802 research outputs found
Net ecosystem CO2 exchange in mountain grasslands is seriously endangered by the temperature increase in the eastern pyrenees
Mediterranean mountain grasslands, including the Pyrenees, are highly vulnerable to climate change, due to the increasing temperatures and heat weaves frequency, among other factors. However, the effects of the increased temperatures on CO2 fluxes in those ecosystems have been barley explored. To address this gap of knowledge, we established the FLUXPYR-ECOFUN micrometeorological flux network, which included three eddy covariance flux stations in grasslands along a management and a climatic gradient (montane to subalpine) at the Pyrenees; we aimed at assessing interactions among environmental and phenological drivers on CO2 fluxes, with special attention at the role of temperature as CO2 flux driver under the different climatic and management conditions across the studied gradient. Our results showed that temperature drove CO2 dynamics along the studied gradient in different ways. At the subalpine grassland net CO2 uptake was linearly enhanced by temperature and CO2 fluxes had not reached a temperature shifting point yet (according to the segmented linear models) at which the net uptake would become CO2 emissions. This suggests that in the short term, and under the incoming enhanced temperatures, sub-alpine grasslands in the Pyrenees might increase their net CO2 uptake, although the mid long-term uptake may be compromised. On the contrary, the montane grasslands already presented CO2 emissions at the highest temperatures, most likely driven by a decrease in the greenness and photosynthesis, which suggests that montane grasslands are expected to reduce their CO2 sink capacity under the increasing temperatures. Overall, mountain grasslands in the mid- to long-term in the Pyrenees may experience a reduction in their net CO2 uptake capacity under the current climate change scenario
A Geometry of the Generations
We propose a geometric theory of flavor based on the discrete group
, in the context of the minimal supersymmetric standard model. The
group treats three objects symmetrically, while making fundamental distinctions
between the generations. The top quark is the only heavy quark in the symmetry
limit, and the first and second generation squarks are degenerate. The
hierarchical nature of Yukawa matrices is a consequence of a sequential
breaking of .Comment: 10 pages, 1 EPS figure as uuencoded tar-compressed file, uses
psfig.st
Variaciones estacionales en ovario de InambĂş Chico ComĂşn (<i>Nothura maculosa</i>)
Seasonal variations of the structure of the Spotted Tinamous ( <i>Nothura maculosa</i> ). Morphological data obtained by means of observation under optic microscope in ovaries of the Spotted Tinamous.(<i>Nothura maculosa</i> ), are presented. The characteristics of the ovaries in winter recess and in time of breeding activity are compared. In the first period it is noticed the very redueed size of the organ; small follieles; numerous masses of folicle atresia and groups of vacuolated cells (full of lipids). In the second period the ovaries are well developed, the rate of follicle growth has increased, and active vitellogenesis takes place a minor number of atresic follicles and of masses of cells full of lipids are observed. These characteristics and some less relevant ones are described and its significance is briefiy discussed
More on Supersymmetric Domain Walls, N Counting and Glued Potentials
Various features of domain walls in supersymmetric gluodynamics are
discussed. We give a simple field-theoretic interpretation of the phenomenon of
strings ending on the walls recently conjectured by Witten. An explanation of
this phenomenon in the framework of gauge field theory is outlined. The
phenomenon is argued to be particularly natural in supersymmetric theories
which support degenerate vacuum states with distinct physical properties. The
issue of existence (or non-existence) of the BPS saturated walls in the
theories with glued (super)potentials is addressed. The amended
Veneziano-Yankielowicz effective Lagrangian belongs to this class. The physical
origin of the cusp structure of the effective Lagrangian is revealed, and the
limitation it imposes on the calculability of the wall tension is explained.
