Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scali...Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling.展开更多
The approach of Obukhov assuming a constant skewness was used to obtain analytical corrections to the scaling of the second order structure function, starting from Kolmogorov＇s 4/5 law. These corrections can be used ...The approach of Obukhov assuming a constant skewness was used to obtain analytical corrections to the scaling of the second order structure function, starting from Kolmogorov＇s 4/5 law. These corrections can be used in model applications in which explicit expressions, rather than numerical solutions are needed. The comparison with an interpolation formula proposed by Batchelor, showed that the latter gives surprisingly precise results. The modification of the same method to obtain analytical corrections to the scaling law, taking into account the possible corrections induced by intermittency, is also proposed.展开更多
Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wak...Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.展开更多
Closure models started from Chou＇s work have been developed for more than 70 years, aiming at providing analytical tools to describe turbulent flows in the spectral space. In this study, a preliminary attempt is pres...Closure models started from Chou＇s work have been developed for more than 70 years, aiming at providing analytical tools to describe turbulent flows in the spectral space. In this study, a preliminary attempt is presented to introduce a closure model in the physical space, using the velocity structure functions as key parameters. The present closure model appears to qualitatively reproduce the asymptotic scaling behav- iors at small and large scales, despite some inappropriate behaviors such as oscillations. Therefore, further improvements of the present model are expected to provide appropriate descriptions of turbulent flows in the physical space.展开更多
Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)d...Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium scalings.Moreover,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows.These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.展开更多
Van der Waals(vdW)layered two-dimensional(2D)materials,which may have high carrier mobility,valley polarization,excellent mechanical properties and air stability,have been widely investigated before.We explore the pos...Van der Waals(vdW)layered two-dimensional(2D)materials,which may have high carrier mobility,valley polarization,excellent mechanical properties and air stability,have been widely investigated before.We explore the possibility of producing a spin-polarized two-dimensional electron gas(2DEG)in the heterojunction composed of insulators MoSi_(2)N_(4)and VSi_(2)N_(4)by using first-principles calculations.Due to the charge transfer effect,the 2DEG at the interface of the MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunction is found.Further,for different kinds of stacking of heterojunctions,lattice strain and electric fields can effectively tune the electronic structures and lead to metal-to-semiconductor transition.Under compressive strain or electric field parallel to c axis,the 2DEG disappears and band gap opening occurs.On the contrary,interlayer electron transfer enforces the system to become metallic under the condition of tensile strain or electric field anti-parallel to c axis.These changes are mainly attributed to electronic redistribution and orbitals’reconstruction.In addition,we reveal that MoSi_(2)N_(4)/VSi_(2)N_(4)lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties,such as a large band gap semiconductor and a metallic state.Our findings provide insights into electronic band engineering of MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunctions and pave the way for future spintronics applications.展开更多
The turbulence governed by the Navier-Stokes equation is paramount in many physical processes.However,it has been considered as a challenging problem due to its inherent nonlinearity,non-equilibrium,and complexity.Her...The turbulence governed by the Navier-Stokes equation is paramount in many physical processes.However,it has been considered as a challenging problem due to its inherent nonlinearity,non-equilibrium,and complexity.Herein,we review the connections between the velocity derivative skewness Sk and the non-equilibrium properties of turbulence.Sk,a reasonable candidate for describing the non-equilibrium turbulence,which varies during the non-equilibrium procedure.A lot of experimental or numerical evidences have shown that the perturbation