Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils shou...Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.展开更多
Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core,lithosphere,ocean,ionosphere,and magnetosphere,and also from field-aligned currents ...Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core,lithosphere,ocean,ionosphere,and magnetosphere,and also from field-aligned currents coupling the ionosphere and magnetosphere—the meridional currents that connect the two hemispheres and the induced currents due to the variations of fields over time.The fluctuation of magnetic fields generated by these highly dynamic space currents greatly limits the accuracy of the geomagnetic models.In order to better accomplish the scientific objectives of Macao Science Satellite-1(MSS-1),and to improve existing geomagnetic field models,we present here for the first time a self-consistent coupling of solar wind,magnetosphere,and ionosphere,which represents the most developed numerical simulation method for space physics research so far,making it possible to quantify the contribution of different current systems to the total observed magnetic field(B).The results show that numerical simulation can capture main magnetic disturbance characteristics with significant precision.Partial ring current is a major contributor to the latitudinal magnetic perturbation near the equator.Magnetopause and magnetotail currents affect the radial magnetic perturbation around the mid-latitudes.Field-aligned and Pedersen currents produce significant longitudinal and latitudinal magnetic perturbations at high latitudes.展开更多
A stochastic wheelset model with a nonlinear wheel-rail contact relationship is established to investigate the stochastic stability and stochastic bifurcation of the wheelset system with the consideration of the stoch...A stochastic wheelset model with a nonlinear wheel-rail contact relationship is established to investigate the stochastic stability and stochastic bifurcation of the wheelset system with the consideration of the stochastic parametric excitations of equivalent conicity and suspension stiffness.The wheelset is systematized into a onedimensional(1D)diffusion process by using the stochastic average method,the behavior of the singular boundary is analyzed to determine the hunting stability condition of the wheelset system,and the critical speed of stochastic bifurcation is obtained.The stationary probability density and joint probability density are derived theoretically.Based on the topological structure change of the probability density function,the stochastic Hopf bifurcation form and bifurcation condition of the wheelset system are determined.The effects of stochastic factors on the hunting stability and bifurcation characteristics are analyzed,and the simulation results verify the correctness of the theoretical analysis.The results reveal that the boundary behavior of the diffusion process determines the hunting stability of the stochastic wheelset system,and the left boundary characteristic value cL=1 is the critical state of hunting stability.Besides,stochastic D-bifurcation and P-bifurcation will appear in the wheelset system,and the critical speeds of the two kinds of stochastic bifurcation decrease with the increase in the stochastic parametric excitation intensity.展开更多
Common strategies for catalytic graphitization of biochar into graphitic porous carbon(GPC)still face great challenges,such as the realization of simple procedures,energy conservation,and green processes.Controlling o...Common strategies for catalytic graphitization of biochar into graphitic porous carbon(GPC)still face great challenges,such as the realization of simple procedures,energy conservation,and green processes.Controlling over the graphitization degree and pore structure of biochar is the key to its structural diversification.Herein,a clean and energy-efficient method is developed to synthesize adjustable graphitic degree and structure porosity GPC from rice husk-based carbon(RHC)at a relatively low temperature of 800–1000°C with environment-benign organometallic catalyst ethylenediaminetetraacetic acid ferric sodium salt(EDTA-iron)and the recovery ratio of catalyst is as high as 97%.The formed by the organic ligands of EDTA-iron facilitates the etching of RHC surface and pore by iron,resulting in highly graphitized and developed porous GPCs.The pore structure and graphitization degree of GPCs can be adjusted by altering the catalyst loading,temperature,and holding time.The catalyst EDTA-iron with a lower concentration mainly plays the role of etching,which promotes the formation of porous carbon with larger surface area(SBET=1187.2 m^(2)·g^(-1)).The catalyst with higher concentration mainly plays the role of catalyzing graphitization and promotes the obtaining of graphitic carbon with high graphitization degree(ID/IG=0.19).The mechanism of EDTA-iron catalyzed graphitization of RHC is explored by the comprehensive analysis of BET,XRD,Raman,TEM and TGA.This research not only provides an efficient method for the preparation of high-quality biomass-based graphite carbon,but also provides a feasible method for the preparation of biomass-based porous carbon.展开更多
Adsorption dynamics of ethane in two granular fixed beds and structured fixed beds with microfibrous composites was studied.5A zeolite membrane 5A/PSSF(paper-like sintered stainless steel fiber)and microfibrous entrap...Adsorption dynamics of ethane in two granular fixed beds and structured fixed beds with microfibrous composites was studied.5A zeolite membrane 5A/PSSF(paper-like sintered stainless steel fiber)and microfibrous entrapped activated carbon(MEAC)composites were prepared by wet layup papermaking/sintering technique and in-situ hydrothermal method.Microfibrous composites were characterized by X-ray diffraction,scanning electron microscopy and N2 adsorption/desorption.Structured fixed beds were designed by filling granular adsorbents(5A zeolite or activated carbon)and microfibrous composites at the inlet and outlet of the beds,respectively.Effects of flow rate,bed height and structure on the breakthrough curves were investigated.The length of unused bed(LUB)was determined,and Yoon–Nelson model was used to fit the breakthrough curves.The experimental results showed ethane was effectively adsorbed on the granular adsorbents and microfibrous composites.Both composites could decrease the LUB values and enhance bed utilization.All breakthrough curves fitted well to Yoon–Nelson model,with correlation coefficient exceeding 0.89.The adsorption rate of ethane could be improved in the structured fixed beds,which showed an enhanced mass transfer efficiency for ethane adsorption.LUB values of structured fixed beds with 5A/PSSF composites were larger,the bed utilization values were lower,and the adsorption rate constants were higher than those with MEAC composites under the same conditions.展开更多
The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_...The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage.A negative magnetoresistance is observed first in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)tunnel junctions,where the resistance with antiparallel aligned magnetization of two Fe_(3)GeTe_(2)electrodes is lower than that with parallel alignment,which is due to the opposite spin polarizations of two Fe_(3)GeTe_(2)electrodes.With the bias voltage increasing,the spin polarization of the biased Fe_(3)GeTe_(2)electrode is changed so that the spin orientations of two Fe_(3)GeTe_(2)electrodes are the same.Our experimental observations are supported by the calculated spin-dependent density of states for Fe_(3)GeTe_(2)electrodes under a finite bias.The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.展开更多
