bluuebunny/crossref_metadata_2025 huggingface dataset:
Scale and rotation statistic-based self-adaptive function for ground penetrating radar denoising in curvelet domain
Authors: Li Jing-He , He Zhan-Xiang , Yang Jun , Meng Shu-Jun , Li Wen-Jie , Liao Xiao-Qian ,   College of Earth Sciences, Guilin University of Technology, Guilin 541004, China,   Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen 518055, China
Published: December 2020

Nonlinear and non-stationary ground penetrating radar (GPR) data for geophysics exploration are often mixed with various complex noise sources, such as random and coherent noise. Those complex noise sources are introduced by the acquisition system and other sources of measurement uncertainty. The data sets which are contaminated by the above noises have a serious influence on the accurate extraction of weak reflected signals and the effective identification of diffracted wave hyperbolic coaxial characteristics. The ignorance of the influence of noise will cause great errors in the interpretation of GPR data and the subsequent migration imaging with full waveform. The curvelet transform not only is related to position and frequency as compared with the wavelet transform, but also is controlled by the translation angle. With such a unique advantage, curvelets are used for ground roll whitening, coherent noise denoising and separation of overlapping events. The traditional curvelet transform denoising with a hard threshold function needs to give a reasonable threshold function control coefficient according to the noise level of GPR data. As a result, an appropriate choice of a hard threshold is a basic requirement, and this presents a challenging task in curvelet denoising. To overcome these shortcomings, an self-adaptive threshold function for GPR data denoising with curve transform is proposed in this paper. For detailing the reasonable control coefficient of the threshold function, the complex block threshold function algorithm is used to analyze the distribution of peak-signal-to-noise ratio value of the noisy synthetic GPR data contaminated with random and coherent noise by using the traditional threshold function curvelet transform. Based on the high order statistical theory, the accuracy distribution of the curvelet coefficient for useful signals in scale and rotation direction are correlatively stacked and determined by using the statistical self-adaptive function. And then the threshold range of noise removal components is given by the statistical self-adaptive function. The effectiveness of the proposed denoising algorithm for the noisy synthetic contaminated with different types of noise (i.e., Gaussian random and coherent), and field GPR data is demonstrated by comparing the denoising results via curvelet transform with those from traditional thresholding function. The presented denoising results by the statistical self-adaptive function is helpful and instructive for the accurate inference and interpretation of complex GPR data.
Influence of mass sample thickness on quantitative analysis of neutron activation and its modification
Authors: Sun Yuan-Ming , Xu Xu , Tang Wan-Yue , Chang Yi , Lu Jing-Bin , Zhao Long , Liu Yu-Min ,   College of Physics Jilin University, Changchun 130012, China
Published: December 2020

With traditional neutron activation analysis, the increase of sample quality leads to some problems in both irradiation process and measurement process. These problems include the neutron flux gradient in the range of the sample, the decrease of the thermal neutron flux rate around the sample and the influence of self-shielding in the sample in the irradiation process, In the process of measurement, the self-attenuation of γ-ray in the sample and the geometric effect of the sample lead to the effect of the detector on the measurement of characteristic γ-ray emissivity due to the difference in the detection efficiency of each point of the sample. So the neutron activation analysis of mass sample needs to make some additional modifications. By using the neutron activation analysis technique, the content of 24Mg and 28Si in a large amount of flour can be detected, and the content of talc powder in the flour can be given, so that the quality of flour can be monitored. The flour mainly contains C, H, O, N, Ca, and F element, but the main chemical constituent of talc powder is Mg3[Si4010](OH)2. Therefore, the measured content of Si and Mg element can be used to judge whether the flour contains talcum powder and to determine its exact content. When the content of 24Mg and 28Si in flour are measured by the neutron activation analysis, the variation of neutron flux and energy with thickness in the measured sample and the effect of γ-ray self-absorption will have great influence on the measurement results. The relationship between the neutron flux and energy and the thickness of the sample is simulated by MCNP5 (Monte Carlo N-particle transport code system 5), and the neutron fluxes at different thickness of the sample are measured by a 3He proportional counter tube. The results show that the simulation results of MCNP5 are basically consistent with the experimental results. Using the simulation by MCNP5 and the measurements by a sodium iodide detector, the relationship between γ-ray self-absorption effect and sample thickness is studied, and the sample thickness is determined to be 6.6.cm that is adopted as an optimal experimental condition. Based on the simulated data, the function relationship between the counting of 1.779 MeV γ-ray and the thickness of the sample is obtained as follows: A = 1401 + 3815x – 720x2 + 64x3 – 2.8x4 + 0.05x5. The curve trend of the experimental results is basically the same as that of the simulation results.
Optical properties of BaTiO3 and its volume effects
Authors: Sun Zhi-Zheng , Xun Wei , Zhang Jia-Yong , Liu Chuan-Yang , Zhong Jia-Lin , Wu Yin-Zhong ,   School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China,   School of Electronics and Information Engineering, Suzhou University of Science and Technology, Suzhou 215009, China
Published: December 2020

