1,562 research outputs found
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Resonant solar neutrino oscillation versus laboratory neutrino oscillation experiments
The interplay between resonant solar neutrino oscillations and neutrino oscillations in laboratory experiments is investigated in a 3 generation model. Due to the assumed hierarchy of neutrino masses, together with our choice of a convenient parameterization of the 3 generation mixing matrix, we can derive a simple analytic formula which reduces the solar neutrino problem to an effective 2 generation problem. The reduction makes it apparent that the allowed range of mixing and mass parameters crucially depend on whether the survival probability of solar neutrinos S satisfies S greater than or equal to 1/3 or not. The formulae for probabilities of laboratory neutrino oscillations are also greatly simplified. We argue that a combination of the observed solar neutrino depletion and data obtained from reactor experiments seems to rule out some range of neutrino masses. If a sizable nu/sub ..mu../ ..-->.. nu/sub e/ oscillation is observed at accelerators, as suggested at this Workshop, it severely restricts the range of 2 mixing angles
A scalar field instability of rotating and charged black holes in (4+1)-dimensional Anti-de Sitter space-time
We study the stability of static as well as of rotating and charged black
holes in (4+1)-dimensional Anti-de Sitter space-time which possess spherical
horizon topology. We observe a non-linear instability related to the
condensation of a charged, tachyonic scalar field and construct "hairy" black
hole solutions of the full system of coupled Einstein, Maxwell and scalar field
equations. We observe that the limiting solution for small horizon radius is
either a hairy soliton solution or a singular solution that is not a regular
extremal solution. Within the context of the gauge/gravity duality the
condensation of the scalar field describes a holographic
conductor/superconductor phase transition on the surface of a sphere.Comment: 16 pages including 8 figures, v2: discussion on soliton solutions
extended; v3: matches version accepted for publication in JHE
A soliton menagerie in AdS
We explore the behaviour of charged scalar solitons in asymptotically global
AdS4 spacetimes. This is motivated in part by attempting to identify under what
circumstances such objects can become large relative to the AdS length scale.
We demonstrate that such solitons generically do get large and in fact in the
planar limit smoothly connect up with the zero temperature limit of planar
scalar hair black holes. In particular, for given Lagrangian parameters we
encounter multiple branches of solitons: some which are perturbatively
connected to the AdS vacuum and surprisingly, some which are not. We explore
the phase space of solutions by tuning the charge of the scalar field and
changing scalar boundary conditions at AdS asymptopia, finding intriguing
critical behaviour as a function of these parameters. We demonstrate these
features not only for phenomenologically motivated gravitational Abelian-Higgs
models, but also for models that can be consistently embedded into eleven
dimensional supergravity.Comment: 62 pages, 21 figures. v2: added refs and comments and updated
appendice
Rotating BPS black holes in matter-coupled AdS(4) supergravity
Using the general recipe given in arXiv:0804.0009, where all timelike
supersymmetric solutions of N=2, D=4 gauged supergravity coupled to abelian
vector multiplets were classified, we construct genuine rotating supersymmetric
black holes in AdS(4) with nonconstant scalar fields. This is done for the
SU(1,1)/U(1) model with prepotential F=-iX^0X^1. In the static case, the black
holes are uplifted to eleven dimensions, and generalize the solution found in
hep-th/0105250 corresponding to membranes wrapping holomorphic curves in a
Calabi-Yau five-fold. The constructed rotating black holes preserve one quarter
of the supersymmetry, whereas their near-horizon geometry is one half BPS.
Moreover, for constant scalars, we generalize (a supersymmetric subclass of)
the Plebanski-Demianski solution of cosmological Einstein-Maxwell theory to an
arbitrary number of vector multiplets. Remarkably, the latter turns out to be
related to the dimensionally reduced gravitational Chern-Simons action.Comment: 23 pages, uses JHEP3.cl
Conformal Symmetry of a Black Hole as a Scaling Limit: A Black Hole in an Asymptotically Conical Box
We show that the previously obtained subtracted geometry of four-dimensional
asymptotically flat multi-charged rotating black holes, whose massless wave
equation exhibit symmetry may be
obtained by a suitable scaling limit of certain asymptotically flat
multi-charged rotating black holes, which is reminiscent of near-extreme black
holes in the dilute gas approximation. The co-homogeneity-two geometry is
supported by a dilation field and two (electric) gauge-field strengths. We also
point out that these subtracted geometries can be obtained as a particular
Harrison transformation of the original black holes. Furthermore the subtracted
metrics are asymptotically conical (AC), like global monopoles, thus describing
"a black hole in an AC box". Finally we account for the the emergence of the
symmetry as a consequence of the
subtracted metrics being Kaluza-Klein type quotients of .
