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Chin. Phys. B  
  Chin. Phys. B--2019, Vol.28, No.4
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SPECIAL TOPIC—Recent advances in thermoelectric materials and devices
TOPICAL REVIEW—Photodetector: materials, physics, and applications
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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

Suhui Deng, Mingping Liu
Chin. Phys. B 2019, 28 (4): 044101;  doi: 10.1088/1674-1056/28/4/044101
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The self-injection and acceleration of electrons in a hollow plasma channel driven by ultrashort intense laser pulses is investigated by Particle-in-Cell (PIC) simulations. It is shown that electrons from the bubble sheath will be self-injected into the hollow plasma channel and move radially towards the channel border due to the lack of focusing force in the hollow plasma channel. After several reflections near the channel wall by the strong focusing force, a self-injected electron bunch can be confined in the hollow plasma channel and quasi-phase-stably accelerated forward for the whole laser-plasma interaction process. These electrons using optical and plasma-related self-injection method can be self-organized to remain in the rear of the bubble, where the accelerating electric field is transversely uniform and nearly plateau along the propagation axis. Therefore, the self-injected electron bunch can be accelerated in a steady state without obvious oscillation and has a high quality with narrow energy spread and low divergence.

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

Xiangxian Wang, Jiankai Zhu, Huan Tong, Xudong Yang, Xiaoxiong Wu, Zhiyuan Pang, Hua Yang, Yunping Qi
Chin. Phys. B 2019, 28 (4): 044201;  doi: 10.1088/1674-1056/28/4/044201
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A plasmonic refractive index (RI) sensor with high RI sensitivity based on a gold composite structure is proposed. This composite structure is constructed from a perfect gold nano-disk square array on a gold film, with a SiO2 spacer. The reflection spectra of the composite structure, with analyte RI in the range of 1.30 to 1.40, are theoretically studied using the finite-difference time-domain method. The incident light beam is partly coupled to the localized surface plasmons (LSP) of the single nano-disks and partly transferred to the propagating surface plasmons (PSP) by grating coupling. The reflectivity is nearly zero at the valley of the reflection spectrum because of the strong coupling between LSP and PSP. Also, the full width at half maximum (FWHM) of one of the surface plasmon polaritons (SPPs) modes is very narrow, which is helpful for RI sensing. An RI sensitivity as high as 853 nm/RIU is obtained. The influence of the structure parameters on the RI sensitivity and the sensor figure of merit (FOM) are investigated in detail. We find that the sensor maintains high RI sensitivity over a large range of periods and nano-disk diameters. Results of the theoretical simulation of the composite structure as a plasmonic sensor are promising. Thus, this composite structure could be extensively applied in the fields of biology and chemistry.

Enhancement of spatial resolution of ghost imaging via localizing and thresholding

Yunlong Wang, Yingnan Zhou, Shaoxiong Wang, Feiran Wang, Ruifeng Liu, Hong Gao, Pei Zhang, Fuli Li
Chin. Phys. B 2019, 28 (4): 044202;  doi: 10.1088/1674-1056/28/4/044202
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In ghost imaging, an illumination light is split into test and reference beams which pass through two different optical systems respectively and an image is constructed with the second-order correlation between the two light beams. Since both light beams are diffracted when passing through the optical systems, the spatial resolution of ghost imaging is in general lower than that of a corresponding conventional imaging system. When Gaussian-shaped light spots are used to illuminate an object, randomly scanning across the object plane, in the ghost imaging scheme, we show that by localizing central positions of the spots of the reference light beam, the resolution can be increased by a factor of √2 same as that of the corresponding conventional imaging system. We also find that the resolution can be further enhanced by setting an appropriate threshold to the bucket measurement of ghost imaging.

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

Li-Li Hou, Yong-Xing Sui, Shuai Wang, Xue-Fen Xu
Chin. Phys. B 2019, 28 (4): 044203;  doi: 10.1088/1674-1056/28/4/044203
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We theoretically investigate the phase sensitivity with parity measurement on a Mach-Zehnder interferometer with a coherent state combined with a squeezed number state. Within a constraint on the total mean photon number, we find, via parity measurement, that the mixing of a coherent state and squeezed number state can give better phase sensitivity than mixing a coherent state and squeezed vacuum state when the phase shift deviates from the optimal phase φ=0. In addition, we show that the classical Fisher information for parity measurement saturates the quantum Fisher information when the phase shift approaches to zero. Thus, the quantum Cramér-Rao bound can be reached via the parity measurement in the case of φ=0.

Anisotropic stimulated emission cross-section measurement in Nd: YVO4

Rui Guo, Yijie Shen, Yuan Meng, Mali Gong
Chin. Phys. B 2019, 28 (4): 044204;  doi: 10.1088/1674-1056/28/4/044204
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As a crucial parameter in the design and analysis of laser performances, stimulated emission (SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention. In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition 4F3/24I11/2 in Nd:YVO4 are measured in different propagating directions. Based on Fuchtbauer-Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO4 are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.

7.6-W diode-pumped femtosecond Yb: KGW laser

Yan-Fang Cao, Xiang-Hao Meng, Jun-Li Wang, Zhao-Hua Wang, Meng-Yao Cheng, Jiang-Feng Zhu, Zhi-Yi Wei
Chin. Phys. B 2019, 28 (4): 044205;  doi: 10.1088/1674-1056/28/4/044205
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We have demonstrated a high power diode-pumped mode-locked femtosecond Yb:KGW laser with semiconductor saturable absorber mirror (SESAM). By using an output coupler with 10% transmittance, the laser delivered 160-fs pulses with average output power of 7.6 W at a repetition rate of 78 MHz, corresponding to pulse energy of 97 nJ and peak power of 606 kW.

