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Chin. Phys. B  
  Chin. Phys. B--2020, Vol.29, No.6
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SPECIAL TOPIC—Recent advances in thermoelectric materials and devices
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Extraordinary propagation characteristics of electromagnetic waves in one-dimensional anti-PT-symmetric ring optical waveguide network

Jie-Feng Xu, Xiang-Bo Yang, Hao-Han Chen, Zhan-Hong Lin
Chin. Phys. B 2020, 29 (6): 064201;  doi: 10.1088/1674-1056/ab8371
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In this paper, we design a one-dimensional anti-PT-symmetric ring optical waveguide network (1D APTSPROWN). Using the three-material network equation and the generalized Floquet-Bloch theorem, we investigate its photonic mode distribution, and observe weak extremum spontaneous anti-PT-symmetric breaking points (WBPs) and strong extremum spontaneous anti-PT-symmetric breaking points (SBPs). Then the transmission spectrum is obtained by using the three-material network equation and the generalized eigenfunction method. The 1D APTSPROWN is found to generate ultra-strong transmission near SBPs and ultra-weak transmission near WBPs and SBPs, with the maximal and minimal transmissions being 4.08×1012 and 7.08×10-52, respectively. The maximal transmission has the same order of magnitude as the best-reported result. It is not only because the distribution of photonic modes generated by the 1D APTSROWN results in the coupling resonance and anti-resonance, but also because the 1D APTSROWN composed of materials whose real parts of refractive indices are positive and negative has two kinds of phase effects, which results in the resonance and anti-resonance effects in the same kind of photonic modes. This demonstrates that the anti-PT-symmetric and PT-symmetric optical waveguide networks are quite different, which leads to a more in-depth understanding of anti-PT-symmetric and PT-symmetric structures. This work has the potential for paving a new approach to designing single photon emitters, optical amplifiers, and high-efficiency optical energy saver devices.

Propagation properties of radially polarized Pearcey-Gauss vortex beams in free space

Xinpeng Chen, Chuangjie Xu, Qian Yang, Zhiming Luo, Xixian Li, Dongmei Deng
Chin. Phys. B 2020, 29 (6): 064202;  doi: 10.1088/1674-1056/ab8202
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We investigate a family of radially polarized Pearcey-Gauss vortex beams (RPPGVBs), obtain the general propagation expressions of an RPPGVB, and study the intensity distribution, phase pattern, spin currents as well as the orbital currents when the RPPGVB propagates in free space. The focal plane and the intensity of the focal point can be adjusted by changing the position of the vortex and the scaling factors. We also investigate how the waist size influences the propagation properties.

Three-Airy autofocusing beams

Xiao-Hong Zhang, Fei-Li Wang, Lu-Yang Bai, Ci-Bo Lou, Yi Liang
Chin. Phys. B 2020, 29 (6): 064204;  doi: 10.1088/1674-1056/ab84d2
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We numerically and experimentally demonstrate that a three-Airy autofocusing beam can be generated by superposing three deformed two-dimensional (2D) Airy beams with a triangle symmetry. When the initial angle between two wings of the deformed 2D Airy beams increases, such a three-Airy autofocusing beam exhibits that the focusing length decreases and the intensity contrast at the focal point changes. Moreover, after introducing an optical vortex phase, this three-Airy autofocusing beam displays a transverse rotation in propagation. The rotation angle is determined by the topological charge of the vortex and the initial wing angle. Our results may have some potential applications in optical manipulation.

Gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging for detection of submucosal gastric cancer: in vitro study

Huaqin Wu, Haiyang Song, Yudian Huang, Zhifang Li, Shulian Wu, Xiaoman Zhang, Hui Li
Chin. Phys. B 2020, 29 (6): 064205;  doi: 10.1088/1674-1056/ab84d4
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This paper presents photoacoustic and ultrasonic dual-mode imaging for real-time detection of submucosal gastric cancer with a combination of gastroscopy. The diagnostic capacity was directly addressed via several phantoms and ex vivo experiments. Results demonstrated that superficial and submucosal gastric cancer can be diagnosed with a perceptible depth of 6.33 mm, a lateral accuracy of 2.23 mm, and a longitudinal accuracy of 0.17 mm though capturing the morphology of angiogenesis, which is a main character of the therioma-related change. The capability of gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging system will own great potential in improving the clinical diagnostic rate of submucosal gastric cancer.

M2-factor of high-power laser beams through a multi-apertured ABCD optical system

Xiangmei Zeng, Meizhi Zhang, Dongmei Cao, Dingyu Sun, Hua Zhou
Chin. Phys. B 2020, 29 (6): 064206;  doi: 10.1088/1674-1056/ab81f1
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Based on the generalized truncated second-order moments, an approximate analytical formula of the beam propagation factor M2 of high-power laser beams passing through the optical system with multiple hard-edged apertures is deduced. Numerical examples of the beams passing through an aperture-spatial filter are enclosed, and the influences of amplitude modulations (AMs) and phase fluctuations (PFs) on the beam propagation quality of high-power laser beams passing through the multi-apertured ABCD optical system are considered and discussed. It is shown that PFs are able to degrade the beam propagation quality of laser beams more than AMs when the high-power laser beams passing through the aperture-spatial filter, furthermore, one or two aperture-lens optical systems configured appropriate aperture parameters are both able to upgrade the beam propagation quality of high-power laser beams. The M2 factor of Gaussian beam passing through the multi-aperture optical system is a special case in this paper.

Inhibiting radiative recombination rate to enhance quantum yields in a quantum photocell

Jing-Yi Chen, Shun-Cai Zhao
Chin. Phys. B 2020, 29 (6): 064207;  doi: 10.1088/1674-1056/ab836f
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Inhibiting the radiative radiation is an efficient approach to enhance quantum yields in a solar sell. This work carries out the inhibition of radiative recombination rate (RRR) in a quantum photocell with two coupled donors. We perform explicit calculations of the transition rates, energy gaps and the absorbed solar wavelength-dependent RRR, and find that two different regimes play the crucial roles in inhibiting RRR. One is the quantum coherence generated from two different transition channels, the other includes the absorbed photon wavelength and gaps between the donor and acceptor in this proposed photocell model. The results imply that there may be some efficient ways to enhance the photoelectron conversion compared to the classic solar cell.

Simple and robust method for rapid cooling of 87Rb to quantum degeneracy

Chun-Hua Wei, Shu-Hua Yan
Chin. Phys. B 2020, 29 (6): 064208;  doi: 10.1088/1674-1056/ab8625
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We demonstrate a simple and fast way to produce 87Rb Bose-Einstein condensates. A digital optical phase lock loop (OPLL) board is introduced to lock and adjust the frequency of the trap laser, which simplifies the optical design and improves the experimental efficiency. We collect atoms in a magneto-optical trap, then compress the cloud and cut off hot atoms by rf knife in a magnetic quadrupole trap. The atom clouds are then transferred into a spatially mode-matched optical dipole trap by lowering the quadrupole field gradient. Our system reliably produces a condensate with 2×106 atoms every 7.5 s. The compact optical design and rapid preparation speed of our system will open the gate for mobile quantum sensing.

Microwave frequency transfer over a 112-km urban fiber link based on electronic phase compensation

Wen-Xiang Xue, Wen-Yu Zhao, Hong-Lei Quan, Cui-Chen Zhao, Yan Xing, Hai-Feng Jiang, Shou-Gang Zhang
Chin. Phys. B 2020, 29 (6): 064209;  doi: 10.1088/1674-1056/ab84d6
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We demonstrate the transmission of a microwave frequency signal at 10 GHz over a 112-km urban fiber link based on a novel simple-architecture electronic phase compensation system. The key element of the system is the low noise frequency divider by 4 to differentiate the frequency of the forward signal from that of the backward one, thus suppressing the effect of Brillouin backscattering and parasitic reflection along the link. In terms of overlapping Allan deviation, the frequency transfer instability of 4.2×10-15 at 1-s integration time and 1.6×10-18 at one-day integration time was achieved. In addition, its sensitivity to the polarization mode dispersion in fiber is analyzed by comparing the results with and without laser polarization scrambling. Generally, with simplicity and robustness, the system can offer great potentials in constructing cascaded frequency transfer system and facilitate the building of fiber-based microwave transfer network.

