Compensated Current Injection circuit, theory and applications

This paper presents a detailed description, analysis and example of practical application of a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops. This feature allows compensation for parasitic impedance connected in parallel with the useful load, which in turn keeps an excitation current flowing through the useful load independent of its impedance. The simplicity of the circuit and its good electrical properties are additional advantages of the scheme.Comment: 9 pages and 7 figures in one PDF fil

Hanté par la machine

International audienceLa fictionosphère regorge d'histoire de machines hantées par des esprits, mais les êtres humains ne peuvent-ils pas à leur tour être hantés par des machines

Gérer les risques avec les jeunes : État, cultures jeunes et (in)civilité

Si les jeunes se retrouvent sur le banc des accusés lors des débats sur l’insécurité, leurs pratiques culturelles sont également incriminées : c’est le cas, en France, de la culture hip-hop et des rave parties. Pourtant, il existe des formes de civilité « spontanée » à l’oeuvre dans ces pratiques, que l’État reconnaît et soutient progressivement. Le paradoxe est saisissant : d’un côté, l’État contribue à produire une demande de sécurité en investissant le domaine culturel et participe de la stigmatisation de la jeunesse ; de l’autre, l’État encourage certaines de ces pratiques dans l’optique d’une gestion des risques : risque d’exclusion sociale et territoriale, risque sanitaire, risque environnemental.Youth often stand accused in debates about insecurity, and their cultural practices are also incriminated. This is the case for hip-hop culture and raves in France. Nonetheless, there are forms of “spontaneous” civility in these practices, ones that the state recognises and increasingly supports. There is a striking paradox. On the one hand the state contributes to demands for security, by investing in the cultural field and stigmatising youth. On the other the state encourages certain practices, in order to manage risks such as the risk of social exclusion, health risks, and environmental risk

An insight into polarization states of solid-state organic lasers

The polarization states of lasers are crucial issues both for practical applications and fundamental research. In general, they depend in a combined manner on the properties of the gain material and on the structure of the electromagnetic modes. In this paper, we address this issue in the case of solid-state organic lasers, a technology which enables to vary independently gain and mode properties. Different kinds of resonators are investigated: in-plane micro-resonators with Fabry-Perot, square, pentagon, stadium, disk, and kite shapes, and external vertical resonators. The degree of polarization P is measured in each case. It is shown that although TE modes prevail generally (P>0), kite-shaped micro-laser generates negative values for P, i.e. a flip of the dominant polarization which becomes mostly TM polarized. We at last investigated two degrees of freedom that are available to tailor the polarization of organic lasers, in addition to the pump polarization and the resonator geometry: upon using resonant energy transfer (RET) or upon pumping the laser dye to an higher excited state. We then demonstrate that significantly lower P factors can be obtained.Comment: 12 pages, 12 figure

On the statistical interpretation of optical rogue waves

Numerical simulations are used to discuss various aspects of "optical rogue wave" statistics observed in noise-driven fiber supercontinuum generation associated with highly incoherent spectra. In particular, we consider how long wavelength spectral filtering influences the characteristics of the statistical distribution of peak power, and we contrast the statistics of the spectrally filtered SC with the statistics of both the peak power of the most red-shifted soliton in the SC and the maximum peak power across the full temporal field with no spectral selection. For the latter case, we show that the unfiltered statistical distribution can still exhibit a long-tail, but the extreme-events in this case correspond to collisions between solitons of different frequencies. These results confirm the importance of collision dynamics in supercontinuum generation. We also show that the collision-induced events satisfy an extended hydrodynamic definition of "rogue wave" characteristics.Comment: Paper accepted for publication in the European Physical Journal ST, Special Topics. Discussion and Debate: Rogue Waves - towards a unifying concept? To appear 201