bluuebunny/crossref_metadata_2025 huggingface dataset:
NH3 aliasing absorption spectra at 1103.4 cm–1 based on continuous quantum cascade laser
Authors: Li Meng-Qi , Zhang Yu-Jun , He Ying , You Kun , Fan Bo-Qiang , Yu Dong-Qi , Xie Hao , Lei Bo-En , Li Xiao-Yi , Liu Jian-Guo , Liu Wen-Qing ,   Key Laboratory of Environmental Optics and Technology, Chinese Academy of Sciences, Anhui Institute of Optics and Fine Mechanics, Hefei 230031, China,   University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Due to the important role of NH3 in atmospheric aerosol chemistry, rapid and accurate inversion of ammonia concentration is very important for environmental issues. In this paper, a 9.05 μm continuous quantum cascade laser (QCL) is used as the light source at room temperature, and the scanned-wavelength direct-absorption tunable diode laser absorption spectroscopy (TDLAS) is used to study the spectral characteristics of the QCL at 1103.4 cm–1. A low-pressure experimental platform based on two-level temperature control was designed to measure the six aliasing absorption lines of ammonia at 1103.4 cm–1. The broadening of spectral line becomes smaller under the condition of reducing the pressure, and the aliasing spectra are separated. The line strength of each absorption line is calculated, and the measurement uncertainty is further analyzed. A method for accurate inversion of single-spectrum gas concentration by low-pressure separation was proposed for severely aliased spectra, and experimental verification was performed. By comparing the results with the HITRAN database, it is concluded that the experimental measured line strength of ammonia gas at 1103.4 cm–1 has a deviation from the database of . The uncertainty of the line intensity measurement is mainly related to the separation and extraction of aliasing absorbance, which is about 2.42%–8.92%. The deviation between the inversion concentration and the actual value under the condition of extreme low pressure is between 1% and 3%, while the calculated deviation of the line intensity value in the 2.71%–4.71% HITRAN database is about 3% to 5%. The results above indicate that the experimental data are reliable. The non-separative aliasing spectral line method is used to invert the concentration at normal pressure, and the low-pressure separated single spectral line method is used to invert the concentration at low pressure. The results of the two are compared. The analysis results show that the low-pressure separation single-spectrum spectral line inversion concentration value has smaller deviation and higher accuracy from the original concentration. The study of this method provides reference for future inversion of gas concentrations inversion in the atmospheric environment and other fields.
Thermodynamic limit and optimal performance prediction of thermophotovoltaic energy conversion devices
Authors: Liao Tian-Jun , Lü Yi-Xiang ,   Department of Physics and Energy, Chongqing University of Technology, Chongqing 400054, China
Published: December 2020

The application of thermophotovoltaic energy conversion device to recovery and utilization of high-grade thermal energy are limited by its irreversible loss. In this work, we reveal the source of irreversible loss and provide a strategy for improving the performance of thermophotovoltaic energy conversion device. The maximum efficiency of thermophotovoltaic energy conversion device under ideal condition is determined by using the theory of semiconductor physics and Planck thermal radiation. Moreover, the effects of non-radiative recombination and irreversible heat transfer loss on the electrical, optical, and thermal characteristics of thermophotovoltaic device are considered to predict the optimal performance of thermophotovoltaic device. The optimal region of power density, efficiency, and photon cut-off energy are determined. The obtained results show that the open-circuit voltage, short-circuit current density and efficiency of non-ideal device are lower than those of ideal device. The voltage output and photon cut-off energy of thermophotovoltaic device and heat source temperature can be optimized to improve the power density and efficiency of the device. It is found that the theoretical results are in good agreement with the experimental results, which can provide some guidances fordeveloping the practical thermophotovoltaic devices.
Electron transport through a quantum-dot-Su-Schrieffer-Heeger-chain system
Authors: Zhang Lan-Yun , Xue Hai-Bin , Chen Bin , Chen Jian-Bin , Xing Li-Li ,   Key Laboratory of Interface Science and Engineering in Advanced Materials of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China,   College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

