7,111 research outputs found
The classifying space of a bound quiver
We associate to a bound quiver (Q,I) a CW-complex which we denote by B(Q,I),
and call the classifying space of (Q,I). We show that the fundamental group of
B(Q,I) is isomorphic to the fundamental group of (Q,I). Moreover, we show that
this construction behaves well with respect to coverings. On the other hand, we
study the (co)homology groups of B(Q,I), and compare them with the simplicial
and the Hochschild (co)homology groups of the algebra A=kQ/I. More precisely,
we give sufficient conditions for these groups to be isomorphic. This
generalizes a theorem due to Gerstenhaber and Schack.Comment: Revised version. To appear in J. Algebra. 22 pages, 3 postscript
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The response of Musa cultivar root systems to a tree shade gradient
Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Merger-Induced Metallicity Dilution in Cosmological Galaxy Formation Simulations
Observational studies have revealed that galaxy pairs tend to have lower
gas-phase metallicity than isolated galaxies. This metallicity deficiency can
be caused by inflows of low-metallicity gas due to the tidal forces and
gravitational torques associated with galaxy mergers, diluting the metal
content of the central region. In this work we demonstrate that such
metallicity dilution occurs in state-of-the-art cosmological simulations of
galaxy formation. We find that the dilution is typically 0.1 dex for major
mergers, and is noticeable at projected separations smaller than kpc. For
minor mergers the metallicity dilution is still present, even though the
amplitude is significantly smaller. Consistent with previous analysis of
observed galaxies we find that mergers are outliers from the \emph{fundamental
metallicity relation}, with deviations being larger than expected for a
Gaussian distribution of residuals. Our large sample of mergers within full
cosmological simulations also makes it possible to estimate how the star
formation rate enhancement and gas consumption timescale behave as a function
of the merger mass ratio. We confirm that strong starbursts are likely to occur
in major mergers, but they can also arise in minor mergers if more than two
galaxies are participating in the interaction, a scenario that has largely been
ignored in previous work based on idealised isolated merger simulations.Comment: Submitted to MNRA
Force induced stretched state: Effects of temperature
A model of self avoiding walks with suitable constraint has been developed to
study the effect of temperature on a single stranded DNA (ssDNA) in the
constant force ensemble. Our exact calculations for small chains show that the
extension (reaction co-ordinate) may increase or decrease with the temperature
depending upon the applied force. The simple model developed here which
incorporates semi-microscopic details of base direction provide an explanation
of the force induced transitions in ssDNA as observed in experiments.Comment: 5 pages, 8 figures, RevTex
Biomass partitioning and gas exchange parameters in different Musa cultivars as influenced by natural shade
Poster presented at Tropentag 2011 Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Photosynthesis of three dessert banana cultivars along an altitudinal gradient
Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Development of organic fertilizers from food market waste and urban gardening by composting in Ecuador
Currently, the management of urban waste streams in developing countries is not optimized yet, and in many cases these wastes are disposed untreated in open dumps. This fact causes serious environmental and health problems due to the presence of contaminants and pathogens. Frequently, the use of specific low-cost strategies reduces the total amount of wastes. These strategies are mainly associated to the identification, separate collection and composting of specific organic waste streams, such as vegetable and fruit refuses from food markets and urban gardening activities. Concretely, in the Chimborazo Region (Ecuador), more than 80% of municipal solid waste is dumped into environment due to the lack of an efficient waste management strategy. Therefore, the aim of this study was to develop a demonstration project at field scale in this region to evaluate the feasibility of implanting the composting technology not only for the management of the organic waste fluxes from food market and gardening activities to be scaled-up in other developing regions, but also to obtain an end-product with a commercial value as organic fertilizer. Three co-composting mixtures were prepared using market wastes mixed with pruning of trees and ornamental palms as bulking agents. Two piles were created using different proportions of market waste and prunings of trees and ornamental palms: pile 1 (50:33:17) with a C/N ratio 25; pile 2: (60:30:10) with C/N ratio 24 and pile 3 (75:0:25) with C/N ratio 33), prepared with market waste and prunings of ornamental palm. Throughout the process, the temperature of the mixtures was monitored and organic matter evolution was determined using thermogravimetric and chemical techniques. Additionally, physico-chemical, chemical and agronomic parameters were determined to evaluate compost quality. The results obtained indicated that all the piles showed a suitable development of the composting process, with a significant organic matter decomposition, reached in a shorter period of time in pile 3. At the end of the process, all the composts showed absence of phytotoxicity and suitable agronomic properties for their use as organic fertilizers. This reflects the viability of the proposed alternative to be scaled-up in developing areas, not only to manage and recycle urban waste fluxes, but also to obtain organic fertilizers, including added value in economic terms related to nutrient contents.Peer ReviewedPostprint (published version
Epidemic model on a network: analysis and applications to COVID-19
We analyze an epidemic model on a network consisting of
susceptible-infected-recovered equations at the nodes coupled by diffusion
using a graph Laplacian. We introduce an epidemic criterion and examine
different vaccination/containment strategies: we prove that it is most
effective to vaccinate a node of highest degree. The model is also useful to
evaluate deconfinement scenarios and prevent a so-called second wave. The model
has few parameters enabling fitting to the data and the essential ingredient of
importation of infected; these features are particularly important for the
current COVID-19 epidemic
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