The jasmonic acid(JA)signaling pathway is involved in plant growth,development,and response to abiotic or biotic stresses.MYC2,a bHLH transcription factor,is a regulatory hub in the pathway.The function of ZmMYC7,a pu...The jasmonic acid(JA)signaling pathway is involved in plant growth,development,and response to abiotic or biotic stresses.MYC2,a bHLH transcription factor,is a regulatory hub in the pathway.The function of ZmMYC7,a putative MYC2 ortholog,in jasmonate-signaled defense responses of maize has not been reported.In this study,we found that ZmMYC7 possesses JID,TAD,bHLH and Zip domains and essential characteristics of transcription factors:a nuclear location and transactivation activity.The ZmMYC7mutants showed markedly increased sensitivity to Fusarium graminearum and Setosphaeria turcica.The expression levels of the defense-associated genes ZmPR1,ZmPR2,ZmPR3,ZmPR5,ZmPR6,and ZmPR7 in response to F.graminearum infection were downregulated in ZmMYC7 mutants,while ZmPR4 and ZmPR10 were up-regulated.ZmMYC7 interacted with members of the ZmJAZ family,including ZmJAZ8,ZmJAZ11,and ZmJAZ12.ZmMYC7 physically interacted with G-box cis-elements in the ZmERF147 promoter in vitro and transcriptional activation of ZmERF147 by ZmMYC7 was inhibited by ZmJAZ11 and ZmJAZ12.ZmERF147 mutants were more susceptible to F.graminearum infection than inbred line B73with concomitant down-regulation of all defense-associated ZmPRs except ZmPR4.These findings indicate that ZmMYC7 functions in maize resistance to F.graminearum and sheds light on maize defense responses to pathogenic fungi via the JA signaling pathway.展开更多
Thermogenic features are often invoked to illustrate animal’s colonization,distribution,and response to climate change.To understand why the White-browed Laughingthrush(Pterorhinus sannio)has expanded its distributio...Thermogenic features are often invoked to illustrate animal’s colonization,distribution,and response to climate change.To understand why the White-browed Laughingthrush(Pterorhinus sannio)has expanded its distribution to temperate zones in recent years,we compared its thermogenic features with three species of songbirds that cooccur in its newly colonized areas.Thermogenic parameters of these four species were measured under different ambient temperatures,ranging from 0 to 40℃.The results showed that basal metabolic rate(BMR)was 44.5±3.9 mL O2/h in P.sannio,which is lower than predicted value by its body weight.This is also lower than the BMR of both its temperate congener the Plain Laughingthrush(P.davidi)and the montane,similar species Elliot’s Laughingthrush(Trochalopteron elliotii).The thermal neutral zone(TNZ)in P.sannio was 15-35℃,as compared to 10-27.5℃in P.davidi,25-30℃in T.elliotii,and 7.5-32.5℃in the Green-capped Greenfinch(Chloris sinica).Thermal conductance was lowest in P.sannio,with the minimum value lower than the predicted value based on its body weight.Our results showed that the northward-colonizing P.sannio exhibited different thermogenic characteristics compared with its coexisting species in the new habitat,even its congener P.davidi,which shared similar microhabitats to P.sannio.We suggest that researchers further explore the physiological mechanisms of birds’northward expansion.展开更多
Foam drainage is theflow of liquid through the interstitial spaces between bubbles driven by capillarity and grav-ity and resisted by viscous damping.The so-called foam drainage gas recovery technology is a technique ...Foam drainage is theflow of liquid through the interstitial spaces between bubbles driven by capillarity and grav-ity and resisted by viscous damping.The so-called foam drainage gas recovery technology is a technique tradi-tionally used to mitigate the serious bottom-hole liquid loading in the middle and late stages of gas well production.In this context,determining the optimal concentration of the bubble drainage agent is generally cru-cial for the proper application of this method.In this study,a combination of indoor experiments and theoretical analysis have been used to determine the pressure drop related to the foam-carrying capacity in a representative gasfield.Dynamic and static experiments were designed with a bubble drainage agent concentration varying in the range 0.3%–0.6%.Using thefield formation water data,the optimal soaking agent concentration was obtained and pressure drop test experiments on the foam carrying capacity were conducted accordingly.These tests have revealed that the optimal foam displacement agent concentration is 0.5%,and the foam quality at the optimum concentration is between 0.78–0.98.A theoretical method for calculating the pressure drop at the optimum soak-away concentration based on experimental data has also been introduced.The error of the proposed method is within 15%compared to the experimental measured value,demonstrating that it is highly accurate and simple.展开更多
The Earth’s“lithosphere”is its outer shell,made up of the Earth’s crust and outermost mantle.The part of the Earth’s magnetic field that originates in the lithosphere consists of a superposition of magnetic anoma...The Earth’s“lithosphere”is its outer shell,made up of the Earth’s crust and outermost mantle.The part of the Earth’s magnetic field that originates in the lithosphere consists of a superposition of magnetic anomalies with a broad spectrum of sizes and intensities,which arise from geological and tectonic features.The lithospheric magnetic field is known from surface observations,and on larger scales from above-surface measurements.The increase in recent decades of satellites dedicated to measuring the Earth’s magnetic field has improved significantly our models of the Earth’s magnetic environment.Based on these increasing observations,a number of comprehensive field models have been constructed,some of which focus solely on the lithosphere,such as the MF model series.We present a map of lithospheric magnetic anomalies at 400 km altitude,based on a vertically integrated magnetization model.This height was chosen because it is the expected orbital altitude of the Macao Science Satellite-1(MSS-1)mission.The model presented herein indicates that the amplitude of the lithospheric anomalies at 400 km altitude is between-14.8 n T and 18.2 n T.This information is useful because it provides a reference for the lithospheric source of the Earth’s magnetic field that contributes to the magnetic measurements made from satellite instruments.The low inclination orbit of the MSS-1 mission will provide information that is sensitive to lateral variation within the lithosphere;these variations arise from plate tectonic features with longitudinal extent.In conclusion,the new MSS-1mission will provide valuable information in detecting compositional variations in the lithosphere,and in delineating large-scale geological structures.展开更多
