The solvability of groups with nilpotent minimal coverings

A covering of a group is a finite set of proper subgroups whose union is the whole group. A covering is minimal if there is no covering of smaller cardinality, and it is nilpotent if all its members are nilpotent subgroups. We complete a proof that every group that has a nilpotent minimal covering is solvable, starting from the previously known result that a minimal counterexample is an almost simple finite group

Potential Response of Soil-Borne Fungal Pathogens Affecting Crops to a Scenario of Climate Change in Europe

A study was carried out on the potential response of soil-borne pathogens causing crop yield losses under a climate change scenario in Europe. A controlled chamber set of experiments was carried out to quantify pathogen response to temperature using pure colonies of three soil-borne fungi, representative of low (Fusarium nivale), medium-high (Athelia rolfsii) and high (Macrophomina phaseolina) temperature requirements. A generic model to simulate fungal growth response to temperature based on these experiments was developed and linked to a soil temperature model component, and to components to simulate soil water content accounting for crop water uptake of potential hosts. Pathogens relative growth was simulated over Europe using the IPCC A1B emission scenario as realization of the Hadley-CM3 global climate model, available from the European Commission and processed for use with biophysical models. The simulations resulting from using the time span centred on 2030 were compared to the baseline, centred on the year 2000, using a sample of 30 years of daily weather. The general trend of soil-borne pathogens response to the scenario of climate change is a relative increase in growth in colder areas of Europe, as a function of their temperature requirements. Projections of F. nivale in the future indicate a relative increase of this winter pathogen of wheat in Northern European countries. A. rolfsii and M. phaseolina, two soil-borne pathogens typical of warmer agricultural areas, could find more favourable conditions in areas of the Central Europe, but they differentiated in Southern Europe where A. rolfsii resulted affected by summer soil temperatures above optimum

Modeling the Effects of Star Formation Histories on Halpha and Ultra-Violet Fluxes in Nearby Dwarf Galaxies

We consider the effects of non-constant star formation histories (SFHs) on Halpha and GALEX far ultra-violet (FUV) star formation rate (SFR) indicators. Under the assumption of a fully populated Chabrier IMF, we compare the distribution of Halpha-to-FUV flux ratios from ~ 1500 simple, periodic model SFHs with observations of 185 galaxies from the Spitzer Local Volume Legacy survey. We find a set of SFH models that are well matched to the data, such that more massive galaxies are best characterized by nearly constant SFHs, while low mass systems experience bursts amplitudes of ~ 30 (i.e., an increase in the SFR by a factor of 30 over the SFR during the inter-burst period), burst durations of tens of Myr, and periods of ~ 250 Myr; these SFHs are broadly consistent with the increased stochastic star formation expected in systems with lower SFRs. We analyze the predicted temporal evolution of galaxy stellar mass, R-band surface brightness, Halpha-derived SFR, and blue luminosity, and find that they provide a reasonable match to observed flux distributions. We find that our model SFHs are generally able to reproduce both the observed systematic decline and increased scatter in Halpha-to-FUV ratios toward low mass systems, without invoking other physical mechanisms. We also compare our predictions with those from the Integrated Galactic IMF theory with a constant SFR. We find that while both predict a systematic decline in the observed ratios, only the time variable SFH models are capable of producing the observed population of low mass galaxies ($M_{*}$ < 10$^{7}$ Msun) with normal Halpha-to-FUV ratios. These results demonstrate that a variable IMF alone has difficulty explaining the observed scatter in the Halpha-to-FUV ratios. We conclude by considering the limitations of the model SFHs, and discuss the use of additional empirical constraints to improve future SFH modeling efforts.Comment: 15 pages, 11 Figures. Accepted for publication in Ap

Accessing and assessing lunar resources with PROSPECT

PROSPECT is a package in development by ESA to assess the in-situ resource potential of lunar regolith. PROSPECT will: obtain sub-surface regolith samples, extract volatiles, identify chemical species, quantify abundances, and characterize isotopes

Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers

Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (~1.2nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5–300K, has almost bulk- like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy

Atomic hydrogen, star formation and feedback in the lowest mass Blue Compact Dwarf galaxies

We present the results from a search for HI emission from a sample of newly discovered dwarf galaxies in the M81 group. HI is detected in three galaxies, all of which are classified as BCDs. The HI masses of these galaxies are ~ 10^6 M_sun, making these some of the lowest mass BCDs known. For these three galaxies FUV images (from GALEX) and H-alpha images (from the Russian 6m BTA telescope) are available.The H-alpha emission is very faint, and, in principle could be produced by a single O star. Further, in all cases we find offsets between the peak of the FUV emission and that of the H-alpha emission. Offsets between the most recent sites of star formation (i.e. those traced by H-alpha) and the older sites (i.e. those traced by FUV) would be natural if the star formation is stochastic. In spite of the expectation that the effects of mechanical feedback from star formation would be most directly seen in the smallest galaxies with low gravitational potentials, we only see tentative evidence of outflowing HI gas associated with the star forming region in one of the galaxies.Comment: 9 pages, 5 figures, 5 tables. Accepted for publication in MNRAS. The definitive version is available at www.blackwell-synergy.co

Gas Accretion in Star-Forming Galaxies

Cold-mode gas accretion onto galaxies is a direct prediction of LCDM simulations and provides galaxies with fuel that allows them to continue to form stars over the lifetime of the Universe. Given its dramatic influence on a galaxy's gas reservoir, gas accretion has to be largely responsible for how galaxies form and evolve. Therefore, given the importance of gas accretion, it is necessary to observe and quantify how these gas flows affect galaxy evolution. However, observational data have yet to conclusively show that gas accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is a challenging endeavor and we now have obtained a significant amount of observational evidence to support it. This chapter reviews the current observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springer. This chapter includes 22 pages with 7 Figure

“Not walled facts, their essence”: Derek Walcott’s Tiepolo’s Hound and Camille Pissarro

Life-writing — a genre which goes beyond traditional biography, includes both fact and fiction, and is concerned with either entire lives or days-in-the-lives of individuals, communities, objects, or institutions — has always played an important role in Derek Walcott’s work, from Another Life (1973),Walcott’s autobiography in verse, to his last play O Starry Starry Night (2014), where he re-imagines Paul Gauguin and Vincent Van Gogh’s (often tempestuous) cohabitation in the so-called “Yellow House” in 1888 Arles. In Tiepolo’s Hound (2000), Walcott’s life rhymes with that of the Impressionist painter Jacob Camille Pissarro, who was born in the Caribbean island of St Thomas in 1830. In this work, biographical and autobiographical impulses, fact and fiction, are productively combined, as “creation” (what “might have happened”) shapes Walcott’s life-writing as much as “recreation” (what “actually” happened). Walcott’s Pissarro is an individual immersed in a set of historical networks but also a figure at the centre of a web of imagined relations which illuminate the predicament of present and past artists in the Caribbean region and the ways in which they articulate their vision vis-à-vis the metropolitan centre, their relationship with their social and natural environment, and their individual and collective identity. Tiepolo’s Hound is enriched by the inclusion of twenty-six of Walcott’s own paintings which engage in conversation with the poet’s words and add complexity to his meditation on the nature and purpose of (re)writing and (re)creating lives. Extending the catholicity of life-writing to animals, in this case dogs and, in particular, mongrels, Tiepolo’s Hound also entails a careful, if counterintuitive, evaluation of anonymity