Publication Search Results
Results per page
Now showing 1 - 5 of 5
(2007) Wright, Christopher; Burton, Michael; Van Dishoeck, Ewine; van Langevelde, Huib-Jan; Wilner, David; Hughes, Annie; Lommen, Dave; Maddison, Sarah; Jorgensen, Jes; Bourke, TylerJournal ArticleContext. Low-mass stars form with disks in which the coagulation of grains may eventually lead to the formation of planets. It is not known when and where grain growth occurs, as models that explain the observations are often degenerate. A way to break this degeneracy is to resolve the sources under study. Aims. Our aim is to find evidence for the existence of grains of millimetre sizes in disks around T Tauri stars, implying grain growth. Methods. The Australia Telescope Compact Array (ATCA) was used to observe 15 southern T Tauri stars, five in the constellation Lupus and ten in Chamaeleon, at 3.3 mm. The five Lupus sources were also observed with the SubMillimeter Array (SMA) at 1.4 mm. Our new data are complemented with data from the literature to determine the slopes of the spectral energy distributions in the millimetre regime. Results. Ten sources were detected at better than 3 sigma with the ATCA, with sigma approximate to 1-2 mJy, and all sources that were observed with the SMA were detected at better than 15 sigma, with sigma approximate to 4 mJy. Six of the sources in our sample are resolved to physical radii of similar to 100 AU. Assuming that the emission from such large disks is predominantly optically thin, the millimetre slope can be related directly to the opacity index. For the other sources, the opacity indices are lower limits. Four out of six resolved sources have opacity indices <= 1, indicating grain growth to millimetre sizes and larger. The masses of the disks range from < 0.01 to 0.08 M-circle dot, which is comparable to the minimum mass solar nebula. A tentative correlation is found between the millimetre slope and the strength and shape of the 10-mu m silicate feature, indicating that grain growth occurs on similar (short) timescales in both the inner and outer disk.
(2006) Maercker, M; Burton, Michael; Wright, ChristopherJournal ArticleContext. We present a JHK(s)L survey of the massive star forming region RCW 57 (NGC 3576) based on L-band data at 3.5 mu m taken with SPIREX ( South Pole Infrared Explorer), and 2MASS JHK(s) data at 1.25-2.2 mu m. This is the second of two papers, the first one concerning a similar JHK(s)L survey of 30 Doradus. Aims. Colour-colour and colour-magnitude diagrams are used to detect sources with infrared excess. This excess emission is interpreted as coming from circumstellar disks, and hence gives the cluster disk fraction (CDF). Based on the CDF and the age of RCW 57, it is possible to draw conclusions on the formation and early evolution of massive stars. Methods. The infrared excess is detected by comparing the locations of sources in JHKsL colour-colour and L vs. (K-s - L) colour - magnitude diagrams to the reddening band due to interstellar extinction. Results. A total of 251 sources were detected. More than 50% of the 209 sources included in the diagrams have an infrared excess. Conclusions. Comparison with other JHKsL surveys, including the results on 30 Doradus from the first paper, support a very high initial disk fraction (> 80%) even for massive stars, although there is an indication of a possible faster evolution of circumstellar disks around high mass stars. 33 sources only found in the L-band indicate the presence of heavily embedded, massive Class I protostars. We also report the detection of diffuse PAHs emission throughout the RCW 57 region.
(2012) Eggert, PaulJournal ArticleThis essay is based on the seventeenth annual D. F. McKenzie lecture given at the University of Oxford on 2 March 2011. McKenzie is best known for his tolerant unrolling of the bibliographical into wider cultural and social realms, together with his implication that the material book can be treated as an index of them. Eggert’s essay argues for a timely counterbalance: the need for a regathering of the concept of the work, which largely fell from view during the period of high literary theory. A new model for interpretation is proposed by building reading, and thus the aesthetic, into the definition of the work, while retaining the evidentiary witness of the material book. The model offers, in other words, a justification for folding book history and bibliography into the literary study of all works that have enjoyed an extended history of printing and reprinting.
(2008) Tranter, Paul Joseph; Sharpe, ScottJournal ArticleIn Monstropolis, the virtual world of monsters in the 2001 Pixar-animated Disney movie Monsters, Inc., the screams of human children are the source of energy. In this paper, the energy shortage (or ‘scream shortage’) depicted in Monsters, Inc. serves as a subtle and engaging allegory, drawing attention to the non-virtual world’s concerns with energy supplies, particularly oil. Peak oil, the time at which the global production of oil reaches its maximum, is arguably one of the most important issues that will affect the conceptualisation of children and our ability to create and maintain child-friendly cities. This paper derives new ways of conceptualising the relationship between peak oil and children in modern western societies, through a critical analysis of a number of themes from Monsters, Inc. The value of such an analysis is that in Monsters, Inc. the issues of children, lifestyle and energy acquisition and use are all brought together in a common problematic. Thus, the underlying descriptions in Monsters, Inc. provide a catalyst for a wider debate about children and peak oil
(2001) Malomed, Boris; Peng, Gang-Ding; Chu, Pak; Towers, Isaac; Buryak, Alexander; Sammut, RowlandJournal ArticleWe present a review of new results which suggest the existence of fully stable spinning solitons (self-supporting localised objects with an internal vorticity) in optical fibres with selffocusing Kerr (cubic) nonlinearity, and in bulk media featuring a combination of the cubic selfdefocusing and quadratic nonlinearities. Their distinctive difference from other optical solitons with an internal vorticity, which were recently studied in various optical media, theoretically and also experimentally, is that all the spinning solitons considered thus far have been found to be unstable against azimuthal perturbations. In the first part of the paper, we consider solitons in a nonlinear optical fibre in a region of parameters where the fibre carries exactly two distinct modes, viz., the fundamental one and the first-order helical mode. From the viewpoint of application to communication systems, this opens the way to doubling the number of channels carried by a fibre. Besides that, these solitons are objects of fundamental interest. To fully examine their stability, it is crucially important to consider collisions between them, and their collisions with fundamental solitons, in (ordinary or hollow) optical fibres. We introduce a system of coupled nonlinear Schr¨ odinger equations for the fundamental and helical modes with nonstandard values of the cross-phase-modulation coupling constants, and show, in analytical and numerical forms, results of collisions between solitons carried by the two modes. In the second part of the paper, we demonstrate that the interaction of the fundamental beam with its second harmonic in bulk media, in the presence of self-defocusing Kerr nonlinearity, gives rise to the first ever example of completely stable spatial ring-shaped solitons with intrinsic vorticity. The stability is demonstrated both by direct simulations and by analysis of linearized equations.