The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes f...The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes from three nearest Nb ions forming a molecular cluster with spin 1/2.Previous bulk measurements including magnetic susceptibility and specific heat suggested the existence of spinon Fermi surfaces.Here we further probe the spin system by nuclear magnetic resonance(NMR)and muon spin rotation and relaxation(μSR)techniques.We confirm that there is no magnetic long-range order and the dynamical spin fluctuations persist down to 0.075 K.These results provide further evidence that Nb_(3)Cl_(8)may host a quantum spin liquid.展开更多
By using muon spin relaxation(μSR)measurements,we perform a comparative study of the microscopic magnetism in the parent compounds of infinite-layer nickelate superconductors RNiO_(2)(R=La,Nd).In either compound,the ...By using muon spin relaxation(μSR)measurements,we perform a comparative study of the microscopic magnetism in the parent compounds of infinite-layer nickelate superconductors RNiO_(2)(R=La,Nd).In either compound,the zero-fieldμSR spectra down to the lowest measured temperature reveal no long-range magnetic order.In LaNiO_(2),short-range spin correlations appear below T=150 K,and spins fully freeze below T∼10 K.NdNiO_(2)exhibits a more complex spin dynamics driven by the Nd 4f and Ni3d electron spin fluctuations.Further,it shows features suggesting the proximity to a spin-glass state occurring below T=5 K.In both compounds,the spin behavior with temperature is further confirmed by longitudinal-field μSR measurements.These results provide new insight into the magnetism of the parent compounds of the superconducting nickelates,crucial to understanding the microscopic origin of their superconductivity.展开更多
Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we ap...Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we applied x-ray diffraction,magnetization,heat capacity and powder inelastic neutron scattering measurements,along with theoretical calculations,to study the exotic properties of chromite-spinel oxides CoCr_(2)O_(4) and MnCr_(2)O_(4).The temperature dependence of the phonon spectra provides an insight into the correlation between oxygen motion and the magnetic order,as well as the magnetoelectric effect in the ground state of MnCr_(2)O_(4).Moreover,spin-wave excitations in CoCr_(2)O_(4) and MnCr_(2)O_(4) are compared with Heisenberg model calculations.This approach enables the precise determination of exchange energies and offers a comprehensive understanding of the spin dynamics and relevant exchange interactions in complicated spiral spin ordering.展开更多
Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and s...Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and skilled workers. Another solution is the use of welding. However, the weldability of old steels is poor. Bolts are very attractive alternative solutions, and are most commonly used to repair old metallic bridges. Fitted bolts are expensive solutions; the alternative is the use of resin-injected bolts. The behavior of bolted joints with preloaded resin-injected bolts has been studied using quasi-static and creep tests; however, few studies on the slip and fatigue behavior of these joints can be found in the literature. This paper presents an overview of a few experimental programs that were carried out by several authors aiming at evaluating the fatigue behavior of single and double shear resin-injected bolted connections. A comparison between the experimental data of joints with preloaded standard bolts and preloaded resin- injected bolts shows a fatigue strength reduction in the latter. Since Eurocode 3 （EC3） suggests the same fatigue strength curve for joints made of resin-injected bolts and standard bolts, this may raise some con- cerns. Furthermore, research on the feasibility of using both bonded and bolted connections is shown. This last study was performed with high-strength low-alloy structural steel plates and an acrylic struc- tural adhesive for metal bonding. For both case studies, a statistical analysis is performed on fatigue experimental data using linearized boundaries and the Castillo and Fernandez-Canteli model. Fatigue design curves are proposed and compared with the design suggestions of several European and North American standards,展开更多
The buildings＇ capacity to maintain minimum structural safety levels during natural disasters, such as earthquakes, is recognisably one of the aspects that most influence urban resilience. Moreover, the public invest...The buildings＇ capacity to maintain minimum structural safety levels during natural disasters, such as earthquakes, is recognisably one of the aspects that most influence urban resilience. Moreover, the public investment in risk mitigation strategies is fimdamental, not only to promote social and urban and resilience, but also to limit consequent material, human and environmental losses. Despite the growing awareness of this issue, there is still a vast number of traditional masonry buildings spread throughout many European old city centres that lacks of adequate seismic resistance, requiring therefore urgent retrofitting interventions in order to both reduce their seismic vulnerability and to cope with the increased seismic requirements of recent code standards. Thus, this paper aims at contributing to mitigate the social and economic impacts of earthquake damage scenarios through the development of vulnerability-based comparative analysis of some of the most popularretrofitting techniques applied after the 1998 Azores earthquake. The influence of each technique individually and globally studied resorting to a seismic vulnerability index methodology integrated into a GIS tool and damage and loss scenarios are constructed and critically discussed. Finally, the economic balance resulting from the implementation of that techniques are also examined.展开更多
