bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphologies, compositions and spectrum features of palm leaves
Authors: Liu Yi-Ke  , Liu Yu-Tong  , Xu Xiang-Dong  , Yan Wei  , Ma Miao  , Zhu Hong-Zhao  , Ma Chun-Qian  , Zou Rui-Jiao  , Ding Lian  , Luo Meng-Jia  ,   School of Optoelectronic Information, University of Electronic Science and Tecnology of China, Chengdu 610054, China
Published: December 2020

Terahertz (THz) spectra for different palm leaves are measured by Fourier transformed infrared spectroscopy-attenuated total reflection, and the physical morphologies and chemical compositions of the leaves are characterized by scanning electron microscopy and infrared spectroscopy, respectively. Accordingly, the THz fingerprint peaks of chlorophyll and carotenoid are experimentally identified. In addition, the results indicate that the influence of the chemical composition in plant leave on optical response is significantly stronger than that of the physical morphology. Moreover, among the main chemical components of palm leave, the THz response of chlorophyll is stronger than that of carotenoid. In this work, new methods of investigating the optical properties of the planes and of developing novel THz sensitive organic materials are also proposed. Particularly, some important results are reported for the first time in this article. These valuable results will be helpful not only for an in-depth understanding of the physiological behavior of the plants, but also for the obtaining of inspiration for designing functional materials of device with higher performance, higher pertinency and wider applications, and thus promoting the development of related theories and applications.
Diffusing loss effects of radiation belt energetic electrons caused by typical very low frequency electromagnetic wave
Authors: Luo Xu-Dong  , Niu Sheng-Li  , Zuo Ying-Hong  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Radiation belt energetic electrons can interact with very low frequency (VLF) electromagnetic wave due to wave-particle resonance; then the particles are imposed to enter into the loss cone and sink to dense atmosphere resulting from changing of its pitch angle. To investigate the diffusion mechanism of interaction of VLF electromagnetic wave with radiation belt energetic electrons, according to quasi-linear diffusion theory, in this paper we use a physical model to calculate diffusion coefficients of Coulomb scatting and wave-particle resonance interaction. Bounce-averaged pitch angle diffusion coefficients of energetic electrons due to the interaction of wave-particle resonance with two groups of VLF electromagnetic waves are obtained. The influence of interaction caused by VLF electromagnetic wave and Coulomb scatting on diffusion of radiation belt energetic electrons for different L shells and various energies are analyzed. Take the case for example, where L equals 2.2 and electron energy E equals 0.5 MeV, the diffusion equation of energetic electrons are solved by using the finite difference method. The time evolutions of precipitation of directional particle flux and omnidirectional particle flux are analyzed. The results show that the resonance interaction caused by VLF electromagnetic wave plays a dominant role when E>0.5 MeV and L>1.6; the higher the L shell or electron energy value, the more significant the high order resonance interaction caused by the oblique propagation VLF electromagnetic wave will be; approximately, the omnidirectional particle flux of radiation belt energetic electrons decreases exponentially with time.
A recovery algorithm for multitask compressive sensing based on block sparse Bayesian learning
Authors: Wen Fang-Qing  , Zhang Gong  , Ben De  ,   College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;,   Key Laboratory of Radar Imaging and Microwave Photonics, Ministry of Education, Nanjing 210016, China;,   Nanjing Research Institute of Electronics Technology, Nanjing 210039, China
Published: December 2020

As a widely applied model for compressive sensing, the multitask compressive sensing can improve the performance of the inversion by appropriately exploiting the interrelationships of the tasks. The existing multitask compressive sensing recovery algorithms only utilize the statistical characteristics of a sparse signal, the structural characteristics of the sparse signal have not been taken into consideration. A multitask compressive sensing recovery algorithm is proposed in this paper based on the block sparse Bayesian learning. The block sparse single measurement vector model is applied to the multi-task problem. Both statistical and block structural characteristics of the sparse signal are used to build a mathematical model, and the sparse inverse problem is linked to the parameter iteration problems in the Bayesian framework. The proposed algorithm does not require the sparseness information and noise beforehand, which turns out to be an effective blind recovery algorithm. Extensive numerical experiments show that the proposed algorithm can exploit both statistical and structural characteristics of the signal, therefore it may reach a good trade-off between the recovery accuracy and the convergence rate.
Research of the impact of group velocity dispersion on the second-order correlation of entangled light field
Authors: Han Xiao-Chun  , Huang Jing-Zheng  , Fang Chen  , Zeng Gui-Hua  ,   Center for Quantum Information Sensing and Processing Research, State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiaotong University, Shanghai 200240, China
Published: December 2020

