bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of parameter prior information on effect of colored noise in Bayesian frequency estimation
Authors: Yang Di  , Wang Yuan-Mei  , Li Jun-Gang  ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Parameter estimation, which undertakes one of the vital missions in quantum metrology, has attracted a lot of attention in recent years. A large number of investigations on the frequency estimation have been carried out. Most of them are based on Cramér-Rao bound estimation approach in which almost perfect knowledge of the parameter to be estimated is given. In reality, however, one has inadequate prior knowledge about the parameter to be estimated. Then the Bayesian estimation approach in which we can perform the estimation even if we only have partial prior information about the parameter would be an ideal choice. Prior information about the parameter can play a significant role in Bayesian statistical inference. So it is interesting to know how the prior knowledge affects the estimation accuracy in the estimation process. In the solid-state realization of probe system, material-specific fluctuations typically lead to the major contribution to the intrinsic noise. Then it is interesting to study the effects of colored noise on the quantum parameter estimation. In this work, we study the inhibitory effects of prior probability distribution of the parameter to be estimated on the effects of colored noise under the framework of Bayesian parameter estimation theory. In particular, we estimate the intensity of a magnetic field by adopting a spin-1/2 system which is influenced by the colored noise with 1/fα spectrum. To evaluate the accuracy of estimation, we obtain the Bayes cost analytically which can be applied to the noisy channels. We mainly focus on the inhibitory effect of prior probability distribution of measured parameter on the non-Gaussianity of noise. We find that for the case of broad prior frequency distribution, the influence of non-Gaussianity on the estimation is very weak. While for the case of narrow prior frequency distribution, the influence of non-Gaussianity on the estimation is strong. That means that in the Bayesian approach, when we have enough prior information about the frequency, the non-Gaussianity can conduce to the improvement of the accuracy of the estimation of the frequency. When we lose the prior information, we also lose the improvement of the accuracy from the non-Gaussianity. The uncertainty of the prior information tends to eliminate the effects of the non-Gaussianity of the noise.
Fabrication and electrical transport characteristics of the polycrystalline Ca12Al14O33 electride
Authors: Feng Qi  , Zhang Xin  , Liu Hong-Liang  , Zhao Ji-Ping  , Jiang Hao  , Xiao Yi-Xin  , Li Fan  , Zhang Jiu-Xing  ,   Key Laboratory of Advanced Functional Materials, Ministry of Education, College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China;,   School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China
Published: December 2020

The[Ca24Al28O64]4+:4e- (C12A7:e-) electride composed of densely packed, subnanometer-sized cages. This unique structure makes it possess distinctive applications in fields of electronic emission, superconductor, electrochemical reaction. In this paper, we explore a new method to prepare the bulk of C12A7:e- electride. The following areare systematically studied in this work. 1) the condition of preparing bulk of C12A7:e- electride by solid reaction combining spark plasma sintering and reduction with Ti particles at high temperature, CaCO3 and Al2O3 powders are used as raw materials; 2) the first principle calculations of band structure and density of states of the C12A7:e- electride; 3) the analysis of the electrical transport properties of the C12A7:e- electride. The bulk of C12A7:e- electride is successfully prepared by this method, so the results show that the bulk of C12A7:e- electrode with the electron concentration 1018-1020 cm-3 is synthesized at 1100 ℃ and a vacuum pressure of 10-5 Pa for 10-30 h. In the process of Ti reduction, Ti particles become evaporated and deposit on the surface of C12A7, the free O2- atom in the cages diffuse to the sample surface, the Ti vapor reacts with the O2-, forming a loose TiO_x layer. In order to maintain electrical neutrality, the electrons of the free O2- atom leave from the cages, forming the C12A7:e- electride. In addition, the loose TiO_x layer also provides a channel for the diffusion of the O2- atoms in the cage, ensuring the continuation of the reduction reaction. The calculated band structure and density of states of the bulk C12A7:e- electride show that when electrons replace the O2- atoms in the cage, the Fermi level of C12A7:e- crosses over the cage conduction band (CCB). Thus the free movement of the electron is the main reason for the insulator C12A7 to convert into conductor C12A7:e-. At the same time the electrons near the Fermi level in the cages are easy to jump from the CCB to the frame conduction band (FCB). Combination of the above experimental results suggests that the electrons in cages are easier to escape to vacuum under the action of electric field or thermal field, which is the main reason for low work function of C12A7:e-. This way provides an new approach to the realization of the insulator C12A7 converting into C12A7:e- electride. And the C12A7:e- is a good electronic emission material due to low work function, low working temperature, and highly anti-poisoning ability, so this method of preparing bulk C12A7:e- electride provides a good new way to synthesize a new electronic emission material.
Interfacial reaction and failure mechanism of Cu/Ni/SnAg1.8/Cu flip chip Cu pillar bump under thermoelectric stresses
Authors: Zhou Bin  , Huang Yun  , En Yun-Fei  , Fu Zhi-Wei  , Chen Si  , Yao Ruo-He  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China;,   Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, The 5th Electronics Research Institute of the Ministry of Industry and Information Technology, Guangzhou 510610, China
Published: December 2020

