Experimental investigation on dynamic behaviour of heavy-haul railway track induced by heavy axle load

The damage to the track structure and the influence to the line deformation have greatly deteriorated with the increase of the axle load compared with that of the ordinary trains. However, there is a paucity of experimental research on the dynamic influence of the heavier haul freight trains on the railway tracks. The objective of this study is to investigate the dynamic behaviour of heavy-haul railway track induced by heavy axle load by field experimental tests. The wheel–rail dynamic force, the track structure dynamic deformation and the track vibration behaviour are measured and analysed when the train operates in the speed range from 10 to 75 km/h and the axle load of vehicles varies from 21 to 30 t. Comparisons between the results for the axle conditions of 25 and 30 t are made in this paper to reveal the axle load effects. It is demonstrated that part of the indicators reflecting the dynamic behaviour of the railway track increases approximately linearly with the train running speed and axle load, while others are influenced negligibly

Comparison of staged-stent and stent-assisted coiling technique for ruptured saccular wide-necked intracranial aneurysms: Safety and efficacy based on a propensity score-matched cohort study

BackgroundApplication of stent-assisted coiling and FD in acute phase of ruptured wide-necked aneurysms is relatively contraindicated due to the potential risk of ischemic and hemorrhagic complications. Scheduled stenting after initial coiling has emerged as an alternative paradigm for ruptured wide-necked aneurysms. The objective of this study is to evaluate the safety and efficacy of a strategy of staged stent-assisted coiling in acutely ruptured saccular wide-necked intracranial aneurysms compared with conventional early stent-assisted coiling strategy via propensity score matching in a high-volume center.MethodsA retrospective review of patients with acutely ruptured saccular wide-necked intracranial aneurysms who underwent staged stent-assisted coiling or conventional stent-assisted coiling from November 2014 to November 2019 was performed. Perioperative procedure-related complications and clinical and angiographic follow-up outcomes were compared.ResultsA total of 69 patients with staged stent-assisted coiling and 138 patients with conventional stent-assisted coiling were enrolled after 1:2 propensity score matching. The median interval time between previous coiling and later stenting was 4.0 weeks (range 3.5–7.5 weeks). No rebleeding occurred during the intervals. The rate of immediate complete occlusion was lower with initial coiling before scheduled stenting than with conventional stent-assisted coiling (21.7 vs. 60.9%), whereas comparable results were observed at follow-up (82.5 vs. 72.9%; p = 0.357). The clinical follow-up outcomes, overall procedure-related complications and procedure-related mortality between the two groups demonstrated no significant differences (P = 0.232, P = 0.089, P = 0.537, respectively). Multivariate analysis showed that modified Fisher grades (OR = 2.120, P = 0.041) were independent predictors for overall procedure-related complications and no significant predictors for hemorrhagic and ischemic complications.ConclusionsStaged stent-assisted coiling is a safe and effective treatment strategy for acutely ruptured saccular wide-necked intracranial aneurysms, with comparable complete occlusion rates, recurrence rates at follow-up and overall procedure-related complication rates compared with conventional stent-assisted coiling strategy. Staged stent-assisted coiling could be an alternative treatment option for selected ruptured intracranial aneurysms in the future

Cycloaddition de Diels-Alder à demande inverse en électron asymétrique entre une 2-pyrone et un éther d'énol acyclique et synthèse totale de la (+)-lucidumone à l'échelle du gramme

