bluuebunny/crossref_metadata_2025 huggingface dataset:
Relaxation behavior simulation of power lithium-ion battery in high-rate charging-discharging process
Authors: Tang Yi-Wei  , Ai Liang  , Cheng Yun  , Wang An-An  , Li Shu-Guo  , Jia Ming  ,   School of Metallurgy and Environment, Central South University, Changsha 410083, China;,   Hunan Aihua Group Co., LTD, Yiyang 413002, China
Published: December 2020

The relaxation behaviors of a power lithium-ion battery significantly affect its performance, and these properties are greatly affected by temperature. This study presents a validated electrochemical-thermal model battery model covering the conservations of charge, mass, and energy and the electrochemical reaction kinetics, and considering the effect of heat on electrochemical performance of a battery. Using this battery model, the relaxation behavior of power lithium-ion battery in high-rate charging-discharging process and the effect of difference among charge-discharge systems are investigated. It is found that ohmic polarization is the main reason for voltage change in charging-discharging process. Constant-current-constant-voltage charging mode can effectively remit ohmic polarization and then avoid changing the voltage rapidly. In the shelving process after constant-current-constant-voltage charging, voltage change is smaller and the time for it to take to reach open circuit potential is shorter than in the shelving process after constant-current charging. In charging-discharging process, the values of polarization at positive and negative electrode are almost the same. Power lithium-ion battery can be charged into more energy by constant-current-constant-voltage charging modes, meaning that it is beneficial to battery performance. Because active material particles in electrodes have certain sizes, in discharging process, there is some gradient between the surface and center of solid particle, and the electrodes each have a certain thickness, different place of electrode has a different lithium-ion concentration. In the shelving process after discharging, there is no outer current, so the gradient of lithium-ion concentration disappears due to the effect of diffusion process. The relaxation time of lithium-ion concentration in solid phase is longer than in liquid phase. The ratio between characteristic time of solid diffusion and that of liquid diffusion increases constantly near the end of the discharge, thus the polarization due to solid diffusion cannot be neglected in the whole discharging process.
Investigation of photo-chromic properties of remote phosphor film and white light emitting diode mixed with TiO2 particles
Authors: Zhuo Ning-Ze  , Zhang Na  , Li Bo-Chao  , Li Wen-Quan  , He Qing-Yang  , Shi Feng-Hua  , Zhu Yue-Hua  , Xing Hai-Dong  , Wang Hai-Bo  ,   Research Institute of Electric Light Source Materials, Nanjing Tech University, Nanjing 210015, China;,   College of materials science and engineering, Nanjing Tech University, Nanjing 210009, China
Published: December 2020

Based on the hot pressing method, the remote phosphor films are prepared by adding TiO2 particles into YAG:Ce and silicon binder, and then they are packaged into white light emitting diode (WLED) device with chip on board (COB) blue light source. The photo-chromic properties and mechanism are studied and calculated. Based on Mie theory and Henyey-Greenstein function, forward scattering is the main light scattering form of YAG:Ce phosphor powder, while the forward scattering intensity is close to the back scattering intensity of TiO2 particles. The emission spectral intensity and relative luminance of remote phosphor film change with increasing the concentration of TiO2 particles, and the optimum concentration is 0.966 g/cm3. Forward transmission intensity and back reflection intensity are calculated and analyzed, when the concentration of TiO2 is low, the forward transmission intensity of blue light is stronger than that of yellow light and the main transmission form is forward transmission, while the forward and backward intensity of yellow light are similar because of isotropy. With increasing the concentration of TiO2, the forward intensity of blue light gradually decreases, and the transmission intensity is lower than that of yellow light. The forward and backward intensity of yellow light reach their maxima when the TiO2 concentration is 0.966 g/cm3. The main reason for this phenomenon is that the increasing of the utilization ratio between blue light and transmission of yellow light is affected by the strong scattering ability of TiO2. Finally the WLEDs are packaged by remote phosphor films and COB blue light source, the luminous flux of WLED reaches 415.28 lm (at 300 mA and 9.3 V) at a concentration of 0.966 g/cm3, which is increased by 8.15% compared with the concentration in the case of no TiO2 mixing. Besides, the correlated color temperature changes from cool white 6900 K to warm white 3832 K gradually. Consequently, the adding of TiO2 particles can not only improve the emission intensity of remote phosphor film and the luminous flux of WLED, but also regulate the correlated color temperature.
Quantitative analysis of the field of view for X-ray differential phase contrast imaging
Authors: Du Yang  , Liu Xin  , Lei Yao-Hu  , Huang Jian-Heng  , Zhao Zhi-Gang  , Lin Dan-Ying  , Guo Jin-Chuan  , Li Ji  , Niu Han-Ben  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

