Xin Chen - Beijing Key Laboratory of Intelligent Telecommunications Software and Multimedia, Beijing University of Posts and Telecommunications, Beijing, China

Xin Chen
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Name
Xin Chen
Affiliation
Beijing Key Laboratory of Intelligent Telecommunications Software and Multimedia, Beijing University of Posts and Telecommunications, Beijing, China
City
Beijing
Country
China

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Mathematics - Probability (14)
 
Quantum Physics (9)
 
Physics - Materials Science (8)
 
Solar and Stellar Astrophysics (3)
 
Physics - Statistical Mechanics (3)
 
Mathematics - Statistics (3)
 
Mathematics - Functional Analysis (3)
 
Statistics - Theory (3)
 
Quantitative Biology - Genomics (3)
 
Physics - Chemical Physics (2)
 
Mathematical Physics (2)
 
Physics - Strongly Correlated Electrons (2)
 
Physics - Soft Condensed Matter (2)
 
Mathematics - Mathematical Physics (2)
 
Mathematics - Analysis of PDEs (1)
 
Quantitative Biology - Neurons and Cognition (1)
 
Computer Science - Logic in Computer Science (1)
 
Computer Science - Software Engineering (1)
 
Physics - Disordered Systems and Neural Networks (1)
 
Mathematics - Combinatorics (1)
 
Physics - Mesoscopic Systems and Quantum Hall Effect (1)
 
Computer Science - Computers and Society (1)
 
Computer Science - Human-Computer Interaction (1)
 
High Energy Physics - Experiment (1)
 
Computer Science - Computational Engineering; Finance; and Science (1)
 
Mathematics - Dynamical Systems (1)
 
High Energy Physics - Phenomenology (1)
 
Mathematics - Differential Geometry (1)

Publications Authored By Xin Chen

We present a quantum framework based on a density matrix of a dimer system to investigate the quantum dynamics of excitation energy transfer (EET) in the presence of the evanescent field from the metal and the phonon bath. Due to the spatial correlation of the electric field in the vicinity of the metal, the spectral density of the evanescent field is similar to that of a shared phonon bath. However, the EET dynamics under the influence of the evanescent field is an open and a new problem. Read More

Two-dimensional (2D) carbon nitride materials play an important role in energy-harvesting, energy-storage and environmental applications. Recently, a new carbon nitride, 2D polyaniline (C3N) was proposed [PNAS 113 (2016) 7414-7419]. Based on the structure model of this C3N monolayer, we propose two new carbon nitride monolayers, named dumbbell (DB) C4N-I and C4N-II. Read More

In this letter we show how the topological number of a static Hamiltonian can be measured from a dynamical quench process. We focus on a two-band Chern insulator in two-dimension, for instance, the Haldane model, whose dynamical process can be described by a mapping from the $[k_x,k_y,t]$ space to the Bloch sphere, characterized by the Hopf invariant. Such a mapping has been constructed experimentally by measurements in cold atom systems. Read More

Quantum Spin Hall (QSH) insulators with a large topologically nontrivial bulk gap are crucial for future applications of the QSH effect. Among these, group III-V monolayers and their halides with chair structure (regular hexagonal framework, RHF) were widely studied. Using first-principles calculations, we propose a new structure model for the functionalized group III-V monolayers, which consist of rectangular GaBi-X2 (X=I, Br, Cl) monolayers with a distorted hexagonal framework (DHF). Read More

The high density of evanescent modes in the vicinity of a metal leads to enhancement of the near-field F\"{o}rster resonant energy transfer (FRET) rate. We present a classical approach to calculate the FRET rate based on the dyadic Green's function of an arbitrary dielectric environment, and consider non-local limit of material permittivity in case of metallic halfspace and thin film. In a dimer system, we find that the FRET rate is enhanced due to shared evanescent photon modes bridging a donor and an acceptor. Read More

Nowadays, quantum router is playing a key role in quantum communication and quantum network- s. Here we propose a tunable single-photon routing scheme, based on quantum interference, which uses two distant artificial atoms coupling to two transmission lines. Depending on the distance between the two atoms, the collective effect will lead to destructive or constructive interference between the scattered photons. Read More

The search for new quantum spin Hall (QSH) phase and effective manipulations of their edge states are very important for both fundamental sciences and practical applications. Here, we use first-principles calculations to study the strain-driven topological phase transition of two-dimensional (2D) arsenene monolayer. We find that the band gap of arsenene decreases with increasing strain and changes from indirect to direct, and then the s-p band inversion takes place at {\Gamma} point as the tensile strain is larger than 11. Read More