Femtosecond enhancement cavity with kilowatt average power

Jin Zhang, Lin-Qiang Hua, Shao-Gang Yu, Zhong Chen, Xiao-Jun Liu
Chin. Phys. B 2019, 28 (4): 044206;  doi: 10.1088/1674-1056/28/4/044206
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Femtosecond enhancement cavity (fsEC) has been proved to be a powerful tool in a diverse range of applications. Here, we report the recent progresses in building an fsEC on kilowatt level average power, with the aim of realization of intracavity high harmonic generation (HHG) and extension of the wavelength of femtosecond optical frequency comb from infrared (IR) to extreme ultraviolet (XUV). Upon mode-matching optimization and cavity length locking, an intracavity average power of 6.08 kW is reached and the corresponding buildup is 225. After introducing noble gas of Xe into the focus region, clear sign of plasma has been observed. The generated HHG is also coupled out by a sapphire plate placed at Brewster's angle for the fundamental laser. Our work paves the way for the realization of an XUV comb.

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

Ji-Hou Wang, Chang-Ming Chen, Ke-Wei Hu, Ru Cheng, Chun-Xue Wang, Yun-Ji Yi, Xiao-Qiang Sun, Fei Wang, Zhi-Yong Li, Da-Ming Zhang
Chin. Phys. B 2019, 28 (4): 044207;  doi: 10.1088/1674-1056/28/4/044207
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In this work, a dual-side parabolic structural (DSPS) multimode interference (MMI) thermo-optic (TO) waveguide switch is designed and fabricated by using novel low-loss fluorinated photopolymer materials. Comparing with the traditional dual-side linear structural (DSLS) MMI device, the effective length of the MMI coupling region proposed can be effectively reduced by 40%. The thermal stability of the waveguide material is analyzed, and the optical characteristics of the switching chip are simulated. The actual performances of the entire MMI switch are measured with an insertion loss of 7 dB, switching power of 15 mW and an extinction ratio of 28 dB. In contrast to the traditional MMI optical switch, the new type of parabolic structural MMI TO waveguide switch exhibits lower power consumption and larger extinction ratio. The compact fluorinated polymer MMI TO switches are suitable well for realizing miniaturization, high-properties, and lower cost of photonic integrated circuits.

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

Ming-Liang Li, Liang-Bing Liu, Guang-Jian Gao, Ming-Xi Deng, Ning Hu, Yan-Xun Xiang, Wu-Jun Zhu
Chin. Phys. B 2019, 28 (4): 044301;  doi: 10.1088/1674-1056/28/4/044301
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A theoretical model to analyze the nonlinear circumferential guided wave (CGW) propagation in a composite circular tube (CCT) is established. The response features of nonlinear CGWs to early damage[denoted by variations in third-order elastic constants (TOECs)] in an inner layer of CCT are investigated. On the basis of the modal expansion approach, the second-harmonic field of primary CGW propagation can be assumed to be a linear sum of a series of double-frequency CGW (DFCGW) modes. The quantitative relationship of DFCGW mode versus the relative changes in the inner layer TOECs is then investigated. It is found that the changes in the inner layer TOECs of CCT will obviously affect the driving source of DFCGW mode and its modal expansion coefficient, which is intrinsically able to influence the efficiency of cumulative second-harmonic generation (SHG) by primary CGW propagation. Theoretical analyses and numerical simulations demonstrate that the second harmonic of primary CGW is monotonic and very sensitive to the changes in the inner layer TOECs of CCT, while the linear properties of primary CGW propagation almost remain unchanged. Our results provide a potential application for accurately characterizing the level of early damage in the inner layer of CCT through the efficiency of cumulative SHG by primary CGW propagation.

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

Yan-Hong Li, Guo-Qiang Liu, Jia-Xiang Song, Hui Xia
Chin. Phys. B 2019, 28 (4): 044302;  doi: 10.1088/1674-1056/28/4/044302
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Thermoacoustic imaging with current injection (TAI-CI) is a novel imaging technology that couples with electromagnetic and acoustic research, which combines the advantages of high contrast of the electrical impedance tomography and the high spatial resolution of sonography, and therefore has the potential for early diagnosis. To verify the feasibility of TAI-CI for complex bone-containing biological tissues, the principle of TAI-CI and the coupling characteristics of fluid and solid were analyzed. Meanwhile, thermoacoustic (TA) effects for fluid model and fluid-solid coupling model were analyzed by numerical simulations. Moreover, we conducted experiments on animal cartilage, hard bone and biological soft tissue phantom with low conductivity (0.5 S/m). By injecting a current into the phantom, the thermoacoustic signal was detected by the ultrasonic transducer with a center frequency of 1 MHz, thereby the B-scan image of the objects was obtained. The B-scan image of the cartilage experiment accurately reflects the distribution of cartilage and gel, and the hard bone has a certain attenuation effect on the acoustic signal. However, compared with the ultrasonic imaging, the thermoacoustic signal is only attenuated during the outward propagation. Even in this case, a clear image can still be obtained and the images can reflect the change of the conductivity of the gel. This study confirmed the feasibility of TAI-CI for the imaging of biological tissue under the presence of cartilage and the bone. The novel TAI-CI method provides further evidence that it can be used in the diagnosis of human diseases.