The type of subgrade of a railroad foundation is vital to the overall performance of the track structure.With the train speed and tonnage increase,as well as environmental changes,the evaluation and influence of subgr...The type of subgrade of a railroad foundation is vital to the overall performance of the track structure.With the train speed and tonnage increase,as well as environmental changes,the evaluation and influence of subgrade are even more paramount in the railroad track structure performance.A geomechanics classification for subgrade is proposed coupling the stiffness(resilient modulus)and permanent deformation behaviour evaluated by means of repeated triaxial loading tests.This classification covers from fine-to coarse-grained soils,grouped by UIC and ASTM.For this achievement,we first summarize the main models for estimating resilient modulus and permanent deformation,including the evaluation of their robustness and their sensitivity to mechanical and environmental parameters.This is followed by the procedure required to arrive at the geomechanical classification and rating,as well as a discussion of the influence of environmental factors.This work is the first attempt to obtain a new geomechanical classification that can be a useful tool in the evaluation and modelling of the foundation of railway structures.展开更多
Eurofer97 steel is a primary structural material for applications in fusion reactors. Laser welding is a promising technique to join Eurofer97 plasma-facing components and overcome remote handling and maintenance chal...Eurofer97 steel is a primary structural material for applications in fusion reactors. Laser welding is a promising technique to join Eurofer97 plasma-facing components and overcome remote handling and maintenance challenges. The interaction of the induced residual stress and the heterogeneous microstructure degrades the mechanical performance of such fusion components. The present study investigates the distribution of residual stress in as-welded and post-heat treated Eurofer97 joints. The mechanistic connections between microstructure, material properties, and residual stress are also studied. Neutron diffraction is used to study the through-thickness residual stress distribution in three directions,and neutron Bragg edge imaging(NBEI) is applied to study the residual strain in high spatial resolution.The microstructures and micro-hardness are characterised by electron backscatter diffraction and nanoindentation, respectively. The M-shaped residual stress distribution through the thickness of the as-welded weldment is observed by neutron diffraction line scans over a region of 1.41 × 10 mm^(2). These profiles are cross-validated over a larger area(∼56 × 40 mm^(2)) with the higher spatial resolution by NBEI. The micro-hardness value in the fusion zone of the as-welded sample almost doubles from 2.75 ± 0.09 GPa to 5.06 ± 0.29 GPa due to a combination of residual stress and cooling-induced martensite. Conventional post weld heat treatment(PWHT) is shown to release ∼90% of the residual stress but not fully restore the microstructure. By comparing its hardness with that of stress-free samples, it is found that the microstructure is the primary contribution to the hardening. This study provides insight into the prediction of structural integrity for critical structural components of fusion reactors.展开更多
An experimental muon source(EMuS) will be built at the China Spallation Neutron Source(CSNS). In phase I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A ...An experimental muon source(EMuS) will be built at the China Spallation Neutron Source(CSNS). In phase I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A 128-channel muon spin rotation/relaxation/resonance(μSR) spectrometer is proposed as a prototype surface muon spectrometer in a sub-branch of EMuS. The prototype spectrometer includes a detection system, sample environment, and supporting mechanics. The current design has two rings located at the forward and backward directions of the muon spin with 64 detectors per ring. The simulation shows that the highest asymmetry of approximately 0.28 is achieved by utilizing two 10-mm-thick brass degraders. To obtain the optimal asymmetry, the two-ring structure is updated to a four-ring structure with 32 segments in each ring. An asymmetry of 0.42 is obtained through the simulation, which is higher than that of all the current μSR spectrometers in the world.展开更多
