bluuebunny/crossref_metadata_2025 huggingface dataset:
TAFONOMÍA DE LOS CARBONATOS TEMPLADOS PLIOCENOS DE LA CUENCA DE ALMAYATE (MÁLAGA, S DE ESPAÑA)
Authors: Aguirre Julio , Méndez-Chazarra Nahum
Published: December 2020

Se analizan los procesos tafonómicos que afectan a las asociaciones de fósiles de los carbonatos templados del Plioceno que afloran en la Cuenca de Almayate (Málaga, S de España). El estudio tafonómico se ha realizado cuantificando varias propiedades tafonómicas. Los valores obtenidos han servido para realizar un análisis multivariante de agrupamiento de muestras, con objeto de establecer modelos de tafofacies. Los resultados obtenidos indican unas condiciones de depósito de alta energía donde los restos esqueléticos permanecieron durante prolongados períodos de tiempo en la zona tafonómicamente activa. En este contexto, durante los periodos de sedimentación normal se produjo un efecto combinado de destrucción tafonómica: 1) destrucción física, como consecuencia de la alta energía, 2) destrucción biológica, debido al efecto de los organismos bioperforadores, y 3) destrucción química, por disolución de las fases inestables del carbonato cálcico. Estos procesos tafonómicos son los que de forma habitual afectan a los carbonatos templados. Además de estos procesos normales, la acción esporádica de tormentas dejó señales sedimentológicas (presencia de niveles de tempestitas) y tafonómicas propias. En este sentido, el análisis cluster individualiza un conjunto de muestras tomadas en niveles de tempestitas. Finalmente, el análisis cluster separa un tercer grupo de muestras donde domina la presencia de moldes de organismos originalmente aragoníticos sobre restos que mantienen la mineralogía original de la concha. Una cementación temprana debió jugar un papel decisivo en la formación de esta asociación.
First xiphosuran traceway in the middle Muschelkalk facies (Middle Triassic) of the Catalan Basin (NE Iberian Peninsula)
Authors: De Jaime-Soguero Chabier , Mujal Eudald , Fortuny Josep
Published: December 2020

In the last decade, the first ichnoassamblages from the middle Muschelkalk facies (upper Anisian–middle Ladinian) of the Catalan Basin (NE Iberian Peninsula) have been discovered. Herein, the first xiphosuran trace fossils are described from the locality of Penya Rubí, a newly discovered ichnosite from the Catalan Basin. The finding opens a window into peri-Tethys ecosystems with coastal influence. The traceway is referred to the ichnogenus Kouphichnium, a locomotion trace attributed to xiphosurans. The traceway preserves telson grooves and different imprint morphologies from the various appendages. The traceway pattern and arrangement of the different traces suggest a crawling locomotion style. The sedimentology suggests a coastal zone with areas influenced by tides (intertidal flat). The morphological variations of the ichnites are correlated to substrate rheology, the locomotion of the tracemaker and environmental conditions.
Reconstrucción alométrica de la capacidad de vuelo de Pelagornis chilensis Mayr & Rubilar-Rogers, 2010 (Aves: Pelagornithidae)
Authors: Meza-Vélez Ivan
Published: December 2020

Las aves fósiles de la familia Pelagornithidae fueron grandes aves marinas planeadoras que habitaron desde el Paleoceno tardío hasta el Plioceno. En este trabajo se estudia la capacidad de vuelo de Pelagornis chilensis, una especie de esa familia. Utilizando la fórmula de sustentación y fórmulas alométricas se demostró que diferentes tipos de velocidades del ave extinta son significativamente mayores a las de Thalassarche chrysostoma, el albatros de cabeza gris, el ave marina actual que más se asemeja morfológicamente al ave extinta. Además, en coherencia con los resultados anteriores, se determinó que la potencia parásita, la potencia inducida, la fuerza muscular y el número de Reynolds de P. chilensis son significativamente mayores que las de T. chrysostoma. El método fue utilizado en el albatros Diomedea exulans para comprobar la cercanía de los valores observados con los calculados y estimar un porcentaje de error. La diferencia obtenida entre estos resultados es de un 2,7%, demostrando la efectividad del método. Finalmente, se estudian las condiciones y forma de vuelo de los grandes albatros y su posible aplicación al vuelo de los Pelagornítidos. Se hipotetiza que por el gran tamaño de las especies estudiadas y por tener una morfología semejante, dichos patrones de vuelo serían similares.
Simulation and prediction of the weld-line in the filling process using a corrected smoothed particle hydrodynamics method
Authors: Ren Jin-Lian  , Lu Wei-Gang  , Jiang Tao  ,   Department of Mathematics, School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou 225002, China
Published: December 2020

