bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of spherical stress wave propagation in the standard linear solid material
Authors: Lu Qiang  , Wang Zhan-Jiang  ,   State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, China;,   Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

Based on the standard linear solid model, the solutions in Laplace domain, such as particle velocity v, particle displacement u, radial stress σr, tangential stress σθ, radial strain εr, tangential strain εθ, reduced velocity potential γ (RVP), and reduced displacement potential ψ (RDP), are derived from the spherical wave equations. The propagating characteristics of these physical quantities, as mentioned above, are calculated by using Crump algorithm for inverse Laplace transformation. The numerical inversion results reveal that the initial response to strong discontinuity spherical stress wave in viscoelastic material is purely elastic response. The strong discontinuities, such as σr, σθ, εr, εθ and v, contain geometrical attenuation and viscoelastic damping in the process of wave propagation. The variables, such as σr, σθ, εr, εθ,u and ψ, converge to steady values as time approaches to infinity. The peak values of RVP γ and RDP ψ, which are constant in a purely elastic material, are steadily reduced with the spreading distance increasing in viscoelastic material. The steady values of ψ are in inverse relation to the static shear modulus Ga, and directly proportional to the steady cavity pressure and the cube of the cavity radius r.
Analysis and design of a Ka-band sheet beam relativistic extended interaction klystron amplifier
Authors: Liu Zhen-Bang  , Zhao Yu-Cong  , Huang Hua  , Jin Xiao  , Lei Lu-Rong  ,   Institute of Applied Electronics, Science and Technology on High Power Microwave Laboratory, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The sheet beam klystron is a kind of novel powerful microwave and millimeter-wave vacuum electron device, in which used is a thin rectangular sheet beam with high aspect ratio in order to improve beam-wave interaction efficiency by improving space-charge-limiting current of electron beam and obtaining big electric current, and it has many actual and potential applications. Based on the motion of the single electron under the small signal condition, the transit-time effect of electron beam in 2π-mode standing wave electric field in a multiple-cavity resonator is investigated, the expression of electron load conductance in a multiple-cavity resonator is presented, and the influence of the cavity number N on transit-time effect in a multiple-cavity resonator is discussed. The high frequency characteristics of the three-gap extended cavity are studied. The abilities for the single-gap cavity and three-gap cavity to modulate the sheet beam are compared by 3D PIC simulation. The simulation result shows that the three-gap extended interaction cavity operating at 2πmode is better than the single-gap cavity. The electron load conductance is derived and corrected based on the theory of relativity, by which a more accurate relation of electron load conductance to transmit angle can be obtained. In order to improve the output power and electron efficiency, the three-gap extended output cavity is used in the relativistic klystron to replace the single gap output cavity. By using the electromagnetic simulation software and 3D PIC code, a Ka-band sheet beam relativistic extended interaction klystron amplifie is designed. A sheet electron beam with a width-to-height ratio of 30 is adopted to reduce the space charge effect. In the PIC simulation, when the beam voltage is 500 kV and current is 1 kA, the device can generate a 190 MW output power at 40 GHz with an efficiency of 38% and a gain of 69 dB. The 3 dB bandwidth of the EISBK is about 150 MHz. Meanwhile, the output microwave is without the clutter jamming, which makes the contribution avoid the shrinkage of output microwave impulse. This study is of great importance for the physical design and process in engineering of the Ka-band sheet beam extended interaction relativistic klystron amplifier.
Low frequency noise behaviors in the partially depleted silicon-on-insulator device
Authors: Wang Kai  , Liu Yuan  , Chen Hai-Bo  , Deng Wan-Ling  , En Yun-Fei  , Zhang Ping  ,   School of Information Science and Technology, Jinan University, Guangzhou 510632, China;,   Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, CEPREI, Guangzhou 510610, China;,   No. 58th Research Institute of China Electronics Technology Group Corporation, Wuxi 214035, China
Published: December 2020

Low frequency noise in the partially depleted silicon-on-insulator (SOI) NMOS device is investigated in this paper. The experimental results show low frequency noise behaviors are in good consistence with classical noise model. Based on McWhorter model, the low frequency noise in the SOI device results from the exchange of carriers between channel and oxide. The densities of trapped charges in the front gate oxide and buried oxide are extracted. Due to the difference between manufacture processes, the extracted density of trapped charges in the buried oxide (Nt=8×1017 eV-1·cm-3) is larger than that in the gate oxide (Nt=2.767×1017 eV-1·cm-3), and the result is in good agreement with testing result of transfer characteristics in part 2. Based on the charge tunneling mechanism, the spatial distribution of trapped charges in the gate oxide and buried oxide are extracted by using the tunneling attenuation coefficient (λ=0.1 nm for SiO2) and time constant (τ0=10-10 s), and the result also proves that the trap in buried oxide is larger than that in gate oxide. In addition, the influence of channel length on the low frequency noise in the SOI device is discussed. The variations of normalized channel current noise power spectral density with channel length are investigated at four frequencies(10 Hz, 25 Hz, 50 Hz, and 100 Hz). The experimental results show that the normalized noise power spectral density decreases linearly with the increase of channel length, which indicates the low frequency noise of SOI device is mainly caused by the flicker noise in the channel, and the contribution of source/drain contact and parasitic resistances could be ignored. Finally, the dependences of back gate voltage on the front gate threshold voltage, front channel current and front channel noise are discussed by considering the charge coupling effect. The experimental results show the measured channel current and channel noise with applying front gate voltage and back gate voltage simultaneously are larger than those with applying the front gate voltage and back gate voltage separately.
Dynamical balance between excitation and inhibition of feedback neural circuit via inhibitory synaptic plasticity
Authors: Wang Mei-Li  , Wang Jun-Song  ,   School of Biomedical Engineering, Tianjin Medical University, Tianjin 300070, China
Published: December 2020

