Statistical learning prediction of fatigue crack growth via path slicing and re-weighting

Predicting potential risks associated with the fatigue of key structural components is crucial in engineering design.However,fatigue often involves entangled complexities of material microstructures and service conditions,making diagnosis and prognosis of fatigue damage challenging.We report a statistical learning framework to predict the growth of fatigue cracks and the life-to-failure of the components under loading conditions with uncertainties.Digital libraries of fatigue crack patterns and the remaining life are constructed by high-fidelity physical simulations.Dimensionality reduction and neural network architectures are then used to learn the history dependence and nonlinearity of fatigue crack growth.Path-slicing and re-weighting techniques are introduced to handle the statistical noises and rare events.The predicted fatigue crack patterns are self-updated and self-corrected by the evolving crack patterns.The end-to-end approach is validated by representative examples with fatigue cracks in plates,which showcase the digital-twin scenario in real-time structural health monitoring and fatigue life prediction for maintenance management decision-making.

Mechanical responses of the bio-nano interface: A molecular dynamics study of graphene-coated lipid membrane

Bio-nano interfaces between biological materials and functional nanodevices are of vital importance in relevant energy and information exchange processes, which thus demand an in-depth understanding. One of the critical issues from the application viewpoint is the stability of the bio-nano hybrid under mechanical perturbations. In this work we explore mechanical responses of the interface between lipid bilayer and graphene under hydrostatic coating provides remarkable resistance to the pressure or indentation loads, We find that graphene loads, and the intercalated water layer offers additional protection. These findings are discussed based on molecular dynamics simulation results that elucidate the molecular level mechanisms, which provide a basis for the rational design of bionanotechnology- enabled aoolications such as biomedical devices and nanotheraoeutics.

Two-dimensional modeling of the self-limiting oxidation in silicon and tungsten nanowires

Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.

Heat transport in low-dimensional materials: A review and perspective

Heat transport is a key energetic process in materials and devices. The reduced sample size, low dimension of the problem and the rich spectrum of material imperfections introduce fruitful phenomena at nanoscale. In this review, we summarize recent progresses in the understanding of heat transport process in low-dimensional materials, with focus on the roles of defects, disorder, interfaces, and the quantum- mechanical effect. New physics uncovered from computational simulations, experimental studies, and predictable models will be reviewed, followed by a perspective on open challenges.

Crustal density structure of the southern segment of the Liaocheng-Lankao fault, China

The 1:200,000 middle-large scale Bouguer gravity anomaly data covering the southern segment of the Liaocheng-Lankao fault(SLLF)and its vicinity are analyzed with two methods.First,the Bouguer gravity anomaly data are decomposed by two-dimensional(2 D)wavelet to make the family of multi-scale modes correspond with density structure at different depths.Second,a two and half dimension(2.5 D)human-computer interaction inversion of the Bouguer gravity anomaly data are conducted with the constraints provided by two deep seismic sounding profiles(DSS1 and DSS2)crossing the study area to get the crustal density profiles.Based on the integrated study,we can draw the following conclusions:1)SLLF appears to be a deep fault with almost vertical dipping and rooted into the uppermost mantle;2)In the middle to upper crust SLLF shows an clear turning patterns and segmentation features;3)In the study area the epicentral distributions of the precisely re-located small earthquakes and the historical large earthquakes have a good correspondence with the turning patterns and segmentation features of SLLF;and 4)The results of the horizontal slices from 2 D wavelet decomposition show that there are significant differences in the density structure on the two sides of the fault.A well-defined concave structure with low density exists in the upper crust of the Dongming Depression on the west side of the fault,with the concave center being estimated at a depth of about 8 km.In contrast,the upper crust on the east side presents a relative thinner pattern in depth with a bit higher density.Meanwhile,the low-density structure in the middle crust underneath the fault is presumably caused by the uplift of the upper mantle materials and their intrusion along the deep rupture system.This paper clarified the inconsistency of fault system and epicenters of small earthquakes from upper to lower crust.The results indicated that the fault system plays an important governing role to the seismicity in this area.

Mechanics of soft particle capture using nanofiber networks

Nano-particle capture is a key process in filtration, separation, and biomedical applications. Here we explored the mechanisms of soft particle capture using nanofiber networks. We identified possible states of the capture process, which are defined by their structural and material parameters. By performing numerical analysis, we provided a phase diagram in the parametric space of the network structure and interracial adhesion. The work provides a conceptual model for rational design of synthetic materials in related applications that focus on the protection against or removal of virus, as well as other soft particles.

