arXiv subjects

Wei Sun

Publications and source records attributed to Wei Sun.

At least 433 records · Page 24Linked to original sources

arXiv2018

Uncover Topology by Quantum Quench Dynamics

Topological quantum states are characterized by nonlocal invariants, and their detection is intrinsically challenging. Various strategies have been developed to study topological Hamiltonians through their equilibrium states. We present a fundamentally new, high-precision dynamical approach, revealing topology through the unitary evolution after a quench from a topological trivial initial state with a two-dimensional Chern band realized in an ultracold $^{87}$Rb atom gas. The emerging ring structure in the spin dynamics uniquely determines the Chern number for the post-quench band and enables probing the full phase diagram of the band topology with high precision. Besides, we also measure the topological band gap and the domain wall structure dynamically formed in the momentum space during the long-term evolution. Our dynamical approach provides a way towards observing a universal bulk-ring correspondence, and has broad applications in exploring topological quantum matter.

cond-mat.quant-gas↗

arXiv2018

Convergence rates in the law of large numbers and new kinds of convergence of random variables

In this paper, we first study convergence rates in the law of large numbers for independent and identically distributed random variables. We obtain a strong $L^p$-convergence version and a strongly almost sure convergence version of the law of large numbers. Second, we investigate several new kinds of convergence of random variables and discuss their relations and properties.

math.PR↗

arXiv2018

Anatomy of the $ρ$ resonance from lattice QCD at the physical point

We propose a strategy to access the $q\bar{q}$ component of the $ρ$ resonance in lattice QCD. Through a mixed action formalism (overlap valence on domain wall sea), the energy of the $q\bar{q}$ component is derived at different valence quark masses, and shows a linear dependence on $m_π^2$. The slope is determined to be $c_1=0.505(3)\,{\rm GeV}^{-1}$, from which the valence $πρ$ sigma term is extracted to be $σ_{πρ}^{(\rm val)}=9.82(6)$ MeV using the Feynman-Hellman theorem. At the physical pion mass, the mass of the $q\bar{q}$ component is interpolated to be $m_ρ=775.9\pm 6.0\pm 1.8$ MeV, which is close to the $ρ$ resonance mass. We also obtain the leptonic decay constant of the $q\bar{q}$ component to be $f_{ρ^-}=208.5\pm 5.5\pm 0.9$ MeV, which can be compared with the experimental value $f_ρ^{\rm exp}\approx 221$ MeV through the relation $f_ρ^{\rm exp}=\sqrt{Z_ρ}f_{ρ^\pm} $ with $Z_ρ\approx 1.13$ being the on-shell wavefunction renormalization of $ρ$ owing to the $ρ-π$ interaction. We emphasize that $m_ρ$ and $f_ρ$ of the $q\bar{q}$ component, which are obtained for the first time from QCD, can be taken as the input parameters of $ρ$ in effective field theory studies where $ρ$ acts as a fundamental degree of freedom.

hep-ph↗

arXiv2018

Dissipative solitary wave at the interface of a binary complex plasma

The propagation of a dissipative solitary wave across an interface is studied in a binary complex plasma. The experiments were performed under microgravity conditions in the PK-3 Plus Laboratory on board the International Space Station using microparticles with diameters of 1.55 micrometre and 2.55 micrometre immersed in a low-temperature plasma. The solitary wave was excited at the edge of a particle-free region and propagated from the sub-cloud of small particles into that of big particles. The interfacial effect was observed by measuring the deceleration of particles in the wave crest. The results are compared with a Langevin dynamics simulation, where the waves were excited by a gentle push on the edge of the sub-cloud of small particles. Reflection of the wave at the interface is induced by increasing the strength of the push. By tuning the ion drag force exerted on big particles in the simulation, the effective width of the interface is adjusted. We show that the strength of reflection increases with narrower interfaces.

