Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among th...Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).展开更多
Three-dimensional finite element(FE)models of carbon/epoxy composite laminates with copper mesh and aluminum mesh protection were established subjected to lightning strike,in which different mesh spacing was selected....Three-dimensional finite element(FE)models of carbon/epoxy composite laminates with copper mesh and aluminum mesh protection were established subjected to lightning strike,in which different mesh spacing was selected.Effectiveness of numerical method was verified and impulse current waveforms with different current peaks were applied according to aircraft lightning zones.Thermal-electrical material parameters varying with temperature were added into numerical models.Element deletion method was used to deal with lightning ablation elements of composite structures.The results show that ablation area and depth of composite laminates with metal mesh protection are significantly smaller,which proves good protection effectiveness of metal meshes on anti-lightning strike.The denser the mesh spacing,the better the anti-lightning strike will be.Protection of composite laminates with copper mesh has better effects than that of aluminum mesh.Considering the effect of mesh spacing variation on composite structural weight and anti-lightning strike,the ideal mesh spacing was obtained.展开更多
To address the main stumbling-block of bulk metallic glasses （BMGs）, i.e., room temperature brittleness, designing BMG matrix composites has been attracted extensive attention. Up to date, BMG composites in various ...To address the main stumbling-block of bulk metallic glasses （BMGs）, i.e., room temperature brittleness, designing BMG matrix composites has been attracted extensive attention. Up to date, BMG composites in various alloy systems have been successfully developed by forming crystalline phases embedded in the amorphous matrix through either ex-situ or in-situ methods. In this paper, a brief review of our recent work in this topic will be presented and the novel approaches to improving composite formability and mechanical properties will also be highlighted. The main purpose of this manuscript is not to offer a comprehensive review of all the BMG composites, but instead focuses will be placed on illustrating recently developed advanced BMG composites including Fe-based BMG composite with no metalloids, AI-based BMG composite and BMG composites reinforced by the TRIP （transformation-induced plasticity） effects. The basic ideas and related mechanisms underlying the development of these novel BMG composites will be discussed.展开更多
The theory of time scales,which unifies continuous and discrete analysis,provides a powerful mathematical tool for the study of complex dynamic systems.It enables us to understand more clearly the essential problems o...The theory of time scales,which unifies continuous and discrete analysis,provides a powerful mathematical tool for the study of complex dynamic systems.It enables us to understand more clearly the essential problems of continuous systems and discrete systems as well as other complex systems.In this paper,the theory of generalized canonical transformation for second-order Birkhoffian systems on time scales is proposed and studied,which extends the canonical transformation theory of Hamilton canonical equations.First,the condition of generalized canonical transformation for the second-order Birkhoffian system on time scales is established.Second,based on this condition,six basic forms of generalized canonical transformation for the second-order Birkhoffian system on time scales are given.Also,the relationships between new variables and old variables for each of these cases are derived.In the end,an example is given to show the application of the results.展开更多
In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar ...In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar collision species alternated frequently between 9644 Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr.In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data,STAR developed a three-step blind analysis procedure.Analysts are initially provided a"reference sample"of data,comprised of a mix of events from the two species,the order of which respects time-dependent changes in run conditions.After tuning analysis codes and performing time-dependent quality assurance on the reference sample,analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual≈30-min data-taking runs.For this sample,species-specific information is disguised,but individual output files contain data from a single isobar species.Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage.Following these modifications,the"frozen"code is passed over the fully un-blind data,completing the blind analysis.As a check of the feasibility of the blind analysis procedure,analysts completed a"mock data challenge,"analyzing data from Au+Au collisions at√^(S)NN=27 Ge V,collected in 2018.The Au+Au data were prepared in the same manner intended for the isobar blind data.The details of the blind analysis procedure and results from the mock data challenge are presented.展开更多
Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardeni...Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardening and shot peening, respectively, to reveal the mechanism of fatigue property improvement by microstructure characterization, microhardness measurement, residual stress analysis, roughness measurement, and rotary bending fatigue tests. The results indicate that both quenching and tempering treatment can effectively improve the fatigue properties of the modified axle steel. In addition, induction hardening can create an ideal hardened layer on the sample surface by phase transformation from the microstructure of ferrite and pearlite to martensite. By comparison, shot peening can modify the microstructure in surface layer by surface severe plastic deformation introducing a large number of dislocation and even cause grain refinement. Both induction hardening and shot peening create compressive residual stress into the surface layer of axle steel sample, which can effectively reduce the stress level applied to the metal surface during the rotary bending fatigue tests. On the whole, the contribution of induction hardening to the fatigue life of axle steel sample is better than that of the shot peening, and induction hardening shows obvious advantages in improving the fatigue life of axle steel.展开更多
The deformation mechanisms and the flow stress behavior of a medium-manganese high-carbon steel during cold deformation at a strain rate of 10×5 s^-1 were explored using a universal testing machine,an X-ray diffr...The deformation mechanisms and the flow stress behavior of a medium-manganese high-carbon steel during cold deformation at a strain rate of 10×5 s^-1 were explored using a universal testing machine,an X-ray diffractometer,a field emission scanning electron microscope and a high-resolution transmission electron microscope.The results show that continuous step-up serrated flow behavior appears after the yielding point,and the true stress-strain curve is roughly divided into five stages based on distinctive densities and amplitudes of serration.The strengthening mechanisms of the experimental steel involve Cottrell atmosphere,twinning-induced plasticity(TWIP)efect and transformation-induced plasticity(TRIP)effect.TWIP effect is the dominant deformation mechanism,and deformation twins formed by TWIP effect comprise primary,secondary and nanotwins.Furthermore,TRIP effect arises in the local high-strain region.Carbon element plays a key role in the transformation of the deformation mechanism.A small amount of carbide precipitates around twin boundaries lead to the formation of local carbon-poor regions,and Md temperature and stacking fault energy of medium-manganese high-carbon steel are propitious to the occurrence of TRIP effect.In addition,the contributions of various deformation mechanisms to plasticity are calculated,and that of TWIP effect is the greatest.展开更多
The isothermal single-stage compression of 35CrMo structural steel has been carried out by using Gleeble 1500 simulator at the temperature range of 950℃ to 1150℃ and strain rate range of 0.01s-1 to 10s-1. The effect...The isothermal single-stage compression of 35CrMo structural steel has been carried out by using Gleeble 1500 simulator at the temperature range of 950℃ to 1150℃ and strain rate range of 0.01s-1 to 10s-1. The effect of hot deformation parameters, such as strain rate, deformed temperature and initial grain size on the flow stress behavior was investigated. The activation energy of tested alloy was calculated, which is 378.16kJ/mol; The relationships between the peak stress (σp), the peak stain (εp), the critical strain (εc) and Z parameter were established. The micro structure evolution shows the pre-existing austenite grain boundaries constitute the principal nucleation sites for dynamic recrystallization (DRX), and the initial austenite grain size affects the grain size of DRX slightly. The kinetic mathematical model of DRX of 35CrMo is: XDRX=1-exp(-3.23-2.28) and Ddyn = 2.252× 10Z-0.22.展开更多
The stability and singularity problem of agile small satellite （ASS） with actuator failure is discussed in this paper. Firstly, the three-axis stabilized controller of an ASS is designed, where micro control moment ...The stability and singularity problem of agile small satellite （ASS） with actuator failure is discussed in this paper. Firstly, the three-axis stabilized controller of an ASS is designed, where micro control moment gyros （MCMG＇s） in pyramid configuration （PC） is used as the actuator. By using the same controller and steering law, the control results before and after one gyro fails are compared by simulation. The variation of singular momentum envelope before and after one gyro fails is also compared. The simulation results show that the failure intensively decreases the capacity of output torque, which leads to the emergence of more singular points and the rapid saturation of MCMG＇s. Finally, the parameters of system controller are changed to compare the control effect.展开更多