The Su-Schrieffer-Heeger (SSH) is a typical one-dimensional system with topological edge states, which has been experimentally realized in the photon and cold atom systems.Therefore, how to confirm the existence of the edge states from theoretical and experimental has become one of the most important topics in condensed matter physics. In this paper, using the tight-binding approximation and transfer-matrix method, we have studied the transport signatures of electron through a quantum dot-SSH chain hybrid system. Here,the two quantum dots play a role in modulating the tunneling coupling strength between the SSH chain and the two electrodes.When the quantum dots are weakly coupled to the SSH chain, the quadruple-degenerate edge states of the quantum dot-SSH chain hybrid system correspond to that the SSH chain has two degenerate zero-energy edge states; whereas the twofold-degenerate ones correspond to that the SSH chain has no edge states. While the quantum dots are strongly coupled to the SSH chain, the edge states only exist when the intra-cell hopping amplitude is larger than the inter-cell hopping amplitude. In this situation, however, there is no edge states in the SSH chain. In particular, when the quantum dot-SSH chain hybrid system is strongly coupled to the two external electrodes, the number of transmission resonance peaks of the edge states of the quantum dot-SSH chain hybrid system will be reduced by 2. For example, in the case of the quadruple-degenerate edge states, the number of transmission resonance peaks will be two; whereas in the case of twofold-degenerate ones, that will disappear. Therefore, by modulating the tunneling coupling strength between the quantum dots and the SSH chain and that between the quantum dots and the two external electrodes, we can observe the variation of the number of transmission resonance peaks of edge states to detect whether the SSH chain is in the nontrivial topological state or not.
Time delay signature and bandwidth of chaotic laser output from semiconductor laser
Authors: Zhang Yi-Ning , Feng Yu-Ling , Wang Xiao-Qian , Zhao Zhen-Ming , Gao Chao , Yao Zhi-Hai ,   Department of Physics, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

 Semiconductor laser (SL) can output chaotic lasers under external disturbances such as optical injection or optical feedback, and the bandwidth can reach up to GHz magnitude. External-cavity feedback semiconductor lasers can output high-dimensional chaotic lasers and are considered to be better sources of chaotic entropy. However, due to external cavity feedback and other effects, it will give rise to obvious external cavity time delay signature (TDS) in the output chaotic laser, which restricts the application of chaotic lasers. On the other hand, the bandwidth of chaotic laser determines the transmission rate of confidential communication, and therefore TDS and bandwidth are two important parameters that will affect chaotic laser’s applications. Therefore, it is significant to take appropriate measures to suppress the TDS and increase the bandwidth of chaotic laser output by semiconductor laser.

 In this paper the output laser from a semiconductor laser with single optical feedback is partially injected to another semiconductor laser with double filtered optical feedback. Thus they form a semiconductor laser system with external optical injection and double filtered optical feedback, i.e. a master-slave laser system which is used to suppress the TDS of chaotic laser and investigate its bandwidth. We numerically investigate the influences of external light injection coefficient, feedback intensity, pumping factor, and filter bandwidth on TDS. Then the suppression effects of this system on TDS are analyzed and compared with those of semiconductor laser system with external optical injection and single optical feedback, those of semiconductor laser system with external optical injection and double optical feedback, those of semiconductor laser system with external optical injection and single filtered optical feedback, and those of semiconductor laser system with double filtered optical feedback. The results show that the proposed scheme in this paper has the best suppression effect on TDS. Then the bandwidth of the chaotic laser output from the system is investigated under the condition of parameters of effectively suppressing TDS. The results show that the system proposed in this paper can increase the bandwidth of the system output chaotic laser by properly selecting the parametric values, and the maximum bandwidth value of the obtained chaotic laser is about 8.8 GHz. The above investigations indicate the effectiveness of the proposed scheme. The results of this investigation are significant for the application of chaotic lasers.
An integrable reverse space-time nonlocal Sasa-Satsuma equation
Authors: Song Cai-Qin , Zhu Zuo-Nong ,   College of Sciences, University of Shanghai for Science and Technology, Shanghai 200093, China,   School of Mathematical Sciences, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

In this paper, we introduce an integrable reverse space-time nonlocal Sasa-Satsuma equation. The Darboux transformation and soliton solutions for this nonlocal integrable equation are constructed.
Simulation and architectural design for Schottky structure perovskite solar cells
Authors: Liang Xiao-Juan , Cao Yu , Cai Hong-Kun , Su Jian , Ni Jian , Li Juan , Zhang Jian-Jun ,   College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300350, China,   College of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China,   Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin, Tianjin 300350, China
Published: December 2020

