Improved model for the analysis of air fluorescence induced by electrons

A model recently proposed for the calculation of air-fluorescence yield excited by electrons is revisited. Improved energy distributions of secondary electrons and a more realistic Monte Carlo simulation including some additional processes have allowed us to obtain more accurate results. The model is used to study in detail the relationship between fluorescence intensity and deposited energy in a wide range of primary energy (keVs - GeVs). In addition, predictions on the absolute value of the fluorescence efficiency in the absence of collisional quenching will be presented and compared with available experimental data.Comment: Contribution to the 5th Fluorescence Workshop, El Escorial, Madrid, Spain, September 2007, to appear in Nuclear Instruments and Methods A. Revised version.- More details on the comparison with experimental dat

A first approach to model the low-frequency wave activity in the plasmasphere

International audienceA comprehensive empirical model of waves is developed in the objective to simulate wave-particle interactions involved in the loss and acceleration of radiation belt electrons. Three years of measured magnetic wave field components from the Plasma Wave Instrument on board the DE-1 satellite are used to model the amplitude spectral density of the magnetic wave field of each type of emission observed in the equatorial regions of the plasmasphere: VLF transmitter emissions, chorus emissions, plasmaspheric hiss emissions and equatorial emissions below ~ 200 Hz. Each model is a function of the wave frequency f , the MLT, L and Mlat parameters, and the Kp values. The performances of the plasmaspheric hiss and chorus models are tested on amplitude spectra recorded on board the OGO-5 and GEOS-1 satellites

Low-latitude ionospheric turbulence observed by Aureol-3 satellite

Using PSD (Power Spectral Density) data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form <i>k<sup>-α</sup></i>, where <i>k</i> is the wave number and α is the spectral index. At first, high-resolution data in the near-equator region for several orbits have been processed. In this case the frequency range is from 6Hz to 100Hz (corresponding spatial scales from 80m to 1.3km), each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with α<sub><i>N</i></sub>=2.2±0.3 and α<sub><i>E</i></sub>=1.8±0.2, for the density and electric field, respectively. Then we produce a statistical study of 96 electric field bursts in the frequency range 10-100Hz from low-time resolution data (filter bank envelope). These bursts concentrate on the side of the Equatorial Anomaly crest (geomagnetic latitude 30-40°). Spectral indices of the bursts vary in the interval α<sub><i>E</i></sub>=2.0-2.5 but are fairly stable in seasons and local times. The electric field power of the burst has rather a large variability but has a relative increase in mean values for the summer and winter, as well as the daytime. The effect of major seismic activities toward the ionospheric turbulence is not conclusive either for the refractive index or for the electric field power. However, the mean value for the electric field power of bursts during seismic periods is larger than that for non seismic periods, and the statistical difference of the mean values is rather significant

Utilisation de tests basés sur des statistiques d'ordre supérieur dans l'analyse de séries temporelles mesurées dans l'espace

Tests of hypotheses based on Higher Order Statistics (HOS) are reviewed in the particular context of the identification of nonlinear processes in space plasma. The time series under study are associated with the measurements of electric or/and magnetic field components, or/and counting rates of particles. The basic principles of HOS techniques are reviewed. A general and unified procedure is suggested in order to construct statistical tests: (1) for detecting a non-gaussian or transient signal in a gaussian (or non-gaussian) noise, (2) testing a stochastic time series for non-gaussianity (including non-linearity), (3) studying non-linear wave interactions by using the kth-order coherency function. Asymptotic theory of estimates of the kthorder spectra is implemented in a digital signal processing framework. The effectiveness of the signal detection algorithms is demonstrated through computer simulations. Examples of application on the analysis of satellite data are given.Des tests d'hypothèses basés sur des statistiques d'ordre supérieur sont revus dans le contexte particulier de l'identification de processus non-linéaires dans les plasmas spatiaux. Les séries temporelles étudiées sont associées à la mesure de composantes du champ électrique et/ou magnétique d'ondes ou de turbulences, et/ou de données particules. Les principes de base des statistiques d'ordre supérieur sont brièvement rappelés. Une procédure générale et unifiée est suggérée afin de construire des tests statistiques permettant: (1) de détecter des signaux non-gaussiens ou transitoires au sein d'un bruit gaussien (ou non-gaussien), (2) de tester si une série temporelle est associée ou non à un processus stochastique issu d'un processus non-linéaire, (3) d'étudier des interactions non-linéaires à plusieurs ondes par l'utilisation de la fonction de cohérence d'ordre k. La théorie asymptotique des estimés des spectres d'ordre k est mise en oeuvre dans le cas discret. L'efficacité des algorithmes de détection est démontrée par le biais de simulations numériques. Des exemples d'applications à des données satellites sont présentés

