Philippe Gaucher

Correlation between structure, microstructure, and ferroelectric properties of PbZr0.2Ti0.8O3 integrated film: Influence of the sol-gel process and the substrate

The properties of a ferroelectric material deposed as a thin film on a substrate depend on the method of preparation and on the nature of the substrate used. The present work reports fine characterization by x-ray diffraction of structural modifications (cell parameters, preferential orientations) and microstructural modifications (ferroelectric domain arrangement) and electric measurements of a ferroelectric film as a function of its method of preparation (sol-gel process, pyrolysis, annealing) and the nature of its substrate (crystalline structure, crystallographic orientation, thermal coefficient of dilation). Due to the elaboration process, lead zirconate titanate (PZT) films have grain size smaller than 0.3 μm and consequently modified cell parameters (higher a parameter, smaller c parameter, and consequently smaller c/a tetragonality). Thermal treatment induces specific stresses between the PZT film and the substrate that modify the ferroelectric domain microstructure of the PZT grains: the microstr...

Temporal and spatial variability of animal sound within a neotropical forest

article i nfo Soundscape ecology aims to use biological, geophysical and anthropogenic sound to understand natural-human landscape dynamics. The analysis of natural soundscapes with no human noise is a prerequisite to understand and quantify the effects of human activity on animal ecology linked to sound. Preserved tropical forests are the lo- cation of unique, highly diverse, and animal sound. However, although the acoustic behavior of several tropical spe- cies has been examined, very few analyses have attempted tropical sounds at a spatial scale able to incorporate landscape characters. Here we analyze the acoustic structure of a neotropical forest landscape in French Guiana. We used a four dimensional synchronous acoustic sampling (three spatial dimensions and the temporal dimen- sion) by deploying an array of 24 microphones in the understory and canopy of the Nouragues Nature Reserve dur- ing a 43 day period and we undertook a detailed signal analysis to detect spatial and temporal animal acoustic heterogeneity. We identified a clear pattern of acoustic activity with four distinct periods of activity that differed by their spectral characteristics indicating acoustic heterogeneity along the 24-hour cycle but periodicity at a longer time scale. We revealed acoustic divergences between the understory and the canopy layers in terms of amplitude level and frequency content. We highlighted vertical (understory/canopy) and horizontal acoustic heterogeneities with a more diverse (frequency) patch in the north of the study area sampled and a more active (intensity) patch in the southeast of the study area. Our results show that the soundscape of a tropical forest, in the absence of human disturbance, is subtly structured in time and is heterogeneous in space. This structure is probably linked to endogenous factors that rule out the acoustic time activity of animal species, to the vertical stratification of singing communities or guilds, to horizontal variations in the distributions of species and to veg- etation spatial heterogeneity. Our study emphasizes that tropical soundscapes need to be recorded and analyzed in considerable spatial and temporal detail to understand their dynamics without the presence of human pro- duced noise. Our analysis also suggests that tropical forests are unique places for acoustic diversity, supporting the need for preservation from all perturbations including anthropic noise.

Domain Structures in Monoclinic Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Poled Single Crystals

A tetragonal (T) ?monoclinic (M) phase transition characterized by a wide thermal hysteresis is observed in Pb(Zn1/3Nb2/3)O3?PbTiO3 (PZN?PT) single crystals close to the morphotropic composition PZN?9%PT. The domain structure of crystals, determined by X-ray diffraction and optical observations, is dependent on the poling crystallographic direction. A monoclinic quasi-single domain structure is obtained by poling along the pseudocubic [101] direction whereas an unexpected monoclinic multidomain state with macroscopic 2 mm symmetry can be obtained for [001] poled crystals. Finally it is shown that the largest piezoelectric response corresponds to the monoclinic multidomain state of [001] poled crystals.

Electric-field-induced orthorhombic phase in Pb[(Zn1∕3Nb2∕3)0.955Ti0.045]O3 single crystals

The ferroelectric phase transitions of [1¯01]-, [001]-, and [111]-oriented Pb[Zn1∕3Nb2∕3]O3–4.5%PbTiO3 (PZN–4.5%PT) single crystals were investigated as a function of temperature (T between 300 and 450K), and electric field (E field between 0 and 300kV∕m) by dielectric and x-ray diffraction combined measurements. Under null E field, PZN–4.5%PT exhibits the following phase transitions: cubic (C)→tetragonal (T)→rhombohedral (R), during cooling. Under E field applied on a [1¯01]-oriented single crystal, an intermediate orthorhombic (O) ferroelectric phase is induced at temperatures intermediate between that of the T and R phases. The temperature range of existence of this O phase depends both on the crystal orientation and on the measurement conditions: field cooling (FC), zero-field heating after field cooling (ZFHAFC), or field heating (FH). When E field is applied along [1¯01], the stability range is within 40K in FC and only 15K in ZFHAFC; when E field is applied along [001] or [111], this range is still...

From Concurrency to Algebraic Topology

This paper is a survey of the new notions and results scattered in [13,11,12]. However the speculations of Section 5 and Section 6 are new. Starting from a formalization of higher dimensional automata (HDA) by strict globular ω-categories, the construction of a diagram of simplicial sets over the three-object small category −← gl → + is exposed. Some of the properties discovered so far on the corresponding simplicial homology theories are explained, in particular their links with geometric problems coming from concurrency theory in computer science.

Widespread occurrence of bd in French Guiana, South America.

