Traditional tracking algorithms based on static sensors have several problems. First, the targets only occur in a part of the interested area; however, a large number of static sensors are distributed in the area to guarantee entire coverage, which leads to wastage of sensor resources. Second, many static sensors have to remain in active mode to track the targets, which causes an increase of energy consumption. To solve these problems, a target group tracking algorithm based on a hybrid sensor network is proposed in this paper, which includes static sensors and mobile sensors. First, an estimation algorithm is proposed to estimate the objective region by static sensors, which work in low-power sensing mode. Second, a movement algorithm based on sliding windows is proposed for mobile sensors to obtain the destinations. Simulation results show that this algorithm can reduce the number of mobile sensors participating in the tracking task and prolong the network lifetime.

In a wireless sensor network (WSN), the energy of nodes is limited and cannot be charged. Hence, it is necessary to reduce energy consumption. Both the transmission power of nodes and the interference among nodes influence energy consumption. In this paper, we design a power control and channel allocation game model with low energy consumption (PCCAGM). This model contains transmission power, node interference, and residual energy. Besides, the interaction between power and channel is considered. The Nash equilibrium has been proved to exist. Based on this model, a power control and channel allocation optimization algorithm with low energy consumption (PCCAA) is proposed. Theoretical analysis shows that PCCAA can converge to the Pareto Optimal. Simulation results demonstrate that this algorithm can reduce transmission power and interference effectively. Therefore, this algorithm can reduce energy consumption and prolong the network lifetime.

Instead of normally tackling electric circuits by virtue of the Kirchhoff's theorem whose aim is to derive voltage, electric current, and electric impedence, our aim in this paper is to derive the characteristic frequency of a three-loop mesoscopic LC circuit with three mutual inductances, e.g., for the radiating frequency of the three-loop LC oscillator, we adopt the invariant eigen-operator (IEO) method to realize our aim.

The dynamical effects on electron-positron pair creation from a vacuum caused by the switching processes of a super-critical well potential are investigated in detail. The results show that only when the switching on and switching off time both increase will the final pair yield converge to the integer of embedded bound states nearly exponentially. But a single adiabatic switching on or switching off cannot lead to an integer pair yield. If the potential is turned on abruptly, associated with the discrete and embedded bound states, there is multi-frequency oscillation around the pair number's saturation. The slowly switching on can suppress the amplitude of this oscillation and reduce the final pair yield. The switching off can also reduce the final pair number in the same order of magnitude. The evolution of a single-pair number shows a robust long range correlation between particle and antiparticle. For an adiabatic switching case, the single-pair dominates the early pair creation, their upper limit value is equal to the integer, and these single-pairs will totally disentangle during the switching off.

We study the spherical quantum pseudodots in the Schrödinger equation by using the pseudo-harmonic plus harmonic oscillator potentials considering the effect of the external electric and magnetic fields. The finite energy levels and the wave functions are calculated. Furthermore, the behavior of the essential thermodynamic quantities such as, the free energy, the mean energy, the entropy, the specific heat, the magnetization, the magnetic susceptibility, and the persistent currents are also studied by using the characteristic function. Our analytical results are found to be in good agreement with the other works. The numerical results on the energy levels as well as the thermodynamic quantities have also been given.

To solve the problems of updating sub-secrets or secrets as well as adding or deleting agents in the quantum secret sharing protocol, we propose a two-particle transform of Bell states, and consequently present a novel dynamic quantum secret sharing protocol. The new protocol can not only resist some typical attacks, but also be more efficient than the existing protocols. Furthermore, we take advantage of the protocol to establish the dynamic secret sharing of a quantum state protocol for two-particle maximum entangled states.

GHz single-photon detector (SPD) is a crucial part in the practical high speed quantum key distribution (QKD) system. However, any imperfections in a practical QKD system may be exploited by an eavesdropper (Eve) to collect information about the key without being discovered. The sine wave gating SPD (SG-SPD) based on InGaAs/InP avalanche photodiode, one kind of practical high speed SPD, may also contain loopholes. In this paper, we study the principle and characteristic of the SG-SPD and find out the filtering loophole of the SG-SPD for the first time. What is more, the proof-of-principle experiment shows that Eve could blind and control Bob's SG-SPD by exploiting this loophole. We believe that giving enough attention to this loophole can improve the practical security of the existing QKD system.

Newton's gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been obtained by using torsion balances. However, the uncorrected anelasticity of torsion fibers makes the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The superconducting gravity gradiometer is rotated to generate a centrifugal acceleration that nulls the gravity field of the source mass, forming an artificial planetary system. This experiment has a potential accuracy of G better than 10 ppm.

In a test of the weak equivalence principle (WEP) with a rotating torsion pendulum, it is important to estimate the amplitude of the modulation signal with high precision. We use a torsional filter to remove the free oscillation signal and employ the correlation method to estimate the amplitude of the modulation signal. The data analysis of an experiment shows that the uncertainties of amplitude components of the modulation signal obtained by the correlation method are in agreement with those due to white noise. The power spectral density of the modulation signal obtained by the correlation method is about one order higher than the thermal noise limit. It indicates that the correlation method is an effective way to estimate the amplitude of the modulation signal and it is instructive to conduct a high-accuracy WEP test.

We systematically investigate the periodic orbits of the Lorenz flow up to certain topological length. As an alternative to Poincaré section map analysis, we propose a new approach for establishing one-dimensional symbolic dynamics based on the topological structure of the orbit. A newly designed variational method is stable numerically for cycle searching, and two orbital fragments can be used as basic building blocks for initialization. The topological classification based on the entire orbital structure is revealed to be effective. The deformation of periodic orbits with the change of parameters provides a chart to the periods of cycles. The current research may provide a methodology for finding and systematically classifying periodic orbits in other similar chaotic flows.

Depending on double compound synchronization and compound combination synchronization, a new kind of synchronization is introduced which is the double compound combination synchronization (DCCS) of eight n-dimensional chaotic systems. This kind may be considered as a generalization of many types of synchronization. In the communication, based on many of drive and response systems, the transmitted and received signals will be more secure. Using the Lyapunov stability theory and nonlinear feedback control, analytical formulas of control functions are obtained to insure our results. The corresponding analytical expression and numerical treatment are used to show the validity and feasibility of our proposed synchronization scheme. The eight memristor-based Chua oscillators are considered as an example. Other examples can be similarly investigated. The proposed synchronization technique is supported using the MATLAB simulation outcomes. We obtain the same results of numerical treatment of our synchronization using simulation observations of our example.

Using the tensor renormalization group method based on the higher-order singular value decomposition, we have studied the phase transitions of the five-state clock model on the square lattice. The temperature dependence of the specific heat indicates the system has two phase transitions, as verified clearly by the correlation function at three representative temperatures. By calculating the magnetic susceptibility, we obtained only the upper critical temperature as T_{c2}=0.9565(7). Investigating the fixed-point tensor, we precisely locate the transition temperatures at T_{c1}=0.9029(1) and T_{c2}=0.9520(1), consistent well with the Monte Carlo and the density matrix renormalization group results.

We numerically investigate the trapping behaviors of aligning particles in two-dimensional (2D) random obstacles system. Under the circumstances of the effective diffusion rate and the average velocity tend to zero, particles are in trapped state. In this paper, we examine how the system parameters affect the trapping behaviors. At the large self-propelled speed, the ability of nematic particles escape from trapping state is enhancing rapidly, in the meanwhile the polar and free particles are still in trapped state. For the small rotation diffusion coefficient, the polar particles circle around (like vortices) the obstacles and here particles are in trapped state. Interestingly, only the partial nematic particles are trapped in the confined direction and additional particles remain flowing. In the free case, the disorder particle-particle collisions impede the motion in each other's directions, leading the free particles to be trapped. At the large rotation diffusion coefficient, the ordered motion of aligning particles disappear, particles fill the sample evenly and are self-trapped around obstacles. As the particles approach the trapping density due to the crowding effect the particles become so dense that they impede each other's motion. With the increasing number of obstacles, the trajectories of particles are blocked by obstacles, which obstruct the movement of particles. It is worth noting that when the number of the obstacles are large enough, once the particles are trapped, the system is permanently absorbed into a trapped state.

Single or multiple S-boxes are widely used in image encryption schemes, and in many image encryption schemes the asynchronous encryption structure is utilized, which separates the processes of substitution and diffusion. In this paper, we analyze the defects of this structure based on the example of an article and crack it using a simpler method. To address the defects of the asynchronous encryption structure, a novel encryption scheme is proposed, in which the structure of synchronous substitution and diffusion based on double S-boxes is utilized, so the processes of substitution and diffusion are combined together and the attackers cannot crack the cryptosystem by any of the processes. The simulation results and security analysis show that the proposed encryption scheme is safer and more efficient to expediently use in the real-time system.

