1,098 research outputs found
Conformal Symmetries of Adiabatic Modes in Cosmology
We remark on the existence of non-linearly realized conformal symmetries for
scalar adiabatic perturbations in cosmology. These conformal symmetries are
present for any cosmological background, beyond any slow-roll or quasi-de
Sitter approximation. The dilatation transformation shifts the curvature
perturbation by a constant, and corresponds to the well-known symmetry under
spatial rescaling. We argue that the scalar sector is also invariant under
special conformal transformations, which shift the curvature perturbation by a
term linear in the spatial coordinates. We discuss whether these conformal
symmetries can be extended to include tensor perturbations. Tensor modes
introduce their own set of non-linearly realized symmetries. We identify an
infinite set of large gauge transformations which maintain the transverse,
traceless gauge condition, while shifting the tensor mode non-trivially.Comment: 16 page
Effect of reaction atmosphere on catalytic CO oxidation over Cu-based bimetallic nanoclusters on a CeO2 support
Understanding the nature of active sites and the catalytic properties of oxide-supported bimetallic clusters under reaction conditions remains challenging. In this study, we combine first-principles calculations with genetic algorithm and grand canonical Monte Carlo methods to reveal the structures and compositions of CeO2-supported Cu-based bimetallic clusters in an oxygen-rich environment. Oxidized Cu4X4 (X = Pd, Pt, and Rh) bimetallic clusters on CeO2(111) are stable and exhibit different catalytic properties during CO oxidation compared with the pristine bimetallic clusters. Microkinetic simulations predict that CeO2(111)-supported Cu4Pd4O10, Cu4Pt4O11, and Cu4Rh4O14 clusters have much higher CO oxidation activity than the supported Cu4Pd4, Cu4Pt4, and Cu4Rh4 clusters; this is ascribed to the moderate CO adsorption strength and active oxygen on oxidized alloy clusters. A mechanistic study suggests that CO oxidation occurs via the O2 associative reaction mechanism on the Cu4Pd4O10 and Cu4Pt4O11 clusters, while it proceeds through the O2 dissociative reaction mechanism on the Cu4Rh4O14 cluster. Our calculations further predict that CO oxidation on the Cu4Rh4O14 cluster exhibits a low apparent activation energy, indicating that the oxidized cluster possesses excellent CO oxidation activity. This work demonstrates that the catalytic activity and reaction mechanism vary with the composition and oxidation state of the alloy nanocluster under the reaction conditions and emphasizes the influence of the reaction atmosphere on the reaction mechanisms and catalytic activity of oxide-supported alloy catalysts
The Significance of the Lingual Nerve During Periodontal/Implant Surgery
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141105/1/jper0372.pd
Tissue Biotype and Its Relation to the Underlying Bone Morphology
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142069/1/jper0569.pd
Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant
We compute the dimensionality dependence of for charged black branes
with Gauss-Bonnet correction. We find that both causality and stability
constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in
the infinite dimensionality limit. We further show that higher dimensionality
stabilize the gravitational perturbation. The stabilization of the perturbation
in higher dimensional space-time is a straightforward consequence of the
Gauss-Bonnet coupling constant bound.Comment: 16 pages,3 figures+3 tables,typos corrected, published versio
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Shade alters savanna grass layer structure and function along a gradient of canopy cover:Savanna grasses turnover across the light gradient
The Harris-Luck criterion for random lattices
The Harris-Luck criterion judges the relevance of (potentially) spatially
correlated, quenched disorder induced by, e.g., random bonds, randomly diluted
sites or a quasi-periodicity of the lattice, for altering the critical behavior
of a coupled matter system. We investigate the applicability of this type of
criterion to the case of spin variables coupled to random lattices. Their
aptitude to alter critical behavior depends on the degree of spatial
correlations present, which is quantified by a wandering exponent. We consider
the cases of Poissonian random graphs resulting from the Voronoi-Delaunay
construction and of planar, ``fat'' Feynman diagrams and precisely
determine their wandering exponents. The resulting predictions are compared to
various exact and numerical results for the Potts model coupled to these
quenched ensembles of random graphs.Comment: 13 pages, 9 figures, 2 tables, REVTeX 4. Version as published, one
figure added for clarification, minor re-wordings and typo cleanu
Inhibition of STAT3 dimerization and acetylation by garcinol suppresses the growth of human hepatocellular carcinoma in vitro and in vivo
10.1186/1476-4598-13-66Molecular Cancer131-MCOA
Transverse polarization in inclusive quasi-real photoproduction at the current fragmentation
It is shown that the recent HERMES data on the transverse
polarization in the inclusive quasi-real photoproduction at can be
accommodated by the strange quark scattering model. Relations with the quark
recombination approach are discussed.Comment: 5 pages, 3 figures, accepted by Eur. Phys. J.
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