Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ig...Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ignition mechanism of EFIs directly igniting pyrotechnics.An oscilloscope,a photon Doppler velocimetry,and a plasma spectrum measurement system were employed to obtain information of electric characteristics,impact pressure,and plasma temperature.The results of the electric characteristics and the impact pressure were inconsistent with ignition results.The only thing that the ignition success tests had in common was that their plasma all had a relatively long period of high-temperature duration(HTD).It eventually concludes that the ignition mechanism in this research is the microconvection heat transfer rather than the shock initiation,which differs from that of exploding foil initiators detonating explosives.Furthermore,the methods for evaluating the ignition success of semiconductor bridge initiators are not entirely applicable to the tests mentioned in this paper.The HTD is the critical parameter for judging the ignition success,and it is influenced by two factors:the late time discharge and the energy of the electric explosion.The longer time of the late time discharge and the more energy of the electric explosion,the easier it is to expand the HTD,which improves the probability of the ignition success.展开更多
Understanding the response of solid combustibles under high radiant fluxes is critical in predicting the thermal damage from extreme scenarios.Unlike the more moderate radiant fluxes in conventional hydrocarbon fires,...Understanding the response of solid combustibles under high radiant fluxes is critical in predicting the thermal damage from extreme scenarios.Unlike the more moderate radiant fluxes in conventional hydrocarbon fires,extreme events such as strong explosion,concentrated sunlight and directed energy can generate dynamic radiant fluxes at the MW/m^(2) level,creating a unique threat to materials.This study investigates the pyrolysis and spontaneous ignition behaviors of corrugated cardboard by using both experimental and numerical methods,under 10-cm dynamic high radiant fluxes ranging from 0.2 to 1.25 MW/m^(2) for 10 s.The spontaneous ignition process at dynamic high radiant fluxes was recorded and quantified.Two ignition modes were found at the critical radiant flux of 0.4 MW/m^(2),namely hot-gas spontaneous ignition and hot-residue piloted ignition.The latter is not the focus of this paper due to its extremely small probability of occurrence.The research reveals that the increase in flux intensity induces shorter delay times for both pyrolysis and ignition,lower ignition energy density,along with a corresponding rise in the critical mass flux and surface temperature at ignition moment.The simulation results are generally aligned with the experimental findings,despite some divergences may be attributed to model simplifications and parameter assumptions.The work contributes to a deeper insight into material behavior under extreme radiation,with valuable implications for fire safety and hazard assessment.展开更多
Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)an...Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.展开更多
The non-linear effects of different initial melt temperatures on the microstructure evolution during the solidification process of liquid Mg7Zn3 alloys were investigated by molecular dynamics simulation, The microstru...The non-linear effects of different initial melt temperatures on the microstructure evolution during the solidification process of liquid Mg7Zn3 alloys were investigated by molecular dynamics simulation, The microstructure transformation mechanisms were analyzed by several methods. The system was found to be solidified into amorphous structures from different initial melt temperatures at the same cooling rate of 1×10^12 K/s, and the 1551 bond-type and the icosahedron basic cluster (12 0 12 0 ) played a key role in the microstructure transition. Different initial melt temperatures had significant effects on the final microstructures. These effects only can be clearly observed below the glass transition temperature Tg; and these effects are non-linearly related to the initial melt temperatures, and fluctuated in a certain range. However, the changes of the average atomic energy of the systems are still linearly related with the initial melt temperatures, namely, the higher the initial melt temperature is, the more stable the amorphous structure is and the stronger the glass forming ability will be.展开更多
Application of the Semenov theory of spontaneous ignition to evaluation of the critical temperature (Tc) in thermal explosion (TE) synthesis was conducted with the Ti-75at pct Al binary system using nonisothermal diff...Application of the Semenov theory of spontaneous ignition to evaluation of the critical temperature (Tc) in thermal explosion (TE) synthesis was conducted with the Ti-75at pct Al binary system using nonisothermal differential scanning calorimetry (DSC) at different heating rates. And the critical temperature for isothermal TE is predicted to be 728.9癈 by the multiple linear regression of Tcs evaluated according to Semenov theory, which is close to the range of 740~745癈 obtained from the isothermal DSC observation. This result proves that Semenov theory of spontaneous ignition is also feasible for TE synthesis in binary metallic systems like Ti-75 at. pct Al system.展开更多
