1,236 research outputs found
Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature
In this paper we present the effects produced by the temperature in the
renormalized vacuum expectation value of the zero-zero component of the
energy-momentum tensor associated with massless left-handed spinor field in the
pointlike global monopole spacetime. In order to develop this calculation we
had to obtain the Euclidean thermal Green function in this background. Because
the expression obtained for the thermal energy density cannot be expressed in a
closed form, its explicit dependence on the temperature is not completely
evident. So, in order to obtain concrete information about its thermal
behavior, we develop a numerical analysis of our result in the high-temperature
limit for specific values of the parameter which codify the presence
of the monopole.Comment: 22 pages, LaTex format, 5 figure
Vacuum Polarization by a Magnetic Flux Tube at Finite Temperature in the Cosmic String Spacetime
In this paper we analyse the effect produced by the temperature in the vacuum
polarization associated with charged massless scalar field in the presence of
magnetic flux tube in the cosmic string spacetime. Three different
configurations of magnetic fields are taken into account: a homogeneous
field inside the tube, a field proportional to and a
cylindrical shell with -function. In these three cases, the axis of the
infinitely long tube of radius coincides with the cosmic string. Because
the complexity of this analysis in the region inside the tube, we consider the
thermal effect in the region outside. In order to develop this analysis, we
construct the thermal Green function associated with this system for the three
above mentioned situations considering points in the region outside the tube.
We explicitly calculate in the high-temperature limit, the thermal average of
the field square and the energy-momentum tensor.Comment: 16 pages, 1 figur
Sistemas de manejo de solo litorâneo cultivado com cajueiro anão precoce.
O cultivo do cajueiro (Anacardium occidentale L.) e bastante expressivo nos solos dos tabuleiros costeiros da regiao Nordeste Ocidental, em face da sua rusticidade e adaptabilidade as condicoes edafoclimaticas locais. A regiao litoranea do Ceara e constituida, igualmente, de solos arenosos com problemas de deficiencia hidrica e baixa fertilidade natural, exigindo o conhecimento detalhado de suas caracteristicas para o desenvolvimento das tecnicas de manejo mais apropriadas. Nestas areas, verifica-se uma exploracao continua para atender a demanda de alimentos e de materia-prima para a agroindustria do caju, intensificada pelo uso crescente de mecanizacao em substituicao ao trabalho humano.bitstream/CNPAT-2010/2157/1/Pa-009.pd
Vacuum polarization for neutral particles in 2+1 dimensions
In 2+1 dimensions there exists a duality between a charged Dirac particle
coupled minimally to a background vector potential and a neutral one coupled
nonminimally to a background electromagnetic field strength. A constant uniform
background electric current induces in the vacuum of the neutral particle a
fermion current which is proportional to the background one. A background
electromagnetic plane wave induces no current in the vacuum. For constant but
nonuniform background electric charge, known results for charged particles can
be translated to give the induced fermion number. Some new examples with
infinite background electric charge are presented. The induced spin and total
angular momentum are also discussed.Comment: REVTeX, 7 pages, no figur
Occurrence of geminivirus in tomato-producing areas in Submedio Sao Francisco.
This is the first report of geminivirus in Submedio Sao Francisco and reveals a wide dispersal of this virus that was previously described in the Federal District (1994) and state of Sao Paulo (1997), Minas Gerais (1996) and Bahia (1996).Suplemento. Edição dos Resumos do 30 Congresso Brasileiro de Fitopatologia, Poços de Caldas, 1997
Comment on "On the temperature dependence of the Casimir effect"
Recently, Brevik et al. [Phys. Rev. E 71, 056101 (2005)] adduced arguments
against the traditional approach to the thermal Casimir force between real
metals and in favor of one of the alternative approaches. The latter assumes
zero contribution from the transverse electric mode at zero frequency in
qualitative disagreement with unity as given by the thermal quantum field
theory for ideal metals. Those authors claim that their approach is consistent
with experiments as well as with thermodynamics. We demonstrate that these
conclusions are incorrect. We show specifically that their results are
contradicted by four recent experiments and also violate the third law of
thermodynamics (the Nernst heat theorem).Comment: 11 pages, 3 figures, changed in accordance with the final published
versio
Three new geminiviruses in tomato in the state of Pernambuco.
These clones were used as probes in hybridization test, allowing the detection of each virus separately, with no cross-reactivity.Suplemento. Edição dos Resumos do 31 Congresso Brasileiro de Fitopatologia, Fortaleza, 1998
Embedded System for Real Color Composition in Experimental Physics
Software can be considered educational when properly contextualized in a relationship of teaching and learning. This paper describes an embedded system and an educational software developed and applied in experimental physics to real and virtual colors composition. The educational system developed allows student interaction by voice commands, which makes the assimilation process of red/green/blue (RGB) color formation concepts more didactic and playful. The application of educational software in experiments also allows to verify, in real time, the influence of programs change on the physical phenomena and stimulates the logical reasoning development and consequently the autonomy of the students, to the measure that can raise hypothesis, make modifications in the programming and take off conclusions from the practical results obtained
New species emergence via recombination among isolates of the Brazilian tomato infecting Begomovirus complex.
Effect of Dichlorvos on the acetylcholinesterase from tambaqui (Colossoma macropomum) Brain.
Dichlorvos is an acutely toxic organophosphorous pesticide that is known as a classical acetylcholinesterase (AChE; EC 3.1.1.7) inhibitor. Here, the brain AChE from the important Amazonian fish tambaqui (Colossoma macropomum) was assayed in the presence of this insecticide and also of deltamethrin, a classical sodium and potassium channel inhibitor (negative control). Four tissue homogenates were analyzed in triplicate for AChE activity using acetylthiocholine as the substrate and 5,5'-dithiobis(2-nitrobenzoic) acid (DTNB) as the color-developing agent. Each tissue homogenate represented pooled brains from five fish. The inhibitory effect of dichlorvos on AChE activities was determined at concentrations from 0.001 to 10 ppm and compared to controls. This effect followed an exponential decay model (y = 9.420 + 26.192e(-x/5.380); r2 = 0.989), presenting IC50 (the concentration of dichlorvos that is required for 50% of AChE inhibition) of 0.081 ppm (0.368 umol/L). No effect was observed for the deltamethrin, and the concentration 0.0452 umol/L of dichlorvos was significantly different from this control. These results suggest that tambaqui brain AChE can be proposed as a biomarker for dichlorvos and can be used as a tool for aquatic environment monitoring
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