BaTiO3 (BTO) is a typical studying object both in ferroelectrics and in material science. By the GW method, optical property of BTO is investigated, and its volume effect under the case of iso-strain is also studied. It is found that the results of excited states are closer to the experimental results with the consideration of electron-hole interaction in the framework of GW method. Considering the volume effect, we obtain that the red shift of the peaks of optical absorption occurs under the expansion of volume, and the blue shift appears when the BTO is compressed. At the same time, the polarization and the hybridization between d orbital of Ti atom and p orbital of O atom are enhanced for the case of volume expansion, however, things will be opposite under the compression of volume. Furthermore, the volume effect in the iso-strain case is less dramatic than in the iso-stress case.
Leakage current model of InGaZnO thin film transistor
Authors: Deng Xiao-Qing , Deng Lian-Wen , He Yi-Ni , Liao Cong-Wei , Huang Sheng-Xiang , Luo Heng ,   School of Physics and Electronics, Central South University, Changsha 410083, China,   Hunan Province Engineering Technology Research Center in Novel Chip Inductance and Advanced Manufacturing Equipment, Huaihua 419600, China
Published: December 2020

In recent years, amorphous InGaZnO thin-film transistor (InGaZnO TFT) has attracted intensive attention. Due to its high mobility, low off-state current, and excellent uniformity over large fabrication area, the InGaZnO TFTs promise to replace silicon-based TFTs in flat panel displays, optical image sensors, touch sensing and fingerprint sensing area. The on-state performances of InGaZnO TFT are used in thin film transistor liquid crystal display, active-matrix organic light emitting display, etc. Consequently, numerous on-current models have been proposed previously. However, for lots of the emerging sensing applications such as optical image sensors, the leakage current of InGaZnO TFTs is critical.

Previous literature has shown that the leakage current generation mechanisms in TFTs include trap-assisted thermal emission, trap-assisted field emission, inter-band tunneling, and auxiliary thermal electron field emission containing Poole-Frenkel effect. However, up to now, there has been few reports on the leakage current model of InGaZnO TFT, which hinders further the development of emerging applications in InGaZnO TFTs for sensor and imagers integrated in display panels.

In this paper, the leakage current model of InGaZnO TFT is established on the basis of carrier generation recombination rate. The feasibility of the proposed model is proved by comparing the TCAD simulations with the measured results. In addition, the influences of geometrical parameters on the leakage current of InGaZnO TFT, i.e. the channel width, the active layer thickness, and the gate dielectric thickness, are analyzed in detail. This research gives insightful results for designing the sensors and circuits by using the InGaZnO TFTs.
Spectrum and dissociation properties of fluoro trichloro methane molecule in radiational field
Authors: Wu Yong-Gang , Liu Jia-Xing , Liu Hong-Ling , Xu Mei , Linghu Rong-Feng ,   School of Physics and Electronic Science, Guizhou Education University, Guiyang 550018, China,   School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, China
Published: December 2020

The ozone layer in the stratosphere of the earth’s atmosphere, which can be destroyed by CFC-11 molecule, plays a crucial role in human survival because it can absorb most of the harmful radiation from the sun and effectively protect the earth’s biology. Therefore, it is of evident significance to investigate the properties of CFC-11 molecule. By Motivated by this and the adoption of B3LYP complex function at a level of 6-311++g(3df, 3pd) basis set, we carry out a series of theoretical studies of the Freon material CFC-11 (CFCl3) molecules, including the studies of the equilibrium structure, electric dipole moment, total energy, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) level, energy gap, infrared and Raman spectrum, C—F dissociation characteristics of CFC-11 molecule, and the effect of the applied electric field on CFC-11 molecule as well. The results show that the maximum error between the theoretical calculation value and the experimental value is less than 2% for an optimized ground state structure; the C—F bond length and C—Cl bond length extend with the increase of electric field intensity, but the degree of change of C—F bond length is much stronger than that of C—Cl; the HOMO energy level and total energy go up and then come down as the external field rises, while the LUMO energy level goes up as the field increases. The energy gap Eg first increases and then decreases with the variation of EH and EL. The dipole moment without electric field is a minimum value, and the external electric field leads the molecular polarity to increase and the molecular activity to strengthen. The electric field influences the absorption intensity of infrared and Raman spectrum. The infrared and Raman spectrum move toward the long wave under the action of positive electric field, while they move toward the short wave under the action of negative electric field. The red- or blue-shift of infrared and Raman spectrum occur with the change of electric field. The electric field can be adopted as an auxiliary means to separate the overlapping or quasi-overlapping spectral lines. The potential well depth decreases with the increase of the reverse electric field until it vanishes, which causes the bound state ability of C—F bond of CFC-11 molecule to gradually degrade. This paper is expected to provide a feasible and effective tunable means for the final dissociation and degradation of CFC-11 molecules.
Optimal microwave imaging with random field illuminations
Authors: Zhou Tian-Yi ,   College of Information Science and Engineering, Ningbo University, Ningbo 315211, China
Published: December 2020

