Angiotensin-converting enzyme 2 (ACE2) is the cellular receptor for severe acute respiratory syndrome-coronavirus (SARS-CoV) and the new coronavirus (SARS-CoV-2) that is causing the serious ...coronavirus disease 2019 (COVID-19) epidemic. Here, we present cryo-electron microscopy structures of full-length human ACE2 in the presence of the neutral amino acid transporter B
AT1 with or without the receptor binding domain (RBD) of the surface spike glycoprotein (S protein) of SARS-CoV-2, both at an overall resolution of 2.9 angstroms, with a local resolution of 3.5 angstroms at the ACE2-RBD interface. The ACE2-B
AT1 complex is assembled as a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues. These findings provide important insights into the molecular basis for coronavirus recognition and infection.
The shear resistance of 3D printed periodic auxetic chiral mechanical metamaterial was quantified via a picture-frame apparatus. The experimental set-up allowed the accurate measurement of the ...effective shear modulus of the material. Also, a rigid-rod-rotational spring model shows that the effective shear modulus of the material is directly related to the chiral geometry and the rotational rigidity of the center joints and the corner joints in the chiral cell. To facilitate practical design, design guidelines were developed through an integrated analytical, numerical and experimental approach. The influences of the chiral geometry and the joint rigidity on the shear resistance of the periodic auxetic chiral mechanical metamaterial were quantified. The design guidelines were verified by systematic finite element (FE) simulations.
•A novel EMD–ENN model is proposed to forecast wind speed.•In EMD–ENN, the EMD is adopted to decompose the original data.•In EMD–ENN, the ENN is used to build the prediction models for each ...sub-series.•Four datasets of wind speed are used to demonstrate the proposed approach.•It is concluded that the proposed approach can improve the prediction accuracy and is very effective.
Because of the chaotic nature and intrinsic complexity of wind speed, it is difficult to describe the moving tendency of wind speed and accurately forecast it. In our study, a novel EMD–ENN approach, a hybrid of empirical mode decomposition (EMD) and Elman neural network (ENN), is proposed to forecast wind speed. First, the original wind speed datasets are decomposed into a collection of intrinsic mode functions (IMFs) and a residue by EMD, yielding relatively stationary sub-series that can be readily modeled by neural networks. Second, both IMF components and residue are applied to establish the corresponding ENN models. Then, each sub-series is predicted using the corresponding ENN. Finally, the prediction values of the original wind speed datasets are calculated by the sum of the forecasting values of every sub-series. Moreover, in the ENN modeling process, the neuron number of the input layer is determined by a partial autocorrelation function. Four prediction cases of wind speed are used to test the performance of the proposed hybrid approach. Compared with the persistent model, back-propagation neural network, and ENN, the simulation results show that the proposed EMD–ENN model consistently has the minimum statistical error of the mean absolute error, mean square error, and mean absolute percentage error. Thus, it is concluded that the proposed approach is suitable for wind speed prediction.
Developing therapeutics against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could be guided by the distribution of epitopes, not only on the receptor binding domain (RBD) of the ...Spike (S) protein but also across the full Spike (S) protein. We isolated and characterized monoclonal antibodies (mAbs) from 10 convalescent COVID-19 patients. Three mAbs showed neutralizing activities against authentic SARS-CoV-2. One mAb, named 4A8, exhibits high neutralization potency against both authentic and pseudotyped SARS-CoV-2 but does not bind the RBD. We defined the epitope of 4A8 as the N-terminal domain (NTD) of the S protein by determining with cryo-eletron microscopy its structure in complex with the S protein to an overall resolution of 3.1 angstroms and local resolution of 3.3 angstroms for the 4A8-NTD interface. This points to the NTD as a promising target for therapeutic mAbs against COVID-19.
By incorporating concepts from auxeticity, kinematic constraints, pre-tension induced compression (PIC), and suture tessellations, tiled sandwich composites are designed, demonstrating behaviors ...attributed to the synergy between auxeticity and pre-tension induced contact and compression, simultaneously triggered by a threshold strain. The designs can theoretically achieve on-demand Poisson’s ratio in the widest range (−∞, +∞), and once triggered, the Poisson’s ratio is stable under large deformation. Also, once the overall strain goes beyond the threshold, the designs enter into a PIC stage, ensuring the middle soft layer takes the tensile load, while the tiles are under compression via contact and the 3D articulation of the tooth-channel pairs. In this PIC stage, the tooth-channel pairs provide kinematic constraints via the contact and relative sliding between teeth and channels. The deformation mechanisms and mechanical properties of them are systematically explored via an integrated analytical, numerical, and experimental approach. Mechanical experiments are performed on 3D printed specimens. It is found that the length aspect ratio and the obliqueness of the teeth significantly influence the constraint angle and therefore the auxeticity and strength of the designs.New tiled sandwich composites demonstrate on-demand auxeticity and a pseudo tensegrity deformation stage, achieving Poisson’s ratios from -∞ to +∞, maintaining stability under large deformation and increasing strength under tension and indentation.