The wx-AMPS simulation software is used to model and simulate the Schottky perovskite thin film solar cells. The front and back electrodes with different work functions are applied to the Schottky perovskite solar cells to study the effect of band structure on the performance of solar cells. The results show that in a range from 3.8 to 4.4 eV, as the work function of the front electrode decreases, the conversion efficiency of the Schottky solar cells gradually increases. When the work function of the front electrode is low, the electric field strength is large, which facilitates the transport of carriers in the light-absorbing layer of the perovskite and reduces the carrier recombination rate of the perovskite layer. In addition, the recombination ratio of the light absorbing layer is reduced due to the increase of the electric field strength, and the parallel resistance is increased to a certain extent thereby increasing the FF and improving the output efficiency of the battery. At the same time, when the current electrode work function is maintained at 3.8 eV, in a range from 4.3 to 5.5 eV, the higher the work function of the back electrode, the greater the conversion efficiency of the Schottky solar cell is. This conduces to the band alignment in contact between perovskite and back electrode. Under the premise that the common electrode Au is used as a back electrode, the work function of the front electrode is 3.8 eV and the conversion efficiency of the Schottky perovskite solar cell is 17.93%. In addition, by using the optimized front and rear contact electrodes, the quality of the perovskite layer material, thus the performance of the solar cell can be further improved. Doping till a certain concentration and removing the defects of the perovskite layer, the conversion efficiency of the solar cell with a thickness of 500 nm can be increased from 17.93% to 20.1%. The simulation results show that the Schottky perovskite thin film solar cells can obtain excellent performance with simple device structure and have great potential applications.
Radiative heat transfer in nanophotonics: From thermal radiation enhancement theory to radiative cooling applications
Authors: Liu Yang , Pan Deng , Chen Wen , Wang Wen-Qiang , Shen Hao , Xu Hong-Xing ,   School of Physics and Technology, Wuhan University, Wuhan 430072, China,   The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China,   ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Barcelona 08860, Spain,   School of Science, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

Thermal radiation, as a ubiquitous physical phenomenon, plays an important role in various research fields of science and engineering. Traditional understanding of thermal radiation mainly relies on Planck’s law, which describes the energy exchanging efficiency of entire thermal radiation process. However, recent studies indicated that comparing with the macroscopic object obeying Planck’s law, the thermal radiation in nanophotonic structures is obviously abnormal. This is due to the fact that the nanostructures’ featured size or neighboring space are much smaller than the thermal wavelength. It is important to notice that by well designing the material, size, and structure pattern, the thermal radiation is tunable and controllable. Furthermore, the nanophotonic structures enabling the radiative cooling effects promise to possess the tremendous applications including energy, ecology, etc. In this review paper, firstly, we briefly describe the fundamental theory of thermal radiation, as well as the history and latest progress, such as, enhanced radiative heat transfer, the near-field radiation in two-dimensional materials, and the overall far-field enhancement. Secondly, we focus on the newly available daytime radiative cooling system, which is based on metamaterials or desired nanophotonic structures, pursuing the best cooling performances. Finally, we detail the checklists of remarkable applications, ranging from building cooling and dew collection to solar cell cooling. In addition, we also point out the broad future of radiation cooling technology of nanometer optical materials in promoting the management and transformation of desert ecological environment.
High-speed and large-scaled light-sheet microscopy with electrically tunable lens
Authors: Hu Yu-Yao , Liang Dong , Wang Jing , Liu Jun ,   State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Fluorescence microscopic imaging technology realizes specific imaging by labeling biological tissue with fluorescence molecules, which has a high signal-to-noise ratio and has been widely used in the field of medical biology research. Some typical fluorescence microscopy techniques, such as confocal microscopy and two-photon microscopy, have high fluorescence intensity, but the long exposure can cause phototoxicity and photobleaching of biological tissue, which is difficult to meet the demand for long-time observation or noninvasive imaging. Then, light sheet fluorescence microscopy (LSFM) has become a hot research topic in fluorescence micro-imaging in recent years due to its fast speed, high resolution, low photobleaching and low phototoxicity. The imaging speed of a typical light sheet microscopy is not fast enough to observe fast biological activities such as transmission of neural signals, blood flow, and heart beats. At present, many reported light-sheet fluorescence microscopies still have some problems such as fixed imaging surface, slow imaging speed, small imaging depth or residual artifacts. Therefore, in this paper, a rapid light-sheet fluorescence microscopy based on electrically tunable lens is built. To achieve the rapid movement of the focal plane of the detection objective lens, the electrically tunable lens is introduced to meet the reqirement for fast changing of the diopter. Similarly, the rapid movement of light sheet is achieved by introducing one-dimensional galvanometer to change the rotation angle. Fast imaging requires the light sheet and focal plane to overlap in real time, which is then combined with a high-speed sCMOS receiving fluorescence to complete the whole imaging. In the experiment, the vertical depth significantly increases by modifying the optical path, and the LABVIEW programming is used to coordinate and improve the dynamic imaging quality, which effectively reduces the artifacts generated in rapid imaging. Finally, an imaging speed of 275 frames/s with a lateral resolution of ~0.73 μm, vertical resolution of ~5.5 μm, and an imaging depth of ~138 μm is achieved. This is of significance for developing the real-time and non-invasive imaging of living biological tissues.
Preparing GaN nanowires on Al2O3 substrate without catalyst and its optical property
Authors: Liang Qi , Wang Ru-Zhi , Yang Meng-Qi , Wang Chang-Hao , Liu Jin-Wei ,   Key Laboratory of Advanced Functional Materials, Education Ministry of China, College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