In the recent years, the theory and technologies of electromagnetic computational imaging have been well developed and several novel imaging methods have been proposed, one of which is known as the microwave imaging under random field illumination. In order to solve the matrix equation of imaging model, the key of such an imaging system is to generate the random electromagnetic radiation field distribution, implementing the independent measurements under random field illuminations. In this work, an optimal microwave imaging system for the desired imaging region and resolution is theoretically analyzed and experimentally implemented. In the randomness analysis, the correlation between different measurements is evaluated by the singular value decomposition, which is also adopted as a criterion for choosing the optimal parameters of the imaging system. Based on random field illuminations generated by the least number of antenna elements, a full-rank matrix equation can be used to reconstruct the object by direct matrix inversion, which can be completed in nearly real-time once the system calibration is implemented in advance. The numerical simulation and experimental investigation are performed, and the results prove the effectiveness of the proposed optimal imaging system. By using the traditional array theory, it is found that for an N-element phase array, N illuminations with each element excited by a single frequency, equal amplitude and randomized 0 or \begin{document}${\text{π}}$\end{document} phase signal will result in N independent measurements. Theoretically, any additional measurement under random illumination will be correlated with the previous N measurements. Since the random field illumination is obtained by array antennas with 1-bit random phase modulation, the power radiated by each transmitting element is not sacrificed, resulting in an optimal power efficiency of the imaging system compared with those of earlier metasurface-based imaging systems. Besides, a single frequency signal source is used in the system, which also realizes the optimal spectrum efficiency. In conclusion, there are two major innovations of the proposed imaging system: 1) the completely random field illuminations based on 1-bit phase modulation; 2) the approach to optimizing the system on desired demand. The compact and low-cost imaging system promises to have various imaging applications, such as public security and indoor localization.
A review of research on active noise control near human ear in complex sound field
Authors: Zou Hai-Shan , Qiu Xiao-Jun ,   Key Laboratory of Modern Acoustics, Ministry of Education, Institute of Acoustics of Nanjing University, Nanjing 210093, China,   Centre for Audio, Acoustics and Vibration, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney 2007, Australia
Published: December 2020

Local control of sound around human ears in complex acoustic environments is important for both active noise control and sound reproduction. Two typical active noise control approaches for this objective are active headrest systems and virtual sound barrier systems. In this paper, the history and the present status for the active headrest systems and virtual sound barrier systems are briefed first, then the theoretical principles, the design methods and the applications of these approaches are reviewed. Their advantages and limitations are discussed, and finally, the currently existing problems and future research directions are presented. The feasibility of these approaches to generating a quiet zone near a human ear has been verified by the theoretical research, numerical simulations and experiments. The active headrest systems require less control sources and are simpler for implementation; however, they suffer the problem of small-sized quiet zones. This results in the restrictions on the head movement since the error sensor needs to be close to the human ear to obtain better noise reduction performance. Based on the virtual sensor technology, a physical error sensor can be placed farther away from the human head, and create the quiet zone at the virtual sensor position near the human ear. Moreover, combined with the virtual sensor technology and the head-tracking technology, an active headrest system can generate a moving zone of quiet following the head movement, and the noise reduction can be achieved in a middle-to-high frequency range. A virtual sound barrier system reduces the sound pressure inside a volume, through controlling the sound pressure and normal gradient on the boundary of the volume. Two main design methods are the expansion method of the primary sound field which is suitable for steady primary sound fields, and the least mean square method which is applicable to time-varying primary sound fields. It can generate larger quiet zone at the cost of more control sources, more complexity and high cost. Optimizing cost functions and control sources and using hybrid active and passive control techniques can increase the effective frequency range and reduce the number of control sources. Although the feasibility of these two systems has been verified, more research work is needed to develop practical systems. An active-passive hybrid structure for specific application scenarios, which combines these two approaches together as well as the virtual sensor technology and sound field estimation technology, may most likely be practical methods to achieve effective noise reduction near the human ear in a complex sound field in the near future.
First-principles calculations of high pressure phase transition of Ce-La-Th alloy
Authors: Wang Yan , Cao Qian-Hui , Hu Cui-E , Zeng Zhao-Yi ,   School of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China
Published: December 2020

