bluuebunny/crossref_metadata_2025 huggingface dataset:
Hardening of reduced activation ferritic/martensitic steels under the irradiation of high-energy heavy-ion
Authors: Ding Zhao-Nan  , Yang Yi-Tao  , Song Yin  , Zhang Li-Qing  , Gou Jie  , Zhang Chong-Hong  , Luo Guang-Nan  ,   Institution of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

In order to study the irradiation responses of reduced activation ferritic/martensitic (RAFM) steels which are candidates for fusion reactors, a reduced activation steel is irradiated at a terminal of HIRFL (heavy ion research facility in Lanzhou) with 63 MeV 14N ions and 336 MeV 56Fe ions at -50 ℃. The energies of the incident N/Fe ions are varied from 0.22 MeV/u to 6.17 MeV/u by using an energy degrader at the terminal, so that a plateau region of an atomic displacement damage (0.05-0.2 dpa) is obtained from the near surface to a depth of 24 μm in the specimens. Nanoindentation technique is used to investigate the nano-hardness changes of the samples before and after irradiation. The constant stiffness measurement is used to obtain the depth profile of hardness. The Nix-Gao model taking account of the indentation size effect (ISE) is used to fit the measured hardness and thus a hardness value excluding ISE is obtained. Consequently, the soft substrate effect for lower energy ion irradiation is effectively avoided. It is observed that there seems to be a power function relationship between the hardness and damage for the RAFM steel. The hardness initially increases significantly with the increase of irradiation damage, then increases slowly when the damage reaches to about 0.2 dpa. Positron annihilation is performed to investigate the defect evolution in the material. The positron annihilation lifetime spectra show that the long-lifetime proportion of the RAFM steel increases significantly after being irradiated. This means vacancy clusters are produced by the irradiation, resulting in the change of mechanics property. Even at low irradiation dose, point defects with high density are generated in the steel specimens, and subsequently aggregate into defect clusters, thereby suppressing the dislocation slip.The defect concentration in the material increases continuously with the increase of irradiation damage, which leads to the obvious irradiation hardening phenomenon. When the damage is higher than 0.1 dpa, the increment of mean lifetime gradually decreases due to the existence of a large number of vacancies and dislocations, and it eventually tends to be saturated, which explains why the irradiation hardening increment rate decreases with the increase of irradiation damage in the material.
Quantum efficiency calibration for low energy detector in hard X-ray modulation telescope satellite
Authors: Zhu-Yue  , Zhang Zi-Liang  , Yang Yan-Ji  , Xue Rong-Feng  , Cui Wei-Wei  , Lu Bo  , Wang Juan  , Chen Tian-Xiang  , Wang Yu-Sa  , Li Wei  , Han Da-Wei  , Huo Jia  , Hu Wei  , Li Mao-Shun  , Zhang Yi  , Zhu Yu-Xuan  , Liu Miao  , Zhao Xiao-Fan  , Chen Yong  ,   Key Laborotary of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;,   Department of Radio Physics, Jilin University, Changchun 130012, China
Published: December 2020

Low energy X-ray telescope, working over 0.7-15 keV energy band, is one of the main payloads in the hard X-ray modulation telescope satellite. The primary scientific objectives are to survey large sky area to investigate galactic X-ray transient sources as well as the cosmic X-ray background, and to observe X-ray binaries or black holes for studying the dynamics and emission mechanism in strong gravitational or magnetic field. The detector of low energy X-ray telescope is CCD236, a new generation of swept charge device, which has good time and energy resolution. Quantum efficiency (QE) of the detector has a crucial influence on X-ray spectrum fitting and absolute luminosity calculation. To provide valuable scientific data, QE should be calibrated in detail. In this paper, QE calibration is accomplished with respect to a silicon drift detector (SDD), using an Fe-55 radioactive source, at energy points Mn-Kα (5.899 keV) and Mn-Kβ (6.497 keV). The energies of Mn-Kα and Mn-Kβ are near that of iron-K, which is an important line in X-ray observation. Additionally, Mn-Kα and Mn-Kβ X-ray will partially pass through the depletion region of CCD236, and these energy points can be used to measure the depletion thickness. This experiment is set up in a vacuum cooling chamber. The X-ray source perpendicularly illuminates SDD and CCD236 through a small hole, whose area is far less than those of two detectors; therefore, QE measurements are irrelevant to neither the distance nor the azimuth angle between the X-ray source and the detector. For CCD236, split events should be corrected. Energy spectra of SDD and CCD236 are fitted with two Gaussian distributions, respectively, to obtain peak positions and standard variations of Mn-Kα and Mn-Kβ. With known structure of SDD, the QE of CCD236 can be calculated. QE values at Mn-Kα and Mn-Kβ are 71% and 62%, respectively. QE and temperature are uncorrelated with each other in a temperature range from -95 ℃ to -30 ℃. According to the specific structure of CCD236 and the measured QE, without considering the effect of channel stop, the best-fit thickness of depletion region is obtained to be 38 μm. When CCD236 is applied with different driving or substrate voltages, no obvious variation of QE is observed. It indicates that the thickness values of depletion region with high and low level voltages are equal. Furthermore, it shows that working CCD236 is deep depleted, and the thickness of depletion region will not change because it reaches its maximum, the edge of epitaxial layer and substrate layer.
Four-element division algorithm for focusing light through scattering medium
Authors: Zhang Cheng  , Fang Long-Jie  , Zhu Jian-Hua  , Zuo Hao-Yi  , Gao Fu-Hua  , Pang Lin  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610065, China
Published: December 2020

