8,384 research outputs found
From Topology to Generalised Dimensional Reduction
In the usual procedure for toroidal Kaluza-Klein reduction, all the
higher-dimensional fields are taken to be independent of the coordinates on the
internal space. It has recently been observed that a generalisation of this
procedure is possible, which gives rise to lower-dimensional ``massive''
supergravities. The generalised reduction involves allowing gauge potentials in
the higher dimension to have an additional linear dependence on the toroidal
coordinates. In this paper, we show that a much wider class of generalised
reductions is possible, in which higher-dimensional potentials have additional
terms involving differential forms on the internal manifold whose exterior
derivatives yield representatives of certain of its cohomology classes. We
consider various examples, including the generalised reduction of M-theory and
type II strings on K3, Calabi-Yau and 7-dimensional Joyce manifolds. The
resulting massive supergravities support domain-wall solutions that arise by
the vertical dimensional reduction of higher-dimensional solitonic p-branes and
intersecting p-branes.Comment: Latex, 24 pages, no figures, typo corrected, reference added and
discussion of duality extende
AdS and Lifshitz Black Holes in Conformal and Einstein-Weyl Gravities
We study black hole solutions in extended gravities with higher-order
curvature terms, including conformal and Einstein-Weyl gravities. In addition
to the usual AdS vacuum, the theories admit Lifshitz and Schr\"odinger vacua.
The AdS black hole in conformal gravity contains an additional parameter over
and above the mass, which may be interpreted as a massive spin-2 hair. By
considering the first law of thermodynamics, we find that it is necessary to
introduce an associated additional intensive/extensive pair of thermodynamic
quantities. We also obtain new Liftshitz black holes in conformal gravity and
study their thermodynamics. We use a numerical approach to demonstrate that AdS
black holes beyond the Schwarzschild-AdS solution exist in Einstein-Weyl
gravity. We also demonstrate the existence of asymptotically Lifshitz black
holes in Einstein-Weyl gravity. The Lifshitz black holes arise at the boundary
of the parameter ranges for the AdS black holes. Outside the range, the
solutions develop naked singularities. The asymptotically AdS and Lifshitz
black holes provide an interesting phase transition, in the corresponding
boundary field theory, from a relativistic Lorentzian system to a
non-relativistic Lifshitz system.Comment: typos corrected, references adde
Saturation of Turbulent Drag Reduction in Dilute Polymer Solutions
Drag reduction by polymers in turbulent wall-bounded flows exhibits universal
and non-universal aspects. The universal maximal mean velocity profile was
explained in a recent theory. The saturation of this profile and the crossover
back to the Newtonian plug are non-universal, depending on Reynolds number Re,
concentration of polymer and the degree of polymerization . We
explain the mechanism of saturation stemming from the finiteness of
extensibility of the polymers, predict its dependence on and in the
limit of small and large Re, and present the excellent comparison of our
predictions to experiments on drag reduction by DNA.Comment: 4 pages, 4 figs., included, PRL, submitte
Euclidean-signature Supergravities, Dualities and Instantons
We study the Euclidean-signature supergravities that arise by compactifying
D=11 supergravity or type IIB supergravity on a torus that includes the time
direction. We show that the usual T-duality relation between type IIA and type
IIB supergravities compactified on a spatial circle no longer holds if the
reduction is performed on the time direction. Thus there are two inequivalent
Euclidean-signature nine-dimensional maximal supergravities. They become
equivalent upon further spatial compactification to D=8. We also show that
duality symmetries of Euclidean-signature supergravities allow the harmonic
functions of any single-charge or multi-charge instanton to be rescaled and
shifted by constant factors. Combined with the usual diagonal dimensional
reduction and oxidation procedures, this allows us to use the duality
symmetries to map any single-charge or multi-charge p-brane soliton, or any
intersection, into its near-horizon regime. Similar transformations can also be
made on non-extremal p-branes. We also study the structures of duality
multiplets of instanton and (D-3)-brane solutions.Comment: Latex, 50 pages, typos corrected and references adde
U-duality as General Coordinate Transformations, and Spacetime Geometry
We show that the full global symmetry groups of all the D-dimensional maximal
supergravities can be described in terms of the closure of the internal general
coordinate transformations of the toroidal compactifications of D=11
