Copper particles emitted from braking have become a significant source of environmental pollution.However,copper plays a crucial role in resin-based braking materials.Developing high-performance braking materials with...Copper particles emitted from braking have become a significant source of environmental pollution.However,copper plays a crucial role in resin-based braking materials.Developing high-performance braking materials without copper has become a significant challenge.In this paper,the resin-based braking materials were filled with flyash cenospheres to develop copper-free braking materials.The effects of fly-ash cenospheres on the physical properties,mechanical and friction and wear properties of braking materials were studied.Furthermore,the wear mechanism of copper-free resin-based braking materials filled with fly-ash cenospheres was discussed.The results indicate that the inclusion of fly-ash cenospheres in the braking materials improved their thermal stability,hardness and impact strength,reduced their density,effectively increased the friction coefficient at medium and high temperatures,and enhanced the heat-fade resistance of the braking materials.The inclusion of fly-ash cenospheres contributed to the formation of surface friction film during the friction process of the braking materials,and facilitated the transition of form from abrasive wear to adhesive wear.At 100-350℃,the friction coefficient of the optimal formulation is in the range of 0.57-0.61,and the wear rate is in the range(0.29-0.65)×10^(-7) cm^(3)·N^(-1)·m^(-1),demonstrating excellent resistance to heat-fade and stability in friction coefficient.This research proposes the use of fly-ash cenospheres as a substitute for environmentally harmful and expensive copper in brake materials,which not only improves the performance of braking materials but also reduces their costs.展开更多
This study explores the impact of street pattern measurements on urban heat islands(UHI)in the arid climate of Mashhad,Iran.The Landsat-8 top-of-the-atmosphere(TOA)brightness images from 2013 to 2021,average values of...This study explores the impact of street pattern measurements on urban heat islands(UHI)in the arid climate of Mashhad,Iran.The Landsat-8 top-of-the-atmosphere(TOA)brightness images from 2013 to 2021,average values of normalized difference vegetation index(NDvI)and land surface temperature(LST)were calculated.Street pattern measurements,including closeness-centrality,straightness,and street orientation,were employed to analyse the patterns in each district.The results indicated that districts with higher straightness and lower closeness-centrality exhibit,cooler surface temperatures.Strong correlations were observed between LST and NDVl,straightness,and local closeness-centrality.The research highlighted the importance of considering street network measurements in long-term urban planning and design to mitigate the UHI effect in arid regions.A moderate grid street pattern with a reasonable distribution of green spaces throughout the region is suggested to reduce surface temperatures sustainably.Street pattern indexes,such as straightness and local closeness-centrality,are identified as significant factors in urban design to mitigate UHl.These findings have implications for urban planners,who can use this information to create street network patterns with lower UHI effects by reducing local closeness-centrality and increasing straightness.展开更多
Some of the variation formulas of a metric were derived in the literatures by using the local coordinates system, In this paper, We give the first and the second variation formulas of the Riemannian curvature tensor, ...Some of the variation formulas of a metric were derived in the literatures by using the local coordinates system, In this paper, We give the first and the second variation formulas of the Riemannian curvature tensor, Ricci curvature tensor and scalar curvature of a metric by using the moving frame method. We establish a relation between the variation of the volume of a metric and that of a submanifold. We find that the latter is a consequence of the former. Finally we give an application of these formulas to the variations of heat invariants. We prove that a conformally flat metric g is a critical point of the third heat invariant functional for a compact 4-dimensional manifold M, then （M, g） is either scalar flat or a space form.展开更多
Using parabolic maximum principle, we apply the analytic method to obtain lower comparison inequalities for non-negative weak supersolutions of the heat equation associated with a regular strongly p-local Dirichlet fo...Using parabolic maximum principle, we apply the analytic method to obtain lower comparison inequalities for non-negative weak supersolutions of the heat equation associated with a regular strongly p-local Dirichlet form on the abstract metric measure space. As an application we obtain lower estimates for heat kernels on some Riemannian manifolds.展开更多
In this paper, we discuss necessary and sufficient conditions on jumping kernels for a class of jump-type Markov processes on metric measure spaces to have scale-invariant finite range parabolic Harnack inequality.