Light transport in complex disordered medium, such as white paint, milk, is a fundamental physical phenomenon, and it plays an important role in numerous applications including imaging through turbid layers, and quantum information processes. However, all spatial coherence is lost due to the distorted incident wavefront caused by repeated scattering and interference. Incident coherent light diffuses through the medium and cannot form a geometric focus but a volume speckle field on the imaging plane. In this paper, we propose a four-element division algorithm and experimentally demonstrate that using this algorithm to modulate the incident light, the shaped wavefront can focus through disordered material. At the beginning, we start with four segments on spatial light modulator (SLM), changing the phase of each segment from 0-2πup to search for the optimal phase in terms of the maximal output intensity at a certain field. After the optimal phase of these four segments is found, each of all segments is divided further into four subsegments, so 16 subsegments are formed on the SLM. Just like the first step, the optimal phase is found by cycling the phases of these 16 subsegments. Sequentially, this procedure is repeated several times, so more and more subsegments are obtained. As a result, the modulated input light from SLM can be focused after it has passed through the turbid scattering medium. By employing this approach in the forward scattered experiment, the total pixels of spatial light modulator are divided into 4-4096 segments to shape the incident light. After separately searching for all the optimal phase distributions, we can see that a sharp focusing is gradually achieved. Likewise, in backscattered experiment, 4-1024 segments are used to focus the incident light after passing through the diffuse material. In comparison with stepwise sequential algorithm, the main advantage of our method is that the interference effect of all segments on SLM is taken into consideration, which means that the modulated and the modulating segments are connected with each other. In this way, the signal-to-noise ratio is higher and no iteration is needed. All this experiment shows that the four-element division algorithm can be employed to focus the incident light passing through a disorder material efficiently, which maybe provide a new idea and method in the field of biomedical imaging through scattering medium.
A full spectrum resamping method in polygon tunable laser-based swept-source optical coherence tomography
Authors: Fan Jin-Yu  , Gao Feng  , Kong Wen  , Li Hai-Wen  , Shi Guo-Hua  ,   Jiangsu Key Laboratory of Medical Optics, Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou 215163, China
Published: December 2020

Swept-source optical coherence tomography (SS-OCT) has high sensitivity and signalnoise ratio compare with time-domain optical coherence tomography and spectral-domain optical coherence tomography. Therefore, SS-OCT is the form of Fourier domain optical coherence tomography predominantly used in experimental research and biomedical image. However, polygon tunable laser-based SS-OCT suffers sweep range fluctuation and spectral misplacement. Under certain circumstances, in the current resampling methods cross-correlation is widely used to align spectrum misplacement, and truncate A-lines in order to ensure the consistency of frequency-scanning range, which, however, degrades the image SNR and resolution. We use the Mach-Zehnder interference (MZI) signal to quantify and analyze this problem in two typical polygon tunable lasers. The periodical change of sweep range and spectrum misplacement show the instability derived from polygon mirror. The parallelism among unwrapped phase curves indicates that polygon tunable laser output spectra have consistent wavelength distributions, and thus it is suited to implement cross-correlation between MZI signals in time domain, and an unwrapped phase curve can represent the wavelength distribution of all A-lines.According to the above conclusions, we demonstrate a resampling method in which the zero-padding interpolation and cross-correlation are used to align A-lines in time domain and eliminate the residual phase noise caused by integer shift. Then the unwrapped phase curve that has a largest sweep range is used to resample all the aligned A-lines, and the interference signals can be fully utilized. The experiments for signal truncation and Pomelo fruit flesh indicate that the proposed method can improve image SNR but does not make the intensity image dislocated. The phase noise (3.9 mrad for a 49 dB SNR) from static mirror is close to theory limit after resampling, thus showing good phase stability and resampling precision. The proposed resampling method also needs less computational work than one-to-one resampling method because it only fits unwrapped phase curve and calculates interpolation coefficient once.
Concept of waveguide invariant spectrum and algorithm for its extraction
Authors: Song Wen-Hua  , Wang Ning  , Gao Da-Zhi  , Wang Hao-Zhong  , Qu Ke  ,   Department of Marine Technology, Ocean University of China, QingDao 266100, China;,   School of Electronic and Information Engineering, Guangdong Ocean University, Zhanjiang 524088, China
Published: December 2020