The RMR system is still very much applied in rock mechanics engineering context. It is based on the evaluation of six weights to obtain a final rating. To obtain the final rating a considerable amount of information i...The RMR system is still very much applied in rock mechanics engineering context. It is based on the evaluation of six weights to obtain a final rating. To obtain the final rating a considerable amount of information is needed concerning the rock mass which can be difficult to obtain in some projects or project stages at least with accuracy. In 2007 an alternative classification scheme based on the RMR, the Hierarchical Rock Mass Rating(HRMR) was presented. The main feature of this system was the adaptation to the level of knowledge existent about the rock mass to obtain the classification of the rock mass since it followed a decision tree approach. However, the HRMR was only valid for hard rock granites with low fracturing degrees. In this work, the database was enlarged with approximately 40% more cases considering other types of granite rock masses including weathered granites and based on this increased database the system was updated. Granite formations existent in the north of Portugal including Porto city are predominantly granites. Some years ago a light rail infrastructure was built in the city of Porto and surrounding municipalities which involved considerable challenges due to the high heterogeneity levels of the granite formations and the difficulties involved in their geomechanical characterization. In this work it is intended to provide also a contribution to improve the characterization of these formations with special emphasis to the weathered horizons. A specific subsystem applicable to the weathered formations was developed. The results of the validation of these systems are presented and show acceptable performances in identifying the correct class using less information than with the RMR system.展开更多
We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield s...We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.However,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated to be 63 mJ m^(-2) at 293 K and 47 mJ m^(-2) at 15 K.This work highlights the significance of lattice distortion and dislocations played in this alloy,providing insights into the design of new multicomponent alloys with superb mechanical performance for cryogenic applications.展开更多
The ballastless track is nowadays the most popular railway system due to the required low number of maintenance opera-tions and costs,despite the high investment.The gradual change from ballasted to ballastless tracks...The ballastless track is nowadays the most popular railway system due to the required low number of maintenance opera-tions and costs,despite the high investment.The gradual change from ballasted to ballastless tracks has been occurring in Asia,but also in Europe,increasing the number of transition zones.The transition zones are a special area of the railway networks where there is an accelerated process of track degradation,which is a major concern of the railway infrastructure managers.Thus,the accurate prediction of the short-and long-term performance of ballastless tracks in transition zones is an important topic in the current paradigm of building/rehabilitating high-speed lines.This work purposes the development of an advanced 3D model to study the global performance of a ballastless track in an embankment-tunnel transition zone considering the influence of the train speed(220,360,500,and 600 km/h).Moreover,a mitigation measure is also adopted to reduce the stress and displacements levels of the track in the transition.A resilient mat placed in the tunnel and embank-ment aims to soften the transition.The behaviour of the track with the resilient mat is evaluated considering the influence of the train speed,with special attention regarding the critical speed.The used methodology is a novel and hybrid approach that allows including short-term and long-term performance,through the development of a powerful 3D model combined with the implementation of a calibrated empirical permanent deformation model.展开更多
Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.T...Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.The interactions between dislocations andγ"precipitates vary according to theγ"orienta-tion variants,which makes the deformation behaviour complicated and difficult to reveal experimentally.In this work,γ"variant distributions of Inconel 718 samples were tailored by ageing heat treatment under either tensile or compressive stress.Theγ"variant-sensitive deformation behaviours were then studied by in situ tensile tests via neutron diffraction at room temperature.It is demonstrated that yield-ing first takes place in grains oriented with<110>parallel to the loading direction.An identical lattice strain response to applied stress of both theγmatrix and theγ"precipitates was observed during yield-ing,suggesting that dislocations shearing through theγ"precipitates is predominant at this stage.Vari-ations in yield strength for samples with differentγ"variant distributions were observed,which can be attributed to different strengthening that arises from interactions between dislocation and differentγ"variants.展开更多
