The wheat roots membrane separates the cell from the environment around it and encloses the cell contents. The pro-tein secondary structure and thermal stability of the plasma membrane of wheat root have been characte...The wheat roots membrane separates the cell from the environment around it and encloses the cell contents. The pro-tein secondary structure and thermal stability of the plasma membrane of wheat root have been characterized in D2O buffer from 20°C to 90°C by Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Quantitative analysis of the amide I band (1700 - 1600 cm–1) showed that the plasma membrane proteins contains 41% α-helix, 16% β-sheet, 18% turn, and 25% disorder structures at 20°C. At elevated temperatures from 25°C up to 90°C, the α-helix and the β-sheet structure unfold into turns and the disorder structure, with a major conformational transition occurring at 50°C. There is a rapid decline in H+-ATPase activity of plasma membrane from 35°C to 55°C and it remain very low level H+-ATPase activity of PM from 55°C to 90°C. Therefore the protein conformational transition was one of reasons of loses H+-ATPase activity of plasma membrane.展开更多
With the two-scale expansion technique proposed by Yoshizawa,the turbulent fluctuating field is expanded around the isotropic field.At a low-order two-scale expansion,applying the mode coupling approximation in the Ya...With the two-scale expansion technique proposed by Yoshizawa,the turbulent fluctuating field is expanded around the isotropic field.At a low-order two-scale expansion,applying the mode coupling approximation in the Yakhot-Orszag renormalization group method to analyze the fluctuating field,the Reynolds-average terms in the Reynolds stress transport equation,such as the convective term,the pressure-gradient-velocity correlation term and the dissipation term,are modeled.Two numerical examples：turbulent flow past a backward-facing step and the fully developed flow in a rotating channel,are presented for testing the efficiency of the proposed second-order model.For these two numerical examples,the proposed model performs as well as the Gibson-Launder （GL） model,giving better prediction than the standard k-ε model,especially in the abilities to calculate the secondary flow in the backward-facing step flow and to capture the asymmetric turbulent structure caused by frame rotation.展开更多
Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations betwee...Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries.展开更多
The velocity field and the associated shear stress corresponding to the longitudinal oscillatory flow of a generalized second grade fluid, between two infinite coaxial circular cylinders, are determined by means of th...The velocity field and the associated shear stress corresponding to the longitudinal oscillatory flow of a generalized second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. Initially, the fluid and cylinders are at rest and at t = 0＋ both cylinders suddenly begin to oscillate along their common axis with simple harmonic motions having angular frequencies Ω1 and Ω2. The solutions that have been obtained are presented under integral and series forms in terms of the generalized G and R functions and satisfy the governing differential equation and all imposed initial and boundary conditions. The respective solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for the similar flow of ordinary second grade fluid and Newtonian fluid are also obtained as limiting cases of our general solutions. At the end, the effect of different parameters on the flow of ordinary second grade and generalized second grade fluid are investigated graphically by plotting velocity profiles.展开更多
The velocity field and the adequate shear stress corresponding to the longitudinal flow of a fractional second grade fluid,between two infinite coaxial circular cylinders,are determined by applying the Laplace and fin...The velocity field and the adequate shear stress corresponding to the longitudinal flow of a fractional second grade fluid,between two infinite coaxial circular cylinders,are determined by applying the Laplace and finite Hankel transforms.Initially the fluid is at rest,and at time t=0^+, the inner cylinder suddenly begins to translate along the common axis with constant acceleration. The solutions that have been obtained are presented in terms of generalized G functions.Moreover, these solutions satisfy both the governing differential equations and all imposed initial and boundary conditions.The corresponding solutions for ordinary second grade and Newtonian fluids are obtained as limiting cases of the general solutions.Finally,some characteristics of the motion,as well as the influences of the material and fractional parameters on the fluid motion and a comparison between models,are underlined by graphical illustrations.展开更多
GH4169 superalloy stress relaxation test was investigated to study its characteristics of stress relaxation curves at various temperatures( 550,650,and 750 ℃). These curves presented jointly two distinct stages,the s...GH4169 superalloy stress relaxation test was investigated to study its characteristics of stress relaxation curves at various temperatures( 550,650,and 750 ℃). These curves presented jointly two distinct stages,the stage of inner stress relaxing quickly,and the stage of inner stress relaxing slowly and closing to the stress relaxation limit. And these curves obtained could be fitted by second order exponential decay function well. Based on the experimental stress relaxation curves,the relationship between stress relaxation rate and time were derived, which showed that the higher relaxation temperature and the greater initial rate of stress relaxation. The whole process presented two different stages,the stage of stress relaxation rate falling rapidly and the stage of stress relaxation rate slowing down and tending to be constant. The relation curve between creep strain rate and stress of GH4169 superalloy can be divided into three stages,low stress stage,transition stage,and high stress stage.Both the high stage and the low stage present linear correlation.展开更多
