bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and research of magnetic tunable frequency selective surface based on dielectric and ferrite
Authors: Han Peng  , Wang Jun  , Wang Jia-Fu  , Ma Hua  , Shao Teng-Qiang  , Chen Hong-Ya  , Zhang Jie-Qiu  , Qu Shao-Bo  ,   College of Science, Air Force Engineering University, Xi'an 710051, China;,   Air Force Aviation University Flight Instructor Training Base, Bengbu 233000, China
Published: December 2020

In this paper, a method of designing tunable bandpass frequency selective surface via ceramics and ferrite material is proposed. The ferromagnetic resonance frequency can be tuned when magnetic field is applied. According to this property, the center-frequencies of the pass and stop band can be adjusted. The proposed model is composed of the ceramic part and ferrite part, and CST simulation under C band waveguide condition is employed in the research. For the ceramic part, five high-permittivity rectangular blocks are included. The aim is to achieve negative permittivity in broad band. The band-pass and band-stop properties of the frequency selective surface are clarfied based on the effective medium theory. The stop band originates from a similar Drude resonant electric monopole in the medium. The part of ferrite is composed of ten rectangular blocks. By adjusting the applied magnetic field, the ferromagnetic resonance and negative permeability are obtained at corresponding frequencies. Based on the double negative characteristics, the two parts are combined together to realize the pass band. For instance, when the magnetic field H0 is 1700 Oe, the ferromagnetic resonance appears at a frequency of 6.778 GHz. In this case, the center frequency of the pass band is at 6.758 GHz. By interacting with the electromagnetic wave, the electric resonance can take place in the ceramic blocks, and the ferromagnetic precession will appear in the ferrite blocks. The simulation results indicate that the pass band is switchable and tunable in a range of 6-8 GHz by changing the bias magnetic field. The distributions of electric and magnetic fields, and the parameters of perimittivity, permeability and impedance are obtained and discussed. Finally, the samples are fabricated and tested. The experimental results are basically consistent with the simulation results, indicating that the double negative passband can be adjusted via the applied magnetic field. This proposal provides a route to designing all-dielectric frequency selective surface and it can be used to design multi-band or tunable frequency selective surface.
Controlling spiral wave and spatiotemporal chaos in cardiac tissues by slowing sodium channel activation and inactivation
Authors: Pan Fei  , Wang Xiao-Yan  , Wang Peng  , Li Wei-Xin  , Tang Guo-Ning  ,   College of Physical science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Much evidence shows that the appearance and instability of the spiral wave in cardiac tissue can be linked to a kind of heart disease. Therefore there needs a method of controlling spiral wave more safely and effectively. The intelligent modification of specific ion channel to achieve desired control is the future direction of gene therapy in heart disease. The key question that has to be answered is which ion channel is the best candidate for controlling spiral wave. Modern biological technology has been able to make the mutation of sodium channel gene to change its relaxation time constant. In this paper, we adopt the Luo-Rudy phase I model to investigate how to regulate the relaxation time constant of sodium channel gate to control spiral wave and spatiotemporal chaos in cardiac tissues. We suggest a control strategy which slows down the rate of sodium current activation and inactivation by increasing the relaxation time constant of the sodium activation gate by up to times while its fast inactivation gate is clamped to 0.77. Numerical simulation results show that a gradual increase of will cause the activation gate of sodium current to reach maximum more slowly, and its amplitude is gradually reduced, so that the amplitude and duration of the action potential of cardiomyocyte are gradually reduced. When the factor is large enough, the spiral wave and spatiotemporal chaos cannot propagate in the medium except planar wave with low frequency. The reason is that the excitabilities of medium and wave speed significantly decrease. Therefore, the spiral waves and spatiotemporal chaos can be effectively eliminated when the control time is properly selected and the factor is large enough. Spiral wave and spatiotemporal chaos disappear mainly due to conduction obstacle. In some cases, spiral wave can disappear through the transition from spiral wave to target wave or tip retraction. Spatiotemporal chaos disappears after spatiotemporal chaos has evolved into meandering spiral wave. When the parameters are chosen properly, the phenomenon that spiral wave evolves into a self-sustained target wave is also observed. The corresponding target wave source is the pair of spiral waves with opposite rotation directions. These results can provide useful information for gene therapy in heart disease.