It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation mo...It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g., the secondary dendrite arm spacing(λ), cooling rate( ˙T) or actual solidification range(△T). This requirement disables these models for alloy solidification with no measured values for λ,˙T and △T. Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input,akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions(f_(s)) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e.,it allows the Lever rule solid fraction fsto be greater than one(f_(s)> 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until fsreaches about 0.9, beyond which(f_(s)> 0.9) its applicability is dictated by both the equilibrium solute partition coefcient(k) and the solute diffusion coefcient in the solid(Ds), which has been tabulated in detail.展开更多
A nonlocal elastic micro/nanobeam is theoretically modeled with the consideration of the surface elasticity, the residual surface stress, and the rotatory inertia,in which the nonlocal and surface effects are consider...A nonlocal elastic micro/nanobeam is theoretically modeled with the consideration of the surface elasticity, the residual surface stress, and the rotatory inertia,in which the nonlocal and surface effects are considered. Three types of boundary conditions, i.e., hinged-hinged, clamped-clamped, and clamped-hinged ends, are examined. For a hinged-hinged beam, an exact and explicit natural frequency equation is derived based on the established mathematical model. The Fredholm integral equation is adopted to deduce the approximate fundamental frequency equations for the clamped-clamped and clamped-hinged beams. In sum, the explicit frequency equations for the micro/nanobeam under three types of boundary conditions are proposed to reveal the dependence of the natural frequency on the effects of the nonlocal elasticity, the surface elasticity, the residual surface stress, and the rotatory inertia, providing a more convenient means in comparison with numerical computations.展开更多
Spherical nanoindentation of an iron-chromium-aluminum alloy was conducted to study the effect of ferric-ion(Fe 3+)irradiation on the time-dependent plasticity behavior in the surface layers of this alloy.It was obser...Spherical nanoindentation of an iron-chromium-aluminum alloy was conducted to study the effect of ferric-ion(Fe 3+)irradiation on the time-dependent plasticity behavior in the surface layers of this alloy.It was observed that the initiation of plasticity by the appearance of displacement burst or“pop-in”event occurred after a period of waiting time in the apparent elastic regime and that Fe^(3+)irradiation at 360°C and up to∼0.5 displacements per atom could make it happen under the lower applied loads but with a reduced magnitude.Through the experimental data,an activation volume and activation energy were extracted for the delayed plasticity.The results show that Fe^(3+)-irradiation significantly reduced its acti-vation volume from∼3.05 b 3 to∼1.75 b 3(where b=Burgers vector),but slightly increased its activation energy from∼0.65 to∼0.71 eV.On the other hand,high-resolution scanning transmission electron mi-croscopy observations reveal that the irradiation at the elevated temperature created interstitial atom pair onto the(100)habit plane that can serve as the nucleation site of a100dislocation loop while elim-inating the pre-existing dislocations.Consequently,it is indicated that heterogeneous nucleation of the dislocation loop was predominant in the delayed plasticity initiation of this alloy and that the nucleation of the interstitial-type dislocation loop was involved due to Fe^(3+)-irradiation.展开更多
The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk ...The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk materials can be very severe,particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features.Here,we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones.The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise.The information in the missing wedge can be partly recovered by this technique.Thus,both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image.Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography,in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.展开更多
The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A d...The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A double-layer skin tissue model embedded with a single blood vessel was established,and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent.808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the e®ect of optical clearing agents(OCAs)on photon deposition in tissues.Results show that the photon energy deposition density in the epidermis increases with the amount of tissue°uid replaced by OCA.Compared with glucose solution,polyethylene glycol 400(PEG 400)and glycerol can considerably increase the average penetration depth of photons in the skin tissue,thereby raising the sampling depth of the LSI.After the action of glycerol,PEG 400,and glucose,the average photon penetration depth is increased by 51.78%,51.06%,and 21.51%for 808nm,68.93%,67.94%,and 26.67%for 632.8 nm lasers,respectively.In vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood°ow rate,whereas PEG 400 can signicantly improve the capability of light penetration without a®ecting blood velocity,which exhibits considerable potential in the monitoring of blood°ow in skin tissues.展开更多
