Serendipity Face and Edge VEM Spaces

We extend the basic idea of Serendipity Virtual Elements from the previous case (by the same authors) of nodal ($H^1$-conforming) elements, to a more general framework. Then we apply the general strategy to the case of $H(div)$ and $H(curl)$ conforming Virtual Element Methods, in two and three dimensions

Serendipity Nodal VEM spaces

We introduce a new variant of Nodal Virtual Element spaces that mimics the "Serendipity Finite Element Methods" (whose most popular example is the 8-node quadrilateral) and allows to reduce (often in a significant way) the number of internal degrees of freedom. When applied to the faces of a three-dimensional decomposition, this allows a reduction in the number of face degrees of freedom: an improvement that cannot be achieved by a simple static condensation. On triangular and tetrahedral decompositions the new elements (contrary to the original VEMs) reduce exactly to the classical Lagrange FEM. On quadrilaterals and hexahedra the new elements are quite similar (and have the same amount of degrees of freedom) to the Serendipity Finite Elements, but are much more robust with respect to element distortions. On more general polytopes the Serendipity VEMs are the natural (and simple) generalization of the simplicial case

Lowest order Virtual Element approximation of magnetostatic problems

We give here a simplified presentation of the lowest order Serendipity Virtual Element method, and show its use for the numerical solution of linear magneto-static problems in three dimensions. The method can be applied to very general decompositions of the computational domain (as is natural for Virtual Element Methods) and uses as unknowns the (constant) tangential component of the magnetic field $\mathbf{H}$ on each edge, and the vertex values of the Lagrange multiplier $p$ (used to enforce the solenoidality of the magnetic induction $\mathbf{B}=\mu\mathbf{H}$). In this respect the method can be seen as the natural generalization of the lowest order Edge Finite Element Method (the so-called "first kind N\'ed\'elec" elements) to polyhedra of almost arbitrary shape, and as we show on some numerical examples it exhibits very good accuracy (for being a lowest order element) and excellent robustness with respect to distortions

Acquisition of fungi from the environment modifies ambrosia beetle mycobiome during invasion

Microbial symbionts can play critical roles when their host attempts to colonize a new habitat. The lack of symbiont adaptation can in fact hinder the invasion process of their host. This scenario could change if the exotic species are able to acquire microorganisms from the invaded environment. Understanding the ecological factors that influence the take-up of new microorganisms is thus essential to clarify the mechanisms behind biological invasions. In this study, we tested whether different forest habitats influence the structure of the fungal communities associated with ambrosia beetles. We collected individuals of the most widespread exotic (Xylosandrus germanus) and native (Xyleborinus saxesenii) ambrosia beetle species in Europe in several old-growth and restored forests. We characterized the fungal communities associated with both species via metabarcoding. We showed that forest habitat shaped the community of fungi associated with both species, but the effect was stronger for the exotic X. germanus. Our results support the hypothesis that the direct contact with the mycobiome of the invaded environment might lead an exotic species to acquire native fungi. This process is likely favored by the occurrence of a bottleneck effect at the mycobiome level and/or the disruption of the mechanisms sustaining co-evolved insect-fungi symbiosis. Our study contributes to the understanding of the factors affecting insect-microbes interactions, helping to clarify the mechanisms behind biological invasions

Evidence of a pressure-induced metallization process in monoclinic VO2_2

Raman and combined trasmission and reflectivity mid infrared measurements have been carried out on monoclinic VO$_2$ at room temperature over the 0-19 GPa and 0-14 GPa pressure ranges, respectively. The pressure dependence obtained for both lattice dynamics and optical gap shows a remarkable stability of the system up to P*$\sim$10 GPa. Evidence of subtle modifications of V ion arrangements within the monoclinic lattice together with the onset of a metallization process via band gap filling are observed for P$>$P*. Differently from ambient pressure, where the VO$_2$ metal phase is found only in conjunction with the rutile structure above 340 K, a new room temperature metallic phase coupled to a monoclinic structure appears accessible in the high pressure regime, thus opening to new important queries on the physics of VO$_2$.Comment: 5 pages, 3 figure

Analysis of enhanced-performance fibre Brillouin ring laser for Brillouin sensing applications

In this work, we present an enhanced design for a Brillouin ring laser (BRL), which employs a double resonant cavity (DRC) with short fiber length, paired with a heterodyne-based wavelength-locking system, to be employed as a pump-probe source for Brillouin sensing. The enhanced source is compared to traditional long-cavity pump-probe source, showing a significantly lower relative intensity noise (~-145 dB/Hz in the whole 0\u2013800 MHz range), a narrow linewidth (10 kHz), and large tunability features, resulting in an effective pump-probe source in BOTDA systems, with an excellent pump-probe frequency stability (~200 Hz), which is uncommon for fiber lasers. The enhanced source showed an improved signal-to-noise ratio (SNR) of about 22 dB with respect to standard BRL schemes, resulting in an improved temperature/strain resolution in BOTDA applications up to 5.5 dB, with respect to previous high-noise BRL designs

Positive regional species-people correlations: A sampling artefact or a key issue for sustainable development?

Many studies are documenting positive large-scale species– people correlations (Luck, 2007; Schuldt & Assmann, 2010). The issue is scale dependent: the local association of species richness and people is in many cases a negative one (Pautasso, 2007; Pecher et al., 2010). This biogeographical pattern is thus important for conservation. If species-rich regions are also densely populated, preserving biodiversity becomes more difficult, ceteris paribus, than if species-rich regions were sparsely populated. At the same time, positive, regional species–people correlations are an opportunity for the biodiversity education of the majority of the human population and underline the importance of conservation in human-modified landscapes (e.g. Sheil & Meijaard, 2010; Ward, 2010)

Is the human population a large-scale indicator of the species richness of ground beetles?

Aim Positive regional correlations between biodiversity and human population have been detected for several taxonomic groups and geographical regions. Such correlations could have important conservation implications and have been mainly attributed to ecological factors, with little testing for an artefactual explanation: more populated regions may show higher biodiversity because they are more thoroughly surveyed. We tested the hypothesis that the correlation between people and herptile diversity in Europe is influenced by survey effor