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Chin. Phys. B  
  Chin. Phys. B--2018, Vol.27, No.3
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GENERAL

Solitary wave for a nonintegrable discrete nonlinear Schrödinger equation in nonlinear optical waveguide arrays

Li-Yuan Ma, Jia-Liang Ji, Zong-Wei Xu, Zuo-Nong Zhu
Chin. Phys. B 2018, 27 (3): 030201;  doi: 10.1088/1674-1056/27/3/030201
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We study a nonintegrable discrete nonlinear Schrödinger (dNLS) equation with the term of nonlinear nearest-neighbor interaction occurred in nonlinear optical waveguide arrays. By using discrete Fourier transformation, we obtain numerical approximations of stationary and travelling solitary wave solutions of the nonintegrable dNLS equation. The analysis of stability of stationary solitary waves is performed. It is shown that the nonlinear nearest-neighbor interaction term has great influence on the form of solitary wave. The shape of solitary wave is important in the electric field propagating. If we neglect the nonlinear nearest-neighbor interaction term, much important information in the electric field propagating may be missed. Our numerical simulation also demonstrates the difference of chaos phenomenon between the nonintegrable dNLS equation with nonlinear nearest-neighbor interaction and another nonintegrable dNLS equation without the term.

On fairness, full cooperation, and quantum game with incomplete information

Zhen-Zhou Lei, Bo-Yang Liu, Ying Yi, Hong-Yi Dai, Ming Zhang
Chin. Phys. B 2018, 27 (3): 030202;  doi: 10.1088/1674-1056/27/3/030202
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Quantum entanglement has emerged as a new resource to enhance cooperation and remove dilemmas. This paper aims to explore conditions under which full cooperation is achievable even when the information of payoff is incomplete. Based on the quantum version of the extended classical cash in a hat game, we demonstrate that quantum entanglement may be used for achieving full cooperation or avoiding moral hazards with the reasonable profit distribution policies even when the profit is uncertain to a certain degree. This research further suggests that the fairness of profit distribution should play an important role in promoting full cooperation. It is hopeful that quantum entanglement and fairness will promote full cooperation among distant people from various interest groups when quantum networks and quantum entanglement are accessible to the public.

Analytical model of tilted driver-pickup coils for eddy current nondestructive evaluation

Bing-Hua Cao, Chao Li, Meng-Bao Fan, Bo Ye, Gui-Yun Tian
Chin. Phys. B 2018, 27 (3): 030301;  doi: 10.1088/1674-1056/27/3/030301
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A driver-pickup probe possesses better sensitivity and flexibility due to individual optimization of a coil. It is frequently observed in an eddy current (EC) array probe. In this work, a tilted non-coaxial driver-pickup probe above a multilayered conducting plate is analytically modeled with spatial transformation for eddy current nondestructive evaluation. Basically, the core of the formulation is to obtain the projection of magnetic vector potential (MVP) from the driver coil onto the vector along the tilted pickup coil, which is divided into two key steps. The first step is to make a projection of MVP along the pickup coil onto a horizontal plane, and the second one is to build the relationship between the projected MVP and the MVP along the driver coil. Afterwards, an analytical model for the case of a layered plate is established with the reflection and transmission theory of electromagnetic fields. The calculated values from the resulting model indicate good agreement with those from the finite element model (FEM) and experiments, which validates the developed analytical model.

Separability criteria based on Heisenberg-Weyl representation of density matrices

Jingmei Chang, Meiyu Cui, Tinggui Zhang, Shao-Ming Fei
Chin. Phys. B 2018, 27 (3): 030302;  doi: 10.1088/1674-1056/27/3/030302
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Separability is an important problem in theory of quantum entanglement. By using the Bloch representation of quantum states in terms of the Heisenberg-Weyl observable basis, we present a new separability criterion for bipartite quantum systems. It is shown that this criterion can be better than the previous ones in detecting entanglement. The results are generalized to multipartite quantum states.

Effect of Raman-pulse duration related to the magnetic field gradient in high-precision atom gravimeters

Yuan Cheng, Yu-Jie Tan, Min-Kang Zhou, Xiao-Chun Duan, Cheng-Gang Shao, Zhong-Kun Hu
Chin. Phys. B 2018, 27 (3): 030303;  doi: 10.1088/1674-1056/27/3/030303
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The effect of the Raman-pulse duration related to the magnetic field gradient, as a systematic error, is playing an important role on evaluating the performance of high-precision atomic gravimeters. We study this effect with a simplified theoretical model of the time-propagation operator. According to the typical parameters, we find that this effect should be taken into account when the gravimeter reaches an accuracy of 10-10g, and the larger the pulse duration is, the more obvious the systematic effect will be. Finally, we make a simple discussion on the possibility of testing this effect.

The global monopole spacetime and its topological charge

Hongwei Tan, Jinbo Yang, Jingyi Zhang, Tangmei He
Chin. Phys. B 2018, 27 (3): 030401;  doi: 10.1088/1674-1056/27/3/030401
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We show that the global monopole spacetime is one of the exact solutions of the Einstein equations by treating the matter field as a non-linear sigma model, without the weak field approximation applied in the original derivation by Barriola and Vilenkin. Furthermore, we find the physical origin of the topological charge in the global monopole spacetime. Finally, we generalize the proposal which generates spacetime from thermodynamical laws to the case of spacetime with global monopole charge.

Effects of intrinsic and extrinsic noises on transposons kinetics

Alssadig A M Yousif, Lulu Lu, Mengyan Ge, Ying Xu, Ya Jia
Chin. Phys. B 2018, 27 (3): 030501;  doi: 10.1088/1674-1056/27/3/030501
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The absolute concentration robustness (ACR) steady state of a biochemical system can protect against changing a large concentration of the system's components. In this paper, a minimal model of autonomous-nonautonomous transposons driven by intrinsic and extrinsic noises is investigated. The effects of intrinsic and extrinsic noises on ACR steady state of the transposons kinetics are studied by numerical simulations. It is found that the predator-prey-like oscillations around the ACR steady state are induced by the intrinsic or extrinsic noises. Comparing with the case of intrinsic noises, the extrinsic noises can inhibit the amplitude of oscillations of transposon kinetics. To characterize the predator-prey-like oscillations, we calculate the probability distributions and the normalized correlation functions of a system in the stability domain. With the increasing of noise intensity, the peak of the probability distribution is shifted from the ACR steady state to the trivial steady state. The normalized autocorrelation and cross-correlation functions indicate that the state of the predator-prey oscillator is transmitted to 50 successive generations at least.

Image encryption technique based on new two-dimensional fractional-order discrete chaotic map and Menezes-Vanstone elliptic curve cryptosystem

Zeyu Liu, Tiecheng Xia, Jinbo Wang
Chin. Phys. B 2018, 27 (3): 030502;  doi: 10.1088/1674-1056/27/3/030502
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We propose a new fractional two-dimensional triangle function combination discrete chaotic map (2D-TFCDM) with the discrete fractional difference. Moreover, the chaos behaviors of the proposed map are observed and the bifurcation diagrams, the largest Lyapunov exponent plot, and the phase portraits are derived, respectively. Finally, with the secret keys generated by Menezes-Vanstone elliptic curve cryptosystem, we apply the discrete fractional map into color image encryption. After that, the image encryption algorithm is analyzed in four aspects and the result indicates that the proposed algorithm is more superior than the other algorithms.

Reconstruction of dynamic structures of experimental setups based on measurable experimental data only

Tian-Yu Chen, Yang Chen, Hu-Jiang Yang, Jing-Hua Xiao, Gang Hu
Chin. Phys. B 2018, 27 (3): 030503;  doi: 10.1088/1674-1056/27/3/030503
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Nowadays, massive amounts of data have been accumulated in various and wide fields, it has become today one of the central issues in interdisciplinary fields to analyze existing data and extract as much useful information as possible from data. It is often that the output data of systems are measurable while dynamic structures producing these data are hidden, and thus studies to reveal system structures by analyzing available data, i.e., reconstructions of systems become one of the most important tasks of information extractions. In the past, most of the works in this respect were based on theoretical analyses and numerical verifications. Direct analyses of experimental data are very rare. In physical science, most of the analyses of experimental setups were based on the first principles of physics laws, i.e., so-called top-down analyses. In this paper, we conducted an experiment of “Boer resonant instrument for forced vibration” (BRIFV) and inferred the dynamic structure of the experimental set purely from the analysis of the measurable experimental data, i.e., by applying the bottom-up strategy. Dynamics of the experimental set is strongly nonlinear and chaotic, and it's subjects to inevitable noises. We proposed to use high-order correlation computations to treat nonlinear dynamics; use two-time correlations to treat noise effects. By applying these approaches, we have successfully reconstructed the structure of the experimental setup, and the dynamic system reconstructed with the measured data reproduces good experimental results in a wide range of parameters.