The bending of the Euler-Bernoulli micro-beam has been extensively modeled based on the modified couple stress(MCS)theory.Although many models have been incorporated into the literature,there is still room for introdu...The bending of the Euler-Bernoulli micro-beam has been extensively modeled based on the modified couple stress(MCS)theory.Although many models have been incorporated into the literature,there is still room for introducing an improved model in this context.In this work,we investigate the thermoelastic vibration of a micro-beam exposed to a varying temperature due to the application of the initial stress employing the MCS theory and generalized thermoelasticity.The MCS theory is used to investigate the material length scale effects.Using the Laplace transform,the temperature,deflection,displacement,flexure moment,and stress field variables of the micro-beam are derived.The effects of the temperature pulse and couple stress on the field distributions of the micro-beam are obtained numerically and graphically introduced.The numerical results indicate that the temperature pulse and couple stress have a significant effect on all field variables.展开更多
Global warming has become a topic of widespread attention. The climate change will affect the change of agricultural climate resource,thereby affecting the agricultural planting structure,the grain yield,etc. Based on...Global warming has become a topic of widespread attention. The climate change will affect the change of agricultural climate resource,thereby affecting the agricultural planting structure,the grain yield,etc. Based on the daily temperature of Zhangjiakou from 1960 to 2011,the temporal changes of ≥0 ℃ and ≥10 ℃ accumulated temperatures were analyzed by using the methods of linear trend estimation and M-K mutation test. The results indicated that(1) the annual average temperature showed an increasing trend with the linear warming rate of 0. 42 ℃ /10 a in the past 52 years. In 1982,the annual average temperature had abrupt change,especially after 1983,the warming trend increased significantly.(2) In the past 52 years,≥0 ℃ accumulated temperature showed an increasing trend with the warming rate of 89. 4 ℃ /10 a. Mutation point of ≥0 ℃ accumulated temperature appeared in 1983,and after 1985,≥0 ℃ accumulated temperature increased sharply. At the same time,the ≥10 ℃ accumulated temperature had abrupt change in 1983,especially from 1987 to 1995 and after 1986,the warming trend increased sharply.(3) The initial date of ≥0 ℃ presented significant advancing trend,and that of ≥10 ℃ had little change,while their terminal dates presented delaying trend,so the sustained days of ≥0 ℃ and ≥10 ℃ increased significantly.(4) In the past 52 years,the delay of the terminal dates of ≥0 ℃ and ≥10 ℃ was greater than the advancing of the initial dates,and ≥0 ℃ accumulated temperature had a greater increase than ≥10 ℃ accumulated temperature.展开更多
This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2...This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) alloy was discussed in depth through ignition-proof testing and microstructure observation. The results showed that the AZ91D-3 Nd-2 Dy alloy exhibited the highest ignition-point of 893 K, increased by 69 K as compared to the AZ91D alloy. The ignition-proof mechanism of Nd and Dy additions lay in three aspects:(1) the formation of denser oxide film consisting of Dy_2O_3 and MgO improves the oxidation resistance of the alloy,(2) the great reduction of the low melting-point phase β-Mg_(17)Al_(12), which leads to the decrease in the oxygen diffusion channels, and(3) the newly formed high melting-point phases(Al_2Nd and Al_2Dy), which block the oxygen diffusion channels and prevent the chemical reaction of Mg and oxygen.展开更多
To assess the influence of the initial temperature field on ocean temperature and sea ice simulations,a climatological dataset(WOA18),a real-time varying dataset(SODA),and an analysis field obtained after applying the...To assess the influence of the initial temperature field on ocean temperature and sea ice simulations,a climatological dataset(WOA18),a real-time varying dataset(SODA),and an analysis field obtained after applying the“vertical projection”assimilation scheme were selected to obtain the initial temperature field(the initial moment was December 1,2015)for use in the sea ice simulation of the HAMSOM ice-ocean coupled model,considering the Bohai Sea in the 2015/2016 winter.In this study,after using this assimilation scheme,the analysis initial temperature field showed significant improvement.The simulated SST results showed that the initial temperature field had a considerable effect on the SST results in the first 45 days of the model run;after this period,the effect became negligible and the model internal dynamics and atmospheric forcing became dominant.The simulated sea ice results showed that the ice area and ice edge distance(i.e.,the distance between the intersection of the central axis and the ice edge line and axis apex)results obtained in experiment E3 which used the analysis initial temperature field were improved by~14%and~35%,respectively,and those obtained in experiment E2 which used the real-time varying initial temperature field were improved by~10%and~22%,respectively,compared to the results of experiment E1 which used the climatological initial temperature field.展开更多