There are two kinds of definitions for waveguide invariant β. One is defined according to the striation slope of acoustic interference patterns, and the other is defined on the basis of dispersion characteristics of acoustic modes. The first definition is appropriate for engineering applications, while the second is suitable for theoretical analysis. However, the two definitions are not consistent with each other for a waveguide with thermoclines, because modal dispersion in such a waveguide can be very different for different modes and different frequencies. In such cases, the waveguide invariant defined according to modal dispersion can take many different values, which are referred to as the spectrum of waveguide invariant (β spectrum for short) in the paper. Each β spectrum can be related to some interference striation patterns with corresponding striation slopes. The sound field is composed of many modes, so the interference pattern is the summation of many components of different striation slopes and may be very complicated as a result of the diversity of β spectrum. In such a case one single β is not able to describe the complicated interference pattern adequately; instead multiple values of β spectrum are required. From the point of view of engineering application, however, the present β-extracting methods can only give one optimal value, and thus a lot of information is lost. In this paper an algorithm for doing so, called β spectrum separation technique, is proposed. By adopting the concept of integral projection used in digital image processing, the image of acoustic intensity is projected at different angles to separate out the striations of different slopes; and then fast Fourier transform (FFT) is applied to the projected curve in order to isolate striations of different spacing from each other. The values for β spectrum can be computed according to striation slopes, which are also mapped into the positions of their corresponding acoustic modal horizontal wavenumber differences in the wavenumber domain. The applicability of this algorithm for the extraction of β spectrum is tested and verified by simulation results and experiment data. It is shown that the algorithm can separate out each β spectrum of different intensity components from acoustic interference structure. The algorithm maps β spectrum into a two-dimensional plane thereby being able to suppress noise more effectively and work in the condition of low signal-to-noise ratio compared with the already-existing β-extracting algorithms.
Design and research of columnar thermal cloak with arbitrary shape in inhomogeneous backgrounds
Authors: Xia Ge  , Yang Li  , Kou Wei  , Du Yong-Cheng  ,   School of Power Engineering, Naval University of Engineering, Wuhan 430033, China
Published: December 2020

Recently, thermal metamaterials have attracted more and more attention, and they have been used to manipulate the flow of heat flux. As a typical case, the thermal cloak can conceal the heat signature of an object. To the best of our knowledge, most of researches on cloak have focused on the case in which the background is a single homogeneous medium. However, cloaking in the layered and gradually changing backgrounds is very common in our real life such as hiding the buried mines in several soil backgrounds. In this paper, on the basis of transformation thermodynamics, a general expression of the thermal conductivity for two-dimensional thermal cloak with arbitrary shape in the layered and gradually changing backgrounds is derived by the coordinate transformation method. According to the expression, we design the thermal cloak in different inhomogeneous backgrounds. Results of full wave simulation show that heat flux can travel around the protection area and eventually return to their original path. The temperature profile inside the thermal cloak keeps unchanged, and the temperature field outside the thermal cloak is not distorted, which proves that the cloak has a thermal protection and thermal stealth function. In the end, we propose a useful method of utilizing homogeneous isotropic materials to construct a thermal device according to the equivalent medium theory. The method is closer to the practical application of the project because of considering the complex backgrounds. At the same time, this technology provides a feasible method to control heat transfer in the future and has great significance for thermal stealth and thermal protection.
Cyclic capacity fading of the power lithium ion battery based on a numerical modelling with dynamic responses
Authors: Jiang Yue-Hui  , Ai Liang  , Jia Ming  , Cheng Yun  , Du Shuang-Long  , Li Shu-Guo  ,   School of Metallurgy and Environment, Central South University, Changsha 410083, China;,   Hunan Aihua Group Co., LTD, Yiyang 413002, China
Published: December 2020

