•Steel-PVA -CW hybrid fiber improves the strength of mortar after elevated temperatures.•MSFRC has better high temperature resistance than concrete, RPC and ECC.•Digital camera and optical microscope ...are useful to evaluate changes of fiber at high temperature.
By experimental research on the steel- polyvinyl alcohol (PVA) fibers- calcium carbonate whisker (CW) multi scale fiber-reinforced cement-based composites (MSFRC) after exposure of temperatures up to 900 °C, the flexural, compressive strength, and microstructures of multi scale fibers were investigated in this paper. The incorporation of steel-PVA fibers-CW can effectively improve the flexural and compressive strength of mortar after elevated temperatures. Compared with normal concrete, hybrid fiber reactive powder concrete (RPC) and engineered cement-based composites (ECC), the MSFRC present better capacity of high temperature resistance. The flexural and compressive strength increase first and then decrease with the increasing temperature, and the critical temperatures are 200 °C and 400 °C respectively. Models for describing the relationship between strength, CW content and temperature are proposed. The good high temperature resistance of MSFRC relates to the hybrid effect of melt of PVA fiber, good heat conduction of steel, and the phase transformation from aragonite to calcite of CW. Comprehensive morphology observations by digital camera and optical microscope are simple and useful way to evaluate the changes of fibers and CW at high temperature. This research is very beneficial for the applications of MSFRC in construction project with fire risk.
This study investigates the penetration characteristics of water and temperature effect, aiming to understand the mechanism of water intrusion and provide a basis for studying the transport of ...aggressive ions in concrete. Molecular dynamics simulations were employed to simulate the capillary motion of water in hydrated calcium silicate (C-S-H) slit. The effects of temperature on water density, chemical bond of atomic pairs, flow velocity distribution, and slip length during the flow process were analysed, and the flow equations were modified. It was found that the density of water in the region of 0.55 nm from the interior wall of the C-S-H slit manifests significant inhomogeneity. The stronger the chemical bond of atomic pairs, the less the residence time is influenced by temperature. Increasing the temperature from 280 K to 360 K results in a significant increase in the cross-sectional flow velocity within the nanoslit, while the changes in the size of the inhomogeneous region and the slip length are insignificant. The modified Bosanquet equation is suitable for describing the second stage of nanocapillary flow, while the Lucas-Washburn equation is suitable for describing the third stage.
•The thermal fatigue test of concrete was carried out under constant ambient humidity.•The macroscopic mechanical properties and ultrasonic wave velocity were decreased.•The splitting tensile ...strength was more sensitive than the compressive strength.•The pore structure showed the characteristics of coarsening and deterioration.
The daily and annual temperature differences in mid and high latitudes areas vary greatly, which leads to thermal fatigue deterioration of concrete. The deterioration of concrete properties can also be generated by the cyclic change of humidity in concrete. In the experiment, the thermal fatigue tests of concrete with two strength grades were carried out at the temperature difference of 20 °C, 30 °C, and 40 °C (the initial temperature is 20 °C) under the condition of constant ambient humidity. The macroscopic properties change of concrete such as compressive strength and splitting tensile strength were measured. The microstructure changes of concrete were determined by ultrasonic nondestructive testing technique and mercury intrusion test. The results indicated that thermal fatigue has obvious deterioration effect on concrete. With the increase of temperature difference and cycle number, the strength of concrete decreased dramatically and the decrease of C40 concrete was greater than that of C25 concrete. The splitting tensile strength was more sensitive to thermal fatigue than compressive strength. The ultrasonic wave velocity gradually decreased and the damage factor increased, indicating the internal crack defects of concrete increased. At the same temperature difference, the porosity, total pore volume, average pore diameter, medium pore diameter, and the most probable pore diameter of concrete increased gradually with the increase of the cycle number, while the total pore surface area decreased. The pore structure showed the characteristics of coarsening and the trend of deterioration. The porosity of C40 concrete was less than that of C25 concrete, but the relative change value of porosity was larger, which reveals the internal reason for the strength damage of concrete under thermal fatigue at the microscopic level.