The Euler angle estimation is a calibration method for vector data measured by the magnetometer on a satellite.It is used to find the relative rotation between the coordinate system of the magnetometer and the satelli...The Euler angle estimation is a calibration method for vector data measured by the magnetometer on a satellite.It is used to find the relative rotation between the coordinate system of the magnetometer and the satellite(usually determined by Star Imagers).Before launch of the low-orbit,low-inclination Macao Science Satellite-1(known as MSS-1),we simulated the estimation of Euler angles by using the magnetic measurements of the in-orbit Swarm and China Seismo-Electromagnetic Satellite(noted as CSES),with various data combinations.In this study,11 data sets were designed to analyze the estimation results for the MSS-1 orbit by using a joint estimation method of the geomagnetic field model parameters and Euler angles.For the model results,we found that all the spatial power spectral lines showed behavior consistent with that of the CHAOS-7.8 model at low degrees(corresponding to large-scale magnetic signals).The spectra of models without global data coverage deviated much more(by a maximum of~10^(4) nT^(2))from those of the CHAOS-7.8 model at higher degrees.For models with global data coverage and with various data combinations,the spectral lines were distributed similarly.Moreover,the models with accordant power spectral distributions demonstrated different Euler angle estimations.As more vector data at higher latitudes were included,the estimated Euler angles varied monotonically in all three directions.The models with vector data in the same latitude range showed similar Euler angle results,regardless of whether the poleward scalar data were included.The largest value difference was found between the models using vector data within±40°latitudes and those using vector data within±60°latitudes,which reached to~28″.Therefore,we concluded that the inversion of the spherical harmonic Gauss coefficients in our tests was mainly affected by the spatial coverage range of the data,whereas the estimation of Euler angles largely depended on the latitude range where the vector data could be obtained.These results can be used for future in-flight data testing.We expect the estimation of Euler angles to improve as other methods are adopted.展开更多
In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it ...In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU(2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb_(3)S_(6), paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.展开更多
As a vital and integral component of transportation infrastructure,pavement has a direct and tangible impact on socio-economic sustainability.In recent years,an influx of groundbreaking and state-of-the-art materials,...As a vital and integral component of transportation infrastructure,pavement has a direct and tangible impact on socio-economic sustainability.In recent years,an influx of groundbreaking and state-of-the-art materials,structures,equipment,and detection technologies related to road engineering have continually and progressively emerged,reshaping the landscape of pavement systems.There is a pressing and growing need for a timely summarization of the current research status and a clear identification of future research directions in these advanced and evolving technologies.Therefore,Journal of Road Engineering has undertaken the significant initiative of introducing a comprehensive review paper with the overarching theme of“advanced road materials,structures,equipment,and detection technologies”.This extensive and insightful review meticulously gathers and synthesizes research findings from 39 distinguished scholars,all of whom are affiliated with 19 renowned universities or research institutions specializing in the diverse and multidimensional field of highway engineering.It covers the current state and anticipates future development directions in the four major and interconnected domains of road engineering:advanced road materials,advanced road structures and performance evaluation,advanced road construction equipment and technology,and advanced road detection and assessment technologies.展开更多
Concrete pavement is accompanied by two major functional properties,namely noise emission and friction,which are closely related to pavement surface texture.While several technologies have been developed to mitigate t...Concrete pavement is accompanied by two major functional properties,namely noise emission and friction,which are closely related to pavement surface texture.While several technologies have been developed to mitigate tirepavement noise and improve driving friction by surface texturization,limited information is available to compare the advantages and disadvantages of different surface textures.In this study,a state-of-the-art and state-of-thepractice review is conducted to investigate the noise reduction and friction improvement technologies for concrete pavement surfaces.The commonly used tests for characterizing the surface texture,skid resistance,and noise emission of concrete pavement were first summarized.Then,the texturing methods for both fresh and hardened concrete pavement surfaces were discussed,and the friction,noise emission and durability performances of various surface textures were compared.It is found that the next generation concrete surface(NGCS)texture generally provides the best noise emission performance and excellent friction properties.The exposed aggregate concrete(EAC)and optimized diamond grinding textures are also promising alternatives.Lastly,the technical parameters for the application of both diamond grinding and diamond grinding&grooving textures were recommended based on the authors'research and practical experience in Germany and the US.This study offers a convenient reference to the pavement researchers and engineers who seek to quickly understand relevant knowledge and choose the most appropriate surface textures for concrete pavements.展开更多
通过'人工光合成'过程,将太阳能转化成氢能的形式加以存储和利用,是替代传统化石能源的清洁能源的制备有效途径.其中,光电化学分解水是氢能制备的最有潜力的路径之一.n型BiVO_4由于具有丰富的储量、较窄的带隙以及合适的能带位...通过'人工光合成'过程,将太阳能转化成氢能的形式加以存储和利用,是替代传统化石能源的清洁能源的制备有效途径.其中,光电化学分解水是氢能制备的最有潜力的路径之一.n型BiVO_4由于具有丰富的储量、较窄的带隙以及合适的能带位置,被称为光电化学领域的研究热点.然而,未修饰的BiVO_4光阳极性能并不理想,主要原因在于载流子复合严重、导电性差以及表面催化动力学低等性质的制约.科研工作者们针对这些方面已进行了非常多的研究,例如与电子传输层的复合、产氧电催化剂的担载以及异质结的构建等.其中表面动力学和电荷分离的同时提升是更理想的改善BiVO_4光阳极性能的方法.我们在上述研究基础上,采用光化学沉积法在纳米多孔BiVO_4电极表面担载无定形氧化铁层,将电极在1.23 V vs.RHE电位下的光电流提升至2.52 m A/cm2,是初始光电化学性能的3倍.采用间歇光照计时电流(i-t)测试,电化学交流阻抗谱(EIS),X射线光电子能谱(XPS),原位和非原位的X射线精细结构能谱(in-situ and ex-situ XAFS)等表征手段研究了无定形氧化铁层的成分和光电化学反应过程中的价态变化,从而分析出光电化学性能提升的原因.间歇光照i-t测试和EIS测试结果表明,无定形氧化铁沉积在BiVO_4使电荷累积减少,复合率降低.XPS测试结果发现无定形氧化铁层存在少量的二价铁成分.通过原位XAFS测试发现,BiVO_4/Fe Ox电极中Fe原子的价态在光照和施加外加偏压条件下会有价态的升高,而撤去光照和偏压后Fe原子的价态状态与最初非原位的测试结果重合.这样的结果证明了无定型氧化铁层在光电化学反应过程中由于二价铁成分的存在,能够很好的通过价态改变实现空穴的吸附和传输,即吸附空穴,被空穴氧化成三价或四价,同时结合自身电催化活性,促进表面分解水反应的进行.而水的氧化反应结束时,则伴随着二价铁离子的再生成.这种反应机理为开发更高效的电催化剂,匹配光电极使用,有着重大的指导意义.展开更多
Among the various treatment methods for stroke, increasing attention has been paid to traditional Chinese medicines. Buyang Huanwu decoction is a commonly used traditional Chinese medicine for the treatment of stroke....Among the various treatment methods for stroke, increasing attention has been paid to traditional Chinese medicines. Buyang Huanwu decoction is a commonly used traditional Chinese medicine for the treatment of stroke. This paper summarizes the active components of the Chinese herb, which is composed of Huangqi(Radix Astragali seu Hedysari), Danggui(Radix Angelica sinensis), Chishao(Radix Paeoniae Rubra), Chuanxiong(Rhizoma Ligustici Chuanxiong), Honghua(Flos Carthami), Taoren(Semen Persicae) and Dilong(Pheretima), and identifies the therapeutic targets and underlying mechanisms that contribute to the neuroprotective properties of Buyang Huanwu decoction.展开更多