The Magnetic Distortion Calibration System of the LHCb RICH1 Detector

The LHCb RICH1 detector uses hybrid photon detectors (HPDs) as its optical sensors. A calibration system has been constructed to provide corrections for distortions that are primarily due to external magnetic fields. We describe here the system design, construction, operation and performance.Comment: 9 pages, 14 figure

Comparison of available measurements of the absolute fluorescence yield

The uncertainty in the absolute value of the fluorescence yield is still one of the main contributions to the total error in the reconstruction of the primary energy of ultra-energetic air showers using the fluorescence technique. A significant number of experimental values of the fluorescence yield have been published in the last years, however reported results are given very often in different units (photons/MeV or photons/m) and for different wavelength intervals. In this work we present a comparison of available results normalized to its value in photons/MeV for the 337 nm band at 800 hPa and 293 K. The conversion of photons/m to photons/MeV requires an accurate determination of the energy deposited by the electrons in the field of view of the experimental setup. We have calculated the energy deposition for each experiment by means of a detailed Monte Carlo simulation including when possible the geometrical details of the particular setup. Our predictions on deposited energy, as well as on some geometrical factors, have been compared with those reported by the authors of the corresponding experiments and possible corrections to the fluorescence yields are proposed.Comment: 29 pages, 5 figures Revised version submitted to Astroparticle Physic

Cadmium isotope fractionation in soil-cacao systems of Ecuador: a pilot field study

The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil – cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0–80 cm depth have very similar δ114/110Cd of about −0.1‰ to 0‰. Two 0–5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ114/110Cd ≈ 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Δ114/110Cdleaf–soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ114/110Cdbean–leaf that may be linked to distinct cacao cultivars. In detail, Δ114/110Cdbean–leaf values of −0.34‰ to −0.40‰ were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (−0.08 ± 0.13‰). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated

Possible seismo-ionosphere perturbations revealed by VLF signals collected on ground and on a satellite

The results of the monitoring of three VLF/LF signals collected in Petropavlovsk station (Kamchatka, Russia) and one VLF signal collected on board of the DEMETER French satellite are presented. Two periods of the seismic activity occurred in the Japan-Kamchatka area during November–December 2004 and July–September 2005 were investigated and the earthquakes with M≥6.0 in the Japan-Kamchatka area, located inside one or more of the third Fresnel zones of the three radio paths were considered. The ground data were analysed using residual signal of phase <i>dP</i> or of amplitude <i>dA</i>, defined as the difference between the signal and the average of few quiet days (±5 days) immediately preceding or following the current day. Also the satellite data were processed by a method based on the difference between the real signal and the reference one, but in order to obtain this last signal it was necessary to construct previously a model of the signal distribution over the selected area. The method consists: (a) in averaging all the data available in the considered region over a period characterized by low level seismicity, regardless of the global disturbances, in particular, of the magnetic activity; (b) in computing a polynomial expression for the surface as a function of the longitude and the latitude. The model well describes the real data in condition of their completeness and in absence of magnetic storms or seismic forcing. In the quoted periods of seismic activity clear anomalies both in the ground and in satellite data were revealed. The influence of the geomagnetic activity cannot to be excluded, but the seismic forcing seems more probable