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Using the 1.26 m National Astronomical Observatory-Guangzhou University Infrared/Optical Telescope (NGT), we monitor one BL Lac object, OJ 287. For this source, we obtain 15 094 gri observations (4900 at g band, 5184 at r band and 5010 at i band) in 155 nights from 2014 December 13 to 2019 March 15. Based on the upper observations, we obtain the following results. (1) The total variation amplitude is ∼2.3 mag. (2) There are intra-day variabilities (IDVs). The IDV timescales (Δ T) are in the range from 7.69 min (Δ m = 0.06 ± 0.02 mag) to 371.09 min (Δ m = 0.26 ± 0.04 mag). (3) There are strong correlations between Δ T and Δ m, Δ m = (2.91 ± 0.66) × 10−4ΔT + (0.08 ± 0.009), with r = 0.52, p = 5.33 × 10−5. (4) There are intra-day periods in this source, with the period P ≈ 94 min on 2017 December 10. When we supplement the observations from the literature, we can obtain that the long-term period is about 12.02 ± 0.41 yr. (5) The spectral properties of OJ 287 show the bluer-when-brighter behavior, whatever state the source is at.

In this paper, the electronic structure and photo-electric properties of N and Fe co-doped ZnO systems have been studied by using Density functional theory method. The results show that the formation energy of ZnO-N, ZnO-Fe, ZnO-N-Fe and ZnO-N-2Fe systems decreases in turn, the doping is easier to realize. Compared with the ZnO system, the activity of ZnO-Fe, ZnO-N-Fe and ZnO-N-2Fe systems increases in turn, the band gap of ZnO-N and ZnO-N-2Fe systems decreases, and the electron transition is easier in the doped system. The peak of the dielectric function shifts to the left, the absorption of the electron to the photon increases obviously, and the absorption spectrum appears red shift. It can be concluded that the electronic structure and optical properties of ZnO are greatly affected by the single and co-doping of N and Fe, which provides a theoretical basis for the further study.

In this paper, the electronic structure and photoelectric properties of P and Cu doped ZnO systems have been studied by Density functional theory method. The results show that the formation energies of ZnO-P-Cu, ZnO-P-2Cu, ZnO-P and ZnO-Cu systems decrease in turn Compared with the intrinsic ZnO system, the ZnO-P, ZnO-P-Cu, ZnO-P-2Cu and ZnO-Cu systems have higher activity, the band gap of ZnO-P and ZnO-P-2Cu systems is reduced, and the electron transition is easier. In the doped system, the peak of the dielectric function shifts to the left and increases, the absorption of the electron to the photon increases obviously, and the absorption spectrum appears red shift, from the calculated results, it can be concluded that P and Cu single-doped and co-doped ZnO have great influence on the electronic structure and optical properties of ZnO system, which provides a theoretical basis for further study of the influence of doping on the properties of ZnO.

The behavior of graphene bombarded by fullerene (C60 and C70) and its derivatives through using non-equilibrium molecular dynamics method are studied. The microscopic mechanism of passing through graphene is obviously related to the initial structure of destroying carbon-carbon bonds and the strong interaction between the circular region of graphene and the cluster. The probability of passing through graphene depends on the incident velocity of clusters, the species of clusters, the temperature of heat baths, and the defect of graphene. Our results can provide a perspective for further understanding the mechanism of generating nanopores in graphene. The clusters used here may also bring about some potential utilities in the functionalization of graphene and the production of nanopores.

The performance of helicopter is limited by the phenomenon of dynamic stall. Dynamic stall is attributed to the time-varying angle of attack (AOA) of blade element resulting from blade flapping cyclic pitch inputs and wake flow. Co-flow jet(CFJ), as a novel flow control technique proposed by the joint research team from University Miami (UM) and AFRL has shown great improvement on lift enhancement, drag reduction due to its strong circulation improvement and turbulent mixing effect. Focusing on dynamic stall characteristics, this paper studies the effect of co-flow jet technique applying to rotor airfoil OA309. Numerical simulations show that CFJ can remove dynamic stall phenomenon occurring on rotor airfoils but the momentum coefficient should be carefully chosen so as to obtain high-efficient control effect.

Based on density functional theory, using the scheme of the linearized augmented plane wave and the improved local orbital (APW+lo), this paper analyses and calculates the lattice parameters, formation energy and magnetism of the rare-earth permanent magnetic materials YFe12−xCrx (x = 0 ~ 5). The stabilization effect and the possible positions of the substituted atom Cr are analysed. Magnetic moments for the system and the atoms are obtained.

We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however, leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment, whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.

We present an experimental scheme of a cold atom space clock with a movable cavity. By using a single microwave cavity, we find that the clock has a significant advantage, i.e. the longitudinal cavity phase shift is eliminated. A theoretical analysis has been carried out in terms of the relation between the atomic transition probability and the velocity of the moving cavity by taking into account the velocity distribution of cold atoms. The requirements for the microwave power and its stability for atomic pi/2 excitation at different moving velocities of the cavity lead to the determination of the proper working parameters of the rubidium clock in frequency accuracy 10(-17). Finally, the mechanical stability for the scheme is analysed and the ways of solving the possible mechanical instability of the device are proposed.

Another algorithm for chaotification of any given linear time-invariant discrete-time systems is presented. The new chaotification algorithm uses the decentralized control and the continuous sawtooth function, which can generate discrete chaos with an arbitrarily desired amplitude bound. Based on the Marotto theorem, we mathematically prove that the controlled system is chaotic in the sense of Li and Yorke. Finally, a simple example is used to illustrate the effectiveness of the proposed theory and method.