A light field modulated imaging spectrometer (LFMIS) can acquire the spatial-spectral datacube of targets of interest or a scene in a single shot. The spectral information of a point target is imaged on the pixels covered by a microlens. The pixels receive spectral information from different spectral filters to the diffraction and misalignments of the optical components. In this paper, we present a linear spectral multiplexing model of the acquired target spectrum. A calibration method is proposed for calibrating the center wavelengths and bandwidths of channels of an LFMIS system based on the liner-variable filter (LVF) and for determining the spectral multiplexing matrix. In order to improve the accuracy of the restored spectral data, we introduce a reconstruction algorithm based on the total least square (TLS) approach. Simulation and experimental results confirm the performance of the spectrum reconstruction algorithm and validate the feasibility of the proposed calibrating scheme.

SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

The potential energy curves (PECs) of 14 Λ-S states for magnesium chloride (MgCl) have been calculated by using multi-reference configuration interaction method with Davidson correction (MRCI+Q). The core-valence correlation (CV), scalar relativistic effect, and spin-orbit coupling (SOC) effect are considered in the electronic structure computations. The spectroscopic constants of X^{2}Σ^{+} and A^{2}Π states have been obtained, which are in good agreement with the existing theoretical and experimental results. Furthermore, other higher electronic states are also characterized. The permanent dipole moments (PDMs) of Λ-S states and the spinorbit (SO) matrix elements between Λ-S states are also computed. The results indicate that the abrupt changes of PDMs and the SO matrix elements are attributed to the avoided crossing between the states with the same symmetry. The SOC effect is taken into account with Breit-Pauli operator, which makes the 14 Λ-S states split into 30 Ω states, and leads to a double-well potential of the Ω=(3)1/2 state. The energy splitting for the A^{2}Π is calculated to be 53.61 cm^{-1} and in good agreement with the experimental result 54.47 cm^{-1}. The transition dipole moments (TDMs), Franck-Condon factors (FCFs), and the corresponding radiative lifetimes of the selected transitions from excited Ω states to the ground state X^{2}Σ+1/2 have been reported. The computed radiative lifetimes τ_{ν'} of low-lying excites Ω states are all on the order of 10 ns. Finally, the feasibility of laser cooling of MgCl molecule has been analyzed.

Based on relativistic wave functions from multiconfiguration Dirac-Hartree-Fock and configuration interaction calculations, E2 and M1 transition probabilities of 2p^{3 4}S_{3/2}-2p^{3 2}D_{3/2,5/2} are investigated in the nitrogen-like sequence with 7 ≤ Z ≤ 16. The contributions of the electron correlations, Breit interaction, and the quantum electrodynamic (QED) effects on the transition properties are analyzed. The present results can be used for diagnosing plasma. In addition, several N-like ions can also be recommended as a promising candidate for a highly charged ion (HCI) clock with a quality factor (Q) of transition as high as 10^{20}.

We present a systematic investigation of the impact of changing the geometry structure of the SPC/E water model by performing a series of molecular dynamic simulations at 1 bar (1 bar=10^{5} Pa) and 298.15 K. The geometric modification includes altering the H-O-H angle range from 90° to 115° and modifying the O-H length range from 0.90 Å to 1.10 Å in the SPC/E model. The former is achieved by keeping the dipole moment constant by modifying the O-H length, while in the latter only the O-H length is changed. With the larger bond length and angle, we find that the liquid shows a strong quadrupole interaction and high tetrahedral structure order parameter, resulting in the enhancement of the network structure of the liquid. When the bond length or angle is reduced, the hydrogen bond lifetime and self-diffusion constant decrease due to the weakening of the intermolecular interaction. We find that modifying the water molecular bond length leading to the variation of the intermolecular interaction strength is more intensive than changing the bond angle. Through calculating the average reduced density gradient and thermal fluctuation index, it is found that the scope of vdW interaction with neighbouring water molecules is inversely proportional to the change of the bond length and angle. The effect is mainly due to a significant change of the hydrogen bond network. To study the effect of water models as a solvent whose geometry has been modified, the solutions of ions in different solvent environments are examined by introducing NaCl. During the dissolving process, NaCl ions are ideally dissolved in SPC/E water and bond with natural water more easily than with other solvent models.

The photoionization cross section of the ground state 2s^{2}2p 2P_{1/2}^{o} and the first excited state 2s^{2}2p 2P_{3/2}^{o} of C Ⅱ ions are systematically calculated using the fully relativistic R-matrix code DARC. The detailed resonances are presented and identified for the photon energy ranging from threshold (24.38 eV) up to 41.5 eV where the L-shell (2p, 2s) photoionization process is dominant. In the calculations, the relativistic effect and electronic correlation effect are well considered. It is found that the relativistic effect is very important for the light atomic system CⅡ, which accounts for experimentally observed fine structure resonance peaks. A careful comparison is made between the present results and the experimental values, and also other theoretical data available in the literature, showing that good agreement is obtained for the resonance peaks.

We simultaneously investigate variations of a low order harmonic and photoelectron emission with an incident laser intensity by solving the time-dependent Schrödinger equation in a momentum space. It can be found that, the intensity of low order harmonic and photoelectron are gradually enhanced with the increase of the laser intensity, when the laser frequency is not in resonance with the transition frequency between the laser-induced high excited states and the ground state. If the resonance occurs, the intensity of the lower order harmonic is reduced and the interference can be observed in the lower order photoelectron spectra.

The twisted intramolecular charge transfer and the excited state relaxation of 1-aminoanthraquinone (1-NH_{2}-AQ) in different solvents are investigated using quantum chemical calculations in this paper. The geometries of the ground state are optimized both in gas and solvents based on the high-level ab initio calculations, the lowest excited singlet state geometry is optimized only in gas for simplicity. An intramolecular charge transfer property is substantiated by the large change of dipole moments between the S_{0} and S_{1} states. The mechanism of twisted intramolecular charge transfer is proposed by the conformational relaxation on the potential surface of the S_{1} state. Quantum chemical calculations present that internal conversion and intersystem crossing are important approaches to the ultrafast deactivation of the S_{1} state via the twisting of the amino group. The smaller energy difference between the S_{0} and S_{1} state shows that the internal conversion process is much faster in a polar solvent than in a nonpolar solvent. Energy intersections between the T_{2} and S_{1} state in cyclohexane and dioxane indicate a faster intersystem crossing process in them than in ethanol. These theoretical results agree well with the previous experimental results. Energy barriers are predicted on the potential surface of the S_{1} state, and they have a positive correlation to solvent viscosity, and the timescale of twisted intra-molecular charge transfer in dioxane is predicted to be longer than in cyclohexane and ethanol.

Structural, electronic, and magnetic properties of Au_{n}Gd (n=6-15) small clusters are investigated by using first principles spin polarized calculations and combining with the ab-initio evolutionary structure simulations. The calculated binding energies indicate that after doping a Gd atom Au_{n}Gd cluster is obviously more stable than a pure Au_{n+1} cluster. Au_{6}Gd with the quasiplanar structure has a largest magnetic moment of 7.421 μ_{B}. The Gd-4f electrons play an important role in determining the high magnetic moments of Au_{n}Gd clusters, but in Au_{6}Gd and Au_{12}Gd clusters the unignorable spin polarized effects from the Au-6s and Au-5d electrons further enhance their magnetism. The HOMO-LUMO (here, HOMO and LUMO stand for the highest occupied molecular orbital, and the lowest unoccupied molecular orbital, respectively) energy gaps of Au_{n}Gd clusters are smaller than those of pure Au_{n+1} clusters, indicating that Au_{n}Gd clusters have potential as new catalysts with enhanced reactivity.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Circularly polarized (CP) lens antenna has been applied to numerous wireless communication systems based on its unique advantages such as high antenna gain, low manufacturing cost, especially stable data transmission between the transmitter and the receiver. Unfortunately, current available CP lens antennas mostly suffer from high profile, low aperture efficiency as well as complex design. In this paper, we propose an ultra-thin CP lens antenna based on the designed single-layered Pancharatnam-Berry (PB) transparent metasurface with focusing property. The PB metasurface exhibits a high transmissivity, which ensures a high efficiency of the focusing property. Launched the metasurface with a CP patch antenna at its focal point, a low-profile lens antenna is simulated and measured. The experimental results show that our lens antenna exhibits a series of advantages including high radiation gain of 20.7 dB, aperture efficiency better than 41.3%, and also narrow half power beam width (HPBW) of 13° at about 14GHz. Our finding opens a door to realize ultra-thin transparent metasurface with other functionalities or at other working frequencies.

