Atmospheric models are physical equations based on the ideal gas law. Applied to the atmosphere, this law yields equations for water, vapor (gas), ice, air, humidity, dryness, fire, and heat, thus defining the model o...Atmospheric models are physical equations based on the ideal gas law. Applied to the atmosphere, this law yields equations for water, vapor (gas), ice, air, humidity, dryness, fire, and heat, thus defining the model of key atmospheric parameters. The distribution of these parameters across the entire planet Earth is the origin of the formation of the climatic cycle, which is a normal climatic variation. To do this, the Earth is divided into eight (8) parts according to the number of key parameters to be defined in a physical representation of the model. Following this distribution, numerical models calculate the constants for the formation of water, vapor, ice, dryness, thermal energy (fire), heat, air, and humidity. These models vary in complexity depending on the indirect trigonometric direction and simplicity in the sum of neighboring models. Note that the constants obtained from the equations yield 275.156˚K (2.006˚C) for water, 273.1596˚K (0.00963˚C) for vapor, 273.1633˚K (0.0133˚C) for ice, 0.00365 in/s for atmospheric dryness, 1.996 in<sup>2</sup>/s for humidity, 2.993 in<sup>2</sup>/s for air, 1 J for thermal energy of fire, and 0.9963 J for heat. In summary, this study aims to define the main parameters and natural phenomena contributing to the modification of planetary climate. .展开更多
The Ga_(2)O_(3) films are deposited on the Si and quartz substrates by magnetron sputtering, and annealing. The effects of preparation parameters(such as argon–oxygen flow ratio, sputtering power, sputtering time and...The Ga_(2)O_(3) films are deposited on the Si and quartz substrates by magnetron sputtering, and annealing. The effects of preparation parameters(such as argon–oxygen flow ratio, sputtering power, sputtering time and annealing temperature)on the growth and properties(e.g., surface morphology, crystal structure, optical and electrical properties of the films) are studied by x-ray diffractometer(XRD), scanning electron microscope(SEM), and ultraviolet-visible spectrophotometer(UV-Vis). The results show that the thickness, crystallization quality and surface roughness of the β-Ga_(2)O_(3) film are influenced by those parameters. All β-Ga_(2)O_(3) films show good optical properties. Moreover, the value of bandgap increases with the enlarge of the percentage of oxygen increasing, and decreases with the increase of sputtering power and annealing temperature, indicating that the bandgap is related to the quality of the film and affected by the number of oxygen vacancy defects. The I–V curves show that the Ohmic behavior between metal and β-Ga_(2)O_(3) films is obtained at 900℃. Those results will be helpful for the further research of β-Ga_(2)O_(3) photoelectric semiconductor.展开更多
An engineering system approach of 2-D cylindrical model of transient mass balance calculations of ozone and other concerned chemicals along with fourteen photolysis, ozone-generating and ozone-depleting chemical react...An engineering system approach of 2-D cylindrical model of transient mass balance calculations of ozone and other concerned chemicals along with fourteen photolysis, ozone-generating and ozone-depleting chemical reaction equations was developed, validated, and used for studying the ozone concentrations, distribution and peak of the layer, ozone depletion and total ozone abundance in the stratosphere. The calculated ozone concentrations and profile at both the Equator and a 60˚N location were found to follow closely with the measured data. The calculated average ozone concentration was within 1% of the measured average, and the deviation of ozone profiles was within 14%. The monthly evolution of stratospheric ozone concentrations and distribution above the Equator was studied with results discussed in details. The influences of slow air movement in both altitudinal and radial directions on ozone concentrations and profile in the stratosphere were explored and discussed. Parametric studies of the influences of gas diffusivities of ozone D<sub>O3</sub> and active atomic oxygen D<sub>O</sub> on ozone concentrations and distributions were also studied and delineated. Having both influences through physical diffusion and chemical reactions, the diffusivity (and diffusion) of atomic oxygen D<sub>O</sub> was found to be more sensitive and important than that of ozone D<sub>O3</sub> on ozone concentrations and distribution. The 2-D ozone model present in this paper for stratospheric ozone and its layer and depletion is shown to be robust, convenient, efficient, and executable for analyzing the complex ozone phenomena in the stratosphere. .展开更多
CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that a...CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that affects the final gas production effect.However,there have been few studies focusing on the flowback characteristics after CO_(2) dry fracturing.In this study,an extensive core-to-field scale study was conducted to investigate CO_(2) flowback characteristics and CH_(4) production behavior.Firstly,to investigate the impact of core properties and production conditions on CO_(2) flowback,a series of laboratory experiments at the core scale were conducted.Then,the key factors affecting the flowback were analyzed using the grey correlation method based on field data.Finally,taking the construction parameters of Well S60 as an example,a dual-permeability model was used to characterize the different seepage fields in the matrix and fracture for tight gas reservoirs.The production parameters after CO_(2) dry fracturing were then optimized.Experimental results demonstrate that CO_(2) dry fracturing is more effective than slickwater fracturing,with a 9.2%increase in CH_(4) recovery.The increase in core permeability plays a positive role in improving CH_(4) production and CO_(2) flowback.The soaking process is mainly affected by CO_(2) diffusion,and the soaking time should be controlled within 12 h.Increasing the flowback pressure gradient results in a significant increase in both CH_(4) recovery and CO_(2) flowback efficiency.While,an increase in CO_(2) injection is not conducive to CH_(4) production and CO_(2) flowback.Based on the experimental and field data,the important factors affecting flowback and production were comprehensively and effectively discussed.The results show that permeability is the most important factor,followed by porosity and effective thickness.Considering flowback efficiency and the influence of proppant reflux,the injection volume should be the minimum volume that meets the requirements for generating fractures.The soaking time should be short which is 1 day in this study,and the optimal bottom hole flowback pressure should be set at 10 MPa.This study aims to improve the understanding of CO_(2) dry fracturing in tight gas reservoirs and provide valuable insights for optimizing the process parameters.展开更多
Photocatalytic solar to energy conversion is considered an attractive approach for overcoming energy crises and environmental concerns.Recently,titanium carbide(Ti_(3)C_(2))MXenes have been recognized as promising coc...Photocatalytic solar to energy conversion is considered an attractive approach for overcoming energy crises and environmental concerns.Recently,titanium carbide(Ti_(3)C_(2))MXenes have been recognized as promising cocatalysts based on their metallic conductivity,excessive active reaction sites,and enlarged surface area.The current review focuses on the properties and applications of Ti_(3)C_(2)MXenes useful in the field of photocatalysis.More specifically,surface modification of Ti_(3)C_(2)MXenes by varying synthesis parameters to get pure materials and also composites with the role of functional groups towards solar energy conversion applications is highlighted in this review.The effect of etching and oxidizing pathways to get an efficient cocatalyst has been discussed in detail.Considering the significant effect of parameters,optimum synthesis conditions such as etchant type,concentration,time and type of intercalant in both the Ti_(3)C_(2)synthesis approaches for improved photoactivity are discussed.Additionally,the surface modification of Ti_(3)C_(2)through oxidation for TiO2growth on its surface is deliberated with a detailed discussion on etchant type,concentration,etching time,and environmental factors.The optimum oxidation condition,including temperature,time,and environment for thermal treatment of Ti_(3)C_(2),were also included.Lastly,the review summarizes the conclusion and future perspectives for solar energy conversion applications.展开更多
The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological ...The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method and found focal mechanism solutions using gird test method. The inversion results are as follows: the strike is 21.6°, the dip angle is 89.5°, the slip angle is 170°, the fault length is about 160 km, the lower-boundary depth is about 32 km and the buried depth of upper boundary is about 4 km. This shows that the seismic fault is a NNE-trending upright right-lateral strike-slip fault and has cut through the crust. Moreover, the surface seismic fault, intensity distribution of the earthquake, earthquake-depth distribution and seismic-wave velocity profile in the focal area all verified our study result.展开更多
The robust stability test of time-delay systems with interval parameters can be concluded into the robust stability of the interval quasipolynomials. It has been revealed that the robust stability of the quasipolynomi...The robust stability test of time-delay systems with interval parameters can be concluded into the robust stability of the interval quasipolynomials. It has been revealed that the robust stability of the quasipolynomials depends on that of their edge polynomials. This paper transforms the interval quasipolynomials into two-dimensional (2-D) interval polynomials (2-D s-z hybrid polynomials), proves that the robust stability of interval 2-D polynomials are sufficient for the stability of given quasipolynomials. Thus, the stability test of interval quasipolynomials can be completed in 2-D s-z domain instead of classical 1-D s domain. The 2-D s-z hybrid polynomials should have different forms under the time delay properties of given quasipolynomials. The stability test proposed by the paper constructs an edge test set from Kharitonov vertex polynomials to reduce the number of testing edge polynomials. The 2-D algebraic tests are provided for the stability test of vertex 2-D polynomials and edge 2-D polynomials family. To verify the results of the paper to be correct and valid, the simulations based on proposed results and comparison with other presented results are given.展开更多