Time reversal symmetry(TRS)is a key symmetry for classification of unconventional superconductors,and the violation of TRS often results in a wealth of novel properties.Here we report the synthesis and superconducting...Time reversal symmetry(TRS)is a key symmetry for classification of unconventional superconductors,and the violation of TRS often results in a wealth of novel properties.Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr1-δPt4Ge12.The results from x-ray diffraction and magnetization measurements show that the[Pt4 Ge12]cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature Tc = 7.80 K.The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model,providing strong evidence of multi-band superconductivity.TRS breaking is observed using zero Held muon-spin relaxation experiments,and the magnitude of the spontaneous field is nearly half of that in PrPt4Ge12.展开更多
Two-phase flow in porous media is a very active field of research,due to its important applications in groundwater pollution,CO_(2)sequestration,or oil and gas production from petroleum reservoirs,just to name a few o...Two-phase flow in porous media is a very active field of research,due to its important applications in groundwater pollution,CO_(2)sequestration,or oil and gas production from petroleum reservoirs,just to name a few of them.Fractional flow equations,which make use of Darcy's law,for describing the movement of two immiscible fluids in a porous medium,are among the most relevant mathematical models in reservoir simulation.This work aims to solve a fractional flow model formed by an elliptic equation,representing the spatial distribution of the pressure,and a hyperbolic equation describing the space-time evolution of water saturation.The numerical solution of the elliptic part is obtained using a finite-element(FE)scheme,while the hyperbolic equation is solved by means of two dif-ferent numerical approaches,both in the finite-volume(FV)framework.One is based on a monotonic upstream-centered scheme for conservation laws(MUSCL)-Hancock scheme,whereas the other makes use of a weighted essentially non-oscillatory(ENO)reconstruc-tion.In both cases,a first-order centered(FORCE)-αnumerical scheme is applied for inter-cell flux reconstruction,which constitutes a new contribution in the field of fractional flow models describing oil-water movement.A relevant feature of this work is the study of the effect of the parameterαon the numerical solution of the models considered.We also show that,in the FORCE-αmethod,when the parameterαincreases,the errors diminish and the order of accuracy is more properly attained,as verified using a manufactured solution technique.展开更多
The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The...The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The existence of a small amount of Tm/Mg site-mixing disorder is revealed.DC magnetic susceptibility measurement shows that Tm^(3+)magnetic moments are antiferromagnetically correlated with a negative Curie-Weiss temperature of−26.3 K.Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility,and confirmed by μSR experiment down to 0.1 K.However,the emergence of short-range magnetic order is indicated by the zero-field μSR experiments,and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique.Compared with the results of Tm_(3)Sb_(3)Zn_(2)O_(14),another Tm-based Kagomé lattice with much more site-mixing disorder,the gapless spin liquid like behaviors in Tm_(3)Sb_(3)Zn_(2)O_(14)can be induced by disorder effect.Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403800,2022YFA1403400,2021YFA1400400,2023YFA1406100,and 2024YFA1409200)the National Natural Science Foundation of China(Grant Nos.12274444,12374142,and 12304170)+1 种基金the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2025PG0007)We thank ISIS Facility for beam time(Grant No.RB2310088).
文摘The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes from three nearest Nb ions forming a molecular cluster with spin 1/2.Previous bulk measurements including magnetic susceptibility and specific heat suggested the existence of spinon Fermi surfaces.Here we further probe the spin system by nuclear magnetic resonance(NMR)and muon spin rotation and relaxation(μSR)techniques.We confirm that there is no magnetic long-range order and the dynamical spin fluctuations persist down to 0.075 K.These results provide further evidence that Nb_(3)Cl_(8)may host a quantum spin liquid.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1402203)the National Natural Science Foundation of China(Grant No.12174065)supported by the Shenzhen Fundamental Research Program(Grant Nos.JCYJ20220818100405013 and JCYJ20230807093204010)。
文摘By using muon spin relaxation(μSR)measurements,we perform a comparative study of the microscopic magnetism in the parent compounds of infinite-layer nickelate superconductors RNiO_(2)(R=La,Nd).In either compound,the zero-fieldμSR spectra down to the lowest measured temperature reveal no long-range magnetic order.In LaNiO_(2),short-range spin correlations appear below T=150 K,and spins fully freeze below T∼10 K.NdNiO_(2)exhibits a more complex spin dynamics driven by the Nd 4f and Ni3d electron spin fluctuations.Further,it shows features suggesting the proximity to a spin-glass state occurring below T=5 K.In both compounds,the spin behavior with temperature is further confirmed by longitudinal-field μSR measurements.These results provide new insight into the magnetism of the parent compounds of the superconducting nickelates,crucial to understanding the microscopic origin of their superconductivity.