Excitation-wavelength-dependent THz wave modulation via external bias electric field

Shi-Jia Feng, Li-Quan Dong, Dan-Ni Ma, Tong Wu, Yong Tan, Liang-Liang Zhang, Cun-Lin Zhang, Yue-Jin Zhao
Chin. Phys. B 2020, 29 (6): 064210;  doi: 10.1088/1674-1056/ab84d7
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A theoretical model was proposed to describe the effects of external bias electric field on terahertz (THz) generated in air plasma. The model predicted that for a plasma in a bias electric field, the amplification effect of the THz wave intensity increases with the increase of the excitation laser wavelength. We experimentally observed the relationship between the THz enhancement effect and the electric field strength at different wavelengths. Experimental results showed a good agreement with the model predictions. These results enhance our understanding of the physical mechanism by which femtosecond lasers excite air to generate THz and extend the practical applications of THz generation and modulation.

Four-soliton solution and soliton interactions of the generalized coupled nonlinear Schrödinger equation

Li-Jun Song, Xiao-Ya Xu, Yan Wang
Chin. Phys. B 2020, 29 (6): 064211;  doi: 10.1088/1674-1056/ab84ce
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Based on the generalized coupled nonlinear Schrödinger equation, we obtain the analytic four-bright-bright soliton solution by using the Hirota bilinear method. The interactions among four solitons are also studied in detail. The results show that the interaction among four solitons mainly depends on the values of solution parameters; k1 and k2 mainly affect the two inboard solitons while k3 and k4 mainly affect the two outboard solitons; the pulse velocity and width mainly depend on the imaginary part of ki (i=1, 2, 3, 4), while the pulse amplitude mainly depends on the real part of ki (i=1, 2, 3, 4).

Effect of dark soliton on the spectral evolution of bright soliton in a silicon-on-insulator waveguide

Zhen Liu, Wei-Guo Jia, Hong-Yu Wang, Yang Wang, Neimule Men-Ke, Jun-Ping Zhang
Chin. Phys. B 2020, 29 (6): 064212;  doi: 10.1088/1674-1056/ab84d9
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The spectral evolution of bright soliton in a silicon-on-insulator optical waveguide is numerically simulated using the split-step Fourier method. The power and input chirp of the dark soliton and the second-order dispersion are varied to investigate the effect of dark soliton on the spectrum of bright soliton. The simulations prove that the dark soliton modifies the spectral shape of the bright soliton. Further, the variation in the power of dark soliton affects the splitting of bright soliton. Furthermore, the chirped dark soliton can improve the spectral width and flatness. The variation in the dispersion of dark soliton modifies the phase matching of the bright soliton and the dispersive wave emission, thereby affecting the spectral evolution.

Properties of off-axis hollow Gaussian-Schell model vortex beam propagating in turbulent atmosphere

Yan-Song Song, Ke-Yan Dong, Shuai Chang, Yan Dong, Lei Zhang
Chin. Phys. B 2020, 29 (6): 064213;  doi: 10.1088/1674-1056/ab836c
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The analytical expression of off-axis hollow Gaussian-Schell model vortex beam (HGSMVB) generated by anisotropic Gaussian-Schell model source is first introduced. The evolution properties of off-axis HGSMVB propagating in turbulent atmosphere are analyzed. The results show that the off-axis HGSMVB with smaller coherence length or propagating in stronger turbulent atmosphere will evolve from dark hollow beam into Gaussian-like beam with a larger beam spot faster. The beams with different values of integer order N or the position for hollow and vortex factor R will have almost the same Gaussian-like spot distribution at the longer propagation distance.

Extended validity of weak measurement

Jiangdong Qiu, Changliang Ren, Zhaoxue Li, Linguo Xie, Yu He, Zhiyou Zhang, Jinglei Du
Chin. Phys. B 2020, 29 (6): 064214;  doi: 10.1088/1674-1056/ab8622
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We introduce a modified weak value that is related to the mean value of input meter variable. With the help of the modified weak value, the validity conditions for various modified versions of weak value formalism are investigated, in terms of the dependence of the pointer shift on the mean value of the input meter. The weak value formalism, often used to represent the pointer shift, with the modified weak value is of great use in simplifying calculations and giving guidance of practical experiments whenever the mean value of the input meter variable is nonzero. The simulation in a qubit system is presented and coincident well with our theoretical result.

Extra-narrowband metallic filters with an ultrathin single-layer metallic grating

Ran Wang, Qi-Huang Gong, Jian-Jun Chen
Chin. Phys. B 2020, 29 (6): 064215;  doi: 10.1088/1674-1056/ab8899
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Narrowband and high-transmission optical filters are extensively used in color display technology, optical information processing, and high-sensitive sensing. Because of large ohmic losses in metallic nanostructures, metallic filters usually exhibit low transmittances and broad bandwidths. By employing both strong field enhancements in metallic nano-slits and the Wood's anomaly in a periodic metallic grating, an extra-narrowband and high-transmission metallic filter is numerically predicted in an ultrathin single-layer metallic grating. Simulation results show that the Wood's anomaly in the ultrathin (thickness H=60 nm) single-layer metallic grating results in large field enhancements in the substrate and low losses in the metallic grating. As a result, the transmission bandwidth (transmittance T > 60%) at λ=1200 nm is as small as ΔλFWHM=1.6 nm, which is smaller than 4% of that in the previous thin dielectric and metallic filters. The corresponding quality factor is as high as Q=λλFWHM=750, which is 40 times greater than that in the previous reports. Moreover, the thickness of our metallic filter (H=60 nm) is smaller than 40% of that in the previous reports, and its maximum transmittance can reach up to 80%. In experiments, a narrowband metallic filter with a bandwidth of about ΔλFWHM=10 nm, which is smaller than 25% of that in the previous metallic filters, is demonstrated.

Frequency-dependent reflection of elastic wave from thin bed in porous media

Hong-Xing Li, Chun-Hui Tao, Cai Liu, Guang-Nan Huang, Zhen-An Yao
Chin. Phys. B 2020, 29 (6): 064301;  doi: 10.1088/1674-1056/ab888b
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The reflection of elastic wave from thin bed in porous media is important for oil and gas reservoir seismic exploration. The equations for calculating frequency-dependent reflection amplitude versus incident angle (FDAVA) from thin bed in porous media are obtained based on porous media theory. Some conclusions are obtained from numerical analysis, specifically, slow compression wave may be ignored when considering boundary conditions in most situations; the dispersion of reflection from thin bed is much higher than that from thick layer and is periodic in frequency domain, which is affected by the thickness of thin bed, velocity, and incident angle; the reflection amplitude envelope in frequency domain decays exponentially, which is affected by the thickness of thin bed, attenuation, and incident angle; the reflection amplitude increases with thickness of thin bed increasing, and then it decreases when the thickness reaches to a quarter of wavelength.

Quasi-canonicalization for linear homogeneous nonholonomic systems

Yong Wang, Jin-Chao Cui, Ju Chen, Yong-Xin Guo
Chin. Phys. B 2020, 29 (6): 064501;  doi: 10.1088/1674-1056/ab8627
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For conservative linear homogeneous nonholonomic systems, there exists a cotangent bundle with the symplectic structure dπμ∧dξμ, in which the motion equations of the system can be written into the form of the canonical equations by the set of quasi-coordinates πμ and quasi-momenta ξμ. The key to construct this cotangent bundle is to define a set of suitable quasi-coordinates πμ by a first-order linear mapping, so that the reduced configuration space of the system is a Riemann space with no torsion. The Hamilton-Jacobi method for linear homogeneous nonholonomic systems is studied as an application of the quasi-canonicalization. The Hamilton-Jacobi method can be applied not only to Chaplygin nonholonomic systems, but also to non-Chaplygin nonholonomic systems. Two examples are given to illustrate the effectiveness of the quasi-canonicalization and the Hamilton-Jacobi method.

Large eddy simulations of a triangular jet and its counterpart through a chamber

Xiu Xiao, Guo-Chang Wang, Min-Yi Xu, Jian-Chun Mi
Chin. Phys. B 2020, 29 (6): 064701;  doi: 10.1088/1674-1056/ab8623
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A free triangular jet (TJ1) and its counterpart initially passing a short circular chamber (TJ2) are numerically modeled using large eddy simulation (LES). This paper compares the near-field characteristics of the two jets in detail. To enable some necessary experimental validations, the LES conditions of TJ1 and TJ2 are taken to be identical to those measured by Xu et al. (Sci. China Phys. 56 1176 (2013)) and England et al. (Exp. Fluids. 48 69 (2010)), respectively. The LES predictions are found to agree well with those measurements. It is demonstrated that a strong swirl occurs near the chamber inlet plane for the TJ2 flow. At the center of the swirl, there is a cluster of three sink foci, where each focus is aligned midway between the original triangular apexes. In the vortex skeleton constructed from the time-averaged flow field, the vortices arising from the foci are helically twisted around the core of the jet. As the flow passes through the chamber, the foci merge to form a closed-loop “bifurcation line”, which separates the inward swirling flow and the outward oscillating jet. This global oscillation is regarded as a source node near the centerline of the chamber. If the chamber is removed for a “free” jet, i.e., TJ1, a cluster of three pairs of counter-rotating foci is produced and the net swirl circulation is zero, so the overall oscillation of the jet does not occur.

