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Chaos Identification Based on Component Reordering and Visibility Graph
Sheng-Li Zhu, Lu Gan
Chin. Phys. Lett. 2017, 34 (5):
050501
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DOI: 10.1088/0256-307X/34/5/050501
The identification between chaotic systems and stochastic processes is not easy since they have numerous similarities. In this study, we propose a novel approach to distinguish between chaotic systems and stochastic processes based on the component reordering procedure and the visibility graph algorithm. It is found that time series and their reordered components will show diverse characteristics in the 'visibility domain'. For chaotic series, there are huge differences between the degree distribution obtained from the original series and that obtained from the corresponding reordered component. For correlated stochastic series, there are only small differences between the two degree distributions. For uncorrelated stochastic series, there are slight differences between them. Based on this discovery, the well-known Kullback–Leible divergence is used to quantify the difference between the two degree distributions and to distinguish between chaotic systems, correlated and uncorrelated stochastic processes. Moreover, one chaotic map, three chaotic systems and three different stochastic processes are utilized to illustrate the feasibility and effectiveness of the proposed method. Numerical results show that the proposed method is not only effective to distinguish between chaotic systems, correlated and uncorrelated stochastic processes, but also easy to operate.
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Phase Transition of the q-State Clock Model: Duality and Tensor Renormalization
Jing Chen, Hai-Jun Liao, Hai-Dong Xie, Xing-Jie Han, Rui-Zhen Huang, Song Cheng, Zhong-Chao Wei, Zhi-Yuan Xie, Tao Xiang
Chin. Phys. Lett. 2017, 34 (5):
050503
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DOI: 10.1088/0256-307X/34/5/050503
We investigate the critical behavior and the duality property of the ferromagnetic $q$-state clock model on the square lattice based on the tensor-network formalism. From the entanglement spectra of local tensors defined in the original and dual lattices, we obtain the exact self-dual points for the model with $q \leq 5 $ and approximate self-dual points for $q \geq 6$. We calculate accurately the lower and upper critical temperatures for the six-state clock model from the fixed-point tensors determined using the higher-order tensor renormalization group method and compare with other numerical results.
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Direct Laser Cooling Al$^+$ Ion Optical Clocks
Jie Zhang, Ke Deng, Jun Luo, Ze-Huang Lu
Chin. Phys. Lett. 2017, 34 (5):
050601
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DOI: 10.1088/0256-307X/34/5/050601
The Al$^+$ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al$^+$ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al$^+$ traps are utilized. The first trap is used to trap a large number of Al$^+$ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al$^+$ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach $9.0\times10^{-17}/\sqrt{\tau}$. For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed 234 nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about $1\times10^{-18}$. The proposed Al$^+$ ion optical clock has the potential to become the most accurate and stable optical clock.
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High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC
Yu-Zhu Liu, Bing-Sheng Li, Li Zhang
Chin. Phys. Lett. 2017, 34 (5):
052801
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DOI: 10.1088/0256-307X/34/5/052801
Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The $\langle0001\rangle$-oriented 6H-SiC wafers are implanted with 15 keV helium ions at a dose of 1$\times$10$^{17}$ cm$^{-2}$ at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473 K for 30 min. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273 K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealing abides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120–135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236 eV.
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Beam Line Design of Compact Laser Plasma Accelerator
Jun-Gao Zhu, Kun Zhu, Li Tao, Yi-Xing Geng, Chen Lin, Wen-Jun Ma, Hai-Yang Lu, Yan-Ying Zhao, Yuan-Rong Lu, Jia-Er Chen, Xue-Qing Yan
Chin. Phys. Lett. 2017, 34 (5):
054101
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DOI: 10.1088/0256-307X/34/5/054101
A compact laser plasma accelerator that is a novel accelerator based on the interaction of ultra-intense laser and plasmas is being built now at Peking University. According to the results of experiments and numerical simulations, a beam line combining the advantages of quadrupole and analyzing magnets is designed to deliver proton beams with energy ranging from 1 to 44 MeV, energy spread within $\pm$5% and $10^{6-8}$ protons per pulse. It turns out that the existence of space charge force of protons can be ignored for the increase of transverse and longitudinal envelopes even in the case of 10$^{9}$ protons in one pulse. To cope with the challenge to obtain a uniform distribution of protons at the final experiment target in laser acceleration, we manipulate the envelope beam waist in the $Y$ direction to a proper position and obtain a relatively good distribution uniformity of protons with an energy spread of 0–$\pm$5%.
