Cyclic lateral response of FRP-confined circular concrete-filled steel tubular columns

Concrete-filled steel tubular (CFT) columns are widely used as columns in many structural systems and a common failure mode of such tubular columns is inelastic outward local buckling near a column end. The use of fibre-reinforced polymer (FRP) jackets/wraps for the suppression of such local buckling has recently been proposed and has been proven to possess excellent potential in both retrofit/strengthening and new construction. This paper presents the results of an experimental study into the behaviour of large-scale FRP-confined CFT (CCFT) columns under combined axial compression and lateral loading. The test parameters included the stiffness of the FRP jacket and the loading scenario. The test results showed that the FRP jacket can effectively delay or even prevent outward local buckling at the end of a cantilevered CFT column, leading to significantly improved structural performance under combined constant axial compression and cyclic lateral loading. Compared to monotonic lateral loading, cyclic lateral loading was found to introduce more severe localized deformation near the column end and may lead to earlier FRP rupture within that region

Avalanche-mechanism loss at an atom-molecule Efimov resonance

The avalanche mechanism has been used to relate Efimov trimer states to certain enhanced atom loss features observed in ultracold-atom-gas experiments. These atom loss features are argued to be a signature of resonant atom-molecule scattering that occurs when an Efimov trimer is degenerate with the atom-molecule scattering threshold. However, observation of these atom loss features has yet to be combined with the direct observation of atom-molecule resonant scattering for any particular atomic species. In addition, recent Monte Carlo simulations were unable to reproduce a narrow loss feature. We experimentally search for enhanced atom loss features near an established scattering resonance between K40 Rb87 Feshbach molecules and Rb87 atoms. Our measurements of both the three-body recombination rate in a gas of K40 and Rb87 atoms and the ratio of the number loss for the two species do not show any broad loss feature and are therefore inconsistent with theoretical predictions that use the avalanche mechanism

Rigid vortices in MgB2

Magnetic relaxation of high-pressure synthesized MgB$_2$ bulks with different thickness is investigated. It is found that the superconducting dia-magnetic moment depends on time in a logarithmic way; the flux-creep activation energy decreases linearly with the current density (as expected by Kim-Anderson model); and the activation energy increases linearly with the thickness of sample when it is thinner than about 1 mm. These features suggest that the vortices in the MgB$_2$ are rather rigid, and the pinning and creep can be well described by Kim-Anderson model.Comment: Typo corrected & reference adde

Influence of oil film stiffness on natural characteristics of single-rotor three-input helicopter main gearbox

The elastohydrodynamic lubrication (EHL) contact model is established, the oil film stiffness is calculated based on Dowson-Higginson empirical minimum thickness equation. The vibration model of single-rotor three-input helicopter main reducer is proposed by lumped mass method, and nonlinear factors like oil film stiffness, dynamic meshing force are taken into account. The influence of oil film stiffness on system natural frequency is analyzed as well. The results show that oil film stiffness of the internal and external meshing pairs in the planetary gear system have greater impact on the natural frequency, which tends to destabilize the system. Therefore, the planetary gear train is the most crucial branch regarding the system splash lubrication. When all the oil film stiffness in the system are greater than 4×109 N/m, the natural frequencies tend to be stable. This study can provide the theoretical reference for the lubrication characteristics in the single-rotor multi-input helicopter