Wetting failure condition on rough surfaces

Feng-Chao Yang, Xiao-Peng Chen
Chin. Phys. B 2019, 28 (4): 044701;  doi: 10.1088/1674-1056/28/4/044701
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Wetting states and processes attract plenty of interest of scientific and industrial societies. Air entrainment, i.e., wetting failure, on smooth plate in wetting process has been investigated carefully before. Liquid bath entries of “rough” silicon wafers are studied experimentally in the present work, and the air entrainment condition is analyzed specially with the lubrication theory. The roughness effects on the moving contact lines are therefore explored. The contact line pinning is found to be the main reason for the dynamically enhanced hydrophobicity of rough surface, which implies an effective microscopic contact angle of θe=θY+90° where θY is the Young's contact angle of the material. Our results suggest that the solid surfaces can be considered as hydrophobic ones for a wide range of dynamic process, since they are normally rough. The work can also be considered as a starting point for investigating the high-speed advancing of moving contact line on rough surfaces.

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

Shaolong Zhang, Wei Liu, Guilin Wang, Zhengwei Zhang, Qizhi Sun, Zhaohui Zhang, Jun Li, Yuan Chi, Nanchuan Zhang
Chin. Phys. B 2019, 28 (4): 044702;  doi: 10.1088/1674-1056/28/4/044702
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The Richtmyer-Meshkov instability at the interface of solid state tin material and xenon gases under cylinder geometry is studied in this paper. The experiments were conducted at FP-1 facility in Institute of Fluid Physics, China Academy of Engineering Physics (CAEP). The FP-1 facility is a pulsed power driver which could generate high amplitude magnetic field to drive metal liner imploding. Convergent shock wave was generated by impacting a magnetic-driven aluminium liner onto a inner mounted tin liner. The convergent evolution of the disturbance pre-machined onto the tin liner's inner surface was diagnosed by x-radiography. The spike amplitudes were derived from x-ray frames and were compared with linear theory. An analytical model containing material strength effect was derived and matched well to the experimental results. This sensibility of the disturbance evolution to material strength property shines light to the application of Richtmyer-Meshkov instability to infer material strength.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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

Yan Huang, Ji-Zhong Sun, Juan Cai, Zhen-Yue Sun, Chao-Feng Sang, De-Zhen Wang
Chin. Phys. B 2019, 28 (4): 045201;  doi: 10.1088/1674-1056/28/4/045201
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The influence of the J×B force on the topographical modification of W targets during a type-I-like ELM in ITER has been studied numerically. A two-dimensional (2D) fluid dynamics model is employed by solving liquid hydrodynamic Navier-Stokes equation with the 2D heat conduction equation in addition to driving forces for surface topography, such as surface tension and pressure gradient, the J×B force is particularly addressed. The governing equations are solved with the finite volume method by adequate prediction of the moving solid-liquid interface. Numerical simulations are carried out for a range of type-I ELM characteristic parameters. Our results indicate that both the surface tension and the J×B force contributes to the melt motion of tungsten plates when the energy flux is under 3000 MW·m-2, the surface tension is a major driving force while the pressure gradient is negligible. Our results also indicate that the J×B force makes the small hills grow at different rates at both the crater edges under a type-I-like ELM heat load with a Gaussian power density profile.

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

Cui-Kun Yang, Ming-Sheng Chu, Wen-Feng Guo
Chin. Phys. B 2019, 28 (4): 045202;  doi: 10.1088/1674-1056/28/4/045202
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The effect of an edge transport barrier on the toroidal field required for the ignition of an elongated tokamak is studied by modifying an analytic model which was calibrated against a transport code. It is found that the presence of the edge transport barrier will lead to a higher marginal toroidal field needed for ignition. This seemingly counter intuitive result is explained as being due to the equivalent effect of profile broadening by the edge transport barrier. This effect is further traced to its physical origin:in the case close to ignition, the fusion power input is predominantly concentrated in the center of plasma. It is demonstrated that if the fusion power input could be shifted from the center to the edge by a sufficient amount, then the presence of an edge transport barrier would lead to a reduction of the required toroidal field for ignition.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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

Zhi-Bin Ling, Gui-Ju Liu, Cheng-Peng Yang, Wen-Shuang Liang, Yi-Qian Wang
Chin. Phys. B 2019, 28 (4): 046101;  doi: 10.1088/1674-1056/28/4/046101
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The interfacial electrical potentials and charge distributions of two manganite-based heterojunctions, i.e., La0.67Ca0.33MnO3/SrTiO3:0.05 wt% Nb (LCMO/STON) and La0.67Ca0.33MnO3/LaMnO3/SrTiO3:0.05 wt% Nb (simplified as LCMO/LMO/STON), are studied by means of off-axis electron holography in a transmission electron microscope. The influences of buffer layer on the microstructure and magnetic properties of the LCMO films are explored. The results show that when a buffer layer of LaMnO3 is introduced, the tensile strain between the STON substrate and LCMO film reduces, misfit dislocation density decreases near the interfaces of the heterojunctions, and a positive magnetoresistance is observed. For the LCMO/STON junction, positive and negative charges accumulate near the interface between the substrate and the film. For the LCMO/LMO/STON junction, a complex charge distribution takes place across the interface, where notable negative charges accumulate. The difference between the charge distributions near the interface may shed light on the observed generation of positive magnetoresistance in the junction with a buffer layer.