This paper puts forward for the first time a combined transmission matrix (TM) method to measure the monochromatic TM of scattering media without a reference beam. This method can be named a sequential semi-definite programming method which combines the sequential algorithm and the semi-definite programming method. Firstly, each part of the TM is calculated respectively in proper sequence. Then every part of TM is combined to form a complete TM in accordance with a certain rule. The phase modulation of the incident light is achieved by using a high speed digital mirror device with the superpixel method. We have experimentally demonstrated that the incident light field is focused at the target through scattering media using the measured TM to optimize the wavefront of the incident light. Compared with the semi-definite programming method, our method takes less computational time and occupies less memory space. The sequential semi-definite programming method shows potential applications in imaging through biological tissues.

We couple a ladder-type three-level superconducting artificial atom to a cavity. Adjusting the artificial atom to make the cavity be resonant with the two upper levels, we then probe the lower two levels of the artificial atom. When driving the cavity to a coherent state, the probe spectrum shows energy level splitting induced by the quantized electromagnetic field in the cavity. This splitting size is related to the coupling strength between the cavity and the artificial atom and, thus, is fixed after the sample is fabricated. This is in contrast to the classical Autler-Townes splitting of a three-level system in which the splitting is proportional to the driving amplitude, which can be continuously changed. Our experiment results show the difference between the classical microwave driving field and the quantum field of the cavity.

We propose a scheme for measuring the angular velocity of absolute rotation using a three-mode optomechanical system in which one mode of the two-dimensional (2D) mechanical resonator is coupled to an optical cavity. When the total system rotates, the Coriolis force acting on the 2D mechanical resonator due to the absolute rotation will affect the mechanical motion and thus change the phase of the output field from the cavity. The angular velocity of the absolute rotation can be estimated by monitoring the spectrum of the output field from the cavity via homodyne measurement. The minimum measurable angular velocity, which is determined by the noise spectrum, is calculated. The working range of the gyroscope for measuring angular velocity is discussed.

We investigate the fundamental limits to the achievable tripartite continuous-variable (CV) entanglement criterion of a generalized V_{1} criterion. Our numerical simulation results show that the non-degenerate eigenvalues do effect the performances of the estimated minimum variances. From below the threshold to above the threshold, with the increase of the pump parameter, the tripartite CV entanglement gradually disappears. The different off-diagonal elements seriously distort the weights for entanglement. We can obtain a good tripartite CV entanglement by appropriately controlling the values of off-diagonal elements ε_{ij}.

High power optically pumped vertical-external-cavity surface-emitting lasers with front and end pump are reported. The gain chip consists of 15 repeats of In_{0.26}GaAs/GaAsP_{0.02} multiple quantum wells and 30 pairs of Al_{0.2}GaAs/Al_{0.98}GaAs distributed Bragg reflectors. The maximum output power of 3 W, optical-to-optical conversion efficiency of 22.4%, and slope efficiency of 29.8% are obtained with 5-℃ heatsink temperature under the front pump, while the maximum output power of 1.1 W, optical-to-optical conversion efficiency of 23.2%, and slope efficiency of 30.8% are reached with 5-℃ heatsink temperature under the end pump. Influences of thermal effects on the output power of the laser with front and end pump are discussed.

We report the implementation of qubit-qubit coupling in a three-dimensional (3D) cavity, using the exchange of virtual photons, to realize logical operations. We measure single photon and multi-photon transitions in this qubit-qubit coupling system and obtain its energy avoided-crossing spectrum. With ac-Stark effect, fast control of the qubits is achieved to tune the effective coupling on and off and the state-swap gate √SWAP is successfully constructed. Moreover, using two-photon transition between the ground state and doubly excited states, a kind of two-photon Rabi-like oscillation is observed. A quarter period of this oscillation corresponds to the logical gate √bSWAPP, which is used for generating Bell states. √bSWAPP and √iSWAP are the foundations of future preparation of two-qubit Bell states and realization of CNOT gate.

We study theoretically intense terahertz radiation from multi-color laser pulse with uncommon frequency ratios. Comparing the two-color laser scheme, of which the uncommon frequency ratio should be set to be a specific value, we show that by using multi-color harmonic laser pulses as the first pump component, the lasers as the second pump component can be adjusted in a continuous frequency range. Moreover, these multi-color laser pulses can effectively modulate and enhance the terahertz radiation, and the terahertz yield increases with the increase of the wavelength of the uncommon pump component and is stable to the laser relative phase. Finally, we utilize the electron densities and velocities of ionization events to illustrate the physical mechanism of the intense terahertz generation.

According to density functional theory, we investigate the effects of BF_{3}, BF_{4}, BCl_{3}, AlF_{3}, AlCl_{3}, AlBr_{3}, BeF_{3}, GaF_{3}, GaCl_{3}, GaBr_{3}, NO_{3}, BS_{2}, BSO, BO_{2}, F_{2}, PF_{5}, PCl_{5}, and ASF_{5} molecules on the geometric, electronic, linear, and nonlinear optical properties of an Mg_{12}O_{12} nanocage. The thermodynamic stability and feasibility of the adsorption process are investigated by analyzing the free energy. It is shown that the adsorptions of almost all molecules on the Mg_{12}O_{12} surface are exothermic. The calculations of the polarizability of these nanoclusters show that among the studied molecules, BeF_{3} has the largest influence on the polarizability value (α≈315 a.u., the unit a.u. is short for atomic unit). The static first hyperpolarizability (β_{0}) value is increased in the presence of these superhalogens. This increase is greatest for BeF_{3} and BF_{4} of which the highest value of the first hyperpolarizability (β_{0}≈5775 a.u.) is related to a BeF_{3}_c(e@Mg_{12}O_{12}) nanocluster. The adsorption position is a key to estimating the value of increasing the first hyperpolarizability.

We have designed and proposed the edge modes supported by graphene ribbons and the planar band-pass filter consisting of graphene ribbons coupled to a graphene ring resonator by using the finite-difference time-domain numerical method. Simulation results show that the edge modes improve the electromagnetic coupling between devices. This structure works as a novel, tunable mid-infrared band-pass filter. Our studies will benefit the fabrication of planar, ultra-compact nano-scale devices in the mid-infrared region. A power splitter consisting of two output ribbons that is useful in photonic integrated devices and circuits is also designed and simulated. These devices are useful for designing ultra-compact planar devices in photonic integrated circuits.

Resonator integrated optic gyro (RIOG) is a high-accuracy gyroscope based on the Sagnac effect. The waveguide-type ring resonator is a key rotation sensing element in the RIOG. An asymmetric resonance line shape is found in the optic resonator. These asymmetries will induce offset errors when the phase modulation spectroscopy technique (PMST) is applied to the RIOG. The polarization errors and the difference among normal mode losses are found to be the two main sources of resonance asymmetry in an experiment. These sources are fully investigated and their contributions to the offset errors are compared. The analysis shows that proper modulation frequencies in clockwise (CW) and counterclockwise (CCW) directions can reduce an RIOG bias error. A transmissive resonator is recommended to obtain a better resonance line shape.

Using graphene-covered-microfiber (GCM) as a saturable absorber, the generation and evolution of multiple operation states are proposed and demonstrated in passively mode-locked thulium-doped fiber laser. The microfiber was fabricated using the flame brushing method to an interaction length of~1.2 cm with a waist diameter of~10 μm. Graphene layers were grown on copper foils by chemical vapor deposition and transferred onto the polydimethylsiloxane (PDMS) to form a PDMS/graphene film, which allowed light-graphene interaction via evanescent field. With the increase of the pump power from 1.25 W to 2.15 W, five different lasing regimes, including continuous-wave, conventional soliton mode-locking, multi-soliton mode-locking, a period of transition, and noise-like mode-locking, were achieved in a fiber ring cavity. To the best of our knowledge, it is the first report of the generation and evolution of multiple operation states by covering graphene on the microfiber in the 2-μm region. The results demonstrate that GCM can be a promising method for fabricating all fiber SA, and the switchable operation states can provide more portability in complex application domain.

In this paper, we investigate a method of selectively enhancing the single mode signal of a Lamb wave by using a meander-coil electromagnetic acoustic transducer (EMAT) with a new magnetic configuration. We use the Lamb antisymmetric (A0) mode and symmetric (S0) mode as an example for analysis. The analytical expression of the magnitude of the spatial Fourier transform of the Lorentz force generated by different meander coils is used to determine the optimal driving frequency for single mode generation. The numerical calculation is used to characterize the new magnetic configuration and the conventional EMAT magnet. Experimental examinations of each meander coil in combination with the conventional and new magnetic configuration show that the Lamb wave signal can be selectively enhanced by choosing the appropriate driving frequency and coil parameters through using the improved meander-coil EMAT.