The lanthanide and actinide metals and alloys are of great interest in experimental and theoretical high-pressure research, because of the unique behavior of the f electrons under pressure and their delocalization and participation in bonding. Cerium (Ce) metal is the first lanthanide element with a 4f electron. It has a very complex phase diagram and displays intriguing physical and chemical properties. In addition, it is expected to be an excellent surrogate candidate for plutonium (Pu), one of the radioactive transuranic actinides with a 5f electron. The bulk properties and phase transformation characteristics of Ce-based alloys are similar to those of Pu and its compounds. Thus, the investigations of Ce-based alloys are necessary and can potentially advance the understanding of the behavior of Pu. In this work, the equation of state, phase transition, elastic and thermodynamic properties of Ce0.8La0.1Th0.1 alloy at high pressure are investigated by using first-principles calculations based on the density-functional theory. The structural properties of the Ce0.8La0.1Th0.1 alloy are in good agreement with the available experimental and theoretical data. The lattice constant a decreases with pressure increasing, while c shows an opposite variation. It is found that the lattice parameter c shows abnormal jump. And the critical volume is located at 20.1 Å3. The axial ratio jumps from a value of about \begin{document}$\sqrt 2 $\end{document} (corresponding to the fcc structure) to a higher value, which indicates that the fcc-bct transition occurs. And the corresponding transition pressure is located at ~31.6 GPa. When the pressure rises to 34.9 GPa, the bct structure displays a saturated c/a axial ratio close to about 1.67. The Young's modulus E, shear modulus G and the Debye temperature of the fcc phase tend to be " softened” around the phase transition pressure. The vibrational free energy is obtained by using the quasi-harmonic Debye model. And then the thermodynamic properties including the thermal equation of state, heat capacity and entropy under high pressure and high temperature are also predicted successfully. The results show that the heat capacity and entropy increase rapidly with temperature increasing, and decrease with pressure increasing. The high pressure can suppress part of the anharmonicity caused by temperature.
Experimental progress of quantum computation based on trapped single neutral atoms
Authors: Xu Peng , He Xiao-Dong , Liu Min , Wang Jin , Zhan Ming-Sheng ,   State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China,   Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071, China
Published: December 2020

As an important candidate for quantum simulation and quantum computation, a microscopic array of single atoms confined in optical dipole traps is advantageous in controlled interaction, long coherence time, and scalability of providing thousands of qubits in a small footprint of less than 1 mm2. Recently, several breakthroughs have greatly advanced the applications of neutral atom system in quantum simulation and quantum computation, such as atom-by-atom assembling of defect-free arbitrary atomic arrays, single qubit addressing and manipulating in two-dimensional and three-dimensional arrays, extending coherence time of atomic qubits, controlled-NOT (C-NOT) gate based on Rydberg interactions, high fidelity readout, etc.In this paper, the experimental progress of quantum computation based on trapped single neutral atoms is reviewed, along with two contributions done by single atom group in Wuhan Institute of Physics and Mathematics of Chinese Academy of Sciences. First, a magic-intensity trapping technique is developed and used to mitigate the detrimental decoherence effects which are induced by light shift and substantially enhance the coherence time to 225 ms which is 100 times as large as our previous coherence time thus amplifying the ratio between coherence time and single qubit operation time to 105. Second, the difference in resonant frequency between the two atoms of different isotopes is used to avoid crosstalking between individually addressing and manipulating nearby atoms. Based on this heteronuclear single atom system, the heteronuclear C-NOT quantum gate and entanglement of an Rb-85 atom and an Rb-87 atom are demonstrated via Rydberg blockade for the first time. These results will trigger the quests for new protocols and schemes to use the double species for quantum computation with neutral atoms. In the end, the challenge and outlook for further developing the neutral atom system in quantum simulation and quantum computation are also reviewed.
Influence of spectral filtering on mode-locking operation of figure-eight Er-doped fiber laser
Authors: Shi Jun-Kai , Wang Guo-Ming , Li Yao , Gao Shu-Yuan , Liu Li-Tuo , Zhou Wei-Hu ,   Laboratory of Laser Measurement Technology, Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Over the last decades, passive mode-locked fiber laser has received considerable attention because of ultrashort pulse, compactness, and low cost. As a saturable absorber, nonlinear optical loop mirror (NOLM) has shown the advantages of high damage threshold, possibility of all-PM fiber implementation, short response time and therefore potentially low intrinsic noise. Spectral filtering plays an important role in NOLM mode locked fiber laser, but the influence of filtering parameters on mode locking operation is rarely reported. In this paper, the influence of filtering bandwidth on mode locking operation and on output pulse characteristics are experimentally investigated. A 2 × 2 optical coupler with a splitting ratio of 10 : 90 is introduced at one end of fiber loop to form a loss-imbalanced NOLM, and extracts 90% of intracavity pulse energy as outputs. With this architecture, an all polarization-maintaining figure-8 Er-doped fiber ultrafast laser is achieved. A home-made bandwidth and wavelength tunable bandpass filter is utilized in the cavity, and the filtering bandwidth is defined by 10 dB bandwidth. The clockwise and counter-clockwise mode locked output power are 8.4 mW and 8.6 mW, respectively, with a repetition rate of 2.734 MHz. With a spectral bandwidth of 2.1 nm, the intracavity pulse is shaped by spectral filtering and soliton effect. The 3 dB bandwidth of the clockwise and counter-clockwise mode locked output pulse are 10.1 nm and 1.8 nm, and the values of corresponding full width at half maximum (FWHM) of the direct outputs are 583.7 fs and 2.94 ps, respectively. As the filtering bandwidth increases, the role of filter in spectral shaping weakens, and the parameters of two output pulses become close. When spectral bandwidth is larger than 7.3 nm, the intracavity pulse is shaped by gain spectrum and soliton effect. Both of the clockwise and counter-clockwise output pulses become the transform-limited pulses with almost the same FWHMs of 440 fs. Besides, the wavelength of the figure-8 fiber laser can be adjusted in a range larger than 30 nm by modulating the wavelength of the filter. The tunable mode-locked fiber laser has great potential applications in various application fields.
Identification and tracking of different types of crystalline nucleiduring isothermal crystallization of amorphous Ag
Authors: Li Yuan , Peng Ping ,   School of Materials Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