In the experiment presented in the paper, HBT (Hanbury-Brown and Twiss) interferometer is used to measure the second-order correlation function (G2) for two entangled photons, denoted as signal and idle ones, generated by the spontaneous parametric down-conversion process. When an extra optical fiber is inserted in the signal's path, the arrival times of these two photons are different, so that the length of the fiber can be estimated by measuring the time offset in the G2 function.#br#As the laser light we used is not monochromatic, the experimental result is affected by the group velocity dispersion (GVD). Light of different wavelength has different velocity and leads to different travelling time in the fiber. Through calculation, we find that the G2 function of each wavelength has the same shape but different center time offset. Thus, the final G2 function, as a superimposition of the functions with different wavelengths, is broadened in a long-distance measurement, which seriously reduces the estimation accuracy. We analyze this phenomenon in both theory and experiment, and the experimental results fit our theoretical simulations quite well.#br#In the theoretical analysis, we find that the group velocity dispersion introduces an additional time offset to the final G2 function which is proportional to the total time offset. In our experiment, this additional time offset is about 1% of the total time offset. In particular, this effect results in a 63600 ps extra time offset, which can be compensated in post process, with a time accuracy of about 1 ps.#br#This paper focuses on the G2 function affected by the group velocity dispersion, and also calculates the additional time offset produced by group velocity dispersion, and thus gives a method to compensate the additional time offset through calculation.
Study on partial discharge signals detection by extended Duffing oscillator
Authors: Zeng Zhe-Zhao  , Zhou Yong  , Hu Kai  ,   College of Electric and Information Engineering, Changsha University of Science and Technology, Changsha 410076, China
Published: December 2020

At present, commonly used methods of weak signal detection such as the wavelet threshold denoising method, digital filtering method, the Fourier frequency domain transformation etc. can achieve the lowest detection of signal-to-noise ratio (SNR) of -10 dB, and the bidirectional ring coupled Duffing oscillator can reach the lowest detected SNR of -20 dB. But the discharge pulse signal with a lower SNR often appears in on-site testing, so the existing detection methods are difficult to meet the practical requirements of weak signal detection. In order to effectively solve the problem, a new method for weak pulse signal detection is proposed based on an extended-Duffing oscillator. The main idea of this method is to make the Duffing oscillator model transform to an extended-Duffing oscillator model by using the general time scale transformation. This approach can effectively expand the frequency detection range for weak signal detection. In addition, because the critical amplitude of the Duffing system depends on various parameters, such as system parameters, initial values, driving signal frequency, and calculation step of Runge - Kutta method etc.. However, the Melnikov method is an approximate analytical method, which does not take into account the factors such as initial values and calculation step, therefore, the Melnikov method is not suitable for numerical simulations, and lack of practicality. For this, the critical amplitude of chaos with high accuracy is determined only through the simulation experiment. Experimental results show that the critical amplitude is equal to 0.825010 when the incentive angular frequency of the extended-Duffing oscillator equals 10000 rad/s, and the extended-Duffing oscillator changes from the critical chaotic state to the large scale cycle state for small changes (10-6) of the driving amplitude. The simulation results show that the extended-Duffing oscillator not only has a good noise immunity performance, but also can effectively detect weak partial discharge pulse signal so that the signal-to-noise ratio can be lower than -40 dB. This method further expands the detection range and application fields of weak signals.
Vibrational resonance in an asymmetric bistable system with time-delay feedback
Authors: Yang Xiu-Ni  , Yang Yun-Feng  ,   School of Science, Xi'an University of Science and Technology, Xi'an 710054, China
Published: December 2020

