On the bend number of circular-arc graphs as edge intersection graphs of paths on a grid

Golumbic, Lipshteyn and Stern \cite{Golumbic-epg} proved that every graph can be represented as the edge intersection graph of paths on a grid (EPG graph), i.e., one can associate with each vertex of the graph a nontrivial path on a rectangular grid such that two vertices are adjacent if and only if the corresponding paths share at least one edge of the grid. For a nonnegative integer $k$, $B_k$-EPG graphs are defined as EPG graphs admitting a model in which each path has at most $k$ bends. Circular-arc graphs are intersection graphs of open arcs of a circle. It is easy to see that every circular-arc graph is a $B_4$-EPG graph, by embedding the circle into a rectangle of the grid. In this paper, we prove that every circular-arc graph is $B_3$-EPG, and that there exist circular-arc graphs which are not $B_2$-EPG. If we restrict ourselves to rectangular representations (i.e., the union of the paths used in the model is contained in a rectangle of the grid), we obtain EPR (edge intersection of path in a rectangle) representations. We may define $B_k$-EPR graphs, $k\geq 0$, the same way as $B_k$-EPG graphs. Circular-arc graphs are clearly $B_4$-EPR graphs and we will show that there exist circular-arc graphs that are not $B_3$-EPR graphs. We also show that normal circular-arc graphs are $B_2$-EPR graphs and that there exist normal circular-arc graphs that are not $B_1$-EPR graphs. Finally, we characterize $B_1$-EPR graphs by a family of minimal forbidden induced subgraphs, and show that they form a subclass of normal Helly circular-arc graphs

A laboratory facility to study gas-aerosol-cloud interactions in a turbulent environment: The Π Chamber

A detailed understanding of interactions of aerosols, cloud droplets/ice crystals, and trace gases within the atmosphere is of prime importance for an accurate understanding of Earth’s weather and climate. One aspect that remains especially vexing is that clouds are ubiquitously turbulent, and therefore thermodynamic and compositional variables, such as water vapor supersaturation, fluctuate in space and time. With these problems in mind, a multiphase, turbulent reaction chamber—called the Π chamber because of the internal volume of 3.14 m3 with the cylindrical insert installed—has been developed. It is capable of pressures ranging from 1,000 to –60 hPa and can sustain temperatures of –55° to 55°C, thereby spanning much of the range of tropospheric clouds. To control the relative humidity in the chamber, it can be operated with a stable, unstable, or neutral temperature difference between the top and bottom surfaces, with or without expansion. A negative temperature difference induces turbulent Rayleigh–Bénard convection and associated supersaturation generation through isobaric mixing. Supporting instrumentation includes a suite of aerosol generation and characterization techniques; temperature, pressure, and humidity sensors; and a phase Doppler interferometer. Initial characterization experiments demonstrate the ability to sustain steady-state turbulent cloud conditions for times greater than 1 day, with droplet diameters typically in the range of 5–40 µm. Typical turbulence has root-mean-square velocity fluctuations on the order of 10 cm s–1 and kinetic energy dissipation rates of 1 × 10–3 W kg–1

Fungal endophytes affect plant response to leaf litter with contrasting chemical traits

Abstract Plant litter decomposition is a crucial process of nutrient cycling within ecosystems. However, many studies have shown that, apart from its several beneficial effects, organic matter decomposition can be disadvantageous to seed germination, seedling growth, and physiological activity of plants. Litter decomposition was reported to affect both plants and their associated soil microbial communities. The aim of this work was to test the relationships between seed-associated endophytic fungi on the either positive or negative plant's response to different litter types. Leaf material of four species was collected and used in a decomposition experiment inside a growth chamber for 120 days. The plant growth experiment was set in a greenhouse using Trifolium repens and Triticum durum with and without their associated endophytic fungi in the presence of the different litter species at two decay levels (fresh litter and after 120 days of decomposition). Results demonstrated that fresh litter exerted a strong inhibition effect on the plant total biomass when compared to decomposed litter. Moreover, seed-associated endophytic fungi enhanced the inhibitory effect of litter in the observed experimental conditions. The removal of seed-associated endophytic fungi improved the capacity of tested plants to resist to litter inhibitory effect

Corroborating the autoptic identification of archeological glyptics in museum collections: the contribution of portable Raman spectroscopy