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

Ali Bahrami, Mahyar Dehdast, Shahram Mohammadnejad, Habib Badri Ghavifekr
Chin. Phys. B 2019, 28 (4): 046102;  doi: 10.1088/1674-1056/28/4/046102
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We propose a novel structure for tunnel junction based on delta-doped AlGaAs/GaAs quantum wires. Higher spatial confinement of quantum wires alongside the increased effective doping concentration in the delta-doped regions extremely increase the peak tunneling current and enhance the performance of tunnel junction. The proposed structure can be used as tunnel junction in the multijunction solar cells under the highest possible thermodynamically limited solar concentration. The combination of the quantum wire with the delta-doped structure can be of benefit to the solar cells' advantages including higher number of sub-bands and high degeneracy. Simulation results show a voltage drop of 40 mV due to the proposed tunnel junction used in a multijunction solar cell which presents an extremely low resistance to the achieved peak tunneling current.

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

Shaoqin Jiang, Yong Huang, Maozhi Li
Chin. Phys. B 2019, 28 (4): 046103;  doi: 10.1088/1674-1056/28/4/046103
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Classical molecular dynamics simulations have been performed to investigate the structural evolution in deformation-induced rejuvenation in Cu80Zr20 metallic glass. Metallic glasses obtained by different cooling rates can be rejuvenated into the glassy state with almost the same potential energy by compressive deformation. The aging effect in different metallic glasses in cooling process can be completely erased by the deformation-induced rejuvenation. The evolution of cavities has been analyzed to understand the structural evolution in rejuvenation. It is found that as metallic glasses are rejuvenated by mechanical deformation, a lot of cavities are created. The lower the potential energy is, the more the cavities are created. The cavities are mainly created in the regions without cavities or with small cavities populated, indicating that the irreversible rearrangements induced by deformation are accompanied by the creation of cavity. This finding elucidates the underlying structural basis for rejuvenation and aging in metallic glasses from the cavity perspective.

Effects of helium implantation on mechanical properties of (Al0.31Cr0.20Fe0.14Ni0.35)O high entropy oxide films

Zhao-Ming Yang, Kun Zhang, Nan Qiu, Hai-Bin Zhang, Yuan Wang, Jian Chen
Chin. Phys. B 2019, 28 (4): 046201;  doi: 10.1088/1674-1056/28/4/046201
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It is widely accepted that helium (He) bubbles can prevent dislocations from moving and causing hardening and embrittlement of the material. However, He can affect the mechanical properties of materials in various ways. In this work, ultrafine nanocrystal high entropy oxide (HEO) films with He implantation are prepared by using a radio frequency (RF) reactive magnetron sputtering system to investigate the effects of He bubbles located at grain boundary on the mechanical properties of the films. The mechanical properties of the HEO films are investigated systematically via nanoindentation measurements. The results indicate that the grain boundary cavities induced by He implantation can degrade the hardness, the elastic modulus, and the creep resistance of the HEO films. The mechanical properties of the HEO films are sensitive to the interaction between the He bubbles and the dominating defects.

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

Ning-Ning Zhang, Yu-Juan Zhang, Yu Yang, Ping Zhang, Chang-Chun Ge
Chin. Phys. B 2019, 28 (4): 046301;  doi: 10.1088/1674-1056/28/4/046301
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The structural, mechanical and electronic properties of W1-xZrx (x=0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstrate that the W-Zr binary substitutional solid solution remaining bcc structure can be formed at an atom level. In addition, the derived bulk modulus (B), shear modulus (G), Young's modulus (E) for each of W-Zr alloys decrease gradually with the increase of Zr concentration, suggesting that W alloying with higher Zr concentration becomes softer than pure W metal. Based on the mechanical characteristic B/G ratio, Poisson's ratio ϒ and Cauchy pressure C', all W1-xZrx alloys are regarded as ductile materials. The ductility for each of those materials is improved with the increase of Zr concentration. The calculated density of states indicates that the ductility of W1-xZrx is due to the fact that the bonding in the alloy becomes more metallic through increasing the Zr concentration in tungsten. These results provide incontrovertible evidence for the fact that Zr has a significant influence on the properties of W.

Interaction of two symmetric monovacancy defects in graphene Hot!

Wen-Yan Xu, Li-Zhi Zhang, Li Huang, Yan-De Que, Ye-Liang Wang, Xiao Lin, Shi-Xuan Du
Chin. Phys. B 2019, 28 (4): 046801;  doi: 10.1088/1674-1056/28/4/046801
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We investigate the interactions between two symmetric monovacancy defects in graphene grown on Ru (0001) after silicon intercalation by combining first-principles calculations with scanning tunneling microscopy (STM). First-principles calculations based on free-standing graphene show that the interaction is weak and no scattering pattern is observed when the two vacancies are located in the same sublattice of graphene, no matter how close they are, except that they are next to each other. For the two vacancies in different sublattices of graphene, the interaction strongly influences the scattering and new patterns' emerge, which are determined by the distance between two vacancies. Further experiments on silicon intercalated graphene epitaxially grown on Ru (0001) shows that the experiment results are consistent with the simulated STM images based on free-standing graphene, suggesting that a single layer of silicon is good enough to decouple the strong interaction between graphene and the Ru (0001) substrate.