Soliton structures in the (1+1)-dimensional Ginzburg-Landau equation with a parity-time-symmetric potential in ultrafast optics

Wenyi Li, Guoli Ma, Weitian Yu, Yujia Zhang, Mengli Liu, Chunyu Yang, Wenjun Liu
Chin. Phys. B 2018, 27 (3): 030504;  doi: 10.1088/1674-1056/27/3/030504
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In this paper, the (1+1)-dimensional variable-coefficient complex Ginzburg-Landau (CGL) equation with a parity-time (PT) symmetric potential U(x) is investigated. Although the CGL equations with a PT-symmetric potential are less reported analytically, the analytic solutions for the CGL equation are obtained with the bilinear method in this paper. Via the derived solutions, some soliton structures are presented with corresponding parameters, and the influences of them are analyzed and studied. The single-soliton structure is numerically verified, and its stability is analyzed against additive and multiplicative noises. In particular, we study the soliton dynamics under the impact of the PT-symmetric potential. Results show that the PT-symmetric potential plays an important role for obtaining soliton structures in ultrafast optics, and we can design fiber lasers and all-optical switches depending on the different amplitudes of soliton-like structures.

Hydrophobic nanochannel self-assembled by amphipathic Janus particles confined in aqueous nano-space

Gang Fang, Nan Sheng, Tan Jin, Yousheng Xu, Hai Sun, Jun Yao, Wei Zhuang, Haiping Fang
Chin. Phys. B 2018, 27 (3): 030505;  doi: 10.1088/1674-1056/27/3/030505
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Hydrophobic nanochannel plays a significant role in many physical, biological, and geological phenomena and exhibits impressive applications due to both its ubiquitous distribution and great ability to transport hydrophobic molecules, including various oils and gases. Based on theoretical modeling, we herein reveal that the amphipathic Janus nanoparticles have a large probability to self-assemble into uninterrupted hydrophobic nanochannels inside the aqueous nano-space, although there are large portions of the Janus nanoparticles to be hydrophilic. The key to this observation is the attractions between the hydrophobic regimes on neighboring amphipathic Janus particles through hydrophobic interaction in aqueous nano-space. More surprisingly, the permeation efficiency of hydrophobic molecules through the uninterrupted hydrophobic channel in Janus particles aggregate is even higher than that in the aggregate of hydrophobic particles. We note that the proposed amphipathic Janus particles can be transported to the appropriate positions by the water since the hydrophilic regimes still remain a strong particle-water interaction. We also note that most natural subsurface rocks are not completely hydrophobic or hydrophilic but have complex surfaces with inhomogeneous wetting property. Our work therefore provides a detailed molecular level understanding of the formation of underground strata as well as the new insight for constructing the artificial hydrophobic channels for various applications, such as the design of proppants to enhance the recovery of the unconventional oil/gas.

Photonic generation of RF and microwave signal with relative frequency instability of 10-15 Hot!

Lu-Lu Yan, Wen-Yu Zhao, Yan-Yan Zhang, Zhao-Yang Tai, Pan Zhang, Bing-Jie Rao, Kai Ning, Xiao-Fei Zhang, Wen-Ge Guo, Shou-Gang Zhang, Hai-Feng Jiang
Chin. Phys. B 2018, 27 (3): 030601;  doi: 10.1088/1674-1056/27/3/030601
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We demonstrate the ultra-stable frequency sources aiming to improve the short-time instability of primary frequency standards. These sources are realized by using photonic generation approach, and composed of ultra-stable lasers, optical-frequency-combs, optical signal detecting parts, and synthesizers. Preliminary evaluation shows that the sources produce fixed-frequency at 9.54(/9.63) GHz, 10 MHz, and tunable-frequency around 9.192 GHz with relative frequency instability of 10-15 for short terms.

4.3 THz quantum-well photodetectors with high detection sensitivity Hot!

Zhenzhen Zhang, Zhanglong Fu, Xuguang Guo, Juncheng Cao
Chin. Phys. B 2018, 27 (3): 030701;  doi: 10.1088/1674-1056/27/3/030701
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We demonstrate a high performance GaAs/AlGaAs-based quantum-well photodetector (QWP) device with a peak response frequency of 4.3 THz. The negative differential resistance (NDR) phenomenon is found in the dark current-voltage (I-V) curve in the current sweeping measurement mode, from which the breakdown voltage is determined. The photocurrent spectra and blackbody current responsivities at different voltages are measured. Based on the experimental data, the peak responsivity of 0.3 A/W (at 0.15 V, 8 K) is derived, and the detection sensitivity is higher than 1011 Jones, which is in the similar level as that of the commercialized liquid-helium-cooled silicon bolometers. We attribute the high detection performance of the device to the small ohmic contact resistance of ~2Ω and the big breakdown bias.

Weak wide-band signal detection method based on small-scale periodic state of Duffing oscillator

Jian Hou, Xiao-peng Yan, Ping Li, Xin-hong Hao
Chin. Phys. B 2018, 27 (3): 030702;  doi: 10.1088/1674-1056/27/3/030702
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The conventional Duffing oscillator weak signal detection method, which is based on a strong reference signal, has inherent deficiencies. To address these issues, the characteristics of the Duffing oscillator's phase trajectory in a small-scale periodic state are analyzed by introducing the theory of stopping oscillation system. Based on this approach, a novel Duffing oscillator weak wide-band signal detection method is proposed. In this novel method, the reference signal is discarded, and the to-be-detected signal is directly used as a driving force. By calculating the cosine function of a phase space angle, a single Duffing oscillator can be used for weak wide-band signal detection instead of an array of uncoupled Duffing oscillators. Simulation results indicate that, compared with the conventional Duffing oscillator detection method, this approach performs better in frequency detection intervals, and reduces the signal-to-noise ratio detection threshold, while improving the real-time performance of the system.

Demonstration of multi-Watt all-fiber superfluorescent source operating near 980 nm

Yankun Ren, Jianqiu Cao, Hanyuan Ying, Heng Chen, Zhiyong Pan, Shaojun Du, Jinbao Chen
Chin. Phys. B 2018, 27 (3): 030703;  doi: 10.1088/1674-1056/27/3/030703
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The superfluorescent Yb-doped fiber source operating near 980 nm is studied. The design requirement is theoretically discussed aiming to suppress the amplified spontaneous emission around 1030 nm in the 980-nm superfluorescent fiber source. Based on the theoretical study, a multi-Watt, all-fiber, bi-directional, pumped, superfluorescent source operating near 980 nm is designed and experimentally demonstrated for the first time, to the best of our knowledge. The recorded 8.38-W combined output power is obtained with a 3-dB bandwidth about 3.5 nm. The power scaling of the 980-nm superfluorescent fiber source is limited by the parasitic laser oscillation.
TOPIC REVIEW—Thermal and thermoelectric properties of nano materials
ATOMIC AND MOLECULAR PHYSICS

Ab-initio calculations of structural, electronic, and optical properties of Zn3(VO4)2

Nisar Ahmed, S Mukhtar, Wei Gao, Syed Zafar Ilyas
Chin. Phys. B 2018, 27 (3): 033101;  doi: 10.1088/1674-1056/27/3/033101
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The structural, electronic, and optical properties of Zn3(VO4)2 are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). Various approaches are adopted to treat the exchange and correlation potential energy such as generalized gradient approximation (GGA), GGA+U, and the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The calculated band gap of 3.424 eV by TB-mBJ is found to be close to the experimental result (3.3 eV). The optical anisotropy is analyzed through optical constants, such as dielectric function and absorption coefficient along parallel and perpendicular crystal orientations. The absorption coefficient reveals high absorption (1.5×106 cm-1) of photons in the ultraviolet region.

Exploration of strong-field double ionization of C3H6 with the structures of propene and cyclopropane in intense laser fields

Qing-Yun Xu, Yan-Rong Tian, Hui-Zhong Lu, Jun Zhang, Tong-Tong Xu, Hong-Dan Zhang, Xue-Shen Liu, Jing Guo
Chin. Phys. B 2018, 27 (3): 033202;  doi: 10.1088/1674-1056/27/3/033202
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By using classical ensemble method, we investigate the double ionization of C3H6 molecule with different structures (propene and cyclopropane) in intense laser fields. The numerical results show that the non-sequential double ionization occurs in propene molecule rather than cyclopropane molecule in 1200 nm laser field. To further explain this interesting phenomenon, the momentum distribution of double ionized electrons is presented and the result presents the “finger-like” structure at about 30 TW/cm2 of propene molecule, and this structure is more obvious than that in cyclopropane molecule. The above phenomena are also demonstrated by analysing the energy distributions of double-ionized electrons versus time. Moreover, we also investigated the angular distribution at the end of pulse, which is different between propene and cyclopropane.

Influence factor analysis of field-free molecular orientation

Jing-Song Liu, Qi-Yuan Cheng, Da-Guang Yue, Xu-Cong Zhou, Qing-Tian Meng
Chin. Phys. B 2018, 27 (3): 033301;  doi: 10.1088/1674-1056/27/3/033301
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The effects of the characteristics of molecules and external fields on field-free molecular orientation are investigated through the comparison of HBr with LiH driven by the combination of a two-color laser pulse and a time-delayed THz laser pulse. It is shown that the dipole interaction has greater influence on field-free orientation than the hyperpolarizability interaction. In addition to the temperature dependence of orientation degree, the effects of the amplitudes of the two-color laser pulse and THz laser pulse, rising time, and THz laser frequency on molecular orientation are also discussed.

