bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiphoton ionization and dissociation dynamics of Freon-113 induced by femtosecond laser pulse
Authors: Liu Yu-Zhu  , Chen Yun-Yun  , Zheng Gai-Ge  , Jin Feng  , Gregor Knopp  ,   School of Physics and Opto-electronics Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology (CICAEET), Nanjing 210044, China;,   C. Eugene Benett Department of Chemistry, West Virginia University, Morgantown WV 26506, USA;,   Paul Scherrer Institute, Villigen 5232, Switzerland
Published: December 2020

The ozone layer which absorbs harmful solar UV radiation is an essential umbrella for human. However, a large number of exhausts of Freon released by human activity into the atmosphere pose a great threat to the ozone layer. The UV sunlight radiation induced Freon dissociation produces chlorine radicals, which are found to be the main culprit for destroying the atmospheric ozone. In this paper, multiphoton ionization and dissociation dynamics of Freon-113 (CF2ClCFCl2) induced by femtosecond laser pulse are studied by time-of-flight mass spectrometry coupled with velocity map imaging technique. Fragment mass spectra of Freon-113 are measured by time-of-flight mass spectrometry. No parent ions are discovered in the time-of-flight mass spectra, and all the detected ions are from the fragmentation induced by the laser pulse. Daughter ions CFCl2+, CF2Cl+, C2F3Cl2+ are found to be the three major fragmentation ions in the multi-photon ionization and dissociation. Several photodissociation channels are discussed and concluded by further analysis and calibration (via the ratio of mass to charge) of the measured time-of-flight mass spectra. Three main photodissociation mechanisms are found as follows: 1) C2F3Cl3+→C2F3Cl2++Cl with breaking C--Cl bond and directly producing the Cl radical; 2) C2F3Cl3+ →CFCl2++CF2Cl with breaking the C--C; 3) C2F3Cl3+ →CF2Cl++CFCl2 with breaking the C--C bond. Ion images of the three main fragments C2F3Cl2+, CFCl2+ and CF2Cl+ are measured by the velocity map imaging setup. The speed distributions of these three fragment ions are obtained from the velocity map imaging. The speed distribution of C2F3Cl2+ with breaking C--Cl bond can be fitted by two Gaussian distributions while the speed distributions of both CFCl2+ and CF2Cl+ with breaking the C--C bond can be well fitted by one Gaussian distribution. The different fittings reflect different production channels. The detailed photodissociation dynamics is obtained by analyzing the kinetic energy distribution and angular distribution of the fragment ions. Additionally, density functional theory calculations on high-precision level are also performed on photodissociation dynamics for further analysis and discussion. An in-depth understanding of dissociation dynamics of freon can provide theoretical reference and experimental basis for further controlling the dissociation process that can do destruction to the ozone layer.
Total internal reflection orders in transmission grating
Authors: Wu Rong  , Tian Yu-Ting  , Zhao Dong-Feng  , Li Da-Wei  , Hua Neng  , Shao Ping  ,   National Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In a current high-power laser system, transmission grating has been used to sample, separate and focus laser beam. Under high power laser irradiation, besides the 0-order shooting beam and target sampling beam, the detrimental influence of other diffraction orders should be taken into consideration seriously. These useless orders may damage other nearby optical elements and mechanical devices, disturb and confuse the measurement of time pulse and near/far-field intensity. Especially the total internal diffraction order will lead to some series diffraction patterns, causing the above problems. First, relevant theoretical calculation and analysis are carried out for transmission grating (including beam sample grating and focusing grating), which can predict and indicate these inconspicuous diffraction orders. These orders appear on four receiving screens regularly and periodically, and the periodic distance between them is determined by ray-tracing draft. Second, the phenomenon of total internal reflection order is observed and measured by combining with anti-reflection film. The measured periodic spacings on three screens are 24 mm, 26 mm and 35 mm, respectively. Moreover, energy intensities of these redundant orders are measured finely, which shows that their contrasts or SNRs to 0-order main laser is in a range of 10-8-10-4). Finally, some appropriate and effective approaches to eliminating or avoiding total internal reflection and other useless orders are proposed and discussed, which include 1) coating by anti-reflection film with pre-deep etching; 2) optimizing the grating design to make redundant orders far from target spot; 3) placing laser scattering or absorbing devices at corresponding position to avoid being damaged by the side-leakage energy and ghost image of total internal reflection and other redundant orders.
