bluuebunny/crossref_metadata_2025 huggingface dataset:
A review of correlative modeling for transport properties, microstructures, and compositions of granular materials in soft matter
Authors: Xu Wen-Xiang  , Sun Hong-Guang  , Chen Wen  , Chen Hui-Su  ,   Institute of Soft Matter Mechanics, College of Mechanics and Materials, Hohai University, Nanjing 211100, China;,   Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China
Published: December 2020

The transport property of granular material that is a typical of soft matter, plays a significant role in durability and service life in a relevant practical engineering structure. Physical properties of material is generally dependent on its microstructure. Meanwhile, the formation of microstructure is directly related to compositions of granular material. Understanding the intrinsic mechanisms of composition, microstructure, and transport property are of great importance for improving mechanical properties and durability of granular material. In this article, we review the new progress of modeling transport properties of granular multiphase materials. We focus on the three main aspects involving the simulations for geometrical models of composition structures, the quantitative characterizations for microstructures of pore and interface phases, and the theoretical and numerical strategies for transport properties of granular multiphase materials. In the first aspect, in-depth reviews of realizing complex morphologies of geometrical particles, detecting the overlap between adjacent non-spherical particles, and packing randomly non-spherical particles are presented. In the second aspect, we emphasize the development progress of the interfacial thickness and porosity distribution, the interfacial volume fraction, and the continuum percolation of soft particles such as compliant interfaces and discrete pores. In the final aspect, the modeling the transport properties and the frontier issues of the effective diffusion and anomalous diffusion in granular multiphase materials are elucidated. Finally, some conclusions and perspectives for future studies are provided.
Development and application of bio-inspired and biomimetic microfluidics
Authors: Min Ling-Li  , Chen Song-yue  , Sheng Zhi-Zhi  , Wang Hong-Long  , Wu Feng  , Wang Miao  , Hou Xu  ,   Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, Xiamen University, Xiamen 361005, China;,   School of Physics and Mechanical & Electrical Engineering, Xiamen University, Xiamen 361005, China;,   College of Aeronautics and Astronautics, Xiamen University, Xiamen 361005, China;,   College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China;,   Collaborative Innovation Center of Chemistry for Energy Materials, Xiamen 361005, China
Published: December 2020

Biomimetic microfluidic systemscan be obtained through multidisciplinary approaches by using bio-inspired structural and functional designsfor the microfluidic devices. This review mainly focuseson the concept of biomimetic microfluidics to improve the properties of microfluidic systemsfor breaking through the bottlenecks of the current microfluidic devices, such as antifoulingsmart, anddynamic response insidethe microchannelsunder different environments. In addition, herewe showthecurrentresearch progress ofbiomimetic microfluidic systems in applicationsrelatedtoantifoulingandsmartdevices, andbiomedicalresearch The review discusses both physical theories and critical technologies in thebiomimetic microfluidics, from biomimetic design to real-worldapplications, so as to offer new ideas for the design and application of smart microfluidics, and the authors hope this review will inspire the active interest of many scientists in the area of the development and application of soft matter, and multi-functional and smart biomimetic devices.
Dynamics of actin monomers assembled into long filaments
Authors: Guo Kun-Kun  , Yi Xie  ,   College of Materials Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

We investigate the dynamics of actin monomers that are assembled into long filaments via the particle-based Brownian dynamics simulations. In order to study the dynamics of long filaments containing up to several hundred protomers, a coarse-grained model for actin polymerization involving several simplifications is used. In order to overcome the large separation of time scales between the diffusive motion of the free monomers and the relatively slow polymerized and depolymerized processes at the two ends of the filaments, all polymerized and depolymerized rates are rescaled by a dimensionless parameter. Actin protomers within a filament generally possess three nucleotide states corresponding to a bound adenosine triphosphate (ATP), adenosine diphosphate with inorganic phosphate (ADP. Pi), and ADP molecules in the presence of ATP hydrolysis. Here in this paper, single nucleotide state and two nucleotide states of actin protomers are described by the simplified theoretical model, giving the dependence of the growth rate on actin concentration. The simplest case where all protomers are identical, is provided by the assembly of ADP-actins. In the simulations, the growth rate is found to increase linearly with free monomer concentration, which agrees quantitatively with in vitro experimental result. These surprised phenomena observed in the experiments, such as treadmilling processes and length diffusion of actin filaments at the steady state, are presented in detail by Brownian dynamics simulations. For free actin concentrations close to the critical concentration, cT ccr, T, the filaments undergo treadmilling, that is, they grow at the barbed end and shrink at the pointed end, leading to the directed translational motion of the filament. In the absence of ATP hydrolysis, the functional dependence of a length diffusion constant on ADP-actin monomer concentration implies that a length diffusion constant is found to increase linearly with ADP-actin monomer concentration. With the coupling of ATP hydrolysis, a peak of the filament length diffusion as a function of ATP-actin monomer concentration is observed i. e. , the length diffusion coefficient is peaked near to 35 mon2/s below the critical concentration and recovers to the expected estimate of 1 mon2/s above the critical concentration. These obtained results are well consistent with the experimental results and stochastic theoretical analysis. Furthermore, several other quantities and relations that are difficult to study experimentally but provide nontrivial crosschecks on the consistency of our simulations, are investigated in the particle-based simulations. The particle-based simulations developed in our studies would easily extend to study a variety of more complex systems, such as the assembly process of other dynamic cytoskeletons
Thermodynamics of trapped finite unitary Fermi gas
Authors: Yuan Du-Qi  ,   College of Physics and Photoelectric Technology, Baoji University of Science and Arts, Baoji 721016, China
Published: December 2020