Discharge and flow characterizations of the double-side sliding discharge plasma actuator

Qi-Kun He, Hua Liang, Bo-Rui Zheng
Chin. Phys. B 2020, 29 (6): 064702;  doi: 10.1088/1674-1056/ab8624
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We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current (DC) voltage. The discharge tests show that sliding discharge and extended discharge are filamentary discharge. The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle, ultimately expands the discharge channel. The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge (DBD). The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge, which causes a bulge structure in the discharge channel. The bias DC electrode can deflect the direction of the induced jet, then modifying the properties of the boundary layer. Extended discharge can accelerate the velocity of the starting vortex, improving the horizontal velocity profile by 203%. The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate, compared with sliding discharge and DBD. However, the momentum growth of sliding discharge lasts longer in the whole pulsed cycle, indicating that sliding discharge can also inject more momentum.

Forebody asymmetric vortex control with extended dielectric barrier discharge plasma actuators

Borui Zheng, Ming Xue, Chang Ge
Chin. Phys. B 2020, 29 (6): 064703;  doi: 10.1088/1674-1056/ab8372
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Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge (DBD) plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a single-direction induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry (PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuation-induced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved. There exists an optimal normalized reduced frequency (f+=2πfpd/U=2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Simulation of helium supersonic molecular beam injection in tokamak plasma

Xue-Ke Wu, Zhan-Hui Wang, Hui-Dong Li, Li-Ming Shi, Di Wan, Qun-Chao Fan, Min Xu
Chin. Phys. B 2020, 29 (6): 065201;  doi: 10.1088/1674-1056/ab81fd
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To study helium (He) supersonic molecular beam injection (SMBI) into H-mode tokamak plasma, a simplified multicomponent-plasma model under the assumption of quasi-neutral condition is developed and implemented in the frame of BOUT ++. The simulation results show that He species propagate inwards after He SMBI, and are deposited at the bottom of the pedestal due to intensive ionization and weak spreading speed. It is found that almost all injected helium particles strip off all the bounded electrons. He species interact intensively with background plasma along the injection path during He SMBI, making deuterium ion density profile drop at the He-deposited location and resulting in a large electron temperature decreasing, but deuterium ion temperature decreasing a little at the top of the pedestal.

Oblique collisional effects of dust acoustic waves in unmagnetized dusty plasma

M S Alam, M R Talukder
Chin. Phys. B 2020, 29 (6): 065202;  doi: 10.1088/1674-1056/ab829b
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Effects of oblique collisions of the dust acoustic (DA) waves in dusty plasma are studied by considering unmagnetized fully ionized plasma. The plasma consists of inertial warm negatively charged massive dusts, positively charged dusts, superthermal kappa distributed electrons, and isothermal ions. The extended Poincaré-Lighthill-Kuo (ePLK) method is employed for the drivation of two-sided Korteweg-de Vries (KdV) equations (KdVEs). The KdV soliton solutions are derived by using the hyperbolic secant method. The effects of superthermality index of electrons, temperature ratio of isothermal ion to electron, and the density ratio of isothermal ions to negatively charged massive dusts on nonlinear coefficients are investigated. The effects of oblique collision on amplitude, phase shift, and potential profile of right traveling solitons of DA waves are also studied. The study reveals that the new nonlinear wave structures are produced in the colliding region due to head-on collision of the two counter propagating DA waves. The nonlinearity is found to decrease with the increasing density ratio of ion to negative dust in the critical region. The phase shifts decrease (increase) with increasing the temperature ratio of ion to electron (κe). The hump (compressive, κe < κec) and dipshaped (rarefactive, κe > κec) solitons are produced depending on the angle (θ) of oblique collision between the two waves.

Influence of polarization of laser beam on emission intensity of femtosecond laser-induced breakdown spectroscopy

Lan Yang, Miao Liu, Yi-Tong Liu, Qing-Xue Li, Su-Yu Li, Yuan-Fei Jiang, An-Min Chen, Ming-Xing Jin
Chin. Phys. B 2020, 29 (6): 065203;  doi: 10.1088/1674-1056/ab84dc
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Laser-induced breakdown spectroscopy (LIBS) is an important technique which is widely used to analyze element composition. In order to improve the sensitivity of LIBS, much effort has been made to enhance the spectral intensity of LIBS by proposing a number of methods. In addition, we find that laser polarization has great influence on the emission intensity of femtosecond LIBS. By comparing the emission intensity of femtosecond LIBS in the circular polarization with that in the linear polarization, the spectral intensity in the case of circular polarization is stronger than that in the case of linear polarization. Moreover, this phenomenon is more obvious as laser energy increases. The polarization plays an important role in LIBS signal intensity. Based on the observation, the enhanced mechanism of the laser polarization for the spectral intensity is discussed in this paper, which will be helpful in spectral analysis and component analysis.

Tests of the real-time vertical growth rate calculation on EAST

Na-Na Bao, Yao Huang, Jayson Barr, Zheng-Ping Luo, Yue-Hang Wang, Shu-Liang Chen, Bing-Jia Xiao, David Humphreys
Chin. Phys. B 2020, 29 (6): 065204;  doi: 10.1088/1674-1056/ab84da
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In order to measure controllability of vertical instability in EAST, the calculation of model-based vertical growth rate, called rt-gamma, has been successfully carried out in real time. The numerical computing method is adapted from rigid plasma response model in TokSys, which is a widely-used analysis tool for tokamak devices in Matlab environment, but the code is rewritten by taking advantage of GPU parallel computing capability to accelerate the computation. The calculation of rt-gamma is validated by comparing it with the corresponding result generated by TokSys for totally 3508 cases. It is shown that the average absolute value of relative errors is about 0.85%. In addition, the calculation program of rt-gamma has been successfully applied during 2019 EAST campaign. The comparison with experimental results is discussed in this paper. The real-time calculation tool is well able to calculate model-based vertical growth rate, which is convenient for fast and continuous evaluations of EAST control system stability performances.

Determination of activation energy of ion-implanted deuterium release from W-Y2O3

Xue-Feng Wang, Ji-Liang Wu, Qiang Li, Rui-Zhu Yang, Zhan-Lei Wang, Chang-An Chen, Chun-Rong Feng, Yong-Chu Rao, Xiao-Hong Chen, Xiao-Qiu Ye
Chin. Phys. B 2020, 29 (6): 065205;  doi: 10.1088/1674-1056/ab8204
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The retention and release of deuterium in W-2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma (flux ~3.71×1021 D/m2·s, energy ~25 eV, and fluence up to 1.3×1026 D/m2) are studied. The results show that the total amount of deuterium released from W-2%Y2O3 is 5.23×1020 D/m2(2.5 K/min), about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra (TDS) at different heating rates (2.5 K/min-20 K/min) reveal that both W and W-2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV (grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV (vacancy) in W and 1.73 eV (vacancy) in W-2%Y2O3.

Measurement of molybdenum ion density for L-mode and H-mode plasma discharges in the EAST tokamak

Yongcai Shen, Hongming Zhang, Bo Lyu, Yingying Li, Jia Fu, Fudi Wang, Qing Zang, Baonian Wan, Pan Pan, Minyou Ye, the EAST team
Chin. Phys. B 2020, 29 (6): 065206;  doi: 10.1088/1674-1056/ab8456
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We report the measurement of total molybdenum ion density for L-mode and H-mode plasmas on EAST using spectral lines observation and calculation based on an impurity transport code. A flat-filed extreme ultraviolet spectrometer with some spatial resolution is used to obtain the radial profiles of molybdenum spectral line emissions. The absolute calibration for the extreme ultraviolet spectrometer is finished by comparing the calculated bremsstrahlung intensity with the readings of CCD detector. Molybdenum ion transport study is performed using the radial ion density profiles and one-dimensional impurity transport code STRAHL. The total molybdenum density profiles are determined from the transport analysis. The molybdenum density during L-mode and H-mode phases are obtained, which are about 3 and 4 orders of magnitude smaller than the electron density, respectively. An inward pinch is found during the H-mode phase that leads to the peaked profile of molybdenum density.

