中国物理B

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Dynamics of traveling wave solutions to a highly nonlinear Fujimoto-Watanabe equation

师利娟, 温振庶

2019 (4): 40201-040201. doi: 10.1088/1674-1056/28/4/040201

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In this work, we apply the bifurcation method of dynamical systems to investigate the underlying complex dynamics of traveling wave solutions to a highly nonlinear Fujimoto-Watanabe equation. We identify all bifurcation conditions and phase portraits of the system in different regions of the three-dimensional parametric space, from which we present the sufficient conditions to guarantee the existence of traveling wave solutions including solitary wave solutions, periodic wave solutions, kink-like (antikink-like) wave solutions, and compactons. Furthermore, we obtain their exact expressions and simulations, which can help us understand the underlying physical behaviors of traveling wave solutions to the equation.

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Quantifying quantum non-Markovianity via max-relative entropy

罗宇, 李永明

2019 (4): 40301-040301. doi: 10.1088/1674-1056/28/4/040301

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We investigate the non-Markovian behavior in open quantum systems from an information-theoretic perspective. Our main tool is the max-relative entropy, which quantifies the maximum probability with which a state ρ can appear in a convex decomposition of a state σ. This operational interpretation provides a new view for the non-Markovian process. We also find that max-relative entropy can be the witness and measure of non-Markovian processes. As applications, some examples are also given and compared with other measures in this paper.

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Novel quantum secret image sharing scheme

罗高峰, 周日贵, 胡文文

2019 (4): 40302-040302. doi: 10.1088/1674-1056/28/4/040302

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In this paper, we propose a novel quantum secret image-sharing scheme which constructs m quantum secret images into m+1 quantum share images. A chaotic image generated by the logistic map is utilized to assist in the construction of quantum share images first. The chaotic image and secret images are expressed as quantum image representation by using the novel enhanced quantum representation. To enhance the confidentiality, quantum secret images are scrambled into disordered images through the Arnold transform. Then the quantum share images are constructed by performing a series of quantum swap operations and quantum controlled-NOT operations. Because all quantum operations are invertible, the original quantum secret images can be reconstructed by performing a series of inverse operations. Theoretical analysis and numerical simulation proved both the security and low computational complexity of the scheme, which has outperformed its classical counterparts. It also provides quantum circuits for sharing and recovery processes.

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Research on co-propagation of QKD and classical communication by reducing the classical optical power

何如适, 江木生, 汪洋, 甘亚辉, 周淳, 鲍皖苏

2019 (4): 40303-040303. doi: 10.1088/1674-1056/28/4/040303

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We investigate the crosstalk noise, especially the spontaneous Raman scattering, in the optical fiber of a co-propagation system between quantum key distribution (QKD) and classical communications. Although many methods have been proposed, such as increasing the wavelength spacing and narrowband filtering technique, to suppress Raman scattering noise, these methods greatly affect the performance of QKD. One way to solve the obstacle restricting the coexistence is to decrease the classical signal power. Based on the high gain of the gated avalanche photodiode and pulse position modulation, we demonstrate that the co-propagation system works effectively with only a small effect on long-haul fibers, which has great significance for the practical widespread commercialization of QKD.

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Entangled multi-knot lattice model of anyon current

司铁岩

2019 (4): 40501-040501. doi: 10.1088/1674-1056/28/4/040501

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We proposed an entangled multi-knot lattice model to explore the exotic statistics of anyons. Long-range coupling interaction is a fundamental character of this knot lattice model. The short-range coupling models, such as the Ising model, Hamiltonian model of quantum Hall effect, fermion pairing model, Kitaev honeycomb lattice model, and so on, are the short-range coupling cases of this knot lattice model. The long-range coupling knot lattice model bears Abelian and non-Abelian anyons, and shows integral and fractional filling states like the quantum Hall system. The fusion rules of anyons are explicitly demonstrated by braiding crossing states. The eigenstates of quantum models can be represented by a multi-layer link lattice pattern whose topology is characterized by the linking number. This topological linking number offers a new quantity to explain and predict physical phenomena in conventional quantum models. For example, a convection flow loop is introduced into the well-known Bardeen-Cooper-Schrieffer fermion pairing model to form a vortex dimer state that offers an explanation of the pseudogap state of unconventional superconductors, and predicts a fractionally filled vortex dimer state. The integrally and fractionally quantized Hall conductance in the conventional quantum Hall system has an exact correspondence with the linking number in this multi-knot lattice model. The real-space knot pattern in the topological insulator model has an equivalent correspondence with the Lissajous knot in momentum space. The quantum phase transition between different quantum states of the quantum spin model is also directly quantified by the change of topological linking number, which revealed the topological character of phase transition. Circularized photons in an optical fiber network are a promising physical implementation of this multi-knot lattice, and provide a different path to topological quantum computation.

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Ratchet transport of overdamped particles in superimposed driven lattices

黄淑娜, 朱薇静, 黄小群, 艾保全, 李丰果

2019 (4): 40502-040502. doi: 10.1088/1674-1056/28/4/040502

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Ratchet transport of overdamped particles is investigated in superimposed driven lattices using Langevin dynamics simulations. It is found that noise can strongly affect the transport of the particles. When lattices driving dominates the transport, the noise acts as a disturbance of the directed transport and slows down the average velocity of the particles. When the driving phase has less impact on particle transport, Gaussian white noise can play a positive role. By simply modulating these two parameters, we can control efficiency and the direction of the directed currents.

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Intrinsic fluctuation and susceptibility in somatic cell reprogramming process

沈健, 张小敏, 李齐亮, 王歆宇, 赵蕴杰, 贾亚

2019 (4): 40503-040503. doi: 10.1088/1674-1056/28/4/040503

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Based on the coherent feedforward transcription regulation loops in somatic cell reprogramming process, a stochastic kinetic model is proposed to study the intrinsic fluctuations in the somatic cell reprogramming. The Fano factor formulas of key genes expression level in the coherent feedforward transcription regulation loops are derived by using of Langevin theory. It is found that the internal fluctuations of gene expression levels mainly depend on itself activation ratio and degradation ratio. When the self-activation ratio (or self-degradation ratio) is increased, the Fano factor increases reaches a maximum and then decreases. The susceptibility is used to measure the sensitivity of steady-state response to the variation in systemic parameters. It is found that with the increase of the self-activation ratio (or self-degradation ratio), the susceptibility of steady-state increases at first, it reaches a maximum, and it then decreases. The magnitude of the maximum is increased with the increase of activated ratio by the upstream transcription factor.

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New chaotical image encryption algorithm based on Fisher-Yatess scrambling and DNA coding

王兴元, 张钧荐, 张付臣, 曹光辉

2019 (4): 40504-040504. doi: 10.1088/1674-1056/28/4/040504

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Based on the Fisher-Yatess scrambling and DNA coding technology, a chaotical image encryption method is proposed. First, the SHA-3 algorithm is used to calculate the hash value of the initial password, which is used as the initial value of the chaotic system. Second, the chaotic sequence and Fisher-Yatess scrambling are used to scramble the plaintext, and a sorting scrambling algorithm is used for secondary scrambling. Then, the chaotic sequence and DNA coding rules are used to change the plaintext pixel values, which makes the ciphertext more random and resistant to attacks, and thus ensures that the encrypted ciphertext is more secure. Finally, we add plaintext statistics for pixel-level diffusion to ensure plaintext sensitivity. The experimental results and security analysis show that the new algorithm has a good encryption effect and speed, and can also resist common attacks.

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Coexistence and local Mittag-Leffler stability of fractional-order recurrent neural networks with discontinuous activation functions

黄玉娇, 陈时俊, 杨旭华, 肖杰

2019 (4): 40701-040701. doi: 10.1088/1674-1056/28/4/040701

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In this paper, coexistence and local Mittag-Leffler stability of fractional-order recurrent neural networks with discontinuous activation functions are addressed. Because of the discontinuity of the activation function, Filippov solution of the neural network is defined. Based on Brouwer's fixed point theorem and definition of Mittag-Leffler stability, sufficient criteria are established to ensure the existence of (2k+3)ⁿ (k ≥ 1) equilibrium points, among which (k+2)ⁿ equilibrium points are locally Mittag-Leffler stable. Compared with the existing results, the derived results cover local Mittag-Leffler stability of both fractional-order and integral-order recurrent neural networks. Meanwhile discontinuous networks might have higher storage capacity than the continuous ones. Two numerical examples are elaborated to substantiate the effective of the theoretical results.

