arXiv subjects

Wei Li

Publications and source records attributed to Wei Li.

At least 1,477 records · Page 82Linked to original sources

arXiv2011

Correlations and fluctuations measured by the CMS experiment in pp and PbPb

Measurements of charged dihadron angular correlations are presented in proton-proton (pp) and Lead-Lead (PbPb) collisions, over a broad range of pseudorapidity and azimuthal angle, using the CMS detector at the LHC. In very high multiplicity pp events at center-of-mass energy of 7 TeV, a striking "ridge"-like structure emerges in the two-dimensional correlation function for particle pairs with intermediate pt of 1-3 GeVc, in the kinematic region 2.0<|Δη|<4.8 and small Δϕ, which is similar to observations in heavy-ion collisions. Studies of this new effect as a function of particle transverse momentum are discussed. The long-range and short-range dihadron correlations are also studied in PbPb collision at a nucleon-nucleon center-of-mass energy of 2.76 TeV, as a function of transverse momentum and collision centrality. A Fourier analysis of the long-range dihadron correlations is presented and discussed in the context of CMS measurements of higher order flow coefficients.

nucl-ex↗

arXiv2011

Low-threshold directional plasmon lasing assisted by spatially coherent surface plasmon polaritons

We theoretically propose directional, low-threshold plasmon lasing in both the near-infrared and visible wavelengths by utilizing spatially coherent surface plasmon polaritons on a meta-surface. The gain strength required for threshold lasing can be tuned down to a large extent through compatible structural parameters. Our calculations show that no more than 65 cm$^{-1}$ at 193.5 THz (1.55 $μ$m) or 267 cm$^{-1}$at 474THz (0.633 $μ$m) of gain coefficient is sufficient to compensate for the dissipation of metal films for threshold lasing; these values are smaller than any reported studies at the same frequencies. These findings present a planar solid-state route for plasmon lasing that is highly efficient and spatially coherent.

physics.optics↗

arXiv2011

Financial factor influence on scaling and memory of trading volume in stock market

We study the daily trading volume volatility of 17,197 stocks in the U.S. stock markets during the period 1989--2008 and analyze the time return intervals $τ$ between volume volatilities above a given threshold q. For different thresholds q, the probability density function P_q(τ) scales with mean interval <τ> as P_q(τ)=<τ>^{-1}f(τ/<τ>) and the tails of the scaling function can be well approximated by a power-law f(x)~x^{-γ}. We also study the relation between the form of the distribution function P_q(τ) and several financial factors: stock lifetime, market capitalization, volume, and trading value. We find a systematic tendency of P_q(τ) associated with these factors, suggesting a multi-scaling feature in the volume return intervals. We analyze the conditional probability P_q(τ|τ_0) for $τ$ following a certain interval τ_0, and find that P_q(τ|τ_0) depends on τ_0 such that immediately following a short/long return interval a second short/long return interval tends to occur. We also find indications that there is a long-term correlation in the daily volume volatility. We compare our results to those found earlier for price volatility.

q-fin.TR↗

arXiv2011

Power-Law Decay of Standing Waves on the Surface of Topological Insulators

We propose a general theory on the standing waves (quasiparticle interference pattern) caused by the scattering of surface states off step edges in topological insulators, in which the extremal points on the constant energy contour of surface band play the dominant role. Experimentally we image the interference patterns on both Bi$_2$Te$_3$ and Bi$_2$Se$_3$ films by measuring the local density of states using a scanning tunneling microscope. The observed decay indices of the standing waves agree excellently with the theoretical prediction: In Bi$_2$Se$_3$, only a single decay index of -3/2 exists; while in Bi$_2$Te$_3$ with strongly warped surface band, it varies from -3/2 to -1/2 and finally to -1 as the energy increases. The -1/2 decay indicates that the suppression of backscattering due to time-reversal symmetry does not necessarily lead to a spatial decay rate faster than that in the conventional two-dimensional electron system. Our formalism can also explain the characteristic scattering wave vectors of the standing wave caused by non-magnetic impurities on Bi$_2$Te$_3$.