The analytic expressions of temperature and stress in directly liquid cooled thin slab laser
Authors: Li Ce  , Feng Guo-Ying  , Yang Huo-Mu  ,   College of Electronics & Information Engineering, Sichuan University, Chengdu 610065, China
Published: December 2020

In this paper, based on the convective heat transfer and conduction principle, the thermal effect analysis model of the directly liquid cooled uniformly pumped thin slab laser is established. The approximate plane stress and the principle of minimum are introduced to describe thermal stress distribution in the thin slab. Firstly, the relationships between the flow velocities in different flow channel thickness values and the convection heat transfer coefficients and also the relationship between flow velocity and coolant temperature rise are studied. Moreover, the influences of different flow channel thickness values on temperature field and thermal stress distribution are analyzed. Finally, the variation trends of wave-front phase distortion with the change of heat power in the case of Zig-zag path and direct path are investigated, respectively. The results reveal that thicker flow channel can achieve stronger heat treatment effects in an appropriate range of the cooled liquid flow rate, and the thermal profile is symmetrical with respect to the center plane of slab. In addition, the longitudinal maximum temperature rise occurs in the outlet; the maximum stress distortions centralize on the both ends and partial sides of slab. It is worthy to mention that the one-dimensional temperature gradient and smaller stress form more probably for thicker flow channel., Furthermore, zig-zag path can alleviate obviously wave-front aberration due to thermo-optic effect. In this paper the thermal effect of the liquid direct cooled thin slab laser is investigated. The research results are beneficial to the design and optimization of the directly liquid cooled thin slab laser.
Experimental study of the communication performance of electromagnetic wave in time-varying and magnetized plasma channel
Authors: Bo Yong  , Zhao Qing  , Luo Xian-Gang  , Fan Jia  , Liu Ying  , Liu Jian-Wei  ,   School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China;,   State Key Laboratory of Optical Technologies for Microfabrication, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
Published: December 2020

In this paper the influences of the time-varying plasma and magnetized time-varying plasma on the communication performance are investigated. Using a 5.8 GHz microwave source, the electron density and collision frequency of the time-varying glow discharge plasma are measured. An experimental platform is set up to test the bit error rates (BERs) of a variety of the modulation signals after going though the time-varying plasma channel. The experimental results show that the binary phase shift keying (BPSK) modulation signal has a minimal communication BER. Meanwhile, the variations of L-band BPSK and S-band QPSK (quadrature phase shift keying) signal's eye diagram and the constellation diagram, and the variation of energy after a magnetized plasma are observed. Compared with the un-magnetized situation, the magnetized plasma communication performance is greatly improved and the BER becomes much lower. The results prove that the magnetic field can effectively relieve the amplitude modulation and phase modulation caused by the plasma channel.
Evolution of electron energy distribution function in capacitively coupled argon plasma driven by very high frequency
Authors: Wang Jun  , Wang Tao  , Tang Cheng-Shuang  , Xin Yu  ,   College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
Published: December 2020

Capacitively coupled plasma driven by a very high frequency power has attracted much attention due to its rather independent control of ion flux and energy. In this paper, Langmuir probe diagnostic technique is used to observe the evolution of plasma properties such as electron energy distribution function, electron temperature and density, etc. Our experiment is performed in capacitively coupled argon plasma driven by a 40.68 MHz frequency. Experimental results show that the electron energy probability function changes from bi-Maxwellian type to single-Maxwellian type and then to Druyvesteyn type with the increase of the discharge pressure. At a low gas pressure, the electron collisionless heating in bulk plasma leads to bi-Maxwellian type in electron energy possibility function (EEPF), which has a double temperatures structure in EEPF. As the gas pressure increases, the electrons with low energy are able to collide with the neutral species more frequently, thus they gain energies through collisional heating. Therefore, these electrons can overcome the dc ambipolar potential and the collisional heating becomes a main electron heating mechanism. Increasing the input power enhances the electron population with low energy. From the discharge center to the edge, electron population with low energy decreases clearly due to the dc ambipolar potential, and they are unable to reach an oscillating sheath where collisionless heating occurs. However, electron population with high energy is slightly increased. The result indicates that more uniform plasma can be achieved at a high gas pressure. Additionally, EEPFs are measured for different discharge gaps between electrodes. The change of electrode gap for the plasma leads to a transition of electron heating mode along the axial direction. In order to characterize the electron behavior further, we introduce the ratio of the cold electron density to hot electron density (α) and the ratio of cold electron temperature to hot electron temperature (β). The ratios also show the proportional distributions of the cold and hot electron populations. The electrode gap has a great influences on α while little influence on β. When the discharge gap between electrodes varies from 20 to 40 mm, α changes from 0.2 to 0.5 while β has the same trend. Spatial distributions of electron density and temperature with low and high energy are also discussed.