The isothermal crystallization of amorphous Ag is investigated by a molecular dynamics (MD) simulation, and the heredity and evolution of different types of crystalline clusters aretracked and analyzed by a reverse tracking method of atom trajectories with the help of cluster-type index method (CTIM) based on Honeycutt-Anderson (H-A) bond-type index. According to the difference in the type of crystalline cluster and the linkage mode, i.e., vertex-sharing (VS), edge-sharing (ES), face-sharing (FS) and intercross-sharing (IS), a cluster analysis method which can efficiently characterize fcc single-crystal, fcc poly-crystal and fcc hydrid-crystal, is proposed. That is, the IS-linkage of fcc basic clusters, i.e., a fcc medium range order, is defined as a fcc single-crystal cluster. The extended cluster of fccbasic clusterslinked by ISand FS modes is named fcc poly-crystal clusters. In the case of IS-linkages, if the majority of core atoms arefcc atoms, the extended cluster composed of fcc, hcp and bcc basic clusters will be regarded as a fcc hydrid-crystal cluster. Moreover, a structural analysis method of critical nuclei distinguishing embryosis also developed in terms of the hereditary characteristics of various crystalline clusters. In this scheme, the extended cluster which has only transient heredity and no continuous heredity is defined as an embryo, while it will be named nuclei if part of core atoms in extended clusters can keep cluster type of atoms unchanged and be continuously passed down in the early stage of crystallization. Thus, corresponding to the onset time/temperature of continuous heredity, the critical nuclei of fcc singe-crystals, fcc poly-crystals and fcc hybrid-crystals can be identified and characterized. It is found that the nuclei of fcc crystalsemerge after the steep drop of total energy of system and before the abrupt increase of sizesof tracked clusters. And regardless of critical sizes or geometric configurations, an evident difference exists among fcc singe-crystal, hybrid-crystal clusters and fcc poly-crystal clusters, of which the fcc single-crystal nucleus is the smallest (~1.6 nm ×1.0 nm × 1.1 nm), followed by poly-crystal nucleus (~1.7 nm × 1.0 nm × 1.6 nm) and hydrid-crystal nucleus (~2.3 nm × 2.0 nm × 2.4 nm) in sequence. There are a few hcp and bcc atoms at surfaces, i.e. shells, of single-crystal and poly-crystal nucleus, but neither hcp nor bcc atom can be detected at the shell of fcc hydrid-crystal nucleus. And theconfiguration of fcc single-crystal, poly-crystal and hydrid-crystal critical nuclei are all non-spherical.
Influence of distance between focusing lens and sample surface on laser-induced breakdown spectroscopy of brass at different sample temperatures
Authors: Yang Xue , Li Su-Yu , Jiang Yuan-Fei , Chen An-Min , Jin Ming-Xing ,   College of Science, Jilin Institute of Chemical Technology, Jilin 132022, China,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012, China
Published: December 2020

