formulation allows for the use of nonconforming and independent meshes for each fracture. The arising algebraic problem produces a symmetric saddle-point matrix with a rank-deficient leading block. In our work, we investigate the properties of the system to design a block preconditioning strategy to accelerate the iterative solution of the linearized algebraic problem. The matrix is first permuted and then projected in the symmetric positive-definite Schur-complement space. The proposed strategy is tested in applications of increasing size, in order to investigate its capabilities.Gazzola, L.; Ferronato, M.; Berrone, S.; Pieraccini, S.; Scialò, S. (2022). Numerical investigation on a block preconditioning strategy to improve the computational efficiency of DFN models. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 346-354. https://doi.org/10.4995/YIC2021.2021.12234OCS34635