physics.plasm-ph↗

arXiv2017

Partial Labeled Gastric Tumor Segmentation via patch-based Reiterative Learning

Gastric cancer is the second leading cause of cancer-related deaths worldwide, and the major hurdle in biomedical image analysis is the determination of the cancer extent. This assignment has high clinical relevance and would generally require vast microscopic assessment by pathologists. Recent advances in deep learning have produced inspiring results on biomedical image segmentation, while its outcome is reliant on comprehensive annotation. This requires plenty of labor costs, for the ground truth must be annotated meticulously by pathologists. In this paper, a reiterative learning framework was presented to train our network on partial annotated biomedical images, and superior performance was achieved without any pre-trained or further manual annotation. We eliminate the boundary error of patch-based model through our overlapped region forecast algorithm. Through these advisable methods, a mean intersection over union coefficient (IOU) of 0.883 and mean accuracy of 91.09% on the partial labeled dataset was achieved, which made us win the 2017 China Big Data & Artificial Intelligence Innovation and Entrepreneurship Competitions.

cs.CV↗

arXiv2017

Joint Fit of Warm Absorbers in COS & HETG Spectra of NGC 3783

Warm Absorbers (WAs), as an important form of AGN outflows, show absorption in both UV and X-ray band. Using XSTAR generated photoionization models, for the first time we present a joint fit to the simultaneous observations of HST/COS and Chandra/HETGS on NGC 3783. A total of five WAs explain well all absorption features from the AGN outflows, which are spread over a wide range of parameters: ionization parameter logξ from 0.6 to 3.8, column density log N_H from 19.5 to 22.3 cm^{-2}, velocity v from 380 to 1060 km s^{-1}, and covering factor from 0.33 to 0.75. Not all the five WAs are consistent in pressure. Two of them are likely different parts of the same absorbing gas, and two of the other WAs may be smaller discrete clouds that are blown out from the inner region of the torus at different periods. The five WAs suggest a total mass outflowing rate within the range of 0.22-4.1 solar mass per year.

astro-ph.HE↗

arXiv2017

Disc-corona interaction in the heartbeat state of GRS 1915+105

Timing analysis provides information about the dynamics of matter accreting on to neutron stars and black holes, and hence is crucial for studying the physics of the accretion flow around these objects. It is difficult, however, to associate the different variability components with each of the spectral components of the accretion flow. We apply several new methods to two Rossi X-ray Timing Explorer observations of the black hole binary GRS 1915+105 during its heartbeat state to explore the origin of the X-ray variability and the interactions of the accretion-flow components. We offer a promising window into the disc--corona interaction through analysing the formation regions of the disc aperiodic variabilities with different time-scales via comparing the corresponding transition energies of the amplitude-ratio spectra. In a previous paper, we analysed the Fourier power density as a function of energy and frequency to study the origin of the aperiodic variability, and combined that analysis with the phase lag as a function of frequency to derive a picture of the disc--corona interaction in this source. We here, for the first time, investigate the phase lag as a function of energy and frequency, and display some interesting details of the disc--corona interaction. Besides, the results from the shape of amplitude-ratio spectrum and from several other aspects suggest that the quasi-periodic oscillation originates from the corona.

astro-ph.HE↗

arXiv2017

The parabolic flows for complex quotient equations

We apply the parabolic flow method to solving complex quotient equations on closed Kähler manifolds. We study the parabolic equation and prove the convergence. As a result, we solve the complex quotient equations.

math.AP↗

arXiv2017

Glueball relevant study on isoscalars from $N_f=2$ lattice QCD

We perform a glueball-relevant study on isoscalars based on anisotropic $N_f=2$ lattice QCD gauge configurations. In the scalar channel, we identify the ground state obtained through gluonic operators to be a single-particle state through its dispersion relation. When $q\bar{q}$ operator is included, we find the mass of this state does not change, and the $q\bar{q}$ operator couples very weakly to this state. So this state is most likely a glueball state. For pseudoscalars, along with the exiting lattice results, our study implies that both the conventional $q\bar{q}$ state $η_2$ (or $η'$ in flavor $SU(3)$) and a heavier glueball-like state with a mass of roughly 2.6 GeV exist in the spectrum of lattice QCD with dynamical quarks.