Micro-interconnection copper pillar bumps are being widely used in the packaging areas of memory chip and high performance computer due to their high density, good conductivity and low noise. Studying the interfacial behavior of copper pillar bump is of great significance for understanding its failure mechanism and microstructure evolution in order to improve the reliability of flip chip package. The thermoelectric stress test, in-situ monitor, infrared thermography test, and microstructure analysis method are employed to study the interfacial reaction, life distribution, failure mechanism and their effect factors of Cu/Ni/SnAg1.8/Cu flip chip copper pillar interconnects under 9 groups of thermoelectric stresses including 2104-3104 A/cm2 and 100-150℃. Under thermoelectric stresses, the interfacial reaction of Cu pillar can be divided into three stages:Cu6Sn5 growth and Sn solder exhaustion; the Cu6Sn5 phase transformation, exhaustion and the Cu3Sn phase growth; voids formation and crack propagation. The rate of Cu6Sn5 phase transforming into Cu3Sn phase is positively correlated with the current density. There are four kinds of failure modes including Cu pad consumption, solder complete consumption and transformation into Cu3Sn, Ni plating layer erosion and strip voids. An obvious polar effect is observed during the dissolution of Cu pads on the substrate side and the Ni layer on the Cu pillar side. When Cu pad is located at the cathode, the direction of electron flow is the same as that of the heat flow, and it can accelerate the consumption of Cu pad and the growth of Cu3Sn. When Ni layer serves as the cathode, the electron flow can enhance the consumption of Ni layer. Under 150℃ and 2.5104 A/cm2, the local Ni barrier layer is eroded after 2.5 h, which results in the transformation of Cu pillar on the Ni side into (Cux, Niy)6Sn5 and Cu3Sn alloy. The life of Cu pillar interconnection complies well to the 2-parameter Weibull distribution with a shape parameter of 7.78, which is a typical characteristic of cumulative wear-out failure. The results show that the intermitallic growth behavior and failure mechanism at Cu pillar interconnects are significantly accelerated and changed under thermoelectric stresses compared with the scenario under the single high temperature stress.
Performance analysis of a refrigerator operating between an infinite-sized hot reservoir and a finite-sized cold one within linear irreversible thermodynamics
Authors: Zhang Rong  , Lu Can-Can  , Li Qian-Wen  , Liu Wei  , Bai Long  ,   School of Physical Science and Technology, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

How to optimize the performances of heat devices operating between finite-sized heat sources and sinks has become a very important issue in the field of finite-time thermodynamics. In this paper, a physical model of the refrigerator operating between an infinite-sized hot reservoir and a finite-sized cold one is proposed, and by using the principles of finite-time thermodynamics and the theory of linear irreversible thermodynamics, we present the analytical expressions of the input power and the coefficient of performance (COP) under the tight-coupling condition, and analyze the performance characteristics of the refrigerator in detail. When the temperature of the cold reservoir is changed with fixing the environment temperature (the temperature of the hot reservoir), it is found that there does not exist a well-defined optimal relation between the input power and a duration time of the refrigerating process, which is a remarkable difference from the working process of a heat engine operating between a finite-sized hot reservoir and an infinite-sized cold one. We further find that the COP exhibits the monotonically decreasing trend with the increase of the input power, but the increase of the exergy leads to the enhancement of the COP. This feature can be understood as follows:when P is small, this means that the duration time is large, thus the refrigerating process approaches to the quasistatic operation, which induces the large COP. In particular, when P0, the COP max. The increase of P implies the reduction of , thus the refrigerating process keeps away from the quasistatic process and approaches to the actual irreversible process, which causes the COP to decrease. On the contrary, shows the increasing trend with the increase of the exergy E. This is because the increase of E means the enhancement of at fixing the input power P, which corresponds to a slow refrigerating process. As a result, E exhibits the increasing behaviors due to the emergence of the quasistatic process. From the above analyses, we can find that an appropriate proposal to optimize the refrigerating performance of heat devices should be based on the actual parameters and the real external environment, thus it is possible to obtain the optimal refrigerating objective at the expense of the suitable input power. These results are not only helpful in the in-depth understanding of the refrigerator operating between an infinite-sized hot reservoir and a finite-sized cold one, but also of great engineering interest in designing realistic heat deices. Our method can also generalize the investigation of heat pumps. In addition, when the tight-coupling condition is false due to the breaking of time-reversal symmetry, there needs to be further consideration about it from the angle of physics.
High-power wideband radio-frequency intensity modulated continuous wave laser
Authors: Cheng Li-Jun  , Yang Su-Hui  , Zhao Chang-Ming  , Zhang Hai-Yang  ,   School of Optics and Photonics, Beijing Institute of Technology, Beijing 100081, China;,   Beijing Key Laboratory for Precision Optoelectronics Measurement Instrument and Technology, Beijing 100081, China
Published: December 2020