The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within ab...The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 rain. The crystalline forms all grew with experimental time increase. Scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and X-ray diffraction spectroscopy （XRD） techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.展开更多
We establish conditions ensuring either existence or blow-up of nonnegative solutions for the heat equation generated by the Dirichlet fractional Laplacian perturbed by negative potentials on bounded sets. The elabora...We establish conditions ensuring either existence or blow-up of nonnegative solutions for the heat equation generated by the Dirichlet fractional Laplacian perturbed by negative potentials on bounded sets. The elaborated theory is supplied by some examples.展开更多
The factors of heat treatments were discussed, which affect the formability of two low carbon, low alloy steels. Experiment concerns mechanical properties, R-values, orientation intensity, texture internal friction an...The factors of heat treatments were discussed, which affect the formability of two low carbon, low alloy steels. Experiment concerns mechanical properties, R-values, orientation intensity, texture internal friction and their relationship with annealing and ageing.展开更多
Effects of the form factor on natural convection heat transfer and fluid flow in a two-dimensional cavity filled with Al2O3-nanofluid has been analyzed numerically. A model was developed to explain the behavior of nan...Effects of the form factor on natural convection heat transfer and fluid flow in a two-dimensional cavity filled with Al2O3-nanofluid has been analyzed numerically. A model was developed to explain the behavior of nanofluids taking account of the volume fraction φ. The Navier-Stokes equations are solved numerically by alternating an implicit method (Method ADI) for various Rayleigh numbers varies as 103, 104 and 105. The nanofluid used is aluminum oxide with water Pr = 6.2;solid volume fraction φ is varied as 0%, 5% and 10%. Inclination angle Φ varies from 0° to 90° with a step the 15° and the form report varies as R = 0.25, 0.5, 1 and 4. The problem considered is a two-dimensional heat transfer enclosure. The vertical walls are differentially heated;the right is cold when the left is hot. The horizontal walls are assumed to be insulated. The nanofluid in the cavity is considered as incompressible, Newtonian and laminar flow. The nanoparticles are assumed to have a shape and a uniform size. However, it is supposed that the two fluid phases and nanoparticles are in a state of thermal equilibrium and they sink at the same speed. The thermophysical properties of nanofluids are assumed to be constant at the exception of the variation of density in the force of buoyancy, which is based on the approximation of Boussinesq values.展开更多
Small brown planthopper, Laodelphax striatellus （Fall6n） numbers usually drop sharply in the summer and revive quickly in the autumn. However, it is unclear whether and how the high temperature plays a role in this ...Small brown planthopper, Laodelphax striatellus （Fall6n） numbers usually drop sharply in the summer and revive quickly in the autumn. However, it is unclear whether and how the high temperature plays a role in this process. The effects of durations of heat exposure （33~C） on life-history traits were examined here. Exposure of adults for 1 day during the oviposition stage led to a very low survival of nymphs. The average longevity ofL. striatellus exposed for 1-31 days from oviposition was significantly longer than that of the control （27℃）. Short-term （1-5 days） heat exposure of the third instar nymphs did not significantly influence eclosion, but exposure of the fourth instar nymphs significantly increased eclosion. Lifespan from egg to adult was significantly lengthened when the third instar nymphs were exposed to heat for 2-15 days, or the fourth instar were exposed for 10 days. The preoviposition period was prolonged by heat exposure of the third or fourth instar nymphs. Short-term heat exposure of less than 3 days of the third or fourth instar nymphs did not restrict fecundity, but when the exposure duration exceeded 5 days the total eggs per female and hatchability decreased. Exposure to high temperature increased the brachypter rate of adults. In summary, low survival and slowing development under heat exposure resulted in population decline in the summer, and the relatively high fecundity and brachypter rate led to quick revival in autumn. Temperature in the summer determines the rise and fall in numbers ofL. striatellus.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.52275178)Fujian Provincial Natural Science Foundation of China(Grant Nos.2020J05115,2022J01073)Project National United Engineering Laboratory for Advanced Bearing Tribology,Henan University of Science and Technology of China(Grant No.202103).
