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The great catastrophe: causes of the Permo-Triassic marine mass extinction

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National Science Review 2024年第1期11卷 37-50页

作者： Paul B.Wignall David P.G.Bond School of Earth & Environment University of Leeds School of Environmental Sciences University of Hull

The marine losses during the Permo-Triassic mass extinction were the worst ever experienced. All groups were badly affected, especially amongst the benthos(e.g. brachiopods, corals, bryozoans, foraminifers,ostracods). Planktonic populations underwent a fundamental change with eukaryotic algae being replaced by nitrogen-fixing bacteria, green-sulphur bacteria, sulphate-reducing bacteria and prasinophytes. Detailed studies of boundary sections, especially those in South China, have resolved the crisis to a ～55 kyr interval straddling the Permo-Triassic boundary. Many of the losses occur at the beginning and end of this interval painting a picture of a two-phase extinction. Improved knowledge of the extinction has been supported by numerous geochemical studies that allow diverse proposed extinction mechanisms to be studied. A transition from oxygenated to anoxic-euxinic conditions is seen in most sections globally, although the intensity and timing shows regional variability. Decreased ocean ventilation coincides with rapidly rising temperatures and many extinction scenarios attribute the losses to both anoxia and high temperatures.Other kill mechanisms include ocean acidification for which there is conflicting support from geochemical proxies and, even less likely, siltation(burial under a massive influx of terrigenous sediment) which lacks substantive sedimentological evidence. The ultimate driver of the catastrophic changes at the end of the Permian was likely Siberian Trap eruptions and their associated carbon dioxide emissions with consequences such as warming, ocean stagnation and acidification. Volcanic winter episodes stemming from Siberian volcanism have also been linked to the crisis, but the short-term nature of these episodes(

关键词： ocean anoxia ocean acidification siltation productivity collapse volcanic winter

A numerical model to simulate the transient frictional viscoelastic sliding contact

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Friction 2024年第2期12卷 319-339页

作者： Dongze WANG Gregory de BOER Anne NEVILLE Ali GHANBARZADEH School of Mechanical Engineering University of LeedsLeeds LS29JTUK

Sliding motion has always been one of the major concerns when it comes to the analysis of viscoelastic contact problems.A new model simulating the transient sliding contact of smooth viscoelastic surfaces is developed in this paper.By taking the dry contact friction and the coupling between shear tractions and normal pressure into account,the effect of the early partial slip period,which is often neglected in the study of viscoelastic sliding contact problems,is investigated numerically.Compared with solutions based on the frictionless assumption,the steady-state pressure profile is found to be slightly different under the effect of the partial slip regime,including a lower peak pressure and the shift of the contacting region in the direction opposite to the sliding motion.Furthermore,the time required for the viscoelastic contact to reach its steady state is delayed owing to the partial slip period preceding the global sliding motion.

关键词： contact mechanics frictional sliding viscoelasticity viscoelastic friction

Three-stage pyrolysis–steam reforming–water gas shift processing of household,commercial and industrial waste plastics for hydrogen production

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Waste Disposal and Sustainable Energy 2024年第1期6卷 25-37页

作者： Rayed Alshareef Robert Sait-Stewart Mohamad A.Nahil Paul T.Williams School of Chemical and Process Engineering University of LeedsLeedsLS29JTUK