A high-power wideband radio-frequency (RF) intensity modulated continuous wave light source is demonstrated. The high-power dual-frequency light source is obtained via a dual-frequency laser signal seeding fiber power amplifier. A diode laser pumped dual-frequency laser is built as the seed and a diode laser pumped three-stage Yb3 + doped large mode area fiber power amplifier is used to enhance the output power to 50 W. In the dual-frequency seed laser, a coupled cavity composed of the Nd:YAG gain crystal and output coupler is used as the mode selector and enforces single longitude mode to oscillate. Two quarter wave plates are inserted in the laser cavity to lift the frequency degeneration of the two orthogonally polarized modes. By changing the angle between the fast axes of the two quarter wave plates, the frequency difference between the two orthogonally polarized modes can be tuned from 30 MHz to 1.5 GHz. The standard difference of beat frequency is 1.6144 MHz and stability is 1.52% when a frequency difference of output dual-frequency laser is 250 MHz. This stable dual-frequency seed signal is amplified via a diode pumped Yb3 +-doped fiber power amplifier. In order to suppress amplified spontaneous emission and other nonlinear effects, a three-stage fiber amplification system is used. The first stage is a diode pumped fiber (5 m, 6/125 m, NA = 0.13) power amplifier. The pump power is fixed at 600 mW. The input dual frequency signal is 3.2 mW, and it is amplified to several hundred mW by the first fiber power amplifier. The second fiber amplifier is a diode laser pumped fiber (5 m, 10/125 m, NA = 0.075/0.46) amplifier. The pump power is fixed at 10 W, and the dual frequency signal is amplified to sub watts after the second fiber amplifier. A 5 m large mode area fiber (25/250 m, NA=0.065/0.46) is used in the final amplification. A maximum amplified power of 50.2 W is obtained when the pump power is 70 W in the experiment. The signal-to-noise ratio of the beat note increases from 25 dB to 40 dB via amplification. The output power fluctuation of the amplified signal at 50 W is smaller than 0.1 W during 30 min. The RF frequency stability is well maintained during the amplification, and the beat-note frequency instability is 1.777 MHz. This high-power dual-frequency light source with wide beat note frequency bandwidth has potential applications in dual-frequency coherent lidar system for long distance ranging and imaging or underwater detections after the frequency has been doubled to 532 nm.
Investigation of external electric field effect on C24H38O4 molecule by density functional theory
Authors: Du Jian-Bin  , Zhang Qian  , Li Qi-Feng  , Tang Yan-Lin  ,   College of Physics and Electrical Information, Langfang Normal University, Langfang 065000, China;,   College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China;,   Department of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

The C24H38O4 (dioctyl phthalate, DOP) is a main component of the plasticizer. In order to study the influence of external electrical field on molecular structure and spectrum of DOP, the method B3LYP of the density functional theory at B3LYP/6-311G(d,p) level is employed to calculate geometrical parameters of the ground state of DOP molecule under different external electric fields (from 0 to 0.0125 a.u.) in this article. On this basis, the ultraviolet-visible absorption spectrum of DOP is calculated by using the time-dependent density functional theory in the same fundamental group and compared with the ultraviolet absorption peak of the molecules, measured by UNICO ultraviolet and visible spectrophotometer. Finally, by using the time-dependent density functional theory in the same fundamental group, we study wavelengths and oscillator strengths of the first twenty-six excited states of DOP molecule in external electric field. The obtained results are as follows. The strongest absorption of ultraviolet-visible absorption spectrum appears in the end absorption band from n to σ* transition. The stronger absorption occurs in the E band of benzene electronic transition from π to π*. The molecular geometry parameters are strongly dependent on the external field intensity. The dipole moment of DOP molecule is proved to first decrease and then increase with the sharp increase of external field, but the total energy first increases and then decreases with the increase of the external field intensity. The ultraviolet absorption peaks of excited states of DOP are proved to have observably red shift, and the oscillator strength sharply decreases with the increasing of the field intensity.
Control of evolutionary atomic system of excited atom by using ideal photonic band-gap model
Authors: Zhang Si-Qi  , Lu Jing-Bin  , Liu Xiao-Jing  , Liu Ji-Ping  , Li Hong  , Liang Yu  , Zhang Xiao-Ru  , Liu Han  , Wu Xiang-Yao  , Guo Yi-Qing  ,   College of Physics, Jilin University, Changchun 130012, China;,   College of Physics, Jilin Normal University, Siping 136000, China;,   School of Physics, Northeast Normal University, Changchun 130012, China;,   Institute of High Energy Physics, Chinese Academy of Siences, Beijing 100049, China
Published: December 2020