Grating-based X-ray differential phase contrast imaging provides excellent image contrast for low-Z objects that cannot be acquired by conventional X-ray imaging, which has great potential applications in the early diagnosis of cancer and non-destructive detections of low-Z materials and devices. Large field of view imaging is a crucial factor for this technology from the laboratory to practical application. For the objective need of large field of view, on the basis of the Fresnel diffraction theory and the structure characteristics of gratings, we establish a quantitative physical model to analyze the factors that affect the imaging field of view and give a feasible way for large imaging field of view. This work provides a theoretical basis for the large field of view grating-based X-ray differential phase contrast imaging in the future.
Resonance transmission of one-dimensional quantum walk with phase defects
Authors: Wang Dan-Dan  , Li Zhi-Jian  ,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China
Published: December 2020

In this paper, the resonance transmission of discrete time quantum walk is studied when it walks on one-dimensional lattice in which two-phase defects or a piece of phase defects exists. The quasi energy of discrete time quantum walk has a unique dispersion relation with the momentum, from which we first discuss the wave velocity direction versus the values of momentum, and distinguish the incident wave and the reflected wave. The gap between two energy bands depends on the parameters of coincident operator, so the phase defects, which break down the translation invariance of quantum walk on uniform lattices, can be regarded as an analogue of quantum potential. Then we use the condition of energy conversion at the boundary points to obtain the transmission rate and discuss its variation with the incident momentum for different strengths and widths of defects in detail. The multiple resonant peaks are observed due to the enhanced interference effect. Different resonant behaviors are shown when the strength of defect is less or greater than /2, correspondingly the resonances occur in a wide region of incident momentum or the sharp resonant peaks appear at discrete values of momentum. Under the condition of strong defect strength, i.e., approaching to , the qualitative relation between the number of resonant peaks and the widths of defect region is given. The number of resonant peaks is 2(N-1) when the two phase defects are located at N sites symmetric about the origin, while the number is 2N when a piece of phase defects is located at -N to N sites. In the case of a piece of phase defects, we also present the phase diagram in parameter space of (k, ) to show the discrete time of quantum walk propagating or tunneling through the defect region. In terms of this phase diagram, the variations of transmission rate with the incident momentum are reasonably explained. One special phenomenon is that the quantum walk is almost totally reflected in the tunneling case except for =/2 and k being slightly off -/2. Moreover, this behavior seems little affecting the defect strength, just similar to a classical particle. As a result of this research, we hope to deepen the insight of the quantum walk and provide methods to control the spreading of quantum walk through artificial defects.
General robust stability controller design method for a class of hopf bifurcation systems
Authors: Lu Jin-Bo  , Hou Xiao-Rong  , Luo Min  ,   School of Energy Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

For the nonlinear Hopf bifurcation system, the change of bifurcation parameter has an important influence on the state of the system. In order to control the Hopf bifurcations of the nonlinear dynamic system, the parameter values of bifurcation points in the system need to be found out before controller designing. However, due to uncertainties of the system structure and parameters in the nonlinear system, or disturbance, it is difficult to determine the bifurcation point precisely. So it is a good way of designing a robust controller near the bifurcation point. Although, lots of works have discussed the robust control of a Hopf bifurcation in a nonlinear dynamic system, the solutions are not satisfactory and there are still many problems. The controller is always designed for some special system. Its structure is usually complex, not general, and the design process is complicated. And before controller design, the value of bifurcation point must be solved accurately.In this paper, a parametric robust stability controller design method is proposed for a class of polynomial form Hopf bifurcation systems. Using this method, it is not necessary to solve the exact values of the bifurcation parameter, it is only needed to determine the bifurcation parameter range. The designed controller includes a system state polynomial; its structure is general, simple and keeps the equilibrium of the original system unchanged. By using the Hurwitz criterion, the system stability constraints for bifurcation parameter boundaries are obtained at equilibrium, and they are described by algebraic inequalities. Cylindrical algebraic decomposition is applied to calculate the stability region of the controller parameters. And then, in the region, parameters of the robust controller can be calculated to make the dynamic system stable. In this paper, the Lorenz system without disturbance is used as an example to show the designing process of the method, and then the controller of the van der Pol oscillator system with disturbance is designed by this method as an engineering application. Simulations of the two systems are given to demonstrate that the proposed controller designing method can be effectively applied to the robust stability control of the Hopf bifurcation systems.
Algorithm researches for efficient global tallying in criticality calculation of Monte Carlo method
Authors: ShangGuan Dan-Hua  , Deng Li  , Li Gang  , Zhang Bao-Yin  , Ma Yan  , Fu Yuan-Guang  , Li Rui  , Hu Xiao-Li  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   CAEP Software Center for High Performance Numerical Simulation, Beijing 100083, China
Published: December 2020

