In this paper,we investigate the periodic traveling wave solutions problem for a single population model with advection and distributed delay.By the bifurcation analysis method,we can obtain periodic traveling wave so...In this paper,we investigate the periodic traveling wave solutions problem for a single population model with advection and distributed delay.By the bifurcation analysis method,we can obtain periodic traveling wave solutions for this model under the influence of advection term and distributed delay.The obtained results indicate that weak kernel and strong kernel can both deduce the existence of periodic traveling wave solutions.Finally,we apply the main results in this paper to Logistic model and Nicholson’s blowflies model.展开更多
Lithium ion batteries are complicated distributed parameter systems that can be described preferably by partial differential equations and a field theory. To reduce the solution difficulty and the calculation amount, ...Lithium ion batteries are complicated distributed parameter systems that can be described preferably by partial differential equations and a field theory. To reduce the solution difficulty and the calculation amount, if a distributed parameter system is described by ordinary differential equations （ODE） during the analysis and the design of distributed parameter system, the reliability of the system description will be reduced, and the systemic errors will be introduced. Studies on working condition real-time monitoring can improve the security because the rechargeable LIBs are widely used in many electronic systems and electromechanical equipment. Single particle model （SPM） is the simplification of LIB under some approximations, and can estimate the working parameters of a LIB at the faster simulation speed. A LIB modelling algorithm based on PDEs and SPM is proposed to monitor the working condition of LIBs in real time. Although the lithium ion concentration is an unmeasurable distributed parameter in the anode of LIB, the working condition monitoring model can track the real time lithium ion concentration in the anode of LIB, and calculate the residual which is the difference between the ideal data and the measured data. A fault alarm can be triggered when the residual is beyond the preset threshold. A simulation example verifies that the effectiveness and the accuracy of the working condition real-time monitoring model of LIB based on PDEs and SPM.展开更多
Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mecha...Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of ferroelectric ceramic and used to study the nonlinear constitutive behavior of ferroelectric body in this paper. The principle of stationary total energy is put forward in which the basic unknown quantities are the displacement ui, electric displacement Di and volume fraction pI of the domain switching for the variant I. Mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion. On the basis of the domain switching criterion, a set of linear algebraic equations for the volume fraction PI of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. Then a single domain mechanical model is proposed in this paper. The poled ferroelectric specimen is considered as a transversely isotropic single domain. By using the partial experimental results, the hardening relation between the driving force of domain switching and the volume fraction of domain switching can be calibrated. Then the electromechanical response can be calculated on the basis of the calibrated hardening relation. The results involve the electric butterfly shaped curves of axial strain versus axial electric field, the hysteresis loops of electric displacement versus electric filed and the evo- lution process of the domain switching in the ferroelectric specimens under uniaxial coupled stress and electric field loading. The present theoretic prediction agrees reasonably with the experimental results given by Lynch.展开更多
The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM;...The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM; post-CMIP5, hereafter P5）. In this study, single column model （SCM_P5） simulated cloud fractions （CFs）, cloud liquid water paths （LWPs） and precipitation were compared with Atmospheric Radiation Measurement （ARM） Southern Great Plains （SGP） groundbased observations made during the period 2002-08. CMIP5 SCM simulations and GCM outputs over the ARM SGP region were also used in the comparison to identify whether the causes of cloud and precipitation biases resulted from either the physical parameterization or the dynamic scheme. The comparison showed that the CMIP5 SCM has difficulties in simulating the vertical structure and seasonal variation of low-level clouds. The new scheme implemented in the turbulence parameterization led to significantly improved cloud simulations in P5. It was found that the SCM is sensitive to the relaxation time scale. When the relaxation time increased from 3 to 24 h, SCM_P5-simulated CFs and LWPs showed a moderate increase （10%-20%） but precipitation increased significantly （56%）, which agreed better with observations despite the less accurate atmospheric state. Annual averages among the GCM and SCM simulations were almost the same, but their respective seasonal variations were out of phase. This suggests that the same physical cloud parameterization can generate similar statistical results over a long time period, but different dynamics drive the differences in seasonal variations. This study can potentially provide guidance for the further development of the GISS model.展开更多