The evolution of two-level atomic system, in which the initial state is excited state, is investigated by adjusting the structural parameters of the dynamic and static ideal photonic band-gap environment reservoir. In a static state (no modulation), we study the effects of half width, center resonant frequency, and specific gravity on the evolution of energy level population. The results show that when the half width or the specific gravity decreases, in the atomic system there happens decoherence, and the energy dissipation to the outside becomes slower. When the center resonant frequency increases, there exists no resonance between the library central resonant frequency and the atom transition frequency, then the attenuation suppression effect occurs, and the time of atomic attenuation to ground state is longer. An actual quantum system is not isolated, so it is inevitable that it interacts with its ambient environment. Owing to the influence of environment, in the system there appears an irreversible quantum decoherence phenomenon. Therefore, how to effectively suppress the decoherence of quantum system becomes an important problem in quantum information science. Linington and Garraway (2008 Phys. Rev. A 77 033831) pointed out that the evolution process of a two-level atom quantum state can be manipulated by a dynamic dissipative environment. So, we use the dynamic cavity environment to control the evolution of spontaneous emission from an excited two-level atom. The dynamic modulation form for the center resonant frequency of the ideal photonic band-gap environment reservoir includes the rectangular single pulse, rectangular periodic pulse, and slow continuous period. Owing to the periodic modulation, the atoms are affected by different environments. On this basis, the influence of dynamic modulation form on the atomic population evolution is discussed. It is found that no matter what form the dynamic modulation is in, the attenuation inhibition in the evolution of atomic system is evident. These conclusions make the idea of using the environmental change to modulate the coherent evolution of atomic system become true.
Comparative studies of irradiation effects in borosilicate glass and fused silica irradiated by energetic Xe ions
Authors: Peng Hai-Bo  , Liu Feng-Fei  , Zhang Bing-Tao  , Zhang Xiao-Yang  , Sun Meng-Li  , Du Xin  , Wang Peng  , Yuan Wei  , Wang Tie-Shan  , Wang Jian-Wei  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China;,   School of Physics Science and Technology, Lanzhou University, Lanzhou 730000, China;,   Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, China
Published: December 2020

As the first safety barrier of high level radioactive waste, the tolerance to radiation of vitrification is critical. Vitrification is a kind of specialized glass used as the package of high-level radioactive waste in nuclear power industry. Because of its structural consistency with the main structure of vitrification (silicon-oxygen tetrahedron), fused silica is used to study the irradiation effect on network of vitrification in the present study. Borosilicate glass, a simplified version of vitrification, is studied under the same conditions for comparison. Hardness values, moduli and refractive indexes of fused silica and borosilicate glass are measured before and after irradiation with nanoindentation technology and elliptic polarization instrument. It is shown in this study that the hardness values of fused silica and borosilicate glass decrease with increasing dose. On the other hand, with dose increasing, the modulus of borosilicate glass decreases but the modulus of silica increases. Change in modulus might be attributed to the change of density, which is consistent with results from the refractive index.
Beat frequency error rectifying in multi-beam laser coherent remote tmaging
Authors: Zhang Yu  , Luo Xiu-Juan  , Liu Hui  , Chen Ming-Lai  , Lan Fu-Yang  , Jia Hui  , Cao Bei  ,   Xi'an Institute of Optics and Precision Mechanics of Chinese Academy of Sciences, Xi'an 710119, China
Published: December 2020

Coherent imaging with a multi-beam laser is considered as a key technique in ground based imaging. The image quality is directly determined by stability and consistency of each beam in transmitter. Although the stabilities of laser frequency and the drifting compensation methods have been studied previously, they mostly focused on the laser source. In most cases, especially in large transmitter array, however, transmitted beams are always disturbed by different influential factors, such as frequency drift induced by acoustic-optical modulation (AOM) and high power driven amplification. Therefore this kind of frequency drifting needs further rectification. Aiming at this problem, in this paper we propose two new methods called dynamic demodulation and dependence range demodulation. Firstly, the dynamic demodulation takes the whole drifting frequency drift as a changing procedure. It is believed that the beat frequency drifted at any position still carries the target information, so the system demodulates the signal at that drifted position. According to this method, the response speed of the demodulation system should be very high. But in a real system this acquisition is too high to be satisfied. It cannot work as quickly as expected. In computer simulation some slow varying drifts are induced at the beat frequency and the variation is distributed only in three parts of spatial frequency of transmitter interfering array. Simulation results show that this method may well compensate for slow drifting beat frequency. While its response speed is often limited by hardware system. On the other hand, for the dependence range demodulation, the beat drifting range is considered as a useful district, in which all the beat energy is added and demodulated at a preset position. An experiment is carried out to verify this method. The result demonstrates that it can well restrict the beat frequency drift within 100 Hz, which often happens in the procedure of AOM and driving amplification. Besides the laboratory setup research, the field experiments in 200 m and 1.5 km range are also carried out. The dependence range demodulation is proved to be well performed as well. The resolution of the 25 cm simulated target in 1.5 km reaches 0.008 rad. In the consideration of real system, the imaging range is further expanded and the amplifier power is stronger. The field experiments reveal that this demodulation method is applicable in such a condition. Therefore the research in this article provides some new techniques for the remote high resolution imaging in multi-beam laser interfering imaging.
New experimental discovery of channel crystal plane and orientation selection for small-sized uniaxial strained Si PMOS
Authors: Chen Hang-Yu  , Song Jian-Jun  , Zhang Jie  , Hu Hui-Yong  , Zhang He-Ming  ,   Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

