Double-edge scan wavefront metrology and its application in crystal diffraction wavefront measurements.

Achieving diffraction-limited performance in fourth-generation synchrotron radiation sources demands monochromator crystals that can preserve the wavefront across an unprecedented extensive range. There is an urgent need for techniques of absolute crystal diffraction wavefront measurement. At the Beijing Synchrotron Radiation Facility (BSRF), a novel edge scan wavefront metrology technique has been developed. This technique employs a double-edge tracking method, making diffraction-limited level absolute crystal diffraction wavefront measurement a reality. The results demonstrate an equivalent diffraction surface slope error below 70 nrad (corresponding to a wavefront phase error of 4.57% λ) r.m.s. within a nearly 6 mm range for a flat crystal in the crystal surface coordinate. The double-edge structure contributes to exceptional measurement precision for slope error reproducibility, achieving levels below 15 nrad (phase error reproducibility < λ/100) even at a first-generation synchrotron radiation source. Currently, the measurement termed double-edge scan (DES) has already been regarded as a critical feedback mechanism in the fabrication of next-generation crystals.

PIS-Net: Efficient Medical Image Segmentation Network with Multivariate Downsampling for Point-of-Care.

Recently, with more portable diagnostic devices being moved to people anywhere, point-of-care (PoC) imaging has become more convenient and more popular than the traditional "bed imaging". Instant image segmentation, as an important technology of computer vision, is receiving more and more attention in PoC diagnosis. However, the image distortion caused by image preprocessing and the low resolution of medical images extracted by PoC devices are urgent problems that need to be solved. Moreover, more efficient feature representation is necessary in the design of instant image segmentation. In this paper, a new feature representation considering the relationships among local features with minimal parameters and a lower computational complexity is proposed. Since a feature window sliding along a diagonal can capture more pluralistic features, a Diagonal-Axial Multi-Layer Perceptron is designed to obtain the global correlation among local features for a more comprehensive feature representation. Additionally, a new multi-scale feature fusion is proposed to integrate nonlinear features with linear ones to obtain a more precise feature representation. Richer features are figured out. In order to improve the generalization of the models, a dynamic residual spatial pyramid pooling based on various receptive fields is constructed according to different sizes of images, which alleviates the influence of image distortion. The experimental results show that the proposed strategy has better performance on instant image segmentation. Notably, it yields an average improvement of 1.31% in Dice than existing strategies on the BUSI, ISIC2018 and MoNuSeg datasets.

A magnetically controlled chemical-mechanical polishing (MC-CMP) approach for fabricating channel-cut silicon crystal optics for the High Energy Photon Source.

Crystal monochromators are indispensable optical components for the majority of beamlines at synchrotron radiation facilities. Channel-cut monochromators are sometimes chosen to filter monochromatic X-ray beams by virtue of their ultrahigh angular stability. Nevertheless, high-accuracy polishing on the inner diffracting surfaces remains challenging, thus hampering their performance in preserving the coherence or wavefront of the photon beam. Herein, a magnetically controlled chemical-mechanical polishing (MC-CMP) approach has been successfully developed for fine polishing of the inner surfaces of channel-cut crystals. This MC-CMP process relieves the constraints of narrow working space dictated by small offset requirements and achieves near-perfect polishing on the surface of the crystals. Using this method, a high-quality surface with roughness of 0.614 nm (root mean square, r.m.s.) is obtained in a channel-cut crystal with 7 mm gap designed for beamlines at the High Energy Photon Source, a fourth-generation synchrotron radiation source under construction. On-line X-ray topography and rocking-curve measurements indicate that the stress residual layer on the crystal surface was removed. Firstly, the measured rocking-curve width is in good agreement with the theoretical value. Secondly, the peak reflectivity is very close to theoretical values. Thirdly, topographic images of the optics after polishing were uniform without any speckle or scratches. Only a nearly 2.5 nm-thick SiO2 layer was observed on the perfect crystalline matrix from high-resolution transmission electron microscopy photographs, indicating that the structure of the bulk material is defect- and dislocation-free. Future development of MC-CMP is promising for fabricating wavefront-preserving and ultra-stable channel-cut monochromators, which are crucial to exploit the merits of fourth-generation synchrotron radiation sources or hard X-ray free-electron lasers.

Stitching method based on dual quaternion for cylindrical mirrors.