Solvent effects and potential of mean force study of the SN2 reaction of CH3F+CN- in water

Chen Li, Peng Liu, Yongfang Li, Dunyou Wang
Chin. Phys. B 2018, 27 (3): 033401;  doi: 10.1088/1674-1056/27/3/033401
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We used a combined quantum mechanics and molecular mechanics (QM/MM) method to investigate the solvent effects and potential of mean force of the CH3F+CN- reaction in water. Comparing to gas phase, the water solution substantially affects the structures of the stationary points along the reaction path. We quantitatively obtained the solvent effects' contributions to the reaction:1.7 kcal/mol to the activation barrier and -26.0 kcal/mol to the reaction free energy. The potential mean of force calculated with the density functional theory/MM theory has a barrier height at 19.7 kcal/mol, consistent with the experimental result at 23.0 kcal/mol; the calculated reaction free energy at -43.5 kcal/mol is also consistent with the one estimated based on the gas-phase data at -39.7 kcal/mol.

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

Further analysis of scintillation index for a laser beam propagating through moderate-to-strong non-Kolmogorov turbulence based on generalized effective atmospheric spectral model

Jing Ma, Yu-Long Fu, Si-Yuan Yu, Xiao-Long Xie, Li-Ying Tan
Chin. Phys. B 2018, 27 (3): 034201;  doi: 10.1088/1674-1056/27/3/034201
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A new expression of the scintillation index (SI) for a Gaussian-beam wave propagating through moderate-to-strong non-Kolmogorov turbulence is derived, using a generalized effective atmospheric spectrum and the extended Rytov approximation theory. Finite inner and outer scale parameters and high wave number “bump” are considered in the spectrum with a generalized spectral power law in the range of 3-4, instead of the fixed classical Kolmogorov power law of 11/3. The obtained SI expression is then used to analyze the effects of the spectral power law and the inner scale and outer scale on SI under various non-Kolmogorov fluctuation conditions. These results will be useful in future investigations of optical wave propagation through atmospheric turbulence.

Optical encryption of multiple three-dimensional objects based on multiple interferences and single-pixel digital holography

Ying Wang, Qi Liu, Jun Wang, Qiong-Hua Wang
Chin. Phys. B 2018, 27 (3): 034202;  doi: 10.1088/1674-1056/27/3/034202
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We present an optical encryption method of multiple three-dimensional objects based on multiple interferences and single-pixel digital holography. By modifying the Mach-Zehnder interferometer, the interference of the multiple objects beams and the one reference beam is used to simultaneously encrypt multiple objects into a ciphertext. During decryption, each three-dimensional object can be decrypted independently without having to decrypt other objects. Since the single-pixel digital holography based on compressive sensing theory is introduced, the encrypted data of this method is effectively reduced. In addition, recording fewer encrypted data can greatly reduce the bandwidth of network transmission. Moreover, the compressive sensing essentially serves as a secret key that makes an intruder attack invalid, which means that the system is more secure than the conventional encryption method. Simulation results demonstrate the feasibility of the proposed method and show that the system has good security performance.

Implication of two-coupled tri-stable stochastic resonance in weak signal detection

Quan-Quan Li, Xue-Mei Xu, Lin-Zi Yin, Yi-Peng Ding, Jia-Feng Ding, Ke-Hui Sun
Chin. Phys. B 2018, 27 (3): 034203;  doi: 10.1088/1674-1056/27/3/034203
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Stochastic resonance (SR) has been proved to be an effective approach to extract weak signals overwhelmed in noise. However, the detection effect of current SR models is still unsatisfactory. Here, a coupled tri-stable stochastic resonance (CTSSR) model is proposed to further increase the output signal-to-noise ratio (SNR) and improve the detection effect of SR. The effects of parameters a, b, c, and r in the proposed resonance system on the SNR are studied, by which we determine a set of parameters that is relatively optimal to implement a comparison with other classical SR models. Numerical experiment results indicate that this proposed model performs better in weak signal detection applications than the classical ones with merits of higher output SNR and better anti-noise capability.

Multi-window transparency and fast-slow light switching in a quadratically coupled optomechanical system assisted with three-level atoms

Wan-Ying Wei, Ya-Fei Yu, Zhi-Ming Zhang
Chin. Phys. B 2018, 27 (3): 034204;  doi: 10.1088/1674-1056/27/3/034204
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We study theoretically the features of the output field of a quadratically coupled optomechanical system assisted with three-level atoms. In this system, the atoms interact with the cavity field and are driven by a classical field, and the cavity is driven by a strong coupling field and a weak signal field. We find that there exists a multi-window transparency phenomenon. The width of the transparent windows can be adjusted by controlling the system parameters, including the number of the atoms, the powers of the lasers driving the atoms and driving the cavity, and the environment temperature. We also find that a tunable switch from fast light to slow light can be realized in this system.

Optomechanically induced transparency with Bose–Einstein condensate in double-cavity optomechanical system

Li-Wei Liu, Duo-Jie Gengzang, Xiu-Jia An, Pei-Yu Wang
Chin. Phys. B 2018, 27 (3): 034205;  doi: 10.1088/1674-1056/27/3/034205
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We propose a novel technique of generating multiple optomechanically induced transparency (OMIT) of a weak probe field in hybrid optomechanical system. This system consists of a cigar-shaped Bose-Einstein condensate (BEC), trapped inside each high finesse Fabry-Pérot cavity. In the resolved sideband regime, the analytic solutions of the absorption and the dispersion spectrum are given. The tunneling strength of the two resonators and the coupling parameters of the each BEC in combination with the cavity field have the appearance of three distinct OMIT windows in the absorption spectrum. Furthermore, whether there is BEC in each cavity is a key factor in the number of OMIT windows determination. The technique presented may have potential applications in quantum engineering and quantum information networks.

Effect of multiple rescattering processes on harmonic emission in spatially inhomogeneous field

Cai-Ping Zhang, Chang-Long Xia, Xiang-Fu Jia, Xiang-Yang Miao
Chin. Phys. B 2018, 27 (3): 034206;  doi: 10.1088/1674-1056/27/3/034206
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The effect of multiple rescattering processes on the harmonic emission from He atom in a spatially inhomogeneous field is discussed by solving the one-dimensional time-dependent Schrödinger equation and the classical equation of motion. By establishing the physical model of the harmonic emission in the inhomogeneous field, we discuss the related characters of the multiple rescatterings process in the harmonic generation process. It shows that the second rescattering rather than the first rescattering tends to determine the harmonic cutoff energy when the inhomogeneous parameter is larger than 0.0055. Additionally, with the classical simulation, the underlying physical mechanism of the continuum-continuum harmonics is also revealed. Moreover, this work may provide new physical insight into the harmonic generation in an inhomogeneous field, and is beneficial to further extract the harmonic emission from molecular systems.

Enhanced second harmonic generation in a two-dimensional optical micro-cavity

Jian-Jun Zhang, Hui-Fang Wang, Jun-Hua Hou
Chin. Phys. B 2018, 27 (3): 034207;  doi: 10.1088/1674-1056/27/3/034207
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We introduce a two-dimensional Bose-Einstein condensation model consisting of massive photon and photon-pair. Based on the new nonlinear model, the traditional process of second harmonics generation is reinvestigated. In order to describe the process, a new quantum phase, the harmonic phase, is introduced. The order parameter of the new physical phase is also given in this paper.

Random phase screen influence of the inhomogeneous tissue layer on the generation of acoustic vortices

Zhiyao Ma, Jun Ma, Dong Zhang, Juan Tu
Chin. Phys. B 2018, 27 (3): 034301;  doi: 10.1088/1674-1056/27/3/034301
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The influence of the inhomogeneous tissue layer on the generation of acoustic vortices (AV) is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phase screen, the formula of acoustic pressure for the AV beam generated by a circular array of eight planar piston sources is derived. With the actual correlation length of the abdominal wall, numerical simulations before and after the insertion of the inhomogeneous tissue layer are conducted, and also demonstrated by experimental measurements. It is proved that, when the thickness variation of the phase screen is less than one wavelength, no significant influence on the generation of AVs can be produced. The variations of vortex nodes and antinodes in terms of the location, shape, and size of AVs are not obvious. Although the circular pressure distribution might be deformed by the phase interference with a larger thickness variation, AVs can still be generated around the center axis with perfect phase spirals in a reduced effective radius. The favorable results provide the feasibility of AV generation inside the human body and suggest the application potential of AVs in object manipulation for biomedical engineering.

