Numerical simulation study of the dynamical behavior of the Niedermayer algorithm

We calculate the dynamic critical exponent for the Niedermayer algorithm applied to the two-dimensional Ising and XY models, for various values of the free parameter $E_0$. For $E_0=-1$ we regain the Metropolis algorithm and for $E_0=1$ we regain the Wolff algorithm. For $-1<E_0<1$, we show that the mean size of the clusters of (possibly) turned spins initially grows with the linear size of the lattice, $L$, but eventually saturates at a given lattice size $\widetilde{L}$, which depends on $E_0$. For $L>\widetilde{L}$, the Niedermayer algorithm is equivalent to the Metropolis one, i.e, they have the same dynamic exponent. For $E_0>1$, the autocorrelation time is always greater than for $E_0=1$ (Wolff) and, more important, it also grows faster than a power of $L$. Therefore, we show that the best choice of cluster algorithm is the Wolff one, when compared to the Nierdermayer generalization. We also obtain the dynamic behavior of the Wolff algorithm: although not conclusive, we propose a scaling law for the dependence of the autocorrelation time on $L$.Comment: Accepted for publication in Journal of Statistical Mechanics: Theory and Experimen

Evolution of stellar structure in the Small Magellanic Cloud

The projected distribution of stars in the Small Magellanic Cloud (SMC) from the Magellanic Clouds Photometric Survey is analysed. Stars of different ages are selected via criteria based on V magnitude and V-I colour, and the degree of `grouping' as a function of age is studied. We quantify the degree of structure using the two-point correlation function and a method based on the Minimum Spanning Tree and find that the overall structure of the SMC is evolving from a high degree of sub-structure at young ages (~10 Myr) to a smooth radial density profile. This transition is gradual and at ~75 Myr the distribution is statistically indistinguishable from the background SMC distribution. This time-scale corresponds to approximately the dynamical crossing time of stars in the SMC. The spatial positions of the star clusters in the SMC show a similar evolution of spatial distribution with age. Our analysis suggests that stars form with a high degree of (fractal) sub-structure, probably imprinted by the turbulent nature of the gas from which they form, which is erased by random motions in the galactic potential on a time-scale of a galactic crossing time.Comment: Updated to match final journal styl

The tidal tails of NGC 2298

We present an implementation of the matched-filter technique to detect tidal tails of globular clusters. The method was tested using SDSS data for the globular cluster Palomar 5 revealing its well known tidal tails. We also ran a simulation of a globular cluster with a tidal tail where we successfully recover the tails for a cluster at the same position and with the same characteristics of NGC 2298. Based on the simulation we estimate that the matched-filter increases the contrast of the tail relative to the background of stars by a factor of 2.5 for the case of NGC 2298. We also present the photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit of a King profile to the radial density profile of NGC 2298 shows that this cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the literature. The application of the matched-filter to NGC 2298 reveals several extra-tidal structures, including a leading and trailing tail. We also find that NGC 2298 has extra-tidal structures stretching towards and against the Galactic disk, suggesting strong tidal interaction. Finally, we assess how the matched-filter performs when applied to a globular cluster with and without mass segregation taken into account. We find that disregarding the effects of mass segregation may significantly reduce the detection limit of the matched-filter.Comment: 11 pages, 9 figures, 1 table. Accepted for publication on MNRAS main journa

Fixadores e porta-enxertos para enxertia hipocotiledonar de maracujazeiro amarelo.

O maracujazeiro-amarelo (Passiflora edulis Sims. f. flavicarpa Deg.) é a principal Passifloraceae cultivada no Brasil. Mas apesar da posição de destaque, a vida útil do maracujazeiro vem sendo reduzida, principalmente em decorrência dos danos causados por doenças do sistema radicular, com destaque para a fusariose, cujo agente causal é o fungo Fusarium oxysporum f. sp. passiflorae (FOP)

Produtividade de Laranjeira Pêra sob porta-enxertos híbridos de Trifoliata.

No Brasil, o principal porta-enxerto utilizado para laranjeira Pera [Citrus sinensis (L.) Osbeck] é o limoeiro Cravo (C. limonia Osbeck). Todavia, este apresenta suscetibilidade ao declínio e à morte súbita dos citros (MSC), além de conferir aos frutos qualidade inferior à relacionada a outros porta-enxertos, como a tangerineira Sunki [C. sunki (Hayata) hort. ex Tanaka]

Produtividade de 13 variedades de Laranjeira Doce no Litoral Norte da Bahia..

O Brasil é o maior produtor mundial de laranja doce [Citrus sinensis (L.) Osbeck], respondendo por metade do suco de laranja produzido globalmente. Objetivou-se com esse estudo avaliar a produtividade de 13 variedades de laranjeira doce no Litoral Norte da Bahia

Analysing observed star cluster SEDs with evolutionary synthesis models: systematic uncertainties

The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2004.07197.xWe discuss the systematic uncertainties inherent to analyses of observed (broad-band) Spectral Energy Distributions (SEDs) of star clusters with evolutionary synthesis models. We investigate the effects caused by restricting oneself to a limited number of available passbands, choices of various passband combinations, finite observational errors, non-continuous model input parameter values, and restrictions in parameter space allowed during analysis. Starting from a complete set of UBVRIJH passbands (respectively their Hubble Space Telescope/WFPC2 equivalents) we investigate to which extent clusters with different combinations of age, metallicity, internal extinction and mass can or cannot be disentangled in the various evolutionary stages throughout their lifetimes and what are the most useful passbands required to resolve the ambi- guities. We find the U and B bands to be of the highest significance, while the V band and near-infrared data provide additional constraints. A code is presented that makes use of luminosities of a star cluster system in all of the possibly available passbands, and tries to find ranges of allowed age-metallicity-extinction-mass combinations for individual members of star cluster systems. Numerous tests and examples are pre- sented. We show the importance of good photometric accuracies and of determining the cluster parameters independently without any prior assumptions.Peer reviewe