Cortical cortex is mainly composed of excitatory and inhibitory neurons. Balance between excitation and inhibition is a ubiquitous experimental phenomenon in brain. On the one hand, balanced excitation and inhibition plays a crucial role in maintaining normal brain functions; on the other hand, the loss of balance between the two opposing forces will cause neural diseases, such as epilepsy, Parkinson, schizophrenia, etc. Thus the research on balance between excitation and inhibition increasingly focuses on the field of neuroscience. Feedback neural circuit with recurrent excitatory and inhibitory connections is ubiquitous in cortical cortex. However, it is still little known how to achieve and maintain the balance between excitation and inhibition in feedback neural circuit. In this study it is proposed that inhibitory synaptic plasticity should play a key role in regulating the balance between excitation and inhibition. Firstly, the feedback neural circuit model is constructed using leaky integrate-and-fire neuron model, mainly composed of excitatory feed-forward loop, and excitatory and inhibitory recurrent connections. The proposed inhibitory synaptic model is incorporated into the feedback neural circuit model, and whose mathematical formulation is presented in detail. Secondly, the excitatory and inhibitory synaptic currents are obtained through numerical simulations, which demonstrate that the precise balance between excitation and inhibition is achieved under the regulation of inhibitory synaptic plasticity. Furthermore, the research results show that this balance is robust to the fluctuation inputs and disturbances. Thirdly, the balance mechanism underlined by inhibitory synaptic plasticity is elucidated through theoretical and simulation analysis, separately, which provides a clear explanation and an insight into how to achieve and maintain the balance between excitation and inhibition in a feedback neural circuit. Finally, the numerical results reveal that the neuron numbers in excitatory and inhibitory feedback loop exert an influence on the balance, and the larger number can enhance the balance between excitation and inhibition, which explains, to some extent, why there are dense connections between neurons in brain. The results in this study shed light on the balance mechanism of feedback neural circuit, and provide some clues for understanding the mechanism of balance between excitation and inhibition in the brain area.
Effects of bathocuproine/Ag composite anode on the performances of stability polymer photovoltaic devices
Authors: Yang Bing-Yang  , He Da-Wei  , Wang Yong-Sheng  ,   Key Laboratory of Luminescence and Optical Information, Beijing Jiaotong University, Ministry of Education, Beijing 100044, China;,   Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In this work, the composite anode of BCP/Ag replaces the composite anode of Ca/Al, and the PTB7:PC71BM acts an as active layer for polymer solar cells. Calcium (Ca) is not a desirable candidate as electron extraction layer (EEL) for long-term stability polymer solar cells (PSCs) on account of its nature of active metal. And then, due to the poor stability of Al, which is not a desirable candidate as electrode, the bathocuproine (BCP) layer acts as an exciton blocking layer in organic device such OLEDs and small molecule solar cells, which has a k value that is close to zero for a broad range of wavelengths. The Ag has the nature of better chemical stability and conductivity than Al. In the device architecture described below, we replace the typical back metal electrode composed of a thin Ca layer and a thicker Al electrode by a few nanometer thick bathocuproine (BCP) layer and a thick 150 nm Ag layer. We investigate the effects of BCP thickness on the power conversion efficiency (PCE) and stability. The results reveal that the photovoltaic performances are improved, and a PCE of 6.82% at the 5 nm of BCP thickness, higher than the PCE of Ca/Al acted composite anode, is achieved. The substitution of BCP for Ca, can largely enhance light harvesting and exhibits an optimal light absorption by the active layer. This enhanced reflectivity of the buffer layer/electrode back contact results in an increase of the short circuit current. Compared with the devices of Ca/Al composite anode, it increases Jsc and external quantum efficiency with BCP/Ag composite anode. At the same time, it has the better stability of BCP/Ag composite anode of device, and almost the same PCE decrease ratio as free BCP devices and significantly improves the stability compared with Ca/Al composite anode. The stability test shows the better stability of BCP/Ag as composite anode than that of Ca/Al composite anode. The PCE of the device with Ca/Al as composite anode rapidly decreases by about 70% after 50 hour servicing due to the poor stabilities of Ca and Al. The device with BCP/Ag as composite anode shows favorable stability, owing to the PCE moderate decrease by less than 30% after the same story time. Our results indicate that substitution of BCP/Ag for Ca/Al composite anode is an alternative candidate for high performance and longterm photo stability PSCs.
Carrier transport mechanism of GaAs/Ge solar cells under electrons irradiation
Authors: Qi Jia-Hong  , Hu Jian-Min  , Sheng Yan-Hui  , Wu Yi-Yong  , Xu Jian-Wen  , Wang Yue-Yuan  , YANG Xiao-Ming  , Zhang Zi-Rui  , Zhou Yang  ,   Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025, China;,   School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;,   Shanghai Institute of Space Power Sources, Shanghai 200233, China
Published: December 2020