Infrared laser protection of multi-wavelength with high optical switching efficiency VO2 film
Authors: Wang Ya-Qin  , Yao Gang  , Huang Zi-Jian  , Huang Ying  ,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Vanadium dioxide (VO2) film with nanoparticles is fabricated by reactive ion beam deposition (RIBD) technology and post-annealing method on a quartz glass substrate. RIBD can enhance the damage threshold of VO2 film and reduce its scattering at insulator-state. And post-annealing can eliminate the structure defects and residual stress. VO2 film exhibits first-order and reversible metal-to-insulator (MIT) phase transition at a temperature of 68 ℃. It also exhibits photo-induced MIT, in which process a metal-like phase of monoclinic VO2 appears. With many surprising features in heat-induced and photo-induced MIT processes, VO2 film turn to satisfy all the characteristics needed for a laser protection system. The thickness of VO2 film used in these experiments and simulations is about 100 nm. The double-frequency He-Ne laser at a wavelength of 3 m is used to perform the experiment of heat-induced MIT, with a temperature controlling system. The exact optimal annealing temperature is demonstrated to be 465 ℃, as the sample annealing at this temperature shows the sharpest transition properties and unmixed VO2 phase peaks in X-ray diffraction pattern. Drude and Drude-Lorentz dispersion models are taken to analyze the dielectric constant of VO2. Then, the complex refractive index is calculated for simulation. Simulations with the TFCale software show that the transmissions at high temperature and low temperature have high contrasts in the infrared range. MIT experiments at multi-wavelength, which cover heat-induced and photo-induced MIT phase transition, are performed to investigate the applicability of VO2 film in multi-wavelength laser protection for both continuous wave and pulsed lasers Thus the excellent performance of VO2 film for laser protection is roundly verified. The laser protection experiments on silicon photocell exhibit that the VO2 film enhances the anti-jamming capability of photocell system by about 2.6 times, demonstrating the applicability of VO2 film to laser protection system. The power density of MIT transition threshold of VO2 film with a thickness of 100 nm is 4.35 W/cm2 at room temperature, which is investigated with a continuous wave laser at a wavelength of 1.08 m with a continuous tunable system. In addition, atomic force microscope is used to observe the film surfaces, which are irradiated by lasers with different power densities for different times The experimental results demonstrate that the power density damage threshold of VO2 film becomes very high (404 W/cm2). The low MIT transition threshold and high damage threshold of VO2 film further demonstrate its applicability as a key role for a laser protection system. With the high switching efficiency ratio and high damage threshold, VO2 thin film can be used in optical switch, smart windows and photoelectric device.
Theoretical studies of the site preference, electronic and lattice vibration properties of La3Co29-xFexSi4B10
Authors: Wang Xiao-Xu  , Zhao Liu-Tao  , Cheng Hai-Xia  , Qian Ping  ,   Beijing Computing Center, Beijing 100094, China;,   Institute of Applied Physics, Beijing University of Science and Technology, Beijing 100083, China
Published: December 2020

In this work, the initial configuration is first optimized by the first principle and interatomic pair potentials separately, the lattice parameters of the stable structure are in good agreement with the experimental values. The site preferences of La3Co29-xFexSi4B10 compounds are studied by using the first principle with density function theory method. The calculated results show that the substitution of Fe for Co has a strong preference for the 2c site, and the substitution sequence is 2c 8j1 8i2 8j2 8i3 16k 8i1, which is in good agreement with the experimental result The lattice parameters of La3Co29-xFexSi4B10 system change little, but the magnetic moment changes obviously, when only one Co atom is substituted by Fe atoms each time. We calculate the electronic densities of states and magnetic moments of La3Co29-xFexSi4B10 compound when all the Co atoms from different sites are substituted by Fe atoms with the preferential order With the increases of Fe content values in the La3Co29-xFexSi4B10, the curves of density of states move leftwards gradually. And the magnetic moment of the La3Fe29Si4B10 is larger than that of La3Co29Si4B10. Furthermore, the lattice vibrational and thermodynamic properties are predicted by using a series of interatomic pair potentials. The Co, Fe and La atoms contribute to the lower frequency vibrations because of their heavier mass. With the increase of Fe content the cut-off frequencies of La3Co29-xFexSi4B10 first decrease and then increase, and the vibration mode induced by Si element decreases in medium frequency. The very strong B-B interaction causes higher frequency vibrations. Furthermore, the specific heat, vibrational entropy and Debye temperature are predicted based on the phonon densities of states of the La3Co29-xFexSi4B10 with the different content values of Fe. The Debye temperature rises when the Fe content is bigger than Co content in La3Co29-xFexSi4B10compound.