A three-dimensional incompressible annular jet is simulated by the large eddy simulation(LES)method at a Reynolds number Re=8500.The time-averaged velocity field shows an asymmetric wake behind the central bluff-body ...A three-dimensional incompressible annular jet is simulated by the large eddy simulation(LES)method at a Reynolds number Re=8500.The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric.The proper orthogonal decomposition(POD)analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow.The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1%of the turbulent kinetic energy,and hence their impact on the wake dynamics is studied.The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point.The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction.In addition,the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.展开更多
An educational intervention targeting medical students and aiming to develop skills useful to the writing of a health science research protocol over a short period of time has been developed in the Shanghai Jiao Tong ...An educational intervention targeting medical students and aiming to develop skills useful to the writing of a health science research protocol over a short period of time has been developed in the Shanghai Jiao Tong University School of Medicine. The methodology blending the principles of PBL and TBL is detailed and key issues of this implementation are discussed. Twenty-one students were enrolled in a research master degree and participated to three mandatory 180-minutes sessions. Beyond classical skills useful to solve a problem, this new intervention focused on the transformation of knowledge to create an authentic content, which is a feature of the project-based learning(PBL). The training process was designed according to team-based learning(TBL) procedure except that work sharing between groups and pooling resources and outcomes of each group allowed the construction of one final class original research project in the field of respiratory pharmacology. The combination of both learning methods allowed promoting individual and group accountability necessary to improve self-learning and the quality of the final joint project. The peer reviewing was an essential factor in creating the students' motivation and improving of team discussion. The grades individually assigned for skills and quality of the project by an external teacher suggested that key objectives of the intervention were reached. In conclusion, the educational intervention described in this paper appears as an appropriate method to develop specific skills necessary to write and discuss a research project within a research team.Further works are necessary to measure the degree of satisfaction of students and improvement of performance.展开更多
FeGa thin film has been deposited on（100）-oriented GaAs and（001）-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system.Materials st...FeGa thin film has been deposited on（100）-oriented GaAs and（001）-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system.Materials structure and static magnetic of FeGa film have great changes depending on the substrate and energy density of pulsed laser.X-ray diffraction reveals the presence of first-order order–disorder structure ofgrain phase and disordered bcc A2 structure on GaAs substrate.The coercivity and remanence of FeGa film on GaAs substrate ratio show a regular dependence on the thickness and energy densities.However,film on Si substrate did not exhibit structure change,which can be attributed to a large lattice mismatch between FeGa and Si.展开更多
The cooling rate during vitrification is critical for determining the mechanical properties of metallic glasses.However,the structural origin of the cooling rate effect on mechanical behaviors is unclear.In this work,...The cooling rate during vitrification is critical for determining the mechanical properties of metallic glasses.However,the structural origin of the cooling rate effect on mechanical behaviors is unclear.In this work,a systematical investigation of the cooling rate effect on the deformation mode,shear band nucleation,and nanoscale heterogeneous structure was conducted in three Fe-based metallic glasses.The brittle to ductile deformation transition was observed when increasing the cooling rate.Meanwhile,the governing shear band nucleation site from high load site to low load site appears the synchronous tran-sition.By studying the corresponding nanoscale heterogeneous structure,it was found that nanoscale viscoelastic transition from solid-like to liquid-like as increasing cooling rate enables ductile deformation.The current work not only reveals the nanoscale structural origin of the cooling rate effect on the de-formation behaviors,but also provides a new route to design ductile metallic glasses by freezing more nanoscale liquid-like regions during cooling.展开更多
基金supported by the National Nature Science Foundation of China[Grant Nos.92365204 and 12274298(Z.K.Liu)]the National Key R&D program of China[Grant No.2022YFA1604400/03(Z.K.Liu)]Zhangjiang Laboratory(Y.M.Zhang).The authors thank BL02B at the Shanghai Synchrotron Radiation Facility supported by the National Natural Science Foundation of China(Contract No.11227902).
文摘Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).
