39,425 research outputs found
Spectrum-enhanced Pairwise Learning to Rank
To enhance the performance of the recommender system, side information is
extensively explored with various features (e.g., visual features and textual
features). However, there are some demerits of side information: (1) the extra
data is not always available in all recommendation tasks; (2) it is only for
items, there is seldom high-level feature describing users. To address these
gaps, we introduce the spectral features extracted from two hypergraph
structures of the purchase records. Spectral features describe the
\textit{similarity} of users/items in the graph space, which is critical for
recommendation. We leverage spectral features to model the users' preference
and items' properties by incorporating them into a Matrix Factorization (MF)
model. In addition to modeling, we also use spectral features to optimize.
Bayesian Personalized Ranking (BPR) is extensively leveraged to optimize models
in implicit feedback data. However, in BPR, all missing values are regarded as
negative samples equally while many of them are indeed unseen positive ones. We
enrich the positive samples by calculating the similarity among users/items by
the spectral features. The key ideas are: (1) similar users shall have similar
preference on the same item; (2) a user shall have similar perception on
similar items. Extensive experiments on two real-world datasets demonstrate the
usefulness of the spectral features and the effectiveness of our
spectrum-enhanced pairwise optimization. Our models outperform several
state-of-the-art models significantly.Comment: 11 pages; submitted to World Wide Web Conference (WWW 2019
On Okounkov's conjecture connecting Hilbert schemes of points and multiple q-zeta values
We compute the generating series for the intersection pairings between the
total Chern classes of the tangent bundles of the Hilbert schemes of points on
a smooth projective surface and the Chern characters of tautological bundles
over these Hilbert schemes. Modulo the lower weight term, we verify Okounkov's
conjecture [Oko] connecting these Hilbert schemes and multiple -zeta values.
In addition, this conjecture is completely proved when the surface is abelian.
We also determine some universal constants in the sense of Boissi\' ere and
Nieper-Wisskirchen [Boi, BN] regarding the total Chern classes of the tangent
bundles of these Hilbert schemes. The main approach of this paper is to use the
set-up of Carlsson and Okounkov outlined in [Car, CO] and the structure of the
Chern character operators proved in [LQW2].Comment: 35 pages, comments are welcom
- mixing parameter in the factorization-assisted topological-amplitude approach
We calculate the - mixing parameter in the
factorization-assisted topological-amplitude (FAT) approach, considering
contributions from , , and modes, where () stands
for a pseudoscalar (vector) meson. The and decay amplitudes
are extracted in the FAT approach, and the decay amplitudes with
final states in the longitudinal polarization are estimated via the parameter
set for . It is found that the contribution to , being of
order of , is negligible, and that the and contributions
amount only up to , a prediction more precise than
those previously obtained in the literature, and much lower than the
experimental data . We conclude that meson
decays into other two-body and multi-particle final states are relevant to the
evaluation of , so it is difficult to understand it fully in an exclusive
approach.Comment: 13 page
Circularly polarized extreme ultraviolet high harmonic generation in graphene
Circularly polarized extreme ultraviolet (XUV) radiation is highly
interesting for investigation of chirality-sensitive light-matter interactions.
Recent breakthroughs have enabled generation of such light sources via high
harmonic generation (HHG) from rare gases. There is a growing interest in
extending HHG medium from gases to solids, especially to 2D materials, as they
hold great promise to develop ultra-compact solid-state photonic devices and
provide insights into electronic properties of the materials themselves.
However, HHG in graphene driven by terahertz to mid-infrared fields reported so
far only generate low harmonic orders, and furthermore no harmonics driven by
circularly polarized lasers. Here, using first-principles simulations within a
time-dependent density-functional theory framework, we show that it is possible
to generate HHG extending to the XUV spectral region in monolayer extended
graphene excited by near-infrared lasers. Moreover, we demonstrate that a
single circularly polarized driver is enough to ensure HHG in graphene with
circular polarization. The corresponding spectra reflect the six-fold
rotational symmetry of the graphene crystal. Extending HHG in graphene to the
XUV spectral regime and realizing circular polarization represent an important
step towards the development of novel nanoscale attosecond photonic devices and
numerous applications such as spectroscopic investigation and nanoscale imaging
of ultrafast chiral and spin dynamics in graphene and other 2D materials.Comment: 5 figure
Parameter Reconstruction for general transport equation
We consider the inverse problem for the general transport equation with
external field, source term and absorption coefficient. We show that the source
and the absorption coefficients can be uniquely reconstructed from the boundary
measurement, in a Lipschitz stable manner. Specifically, the uniqueness and
stability are obtained by using the Carleman estimate in which a special weight
function is designed to pick up information on the desired parameter.Comment: 23 pages, 3 figure
Strain-controlled high harmonic generation with Dirac fermions in silicene
Two-dimensional (2D) materials with zero band gap exhibit remarkable
electronic properties with wide tunability. High harmonic generation (HHG) in