Related problems are considered. In particular, it is shown that the so called
discrete anomaly matching, when properly implemented, does not rule out the
chirally symmetric phase of supersymmetric gluodynamics, contrary to recent
claims.Comment: 40 pages, Latex, 5 figures. Several references added, final version
to be published in Physical Review
Genetically controlled environmental variance for sternopleural bristles in Drosophila melanogaster - an experimental test of a heterogeneous variance model
This is an Accepted Manuscript of an article published by Taylor & Francis in Acta Agriculturae Scandinavica Section A - Animal Science on2007, available online: http://doi.org/10.1080/09064700801959403[EN] objective of this study was to test the hypothesis that the environmental variance of sternopleural bristle number in Drosophila melanogaster is partly under genetic control. We used data from 20 inbred lines and 10 control lines to test this hypothesis. Two models were used: a standard quantitative genetics model based on the infinitesimal model, and an extension of this model. In the extended model it is assumed that each individual has its own environmental variance and that this heterogeneity of variance has a genetic component. The heterogeneous variance model was favoured by the data, indicating that the environmental variance is partly under genetic control. If this heterogeneous variance model also applies to livestock, it would be possible to select for animals with a higher uniformity of products across environmental regimes. Also for evolutionary biology the results are of interest as genes affecting the environmental variance may be important for adaptation to changing environmental conditions.Sørensen, AC.; Kristensen, TN.; Loeschcke, V.; Ibañez Escriche, N.; Sorensen, D. (2007). Genetically controlled environmental variance for sternopleural bristles in Drosophila melanogaster - an experimental test of a heterogeneous variance model. Acta Agriculturae Scandinavica Section A - Animal Science. 57(4):196-201. https://doi.org/10.1080/09064700801959403S19620157
Duality in Superstring Compactifications with Magnetic Field Backgrounds
Motivated by the work of Polchinski and Strominger on type IIA theory, where
the effect of non-trivial field strengths for p-form potentials on a Calabi-Yau
space was discussed, we study four-dimensional heterotic string theory in the
presence of magnetic field on a 2-cycle in the internal manifold, for both N=4
and N=2 cases. We show that at special points in the moduli space, certain
perturbative charged states become tachyonic and stabilize the vacuum by
acquiring vacuum expectation values, thereby restoring supersymmetry. We
discuss both the cases where the tachyons appear with a tower of Landau levels,
which become light in the limit of large volume of the 2-cycle, and the case
where such Landau levels are not present. In the latter case it is sufficient
to restrict the analysis to the quartic potential for the tachyon. On the other
hand, in the former case it is necessary to include the Landau levels in the
analysis of the potential; for toroidal and orbifold examples, we give an
explicit CFT description of the new supersymmetric vacuum. The resulting new
vacuum turns out to be in the same class as the original supersymmetric one.
Finally, using duality, we discuss the role of the Landau levels on the type
IIA side.Comment: 26 pages, LaTeX, 1 figure; Nucl. Phys. B version with typos corrected
and references adde
Neutrinos: Key to New Physics
The Seesaw mechanism predicted tiny neutrino masses by postulating a new
large scale in particle physics, using new theoretical ideas prompted by the
Standard Model. It adds credence to a theoretical vista that is a quarter
century old, and fits with the most endearing speculations of ultimate
unification. By relating the measurement of static neutrino properties to
near-Planck physics, it may even prove key to solving the riddles of flavor.Comment: Invited Talk, Fujihara Seminar " Neutrino Masses and Seesaw
Mechanism", February 23-25, 2004, KEK, Japa
Anomalies in field theories with extra dimensions
We give an overview of the issue of anomalies in field theories with extra
dimensions. We start by reviewing in a pedagogical way the computation of the
standard perturbative gauge and gravitational anomalies on non-compact spaces,
using Fujikawa's approach and functional integral methods, and discuss the
available mechanisms for their cancellation. We then generalize these analyses
to the case of orbifold field theories with compact internal dimensions,
emphasizing the new aspects related to the presence of orbifold singularities
and discrete Wilson lines, and the new cancellation mechanisms that are
becoming available. We conclude with a very brief discussion on global and
parity anomalies.Comment: Review article written for Int.J.Mod.Phys. A, 63 pages; v2: mistake
in subsection 4.3 corrected, some comments and references added, a few
misprints fixe
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