Wire rolling is a typical large deformation process and its principle is very complex,which includes material non- linearity,geometry non-linearity and boundary non-linearity.It is difficult to obtain theory analytica...Wire rolling is a typical large deformation process and its principle is very complex,which includes material non- linearity,geometry non-linearity and boundary non-linearity.It is difficult to obtain theory analytical results by trying to roll or physical experiment because they will induce many problems such as high cost,waste time and venture.With the rapid advance- ment of computing technology and numerical method,the finite element method is regarded as the best one,which can account for the large plastic deformation,thermo-mechanical coupling and complex boundary conditions of the rollers and the workpiece inter- actions in the rolling process.Under the different initial rolling temperature,the two-pass hot continuous rolling process of high- speed wire has been simulated accurately for the pre-finishing rolling section.The metal fluxion law and the deformation field have been obtained.Strain,temperature,rolling force and torque also have been simulated and discussed.The results of simulation are useful for practical manufacture and the optimization of process-parameters.展开更多
Due to climate change, extreme heat stress events have become more frequent, adversely affecting rice yield and grain quality. The accumulation and translocation of dry matter and nitrogen substances are essential for...Due to climate change, extreme heat stress events have become more frequent, adversely affecting rice yield and grain quality. The accumulation and translocation of dry matter and nitrogen substances are essential for rice yield and grain quality. To assess the impact of high temperature stress(HTS) at the early panicle initiation(EPI) stage on the accumulation, transportation, and distribution of dry matter and nitrogen substances in various organs of rice, as well as the resulting effects on rice yield and grain quality, pot experiments were conducted using an indica rice cultivar Yangdao 6(YD6) and a japonica rice cultivar Jinxiangyu 1(JXY1) under both normal temperature(32 ℃/26 ℃) and high temperature(38 ℃/29 ℃) conditions. The results indicated that exposure to HTS at the EPI stage significantly decreased rice yield by reducing spikelet number per panicle, grain-filling rate, and grain weight. However, it improved the nutritional quality of rice grains by increasing protein and amylose contents. The reduction in nitrogen and dry matter accumulation accounted for the changes in spikelet number per panicle, grain-filling rate, and grain size. Under HTS, the decrease in nitrogen accumulation accompanied by the reduction in dry matter may be due to the down-regulation of leaf net photosynthesis and senescence, as evidenced by the decrease in nitrogen content. Furthermore, the decrease in sink size limited the translocation of dry matter and nitrogen substances to grains, which was closely related to the reduction in grain weight and the deterioration of grain quality. These findings significantly contribute to our understanding of the mechanisms of HTS on grain yield and quality formation from the perspective of dry matter and nitrogen accumulation and translocation. Further efforts are needed to improve the adaptability of rice varieties to climate change in the near future.展开更多
High temperatures cause physiological and biochemical changes and significantly affect young panicle development of rice(Oryza sativa L.).Brassinosteroids play important roles in enhancing crop stress resistance.In th...High temperatures cause physiological and biochemical changes and significantly affect young panicle development of rice(Oryza sativa L.).Brassinosteroids play important roles in enhancing crop stress resistance.In this study,we subjected rice cultivars Huanghuazhan(heat-resistant)and IR36(heat-sensitive)to high temperature(HT,40 oC)or normal temperature(NT,33 oC)for 7 d at the panicle initiation stage,in conjunction with application of 24-epibrassinolide[EBR,a synthetic brassinolide(BR)]or brassinazole(BRZ,a BR biosynthesis inhibitor)at the beginning of the treatments.HT exacerbated spikelet degeneration and inhibited young panicle growth,which were partially prevented by EBR application,while BRZ application aggravated the reduction in spikelet number.HT decreased the contents of BR,active cytokinins(aCTK),active gibberellins(aGA)and indole-3-acetic acid(IAA),but increased the content of abscisic acid(ABA)in young panicles.The activities of key enzymes involved in sucrose hydrolysis,glycolysis and the tricarboxylic acid cycle in young panicles were decreased with the change of endogenous hormone levels under HT.In addition,the contents of H2O2 and malondialdehyde(MDA)were increased and the activities of antioxidant enzymes were decreased in young panicles.Exogenous application of EBR induced the expression of phytohormone biosynthesis-related genes and down-regulated the expression of phytohormone catabolism-related genes to increase the contents of endogenous BR,aCTK,aGA and ABA,thus promoting the decomposition and utilization of sucrose in young panicles,enhancing the activities of superoxide dismutase,catalase and peroxidase,and reducing the accumulation of H2O2 and MDA in young panicles,whereas application of BRZ had the opposite physiological effects.These results showed that brassinosteroids mediate endogenous phytohormone metabolism to alleviate HT injury at the panicle initiation stage in rice.展开更多
