471,381 research outputs found
Modeling Occasion Evolution in Frequency Domain for Promotion-Aware Click-Through Rate Prediction
Promotions are becoming more important and prevalent in e-commerce to attract
customers and boost sales, leading to frequent changes of occasions, which
drives users to behave differently. In such situations, most existing
Click-Through Rate (CTR) models can't generalize well to online serving due to
distribution uncertainty of the upcoming occasion. In this paper, we propose a
novel CTR model named MOEF for recommendations under frequent changes of
occasions. Firstly, we design a time series that consists of occasion signals
generated from the online business scenario. Since occasion signals are more
discriminative in the frequency domain, we apply Fourier Transformation to
sliding time windows upon the time series, obtaining a sequence of frequency
spectrum which is then processed by Occasion Evolution Layer (OEL). In this
way, a high-order occasion representation can be learned to handle the online
distribution uncertainty. Moreover, we adopt multiple experts to learn feature
representations from multiple aspects, which are guided by the occasion
representation via an attention mechanism. Accordingly, a mixture of feature
representations is obtained adaptively for different occasions to predict the
final CTR. Experimental results on real-world datasets validate the superiority
of MOEF and online A/B tests also show MOEF outperforms representative CTR
models significantly
Symmetry protected topological orders and the group cohomology of their symmetry group
Symmetry protected topological (SPT) phases are gapped short-range-entangled
quantum phases with a symmetry G. They can all be smoothly connected to the
same trivial product state if we break the symmetry. The Haldane phase of
spin-1 chain is the first example of SPT phase which is protected by SO(3) spin
rotation symmetry. The topological insulator is another exam- ple of SPT phase
which is protected by U(1) and time reversal symmetries. It has been shown that
free fermion SPT phases can be systematically described by the K-theory. In
this paper, we show that interacting bosonic SPT phases can be systematically
described by group cohomology theory: distinct d-dimensional bosonic SPT phases
with on-site symmetry G (which may contain anti-unitary time reversal symmetry)
can be labeled by the elements in H^{1+d}[G, U_T(1)] - the Borel (1 +
d)-group-cohomology classes of G over the G-module U_T(1). The boundary
excitations of the non-trivial SPT phases are gapless or degenerate. Even more
generally, we find that the different bosonic symmetry breaking
short-range-entangled phases are labeled by the following three mathematical
objects: (G_H, G_{\Psi}, H^{1+d}[G_{\Psi}, U_T(1)], where G_H is the symmetry
group of the Hamiltonian and G_{\Psi} the symmetry group of the ground states.Comment: 55 pages, 42 figures, RevTeX4-1, included some new reference
Online Deep Metric Learning
Metric learning learns a metric function from training data to calculate the
similarity or distance between samples. From the perspective of feature
learning, metric learning essentially learns a new feature space by feature
transformation (e.g., Mahalanobis distance metric). However, traditional metric
learning algorithms are shallow, which just learn one metric space (feature
transformation). Can we further learn a better metric space from the learnt
metric space? In other words, can we learn metric progressively and nonlinearly
like deep learning by just using the existing metric learning algorithms? To
this end, we present a hierarchical metric learning scheme and implement an
online deep metric learning framework, namely ODML. Specifically, we take one
online metric learning algorithm as a metric layer, followed by a nonlinear
layer (i.e., ReLU), and then stack these layers modelled after the deep
learning. The proposed ODML enjoys some nice properties, indeed can learn
metric progressively and performs superiorly on some datasets. Various
experiments with different settings have been conducted to verify these
properties of the proposed ODML.Comment: 9 page
Group Theory of Circular-Polarization Effects in Chiral Photonic Crystals with Four-Fold Rotation Axes, Applied to the Eight-Fold Intergrowth of Gyroid Nets
We use group or representation theory and scattering matrix calculations to
derive analytical results for the band structure topology and the scattering
parameters, applicable to any chiral photonic crystal with body-centered cubic
symmetry I432 for circularly-polarised incident light. We demonstrate in
particular that all bands along the cubic [100] direction can be identified
with the irreducible representations E+/-,A and B of the C4 point group. E+ and
E- modes represent the only transmission channels for plane waves with wave
vector along the ? line, and can be identified as non-interacting transmission
channels for right- (E-) and left-circularly polarised light (E+),
respectively. Scattering matrix calculations provide explicit relationships for
the transmission and reflectance amplitudes through a finite slab which
guarantee equal transmission rates for both polarisations and vanishing
ellipticity below a critical frequency, yet allowing for finite rotation of the
polarisation plane. All results are verified numerically for the so-called
8-srs geometry, consisting of eight interwoven equal-handed dielectric Gyroid
networks embedded in air. The combination of vanishing losses, vanishing
ellipticity, near-perfect transmission and optical activity comparable to that
of metallic meta-materials makes this geometry an attractive design for
nanofabricated photonic materials
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