Research and analysis on lidar performance with intrinsic fluorescence biological aerosol measurements
Authors: Rao Zhi-Min  , Hua Deng-Xin  , He Ting-Yao  , Le Jing  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Biological aerosols which could cause diseases of human beings, animals and plants, are living particles suspended in the atmosphere. Ultraviolet laser induced fluorescence has been developed as a standard technique used to discriminate between biological and non-biological particles. As an effective tool of remote sensing, fluorescence lidar is capable of detecting concentration of biological aerosols with high spatial and temporal resolutions. Intrinsic fluorescence, one of the most important characteristics of biological aerosols, has quite a large effect on the performances of fluorescence lidar. To investigate the effects of intrinsic fluorescence on biological aerosols, we design an ultraviolet laser induced fluorescence lidar at an excited wavelength of 266 nm, with a repetition rate of 10 Hz. Fluorescence signals are collected by a Cassegrain telescope with a diameter of 254 mm, in which fluorescence spectra of 300-800 nm are mainly considered. A spectrograph and a multichannel photomultiplier tube (PMT) array detector are employed to achieve the fine separation and highefficiency detection of fluorescence signals. According to the present configuration, we perform a series of simulations to estimate the measurement range and the concentration resolution of biological aerosols, with a certain pulse energy. With a relative error less than 10%, theoretical analysis shows that designed fluorescence lidar is able to detect the biological aerosols within a range of 1.5 km at a concentration of 1000 particles·L-1. When the detection distance enlarges to 2.1 km, detectable wavelength range is limited to 300-310 nm. In addition, the lidar is capable of identifying minimum concentrations of biological aerosols with 2 particles·L-1 and 4 particles·L-1 at fluorescence wavelengths of 350 nm and 600 nm, respectively, where the induced pulse energy is set to be 60 mJ and detected range 0.1 km. With setting energies of 40 mJ and 20 mJ, minimum concentrations of biological aerosols decrease to 3 particles·L-1 and 6 particles·L-1, respectively, at a fluorescence wavelength of 350 nm. The relative error of minimum concentration resolution is about 2 particles·L-1, increasing rapidly with range. For a fluorescence wavelength of 600 nm, both the minimum concentration and the relative error show relatively high values, 5 particles·L-1 at 40 mJ and 10 particles·L-1 at 20 mJ, where the relative errors are found to be 2 particles·L-1 and 4 particles·L-1, respectively. The results prove that a shorter intrinsic fluorescence wavelength has a better effect on biological aerosol measurement. We believe that a proper intrinsic fluorescence wavelength will further improve the detection accuracy of biological aerosols.
Ultra-low-frequency vertical vibration isolator based on a two-stage beam structure
Authors: Wang Guan  , Hu Hua  , Wu Kang  , Li Gang  , Wang Li-Jun  ,   Department of Precision Instrument, Tsinghua University, Beijing 100084, China;State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China
Published: December 2020

High-performance vertical vibration isolators are required in precision instruments and physical experiments to reduce the seismic noise, which limits the instrument performance and measurement results. For example, inertial references are needed in interferometric gravitational wave detectors and absolute gravimeters, in order to separate the useful signal from noise. Microseisms typically occur at around 0.07 Hz. The secondary microseisms occur at about 0.14 Hz. Buildings usually wobble at frequencies between 0.1 and 1 Hz. To reduce all these vibrations would require a spring-mass system with a resonance frequency lower than 0.05 Hz. The most commonly applied techniques use a passive vertical isolation system, which is easy to set up and cheap to build. However, to achieve low cut-off frequency, such as 0.05 Hz, there requires longer than 100 m static deflection for a simple passive isolator, which is impractical in most applications. An ultra-low-frequency active vertical vibration isolator, based on a two-stage beam structure, is proposed and demonstrated in this paper. Two beams are connected to a frame with flexural pivots. The upper beam is suspended from the frame with a normal hex spring. The lower beam is suspended from the upper one by a zero-length spring. The flexural pivots of the upper beam are not vertically placed above the pivots of the lower beam. With this special design, the attachment points of the zero-length spring to the beams can be moved to change the effective stiffness. A laser reflectometry is used to detect the angle between the two beams. A laser collimator, a mirror, a beam splitter and an optical detector are fixed to the upper beam, and another mirror is fixed to the lower beam. A laser beam from the collimator is directed to the detector via the mirrors and the beam splitter. The output of the detector is proportional to the angle between the two beams. The minimum detectable angle is 36 nrad. The angle signal is sent to a circuit to generate a control signal, which drives a voice coil mounted between the lower beam and the frame to maintain the angle between the two beams to a fixed value. The isolation system can achieve a natural period of 100 s by carefully adjusting the attachment points of the zero-length spring and the feedback parameters. This type of isolator has a simpler and more robust structure than the famous active vibration isolator-the super spring. The system is promising in applications such as precision instruments and experiments, especially in absolute gravimeters.