It is revealed that the dynamic stability of 2-D recursive continuous-discrete systems with interval parameters involves the problem of robust Hurwitz-Schur stability of bivariate polynomials family. It is proved that...It is revealed that the dynamic stability of 2-D recursive continuous-discrete systems with interval parameters involves the problem of robust Hurwitz-Schur stability of bivariate polynomials family. It is proved that the Hurwitz-Schur stability of the denominator polynomials of the systems is necessary and sufficient for the asymptotic stability of the 2-D hybrid systems. The 2-D hybrid transformation, i. e. 2-D Laplace-Z transformation, has been proposed to solve the stability analysis of the 2-D continuous-discrete systems, to get the 2-D hybrid transfer functions of the systems. The edge test for the Hurwitz-Schur stability of interval bivariate polynomials is introduced. The Hurwitz-Schur stability of the interval family of 2-D polynomials can be guaranteed by the stability of its finite edge polynomials of the family. An algorithm about the stability test of edge polynomials is given.展开更多
The inter-relation between zero-field splitting (ZFS) parameters and local lattice structures of the (CrSe4)6 clusters in ZnSe semiconductors has been established by using the complete diagonalization (of the ene...The inter-relation between zero-field splitting (ZFS) parameters and local lattice structures of the (CrSe4)6 clusters in ZnSe semiconductors has been established by using the complete diagonalization (of the energy matrix) method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr2+ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters AR = 0.091A and Aθ = 4.28° of Cr2+ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of (CrSe4)6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.展开更多
2,4(5)-Dinitroimidazole(2,4(5)-DNI)is an important organic intermediate,and itself can also be used for energetic material.In this work,the solubility of 2,4(5)-DNI in(methanol+water,acetonitrile+water,acetone+water)b...2,4(5)-Dinitroimidazole(2,4(5)-DNI)is an important organic intermediate,and itself can also be used for energetic material.In this work,the solubility of 2,4(5)-DNI in(methanol+water,acetonitrile+water,acetone+water)binary solvents were measured by using a dynamic test method from 278.15 K to 323.15 K under 101.1 k Pa.The Jouyban–Acree model,van't Hoff–Jouyban–Acree model,Apelblat–Jouyb an–Acree model,Ma model,and Sun model were used to correlate the experimental data.The values of relative average deviation(RAD)and root-mean-square deviation(RMSD)were very small,indicating that the error between the experimental value and the correlated value was very small.The thermodynamic parameters such as dissolution enthalpy,dissolution entropy and Gibbs energy were calculated based on solubility data.High-purity of 2,4(5)-DNI was efficiently obtained by using cooling and dilution crystallization method.展开更多
The statistical probability and their variation regularity of the measurable characteristic parameters in the CO 2 arc welding droplet short circuiting transfer process have been studied. The statistical analysis sh...The statistical probability and their variation regularity of the measurable characteristic parameters in the CO 2 arc welding droplet short circuiting transfer process have been studied. The statistical analysis shows that the sensitivity of each characteristic parameter with regard to the variation of the short circuiting transfer process is different. The sensitivity of 4 kinds among these characteristic parameters is more intense than that of the short circuiting transfer frequency. In order to take account of the synthetic influence of these characteristic parameters, by means of the characteristic parameters synthetic value, a quantitative evaluation function is built up to describe and evaluate the short circuiting transfer process of CO 2 arc welding in real time. The testing shows that the evaluation function can give a suitable synthetic valuation for the short circuiting transfer process with a variety of welding variables.展开更多
This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that differ...This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.展开更多
The spectral parameters of Nd^3+ ions in Nd^3+-doped NaGd(MoO4)2 crystal have been investigated based on Judd-Ofelt theory and obtained as follows: The intensity parameters Ωeff are Ω2 = 24.77×10^20, Ω4 =...The spectral parameters of Nd^3+ ions in Nd^3+-doped NaGd(MoO4)2 crystal have been investigated based on Judd-Ofelt theory and obtained as follows: The intensity parameters Ωeff are Ω2 = 24.77×10^20, Ω4 = 7.31×10^-20 and Ω6 = 6.91×10^-20 cm^2. The radiative lifetime is 100 μs, and the quantum efficiency is 93.9%. The fluorescence branch ratios were calculated to be β1 = 0.441, β2 = 0.469,β3 = 0.086 and β4=0.004.展开更多