Decreasing in emissions of greenhouse gases to confront the global warming needs to replace fossil fuels as the main doer of the world climate changes by renewable and clean fuels produced from biomass like wood waste...Decreasing in emissions of greenhouse gases to confront the global warming needs to replace fossil fuels as the main doer of the world climate changes by renewable and clean fuels produced from biomass like wood waste which is neutral on the amount of CO2. An analytical and engineering model for pyrolysis process of a single biomass particle has been presented. Using a two-stage semi global kinetic model which includes both primary and secondary reactions, the effects of parameters like shape and size of particle as well as porosity on the particle temperature profile and product yields have been investigated. Comparison of the obtained results with experimental data shows that our results are in a reasonable agreement with previous researchers' works. Finally, a sensitivity analysis is done to determine the importance of each parameter on pyrolysis of a single biomass particle which is affected by many constant parameters.展开更多
This research appraises comparative analysis between single diode and double diode model of photovoltaic (PV) solar cells to enhance the conversion efficiency of power engendering PV solar systems. Single diode model ...This research appraises comparative analysis between single diode and double diode model of photovoltaic (PV) solar cells to enhance the conversion efficiency of power engendering PV solar systems. Single diode model is simple and easy to implement, whereas double diode model has better accuracy which acquiesces for more precise forecast of PV systems performance. Exploration is done on the basis of simulation results and MATLAB tool is used to serve this purpose. Simulations are performed by varying distinct model parameters such as solar irradiance, temperature, value of parasitic resistances, ideality factor of diode and number of series and parallel connected solar cells used to assemble PV array. Conspicuous demonstration is executed to analyze effects of these specifications on the efficiency curve and power vs. voltage output characteristics of PV cell for specified models.展开更多
A geometric analysis technique for crystal growth and microstructure development in single-crystal welds had been previously developed.And the effect of welding conditions on the tendency of stray grains formation dur...A geometric analysis technique for crystal growth and microstructure development in single-crystal welds had been previously developed.And the effect of welding conditions on the tendency of stray grains formation during solidification was researched.In the present work,these analytical methods were further extended.Combined with an original vectorization method,a 3D Rosenthal solution was used to determine thermal conditions of the welds.Afterward,the dendrite growth orientation,the dendrite growth velocity and the thermal gradient along dendrite direction were calculated and lively plotted.Finally,the tendency of stray grains formation in the solidification front was forecasted and its distribution was presented with a 3D plot.The results indicate that substrate orientation has some impacts on the crystal growth pattern,dendrite growth velocity,distribution of thermal gradient and stray grain.Based on the research methods proposed in this work,any substrate crystallographic orientation can be studied,and predicted stray grains distribution can be visualized.展开更多
A single column model (SCM) is constructed by extracting the physical subroutines from the NCAR Community Climate Model version 1 (CCM1).Simulated data are generated by CCM1 and used to validate the SCM and to study t...A single column model (SCM) is constructed by extracting the physical subroutines from the NCAR Community Climate Model version 1 (CCM1).Simulated data are generated by CCM1 and used to validate the SCM and to study the sensitivity of the SCM to errors in its input data.It is found that the SCM temperature predictions are moderately sensitive to errors in the input horizontal temperature flux convergence and moisture flux convergence.Two types of error are concerned in this study,random errors due to insufficient data resolution,and errors due to insufficient data area coverage.While the first type of error can be reduced by filtering and/or increasing the data resolution,it is shown that the second type of error can be reduced by enlarging the data area coverage and using a suitable method to compute the input flux convergence terms.展开更多