In this paper, the basic laws of spectral response, open-circuit voltage and short circuit current of GaAs/Ge solar cells are obtained by ground simulation irradiation test under the different-energy electrons’ irradiations, such as 1, 1.8 and 10 MeV. The carriers’ transport mechanism in cells is analyzed using the PC1 D simulation program. The variations of the majority carriers’ concentration and the minority carriers’ diffusion length with the irradiation particle fluence are obtained in GaAs/Ge solar cells under different-energy electrons’ irradiation. Majority carriers’ removal rate and minority carriers’ diffusion length damage coefficient are calculated under different-energy electron irradiations. The results show that majority carriers’ concentration and minority carriers’ diffusion length decrease with increasing the incident electron fluence. The majority carriers’ removal rate and the damage coefficient of minority carriers’ diffusion length increase with increasing the electrons energy. The majority carriers’ removal effect and the minority carriers’ diffusion length shortened are the main reasons of open-circuit voltage and short circuit current degradation of the solar cells, respectively.
Effect of gas bubble on acoustic characteristic of sediment: taking sediment from East China Sea for example
Authors: Li Hong-Xing  , Tao Chun-Hui  , Liu Fu-Lin  , Zhou Jian-Ping  ,   College of Nuclear Engineering and Geophysics, East China Institute of Technology, Nanchang 330013, China;,   Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
Published: December 2020

The effect of gas bubble on acoustic characteristic of sediment is important for ocean science, ocean geology, ocean geophysics, etc. Twenty five samples of ocean bottom sediments are extracted through gravity sampling equipment from the East China Sea and are sealed in PVC pipes for storage in order to study the effect of gas bubble on acoustic characteristic of sediment. In order to obtain the gas content of sediment, in this the paper the Micro-CT scanning technology is introduced into sediment measuring method. The different X ray absorption rates of water, gas and solid particles in sediment samples are obtained through Micro-CT scanning using Siemens Micro-CT scanner. The gas volume content and water volume content in sediment can be obtained according to CT number distribution. The acoustic measurement is carried out in laboratory using intelligent nonmetal ultrasonic detector and the 40 kHz waves are launched from one side of the sediment sample and obtained from another side. The acoustic attenuation can be obtained according to the amplitudes of launched and received waves and the acoustic velocity can be obtained according to travelling time when acoustic wave goes through the sediment. The attenuation of sediment sample is about a few to twenty and the velocity is about 1100 to 1700 m-1. By mean of analysis of regression, the correlations are obtained among gas content, fluid content, acoustic velocity, attenuation and power function, which better match the measuring data. The result of study indicates that slight augment of gas content can cause sharp decrease of acoustic velocity and rapid increase of acoustic attenuation. The increment and decrement decrease obviously when the gas content exceeds 10%. The result in this paper is useful to explore oil and gas seismic.
Study on the super transmission in a typical dielectric structure
Authors: Wang Juan-Juan  , Huang Zhi-Xiang  , Fang Ming  , Zhang Ya-Guang  , Wu Xian-Liang  ,   Key Laboratory of Intelligent Computing and Signal Processing, Anhui University, Hefei 230039, China;,   Electronics and Information Engineering of Hefei Normal University, Hefei 230061, China
Published: December 2020