Although thermally conductive graphene sheets are efficient in enhancing in-plane thermal conductivities of polymers,the resulting nanocomposites usually exhibit low through-plane thermal conductivities,limiting their...Although thermally conductive graphene sheets are efficient in enhancing in-plane thermal conductivities of polymers,the resulting nanocomposites usually exhibit low through-plane thermal conductivities,limiting their application as thermal interface materials.Herein,lamellarstructured polyamic acid salt/graphene oxide(PAAS/GO)hybrid aerogels are constructed by bidirectional freezing of PAAS/GO suspension followed by lyophilization.Subsequently,PAAS monomers are polymerized to polyimide(PI),while GO is converted to thermally reduced graphene oxide(RGO)during thermal annealing at 300℃.Final graphitization at 2800℃ converts PI to graphitized carbon with the inductive effect of RGO,and simultaneously,RGO is thermally reduced and healed to high-quality graphene.Consequently,lamellar-structured graphene aerogels with superior through-plane thermal conduction capacity are fabricated for the first time,and its superior through-plane thermal conduction capacity results from its vertically aligned and closely stacked high-quality graphene lamellae.After vacuum-assisted impregnation with epoxy,the resultant epoxy composite with 2.30 vol% of graphene exhibits an outstanding through-plane thermal conductivity of as high as 20.0 W m^−1 K^−1,100 times of that of epoxy,with a record-high specific thermal conductivity enhancement of 4310%.Furthermore,the lamellar-structured graphene aerogel endows epoxy with a high fracture toughness,~1.71 times of that of epoxy.展开更多
It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of ...It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of seedling pickup mechanism with planetary gear train was studied based on the data of given key points and the trajectory of the endpoint of seedling pick-up mechanism.Given the positions and orientations requirements of the five key points,the study first conducted a dimensional synthesis of the linkage size and center of rotation.The next steps were to select a reasonable solution and optimize the data values based on the ideal seedling trajectory.The link motion was driven by the planetary gear train of the two-stage gear.Four pitch curves of noncircular gears were obtained by calculating and distributing the transmission ratio according to the data.For the pitch curve with two convex points,the tooth profile design method of incomplete noncircular gear was applied.The seedling pick-up mechanism was tested by a virtual prototype and a physical prototype designed with the obtained parameter values.The results were consistent with the theoretical design requirements,confirming that the mechanism meets the expected requirements for picking seedlings up.This paper presents a new design method of vegetable pot seedling pick-up mechanism for an automatic vegetable transplanter.展开更多
In this study,to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete,a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive ...In this study,to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete,a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive experiments under confined and unconfined conditions.The confining pressure was achieved by applying a lateral metal sleeve on the testing specimen which was loaded in the axial direction.The experimental results prove that dynamic peak axial stress,dynamic peak lateral stress,and peak axial strain of concrete are strongly sensitive to the strain rate under confined conditions.Moreover,the failure patterns are significantly affected by the stress-loading rate and confining pressure.Concrete shows stronger strain rate effects under an unconfined condition than that under a confined condition.More cracks are created in concrete subjected to uniaxial dynamic compression at a higher strain rate,which can be explained by a thermal-activated mechanism.By contrast,crack generation is prevented by confinement.Fitting formulas of the dynamic peak stress and dynamic peak axial strain are established by considering strain rate effects(50–250 s-1)as well as the dynamic confining increase factor(DIFc).展开更多
Reid, Lancaster, Tuxpeno and Suwan are the most common maize (Zea mays L.) germplasms. Reid × Lancaster and Suwan × Tuxpeno are very important heterotic patterns in temperate areas and tropical areas, respec...Reid, Lancaster, Tuxpeno and Suwan are the most common maize (Zea mays L.) germplasms. Reid × Lancaster and Suwan × Tuxpeno are very important heterotic patterns in temperate areas and tropical areas, respectively. Broadening the genetic basis of maize has usually been conducted in inter-populations formed by crossing temperate and tropical germplasms. Reciprocal recurrent selection (RRS) is a breeding procedure to improve the inter-populational cross of two base populations. The objective of this study was to evaluate the direct and indirect effects of reciprocal recurrent selection on grain yield in the TR (Tuxpeno-Reid) and SL (Suwan-Lancaster) maize populations. The populations and the inter-populational crosses of each selection cycle, as well as two commercial hybrids, were evaluated in four environments. The effect of mean grain yield on TR × SL inter-population crosses was 4.63% (or 0.365 Mg·ha-1) cycle-1. The grain yield of SL increased by 2.78% (or 0.20 Mg·ha-1) cycle-1, but the grain yield of TR essentially did not change. Most changes in other agronomic traits occurred in the desired direction. After 3 selection cycles, the ear tip-barrenness length decreased in TR × SL, TR and SL by 39.70%, 37.50% and 24.57%, respectively, which indicates that the increase in grain yield may be largely due to a decreasing ear tip-barrenness length. The mid-parent heterosis of grain yield of the inter-populational cross increased from 15.49% to 25.96% from C0 to C3. The mean grain yields of TRC3 × SLC3 were 100.01% and 103.88% of the mean grain yields of the commercial single-crosses GD8 and QD16, respectively. The results suggest that Tuxpeno-Reid × Suwan-Lancaster may be possible new heterotic patterns in the southern region of China.展开更多
基金The financial support from the National Natural Science Foun-dation of China(Grant Nos.52022112 and 51778637)the Sci-ence and Technology Innovation Program of Hunan Province(Grant No.2021RC3015)are acknowledged and appreciated.
文摘Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.
基金supported by the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)Natural Science Foundation of Shanghai’s Science and Technology Innovation Action Plan(General Program:No.22ZR1472900)+4 种基金Study on the Environment and Dynamics of Earth’s Inner Magnetospheric Particles and the Needs of Space-based Exploration(Grant No.D-2022-09-13-001)Hong Kong-Macao-Taiwan Cooperation Funding of Shanghai Committee of Science and Technology(Grant No.19590761300)Shanghai 2022“Science and Technology Innovation Action Plan”Hong Kong,Macao and Taiwan Science and Technology Cooperation Project(Grant No.22590760900)Shanghai Postdoctoral Daily Funding(Grant No.K-2021-12-16001)。
文摘Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core,lithosphere,ocean,ionosphere,and magnetosphere,and also from field-aligned currents coupling the ionosphere and magnetosphere—the meridional currents that connect the two hemispheres and the induced currents due to the variations of fields over time.The fluctuation of magnetic fields generated by these highly dynamic space currents greatly limits the accuracy of the geomagnetic models.In order to better accomplish the scientific objectives of Macao Science Satellite-1(MSS-1),and to improve existing geomagnetic field models,we present here for the first time a self-consistent coupling of solar wind,magnetosphere,and ionosphere,which represents the most developed numerical simulation method for space physics research so far,making it possible to quantify the contribution of different current systems to the total observed magnetic field(B).The results show that numerical simulation can capture main magnetic disturbance characteristics with significant precision.Partial ring current is a major contributor to the latitudinal magnetic perturbation near the equator.Magnetopause and magnetotail currents affect the radial magnetic perturbation around the mid-latitudes.Field-aligned and Pedersen currents produce significant longitudinal and latitudinal magnetic perturbations at high latitudes.
