1,334 research outputs found
Topological interface engineering and defect crossing in ultracold atomic gases
We propose an experimentally feasible scheme for topological interface
engineering and show how it can be used for studies of dynamics of
topologically nontrivial interfaces and perforation of defects and textures
across such interfaces. The method makes use of the internal spin structure of
the atoms together with locally applied control of interaction strengths to
create many-particle states with highly complex topological properties. In
particular, we consider a constructed coherent interface between topologically
distinct phases of spinor Bose-Einstein condensates.Comment: 9 pages, 7 figure
Characteristics of the polymer transport in ratchet systems
Molecules with complex internal structure in time-dependent periodic
potentials are studied by using short Rubinstein-Duke model polymers as an
example. We extend our earlier work on transport in stochastically varying
potentials to cover also deterministic potential switching mechanisms,
energetic efficiency and non-uniform charge distributions. We also use currents
in the non-equilibrium steady state to identify the dominating mechanisms that
lead to polymer transportation and analyze the evolution of the macroscopic
state (e.g., total and head-to-head lengths) of the polymers. Several numerical
methods are used to solve the master equations and nonlinear optimization
problems. The dominating transport mechanisms are found via graph optimization
methods. The results show that small changes in the molecule structure and the
environment variables can lead to large increases of the drift. The drift and
the coherence can be amplified by using deterministic flashing potentials and
customized polymer charge distributions. Identifying the dominating transport
mechanism by graph analysis tools is found to give insight in how the molecule
is transported by the ratchet effect.Comment: 35 pages, 17 figures, to appear in Phys. Rev.
A Quantum Tweezer for Atoms
We propose a quantum tweezer for extracting a desired number of neutral atoms
from a reservoir. A trapped Bose-Einstein condensate (BEC) is used as the
reservoir, taking advantage of its coherent nature, which can guarantee a
constant outcome. The tweezer is an attractive quantum dot, which may be
generated by red-detuned laser light. By moving with certain speeds, the dot
can extract a desired number of atoms from the BEC through Landau-Zener
tunneling. The feasibility of our quantum tweezer is demonstrated through
realistic and extensive model calculations.Comment: 4 pages, 6 figures Revised versio
Covariant generalization of cosmological perturbation theory
We present an approach to cosmological perturbations based on a covariant
perturbative expansion between two worldlines in the real inhomogeneous
universe. As an application, at an arbitrary order we define an exact scalar
quantity which describes the inhomogeneities in the number of e-folds on
uniform density hypersurfaces and which is conserved on all scales for a
barotropic ideal fluid. We derive a compact form for its conservation equation
at all orders and assign it a simple physical interpretation. To make a
comparison with the standard perturbation theory, we develop a method to
construct gauge-invariant quantities in a coordinate system at arbitrary order,
which we apply to derive the form of the n-th order perturbation in the number
of e-folds on uniform density hypersurfaces and its exact evolution equation.
On large scales, this provides the gauge-invariant expression for the curvature
perturbation on uniform density hypersurfaces and its evolution equation at any
order.Comment: Minor changes to match the version published in PRD. RevTex, 22
pages, 1 figur
Geodynamic implications for zonal and meridional isotopic patterns across the northern Lau and North Fiji Basins
We present new Sr-Nd-Pb-Hf-He isotopic data for sixty-five volcanic samples from the northern Lau and North Fiji Basin. This includes forty-seven lavas obtained from forty dredge sites spanning an east-west transect across the Lau and North Fiji basins, ten ocean island basalt (OIB)-type lavas collected from seven Fijian islands, and eight OIB lavas sampled on Rotuma. For the first time we are able to map clear north-south and east-west geochemical gradients in 87Sr/86Sr across the northern Lau and North Fiji Basins: lavas with the most geochemically enriched radiogenic isotopic signatures are located in the northeast Lau Basin, while signatures of geochemical enrichment are diminished to the south and west away from the Samoan hotspot. Based on these geochemical patterns and plate reconstructions of the region, these observations are best explained by the addition of Samoa, Rurutu, and Rarotonga hotspot material over the past 4 Ma. We suggest that underplated Samoan material has been advected into the Lau Basin over the past ∼4 Ma. As the slab migrated west (and toward the Samoan plume) via rollback over time, younger and hotter (and therefore less viscous) underplated Samoan plume material was entrained. Thus, entrainment efficiency of underplated plume material was enhanced, and Samoan plume signatures in the Lau Basin became stronger as the trench approached the Samoan hotspot. The addition of subducted volcanoes to the Cook-Austral Volcanic Lineament material, first from the Rarotonga hotspot, then followed by the Rurutu hotspot, contributes to the extreme geochemical signatures observed in the northeast Lau Basin
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