Acoustic radiation force on a multilayered sphere in a Gaussian standing field

Haibin Wang, Xiaozhou Liu, Sha Gao, Jun Cui, Jiehui Liu, Aijun He, Gutian Zhang
Chin. Phys. B 2018, 27 (3): 034302;  doi: 10.1088/1674-1056/27/3/034302
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We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach. An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid. The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed, with particular emphasis on the shell thickness of every layer, and the width of the Gaussian beam. The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka, as well as the shell thickness of each layer. This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave, which may benefit the improvement and development of acoustic control technology, such as trapping, sorting, and assembling a cell, and drug delivery applications.

Numerical analysis of plasma arc physical characteristics under additional constraint of keyhole

Bin Xu, Fan Jiang, Shujun Chen, Manabu Tanaka, Shinichi Tashiro, Nguyen Van Anh
Chin. Phys. B 2018, 27 (3): 034701;  doi: 10.1088/1674-1056/27/3/034701
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The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding (KPAW). There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration. Therefore, in order to obtain the temperature field, flow field, and arc pressure of a plasma arc under the reaction of the keyhole, the physical model of a plasma arc with a pre-set keyhole was established. In addition, the tungsten and base metal were established into the calculated domain, which can reflect the effect of plasma arc to weld pool further. Based on magneto hydrodynamics and Maxwell equations, a two-dimensional steady state mathematical model was established. Considering the heat production of anode and cathode, the distribution of temperature field, flow field, welding current density, and plasma arc pressure were solved out by the finite difference method. From the calculated results, it is found that the plasma arc was compressed a second time by the keyhole. This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole, while the temperature field is impacted slightly. Finally, the observational and metallographic experiments are conducted, and the shapes of plasma arc and fusion line agree with the simulated results generally.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Laser-driven relativistic electron dynamics in a cylindrical plasma channel

Pan-Fei Geng, Wen-Juan Lv, Xiao-Liang Li, Rong-An Tang, Ju-Kui Xue
Chin. Phys. B 2018, 27 (3): 035201;  doi: 10.1088/1674-1056/27/3/035201
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The energy and trajectory of the electron, which is irradiated by a high-power laser pulse in a cylindrical plasma channel with a uniform positive charge and a uniform negative current, have been analyzed in terms of a single-electron model of direct laser acceleration. We find that the energy and trajectory of the electron strongly depend on the positive charge density, the negative current density, and the intensity of the laser pulse. The electron can be accelerated significantly only when the positive charge density, the negative current density, and the intensity of the laser pulse are in suitable ranges due to the dephasing rate between the wave and electron motion. Particularly, when their values satisfy a critical condition, the electron can stay in phase with the laser and gain the largest energy from the laser. With the enhancement of the electron energy, strong modulations of the relativistic factor cause a considerable enhancement of the electron transverse oscillations across the channel, which makes the electron trajectory become essentially three-dimensional, even if it is flat at the early stage of the acceleration.

Areal density and spatial resolution of high energy electron radiography

Jiahao Xiao, Zimin Zhang, Shuchun Cao, Ping Yuan, Xiaokang Shen, Rui Cheng, Quantang Zhao, Yang Zong, Ming Liu, Xianming Zhou, Zhongping Li, Yongtao Zhao, Chuanxiang Tang, Wenhui Huang, Yingchao Du, Wei Gai
Chin. Phys. B 2018, 27 (3): 035202;  doi: 10.1088/1674-1056/27/3/035202
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Ultrafast imaging tools are of great importance for determining the dynamic density distribution in high energy density (HED) matter. In this work, we designed a high energy electron radiography (HEER) system based on a linear electron accelerator to evaluate its capability for imaging HED matter. 40 MeV electron beams were used to image an aluminum target to study the density resolution and spatial resolution of HEER. The results demonstrate a spatial resolution of tens of micrometers. The interaction of the beams with the target and the beam transport of the transmitted electrons are further simulated with EGS5 and PARMELA codes, with the results showing good agreement with the experimental resolution. Furthermore, the experiment can be improved by adding an aperture at the Fourier plane.

Experimental investigation on electrical characteristics and ignition performance of multichannel plasma igniter

Sheng-Fang Huang, Hui-Min Song, Yun Wu, Min Jia, Di Jin, Zhi-Bo Zhang, Bing-Xuan Lin
Chin. Phys. B 2018, 27 (3): 035203;  doi: 10.1088/1674-1056/27/3/035203
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Relighting of jet engines at high altitudes is very difficult because of the high velocity, low pressure, and low temperature of the inlet airflow. Successful ignition needs sufficient ignition energy to generate a spark kernel to induce a so-called critical flame initiation radius. However, at high altitudes with high-speed inlet airflow, the critical flame initiation radius becomes larger; therefore, traditional ignition technologies such as a semiconductor igniter (SI) become infeasible for use in high-altitude relighting of jet engines. In this study, to generate a large spark kernel to achieve successful ignition with high-speed inlet airflow, a new type of multichannel plasma igniter (MCPI) is proposed. Experiments on the electrical characteristics of the MCPI and SI were conducted under normal and sub-atmospheric pressures (P=10-100 kPa). Ignition experiments for the MCPI and SI with a kerosene/air mixture in a triple-swirler combustor under different velocities of inlet airflow (60-110 m/s), with a temperature of 473 K at standard atmospheric pressure, were investigated. Results show that the MCPI generates much more arc discharge energy than the SI under a constant pressure; for example, the MCPI generated 6.93% and 16.05% more arc discharge energy than that of the SI at 30 kPa and 50 kPa, respectively. Compared to the SI, the MCPI generates a larger area and height of plasma heating zone, and induces a much larger initial spark kernel. Furthermore, the lean ignition limit of the MCPI and SI decreases with an increase in the velocity of the inlet airflow, and the maximum velocity of inlet airflow where the SI and MCPI can achieve successful and reliable ignition is 88.7 m/s and 102.2 m/s, respectively. Therefore, the MCPI has the advantage of achieving successful ignition with high-speed inlet airflow and extends the average ignition speed boundary of the kerosene/air mixture by 15.2%.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Structural phase transition, strength, and texture in vanadium at high pressure under nonhydrostatic compression

Lun Xiong, Jing Liu
Chin. Phys. B 2018, 27 (3): 036101;  doi: 10.1088/1674-1056/27/3/036101
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The structural phase transition, strength, and texture of vanadium have been studied under nonhydrostatic compression up to 70 GPa using an angle-dispersive radial x-ray diffraction technique in a 2-fold paranomic diamond anvil cell and up to 38 GPa using an angle-dispersive x-ray diffraction technique in a modified Mao-Bell diamond anvil cell at room temperature. We have confirmed a phase transition from body-centered cubic structure to rhombohedral structure at 27-32 GPa under nonhydrostatic compression. The radial x-ray diffraction data yields a bulk modulus K0=141(5) GPa and its pressure derivative K'0=5.4(7) for the bcc phase and K0=154(13) GPa with K'0=3.8(3) for the rhombohedral phase at ψ=54.7°. The nonhydrostatic x-ray diffraction data of both bcc and rhombohedral phases yields a bulk modulus K0=188(5) GPa with K'0=2.1(3). Combined with the independent constraints on the high-pressure shear modulus, it is found that the vanadium sample can support a differential stress of ~1.6 GPa when it starts to yield with plastic deformation at ~36 GPa. A maximum differential stress as high as ~1.7 GPa can be supported by vanadium at the pressure of ~47 GPa. In addition, we have investigated the texture up to 70 GPa using the software package MAUD. It is convinced that the body-centered cubic to rhombohedral phase transition and plastic deformation due to stress under high pressures are responsible for the development of texture.

Estimation of enhanced low dose rate sensitivity mechanisms using temperature switching irradiation on gate-controlled lateral PNP transistor

Xiao-Long Li, Wu Lu, Xin Wang, Xin Yu, Qi Guo, Jing Sun, Mo-Han Liu, Shuai Yao, Xin-Yu Wei, Cheng-Fa He
Chin. Phys. B 2018, 27 (3): 036102;  doi: 10.1088/1674-1056/27/3/036102
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The mechanisms occurring when the switched temperature technique is applied, as an accelerated enhanced low dose rate sensitivity (ELDRS) test technique, are investigated in terms of a specially designed gate-controlled lateral PNP transistor (GLPNP) that used to extract the interface traps (Nit) and oxide trapped charges (Not). Electrical characteristics in GLPNP transistors induced by 60Co gamma irradiation are measured in situ as a function of total dose, showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP. Based on the analysis of the variations of Nit and Not, with switching the temperature, the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation. Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup. In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP, which provides us with a new insight into the test technique for ELDRS.

