Heterogeneity induced strain localization in block-in-matrix-soils subjected to uniaxial loading using real-time CT scanning

Block-in-matrix-soils(bimsoils)are geological mixtures that have distinct structures consisting of relatively strong rock blocks and weak matrix soils.It is still a challenge to evaluate the mechanical behaviors of bimsoils because of the heterogeneity,chaotic structure,and lithological variability.As a result,only very limited laboratory studies have been reported on the evolution of their internal deformation.In this study,the deformation evolution of bimsoils under uniaxial loading is investigated using real-time X-ray computed tomography(CT)and image correlation algorithm(with a rock block percentage(RBP)of 40%).Three parameters,i.e.heterogeneity coefficient(K),correlation coefficient(CC),and standard deviation(STD)of displacement fields,are proposed to quantify the heterogeneity of the motion of the rock blocks and the progressive deformation of the bimsoils.Experimental results show that the rock blocks in bimsoils are prone to forming clusters with increasing loading,and the sliding surface goes around only one side of a cluster.Based on the movement of the rock blocks recorded by STD and CC,the progressive deformation of the bimsoils is quantitatively divided into three stages:initialization of the rotation of rock blocks,formation of rock block clusters,and formation of a shear band by rock blocks with significant rotation.Moreover,the experimental results demonstrate that the meso-motion of rock blocks controls the macroscopic mechanical properties of the samples.

VEGFR-3 ligand-binding and kinase activity are required for lymphangiogenesis but not for angiogenesis

Although VEGFR-3 deficiency disrupts blood vascular development during early embryogenesis, the underlying mechanism was not clear. To characterize its function in angiogenesis and lymphangiogenesis, we employed two genetically modified mouse models in this study, targeting the coding region for the ligand-binding domain （Vegfr△LBD） or the tyrosine kinase domain with an inactivation point mutation （Vegfr3^TKmat）. We show that lymphatic growth was disrupted in Vegfr3△LBD/△LBD and Vegfr3^TKmut3^TKmat mice, but blood vessels developed normally in both embryo and yolk sac. Interestingly, in Vegfr3△LBD/△LBD but not Vegfr3^TKmut3^TKmat mice, lymph sac was present but there was lack of iym- phangiogenic sprouting. We further demonstrate that both the wild-type and mutant forms of VEGFR-3 could form heterodimers with VEGFR-2, and decreased the level of phospho-VEGFR-2 and the downstream phospho-Erk1/2 in endothelial cells when they were treated with VEGF-A. These findings indicate that signaling mediated via VEGFR-3 activation by its cognate ligands （VEGF-C/-D） is not required for angiogenesis, and that VEGFR-3 may play a role in this process by modulating VEGFR-2-mediated signals.

Constructing nanocomposites with robust covalent connection between nanoparticles and polymer for high discharged energy density and excellent tensile properties

High discharged energy density and excellent flexible properties in dielectric materials are significantly sought to meet the rapid advancements in the electronics industry. In this study, covalent bonds are constructed between poly(vinylidene fluoride-chlorotrifluoroethylene), which contains olefinic bonds, and thiol-modified BaTiO_(3) at the interface before the nanocomposite films are fabricated. The presence of the covalent bonds is proved to promote the dispersibility of the modified BaTiO_(3) and enhance the interfacial adhesion between the modified BaTiO_(3) and the polymer, followed by a remarkably positive effect in suppressing the dielectric loss(tanδ) and increasing the breakdown strength(Eb) of the nanocomposite films. In addition, the cross-linking treatment in the preparation process is found to be favourable for improving the mechanical properties of the nanocomposite films, which benefits the enhancement of Eb. Furthermore, at 400% elongation, the stretched nanocomposite film doped with 5 vol% modified BaTiO_(3) exhibits an Eb15.6% greater than that of the unstretched film, and the discharged energy density reaches 11.4 J/cm^(3) with a high discharge energy efficiency of 84.5%. This study provides a novel strategy for preparing flexible nanocomposites with powerful interfacial adhesion at high filler content to achieve high discharged energy density.

