Specialist knowledge practices of craftsmen and clerics in Senegal

Special Issue: Knowledge in Practice: Expertise and the Transmission of Knowledge. Guest Editor: Kai Kresse and Trevor H. J. MarchandThis article examines the specialized knowledge practices of two sets of culturally recognized ‘experts’ in Senegal: Islamic clerics and craftsmen. Their respective bodies of knowledge are often regarded as being in opposition, and in some respects antithetical, to one another. The aim of this article is to examine this claim by means of an investigation of how knowledge is conceived by each party. The analysis attempts to expose local epistemologies, which are deduced from an investigation of ‘expert’ knowledge practices and indigenous claims to knowledge. The social processes of knowledge acquisition and transmission are also examined with reference to the idea of initiatory learning. It is in these areas that commonalities between the bodies of knowledge and sets of knowledge practices are to be found. Yet, despite parallels between the epistemologies of both bodies of expertise and between their respective modes of knowledge transmission, the social consequences of ‘expertise’ are different in each case. The hierarchical relations of power that inform the articulation of the dominant clerics with marginalized craftsmen groups serve to profile ‘expertise’ in different ways, each one implying its own sense of authority and social range of legitimacy.Publisher PDFPeer reviewe

Phase Behavior of Type-II Superconductors with Quenched Point Pinning Disorder: A Phenomenological Proposal

A general phenomenology for phase behaviour in the mixed phase of type-II superconductors with weak point pinning disorder is outlined. We propose that the ``Bragg glass'' phase generically transforms via two separate thermodynamic phase transitions into a disordered liquid on increasing the temperature. The first transition is into a glassy phase, topologically disordered at the largest length scales; current evidence suggests that it lacks the long-ranged phase correlations expected of a ``vortex glass''. This phase has a significant degree of short-ranged translational order, unlike the disordered liquid, but no quasi-long range order, in contrast to the Bragg glass. This glassy phase, which we call a ``multi-domain glass'', is confined to a narrow sliver at intermediate fields, but broadens out both for much larger and much smaller field values. The multi-domain glass may be a ``hexatic glass''; alternatively, its glassy properties may originate in the replica symmetry breaking envisaged in recent theories of the structural glass transition. Estimates for translational correlation lengths in the multi-domain glass indicate that they can be far larger than the interline spacing for weak disorder, suggesting a plausible mechanism by which signals of a two-step transition can be obscured. Calculations of the Bragg glass-multi-domain glass and the multi-domain glass-disordered liquid phase boundaries are presented and compared to experimental data. We argue that these proposals provide a unified picture of the available experimental data on both high-T$_c$ and low-T$_c$ materials, simulations and current theoretical understanding.Comment: 70 pages, 9 postscript figures, modified title and minor changes in published versio

Anomalous Peak Effect in CeRu2 and NbSe2 : Fracturing of a Flux Line Lattice?

CeRu2 and 2H-NbSe2 display remarkable similarities in their magnetic response, reflecting the manner in which the weakly pinned flux line lattice (FLL) loses spatial order in the Peak Effect (PE) regime. The discontinuous change in screening response near the onset of PE and the history dependence in it are attributed to a disorder-induced fracturing transition of the FLL, as an alternative to the scenario involving the appearance of a spatial modulation in superconducting order parameter in CeRu2.Comment: 4 pages of text and figures in ps for