In order to improve the measurement precision and increase the reliability of the femtosecond laser transient thermoreflectance system, the relative optical path difference between pump and probe beams is prolonged, w...In order to improve the measurement precision and increase the reliability of the femtosecond laser transient thermoreflectance system, the relative optical path difference between pump and probe beams is prolonged, which can improve the fitting accuracy of the experimental data to the theoretical model. A modified experimental setup is devised with the pump path intercalated a moving stage identical to the one in the probe path, which extends the optical path difference of the probe beam relative to the pump beam from 4 to 8 ns. The measured results indicate that the uncertainty from the misalignment and divergence of both beams can be ignored when the last 4 ns experimental data are connected with those of the first 4 ns smoothly. The as-obtained thermal conductance of AI/Si and Cr/Si interfaces agrees well with the reported experimental values, which verifies the reliability of this modified version of this measurement.展开更多
In order to well understand the elementary mechanisms that govern the hot working process of a V?5Cr?5Ti alloy (mass fraction, %), thermal activation parameters under compression were measured in a temperature ran...In order to well understand the elementary mechanisms that govern the hot working process of a V?5Cr?5Ti alloy (mass fraction, %), thermal activation parameters under compression were measured in a temperature range of 1373?1673 K by a Gleeble?3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy (270?300 kJ/mol) by introducing a threshold stress(σ0) variable. The typical values of physical activation volume (Vp) and strain rate sensitivity (m) are measured as (120?700)b3 and 0.075?0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V?5Cr?5Ti alloy compressed in ranges of 1373?1673 K and 0.001?1.0 s?1 is the dislocation climb by overcoming of forest dislocations.展开更多
It is a very important and complex task to estimate the thermo-elasticproperties of a textile structural composite. In this paper, the finite element method (FEM) wasused for the prediction of the orthotropic thermo-e...It is a very important and complex task to estimate the thermo-elasticproperties of a textile structural composite. In this paper, the finite element method (FEM) wasused for the prediction of the orthotropic thermo-elastic properties of a composite reinforced byglass fiber knitted fabric. In order to define the final 3-D configuration of the loop reinforcingstructure, the interactions between the adjacent loops, the large displacement and the contactelements without friction were considered. The values predicted were compared with the experimentalresults.展开更多
With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG:Cr^3+ at normal pre...With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG:Cr^3+ at normal pressure and low temperature has been calculated. The g factor of the ground-state has been evaluated in terms of the energy spectrum. At the same time, by using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix and Thermal Shifts theory, we calculate the thermal shifts of the sharp lines of YGG:Cr^3+ and determine the relevant parameters. The calculated results are all in good agreement with the optical-spectrum and EPR experimental data. It is demonstrated that the obtained wavefunctions and the values of parameters are reasonable.展开更多
A great improvement on a previous work (Phys. Rev. B48 (1993) 14067) has been made. By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as a...A great improvement on a previous work (Phys. Rev. B48 (1993) 14067) has been made. By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration, the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) from EPI for the ground level, R level and R line of MgO:V<SUP>2+</SUP> have microscopically been evaluated; and then, both the TS and TB of R line and various contributions to them have uniformly been calculated. The results are in very good agreement with the experimental data. It is found that all the three terms of TS from EPI are red shifts; the term of the contribution to TS from thermal expansion is blue shift. The Raman term is the largest, and the other terms are also important for TS. The R-line TS of MgO:V<SUP>2+</SUP> comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:V<SUP>2+</SUP>. For calculations of both the TS and TB, it is very important to take into account all the admixtures of wavefunctions.展开更多
By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d<SUP>3</SUP...By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration, the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) due to EPI for the ground level, R level and R line of MgO:Cr<SUP>3+</SUP> have microscopically been evaluated; and then, TS and TB of R line and various contributions to them have uniformly been calculated. The results are in very good agreement with the experimental data. It is found that all the three terms of TS due to EPI are red shifts; the Raman term is the largest one, and the optical-branch term and neighbor-level term are important for TS; the contribution to TS from thermal expansion is blue shift, which is also important. The R-line TS of MgO:Cr<SUP>3+</SUP> comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:Cr<SUP>3+</SUP>. For both TS and TB, it is very important to take into account all the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration.展开更多
Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical P...Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical Pacific sea surface temperature (SST) anomalies associated with meridional displacement of the monthly EAJS during the summer.The meridional displacement of the EAJS in June is significantly associated with the tropical central Pacific SST anomaly in the winter of previous years,while displacements in July and August are related to tropical eastern Pacific SST anomalies in the late spring and concurrent summer.The EAJS tends to shift southward in the following June (July and August) corresponding to a warm SST anomaly in the central (eastern) Pacific in the winter (late spring-summer).The westerly anomaly south of the Asian jet stream is a result of tropical central Pacific warm SST anomaly-related warming in the tropical troposphere,which is proposed as a possible reason for southward displacement of the EAJS in June.The late spring-summer warm SST anomaly in the tropical eastern Pacific,however,may be linked to southward displacement of the EAJS in July and August through a meridional teleconnection over the western North Pacific (WNP) and East Asia.展开更多
In the processes of manufacturing, MT (machine tools) plays an important role in the manufacture of work pieces with complex and high dimensional and geometric accuracy. Much of the errors of a machine tool are thos...In the processes of manufacturing, MT (machine tools) plays an important role in the manufacture of work pieces with complex and high dimensional and geometric accuracy. Much of the errors of a machine tool are those which are thermally induced which are from internal and external heat sources acting on the machine. In this paper, a methodology for determining and analyzing the thermal deformation of machine tools using FEM (finite element method) and ANN (artificial neural networks) is presented. After modeling the machine using FEM is defined the location of the heat sources, it is possible to obtain the temperature gradient and the corresponding thermal deformation at predetermined periods. Results obtained with simulations using the software NX.7.5 showed that this methodology is an effective tool in determining the thermal deformation of the machine, correlating the temperature reading at strategic points with volumetric deformation at the tool tip. Therefore, the thermal analysis of the errors in the pair tool part can be established. After training and validation process, the network will be able to make the prediction of thermal errors just stating the temperature values of specific points of each heat source, providing a way for compensation of thermally induced errors.展开更多
According to the two-dimensional(2-D) thermo-elasticity theory, the exact elasticity solution of the simply supported laminated beams subjected to thermo-loads was studied. An analytical method was presented to obtain...According to the two-dimensional(2-D) thermo-elasticity theory, the exact elasticity solution of the simply supported laminated beams subjected to thermo-loads was studied. An analytical method was presented to obtain the temperature, displacement and stress fields in the beam. Firstly, the general solutions of temperature, displacements and stresses for a single-layered simply supported beam were obtained by solving the 2-D heat conduction equation and the 2-D elasticity equations, respectively. Then, based on the continuity of temperature, heat flux, displacements and stresses on the interface of two adjacent layers, the formulae of temperature, displacements and stresses between the lowest layer and the top layer of the beam were derived out in a recurrent manner. Finally, the unknown coefficients in the solutions were determined by the use of the upper surface and lower surface conditions of the beam. The distributions of temperature, displacement and stress in the beam were obtained by substituting these coefficients back to the recurrence formulae and the solutions. The excellent convergence of the present method has been demonstrated and the results obtained by the present method agree well with those from the finite element method. The effects of surface temperatures, thickness, layer number and material properties of the plate on the temperature distribution were discussed in detail. Numerical results reveal that the displacements and stresses monotonically increase with the increase of surface temperatures. In particular, the horizontal stresses are discontinuous at the interface.展开更多
We have considered the basic dynamic homogeneous system of partial differential equations of generalized Green-Lindsay couple-stress thermodiffusion on the plane for homogeneous, isotropic elastic media with the centr...We have considered the basic dynamic homogeneous system of partial differential equations of generalized Green-Lindsay couple-stress thermodiffusion on the plane for homogeneous, isotropic elastic media with the centre of symmetry. We have constructed regular solution of the boundary problems on the line. In the works are obtained in quadrates the solution of the boundary-value problem of the generalized Green-Lindsay theory of couple-stress thermodiffusion, when on border of area are given: the component of normal of displacement vector, the component of touching of stress vector, rotations, flow of heat and flow of diffusion.展开更多
