Lei Wang

Renmin University of China | RUC

Thermal broadening of the quasi-particle peak in the spectral function is an important physical feature in many statistical systems, but difficult to calculate. Within the projective truncation approximation (PTA) of Green's function equation of motion for classical systems, we produce the spectral function with thermal broadened quasi-particles pe...

It is expected that the energy-diffusion propagator in a one-dimensional nonlinear lattice with three conserved quantities: energy, momentum, and stretch, consists of a central heat mode and two sound modes. The heat mode follows a Lévy distribution. Consequently, the heat diffusion is super, i.e., the second moment of the diffusion propagator dive...

We study the thermalization process in a one-dimensional lattice with two-dimensional motions. The phonon modes in such a lattice consist of two branches. Unlike in general nonlinear Hamiltonian systems, for which the only conserved quantity is the total energy, the total angular momentum J is also conserved in this system. Consequently, the intra-...

Stochastic dynamics of a nonlinear thermal circuit is studied. Due to the existence of negative differential thermal resistance, there exist two stable steady states that satisfy both the continuity and stability conditions. The dynamics of such a system is governed by a stochastic equation which describes originally an overdamped Brownian particle...

The energy diffusion process in a few two-dimensional Fermi-Pasta-Ulam-type lattices is numerically simulated via the equilibrium local energy spatiotemporal correlation. Just as the nonlinear fluctuating hydrodynamic theory suggested, the diffusion propagator consists of a bell-shaped central heat mode and a sound mode extending with a constant sp...

In this paper, we first develop the projective truncation approximation (PTA) in the Green's function equation of motion (EOM) formalism for classical statistical models. To implement PTA for a given Hamiltonian, we choose a set of basis variables and projectively truncate the hierarchical EOM. We apply PTA to the one-dimensional ϕ^{4} lattice mode...

We study the equilibration process of a one-dimensional lattice with transverse motions and external magnetic field. Starting from certain initial states, the system commonly reaches a metastable transient state shortly and then stays there for an extremely long time before it finally arrives in the ergodic equilibrium state. The relaxation time Te...

Heat current J that flows through a few typical two-dimensional nonlinear lattices is systematically studied. Each lattice consists of two identical segments that are coupled by an interface with strength kint. It is found that the two-universality-class scenario that is revealed in one-dimensional systems is still valid in the two-dimensional syst...

A thermal transistor consists of three segments, the drain, the source, and the gate. We study the influence of the thermal resistance RG in the gate segment systematically and reveal its key importance. In contrast to the negative differential thermal resistance between the drain and the source that has been studied extensively due to its indispen...

Green-Kubo algorithm is an effective method for the calculation of transport coefficients in terms of integral of the current correlation function. In this paper, we investigate two important issues of this algorithm in the calculation of anomalous heat conduction. Firstly, since the correlation function should be calculated in the thermodynamic li...

It is well known that the price time series of an efficient market display a Brownian motion. In such a case the best prediction of a future price is the last-known price thus no arbitrage is possible. A real market is, however, possibly not perfectly efficient. In this paper, we apply an error back-propagation neural network to tick-by-tick high-f...

The grain size effect on the thermal transport properties of hexagonal boron nitride (h-BN) thin films was experimentally investigated using the opto-thermal Raman technique. High-quality monolayer h-BN with mean grain sizes ranging from~7μm to~19nm were successfully synthesized on Pt foil by chemical vapor deposition (CVD). The thermal conductivit...

Local thermal equilibrium (LTE) is a general presumption of many theoretical analyses in nonequilibrium statistical physics. It describes a situation that although the system is not in global thermal equilibrium, each small portion of the system may still be described approximately by the laws of thermal equilibrium. The validity of LTE has however...

We systematically study heat current J that flows through a few one-dimensional nonlinear lattices, each of which consists of two identical segments that are coupled by a weak interface. Existing theoretical analyses expect that J is generally proportional to the square of the interface strength when the temperature drop is fixed and small. However...