cond-mat.mes-hall↗

arXiv2011

Kinetics of microribbon formation in a simplified model of amelogenin biomacromolecules

We show that the kinetics of microribbon formation of amelogenin molecules is well described by a combination of translational and rotational diffusion of a simplified anisotropic bipolar model consisting of hydrophobic spherical colloid particles and a point charge located on each particle surface. The colloid particles interact via a standard depletion attraction while the point charges interact through a screened Coulomb repulsion. We study the kinetics via a Brownian dynamics simulation of both translational and rotational motions and show that the anisotropy brought in by the charge dramatically affects the kinetic pathway of cluster formation and our simple model captures the main features of the experimental observations.

cond-mat.soft↗

arXiv2011

Linearized Tensor Renormalization Group Algorithm for Thermodynamics of Quantum Lattice Models

A linearized tensor renormalization group (LTRG) algorithm is proposed to calculate the thermodynamic properties of one-dimensional quantum lattice models, that is incorporated with the infinite time-evolving block decimation technique, and allows for treating directly the two-dimensional transfer-matrix tensor network. To illustrate its feasibility, the thermodynamic quantities of the quantum XY spin chain are calculated accurately by the LTRG, and the precision is shown to be comparable with (even better than) the transfer matrix renormalization group (TMRG) method. Unlike the TMRG scheme that can only deal with the infinite chains, the present LTRG algorithm could treat both finite and infinite systems, and may be readily extended to boson and fermion quantum lattice models.

cond-mat.str-el↗

arXiv2011

Holography and Entanglement in Flat Spacetime

We propose a holographic correspondence of the flat spacetime based on the behavior of the entanglement entropy and the correlation functions. The holographic dual theory turns out to be highly non-local. We argue that after most part of the space is traced out, the reduced density matrix gives the maximal entropy and the correlation functions become trivial. We present a toy model for this holographic dual using a non-local scalar field theory that reproduces the same property of the entanglement entropy. Our conjecture is consistent with the entropy of Schwarzschild black holes in asymptotically flat spacetimes.

hep-th↗

arXiv2011

A rigorous proof of non-existence of edge state in the semi-infinite armchair edged graphene

With the help of transfer matrix method, the conditions for the existence of the edge states in the semi-infinite armchair edged graphene is given. We discuss zero-energy and non-zero-energy edge states separately, and show the nonexistence of the edge states in the model analytically and rigorously.

cond-mat.mes-hall↗

arXiv2011

Giant topological magnetoelectric and optical Hall effects for topological insulator as a defect in photonic crystal

A system with a topological insulator slab sandwiched by two one-dimensional photonic crystals as a defect is investigated. A giant topological magnetoelectric effect is proposed which is characterized by two resonant peaks with half-unit transmissions and rich polarization behaviors in the photonic band gap. We also predict a giant optical Hall effect in our system, in which the transverse shift of the transmitted light could be thousand times larger than the wavelength. These effects are purely from the $Θ$-domain walls at the topological insulator interfaces and could be observed easily. These effects can also be used as the sensitive detection of basic physical constants.

cond-mat.mes-hall↗

arXiv2011

Effect of edge decoration on the energy spectrum of semi-infinite lattices

Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional (1D) lattice chain with Peierls phase transition and zigzag edged graphene (ZEG) are presented by means of transfer matrix method, in the frame of which the sufficient and necessary conditions for the existence of the edge states are determined. For 1D lattice chain, the zero-energy edge state exists when Peierls phase transition happens regardless whether the decoration exists or not, while the non-zero-energy edge states can be induced and manipulated through adjusting the edge decoration. On the other hand, the semi-infinite ZEG model with nearest-neighbor interaction can be mapped into the 1D lattice chain case. The non-zero-energy edge states can be induced by the decoration as well, and we can obtain the condition of the decoration on the edge for the existence of the novel edge states.

