The origins of electromechanical indentation size effect in ferroelectrics

Metals exhibit a size-dependent hardening when subject to indentation. Mechanisms for this phenomenon have been intensely researched in recent times. Does such a size-effect also exist in the electromechanical behavior of ferroelectrics?--if yes, what are the operative mechanisms? Our experiments on BaTiO3 indeed suggest an electromechanical size-effect. We argue, through theoretical calculations and differential experiments on another non-ferroelectric piezoelectric (Quartz), that the phenomenon of flexoelectricity(as opposed to dislocation activity) is responsible for our observations. Flexoelectricity is the coupling of strain gradients to polarization and exists in both ordinary and piezoelectric dielectrics. In particular, ferroelectrics exhibit an unusually large flexoelectric response.Comment: in revie

Sensitivity of a Red Sea numerical wave model to spatial and temporal resolution of forcing wind field

566-575Simulating waves using numerical wave models provide essential wave information for navigational safety and coastal protection applications. Accuracy of such simulations depends mainly on the accuracy of the forcing wind fields, which are influenced by the wind fields’ spatial and temporal resolutions. In this study, the sensitivity of a SWAN-based Red Sea wave model to spatial and temporal resolutions of forcing wind fields was investigated. The sensitivity analysis showed that forcing the wave model with wind fields of low spatial and/or temporal resolutions will affect the quality of wave model outputs, not only in terms of integrated wave parameters, but also in terms of the overall wave energy distribution in both frequency and directional domains. This study suggests that the spatial resolution of the forcing wind filed plays more significant role than the temporal resolution on the quality of the wave model predictions

Topological defects at smectic interfaces as a potential tool for the biosensing of living microorganisms

Characterizing the anchoring properties of smectic liquid crystals (LCs) in contact with bacterial solutions is crucial for developing biosensing platforms. In this study, we investigate the anchoring properties of a smectic LC when exposed to Bacillus Subtilis and Escherichia coli bacterial solutions using interfaces with known anchoring properties. By monitoring the optical response of the smectic film, we successfully distinguish different types of bacteria, leveraging the distinct changes in the LC's response. Through a comprehensive analysis of the interactions between bacterial proteins and the smectic interface, we elucidate the potential underlying mechanisms responsible for these optical changes. Additionally, we introduce the utilization of topological defects; the focal conic domains (FCDs), at the smectic interface as an indicative measure of the bacterial concentration. Our findings demonstrate the significant potential of smectic LCs and their defects for biosensing applications and contribute to our understanding of bacteria- LC interactions, paving the way for advancements in pathogen detection and protein-based sensing

Multiscale identification of the random elasticity field at mesoscale of a heterogeneous microstructure using multiscale experimental observations

International audienceThis paper deals with a multiscale statistical inverse method for performing the experimental identification of the elastic properties of materials at macroscale and at mesoscale within the framework of a heterogeneous microstructure which is modeled by a random elastic media. New methods are required for carrying out such multiscale identification using experimental measurements of the displacement fields carried out at macroscale and at mesoscale with only a single specimen submitted to a given external load at macroscale. In this paper, for a heterogeneous microstructure, a new identification method is presented and formulated within the framework of the three-dimensional linear elasticity. It permits the identification of the effective elasticity tensor at macroscale, and the identification of the tensor-valued random field, which models the apparent elasticity field at mesoscale. A validation is presented first with simulated experiments using a numerical model based on the hypothesis of 2D-plane stresses. Then, we present the results given by the proposed identification procedure for experimental measurements obtained by digital image correlation (DIC) on cortical bone

Determination of the interfacial heat transfer coefficient for a hot aluminium stamping process

The interfacial heat transfer coefficient (IHTC) is an important thermophysical parameter in hot stamping processes and must be identified not only to retain the full mechanical strength of formed components, but also to optimise the production rate. In this work, a novel experimental facility was developed and applied to measure the temperature evolutions of the specimens and tools in stamping processes. Simulated temperature evolutions obtained using the FE software PAM-STAMP were then fit to this data. The IHTC values between AA7075 and three different tool materials were characterized at different contact pressures under both dry and lubricated conditions. In addition, a mechanism based IHTC model was developed and validated as a function of contact pressure, tool material and lubricant thickness to predict the IHTC values under different conditions

Molecular prevalence of Chlamydia and Chlamydia-like bacteria in Tunisian domestic ruminant farms and their influencing risk factors

Chlamydia and Chlamydia-like bacteria are well known to infect several organisms and may cause a wide range of diseases, particularly in ruminants. To gain insight into the prevalence and diversity of these intracellular bacteria, we applied a pan-Chlamydiales real-time PCR to 1,134 veterinary samples taken from 130 Tunisian ruminant herds. The true adjusted animal population-level prevalence was 12.9% in cattle, against 8.7% in sheep. In addition, the true adjusted herd-level prevalence of Chlamydiae was 80% in cattle and 25.5% in sheep. Chlamydiales from three familylevel lineages were detected indicating a high biodiversity of Chlamydiales in ruminant herds. Our results showed that Parachlamydia acanthamoebae could be responsiblefor bovine and ovine chlamydiosis in central-eastern Tunisia. Multivariable logistic regression analysis at the animal population level indicated that strata and digestive disorders variables were the important risk factors of bovine and ovine chlamydiosis. However, origin and age variables were found to be associated withbovine and ovine chlamydiosis, respectively. At the herd level, risk factors for Chlamydia positivity were as follows: abortion and herd size for cattle against breeding system, cleaning frequency, quarantine, use of disinfectant and floor type for sheep. Paying attention to these risk factors will help improvement of control programs against this harmful zoonotic disease

Preliminary results of a paleoseismological analysis along the Sahel fault (Algeria): New evidence for historical seismic events

International audienceThe ∼60 km-long Sahel ridge west of Algiers (Tell Atlas, north Algeria) is considered as an ENE-WSW fault-propagation fold running along the Mediterranean coast and associated with a north-west dipping thrust. Its proximity with Algiers makes this structure a potential source of destructive earthquakes that could hit the capital city, as occurred in 1365 AD and 1716 AD. The first paleoseismologic investigation on the Sahel ridge was conducted in order to detect paleo-ruptures related to active faulting and to date them. From the first investigations in the area, a first trench was excavated across bending-moment normal faults induced by flexural slip folding in the hanging wall of the Sahel anticline thrust ramp. Paleoseismological analyses recognize eight rupture events affecting colluvial deposits. 14C dating indicates that these events are very young, six of them being younger than 778 AD. The first sedimentary record indicates two ruptures before 1211 AD, i.e. older than the first historical earthquake documented in the region. Three events have age ranges compatible with the 1365, 1673 and 1716 Algiers earthquakes, whereas three other ones depict very recent ages, i.e. younger than 1700 AD. Potential of these secondary extrados faults for determining paleoseismic events and thrust behaviour is discussed