« Britain’s best kept secret » : la machine Enigma et le décodage des messages durant la Seconde Guerre mondiale

L’Enigma et ses cylindres permutables (Coll. Württembergische Landesbibliothek Stuttgart) © et cliché Württembergische Landesbibliothek Stuttgart / Larissa Arlt Un des plus grands mystères de la Seconde Guerre mondiale fut le décodage réussi des messages radio que les Allemands avaient cryptés grâce à la machine à coder « Enigma » (voir ill. ci-dessus). Jürgen Rohwer, ancien directeur de la Bibliothèque d’histoire contemporaine (Bibliothek für Zeitgeschichte–BfZ), s’est livré à des recherche..

A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes

Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth, time-averaged over extended periods. Although the technique lacks statistical power to make the critical hourly measurements that only specialized active instruments can achieve, we note the technique does not depend on absolute calibration of the detector hardware, and requires no additional equipment beyond the fluorescence detectors that observe the air showers. This paper describes the technique, and presents results based on analysis of 1258 air-showers observed in stereo by the High Resolution Fly's Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics Journa

Search for Global Dipole Enhancements in the HiRes-I Monocular Data above 10^{18.5} eV

Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs) consist of dipole distributions oriented towards major astrophysical landmarks such as the galactic center, M87, or Centaurus A. We use a comparison between real data and simulated data to show that the HiRes-I monocular data for energies above 10^{18.5} eV is, in fact, consistent with an isotropic source model. We then explore methods to quantify our sensitivity to dipole source models oriented towards the Galactic Center, M87, and Centaurus A.Comment: 17 pages, 31 figure

Observation of the Ankle and Evidence for a High-Energy Break in the Cosmic Ray Spectrum

We have measured the cosmic ray spectrum at energies above $10^{17}$ eV using the two air fluorescence detectors of the High Resolution Fly's Eye experiment operating in monocular mode. We describe the detector, PMT and atmospheric calibrations, and the analysis techniques for the two detectors. We fit the spectrum to models describing galactic and extragalactic sources. Our measured spectrum gives an observation of a feature known as the ``ankle'' near $3\times 10^{18}$ eV, and strong evidence for a suppression near $6\times 10^{19}$ eV.Comment: 14 pages, 9 figures. To appear in Physics Letters B. Accepted versio

Fundamental properties of Ca²⁺ signals

Background Ca²⁺ is a ubiquitous and versatile second messenger that transmits information through changes of the cytosolic Ca²⁺ concentration. Recent investigations changed basic ideas on the dynamic character of Ca²⁺ signals and challenge traditional ideas on information transmission. Scope of review We present recent findings on key characteristics of the cytosolic Ca²⁺ dynamics and theoretical concepts that explain the wide range of experimentally observed Ca²⁺ signals. Further, we relate properties of the dynamical regulation of the cytosolic Ca²⁺ concentration to ideas about information transmission by stochastic signals. Major conclusions We demonstrate the importance of the hierarchal arrangement of Ca²⁺ release sites on the emergence of cellular Ca²⁺ spikes. Stochastic Ca²⁺ signals are functionally robust and adaptive to changing environmental conditions. Fluctuations of interspike intervals (ISIs) and the moment relation derived from ISI distributions contain information on the channel cluster open probability and on pathway properties. General significance Robust and reliable signal transduction pathways that entail Ca²⁺ dynamics are essential for eukaryotic organisms. Moreover, we expect that the design of a stochastic mechanism which provides robustness and adaptivity will be found also in other biological systems. Ca2 + dynamics demonstrate that the fluctuations of cellular signals contain information on molecular behavior. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling. Highlights ► We review recent findings on key characteristics of cytosolic Ca²⁺ dynamics. ► We demonstrate the importance of the hierarchal arrangement of Ca²⁺ release sites. ► New theoretical concepts exploit emergent behavior of cellular Ca²⁺ spikes. ► We relate the dynamical regulation of [Ca²⁺] to information transmission. ► Stochastic Ca²⁺ signals are functionally robust and adaptive to changing conditions

Search for Point Sources of Ultra-High Energy Cosmic Rays Above 40 EeV Using a Maximum Likelihood Ratio Test

We present the results of a search for cosmic ray point sources at energies above 40 EeV in the combined data sets recorded by the AGASA and HiRes stereo experiments. The analysis is based on a maximum likelihood ratio test using the probability density function for each event rather than requiring an a priori choice of a fixed angular bin size. No statistically significant clustering of events consistent with a point source is found.Comment: 7 pages, 7 figures. Accepted for publication in The Astrophysical Journa