of energy spectrum,which associated with the excitation of large scales,results in an obvious variation of Sk,and Sk is a negative value in this rapid energy decay process.The variation of positive Sk is closely related to the perturbation of transfer spectrum,and this corresponds to the backward energy transfer process.In addition,the skewness characterizes the production(or reduction)rate of enstrophy due to vortex stretching(or compression).Using the transport equation of turbulent energy dissipation rate and enstrophy,it is possible to establish a theoretical connection between skewness and the non-equilibrium turbulence.It is expected that this work could trigger the rapid advancement of the future studies of non-equilibrium turbulence,and also the improvement of turbulence models.展开更多
By introducing the Fourier filters, we analyse the correlation between large- and small-scale velocity components in homogeneous isotropic turbulence theoretically. We show that different Fourier filters act similarly...By introducing the Fourier filters, we analyse the correlation between large- and small-scale velocity components in homogeneous isotropic turbulence theoretically. We show that different Fourier filters act similarly on this multiscale correlation with a ＂natural＂ mechanism of removing the physical correlations between large- and small-scale velocity components. This conclusion calls for the further investigation on the Hilbert-Huang decomposition to investigate the mechanism of Marusic et al （2008）.展开更多
Excessive radiation exposure may lead to edema of the spinal cord and deterioration of the nervous system. Magnetic resonance imaging can be used to judge and assess the extent of edema and to evaluate pathological ch...Excessive radiation exposure may lead to edema of the spinal cord and deterioration of the nervous system. Magnetic resonance imaging can be used to judge and assess the extent of edema and to evaluate pathological changes and thus may be used for the evaluation of spinal cord injuries caused by radiation therapy. Radioactive ^125I seeds to irradiate 90% of the spinal cord tissue at doses of 40–100 Gy （D90） were implanted in rabbits at T10 to induce radiation injury, and we evaluated their safety for use in the spinal cord. Diffusion tensor imaging showed that with increased D90, the apparent diffusion coefficient and fractional anisotropy values were increased. Moreover, pathological damage of neurons and microvessels in the gray matter and white matter was aggravated. At 2 months after implantation, obvious pathological injury was visible in the spinal cords of each group. Magnetic resonance diffusion tensor imaging revealed the radiation injury to the spinal cord, and we quantified the degree of spinal cord injury through apparent diffusion coefficient and fractional anisotropy.展开更多
BaSO_(4) nanoparticles as important functional materials have attracted considerable research interests,due to their X-rays barrier and absorption properties.However,most of BaSO_(4) nanoparticles prepared by traditio...BaSO_(4) nanoparticles as important functional materials have attracted considerable research interests,due to their X-rays barrier and absorption properties.However,most of BaSO_(4) nanoparticles prepared by traditional technology are nanopowders with broad size distribution and poor dispersibility,which may greatly limit their applications.To the best of our knowledge,the synthesis of transparent BaSO_(4) nanodispersions was rarely reported.Here,we firstly present a novel and efficient method to prepare transparent and stable BaSO_(4) nanodispersions with a relatively small particle size around 10 to 17 nm using a precipitation method in a rotating packed bed(RPB),followed by a modification treatment using stearic acid.Compared with the BaSO_(4) prepared in a traditional stirred tank,the product prepared using an RPB has much smaller particle size and narrower size distribution.More importantly,by using RPB,the reaction time can be significantly decreased from 20 min to 18 s.Furthermore,the transparent BaSO_(4)-polyvinyl butyral nanocomposite films with good X-ray shielding performance can be easily fabricated.We believe that the stable BaSO_(4) nanodispersions may have a wide range of applications for transparent composite materials and coatings with X-ray shielding performance for future research.展开更多