hep-lat↗

arXiv2017

Multimodal Content Analysis for Effective Advertisements on YouTube

The rapid advances in e-commerce and Web 2.0 technologies have greatly increased the impact of commercial advertisements on the general public. As a key enabling technology, a multitude of recommender systems exists which analyzes user features and browsing patterns to recommend appealing advertisements to users. In this work, we seek to study the characteristics or attributes that characterize an effective advertisement and recommend a useful set of features to aid the designing and production processes of commercial advertisements. We analyze the temporal patterns from multimedia content of advertisement videos including auditory, visual and textual components, and study their individual roles and synergies in the success of an advertisement. The objective of this work is then to measure the effectiveness of an advertisement, and to recommend a useful set of features to advertisement designers to make it more successful and approachable to users. Our proposed framework employs the signal processing technique of cross modality feature learning where data streams from different components are employed to train separate neural network models and are then fused together to learn a shared representation. Subsequently, a neural network model trained on this joint feature embedding representation is utilized as a classifier to predict advertisement effectiveness. We validate our approach using subjective ratings from a dedicated user study, the sentiment strength of online viewer comments, and a viewer opinion metric of the ratio of the Likes and Views received by each advertisement from an online platform.

cs.AI↗

arXiv2017

Dirac, Rashba and Weyl type spin-orbit couplings: toward experimental realization in ultracold atoms

We propose a hierarchy set of minimal optical Raman lattice schemes toward the experimental realization of spin-orbit (SO) couplings of various types for ultracold atoms, including two-dimensional (2D) Dirac type of $C_4$ symmetry, 2D Rashba and 3D Weyl types. These schemes are well accessible with current cold-atom technology, and in particular, a long-lived Bose-Einstein condensation of the 2D Dirac SO coupling has been experimentally proved. The generation of 2D Rashba and 3D Weyl types has an exquisite request that two sources of laser beams have distinct frequencies of factor-two difference. Surprisingly, we find that $^{133}$Cs atoms provide an ideal candidate for the realization. A common and essential feature is the absence of any fine-tuning and phase-locking in the realization, and the resulted SO coupled ultracold atoms have a long lifetime. These schemes essentially improve over the current experimental accessibility and controllability, and open new experimental platforms to study high-dimensional SO physics and novel topological phases with ultracold atoms.

cond-mat.mes-hall↗

arXiv2017

A dynamic model for the two-parameter Dirichlet process

Let $α=1/2$, $θ>-1/2$, and $ν_0$ be a probability measure on a type space $S$. In this paper, we investigate the stochastic dynamic model for the two-parameter Dirichlet process $Π_{α,θ,ν_0}$. If $S=\mathbb{N}$, we show that the bilinear form \begin{eqnarray*} \left\{ \begin{array}{l} {\cal E}(F,G)=\frac{1}{2}\int_{{\cal P}_1(\mathbb{N})}\langle \nabla F(μ),\nabla G(μ)\rangle_μ Π_{α,θ,ν_0}(dμ),\ \ F,G\in {\cal F},\\ {\cal F}=\{F(μ)=f(μ(1),\dots,μ(d)):f\in C^{\infty}(\mathbb{R}^d), d\ge 1\} \end{array} \right. \end{eqnarray*} is closable on $L^2({\cal P}_1(\mathbb{N});Π_{α,θ,ν_0})$ and its closure $({\cal E}, D({\cal E}))$ is a quasi-regular Dirichlet form. Hence $({\cal E}, D({\cal E}))$ is associated with a diffusion process in ${\cal P}_1(\mathbb{N})$ which is time-reversible with the stationary distribution $Π_{α,θ,ν_0}$. If $S$ is a general locally compact, separable metric space, we discuss properties of the model \begin{eqnarray*} \left\{ \begin{array}{l} {\cal E}(F,G)=\frac{1}{2}\int_{{\cal P}_1(S)}\langle \nabla F(μ),\nabla G(μ)\rangle_μ Π_{α,θ,ν_0}(dμ),\ \ F,G\in {\cal F},\\ {\cal F}=\{F(μ)=f(\langle ϕ_1,μ\rangle,\dots,\langle ϕ_d,μ\rangle): ϕ_i\in B_b(S),1\le i\le d,f\in C^{\infty}(\mathbb{R}^d),d\ge 1\}. \end{array} \right. \end{eqnarray*} In particular, we prove the Mosco convergence of its projection forms.

