Presence Of External Confinement Research Articles

Reactive collisions in confined geometries

We consider low energy threshold reactive collisions of particles interacting via a van der Waals potential at long range in the presence of external confinement and give analytic formulas for the confinement modified scattering in such circumstances. The reaction process is described in terms of the short range reaction probability. Quantum defect theory is used to express elastic and inelastic or reaction collision rates analytically in terms of two dimensionless parameters representing phase and reactivity. We discuss the modifications to Wigner threshold laws for quasi-one-dimensional and quasi-two-dimensional geometries. Confinement-induced resonances are suppressed due to reactions and are completely absent in the universal limit where the short-range loss probability approaches unity.

Stable Vortex–Bright-Soliton Structures in Two-Component Bose-Einstein Condensates

We report the numerical realization of robust two-component structures in 2D and 3D Bose-Einstein condensates with nontrivial topological charge in one component. We identify a stable symbiotic state in which a higher-dimensional bright soliton exists even in a homogeneous setting with defocusing interactions, due to the effective potential created by a stable vortex in the other component. The resulting vortex-bright-solitons, generalizations of the recently experimentally observed dark-bright solitons, are found to be very robust both in the homogeneous medium and in the presence of external confinement.

Experimental Analysis of Flexural Hinging in Hollow Marine Prestressed Pile Shafts

Parametric analysis of hollow precast prestressed piles indicated that under certain conditions of loading and geometry, plastic hinge formation could be expected in the pile shaft below ground level. Four half-scale model precast prestressed piles were tested in flexure to characterize plastic hinge development. The test rig simulated the subgrade moment pattern found in an in situ pile, and simulated external confinement from the soil around the pile shaft. Parameters varied were transverse reinforcement ratio, presence of external confinement, and presence of nonprestressed longitudinal steel in the plastic hinge region. The model piles were found to be insensitive to parameter variation. Failure occurred at similar levels of structural displacement in all cases, and in all cases took the form of compression failure of the pile wall. The piles had limited ductility, less than μΔ = 4 in all cases.