基金the financial support from the National Key Research and Development Program of China(Grant No.2022YFA1402702)the National Science Foundation of China(Grant Nos.U2032213 and 12004243)+8 种基金the National Science Foundation of China(Grant No.12274412)the Interdisciplinary Program of Wuhan National High Magnetic Field Center(Grant No.WHMFC 202122)Huazhong University of Science and Technologythe support from the National Natural Science Foundation of China(Grant No.52101236)Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515140014)the Guangdong Provincial Key Laboratory of Extreme Conditionsfinancial support from the National Key Research and Development Program of China(Grant Nos.2021YFA1600201 and 2023YFA1607402)the support of NSF-DMR-2003117supported by a beamtime allocation RB1910163 from the Science and Technology Facilities Council。
文摘Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we applied x-ray diffraction,magnetization,heat capacity and powder inelastic neutron scattering measurements,along with theoretical calculations,to study the exotic properties of chromite-spinel oxides CoCr_(2)O_(4) and MnCr_(2)O_(4).The temperature dependence of the phonon spectra provides an insight into the correlation between oxygen motion and the magnetic order,as well as the magnetoelectric effect in the ground state of MnCr_(2)O_(4).Moreover,spin-wave excitations in CoCr_(2)O_(4) and MnCr_(2)O_(4) are compared with Heisenberg model calculations.This approach enables the precise determination of exchange energies and offers a comprehensive understanding of the spin dynamics and relevant exchange interactions in complicated spiral spin ordering.
基金the financial support of the Portuguese Foundation for Science and Technology (FCT) through the postdoctoral grant (SFRH/BPD/107825/2015)the funding of Pro-Life-Prolonging the Lifetime of Old Steel and Steel-Concrete Bridges (RFSR-CT-2015-00025) by the Research Fund for Coal and Steel (RFCS)
文摘Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and skilled workers. Another solution is the use of welding. However, the weldability of old steels is poor. Bolts are very attractive alternative solutions, and are most commonly used to repair old metallic bridges. Fitted bolts are expensive solutions; the alternative is the use of resin-injected bolts. The behavior of bolted joints with preloaded resin-injected bolts has been studied using quasi-static and creep tests; however, few studies on the slip and fatigue behavior of these joints can be found in the literature. This paper presents an overview of a few experimental programs that were carried out by several authors aiming at evaluating the fatigue behavior of single and double shear resin-injected bolted connections. A comparison between the experimental data of joints with preloaded standard bolts and preloaded resin- injected bolts shows a fatigue strength reduction in the latter. Since Eurocode 3 （EC3） suggests the same fatigue strength curve for joints made of resin-injected bolts and standard bolts, this may raise some con- cerns. Furthermore, research on the feasibility of using both bonded and bolted connections is shown. This last study was performed with high-strength low-alloy structural steel plates and an acrylic struc- tural adhesive for metal bonding. For both case studies, a statistical analysis is performed on fatigue experimental data using linearized boundaries and the Castillo and Fernandez-Canteli model. Fatigue design curves are proposed and compared with the design suggestions of several European and North American standards,
基金URBSIS:Assessing Vulnerability and Managing Earthquake Risk at Urban Scale(PTDC/ECM-URB/2564/2012)
文摘The buildings＇ capacity to maintain minimum structural safety levels during natural disasters, such as earthquakes, is recognisably one of the aspects that most influence urban resilience. Moreover, the public investment in risk mitigation strategies is fimdamental, not only to promote social and urban and resilience, but also to limit consequent material, human and environmental losses. Despite the growing awareness of this issue, there is still a vast number of traditional masonry buildings spread throughout many European old city centres that lacks of adequate seismic resistance, requiring therefore urgent retrofitting interventions in order to both reduce their seismic vulnerability and to cope with the increased seismic requirements of recent code standards. Thus, this paper aims at contributing to mitigate the social and economic impacts of earthquake damage scenarios through the development of vulnerability-based comparative analysis of some of the most popularretrofitting techniques applied after the 1998 Azores earthquake. The influence of each technique individually and globally studied resorting to a seismic vulnerability index methodology integrated into a GIS tool and damage and loss scenarios are constructed and critically discussed. Finally, the economic balance resulting from the implementation of that techniques are also examined.
