The governing equations of a transversely isotropic dissipative medium are solved analytically to obtain the speeds of plane waves. The appropriate solutions satisfy the required boundary conditions at the stress-free...The governing equations of a transversely isotropic dissipative medium are solved analytically to obtain the speeds of plane waves. The appropriate solutions satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflection coefficients of reflected quasi-P (qP) and quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter. The impact of initial stress parameter on the reflection coefficients is observed significantly.展开更多
Investigation concerning peristaltic motion of couple stress fluid is made. An incompressible couple stress fluid occupies the porous medium. Mathematical anal- ysis is presented through large wavelength and low Reyno...Investigation concerning peristaltic motion of couple stress fluid is made. An incompressible couple stress fluid occupies the porous medium. Mathematical anal- ysis is presented through large wavelength and low Reynolds number. Exact analytical expressions of axial velocity, volume flow rate, pressure gradient, and stream function are calculated as a function of couple stress parameter. The essential feature of the analysis is a full description of influence of couple stress parameter and permeability parameter on the pressure, frictional force, mechanical efficiency, and trapping.展开更多
The strain and stress fields of a rectangular dislocation loop in an isotropic solid that is a semi-infinite medium (half medium) are developed here for a Volterra-type dislocation. Specifically, the loop is parallel ...The strain and stress fields of a rectangular dislocation loop in an isotropic solid that is a semi-infinite medium (half medium) are developed here for a Volterra-type dislocation. Specifically, the loop is parallel to the free surface of the solid. The elastic fields of the dislocation loop are developed by integrating the displacement equation of infinitesimals dislocation loops over a finite rectangular loop area below the free surface. The strains and stress then follow from the small strain tensor and Hooke’s law for isotropic materials, respectively. In this paper, analytical verification and numerical verification for the elastic fields are both demonstrated. Equilibrium equations and strain compatibility equations are applied in the verification. Also, a comparison with a newly-developed numerical method for dislocations near a free surface is performed as well. The developed solution is a function of the loop depth beneath the surface and can be used as a fundamental solution to solve elasticity, plasticity or dislocation problems.展开更多
In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 ...In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 and 7039 aluminum alloys. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of LC52 and 7039 alloy was investigated. The results show that the near solvus pre precipitation can be limited on grain boundary and can enhance the discontinuity of grain boundary precipitates. The stress corrosion cracking resistance of aged Al Zn Mg alloys can be improved with non deteriorated strength and plasticity via pre precipitation.展开更多
The governing equations of an initially stressed rotating orthotropic dissipative medium are solved analytically to obtain the velocity equation which indicates the existence of two quasi-planar waves. The appropriate...The governing equations of an initially stressed rotating orthotropic dissipative medium are solved analytically to obtain the velocity equation which indicates the existence of two quasi-planar waves. The appropriate particular solutions in the half-space satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflec-tion coefficients of the reflected quasi-P (qP) and reflected quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter and rotation parameter. The impact of initial stress and rotation parameters on the reflection coefficients is observed significantly.展开更多
In this paper, we discussed the influence of the initial tectonic stress on the relative measurement value of the ground stress when a long cylindrical straingauge is used in the viscoelastic media. We simulate the...In this paper, we discussed the influence of the initial tectonic stress on the relative measurement value of the ground stress when a long cylindrical straingauge is used in the viscoelastic media. We simulate the whole system consisting of the stratum, cement ring and the straingauge cylinder with a three layer medium model and obtain the solution of radial displacement on the inner wall of the straingauge under the action of initial tectonic stress by using the correspondence principle. The result showes: 1) The influence of initial stress making of the radial displacement on the inner wall of the straingauge increases gradually with time at a gradually reduced rate and tends to a certain value eventually; 2) The principal stress with a magnitude of [C 0+C 1 exp (- ω 1t)+ C 2 exp(- ω 2t )] σ i0 in the opposite direction of initial stress will be superimposed to the measuring result of stress change without considering the initial stress. where C 0, C 1, C 2 and ω 1, ω 2 are related only to the mechanical property of the stratum, σ i0 (i=1, 2) are the two principal components of the initial tectonic stress. It is pointed out that the initial tectonic stress affects obviously on the measurement of the relative change of ground stress in the cases of soft strata and high initial stress.展开更多
Both the orthotropy and the stress concentration are common issues in modem structural engineering. This paper introduces the boundary element method （BEM） into the elastic and elastoplastic analyses for 2D orthotro...Both the orthotropy and the stress concentration are common issues in modem structural engineering. This paper introduces the boundary element method （BEM） into the elastic and elastoplastic analyses for 2D orthotropic media with stress concentration. The discretized boundary element formulations are established, and the stress formulae as well as the fundamental solutions are derived in matrix notations. The numerical procedures are proposed to analyze both elastic and elastoplastic problems of 2D orthotropic me- dia with stress concentration. To obtain more precise stress values with fewer elements, the quadratic isoparametric element formulation is adopted in the boundary discretization and numerical procedures. Numerical examples show that there are significant stress concentrations and different elastoplastic behaviors in some orthotropic media, and some of the computational results are compared with other solutions. Good agreements are also observed, which demonstrates the efficiency and reliability of the present BEM in the stress concentration analysis for orthotropic media.展开更多