Spatio-temporal variation of soil CO_(2) concentration in Loess Area of northwestern Shanxi Province,China

CO_(2) released by soil serves as an important link between terrestrial ecosystems and atmospheric CO_(2), whose small chang‐es may significantly affect the global carbon cycle. In order to reveal the spatio-temporal variations of CO_(2) concentrations in deep loess, this paper takes Qingliangsi Gully watershed in northwestern Shanxi Province, China as an example to sys‐tematically study soil CO_(2)concentration and its spatio-temporal variations and carbon sink significance under different watershed locations and different land use types. Results show that: (1) The release potential of the loess soil is larger in the depth range of 2 m, which is much more likely to be the CO_(2) release area. (2) Grassland and forest are more advanta‐geous in terms of soil microbial activity and soil carbon reserve compared with farmland. In addition, the change of land use type from farmland to grassland can increase soil organic carbon reserve, which is of far-reaching significance to the global carbon cycle. This is especially true in an area like the Loess Plateau with densely covered hills, gullies, and serious soil erosion in an area of 64×104 km2. (3) In the study area, the diurnal concentration of soil CO_(2) at different depths shows a weak "high-low-high-low" trend from 08:00 to 07:00 next day;and in deep soil it has a lag time compared with the daily change of temperature, generally about 4−12 h, which may be caused largely by the more compact loess structure. It is worth pointing out that the Loess Plateau in China, with a thickness of the loess of tens to hundreds of meters, has the most abundant soil resources in the world, and also stores a large amount of terrestrial soil carbon, which carries the hope of promoting the research of global carbon cycle.

Efficacy of Danshen Injection Combined with Phosphocreatine Disodium in Treating Frequent Premature Contractions during Pregnancy and Its Effects on Maternal and Infant Outcomes

[Objectives]To explore the efficacy of Danshen Injection combined with phosphocreatine disodium in treating frequent premature contractions during pregnancy and its effect on maternal and infant outcomes.[Methods]A total of 200 pregnant women with normal pregnancy and frequent premature contractions who were treated in the outpatient department of internal medicine in Women and Children's Hospital of Hubei Province and Xinzhou District People's Hospital of Wuhan Central Hospital during September 2015 and October 2018 were selected and randomly divided into the control group and observation group,100 cases for each group.The observation group was treated with Danshen Injection combined with phosphocreatine disodium,and the control group was treated with phosphocreatine disodium alone.The course of treatment in both groups was one week.During the treatment,the changes of heart rate,heart rhythm,electrocardiogram and 24-h dynamic electrocardiogram(DCG)of both groups were observed.[Results]After treatment,the clinical efficacy of the observation group was better than that of the control group,and the difference was statistically significant(P<0.01).There were no adverse drug reactions in both groups.However,in the control group,non-sustained ventricular tachycardia(NSVT)was found in 24-h dynamic electrocardiogram(DCG)of 2 pregnant women with premature ventricular contraction.The pregnancy process was smooth,with full-term natural delivery and no fetal malformation.There was no significant difference in gestational age and neonatal weight between the two groups(P>0.05).However,there was a statistically significant difference in Apgar score between the two groups(P<0.05).During the 6-month postpartum follow-up,the mother and child were unharmed,and examination of repeated electrocardiograms showed that the conditions were normal.[Conclusions]Danshen Injection combined with phosphocreatine disodium has better efficacy in the treatment of frequent premature contractions during pregnancy and the maternal and infant outcomes than the treatment with phosphocreatine disodium alone,and it has good safety and can prevent premature contractions from progressing to tachyarrhythmias.

Design,synthesis and bioassay of the emerging photo-responsive fungicides

Precise and spatiotemporal control over the pesticide remains to be a challenge.More efficient controlled release systems(CRSs)have been developed to support the precise delivery of active ingredients.Herein,we incorporated the photoremovable protecting groups(PRPGs)into phenamacril(PHE)and obtained two photo-responsive fungicides of NV-PHE and DEACM-PHE.The 4,5-dimethoxy-o-nitrobenzyl(NV)or 7-diethylaminocoumarin(DEACM)-caged PHE could release the active molecule PHE after irradiation of UV light and blue light,respectively.Optical properties and in-vitro/vivo fungicidal activities of NV-PHE and DEACM-PHE demonstrated the feasibility for light controlled release of PHE.DEACM-PHE could release 98%PHE by illumination of blue light.The irradiated DEACM-PHE could preserve the similar bioactivity of PHE,and significantly improve the in-vitro/vivo fungicidal activities compared to the non-irradiated DEACM-PHE.The optical controlled release of PHE from DEACM-PHE enabled the precise and spatiotemporal delivery of PHE,diversifying the development of CRSs for pesticide,and providing environmentfriendly agricultural applications with high pesticide efficiency.

Controlled Nanocutting of Graphene

Rapid progress in graphene-based applications is calling for new processing techniques for creating graphene components with different shapes,sizes,and edge structures.Here we report a controlled cutting process for graphene sheets,using nickel nanoparticles as a knife that cuts with nanoscale precision.The cutting proceeds via catalytic hydrogenation of the graphene lattice,and can generate graphene pieces with specifi c zigzag or armchair edges.The size of the nanoparticle dictates the edge structure that is produced during the cutting.The cutting occurs along straight lines and along symmetry lines,defined by angles of 60ºor 120º,and is defl ected at free edges or defects,allowing practical control of graphene nano-engineering.