Reflection is a natural phenomenon that occurs when light passes the interface between materials with different refractive index. In many applications, such as solar cells, introduction of a substrate will result in an increase in reflection. There are many ways to reduce the reflection from a substrate, which have been investigated so far, including dielectric interference coatings, surface texturing, adiabatic index matching, and scattering from plasmonic nanoparticles etc. Here we present an entirely new concept to eliminate reflection from a silicon wafer, which makes use of much simpler method than the ones reported before, and can be applied to any high-index material. Finite-difference-time-domain (FDTD) method and auxiliary differential equations are used in this paper to simulate a new structure that can suppress the reflection of light from a silicon surface over a broad spectral range. A two-dimensional periodic array of subwavelength silicon nanocylinders is designed, which possesses a phenomenon strongly substrate-coupled to the Mie resonances, and which can produce an extraordinary transmission phenomenon similar to the metal surface plasmon that yields almost zero total reflectance over the entire spectral range from ultraviolet to near-infrared. This new antireflection concept relies on the strong forward scattering that occurs when a scattering structure is placed in close proximity to a high-index substrate with a high optical density of states. For a detailed description of the problem, we have carried out some simulations. From the results, one can see that although nano-pillar covers only 30% of the substrate surface area, it can reduce the reflection from the surface from 30% to under 10% at the Mie resonance. For the purpose of reducing reflection from the substrate, this new structure designed may provide a reference for the actual solar cells and optical antenna design.
Analysis on quantum bit error rate in measurement-device-independent quantum key distribution using weak coherent states
Authors: Du Ya-Nan  , Xie Wen-Zhong  , Jin Xuan  , Wang Jin-Dong  , Wei Zheng-Jun  , Qin Xiao-Juan  , Zhao Feng  , Zhang Zhi-Ming  ,   Laboratory of Nanophotonic Functional Materials and Devices (SIPSE), and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China;,   Engineering Technology Department, Guangdong Polytechnic Institute, Guangzhou 510091, China;,   School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723000, China
Published: December 2020

A measurement-device-independent quantum key distribution (MDI-QKD) protocol is immune to all detection side-channel attacks and guarantees the information-theoretical security even with uncharacterized single photon detectors. A weak coherent source is used in the current MDI-QKD experiments, it inevitably contains a certain percentage of vacuum and multi-photon pulses. The security issues introduced by these source imperfections can be avoided by applying the decoy state method. Here, through modeling experimental devices, and taking into account the weak coherent source and the threshold detectors, we have evaluated the gain, the probability to get successful Bell measurement and incorrect Bell measurement, and the quantum bit error rate (QBER), given a practical setup. In our simulation, we show how QBER varies with different transmission distances in the cases when the average photon numbers per pulse from Alice and Bob are symmetric and asymmetric. Result shows that the multi-photon pulses do not cause error in the Z basis of polarization encoding scheme, but produce a large QBER in phase encoding scheme and in the X basis of polarization encoding scheme. QBER is affected by the dark count rate and the system optical error associated with the multi-photon pulses. For different encoding schemes, QBER caused by each kind of average photon numbers from Alice and Bob increases to different degrees with the transmission distance, and finally is close to 50%. With the increase of the transmission distance, the average photon number per pulse decreases and the fraction of the dark count rate causing QBER gradually increases. Under the same effect of the dark count rate, the smaller the average photon number per pulse, the bigger the QBER. After a certain transmission and at the same transmission distance, the QBER is largest when average photon numbers used by Alice and Bob are both smallest. For the short distance transmission of phase encoding scheme and the X basis, we find that QBER is larger when average photon numbers from the two arms are asymmetric, as compared to the symmetric case. For the Z basis, the QBER caused by the system optical error and the dark count rate is very small.
Fractal property of sea clutter FRFT spectrum for small target detection
Authors: Xing Hong-Yan  , Zhang Qiang  , Xu Wei  ,   Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China;,   Key Laboratory for Aerosol-Cloud-Precipitation, China Meteorological Administration, Nanjing University of Information Science & Technology, Nanjing 210044, China
Published: December 2020

Because the detection of small target in the background of sea clutter is strongly influenced by the sea condition, this paper studies the fractal property of sea clutter in fractional Fourier transform (FRFT) domain and proposes the fractal detection method in single and high dimensions. The FRFT deduced from mathematical definition is not consistent with the self-similar properties in orders and scales. Multifractal detrended fluctuation analysis (MF-DFA) method is used to determine the fractal parameter H(q) and analyze the fractal property of the sea clutter in different situations, distances, and polarizations. In single dimension, the small target detection method is proposed based on an adaptive order. By comparing different factors of the multifractal parameters, the results show that the transform order method in sea clutter FRFT domain can detect small signals under complicated sea conditions. The detection threshold mostly increases above 200%, which is 26.3% higher than the method of time domain signal. H(q) has an obvious multifractal difference on high negative scale, the H(q)-q curve satisfies the arctangent distribution. The fitting amplitude ratios of pure sea clutter and target data are greater than 1.8 (HH) and 1.4 (VV), which provide the basis for the small target detection in sea clutter background.
Internet public opinion chaotic prediction based on chaos theory and the improved radial basis function in neural networks
Authors: Wei De-Zhi  , Chen Fu-Ji  , Zheng Xiao-Xue  ,   School of Economics and Management, Fuzhou University, Fuzhou 350108, China;,   Jimei University Chengyi College, Xiamen 361021, China
Published: December 2020