文摘Copper particles emitted from braking have become a significant source of environmental pollution.However,copper plays a crucial role in resin-based braking materials.Developing high-performance braking materials without copper has become a significant challenge.In this paper,the resin-based braking materials were filled with flyash cenospheres to develop copper-free braking materials.The effects of fly-ash cenospheres on the physical properties,mechanical and friction and wear properties of braking materials were studied.Furthermore,the wear mechanism of copper-free resin-based braking materials filled with fly-ash cenospheres was discussed.The results indicate that the inclusion of fly-ash cenospheres in the braking materials improved their thermal stability,hardness and impact strength,reduced their density,effectively increased the friction coefficient at medium and high temperatures,and enhanced the heat-fade resistance of the braking materials.The inclusion of fly-ash cenospheres contributed to the formation of surface friction film during the friction process of the braking materials,and facilitated the transition of form from abrasive wear to adhesive wear.At 100-350℃,the friction coefficient of the optimal formulation is in the range of 0.57-0.61,and the wear rate is in the range(0.29-0.65)×10^(-7) cm^(3)·N^(-1)·m^(-1),demonstrating excellent resistance to heat-fade and stability in friction coefficient.This research proposes the use of fly-ash cenospheres as a substitute for environmentally harmful and expensive copper in brake materials,which not only improves the performance of braking materials but also reduces their costs.
文摘This study explores the impact of street pattern measurements on urban heat islands(UHI)in the arid climate of Mashhad,Iran.The Landsat-8 top-of-the-atmosphere(TOA)brightness images from 2013 to 2021,average values of normalized difference vegetation index(NDvI)and land surface temperature(LST)were calculated.Street pattern measurements,including closeness-centrality,straightness,and street orientation,were employed to analyse the patterns in each district.The results indicated that districts with higher straightness and lower closeness-centrality exhibit,cooler surface temperatures.Strong correlations were observed between LST and NDVl,straightness,and local closeness-centrality.The research highlighted the importance of considering street network measurements in long-term urban planning and design to mitigate the UHI effect in arid regions.A moderate grid street pattern with a reasonable distribution of green spaces throughout the region is suggested to reduce surface temperatures sustainably.Street pattern indexes,such as straightness and local closeness-centrality,are identified as significant factors in urban design to mitigate UHl.These findings have implications for urban planners,who can use this information to create street network patterns with lower UHI effects by reducing local closeness-centrality and increasing straightness.
基金supported by National Natural Science Foundation of China(Grant Nos.11025107,10831008 and 10901165)the Fundamental Research Funds for Central Universities(Grant No.201034000-3162643)+2 种基金High Level Talent Project in High Schools in Guangdong Province(Grant No.34000-5221001)the Fundamental Research Funds for the Central Universities(Grant No.101gpy25)China Post-doctoral Science Foundation(Grant No.201003382)
文摘We construct the canonical solitons,in terms of Cabezas-Rivas and Topping,associated with some generalized Ricci flows.
基金Supported by National Natural Science Foundation of China (Grant No. 10571088)
文摘Some of the variation formulas of a metric were derived in the literatures by using the local coordinates system, In this paper, We give the first and the second variation formulas of the Riemannian curvature tensor, Ricci curvature tensor and scalar curvature of a metric by using the moving frame method. We establish a relation between the variation of the volume of a metric and that of a submanifold. We find that the latter is a consequence of the former. Finally we give an application of these formulas to the variations of heat invariants. We prove that a conformally flat metric g is a critical point of the third heat invariant functional for a compact 4-dimensional manifold M, then （M, g） is either scalar flat or a space form.
