Nonconservative current-driven dynamics: beyond the nanoscale

Long metallic nanowires combine crucial factors for nonconservative current-driven atomic motion. These systems have degenerate vibrational frequencies, clustered about a Kohn anomaly in the dispersion relation, that can couple under current to form nonequilibrium modes of motion growing exponentially in time. Such motion is made possible by nonconservative current-induced forces on atoms, and we refer to it generically as the waterwheel effect. Here the connection between the waterwheel effect and the stimulated directional emission of phonons propagating along the electron flow is discussed in an intuitive manner. Nonadiabatic molecular dynamics show that waterwheel modes self-regulate by reducing the current and by populating modes in nearby frequency, leading to a dynamical steady state in which nonconservative forces are counter-balanced by the electronic friction. The waterwheel effect can be described by an appropriate effective nonequilibrium dynamical response matrix. We show that the current-induced parts of this matrix in metallic systems are long-ranged, especially at low bias. This nonlocality is essential for the characterisation of nonconservative atomic dynamics under current beyond the nanoscale.

Shadow policing: the boundaries of community-based ‘policing’ in Northern Ireland

The intention of this article is to provide a structural and operational analysis of policing beyond the police in Northern Ireland. While the polity enjoys low levels of ‘officially’ recorded crime as part of its post-conflict status, little empirical analysis exists as to the epistemological roots of security production outside that of the Police Service of Northern Ireland. The empirical evidence presented seeks to establish that beyond more prominent analyses related to paramilitary ‘policing’, the country is in fact replete with a substantial reservoir of legitimate civil society policing – the collective mass of which contributes to policing, community safety and quality of life issues. While such non-state policing at the level of locale was recognised by the Independent Commission for Policing, structured understandings have rarely permeated governmental or academic discourse beyond anecdotal contentions. Thus, the present argument provides an empirical assessment of the complex, non-state policing landscape beyond the formal state apparatus; examines definitions and structures of such community-based policing activities; and explores issues related to co-opting this non-state security ‘otherness’ into more formal relations with the state.