Vibrational resonance is a resonant dynamics induced by a high-frequency periodic force at the low-frequency of the input periodic signal, and the input periodic signal is enhanced by a high-frequency signal. In this paper, a linear time-delayed feedback bistable system with an asymmetric double-well potential driven by both low-frequency and high-frequency periodic forces is constructed. Based on this model, the vibrational resonance phenomenon is investigated. Making use of the method of separating slow motion from fast motion under the conditions of Ω>>ω (Ω is the frequency of the high-frequency signal and ω is the one of the low-frequency signal), equivalent equations to the slow motion and the fast motion are obtained. Neglecting the nonlinear factors, the analytical expression of the response amplitude Q can be obtained, and the effects of the time-delay parameter α and the asymmetric parameter r on the vibrational resonance are discussed in detail. Moreover, the locations at which the vibrational resonance occurs, are obtained by means of solving the condition for a resonance to occur. A major consequence of time-delayed feedback is that it gives rise to a periodic or quasiperiodic pattern of vibrational resonance profile with respect to the time-delayed parameter, i.e. in Q-α plot, α can induce the Q which is periodic with the periods of the high-frequency signal and the low-frequency signal. The locations at which the vibrational resonance occurs are not changed by the asymmetric parameter r. However, the resonance amplitude is enhanced with increasing r. Specifically, the resonance amplitude is greatly enhanced when r>0.15. On the other hand, in the symmetric case (r=0), BVR at which the vibrational resonance occurs is periodic with the periods of high-frequency signal and low-frequency signal as α increases, which is shown in BVR-α (B is the amplitude of the high-frequency signal) plot. In Q-Ω plot, Q is presented by multi-resonance at the small values of B and Ω, but Q tends to a fixed value at the small values of B and the large values of Ω. We believe that the above theoretical observations will stimulate the experimental study of vibrational resonance in nonlinear oscillators and electronic circuits with time-delayed feedback.
Influence of initial indentation point on nanoindentation of Ni-based single crystal line alloys
Authors: Hu Xing-Jian  , Zheng Bai-Lin  , Yang Biao  , Yu Jin-Gui  , He Peng-Fei  , Yue Zhu-Feng  ,   Institute of Applied Mechanics, Tongji University, Shanghai 200092, China;,   School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan 430070, China;,   School of Mechanics and Civil&Architecture, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Ni-based single crystal line alloy is constituted with γ phase and γ' phase in the form of coherency. Since an indenter for two-phase coherent structure is bigger than the usual nano-scale indenter, the press location of indenter may be unclear in nanoindentation simulation. Both γ phase and γ' phase may be pressed initially, and the mechanical properties shown are different because of the initial press locations. The nanoindentation of Ni-based single crystal line alloys is simulated by molecular dynamics method. Two models are used to study about the hardness in [001] crystal orientation, one is the model γ /γ' with the initial indentation on γ phase, and the other is the model γ'/γ with the initial indentation on γ' phase. The influence of misfit dislocation at (001) interface on nanoindentation of the two models is analyzed using a center-symmetry parameter. Results show that the misfit dislocation shape of the two models are different after relaxation. Lomer-Cottrell dislocation occurs on (001) interface in the γ'/γ model. Before 0.930 nm press depth is reached, there is little change in the (001) interface misfit dislocation of the two models. Relationship between press load and press depth is similar for the two models, and it is the same in the relationship between hardness and press depth. After press depth reaches 0.930 nm, the misfit dislocation at (001) interface for model γ'/γ grows big, which results in a smaller press load and a smaller hardness computation in the model γ'/γ than that in model γ /γ'. When the press depth reach 2.055 nm, we find only a small amount of dislocations in γ phase that can go into γ' phase since the misfit dislocation at (001) interface in model γ /γ' hinders the process. However, none of dislocations can go into γ phase because of the prevention caused by Lomer-Cottrell dislocation at the (001) interface in the model γ'/γ . That means the Lomer-Cottrell dislocation reinforces the material obviously. So the press load in model γ'/γ grows faster than that in model γ /γ'.
Structural and electronic properties of hydrogenated bilayer silicene
Authors: Gao Tan-Hua  ,   School of Electromechanical Engineering, Wuyi University, Wuyishan 354300, China
Published: December 2020

Using the density functional theory (DFT) with both the generalized gradient approximation (GGA) and HSE06 hybrid functional calculation, we have investigated the structural and electronic properties of hydrogenated bilayer silicene. Results show that the hydrogenated bilayer silicene may have three configurations: AA-chair-like, AB-chair-like and AA-boat-like forms; after hydrogenation the material properties change from zero band gap semimetal into an indirect band gap semiconductor with forbidden band widths of 1.208, 1.437, and 1.111 eV. We have performed a hybrid HSB06 functional calculation and the correction for the band gaps: 1.595, 1.785, and 1.592 eV. Further analysis of the hydrogenated bilayer silicene with a strained band gap, the relationship between strain and the band gap can be continuously adjusted. Possible applications may be found in future nano-electronic devices.
Density functional theory studies of (TiO2)12 quantum ring and its electronic properties when doped with transition metal compounds
Authors: Yang Zhen-Qing  , Bai Xiao-Hui  , Shao Chang-Jin  ,   Surface Physics Laboratory of Science College, China University of Petroleum, Beijing 102249, China
Published: December 2020

In this paper, we have designed a new (TiO2)12 quantum ring structure and studied its geometry, average binding energy, and the electron density distributions using the generalized gradient approximation (GGA), which is based on the density functional theory (DFT) with the first-principles calculations. This new quantum ring structure is doped with transition metal compounds MoS2, MoSe2, MoTe2, WS2, WSe2 and WTe2 respectively, to modify its properties. Thus we can calculate and analyze their geometrics and electronic properties (such as average binding energies, energy levels, electronic density of states and the HOMO-LUMO electron density distributionsatc). We find that the (TiO2)12 quantum ring with a diameter of 1.059 nm seems to be of a two-dimensional structure with a center symmety which ensurs it a stable structure. In addition, the HOMO-LUMO orbital electron density in the quantum ring distributes evenly, and its energy gap is 3.17 eV which is very close to the experimental value of TiO2 semiconductor materials (3.2 eV). The energy gaps decrease substantially after introducing the transition metal compounds into the quantum ring. Among these results, the ring doped with WTe2 has the smallest energy gap (0.61 eV), and that with MoTe2 has the biggest energy gap (1.16 eV), but it is still smaller by about 2 eV than that of the (TiO2)12 quantum ring. Furthermore, other doping results have energy gap variation around 1 eV. The TiO2 clusters with this energy gap could make use most of the solar energy and so expand applications of TiO2.
Effects of protons within SiO2 solid-state electrolyte on performances of oxide electric-double-layer thin film transistor
Authors: Guo Wen-Hao  , Xiao Hui  , Men Chuan-Ling  ,   School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China;,   Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
Published: December 2020