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) is a purported agent of decline and extinction of many amphibian populations worldwide. Its occurrence remains poorly documented in many tropical regions, including the Guiana Shield, despite the area’s high amphibian diversity. We conducted a comprehensive assessment of Bd in French Guiana in order to (1) determine its geographical distribution, (2) test variation of Bd prevalence among species in French Guiana and compare it to earlier reported values in other South American anuran species (http://www.bd-maps.net; 123 species from 15 genera) to define sentinel species for future work, (3) track changes in prevalence through time and (4) determine if Bd presence had a negative effect on one selected species. We tested the presence of Bd in 14 species at 11 sites for a total of 1053 samples (306 in 2009 and 747 in 2012). At least one Bd-positive individual was found at eight out of 11 sites, suggesting a wide distribution of Bd in French Guiana. The pathogen was not uniformly distributed among the studied amphibian hosts, with Dendrobatidae species displaying the highest prevalence (12.4%) as compared to Bufonidae (2.6 %) and Hylidae (1.5%). In contrast to earlier reported values, we found highest prevalence for three Dendrobatidae species and two of them displayed an increase in Bd prevalence from 2009 to 2012. Those three species might be the sentinel species of choice for French Guiana. For Dendrobates tinctorius, of key conservation value in the Guiana Shield, smaller female individuals were more likely to be infected, suggesting either that frogs can outgrow their chytrid infections or that the disease induces developmental stress limiting growth. Generally, our study supports the idea that Bd is more widespread than previously thought and occurs at remote places in the lowland forest of the Guiana shield.

Soil community assembly varies across body sizes in a tropical forest

The relative influence of deterministic niche-based (i.e. abiotic conditions, biotic interactions) and stochastic-distance dependent neutral processes (i.e. demography, dispersal) in shaping communities has been extensively studied for various organisms, but is far less explored jointly across the tree of life, in particular in soil environments. Here, using a thorough DNA-based census of the whole soil biota in a large tropical forest plot, we show that soil aluminium, topography, and plant species identity are all important drivers of soil richness and community composition. Body size emerges as an important feature of the comparative ecology of the different taxa at the studied spatial scale, with microorganisms being more importantly controlled by environmental factors, while soil mesofauna rather display random spatial distribution. We infer that niche-based processes contribute differently to community assembly across trophic levels due to spatial scaling. Body size could hence help better quantifying important properties of multitrophic assemblages.

Phenotypic and life-history diversification in Amazonian frogs despite past introgressions

The advent of genomics in phylogenetics and population genetics strengthened the perception that conflicts among gene trees are frequent and often due to introgression. However, hybridization occurs mostly among species that exhibit little phenotypic differentiation. A recent study delineating species in Anomaloglossus, a frog genus endemic to the Guiana Shield, identified an intriguing pattern in the A. baeobatrachus species complex. This complex occurs in French Guiana and Amapá (Brazil) and comprises two sympatric phenotypes contrasting not only in body size, habitat, and advertisement call, but also in larval development mode (endotrophic vs exotrophic tadpoles). However, molecular and phenotypic divergences are, in some cases, incongruent, i.e specimens sharing mtDNA haplotypes are phenotypically distinct, suggesting a complex evolutionary history. Therefore, we genotyped 106 Anomaloglossus individuals using ddRADseq to test whether this phenotype/genotype incongruence was a product of phenotypic plasticity, incomplete lineage sorting, multiple speciation events, or admixture. Based on more than 16,000 SNPs, phylogenetic and population genetic approaches demonstrated that exotrophic populations are paraphyletic. Species tree and admixture analyses revealed a strikingly reticulate pattern, suggesting multiple historical introgression events. The evolutionary history of one exotrophic population in northern French Guiana is particularly compelling given that it received genetic material from exotrophic ancestors but shows very strong genetic affinity with the nearby endotrophic populations. This suggests strong selection on larval development and mating call after secondary contact and hybridization. The case of A. baeobatrachus represents a striking example of introgression among lineages that are phenotypically distinct, even in their larval development mode, and highlights how high-resolution genomic data can unravel unexpectedly complex evolutionary scenarios.

New records and geographic distribution map of Adenomera heyeri Boistel, de Massary and Angulo, 2006 (Anura: Leptodactylidae)

Here we report new distributional data for Adenomera heyeri , a recently described species of the lowlands of the Guiana Shield. We compiled available and new occurrence data as well as the absence of records from field surveys that were undertaken in the Guiana Shield in order to evaluate the actual range of the species. We confirm that A. heyeri is potentially distributed over most forested part of the northern Guiana Shield lowlands. The pattern of distribution also reveals valuable information on the ecology of the species.

Lambda-Opérations sur l'Homologie d'une Algèbre de Lie de Matrices

Le propos de cet article est de definir des operations k pour k > 0 sur l’homologie de l’algebre de Lie gl1(A) a coefficients triviaux, notee H (gl1(A)), a l’aide des puissances exterieures de matrices, A etant une K-algebre commutative sur un corps K de caracteristique 0, et d’en etudier les proprietes. En particulier, leur restriction a la partie primitive redonnera les operations de Loday–Procesi sur l’homologie cyclique de A, notee HC 1(A). Dans toute la suite, tous les produits qui apparaitront seront supposes etre commutatifs et sauf mention du contraire, K sera un anneau commutatif unitaire quelconque. Soit V un K-module et S (V ) l’algebre symetrique de V sur K , i.e.