From previously published results of laser-induced breakdown spectroscopy, one can know that the change in the distance from the sample surface to the focusing lens has an important influence on the interaction between the sample and the laser, and increasing the sample temperature can enhance the coupling between the laser and the sample. However, almost no work has devoted to directly studying the influence of the distance between focusing lens and sample surface on the spectral intensity of laser-induced breakdown spectroscopy under different sample temperatures. In this paper, we investigate experimentally this subject. An Nd:YAG laser is used to excite the sample to produce the plasma. The detected spectral lines are Cu (I) 510.55 nm, Cu (I) 515.32 nm, and Cu (I) 521.82 nm. The focal length of focusing lens is 200 mm. The distance between focusing lens and sample surface ranges from 170 mm to 200 mm. The sample is heated from 25 ℃ to 270 ℃, and the laser energy is 26 mJ. In general, the spectral intensity of laser-induced breakdown spectroscopy can be effectively enhanced by increasing the sample temperature. At the sample temperatures of 25 ℃ and 100 ℃, the spectral intensity increases monotonically with the increase of the distance between focusing lens and sample surface; at higher sample temperatures (150, 200, 250, and 270 ℃), the spectral intensity first increases and then decreases with the increase of the distance between focusing lens and sample surface. In addition, near the focal point, with the increase of sample temperature, the increase of the spectral intensity is not obvious, and the spectral intensity decreases with the increase of sample temperature, which is particularly noteworthy in improving the spectral intensity of laser-induced breakdown spectroscopy by increasing sample temperature. In order to further understand the influences of these two conditions on laser-induced breakdown spectroscopy, we also calculate the plasma temperature and electron density, and find that the variation of plasma temperature and electron density are almost the same as that of spectral intensity. The plasma temperature and electron density at higher sample temperature are higher.
Recent advances in probing surface/interfacial water by scanning probe microscopy
Authors: You Si-Fan  , Sun Lu-Ye  , Guo Jing  , Qiu Xiao-Hui  , Jiang Ying  ,   1. International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China;,   2. National Center for Nanoscience and Technology, Beijing 100190, China;,   3. University of Chinese Academy of Sciences, Beijing 100049, China;,   4. Department of Chemistry, Beijing Normal University, Beijing 100875, China;,   5. Collaborative Innovation Center of Quantum Matter, Beijing 100871, China;,   6. CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Surface and interfacial water is ubiquitous in nature and modern technology.It plays vital roles in an extremely wide range of basic and applied fields including physics,chemistry,environmental science,material science,biology,geology, etc.Therefore,the studies of surface/interfacial water lies at the heart of water science.When water molecules are brought into contact with various materials,a variety of phenomena can show up,such as wetting,corrosion,lubrication, nanofluidics,ice nucleation,to name just a few.Due to the complexity of hydrogen-bonding interactions between water molecules and the competition between water-water interaction and water-solid interaction,surface/interfacial water is very sensitive to local environment,which makes it necessary to study the structure and dynamics of water at the molecular level.In recent years,the development of new scanning probe techniques allows detailed real-space research on surface/interfacial water at single-molecule or even submolecular scale.In Section 2,several representative scanning probe techniques and their applications in surface/interfacial water are reviewed.The first one is ultra-high vacuum scanning tunneling microscopy,which allows molecular imaging of single water molecules,water clusters,wetting layers,and even water multilayers on metal surfaces as well as ultrathin insulating films.Based on scanning tunneling microscopy,the single-molecule vibrational spectroscopy can be further developed to probe the vibration and movement of individual water molecules,which assist us in understanding water diffusion,dissociation and quantum nature of hydrogen bonds.As a versatile tool at liquid/solid interfaces,electrochemical scanning tunneling microscopy opens up the unique possibility of probing the double electric layer and identifying water dynamics during electrochemical reactions. Moreover,non-contact atomic force microscopy yields higher resolution than scanning tunneling microscopy,such that the topology of hydrogen-bonding skeleton of surface/interfacial water and even the degree of freedom of hydrogen atoms can be discerned.To conclude this review,the challenges and future directions of this field are discussed in Section 3, focusing on non-invasive imaging under ambient conditions,ultrafast molecular dynamics,and novel structures under high pressures.
Effect of intrinsic defects and copper impurities co-existing on electromagnetic optical properties of ZnO: First principles study
Authors: Zhang Mei-Ling , Chen Yu-Hong , Zhang Cai-Rong , Li Gong-Ping ,   School of Science, Lanzhou University of Technology, Lanzhou 730050, China,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
Published: December 2020

For ZnO which is not magnetic itself, it is of great significance to study the source of ferromagnetism and its photoelectric properties when Cu doped ZnO coexists with internal defects. The effects of intrinsic defects on the electronic structures, magnetic and optical properties of Cu-doped ZnO (CuZn) are studied by using first principle calculations based on the density functional theory combined with the Hubbard U (DFT + Ud + Up). The results indicate that the doped Cu is a substitute acceptor, and the manufacturing environment plays an important role in forming the CuZn with internal defects. Under the oxygen-rich condition, the doped Cu is favorable for forming internal defects, and the CuZn—Oi bonds are easily formed. On the contrary, the Cu-doped ZnO is not conducive to forming internal defects under the O-poor condition. The 3d electrons of the substitute Cu form the unoccupied accepter energy level at the top of valence band, generating p-type conduction. Comparing with CuZn system, the carrier concentration of positive hole decreases in CuZn-VO system and the conductivity is poor. In the CuZn-VZn system, the number of carrier holes is almost constant, and the conductivity has no effect. In the CuZn-Oi model, the carrier concentration of positive holes increases and the conductivity gets better. The pure ZnO system exhibits non-magnetic behavior. The study also reveals that the smaller the electro-negativity, the greater the contribution to magnetic moment is when O atom is connected with Cu atom. The magnetic moments in CuZn and CuZn-Oi system are mainly generated by the coupling between the Cu 3d and the O 2p orbital on the c axis. When VO and VZn exist in CuZn, the magnetic moment is mainly caused by the strong coupling of Cu 3d with O 2p in ab plane. In the presence of VZn in CuZn, the magnetism also contains the contribution of the spin polarization of O(5, 6) atoms around VZn. In the defect states of CuZn-VZn and CuZn-Oi, the induced states in the deep energy levels are generated by the interaction between the O-O 2s orbital electrons. The reduced optical band gap of the CuZn model results in the red shift of absorption spectrum. The enhanced absorption and reflection of the CuZn-VZn model reduce the transmission.
Double Fano resonance in gold nanotube embedded with a concentric elliptical cylinder
Authors: Zhang Xing-Fang , Liu Feng-Shou , Yan Xin , Liang Lan-Ju , Wei De-Quan ,   School of Opt-Electronic Engineering, Zaozhuang University, Zaozhuang 277160, China,   Laboratory of Optoelectronic Information Processing and Display of Shandong, Zaozhuang 277160, China
Published: December 2020

