arXiv subjects

Hui Liu

Publications and source records attributed to Hui Liu.

At least 541 records · Page 30Linked to original sources

arXiv2019

INS: An Interactive Chinese News Synthesis System

Nowadays, we are surrounded by more and more online news articles. Tens or hundreds of news articles need to be read if we wish to explore a hot news event or topic. So it is of vital importance to automatically synthesize a batch of news articles related to the event or topic into a new synthesis article (or overview article) for reader's convenience. It is so challenging to make news synthesis fully automatic that there is no successful solution by now. In this paper, we put forward a novel Interactive News Synthesis system (i.e. INS), which can help generate news overview articles automatically or by interacting with users. More importantly, INS can serve as a tool for editors to help them finish their jobs. In our experiments, INS performs well on both topic representation and synthesis article generation. A user study also demonstrates the usefulness and users' satisfaction with the INS tool. A demo video is available at \url{https://youtu.be/7ItteKW3GEk}.

cs.CL↗

arXiv2019

Transformation optics based on metasurfaces

Recently, new artificial material has been proposed to control an electromagnetic wave-metasurface, a two-dimensional metamaterial. Compared with a three-dimensional bulky metamaterial, this artificial plane material with sub-wavelength thickness greatly reduces fabrication time and mitigates fabrication complexity. Additionally, traditional metamaterials usually control the wavefront of an electromagnetic wave by accumulating the phase through propagating at a distance far larger than the wavelength. However, a metasurface can efficiently manipulate the wavefront of an incident electromagnetic wave through just the subwavelength propagation distance. Therefore, this can largely alleviate the propagation loss. Given the fact that a metasurface has high manipulation efficiency for an electromagnetic wave in the near filed regime, our group investigated experimental work on the analogy of gravity using a metasurface.

physics.optics↗

arXiv2019

Towards Explainable NLP: A Generative Explanation Framework for Text Classification

Building explainable systems is a critical problem in the field of Natural Language Processing (NLP), since most machine learning models provide no explanations for the predictions. Existing approaches for explainable machine learning systems tend to focus on interpreting the outputs or the connections between inputs and outputs. However, the fine-grained information is often ignored, and the systems do not explicitly generate the human-readable explanations. To better alleviate this problem, we propose a novel generative explanation framework that learns to make classification decisions and generate fine-grained explanations at the same time. More specifically, we introduce the explainable factor and the minimum risk training approach that learn to generate more reasonable explanations. We construct two new datasets that contain summaries, rating scores, and fine-grained reasons. We conduct experiments on both datasets, comparing with several strong neural network baseline systems. Experimental results show that our method surpasses all baselines on both datasets, and is able to generate concise explanations at the same time.

cs.CL↗

arXiv2019

Continuum Limit Matrix Elements for the Tonks-Girardeau Ground State

The Tonks-Girardeau model is a quantum mechanical model of N impenetrable bosons in 1+1 dimensions. A Vandermonde determinant provides the exact N-particle wave function of the ground state, or equivalently the matrix elements with respect to position eigenstates. We consider the large $N$ limit of these matrix elements. We present a binning prescription which calculates the leading terms of the matrix elements in a time which is independent of $N$, and so is suitable for this limit. In this sense, it allows one to solve for the ground state of a strongly coupled continuum quantum field theory in the field eigenstate basis. As examples, we calculate the matrix elements with respect to states with uniform density and also states consisting of two regions with distinct densities.

hep-th↗

arXiv2019

The optimal lower bound estimation of the number of closed geodesics on Finsler compact space form $S^{2n+1}/ Γ$

Let $M=S^{2n+1}/ Γ$, $Γ$ is a finite group which acts freely and isometrically on the $(2n+1)$-sphere and therefore $M$ is diffeomorphic to a compact space form. In this paper, we first investigate Katok's famous example about irreversible Finsler metrics on the spheres to study the topological structure of the contractible component of the free loop space on the compact space form $M$, then we apply the result to establish the resonance identity for homologically visible contractible minimal closed geodesics on every Finsler compact space form $(M, F)$ when there exist only finitely many distinct contractible minimal closed geodesics on $(M, F)$. As its applications, using this identity and the enhanced common index jump theorem for symplectic paths proved by Duan, Long and Wang in \cite{DLW2}, we show that there exist at least $2n+2$ distinct closed geodesics on every compact space form $S^{2n+1}/ Γ$ with a bumpy irreversible Finsler metric $F$ under some natural curvature condition, which is the optimal lower bound due to Katok's example.

