A frictional Cosserat model for the flow of granular materials through a vertical channel

A rigid-plastic Cosserat model has been used to study dense, fully developed flow of granular materials through a vertical channel. Frictional models based on the classical continuum do not predict the occurrence of shear layers, at variance with experimental observations. This feature has been attributed to the absence of a material length scale in their constitutive equations. The present model incorporates such a material length scale by treating the granular material as a Cosserat continuum. Thus localised couple stresses exist and the stress tensor is asymmetric. The velocity profiles predicted by the model are in close agreement with available experimental data. The predicted dependence of the shear layer thickness on the width of the channel is in reasonable agreement with data. In the limit of the ratio of the particle diameter to the half-width of the channel being small, the model predicts that the shear layer thickness scaled by the particle diameter grows.Comment: 17 pages, 12 PostScript figures, uses AmsLaTeX, psfrag and natbib. Accepted for publication in Acta Mechanic

Exploration of The Duality Between Generalized Geometry and Extraordinary Magnetoresistance

We outline the duality between the extraordinary magnetoresistance (EMR), observed in semiconductor-metal hybrids, and non-symmetric gravity coupled to a diffusive $U(1)$ gauge field. The corresponding gravity theory may be interpreted as the generalized complex geometry of the semi-direct product of the symmetric metric and the antisymmetric Kalb-Ramond field: ($g_{\mu\nu}+\beta_{\mu\nu}$). We construct the four dimensional covariant field theory and compute the resulting equations of motion. The equations encode the most general form of EMR within a well defined variational principle, for specific lower dimensional embedded geometric scenarios. Our formalism also reveals the emergence of additional diffusive pseudo currents for a completely dynamic field theory of EMR. The proposed equations of motion now include terms that induce geometrical deformations in the device geometry in order to optimize the EMR. This bottom-up dual description between EMR and generalized geometry/gravity lends itself to a deeper insight into the EMR effect with the promise of potentially new physical phenomena and properties.Comment: 13 pages and 6 figures. Revised/edited for clarity and purpose. Several references added. Updated title based on suggestions and comments received. Version accepted for publication in Phys.Rev.

The poetic is political….and other notes on engaged scholarship

Instrumental and objectivist logics maintain a hegemonic place in Western scholarship, reasoning skills powerfully equipped to address certain dilemmas even as they may obscure other ways of knowing. In this chapter, we enlarge dominant notions of rationality by offering an aesthetic view of knowledge as vital for engaged communication scholarship. Our interest in aesthetic logics parallels concerns that have led scholars to develop feminist practices of inquiry (e.g., Harding, 1998; Hesse-Biber, 2007), interrogate the aesthetics of representations in West-centric knowledge structures from postcolonial and Subaltern Studies standpoints (e.g., Broadfoot & Munshi, 2007; Dutta, 2007, 2008), focus on autoethnographic and poetic accounts ( e.g., Carr, 2003; Ellingson, 2009), introduce reflexivity and the politics of personhood in the scholarly process ( e.g., Harding, 1991; Reinharz, 1992), and adopt narrative and dialogic understandings of knowledge constructions (e.g., Frank, 2005; Harter, 2005). Loosely coupled, these research trajectories advance alternative rationalities for witnessing and answering salient social issues. We argue for the theoretical and practical incorporation of aesthetic rationalities in engaged scholarship-logics of poss ibility that cultivate individuals \u27 capacities to imagine otherwise. Reimagining scholarly inquiry to reflect and embrace aesthetic logics requires us to rethink our methods of data collection, analysis, and representation and our own roles as researchers and writers . When we resist the art/science dichotomy, opportunities abound for sensemaking and representation that embody aesthetic ways of knowing. Furthermore, rejection of dichotomous thinking opens up possibilities for listening to ways of knowing that lie beyond the realm of Eurocentric knowledge structures (Dutta, in press). Even after the interpretive turn, instrumental and objectivist logics often underlie and sometimes constrain the processes and products of social scientific research (Denzin & Lincoln, 2005). Traditional structures and modes of research offer important but limited conceptualizations of knowing. We can open ourselves to other ways of asking questions that include overt attention to aesthetic sensibilities . We need not reject or abandon traditional modes of research. Instead, we can enlarge the realm of possibilities for what counts as accepted research practices and advance methods for studying the aesthetic nature of communal life (Ellingson, 2009). In this chapter, we develop an understanding of rationality that incorporates imagination, and we explore methodologies that draw on creative sensibilities. We then articul ate the salience of creativity for rendering credible previously subjugated voices, and we articulate its value for engaged communication theory and research

Development of high resolution simulations of the atmospheric environment using the MASS model

Numerical simulations were performed with a very high resolution (7.25 km) version of the MASS model (Version 4.0) in an effort to diagnose the vertical wind shear and static stability structure during the Shuttle Challenger disaster which occurred on 28 January 1986. These meso-beta scale simulations reveal that the strongest vertical wind shears were concentrated in the 200 to 150 mb layer at 1630 GMT, i.e., at about the time of the disaster. These simulated vertical shears were the result of two primary dynamical processes. The juxtaposition of both of these processes produced a shallow (30 mb deep) region of strong vertical wind shear, and hence, low Richardson number values during the launch time period. Comparisons with the Cape Canaveral (XMR) rawinsonde indicates that the high resolution MASS 4.0 simulation more closely emulated nature than did previous simulations of the same event with the GMASS model