A numerical simulation is performed for thermal instability and heat transfer of viscoelastic fluids in bounded porous media under the bottom constant heat flux boundary condition. The results for six different combin...A numerical simulation is performed for thermal instability and heat transfer of viscoelastic fluids in bounded porous media under the bottom constant heat flux boundary condition. The results for six different combinations of relaxation and retardation times demonstrate the existence of the thermal instability induced flow bifurcation. It is found that the increase of the relaxation time can enhance the heat transfer efficiency by disturbing the fluid flow and facilitating the bifurcation. The increase of the retardation time can stabilize the flow and postpone the bifurcation, leading to simpler flow pattern and lower heat transfer rate.展开更多
The authors examined the thermal change in the aroma profile of myrrh. The fresh odor of raw myrrh and its hexane extract depended on the amount of （E）-13-ocimene. Myrrh was extracted with hexane to avoid inducing c...The authors examined the thermal change in the aroma profile of myrrh. The fresh odor of raw myrrh and its hexane extract depended on the amount of （E）-13-ocimene. Myrrh was extracted with hexane to avoid inducing changes in the constituents and odor. The main constituent, （E）-L3-ocimene （group A; low boiling point）, and the other constituents （group B; high boiling point） of the hexane extract were separated by bulb-to-bulb distillation. The constituents of groups A and B were analyzed over time by nuclear magnetic resonance analysis and the odors were evaluated. Myrrh＇s odor depended on both the amount of thermally unstable （E）-[3-ocimene, which contributed to the fresh odor, and the constituents of group B （thermally stable）, which contributed to the myrrh-like odor. Six compounds （c^-santalene, （Z）-a-bisabolene, c^-bergamotene, （E）-ct-santalal, c^-photosantalol and campherenol） were isolated from group B. No individual group B component had a myrrh-like odor, although the combined odor of group B was myrrh like. The authors demonstrated that the aroma profile of myrrh depends on the thermal instability of （E）-^-ocimene and a combination of six thermally stable terpenes with similar molecular structures.展开更多
The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. T...The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. Two sandwich models corresponding to CNTRC and FGM face sheets are proposed. Carbon nanotubes(CNTs) in the CNTRC layer are embedded into a matrix according to functionally graded distributions. The effects of porosity in the FGM and the temperature dependence of properties of all constituent materials are considered. The effective properties of the porous FGM and CNTRC are determined by using the modified and extended versions of a linear mixture rule, respectively. The basic equations governing the stability problem of thin sandwich cylindrical shells are established within the framework of the Donnell shell theory including the von K’arm’an-Donnell nonlinearity. These equations are solved by using the multi-term analytical solutions and the Galerkin method for simply supported shells.The critical buckling temperatures and postbuckling paths are determined through an iteration procedure. The study reveals that the sandwich shell model with a CNTRC core layer and relatively thin porous FGM face sheets can have the best capacity of thermal load carrying. In addition, unlike the cases of mechanical loads, porosities have beneficial effects on the nonlinear stability of sandwich shells under the thermal load. It is suggested that an appropriate combination of advantages of FGM and CNTRC can result in optimal efficiency for advanced sandwich structures.展开更多
We investigate the thermal instability of a three-dimensional Rayleigh–Bénard(RB for short)problem without thermal diffusion in a bounded domain.First we construct unstable solutions in exponential growth modes ...We investigate the thermal instability of a three-dimensional Rayleigh–Bénard(RB for short)problem without thermal diffusion in a bounded domain.First we construct unstable solutions in exponential growth modes for the linear RB problem.Then we derive energy estimates for the nonlinear solutions by a method of a prior energy estimates,and establish a Gronwall-type energy inequality for the nonlinear solutions.Finally,we estimate for the error of L^(1)-norm between the both solutions of the linear and nonlinear problems,and prove the existence of escape times of nonlinear solutions.Thus we get the instability of nonlinear solutions under L^(1)-norm.展开更多
In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot...In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot during the O-mode heating period.The second experiment,which used cold-start X-mode heating,showed the generation of parametric decay instability,whereas overshoot was not observed.The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage.Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect,which implies suppression of the thermal parametric instability with X-mode heating.We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.展开更多