基金Project supported by the National Natural Science Foundation of China(Nos.11790282,12172235,12072208,and 52072249)the Opening Foundation of State Key Laboratory of Shijiazhuang Tiedao University of China(No.ZZ2021-13)。
文摘A stochastic wheelset model with a nonlinear wheel-rail contact relationship is established to investigate the stochastic stability and stochastic bifurcation of the wheelset system with the consideration of the stochastic parametric excitations of equivalent conicity and suspension stiffness.The wheelset is systematized into a onedimensional(1D)diffusion process by using the stochastic average method,the behavior of the singular boundary is analyzed to determine the hunting stability condition of the wheelset system,and the critical speed of stochastic bifurcation is obtained.The stationary probability density and joint probability density are derived theoretically.Based on the topological structure change of the probability density function,the stochastic Hopf bifurcation form and bifurcation condition of the wheelset system are determined.The effects of stochastic factors on the hunting stability and bifurcation characteristics are analyzed,and the simulation results verify the correctness of the theoretical analysis.The results reveal that the boundary behavior of the diffusion process determines the hunting stability of the stochastic wheelset system,and the left boundary characteristic value cL=1 is the critical state of hunting stability.Besides,stochastic D-bifurcation and P-bifurcation will appear in the wheelset system,and the critical speeds of the two kinds of stochastic bifurcation decrease with the increase in the stochastic parametric excitation intensity.
基金the Science and Technology Research Project of Education Department of Jilin Province(JJKH20220683KJ)Natural Science Foundation of Jilin Province(20220101093JC).
文摘Common strategies for catalytic graphitization of biochar into graphitic porous carbon(GPC)still face great challenges,such as the realization of simple procedures,energy conservation,and green processes.Controlling over the graphitization degree and pore structure of biochar is the key to its structural diversification.Herein,a clean and energy-efficient method is developed to synthesize adjustable graphitic degree and structure porosity GPC from rice husk-based carbon(RHC)at a relatively low temperature of 800–1000°C with environment-benign organometallic catalyst ethylenediaminetetraacetic acid ferric sodium salt(EDTA-iron)and the recovery ratio of catalyst is as high as 97%.The formed by the organic ligands of EDTA-iron facilitates the etching of RHC surface and pore by iron,resulting in highly graphitized and developed porous GPCs.The pore structure and graphitization degree of GPCs can be adjusted by altering the catalyst loading,temperature,and holding time.The catalyst EDTA-iron with a lower concentration mainly plays the role of etching,which promotes the formation of porous carbon with larger surface area(SBET=1187.2 m^(2)·g^(-1)).The catalyst with higher concentration mainly plays the role of catalyzing graphitization and promotes the obtaining of graphitic carbon with high graphitization degree(ID/IG=0.19).The mechanism of EDTA-iron catalyzed graphitization of RHC is explored by the comprehensive analysis of BET,XRD,Raman,TEM and TGA.This research not only provides an efficient method for the preparation of high-quality biomass-based graphite carbon,but also provides a feasible method for the preparation of biomass-based porous carbon.
基金support from the National Natural Science Foundation of China(21776101)the National Natural Science Foundation of China(22178122)for this work.
文摘Adsorption dynamics of ethane in two granular fixed beds and structured fixed beds with microfibrous composites was studied.5A zeolite membrane 5A/PSSF(paper-like sintered stainless steel fiber)and microfibrous entrapped activated carbon(MEAC)composites were prepared by wet layup papermaking/sintering technique and in-situ hydrothermal method.Microfibrous composites were characterized by X-ray diffraction,scanning electron microscopy and N2 adsorption/desorption.Structured fixed beds were designed by filling granular adsorbents(5A zeolite or activated carbon)and microfibrous composites at the inlet and outlet of the beds,respectively.Effects of flow rate,bed height and structure on the breakthrough curves were investigated.The length of unused bed(LUB)was determined,and Yoon–Nelson model was used to fit the breakthrough curves.The experimental results showed ethane was effectively adsorbed on the granular adsorbents and microfibrous composites.Both composites could decrease the LUB values and enhance bed utilization.All breakthrough curves fitted well to Yoon–Nelson model,with correlation coefficient exceeding 0.89.The adsorption rate of ethane could be improved in the structured fixed beds,which showed an enhanced mass transfer efficiency for ethane adsorption.LUB values of structured fixed beds with 5A/PSSF composites were larger,the bed utilization values were lower,and the adsorption rate constants were higher than those with MEAC composites under the same conditions.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1405100)the Beijing Natural Science Foundation Key Program(Grant No.Z190007)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB44000000 and XDB28000000)the National Natural Science Foundation of China(Grant Nos.12241405,11734004,and 12174028)。
文摘The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage.A negative magnetoresistance is observed first in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)tunnel junctions,where the resistance with antiparallel aligned magnetization of two Fe_(3)GeTe_(2)electrodes is lower than that with parallel alignment,which is due to the opposite spin polarizations of two Fe_(3)GeTe_(2)electrodes.With the bias voltage increasing,the spin polarization of the biased Fe_(3)GeTe_(2)electrode is changed so that the spin orientations of two Fe_(3)GeTe_(2)electrodes are the same.Our experimental observations are supported by the calculated spin-dependent density of states for Fe_(3)GeTe_(2)electrodes under a finite bias.The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.
基金supported by the State Key Laboratory of North China Crop Improvement and Regulation(NCCIR2021ZZ-14)the Natural Science Foundation of Hebei Province(C2019204246,C2019204141)+2 种基金the Central Government Guides Local Science and Technology Development Projects(216Z6501G,216Z6502G)the Research Project of Basic Scientific Research Business Fees in Provincial Universities of Hebei Province(KY2021043,KY2021044)the China Agriculture Research System(CARS-02)。
文摘The jasmonic acid(JA)signaling pathway is involved in plant growth,development,and response to abiotic or biotic stresses.MYC2,a bHLH transcription factor,is a regulatory hub in the pathway.The function of ZmMYC7,a putative MYC2 ortholog,in jasmonate-signaled defense responses of maize has not been reported.In this study,we found that ZmMYC7 possesses JID,TAD,bHLH and Zip domains and essential characteristics of transcription factors:a nuclear location and transactivation activity.The ZmMYC7mutants showed markedly increased sensitivity to Fusarium graminearum and Setosphaeria turcica.The expression levels of the defense-associated genes ZmPR1,ZmPR2,ZmPR3,ZmPR5,ZmPR6,and ZmPR7 in response to F.graminearum infection were downregulated in ZmMYC7 mutants,while ZmPR4 and ZmPR10 were up-regulated.ZmMYC7 interacted with members of the ZmJAZ family,including ZmJAZ8,ZmJAZ11,and ZmJAZ12.ZmMYC7 physically interacted with G-box cis-elements in the ZmERF147 promoter in vitro and transcriptional activation of ZmERF147 by ZmMYC7 was inhibited by ZmJAZ11 and ZmJAZ12.ZmERF147 mutants were more susceptible to F.graminearum infection than inbred line B73with concomitant down-regulation of all defense-associated ZmPRs except ZmPR4.These findings indicate that ZmMYC7 functions in maize resistance to F.graminearum and sheds light on maize defense responses to pathogenic fungi via the JA signaling pathway.