SiO2-based solid state electrolyte films are deposited at room temperature by using the plasma-enhanced chemical vapor deposition (PECVD) technique. An electric-double-layer (EDL) effect has been observed. Then, indium-zinc-oxide thin-film transistors (IZO TFTs) are fabricated by using such SiO2 films as dielectrics in a self-assembling process through a shadow mask. The IZO films for source/drain electrodes and channel are deposited on the nanogranular SiO2 film by RF sputtering the IZO target in an Ar ambient. Such TFTs exhibit a good performance at an ultralow operation voltage of 1.5 V, with a high field-effect mobility of 11.9 cm2/Vs, a small subthreshold swing of 94.5 mV/decade, and a large current on-off ratio of 7.14×106. Effects of protons in the SiO2-based solid state electrolyte films on the electrical performances of the IZO TFTs are also studied. It is observed that a big EDL capacitance can be obtained for SiO2 films dipped in pure water, as a result of the fact that there are more protons in such SiO2 films. Because of the migration of protons in SiO2 electrolytes, an anti-clockwise hysteresis is observed on the transfer curve. Moreover, a bigger hysteresis is observed at a higher gate voltage scan rate. Gate bias stressing stabilities are also studied the shifts in threshold voltage are observed to obey a stretched exponential function.
Graphene/h-BN Moiré superlattice
Authors: Lu Xiao-Bo  , Zhang Guang-Yu  ,   Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences, Beijing 100190, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
Published: December 2020

Graphene Moiré superlattice, a unique 2D periodical structure originated from the interaction between graphene and its supporting substrate h-BN, has attracted great interest recently. Employing epitaxial graphene on h-BN single crystals, we have investigated systematically the physical properties related to the Moiré superlattice. From transport measurements, we can observe the superlattice Dirac points at both electron side and hole side. Similar to the Dirac point, the superlattice Dirac points have insulator behaviors. Under the action of magnetic field, the quantum Hall effects both in monolayer and bilayer graphenes are observed. Also, the Moiré superlattice can lead to the formation of self-similar mini-bands from the Landau fan diagram. According to the infrared optical spectroscopy measurements, the transitions between different Landau levels are characterized by massive Dirac fermions and thus reveal a band-gap of ～38 meV. Moreover, without magnetic fields, an optical conductivity peak related to the Moiré superlattice appears. We use three spinor potential components to explain the optical conductivity peak and demonstrate that the pseudospin-mixing component plays a dominant role in the spinor potential. In addition, the spinor potential depends sensitively on the gate voltage, indicating that the electron–electron interactions play an important part in the renormalization of the spinor potential.
Effect of Ni2O3 doping on the properties of single domain GdBCO bulk superconductors fabricated by a new modified top-seeding infiltration and growth process
Authors: Guo Li-Ping  , Yang Wan-Min  , Guo Yu-Xia  , Chen Li-Ping  , Li Qiang  ,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