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Observing the steady-state visual evoked potentials with a compact quad-channel spin exchange relaxation-free magnetometer

杜鹏程, 李建军, 杨思嘉, 王旭桐, 卓彦, 王帆, 王如泉

2019 (4): 40702-040702. doi: 10.1088/1674-1056/28/4/040702

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We observed the steady-state visually evoked potential (SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free (SERF) optically pumped magnetometer (OPM). To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 fT were observed for all four channels. The corresponding signal to noise ratio (SNR) was in the range of 3.5-5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography (MEG) paradigms that require good noise cancellation. Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces (BCI).

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Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography

李建军, 杜鹏程, 伏吉庆, 王旭桐, 周庆, 王如泉

2019 (4): 40703-040703. doi: 10.1088/1674-1056/28/4/040703

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A miniature quad-channel optically pumped atomic magnetometer (OPM) has been developed based on the spin-exchange relaxation-free (SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography (MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^1/2, which is also good enough for MEG measurement. The vapor cell is heated to 160℃ by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.

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Low-lying electronic states of aluminum monoiodide

袁翔, 阴爽, 连艺, 颜培源, 徐海峰, 闫冰

2019 (4): 43101-043101. doi: 10.1088/1674-1056/28/4/043101

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High-level ab initio calculations of aluminum monoiodide (AlI) molecule are performed by utilizing the multi-reference configuration interaction plus Davidson correction (MRCI+Q) method. The core-valence correlation (CV) and spin-orbit coupling (SOC) effect are considered. The adiabatic potential energy curves (PECs) of a total of 13 Λ-S states and 24Ω states are computed. The spectroscopic constants of bound states are determined, which are in accordance with the results of the available experimental and theoretical studies. The interactions between the Λ-S states are analyzed with the aid of the spin-orbit matrix elements. Finally, the transition properties including transition dipole moment (TDM), Frank-Condon factors (FCF) and radiative lifetime are obtained based on the computed PEC. Our study sheds light on the electronic structure and spectroscopy of low-lying electronic states of the AlI molecule.

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Explicitly correlated configuration interaction investigation on low-lying states of SiO⁺ and SiO

李瑞, 梁桂颖, 林晓贺, 朱宇豪, 赵书涛, 吴勇

2019 (4): 43102-043102. doi: 10.1088/1674-1056/28/4/043102

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SiO⁺ and SiO, which play vital roles in astrophysics and astrochemistry, have long attracted considerable attention. However, accurate information about excited states of SiO⁺ is still limited. In this work, the structures of 14 Λ-S states and 30Ω states of SiO⁺ are computed with explicitly correlated configuration interaction method. On the basis of the calculated potential energy curves of those Λ-S states and Ω states, the spectroscopic constants of bound states are evaluated, which are in good agreement with the latest experimental results. The predissociation mechanism of B²Σ⁺ state is illuminated with the aid of spin-orbit coupling matrix elements. On the basis of the calculated potential energy curves and transition dipole moments, the radiative lifetime for each of low-lying vibrational states B²Σ⁺ and A²Π is estimated. The laser cooling scheme of SiO⁺ is proposed by employing B²Σ⁺-X²Σ⁺ transition. Finally, the vertical ionization energy values from SiO (X¹Σ⁺) to ionic states:SiO⁺, X²Σ⁺, B²Σ⁺, and A²Π are calculated, which agree well with experimental measurements.

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Cavity enhanced measurement of trap frequency in an optical dipole trap

杨鹏飞, 贺海, 王志辉, 韩星, 李刚, 张鹏飞, 张天才

2019 (4): 43701-043701. doi: 10.1088/1674-1056/28/4/043701

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We demonstrate a direct, fluorescence-free measurement of the oscillation frequency of cold atoms in an optical dipole trap based on a high-finesse optical cavity strongly coupled to atoms. The parametric heating spectra of the trapped atoms are obtained by recording the transmitted photons from the cavity with the trap depth is modulated by different frequency. Moreover, in our method the oscillation can be observed directly in the time scale. Being compared to the conventional fluorescence-dependent method, our approach avoids uncertainties associated with the illuminating light and auxiliary imaging optics. This method has the potential application of determining the motion of atoms with stored quantum bits or degenerate gases without destroying them.

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Laser-assisted Stark deceleration of CaF in its rovibronic ground (high-field-seeking) state

顾跃凤, 陈凯, 黄云霞, 杨晓华

2019 (4): 43702-043702. doi: 10.1088/1674-1056/28/4/043702

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A near-resonant, red-detuning laser-assisted Stark deceleration scheme is proposed to slow CaF in its high-field-seeking rovibronic ground state. The assisting Gaussian laser beam can confine CaF molecules transversely owing to the optical Stark effect. Simulations suggest that the present scheme is superior to previous Stark decelerators. Under typical experimental conditions, when the assisting laser frequency is red-detuned to the molecular transition (λ~606.3 nm) by 5.0 GHz and the laser power is about 5.6 W, the proposed decelerator can achieve a total number at the order of 10⁴ CaF molecules with a number density at the order of 10⁸ cm^-3. The equivalent temperature of the obtained cold CaF molecules is 2.3 mK. Additionally, the desired assisting laser power can be as low as about 1.2 W if keeping the red-detuning value to be 1.0 GHz, which further suggests its experimental feasibility.

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Electron self-injection and acceleration in a hollow plasma channel driven by ultrashort intense laser pulses

邓素辉, 刘明萍

2019 (4): 44101-044101. doi: 10.1088/1674-1056/28/4/044101

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The self-injection and acceleration of electrons in a hollow plasma channel driven by ultrashort intense laser pulses is investigated by Particle-in-Cell (PIC) simulations. It is shown that electrons from the bubble sheath will be self-injected into the hollow plasma channel and move radially towards the channel border due to the lack of focusing force in the hollow plasma channel. After several reflections near the channel wall by the strong focusing force, a self-injected electron bunch can be confined in the hollow plasma channel and quasi-phase-stably accelerated forward for the whole laser-plasma interaction process. These electrons using optical and plasma-related self-injection method can be self-organized to remain in the rear of the bubble, where the accelerating electric field is transversely uniform and nearly plateau along the propagation axis. Therefore, the self-injected electron bunch can be accelerated in a steady state without obvious oscillation and has a high quality with narrow energy spread and low divergence.

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A theoretical study of a plasmonic sensor comprising a gold nano-disk array on gold film with a SiO₂ spacer

王向贤, 朱剑凯, 童欢, 杨旭东, 吴枭雄, 庞志远, 杨华, 祁云平

2019 (4): 44201-044201. doi: 10.1088/1674-1056/28/4/044201

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A plasmonic refractive index (RI) sensor with high RI sensitivity based on a gold composite structure is proposed. This composite structure is constructed from a perfect gold nano-disk square array on a gold film, with a SiO₂ spacer. The reflection spectra of the composite structure, with analyte RI in the range of 1.30 to 1.40, are theoretically studied using the finite-difference time-domain method. The incident light beam is partly coupled to the localized surface plasmons (LSP) of the single nano-disks and partly transferred to the propagating surface plasmons (PSP) by grating coupling. The reflectivity is nearly zero at the valley of the reflection spectrum because of the strong coupling between LSP and PSP. Also, the full width at half maximum (FWHM) of one of the surface plasmon polaritons (SPPs) modes is very narrow, which is helpful for RI sensing. An RI sensitivity as high as 853 nm/RIU is obtained. The influence of the structure parameters on the RI sensitivity and the sensor figure of merit (FOM) are investigated in detail. We find that the sensor maintains high RI sensitivity over a large range of periods and nano-disk diameters. Results of the theoretical simulation of the composite structure as a plasmonic sensor are promising. Thus, this composite structure could be extensively applied in the fields of biology and chemistry.