A green and low-cost method to prepare high-quality GaN (gallium nitride) nanowires is important for the applications of GaN-based devices on a large scale. In this work, high-quality GaN nanowires are successfully prepared by a green plasma enhanced chemical vapor deposition method without catalyst, with Al2O3 used as a substrate, metal Ga as a gallium source and N2 as a nitrogen source. The obtained GaN nanomaterials are investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy. The XRD results demonstrate that hexagonal-wurtzite GaN is obtained and no other phases exist. The SEM results show that GaN nanowires and hexagonal GaN microsheets are obtained at different temperatures. When the growth temperature is at 950 ℃ (reaction time for 2 h), the hexagonal GaN microsheets each with a size of 15 μm are obtained. When the growth temperature is at 1000 ℃(reaction time for 2 h), the GaN nanowires with the lengths in a range of 10–20 μm are obtained. With the reaction temperature increasing from 0.5 h to 2 h, the lengths of GaN nanowires increase. The TEM results suggest that the GaN nanowires are of high crystallinity and the growth direction of GaN nanowires is in the [0001] direction. The Raman results indicate that there exists a compressive stress in the GaN nanowires and its value is 0.84 GPa. Meanwhile, the growth mechanism of GaN nanowires is also proposed. The morphologies of GaN nanomaterials are tailed by the growth temperature, which may be caused by Ga atomic surface diffusion. Ga atoms have low diffusion energy and small diffusion length at 950 ℃. They gather in the non-polar m-plane. The (0001) plane with the lowest energy begins to grow. Then, hexagonal GaN microsheets are obtained. When reaction temperature is at 1000 ℃, the diffusion length of Ga atoms increases. Ga atoms can diffuse into (0001) plane. In order to maintain the lowest surface energy, the GaN nanowires grow along the [0001] direction. The PL results indicate that the obtained GaN nanowires have just an intrinsic and sharp luminescence peak at 360 nm, which possesses promising applications in photoelectric devices such as ultraviolet laser emitter. Our research will also provide a low-cost and green technical method of fabricating the new photoelectric devices.
Thermodynamics of laser plasma removal of micro and nano-particles
Authors: Luo Ju , Feng Guo-Ying , Han Jing-Hua , Shen Xiong , Zhang Li-Jun , Ding Kun-Yan ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China
Published: December 2020

Micro-impurity pollution is always one of the key factors affecting the quality and service life of precision devices. Micro-nano impurity particles are difficult to remove by traditional cleaning methods (ultrasonic cleaning, etc.) and low removal efficiency by laser cleaning methods (dry laser cleaning, etc.). The laser plasma shock wave has high pressure and high temperature characteristics, which can remove nano-scaled impurity particles, and has great potential applications. In this work, we mainly study the thermodynamic effect of the laser plasma in the process of removing micro- and nano-particles. In this work, the Al particles on the Si substrate are removed by laser plasma shock wave, and the transformation of the particle state is discussed through the changes of the experimental sample morphology after different pulse effects. The experimental results show as follows With the increase of the pulse number, the micro- and nano-particle residues gradually decrease. At the same time, on the surface of the sample after these particles are removed, it can be found that large particles break up into small particles, and some of the particles will change into smooth spheres when their temperatures reach the melting point. These phenomena are the result of the interaction of the thermodynamic effect of the plasma. In order to study the transformation process of particle state, based on the plasma shock wave propagation theory, the evolution law of pressure characteristic and temperature characteristic of shock wave are obtained. From the evolution law, it can be seen that with the increase of shock wave radius, the pressure and temperature gradually decrease. When the shock wave propagates to the surface of a sample, it can reach the compression threshold and correspondingly the surface temperature arrives at melting temperature of particles, which are consistent with the experimental results. By using the finite element simulation method, the pressure and temperature of laser plasma shock wave acting on particles are studied. The stress distribution and temperature distribution in particles varying with time are obtained. The analysis results are consistent with the experimental results, and therefore the thermodynamic mechanism of plasma on particles is obtained.
Influence of magentic annealing temperature on microstructure and magnetic properties of NiCu alloy film
Authors: Liu Wen-Shu , Gao Run-Liang , Feng Hong-Mei , Liu Yue-Yue , Huang Yi , Wang Jian-Bo , Liu Qing-Fang ,   Key Laboratory of Magnetism and Magnetic Materials, Ministry of Education, Lanzhou University, Lanzhou 730000, China,   Key Laboratory of Special Function Materials and Structural Design, Ministry of Education, Lanzhou University, Lanzhou 730000, China
Published: December 2020

