982,549 research outputs found
Tropical curves, graph complexes, and top weight cohomology of M_g
We study the topology of a space parametrizing stable tropical curves of
genus g with volume 1, showing that its reduced rational homology is
canonically identified with both the top weight cohomology of M_g and also with
the genus g part of the homology of Kontsevich's graph complex. Using a theorem
of Willwacher relating this graph complex to the Grothendieck-Teichmueller Lie
algebra, we deduce that H^{4g-6}(M_g;Q) is nonzero for g=3, g=5, and g at least
7. This disproves a recent conjecture of Church, Farb, and Putman as well as an
older, more general conjecture of Kontsevich. We also give an independent proof
of another theorem of Willwacher, that homology of the graph complex vanishes
in negative degrees.Comment: 31 pages. v2: streamlined exposition. Final version, to appear in J.
Amer. Math. So
The polarisation of afterglow emission reveals GRB jet structure
We numerically compute light and polarisation curves of gamma-ray burst
afterglows for various configurations of the jet luminosity structure and for
different dynamical evolutions. We especially consider the standard homogeneous
``top hat'' jet and the ``universal structured jet'' with power-law wings. We
also investigate a possible more physical variation of the ``top hat'' model:
the ``Gaussian jet''. The polarisation curves for the last two jet types are
shown here for the first time together with the computation of X-ray and radio
polarised fluxes. We show that the lightcurves of the total flux from these
configurations are very similar to each other, and therefore only very high
quality data could allow us to pin down the underlying jet structure. We
demonstrate instead that polarisation curves are a powerful means to solve the
jet structure, since the predicted behaviour of polarisation and its position
angle at times around the jet break are very different if not opposite. We
conclude that the afterglow polarisation measurements provide clear footprints
of any outflow energy distribution (unlike the lightcurves of the total flux)
and the joint analysis of the total and polarised flux should reveal GRBs jet
structure.Comment: 16 pages, 18 figures, MNRAS, temp, 321. Light curves and polarisation
curves for a Gaussian jet added. Cartoon of the three jet structures adde
Guided Surface Plasmon Mode of Semicircular Cross Section Silver Nanoridges
Tightly confined plasmon waveguide modes supported by semicircular cross
section top silver nanoridges are investigated in this paper. Mode field
profiles, dispersion curves, propagation distances, confinement factors, and
figure-of-merits of semicircular top silver nanoridge plasmon waveguide mode
are calculated for different radii of curvature at different wavelengths. It is
found that semicircular top silver nanoridges support tightly confined
quasi-TEM plasmon waveguide modes. Semicircular top silver nanoridge mode has
longer propagation distance and higher figure-of-merit than that of the
cylindrical silver nanowire of the same radius of curvature.Comment: 21 pages, 11 figure
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