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Enhancement of spatial resolution of ghost imaging via localizing and thresholding

王云龙, 周英男, 王少雄, 王斐然, 刘瑞丰, 高宏, 张沛, 李福利

2019 (4): 44202-044202. doi: 10.1088/1674-1056/28/4/044202

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In ghost imaging, an illumination light is split into test and reference beams which pass through two different optical systems respectively and an image is constructed with the second-order correlation between the two light beams. Since both light beams are diffracted when passing through the optical systems, the spatial resolution of ghost imaging is in general lower than that of a corresponding conventional imaging system. When Gaussian-shaped light spots are used to illuminate an object, randomly scanning across the object plane, in the ghost imaging scheme, we show that by localizing central positions of the spots of the reference light beam, the resolution can be increased by a factor of √2 same as that of the corresponding conventional imaging system. We also find that the resolution can be further enhanced by setting an appropriate threshold to the bucket measurement of ghost imaging.

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Quantum interferometry via a coherent state mixed with a squeezed number state

侯丽丽, 眭永兴, 王帅, 许雪芬

2019 (4): 44203-044203. doi: 10.1088/1674-1056/28/4/044203

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We theoretically investigate the phase sensitivity with parity measurement on a Mach-Zehnder interferometer with a coherent state combined with a squeezed number state. Within a constraint on the total mean photon number, we find, via parity measurement, that the mixing of a coherent state and squeezed number state can give better phase sensitivity than mixing a coherent state and squeezed vacuum state when the phase shift deviates from the optimal phase φ=0. In addition, we show that the classical Fisher information for parity measurement saturates the quantum Fisher information when the phase shift approaches to zero. Thus, the quantum Cramér-Rao bound can be reached via the parity measurement in the case of φ=0.

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Anisotropic stimulated emission cross-section measurement in Nd: YVO₄

郭瑞, 申艺杰, 孟鸢, 巩马理

2019 (4): 44204-044204. doi: 10.1088/1674-1056/28/4/044204

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As a crucial parameter in the design and analysis of laser performances, stimulated emission (SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention. In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition ⁴F_3/2→⁴I_11/2 in Nd:YVO₄ are measured in different propagating directions. Based on Fuchtbauer-Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO₄ are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.

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7.6-W diode-pumped femtosecond Yb: KGW laser

曹艳芳, 孟祥昊, 王军利, 王兆华, 程梦尧, 朱江峰, 魏志义

2019 (4): 44205-044205. doi: 10.1088/1674-1056/28/4/044205

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We have demonstrated a high power diode-pumped mode-locked femtosecond Yb:KGW laser with semiconductor saturable absorber mirror (SESAM). By using an output coupler with 10% transmittance, the laser delivered 160-fs pulses with average output power of 7.6 W at a repetition rate of 78 MHz, corresponding to pulse energy of 97 nJ and peak power of 606 kW.

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Femtosecond enhancement cavity with kilowatt average power

张津, 华林强, 余少刚, 陈忠, 柳晓军

2019 (4): 44206-044206. doi: 10.1088/1674-1056/28/4/044206

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Femtosecond enhancement cavity (fsEC) has been proved to be a powerful tool in a diverse range of applications. Here, we report the recent progresses in building an fsEC on kilowatt level average power, with the aim of realization of intracavity high harmonic generation (HHG) and extension of the wavelength of femtosecond optical frequency comb from infrared (IR) to extreme ultraviolet (XUV). Upon mode-matching optimization and cavity length locking, an intracavity average power of 6.08 kW is reached and the corresponding buildup is 225. After introducing noble gas of Xe into the focus region, clear sign of plasma has been observed. The generated HHG is also coupled out by a sapphire plate placed at Brewster's angle for the fundamental laser. Our work paves the way for the realization of an XUV comb.

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Compact 2×2 parabolic multimode interference thermo-optic switches based on fluorinated photopolymer

王继厚, 陈长鸣, 胡珂玮, 程儒, 王春雪, 衣云骥, 孙小强, 王菲, 李智勇, 张大明

2019 (4): 44207-044207. doi: 10.1088/1674-1056/28/4/044207

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In this work, a dual-side parabolic structural (DSPS) multimode interference (MMI) thermo-optic (TO) waveguide switch is designed and fabricated by using novel low-loss fluorinated photopolymer materials. Comparing with the traditional dual-side linear structural (DSLS) MMI device, the effective length of the MMI coupling region proposed can be effectively reduced by 40%. The thermal stability of the waveguide material is analyzed, and the optical characteristics of the switching chip are simulated. The actual performances of the entire MMI switch are measured with an insertion loss of 7 dB, switching power of 15 mW and an extinction ratio of 28 dB. In contrast to the traditional MMI optical switch, the new type of parabolic structural MMI TO waveguide switch exhibits lower power consumption and larger extinction ratio. The compact fluorinated polymer MMI TO switches are suitable well for realizing miniaturization, high-properties, and lower cost of photonic integrated circuits.

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Response features of nonlinear circumferential guided wave on early damage in inner layer of a composite circular tube

李明亮, 刘良兵, 高广健, 邓明晰, 胡宁, 项延训, 朱武军

2019 (4): 44301-044301. doi: 10.1088/1674-1056/28/4/044301

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A theoretical model to analyze the nonlinear circumferential guided wave (CGW) propagation in a composite circular tube (CCT) is established. The response features of nonlinear CGWs to early damage[denoted by variations in third-order elastic constants (TOECs)] in an inner layer of CCT are investigated. On the basis of the modal expansion approach, the second-harmonic field of primary CGW propagation can be assumed to be a linear sum of a series of double-frequency CGW (DFCGW) modes. The quantitative relationship of DFCGW mode versus the relative changes in the inner layer TOECs is then investigated. It is found that the changes in the inner layer TOECs of CCT will obviously affect the driving source of DFCGW mode and its modal expansion coefficient, which is intrinsically able to influence the efficiency of cumulative second-harmonic generation (SHG) by primary CGW propagation. Theoretical analyses and numerical simulations demonstrate that the second harmonic of primary CGW is monotonic and very sensitive to the changes in the inner layer TOECs of CCT, while the linear properties of primary CGW propagation almost remain unchanged. Our results provide a potential application for accurately characterizing the level of early damage in the inner layer of CCT through the efficiency of cumulative SHG by primary CGW propagation.

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Influence exerted by bone-containing target body on thermoacoustic imaging with current injection

李艳红, 刘国强, 宋佳祥, 夏慧

2019 (4): 44302-044302. doi: 10.1088/1674-1056/28/4/044302

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Thermoacoustic imaging with current injection (TAI-CI) is a novel imaging technology that couples with electromagnetic and acoustic research, which combines the advantages of high contrast of the electrical impedance tomography and the high spatial resolution of sonography, and therefore has the potential for early diagnosis. To verify the feasibility of TAI-CI for complex bone-containing biological tissues, the principle of TAI-CI and the coupling characteristics of fluid and solid were analyzed. Meanwhile, thermoacoustic (TA) effects for fluid model and fluid-solid coupling model were analyzed by numerical simulations. Moreover, we conducted experiments on animal cartilage, hard bone and biological soft tissue phantom with low conductivity (0.5 S/m). By injecting a current into the phantom, the thermoacoustic signal was detected by the ultrasonic transducer with a center frequency of 1 MHz, thereby the B-scan image of the objects was obtained. The B-scan image of the cartilage experiment accurately reflects the distribution of cartilage and gel, and the hard bone has a certain attenuation effect on the acoustic signal. However, compared with the ultrasonic imaging, the thermoacoustic signal is only attenuated during the outward propagation. Even in this case, a clear image can still be obtained and the images can reflect the change of the conductivity of the gel. This study confirmed the feasibility of TAI-CI for the imaging of biological tissue under the presence of cartilage and the bone. The novel TAI-CI method provides further evidence that it can be used in the diagnosis of human diseases.