The prospects of searching for the flavor changing neutral current effect in the decay of $t\to H c, H\to \tau\tau$ are investigated with the simulated $p-p$ collision data for the ATLAS detector at the LHC, where the Higgs mass is assumed to be 125~GeV. A fit based on the constraints from the Higgs mass and the tau decay kinematics is performed for each event, which improves significantly the Higgs and top mass reconstruction and helps the signal-background separation. Boosted Decision Trees discriminants are developed to achieve an optimal sensitivity of searching for the FCNC signal. Read More

We develop symmetry reduction for material stochastic Lagrangian systems with advected quantities whose configuration space is a Lie group, obtaining deterministic constrained variational principles and dissipative equations of motion in spatial representation. We discuss in detail the situation when the group in the general theory is a group of diffeomorphisms and derive, as an application, an MHD system for viscous compressible fluids. Read More

Quantum spin Hall (QSH) effect is quite promising for applications in spintronics and quantum computations, but presently can only be achieved at ultralow temperature. Searching for large-gap QSH insulators is the key to increase the operating temperature. Using first-principles calculations, we demonstrate that the stable hydrogenated stanene with a dumbbell-like structure (DB stanane) has large topological nontrivial band gaps of 312 meV (gamma point) and 160 meV for bulk characterized by a topological invariant of Z2=1, due to the s-pxy band inversion. Read More

Wearable devices are a new form of mobile computer system that provides exclusive and user-personalized services. Wearable devices bring new issues and challenges to computer science and technology. This paper summarizes the development process and the categories of wearable devices. Read More

The study of genetic map linearization leads to a combinatorial hard problem, called the {\em minimum breakpoint linearization} (MBL) problem. It is aimed at finding a linearization of a partial order which attains the minimum breakpoint distance to a reference total order. The approximation algorithms previously developed for the MBL problem are only applicable to genetic maps in which genes or markers are represented as signed integers. Read More

Background: Identifying all possible mapping locations of next-generation sequencing (NGS) reads is highly essential in several applications such as prediction of genomic variants or protein binding motifs located in repeat regions, isoform expression quantification, metagenomics analysis, etc. However, this task is very time-consuming and majority of mapping tools only focus on one or a few best mapping locations. Results: We propose AMAS, an alignment tool specialized in identifying all possible mapping locations of NGS reads in a reference sequence. Read More

Let $(X_t)_{t\ge 0}$ be a symmetric strong Markov process generated by non-local regular Dirichlet form $(D,\D(D))$ as follows \begin{equation*} \begin{split} & D(f,g)=\int_{\R^d}\int_{\R^d}\big(f(x)-f(y)\big)\big(g(x)-g(y)\big) J(x,y)\,dx\,dy, \quad f,g\in \D(D) \end{split} \end{equation*} where $J(x,y)$ is a strictly positive and symmetric measurable function on $\R^d\times \R^d$. We study the intrinsic hypercontractivity, intrinsic supercontractivity and intrinsic ultracontractivity for the Feynman-Kac semigroup $$ T^V_t(f)(x)=\Ee^x\left(\exp\Big(-\int_0^tV(X_s)\,ds\Big)f(X_t)\right),\,\, x\in\R^d, f\in L^2(\R^d;dx).$$ In particular, we prove that for $$J(x,y)\asymp|x-y|^{-d-\alpha}\I_{\{|x-y|\le 1\}}+e^{-|x-y|}\I_{\{|x-y|> 1\}}$$ with $\alpha \in (0,2)$ and $V(x)=|x|^\lambda$ with $\lambda>0$, $(T_t^V)_{t\ge 0}$ is intrinsically ultracontractive if and only if $\lambda>1$; and that for symmetric $\alpha$-stable process $(X_t)_{t\ge0}$ with $\alpha \in (0,2)$ and $V(x)=\log^\lambda(1+|x|)$ with some $\lambda>0$, $(T_t^V)_{t\ge 0}$ is intrinsically ultracontractive (or intrinsically supercontractive) if and only if $\lambda>1$, and $(T_t^V)_{t\ge 0}$ is intrinsically hypercontractive if and only if $\lambda\ge1$. Read More

We prove that a general (not necessarily symmetric) L\'evy process killed on exiting a bounded open set (without regular condition on the boundary) is intrinsically ultracontractive, provided that $B(0,R_0)\subseteq \rm{supp}(\nu)$ for some constant $R_0>0$, where $\rm{supp}(\nu)$ denotes the support of the associated L\'evy measure $\nu$. For a symmetric L\'evy process killed on exiting a bounded H\"older domain of order $0$, we also obtain the intrinsic ultracontractivity under much weaker assumption on the associated L\'evy measure. Read More