Back analysis of long-term stability of a 92 m span ancient quarrying cavern

Long-term stability of large-span caverns is a challenging issue for design and construction of underground rock engineering.The Heidong cavern group consisting of 21 caverns was constructed about 1400 years ago for quarrying in massive Cretaceous tuff.The cavern No.5 of the Heidong cavern group is characterized by an unsupported span up to 92 m,with the overburden thickness of only 3-25 m.To analyze its long-term stability,a detailed investigation was conducted to obtain its geometry and rock mass characteristics,and to monitor surrounding rock displacements.Based on field survey and laboratory tests,numerical simulations were performed using the finite difference code FLAC;.The analysis results revealed that for the long-term stability of the cavern No.5,some major factors should be carefully considered,such as cavern excavation method in hard massive rocks,site investigation using trial pits,tools like short iron chisel and hammer for manual excavation,geometric dome roof,and waste rocks within abutment or on the floor.The highlights of the technologies obtained from this large-scale ancient underground project can provide reference for other similar project excavations in practice.

A hypothesis for crack free interior surfaces of Longyou caverns caved in argillaceous siltstone 2000 years ago

Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.

Preparation of slightly crosslinked monodisperse poly(maleic anhydride-cyclohexyl vinyl ether-divinylbenzene)functional microspheres with anhydride groups via precipitation polymerization

Slightly crosslinked monodisperse poly（maleic anhydride-cyclohexyl vinyl ether-divinylbenzene） （MA-CHVE-DVB） microspheres were prepared via precipitation polymerization while using 2,2- azobisisobutyronitrile as an initiator in a mixture of methyl ethyl ketone and n-heptane without any stabilizer. The number-average diameter of the resultant poly（MA-CHVE-DVB） microspheres ranged from 0.478 to 1.386 μm with a polydispersity index of 1.00 to 1.02 that depended on the feed ratios of the MA/CHVE/DVB monomers. The introduction of one electron donor monomer cyclohexyl vinyl ether strongly affected the yield, size, and morphology of these slightly crosslinked microspheres. Quinoline- type chelating resins were obtained after combining the poly（MA-CHVE-DVB） with 8-hydroxyquinoline; the adsorption properties of these materials were measured through their ability to remove Cu^2＋ ions from water. The poly（MA-CHVE-DVB） microspheres with low degrees of crosslinking provided more effective functional groups and therefore better ion removal capabilities. These slightly crosslinked microspheres may have applications in water treatment as well as in sensing and drug delivery.

The effect of oxidation on physicochemical properties and aqueous stabilization of multiwalled carbon nanotubes：comparison of multiple analysis methods

Surface oxidation can alter physicochemical properties of multiwalled carbon nanotubes(MWCNTs) and influence their aqueous stabilization.Many techniques have been used to characterize the physicochemical properties and aqueous stabilization of MWCNTs.However,the relationship between the change in physicochemical property and the aqueous stabilization of MWCNTs merits more studies,and the multiple characterization techniques have not been well compared.This study systematically and comparatively investigated the effect of oxidation on the physicochemical properties and aqueous stabilization of MWCNTs using multiple analysis methods.Increased surface area,disclosed tube ends,defects on the sidewalls,disruption of the electronic structure,and removal of metal catalysts and amorphous carbon were observed for the oxidized MWCNTs(o-MWCNTs) using the multipoint Brunauer-Emmett-Teller(BET) method,transmission electron microscope observation,Raman spectroscopy,UV-Vis spectroscopy,and thermogravimetric analysis.An oxidation-time-dependent increase in oxygen content of the MWCNTs was verified by the methods of elemental analysis,mass difference calculation,and X-ray photoelectron spectroscopy(XPS).Fourier transform infrared spectroscopy,XPS,and the Boehm titration were employed to study the functionalities on the MWCNT surfaces.Despite the limitations of these techniques,the results indicated that the dramatic increase in carboxyl groups was mainly responsible for the significant increase in oxygen content after the oxidation.The dissociation of the grafted functional groups increased electronegativity of the o-MWCNTs and facilitated the aqueous stabilization of o-MWCNTs through electrostatic repulsions.The oxidation affected the UV-Vis absorbance of MWCNT suspensions.The absorbances at 800 nm of the stabilized MWCNT suspensions had a good correlation with the MWCNT concentrations and could be used to quantify the MWCNT suspensions.The findings of this work are expected to boost the research on carbon nanotubes and their environmental behaviors.