5,081 research outputs found
Normal ordering and boundary conditions in open bosonic strings
Boundary conditions play a non trivial role in string theory. For instance
the rich structure of D-branes is generated by choosing appropriate
combinations of Dirichlet and Neumann boundary conditions. Furthermore, when an
antisymmetric background is present at the string end-points (corresponding to
mixed boundary conditions) space time becomes non-commutative there.
We show here how to build up normal ordered products for bosonic string
position operators that satisfy both equations of motion and open string
boundary conditions at quantum level. We also calculate the equal time
commutator of these normal ordered products in the presence of antisymmetric
tensor background.Comment: 7 pages no figures, References adde
Linear Pinch Equilibrium of Non-Neutral Plasma Revisited: Phenomenological Consequences of a Numerical Accuracy Problem
Weibel in 1959 under considerations of a collisionless non-neutral cylindrical plasma column studied a linear pinch confinement equilibrium. As reported here, due to non-linearity of the ordinary differential equations obtained for the electrostatic and magnetostatic fields is possible to demonstrate that the confining features previously obtained are extremely dependent on the initial conditions, and the arrangement of two parameters (β - the ratio between ion and electron mass; M/KT - ratio between relativistic rest energy associated with the pair electron-ion and thermal energy kT ) related to the plasma column characteristics. We investigated in this paper the plasma column behavior (confining or non-confining) under modifications of that set of parameters. We detected a set of parameters values that imposes a confining configuration with an electronic skin effect on the plasma column, not yet reported or discussed in the literature
Fish, Corumbataí and Jacaré-Pepira river basins, São Paulo State, Brazil
Fish were studied in two river basins (Corumbataí and Jacaré-Pepira) subjected to strong human pressure, in the interior of the State of São Paulo, southeastern Brazil. In the Corumbataí basin, four sites were sampled: Cabeça river, Lapa stream, Passa-Cinco river, and Corumbataí river; in the Jacaré-Pepira basin, three sites were sampled: Tamanduá stream, Jacaré-Pepira river, and Água Branca stream. A total of 4,050 specimens belonging to 48 species and 13 families were caught and analyzed
Extended BRST invariance in topological Yang Mills theory revisited
Extended BRST invariance (BRST plus anti-BRST invariances) provides in
principle a natural way of introducing the complete gauge fixing structure
associated to a gauge field theory in the minimum representation of the
algebra. However, as it happens in topological Yang Mills theory, not all gauge
fixings can be obtained from a symmetrical extended BRST algebra, where
antighosts belong to the same representation of the Lorentz group of the
corresponding ghosts. We show here that, at non interacting level, a simple
field redefinition makes it possible to start with an extended BRST algebra
with symmetric ghost antighost spectrum and arrive at the gauge fixing action
of topological Yang Mills theory.Comment: Interaction terms heve been included in all the calculations. Two
references added. Version to be published in Phys. Rev. D. 7 pages, Latex, no
figure
Examining Social, Cognitive and Teaching Presences in an Online Teacher Development Course Using WhatsApp and Community of Inquiry
Over the last decade, advancements in digital technologies have raised the interest of educators in all areas. Mobile learning, specifically, has drawn great attention for its potential to promote opportunities for mediating peer interactions. Drawing on the Community of Inquiry framework Garrison, Anderson and Archer’s (2000), this paper reports a quantitative analysis of the 1,670 interactions among 38 [elementary/high school teachers of Portuguese from around Brazil who participated in a 7-week continuing education course via WhatsApp. The findings show a high level of social presence at moments that the construction of collective knowledge takes place during the course
Structure and Composition of Rhodolith Beds from the Sergipe-Alagoas Basin (NE Brazil, Southwestern Atlantic)
This study was funded by the CoordenacAo de Aperfeicoamento de Pessoal de Nivel Superior (CAPES-Finance Code 001) and FundacAo de Amparo a Pesquisa do Estado do Rio de Janeiro- Jovem Cientista do Nosso Estado (FAPERJ/JCNE-Fellow to Leonardo T. Salgado).Rhodolith beds are biogenic benthic habitats mainly formed by unattached, non-geniculate
coralline algae, which can be inhabited by many associated species. The Brazilian continental shelf
encompasses the largest continuous rhodolith bed in the world. This study was based on samples
obtained from seven sites and videos taken by a Remotely Operated Vehicle (ROV) at four transects
off the Sergipe-Alagoas Coast on the northeast Brazilian shelf. ROV operations and bottom trawl
sampling revealed the occurrence of rhodolith beds between 25 and 54 m depths. At the shallower
depths, fruticose (branching) rhodoliths (maërl) appear in troughs of ripples, and other non-branching
rhodoliths occur associated with corals and sponge patches surrounded by bioclastic sand. Rhodoliths
also occur in patches from 30 to 39 m depth; some are fused, forming larger, complex tridimensional
structures. At deeper depths, from 40 to 54 m, the abundance of rhodoliths increases and occur
associated with fleshy macroalgae on a smooth seafloor; some rhodoliths are fused into complex
structures, locally some are fruticose (maërl), and others are partially buried by fine-grained sediment.
The collected rhodoliths vary from fruticose in two sites to encrusting to lumpy, concentric and
boxwork nodules in the rest; their size ranges from small (<1.5 cm) to large (~6 cm) and are mostly
sub-spheroidal to spheroidal. A total of 16 red algal morpho-taxa were identified in the study sites.
Two phases of growth can be distinguished in some rhodoliths by changes in color. The brownish
inner cores yielded ages of 1600–1850 cal years before the present, whereas outer layers were much
younger (180–50 years BP old). Growth layers appeared to have been separated by a long period of
burial in the seafloor sediment. Other rhodoliths have ages of hundreds of years.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) 001Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro-Jovem Cientista do Nosso Estado (FAPERJ/JCNE
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The effect of weather on respiratory and cardiovascular deaths in 12 U.S. cities.
We carried out time-series analyses in 12 U.S. cities to estimate both the acute effects and the lagged influence of weather on respiratory and cardiovascular disease (CVD) deaths. We fit generalized additive Poisson regressions for each city using nonparametric smooth functions to control for long time trend, season, and barometric pressure. We also controlled for day of the week. We estimated the effect and the lag structure of both temperature and humidity based on a distributed lag model. In cold cities, both high and low temperatures were associated with increased CVD deaths. In general, the effect of cold temperatures persisted for days, whereas the effect of high temperatures was restricted to the day of the death or the day before. For myocardial infarctions (MI), the effect of hot days was twice as large as the cold-day effect, whereas for all CVD deaths the hot-day effect was five times smaller than the cold-day effect. The effect of hot days included some harvesting, because we observed a deficit of deaths a few days later, which we did not observe for the cold-day effect. In hot cities, neither hot nor cold temperatures had much effect on CVD or pneumonia deaths. However, for MI and chronic obstructive pulmonary disease deaths, we observed lagged effects of hot temperatures (lags 4-6 and lags 3 and 4, respectively). We saw no clear pattern for the effect of humidity. In hierarchical models, greater variance of summer and winter temperature was associated with larger effects for hot and cold days, respectively, on respiratory deaths
Levantamento e importância de inimigos naturais da broca-das-pontas e da traça-da-castanha do cajueiro.
bitstream/CNPAT-2010/5603/1/Pa-032.pd
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