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Wetting failure condition on rough surfaces

杨冯超, 陈效鹏

2019 (4): 44701-044701. doi: 10.1088/1674-1056/28/4/044701

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Wetting states and processes attract plenty of interest of scientific and industrial societies. Air entrainment, i.e., wetting failure, on smooth plate in wetting process has been investigated carefully before. Liquid bath entries of “rough” silicon wafers are studied experimentally in the present work, and the air entrainment condition is analyzed specially with the lubrication theory. The roughness effects on the moving contact lines are therefore explored. The contact line pinning is found to be the main reason for the dynamically enhanced hydrophobicity of rough surface, which implies an effective microscopic contact angle of θ_e=θ_Y+90° where θ_Y is the Young's contact angle of the material. Our results suggest that the solid surfaces can be considered as hydrophobic ones for a wide range of dynamic process, since they are normally rough. The work can also be considered as a starting point for investigating the high-speed advancing of moving contact line on rough surfaces.

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Investigation of convergent Richtmyer-Meshkov instability at tin/xenon interface with pulsed magnetic driven imploding

张绍龙, 刘伟, 王贵林, 章征伟, 孙奇志, 张朝辉, 李军, 池原, 张南川

2019 (4): 44702-044702. doi: 10.1088/1674-1056/28/4/044702

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The Richtmyer-Meshkov instability at the interface of solid state tin material and xenon gases under cylinder geometry is studied in this paper. The experiments were conducted at FP-1 facility in Institute of Fluid Physics, China Academy of Engineering Physics (CAEP). The FP-1 facility is a pulsed power driver which could generate high amplitude magnetic field to drive metal liner imploding. Convergent shock wave was generated by impacting a magnetic-driven aluminium liner onto a inner mounted tin liner. The convergent evolution of the disturbance pre-machined onto the tin liner's inner surface was diagnosed by x-radiography. The spike amplitudes were derived from x-ray frames and were compared with linear theory. An analytical model containing material strength effect was derived and matched well to the experimental results. This sensibility of the disturbance evolution to material strength property shines light to the application of Richtmyer-Meshkov instability to infer material strength.

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Numerical study of influence of J×B force on melt layer under conditions relevant to ITER ELMs

黄艳, 孙继忠, 蔡娟, 孙振月, 桑超峰, 王德真

2019 (4): 45201-045201. doi: 10.1088/1674-1056/28/4/045201

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The influence of the J×B force on the topographical modification of W targets during a type-I-like ELM in ITER has been studied numerically. A two-dimensional (2D) fluid dynamics model is employed by solving liquid hydrodynamic Navier-Stokes equation with the 2D heat conduction equation in addition to driving forces for surface topography, such as surface tension and pressure gradient, the J×B force is particularly addressed. The governing equations are solved with the finite volume method by adequate prediction of the moving solid-liquid interface. Numerical simulations are carried out for a range of type-I ELM characteristic parameters. Our results indicate that both the surface tension and the J×B force contributes to the melt motion of tungsten plates when the energy flux is under 3000 MW·m^-2, the surface tension is a major driving force while the pressure gradient is negligible. Our results also indicate that the J×B force makes the small hills grow at different rates at both the crater edges under a type-I-like ELM heat load with a Gaussian power density profile.

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Effect of edge transport barrier on required toroidal field for ignition of elongated tokamak

杨翠坤, 朱名盛, 郭文峰

2019 (4): 45202-045202. doi: 10.1088/1674-1056/28/4/045202

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The effect of an edge transport barrier on the toroidal field required for the ignition of an elongated tokamak is studied by modifying an analytic model which was calibrated against a transport code. It is found that the presence of the edge transport barrier will lead to a higher marginal toroidal field needed for ignition. This seemingly counter intuitive result is explained as being due to the equivalent effect of profile broadening by the edge transport barrier. This effect is further traced to its physical origin:in the case close to ignition, the fusion power input is predominantly concentrated in the center of plasma. It is demonstrated that if the fusion power input could be shifted from the center to the edge by a sufficient amount, then the presence of an edge transport barrier would lead to a reduction of the required toroidal field for ignition.

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Off-axis electron holography of manganite-based heterojunctions: Interface potential and charge distribution

令志斌, 刘桂菊, 杨成鹏, 梁文双, 王乙潜

2019 (4): 46101-046101. doi: 10.1088/1674-1056/28/4/046101

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The interfacial electrical potentials and charge distributions of two manganite-based heterojunctions, i.e., La_0.67Ca_0.33MnO₃/SrTiO₃:0.05 wt% Nb (LCMO/STON) and La_0.67Ca_0.33MnO₃/LaMnO₃/SrTiO₃:0.05 wt% Nb (simplified as LCMO/LMO/STON), are studied by means of off-axis electron holography in a transmission electron microscope. The influences of buffer layer on the microstructure and magnetic properties of the LCMO films are explored. The results show that when a buffer layer of LaMnO₃ is introduced, the tensile strain between the STON substrate and LCMO film reduces, misfit dislocation density decreases near the interfaces of the heterojunctions, and a positive magnetoresistance is observed. For the LCMO/STON junction, positive and negative charges accumulate near the interface between the substrate and the film. For the LCMO/LMO/STON junction, a complex charge distribution takes place across the interface, where notable negative charges accumulate. The difference between the charge distributions near the interface may shed light on the observed generation of positive magnetoresistance in the junction with a buffer layer.

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Delta-doped quantum wire tunnel junction for highly concentrated solar cells

Ali Bahrami, Mahyar Dehdast, Shahram Mohammadnejad, Habib Badri Ghavifekr

2019 (4): 46102-046102. doi: 10.1088/1674-1056/28/4/046102

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We propose a novel structure for tunnel junction based on delta-doped AlGaAs/GaAs quantum wires. Higher spatial confinement of quantum wires alongside the increased effective doping concentration in the delta-doped regions extremely increase the peak tunneling current and enhance the performance of tunnel junction. The proposed structure can be used as tunnel junction in the multijunction solar cells under the highest possible thermodynamically limited solar concentration. The combination of the quantum wire with the delta-doped structure can be of benefit to the solar cells' advantages including higher number of sub-bands and high degeneracy. Simulation results show a voltage drop of 40 mV due to the proposed tunnel junction used in a multijunction solar cell which presents an extremely low resistance to the achieved peak tunneling current.

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Structural evolution in deformation-induced rejuvenation in metallic glasses: A cavity perspective

江少钦, 黄勇, 李茂枝

2019 (4): 46103-046103. doi: 10.1088/1674-1056/28/4/046103

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Classical molecular dynamics simulations have been performed to investigate the structural evolution in deformation-induced rejuvenation in Cu₈₀Zr₂₀ metallic glass. Metallic glasses obtained by different cooling rates can be rejuvenated into the glassy state with almost the same potential energy by compressive deformation. The aging effect in different metallic glasses in cooling process can be completely erased by the deformation-induced rejuvenation. The evolution of cavities has been analyzed to understand the structural evolution in rejuvenation. It is found that as metallic glasses are rejuvenated by mechanical deformation, a lot of cavities are created. The lower the potential energy is, the more the cavities are created. The cavities are mainly created in the regions without cavities or with small cavities populated, indicating that the irreversible rearrangements induced by deformation are accompanied by the creation of cavity. This finding elucidates the underlying structural basis for rejuvenation and aging in metallic glasses from the cavity perspective.

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Effects of helium implantation on mechanical properties of (Al_0.31Cr_0.20Fe_0.14Ni_0.35)O high entropy oxide films

杨朝明, 张坤, 裘南, 张海斌, 汪渊, 陈坚

2019 (4): 46201-046201. doi: 10.1088/1674-1056/28/4/046201

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It is widely accepted that helium (He) bubbles can prevent dislocations from moving and causing hardening and embrittlement of the material. However, He can affect the mechanical properties of materials in various ways. In this work, ultrafine nanocrystal high entropy oxide (HEO) films with He implantation are prepared by using a radio frequency (RF) reactive magnetron sputtering system to investigate the effects of He bubbles located at grain boundary on the mechanical properties of the films. The mechanical properties of the HEO films are investigated systematically via nanoindentation measurements. The results indicate that the grain boundary cavities induced by He implantation can degrade the hardness, the elastic modulus, and the creep resistance of the HEO films. The mechanical properties of the HEO films are sensitive to the interaction between the He bubbles and the dominating defects.