Phosphorus(P)recovery from incinerated sewage sludge ash(ISSA)has been extensively investigated,but insufficient research has been conducted to evaluate the effect of different kinds of recovered phosphate fertilizers...Phosphorus(P)recovery from incinerated sewage sludge ash(ISSA)has been extensively investigated,but insufficient research has been conducted to evaluate the effect of different kinds of recovered phosphate fertilizers(RPFs)on plant growth with respect to the P and heavy metal contents of RPFs.In this study,three kinds of RPFs,precipitated calcium phosphate fertilizer(CaP),struvite phosphate fertilizer(SP),and P-loaded biochar(BP),produced from ISSA were characterized,and their agronomic effectiveness was verified by hydroponic and soil cultivation.In addition to the three kinds of RPFs,a control group(mono-phosphate fertilizer in hydroponic group/compound fertilizer in soil cultivation group)and a blank control group(BC,with zero P)were tested on choy sum and ryegrass at the same time.SP has the highest P purity(76.0%of struvite)while the BP has the most complex P species(P was co-exist with Fe,Al,and Mg).Plant growth results showed that the RPFs greatly facilitated plant growth and demonstrated superior/comparable effects to those of control group.In hydroponics testing,SP showed the best effect(shoot length of 17.0 cm,chlorophyll content of 2.05 mg/g)due to the Mg involved and the high P purity of SP,while BP performed the best(shoot length of 13.7 cm,chlorophyll content of 2.42 mg/g)in the soil testing system among all of the groups because of the additional nutritional elements and the high P availability of BP.Additionally,the accumulation of heavy metals in the plants under all conditions did not exceed the limits stipulated in the regulations.These results indicate that recovering P from ISSA is an attractive technology to produce P fertilizers,which can alleviate both the scarcity of phosphate resources and the burden of ISSA management.展开更多
In this article,the affiliation details for Author Chi Sun Poon were incorrectly given as'State Key Laboratory of Water Environment Simulation,School of Environment,Beijing Normal University,Beijing 100875,China&#...In this article,the affiliation details for Author Chi Sun Poon were incorrectly given as'State Key Laboratory of Water Environment Simulation,School of Environment,Beijing Normal University,Beijing 100875,China'and'State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China'but should have been'Department of Civil and Environmental Engineering,The Hong Kong Polytechnic University,Kowloon,Hong Kong,China'and'IRSM-CAS/HK PolyU Joint Laboratory on Solid Waste Science,Kowloon,Hong Kong,China'.The original article has been corrected.展开更多
基金supported by the National Natural Science Foundation of China(11202013 and 51136003)the National Basic Research Program of China(2012CB720200)the Opening fundof State Key Laboratory of Nonlinear Mechanics
文摘Eddy-damping quasinormal Markovian （EDQNM） theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling.
基金supported by the National Natural Science Foundation of China(10828204 and A020401)BUAA SJP 111 program
文摘The approach of Obukhov assuming a constant skewness was used to obtain analytical corrections to the scaling of the second order structure function, starting from Kolmogorov＇s 4/5 law. These corrections can be used in model applications in which explicit expressions, rather than numerical solutions are needed. The comparison with an interpolation formula proposed by Batchelor, showed that the latter gives surprisingly precise results. The modification of the same method to obtain analytical corrections to the scaling law, taking into account the possible corrections induced by intermittency, is also proposed.
基金Project supported by the National Natural Science Foundation of China(Nos.11572025,11772032,and 51420105008)the National Basic Research Program of China(No.2014CB046405)the U.K.Engineering and Physical Sciences Research Council(EPSRC)(Nos.EP/K024574/1 and EP/L000261/1)
文摘Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.
基金supported by the National Natural Science Foundation of China(Nos.11572025,11202013,and 51420105008)
文摘Closure models started from Chou＇s work have been developed for more than 70 years, aiming at providing analytical tools to describe turbulent flows in the spectral space. In this study, a preliminary attempt is presented to introduce a closure model in the physical space, using the velocity structure functions as key parameters. The present closure model appears to qualitatively reproduce the asymptotic scaling behav- iors at small and large scales, despite some inappropriate behaviors such as oscillations. Therefore, further improvements of the present model are expected to provide appropriate descriptions of turbulent flows in the physical space.