math.PR↗

arXiv2017

Fast MPEG-CDVS Encoder with GPU-CPU Hybrid Computing

The compact descriptors for visual search (CDVS) standard from ISO/IEC moving pictures experts group (MPEG) has succeeded in enabling the interoperability for efficient and effective image retrieval by standardizing the bitstream syntax of compact feature descriptors. However, the intensive computation of CDVS encoder unfortunately hinders its widely deployment in industry for large-scale visual search. In this paper, we revisit the merits of low complexity design of CDVS core techniques and present a very fast CDVS encoder by leveraging the massive parallel execution resources of GPU. We elegantly shift the computation-intensive and parallel-friendly modules to the state-of-the-arts GPU platforms, in which the thread block allocation and the memory access are jointly optimized to eliminate performance loss. In addition, those operations with heavy data dependence are allocated to CPU to resolve the extra but non-necessary computation burden for GPU. Furthermore, we have demonstrated the proposed fast CDVS encoder can work well with those convolution neural network approaches which has harmoniously leveraged the advantages of GPU platforms, and yielded significant performance improvements. Comprehensive experimental results over benchmarks are evaluated, which has shown that the fast CDVS encoder using GPU-CPU hybrid computing is promising for scalable visual search.

cs.MM↗

arXiv2017

A system of nonlinear equations with application to large deviations for Markov chains with finite lifetime

In this paper, we first show the existence of solutions to the following system of nonlinear equations \begin{eqnarray*}\left\{\begin{array}{l} a_{11}x_1+a_{12}x_2+a_{13}x_3+\cdots+a_{1n}x_{n} = b_{11}\frac{1}{x_1}+b_{12}\frac{1}{x_2}+b_{13}\frac{1}{x_3}+\cdots+b_{1n}\frac{1}{x_{n}},\\ a_{21}\frac{1}{x_1}+a_{22}\frac{x_2}{x_1}+a_{23}\frac{x_3}{x_1}+\cdots+a_{2n}\frac{x_{n}}{x _1}=b_{21}x_1+b_{22}\frac{x_1}{x_2}+b_{23}\frac{x_1}{x_3}+\cdots+b_{2n}\frac{x_1}{x_{n}},\\ a_{31}\frac{x_1}{x_2}+a_{32}\frac{1}{x_2}+a_{33}\frac{x_3}{x_2}+\cdots+a_{3n}\frac{x_{n}}{x _2}=b_{31}\frac{x_2}{x_1}+b_{32}x_2+b_{33}\frac{x_2}{x_3}+\cdots+b_{3n}\frac{x_2}{x_{n}},\\ \cdots\cdots\\ a_{n1}\frac{x_1}{x_{n-1}}+a_{n2}\frac{x_2}{x_{n-1}}+a_{n3}\frac{x_3}{x_{n-1}}+ \cdots+a_{n,n-1}\frac{1}{x_{n-1}}+a_{nn}\frac{x_{n}}{x_{n-1}}\\ =b_{n1}\frac{x_{n-1}}{x_1}+b_{n2}\frac{x_{n-1}}{x_2}+b_{n3}\frac{x_{n-1}}{x_3}+\cdots+b_{n, n-1}x_{n-1} +b_{nn}\frac{x_{n-1}}{x_{n}}, \end{array} \right. \end{eqnarray*} where $n\ge 3$ and $a_{ij},b_{ij},1\le i,j\le n$, are positive constants. Then, we make use of this result to obtain the large deviation principle for the occupation time distributions of continuous-time finite state Markov chains with finite lifetime.