Theoretical studies on the multi-bubble interaction are crucial for the in-depth understanding of the mechanism behind the applications of ultrasound contrast agents (UCAs) in clinics. A two-dimensional (2D) axisymmetric finite element model (FEM) is developed here to investigate the bubble-bubble interactions for UCAs in a fluidic environment. The effect of the driving frequency and the bubble size on the bubble interaction tendency (viz., bubbles' attraction and repulsion), as well as the influences of bubble shell mechanical parameters (viz., surface tension coefficient and viscosity coefficient) are discussed. Based on FEM simulations, the temporal evolution of the bubbles' radii, the bubble-bubble distance, and the distribution of the velocity field in the surrounding fluid are investigated in detail. The results suggest that for the interacting bubble-bubble couple, the overall translational tendency should be determined by the relationship between the driving frequency and their resonance frequencies. When the driving frequency falls between the resonance frequencies of two bubbles with different sizes, they will repel each other, otherwise they will attract each other. For constant acoustic driving parameters used in this paper, the changing rate of the bubble radius decreases as the viscosity coefficient increases, and increases first then decreases as the bubble shell surface tension coefficient increases, which means that the strength of bubble-bubble interaction could be adjusted by changing the bubble shell visco-elasticity coefficients. The current work should provide a powerful explanation for the accumulation observations in an experiment, and provide a fundamental theoretical support for the applications of UCAs in clinics.

Energy dissipation is one of the most important properties of granular gas, which makes its behavior different from that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics (MD) simulation for comparison. While our experimental and simulation results support Haff's law that the kinetic energy dissipates with time t as E(t)~(1+t/τ)^{-2}, we modify τ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff's kinetic energy dissipation.

This work is motivated by previous experimental and numerical studies which reveal that the hairpin vortex could be formed by the interaction between spanwise adjacent low-speed streaks. To prove that such an interaction mechanism is still applicable in the normal direction, two sinuous low-speed streaks with the same streamwise phase are set to be in the upper half and bottom half of a small size channel, respectively, and their evolution and interaction are investigated by direct numerical simulation. A new kind of hairpin-like vortical structure, distributed in the normal direction and straddled across both halves of the channel, is found during the cross-interaction process of the low-speed streaks. The influence of such a normal-distributed hairpin-like vortex (NHV) on the turbulent statistical regularity is also revealed. It is observed that the NHV can lead to a sudden surge of wall skin friction, but the value of the normal velocity as well as the streamwise and spanwise vorticity sharply decrease to zero in the center of the channel.

Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases:slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.

The study on deflagration-to-detonation transition (DDT) is very important because this mechanism has relevance to safety issues in industries, where combustible premixed gases are in general use. However, the quantitative prediction of DDT is one of the major unsolved problems in combustion and detonation theory to date. In this paper, the DDT process is studied theoretically and the critical condition is given by a concise theoretical expression. The results show that a deflagration wave propagating with about 60% Chapman-Jouguet (CJ) detonation velocity is a critical condition. This velocity is the maximum propagating velocity of a deflagration wave and almost equal to the sound speed of combustion products. When this critical condition is reached, a CJ detonation is triggered immediately. This is the quantitative criteria of the DDT process.

Chalcogenide glasses (ChGs) are a promising candidate for applications in nonlinear photonic devices. In this paper, we review the research progress of the third-order optical nonlinearity (TONL) of ChGs from the following three aspects:chemical composition, excitation condition, and post processing. The deficiencies in previous studies and further research of the TONL property of ChGs are also discussed.

Liquid phase epitaxy (LPE) is a mature technology. Early experiments on single magnetic crystal films fabricated by LPE were focused mainly on thick films for microwave and magneto-optical devices. The LPE is an excellent way to make a thick film, low damping magnetic garnet film and high-quality magneto-optical material. Today, the principal challenge in the applied material is to create sub-micrometer devices by using modern photolithography technique. Until now the magnetic garnet films fabricated by LPE still show the best quality even on a nanoscale (about 100 nm), which was considered to be impossible for LPE method.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Pseudowaves, known as burst-ion signals, which are different from plasma normal modes, exist frequently in ion-wave excitation experiments when launching the waves by applying a pulsed voltage to a negatively biased grid. In previous experiments, only one kind of the pseudowave was observed. In this paper, we report the observation and identification of double pseudowaves in an ion-beam-plasma system. These pseudowaves originate from two ion groups:the burst of the beam ions and the burst of the background ions. It was observed that the burst of the background ions was in the case of high ion beam energy, while the burst of the beam ions was in the case of low ion beam energy. By observing the dependence of the signal velocities on the characteristics of the excitation voltage, these pseudowaves can be identified. It was also observed that the burst ion signal originating from the background ions can interact with slow beam mode and that originating from the beam ions can interact with fast beam mode.

We report on the observation of new fluorescence emission spectral transitions obtained from NO diatomic molecule in the region from ultraviolet (UV) to near infrared (NIR) in a low power glow discharge system. This glow discharge electronic excitation populates different quartet and doublet states of NO in its proximity such as the A^{2}Σ (υ=2), b^{4}Σ^{-} (υ=3), B^{2}Π (υ=4), and X^{2}Π (υ=33-32) states. Due to inter-system crossing, emission lines originating from these levels to lower lying states are recorded and spectral line assignments are performed. The observed systems include b^{4}Σ^{-}-a^{4}Π, B^{2}Π-a^{4}Π, a^{4}Π-X^{2}Π, A^{2}Σ-X^{2}Π, X^{2}Π-X^{2}Π (33-15), X^{2}Π-X^{2}Π (33-17), X^{2}Π-X^{2}Π (33-20), and X^{2}Π-X^{2}Π (33-18). This new information will conduce to the better understanding of the interesting features of NO molecule. Such parameters that affect the recording of low density of NO molecules are also discussed In addition to the factors such as the time evolution, argon gas concentration relative to NO mixture, the percentage of NO molecular gas concentration, discharge electric current signals and discharge applied voltage are studied. Those factors would enhance the fluorescence signal intensity of NO molecules. The recent results might be significant as reference data for optimizing the glow discharge spectrometer and diagnostics of NO gas.

The multiple filamentation of terawatt femtosecond (fs) laser pulses is experimentally studied in a natural environment. A more than 30-m long plasma filament with a millimeter diameter is formed by the collimated fs laser pulse freely propagating in an open atmosphere. This study provides the first quantitative experimental data about the electron density of a long range light filament in the atmosphere. The electron density of such a filament is quantitatively detected by using an electric method, showing that it is at the 10^{11}-cm^{-3} level.

Hall thruster has the advantages of simple structure, high specific impulse, high efficiency, and long service life, and so on. It is suitable for spacecraft attitude control, North and South position keeping, and other track tasks. The anode layer Hall thruster is a kind of Hall thruster. The thruster has a longer anode area and a relatively short discharge channel. In this paper, the effect of the channel length on the performance of the anode layer Hall thruster is simulated by the PIC simulation method. The simulation results show that the change of the channel length has significant effect on the plasma parameters, such as potential and plasma density and so on. The ionization region mainly concentrates at the hollow anode outlet position, and can gradually move toward the channel outlet as the channel length decreases. The collision between the ions and the wall increases with the channel length increasing. So the proper shortening of the channel length can increase the life of the thruster. Besides, the results show that there is a best choice of the channel length for obtaining the best performance. In this paper, thruster has the best performance under a channel length of 5 mm.

The electrical and thermal characterization of near-surface electrical discharge plasma driven by radio frequency voltage are investigated experimentally in this paper. The influences of operating pressure, electrode distance, and duty cycle on the discharge are studied. When pressure reaches 60 Torr (1 Torr=1.33322×10^{2} Pa) the transition from diffuse glow mode to constricted mode occurs. With the operating pressure varying from 10 Torr to 60 Torr, the discharge energy calculated from the charge-voltage (Q-V) Lissajous figure decreases rapidly, while it remains unchanged between 60 Torr and 460 Torr. Under certain experimental conditions, there exists an optimized electrode distance (8 mm). As the duty cycle of applied voltage increases, the voltage-current waveforms and Q-V Lissajous figures show no distinct changes.

In order to validate the similarity principle of microwave breakdown, a two-dimensional (2D) fluid model of low-pressure microwave argon plasma is established and solved by the finite-element method. Proportional conditions are used in this model to build three different breakdown processes that meet the premise of a similarity principle, and these breakdown processes are called “similar cases” in this paper. Similar cases have proportionately sized breakdown regions, where the ratio of frequency of incident microwave f to gas pressure p (f/p), and the reduced field E/p in them are kept the same. All the important physical parameters such as electron density, electron temperature, and reduced electric field can be obtained from the simulation of this model. The results show that the parameters between similar cases are in constant ratio without changing with time, which means that the similarity principle is also valid in microwave breakdown.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Undoped and praseodymium-doped zinc oxide (Pr-doped ZnO) (with 2.0-mol%-6.0-mol% Pr) nanoparticles as sunlight-driven photocatalysts are synthesized by means of co-precipitation with nitrates followed by thermal annealing. The structure, morphology, and chemical bonding of the photocatalysts are studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray emission spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The optical properties are studied by photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). We find that Pr doping does not change the crystallinity of ZnO; but it reduces the bandgap slightly, and restrains the recombination of the photogenerated electron-hole pairs. The photocatalytic performance of the photocatalysts is investigated by the photodegradation reaction of 10-mg/L rhodamine B (RhB) solution under simulated sunlight irradiation, showing a degradation rate of 93.75% in ZnO doped with 6.0-mol% Pr.