Mechanical models of residually stressed fibre-reinforced solids,which do not resist bending,have been developed in the literature.However,in some residually stressed fibre-reinforced elastic solids,resistance to fibr...Mechanical models of residually stressed fibre-reinforced solids,which do not resist bending,have been developed in the literature.However,in some residually stressed fibre-reinforced elastic solids,resistance to fibre bending is significant,and the mechanical behavior of such solids should be investigated.Hence,in this paper,we model the mechanical aspect of residually stressed elastic solids with bending stiffness due to fibre curvature,which up to the authors’knowledge has not been mechanically modeled in the past.The proposed constitutive equation involves a nonsymmetric stress and a couple-stress tensor.Spectral invariants are used in the constitutive equation,where each spectral invariant has an intelligible physical meaning,and hence they are useful in experiment and analysis.A prototype strain energy function is proposed.Moreover,we use this prototype to give results for some cylindrical boundary value problems.展开更多
This paper deals with the rotational flow of a generalized second grade fluid, within a circular cylinder, due to a torsional shear stress. The fractional calculus approach in the constitutive relationship model of a ...This paper deals with the rotational flow of a generalized second grade fluid, within a circular cylinder, due to a torsional shear stress. The fractional calculus approach in the constitutive relationship model of a second grade fluid is introduced. The velocity field and the resulting shear stress are determined by means of the Laplace and finite Hankel transforms to satisfy all imposed initial and boundary conditions. The solutions corresponding to second grade fluids as well as those for Newtonian fluids are obtained as limiting cases of our general solutions. The influence of the fractional coefficient on the velocity of the fluid is also analyzed by graphical illustrations.展开更多
The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and H...The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. At time t = 0, the fluid and both the cylinders are at rest and at t = 0 ＋ , cylinders suddenly begin to oscillate around their common axis in a simple harmonic way having angular frequencies ω 1 and ω 2 . The obtained solutions satisfy the governing differential equation and all imposed initial and boundary conditions. The solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for Newtonian fluid are also obtained as limiting cases of our general solutions.展开更多
The areas affected by the L1 transfer to L2,such as phonotactics and stress,appear to have different degrees of erasability through training and practice.This paper attempts a theoretical analysis to account for empir...The areas affected by the L1 transfer to L2,such as phonotactics and stress,appear to have different degrees of erasability through training and practice.This paper attempts a theoretical analysis to account for empirical observations of L1 transfer in diphthong-coda coalescence and in sentence stress for Chinese learners of English in an American accent training course.Using the framework and tableau method of Optimality Theory(Prince and Smolensky 1993),the phonological paradigm that views languages’differences as symptomatic of differences in rankings of a set of universal violable constraints,this paper posits the underlying ranking at work in(a)the segmental case where[aŋ]is the observed output for/aʊn/;(b)the suprasegmental case where no stress contrast is observed for a pair of phonologically similar sentences with contrastive stress.It is argued that,in the segmental case,the coalescence of the second vowel of a diphthong with an alveolar nasal coda results from the high ranking of markedness constraints,including Complex Syllable;and in the suprasegmental case,sentence stress is greatly affected by changes in the ranking of the constraint culminativity.Aside from shedding light on the understudied issue of diphthong-coda coalescence,this research also contributes to the discussion of the comparative erasability of L1 transfer for the two areas and demonstrates how a deduction-based theoretical method may actually have practical implications for guiding the design of L2 teaching methodology of English pronunciation as well as for promoting native English speakers’clearer understanding of Chinese learners of English on the global stage.展开更多
The USM-θ model of Bingham fluid for dense two-phase turbulent flow was developed, which combines the second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collisi...The USM-θ model of Bingham fluid for dense two-phase turbulent flow was developed, which combines the second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collision. In this model, phases interaction and the extra term of Bingham fluid yield stress are taken into account. An algorithm for USM-θ model in dense two-phase flow was proposed, in which the influence of particle volume fraction is accounted for. This model was used to simulate turbulent flow of Bingham fluid single-phase and dense liquid-particle two-phase in pipe. It is shown USM-θ model has better prediction result than the five-equation model, in which the particle-particle collision is modeled by the particle kinetic theory, while the turbulence of both phase is simulated by the two-equation turbulence model. The USM-θ model was then used to simulate the dense two-phase turbulent up flow of Bingham fluid with particles. With the increasing of the yield stress, the velocities of Bingham and particle decrease near the pipe centre. Comparing the two-phase flow of Bingham-particle with that of liquid-particle, it is found the source term of yield stress has significant effect on flow.展开更多