In this paper, Ni88Cu12 thin films are prepared on Si substrates by radio-frequency magnetron co-sputtering. The effects of film thickness and heat treatment on domain structure and magnetic properties are studied. The Ni88Cu12 films with thickness less than 210 nm show weak in-plane anisotropy. After the vacuum magnetic field heat treatment, the crystal grains of all films grow, and the in-plane anisotropy extents of Ni88Cu12 films with thickness less than 210 nm become weaker. The films have different morphological characteristics at different heat treatment temperatures. The surface of the film is very dense before heat treatment. After heat treatment at 300 °C, it forms island shape due to the solid solution between the grains. Compared with the grains on the surface of the heat-treated film at 300 °C, the grains grow further after being heat-treated at 400 °C. Grown grains cover the gaps between the grains, which makes the film surface flat. The results of in-plane normalized hysteresis loop of the films show that the critical thickness of the stripe domains decreases after heat treatment. The stripe domain structure appears in the 210-nm-thick films without being heat-treated. For the film with the heat treatment, its remanence ratio Mr/Ms decreases, and the saturation field Hs increases, and thus leading the perpendicular anisotropy constant Kp to increase. Therefore, the thickness of the stripe domain in the film after being heat-treated decreases. Compared with the films after being heat-treated, the 105-nm-thick as-prepared Ni88Cu12 film has a maximum natural resonance frequency of 2.1 GHz, which is attributed to the uniaxial anisotropy of the as-prepared Ni88Cu12 film. The saturation magnetization of the 300 °C-treated 105-nm-thick film decreases to 3.01 × 105 A/m. However, the saturation magnetization decreases to 5.9 × 105 A/m after heat treatment at 400 °C. Moreover, the ferromagnetic resonance peak of the film narrows after being treated at 300 °C, and the resonance frequency decreases to 1.95 GHz.
Intensity noise of tunable infrared laser based on singly resonant optical parametric oscillator
Authors: Nie Dan-Dan , Feng Jin-Xia , Qi Meng , Li Yuan-Ji , Zhang Kuan-Shou ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The infrared laser sources have important applications in many fields such as real-time detection, gas sensing or tracing, high-resolution spectral analysis and quantum optics. In this paper, we develop an infrared laser source with mode-hop-free broadband tunability by using a singly optical parametric oscillator (SRO) based on the magnesium-oxide doped periodically poled lithium niobite (MgO:PPLN) crystal. A polished lithium niobite crystal with a thickness of 1 mm is used as an etalon that is inserted into the cavity of SRO to realize continuous mode-hop-free tuning. The resonant signal in SRO is frequency stabilized to the transmission peak of intracavity etalon. Owing to the high stability of the resonator, continuous mode-hop-free tuning with a bandwidth of 2063.7 GHz for both signal and idler is realized. The oscillation threshold of SRO is 7.3 W. The signal of 4.3 W over 1551.9－1568.6 nm and idler of 2.1 W over 3307.3－3384.3 nm are generated for 22 W of pump power by tuning the temperature of the crystal from 20 ℃ to 70 ℃. The slope efficiency of 42.6% and optical conversion efficiency of 29% are obtained. Then the intensity noise characteristics of generated infrared laser are further studied theoretically and experimentally. The fluctuation characteristics of the SRO emission can be computed just by using a semiclassical approach. We analyze theoretically the factors that affect the intensity noise of the signal and idler. The temperature of the MgO:PPLN crystal and the modulation frequency of the etalon are important parameters, which can affect the intensity noise characteristics of signal and idler laser. Therefore, we investigate experimentally the variation of the intensity noise characteristics by changing the temperature of the crystal and the modulation frequency of the etalon. The intensity noise of the signal and idler laser are optimized through controlling the temperature in a range of 20－60 ℃ and the modulation frequency ranging from 2 kHz to 8 kHz, respectively. The experimental data basically accord with the theoretical calculations. When the operating temperature of the MgO:PPLN crystal is controlled at 60 ℃ and the modulation frequency of the etalon is 8 kHz, the intensity noise of the signal and the idler laser are reduced by 11 dB and 8 dB, respectively. The optimized infrared laser can provide a high-quality laser source for subsequent quantum optics research.
Current phases in Hofstadter ladder with staggered hopping
Authors: Liu Biao , Zhou Xiao-Fan , Chen Gang , Jia Suo-Tang ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China,   Center of Light Manipulations and Applications, College of and Electronics, Shandong Normal University, Jinan 250358, China
Published: December 2020