First principles study of ceramic materials (IVB group carbides) under ultrafast laser irradiation

Nan-Lin He, Xin-Lu Cheng, Hong Zhang, Gai-Qin Yan, Jia Zhang
Chin. Phys. B 2018, 27 (3): 036301;  doi: 10.1088/1674-1056/27/3/036301
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Group IVB carbides have been applied in extreme aerospace environments as hard ceramic coatings; ZrC is being considered as a replacement for SiC in nuclear reactors. Therefore, a thorough understanding of the laser irradiation response of group IVB carbides is of clear significance. However, the existing knowledge on the fundamental properties of IVB group carbides is limited and insufficient with regard to both irradiated and non-irradiated characteristics. We investigate the effect of ultrafast laser irradiation on the lattice stability of ceramic materials (IVB group carbides) using the density functional perturbation theory (DFPT). The calculated phonon frequencies of TiC and ZrC at the ground state are in good agreement with previous calculations and experimental values. The phonon frequencies of IVB group carbides are positive, even though the electronic temperature reached 5 eV. Thus, IVB group carbides are more stable under ultrafast laser irradiation, which has greater benefits in nuclear and aeronautical applications compared to metals (W, Na), semimetals (Bi), and semiconductors (Si, SiC). The thermodynamic properties of ZrC are calculated as functions of their lattice temperature at different electronic temperatures. The elastic shear constants of IVB group carbides satisfy the Born stability criteria at Te=5 eV. In addition, a comparison of the predicted melting temperatures of IVB group carbides, reveal that HfC is better suited for extreme high-temperature environments.

Power flow analysis in a hybrid phononic crystal structure

Hanbei Guo, Qiang Li, Liubin Zhou, Lei Qiang
Chin. Phys. B 2018, 27 (3): 036302;  doi: 10.1088/1674-1056/27/3/036302
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To reveal the energy transmission through a hybrid phononic crystal structure, power flow analysis is carried out in this paper. Hysteretic damping having significant relationship with power flow is added and corresponding theoretical formulas of the dispersion relation are derived. Besides, the power flow in the hybrid structure is calculated by using the finite element method. The results show that as the damping increases, the boundaries of the band gaps become smoother and dimmer, i.e., broader width. With the increase of damping, the power flow is lowered at the resonance frequencies, while slightly increases near the resonance frequencies. The power flow maps manifest energy distribution in the hybrid structure within and out of the band gaps, which can be exploited in the optimization of the structure design.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Phase diagram, correlations, and quantum critical point in the periodic Anderson model Hot!

Jian-Wei Yang, Qiao-Ni Chen
Chin. Phys. B 2018, 27 (3): 037101;  doi: 10.1088/1674-1056/27/3/037101
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Periodic Anderson model is one of the most important models in the field of strongly correlated electrons. With the recent developed numerical method density matrix embedding theory, we study the ground state properties of the periodic Anderson model on a two-dimensional square lattice. We systematically investigate the phase diagram away from half filling. We find three different phases in this region, which are distinguished by the local moment and the spin-spin correlation functions. The phase transition between the two antiferromagnetic phases is of first order. It is the so-called Lifshitz transition accompanied by a reconstruction of the Fermi surface. As the filling is close to half filling, there is no difference between the two antiferromagnetic phases. From the results of the spin-spin correlation, we find that the Kondo singlet is formed even in the antiferromagnetic phase.

First-principles investigations of proton generation in α-quartz

Yunliang Yue, Yu Song, Xu Zuo
Chin. Phys. B 2018, 27 (3): 037102;  doi: 10.1088/1674-1056/27/3/037102
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Proton plays a key role in the interface-trap formation that is one of the primary reliability concerns, thus learning how it behaves is key to understand the radiation response of microelectronic devices. The first-principles calculations have been applied to explore the defects and their reactions associated with the proton release in α -quartz, the well-known crystalline isomer of amorphous silica. When a high concentration of molecular hydrogen (H2) is present, the proton generation can be enhanced by cracking the H2 molecules at the positively charged oxygen vacancies in dimer configuration. If the concentration of molecular hydrogen is low, the proton generation mainly depends on the proton dissociation of the doubly-hydrogenated defects. In particular, a fully passivated E'2 center can dissociate to release a proton barrierlessly by structure relaxation once trapping a hole. This research provides a microscopic insight into the proton release in silicon dioxide, the critical step associated with the interface-trap formation under radiation in microelectronic devices.

Magnetism, optical, and thermoelectric response of CdFe2O4 by using DFT scheme

Q Mahmood, M Yaseen, K C Bhamu, Asif Mahmood, Y Javed, Shahid M Ramay
Chin. Phys. B 2018, 27 (3): 037103;  doi: 10.1088/1674-1056/27/3/037103
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Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe2O4, calculated by employing PBEsol+mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John-Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electrical and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe2O4 as the potential candidate for renewable energy applications.

Structural, electronic, elastic, and thermal properties of CaNiH3 perovskite obtained from first-principles calculations

S Benlamari, H Bendjeddou, R Boulechfar, S Amara Korba, H Meradji, R Ahmed, S Ghemid, R Khenata, S Bin Omran
Chin. Phys. B 2018, 27 (3): 037104;  doi: 10.1088/1674-1056/27/3/037104
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A theoretical study of the structural, elastic, electronic, mechanical, and thermal properties of the perovskite-type hydride CaNiH3 is presented. This study is carried out via first-principles full potential (FP) linearized augmented plane wave plus local orbital (LAPW+lo) method designed within the density functional theory (DFT). To treat the exchange-correlation energy/potential for the total energy calculations, the local density approximation (LDA) of Perdew-Wang (PW) and the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) are used. The three independent elastic constants (C11, C12, and C44) are calculated from the direct computation of the stresses generated by small strains. Besides, we report the variation of the elastic constants as a function of pressure as well. From the calculated elastic constants, the mechanical character of CaNiH3 is predicted. Pertaining to the thermal properties, the Debye temperature is estimated from the average sound velocity. To further comprehend this compound, the quasi-harmonic Debye model is used to analyze the thermal properties. From the calculations, we find that the obtained results of the lattice constant (a0), bulk modulus (B0), and its pressure derivative (B'0) are in good agreement with the available theoretical as well as experimental results. Similarly, the obtained electronic band structure demonstrates the metallic character of this perovskite-type hydride.

Effect of P impurity on mechanical properties of NiAlΣ5 grain boundary: From perspectives of stress and energy

Xue-Lan Hu, Ruo-Xi Zhao, Jiang-Ge Deng, Yan-Min Hu, Qing-Gong Song
Chin. Phys. B 2018, 27 (3): 037105;  doi: 10.1088/1674-1056/27/3/037105
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In this paper, we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiAl grain boundary (GB). According to “energy”, the segregation of P atom in NiAlΣ5 GB reduces the cleavage energy and embrittlement potential, demonstrating that P impurity embrittles NiAlΣ5 GB. The first-principle computational tensile test is conducted to determine the theoretical tensile strength of NiAlΣ5 GB. It is demonstrated that the maximum ideal tensile strength of NiAlΣ5 GB with P atom segregation is 144.5 GPa, which is lower than that of the pure NiAlΣ5 GB (164.7 GPa). It is indicated that the segregation of P weakens the theoretical strength of NiAlΣ5 GB. The analysis of atomic configuration shows that the GB fracture is caused by the interfacial bond breaking. Moreover, P is identified to weaken the interactions between Al-Al bonds and enhance Ni-Ni bonds.

Spin flip in single quantum ring with Rashba spin-orbit interation

Duan-Yang Liu, Jian-Bai Xia
Chin. Phys. B 2018, 27 (3): 037201;  doi: 10.1088/1674-1056/27/3/037201
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We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin-orbit interaction. It is shown that when Rashba spin-orbit interaction is relatively weak, a single circular ring can not realize spin flip, however an elliptical ring may work as a spin-inverter at this time, and the influence of the defect of the geometry is not obvious. Howerver if a giant Rashba spin-orbit interaction strength has been obtained, a circular ring can work as a spin-inverter with a high stability.

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

Runrun Hao, Hai Zhong, Yun Kang, Yufei Tian, Shishen Yan, Guolei Liu, Guangbing Han, Shuyun Yu, Liangmo Mei, Shishou Kang
Chin. Phys. B 2018, 27 (3): 037202;  doi: 10.1088/1674-1056/27/3/037202
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The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents (σsc), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe20Ni80 (Py) than that of Ni is obtained from the nonlocal voltage measurements.

Electro-statically controllable graphene local heater

Hui-Shan Wang, Lian-Wen Deng, Lei Li, Qiu-Juan Sun, Hong Xie, Hao-Min Wang
Chin. Phys. B 2018, 27 (3): 037203;  doi: 10.1088/1674-1056/27/3/037203
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We report on current-induced thermal power investigation of graphene nanostructure for potential local-heating applications. It is found that the efficiency of heating can be greatly improved if graphene is patterned into structures with narrow width and long channel. In a narrow graphene-ribbon, the Joule heating power exhibits an obvious dependence on the back-gate voltage. By monitoring Raman spectra, the temperature of graphene-ribbon can be determined. The temperature of graphene-ribbon is modulated by the electric field effect when the sample is sourced with a relatively high current.