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Transport properties of topological nodal-line semimetal candidate CaAs₃ under hydrostatic pressure

李婧, 赵凌霄, 王义炎, 王欣敏, 麻朝阳, 朱文亮, 高默然, 张帅, 任治安, 陈根富

2019 (4): 46202-046202. doi: 10.1088/1674-1056/28/4/046202

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We report the transport properties of the CaAs₃ single crystal, which has been predicted to be a candidate for topological nodal-line semimetals. At ambient pressure, CaAs₃ exhibits semiconducting behavior with a small gap, while in some crystals containing tiny defects or impurities, a large “hump” in the resistivity is observed around 230 K. By applying hydrostatic pressure, the samples appear to a tendency towards metallic behavior, but not fully metallized up to 2 GPa. Further high pressure studies are needed to explore the topological characteristics for CaAs₃.

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First-principles study of structural, mechanical, and electronic properties of W alloying with Zr

张宁宁, 张玉娟, 杨宇, 张平, 葛昌纯

2019 (4): 46301-046301. doi: 10.1088/1674-1056/28/4/046301

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The structural, mechanical and electronic properties of W_1-xZr_x (x=0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstrate that the W-Zr binary substitutional solid solution remaining bcc structure can be formed at an atom level. In addition, the derived bulk modulus (B), shear modulus (G), Young's modulus (E) for each of W-Zr alloys decrease gradually with the increase of Zr concentration, suggesting that W alloying with higher Zr concentration becomes softer than pure W metal. Based on the mechanical characteristic B/G ratio, Poisson's ratio ϒ and Cauchy pressure C', all W_1-xZr_x alloys are regarded as ductile materials. The ductility for each of those materials is improved with the increase of Zr concentration. The calculated density of states indicates that the ductility of W_1-xZr_x is due to the fact that the bonding in the alloy becomes more metallic through increasing the Zr concentration in tungsten. These results provide incontrovertible evidence for the fact that Zr has a significant influence on the properties of W.

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Interaction of two symmetric monovacancy defects in graphene

徐文焱, 张礼智, 黄立, 阙炎德, 王业亮, 林晓, 杜世萱

2019 (4): 46801-046801. doi: 10.1088/1674-1056/28/4/046801

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We investigate the interactions between two symmetric monovacancy defects in graphene grown on Ru (0001) after silicon intercalation by combining first-principles calculations with scanning tunneling microscopy (STM). First-principles calculations based on free-standing graphene show that the interaction is weak and no scattering pattern is observed when the two vacancies are located in the same sublattice of graphene, no matter how close they are, except that they are next to each other. For the two vacancies in different sublattices of graphene, the interaction strongly influences the scattering and new patterns' emerge, which are determined by the distance between two vacancies. Further experiments on silicon intercalated graphene epitaxially grown on Ru (0001) shows that the experiment results are consistent with the simulated STM images based on free-standing graphene, suggesting that a single layer of silicon is good enough to decouple the strong interaction between graphene and the Ru (0001) substrate.

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Tunable 2H-TaSe₂ room-temperature terahertz photodetector

王瑾, 郭程, 郭万龙, 王林, 石旺舟, 陈效双

2019 (4): 46802-046802. doi: 10.1088/1674-1056/28/4/046802

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Two-dimensional transition metal dichalcogenides (TMDs) provide fertile ground to study the interplay between dimensionality and electronic properties because they exhibit a variety of electronic phases, such as semiconducting, superconducting, charge density waves (CDW) states, and other unconventional physical properties. Compared with other classical TMDs, such as Mott insulator 1T-TaS₂ or superconducting 2H-NbSe₂, bulk 2H-TaSe₂ has been a canonical system and a touchstone for modeling the CDW measurement with a less complex phase diagram. In contrast to ordinary semiconductors that have only single-particle excitations, CDW can have collective excitation and carry current in a collective fashion. However, manipulating this collective condensation of these intriguing systems for device applications has not been explored. Here, the CDW-induced collective driven of non-equilibrium carriers in a field-effect transistor has been demonstrated for the sensitive photodetection at the highly-pursuit terahertz band. We show that the 2H-TaSe₂-based photodetector exhibits a fast photoresponse, as short as 14 μs, and a responsivity of over 27 V/W at room temperature. The fast response time, relative high responsivity and ease of fabrication of these devices yields a new prospect of exploring CDW condensate in TMDs with the aim of overcoming the existing limitations for a variety of practical applications at THz spectral range.

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Band engineering of B₂H₂ nanoribbons

雷宝, 张余洋, 杜世萱

2019 (4): 46803-046803. doi: 10.1088/1674-1056/28/4/046803

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Freestanding honeycomb borophene is unstable due to the electron-deficiency of boron atoms. B₂H₂ monolayer, a typical borophene hydride, has been predicted to be structurally stable and attracts great attention. Here, we investigate the electronic structures of B₂H₂ nanoribbons. Based on first-principles calculations, we have found that all narrow armchair nanoribbons with and without mirror symmetry (ANR-s and ANR-as, respectively) are semiconducting. The energy gap has a relation with the width of the ribbon. When the ribbon is getting wider, the gap disappears. The zigzag ribbons without mirror symmetry (ZNR-as) have the same trend. But the zigzag ribbons with mirror symmetry (ZNR-s) are always metallic. We have also found that the metallic ANR-as and ZNR-s can be switched to semiconducting by applying a tensile strain along the nanoribbon. A gap of 1.10 eV is opened under 16% strain for the 11.0-Å ANR-as. Structural stability under such a large strain has also been confirmed. The flexible band tunability of B₂H₂ nanoribbon increases its possibility of potential applications in nanodevices.

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Prediction of high-mobility two-dimensional electron gas at KTaO₃-based heterointerfaces

王芙凝, 李吉超, 李宜, 张鑫淼, 王学晋, 陈宇飞, 刘剑, 王春雷, 赵明磊, 梅良模

2019 (4): 47101-047101. doi: 10.1088/1674-1056/28/4/047101

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First-principles calculations are performed to explore the possibility of generating the two-dimensional electron gas (2DEG) at the interface between LaGaO₃/KTaO₃ and NdGaO₃/KTaO₃ (001) heterostructures. Two different models – i.e., the superlattice model and the thin film model–are used to conduct a comprehensive investigation of the origin of charge carriers. For the symmetric superlattice model, the LaGaO₃ (or NdGaO₃) film is nonpolar. The 2DEG with carrier density on the order of 10¹⁴ cm^-2 originates from the Ta d_xy electrons contributed by both LaGaO₃ (or NdGaO₃) and KTaO₃. For the thin film model, large polar distortions occur in the LaGaO₃ and NdGaO₃ layer, which entirely screens the built-in electric field and prevents electrons from transferring to the interface. Electrons of KTaO₃ are accumulated at the interface, contributing to the formation of the 2DEG. All the heterostructures exhibit conducting properties regardless of the film thickness. Compared with the Ti d_xy electrons in SrTiO₃-based heterostructures, the Ta d_xy electrons have small effective mass and they are expected to move with higher mobility along the interface. These findings reveal the promising applications of 2DEG in novel nanoelectronic devices.

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Controllable precision of the projective truncation approximation for Green's functions

范鹏, 同宁华

2019 (4): 47102-047102. doi: 10.1088/1674-1056/28/4/047102

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Recently, we developed the projective truncation approximation for the equation of motion of two-time Green's functions (Fan et al., Phys. Rev. B 97, 165140 (2018)). In that approximation, the precision of results depends on the selection of operator basis. Here, for three successively larger operator bases, we calculate the local static averages and the impurity density of states of the single-band Anderson impurity model. The results converge systematically towards those of numerical renormalization group as the basis size is enlarged. We also propose a quantitative gauge of the truncation error within this method and demonstrate its usefulness using the Hubbard-I basis. We thus confirm that the projective truncation approximation is a method of controllable precision for quantum many-body systems.