Information of internet public opinion is influenced by many netizens and net medias; characteristics of this information are non regular, stochastic, and may be expressed by a nonlinear complex evolution system. Corresponding model is difficult to establish and effectively predicted using the traditional methods based on statistical and machine learning. Characteristics of internet public opinion are chaotic, so the chaos theory can be introduced to research first, then the information of internet public opinion having chaotic characteristic is proved by the Lyapunov index. The model to predict the development trend of internet public opinion is next established by the phase space reconstruction theory. Finally, the hybrid algorithm EMPSO-RBF which is based on EM algorithm and the RBF neural network optimized by the improved PSO algorithm is proposed to solve the model. The hybrid algorithm fully takes the advantage of the EM clustering algorithm and the improved PSO, so the RBF neural network is improved by initializing the network structure in the early stage and optimizing the network parameters later. First, the EM clustering algorithm is used to obtain the center value and variance, and the radial basis function is improved with the combination of traditional Gauss model. Then the relevant network parameters are obtained by the improved PSO algorithm which is based on error optimizing the network parameters constantly. The model algorithm can be accurately simulated in the time series of chaotic information by experiments which are validated by different chaotic time series information; and it can better describe the development trend of different information of internet public opinion. The predicted results are made for government to monitor and guide the information of internet public opinion and benefit the social harmony and stability.
Accurate determination of thickness values and optical constants of absorbing thin films on opaque substrates with spectroscopic ellipsometry
Authors: Li Jiang  , Tang Jing-You  , Pei Wang  , Wei Xian-Hua  , Huang Feng  ,   Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China;,   School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China
Published: December 2020

The determination of the optical constants of absorbing films, particularly on opaque substrates, is a difficult problem when solely using spectroscopic ellipsometry. First, unwanted backside reflections are incoherent with the desired reflection from the front side, which makes the fitting of optical constants difficult. Second, the optical constants of substrate must be carefully characterized in advance, as any small absorption in the substrate would be mixed into the film’s overall optical constants. Third, thickness and optical constants are strongly correlated with each other, which may prevent a unique solution for absorbing films. For the above reasons, quartz, glass slide, cover glass and float glass substrates are studied. Backside reflections of the substrates are suppressed by index matching technique. The results show that the simple technique works well for substrate materials with refractive index in a range from 1.43 to 1.64, including materials such as fused silica, float glass, etc. in a spectral range from 190 nm to 1700 nm. The refractive index and extinction coefficient of the substrate are fitted by ellipsometricψdata and the normal spectral transmittance T0. The results are consistent with the literature reported. Finally, a Combined ellipsometry and transmission approach is used to determine the thickness values and optical constants of the diamond-like carbon (DLC) film coated on the quartz and the amorphous silicon (a-Si) film coated on the glass slide and cover glass accurately.
Design of multiband Salisbury screen based on high impedance surfaces
Authors: Dang Ke-Zheng  , Shi Jia-Ming  , Li Zhi-Gang  , Meng Xiang-Hao  , Wang Qi-Chao  ,   State Key Laboratory of Pulsed Power Laser, Hefei 230037, China;,   Electric Engineering Institute, Hefei 230037, China
Published: December 2020

High impedance surface, due to its unique property of in-phase reflection at some frequency, could be used in designing multiband Salisbury screen by replacing the metallic ground plane in a traditional structure, which is proposed, in this paper, to enhance the microwave absorbing performance of the conventional Salisbury screen. First, electromagnetic wave field intensity of different frequency in space after being reflected by a high impedance surface is analyzed, which implies that new absorption bands can be introduced at about the frequencies of in-phase reflection by sharing Salisbury screen’s resistive sheet, without adding extra lossy materials such as lumped elements or others. Then, by taking a single band high impedance surface at 6.25 GHz and a dual-band high impedance surface at 6.27 and 8.17 GHz, which are both composed of patches array with varying periodic size and a thickness of 0.6 mm, the multiband Salisbury screens can be constructed utilizing a conventional one with an absorbing peak at about 10.5 GHz. The reflectivity of these multiband absorbers are simulated by employing the commercial CST microwave studio and later measured using a reflectivity measurement system comprising two polarized horns and a vector network analyzer. Experimental results agree well with the simulations, and all results verify that the method presented at the beginning is effective. Results also show that new additional absorptions appear at the frequencies where microwaves are nearly reflected in phase from the high impedance surface, with the same number of the in-phase reflection bands. Meanwhile, the original microwave absorbing capability of the traditional Salisbury screen is reserved mostly. Compared to the single band high impedance surface, the dual-band high impedance surface performs better in the design as the absorbing bandwidth is wider and the absorbing frequency is lower. With an additional thickness of the high impedance surface (no more than 1 mm), the total absorption bandwidth of the multiband Salisbury screen with a reflection below -10 dB increases from 8.5 to 10.1 GHz, and the lowest frequency with 10 dB absorption falls from 7.5 to 5.98 GHz. So it could be concluded that the design of multiband Salisbury screen is helpful to widen the absorption, especially towards the lower frequency direction.
Manipulation of the polarization switching and the nonlinear dynamic behaviors of the vertical-cavity surface-emitting laser subjected to optical injection by EO modulation
Authors: Zhong Dong-Zhou  , Ji Yong-Qiang  , Deng Tao  , Zhou Kai-Li  ,   School of Information Engineering, Wuyi University, Jiangmen 529020, China;,   School of Physics, Southwest University, Chongqing 400715, China
Published: December 2020

