Stability and Stress State of an Underground Pipeline Joined to a Unit

International Applied Mechanics - The stability of a pipeline jointed to a unit interacting with the surrounding soil is analyzed. The pipeline is subject to axial compression. The stress state of...     

Transverse Vibrations of Buried Pipelines Under Axial Loading Within Geometrically Nonlinear Theory

International Applied Mechanics - The transverse motions of an underground pipeline located in water-saturated fine-grained soil are studied using the developed models of interaction in the...     

Macroscopic properties of triplon Bose–Einstein condensates

Magnetic insulators can be characterized by a gap separating the singlet ground state from the lowest-energy triplet, S=1 excitation. If the gap can be closed by the Zeeman interaction in applied magnetic field, the resulting quasiparticles, triplons, can have concentrations sufficient to undergo the Bose–Einstein condensates transition. We consider macroscopic properties of the triplon Bose–Einstein condensates in the Hartree–Fock–Bogoliubov approximation taking into account the anomalous averages. We prove that these averages play the qualitative role in the condensate properties. As a result, we show that with the increase in the external magnetic field at a given temperature, the condensate demonstrates an instability related to the appearance of nonzero phonon damping and a change in the characteristic dependence of the speed of sound on the magnetic field. The calculated magnetic susceptibility diverges when the external magnetic field approaches this instability threshold, providing a tool for the experimental verification of this approach.     

Quasi-equilibrium mixture of itinerant and localized bose atoms in optical lattice

Conditions are studied under which there can exist a quasi-equilibrium mixture of itinerant and localized bosonic atoms in an optical lattice, even at zero temperature and at integer filling factor, when such a coexistence is impossible for an equilibrium lattice. The consideration is based on a model having the structure of a two-band, or two-component, boson Hubbard Hamiltonian. The minimal value for the ratio of onsite repulsion to tunneling parameter, necessary for the occurrence of such a mixture, is found.