We propose a novel atomic fountain clock which is compact and transportable. The clock is 60-cm in height. Its linewidth is expected to be 1.75 Hz, with accuracy 10−14, stability 10−14 and signal–noise ratio 103. A hollow beam is applied as atomic wave-guide, which can increase the stability and the signal–noise ratio by one order. The hollow beam will not affect the accuracy of the clock, if the frequency shift due to the hollow beam is amended and the fluctuation of the hollow beam intensity is controlled to be smaller than 0.6%.

We introduce a new method of frequency-shifting for a diode laser in laser cooling experiments, the method is based on the Zeeman effect of 87Rb atoms. The laser frequency is stabilized by absorption spectrum line of atoms in magnetic field. We show that a magnetic field can be added up to 10-2T. The corresponding frequency shift is 102MHz and the response time is about 1 ms. The large range of the frequency shift is sufficient for laser-cooling experiments.

We study the rectified efficiency of self-propelled particles in a confined structure in the presence of ferromagnetic (polar) and nematic alignments. It is found that purely polar alignment can greatly facilitate the rectification, and the rectified efficiency can even be up to 1. However, the purely nematic alignment suppresses the rectification for large self-propulsion speed and slightly facilitates the rectification for small self-propulsion speed. With an increase in the relative weight of polar interactions, the rectified efficiency is suddenly increased from 0–1, with the jump depending on the order switching from nematic to polar. From the point of view of dynamic ordering, we can conclude that the perfect polarly ordered phase will cause the maximal rectified efficiency, while the genuine apolarly ordered phase will suppress the rectification.

We propose a novel method to generate a collimated doughnut-beam (DB) using only one single-cone axicon and realize it experimentally. The diameter of the DB is estimated by ray optics and is in good agreement with the experimental results. The CCD image of the DB and the radial light intensity distribution are experimentally obtained. The light intensity of the DB dark inner region is about 1% of the peak intensity of the DB. The far-field divergent angle is about 6 mrad and seems to be well-collimated. With optimum values of the power and the positive detuning of the laser field, the optical dipole potential of the DB can be chosen to be very large as a good confinement for atom trapping.

Using non-equilibrium molecular dynamics and Monte Carlo methods, we study the collective diffusion of helium in carbon nanotubes. The results show that the collective diffusion coefficient (CDC) increases with the dimension of the channel. The collective diffusion coefficient has a linear relationship with the temperature and the concentration. There exist a ballistic transport in short carbon nanotubes and a diffusive transport in long carbon nanotubes. Fick's law has an invalid region in the nanoscale channel.

In order to investigate the thermal transport in one-dimensional (1D) superlattice and quasicrystal chains, the simple harmonic-oscillator model and the C60 chains model, are studied through non-equilibrium molecular dynamics simulation. In the simple harmonic-oscillator model, we construct a simple periodic harmonic-oscillator chain by using two different stiffness coefficients alternatively. It is found that its thermal conductivity is smaller than in non-periodic chains, no matter which stiffness coefficient is used in the non-periodic chains. In order to test if this is true in a real material structure, a superlattice C60 chain is constructed by connecting perfect and defective C60 alternatively. The calculation outcome of the C60 chains coincides with the results of the simple harmonic-oscillator model, that the thermal conductivity of the superlattice C60 chain is smaller than that of perfect and defective crystal C60 chains. Besides this, we also studied the thermal transport properties of the quasicrystal C60 chain, which consists of a random defective C60 molecular structure. It is found that the thermal conductivity of the quasicrystal structure is far less than that of the crystal and superlattice chains. The phonon spectra of the perfect, defective and superlattice C60 chain are provided to give corresponding supports. Our results also propose a controllable method for the thermal management in nanoscale materials.

We design some graphene superlattice structures with ultra-low thermal conductivity 121 W/mK, which is only 6% of the straight graphene nanoribbons. The thermal conductivity of graphene superlattice nanoribbons (GSNRs) is investigated by using molecular dynamics simulations. It is reported that the thermal conductivity of graphene superlattice nanoribbons is significantly lower than that of the straight graphene nanoribbons (GNRs). Compared with the phonon spectra of straight GNRs, GSNRs have more forbidden bands. The overlap of phonon spectra between two supercells is shrinking.

Heat transport in one kind of double-bond linear chains of fullerenes (C60's) is investigated by the classical nonequilibrium molecular dynamics method. It is found that the negative differential thermal resistance (NDTR) is more likely to occur at larger temperature difference and shorter length. In addition, with the increase of the length, the thermal conductivity of the chains increases, and NDTR region shrinks and vanishes in the end. The temperature profiles reveal that a large temperature jump exists at a high-temperature boundary of the chains when NDTR occurs. These results may be helpful for designing thermal devices where low-dimensional C60 polymers can be used.

We deal with the thermal conductance and the denaturation of a three-dimensional DNA double helix based on the Peyrard—Bishop—Dauxois model by using non-equilibrium molecular dynamics simulations. It is reported that the thermal conductance of DNA has a substantial decrease near the denaturation where the DNA double helix separates into two single chains. We explain this phenomenon through the phonon spectra at different temperatures. It is suggested that the denaturation of DNA can also be characterized by the change of the thermal conductance.

A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors is proposed. The proposed TLE is highly reconfigurable, which can perform all two-variable logic functions directly or indirectly, including OR, NOR, AND, NAND, XOR and XNOR. The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters. The design methodology can also be applied in the design of a multi-variable TLE. The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation. The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.