12,857 research outputs found
Quantum knots in Bose-Einstein condensates created by counterdiabatic control
We theoretically study the creation of knot structures in the polar phase of
spin-1 BECs using the counterdiabatic protocol in an unusual fashion. We
provide an analytic solution to the evolution of the external magnetic field
that is used to imprint the knots. As confirmed by our simulations using the
full three-dimensional spin-1 Gross-Pitaevskii equation, our method allows for
the precise control of the Hopf charge as well as the creation time of the
knots. The knots with Hopf charge exceeding unity display multiple nested Hopf
links.Comment: 7 pages, 6 figure
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In vitro microtubule-nucleating activity of spindle pole bodies in fission yeast Schizosaccharomyces pombe: cell cycle-dependent activation in xenopus cell-free extracts.
The spindle pole body (SPB) is the equivalent of the centrosome in fission yeast. In vivo it nucleates microtubules (MTs) during mitosis, but, unlike animal centrosomes, does not act as a microtubule organizing center (MTOC) during interphase. We have studied the MT-nucleating activity of SPBs in vitro and have found that SPBs in permeabilized cells retain in vivo characteristics. SPBs in cells permeabilized during mitosis can nucleate MTs, and are recognized by two antibodies: anti-gamma-tubulin and MPM-2 which recognizes phosphoepitopes. SPBs in cells permeabilized during interphase cannot nucleate MTs and are only recognized by anti-gamma-tubulin. Interphase SPBs which cannot nucleate can be converted to a nucleation competent state by incubation in cytostatic factor (CSF)-arrested Xenopus egg extracts. After incubation, they are recognized by MPM-2, and can nucleate MTs. The conversion does not occur in Xenopus interphase extract, but occurs in Xenopus interphase extract driven into mitosis by preincubation with exogenous cyclin B. The conversion is ATP dependent and inhibited by protein kinase inhibitors and alkaline phosphatase. Purified, active, cdc2 kinase/cyclin B complex in itself is not effective for activation of MT nucleation, although some interphase SPBs are now stained with MPM-2. These results suggest that the ability of SPBs in vitro to nucleate MTs after exposure to CSF-arrested extracts is activated through a downstream pathway which is regulated by cdc2 kinase
Temporal networks: slowing down diffusion by long lasting interactions
Interactions among units in complex systems occur in a specific sequential
order thus affecting the flow of information, the propagation of diseases, and
general dynamical processes. We investigate the Laplacian spectrum of temporal
networks and compare it with that of the corresponding aggregate network.
First, we show that the spectrum of the ensemble average of a temporal network
has identical eigenmodes but smaller eigenvalues than the aggregate networks.
In large networks without edge condensation, the expected temporal dynamics is
a time-rescaled version of the aggregate dynamics. Even for single sequential
realizations, diffusive dynamics is slower in temporal networks. These
discrepancies are due to the noncommutability of interactions. We illustrate
our analytical findings using a simple temporal motif, larger network models
and real temporal networks.Comment: 5 pages, 2 figures, v2: minor revision + supplemental materia
Magnetic excitation in a new spin gap compound CuScGeO: Comparison to CuFeGeO
The compound \CuScGeO is presented as a new member of the family of weakly
coupled spin chain and dimer compounds \CuMGeO. Magnetic susceptibility, heat
capacity, and neutron inelastic scattering measurements reveal that the
compound has the same spin dimer component as \CuFeGeO. The observed narrow
band excitation in bulk measurements is consistent with spin gap behavior. The
energy scale of the weakly coupled dimers in the Sc compound is perfectly
coincident with that in the Fe compound.Comment: 5 page
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