Hofstadter ladder describes a Boson ladder under a uniform magnetic field and supports nontrivial energy band and fractional quantum Hall states. Staggered hopping is illuminated from the SSH model and proved to have non-trivial effects on current phases. We introduce staggered hopping on Hofstadter ladder to study the novel current phases. Exact diagonalization (ED) and density matrix renormalization group (DMRG) methods have been employed to study the current phases of the ladder in noninteraction and strong interaction (hard core boson) cases. By observing energy singularities and the new flux patterns when increasing the staggered hopping strength, we extend Meissner and vortex phase to horizontal current phase, vertical current phase and vortex phase. The horizontal current phase has stronger chiral currents in horizontal direction, which is the long direction of the ladder. The vertical current phase has stronger chiral currents in vertical direction. The above two phases do not break translational invariance while the vortex phase does. The current patterns of horizontal current phase are proved to be continuously deformed form the Meissner phase, and the vortex phase has similar signatures. The vertical current phase is only visible when the hopping is staggered. These phases generally exist in noninteraction regimes and interacting superfluid regimes. We have defined new quantities (i.e. current inhomogeneity and nearest overlap) to characterize different quantum phases. In noninteraction case, the horizontal current phase go through the vortex phase to enter the vertical current phase by second order phase transitions, but in strong interaction case such a change can be directly made in a first order phase transition. The direct transition is made in higher fillings with almost identical flux. Surprisingly, the three phases turn into only two phases in Mott regimes, and the phase transition between the horizontal current phase and the vertical current phase has disappeared. We call the new phase as Mott-homogenous phase. The staggered hopping has exotic effects in strong interaction case. For n = 0.25 filling, the staggered hopping shrinks the region of vortex phases and produces Mott-SF transition. When the staggered hopping is weak, the system achieves Mott-SF transition just by varying the flux. This research can enrich current phases in lattice systems and illuminate further studies on chiral currents.
Synchronization of coupled phase oscillators: Order parameter theory
Authors: Zheng Zhi-Gang , Zhai Yun , Wang Xue-Bin , Chen Hong-Bin , Xu Can ,   Institute of Systems Science, Huaqiao University, Xiamen 361021, China,   College of Information Science and Engineering, Huaqiao University, Xiamen 361201, China,   School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

Rhythmic behaviors, i.e. temporally periodic oscillations in a system, can be ubiquitously found in nature. Interactions among various rhythms can lead to self-organized behaviors and synchronizations. This mechanism is also responsible for many phenomena such as nonlinear waves, spatiotemporal patterns, and collective behaviors in populations emerging in complex systems. Mathematically different oscillations are described by limit-cycle oscillators (pacemakers) with different intrinsic frequencies, and the synchrony of these units can be described by the dynamics of coupled oscillators. Studies of microscopic dynamics reveal that the emergence of synchronization manifests itself as the dimension reduction of phase space, indicating that synchrony can be considered as no-equilibrium phase transition and can be described in terms of order parameters. The emergence of order parameters can be theoretically explored based on the synergetic theory, central manifold theorem and statistical physics. In this paper, we discuss the order-parameter theory of synchronization in terms of statistical physics and set up the dynamical equations of order parameters. We also apply this theory to studying the nonlinear dynamics and bifurcation of order parameters in several typical coupled oscillator systems.
Internal dynamic detection of soliton molecules in Ti:sapphire femtosecond laser
Authors: Zhou Feng , Cai Yu , Zou De-Feng , Hu Ding-Tong , Zhang Ya-Jing , Song You-Jian , Hu Ming-Lie ,   Key Laboratory of Opto-electronic Information Technology, Ministry of Education, Ultrafast Laser Laboratory, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Soliton is a universal format of nonlinear wave propagation in nature. Soliton can maintain its shape during propagation. This unique property has been widely observed in plasma physics, high energy electromagnetics, hydrodynamics, and nonlinear optics. Soliton interactions can reflect collective dynamic behaviors in complex nonlinear systems, showing significant basic research value. Passive mode-locked laser is an ideal platform for studying soliton interaction. The attraction and repulsion between two optical solitons can form soliton molecules. Their properties have been intensively studied by optical spectral analysis. However, conventional optical spectrum analyzers show low resolution and long average time. Time-stretched dispersive Fourier transformation (TS-DFT) is an emerging-powerful measurement technology, which can map the spectrum of an optical pulse to a temporal waveform under sufficient dispersion. The TS-DFT makes it possible to detect the dynamics of the solitons in real time. Based on TS-DFT, the internal dynamics of the solitons in Ti:sapphire femtosecond laser is studied in experiment. By changing the pump power, the stable soliton molecules with a separation of 180 fs and the weak phase oscillatory soliton molecules with a separation of 105 fs are observed. The amplitude in the weak oscillation state is merely 0.05 rad. We also find that the soliton molecules in stable state can transform into phase sliding state under environmental perturbation. These optical soliton molecules with a binding separation of 100 fs are of great significance for studying the short-range nonlinear interactions of solitons.
Design and application of gas cluster accelerator for surface smoothing and nanostructures formation
Authors: Zeng Xiao-Mei , Vasiliy Pelenovich , Rakhim Rakhimov , Zuo Wen-Bin , Xing Bin , Luo Jin-Bao , Zhang Xiang-Yu , Fu De-Jun ,   School of Physical Science and Technology, Wuhan University, Wuhan 430072, China,   School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China
Published: December 2020