Single-domain GdBCO bulk superconductor (20 mm in diameter) has been fabricated by a top-seeding infiltration and growth (TSIG) mathod, it has a new solid phase of [(1-x)(Gd2O3+1.2BaCuO2) + x Ni2O3] (where x =0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%). Effect of Ni2O3 additions on the growth morphology, microstructure, critical temperature Tc, magnetic levitation force, and trapped flux of single-domain GdBCO bulks have been investigated. Results show that the single-domain GdBCO bulk can be gained when x is in the range of 0-0.50 wt%; and the Gd211 particles are not affected by the Ni2O3 doping in the samples. The Tc of the samples decrease from 92.5 K (x=0 wt%) to 86.5 K (x=0.50 wt%) when x increases from 0 to 0.50 wt%, which is caused by the substitution of Ni3+ for Cu2 +. Both of the levitation force and trapped field of the samples increase first and then decrease with the increase of x; the largest levitation force of 34.2 N is obtained for the samples with x=0.14 wt%, and the largest trapped field of 0.354 T is obtained for the samples with x=0.10 wt%. The change of the levitation force and trapped field of the samples is closely related to the doping content x. As is known, the doping of Ni2O3 can result in substitution of Ni3+ for Cu2+ at its site in GdBCO crystals, which can reduce the critical temperature Tc of the samples; although Tc and the physical properties of the samples is reduced with the increase in the doping amount of Ni2O3, but at the same time, the substitutions of Ni3 + for Cu2 + in GdBCO crystals can produce local lattice distortions, which can act as magnetic flux pinning centers to improve the properties of the samples. The highest Tc is obtained in the samples without any Ni2O3 additions (x=0), but the magnetic flux pinning force of the samples is weak, so both of the levitation force and trapped field of the samples are relatively lower. When the doping content x ≤ 0.14 wt%, although the Tc is reduced slightly, it still has a value higher than 90 K; and the magnetic flux pinning force in the samples, due to the substitutions of Ni3+ for Cu2 +, would increase with the increase of doping content x, and result in an enhancement of levitation force and trapped field. When the doping content x is greater than 0.14 wt%, the magnetic flux pinning force of the samples is still increasing with the increase of x, but the Tc of the sample is significantly reduced and even less than 90 K, and finally result in an decrease of levitation force and trapped field. Only when the doping amount of Ni2O3 is appropriate, both of Tc and magnetic flux pinning force are of a relative optimal value, and lead to an enhancement of levitation force and trapped field.
Molecular-beam epitaxy of high-quality diluted magnetic semiconductor (Ga, Mn)Sb single-crystalline films
Authors: Zhu Meng-Yao  , Lu Jun  , Ma Jia-Lin  , Li Li-Xia  , Wang Hai-Long  , Pan Dong  , Zhao Jian-Hua  ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Diluted magnetic semiconductor (Ga, Mn)Sb and its related hetero-structures have attracted much attention in recent years since they are predicted to have some novel properties, such as the quantum anomalous Hall effect etc. However, it is not easy to grow high-quality (Ga, Mn)Sb films due to their narrow growth window. In this article, a series of 10 nm thick (Ga, Mn)Sb films with different Mn contents from 0.016 to 0.039 have been grown by molecular-beam epitaxy at low temperaturs (～230 ℃). The films have high crystalline quality as confirmed by in situ reflection high-energy electron diffraction and ex situ atomic force microscopy, and no MnSb phase could be observed. Curie temperature up to 30 K has been obtained in one (Ga, Mn)Sb film after post-growth thermal annealing. The magneto-resistance and anomalous Hall effect of this film have also been investigated at different temperatures.
Radiation effects on the low frequency noise in partially depleted silicon on insulator transistors
Authors: Liu Yuan  , Chen Hai-Bo  , He Yu-Juan  , Wang Xin  , Yue Long  , En Yun-Fei  , Liu Mo-Han  ,   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;,   Xinjiang Technical Institute of Physics & Chemistry of CAS, Urumqi 830011, China
Published: December 2020

The transfer characteristics and low-frequency noise behavior of partially depleted silicon on insulator n-channel metal-oxide-semiconductor transistors after γ-ray irradiation up to a total dose of 1M rad (Si) have been investigated in this paper. Due to the radiation-induced positive buried-oxide trapped charges and the interface traps, the back gate threshold voltage decreases from 44.72 to 12.88 V, and the electron field effect on mobility decreases from 473.7 to 419.8 cm2/V·s; while the sub-threshold swing increases from 2.47 to 3.93 V/dec. Based on the measurements of sub-threshold swing and the back gate threshold voltage, the variations of extracted radiation-induced buried oxide trapped charge and interface trap densities, are about 2.36×1012 cm-2 and 5.33×1011 cm-2 respectively. In addition, the normalized back gate flat-band voltage noise power spectral density is a sensitive function of radiation-induced buried oxide trapped charges and interface traps, which increases from 7×10-10 V2·Hz-1 to 1.8×10- 9 V2·Hz-1. According to the carrier number fluctuation model, the extracted trap density near the interface between channel and buried oxide increases from 1.42×1017 to 3.66×1017 cm- 3·eV-1. By considering the tunneling attenuation coefficient of the electron wave function and the tunneling depth of the electron in the buried oxide, the spatial distribution of trapped charges in the buried oxide before and after radiation are calculated and discussed.
Stark structure of atomic gallium
Authors: Dong Hui-Jie  , Wang Xin-Yu  , Li Chang-Yong  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