Experimental study on energy characteristics and ignition performance of recessed multichannel plasma igniter

Bang-Huang Cai, Hui-Min Song, Min Jia, Yun Wu, Wei Cui, Sheng-Fang Huang
Chin. Phys. B 2020, 29 (6): 065207;  doi: 10.1088/1674-1056/ab820c
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In the extreme conditions of high altitude, low temperature, low pressure, and high speed, the aircraft engine is prone to flameout and difficult to start secondary ignition, which makes reliable ignition of combustion chamber at high altitude become a worldwide problem. To solve this problem, a kind of multichannel plasma igniter with round cavity is proposed in this paper, the three-channel and five-channel igniters are compared with the traditional ones. The discharge energy of the three igniters was compared based on the electric energy test and the thermal energy test, and ignition experiments was conducted in the simulated high-altitude environment of the component combustion chamber. The results show that the recessed multichannel plasma igniter has higher discharge energy than the conventional spark igniter, which can increase the conversion efficiency of electric energy from 26% to 43%, and the conversion efficiency of thermal energy from 25% to 73%. The recessed multichannel plasma igniter can achieve greater spark penetration depth and excitation area, which both increase with the increase of height. At the same height, the inlet flow helps to increase the penetration depth of the spark. The recessed multichannel plasma igniter can widen the lean ignition boundary, and the maximum enrichment percentage of lean ignition boundary can reach 31%.

Interaction of supersonic molecular beam with low-temperature plasma

Dong Liu, Guo-Feng Qu, Zhan-Hui Wang, Hua-Jie Wang, Hao Liu, Yi-Zhou Wang, Zi-Xu Xu, Min Li, Chao-Wen Yang, Xing-Quan Liu, Wei-Ping Lin, Min Yan, Yu Huang, Yu-Xuan Zhu, Min Xu, Ji-Feng Han
Chin. Phys. B 2020, 29 (6): 065208;  doi: 10.1088/1674-1056/ab8457
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The interaction between the supersonic molecular beam (SMB) and the low-temperature plasma is a critical issue for the diagnosis and fueling in the Tokamak device. In this work, the interaction process between the argon SMB and the argon plasma is studied by a high-speed camera based on the Linear Experimental Advanced Device (LEAD) in Southwestern Institute of Physics, China. It is found that the high-density SMB can extinct the plasma temporarily and change the distribution of the plasma density significantly, while the low-density SMB can hardly affect the distribution of plasma density. This can be used as an effective diagnostic technique to study the evolution of plasma density in the interaction between the SMB and plasma. Moreover, the related simulation based on this experiment is carried out to better understand the evolution of electron density and ion density in the interaction. The simulation results can be used to analyze and explain the experimental results well.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Effects of 3d-transition metal doping on the electronic and magnetic properties of one-dimensional diamond nanothread

Zhenzhen Miao, Can Cao, Bei Zhang, Haiming Duan, Mengqiu Long
Chin. Phys. B 2020, 29 (6): 066101;  doi: 10.1088/1674-1056/ab84dd
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The diamond nanothread (DNT), a new one-dimensional (1D) full carbon sp3 structure that has been successfully synthesized recently, has attracted widespread attention in the carbon community. By using the first-principles calculation method of density functional theory (DFT), we have studied the effects of 3d transition metal (TM) atomic doping on the electronic and magnetic properties of DNT. The results show that the spin-polarized semiconductor characteristics are achieved by doping Sc, V, Cr, Mn, and Co atoms in the DNT system. The magnetic moment ranges from 1.00 μB to 3.00 μB and the band gap value is from 0.35 eV to 2.54 eV. The Fe-doped DNT system exhibits spin-metallic state with a magnetic moment of 2.58 μB, while the Ti and Ni-doped DNT systems are nonmagnetic semiconductors. These results indicate that the 3d TM atoms doping can modulate the electronic and magnetic properties of 1D-DNT effectively, and the TM-doped DNT systems have potential applications in the fields of electronics, optoelectronics, and spintronics.

Exploring ferromagnetic half-metallic nature of Cs2NpBr6 via spin polarized density functional theory

Malak Azmat Ali, G Murtaza, A Laref
Chin. Phys. B 2020, 29 (6): 066102;  doi: 10.1088/1674-1056/ab7da4
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By employing the spin resolved density functional theory, half-metallic character is investigated in Cs2NpBr6 having a K2PtCl6-type structure. The results precisely predict the half-metallic behavior of Cs2NpBr6. In spin-down state it presents an indirect band gap, while in spin-up channel it turns metallic. The structure optimization confirms the half-metallic nature in ferromagnetic configuration. The calculated magnetic moment is 3 μB toward which the main contributor is the Np atom. Furthermore, all the computed results are compared with the available experimental and theoretical values. According to the present analysis, we recommend Cs2NpBr6 for spintronic applications.

First-principles calculations of solute-vacancy interactions in aluminum

Sha-Sha Zhang, Zheng-Jun Yao, Xiang-Shan Kong, Liang Chen, Jing-Yu Qin
Chin. Phys. B 2020, 29 (6): 066103;  doi: 10.1088/1674-1056/ab8458
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The interactions of solute atoms with vacancies play a key role in diffusion and precipitation of alloying elements, ultimately influencing the mechanical properties of aluminum alloys. In this study, first-principles calculations are systematically performed to quantify the solute-vacancy interactions for the 3d-4p series and the 4d-5p series. The solute-vacancy interaction gradually transforms from repulsion to attraction from left to right. The solute-vacancy binding energy is sensitive to the supercell size for elements at the beginning. These behaviors of the solute-vacancy binding energy can be understood in terms of the combination and competition between the elastic and electronic interactions. Overall, the electronic binding energy follows a similar trend to the total binding energy and plays a major role in the solute-vacancy interactions.

Extended damage range of (Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide films induced by surface irradiation

Jian-Cong Zhang, Sen Sun, Zhao-Ming Yang, Nan Qiu, Yuan Wang
Chin. Phys. B 2020, 29 (6): 066104;  doi: 10.1088/1674-1056/ab8374
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Irradiation makes structural materials of nuclear reactors degraded and failed. However, the damage process of materials induced by irradiation is not fully elucidated, mostly because the charged particles only bombarded the surface of the materials (within a few microns). In this work, we investigated the effects of surface irradiation on the indirect irradiation region of the (Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide (HEO) films in detail by plasma surface interaction. The results show that the damage induced by surface irradiation significantly extends to the indirect irradiation region of HEO film where the helium bubbles, dislocations, phase transformation, and the nickel oxide segregation were observed.

Balancing strength and plasticity of dual-phase amorphous/crystalline nanostructured Mg alloys

Jia-Yi Wang, Hai-Yang Song, Min-Rong An, Qiong Deng, Yu-Long Li
Chin. Phys. B 2020, 29 (6): 066201;  doi: 10.1088/1674-1056/ab84d5
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The dual-phase amorphous/crystalline nanostructured model proves to be an effective method to improve the plasticity of Mg alloys. The purpose of this paper is to explore an approach to improving the ductility and strength of Mg alloys at the same time. Here, the effect of amorphous phase strength, crystalline phase strength, and amorphous boundary (AB) spacing on the mechanical properties of dual-phase Mg alloys (DPMAs) under tensile loading are investigated by the molecular dynamics simulation method. The results confirm that the strength of DPMA can be significantly improved while its excellent plasticity is maintained by adjusting the strength of the amorphous phase or crystalline phase and optimizing the AB spacing. For the DPMA, when the amorphous phase (or crystalline phase) is strengthened to enhance its strength, the AB spacing should be increased (or reduced) to obtain superior plasticity at the same time. The results also indicate that the DPMA containing high strength amorphous phase exhibits three different deformation modes during plastic deformation with the increase of AB spacing. The research results will present a theoretical basis and early guidance for designing and developing the high-performance dual-phase hexagonal close-packed nanostructured metals.

