Nonlinear development of matrix-converter instabilities

Matrix converters convert a three-phase alternating-current power supply to a power supply of a different peak voltage and frequency, and are an emerging technology in a wide variety of applications. However, they are susceptible to an instability, whose behaviour is examined herein. The desired “steady-state” mode of operation of the matrix converter becomes unstable in a Hopf bifurcation as the output/input voltage transfer ratio, q, is increased through some threshold value, qc. Through weakly nonlinear analysis and direct numerical simulation of an averaged model, we show that this bifurcation is subcritical for typical parameter values, leading to hysteresis in the transition to the oscillatory state: there may thus be undesirable large-amplitude oscillations in the output voltages even when q is below the linear stability threshold value qc.

The dynamics of professions and development of new roles in public services organizations: the case of modern matrons in the English NHS

This study contributes to research examining how professional autonomy and hierarchy impacts upon the implementation of policy designed to improve the quality of public services delivery through the introduction of new managerial roles. It is based on an empirical examination of a new role for nurses – modern matrons – who are expected by policy-makers to drive organizational change aimed at tackling health care acquired infections (HCAI) in the National Health Service (NHS) within England. First, we show that the changing role of nurses associated with their ongoing professionalization limits the influence of modern matrons over their own ranks in tackling HCAI. Second, the influence of modern matrons over doctors is limited. Third, government policy itself appears inconsistent in its support for the role of modern matrons. The attempts of modern matrons to tackle HCAI appear more effective where infection control activity is situated in professional practice and where modern matrons integrate aspirations for improved infection control within mainstream audit mechanisms in a health care organization.