The influences of total ionizing dose (TID) on the single event effect (SEE) sensitivity of 34-nm and 25-nm NAND flash memories are investigated in this paper. The increase in the cross section of heavy-ion single event upset (SEU) in memories that have ever been exposed to TID is observed, which is attributed to the combination of the threshold voltage shifts induced by γ-rays and heavy ions. Retention errors in floating gate (FG) cells after heavy ion irradiation are observed. Moreover, the cross section of retention error increases if the memory has ever been exposed to TID. This effect is more evident at a low linear energy transfer (LET) value. The underlying mechanism is identified as the combination of the defects induced by γ-rays and heavy ions, which increases the possibility to constitute a multi-trap assisted tunneling (m-TAT) path across the tunnel oxide.

In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge (BEC), and spontaneous polarization of Sr_{2}M_{2}O_{7}, the method used in our study was a well-known density functional theory based on first-principles. The optimized results were in good agreement with previous experiments and calculations, which indicates that our calculated method is reasonable. The research we have done suggested that greater piezoelectric components of Sr_{2}Nb_{2}O_{7} were e_{31} and e_{33}, and the contributions were derived from the A_{1}. By studying the Born effective charge, it could be seen that the valence of ions changed, and the O of Sr_{2}Nb_{2}O_{7} were most obviously that caused by the covalent character of ions and the hybridization of O-2p and Nb-4d. The spontaneous polarization of Sr_{2}Nb_{2}O_{7} in the[001] direction is 25 μC/cm^{2}, while for Sr_{2}Ta_{2}O_{7}, there was no spontaneous polarization in the paraelectric state. Finally, the effect of pressure on the piezoelectric properties were also investigated, the polarization of Sr_{2}Nb_{2}O_{7} decreased linearly with the increase after pressure. All our preliminary results throw light on the nature of dielectric, piezoelectric properties, Born effective charge, and spontaneous polarization of Sr_{2}M_{2}O_{7}, it was helpful for experimental research, the development of new materials, and future applications.

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional (2D) systems, few-layer h-BN and indium iodide (InI). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.

The structural parameters, the formation energies, and the elastic and thermodynamic properties of the (Cu_{x}Ni_{1-x})_{3}Sn phase with different structures are studied by the virtual crystal approximation (VCA) and super-cell (SC) methods. The lattice constants, formation energies, and elastic constants obtained by SC and VCA are generally consistent with each other. It can be inferred that the VCA method is suitable for (Cu_{x}Ni_{1-x})_{3}Sn ordered phase calculation. The calculated results show that the equilibrium structures of Cu_{3}Sn and Ni_{3}Sn are D0_{a} and D0_{19} respectively. (Cu_{x}Ni_{1-x})_{3}Sn-D0_{3} with various components are the metastable phase at temperature of 0 K, just as D0_{22} and L_{12}. With the temperature increase, the free energy of the D03 is lower than those of D0_{22} and L_{12}, and D0^{22} and L^{12} eventually turn into D0^{3} in the aging process. The (Cu_{x}Ni_{1-x})_{3}Sn-D0^{22} is first precipitated in a solid solution because its structure and cell volume are most similar to those of a solid solution matrix. The L^{12} and the D0^{22} possess better mechanical stability than the D0^{3}. Also, they may play a more important role in the strengthening of Cu-Ni-Sn alloys. This study is valuable for further research on Cu-Ni-Sn alloys.

The thermodynamic properties of Ta metal under high pressure are studied by molecular dynamics simulation. For dislocation-free Ta crystal, all the thermodynamic properties considered are in good agreement with the results from experiments or higher level calculations. If dislocations are included in the Ta crystal, it is found that as the dislocation density increases, the hydrostatic pressure at the phase transition point of bcc→hcp and hcp→fcc decreases, while the Hugoniot temperature increases. Meanwhile, the impact pressure at the elastic-plastic transition point is found to depend on the crystallographic orientation of the pressure. As the dislocation density increases, the pressure of the elastic-plastic transition point decreases rapidly at the initial stage, then gradually decreases with the increase of the dislocation density.

The expressions of interface free energy (IFE) of composite droplets with meniscal liquid-air interface in metastable state on micro/nano textured surfaces were formulated. Then the parameters to describe the meniscus were determined based on the principle of minimum IFE. Furthermore, the IFE barriers and the necessary and sufficient conditions of drop wetting transition from Cassie to Wenzel were analyzed and the corresponding criteria were formulated. The results show that the liquid-air interface below a composite droplet is flat when the post pitches are relatively small, but in a shape of curved meniscus when the piteches are comparatively large and the curvature depends on structural parameters. The angle between meniscus and pillar wall is just equal to the supplementary angle of intrinsic contact angle of post material. The calculations also illustrate that Cassie droplets will transform to Wenzel state when post pitch is large enough or when drop volume is sufficiently small. The opposite transition from Wenzel to Cassie state, however, is unable to take place spontaneously because the energy barrier is always positive. Finally, the calculation results of this model are well consistent with the experimental observations in literatures for the wetting transition of droplets from Cassie to Wenzel state.

The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work, we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate (PMMA) and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable, unlimitedly reusable substrates for the kerfless technology.

The properties and stability of the reported surface nanobubbles are related to the substrate used and the generation method. Here, we design a series of experiments to study the influence of the hydrophobicity of the substrate and the production method on the formation and properties of nanobubbles. We choose three different substrates, dodecyltrichlorosilane (DTS) modified silicon, octadecyltrichlorosilane (OTS) modified silicon, and highly oriented pyrolytic graphite (HOPG) as nanobubble substrates, and two methods of ethanol-water exchange and 4-℃ cold water to produce nanobubbles. It is found that using ethanol-water exchange method could produce more and larger nanobubbles than the 4-℃ cold water method. The contact angle of nanobubbles produced by ethanol-water exchange depends on the hydrophobicity of substrates, and decreases with the increase of the hydrophobicity of substrates. More interestingly, nanoscopic contact angle approaches the macroscopic contact angle as the hydrophobicity of substrates increases. It is believed that these results would be very useful to understand the stability of surface nanobubbles.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Dirac states composed of p_{x,y} orbitals have been reported in many two-dimensional (2D) systems with honeycomb lattices recently. Their potential importance has aroused strong interest in a comprehensive understanding of such states. Here, we construct a four-band tight-binding model for the p_{x,y}-orbital Dirac states considering both the nearest neighbor hopping interactions and the lattice-buckling effect. We find that p_{x,y}-orbital Dirac states are accompanied with two additional narrow bands that are flat in the limit of vanishing π bonding, which is in agreement with previous studies. Most importantly, we analytically obtain the linear dispersion relationship between energy and momentum vector near the Dirac cone. We find that the Fermi velocity is determined not only by the hopping through π bonding but also by the hopping through σ bonding of p_{x,y} orbitals, which is in contrast to the case of p_{z}-orbital Dirac states. Consequently, p_{x,y}-orbital Dirac states offer more flexible engineering, with the Fermi velocity being more sensitive to the changes of lattice constants and buckling angles, if strain is exerted. We further validate our tight-binding scheme by direct first-principles calculations of model-materials including hydrogenated monolayer Bi and Sb honeycomb lattices. Our work provides a more in-depth understanding of p_{x,y}-orbital Dirac states in honeycomb lattices, which is useful for the applications of this family of materials in nanoelectronics.

Mesa width (W_{M}) is a key design parameter for SiC super junction (SJ) Schottky diodes (SBD) fabricated by the trench-etching-and-sidewall-implant method. This paper carries out a comprehensive investigation on how the mesa width design determines the device electrical performances and how it affects the degree of performance degradation induced by process variations. It is found that structures designed with narrower mesa widths can tolerant substantially larger charge imbalance for a given BV target, but have poor specific on-resistances. On the contrary, structures with wider mesa widths have superior on-state performances but their breakdown voltages are more sensitive to p-type doping variation. Medium W_{M} structures (~2 μ) exhibit stronger robustness against the process variation resulting from SiC deep trench etching. Devices with 2-μ mesa width were fabricated and electrically characterized. The fabricated SiC SJ SBDs have achieved a breakdown voltage of 1350 V with a specific on-resistance as low as 0.98 mΩ·cm^{2}. The estimated specific drift on-resistance by subtracting substrate resistance is well below the theoretical one-dimensional unipolar limit of SiC material. The robustness of the voltage blocking capability against trench dimension variations has also been experimentally verified for the proposed SiC SJ SBD devices.