Time reversal multi-target imaging technique based on eliminating the diffusion of the time reversal field
Authors: Zang Rui  , Wang Bing-Zhong  , Ding Shuai  , Gong Zhi-Shuang  ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Time reversal technique has the adaptive time-space focusing characteristics, which has been widely used in communication systems, imaging systems, and power combining systems. However, the ideal time reversal processing cannot be implemented in an actual imaging system and some diffusion phenomenon has been observed. In this paper, the diffusion phenomenon of the time reversal field in an imaging system is analyzed based on the time reversal cavity theory. Since the corresponding absorption source cannot be set in an imaging process, the time reversal field will continue to disperse after the convergence. Therefore, the field produced by the time reversal cavity will be similar to the sinc-function near the source. The diffusion field will result in mutual interference between the imaging targets. In a traditional time reversal multi-target imaging system, weaker targets can easily be concealed and artifacts may occur. In this paper, a multi-target imaging technique based on the elimination of the time reversal field diffusion is proposed. In order to eliminate the effect of the diffusion field, the Clean algorithm is used. The Clean algorithm is a de-convolution algorithm, which can effectively suppress the side lobe signal. By using the Clean algorithm in the time reversal imaging system, the interaction between multi-targets can be eliminated. Full-wave simulation shows a good performance of the proposed method. In practice, the time reversal mirrors are used to replace the time reversal cavity, for the fully closed time reversal cavity cannot be implemented. The effects of the time reversal mirrors have also been analyzed in this paper. The result shows that the positions of the time reversal mirrors have an significant influence on the reversed field distribution, which affects the Clean algorithm and the proposed imaging method. In order to eliminate the influence of time-reversal mirror position, an effective time reversal signal equalization algorithm is proposed. In the equalization algorithm, the amplitude of the time reversal signal in the time reversal mirrors is adjusted according to both the distance and the intensity. The proposed equalization algorithm can keep the time reversal field stable and provide effective support for the imaging method.
A new scheme of spectral dispersion smoothing based on hybrid grating
Authors: Wang Jian  , Hou Peng-Cheng  , Zhang Bin  ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China
Published: December 2020

The irradiance uniformity on target plane is a key issue in laser-driven inertial confinement facilities. In the typical schemes of one-dimensional smoothing by spectral dispersion (1D-SSD) and the “star” grating, the stripe pattern inside the focal spot appears inevitably, besides, the fabrication of the “star” grating is relatively difficult. Thus, a new spectral dispersion smoothing scheme based on a hybrid grating is proposed, which not only achieves the better smoothing effect, but also exhibits some specific advantages in the fabrication and the dispersion way. According to the different direction of the spectral dispersion, the hybrid grating is divided into inner and outer dispersion areas. That is, the dispersion direction of the inter dispersion area is in the horizontal or vertical direction, and the dispersion direction of the outer dispersion area is in the azimuthal direction. When the laser beam with the temporal phase modulation propagates through the hybrid grating, the dispersion directions of the laser beam in the inner and the outer dispersion areas are different, leading to the redistribution of the speckles inside the focal spot in the resultant direction of the translation and rotation on the target plane. Consequently, the focal spot on the target plane achieves the beam smoothing in radial and horizontal or vertical direction. In the present paper, the theoretical model of the hybrid grating scheme based on the spectral dispersion smoothing is built up. Using the theoretical model, the smoothing effect of the hybrid grating scheme is analyzed, and compared with those of the typical schemes of 1D-SSD and the “star” grating. The contrast and the fractional power above the intensity (FOPAI) are used to evaluate the smoothing characteristic of the focal spot. In addition, the influences of the area ratio and groove density in the different dispersion areas of the hybrid grating on beam-smoothing effect are also discussed. Results indicate that when the inner dispersion area accounts for the 0.3-0.5 of the total dispersion area, the hybrid grating scheme can effectively suppress the stripe intensity modulation both in the radial direction and the vertical direction. With increasing the groove densities of the inner and the outer dispersion area in a certain range, the irradiance uniformity of the focal spot is further improved. However, considering the actual processing of the hybrid grating, the appropriate groove density should be selected. Compared with the typical scheme of the 1D-SSD, the scheme of the hybrid grating can achieve the better smoothing effect with the multi-direction spectral dispersion smoothing. Furthermore, the fabrication of the hybrid grating is relatively simple and the irradiation uniformity on the target plane is also good compared with those of the “star” grating scheme.
