Toppling is a representative failure mode of discontinuity-controlled rock slopes. As a discrete numerical method, discontinuous deformation analysis (DDA) is well-suited for simulating the movement ...process, contact transformation, and large displacement and deformation of rock block systems, which are formed in jointed rock masses. In the present study, a three-dimensional (3D) DDA method was conducted to study the toppling failure mechanisms of rock slopes by introducing the global contact theory. Considering dynamic equilibrium conditions, the analyses of toppling slopes were performed and the corresponding formulations were derived. The algebraic and mechanical computation of the global contact theory was illustrated and implemented into the 3D DDA method. An experimental apparatus for studying the toppling process of blocks was developed and a series of laboratory experiments were carried out for different block distributions under different conditions. By comparing with the results of the analytical methods and laboratory experiments, the accuracy of the 3D DDA method was verified. Numerical examples, including a classical toppling slope, an ideal mountain slope, and a real toppling case were analyzed to further research the toppling failure mechanisms. The results revealed that the 3D DDA method can effectively predict slope instability and simulate the failure process of toppling slopes. The results of the dynamics-based formulations, experiments and 3D DDA enrich the instability conditions of slope-toppling. Moreover, the general phenomena and laws of the toppling failure were presented.
Three-dimensional (3D) printing continuous carbon fiber-reinforced polylactic acid (PLA) composites offer excellent tensile mechanical properties. The present study aimed to research the effect of ...process parameters on the tensile mechanical properties of 3D printing composite specimens through a series of mechanical experiments. The main printing parameters, including layer height, extrusion width, printing temperature, and printing speed are changed to manufacture specimens based on the modified fused filament fabrication 3D printer, and the tensile mechanical properties of 3D printing continuous carbon fiber-reinforced PLA composites are presented. By comparing the outcomes of experiments, the results show that relative fiber content has a significant impact on mechanical properties and the ratio of carbon fibers in composites is influenced by layer height and extrusion width. The tensile mechanical properties of continuous carbon fiber-reinforced composites gradually decrease with an increase of layer height and extrusion width. In addition, printing temperature and speed also affect the fiber matrix interface, i.e., tensile mechanical properties increase as the printing temperature rises, while the tensile mechanical properties decrease when the printing speed increases. Furthermore, the strengthening mechanism on the tensile mechanical properties is that external loads subjected to the components can be transferred to the carbon fibers through the fiber-matrix interface. Additionally, SEM images suggest that the main weakness of continuous carbon fiber-reinforced 3D printing composites exists in the fiber-matrix interface, and the main failure is the pull-out of the fiber caused by the interface destruction.
Abstract
Zwitterionic hydrogels exhibit eminent nonfouling and hemocompatibility. Several key challenges hinder their application as coating materials for blood-contacting biomedical devices, ...including weak mechanical strength and low adhesion to the substrate. Here, we report a poly(carboxybetaine) microgel reinforced poly(sulfobetaine) (pCBM/pSB) pure zwitterionic hydrogel with excellent mechanical robustness and anti-swelling properties. The pCBM/pSB hydrogel coating was bonded to the PVC substrate via the entanglement network between the pSB and PVC chain. Moreover, the pCBM/pSB hydrogel coating can maintain favorable stability even after 21 d PBS shearing, 0.5 h strong water flushing, 1000 underwater bends, and 100 sandpaper abrasions. Notably, the pCBM/pSB hydrogel coated PVC tubing can not only mitigate the foreign body response but also prevent thrombus formation ex vivo in rats and rabbits blood circulation without anticoagulants. This work provides new insights to guide the design of pure zwitterionic hydrogel coatings for biomedical devices.
Abstract Cancer-associated fibroblasts (CAFs) play a pivotal role in regulating tumour progression. Therefore, understanding how CAFs communicate with hepatocellular carcinoma (HCC) is crucial for ...HCC therapy. Recently, exosomes have been considered an important “messenger” between cells. In this study, we performed microRNA (miRNA) sequencing of exosomes derived from CAFs and corresponding para-cancer fibroblasts (PAFs) of HCC patients. We found a significant reduction in the miR-320a level in CAF-derived exosomes. Using exogenous miRNAs, we demonstrated that stromal cells could transfer miRNA to HCC cells. In vitro and in vivo studies further revealed that miR-320a could function as an antitumour miRNA by binding to its direct downstream target PBX3 to suppress HCC cell proliferation, migration and metastasis. The miR-320a-PBX3 pathway inhibited tumour progression by suppressing the activation of the MAPK pathway, which could induce the epithelial-mesenchymal transition and upregulate cyclin-dependent kinase 2 (CDK2) and MMP2 expression to promote cell proliferation and metastasis. In xenograft experiments involving CAFs mixed with MHCC97-H cells, miR-320a overexpression in CAFs could inhibit tumourigenesis. Therefore, these data suggest that CAF-mediated HCC tumour progression is partially related to the loss of antitumour miR-320a in the exosomes of CAFs and that promoting the transfer of stromal cell-derived miR-320a might be a potential treatment option to overcome HCC progression.
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•Decreasing the Pd particle size increases the catalytic activity of Pd/C in FA dehydrogenation.•The 2.1nm Pd/C catalyst showed a TOF of 835h−1 at 25°C among the highest activities ...for monometallic Pd catalysts.•Both low- and high-coordination Pd surface atoms are the active sites in FA dehydrogenation.•The improved catalytic activity on smaller Pd nanoparticles is likely attributed to the positive charged Pd species.
