arXiv subjects

Rui Chen

Publications and source records attributed to Rui Chen.

At least 433 records · Page 24Linked to original sources

arXiv2019

Finite-size effects in non-Hermitian topological systems

We systematically investigate the finite-size effects in non-Hermitian one-dimensional (1D) Su-Schrieffer-Heeger (SSH) and two-dimensional (2D) Chern insulator models. Using a combination of analytical and numerical calculations, we show that the non-Hermitian intra-cell hoppings in the SSH model can modify the localization lengths of bulk and end states, giving rise to a complex finite-size energy gap that exhibits an oscillating exponential decay as the chain length grows. However, the imaginary staggered on-site potentials in the SSH model only change the end-state energy, leaving the localization lengths of the system unchanged. In this case, the finite-size energy gap can undergo a transition from real values to imaginary values. We observed similar phenomena for the finite-size effect in 2D Chern insulator systems.

cond-mat.mes-hall↗

arXiv2019

Possible triple-charm molecular pentaquarks from $Ξ_{cc}D_1/Ξ_{cc}D_2^*$ interactions

In this work, we explore a systematic investigation on $S$-wave interactions between a doubly charmed baryon $Ξ_{cc}(3621)$ and a charmed meson in a $T$ doublet $(D_1,\,D_2^*)$. We first analyze the possibility for forming $Ξ_{cc}D_1/Ξ_{cc}D_2^*$ bound states with the heavy quark spin symmetry. Then, we further perform a dynamical study on the $Ξ_{cc}D_1/Ξ_{cc}D_2^*$ interactions within a one-boson-exchange model by considering both the $S$-$D$ wave mixing and coupled channel effect. Finally, our numerical results conform the proposals from the heavy quark spin symmetry analysis: the $Ξ_{cc}D_1$ systems with $I(J^P)=$ $0(1/2^+,\,3/2^+)$ and the $Ξ_{cc}D_2^*$ systems with $I(J^P)=$ $0(3/2^+,\,5/2^+)$ can possibly be loose triple-charm molecular pentaquarks. Meanwhile, we also extend our model to the $Ξ_{cc}\bar{D}_1$ and $Ξ_{cc}\bar D_2^*$ systems, and our results indicate the isoscalars of $Ξ_{cc}\bar{D}_1$ and $Ξ_{cc}\bar{D}_2^*$ can be possible molecular candidates.

hep-ph↗

arXiv2019

Micro- and Macro-Level Churn Analysis of Large-Scale Mobile Games

As mobile devices become more and more popular, mobile gaming has emerged as a promising market with billion-dollar revenues. A variety of mobile game platforms and services have been developed around the world. A critical challenge for these platforms and services is to understand the churn behavior in mobile games, which usually involves churn at micro level (between an app and a specific user) and macro level (between an app and all its users). Accurate micro-level churn prediction and macro-level churn ranking will benefit many stakeholders such as game developers, advertisers, and platform operators. In this paper, we present the first large-scale churn analysis for mobile games that supports both micro-level churn prediction and macro-level churn ranking. For micro-level churn prediction, in view of the common limitations of the state-of-the-art methods built upon traditional machine learning models, we devise a novel semi-supervised and inductive embedding model that jointly learns the prediction function and the embedding function for user-app relationships. We model these two functions by deep neural networks with a unique edge embedding technique that is able to capture both contextual information and relationship dynamics. We also design a novel attributed random walk technique that takes into consideration both topological adjacency and attribute similarities. To address macro-level churn ranking, we propose to construct a relationship graph with estimated micro-level churn probabilities as edge weights and adapt link analysis algorithms on the graph. We devise a simple algorithm SimSum and adapt two more advanced algorithms PageRank and HITS. The performance of our solutions for the two-level churn analysis problems is evaluated on real-world data collected from the Samsung Game Launcher platform.