Les cycloadditions de Diels-Alder à demande inverse en électron impliquant des 2-pyrones appauvries en électrons en tant que diène électrophile on fait l'objet de nombreuses études au cours des 50 dernières années. Cette réaction offre une voie d'accès efficace à des lactones bicycliques pontées et leurs dérivés, tels que des 1,3-cyclohexadiènes hautement fonctionnalisés après extrusion de CO₂ est des composés aromatiques polysubstitués après élimination. Ainsi, les Diels-Alder à demande inverse ont été utilisées pour la synthèse de nombreuses molécules bioactives et/ou naturelles ainsi que des candidats médicaments. Cette thèse s'intéresse à la Diels-Alder à demande inverse en électrons entre une 2-pyrone appauvrie en électrons et un éther d'énol acyclique. En utilisant un système catalytique comportant un complexe Cu(II)-BOX, de nombreuses lactones bicycliques sont obtenues avec d'excellents rendements (jusqu'à 99%) et énantiosélectivités (jusqu'à 99% d'excès). Une étude mécanistique ainsi que des calculs de DFT indiquent que le mécanisme à lieu en deux étapes. Le potentiel synthétique des lactones bicycliques est mis en évidence par la synthèse totale à l'échelle du gramme de la (+)-lucidumone. Les étapes clés comportent la formation d'une lactone bicyclique pontée par la cycloaddition énantiosélective susmentionnée, formation d'une liaison C-O pour assembler deux fragments dans des conditions de Mitsunobu, et une cascade d'extrusion de CO₂ / cycloaddition [4+2] intramoléculaire.The inverse-electron-demand Diels-Alder (IEDDA) cycloaddition of electron-poor 2-pyrones as electrophilic dienes has been extensively studied in the past fifty years. The reaction provides an efficient access to bridged bicyclic lactones and their derivatives, such as densely functionalized 1,3-cyclohexadienes after CO₂ extrusion and polysubstituted aromatic compounds through elimination. Thus, the IEDDA cycloaddition has been used for the synthesis of many biologically active natural products and drug candidates. This thesis focused on the inverse-electron-demand Diels-Alder reaction of electron-poor 2-pyrones and its appliactions in total synthesis. We developed a broadly applicable diastereo- and enantioselective inverse-electron-demand Diels-Alder reaction of 2-pyrones and acyclic enol ethers. Using a copper(II)-BOX catalytic system, numerous bridged bicyclic lactones were obtained in very high yields (up to 99% yield) and enantioselectivities (up to 99% ee). Mechanistic experiments as well as DFT calculations indicate the occurrence of a stepwise mechanism. To showcase the synthetic utility of this methodology, we developed a gram-scale total synthesis of (+)-Lucidumone. The features of the total synthesis involve the formation of a bridged bicyclic lactone by the IEDDA cycloaddition, C-O bond formation under Mitsunobu conditions and a one-pot CO₂ extrusion/intramolecular Diels-Alder cycloaddition cascade

Cycloaddition de Diels-Alder à demande inverse en électron asymétrique entre une 2-pyrone et un éther d'énol acyclique et synthèse totale de la (+)-lucidumone à l'échelle du gramme

The inverse-electron-demand Diels-Alder (IEDDA) cycloaddition of electron-poor 2-pyrones as electrophilic dienes has been extensively studied in the past fifty years. The reaction provides an efficient access to bridged bicyclic lactones and their derivatives, such as densely functionalized 1,3-cyclohexadienes after CO₂ extrusion and polysubstituted aromatic compounds through elimination. Thus, the IEDDA cycloaddition has been used for the synthesis of many biologically active natural products and drug candidates. This thesis focused on the inverse-electron-demand Diels-Alder reaction of electron-poor 2-pyrones and its appliactions in total synthesis. We developed a broadly applicable diastereo- and enantioselective inverse-electron-demand Diels-Alder reaction of 2-pyrones and acyclic enol ethers. Using a copper(II)-BOX catalytic system, numerous bridged bicyclic lactones were obtained in very high yields (up to 99% yield) and enantioselectivities (up to 99% ee). Mechanistic experiments as well as DFT calculations indicate the occurrence of a stepwise mechanism. To showcase the synthetic utility of this methodology, we developed a gram-scale total synthesis of (+)-Lucidumone. The features of the total synthesis involve the formation of a bridged bicyclic lactone by the IEDDA cycloaddition, C-O bond formation under Mitsunobu conditions and a one-pot CO₂ extrusion/intramolecular Diels-Alder cycloaddition cascade.Les cycloadditions de Diels-Alder à demande inverse en électron impliquant des 2-pyrones appauvries en électrons en tant que diène électrophile on fait l'objet de nombreuses études au cours des 50 dernières années. Cette réaction offre une voie d'accès efficace à des lactones bicycliques pontées et leurs dérivés, tels que des 1,3-cyclohexadiènes hautement fonctionnalisés après extrusion de CO₂ est des composés aromatiques polysubstitués après élimination. Ainsi, les Diels-Alder à demande inverse ont été utilisées pour la synthèse de nombreuses molécules bioactives et/ou naturelles ainsi que des candidats médicaments. Cette thèse s'intéresse à la Diels-Alder à demande inverse en électrons entre une 2-pyrone appauvrie en électrons et un éther d'énol acyclique. En utilisant un système catalytique comportant un complexe Cu(II)-BOX, de nombreuses lactones bicycliques sont obtenues avec d'excellents rendements (jusqu'à 99%) et énantiosélectivités (jusqu'à 99% d'excès). Une étude mécanistique ainsi que des calculs de DFT indiquent que le mécanisme à lieu en deux étapes. Le potentiel synthétique des lactones bicycliques est mis en évidence par la synthèse totale à l'échelle du gramme de la (+)-lucidumone. Les étapes clés comportent la formation d'une lactone bicyclique pontée par la cycloaddition énantiosélective susmentionnée, formation d'une liaison C-O pour assembler deux fragments dans des conditions de Mitsunobu, et une cascade d'extrusion de CO₂ / cycloaddition [4+2] intramoléculaire