Magnesium alloys are well known for their excellent properties, but the potential issues with oxidation and burning during melting and casting largely limit its industrial applications. The addition of Ce in magnesium...Magnesium alloys are well known for their excellent properties, but the potential issues with oxidation and burning during melting and casting largely limit its industrial applications. The addition of Ce in magnesium alloys can significantly raise ignition-proof performance and change the structure of the oxide film on the surface of the molten metal as well as the surface tension values. Surface tension is an important physical parameter of the metal melts, and it plays an important role in the formation of surface oxide film. In this present work, the ignition temperature and the surface tension of Mg-9wt.%AI alloy with different Ce concentrations were studied. Surface tensions was measured using the maximum bubble pressure method (MBPM). Ignition temperature was measured using NiCr-NiSi type thermocouples and was monitored and recorded via a WXT-604 desk recording device. The results show that the ignition point of Mg-9wt.%AI alloy can be effectively elevated by adding Ce. The ignition temperature reaches its highest point of 720 ℃ when the addition of Ce is lwt.%. The surface tension of the molten Mg-9wt.%AI alloy decreases exponentially with the increase of Ce addition at the same temperature. Similarly, the experiment also shows that the surface tension of Mg-9wt.%AI alloy decreases exponentially with the increase of temperature.展开更多
<span style="font-family:Verdana;">The objective of this study was to investigate performance characteristics of a spark ignition engine, particularly, the correlation between performance, exhaust gas ...<span style="font-family:Verdana;">The objective of this study was to investigate performance characteristics of a spark ignition engine, particularly, the correlation between performance, exhaust gas temperature and speed, using Kiva4. Test data to validate kiva4 si</span><span style="font-family:Verdana;">mulation</span><span style="font-family:Verdana;"> results were conducted on a 3-cylinder, four-stroke Volkswagen (</span><span style="font-family:Verdana;">VW) Polo 6 TSI 1.2 gasoline engine. Three different tests were, therefore, carried out. In one set, variations in exhaust gas temperature were studied by varying the engine load, while keeping the engine speed constant. In another test, exhaust gas temperature variations were studied by keeping the engine at idling whilst varying the speeds. A third test involved studying variations in exhaust gas temperature under a constant load with variable engine speeds. To study </span><span style="font-family:Verdana;">variations in exhaust gas temperatures under test conditions, a basic grid/</span><span style="font-family:Verdana;">mesh generator, K3PREP, was employed to write an itape17 file comprising of a 45</span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">°</span><span> <span style="font-family:Verdana;">asymmetrical mesh. This was based on the symmetry of the combustion ch</span><span style="font-family:Verdana;">amber of </span><span style="font-family:Verdana;">the engine used in carrying out experimental tests. Simulati</span><span style="font-family:Verdana;">ons were therefore p</span><span style="font-family:Verdana;">erformed based on the input parameters established in</span><span style="font-family:Verdana;"> the conducted tests. Simulations with the kiva4 code showed a significant predictability of the performance characteristics of the engine. This was evident in the appreciable agreement obtained in the simulation results when compared </span><span style="font-family:Verdana;">with the test data, under the considered test conditions. A percentage error, be</span><span style="font-family:Verdana;">tween experimental results and results from simulations with the kiva4 code of only between 2% to 3% was observed.</span></span></span></span></span>展开更多
It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics li...It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics like SrTiO<sub>3</sub> under the temperatures 60 - 200 K, these crystals possess the cubic nonlinearity. The bias electric field is applied to provide the dominating quadratic nonlinearity. The initial focusing of the beams not only increases the efficiency of generation of higher harmonics, but alto makes possible to select maxima of different higher harmonics at some distances from the input. At lower temperatures the nonlinearity behaves at smaller input amplitudes, whereas at higher temperatures the harmonic generation can be observed at higher frequencies up to 1.5 THz. In three-dimensional beams the peak amplitudes of higher harmonics can be bigger than in two-dimensional beams, but the ratios of these peak values to the maximum values of the focused first harmonic are smaller than in two-dimensional beams.展开更多
文摘Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ignition mechanism of EFIs directly igniting pyrotechnics.An oscilloscope,a photon Doppler velocimetry,and a plasma spectrum measurement system were employed to obtain information of electric characteristics,impact pressure,and plasma temperature.The results of the electric characteristics and the impact pressure were inconsistent with ignition results.The only thing that the ignition success tests had in common was that their plasma all had a relatively long period of high-temperature duration(HTD).It eventually concludes that the ignition mechanism in this research is the microconvection heat transfer rather than the shock initiation,which differs from that of exploding foil initiators detonating explosives.Furthermore,the methods for evaluating the ignition success of semiconductor bridge initiators are not entirely applicable to the tests mentioned in this paper.The HTD is the critical parameter for judging the ignition success,and it is influenced by two factors:the late time discharge and the energy of the electric explosion.The longer time of the late time discharge and the more energy of the electric explosion,the easier it is to expand the HTD,which improves the probability of the ignition success.