Band engineering of B2H2 nanoribbons

Bao Lei, Yu-Yang Zhang, Shi-Xuan Du
Chin. Phys. B 2019, 28 (4): 046803;  doi: 10.1088/1674-1056/28/4/046803
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Freestanding honeycomb borophene is unstable due to the electron-deficiency of boron atoms. B2H2 monolayer, a typical borophene hydride, has been predicted to be structurally stable and attracts great attention. Here, we investigate the electronic structures of B2H2 nanoribbons. Based on first-principles calculations, we have found that all narrow armchair nanoribbons with and without mirror symmetry (ANR-s and ANR-as, respectively) are semiconducting. The energy gap has a relation with the width of the ribbon. When the ribbon is getting wider, the gap disappears. The zigzag ribbons without mirror symmetry (ZNR-as) have the same trend. But the zigzag ribbons with mirror symmetry (ZNR-s) are always metallic. We have also found that the metallic ANR-as and ZNR-s can be switched to semiconducting by applying a tensile strain along the nanoribbon. A gap of 1.10 eV is opened under 16% strain for the 11.0-Å ANR-as. Structural stability under such a large strain has also been confirmed. The flexible band tunability of B2H2 nanoribbon increases its possibility of potential applications in nanodevices.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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

Fu-Ning Wang, Ji-Chao Li, Yi Li, Xin-Miao Zhang, Xue-Jin Wang, Yu-Fei Chen, Jian Liu, Chun-Lei Wang, Ming-Lei Zhao, Liang-Mo Mei
Chin. Phys. B 2019, 28 (4): 047101;  doi: 10.1088/1674-1056/28/4/047101
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First-principles calculations are performed to explore the possibility of generating the two-dimensional electron gas (2DEG) at the interface between LaGaO3/KTaO3 and NdGaO3/KTaO3 (001) heterostructures. Two different models – i.e., the superlattice model and the thin film model–are used to conduct a comprehensive investigation of the origin of charge carriers. For the symmetric superlattice model, the LaGaO3 (or NdGaO3) film is nonpolar. The 2DEG with carrier density on the order of 1014 cm-2 originates from the Ta dxy electrons contributed by both LaGaO3 (or NdGaO3) and KTaO3. For the thin film model, large polar distortions occur in the LaGaO3 and NdGaO3 layer, which entirely screens the built-in electric field and prevents electrons from transferring to the interface. Electrons of KTaO3 are accumulated at the interface, contributing to the formation of the 2DEG. All the heterostructures exhibit conducting properties regardless of the film thickness. Compared with the Ti dxy electrons in SrTiO3-based heterostructures, the Ta dxy electrons have small effective mass and they are expected to move with higher mobility along the interface. These findings reveal the promising applications of 2DEG in novel nanoelectronic devices.

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

Peng Fan, Ning-Hua Tong
Chin. Phys. B 2019, 28 (4): 047102;  doi: 10.1088/1674-1056/28/4/047102
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Recently, we developed the projective truncation approximation for the equation of motion of two-time Green's functions (Fan et al., Phys. Rev. B 97, 165140 (2018)). In that approximation, the precision of results depends on the selection of operator basis. Here, for three successively larger operator bases, we calculate the local static averages and the impurity density of states of the single-band Anderson impurity model. The results converge systematically towards those of numerical renormalization group as the basis size is enlarged. We also propose a quantitative gauge of the truncation error within this method and demonstrate its usefulness using the Hubbard-I basis. We thus confirm that the projective truncation approximation is a method of controllable precision for quantum many-body systems.

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

Tie-Cheng Han, Hong-Dong Zhao, Xiao-Can Peng
Chin. Phys. B 2019, 28 (4): 047302;  doi: 10.1088/1674-1056/28/4/047302
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Using the semi-insulating property and small lattice constant a of wurtzite BGaN alloy, we propose a BGaN buffer with a B-content of 1% to enhance two-dimensional electron gas (2DEG) confinement in a short-gate AlGaN/GaN high-electron mobility transistor (HEMT). Based on the two-dimensional TCAD simulation, the direct current (DC) and radio frequency (RF) characteristics of the AlGaN/GaN/B0.01Ga0.99N structure HEMTs are theoretically studied. Our results show that the BGaN buffer device achieves good pinch-off quality and improves RF performance compared with GaN buffer device. The BGaN buffer device can allow a good immunity to shift of threshold voltage for the aspect ratio (LG/d) down to 6, which is much lower than that the GaN buffer device with LG/d=11 can reach. Furthermore, due to a similar manner of enhancing 2DEG confinement, the B0.01Ga0.99N buffer device has similar DC and RF characteristics to those the AlGaN buffer device possesses, and its ability to control short-channel effects (SCEs) is comparable to that of an Al0.03Ga0.97N buffer. Therefore, this BGaN buffer with very small B-content promises to be a new method to suppress SCEs in GaN HEMTs.

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

Li-Jun Cui, Ping-Xiang Zhang, Jin-Shan Li, Guo Yan, Yong Feng, Xiang-Hong Liu, Jian-Feng Li, Xi-Feng Pan, Fan Yang, Sheng-Nan Zhang, Xiao-Bo Ma, Guo-Qing Liu
Chin. Phys. B 2019, 28 (4): 047401;  doi: 10.1088/1674-1056/28/4/047401
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The phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method is studied with different heat treatment parameters. The results show that the reaction temperature and phase composition of precursor powder depend on heat treatment atmosphere. Phase assemblage of (Bi,Pb)-2212, AEC, CuO, and small Bi-2201 can be obtained by heat-treated in N2-0.1%O2 atmosphere. For precursor powder, there is sufficient reaction process at 770℃, and the dimension of Bi-2212 phase increases rapidly with the increase of heat treatment temperature and time. The dimension of AEC phase also increases by extending heat treatment time. As a balance among phase assemblage, dimension of particle and adequate reaction, a reasonable precursor powder can be obtained by heat-treated at 770℃ for 12 h-16 h in N2-0.1%O2 atmosphere. Critical current of 37-filament Bi-2223 tape is about 120 A, which confirms that these heat treatment parameters are reasonable.