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Holmium Oxide Film as a Saturable Absorber for 2μm Q-Switched Fiber Laser
M. F. A. Rahman, M. F. M. Rusdi, M. Q. Lokman, M. B. H. Mahyuddin, A. A. Latiff, A. H. A. Rosol, K. Dimyati, S. W. Harun
Chin. Phys. Lett. 2017, 34 (5):
054201
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DOI: 10.1088/0256-307X/34/5/054201
This work reports on the use of the holmium oxide (Ho$_{2}$O$_{3})$ polymer film as a saturable absorber (SA) for generating stable Q-switching pulses operating in a 2-μm region in a thulium-doped fiber laser cavity. The SA is prepared by diluting a commercial Ho$_{3}$O$_{2}$ powder and then mixing it with polyvinyl alcohol (PVA) solution to form a Ho$_{2}$O$_{3}$-PVA film. A tiny part of the film about 1 mm$\times$1 mm in size is sandwiched between two fiber ferrules with the help of index matching gel. When incorporated in a laser cavity driven by a 1552-nm pump, stable Q-switching pulses are observed at 1955 nm within the pump power range of 363–491 mW. As the pump power increases within this range, the repetition rate rises from 26 kHz to 39 kHz, as the pulse width drops from 4.22 μs to 2.57 μs. The laser operates with a signal-to-noise ratio of 47 dB, and the maximum output power and the pulse energy obtained are 2.67 mW and 69 nJ, respectively. Our results successfully demonstrate that the Ho$_{2}$O$_{3 }$ film can be used as a passive SA to generate a 2-μm pulse laser.
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Single-Shot Measurement of Transient Phase Shift Induced by Laser Wake
Jun Dong, Zhong-Gui Lu, Bo Zhang, Zhi-Tao Peng, Zhi-Hong Sun, Yan-Wen Xia, Hao-Yu Yuan, Jun Tang, De-Yan Zhu, Hua Liu, Jia-Kun Lv
Chin. Phys. Lett. 2017, 34 (5):
054204
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DOI: 10.1088/0256-307X/34/5/054204
Based on the frequency-to-time mapping relation of the linearly chirped pulse, the temporal phase shift induced by a laser-excited wake in a helium gas jet is measured using a chirped-pulse spectral interferometry with $\sim$140 fs resolution over a temporal region of 1 ps in a single shot. In this measurement, the image of the wake is obtained with one-dimensional spatial resolution and temporal resolution limited only by the bandwidth and chirp of the pulse. The 'bubbles' feature of the wake structure, along with multiple wakes excited by the main lobe and the side lobe of a laser focal-spot, is captured simultaneously.
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Robust Ghost Imaging Based on Degenerate Spontaneous Parametric Down-Conversion
Ling-Jun Kong, Yu Si, Rui Liu, Zhou-Xiang Wang, Wen-Rong Qi, Chenghou Tu, Yongnan Li, Hui-Tian Wang
Chin. Phys. Lett. 2017, 34 (5):
054206
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DOI: 10.1088/0256-307X/34/5/054206
In traditional ghost imaging, the entangled photon pairs produced from the spontaneous parametric down conversion (SPDC) process are used. There is an intrinsic disadvantage that the utilization efficiency of the photon pairs is very low. Inasmuch as all the correlated photon pairs produced by the degenerate SPDC process can be used to record the image of an object, the ghost imaging scheme we present here has a higher utilization efficiency of the photon pairs. We also investigate the robustness of our experimental scheme. The experimental results show that, no matter whether the photon-pair source is two light cones or two beam-like spots, the clear image of the object can be obtained. The slight rotation of the nonlinear crystal has no influence on the imaging quality. Our experimental results also demonstrate that when the part of the photon-pair source in the signal path or the idler path is blocked by unwanted things, the clear ghost image of the object can still be recorded.
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Hydrodynamic Effects on Surface Morphology Evolution of Titanium Alloy under Intense Pulsed Ion Beam Irradiation
Ting-Jian Dong, Cui-Hua Rong, Jia-Chang Liang, Bo Liu, Xiao-Yong Zhao, Dong-Yan Chen, Bin Zhang, Hao Wang, Hai-Bo Li, Shi-Gui Zhang, Yu-Ping Jiang, Bing Luo, Xiao-Wen Zhou, Tao Wang, Xiao Yu, Xiao-Yun Le
Chin. Phys. Lett. 2017, 34 (5):
056101
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DOI: 10.1088/0256-307X/34/5/056101
The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam (IPIB) irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses, the surface morphology of titanium alloy in a spatial scale of μm exhibits an obvious smoothening trend. The mechanism of this phenomenon is explained by the mass transfer caused by the surface tension of molten metal. Hydrodynamic simulation with a combination of the finite element method and the level set method reveals that the change in curvature on the molten surface leads to uneven distribution of surface tension. Mass transfer is caused by the relief of surface tension, and meanwhile a flattening trend in the surface morphology evolution is achieved.