In this study, a stitching method based on dual quaternion is proposed. The application of a dual quaternion in sub-aperture stitching interferometry is analyzed in detail, and a calculation method for sub-aperture stitching based on a dual quaternion is deduced. The experimental results demonstrate the accuracy of the stitching method proposed in this study (residuals of overlapping area approximately 0.22 nm RMS). Finally, the residual differences of 0.79 nm RMS between the figure errors are acquired with a stitching by parts algorithm based on the dual quaternion and long trace profiler (FSP at HEPS). The high-accuracy and high-efficiency stitching method proposed in this study will expand its application in the metrology and manufacture of long cylindrical mirrors.

In situ Observation of Compression Damage in a Three-Dimensional Braided Carbon Fiber Reinforced Carbon and Silicon Carbide (C/C-SiC) Ceramic Composite.

Deformation and mechanical damage in a three-dimensional braided carbon fiber reinforced carbon and silicon carbide ceramic composite, subjected to compressive loading, has been studied in situ by laboratory X-ray computed tomography. Dimensional change was measured and damage visualized by digital volume correlation analysis of tomographs. Cracks nucleated from defects within the fiber bundles and tended to propagate along the fiber bundle/matrix interface. For longitudinal compression, parallel to the fiber bundles, the initial elastic modulus decreased with increasing compressive strain while significant transverse tensile strains developed due to distributed cracking. For transverse compression, perpendicular to the fiber bundles, the compressive elastic modulus was effectively constant; the tensile strains developed along the fiber direction were small, whereas macroscopic fracture between the fiber bundles caused very large bulk tensile strain perpendicular to the loading. The observations suggest that the mechanical strength might be improved through control of pre-existing defects and application of stitch fibers in the transverse direction.

[A comparison study of post-cerebral hemorrhage stress ulcer with two interventional treatments aimed at endogenous endothelin in rat].

OBJECTIVE: To observe the respective effects of intervention either with endothelin (ET) antibody or with ET receptor antagonist on acute stress ulcer (ASU) subsequent to cerebral hemorrhage in rats. METHODS: Forty Sprague-Dawley (SD) rats were randomly divided into control group (group A, n=10), model group (group B, n=10), ET antibody (group C, n=10), and ET receptor antagonist group (group D, n=10). Right intracerebral hemorrhage was reproduced by injection of 200 microl autologous venous blood. Normal saline, ET antibody, or ET receptor antagonist was respectively administered intravenously per day for designated group. The rats were sacrificed at 3 days of the experiment. The incidence of ASU and ulcer index were assessed, serum ET-1 level, malondialdehyde (MDA) content and superoxide dismutase (SOD) activity in serum, Rsvmit (Rsv) and Vvmit (Vv) of cerebral and gastric mucosa were measured, and pathological examination of the cerebral tissue and gastric mucosa was performed with light microscopy and electron microscopy. RESULTS: In group B, serum ET-1 level did not changed. MDA content were markedly increased in serum, cerebral and gastric mucosa, SOD activity were markedly decreased, cerebral water content were markedly increased; Rsv in neuron and gastric parietal cell, Vv in gastric parietal cell both were markedly decreased (P<0.05 or P<0.01). ASU was only observed in group B (the incidence was 30%, ulcer index was 15). It was not observed in other groups. Compared with group B, MDA content were significantly decreased, and SOD activity were significantly increased in serum, cerebral and gastric mucosa in groups C and D, cerebral water content in group C were dramatically decreased (all P<0.01), but these were not statistically different between groups C and D. Rsv and Vv in neuron and gastric parietal cell in groups B, C and D were not statistically different, and serum ET-1 level were not statistically different among the groups (all P>0.05). CONCLUSION: Intervention of ET antibody and ET receptor antagonist can both reduce occurrence and development of ASU subsequent to cerebral hemorrhage in rats.

Synthesis of silicon nitride nanowires by the pyrolysis of perhydropolysilazane.

Silicon nitride nanowires synthesized by the pyrolysis of perhydropolysilazane without using any catalysts are reported. After pyrolysis at 1073 K in N2/NH3 atmosphere, the synthetic nanowires are discrete and curly with diameters about tens of nanometers and lengths of hundreds of nanometers. While after post-treatment at 1873 K in N2 atmosphere, the nanowires are continuous and randomly distributed with diameters about tens of nanometers and several microns in length. There are no bulbs or droplets on the tips of the nanowires, and two gas-solid mechanisms are proposed to explain their growth.