cs.LG↗

arXiv2019

Optimization of Ride Sharing Systems Using Event-driven Receding Horizon Control

We develop an event-driven Receding Horizon Control (RHC) scheme for a Ride Sharing System (RSS) in a transportation network where vehicles are shared to pick up and drop off passengers so as to minimize a weighted sum of passenger waiting and traveling times. The RSS is modeled as a discrete event system and the event-driven nature of the controller significantly reduces the complexity of the vehicle assignment problem, thus enabling its real-time implementation. Simulation results using actual city maps and real taxi traffic data illustrate the effectiveness of the RH controller in terms of real-time implementation and performance relative to known greedy heuristics.

eess.SY↗

arXiv2018

Floquet topological insulator phase in a Weyl semimetal thin film with disorder

We investigate the effects of periodic fields and disorder on topological properties of a Weyl-semimetal thin film. The two periodic fields, i.e., a periodic magnetic field and elliptically polarized light, are discussed respectively. By use of the Floquet theory, we find that both the two periodic drives can resonantly induce the topological transitions from normal insulator (NI) phases to Floquet topological insulator (FTI) phases. The Floquet topological transitions are characterized by variation of Chern number. Moreover, we show that the Floquet topological transitions can be explained by a combination of the quantum well approximation and the rotating wave approximation. In the disordered Weyl-semimetal thin film model under periodic fields, we calculate the Bott index to characterize topological phase. It is found that the FTI phase is robust against weak disorder, and collapses for strong disorder strength. Interestingly, we find that disorder can also induce a topological transition from a topological trivial phase to an FTI phase, establishing the Floquet topological Anderson insulator (FTAI) phase. Finally, an effective-medium theory based on the Born approximation further confirms the numerical conclusions.

cond-mat.mes-hall↗

arXiv2018

Streaming Network Embedding through Local Actions

Recently, considerable research attention has been paid to network embedding, a popular approach to construct feature vectors of vertices. Due to the curse of dimensionality and sparsity in graphical datasets, this approach has become indispensable for machine learning tasks over large networks. The majority of existing literature has considered this technique under the assumption that the network is static. However, networks in many applications, nodes and edges accrue to a growing network as a streaming. A small number of very recent results have addressed the problem of embedding for dynamic networks. However, they either rely on knowledge of vertex attributes, suffer high-time complexity or need to be re-trained without closed-form expression. Thus the approach of adapting the existing methods to the streaming environment faces non-trivial technical challenges. These challenges motivate developing new approaches to the problems of streaming network embedding. In this paper, We propose a new framework that is able to generate latent features for new vertices with high efficiency and low complexity under specified iteration rounds. We formulate a constrained optimization problem for the modification of the representation resulting from a stream arrival. We show this problem has no closed-form solution and instead develop an online approximation solution. Our solution follows three steps: (1) identify vertices affected by new vertices, (2) generate latent features for new vertices, and (3) update the latent features of the most affected vertices. The generated representations are provably feasible and not far from the optimal ones in terms of expectation. Multi-class classification and clustering on five real-world networks demonstrate that our model can efficiently update vertex representations and simultaneously achieve comparable or even better performance.

cs.LG↗

arXiv2018

Capacitated Assortment Optimization with Pricing under the Paired Combinatorial Logit Model

In this paper, we investigate the capacitated assortment optimization problem with pricing under the paired combinatorial logit model, whose goal is to identify the revenue-maximizing subset of products as well as their selling prices subject to a known capacity limit. We model customers' purchase behavior using the paired combinatorial logit model, which allows for covariance among any pair of products. We formulate this problem as a non-linear mixed integer program. Then, we propose a two-step approach to obtain the optimal solution based on solving a mixed integer program and Lambert-W function. To further improve its performance, we design a greedy heuristic algorithm and a greedy randomized adaptive search procedure to obtain high-quality solutions so as to balance the tradeoff between accuracy and computational efficiency. A series of numerical experiments are conducted to gauge the efficiency and quality of our proposed approaches.

math.OC↗

arXiv2018

A Semi-Supervised and Inductive Embedding Model for Churn Prediction of Large-Scale Mobile Games

