214,379 research outputs found
Learning SO(3) Equivariant Representations with Spherical CNNs
We address the problem of 3D rotation equivariance in convolutional neural
networks. 3D rotations have been a challenging nuisance in 3D classification
tasks requiring higher capacity and extended data augmentation in order to
tackle it. We model 3D data with multi-valued spherical functions and we
propose a novel spherical convolutional network that implements exact
convolutions on the sphere by realizing them in the spherical harmonic domain.
Resulting filters have local symmetry and are localized by enforcing smooth
spectra. We apply a novel pooling on the spectral domain and our operations are
independent of the underlying spherical resolution throughout the network. We
show that networks with much lower capacity and without requiring data
augmentation can exhibit performance comparable to the state of the art in
standard retrieval and classification benchmarks.Comment: Camera-ready. Accepted to ECCV'18 as oral presentatio
Reconsidering Linear Transmit Signal Processing in 1-Bit Quantized Multi-User MISO Systems
In this contribution, we investigate a coarsely quantized Multi-User
(MU)-Multiple Input Single Output (MISO) downlink communication system, where
we assume 1-Bit Digital-to-Analog Converters (DACs) at the Base Station (BS)
antennas. First, we analyze the achievable sum rate lower-bound using the
Bussgang decomposition. In the presence of the non-linear quanization, our
analysis indicates the potential merit of reconsidering traditional signal
processing techniques in coarsely quantized systems, i.e., reconsidering
transmit covariance matrices whose rank is equal to the rank of the channel.
Furthermore, in the second part of this paper, we propose a linear precoder
design which achieves the predicted increase in performance compared with a
state of the art linear precoder design. Moreover, our linear signal processing
algorithm allows for higher-order modulation schemes to be employed
NLTE and LTE Lick indices for red giants from [M/H] 0.0 to -6.0 at SDSS and IDS spectral resolution
We investigate the dependence of the complete system of 22 Lick indices on
overall metallicity scaled from solar abundances, [M/H], from the solar value,
0.0, down to the extremely-metal-poor (XMP) value of -6.0, for late-type giant
stars (MK luminosity class III, log(g)=2.0) of MK spectral class late-K to
late-F (3750 < Teff < 6500 K) of the type that are detected as "fossils" of
early galaxy formation in the Galactic halo and in extra-galactic structures.
Our investigation is based on synthetic index values, I, derived from
atmospheric models and synthetic spectra computed with PHOENIX in LTE and
Non-LTE (NLTE), where the synthetic spectra have been convolved to the spectral
resolution, R, of both IDS and SDSS (and LAMOST) spectroscopy. We identify nine
indices, that we designate "Lick-XMP", that remain both detectable and
significantly [M/H]-dependent down to [M/H] values of at least ~-5.0, and down
to [M/H] ~ -6.0 in five cases, while also remaining well-behaved . For these
nine, we study the dependence of I on NLTE effects, and on spectral resolution.
For our LTE I values for spectra of SDSS resolution, we present the fitted
polynomial coefficients, C_n, from multi-variate linear regression for I with
terms up to third order in the independent variable pairs (Teff, [M/H]), and
(V-K, [M/H]), and compare them to the fitted C_n values of Worthey et al.
(1994) at IDS spectral resolution.Comment: Accepted for publication in the Astrophysical Journal. Tables 6 and 7
available electronically from the autho
Transmission of natural scene images through a multimode fibre
The optical transport of images through a multimode fibre remains an
outstanding challenge with applications ranging from optical communications to
neuro-imaging. State of the art approaches either involve measurement and
control of the full complex field transmitted through the fibre or, more
recently, training of artificial neural networks that however, are typically
limited to image classes belong to the same class as the training data set.
Here we implement a method that statistically reconstructs the inverse
transformation matrix for the fibre. We demonstrate imaging at high frame
rates, high resolutions and in full colour of natural scenes, thus
demonstrating general-purpose imaging capability. Real-time imaging over long
fibre lengths opens alternative routes to exploitation for example for secure
communication systems, novel remote imaging devices, quantum state control
processing and endoscopy
General relativistic null-cone evolutions with a high-order scheme
We present a high-order scheme for solving the full non-linear Einstein
equations on characteristic null hypersurfaces using the framework established
by Bondi and Sachs. This formalism allows asymptotically flat spaces to be
represented on a finite, compactified grid, and is thus ideal for far-field
studies of gravitational radiation. We have designed an algorithm based on
4th-order radial integration and finite differencing, and a spectral
representation of angular components. The scheme can offer significantly more
accuracy with relatively low computational cost compared to previous methods as
a result of the higher-order discretization. Based on a newly implemented code,
we show that the new numerical scheme remains stable and is convergent at the
expected order of accuracy.Comment: 24 pages, 3 figure
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