A custom-built gas cluster ion source with energy up to 50 keV is constructed, and Ar, CO2, N2, and O2 are used as the working gases. The clusters are formed by a metal supersonic conical nozzle with critical diameter in a range of 65–135 μm and a cone angle of 14°. The nozzle is powered in the pulsed mode, which improves the pumping conditions, and also makes it possible to increase the gas pressure in the stagnation zone to 15 atm and thereby obtain larger clusters. Based on the principle of ultrasonic expansion, gas cluster ions with an average size of 3000 atoms are obtained. The cluster beam current of 50 μA is obtained. The Ar cluster beam, which is less reactive, is used for treating surface, namely, surface smoothing and formation of self-assembled nanostructures. The Ar cluster bombardment perpendicular to the surface of the substrate is used to demonstrate the smoothing of the surface of Si wafers, Ti coating, and Au film. For the initial Si wafer, its root-mean-square (RMS) roughness of 1.92 nm decreases down to 0.5 nm after cluster beam treatment. The cleaning effect of the cluster beam is also observed very well. The one-dimensional (1D) isotropic power spectral density of the Si surface topography before and after smoothing are also discussed. The off-normal irradiation Ar cluster beam is also used to form self-assembled surface nanoripple arrays on the surface of flat ZnO single crystal substrates. The ripple formation is observed when the incident angle of the cluster beam is in a range of 30°–60°. The process of nanoripple fabrication is significantly governed by the cluster beam incident angle, energy and dose. The nano-ripples formed on the flat substrates remain eolian sand ripples and their formation starts at the incident angle of 30°. The most developed nanoripples are observed at the incident angle within a range of 45°–60°. The surface morphology and characteristic distribution of the nano-structures on the flat ZnO substrate are also analyzed by the two-dimensional (2D) power spectral density function. Next, Ar cluster beam is used for irradiating the ZnO nanorod arrays grown on the Si substrate. Due to various angles between the nanorod’s axis and the substrate normal, the conditions of the ripple formation on the nanorod facets are also realized. The dependence of wavelength on the accelerating voltage of the cluster ions and the dose are studied. Similar dependence of wavelength on accelerating voltage and dose are found for nanorods. Comparing with the flat ZnO surface, nanoripples on the ZnO nanorod faces at high irradiation doses demonstrate an ordering effect, and morphology of the ripples resembles that of more parallel steps rather than eolian ripples.
Overview of precaution and recovery strategies for cascading failures in multilayer networks
Authors: Jiang Wen-Jun , Liu Run-Ran , Fan Tian-Long , Liu Shuang-Shuang , Lü Lin-Yuan ,   Alibaba Research Center for Complexity Sciences, Hangzhou Normal University, Hangzhou 311121, China,   Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

In real life, most of the infrastructure networks closely related to the national economy and people's livelihood do not exist independently, but are interconnected with or dependent on each other, so the multilayer network model is proposed to study the independent complex systems and infrastructures. When the nodes in the multilayer network suffer initial failure or attack, the cascade occurs due to the interaction between the “intra-layer” and “inter-layer”, and the failure can propagate in the network layer and across the layers iteratively, so that the scale of the failures is enlarged gradually. As a result, many multilayer networks are more fragile than single networks. The cascading failure of multilayer network usually brings very serious catastrophes to our society. So, conducting the research on preventing the multilayer network from cascading failure and recovering is of great significance. As far as the prevention of cascading failure is concerned, what are mainly included are the strategies such as the fault detection, the protection of important nodes, the optimization of the coupling method of networks, and the backup of nodes. As for the recovery of multi-layer network, included mainly are the strategies such as common boundary node recovery, the idle connected link recovery, the link addition, the priority recovery of important nodes, the topology perturbation, and the repairing of localized attack and adaptive link.
Complex system reconstruction
Authors: Zhang Hai-Feng , Wang Wen-Xu ,   School of Mathematical Science, Anhui University, Hefei 230601, China,   State Key Laboratory of Cognitive Neuroscience and Learning IDG/McGovern Institute for Brain & Research, School of Systems Science, Beijing Normal University, Beijing 100875, China
Published: December 2020