At zero-temperature and finite-temperature, the thermodynamic properties of finite unitary Fermi gas in a three-dimensional harmonic trap are investigated by using fractional exclusion statistics, and the results are compared with those of the system which satisfies the thermodynamic limit. At zero-temperature, Fermi energy and average energy of per particle increase with the increase of the number of particles for finite unitary Fermi gas, and their limits are the corresponding parameters of the system which satisfy thermodynamic limits. Fermi energy and average energy of per particle each have a maximum value changing with the boundary of the potential well. For the finite-temperature trapped unitary Fermi system, when the number of particles is certain the average energy of per particle, average entropy of per particle, average heat capacity of per particle each have a characteristic temperature, respectively, when the temperature is equal to the characteristic temperature of the physical parameter, the corresponding parameters for the finite system and the thermodynamic limit system are equal, when the temperature is lower (or higher) than the characteristic temperature of parameter, the physical parameter of the finite system will be greater (or less) than the corresponding parameter of the thermodynamic limit system. The characteristic temperature has particle number effect and boundary effect. When the temperature is determined, the average energy of per particle, average entropy of per particle and average heat capacity of per particle each have a characteristic number of particles, respectively, when the number of particles is equal to the characteristic number of particles for physical parameter, the corresponding parameters for the finite system and the thermodynamic limit system are equal, when the number of particles is less (or more) than the characteristic number of particles for corresponding parameter, the corresponding parameter of the finite system will be less (or larger) than the thermodynamic limit of system.
Crises in a non-autonomous fractional-order Duffing system
Authors: Liu Xiao-Jun  , Hong Ling  , Jiang Jun  ,   College of Science, Northwest A&F University, Yangling 712100, China;,   State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In this paper, the crises in a non-autonomous fractional-order Duffing system are investigated. Firstly, based on the short memory principle of fractional derivative, a global numerical method called an extended generalized cell mapping (EGCM), which combines the generalized cell mapping with the improved predictor-corrector algorithm, is proposed for fractional-order nonlinear systems. The one-step transition probability matrix of Markov chain of the EGCM is generated by the improved predictor-corrector approach for fractional-order systems. The one-step mapping time of the proposed method is evaluated with the help of the short memory principle for fractional derivative to deal with its non-local property and to properly define a bound of the truncation error by considering the features of cell mapping. On the basis of the characteristics of the cell state space, the bound of the truncation error is defined to ensure that the truncation error is less than half a cell size. For a fractional-order Duffing system, boundary and interior crises with varying the derivative order and the intensity of external excitation are determined by the EGCM method. A boundary crisis results from the collision of a chaotic (or regular) saddle in the fractal (or smooth) basin boundary with a periodic (or chaotic) attractor. An interior crisis happens when an unstable chaotic set in the basin of attraction collides with a periodic attractor, which causes a chaotic attractor to occur, and simultaneously the previous attractor and the unstable chaotic set are converted into a part of the chaotic attractor. It is found that a crisis can be generally defined as a collision between a chaotic basic set and a basic set, either periodic or chaotic, to cause the chaotic set to have a sudden discontinuous change. Here the chaotic set involves three different kinds of chaotic basic sets: a chaotic attractor, a chaotic saddle on a fractal basin boundary, and a chaotic saddle in the interior of a basin and disjoint from the attractor. The results further reveal that the EGCM is a powerful tool to determine the global dynamics of fractional-order systems.
Precise controll of hollow beam size
Authors: Zhu Qing-Zhi  , Wu Feng-Tie  , Hu Run  , Feng Cong  ,   Fujian Provincial Key Laboratory of Light Propagation and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