The Mg_(2)Si-matrix thermoelectric material was synthesized by low temperature solid-state reaction.This paper studies the effects of holding time and reaction temperature on the particle size and the properties of th...The Mg_(2)Si-matrix thermoelectric material was synthesized by low temperature solid-state reaction.This paper studies the effects of holding time and reaction temperature on the particle size and the properties of the material,and also studies effects of doping elemental Sb,Te and their doping seqence on the properties of the material.The result shows that excessively high temperature and elongated holding time of solid-state reaction are harmful,there is a range of particle size to ensure optimum properties and the doping sequence of Sb or Te without influencing the properties.展开更多
文摘Atmospheric models are physical equations based on the ideal gas law. Applied to the atmosphere, this law yields equations for water, vapor (gas), ice, air, humidity, dryness, fire, and heat, thus defining the model of key atmospheric parameters. The distribution of these parameters across the entire planet Earth is the origin of the formation of the climatic cycle, which is a normal climatic variation. To do this, the Earth is divided into eight (8) parts according to the number of key parameters to be defined in a physical representation of the model. Following this distribution, numerical models calculate the constants for the formation of water, vapor, ice, dryness, thermal energy (fire), heat, air, and humidity. These models vary in complexity depending on the indirect trigonometric direction and simplicity in the sum of neighboring models. Note that the constants obtained from the equations yield 275.156˚K (2.006˚C) for water, 273.1596˚K (0.00963˚C) for vapor, 273.1633˚K (0.0133˚C) for ice, 0.00365 in/s for atmospheric dryness, 1.996 in<sup>2</sup>/s for humidity, 2.993 in<sup>2</sup>/s for air, 1 J for thermal energy of fire, and 0.9963 J for heat. In summary, this study aims to define the main parameters and natural phenomena contributing to the modification of planetary climate. .
基金Project supported by the Science and Technology Major Project of Shanxi Province,China (Grant No.20181102013)the “1331 Project” Engineering Research Center of Shanxi Province,China (Grant No.PT201801)the Natural Science Foundation of Shanxi Province,China (Grant No.201801D221131)。
文摘The Ga_(2)O_(3) films are deposited on the Si and quartz substrates by magnetron sputtering, and annealing. The effects of preparation parameters(such as argon–oxygen flow ratio, sputtering power, sputtering time and annealing temperature)on the growth and properties(e.g., surface morphology, crystal structure, optical and electrical properties of the films) are studied by x-ray diffractometer(XRD), scanning electron microscope(SEM), and ultraviolet-visible spectrophotometer(UV-Vis). The results show that the thickness, crystallization quality and surface roughness of the β-Ga_(2)O_(3) film are influenced by those parameters. All β-Ga_(2)O_(3) films show good optical properties. Moreover, the value of bandgap increases with the enlarge of the percentage of oxygen increasing, and decreases with the increase of sputtering power and annealing temperature, indicating that the bandgap is related to the quality of the film and affected by the number of oxygen vacancy defects. The I–V curves show that the Ohmic behavior between metal and β-Ga_(2)O_(3) films is obtained at 900℃. Those results will be helpful for the further research of β-Ga_(2)O_(3) photoelectric semiconductor.
文摘An engineering system approach of 2-D cylindrical model of transient mass balance calculations of ozone and other concerned chemicals along with fourteen photolysis, ozone-generating and ozone-depleting chemical reaction equations was developed, validated, and used for studying the ozone concentrations, distribution and peak of the layer, ozone depletion and total ozone abundance in the stratosphere. The calculated ozone concentrations and profile at both the Equator and a 60˚N location were found to follow closely with the measured data. The calculated average ozone concentration was within 1% of the measured average, and the deviation of ozone profiles was within 14%. The monthly evolution of stratospheric ozone concentrations and distribution above the Equator was studied with results discussed in details. The influences of slow air movement in both altitudinal and radial directions on ozone concentrations and profile in the stratosphere were explored and discussed. Parametric studies of the influences of gas diffusivities of ozone D<sub>O3</sub> and active atomic oxygen D<sub>O</sub> on ozone concentrations and distributions were also studied and delineated. Having both influences through physical diffusion and chemical reactions, the diffusivity (and diffusion) of atomic oxygen D<sub>O</sub> was found to be more sensitive and important than that of ozone D<sub>O3</sub> on ozone concentrations and distribution. The 2-D ozone model present in this paper for stratospheric ozone and its layer and depletion is shown to be robust, convenient, efficient, and executable for analyzing the complex ozone phenomena in the stratosphere. .
