158 research outputs found
Early cosmic ray research in France
International audienceThe French research on cosmic rays in the first half of the 20th century is summarized. The main experiments are described as the discovery of air cosmic ray showers by Pierre Auger. The results obtained at the French altitude laboratories like the "Pic du Midi de Bigorre" are also briefly presented
Are vertical cosmic rays the most suitable to radio detection ?
The electric field induced by extensive air showers generated by high energy
cosmic rays is considered and, more specifically, its dependence on the shower
incident angle. It is shown that for distances between the shower axis and the
observation point larger than a few hundred meters, non-vertical showers
produce larger fields than vertical ones. This may open up new prospects since,
to some extent, the consideration of non-vertical showers modifies the scope of
the radio-detection domain.Comment: 8 pages, 4 figure
Development of a radio-detection method array for the observation of ultra-high energy neutrino induced showers
The recent demonstration by the CODALEMA Collaboration of the ability of the
radio-detection technique for the characterization of UHE cosmic-rays calls for
the use of this powerful method for the observation of UHE neutrinos. For this
purpose, an adaptation of the existing 21CM Array (China) is presently under
achievment. In an exceptionally low electromagnetic noise level, 10160
log-periodic 50-200 MHz antennas sit along two high valleys, surrounded by
mountain chains. This lay-out results in 30-60 km effective rock thicnesses for
neutrino interactions with low incidence trajectories along the direction of
two 4-6 km baselines. We will present first in-situ radio measurements
demonstrating that this environment shows particularly favourable conditions
for the observation of electromagnetic decay signals of taus originating from
the interaction of 10^17-20 eV tau neutrinos.Comment: 4pages, 3 figures, Contribution to appear in the proceedings of ARENA
2008 conferenc
Réalisation d'un systÚme d'émission-réception 4 canaux dédié au cerveau de rat pour un systÚme RM à 7T
International audienceUn systÚme ainsi qu'une bobine d'émission-réception ont été réalisés pour un systÚme RM à 7 T. Ce systÚme d'émission-réception 4 canaux permet de créer un champ magnétique RF B1+ polarisé circulairement. La combinaison constructive des phases des 4 canaux a été démontrée par des images RM
Circadian rhythms regulate the environmental responses of net CO2 exchange in bean and cotton canopies
Studies on the dependence of the rates of ecosystem gas exchange on environmental parameters often rely on the up-scaling of leaf-level response curves ('bottom-up' approach), and/or the down-scaling of ecosystem fluxes ('top-down' approach), where one takes advantage of the natural diurnal covariation between the parameter of interest and photosynthesis rates. Partly independent from environmental variation, molecular circadian clocks drive âŒ24 h oscillations in leaf-level photosynthesis, stomatal conductance and other physiological processes in plants under controlled laboratory conditions. If present and of sufficient magnitude at ecosystem scales, circadian regulation could lead to different results when using the bottom-up approach (where circadian regulation exerts a negligible influence over fluxes because the environment is modified rapidly) relative to the top-down approach (where circadian regulation could affect fluxes as it requires the passage of a few hours). Here we dissected the drivers of diurnal net CO2 exchange in canopies of an annual herb (bean) and of a perennial shrub (cotton) through a set of experimental manipulations to test for the importance of circadian regulation of net canopy CO2 exchange, relative to that of temperature and vapor pressure deficit, and to understand whether circadian regulation could affect the derivation of environmental flux dependencies. Contrary to conventional wisdom, we observed how circadian regulation exerted controls over net CO2 exchange that were of similar magnitude to the controls exerted by direct physiological responses to temperature and vapor pressure deficit. Diurnal patterns of net CO2 exchange could only be explained by considering effects of environmental responses combined with circadian effects. Consequently, we observed significantly different results when inferring the dependence of photosynthesis over temperature and vapor pressure deficit when using the top-down and the bottom up approaches.We remain indebted to E. Gerardeau, D. Dessauw, J. Jean, P. Prudent (AĂŻda CIRAD), J.