A novel technique to generate precisely size-controlled hollow beams by controlling the diameter of circular slit is proposed. Firstly, a laser beam is transformed into a quasi-monochromatic incoherent annular source by a rotating ground-glass disk and circular slit. Then, after passing through a thin converging lens, a J0-correlated Schell-model beam is synthesized by placing the annular incoherent source in the first focal plane of the thin lens. Finally, a partially coherent hollow beam is generated by focusing the J0-correlated Schell-model beam with an axicon. Based on the diffraction theory and the propagation law of partially coherent beams, the cross-spectral density function is derived to calculate the intensity distribution of the cross section and the radial intensity distribution along the propagation axis behind the axicon. By carrying out the theoretical calculation, the proposed optical system generates a partially hollow beam, and the size of the hollow beam expands continuously as the propagation distance increases. Before further investigating the effect of the diameter of incoherent annular source on the hollow beam behind the axicon, we also calculate the intensity distribution of the cross section and the size of hollow beams along the propagation axis at z=70 mm with the source diameters being 1, 2, 3, 4 and 5 mm, respectively. Results show that the size of the hollow beam also increases with the diameter of incoherent annular source increasing. In this case, the size of the hollow beam can be precisely controlled by tuning the diameter of incoherent annular source through circular slit. We also design and conduct an experimental generation of the hollow beam and investigate the propagation properties. In the experiment, we control the diameter of the annular source by tuning the diameter of the circular slit located before the rotating ground-glass disk. And the diameter of the annular source is equal to that of the circular slits. When the sizes of circular slits are 1, 2, 3, 4 and 5 mm, respectively, the corresponding hollow beams are measured by CCD. Experimental results show that the size of hollow beam can be controlled by the propagation distance and the diameter of the circular slit. The intensity profiles are in good agreement with theoretical predictions. Therefore, the size of hollow beams can be precisely generated and controlled by the proposed system so that the optical system can be flexibly employed in optical trapping and manipulation of particles with different sizes. The results may provide a powerful tool for manipulating the micro- and nano-particles.
Theory and calculations of colloidal depletion interaction
Authors: Ma Hong-Ru  ,   School of Mechanical Engineering, Shanghai Jiaotong University, Shanghai 200240, China;,   Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shanghai Jiaotong University, Shanghai 200240, China
Published: December 2020

Colloidal suspension is composed of particles with sizes between 1 nm and 1 m, suspended in liquid phase. The interaction between the particles consists of a hard core repulsive interaction and other kinds of repulsive and attractive interacions. Hard interaction forbids the particles from occupying the same places, resulting in a depletion effect. When big colloid particles are immersed in a colloid of small particles, each big particle has a depletion layer where the small particles cannot enter due to the hard interaction. The depletion layers of two big particles overlap when they are close enough so that extra free volume of the small particles increases and therefore the entropy of the small particles increase, thus an effective interaction between big particles is induced. This effective interaction is the so-called depletion interaction. In this review the concepts and an intuitive explanation of depletion interaction of colloidal suspensions are presented. The numerical calculation methods, including the acceptance ratio method, Wang-Landau-type method, and density functional theory method, are briefly reviewed. Several useful analytic approximations are presented. Stating from the depletion interaction between two flat plates, the Derjaguin approximation is introduced through the Asakura- Oosawa model. With this approximation, the approximate formulas of depletion interaction between two hard spheres, between a hard sphere and a hard wall, and between a hard sphere and curved hard walls in a small hard sphere colloid are derived. The depletion interaction between two hard spheres in a thin rod colloid and a thin disk colloid are also derived in the Derjaguin approximation.
Numerical solutions of Grad-Shafranov equation in a field-reversed configuration
Authors: Zhao Xiao-Ming  , Sun Qi-Zhi  , Fang Dong-Fan  , Jia Yue-Song  , Liu Zheng-Fen  , Sun Cheng-Wei  ,   Key Laboratory of Pulse Power, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

The solution of Grad-Shafranov equation in field-reversed configuration (FRC) is a basic problem. The solution of Grad-Shafranov equation can help to understand most of physical processes in FRC plasma, such as magnetohydrodynamic (MHD) instabilities and plasma transport. In the present paper, based on the FRC asymptotic theory by Barnes D C, the code for solving the two-dimensional Grad-Shafranov equation in FRC is developed. By using the code, the equilibriums of FRC with different elongations and separatrix radii are investigated in the present paper. The one-dimensional numerical results show that the plasma density gradient increases linearly with magnetic flux increasing in the FRC center, while, it steepens due to the high magnetic field distribution at the separatrix. The results also show that the plasma density in the closed field region increases with the density at the separatrix increasing, which implies that FRC embodies the strong confinement ability. It is a key problem to choose equations determining the shape of the separatrix in a two-dimensional numerical investigation. In the present paper, the shape equation is described as rs = rs max (1 - z2a), in which a is the shaping parameter. When a=1, the separatrix shape is elliptical, and when a1, the separatrix shape is like a racetrack. The geometry character of the separatrix appears in the one-order equations (in one-order equations: (0)/(z) = (0)/(rs)(rs)/(z), where (0)/(rs) is determined by lead equations and (rs)/(z) is given by separatrix equation). The two-dimensional numerical results show that O-point moves outward as the sparatrix radius increases. The curvature radius of magnetic flux surface increases with the separatrix radius increasing. The O-point of magnetic flux surface is just at the curvature center. Thus O-point moves outward as the sparatrix radius increases.
Cylindric high power impulse magnetron sputtering source and its discharge characteristics
Authors: Xiao Shu  , Wu Zhong-Zhen  , Cui Sui-Han  , Liu Liang-Liang  , Zheng Bo-Cong  , Lin Hai  , Ricky K Y Fu  , Tian Xiu-Bo  , Pan Feng  , Paul K Chu  ,   School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen 518055, China;,   Department of Physics and Materials Science, City University of Hong Kong, Hong Kong 999077, China
Published: December 2020

