Dissociative electron attachment to gas phase thiothymine: experimental and theoretical approaches

International audienceIn this contribution we have investigated experimentally and theoretically the interaction of low energy electrons with gas phase thiothymine (a sulphur containing analogue of thymine). We observe that the presence of the sulphur atom within thiothymine strongly controls the fragmentation dynamics. With the exception of the (M - H)(-) anion formation, the most favorable reaction channels are associated with a loss of sulphur containing negative fragments (i.e., the formation of S(-), SCN(-) and (M - S)(-)) suggesting that these resonances are localized at the C[double bond, length as m-dash]S group. Hence the present results demonstrate that certain reactions can be controlled by substitution of the sulphur atom at specific molecular sites within nucleobases. Our study thus represents a starting point for a physicochemical understanding of the action of sulphur-containing antimetabolites when used in chemoradiotherapy. Dissociative electron attachment to gas phase thiothymine: Experimental and theoretical approaches (PDF Download Available). Available from: http://www.researchgate.net/publication/260093855_Dissociative_electron_attachment_to_gas_phase_thiothymine_Experimental_and_theoretical_approache

Mechanical testing of wood-glass composite mast sections

Glass fibre-sheathed wood cored composite materials may offer a lightweight, stiff alternative to carbon fibre for manufacturing masts for sailing dinghies. However, at present, very little data quantifying the mechanical response of these materials when loaded is available. Before manufacturing a prototype mast from these materials, it is necessary to acquire such data and determine how the various fabrication parameters influence the behaviour of these materials when loaded. To address this need, a series of wood-glass composite tubular structures representative of typical mast sections were constructed and loaded in a suitable testing machine. This paper reports the results of these tests and discusses how the parameters investigated influence the stiffness and strength of the structures. The results provide useful data on which to base the design of prototype masts

Flight in slow motion: aerodynamics of the pterosaur wing

The flight of pterosaurs and the extreme sizes of some taxa have long perplexed evolutionary biologists. Past reconstructions of flight capability were handicapped by the available aerodynamic data, which was unrepresentative of possible pterosaur wing profiles. I report wind tunnel tests on a range of possible pterosaur wing sections and quantify the likely performance for the first time. These sections have substantially higher profile drag and maximum lift coefficients than those assumed before, suggesting that large pterosaurs were aerodynamically less efficient and could fly more slowly than previously estimated. In order to achieve higher efficiency, the wing bones must be faired, which implies extensive regions of pneumatized tissue. Whether faired or not, the pterosaur wings were adapted to low-speed flight, unsuited to marine style dynamic soaring but adapted for thermal/slope soaring and controlled, low-speed landing. Because their thin-walled bones were susceptible to impact damage, slow flight would have helped to avoid injury and may have contributed to their attaining much larger sizes than fossil or extant birds. The trade-off would have been an extreme vulnerability to strong or turbulent winds both in flight and on the ground, akin to modern-day paragliders

Performance Variations of Leading-Edge Tubercles for Distinct Airfoil Profiles

An experimental investigation has been undertaken to determine the influence of sinusoidal leading-edge protrusions on the performance of two NACA airfoils with different aerodynamic characteristics. Force measurements on full-span airfoils with various combinations of tubercle amplitude and wavelength reveal that when compared to the unmodified equivalent, tubercles are more beneficial for the NACA 65-021 airfoil than the NACA 0021 airfoil. It was also found that for both airfoil profiles, reducing the tubercle amplitude leads to a higher maximum lift coefficient and larger stall angle. In the poststall regime, however, the performance with largeramplitude tubercles is more favorable. Reducing the wavelength leads to improvements in all aspects of lift performance, including maximum lift coefficient, stall angle, and poststall characteristics. Nevertheless, there is a certain point at which further reduction in wavelength has a negative impact on performance. The results also suggest that tubercles act in a manner similar to conventional vortex generators.Kristy L. Hansen, Richard M. Kelso, and Bassam B. Dall

The belt-rib concept: a structronic approach to variable camber.

The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a "mechatronic" solution with hinges or linear bearings a "structronic" solution is chosen, where distributed flexibility allows the desired shape changes. The resulting system is not only easier to maintain due to the absence of wear, but also is structurally more reliable and substantially lighter. The new concept evolves from the classical wing structure. The classical rib, which i s in charge of the wing section's stiffness, is replaced by a "belt rib," which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged. The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. After a first development stage, in which mainly the system's shape adaptability and the overall stiffness properties were investigated, further steps followed, focused on manufacturing, weight optimization and strength aspects. Recent developments dealt with the construction of a model with solid-state hinges, realized as hybrid glass fiber-carbon-fiber reinforced composite s tructure. The model is actuated mechanically by cables, which can be replaced by multifunctional actuators-like shape memory wires-in the future. The paper opens with an introduction about shape control of aerospace structures and variable camber in particular, in which the major advantages of a "structronic" approach with respect to classical solutions are discussed. Then the fundamentals of the belt-rib concept are sketched, with some significant results of the feasibility proof phase, followed by the description of the last developments. The conclusion summarizes the potential of a structronic approach to shape control with an outline of possible future work