Conductivity of underdoped YBa2Cu3O7-d : evidence for incoherent pair correlations in the pseudogap regime

Conductivity due to superconducting fluctuations studied in optimally doped YBa2Cu3O7-d films displays a stronger decay law in temperature than explainable by theory. A formula is proposed, which fits the data very well with two superconductive parameters, Tc and the coherence length ksi_c0, and an energy scale Delta*. This is also valid in underdoped materials and enables to describe the conductivity up to 300 K with a single-particle excitations channel in parallel with a channel whose contribution is controlled by ksi_c0, Tc and Delta*. This allows to address the nature of the pseudogap in favour of incoherent pairing.Comment: 14 pages, 4 figures, 1 tabl

Identification of hip fracture patients from radiographs using Fourier analysis of the trabecular structure: a cross-sectional study

Peer reviewedPublisher PD

Determination of the trabecular bone direction from digitised radiographs

There is increasing evidence for monitoring the bone trabecular structure to explain, in part, the mechanical properties of bone. Despite the emergence of Computed Tomography, a radiograph is the standard format as it is cheap and used for assessing implant performance. Furthermore, various image-processing techniques developed to assess the trabecular structure from radiographs have regained interest owing to improvements in imaging equipment. This study assessed the precision and accuracy of the Co-occurrence and Run-length matrix, Spatial-frequency and Minkowski-fractal techniques to infer the trabecular direction from radiographs. Ten clinical images of femoral neck regions were obtained from digitised pelvic radiographs and subsequently analysed. These data were also used to generate synthetic images where the trabecular thickness, separation and directions were controlled in order to calculate the accuracy of the techniques. Additionally, a Laplacian noise was added in order to infer the precision of the techniques. All methods assessed the trabecular direction with a high degree of accuracy in these synthetic images including a single direction and no noise. However, only the Spatial-frequency and Co-occurrence matrix methods performed well on the clinical and heavily corrupted synthetic images. This demonstrated the possibility of inferring a linear trabecular direction in clinical conditions.</p

Impact of soil water content on the overturning resistance of young Pinus Pinaster in sandy soil

Background and aims: The tree resistance to uprooting is crucial to face wind damage in temperate forest. Tree anchorage varies considerably with site conditions, species, and tree age. Only few studies have focused on the influence of the site soil properties on the tree anchorage. With ongoing climate change, the soil hydrologic conditions are changing in Europe due to higher precipitations during winter, with possible higher risk of wind damage in forests.Methods: This study investigates the role of soil hydrology on tree anchorage of Pinus pinaster in sandy soil with a combination of field experiments and simulations. Tree pulling experiments until root-soil system failure were performed for 12 Pinus pinaster of 14 years-old growing in podzol to measure the tree resistance to uprooting M-c for two contrasted soil water conditions. In addition, simulations were conducted to analyze how M-c changes during the progressive wetting of the layered soil. For that purpose, a new model was developed for M-c. This model also includes a sub-model for the shear mechanical strengths of the sandy soil layers and their variation with soil water content. The model was calibrated with different data sets: (1) the M-c-data obtained from the tree pulling experiments performed on 14 years-old Pinus pinaster; (2) the 3D root system architectures of the pulled trees; and (3) the soil shear mechanical strength as function of the soil water content measured in laboratory by direct shear tests and soil water retention curve measurements. After calibration,-calculations were performed when simulating a progressive soil wetting by water table increase or by water saturation front progression.Results: Field-data and simulations show that M-c depends little on soil water content outside the domain of complete soil saturation. Close to saturation, simulations show that M-c decreases drastically up to 40 % of its value. This is specific to sandy soil whose mechanical strength is mainly due to the capillarity forces between grains. As illustrated by simulations, the anchorage resistance results from two components. The first friction component slightly increases with soil water content. The second suction component decreases little with soil water content and drops down at saturation when all the interstitial water in the soil porous network merges.Conclusions: This loss of anchorage resistance at full saturation may increase considerably the risk of wind damage of forest growing in sandy soil as floods increase with climate change in Europe.Réponse de l'arbre aux vents fortsAdaptation sylvicole et économique de l'aménagement forestier au risque ventCOntinental To coastal Ecosystems: evolution, adaptability and governanc