Experimental study of diode-pumped Nd, Y:CaF2 amplifier for inertial confinement fusion laser driver
Authors: Tang Xiong-Xin  , Qiu Ji-Si  , Fan Zhong-Wei  , Wang Hao-Cheng  , Liu Yue-Liang  , Liu Hao  , Su Liang-Bi  ,   Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   National Engineering Research Center for DPSSL, Beijing 100094, China;,   Zhongkeheguang Applied Laser Technology Institute Company, Ltd. Tianjin 300304, China;,   Synthetic Single Crystal Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China;,   Key Laboratory of Transparent and Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China
Published: December 2020

In a conventional laser-driven inertial confinement fusion (ICF), Nd-doped phosphate glass is used as a gain medium. However, the repetition frequency operation of such a laser system is restricted by the low thermal conductivity of the phosphate glass. To attain a high ICF performance, the laser driver must be able to operate at a repetition frequency of no less than 10 Hz. Typically, an Nd-doped laser glass operates at a repetition frequency well below 10 Hz. In this paper, an Nd, Y:CaF2 crystal is taken as a gain medium for the laser amplifier, and experiments are carried out to demonstrate the capability of Nd, Y:CaF2 crystal to act as a gain medium for ICF laser driver. A laser-diode plane-array five-direction horizontal-side-pumped Nd, Y:CaF2 laser amplifier 5 mm70 mm is developed and an experimental study is carried out. The absorption spectrum and emission spectrum of Nd, Y:CaF2 crystal and the fluorescence distribution of the amplifier are measured. The Nd:CaF2 co-doped with Y3+ ions results in a broad absorption band, which makes the laser diode pumping more efficient. The strongest excitation band peak is centered around 796 nm. The small signal gains of Nd, Y:CaF2 and Nd:Glass working respectively at repetition frequencies of 10 and 1 Hz under the same pump power are measured. The small signal gain of Nd, Y:CaF2 amplifier reaches 6.12 under a pump power of 9.63 kW, which is 1.5 times that of Nd:Glass amplifier. The measurements of the spectrum of the seed beam and the spectrum from Nd, Y:CaF2 amplifier show that the signals have no change before and after being amplified. Most likely the Nd, Y:CaF2 crystal is a promising laser material for repetitive ICF laser drivers.
First-principles studies of multiple trapped impurity C by Ni vacancy and temperature effects in NiAl intermetallics
Authors: Hu Xue-Lan  , Luo Yang  , Zhao Ruo-Xi  , Hu Yan-Min  , Song Qing-Gong  ,   Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin 300300, China;,   College of Science, Civil Aviation University of China, Tianjin 300300, China
Published: December 2020

By using a first-principles pseudopotential method based on the density functional theory and Vienna ab initio Simulation Package (VASP), we investigate the multiple trapping of C by Ni vacancy (VNi) and its temperature effects in NiAl intermetallics. A single C atom is energetically and favorably situated at the Ni-rich octahedron interstitial site that surrounds Ni vacancy, which is shown via calculating the formation energy of C atom in NiAl with Ni vacancy system. Single C atom prefers to interact with neighboring Ni atom and Al atom to form a covalent bond. In NiAl intermetallics, C atoms prefer to be trapped in the Ni vacancy in the sequential way, thus easily forming the CnVNi (n=1, 2, 3, 4) clusters, in which the C4VNi clusters are most energetically favorable. It is interesting to find that when C atoms are trapped by Ni vacancy, all the C atoms themselves prefer to be combined with each other to form a bond, surrounding Ni vacancy. With the C atoms further added, both the charge density and the deformation charge prefer to bind with each other despite the Ni or Al environment and the intrinsic bonding properties of CC bond contain obvious covalent characteristics. Furthermore, using first-principles calculations combined with statistical model, we quantitatively predict point defect concentration as a function of temperature in NiAl intermetallics. It is concluded that the concentration of intrinsic Ni vacancies (VNi) will obviously increase as temperature increases. With the increase of temperature, the concentration of C atoms in the CnVNi cluster is higher than that at the intrinsic position. Besides, it indicates that most of C atoms in NiAl intermetallics are trapped by Ni vacancy, which is due to the larger binding energy of the CnVNi clusters and most of the C atoms are trapped directly by vacancies at room temperature or high temperature to form CnVNi clusters. Since the formation of CnVNi clusters is a process of heat releasing which will further increase the temperature of the NiAl system and produce more and more Ni vacancies, we can conclude that much more vacancies are created as a result of the presence of C impurity in NiAl intermetallics. However, the Ni vacancies exist in the form of CnVNi clusters from our calculation in a certain temperature range (less than 700 K). The existence of this kind of CnVNi cluster can effectively restrain the generations of cracks in the vacancies, which will produce some influences on the mechanical properties of NiAl intermetallic compound. Consequently, our results will provide a valuable reference for understanding the effects of C and vacancy on the mechanical properties of the NiAl intermetallics.
