2,603 research outputs found
La disputa por el maĂz en MĂ©xico: Âżbien comĂşn o mercancĂa?
Profunda investigaciĂłn donde se clarifican los avances tecnolĂłgicos que pueden ayudar a combatir el hambre en el mundo y los riesgos de que estos sean manejados por unas cuantas ambiciosas empresas biotecnolĂłgicas.ITESO, A.C
Onthophagus pilauco sp. nov. (Coleoptera, Scarabaeidae): evidence of beetle extinction in the Pleistocene–Holocene transition in Chilean Northern Patagonia
The South American Pleistocene–Holocene transition has been characterized by drastic climatic and diversity changes. These rapid changes induced one of the largest and most recent extinctions in the megafauna at the continental scale. However, examples of the extinction of small animals (e.g., insects) are scarce, and the underlying causes of the extinction have been little studied. In this work, a new extinct dung beetle species is described from a late Pleistocene sequence (~15.2 k cal yr BP) at the paleoarcheological site Pilauco, Chilean Northern Patagonia. Based on morphological characters, this fossil is considered to belong to the genus Onthophagus Latreille, 1802 and named Onthophagus pilauco sp. nov. We carried out a comprehensive revision of related groups, and we analyzed the possible mechanism of diversification and extinction of this new species. We hypothesize that Onthophagus pilauco sp. nov. diversified as a member of the osculatii species-complex following migration processes related to the Great American Biotic Interchange (~3 Ma). The extinction of O. pilauco sp. nov. may be related to massive defaunation and climatic changes recorded in the Plesitocene-Holocene transition (12.8 k cal yr BP). This finding is the first record of this genus in Chile, and provides new evidence to support the collateral-extinction hypothesis related to the defaunation.FT was supported by CONICYT doctoral scholarship Grant #21171980 and Ilustre Municipalidad de Osorno, Osorno, Chile
Searching for galactic sources in the Swift GRB catalog
Since the early 1990s Gamma Ray Bursts have been accepted to be of
extra-galactic origin due to the isotropic distribution observed by BATSE and
the redshifts observed via absorption line spectroscopy. Nevertheless, upon
further examination at least one case turned out to be of galactic origin. This
particular event presented a Fast Rise, Exponential Decay (FRED) structure
which leads us to believe that other FRED sources might also be Galactic. This
study was set out to estimate the most probable degree of contamination by
galactic sources that certain samples of FREDs have. In order to quantify the
degree of anisotropy the average dipolar and quadripolar moments of each sample
of GRBs with respect to the galactic plane were calculated. This was then
compared to the probability distribution of simulated samples comprised of a
combination of isotropically generated sources and galactic sources. We observe
that the dipolar and quadripolar moments of the selected subsamples of FREDs
are found more than two standard deviations outside those of random
isotropically generated samples.The most probable degree of contamination by
galactic sources for the FRED GRBs of the Swift catalog detected until February
2011 that do not have a known redshift is about 21 out of 77 sources which is
roughly equal to 27%. Furthermore we observe, that by removing from this sample
those bursts that may have any type of indirect redshift indicator and multiple
peaks gives the most probable contamination increases up to 34% (17 out of 49
sources). It is probable that a high degree of contamination by galactic
sources occurs among the single peak FREDs observed by Swift.Comment: Published to A&A, 4 pages, 5 figures, this arXiv version includes
appended table with all the bursts considered in this stud
Aspectos sobre la presencia del picudo del algodonero (Anthonomus grandis Boh) en la Dorada Caldas.
AlgodĂłn-Gossypium herbaceu
First European leaf-feeding grape phylloxera (Daktulosphaira vitifoliae Fitch) survey in Swiss and German commercial vineyards
Recent observations report the worldwide incidence of leaf-feeding grape phylloxera in formerly resistant scions of commercial vineyards. To analyze the genetic structure of leaf-feeding phylloxera, we performed an extensive sampling of leaf-feeding phylloxera populations in seven regions (“cantons”) in Switzerland and Germany. The use of polymorphic microsatellite markers revealed presence of 203 unique grape phylloxera multilocus genotypes. Genetic structure analyses showed a high genetic similitude of these European samples with phylloxera samples from its native habitat on Vitis riparia (northeastern America). Nevertheless, no genetic structure within the European samples was observed, and neither host, geography nor sampling date factors caused clear effects on phylloxera genetic stratification. Clonality was high in commercial vineyards and leaf-feeding grape phylloxera strains were found to be present in scion leaves and rootstock roots in the same vineyard, potentially indicating migration between both habitats. We found indications of sexual reproduction, as shown by high degrees of genetic variation among collection sites
Análisis de la estructura genética de poblaciones del caracol rosado, Strombus gigas (L.) en la Peninsula de Yucatán
Jahn-Teller EPA spectra of Cu2 + in MgSif6.6H20
The 34 GHz EPR spectrum ofCu2+ in MgSiF6-6H20 showed a "static" Jahn-Teller effect at 4.2
K with two inequivalent Jahn- Teller sites per unit cell. The six axially symmetric sets of Cu2+
lines had their z axes parallel to the three tetragonal axes of two cubes, which were rotated by
approximately 40" with respect to each other about a common (Ill) axis, which is the crystal c
axis. The measured spin-Hamiltonian parameters at 4.2 K for each set of lines were
g11 = 2.47 ± 0.01, g1 = 2.10 ± 0.01 , and lA 11 1 = (110 ± 3)X 10- 4 em- •. There was a gradual
decrease in the anisotropy of the spectrum on warming the crystal, with a single, nearly isotropic
line being observed above 220 K. At 270 K the spectrum had axial symmetry about the c axis with
Kn = 2.23 ± 0.01 and g~ = 2.25 ± 0.01 . The temperature evolution of the spectrum was
interpreted in terms of a Boltzmann distribution over inequivalent distorted Jahn-Teller
configurations, with one potential well lowered by an amount L1:::::: I 05 em- 1 below the other two
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