High power impulse magnetron sputtering (HiPIMS) is a popular physical vapor deposition (PVD) technology because of the high ionization of the sputtering materials, large coating density, good adhesion, and other favorable properties. However, this technique suffers some disadvantages such as the small deposition rate induced by the high target potential, the metallic droplets produced by the unstable discharge, and different ionizations for different sputtering materials, thereby hampering wider acceptance by the industry. A cylindric HiPIMS source in which the discharge is restricted in the cylinder is described in this paper. By using this source, coatings can be deposited with 100% ions without metallic droplets arising from the unstable discharge, and the unionized sputtered atoms cannot be extracted by the extraction grid with negative potential. Electron oscillation and repetitive sputtering of the unionized atoms occur in the cylinder to enhance collision and ionization. Due to the enlarged discharge area by the cylinder internal surface comparing with the area of the ion outlet (end face of the cylinder), the sputtering ions converge from the inwall to the center of the cylinder target and form an enhanced flow to spray out from the source, which will improve the deposition rate. The structure and discharge characteristics of the novel HiPIMS source are investigated by simulation and experiments. Our results indicate that 8 magnets can provide the reasonable magnetic field and the highest target utilization rate. The distributions of electrons and ions in the target each consist of 8 petals in the optimized magnetic structure, and the highest plasma density happens near the target, which is above 1.31017 m-3. The discharge characteristics confirm that the cylindric sputtering source can be operated under HiPIMS conditions and the evolution of the target currents with target voltage exhibits I-V characteristics typical of HiPIMS. An obvious pre-ionization is observed on the discharge glow and discharge current curves when the extra direct current (DC) is added. The racetrack area is about 60.0% of the target surface. The ion current curves are similar to those of the target currents, but a 40 s delay and about one-tenth current value are observed compared with the target currents. The sputtering is improved by the extra DC, inducing the increased metallic ions and the opposite evolution of gas ions. The results suggest that the cylindric sputtering source can be effectively used to conduct HiPIMS and is a novel way to improve and promote the application of HiPIMS.
Recent development on the theory of polymer crystallization
Authors: Yan Da-Dong  , Zhang Xing-Hua  ,   Department of Physics, Beijing Normal University, Beijing 100875, China;,   School of Science, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In this paper, the history and the recent development of polymer crystallization have been reviewed briefly. After introducing the conventional Hoffman-Lauritzen theory, the recent new experimental results, especially on X-ray scattering, have been summarized. Some new models of crystallization have been reviewed, such as Strobl's mesomorphic phase model, Olmsted's spinodal-assisted crystallization theory, and Muthukumar's molecular modeling of polymer crystallization.
Three-dimensional morphological wrinkling of cylindrical soft tissues
Authors: Xie Wei-Hua  , Yin Si-Fan  , Li Bo  , Cao Yan-Ping  , Feng Xi-Qiao  ,   Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
Published: December 2020