Distinct edge states and optical conductivities in the zigzag and armchair silicene nanoribbons under exchange and electric fields

Jianfei Zou, Jing Kang
Chin. Phys. B 2018, 27 (3): 037301;  doi: 10.1088/1674-1056/27/3/037301
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Based on the tight binding model, we investigate the low energy bandstructures, edge states, and optical absorptions for the silicene nanoribbons (SiNRs) with different terminations under an in-plane exchange field and/or a perpendicular electric field. We find that the zigzag SiNRs are gapped by the exchange field, but they could reenter the metallic state after the application of the electric field. Contrarily, a certain kind of armchair SiNRs remain gapless even if a weak exchange field is present. Furthermore, the combination of the exchange and electric fields could effectively modulate the penetration length and the components of the edge states in the SiNRs. The corresponding optical conductivities for the SiNRs are also calculated, which show remarkable dependence on the edge types of the SiNRs and the two external fields.

Distinctive distribution of defects in CdZnTe: In ingots and their effects on the photoelectric properties

Xu Fu, Fang-Bao Wang, Xi-Ran Zuo, Ze-Jian Wang, Qian-Ru Wang, Ke-Qin Wang, Ling-Yan Xu, Ya-Dong Xu, Rong-Rong Guo, Hui Yu, Wan-Qi Jie
Chin. Phys. B 2018, 27 (3): 037302;  doi: 10.1088/1674-1056/27/3/037302
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Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques. Samples cut from the head (T04) and tail (W02) regions of a crystal ingot show distinct differences in Te inclusion distribution. Obvious difference is not observed in Fourier transform infrared (FTIR) spectra, UV-Vis-NIR transmittance spectra, and I-V measurements. However, carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current (LBIC) measurements. Low temperature photoluminescence (PL) measurement presents sharp emission peaks of D0X and A0X, and relatively large peak of D0X (or A0X)/Dcomplex for T04, indicating a better crystalline quality. Thermally stimulated current (TSC) spectrum shows higher density of shallow point defects, i.e., Cd vacancies, InCd+, etc., in W02 sample, which could be responsible for the deterioration of electron mobility.

Strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2

Wen Zhang, Yi Liu, Xiaoying Wang, Yun Zhang, Donghua Xie
Chin. Phys. B 2018, 27 (3): 037501;  doi: 10.1088/1674-1056/27/3/037501
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The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band-like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons. Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below TC ≈ 52 K, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at TX ≈ 28 K, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.

NMR evidence of charge fluctuations in multiferroic CuBr2 Hot!

Rui-Qi Wang, Jia-Cheng Zheng, Tao Chen, Peng-Shuai Wang, Jin-Shan Zhang, Yi Cui, Chong Wang, Yuan Li, Sheng Xu, Feng Yuan, Wei-Qiang Yu
Chin. Phys. B 2018, 27 (3): 037502;  doi: 10.1088/1674-1056/27/3/037502
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We report combined magnetic susceptibility, dielectric constant, nuclear quadruple resonance (NQR), and zero-field nuclear magnetic resonance (NMR) measurements on single crystals of multiferroics CuBr2. High quality of the sample is demonstrated by the sharp magnetic and magnetic-driven ferroelectric transition at TN=TC≈ 74 K. The zero-field 79Br and 81Br NMR are resolved below TN. The spin-lattice relaxation rates reveal charge fluctuations when cooled below 60 K. Evidences of an increase of NMR linewidth, a reduction of dielectric constant, and an increase of magnetic susceptibility are also seen at low temperatures. These data suggest an emergent instability which competes with the spiral magnetic ordering and the ferroelectricity. Candidate mechanisms are discussed based on the quasi-one-dimensional nature of the magnetic system.

Formation of unusual Cr5+ charge state in CaCr0.5Fe0.5O3 perovskite Hot!

Jian-Hong Dai, Qing Zhao, Qian Sun, Shuo Zhang, Xiao Wang, Xu-Dong Shen, Zhe-Hong Liu, Xi Shen, Ri-Cheng Yu, Ting-Shan Chan, Lun-Xiong Li, Guang-Hui Zhou, Yi-feng Yang, Chang-Qing Jin, You-Wen Long
Chin. Phys. B 2018, 27 (3): 037503;  doi: 10.1088/1674-1056/27/3/037503
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A new oxide CaCr0.5Fe0.5O3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr5+/Fe3+ with the presence of unusual Cr5+ state in octahedral coordination, although Cr4+ and Fe4+ occur in the related perovskites CaCrO3 and CaFeO3. The randomly distributed Cr5+ and Fe3+ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe3+-O-Fe3+ interaction. In spite of the B-site Cr5+/Fe3+ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr0.55+Fe0.53+O3 charge combination, and the electron correlation effect of Fe3+ plays an important role for the insulting ground state. CaCr0.5Fe0.5O3 provides the first Cr5+ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states.

Magnetostructural transformation and magnetocaloric effect in Mn48-xVxNi42Sn10 ferromagnetic shape memory alloys

Najam ul Hassan, Ishfaq Ahmad Shah, Tahira Khan, Jun Liu, Yuanyuan Gong, Xuefei Miao, Feng Xu
Chin. Phys. B 2018, 27 (3): 037504;  doi: 10.1088/1674-1056/27/3/037504
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In this work, we tuned the magnetostructural transformation and the coupled magnetocaloric properties of Mn48-xVxNi42Sn10 (x=0, 1, 2, and 3) ferromagnetic shape memory alloys prepared by means of partial replacement of Mn by V. It is observed that the martensitic transformation temperatures decrease with the increase of V content. The shift of the transition temperatures to lower temperatures driven by the applied field, the metamagnetic behavior, and the thermal hysteresis indicates the first-order nature for the magnetostructural transformation. The entropy changes with a magnetic field variation of 0-5 T are 15.2, 18.8, and 24.3 J·kg-1·K-1 for the x=0, 1, and 2 samples, respectively. The tunable martensitic transformation temperature, enhanced field driving capacity, and large entropy change suggest that Mn48-xVxNi42Sn10 alloys have a potential for applications in magnetic cooling refrigeration.

Calculation of electric field-temperature (E, T) phase diagram of a ferroelectric liquid crystal near the SmA-SmCα* transition

F Trabelsi, H Dhaouadi, O Riahi, T Othman
Chin. Phys. B 2018, 27 (3): 037701;  doi: 10.1088/1674-1056/27/3/037701
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In this work we perform a theoretical calculation in order to reconstitute the (E-T) phase diagram of a chiral smectic liquid crystal in the vicinity of the SmA-SmCα* transition. This reconstruction is carried out on the basis of a thermodynamic calculation of the slope of the curve joining the SmCα* domain and the unwound SmC*. An empiric correction of the mean field term of Landau De-Gennes development is necessary to accomplish this reconstruction. Thereafter, an experimental validation is performed to verify our calculations.

Particle swarm optimization and its application to the design of a compact tunable guided-mode resonant filter

Dan-Yan Wang, Qing-Kang Wang
Chin. Phys. B 2018, 27 (3): 037801;  doi: 10.1088/1674-1056/27/3/037801
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A compact tunable guided-mode resonant filter (GMRF) in the telecommunication region near the 1550 nm wavelength is proposed in this paper. Particle swarm optimization (PSO) is used to design the GMRF. The tunability of the GMRF is achieved by an MEMS-based physical movement (in the horizontal or vertical direction) combined with an incident angle in a certain range. The results show that the resonant wavelength tuning of 110 nm (140 nm) is obtained by horizontal movement of 168 nm (vertical movement of 435 nm) combined with an about 11° variation of incident angle.

Influence of fluorescence time characteristics on the spatial resolution of CW-stimulated emission depletion microscopy

Haiyun Qin, Wei Zhao, Chen Zhang, Yong Liu, Guiren Wang, Kaige Wang
Chin. Phys. B 2018, 27 (3): 037803;  doi: 10.1088/1674-1056/27/3/037803
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As one of the most important realizations of stimulated emission depletion (STED) microscopy, the continuous-wave (CW) STED system, constructed by using CW lasers as the excitation and STED beams, has been investigated and developed for nearly a decade. However, a theoretical model of the suppression factors in CW STED has not been well established. In this investigation, the factors that affect the spatial resolution of a CW STED system are theoretically and numerically studied. The full-width-at-half-maximum (FWHM) of a CW STED with a doughnut-shaped STED beam is also reanalyzed. It is found that the suppression function is dominated by the ratio of the local STED and excitation beam intensities. In addition, the FWHM is highly sensitive to both the fluorescence rate (inverse of fluoresce lifetime) and the quenching rate, but insensitive to the rate of vibrational relaxation. For comparison, the suppression function in picosecond STED is only determined by the distribution of the STED beam intensity scaled with the saturation intensity. Our model is highly consistent with published experimental data for evaluating the spatial resolution. This investigation is important in guiding the development of new CW STED systems.

