Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes

Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes were investigated using X-ray diffraction （XRD） and electron back scatter diffraction （EBSD） techniques. The experimental results show that the 〈111〉 and 〈100〉 fibre textures are the main texture components, and crystalline grains in the surface are more fine and uniform than those in the center of Fe-Ni alloy wires during cold-drawing processes. It is found that the volume fraction of the 〈111〉 fibre texture component determined by quantitative regression calculation of the Gaussian distribution function reaches more than 60% and the strong 〈111〉 fibre texture component favors the torsional property of Fe-Ni alloy wires.

Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation

We use laser-scanning nonlinear imaging microscopy in atomically thin transition metal dichalcogenides(TMDs)to reveal information on the crystalline orientation distribution,within the 2D lattice.In particular,we perform polarization-resolved second-harmonic generation(PSHG)imaging in a stationary,raster-scanned chemical vapor deposition(CVD)-grown WS2 flake,in order to obtain with high precision a spatially resolved map of the orientation of its main crystallographic axis(armchair orientation).By fitting the experimental PSHG images of sub-micron resolution into a generalized nonlinear model,we are able to determine the armchair orientation for every pixel of the image of the 2D material,with further improved resolution.This pixel-wise mapping of the armchair orientation of 2D WS2 allows us to distinguish between different domains,reveal fine structure,and estimate the crystal orientation variability,which can be used as a unique crystal quality marker over large areas.The necessity and superiority of a polarization-resolved analysis over intensity-only measurements is experimentally demonstrated,while the advantages of PSHG over other techniques are analysed and discussed.

Super-resolution dipole orientation mapping via polarization demodulation

Fluorescence polarization microscopy(FPM)aims to detect the dipole orientation of fluorophores and to resolve structural information for labeled organelles via wide-field or confocal microscopy.Conventional FPM often suffers from the presence of a large number of molecules within the diffraction-limited volume,with averaged fluorescence polarization collected from a group of dipoles with different orientations.Here,we apply sparse deconvolution and least-squares estimation to fluorescence polarization modulation data and demonstrate a super-resolution dipole orientation mapping(SDOM)method that resolves the effective dipole orientation from a much smaller number of fluorescent molecules within a sub-diffraction focal area.We further apply this method to resolve structural details in both fixed and live cells.For the first time,we show that different borders of a dendritic spine neck exhibit a heterogeneous distribution of dipole orientation.Furthermore,we illustrate that the dipole is always perpendicular to the direction of actin filaments in mammalian kidney cells and radially distributed in the hourglass structure of the septin protein under specific labelling.The accuracy of the dipole orientation can be further mapped using the orientation uniform factor,which shows the superiority of SDOM compared with its wide-field counterpart as the number of molecules is decreased within the smaller focal area.Using the inherent feature of the orientation dipole,the SDOM technique,with its fast imaging speed(at sub-second scale),can be applied to a broad range of fluorescently labeled biological systems to simultaneously resolve the valuable dipole orientation information with super-resolution imaging.

Prior-Free Dependent Motion Segmentation Using Helmholtz-Hodge Decomposition Based Object-Motion Oriented Map

Motion segmentation in moving camera videos is a very challenging task because of the motion dependence between the camera and moving objects. Camera motion compensation is recognized as an effective approach. However, existing work depends on prior-knowledge on the camera motion and scene structure for model selection. This is not always available in practice. Moreover, the image plane motion suffers from depth variations, which leads to depth-dependent motion segmentation in 3D scenes. To solve these problems, this paper develops a prior-free dependent motion segmentation algorithm by introducing a modified Helmholtz-Hodge decomposition （HHD） based object-motion oriented map （OOM）. By decomposing the image motion （optical flow） into a curl-free and a divergence-free component, all kinds of camera-induced image motions can be represented by these two components in an invariant way. HHD identifies the camera-induced image motion as one segment irrespective of depth variations with the help of OOM. To segment object motions from the scene, we deploy a novel spatio-temporal constrained quadtree labeling. Extensive experimental results on benchmarks demonstrate that our method improves the performance of the state-of-the-art by 10%-20% even over challenging scenes with complex background.

Ultrahigh-resolution nonlinear optical imaging of the armchair orientation in 2D transition metal dichalcogenides

We used nonlinear laser scanning optical microscopy to study atomically thin transition metal dichalcogenides(TMDs)and revealed,with unprecedented resolution,the orientational distribution of armchair directions and their degree of organization in the two-dimensional(2D)crystal lattice.In particular,we carried out polarization-resolved second-harmonic generation(PSHG)imaging for monolayer WS2 and obtained,with high-precision,the orientation of the main crystallographic axis(armchair orientation)for each individual 120×120 nm^(2) pixel of the 2D crystal area.Such nanoscale resolution was realized by fitting the experimental PSHG images,obtained with sub-micron precision,to a new generalized theoretical model that accounts for the nonlinear optical properties of TMDs.This enabled us to distinguish between different crystallographic domains,locate boundaries and reveal fine structure.As a consequence,we can calculate the mean orientational average of armchair angle distributions in specific regions of interest and define the corresponding standard deviation as a figure-of-merit for the 2D crystal quality.

Development of micro-Laue technique at Shanghai Synchrotron Radiation Facility for materials sciences

Synchrotron radiation-based micro-Laue technique has showcased great application potentials in materials science study for its unprecedented crystal orientation and lattice strain/stress resolution.Here we report the updated progress in the development of the micro-Laue technique on the X-ray test beamline at Shanghai Synchrotron Radiation Facility.So far,40μm(h)×50μm(v)X-ray beam spot is routinely obtained,with the convergent angle of 0.2 mrad(h)×0.12 mrad(v).Area scans are conducted on a GH3535 Nibased superalloy base metal and weld joint with the same chemical composition.By analyzing the tremendous amount of Laue diffraction patterns using in-house developed software packages,the crystal orientation,elastic strain,and defect distributions are mapped and investigated.Such a successful proof-of-principle study offers first-hand experience on the further optimization of the design and construction of the scanning micro-Laue facility on the superbend beamline with improved spatial resolution and multiple functions for simultaneous chemical fluorescence mapping and in-situ microstructural evolution studies.The micro-Laue diffraction beamline at Shanghai Synchrotron Radiation Facility will provide a versatile and powerful tool for the orientation and strain/stress mapping combined with phase identification with micron-sized spatial resolution.