Spectral computed tomography (CT) can reconstruct scanned objects at different energy-bins and thus solve the multimaterial decomposition (MMD) problem. Because the linear attenuation coefficients of different basis materials may be extremely close, the decomposition problem is often ill-conditioned. Meanwhile, traditional material decompositions with image-domain algorithms are usually voxelwise based. Therefore, these algorithms rely heavily on image quality. Ring artifacts often exist in the reconstructed images of spectral CT due to the inconsistency feature of energy-resolved detectors and beam-hardening effect. Considering the enlargement of the receptive field and taking advantage of the modeling ability of convolutional neural networks in deep learning, we proposed a convolutional material decomposition algorithm to solve the MMD problem through a basis of patches instead of pixels of the spectral CT images. Simulations and physical experiments were performed to validate the proposed algorithm, and its quality was compared with a traditional MMD algorithm in the image domain. Results show that the proposed method achieves good accuracy, reduces mean squared errors by one to two orders, and exhibits robustness in the MMD of spectral CT images even in the case that obvious ring artifacts is presented.
To improve the moisture absorption and air permeability of polyamide (PA) fibers, the modified fibers with porous structure were fabricated by melt spinning using polyethylene glycol (PEG) as the pore-forming agent due to its high solubility in water. The effects of pores caused by different PEG contents on the structure and properties of modified fibers were analyzed by electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and water contact angle. These results indicate that the porosity of modified fibers increases with PEG content increasing. Moreover, the formation of pores obviously affects the crystal forms of modified fibers. The alpha crystal gradually decreases and the gamma crystal increases with the porosity increasing. Furthermore, with respect to the modified fibers obtained from 47.33% PEG content, its water absorption increases from 3.78% of pure PA to 19.76% and its contact angle decreases from 116° to 85°. In addition, due to the interaction of hydrogen bond occurring between PA and PEG during the spinning process, the elongation at break, rupture work, and initial modulus of modified fibers were improved when the porosity was not more than 4.23%.
Flexibility, waterproof and breathability of substrates are the key issues restricting the application of electronic skin. Composite nanofibrous membranes (CNFMs) as substrates of electronic skin are prepared from polyvinylidene fluoride and silver nitrate blended solution by electrospinning technique. The microstructure and performances of the CNFMs are characterized by scanning electron microscopy, x-ray diffraction, capillary pore size analyzer, gravimetric method, water vapor permeability tester, optical contact angle tester, water permeability tester, intelligent electronic strength tester, hand-held electronic thickness meter and seveneasy conductivity meter. The results indicate that with the introduction of silver nitrate, the waterproof and breathability of CNFMs are balanced and optimized. The moisture permeability increases by 22%–69% from 2915.9 g · m−2 · 24 h−1 of pristine nanofibrous membrane (PNFM) to 3801.2–4151.5 g · m−2 · 24 h−1 of CNFMs and the hydraulic pressure decreases from 23.4 kPa to 21.6–16.5 kPa. However, the change of contact angle is irregular, which depends on the presence of like lotus-leaf-papillae morphology on fiber surface. The tensile strength of CNFMs decreases greatly and the elongation increases by 3–8 times from 7.7% of PNFM to 25.1%–63.2% of the CNFMs. The improvement of CNFMs flexibility is attributed to the hierarchical roughness of nanofiber surface, the unlock bonding between fibers and various combination forms of silver particles in CNFMs. Thus it was suitable to be applied as the substrate of electronic skin.
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