2,281 research outputs found
Fourier modal method for inverse design of metasurface-enhanced micro-LEDs
We present a simulation capability for micro-scale light-emitting diodes
(uLEDs) that achieves comparable accuracy to CPU-based finite-difference
time-domain simulation but is more than 10^7 times faster. Our approach is
based on the Fourier modal method (FMM) -- which, as we demonstrate, is well
suited to modeling thousands of incoherent sources -- with extensions that
allow rapid convergence for uLED structures that are challenging to model with
standard approaches. The speed of our method makes the inverse design of uLEDs
tractable, which we demonstrate by designing a metasurface-enhanced uLED that
doubles the light extraction efficiency of an unoptimized device.Comment: 15 pages, 10 figure
Data-driven acceleration of Photonic Simulations
Designing modern photonic devices often involves traversing a large parameter
space via an optimization procedure, gradient based or otherwise, and typically
results in the designer performing electromagnetic simulations of correlated
devices. In this paper, we present an approach to accelerate the Generalized
Minimal Residual (GMRES) algorithm for the solution of frequency-domain
Maxwell's equations using two machine learning models (principal component
analysis and a convolutional neural network) trained on simulations of
correlated devices. These data-driven models are trained to predict a subspace
within which the solution of the frequency-domain Maxwell's equations lie. This
subspace can then be used for augmenting the Krylov subspace generated during
the GMRES iterations. By training the proposed models on a dataset of grating
wavelength-splitting devices, we show an order of magnitude reduction () in the number of GMRES iterations required for solving frequency-domain
Maxwell's equations
Photon-Graviton Amplitudes from the Effective Action
We report on the status of an ongoing effort to calculate the complete
one-loop low-energy effective actions in Einstein-Maxwell theory with a massive
scalar or spinor loop, and to use them for obtaining the explicit form of the
corresponding M-graviton/N-photon amplitudes. We present explicit results for
the effective actions at the one-graviton four-photon level, and for the
amplitudes at the one-graviton two-photon level. As expected on general
grounds, these amplitudes relate in a simple way to the corresponding
four-photon amplitudes. We also derive the gravitational Ward identity for the
1PI one-graviton -- N photon amplitude.Comment: 9 pages, 2 figures, talk given by C. Schubert at "Supersymmetries and
Quantum Symmetries - SQS`2011", JINR Dubna, July 18 - 23, 2011 (to appear in
the Proceedings
Dimensional renormalization of Yukawa theories wia Wilsonian methods
In the 't Hooft-Veltman dimensional regularization scheme it is necessary to
introduce finite counterterms to satisfy chiral Ward identities. It is a
non-trivial task to evaluate these counterterms even at two loops. We suggest
the use of Wilsonian exact renormalization group techniques to reduce the
computation of these counterterms to simple master integrals. We illustrate
this method by a detailed study of a generic Yukawa model with massless
fermions at two loops.Comment: 32 pages, 9 figures, revised version: minor errors corrected, a
reference adde
Euler-Heisenberg lagrangians and asymptotic analysis in 1+1 QED, part 1: Two-loop
We continue an effort to obtain information on the QED perturbation series at
high loop orders, and particularly on the issue of large cancellations inside
gauge invariant classes of graphs, using the example of the l - loop N - photon
amplitudes in the limit of large photons numbers and low photon energies. As
was previously shown, high-order information on these amplitudes can be
obtained from a nonperturbative formula, due to Affleck et al., for the
imaginary part of the QED effective lagrangian in a constant field. The
procedure uses Borel analysis and leads, under some plausible assumptions, to a
number of nontrivial predictions already at the three-loop level. Their direct
verification would require a calculation of this `Euler-Heisenberg lagrangian'
at three-loops, which seems presently out of reach. Motivated by previous work
by Dunne and Krasnansky on Euler-Heisenberg lagrangians in various dimensions,
in the present work we initiate a new line of attack on this problem by
deriving and proving the analogous predictions in the simpler setting of 1+1
dimensional QED. In the first part of this series, we obtain a generalization
of the formula of Affleck et al. to this case, and show that, for both Scalar
and Spinor QED, it correctly predicts the leading asymptotic behaviour of the
weak field expansion coefficients of the two loop Euler-Heisenberg lagrangians.Comment: 28 pages, 1 figures, final published version (minor modifications,
refs. added
Telepresence and the Role of the Senses
The telepresence experience can be evoked in a number of ways. A well-known example is a player of videogames who reports about a telepresence experience, a subjective experience of being in one place or environment, even when physically situated in another place. In this paper we set the phenomenon of telepresence into a theoretical framework. As people react subjectively to stimuli from telepresence, empirical studies can give more evidence about the phenomenon. Thus, our contribution is to bridge the theoretical with the empirical. We discuss theories of perception with an emphasis on Heidegger, Merleau-Ponty and Gibson, the role of the senses and the Spinozian belief procedure. The aim is to contribute to our understanding of this phenomenon. A telepresence-study that included the affordance concept is used to empirically study how players report sense-reactions to virtual sightseeing in two cities. We investigate and explore the interplay of the philosophical and the empirical. The findings indicate that it is not only the visual sense that plays a role in this experience, but all senses
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