math.DS↗

arXiv2019

Closed geodesics on positively curved spheres $S^n$ with Finsler metric induced by $(\mathbb{R}P^n,F)$

It's well known that the n-sphere $S^n$ is the universal double covering of the $n$-dimensional real projective space $\mathbb{R}P^n$ and then any Finsler metric on $\mathbb{R}P^n$ induces a Finsler metric of $S^n$. In this paper, we prove that for every Finsler $(S^n, F)$ for $n\geq3$ whose metric is induced by irreversible Finsler $(\mathbb{R}P^n,F)$ with reversibility $λ$ and flag curvature $K$ satisfying $(\fracλ{λ+1})^2<K\leq 1$, there exist at least $n-1$ prime closed geodesics on $(S^n, F)$. Furthermore, if there exist finitely many distinct closed geodesics on $(S^n, F)$, then there exist at least $2[\frac{n}{2}]-1$ of them are non-hyperbolic.

math.DG↗

arXiv2019

Experimental 4-intensity decoy-state quantum key distribution with asymmetric basis detector efficiency

The decoy-state method has been developed rapidly in quantum key distribution (QKD) since it is immune to photon-number splitting attacks. However, two basis detector efficiency asymmetry, which exists in realistic scenarios, has been ignored in the prior results. By using the recent 4-intensity decoy-state optimization protocol, we report the first implementation of high-rate QKD with asymmetric basis detector efficiency, demonstrating 1.9 to 33.2 times higher key rate than previous protocols in the situation of large basis detector efficiency asymmetry. The results ruled out an implicitly assumption in QKD that the efficiency of Z basis and X basis are restricted to be same. This work paves the way towards a more practical QKD setting.

quant-ph↗

arXiv2019

Effective Spin-2 Quasi-particles at Linear Dispersive Five-fold Degenerate Points with Tunable Topological Chern Numbers

In this work, which is based on spin-2 vectors and traceless spin-2 tensors, an effective Hamiltonian is constructed with a linearly dispersive five-fold degenerate point with spin-2 vector-momentum couplings. For the model without spin-2 vector-tensor coupling, the topological Chern numbers of five bands are calculated as 4, 2, 0, -2, -4. After including spin-2 vector-tensor coupling, separate topological Chern numbers are obtained for different couplings. A cubic lattice of atoms with five internal states is designed to realize two five-fold degenerate points. The Chern numbers of the bands can be changed by tuning the coupling coefficient. In this work we propose a theoretical design to obtain spin-2 quasi-particles.

cond-mat.quant-gas↗

arXiv2019

Low Complexity Algorithms for Robust Multigroup Multicast Beamforming

Existing methods for robust multigroup multicast beamforming obtain feasible points using semidefinite relaxation (SDR) and Gaussian randomization, and have high computational complexity. In this letter, we consider the robust multigroup multicast beamforming design to minimize the sum power (SP) or per-antenna power (PAP) under the signal-to-interference-plus-noise ratio (SINR) constraints and to maximize the worst-case SINR under the SP constraint or PAP constraints, respectively. The resulting optimization problems are challenging non-convex problems with infinitely many constraints. For each problem, using the majorization-minimization (MM) approach, we propose an iterative algorithm to obtain a feasible solution which is shown to be a stationary point under certain conditions. We also show that the proposed algorithms have much lower computational complexity than existing SDR-based algorithms.

cs.IT↗

arXiv2019

Experimental demonstration of high-rate measurement-device-independent quantum key distribution over asymmetric channels

Measurement-device-independent quantum key distribution (MDI-QKD) can eliminate all detector side channels and it is practical with current technology. Previous implementations of MDI-QKD all use two symmetric channels with similar losses. However, the secret key rate is severely limited when different channels have different losses. Here we report the results of the first high-rate MDI-QKD experiment over $asymmetric$ channels. By using the recent 7-intensity optimization approach, we demonstrate $>$10x higher key rate than previous best-known protocols for MDI-QKD in the situation of large channel asymmetry, and extend the secure transmission distance by more than 20-50 km in standard telecom fiber. The results have moved MDI-QKD towards widespread applications in practical network settings, where the channel losses are asymmetric and user nodes could be dynamically added or deleted.

