45,599 research outputs found
Fractional Quantum Hall Physics in Jaynes-Cummings-Hubbard Lattices
Jaynes-Cummings-Hubbard arrays provide unique opportunities for quantum
emulation as they exhibit convenient state preparation and measurement, and
in-situ tuning of parameters. We show how to realise strongly correlated states
of light in Jaynes-Cummings-Hubbard arrays under the introduction of an
effective magnetic field. The effective field is realised by dynamic tuning of
the cavity resonances. We demonstrate the existence of Fractional Quantum Hall
states by com- puting topological invariants, phase transitions between
topologically distinct states, and Laughlin wavefunction overlap.Comment: 5 pages, 3 figure
Organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium or azolium enolates
This tutorial review highlights the organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium/azolium enolates. The generation and synthetic utility of these powerful intermediates is highlighted through their application in various methodologies including aldol-lactonisations, Michael-lactonisations/lactamisations and [2,3]-rearrangements.Publisher PDFPeer reviewe
Tensor Networks with a Twist: Anyon-permuting domain walls and defects in PEPS
We study the realization of anyon-permuting symmetries of topological phases
on the lattice using tensor networks. Working on the virtual level of a
projected entangled pair state, we find matrix product operators (MPOs) that
realize all unitary topological symmetries for the toric and color codes. These
operators act as domain walls that enact the symmetry transformation on anyons
as they cross. By considering open boundary conditions for these domain wall
MPOs, we show how to introduce symmetry twists and defect lines into the state.Comment: 11 pages, 6 figures, 2 appendices, v2 published versio
Contrast sensitivity of insect motion detectors to natural images
How do animals regulate self-movement despite large variation in the luminance contrast of the environment? Insects are capable of regulating flight speed based on the velocity of image motion, but the mechanisms for this are unclear. The Hassenstein–Reichardt correlator model and elaborations can accurately predict responses of motion detecting neurons under many conditions but fail to explain the apparent lack of spatial pattern and contrast dependence observed in freely flying bees and flies. To investigate this apparent discrepancy, we recorded intracellularly from horizontal-sensitive (HS) motion detecting neurons in the hoverfly while displaying moving images of natural environments. Contrary to results obtained with grating patterns, we show these neurons encode the velocity of natural images largely independently of the particular image used despite a threefold range of contrast. This invariance in response to natural images is observed in both strongly and minimally motion-adapted neurons but is sensitive to artificial manipulations in contrast. Current models of these cells account for some, but not all, of the observed insensitivity to image contrast. We conclude that fly visual processing may be matched to commonalities between natural scenes, enabling accurate estimates of velocity largely independent of the particular scene
Unexpected evolutionary proximity of eukaryotic and cyanobacterial enzymes responsible for biosynthesis of retinoic acid and its oxidation
Biosynthesis of retinoic acid from retinaldehyde (retinal) is catalysed by an aldehyde dehydrogenase (ALDH) and its oxidation by cytochrome P450 enzymes (CYPs). Herein we show by phylogenetic analysis that the ALDHs and CYPs in the retinoic acid pathway in animals are much closer in evolutionary terms to cyanobacterial orthologs than would be expected from the standard models of evolution
Implications of very rapid TeV variability in blazars
We discuss the implications of rapid (few-minute) variability in the TeV flux
of blazars, which has been observed recently with the HESS and MAGIC
telescopes. The variability timescales seen in PKS 2155-304 and Mrk 501 are
much shorter than inferred light-crossing times at the black hole horizon,
suggesting that the variability involves enhanced emission in a small region
within an outflowing jet. The enhancement could be triggered by dissipation in
part of the black hole's magnetosphere at the base of the outflow, or else by
instabilities in the jet itself. By considering the energetics of the observed
flares, along with the requirement that TeV photons escape without producing
pairs, we deduce that the bulk Lorentz factors in the jets must be >50. The
distance of the emission region from the central black hole is less
well-constrained. We discuss possible consequences for multi-wavelength
observations.Comment: 5 pages, no figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
Injecting, Controlling, and Storing Magnetic Domain Walls in Ferromagnetic Nanowires
Domain walls in ferromagnetic nanowires are important for proposed devices in recording, logic, and sensing. The realization of such devices depends in part on the ability to quickly and accurately control the domain wall from creation until placement. Using micromagnetic computer simulation we demonstrate how a combination of externally applied magnetic fields is used to quickly inject, move, and accurately place multiple domain walls within a single wire for potential recording and logical operations. The use of a magnetic field component applied perpendicular to the principle domain wall driving field is found to be critical for increased speed and reliability. The effects of the transverse field on the injection and trapping of the domain wall will be shown to be of particular importance
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