9,440 research outputs found
Quantum effects in Acoustic Black Holes: the Backreaction
We investigate the backreaction equations for an acoustic black hole formed
in a Laval nozzle under the assumption that the motion of the fluid is
one-dimensional. The solution in the near-horizon region shows that as phonons
are (thermally) radiated the sonic horizon shrinks and the temperature
decreases. This contrasts with the behaviour of Schwarzschild black holes, and
is similar to what happens in the evaporation of (near-extremal)
Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by
appropriate boundary conditions the solution is extended in both the asymptotic
regions of the nozzle.Comment: 23 pages, latex, 1 figure; revised version, to appear in Phys. Rev.
A Planck-like problem for quantum charged black holes
Motivated by the parallelism existing between the puzzles of classical
physics at the beginning of the XXth century and the current paradoxes in the
search of a quantum theory of gravity, we give, in analogy with Planck's black
body radiation problem, a solution for the exact Hawking flux of evaporating
Reissner-Nordstrom black holes. Our results show that when back-reaction
effects are fully taken into account the standard picture of black hole
evaporation is significantly altered, thus implying a possible resolution of
the information loss problem.Comment: 6 pages, LaTeX file, Awarded Fifth Prize in the Gravity Research
Foundation Essay Competition for 200
Testing Hawking particle creation by black holes through correlation measurements
Hawking's prediction of thermal radiation by black holes has been shown by
Unruh to be expected also in condensed matter systems. We show here that in a
black hole-like configuration realised in a BEC this particle creation does
indeed take place and can be unambiguously identified via a characteristic
pattern in the density-density correlations. This opens the concrete
possibility of the experimental verification of this effect.Comment: 13 pages, 2 figures. Honorable mention in the 2010 GRF Essay
Competitio
Running coupling in electroweak interactions of leptons from f(R)-gravity with torsion
The f(R)-gravitational theory with torsion is considered for one family of
leptons; it is found that the torsion tensor gives rise to interactions having
the structure of the weak forces while the intrinsic non-linearity of the f(R)
function provides an energy-dependent coupling: in this way, torsional f(R)
gravity naturally generates both structure and strength of the electroweak
interactions among leptons. This implies that the weak interactions among the
lepton fields could be addressed as a geometric effect due to the interactions
among spinors induced by the presence of torsion in the most general f(R)
gravity. Phenomenological considerations are addressed.Comment: 9 pages. arXiv admin note: text overlap with arXiv:1012.5529 by other
author
Direct evidence for efficient ultrafast charge separation in epitaxial WS/graphene heterostructure
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to
investigate ultrafast charge transfer in an epitaxial heterostructure made of
monolayer WS and graphene. This heterostructure combines the benefits of a
direct gap semiconductor with strong spin-orbit coupling and strong
light-matter interaction with those of a semimetal hosting massless carriers
with extremely high mobility and long spin lifetimes. We find that, after
photoexcitation at resonance to the A-exciton in WS, the photoexcited holes
rapidly transfer into the graphene layer while the photoexcited electrons
remain in the WS layer. The resulting charge transfer state is found to
have a lifetime of \,ps. We attribute our findings to differences in
scattering phase space caused by the relative alignment of WS and graphene
bands as revealed by high resolution ARPES. In combination with spin-selective
excitation using circularly polarized light the investigated WS/graphene
heterostructure might provide a new platform for efficient optical spin
injection into graphene.Comment: 28 pages, 14 figure
Direct evidence for efficient ultrafast charge separation in epitaxial WS<sub>2</sub>/graphene heterostructures
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2 and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS2, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS2 layer. The resulting charge-separated transient state is found to have a lifetime of âŒ1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS2 and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS2/graphene heterostructure might provide a platform for efficient optical spin injection into graphene
Epilepsy and phenylketonuria: a case description and EEG-fMRI findings.
Phenylketonuria (PKU) is characterized by phenylalanine accumulation due to phenylalanine hydroxylase deficiency. Up to 50% of PKU patients experience seizures. We evaluated an adult PKU patient who suffered from absences and primarily generalized tonicclonic seizures, associated with generalized spikeand-wave discharges (GSWs) on EEG. An analysis of blood oxygenation level-dependent (BOLD) signal changes during interictal epileptiform discharges showed early activation of the left perirolandic cortex followed by a BOLD signal decrease within cortical regions belonging to the default mode network and left frontoparietal cortex. Moreover, deactivation of the head of the right caudate nucleus and the left thalamus was observed. The fMRI pattern observed in our patient during GSWs is similar but not identical to that observed in idiopathic generalized epilepsy, suggesting different neurophysiological mechanisms. This is the first description of BOLD-fMRI patterns in a PKU patient with epilepsy. Similar studies in more patients might help to uncover the pathophysiology of seizures in this disease
Resolving the M2-brane
We construct deformed, T^2 wrapped, rotating M2-branes on a resolved cone
over Q^{1,1,1} and Q^{1,1,1}/Z_2, as well as on a product of two Eguchi-Hanson
instantons. All worldvolume directions of these supersymmetric and regular
solutions are fibred over the transverse space. These constitute gravity duals
of D=3, N=2 gauge theories. In particular, the deformed M2-brane on a resolved
cone over Q^{1,1,1} and the S^1 wrapped M2-brane on a resolved cone over
Q^{1,1,1}/Z_2 provide explicit realizations of holographic renormalization
group flows in M-theory for which both conformal and Lorentz symmetries are
broken in the IR region and restored in the UV limit. These solutions can be
dualized to supersymmetric type IIB pp-waves, which are rendered non-singular
either by additional flux or a twisted time-like direction.Comment: Latex, 23 pages, references adde
- âŠ