quant-ph↗

arXiv2019

Global classical solutions to an evolutionary model for magnetoelasticity

In this paper, we first prove the local-in-time existence of the evolutionary model for magnetoelasticity with finite initial energy by employing the nonlinear iterative approach given in \cite{Jiang-Luo-2019-SIAM} to deal with the geometric constraint $M \in \mathbb{S}^{d-1}$ in the Landau-Lifshitz-Gilbert (LLG) equation. Inspired by \cite{Lin-Liu-Zhang-CPAM2005, Lin-Zhang-2008-CPAM}, we reformulate the evolutionary model for magnetoelasticity with vanishing external magnetic field $H_{ext}$, so that a further dissipative term will be sought from the elastic stress. We thereby justify the global well-posedness to the evolutionary model for magnetoelasticity with zero external magnetic field under small size of initial data.

math.AP↗

arXiv2019

Three-Dimensional Radiotherapy Dose Prediction on Head and Neck Cancer Patients with a Hierarchically Densely Connected U-net Deep Learning Architecture

The treatment planning process for patients with head and neck (H&N) cancer is regarded as one of the most complicated due to large target volume, multiple prescription dose levels, and many radiation-sensitive critical structures near the target. Treatment planning for this site requires a high level of human expertise and a tremendous amount of effort to produce personalized high quality plans, taking as long as a week, which deteriorates the chances of tumor control and patient survival. To solve this problem, we propose to investigate a deep learning-based dose prediction model, Hierarchically Densely Connected U-net, based on two highly popular network architectures: U-net and DenseNet. We find that this new architecture is able to accurately and efficiently predict the dose distribution, outperforming the other two models, the Standard U-net and DenseNet, in homogeneity, dose conformity, and dose coverage on the test data. Averaging across all organs at risk, our proposed model is capable of predicting the organ-at-risk max dose within 6.3% and mean dose within 5.1% of the prescription dose on the test data. The other models, the Standard U-net and DenseNet, performed worse, having an averaged organ-at-risk max dose prediction error of 8.2% and 9.3%, respectively, and averaged mean dose prediction error of 6.4% and 6.8%, respectively. In addition, our proposed model used 12 times less trainable parameters than the Standard U-net, and predicted the patient dose 4 times faster than DenseNet.

physics.med-ph↗

arXiv2019

Bandwidth Gain from Mobile Edge Computing and Caching in Wireless Multicast Systems

In this paper, we present a novel mobile edge computing (MEC) model where the MEC server has the input and output data of all computation tasks and communicates with multiple caching-and-computing-enabled mobile devices via a shared wireless link. Each task request can be served from local output caching, local computing with input caching, local computing or MEC computing, each of which incurs a unique bandwidth requirement of the multicast link. Aiming to minimize the transmission bandwidth, we design and optimize the local caching and computing policy at mobile devices subject to latency, caching, energy and multicast transmission constraints. The joint policy optimization problem is shown to be NP-hard. When the output data size is smaller than the input data size, we reformulate the problem as minimization of a monotone submodular function over matroid constraints and obtain the optimal solution via a strongly polynomial algorithm of Schrijver. On the other hand, when the output data size is larger than the input data size, by leveraging sample approximation and concave convex procedure together with the alternating direction method of multipliers, we propose a low-complexity high-performance algorithm and prove it converges to a stationary point. Furthermore, we theoretically reveal how much bandwidth gain can be achieved from computing and caching resources at mobile devices or the multicast transmission for symmetric case. Our results indicate that exploiting the computing and caching resources at mobile devices as well as multicast transmission can provide significant bandwidth savings.

cs.IT↗

arXiv2018

Numerical Simulations of Polymer Flooding Process in Porous Media on Distributed-memory Parallel Computers