Based on the research of the uniform fission site algorithm, the uniform tally density algorithm and the uniform track number density algorithm are proposed and compared with the original uniform fission site algorithm in this paper for seeking high performance of global tallying in Monte Carlo criticality calculation. Because reducing the largest uncertainties to an acceptable level simply by running a large number of neutron histories is often prohibitively expensive, the researches are indispensable for the calculation to reach the goal of practical application (the so called 95/95 standard). Using the global volume-averaged cell flux tally and energy deposition tally of the pin-by-pin model of Dayawan nuclear reactor as two examples, these new algorithms show better results. Although the uniform tally density algorithm has the best performance, the uniform track number density algorithm still has the advantage of being applicable to any type of tally, which is based on the track length estimator without any modification. All the algorithms are realized in a recently developed parallel Monte Carlo particle transport code JMCT.
Preparation and characterization of self-cleaning and anti-reflection ZnO-SiO2 nanometric films
Authors: Guo Zhao-Long  , Zhao Hai-Xin  , Zhao Wei  ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of the Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Unlike the general anti-reflection and self-cleaning film such as SiO2 and TiO2-SiO2, the ZnO-SiO2 nanometric film used as a substrate of excellent transparency in visible region and effective photo-catalytic self-cleaning under UV illumination is seldom studied in the application as a substrate; however, it has a lot of advantages including high transmittance and low refractivity. In this paper, a self-cleaning and anti-reflection ZnO-SiO2 nanometric film is successfully fabricated by using a sol-gel dip-coating method. The morphology, crystal structure, surface microstructure and light transmittance of the obtained products are characterized by techniques such as TEM, SAD, XRD, SEM, DTA and UV-vis. Photo-catalytic degradation of the methylene blue (MB) in aqueous solution is used as probe reaction to evaluate the photo-catalytic activity of ZnO-SiO2 nanometric film. The TEM images reveal that the as-prepared ZnO nanoparticles are spherical grains with diameters of 12-20 nm, the average grain diameter is about 14.51 nm. ZnO nanoparticles obtained are of hexagonal wurtzite structure revealed by XRD pattern and there exist no other diffraction peaks, Furthermore, the SAD results show that ZnO microstructurs have good crystallinity. In addition, the ZnO grain size is about 14.41 nm by using the Scherrer formula calculation, which is consistent with the TEM results by the Gauss simulation. The UV-vis spectra reveal that the ultraviolet characteristic absorption peak of ZnO-SiO2 composite films is located at 368 nm and 375 nm after annealing at different temperatures such as 300℃ and 450℃, corresponding to the band gaps of 3.37 eV and 3.31 eV, respectively. It is highly consistent with that obtained from pure ZnO nanoparticles. Increasing the annealing temperature results in a lower refractive index and the increases of the porosity in of the ZnO-SiO2 composite films. It has a uniformly refractive index value about 1.23-1.25 and a high porosity value about 50.3-54.7% when the annealing temperature is 450 ℃. Experimental results show that the ZnO-SiO2 composite film can enhance the light transmittance of the quartz substrate, due to its lower reflective index and higher porosity. Compared with the quartz substrate, the average optical transmission rate of the quartz glass coated with ZnO-SiO2composite films is increased by about 4.17% at 400-800 nm, which favors greatly anti-reflection characteristics in a wide spectrum range. Meanwhile, the ZnO-SiO2 composite films are found to be efficient for photo-catalytically degradation of methylene blue dye under UV illumination, which favors greatly the self-cleaning function.
Analysis of the magnetohydrodynamic heat shield system for hypersonic vehicles
Authors: Li Kai  , Liu Wei-Qiang  ,   College of Aerospace Science and Engineering, NUDT, Changsha 410073, China
Published: December 2020

