Non-linear photochemical pathways in laser induced atmospheric aerosol formation

We measured the chemical composition and the size distribution of aerosols generated by femtosecond-Terawatt laser pulses in the atmosphere using an aerosol mass spectrometer (AMS). We show that nitric acid condenses in the form of ammonium nitrate, and that oxidized volatile organics also contribute to particle growth. These two components account for two thirds and one third, respectively, of the dry laser-condensed mass. They appear in two different modes centred at 380 nm and 150 nm. The number concentration of particles between 25 and 300 nm increases by a factor of 15. Pre-existing water droplets strongly increase the oxidative properties of the laser-activated atmosphere, substantially enhancing the condensation of organics under laser illumination.Comment: 19 pages, 5 figure

On the groove pressing of Ni-W alloy: microstructure, texture and mechanical properties evolution

International audienceThe microstructure, texture and mechanical properties of the Ni-14%W(wt.%) alloy with two different initial grain sizes and textures were investigated after groove pressing (GP) at 450 °C to 4 cycles using Electron Back Scatter Diffraction (EBSD) and microhardness measurements. The initial first series was characterized by small equiaxed grains and Cube dominant texture component. The second series has elongated grains and β-fiber texture. EBSD analysis has shown that GP processing led to a slight refinement (less than 15%) of equiaxed grains in series I while greater refinement (~55%) of the mean spacing along normal direction was observed in series II. The texture did not drastically change from the initial ones and was characterized by the weakening of the Cube component in series I and rapid decrease of Copper component for series II. GP processing reduces very slightly the plastic anisotropy of the alloy with initial elongated granular microstructure

Synthesis, electrochemical and photochromic behaviour of a series of (1,4-dithiafulven-6-yl)substituted 3H-naphtho[2,1-b]pyran derivatives

The synthesis and electrochemical and photochromic properties of new 3,3-diphenyl-8-(1,4-dithiafulven-6-yl)-[3H]-naphtho[2,1-b]pyran derivatives containing differently substituted dithiafulvenyl units are described. An example of electrochemical dimerization is shown which gives access to electroactive bichromophoric systems. Such systems could allow the study of the interplay of photochromic and electrochemical properties

Primary recrystallization of a magnesium hybrid material fabricated by high-pressure torsion

The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt.%) material fabricated by high-pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 °C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 °C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 °C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 °C and of Mg5Gd and Mg12Gd phases at 350 and 450 °C. The distribution of the basal texture in both regions was strongly controlled by dynamic recrystallization, precipitation and grain growth. The values of the microhardness over the radial cross-sections of the hybrid discs decrease and become more uniform, in the range of ~35–66 Hv, with increasing annealing temperature

Evaluating the textural and mechanical properties of an Mg-Dy alloy processed by high-pressure torsion

Samples of an Mg-0.41Dy (wt. %) alloy were severely deformed by high-pressure torsion (HPT) at room temperature up to 15 turns and the texture, microstructure and microhardness values in the centres, mid-radial points and edges of the HPT-deformed discs were investigated using X-ray diffraction, Electron BackScatter Diffraction and Vickers microhardness measurements. The textures in the centres of discs were characterized by a typical weak basal fiber whereas at both the mid-points and edges of the discs there was a strong basal texture where the c-axis of most grains was shifted 15° away from the shear direction. An almost homogeneous ultrafine-grained structure with a grain size of about 0.75 μm was achieved after 15 HPT turns. The microhardness values in these three positions increased with increasing numbers of turns, reached a maximum and then decreased to a lower steady-state level at large strains. In addition to dislocation and grain size hardening, the results show that texture strengthening contributes significantly to the rapid increase in hardening in the early stages of deformation

Electroactive polyacrylates bearing linear conjugated systems based on EDOT moieties

New polyacrylates bearing an electropolymerizable bi or terthiophene group have been synthesized via classical radical polymerization and via RAFT process. Polymerizations can be controlled if thiophene moieties have protected α positions; otherwise polymerization is difficult or impossible. Cross-linked polymers can be obtained after film electropolymerizations on different electrodes (gold, carbon and platinum)

A Fixed-Wing Biplane MAV for Low Speed Missions

Practical MAVs missions, such as outdoor urban environment recognitions, simultaneously require a capability of both dashing to escape enemy fire and slowly loitering over a target in order to capture and transmit clear images to a ground station. Since an MAV intrinsically offers better payload and endurance capabilities than a rotorcraft of an equal size, fixed-wing MAVs can be considered as promising platforms to start with. The objective of this study is to investigate the possibility of developing a fixed-wing MAV which can both perform rapid translations and low-speed flights through urban canyons. Alow-speed wind tunnel testing is conducted to compare several powered configurations including monoplane, biplane and tandem wing combinations. The testing also focuses on wing-propeller interactions. Results indicate that a positive stagger biplane configuration powered by counter-rotating propellers placed in pusher position provides the best trade-off between a high-speed performance and a low-speed capability with a limited electric consumption. Consequently, a 30 cm span MAV biplane prototype, named TYTO-30, has been designed and built. TYTO-30 is equipped with a 110g-payload which includes a video camera, navigation and autopilot system and has been flight tested successfully