A corrected smoothed particle hydrodynamics (SPH) method for viscoelastic fluid is proposed and used to tentatively simulate and predict the behavior of the molecule near the weld line in the filling process of the FENE-P fluid in this paper. And the corrected SPH scheme for the viscoelastic fluid is simultaneously presented. Firstly, a coupled macro-micro model based on the SPH method for the viscoelatic fluid is set up. Then, some benchmarks, such as the flow behavior of the periodic cylinders of FENE-P fluid and the non-isothermal Poiseuille flow based on the Oldroyd-B model which is a simplified model of FENE-P model, are simulated to verify their validity and the convergence of the corrected SPH method of solving the coupled macro-micro problem of the polymer and the discrete SPH temperature model for viscoelastic fluid. Finally, the filling process of the viscoelastic fluid based on the FENE-P model in a ring-shaped mold is simulated, and the behavior of the micro molecules in the filling process is tentatively shown by orientation ellipse. Meanwhile the non-isothermal filling process of the FENE-P fluid is also implemented. The numerical results show clearly the behavior of the molecules in the filling process of the FENE-P fluid, the weld line is indeed observed in the filling process of the FENE-P fluid in the ring-shaped mold, and the non-isothermal filling process can improve the weld line to some extent. In order to further discuss the improvement of the weld line, the filling processes of different cases are simulated in the multiple-gating C-shaped mold by using the pattern of the hot runner and valve gates, and the obtained results are compared with other available data. Moreover, the effect of the delay time needed for the fluid to be injected on the flow is also investigated. The numerical results show that the pattern of the hot runner and valve gates can improve and even remove the weld-line in the filling process of the polymer melt, especially for the big-sized product, and the shorter the delay time is, the faster the flow is, and the bigger the appearance probability of the weld line is.
Effects of Dzyaloshinskii-Moriya interaction and intrinsic decoherence on quantum dense coding via a two-qubit Heisenberg spin system
Authors: Zou Qin  , Hu Xiao-Mian  , Liu Jin-Ming  ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

By solving the Milburn equation, we investigate the properties of optimal channel capacity for the quantum dense coding via a two-qubit Heisenberg spin system with Dzyaloshinskii-Moriya (DM) interaction in the presence of intrinsic decoherence. The influences of different DM interactions, different initial states, anisotropic coupling parameters, and intrinsic decoherence on optimal coding capacity are analyzed in detail. It is found that the initial state of the system affects optimal coding capacity greatly, whose dependent parameters are not identical for different types of initial states. When the system is initially in the form of the nonmaximally entangled state cft| {01} ightangle + dft| {10} ightangle , a weak z-component DM interaction can enhance the value of optimal coding capacity as compared with the value without DM interaction, and the phase decoherence effect can suppress the oscillation of optimal coding capacity and make the capacity decrease to a stable value for the long-time evolution. It is also found that under the influence of intrinsic decoherence, the optimal transmission capacity of dense coding can keep an ideal maximal value of 2 by choosing the proper initial maximally entangled state. Moreover, no matter from which direction the DM interaction is introduced, the optimal coding capacity via the two-qubit Heisenberg spin system is always larger than the transmission capacity of any classical communication.
Effect of anomalous magnetic moment on thermodynamic properties of weakly interacting Fermi gas in weak magnetic field
Authors: Chen Xin-Long  , Men Fu-Dian  , Tian Qing-Song  ,   College of Science, China University of Petroleum (East China), Qingdao 266580, China
Published: December 2020

Taking the anomalous magnetic moment into consideration, the analytical expression of the free energy for a weakly interacting Fermi gas in a weak magnetic field is derived by using the pseudopotential method and thermodynamic theory, therefore the thermodynamic properties can be studied. Based on the derived expression, the thermodynamic properties of this system at both high and low temperatures are given, and the effect of anomalous magnetic moment on thermodynamic properties can be analyzed. The effect of anomalous magnetic moment on the thermodynamic properties is related to temperature, and with the rise of temperature this effect increases in the low temperature zone, but decreases in the high temperature zone. For the chemical potential and internal energy of the system, the anomalous magnetic moment strengthens the influence of the magnetic field, but weakens the influence of the interaction. Under the influence of anomalous magnetic moment, the heat capacity of the system decreases in the low temperature zone, but increases in the high temperature zone.
Simulation and experiment for electrode capacitance based on Vernier anode photon counting detector
Authors: Xing Yan  , Chen Bo  , Wang Hai-Feng  , Zhang Hong-Ji  , He Ling-Ping  , Jin Fang-Yuan  ,   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