For the polarization switching (PS) and the nonlinear dynamic behaviors (NDBs) of the optically injected laser system composed of master vertical-cavity surface-emitting laser (M-VCSEL) and slave vertical-cavity surface-emitting laser (S-VCSEL), we put forward a novel manipulation scheme and explore their control law by means of electro-optic (EO) modulation with quasi-phase matched technology in periodically poled LiNbO3. It is found that the PS of the S-VCSEL subjected to parallel or orthogonal optical injection undergoes a change of periodic oscillation with the applied transverse electric field. The envelope trajectory of the oscillation peak appears to be a cosine curve, and that of the oscillation wave trough becomes a sine curve. Besides, the PS of the S-VCSEL only depends on the applied transverse electric field and the bias current of the M-VCSEL, and is independent of the bias current of the S-VCSEL. When the bias current of the M-VCSEL takes a different value, the PS of the S-VCSEL shows a different evolution law in one period of the applied electric field. For a certain fixed bias current of the M-VCSEL, the optically injected S-VCSEL can emit an arbitrary polarization mode and its NDBs experience different evolutions when the light from the M-VCSEL goes through EO intensity modulation. If the output light of the M-VCSEL is subjected to EO intensity modulation and EO phase modulation simultaneously, while the bias current of the S-VCSEL is fixed at 1.06, that of the M-VCSEL is fixed at 1.18, and the optical injection strength is set at 5 ns-1, then the output polarization of the S-VCSEL is in turn switched from the y-LP to the left-handed elliptic polarization (EP), then the right-handed EP circular polarization, and lastly the left-handed EP. And its NDB shows in turn a single period, four doubled periods, chaos, four doubled periods, and chaos with the increase of the applied electric field.
Rapid measurement of the diffusion coefficient of liquids using a liquid-core cylindrical lens:a method for analysing an instantaneous diffusive picture
Authors: Meng Wei-Dong  , Sun Li-Cun  , Zhai Ying  , Yang Rui-Fen  , Pu Xiao-Yun  ,   Department of Physics, Yunnan University, Kunming 650091, China
Published: December 2020

This paper studies the equivalent refractive index method and other methods to measure the liquid diffusion coefficient. Based on this, a quick method to measure the liquid diffusion coefficient is proposed, i.e. using a specially designed asymmetric liquid-core cylindrical lens as both diffusive pool and imaging element. By means of this system with the liquid-core cylindrical lens to measure the diffusion coefficient, we can eliminate the spherical aberration and improve the accuracy in refractive index measurement. Based on the spatially resolving ability of the cylindrical lens in measuring the refractive index, only one instantaneous diffusive picture is required. Depending on the correspondence between the image width and the refractive index, we thus can quickly calculate the diffusion coefficient D by the Ficks second law. Then the diffusive process of ethylene glycol in water at 25℃ is investigated by this method. We calculate the diffusion coefficient between 660-3000 s with the method to analyse an instantaneous diffusion picture. At the beginning, injection will cause the liquid turbulent, and thus create a larger diffusion coefficient. In the course of diffusion, the influence of turbulence on the diffusion coefficient gradually decreases, but the image narrowing can make inaccurate results. Therefore, this method is required to be used at an appropriate time and an appropriate position to reduce experimental errors. After repeated experiments we can conclude that, between 1500-2700 s we may select the appropriate measurement of location for measuring liquid diffusion coefficient by the method to analyze an instantaneous diffusive picture. This not only can avoid the effect of turbulence but also avoid the effect of fewer sampling points. Compared with other methods reported in the literature, the results show that this method is characterized by short time (~20 ms) in data acquisition, faster measurement ( 1 s), high-accuracy (relative error 3%), and easy operation, thus providing a new method for measuring the diffusion coefficient of liquids rapidly.
False-color terahertz imaging system based on terahertz time domain spectrocsopy
Authors: Lu Wen-Liang  , Lou Shu-Qin  , Wang Xin  , Shen Yan  , Sheng Xin-Zhi  ,   School of Electronic and Information Engeering, Beijing Jiaotong University, Beijing 100044, China;,   School of Science, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Based on terahertz time domain spectroscopy, a false-color imaging system is demonstrated by experiments. Three frequency ranges are defined as color ranges for three primary colors (red, green and blue). The mixture of the spectral integral values in each color range presents the final color of each pixel on the false-color THz image. Since the absorption frequencies of different materials are different, the spectral integral values in defined ranges are different, leading to different color on the false-color THz image. The false-color THz images of two kinds of white powder which are lactose and 4-aminobenzonic acid are obtained from the imaging system with two different definitions of color ranges. From the first color range definition, the absorption frequency of lactose lies in the green range, so only the green light is absorbed, and the color of lactose is magenta. In the meanwhile, there are two absorption frequencies for 4-aminobenzonic acid lying in the green and blue ranges, so both green and blue light are absorbed, and the color of 4-aminobenzonic acid is red. They can be told easily by different colors on the false-color THz image. From the second color range definition, the colors of two kinds of powder are more different. Both false-color THz images can present the cuvette and two kinds of powder clearly. By comparing the THz imaging with grayscale images, false-color THz imaging can display different materials by different colors in one image, instead of the requirement of many grayscale images. It is no need to generate grayscale images at each frequency, making false-color THz imaging consume less time. The false-color imaging is clearer and more efficient, which is more suitable for recognition in a rapid security check. In the situation of complex materials, more false-color THz images can be generated by different color range definitions to assist the detection. The spatial resolution of the imaging system is also investigated. The resolution of imaging system is investigated by imaging home-made standard sample plate. For the frequency range that is higher than 0.3 THz, the resolution can reach 0.4 mm, which is larger than enough for most practical applications.
End-face reflected LiNbO3 waveguide based stationary miniature Fourier transform spectrometer with two-fold enhanced spectral resolution
Authors: Li Jin-Yang  , Lu Dan-Feng  , Qi Zhi-Mei  ,   State Key Laboratory of Transducer Technology, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China;,   State Key Laboratory of NBC Protection for Civilian, Beijing 102205, China
Published: December 2020