During hypersonic flight, the weakly-ionized plasma layer post shock can be utilized for flow control by externally applying a magnetic field. The Lorentz force, which is induced by the interaction between the ionized air and the magnetic field, decelerates the flow in the shock layer. Consequently, the thickness of the shock layer is increased and the convective heat flux can be mitigated. This so-called magnetohydrodynamic (MHD) heat shield system has been proved to be effective in heat flux mitigation by many researchers.Different from the dipole magnet conventionally used in previous researches on MHD heat shield, a normal columned solenoid-based MHD thermal protection system model is built in this paper. The present numerical analysis is mainly based on the low magneto-Reynolds MHD model, which neglects the induction magnetic field. Hall effect and the ion-slip effect are also neglected here because an insulating wall is assumed. With these hypothesis, a series of axisymmetric simulations on the flow field of Japanese Orbital Reentry Experimental Capsule (OREX) are performed to analyze the influence of different externally applied magnetic fields on the efficiency of MHD thermal protection. First, based on the dipole magnet field, the influence of magnetic induction density is analyzed. Second， differences between the efficiency of MHD thermal protection under three types of magnetic field, namely dipole magnet, solenoid magnet, and uniform magnet field are compared. Finally, the influence of the geometric parameters of solenoid magnet on the MHD thermal protection is analyzed. Results show that, saturation effect exists in the process of MHD heat flux mitigation and it confines the effectiveness of MHD heat shield system. Thermal protection capabilities under three types of magnetic field are ranked from weak to strong as dipole magnet, solenoid magnet, and uniform magnet field. Under the same magnetic induction intensity at the stagnation point, first， the increase of solenoid radius improves its effectiveness in MHD thermal protection; second, the influence of solenoid length on the efficiency of MHD thermal protection is weak, indicating that the solenoid length can be optimized with the remaining two factors, namely the exciting current density and the total weight of solenoid magnet. Finally, the closer distance between the solenoid and stagnation point has negative influence on MHD thermal protection for the stagnation and the shoulder area of the reentry capsule.
Plasma distribution properties of vacuum ribbon-like cathodic arc plasma fliter and Raman studies of diamond-like carbon films perpared by it
Authors: Li Liu-He  , Liu Hong-Tao  , Luo Ji  , Xu Yi  ,   School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China
Published: December 2020

As is well known, most filtered cathodic vacuum arc deposition technology adopts filters with various geometries to remove macro particles in the last three decades, but almost all of them have a circular cross-section. Compared with the traditional toroidal duct filters, the rectangular graphite cathodic arc source can have a larger area which can be an arc source of a ribbon-like cathodic arc plasma filter, which has a higher coating efficiency due to its larger area arc source and may be more suitable for a larger scale industrial production. Thus, the research on the plasma distribution properties within the vacuum ribbon-like cathodic arc plasma filter is of great significance. In this paper, a rectangular graphite cathodic arc source is used to produce the ribbon-like cathodic arc plasma. Within the filter, a 90 curved magnetic duct with a rectangular cross-section is used as the arc filter. The ribbon-like cathodic arc plasma is transmitted from cathode to the deposition area along the magnetic line produced by external coils. A Faraday cup ion energy analyzer and a Langmuir probe are used to characterize the distribution properties of the filtered plasma at 15 places on the exit plane. Ion energies and ion density at these positions are obtained. For the special retrograde motion of the cathode spot on the rectangular target surface, the ion energies and ion density data are not stable. In order to obtain representative values, the net results are the average value of 3 measurements. Diamond-like carbon (DLC) films are deposited by the ribbon-like cathodic arc plasma filter at the same exit plane and their structures are characterized by Raman shift. To compare the distinctness of the 15 Raman spectrums, each Raman spectrum of the DLC films is normalized and shown in a figure. Meanwhile, the thicknesses of all the DLC films are measured by step profiler. Results show that the ion energies are of Maxwell distributions at all the 15 places on the exit plane. The ion energies vary from 0 to 60 eV, most being in the range from 20 to 30 eV. The arc voltage is 30 eV, which exactly coincides with the ion energies. While Raman spectra of the DLC films show an obvious correspondence relationship with the ion energies as well as the ion density and the DLC film thickness. The nano-hardness of the DLC films lies in a range of 25-43 GPa. Although the ion energies, ion density, DLC film thickness and nano-hardness are slightly different at different locations, they are not significant. Owing to the relatively evenly distributed properties of the ribbon-like arc plasma this may open great opportunities for a large area filtered arc deposition technique.
The first-principles study on the interaction of Ni with the yttria-stabilized zirconia and the activity of the interface
Authors: Dong Shan  , Zhang Yan-Xing  , Zhang Xi-Lin  , Xu Xiao-Pei  , Mao Jian-Jun  , Li Dong-Lin  , Chen Zhi-Ming  , Ma Kuan  , Fan Zheng-Quan  , Wei Dan-Dan  , Yang Zong-Xian  ,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

