Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks,provide safe and smooth rides,and reduce the maintenance frequency.In this paper,the elastic performance of a ...Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks,provide safe and smooth rides,and reduce the maintenance frequency.In this paper,the elastic performance of a novel slab trackform for high-speed railways is investigated using three-dimensional finite element modelling in Abaqus.It is then compared to the performance of a ballasted track.First,slab and ballasted track models are developed to replicate the full-scale testing of track sections.Once the models are calibrated with the experimental results,the novel slab model is developed and compared against the calibrated slab track results.The slab and ballasted track models are then extended to create linear dynamic models,considering the track geodynamics,and simulating train passages at various speeds,for which the Ledsgard documented case was used to validate the models.Trains travelling at low and high speeds are analysed to investigate the track deflections and the wave propagation in the soil,considering the issues associated with critical speeds.Various train loading methods are discussed,and the most practical approach is retained and described.Moreover,correlations are made between the geotechnical parameters of modern high-speed rail and conventional standards.It is found that considering the same ground condition,the slab track deflections are considerably smaller than those of the ballasted track at high speeds,while they show similar behaviour at low speeds.展开更多
Compacted granular material,integral to geotechnical engineering,undergoes translation,rotation,and interlocking when subject to shear displacements or external loads.The present study focuses on the interlocking of h...Compacted granular material,integral to geotechnical engineering,undergoes translation,rotation,and interlocking when subject to shear displacements or external loads.The present study focuses on the interlocking of heterogeneous granular materials,a complex behavior influenced by gradation,compaction,and varying particle geometry,and has consequently received limited attention in existing research.To address this research gap,we conducted an analysis on the effect of grain interlocking on the shear resistance of granular assemblies,using a combination of laboratory testing and the discrete element method(DEM).Initially,large-scale direct shear tests were conducted on gravel−sand mixes with varying degrees of compaction and normal pressure.One of the mixes also underwent subsequent shear reversal to explore the differences in grain interlocking between the two shearing processes on the shear plane.After analyzing the laboratory results,a mesoscopic scale investigation was performed by replicating the test using discrete element simulations.To facilitate this,granular particle geometries were measured using 3D laser scanning based on the physical lab tests.Subsequently,based on these scans,discrete element R-block and ball models were utilized to construct both the coarse and fine particles within the mix.Surface vibro-compaction was employed to regulate the degree of compaction.The results indicate that an increase in vertical pressure,coupled with a zero dilatancy angle,results in a rising stress ratio,indicative of grain interlocking.This interlocking exhibits a positive correlation with both the coarse content and the degree of compaction,and varies depending on the shear displacement.As interlocking progresses,the shear band,induced by particle movement,expands and is associated with reduced particle rotation near the shear band.The study further reveals a consistent positive correlation between interlocking and the principal orientation angle of strong normal contact forces,as well as a correlation between展开更多
Resonance effects in parallel jointed rocks subject to stress waves are investigated using transfer functions,derived from signals generated through numerical modelling.Resonance is important for a range of engineerin...Resonance effects in parallel jointed rocks subject to stress waves are investigated using transfer functions,derived from signals generated through numerical modelling.Resonance is important for a range of engineering situations as it identifies the frequency of waves which will be favourably transmitted.Two different numerical methods are used for this study,adopting the finite difference method and the combined discrete element-finite difference method.The numerical models are validated by replicating results from previous studies.The two methods are found to behave similarly and show the same resonance effects;one operating at low frequency and the other operating at relatively high frequency.These resonance effects are interpreted in terms of simple physical systems and analytical equations are derived to predict the resonant frequencies of complex rock masses.Low frequency resonance is shown to be generated by a system synonymous with masses between springs,described as spring resonance,with an equal number of resonant frequencies as the number of blocks.High frequency resonance is generated through superposition of multiple reflected waves developing standing waves within intact blocks,described as superposition resonance.While resonance through superposition has previously been identified,resonance based on masses between springs has not been previously identified in jointed rocks.The findings of this study have implications for future analysis of multiple jointed rock masses,showing that a wave travelling through such materials can induce other modes of propagation of waves,i.e.spring resonance.展开更多
Walking is the most commonly chosen type of physical activity(PA)during pregnancy and provides several health benefits to both mother and child.National initiatives have promoted the importance of walking in general,b...Walking is the most commonly chosen type of physical activity(PA)during pregnancy and provides several health benefits to both mother and child.National initiatives have promoted the importance of walking in general,but little emphasis is directed toward pregnant women,the majority of whom are insufficiently active.Pregnant women face a variety of dynamic barriers to a physically active lifestyle,some of which are more commonly experienced during specific times throughout the pregnancy experience.Walking is unique in that it appears resistant to a number of these barriers that limit other types of PA participation,and it can be meaningfully integrated into some transportation and occupational activities when leisure-time options are unavailable.Preliminary intervention work suggests that walking programs can be effectively adopted into a typical pregnancy lifestyle.However,a great deal of work remains to administer successful pregnancy walking interventions,including developing and using validated methods of PA and walking assessment.This narrative review discusses the unique advantages of walking during pregnancy,provides recommendations for future intervention work,and outlines the need for pregnancy-focused community walking initiatives.Standard search procedures were followed to determine sources from the literature specific to walking during pregnancy for use in each section of this review.展开更多