基金the Presidential Foundation of CAEP(Grant No.YZJJZQ2023008)the National Natural Science Foundation of China(Grant No.NSFC 12372342)for financial support of this work.
文摘Understanding the response of solid combustibles under high radiant fluxes is critical in predicting the thermal damage from extreme scenarios.Unlike the more moderate radiant fluxes in conventional hydrocarbon fires,extreme events such as strong explosion,concentrated sunlight and directed energy can generate dynamic radiant fluxes at the MW/m^(2) level,creating a unique threat to materials.This study investigates the pyrolysis and spontaneous ignition behaviors of corrugated cardboard by using both experimental and numerical methods,under 10-cm dynamic high radiant fluxes ranging from 0.2 to 1.25 MW/m^(2) for 10 s.The spontaneous ignition process at dynamic high radiant fluxes was recorded and quantified.Two ignition modes were found at the critical radiant flux of 0.4 MW/m^(2),namely hot-gas spontaneous ignition and hot-residue piloted ignition.The latter is not the focus of this paper due to its extremely small probability of occurrence.The research reveals that the increase in flux intensity induces shorter delay times for both pyrolysis and ignition,lower ignition energy density,along with a corresponding rise in the critical mass flux and surface temperature at ignition moment.The simulation results are generally aligned with the experimental findings,despite some divergences may be attributed to model simplifications and parameter assumptions.The work contributes to a deeper insight into material behavior under extreme radiation,with valuable implications for fire safety and hazard assessment.
基金the National Natural Science Foundation of China(Grant No.U20A2081)West Light Foundation of the Chinese Academy of Sciences(Grant No.xbzg-zdsys-202102)the Second Tibetan Plateau Scientific Expedition and Research(STEP)Project(Grant No.2019QZKK0105).
文摘Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.
基金Projects(50831003,51071065,51101022,51102090) supported by the National Natural Science Foundation of China
文摘The non-linear effects of different initial melt temperatures on the microstructure evolution during the solidification process of liquid Mg7Zn3 alloys were investigated by molecular dynamics simulation, The microstructure transformation mechanisms were analyzed by several methods. The system was found to be solidified into amorphous structures from different initial melt temperatures at the same cooling rate of 1×10^12 K/s, and the 1551 bond-type and the icosahedron basic cluster (12 0 12 0 ) played a key role in the microstructure transition. Different initial melt temperatures had significant effects on the final microstructures. These effects only can be clearly observed below the glass transition temperature Tg; and these effects are non-linearly related to the initial melt temperatures, and fluctuated in a certain range. However, the changes of the average atomic energy of the systems are still linearly related with the initial melt temperatures, namely, the higher the initial melt temperature is, the more stable the amorphous structure is and the stronger the glass forming ability will be.
文摘Application of the Semenov theory of spontaneous ignition to evaluation of the critical temperature (Tc) in thermal explosion (TE) synthesis was conducted with the Ti-75at pct Al binary system using nonisothermal differential scanning calorimetry (DSC) at different heating rates. And the critical temperature for isothermal TE is predicted to be 728.9癈 by the multiple linear regression of Tcs evaluated according to Semenov theory, which is close to the range of 740~745癈 obtained from the isothermal DSC observation. This result proves that Semenov theory of spontaneous ignition is also feasible for TE synthesis in binary metallic systems like Ti-75 at. pct Al system.
