CO2 Binding and Splitting by Boron–Boron Multiple Bonds

The room‐temperature, ambient‐pressure reactions of CO₂ with two species containing boron–boron multiple bonds led to the incorporation of either one or two CO₂ molecules. The structural characterization of a thermally unstable intermediate in one case indicates that an initial [2+2] cycloaddition is the key step in the reaction mechanism.     

Semi-active friction tendons for vibration control of space structures

Semi-active vibration control systems are becoming popular because they offer both the reliability of passive systems and the versatility of active control without high power demands. In this work, a new semi-active control system is proposed and studied numerically. The system consists of variable-friction dampers linked to the structure through cables. Auxiliary soft springs in parallel with these friction dampers allow them to return to their initial pre-tensioned state. Using cables makes the system suitable for deployable, flexible and lightweight structures, such as space structures (spacecraft). A control system with three control laws applied to a single-degree-of-freedom structure is studied. Two of these laws are derived by using Lyapunov theory, whereas the third one is developed heuristically. In order to assess the performance of the control system, a parametric study is carried out through numerical simulations. An application of the proposed method to multi-degree-of-freedom structures is also presented and demonstrated through a numerical example. The system in semi-active mode is more effective than in passive mode and its effectiveness is less sensitive to loss of pre-tension.     

Extended WKB Method,Resonances and Supersymmetric Radial Barriers

Semiclassical approximations are implemented in the calculation of position and width of low-energy resonances for radial barriers. The numerical integrations are delimited by τ/τ _life≪8, with τ the period of a classical particle in the barrier trap and τ _life the resonance lifetime. These energies are used in the construction of ‘haired’ short-range potentials as the supersymmetric partners of a given radial barrier. The new potentials could be useful in the study of the transient phenomena which give rise to the Moshinsky’s diffraction in time.