Five common single plastics and nine different household,commercial and industrial waste plastics were processed using a three-stage(i)pyrolysis,(ii)catalytic steam reforming and(iii)water gas shift reaction system to produce hydrogen.Pyrolysis of plastics produces a range of different hydrocarbon species which are subsequently catalytically steam reformed to produce H_(2)and CO and then undergo water gas shift reaction to produce further H_(2).The process mimics the commercial process for hydrogen production from natural gas.Processing of the single polyalkene plastics(high-density polyethylene(HDPE),low-density polyethylene(LDPE),and polypropylene(PP))produced similar H_(2)yields between 115 mmol and 120 mmol per gram plastic.Even though PS produced an aromatic product slate from the pyrolysis stage,further stages of reforming and water gas shift reaction produced a gas yield and composition similar to that of the polyalkene plastics(115 mmol H_(2)per gram plastic).PET gave significantly lower H_(2)yield(41 mmol per gram plastic)due to the formation of mainly CO,CO_(2)and organic acids from the pyrolysis stage which were not conducive to further reforming and water gas shift reaction.A mixture of the single plastics typical of that found in municipal solid waste produced a H_(2)yield of 102 mmol per gram plastic.Knowing the gas yields and composition from the single plastics enabled an estimation of the yields from a simulated waste plastic mixture and a‘real-world’waste plastic mixture to be determined.The different household,commercial and industrial waste plastic mixtures produced H_(2)yields between 70 mmol and 107 mmol per gram plastic.The H_(2)yield and gas composition from the single waste plastics gave an indication of the type of plastics in the mixed waste plastic samples.

关键词： Waste plastic Hydrogen Catalyst Pyrolysis reforming Water gas shift

Simulation of the deformable lateral boundaries in biaxial test using DEM

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Particuology 2024年第5期88卷 161-175页

作者： Ali Momeni Barry Clarke Yong Sheng Ali Hassanpour WSP 3 Wellington PlaceLeedsLS1 4APUK Hull university HullHU6 7RXUK School of Civil Engineering University of LeedsLeedsLS2 9JTUK School of Computer Science University of HullHullHU6 7RXUK School of Chemical and Process Engineering University of LeedsLeedsLS2 9JTUK

Applying the discrete element method(DEM)in soil mechanics can provide abundant information at the particle-scale and facilitates illustration of the macro-mechanical behaviour of soils based on the inter-particle mechanisms.The triaxial test is one of the most common laboratory methods to study the macro-mechanical behaviour of particulate materials such as soil.However,many problems in geotechnical design can be assumed and simplified as a plane strain phenomenon.Therefore a biaxial test can be conducted to reproduce the macro-mechanical behaviour of soil,where the sample is enclosed by two horizontal rigid platens and a vertical latex membrane,which is a deformable continuous element and allows the enclosed specimen to deform freely while maintaining confining stress during loading.This paper presents an algorithm to represent physical and mechanical characteristics of latex membrane in the 2D DEM simulation of biaxial test using the PFC 2D code.To investigate the impact of the lateral boundary conditions on the micro-macro mechanical behaviours of soil samples,two sets of DEM biaxial tests are conducted,i.***.with rigid and deformable lateral boundary conditions.The DEM modeling results indicate that the lateral boundary conditions have a significant effect on the micro-scale fabric properties,thickness and inclination of the shear band.The comparison between these two simulations also demonstrates that the lateral boundary conditions play a major role in the peak and post-peak stress-strain behaviours as well as the dilation and critical state behaviours of granular soils.

关键词： Discrete element method Biaxial test Deformable boundaries Shear band Critical state Fabric anisotropy Geometrical stability index

Semi-analytical solution for drained expansion analysis of a hollow cylinder of critical state soils

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第6期16卷 2326-2340页

作者： He Yang Jialiang Zhang Haisui Yu Peizhi Zhuang School of Qilu Transportation Shandong UniversityJinan250002China School of Civil Engineering University of LeedsLeedsLS29JTUK

The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by the common self-similar-based similarity techniques.This paper proposes a novel,exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils.Considering stress-dependent elastic moduli of soils,new analytical stress and displacement solutions for the nonself-similar problem are developed taking the small strain assumption in the elastic zone.In the plastic zone,the cavity expansion response is formulated into a set of first-order partial differential equations(PDEs)with the combination use of Eulerian and Lagrangian descriptions,and a novel solution algorithm is developed to efficiently solve this complex boundary value problem.The solution is presented in a general form and thus can be useful for a wide range of soils.With the new solution,the non-self-similar nature induced by the finite outer boundary is clearly demonstrated and highlighted,which is found to be greatly different to the behaviour of cavity expansion in infinite soil mass.The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small-sized calibration chambers.