such materials offers unique platforms to develop novel optoelectronic devices
at nanoscale, as well as to investigate strong-field and ultrafast nonlinear
behaviour of massless Dirac fermions. However, control of HHG by modulating
electronic structure of materials remains largerly unexplored to date. Here we
report controllable HHG by tuning the electronic structures via mechanical
engineering. Using an \textit{ab initio} approach based on time-dependent
density-functional theory (TDDFT), we show that the HHG process is sensitive to
the modulation of band structures of monolayer silicene while preserving the
Dirac cones under biaxial and uniaxial strains, which can lead to significant
enhancement of harmonic intensity up to an order of magnitude. With the
additional advantage of silicene in compatibility and integration into the
current silicon-based electronic industry, this study may open a new avenue to
develop efficient solid-state optoelectronic nano-devices, and provide a
valuable tool to understand the strong-field and mechanically induced ultrafast
nonlinear response of Dirac carriers in 2D materials.Comment: 24pages, 7 figure
Strong-field nonlinear optical properties of monolayer black phosphorus
Within the past few years, atomically thin black phosphorus (BP) has been
demonstrated as a fascinating new 2D material that is promising for novel
nanoelectronics and nanophotonics applications, due to its many unique
properties such as direct and widely tunable bandgap, high carrier mobility and
remarkable intrinsic in-plane anisotropy. However, its important extreme
nonlinear behavior and ultrafast dynamics of carriers under strong-field
excitation have yet to be revealed to date. Herein, we report nonperturbative
high harmonic generation (HHG) in monolayer BP by first-principles simulations.
We show that BP exhibits extraordinary HHG properties, with clear advantages
over three major types of 2D materials under intensive study, i.e.,
semimetallic graphene, semiconducting MoS, and insulating hexagonal boron
nitride, in terms of HHG cutoff energy and spectral intensity. This study
advances the scope of current research activities of BP into a new regime,
suggesting its promising future in applications of extreme-ultraviolet and
attosecond nanophotonics, and also opening doors to investigate the
strong-field and ultrafast carrier dynamics of this emerging material.Comment: 24 pages, 5 figure
Distilling Critical Paths in Convolutional Neural Networks
Neural network compression and acceleration are widely demanded currently due
to the resource constraints on most deployment targets. In this paper, through
analyzing the filter activation, gradients, and visualizing the filters'
functionality in convolutional neural networks, we show that the filters in
higher layers learn extremely task-specific features, which are exclusive for
only a small subset of the overall tasks, or even a single class. Based on such
findings, we reveal the critical paths of information flow for different
classes. And by their intrinsic property of exclusiveness, we propose a
critical path distillation method, which can effectively customize the
convolutional neural networks to small ones with much smaller model size and
less computation.Comment: Accepted in NIPS18 CDNNRIA worksho
Computational Soundness Results for Stateful Applied pi Calculus
In recent years, many researches have been done to establish symbolic models
of stateful protocols. Two works among them, the SAPIC tool and StatVerif tool,
provide a high-level specification language and an automated analysis. Their
language, the stateful applied \pi-calculus, is extended from the applied
\pi-calculus by defining explicit state constructs. Symbolic abstractions of
cryptography used in it make the analysis amenable to automation. However, this
might overlook the attacks based on the algebraic properties of the
cryptographic algorithms. In our paper, we establish the computational
soundness results for stateful applied \pi-calculus used in SAPIC tool and
StatVerif tool.
In our approach, we build our results on the CoSP framework. For SAPIC, we
embed the non-monotonic protocol states into the CoSP protocols, and prove that
the resulting CoSP protocols are efficient. Through the embedding, we provide
the computational soundness result for SAPIC (by Theorem 1). For StatVerif, we
encode the StatVerif process into a subset of SAPIC process, and obtain the
computational soundness result for StatVerif (by Theorem 2). Our encoding shows
the differences between the semantics of the two languages. Our work inherits
the modularity of CoSP, which allows for easily extending the proofs to
specific cryptographic primitives. Thus we establish a computationally sound
automated verification result for the input languages of SAPIC and StatVerif
that use public-key encryption and signatures (by Theorem 3).Comment: to appear in POST 201
Interplay between superconductivity and pseudogap state in bilayer cuprate superconductors
The interplay between the superconducting gap and normal-state pseudogap in
the bilayer cuprate superconductors is studied based on the kinetic energy
driven superconducting mechanism. It is shown that the charge carrier
interaction directly from the interlayer coherent hopping in the kinetic energy
by exchanging spin excitations does not provide the contribution to the
normal-state pseudogap in the particle-hole channel and superconducting gap in
the particle-particle channel, while only the charge carrier interaction
directly from the intralayer hopping in the kinetic energy by exchanging spin
excitations induces the normal-state pseudogap in the particle-hole channel and
superconducting gap in the particle-particle channel, and then the two-gap
behavior is a universal feature for the single layer and bilayer cuprate
superconductors.Comment: 7 pages, 2 figure
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