math.PR↗

arXiv2017

Joint estimation of genetic and parent-of-origin effects using RNA-seq data from human

RNA sequencing allows one to study allelic imbalance of gene expression, which may be due to genetic factors or genomic imprinting. It is desirable to model both genetic and parent-of-origin effects simultaneously to avoid confounding and to improve the power to detect either effect. In a study of experimental cross, separation of genetic and parent-of-origin effects can be achieved by studying reciprocal cross of two inbred strains. In contrast, this task is much more challenging for an outbred population such as human population. To address this challenge, we propose a new framework to combine experimental strategies and novel statistical methods. Specifically, we propose to collect genotype data from family trios as well as RNA-seq data from the children of family trios. We have developed a new statistical method to estimate both genetic and parent-of-origin effects from such data sets. We demonstrated this approach by studying 30 trios of HapMap samples. Our results support some of previous finding of imprinted genes and also recover new candidate imprinted genes.

stat.AP↗

arXiv2017

Hunt's Hypothesis (H) for the Sum of Two Independent Levy Processes

Which Levy processes satisfy Hunt's hypothesis (H) is a long-standing open problem in probabilistic potential theory. The study of this problem for one-dimensional Levy processes suggests us to consider (H) from the point of view of the sum of Levy processes. In this paper, we present theorems and examples on the validity of (H) for the sum of two independent Levy processes. We also give a novel condition on the Levy measure which implies (H) for a large class of one-dimensional Levy processes.

math.PR↗

arXiv2016

A timing view of the heartbeat state of GRS 1915+105

We present a timing analysis of two Rossi X-ray Timing Explorer observations of the microquasar GRS 1915+105 during the heartbeat state. The phase-frequency-power maps show that the intermediate-frequency aperiodic X-ray variability weakens as the source softens in the slow rise phase, and when the quasi-periodic oscillation disappears in the rise phase of the pulse of the double-peaked class its sub-harmonic is still present with a hard phase lag. In the slow rise phase, the energy-frequency-power maps show that most of the aperiodic variability is produced in the corona, and may also induce the aperiodic variability observed at low energies from an accretion disk, which is further supported by the soft phase lag especially in the intermediate-frequency range (with a time delay up to 20 ms). In the rise phase of the pulse, the low-frequency aperiodic variability is enhanced significantly and there is a prominent hard lag (with a time delay up to 50 ms), indicating that the variability is induced by extension of the disk toward small radii as implied by the increase in flux and propagates into the corona. However, during the hard pulse of the double-peaked class, the variability shows no significant lag, which may be attributed to an optically thick corona. These timing results are generally consistent with the spectral results presented by Neilsen et al. (2011, 2012) which indicated that the slow rise phase corresponds to a local Eddington limit and the rise phase of the pulse corresponds to a radiation pressure instability in the disk.

astro-ph.HE↗

arXiv2016

Long distance co-propagation of quantum key distribution and terabit classical optical data channels

Quantum key distribution (QKD) generates symmetric keys between two remote parties, and guarantees the keys not accessible to any third party. Wavelength division multiplexing (WDM) between QKD and classical optical communications by sharing the existing fibre optics infrastructure is highly desired in order to reduce the cost of QKD applications. However, quantum signals are extremely weak and thus easily affected by the spontaneous Raman scattering effect from intensive classical light. Here, by means of wavelength selecting and spectral and temporal filtering, we realize the multiplexing and long distance co-propagation of QKD and Terabit classical coherent optical communication system up to 80km. The data capacity is two orders of magnitude larger than the previous results. Our demonstration verifies the feasibility of QKD and classical communication to share the resources of backbone fibre links, and thus taking the utility of QKD a great step forward.

quant-ph↗