Metakaolin (MK) and silica fume (SF) have been added either individually or in combination to improve concrete performance. Recent studies proved that the combined addition of MK and SF offers ...synergistic effects, but the mechanism behind is still not unclear. Herein, it is postulated that the synergistic effects arise mainly from the successive filling effects of the MK and SF into voids between larger size particles, which increase the wet packing density (WPD). The present work indicated that the slurry formed of the water and ultrafine particles plays an important role. Good correlation of the workability measures to the slurry film thickness (SFT) revealed the governing factor of SFT for the first time. Moreover, the synergistic effects of MK and SF on the compressive and flexural strengths have been studied based on cementing efficiency and synergistic factors. Correlation of the synergistic factor to the WPD revealed that the WPD plays an important role.
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•The simultaneous use of metakaolin and silica fume is explored.•The concept of slurry film thickness is established for modeling.•Formulas based on slurry film thickness are derived for workability.•Synergistic factor and particle packing are associated with strengths.
Vaccines against COVID-19 are now available for adolescents in Hong Kong but vaccine hesitancy is a major barrier to herd immunity. This survey study explores Hong Kong adolescents’ attitudes towards ...the COVID-19 vaccination. 2609 adolescents from across Hong Kong completed an online survey focused on the intent to vaccinate and the reasons for their choice. 39% of adolescents intended to take the COVID-19 vaccination and significant factors for this decision include: having at least one parent vaccinated, knowing somebody diagnosed with COVID-19 and receiving the influenza vaccine. Adolescents’ major concerns were either the safety and efficacy of the vaccine or the risk of infection. This study has proved that even in adolescents the vaccine hesitancy model is prominent with adolescents’ intentions highly related to confidence in the vaccine and perception of disease risk. Future interventions should target these specific concerns to ensure adolescents are well educated to overcome vaccine hesitancy.
•A new FE model considering lateral dilation of concrete has been developed.•Non-uniform confinement in eccentrically loaded CFST columns can be simulated.•Accuracy of the model is verified by ...comparing the test results to the predictions thereof.•The FE model provides a framework for any equivalent models of confined concrete.
The casting of concrete in concrete-filled steel tube (CFST) can, via the confinement effect of the steel tube, significantly increase the ductility of the concrete and, in the case of high-strength concrete (HSC), alleviate the shortfall in ductility of the HSC. This kind of structure is gaining popularity but its behaviour is quite complicated. In an axially loaded circular CFST column, the confinement is uniform and equi-biaxial (isotropic within the cross-section). But, when the circular CFST column is under eccentric load, the confinement becomes non-uniform and anisotropic. Such complicated confinement effect is not easy to analyse and for such analysis, a rigorous finite element (FE) method is generally needed. In this paper, a new FE model considering the lateral strain-axial strain relation of the confined concrete covering the full range from the initial elastic stage to the inelastic stage is developed for the analysis of circular CFST columns under eccentric load. The FE model is used to analyse a total of 95 CFST specimens tested by other researchers and the numerical results are compared to the published test results for verification.
Landslide debris is a common occurrence in mountainous regions around the world that can potentially result in disastrous consequences to downstream facilities. Flow-impeding structures are often ...constructed along the flow path to impede this hazardous phenomenon. Baffles are a type of flow-impeding structure regularly installed using empirical and prescriptive design methods as the interaction mechanism and the influence of baffle configuration on flow impedance is not well understood. A series of flume experiments were carried out to investigate flows characterizing landslide debris impacting an array of baffles using dry uniform sand. The influence of baffle height, row number, and spacing between successive rows was examined. Photoconductive sensors were used to estimate flow velocity, laser sensors were installed to measure flow depth profiles, and high-speed cameras were used to capture flow kinematics. Experimental results reveal that baffles can be categorized relative to the approach flow depth (h) and increasing the baffle height from 0.75h to 1.5h leads to a 40% increase in upstream flow depths from backwater effects, more effective development of subcritical conditions, and additional energy losses of up to 9%. Increasing the number of rows of 1.5h baffles from a single row to a three-row staggered array results in up to 72% additional energy loss. The energy loss is attributed to the deflection of granular jets and additional backwater effects. Increasing the row spacing from 50 to 100 mm results in up to a 14% increase in energy loss.
The impulse load of boulders at the front of debris flows is critical to the design of structural defense measures, which are commonly constructed on hillsides to mitigate landslide risk. Field ...evidences have demonstrated the capability of some steel flexible barriers in intercepting debris flows with bouldery inclusions. However, there is still a lack of fundamental understanding of the load-attenuation mechanisms of flexible barriers, especially under bouldery debris flow impact. In this study, systematic tests of mono-disperse and bi-disperse bouldery flows impacting an instrumented flexible barrier were conducted using a geotechnical centrifuge. The impact kinematics and barrier responses, such as mobilized structural forces and elongation of cables, were recorded synchronously. The results reveal that the load-attenuation mechanism of flexible barriers for the frontal impact originates from the barrier deflections and extended interaction duration. Only 30% of the frontal momentum is transferred to the flexible barrier. The performance of the flexible barrier is compared with that of a rigid barrier model under identical testing conditions. It is found that the boulder impulse loads on flexible barrier are significantly attenuated, resulting in a “plateau” pattern of the impact time history. The practical implication is that the design of flexible barriers may not demand separate considerations of the bulk debris and individual boulder impact loads. Detailed examination of the state of debris deposited behind the flexible barrier indicates that the static dry debris is close to the active failure state due to the large barrier deflection.
