Labour mobility in the public sector: the impact of job opportunities

This paper investigates the mobility of highly skilled labour, using doctors in public hospitals in Denmark as an example. From the perspective of regional development, the concentration of human capital is one of the contributors to regional growth and consequently to inequality between places, being associated most often with differences in economic growth between regions. The decentralisation of highly skilled public jobs to even out the concentration of human capital could be one way to stimulate growth outside city regions. However, such initiatives are somewhat dependent upon the cooperation of the highly skilled public employees, whose preferences have been little studied thus far. Based on data from a survey of 1600 publicly employed doctors, PLUM regression modelling was applied to test the relative significance of four professional preferences influencing choice of workplace. It was found that professional preferences have different influences on doctors’ choices, depending on their place of residence measured in terms of a location’s population density. The paper concludes that opportunities in employment depend on one’s stage in life and can serve to explain choices and mobility among highly skilled public employees.     

Linear Waveform Tomography Inversion Using Machine Learning Algorithms

Mathematical Geosciences - A linear probabilistic waveform inversion strategy is proposed for crosshole tomographic data using machine learning algorithms that integrates a priori information...     

Laboratory Simulations of Supernova Shockwave Propagation

Supernovae launch spherical shocks into the circumstellar medium (CSM). These shocks have high Mach numbers and may be radiative. We have created similar shocks in the laboratory by focusing laser pulses onto the tip of a solid pin surrounded by ambient gas; ablated material from the pin rapidly expands and launches a shock through the surrounding gas. Laser pulses were typically 5 ns in duration with ablative energies ranging from 1–150 J. Shocks in ambient gas pressures of ~1 kPa were observed at spatial scales of up to 5 cm using optical cameras with schlieren. Emission spectroscopy data were obtained to infer electron temperatures (< 10 eV). In this experiment we have observed a new phenomena; at the edge of the radiatively heated gas ahead of the shock, a second shock forms. The two expanding shocks are simultaneously visible for a time, until the original shock stalls from running into the heated gas. The second shock remains visible and continues to expand. A minimum condition for the formation of the second shock is that the original shock is super-critical, i.e., the temperature distribution ahead of the original shock has an inflexion point. In a non-radiative control experiment the second shock does not form. We hypothesize that a second shock could form in the astrophysical case, possibly in radiative supernova remnants such as SN1993J, or in shock-CSM interaction.     

Differential rotation and reconnection as basic causes of some coronal reorientations

A process is suggested by which a coronal structure (with underlying filament) may form between a polar crown structure and a low-latitude bipolar region. During the ascending phase of the solar cycle the identifying underlying filament should lie poleward and westward of the active region, but during the descending phase it should appear as an eastward extension of the filament separating leader and follower photospheric fields within the active region.     

Refraction Scattering in the Anomalous Reflections from Icy Surfaces

The modes of scatter at radar targets are discussed and in particular the mode due to internal refraction in the target material whenever a gradual transition in the refractive index occurs. The importance of this arises mainly in planetary radar, as this could account for the unusual polarization effects observed on the icy satellites of the major planets and in certain parts of Mercury and Mars. Ices with their low radar surface reflectivity and low internal absorption would be the best naturally occurring materials to cause these effects. Indeed similar effects have been reported in radar observations over sections of the Greenland ice shelf. The nature of these effects can most easily be seen in the simple approximation of geometrical optics, and a more detailed discussion presented in the applicable electromagnetic theory confirms these results, even when the size of the inclusions is only on the order of a wavelength.     

On the prograde rotation of asteriods

Sets of diameter determinations before and after opposition for the asteriods Ceres, Pallas, Vesta, and Fortuna have been studied statistically for indications of spin direction. All four asteriods are tentatively found to have prograde spin. For Ceres, that conclusion is virtually certain.     

Dynamics of flare sprays

During solar cycle No. 20 new insight into the flare-spray phenomenon has been attained due to several innovations in solar optical-observing techniques (higher spatial resolution cinema-photography, tunable pass-band filters, multi-slit spectroscopy and extended angular field coronagraphs). From combined analysis of 13 well-observed sprays which occurred between 1969–1974 we conclude that (i) the spray material originates from a preexisting active region filament which undergoes increased absorption some tens of minutes prior to the abrupt chromospheric brightening at the flare-start, and (ii) the spray material is confined within a steadily expanding, loop-shaped (presumably magnetically controlled) envelope with part of the material draining back down along one or both legs of the loop.