High mobility ultrathin ZnO p-n homojunction modulated by Zn0.85Mg0.15O quantum barriers

Jing-Jing Yang, Qing-Qing Fang, Wen-Han Du, Ke-Ke Zhang, Da-Shun Dong
Chin. Phys. B 2018, 27 (3): 037804;  doi: 10.1088/1674-1056/27/3/037804
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The adding of ZnMgO asymmetric double barriers (ADB) in p-ZnO:(Li, N)/n-ZnO homojunction affects the p-n junction device performance prominently. Two different homojunctions are fabricated on Si (100) substrates by pulsed laser deposition; one is the traditional p-ZnO:(Li, N)/n-ZnO homojunction with different thicknesses named as S1 (250 nm) and S2 (500 nm), the other is the one with ADB embedded in the n-layer named as Q (265 nm). From the photoluminescence spectra, defect luminescence present in the S-series devices is effectively limited in the Q device. The current-voltage curve of the Q device shows Zener-diode rectification property because the two-dimensional electron gas tunnels through the narrow ZnMgO barrier under a reverse bias, thus decreasing the working p-n homojunction thickness from 500 nm to 265 nm. The ADB-modified homojunction shows higher carrier mobility in the Q device. The electroluminescence of the ZnO homojunction is improved in Q compared to S2, because the holes in p-type ZnO (Li, N) can cross the wide ZnMgO barrier under a forward bias voltage into the ZnO quantum well. Therefore, electron-hole recombination occurs in the narrow bandgap of n-type ZnO, creating an ultraviolet light-emitting diode using the ZnO homojunction.

Thermomechanical response of aluminum alloys under the combined action of tensile loading and laser irradiations

Mohsan Jelani, Zewen Li, Zhonghua Shen, Maryam Sardar
Chin. Phys. B 2018, 27 (3): 037901;  doi: 10.1088/1674-1056/27/3/037901
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This study reports the investigation of the thermomechanical behavior of aluminum alloys (Al-1060, Al-6061, and Al-7075) under the combined action of tensile loading and laser irradiations. The continuous wave ytterbium fiber laser (wavelength 1080 nm) was employed as the irradiation source, while tensile loading was provided by the tensile testing machine. The effects of various pre-loading and laser power densities on the failure time, temperature distribution, and the deformation behavior of aluminum alloys are analyzed. The experimental results represent the significant reduction in failure time for higher laser power densities and for high preloading values, which implies that preloading may contribute a significant role in the failure of the material at elevated temperature. Fracture on a microscopic scale was predominantly ductile comprising micro-void nucleation, growth, and coalescence. The Al-1060 specimens behaved plastically to some extent, while Al-6061 and Al-7075 specimens experienced catastrophic failure. The reason and characterization of material failure by tensile and laser loading are explored in detail. A comparative behavior of under-tested materials is also investigated. This work suggests that studies considering only combined loading are not enough to fully understand the mechanical behavior of under-tested materials. For complete characterization, one should consider the effect of heating as well as loading rate and the corresponding involved processes with the help of thermomechanical coupling and the thermal elastic-plastic theory.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Synthesis of strong SiV photoluminescent diamond particles on silica optical fiber by chemical vapor deposition

Zongchun Yang, Yingshuang Mei, Chengke Chen, Yinlan Ruan, Xiaojun Hu
Chin. Phys. B 2018, 27 (3): 038101;  doi: 10.1088/1674-1056/27/3/038101
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The separated silicon-vacancy (SiV) photoluminescent diamond particles were synthesized on a silica optical fiber by hot filament chemical vapor deposition (HFCVD). The effects of the pre-treated method and chamber pressure on the microstructure and photoluminescence of the diamond particles were investigated. The results show that the diamond particles are homogeneously distributed on the surface of the optical fiber. With the chamber pressure increasing from 1.6 kPa to 3.5 kPa, the shape of the particles transforms from flake to circle, while the diamond particles cannot be deposited on the fiber with the pressure further increased to 4.5 kPa. The samples synthesized under 2.5 kPa chamber pressure are composed of diamond particles with size around 200-400 nm, exhibiting stronger SiV photoluminescence with the width of around 6 nm.

Quantitative deformation measurements and analysis of the ferrite-austenite banded structure in a 2205 duplex stainless steel at 250℃

Ji-Hua Liu
Chin. Phys. B 2018, 27 (3): 038102;  doi: 10.1088/1674-1056/27/3/038102
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The deformation process of the microstructure in 2205 duplex stainless steel (DSS) under thermo-mechanical coupling at 250℃ was investigated using digital image correlation (DIC). A thermal tension test of duplex stainless steel (2205DSS) with a banded structure was carried out to observe the initial deformation of the microstructure. It was found that inhomogeneous strain fields occurred primarily in austenite. The maximum normal strain in austenite was almost positive, while that in ferrite was almost negative. In addition, a thermal cyclic-loading test was conducted, and the strain field was characterized by e11. Strain heterogeneities were induced after 400 cycles, which spread within the austenite and at the phase boundaries with the load increasing. The high tensile-strain regions were always located adjacent to regions of intense compressive strain. Based on the strain matrix sum vs. cycle number, we found that hardening occurred in the early cycles followed by softening.

Enhanced ionic conductivity in LAGP/LATP composite electrolyte

Shi-Gang Ling, Jia-Yue Peng, Qi Yang, Ji-Liang Qiu, Jia-Ze Lu, Hong Li
Chin. Phys. B 2018, 27 (3): 038201;  doi: 10.1088/1674-1056/27/3/038201
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Nasicon materials (sodium superionic conductors) such as Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and Li1.4Al0.4Ti1.6(PO4)3 (LATP) have been considered as important solid electrolytes due to their high ionic conductivity and chemical stability. Compared to LAGP, LATP has higher bulk conductivity around 10-3 S/cm at room temperature; however, the apparent grain boundary conductivity is almost two orders of magnitude lower than the bulk, while LAGP has similar bulk and grain boundary conductivity around the order of 10-4 S/cm. To make full use of the advantages of the two electrolytes, pure phase Li1.5Al0.5Ge1.5(PO4)3 and Li1.4Al0.4Ti1.6(PO4)3 were synthesized through solid state reaction, a series of composite electrolytes consisting of LAGP and LATP with different weight ratios were designed. XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes. The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80:20 achieved the highest bulk conductivity which shall be due to the formation of solid solution phase Li1.42Al0.42Ge0.3Ti1.28(PO4)3, while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20:80 which may be due to the excellent interfacial phase between Li1+xAlxGeyTi2-x-y(PO4)3/LATP. All the composite electrolytes demonstrated higher total conductivity than the pure LAGP and LATP, which highlights the importance of heterogeneous interface on regulating the ion transport properties.

An improved secondary electrons energy spectrum model and its application in multipactor discharge

Wan-Zhao Cui, Heng Zhang, Yun Li, Yun He, Qi Wang, Hong-Tai Zhang, Hong-Guang Wang, Jing Yang
Chin. Phys. B 2018, 27 (3): 038401;  doi: 10.1088/1674-1056/27/3/038401
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Secondary electron emission (SEE) of metal and dielectric materials plays a key role in multipactor discharge, which is a bottle neck problem for high-power satelliate components. Measurements of both the secondary electron yield (SEY) and the secondary electron energy spectrum (SES) are performed on metal samples for an accurate description of the real SEE phenomenon. In order to simplify the fitting process and improve the simulation efficiency, an improved model is proposed for the description of secondary electrons (SE) emitted from the material surface, including true, elastic, and inelastic SE. Embedding the novel SES model into the electromagnetic particle-in-cell method, the electronic resonant multipactor in microwave components is simulated successfully and hence the discharge threshold is predicted. Simulation results of the SES variation in the improved model demonstrate that the multipactor threshold is strongly dependent on SES. In addition, the mutipactor simulation results agree quite well with the experiment for the practical microwave component, while the numerical model of SEY and SES fits well with the sample data taken from the microwave component.

Factors influencing the performance of paintable carbon-based perovskite solar cells fabricated in ambient air

Wei-Kang Xu, Feng-Xiang Chen, Gong-Hui Cao, Jia-Qi Wang, Li-Sheng Wang
Chin. Phys. B 2018, 27 (3): 038402;  doi: 10.1088/1674-1056/27/3/038402
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To date, many efforts have been made to improve the performance of paintable carbon-based (PC-based) perovskite solar cells (PSCs). Though great progress has been achieved, their power conversion efficiencies are still relatively low compared with hole-transport-materials-based PSCs. General research on influencing factors of performance in PC-based PSCs is still insufficient. In this work, PC-based PSCs were fabricated in ambient air and four groups of controlled experiments were performed in which the PbI2 layers were prepared with or without antisolvent extraction treatment. These four groups of experiments were designed to find out the effect of different influencing factors on PC-based PSCs performance, for example, PbI2 residual, the surface morphology of the perovskite film, the surface roughness of the perovskite film, and the contact status of the perovskite/carbon electrode interface. With a systematic analysis, we demonstrated that the contact status of the perovskite/carbon electrode interface played a vital role in PC-based PSCs, and a flat, smooth perovskite surface could help to improve this contact status significantly. Besides, on the precondition of a poor contact interface, no PbI2 residual and a good surface morphology only brought limited benefits to the performances of PC-based PSCs.

