Train-induced aerodynamic characteristics of vertical sound barriers influenced by several factors

Investigations into the aerodynamic properties of vertical sound barriers exposed to high-speed operations employ computational fluid dynamics.The primary focus of this research is to evaluate the influence of train speed and the distance(D)from the track centerline under various operating conditions.The findings elucidate a marked elevation in the aerodynamic effect amplitude on sound barriers as train speeds increase.In single-train passages,the aerodynamic effect amplitude manifests a direct relationship with the square of the train speed.When two trains pass each other,the aerodynamic amplitude intensifies due to an additional aerodynamic increment on the sound barrier.This increment exhibits an approximate quadratic correlation with the retrograde train speed.Notably,the impact of high-speed trains on sound barrier aerodynamics surpasses that of low-speed trains,and this discrepancy amplifies with larger speed differentials between trains.Moreover,the train-induced aerodynamic effect diminishes significantly with greater distance(D),with occurrences of pressure coefficient(CP)exceeding the standard thresholds during dual-train passages.This study culminates in the formulation of universal equations for quantifying the influence of train speed and distance(D)on sound barrier aerodynamic characteristics across various operational scenarios.

Aerodynamic characteristics of a high-speed train crossing the wake of a bridge tower from moving model experiments

In a strong crosswind,the wake of a bridge tower will lead to an abrupt change of the aerodynamic forces acting on a vehicle passing through it,which may result in problems related to the transportation safety.This study investigates the transient aerodynamic characteristics of a high-speed train moving in a truss girder bridge and passing by a bridge tower in a wind tunnel.The scaled ratio of the train,bridge,and tower are 1:30.Effects of various parameters such as the incoming wind speed,train speed,and yaw angle on the aerodynamic performance of the train were considered.Then the sudden change mechanism of aerodynamic loads on the train when it crosses over the tower was further discussed.The results show that the bridge tower has an apparent shielding effect on the train passing through it,with the influencing width being larger than the width of the tower.The train speed is the main factor affecting the influencing width of aerodynamic coefficients,and the mutation amplitude is mainly related to the yaw angle obtained by changing the incoming wind speed or train speed.The vehicle movement introduces an asymmetry of loading on the train in the process of approaching and leaving the wake of the bridge tower,which should not be neglected.

Wind tunnel measurement of aerodynamic characteristics of trains passing each other on a simply supported box girder bridge

The aerodynamic performance of high-speed trains passing each other was investigated on a simply supported box girder bridge,with a span of 32 m,under crosswinds.The bridge and train models,modeled at a geometric scale ratio of 1:30,were used to test the aerodynamic forces of the train,with the help of a designed moving test rig in the XNJD-3 wind tunnel.The effects of wind speed,train speed,and yaw angle on the aerodynamic coefficients of the train were analyzed.The static and moving model tests were compared to demonstrate how the movement of the train influences its aerodynamic characteristics.The results show that the sheltering effect introduced by trains passing each other can cause a sudden change in force on the leeward train,which is further influenced by the wind and running speeds.Detailed analyses related to the effect of wind and train speeds on the aerodynamic coefficients were conducted.The relationship between the change in aerodynamic coefficients and yaw angle was finally described by a series of proposed fitting formulas.

Review of recent progress in studies on noise emanating from rail transit bridges

In recent years, there has been rapid growth of Chinese rail transit networks. Many of these networks require elevated bridges. This results in a bridge-borne noise source, which occurs in addition to the main noise source （i.e., wheel-rail interactions）. Bridge-borne noise is attracting increasing attention because of its low-frequency noise characteristics. This review paper first analyzes the space distribution, spectral characteristics, and sound pressure levels of noise radiated by all-concrete, steel- concrete composite, and all-steel bridges, mainly according to experimental studies. Second, this paper reviews exist- ing theoretical prediction models of noise emanating from bridges： the semianalytical method, the Rayleigh integral method, the boundary element method, and statistical energy analysis. Several case studies are reviewed, and their results are discussed. Finally, according to the results of the current review, the main factors affecting bridgeborne noise are analyzed, several noise reduction measures are proposed for different types of bridges, and their effectiveness is demonstrated.

Construction of coxsackievirus B5 viruses with luciferase reporters and their applications in vitro and in vivo

Coxsackievirus belongs to the Picornaviridae family and is one of the major pathogens that cause hand,foot and mouth disease(HFMD)in infants and children with potential serious complications and even deaths.The pathogenesis of this virus is not fully elucidated and no vaccine or antiviral drug has been approved.In this study,a full-length infectious cDNA clone of coxsackievirus B5 virus was assembled and the recombinant virus displayed similar growth kinetics and ability to cause cytopathic effects as the parental virus.Luciferase reporter was then incorporated to generate both full-length and subgenomic replicon(SGR)reporter viruses.The full-length reporter virus is suitable for high-throughput antiviral screening,while the SGR is a useful tool to study viral-host interactions.More importantly,the full-length reporter virus has also been shown to infect the suckling mouse model and the reporter gene could be detected using an in vivo imaging system,thus providing a powerful tool to track viruses in vivo.In summary,we have generated coxsackievirus B5 reporter viruses and provided unique tools for studying virus-host interactions in vitro and in vivo as well as for high-throughput screenings(HTS)to identify novel antivirals.