文摘Using parabolic maximum principle, we apply the analytic method to obtain lower comparison inequalities for non-negative weak supersolutions of the heat equation associated with a regular strongly p-local Dirichlet form on the abstract metric measure space. As an application we obtain lower estimates for heat kernels on some Riemannian manifolds.
基金supported by NSF (Grant No. DMS-0600206)supported by the Korea Science Engineering Foundation (KOSEF) Grant funded by the Korea government (MEST) (No. R01-2008-000-20010-0)supported by the Grant-in-Aid for Scientific Research (B) 18340027
文摘In this paper, we discuss necessary and sufficient conditions on jumping kernels for a class of jump-type Markov processes on metric measure spaces to have scale-invariant finite range parabolic Harnack inequality.
基金Project supported by the National Natural Science Foundation of China （No. 20073047） and Doctor Foundation of Shandong Province （No. 2004BS04021）.
文摘The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 rain. The crystalline forms all grew with experimental time increase. Scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and X-ray diffraction spectroscopy （XRD） techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.
文摘We establish conditions ensuring either existence or blow-up of nonnegative solutions for the heat equation generated by the Dirichlet fractional Laplacian perturbed by negative potentials on bounded sets. The elaborated theory is supplied by some examples.
基金This boas was financially seaported by SAIC FUND 3166A.
文摘The factors of heat treatments were discussed, which affect the formability of two low carbon, low alloy steels. Experiment concerns mechanical properties, R-values, orientation intensity, texture internal friction and their relationship with annealing and ageing.
文摘Effects of the form factor on natural convection heat transfer and fluid flow in a two-dimensional cavity filled with Al2O3-nanofluid has been analyzed numerically. A model was developed to explain the behavior of nanofluids taking account of the volume fraction φ. The Navier-Stokes equations are solved numerically by alternating an implicit method (Method ADI) for various Rayleigh numbers varies as 103, 104 and 105. The nanofluid used is aluminum oxide with water Pr = 6.2;solid volume fraction φ is varied as 0%, 5% and 10%. Inclination angle Φ varies from 0° to 90° with a step the 15° and the form report varies as R = 0.25, 0.5, 1 and 4. The problem considered is a two-dimensional heat transfer enclosure. The vertical walls are differentially heated;the right is cold when the left is hot. The horizontal walls are assumed to be insulated. The nanofluid in the cavity is considered as incompressible, Newtonian and laminar flow. The nanoparticles are assumed to have a shape and a uniform size. However, it is supposed that the two fluid phases and nanoparticles are in a state of thermal equilibrium and they sink at the same speed. The thermophysical properties of nanofluids are assumed to be constant at the exception of the variation of density in the force of buoyancy, which is based on the approximation of Boussinesq values.
文摘Small brown planthopper, Laodelphax striatellus （Fall6n） numbers usually drop sharply in the summer and revive quickly in the autumn. However, it is unclear whether and how the high temperature plays a role in this process. The effects of durations of heat exposure （33~C） on life-history traits were examined here. Exposure of adults for 1 day during the oviposition stage led to a very low survival of nymphs. The average longevity ofL. striatellus exposed for 1-31 days from oviposition was significantly longer than that of the control （27℃）. Short-term （1-5 days） heat exposure of the third instar nymphs did not significantly influence eclosion, but exposure of the fourth instar nymphs significantly increased eclosion. Lifespan from egg to adult was significantly lengthened when the third instar nymphs were exposed to heat for 2-15 days, or the fourth instar were exposed for 10 days. The preoviposition period was prolonged by heat exposure of the third or fourth instar nymphs. Short-term heat exposure of less than 3 days of the third or fourth instar nymphs did not restrict fecundity, but when the exposure duration exceeded 5 days the total eggs per female and hatchability decreased. Exposure to high temperature increased the brachypter rate of adults. In summary, low survival and slowing development under heat exposure resulted in population decline in the summer, and the relatively high fecundity and brachypter rate led to quick revival in autumn. Temperature in the summer determines the rise and fall in numbers ofL. striatellus.
