Single- and double-vortex vector solitons in self-focusing nonlinear media

We study two-component spatial optical solitons carrying an angular momentum and propagating in a self-focusing saturable nonlinear medium. When one of the components is small, such vector solitons can be viewed as a self-trapped vortex beam that guides either the fundamental or first-order guided mode, and they are classified as single- and double-vortex vector solitons. For such composite vortex beams, we demonstrate that a large-amplitude guided mode can stabilize the ring-like vortex beam which usually decays due to azimuthal modulational instability. We identify different types of these vector vortex solitons and demonstrate both vortex bistability and mutual stabilization effect.Comment: 7 pages, 13 figure

The young cluster NGC 2282 : a multi-wavelength perspective

We present the analysis of the stellar content of NGC~2282, a young cluster in the Monoceros constellation, using deep optical $BVI$ and IPHAS photometry along with infrared (IR) data from UKIDSS and $Spitzer$-IRAC. Based on the stellar surface density analysis using nearest neighborhood method, the radius of the cluster is estimated as $\sim$ 3.15\arcmin. From optical spectroscopic analysis of 8 bright sources, we have classified three early B-type members in the cluster, which includes, HD 289120, a previously known B2V type star, a Herbig Ae/Be star (B0.5 Ve) and a B5 V star. From spectrophotometric analyses, the distance to the cluster has been estimated as $\sim$ 1.65 kpc. The $K$-band extinction map is estimated using nearest neighborhood technique, and the mean extinction within the cluster area is found to be A$_V$ $\sim$ 3.9 mag. Using IR colour-colour criteria and H$_\alpha$-emission properties, we have identified a total of 152 candidate young stellar objects (YSOs) in the region, of which, 75 are classified as Class II, 9 are Class I YSOs. Our YSO catalog also includes 50 H$_\alpha$-emission line sources, identified using slitless spectroscopy and IPHAS photometry data. Based on the optical and near-IR colour-magnitude diagram analyses, the cluster age has been estimated to be in the range of 2 $-$ 5 Myr, which is in agreement with the estimated age from disc fraction ($\sim$ 58\%). Masses of these YSOs are found to be $\sim$ 0.1$-$2.0 M$_\odot$. Spatial distribution of the candidate YSOs shows spherical morphology, more or less similar to the surface density map.Comment: 16 pages, 19 Figure

Glasgow University at TRECVID 2006

In the first part of this paper we describe our experiments in the automatic and interactive search tasks of TRECVID 2006. We submitted five fully automatic runs, including a text baseline, two runs based on visual features, and two runs that combine textual and visual features in a graph model. For the interactive search, we have implemented a new video search interface with relevance feedback facilities, based on both textual and visual features. The second part is concerned with our approach to the high-level feature extraction task, based on textual information extracted from speech recogniser and machine translation outputs. They were aligned with shots and associated with high-level feature references. A list of significant words was created for each feature, and it was in turn utilised for identification of a feature during the evaluation

Stacking boundaries and transport in bilayer graphene

Pristine bilayer graphene behaves in some instances as an insulator with a transport gap of a few meV. This behaviour has been interpreted as the result of an intrinsic electronic instability induced by many-body correlations. Intriguingly, however, some samples of similar mobility exhibit good metallic properties, with a minimal conductivity of the order of $2e^2/h$. Here we propose an explanation for this dichotomy, which is unrelated to electron interactions and based instead on the reversible formation of boundaries between stacking domains (`solitons'). We argue, using a numerical analysis, that the hallmark features of the previously inferred many-body insulating state can be explained by scattering on boundaries between domains with different stacking order (AB and BA). We furthermore present experimental evidence, reinforcing our interpretation, of reversible switching between a metallic and an insulating regime in suspended bilayers when subjected to thermal cycling or high current annealing.Comment: 13 pages, 15 figures. Published version (Nano Letters