<span style="font-family:Verdana;">A successful single parameter model has be</span><span style="font-family:Verdana;">en </span><span style="font-family:Verdana;&qu...<span style="font-family:Verdana;">A successful single parameter model has be</span><span style="font-family:Verdana;">en </span><span style="font-family:Verdana;">formulated to match the observations of photons from type 1a supernovae which were previously used to corroborate the standard </span><span style="font-family:Verdana;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">𝛬</span></span></span><span style="font-family:;" "=""><span style="font-family:Verdana;"> cold dark matter model. The new single parameter model extrapolates all the way back to the cosmic background radiation (CMB) without requiring a separate model to describe inflation of the space dimensions after the Big Bang. This single parameter model assumes that spacetime forms a finite symmetrical manifold with positive curvature. For the spacetime manifold to be finite, the time dimension must also have positive curvature. This model was formulated to consider whether the curvature of the time dimension may be related to the curvature of the space dimensions. This possibility is not considered in the more complex models previously used to fit the available redshift data. The geometry for the finite spacetime manifold was selected to be compatible with the Friedmann equation with positive curvature. The manifold shape was motivated by an assumption that there exists a matter hemisphere (when considering time together with a single space dimension) and an antimatter hemisphere to give a symmetrical and spherical overall spacetime manifold. Hence, the space dimension expands from a pole to the equator, at a maximum value for the time dimension. This is analogous to the expansion of a circle of latitude on a globe from a pole to the equator. The three space dimensions are identical so that any arbitrary single space direction may be selected. The initial intention was to modify the assumed geometry for the spacetime manifold to account for the presence of matter. It was surprisingly found that, within the error of the reported measurements, no further modification was necessary to fit the data. The Friedmann equation reduces to the Schwarzschild equation at the equator so this can be used to predict the total amount of mass in the Universe. The resulting prediction is of the order of 10</span><sup><span style="font-family:Verdana;">51</span></sup><span style="font-family:Verdana;"> kg. The corresponding density of matter at the current time is approxima</span></span><span style="font-family:;" "=""><span style="font-family:Verdana;">tely 1.6 × 10</span><sup><span style="font-family:Verdana;">-28</span></sup><span style="font-family:Verdana;"> kg<span style="color:#636363;"><span style="font-size:13.3333px;"><span style="white-space:nowrap;">·</span></span></span>m</span><sup><span style="font-family:Verdana;">-3</span></sup><span style="font-family:Verdana;">.</span></span>展开更多
Current research focuses on the performance degradation of photovoltaic(PV)modules,examining both crystalline silicon(p-Si and m-Si)and thin-film technologies,including a-Si/μc-Si,HIT,CdTe and CIGS.These modules were...Current research focuses on the performance degradation of photovoltaic(PV)modules,examining both crystalline silicon(p-Si and m-Si)and thin-film technologies,including a-Si/μc-Si,HIT,CdTe and CIGS.These modules were operated outdoors in two distinct climatic zones in the United States(US)over a period of three years.The degradation analysis includes the study of various quantities,such as the decrease in peak power,the reduction in current and voltage,and the variation in the fill factor.The annual degradation rate(DR)of PV modules is obtained by a linear fit of the effective maximum power evolution over time.The results indicate that m-Si and p-Si modules experienced a slight decrease in performance,with DRs of−0.83%and−1.07%,respectively.Subsequently,the HIT module exhibited a DR of−1.75%,while CdTe and CIGS modules demonstrated DRs of−2.03%and−2.45%,respectively.The a-Si/μc-Si module showed the highest DR at−3.26%.Using the Single Diode Model(SDM),we monitored the temporal evolution of physical parameters as well as changes in the shape of the I-V and P-V curves over time.We found that the key points of the I-V curve degrade over time,as do the I-V and P-V characteristics between two days approximately 30 months apart.展开更多
A comprehensive single particle model which includes the mesoscale and microscale models was developed to study the influence of particle diameter on mass and heat transfer occurring within a ferrite catalyst during t...A comprehensive single particle model which includes the mesoscale and microscale models was developed to study the influence of particle diameter on mass and heat transfer occurring within a ferrite catalyst during the oxidative dehydrogenation of butene to butadiene process. The verified model can be used to investigate the influence of catalyst diameter on the flow distribution inside the particle. The simulation results demonstrate that the mass fraction gradients of all species, temperature gradient and pressure gradient increase with the increase of the particle diameter. It means that there is a high intraparticle transfer resistance and strong diffusion when applying the large catalysts. The external particle mass transfer resistance is nearly constant under different particle diameters so that the effect of particle diameter at external diffusion can be ignored. A large particle diameter can lead to a high surface temperature, which indicates the external heat transfer resistance. Moreover, the selectivity of reaction may be changed with a variety of particle diameters so that choosing appropriate particle size can enhance the production of butadiene and optimize the reaction process.展开更多