Miniature Fourier transform spectrometer (FTS) has attracted considerable interest because of its important application in spaceborne spectroscopy and as a portable analytical tool for rapid on-site chemical/biochemical detection. In a previous paper, a stationary miniature FTS constructed with an electro-optic (EO) modulator of a LiNbO3 (LN) waveguide Mach-Zehnder interferometer (MZI) containing push-pull electrodes was demonstrated. This stationary miniature FTS is operated in the near-infrared region with either nonlinear or linear scanning of the modulating voltage. The simple and mirrorless structure renders the device compact, vibration resistant, and cost-effective. However, the spectral resolution of the proposed prototype FTS was not satisfactory due to the limited optical pathlength difference (OPD), thereby limiting the device application. To improve its spectral resolution, the factors affecting the spectral resolution of the LN waveguide-based FTS is investigated in this paper. Findings show that the spectral resolution is inversely proportional to the maximum OPD, which is proportional to the length of the EO modulating region. A simple method for two-fold enhancement of the spectral resolution of the FTS is proposed based on the end-face reflection in LN waveguide interferometer. With the end-face reflection geometry the guided mode can propagate back and forth in the LN waveguide, making the mode passing through the EO modulating region twice and consequently leading to two times enhancement of the OPD. Therefore, the end-face reflection geometry enables to double the maximum OPD of the interferometer without increasing the device size and thus to offer the device a two-fold enhanced spectral resolution according to the equation for FTS resolution. Two prototypes of FTS with and without the end-face reflection structure are prepared using the same commercial LN waveguide EO modulator. The spectral resolutions in terms of the full-width at half maximum (FWHM) at different wavelengths for the two prototypes of FTS are measured using a series of distributed feedback lasers. The FWHM measured at a specific wavelength with the end-face reflection structure is half as large as that obtained without the end-face reflection structure. Experimental results are in excellent agreement with the theoretical data, demonstrating the applicability of the end-face reflection method to the spectral resolution enhancement.
Super resolution of aerial image by means of polyphase components reconstruction
Authors: He Lin-Yang  , Liu Jing-Hong  , Li Gang  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Multi-frame super resolution reconstruction is a technology for obtaining a high resolution image from a set of blurred and aliased low resolution images. The most popular and widely used super resolution methods are motion based. However, the estimation of motion information (registration) is very difficult, computationally expensive and inaccurate, especially for aerial image. The sub-pixel registration error restricts the performance of the subsequent super resolution. Instead of trying to parameterize the motion estimation model, this paper proposes an image super resolution framework based on the polyphase components reconstruction algorithm and an improved steering kernel regression algorithm. Given an image observation model, a reversible 2D polyphase decomposition, which breaks down a high resolution image into polyphase components, is obtained. Though the assumption of diversity sampling, this paper adopts a fundamentally different approach, in which the low-resolution frames is used as the basis and the reference frame as the reference sub-polyphase component of the high resolution image for recovering the polyphase components of the high resolution image. The polyphase components, which fuse the low resolution frames with the complementary details, can be obtained by computing their expansion coefficients in terms of this basis using the available sub-polyphase components and then inversely transforming them into a high resolution image. This paper accomplishes this by formulating the problem as the maximum likelihood estimation, which guarantees a close-to-perfect solution. Furthermore, this paper proposes an improved steering kernel regression algorithm, to help restore the fusion image with mild blur and random noise. This paper adaptively refines the steering kernel regression function according to the local region context and structures. Thus, this new algorithm not only effectively combines denoising and deblurring together, but also preserves the edge information. Our framework develops an efficient and stable algorithm to tackle the huge size and ill-posedness of the super resolution problem, and improves the computational efficiency via avoiding registration and iterative computation. Several experimental results on synthetic data illustrate that our method outperforms the state-of-the-art methods in quantitative and qualitative comparisons. The proposed super resolution algorithm can indeed reconstruct high-frequency information which is otherwise unavailable in the single LR image. It can effectively suppress blur and noise, and produce visually pleasing resolution enhancement in aerial images.
Spatial correlation experimental analysis of atmospheric optical turbulence in the near ground layer
Authors: Wang Qian  , Mei Hai-Ping  , Qian Xian-Mei  , Rao Rui-Zhong  ,   Key Laboratory of Atmospheric Composition and Optical Radiation, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Atmospheric optical turbulence means refractive index random fluctuation of atmosphere. In this article, according to the concept of correlation function, the measurement principle, measurement schemes, and data processing method of spatial correlation function are given based on a high-quality fiber optical turbulence sensing array. Determining the statistical time and the calculation principle of the spatial correlation is the main point of current research. Emphasis is put on demonstrating the kinds of structural forms and analyzing the impact elements of spatial correlation function in turbulence as clear as possible. Using the sensing array, experimental measurement is promoted in the near ground layer and many forms of correlation functions are revealed. Results show that there are two main structural forms of the spatial correlation function:the first one shows an isotropy-model form, which tends to decrease with the increase of spatial displacement, and then tends to zero after outer scale, the coincidence rate is about 58.7%. The other one tends to oscillate around zero, and the coincidence rate is about 37.9%. By analyzing the probability and impact elements, it is not difficult to know that the spatial correlation of an optical turbulence mainly depends on the intensity and development degree of the optical turbulence; and the coherent structure is an important factor of oscillation in the correlation functions. On the one hand, the value of correlation coefficient is mainly determined by the intensity of the optical turbulence; and on a certain scale, the stronger the turbulence, the bigger the value of correlation coefficient becomes. On the other hand, the variation tendency of correlation function is not only determined by the intensity of turbulence, but also by the development degree of the optical turbulence. When the atmosphere is in advection or anisotropy, its spatial correlation coefficient will oscillate around zero and be unrelated to the spatial displacement. The spatial correlation function obtained by the sensor array set is not only the foundation of analyzing the spatial structure, but also the beginning of giving non-Kolmogorov model of turbulence.
First-principles study on the band-gap changes of Zn2GeO4 under high pressure
Authors: Wu Cheng-Guo  , Wu Wen-Yuan  , Gong Yan-Chun  , Dai Bin-Fei  , He Su-Hong  , Huang Yan-Hua  ,   College of Science, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