Insects rely on olfaction for mating, finding oviposition sites, and locating hosts. Hyphantria cunea is a serious pest that severely damages forests. Differential expression analysis of ...olfactory-related genes between males and females is the basis for elucidating the functions of olfactory-related proteins in H. cunea. In this study, Illumina HiSeqTM 4000 high-throughput sequencing technology was used to perform transcriptome sequencing of the antennal tissues of adult male and female H. cunea. Functional annotation was conducted using the NR, Swiss-Prot, KOG, KEGG, and GO databases, and the results showed that the antennal transcriptome of adult H. cunea contained 50,158 unigenes. Differential expression analysis identified 3923 genes that were significantly differentially expressed between male and female antennae. A total of 221 olfactory-related genes were annotated, and 96 sex-biased genes were identified, including 13 odorant receptors (ORs), 48 odorant binding proteins (OBPs), 7 chemosensory proteins (CSPs), 10 ionotropic receptors (IRs), 10 sensory neuron membrane proteins (SNMPs), 2 gustatory receptors (GRs), and 6 odorant-degrading enzymes (ODEs), indicating that there were differences in olfaction between male and female H. cunea. Quantitative real-time PCR was used to verify the expression levels of 21 putative general odorant receptor genes in male and female antennae. HcunOR4 and HcunOR5 showed female-biased expression; HcunOR48, HcunOR49 and HcunOR50 showed male-biased expression. The results were consistent with the transcriptome differential analysis. The screening of male-biased odorant receptor genes might provide a theoretical basis for the functional characterization of odorant receptors for recognizing sex pheromones in H. cunea.
In this investigation, the three-parameter Modified Mohr–Coulomb (MMC) fracture model and the determination of the material parameters are briefly described. The formulation of the post-initiation ...behavior is proposed by defining both the explicit softening law and the incremental damage evolution law. As opposed to the existing attempts to simulate slant fracture with material weakening before crack formation, softening is assumed to occur only in the post-initiation range. The justification of this assumption can be provided by the interrupted fracture tests, for example,
Spencer et al. (2002).
Element deletion with a gradual loss of strength is used to simulate crack propagation after fracture initiation. The main emphasis of the paper is the numerical prediction of slant fracture which is almost always observed in thin sheets. For that purpose, VUMAT subroutines of ABAQUS are coded with post-initiation behavior for both shell elements and plane strain elements. Fracture of flat-grooved tensile specimens cut from advanced high strength steel (AHSS) sheets are simulated by 2D plane strain element and shell element models.
Necking has been the dominant failure mode in sheet metal forming industry and several analytical and numerical tools were developed to predict the onset of necking. However, the introduction of ...Advanced High Strength Steels (AHSS) with reduced ductility brought up an issue of a shear fracture which could not be predicted using the concept of Forming Limit Curve (FLC). The Modified Mohr-Coulomb fracture criterion (MMC) was recently shown to be applicable to problems involving ductile fracture of materials and sheets. In the limiting case of plane stress, the fracture locus consists of four branches when represented on the plane of the equivalent strain to fracture and the stress triaxiality. A transformation of above 2D fracture locus to the space of principal strains was performed which revealed the existence of two new branches not extensively studied before. The existence of those branches explains the formation of shear-induced fracture. As an illustration of this new approach, initiation and propagation of cracks is predicted and compared with series of deep-drawing punch tests of ThyssenKrupp AHSS (grade RA-K 40/70, standard HCT690T) performed at ThyssenKrupp. It was shown that the location of fracture as well as the magnitude of punch travel corresponding to first fracture was correctly predicted by MMC fracture criterion for both circular and square punch.
Aiming to assist stroke patients who suffer from motor dysfunction after stroke and reduce the stress of physiotherapists, a 3-degree-of-freedom (3DOF) lower limb rehabilitation robot (LLRR) has been ...developed for the motion recovery in this paper. At first, a simple and flexible structure of LLRR is designed, which involves hip, knee and ankle joints and can also be adjusted to fit for the different heights of patients. Then, for the controller design, control-oriented model of LLRR is studied and validated by both simulation and experiments, including the kinematic model of mechanical system, friction model of rotation joints and motor model of actuators. Based on the proposed models, an adaptive robust sub-controller is synthesized to make each joint track its designed training trajectory, overcome system uncertainties and reject the disturbances from patient. At last, experiments are carried out to validate the proposed LLRR by the passive movement training.
•The lowest energy interlayer bright exciton (IXB) in 1-WSO has a higher percentage of allowed transitions compared to 2-WSO.•The intrinsic electric field facilitates the transition of IXB in ...1-WSO.•The radiative lifetime of the IXB is extremely short, around 10−10 s at 300 K in 1-WSO.
The intrinsic electric field of Janus layer has an important impact on interlayer excitons of heterostructures constructed by Janus components. In this study, we employ the GW-BSE method to investigate the influence of the intrinsic electric field on interlayer excitons in WSO/MoSi2N4 heterostructures with different stacking configurations. Our findings reveal that reverse the Janus WSO layer strongly alters the electronic structures while keeping the type-Ⅱ band alignment feature. Both structures demonstrate tightly bound bright interlayer excitons. We also observe that the lowest energy interlayer bright exciton (IXB) in 1-WSO has a higher percentage of allowed transitions compared to 2-WSO, due to the multi-band transition characteristic of the participating states. And thus the intrinsic electric field facilitates the transition of IXB in 1-WSO. Consequently, the radiative lifetime of the IXB is extremely short, around 10−10 s at 300 K. Our exploration underscores the significance of the intrinsic electric field in determining the lifetime of IXs.
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