Investigations of the growth-induced deformations of soft biological tissues may help understand the underlying mechanical mechanisms of their morphogenesis and provide clues for diagnosing some diseases. In the framework of continuum mechanics, we establish a three-dimensional model to analyze the instabilities of cylindrical soft tissues induced by volumetric growth. The different three-dimensional wrinkling patterns under either free or fixed boundary conditions at the outer surface are considered. It is found that Euler buckling, axially symmetrical wrinkling, and checkerboard wrinkling may occur under the traction-free boundary conditions, while axisymmetric pattern and checkerboard pattern often appear under the fixed boundary conditions. Phase diagrams are constructed to predict the morphologies in terms of the geometrical and material parameters of the system. Besides, a pseudo-dynamic numerical method is invoked to simulate the postbuckling evolutions of the wrinkling patterns.
In vitro experimental models and their molding technology of tumor cell
Authors: Wang Gao  , Wang Xiao-Chen  , Liu Ting  , Liu Ru-Chuan  , Liu Li-Yu  ,   College of Physics, Chongqing University, Chongqing 401331, China;,   Key Laboratory of Soft Matter, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Traditional cancer researches focus on the analyses of the mice biopsy in order to understand the formation of cancer and the stage of cancer development. In contrast to in vivo experiments, in vitro investigation of cancer cells provides the flexible manipulation of the experimental parameters and the real time observation of the growth and reproduction of cancer cells, thus has been developing rapidly. However, further studies have demonstrated that cells' behavior in a two-dimensional (2D) environment, e.g. Petri dish, is dramatically different from that in a three-dimensional (3D) environment. Therefore, with assistance of bio-microfluidic chips, 3D bio-printing, direct femtosecond laser writing technology and UV curing hydrogel technology, an increasing number of 3D models have been developed to investigate the behaviors of cancer cells in vitro. Nevertheless, the existing technology is also facing the contradiction between accuracy and speed requirements, as well as the biocompatibility and biodegradability of scaffold materials in use. In this paper, we first summarize and compare present 2D models, e. g. Agar Plate and Boyden Assay, and the developing 3D models in vitro experimental approaches as mentioned above, and discuss the merits of these fabricating technologies. Then we focus on the recent progress and achievements of 3D bio-techniques, especially the successful applications in probing the invasion behaviors of cancer cells. Though significant progress has been made from 2D to 3D approaches and these in vitro experimental models are becoming more flawless in simulating the in vivo environment of cells, the following challenges remain: 1) biocompatible material with the appropriate mechanic properties simulating the environment in vivo; 2) the viability of cells in the complex 3D model with of biomaterial, especially during the laser or UV-assisted gelation of hydrogels; 3) the speed and resolution of the present 3D fabrication technologies; 4) the in situ observation and control of cells. Nevertheless, with the development of 3D bio-technologies, breakthroughs can be expected in solving those problems, and thus will guide the 3D experimental models for the invasion of cancer cells in next few years. This will eventually help people in the war towards cancers, and at the same time provide new experimental approaches for other relevant researches in the interdisciplinary fields of biology, physics, chemistry, materials and engineering.
Multi-photon dissociation dynamics of Freon 114B2 under UV radiation by femtosecond laser pulse
Authors: Liu Yu-Zhu  , Deng Xu-Lan  , Li Shuai  , Guan Yue  , Li Jing  , Long Jin-You  , Zhang Bing  ,   School of Physics and Opto-electronics Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology(CICAEET), Nanjing 210044, China;,   State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430074, China
Published: December 2020

The ozone layer which absorbs harmful solar UV radiation is a necessary umbrella for human beings and biosphere. A large amount of alkyl halide including freon exhausted by human into the atmosphere poses a great threat to the ozone layer. Freon dissociates into the product of halogen radical, like Br and Cl, induced by UV sunlight radiation, which is found to be the main culprit for the destruction of atmospheric ozone. In this paper, time-of-flight (TOF) mass spectrometry and velocity map imaging technique are employed for investigating the multiphoton dissociation dynamics of Freon F114B2 (C2F4Br2) induced by femtosecond UV radiation at 267 nm. Fragment mass spectra of C2F4Br2 under UV radiation at 266 nm are obtained by TOF mass spectrometry. Three daughter ions C2F4Br+, C2F4+ and CF2Br+are discovered together with the parent ions C2F4Br2+. And three corresponding photodissociation mechanisms are concluded as follows: 1) C2F4Br2+C2F4Br++Br with single CBr bond breaking and direct production of Br radical; 2) C2F4Br2+C2F4++2Br with double CBr bonds breaking and production of two Br radical; 3) C2F4Br2+CF2Br++CF2Br with CC bond breaking. Velocity map images of the strongest daughter ion C2F4Br+with CBr breaking are measured by imaging apparatus. The kinetic energy distribution of C2F4Br+ ions is obtained from the measured velocity map images. And it can be well fitted by three Gaussian curves which describe normal distribution. It indicates that the production of the fragment C2F4Br+ stems from three different dissociation channels. Additional photodissociation dynamics is obtained by analyzing the angular distribution of the measured image. The values of anisotropy parameter are measured to be 0.1 (for the low energy channel), 0.8 (for the middle energy channel) and 1.4 (for the high energy channel) for the fragment C2F4Br+, respectively. The ratios of parallel transition to perpendicular transition are determined for three different channels. In addition, density functional theory calculations are also performed for further analysis and discussion. The optimized geometries of ground state and ionic state of C2F4Br2 are obtained and compared at the level of B3LYP/6-311G++(d, p). The calculated information about ionic states, including energy level and oscillator strength for the ionic excited states, are given.
A method of detecting stomach tumour based on capsule endoscopy
Authors: Chen Gong  , Zhang Ye-Rong  ,   College of Electronics Science and Technology, Nanjing University of Post and Telecommunications, Nanjing 210003, China
Published: December 2020

