Search

Introduction Phyllosphere microbiome is intrinsically linked to plant performance and ecosystem functioning. However, our knowledge about the role of ecological processes in shaping the biogeography of different phyllosphere microbial communities is scarce. Materials and Methods Here, we compared the biogeographic patterns of bacterial and fungal communities in phyllosphere samples of plants belonging to the genus of Eucalyptus of the Myrtaceae family collected from an over 4000 km transect. We investigated the relative importance of two major ecosystem processes (stochastic vs. deterministic) in shaping phyllosphere microbial community assemblies. Results Our results demonstrated that the neutral community model, which can quantify the degree of a community assembly determined by stochastic processes, explained 64.2% of the variations in bacterial community assembly, which had a normalized stochasticity ratio of 71.8%. These results suggest that the dominant role of stochastic processes in shaping bacterial community assembly. In contrast, phyllosphere fungal community assembly was mainly shaped by deterministic processes as revealed by a relatively small explanation rate of the neutral community model (48.7%) and a normalized stochasticity ratio of 25.1%. Variation partitioning analysis and random forest modelling results indicated that climatic factors, particularly mean annual precipitation and aridity index, were important in driving both bacterial and fungal biogeographic patterns in the phyllosphere. Edaphic factors, such as soil organic and mineral nitrogen content, were more closely related to fungal community assembly than to bacterial community assembly. The differential responses of bacterial and fungal communities to environmental factors could be attributed to the different traits of bacteria and fungi, that is, the higher potential dispersal rate and wider habitat niche of bacteria than fungi. Conclusion Our findings demonstrated that phyllos

© 2019 The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s −1 , is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s −1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading.

© 2019 The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s −1 , is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s −1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading.

© 2017 Elsevier Ltd In this study, the effects of graphene oxide (GO) agglomerates on the workability, hydration, microstructure, and compressive strength of cement paste were addressed. The workability of cement paste was reduced because of the presence of GO agglomerates, which entrap a large amount of water. The mini-slump diameter was reduced by 21% with the incorporation of 0.03% by weight GO in cement paste. Hydration of the cement paste was accelerated due to nucleation sites provided by GO agglomerates serving as seeding material in the cement paste. The incorporation of GO refined the pore structure of the cement paste. The incorporation of GO was found to have much greater impact on macropores than on large and small mesopores. At 28 days, the incorporation of 0.04% by weight GO produced a 14% improvement in the compressive strength of cement paste. Below 0.03%, the incorporation of GO had no positive effects on compressive strength.

© 2017 Elsevier Ltd In this study, the effects of graphene oxide (GO) agglomerates on the workability, hydration, microstructure, and compressive strength of cement paste were addressed. The workability of cement paste was reduced because of the presence of GO agglomerates, which entrap a large amount of water. The mini-slump diameter was reduced by 21% with the incorporation of 0.03% by weight GO in cement paste. Hydration of the cement paste was accelerated due to nucleation sites provided by GO agglomerates serving as seeding material in the cement paste. The incorporation of GO refined the pore structure of the cement paste. The incorporation of GO was found to have much greater impact on macropores than on large and small mesopores. At 28 days, the incorporation of 0.04% by weight GO produced a 14% improvement in the compressive strength of cement paste. Below 0.03%, the incorporation of GO had no positive effects on compressive strength.

It can facilitate the understanding of the mechanical properties and failure laws of rocks to research on the rock failure mechanism and evolution characteristics of Acoustic Emission (AE). Under the concentrated loading condition, the fracture and instability test of a rock plate was conducted by using the rock Mechanics Testing System (MTS), meanwhile, these AE events were recorded through the AE recording system. Based on the laboratory test, the numerical simulation was completed by using FLAC3D technique under the criterion that the rupture of a cell or several adjacent cells was regarded as an AE event. The results show that the process of the fracture and instability of the rock plate can be divided into four stages, such as the stress adjusting stage, the brittle fracture stage, the rock-arch bearing load stage and the rock-arch instability stage. And the acoustic emissions display the different characteristics in each one of the four stages. The temporal and spatial distribution characteristics of the AE events with large magnitudes are very similar to those of the natural earthquakes.

Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10-20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north-south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present-day Tibetan Plateau, deformed, and its north-south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since ~15 Ma and a less precisely dated change in orientation of crustal shortening since ~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE-SSW in northern Tibet to more NE-SW and even ENE-WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation. Key Points The north-south limits of Tibet were set by lateral variations in strength Roughly 15 million years ago, deformation of NE Tibet accelerated Since 20-15 million years ago, the orientation of shortening rotated eastward ©2013. American Geophysical Union. All Rights Reserved.

Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10-20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north-south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present-day Tibetan Plateau, deformed, and its north-south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since ~15 Ma and a less precisely dated change in orientation of crustal shortening since ~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE-SSW in northern Tibet to more NE-SW and even ENE-WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation. Key Points The north-south limits of Tibet were set by lateral variations in strength Roughly 15 million years ago, deformation of NE Tibet accelerated Since 20-15 million years ago, the orientation of shortening rotated eastward ©2013. American Geophysical Union. All Rights Reserved.

We observed the transverse magnetic field induced transition from static to dynamic electric field domain formation in doped GaAs/AlAs superlattices. A dynamic dc voltage band was found emerging from each sawtooth-like branch of the current-voltage characteristics in the transition process. Within each dynamic dc voltage band at a fixed magnetic field the current self-oscillation frequency was increased while the average current was decreased. These results were explained by a general analysis of stability of the sequential tunneling current in superlattices.

We observed the transverse magnetic field induced transition from static to dynamic electric field domain formation in doped GaAs/AlAs superlattices. A dynamic dc voltage band was found emerging from each sawtooth-like branch of the current-voltage characteristics in the transition process. Within each dynamic dc voltage band at a fixed magnetic field the current self-oscillation frequency was increased while the average current was decreased. These results were explained by a general analysis of stability of the sequential tunneling current in superlattices.

HEPTYLENE-LINKED bis-(9-amino-1,2,3,4-tetrahydroacridine) (bis(7)-tacrine) is a potential palliative therapeutic agent for Alzheimer's disease (AD), on the basis of its superior acetylcholinesterase (AChE) inhibition and memory-enhancing potency relative to tacrine. In this study we report that bis(7)-tacrine exhibits a potentially complementary central nervous system action, antagonism of GABA(A) receptor function. Bis(7)tacrine displaced [H-3]muscimol from rat brain membranes with an apparent K-i of 6.0 mu M; tacrine and physostigmine were shown to be 18 and 170 times less potent, respectively. In whole-cell patch-clamp recordings, bis(7)-tacrine inhibited GABA-induced inward current with an IC50 of 5.6 mu M, and shifted the GABA concentration-response curve to the right in a parallel manner. These results suggest that bis(7)-tacrine is a competitive antagonist of the GABA(A) receptor. NeuroReport 10:795-800 (C) 1999 Lippincott Williams & Wilkins.

HEPTYLENE-LINKED bis-(9-amino-1,2,3,4-tetrahydroacridine) (bis(7)-tacrine) is a potential palliative therapeutic agent for Alzheimer's disease (AD), on the basis of its superior acetylcholinesterase (AChE) inhibition and memory-enhancing potency relative to tacrine. In this study we report that bis(7)-tacrine exhibits a potentially complementary central nervous system action, antagonism of GABA(A) receptor function. Bis(7)tacrine displaced [H-3]muscimol from rat brain membranes with an apparent K-i of 6.0 mu M; tacrine and physostigmine were shown to be 18 and 170 times less potent, respectively. In whole-cell patch-clamp recordings, bis(7)-tacrine inhibited GABA-induced inward current with an IC50 of 5.6 mu M, and shifted the GABA concentration-response curve to the right in a parallel manner. These results suggest that bis(7)-tacrine is a competitive antagonist of the GABA(A) receptor. NeuroReport 10:795-800 (C) 1999 Lippincott Williams & Wilkins.

HEPTYLENE-LINKED bis-(9-amino-1,2,3,4-tetrahydroacridine) (bis(7)-tacrine) is a potential palliative therapeutic agent for Alzheimer's disease (AD), on the basis of its superior acetylcholinesterase (AChE) inhibition and memory-enhancing potency relative to tacrine. In this study we report that bis(7)-tacrine exhibits a potentially complementary central nervous system action, antagonism of GABA(A) receptor function. Bis(7)tacrine displaced [H-3]muscimol from rat brain membranes with an apparent K-i of 6.0 mu M; tacrine and physostigmine were shown to be 18 and 170 times less potent, respectively. In whole-cell patch-clamp recordings, bis(7)-tacrine inhibited GABA-induced inward current with an IC50 of 5.6 mu M, and shifted the GABA concentration-response curve to the right in a parallel manner. These results suggest that bis(7)-tacrine is a competitive antagonist of the GABA(A) receptor. NeuroReport 10:795-800 (C) 1999 Lippincott Williams & Wilkins.