The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck.Silicon/perovskite tandem solar cells are a solution,which is attracting much atte...The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck.Silicon/perovskite tandem solar cells are a solution,which is attracting much attention.While silicon/perovskite tandem cells in 2-terminal and 4-terminal configurations are well documented,the three-terminal concept is still in its infancy.It has significant advantages under low light intensities as opposed to concentrated sunlight,which is the critical factor in designing tandem solar cells for low-cost terrestrial applications.This study pre-sents novel studies of the sub-cell performance of the first three-terminal perovskite/silicon selective band offset barrier tandem solar cells fabricated in an ongoing research project.This study focuses on short circuit current and operating voltages of the subcells under light intensities of one sun and below.Lifetime studies show that the perovskite bulk carrier lifetime is insensitive to illumination,while the silicon cell's lifetime decreases with decreasing light intensity.The combination of perovskite and silicon in the 3T perovskite-silicon tandem therefore reduces the sensitivity of V_(OC) to light intensity and maintains a relatively higher V_(OC) down to low light intensities,whereas silicon single-junction cells show a marked decrease.This technological advantage is proposed as a novel advantage of three-terminal perovkite/silicon solar cells for low light intensities of one sun or less.展开更多
Chemical reactions in homogenous systems are generally associated with positive-order kinetics;that is,the reaction rate increases with the increased concentration of reactants.In this work,we report a coordination re...Chemical reactions in homogenous systems are generally associated with positive-order kinetics;that is,the reaction rate increases with the increased concentration of reactants.In this work,we report a coordination reaction of Cu^(2+)ions,cyanuric acid(CA),and pyridine in aqueous solution which shows negative-order kinetics with respect to the concentration of pyridine.As the pyridine concentration increases,the complexation of CA with pyridine overwhelms its dissociation in water,resulting in the redistribution of CA;that is,CA is sealed in the pyridine phase by forming an unreactive hydrogenbonded complex.As a result,the number of accessible anionic CA for crystallization in water decreases,and thus the crystallization slows down and almost terminates.Further,the crystallization yields two types of crystals with similar structures but disparate colors(red and blue),and the origin is investigated by the ligand field analysis.展开更多
基金Engineering and Physical Sciences Research Council (EPSRC) is also acknowledged for funding this work under Grant Number EP/N009207/1.
文摘Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks,provide safe and smooth rides,and reduce the maintenance frequency.In this paper,the elastic performance of a novel slab trackform for high-speed railways is investigated using three-dimensional finite element modelling in Abaqus.It is then compared to the performance of a ballasted track.First,slab and ballasted track models are developed to replicate the full-scale testing of track sections.Once the models are calibrated with the experimental results,the novel slab model is developed and compared against the calibrated slab track results.The slab and ballasted track models are then extended to create linear dynamic models,considering the track geodynamics,and simulating train passages at various speeds,for which the Ledsgard documented case was used to validate the models.Trains travelling at low and high speeds are analysed to investigate the track deflections and the wave propagation in the soil,considering the issues associated with critical speeds.Various train loading methods are discussed,and the most practical approach is retained and described.Moreover,correlations are made between the geotechnical parameters of modern high-speed rail and conventional standards.It is found that considering the same ground condition,the slab track deflections are considerably smaller than those of the ballasted track at high speeds,while they show similar behaviour at low speeds.
基金the National Natural Science Foundation of China(grant No.52078435)the Natural Science Foundation of Sichuan Province(grant No.2023NSFSC0391)the 111 Project(grant No.B21011)and the Leverhulme Trust UK(grant No.PLP-2016-270).
文摘Compacted granular material,integral to geotechnical engineering,undergoes translation,rotation,and interlocking when subject to shear displacements or external loads.The present study focuses on the interlocking of heterogeneous granular materials,a complex behavior influenced by gradation,compaction,and varying particle geometry,and has consequently received limited attention in existing research.To address this research gap,we conducted an analysis on the effect of grain interlocking on the shear resistance of granular assemblies,using a combination of laboratory testing and the discrete element method(DEM).Initially,large-scale direct shear tests were conducted on gravel−sand mixes with varying degrees of compaction and normal pressure.One of the mixes also underwent subsequent shear reversal to explore the differences in grain interlocking between the two shearing processes on the shear plane.After analyzing the laboratory results,a mesoscopic scale investigation was performed by replicating the test using discrete element simulations.To facilitate this,granular particle geometries were measured using 3D laser scanning based on the physical lab tests.Subsequently,based on these scans,discrete element R-block and ball models were utilized to construct both the coarse and fine particles within the mix.Surface vibro-compaction was employed to regulate the degree of compaction.The results indicate that an increase in vertical pressure,coupled with a zero dilatancy angle,results in a rising stress ratio,indicative of grain interlocking.This interlocking exhibits a positive correlation with both the coarse content and the degree of compaction,and varies depending on the shear displacement.As interlocking progresses,the shear band,induced by particle movement,expands and is associated with reduced particle rotation near the shear band.The study further reveals a consistent positive correlation between interlocking and the principal orientation angle of strong normal contact forces,as well as a correlation between
基金supported by the Engineering and Physical Sciences Research Council(EPSRC)(EP/R513258/1).