Effect of Sn and Al additions on the microstructure and mechanical properties of amorphous Ti-Cu-Zr-Ni alloys

Fu-Chuan Chen, Fu-Ping Dai, Xiao-Yi Yang, Ying Ruan, Bing-Bo Wei
Chin. Phys. B 2020, 29 (6): 066401;  doi: 10.1088/1674-1056/ab8628
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Amorphous Ti-Cu-Zr-Ni alloys with minor addition of Sn and Al were prepared by melt spinning technique. The effects of Sn and Al additions on the microstructures and mechanical properties of glassy ribbons were investigated. The amorphous state of ribbons was confirmed by x-ray diffraction and transmission electron microscopy, where those ribbons with Sn addition exhibited a fully amorphous state. The characteristic temperature indicates that Ti45Cu35Zr10Ni5Sn5 alloy has a stronger glass-forming ability, as proven by differential scanning calorimetry. Ti45Cu35Zr10Ni5Al5 alloy showed a better hardness of 9.23 GPa and elastic modulus of 127.15 GPa and good wear resistance. Ti45Cu35Zr10Ni5Sn5 alloy displayed a pop-in event related to discrete plasticity according to nanoindentation. When the temperature is below 560 K, Ti45Cu35Zr10Ni5Sn5 alloy mainly exhibits elasticity. When the temperature rises between 717 K and 743 K, it shows a significant increase in elasticity but decrease in viscoelasticity after the ribbon experiences the main relaxation at 717 K. When the temperature is above 743 K, the ribbon shows viscoplasticity.

Growth and aggregation of Cu nanocrystals on ionic liquid surfaces

Jia-Wei Shen, Xun-Heng Ye, Zhi-Long Bao, Lu Li, Bo Yang, Xiang-Ming Tao, Gao-Xiang Ye
Chin. Phys. B 2020, 29 (6): 066801;  doi: 10.1088/1674-1056/ab8896
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We report a catalyst-free growth of Cu nanocrystals on ionic liquid surfaces by thermal evaporation method at room temperature. After deposition of Cu on ionic liquid surfaces, ramified Cu aggregates form. It is found that the aggregates are composed of both granules and nanocrystals with triangular or hexagonal appearances. The sizes of the nanocrystals are in the range of tens to hundreds of nanometers and increase with the nominal deposition thickness. The growth mechanism of the Cu aggregates and nanocrystals is presented.

Scalable preparation of water-soluble ink of few-layered WSe2 nanosheets for large-area electronics Hot!

Guoyu Xian, Jianshuo Zhang, Li Liu, Jun Zhou, Hongtao Liu, Lihong Bao, Chengmin Shen, Yongfeng Li, Zhihui Qin, Haitao Yang
Chin. Phys. B 2020, 29 (6): 066802;  doi: 10.1088/1674-1056/ab889e
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Few-layer two-dimensional (2D) semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics. A general approach is developed to fast prepare uniform and phase-pure 2H-WSe2 semiconducting nanosheets at a large scale, which involves the supercritical carbon dioxide (SC-CO2) treatment and a mild sonication-assisted exfoliation process in aqueous solution. The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures, as confirmed by Raman, x-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscope (STEM). The uniform 2H-WSe2 nanosheets can disperse well in water for over six months. Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics. The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Significant role of nanoscale Bi-rich phase in optimizing thermoelectric performance of Mg3Sb2

Yang Wang, Xin Zhang, Yan-Qin Liu, Jiu-Xing Zhang, Ming Yue
Chin. Phys. B 2020, 29 (6): 067201;  doi: 10.1088/1674-1056/ab84cd
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Mg3Sb1.5Bi0.5-based alloys have received much attention, and current reports on this system mainly focus on the modulation of doping. However, there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix. Here in this work, the thermoelectric properties of Mg3Sb2-xBix (0.4 ≤ x ≤ 0.55) compounds are systematically investigated by using the first principles calculation combined with experiment. The calculated results show that the band gap decreases after Bi has been substituted for Sb site, which makes the thermal activation easier. The maximum figure of merit (ZT) is 0.27 at 773 K, which is attributed to the ultra-low thermal conductivity 0.53 W·m-1·K-1 for x=0.5. The large mass difference between Bi and Sb atoms, the lattice distortion induced by substituting Bi for Sb, and the nanoscale Bi-rich particles distributed on the matrix are responsible for the reduction of thermal conductivity. The introduction of Bi into Mg3Sb2-based materials plays a vital role in regulating the transport performance of thermoelectric materials.

Theoretical design of single-molecule NOR and XNOR logic gates by using transition metal dibenzotetraaza[14]annulenes

Zi-Qun Wang, Fei Tang, Mi-Mi Dong, Ming-Lang Wang, Gui-Chao Hu, Jian-Cai Leng, Chuan-Kui Wang, Guang-Ping Zhang
Chin. Phys. B 2020, 29 (6): 067202;  doi: 10.1088/1674-1056/ab84cf
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The idea of replacing traditional silicon-based electronic components with the ones assembled by organic molecules to further scale down the electric circuits has been attracting extensive research focuses. Among the molecularly assembled components, the design of molecular logic gates with simple structure and high Boolean computing speed remains a great challenge. Here, by using the state-of-the-art nonequilibrium Green's function theory in conjugation with first-principles method, the spin transport properties of single-molecule junctions comprised of two serially connected transition metal dibenzotetraaza[14]annulenes (TM(DBTAA), TM=Fe, Co) sandwiched between two single-walled carbon nanotube electrodes are theoretically investigated. The numerical results show a close dependence of the spin-resolved current-voltage characteristics on spin configurations between the left and right molecular kernels and the kind of TM atom in TM(DBTAA) molecule. By taking advantage of spin degree of freedom of electrons, NOR or XNOR Boolean logic gates can be realized in Fe(DBTAA) and Co(DBTAA) junctions depending on the definitions of input and output signals. This work proposes a new kind of molecular logic gates and hence is helpful for further miniaturization of the electric circuits.

Experimental evaluation of interface states during time-dependent dielectric breakdown of GaN-based MIS-HEMTs with LPCVD-SiNx gate dielectric

Ya-Wen Zhao, Liu-An Li, Tao-Tao Que, Qiu-Ling Qiu, Liang He, Zhen-Xing Liu, Jin-Wei Zhang, Qian-Shu Wu, Jia Chen, Zhi-Sheng Wu, Yang Liu
Chin. Phys. B 2020, 29 (6): 067203;  doi: 10.1088/1674-1056/ab8895
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We experimentally evaluated the interface state density of GaN MIS-HEMTs during time-dependent dielectric breakdown (TDDB). Under a high forward gate bias stress, newly increased traps generate both at the SiNx/AlGaN interface and the SiNx bulk, resulting in the voltage shift and the increase of the voltage hysteresis. When prolonging the stress duration, the defects density generated in the SiNx dielectric becomes dominating, which drastically increases the gate leakage current and causes the catastrophic failure. After recovery by UV light illumination, the negative shift in threshold voltage (compared with the fresh one) confirms the accumulation of positive charge at the SiNx/AlGaN interface and/or in SiNx bulk, which is possibly ascribed to the broken bonds after long-term stress. These results experimentally confirm the role of defects in the TDDB of GaN-based MIS-HEMTs.

Capacitive coupling induced Kondo-Fano interference in side-coupled double quantum dots

Fu-Li Sun, Yuan-Dong Wang, Jian-Hua Wei, Yi-Jing Yan
Chin. Phys. B 2020, 29 (6): 067204;  doi: 10.1088/1674-1056/ab8ac1
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We report capacitive coupling induced Kondo-Fano (K-F) interference in a double quantum dot (DQD) by systematically investigating its low-temperature properties on the basis of hierarchical equations of motion evaluations. We show that the interdot capacitive coupling U12 splits the singly-occupied (S-O) state in quantum dot 1 (QD1) into three quasi-particle substates: the unshifted S-O0 substate, and elevated S-O1 and S-O2. As U12 increases, S-O2 and S-O1 successively cross through the Kondo resonance state at the Fermi level (ω=0), resulting in the so-called Kondo-I (KI), K-F, and Kondo-II (KII) regimes. While both the KI and KII regimes have the conventional Kondo resonance properties, remarkable Kondo-Fano interference features are shown in the K-F regime. In the view of scattering, we propose that the phase shift η(ω) is suitable for analysis of the Kondo-Fano interference. We present a general approach for calculating η(ω) and applying it to the DQD in the K-F regime where the two maxima of η(ω=0) characterize the interferences between the Kondo resonance state and S-O2 and S-O1 substates, respectively.

Optical spin-to-orbital angular momentum conversion instructured optical fields Hot!