The inversion layer mobility of small-sized uniaxial strained Si p-channel metal oxide semiconductor (PMOS) channel is closely related to the crystal plane and crystal orientation. When optimally designing the strained PMOS, the crystal plane and crystal orientation of the channel should be chosen reasonably. At present, there is a theoretical sort model for the inversion layer mobility of Si PMOS channel at 1.5 GPa stress according to the crystal plane and crystal orientation. However, in the actual manufacturing process of device, the process of covering the SiN stress film is fixed, because the channel coefficient of stiffness is aeolotropic. So, the stress intensities of strained PMOS in different crystal planes and orientation channels are different, which causes the theoretical sort model for the inversion layer mobility to be invalid. To solve this problem, the small-sized uniaxial strained Si PMOS and unstrained Si PMOS with different crystal planes and orientations are fabricated by 40 nm technological process of Chinese Academy of Sciences. The result for the inversion layer mobility of Si PMOS channel according to the crystal plane and crystal orientation is obtained by the device transfer characteristic test. Considering the process implementation factors, the relevant conclusion about the inversion layer mobility of small-sized uniaxial strained Si PMOS channel according to the crystal plane and crystal orientation is more suitable to guide the actual device manufacturing than the theoretical sort result predicted in the literature. At the same time, the relevant analysis method can also provide important technical reference for the solution of other strained material MOS.
Decoupled two-dimensional direction of arrival estimation of single distributed source by vectoring differential phases
Authors: Dai Zheng-Liang  , Cui Wei-Jia  , Wang Da-Ming  , Zhang Yan-Kui  ,   The PLA Information Engineering University, Zhengzhou 450001, China
Published: December 2020