A theoretical model which describes the small-scale irregularities excited by powerful high frequency （3–30 MHz） electromagnetic wave in ionosphere heating is investigated quantitatively in this paper. The model is...A theoretical model which describes the small-scale irregularities excited by powerful high frequency （3–30 MHz） electromagnetic wave in ionosphere heating is investigated quantitatively in this paper. The model is based on the transport equation in magnetic plasma and mode conversion from electromagnetic wave to electrostatic wave in ionospheric modification.Threshold electric field for exciting small-scale （meter scale） irregularities and spatial spectra of irregularities are analytically calculated by this model. The results indicate that background electron density and geomagnetic field play an important role for the threshold electric field and the spatial scale of the electron density irregularities. The results demonstrate that the electric field threshold increases with the decrease of the spatial scale of the irregularities. For exciting meter scale irregularities, the threshold electric field is about tens of mV m^（-1）. The theoretical results are consistent with those of the experiments.展开更多
Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable imp...Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy （TEM） technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism （with 〈 100 ~C temperature rise）, we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM （HRTEM） observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level which may pave the way for their interconnect applications in future ultra- large-scale integrated ciroaits.展开更多
Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded nea...Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by iGOs. This work demonstrated that the iGOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures （Tg）. Via annealing the 50-120 nm thick composite and associated neat PS films at temperatures ranging from 35℃ to 70 ℃ above Tg, surface morphology evolution of the films was monitored by atomic force microscopy （AFM）. The iGOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.展开更多
基金Project supported by the National Key Basic Research Development Program of China(973 Program,Grant Nos.2006CB705803,2013CB531200)the National Natural Science Foundation of China(Grant No.21571188)
文摘A numerical simulation is performed for thermal instability and heat transfer of viscoelastic fluids in bounded porous media under the bottom constant heat flux boundary condition. The results for six different combinations of relaxation and retardation times demonstrate the existence of the thermal instability induced flow bifurcation. It is found that the increase of the relaxation time can enhance the heat transfer efficiency by disturbing the fluid flow and facilitating the bifurcation. The increase of the retardation time can stabilize the flow and postpone the bifurcation, leading to simpler flow pattern and lower heat transfer rate.
文摘The authors examined the thermal change in the aroma profile of myrrh. The fresh odor of raw myrrh and its hexane extract depended on the amount of （E）-13-ocimene. Myrrh was extracted with hexane to avoid inducing changes in the constituents and odor. The main constituent, （E）-L3-ocimene （group A; low boiling point）, and the other constituents （group B; high boiling point） of the hexane extract were separated by bulb-to-bulb distillation. The constituents of groups A and B were analyzed over time by nuclear magnetic resonance analysis and the odors were evaluated. Myrrh＇s odor depended on both the amount of thermally unstable （E）-[3-ocimene, which contributed to the fresh odor, and the constituents of group B （thermally stable）, which contributed to the myrrh-like odor. Six compounds （c^-santalene, （Z）-a-bisabolene, c^-bergamotene, （E）-ct-santalal, c^-photosantalol and campherenol） were isolated from group B. No individual group B component had a myrrh-like odor, although the combined odor of group B was myrrh like. The authors demonstrated that the aroma profile of myrrh depends on the thermal instability of （E）-^-ocimene and a combination of six thermally stable terpenes with similar molecular structures.
基金the Vietnam National Foundation for Science and Technology Development(NAFOSTED)(No.107.02-2019.318)。
文摘The nonlinear stability of sandwich cylindrical shells comprising porous functionally graded material(FGM) and carbon nanotube reinforced composite(CNTRC)layers subjected to uniform temperature rise is investigated. Two sandwich models corresponding to CNTRC and FGM face sheets are proposed. Carbon nanotubes(CNTs) in the CNTRC layer are embedded into a matrix according to functionally graded distributions. The effects of porosity in the FGM and the temperature dependence of properties of all constituent materials are considered. The effective properties of the porous FGM and CNTRC are determined by using the modified and extended versions of a linear mixture rule, respectively. The basic equations governing the stability problem of thin sandwich cylindrical shells are established within the framework of the Donnell shell theory including the von K’arm’an-Donnell nonlinearity. These equations are solved by using the multi-term analytical solutions and the Galerkin method for simply supported shells.The critical buckling temperatures and postbuckling paths are determined through an iteration procedure. The study reveals that the sandwich shell model with a CNTRC core layer and relatively thin porous FGM face sheets can have the best capacity of thermal load carrying. In addition, unlike the cases of mechanical loads, porosities have beneficial effects on the nonlinear stability of sandwich shells under the thermal load. It is suggested that an appropriate combination of advantages of FGM and CNTRC can result in optimal efficiency for advanced sandwich structures.
