591 research outputs found

    Syngenetic sand veins and anti-syngenetic sand wedges, Tuktoyaktuk Coastlands, western Arctic Canada

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    Sand-sheet deposits of full-glacial age in the Tuktoyaktuk Coastlands, western Arctic Canada, contain syngenetic sand veins 1-21 cm wide and sometimes exceeding 9 m in height. Their tall and narrow, chimney-like morphology differs from that of known syngenetic ice wedges and indicates an unusually close balance between the rate of sand-sheet aggradation and the frequency of thermal-contraction cracking. The sand sheets also contain rejuvenated (syngenetic) sand wedges that have grown upward from an erosion surface. By contrast, sand sheets of postglacial age contain few or sometimes no intraformational sand veins and wedges, suggesting that the climatic conditions were unfavourable for thermal-contraction cracking. Beneath a postglacial sand sheet near Johnson Bay, sand wedges with unusually wide tops (3.9 m) extend down from a prominent erosion surface. The wedges grew vertically downward during deflation of the ground surface, and represent anti-syngenetic wedges. The distribution of sand veins and wedges within the sand sheets indicates that the existence of continuous permafrost during sand-sheet aggradation can be inferred confidently only during full-glacial conditions

    Surface acoustic wave attenuation by a two-dimensional electron gas in a strong magnetic field

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    The propagation of a surface acoustic wave (SAW) on GaAs/AlGaAs heterostructures is studied in the case where the two-dimensional electron gas (2DEG) is subject to a strong magnetic field and a smooth random potential with correlation length Lambda and amplitude Delta. The electron wave functions are described in a quasiclassical picture using results of percolation theory for two-dimensional systems. In accordance with the experimental situation, Lambda is assumed to be much smaller than the sound wavelength 2*pi/q. This restricts the absorption of surface phonons at a filling factor \bar{\nu} approx 1/2 to electrons occupying extended trajectories of fractal structure. Both piezoelectric and deformation potential interactions of surface acoustic phonons with electrons are considered and the corresponding interaction vertices are derived. These vertices are found to differ from those valid for three-dimensional bulk phonon systems with respect to the phonon wave vector dependence. We derive the appropriate dielectric function varepsilon(omega,q) to describe the effect of screening on the electron-phonon coupling. In the low temperature, high frequency regime T << Delta (omega_q*Lambda /v_D)^{alpha/2/nu}, where omega_q is the SAW frequency and v_D is the electron drift velocity, both the attenuation coefficient Gamma and varepsilon(omega,q) are independent of temperature. The classical percolation indices give alpha/2/nu=3/7. The width of the region where a strong absorption of the SAW occurs is found to be given by the scaling law |Delta \bar{\nu}| approx (omega_q*Lambda/v_D)^{alpha/2/nu}. The dependence of the electron-phonon coupling and the screening due to the 2DEG on the filling factor leads to a double-peak structure for Gamma(\bar{\nu}).Comment: 17 pages, 3 Postscript figures, minor changes mad

    In search of lost hybridity: the French Daniel Deronda

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    Starting from a set of examples of borrowings from French in George Eliot’s Daniel Deronda, I explore the various ways in which the characters’ and narrator’s use of mixed English–French utterances generates inferences which make the transcending of their mono-cultural self possible. I go on to argue that in Jumeau’s recent French translation of the novel, the reader is not given access to those inferences, resulting in the erasing of an Anglo-European, cosmopolitan identity

    Communicative competence and institutional affiliation: interactional processes of identity construction by immigrant students in Catalonia

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    The growing presence of children of immigrant families in the public school system in the bilingual region of Catalonia provides us with an opportunity to study how young multilingual and multicultural speakers construct their social competencies and their identity within the specific context of a gate-keeping social institution such as the school. The study reported in this paper approaches language learning as a process of socialisation that involves not only learning how to make sense of linguistic signs but also learning how to enact different social roles in particular institutions. The analysis focuses on the interactional profiles of two immigrant students in two types of communicative activities that are representative of the school context: responding to questions from an adult and cooperating with a peer in the resolution of a learning task. By shifting the focus of analysis from a decontextualised notion of communicative competence to the notion of 'institutionally affiliated communicative competence' and concentrating on issues such as the (1) the relationship between knowledge and participation, (2) language choice inside and outside school and (3) definitions of correctness in language use, the study reveals how the two students construct a highly 'affiliated' identit

    Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer Quantized-Hall Regime

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    The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs heterostructure is studied (in the clean limit) where the 2D electron-gas (2DEG), being in an odd-integer quantum-Hall state, is in fact a spin dielectric. Of the two channels of phonon absorption associated with excitation of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons, involves a change of the spin state of the system and the other does not. We show that the phonon-absorption rate corresponding to the former channel (in the paper designated as the second absorption channel) is finite at zero temperature (TT), whereas that corresponding to the latter (designated as the first channel) vanishes for T0T\to 0. The long-wavelength limit, being the special case of the first absorption channel, corresponds to sound (bulk and surface) attenuation by the 2DEG. At the same time, the ballistic phonon propagation and heat absorption are determined by both channels. The 2DEG overheat and the attendant spin-state change are found under the conditions of permanent nonequilibrium phonon pumping.Comment: 26 pages, 2 figure

    A long view of liberal peace and its crisis

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    The ‘crisis’ of liberal peace has generated considerable debate in International Relations. However, analysis is inhibited by a shared set of spatial, cultural and temporal assumptions that rest on and reproduce a problematic separation between self-evident ‘liberal’ and ‘non-liberal’ worlds, and locates the crisis in presentist terms of the latter’s resistance to the former’s expansion. By contrast, this article argues that efforts to advance liberal rule have always been interwoven with processes of alternative order-making, and in this way are actively integral, not external, to the generation of the subjectivities, contestations, violence and rival social orders that are then apprehended as self-evident obstacles and threats to liberal peace and as characteristic of its periphery. Making visible these intimate relations of co-constitution elided by representations of liberal peace and its crisis requires a long view and an analytical frame that encompasses both liberalism and its others in the world. The argument is developed using a Foucauldian governmentality framework and illustrated with reference to Sri Lanka

    To what extent does a regional dialect and accent impact on the development of reading and writing skills?

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    The issue of whether a regional accent and/or dialect impact(s) on the development of literacy skills remains current in the UK. For decades the issue has dogged debate about education outcomes, portable skills and employability. The article summarizes research on the topic using systematic review methodology. A scoping review was undertaken with the research question ‘To what extent does a regional dialect and accent impact on the development of reading and writing skills?’. The review covers research relevant to the teaching of 5-16 year olds in England, but also draws on research within Europe, the USA, Australia and the Caribbean. The results suggest that curricula have marginalized language variation; that the impact of regional accent and dialect on writing is relatively minor; that young people are adept at style-shifting between standard and non-standard forms; and that inappropriate pedagogical responses to regional variation can have detrimental effects on children’s educational achievement
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