基金supported financially by the National Natural Science Foundation of China (No.51875463)the Natural Science Basic Research Plan in Shaanxi Province of China (No.2018JM1001)the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University (No.ZZ2018107)
文摘Three-dimensional finite element(FE)models of carbon/epoxy composite laminates with copper mesh and aluminum mesh protection were established subjected to lightning strike,in which different mesh spacing was selected.Effectiveness of numerical method was verified and impulse current waveforms with different current peaks were applied according to aircraft lightning zones.Thermal-electrical material parameters varying with temperature were added into numerical models.Element deletion method was used to deal with lightning ablation elements of composite structures.The results show that ablation area and depth of composite laminates with metal mesh protection are significantly smaller,which proves good protection effectiveness of metal meshes on anti-lightning strike.The denser the mesh spacing,the better the anti-lightning strike will be.Protection of composite laminates with copper mesh has better effects than that of aluminum mesh.Considering the effect of mesh spacing variation on composite structural weight and anti-lightning strike,the ideal mesh spacing was obtained.
基金supported in part by the National Natural Science Foundation of China (Nos. 51010001, 51371003, 51001009 and 51271212)111 Project (No. B07003)+2 种基金Program for Changjiang Scholars and Innovative Research Team in Universityfinancial support from the Fundamental Research Funds for the Central Universities (Nos. FRF-SD-12-005A and FRF-TP-11-005A)financial support from the Research Project of State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing (No. 2011Z-13)
文摘To address the main stumbling-block of bulk metallic glasses （BMGs）, i.e., room temperature brittleness, designing BMG matrix composites has been attracted extensive attention. Up to date, BMG composites in various alloy systems have been successfully developed by forming crystalline phases embedded in the amorphous matrix through either ex-situ or in-situ methods. In this paper, a brief review of our recent work in this topic will be presented and the novel approaches to improving composite formability and mechanical properties will also be highlighted. The main purpose of this manuscript is not to offer a comprehensive review of all the BMG composites, but instead focuses will be placed on illustrating recently developed advanced BMG composites including Fe-based BMG composite with no metalloids, AI-based BMG composite and BMG composites reinforced by the TRIP （transformation-induced plasticity） effects. The basic ideas and related mechanisms underlying the development of these novel BMG composites will be discussed.
基金supported by the National Natural Science Foundation of China(Grants 11972241 and 11572212)
文摘The theory of time scales,which unifies continuous and discrete analysis,provides a powerful mathematical tool for the study of complex dynamic systems.It enables us to understand more clearly the essential problems of continuous systems and discrete systems as well as other complex systems.In this paper,the theory of generalized canonical transformation for second-order Birkhoffian systems on time scales is proposed and studied,which extends the canonical transformation theory of Hamilton canonical equations.First,the condition of generalized canonical transformation for the second-order Birkhoffian system on time scales is established.Second,based on this condition,six basic forms of generalized canonical transformation for the second-order Birkhoffian system on time scales are given.Also,the relationships between new variables and old variables for each of these cases are derived.In the end,an example is given to show the application of the results.
文摘In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar collision species alternated frequently between 9644 Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr.In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data,STAR developed a three-step blind analysis procedure.Analysts are initially provided a"reference sample"of data,comprised of a mix of events from the two species,the order of which respects time-dependent changes in run conditions.After tuning analysis codes and performing time-dependent quality assurance on the reference sample,analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual≈30-min data-taking runs.For this sample,species-specific information is disguised,but individual output files contain data from a single isobar species.Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage.Following these modifications,the"frozen"code is passed over the fully un-blind data,completing the blind analysis.As a check of the feasibility of the blind analysis procedure,analysts completed a"mock data challenge,"analyzing data from Au+Au collisions at√^(S)NN=27 Ge V,collected in 2018.The Au+Au data were prepared in the same manner intended for the isobar blind data.The details of the blind analysis procedure and results from the mock data challenge are presented.