Solid oxide fuel cell (SOFC) is expected to be a crucial technology in future power generation due to its advantages of high efficiency, fuel adaptability, all-solid state, modular assembly, and low pollution. The Ni/YSZ (yttrium-stabilized zirconia) cermet is the most popular anode material in SOFCs. However, a major problem is that it can be easily oxidized, thus resulting in the decline of long-term stability and activity as an anode catalyst. A better performance of the Ni/YSZ cermet can be obtained by improving its microstructure as well as the Ni distribution in it. Interactions between Ni and the yttria-stabilized zirconia (YSZ) (111) or oxygen-enriched YSZ(111) (YSZ+O) surface are studied in terms of the first-principles method based on the density functional theory with particular focus put on the activity of the Ni atom at the interface. The geometric and electronic structures of CO and O2 on the Ni1 (the single Ni atom)/YSZ and Ni1/YSZ+O surfaces are also studied. It is found that the Ni atom tends to be adsorbed to O sites and away from the Y atoms on both the surfaces. The most favorable adsorption site is the oxygen vacancy, which has an adsorption energy of 2.85 eV. Compared with YSZ, the single Ni atom loses 1.06 electrons and is oxidized as Ni+ on YSZ+O, which produces a strong interaction between the Ni atom and YSZ+O. Strong adsorption is mainly attributed to the interaction between Ni 3d and Ou 2p orbitals. And the oxidation of Ni can lead to the decrease of electrocatalytic activity of the Ni catalyst. The d-band DOS (density of states) peaks of the Ni1/YSZ+O are lower than that of the Ni1/YSZ, and the corresponding d-band centers are shifted away from the Fermi level to lower energy with the d value of -3.69 eV; therefore the CO and O2 adsorption is weakened. While the adsorption energy for CO on the Ni1/YSZ+O (0.42 eV) is much lower than that on the Ni1/YSZ surface (1.78 eV). In addition, the adsorbed CO gains 0.07 electrons, less than those on the Ni1/YSZ surface (0.34 e). The adsorption energy of O2 on Ni1/YSZ+O also decreases (0.34 eV) and gains fewer electrons (0.24 e) as compared with the corresponding values (2.57 eV, 1.15 eV) on Ni1/YSZ. Results would improve our understanding on the mechanism of oxidation of Ni on the Ni/YSZ anode of SOFCs and would be of great importance for designing highly active catalysts used for fuel cells.
Double resonant sum-frequency generation in an external-cavity under high-efficiency frequency conversion
Authors: Tan Wei  , Qiu Xiao-Dong  , Zhao Gang  , Hou Jia-Jia  , Jia Meng-Yuan  , Yan Xiao-Juan  , Ma Wei-Guang  , Zhang Lei  , Dong Lei  , Yin Wang-Bao  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China;,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

In recent years, more than 90% of the signal laser power can be up-converted based on the high-efficiency double resonant external cavity sum-frequency generation (SFG), especially when the whole system runs under the undepleted pump approximation scheme. Therefore it is difficult to directly achieve an error signal with a high signal-to-noise ratio through the signal laser to lock its frequency to the cavity mode. In this paper a novel method, based on the frequency modulation of signal laser and demodulation of the SFG laser, is used to obtain the error signal to realize the cascade frequency locking between the two fundamental lasers and the external cavity. In this experiment, 1064 nm laser is the pump laser and 1583 nm laser is the signal laser. They are coupled into a ring cavity inside which a 5% MgO-doped PPLN (25 mm1 mm0.5 mm) is used to produce the SFG laser of 636 nm. When the pump laser is resonant with the external cavity, a circulating power of 14.3 W is obtained with its input power of 1.3 W. The reflectivity of the input coupling mirror of signal laser is 10% to restrain the impendence mismatch. The temperature of PPLN is set at 68.5 ℃ to reach the optimum SFG temperature. In order to keep the signal laser resonance inside the external cavity, one needs to lock its frequency to the cavity mode. A 28.5 kHz sinusoidal voltage is used to modulate the frequency of the signal laser so that the frequency of 636 nm laser is modulated simultaneously. Then 5% of the output 636 nm laser power is sent into a Si photodiode detector the signal of which is demodulated at the modulation frequency by a lock-in amplifier. Finally the demodulated signal is feedback to the frequency control port of signal laser. Under these conditions, 73% of 1583 nm signal laser power can be converted into 636 nm laser power when the incident power varies from 10 W to demodulation of the transmitted cavity mode of 1583 nm when the incident signal laser power is below 12 mW. When the signal laser power increases from 50 mW to 295 mW, the conversion efficiency linearly drops to 60%, which is mainly caused by depleting the 1064 nm pump laser power. Finally a 440 mW of 636 nm laser is generated with an incident signal laser power of 295 mW. This scheme can realize a high-efficiency SFG with a low input signal laser power or poor single-pass SFG efficiency.
Optical modulation characteristics of all-dielectric grating at terahertz frequencies
Authors: Cui Bin  , Yang Yu-Ping  , Ma Pin  , Yang Xue-Ying  , Ma Li-Wen  ,   School of Science, Minzu University of China, Beijing 100081, China
Published: December 2020