It is one of the important issues for electric vehicle to utilize power batteries which have long lifetime and excellent performance. For optimizing electrochemical performance and lifetime of the lithium ion battery, an electrochemical-thermal model based on dynamic response is developed by COMSOL MULTIPHYSICS. The modeling theory is the reaction mechanism of lithium iron phosphate battery which also includes a parasitic reaction occurring in the constant current and constant voltage charging process. The model consists of three parts: electro-chemical model, thermal model and capacity fade model. A series of temperature-dependent parameters and lithium ion concentration-dependent parameters relevant to the reaction rate and Li+ transport are employed in this model. Comparing with the results of the experimental test, the model shows high accuracy and reliability. The capacity losses and electrochemical behaviors of the battery in cyclic processes with different rates are investigated. The results show that when the battery is cycled at a rate of 1C, the capacity fading rate is about 6.35%, meanwhile the solid electrolyte interface membrane impedance of the battery is increased by 15.6 mm-2 after 800 time cycle. In the charge process, the side reaction rate within the anode shows a decreasing trend along the direction from the cooper current collector to separator, which is consistent with the lithium concentration in the anode. Besides, the effects of charge/discharge rate, negative active material particle radius and negative solid volume fraction on the battery cycle life are also discussed respectively. Compared with the fading rate of 3.31% after 400 time cycle with 1C rate, the capacity fading rates for 2C, 3C, 4C reach to 3.93%, 4.69% and 5.04% respectively. When the average particle radii of the anode are 2 m and 10 m, corresponding capacity fading rates are 2.89% and 3.87%, showing a difference of nearly 1%. The study for solid volume fraction demonstrates that the battery with a solid volume fraction varying in a range of [0.5, 0.6] will keep a longest battery life. These results show that the model has great potential to optimize the design of the battery.
Research and verification for parabolic equation method of radio wave propagation in obstacle environment
Authors: Wei Qiao-Fei  , Yin Cheng-You  , Fan Qi-Meng  ,   National Key Laboratory of Pulsed Power Laser Technology, Electronic Engineering Institute of PLA, Hefei 230037, China
Published: December 2020

In recent years, the two-way parabolic equation method (2WPE) has been widely utilized for studying the tropospheric ground-wave propagation under the irregular terrain. This algorithm can deal with the influences of the irregular terrain characteristic and the different electromagnetic parameters of the surface structure on wave propagation. However, there are still some defects in 2WPE method. Firstly, the method considers the irregular terrain and obstacles as a whole, so it cannot deal with the situation where the medium parameters of obstacles and the ground are different. Secondly, its calculation precision is limited with the inclination of the undulating terrain: if there are obstacles the upper bound of the inclination is easily broken through. Therefore, in this paper, a novel two-way parabolic equation method is proposed for analyzing the radio wave propagation in obstacle environment. According to the principle of domain decomposition, the obstacle zones are divided into two domains in the new algorithm, and the two subdomains are calculated, respectively. Meanwhile, in order to avoid the calculation error caused by the abrupt truncation of the obstacle zone, the field at the upper boundary of obstacles is modified to ensure the continuity of tangential field. To further improve the accuracy of the new algorithm, according to the historical transmission paths, we exactly retrieve the phases of each forward and backward wave, especially when stepping in and out of the obstacles. Furthermore, the method of moment (MoM) is used to verify the calculation accuracy of the new algorithm in obstacle environment. Although the accuracy of the MoM is very high, it also requires a great deal of calculation resources: it can only be employed to compute the fields in short distance. To overcome the difficulty, we use the image principle in the obstacle environment and do not subdivide the ground into segments; therefore the verification accuracy can be improved. On this basis, to unify the source setting of the new algorithm and the MoM, the equivalent source model is used to set the initial field. Finally, through numerical experiments, the simulation results of both methods agree very well, so the effectiveness of the boundary correction and the phase correction which are presented in this paper are both verified. The accuracy and superiority of the new algorithm in obstacle environment are also demonstrated. To sum up, the novel two-way parabolic equation method can be used to accurately calculate the field of the space in the obstacle environment, and lays the foundation for the field calculation of radio wave propagation in real environment.
A collisional-radiative model for lithium impurity in plasma boundary region of Experimental Advanced Superconducting Tokamak
Authors: Zhang Tai-Yang  , Chen Ran  ,   School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230022, China;,   Institute of Plasma Physics, Heifei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

A green emission layer caused by lithium impurity is universally observed in plasma boundary region of Experimental Advanced Superconducting Tokamak (EAST) via a visible-light camera, where lithium coating is normally adopted as a routine technique of wall conditioning. In this article, in order to estimate the spatial distribution of green light intensity of this emission layer according to the given real parameter distributions of edge plasmas, a practicable method is proposed based on a collisional-radiative model. In this model, a finite number of energy levels of lithium are taken into account, and proper simplifications of convection-diffusion equations are made according to the order-of-magnitude analysis. We process the atomic data collected from the OPEN-ADAS database, and develop a corresponding program in Mathematica 10.4.1 to solve the simplified one-dimensional problem numerically. Estimation results are obtained respectively for the two sets of edge plasma profiles of EAST in L-mode and H-mode regimes, and both clearly show a good unimodal structure of the spatial distribution of green light intensity of this emission layer. These analyses actually provide the spatial distributions of lithium impurities at different energy levels, not only indicating the spatial distribution of the intensity of this emission layer induced by lithium impurity but also revealing the physical processes that lithium experiences in edge plasma. There are some different and common characteristics in the spatial distribution of the intensity of this emission layer in these two important cases. This emission layer is kept outside the last closed magnetic surface in both cases while it becomes thinner with a higher intensity peak in H-mode case. Besides, the sensitivity of this algorithm to the measurement error of edge plasma profile is also explored in this work. It is found that the relative errors of the numerical results obtained by our proposed method are comparable to those of edge plasma profiles. This work provides important theoretical references for developing a new practical technique of fast reconstructing edge plasma configurations in EAST based on the emission of lithium impurity, and may further contribute a lot to the studies of edge plasma behaviors when three-dimensional perturbation fields are adopted.
Chemical potential-functional-theory about the properties of one-dimensional Hubbard model at finite temperature
Authors: Lu Zhan-Peng  , Wei Xing-Bo  , Liu Tian-Shuai  , Chen A-Hai  , Gao Xian-Long  ,   Department of Physics, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