supergravity and of type IIB supergravity, with type IIA/IIB T-duality
providing an intertwining between the two pictures. At the quantum level, the
part of the U-duality group that corresponds to the surviving discretised
internal general coordinate transformations in a given picture leaves the
internal torus invariant, while the part that is not described by internal
general coordinate transformations can have the effect of altering the size or
shape of the internal torus. For example, M-theory compactified on a large
torus T^n can be related by duality to a compactification on a small torus, if
and only if n\ge 3. We also discuss related issues in the toroidal
compactification of the self-dual string to D=4. An appendix includes the
complete results for the toroidal reduction of the bosonic sector of type IIB
supergravity to arbitrary dimensions D\ge3.Comment: Latex, 28 page
Single vs. reimplant programs for finishing steers
Finishing yearling beef steers were used to compare various implant programs in a 167-day trial. All implant programs increased daily gain ranging from 6.6 to 25.4% over non-implanted controls and improved feed efficiency ranging from .5 to 13.9%. Steers implanted with Ralgro® initially and reimplanted 75 days later with Synovex-S gained the fastest and mos
Effects of Rumensin or Rumensin-Tylan combination on steer performance and liver abscess control
Combining Tylan with Rumensin dramatically reduced abscessed liver incidence, compared with that of steers fed a non-medicated control ration or Rumensin without Tylan. Only one steer out of 50 on the Rumensin plus Tylan combination had an abscessed liver, whereas livers from 16 of the control steers and 27 on Rumensin were condemned. There were no significant differences in daily gain among treatments; however, Rumensin plus Tylan improved feed efficiency by 9.4% compared with that of the control. Rumensin alone improved efficiency by 6%
Analytical Model of the Time Developing Turbulent Boundary Layer
We present an analytical model for the time-developing turbulent boundary
layer (TD-TBL) over a flat plate. The model provides explicit formulae for the
temporal behavior of the wall-shear stress and both the temporal and spatial
distributions of the mean streamwise velocity, the turbulence kinetic energy
and Reynolds shear stress. The resulting profiles are in good agreement with
the DNS results of spatially-developing turbulent boundary layers at momentum
thickness Reynolds number equal to 1430 and 2900. Our analytical model is, to
the best of our knowledge, the first of its kind for TD-TBL.Comment: 5pages, 9 figs, JETP Letters, submitte
Effect of religious belief on informal reasoning about biotechnology issues
The advances of modern biotechnology provide teachers with a number of opportunities to explore socioscientific issues, and in doing so to enhance students' reasoning skills. Although some attempt has been made to understand cultural differences in students' informal reasoning across international and regional boundaries, there is limited research about the differences that exist between students who identify with a Christian worldview and those students who do not. To investigate the role that students' religious beliefs played in their informal reasoning about biotechnology issues regarding genetically modified food, genetic screening, therapeutic cloning and reproductive cloning, the written responses of 101 students identified as accepting a Christian worldview was compared with 21 students who did not identify with a Christian worldview. Using a qualitative approach, the students' responses to these issues were analysed to identify the modes of informal reasoning incorporated in the justification of their views about the technology. It was shown that students with a higher degree of religious belief demonstrated less use of rational reasoning and a greater reliance on intuitive reasoning in their responses to socioscientific issues when compared with their less-religious peers. The findings highlight the need for initiatives that will develop students' rational and emotive reasoning and encourage them to acknowledge the presuppositions of their belief system and how these influence their attitudes towards controversial issues in science
Effect of Aureomycin and Rumensin on performance of finishing heifers
We used 210 yearling Hereford heifers to evaluate the efficacy of Aureomycin and Rumensin fed alone and in combination. Each product is cleared by the FDA for use in feedlot rations as an individual feed additive, however, additional clearance must be obtained to use the two products in combination in the same ration. Aureomycin effectively controlled live abscessed, and Rumensin improve feed efficiency by 8.7%
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