基金Project supported by the National Natural Science Foundation of China(Nos.12002318,11572025,11772032,and 51420105008)the Science Foundation of North University of China(No.XJJ201929)。
文摘Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium scalings.Moreover,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows.These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074241,52130204,and 11929401)the Science and Technology Commission of Shanghai Municipality(Grant Nos.22XD1400900,20501130600,21JC1402600,and 22YF1413300)+5 种基金High Performance Computing Center,Shanghai UniversityKey Research Project of Zhejiang Lab(Grant No.2021PE0AC02)the supports from the open projects of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(Anhui University of Technology),Ministry of Education(Grant No.GFST2022KF08)State Key Laboratory of Surface Physics(Fudan University)(Grant No.KF202210)State Key Laboratory of Infrared Physics,Shanghai Institute of Technical Physics,Chinese Academy of Sciences(Grant No.SITP-NLIST-YB-2022-08)the support of China Scholarship Council。
文摘Van der Waals(vdW)layered two-dimensional(2D)materials,which may have high carrier mobility,valley polarization,excellent mechanical properties and air stability,have been widely investigated before.We explore the possibility of producing a spin-polarized two-dimensional electron gas(2DEG)in the heterojunction composed of insulators MoSi_(2)N_(4)and VSi_(2)N_(4)by using first-principles calculations.Due to the charge transfer effect,the 2DEG at the interface of the MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunction is found.Further,for different kinds of stacking of heterojunctions,lattice strain and electric fields can effectively tune the electronic structures and lead to metal-to-semiconductor transition.Under compressive strain or electric field parallel to c axis,the 2DEG disappears and band gap opening occurs.On the contrary,interlayer electron transfer enforces the system to become metallic under the condition of tensile strain or electric field anti-parallel to c axis.These changes are mainly attributed to electronic redistribution and orbitals’reconstruction.In addition,we reveal that MoSi_(2)N_(4)/VSi_(2)N_(4)lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties,such as a large band gap semiconductor and a metallic state.Our findings provide insights into electronic band engineering of MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunctions and pave the way for future spintronics applications.
基金Project supported by the National Natural Science Foundation of China(Grant No.11772032)the Science Foundation of North University of China(Grant No.11026829).
文摘The turbulence governed by the Navier-Stokes equation is paramount in many physical processes.However,it has been considered as a challenging problem due to its inherent nonlinearity,non-equilibrium,and complexity.Herein,we review the connections between the velocity derivative skewness Sk and the non-equilibrium properties of turbulence.Sk,a reasonable candidate for describing the non-equilibrium turbulence,which varies during the non-equilibrium procedure.A lot of experimental or numerical evidences have shown that the perturbation of energy spectrum,which associated with the excitation of large scales,results in an obvious variation of Sk,and Sk is a negative value in this rapid energy decay process.The variation of positive Sk is closely related to the perturbation of transfer spectrum,and this corresponds to the backward energy transfer process.In addition,the skewness characterizes the production(or reduction)rate of enstrophy due to vortex stretching(or compression).Using the transport equation of turbulent energy dissipation rate and enstrophy,it is possible to establish a theoretical connection between skewness and the non-equilibrium turbulence.It is expected that this work could trigger the rapid advancement of the future studies of non-equilibrium turbulence,and also the improvement of turbulence models.
基金supported by the National Natural Science Foundation of China(11202013 and51420105008)
文摘By introducing the Fourier filters, we analyse the correlation between large- and small-scale velocity components in homogeneous isotropic turbulence theoretically. We show that different Fourier filters act similarly on this multiscale correlation with a ＂natural＂ mechanism of removing the physical correlations between large- and small-scale velocity components. This conclusion calls for the further investigation on the Hilbert-Huang decomposition to investigate the mechanism of Marusic et al （2008）.
基金supported by the Science and Technology Development Project Funds of Science and Technology Department of Jilin Province in China,No.20120724
文摘Excessive radiation exposure may lead to edema of the spinal cord and deterioration of the nervous system. Magnetic resonance imaging can be used to judge and assess the extent of edema and to evaluate pathological changes and thus may be used for the evaluation of spinal cord injuries caused by radiation therapy. Radioactive ^125I seeds to irradiate 90% of the spinal cord tissue at doses of 40–100 Gy （D90） were implanted in rabbits at T10 to induce radiation injury, and we evaluated their safety for use in the spinal cord. Diffusion tensor imaging showed that with increased D90, the apparent diffusion coefficient and fractional anisotropy values were increased. Moreover, pathological damage of neurons and microvessels in the gray matter and white matter was aggravated. At 2 months after implantation, obvious pathological injury was visible in the spinal cords of each group. Magnetic resonance diffusion tensor imaging revealed the radiation injury to the spinal cord, and we quantified the degree of spinal cord injury through apparent diffusion coefficient and fractional anisotropy.