cond-mat.mes-hall↗

arXiv2010

The generalized connectivity of complete bipartite graphs

Let $G$ be a nontrivial connected graph of order $n$, and $k$ an integer with $2\leq k\leq n$. For a set $S$ of $k$ vertices of $G$, let $κ(S)$ denote the maximum number $\ell$ of edge-disjoint trees $T_1,T_2,...,T_\ell$ in $G$ such that $V(T_i)\cap V(T_j)=S$ for every pair $i,j$ of distinct integers with $1\leq i,j\leq \ell$. Chartrand et al. generalized the concept of connectivity as follows: The $k$-$connectivity$, denoted by $κ_k(G)$, of $G$ is defined by $κ_k(G)=$min$\{κ(S)\}$, where the minimum is taken over all $k$-subsets $S$ of $V(G)$. Thus $κ_2(G)=κ(G)$, where $κ(G)$ is the connectivity of $G$. Moreover, $κ_{n}(G)$ is the maximum number of edge-disjoint spanning trees of $G$. This paper mainly focus on the $k$-connectivity of complete bipartite graphs $K_{a,b}$. First, we obtain the number of edge-disjoint spanning trees of $K_{a,b}$, which is $\lfloor\frac{ab}{a+b-1}\rfloor$, and specifically give the $\lfloor\frac{ab}{a+b-1}\rfloor$ edge-disjoint spanning trees. Then based on this result, we get the $k$-connectivity of $K_{a,b}$ for all $2\leq k \leq a+b$. Namely, if $k>b-a+2$ and $a-b+k$ is odd then $κ_{k}(K_{a,b})=\frac{a+b-k+1}{2}+\lfloor\frac{(a-b+k-1)(b-a+k-1)}{4(k-1)}\rfloor,$ if $k>b-a+2$ and $a-b+k$ is even then $κ_{k}(K_{a,b})=\frac{a+b-k}{2}+\lfloor\frac{(a-b+k)(b-a+k)}{4(k-1)}\rfloor,$ and if $k\leq b-a+2$ then $κ_{k}(K_{a,b})=a. $

math.CO↗

arXiv2010

The tragedy of the commons in a multi-population complementarity game

We study a complementarity game with multiple populations whose members' offered contributions are put together towards some common aim. When the sum of the players' offers reaches or exceeds some threshold K, they each receive K minus their own offers. Else, they all receive nothing. Each player tries to offer as little as possible, hoping that the sum of the contributions still reaches K, however. The game is symmetric at the individual level, but has many equilibria that are more or less favorable to the members of certain populations. In particular, it is possible that the members of one or several populations do not contribute anything, a behavior called defecting, while the others still contribute enough to reach the threshold. Which of these equilibria then is attained is decided by the dynamics at the population level that in turn depends on the strategic options the players possess. We find that defecting occurs when more than 3 populations participate in the game, even when the strategy scheme employed is very simple, if certain conditions for the system parameters are satisfied. The results are obtained through systematic simulations.

q-bio.PE↗

arXiv2010

Learning, evolution and population dynamics

We study a complementarity game as a systematic tool for the investigation of the interplay between individual optimization and population effects and for the comparison of different strategy and learning schemes. The game randomly pairs players from opposite populations. The game is symmetric at the individual level, but has many equilibria that are more or less favorable to the members of the two populations. Which of these equilibria then is attained is decided by the dynamics at the population level. Players play repeatedly, but in each round with a new opponent. They can learn from their previous encounters and translate this into their actions in the present round on the basis of strategic schemes. The schemes can be quite simple, or very elaborate. We can then break the symmetry in the game and give the members of the two populations access to different strategy spaces. Typically, simpler strategy types have an advantage because they tend to go more quickly towards a favorable equilibrium which, once reached, the other population is forced to accept. Also, populations with bolder individuals that may not fare so well at the level of individual performance may obtain an advantage towards ones with more timid players. By checking the effects of parameters such as the generation length or the mutation rate, we are able to compare the relative contributions of individual learning and evolutionary adaptations.

