Study on the cross-correlation of GNSS signals and typical approximations

In global navigation satellite system (GNSS) receivers, the first signal processing stage is the acquisition, which consists of detecting the received GNSS signals and determining the associated code delay and Doppler frequency by means of correlations with a code and carrier replicas. These codes, as part of the GNSS signal, were chosen to have very good correlation properties without considering the effect of a potential received Doppler frequency. In the literature, it is often admitted that the maximum GPS L1 C/A code cross-correlation is about ?24 dB. We show that this maximum can be as high as ?19.2 dB when considering a Doppler frequency in a typical range of [?5, 5] kHz. We also show the positive impact of the coherent integration time on the cross-correlation and that even a satellite with Doppler outside the frequency search space of a receiver impacts the cross-correlation. In addition, the expression of the correlation is often provided in the continuous time domain, while its implementation is typically made in the discrete domain. It is then legitimate to ask the validity of this approximation. Therefore, the purpose of this research is twofold: First, we discuss typical approximations and evaluate their regions of validity, and second, we provide characteristic values such as maximums and quantiles of the auto- and cross-correlation of the GPS L1 C/A and Galileo E1 OS codes in the presence of Doppler, for frequency ranges up to 50 kHz and for different integration times.     

Dislocations in olivine indented at low temperatures

Microhardness experiments have been performed on faces of olivine single crystals oriented at 45° to the [100] and [001] axis. Experiments have been performed between 20°C and 900°C in order to follow the evolution of the slip systems and the evolution of the nature of dislocations with temperature. Slip systems were identified using interferential contrast, decoration and transmission electron microscopy (TEM). Although the two possible Burgers vectors [001] and [100] are acted upon symmetrically, the only activated slip systems are (100) [001] and {110} [001]. The latter system is less developed and appears only at 600°C and above. Dislocations are mainly [001] screws, which are always very straight. Microcracks are observed together with dislocations. Above 600°C there is a clear relationship between both as a narrow plastic zone is developed around the cracks.     

Effect of decompression and suction on macroscopic and microscopic behavior of a clay rock

The goal in this research was to analyze the effects of decompression and suction on the formation of cracks in a clay rock from the Andra (French National Radioactive Waste Management Agency) site at Bure (Meuse–Haute-Marne, France). The article investigates the relationship between the changes in the hydromechanical properties and the changes in microstructure and porosity. Concerning the effect of decompression, at the macroscopic scale, the study highlighted an important effect on the elastic modulus and permeability, but little effect at the microscopic scale except an evolution of mineralogy related to the oxidation of pyrite often present in layers where cracks develop. Concerning the effect of suction, at the macroscopic level, the results showed that, on drying path, the change in the properties of the material was very small, whereas, on wetting path, a large decrease in tensile strength and gas permeability was observed. At the microscopic level, observations with SEM and ESEM, and measurements with MIP, highlighted the evolution of microstructural organization as a function of suction, and the propagation and enlargement of cracks on wetting path, rather than on drying path.     

Initiation and Propagation of Compaction Bands in Dry and Wet Bentheim Sandstone

We investigated initiation and propagation of compaction bands (CB) in six wet and four dry Bentheim sandstone samples deformed in axial compression tests with strain rates ranging from 3.2 × 10^?8 s^?1 to 3.2 × 10^?4 s^?1. Circumferential notches with 0.8-mm width and 5-mm depth served to initiate CB at mid-sample length. Wet samples were saturated with distilled water and deformed at 195 MPa confining pressure and 10 MPa pore pressure. Dry samples were deformed at 185 MPa confining pressure. Twelve P-wave sensors, eight S-wave sensors and two pairs of orthogonally oriented strain-gages were glued to the sample surface to monitor acoustic emission (AE), velocities and local strain during the loading process. Nucleation of compaction bands is indicated by AE clusters close to the notch tips. With progressive loading, AE activity increased and AE hypocenters indicated propagation of a single CB normal to the sample axis. CB propagation from the sample periphery towards the centre was monitored. Microstructural analysis of deformed samples shows excellent agreement between location of AE clusters and CBs. In both dry and wet samples the lateral propagation of CBs was about 100 times faster than axial shortening rates. At the slowest displacement rate, AE activity during band propagation was reduced and CB nucleation in wet samples occurred at 20% lower stresses. This may indicate an increasing contribution of stress corrosion processes to the formation of the compaction bands. In dry and wet samples inelastic compaction energy per area ranged between 16 and 80 kJ m^?2. This is in good agreement with previous estimates from laboratory and field studies.     

Estimates of sediment and nutrient loads in 10 major catchments draining to the Great Barrier Reef during 2006-2009

The Great Barrier Reef (GBR) catchment area has been monitored simultaneously for sediment and nutrient exports from 10 priority catchments discharging into the GBR lagoon between 2006 and 2009. This allows GBR catchment-wide exports to be estimated and spatially compared within a discrete time-frame. Elevated levels of sediment and nutrient exports were recorded in all monitored catchments as compared to pre-European estimates, but vary around previous estimates of mean annual loads. During the period of monitoring, the Burdekin and Fitzroy catchments contributed the highest sediment and nutrient exports, however when loads were normalised for area, these catchments produced the lowest unit yields. In contrast, the highest yields were produced in the wetter and proportionately more intensively cultivated Johnstone, O'Connell, and Pioneer catchments particularly for dissolved nitrogens. This assessment offers the necessary scientific foundation for future monitoring, assessment, and management of sediment and nutrient loads entering the GBR.     

Long-term monitoring of fish farms: application of Nematode/Copepod index to oligotrophic conditions

Interannual variability (2003-2008) of meiofaunal assemblages were analyzed in sediments beneath fish cages (Impact group) and in areas not affected by aquaculture activities (Control group). Organisms responded with spatial and seasonal variation in meiofauna assemblages, with an abrupt increase of abundances in locations beneath fish cages throughout the study period. This increase was greater during the last sampling year (2008) and mainly due to high abundances of nematodes. Univariate analyses showed differences between control and impacted sites at both sites, however, only significant variations were found in Los Gigantes, which are consistent with seasonal meiofauna variations throughout the study period. These results are partially explained by differences in current velocity between both sampling areas. The Ne/Co index showed the same trend and it seems to be a reliable index in sediment slightly affected by aquaculture wastes. This index is especially recommended in oligotrophic areas (e.g. Canary Islands) where meiofaunal assemblages are poorly represented in terms of abundances.