90 research outputs found
Collective excitations of BEC under anharmonic trap position jittering
Collective excitations of a Bose-Einstein condensate under periodic
oscillations of a quadratic plus quartic trap position has been studied. A
coupled set of variational equations is derived for the width and the
condensate wave function center. Analytical expressions for the growth of
oscillation amplitudes in the resonance case are derived. It is shown that
jittering of an anharmonic trap position can cause double resonance of the BEC
width and the center of mass oscillation in the wide range of the BEC
parameters values. The predictions of variational approach are confirmed by
full numerical simulations of the 1D GP equation.Comment: This paper contains a manuscript - SolAnJPB.tex and figures (fig1 -
fig1a.eps and fig1b.eps, fig2 - fig2.eps, fig3 - fig3a.eps and fig3b.eps,
fig4 - fig4a.eps and fig4b.eps). The manuscript has been prepared using
LATEX2e with the iopart class and the figures in encapsulated PostScrip
Local stress and elastic properties of lipid membranes obtained from elastic energy variation
A theory and computational method are provided for the calculation of lipid
membranes elastic parameters, which overcomes the difficulties of the existing
approaches and can be applied not only to single-component but also to
multi-component membranes. It is shown that the major elastic parameters can be
determined as the derivatives of the stress-profile moments with respect to
stretching. The more general assumption of the global incompressibility,
instead of the local one, is employed, which allows the measurement of the
local Poisson's ratio from the response of the stress profile to the isotropic
ambient pressure. In the case of the local incompressibility and quadratic
energy law, a direct relation between the bending modulus and Gaussian
curvature modulus is established
Dynamics of bright matter wave solitons in a quasi 1D Bose-Einstein condensate with a rapidly varying trap
The dynamics of a bright matter wave soliton in a quasi 1D Bose-Einstein
condensate with periodically rapidly varying trap is considered. The governing
equation is derived based on averaging over fast modulations of the
Gross-Pitaevskii (GP) equation. This equation has the form of GP equation with
effective potential of more complicated structure than unperturbed trap. For
the case of inverted (expulsive) quadratic trap corresponding to unstable GP
equation, the effective potential can be stable. For the bounded in space trap
potential it is showed that the bifurcation exists, i.e.,the single well
potential bifurcates to the triple well effective potential. Stabilization of
BEC cloud on-site state in the temporary modulated optical lattice is found.
(analogous to the Kapitza stabilization of the pendulum). The predictions of
the averaged GP equation are confirmed by the numerical simulations of GP
equation with rapid perturbations.Comment: 15 pages, 4 figure
Nonlinear material and ionic transport through membrane nanotubes
Membrane nanotubes (NTs) and their networks play an important role in intracellular membrane transport and intercellular communications. The transport characteristics of the NT lumen resemble those of conventional solid-state nanopores. However, unlike the rigid pores, the soft membrane wall of the NT can be deformed by forces driving the transport through the NT lumen. This intrinsic coupling between the NT geometry and transport properties remains poorly explored. Using synchronized fluorescence microscopy and conductance measurements, we revealed that the NT shape was changed by both electric and hydrostatic forces driving the ionic and solute fluxes through the NT lumen. Far from the shape instability, the strength of the force effect is determined by the lateral membrane tension and is scaled with membrane elasticity so that the NT can be operated as a linear elastic sensor. Near shape instabilities, the transport forces triggered large-scale shape transformations, both stochastic and periodic. The periodic oscillations were coupled to a vesicle passage along the NT axis, resembling peristaltic transport. The oscillations were parametrically controlled by the electric field, making NT a highly nonlinear nanofluidic circuitry element with biological and technological implications.This work was partially supported by NIGMS of the National Institutes of Health under award R01GM121725, RYC-2014-01419 to A.V.S.; Spanish Ministry of Science, Innovation and Universities grants PGC2018-099971-B-I00 and EUR2019-103830 to A.V.S.; Basque Government grant IT1270-19; and the Ministry of Science and Higher Education of the Russian Federation to P.I.K. and G.T.R
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