Mineral chemistry of late Variscan gabbros from central Spain: constraints on crystallisation processes and nature of the parental magmas

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Hypergraphs, the Qualitative Solvability of κ · λ = 0, and Volterra Multipliers for Nonlinear Dynamical Systems

AbstractCertain sign equivalence classes of n-dimensional nonlinear dynamical systems correspond to n-vertex hypergraphs, The global stability of some such dynamical systems can be guaranteed if the associated hypergraphs have a simplicity of structure and meet certain quantitative path product conditions. A purely algebraic version of the same problem can be described as follows. Suppose we are given a rectangular matrix pattern of signs; each entry in the matrix is +, −, or 0. For every real matrix κ of the same sign pattern, is there a real vector λ, each component of which is positive, such that κ · λ = 0? This paper presents graph theoretic sufficient conditions on a hypergraph generated from the sign pattern of κ which guarantee the existence of λ. For κ with more highly connected hypergraphs, this paper also presents sufficient qualitative conditions on the sign pattern of κ and certain quantitative conditions on sums of hypergraph path products which together guarantee the existence of λ

Extending Seqenv: a taxa-centric approach to environmental annotations of 16S rDNA sequences

Understanding how the environment selects a given taxon and the diversity patterns that emerge as a result of environmental filtering can dramatically improve our ability to analyse any environment in depth as well as advancing our knowledge on how the response of different taxa can impact each other and ecosystem functions. Most of the work investigating microbial biogeography has been site-specific, and logical environmental factors, rather than geographical location, may be more influential on microbial diversity. SEQenv, a novel pipeline aiming to provide environmental annotations of sequences emerged to provide a consistent description of the environmental niches using the ENVO ontology. While the pipeline provides a list of environmental terms on the basis of sample datasets and, therefore, the annotations obtained are at the dataset level, it lacks a taxa centric approach to environmental annotation. The work here describes an extension developed to enhance the SEQenv pipeline, which provided the means to directly generate environmental annotations for taxa under different contexts. 16S rDNA amplicon datasets belonging to distinct biomes were selected to illustrate the applicability of the extended SEQenv pipeline. A literature survey of the results demonstrates the immense importance of sequence level environmental annotations by illustrating the distribution of both taxa across environments as well as the various environmental sources of a specific taxon. Significantly enhancing the SEQenv pipeline in the process, this information would be valuable to any biologist seeking to understand the various taxa present in the habitat and the environment they originated from, enabling a more thorough analysis of which lineages are abundant in certain habitats and the recovery of patterns in taxon distribution across different habitats and environmental gradients

WIYN/Hydra Detection of Lithium Depletion in F Stars of the Young Open Cluster M35 and Implications for the Development of the Lithium Gap

We report discovery of significant depletion of Li on the surfaces of F dwarf stars in the 150-Myr-old open cluster M35, analagous to a feature in the 700-Myr-old Hyades cluster that has been referred to as the ``Li gap.'' We have caught the gap in the act of forming: using high resolution, high S/N, WIYN/Hydra observations, we detect Li in all but a few M35 F stars; the maximum depletion lies at least 0.6-0.8 dex below minimally depleted (or undepleted) stars. The M35 Li depletion region, a) is quite wide, with clear depletion seen from 6000K to 6700K or hotter; b) shows a significant dispersion in Li abundance at all T_eff, even with stars of the same T_eff; and c) contains undepleted stars (as well as depleted ones) in the (narrow) classical Hyades gap region, which itself shows no undepleted stars. All of these M35 Li depletion properties support rotationally-induced slow mixing as the primary physical mechanism that forms the gap, and argues against other proposed mechanisms, particularly diffusion and steady main sequence mass loss. When viewed in the context of the M35 Li depletion properties, the Hyades Li gap may well be wider than is usually recognized.Comment: 14 Pages, 3 figures. Accepted to ApJ Letter

The Li Overabundance of J37: Diffusion or Accretion?

In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow "Li-peak" at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most striking of which being no Be in super-Li-rich dwarfs subject to diffusion) the opposing diffusion/accretion predictions can be tested. Initial modelling of the Be line indicates that J37 is as Be rich as it is Li rich; log N(Be) = 2.25 +/- 0.25, and so is broadly consistent with an accretion-fuelled enhancement. However, that both Li and Be are enhanced by much more than the iron-peak elements (as determined in previous studies) suggests that diffusion also plays a role in increasing the abundances of Li and Be specifically. Furthermore, a new data set from the UVES/UT2 combination has allowed the elemental abundance of Iron to be measured, and the set of preliminary stellar parameters determined; Teff ~ 7340 K, log g ~ 4.1, microturbulence ~ 4.3 km/s, [Fe/H] ~ 0.50. This again provides distinct evidence for the effects of accretion in J37 and requires a new synthesis of the Be doublet.Comment: 5 pages, 2 figures. Poster presented at IAU Symposium 224 "The A Star Puzzle", 7-13 July 2004, Poprad, Slovaki

Beryllium Enhancement as Evidence for Accretion in a Lithium-Rich F Dwarf

The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the cosmic value. This contradicts radiative diffusion models that produce a Li over-abundance, as they also predict photospheric Be depletion. Instead, since Be is a highly refractory element, it supports the notion that J37 is the first clear example of a star that has accreted volatile-depleted material with a composition similar to chondritic meteorites, although some diffusion may be necessary to explain the low C and O abundances.Comment: Accepted for publication in MNRAS letters, 5 page