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

Jian-Feng Ye, Zheng Jiao, Kun Ma, Zhi-Yong Huang, Hai-Jiang Lv, Feng-Jian Jiang
Chin. Phys. B 2019, 28 (4): 047601;  doi: 10.1088/1674-1056/28/4/047601
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We carried out a proof-of-principle demonstration of the reconstruction of a static vector magnetic field involving adjacent three nitrogen-vacancy (NV) sensors with corresponding different NV symmetry axes in a bulk diamond. By means of optical detection of the magnetic resonance (ODMR) techniques, our experiment employs the continuous wave (CW) to monitor resonance frequencies and it extracts the information of the detected field strength and polar angles with respect to each NV frame of reference. Finally, the detected magnetic field relative to a fixed laboratory reference frame was reconstructed from the information acquired by the multi-NV sensor.

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

S Mourad, J El Ghoul, K Omri, K Khirouni
Chin. Phys. B 2019, 28 (4): 047701;  doi: 10.1088/1674-1056/28/4/047701
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Pure ZnO and indium-doped ZnO (In-ZO) nanoparticles with concentrations of In ranging from 0 to 5% are synthesized by a sol-gel processing technique. The structural and optical properties of ZnO and In-ZO nanoparticles are characterized by different techniques. The structural study confirms the presence of hexagonal wurtzite phase and indicates the incorporation of In3+ ions at the Zn2+ sites. However, the optical study shows a high absorption in the UV range and an important reflectance in the visible range. The optical band gap of In-ZnO sample varies between 3.16 eV and 3.22 eV. The photoluminescence (PL) analysis reveals that two emission peaks appear:one is located at 381 nm corresponding to the near-band-edge (NBE) and the other is observed in the green region. The aim of this work is to study the effect of indium doping on the structural, morphological, and optical properties of ZnO nanoparticles.

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

Fan Zhang, Yimin Chen, Rongping Wang, Xiang Shen, Junqiang Wang, Tiefeng Xu
Chin. Phys. B 2019, 28 (4): 047802;  doi: 10.1088/1674-1056/28/4/047802
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Ultrafast differential scanning calorimetry (DSC) was employed to investigate the glass transition kinetics of As2S3 and As2Se3. By using the Arrhenius method, a fragility index of~22 can be estimated in both As2S3 and As2Se3. However, when the scanning rate is more than 200 K…-1, non-Arrhenius behavior can be observed in such “strong” liquids where the Vogel-Fulcher method is more accurate to describe the glass transition kinetics. The fragilities of As2S3 and As2Se3 glasses are thus extrapolated as 28.3±1.94 and 23.7±1.80, respectively. This indicates that, As2Se3 glass has a better structural stability and it is a better candidate for device applications.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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

Jia Liu, Ying-Hua Zhang, Zhi-Ming Bai, Zhi-An Huang, Yu-Kun Gao
Chin. Phys. B 2019, 28 (4): 048101;  doi: 10.1088/1674-1056/28/4/048101
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ZnO/graphene/polyaniline (PANI) composite is synthesized and used for photoelectrocatalytic oxidation of methane under simulated sun light illumination with ambient conditions. The photoelectrochemical (PEC) performance of pure ZnO, ZnO/graphene, ZnO/PANI, and ZnO/graphene/PANI photoanodes is investigated by cyclic voltammetry (CV), chronoamerometry (J-t) and electrochemical impedance spectroscopy (EIS). The yields of methane oxidation products, mainly methanol (CH3OH) and formic acid (HCOOH), catalysed by the synthesized ZnO/graphene/PANI composite are 2.76 and 3.20 times those of pure ZnO, respectively. The mechanism of the photoelectrocatalytic process converting methane into methanol and formic acid is proposed on the basis of the experimental results. The enhanced photoelectrocatalytic activity of the ZnO/graphene/PANI composite can be attributed to the fact that graphene can efficiently transfer photo-generated electrons from the inner region to the surface reaction to form free radicals due to its superior electrical conductivity as an inter-media layer. Meanwhile, the introduction of PANI promotes solar energy harvesting by extending the visible light absorption and enhances charge separation efficiency due to its conducting polymer characteristics. In addition, the PANI can create a favorable π-conjunction structure together with graphene layers, which can achieve a more effective charge separation. This research demonstrates that the fabricated ZnO/graphene/PANI composite promises to implement the visible-light photoelectrocatalytic methane oxidation.

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

Yuan Guo, Chunmei Tang, Xinbo Wang, Cheng Wang, Ling Fu
Chin. Phys. B 2019, 28 (4): 048102;  doi: 10.1088/1674-1056/28/4/048102
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Membrane technology has been used for H2 purification. In this paper, the systematic density functional simulations are conducted to study the separation of H2 from the impurity gases (H2, N2, H2O, CO, Cl2, and CH4) by the bilayer porous graphitic carbon nitride(g-C3N4) membrane. Theoretically, the bilayer g-C3N4 membrane with a diameter of about 3.25 Å should be a perfect candidate for H2 purification from these mixed gases, which is verified by the high selectivity (S) for H2 over other kinds of gases (3.43×1028 for H2/N2; 1.40×1028 for H2/H2O; 1.60×1026 for H2/CO; 4.30×1014 for H2/Cl2; 2.50×1055 for H2/CH4), and the permeance (P) of H2 (13 mol/m2·s·Pa) across the bilayer g-C3N4 membrane at 300 K, which should be of great potential in energy and environmental research. Our studies highlight a new approach towards the final goal of high P and high S molecular-sieving membranes used in simple structural engineering.