文摘The bending of the Euler-Bernoulli micro-beam has been extensively modeled based on the modified couple stress(MCS)theory.Although many models have been incorporated into the literature,there is still room for introducing an improved model in this context.In this work,we investigate the thermoelastic vibration of a micro-beam exposed to a varying temperature due to the application of the initial stress employing the MCS theory and generalized thermoelasticity.The MCS theory is used to investigate the material length scale effects.Using the Laplace transform,the temperature,deflection,displacement,flexure moment,and stress field variables of the micro-beam are derived.The effects of the temperature pulse and couple stress on the field distributions of the micro-beam are obtained numerically and graphically introduced.The numerical results indicate that the temperature pulse and couple stress have a significant effect on all field variables.
文摘Global warming has become a topic of widespread attention. The climate change will affect the change of agricultural climate resource,thereby affecting the agricultural planting structure,the grain yield,etc. Based on the daily temperature of Zhangjiakou from 1960 to 2011,the temporal changes of ≥0 ℃ and ≥10 ℃ accumulated temperatures were analyzed by using the methods of linear trend estimation and M-K mutation test. The results indicated that(1) the annual average temperature showed an increasing trend with the linear warming rate of 0. 42 ℃ /10 a in the past 52 years. In 1982,the annual average temperature had abrupt change,especially after 1983,the warming trend increased significantly.(2) In the past 52 years,≥0 ℃ accumulated temperature showed an increasing trend with the warming rate of 89. 4 ℃ /10 a. Mutation point of ≥0 ℃ accumulated temperature appeared in 1983,and after 1985,≥0 ℃ accumulated temperature increased sharply. At the same time,the ≥10 ℃ accumulated temperature had abrupt change in 1983,especially from 1987 to 1995 and after 1986,the warming trend increased sharply.(3) The initial date of ≥0 ℃ presented significant advancing trend,and that of ≥10 ℃ had little change,while their terminal dates presented delaying trend,so the sustained days of ≥0 ℃ and ≥10 ℃ increased significantly.(4) In the past 52 years,the delay of the terminal dates of ≥0 ℃ and ≥10 ℃ was greater than the advancing of the initial dates,and ≥0 ℃ accumulated temperature had a greater increase than ≥10 ℃ accumulated temperature.
文摘This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) alloy was discussed in depth through ignition-proof testing and microstructure observation. The results showed that the AZ91D-3 Nd-2 Dy alloy exhibited the highest ignition-point of 893 K, increased by 69 K as compared to the AZ91D alloy. The ignition-proof mechanism of Nd and Dy additions lay in three aspects:(1) the formation of denser oxide film consisting of Dy_2O_3 and MgO improves the oxidation resistance of the alloy,(2) the great reduction of the low melting-point phase β-Mg_(17)Al_(12), which leads to the decrease in the oxygen diffusion channels, and(3) the newly formed high melting-point phases(Al_2Nd and Al_2Dy), which block the oxygen diffusion channels and prevent the chemical reaction of Mg and oxygen.
基金This research was jointly sponsored by the National Key R&D Program of China(2019YFC 1407800)National Natural Science Foundation of China(No.42006154).
文摘To assess the influence of the initial temperature field on ocean temperature and sea ice simulations,a climatological dataset(WOA18),a real-time varying dataset(SODA),and an analysis field obtained after applying the“vertical projection”assimilation scheme were selected to obtain the initial temperature field(the initial moment was December 1,2015)for use in the sea ice simulation of the HAMSOM ice-ocean coupled model,considering the Bohai Sea in the 2015/2016 winter.In this study,after using this assimilation scheme,the analysis initial temperature field showed significant improvement.The simulated SST results showed that the initial temperature field had a considerable effect on the SST results in the first 45 days of the model run;after this period,the effect became negligible and the model internal dynamics and atmospheric forcing became dominant.The simulated sea ice results showed that the ice area and ice edge distance(i.e.,the distance between the intersection of the central axis and the ice edge line and axis apex)results obtained in experiment E3 which used the analysis initial temperature field were improved by~14%and~35%,respectively,and those obtained in experiment E2 which used the real-time varying initial temperature field were improved by~10%and~22%,respectively,compared to the results of experiment E1 which used the climatological initial temperature field.