A reliability sensitivity analysis based on modal stress is presented and applied to predict the influence factors of parameters on drum brake.Firstly,the first 10 modes of prestress of the brake drum are performed in...A reliability sensitivity analysis based on modal stress is presented and applied to predict the influence factors of parameters on drum brake.Firstly,the first 10 modes of prestress of the brake drum are performed in the software ANSYS Workbench.According to the results of brake noise research,it can be detected whether the drum brake meets the results that the noise frequency range of 500-1000 Hz.The reliability sensitivity design of mechanical parts based on the normal distribution parameters for complex mechanical system is discussed.Secondly,according to the first order second moment(FOSM)theory on reliability,the reliability sensitivity of drum brake is analyzed and calculated,and compared with the Monte Carlo(MC)numerical simulation results,The variation rules of reliability sensitivity is given,which provides a theoretical basis for the design of drum brake.展开更多
文摘The wheat roots membrane separates the cell from the environment around it and encloses the cell contents. The pro-tein secondary structure and thermal stability of the plasma membrane of wheat root have been characterized in D2O buffer from 20°C to 90°C by Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Quantitative analysis of the amide I band (1700 - 1600 cm–1) showed that the plasma membrane proteins contains 41% α-helix, 16% β-sheet, 18% turn, and 25% disorder structures at 20°C. At elevated temperatures from 25°C up to 90°C, the α-helix and the β-sheet structure unfold into turns and the disorder structure, with a major conformational transition occurring at 50°C. There is a rapid decline in H+-ATPase activity of plasma membrane from 35°C to 55°C and it remain very low level H+-ATPase activity of PM from 55°C to 90°C. Therefore the protein conformational transition was one of reasons of loses H+-ATPase activity of plasma membrane.
基金supported by the National Natural Science Foundation of China (10872192)
文摘With the two-scale expansion technique proposed by Yoshizawa,the turbulent fluctuating field is expanded around the isotropic field.At a low-order two-scale expansion,applying the mode coupling approximation in the Yakhot-Orszag renormalization group method to analyze the fluctuating field,the Reynolds-average terms in the Reynolds stress transport equation,such as the convective term,the pressure-gradient-velocity correlation term and the dissipation term,are modeled.Two numerical examples：turbulent flow past a backward-facing step and the fully developed flow in a rotating channel,are presented for testing the efficiency of the proposed second-order model.For these two numerical examples,the proposed model performs as well as the Gibson-Launder （GL） model,giving better prediction than the standard k-ε model,especially in the abilities to calculate the secondary flow in the backward-facing step flow and to capture the asymmetric turbulent structure caused by frame rotation.
基金supported by the National Natural Science Foundation of China, No. 81171109
文摘Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries.
文摘The velocity field and the associated shear stress corresponding to the longitudinal oscillatory flow of a generalized second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. Initially, the fluid and cylinders are at rest and at t = 0＋ both cylinders suddenly begin to oscillate along their common axis with simple harmonic motions having angular frequencies Ω1 and Ω2. The solutions that have been obtained are presented under integral and series forms in terms of the generalized G and R functions and satisfy the governing differential equation and all imposed initial and boundary conditions. The respective solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for the similar flow of ordinary second grade fluid and Newtonian fluid are also obtained as limiting cases of our general solutions. At the end, the effect of different parameters on the flow of ordinary second grade and generalized second grade fluid are investigated graphically by plotting velocity profiles.
文摘The velocity field and the adequate shear stress corresponding to the longitudinal flow of a fractional second grade fluid,between two infinite coaxial circular cylinders,are determined by applying the Laplace and finite Hankel transforms.Initially the fluid is at rest,and at time t=0^+, the inner cylinder suddenly begins to translate along the common axis with constant acceleration. The solutions that have been obtained are presented in terms of generalized G functions.Moreover, these solutions satisfy both the governing differential equations and all imposed initial and boundary conditions.The corresponding solutions for ordinary second grade and Newtonian fluids are obtained as limiting cases of the general solutions.Finally,some characteristics of the motion,as well as the influences of the material and fractional parameters on the fluid motion and a comparison between models,are underlined by graphical illustrations.
文摘GH4169 superalloy stress relaxation test was investigated to study its characteristics of stress relaxation curves at various temperatures( 550,650,and 750 ℃). These curves presented jointly two distinct stages,the stage of inner stress relaxing quickly,and the stage of inner stress relaxing slowly and closing to the stress relaxation limit. And these curves obtained could be fitted by second order exponential decay function well. Based on the experimental stress relaxation curves,the relationship between stress relaxation rate and time were derived, which showed that the higher relaxation temperature and the greater initial rate of stress relaxation. The whole process presented two different stages,the stage of stress relaxation rate falling rapidly and the stage of stress relaxation rate slowing down and tending to be constant. The relation curve between creep strain rate and stress of GH4169 superalloy can be divided into three stages,low stress stage,transition stage,and high stress stage.Both the high stage and the low stage present linear correlation.
