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

Emergência 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 −0.1 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 −1.2 and 1.5 km for low clouds and between −1.4 and 2.7 km for high clouds

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

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

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 $^{141}$Ho. The approach also elucidates the softening of kinematic coupling between particle and collective rotation, the Coriolis attenuation problem.Comment: 2 pages, 1 figur

Influência do esterco no crescimento e no acúmulo de nutrientes em mudas de mamão havaí.

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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