Variability in pattern and hydrogen isotope composition(δ^(2)H)of long-chain n-alkanes of surface soils and its relations to climate and vegetation characteristics:A meta-analysis

The average chain length(ACL),carbon preference index(CPI),and hydrogen isotope composition(δ^(2)H)of long-chain n-alkanes in sediments have been used to retrieve information about the paleoclimate.Despite their importance as in-between media from leaves to sediments,n-alkanes of surface soils have not been systematically analyzed at large scale.Such an investigation of the spatial variation of n-alkane properties in soil and their dependence on climatic and botanic(e.g.,vegetation type)factors could provide a rationale for a better estimation of the past environment.We synthesized the patterns andδ^(2)H of long-chain n-alkanes in soil(δ^(2)H_(n-alkanes))with regard to vegetation types(cropland,grassland,shrubland,and woodland)and environmental factors using data from peer-reviewed papers.Our results showed that the ACL and CPI of soil C_(27)–C_(33) n-alkanes were not suitable indicators for differentiating vegetation types at large scale;instead,ACL significantly correlated with water conditions such as mean annual precipitation(MAP)and Palmer drought severity index(PDSI),and CPI significantly correlated with temperature without significant influence of vegetation type.The variation(i.e.,standard deviation)of fractionation between theδ^(2)H values in annual precipitation and in soil n-alkanes(ε_(rain-soil))was smaller than that reported in leaves;therefore,soils were better suited to quantifying the general growing conditions of plants at a certain site.The fractionationε_(rain-soil)correlated with climatic conditions as described by the PDSI and relative humidity(RH).This correlation agreed with the change in leaf water enrichment with changing RH taken from the literature and was independent of the vegetation type at large scale.This meta-analysis may provide useful information for the variations of the patterns andδ^(2)H_(n-alkanes) values in surface soils.

Confocal visible/NIR photoacoustic microscopy of tumors with structural, functional, and nanoprobe contrasts

Distinguishing early-stage tumors from normal tissues is of great importance in cancer diagnosis.We report fiberbased confocal visible/near-infrared(NIR)optical-resolution photoacoustic microscopy that can image tumor microvasculature,oxygen saturation,and nanoprobes in a single scanning.We develop a cost-efficient single laser source that provides 532,558,and 1064 nm pulsed light with sub-microseconds wavelength switching time.Via dual-fiber illumination,we can focus the three beams to the same point.The optical and acoustic foci are confocally aligned to optimize the sensitivity.The visible and NIR wavelengths enable simultaneous tumor imaging with three different contrast modes.Results show obvious angiogenesis,significantly elevated oxygen saturation,and accumulated nanoparticles in the tumor regions,which offer comprehensive information to detect the tumor.This approach also allows us to identify feeding and draining vessels of the tumor and thus to determine local oxygen extraction fraction.In the tumor region,the oxygen extraction fraction significantly decreases along with tumor growth,which can also assist in tumor detection and staging.Fiber-based confocal visible/NIR photoacoustic microscopy offers a new tool for early detection of cancer.

Porcine circovirus type 2(PCV2)and Campylobacter infection induce diarrhea in piglets:Microbial dysbiosis and intestinal disorder

Diarrhea is considered to be associated with microbial dysbiosis caused by infection of pathogens but poorly understood.We herein characterized the colonic microbiota of diarrheal early-weaning piglets infected with porcine circovirus type 2(PCV2)and Campylobacter.Campylobacter infection significantly decreased species richness and Shannon diversity index of colonic microbiota together with a significant increase in the proportion of Campylobacter and Enterobacteriaceae,whereas no significant difference on the above indexes was observed in piglets infected with PCV2 compared with healthy piglets,PCV2 and Campylobacter infection could disturb the homeostasis of colonic microbiota through deterioration of ecological network within microbial community,and specially Campylobacter performed as a module hub in ecological networks.The microbial dysbiosis caused metabolic dysfunction and led to a remarkable reduction in production of short chain fatty acids,following by a higher pH level in colon cavity.Campylobacter infection disturbed the function of colonic tract barrier observed in terms of significant lower relative expression of claudin-1,occluding,and zonula occludens protein-1 genes,and PCV2 infection induced intestinal inflammation together with a higher permeability of colon.Generally,these results suggested that PCV2 and Campylobacter infection could induce microbial dysbiosis and metabolic dysfunction,and cause intestinal disorder,all of which finally were associated to contribute to the diarrhea of early-weaning piglets.