The Stark effect in Rydberg atoms has potential applications in the areas of dipole-dipole interaction, quantum information, quantum control, and so on. Many reflevant theoretical calculations and experimental studies about the Stark effect of alkali metal and alkali earth metals have been reported, but the other atom’s Stark effect is studied still relatively less. Our goal in this paper is to reflearch the third main group atom’s Stark effect in a large electric field. First, according to the level data of gallium atom in zero-field, we obtain the quantum defects from the modified Ritz formula in each state by using a nonlinear least-squares-fitting algorithm. The quantum defects as a function of the principal quantum number are analyzed in detail. Influences of both the core polarization and the penetrating valence electron on the quantum defect are discussed according to the fitting results. Then we use the Numerov algorithm to calculate the radial wave functions of atomic gallium. Finally, the Stark structures of Rydberg states around n=7 and n=18 are numerically calculated by matrix diagonalization. Results show that at the levels above n=7 manifold states, (n+1)P is higher than nD state, and it is in contrast to the levels below the n=7 manifold states. This phenomenon is different from the usual Stark structure of alkali metal atoms, the level’s order of which does not change with the principal quantum number. The Stark levels with the identical |m| anti-cross each other, and those with different |m| cross. Our results give an important reflerence for related reflearches, and are of great significance for insight into the atomic structure and the interaction between the atomic core and the highly excited electrons.
Study on temperature adaptability extension of KTP frequency-doubling device
Authors: Li Xiao-Ming  , Shen Xue-Ju  , Liu Xun  , Wang Lin  ,   Department of Electronics and Optics Engineering, Ordnance Engineering College, Shijiazhuang 050003, China;,   People’s Liberation Army of 77, 108 troops, Chengdu 611233, China
Published: December 2020

For the most commonly used KTP frequency-doubling crystal, its temperature adaptability range should be effectively extended. For this purpose, a compromise design is given by compreflensively considering both its effective nonlinear coefficient and the half-width of temperature range. The design method of KTP frequency-doubling device with a wide temperature range is analyzed in detail; furthermore, the curves of effective nonlinear coefficients, acceptance angles, and walk-off angles as a function of phase-matching angle are plotted via computer simulation. According to the results of theoretical study, a device used in the temperature range from -20 ℃ to 50 ℃ is designed and validated experimentally by the KTP external cavity frequency-doubling laser. Experimental results indicate that a peak conversion efficiency of 22.7% at 15 ℃ with a 70 ℃ temperature halfwidth is achieved by using the designed device. Compared with the commonly designed KTP frequency-doubling device, the temperature adaptability range increases notably although its frequency conversion efficiency decreases a little. Additionally, the effective nonlinear coefficient is still bigger than that of the commonly used crystals such as LBO and BBO when temperature halfwidth increases to 70 ℃. The above method would have the potential for extending the temperature adaptability range of other frequency-doubling devices.
Influnce of polymer additives on the transport process in drag reducing turbulent flow
Authors: Guan Xin-Lei  , Wang Wei  , Jiang Nan  ,   Department of Mechanics, Tianjin University, Tianjin 300072, China;,   Tianjin Key Laboratory of Modern Engineering Mechanics, Tianjin 300072, China;,   Nankai University-Tianjin University Center for LiuHui Applied Mathematics, Tianjin 300072, China
Published: December 2020

The spatial-temporal sequence of velocity fields in wall turbulence with and without polymer additives at the same Reynolds number are measured by time-resolved particle image velocimetry (TRPIV) from the side and top views. Based on this experimental database of a water channel, the mechanism of drag reduction by polymers is explored from the viewpoint of the influence of polymer solution on the transport of momentum and energy in a turbulent boundary layer. Comparison of Reynolds stress profiles confirms that due to the existence of polymer additives, the transport of turbulent momentum is significantly inhibited, as if caused by the decrease of Reynolds shear stress. Furthermore, it is noted that these changes are closely related to the effect of polymer additives on the classical coherent structures, such as vortices and low-speed streaks, which are the dominant structures in near-wall turbulence. The spatial topological mode of hairpin vortex extracted by conditional sampling method shows that the intensity of vortices and ejection event are greatly suppressed by the polymer solution. Not only does the decline of turbulent kinetic energy production indicate that the energy of hairpin vortices that comes from the ensemble average movement is attenuated in the solution, but all this implys that the polymer additives hinder the self-sustaining mechanism, the inherent character of wall turbulence. Then, the analysis of linear stochastic estimation (LSE) suggests that the development of hairpin vortices in the packet is impeded, which is mainly reflected in the reduction of the number of hairpin vortices and the suppression of uplift in the wall-normal direction. To investigate the change of low-speed streaks after the addition of polymers, the spanwise autocorrelation function of streamwise fluctuating velocities has been calculated. In the polymer solution the large-scale vortices areflenhanced while the small-scale vortices are suppressed. This observation refleals that the polymers disrupt the energy transport from large to small scales. To summarize, it is through the action on coherent structures that the polymer additives can damp the transport of momentum and energy between the near-wall region and outer region of the boundary layer. In this way, the polymer solution makes turbulent flow less chaotic, leading to the reduction of friction drag.
A coupled level-set and volume-of-fluid simulation for splashing of single droplet impact on an inclined liquid film
Authors: Dai Jian-Feng  , Fan Xue-Ping  , Meng Bo  , Liu Ji-Fei  ,   School of Sciences, Lanzhou University of Science and Technology, Lanzhou 730050, China
Published: December 2020