We present a set of tools for detecting small-scale solar magnetic cancellations and the disk counterpart of type II spicules (the so-called Rapid Blueshifted Excursions (RBEs)), using line-of-sight photospheric magnetograms and chromospheric spectroscopic observations, respectively. For tracking magnetic cancellation, we improve the Southwest Automatic Magnetic Identification Suite (SWAMIS) so that it is able to detect certain obscure cancellations that can be easily missed. For detecting RBEs, we use a normalized reference profile to reduce false-positive detections caused by the non-uniform background and seeing condition. Read More

Chromospheric rapid blueshifted excursions (RBEs) are suggested to be the disk counterparts of type II spicules at the limb and believed to contribute to the coronal heating process. Previous identification of RBEs was mainly based on feature detection using Dopplergrams. In this paper, we study RBEs on 2011 October 21 in a very quiet region at the disk center, which were observed with the high-cadence imaging spectroscopy of the Ca II 8542 A line from the Interferometric Bidimensional Spectrometer (IBIS). Read More

In this paper, we examine linear programming (LP) based relaxations for synthesizing polynomial Lyapunov functions to prove the stability of polynomial ODEs. A common approach to Lyapunov function synthesis starts from a desired parametric polynomial form of the polynomial Lyapunov function. Subsequently, we encode the positive-definiteness of the function, and the negative-definiteness of its derivative over the domain of interest. Read More

Consider the symmetric non-local Dirichlet form $(D,\D(D))$ given by $$ D(f,f)=\int_{\R^d}\int_{\R^d}\big(f(x)-f(y)\big)^2 J(x,y)\,dx\,dy $$with $\D(D)$ the closure of the set of $C^1$ functions on $\R^d$ with compact support under the norm $\sqrt{D_1(f,f)}$, where $D_1(f,f):=D(f,f)+\int f^2(x)\,dx$ and $J(x,y)$ is a nonnegative symmetric measurable function on $\R^d\times \R^d$. Suppose that there is a Hunt process $(X_t)_{t\ge 0}$ on $\R^d$ corresponding to $(D,\D(D))$, and that $(L,\D(L))$ is its infinitesimal generator. We study the intrinsic ultracontractivity for the Feynman-Kac semigroup $(T_t^V)_{t\ge 0}$ generated by $L^V:=L-V$, where $V\ge 0$ is a non-negative locally bounded measurable function such that Lebesgue measure of the set $\{x\in \R^d: V(x)\le r\}$ is finite for every $r>0$. Read More

We prove the strong completeness for a class of non-degenerate SDEs, whose coefficients are not necessarily uniformly elliptic nor locally Lipschitz continuous nor bounded. Moreover, for each $t$, the solution flow $F_t$ is weakly differentiable and for each $p>0$ there is a positive number $T(p)$ such that for all $tRead More

Enormous volumes of short reads data from next-generation sequencing (NGS) technologies have posed new challenges to the area of genomic sequence comparison. The multiple sequence alignment approach is hardly applicable to NGS data due to the challenging problem of short read assembly. Thus alignment-free methods need to be developed for the comparison of NGS samples of short reads. Read More

In general, gradient estimates are very important and necessary for deriving convergence results in different geometric flows, and most of them are obtained by analytic methods. In this paper, we will apply a stochastic approach to systematically give gradient estimates for some important geometric quantities under the Ricci flow, the mean curvature flow, the forced mean curvature flow and the Yamabe flow respectively. Our conclusion gives another example that probabilistic tools can be used to simplify proofs for some problems in geometric analysis. Read More

Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, $\it{i.e. Read More

We present an analysis of the thermoelectric properties of of $n$-type GeTe and SnTe in relation to the lead chalcogenides PbTe and PbSe. We find that the singly degenerate conduction bands of semiconducting GeTe and SnTe are highly non-ellipsoidal, even very close to the band edges. This leads to isoenergy surfaces with a strongly corrugated shape that is clearly evident at carrier concentrations well below 0. Read More

We prove the existence of the O-U Dirichlet form and the damped O-U Dirichlet form on path space over a general non-compact Riemannian manifold which is complete and stochastically complete. We show a weighted log-Sobolev inequality for the O-U Dirichlet form and the (standard) log-Sobolev inequality for the damped O-U Dirichlet form. In particular, the Poincar\'e inequality (and the super Poincar\'e inequality) can be established for the O-U Dirichlet form on path space over a class of Riemannian manifolds with unbounded Ricci curvatures. Read More

