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Abstract: Tensile tests with Hopkinson bars are monitored with high speed cameras to extract 3D displacement fields and the corresponding strain fields by resorting to stereocorrelation. The aim of the experiments is to analyze the onset and development of necking for various strain rates and samples. Various challenges have to be dealt with, namely small definition of the pictures, large displacements that occur during the experiment, and the need for good spatial resolutions to capture the strain levels within the neck. In order to address all these issues, pre-correction techniques are used to allow for the required stability and accuracy of the analysis. Eight experiments on cylinders and parallelepipeds at different loading rates are analyzed. Either single or multiple neck inceptions were observed, irrespective of the mean strain rate, supporting a random nucleation picture rather than a deterministic result of the constitutive law. Local strains up to about 600% were measured. In the case of multiple necking, a selection leading to the growth of a dominant one is observed, in agreement with Mott''s theory of an “unloading wave” emanating from neck inception. A propagation speed of this wave can be estimated from the analysis and is shown to agree with the theoretical prediction. [Copyright &y& Elsevier]

Abstract: Volumetric strains in a filled SBR specimen subjected to cyclic uniaxial tension with increasing extensions are studied. Digital image correlation is used to follow the kinematics of two orthogonal free faces. A volume expansion is observed past a critical elongation, which can be interpreted as the onset of cavitation. Under unloading, the volume returns to its original value and remains constant upon reloading. Increasing the elongation to higher values than the previous cycle leads again to a volumetric expansion. [Copyright &y& Elsevier]

Abstract: A new method is proposed to estimate arbitrary velocity fields from a time series of images acquired by a single camera. This approach, here focused on a single spatial plus a time dimension, is specialized to the decomposition of the velocity field over rectangular shaped (finite-element) bilinear shape functions. It is therefore assumed that the velocity field is essentially aligned along one direction. The use of a time sequence over which the velocity is assumed to have a smooth temporal change allows one to use elements whose spatial extension is much smaller than in traditional digital image correlation based on successive image pairs. This method is first qualified by using synthetic numerical test cases, and then applied to a dynamic tensile test performed on a tantalum specimen. Improvements with respect to classical digital image correlation techniques are observed in terms of spatial resolution. [ABSTRACT FROM AUTHOR]

Background: Colonization of large part of Europe by the Asian tiger mosquito Aedes albopictus is causing autochthonous transmission of chikungunya and dengue exotic arboviruses. While pyrethroids are recommended only to reduce/limit transmission, they are widely implemented to reduce biting nuisance and to control agricultural pests, increasing the risk of insurgence of resistance mechanisms. Worryingly, pyrethroid resistance (with mortality < 70%) was recently reported in Ae. albopictus populations from Italy and Spain and associated with the V1016G point mutation in the voltage-sensitive sodium channel gene conferring knockdown resistance (kdr). Genotyping pyrethroid resistance-associated kdr mutations in field mosquito samples represents a powerful approach to detect early signs of resistance without the need for carrying out phenotypic bioassays which require availability of live mosquitoes, dedicated facilities and appropriate expertise. Methods: Here we report results on the PCR-genotyping of the V1016G mutation in 2530 Ae. albopictus specimens from 69 sampling sites in 19 European countries. Results: The mutation was identified in 12 sites from nine countries (with allele frequencies ranging from 1 to 8%), mostly distributed in two geographical clusters. The western cluster includes Mediterranean coastal sites from Italy, France and Malta as well as single sites from both Spain and Switzerland. The eastern cluster includes sites on both sides of the Black Sea in Bulgaria, Turkey and Georgia as well as one site from Romania. These results are consistent with genomic data showing high connectivity and close genetic relationship among West European populations and a major barrier to gene flow between West European and Balkan populations. Conclusions: The results of this first effort to map kdr mutations in Ae. albopictus on a continental scale show a widespread presence of the V1016G allele in Europe, although at lower frequencies than those previously reported from Italy. This represents a wake-up call for mosquito surveillance programs in Europe to include PCR-genotyping of pyrethroid resistance alleles, as well as phenotypic resistance assessments, in their routine activities. [ABSTRACT FROM AUTHOR]