基金This work was financially supported by the National Key Research and Development Program of China(Grant No.2016YFA0201701/2016YFA0201700)the National Natural Science Foundation of China(Grant No.21878015).
文摘BaSO_(4) nanoparticles as important functional materials have attracted considerable research interests,due to their X-rays barrier and absorption properties.However,most of BaSO_(4) nanoparticles prepared by traditional technology are nanopowders with broad size distribution and poor dispersibility,which may greatly limit their applications.To the best of our knowledge,the synthesis of transparent BaSO_(4) nanodispersions was rarely reported.Here,we firstly present a novel and efficient method to prepare transparent and stable BaSO_(4) nanodispersions with a relatively small particle size around 10 to 17 nm using a precipitation method in a rotating packed bed(RPB),followed by a modification treatment using stearic acid.Compared with the BaSO_(4) prepared in a traditional stirred tank,the product prepared using an RPB has much smaller particle size and narrower size distribution.More importantly,by using RPB,the reaction time can be significantly decreased from 20 min to 18 s.Furthermore,the transparent BaSO_(4)-polyvinyl butyral nanocomposite films with good X-ray shielding performance can be easily fabricated.We believe that the stable BaSO_(4) nanodispersions may have a wide range of applications for transparent composite materials and coatings with X-ray shielding performance for future research.
基金support from Major Scientific and Technological Innovation Projects of Shandong Province(No.2021CXGC011201)the start-up funding for the new introduced talents of the Beijing Normal University(No.28707-111032107)Hong Kong Research Grants Council(PolyU No.152132/14E)for financial support.
文摘Phosphorus(P)recovery from incinerated sewage sludge ash(ISSA)has been extensively investigated,but insufficient research has been conducted to evaluate the effect of different kinds of recovered phosphate fertilizers(RPFs)on plant growth with respect to the P and heavy metal contents of RPFs.In this study,three kinds of RPFs,precipitated calcium phosphate fertilizer(CaP),struvite phosphate fertilizer(SP),and P-loaded biochar(BP),produced from ISSA were characterized,and their agronomic effectiveness was verified by hydroponic and soil cultivation.In addition to the three kinds of RPFs,a control group(mono-phosphate fertilizer in hydroponic group/compound fertilizer in soil cultivation group)and a blank control group(BC,with zero P)were tested on choy sum and ryegrass at the same time.SP has the highest P purity(76.0%of struvite)while the BP has the most complex P species(P was co-exist with Fe,Al,and Mg).Plant growth results showed that the RPFs greatly facilitated plant growth and demonstrated superior/comparable effects to those of control group.In hydroponics testing,SP showed the best effect(shoot length of 17.0 cm,chlorophyll content of 2.05 mg/g)due to the Mg involved and the high P purity of SP,while BP performed the best(shoot length of 13.7 cm,chlorophyll content of 2.42 mg/g)in the soil testing system among all of the groups because of the additional nutritional elements and the high P availability of BP.Additionally,the accumulation of heavy metals in the plants under all conditions did not exceed the limits stipulated in the regulations.These results indicate that recovering P from ISSA is an attractive technology to produce P fertilizers,which can alleviate both the scarcity of phosphate resources and the burden of ISSA management.
文摘In this article,the affiliation details for Author Chi Sun Poon were incorrectly given as'State Key Laboratory of Water Environment Simulation,School of Environment,Beijing Normal University,Beijing 100875,China'and'State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China'but should have been'Department of Civil and Environmental Engineering,The Hong Kong Polytechnic University,Kowloon,Hong Kong,China'and'IRSM-CAS/HK PolyU Joint Laboratory on Solid Waste Science,Kowloon,Hong Kong,China'.The original article has been corrected.