Analysis of multiple cell upset sensitivity in bulk CMOS SRAM after neutron irradiation

Xiaoyu Pan, Hongxia Guo, Yinhong Luo, Fengqi Zhang, Lili Ding
Chin. Phys. B 2018, 27 (3): 038501;  doi: 10.1088/1674-1056/27/3/038501
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In our previous studies, we have proved that neutron irradiation can decrease the single event latch-up (SEL) sensitivity of CMOS SRAM. And one of the key contributions to the multiple cell upset (MCU) is the parasitic bipolar amplification, it bring us to study the impact of neutron irradiation on the SRAM's MCU sensitivity. After the neutron experiment, we test the devices' function and electrical parameters. Then, we use the heavy ion fluence to examine the changes on the devices' MCU sensitivity pre-and post-neutron-irradiation. Unfortunately, neutron irradiation makes the MCU phenomenon worse. Finally, we use the electric static discharge (ESD) testing technology to deduce the experimental results and find that the changes on the WPM region take the lead rather than the changes on the parasitic bipolar amplification for the 90 nm process.

Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

Haibin Huang, Gangyu Tian, Lang Zhou, Jiren Yuan, Wolfgang R. Fahrner, Wenbin Zhang, Xingbing Li, Wenhao Chen, Renzhong Liu
Chin. Phys. B 2018, 27 (3): 038502;  doi: 10.1088/1674-1056/27/3/038502
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A novel structure of Ag grid/SiNx/n+-c-Si/n-c-Si/i-a-Si:H/p+-a-Si:H/TCO/Ag grid was designed to increase the efficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost. The simulation results show that the new structure obtains higher efficiency compared with the typical bifacial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current (Jsc), while retaining the advantages of a high open-circuit voltage, low temperature coefficient, and good weak-light performance. Moreover, real cells composed of the novel structure with dimensions of 75 mm×75 mm were fabricated by a special fabrication recipe based on industrial processes. Without parameter optimization, the cell efficiency reached 21.1% with the Jsc of 41.7 mA/cm2. In addition, the novel structure attained 28.55% potential conversion efficiency under an illumination of AM 1.5 G, 100 mW/cm2. We conclude that the configuration of the Ag grid/SiNx/n+-c-Si/n-c-Si/i-a-Si:H/p+-a-Si:H/TCO/Ag grid is a promising structure for high efficiency and low cost.

A novel knowledge-based potential for RNA 3D structure evaluation

Yi Yang, Qi Gu, Ben-Gong Zhang, Ya-Zhou Shi, Zhi-Gang Shao
Chin. Phys. B 2018, 27 (3): 038701;  doi: 10.1088/1674-1056/27/3/038701
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Ribonucleic acids (RNAs) play a vital role in biology, and knowledge of their three-dimensional (3D) structure is required to understand their biological functions. Recently structural prediction methods have been developed to address this issue, but a series of RNA 3D structures are generally predicted by most existing methods. Therefore, the evaluation of the predicted structures is generally indispensable. Although several methods have been proposed to assess RNA 3D structures, the existing methods are not precise enough. In this work, a new all-atom knowledge-based potential is developed for more accurately evaluating RNA 3D structures. The potential not only includes local and nonlocal interactions but also fully considers the specificity of each RNA by introducing a retraining mechanism. Based on extensive test sets generated from independent methods, the proposed potential correctly distinguished the native state and ranked near-native conformations to effectively select the best. Furthermore, the proposed potential precisely captured RNA structural features such as base-stacking and base-pairing. Comparisons with existing potential methods show that the proposed potential is very reliable and accurate in RNA 3D structure evaluation.

A computational study of the chemokine receptor CXCR1 bound with interleukin-8

Yang Wang, Cecylia Severin Lupala, Ting Wang, Xuanxuan Li, Ji-Hye Yun, Jae-hyun Park, Zeyu Jin, Weontae Lee, Leihan Tan, Haiguang Liu
Chin. Phys. B 2018, 27 (3): 038702;  doi: 10.1088/1674-1056/27/3/038702
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CXCR1 is a G-protein coupled receptor, transducing signals from chemokines, in particular the interleukin-8 (IL8) molecules. This study combines homology modeling and molecular dynamics simulation methods to study the structure of CXCR1-IL8 complex. By using CXCR4-vMIP-Ⅱ crystallography structure as the homologous template, CXCR1-IL8 complex structure was constructed, and then refined using all-atom molecular dynamics simulations. Through extensive simulations, CXCR1-IL8 binding poses were investigated in detail. Furthermore, the role of the N-terminal of CXCR1 receptor was studied by comparing four complex models differing in the N-terminal sequences. The results indicate that the receptor N-terminal affects the binding of IL8 significantly. With a shorter N-terminal domain, the binding of IL8 to CXCR1 becomes unstable. The homology modeling and simulations also reveal the key receptor-ligand residues involved in the electrostatic interactions known to be vital for complex formation.

Molecular dynamics simulations of membrane deformation induced by amphiphilic helices of Epsin, Sar1p, and Arf1

Zhen-Lu Li
Chin. Phys. B 2018, 27 (3): 038703;  doi: 10.1088/1674-1056/27/3/038703
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The N-terminal amphiphilic helices of proteins Epsin,Sar1p,and Arf1 play a critical role in initiating membrane deformation.The interactions of these amphiphilic helices with the lipid membranes are investigated in this study by combining the all-atom and coarse-grained simulations.In the all-atom simulations,the amphiphilic helices of Epsin and Sar1p are found to have a shallower insertion depth into the membrane than the amphiphilic helix of Arf1,but remarkably, the amphiphilic helices of Epsin and Sar1p induce higher asymmetry in the lipid packing between the two monolayers of the membrane.The insertion depth of amphiphilic helix into the membrane is determined not only by the overall hydrophobicity but also by the specific distributions of polar and non-polar residues along the helix.To directly compare their ability to deform the membrane,the coarse-grained simulations are performed to investigate the membrane deformation under the insertion of multiple helices.

First integrals of the axisymmetric shape equation of lipid membranes

Yi-Heng Zhang, Zachary McDargh, Zhan-Chun Tu
Chin. Phys. B 2018, 27 (3): 038704;  doi: 10.1088/1674-1056/27/3/038704
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The shape equation of lipid membranes is a fourth-order partial differential equation. Under the axisymmetric condition, this equation was transformed into a second-order ordinary differential equation (ODE) by Zheng and Liu (Phys. Rev. E 48 2856 (1993)). Here we try to further reduce this second-order ODE to a first-order ODE. First, we invert the usual process of variational calculus, that is, we construct a Lagrangian for which the ODE is the corresponding Euler-Lagrange equation. Then, we seek symmetries of this Lagrangian according to the Noether theorem. Under a certain restriction on Lie groups of the shape equation, we find that the first integral only exists when the shape equation is identical to the Willmore equation, in which case the symmetry leading to the first integral is scale invariance. We also obtain the mechanical interpretation of the first integral by using the membrane stress tensor.

Spatial memory enhances the evacuation efficiency of virtual pedestrians under poor visibility condition

Yi Ma, Eric Wai Ming Lee, Meng Shi, Richard Kwok Kit Yuen
Chin. Phys. B 2018, 27 (3): 038901;  doi: 10.1088/1674-1056/27/3/038901
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Spatial memory is a critical navigation support tool for disoriented evacuees during evacuation under adverse environmental conditions such as dark or smoky conditions. Owing to the complexity of memory, it is challenging to understand the effect of spatial memory on pedestrian evacuation quantitatively. In this study, we propose a simple method to quantitatively represent the evacuee's spatial memory about the emergency exit, model the evacuation of pedestrians under the guidance of the spatial memory, and investigate the effect of the evacuee's spatial memory on the evacuation from theoretical and physical perspectives. The result shows that (i) a good memory can significantly assist the evacuation of pedestrians under poor visibility conditions, and the evacuation can always succeed when the degree of the memory exceeds a threshold (φ>0.5); (ii) the effect of memory is superior to that of “follow-the-crowd” under the same environmental conditions; (iii) in the case of multiple exits, the difference in the degree of the memory between evacuees has a significant effect (the greater the difference, the faster the evacuation) for the evacuation under poor visibility conditions. Our study provides a new quantitative insight into the effect of spatial memory on crowd evacuation under poor visibility conditions.

Flowrate behavior and clustering of self-driven robots in a channel

Bo Tian, Wang-Ping Sun, Ming Li, Rui Jiang, Mao-Bin Hu
Chin. Phys. B 2018, 27 (3): 038902;  doi: 10.1088/1674-1056/27/3/038902
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In this paper, the collective motion of self-driven robots is studied experimentally and theoretically. In the channel, the flowrate of robots increases with the density linearly, even if the density of the robots tends to 1.0. There is no abrupt drop in the flowrate, similar to the collective motion of ants. We find that the robots will adjust their velocities by a serial of tiny collisions. The speed-adjustment will affect both robots involved in the collision, and will help to maintain a nearly uniform velocity for the robots. As a result, the flowrate drop will disappear. In the motion, the robots neither gather together nor scatter completely. Instead, they form some clusters to move together. These clusters are not stable during the moving process, but their sizes follow a power-law-alike distribution. We propose a theoretical model to simulate this collective motion process, which can reproduce these behaviors well. Analytic results about the flowrate behavior are also consistent with experiments.
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