In this paper, the properties of electronic structure and band-gap change of Zn2GeO4 under high pressures are investigated using the first principles method based on the density functional theory (DFT). We demonstrate that the density functional theory calculations performed with the local density approximation (LDA) allows for a significantly better reproduction of lattice constants, the unit cell volume and the band gap of Zn2GeO4 than those performed with the generalized gradient approximation (GGA), so the electronic structure and the band-gap changes of Zn2GeO4 under high pressures can be systematically investigated by LDA. Result of the state density without application of pressures shows that Zn2GeO4 is a wide direct-band-gap semiconductor, and the top of the valence band is mainly composed of Zn 3d and O 2p states, while the conduction band is dominated by the Zn 4 s and Ge 4p. Calculated results about the energy band structure of Zn2GeO4 show that the band gaps of Zn2GeO4 first increase and have a peak at around 9.7 GPa, and then gradually decrease with increasing pressure. The Mulliken charge populations and the value of net charges of Zn2GeO4 at different pressures reveal that the charge distribution of O atoms does not change obviously, while the s and p orbital charges of Zn and Ge atom distributions have obviously charge transfer above 9.7 GPa, and result in an increase of Zn and Ge atom net charges. Analysis of the state density, the Mulliken charge populations, and the electronic density difference of Zn2GeO4 in (210) plane at different pressures indicate:in the low-pressure region (0PP>9.7 GPa), the delocalization phenomenon becomes dominant due to the fact that the delocalization action exceeds the force between the bonding state and anti-bonding state, which induces the decrease of the band gap. These results will not only help to understand the germanate crystal structures in Zn2GeO4 materials under high pressures and the unique characteristics and laws, and may provide a reference for the design of electronic devices of Zn2GeO4 crystals.