基金financially supported by the National Key Research and Development Project(No.2017YFB0703004)the National Natural Science Foundation of China(NSFC,No.U1664253)the LiaoNing Revitalization Talents Program(No.XLYC1808027)。
文摘Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardening and shot peening, respectively, to reveal the mechanism of fatigue property improvement by microstructure characterization, microhardness measurement, residual stress analysis, roughness measurement, and rotary bending fatigue tests. The results indicate that both quenching and tempering treatment can effectively improve the fatigue properties of the modified axle steel. In addition, induction hardening can create an ideal hardened layer on the sample surface by phase transformation from the microstructure of ferrite and pearlite to martensite. By comparison, shot peening can modify the microstructure in surface layer by surface severe plastic deformation introducing a large number of dislocation and even cause grain refinement. Both induction hardening and shot peening create compressive residual stress into the surface layer of axle steel sample, which can effectively reduce the stress level applied to the metal surface during the rotary bending fatigue tests. On the whole, the contribution of induction hardening to the fatigue life of axle steel sample is better than that of the shot peening, and induction hardening shows obvious advantages in improving the fatigue life of axle steel.
基金The authors gratefully appreciate the financial support by the National Natural Science Foundation of China(Grant Nos.U1860201 and U1960115)the Basic Research Program of Key Laboratory of Liaoning Province(LZ2015035).
文摘The deformation mechanisms and the flow stress behavior of a medium-manganese high-carbon steel during cold deformation at a strain rate of 10×5 s^-1 were explored using a universal testing machine,an X-ray diffractometer,a field emission scanning electron microscope and a high-resolution transmission electron microscope.The results show that continuous step-up serrated flow behavior appears after the yielding point,and the true stress-strain curve is roughly divided into five stages based on distinctive densities and amplitudes of serration.The strengthening mechanisms of the experimental steel involve Cottrell atmosphere,twinning-induced plasticity(TWIP)efect and transformation-induced plasticity(TRIP)effect.TWIP effect is the dominant deformation mechanism,and deformation twins formed by TWIP effect comprise primary,secondary and nanotwins.Furthermore,TRIP effect arises in the local high-strain region.Carbon element plays a key role in the transformation of the deformation mechanism.A small amount of carbide precipitates around twin boundaries lead to the formation of local carbon-poor regions,and Md temperature and stacking fault energy of medium-manganese high-carbon steel are propitious to the occurrence of TRIP effect.In addition,the contributions of various deformation mechanisms to plasticity are calculated,and that of TWIP effect is the greatest.
基金supported by the National Natural Science Foundation of China(Grant No.50075053).
文摘The isothermal single-stage compression of 35CrMo structural steel has been carried out by using Gleeble 1500 simulator at the temperature range of 950℃ to 1150℃ and strain rate range of 0.01s-1 to 10s-1. The effect of hot deformation parameters, such as strain rate, deformed temperature and initial grain size on the flow stress behavior was investigated. The activation energy of tested alloy was calculated, which is 378.16kJ/mol; The relationships between the peak stress (σp), the peak stain (εp), the critical strain (εc) and Z parameter were established. The micro structure evolution shows the pre-existing austenite grain boundaries constitute the principal nucleation sites for dynamic recrystallization (DRX), and the initial austenite grain size affects the grain size of DRX slightly. The kinetic mathematical model of DRX of 35CrMo is: XDRX=1-exp(-3.23-2.28) and Ddyn = 2.252× 10Z-0.22.
基金the National Natural Science Foundation of China (10502006)Excellent Young Scholars Research Fund of Beijing Institute of Technology (2007YS0202)
文摘The stability and singularity problem of agile small satellite （ASS） with actuator failure is discussed in this paper. Firstly, the three-axis stabilized controller of an ASS is designed, where micro control moment gyros （MCMG＇s） in pyramid configuration （PC） is used as the actuator. By using the same controller and steering law, the control results before and after one gyro fails are compared by simulation. The variation of singular momentum envelope before and after one gyro fails is also compared. The simulation results show that the failure intensively decreases the capacity of output torque, which leads to the emergence of more singular points and the rapid saturation of MCMG＇s. Finally, the parameters of system controller are changed to compare the control effect.