q-bio.PE↗

arXiv2010

Maximum Path Information and Fokker-Planck Equation

We present in this paper a rigorous method to derive the nonlinear Fokker-Planck (FP) equation of anomalous diffusion directly from a generalization of the principle of least action of Maupertuis proposed by Wang for smooth or quasi-smooth irregular dynamics evolving in Markovian process. The FP equation obtained may take two different but equivalent forms. It was also found that the diffusion constant may depend on both q (the index of Tsallis entropy) and the time t.

cond-mat.stat-mech↗

arXiv2010

The effect of the forget-remember mechanism on spreading

We introduce a new mechanism---the forget-remember mechanism into the spreading process. Equipped with such a mechanism an individual is prone to forget the "message" received and remember the one forgotten, namely switching his state between active (with message) and inactive (without message). The probability of state switch is governed by linear or exponential forget-remember functions of history time which is measured by the time elapsed since the most recent state change. Our extensive simulations reveal that the forget-remember mechanism has significant effects on the saturation of message spreading, and may even lead to a termination of spreading under certain conditions. This finding may shed some light on how to control the spreading of epidemics. It is found that percolation-like phase transitions can occur. By investigating the properties of clusters, formed by connected, active individuals, we may be able to justify the existence of such phase transitions.

physics.bio-ph↗

arXiv2010

Phase transitions and thermodynamics of the two-dimensional Ising model on a distorted Kagomé lattice

The two-dimensional Ising model on a distorted Kagomé lattice is studied by means of exact solutions and the tensor renormalisation group (TRG) method. The zero-field phase diagrams are obtained, where three phases such as ferromagnetic, ferrimagnetic and paramagnetic phases, along with the second-order phase transitions, have been identified. The TRG results are quite accurate and reliable in comparison to the exact solutions. In a magnetic field, the magnetization ($m$), susceptibility and specific heat are studied by the TRG algorithm, where the $m=1/3$ plateaux are observed in the magnetization curves for some couplings. The experimental data of susceptibility for the complex Co(N$_3$)$_2$(bpg)$\cdot$ DMF$_{4/3}$ are fitted with the TRG results, giving the couplings of the complex $J=22K$ and $J'=33K$.

cond-mat.stat-mech↗

arXiv2010

Computing the permanental polynomials of bipartite graphs by Pfaffian orientation

The permanental polynomial of a graph $G$ is $π(G,x)\triangleq\mathrm{per}(xI-A(G))$. From the result that a bipartite graph $G$ admits an orientation $G^e$ such that every cycle is oddly oriented if and only if it contains no even subdivision of $K_{2,3}$, Yan and Zhang showed that the permanental polynomial of such a bipartite graph $G$ can be expressed as the characteristic polynomial of the skew adjacency matrix $A(G^e)$. In this paper we first prove that this equality holds only if the bipartite graph $G$ contains no even subdivision of $K_{2,3}$. Then we prove that such bipartite graphs are planar. Further we mainly show that a 2-connected bipartite graph contains no even subdivision of $K_{2,3}$ if and only if it is planar 1-cycle resonant. This implies that each cycle is oddly oriented in any Pfaffian orientation of a 2-connected bipartite graph containing no even subdivision of $K_{2,3}$. As applications, permanental polynomials for some types of bipartite graphs are computed.

math.CO↗

arXiv2010

Effect of annealing temperature on morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2

Nanotubed titanic acid (H2Ti2O4(OH)2) was prepared from nanotubed sodium titanate (Na2Ti2O4(OH)2) by an ion exchange reaction in a pH=1 HCl solution. The effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR. The results showed that nanotubed H2Ti2O4(OH)2 is thermally unstable. Its dehydration consists of two steps. In the first-step dehydration, single-electron-trapped oxygen vacancies (SETOVs) were generated. Accompanying the second-step dehydration, the transition of crystal form from orthorhombic system to anatase took place, at the same time the nanotubes broke. At T>300 °C, when the SETOV concentration greatly increased, the interaction between SETOV happened. (VOo)x formed could play the role of recombination center of photogenerated e--h+ and make the photocatalytic behavior of TiO2 (anatase, obtained from 500 °C-treated nanotubed H2Ti2O4(OH)2) to become bad.

cond-mat.mtrl-sci↗