Measurement and study of low-frequency noise in TMR magnetic field sensor
Authors: Cao Jiang-Wei  , Wang Rui  , Wang Ying  , Bai Jian-Min  , Wei Fu-Lin  ,   Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China;,   Lertech Technology, Wuxi 214000, China
Published: December 2020

The magnetic field sensor based on tunnel magnetoresistance (TMR) effect has potential applications in various fields due to its very high field sensitivity and low power comsuption. However, the resolution of magnetic sensor depends on not only field sensitivity, but also intrinsic noise level. The intrinsic noise of an electronic device is normally frequency-dependent and increases in low frequency range. In a magnetic tunneling system, thermal magnetization fluctuation in the magnetic layer can couple to the resistance through the spin-dependent tunneling effect and create low-frequency magnetic noise. In addition, the charge trapping effect in the oxide barrier may also contribute to the external low-frequency noise. Therefore, the depression of the noise in TMR magnetic field sensor, especially the low-frequency noise, is extremely important for the application with high resolution requirement. In this work, a low-frequency noise measurement system for TMR magnetic sensor is built by using a highaccuracy data acquisition card and a low noise preamplifier. After subtracting the circuit noise from the measured noise, the noise spectral patterns of TMR magnetic field sensor with a full Wheatstone bridge structure are obtained under various bias currents and external magnetic fields. It is found that the noise spectra of the TMR sensor exhibit a clear 1/f character in the low frequency region and the noise power spectral intensity is proportional to the square of the bias current. By fitting the power spectral density of the noise versus frequency in the TMR sensor, the Hooge parameters are obtained, which remain unchanged in the measurement. The noise intensity increases abruptly in the magnetization switching region of the free layer in magnetic tunnel junction, suggesting that the 1/f noise mostly comes from the magnetic noise. In a magnetic hysteresis loop, this noise power is strongly field-dependent, which is due to thermal magnetization fluctuations in magnetic layers. We attribute this magnetic fluctuation to thermally excited hopping of the magnetic domain wall between the pinning sites. Finally, according to the R-H transfer curves and the measured noise spectra of the TMR sensor, the detectable minimum magnetic fields of the sensor are 9 nT and 1.3 nT at 100 Hz and 4 kHz with 1 V input voltage, respectively. These results pave a way for optimizing the noise properties of TMR magnetic sensors.
Generation of low-frequency squeezed states
Authors: Liu Zeng-Jun  , Zhai Ze-Hui  , Sun Heng-Xin  , Gao Jiang-Rui  ,   College of Physics and Electronic Eigeneering, Shanxi University, Taiyuan 030006, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Squeezed state of light is an important resource of optical measuerments below the shot noise limit and has been used to improve measurement sensitivity in many areas such as gravitational wave detection, especially in audio frequency region. Compared with the high-frequency squeezed states, the generation of the low-frequency squeezed states is more difficult, because it is limited by several technical noise sources. In this paper we report the observation of more than 2 dB of vacuum squeezing at 1064 nm in the gravitational-wave detection band down to 3 kHz with a double-resonant optical parametric oscillator (OPO). The OPO has a configuration of linear cavity consisting of an input coupling mirror with a transmission of 11% at 532 nm and an output coupling mirror with the transmission of 12% at 1064 nm. The nonlinear materials in the OPO is type-I periodically poled potassium titanyl phosphate (PPKTP) crystal which is chosen for this experiment due to its higher nonlinearity, broader phase matching temperature, and smaller photo-thermal effect. The OPO is pumped by the light of 532 nm from Nd: YVO4/KTP solid-state laser of maximum optical power 3 W. To avoid various noise coupled from the seed beam, the OPO is seeded by vacuum fluctuations instead of coherent field at the fundamental wavelength (1064 nm). A Pound-Drever-Hall (PDH) locking scheme is used to lock the OPO cavity length with the signal derived from the reflected pump beam, so as to lock the pump field and also lock the fundamental field. To make both the pump and seed beams resonant simultaneously, the temperature of the PPKTP is carefully adjusted. The squeezed state can be detected on a homodyne detection by interfering it with the local oscillator (LO) and detected by a balanced detector with two photodiodes (EXT500 T) but having the same quantum efficiency of 86% at 1064 nm. The subsequent electronic noise is analyzed with a low-frequency spectrum analyzer, which shows that the audio noise sources from lab enviroment, locking quality, escape efficiency, propagation loss, homodyne efficiency and detection efficiency have effect on the squeezing pruced by an OPO.