The beam horizontal orbit at Hefei Light Source(HLS)was drifting all along while the storage ring was operating.To study this phenomenon,the displacement and the temperature variation of the BPM chamber were measured....The beam horizontal orbit at Hefei Light Source(HLS)was drifting all along while the storage ring was operating.To study this phenomenon,the displacement and the temperature variation of the BPM chamber were measured.By analyzing the measurement results,the main reason that explained the drifting phenomenon was found. The vacuum chamber following the dipole magnets was heated by the synchrotron light,which caused the increasing of the chamber surface temperature.The variation of the chamber temperature was the main reason why the BPM chamber held the horizontal displacement.To suppress the orbit drifting,a compensation method of BPM movement was proposed and its experimental results were given.展开更多
基金The National Basic Research Program of China(973 Program)(No.2011CB707605)the National Natural Science Foundation of China(No.51205061,50925519,51106029)+1 种基金the Natural Science Foundation of Jiangsu Province(No.BK2012340)the Ph.D.Programs Foundation of Ministry of Education of China(No.20110092120006)
文摘In order to improve the measurement precision and increase the reliability of the femtosecond laser transient thermoreflectance system, the relative optical path difference between pump and probe beams is prolonged, which can improve the fitting accuracy of the experimental data to the theoretical model. A modified experimental setup is devised with the pump path intercalated a moving stage identical to the one in the probe path, which extends the optical path difference of the probe beam relative to the pump beam from 4 to 8 ns. The measured results indicate that the uncertainty from the misalignment and divergence of both beams can be ignored when the last 4 ns experimental data are connected with those of the first 4 ns smoothly. The as-obtained thermal conductance of AI/Si and Cr/Si interfaces agrees well with the reported experimental values, which verifies the reliability of this modified version of this measurement.
基金Project(11105127)supported by the National Natural Science Foundation of China
文摘In order to well understand the elementary mechanisms that govern the hot working process of a V?5Cr?5Ti alloy (mass fraction, %), thermal activation parameters under compression were measured in a temperature range of 1373?1673 K by a Gleeble?3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy (270?300 kJ/mol) by introducing a threshold stress(σ0) variable. The typical values of physical activation volume (Vp) and strain rate sensitivity (m) are measured as (120?700)b3 and 0.075?0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V?5Cr?5Ti alloy compressed in ranges of 1373?1673 K and 0.001?1.0 s?1 is the dislocation climb by overcoming of forest dislocations.
文摘It is a very important and complex task to estimate the thermo-elasticproperties of a textile structural composite. In this paper, the finite element method (FEM) wasused for the prediction of the orthotropic thermo-elastic properties of a composite reinforced byglass fiber knitted fabric. In order to define the final 3-D configuration of the loop reinforcingstructure, the interactions between the adjacent loops, the large displacement and the contactelements without friction were considered. The values predicted were compared with the experimentalresults.
基金supported by National Natural Science Foundation of China under Grant No.10775102
文摘With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG:Cr^3+ at normal pressure and low temperature has been calculated. The g factor of the ground-state has been evaluated in terms of the energy spectrum. At the same time, by using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix and Thermal Shifts theory, we calculate the thermal shifts of the sharp lines of YGG:Cr^3+ and determine the relevant parameters. The calculated results are all in good agreement with the optical-spectrum and EPR experimental data. It is demonstrated that the obtained wavefunctions and the values of parameters are reasonable.
文摘A great improvement on a previous work (Phys. Rev. B48 (1993) 14067) has been made. By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration, the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) from EPI for the ground level, R level and R line of MgO:V<SUP>2+</SUP> have microscopically been evaluated; and then, both the TS and TB of R line and various contributions to them have uniformly been calculated. The results are in very good agreement with the experimental data. It is found that all the three terms of TS from EPI are red shifts; the term of the contribution to TS from thermal expansion is blue shift. The Raman term is the largest, and the other terms are also important for TS. The R-line TS of MgO:V<SUP>2+</SUP> comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:V<SUP>2+</SUP>. For calculations of both the TS and TB, it is very important to take into account all the admixtures of wavefunctions.
文摘By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration, the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) due to EPI for the ground level, R level and R line of MgO:Cr<SUP>3+</SUP> have microscopically been evaluated; and then, TS and TB of R line and various contributions to them have uniformly been calculated. The results are in very good agreement with the experimental data. It is found that all the three terms of TS due to EPI are red shifts; the Raman term is the largest one, and the optical-branch term and neighbor-level term are important for TS; the contribution to TS from thermal expansion is blue shift, which is also important. The R-line TS of MgO:Cr<SUP>3+</SUP> comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:Cr<SUP>3+</SUP>. For both TS and TB, it is very important to take into account all the admixtures of basic wavefunctions within d<SUP>3</SUP> electronic configuration.
