3,605 research outputs found

    D1 and D5-brane giant gravitons on AdS3×S3×S3×S1AdS_3 \times S^3 \times S^3 \times S^1

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    We construct various examples of 1/4-BPS giant gravitons embedded into the type IIB supergravity background AdS3×S+3×S3×S1AdS_{3} \times S^{3}_{+} \times S^{3}_{-} \times S^{1} with pure R-R flux: two D1-brane giants wrapping 1-cycles in AdS3AdS_{3} and S+3×S3S^{3}_{+} \times S^{3}_{-}, and one D5-brane giant wrapping a 4-cycle in S+3×S3S^{3}_{+} \times S^{3}_{-} and the S1S^{1}. These D-branes are supported by angular momenta α\alpha P on one 3-sphere and (1α)(1-\alpha) P on the other. We then construct a general class of 1/8-BPS D5-brane giant gravitons wrapping 4-cycles Σ\Sigma in S+3×S3S^{3}_{+} \times S^{3}_{-} and the S1S^{1}. Here Σ\Sigma is the intersection of a holomorphic surface C\mathcal{C} in C+2×C2\mathbb{C}^{2}_{+} \times \mathbb{C}^{2}_{-} with the S+3×S3S^{3}_{+} \times S^{3}_{-} submanifold. The holomorphic surface C\mathcal{C} is defined by f(y1z1,y1z2,y2z1,y2z2)=0f(y_{1}z_{1},y_{1}z_{2},y_{2}z_{1},y_{2}z_{2}) = 0, with yay_{a} and zaz_{a} the C±2\mathbb{C}^{2}_{\pm} complex coordinates. There is supersymmetry enhancement to 1/4-BPS in the special case f(y1z1)=0f(y_{1}z_{1}) = 0 of which our original D5-brane giant graviton is an example.Comment: 30 pages, 4 figures. reference and figure added, minor change

    In the eye of the storm: preliminary evidence on the use of online learning diaries

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    The surprising lack of pressure and speed in the centre of the vortex of a storm are in stark contrast to the force and destruction often experienced at its periphery. Many spectators watching a developing storm will be caught between fear and a desire to escape. The metaphor of a storm has been applied here to the emotions experienced by many students enrolling in online learning courses. Not only do the requirements of studying online collide with personal and professional commitments, the experience of learning online (often in groups) results in many students feeling displaced, scared or out of control. Learning diaries, especially in an online environment, present students with an opportunity to reach the centre of the vortex, though this may not be as quiet and safe as we may have presumed. This paper reports on students’ reflections in their learning diaries as a prescriptive part of the Professional Certificate in Management offered by the Open University. The research focused on the unstructured learning diary entries of 12 students from one tutor group over an 18 day period of a short compulsory online course. This phenomenographic study used grounded theory as methodology to analyse and describe students’ use of their learning diaries. The research found ample evidence that online learning diaries provide students with a safe space to reflect on the vortex around them. Without a quiet and reflective centre, students may be overwhelmed by the wider forces impacting on them. Students’ postings provided rich descriptions of the vortex of studying online and the function of having a centre to which to withdraw. There is, however, also evidence that posting reflections in learning diaries can itself be a dislocating and uncomfortable experience for some learners, while others question its usefulness. The work provides practical and useful information for managers of online learning experiences, instructional designers and curriculum developer

    Towards Official Balance Sheet Estimates for South Africa’s Household Sector

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    Official balance sheet estimates for the household sector are not currently available in South Africa. Yet with South Africa.s well-developed financial sector and deep capital markets, asset market channels are likely to be important determinants of aggregate consumer spending and saving, consumers. demand for credit and their broad money holdings. The current paper aims to produce comprehensive estimates of household balance sheets for South Africa. The paper draws, where feasible, on best practice from the Office of National Statistics of the U.K.. The paper assesses the quality of the data sources and suggests areas where additional surveys or improvements in data collection procedures would be helpful to further improve the quality of the balance sheet estimates. Furthermore, quarterly balance sheet measures to 2003 are provided, and linked to quarterly measures constructed in Aron and Muellbauer (2006a). The main balance sheet categories are liquid assets, household debt and various categories of illiquid financial and tangible assets, including pension wealth, directly held shares and bonds, and housing. Revised debt estimates and new estimates of tangible assets for households and unincorporated businesses are provided. The South African Reserve Bank aims to publish selected items of the quarterly household balance sheets in its Quarterly Bulletin on an ongoing basis. The paper describes the trends of the estimates of the household sector.s balance sheets and of total net wealth. The paucity of data for developing and emerging market countries is illustrated by means of a survey, and lessons are drawn from the South African research for the compilation of household sector balance sheets.

    Critical media literacy: a design for the future

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    [From OPENSPACE Editor Alice Kanengoni's editorial]: Professor Jeanne Prinsloo notes in her article that "In fact, it has been argued that the significance of the media in people’s lives has increased to the extent that it has been described as their primary curriculum, thereby recasting formal education as the secondary curriculum." This therefore requires an incestment in media literacy; people's ability to to understand the world around them, as represented in the media. Thus, Professor Prinsloo argues for critical media literacy, citing the role that the media played in fuelling the genocide in Rwanda, as an illustrative case in point. She states that "While we can not attribute all blame in the Rwandan scenario to the radio use, it is clear that the media mattered." She indicates that "media representations and engagements play a significant role in the way we understand the world, its people and events, and ourselves therein." As such, societies should invest in building a critical citizenry that can read and deconstruct the various ideologies that are often carries in and through the media
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