Single-pixel remote imaging based on Walsh-Hadamard transform
Authors: Li Ming-Fei  , Mo Xiao-Fan  , Zhao Lian-Jie  , Huo Juan  , Yang Ran  , Li Kai  , Zhang An-Ning  ,   Beijing Institute of Aerospace Control Devices, China Aerospace Science and Technology Corporation, Beijing 100094, China;,   Quantum Engineering Research Center, China Aerospace Science and Technology Corporation, Beijing 100094, China
Published: December 2020

Single-pixel imaging has become a topic of intense interest amongst theoreticians and experimentalists in recent years, and is still attracting great attention due to its potential applications in biomedical imaging, remote sensing, defence monitoring, etc. Two main fields should be involved in single-pixel imaging scheme: single-pixel camera and computational quantum imaging, which are proposed in the year 2006 and 2008, respectively. Although these two single-pixel imaging schemes belong to different research fields, they are nearly identical in the realization setup and using the similar image recovering algorithm. The single-pixel camera scheme is mainly based on compressive sensing algorithms, which can recover the image with about 30 percent measurements of its total pixels (raster scan method), but need the prior knowledge of the image. While the computational quantum imaging method usually recovers the image by using the second-order correlation function, which is computational fast but need more measurements to retrieve a high quality image. Thus, both the methods mentioned above are time consuming. In this paper, a single-pixel imaging scheme based on Walsh-Hadamard transform is proposed and is demonstrated both theoretically and experimentally. The retrieving times of different algorithms are discussed and compared with each other. An image of 10241024 pixels can be acquired around 1 second with our method while it will take 8 seconds by using TVAL3 algorithm on the general computer in our numerical simulation experiment. It is also experimentally demonstrated that the nature targets from 500 meters to 5000 meters away are acquired, with pixels of 128128 and in the waveband of 350-900 nm, and the speed of the imaging frame rate is achieved at 0.5 frame per second. The differences and commons between single-pixel imaging and computational quantum imaging are also discussed in this article. It is found that the Walsh-Hadamard transform we proposed is stable and can be sufficiently saving the imaging time of the single-pixel imaging schemes while maintaining a high imaging quality. Moreover, the single-pixel remote imaging scheme can be used in other wave band such as infrared and micro wave imaging, or will be useful in the case when the array detector technique is difficult to meet the requirements such as the sensitivity or the volume. And our scheme proposed here can make the single-pixel imaging technique step further toward its real applications.
Acoustic scattering from elastic target buried in water-sand sediment
Authors: Hu Zhen  , Fan Jun  , Zhang Pei-Zhen  , Wu Yu-Shuang  ,   Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;,   Information Institute, Guangdong Ocean University, Zhanjiang 524088, China;,   Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Acoustic scattering from objects buried in water-sand sediment is the foundation of target detection and identification. It is also a research hotspot in areas of acoustic scattering while the domestic research on scattered field from buried targets is not deep. This paper deduces an approximate Green's function of acoustic scattering from targets buried in water-sand sediment, which describes clearly the whole physical process during the propagation of scattered waves. Next, on basis of geometric acoustics, the corresponding Helmholtz-Kirchhoff formula of integration is presented. Complicated integration of the full wave number spectral representation of the Green's function is avoided by employing approximate formula derived from the method of ray acoustics. As a result of neglecting the influence from lateral waves, the Helmholtz-Kirchhoff integral given applies to supercritical incidence case. The function of COMSOL Multiphysics software is expanded by writing this formula of integration into it. By means of finite-element method, numerical calculation models for two-dimensional axisymmetric targets are established on the software platform. The proposed model built in free field is verified through comparing numerical results obtained with the Rayleigh method which has been validated in previous research achievements of acoustics. The target strength of buried elastic solid sphere is calculated under different conditions in order to analyze the change regularity of buried scattered field. We provide a summary about the law of target strength of the elastic sphere varying with frequency, buried depth, and the attenuation of sand. Finally, we conduct acoustic scattering experiments in free space and shallow buried conditions and process the data with the method of isolation and identification of resonance to separate eliastic echoes from reverberation echo and specular echo. Results from the experiment of free field show that components of the scattered wave should include Rayleigh waves and whispering gallery waves. The processed data of objects buried inside layered fluid media indicate that characteristics of resonance spectra can be used to identify and detect the target effectively while echo signal is not available for identification of target. The proposed technique is verified through the comparison of data from total scattered field between experiment and theoretical prediction. This study has important guiding significance for detecting and identifying targets embedded within layered acoustic media in practical applications.
Spin transport properties for iron-doped zigzag-graphene nanoribbons interface
Authors: Deng Xiao-Qing  , Sun Lin  , Li Chun-Xian  ,   School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China
Published: December 2020

By using the first-principles method based on the density-functional theory, the spin transport properties for the systems consisting of iron-doped zigzag-edged graphene nanoribbons (ZGNRs) with iron doping at the interface, where the connection is realized between electrodes and the central scattering region, are investigated theoretically. The ribbon widths of ZGNRs are four zigzag C chains (4 ZGNRs), and the length of scattering region is N unit cells (here, N=4, 6, 8, 10). Results show that -spin current is obviously greater than the -spin current under the ferromagnetic (FM) configuration, which is the spin filtering effect. The reason of spin filtering effect cames from two aspects: a) The symmetry-dependent transport properties which arise from different coupling rules between the up and * subbands around the Fermi level, that are dependent on the wave-function symmetry of the two subbands; b) the distribution of molecular orbit within the bias windows, location, or delocalization. While for antiferromagnetic (AFM) spin state, both and spin currents are very small and both the positive and negative bias regions originate from the existence of band gap; therefore, no obvious spin filtering effect can be obtained. For antiparallel (AP) magnetism configuration, spin filtering effect also can be obtained at high bias. Next, we also investigate the other models: the ribbon width of ZGNRs is five (six) zigzag C chains, namely, 5 ZGNRs (6 ZGNRs), and the scattering region is 6 unit cells length. The currents in 6 ZGNRs are less than that of 5 ZGNRs obviously, and this difference is revealed to arise from different couplings between the conducting subbands around the Fermi level, which is dependent on the symmetry of the systems. However, both of the two models show the similar characteristic: spin filtering effect. The spin current is obviously greater than the -spin current with the whole bias under the ferromagnetic (FM) configuration, The analysis on the electronic structure, transmission spectra, the molecular projected self-consistent Hamiltonian (MPSH) which have been modified by the electrodes, local density (LDOS) and the spin density give an insight into the observed results for the systems. These results indicate that the iron doping at interface between electrodes and central scattering region for ZGNRs can modulate effectively the spin electrons. It is of important significance for developing high spin polarization filtering device based on GNRs.
