Communication Efficiency in Self-stabilizing Silent Protocols

Self-stabilization is a general paradigm to provide forward recovery capabilities to distributed systems and networks. Intuitively, a protocol is self-stabilizing if it is able to recover without external intervention from any catastrophic transient failure. In this paper, our focus is to lower the communication complexity of self-stabilizing protocols \emph{below} the need of checking every neighbor forever. In more details, the contribution of the paper is threefold: (i) We provide new complexity measures for communication efficiency of self-stabilizing protocols, especially in the stabilized phase or when there are no faults, (ii) On the negative side, we show that for non-trivial problems such as coloring, maximal matching, and maximal independent set, it is impossible to get (deterministic or probabilistic) self-stabilizing solutions where every participant communicates with less than every neighbor in the stabilized phase, and (iii) On the positive side, we present protocols for coloring, maximal matching, and maximal independent set such that a fraction of the participants communicates with exactly one neighbor in the stabilized phase

500 FS STREAK CAMERA FOR UV-HARD X RAYS IN 1KHZ ACCUMULATING MODE WITH OPTICAL -JITTER FREE-SYNCHRONISATION

Abstract The development at the ESRF of a jitter-free, laser triggered Streak Camera has now yielded time resolution results as short as 460fs while operating in accumulating mode. The so-called jitter-free synchronisation between the laser light and the Streak Camera is performed through a GaAs photo-switch in a simple HV circuit that connects directly to the Streak tube's deflection plates. The novelty of this technique permits to obtain excellent dynamic range measurements in a shot-to-shot accumulation of ultra fast (laser stimulated) events at up to 1Khz without degrading the time resolution. Important insight was obtained on the quality of this optical synchronisation and its dependence on the laser characteristics, the switch circuit, and the structure of the GaAs switch itself. This permitted to suppress the jitter causes and today the 500fs limitation is imposed by the streak tube's intrinsic time resolution. This work was done by measuring (with Au or Pd photo-cathodes) the 3 rd harmonic (i.e. 267nm) of a 100fs Ti:Saph laser. Also important progress was made with the reliability of the photo-switch and problems of HV break-down and structural degradation have been completely resolved. Since the principal use of this system at the ESRF is in ultra-fast X-ray diffraction experiments the exchangeable photo-cathode structure of this tube covers the entire UV-to-X-rays spectrum. The QE of various photo-cathode materials was measured in the 8-30KeV range