-J. Drevon, C. Pernot (Eco&Sol INRA), B. Buatois, A. Rocheteau (CEFE CNRS), A. Pra, A. Mokhtar and the full Ecotron team, in particular C. Escape, for outstanding technical assistance during experiment set-up, plant cultivation and measurements. Earlier versions of the manuscript benefitted from comments by M. Dietze, B. Medlyn, R. Duursma and Y.-S. Lin. This study benefited from the CNRS human and technical resources allocated to the ECOTRONS Research Infrastructures as well as from the state allocation âInvestissement d'Avenirâ ANR-11-INBS-0001, ExpeER Transnational Access program, RamĂłn y Cajal fellowships (RYC-2012-10970 to VRD and RYC-2008-02050 to JPF), the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR) and internal grants from UWS-HIE to VRD and ZALF to AG. We thank the Associate Editor T. Vesala and two anonymous reviewers for their help to improve this manuscript
Post-starburst galaxies: more than just an interesting curiosity
From the VIMOS VLT DEEP Survey (VVDS) we select a sample of 16 galaxies with
spectra which identify them as having recently undergone a strong starburst and
subsequent fast quenching of star formation. These post-starburst galaxies lie
in the redshift range 0.510^9.75Msun. They have a number
density of 1x10^-4 per Mpc^3, almost two orders of magnitude sparser than the
full galaxy population with the same mass limit. We compare with simulations to
show that the galaxies are consistent with being the descendants of gas rich
major mergers. Starburst mass fractions must be larger than ~5-10% and decay
times shorter than ~10^8 years for post-starburst spectral signatures to be
observed in the simulations. We find that the presence of black hole feedback
does not greatly affect the evolution of the simulated merger remnants through
the post-starburst phase. The multiwavelength spectral energy distributions of
the post-starburst galaxies show that 5/16 have completely ceased the formation
of new stars. These 5 galaxies correspond to a mass flux entering the
red-sequence of rhodot(A->Q, PSB) = 0.0038Msun/Mpc^3/yr, assuming the defining
spectroscopic features are detectable for 0.35Gyr. If the galaxies subsequently
remain on the red sequence, this accounts for 38(+4/-11)% of the growth rate of
the red sequence. Finally, we compare our high redshift results with a sample
of galaxies with 0.05<z<0.1 observed in the SDSS and UKIDSS surveys. We find a
very strong redshift evolution: the mass density of strong post-starburst
galaxies is 230 times lower at z~0.07 than at z~0.7.Comment: 18 pages, 12 figures, to match version accepted to MNRAS. Minor
reordering of text in places and Sec 2.2 on SPH simulation comparisons
expande
The zCOSMOS 10k-Bright Spectroscopic Sample
We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(â1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed
Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions
Background Molecular clocks drive oscillations in leaf photosynthesis,
stomatal conductance, and other cell and leaf-level processes over ~24 h under
controlled laboratory conditions. The influence of such circadian regulation
over whole-canopy fluxes remains uncertain; diurnal CO2 and H2O vapor flux
dynamics in the field are currently interpreted as resulting almost
exclusively from direct physiological responses to variations in light,
temperature and other environmental factors. We tested whether circadian
regulation would affect plant and canopy gas exchange at the Montpellier
European Ecotron. Canopy and leaf-level fluxes were constantly monitored under
field-like environmental conditions, and under constant environmental
conditions (no variation in temperature, radiation, or other environmental
cues). Results We show direct experimental evidence at canopy scales of the
circadian regulation of daytime gas exchange: 20â79 % of the daily variation
range in CO2 and H2O fluxes occurred under circadian entrainment in canopies
of an annual herb (bean) and of a perennial shrub (cotton). We also observed
that considering circadian regulation improved performance by 8â17 % in
commonly used stomatal conductance models. Conclusions Our results show that
circadian controls affect diurnal CO2 and H2O flux patterns in entire canopies
in field-like conditions, and its consideration significantly improves model
performance. Circadian controls act as a âmemoryâ of the past conditions
experienced by the plant, which synchronizes metabolism across entire plant
canopies
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