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Tunable Weyl fermions and Fermi arcs in magnetized topological crystalline insulators

刘军伟, 方辰, 傅亮

2019 (4): 47301-047301. doi: 10.1088/1674-1056/28/4/047301

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Based on k·p analysis and realistic tight-binding calculations, we find that time-reversal-breaking Weyl semimetals can be realized in magnetically-doped (Mn, Eu, Cr, etc.) Sn_1-xPb_x(Te, Se) class of topological crystalline insulators. All the Weyl points are well separated in momentum space and possess nearly the same energy due to high crystalline symmetry. Moreover, both the Weyl points and Fermi arcs are highly tunable by varying Pb/Sn composition, pressure, magnetization, temperature, surface potential, etc., opening up the possibility of manipulating Weyl points and rewiring the Fermi arcs.

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Short-gate AlGaN/GaN high-electron mobility transistors with BGaN buffer

韩铁成, 赵红东, 彭晓灿

2019 (4): 47302-047302. doi: 10.1088/1674-1056/28/4/047302

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Using the semi-insulating property and small lattice constant a of wurtzite BGaN alloy, we propose a BGaN buffer with a B-content of 1% to enhance two-dimensional electron gas (2DEG) confinement in a short-gate AlGaN/GaN high-electron mobility transistor (HEMT). Based on the two-dimensional TCAD simulation, the direct current (DC) and radio frequency (RF) characteristics of the AlGaN/GaN/B_0.01Ga_0.99N structure HEMTs are theoretically studied. Our results show that the BGaN buffer device achieves good pinch-off quality and improves RF performance compared with GaN buffer device. The BGaN buffer device can allow a good immunity to shift of threshold voltage for the aspect ratio (L_G/d) down to 6, which is much lower than that the GaN buffer device with L_G/d=11 can reach. Furthermore, due to a similar manner of enhancing 2DEG confinement, the B_0.01Ga_0.99N buffer device has similar DC and RF characteristics to those the AlGaN buffer device possesses, and its ability to control short-channel effects (SCEs) is comparable to that of an Al_0.03Ga_0.97N buffer. Therefore, this BGaN buffer with very small B-content promises to be a new method to suppress SCEs in GaN HEMTs.

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Heat treatment on phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method

崔利军, 张平祥, 李金山, 闫果, 冯勇, 刘向宏, 李建峰, 潘熙峰, 杨帆, 张胜楠, 马晓波, 刘国庆

2019 (4): 47401-047401. doi: 10.1088/1674-1056/28/4/047401

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The phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method is studied with different heat treatment parameters. The results show that the reaction temperature and phase composition of precursor powder depend on heat treatment atmosphere. Phase assemblage of (Bi,Pb)-2212, AEC, CuO, and small Bi-2201 can be obtained by heat-treated in N₂-0.1%O₂ atmosphere. For precursor powder, there is sufficient reaction process at 770℃, and the dimension of Bi-2212 phase increases rapidly with the increase of heat treatment temperature and time. The dimension of AEC phase also increases by extending heat treatment time. As a balance among phase assemblage, dimension of particle and adequate reaction, a reasonable precursor powder can be obtained by heat-treated at 770℃ for 12 h-16 h in N₂-0.1%O₂ atmosphere. Critical current of 37-filament Bi-2223 tape is about 120 A, which confirms that these heat treatment parameters are reasonable.

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Reconstruction of vector static magnetic field by different axial NV centers using continuous wave optically detected magnetic resonance in diamond

叶剑锋, 焦铮, 马堃, 黄志永, 吕海江, 蒋峰建

2019 (4): 47601-047601. doi: 10.1088/1674-1056/28/4/047601

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We carried out a proof-of-principle demonstration of the reconstruction of a static vector magnetic field involving adjacent three nitrogen-vacancy (NV) sensors with corresponding different NV symmetry axes in a bulk diamond. By means of optical detection of the magnetic resonance (ODMR) techniques, our experiment employs the continuous wave (CW) to monitor resonance frequencies and it extracts the information of the detected field strength and polar angles with respect to each NV frame of reference. Finally, the detected magnetic field relative to a fixed laboratory reference frame was reconstructed from the information acquired by the multi-NV sensor.

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Indium doping effect on properties of ZnO nanoparticles synthesized by sol-gel method

S Mourad, J El Ghoul, K Omri, K Khirouni

2019 (4): 47701-047701. doi: 10.1088/1674-1056/28/4/047701

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Pure ZnO and indium-doped ZnO (In-ZO) nanoparticles with concentrations of In ranging from 0 to 5% are synthesized by a sol-gel processing technique. The structural and optical properties of ZnO and In-ZO nanoparticles are characterized by different techniques. The structural study confirms the presence of hexagonal wurtzite phase and indicates the incorporation of In³⁺ ions at the Zn²⁺ sites. However, the optical study shows a high absorption in the UV range and an important reflectance in the visible range. The optical band gap of In-ZnO sample varies between 3.16 eV and 3.22 eV. The photoluminescence (PL) analysis reveals that two emission peaks appear:one is located at 381 nm corresponding to the near-band-edge (NBE) and the other is observed in the green region. The aim of this work is to study the effect of indium doping on the structural, morphological, and optical properties of ZnO nanoparticles.

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Optical investigation of topological semimetal SrMnSb₂

邱子阳, 廖知裕, 邱祥冈

2019 (4): 47801-047801. doi: 10.1088/1674-1056/28/4/047801

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We investigate the temperature-dependent infrared spectroscopy of SrMnSb₂, which is a semimetal with multiple Fermi surfaces. A notable blue shift of the plasma minimum in reflectivity upon cooling indicates that the carrier density varies with temperature. In the real part of the optical conductivity σ₁(ω), a linearly-increased component which extrapolates to zero conductivity at finite frequency has been identified, which suggests dispersion of gapped Dirac band structures near the Fermi level. A two-Drude model, representing two different types of carriers, is introduced to describe the real part of optical conductivity. We separate the contributions of two-Drude model in dc conductivity, and demonstrate that the transport properties of SrMnSb₂ are mainly affected by the narrow-Drude quasiparticles. Compared with the similar phenomena observed in CaMnSb₂ and SrMnBi₂, we can infer that the two-Drude model is an appropriate approach to investigate the multiband materials in AMnSb₂ and AMnBi₂ families.

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Study of glass transition kinetics of As₂S₃ and As₂Se₃ by ultrafast differential scanning calorimetry

张凡, 陈益敏, 王荣平, 沈祥, 王军强, 徐铁峰

2019 (4): 47802-047802. doi: 10.1088/1674-1056/28/4/047802

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Ultrafast differential scanning calorimetry (DSC) was employed to investigate the glass transition kinetics of As₂S₃ and As₂Se₃. By using the Arrhenius method, a fragility index of~22 can be estimated in both As₂S₃ and As₂Se₃. However, when the scanning rate is more than 200 K…^-1, non-Arrhenius behavior can be observed in such “strong” liquids where the Vogel-Fulcher method is more accurate to describe the glass transition kinetics. The fragilities of As₂S₃ and As₂Se₃ glasses are thus extrapolated as 28.3±1.94 and 23.7±1.80, respectively. This indicates that, As₂Se₃ glass has a better structural stability and it is a better candidate for device applications.

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Preparation and photoelectric properties of cadmium sulfide quantum dots

古月, 唐利斌, 郭小鹏, 项金钟, Kar Seng Teng, 刘树平

2019 (4): 47803-047803. doi: 10.1088/1674-1056/28/4/047803

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Cadmium sulfide quantum dots (CdS QDs) are widely used in solar cells, light emitting diodes, photocatalysis, and biological imaging because of their unique optical and electrical properties. However, there are some drawbacks in existing preparation techniques for CdS QDs, such as protection of inert gas, lengthy reaction time, high reaction temperature, poor crystallinity, and non-uniform particle size distribution. In this study, we prepared CdS QDs by liquid phase synthesis under ambient room temperature and atmospheric pressure using sodium alkyl sulfonate, CdCl₂, and Na₂S as capping agent, cadmium, and sulfur sources respectively. This technique offers facile preparation, efficient reaction, low-cost, and controllable particle size. The as-prepared CdS QDs exhibited good crystallinity, excellent monodispersity, and uniform particle size. The responsivity of CdS QDs-based photodetector is greater than 0.3 μA/W, which makes them suitable for use as ultra-violet (UV) detectors.