文摘Resonance effects in parallel jointed rocks subject to stress waves are investigated using transfer functions,derived from signals generated through numerical modelling.Resonance is important for a range of engineering situations as it identifies the frequency of waves which will be favourably transmitted.Two different numerical methods are used for this study,adopting the finite difference method and the combined discrete element-finite difference method.The numerical models are validated by replicating results from previous studies.The two methods are found to behave similarly and show the same resonance effects;one operating at low frequency and the other operating at relatively high frequency.These resonance effects are interpreted in terms of simple physical systems and analytical equations are derived to predict the resonant frequencies of complex rock masses.Low frequency resonance is shown to be generated by a system synonymous with masses between springs,described as spring resonance,with an equal number of resonant frequencies as the number of blocks.High frequency resonance is generated through superposition of multiple reflected waves developing standing waves within intact blocks,described as superposition resonance.While resonance through superposition has previously been identified,resonance based on masses between springs has not been previously identified in jointed rocks.The findings of this study have implications for future analysis of multiple jointed rock masses,showing that a wave travelling through such materials can induce other modes of propagation of waves,i.e.spring resonance.
文摘Walking is the most commonly chosen type of physical activity(PA)during pregnancy and provides several health benefits to both mother and child.National initiatives have promoted the importance of walking in general,but little emphasis is directed toward pregnant women,the majority of whom are insufficiently active.Pregnant women face a variety of dynamic barriers to a physically active lifestyle,some of which are more commonly experienced during specific times throughout the pregnancy experience.Walking is unique in that it appears resistant to a number of these barriers that limit other types of PA participation,and it can be meaningfully integrated into some transportation and occupational activities when leisure-time options are unavailable.Preliminary intervention work suggests that walking programs can be effectively adopted into a typical pregnancy lifestyle.However,a great deal of work remains to administer successful pregnancy walking interventions,including developing and using validated methods of PA and walking assessment.This narrative review discusses the unique advantages of walking during pregnancy,provides recommendations for future intervention work,and outlines the need for pregnancy-focused community walking initiatives.Standard search procedures were followed to determine sources from the literature specific to walking during pregnancy for use in each section of this review.
基金The authors acknowledge the support of the H2020 pro-gram for Solar-ERANET funding of the BOBTANDEM(2019-2022).
文摘The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck.Silicon/perovskite tandem solar cells are a solution,which is attracting much attention.While silicon/perovskite tandem cells in 2-terminal and 4-terminal configurations are well documented,the three-terminal concept is still in its infancy.It has significant advantages under low light intensities as opposed to concentrated sunlight,which is the critical factor in designing tandem solar cells for low-cost terrestrial applications.This study pre-sents novel studies of the sub-cell performance of the first three-terminal perovskite/silicon selective band offset barrier tandem solar cells fabricated in an ongoing research project.This study focuses on short circuit current and operating voltages of the subcells under light intensities of one sun and below.Lifetime studies show that the perovskite bulk carrier lifetime is insensitive to illumination,while the silicon cell's lifetime decreases with decreasing light intensity.The combination of perovskite and silicon in the 3T perovskite-silicon tandem therefore reduces the sensitivity of V_(OC) to light intensity and maintains a relatively higher V_(OC) down to low light intensities,whereas silicon single-junction cells show a marked decrease.This technological advantage is proposed as a novel advantage of three-terminal perovkite/silicon solar cells for low light intensities of one sun or less.
基金the financial support by the Australian Research Council(grant no.DP190101607).
文摘Chemical reactions in homogenous systems are generally associated with positive-order kinetics;that is,the reaction rate increases with the increased concentration of reactants.In this work,we report a coordination reaction of Cu^(2+)ions,cyanuric acid(CA),and pyridine in aqueous solution which shows negative-order kinetics with respect to the concentration of pyridine.As the pyridine concentration increases,the complexation of CA with pyridine overwhelms its dissociation in water,resulting in the redistribution of CA;that is,CA is sealed in the pyridine phase by forming an unreactive hydrogenbonded complex.As a result,the number of accessible anionic CA for crystallization in water decreases,and thus the crystallization slows down and almost terminates.Further,the crystallization yields two types of crystals with similar structures but disparate colors(red and blue),and the origin is investigated by the ligand field analysis.