基金This work was partially carried out under the framework of In2Track,a research project of Shift2Rail.This work was partly financed by FCT/MCTES through national funds(PIDDAC)under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering(ISISE)under reference UIDB/04029/2020It has been also financially supported by national funds through FCT—Foundation for Science and Technology,under grant agreement[PD/BD/127814/2016]attributed to Ana Ramos.
文摘The type of subgrade of a railroad foundation is vital to the overall performance of the track structure.With the train speed and tonnage increase,as well as environmental changes,the evaluation and influence of subgrade are even more paramount in the railroad track structure performance.A geomechanics classification for subgrade is proposed coupling the stiffness(resilient modulus)and permanent deformation behaviour evaluated by means of repeated triaxial loading tests.This classification covers from fine-to coarse-grained soils,grouped by UIC and ASTM.For this achievement,we first summarize the main models for estimating resilient modulus and permanent deformation,including the evaluation of their robustness and their sensitivity to mechanical and environmental parameters.This is followed by the procedure required to arrive at the geomechanical classification and rating,as well as a discussion of the influence of environmental factors.This work is the first attempt to obtain a new geomechanical classification that can be a useful tool in the evaluation and modelling of the foundation of railway structures.
文摘Eurofer97 steel is a primary structural material for applications in fusion reactors. Laser welding is a promising technique to join Eurofer97 plasma-facing components and overcome remote handling and maintenance challenges. The interaction of the induced residual stress and the heterogeneous microstructure degrades the mechanical performance of such fusion components. The present study investigates the distribution of residual stress in as-welded and post-heat treated Eurofer97 joints. The mechanistic connections between microstructure, material properties, and residual stress are also studied. Neutron diffraction is used to study the through-thickness residual stress distribution in three directions,and neutron Bragg edge imaging(NBEI) is applied to study the residual strain in high spatial resolution.The microstructures and micro-hardness are characterised by electron backscatter diffraction and nanoindentation, respectively. The M-shaped residual stress distribution through the thickness of the as-welded weldment is observed by neutron diffraction line scans over a region of 1.41 × 10 mm^(2). These profiles are cross-validated over a larger area(∼56 × 40 mm^(2)) with the higher spatial resolution by NBEI. The micro-hardness value in the fusion zone of the as-welded sample almost doubles from 2.75 ± 0.09 GPa to 5.06 ± 0.29 GPa due to a combination of residual stress and cooling-induced martensite. Conventional post weld heat treatment(PWHT) is shown to release ∼90% of the residual stress but not fully restore the microstructure. By comparing its hardness with that of stress-free samples, it is found that the microstructure is the primary contribution to the hardening. This study provides insight into the prediction of structural integrity for critical structural components of fusion reactors.
基金supported by the National Natural Science Foundation of China(No.11527811)the Key Program of State Key Laboratory of Particle Detection and ElectronicsA part of the work performed in the UKRI ISIS Detector Group was sponsored by the China Scholarship Council
文摘An experimental muon source(EMuS) will be built at the China Spallation Neutron Source(CSNS). In phase I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A 128-channel muon spin rotation/relaxation/resonance(μSR) spectrometer is proposed as a prototype surface muon spectrometer in a sub-branch of EMuS. The prototype spectrometer includes a detection system, sample environment, and supporting mechanics. The current design has two rings located at the forward and backward directions of the muon spin with 64 detectors per ring. The simulation shows that the highest asymmetry of approximately 0.28 is achieved by utilizing two 10-mm-thick brass degraders. To obtain the optimal asymmetry, the two-ring structure is updated to a four-ring structure with 32 segments in each ring. An asymmetry of 0.42 is obtained through the simulation, which is higher than that of all the current μSR spectrometers in the world.
