Attention to Wi-Fi Diversity: Resource Management in WLANs with Heterogeneous APs

Many home networks integrate a small number (typically 2-4) of Wi-Fi Access Points (APs), with heterogeneous characteristics: different 802.11 variants, capabilities and security schemes. This paper proposes the consideration of these specific characteristics in order to improve the management of network resources. Three use cases are presented in order to showcase the potential benefits. By the use of a user-space AP, which works in coordination with a controller, the network is able to assign each connected station to the AP that best fits with its characteristics. The system also manages security, avoiding the need of adding specific elements for authentication, encryption or decryption. Extensions are proposed to an existing protocol that defines the communication between the AP and the controller, in order to communicate and store the specific characteristics of each AP and end device. This includes new association and handoff schemes that do not introduce any additional delay. The system has been implemented in a real environment, and a battery of tests has been run using three hardware platforms of different characteristics. The results show that handoffs between bands are possible, and estimate the processing delays, the Round-Trip Time and the handoff delay, which is small enough in order not to produce any significant disruption to the user (10-50 ms). Finally, the scenarios of interest have been replicated in a simulation environment, showing that significant benefits can be achieved if the specific characteristics of each AP and station are considered

Magnetic field induced by elliptical instability in a rotating spheroid

International audienceThe tidal or elliptical instability of rotating fluid flows is generated by the resonant interaction of inertial waves. In a slightly elliptically deformed rotating sphere, the most unstable linear mode is called the spin-over mode and is a solid body rotation versus an axis aligned with the maximum strain direction. In the non viscous case, this instability corresponds to the median moment of inertia instability of solid rotating bodies. This analogy is furthermore illustrated by an elliptical top experiment, which shows the expected inviscid heteroclinic behaviour. In geophysics, the elliptical instability may appear in the molten liquid cores of rotating planets, which are slightly deformed by tidal gravitational effects of close bodies. It may then participate to the general outer core dynamics and possibly to the geodynamo process. In this context, Kerswell and Malkus (Kerswell, R.R. and Malkus, W.V.R., Tidal instability as the source for Io's magnetic signature, Geophys. Res. Lett., 1998, 25, 603-606) showed that the puzzling magnetic field of the Jovian satellite Io may indeed be induced by the elliptically unstable motions of its liquid core that deflect Jupiter magnetic field. Our magnetohydrodynamics experiment is a toy-experiment of this geophysical situation and demonstrates for the first time the possibility of an induction of a magnetic field by the flow motions due to the elliptical instability. A full analytical calculation of the magnetic dipole induced by the spin-over is presented. Finally, exponential growths of this induced magnetic field in a slightly deformed rotating sphere filled with Galinstan liquid metal are measured for different rotating rates. Their growth rates compare well with theoretical predictions in the limit of a vanishing Lorentz force

Quelle place pour une alimentation low-carb ou à index glycémique bas dans le diabète gestationnel ? [What is the place of a low carbohydrate or low glycemic index diet in gestational diabetes treatment?]

There is no real consensus on the ideal nutritional approach to recommend for gestational diabetes (GDM) treatment. A carbohydrates reduction (low-carb) is frequently suggested, although many studies have not found any consistent beneficial effects. On the other hand, according to recent meta-analyses, a low glycemic index (GI) diet would have favorable effects for the mother and the child. Although the clinical and practical value of GI is still being studied, a low GI diet seems to be the most appropriate approach in GDM. In addition, soluble fibers may have a beneficial metabolic impact in the short time of pregnancy. More evidence on the impact of these nutritional approaches in the short and long term for mother and child is needed