According to the principle of Vernier anode photon counting detector, in this paper we discuss a decoding algorithm of calculating centroid location and interelectrode capacitance between electrodes, which has a close relationship with preamplifier circuit noise. Based on the Poisson's equation, the theoretical model of Vernier anode is established. The method of calculating the irregular shape uniplanar self-capacitance and interelectrode capacitance between electrodes using ANSYS finite element analysis is introduced. In addition, a Vernier anode plate is manufactured with picosencond laser micromachining process on a 1.5 mm thick quartz substrate with gold film as conductors. The Vernier anode pattern has a picth of 9.9 mm, an active area of 19.8 mm×19.8 mm, insulation channel depth of 10 μm, and insulation channel width of 30 μup$m. Comparing the simulated capacitances with the measured capacitances, the validity of the three-dimensional finite-element method is proved. A simulation study on the effects of substrate permittivity, insulation channel width and depth on capacitance change is carried out. The simulation result provides a basis for structure design of Vernier anodes.
Radar cross section reduction of microstrip antenna based on wide-band metamaterial absorber
Authors: Li Wen-Hui  , Zhang Jie-Qiu  , Qu Shao-Bo  , Yuan Hang-Ying  , Shen Yang  , Wang Dong-Jun  , Guo Meng-Chao  ,   College of Science, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

We design a wide-band metamaterial absorber (WBMA) with stable polarization and wide incident angle by loading a lumped resistance. The full-width at half-maximum of the absorber is 98%, the bandwidth of absorbing rate of more than 90% reaches 10.42 GHz, and the peak absorbing rate is 99.9% in the normal wave incidence. Loading the WBMA around the microstrip antenna by sharing the same substrate and ground plane, we fabricate the WBMA antenna, whose radar cross section (RCS) sharply decreases in the wide frequency range. Simulation and experimental results show that the antenna's radiation pattern is almost unchanged: just only the former gain improves 0.53 dB after loading the WBMA. Under different polarized waves, the antenna's monostatic RCS reduction is more than 3 dB within the working frequency band and beyond the working frequency band (6.95-17.91 GHz), the maximum value is 21.2 dB. The bistatic RCS decreases significantly from -48° to 48° at the middle working frequency (8 GHz), which well achieves the antenna stealth at the wide-band frequency and wide angle.
Influence of feedback strength on the characteristics of the random number sequence extracted from an external-cavity feedback semiconductor laser
Authors: Yang Hai-Bo  , Wu Zheng-Mao  , Tang Xi  , Wu Jia-Gui  , Xia Guang-Qiong  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

Under proper feedback strength, an external-cavity feedback semiconductor laser can operate at a chaos state, and its chaotic output can be used as a physical entropy source to generate a physical random number sequence. In this paper, we focus on the influence of feedback strength on the randomness of the obtained binary code sequence. The simulation results show that with the increase of feedback strength, the time delay characteristic peak of the chaotic signal from an external-cavity feedback semiconductor laser first decreases and then increases gradually, meanwhile, the permutation entropy characteristic value of chaotic signal first increases and then decreases gradually, namely, there exists an optimized feedback strength for obtaining the chaotic signal with the weakest time delay signature and high complexity. The randomness of binary code sequences, generated by the chaotic signal from the external-cavity feedback semiconductor laser under different feedback strengths, is tested by NIST Special Publication 800-22, and the influence of feedback strength on the test results is also discussed.
High-efficiency intracavity 2 μm degenerate optical parametric oscillator
Authors: Guo Jing  , He Guang-Yuan  , Jiao Zhong-Xing  , Wang Biao  ,   State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China;,   Institut Franco-Chinois de I'Energie Nucléaire, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

A high-efficiency 2 μm optical parametric oscillator based on MgO-doped periodically poled LiNbO3 intracavity pumped by a 1.064 μm Q-switched Nd:YVO4 laser is reported. With the intense fluence inside the laser cavity, a maximum 2 μm average power of 3.5 W is obtained at 15 kHz repetition rate in a degenerate state. A maximum optical-to-optical conversion efficiency of 17.5% with a slope efficiency of 25% is achieved when the laser diode power is 20 W. To the best of our knowledge, the efficiency is the highest ever achieved from an intracavity degenerate optical parametric oscillator in 2 μm region. The pulse duration of 2 μm is 1.4 ns, which is much shorter than that of 1.064 μm. A bandwidth of 30 nm is obtained at a degenerate wavelength of 2128 nm. The M2 values for the 2 μm beam are 3.47 and 3.54 in the horizontal and vertical directions, respectively. The standard deviation of the power fluctuation is ～ 2% at the maximum power in half an hour.
Reliability of partially-depleted silicon-on-insulator n-channel metal-oxide-semiconductor field-effect transistor under the ionizing radiation environment
Authors: Zhou Hang  , Cui Jiang-Wei  , Zheng Qi-Wen  , Guo Qi  , Ren Di-Yuan  , Yu Xue-Feng  ,   Xinjiang Key Laboratory of Electric Information Materials and Devices, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumuqi 830011, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