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

Dong-Yan Zhang, Jie Zhang, Xiao-Feng Liu, Sha-Sha Chen, Hui-Wen Li, Ming-Qing Liu, Da-Qian Ye, Du-Xiang Wang
Chin. Phys. B 2019, 28 (4): 048501;  doi: 10.1088/1674-1056/28/4/048501
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Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes (LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition (MOCVD) growth of multiple quantum wells (MQWs) in Ⅲ-nitride LEDs, and thus affecting the carrier dynamics of the LEDs. Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells (QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.

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

Chao Yang, Hongwei Liang, Zhenzhong Zhang, Xiaochuan Xia, Heqiu Zhang, Rensheng Shen, Yingmin Luo, Guotong Du
Chin. Phys. B 2019, 28 (4): 048502;  doi: 10.1088/1674-1056/28/4/048502
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A solar-blind photodetector is fabricated on single crystal Ga2O3 based on vertical structure Schottky barrier diode. A Cu Schottky contact electrode is prepared in a honeycomb porous structure to increase the ultraviolet (UV) transmittance. The quantum efficiency is about 400% at 42 V. The Ga2O3 photodetector shows a sharp cutoff wavelength at 259 nm with high solar-blind/visible (=3213) and solar-blind/UV (=834) rejection ratio. Time-resolved photoresponse of the photodetector is investigated at 253-nm illumination from room temperature (RT) to 85.8℃. The photodetector maintains a high reversibility and response speed, even at high temperatures.

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

Zuoxian Xiang, Chuanxiang Tang, Lixin Yan
Chin. Phys. B 2019, 28 (4): 048701;  doi: 10.1088/1674-1056/28/4/048701
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Microtubules (MTs) are part of the cellular cytoskeleton and they play a role in many activities, such as cell division and maintenance of cell shape. In recent years, MTs have been thought to be involved in storing and processing information. Several models have been developed to describe the information-processing ability of MTs. In these models, MTs are considered as a device that can transmit quantum information. However, MTs are affected by the “wet and warm” cellular environment, thus it is essential to calculate the decoherence time. Many researchers have attempted to calculate this parameter but the values that have been obtained vary markedly. Previous studies considered the cellular environment as a distant ion; however, this treatment is somewhat simplified. In this study, we develop a model to determine the decoherence time in neuronal MTs while considering the interaction effects of the neuronal fluid environment. The neuronal environment is considered as a plasmon reservoir. The coupling between MTs and neuronal environment occurs due to the interaction between dipoles and plasmon. The interaction Hamiltonian is derived by using the second quantization method, and the coupling coefficient is calculated. Finally, the decoherence time scale is estimated according to the interaction Hamiltonian. In this paper, the time scale of decoherence in MTs is approximately 1 fs-100 fs. This model may be used as a reference in other decoherence processes in biological tissues.

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

Hai-Tao Yu, Li-Hui Cai, Xin-Yu Wu, Jiang Wang, Jing Liu, Hong Zhang
Chin. Phys. B 2019, 28 (4): 048702;  doi: 10.1088/1674-1056/28/4/048702
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In this study, we investigate the cross-frequency coupling and functional brain networks in the subjects with temporal lobe epilepsy (TLE) using interictal EEG signals. The phase to phase synchronization within and across frequency bands is calculated and a significant difference between the epilepsy and control groups is observed. Compared with the controls, the epilepsy patients exhibit a stronger within-frequency coupling (WFC) within theta and beta bands, and shows a stronger cross-frequency coupling (CFC) in the delta-alpha and theta-alpha band pairs, but a weakened CFC in alpha-beta band pairs. The weakened coupling between alpha and high frequency band reflects a suppression of phase modulation between the brain regions related to epilepsy. Moreover, WFC and CFC are positively correlated, which is higher in the patients relative to controls. We further reconstruct functional brain connectivity and find that both WFC and CFC networks show small-world properties. For the epilepsy, the small-world efficiency is enhanced in the CFC networks in delta-alpha and theta-alpha band pairs, whereas weakened between alpha and beta bands, which suggests a shift away from the optimal operating point in the epileptic brain with a new balance between WFC and CFC. Our results may help us to understand the important role of information communication across different frequency bands and shed new light on the study of pathology of epilepsy.

Effect of terahertz pulse on gene expression in human eye cells

Jin-Wu Zhao, Ming-Xia He, Li-Jie Dong, Shao-Xian Li, Li-Yuan Liu, Shao-Chong Bu, Chun-Mei Ouyang, Peng-Fei Wang, Long-Ling Sun
Chin. Phys. B 2019, 28 (4): 048703;  doi: 10.1088/1674-1056/28/4/048703
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In recent years, the advances in terahertz applications have stimulated interest in the biological effects associated with this frequency range. We study the gene expression profile in three types of cells exposed to terahertz radiation, i.e., human ARPE-19 retinal pigment epithelial cells, simian virus 40-transformed human corneal epithelial cells, and human MIO-M1 Müller cells. We find that the gene expression in response to heat shock is unaffected, indicating that the minimum temperature increases under controlled environment. The transcriptome sequencing survey demonstrates that 6-hour irradiation with a broadband terahertz source results in specific change in gene expression and also the biological functions that are closely related to these genes. Our results imply that the effect of terahertz radiation on gene expression can last over 15 hours and depends on the type of cell.