关键词： Cavity expansion Drained analysis Boundary effect Critical state soil Non-self-similar Eulerian-Lagrangian approach

Piezo1 expression in chondrocytes controls endochondral ossification and osteoarthritis development

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Bone Research 2024年第1期12卷 199-214页

作者： Laura J.Brylka Assil-Ramin Alimy Miriam E.A.Tschaffon-Müller Shan Jiang Tobias Malte Ballhause Anke Baranowsky Simon von Kroge Julian Delsmann Eva Pawlus Kian Eghbalian Klaus Püschel Astrid Schoppa Melanie Haffner-Luntzer David J.Beech Frank Timo Beil Michael Amling Johannes Keller Anita Ignatius Timur A.Yorgan Tim Rolvien Thorsten Schinke Department of Osteology and Biomechanics University Medical Center Hamburg-Eppendorf20246 HamburgGermany Department of Trauma and Orthopedic Surgery University Medical Center Hamburg-Eppendorf20246 HamburgGermany Institute of Orthopedic Research and Biomechanics University Medical Center UlmBadenWürttemberg89081 UlmGermany Department Legal Medicine University Medical Center Hamburg-Eppendorf20246 HamburgGermany leeds Institute of Cardiovascular and Metabolic Medicine School of MedicineUniversity of LeedsLS29JT LeedsUK

Piezo proteins are mechanically activated ion channels,which are required for mechanosensing functions in a variety of cell types.While we and others have previously demonstrated that the expression of Piezo1 in osteoblast lineage cells is essential for boneanabolic processes,there was only suggestive evidence indicating a role of Piezo1 and/or Piezo2 in cartilage.Here we addressed the question if and how chondrocyte expression of the mechanosensitive proteins Piezo1 or Piezo2 controls physiological endochondral ossification and pathological osteoarthritis(OA)development.Mice with chondrocyte-specific inactivation of Piezo1(Piezo1^(Col2a1Cre)),but not of Piezo2,developed a near absence of trabecular bone below the chondrogenic growth plate postnatally.Moreover,all Piezo1^(Col2a1Cre) animals displayed multiple fractures of rib bones at 7 days of age,which were located close to the growth plates.While skeletal growth was only mildly affected in these mice,OA pathologies were markedly less pronounced compared to littermate controls at 60 weeks of age.Likewise,when OA was induced by anterior cruciate ligament transection,only the chondrocyte inactivation of Piezo1,not of Piezo2,resulted in attenuated articular cartilage degeneration.Importantly,osteophyte formation and maturation were also reduced in Piezo1^(Col2a1Cre) mice.We further observed increased Piezo1 protein abundance in cartilaginous zones of human osteophytes.Finally,we identified Ptgs2 and Ccn2 as potentially relevant Piezo1 downstream genes in chondrocytes.Collectively,our data do not only demonstrate that Piezo1 is a critical regulator of physiological and pathological endochondral ossification processes,but also suggest that Piezo1 antagonists may be established as a novel approach to limit osteophyte formation in OA.

关键词： Piezo1 markedly ossification

Grain refinement of Mg-Ca alloys by native MgO particles

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Journal of Magnesium and Alloys 2024年第3期12卷 980-996页

作者： Shihao Wang Yun Wang Quentin M.Ramasse Zhongyun Fan Super STEM Laboratory SciTech Daresbury CampusDaresbury WA44ADUK School of Chemical and Process Engineering University of LeedsLeeds LS29JTUK BCAST Brunel University LondonUxbridgeMiddlesex UB83PHUK

In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.

关键词： Mg-Ca alloy Grain refinement MgO Interfacial segregation STEM/EELS Solidification.

