72 research outputs found
Non-Riemannian vortex geometry of rotational viscous fluids and breaking of the acoustic Lorentz invariance
Acoustic torsion recently introduced in the literature (Garcia de
Andrade,PRD(2004),7,64004) is extended to rotational incompressible viscous
fluids represented by the generalised Navier-Stokes equation. The fluid
background is compared with the Riemann-Cartan massless scalar wave equation,
allowing for the generalization of Unruh acoustic metric in the form of
acoustic torsion, expressed in terms of viscosity, velocity and vorticity of
the fluid. In this work the background vorticity is nonvanishing but the
perturbation of the flow is also rotational which avoids the problem of
contamination of the irrotational perturbation by the background vorticity. The
acoustic Lorentz invariance is shown to be broken due to the presence of
acoustic torsion in strong analogy with the Riemann-Cartan gravitational case
presented recently by Kostelecky (PRD 69,2004,105009). An example of analog
gravity describing acoustic metric is given based on the teleparallel loop
where the acoustic torsion is given by the Lense-Thirring rotation and the
acoustic line element corresponds to the Lense-Thirring metric
Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology
Magneto-curvature stresses could deform magnetic field lines and this would
give rise to back reaction and restoring magnetic stresses [Tsagas, PRL
(2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the
expansion to be slow down in spatial section of negative Riemann curvatures.
From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D
manifold implies negatively constant Riemannian curvature, here one applies the
Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of
Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection
term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In
absence of advection a fast dynamo is also obtained. Viscous and restoring
forces on stretching particles decrease, as magnetic rates increase. From COBE
data (), one computes stretching
.
Zeldovich et al has computed the maximum magnetic growth rate as
. From COBE data one computes
a lower growth rate for the magnetic field as
, well-within Zeldovich et al
estimate. Instead of the Harrison value one obtains the
lower primordial field which yields the
at the Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi
Traversable Wormholes Construction in 2+1 Dimensions
We study traversable Lorentzian wormholes in the three-dimensional low energy
string theory by adding some matter source involving a dilaton field. It will
be shown that there are two-different types of wormhole solutions such as BTZ
and black string wormholes depending on the dilaton backgrounds, respectively.
We finally obtain the desirable solutions which confine exotic matter near the
throat of wormhole by adjusting NS charge.Comment: 12 pages, 4 figures, JHEP style, one reference adde
The torsion cosmology in Kaluza-Klein theory
We have studied the torsion cosmology model in Kaluza-Klein theory. We
considered two simple models in which the torsion vectors are
and ,
respectively. For the first model, the accelerating expansion of the Universe
can be not explained without dark energy which is similar to that in the
standard cosmology. But for the second model, we find that without dark energy
the effect of torsion can give rise to the accelerating expansion of the
universe and the alleviation of the well-known age problem of the three old
objects for appropriated value of the model parameter . These
outstanding features of the second torsion cosmology model have been supported
by the Type Ia supernovae (SNIa) data.Comment: 12 pages, 2 figures. Accepted for publication in JCA
Produção e qualidade de frutos de melancia Ă aplicação de nitrogĂȘnio via fertirrigação
Current status of turbulent dynamo theory: From large-scale to small-scale dynamos
Several recent advances in turbulent dynamo theory are reviewed. High
resolution simulations of small-scale and large-scale dynamo action in periodic
domains are compared with each other and contrasted with similar results at low
magnetic Prandtl numbers. It is argued that all the different cases show
similarities at intermediate length scales. On the other hand, in the presence
of helicity of the turbulence, power develops on large scales, which is not
present in non-helical small-scale turbulent dynamos. At small length scales,
differences occur in connection with the dissipation cutoff scales associated
with the respective value of the magnetic Prandtl number. These differences are
found to be independent of whether or not there is large-scale dynamo action.
However, large-scale dynamos in homogeneous systems are shown to suffer from
resistive slow-down even at intermediate length scales. The results from
simulations are connected to mean field theory and its applications. Recent
work on helicity fluxes to alleviate large-scale dynamo quenching, shear
dynamos, nonlocal effects and magnetic structures from strong density
stratification are highlighted. Several insights which arise from analytic
considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue
"Magnetism in the Universe" (ed. A. Balogh
Estimating the global conservation status of more than 15,000 Amazonian tree species
Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict thatmost of the worldâs >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century
Silagem de grĂŁos Ășmidos de milho em substituição ao milho seco da ração de frangos de corte criados em dois sistemas
NĂveis de urĂ©ia na ração de novilhos de quatro grupos genĂ©ticos: consumo e digestibilidades totais
The performance of the jet trigger for the ATLAS detector during 2011 data taking
The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided protonâproton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleonânucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction
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