Open complex systems far from equilibrium widely exist in the nature and the fields of society and technology, which are the main research objects of complexity science. Through the exchange of energy and material with the outside world, complex systems can form a variety of internal structures, orders and laws by self-organization behaviors, which poses an arduous challenge to the understanding and predicting complex systems. With the improvement of experimental technology and the progress of science and technology, the data reflecting the mechanism of various complex systems are increasing exponentially, thereby providing new opportunities for studying complex systems. Revealing the structures and dynamics of complex systems from the measured data is an inverse problem in the field of physics, which is the premise of understanding complex systems, predicting the evolution of system state, and regulating system state. However, it is very difficult to solve this inverse problem due to the diversity and complexity of complex system. Therefore, we need to fully mine the hidden knowledge and deep mechanism in the data with the help of interdisciplinary integration. In this paper we briefly review the research results of complex system in recent years, especially the reconstruction of complex network structures, hoping to inspire the innovation to the inverse problem of complex systems. Meanwhile, we hope that researchers in different fields can pay much attention to the inverse problems of complex systems, promote the cross and integration of nature, society, economy, biology and technology, and solve the scientific problems that we are facing.
Time evolution law of Wigner operator in diffusion channel
Authors: Zhang Ke , Li Lan-Lan , Ren Gang , Du Jian-Ming , Fan Hong-Yi ,   School of Electronic Engineering, Huainan Normal University, Huainan 232038, China,   Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230031, China
Published: December 2020

As is well known, the evolution of quantum state can be replaced by its Wigner function’s time evolution. The Wigner function of a quantum state is the same as the density matrix of a quantum state, because they both contain many messages, such as the probability distribution and phases. Thus, the important information about the quantum state in the evolution process can be obtained more quickly and effectively by studying the Wigner function of a quantum state. In this paper, based on the classical diffusion equation, the diffusion equation of the quantum state density operator is derived by using the P representation of the density operator. Furthermore, by introducing the Weyl ordering symbol of the quantum operator, the corresponding Weyl quantization scheme is given. In addition, the evolution equation of Wigner operator in diffusion channel is established by using another phase space representation of density operator—Wigner function, and the solution form of Wigner operator is given. In this paper, we derive the evolution law of Wigner operator in quantum diffusion channel for the first time, that is, the form of Wigner operator at any time in the evolution process. Based on this conclusion, the evolution of coherent states through quantum diffusion channels is discussed.
Mechanical behaviors of radial symmetric pyramid kirigami
Authors: Xiao Si , Qin Ying-Lin , Wang Hui , Wang Peng , Ma Hai-Ming , He Jun , Wang Ying-Wei ,   School of Physics and Electronics, Hunan Key Laboratory for Super-Microstructure and Ultrafast,  Central South University, Changsha 410083, China,   School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Kirigami, the art of cutting paper, recently emerged as a powerful tool to substantially modify, reconfigure and program the properties of material. The development of kirigami technology provides an effective solution for designing the inorganic flexible electronic devices. Pyramid kirigami, as a kind of kirigami structure, shows a large vertical extension characteristic. It has been widely used to demonstrate versatile applications, such as graphene kirigami spiral spring, three-dimensional stretchable supercapacitor, and wearable flexible sensors. In the present work, we construct a polygonal radial symmetric pyramid kirigami by introducing some cuts in the elastic sheet. The mechanical behavior of pyramid kirigami is investigated based on the cantilever formula solved by Galerkin method. In addition, a “beam model” is proposed to explain deformation process of pyramid kirigami, which consists of several “beam elements” containing two cantilever beams. The formula for the relationship between the elastic coefficient K and the structural parameters of the regular N-sided pyramid kirigami of n modules is obtained by combining several cantilever beams. The formula for the linear threshold of deformation DT is obtained based on the comparison between the approximate curve of small deflection and the theoretical curve of a cantilever beam. When the deformation of the structure exceeds the linear threshold, the structure cannot keep the elastic coefficient K value linear any more, and the mechanical behaviors become non-linear. The simple geometric relationship of a single module is used to explain the out-of-sheet distortion of the structure. The proposed theoretical model is confirmed by finite element method simulation and experimental methods, and it is used to analyze the mechanical characteristics of graphene krigami reported. The results indicate that the defined parameters can be adjusted to tailor or manipulate the ductility and mechanical behaviors. This work provides theoretical support for the application of pyramid kirigami in the field of flexible devices. In the macroscopic field, the pyramid kirigami structure is expected to be applied to the field of flexible devices as a flexible structure with controllable elastic coefficient. In the microscopic field, it is expected to use two-dimensional materials to make force measurement devices with a simple visual readout and femtonewton force resolution.