基金funding from the Australian Research Council(ARC) via DP180103205。
文摘It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g., the secondary dendrite arm spacing(λ), cooling rate( ˙T) or actual solidification range(△T). This requirement disables these models for alloy solidification with no measured values for λ,˙T and △T. Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input,akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions(f_(s)) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e.,it allows the Lever rule solid fraction fsto be greater than one(f_(s)> 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until fsreaches about 0.9, beyond which(f_(s)> 0.9) its applicability is dictated by both the equilibrium solute partition coefcient(k) and the solute diffusion coefcient in the solid(Ds), which has been tabulated in detail.
基金School of Civil and Environmental Engineering at Nanyang Technological University, Singapore for kindly supporting this research topic.
文摘A nonlocal elastic micro/nanobeam is theoretically modeled with the consideration of the surface elasticity, the residual surface stress, and the rotatory inertia,in which the nonlocal and surface effects are considered. Three types of boundary conditions, i.e., hinged-hinged, clamped-clamped, and clamped-hinged ends, are examined. For a hinged-hinged beam, an exact and explicit natural frequency equation is derived based on the established mathematical model. The Fredholm integral equation is adopted to deduce the approximate fundamental frequency equations for the clamped-clamped and clamped-hinged beams. In sum, the explicit frequency equations for the micro/nanobeam under three types of boundary conditions are proposed to reveal the dependence of the natural frequency on the effects of the nonlocal elasticity, the surface elasticity, the residual surface stress, and the rotatory inertia, providing a more convenient means in comparison with numerical computations.
基金supported by the National Natural Science Foundation of China(grant Nos.52122103 and 51971207)Shenzhen-Hong Kong Science and Technology Innovation Cooper-ation Zone Shenzhen Park Project:HZQB-KCZYB-2020030.
文摘Spherical nanoindentation of an iron-chromium-aluminum alloy was conducted to study the effect of ferric-ion(Fe 3+)irradiation on the time-dependent plasticity behavior in the surface layers of this alloy.It was observed that the initiation of plasticity by the appearance of displacement burst or“pop-in”event occurred after a period of waiting time in the apparent elastic regime and that Fe^(3+)irradiation at 360°C and up to∼0.5 displacements per atom could make it happen under the lower applied loads but with a reduced magnitude.Through the experimental data,an activation volume and activation energy were extracted for the delayed plasticity.The results show that Fe^(3+)-irradiation significantly reduced its acti-vation volume from∼3.05 b 3 to∼1.75 b 3(where b=Burgers vector),but slightly increased its activation energy from∼0.65 to∼0.71 eV.On the other hand,high-resolution scanning transmission electron mi-croscopy observations reveal that the irradiation at the elevated temperature created interstitial atom pair onto the(100)habit plane that can serve as the nucleation site of a100dislocation loop while elim-inating the pre-existing dislocations.Consequently,it is indicated that heterogeneous nucleation of the dislocation loop was predominant in the delayed plasticity initiation of this alloy and that the nucleation of the interstitial-type dislocation loop was involved due to Fe^(3+)-irradiation.
基金financially supported by the National Natural Science Foundation of China(Nos.51831004,11904093,11427806,51671082,51471067)the National Key Research and Development Program of China(No.2016YFB0300801)+2 种基金the Major Science and Technology Program of Changsha(kq1804010)the National Key Laboratory Foundation of National Defense Science and Technology(No.6142907190402)financial support from Aid Program for Innovative Group of National University of Defense Technology。
文摘The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality.The artifacts produced in tomographic reconstruction of bulk materials can be very severe,particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features.Here,we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones.The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise.The information in the missing wedge can be partly recovered by this technique.Thus,both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image.Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography,in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.
基金supported by the National Natural Science Foundation of China(Grant No.51727811).
文摘The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A double-layer skin tissue model embedded with a single blood vessel was established,and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent.808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the e®ect of optical clearing agents(OCAs)on photon deposition in tissues.Results show that the photon energy deposition density in the epidermis increases with the amount of tissue°uid replaced by OCA.Compared with glucose solution,polyethylene glycol 400(PEG 400)and glycerol can considerably increase the average penetration depth of photons in the skin tissue,thereby raising the sampling depth of the LSI.After the action of glycerol,PEG 400,and glucose,the average photon penetration depth is increased by 51.78%,51.06%,and 21.51%for 808nm,68.93%,67.94%,and 26.67%for 632.8 nm lasers,respectively.In vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood°ow rate,whereas PEG 400 can signicantly improve the capability of light penetration without a®ecting blood velocity,which exhibits considerable potential in the monitoring of blood°ow in skin tissues.