基金support from the National Natural Science Foundation of China(No.51904324,No.51974348)the Prospective Basic Major Science and Technology Projects for the 14th Five Year Plan(No.2021DJ2202).
文摘CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that affects the final gas production effect.However,there have been few studies focusing on the flowback characteristics after CO_(2) dry fracturing.In this study,an extensive core-to-field scale study was conducted to investigate CO_(2) flowback characteristics and CH_(4) production behavior.Firstly,to investigate the impact of core properties and production conditions on CO_(2) flowback,a series of laboratory experiments at the core scale were conducted.Then,the key factors affecting the flowback were analyzed using the grey correlation method based on field data.Finally,taking the construction parameters of Well S60 as an example,a dual-permeability model was used to characterize the different seepage fields in the matrix and fracture for tight gas reservoirs.The production parameters after CO_(2) dry fracturing were then optimized.Experimental results demonstrate that CO_(2) dry fracturing is more effective than slickwater fracturing,with a 9.2%increase in CH_(4) recovery.The increase in core permeability plays a positive role in improving CH_(4) production and CO_(2) flowback.The soaking process is mainly affected by CO_(2) diffusion,and the soaking time should be controlled within 12 h.Increasing the flowback pressure gradient results in a significant increase in both CH_(4) recovery and CO_(2) flowback efficiency.While,an increase in CO_(2) injection is not conducive to CH_(4) production and CO_(2) flowback.Based on the experimental and field data,the important factors affecting flowback and production were comprehensively and effectively discussed.The results show that permeability is the most important factor,followed by porosity and effective thickness.Considering flowback efficiency and the influence of proppant reflux,the injection volume should be the minimum volume that meets the requirements for generating fractures.The soaking time should be short which is 1 day in this study,and the optimal bottom hole flowback pressure should be set at 10 MPa.This study aims to improve the understanding of CO_(2) dry fracturing in tight gas reservoirs and provide valuable insights for optimizing the process parameters.
基金supported by United Arab Emirates University(UAEU),United Arab Emirates under research fund no 12N097。
文摘Photocatalytic solar to energy conversion is considered an attractive approach for overcoming energy crises and environmental concerns.Recently,titanium carbide(Ti_(3)C_(2))MXenes have been recognized as promising cocatalysts based on their metallic conductivity,excessive active reaction sites,and enlarged surface area.The current review focuses on the properties and applications of Ti_(3)C_(2)MXenes useful in the field of photocatalysis.More specifically,surface modification of Ti_(3)C_(2)MXenes by varying synthesis parameters to get pure materials and also composites with the role of functional groups towards solar energy conversion applications is highlighted in this review.The effect of etching and oxidizing pathways to get an efficient cocatalyst has been discussed in detail.Considering the significant effect of parameters,optimum synthesis conditions such as etchant type,concentration,time and type of intercalant in both the Ti_(3)C_(2)synthesis approaches for improved photoactivity are discussed.Additionally,the surface modification of Ti_(3)C_(2)through oxidation for TiO2growth on its surface is deliberated with a detailed discussion on etchant type,concentration,etching time,and environmental factors.The optimum oxidation condition,including temperature,time,and environment for thermal treatment of Ti_(3)C_(2),were also included.Lastly,the review summarizes the conclusion and future perspectives for solar energy conversion applications.
基金supported by the National Natural Science Foundation of China(No.90814002)the Natural Science Foundation of Shandong Province(No.Y2005E02)
文摘The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method and found focal mechanism solutions using gird test method. The inversion results are as follows: the strike is 21.6°, the dip angle is 89.5°, the slip angle is 170°, the fault length is about 160 km, the lower-boundary depth is about 32 km and the buried depth of upper boundary is about 4 km. This shows that the seismic fault is a NNE-trending upright right-lateral strike-slip fault and has cut through the crust. Moreover, the surface seismic fault, intensity distribution of the earthquake, earthquake-depth distribution and seismic-wave velocity profile in the focal area all verified our study result.
基金This project was supported by the National Science Foundation of China (60572093).
文摘The robust stability test of time-delay systems with interval parameters can be concluded into the robust stability of the interval quasipolynomials. It has been revealed that the robust stability of the quasipolynomials depends on that of their edge polynomials. This paper transforms the interval quasipolynomials into two-dimensional (2-D) interval polynomials (2-D s-z hybrid polynomials), proves that the robust stability of interval 2-D polynomials are sufficient for the stability of given quasipolynomials. Thus, the stability test of interval quasipolynomials can be completed in 2-D s-z domain instead of classical 1-D s domain. The 2-D s-z hybrid polynomials should have different forms under the time delay properties of given quasipolynomials. The stability test proposed by the paper constructs an edge test set from Kharitonov vertex polynomials to reduce the number of testing edge polynomials. The 2-D algebraic tests are provided for the stability test of vertex 2-D polynomials and edge 2-D polynomials family. To verify the results of the paper to be correct and valid, the simulations based on proposed results and comparison with other presented results are given.
