Predicting the precise impacts of climate change on extreme winds remains challenging,yet strong storms are widely expected to occur more frequently in a warming climate.Wind barriers are commonly used on bridges to r...Predicting the precise impacts of climate change on extreme winds remains challenging,yet strong storms are widely expected to occur more frequently in a warming climate.Wind barriers are commonly used on bridges to reduce aerodynamic loads on trains through blocking effects.This study develops a novel wind barrier based on Tesla valves,which not only blocks incoming flow but also dissipates mechanical energy through fluid collision.To demonstrate this energy-dissipation capability,a Tesla plate is placed in a circular duct to examine its influence on pressure drop.Experimental tests and numerical simulations comparing a Tesla channel and a straight channel of equal porosity show that the Tesla configuration produces a substantially higher pressure drop.Validated simulations are then used to conduct a parametric study to optimize the design.By varying the channel ratio,diversion angle,number of dissipation units,and porosity,velocity–pressure-drop relationships for different Tesla plates are obtained.The results show that larger channel ratios,larger diversion angles,and more dissipation units,combined with lower porosity,all increase pressure drop and thus enhance energy dissipation.Finally,the aerodynamic coefficients of a high-speed train on a bridge deck equipped with a Tesla-type barrier are evaluated and compared with those for a traditional straight-channel barrier.The Tesla-type barrier reduces the train’s lateral force coefficient to only 15%–25%of that produced by the traditional barrier,and it generates an additional stabilizing force that further improves running safety.展开更多
Background and purpose The low-field MRI is a promising tool to accurately diagnose strokes.We here report our study on the accuracy of a 0.23-Tesla(0.23-T)MRI using the haematoma enhanced inversion recovery(HEIR)sequ...Background and purpose The low-field MRI is a promising tool to accurately diagnose strokes.We here report our study on the accuracy of a 0.23-Tesla(0.23-T)MRI using the haematoma enhanced inversion recovery(HEIR)sequence to detect acute ischaemic stroke(AIS)and intracerebral haemorrhage(ICH)within 24 hours of symptom onset.Methods A novel HEIR sequence based on fluid-attenuated inversion recovery T1-weighted,with a scanning time of 1 min and 17 s,was developed using an ICH and AIS pig model on a 0.23-T MRI.Images of the pig model were obtained hourly for 24 hours in order to monitor value changes on T1/T2 and verify the differential diagnosis of AIS and ICH.Then,30 patients with AIS and 30 patients with ICH with confirmed diagnoses by 3T-MRI/CT were included.Diagnostic criteria on a 0.23-T MRI for ICH was the hyperintensity signal on both the diffusion-weighted imaging(DWI)and HEIR sequence,while for AIS was the hyperintensity on DWI and isointensity on the HEIR sequence.Two blinded raters independently assessed the images obtained by the 0.23-T MRI for the presence of ICH/AIS.Results In the pig model,setting the inversion time to 800 ms enabled clear differentiation of ICH from brain parenchymal tissue and AIS.In real patients,a correct 0.23-T MRI diagnosis of either an AIS or ICH was made in all 60 patients within 24 hours of symptom onset(100%overall accuracy).No adverse events occurred.Conclusions The 0.23-T MRI may have the potential to differentiate cerebral haemorrhage from cerebral infarction with both speed and accuracy,making brain MRI scans easier,faster and cheaper.It might be possible to improve the screening imaging process for strokes in the emergency room.Further multicentre studies are needed to validate our findings.展开更多
基金supported by the National Natural Science Foundation of China(52475105)Special Fund for Science and Technology Innovation of Jiangsu Province(BE2022610)National Natural Science Foundation of China(U23A20661).
文摘Predicting the precise impacts of climate change on extreme winds remains challenging,yet strong storms are widely expected to occur more frequently in a warming climate.Wind barriers are commonly used on bridges to reduce aerodynamic loads on trains through blocking effects.This study develops a novel wind barrier based on Tesla valves,which not only blocks incoming flow but also dissipates mechanical energy through fluid collision.To demonstrate this energy-dissipation capability,a Tesla plate is placed in a circular duct to examine its influence on pressure drop.Experimental tests and numerical simulations comparing a Tesla channel and a straight channel of equal porosity show that the Tesla configuration produces a substantially higher pressure drop.Validated simulations are then used to conduct a parametric study to optimize the design.By varying the channel ratio,diversion angle,number of dissipation units,and porosity,velocity–pressure-drop relationships for different Tesla plates are obtained.The results show that larger channel ratios,larger diversion angles,and more dissipation units,combined with lower porosity,all increase pressure drop and thus enhance energy dissipation.Finally,the aerodynamic coefficients of a high-speed train on a bridge deck equipped with a Tesla-type barrier are evaluated and compared with those for a traditional straight-channel barrier.The Tesla-type barrier reduces the train’s lateral force coefficient to only 15%–25%of that produced by the traditional barrier,and it generates an additional stabilizing force that further improves running safety.
基金National Natural Science Foundation of China(grant no.82271329grant no.82471356).
文摘Background and purpose The low-field MRI is a promising tool to accurately diagnose strokes.We here report our study on the accuracy of a 0.23-Tesla(0.23-T)MRI using the haematoma enhanced inversion recovery(HEIR)sequence to detect acute ischaemic stroke(AIS)and intracerebral haemorrhage(ICH)within 24 hours of symptom onset.Methods A novel HEIR sequence based on fluid-attenuated inversion recovery T1-weighted,with a scanning time of 1 min and 17 s,was developed using an ICH and AIS pig model on a 0.23-T MRI.Images of the pig model were obtained hourly for 24 hours in order to monitor value changes on T1/T2 and verify the differential diagnosis of AIS and ICH.Then,30 patients with AIS and 30 patients with ICH with confirmed diagnoses by 3T-MRI/CT were included.Diagnostic criteria on a 0.23-T MRI for ICH was the hyperintensity signal on both the diffusion-weighted imaging(DWI)and HEIR sequence,while for AIS was the hyperintensity on DWI and isointensity on the HEIR sequence.Two blinded raters independently assessed the images obtained by the 0.23-T MRI for the presence of ICH/AIS.Results In the pig model,setting the inversion time to 800 ms enabled clear differentiation of ICH from brain parenchymal tissue and AIS.In real patients,a correct 0.23-T MRI diagnosis of either an AIS or ICH was made in all 60 patients within 24 hours of symptom onset(100%overall accuracy).No adverse events occurred.Conclusions The 0.23-T MRI may have the potential to differentiate cerebral haemorrhage from cerebral infarction with both speed and accuracy,making brain MRI scans easier,faster and cheaper.It might be possible to improve the screening imaging process for strokes in the emergency room.Further multicentre studies are needed to validate our findings.