With the development of semiconductor technology, the small size silicon-on-insulator metal-oxide-semiconductor field-effect transistor devices start to be applied to the aerospace field, which makes the device in use face dual challenges of the deep space radiation environment and conventional reliability. The small size device reliability test under ionizing radiation environment is conducible to the assessing of the comprehensive reliability of the device. With reference to the national standard GB2689.1-81 constant stress life test and accelerated life test method for the general electric stress, the conventional reliability of the sub-micron type partially-depleted silicon-on-insulator n-channel metal-oxide-semiconductor is studied under the ionizing radiation environment. The experiment is divided into three groups marked by A, B and C. For all the experimental devices, the gate oxide tox=12.5 nm, channel length L=0.8 μm and width W=8 μm, and nominal operating voltage V=3.5 V. We carry out the electrical stress test on A group after irradiation with γ -ray dose up to 1×104 Gy (Si) under the bias condition. Before group B is tested, it has been irradiated by the same dose γ -ray and annealed for one week. Group C is not irradiated by γ -ray before the electric stress test. After irradiation we measure the DC characteristics of the devices: the drain current versus gate voltage (IDS-VGS) and the drain current versus drain voltage (IDS-VDS). The hot carrier injection (HCI) experiment is periodically interrupted to measure the DC characteristics of the device. The sensitive parameters of HCI and irradiation are VT, GM and IDlin, and after HCI stress, all parameters are degenerated. Through the contrast test, we qualitatively analyze the influences of the oxide trap charge and interface state on the sensitive parameters. We obtain the curve of the oxide trap charge and interface state versus time, and the influences of the different stages on device parameters. The results show that the combination of the total dose radiation environment and electrical stress causes the sensitive parameters of the device to rapidly degrade, this combination of these two factors gives rise to bigger effect than a single influence factor.
Surface potential dynamic characteristics of the insulating sample under high-energy electron irradiation
Authors: Li Wei-Qin  , Hao Jie  , Zhang Hai-Bo  ,   School of Automation and Information Engineering, Xi'an University of Technology, Xi'an 710048, China;,   Xi'an Aeronautical University, Xi'an 710077, China;,   Department of Electronic Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

The surface potential and electron yield dynamic characteristics of an insulating thick sample under high-energy electron beam irradiation are obtained by combining the numerical simulation and experimental measurement. The numerical model takes into account the electron scattering, charge trapping, and charge transport. The results show that due to the electron scattering and transport, the space charge is weakly positive in the near surface and strongly negative inside sample; along the depth direction, the space potential decreases to a minimum value slowly, and then increases gradually and finally tends to zero; with the electron beam irradiation, the surface potential decreases to the negative kV magnitude gradually, and the total electron yield gradually increases to a stable value that is slightly less than unity. After stopping irradiation, the surface potential increases gradually, but charges are not eliminated completely. The surface potential decreases linearly with the increase of the beam energy, and increases with the increase of the incident angle, however it decreases slightly with the increase of the sample thickness.
Mechanism of high pulsed magnetic field treatment of the plasticity of aluminum matrix composites
Authors: Wang Hong-Ming  , Li Pei-Si  , Zheng Rui  , Li Gui-Rong  , Yuan Xue-Ting  ,   School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

For aluminum matrix composite, the introduced particles will strengthen the matrix, but as the obstacles, the heterogeneous particles will hinder the dislocation movement, generate uneven material structure, and may become a source of stress concentration. Therefore, they are detrimental severely to the elongation and plasticity of composite. It is known that dislocations exhibit a paramagnetic behavior because they contain paramagnetic centers including localized electrons, holes, triplet excitons, ion radicals, etc. The initial radical pair of the dislocation-obstacle S (spin angular momentum) = ± 1/2 is in a singlet state, and the total spin of the radical pair is 0 and in the antiparallel spin direction, offsetting a magnetism of the radical pair. The magnetic field can change the spin direction from singlet state to triplet state. In the triplet state the electron spin is 1 and in the same spin direction. A strong bond of the dislocation-obstacle is formed only in the singlet state when the spins of the two electrons are antiparallel. So an obstacle is able to pin a dislocation only if the radical pair is in the singlet state. Under the condition of high pulsed magnetic field treatment (HPMFT) the conversion of electronic spin will be a fundamental cause of dislocation motion along a glide plane. The movement of pinned dislocations will change the material microstructure and influence the performance of material. By comparing the microstructural evolutions and the residual stresses of samples subjected to HPMFT with different values of magnetic induced density (B), the positive influence of magnetoplastic effect on the plasticity of aluminum matrix composite is investigated in this paper. The results show that the dislocation density is significantly increased when B changes from 2 T to 4 T. When B=4 T the dislocation density is enhanced by 3.1 times compared with that of the sample without HPMFT. Moreover, the residual stress is reduced apparently from 41 MPa (B=0) to -1 MPa (B=3 T). In the view of atomic scale, the high magnetic field leads to a magnetoplastic effect which contributes to the dislocation movement and promotes the dislocation depinning, thereafter, the number of movable dislocations increases up. From the viewing of the internal structure of composite, the magnetic field accelerates the releasing rate of internal stress and lowers the residual stress in material, which is beneficial to improving the plasticity of aluminum matrix composite.
Suppression of metal grating to surface plasma radiation
Authors: Wang Ping  , Hu De-Jiao  , Xiao Yu-Fei  , Pang Lin  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610064, China;,   Fujian CASIX Inc., Fuzhou 350014, China
Published: December 2020