According to generalized characteristic theory, a characteristic analysis for stress wave propagation in transversely isotropic fluid-saturated porous media was performed. The characteristic differential equations an...According to generalized characteristic theory, a characteristic analysis for stress wave propagation in transversely isotropic fluid-saturated porous media was performed. The characteristic differential equations and compatibility relations along bicharacteristics were deduced and the analytical expressions for wave surfaces were obtained. The characteristic and shapes of the velocity surfaces and wave surfaces in the transversely isotropic fluid-saturated porous media were discussed in detail. The results also show that the characteristic equations for stress waves in pure solids are particular cases of the characteristic equations for fluid-saturated porous media.展开更多
Background/Purpose: Multipotent bone marrow-derived mesenchymal stromal cells (BMMSC) have been shown to possess the potential for tissue regeneration. The application of mesenchymal stromal cells (MSC)-derived growth...Background/Purpose: Multipotent bone marrow-derived mesenchymal stromal cells (BMMSC) have been shown to possess the potential for tissue regeneration. The application of mesenchymal stromal cells (MSC)-derived growth factors and cytokines (GF/CKs) has been implicated for the repair and regeneration of the damaged skin that occurs due to aging and exposure to environmental stress factors. Methods: We have used both qualitative and quantitative measurements of the GF/CKs from the conditioned medium (CM) of a pooled population of BMMSC by antibody array analysis as well as by enzyme-linked immunosorbent assay (ELISA). Furthermore, the CM was also used in a variety of in vitro biological assays to measure its protective properties in human skin fibroblasts. Results: We have characterized the secretome of BMMSC by analyzing the composition of the CM using a forty-one growth factor array system. Thirteen of these GF/CK/extra cellular matrix (ECM)/ matrix metalloproteinases (MMP)-inhibitors in the CM were quantified owing to their involvement in skin repair cascade. In addition, we report that the BMMSC-CM was also able to protect dermal fibroblasts against tert-Butyl hydro peroxide (tbOH) induced oxidative stress and ultra violet B (UV-B) radiation induced cell damage. Conclusion: Based on the data presented here, we propose that BMMSC-derived CM may have the potential to promote health and rejuvenation of the aging skin.展开更多
Based on the observations of many years, it has been found that “small earthquake modulation windows” exist inthe situation of some special geological structures, which respond sensitively to the variations of regio...Based on the observations of many years, it has been found that “small earthquake modulation windows” exist inthe situation of some special geological structures, which respond sensitively to the variations of regional stressfields and the activities of earthquake swarms greater than moderate strong magnitude, and can supply some precursory information. More than two “small earthquake modulation windows” can also provide a general orientation of the first main earthquake of a earthquake cluster. Compared with “seismic window” based on frequency itis no doubt that the “modulation-window” has an unique characteristic of applicational significance to mediumterm earthquake prediction with a time scale of two or three years.展开更多
This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of visc...This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of viscoelastic model in seismic stress triggering, the relation between earthquake triggering and volcanic eruption or explosion, other explanation of earthquake triggering, etc. And some suggestions for further study on seismic stress triggering in near future are given.展开更多
文摘The governing equations of a transversely isotropic dissipative medium are solved analytically to obtain the speeds of plane waves. The appropriate solutions satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflection coefficients of reflected quasi-P (qP) and quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter. The impact of initial stress parameter on the reflection coefficients is observed significantly.
文摘Investigation concerning peristaltic motion of couple stress fluid is made. An incompressible couple stress fluid occupies the porous medium. Mathematical anal- ysis is presented through large wavelength and low Reynolds number. Exact analytical expressions of axial velocity, volume flow rate, pressure gradient, and stream function are calculated as a function of couple stress parameter. The essential feature of the analysis is a full description of influence of couple stress parameter and permeability parameter on the pressure, frictional force, mechanical efficiency, and trapping.
文摘The strain and stress fields of a rectangular dislocation loop in an isotropic solid that is a semi-infinite medium (half medium) are developed here for a Volterra-type dislocation. Specifically, the loop is parallel to the free surface of the solid. The elastic fields of the dislocation loop are developed by integrating the displacement equation of infinitesimals dislocation loops over a finite rectangular loop area below the free surface. The strains and stress then follow from the small strain tensor and Hooke’s law for isotropic materials, respectively. In this paper, analytical verification and numerical verification for the elastic fields are both demonstrated. Equilibrium equations and strain compatibility equations are applied in the verification. Also, a comparison with a newly-developed numerical method for dislocations near a free surface is performed as well. The developed solution is a function of the loop depth beneath the surface and can be used as a fundamental solution to solve elasticity, plasticity or dislocation problems.
文摘In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 and 7039 aluminum alloys. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of LC52 and 7039 alloy was investigated. The results show that the near solvus pre precipitation can be limited on grain boundary and can enhance the discontinuity of grain boundary precipitates. The stress corrosion cracking resistance of aged Al Zn Mg alloys can be improved with non deteriorated strength and plasticity via pre precipitation.