Yang Zhao, Cheng-Xi Yang, Jia-Xi Zhu, Feng Lin, Zhe-Yu Fang, Xing Zhu
Chin. Phys. B 2020, 29 (6): 067301;  doi: 10.1088/1674-1056/ab862a
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We investigate the dynamic quantities: momentum, spin and orbital angular momenta (SAM and OAM), and their conversion relationship in the structured optical fields at subwavelength scales, where the spin-orbit interaction (SOI) plays a key role and determines the behaviors of light. Specifically, we examine a nanostructure of a Ag nanoparticle (Ag NP) attached on a cylindrical Ag nanowire (Ag NW) under illumination of elliptically polarized light. These dynamic quantities obey the Noether theorem, i.e., for the Ag nanoparticle with spherical symmetry, the total angular momentum consisting of SAM and OAM conserves; for the Ag NW with translational symmetry, the orbital momentum conserves. Meanwhile, the spin-to-orbital angular momentum conversion is mediated by SOI arising from the spatial variation of the optical potential. In this nanostructure, the conservation of momentum imposes a strict restriction on the propagation direction of the surface plasmon polaritons along the Ag NW. Meanwhile, the orbital momentum is determined by the polarized properties of the excitation light and the topography of the Ag NP. Our work offers insights to comprehend the light behaviors in the structured optical fields in terms of the dynamic quantities and benefits to the design of optical nano-devices based on interactions between spin and orbital degrees of freedom.

Zero-energy modes in serially coupled double quantum dots

Fu-Li Sun, Zhen-Hua Li, Jian-Hua Wei
Chin. Phys. B 2020, 29 (6): 067302;  doi: 10.1088/1674-1056/ab8378
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We investigate symmetrically coupled double quantum dots via the hierarchical equations of motion method and propose a novel zero-energy mode (ZEM) at a temperature above the spin singlet-triplet transition temperature. Owing to the resonance of electron quasi-particle and hole quasi-particle, ZEM has a peak at ω=0 in the spectral density function. We further examine the effect of the magnetic field on the ZEM, where an entanglement of spin and charge has been determined; therefore, the magnetic field can split the ZEM in the spectra.

Multiple Fano resonances in metal-insulator-metal waveguide with umbrella resonator coupled with metal baffle for refractive index sensing

Yun-Ping Qi, Li-Yuan Wang, Yu Zhang, Ting Zhang, Bao-He Zhang, Xiang-Yu Deng, Xiang-Xian Wang
Chin. Phys. B 2020, 29 (6): 067303;  doi: 10.1088/1674-1056/ab888c
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A single baffle metal-insulator-metal (MIM) waveguide coupled with a semi-circular cavity and a cross-shaped cavity is proposed based on the multiple Fano resonance characteristics of surface plasmon polaritons (SPPs) subwavelength structure. The isolated state formed by two resonators interferes with the wider continuous state mode formed by the metal baffle, forming Fano resonance that can independently be tuned into five different modes. The formation mechanism of Fano resonance is analyzed based on the multimode interference coupled mode theory (MICMT). The finite element method (FEM) and MICMT are used to simulate the transmission spectra of this structure and analyze the influence of structural parameters on the refractive index sensing characteristics. And the transmission responses calculated by the FEM simulation are consistent with the MICMT theoretical results very well. The results show that the figure of merit (FOM) can reach 193 and the ultra-high sensitivity is 1600 nm/RIU after the structure parameters have been optimized, and can provide theoretical basis for designing the high sensitive refractive index sensors based on SPPs waveguide for high-density photonic integration with excellent performance in the near future.

Quasiparticle interference testing the possible pairing symmetry in Sr2RuO4

Cong-Cong Zhang, Jin-Hua Sun, Yang Yang, Wan-Sheng Wang
Chin. Phys. B 2020, 29 (6): 067401;  doi: 10.1088/1674-1056/ab8888
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The quasiparticle interference (QPI) patterns of the superconducting state in Sr2RuO4 are theoretically studied by taking into account the spin-orbital coupling and two different pairing modes, chiral p-wave pairing and equal d-wave pairing, in order to propose an experimental method to test them. Both of the QPI spectra for the two pairing modes have clearly peaks evolving with energy, and their locations can be determined from the tips of the constant energy contour. But the number, location, and evolution of these peaks with energy are different between the two pairing modes. The different behaviors of the QPI patterns in these two pairing modes may help to resolve whether Sr2RuO4 is a chiral p-wave or d-wave superconductor.

NMR and NQR studies on transition-metal arsenide superconductors LaRu2As2, KCa2Fe4As4F2, and A2Cr3As3

Jun Luo, Chunguang Wang Zhicheng Wang, Qi Guo, Jie Yang, Rui Zhou, K Matano, T Oguchi, Zhian Ren, Guanghan Cao, Guo-Qing Zheng
Chin. Phys. B 2020, 29 (6): 067402;  doi: 10.1088/1674-1056/ab892d
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We report 75As-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on transition-metal arsenides LaRu2As2, KCa2Fe4As4F2, and A2Cr3As3. In the superconducting state of LaRu2As2, a Hebel-Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T1 just below Tc, which indicates that LaRu2As2 is a full-gap superperconducor. For KCa2Fe4As4F2, antiferromagnetic spin fluctuations are observed in the normal state. We further find that the anisotropy rate RAF=T1c/T1ab is small and temperature independent, implying that the low energy spin fluctuations are isotropic in spin space. Our results indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition. For A2Cr3As3 (A=Na, K, Rb, Cs), we calculate the electric field gradient by first-principle method and assign the 75As-NQR peaks to two crystallographically different As sites, paving the way for further NMR investigation.

Quadruple-stacked Nb/NbxSi1-x/Nb Josephson junctions for large-scale array application

Wenhui Cao, Jinjin Li, Lanruo Wang, Yuan Zhong, Qing Zhong
Chin. Phys. B 2020, 29 (6): 067404;  doi: 10.1088/1674-1056/ab90e3
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Large-scale Josephson junction (JJ) arrays are essential in many applications, especially quantum voltage standards application for which hundreds of thousands of junctions are required to realize a high quantum voltage. For almost all applications, high-quality JJ arrays must be realized in a small chip area. This study proposes vertically quadruple-stacked Nb/(NbxSi1-x/Nb)4 JJs to increase the integration density of junctions in an array. The current-voltage (I-V) characteristics of a single stack of Nb/(NbxSi1-x/Nb)4 JJs have been measured at 4.2 K. The uniformity of junctions in one stack and the uniformity of several stacks over the entire 2 inches wafer have been analyzed. By optimizing the fabrication parameters, a large-scale quadruple-stacked Nb/(NbxSi1-x/Nb)4 array consisting of 400000 junctions is realized. Good DC I-V characteristics are obtained, indicating the good uniformity of the large-scale array.

Exact solution of a topological spin ring with an impurity

Xu-Chu Huang, Yi-Hua Song, Yi Sun
Chin. Phys. B 2020, 29 (6): 067501;  doi: 10.1088/1674-1056/ab8886
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The spin-1/2 Heisenberg chain coupled to a spin-S impurity moment with anti-periodic boundary condition is studied via the off-diagonal Bethe ansatz method. The twisted boundary breaks the U(1) symmetry of the system, which leads to that the spin ring with impurity can not be solved by the conventional Bethe ansatz methods. By combining the properties of the R-matrix, the transfer matrix, and the quantum determinant, we derive the T-Q relation and the corresponding Bethe ansatz equations. The residual magnetizations of the ground states and the impurity specific heat are investigated. It is found that the residual magnetizations in this model strongly depend on the constraint of the topological boundary condition, the inhomogeneity of the impurity comparing with the hosts could depress the impurity specific heat in the thermodynamic limit. This method can be expand to other integrable impurity models without U(1) symmetry.

Physical properties and magnetic structure of a layered antiferromagnet PrPd0.82Bi2

Meng Yang, Changjiang Yi, Fengfeng Zhu, Xiao Wang, Dayu Yan, Shanshan Miao, Yixi Su, Youguo Shi
Chin. Phys. B 2020, 29 (6): 067502;  doi: 10.1088/1674-1056/ab889f
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We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic (AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at TN~7 K. A large Sommerfeld coefficient of 329.23 mJ·mol-1·K-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k=(0 0 0) is formed below TN. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μB at 4 K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μB. PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.