Quantum path interferences or resonances in multilevel dissipative quantum systems play an important and intriguing role in the transport processes of nanoscale systems. Many previous minimalistic models used to describe the quantum path interference driven by incoherent fields are based on the approximations including the second order perturbation for the weak coupling limit, the ad-hoc choices of two-time correlation functions and $\it{etc}$. On the other hand, the similar model to study the non-adiabatic molecular electronic excitation have been extensively developed and many efficient quantum molecular dynamics simulation schemes, such as the Ehrenfest scheme, have been proposed. Read More

Given $n$ samples of a regular discrete distribution $\pi$, we prove in this article first a serial of SLLNs results (of Dvoretzky and Erd\"{o}s' type) which implies a typical power law when $\pi$ is heavy-tailed. Constructing a (random) graph from the ordered $n$ samples, we can establish other laws for the degree-distribution of the graph. The phenomena of small world is also discussed. Read More

The Navier-Stokes equation on Rd (d greater or equal to 3) formulated on Besov spaces is considered. Using a stochastic forward-backward differential system, the local existence of a unique solution in B_ r, with r > 1 + d is obtained. We also show p,p p the convergence to solutions of the Euler equation when the viscosity tends to zero. Read More

We present an unprecedented high-resolution \ha\ imaging spectroscopic observation of a C4.1 flare taken with IBIS on 2011 October 22. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Read More

The recent experimental discoveries about excitation energy transfer (EET) in light harvesting antenna (LHA) attract a lot of interest. As an open non-equilibrium quantum system, the EET demands more rigorous theoretical framework to understand the interaction between system and environment and therein the evolution of reduced density matrix. A phonon is often used to model the fluctuating environment and convolutes the reduced quantum system temporarily. Read More

Perturbations of super Poincar\'e and weak Poincar\'e inequalities for L\'evy type Dirichlet forms are studied. When the range of jumps is finite our results are natural extensions to the corresponding ones derived earlier for diffusion processes; and we show that the study for the situation with infinite range of jumps is essentially different. Some examples are presented to illustrate the optimality of our results. Read More

We used X-ray/neutron diffraction to determine the low temperature (LT) structure of IrTe2. A structural modulation was observed with a wavevector of k =(1/5, 0, 1/5) below Ts?285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed the first principles calculations for high temperature (HT) and LT structures, which elucidate the nature of the phase transition and the LT structure. Read More

High thermoelectric performance in oxides requires stable conductive materials that have suitable band structures. Here we show based on an analysis of the thermopower and related properties using first-principles calculations and Boltzmann transport theory that hole doped Cu2O may be such a material. We find that hole-doped Cu2O has a high thermopower of above 200 microV/K even with doping levels as high as 5. Read More

The paper is a continuation of our paper [12,2], and it studies functional inequalities for non-local Dirichlet forms with finite range jumps or large jumps. Let $\alpha\in(0,2)$ and $\mu_V(dx)=C_Ve^{-V(x)}\,dx$ be a probability measure. We present explicit and sharp criteria for the Poincar\'{e} inequality and the super Poincar\'{e} inequality of the following non-local Dirichlet form with finite range jump $$\mathscr{E}_{\alpha, V}(f,f):= (1/2)\iint_{{|x-y|\le 1}}\frac{(f(x)-f(y))^2}{|x-y|^{d+\alpha}} dy \mu_V(dx);$$ on the other hand, we give sharp criteria for the Poincar\'{e} inequality of the non-local Dirichlet form with large jump as follows $$\mathscr{D}_{\alpha, V}(f,f):= (1/2)\iint_{{|x-y|> 1}}\frac{(f(x)-f(y))^2}{|x-y|^{d+\alpha}} dy \mu_V(dx),$$ and also derive that the super Poincar\'{e} inequality does not hold for $\mathscr{D}_{\alpha, V}$. Read More

Reduced dimensionality has long been regarded as an important strategy for increasing thermoelectric performance, for example in superlattices and other engineered structures. Here we point out and illustrate by examples that three dimensional bulk materials can be made to behave as if they were two dimensional from the point of view of thermoelectric performance. Implications for the discovery of new practical thermoelectrics are discussed. Read More