Optical properties of the concentric composite nanostructure composed of gold nanotube around the center gold elliptical core are investigated based on the finite difference time domain method. According to the simulated absorption and scattering spectra, electric field distributions and charge distributions, we can generate double dipole-dipole Fano resonances by adjusting the angle between the elliptical cylinder core and the linearly polarized excitation light, which is due mainly to the interference between the subradiant dipole mode and the superradiant dipole mode. The narrow, low-energy subradiant mode originates from the symmetric hybrization between the longitudinal or transverse dipole mode of the elliptical cylinder core and the dipole bonding mode of the nanotube, and the broad, high-energy superradiant mode originates from the symmetric hybrization between the core’s dipole mode and the nanotube’s dipole antibonding mode. Moreover, the intensities and spectral positions of the two Fano resonances can be manipulated by modifying the geometric parameters of the composite structure. By increasing the semiminor axis of elliptical core, the high-energy Fano resonance red-shifts faster than the low-energy Fano resonance due to the increase of the interaction coupling between the transverse dipole mode of the core and the dipole mode of the nanotube, and becomes weaker in the scattering spectrum because of the reduced radiation intensity of the superradiant dipole mode. When the semimajor axis is changed, a similar phenomenon occurs in the low-energy Fano resonance. In addition, the two Fano resonances red-shift when outer radius of the nanotube increases, but the shift of low-frequency and high-frequency Fano resonance are inconsistent as the inner radius of the nanotube changes. The high-frequency Fano resonance red-shifts monotonically while the low-frequency Fano resonance first blue-shifts and then red-shifts with the increase of inner radius of nanotube because the red shift of the dipole bonding nanotube mode competes with the spectral shifts induced by the diminishing hybridization between elliptical core and nanotube mode. It can also be concluded that the dipole-dipole Fano resonances become apparent and higher order Fano resonance occurs when the composite nanostructure is scaled to a larger size due to the increased radiative damping. With the core and nanotube size fixed, Fano resonance is insensitive to the change of the external environment, but has a good response to the nuclear material of the nanotube.
Influence of weighting function on accuracy of supersonic mixing layer wave-front variance estimation with linking equation
Authors: Xie Wen-Ke , Liu Jun-Sheng , Fei Jia-Le , Zhou Quan , Xia Hui , Chen Xin , Zhang Pan , Peng Yi-Ming , Yu Tao ,   School of Physics and Electronics, Central South University, Changsha 410083, China,   College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In aero optics, the linking equation proposed by Sutton is an important equation which can link the fluid-mechanic statistical parameters to the statistical optical degradation parameters. However, in the application of simplified linking equation (SLE) to subsonic flowfields, the weighting function is often ignored. The supersonic mixing layer flowfield is generated in the supersonic wind tunnel. The nanoparticle-based planar laser scattering technology is used to obtain the density field of flowfield. The optics errors between supersonic mixing layer wave-front variances calculated from the SLE and the generalized linking equation are analyzed. The results indicate the validity of using the SLE to estimate the wave-front variance of supersonic mixing layer flowfield. Moreover, the SLE with weighting function has better fitting accuracy than the SLE without weighting function. The weighting function for the application of SLE to the high correlated regions in the supersonic mixing layer is necessary.
Ultracold dipolar molecules
Authors: Lu Bo , Wang Da-Jun ,   Laboratory of Quantum Engineering and Quantum Metrology, School of Physics and Astronomy, Sun Yat-Sen University (Zhuhai Campus), Zhuhai 519082, China,   Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Published: December 2020