Two alternative formulations of single crystal plasticity model were introduced respectively and two schemes were implemented in the explicit FE code with software ABAQUS/Explicit by writing the user subroutine VUMAT....Two alternative formulations of single crystal plasticity model were introduced respectively and two schemes were implemented in the explicit FE code with software ABAQUS/Explicit by writing the user subroutine VUMAT.Meshes containing material data were created with solid elements.Each element represented an individual grain,and the grain orientations were explicitly stored and updated at each increment.Tangential modulus method was employed to calculate the plastic shear strain increment of deformation systems in combination with a hardening law to describe the hardening responses.Both two developed subroutines were applied to simulate the texture evolution during the uniaxial tension of copper（FCC）,cold rolling of IF steel（BCC） and uniaxial compression of AZ31 magnesium alloy（HCP）.The predicted texture distributions are in qualitative agreement with the experimental results.展开更多
A Single Column Model(SCM) for Global and Regional Atmospheric Prediction Enhanced System (GRAPES) is constructed for the purpose of evaluating physical process parameterizations.Two observational datasets including W...A Single Column Model(SCM) for Global and Regional Atmospheric Prediction Enhanced System (GRAPES) is constructed for the purpose of evaluating physical process parameterizations.Two observational datasets including Wangara and the third Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study(GABLS-3) SCM field observations have been applied to evaluate this SCM.By these two numerical experiments,the GRAPESSCM is verified to be correctly constructed.Furthermore, the interaction between the land surface process and atmospheric boundary layer(ABL) is discussed through the second experiment.It is found that CASE3(CoLM land surface scheme coupled with ABL scheme) simulates less sensible heat fluxes and smaller surface temperature which corresponds with its lower potential temperature at the bottom of the ABL.Moreover,CASE3 simulates turbulence that is weaker during the daytime and stronger during nighttime,corresponding with its wind speed at 200 m which is bigger during daytime and smaller during nighttime.However,they are generally opposite in CASE2(SLAB coupled with ABL).The initial profile of the water vapor mixing ratio is artificially increased by the experiment setup which results in the simulated water vapor mixing becoming wetter than actually observed.CASE1 (observed surface temperature taken as lower thermal forcing) and CASE2 have no soil moisture prediction and simulate a similar water vapor mixing ratio,while CASE3 has a soil moisture prediction and simulates wetter.It is also shown that the time step may affect the stabilization of the ABL when the vertical levels of the SCM are fixed.展开更多
This paper considers the problem of change point in single index models.In order to obtain asymptotically valid confidence intervals for the estimation of the change point,the convergence rate and asymptotic distribut...This paper considers the problem of change point in single index models.In order to obtain asymptotically valid confidence intervals for the estimation of the change point,the convergence rate and asymptotic distribution of the change point estimate is studied.Some simulation results are presented which show that the numerical performance of our estimator is satisfactory.展开更多
Tests for nonparametric parts on partially linear single index models are considered in this paper.Based on the estimates obtained by the local linear method,the generalized likelihood ratio tests for the models are e...Tests for nonparametric parts on partially linear single index models are considered in this paper.Based on the estimates obtained by the local linear method,the generalized likelihood ratio tests for the models are established.Under the null hypotheses the normalized tests follow asymptotically theχ2-distribution with the scale constants and the degrees of freedom being independent of the nuisance parameters,which is called the Wilks phenomenon.A simulated example is used to evaluate the performances of the testing procedures empirically.展开更多
A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in lo...A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.展开更多
Single index models are widely used in medicine, econometrics and some other fields. In this paper, we consider the inference of a change point problem in single index models. Based on density-weighted average derivat...Single index models are widely used in medicine, econometrics and some other fields. In this paper, we consider the inference of a change point problem in single index models. Based on density-weighted average derivative estimation (ADE) method, we propose a statistic to test whether a change point exists or not. The null distribution of the test statistic is obtained using a permutation technique. The permuted statistic is rigorously shown to have the same distribution in the limiting sense under both null and alternative hypotheses. After the null hypothesis of no change point is rejected, an ADE-based estimate of the change point is proposed under assumption that the change point is unique. A simulation study confirms the theoretical results.展开更多