In this paper, we study systematically a serial of correlation functions in some one-dimensional nonlinear lattices. Due to the energy conservation law, they are implicitly interdependent. Various transport coefficients are thus also connected. In the studies of the autocorrelations of local energy density and of local heat current, a general relat...

We extend a previously proposed resonance phonon approach that is based on the linear response theory. By studying the complex response function in depth, we work out the phonon relaxation time besides the oscillating frequency of the phonons in a few one-dimensional nonlinear lattices. The results in the large wave-number-k regime agree with the e...

Based on the linear response theory, we propose a resonance phonon (r-ph) approach to study the renormalized phonons in a few one-dimensional nonlinear lattices. Compared with the existing anharmonic phonon (a-ph) approach, the dispersion relations derived from this approach agree with the expectations of the effective phonon (e-ph) theory much bet...

The study of heat transport in low-dimensional oscillator lattices presents a formidable challenge. Theoretical efforts have been made trying to reveal the underlying mechanism of diversified heat transport behaviors. In lack of a unified rigorous treatment, approximate theories often may embody controversial predictions. It is therefore of ultimat...

Nonstationary heat conduction in a few one-dimensional nonlinear lattices is studied numerically based on the Maxwell-Cattaneo (MC) law. We simulate the relaxation process and calculate the magnitudes of the temperature oscillation A_{T}(t) and the local heat current oscillation A_{j}(t). A phase difference between A_{T}(t) and A_{j}(t) is observed...

Heat diffusion processes in various one-dimensional total-momentum-conserving nonlinear lattices with symmetric interaction and asymmetric interaction are systematically studied. It is revealed that the asymmetry of interaction largely enhances the heat diffusion; while according to our existing studies for heat conduction in the same lattices, it...

Heat and particle transport in a one-dimensional hard-point gas of elastically colliding particles are studied. In the nonequal mass case, due to the presence of on-site potential, the heat conduction of the model obeys the Fourier law and all the transport coefficients asymptotically approach constants in the thermodynamic limit. The thermoelectri...

The Green-Kubo formula provides a mathematical expression for heat conductivity in terms of integrals of the heat-current correlation function, which should be calculated in the thermodynamic limit. In finite systems this function generally decreases, i.e., it decays faster than it does in infinite systems. We compared the values of the correlation...

A thermal diode that rectifies heat current is one of the basic devices for functional heat control. Frequency response is an important feature of many electric devices, such as diodes and transistors. Frequency response measures the ability of a device to process high-frequency signals. In this paper, we systematically study the frequency response...

We have numerically studied heat conduction in a few one-dimensional momentum-conserving lattices with asymmetric interparticle interactions by the nonequilibrium heat bath method, the equilibrium Green-Kubo method, and the heat current power spectra analysis. Very strong finite-size effects are clearly observed. Such effects make the heat conducti...

Heat conduction in three two-dimensional (2D) momentum-conserving nonlinear lattices are numerically calculated via both nonequilibrium heat-bath and equilibrium Green-Kubo algorithms. It is expected by mainstream theories that heat conduction in such 2D lattices is divergent and the thermal conductivity κ increases with lattice length N logarithmi...

Current limiters and constant current sources, which play important roles in electronic circuits, have been built up for many decades. Their thermal counterparts, heat current limiters and constant heat current sources, are still not available yet. By combining two typical nonlinear lattices, the Frenkel-Kontorova (FK) lattice and a coupled rotator...

The recently developed modified inverse random midpoint displacement (mIRMD) and conventional detrended fluctuation analysis (DFA) algorithms are used to analyze the tick-by-tick high-frequency time series of Chinese A-share stock prices and indexes. A dual-fractal structure with a crossover at about 10 min is observed. The majority of the selected...

The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: By use of tailored models we demonstrate that phonons can be manipulated like electrons and...

Two-dimensional asymmetrical Ising models consisting of two weakly coupled dissimilar segments, coupled to heat baths with different temperatures at the two ends, are studied by Monte Carlo simulations. The heat rectifying effect, namely asymmetric heat conduction, is clearly observed. The underlying mechanisms are the different temperature depende...