文摘The governing equations of an initially stressed rotating orthotropic dissipative medium are solved analytically to obtain the velocity equation which indicates the existence of two quasi-planar waves. The appropriate particular solutions in the half-space satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflec-tion coefficients of the reflected quasi-P (qP) and reflected quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter and rotation parameter. The impact of initial stress and rotation parameters on the reflection coefficients is observed significantly.
文摘In this paper, we discussed the influence of the initial tectonic stress on the relative measurement value of the ground stress when a long cylindrical straingauge is used in the viscoelastic media. We simulate the whole system consisting of the stratum, cement ring and the straingauge cylinder with a three layer medium model and obtain the solution of radial displacement on the inner wall of the straingauge under the action of initial tectonic stress by using the correspondence principle. The result showes: 1) The influence of initial stress making of the radial displacement on the inner wall of the straingauge increases gradually with time at a gradually reduced rate and tends to a certain value eventually; 2) The principal stress with a magnitude of [C 0+C 1 exp (- ω 1t)+ C 2 exp(- ω 2t )] σ i0 in the opposite direction of initial stress will be superimposed to the measuring result of stress change without considering the initial stress. where C 0, C 1, C 2 and ω 1, ω 2 are related only to the mechanical property of the stratum, σ i0 (i=1, 2) are the two principal components of the initial tectonic stress. It is pointed out that the initial tectonic stress affects obviously on the measurement of the relative change of ground stress in the cases of soft strata and high initial stress.
基金The project supported by the Basic Research Foundation of Tsinghua University,the National Foundation for Excellent Doctoral Thesis(200025)the National Natural Science Foundation of China(19902007).
文摘Both the orthotropy and the stress concentration are common issues in modem structural engineering. This paper introduces the boundary element method （BEM） into the elastic and elastoplastic analyses for 2D orthotropic media with stress concentration. The discretized boundary element formulations are established, and the stress formulae as well as the fundamental solutions are derived in matrix notations. The numerical procedures are proposed to analyze both elastic and elastoplastic problems of 2D orthotropic me- dia with stress concentration. To obtain more precise stress values with fewer elements, the quadratic isoparametric element formulation is adopted in the boundary discretization and numerical procedures. Numerical examples show that there are significant stress concentrations and different elastoplastic behaviors in some orthotropic media, and some of the computational results are compared with other solutions. Good agreements are also observed, which demonstrates the efficiency and reliability of the present BEM in the stress concentration analysis for orthotropic media.
文摘According to generalized characteristic theory, a characteristic analysis for stress wave propagation in transversely isotropic fluid-saturated porous media was performed. The characteristic differential equations and compatibility relations along bicharacteristics were deduced and the analytical expressions for wave surfaces were obtained. The characteristic and shapes of the velocity surfaces and wave surfaces in the transversely isotropic fluid-saturated porous media were discussed in detail. The results also show that the characteristic equations for stress waves in pure solids are particular cases of the characteristic equations for fluid-saturated porous media.
文摘Background/Purpose: Multipotent bone marrow-derived mesenchymal stromal cells (BMMSC) have been shown to possess the potential for tissue regeneration. The application of mesenchymal stromal cells (MSC)-derived growth factors and cytokines (GF/CKs) has been implicated for the repair and regeneration of the damaged skin that occurs due to aging and exposure to environmental stress factors. Methods: We have used both qualitative and quantitative measurements of the GF/CKs from the conditioned medium (CM) of a pooled population of BMMSC by antibody array analysis as well as by enzyme-linked immunosorbent assay (ELISA). Furthermore, the CM was also used in a variety of in vitro biological assays to measure its protective properties in human skin fibroblasts. Results: We have characterized the secretome of BMMSC by analyzing the composition of the CM using a forty-one growth factor array system. Thirteen of these GF/CK/extra cellular matrix (ECM)/ matrix metalloproteinases (MMP)-inhibitors in the CM were quantified owing to their involvement in skin repair cascade. In addition, we report that the BMMSC-CM was also able to protect dermal fibroblasts against tert-Butyl hydro peroxide (tbOH) induced oxidative stress and ultra violet B (UV-B) radiation induced cell damage. Conclusion: Based on the data presented here, we propose that BMMSC-derived CM may have the potential to promote health and rejuvenation of the aging skin.
文摘Based on the observations of many years, it has been found that “small earthquake modulation windows” exist inthe situation of some special geological structures, which respond sensitively to the variations of regional stressfields and the activities of earthquake swarms greater than moderate strong magnitude, and can supply some precursory information. More than two “small earthquake modulation windows” can also provide a general orientation of the first main earthquake of a earthquake cluster. Compared with “seismic window” based on frequency itis no doubt that the “modulation-window” has an unique characteristic of applicational significance to mediumterm earthquake prediction with a time scale of two or three years.
基金Chinese Joint Seismological Science Foundation (602005).
文摘This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of viscoelastic model in seismic stress triggering, the relation between earthquake triggering and volcanic eruption or explosion, other explanation of earthquake triggering, etc. And some suggestions for further study on seismic stress triggering in near future are given.