Polymer flooding is a mature enhanced oil recovery technique that has been successfully applied in many field projects. By injecting polymer into a reservoir, the viscosity of water is increased, and the efficiency of water flooding is improved. As a result, more oil can be recovered. This paper presents numerical simulations of a polymer flooding process using parallel computers, where the numerical modeling of polymer retention, inaccessible pore volumes, a permeability reduction and polymer absorption are considered. Darcy's law is employed to model the behavoir of a fluid in porous media, and the upstream finite difference (volume) method is applied to discretize the mass conservation equations. Numerical methods, including discretization schemes, linear solver methods, nonlinearization methods and parallel techniques are introduced. Numerical experiments show that, on one hand, computed results match those from the commercial simulator, Schlumberger-Eclipse, which is widely applied by the petroleum industry, and, on the other hand, our simulator has excellent scalability, which is demonstrated by field applications with up to 27 million grid blocks using up to 2048 CPU cores.

cs.CE↗

arXiv2018

Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping

An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100 % in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140 dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.

physics.optics↗

arXiv2018

Noise investigation of a dual-frequency VECSEL for application to Cesium clocks

We theoretically and experimentally study the noise of a class-A dual-frequency vertical external cavity surface emitting laser operating at Cesium clock wavelength. The intensity noises of the two orthogonally polarized modes and the phase noise of their beatnote are investigated. The intensity noises of the two modes and their correlations are well predicted by a theory based on coupled rate equations. The phase noise of the beatnote is well described by considering both thermal effects and the effect of phase-amplitude coupling. The good agreement between theory and experiment indicates possible ways to further decrease the laser noises.

physics.ins-det↗

arXiv2018

Infrared echo and late-stage rebrightening of nuclear transient PS1-10adi: exploring Torus by tidal disruption event in active galactic nuclei

Tidal disruption events (TDEs) in active galactic nuclei (AGNs) have been overlooked for a long time but tentatively been investigated recently. We report the discovery of a long-lasting luminous mid-infrared (mid-IR) flare in PS1-10adi, which is a newly-identified highly energetic transient event occurred in AGN. The IR luminosity of PS1-10adi, as well as other analogous events, are at least one order of magnitude higher than all known supernova, but can be well interpreted as the dust echoes of TDEs, whose ultra-high IR energy is reprocessed from the dusty torus around the black hole. The torus dust is sublimating during the early stage of the outburst and probably lead to the observed rapid emergence of Fe II lines. Moreover, the UV-optical rebrightening and contemporaneous X-ray onset after $\sim1500$ rest-frame days since the optical peak is also an intriguing feature of PS1-10adi, which could be attributed to the interaction between the high-velocity outflow and torus. We suggest that the luminous IR echo is a very typical phenomenon of TDEs in AGNs and may provide us an ideal opportunity to explore the torus properties.

astro-ph.GA↗

arXiv2018

The Untold Secrets of Operational Wi-Fi Calling Services: Vulnerabilities, Attacks, and Countermeasures

Since 2016, all of four major U.S. operators have rolled out nationwide Wi-Fi calling services. They are projected to surpass VoLTE (Voice over LTE) and other VoIP services in terms of mobile IP voice usage minutes in 2018. They enable mobile users to place cellular calls over Wi-Fi networks based on the 3GPP IMS (IP Multimedia Subsystem) technology. Compared with conventional cellular voice solutions, the major difference lies in that their traffic traverses untrustful Wi-Fi networks and the Internet. This exposure to insecure networks may cause the Wi-Fi calling users to suffer from security threats. Its security mechanisms are similar to the VoLTE, because both of them are supported by the IMS. They include SIM-based security, 3GPP AKA (Authentication and Key Agreement), IPSec (Internet Protocol Security), etc. However, are they sufficient to secure Wi-Fi calling services? Unfortunately, our study yields a negative answer. We conduct the first study of exploring security issues of the operational Wi-Fi calling services in three major U.S. operators' networks using commodity devices. We disclose that current Wi-Fi calling security is not bullet-proof and uncover four vulnerabilities which stem from improper standard designs, device implementation issues and network operation slips. By exploiting the vulnerabilities, together with several state-of-the-art computer visual recognition technologies, we devise two proof-of-concept attacks: user privacy leakage and telephony harassment or denial of voice service (THDoS); both of them can bypass the security defenses deployed on mobile devices and the network infrastructure. We have confirmed their feasibility and simplicity using real-world experiments, as well as assessed their potential damages and proposed recommended solutions.

cs.CR↗