To ensure the safety and stability of power grids with photovoltaic(PV)gen eration integrati on,it is necessary to predict the output perform a nee of PV modules un der varyi ng operating con ditions.In this paper,an ...To ensure the safety and stability of power grids with photovoltaic(PV)gen eration integrati on,it is necessary to predict the output perform a nee of PV modules un der varyi ng operating con ditions.In this paper,an improved artificial neural network(ANN)method is proposed to predict the electrical characteristics of a PV module by combining several neural networks under different environmental conditions.To study the dependenee of the output performance on the solar irradianee and temperature,the proposed neural network model is composed of four neural networks,it called multineural network(MANN).Each neural network consists of three layers,in which the input is solar radiation,and the module temperature and output are five physical parameters of the single diode model.The experimental data were divided into four groups and used for training the neural networks.The electrical properties of PV modules,including l-V curves,PV curves,and normalized root mean square error,were obtained and discussed.The effectiveness and accuracy of this method is verified by the experimental data for d iff ere nt types of PV modules.Compared with the traditional single-ANN(SANN)method,the proposed method shows be社er accuracy under different operating conditions.展开更多
The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the supe...The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.展开更多
基金Supported by the National Natural Science Foundation of China(12261050)Science and Technology Project of Department of Education of Jiangxi Province(GJJ2201612 and GJJ211027)Natural Science Foundation of Jiangxi Province of China(20212BAB202021)。
文摘In this paper,we investigate the periodic traveling wave solutions problem for a single population model with advection and distributed delay.By the bifurcation analysis method,we can obtain periodic traveling wave solutions for this model under the influence of advection term and distributed delay.The obtained results indicate that weak kernel and strong kernel can both deduce the existence of periodic traveling wave solutions.Finally,we apply the main results in this paper to Logistic model and Nicholson’s blowflies model.
文摘Lithium ion batteries are complicated distributed parameter systems that can be described preferably by partial differential equations and a field theory. To reduce the solution difficulty and the calculation amount, if a distributed parameter system is described by ordinary differential equations （ODE） during the analysis and the design of distributed parameter system, the reliability of the system description will be reduced, and the systemic errors will be introduced. Studies on working condition real-time monitoring can improve the security because the rechargeable LIBs are widely used in many electronic systems and electromechanical equipment. Single particle model （SPM） is the simplification of LIB under some approximations, and can estimate the working parameters of a LIB at the faster simulation speed. A LIB modelling algorithm based on PDEs and SPM is proposed to monitor the working condition of LIBs in real time. Although the lithium ion concentration is an unmeasurable distributed parameter in the anode of LIB, the working condition monitoring model can track the real time lithium ion concentration in the anode of LIB, and calculate the residual which is the difference between the ideal data and the measured data. A fault alarm can be triggered when the residual is beyond the preset threshold. A simulation example verifies that the effectiveness and the accuracy of the working condition real-time monitoring model of LIB based on PDEs and SPM.
基金The project supported by the National Natural Science Foundation of China(10572138)
文摘Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of ferroelectric ceramic and used to study the nonlinear constitutive behavior of ferroelectric body in this paper. The principle of stationary total energy is put forward in which the basic unknown quantities are the displacement ui, electric displacement Di and volume fraction pI of the domain switching for the variant I. Mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion. On the basis of the domain switching criterion, a set of linear algebraic equations for the volume fraction PI of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. Then a single domain mechanical model is proposed in this paper. The poled ferroelectric specimen is considered as a transversely isotropic single domain. By using the partial experimental results, the hardening relation between the driving force of domain switching and the volume fraction of domain switching can be calibrated. Then the electromechanical response can be calculated on the basis of the calibrated hardening relation. The results involve the electric butterfly shaped curves of axial strain versus axial electric field, the hysteresis loops of electric displacement versus electric filed and the evo- lution process of the domain switching in the ferroelectric specimens under uniaxial coupled stress and electric field loading. The present theoretic prediction agrees reasonably with the experimental results given by Lynch.