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Fullerene-based electrode interlayers for bandgap tunable organometal perovskite metal-semiconductor-metal photodetectors

罗文, 闫立志, 刘荣, 邹涛隅, 周航

2019 (4): 47804-047804. doi: 10.1088/1674-1056/28/4/047804

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Perovskite photoconductor-type photodetector with metal-semiconductor-metal (MSM) structure is a basic device for photodetection applications. However, the role of electrode interlayer in MSM-type perovskite devices is less investigated compared to that of the pin diode structure. Here, a systematic investigation on the influence of phenyl-C₆₁-butyric acid methyl ester (PCBM) and indene-C₆₀ bisadduct (ICBA) interfacial layers for MSM perovskite photodetectors is reported. It is found that the fullerene-based interlayer significantly enhances the photocurrent of the MSM photodetectors. On one hand, the PCBM interlayer is more suitable for CH₃NH₃PbI₃ photodetector, with the responsivity two times higher than that of the device with ICBA interlayer. The ICBA layer, on the other hand, becomes more effective when the band gap of perovskite is enlarged with bromine composition, denoted as CH₃NH₃Pb(I_1-xBr_x)₃ (0 ≤ x ≤ 1). It is further found that the specific detectivity of photodetectors with ICBA interlayer becomes even higher than those with PCBM when the bromine compositional percentage reaches 0.6 (x > 0.6).

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Photoelectrocatalytic oxidation of methane into methanol and formic acid over ZnO/graphene/polyaniline catalyst

刘佳, 张英华, 白智明, 黄志安, 高玉坤

2019 (4): 48101-048101. doi: 10.1088/1674-1056/28/4/048101

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ZnO/graphene/polyaniline (PANI) composite is synthesized and used for photoelectrocatalytic oxidation of methane under simulated sun light illumination with ambient conditions. The photoelectrochemical (PEC) performance of pure ZnO, ZnO/graphene, ZnO/PANI, and ZnO/graphene/PANI photoanodes is investigated by cyclic voltammetry (CV), chronoamerometry (J-t) and electrochemical impedance spectroscopy (EIS). The yields of methane oxidation products, mainly methanol (CH₃OH) and formic acid (HCOOH), catalysed by the synthesized ZnO/graphene/PANI composite are 2.76 and 3.20 times those of pure ZnO, respectively. The mechanism of the photoelectrocatalytic process converting methane into methanol and formic acid is proposed on the basis of the experimental results. The enhanced photoelectrocatalytic activity of the ZnO/graphene/PANI composite can be attributed to the fact that graphene can efficiently transfer photo-generated electrons from the inner region to the surface reaction to form free radicals due to its superior electrical conductivity as an inter-media layer. Meanwhile, the introduction of PANI promotes solar energy harvesting by extending the visible light absorption and enhances charge separation efficiency due to its conducting polymer characteristics. In addition, the PANI can create a favorable π-conjunction structure together with graphene layers, which can achieve a more effective charge separation. This research demonstrates that the fabricated ZnO/graphene/PANI composite promises to implement the visible-light photoelectrocatalytic methane oxidation.

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Density functional calculations of efficient H₂ separation from impurity gases (H₂, N₂, H₂O, CO, Cl₂, and CH₄) via bilayer g-C₃N₄ membrane

郭源, 唐春梅, 王鑫波, 王成, 付玲

2019 (4): 48102-048102. doi: 10.1088/1674-1056/28/4/048102

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Membrane technology has been used for H₂ purification. In this paper, the systematic density functional simulations are conducted to study the separation of H₂ from the impurity gases (H₂, N₂, H₂O, CO, Cl₂, and CH₄) by the bilayer porous graphitic carbon nitride(g-C₃N₄) membrane. Theoretically, the bilayer g-C₃N₄ membrane with a diameter of about 3.25 Å should be a perfect candidate for H₂ purification from these mixed gases, which is verified by the high selectivity (S) for H₂ over other kinds of gases (3.43×10²⁸ for H₂/N₂; 1.40×10²⁸ for H₂/H₂O; 1.60×10²⁶ for H₂/CO; 4.30×10¹⁴ for H₂/Cl₂; 2.50×10⁵⁵ for H₂/CH₄), and the permeance (P) of H₂ (13 mol/m²·s·Pa) across the bilayer g-C₃N₄ membrane at 300 K, which should be of great potential in energy and environmental research. Our studies highlight a new approach towards the final goal of high P and high S molecular-sieving membranes used in simple structural engineering.

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Orientation and alignment during materials processing under high magnetic fields

任忠鸣, 王江, 赵睿鑫

2019 (4): 48301-048301. doi: 10.1088/1674-1056/28/4/048301

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The characteristics of lattice structures can make crystal possess distinct anisotropic features, such as the varying magnetism in different crystal orientations and different directions. The anisotropic magnetism can also cause the free energy to vary in different orientations of crystal in a magnetic field (magnetic anisotropy energy). Magneto-anisotropy can make the crystal rotate by the magnetic force moment on the crystal with the easy axis towards the direction of the magnetic field, and can also promote the preferential growth along a certain crystal direction at the lowest energy state. By solidification, vapor-deposition, heat treatment, slip casting and electrodeposition under magnetic field, the crystal structure with high grain orientation is obtained in a variety of binary eutectics, peritectic alloys, multicomponent alloys and high temperature superconducting materials. This makes it possible to fabricate texture-functional material by using high magnetic field and magneto-crystalline anisotropy of crystal. The purpose of this article is to review some recent progress of the orientation and alignment in material processing under a high magnetic field.

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Effects of hole-injection through side-walls of large V-pits on efficiency droop in Ⅲ-nitride LEDs

张东炎, 张洁, 刘晓峰, 陈沙沙, 李慧文, 刘明庆, 叶大千, 王笃祥

2019 (4): 48501-048501. doi: 10.1088/1674-1056/28/4/048501

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Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes (LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition (MOCVD) growth of multiple quantum wells (MQWs) in Ⅲ-nitride LEDs, and thus affecting the carrier dynamics of the LEDs. Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells (QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.

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Effect of temperature on photoresponse properties of solar-blind Schottky barrier diode photodetector based on single crystal Ga₂O₃

杨超, 梁红伟, 张振中, 夏晓川, 张贺秋, 申人升, 骆英民, 杜国同

2019 (4): 48502-048502. doi: 10.1088/1674-1056/28/4/048502

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A solar-blind photodetector is fabricated on single crystal Ga₂O₃ based on vertical structure Schottky barrier diode. A Cu Schottky contact electrode is prepared in a honeycomb porous structure to increase the ultraviolet (UV) transmittance. The quantum efficiency is about 400% at 42 V. The Ga₂O₃ photodetector shows a sharp cutoff wavelength at 259 nm with high solar-blind/visible (=3213) and solar-blind/UV (=834) rejection ratio. Time-resolved photoresponse of the photodetector is investigated at 253-nm illumination from room temperature (RT) to 85.8℃. The photodetector maintains a high reversibility and response speed, even at high temperatures.

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Ultraviolet photodetectors based on wide bandgap oxide semiconductor films

周长祺, 艾秋, 陈星, 高晓红, 刘可为, 申德振

2019 (4): 48503-048503. doi: 10.1088/1674-1056/28/4/048503

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Ultraviolet (UV) photodetectors have attracted more and more attention due to their great potential applications in missile tracking, flame detecting, pollution monitoring, ozone layer monitoring, and so on. Owing to the special characteristics of large bandgap, solution processable, low cost, environmentally friendly, etc., wide bandgap oxide semiconductor materials, such as ZnO, ZnMgO, Ga₂O₃, TiO₂, and NiO, have gradually become a series of star materials in the field of semiconductor UV detection. In this paper, a review is presented on the development of UV photodetectors based on wide bandgap oxide semiconductor films.