Mobile gaming has emerged as a promising market with billion-dollar revenues. A variety of mobile game platforms and services have been developed around the world. One critical challenge for these platforms and services is to understand user churn behavior in mobile games. Accurate churn prediction will benefit many stakeholders such as game developers, advertisers, and platform operators. In this paper, we present the first large-scale churn prediction solution for mobile games. In view of the common limitations of the state-of-the-art methods built upon traditional machine learning models, we devise a novel semi-supervised and inductive embedding model that jointly learns the prediction function and the embedding function for user-app relationships. We model these two functions by deep neural networks with a unique edge embedding technique that is able to capture both contextual information and relationship dynamics. We also design a novel attributed random walk technique that takes into consideration both topological adjacency and attribute similarities. To evaluate the performance of our solution, we collect real-world data from the Samsung Game Launcher platform that includes tens of thousands of games and hundreds of millions of user-app interactions. The experimental results with this data demonstrate the superiority of our proposed model against existing state-of-the-art methods.

cs.LG↗

arXiv2018

An "Xcity" Optimization Approach to Designing Proving Grounds for Connected and Autonomous Vehicles

Proving ground, or on-track testing has been an essential part of testing and validation process for connected and autonomous vehicles (CAV). Several world-class CAV proving grounds, such as Mcity at the University of Michigan and The Castle of Waymo, have already been built, and many more are currently under construction. In this paper, we propose the first optimization approach to CAV proving ground designing and refer to any such CAV-centric design problem as "Xcity" to emphasize the enormous investment, the multi-dimensional spatial consideration, and the immense construction effort emerging globally. Inspired by the recent progress on traffic encounter clustering, we further define "road assets" as fundamental building blocks and formulate the whole design process into nonlinear optimization problems. We have shown that such framework can be utilized to adaptively generate CAV proving ground designs with optimized capability and flexibility and can further be extended to evaluate an existing "Xcity" design.

cs.RO↗

arXiv2018

Phase diagrams of Weyl semimetals with competing intraorbital and interorbital disorders

A Weyl semimetal (WSM) is a topological material that hosts Weyl fermions as quasiparticles in the bulk. We study the combined effect of intra- and interorbital disorders on WSMs by adopting a tight-binding model that supports the WSM, three-dimensional quantum anomalous Hall insulator (3D QAHI), and normal insulator (NI) phases in the clean limit. Based on the calculation of the localization length and the Hall conductivity, we present rich phase diagrams due to the interplay of intra- and interorbital disorders. We find that the WSM with well-separated Weyl nodes is stable to both weak intra- and interorbital disorders. However, weak intraorbital disorder can gap out a WSM close to the 3D QAHI phase in the clean phase diagram, forming a 3D QAHI, and it can also drive a NI near the WSM phase to a WSM. By contrast, weak interorbital disorder can cause a 3D QAHI-WSM transition for a 3D QAHI in proximity to the WSM phase in the clean limit, and it can annihilate a WSM near the NI phase, bringing about a WSM-NI transition. We observe a diffusive anomalous Hall metal (DAHM) phase at moderate disorder strength. The DAHM appears in a wide range of the phase diagram when the intraorbital disorder dominates over the interorbital disorder, while the DAHM is found to exist in a narrow region or be missing in the phase diagram when the interorbital disorder dominates.

cond-mat.mes-hall↗

arXiv2018

Exotic triple-charm deuteron-like hexaquarks

Adopting the one-boson-exchange model, we perform a systematic investigation of interactions between a doubly charmed baryon $(Ξ_{cc})$ and an $S$-wave charmed baryon ($Λ_c$, $Σ_c^{(*)}$, and $Ξ_c^{(\prime,*)}$). Both the $S$-$D$ mixing effect and coupled-channel effect are considered in this work. Our results suggest that there may exist several possible triple-charm deuteron-like hexaquarks. Meanwhile, we further study the interactions between a doubly charmed baryon and an $S$-wave anticharmed baryon. We find that a doubly charmed baryon and an $S$-wave anticharmed baryon can be easily bound together to form shallow molecular hexaquarks. These heavy flavor hexaquarks predicted here can be accessible at future experiment like LHCb.

hep-ph↗

arXiv2018

Amino-acid network clique analysis of protein mutation correlation effects: a case study of lysozme