In recent years, metamaterials (MMs) have been widely investigated for their exotic electromagnetic characteristics which cannot be achieved in nature. However, one of the main limitations in traditional metallic-film MMs is a high level of radiation loss in metal and insertion loss of the high-permittivity or thick substrate. Fortunately, all-dielectric MMs with high refractive-index dielectric structures show significantly less material loss than their metallic counterparts. In this paper, an all-dielectric grating is fabricated on a 100-m-thick silicon wafer by using direct-laser-writing technique, and the properties of its Mie resonances are investigated by THz time-domain spectroscopy. Then we measure the spectral response of the all-dielectric grating under the optical modulation by a near-infrared pump-THz probe method. The modulation light source is an 808 nm continuous semiconductor laser with a maximum power (10 W). To give an insight into the underlying mechanisms of the Mie-type resonance effects on the arrayed, silicon pillars, the transmission of the all-dielectric grating is investigated numerically by the finite-element simulations through using CST Microwave Studio. In our experiment, the incident THz magnetic field is along the grating lines. The research results show that three typical Mie resonances are excited from 0 to 1 THz in the all-dielectric structure, and all the three resonant modes are different in the distributions of electric field and magnetic field. Furthermore, it is found that the resonance intensities of these three resonance peaks appear to be weakened variously with the increase of the optical power, and the first resonant peak modulation amplitude maximally reaches more than 50%. Combining the simulation results, we prove that the decrease of Mie resonance intensity under photo-excitation is caused by the absorption and the scattering of the incident THz wave by photo-generated carriers. Besides, we estimate the conductivity values of the all-dielectric grating under different optical excitations and find that the conductivity values reach 1000 S/m and 1500 S/m corresponding to 5 W and 10 W optical excitation, respectively. The estimated conductivity data will play an important role in the prospective optical modulation simulation. All the results mentioned above will provide an important reference for researches on the resonance properties of the all-dielectric metamaterials and the development of related functional devices.
Microstructure of medium energy and high density helium ion implanted tungsten
Authors: Guo Hong-Yan  , Xia Min  , Yan Qing-Zhi  , Guo Li-Ping  , Chen Ji-Hong  , Ge Chang-Chun  ,   State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Beijing 100083, China;,   Institute of Special Ceramics and Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;,   Accelerator Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072, China
Published: December 2020

Bulk tungsten and tungsten transmission electron microscopy (TEM) lamella are implanted with 15 keV helium ions at about 873 K to study the microstructure evolution. The samples are implanted to about 11017 He+/cm2. The projected range of the helium ion in tungsten is about 43.9 nm, calculated with the stopping and range of ions in matter program (the SRIM code). The density of pores with diameters ranging from 90 nm to 430 nm is detected on the surface of helium implanted bulk tungsten by field emission scanning electron microscopy. Blistering is also observed on the surface of helium implanted bulk tungsten. The TEM results indicate that fuzz microstructure is formed in helium implanted tungsten TEM lamella, and stacking faults and micro-pores are observed in the fuzz structure. Besides, the density of nano-scaled helium bubbles is detected around the mirco-pores.
Image contrast for different imaging methods in turbid media
Authors: Tian Heng  , Zhu Jing-Ping  , Zhang Yun-Yao  , Guan Jin-Ge  , Hou Xun  ,   Shaanxi Key Laboratory of Information Photonic Technique, Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

The physics-based methods that can effectively improve the image contrast in turbid media while truly preserving all the detailed information, have received great attention in recent years. The range-gated imaging (RGI), polarization difference method (PD) and polarization-based range-gated technology (PRG) are three effective methods of enhancing the contrast. However, the relationship between the extent of contrast enhancement and the imaging distance for each method has not been revealed. In this paper, a compact disc (CD) plate is set to be in the intralipid with different concentrations contained in a glass cell and imaged by RGI, PD, PRG and raw intensity imaging (RI). The Indian ink is used as the absorber which eliminates the multiple scattered photons and achieves the range-gated technology. In order to investigate the number of the scattered photons filtered out by the 4 methods, the image intensity curves are acquired while the imaging distance, the distance between the target surface and the front surface of the cell, is set to be 26 mm. The results indicate that PRG filters out the largest number of the scattered photons, followed by PD and RGI because the long imaging distance results in more multiple scattering photons. Then the influence of the imaging distance on the image intensity is investigated by the 4 methods. The image intensity is recorded while the imaging distance varies from 22 mm to 30 mm with even increments. Then four sets of intensity curves are plotted against the imaging distance corresponding to RI, RGI, PD and PRG respectively. Based on the RI, three sets of image intensity difference curves of RGI, PD and PRG are also calculated. The tendencies of the curves show that these imaging methods have their own imaging distance thresholds. It implies that the numbers of the photons filtered out by these methods are all constant when their imaging distances exceed their thresholds of 22 mm, 30 mm and 30 mm, respectively. Finally, the effect of the imaging distance on the contrast variation is studied in turbid media with two different scattering coefficient 0.714 cm-1 and 1.19 cm-1. The results show that PRG is superior to other methods in contrast enhancement. In addition, the imaging distances of the 4 methods under the same image contrast are obtained, showing that under the same contrast increment, the PRG presents the largest imaging distance enhancement, followed by PD, RGI and RI. The increase of scattering coefficient could also cause the decrease of the imaging distance. These results can be very useful to understand the mechanism of imaging in turbid media and are of great significance for improving the ability to recognize the target.
Concentration and pressure measurement of water vapor in sealed glass containers based on tunable diode laser absorption spectroscopy
Authors: Cao Ya-Nan  , Wang Gui-Shi  , Tan Tu  , Wang Lei  , Mei Jiao-Xu  , Cai Ting-Dong  , Gao Xiao-Ming  ,   Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   University of Science and Technology of China, Hefei 230031, China;,   School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China
Published: December 2020