Sufficient dimension reduction (SDR) in regression, which reduces the dimension by replacing original predictors with a minimal set of their linear combinations without loss of information, is very helpful when the number of predictors is large. The standard SDR methods suffer because the estimated linear combinations usually consist of all original predictors, making it difficult to interpret. In this paper, we propose a unified method - coordinate-independent sparse estimation (CISE) - that can simultaneously achieve sparse sufficient dimension reduction and screen out irrelevant and redundant variables efficiently. Read More

We present first principles calculations of the phonon dispersions of Bi2Te3 and discuss these in relation to the acoustic phonon interface scattering in ceramics. The phonon dispersions show agreement with what is known from neutron scattering for the optic modes. We find a difference between the generalized gradient approximation and local density results for the acoustic branches. Read More

We give a combinatorial interpretation using lattice paths for the super Catalan number $S(m, m+s)$ for $s \leq 3$ and a separate interpretation for $s = 4$. Read More

Let $V$ be a locally bounded measurable function such that $e^{-V}$ is bounded and belongs to $L^1(dx)$, and let $\mu_V(dx):=C_V e^{-V(x)} dx$ be a probability measure. We present the criterion for the weighted Poincar\'{e} inequality of the non-local Dirichlet form $$ D_{\rho,V}(f,f):=\iint(f(y)-f(x))^2\rho(|x-y|) dy \mu_V(dx) $$ on $L^2(\mu_V)$. Taking $\rho(r)={e^{-\delta r}}{r^{-(d+\alpha)}}$ with $0<\alpha<2$ and $\delta\geqslant 0$, we get some conclusions for general fractional Dirichlet forms, which can be regarded as a complement of our recent work Wang and Wang (2012), and an improvement of the main result in Mouhot, Russ, and Sire (2011). Read More

The dynamical evolution of a quantum system composed of two coupled cavities, each containing a two-level atom and a single-mode thermal field, is investigated under different conditions. The entanglement between the two atoms is controlled by the hopping strength and the detuning between the atomic transition and the cavities. We find that when the atomic transition is far off-resonant with both the eigenmodes of the coupled cavity system, the maximally entangled state for the two atoms can be generated with the initial state in which one atom is in the ground state and the other is in the excited state. Read More

We describe a scheme with analytic result that allows to generate steady-state entanglement for two atoms over a dissipative bosonic medium. The resonant coupling between the mediating bosonic mode and cavity modes produces three collective atomic decay channels. This dissipative dynamics, together with the unitary process induced by classical microwave fields, drives the two atoms to the symmetric or asymmetric entangled steady state conditional upon the choice of the phases of the microwave fields. Read More

We propose a scheme for generating steady entanglement between two distant atomic qubits in the coupled-cavity system via laser cooling. With suitable choice of the laser frequencies, the target entangled state is the only ground state that is not excited by the lasers due to large detunings. The laser excitations of other ground states, together with dissipative processes, drive the system to the target state which is the unique steady state of the system. Read More

We prove a Euler-Poincar\'e reduction theorem for stochastic processes taking values in a Lie group and we show examples of its application to SO(3) and to the group of diffeomorphisms. Read More

We propose a scheme for the dissipative preparation of W-type entangled steady-states of three atoms trapped in an optical cavity. The scheme is based on the competition between the decay processes into and out of the target state. By suitable choice of system parameters, we resolve the whole evolution process and employ the effective operator formalism to engineer four independent decay processes, so that the target state becomes the stationary state of the quantum system. Read More

We propose a scheme for the generation of entangled states for two atoms trapped in separate cavities coupled to each other. The scheme is based on the competition between the unitary dynamics induced by the classical fields and the collective decays induced by the dissipation of two delocalized field modes. Under certain conditions, the symmetric or asymmetric entangled state is produced in the steady state. Read More

Collective rhythmic dynamics from neurons is vital for cognitive functions such as memory formation but how neurons self-organize to produce such activity is not well understood. Attractor-based models have been successfully implemented as a theoretical framework for memory storage in networks of neurons. Activity-dependent modification of synaptic transmission is thought to be the physiological basis of learning and memory. Read More

Communication Based Train Control (CBTC) system is the state-of-the-art train control system. In a CBTC system, to guarantee the safety of train operation, trains communicate with each other intensively and adjust their control modes autonomously by computing critical control parameters, e.g. Read More

Elliptic stochastic differential equations (SDE) make sense when the coefficients are only continuous. We study the corresponding linearized SDE whose coefficients are not assumed to be locally bounded. This leads to existence of $W_{\loc}^{1,p}$ solution flows for elliptic SDEs with H\"older continuous and $\cap_{p} W_{\loc}^{1,p}$ coefficients. Read More