Monolayer transition-metal dichalcogenides (TMDs) are considered to be fantastic building blocks for a wide variety of optical and optoelectronic devices such as sensors, photodetectors, and quantum emitters, owing to their direct band gap, transparency, and mechanical flexibility. The core element of many conventional electronic and optoelectronic devices is the p-n junction, in which the p- and n-types of the semiconductor are formed by chemical doping in different regions. Here, we report a series of optoelectronic studies on a monolayer WSe_{2} in-plane p-n photodetector, demonstrating a low-power dissipation by showing an ambipolar behavior with a reduced threshold voltage by a factor of two compared with the previous results on a lateral electrostatically doped WSe_{2} p-n junction. The fabrication of the device is based on a polycarbonates (PC) transfer technique and hence no electron-beam exposure induced damage to the monolayer WSe_{2} is expected. Upon optical excitation, the photodetector demonstrates a photoresponsivity of 0.12 mA·W^{-1} and a maximum external quantum efficiency of 0.03%. Our study provides an alternative platform for a flexible and transparent two-dimensional photodetector, from which we expect to further promote the development of next-generation optoelectronic devices.

Au/Ni/n-type 4H-SiC Schottky alpha particle detectors are fabricated and annealed at temperatures between 400℃ and 700℃ to investigate the effects of thermal stability of the Schottky contact on the structural and electrical properties of the detectors. At the annealing temperature of 500℃, the two nickel silicides (i.e., Ni_{31}Si_{12} and Ni_{2}Si) are formed at the interface and result in the formation of an inhomogeneous Schottky barrier. By increasing the annealing temperature, the Ni_{31}Si_{12} transforms into the more stable Ni_{2}Si. The structural evolution of the Schottky contact directly affects the electrical properties and alpha particle energy resolutions of the detectors. A better energy resolution of 2.60% is obtained for 5.48-MeV alpha particles with the detector after being annealed at 600℃. As a result, the Au/Ni/n-type 4H-SiC Schottky detector shows a good performance after thermal treatment at temperatures up to 700℃.

We propose a new type of quantum spin Hall (QSH) insulator in chemically functionalized As (110) and Sb (110) film. According to first-principles calculations, we find that metallic As (110) and Sb (110) films become QSH insulators after being chemically functionalized by hydrogen (H) or halogen (Cl and Br) atoms. The energy gaps of the functionalized films range from 0.121 eV to 0.304 eV, which are sufficiently large for practical applications at room temperature. The energy gaps originate from the spin-orbit coupling (SOC). The energy gap increases linearly with the increase of the SOC strength λ/λ_{0}. The Z_{2} invariant and the penetration depth of the edge states are also calculated and studied for the functionalized films.

By exactly solving the effective two-body interaction for a two-dimensional electron system with layer thickness and an in-plane magnetic field, we recently found that the effective interaction can be described by the generalized pseudopotentials (PPs) without the rotational symmetry. With this pseudopotential description, we numerically investigate the behavior of the fractional quantum Hall (FQH) states both in the lowest Landau level (LLL) and first excited Landau level (1LL). The enhancements of the 7/3 FQH state on the 1LL for a small tilted magnetic field are observed when layer thickness is larger than some critical values, while the gap of the 1/3 state in the LLL monotonically reduced with increasing the in-plane field. From the static structure factor calculation, we find that the systems are strongly anisotropic and finally enter into a stripe phase with a large tilting. With considering the Landau level mixing correction on the two-body interaction, we find the strong LL mixing cancels the enhancements of the FQH states in the 1LL.

Single-layered zirconium pentatelluride (ZrTe_{5}) has been predicted to be a large-gap two-dimensional (2D) topological insulator, which has attracted particular attention in topological phase transitions and potential device applications. Herein, we investigated the transport properties in ZrTe_{5} films as a function of thickness, ranging from a few nm to several hundred nm. We determined that the temperature of the resistivity anomaly peak (T_{p}) tends to increase as the thickness decreases. Moreover, at a critical thickness of~40 nm, the dominating carriers in the films change from n-type to p-type. A comprehensive investigation of Shubnikov-de Hass (SdH) oscillations and Hall resistance at variable temperatures revealed a multi-carrier transport tendency in the thin films. We determined the carrier densities and mobilities of two majority carriers using the simplified two-carrier model. The electron carriers can be attributed to the Dirac band with a non-trivial Berry phase π, while the hole carriers may originate from surface chemical reaction or unintentional doping during the microfabrication process. It is necessary to encapsulate the ZrTe_{5} film in an inert or vacuum environment to potentially achieve a substantial improvement in device quality.

Low energy metallic ions, generated by a Q-switched Nd:YAG laser (1064-nm wavelength, 10-mJ energy, 9-nm~12-ns-pulse width, 10^{11} W/cm^{2} intensity) irradiated on a silicon substrate to modify various properties, such as electrical, morphological, and structural modifications. Thomson parabola technique is used to calculate the energy of these metallic ions whereas the electrical conductivity is calculated with the help of Four-point probe. Interestingly circular tracks forming chain like damage trails are produced via these energetic ions which are carefully examined by optical microscopy. It is observed that excitation, ionization, and cascade collisions are responsible for surface modifications of irradiated samples. Four-point probe analysis revealed that the electrical conductivity of substrate has reduced with increasing trend of atomic number of irradiated metallic ions (Al, Ti, Cu, and Au). The x-ray diffraction analysis elucidated the crystallographic changes leading to reduction of grain size of N-type silicon substrate, which is also associated with the metallic ions used. The decreasing trend of conductivity and grain size is due to thermal stresses, scattering effect, structural imperfections, and non-uniform conduction of energy absorbed by substrate atoms after the ion irradiation.

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr_{1-x}Ba_{x}Fe_{1.97}Ni_{0.03}As_{2}, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr_{1-x}Ba_{x}Fe_{2}As_{2} is determined by the strength of the magnetic-elastic coupling.

We discuss the concept of typicality of quantum states at quantum-critical points, using projector Monte Carlo simulations of an S=1/2 bilayer Heisenberg antiferromagnet as an illustration. With the projection (imaginary) time τ scaled as τ=aL^{z}, L being the system length and z the dynamic critical exponent (which takes the value z=1 in the bilayer model studied here), a critical point can be identified which asymptotically flows to the correct location and universality class with increasing L, independently of the prefactor a and the initial state. Varying the proportionality factor a and the initial state only changes the cross-over behavior into the asymptotic large-L behavior. In some cases, choosing an optimal factor a may also lead to the vanishing of the leading finite-size corrections. The observation of typicality can be used to speed up simulations of quantum criticality, not only within the Monte Carlo approach but also with other numerical methods where imaginary-time evolution is employed, e.g., tensor network states, as it is not necessary to evolve fully to the ground state but only for sufficiently long times to reach the typicality regime.

In this study, micromagnetism simulation by using finite difference method is carried out on the Nd_{2}Fe_{14}B/α-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size (S) on the magnetic properties and magnetic reversal modes are systematically analyzed. As S increases from 1 nm to 48 nm, the remanence (J_{r}) increases, while the coercivity (H_{ci}) decreases, leading to the result that the magnetic energy product[(BH)_{max}] first increases slowly, and then decreases rapidly, peaking at S=24 nm with the (BH)_{max} of 72.9 MGOe (1 MGOe=7.95775 kJ·m^{-3}). Besides, with the increase of S, the coercivity mechanism of the nanocomposite magnet changes from nucleation to pinning. Furthermore, by observing the magnetic moment evolution in demagnetization process, the magnetic reversal of the soft phase in the nanocomposite magnet can be divided into three modes with the increase of S:coherent rotation (S < 3 nm), quasi-coherent rotation (3 nm ≤ qslant S < 36 nm), and the vortex-like rotation (S ≥ 36 nm).

The detailed information of the electronic structure is the key to understanding the nature of charge density wave (CDW) order and its relationship with superconducting order in the microscopic level. In this paper, we present a high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) study on the three-dimensional (3D) hole-like Fermi surface around the Brillouin zone center in a prototypical quasi-one-dimensional CDW and superconducting system ZrTe_{3}. Double Fermi surface sheets are clearly resolved for the 3D hole-like Fermi surface around the zone center. The 3D Fermi surface shows a pronounced shrinking with increasing temperature. In particular, the quasiparticle scattering rate along the 3D Fermi surface experiences an anomaly near the charge density wave transition temperature of ZrTe_{3} (~63 K). The signature of electron-phonon coupling is observed with a dispersion kink at~20 meV; the strength of the electron-phonon coupling around the 3D Fermi surface is rather weak. These results indicate that the 3D Fermi surface is also closely connected to the charge-density-wave transition and suggest a more global impact on the entire electronic structure induced by the CDW phase transition in ZrTe_{3}.