Optimizing amino-acid mutations has been a most challenging task in modern bio- industrial enzyme designing. It is well known that many successful designs often hinge on extensive correlations among mutations at different sites within the enzyme, however, the underpinning mechanism for these correlations is far from clear. Here, we present a topology-based model to quantitively characterize correlation effects between mutations. The method is based on the molecular dynamic simulations and the amino-acid network clique analysis that simply examines if two single mutation sites belong to some 3-clique. We analyzed 13 dual mutations of T4 phage lysozyme and found that the clique-based model successfully distinguishes highly correlated or non-additive double-site mutations from those with less correlation or additive mutations. We also applied the model to the protein Eglin c whose topology is significantly distinct from that of T4 phage lysozyme, and found that the model can, to some extension, still identify non-additive mutations from additive ones. Our calculations showed that mutation correlation effects may heavily depend on topology relationship among mutation sites, which can be quantitatively characterized using amino-acid network k-cliques. We also showed that double-site mutation correlations can be significantly altered by exerting a third mutation, indicating that more detailed physico-chemistry interactions might be considered with the network model for better understanding of the elusive mutation-correlation principle.

q-bio.QM↗

arXiv2018

Extreme Scale FMM-Accelerated Boundary Integral Equation Solver for Wave Scattering

Algorithmic and architecture-oriented optimizations are essential for achieving performance worthy of anticipated energy-austere exascale systems. In this paper, we present an extreme scale FMM-accelerated boundary integral equation solver for wave scattering, which uses FMM as a matrix-vector multiplication inside the GMRES iterative method. Our FMM Helmholtz kernels treat nontrivial singular and near-field integration points. We implement highly optimized kernels for both shared and distributed memory, targeting emerging Intel extreme performance HPC architectures. We extract the potential thread- and data-level parallelism of the key Helmholtz kernels of FMM. Our application code is well optimized to exploit the AVX-512 SIMD units of Intel Skylake and Knights Landing architectures. We provide different performance models for tuning the task-based tree traversal implementation of FMM, and develop optimal architecture-specific and algorithm aware partitioning, load balancing, and communication reducing mechanisms to scale up to 6,144 compute nodes of a Cray XC40 with 196,608 hardware cores. With shared memory optimizations, we achieve roughly 77% of peak single precision floating point performance of a 56-core Skylake processor, and on average 60% of peak single precision floating point performance of a 72-core KNL. These numbers represent nearly 5.4x and 10x speedup on Skylake and KNL, respectively, compared to the baseline scalar code. With distributed memory optimizations, on the other hand, we report near-optimal efficiency in the weak scalability study with respect to both the logarithmic communication complexity as well as the theoretical scaling complexity of FMM. In addition, we exhibit up to 85% efficiency in strong scaling. We compute in excess of 2 billion DoF on the full-scale of the Cray XC40 supercomputer.

cs.PF↗

arXiv2018

Searching for possible $Ω_c-$like molecular states from $Ξ_{c}^{}\bar{K}/Ξ_c\bar{K}^/Ξ_c'\bar{K}^*$ interaction

Stimulated by the observations of recent observation of $Ω_c$ as well as former one of $P_c(4380)$ and $P_c(4450)$, we perform a coupled channel analysis of $Ξ_c^*\bar{K}/Ω_cη/Ω_c^*η/Ξ_c\bar{K}^*/Ξ_c'\bar{K}^*/Ω_cω$ systems to search for possible $Ω_c-$like molecular states by using a one-boson-exchange potential. Our results suggest there exists a loosely bound molecular state, a $Ξ_c^*\bar{K}/Ω_cη/Ω_c^*η/Ξ_c\bar{K}^*/Ξ_c'\bar{K}^*/Ω_cω$ with $I(J^P)=0(3/2^-)$, it is mainly composed of the $Ξ_c^*\bar{K}$ system. Two-body strong decay width is also studied, where we find that $Ξ_c'\bar{K}$ is the dominant decay channel.