Critical behavior in the layered organic-inorganic hybrid (CH3NH3)2CuCl4

Tina Raoufi, Yinina Ma, Young Sun
Chin. Phys. B 2020, 29 (6): 067503;  doi: 10.1088/1674-1056/ab892c
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The critical properties and the nature of the ferromagnetic-paramagnetic phase transition in the 2D organic-inorganic hybrid (CH3NH3)2CuCl4 single crystal have been investigated by dc magnetization in the vicinity of the magnetic transition. Different techniques were used to estimate the critical exponents near the ferromagnetic-paramagnetic phase transition such as modified Arrott plots, the Kouvel-Fisher method, and the scaling hypothesis. Values of β=0.22, γ=0.82, and δ=4.4 were obtained. These critical exponents are in line with their corresponding values confirmed through the scaling hypothesis as well as the Widom scaling relation, supporting their reliability. It is concluded that this 2D hybrid compound possesses strong ferromagnetic intra-layer exchange interaction as well as weak interlayer ferromagnetic coupling that causes a crossover from 2D to 3D long-range interaction.

Influence of the anisotropy on the magneto-acoustic response of magnetic surface acoustic wave resonators

Yawei Lu, Wenbin Hu, Wan Liu, Feiming Bai
Chin. Phys. B 2020, 29 (6): 067504;  doi: 10.1088/1674-1056/ab8375
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One-port magnetic surface acoustic wave (MSAW) resonators are fabricated by stacking multilayered (FeCoSiB/SiO2)n films directly on top of interdigital electrodes. It is shown that the magneto-acoustic response of the MSAW resonators critically depends the hysteresis of ΔE effect. For the magnetic multilayer without induced magnetic anisotropy, the resonance frequency (fR) exhibits a butterfly-like dependence on the external field, therefore, enabling bipolar detection of magnetic field smaller than its coercive field. However, for the magnetic multilayers with induced magnetic anisotropy, butterfly-like or loop-like fR-H curves are measured along the interdigtial electrode fingers or the SAW propagation direction, which can be attributed to the competition between the magnetic field-induced anisotropy and the stress-induced or shape anisotropy.

Effect of interface magnetization depinning on the frequency shift of ferromagnetic and spin wave resonance in YIG/GGG films

Fanqing Lin, Shouheng Zhang, Guoxia Zhao, Hongfei Li, Weihua Zong, Shandong Li
Chin. Phys. B 2020, 29 (6): 067601;  doi: 10.1088/1674-1056/ab8dac
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Nowadays the yttrium iron garnet (Y3Fe5O12, YIG) films are widely used in the microwave and spin wave devices due to their low damping constant and long propagation distance for spin waves. However, the performances, especially the frequency stability, are seriously affected by the relaxation of the interface magnetic moments. In this study, the effect of out-of-plane magnetization depinning on the resonance frequency shift (Δfr) was investigated for 3-μm YIG films grown on Gd3Ga5O12 (GGG) (111) substrates by liquid-phase epitaxy. It is revealed that the ferromagnetic resonance (FMR) and spin wave propagation exhibit a very slow relaxation with relaxation time τ even longer than one hour under an out-of-plane external magnetic bias field. The Δfr span of 15.15-24.70 MHz is observed in out-of-plane FMR and forward volume spin waves. Moreover, the Δfr and τ depend on the magnetic field. The Δfr can be attributed to that the magnetic moments break away from the pinning layer at the YIG/GGG interface. The thickness of the pinning layer is estimated to be about 9.48 nm to 15.46 nm according to the frequency shifting. These results indicate that Δfr caused by the pinning layer should be addressed in the design of microwave and spin wave devices, especially in the transverse magnetic components.

Effect of deposition temperature on SrFe12O19@carbonyl iron core-shell composites as high-performance microwave absorbers

Yuan Liu, Rong Li, Ying Jia, Zhen-Xin He
Chin. Phys. B 2020, 29 (6): 067701;  doi: 10.1088/1674-1056/ab81fb
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The SrFe12O19@carbonyl iron (CI) core-shell composites used in microwave absorption are prepared by the metal-organic chemical vapor deposition (MOCVD). The x-ray diffractometer, scanning electron microscope, energy dispersive spectrometer, and vector network analyzer are used to characterize the structural, electromagnetic, and absorption properties of the composites. The results show that the SrFe12O19@CI composites with a core-shell structure could be successfully prepared under the condition: deposition temperatures above 180 ℃, deposition time 30 min, and gas flow rate 30 mL/min. The electromagnetic properties of the composites change significantly, and their absorption capacities are improved. Of the obtained samples, those samples prepared at a deposition temperature of 180 ℃ exhibit the best absorption performance. The reflection loss of SrFe12O19@CI (180 ℃) with 1.5 mm-2.5 mm in thickness is less than -10 dB in a frequency range of 8 GHz-18 GHz, which covers the whole X band and Ku band.

First-principles calculation of influences of La-doping on electronic structures of KNN lead-free ceramics

Ting Wang, Yan-Chen Fan, Jie Xing, Ze Xu, Geng Li, Ke Wang, Jia-Gang Wu, Jian-Guo Zhu
Chin. Phys. B 2020, 29 (6): 067702;  doi: 10.1088/1674-1056/ab84db
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The electronic structures of lead-free piezoceramic (K0.5Na0.5)NbO3 (KNN) and La-doped KNN ((K0.5Na0.5)0.994La0.006NbO3) are studied by using first principles calculation on the basis of density functional theory (DFT). The results reveale that the piezoelectricity stems from strong hybridization between the Nb atom and the O atom. At the same time, the K or Na atoms are replaced by the La doping atoms, which brings about the anisotropic relaxation. The La doping reduces the forbidden band, at the same time it makes Fermi surfaces shift toward the energetic conduction band (CB) of KNN. With the increase of La-doping intent, the phase structure of KNN extends from O-phase to T-phase and improves the piezoelectric properties of KNN.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Uncovering the internal structure of five-fold twinned nanowires through 3D electron diffraction mapping

Xin Fu
Chin. Phys. B 2020, 29 (6): 068101;  doi: 10.1088/1674-1056/ab8370
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Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement. Although both of metallic and semiconductor five-fold twinned nanostructures show inhomogeneity in their cross-sectional strain distribution, the evident strain concentration at twin boundaries in the semiconductor systems has been found in contrast to the metallic systems. Naturally, a problem is raised how the chemical bonding characteristics of various five-fold twinned nanosystems affects their strain-relieving defect structures. Here using three-dimensional (3D) electron diffraction mapping methodology, the intrinsic strain and the strain-relieving defects in a pentagonal Ag nanowire and a star-shaped boron carbide nanowire, both of them have basically equal radial twin-plane width about 30 nm, are non-destructively characterized. The non-uniform strain and defect distribution between the five single crystalline segments are found in both of the five-fold twinned nanowires. Diffraction intensity fine structure analysis for the boron carbide five-fold twinned nanowire indicates the presence of high-density of planar defects which are responsible for the accommodation of the intrinsic angular excess. However, for the Ag five-fold twinned nanowire, the star-disclination strain field is still present, although is partially relieved by the formation of localized stacking fault layers accompanied by partial dislocations. Energetic analysis suggests that the variety in the strain-relaxation ways for the two types of five-fold twinned nanowires could be ascribed to the large difference in shear modulus between the soft noble metal Ag and the superhard covalent compound boron carbide.

Photocurrent improvement of an ultra-thin silicon solar cell using the localized surface plasmonic effect of clustering nanoparticles

F Sobhani, H Heidarzadeh, H Bahador
Chin. Phys. B 2020, 29 (6): 068401;  doi: 10.1088/1674-1056/ab836d
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The cluster-shaped plasmonic nanostructures are used to manage the incident light inside an ultra-thin silicon solar cell. Here we simulate spherical, conical, pyramidal, and cylindrical nanoparticles in a form of a cluster at the rear side of a thin silicon cell, using the finite difference time domain (FDTD) method. By calculating the optical absorption and hence the photocurrent, it is shown that the clustering of nanoparticles significantly improves them. The photocurrent enhancement is the result of the plasmonic effects of clustering the nanoparticles. For comparison, first a cell with a single nanoparticle at the rear side is evaluated. Then four smaller nanoparticles are put around it to make a cluster. The photocurrents of 20.478 mA/cm2, 23.186 mA/cm2, 21.427 mA/cm2, and 21.243 mA/cm2 are obtained for the cells using clustering conical, spherical, pyramidal, cylindrical NPs at the backside, respectively. These values are 13.987 mA/cm2, 16.901 mA/cm2, 16.507 mA/cm2, 17.926 mA/cm2 for the cell with one conical, spherical, pyramidal, cylindrical NPs at the backside, respectively. Therefore, clustering can significantly improve the photocurrents. Finally, the distribution of the electric field and the generation rate for the proposed structures are calculated.