文摘The RMR system is still very much applied in rock mechanics engineering context. It is based on the evaluation of six weights to obtain a final rating. To obtain the final rating a considerable amount of information is needed concerning the rock mass which can be difficult to obtain in some projects or project stages at least with accuracy. In 2007 an alternative classification scheme based on the RMR, the Hierarchical Rock Mass Rating(HRMR) was presented. The main feature of this system was the adaptation to the level of knowledge existent about the rock mass to obtain the classification of the rock mass since it followed a decision tree approach. However, the HRMR was only valid for hard rock granites with low fracturing degrees. In this work, the database was enlarged with approximately 40% more cases considering other types of granite rock masses including weathered granites and based on this increased database the system was updated. Granite formations existent in the north of Portugal including Porto city are predominantly granites. Some years ago a light rail infrastructure was built in the city of Porto and surrounding municipalities which involved considerable challenges due to the high heterogeneity levels of the granite formations and the difficulties involved in their geomechanical characterization. In this work it is intended to provide also a contribution to improve the characterization of these formations with special emphasis to the weathered horizons. A specific subsystem applicable to the weathered formations was developed. The results of the validation of these systems are presented and show acceptable performances in identifying the correct class using less information than with the RMR system.
基金supported by the City U grant 9360161 and RGC grant 25202719funding from the Euratom research and training programs 2014–2018 and 2019–2020 under Grant Agreement No.633053+4 种基金the RCUK Energy Programme[Grant No.EP/T012250/1]funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(grant agreement No.714697)support from high-performing computing facility MARCONI(Bologna,Italy)provided by EUROfusiona part of an international project co-financed from the funds of the program of the Polish Minister of Science and Higher Education entitled"PMW"in 2019,Agreement No.5018/H2020-Euratom/2019/2support of the Interdisciplinary center for Mathematical and Computational Modeling(ICM),University of Warsaw,under grant No.GB79–6。
文摘We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.However,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated to be 63 mJ m^(-2) at 293 K and 47 mJ m^(-2) at 15 K.This work highlights the significance of lattice distortion and dislocations played in this alloy,providing insights into the design of new multicomponent alloys with superb mechanical performance for cryogenic applications.
基金financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020 financially supported by: Base Funding-UIDB/04708/2020 of the CONSTRUCT-Institute of R&D in Structures and Construction-national funds through the FCT/ MCTES (PIDDAC)
文摘The ballastless track is nowadays the most popular railway system due to the required low number of maintenance opera-tions and costs,despite the high investment.The gradual change from ballasted to ballastless tracks has been occurring in Asia,but also in Europe,increasing the number of transition zones.The transition zones are a special area of the railway networks where there is an accelerated process of track degradation,which is a major concern of the railway infrastructure managers.Thus,the accurate prediction of the short-and long-term performance of ballastless tracks in transition zones is an important topic in the current paradigm of building/rehabilitating high-speed lines.This work purposes the development of an advanced 3D model to study the global performance of a ballastless track in an embankment-tunnel transition zone considering the influence of the train speed(220,360,500,and 600 km/h).Moreover,a mitigation measure is also adopted to reduce the stress and displacements levels of the track in the transition.A resilient mat placed in the tunnel and embank-ment aims to soften the transition.The behaviour of the track with the resilient mat is evaluated considering the influence of the train speed,with special attention regarding the critical speed.The used methodology is a novel and hybrid approach that allows including short-term and long-term performance,through the development of a powerful 3D model combined with the implementation of a calibrated empirical permanent deformation model.
基金support from the Guangdong Introducing Innovative and Entrepreneurial Teams(No.2016ZT06G025)and the financial support from the Centre for Doctoral Training in Innovative Metal Processing(IMPaCT)funded by the UK Engineering and Physical Sciences Research Council(EPSRC,No.EP/L016206/1).The authors also acknowledge useful discussions by Dr.Xingzhong Liang and the allocation of beam time(RB1820207)at ENGIN-X,ISIS,Rutherford Appleton Labora-tory.Chinnapat Panwisawas would like to acknowledge the funding from Innovation Fellowship by EPSRC,UK Research and Innovation(UKRI,No.EP/S000828/2).Shuyan Zhang gratefully acknowledges the support from the Guangdong Major Project of Basic and Ap-plied Basic Research(No.2020B0301030001)and the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDC04000000).