Surface plasmon polaritons (SPP) are widely investigated in many fields because of the surface confinement of their electrocmagnetic field. Grating coupling is one of the methods to achieve the momentum match between light in free space and the surface plasmon to excite SPP. Because of the nature of the grating coupling, its parameters will greatly affect the coupling efficiency. Varying the grating modulation depth but keeping other parameters unchanged, we investigate the reflection spectra of onedimensional rectangle metallic grating by rigorous coupled-wave theory under the irradiation of incident light of 780 and 1500 nm in wavelength, respectively. According to Fano theory, the reflectance of metallic grating is the result of interference of two components, i.e., a directly reflected mode from the metal surface and a resonance radiation mode coupled out by the SPP propagating along the grating surface. We derive the Fano-type expression to describe the reflection spectra, and explain the contributions of directly reflected mode, SPP resonance radiation mode and the interference between these two effects. Near-filed electromagnetic distribution on metallic grating surface proves that the Fano-type expression is accurate enough to reflect the nature of the interference between the direct and radiation modes. Most importantly, our results from the expressions suggest that in some special grating condition, the metallic grating almost completely suppresses the SPP radiation propagating from grating to free space, which means that the energy of light can be completely trapped inside the grating. The phenomenon can be employed in designing light trapping device.
Experimental study of ultrafast carrier dynamics in polycrystalline ZnTe nanofilm
Authors: Jia Lin  , Tang Da-Wei  , Zhang Xing  ,   Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, School of Aerospace, Tsinghua University, Beijing 100084, China;,   Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Zinc telluride, due to its direct band gap and broadband light absorption, has the good application prospects in terahertz devices, solar cells, waveguide devices, and green light emitting diodes. In the photovoltaic field, it is possible to further improve the photoelectron conversion efficiency of multi-junction tandem solar cells by combining zinc telluride with III-V semiconductors. Ultrafast photo-excited carrier dynamics is fundamental to understand photoelectron conversion process of nanofilm solar cells. In this study, the ultrafast energy carrier dynamics of N-doped polycrystalline zinc telluride is investigated by using the femtosecond laser two-color pump-probe method at room temperature. The polycrystalline zinc telluride nanofilm is grown on a 500 μm GaAs (001) substrate via molecular beam epitaxy and doped by using a nitrogen ratio frequency plasma cell. The laser pulses with a central wavelength of 800 nm are divided into pump beam and probe beam by a beam splitter, after which the pump beam passes through a bismuth triborate crystal and its frequency is doubled to 400 nm. The 400 nm pump beam and 800 nm probe beam are focused on the sample collinearly through the same objective lens. Photo-excited carriers will be generated since the excitation photon energy of 400 nm pump beam (3.1 eV) is higher than the band gap of zinc telluride (～ 2.39 eV). The experimental data are analyzed by using the theoretical fitting model which includes energy relaxation processes of electrons and lattice, and the theoretical curves are consistent well with the experimental data. The fitted results show that the three dominated relaxation processes which affect the initial reflectivity recovery are in sub-picosecond time regime. The positive amplitude electron relaxation process is attributed to inter-band carrier cooling and carrier diffusion through electron-photon interactions, and the deduced decay time of this positive amplitude electron relaxation process is about 0.75 ps. The negative amplitude electron relaxation process is characterized as a photo-generated carrier trapping process induced by defects, and the decay time of this process is about 0.61 ps. The lattice heating process is realized through electron-phonon coupling process, and the calculated time constant of the lattice heating is about 0.86 ps.
Experimental study on scan imaging of silicon wafer by laser-induced photocarrier radiometry
Authors: Liu Jun-Yan  , Song Peng  , Qin Lei  , Wang Fei  , Wang Yang  ,   School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In this paper, the modulated laser-induced excess minority carrier density wave (CDW) of bipolar semiconductor is developed. An analytical expression of CDW in frequency domain is introduced. The numerical simulations are carried out to analyze the effects of minority carrier transport parameters (minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) on response of laser-induced photocarrier radiometry (PCR) signal to frequency for semiconductor silicon wafer. The PCR amplitude increases with increasing the minority carrier lifetime, and decreased with increasing the carrier diffusion coefficient and surface recombination velocity. In contrast, the PCR phase lag decreases with increasing the minority carrier lifetime, and increases with increasing the carrier diffusion coefficient and surface recombination velocity. The silicon (Si) wafer with an artificial defect (mechanical scratch) on the surface is experimentally investigated by PCR scanning image system. The distribution maps of the minority carrier transport parameters are obtained by best-fitting method which is based on the carrier density wave analytical expression, and the influences of the artificial defect on carrier transport parameters are discussed in detail. The experimental results indicate that the surface recombination velocity and carrier diffusivity at artificial damaged location are dramatically increased compared with those in the healthy region. The carrier bulk lifetime of whole Si wafer is obtained to be about 38.33 μs by PCR scanning image measurements. Simultaneously, quasi steady-state photoconductance (QSSPC) method is used to measure the carrier effective lifetime of Si wafer, and it is about 33.85 μs. Therefore, the carrier bulk lifetime of Si wafer by PCR scanning image measurement is in good agreement with the QSSPC measurement. However, QSSPC measurement could obtain only the carrier effective lifetime of Si wafer. Furthermore, PCR scanning image measurement can be employed to measure the carrier transport parameters with high resolution in comparison with QSSPC measurement, and to evaluate the localized imperfection.
Solar cell temperature prediction model of support vector machine optimized by particle swarm optimization algorithm
Authors: Zhao Zhi-Gang  , Zhang Chun-Jie  , Gou Xiang-Feng  , Sang Hu-Tang  ,   School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
Published: December 2020