In order to solve the problems of rapidly recognizing the shapes of the tumour in the stomach, a new kind of capsule endoscopy with through-body radar is utilized for the first time. Finite difference time domain method is used to establish an electromagnetic simulation model of stomach. After being swallowed by a patient, the capsule which consists of the radar moves through esophagus and stomach. Finally it drains out of the body by the self peristalsis of the human GI tract. During this time, the radar is used to transmit accurate radar data of human stomach. Then we will carry out electromagnetic inverse scattering imaging by back projection algorithm with the radar data. The algorithm must consider the influence of various tissues in the human body: the attenuation of the signal strength of electromagnetic waves, the decrease in speed and the refraction due to the different permittivities between the different organs of the body. These factors will eventually lead to image offset, and even generating a virtual image. It is effective to refrain the displacement of image with modifying the time element of the imaging algorithm by iteration. It is shown that ultra-wideband radar built-in capsule endoscopy can track and locate targets in the human's stomach.
Characteristics of the spontaneous emission field and spectrum of a two-level atom in a dynamic photonic crystal
Authors: Xing Rong  , Xie Shuang-Yuan  , Xu Jing-Ping  , Yang Ya-Ping  ,   Ministry of Education Key Laboratory of Advanced Microstructure Materials, School of Physics Science and Engineering, Tongji University Shanghai 200092, China
Published: December 2020

The spontaneous emission field and spectrum of a two-level atom, located in an isotropic photonic crystal with dynamic band edges, are investigated by means of numeric calculation. The investigation is expected to help comprehend the characteristics of the atomic spontaneous emission in the dynamic photonic crystal, and provide a possible way to control dynamically the spontaneous emission in photonic crystal. The expression of the spontaneous radiation field is obtained without using the far-zone approximation and the Weisskopf-Wigner approximation, and expected to be applicable in other relevant researches. In the investigation, the spontaneous radiation field and spectrum are calculated when the band edge frequency is unmodulated, or modulated by a step function or triangle function. In the unmodulated situation, the radiation field intensity tends to a constant which is equal to the intensity of the localized field component. The radiation field pulse presents a wave packet behavior as propagation distance increases. The components of the radiation field correspond one-to-one to the peaks in the spontaneous radiation spectrum. When the band edge frequency is modulated by step function, the radiation field intensity tends to a steady-state value after the modulation has happened. And the steady-state intensity is affected by the time when the modulation happens. The components of the non-localized field and the frequency of the localized field after modulation depend on the atomic transition frequency and the band edge frequency, and are identical to those in the unmodulated situation with the same parameters. When the band edge frequency is modulated by a triangle function, the field intensity presents a decaying quasi-periodic oscillation after a long enough time. The modulation frequency determines the frequency of the oscillation, and influences the decay rate. The radiation energy becomes sharp peaks around a set of the discrete frequencies which are evenly spaced with the modulation frequency. The central frequency of these frequencies depends on the atomic transition frequency and the value range of the band edge frequency. The modulation initial phase affects the intensity of the radiation field emitted in an initial period of time.
203 W all-polarization-maintaining picosecond thulium-doped all-fiber laser
Authors: Liu Jiang  , Liu Chen  , Shi Hong-Xing  , Wang Pu  ,   National Center of Laser Technology, Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

High-power ultrafast fiber lasers are important sources for a number of applications including material processing, pump source for optical parametric oscillator, and supercontinuum generation. Ultrafast thulium-doped fiber lasers, which extend the wavelength range of fiber lasers from 1.8 to 2.1 m, have rapidly developed in the last several years and the average output power of the ultrafast thulium-doped fiber amplifiers has reached a hundredwatt level. The broad and smooth gain spectrum of thulium-doped fiber makes it a well-suited gain medium for generating the ultrashort laser pulses and broad wavelength tunability. However, previous reports on ultrafast thulium-doped fiber lasers and amplifiers were related to non-PM fiber configuration. These ultrafast thulium-doped fiber lasers and amplifiers may suffer the environmental instability, which means that these fiber sources are sensitive to externally-induced changes, like significant temperature variations and mechanical perturbations which will influence the fiber birefringence property. An effective method to eliminate this environmental instability is to build an all-PM, thulium-doped all-fiber MOPA configuration where the light polarizes only along the slow or fast axis in the PM fiber and PM-fiber components. Here, we demonstrate a high-power all-polarization-maintaining picosecond thulium-doped all-fiber master-oscillator power-amplifier (MOPA) system. The linearly-polarized thulium-doped all-fiber MOPA yields 203 W of average output power at central wavelength of 1985 nm with a polarization extinction ratio of 15 dB. The pulse duration of 15 ps at 611.5 MHz repetition-rate results in a peak-power of 22 kW in the final thulium-doped fiber power amplifier. To the best of our knowledge, this is the highest average output power ever reported for a picosecond-pulsed thulium-doped all-fiber laser at 2 m wavelength. Furthermore, high-power linearly-polarized thulium-doped fiber laser with compact and simple design is greatly demanded for a variety of applications, such as coherent polarization beam combination, and frequency conversion in nonlinear crystals.
Research on the time-correlation characterisrtic of correlated photon circles generated by the type-I spontaneous parametric down-conversion
Authors: Liu Yan  , Li Jian-Jun  , Gao Dong-Yang  , Zhai Wen-Chao  , Hu You-Bo  , Guo Yuan-Yuan  , Xia Mao-Peng  , Zheng Xiao-Bing  ,   Key Laboratory of Optical Calibration and Characterization, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