In this paper, Ta/[NiFe(15 nm)/FeMn(10 nm)]/Ta exchange-biased bilayers are fabricated by magnetron sputtering, and their static and dynamic magnetic properties before and after rapid annealing treatment with pulsed current are characterized by using a vibrating sample magnetometer (VSM) and a vector network analyzer (VNA), respectively. The exchange bias field H_{e} and static anisotropy field H_{k}^{sta} decrease from 118.45 Oe (1 Oe=79.5775 A·m^{-1}) and 126.84 Oe at 0 V to 94.75 Oe and 102.31 Oe at 90 V, respectively, with increasing capacitor voltage, which supplies pulsed current to heat the sample. The effect of flash thermal annealing by pulsed current on the rotational anisotropy (H_{rot}), the difference value between static and dynamic magnetic anisotropy, is investigated particularly. The highest H_{rot} is obtained in the sample annealing with 45-V capacitor (3300 μF) voltage. According to the anisotropic magnetoresistance measurements, it can be explained by the fact that the temperature of the sample is around the blocking temperature of the exchange bias system (T_{b}) at 45 V, the critical temperature where the formation of more unstable antiferromagnetic grains occurs.

The impacts of HfO_{x} inserting layer thickness on the electrical properties of the ZnO-based transparent resistance random access memory (TRRAM) device were investigated in this paper. The bipolar resistive switching behavior of a single ZnO film and bilayer HfO_{x}/ZnO films as active layers for TRRAM devices was demonstrated. It was revealed that the bilayer TRRAM device with a 10-nm HfO_{x} inserted layer had a more stable resistive switching behavior than other devices including the single layer device, as well as being forming free, and the transmittance was more than 80% in the visible region. For the HfO_{x}/ZnO devices, the current conduction behavior was dominated by the space-charge-limited current mechanism in the low resistive state (LRS) and Schottky emission in the high resistive state (HRS), while the mechanism for single layer devices was controlled by ohmic conduction in the LRS and Poole-Frenkel emission in the HRS.

Optical properties of metallic edge-like structures known as knife-edges are a topic of interest and possess potential applications in enhanced Raman scattering, optical trapping, etc. In this work, we investigate the near-field optical polarization response at the edge of a triangular gold nanosheet, which is synthesized by a wet chemical method. A homemade scanning near-field optical microscope (SNOM) in collection mode is adopted, which is able to accurately locate its probe at the edge during experiments. An uncoated straight fiber probe is used in the SNOM, because it still preserves the property of light polarization though it has the depolarization to some extent. By comparing near-field intensities at the edge and glass substrate, detected in different polarization directions of incident light, the edge-induced depolarization is found, which is supported by the finite differential time domain (FDTD) simulated results. The depolarized phenomenon in the near-field is similar to that in the far-field.

In this paper, a high refractive index metamaterial (HRM), whose element is composed of bilayer square patch (BSP) spaced by a dielectric plate, is proposed. By reducing the thickness of the dielectric plate and the gap between adjacent patches, the BSP can effectively enhance capacitive coupling and simultaneously suppress diamagnetic response, which significantly increases the refractive index of the proposed metamaterial. Furthermore, the high refractive index region is far away from the resonant region of the metamaterial, resulting in broadband. Based on these characteristics of BSP, a gradient refractive index (GRIN) lens with thin thickness (0.34λ_{0}, where λ_{0} is the wavelength at 5.75 GHz) is designed. By using this lens, we then design a circularly polarized horn antenna with high performance. The measurement results show that the 3-dB axial ratio bandwidth is 34.8% (4.75 GHz~6.75 GHz) and the antenna gain in this frequency range is increased by an average value of 3.4 dB. The proposed method opens up a new avenue to design high-performance antenna.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Thermal transport properties are investigated for out-of-plane phonon modes (FPMs) and in-plane phonon modes (IPMs) in double-stub graphene nanoribbons (GNRs). The results show that the quantized thermal conductance plateau of FPMs is narrower and more easily broken by the double-stub structure. In the straight GNRs, the thermal conductance of FPMs is higher in the low temperature region due to there being less cut-off frequency and more low-frequency excited modes. In contrast, the thermal conductance of IPMs is higher in the high temperature region because of the wider phonon energy spectrum. Furthermore, the thermal transport of two types of phonon modes can be modulated by the double-stub GNRs, the thermal conductance of FPMs is less than that of IPMs in the low temperatures, but it dominates the contribution to the total thermal conductance in the high temperatures. The modulated thermal conductance can provide a guideline for designing high-performance thermal or thermoelectric nanodevices based on graphene.

The large single-crystal diamond with FeS doping along the (111) face is synthesized from the FeNi-C system by the temperature gradient method (TGM) under high-pressure and high-temperature (HPHT). The effects of different FeS additive content on the shape, color, and quality of diamond are investigated. It is found that the (111) face of diamond is dominated and the (100) face of diamond disappears gradually with the increase of the FeS content. At the same time, the color of the diamond crystal changes from light yellow to gray-green and even gray-yellow. The stripes and pits corrosion on the diamond surface are observed to turn worse. The effects of FeS doping on the shape and surface morphology of diamond crystal are explained by the number of hang bonds in different surfaces of diamond. It can be shown from the test results of the Fourier transform infrared (FTIR) spectrum that there exists an S element in the obtained diamond. The N element content values in different additive amounts of diamond are calculated. The XPS spectrum results demonstrate that our obtained diamond contains S elements that exist in S-C and S-C-O forms in a diamond lattice. This work contributes to the further understanding and research of FeS-doped large single-crystal diamond characterization.

Recently, 5d transition metal iridates have been reported as promising materials for the manufacture of exotic quantum states. Apart from the semimetallic ground states that have been observed, perovskite SrIrO_{3} is also predicted to have a lattice-symmetrically protected topological state in the (110) plane due to its strong spin-orbit coupling and electron correlation. Compared with non-polar (001)-SrIrO_{3}, the especial polarity of (110)-SrIrO_{3} undoubtedly adds the difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality (110)-SrIrO_{3} thin films on (110)-SrTiO_{3} substrates by reactive molecular beam epitaxy for the first time. Both reflection high-energy electron diffraction patterns and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A (1×2) surface reconstruction driven from the surface instability, the same as that reported in (110)-SrTiO_{3}, is observed. The electric transport measurements uncover that (110)-SrIrO_{3} exhibits a more prominent semimetallic property in comparison to (001)-SrIrO_{3}.

A lattice Boltzmann (LB)-cellular automaton (CA) model is employed to study the dendrite growth of Al-4.0 wt%Cu-1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferred growth orientation are incorporated into the coupled model by coupling the LB-CA model and the CALPHAD-based phase equilibrium solver, PanEngine. The dendrite growth with single and multiple initial seeds was numerically studied under the conditions of pure diffusion and melt convection. Effects of initial seed number and melt convection strength were characterized by new-defined solidification and concentration entropies. The numerical result shows that the growth behavior of dendrites, the final microstructure, and the micro-segregation are significantly influenced by melt convection during solidification of the ternary alloys. The proposed solidification and concentration entropies are useful characteristics bridging the solidification behavior and the microstructure evolution of alloys.

We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus-doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.

A series of Si/C composites were fabricated based on pitch and Si powders with particle sizes of 30, 100, 500, and 3000 nm. The size effects of the Si particles in the Si/C composites were investigated for lithium-ion battery anodes. The nanoscale Si and Si/C composites exhibited good capacity retentions. Scanning electron microscopy showed that exterior and interior cracks emerging owing to volume expansion as well as parasitic reactions with the electrolyte could well explain the performance failure.

The effects of tungsten W doping and coating on the electrochemical performance of LiCoO_{2} cathode are comparatively studied in this work. The amount of modification component is as low as 0.1 wt% and 0.3 wt% respectively. After 100 cycles between 3.0 V-4.6 V, 0.1 wt% W doping provides an optimized capacity retention of 72.3%. However, W coating deteriorates battery performance with capacity retention of 47.8%, even lower than bare LiCoO_{2} of 55.7%. These different electrochemical performances can be attributed to the surface aggregation of W between doping and coating methods. W substitution is proved to be a promising method to develop high voltage cathodes. Practical performance relies on detailed synthesis method.

The collective motion of rounded squares with different corner-roundness ζ is studied by molecular dynamics (MD) simulation in this work. Three types of translational collective motion pattern are observed, including gliding, hopping and a mixture of gliding and hopping. Quantitatively, the dynamics of each observed ordered phase is characterized by both mean square displacement and van Hove functions for both translation and rotation. The effect of corner-roundness on the dynamics is further studied by comparing the dynamics of the rhombic crystal phases formed by different corner-rounded particles at a same surface fraction. The results show that as ζ increases from 0.286 to 0.667, the translational collective motion of particles changes from a gliding-dominant pattern to a hopping-dominant pattern, whereas the rotational motion pattern is hopping-like and does not change in its type, but the rotational hopping becomes much more frequent as ζ increases (i.e., as particles become more rounded). A simple geometrical model is proposed to explain the trend of gliding motion observed in MD simulations.