Water vapor in a sealed glass container processed by lyophilization is a main factor for drug metamorphism. The key to knowing whether there is a leakage occurring in the container is how to detect water concentration and pressure in the sealed container quickly and accurately. In the present paper, a strong absorption line of H2O near 1.39 m is carefully selected to avoid the interference of neighboring transitions. A distributed feedback laser semiconductor laser near 1.396 m is employed as the light source with a power of 10 mW and typical linewidth of 2 MHz by combining with tunable diode laser absorption spectroscopy technique, the concentrations and pressures of water vapor in the sealed container are successfully detected under static condition and dynamic condition. In order to isolate the interference absorption from the ambient water vapor in the air, a differential absorption technique is employed in our experiment, which makes our system simpler than routine nitrogen purging based system. During the measurement, the second harmonic signal is utilized for measuring the concentration and pressure, the concentration is retrieved by the peak value while the pressure is calculated by the full width at half maximum. For the measurement of concentration ranging from 0.2% to 12%, the linear correlation coefficient between the real values and the inversed values and the standard deviation ratio are 0.9978 and 4.81%, respectively. For the measurement of pressure, the correlation coefficient and standard deviation ratio are 0.982 and 5.6%, respectively. The minimum detection limits of the concentration and pressure are 400 ppm and 2.5 Torr, respectively. Moreover, in order to test the system for on-line applications in the pharmaceutical industry, measurements are performed in vials which are placed on a rotary stage to simulate the process of the assemble line. In particular, the amplitude of sinuous signal without absorption is used as the reference signal to validate whether the vial is in the optical path. Besides, this amplitude is also utilized to normalize the laser power. The results show that our system can handle about 300 bottles in one minute, which can meet well the requirements for rapid and real-time detections. This system can be applied directly to the medicine bottle on-line detection, and multicomponent detection can also be realized by employing two or more lasers (e.g. H2O, oxygen, etc.). In the future, we plan to build a system for detecting water vapor and oxygen simultaneously, as oxygen is another import indicator for drug metamorphism.
Measurement of refractive indices of GdTaO4 crystal by the auto-collimation method
Authors: Wang Xiao-Fei  , Yang Hua-Jun  , Zhang Ge  , Zhang Qing-Li  , Dou Ren-Qin  , Ding Shou-Jun  , Luo Jian-Qiao  , Liu Wen-Peng  , Sun Gui-Hua  , Sun Dun-Lu  ,   Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
Published: December 2020

