Linear differential operators on contact manifolds

We consider differential operators between sections of arbitrary powers of the determinant line bundle over a contact manifold. We extend the standard notions of the Heisenberg calculus: noncommutative symbolic calculus, the principal symbol, and the contact order to such differential operators. Our first main result is an intrinsically defined "subsymbol" of a differential operator, which is a differential invariant of degree one lower than that of the principal symbol. In particular, this subsymbol associates a contact vector field to an arbitrary second order linear differential operator. Our second main result is the construction of a filtration that strengthens the well-known contact order filtration of the Heisenberg calculus

Material, Trace, Trauma: Notes on some Recent Acquisitions at the Canadian War Museum and the Legacy of the First World War

Recent acquisitions at the Canadian War Museum are considered in relation to the radical innovations of soldier-artists who endured the somatic conditions of the First World War trenches, privileging materiality and psychic reality over visual perception. Barbara Steinman and Norman Takeuchi bring the past into the present through the indexical presence of black and white photographic fragments and the emotive presentation of lost objects as signifiers of the desires of the absent. Scott Waters and Mary Kavanagh evoke dread and the contingency of death through anamorphic distortion and blinding luminosity. Like the suggestive surfaces of the Museum itself, these works unsettle us to make palpable the psychic toll of war