基金provided by the National Natural Science Foundation of China(Grant No.32070452,32011530077)。
文摘Thermogenic features are often invoked to illustrate animal’s colonization,distribution,and response to climate change.To understand why the White-browed Laughingthrush(Pterorhinus sannio)has expanded its distribution to temperate zones in recent years,we compared its thermogenic features with three species of songbirds that cooccur in its newly colonized areas.Thermogenic parameters of these four species were measured under different ambient temperatures,ranging from 0 to 40℃.The results showed that basal metabolic rate(BMR)was 44.5±3.9 mL O2/h in P.sannio,which is lower than predicted value by its body weight.This is also lower than the BMR of both its temperate congener the Plain Laughingthrush(P.davidi)and the montane,similar species Elliot’s Laughingthrush(Trochalopteron elliotii).The thermal neutral zone(TNZ)in P.sannio was 15-35℃,as compared to 10-27.5℃in P.davidi,25-30℃in T.elliotii,and 7.5-32.5℃in the Green-capped Greenfinch(Chloris sinica).Thermal conductance was lowest in P.sannio,with the minimum value lower than the predicted value based on its body weight.Our results showed that the northward-colonizing P.sannio exhibited different thermogenic characteristics compared with its coexisting species in the new habitat,even its congener P.davidi,which shared similar microhabitats to P.sannio.We suggest that researchers further explore the physiological mechanisms of birds’northward expansion.
基金support provided by the National Natural Science Foundation of China(No.62173049)the Open Fund of the Key Laboratory of Exploration Technologies for Oil and Gas Resources(Yangtze University),Ministry of Education(Grant K2021-17).
文摘Foam drainage is theflow of liquid through the interstitial spaces between bubbles driven by capillarity and grav-ity and resisted by viscous damping.The so-called foam drainage gas recovery technology is a technique tradi-tionally used to mitigate the serious bottom-hole liquid loading in the middle and late stages of gas well production.In this context,determining the optimal concentration of the bubble drainage agent is generally cru-cial for the proper application of this method.In this study,a combination of indoor experiments and theoretical analysis have been used to determine the pressure drop related to the foam-carrying capacity in a representative gasfield.Dynamic and static experiments were designed with a bubble drainage agent concentration varying in the range 0.3%–0.6%.Using thefield formation water data,the optimal soaking agent concentration was obtained and pressure drop test experiments on the foam carrying capacity were conducted accordingly.These tests have revealed that the optimal foam displacement agent concentration is 0.5%,and the foam quality at the optimum concentration is between 0.78–0.98.A theoretical method for calculating the pressure drop at the optimum soak-away concentration based on experimental data has also been introduced.The error of the proposed method is within 15%compared to the experimental measured value,demonstrating that it is highly accurate and simple.
基金supported by the Macao Foundationby the Preresearch Project on Civil Aerospace Technologies No.D020308/D020303 funded by China National Space Administration+1 种基金by the Macao Science and Technology Development Fund,grant No.0001/2019/A1PF Liu is funded by the Science and Technology Development Fund,Macao SAR(File No.0002/2019/APD)。
文摘The Earth’s“lithosphere”is its outer shell,made up of the Earth’s crust and outermost mantle.The part of the Earth’s magnetic field that originates in the lithosphere consists of a superposition of magnetic anomalies with a broad spectrum of sizes and intensities,which arise from geological and tectonic features.The lithospheric magnetic field is known from surface observations,and on larger scales from above-surface measurements.The increase in recent decades of satellites dedicated to measuring the Earth’s magnetic field has improved significantly our models of the Earth’s magnetic environment.Based on these increasing observations,a number of comprehensive field models have been constructed,some of which focus solely on the lithosphere,such as the MF model series.We present a map of lithospheric magnetic anomalies at 400 km altitude,based on a vertically integrated magnetization model.This height was chosen because it is the expected orbital altitude of the Macao Science Satellite-1(MSS-1)mission.The model presented herein indicates that the amplitude of the lithospheric anomalies at 400 km altitude is between-14.8 n T and 18.2 n T.This information is useful because it provides a reference for the lithospheric source of the Earth’s magnetic field that contributes to the magnetic measurements made from satellite instruments.The low inclination orbit of the MSS-1 mission will provide information that is sensitive to lateral variation within the lithosphere;these variations arise from plate tectonic features with longitudinal extent.In conclusion,the new MSS-1mission will provide valuable information in detecting compositional variations in the lithosphere,and in delineating large-scale geological structures.
基金funded by the Macao Foundation,the pre-research project of Civil Aerospace Technologies(Nos.D020308 and D020303)funded by the China National Space Administration,Macao Science and Technology Development Fund(FDCT+1 种基金No.0001/2019/A1)the opening fund of the State Key Laboratory of Lunar and Planetary Sciences(Macao University of Science and Technology,Macao FDCT No.119/2017/A3)。
文摘The Euler angle estimation is a calibration method for vector data measured by the magnetometer on a satellite.It is used to find the relative rotation between the coordinate system of the magnetometer and the satellite(usually determined by Star Imagers).Before launch of the low-orbit,low-inclination Macao Science Satellite-1(known as MSS-1),we simulated the estimation of Euler angles by using the magnetic measurements of the in-orbit Swarm and China Seismo-Electromagnetic Satellite(noted as CSES),with various data combinations.In this study,11 data sets were designed to analyze the estimation results for the MSS-1 orbit by using a joint estimation method of the geomagnetic field model parameters and Euler angles.For the model results,we found that all the spatial power spectral lines showed behavior consistent with that of the CHAOS-7.8 model at low degrees(corresponding to large-scale magnetic signals).The spectra of models without global data coverage deviated much more(by a maximum of~10^(4) nT^(2))from those of the CHAOS-7.8 model at higher degrees.For models with global data coverage and with various data combinations,the spectral lines were distributed similarly.Moreover,the models with accordant power spectral distributions demonstrated different Euler angle estimations.As more vector data at higher latitudes were included,the estimated Euler angles varied monotonically in all three directions.The models with vector data in the same latitude range showed similar Euler angle results,regardless of whether the poleward scalar data were included.The largest value difference was found between the models using vector data within±40°latitudes and those using vector data within±60°latitudes,which reached to~28″.Therefore,we concluded that the inversion of the spherical harmonic Gauss coefficients in our tests was mainly affected by the spatial coverage range of the data,whereas the estimation of Euler angles largely depended on the latitude range where the vector data could be obtained.These results can be used for future in-flight data testing.We expect the estimation of Euler angles to improve as other methods are adopted.