文摘Mechanical models of residually stressed fibre-reinforced solids,which do not resist bending,have been developed in the literature.However,in some residually stressed fibre-reinforced elastic solids,resistance to fibre bending is significant,and the mechanical behavior of such solids should be investigated.Hence,in this paper,we model the mechanical aspect of residually stressed elastic solids with bending stiffness due to fibre curvature,which up to the authors’knowledge has not been mechanically modeled in the past.The proposed constitutive equation involves a nonsymmetric stress and a couple-stress tensor.Spectral invariants are used in the constitutive equation,where each spectral invariant has an intelligible physical meaning,and hence they are useful in experiment and analysis.A prototype strain energy function is proposed.Moreover,we use this prototype to give results for some cylindrical boundary value problems.
文摘This paper deals with the rotational flow of a generalized second grade fluid, within a circular cylinder, due to a torsional shear stress. The fractional calculus approach in the constitutive relationship model of a second grade fluid is introduced. The velocity field and the resulting shear stress are determined by means of the Laplace and finite Hankel transforms to satisfy all imposed initial and boundary conditions. The solutions corresponding to second grade fluids as well as those for Newtonian fluids are obtained as limiting cases of our general solutions. The influence of the fractional coefficient on the velocity of the fluid is also analyzed by graphical illustrations.
文摘The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. At time t = 0, the fluid and both the cylinders are at rest and at t = 0 ＋ , cylinders suddenly begin to oscillate around their common axis in a simple harmonic way having angular frequencies ω 1 and ω 2 . The obtained solutions satisfy the governing differential equation and all imposed initial and boundary conditions. The solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for Newtonian fluid are also obtained as limiting cases of our general solutions.
文摘The areas affected by the L1 transfer to L2,such as phonotactics and stress,appear to have different degrees of erasability through training and practice.This paper attempts a theoretical analysis to account for empirical observations of L1 transfer in diphthong-coda coalescence and in sentence stress for Chinese learners of English in an American accent training course.Using the framework and tableau method of Optimality Theory(Prince and Smolensky 1993),the phonological paradigm that views languages’differences as symptomatic of differences in rankings of a set of universal violable constraints,this paper posits the underlying ranking at work in(a)the segmental case where[aŋ]is the observed output for/aʊn/;(b)the suprasegmental case where no stress contrast is observed for a pair of phonologically similar sentences with contrastive stress.It is argued that,in the segmental case,the coalescence of the second vowel of a diphthong with an alveolar nasal coda results from the high ranking of markedness constraints,including Complex Syllable;and in the suprasegmental case,sentence stress is greatly affected by changes in the ranking of the constraint culminativity.Aside from shedding light on the understudied issue of diphthong-coda coalescence,this research also contributes to the discussion of the comparative erasability of L1 transfer for the two areas and demonstrates how a deduction-based theoretical method may actually have practical implications for guiding the design of L2 teaching methodology of English pronunciation as well as for promoting native English speakers’clearer understanding of Chinese learners of English on the global stage.
基金Project supported by the National Key Basic Research and Development Program of China(No.G1999-0222-08)
文摘The USM-θ model of Bingham fluid for dense two-phase turbulent flow was developed, which combines the second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collision. In this model, phases interaction and the extra term of Bingham fluid yield stress are taken into account. An algorithm for USM-θ model in dense two-phase flow was proposed, in which the influence of particle volume fraction is accounted for. This model was used to simulate turbulent flow of Bingham fluid single-phase and dense liquid-particle two-phase in pipe. It is shown USM-θ model has better prediction result than the five-equation model, in which the particle-particle collision is modeled by the particle kinetic theory, while the turbulence of both phase is simulated by the two-equation turbulence model. The USM-θ model was then used to simulate the dense two-phase turbulent up flow of Bingham fluid with particles. With the increasing of the yield stress, the velocities of Bingham and particle decrease near the pipe centre. Comparing the two-phase flow of Bingham-particle with that of liquid-particle, it is found the source term of yield stress has significant effect on flow.
基金supported by the Natural Science Foundation of Gansu Provincial Department of Science and Technology(No.18JR3RE422)。
文摘A reliability sensitivity analysis based on modal stress is presented and applied to predict the influence factors of parameters on drum brake.Firstly,the first 10 modes of prestress of the brake drum are performed in the software ANSYS Workbench.According to the results of brake noise research,it can be detected whether the drum brake meets the results that the noise frequency range of 500-1000 Hz.The reliability sensitivity design of mechanical parts based on the normal distribution parameters for complex mechanical system is discussed.Secondly,according to the first order second moment(FOSM)theory on reliability,the reliability sensitivity of drum brake is analyzed and calculated,and compared with the Monte Carlo(MC)numerical simulation results,The variation rules of reliability sensitivity is given,which provides a theoretical basis for the design of drum brake.
