Demonstration of the synchrotron-type spectrum of laser-produced Betatron radiation

Betatron X-ray radiation in laser-plasma accelerators is produced when electrons are accelerated and wiggled in the laser-wakefield cavity. This femtosecond source, producing intense X-ray beams in the multi kiloelectronvolt range has been observed at different interaction regime using high power laser from 10 to 100 TW. However, none of the spectral measurement performed were at sufficient resolution, bandwidth and signal to noise ratio to precisely determine the shape of spectra with a single laser shot in order to avoid shot to shot fluctuations. In this letter, the Betatron radiation produced using a 80 TW laser is characterized by using a single photon counting method. We measure in single shot spectra from 8 to 21 keV with a resolution better than 350 eV. The results obtained are in excellent agreement with theoretical predictions and demonstrate the synchrotron type nature of this radiation mechanism. The critical energy is found to be Ec = 5.6 \pm 1 keV for our experimental conditions. In addition, the features of the source at this energy range open novel perspectives for applications in time-resolved X-ray science.Comment: 5 pages, 4 figure

Data dissemination scheme for distributed storage for IoT observation systems at large scale

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Bias reduction in traceroute sampling: towards a more accurate map of the Internet

Traceroute sampling is an important technique in exploring the internet router graph and the autonomous system graph. Although it is one of the primary techniques used in calculating statistics about the internet, it can introduce bias that corrupts these estimates. This paper reports on a theoretical and experimental investigation of a new technique to reduce the bias of traceroute sampling when estimating the degree distribution. We develop a new estimator for the degree of a node in a traceroute-sampled graph; validate the estimator theoretically in Erdos-Renyi graphs and, through computer experiments, for a wider range of graphs; and apply it to produce a new picture of the degree distribution of the autonomous system graph.Comment: 12 pages, 3 figure

A propos des paysages urbains savoyards : l'importance et le rôle des petites villes dans l'histoire et la civilisation du XVe siècle

Leguay J.-P. A propos des paysages urbains savoyards : l'importance et le rôle des petites villes dans l'histoire et la civilisation du XVe siècle. In: Le Globe. Revue genevoise de géographie, tome 125, 1985. Les Alpes dans le temps et dans l'espace. pp. 171-183

Distributed Data Storage and Retrieval Schemes in RPL/IPv6-based networks

This chapter deals with distributed data storage and retrieval techniques in WSNs. The focus is on WSN systems for the Internet of Things (IoT), a new vision of the Internet aiming at pushing IP conne tivity into smart objects. The range of objects involved in the Internet of Things also encompasses Radio Frequency Identi ation (RFID) and Machine-to-Machine (M2M) systems, to cite a few. These technologies will be also described in detail