文摘Wire rolling is a typical large deformation process and its principle is very complex,which includes material non- linearity,geometry non-linearity and boundary non-linearity.It is difficult to obtain theory analytical results by trying to roll or physical experiment because they will induce many problems such as high cost,waste time and venture.With the rapid advance- ment of computing technology and numerical method,the finite element method is regarded as the best one,which can account for the large plastic deformation,thermo-mechanical coupling and complex boundary conditions of the rollers and the workpiece inter- actions in the rolling process.Under the different initial rolling temperature,the two-pass hot continuous rolling process of high- speed wire has been simulated accurately for the pre-finishing rolling section.The metal fluxion law and the deformation field have been obtained.Strain,temperature,rolling force and torque also have been simulated and discussed.The results of simulation are useful for practical manufacture and the optimization of process-parameters.
基金supported by the Jiangsu Agriculture Science and Technology Innovation Fund,China(Grant No.CX(23)1035)the National Natural Science Foundation of China(Grant Nos.32201888,32071943,and 32272197)+2 种基金the Provincial Natural Science Foundation of Jiangsu,China(Grant No.BK20200923)the National Key Research and Development Program of China(Grant Nos.SQ 2022YFD1500402 and SQ2022YFD2300304)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China.
文摘Due to climate change, extreme heat stress events have become more frequent, adversely affecting rice yield and grain quality. The accumulation and translocation of dry matter and nitrogen substances are essential for rice yield and grain quality. To assess the impact of high temperature stress(HTS) at the early panicle initiation(EPI) stage on the accumulation, transportation, and distribution of dry matter and nitrogen substances in various organs of rice, as well as the resulting effects on rice yield and grain quality, pot experiments were conducted using an indica rice cultivar Yangdao 6(YD6) and a japonica rice cultivar Jinxiangyu 1(JXY1) under both normal temperature(32 ℃/26 ℃) and high temperature(38 ℃/29 ℃) conditions. The results indicated that exposure to HTS at the EPI stage significantly decreased rice yield by reducing spikelet number per panicle, grain-filling rate, and grain weight. However, it improved the nutritional quality of rice grains by increasing protein and amylose contents. The reduction in nitrogen and dry matter accumulation accounted for the changes in spikelet number per panicle, grain-filling rate, and grain size. Under HTS, the decrease in nitrogen accumulation accompanied by the reduction in dry matter may be due to the down-regulation of leaf net photosynthesis and senescence, as evidenced by the decrease in nitrogen content. Furthermore, the decrease in sink size limited the translocation of dry matter and nitrogen substances to grains, which was closely related to the reduction in grain weight and the deterioration of grain quality. These findings significantly contribute to our understanding of the mechanisms of HTS on grain yield and quality formation from the perspective of dry matter and nitrogen accumulation and translocation. Further efforts are needed to improve the adaptability of rice varieties to climate change in the near future.
基金funded by the Natural Science Foundation of Zhejiang Province,China(Grant No.LQ20C130009)the Science and Technology Project of Zhejiang Province,China(Grant No.2022C02034)the Special Fund for China Agricultural Research System(Grant No.CARS-01-22)。
文摘High temperatures cause physiological and biochemical changes and significantly affect young panicle development of rice(Oryza sativa L.).Brassinosteroids play important roles in enhancing crop stress resistance.In this study,we subjected rice cultivars Huanghuazhan(heat-resistant)and IR36(heat-sensitive)to high temperature(HT,40 oC)or normal temperature(NT,33 oC)for 7 d at the panicle initiation stage,in conjunction with application of 24-epibrassinolide[EBR,a synthetic brassinolide(BR)]or brassinazole(BRZ,a BR biosynthesis inhibitor)at the beginning of the treatments.HT exacerbated spikelet degeneration and inhibited young panicle growth,which were partially prevented by EBR application,while BRZ application aggravated the reduction in spikelet number.HT decreased the contents of BR,active cytokinins(aCTK),active gibberellins(aGA)and indole-3-acetic acid(IAA),but increased the content of abscisic acid(ABA)in young panicles.The activities of key enzymes involved in sucrose hydrolysis,glycolysis and the tricarboxylic acid cycle in young panicles were decreased with the change of endogenous hormone levels under HT.In addition,the contents of H2O2 and malondialdehyde(MDA)were increased and the activities of antioxidant enzymes were decreased in young panicles.Exogenous application of EBR induced the expression of phytohormone biosynthesis-related genes and down-regulated the expression of phytohormone catabolism-related genes to increase the contents of endogenous BR,aCTK,aGA and ABA,thus promoting the decomposition and utilization of sucrose in young panicles,enhancing the activities of superoxide dismutase,catalase and peroxidase,and reducing the accumulation of H2O2 and MDA in young panicles,whereas application of BRZ had the opposite physiological effects.These results showed that brassinosteroids mediate endogenous phytohormone metabolism to alleviate HT injury at the panicle initiation stage in rice.