Application of similar Liu system in underwater weak signal detection
Authors: Liu Jian-Ming  , Yang Xia  , Gao Yue-Long  , Liu Fu-Cai  ,   Key Lab of Industrial Computer Control Engineering of Hebei Province, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

Weak signal detection is a vital technology in underwater acoustic communication with strong noise background. In this area, non-autonomous Duffing system is still widely used, and a lot of researches focus on enhancing the ability to detect weak signal and to find out the detection limitation of the Duffing system. Moreover, great achievements have already made. But problems still exist such as non-convergence of the periodic state of the Duffing system and its narrow detection domain. Unfortunately, researches on weak signal detection by using other systems are still rare. In order to solve the above problems, a new three-dimensional similar Liu chaotic system for weak signal detection is proposed. A thorough theoretical analysis for the similar Liu chaotic system is given, and its equilibrium point and the Lyapunov index are deduced and analyzed in detail. The major conclusion is that the variable x of the new system becomes a deformation signal when the input signal amplitude is greater than a certain critical value, the variables y and z converge to zero, and the Lyapunov exponents are less than zero at the same time. This means that no matter how strong the input signal is, the detection can be achieved by using a similar Liu chaotic system as long as its amplitude exceeds the threshold value. The periodic convergence and wide area detection of the similar Liu chaotic system are proved by the Matlab simulation, the Multisim circuit simulation, and the actual circuit test. This new system solves the two problems of the period convergence and narrow detection domain for the traditional Duffing system. The periodic state and chaotic state are easy to distinguish when detected. The periodic state can be maintained when the signal amplitude changes from short distance to long distance in a new system. The spectral signal-to-noise ratio range increases up to -46:57 dB in the similar Liu chaotic system. The characteristics of the new system are only effected by its structure and parameters. The system does not rely on the external factors, and it can be extended. By using some switching devices, the conversion between the chaotic state and periodic state can be realized in the practical engineering applications with a higher detection accuracy. The new design concept of the similar Liu chaotic system shows a very high practical value. It will lay a certain foundation for the underwater acoustic communication of the ocean internet of things in the future.
Influence of power dissipation and case temperature on thermal resistance of AlGaN/GaN high-speed electron mobility transistor
Authors: Guo Chun-Sheng  , Li Shi-Wei  , Ren Yun-Xiang  , Gao Li  , Feng Shi-Wei  , Zhu Hui  ,   College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing 100124, China;,   China Electronics Standardization Institute, Beijing 100176, China
Published: December 2020

The junction temperature is a main factor affecting the device performance and reliability. The thermal resistance is usually used to calculate the junction temperature. However, the thermal resistance is not constant under different operating conditions. In this work, we examine the high-speed electron mobility transistor (HEMT) from the CREE Company to investigate its thermal resistances under different case temperatures and dissipation powers. To avoid the self-oscillating phenomenon of the HEMT device, a circuit is designed to prevent the self-oscillating in experiment. First, the temperatures of the active region of the GaN HEMT device are measured by the infrared image method under different dissipation powers (including 2.8, 5.6, 8.4, 11.2, and 14 W) and different case temperatures, respectively. Then according to the result of infrared image method, the simulation model is set up by using the Sentaurus TCAD. From the final optimized model, we extract the device junction temperature and calculate the thermal resistance. It is expected to ascertain the characteristic of the thermal resistance and compare it with the result from the infrared image method.
It is found that as the device case temperature increases from 80 ℃ to 130 ℃, the thermal resistance changes from 5.9 ℃/W to 6.8 ℃/W, i.e., it is increased by 15%. When the power increases from 2.8 W to 14 W, the thermal resistance changes from 5.3 ℃/W to 6.5 ℃/W, i.e., it is increased by 22%. This phenomenon is mainly attributed to the changes of the thermal conductivity of device materials. According to the formula for the coefficient of the thermal conductivity of nonmetallic material SiC, the phonon scattering rate becomes larger with the increase of temperature. Thus, the phonon mean free path can decrease by reducing the average freedom time. Finally, the coefficient of thermal conductivity becomes smaller. It was reported by Kotchetkov et al. (Kotchetkov D, Zou J, Balandin A A, Florescu D I 2001 Appl. Phys. Lett. 79 4316) that the coefficient of thermal conductivity of GaN becomes smaller under high temperature. All of these have an effect on the heat dissipation of the device, which will cause the thermal resistance to increase.