In this paper, we numerically solve the thermodynamic Bethe-ansatz coupled equations for a one-dimensional Hubbard model at finite temperature and obtain the second order thermodynamics properties, such as the specific heat, compressibility, and susceptibility. We find that these three quantities could embody the phase transitions of the system, from the vacuum state to the metallic state, from the metallic state to the Mott-insulating phase, from the Mott-insulating phase to the metallic state, and from the metallic state to the band-insulating phase. With the increase of temperature, the thermal fluctuation overwhelms the quantum fluctuations and the phase transition points disappear due to the destruction of the Mott-insulating phase. But in the case of the strong interaction strength, the Mott-insulating phase is robust, embodying the compressibility. Furthermore, we study the thermodynamic properties of the inhomogeneous Hubbard model with trapping potential. Making use of the Bethe-ansatz results from the homogeneous Hubbard model, we construct the chemical potential-functional theory (-BALDA) for the inhomogeneous Hubbard model instead of the commonly used density-functional theory, in order to solve the in-convergence problem of the Kohn-Sham equation in the case of the divergence appearing in the exchange-correlation potential. We further point out a multi-dimensional bisection method which changes the Kohn-Shan equation into a problem of finding the fixed points. Through -BALDA we numerically solve the one-dimensional homogeneous Hubbard model of trapping potential. The density profile and the local compressibility are obtained. We find that at a given interaction strength, the metallic phase and the Mott-insulating phase are destroyed and the density profile becomes a Guassian distribution with increasing temperature. To the metallic phase, Friedel oscillation caused by quantum fluctuations is still visible at low temperature. With increasing temperature, Friedel oscillation will disappear. This situation reflects the fact that the thermal fluctuation overwhelms the quantum fluctuations. For the Mott-insulating phase, the Mott-insulating plateau is robust at a certain temperature and only the boundary of the Mott-insulating plateau is destroyed. With increasing temperature, the Mott insulating plateau will be destroyed. And the change of the local compressibility provides the information about such a change. So we conclude that the thermal fluctuation destroys the original quantum phase. Through our analysis, we find that the -BALDA can be used to study the finite temperature properties for the system of the exchange-correlation potential divergence with high efficiency.
Simulation of three-dimensional transient heat conduction problem with variable coefficients based on the improved parallel smoothed particle hydrodynamics method
Authors: Jiang Tao  , Chen Zhen-Chao  , Ren Jin-Lian  , Li Gang  ,   School of Mathematical Sciences, Yangzhou University, Yangzhou 225002, China
Published: December 2020