We numerically study heat conduction in a few one-dimensional Fermi-Pasta-Ulam (FPU)-type lattices by both nonequilibrium heat bath and equilibrium Green-Kubo algorithms. In those lattices, heat conductivity κ is known to diverge with length N as Nα. It is commonly expected that the running exponent α should monotonously decreases with N and a rece...

Heat conduction in three-dimensional anharmonic lattices was numerically studied by the Green-Kubo theory. For a given lattice width W, a dimensional crossover is generally observed to occur at a W-dependent threshold of the lattice length. Lattices shorter than W will display a 3D behavior while lattices longer than W will display a 1D behavior. I...

Heat due to lattice vibration (phonons) is traditionally regarded as harmful for information processing. In this paper, we will demonstrate via numerical simulation, theoretical analysis and experiments that, phonons, can be manipulated like electrons. They can be used to carry and process information. Basic phononic devices such as thermal diode,...

We study heat and particle transport in a classical disordered, one-dimensional, hard-point gas model. We provide convincing numerical evidence that the figure of merit ZT diverges as a power law with the average particle number in the chain. This quite surprising result appears to be related to the ergodic and mixing properties of the system and i...

Memory is an indispensible element for a computer in addition to logic gates. In this Letter we report a model of thermal memory. We demonstrate via numerical simulation that thermal (phononic) information stored in the memory can be retained for a long time without being lost and more importantly can be read out without being destroyed. The possib...

Thermal transistor is an efficient heat control device which can act as a heat switch as well as a heat modulator. In this paper, we study systematically one-dimensional and two-dimensional thermal transistors. In particular, we show how to improve significantly the efficiency of the one-dimensional thermal transistor. The study is also extended to...

When it comes to transporting energy, nature has two vital tools at its disposal: conduction by heat and by electricity. But these two phenomena have never been treated equally by scientists. Electricity, via the transistor and other electronic devices, has enabled technological developments that have transformed many aspects of our lives. But simi...

We study directed transport in a classical deterministic dissipative system. We consider the generic case of mixed phase space and show that large ratchet currents can be generated thanks to the presence, in the Hamiltonian limit, of transporting stability islands embedded in the chaotic sea. Because of the simultaneous presence of chaos and dissip...

Logic gates are basic digital elements for computers. We build up thermal logic gates that can perform similar operations as their electronic counterparts. The thermal logic gates are based on nonlinear lattices, which exhibit very intriguing phenomena due to their temperature dependent power spectra. We demonstrate that phonons, the heat carriers,...

A model of a thermal transistor to control heat flow is reported. Like its electronic counterpart, the thermal transistor is a three-terminal device with the important feature that the heat current through two terminals can be switched or modulated by the temperature of the third terminal. The thermal transistor model is possible because of the neg...

By connecting two dissimilar anharmonic lattices exemplified by Fermi-Pasta-Ulam (FPU) model and Frenkel-kontorova (FK) model, we successfully build up one dimensional thermal diode. We find the rectifying effect is closely related to asymmetric interface thermal resistance (Kapitza resistance). And the asymmetric thermal resistance depends on how...

We study thermal properties of one dimensional(1D) harmonic and anharmonic lattices with mass gradient. It is found that the temperature gradient can be built up in the 1D harmonic lattice with mass gradient due to the existence of gradons. The heat flow is asymmetric in the anharmonic lattices with mass gradient. Moreover, in a certain temperature...

We study how to reduce thermal conductivity of anharmonic lattices. It is shown that high density of interface is an efficient way to get ultralow thermal conductivity, however, it does not work well when the density exceeds a certain value. This behavior is even clearer in harmonic lattices. The saturation of thermal conductivity in the case of di...

We discuss the stability properties of a one-dimensional hard-point gas. We study the decay of the Loschmidt echo which describes the stability of the motion under system perturbations. We show a universal behavior in the echo decay which is intimately connected to the linear dynamical instability of the motion. In particular, in spite of such a we...