Based on the result from the infrared image method and TCAD simulation, the changing characteristic of the thermal resistance is obtained, thereby reducing the errors in the calculation of the junction temperature.
Scheme for protecting multipartite quantum entanglement
Authors: Zong Xiao-Lan  , Yang Ming  ,   Physics and Material Science, Anhui University, Hefei 230601, China
Published: December 2020

Entanglement is a vital resource for many quantum information processes. However, the unavoidable interaction between quantum system and its environment will lead to quantum decoherence. So protecting remote entanglement against decoherence is of great importance for realizing quantum information and quantum communication. In fact, there are many types of decoherences. Besides the depolarization and phase damping, amplitude damping is a typical decoherence mechanism. If we monitor the environments to guarantee that no excitation escapes from the system, the amplitude damping is modified into a weak measurement induced amplitude damping of the system. Amplitude damping decoherence can affect both single-qubit quantum states and multipartite entangled states. However, in most of previous quantum state protection schemes, the authors only pay attention to the single-qubit system or two-qubit system. Compared with bipartite entangled states, multipartite entangled states possess many advantages, but the entanglement property of multipartite entangled state is much more complicated than bipartite entanglement, so bipartite entanglement reversal (protection) scheme may not be suitable for multipartite case. Thus, in this paper, according to local pulse series and weak measurement, we propose an effective scheme for protecting two multipartite entangled states against amplitude damping, and these two multipartite states are Cluster state and Maximal slice (MS) state. Cluster state and MS state are two typical classes of multipartite entangled states, which play important roles in quantum computation and communication, respectively. These two states cannot be converted into each other with local operation and classical communication. Owing to its good operational and computable properties, here we choose negativity as a measure to quantify the multipartite entanglement. For the case of MS sate, no matter what the initial parameter is, when the local pulses are exerted on all qubits, the entanglement can be fixed around the entanglement of the initial state. Similarly, in the four-qubit cluster state case, if a series of flip operations is exerted on all qubits, it is shown that the multipartite entanglement can be recovered to the maximum 1.0. All these results show that this protocol can protect remote multipartite entanglement effectively. The physical mechanism behind this scheme is that the weak measurement combining with flip operation can balance the weight of different terms of the state, and move the entanglement toward the initial value. To summarize, our scheme is much simpler and feasible, which may warrant its experimental realization. Moreover, our scheme could be extended to protect other multipartite states.
Study on the methods of calibrating spectral line position of interference imaging spectrometer
Authors: Wei Yu-Tong  , Liu Shang-Kuo  , Yan Ting-Yu  , Li Qi-Wei  ,   School of Science, Xi'an Jiaotong University, Xi'an 710049, China;,   Institute of Space Optics, Xi'an Jiaotong University, Xi'an 710049, China;,   Xi'an Institute Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China
Published: December 2020

The principle of interference imaging spectrometer is presented. According to the drift of recovery spectral line position, two representative methods of calibrating the laboratory spectral line position are proposed, and the calibration results and their comparative analyses are given. One method of calibration is to correct the principle, which embarks from parameter selection of interference imaging spectrometer and the analysis of the reason why the spectral line position is drifted. Aiming at the problem that the position of spectral line changes with row, the correction scheme is given to improve the accuracy of spectral line position. For four given laser wavelengths, which are 543.5 nm, 594.1 nm, 612 nm, and 632.8 nm, the root-mean-square (RMS) error of spectral line position is reduced from 28.3914 to 5.5371 after calibration. For the interferometer system which has no dispersion, the accuracy of calibration is better than the dispersion system, and can be the same at all detected wavelengths. In this article, the calibration accuracy of long wave is better than that of short wave, which is dependent on the selection of the initial correction wavelength. This method achieves a kind of universality for interference imaging spectrometer and its calibration parameters provide a convenient way to analyze the instrument indexes. Another calibration method is data processing. It makes up the deficiencies of the method mentioned above: a large number of data are needed and the effect of calibration at short wave is not good enough. The RMS error of spectral line position is reduced to 0.9178, which proves that the calibration has a really high precision. This method is simple and can correct all the detected wavelengths and spectral lines by using two united formula. Though this method is not applicable for all the interference imaging spectrometers, the idea that makes hard things simple is deserving of our attention. We can use it in many other fields. The essence of the method is to change a variable quantity into a slowly varying quantity by algorithms, and then establish the relationship between the slowly varying quantity and the standard value. This idea can always make a substantial increase in efficiency of calibration and has a satisfied accuracy. Each of the two methods has advantages and disadvantages: which method we choose to use is dependent on the effect we want to achieve, and it is better to make their combination. This study provides a theoretical and practical guidance for study, design, modulation, experiment and engineering of interference imaging spectrometers.