In this work, an improved parallel SPH method is proposed to accurately solve the three-dimensional (3D) transient heat conduction equation with variable coefficients. The improvements are described as follows. Firstly, the first-order symmetric smoothed particle hydrodynamics (SPH) method is extended to the simulating of the 3D problem based on Taylor expansion. Secondly, the concept of stabilized up-wind technique is introduced into the convection term. Thirdly, the MPI parallel technique based on the neighboring particle mark method is introduced into the above improved SPH method, and named the corrected parallel SPH method for 3D problems (CPSPH-3D). Subsequently, the accuracy, convergence and the computational efficiency of the proposed CPSPH-3D method are tested by simulating the 3D transient heat conduction problems with constant/variable coefficient, and compared with the analytical solution. Meanwhile, the capacity of the proposed CPSPH-3D for solving the 3D heat conduction problems with the Dirichlet and Newmann boundaries is illustrated, in which the change of temperature with time under the complex cylindrical area is also considered. The numerical results show that:1) the proposed CPSPH-3D method has the better stability, higher accuracy and computational efficiency than the conventional SPH method no matter whether the particle distribution is uniform; 2) the calculating time can be well reduced by increasing the number of CPUs when the particle number is refined in the simulations of CPSPH-3D. Finally, the temperature variation in the 3D functionally gradient material is predicted by the corrected parallel SPH method, and compared with the other numerical results. The process of temperature variation in the functionally gradient material can be shown accurately.
Ground state of a rotating Bose-Einstein condensate with in-plane quadrupole field
Authors: Liu Jing-Si  , Li Ji  , Liu Wu-Ming  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Compared with the scalar Bose-Einstein condensate, the spinor Bose-Einstein condensate, in which internal degrees of freedom are essentially free, has aroused the great interest in the study of topological excitations. In particular, the spinor Bose-Einstein condensate with rotation provides a new opportunity for studying novel quantum states including a coreless vortex and vortex lattice. To date, in the presence of rotation, a great many of studies on the topological excitations have focused on the Bose-Einstein condensate system with the uniform Zeeman field or without external magnetic field. However, the ground state structure of a rotating Bose-Einstein condensate in the presence of in-plane gradient-magnetic-field remains an open question. In this work, by using the imaginary-time propagation method, we study the ground state structure of a rotating Bose-Einstein condensate with in-plane quadrupole field. We first examine the effect of in-plane quadrupole field on trapped spinor Bose-Einstein condensate. The numerical results show that Mermin-Ho vortex can be induced only by the cooperation between quadrupole field and rotation. When magnetic field gradient is increased, the vortices around Mermin-Ho vortex display the symmetrical arrangement. For an even larger magnetic field gradient strength, the system only presents the Mermin-Ho vortex because the in-plane quadrupole field can prevent the vortices around Mermin-Ho vortex from occurring. Next, we examine the effect of the rotation on trapped spinor Bose-Einstein condensate. A phase transition from a polar-core vortex to a Mermin-Ho vortex is found through applying a rotational potential, which is caused by the cooperation between the in-plane quadrupole field and the rotation. We further study the combined effects of spin exchange interaction and density-density interaction. The results confirm that in the presence of the quadrupole field both spin exchange interaction and density-density interaction, acting as controllable parameters, can control the number of the vortices around Mermin-Ho vortex. The corresponding number of the vortices shows step behavior with increasing the ratio between spin exchange interaction and density-density interaction, which behaves as hexagon, pentagon, square and triangle. It is found that two types of topology structures, i.e., the hyperbolic meron and half-skyrmion, can occur in the present system. These vortex structures can be realized via time-of-flight absorption imaging technique. Our results not only provide an opportunity to investigate the exotic vortex structures and the corresponding phase transitions in a controlled platform, but also lay the foundation for the study of topological defect subjected to gauge field and dipolar interaction in future.
First principles study of the effect of Cu doping on the martensitic transformation of TiNi alloy
Authors: Yan Shun-Tao  , Jiang Zhen-Yi  ,   Shaanxi Key Laboratory for Theoretical Physics Frontiers, Institute of Model Physics, Northwest University, Xi'an 710069, China
Published: December 2020

As is well known,copper is such an unbelievable element that it can affect the phase transition behaviors of binary TiNi alloy when it displaces Ni element up to near upon 25%.The martensitic transition behaviors of TiNi1-xCux alloys appear from high-temperature cubic B2 phase to intermediate B19 structure with orthorhombic system and then finally to low-temperature B19' phase with monoclinic system with x 10% on cooling,so called two-stage martensitic phase transformation.Whereas,it directly transforms into orthorhombic B19 phase withx 20% on cooling,so called one-stage martensitic phase transformation.The orthorhombic B19 phase becomes final low-temperature phase while monoclinic phase will be unstable on cooling.The electronic structures and the formation energies of various point defects, Mulliken bond orders,etc.are studied for TiNi1-xCuxx alloys,however,the phase transition pathway at an atomic level has not been described at all,and further,the difference in transition pathway between TiNi and Ti1Ni1-xCuxx has not been understood so far.In this work,we optimize the crystal structures of TiNi and Ti50Ni25Cu25 alloys with initial geometry from experimental data.In order to choose the proper positions of Cu atom,we calculate the total energy of each doping system and find the most stable configuration.To study the transformation mechanism of TiNi,we calculate the phonon-dispersion spectra of each phase with both frozen-phonon method and linear response method,and then find the atomic vibrations with the imaginary frequency.Finally,with the help of this atomic vibration direction with negative frequency,we find the intermediate structures by the linear interpolation method and calculate their total energies.The phase transformation of TiNi from cubic to orthorhombic phase is driven by the phonon softening at the M point (0.5,0.5,0) of Brillouin zone.For orthorhombic and monoclinic phase,TiNi has real phonon frequencies for all k points and modes.A barrier of 1.6 meV is calculated between orthorhombic and monoclinic phase while no barrier is found between cubic and orthorhombic phase of TiNi,so it is easy to transform from cubic to orthorhombic and then to monoclinic phase.There exists a potential energy barrier of 10.3 meV at least between orthorhombic and monoclinic phase for Ti50Ni25Cu25,which is too high for its transition to overcome the maximum value of potential energy which corresponds to =93.4.The difference in transition pathway between TiNi and Ti50Ni25Cu25 accords well with the experimental measurement,so that the copper concentration with 25% in binary TiNi alloy will offer a new transition path from cubic to orthorhombic phase.
Investigation on Te-based chalcogenide glasses for far-infrared fiber
Authors: Wu Bo  , Zhao Zhe-Ming  , Wang Xun-Si  , Jang Ling  , Mi Nan  , Pan Zhang-Hao  , Zhang Pei-Qing  , Liu Zi-Jun  , Nie Qiu-Hua  , Dai Shi-Xun  ,   Laboratory of Infrared Material and Devices, Advanced Technology Research Institute, Ningbo University, Ningbo 315211, China;,   Faculty of Electrical Engineering and Computer Science, Ningbo University, Ningbo 315211, China;,   Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province, Ningbo 315211, China;,   Nanhu College, Jiaxing University, Jiaxing 314001, China
Published: December 2020