Research on an pump-probe rubidium magnetometer
Authors: Wang Zhi-Guo  , Luo Hui  , Fan Zhen-Fang  , Xie Yuan-Ping  ,   College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China;,   Interdisciplinary Center of Quantum Information, National University of Defense Technology, Changsha 410073, China;,   College of Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In order to measure a weak alternating magnetic field, an optically-pumped Rb magnetometer based on pump-probe structure is investigated and demonstrated. The pumping light and probing light propagate along the z axis and x axis, respectively. A constant polarization magnetic field along the pumping light is applied, which not only stabilizes the polarization of Rb atoms but also tunes resonance frequency of Rb atoms. When a weak alternating magnetic field is applied perpendicularly to the constant magnetic field, the magnetic moment will tip off the z axis and rotate around the z axis. And then the polarization plane of probing light is modulated correspondingly. The x component of the magnetic moment can be obtained with a balanced detector. As a result, a signal proportional to weak alternating magnetic field can be obtained.In order to obtain the magnetic response of the magnetometer, we analyze the signal amplitude as a function of polarization magnetic field strength B0 and transverse relaxation time 2 with numerical simulation. The amplitude-frequency response of the magnetometer is determined mainly by two parameters, namely cutoff frequency c=1/2 and resonance frequency 0= B0, where is the gyromagnetic ratio of Rb atom. At low frequency, that is a0 and a 0c2, the magnetometer has a flat response, here a is the frequency of the weak alternating magnetic field. If 0c, the signal amplitude will be large for large 0 or small c. For a given c, the peak response appears at 0=c. In the vicinity of resonance frequency, if c0, a peak will appear and if c 0, no peak occurs. At high frequency, the amplitude will decrease with the increase of a.We verify the above analyses in experiment. A vapor cell with a short transverse relaxation time is used to obtain large frequency response bandwidth. Through optimizing the powers and frequencies of pumping laser and probing laser, high polarization and detection sensitivity of atomic spin can be obtained. Moreover, through choosing an appropriate polarization magnetic field, the magnetometer can be maximally sensitive to the magnetic field to be measured. The experimental results show that the magnetometer has a sensitivity of about m 0.2; pT/HzHz and bandwidth of about 3.5 kHz. It can be used to detect low field magnetic resonance and high frequency abnormal physical phenomena.
Experimental investigations on the dynamical characteristics of pulse packages in a monolithically integrated amplified feedback laser
Authors: Chen Xi  , Zhao Ling-Juan  , Chen Jian-Jun  , Wang Hui-Ping  , Wu Zheng-Mao  , Lu Dan  , Xia Guang-Qiong  ,   School of Physical Science and Technology Southwest University, Chongqing 400715, China;,   Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083, China;,   School of Medical Engineering Technology, Xinjiang Medical University, Urumqi 830011, China
Published: December 2020

Under suitable external perturbation such as optical feedback, optical injection or optoelectronic feedback, semiconductor lasers can be driven to realize diverse dynamic outputs including period-one, period-two, multi-period, pulse packages（PPs), chaos, etc., which have potential applications in optical secure communications, microwave photonics, lidar, high speed random signal generation, etc.. For the PPs dynamics, most of previous relevant investigations are usually based on a system composed of discrete elements. In this work, we experimentally investigate the PP dynamical characteristics in a three-section monolithically integrated amplified feedback laser（AFL) composed of a distributed feedback（DFB) laser section, a phase（P) section, and an amplified feedback（A) section. For the AFL, the sections P and A act as a compounded feedback cavity in which the feedback phase and strength can be varied by adjusting the current in section P（IP) and the current in section A（IA), respectively. Via the power spectrum and self-correlation function curve of the time series output from the AFL, the influences of IP and IA on repeated frequency（PP) and regularity of PPs are analyzed in detail. The results indicate that, for the section DFB, whose current（IDFB) is biased at a relatively large level, the AFL can realize two-mode oscillation. After further choosing appropriate IP and IA, the AFL can behave as the dynamical state of PPs. Under IDFB=86.15 mA and IP=96.00 mA, through varying IA in a range of 6.50-10.50 mA, there exist two separated regions for IA to make the AFL operate at PPs. For the region with relatively small value of IA, both PP and the secondary maximum（) of self-correlation curve characterizing the regularity of PPs monotonically decrease with the increase of IA. However, for the region with relatively large value of IA, with the increase of IA, PP first decreases and then fluctuates in a tiny range, but first increases, and further reaches an extreme value, and then decreases. Under IDFB=86.15 mA and IA=9.00 mA, the output characteristics of PPs are significantly affected by IP. With IP increasing from 90.5 mA to 96.5 mA, PP first decreases, and then increases after reaching a minimal value, meanwhile shows an approximately opposite variation trend. Finally, for IDFB=86.15 mA, the mapping of PPs in the parameter space of IP and IA is given and the evolution regularities of PPs are also presented.
Characteristics of surface waves on the granular sheet of dense granular jet impingement
Authors: Qian Wen-Wei  , Li Wei-Feng  , Shi Zhe-Hang  , Liu Hai-Feng  , Wang Fu-Chen  ,   Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, Shanghai Engineering Research Center of Coal Gasification, East China University of Science and Technology, Shanghai 200237, China
Published: December 2020

Dense granular jet impingement widely exists in numerous natural flow phenomena and industrial processes. It is significant to investigate the influencing factors of the flow patterns of dense granular jet impingement and reveal the evolution rules of flow patterns. The dynamic behaviors of dense granular jets impinging on a flat target are experimentally studied by a high-speed camera and image processing software of NIH. The effects of the particle diameter（Dpar), the granular jet velocity（U0) and the solid content of the granular jet（X) on the flow patterns and surface waves of granular sheet are investigated. Two patterns, i.e., the liquid-like granular film and the scattering pattern are identified from the dense granular jet impingement. The results show that with the increase of the particle diameter, the solid content of the granular jet reduces, and the interparticle collision frequency decreases, which results in the granular sheet evolving into the scattering pattern. The opening angle of the granular sheet（) is bigger than that of the liquid sheet, and the granular jet velocity plays an insignificant role in the opening angle. The interesting behaviors of liquid-like surface waves are identified in the granular sheet. The frequency of surface wave of the granular sheet（f) is an order of magnitude smaller than that of the liquid sheet. The surface wave length（) increases and frequency decreases with the increase of radial position, as the surface waves merge during the granular sheet spreading radially. The surface wave spreading velocity normalized by the granular jet velocity is a constant of about 0.4. With the increase of the granular jet velocity, the pulsation of granular jet occurs due to the pressure fluctuation in the discharge process under the effect of gas-solid interaction. The frequencies of surface waves of both the granular sheet and the granular jet pulsation become the same generally. It is indicated that the surface wave is primarily caused by the granular jet pulsation. The results in this paper present the knowledge of the dense granular jet impingement and provide some principles for the steady operation of dense granular jet impingement in industrial process.
