Nonlinear mirror instability

Slow dynamical changes in magnetic-field strength and invariance of the particles' magnetic moments generate ubiquitous pressure anisotropies in weakly collisional, magnetized astrophysical plasmas. This renders them unstable to fast, small-scale mirror and firehose instabilities, which are capable of exerting feedback on the macroscale dynamics of the system. By way of a new asymptotic theory of the early nonlinear evolution of the mirror instability in a plasma subject to slow shearing or compression, we show that the instability does not saturate quasilinearly at a steady, low-amplitude level. Instead, the trapping of particles in small-scale mirrors leads to nonlinear secular growth of magnetic perturbations, $\delta B/B \propto t^{2/3}$. Our theory explains recent collisionless simulation results, provides a prediction of the mirror evolution in weakly collisional plasmas and establishes a foundation for a theory of nonlinear mirror dynamics with trapping, valid up to $\delta B/B =O(1)$.Comment: 5 pages, submitte

La destination finale de l’épargne des ménages.

Après prise en compte des opérations d’intermédiation, le patrimoine financier des ménages apparaît plus fortement investi en titres de dette publique et davantage diversifié au plan géographique que dans sa structure initiale.Ménages, patrimoine financier, enquête patrimoine, épargne, intermédiation, diversification, dépôts, crédits, titres de créance, valeurs mobilières, actions, OPCVM, sociétés d’assurance.

Factors influencing consideration of dental specialisation: a survey of current dental students at the University of Western Australia

Aim. At present, little research exists regarding factors that influence dental students and recent graduates to pursue specialist training. Through the provision of a questionnaire, the study investigated student's perceptions of dental specialities and factors impacting specialisation.Methods. Questionnaires (n=65) were undertaken by Doctor of Dental Medicine students in year three (n=34) and four (n=31) through paper means. An analysis was undertaken of the knowledge of speciality courses, speciality preferences and the main motivating and deterring factors influencing specialisation.Results. A response rate of 70% was observed, revealing that 13% of all participants correctly identified the speciality courses available in Western Australia, with 6% of students wanting to specialise in the long term. Altruistic factors were most motivating and financial most deterring when considering specialisation. Speciality preferences also varied between cohorts.Conclusions. Findings highlight that a small proportion of students want to pursue specialisation and the majority of students are unaware of the speciality courses available in Western Australia. This emphasises the need for greater exposure and education in dental specialties. Further research is advised in this field to better understand factors involved in the pathway to dental specialisation and how to encourage specialisation

ICT spillovers, absorptive capacity and productivity performance

We analyse the impact of ICT spillovers on productivity in the uptake of the new technology using company data for the U.S. We account for inter- and intra-industry spillovers and assess the role played by firm’s absorptive capacity. Our results show that intra-industry ICT spillovers have a contemporaneous negative effect that turns positive 5 years after the initial investment. By contrast, inter-industry spillovers are important both in the short and in the long run. In the short run, companies’ innovative effort is complementary to ICT spillovers, but such complementarity disappears with the more pervasive adoption and diffusion of the technology