Hydrogen generation from formic acid (FA) under mild conditions has received significant attention, where Pd-based catalysts have been widely employed due to their superior activities. However, the Pd particle size effect has been much less systematically investigated. In this study, carbon-supported Pd nanoparticles (NPs) with five different Pd particle sizes, ranging from 2.1 to 4.5nm were synthesized using sodium citrate as the stabilizing agent. The Pd particle sizes were determined by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The FA dehydrogenation reaction was conducted in a FA-sodium formate (SF) aqueous solution in a batch reactor at room temperature. We found that decreasing the Pd particle size from 4.5±0.5 to 2.1±0.3nm remarkably boosted the catalytic activity by about 3.6 times, resulting in a turnover frequency of 835h−1, which is among the highest values for supported monometallic Pd catalysts in the literature. Our results suggest that both low- and high-coordination Pd surface atoms participated in the reaction. The remarkably higher activity of smaller Pd NPs was attributed to both higher Pd dispersion and the presence of a larger proportion of Pd species with positive charge, through which the Coulomb interaction between the positive Pd species and negative charged formate ions, the key reaction intermediate, is enhanced. Finally, the deactivation and regeneration of Pd/C catalysts were also discussed.
The microstructure evolution of grains with different orientations during directional solidification is investigated by the phase-field method. For converging dendrites, in addition to the usually ...accepted overgrowth pattern wherein the favorably oriented dendrites block the unfavorably oriented ones, the opposite pattern of overgrowth observed in some recent experiments is also found in our simulations. The factors which may induce this unusual overgrowth are analyzed. It is found that in addition to the difference in tip undercooling, the solute interaction of converging dendrites, which has been ignored in the classical theoretical model, also has a significant effect on the nature of the overgrowth at low pulling velocities. Solute interaction can retard the growth of dendrites at the grain boundary (GB) and induce a lag of these dendrites relative to their immediate neighbors, which gives the unfavorably oriented dendrite the possibility to overgrow the favorably oriented one. However, this unusual overgrowth only occurs when the spacing between the favorably oriented GB dendrite and its immediate favorably oriented neighbor decreases to a certain level through lateral motion. These findings can broaden our understanding of the overgrowth mechanism of converging dendrites.
Remote sensing images are inevitably affected by the degradation of haze with complex appearance and non-uniform distribution, which remarkably affects the effectiveness of downstream remote sensing ...visual tasks. However, most current methods principally operate in the original pixel space of the image, which hinders the exploration of the frequency characteristics of remote sensing images, resulting in these models failing to fully exploit their representation ability to produce high-quality images. This paper proposes a frequency-oriented remote sensing dehazing Transformer named FOTformer, to explore information in the frequency domain to eliminate disturbances caused by haze in remote sensing images. It contains three components. Specifically, we developed a frequency-prompt attention evaluator to estimate the self-correlation of features in the frequency domain rather than the spatial domain, improving the image restoration performance. We propose a content reconstruction feed-forward network that captures information between different scales in features and integrates and processes global frequency domain information and local multi-scale spatial information in Fourier space to reconstruct the global content under the guidance of the amplitude spectrum. We designed a spatial-frequency aggregation block to exchange and fuse features from the frequency domain and spatial domain of the encoder and decoder to facilitate the propagation of features from the encoder stream to the decoder and alleviate the problem of information loss in the network. The experimental results show that the FOTformer achieved a more competitive performance against other remote sensing dehazing methods on commonly used benchmark datasets.
Conventional metasurface holograms relying on metal antennas for phase manipulation suffer from strong Ohmic loss and incomplete polarization conversion. The efficiency is limited to rather small ...values when operating in transmission mode. Here, we implement a high-efficiency transmissive metasurface hologram by leveraging the recently developed Huygens' metasurface to construct an electric and magnetic sheet with a transmission efficiency up to 86% and optical efficiency of 23.6%. The high-efficiency originates from the simultaneous excitations of the Mie-type electric and magnetic dipole resonances in the meta-atoms composed of silicon nanodisks. Our hologram shows high fidelity over a wide spectral range and promises to be an outstanding alternative for display applications.
Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism ...spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light–matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and biophotonics.
The improved antioxidant system of cancer cells renders them well-adaptive to the intrinsic oxidative stress in tumor tissues. On the other hand, cancer cells are more sensitive to elevated tumor ...oxidative stress as compared with normal cells due to their deficient reactive oxygen species-eliminating systems. Oxidation therapy of cancers refers to the strategy of killing cancer cells through selectively increasing the oxidative stress in tumor tissues. In this article, to amplify the oxidation therapy, we develop integrated nanoparticles with the properties to elevate tumor oxidative stress and concurrently suppress the antioxidative capability of cancer cells. The amphiphilic block copolymer micelles of poly(ethylene glycol)-b-poly2-(((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)carbonyl)oxy)ethyl methacrylate (PEG-b-PBEMA) are integrated with palmitoyl ascorbate (PA) to form hybrid micelles (PA-Micelle). PA molecules at pharmacologic concentrations serve as a prooxidant to upregulate the hydrogen peroxide (H2O2) level in tumor sites and the PBEMA segment exhibits H2O2-triggered release of quinone methide for glutathione depletion to suppress the antioxidative capability of cancer cells, which synergistically and selectively kill cancer cells for tumor growth suppression. Given the significantly low side toxicity against normal tissues, this novel integrated nanoparticle design represents a novel class of nanomedicine systems for high-efficiency oxidation therapy with the potentials to be translated to clinical applications.
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