When infrared (IR) is over 12 m, conventional chalcogenide (ChG) fibers are confused by the multiphonon absorption of Se, and novel glass materials for far-IR have become one of hot research points in recent years. Here, a novel ChG glass and fiber for far-IR without containing Se/As is well investigated. The glasses GeTe-AgI are purified by distillation and synthesized by melt-quenching method. The thermal properties and the infrared transmissions are reported. The step-index fiber, fabricated via a novel extrusion method, exhibits excellent transmission at 8-15 m: 24 dB/m in a range of 8-15 m and 15.6 dB/m at 10.6 m. The influences of oxygen contaminant and the purity of AgI on the glass transmission and fiber attenuation are discussed. Structural and physical properties of GeTe-AgI glass system are studied with differential scanning calorimetry and ellipsometer instrument. Optical spectra of GeTe-AgI glass system are obtained by spectrophotometer and infrared spectrometer. Main purification process with oxygen-getters (magnesium) is disclosed. The fiber attenuation is measured by the cut-back method with a Fourier transform infrared spectrometer. The lowest loss of this fiber can be reduced to 15.6 dB/m at 10.6 m. The results show that these glasses are well transparent in a wide IR window from 1.7 to 25 m, and these glass fibers can transmit light up to 15 m, thus the GeTe-AgI glass system is one of good candidates for far-IR. The fiber attenuation can be reduced effectively by the reasonable purification and novel extruded-processing. These environment friendly fibers are suited for far-IR applications, such as greenhouse gas sensing and the power delivery of CO2 laser.
Effect of ZnO twin grain boundary on p-type conductivity of VZn-NO-H complex:a GGA+U study
Authors: Wu Jing-Jing  , Tang Xin  , Long Fei  , Tang Bi-Yu  ,   Key Laboratory of New Processing Technology for Nonferrous Metal and Materials, Ministry of Education, Guilin University of Technology, Guilin 541004, China;,   College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, China;,   School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
Published: December 2020

The origin of the p-type conductivity in N-doped ZnO has been a controversial issue for years, since isolated N substituted for O site (NO) was found to have high ionization energy. A recent experiment demonstrates that the p-type conductivity is attributed to the VZn-NO-H shallow acceptor complex. However, besides the complex, there are many other defects in ZnO, such as twin grain boundaries. They are commonly two-dimensional defects, and inevitably affect the p-type conductivity of the complex. By applying first principle calculations, we present the electronic structures and p-type conductivity of ZnO ∑7 (1230) twin grain boundaries containing VZn-NO-H complexes. Four types of ∑7 twin grain boundaries are investigated, and the VZn-NO-H complex is found to have a tendency to appearing in the stress raisers of the twin grain boundaries. The lowest formation energy under Zn-rich condition is only 0.52 eV for the complex in GB7a, a type of ∑7 twin grain boundary with anion-anion bonds, while the value is 3.25 eV for the complex in bulk ZnO. For the ionization energy, the complex in GB7a is more easily ionized, and has a value of 0.38 eV, compared with 0.67 eV in bulk ZnO. The result of density of states shows that the electron transition is dominated by the empty defect levels in forbidden band, which are occupied by O 2p and N 2p orbital. Further analysis indicates that the special structure of GB7a shortens the distances between NO and its neighbor O atoms, and the shortest N–O bond is only 2.38 Å, which also means a strong orbital hybridization between O and N. As a result, the energy level splitting is enhanced, and the empty energy level in the forbidden band is shifted down to valence band maximum. So, GB7a can favor the ionization in VZn-NO-H complex. Although GB7a is a special case of the twin grain boundaries, the result also gives us a new idea to understand the origin of p-type conductivity in N-doped ZnO.
Terminating spiral wave and spatiotemporal chaos in cardiac tissues by using late sodium current
Authors: Wang Xiao-Yan  , Wang Peng  , Li Qian-Yun  , Tang Guo-Ning  ,   College of Physical science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Most Na+ channels open transiently upon depolarization of cardiac cell membrane and then are quickly inactivated. However, some Na+ channels remain active, which generate the late sodium current during the action potential plateau. So far, late sodium current has been regarded as a relevant contributor to arrhythmias and its inhibition can suppress re-entrant and multifocal ventricular fibrillation so that its inhibition may become a novel therapeutic strategy to treat cardiac arrhythmias in the future. Therefore, how to inhibit late sodium current has received special attention. Since both the late sodium current and defibrillation shocks can lead to the increase of action potential duration, the late sodium current can be used to terminate ventricular fibrillation. However, the suppression of spiral wave and spatiotemporal chaos in cardiac tissues via late sodium current has been neglected. In this paper, we use the model of human heart to study the suppression of spiral wave and spatiotemporal chaos in two-dimensional cardiac tissue by generating late sodium current. We suggest that such a control strategy to induce late sodium current. The slow inactivation gate of sodium channel is clamped to 0.7 while the threshold voltage of corresponding fast inactivation gate is real-timely modulated. We first reduce the threshold voltage from 71.55 mV to 50.55 mV within the time interval T1, and then increase it from 50.55 mV to 71.55 mV within the time interval T2. When the threshold voltage returns to 71.55 mV, the changes of the relevant inactivation gates of sodium channel go back to normal dynamic state. Numerical simulation results show that when the control parameters are properly chosen, the control-induced late sodium current can effectively suppress spiral wave and spatiotemporal chaos even if there are some cardiac cells with spontaneous late sodium current. The advantage of the control scheme is that the control-induced late sodium current is small. The control duration is short because the spiral wave and spatiotemporal chaos disappear mainly due to the conduction obstacle. In a few cases, the spatiotemporal chaos disappears through the transition from spiral wave to target wave. We hope that these results may provide a new strategy to treat heart disease.
Super-resolution microscopic effect of microsphere based on the near-field optics
Authors: Zhou Rui  , Wu Meng-Xue  , Shen Fei  , Hong Ming-Hui  ,   School of Aerospace Engineering, Xiamen University, Xiamen 361005, China;,   Department of Electronics and Computer Engineering, National University of Singapore, Singapore 117576, Singapore
Published: December 2020

