Morphologie, croissance individuelle et dynamique des populations de la tortue verte (Chelonia mydas L.) au banc d'arguin (République islamique de Mauritanie)

The carapace morphology and growth of the Green turtle (Chelonia mydas L.) has been studied in a large (n = 177) sample of animals collected by the Imragen fishermen on the Banc d'Arguin (lslamic Republic of Mauretania). The frequency of anomalies of the scales decreases with age in this species, possibly due to a differentiai mortality between normal and abnormal individuals. The mathematical relation between length and width of the carapace is discussed and the Mauretanian data are compared with those of other areas. There are obvious differences in the shape of the carapace between different breeding populations of green turtles, which quite likely correspond to genetic differences between various breeding populations. The Mauretanian green turtles are quite similar to those breeding on the eastern coast of South-America. Seven age classes can be recognized on the basis of the carapace length. A growth curve of the Mauretanian population of Chelonia mydas L., based upon von Bertalanffy equation, is proposed. The rate of growth decreases sharply after the first breeding season. Sexual maturity takes place at 5.5 years of age, but age at first reproduction apparently varies from one population to the other, probably depending upon fishing pressure. The number of "bachelors" (mature individuals not taking part in reproduction) is apparently greater in areas with the smallest fishing pressur

The (theta, wheel)-free graphs Part I: Only-prism and only-pyramid graphs

Truemper configurations are four types of graphs (namely thetas, wheels, prisms and pyramids) that play an important role in the proof of several decomposition theorems for hereditary graph classes. In this paper, we prove two structure theorems: one for graphs with no thetas, wheels and prisms as induced subgraphs, and one for graphs with no thetas, wheels and pyramids as induced subgraphs. A consequence is a polynomial time recognition algorithms for these two classes. In Part II of this series we generalize these results to graphs with no thetas and wheels as induced subgraphs, and in Parts III and IV, using the obtained structure, we solve several optimization problems for these graphs

Observations of the relationship between frequency sweep rates of chorus wave packets and plasma density

International audience[1] Chorus emissions are generated by a nonlinear mechanism involving wave‐particle interactions with energetic electrons. Discrete chorus wave packets are narrowband tones usually rising (sometimes falling) in frequency. We investigate frequency sweep rates of chorus wave packets measured by the Wideband data (WBD) instrument onboard the Cluster spacecraft. In particular, we study the relationship between the sweep rates and the plasma density measured by the WHISPER active sounder. We have observed increasing values of the sweep rate for decreasing plasma densities. We have compared our results with results of simulations of triggered emissions as well as with estimates based on the backward wave oscillator model for chorus emissions. We demonstrate a reasonable agreement of our experimental results with theoretical ones. Citation: Macúšová, E., et al. (2010), Observations of the relationship between frequency sweep rates of chorus wave packets and plasma density

Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 1. Boundary structure and motion

We study plasma transport at a thin magnetopause (MP), described hereafter as a thin current sheet (TCS), observed by Cluster at the southern cusp on 13 February 2001 around 20:01 UT. The Cluster observations generally agree with the predictions of the Gas Dynamic Convection Field (GDCF) model in the magnetosheath (MSH) up to the MSH boundary layer, where significant differences are seen. We find for the MP a normal roughly along the GSE x-axis, which implies a clear departure from the local average MP normal, a ~90 km thickness and an outward speed of 35 km/s. Two populations are identified in the MSH boundary layer: the first one roughly perpendicular to the MSH magnetic field, which we interpret as the &quot;incident&quot; MSH plasma, the second one mostly parallel to <b>B</b>. Just after the MP crossing a velocity jet is observed with a peak speed of 240 km/s, perpendicular to <b>B</b>, with <i>M_A</i>=3 and &beta;>10 (peak value 23). The magnetic field clock angle rotates by 70&deg; across the MP. <i>E_x</i> is the main electric field component on both sides of the MP, displaying a bipolar signature, positive on the MSH side and negative on the opposite side, corresponding to a ~300 V electric potential jump across the TCS. The <i>E</i>&times;<i>B</i> velocity generally coincides with the perpendicular velocity measured by CIS; however, in the speed jet a difference between the two is observed, which suggests the need for an extra flow source. We propose that the MP TCS can act locally as an obstacle for low-energy ions (&lt;350 eV), being transparent for ions with larger gyroradius. As a result, the penetration of plasma by finite gyroradius is considered as a possible source for the jet. The role of reconnection is briefly discussed. The electrodynamics of the TCS along with mass and momentum transfer across it are further discussed in the companion paper by Savin et al. (2006)

Trimetric Imaging of the Martian Ionosphere Using a CubeSat Constellation

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143020/1/6.2017-5252.pd

Rosetta and Mars Express observations of the influence of high solar wind pressure on the Martian plasma environment

International audienceWe report on new simultaneous in-situ observations at Mars from Rosetta and Mars Express (MEX) on how the Martian plasma environment is affected by high pressure solar wind. A significant sharp increase in solar wind density, magnetic field strength and turbulence followed by a gradual increase in solar wind velocity is observed during ~24 h in the combined data set from both spacecraft after Rosetta's closest approach to Mars on 25 February 2007. The bow shock and magnetic pileup boundary are coincidently observed by MEX to become asymmetric in their shapes. The fortunate orbit of MEX at this time allows a study of the inbound boundary crossings on one side of the planet and the outbound crossings on almost the opposite side, both very close to the terminator plane. The solar wind and interplanetary magnetic field (IMF) downstream of Mars are monitored through simultaneous measurements provided by Rosetta. Possible explanations for the asymmetries are discussed, such as crustal magnetic fields and IMF direction. In the same interval, during the high solar wind pressure pulse, MEX observations show an increased amount of escaping planetary ions from the polar region of Mars. We link the high pressure solar wind with the observed simultaneous ion outflow and discuss how the pressure pulse could also be associated with the observed boundary shape asymmetry