Effects of surface regulation on monolayers SbAs and BiSb
Authors: Yuan Jun-Hui  , Xie Qing-Xing  , Yu Nian-Nian  , Wang Jia-Fu  ,   School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: December 2020

Using the first principle calculation based on the density functional theory, we systematically investigate the stabilities and the structural and electronic structures of fully hydrogenated and fully fluorinated SbAs and BiSb. The results show that the SbAs and BiSb transform the buckled structure into quasi-planar structure after being fully hydrogenated or low-buckled structure after being fully fluorinated. Stability studies show that both the SbAs and BiSb structures（intrinsic, full hydrogenated, and fully fluorinated) are highly stable, and thus likely to be obtained in experiment. The electronic structure study shows that both SbAs and BiSb turn from wide band gap semiconductors into narrow direct-gap semiconductors after being fully hydrogenated and fully fluorinated, meanwhile the band structures still have good linear dispersion. Based on further analyses of the electronic structures of quasi-planar or low-buckled SbAs and BiSb, the reasons for the changes of band structures are revealed. Calculations show that the fX-SbAs（X=H, F) films on h-BN substrate can maintain the direct band gap characteristics because of the weak coupling between them, indicating that they may have great applications in the field of optoelectronic devices in the future.
Local energy of magnetic vortex core reversal
Authors: Lü Gang  , Cao Xue-Cheng  , Zhang Hong  , Qin Yu-Feng  , Wang Lin-Hui  , Li Gui-Hua  , Gao Feng  , Sun Feng-Wei  ,   Information Science and Engineering School, Shandong Agricultural University, Tai'an 271018, China
Published: December 2020

The polarity of magnetic vortex core can be switched by current or magnetic field through a vortex-antivortex pair creation and annihilation process, in which the significant change of the exchange energy during the switching takes an important role. To further unveil the energetic origin of magnetic vortex switching, we investigate the evolution of the maximum exchange energy density of the sample by using micromagnetic finite-element simulations based on the Landau-Lifshitz-Gilbert equation including the adiabatic and the nonadiabatic spin torque terms. Our micromagnetic calculations indicate that maximum exchange energy density for the considered sample must exceed a critical value of ~3.0106 J/m3 in order to achieve the magnetic vortex switching. The threshold value corresponds to the maximum exchange energy density at the time of creation of new vortex-antivortex pair. Following the nucleation of antivortex, the maximum exchange energy density increases rapidly with the antivortex approaching the original vortex. The maximum exchange energy density can become large at the time of annihilation of two vortexes. To explain well the critical value of the local maximum exchange energy density, we use the rigid vortex model（in which the spin distribution is unchangeable while vortex is displaced) to develop an analytical model. For a magnetic vortex confined in a thin ferromagnetic nanodisk, the magnetization distribution is unchanged along the thickness and can be seen as a two-dimensional model when the thickness is less than or on the order of the exchange length. The components of vortex magnetization vector in a ferromagnetic dot can be expressed by using a complex function w(,). Corresponding to the trivortex state appearing in vortex core reversal process, the local exchange energy density Wex around the vortexes cores is obtained. Simultaneously, we obtain the maximum exchange energy density:Wex2.3106 J/m3. In a realistic system, the shape of vortexes will deform during the vortex core reversal, which leads to the analytical result lower than the simulation value. Based on this reason, the analytical result matches well with our simulation value.