In large-scale electric machines, unbalanced magnetic pull (UMP) caused by eccentricity usually results in stator-rotor rub, so it is necessary to investigate the amplitude and the influencing factors. This paper takes the squirrel-cage induction motor as an example. A magnetic loop model of an induction motor is established by an analytical method. The impact of stator winding setup (parallel branch and pole pairs) on each magnetomotive force (MMF) and unbalanced magnetic pull is analyzed. Using the finite element simulation method, the spatial and time distribution of flux density of the rotor outer circle under static eccentricity is obtained, and the unbalanced magnetic pull calculation caused by static eccentricity is completed. The conclusion of the influence of stator winding on the size of unbalanced magnetic pull provides reliable gist for motor noise and vibration analysis, and especially provides an important reference for large induction motor design.

A reverse-conducting lateral insulated-gate bipolar transistor (RC-LIGBT) with a trench oxide layer (TOL), featuring a vertical N-buffer and P-collector is proposed. Firstly, the TOL enhances both of the surface and bulk electric fields of the N-drift region, thus the breakdown voltage (BV) is improved. Secondly, the vertical N-buffer layer increases the voltage drop V_{PN} of the P-collector/N-buffer junction, thus the snapback is suppressed. Thirdly, the P-body and the vertical N-buffer act as the anode and the cathode, respectively, to conduct the reverse current, thus the inner diode is integrated. As shown by the simulation results, the proposed RC-LIGBT exhibits trapezoidal electric field distribution with BV of 342.4 V, which is increased by nearly 340% compared to the conventional RC-LIGBT with triangular electric fields of 100.2 V. Moreover, the snapback is eliminated by the vertical N-buffer layer design, thus the reliability of the device is improved.

A two-dimensional model of the silicon NPN monolithic composite transistor is established for the first time by utilizing the semiconductor device simulator, Sentaurus-TCAD. By analyzing the internal distributions of electric field, current density, and temperature of the device, a detailed investigation on the damage process and mechanism induced by high-power microwaves (HPM) is performed. The results indicate that the temperature elevation occurs in the negative half-period and the temperature drop process is in the positive half-period under the HPM injection from the output port. The damage point is located near the edge of the base-emitter junction of T2, while with the input injection it exists between the base and the emitter of T2. Comparing these two kinds of injection, the input injection is more likely to damage the device than the output injection. The dependences of the damage energy threshold and the damage power threshold causing the device failure on the pulse-width are obtained, and the formulas obtained have the same form as the experimental equations, which demonstrates that more power is required to destroy the device if the pulse-width is shorter. Furthermore, the simulation result in this paper has a good coincidence with the experimental result.

Photo-generated carriers may diffuse into the adjacent cells to form the electrical crosstalk, which is especially noticeable after the pixel cell size has been scaled down. The electrical crosstalk strongly depends on the structure and electrical properties of the photosensitive areas. In this work, time-dependent crosstalk effects considering different isolation structures are investigated. According to the different depths of photo-diode (PD) and isolation structure, the transport of photo-generated carriers is analyzed with different regions in the pixel cell. The evaluation of crosstalk is influenced by exposure time. Crosstalk can be suppressed by reducing the exposure time. However, the sensitivity and dynamic range of the image sensor need to be considered as well.

An ill-posed inverse problem in quantitative susceptibility mapping (QSM) is usually solved using a regularization and optimization solver, which is time consuming considering the three-dimensional volume data. However, in clinical diagnosis, it is necessary to reconstruct a susceptibility map efficiently with an appropriate method. Here, a modified QSM reconstruction method called weighted total variation using split Bregman (WTVSB) is proposed. It reconstructs the susceptibility map with fast computational speed and effective artifact suppression by incorporating noise-suppressed data weighting with split Bregman iteration. The noise-suppressed data weighting is determined using the Laplacian of the calculated local field, which can prevent the noise and errors in field maps from spreading into the susceptibility inversion. The split Bregman iteration accelerates the solution of the L_{1}-regularized reconstruction model by utilizing a preconditioned conjugate gradient solver. In an experiment, the proposed reconstruction method is compared with truncated k-space division (TKD), morphology enabled dipole inversion (MEDI), total variation using the split Bregman (TVSB) method for numerical simulation, phantom and in vivo human brain data evaluated by root mean square error and mean structure similarity. Experimental results demonstrate that our proposed method can achieve better balance between accuracy and efficiency of QSM reconstruction than conventional methods, and thus facilitating clinical applications of QSM.

Accurate identification of Alzheimer's disease (AD) and mild cognitive impairment (MCI) is crucial so as to improve diagnosis techniques and to better understand the neurodegenerative process. In this work, we aim to apply the machine learning method to individual identification and identify the discriminate features associated with AD and MCI. Diffusion tensor imaging scans of 48 patients with AD, 39 patients with late MCI, 75 patients with early MCI, and 51 age-matched healthy controls (HCs) are acquired from the Alzheimer's Disease Neuroimaging Initiative database. In addition to the common fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity metrics, there are two novel metrics, named local diffusion homogeneity that used Spearman's rank correlation coefficient and Kendall's coefficient concordance, which are taken as classification metrics. The recursive feature elimination method for support vector machine (SVM) and logistic regression (LR) combined with leave-one-out cross validation are applied to determine the optimal feature dimensions. Then the SVM and LR methods perform the classification process and compare the classification performance. The results show that not only can the multi-type combined metrics obtain higher accuracy than the single metric, but also the SVM classifier with multi-type combined metrics has better classification performance than the LR classifier. Statistically, the average accuracy of the combined metric is more than 92% for all between-group comparisons of SVM classifier. In addition to the high recognition rate, significant differences are found in the statistical analysis of cognitive scores between groups. We further execute the permutation test, receiver operating characteristic curves, and area under the curve to validate the robustness of the classifiers, and indicate that the SVM classifier is more stable and efficient than the LR classifier. Finally, the uncinated fasciculus, cingulum, corpus callosum, corona radiate, external capsule, and internal capsule have been regarded as the most important white matter tracts to identify AD, MCI, and HC. Our findings reveal a guidance role for machine-learning based image analysis on clinical diagnosis.

ITIC is the milestone of non-fullerene small molecule acceptors used in organic solar cells. We study the electronic states and molecular orientation of ITIC film using photoelectron spectroscopy and x-ray absorption spectroscopy. The negative integer charge transfer energy level is determined to be 4.00±0.05 eV below the vacuum level, and the ionization potential is 5.75±0.10 eV. The molecules predominantly have the face-on orientation on inert substrates as long as the surfaces of the substrates are not too rough. These results provide the physical understanding of the high performance of ITIC-based solar cells, which also afford implications to design more advanced photovoltaic small molecules.

In this study, TiO_{2} nanoforest films consisting of nanotubes have been synthesized by a simple hydrothermal method and a subsequent sintering technique. The hydrothermal reaction time is important for the controlling of the nanotube diameter and the specific surface area of holistic TiO_{2} films. When the hydrothermal process reaction time is up to 8 hours, the diameter of the nanotube is about 10 nm, and the specific surface area of TiO_{2} nanoforest films reaches the maximum. CdS nanoparticles are synthesized on TiO_{2} nanoforest films by the successive ionic layer adsorption and reaction (SILAR) technique. The transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDX) mapping results verify that TiO_{2}/CdS heterostructures are realized. A significant red-shift of the absorption edge from 380 nm to 540 nm can be observed after the pure TiO_{2} film is sensitized by CdS nanoparticles. Under irradiation of light, the current density of the optimal TiO_{2}/CdS photoanode is 2.30 mA·cm^{-2} at 0 V relative to the saturated calomel electrode (SCE), which is 6 times stronger than that of the pure TiO_{2} photoanode. This study suggests that the TiO_{2} nanoforest consisting of interlinked pony-size nanotubes is a promising nanostructure for photoelectrochemical.

By means of game theory, the effect of compassion mechanism on the evacuation dynamics of pedestrians from a room is studied based on a cellular automaton model. Pedestrians can choose to cooperate or defect in a snowdrift game during the movement. With the compassion mechanism, pedestrians share their payoff to the poorest peer when several pedestrians compete for the same empty cell. Simulation results show that the escape time grows with fear degree r of the snowdrift game, and the compassion mechanism will have a different effect on the system compared with the situation of a spatial game with fixed population. By payoff redistribution, the compassion can help the minor strategy to survive. When the fear degree r is large, the compassion can sustain the cooperative behavior, and spontaneously decreases the escape time. When the fear degree r is small, the compassion will decrease the cooperation frequency, and slightly increase the escape time. The phenomenon is explained by the evolution and competition of defectors and cooperators in the system. Finally, the effect of initial cooperator proportion, the effect of two exits, and the effect of “Richest-Following” strategy, and the effect of initial density are also discussed.

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