Establishing a general and precise solar cell temperature model is of crucial importance for photovoltaic system modeling, the loss analysis of output power, and conversion efficiency. According to the complex mechanism of solar cell temperature, in this paper we study the steady state thermal model (SSTM) of solar cell temperature and accurate prediction model of method of support vector machine (SVM). Firstly, based on the approximate linear relationship among air temperature, solar radiation intensity, wind speed and solar cell temperature, the polynomial model of solar cell temperature is established and the unknown parameters of the model are extracted with the improved differential evolution algorithm. Secondly, in order to improve the accuracy of SVM prediction model, the particle swarm optimization algorithm is adopted to optimize the parameters (including kernel parameter g and penalty factor C from the radial basis function kernel) of SVM. After the input/output sample set is determined and the training set and test set are classified, a prediction model of solar cell temperature based on particle swarm optimization support vector machine is established. Finally, experimental acquisition platform is built to reduce the influences of air humidity, solar incidence angle, and thermal hysteresis effects on PV cell temperature. Through contrasting experiments, it is shown that the established fitting of the SSTM is better than the models given in other literature, and the prediction model is reliable, comprehensive and simple. The selected parameter optimization algorithm is superior to genetic algorithm and cross-validation method established on the optimization performance, and the accuracy of prediction model is superior to the prediction performance of back propagation neural network and identified SSTM.
Nonlinear electron transport in superlattice driven by a terahertz field and a tilted magnetic field
Authors: Wang Chang  , Cao Jun-Cheng  ,   Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
Published: December 2020

Vertical electron transport in semiconductor superlattice has been the focus of science and technology during the past two decades due to the potential application of superlattice in terahertz devices. When driven by electromagnetic field, many novel phenomena have been found in superlattice. Here we study the chaotic electron transport in miniband superlattice driven by dc+ac electric fields along the growth axis (z-axis) and a magnetic field tilted to z-axis using semiclassical equations of motion in the preflence of dissipation. We calculate the electron momentum by changing the magnetic field or amplitude of the terahertz field. It is shown that the momentum py(t) of miniband electron exhibits complicated oscillation modes while changing the control parameters. Poincaré bifurcation diagram and power spectrum are adopted to analyze the nonlinear electron states. Poincaré bifurcation diagram is obtained by plotting pym = py(mTac) (with m = 1, 2, 3,… and Tac the period of ac terahertz field) as functions of ac amplitude E1 after the transients decay. The periodic and aperiodic regions can be distinguished from each other since there are a large number of points in the chaotic regions. When the magnetic field is increased from 1.5 to 2 T, the Poincaré bifurcation diagram changes dramatically due to the strong effect of magnetic field on electron motion. The oscillating state of py(t) may be changed between periodic and chaotic syates. Power spectra of electron momentum py for different values of E1 (= 2.06, 2.18, 2.388, and 2.72) are calculated for a deep insight into the nonlinear oscillating mode. It is found that the power spectra of n-periodic states show peaks at frequencies ifac/n (with i = 1, 2, 3,…); the power spectra of chaotic states are very irregular with a large number of peaks. We demonstrate that the dissipation and resonance between Bloch oscillation frequency and cyclotron frequency play an important role in the electron transport process. We attribute the emerging of periodic and chaotic states in a superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode related to Bloch oscillation and cyclotron oscillation. In the case of ωB≠iωc, the time-dependent electron motion is chaotic in most regions of the parameter space. Results of the preflent paper are useful for designing terahertz devices based on the semiconductor superlattices.
Fabrication and X-ray photoemission characteristics of Au spherical shell photocathodes
Authors: Wang Yu-Ying  , Yan Da-Wei  , Tan Xiu-Lan  , Wang Xue-Min  , Gao Yang  , Peng Li-Ping  , Yi You-Gen  , Wu Wei-Dong  ,   College of Physics and Electronics, Central South University, Changsha 410083, China;,   Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, CAEP, Mianyang 621900, China
Published: December 2020