Mitochondria, chloroplasts and Gram-negative bacteria are encased in a double layer of membranes. The outer membrane contains proteins with a β-barrel structure
. β-Barrels are sheets of β-strands ...wrapped into a cylinder, in which the first strand is hydrogen-bonded to the final strand. Conserved multi-subunit molecular machines fold and insert these proteins into the outer membrane
. One subunit of the machines is itself a β-barrel protein that has a central role in folding other β-barrels. In Gram-negative bacteria, the β-barrel assembly machine (BAM) consists of the β-barrel protein BamA, and four lipoproteins
. To understand how the BAM complex accelerates folding without using exogenous energy (for example, ATP)
, we trapped folding intermediates on this machine. Here we report the structure of the BAM complex of Escherichia coli folding BamA itself. The BamA catalyst forms an asymmetric hybrid β-barrel with the BamA substrate. The N-terminal edge of the BamA catalyst has an antiparallel hydrogen-bonded interface with the C-terminal edge of the BamA substrate, consistent with previous crosslinking studies
; the other edges of the BamA catalyst and substrate are close to each other, but curl inward and do not pair. Six hydrogen bonds in a membrane environment make the interface between the two proteins very stable. This stability allows folding, but creates a high kinetic barrier to substrate release after folding has finished. Features at each end of the substrate overcome this barrier and promote release by stepwise exchange of hydrogen bonds. This mechanism of substrate-assisted product release explains how the BAM complex can stably associate with the substrate during folding and then turn over rapidly when folding is complete.
Na(+)-activated K(+) channels are members of the Slo family of large conductance K(+) channels that are widely expressed in the brain, where their opening regulates neuronal excitability. These ...channels fulfil a number of biological roles and have intriguing biophysical properties, including conductance levels that are ten times those of most other K(+) channels and gating sensitivity to intracellular Na(+). Here we present the structure of a complete Na(+)-activated K(+) channel, chicken Slo2.2, in the Na(+)-free state, determined by cryo-electron microscopy at a nominal resolution of 4.5 ångströms. The channel is composed of a large cytoplasmic gating ring, in which resides the Na(+)-binding site and a transmembrane domain that closely resembles voltage-gated K(+) channels. In the structure, the cytoplasmic domain adopts a closed conformation and the ion conduction pore is also closed. The structure reveals features that can explain the unusually high conductance of Slo channels and how contraction of the cytoplasmic gating ring closes the pore.
Chronic obstructive pulmonary disease (COPD) is a common disease with high morbidity and mortality, where early detection benefits the population. However, the early diagnosis rate of COPD is low due ...to the absence or slight early symptoms. In this paper, a novel method based on graph convolution network (GCN) for early detection of COPD is proposed, which uses small and weakly labeled chest computed tomography image data from the publicly available Danish Lung Cancer Screening Trial database. The key idea is to construct a graph using regions of interest randomly selected from the segmented lung parenchyma and then input it into the GCN model for COPD detection. In this way, the model can not only extract the feature information of each region of interest but also the topological structure information between regions of interest, that is, graph structure information. The proposed GCN model achieves an acceptable performance with an accuracy of 0.77 and an area under a curve of 0.81, which is higher than the previous studies on the same dataset. GCN model also outperforms several state-of-the-art methods trained at the same time. As far as we know, it is also the first time using the GCN model on this dataset for COPD detection.
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This paper presents an experiment to investigate the influence of moisture on the static mechanical properties of concrete, and prediction equations for strength and fracture toughness of concrete at ...different strength grades, relative to water saturation, were established respectively. The research results show that all of the compressive strength, splitting tensile strength, and fracture toughness of concrete exhibit an approximately linearly decreasing trend with the increase in water saturation. For saturated concrete specimens with w/c 0.65, 0.55, 0.42 compared with dry ones, compressive strength decreases by 40.08%, 36.08%, and 33.73%, respectively, splitting tensile strength decreases by 45.39%, 42.61%, and 35.18%, respectively, and fracture toughness decreases by 57.31%, 49.92%, and 46.76%, respectively. The higher the water saturation of concrete, the larger the slope of the ascending part of the uniaxial compressive stress-strain curve, and the smaller the peak strain corresponding to the peak compressive stress, then in this case, both crack mouth opening displacement and loading point deflection corresponding to the critical load on three-point bending beam, decrease. Ingress of water causes the deformation capacity to decrease, and the toughness to weaken, which are unfavorable to the mechanical properties of concrete.