文摘Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.The interactions between dislocations andγ"precipitates vary according to theγ"orienta-tion variants,which makes the deformation behaviour complicated and difficult to reveal experimentally.In this work,γ"variant distributions of Inconel 718 samples were tailored by ageing heat treatment under either tensile or compressive stress.Theγ"variant-sensitive deformation behaviours were then studied by in situ tensile tests via neutron diffraction at room temperature.It is demonstrated that yield-ing first takes place in grains oriented with<110>parallel to the loading direction.An identical lattice strain response to applied stress of both theγmatrix and theγ"precipitates was observed during yield-ing,suggesting that dislocations shearing through theγ"precipitates is predominant at this stage.Vari-ations in yield strength for samples with differentγ"variant distributions were observed,which can be attributed to different strengthening that arises from interactions between dislocation and differentγ"variants.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2017YFA0303104 and2016YFA0300503the National Natural Science Foundation of China under Grant No 11774061the Chinese Government Scholarship of China Scholarship Council
文摘Time reversal symmetry(TRS)is a key symmetry for classification of unconventional superconductors,and the violation of TRS often results in a wealth of novel properties.Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr1-δPt4Ge12.The results from x-ray diffraction and magnetization measurements show that the[Pt4 Ge12]cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature Tc = 7.80 K.The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model,providing strong evidence of multi-band superconductivity.TRS breaking is observed using zero Held muon-spin relaxation experiments,and the magnitude of the spontaneous field is nearly half of that in PrPt4Ge12.
文摘Two-phase flow in porous media is a very active field of research,due to its important applications in groundwater pollution,CO_(2)sequestration,or oil and gas production from petroleum reservoirs,just to name a few of them.Fractional flow equations,which make use of Darcy's law,for describing the movement of two immiscible fluids in a porous medium,are among the most relevant mathematical models in reservoir simulation.This work aims to solve a fractional flow model formed by an elliptic equation,representing the spatial distribution of the pressure,and a hyperbolic equation describing the space-time evolution of water saturation.The numerical solution of the elliptic part is obtained using a finite-element(FE)scheme,while the hyperbolic equation is solved by means of two dif-ferent numerical approaches,both in the finite-volume(FV)framework.One is based on a monotonic upstream-centered scheme for conservation laws(MUSCL)-Hancock scheme,whereas the other makes use of a weighted essentially non-oscillatory(ENO)reconstruc-tion.In both cases,a first-order centered(FORCE)-αnumerical scheme is applied for inter-cell flux reconstruction,which constitutes a new contribution in the field of fractional flow models describing oil-water movement.A relevant feature of this work is the study of the effect of the parameterαon the numerical solution of the models considered.We also show that,in the FORCE-αmethod,when the parameterαincreases,the errors diminish and the order of accuracy is more properly attained,as verified using a manufactured solution technique.
基金the ISIS cryogenics Group for their valuable help during the μSR experiments (10.5286/ISIS.E.RB1820271)supported by the National Natural Science Foundation of China (Grant Nos.12034004 and 12174065)the Shanghai Municipal Science and Technology (Major Project Grant Nos.2019SHZDZX01 and 20ZR1405300)
文摘The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The existence of a small amount of Tm/Mg site-mixing disorder is revealed.DC magnetic susceptibility measurement shows that Tm^(3+)magnetic moments are antiferromagnetically correlated with a negative Curie-Weiss temperature of−26.3 K.Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility,and confirmed by μSR experiment down to 0.1 K.However,the emergence of short-range magnetic order is indicated by the zero-field μSR experiments,and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique.Compared with the results of Tm_(3)Sb_(3)Zn_(2)O_(14),another Tm-based Kagomé lattice with much more site-mixing disorder,the gapless spin liquid like behaviors in Tm_(3)Sb_(3)Zn_(2)O_(14)can be induced by disorder effect.Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.