Estimation of sea clutter inherent Doppler spectrum from shipborne S-band radar sea echo

Jin-Peng Zhang, Yu-Shi Zhang, Xin-Yu Xu, Qing-Liang Li, Jia-Ji Wu
Chin. Phys. B 2020, 29 (6): 068402;  doi: 10.1088/1674-1056/ab888a
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Measurement of shipborne radar sea echo is instrumental in collecting the sea clutter data in open sea areas. However, the ship movement would introduce an extra Doppler component into the spectrum of the sea clutter, so the sea clutter inherent spectrum must be estimated prior to investigating the sea clutter Doppler characteristics from the shipborne radar sea echo. In this paper we show some results about a shipborne sea clutter measurement experiment that was conducted in the South China Sea in a period between 2017 and 2018; abundant clutter data have been collected by using a shipborne S-band clutter measurement radar. To obtain the sea clutter inherent Doppler spectrum from these data, an estimation method, based on the mapping relationship between the shipborne clutter spectrum and the inherent clutter spectrum, is proposed. This method is validated by shipborne clutter data sets under the same measuring conditions except for the ship speed. Using this method, the characteristics of the Doppler spectrum lineshapes in the South China Sea are calculated and analyzed according to different sea states, wave directions, and radar resolutions, which can be instrumental in designing the radar target detection algorithms.

High-performance midwavelength infrared detectors based on InAsSb nBn design

Xuan Zhang, Qing-Xuan Jia, Ju Sun, Dong-Wei Jiang, Guo-Wei Wang, Ying-Qiang Xu, Zhi-Chuan Niu
Chin. Phys. B 2020, 29 (6): 068501;  doi: 10.1088/1674-1056/ab8377
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we report nBn photodetectors based on InAs0.91Sb0.09 with a 100% cut-off wavelength of 4.75 μm at 300 K. The band of an nBn detector is similar to that of a standard pin detector, but there is special wide bandgap AlAs0.08Sb0.92 barrier layer in the nBn detector, in which the depletion region of nBn detector exists. The nBn design has many advantages, such as low dark current and high quantum efficiency, because the nBn design can suppress the generation-recombination (GR) current that is the main composition of standard pin detector dark current. The constant slope of the Arrhenius plot of J0-1/T indicates the absence of the generation-recombination dark current. We fabricate an nBn detector with a quantum efficiency (QE) maximum of ~ 60% under -0.2-V bias voltage. The InAsSb nBn detectors may be a competitive candidate for midwavelength infrared detector.

Compact ultra-narrowband superconducting filter using N-spiral resonator with open-loop secondary coupling structure

Lin Tao, Bin Wei, Xubo Guo, Hongcheng Li, Chenjie Luo, Bisong Cao, Linan Jiang
Chin. Phys. B 2020, 29 (6): 068502;  doi: 10.1088/1674-1056/ab888d
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A novel N-spiral resonator with open-loop secondary coupling structure (OLSCS) is proposed to realize a compact ultra-narrowband high temperature superconducting (HTS) filter. The coupling strength and polarity between the resonators can be significantly reduced and changed by introducing OLSCS, thus the required weak coupling can be achieved in a very compact size. A six-pole superconducting filter at 1701 MHz with a fractional bandwidth of 0.19% is designed to validate this method. The filter is fabricated on MgO substrate with a compact size of 15 mm×10 mm. The measured insertion loss is 0.79 dB, and the return loss is better than 17.4 dB. The experimental results show a good agreement with the simulations.

Design of a novel high holding voltage LVTSCR with embedded clamping diode

Ling Zhu, Hai-Lian Liang, Xiao-Feng Gu, Jie Xu
Chin. Phys. B 2020, 29 (6): 068503;  doi: 10.1088/1674-1056/ab836e
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In order to reduce the latch-up risk of the traditional low-voltage-triggered silicon controlled rectifier (LVTSCR), a novel LVTSCR with embedded clamping diode (DC-LVTSCR) is proposed and verified in a 0.18-μm CMOS process. By embedding a p+ implant region into the drain of NMOS in the traditional LVTSCR, a reversed Zener diode is formed by the p+ implant region and the n+ bridge, which helps to improve the holding voltage and decrease the snapback region. The physical mechanisms of the LVTSCR and DC-LVTSCR are investigated in detail by transmission line pulse (TLP) tests and TCAD simulations. The TLP test results show that, compared with the traditional LVTSCR, the DC-LVTSCR exhibits a higher holding voltage of 6.2 V due to the embedded clamping diode. By further optimizing a key parameter of the DC-LVTSCR, the holding voltage can be effectively increased to 8.7 V. Therefore, the DC-LVTSCR is a promising ESD protection device for circuits with the operation voltage of 5.5-7 V.

Entrainment range affected by the difference in sensitivity to light-information between two groups of SCN neurons

Bao Zhu, Jian Zhou, Mengting Jia, Huijie Yang, Changgui Gu
Chin. Phys. B 2020, 29 (6): 068702;  doi: 10.1088/1674-1056/ab8897
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The mammals can not only entrain to the natural 24-h light-dark cycle, but also to the artificial cycle with non 24-h period through the main clock named suprachiasmatic nucleus in the brain. The range of the periods of the artificial cycles which the suprachiasmatic nucleus (SCN) can entrain, is called entrainment range reflecting the flexibility of the SCN. The SCN can be divided into two groups of neurons functionally, based on the different sensitivities to the light information. In the present study, we examined whether the entrainment range is affected by this difference in the sensitivity by a Poincaré model. We found that the relationship of the entrainment range to the difference depends on the coupling between two groups. When the coupling strength is much smaller than the light intensity, the relationship is parabolic-like, and the maximum of the entrainment range is obtained with no difference of the sensitivity. When the coupling strength is much larger than the light intensity, the relationship is monotonically changed, and the maximum of the entrainment range is obtained when the difference is the largest. Our finding may provide an explanation for the exitance of the difference in the sensitivity to light-information as well as shed light on how to increase the flexibility of the SCN represented by widening the entrainment range.

Biases of estimated signals in x-ray analyzer-based imaging

Jianlin Xia, Wen Xu, Ruicheng Zhou, Xiaomin Shi, Kun Ren, Heng Chen, Zhili Wang
Chin. Phys. B 2020, 29 (6): 068703;  doi: 10.1088/1674-1056/ab8887
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Recently, a novel three-image algorithm has been proposed to retrieve the sample's absorption, refraction, and scattering properties in x-ray analyzer-based imaging. The feasibility of the three-image algorithm was validated by synchrotron radiation experiments. However, it is unclear yet whether the estimated refraction and scattering signals are biased or not and how the analyzer angular position affects the biases in the estimated signals. For this purpose, the biases of the extracted refraction and scattering signals are theoretically derived for the three-image algorithm. The theoretical models are further confirmed by numerical experiments. The results show that both the estimated refraction and scattering signals are biased, and the biases are strongly dependent on the analyzer angular position. Besides, the biases also show dependence on the sample's refraction and scattering properties locally. Those results can be used as general guidelines to optimize experimental parameters for bias reduction and accurate imaging of different features within the sample.

Potential dynamic analysis of tumor suppressor p53 regulated by Wip1 protein

Nan Liu, Dan-Ni Wang, Hai-Ying Liu, Hong-Li Yang, Lian-Gui Yang
Chin. Phys. B 2020, 29 (6): 068704;  doi: 10.1088/1674-1056/ab84d1
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The tumor suppressor p53 plays a key role in protecting genetic integrity. Its dynamics have important physiological significance, which may be related to the cell fate. Previous experiments have shown that the wild-type p53-induced phosphatase 1 (Wip1) protein could maintain p53 oscillation. Therefore, we add Wip1 to remodel the p53 network. Firstly, we use the binomial τ-leap algorithm to prove our model stable under internal noise. Then, we make a series of bifurcation diagrams, that is, p53 levels as a function of p53 degradation rate at different Wip1 generation rates. The results illustrate that Wip1 is essential for p53 oscillation. Finally, a two-dimensional bifurcation diagram is made and the stability of some p53 dynamics under external noise is analyzed by potential landscape. Our results may have some implications for artificially interfering with p53 dynamics to achieve tumor suppression.
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