1,298 research outputs found
Nucleon and gamma N -> Delta lattice form factors in a constituent quark model
A covariant quark model, based both on the spectator formalism and on vector
meson dominance, and previously calibrated by the physical data, is here
extended to the unphysical region of the lattice data by means of one single
extra adjustable parameter - the constituent quark mass in the chiral limit. We
calculated the Nucleon (N) and the gamma N -> Delta form factors in the
universe of values for that parameter described by quenched lattice QCD. A
qualitative description of the Nucleon and gamma N -> Delta form factors
lattice data is achieved for light pions.Comment: To appear in J.Phys.
A pure S-wave covariant model for the nucleon
Using the manifestly covariant spectator theory, and modeling the nucleon as
a system of three constituent quarks with their own electromagnetic structure,
we show that all four nucleon electromagnetic form factors can be very well
described by a manifestly covariant nucleon wave function with zero orbital
angular momentum. Since the concept of wave function depends on the formalism,
the conclusions of light-cone theory requiring nonzero angular momentum
components are not inconsistent with our results. We also show that our model
gives a qualitatively correct description of deep inelastic scattering,
unifying the phenomenology at high and low momentum transfer. Finally we review
two different definitions of nuclear shape and show that the nucleon is
spherical in this model, regardless of how shape is defined.Comment: 20 pages and 10 figures; greatly expanded version with new fits and
discussion of DIS; similar to published versio
Occurrence of 15 haplotypes of linepithema micans (Hymenoptera: Formicidae) in southern Brazil.
The ant genus Linepithema is widely known, thanks to the pest species Linepithema humile (Mayr), which is easily mistaken for Linepithema micans (Forel) due to their morphological similarity. Like L. humile , L. micans is associated to the main grapevine pest in Brazil, Eurhizococcus brasiliensis (Wille), also known as ground pearl. Therefore, the present study uses mtDNA fragments to expand the knowledge of haplotype diversity and distri- bution of L. micans in the state of Rio Grande do Sul Brazil), to understand the genetic differences of the popu- lations identified in this study. We identified 15 haplotypes of L. micans spread across different localities. Twelve of these haplotypes were new for the species. The high haplotype diversity uncovered in Rio Grande do Sul (Brazil) for this species was predictable, as L. micans is in its native environment. Additional studies that take gene flow into account may reveal interesting aspects of diversity in these populations. Keywords: mitotype, ground pearl, Rio Grande do Su
Megafauna communities from abyssal sites along the Gloria Fracture Zone (NE Atlantic)
Fracture zones are areas of poorly known abyssal landscapes
and benthic faunal communities. During the R/V Meteor
M162 cruise several imagery surveys were performed using a
TV-CTD guided camera system along four main areas of the
Gloria fault system, between the Terceira ridge and the
Madeira Tore Rise. Based on these records, we were able to
characterize - for the first time - the megafaunal composition,
their abundance and diversity along the sub-basin of the
Gloria fault at depths between 3500 and 4500m. Quantitative
annotations of the observed fauna, as well as evidence of
animal traces on the seafloor were explored in relation to
topography, substrate type, and geochemical data acquired
during surveys. Preliminary observations revealed a total of
121 morphospecies, of which Holothuroidea is the most
diverse group, with 12 morphospecies. Deepest transects
carried out along the main trace of Gloria Fault system
showed the highest similarity among dives, predominantly
characterised by soft sediment areas with Elpidiidae
holothurians frequently observed. In contrast, the survey
carried out at the Terceira ridge showed more diverse
communities, which is likely due to a larger variability in
substrate and topography. Specifically, soft-sediment
sections showed a higher proportion of holothurians,
ophiuroids and acorn worms, while unique Anthozoan and
Porifera morphospecies were observed in areas with
presence of hard substrates. The findings of this study provide
unique knowledge of abyssal fauna associated with the Gloria
Fault System, including areas inside of national jurisdiction
and of relevance for management and conservation actions
Occurrence of marine litter along abyssal areas of the Gloria Fracture Zone (NE Atlantic).
Marine litter pollution is a recognized form of anthropogenic
disturbance that affects widely the marine environment,
particularly near the continental margins, although also
present at abyssal and bathyal depths. This study reports the
occurrence of marine litter distribution and abundance in four
abyssal basins along the Gloria fracture zone in the NE
Atlantic. Litter items occurrences were analysed using TV-CTD
video surveys carried out during the multidisciplinary
activities of the R/V Meteor M162 cruise. The surveys reached
depths between 3500-4500m and covered 16 km of seafloor,
between the Terceira ridge and the Madeira-Tore Rise. Litter
items were annotated and categorized by type (i.e., plastic,
fishing gear, metal, glass, other unknown items). Results
revealed that litter was exclusively found on soft sediment
habitats across all areas, i.e. depositional areas, with the
overwhelming dominance of plastics items (71%), such as
plastic containers, cups and bag fragments. Although less
common (6-8%), metal, glass and lost fishing gear were also
observed. Litter density was on average 9 times higher in the
easternmost area near the Madeira-Tore ridge, when
compared to the other areas. Higher litter densities are likely
explained due to the proximity to the Madeira-Tore
seamount complex targeted by the fishing industry and
nearimportant corridors of marine traffic between various
Atlantic and Mediterranean locations
Variabilidade genética em acessos de mandioca amarela coletadas na Amazônia.
A Amazônia brasileira é conhecida como fonte de variabilidade genética da mandioca. Além disso, costumes locais privilegiaram a conservação de materiais com raiz amarela, rico em carotenóides. O objetivo deste trabalho foi caracterizar uma amostra dos acessos de raiz amarela presentes no BAG da Embrapa Amazônia Oriental. Foram selecionados 18 acessos de mandioca pertencentes ao BAG, sendo 14 materiais com raiz amarela e quatro com raiz branca, por meio de sete locos microssatélites. Todos os locos foram polimórficos, sendo obtido um total de 42 alelos, com média de seis alelos por loco. Quando se avaliou somente as mandiocas amarelas, foram amplificados 36 alelos, com média de 5,12 alelos por loco. A diversidade genética, medida pela heterozigosidade esperada para o grupo das mandiocas amarelas foi de 0,62. O dendrograma não mostrou separação de grupos para as mandiocas, de raiz amarela e raiz branca. No geral, observou-se que é grande a variabilidade genética existente para os materiais de raiz amarela mantidos no BAG da instituição.PIBIC-2011
Role of a Transbilayer pH Gradient in the Membrane Fusion Activity of the Influenza Virus Hemagglutinin: Use of the R18 Assay to Monitor Membrane Merging
It had been suggested that influenza virus-mediated membrane fusion might be dependent on a pH gradient across a target membrane. We have designed experiments in which this issue could be addressed. Two populations of liposomes were prepared, both simulating the plasma membrane of target cells, but with the pH of the internal aqueous medium buffered either at pH 7.4 (physiological cytosol pH) or at pH 5.0 (endosomal pH at which influenza virus displays maximal fusion activity). By monitoring fusion using the R18 assay, we found that the internal pH of the target liposomes did not influence membrane merging as mediated by the influenza virus hemagglutinin, thus demonstrating that a transmembrane pH gradient is not required in this fusion process
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