40,822 research outputs found
Comment on ``Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms''
In a recent Letter (Phys. Rev. Lett. \textbf{98}, 083601 (2007),
arXiv:cond-mat/0610804), O. Assaf and E. Akkermans claim that the angular
correlations of the light intensity scattered by a cloud of cold atoms with
internal degeneracy (Zeeman sublevels) of the ground state overcome the usual
Rayleigh law. More precisely, they found that they become exponentially large
with the size of the sample. In what follows, we will explain why their results
are wrong and, in contrary, why the internal degeneracy leads to lower
intensity correlations.Comment: 1 page. Comment submitted to PR
EmergĂȘncia de sementes de castanha-do-brasil em função do tamanho e da idade.
bitstream/item/40153/1/Circ-Tec-56-CPATU.pd
The size distribution of magnetic bright points derived from Hinode/SOT observations
Context. Magnetic Bright Points (MBPs) are small-scale magnetic features in
the solar photosphere. They may be a possible source of coronal heating by
rapid footpoint motions that cause magnetohydrodynamical waves. The number and
size distribution are of vital importance in estimating the small
scale-magnetic-field energy. Aims. The size distribution of MBPs is derived for
G-band images acquired by the Hinode/SOT instrument. Methods. For
identification purposes, a new automated segmentation and identification
algorithm was developed. Results. For a sampling of 0.108 arcsec/pixel, we
derived a mean diameter of (218 +- 48) km for the MBPs. For the full resolved
data set with a sampling of 0.054 arcsec/pixel, the size distribution shifted
to a mean diameter of (166 +- 31) km. The determined diameters are consistent
with earlier published values. The shift is most probably due to the different
spatial sampling. Conclusions. We conclude that the smallest magnetic elements
in the solar photosphere cannot yet be resolved by G-band observations. The
influence of discretisation effects (sampling) has also not yet been
investigated sufficiently.Comment: Astronomy and Astrophysics, Volume 498, Issue 1, 2009, pp.289-29
Assessment of MISR and MODIS cloud top heights through inter-comparison with a back-scattering lidar at SIRTA
One year of back-scattering lidar cloud boundaries and optical depth were analysed for coincident inter-comparison with the latest processed versions of the NASA-TERRA MISR stereo and MODIS CO2-slicing operational cloud top heights. Optically thin clouds were found to be accurately characterised by the MISR cloud top height product as long as no other cloud was present at lower altitude. MODIS cloud top heights were generally found within the cloud extent retrieved by lidar; agreement improved as cloud optical depth increased and when CO2-slicing was the only technique used for the retrieval. The difference between Lidar and MISR cloud top heights was found to lie between â0.1 and 0.4 km for low clouds and between 0.1 and 3.1 km for high clouds. The difference between Lidar and MODIS cloud top heights was found to lie between â1.2 and 1.5 km for low clouds and between â1.4 and 2.7 km for high clouds
Classical Optimizers for Noisy Intermediate-Scale Quantum Devices
We present a collection of optimizers tuned for usage on Noisy Intermediate-Scale Quantum (NISQ) devices. Optimizers have a range of applications in quantum computing, including the Variational Quantum Eigensolver (VQE) and Quantum Approximate Optimization (QAOA) algorithms. They are also used for calibration tasks, hyperparameter tuning, in machine learning, etc. We analyze the efficiency and effectiveness of different optimizers in a VQE case study. VQE is a hybrid algorithm, with a classical minimizer step driving the next evaluation on the quantum processor. While most results to date concentrated on tuning the quantum VQE circuit, we show that, in the presence of quantum noise, the classical minimizer step needs to be carefully chosen to obtain correct results. We explore state-of-the-art gradient-free optimizers capable of handling noisy, black-box, cost functions and stress-test them using a quantum circuit simulation environment with noise injection capabilities on individual gates. Our results indicate that specifically tuned optimizers are crucial to obtaining valid science results on NISQ hardware, and will likely remain necessary even for future fault tolerant circuits
Emission of Massive Scalar Fields by a Higher-Dimensional Rotating Black-Hole
We perform a comprehensive study of the emission of massive scalar fields by
a higher-dimensional, simply rotating black hole both in the bulk and on the
brane. We derive approximate, analytic results as well as exact numerical ones
for the absorption probability, and demonstrate that the two sets agree very
well in the low and intermediate-energy regime for scalar fields with mass
m_\Phi < 1 TeV in the bulk and m_\Phi < 0.5 TeV on the brane. The numerical
values of the absorption probability are then used to derive the Hawking
radiation power emission spectra in terms of the number of extra dimensions,
angular-momentum of the black hole and mass of the emitted field. We compute
the total emissivities in the bulk and on the brane, and demonstrate that,
although the brane channel remains the dominant one, the bulk-over-brane energy
ratio is considerably increased (up to 33%) when the mass of the emitted field
is taken into account.Comment: 28 pages, 18 figure
Nuclear pairing and Coriolis effects in proton emitters
We introduce a Hartree-Fock-Bogoliubov mean-field approach to treat the
problem of proton emission from a deformed nucleus. By substituting a rigid
rotor in a particle-rotor-model with a mean-field we obtain a better
description of experimental data in Ho. The approach also elucidates
the softening of kinematic coupling between particle and collective rotation,
the Coriolis attenuation problem.Comment: 2 pages, 1 figur
InfluĂȘncia do esterco no crescimento e no acĂșmulo de nutrientes em mudas de mamĂŁo havaĂ.
bitstream/item/59119/1/CPATU-ComTec30.pd
Jet Modification in a Brick of QGP Matter
We have implemented the LPM effect into a microscopic transport model with
partonic degrees of freedom by following the algorithm of Zapp & Wiedemann. The
Landau-Pomeranchuk-Migdal (LPM) effect is a quantum interference process that
modifies the emission of radiation in the presence of a dense medium. In QCD
this results in a quadratic length dependence for radiative energy loss. This
is an important effect for the modification of jets by their passage through
the QGP.
We verify the leading parton energy loss in the model against the leading
order Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPS-Z) result.
We apply our model to the recent observations of the modification of di-jets
at the LHC.Comment: Presented at Panic 1
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