In practical applications such as radar, sonar, and mobile communications, transmitted signals are often affected by the scattering and reflection phenomena, which causes the signal energy received by the antenna array to be distributed into a certain space. In this case, a distributed source model will be more applicable. In general, the distributed sources have been classified as coherently distributed (CD) source and incoherently distributed (ID) source, which prove to be suitable for the cases of slowly time-varying and rapidly time-varying channels, respectively.In this paper, we consider the two-dimensional direction of arrival (DOA) estimation of distributed sources (including CD source or ID source). Specifically, uniform circular array (UCA) is widely used because of its ability to measure full azimuth angle and high resolution. However, the existing estimation algorithms all require spectral peak searching and the eigenvalue decomposition, which can bring a large computational complexity. To solve this problem, a decoupled rapid two-dimensional DOA estimation algorithm is proposed based on vectoring differential phases considering the two cases of single CD source and ID source. Firstly, based on spatial frequency approximation model, it is proved that none of differential phases between the received signals of different sensors in the UCA is affected by angle spread parameters when there is only a single distributed source. Under the premise of such a property, the central DOAs can be decoupled through obtaining the differential phases. Next, we can obtain the phase angles of strictly upper triangular elements in the sample covariance matrix, which correspond to differential phases between different sensors. Finally, by vectoring these differential phases, the central azimuth and elevation DOAs are estimated in the closed form from a least-squared problem, where the spectral peak searching and eigenvalue decomposition can be avoided, hence the computational complexity is reduced greatly. Theoretical analysis and simulation results show that the proposed algorithm has higher estimation accuracy and does not require prior information about the distribution of angular signals. With both low computational complexity and low hardware complexity, the proposed algorithm is beneficial to the engineering practice of array direction finding in complex environment.
Dendrite growth and Vickers microhardness of Co7Mo6 intermetallic compound under large undercooling condition
Authors: Sha Sha  , Wang Wei-Li  , Wu Yu-Hao  , Wei Bing-Bo  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The dendritic growth process and Vickers microhardness enhancement of primary Co7Mo6 phase in undercooled liquid Co-50%Mo hypereutectic alloy are systematically investigated by using electromagnetic levitation and drop tube. It is found that the rapid solidification microstructures are mainly characterized by primary Co7Mo6 dendrites plus interdendritic (Co7Mo6+Co) eutectic irrespective of experimental conditions. In electromagnetic levitation experiment, the obtained maximum undercooling reaches 203 K (0.12TL). With the rise in bulk undercooling, primary Co7Mo6 dendrite growth velocity monotonically increases according to a power function and reaches 22.5 mm-1 at the highest undercooling. The secondary dendrite spacing decreases from 45.8 to 13.6 m, while Co content in primary dendrites shows an increasing trend. This indicates that an evident grain refinement and solute trapping take place for primary Co7Mo6 dendrites during rapid solidification. The dependence of Vickers microhardness on Co content follows an exponential function. Moreover, the variation of Vickers microhardness with the grain size also satisfies an exponential relationship. In addition, Lipton-Kurz-Trivedi/Boettinger-Coriel-Trivedi model is used to analyze the growth kinetics of primary Co7Mo6 dendrites. In the experimental undercooling range, the growth process of primary Co7Mo6 dendrites is controlled mainly by solute diffusion and they grow sluggishly. Under free fall condition, liquid Co-50%Mo alloy is subdivided into many droplets inside a drop tube and their diameters range from 1379 to 139 m. With alloy droplet size decreasing, both droplet undercooling and cooling rate increase rapidly. In a large droplet-diameter regime above 392 m, primary Co7Mo6 phase displays faceted-growth characteristics. Furthermore, primary Co7Mo6 dendrites are refined greatly and their solute solubility is significantly extended as droplet size becomes smaller. Once the alloy droplet diameter decreases to a value below this threshold value, the faceted-growth characteristics start to disappear gradually, which is accompanied with a conspicuous grain refinement and a solute solubility extension. Both the solute solubility enhancement and grain size refinement contribute significantly to the exponential improvement in microhardness if primary Co7Mo6 phase grows in a faceted way. Otherwise, the solute solubility enhancement and grain size refinement result in the linear increase of Vickers microhardness. Theoretical analyses demonstrate that the primary phase microhardness is strongly dependent on its solute content and morphology characteristic.
Three-body fragmentation dynamics of OCS3+ induced by intermediate energy Ne4+ ion impact
Authors: Shen Li-Li  , Yan Shun-Cheng  , Ma Xin-Wen  , Zhu Xiao-Long  , Zhang Shao-Feng  , Feng Wen-Tian  , Zhang Peng-Ju  , Guo Da-Long  , Gao Yong  , Hai Bang  , Zhang Min  , Zhao Dong-Mei  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The fragmentation experiment of OCS3+ induced by 56 keV/u Ne4+ ions is performed using reaction microscope, and the corresponding dissociation dynamics is investigated. By detecting the three fragment ions in coincidence, the three-dimensional (3D) momenta of all ions and the corresponding kinetic energy release (KER) distributions are reconstructed. It is found that a peak maximum of the KER distribution is locates at about 25 eV, and a shoulder structure appears around 18 eV. This result is consistent with previous heavy ion experimental results with different perturbation strengths. Taking into account that the KER distribution is related to the initial state population of the OCS3+ parent ions, it can be concluded that the perturbation strength is not a decisive parameter leading to the initial state population of OCS3+ ions. We also reconstruct the Newton diagram and Dalitz plot for the three-body fragmentation of OCS3+ ion, from which the sequential dissociation is distinguished from nonsequential dissociation clearly. By analyzing the kinetic energy of ions from each fragmentation process, we find that the KER peak at 25 eV corresponds to nonsequential dissociation process, but the shoulder at 18 eV arises from both sequential and nonsequential dissociation processes. This phenomenon suggests that the parent OCS3+ ions in ground state and low excitation states tend to fragment through sequential dissociation, while those in high excitation states tend to fragment through nosequential dissociation. Furthermore, we reconstruct the KER distributions in the second fragmentation step of sequential dissociation, whose peak maximum is at 6.2 eV, corresponding to X3, 1+ and 1 metastable states of CO2+ ion. A similar KER distribution is obtained for the second fragmentation step of the OCS4+ ion. By comparing our experimental results with previous ones, we conclude that the origin of sequential dissociation process is the existence of metastable state, and the reconstructed KER in the second step reflects the initial state information about the metastable state.
Softening of sound velocity and Hugoniot parameter measurement for shocked bismuth in the solid-liquid mixing pressure zone
Authors: Li Xue-Mei  , Yu Yu-Ying  , Tan Ye  , Hu Chang-Ming  , Zhang Zu-Gen  , Lan Qiang  , Fu Qiu-Wei  , Jing Hai-Hua  ,   Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, CAEP, Mianyang 621900, China
Published: December 2020