Micro- and nano-mechanics in China： A brief review of recent progress and perspectives

The past three decades have witnessed the explosion of nanoscience and technology, where notable research efforts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro-and nano-mechanics, and to outline the perspectives in this fast-evolving field.

Light-triggered release of insecticidally active spirotetramat-enol

Spirotetramat metabolizes to its active enol form in the plant. We described here a photocaged pesticide delivery system that can release insecticidal spirotetramat enol form upon light irradiation. Covalently linking spirotetramat-enol with photoresponsive coumarin generated the caged insecticide. The photophysical and photochemical properties, deprotection photolysis and insecticidal activities of the caged spirotetramat enol were studied. This light-triggered system can undergo cleavage to release free spirotetramat enol form at the presence of blue light （420 nm） or sunlight, Bioassays indicated that the triggered molecule has no obvious insecticidal activity against Aphis craccivora Koch at dark and could be activated by light to release the insecticidal ingredients, which provides precise control over insecticide delivery.

Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface:A first-principles study

The application of silicon as ultrahigh capacity electrodes in lithiumion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segre- gate at the （lithiated） Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene. These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.

Robustness of structural superlubricity beyond rigid models

Structural superlubricity is a theoretical concept stating that the friction force is absent between two rigid,incommensurate crystalline surfaces.However,elasticity of the contact pairs could modify the lattice registry at interfaces by nucleating local slips,favoring commeasure.The validity of structural superlubricity is thus concerned for large-scale systems where the energy cost of elastic distortion to break the lattice registry is low.In this work,we study the size dependence of superlubricity between single-crystal graphite flakes.Molecular dynamics simulations show that with nucleation and propagation of out-of-plane dislocations and strained solitons at Bernal interfaces,the friction force is reduced by one order of magnitude.Elastic distortion is much weaker for non-Bernal or incommensurate ones,remaining notable only at the ends of contact.Lattice self-organization at small twist angles perturbs the state of structural superlubricity through a reconstructed potential energy surface.Theoretical models are developed to illustrate and predict the interfacial elastoplastic behaviors at length scales beyond those in the simulations.These results validate the rigid assumption for graphitic superlubricity systems at microscale,and reveal the intrinsic channels of mechanical energy dissipation.The understandings lay the ground for the design of structural superlubricity applications.

Computational Investigations about the Effects of Heteromolecular Aggregation on Bioactivities:a Case of Neonicotinoids and Water

Molecular aggregation state of bioactive compounds plays a key role in bio-interactive procedure.Diverse ag-gregation states of bioactive compounds contribute to different biological or chemical properties.Water-bridge,as the simple hetero-molecular aggregation,has been found bridging the binding between many bioactive compounds and their targets through hydrogen bonding network,e.g.in the recognition of neonicotinoids with insect nAChRs.To better understanding the roles of water-bridge on bioactivities of compounds,an approach of hetero-dimeric ag-gregation with water was proposed.Quantitative structure-activity relationship(QSAR)and pharmacophore mod-eling investigations were applied on 19 neonicotinoids,as well as their aggregates with water.The aggregate-based CoMSIA,PHASE and linear QSAR models presented better statistical significance and predictabilities than the monomer ones,which indicated that the bioactivities correlated with the aggregate properties and water bridged hy-drogen bond of the active site.All results revealed the essential roles of water-bridge in ligand recognition,which should be considered in future ligand design and optimization.

SARS-CoV-2 infection causes immunodeficiency in recovered patients by downregulating CD19 expression in B cells via enhancing B-cell metabolism

The SARS-CoV-2 infection causes severe immune disruption.However,it is unclear if disrupted immune regulation still exists and pertains in recovered COVID-19 patients.In our study,we have characterized the immunephe no type of B cells from 15 recovered COVID-19 patients,and found that healthy controls and recovered patients had similar B-cell populations before and after BCR stimulation,but the frequencies of PBC in patients were significantly increased when compared to healthy controls before stimulation.However,the percentage of unswitched memory B cells was decreased in recovered patients but not changed in healthy controls upon BCR stimulation.Interestingly,we found that CD19 expression was significantly reduced in almost all the B-cell subsets in recovered patients.Moreover,the BCR signaling and early B-cell response were disrupted upon BCR stimulation.Mechanistically,we found that the reduced CD19 expression was caused by the dysregulation of cell metabolism.In conclusion,we found that SARS-CoV-2 infection causes immunodeficiency in recovered patients by downregulating CD19 expression in B cells via enhandng B-cell metabolism,which may provide a new intervention target to cure COVID-19.