In the field of optical imaging, the conventional imaging resolution is about 200 nm due to the diffraction limit. The higher resolution is urgently needed for further developing scientific research. Therefore, how to break through this limitation to acquire high quality and high resolution image has become a hot research topic. The microspheres with the size of tens of micrometers exhibit the ability to improve the imaging resolution of the conventional optical microscope by locating them directly on the sample surface. Due to its simplicity, the microsphere optical nanoscope technology is widely studied. This paper introduces the research background of the optical microscope and the research progress of microsphere optical nanoscope technology. At the same time, approaches to adjusting the photonic nanojet generated by the microspheres by fabricating concentric ringing, central mask, and surface coating of microspheres are reviewed. The possible reasons for this improved resolution are discussed. The applications and development of the microsphere ultra-microscopic technology in the future are discussed.
Measurement and simulation of the hybrid structure gaseous detector gain
Authors: Zhang Yu-Lian  , Qi Hui-Rong  , Hu Bi-Tao  , Wen Zhi-Wen  , Wang Hai-Yun  , Ouyang Qun  , Chen Yuan-Bo  , Zhang Jian  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China;,   State Key Laboratory of Particle Detection and Electronics, Beijing 100049, China;,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

As one of the most popular micro pattern gaseous detectors, gas electron multiplier (GEM) has been extensively studied and applied in recent years. The studies of the detector gain measurement and simulation are important, especially on a low gain scale. Traditionally, the gain measurement is realized by measuring the current or the pulse height spectrum. The former needs complicated electronic chain calibration and the latter needs necessarily to calculate the primary electron number. In this paper, an alternative method to determine the effective gain of GEM is introduced. The GEM gain can be precisely achieved through a gaseous detector of hybrid structure which combines GEM with micro-mesh gaseous structure (MM). The hybrid structure is called GEM-MM for short. The GEM-MM detector consists of drift cathode, standard GEM foil, stainless steel micro mesh, and readout anode. In this detector, the space between the cathode and the GEM foil is called drift gap and the other space between the GEM foil and the mesh is named transfer gap. When the X-rays irradiate into the gas volume of GEM-MM, the primary ionization occurs in both regions. Photoelectrons in the drift gap transfer from the drift region to amplification sensitive areas of the GEM and the MM detector while those in the transfer region are only amplified by the MM detector. In the energy spectrum of 55Fe, there is a clear energy profile including two sets of peaks. The gain of GEM can be easily obtained from the energy spectrum. Meanwhile, detailed simulations are carried out with Garfield++ software package. Simulation of the electron transport parameters has been optimized. and the gains of GEM detector are also calculated for three different gas mixtures. Experimental results of the gains ranging from 3 to 24 are obtained. The gains of GEM under different working voltages are studied precisely from the spectrum measurements. The Penning transfer rate could reach 0.32±0.01 when the simulated value matches the measurement within 1σ error.