Vegetation deterioration and soil loss are the main causes of more precipitation leakages and surface water shortages in degraded karst areas. In order to improve the utilization of water resources ...in such regions, water storage engineering has been considered; however, site selection and cost associated with the special karstic geological structure have made this difficult. According to the principle of the Soil Plant Atmosphere Continuum, increasing both vegetation cover and soil thickness would change water cycle process, resulting in a transformation from leaked blue water (liquid form) into green water (gas or saturated water form) for terrestrial plant ecosystems, thereby improving the utilization of water resources. Using the Soil Vegetation Atmosphere Transfer model and the geographical distributed approach, this study simulated the conversion from leaked blue water (leakage) into green water in the environs of Guiyang, a typical degraded karst area. The primary results were as follows: (1) Green water in the area accounted for <50% of precipitation, well below the world average of 65%; (2) Vegetation growth played an important role in converting leakage into green water; however, once it increased to 56%, its contribution to reducing leakage decreased sharply; (3) Increasing soil thickness by 20 cm converted the leakage considerably. The order of leakage reduction under different precipitation scenarios was dry year > normal year > rainy year. Thus, increased soil thickness was shown effective in improving the utilization ratio of water resources and in raising the amount of plant ecological water use; (4) The transformation of blue water into green water, which avoids constructions of hydraulic engineering, could provide an alternative solution for the improvement of the utilization of water resources in degraded karst area. Although there are inevitable uncertainties in simulation process, it has important significance for overcoming similar problems.
To evaluate the role of radiomics based on Chest Computed Tomography (CT) in the identification and severity staging of chronic obstructive pulmonary disease (COPD).
This retrospective analysis ...included 322 participants (249 COPD patients and 73 control subjects). In total, 1395 chest CT-based radiomics features were extracted from each participant's CT images. Three feature selection methods, including variance threshold, Select K Best method, and least absolute shrinkage and selection operator (LASSO), and two classification methods, including support vector machine (SVM) and logistic regression (LR), were used as identification and severity classification of COPD. Performance was compared by AUC, accuracy, sensitivity, specificity, precision, and F1-score.
38 and 10 features were selected to construct radiomics models to detect and stage COPD, respectively. For COPD identification, SVM classifier achieved AUCs of 0.992 and 0.970, while LR classifier achieved AUCs of 0.993 and 0.972 in the training set and test set, respectively. For the severity staging of COPD, the mentioned two machine learning classifiers can better differentiate less severity (GOLD1 + GOLD2) group from greater severity (GOLD3 + GOLD4) group. The AUCs of SVM and LR is 0.907 and 0.903 in the training set, and that of 0.799 and 0.797 in the test set.
The present study showed that the novel radiomics approach based on chest CT images that can be used for COPD identification and severity classification, and the constructed radiomics model demonstrated acceptable performance.
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•Compressive strength decreases and then increases with increase in temperature.•Splitting tensile strength decreases with increase in drying temperature.•Drying control condition ...with minimal effect was obtained on concrete strength.•Components and defects of concrete after nondestructive drying was analyzed.
In order to obtain the drying control condition with no or minimal effect on concrete strength, various drying temperatures conditions are used as 150°C, 120°C, 105°C, 85°C and 60°C, and the drying procedure of continuous and intermittent cyclic are presented independently in this study. The change of specimen mass is recorded in the drying process, and the compressive strength and splitting tensile strength are measured after the natural cooling. The results show that the concrete compressive strength initially decreases and then increases with the increase in drying temperature, while the splitting tensile strength always decreases. The relative compressive and splitting tensile strength of concrete in dry state are 1 and 0.99 respectively after 115.5h of continuous drying at 105°C, which denotes the optimal drying control condition has minimal effect on the strength, and efficiency is suitable. Finally, the change in components and defects structure of the concrete after minimal damage drying is analyzed through the thermo-gravimetric analysis, electron microscope scanning and industrial CT scanning.
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