Present-day movement characteristics of the Qinghai Nanshan fault and its surrounding area from GPS observation

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Geodesy and Geodynamics 2024年第2期15卷 133-141页

作者： Yang Liu Yuxuan Qiu Jialiang Liu Luyun Xiong Caijun Xu Jianghui Geng Gang Zheng Tianchen Sheng School of Geodesy and Geomatics Wuhan UniversityWuhan 430079China Key Laboratory of Geospace Environment and Geodesy Ministry of EducationWuhan UniversityWuhan 430079China Key Laboratory of Geophysical Geodesy Ministry of Natural ResourcesWuhan UniversityWuhan 430079China GNSS Research Center Wuhan UniversityWuhan 430079China School of Earth and Environment University of LeedsLeeds LS29JTUK Qinghai Basic Surveying and Mapping Institute Xining 810101China

The Qinghai Nanshan fault is a larger fault in the Northeastern Xizang Plateau.In previous studies,its movement characteristics are mainly investigated with geological and seismic observations,and the tectonic transformation role of the fault on its east is not yet clear.This study uses data fusion to obtain denser GPS observations near the Qinghai Nanshan fault.Based on tectonic characteristics,we establish a block model to investigate the fault slip rate,locking degree,and slip deficit.The results show that the Qinghai Nanshan fault slip rate is characterized by sinistral and convergent movement.Both the sinistral and convergent rates display a decreasing trend from west to east.The locking degree and slip deficit are higher in the western segment(with an average of about 0.74 and 1.1 mm/a)and lower in the eastern segment.Then,we construct a strain rate field using GPS observations to analyze the regional strain characteristics.The results indicate that along the fault,the western segment shows a larger shear strain rate and negative dilation rate.Regional earthquake records show that the frequency of earthquakes is lower near the fault.The joint results suggest that the western segment may have a higher earthquake risk.In addition,the insignificant fault slip rate in the eastern segment may indicate that it does not participate in the tectonic transformation among the Riyueshan,Lajishan,and West Qinling faults.

关键词： The Qinghai Nanshan fault Movement characteristics Block model Slip rate GPS

A framework for dynamic modelling of railway track switches considering the switch blades,actuators and control systems

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Railway Engineering Science 2024年第2期32卷 162-176页

作者： Saikat Dutta Tim Harrison Christopher Ward Roger Dixon Phil Winship Institute of Thermofluids School of Mechanical EngineeringUniversity of LeedsLeedsWest YorkshireUK Wolfson School of Mechanical Electrical and Manufacturing EngineeringLoughborough UniversityLoughboroughLeicestershireUK Birmingham Centre for Railway Research and Education School of EngineeringUniversity of BirminghamBirminghamWest MidlandsUK Network Rail Milton KeynesBuckinghamshireUK

The main contribution of this paper is the development and demonstration of a novel methodology that can be followed to develop a simulation twin of a railway track switch system to test the functionality in a digital environment.This is important because,globally,railway track switches are used to allow trains to change routes;they are a key part of all railway networks.However,because track switches are single points of failure and safety-critical,their inability to operate correctly can cause significant delays and concomitant costs.In order to better understand the dynamic behaviour of switches during operation,this paper has developed a full simulation twin of a complete track switch system.The approach fuses finite element for the rail bending and motion,with physics-based models of the electromechanical actuator system and the control system.Hence,it provides researchers and engineers the opportunity to explore and understand the design space around the dynamic operation of new switches and switch machines before they are built.This is useful for looking at the modification or monitoring of existing switches,and it becomes even more important when new switch concepts are being considered and evaluated.The simulation is capable of running in real time or faster meaning designs can be iterated and checked interactively.The paper describes the modelling approach,demonstrates the methodology by developing the system model for a novel“REPOINT”switch system,and evaluates the system level performance against the dynamic performance requirements for the switch.In the context of that case study,it is found that the proposed new actuation system as designed can meet(and exceed)the system performance requirements,and that the fault tolerance built into the actuation ensures continued operation after a single actuator failure.

关键词： Railway track switch Mathematical modelling Redundant actuation Finite element analysis