The research field of ultracold atoms has expanded from atomic and molecular physics to a variety of fields. Ultracold polar molecules have long range and anisotropic dipole-dipole interactions, and similar to atoms, can also be conveniently manipulated by laser and other electromagnetic fields. Thus, ultracold molecules offer promising applications such as ultracold chemistry, quantum simulation, and quantum information. However, due to the difficulty in creating ultracold ground state molecules, expanding the horizon of ultracold physics from atoms to molecules is still under development. In the past decade, many research groups have successfully created bi-alkali rovibrational ground state polar molecules using magneto association and stimulated Raman adiabatic passage (STIRAP). This paper presents a review of the recent progress including creating and manipulating ultracold molecules with this method, and the collision property of molecules at ultracold temperature.
Observation of ejecta tin particles into polymer foam through high-energy X-ray radiograpy using high-intensity short-pulse laser
Authors: Shui Min , Yu Ming-Hai , Chu Gen-Bai , Xi Tao , Fan Wei , Zhao Yong-Qiang , Xin Jian-Ting , He Wei-Hua , Gu Yu-Qiu ,   Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Micron-scale fragment ejection of metal is a kind of surface dynamic fragmentation phenomenon upon shock loading. The study of ejecta is crucial in many fields, such as inertial confinement fusion and pyrotechnics. Due to the particular advantages of laser experiments, a lot of studies of ejecta by strong laser-induced shock loading have been conducted in recent years. The shapes, size and mass of particle can be obtained via static soft recovery technique with foam. However, the stagnation and succedent mixing of the ejecta in the foam could not be deduced by this technique. To study the mixing between the ejecta and foam, a radiography experiment is performed by using the X-ray generated through the irradiation of picosecond laser on the golden wire. This radiography technique has not only high spatial resolution but also high temporal resolution. Two kind of experiments are designed and performed. In the first one, the tin sample and the foam are close to each other while a vacuum gap is arranged between them in the other one. The mixing process is analyzed with the determined areal density and volume density, as well as the results of recovery. The areal density of the front mixing area is similar to the scenario in the case with a vacuum gap, suggesting that the ejecta have not underwent a secondary fragmentation due to the collision with foam. Furthermore, the static recovery results show a different characteristic of penetration depth for the ejecta in the foam. When the tin sample is not close to the foam, the penetration depth in the foam increases with the loading pressure increasing. However, the penetration depth begins to decrease at a critical pressure after a brief increase, which is attributed to the interaction between the shock and the foam before the ejecta coming, and also to the ejecta size and composition. The shock pressure is high enough to change the foam performance, thus enhancing the stagnation ability for ejecta penetration. Moreover, the size and composition vary with loading pressure, thereby leading to the momentum change of the ejecta related to the penetration depth. In the future work, we will improve the field of view of the X-ray radiography to achieve a direct comparison between the dynamic results and the recovery results. Moreover, we will arrange perturbations at the interface to study the mixing between the micro-jetting and the foam and the interface instability.
Evaluation of blackbody-radiation frequency shift in strontium optical lattice clock
Authors: Li Ting , Lu Xiao-Tong , Zhang Qiang , Kong De-Huan , Wang Ye-Bing , Chang Hong ,   Key Laboratory of Time and Frequency Primary Standards of Chinese Academy of Sciences, National Time Service Center, Xi’an 710600, China,   School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China,   College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China
Published: December 2020

The frequency shift caused by blackbody radiation is one of the dominant corrections to the evaluation of the optical lattice clock. The frequency shift of blackbody radiation is closely related to the dynamic and static correction factor, ambient temperature and atomic polarizability. The blackbody radiation shift is mainly affected by ambient temperature. During the normal operation of the strontium atom optical lattice clock, the experimental environment and other heat sources around the vacuum cavity have complicated the environment around the vacuum cavity, resulting in the fact that the external surface temperature of the vacuum cavity does not truly reflect the temperature change of the vacuum cavity. For the strontium atomic optical clock experimental apparatus of the National Time Service Center, the uncertainty and correctionof the blackbody radiation frequency shift are evaluated by the theoretical analysis, measurement of the temperature of the vacuum cavity outer surface, and software simulation. Among them, the frequency shift of black body radiation caused by strontium atom furnace, sapphire heating window, room temperature radiation entering into the vacuum cavity through the window plate, and the thermal radiation at the atomic group caused by Zeeman reducer are analyzed. Five temperature measuring points are set on the external surface of the vacuum chamber, and the temperature changes on the external surface of the vacuum chamber are monitored in real time by using the calibrated platinum resistance temperature sensor while the system is running normally. We obtain the average temperature of the five temperature measuring points. The model of vacuum cavity is established by using the SolidWorks. The method of finite element analysis is used to simulate the variation of the temperature around atom samples. We also obtain the temperature distribution around the atomic groups in the vacuum cavity. The result shows that the temperature around atoms varies with the temperature of the vacuum cavity. When the temperature of the ambient temperature changes 0.72 K, the fluctuation of the temperature around the atoms is 0.34 K. Finally, the total correction of blackbody radiation of the system is evaluated to be –2.13(1) Hz, and the correction uncertainty is about 2.4 × 10–17.