21,682 research outputs found
Combinatorics of tight geodesics and stable lengths
We give an algorithm to compute the stable lengths of pseudo-Anosovs on the
curve graph, answering a question of Bowditch. We also give a procedure to
compute all invariant tight geodesic axes of pseudo-Anosovs.
Along the way we show that there are constants such that the
minimal upper bound on `slices' of tight geodesics is bounded below and above
by and , where is the complexity of the
surface. As a consequence, we give the first computable bounds on the
asymptotic dimension of curve graphs and mapping class groups.
Our techniques involve a generalization of Masur--Minsky's tight geodesics
and a new class of paths on which their tightening procedure works.Comment: 19 pages, 2 figure
Multiplexed communication over a high-speed quantum channel
In quantum information systems it is of particular interest to consider the
best way in which to use the non-classical resources consumed by that system.
Quantum communication protocols are integral to quantum information systems and
are amongst the most promising near-term applications of quantum information
science. Here we show that a multiplexed, digital quantum communications system
supported by comb of vacuum squeezing has a greater channel capacity per photon
than a source of broadband squeezing with the same analogue bandwidth. We
report on the time-resolved, simultaneous observation of the first dozen teeth
in a 2.4 GHz comb of vacuum squeezing produced by a sub-threshold OPO, as
required for such a quantum communications channel. We also demonstrate
multiplexed communication on that channel
Study of V/STOL aircraft implementation. Volume 2: Appendices
An analysis of V/STOL aircraft implementation and utilization is presented. The subjects discussed are: (1) short haul air transportation requirements, (2) available aircraft technology, (3) aircraft production requirements, (4) airport requirements, (5) roles and responsibilities, and (6) cost and funding
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Determining the orientations of ocean bottom seismometers using ambient noise correlation
The cross-correlation of multicomponent ambient seismic noise can reveal both the velocity and polarization of surface waves propagating between pairs of stations. We explore this property to develop a novel method for determining the horizontal orientation of ocean bottom seismometers (OBS) by analyzing the polarization of Rayleigh waves retrieved from ambient noise cross-correlation. We demonstrate that the sensor orientations can be estimated through maximizing the correlation between the radial-vertical component and the phase-shifted vertical-vertical component of the empirical Green's tensor. We apply this new method to the ELSC (Eastern Lau Spreading Center) OBS experiment data set and illustrate its robustness by comparing the obtained orientations with results from a conventional method utilizing teleseismic P and Rayleigh wave polarizations. When applied to a large OBS array, the ambient noise method provides a larger number of orientation estimates and better azimuthal coverage than typically is possible with traditional methods
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