Polymorphic phase transformation and melting under shock wave loading are important for studying the material dynamic mechanical behavior and equation of state in condensed matter physics. In this paper, the accurate Hugoniot parameter and sound velocity of shocked pure bismuth (Bi) in a pressure range of 17.3-28.3 GPa are obtained by using flyer impact method and rarefaction overtaking technique, respectively, and the sound velocity softening trend in shock-induced melting zone and the melting kinetics of Bi are then analyzed. In each experiment, six Bi samples with different thickness values are affected by oxygen-free-high-conducticity copper flyer fired through power gun. Shock wave velocity and particle velocity in Bi are experimentally determined through measuring the impact velocity and shock wave time in the thickest sample by photon Doppler velocimetry (PDV) technique. The velocity profiles on each interface between Bi and lithium fluoride (LiF) window are measured by displacement interferometer system of any reflector (DISAR), and then the sound velocity of shocked Bi is determined using the rarefaction overtaking method. The analyses of our results show that the softening of sound velocity of Bi approximatively satisfies the linear relation of Cs=3.682-0.015 p in the solid-liquid coexistence zone, and the pressure zone of the solid-liquid coexistence phase is further affirmed to be in a range of 18-27.4 GPa. Additionally, the obtained Hugoniot data for Bi in this paper supply a gap in the pressure zone of solid-liquid mixing phase. The quadratic equation with the expression of Ds=0.401+ 3.879 up-0.876 up2 can better demonstrate the relation between shock wave velocity and particle velocity than a linear one when the particle velocity lies in a range of 0.5-1.0 km/s, and this non-linear property maybe has a relationship with the shock-induced melting of Bi. Finally, our wave profile measurement of the Bi/LiF interface shows peculiar ramp characteristics in the expected velocity plateau zone in the pressure zone of solid-liquid coexistence phase, which may be associated with both the nonhomogeneous melting kinetics and the long time scale of melting for bismuth.
An extended single particle model-based parameter identification scheme for lithium-ion cells
Authors: Pang Hui  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

The accurate modeling and parameter identification of lithium-ion battery are of great significance in real-time control and high-performance operation for advanced battery management system (BMS) in electrified vehicles (EVs). However, it is difficult to obtain the information about the interior state inside battery, because it cannot be directly measured by some electric devices. In order to accurately identify the key state parameters of lithium-ion cell applied to electric ground vehicles, an extended single particle model of lithium-ion cell with electrolyte dynamics behaviors is first built up based on the porous electrode theory and concentration theory in this article. Compared with the conventional single particle cell model, the parameter description of the solid electrolyte interface film is incorporated into this model, and the coupled effects of temperature-dependent and electrolyte-dependent electrochemical parameters on the cell discharge are also taken into consideration. Based on this extended single particle cell model, a simplified parameter sensitivity analysis method and a comprehensive parameter identification scheme for lithium-ion cell are proposed herein, in which a sensitivity analysis of the capacity to a subset of electrochemical parameters that are hypothesized to evolve throughout the battery's life, is conducted to determine the highly sensitive parameters to be identified under some particular operation scenarios, and further to solve the parameter optimization problem using the genetic algorithm. Based on this method, the test data under the working condition of 1 C discharge rate at 23℃ are employed to evaluate the identified parameters of lithium-ion battery cell with a peak value of voltage error less than 3.8%. Afterwards, the effectiveness and feasibility of the proposed parameter identification scheme are validated by the comparative study of the simulated output voltage and the experimental output voltage under the same input current profile. Specifically, the 0.05 C discharge and HPPC (hybrid pulse power characterization) current profile are used to verify the evaluated parameters under the 1 C discharge condition, and the maximum relative errors of voltage with 0.05 C galvanostatic discharge profile at 23 and 45℃ are 3.4% and 2.6% by using our proposed SPMe_SEI model, and 5.7% and 4.0% by using the traditional SPMe model, respectively. Moreover, the maximum relative errors of voltage with HPPC discharge profile at 23 and 45℃ are 1.9% and 1.5% by using our proposed SPMe_SEI model, and 2.1% and 1.8% by using the traditional SPMe model, respectively. It is concluded that the proposed parameter identification scheme for a lithium-ion cell model can provide a solid theory foundation for facilitating the estimation of state-of-health in BMS application.
Influneces of different oxygen partial pressures on switching properties of Ni/HfOx/TiN resistive switching devices
Authors: Zhang Zhi-Chao  , Wang Fang  , Wu Shi-Jian  , Li Yi  , Mi Wei  , Zhao Jin-Shi  , Zhang Kai-Liang  ,   Tianjin Key Laboratory of Film Electronic & Communication Devices, School of Electrical and Electronic Engineering, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