[Preparation and infrared spectral analysis of nanoporous silica thin film].

Crack-free homogeneous nanoporous silica films on silicon wafer have been synthesized via supercritical drying of wet gel films obtained by spin-coating the polymeric silica sol, which was prepared using sol-gel method with tetraethoxysilane (TEOS) as precursor. The film is amorphous and nanoporous, and three-dimensional network, cross-linked by the primary particles whose sizes distribute between 10-20 nm showed respectively by XRD and SEM micrograph. The structure of the nanoporous SiO2 thin film was studied by FTIR spectra. The SiO2 thin film was composed of Si-O-Si and Si-OR, and was hydrophobic. The film contained Si-OH and became hydrophilic after being heat-treated at 250 degrees C or above in air. The heat-treated SiO2 thin film becomes hydrophobic by reacting with trimethylchlorosilane(TMCS). The TMCS-modified SiO2 thin film remains hydrophobic and can keep its nanoporous structure at a temperature lower than 450 degrees C in nitrogen.

Ultralight boron nitride aerogels via template-assisted chemical vapor deposition.

Boron nitride (BN) aerogels are porous materials with a continuous three-dimensional network structure. They are attracting increasing attention for a wide range of applications. Here, we report the template-assisted synthesis of BN aerogels by catalyst-free, low-pressure chemical vapor deposition on graphene-carbon nanotube composite aerogels using borazine as the B and N sources with a relatively low temperature of 900 (°)C. The three-dimensional structure of the BN aerogels was achieved through the structural design of carbon aerogel templates. The BN aerogels have an ultrahigh specific surface area, ultralow density, excellent oil absorbing ability, and high temperature oxidation resistance. The specific surface area of BN aerogels can reach up to 1051 m(2) g(-1), 2-3 times larger than the reported BN aerogels. The mass density can be as low as 0.6 mg cm(-3), much lower than that of air. The BN aerogels exhibit high hydrophobic properties and can absorb up to 160 times their weight in oil. This is much higher than porous BN nanosheets reported previously. The BN aerogels can be restored for reuse after oil absorption simply by burning them in air. This is because of their high temperature oxidation resistance and suggests broad utility as water treatment tools.

Van der Waals epitaxy and characterization of hexagonal boron nitride nanosheets on graphene.

Graphene is highly sensitive to environmental influences, and thus, it is worthwhile to deposit protective layers on graphene without impairing its excellent properties. Hexagonal boron nitride (h-BN), a well-known dielectric material, may afford the necessary protection. In this research, we demonstrated the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by chemical vapor deposition, using borazine as the precursor to h-BN. The h-BN nanosheets had a triangular morphology on a narrow graphene belt but a polygonal morphology on a larger graphene film. The h-BN nanosheets on graphene were highly crystalline, except for various in-plane lattice orientations. Interestingly, the h-BN nanosheets preferred to grow on graphene than on SiO2/Si under the chosen experimental conditions, and this selective growth spoke of potential promise for application to the preparation of graphene/h-BN superlattice structures fabricated on SiO2/Si.

Improvement of crystallization of borazine-derived boron nitride using small amounts of Fe or Ni nanoparticles.

Homogenously dispersed Fe and Ni nanoparticles (NPs) are introduced into boron nitride (BN) by pyrolysis of cured borazine containing soluble ferrocene or nickelocene. The crystallization of the borazine-derived BN is significantly improved by using no more than 1 wt% NPs. X-ray diffraction (XRD) suggests that the improved BN obtained at 1200 °C exhibits a higher degree of crystallization close to that obtained at 1600 °C without additives. Transmission electron microscopy (TEM) indicates the formation of Fe or Ni NP-core multilayer BN spheres embedded in amorphous BN, and a corresponding core-shell model is suggested. The Ni NPs exhibit a higher crystallization than Fe NPs, possibly due to the higher solubility of boron in Ni NPs at elevated temperatures. In addition, we discuss the mechanisms by which Fe and Ni NPs improve the crystallization of BN from borazine.

Carbon aerogel composites prepared by ambient drying and using oxidized polyacrylonitrile fibers as reinforcements.

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m(-1) K(-1) at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system.