Countermeasures and Prevention of Railway Traffic Accidents in the Early Days of the Founding of the People’s Republic of China

In the early days of the founding of the People’s Republic of China,in order to restore the national economy as soon as possible,the Communist Party of China carried out maintenance and repairs on the railways that caused serious damage to transportation tasks through war-torn smoke,and carried out large-scale railway construction.However,in the course of operation,railway safety accidents occur frequently due to outdated equipment,low quality of staff,lack of rules and regulations,vandalism,and various natural disasters.In the face of severe conditions,the railway authorities summed up the accidents and learned the safety of the railways,so that the railway transportation industry,which started after the founding of the country,was gradually on the right track,and laid a solid foundation for the safe development of the railway industry.

Nickel-Catalyzed Regioselective Hydrosilylation of Conjugated Dienes

With the increasing demand for homoallylic silanes and allylic silanes,the highly efficient and regioselective hydrosilylations of conjugated dienes are urgently needed.Herein,we developed a Ni-catalyzed regiodivergent hydrosilylation of aromatic conjugated dienes by adjusting the temperature and ligands.Under low temperature(-30℃),an eternal-ligand-free system(Ni/t-BuOk)can efficiently facilitate the 3,4-anti-Markovnikov hydrosilylation to provide homoallylic silanes via electrophilic activation process;under room temperature(25℃),a ligand-controlled system(Ni/t-BuOk/PPh3)can eventuate the 3,4-Markovnikov hydrosilylation to produce allylic silanes via Chalk-Harrod process.Both systems are compatible with various conjugated dienes and primary silanes in excellent yields andregioselectivities.

Calibration and experimental verification of discrete element parameters of Panax notoginseng root

Existing discrete element method-based simulation analysis of Panax notoginseng root soil separation still has the challenge to get the accurate and reliable basic parameters,which are necessary for discrete element simulation.In this paper,the P.notoginseng roots suitable for harvesting period were taken as the experimental object.Then using 3D scanning reverse modeling technology and EDEM software to establish the discrete element model of P.notoginseng,based on which,the physical and virtual tests were carried out to calibrate the simulation parameters.First,the basic physical parameters(density,triaxial geometric size,moisture content,shear modulus,and elastic modulus)and contact coefficients(static friction coefficient,rolling friction coefficient,and crash recovery coefficient between P.notoginseng roots and 65Mn steel)were measured by physical tests.Furthermore,treating the contact coefficients of P.notoginseng roots as the influence factor,the steepest uphill test,and four factors combing five levels of rotational virtual simulation are conducted.The measured relative error accumulation angle and simulation accumulation angle are set as the performance indices.The results show that the static friction coefficient,rolling friction coefficient,crash recovery coefficient,and surface energy coefficient of P.notoginseng roots are 0.55,0.35,0.16,and 19.5 J/m2,respectively.Using calibration results as parameters of the vibration separation simulation test of P.notoginseng soil,the Box-Behnken vibration separation simulation tests were carried out,in which the vibration frequency,inclination angle,and vibration amplitude of separation device as factors,screening rate and damage rate of P.notoginseng soil complex are regarded as indices.The results show that the optimal operating parameters of the separation device are the vibration frequency of 10 Hz,the inclination angle of 5°,and the amplitude of 6 cm.Based on the optimal operation parameters,the discrete element simulation experiment and field experiment of P.notoginseng roots soil separation are also performed to compare the soil three-dimensional trajectory space coordinates of P.notoginseng roots.From the results,three axis coordinate error is less than 15%.This proves that the calibration results are reliable.It can also provide the theoretical basis and technical support for the further study of the P.notoginseng root soil separation platform.

脱烯丙基反应研究进展

烯丙基是有机合成中常用的保护基团,具有引入简单,在酸/碱性及还原剂等条件下稳定,在相对温和的条件下选择性地脱保护等特点,在有机合成特别是药物和天然产物的合成研究中具有重要地位.近几十年来,研究者们对各类烯丙基的脱保护方法进行了广泛研究.按碱及还原剂促进、氧化及自由基过程、路易斯酸促进、碘促进、过渡金属催化及电化学方法等分类,对脱烯丙基保护方法的研究进展进行了综述.