Une méthode de décomposition en temps avec des schémas dʼintégration réversible pour la résolution de système dʼéquations différentielles ordinaires

We propose a time domain decomposition method that breaks the sequentiality of the integration scheme for systems of ODE. Under the condition of differentiability of the flow, we transform the initial value problem into a well-posed boundary values problem using the symmetrization of the interval of time integration and time-reversible integration scheme. For systems of linear ODE, we explicitly construct the block tridiagonal system satisfied by the solutions at the time sub-intervals extremities. We then propose an iterative algorithm of Schwarz type for updating the interfaces conditions which can extend the method to systems of nonlinear ODE.     

On the value of the critical point in fractal percolation

We derive a new lower bound p_c>0.8107 for the critical value of Mandelbrot's dyadic fractal percolation model. This is achieved by taking the random fractal set (to be denoted A_∞) and adding to it a countable number of straight line segments, chosen in a certain (nonrandom) way as to simplify greatly the connectivity structure. We denote the modified model thus obtained by C_∞, and write C_n for the set formed after n steps in its construction. Now it is possible, using an iterative technique, to compute the probability of percolating through C_n for any parameter value p and any finite n. For p=0.8107 and n=360 we obtain a value less than 10^?5; using some topological arguments it follows that 0.8107 is subcritical for C_∞ and hence (since _∞ dominates A_∞) for A_∞. ©2001 John Wiley & Sons, Inc. Random Struct. Alg., 18: 332–345, 2001.     

Formation and Etching of the Insulating Sr-Rich V5+ Phase at the Metallic SrVO3 Surface Revealed by Operando XAS Spectroscopy Characterizations

In the search of low cost and more efficient electronic devices, here the properties of SrVO₃ transparent conductor oxide (TCO) thin film are investigated, both visible-range optically transparent and highly conductive, it stands as a promising candidate to substitute the standard indium-tin-oxide (ITO) in applications. Its surface stability under water (both liquid and vapor) and other gaseous atmospheres is especially addressed. Through the use of spectroscopy characterizations, X-ray photoemission and operando X-ray absorption measurements, the formation of a thin Sr-rich V⁵⁺ layer located at the surface of the polycrystalline SrVO₃ film with aging is observed, and for the first time how it can be removed from the surface by solvating in water atmosphere. The surface recovery is associated to an etching process, here spectroscopically characterized in operando conditions, allowing to follow the stoichiometric modification under reaction. Once exposed in oxygen atmosphere, the Sr-rich V⁵⁺ layer forms again. The findings improve the understanding of aging effects in perovskite oxides, allowing for the development of functionalized films in which it is possible to control or to avoid an insulating surface layer. This constitutes an important step towards the large-scale use of V-based TCOs, with possible implementations in oxide-based electronics.     

The Playground Shade Index: A New Design Metric for Measuring Shade and Seasonal Ultraviolet Protection Characteristics of Parks and Playgrounds

Current shading strategies used to protect outdoor playgrounds from harmful solar radiation include the placement of artificial cloth weaves or permanent roofing over a playground site, planting trees in proximity to playground equipment, and using vegetation or surface texture variations to cool playground surfaces. How and where an artificial shade structure is placed or a tree is planted to maximize the shade protection over specific playground areas, requires careful assessment of local seasonal sun exposure patterns. The Playground Shade Index (PSI) is introduced here as a design metric to enable shade and solar ultraviolet exposure patterns to be derived in an outdoor space using conventional aerial views of suburban park maps. The implementation of the PSI is demonstrated by incorporating a machine learning design tool to classify the position of trees from an aerial image, thus enabling the mapping of seasonal shade and ultraviolet exposure patterns within an existing 7180 m² parkland. This is achieved by modeling the relative position of the sun with respect to nearby buildings, shade structures, and the identified evergreen and deciduous tree species surrounding an outdoor playground.     

Drug Delivery and Drug Efficacy from Amorphous Poly(thioether anhydrides)

The correlation between erosion and drug (lidocaine and 6‐mercaptopurine, 6‐MP) release from amorphous poly(thioether anhydrides), which are synthesized using radical‐mediated thiol‐ene polymerization, is reported. Cytotoxicity studies of the polymer toward human fibroblast human dermal fibroblasts adult, melanoma A‐375, and breast cancer MCF‐7 cells are conducted, and drug efficacy of a cancer and autoimmune disease drug (6‐MP) when released from the poly(thioether anhydrides) is examined against two cancerous cell types (A‐375 and MCF‐7). Erosion and drug release studies reveal that lidocaine release is governed by network erosion whereas 6‐MP is released by a combination of erosion and diffusion. The cytotoxicity studies show that all three cell types demonstrate high viability, thus cytocompatibility, to poly(thioether anhydrides). Toxicity to the material is dose dependent and comparable to other polyanhydride systems. The 6‐MP cancer drug is shown to remain bioactive after encapsulation in the poly(thioether anhydride) matrix and the polymer does not appear to modify the efficacy of the drug.     

Using Mechanoluminescent Materials to Visualize Interparticle Contact Intensity in Granular Media

Mechanoluminescent materials have the property of emitting light when they are mechanically deformed. The paper deals with the potential use of these active substances to reveal interparticle contact force networks in granular media under mechanical loading. Preliminary uniaxial tensile tests were first performed on two types of longitudinal specimens for comparison purposes: pure epoxy resin and epoxy resin containing mechanoluminescent powders. Stress-strain curves showed that the powder acted as a reinforcement, but fractographic analysis by SEM revealed that debonding occurred between the epoxy matrix and powder grains during mechanical loading. Various two-dimensional cohesionless granular systems were then studied, using mechanoluminescent cylinders subjected to compression. Whereas uniaxial tensile tests featured homogeneous light emission, localized mechanoluminescence intensities were revealed in the contact zones between cylinders. The study shows that mechanoluminescent materials open perspectives for the identification of interparticle contact intensities in granular media.