基金supported by the Southeast University Innovation Foundation under the contract No.0941701
文摘Magnesium alloys are well known for their excellent properties, but the potential issues with oxidation and burning during melting and casting largely limit its industrial applications. The addition of Ce in magnesium alloys can significantly raise ignition-proof performance and change the structure of the oxide film on the surface of the molten metal as well as the surface tension values. Surface tension is an important physical parameter of the metal melts, and it plays an important role in the formation of surface oxide film. In this present work, the ignition temperature and the surface tension of Mg-9wt.%AI alloy with different Ce concentrations were studied. Surface tensions was measured using the maximum bubble pressure method (MBPM). Ignition temperature was measured using NiCr-NiSi type thermocouples and was monitored and recorded via a WXT-604 desk recording device. The results show that the ignition point of Mg-9wt.%AI alloy can be effectively elevated by adding Ce. The ignition temperature reaches its highest point of 720 ℃ when the addition of Ce is lwt.%. The surface tension of the molten Mg-9wt.%AI alloy decreases exponentially with the increase of Ce addition at the same temperature. Similarly, the experiment also shows that the surface tension of Mg-9wt.%AI alloy decreases exponentially with the increase of temperature.
文摘<span style="font-family:Verdana;">The objective of this study was to investigate performance characteristics of a spark ignition engine, particularly, the correlation between performance, exhaust gas temperature and speed, using Kiva4. Test data to validate kiva4 si</span><span style="font-family:Verdana;">mulation</span><span style="font-family:Verdana;"> results were conducted on a 3-cylinder, four-stroke Volkswagen (</span><span style="font-family:Verdana;">VW) Polo 6 TSI 1.2 gasoline engine. Three different tests were, therefore, carried out. In one set, variations in exhaust gas temperature were studied by varying the engine load, while keeping the engine speed constant. In another test, exhaust gas temperature variations were studied by keeping the engine at idling whilst varying the speeds. A third test involved studying variations in exhaust gas temperature under a constant load with variable engine speeds. To study </span><span style="font-family:Verdana;">variations in exhaust gas temperatures under test conditions, a basic grid/</span><span style="font-family:Verdana;">mesh generator, K3PREP, was employed to write an itape17 file comprising of a 45</span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">°</span><span> <span style="font-family:Verdana;">asymmetrical mesh. This was based on the symmetry of the combustion ch</span><span style="font-family:Verdana;">amber of </span><span style="font-family:Verdana;">the engine used in carrying out experimental tests. Simulati</span><span style="font-family:Verdana;">ons were therefore p</span><span style="font-family:Verdana;">erformed based on the input parameters established in</span><span style="font-family:Verdana;"> the conducted tests. Simulations with the kiva4 code showed a significant predictability of the performance characteristics of the engine. This was evident in the appreciable agreement obtained in the simulation results when compared </span><span style="font-family:Verdana;">with the test data, under the considered test conditions. A percentage error, be</span><span style="font-family:Verdana;">tween experimental results and results from simulations with the kiva4 code of only between 2% to 3% was observed.</span></span></span></span></span>
文摘It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics like SrTiO<sub>3</sub> under the temperatures 60 - 200 K, these crystals possess the cubic nonlinearity. The bias electric field is applied to provide the dominating quadratic nonlinearity. The initial focusing of the beams not only increases the efficiency of generation of higher harmonics, but alto makes possible to select maxima of different higher harmonics at some distances from the input. At lower temperatures the nonlinearity behaves at smaller input amplitudes, whereas at higher temperatures the harmonic generation can be observed at higher frequencies up to 1.5 THz. In three-dimensional beams the peak amplitudes of higher harmonics can be bigger than in two-dimensional beams, but the ratios of these peak values to the maximum values of the focused first harmonic are smaller than in two-dimensional beams.