8,385 research outputs found
Axisymmetric Stationary Solutions as Harmonic Maps
We present a method for generating exact solutions of Einstein equations in
vacuum using harmonic maps, when the spacetime possesses two commutating
Killing vectors. This method consists in writing the axisymmetric stationry
Einstein equations in vacuum as a harmonic map which belongs to the group
SL(2,R), and decomposing it in its harmonic "submaps". This method provides a
natural classification of the solutions in classes (Weil's class, Lewis' class
etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
Asymmetric band diagrams in photonic crystals with a spontaneous nonreciprocal response
We study the propagation of electromagnetic waves in layered photonic crystals formed by materials with a spontaneous nonreciprocal response, such as Tellegen (axion) media or topological insulators. Surprisingly, it is proven that stratified Tellegen photonic crystals that break simultaneously the space inversion and time-reversal symmetries have always symmetric dispersion diagrams. Interestingly, we show that by combining chiral and nonreciprocal materials the photonic band diagrams can exhibit a spectral asymmetry such that omega(k) not equal omega(-k). Furthermore, it is demonstrated that in some conditions two juxtaposed Tellegen medium layers have an electromagnetic response analogous to that of a biased ferrite slab.info:eu-repo/semantics/publishedVersio
Efeito do armazenamento na qualidade de sementes de linhagens de sorgo.
bitstream/item/46073/1/circ-163.pd
Single observable concurrence measurement without simultaneous copies
We present a protocol that allows us to obtain the concurrence of any two
qubit pure state by performing a minimal and optimal tomography of one of the
subsystems through measuring a single observable of an ancillary four
dimensional qudit. An implementation for a system of trapped ions is also
proposed, which can be achieved with present day experimental techniques.Comment: 4 pages, 1 figur
Controle genético do comprimento e do número de nós do ramo principal em feijão-caupi.
O feijão-caupi [Vigna unguiculata (L.) Walp.] é uma importante leguminosa, fonte de proteÃna cuja plasticidade permite a adaptação em diferentes condições ambientais. A tendência atual é a utilização de tecnologia na lavoura, que possibilite a colheita mecanizada, sendo imprescindÃvel à definição do ideotipo da cultura. Neste sentido, objetivou-se estudar a herança dos caracteres relacionados à arquitetura da planta, comprimento e número de nós do ramo principal. Avaliou-se as linhagens parentais de feijão-caupi e as populações F1's, F2's e RC's dos cruzamentos TE96-282-22G (P1) x TVX-5058-09C (P2) e TE96-282-22G (P1) x IT81D-1332 (P3), na Embrapa Meio-Norte, em Teresina, PI, no delineamento em blocos casualizados, com quatro repetições. Foram estimadas as variâncias fenotÃpica, genotÃpica, aditiva, devido à dominância e ambiental; herdabilidades no sentido amplo e restrito; número de genes e grau médio de dominância. O modelo reduzido, aditivo-dominante, explica a variação observada no comprimento e número de nós do ramo principal. Os componentes de maior relevância no controle dos caracteres foram a média e o efeito aditivo. Em programas de melhoramento, o comprimento e o número de nós do ramo principal devem ser considerados na seleção para aumento de produtividade
Biofilm technology : from support design to reactor operation
The aim of this work was to assess the feasibility of a Sequential Batch Biofilm Reactor
(SBBR) to perform carbon and nitrogen removal: from support design to reactor operation.
The experimental part was conducted in two phases. In the first phase, different supports
were tested to select the most suitable one for SBBR operation. In the second phase, the
most appropriate support was used in a SBBR to perform carbon and nitrogen removal. The
results demonstrate that the support with the highest internal surface area presented a
higher biomass accumulation. Time profiles of nitrogen ions and acetate concentration
showed the typical behaviour of a SBBR performing carbon and nitrogen removal. Poly-bhydroxybutyrate
(PHB) was formed immediately after acetate depletion and was
subsequently consumed for biomass growth, owing to the high oxygen concentration in the
reactor
Design of an all-metal broadband Rotman lens for satellite communications at K/Ka-Band
In this work an all-metal Rotman lens antenna design is presented. Ridge waveguides are used for the input and output ports of the lens to achieve broadband behavior in the K/KA bands of the new generation of satellite communications (17.3 GHz to 31 GHz). The Rotman lens is composed by 5 input and 5 output ports, with a maximum beam scanning of 20 degrees. The connection between the input and output ports is done through a parallel plate waveguide (PPW) in the TEM regime. This simple configuration allows to have an initial assessment of the antenna port isolation and return losses, for the designed ridge to parallel plate waveguide transitions. This preliminary work shows promising results which pave the way for future improvements in terms of bandwidth and scanning performance.info:eu-repo/semantics/acceptedVersio
Synthesis and degradation of poly-β-hydroxybutyrate in a sequencing batch biofilm reactor
The aim of this work was the study of poly-β-hydroxybutyrate (PHB) formation and degradation in a sequencing batch biofilm reactor (SBBR). The SBBR was operated in cycles comprising three individual phases: mixed fill, aeration and draw. A synthetic substrate solution with acetate and ammonium was used.
PHB was formed during the aeration phase immediately after acetate depletion, and was subsequently consumed for biomass growth, owing to the high oxygen concentration in the reactor. It was observed a combination of suspended and biofilm growth in the SBBR with predominance of the fixed form of biomass (506 Cmmol and 2102 Cmmol, respectively). Maximum PHB fraction of suspended biomass (0.13 Cmol/Cmol) was considerably higher than that of biofilm (0.01 Cmol/Cmol). This may possibly be explained by a combination of two factors: lower mass transfer limitation of acetate and higher fraction of heterotrophs in suspended biomass compared to the ones of biofilm.Fundo Europeu de Desenvolvimento Regional (FEDER) - POCI 2010 (POCI/AMB/61155/2004)Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI BD/19687/9
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