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Segregation of the solidification structure of an immiscible alloy is related to the convection induced by the density differences of the components under gravity during solidification. Here, the solidification of the Al–Bi alloy in both opposing and parallel directions to the gravity force was investigated in situ using radiography and optical flow techniques. A quantitative analysis was performed on the flow, solute, and constitutional undercooling fields at the interface. During upward solidification, a flat solute-enriched layer was observed, with the melt flowing toward the center from both sides of the interface. During downward solidification, the solute-enriched layer was deformed, and solute plumes were observed, with the melt flowing toward the sides from the center of the interface. A high solute concentration gradient enhances the local flow and solute transport. The elongation of the plumes was attributed not only to the convective diffusion of the solute but also to the dispersion of droplet clusters. The forces acting on the droplets were calculated, and it was found that the resultant force on the droplets increased the area of the solute-enriched layer. Convection within the bulk melt and the motion of the droplets have synergistic effects on the flow pattern and solute distribution. Distinct microstructures were observed in opposite directions of solidification owing to the differences in constitutional undercooling and flow instability. This work offers insights into the quantitative measurement and understanding of the multi-physics fields during the solidification process. [ABSTRACT FROM AUTHOR]

BackgroundCustoms biosafety inspection is of great significance for maintaining ecological balance and protecting rare wild animals and plants.PurposeTo overcome the problem of poor contrast in traditional X-ray imaging systems for customs biosecurity inspections, an inspection instrument based on X-ray phase contrast imaging planned to be developed in this work.MethodsThe on-line phase contrast imaging method with high photon utilization efficiency was adopted in order to meet the requirements of high-efficiency data acquisition and fast imaging for the customs inspection. The protective shed shielding, security linkage and automatic sample stage were used in the instrument to ensure radiation safety in the inspection and the convenience of sample switching and adjustment. The methods of phase contrast micro-CT and three-dimensional micro-structure quantitative analysis were applied for biometrics recognition of specimens.ResultsA biometrics recognition instrument based on X-ray phase contrast imaging is developed. The test results of JIMA chart and actual samples show that the spatial resolution of the instrument is 3 μm and that the instrument enables high contrast imaging and quantitative analysis of weakly absorbing samples and can be used for the inspection of most biological specimens.ConclusionsThe instrument developed in this work provides a new tool for customs biosafety inspection. Due to its phase contrast imaging characteristics, the instrument can also be applied to the research of microscopic identification of Chinese medicinal materials, structural pharmaceutics and polymer materials.

BackgroundAs one of the most visible organs, human hair has received intense attention in both basic and applied research. Melanin, produced by the melanosomes in human hair, imparts hair color while serving many complex biological functions. Due to the small size of human hair melanosomes, it is difficult to observe and study the chemical properties of melanosomes. In previous study on melanosome, chemical treatment methods were often used to extract melanosomes, which would affect their chemical properties and structures.PurposeThis study aims to apply infrared nano-spectroscopy to exploring the structure, distribution and chemical properties of melanosomes in hair.MethodsPhotothermal induced resonance (PTIR, also known as AFM-IR), a popular technique for infrared imaging and infrared spectroscopy measurements unrestricted by diffraction limit, was used to study melanosomes in hair slices. Synchrotron radiation infrared spectroscopy, together with AFM-IR were employed to characterize the distribution of melanosomes in the cortex in situ, and to measure the infrared characteristics and infrared chemical imaging of melanosomes spectroscopy at nanoscale spatial resolution.ResultsThe experimental results show that there are melanosomes in black hair but not found in white hair. Melanosomes are ellipsoidal, and the average lengths of long axis and short axis are 423 nm and 337 nm, respectively. The average length-to-short axis ratio is 1.26. The distribution of melanosomes in black hair gradually increases from the center to the outer layer.ConclusionsExploring the distribution and chemical information of melanosomes in hair carried out in this study provides an experimental basis for a better understanding of the involvement of melanosomes in hair color and biological function.

The growth of lithium dendrites and the shuttle of polysulfides in lithium metal batteries (LMBs) have hindered their development. In LMBs, the cathode and anode are separated by a separator, although this does not solve the battery's issues. The use of biomass materials is widespread for modifying the separator due to their porous structure and abundant functional groups. LMBs perform more electrochemically when lithium ions are deposited uniformly and polysulfide shuttling is reduced using biomass separators. In this review, we analyze the growth of lithium dendrite and the shuttle of polysulfide in LMBs, summarize the types of biomass separator materials and the mechanisms of action (providing mechanical barriers, promoting uniform deposition of metal ions, capturing polysulfides, shielding polysulfide). The prospect of developing new separator materials from the perspective of regulating ion transport and physical sieving efficiency as well as the application of advanced technologies such as synchrotron radiation to characterize the mechanism of action of biomass separators is also proposed. [ABSTRACT FROM AUTHOR]

BackgroundMassive projection data are produced by user experiments with the X-ray dynamic micro-computed tomography (CT) method on the X-ray imaging beamline at Shanghai synchrotron radiation facility (SSRF). CT reconstruction method based on central processing unit (CPU) serial computing is slow, which leads to a large backlog of experimental data. Graphics processing unit (GPU) is widely used in the field of high-performance computing because of its multi-core architecture and large-scale parallelization.PurposeThis study aims to speed up CT reconstruction by making use of GPU parallel computation for X-ray dynamic micro-CT on the X-ray imaging beamline at SSRF.MethodsAccording to computer unified device architecture (CUDA) programming standard, the back projection process of the filtered back projection (FBP) CT reconstruction algorithm was parallelized, and fast reconstruction of X-ray dynamic micro-CT was implemented on GPU of NVDIA RTX2080. CT reconstruction time was compared with that of CPU-based reconstruction method.ResultsThe comparison of CT reconstruction time shows that the CT reconstruction based on GPU parallel computing achieves about 200 times speedup compared with the CT reconstruction based on CPU serial computing, and the reconstruction time of a set of CT projection data is reduced from minutes to seconds.ConclusionsWith the powerful computing power of GPU, the fast reconstruction of X-ray dynamic micro-CT can be realized.