4,133 research outputs found
Black hole solutions to the -model and their orbits (I)
In this paper we continue the program of the classification of nilpotent
orbits using the approach developed in arXiv:1107.5986, within the study of
black hole solutions in D=4 supergravities. Our goal in this work is to
classify static, single center black hole solutions to a specific N=2 four
dimensional "magic" model, with special K\"ahler scalar manifold , as orbits of geodesics on the
pseudo-quaternionic manifold with respect to the action of the isometry group . Our analysis amounts to the classification of the orbits of the
geodesic "velocity" vector with respect to the isotropy group , which include a thorough
classification of the \emph{nilpotent orbits} associated with extremal
solutions and reveals a richer structure than the one predicted by the
labels alone, based on the Kostant Sekiguchi approach. We
provide a general proof of the conjecture made in arXiv:0908.1742 which states
that regular single center solutions belong to orbits with coinciding
labels. We also prove that the reverse is not true by finding
distinct orbits with the same labels, which are distinguished by
suitably devised tensor classifiers. Only one of these is generated by regular
solutions. Since regular static solutions only occur with nilpotent degree not
exceeding 3, we only discuss representatives of these orbits in terms of black
hole solutions. We prove that these representatives can be found in the form of
a purely dilatonic four-charge solution (the generating solution in D=3) and
this allows us to identify the orbit corresponding to the regular
four-dimensional metrics.Comment: 81 pages, 24 tables, new section 4.4 about the fake superpotential
added, typos corrected, references added, accepted in Nuclear Physics B.
Experimental Investigation of Sublimation of Ice at Subsonic and Supersonic Speeds and Its Relation to Heat Transfer
An experimental investigation was conducted in a 3.84- by 10-inch tunnel to determine the mass transfer by sublimation, heat transfer, and skin friction for an iced surface on a flat plate for Mach numbers of 0.4, 0.6, and 0.8 and pressure altitudes to 30,000 feet. Measurements of rates of sublimation were also made for a Mach number of 1.3 at a pressure altitude of 30,000 feet. The results show that the parameters of sublimation and heat transfer were 40 to 50 percent greater for an iced surface than was the bare-plate heat-transfer parameter. For iced surfaces of equivalent roughness, the ratio of sublimation to heat-transfer parameters was found to be 0.90. The sublimation data obtained at a Mach number of 1.3 showed no appreciable deviation from that obtained at subsonic speeds. The data obtained indicate that sublimation as a means of removing ice formations of appreciable thickness is usually too slow to be of mach value in the de-icing of aircraft at high altitudes
Method for prediction of pump cavitation performance for various liquids, liquid temperatures, and rotative speeds
Prediction of cavitation performance of centrifugal pump
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Developmental changes in children’s training strategies
Effective practice is key to learning. Yet, it is unclear whether
young children have the ability to make effective and adaptive
training choices. In this project, we investigated 4- to 7-year-old
children’s (n=146) ability to tailor their training strategies
to optimize performance outcomes. Children were presented
with one easy and one difficult guessing game and were asked
to choose which game they wanted to practice. Crucially, before
they chose, they were told that they would eventually be
tested either on the game of their choice (Choice condition) or
on the game the computer would randomly pick (Random condition).
Contrary to our hypotheses, we found that condition
per se did not predict children’s training choices. However, we
found that older children were more likely to make effective
and adaptive training choices than younger children. Overall,
our results indicate that children’s training choices improve
from ages 4 to 7 and inform the development of interventions
to support strategic learning
First principles theory of fluctuations in vortex liquids and solids
Consistent perturbation theory for thermodynamical quantities in type II
superconductors in magnetic field at low temperatures is developed. It is
complementary to the existing expansion valid at high temperatures.
Magnetization and specific heat are calculated to two loop order and compare
well to existing Monte Carlo simulations and experiments.Comment: 3 .ps fig. In press Phys. Rev.
Coupling of dynamical micromagnetism and a stationary spin drift-diffusion equation: A step towards a fully self-consistent spintronics framework
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.We consider the coupling of the Landau-Lifshitz-Gilbert equation with a quasilinear diffusion equation to describe the interplay of magnetization and spin accumulation in magnetic-nonmagnetic multilayer structures. For this problem, we propose and analyze a convergent finite element integrator, where, in contrast to prior work, we consider the stationary limit for the spin diffusion. Numerical experiments underline that the new approach is more effective, since it leads to the same experimental results as for the model with time-dependent spin diffusion, but allows for larger time-steps of the numerical integrator.The authors acknowledge support from the Vienna Science and Technology Fund (WWTF) under grant MA14-44 (GH, DP, DS), from the Austrian Science Fund (FWF) under grant W1245 (DP, MR), from TU Wien through the innovative projects initiative (DP, MR), from the Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development (CA, DS), through the EPSRC grant EP/K008412/1 (GH), from the Royal Society under grant UF080837 (GH)
The saturation assumption yields optimal convergence of two-level adaptive BEM
We consider the convergence of adaptive BEM for weakly-singular and hypersingular integral equations associated with the Laplacian and the Helmholtz operator in 2D and 3D. The local mesh-refinement is driven by some two-level error estimator. We show that the adaptive algorithm drives the underlying error estimates to zero. Moreover, we prove that the saturation assumption already implies linear convergence of the error with optimal algebraic rates
Instantons and wormholes in AdS(3) x S-3 x CY2
We study supergravity instantons sourced by axion (and saxion) fields in the Euclidean AdS(3) x S-3 x CY2 vacua of IIB supergravity. Such instantons are described by geodesic curves on the moduli space; the timelike geodesics can describe Euclidean wormholes, the lightlike geodesics describe (generalizations of) D instantons, and spacelike geodesics are subextremal versions thereof. We perform a concrete classification of such geodesics and find that, despite earlier claims, the wormholes fail to be regular. A subclass of the lightlike geodesics is supersymmetric and, up to dualities, lifts to Euclidean strings wrapping 2-cycles in the CY2. The dual of these instantons is expected to be worldsheet instantons of the D1-D5 conformal field theory
The 3D printing of a polymeric electrochemical cell body and its characterisation
An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell ishighlighted
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