We study interface thermal resistance (ITR) in a system consisting of two dissimilar anharmonic lattices exemplified by the Fermi-Pasta-Ulam and Frenkel-Kontorova models. It is found that the ITR is asymmetric; namely, it depends on how the temperature gradient is applied. The dependence of the ITR on the coupling constant, temperature, temperature...

We study anomalous heat conduction and anomalous diffusion in low-dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is sigma(2)(t)=2Dt(alpha) (...

We report on the first model of a thermal transistor to control heat flow. Like its electronic counterpart, our thermal transistor is a three-terminal device with the important feature that the current through the two terminals can be controlled by small changes in the temperature or in the current through the third terminal. This control feature a...

A thermal diode model that works in a wide range of system parameters was demonstrated by coupling two nonlinear one dimensional lattices. A numerical and anlytical evidence for the mechanism which allows heat flux in one direction while the system acts like an insulator when the temperature gradient was reversed was also provided. The study of pos...

A Comment on the Letter by Lei Yang, Phys. Rev. Lett.PRLTAO0031-9007 88, 094301 (2002). The author of the Letter offers a Reply.

We propose and study a one-dimensional traffic flow cellular automaton (CA) model of high speed vehicles with rapid acceleration as in Fukui-Ishibashi (FI) model and with stochastic delay as in Nagel-Schreckenberg (NS) model. This model is different from the NS model in that only the cars following the trail of the ahead car can be delayed. In othe...

We propose and study a one-dimensional traffic flow cellular automaton (CA) model of high speed vehicles with rapid acceleration for all cars as in the Fukui-Ishibashi (FI) model and with stochastic delay applying only to the cars following the trail of the ahead car. The main difference comparing to the Nagel-Schreckenberg (NS) model is that a car...

Heat conduction in three types of 1D channels is studied. The channels consist of two parallel walls, right triangles as scattering obstacles, and noninteracting particles. The triangles are placed along the walls in three different ways: (i) periodic, (ii) disordered in height, and (iii) disordered in position. The Lyapunov exponents in all three...

We propose and study a one-dimensional traffic flow cellular automaton model of high-speed vehicles with the Fukui-Ishibashi-type acceleration for all cars, and the Nagel-Schreckenberg-type (NS) stochastic delay only for cars following the trail of the car ahead. The main difference in the delay scenario between our model and the NS model is that a...

A new traffic flow cellular automaton (CA) model situated between Nagel-Schreckenberg (NS) type and Fukui-Ishibashi (FI) type is defined and studied. This new model adopes the gradual acceleration scenario for all cars as NS model and the stochastic delay scenario for only the car with speed limit as FI model. It is proved that the fundamental diag...

The asymptotic steady state of deterministic Nagel–Schreckenberg (NS) traffic flow cellular automaton (CA) model for high-velocity cars () is studied. It is shown that the fundamental diagram, i.e., the relationship between the average car velocity and the car density, of the NS model in which the velocity of a car may increase by at most one unit...

A new cellular automaton model for traffic flow, which is situated between Nagel-Schreckenberg (NS) type and Fukui-Ishibashi (FI) type, is defined and studied. This new model adopts the gradual acceleration scenario for all cars as NS model and the stochastic delay scenario for only the car with speed limit as FI model. It is proved that the fundam...

In this paper, the fundamental diagram of the average traffic flow speed in the asymptotic steady state as a function of vehicle density for deterministic Nagel-Schreckenberg(NS) traffic flow cellular automaton model of high speed car without stochastic delay has been studied. It is proved that due to self organization of traffic flow, the fundamen...

In this paper, the fundamental diagram of the average traffic flow speed in the asymptotic steady state as a function of vehicle density for deterministic Nagel-Schreckenberg(NS) traffic flow cellular automaton model of high speed car without stochastic delay has been studied. It is proved that due to self organization of traffic flow, the fundamen...

Exact mean field equations are derived analytically to give the fundamental diagrams, i.e., the average speed - car density relations, for the Fukui-Ishibashi one-dimensional traffic flow cellular automaton model of high speed vehicles $(v_{max}=M>1) $ with stochastic delay. Starting with the basic equation describing the time evolution of the numb...