文摘A three-dimensional incompressible annular jet is simulated by the large eddy simulation(LES)method at a Reynolds number Re=8500.The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric.The proper orthogonal decomposition(POD)analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow.The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1%of the turbulent kinetic energy,and hence their impact on the wake dynamics is studied.The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point.The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction.In addition,the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.
文摘An educational intervention targeting medical students and aiming to develop skills useful to the writing of a health science research protocol over a short period of time has been developed in the Shanghai Jiao Tong University School of Medicine. The methodology blending the principles of PBL and TBL is detailed and key issues of this implementation are discussed. Twenty-one students were enrolled in a research master degree and participated to three mandatory 180-minutes sessions. Beyond classical skills useful to solve a problem, this new intervention focused on the transformation of knowledge to create an authentic content, which is a feature of the project-based learning(PBL). The training process was designed according to team-based learning(TBL) procedure except that work sharing between groups and pooling resources and outcomes of each group allowed the construction of one final class original research project in the field of respiratory pharmacology. The combination of both learning methods allowed promoting individual and group accountability necessary to improve self-learning and the quality of the final joint project. The peer reviewing was an essential factor in creating the students' motivation and improving of team discussion. The grades individually assigned for skills and quality of the project by an external teacher suggested that key objectives of the intervention were reached. In conclusion, the educational intervention described in this paper appears as an appropriate method to develop specific skills necessary to write and discuss a research project within a research team.Further works are necessary to measure the degree of satisfaction of students and improvement of performance.
基金financially supported by the National Youth Natural Science Foundation (nos. 61601293 and 61404085)the Yangfan Plan of Shanghai Youth Science and Technology Talents (no. 15YF408800)the National Natural Science Foundation of China (nos. 11574214, 61376010)
文摘FeGa thin film has been deposited on（100）-oriented GaAs and（001）-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system.Materials structure and static magnetic of FeGa film have great changes depending on the substrate and energy density of pulsed laser.X-ray diffraction reveals the presence of first-order order–disorder structure ofgrain phase and disordered bcc A2 structure on GaAs substrate.The coercivity and remanence of FeGa film on GaAs substrate ratio show a regular dependence on the thickness and energy densities.However,film on Si substrate did not exhibit structure change,which can be attributed to a large lattice mismatch between FeGa and Si.
基金supported by the National Natural Science Foun-dation of China(Nos.52201194,52222105,52261028,52001269,92163108,52231006)the 3315 Innovation Youth Talent in Ningbo City(No.2021A123G)+3 种基金the Youth Innovation Promotion Association CAS(No.2019296)the Zhejiang Provincial Natural Science Foun-dation of China(No.LR22E010004)the Zhejiang Provincial Natu-ral Science Foundation Regional Innovation and Development Joint Foundation with Quzhou City(No.LZY23E010002)the Nat-ural Science Foundation of Xinjiang Uygur Autonomous Region of China(No.2022D01C383).
文摘The cooling rate during vitrification is critical for determining the mechanical properties of metallic glasses.However,the structural origin of the cooling rate effect on mechanical behaviors is unclear.In this work,a systematical investigation of the cooling rate effect on the deformation mode,shear band nucleation,and nanoscale heterogeneous structure was conducted in three Fe-based metallic glasses.The brittle to ductile deformation transition was observed when increasing the cooling rate.Meanwhile,the governing shear band nucleation site from high load site to low load site appears the synchronous tran-sition.By studying the corresponding nanoscale heterogeneous structure,it was found that nanoscale viscoelastic transition from solid-like to liquid-like as increasing cooling rate enables ductile deformation.The current work not only reveals the nanoscale structural origin of the cooling rate effect on the de-formation behaviors,but also provides a new route to design ductile metallic glasses by freezing more nanoscale liquid-like regions during cooling.
