Pascal Tardy

Defensive behaviour of Apis mellifera against Vespa velutina in France: Testing whether European honeybees can develop an effective collective defence against a new predator

We investigated the prey-predator interactions between the European honeybee, Apis mellifera, and the invasive yellow-legged hornet, Vespa velutina, which first invaded France in 2004 and thereafter spread to neighbouring European countries (Spain, Portugal and Italy). Our goal was to determine how successfully honeybees are able to defend their colonies against their new predator in Europe. Experiments were conducted in the southwest of France-the point of entry of the hornet in Europe-under natural and semi-controlled field conditions. We investigated a total of eight apiaries and 95 colonies subjected to either low or high levels of predation. We analyzed hornet predatory behaviour and collective response of colonies under attack. The results showed that A. mellifera in France exhibit an inefficient and unorganized defence against V. velutina, unlike in other regions of Europe and other areas around the globe where honeybees have co-evolved with their natural Vespa predators.

Cumulative effects of electrode and dielectric surface modifications on pentacene-based transistors

Surface modifications of the dielectric and the metal of pentacene-based field effect transistors using self-assembled monolayer (SAM) were studied. First, a low interfacial trap density and pentacene 2D-growth were favored by the nonpolar and low surface energy of octadecyltrichlorosilane-based SAM. This treatment leaded to increased mobility up to 0.4 cm2 V−1 s−1 and no observable hysteresis on transfer curves. Second, reduced hole injection barrier and contact resistance were achieved by fluorinated thiols deposited on gold contacts resulting in an increased mobility up to 0.6 cm2 V−1 s−1. Finally, a high mobility of 2.6 cm2 V−1 s−1 was achieved by cumulative effects of both treatments.

Lanthanum Hexaboride As Novel Interlayer for Improving the Thermal Stability of P3HT:PCBM Organic Solar Cells

For efficient organic photovoltaic (OPV) solar cells, a low work function electrode is necessary to enhance the built-in voltage of the active layer, thereby improving the overall efficiency. Calcium is often used for this purpose in the laboratory; however, its development on a larger scale is impaired by its high reactivity with oxygen and water and the resulting low stability of solar cells under operation. The influence of a novel interlayer, lanthanum hexaboride (LaB6), on the electronic properties of OPV is studied in this work. Similarly to calcium, when LaB6 is used as an interlayer, it enhances the built-in voltage in the device, leading to a higher fill factor (FF) and optimal open circuit voltage (V(oc)). As a result, optimized LaB6-based devices present significantly improved power conversion efficiencies. More importantly, while calcium/aluminum (Ca/Al) and aluminum (Al) cathodes lose their capacity to enhance the internal electrical field during thermal aging, the LaB6/aluminum (LaB6/Al) electrode remains stable. This remarkable effect results in a highly stable V(oc) and flat-band potential during aging.

New Type of Thermal Conductivity Sensor for Gas Detection

A new sensor for gas detection based on the transient thermal response of a SiC microplate slightly heated by a screen printed Pt resistance is described.