A coupled level set and volume of fluid (CLSVOF) method is utilized to simulate the droplet evolution, during splashing after impacting on an inclined liquid film, and the bubble entrainment by the droplet impacting of the liquid. The influence of impact angles of bubble entrainment, the processes of splashing pressure field and velocity field after impingement are studied and discussed. Compared with the results obtained by experiment, the validity of CLSVOF method is verifiled by simulating the droplet splashing on an inclined liquid film. Results indicate that the mechanisms of front and back splashing are different. The front splashing is caused by pressure difference in the neck region, and the back splashing is produced by radial flow in the liquid film. It is also found that along with the impact angle moving towards the large angle direction, the bubble entrainment number shows a reducing trend.
Observation of colloidal particle deposition during the confined droplet evaporation process
Authors: Wu Sai  , Li Wei-Bin  , Shi Feng  , Jiang Shi-Chun  , Lan Ding  , Wang Yu-Ren  ,   School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China;,   Key Laboratory of Microgravity Science, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

A circular silicone sheet as a masker was used to cover a glass slide, and then the super-hydrophobic coating was sprayed on the glass slide free of silicone sheet masker, thus a round hydrophilic area surrounded by a super-hydrophobic coating is obtained. The PS colloidal droplets are confined in the hydrophilic area, and the droplet volume can be changed within a large range. Variation of the droplet volume influences the initial apparent contact angle. We investigate the particle deposition behavior of the confined colloidal droplet for a hydrophobic apparent contact angle in evaporation process by using an in situ optical observation system. In the whole evaporation process the contact-line of the confined droplet is pinned at the junction between the hydrophilic area and hydrophobic area. In the particle deposition process the main driving flow is different, and the final deposition pattern is controlled by three flow behaviors. In the early stage, the main flow is the Marangoni flow, which drives the particle clusters float on the droplet surfaces, part of them accumulated at the boundaries. As the evaporation proceeds, when the apparent contact angle decreases (<60°), the evaporation flux becomes singular near the contact line, Capillary flow towards the contact inside the drop as a compensation to the solvent loss at the drop boundary, which drives the particles in the droplet to rapidly accumulate at the contact-line. In the last evaporation stage, the thickness of the film in the hydrophilic area becomes very thin, and there is only one layer of particles in this thin film, the thin liquid film instability triggers the particles in the middle area to rapidly aggregate and then form a kind of network pattern, due to the decrease of distances between the particles. Capillary force between particles also takes part in this aggregate process.
Effects of dopants on the growth of oxidation-induced stacking faults in heavily doped n-type Czochralaki silicon
Authors: Zhang Yue  , Zhao Jian  , Dong Peng  , Tian Da-Xi  , Liang Xing-Bo  , Ma Xiang-Yang  , Yang De-Ren  ,   State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China;,   QL Electronics Co. LTD, Ningbo 315800, China
Published: December 2020

Through comparative investigation on the growth of oxidation-induced stacking faults (OSFs) in heavily antimony (Sb)-doped and phosphorus (P)-doped Czochralaki (Cz) silicon wafers with almost the same resistivity, effects of dopants on the growth of OSF in heavily doped n-type Cz silicon are studied experimentally. Moreover, the influences of Sb and P atoms on the recombination of self-interstitials and vacancies are also explored on the basis of the first-principles calculations. It is shown experimentally that all the OSF lengths are almost identical regardless of the type and density of OSF nucleation centers, such as copper precipitates and mechanical scratches etc.. However, it is found that the OSF length of heavily Sb-doped Cz silicon wafer is larger than that of heavily P-doped Cz silicon wafer under the same oxidation condition. Essentially, the OSFs are formed by the aggregation of silicon self-interstitials refleased at the Si/SiO2interface during the oxidation. Therefore, a longer OSF implies that a higher quantity of silicon self-interstitials remains after the recombination of vacancies and silicon self-interstitials in the heavily Sb-doped Cz silicon wafer. The first-principles calculations based on density functional theory (DFT) indicate that Sb atoms combine with vacancies more readily than P atoms. This is actually due to the fact that Sb has a much larger atomic size than P. In other words, as compared with P atoms, the Sb atoms are the moreflefficient vacancy-trapping centers, thus retarding the recombination of vacancies and silicon self-interstitials. Consequently, the silicon self-interstitials remain after recombination with the vacancies that are much more in heavily Sb-doped Cz silicon wafer than in heavily P-doped counterpart when undergoing the same oxidation. In turn, the OSFs in heavily Sb-doped silicon wafers are relatively longer.
Investigation of scanning tunneling spectra on iron-based superconductor FeSe0.5Te0.5
Authors: Du Zeng-Yi  , Fang De-Long  , Wang Zhen-Yu  , Du Guan  , Yang Xiong  , Yang Huan  , Gu Gen-Da  , Wen Hai-Hu  ,   Center for Superconducting Physics and Materials, School of Physics, Nanjing University, Nanjing 210093, China;,   National Laboratory for Superconductivity, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Condensed Matter Physics & Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
Published: December 2020

FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73 0.03 which is consistent with the lattice constant 3.78 . The Se and Te atoms with a height difference of about 0.35 are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2 = 5.5 meV, and the reduced gap 2/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature /kBTc 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.
Exploring multiferroic materials based on artificial superlattice LaFeO3-YMnO3 and natural superlattice n-LaFeO3-Bi4Ti3O12 thin films
Authors: Chen Yan-Bin  , Zhang Fan  , Zhang Lun-Yong  , Zhou Jian  , Zhang Shan-Tao  , Chen Yan-Feng  ,   National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China;,   National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Combining ferroelectric with antiferromagentic materials in nanometer scale is an effective method for exploring multiferroic materials. We preflent two kinds of systems to show the possibility of multiferroic properties in such nanometer composites. One is the artificial superlattice LaFeO3-YMnO3, and the other is the natural layered Aurivillius material Bi4Ti3O12 doped with different layers of LaFeO3, BiFeO3. Both materials were synthesized by pulsed laser deposition method on SrTiO3 substrates. Microstructural charterizations with XRD, TEM, and EELS in scanning transmission electron microscopy mode substantiate that the samples have atomically sharp interfaces between neighboring layers; this is important for producing possible magneto-electric coupling in multiferroic materials. Magnetic characterization proves that these materials have ferrimagnetic properties, in spite of their anti-ferromagnetic nature before coupling. Magnetic characterization also proves that there is 0.55-0.9 B remanant magnetization generated at LaFeO3-YMnO3 interface. And the 0.5 and 1.5LaFeO3-Bi4Ti3O12 samples show ferrimagnetism which can remain even up to room temperature. Ferroelectric tests prove that there is a large leakage current in LaFeO3-YMnO3 superlattice and BiFeO3-inserted Bi4Ti3O12, but 0.5LaFeO3-Bi4Ti3O12 shows ferroelectric hysteresis loops. It can be therefore concluded that 0.5LaFeO3-Bi4Ti3O12 is a multiferroic material. If more perovskite layers (3-layer SrTiO3 or 2.5-layer LaFeO3) are inserted, the Aurivillius structure of Bi4Ti3O12 may appear structural instability that can be observed in our HRTEM measureflent. Our first principles calculations show that the degeneracy of formation enthalpies is the reason why the intergrowth in these materials forms and their structures are not stable. Our work may provide some examples for exploring new multiferroics by means of nano-meter composite.
Progress in sol-gel autocombustion synthesis of metals and alloys
Authors: Zhang Xin-Wei  , Hua Zheng-He  , Jiang Yu-Wen  , Yang Shao-Guang  ,   School of Physics, Nanjing University, National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
Published: December 2020

This paper is an overview of the progress of sol-gel autocombustion synthesis of metals and metal alloys. Sol-gel is a convenient method to synthesize a variety of oxides by mixing of different elements at an atomic level. Autocombustion synthesis is a self-sustaining process caused by the heat generated from its exothermic reaction. By combining these two methods, the sol-gel autocombustion method is introduced in the synthesis of metals and metal alloys. The experimental principle and technological route are introduced in detail in this review. By using metal nitrate, citric acid etc. as starting materials, the dried gels are prepared through sol-gel routine. Under the protection of inert gas, the autocombustion could be activated at low temperature in a tube furnace. After the autocombustion was activated, the gel burned violently, and a large amount of white gas was refleased. During heating the gel, mass spectrum shows that the H2, CO and CH4 areflevidently identified near the combustion temperature. They are well known reducing agents, which can be used in the redox reaction for synthesizing metals from oxides. Based on the data obtained from the TG-DTA and mass spectrum analysis, it is speculated that there are mainly five reactions appearing during the burning of the gel at high temperature: exothermic reaction between fuel and oxidant; metal oxide(s) formation by decomposition of the nitrate(s); generation of CH4, CO and H2 by the decomposition of CHx containing groups of complexing agent; exothermic reaction between CH4/CO/H2 and oxidant; the reduction of metals from their corresponding metal oxides by CH4 and H2 in nascent product. The application of this method to the synthesis of metals and metal alloys is shown by realized examples. This method shows many advantages in the synthesis of metals, such as simple apparatus, inexpensive raw materials, a relatively simple preparation process, and fine powder products with high homogeneity. Moreover, very low temperature is required to activate the reaction, and then the combustion can continue to take place without needing additional energy supply. This method has potential applications in experimental material reflearches.