Optimization of magnetic resonance imaging high-order axial shim coils using boundary element method
Authors: Hu Yang  , Wang Qiu-Liang  , Li Yi  , Zhu Xu-Chen  , Niu Chao-Qun  ,   Key Laboratory of Applied Superconductivity, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In this paper, we present a novel nonlinear optimization algorithm for designing a shim coil system, especially a high-order axial shim coil, for a magnetic resonance imaging（MRI) system. In an MRI equipment, in order to eliminate higher-order harmonic components of the magnetic field within the volume of interest（VOI), passive shimming（PS) is adopted in traditional methods. However, such a method is suitable for the global shimming with low accuracy and poor target. Active shimming（AS) makes up for the shortcomings from PS with a set of shim coils which are designed to generate a specific magnetic fields to improve magnetic field homogeneity within the VOI. Because the complexity of wire pattern increases with the order of AS coil increasing, conventional optimization model cannot meet the design requirements for producing the complicated magnetic field. In this paper, we propose a nonlinear optimization method of designing the axial shim coils for an open-style bi-planar MRI system, based on boundary element method. The optimization model is built in light of influence extents of the various parameters on the coil characteristics for different shim coils. In such a new method, the field error between the magnetic field produced by designed shim coil and the desired target value is selected to be an optimal value subjected to some constraints including line spacing and coil radius, which makes it possible to realize the manufacture process. Meanwhile, the more design parameters, which involve not only the stream function values at each node, but also the compensation parameters and/or the number of grid nodes, are regarded as optimized variables to control the magnetic deviation and characteristics of designed coil. By using some designed shim coils for a 0.5 T open style bi-planar superconducting MRI, including Z1, Z2, Z3 and Z4, the efficiency of such a numerical design method is displayed. Especially for high-order shim coils, more optimized parameters are involved to control the magnetic deviation of the coils, thereby providing a more flexible and straightforward method of designing the axial shim coils.
Combination of magnetic tweezers with DNA hairpin as a potential approach to the study of RecA-mediated homologous recombination
Authors: Zhang Yu-Wei  , Yan Yan  , Nong Da-Guan  , Xu Chun-Hua  , Li Ming  ,   Key Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Department of Physics, Emory University, Atlanta GA 30322, USA
Published: December 2020

Homologous recombination（HR) is essential for maintaining the genome fidelity and generating genetic diversity. As a prototypical member of the recombinases, RecA from Escherichia coli has been extensively studied by using single-molecule FRET（smFRET), magnetic tweezers, optical tweezers, etc. However, these methods cannot meet the needs of wide-ranged observations nor high spatial resolution at the same time. For sequence comparison, the average base-to-base distance of the homologous dsDNA will be stretched from 0.34 nm to 0.51 nm. The increment for per base pair is 0.17 nm, which is far beyond the spatial resolution of magnetic tweezers so that it cannot be directly measured. As a high-resolution technique, the smFRET enables us to observe more details of reactions. However, its valid measuring distance is 3-8 nm, which limits the observation range. Here, we propose an approach by combining magnetic tweezers with DNA hairpin, which may solve the problem effectively in the study of HR. In this paper, one end of the DNA molecule with a 270 bp hairpin is immobilized onto the surface of the flow cell, while a magnetic bead is attached to the other end. An external magnetic force is applied to the magnetic bead by placing a permanent magnet above the flow cell. The first 90 bp（from the junction of the hairpin) of the hairpin is homologous to the ssDNA within the ssDNA-RecA filament. Thus, the filament searches for homology along the hairpin, and incorporates into the homologous segment for strand exchange. After that, the displaced strand can be opened by pulling at a force of ~7 pN, and each opened base pair results in a 0.82 nm increase in DNA extension. By using this approach, we show that 1) RecA-mediated strand exchange proceeds in a stepwise manner and the average speed is ~7.6 nt/s, which is in accordance with previous result; 2) the dynamic interaction between the second DNA-binding site（SBS) and the displaced strand can be observed in real-time, and the binding force is calculated accurately through the x-dimensional fluctuations; 3) the processes of strand-exchange in different directions can be observed, and the directions are distinguishable through the reaction patterns. The results suggest that the combination of magnetic tweezers with DNA hairpin is a potential approach to the study of RecA or other recombinases. Therefore, our design can be an important single-molecule approach to the research of HR mechanism.
Two differet self-propulsion types of Janus microspheres: from the comparative experiments and driving mechanisms
Authors: Wang Lei-Lei  , Cui Hai-Hang  , Zhang Jing  , Zheng Xu  , Wang Lei  , Chen Li  ,   School of Environment and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China;,   State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, CAS, Beijing 100190, China
Published: December 2020

A Janus particle is a general term for a non-uniform particle that has different properties on different sides of particle. For a Pt-SiO2 type of Janus microsphere, Pt side serves as the catalysis surface to decompose H2O2 solution, leading to the self-propulsion motion of particle. In this paper, the relevant experimental phenomena in two driven modes are compared first. The results show that under the same concentration of solution, the microsphere with a diameter of about 1 m experiences self-diffusiophoresis propulsion; whereas, the one with an about 20 m diameter experiences bubble self-propulsion. Significant differences in motional trajectory and propulsion velocity are found between them. Then, the dominated physical factors are analyzed and the multi-field coupling numerical model is constructed based on the simplified force balance analysis. Subsequently, the velocity field distribution and O2 concentration distribution around Janus microsphere are also studied. According to these studies, we explain the position and size of the bubble generated. Further more, we infer that the wall slip coefficient is a key matching parameter in the numerical model, and two slip coefficients with a difference of an order of magnitude are given corresponding to the two types of self-propulsion modes. Then we explain the possible mechanism for the changes of wall slip coefficient under different particle sizes. The present study is beneficial to the in-depth exploration of the self-propulsion mechanism and also provides the theoretical foundation for improving the performance of self-propellant device.
