A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the all...A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.展开更多
In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate wh...In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. Relatively high rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during flight and upon impacting with the substrate. The processing method uses codeposition of the metallic semi-solidified droplets (metallic matrix) with the injected reinforcement ceramic particles. In the present paper, the microstructures, mechanical properties, interfacial properties, thermal stability and aging behaviour of spray atomized and codeposited Al-Li-X MMC’s (injected X=SiC, Al2O3) are reported and correlated to the processing conditions.展开更多
We investigate the above-threshold ionization of an atom in a combined infrared(IR) and extreme ultraviolet(XUV) two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization(HA...We investigate the above-threshold ionization of an atom in a combined infrared(IR) and extreme ultraviolet(XUV) two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization(HATI)process. It is demonstrated that, in stark contrast to previous studies, the XUV laser may play a significant role in atomic HATI process, and in particular, the XUV laser can accelerate the ionized electron in a quantized way during the collision between the electron and its parent ion. This process cannot be explained by the classical three-step model. Our results indicate that the previously well-established concept that HATI is an elastic recollision process is broken down.展开更多
As the width-thickness ratio of the discrete nozzle atomizer’s discrete hole greatly influences the loss of atomizing gas flow rate,the discrete nozzle atomizer was transformed into an annular slit atomizer with the ...As the width-thickness ratio of the discrete nozzle atomizer’s discrete hole greatly influences the loss of atomizing gas flow rate,the discrete nozzle atomizer was transformed into an annular slit atomizer with the same total nozzle outlet area.A numerical simulation study on the effect of various parameters on the atomization in the annular slit atomizer was carried out by coupling both the large eddy simulation(LES)and volume of fluid(VOF)model,which is based on the applicability of LES in capturing the breakup behavior of transient liquid droplets and the advantage of VOF method in directly capturing the phase interface.The simulation results showed that the increase in the atomization pressure makes the gas gain higher momentum,while the increase in the nozzle intersection angle decreases the distance between the nozzle exit and the computational domain axis.The increase in these two variables results in enhancing the gas-liquid interaction in the primary atomization zone and the formation of more aluminum droplets simultaneously.It is considered that the atomization effect becomes better when atomization pressure is 2.5 MPa,and the nozzle intersection angle is 60°.Industrial tests showed that the aluminum powder prepared by the optimized annular slit atomizer has a finer mean particle size and a higher yield of fine powder.The numerical simulation results agree well with the industrial test data of the powder particle size.展开更多
Observations of the second solar spectrum(SSS) revealed the existence of prominent linear polarization signals due to lines of the C2 molecule.Interpretation of the SSS is the only tool to obtain the weak and turbulen...Observations of the second solar spectrum(SSS) revealed the existence of prominent linear polarization signals due to lines of the C2 molecule.Interpretation of the SSS is the only tool to obtain the weak and turbulent magnetic field which is widespread in the Quiet Sun.However,this interpretation is conditioned by the determination of accurate collisional data.In this context,we present a formulation of the problem of the calculation of the polarization transfer rates by collisions of polarized C2 states with electrons.The obtained formulae are applied to determine,for the first time,the polarization transfer rates between the C2 states of the Swan band electronic system(a 3Πu d 3Πq) and electrons for temperatures going up from 1000 to 10000 K.However,due to the closeness of the electronic states of the C2 molecule,the two electronic d 3Πg and a 3Πu cannot be disconnected from the other electronic levels and,thus,a model based on only two states is not sufficient to describe the formation of the lines in the Swan band.Consequently,we also calculated the collisional polarization transfer rates in the case where the first eight electronic states of C2 are taken into account.All rates are given as functions of the temperature by power laws.Our results should be useful for future solar applications.展开更多
The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma.We calculate the electric resistivity in the solar photosphere and chromosphere,which is the key parameter that controls the...The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma.We calculate the electric resistivity in the solar photosphere and chromosphere,which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet.The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions.We find that under the typical conditions of the quiet Sun,electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere,and mostly by the ion-hydrogen collisions,i.e.ambipolar diffusion,in the chromosphere.In magnetic reconnection events with strong magnetic fields,the ambipolar diffusion,however,may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms.We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.展开更多
The largest and most detailed map of the distribution of dark matter in the Universe has been recently created by the Dark Energy Survey(DES)team.The distribution was found to be slightly(by a few percent)smoother and...The largest and most detailed map of the distribution of dark matter in the Universe has been recently created by the Dark Energy Survey(DES)team.The distribution was found to be slightly(by a few percent)smoother and less clumpy than predicted by general relativity.This result was considered as a hint of some new physical laws.In the present paper we offer a relatively simple model that could explain the above result without resorting to any new physical laws.The model deals with the dynamics of a system consisting of a large number of gravitating neutral particles,whose mass is equal to the mass of hydrogen atoms.The central point of the model is a partial inhibition of the gravitation for a relatively small subsystem of the entire system.It would be sufficient for this subsystem to constitute just about a few percent of the total ensemble of particles for explaining the few percent more smooth distribution of dark matter(observed by the DES team)compared to the prediction of general relativity.The most viable candidate for the dark matter particles in this model is the second flavor of hydrogen atoms(SFHA)that has only S-states and therefore does not couple to the electric dipole radiation or even to higher multipole radiation,so that the SFHA is practically dark.The SFHA has experimental confirmation from atomic experiments,it does not go beyond the Standard Model,it is based on standard quantum mechanics and it explains puzzling astrophysical observations of the redshifted line 21 cm from the early Universe.Thus,our model explaining the DES result of a little too smooth distribution of dark matter without resorting to any new physical laws seems to be self-consistent.展开更多
基金This work has been supported by the Flu,tda~ion Of harbin institute of Technology for Out standing YOungScientists (No. 1832).