基金supported by the National Key R&D Program of China (Grant Nos. 2020YFA0308900 and 2022YFA1403700)the National Natural Science Foundation of China (Grant Nos. 12074163, 12134020, 11974157, 12104255, 12004159, and 12374146)+8 种基金Guangdong Provincial Key Laboratory for Computational Science and Material Design (Grant No. 2019B030301001)the Science, Technology and Innovation Commission of Shenzhen Municipality (Grant Nos. ZDSYS20190902092905285 and KQTD20190929173815000)Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2022B1515020046, 2021B1515130007, 2022A1515011915, 2019A1515110712, and 2022B1515130005)Shenzhen Science and Technology Program (Grant Nos. RCJC20221008092722009 and RCBS20210706092218039)the Guangdong Innovative and Entrepreneurial Research Team Program (Grant No. 2019ZT08C044)the beam time awarded by Australia’s Nuclear Science and Technology Organisation (ANSTO) (Grant No. P8130)the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC) was performed under a user program (Proposal No. 2019B0140)performed at the Hiroshima Synchrotron Radiation Center (HiSOR) of Japan (Grant Nos. 22BG023 and 22BG029)Shanghai Synchrotron Radiation Facility (SSRF) BL03U (Grant No. 2022-SSRF-PT-020848)。
文摘In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU(2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb_(3)S_(6), paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.
基金support from the European Union's Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement No.101024139,the RILEM technical committee TC 279 WMR(valorisation of waste and secondary materials for roads),RILEM technical committee TC-264 RAP(asphalt pavement recycling)the Swiss National Science Foundation(SNF)grant 205121_178991/1 for the project titled“Urban Mining for Low Noise Urban Roads and Optimized Design of Street Canyons”,National Natural Science Foundation of China(No.51808462,51978547,52005048,52108394,52178414,52208420,52278448,52308447,52378429)+9 种基金China Postdoctoral Science Foundation(No.2023M730356)National Key R&D Program of China(No.2021YFB2601302)Natural Science Basic Research Program of Shaanxi(Program No.2023-JC-QN-0472)Postdoctoral Science Foundation of Anhui Province(2022B627)Shaanxi Provincial Science and Technology Department(No.2022 PT30)Key Technological Special Project of Xinxiang City(No.22ZD013)Key Laboratory of Intelligent Manufacturing of Construction Machinery(No.IMCM2021KF02)the Applied Basic Research Project of Sichuan Science and Technology Department(Free Exploration Type)(Grant No.2020YJ0039)Key R&D Support Plan of Chengdu Science and Technology Project-Technology Innovation R&D Project(Grant No.2019-YF05-00002-SN)the China Postdoctoral Science Foundation(Grant No.2018M643520).
文摘As a vital and integral component of transportation infrastructure,pavement has a direct and tangible impact on socio-economic sustainability.In recent years,an influx of groundbreaking and state-of-the-art materials,structures,equipment,and detection technologies related to road engineering have continually and progressively emerged,reshaping the landscape of pavement systems.There is a pressing and growing need for a timely summarization of the current research status and a clear identification of future research directions in these advanced and evolving technologies.Therefore,Journal of Road Engineering has undertaken the significant initiative of introducing a comprehensive review paper with the overarching theme of“advanced road materials,structures,equipment,and detection technologies”.This extensive and insightful review meticulously gathers and synthesizes research findings from 39 distinguished scholars,all of whom are affiliated with 19 renowned universities or research institutions specializing in the diverse and multidimensional field of highway engineering.It covers the current state and anticipates future development directions in the four major and interconnected domains of road engineering:advanced road materials,advanced road structures and performance evaluation,advanced road construction equipment and technology,and advanced road detection and assessment technologies.
基金The authors gratefully acknowledge the financial support of the National Key Research and Development Program of China(2019YFE0116300)the National Natural Science Foundation of China(52308448,52250610218)the Natural Science Foundation of Heilongjiang Province of China(JJ2020ZD0015).
文摘Concrete pavement is accompanied by two major functional properties,namely noise emission and friction,which are closely related to pavement surface texture.While several technologies have been developed to mitigate tirepavement noise and improve driving friction by surface texturization,limited information is available to compare the advantages and disadvantages of different surface textures.In this study,a state-of-the-art and state-of-thepractice review is conducted to investigate the noise reduction and friction improvement technologies for concrete pavement surfaces.The commonly used tests for characterizing the surface texture,skid resistance,and noise emission of concrete pavement were first summarized.Then,the texturing methods for both fresh and hardened concrete pavement surfaces were discussed,and the friction,noise emission and durability performances of various surface textures were compared.It is found that the next generation concrete surface(NGCS)texture generally provides the best noise emission performance and excellent friction properties.The exposed aggregate concrete(EAC)and optimized diamond grinding textures are also promising alternatives.Lastly,the technical parameters for the application of both diamond grinding and diamond grinding&grooving textures were recommended based on the authors'research and practical experience in Germany and the US.This study offers a convenient reference to the pavement researchers and engineers who seek to quickly understand relevant knowledge and choose the most appropriate surface textures for concrete pavements.
基金supported by the National Natural Science Foundation of China(21373083,21573068)Program of Shanghai Subject Chief Scientist(15XD1501300)+1 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education MinistryScience Technology Commission of Shanghai Municipality(14JC1490900)~~
文摘通过'人工光合成'过程,将太阳能转化成氢能的形式加以存储和利用,是替代传统化石能源的清洁能源的制备有效途径.其中,光电化学分解水是氢能制备的最有潜力的路径之一.n型BiVO_4由于具有丰富的储量、较窄的带隙以及合适的能带位置,被称为光电化学领域的研究热点.然而,未修饰的BiVO_4光阳极性能并不理想,主要原因在于载流子复合严重、导电性差以及表面催化动力学低等性质的制约.科研工作者们针对这些方面已进行了非常多的研究,例如与电子传输层的复合、产氧电催化剂的担载以及异质结的构建等.其中表面动力学和电荷分离的同时提升是更理想的改善BiVO_4光阳极性能的方法.我们在上述研究基础上,采用光化学沉积法在纳米多孔BiVO_4电极表面担载无定形氧化铁层,将电极在1.23 V vs.RHE电位下的光电流提升至2.52 m A/cm2,是初始光电化学性能的3倍.采用间歇光照计时电流(i-t)测试,电化学交流阻抗谱(EIS),X射线光电子能谱(XPS),原位和非原位的X射线精细结构能谱(in-situ and ex-situ XAFS)等表征手段研究了无定形氧化铁层的成分和光电化学反应过程中的价态变化,从而分析出光电化学性能提升的原因.间歇光照i-t测试和EIS测试结果表明,无定形氧化铁沉积在BiVO_4使电荷累积减少,复合率降低.XPS测试结果发现无定形氧化铁层存在少量的二价铁成分.通过原位XAFS测试发现,BiVO_4/Fe Ox电极中Fe原子的价态在光照和施加外加偏压条件下会有价态的升高,而撤去光照和偏压后Fe原子的价态状态与最初非原位的测试结果重合.这样的结果证明了无定型氧化铁层在光电化学反应过程中由于二价铁成分的存在,能够很好的通过价态改变实现空穴的吸附和传输,即吸附空穴,被空穴氧化成三价或四价,同时结合自身电催化活性,促进表面分解水反应的进行.而水的氧化反应结束时,则伴随着二价铁离子的再生成.这种反应机理为开发更高效的电催化剂,匹配光电极使用,有着重大的指导意义.