基金This project was supported by National Natural Science Foundation of China (69971002).
文摘It is revealed that the dynamic stability of 2-D recursive continuous-discrete systems with interval parameters involves the problem of robust Hurwitz-Schur stability of bivariate polynomials family. It is proved that the Hurwitz-Schur stability of the denominator polynomials of the systems is necessary and sufficient for the asymptotic stability of the 2-D hybrid systems. The 2-D hybrid transformation, i. e. 2-D Laplace-Z transformation, has been proposed to solve the stability analysis of the 2-D continuous-discrete systems, to get the 2-D hybrid transfer functions of the systems. The edge test for the Hurwitz-Schur stability of interval bivariate polynomials is introduced. The Hurwitz-Schur stability of the interval family of 2-D polynomials can be guaranteed by the stability of its finite edge polynomials of the family. An algorithm about the stability test of edge polynomials is given.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274235 and 11104190)the Doctoral Education Fund of Education Ministry of China(Grant No.20110181120112)
文摘The inter-relation between zero-field splitting (ZFS) parameters and local lattice structures of the (CrSe4)6 clusters in ZnSe semiconductors has been established by using the complete diagonalization (of the energy matrix) method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr2+ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters AR = 0.091A and Aθ = 4.28° of Cr2+ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of (CrSe4)6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.
文摘2,4(5)-Dinitroimidazole(2,4(5)-DNI)is an important organic intermediate,and itself can also be used for energetic material.In this work,the solubility of 2,4(5)-DNI in(methanol+water,acetonitrile+water,acetone+water)binary solvents were measured by using a dynamic test method from 278.15 K to 323.15 K under 101.1 k Pa.The Jouyban–Acree model,van't Hoff–Jouyban–Acree model,Apelblat–Jouyb an–Acree model,Ma model,and Sun model were used to correlate the experimental data.The values of relative average deviation(RAD)and root-mean-square deviation(RMSD)were very small,indicating that the error between the experimental value and the correlated value was very small.The thermodynamic parameters such as dissolution enthalpy,dissolution entropy and Gibbs energy were calculated based on solubility data.High-purity of 2,4(5)-DNI was efficiently obtained by using cooling and dilution crystallization method.
文摘The statistical probability and their variation regularity of the measurable characteristic parameters in the CO 2 arc welding droplet short circuiting transfer process have been studied. The statistical analysis shows that the sensitivity of each characteristic parameter with regard to the variation of the short circuiting transfer process is different. The sensitivity of 4 kinds among these characteristic parameters is more intense than that of the short circuiting transfer frequency. In order to take account of the synthetic influence of these characteristic parameters, by means of the characteristic parameters synthetic value, a quantitative evaluation function is built up to describe and evaluate the short circuiting transfer process of CO 2 arc welding in real time. The testing shows that the evaluation function can give a suitable synthetic valuation for the short circuiting transfer process with a variety of welding variables.
文摘This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.
基金This work was supported by the National Natural Science Foundation of China (60378031) and Key Project of Science and Technology of Fujian Province (2001H1007)
文摘The spectral parameters of Nd^3+ ions in Nd^3+-doped NaGd(MoO4)2 crystal have been investigated based on Judd-Ofelt theory and obtained as follows: The intensity parameters Ωeff are Ω2 = 24.77×10^20, Ω4 = 7.31×10^-20 and Ω6 = 6.91×10^-20 cm^2. The radiative lifetime is 100 μs, and the quantum efficiency is 93.9%. The fluorescence branch ratios were calculated to be β1 = 0.441, β2 = 0.469,β3 = 0.086 and β4=0.004.
文摘The Mg_(2)Si-matrix thermoelectric material was synthesized by low temperature solid-state reaction.This paper studies the effects of holding time and reaction temperature on the particle size and the properties of the material,and also studies effects of doping elemental Sb,Te and their doping seqence on the properties of the material.The result shows that excessively high temperature and elongated holding time of solid-state reaction are harmful,there is a range of particle size to ensure optimum properties and the doping sequence of Sb or Te without influencing the properties.