文摘A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.
文摘In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. Relatively high rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during flight and upon impacting with the substrate. The processing method uses codeposition of the metallic semi-solidified droplets (metallic matrix) with the injected reinforcement ceramic particles. In the present paper, the microstructures, mechanical properties, interfacial properties, thermal stability and aging behaviour of spray atomized and codeposited Al-Li-X MMC’s (injected X=SiC, Al2O3) are reported and correlated to the processing conditions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474348,61275128,11274050,11334009and 11425414the NSERC of Canada+1 种基金the Canadian Computing Facilities of SHARCnet and ACEnetthe National Basic Research Program of China under Grant No 2013CB922200
文摘We investigate the above-threshold ionization of an atom in a combined infrared(IR) and extreme ultraviolet(XUV) two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization(HATI)process. It is demonstrated that, in stark contrast to previous studies, the XUV laser may play a significant role in atomic HATI process, and in particular, the XUV laser can accelerate the ionized electron in a quantized way during the collision between the electron and its parent ion. This process cannot be explained by the classical three-step model. Our results indicate that the previously well-established concept that HATI is an elastic recollision process is broken down.
基金the financial support provided by the National Natural Science Foundation of China(U21A20317)supported by High-Performance Computing Center of Wuhan University of Science and Technology.
文摘As the width-thickness ratio of the discrete nozzle atomizer’s discrete hole greatly influences the loss of atomizing gas flow rate,the discrete nozzle atomizer was transformed into an annular slit atomizer with the same total nozzle outlet area.A numerical simulation study on the effect of various parameters on the atomization in the annular slit atomizer was carried out by coupling both the large eddy simulation(LES)and volume of fluid(VOF)model,which is based on the applicability of LES in capturing the breakup behavior of transient liquid droplets and the advantage of VOF method in directly capturing the phase interface.The simulation results showed that the increase in the atomization pressure makes the gas gain higher momentum,while the increase in the nozzle intersection angle decreases the distance between the nozzle exit and the computational domain axis.The increase in these two variables results in enhancing the gas-liquid interaction in the primary atomization zone and the formation of more aluminum droplets simultaneously.It is considered that the atomization effect becomes better when atomization pressure is 2.5 MPa,and the nozzle intersection angle is 60°.Industrial tests showed that the aluminum powder prepared by the optimized annular slit atomizer has a finer mean particle size and a higher yield of fine powder.The numerical simulation results agree well with the industrial test data of the powder particle size.
基金funded by the Deanship of Scientific Research(DSR)at King Abdulaziz University,Jeddah,under grant no.G:426–130–1440DSR for technical and financial support。
文摘Observations of the second solar spectrum(SSS) revealed the existence of prominent linear polarization signals due to lines of the C2 molecule.Interpretation of the SSS is the only tool to obtain the weak and turbulent magnetic field which is widespread in the Quiet Sun.However,this interpretation is conditioned by the determination of accurate collisional data.In this context,we present a formulation of the problem of the calculation of the polarization transfer rates by collisions of polarized C2 states with electrons.The obtained formulae are applied to determine,for the first time,the polarization transfer rates between the C2 states of the Swan band electronic system(a 3Πu d 3Πq) and electrons for temperatures going up from 1000 to 10000 K.However,due to the closeness of the electronic states of the C2 molecule,the two electronic d 3Πg and a 3Πu cannot be disconnected from the other electronic levels and,thus,a model based on only two states is not sufficient to describe the formation of the lines in the Swan band.Consequently,we also calculated the collisional polarization transfer rates in the case where the first eight electronic states of C2 are taken into account.All rates are given as functions of the temperature by power laws.Our results should be useful for future solar applications.
基金supported by the National Research Foundation of Korea(NRF-2020R1A2C2004616)the support by the Deutsche Forschungsgemeinschaft project(434200803)。
文摘The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma.We calculate the electric resistivity in the solar photosphere and chromosphere,which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet.The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions.We find that under the typical conditions of the quiet Sun,electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere,and mostly by the ion-hydrogen collisions,i.e.ambipolar diffusion,in the chromosphere.In magnetic reconnection events with strong magnetic fields,the ambipolar diffusion,however,may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms.We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.
文摘The largest and most detailed map of the distribution of dark matter in the Universe has been recently created by the Dark Energy Survey(DES)team.The distribution was found to be slightly(by a few percent)smoother and less clumpy than predicted by general relativity.This result was considered as a hint of some new physical laws.In the present paper we offer a relatively simple model that could explain the above result without resorting to any new physical laws.The model deals with the dynamics of a system consisting of a large number of gravitating neutral particles,whose mass is equal to the mass of hydrogen atoms.The central point of the model is a partial inhibition of the gravitation for a relatively small subsystem of the entire system.It would be sufficient for this subsystem to constitute just about a few percent of the total ensemble of particles for explaining the few percent more smooth distribution of dark matter(observed by the DES team)compared to the prediction of general relativity.The most viable candidate for the dark matter particles in this model is the second flavor of hydrogen atoms(SFHA)that has only S-states and therefore does not couple to the electric dipole radiation or even to higher multipole radiation,so that the SFHA is practically dark.The SFHA has experimental confirmation from atomic experiments,it does not go beyond the Standard Model,it is based on standard quantum mechanics and it explains puzzling astrophysical observations of the redshifted line 21 cm from the early Universe.Thus,our model explaining the DES result of a little too smooth distribution of dark matter without resorting to any new physical laws seems to be self-consistent.