基金supported by grants from Health and Family Planning Commission of Heilongjiang Province Research Projects,No. 2014-195Science and Technology Research Projects of Mudanjiang Medical University,No.ZS201305.
文摘Among the various treatment methods for stroke, increasing attention has been paid to traditional Chinese medicines. Buyang Huanwu decoction is a commonly used traditional Chinese medicine for the treatment of stroke. This paper summarizes the active components of the Chinese herb, which is composed of Huangqi(Radix Astragali seu Hedysari), Danggui(Radix Angelica sinensis), Chishao(Radix Paeoniae Rubra), Chuanxiong(Rhizoma Ligustici Chuanxiong), Honghua(Flos Carthami), Taoren(Semen Persicae) and Dilong(Pheretima), and identifies the therapeutic targets and underlying mechanisms that contribute to the neuroprotective properties of Buyang Huanwu decoction.
基金Financial support from the National Natural Science Foundation of China(51773008,51533001,U1905217)the National Key Research and Development Program of China(2016YFC0801302)is gratefully acknowledged.
文摘Although thermally conductive graphene sheets are efficient in enhancing in-plane thermal conductivities of polymers,the resulting nanocomposites usually exhibit low through-plane thermal conductivities,limiting their application as thermal interface materials.Herein,lamellarstructured polyamic acid salt/graphene oxide(PAAS/GO)hybrid aerogels are constructed by bidirectional freezing of PAAS/GO suspension followed by lyophilization.Subsequently,PAAS monomers are polymerized to polyimide(PI),while GO is converted to thermally reduced graphene oxide(RGO)during thermal annealing at 300℃.Final graphitization at 2800℃ converts PI to graphitized carbon with the inductive effect of RGO,and simultaneously,RGO is thermally reduced and healed to high-quality graphene.Consequently,lamellar-structured graphene aerogels with superior through-plane thermal conduction capacity are fabricated for the first time,and its superior through-plane thermal conduction capacity results from its vertically aligned and closely stacked high-quality graphene lamellae.After vacuum-assisted impregnation with epoxy,the resultant epoxy composite with 2.30 vol% of graphene exhibits an outstanding through-plane thermal conductivity of as high as 20.0 W m^−1 K^−1,100 times of that of epoxy,with a record-high specific thermal conductivity enhancement of 4310%.Furthermore,the lamellar-structured graphene aerogel endows epoxy with a high fracture toughness,~1.71 times of that of epoxy.
基金National Key Research and Development Program of China(Grant No.2017YFD0700800)National Science Foundation of China(Grant Nos.51775512,51575496)Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ16E050003).
文摘It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of seedling pickup mechanism with planetary gear train was studied based on the data of given key points and the trajectory of the endpoint of seedling pick-up mechanism.Given the positions and orientations requirements of the five key points,the study first conducted a dimensional synthesis of the linkage size and center of rotation.The next steps were to select a reasonable solution and optimize the data values based on the ideal seedling trajectory.The link motion was driven by the planetary gear train of the two-stage gear.Four pitch curves of noncircular gears were obtained by calculating and distributing the transmission ratio according to the data.For the pitch curve with two convex points,the tooth profile design method of incomplete noncircular gear was applied.The seedling pick-up mechanism was tested by a virtual prototype and a physical prototype designed with the obtained parameter values.The results were consistent with the theoretical design requirements,confirming that the mechanism meets the expected requirements for picking seedlings up.This paper presents a new design method of vegetable pot seedling pick-up mechanism for an automatic vegetable transplanter.
基金supported by the National Natural Science Foundation of China(Nos.52027814 and 51839009)。
文摘In this study,to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete,a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive experiments under confined and unconfined conditions.The confining pressure was achieved by applying a lateral metal sleeve on the testing specimen which was loaded in the axial direction.The experimental results prove that dynamic peak axial stress,dynamic peak lateral stress,and peak axial strain of concrete are strongly sensitive to the strain rate under confined conditions.Moreover,the failure patterns are significantly affected by the stress-loading rate and confining pressure.Concrete shows stronger strain rate effects under an unconfined condition than that under a confined condition.More cracks are created in concrete subjected to uniaxial dynamic compression at a higher strain rate,which can be explained by a thermal-activated mechanism.By contrast,crack generation is prevented by confinement.Fitting formulas of the dynamic peak stress and dynamic peak axial strain are established by considering strain rate effects(50–250 s-1)as well as the dynamic confining increase factor(DIFc).
文摘Reid, Lancaster, Tuxpeno and Suwan are the most common maize (Zea mays L.) germplasms. Reid × Lancaster and Suwan × Tuxpeno are very important heterotic patterns in temperate areas and tropical areas, respectively. Broadening the genetic basis of maize has usually been conducted in inter-populations formed by crossing temperate and tropical germplasms. Reciprocal recurrent selection (RRS) is a breeding procedure to improve the inter-populational cross of two base populations. The objective of this study was to evaluate the direct and indirect effects of reciprocal recurrent selection on grain yield in the TR (Tuxpeno-Reid) and SL (Suwan-Lancaster) maize populations. The populations and the inter-populational crosses of each selection cycle, as well as two commercial hybrids, were evaluated in four environments. The effect of mean grain yield on TR × SL inter-population crosses was 4.63% (or 0.365 Mg·ha-1) cycle-1. The grain yield of SL increased by 2.78% (or 0.20 Mg·ha-1) cycle-1, but the grain yield of TR essentially did not change. Most changes in other agronomic traits occurred in the desired direction. After 3 selection cycles, the ear tip-barrenness length decreased in TR × SL, TR and SL by 39.70%, 37.50% and 24.57%, respectively, which indicates that the increase in grain yield may be largely due to a decreasing ear tip-barrenness length. The mid-parent heterosis of grain yield of the inter-populational cross increased from 15.49% to 25.96% from C0 to C3. The mean grain yields of TRC3 × SLC3 were 100.01% and 103.88% of the mean grain yields of the commercial single-crosses GD8 and QD16, respectively. The results suggest that Tuxpeno-Reid × Suwan-Lancaster may be possible new heterotic patterns in the southern region of China.