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A primary model of decoherence in neuronal microtubules based on the interaction Hamiltonian between microtubules and plasmon in neurons

向左鲜, 唐传祥, 颜立新

2019 (4): 48701-048701. doi: 10.1088/1674-1056/28/4/048701

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Microtubules (MTs) are part of the cellular cytoskeleton and they play a role in many activities, such as cell division and maintenance of cell shape. In recent years, MTs have been thought to be involved in storing and processing information. Several models have been developed to describe the information-processing ability of MTs. In these models, MTs are considered as a device that can transmit quantum information. However, MTs are affected by the “wet and warm” cellular environment, thus it is essential to calculate the decoherence time. Many researchers have attempted to calculate this parameter but the values that have been obtained vary markedly. Previous studies considered the cellular environment as a distant ion; however, this treatment is somewhat simplified. In this study, we develop a model to determine the decoherence time in neuronal MTs while considering the interaction effects of the neuronal fluid environment. The neuronal environment is considered as a plasmon reservoir. The coupling between MTs and neuronal environment occurs due to the interaction between dipoles and plasmon. The interaction Hamiltonian is derived by using the second quantization method, and the coupling coefficient is calculated. Finally, the decoherence time scale is estimated according to the interaction Hamiltonian. In this paper, the time scale of decoherence in MTs is approximately 1 fs-100 fs. This model may be used as a reference in other decoherence processes in biological tissues.

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Cross-frequency network analysis of functional brain connectivity in temporal lobe epilepsy

于海涛, 蔡立辉, 武欣昱, 王江, 刘静, 张宏

2019 (4): 48702-048702. doi: 10.1088/1674-1056/28/4/048702

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In this study, we investigate the cross-frequency coupling and functional brain networks in the subjects with temporal lobe epilepsy (TLE) using interictal EEG signals. The phase to phase synchronization within and across frequency bands is calculated and a significant difference between the epilepsy and control groups is observed. Compared with the controls, the epilepsy patients exhibit a stronger within-frequency coupling (WFC) within theta and beta bands, and shows a stronger cross-frequency coupling (CFC) in the delta-alpha and theta-alpha band pairs, but a weakened CFC in alpha-beta band pairs. The weakened coupling between alpha and high frequency band reflects a suppression of phase modulation between the brain regions related to epilepsy. Moreover, WFC and CFC are positively correlated, which is higher in the patients relative to controls. We further reconstruct functional brain connectivity and find that both WFC and CFC networks show small-world properties. For the epilepsy, the small-world efficiency is enhanced in the CFC networks in delta-alpha and theta-alpha band pairs, whereas weakened between alpha and beta bands, which suggests a shift away from the optimal operating point in the epileptic brain with a new balance between WFC and CFC. Our results may help us to understand the important role of information communication across different frequency bands and shed new light on the study of pathology of epilepsy.

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Effect of terahertz pulse on gene expression in human eye cells

赵晋武, 何明霞, 东莉洁, 李绍限, 刘立媛, 步绍翀, 欧阳春梅, 王鹏騛, 孙珑玲

2019 (4): 48703-048703. doi: 10.1088/1674-1056/28/4/048703

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In recent years, the advances in terahertz applications have stimulated interest in the biological effects associated with this frequency range. We study the gene expression profile in three types of cells exposed to terahertz radiation, i.e., human ARPE-19 retinal pigment epithelial cells, simian virus 40-transformed human corneal epithelial cells, and human MIO-M1 Müller cells. We find that the gene expression in response to heat shock is unaffected, indicating that the minimum temperature increases under controlled environment. The transcriptome sequencing survey demonstrates that 6-hour irradiation with a broadband terahertz source results in specific change in gene expression and also the biological functions that are closely related to these genes. Our results imply that the effect of terahertz radiation on gene expression can last over 15 hours and depends on the type of cell.

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Insight into band alignment of Zn(O,S)/CZTSe solar cell by simulation

姜振武, 高守帅, 王思宇, 王东潇, 高鹏, 孙强, 周志强, 刘玮, 孙云, 张毅

2019 (4): 48801-048801. doi: 10.1088/1674-1056/28/4/048801

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Cd-free kesterite structured solar cells are currently attracting attention because they are environmentally friendly. It is reported that Zn(O,S) can be used as a buffer layer in these solar cells. However, the band alignment is not clear and the carrier concentration of Zn(O,S) layer is low. In this study, the band alignment of the Zn(O,S)/Cu₂ZnSnSe₄ p-n junction solar cell and the effect of In₂S₃/Zn(O,S) double buffer layer are studied by numerically simulation with wxAMPS software. By optimizing the band gap structure between Zn(O,S) buffer layer and Cu₂ZnSnSe₄ absorber layer and enhancing the carrier concentration of Zn(O,S) layer, the device efficiency can be improved greatly. The value of CBO is in a range of 0 eV-0.4 eV for S/(S+O)=0.6-0.8 in Zn(O,S). The In₂S₃ is mainly used to increase the carrier concentration when it is used as a buffer layer together with Zn(O,S).

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Effect of carrier mobility on performance of perovskite solar cells

顾一帆, 杜会静, 李楠楠, 杨蕾, 周春宇

2019 (4): 48802-048802. doi: 10.1088/1674-1056/28/4/048802

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The high carrier mobility and long diffusion length of perovskite material have been regarded because of its excellent photovoltaic performance. However, many studies have shown that a diffusion length longer than 1 μ and higher carrier mobility have no positive effect on the cells' performance. Studies of organic solar cells have demonstrated the existence of an optimal mobility value, while systematic research of the carrier mobility in the PSCs is very rare. To make these questions clear, the effect of carrier mobility on perovskite solar cells' performance is studied in depth in this paper by simulation. Our study shows that the optimal mobility value of the charge transportation layer and absorption layer are influenced by both doping concentration and layer thickness. The appropriate carrier mobility can reduce the carrier recombination rate and enhance the carrier concentration, thus improving the cells' performance. A high efficiency of 27.39% is obtained in the simulated cell with the combination of the optimized parameters in the paper.

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Plasma electrolytic liquefaction of sawdust

蒋匆聪, 刘诗筠, 冯哲, 方志, 张先徽, 梅丹华, 席登科, 栾秉钰, 王兴权, 杨思泽

2019 (4): 48803-048803. doi: 10.1088/1674-1056/28/4/048803

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As a renewable carbon resource, biomass can be converted into polyols, aromatic hydrocarbons, alkanes, and other products by traditional catalytic liquefaction method, which has been widely used in production and life. The efficient development and utilization of biomass energy will play a very positive role in solving the problems of energy and ecological environment. A way of combining the plasma electrolysis with traditional catalytic liquefaction realizes the efficient liquefaction of sawdust, which provides a new liquefaction way for traditional biomass conversion. In this experiment, the effects of solution composition, catalyst content and power supply on solution resistance and liquefaction rate are analyzed. It is found that solution composition and catalyst content have a great influence on solution resistance. The results show that the liquefaction rate is highest and the resistance is smallest when the solution resistance is 500 Ω. The liquefaction rate is greatly affected by the solution temperature, and the solution temperature is determined by the output power between the two electrodes. The output power includes the heating power of the electric field and the discharge power of the plasma. We measure the electric potential field distribution in the solution and the plasma power. It is found that the output power between the two poles increases nonlinearly (from 0 to 270 W) with time. In two minutes, the electric field heating power increases from 0 to 105 W and then decreases to 70 W, while the plasma power increases from 0 to 200 W. It is well known that in the first 70 seconds of the experiment the electric field heating is dominant, and then the plasma heating turns into a main thermal source. In this paper, plasma electrolysis and traditional catalytic liquefaction are combined to achieve the efficient liquefaction of sawdust, which provides a new way for biomass liquefaction.

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Traffic dynamics considering packet loss in finite buffer networks

陈杰, 陈金邕, 李明, 胡茂彬

2019 (4): 48901-048901. doi: 10.1088/1674-1056/28/4/048901

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In real complex systems, the limited storage capacity of physical devices often results in the loss of data. We study the effect of buffer size on packet loss threshold in scale-free networks. A new order parameter is proposed to characterize the packet loss threshold. Our results show that the packet loss threshold can be optimized with a relative small buffer size. Meanwhile, a large buffer size will increase the travel time. Furthermore, we propose a Buffered-Shortest-Path-First (BSPF) queuing strategy. Compared to the traditional First-In-First-Out (FIFO) strategy, BSPF can not only increase the packet loss threshold but can also significantly decrease the travel length and travel time in both identical and heterogeneous node capacity cases. Our study will help to improve the traffic performance in finite buffer networks.

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