基金supported by the NSF of China(Grant No.11901100)the Natural Science Foundation of Fujian Province of China(Grant No.2020J02001)Funds of Education Department of Fujian Province(Grant No.510881/GXRC-20046)。
文摘We investigate the thermal instability of a three-dimensional Rayleigh–Bénard(RB for short)problem without thermal diffusion in a bounded domain.First we construct unstable solutions in exponential growth modes for the linear RB problem.Then we derive energy estimates for the nonlinear solutions by a method of a prior energy estimates,and establish a Gronwall-type energy inequality for the nonlinear solutions.Finally,we estimate for the error of L^(1)-norm between the both solutions of the linear and nonlinear problems,and prove the existence of escape times of nonlinear solutions.Thus we get the instability of nonlinear solutions under L^(1)-norm.
基金EISCAT is an international scientific association supported by research organizations in China(China Research Institute of Radiowave Propagation(CRIRP)),Finland(Suomen Akatemia(SA)),Japan(National Institute of Polar Research(NIPR)and Solar-Terrestrial Environment Laboratory(STEL)),Norway(The Research Council of Norway(NFR)),Sweden(Swedish Research Council(VR)),and the United Kingdom(Natural Environment Research Council(NERC)).This work was supported by the National Natural Science Foundation of China(NSFC,grants 41204111,41574146,41774162,and 41704155)the China Postdoctoral Science Foundation(grant 2017M622504).The experiment described in this work was carried out by the Russian team led by N.F.Blagoveshchenskaya.The data used in this research are available through the EISCAT Madrigal database(http://www.eiscat.se/madrigal/)and EISCAT Dynasonde database(https://dynserv.eiscat.uit.no/).
文摘In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot during the O-mode heating period.The second experiment,which used cold-start X-mode heating,showed the generation of parametric decay instability,whereas overshoot was not observed.The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage.Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect,which implies suppression of the thermal parametric instability with X-mode heating.We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.
基金supported by National Natural Science Foundation of China(NSFC grants 41204111,4157414641774162 and 41704155)China Postdoctoral Science Foundation(2017M622504)
文摘A theoretical model which describes the small-scale irregularities excited by powerful high frequency （3–30 MHz） electromagnetic wave in ionosphere heating is investigated quantitatively in this paper. The model is based on the transport equation in magnetic plasma and mode conversion from electromagnetic wave to electrostatic wave in ionospheric modification.Threshold electric field for exciting small-scale （meter scale） irregularities and spatial spectra of irregularities are analytically calculated by this model. The results indicate that background electron density and geomagnetic field play an important role for the threshold electric field and the spatial scale of the electron density irregularities. The results demonstrate that the electric field threshold increases with the decrease of the spatial scale of the irregularities. For exciting meter scale irregularities, the threshold electric field is about tens of mV m^（-1）. The theoretical results are consistent with those of the experiments.
文摘Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy （TEM） technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism （with 〈 100 ~C temperature rise）, we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM （HRTEM） observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level which may pave the way for their interconnect applications in future ultra- large-scale integrated ciroaits.
基金the start-up fund of Y.G.from both University of Michigan-Shanghai Jiao Tong University Joint InstituteSchool of Materials Science and Engineering at SJTU+4 种基金the National Science Foundation of China for financial support through the General Program(No.2157408)the foundation of Shanghai Sailing Plan(No,16YF1406100)the National Youth 1000 Talent Program of Chinathe Shanghai 1000 Talent Planthe Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry of China
文摘Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by iGOs. This work demonstrated that the iGOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures （Tg）. Via annealing the 50-120 nm thick composite and associated neat PS films at temperatures ranging from 35℃ to 70 ℃ above Tg, surface morphology evolution of the films was monitored by atomic force microscopy （AFM）. The iGOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.