Effective design of mitigation measures against debris flow hazards remains a challenging geotechnical problem. At present, a pseudo-static approach is commonly used for the calculation of impact ...load acting on a rigid debris-resisting barrier. The impact load is normally calculated based on the maximum velocity observed in the transportation zone under free-field conditions without considering debris-barrier interaction. In reality, the impact load acting on a barrier varies with the change of debris momentum flux but this is seldom considered in barrier design. To provide a scientific basis for assessing debris momentum flux during impact, this paper presents results from a study of debris-barrier interaction using physical flume modelling. This study showed that, following the first stage of impact, the accumulated debris behind a barrier formed a stationary zone and caused the remaining debris to slow down in a run-up process. In the experiments, the peak debris momentum was 30 % lower compared to that observed under free-field conditions. A new momentum-based model was developed to take into account attenuation of momentum flux for predicting debris impact load on rigid barriers. The new rationalised model was assessed using data from the notable Yu Tung Road debris flow in Hong Kong. The assessment showed that the design bending moment at the base of the barrier wall could be reduced more than 30 % using the proposed model, compared with the current design approach. The adoption of the proposed model could offer a new opportunity for practitioners to optimise the design of rigid barriers.
Natural terrain landslides are mainly triggered by rainstorms in Hong Kong, which pose great threats to life and property. To mitigate landslide risk, building a prediction model which could provide ...information on both spatial and temporal probabilities of landslide occurrence is essential but challenging. In this paper, real-time rainfall conditions are incorporated into landslide prediction through a unique rainstorm-based database of reported landslides. Other landslide controlling factors related to topography, geology, and land cover are also considered. Five machine learning methods, including logistic regression, random forest, adaboost tree, support vector machine, and multilayer perceptron, are utilized and compared. Validated against historical rainstorms, the machine learning powered landslide prediction model could reasonably forecast the occurrence of landslides in a spatiotemporal context. Moreover, the effects of different rainstorm characteristics in terms of distinct rainfall spatial distribution and intensity on landslide susceptibility could also be captured by this model. For the landslide controlling factors investigated, rolling rainfall factors are proven to play a more important role than antecedent rainfall factors for landslide prediction. Among the five machine learning methods, the random forest model yields the most promising results in terms of all performance indicators (i.e., classification accuracy, recall, precision, area under curve, and overall accuracy).
The mushroom Coprinopsis cinerea is a classic experimental model for multicellular development in fungi because it grows on defined media, completes its life cycle in 2 weeks, produces some 10⁸ ...synchronized meiocytes, and can be manipulated at all stages in development by mutation and transformation. The 37-megabase genome of C. cinerea was sequenced and assembled into 13 chromosomes. Meiotic recombination rates vary greatly along the chromosomes, and retrotransposons are absent in large regions of the genome with low levels of meiotic recombination. Single-copy genes with identifiable orthologs in other basidiomycetes are predominant in low-recombination regions of the chromosome. In contrast, paralogous multicopy genes are found in the highly recombining regions, including a large family of protein kinases (FunK1) unique to multicellular fungi. Analyses of P450 and hydrophobin gene families confirmed that local gene duplications drive the expansions of paralogous copies and the expansions occur in independent lineages of Agaricomycotina fungi. Gene-expression patterns from microarrays were used to dissect the transcriptional program of dikaryon formation (mating). Several members of the FunK1 kinase family are differentially regulated during sexual morphogenesis, and coordinate regulation of adjacent duplications is rare. The genomes of C. cinerea and Laccaria bicolor, a symbiotic basidiomycete, share extensive regions of synteny. The largest syntenic blocks occur in regions with low meiotic recombination rates, no transposable elements, and tight gene spacing, where orthologous single-copy genes are overrepresented. The chromosome assembly of C. cinerea is an essential resource in understanding the evolution of multicellularity in the fungi.
Whole-genome duplication (WGD) results in new genomic resources that can be exploited by evolution for rewiring genetic regulatory networks in organisms. In metazoans, WGD occurred before the last ...common ancestor of vertebrates, and has been postulated as a major evolutionary force that contributed to their speciation and diversification of morphological structures. Here, we have sequenced genomes from three of the four extant species of horseshoe crabs-Carcinoscorpius rotundicauda, Limulus polyphemus and Tachypleus tridentatus. Phylogenetic and sequence analyses of their Hox and other homeobox genes, which encode crucial transcription factors and have been used as indicators of WGD in animals, strongly suggests that WGD happened before the last common ancestor of these marine chelicerates >135 million years ago. Signatures of subfunctionalisation of paralogues of Hox genes are revealed in the appendages of two species of horseshoe crabs. Further, residual homeobox pseudogenes are observed in the three lineages. The existence of WGD in the horseshoe crabs, noted for relative morphological stasis over geological time, suggests that genomic diversity need not always be reflected phenotypically, in contrast to the suggested situation in vertebrates. This study provides evidence of ancient WGD in the ecdysozoan lineage, and reveals new opportunities for studying genomic and regulatory evolution after WGD in the Metazoa.
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