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Positive Bias Temperature Instability Degradation of Buried InGaAs Channel nMOSFETs with InGaP Barrier Layer and Al$_{2}$O$_{3}$ Dielectric
Sheng-Kai Wang, Lei Ma, Hu-Dong Chang, Bing Sun, Yu-Yu Su, Le Zhong, Hai-Ou Li, Zhi Jin, Xin-Yu Liu, Hong-Gang Liu
Chin. Phys. Lett. 2017, 34 (5):
057301
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DOI: 10.1088/0256-307X/34/5/057301
Positive bias temperature instability stress induced interface trap density in a buried InGaAs channel metal-oxide-semiconductor field-effect transistor with a InGaP barrier layer and Al$_{2}$O$_{3}$ dielectric is investigated. Well behaved split $C$–$V$ characteristics with small capacitance frequency dispersion are confirmed after the insertion of the InGaP barrier layer. The direct-current $I_{\rm d}$–$V_{\rm g}$ measurements show both degradations of positive gate voltage shift and sub-threshold swing in the sub-threshold region, and degradation of positive $\Delta V_{\rm g}$ in the on-current region. The $I_{\rm d}$–$V_{\rm g}$ degradation during the positive bias temperature instability tests is mainly contributed by the generation of near interface acceptor traps under stress. Specifically, the stress induced acceptor traps contain both permanent and recoverable traps. Compared with surface channel InGaAs devices, stress induced recoverable donor traps are negligible in the buried channel ones.
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Two-Dimensional Node-Line Semimetals in a Honeycomb-Kagome Lattice
Jin-Lian Lu, Wei Luo, Xue-Yang Li, Sheng-Qi Yang, Jue-Xian Cao, Xin-Gao Gong, Hong-Jun Xiang
Chin. Phys. Lett. 2017, 34 (5):
057302
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DOI: 10.1088/0256-307X/34/5/057302
Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetals, and 3D node-line semimetals (NLSs). In particular, several compounds (e.g., certain 3D graphene networks, Cu$_{3}$PdN, Ca$_{3}$P$_{2}$) were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., graphene), 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice (named as HK lattice) composed by Kagome and honeycomb lattices. It is found that A$_{3}$B$_{2}$ (A is a group-IIB cation and B is a group-VA anion) compounds (such as Hg$_{3}$As$_{2})$ with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-$s$ orbital and the anion As-$p_{z}$ orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, Hg$_{3}$As$_{2}$ with the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities.
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Influence of Al Preflow Time on Surface Morphology and Quality of AlN and GaN on Si (111) Grown by MOCVD
Bo-Ting Liu, Ping Ma, Xi-Lin Li, Jun-Xi Wang, Jin-Min Li
Chin. Phys. Lett. 2017, 34 (5):
058101
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DOI: 10.1088/0256-307X/34/5/058101
We investigate the influence of Al preflow time on surface morphology and quality of AlN and GaN. The AlN and GaN layers are grown on a Si (111) substrate by metal organic chemical vapor deposition. Scanning electron microscopy, atomic force microscopy, x-ray diffraction and optical microscopy are used for analysis. Consequently, we find significant differences in the epitaxial properties of AlN buffer and the GaN layer, which are dependent on the Al preflow time. Al preflow layers act as nucleation sites in the case of AlN growth. Compact and uniform AlN nucleation sites are observed with optimizing Al preflow at an early nucleation stage, which will lead to a smooth AlN surface. Trenches and AlN grain clusters appear on the AlN surface while melt-back etching occurs on the GaN surface with excessive Al preflow. The GaN quality variation keeps a similar trend with the AlN quality, which is influenced by Al preflow. With an optimized duration of Al preflow, crystal quality and surface morphology of AlN and GaN could be improved.
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All-Optical Vector Cesium Magnetometer
Wei-Min Sun, Qiang Huang, Zong-Jun Huang, Ping-Wen Wang, Jun-Hai Zhang
Chin. Phys. Lett. 2017, 34 (5):
058501
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DOI: 10.1088/0256-307X/34/5/058501
Based on power modulation of a pump laser and precessional projection detection, we present an all-optical vector magnetometer of cesium, which has a demonstrated magnitude sensitivity of 80 fT/Hz$^{1/2}$ and an orientation sensitivity of 0.1$^{\circ}$/Hz$^{1/2}$. In the device, four main factors are measured experimentally, which are the Larmor precession frequency of a polarized magnetic moment that depends on the modulus of the measured magnetic field only, two phase shifts and amplitude ratio of the precession projection in the two probe directions relative to the magnetic field orientation. This kind of magnetometer with high sensitivity in the range of the spatial angle is suitable for solving the inverse problem and geomagnetic navigation.
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A Dynamic Evolution Model of Airline Networks
Ze-Jun Xie, Lu-Man Zhang, Sheng-Feng Deng, Wei Li
Chin. Phys. Lett. 2017, 34 (5):
058902
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DOI: 10.1088/0256-307X/34/5/058902
Empirical data show that most of the degree distribution of airline networks assume a double power law. In this work, firstly, we assume cities as sites, flight between two cities as an edge between two sites, and build a dynamic evolution model for airline networks by improving the BA model, in which the conception of attractiveness plays a decisive role in the course of evolution of the networks. To this end, we discuss whether the attractiveness depends on the site label $s$ or not separately, finally we obtain analytic degree distribution. As a result, if the attractiveness of a site is independent of the degree distribution of sites, which will follow the double power law, otherwise, it will be scale-free. Moreover, degree distribution depends on the parameters of the models, and some parameters are more sensitive than others.
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33 articles
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