74,557 research outputs found
GpsTunes: controlling navigation via audio feedback
We combine the functionality of a mobile Global Positioning System (GPS) with that of an MP3 player, implemented on a PocketPC, to produce a handheld system capable of guiding a user to their desired target location via continuously adapted music feedback. We illustrate how the approach to presentation of the audio display can benefit from insights from control theory, such as predictive 'browsing' elements to the display, and the appropriate representation of uncertainty or ambiguity in the display. The probabilistic interpretation of the navigation task can be generalised to other context-dependent mobile applications. This is the first example of a completely handheld location- aware music player. We discuss scenarios for use of such systems
Orbital evolution of a test particle around a black hole: higher-order corrections
We study the orbital evolution of a radiation-damped binary in the extreme
mass ratio limit, and the resulting waveforms, to one order beyond what can be
obtained using the conservation laws approach. The equations of motion are
solved perturbatively in the mass ratio (or the corresponding parameter in the
scalar field toy model), using the self force, for quasi-circular orbits around
a Schwarzschild black hole. This approach is applied for the scalar model.
Higher-order corrections yield a phase shift which, if included, may make
gravitational-wave astronomy potentially highly accurate.Comment: 4 pages, 3 Encapsulated PostScript figure
Controlled cavity-QED using a photonic crystal waveguide-cavity system
We introduce a photonic crystal waveguide-cavity system for controlling
single photon cavity-QED processes. Exploiting Bloch mode analysis, and
medium-dependent Green function techniques, we demonstrate that the propagation
of single photons can be accurately described analytically, for integrated
periodic waveguides with little more than four unit cells, including an output
coupler. We verify our analytical approach by comparing to rigorous numerical
calculations for a range of photonic crystal waveguide lengths. This allows one
to nano-engineer various regimes of cavity-QED with unprecedented control. We
demonstrate Purcell factors of greater than 1000 and on-chip single photon beta
factors of about 80% efficiency. Both weak and strong coupling regimes are
investigated, and the important role of waveguide length on the output emission
spectra is shown, for vertically emitted emission and output waveguide
emission
First passage time for random walks in heterogeneous networks
The first passage time (FPT) for random walks is a key indicator of how fast
information diffuses in a given system. Despite the role of FPT as a
fundamental feature in transport phenomena, its behavior, particularly in
heterogeneous networks, is not yet fully understood. Here, we study, both
analytically and numerically, the scaling behavior of the FPT distribution to a
given target node, averaged over all starting nodes. We find that random walks
arrive quickly at a local hub, and therefore, the FPT distribution shows a
crossover with respect to time from fast decay behavior (induced from the
attractive effect to the hub) to slow decay behavior (caused by the exploring
of the entire system). Moreover, the mean FPT is independent of the degree of
the target node in the case of compact exploration. These theoretical results
justify the necessity of using a random jump protocol (empirically used in
search engines) and provide guidelines for designing an effective network to
make information quickly accessible.Comment: 5 pages, 3 figure
Exploiting long-range disorder in slow-light photonic crystal waveguides
The interplay between order and disorder in photonic lattices opens up a wide
range of novel optical scattering mechanisms, resonances, and applications that
can be obscured by typical ordered design approaches to photonics. Striking
examples include Anderson localization, random lasers, and visible light
scattering in biophotonic structures such as butterfly wings. In this work, we
present a profound example of light localization in photonic crystal waveguides
by introducing long-range correlated disorder. Using a rigorous
three-dimensional Bloch mode expansion technique, we demonstrate how inter-hole
correlations have a negative contribution to the total out-of-plane radiative
losses, leading to a pronounced enhancement of the quality factor, , and
cavity figures of merit in the long-range correlation regime.
Subsequently, the intensity fluctuations of the system are shown to globally
increase with the correlation length, highlighting the non-trivial role of
long-range disorder on the underlying scattering mechanisms. We also explore
the possibility of creating ultra-high quality cavity modes via inter-hole
correlations, which have various functionalities in chip-based nonlinear optics
and waveguide cavity-quantum electrodynamics.Comment: Updated version with DO
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