The HfOx-based resistive random access memory (RRAM) has been extensively investigated as one of the emerging nonvolatile memory (NVM) candidates due to its excellent memory performance and compatibility with CMOS process. In this study, the influences of deposition ambient, especially the oxygen partial pressure during thin film sputtering, on the resistive switching characteristics are discussed in detail for possible nonvolatile memory applications. The Ni/HfOx/TiN RRAMs are fabricated, and the HfOx films with different oxygen content are deposited by a radio frequency magnetron sputtering at room temperature under different oxygen partial pressures. The oxygen partial pressures in the sputter deposition process are 2%, 4% and 6% relative to engineer oxygen content in the HfOx film. Current-voltage (I-V) measurements, X-ray photoelectron spectroscopy, and atomic force microscopy are performed to explain the possible nature of the stable resistive switching phenomenon. Through the current-voltage measurement, typical resistive switching behavior is observed in Ni/HfOx/TiN device cells. It is found that with the increase of the oxygen partial pressure during the preparation of HfOx films, the stoichiometric ratio of O in the film is improved, the root mean square (RMS) of the surface roughness of the film slightly decreases due to the slower deposition rate under a higher oxygen partial pressure, and the high resistance state (HRS) current decreases. In addition, by controlling the oxygen content of the device, the endurance performance of the device is improved, which reaches up to 103 under a 6% oxygen partial pressure. The HfOx films prepared at a higher oxygen partial pressure supply enough oxygen ions to preserve the switching effect. As the oxygen partial pressure increases, the uniformity of the switching voltage is improved, which can be attributed to the fact that better oxidation prevents the point defects (oxygen vacancies) from aggregating into extended defects. Through the linear fitting and temperature test, it is found that the conduction mechanism of Ni/HfOx/TiN RRAM device cells in low resistance state is an ohmic conduction mechanism, while in high resistance state it is a Schottky emission mechanism. The interface between TE and the oxide layer (HfOx) is expected to influence the resistive switching phenomenon. The activation energy of the device is investigated based on the Arrhenius plots in HRS. A switching model is proposed according to the theory of oxygen vacancy conductive filament. Furthermore, the self-compliance behavior is found and explained.
Adaptive imaging by incoherent digital holography based on phase change
Authors: Zhou Hong-Qiang  , Wan Yu-Hong  , Man Tian-Long  ,   College of Applied Sciences, Beijing University of Technology, Beijing 100124, China
Published: December 2020

Fresnel incoherent correlation holography (FINCH) is a unique scanning-free three-dimensional imaging technique which enables holograms to be created from incoherent light illumination. However, the image quality is inclined to be destroyed by various optical aberrations, in the practical application of microscopic imaging. In order to solve this problem, some kinds of adaptive optics are combined with imaging technologies to detect the distorted wavefront and compensate for the aberrations. Phase diversity is an image-based adaptive optics method where two intensity images with a certain phase difference are used for wavefront sensing. In this paper, we develop an adaptive imaging technique by Fresnel incoherent digital holography combined with phase diversity (PD-FINCH). Two recorded phase-shift holograms are applied to wavefront sensing, and the phase of aberration is further extracted by phase diversity reconstruction algorithm. The compensation phase is uploaded on SLM in turn, thus the aberrations are corrected while recording holograms. Both the simulation and experimental results verify the validity of phase diversity in FINCH. All the results show the improvement of reconstructed image quality after wavefront aberration compensation.
Generation of four-photon hyperentangled state using spontaneous parametric down-conversion source with the second-order term
Authors: He Ying-Qiu  , Ding Dong  , Peng Tao  , Yan Feng-Li  , Gao Ting  ,   Department of Biomedical Engineering, Chengde Medical University, Chengde 067000, China;,   College of Science, North China Institute of Science and Technology, Beijing 101601, China;,   College of Physics Science and Information Engineering, Hebei Normal University, Shijiazhuang 050024, China;,   College of Mathematics and Information Science, Hebei Normal University, Shijiazhuang 050024, China
Published: December 2020

Nowadays,the generation of multiphoton entangled states is almost realized by combining the coupled entangled photons emitted from spontaneous parametric down-conversion (SPDC) with the first-order term.In this case,one may focus mainly on the first-order term,and then avoid multipair emission events by restricting experimental parameters.On the other hand,for the higher-order terms in SPDC source,these emitted entangled photons have interesting features.For example,they are entangled maximally not only in photon number for the spatial modes,but also in polarization degree of freedom.In general,two photons,which are entangled in two or more degrees of freedom,are called hyperentangled pair of photons or hyperentangled state.We present a scheme to generate the four-photon hyperentangled state based on four indistinguishable photons emitted from SPDC source with the second-order term.Consider two SPDC sources with equal probability of emission of photons in respective spatial modes.With the passive linear optical devices,i.e., beam splitters,half wave plates,polarizing beam splitters,etc.,under the condition of registering a specified four-photon coincidence,we can obtain the four-photon hyperentangled state in which the photons are entangled in both polarization and spatial-mode degrees of freedom.Here,of course,for an arbitrary fourfold coincidence detection,one obtains a canonical four-photon Greenberger-Horne-Zeilinger (GHZ) state.Then we show the results of fourfold coincidence detections and the corresponding probabilities for the four-photon GHZ states,where the generation of the four-photon hyperentangled state is included as long as we are not to distinguish the two detectors located at the same locations. As a result,our scheme has two notable features.When we only consider the second-order emission,since it is not needed for us to distinguish between the two SPDC sources,the present scheme is simple and feasible.Also,based on the postselection with fourfold coincidence detection,our scheme is suitable for the normal first-order emission where we restrict the four photons emitted from the same source.In this sense,our scheme is efficient.In a word,we describe a method to generate the four-photon hyperentangled state with the second-order emission in SPDC source,which may contribute to the exploration of multipair entanglement with higher-order emissions from the SPDC source.