In this paper, the refractive index of GdTaO4 crystal is measured by the auto-collimation method. GdTaO4 crystal is processed into three rectangular prisms, their planes with longer right angle side are planes a, b and c of the crystal, respectively, and their normal directions are the directions of crystal plane axes a, b and c, respectively. with a side by angle . Plane enclosed by hypotenuse and the longer right angle side is subjected to fine polishing, while the surface plating for the latter is subjected to Al reflectance coating, so that the light is incident along the hypotenuse plane with minimum angle of deviation (), reflects on the plane with longer right angle and returns along the original path.
The rectangular prisms processed by GdTaO4 crystal are placed on the platform of 32 J goniometer with an accuracy of arc seconds. The 473, 532 nm YAG double frequency laser, 633 nm He-Ne laser and 1064 nm YAG laser with stable light intensity are used as a measuring light source, light will refract into the light perpendicular to the longer right angle side when the laser of measuring light source shoots towards the bevel of a prism with a minimum angle of deviation (). The refractive indexes nx, ny, and nz of a crystallographic axis directions can be measured by , and the relationship between refractive index ellipsoid section and prism refraction of light. The constants Ai, Bi, Ci, and Di (i=x, y, z) are given in Sellmeier's equation ni2 =Ai+Bi/(2-Ci)-Di2, and the values of angle Vz included between light axis and refractive index at wavelengths of 473, 532, 632.8 and 1064 nm are calculated to be 22.5, 22.5, 21.9 and 22.0, respectively. It is proved that GdTaO4 crystal is optically positive biaxial crystal.
Efflorescences of confined aqueous sodiumsalt solutions
Authors: Yu Tong-Xu  , Zhang Wen-Bin  , Ji Ai-Ling  , Wang Qiang  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   State Key Laboratory of High-Temperature Gas Dynamics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Owing to its destructive power to porous structures such as buildings and rocks, salt weathering has attracted considerable attention in the community of civil engineers and geomorphologists, who devote their efforts to conservations of architecture and engineering structures afflicted by salt attack, and to the investigation of natural landscape caused by the same group of processes, respectively. Precipitation of dissolved salts is a direct cause of salt weathering effect. Crystallization phenomena in salt weathering can be crudely categorized under efflorescence and subflorescence with respect to the distinct precipitation sites, and the latter is believed to be able to cause more destructions to porous structure. In contrast to subflorescence for which even models of statistical dynamics have been well-established, efflorescence has drawn less attention, partly because of the complexity of constructing a sound theoretical model to describe the mass transport process there involved. As a serie of sodium salts is the main culprit of salt weathering, the current work deals with experimental study of efflorescences of the aqueous NaCl, NaNO3 and Na2SO4 solutions on the surface of porous silica gel particles. We investigate the influences of salt concentration and pore size on the crystal morphology arising in efflorescence by using scanning electron microscopy. It is found that though Na2SO4 effloresces on the specimen surface, its inclination towards subflorescence makes the whiskers appear on specimen with smaller pore radii at low concentrations, which differs obviously from the cases of NaCl and NaNO3. Moreover, unlike the upright growths of NaCl and NaNO3 crystals, the whiskers of Na2SO4 are always oblique to the specimen surface, and the large lateral stress to the specimen thus induced may become another factor of its destructive power apart from the subflorescing trend. The crystallization behaviors of Na2SO4, i.e., both the oblique whiskers and regular crystallites, indicate that mirabilite (Na2SO410H2O) is the main precipitation, which is consistent with the high relative humidity employed in this article. Remarkably, the thinnest whiskers of NaNO3 exhibit the branching and ball-chain structures, indicating that plateau-Rayleigh instablility occurs in the growth process. Our results are expected to inspire more deliberate studies for the full understanding of detailed processes and mechanism involved in efflorescence of aqueous salt solutions.
Synthesis and gas-sensing properties of the silicon nanowires/vanadium oxide nanorods composite
Authors: Zhang Wei-Yi  , Hu Ming  , Liu Xing  , Li Na  , Yan Wen-Jun  ,   School of Electronic Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

As air pollution is becoming more and more serious in recent years, gas-sensing devices have attracted intensive attention. In particular, NO2 is one of the most toxic gases in the atmosphere, which tends to produce acid rain and photochemical smog. Thus, there is a strong demand of cheap, reliable and sensitive gas sensors targeting NO2. Gas sensors fabricated on silicon substrates with room-temperature operation are very promising in power saving, integrated circuit processing and portable detectors. More important, the silicon nanowires (SiNWs)-based devices are compatible with very large scale integration processes and complementary metal oxide semiconductor technologies. In the present work, the novel nanocomposite structure of (SiNWs)/vanadium oxide (V2O5) nanorods for NO2 detection is successfully synthesized. The SiNWs are fabricated by a combination of nanosphere lithography and metal-assisted chemical etching. Vanadium films are deposited on SiNWs by DC magnetron sputtering, and then V2O5 nanorods are synthesized with subsequent thermal annealing process for full oxidation in air. The morphology and crystal structure of product obtained are characterized by field-emission scanning electron microscopy and X-ray diffraction. The characterization results indicate that V2O5 nanorods are uniformly distributed on the surfaces of SiNWs. The increased specific surface area of SiNWs/V2O5 nanocomposite provides more adsorption sites and diffusion conduits for gas molecules. Therefore, the novel structure of the nanocomposite is conducive to gas-sensing. In addition, the sputtering time has an obvious influence on the morphology of vanadium oxide. With the increase of the sputtering time, the specific surface area and the number of p-n heterojunctions formed in the nanocomposite are both less than those of nanocomposite with appropriate sputtering time. The gas-sensing properties are examined by measuring the resistance change towards 0.5-4 ppm NO2 gas at room temperature by the static volumetric method. Results show that the nanocomposite with shorter deposition time has better gas-sensing properties to low-concentration NO2 gas than those of bare SiNWs and nanocomposite with longer deposition time. On the contrary, the responses of the nanocomposite to other high-concentration reducing gases are very low, indicating good selectivity. The enhancement in gas sensing properties may be attributed to the change in width of the space charge region, which is similar to the behavior of p-n junction under forward bias, in the high-density p-n heterojunction structure formed between SiNWs and V2O5 nanorods. In conclusion, these results demonstrate that the SiNWs/V2O5 nanocomposite has great potential for future NO2 gas detection applications with low consumption and good performance.