The optical radiometric calibration method based on correlated photons generated by spontaneous parametric down-conversion (SPDC) is a promising method,because it is based on the basic physical phenomena and does not need radiometric traceability.At the present,the SPDC calibration technology is applicable for the photon-counting detector with a highest calibration accuracy of 0.18%.More and more researchers are making effort to improve its calibration accuracy and expand its applicable targets to analog detectors.Correlated photon circles have the high photon rate characteristic.The photon rates of signal and idle light can be improved significantly by using correlated photon circles in calibration.It has very important significance to study the time-correlation characteristic of correlated photon circles. In this paper,the spatial distribution of emission angle of the broadband (450-1000 nm) correlated photons generated by type-I spontaneous parametric down-conversion is presented through the theoretical calculations.The ZEMAX optical software is used to design the optical system which can receive the broadband correlated photon circles and remove the pump laser which is the main source of stray light.The 355 nm wavelength laser is used to pump -barium borate (BBO) crystal to generate the broadband correlated photon circles.A low-light-level CMOS camera is used to adjust and align the opt-mechanical system.Finally,the 430 nm-860 nm correlated photon circles are received by the optical system and detected by the low-light-level CMOS camera.An experimental measurement system is established to measure the time-correlation characteristics of 685 nm and 736.89 nm correlated photon circles.Using 1.0 mW continuous-wave laser to pump BBO crystal,a coincidence peak is observed evidently.The results show that the correlated photon circles generated by type-I SPDC have the characteristics of time-correlation and high photon rates.It can be conductive to improving optical radiometric calibration accuracy based on correlated photons and promoting the development and application in analog detector calibration.
Multiscale simulations and ductile-brittle analyses of the atomistic cracks in BCC Ta, Fe and W
Authors: Du Hao  , Ni Yu-Shan  ,   Department of Aeronautics and Astronautics, Fudan University, Shanghai 200433, China
Published: December 2020

In order to better understand the fracture mechanism of body-centered-cubic (BCC) metal, the multiscale quasi-continuum method (QC) is employed to analyze the nano-sized mode I cracks of three kinds of BCC metal materials, i.e., Ta, Fe and W. The plastic deformation near the crack tip and the brittle cleavage process are both investigated. The simulation result shows that there are different ductile-brittle behaviors in the cracks of different BCC materials. In the same loading range, the plastic deformation, such as dislocation nucleation and emission, stacking faults and twinning, is the main phenomenon for the crack of BCC-Ta. For the crack of BCC-Fe, plastic deformation and brittle cleavage are observed successively. At the initial stage, plastic deformation is dominant, which is similar to the crack of Ta. As loading increases, the crack begins to propagate, which differs from the crack of Ta. At first, the crack propagates along the initial direction [001], but then turns to [01] as the surface energy of {110} is lower than that of {01}. With the crack propagating, the crack tip is blunted by the plastic deformation, which is consistent with experimental results. As for BCC-W, the crack is found to propagate as brittle cleavage without plastic deformation at first. And the brittle cleavage is dominant all the time, which is a significant difference between W and the other two materials. In addition to the atomistic simulation, some theoretical calculations are also performed to analyze the ductile-brittle behaviors of the cracks. By an atomic slip model, the generalized stacking fault curves of BCC Ta, Fe and W are generated, which exhibit the unstable stacking fault energies of these materials. Based on the unstable stacking fault energy, two theoretical ductile-brittle criterions are analyzed. For the Rice-criterion, the result shows that the dislocation condition is met before cleavage for Ta and Fe, while for W the cleavage occurs before dislocation. For the ductile-brittle-parameter criterion, the result shows that Ta is the most ductile one in the three materials, followed by Fe, and W is the least ductile but the most brittle one. The analysis results of the two theoretical criterions both coincide well with the atomic simulation result, which well validates the simulation and fracture mechanisms.
Effects of silver nanoparticles on Raman spectrum and fluorescence enhancement of nano-diamond
Authors: Liu Li-Shuang  , Chou Xiu-Jian  , Chen Tao  , Sun Li-Ning  ,   College of Mechanical and Electrical Engineering and Jiangsu Provincial Key Labratory of Advanced Robotics and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China
Published: December 2020