Environmental features impacting the spread of invasive species after introduction can be assessed using population genetic structure as a quantitative estimation of effective dispersal at the landscape scale. However, in the case of an ongoing biological invasion, deciphering whether genetic structure represents landscape connectivity or founder effects is particularly challenging.We examined the modes of dispersal (natural and human‐aided) and the factors (landscape or founders history) shaping genetic structure in range edge invasive populations of the Asian tiger mosquito, Aedes albopictus, in the region of Grenoble (Southeast France).Based on detailed occupancy–detection data and environmental variables (climatic, topographic and land‐cover), we modelled A. albopictus potential suitable area and its expansion history since first introduction. The relative role of dispersal modes was estimated using biological dispersal capabilities and landscape genetics approaches using genome‐wide SNP dataset.We demonstrate that both natural and human‐aided dispersal have promoted the expansion of populations. Populations in diffuse urban areas, representing highly suitable habitat for A. albopictus, tend to disperse less, while roads facilitate long‐distance dispersal. Yet, demographic bottlenecks during introduction played a major role in shaping the genetic variability of these range edge populations.The present study is one of the few investigating the role of founder effects and ongoing expansion processes in shaping spatial patterns of genetic variation in an invasive species at the landscape scale. The combination of several dispersal modes and large proportions of continuous suitable habitats for A. albopictus promoted range filling of almost its entire potential distribution in the region of Grenoble only few years after introduction. [ABSTRACT FROM AUTHOR]

Invasion of new territories by insect vector species that can transmit pathogens is one of the most important threats for human health. The spread of the mosquito Aedes albopictus in Europe is emblematic, because of its major role in the emergence and transmission of arboviruses such as dengue or chikungunya. Here, we modeled the spread of this mosquito species in France through a statistical framework taking advantage of a long-term surveillance dataset going back to the first observation of Ae. albopictus in the Metropolitan area. After validating the model, we show that human activities are especially important for mosquito dispersion while land use is a major factor for mosquito establishment. More importantly, we show that Ae. albopictus invasion is accelerating through time in this area, resulting in a geographic range extending further and further year after year. We also show that sporadic “jump” of Ae. albopictus in a new location far from the colonized area did not succeed in starting a new invasion front so far. Finally, we discuss on a potential adaptation to cooler climate and the risk of invasion into Northern latitudes. [ABSTRACT FROM AUTHOR]

Sprays of commercial preparations of the bacterium Bacillus thuringiensis subsp. israelensis are widely used for the control of mosquito larvae. Despite an abundant literature on B. thuringiensis subsp. israelensis field efficiency on mosquito control, few studies have evaluated the fate of spores in the environment after treatments. In the present article, two complementary experiments were conducted to study the effect of different parameters on B. thuringiensis subsp. israelensis persistence and recycling, in field conditions and in the laboratory. First, we monitored B. thuringiensis subsp. israelensis persistence in the field in two contrasting regions in France: the Rhône-Alpes region, where mosquito breeding sites are temporary ponds under forest cover with large amounts of decaying leaf matter on the ground and the Mediterranean region characterized by open breeding sites such as brackish marshes. Viable B. thuringiensis subsp. israelensis spores can persist for months after a treatment, and their quantity is explained both by the vegetation type and by the number of local treatments. We found no evidence of B. thuringiensis subsp. israelensis recycling in the field. Then, we tested the effect of water level, substrate type, salinity and presence of mosquito larvae on the persistence/recycling of B. thuringiensis subsp. israelensis spores in controlled laboratory conditions (microcosms). We found no effect of change in water level or salinity on B. thuringiensis subsp. israelensis persistence over time (75 days). B. thuringiensis subsp. israelensis spores tended to persist longer in substrates containing organic matter compared to sand-only substrates. B. thuringiensis subsp. israelensis recycling only occurred in presence of mosquito larvae but was unrelated to the presence of organic matter. [ABSTRACT FROM AUTHOR]

Nanocavitation was detected for the first time in carbonblack filled styrene–butadiene rubber (CB-SBR) under uniaxialloading by real time small-angle X-ray scattering (SAXS) using synchrotronX-ray radiation. A three phase model was developed to calculate thevoid volume fraction from the scattering invariant Qdetermined from the observed SAXS patterns. The normalized scatteringinvariant Q/Q0, where Q0is the invariant before deformation, greatlyincreased above a critical extension ratio λonsetwhich we attribute to the formation of nanovoids. Analysis of the2D scattering patterns show that voids formed are 20–40 nmin size and elongated along the tensile direction. Cavities formedbeyond λonsetare smaller as λ increases. Resultsfrom the scattering experiments are strongly supported by macroscopicvolume change measurements on the samples under similar uniaxial strain.A nearly constant nanocavitation stress σonset(25MPa) was observed when the filler volume fraction ϕCBwas larger than 14%. This value is much higher than that predictedbased on the elastic instability of small voids in an unfilled elastomerand shows only a weak dependence on the cross-linking density νCin heavily cross-linked samples. An energy based cavitationcriterion stressing the importance of confined domains between particlesor clusters of particles was adopted and found to be consistent withthe observed results. The nanocavities are thought to alter the localstress state and promote local shear motion of filler particles. [ABSTRACT FROM AUTHOR]