We demonstrate that similar properties hold for five-dimensional black holes.Comment: Sections 3 and 4 significantly augmente
Exact Black Holes and Universality in the Backreaction of non-linear Sigma Models with a potential in (A)dS4
The aim of this paper is to construct accelerated, stationary and
axisymmetric exact solutions of the Einstein theory with self interacting
scalar fields in (A)dS4. To warm up, the backreaction of the (non)-minimally
coupled scalar field is solved, the scalar field equations are integrated and
all the potentials compatible with the metric ansatz and Einstein gravity are
found. With these results at hand the non-linear sigma model is tackled. The
scalar field Lagrangian is generic; neither the coupling to the curvature,
neither the metric in the scalar manifold nor the potential, are fixed ab
initio. The unique assumption in the analysis is the metric ansatz: it has the
form of the most general Petrov type D vacuum solution of general relativity;
it is a a cohomogeneity two Weyl rescaling of the Carter metric and therefore
it has the typical Plebanski-Demianski form with two arbitrary functions of one
variable and one arbitrary functions of two variables. It is shown, by an
straightforward manipulation of the field equations, that the metric is
completely integrable without necessity of specifiying anything in the scalar
Lagrangian. This results in that the backreaction of the scalar fields, within
this class of metrics, is universal. The metric functions generically show an
explicit dependence on a dynamical exponent that allows to smoothly connect
this new family of solutions with the actual Plebanski-Demianski spacetime. The
remaining field equations imply that the scalar fields follow geodesics in the
scalar manifold with an affine parameter given by a non-linear function of the
spacetime coordinates and define the on-shell form of the potential plus a
functional equation that it has to satisfy. Finally, a general family of (A)dS4
static hairy black holes is explicitly constructed and its properties are
outlined.Comment: Several typos correcte
Lineage-Specific Methyltransferases Define the Methylome of the Globally Disseminated Escherichia coli ST131 Clone.
UNLABELLED: Escherichia coli sequence type 131 (ST131) is a clone of uropathogenic E. coli that has emerged rapidly and disseminated globally in both clinical and community settings. Members of the ST131 lineage from across the globe have been comprehensively characterized in terms of antibiotic resistance, virulence potential, and pathogenicity, but to date nothing is known about the methylome of these important human pathogens. Here we used single-molecule real-time (SMRT) PacBio sequencing to determine the methylome of E. coli EC958, the most-well-characterized completely sequenced ST131 strain. Our analysis of 52,081 methylated adenines in the genome of EC958 discovered three (m6)A methylation motifs that have not been described previously. Subsequent SMRT sequencing of isogenic knockout mutants identified the two type I methyltransferases (MTases) and one type IIG MTase responsible for (m6)A methylation of novel recognition sites. Although both type I sites were rare, the type IIG sites accounted for more than 12% of all methylated adenines in EC958. Analysis of the distribution of MTase genes across 95 ST131 genomes revealed their prevalence is highly conserved within the ST131 lineage, with most variation due to the presence or absence of mobile genetic elements on which individual MTase genes are located. IMPORTANCE: DNA modification plays a crucial role in bacterial regulation. Despite several examples demonstrating the role of methyltransferase (MTase) enzymes in bacterial virulence, investigation of this phenomenon on a whole-genome scale has remained elusive until now. Here we used single-molecule real-time (SMRT) sequencing to determine the first complete methylome of a strain from the multidrug-resistant E. coli sequence type 131 (ST131) lineage. By interrogating the methylome computationally and with further SMRT sequencing of isogenic mutants representing previously uncharacterized MTase genes, we defined the target sequences of three novel ST131-specific MTases and determined the genomic distribution of all MTase target sequences. Using a large collection of 95 previously sequenced ST131 genomes, we identified mobile genetic elements as a major factor driving diversity in DNA methylation patterns. Overall, our analysis highlights the potential for DNA methylation to dramatically influence gene regulation at the transcriptional level within a well-defined E. coli clone
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Pressure shielding mechanism of canopies for trailing edge noise reduction in aerofoils
Session: Airframe / High-Lift Noise IView Video Presentation: https://doi.org/10.2514/6.2023-3204.vidThe pressure shielding mechanism of bio-inspired surface treatment, called canopies, has been investigated experimentally and applied to reduce trailing edge noise generated by aero- foils. Surface pressure experiments beneath the boundary layer on a flat and aerofoil section show that canopies can attenuate surface pressure in two frequency ranges, â f 1 = 0.1 to 1.0 kHz and âf2 = 2 to 12 kHz, at some critical canopiesâ height from the wall. Canopies with an Open-Area-Ratio (OAR or Ď) of 50 % placed closer (h/δ=0.08) to the surface tend to in- crease attenuation with frequency, without any low-frequency peak attenuation. This high- frequency attenuation is mainly due to the mechanism of dissipation, of small-scale structures in the boundary-layer, provided by the canopies, which have relatively higher wall shear stress compared to flat plate or thicker canopy designs. As h/δ increases, the low-frequency atten- uation in the surface pressure becomes noticeable, with a peak value of 5 dB for a critical height of h/δâ âź 1, indicating the mechanism of blockage or shielding of large structures in the boundary-layer is responsible for the low-frequency attenuation. For h/δ ⼠0.16, both the low- and high-frequency attenuation reduces and becomes almost zero for h/δ = 0.5. Furthermore, the mechanism of pressure shielding provided by the canopy treatment is shown to be a local phenomenon, for 70% <OAR < 90 % and very sensitive to the location of the canopy itself. The maximum attenuation in surface pressure is seen for the canopy geometries with small rod diameters with less spacing. The optimum canopy geometry, based on the surface pres- sure studies, was applied near the trailing edge of the NACA0012 aerofoil. The far-field noise study demonstrates, for the first time, that canopies can reduce broadband noise levels up to 12-14 dB in the frequency range between 2 and 12 kHz, provided they are scaled appropriately based on the incoming turbulent boundary-layer flow.EPSRC under grant No. EP/V038273/1
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