The nano-diamond has been a hot topic in the field of nano-science and nanotechnology for its optical properties. Much effort has been devoted to improving the fluorescence and Raman scattering intensity of nitrogen-vacancy (NV) center in nano-diamond by using plasmon resonance effect in sensing area. A combination of Ag nanoparticle and diamond can not only take advantage of the stability and biocompatibility of diamond, but also enhance the local electric field around NV center through the Ag nanoparticles, thereby speeding up the radiation of the fluorescent near the surface of the substrate, improving the strength and stability of the fluorescence, and greatly broadening the application areas of Raman spectroscopy. In this paper, we mix the nano-diamonds with Ag nanoparticles to improve the fluorescence and Raman scattering intensity on the basis of the localized surface plasmon resonance effect. The influences of Ag mass concentration on the Raman spectrum and fluorescence intensity are investigated. The results show that when the concentration of nano-Ag nanoparticles reaches up to 5 wt%, the light intensity becomes saturated, but the concentration further increases up to a value more than 7 wt% the light intensity begins to decline. Then the corresponding radiative transition rate and the fluorescence quantum efficiency are investigated, and based on these researches, influences and mechanism of surface plasmon resonance (SPR) enhancement are discussed thoroughly. We deduced that the fluorescence enhancement is mainly due to the enhanced surface plasmon field caused by transfer of surface plasmon resonance energy and the energy transfer between surface plasmon and excited state of NV centers. When the concentration of Ag nanoparticles reaches an appropriate value, a suitable distance between metal nanoparticles and diamond is obtained, thereby ensuring the strong local electric field forming on the metal surface, accelerating the emitting photons of diamond in the excited state, and also suppressing the transfer of non-radiative energy, eventually leading to the increase of diamond fluorescence emission intensity.
Numerical investigation on shielding properties of the laser ablation plume of polymer doped metal
Authors: Duan Xing-Yue  , Li Xiao-Kang  , Cheng Mou-Sen  , Li Gan  ,   Department of Aerospace Science and Engineering, National University of Science and Technology, Changsha 410073, China;,   National Key Laboratory of Explosion Shock Disaster Prevention and Reduction of Science and Technology of Liberation Army, Nanjing 210007, China
Published: December 2020

For laser ablation propulsion, the shielding effect of ablation plume on the incident laser is an essential factor affecting the propulsion performance. When the polymer doped metal is utilized as the propellant, the shielding effect would be more significant because the metal dopant is easily ionized. In order to study the shielding effect of ablation plume on the incident laser energy, a laser ablation model with taking into account the plume expansion, ionization and the shielding effect is built in the present work. For the polyoxymethylene doped aluminum particles irradiated by a laser with a fluence of 3-40 J/cm2, the specific impulse of laser ablation is calculated, and the consistency of the numerical results with the experimental data demonstrates the availability of the model. Furthermore, the effects of both the incompletely decomposed polymer chains and the plasma induced by laser ablation on the incident laser are considered. The time variations of electron number density distribution under different laser fluences are calculated based on the laser induced ionization model. Subsequently, the absorption coefficient distributions and the time variations of shielding coefficient under different laser fluences are obtained. The results show that at a low laser fluence (5 J/cm2), the electron number density is small, so the plume shielding effect is dominated by the laser energy absorption of the small polymer chains which are not completely decomposed. While at a high laser fluence (20 J/cm2), small polymer chains are almost completely decomposed into atoms even plasma, hence the shielding effect is dominated by the plasma since the electron number density in the plume increases up to 1020 m-3, and the complicated characteristic in the time variation of shielding coefficient appears. The quantitative analysis results obtained in the present work can be helpful for optimizing the performances of laser ablation propulsion.
Deconvolution optimization in super-resolution optical fluctuation imaging based on cumulant standard deviation
Authors: Wang Xue-Hua  , Chen Dan-Ni  , Yu Bin  , Niu Han-Ben  ,   Key Laboratory of Optoelectronics Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen Key Laboratory of Biomedicine Engineering, College of Optoelectronics Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The super-resolution optical fluctuation imaging (SOFI) technique enhances image spatial resolution by evaluating the independent stochastic intensity fluctuations of emitters. In principle, it eliminates any noise uncorrelated temporally, and provides unlimited spatial resolution since the calculation of the nth-order cumulant followed by a deconvolution results in an image with n-fold resolution improvement in three dimensions. But in practice, due to limited data length, the statistical uncertainty of cumulants will affect the continuity and homogeneity of SOFI image, which results in the fact that the high order SOFI (typically over 3rd order) cannot improve spatial resolution significantly. Since the variance characterizes the statistical uncertainty of cumulant, we deduce its theoretical expression based on a single dataset. In traditional SOFI techniques, due to lack of statistical analysis of cumulant, there is no noise constraint condition of cumulant in the Lucy-Richardson deconvolution to prevent the algorithm from causing noise amplification. In this paper, based on the cumulant variance formula, we calculate the cumulant standard deviation in each pixel of SOFI image and introduce the results into the Lucy-Richardson algorithm as a DAMPAR to suppress the noise generation in such pixels. The simulation and experimental results show that under the same data length, the deconvolution optimization based on cumulant standard deviation significantly improves the uniformity and continuity of SOFI image. On the other hand, under the premise of identical image quality, this optimization technique can also greatly shorten the image frames to less than half the original, thus promoting the development of super-resolution imaging of living cells.