Developing the railway transport sector is a challenging scientific,economic and social research topic starting with ensuring human security.The main topic that should be developed in that sense is the ballast stabili...Developing the railway transport sector is a challenging scientific,economic and social research topic starting with ensuring human security.The main topic that should be developed in that sense is the ballast stability and dynamical behaviour under external loading and environmental changes.This paper investigates the effect of particle size distribution and normal pressure on the mechanical response of a ballast bed.Grading curves of ballast layers with different sizes are illustrated to discuss their strength behaviour under various strains to deduce the significant effect on the direct shear performance of the ballast layer.Direct shear tests with different Particle Size Distribution(PSD)were reproduced using the Discrete Element Method(DEM).It is noticed that when the number of small-sized ballast increases,the shear strength and the friction angle increase to varying degrees under different normal pressures,with an average increase of 27%and 8%,respectively.When the number of large-sized ballast decreases,the shear strength and the friction angle decrease to varying degrees under different normal pressures,with an average decrease of 6%and 3%,respectively.展开更多
Active sites of Fluid catalytic cracking (FCC) catalyst are poisoned during operation in the FCC reactor due to causes including feedstock contaminant metals deposition. This leads to activity, selectivity and increas...Active sites of Fluid catalytic cracking (FCC) catalyst are poisoned during operation in the FCC reactor due to causes including feedstock contaminant metals deposition. This leads to activity, selectivity and increasing coking problems, thereby raising concern to the refiner. This work investigated effect of nickel coexisting with vanadium in the FCC feedstock on the standard FCC catalyst during cracking process, in which destruction of active sites occurs as a result of the metals deposition. Laboratory simulated equilibrium catalysts (E-cats) were studied by XRD, FTIR spectroscopy, N-2 adsorption, solid state MAS-NMR, SEM and H-2-TPR. Results revealed that vanadium, above a certain concentration in the catalyst, under hydrothermal conditions, is highly detrimental to the catalyst's structure and activity. Conversely, nickel hardly affects the catalyst structure, but its co-presence in the catalyst reduces destructive effects of vanadium. The mechanism of nickel inhibition of vanadium poisoning of the catalyst is discussed. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.展开更多
Purpose Position-sensitive detectors play a crucial role in gamma-ray imaging systems.To enhance the detector’s inherent spatial resolution,one promising technique involves the phoswich design,which combines pixelate...Purpose Position-sensitive detectors play a crucial role in gamma-ray imaging systems.To enhance the detector’s inherent spatial resolution,one promising technique involves the phoswich design,which combines pixelated scintillators with different decay times.Method In a previous study,we constructed a phoswich detector comprising a side-by-side GAGG-F/GAGG-T scintillator array coupled to an 8×8 SiPM array.Traditionally,all pulses are distinguished using a parameter with a global cut value.However,due to the non-uniformity of the array,pulse shapes vary with the interaction position of the gamma-ray.In this paper,we propose a novel procedure for crystal discrimination.Initially,the crystal flood map with all events is roughly segmented.Subsequently,the crystal discrimination values of each zone are histogrammed to generate the cut value for each zone.Following this,flood maps of GAGG-F and GAGG-T are generated using these cut values.Finally,flood maps of GAGG-F and GAGG-T are segmented,respectively.Results The novel procedure is compared with the traditional procedure,with results demonstrating that the novel procedure improves pulse discrimination.Conclusion In conclusion,the crystal discrimination for position-sensitive gamma-ray detectors can be enhanced by incorporating interaction position information.展开更多
基金"PSPC Régions n°2"("Projets Structurants des Pôles de Compétitivitéen région")funded by Conseil Régional Hauts-de-France and BPI.
文摘Developing the railway transport sector is a challenging scientific,economic and social research topic starting with ensuring human security.The main topic that should be developed in that sense is the ballast stability and dynamical behaviour under external loading and environmental changes.This paper investigates the effect of particle size distribution and normal pressure on the mechanical response of a ballast bed.Grading curves of ballast layers with different sizes are illustrated to discuss their strength behaviour under various strains to deduce the significant effect on the direct shear performance of the ballast layer.Direct shear tests with different Particle Size Distribution(PSD)were reproduced using the Discrete Element Method(DEM).It is noticed that when the number of small-sized ballast increases,the shear strength and the friction angle increase to varying degrees under different normal pressures,with an average increase of 27%and 8%,respectively.When the number of large-sized ballast decreases,the shear strength and the friction angle decrease to varying degrees under different normal pressures,with an average decrease of 6%and 3%,respectively.
基金financially supported by the Joint Funds of the National Natural Science Foundation of ChinaChina National Petroleum Corporation(U1362202)+4 种基金National Natural Science Foundation of China(21206195)the Fundamental Research Funds for the Central Universities(14CX02050A,14CX02123A)Shandong Provincial Natural Science Foundation(ZR2012BM014)the project sponsored by Scientific Research Foundation for Returned Overseas Chinese Scholarthe support from Chinese Government under the Chinese scholarship scheme for international students
文摘Active sites of Fluid catalytic cracking (FCC) catalyst are poisoned during operation in the FCC reactor due to causes including feedstock contaminant metals deposition. This leads to activity, selectivity and increasing coking problems, thereby raising concern to the refiner. This work investigated effect of nickel coexisting with vanadium in the FCC feedstock on the standard FCC catalyst during cracking process, in which destruction of active sites occurs as a result of the metals deposition. Laboratory simulated equilibrium catalysts (E-cats) were studied by XRD, FTIR spectroscopy, N-2 adsorption, solid state MAS-NMR, SEM and H-2-TPR. Results revealed that vanadium, above a certain concentration in the catalyst, under hydrothermal conditions, is highly detrimental to the catalyst's structure and activity. Conversely, nickel hardly affects the catalyst structure, but its co-presence in the catalyst reduces destructive effects of vanadium. The mechanism of nickel inhibition of vanadium poisoning of the catalyst is discussed. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.
基金supported in part by National Key R&D Program of China(No.2022YFC2402001)the National Natural Science Foundation of China(No.12375337).
文摘Purpose Position-sensitive detectors play a crucial role in gamma-ray imaging systems.To enhance the detector’s inherent spatial resolution,one promising technique involves the phoswich design,which combines pixelated scintillators with different decay times.Method In a previous study,we constructed a phoswich detector comprising a side-by-side GAGG-F/GAGG-T scintillator array coupled to an 8×8 SiPM array.Traditionally,all pulses are distinguished using a parameter with a global cut value.However,due to the non-uniformity of the array,pulse shapes vary with the interaction position of the gamma-ray.In this paper,we propose a novel procedure for crystal discrimination.Initially,the crystal flood map with all events is roughly segmented.Subsequently,the crystal discrimination values of each zone are histogrammed to generate the cut value for each zone.Following this,flood maps of GAGG-F and GAGG-T are generated using these cut values.Finally,flood maps of GAGG-F and GAGG-T are segmented,respectively.Results The novel procedure is compared with the traditional procedure,with results demonstrating that the novel procedure improves pulse discrimination.Conclusion In conclusion,the crystal discrimination for position-sensitive gamma-ray detectors can be enhanced by incorporating interaction position information.