Gold spherical shell photocathode was prepared by seed-mediated growth on polystyrefle template and dispersed on the aluminum substrates by spin-coating procedure. Polystyrefle template was then removed by heat treatment. SEM surface morphology shows that Au spherical shell of ～10 μm in diameter can be self-supported after polystyrefle substrate is removed. The thickness of Au shell is about 70-90 nm and the grain size on the surface is about 30-60 nm. X-ray photoemission characteristics of Au reflection photocathodes in the 400-1400 eV photon energy region are obtained, indicating that the Au shell photocathodes can emit 3 times more photoelectrons than the plane Au photocathode; this results from the special surface morphology of Au spherical shell and the reduction of surface potential.
Photocatalytic application of Z-type system
Authors: Li Ping  , Li Hai-Jin  , Tu Wen-Guang  , Zhou Yong  , Zou Zhi-Gang  ,   National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China;,   Department of Physics, Nanjing University, Nanjing 210093, China;,   Eco-materials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China;,   School of Mathematics and Physics, Anhui University of Technology, Ma’anshan 243002, China
Published: December 2020

Z-type photocatlytic system, reflembling natural photosynthesis, consists of two different photocatalysts and a shuttle redox mediator, involving two-photon excitation process for photocatlysis. One photocatalyst as a photoreduction system offers the reduction sites by conduction band (CB) electrons, and the other photocatalyst as a photooxidation system provides the oxidation sites by valence band (VB) holes. A shuttle redox mediator as an electron conductor transfers the electrons from the CB of the photooxidation system to the VB of the photoreduction system. On the one hand, the separation of photocatalytic reactive sites is advantageous for spatial separation of the electrons and holes, which is beneficial for enhancing the photocatlytic activities. On the other hand, photoreduction system and photooxidation system of different materials effectively inhibit the reflerse reaction involvement of photoreductive and photooxidative products. The Z-type photocatlytic system simultaneously possesses a wide light absorption range and strong redox ability.
Ultrafast spectroscopic study for singlet fission
Authors: Zhang Bo  , Zhang Chun-Feng  , Li Xi-You  , Wang Rui  , Xiao Min  ,   National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, China;,   Department of Science, China University of Petroleum (Huadong), Qingdao 266580, China;,   Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
Published: December 2020

Singlet fission is a spin-allowed process that creates two triplet excitons from one photo-excited singlet exciton in organic semiconductors. This process of carrier multiplication holds the great potential to break the theoretical efficiency limit in single-junction solar cells by making better use of high-energy photons, while capturing lower-energy photons in the usual style. Photovoltaic devices based on singlet fission have achieved external quantum efficiencies in excess of 100%. In this paper, we first introduce the basic concept about singlet fission and review the history of the field briefly. Then, we report some reflent advances in the reflearch of singlet fission progress with the combination of our group’s productions. Tetracene and pentacene are chosen as typical polyacene materials for discuss. We describe how scientists make progresses in understanding the underlying physics in singlet fission process. The experimental methods of transient absorption spectra, time-resolved fluorescence spectra and time-resolved two-photon photoemission spectra render numerous results for analysis. Moreover, a survey about the debate on the direct or indirect mechanism with transient optical study is provided. It has been verified that multiexciton state intermediates in singlet fission process and the factors of energy level alignments, intermolecular interaction as well as lattice vibrations play a role in it. Last, we briefly summarize the implications of singlet fission in organic solar devices by introducing several composite architectures for singlet-fission photovoltaics. Designing efficient and cheap solar cells is the ultimate goal for understanding the intrinsic photophysics of singlet fission. To obtain high efficiencies, it is important to adapt proper materials and new organic/inorganic architectures may become a promising direction. Also, finding a way for efficient triplet exciton dissociation should be considered seriously. It is believable that these guidelines can lead to the development of cheap and efficient fission-based devices.
Broadband target beam-space transformation in generalized likelihood ratio test using acoustic vector sensor array
Authors: Liang Guo-Long  , Tao Kai  , Wang Jin-Jin  , Fan Zhan  ,   Science and Technology on Underwater Acoustic Laboratory Harbin Engineering University, Harbin 150001, Heilongjiang, China;,   College of Underwater Acoustic Engineering Harbin Engineering University, Harbin 150001, Heilongjiang, China
Published: December 2020