New formula for calculating the fidelity of teleportation and its applications
Authors: Jia Fang  , Liu Cun-Jin  , Hu Yin-Quan  , Fan Hong-Yi  ,   Department of Material Science and Engineering, University of Science and Technology of China, Hefei 230026, China;,   Key Laboratory of Optoelectronic and Telecommunication, Jiangxi Normal University, Nanchang 330022, China;,   Center for Quantum Science and Technology, Jiangxi Normal University, Nanchang 330022, China
Published: December 2020

Quantum teleportation plays an important role in quantum information science. In order to obtain the effect of quantum teleportation of a quantum state by using an entangled resource, the fidelity of teleporting the quantum state should be calculated. Braunstein and Kimble[Phys. Rev. Lett. 80 869 (1998)] derived a formula of calculating the fidelity of quantum teleportation for Gaussian entangled resource and any input state to be teleported. Then, the point is how to calculate the quantum teleportation fidelity for any entangled resource. In this paper, werealize this purpose by using the entangled state representation. First, we derive the Weyl expansion of any density operator by using the completeness relation between coherent state and P-representation. Then using the orthogonal property of entangled state representation and the traditional Kimble-Braunstein scheme of quantum teleportation, we further derive the mean density operator of the output state, which means that we establish the relation between the output density operator and the characteristic functions of the input state to be teleported and the entangled resources. The characteristic function of the output state is also derived which is in the concise form relating these two characteristic functions above. Then we further obtain a new formula for calculating the quantum teleportation fidelity for the coherent state input and any two-mode entangled resource. It is shown that the fidelity of teleportation can be easily calculated when the Q-function of the normally ordering form of entangled resource is known. This is a convenient way of obtaining the fidelity of teleportation. As its applications, some Gaussian and non-Gaussian entangled states are examined to teleport the coherent state, whose results are correct.
Stochastic resonance based on frequency information exchange
Authors: Liu Jin-Jun  , Leng Yong-Gang  , Lai Zhi-Hui  , Tan Dan  ,   School of Mechanical Engineering, Tianjin University, Tianjin 300350, China;,   School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China
Published: December 2020

In the past few decades, stochastic resonance (SR) has attracted considerable attention of researchers due to a curious phenomenon appearing in a nonlinear system:an input weak periodic signal can be amplified and optimized by the assistance of noise. It has been proved that the classical stochastic resonance (CSR) has the adiabatic limit, so the performance of CSR in high-frequency signal detection is restricted in practical engineering. To break the restriction, a number of methods have been suggested, such as re-scaling frequency stochastic resonance (RFSR), parameters normalized stochastic resonance, modulated stochastic resonance, etc. Although the high-frequency signal can be detected by the above methods in specific conditions, there are some problems that restrict their applications in different circumstances. In this paper, a new method, stochastic resonance based on frequency-information exchange (FIESR), is developed to deal with the adiabatic limit of CSR. The mechanism of FIESR is analyzed in detail by the theory of single-side band modulation (SSB) which is based on phase shift. The information in small-parameter frequency domain is swapped with the information of the high-frequency target signal. Then the amplitude and phase of the target signal are moved to the small-parameter frequency domain. Consequently the target signal can be enhanced and detected by CSR in small-parameter frequency domain. Besides, a necessary plan, narrow band spectrum exchange, is put forward to diminish the influence of the spectrum leakage of FIESR. It is well known that the RFSR is a method of detecting the practical signal with large-parameter frequency. Through rescaling the time interval of the signal and compressing its frequency according to the scale R, the large-parameter frequency is compressed into a small-parameter frequency. The RFSR has a good performance in mechanical incipient fault diagnosis. However, it has a high sampling ratio limitation. The ratio of sampling frequency to target signal frequency is more than 50. To overcome this weakness of RFSR, frequency-information exchange (FIE) is introduced into RFSR. A new signal detection method based on FIE and RFSR, named F-RFSR, is put forward simultaneously. The flow of F-RFSR consists of three steps. Firstly, the frequency of the original input signal is compressed linearly according to the estimated scale. Then, the frequency information is exchanged between the compressed target signal and the small-parameter signal in the frequency domain. Finally, the CSR is used to amplify and detect the weak target signal processed by re-scaling frequency and FIE. Performance analysis of signal detection and numerical simulation are carried out to demonstrate that F-RFSR has more efficient sampling ratio than RFSR for practical application.