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

Zhen-Wu Jiang, Shou-Shuai Gao, Si-Yu Wang, Dong-Xiao Wang, Peng Gao, Qiang Sun, Zhi-Qiang Zhou, Wei Liu, Yun Sun, Yi Zhang
Chin. Phys. B 2019, 28 (4): 048801;  doi: 10.1088/1674-1056/28/4/048801
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Cd-free kesterite structured solar cells are currently attracting attention because they are environmentally friendly. It is reported that Zn(O,S) can be used as a buffer layer in these solar cells. However, the band alignment is not clear and the carrier concentration of Zn(O,S) layer is low. In this study, the band alignment of the Zn(O,S)/Cu2ZnSnSe4 p-n junction solar cell and the effect of In2S3/Zn(O,S) double buffer layer are studied by numerically simulation with wxAMPS software. By optimizing the band gap structure between Zn(O,S) buffer layer and Cu2ZnSnSe4 absorber layer and enhancing the carrier concentration of Zn(O,S) layer, the device efficiency can be improved greatly. The value of CBO is in a range of 0 eV-0.4 eV for S/(S+O)=0.6-0.8 in Zn(O,S). The In2S3 is mainly used to increase the carrier concentration when it is used as a buffer layer together with Zn(O,S).

Effect of carrier mobility on performance of perovskite solar cells

Yi-Fan Gu, Hui-Jing Du, Nan-Nan Li, Lei Yang, Chun-Yu Zhou
Chin. Phys. B 2019, 28 (4): 048802;  doi: 10.1088/1674-1056/28/4/048802
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The high carrier mobility and long diffusion length of perovskite material have been regarded because of its excellent photovoltaic performance. However, many studies have shown that a diffusion length longer than 1 μ and higher carrier mobility have no positive effect on the cells' performance. Studies of organic solar cells have demonstrated the existence of an optimal mobility value, while systematic research of the carrier mobility in the PSCs is very rare. To make these questions clear, the effect of carrier mobility on perovskite solar cells' performance is studied in depth in this paper by simulation. Our study shows that the optimal mobility value of the charge transportation layer and absorption layer are influenced by both doping concentration and layer thickness. The appropriate carrier mobility can reduce the carrier recombination rate and enhance the carrier concentration, thus improving the cells' performance. A high efficiency of 27.39% is obtained in the simulated cell with the combination of the optimized parameters in the paper.

Plasma electrolytic liquefaction of sawdust

Cong-Cong Jiang, Shi-Yun Liu, Zhe Feng, Zhi Fang, Xian-Hui Zhang, Dan-Hua Mei, Deng-Ke Xi, Bing-Yu Luan, Xing-Quan Wang, Si-Ze Yang
Chin. Phys. B 2019, 28 (4): 048803;  doi: 10.1088/1674-1056/28/4/048803
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As a renewable carbon resource, biomass can be converted into polyols, aromatic hydrocarbons, alkanes, and other products by traditional catalytic liquefaction method, which has been widely used in production and life. The efficient development and utilization of biomass energy will play a very positive role in solving the problems of energy and ecological environment. A way of combining the plasma electrolysis with traditional catalytic liquefaction realizes the efficient liquefaction of sawdust, which provides a new liquefaction way for traditional biomass conversion. In this experiment, the effects of solution composition, catalyst content and power supply on solution resistance and liquefaction rate are analyzed. It is found that solution composition and catalyst content have a great influence on solution resistance. The results show that the liquefaction rate is highest and the resistance is smallest when the solution resistance is 500 Ω. The liquefaction rate is greatly affected by the solution temperature, and the solution temperature is determined by the output power between the two electrodes. The output power includes the heating power of the electric field and the discharge power of the plasma. We measure the electric potential field distribution in the solution and the plasma power. It is found that the output power between the two poles increases nonlinearly (from 0 to 270 W) with time. In two minutes, the electric field heating power increases from 0 to 105 W and then decreases to 70 W, while the plasma power increases from 0 to 200 W. It is well known that in the first 70 seconds of the experiment the electric field heating is dominant, and then the plasma heating turns into a main thermal source. In this paper, plasma electrolysis and traditional catalytic liquefaction are combined to achieve the efficient liquefaction of sawdust, which provides a new way for biomass liquefaction.

Traffic dynamics considering packet loss in finite buffer networks

Jie Chen, Jin-Yong Chen, Ming Li, Mao-Bin Hu
Chin. Phys. B 2019, 28 (4): 048901;  doi: 10.1088/1674-1056/28/4/048901
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In real complex systems, the limited storage capacity of physical devices often results in the loss of data. We study the effect of buffer size on packet loss threshold in scale-free networks. A new order parameter is proposed to characterize the packet loss threshold. Our results show that the packet loss threshold can be optimized with a relative small buffer size. Meanwhile, a large buffer size will increase the travel time. Furthermore, we propose a Buffered-Shortest-Path-First (BSPF) queuing strategy. Compared to the traditional First-In-First-Out (FIFO) strategy, BSPF can not only increase the packet loss threshold but can also significantly decrease the travel length and travel time in both identical and heterogeneous node capacity cases. Our study will help to improve the traffic performance in finite buffer networks.

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