Channeled spectropolarimetry based on division of aperture and field of view
Authors: Quan Nai-Cheng  , Zhang Chun-Min  , Mu Ting-Kui  ,   Institute of Space Optics, School of Science, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In order to obtain accurate image, spectrum and polarization state of target by the interferometric channeled spectropolarimeter, the interferogram and the image need to be separated. Although it can be achieved by digital image processing technology, heavy computations with approximation would be introduced. In the application of channeled spectropolarimetry, an inevitable crosstalk will be present between channels of the interferogram formed on the CCD. Spatial filtering in the optical path difference domain will generate a loss of spectral resolution and the distortion of the recovered spectrum. To overcome these drawbacks, a static imaging channeled spectropolarimeter based on division of aperture and field of view is presented. The aperture is divided by a polarization array, which consists of two polarizers with their transmission axes perpendicular to each other. The field of view is divided by a pair of lenses with the same focal lengths. The spectral modulation module is composed of an achromatic quarter wave plate, a retarder and a polarization array. The interference system consists of an achromatic half wave plate, a Wollaston prism, and a Savart polariscope. Two pairs of in-phase and anti-phase interferogram with different intensity modulations can be obtained simultaneously on a single detector array. The pure image of the target is acquired by the summation of the four interferograms. The background intensity is removed by the subtraction of the interferograms with in-phase and anti-phase, and the pure interference fringes can be acquired. By the summation and subtraction of the two pure interference fringes, the single channeled interference fringes corresponding to spectrum of intensity and linear polarization state can be obtained. Spectral and polarization information of the target are acquired by Fourier transform of the single channeled interference fringes. Compared with previous instruments, the described model has the significant advantage that the background intensity can be removed from the hardware of the layout, and thus avoiding the spatial filtering in the optical path difference domain. The obtained spectra have the same resolutions as those obtained from the interference system, and the distortion of the recovered spectrum can also be vanished. Since there is neither rotating part nor moving part, the system is relatively robust. In the present paper, the principle of the instrument is described, and the interference fringe intensity distribution formula is obtained and analyzed. The performance of the system is demonstrated through a numerical simulation. This work will provide an important theoretical basis and the practical instruction for designing a new type of imaging sepctropolarimeter and its engineering applications.
A hybrid traffic flow model with considering the influence of adaptive cruise control vehicles and on-ramps
Authors: Hua Xue-Dong  , Wang Wei  , Wang Hao  ,   Jiangsu Key Laboratory of Urban ITS, Southeast University, Nanjing 210096, China;,   Jiangsu Province Collaborative Innovation Center of Modern Urban Traffic Technologies, Nanjing 210096, China
Published: December 2020

Recently, autonomous vehicles and the relevant studies have attracted much attention. Adaptive cruise control (ACC), which is a kind of cruise control system for vehicles, automatically adjusts the vehicle speed to maintain a safe distance from vehicles ahead. Since the vehicle with ACC (called ACC vehicles) is semi-autonomous, the performance of ACC vehicle must be quite different from that of manual vehicle. The characteristics of traffic flow with ACC vehicles should be carefully investigated, especially when the traffic system is a bit complicated, such as on-ramp system. The primary objective of this paper is to propose a traffic flow model to simulate the traffic flow with considering the influence of ACC vehicles and on-ramps. Based on the model proposed by Yuan in 2009 [Yuan Y M 2009 Ph. D. Dissertation (Hefei: University of Science and Technology of China)], a hybrid traffic flow model with considering the influence of ACC vehicles and on-ramps is developed. Considering the differences between ACC and manual vehicles, a car-following sub-model based on constant time headway principle is developed for ACC vehicles, while an MCD cellular automata sub-model is proposed for manual vehicles. Besides, a new parameter, , is introduced to show different psychologies of drivers when changing lane from on-ramp to main road. The lane-changing model for vehicles on-ramp is developed as well. At the end, numerical simulation is demonstrated to study the influence of ACC vehicles on traffic flow at on-ramp, and to reveal the influence of parameters on the proposed hybrid model (i.e., the length of merge area, the desired time headway of ACC vehicle and ) on model performance. The results of this paper are as follows. 1) When the ACC vehicles exist in a traffic system, the performance of traffic flow in a on-ramp area is improved: the influence of merged vehicles on main road is reduced, and the average speed and volume are increased. 2) The increase of ACC vehicles can help to alleviate traffic congestion in both congestion duration and scope aspects. 3) The newly proposed hybrid model is sensitive to the length of merge area lw, the desired time headway of ACC vehicle Hd and lane-changing psychology parameter : the decrease of Hd and the increase of can both improve the average speed and volume of traffic flow. In addition, when the volume of on-ramp is small, the speed and volume of main road can be improved by enlarging lw. When the volume of on-ramp is large, a small lw will be better for traffic flow.