Aiming at the problem of passive detection of broadband sources in underwater acoustic vector signal processing, a novel detection algorithm based on beam-space transformation is proposed. The principle of spatial spectrum detection with human eyes is employed for reflerence, and the generalized likelihood ratio test (GLRT) is applied to the beam-space. First, the design criterion of beam-space transformation matrix is studied for the compreflensive consideration of the environment of multiple targets and the characteristic of vector ambient noise field, so that the analytical solution is obtained. Second, assuming that the number of beams not containing the target signal is given, the probability density function (PDF) model of beam-space data is constructed, and the new GLR test is made by calculating the maximum likelihood estimate of the unknown variables in PDF. Finally, the information of theoretical criterion is adopted in order to estimate the number of beams not containing target signals. The processing gain and the threshold value of this test statistics are also discussed, and the specific implement is explained in detail. Theoretical analysis and simulation results show that under the complex conditions of strong target interference and ambient noise with undulated and time-variant power spectrum, the proposed algorithm can give the processing result with higher gain and detection threshold at constant false alarm rate (CFAR); the results of lake experiment further prove the favorable and robust detection performance.
Study on the electronic structure and elastic constants of uranium dioxide by first principles
Authors: Fan Hang  , Wang Shan-Shan  , Li Yu-Hong  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China;,   Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The crystal structure, electronic structure and elastic constants of uranium dioxide are investigated using first-principles calculations, wherein the generalized gradient approximation and Hubbard U terms are used in the framework of density-functional theory. On-site Coulomb interactions with the simplified rotational invariant approach (the Dudarev approach), fully relativistic calculations for the coreflelectrons (repreflented as a pseudopotential), and scalar relativistic approximations for the valence electrons areflemployed to account for the relativistic effects and electron correlation of 5f electrons in UO2. The Hubbard U parameters (Ueff=U-J, U=3.70 eV, J=0.40 eV) are derived by calculating the band gap width of UO2. In addition, the electron density of states calculation suggests that the following value of band gap is appropriate. The calculated lattice constant is 5.54 Å, and the band gap width is 2.17 eV which shows that UO2 is a semiconductor. Its density of states shows that the U 5f orbital contributes to the peaks immediately adjacent to the Fermi level, which agrees with the U 5f2 configuration, while the O 2p orbital plays a dominant role in the bonding band at approximately -6 to -2 eV. Results obtained above have been compared with available experimental data, and also discussed in relation to previous calculations. Above results are better than existing ones gained by others. Analyzing the density of states for different Hubbard U parameters, we find that the Hubbard U parameters can influence the distribution of U 5f electronic orbit.
Surface plasmon polaritons splitting properties of silver cross nanowires
Authors: Zhang Yong-Yuan  , Luo Li-Na  , Zhang Zhong-Yue  ,   School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, China;,   School of Science, Xi’an University of Science and Technology, Xi’an 710054, China
Published: December 2020

Since metallic nanowires can confine light in nanoscale beyond the diffraction limit, metallic nanowires play an important role in nanophotonic integrated circuits. In this paper, a silver nanowire waveguide with a cross is proposed and its surface plasmon polaritons (SPPs) splitting properties of the cross at λ = 532 nm are studied by the finite element method. The nanowire has a square shape with its side length of a. Results show that the outputs for different input modes depend on the geometric parameters of the nanowires. For SPPs with TM0 mode, there are similar intensities in different waveguide directions with smaller side length. With the increase of a, the intensity in the original waveguide direction increases monotonically, and those in the perpendicular direction will decrease monotonically. For SPPs with HE1 mode and HE-1 mode, most of the energy propagate along the original waveguide direction for smaller a. With the increase of a, the intensity in the original waveguide direction decreases dramatically. For SPPs with HE1 mode, the cross blocks most of the energy in three directions for larger a. In addition to the splitting effect of it, the cross also performs a function of mode conversion. For the input SPPs with TM0 mode, the output of SPPs along the perpendicular waveguide direction can be converted to the HE-1 mode. For the input SPPs with HE1 mode, the output of SPPs along the perpendicular waveguide direction can be converted to the TM0 mode. Due to the superposition of electric fields of different SPPs modes in the perpendicular waveguide direction occur the steady-state and periodic electric field distributions.
Magnetic neutron scattering studies on the Fe-based superconductor system Fe1+yTe1-xSex
Authors: Li Shi-Chao  , Gan Yuan  , Wang Jing-Hui  , Ran Ke-Jing  , Wen Jin-Sheng  ,   Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures, Department of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

We preflent a brief overview on the interplay between magnetism and superconductivity in one of the Fe-based superconductor systems, Fe1+yTe1-xSex. The parent compound Fe1+y Te is an antiferromagnet; with Se doping, antiferromagnetic order is suppressed, followed by the appearance of superconductivity; optimal superconductivity is achieved when x～50%, with a superconducting temperature Tc of ～15 K. The parent compound has an in-plane magnetic ordering wave vector around (0.5, 0) (using the tetragonal notation with two Fe atoms per cell). As Se concentration increases, the spectral weight appears to shift to the wave vector around (0.5, 0.5), accompanying the optimization of superconductivity. A neutron-spin resonance is observed around (0.5, 0.5) below Tc, and is suppressed, along with superconductivity, by an external magnetic field. Taking these evidences into account, we conclude that magnetism and superconductivity in this system couple to each other closely-while the static magnetic order around (0.5, 0) competes with superconductivity, the spin excitations around (0.5, 0.5) may be an important ingredient for it. We also discuss the nature of magnetism and substitution effects of 3d transition metals.