A collection of Hellenistic–Roman glyptics, kept at the Regional Archaeological Museum “Paolo Orsi” (Syracuse, Italy), was investigated in situ with portable Raman spectroscopy with the aim of assessing the viability of this approach, not only for the immediate identification of the gemstones but also for a more in-depth successive data treatment. At the same time, a corroboration of the autoptic identification of the materials, both archeological and belonging to historical collections, was looked for in order to verify and potentially correct what reported in the museum catalogue. Actually, most of the identifications could be confirmed, the glyptics being mainly made of chalcedony. Other materials found were garnet, glass, and amber. The larger group of chalcedony Raman spectra was subjected to principal components analysis treatment that, after appropriate pretreatment, resulted successful in separating spectra with higher or lower contribution of the band due to the presence of moganite and Si OH bonds. The garnet spectra were instead subjected to quantitative study to identify the main end member. Both the quick identifications and the more detailed studies on chalcedonies and garnets were achieved thanks to the nondestructive and noninvasive investigation, directly in situ, with no sample preparation and minimal interference with the museum's activities

Spring diet of the pine marten in Sardinia, Italy

Alimentación primaveral de la marta en Cerdeña, ItaliaEl conocimiento del comportamiento de alimentación de un carnívoro es esencial para entender su ecología. La marta Martes martes se define comúnmente como un depredador generalista oportunista, porque su dieta en Europa incluye mamíferos, frutas, aves y invertebrados. A partir del análisis de las heces, hemos descrito los hábitos alimenticios en primavera y la amplitud del nicho trófico de la marta en ambiente mediterráneo en Cerdeña (Italia central). Los pequeños mamíferos (sobre todo Apodemus sylvaticus, Mus musculus y Eliomys quercinus) representan la fuente más importante de alimentación de la marta, ya que constituyen aproximadamente el 52% del volumen medio. Otra fuente importante de alimentos secundarios la constituyen los invertebrados (especialmente escarabajos y larvas de insectos) y las aves (paseriformes casi exclusivamente), mientras que los grandes mamíferos, los lagomorfos, los reptiles y las frutas están poco representados en la dieta. La composición de la dieta y el valor del índice de Levins indican que la marta en Cerdeña es un depredador especialista facultativo, con una especialización en la depredación de los micromamíferos.Knowledge of a carnivore’s foraging behaviour is essential to understand its ecology. The pine marten Martes martes is commonly defined as an opportunistic generalist predator since its diet in Europe includes mammals, fruits, birds and invertebrates. Based on faecal analyses, we evaluated spring feeding habits and trophic niche breadth of the pine marten in a Mediterranean landscape on the island of Sardinia (Central Italy). The most important source of food for the pine marten was small mammals (mainly Apodemus sylvaticus, Mus musculus and Eliomys quercinus), accounting for 52% of the percent mean volume. Important secondary foods were invertebrates (mainly beetles and insect larvae) and birds (almost exclusively passerines), whereas large mammals, lagomorphs, reptiles and fruits made little contribution to the diet. The diet composition and the Levins’ index value suggest that the pine marten in Sardinia behaves as a facultative specialist predator, with a specialization towards small mammals.Alimentación primaveral de la marta en Cerdeña, ItaliaEl conocimiento del comportamiento de alimentación de un carnívoro es esencial para entender su ecología. La marta Martes martes se define comúnmente como un depredador generalista oportunista, porque su dieta en Europa incluye mamíferos, frutas, aves y invertebrados. A partir del análisis de las heces, hemos descrito los hábitos alimenticios en primavera y la amplitud del nicho trófico de la marta en ambiente mediterráneo en Cerdeña (Italia central). Los pequeños mamíferos (sobre todo Apodemus sylvaticus, Mus musculus y Eliomys quercinus) representan la fuente más importante de alimentación de la marta, ya que constituyen aproximadamente el 52% del volumen medio. Otra fuente importante de alimentos secundarios la constituyen los invertebrados (especialmente escarabajos y larvas de insectos) y las aves (paseriformes casi exclusivamente), mientras que los grandes mamíferos, los lagomorfos, los reptiles y las frutas están poco representados en la dieta. La composición de la dieta y el valor del índice de Levins indican que la marta en Cerdeña es un depredador especialista facultativo, con una especialización en la depredación de los micromamíferos