hep-ph↗

arXiv2017

Heavy molecules and one-$σ/ω$-exchange model

In the framework of the one-boson-exchange model, we explore whether the intermediate and short-range forces from $σ/ω$-exchange can be strong enough to bind heavy molecular states. $Λ_cD(\bar{D})$, and $Λ_cΛ_c(\barΛ_c)$ systems have been studied and compared. We find that the force from $σ$-exchange is attractive and dominant, whereas the $ω$-exchange force not. As a consequence, the S-wave $Λ_cD$, $Λ_cΛ_c$, and $Λ_c\barΛ_c$ can be possible molecular candidates. We further indicate that one hadron-hadron system with more light quarks $(u,d)$ can be easier to form a bound state. As a byproduct, by studying the heavy-quark mass dependence for the $Λ_cD(\bar{D})$-like and $Λ_cΛ_c(\barΛ_c)$-like systems, we find that the charm/bottom sector can easily accommodates molecular states. Finally, the $Λ_cN(\bar{N})$ and $Λ_bN(\bar{N})$ systems are investigated. Our results indicate that they are also likely to form bound states. By including one-$π$-exchange forces providing additional attraction when coupled channels are included, we expect many molecular states in heavy quark sectors.

hep-ph↗

arXiv2017

Noise Level Estimation for Overcomplete Dictionary Learning Based on Tight Asymptotic Bounds

In this letter, we address the problem of estimating Gaussian noise level from the trained dictionaries in update stage. We first provide rigorous statistical analysis on the eigenvalue distributions of a sample covariance matrix. Then we propose an interval-bounded estimator for noise variance in high dimensional setting. To this end, an effective estimation method for noise level is devised based on the boundness and asymptotic behavior of noise eigenvalue spectrum. The estimation performance of our method has been guaranteed both theoretically and empirically. The analysis and experiment results have demonstrated that the proposed algorithm can reliably infer true noise levels, and outperforms the relevant existing methods.

eess.SP↗

arXiv2017

Prediction of triple-charm molecular pentaquarks

In a one-boson-exchange model, we study molecular states of double-charm baryon ($Ξ_{cc}(3621)$) and a charmed meson ($D$ and $D^*$). Our model indicates that there exist two possible triple-charm molecular pentaquarks, a $Ξ_{cc}D$ state with $I(J^P)=0(1/2^-)$ and a $Ξ_{cc}D^*$ state with $I(J^P)=0(3/2^-)$. In addition, we also extend our formula to explore $Ξ_{cc}\bar{B}^{(*)}$, $Ξ_{cc}\bar{D}^{(*)}$, and $Ξ_{cc}B^{(*)}$ systems, and find more possible heavy flavor molecular pentaquarks, a $Ξ_{cc}\bar{B}$ state with $I(J^P)=0(1/2^-)$, a $Ξ_{cc}\bar{B}^*$ state with $I(J^P)=0(3/2^-)$, and $Ξ_{cc}\bar{D}^*/Ξ_{cc}B^*$ states with $I(J^P)=0(1/2^-)$. Experimental search for these predicted triple-charm molecular pentaquarks is encouraged.

hep-ph↗

arXiv2017

Disorder-induced topological phase transitions on Lieb lattices

Motivated by the very recent experimental realization of electronic Lieb lattices and research interest on topological states of matter, we study the topological phase transitions driven by Anderson disorder on spin-orbit coupled Lieb lattices in the presence of spin-independent and dependent potentials. By combining the numerical transport and self-consistent Born approximation methods, we found that both time-reversal invariant and broken Lieb lattices can host disorder-induced gapful topological phases, including the quantum spin Hall insulator (QSHI) and quantum anomalous Hall insulator (QAHI) phases. For the time-reversal invariant case, this disorder can induce a topological phase transition directly from normal insulator (NI) to the QSHI. While for the time-reversal broken case, the disorder can induce either a QAHI-QSHI phase transition or a NI-QAHI-QSHI phase transition. Remarkably, the time-reversal broken QSHI phase can be induced by Anderson disorder on the spin-orbit coupled Lieb lattices without time-reversal symmetry.

cond-mat.mes-hall↗