基金supported by the National Natural Science Foundation of China (Grant No. 40810059005)
文摘Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical Pacific sea surface temperature (SST) anomalies associated with meridional displacement of the monthly EAJS during the summer.The meridional displacement of the EAJS in June is significantly associated with the tropical central Pacific SST anomaly in the winter of previous years,while displacements in July and August are related to tropical eastern Pacific SST anomalies in the late spring and concurrent summer.The EAJS tends to shift southward in the following June (July and August) corresponding to a warm SST anomaly in the central (eastern) Pacific in the winter (late spring-summer).The westerly anomaly south of the Asian jet stream is a result of tropical central Pacific warm SST anomaly-related warming in the tropical troposphere,which is proposed as a possible reason for southward displacement of the EAJS in June.The late spring-summer warm SST anomaly in the tropical eastern Pacific,however,may be linked to southward displacement of the EAJS in July and August through a meridional teleconnection over the western North Pacific (WNP) and East Asia.
文摘In the processes of manufacturing, MT (machine tools) plays an important role in the manufacture of work pieces with complex and high dimensional and geometric accuracy. Much of the errors of a machine tool are those which are thermally induced which are from internal and external heat sources acting on the machine. In this paper, a methodology for determining and analyzing the thermal deformation of machine tools using FEM (finite element method) and ANN (artificial neural networks) is presented. After modeling the machine using FEM is defined the location of the heat sources, it is possible to obtain the temperature gradient and the corresponding thermal deformation at predetermined periods. Results obtained with simulations using the software NX.7.5 showed that this methodology is an effective tool in determining the thermal deformation of the machine, correlating the temperature reading at strategic points with volumetric deformation at the tool tip. Therefore, the thermal analysis of the errors in the pair tool part can be established. After training and validation process, the network will be able to make the prediction of thermal errors just stating the temperature values of specific points of each heat source, providing a way for compensation of thermally induced errors.
基金Project(2012CB026205)supported by the National Basic Research Program of ChinaProject(51238003)supported by the National Natural Science Foundation of ChinaProject(2014Y01)supported by the Transportation Department of Jiangsu Province,China
文摘According to the two-dimensional(2-D) thermo-elasticity theory, the exact elasticity solution of the simply supported laminated beams subjected to thermo-loads was studied. An analytical method was presented to obtain the temperature, displacement and stress fields in the beam. Firstly, the general solutions of temperature, displacements and stresses for a single-layered simply supported beam were obtained by solving the 2-D heat conduction equation and the 2-D elasticity equations, respectively. Then, based on the continuity of temperature, heat flux, displacements and stresses on the interface of two adjacent layers, the formulae of temperature, displacements and stresses between the lowest layer and the top layer of the beam were derived out in a recurrent manner. Finally, the unknown coefficients in the solutions were determined by the use of the upper surface and lower surface conditions of the beam. The distributions of temperature, displacement and stress in the beam were obtained by substituting these coefficients back to the recurrence formulae and the solutions. The excellent convergence of the present method has been demonstrated and the results obtained by the present method agree well with those from the finite element method. The effects of surface temperatures, thickness, layer number and material properties of the plate on the temperature distribution were discussed in detail. Numerical results reveal that the displacements and stresses monotonically increase with the increase of surface temperatures. In particular, the horizontal stresses are discontinuous at the interface.
文摘We have considered the basic dynamic homogeneous system of partial differential equations of generalized Green-Lindsay couple-stress thermodiffusion on the plane for homogeneous, isotropic elastic media with the centre of symmetry. We have constructed regular solution of the boundary problems on the line. In the works are obtained in quadrates the solution of the boundary-value problem of the generalized Green-Lindsay theory of couple-stress thermodiffusion, when on border of area are given: the component of normal of displacement vector, the component of touching of stress vector, rotations, flow of heat and flow of diffusion.
文摘The beam horizontal orbit at Hefei Light Source(HLS)was drifting all along while the storage ring was operating.To study this phenomenon,the displacement and the temperature variation of the BPM chamber were measured.By analyzing the measurement results,the main reason that explained the drifting phenomenon was found. The vacuum chamber following the dipole magnets was heated by the synchrotron light,which caused the increasing of the chamber surface temperature.The variation of the chamber temperature was the main reason why the BPM chamber held the horizontal displacement.To suppress the orbit drifting,a compensation method of BPM movement was proposed and its experimental results were given.