基金supported by the DOE ASR program(Grant No.DESC008468)
文摘The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM; post-CMIP5, hereafter P5）. In this study, single column model （SCM_P5） simulated cloud fractions （CFs）, cloud liquid water paths （LWPs） and precipitation were compared with Atmospheric Radiation Measurement （ARM） Southern Great Plains （SGP） groundbased observations made during the period 2002-08. CMIP5 SCM simulations and GCM outputs over the ARM SGP region were also used in the comparison to identify whether the causes of cloud and precipitation biases resulted from either the physical parameterization or the dynamic scheme. The comparison showed that the CMIP5 SCM has difficulties in simulating the vertical structure and seasonal variation of low-level clouds. The new scheme implemented in the turbulence parameterization led to significantly improved cloud simulations in P5. It was found that the SCM is sensitive to the relaxation time scale. When the relaxation time increased from 3 to 24 h, SCM_P5-simulated CFs and LWPs showed a moderate increase （10%-20%） but precipitation increased significantly （56%）, which agreed better with observations despite the less accurate atmospheric state. Annual averages among the GCM and SCM simulations were almost the same, but their respective seasonal variations were out of phase. This suggests that the same physical cloud parameterization can generate similar statistical results over a long time period, but different dynamics drive the differences in seasonal variations. This study can potentially provide guidance for the further development of the GISS model.
文摘Decreasing in emissions of greenhouse gases to confront the global warming needs to replace fossil fuels as the main doer of the world climate changes by renewable and clean fuels produced from biomass like wood waste which is neutral on the amount of CO2. An analytical and engineering model for pyrolysis process of a single biomass particle has been presented. Using a two-stage semi global kinetic model which includes both primary and secondary reactions, the effects of parameters like shape and size of particle as well as porosity on the particle temperature profile and product yields have been investigated. Comparison of the obtained results with experimental data shows that our results are in a reasonable agreement with previous researchers' works. Finally, a sensitivity analysis is done to determine the importance of each parameter on pyrolysis of a single biomass particle which is affected by many constant parameters.
文摘This research appraises comparative analysis between single diode and double diode model of photovoltaic (PV) solar cells to enhance the conversion efficiency of power engendering PV solar systems. Single diode model is simple and easy to implement, whereas double diode model has better accuracy which acquiesces for more precise forecast of PV systems performance. Exploration is done on the basis of simulation results and MATLAB tool is used to serve this purpose. Simulations are performed by varying distinct model parameters such as solar irradiance, temperature, value of parasitic resistances, ideality factor of diode and number of series and parallel connected solar cells used to assemble PV array. Conspicuous demonstration is executed to analyze effects of these specifications on the efficiency curve and power vs. voltage output characteristics of PV cell for specified models.
基金financially supported by the National Natural Science Foundation of China(Nos.51401210 and51271186)the National High Technology Research and Development Program of China(No.2014AA041701)
文摘A geometric analysis technique for crystal growth and microstructure development in single-crystal welds had been previously developed.And the effect of welding conditions on the tendency of stray grains formation during solidification was researched.In the present work,these analytical methods were further extended.Combined with an original vectorization method,a 3D Rosenthal solution was used to determine thermal conditions of the welds.Afterward,the dendrite growth orientation,the dendrite growth velocity and the thermal gradient along dendrite direction were calculated and lively plotted.Finally,the tendency of stray grains formation in the solidification front was forecasted and its distribution was presented with a 3D plot.The results indicate that substrate orientation has some impacts on the crystal growth pattern,dendrite growth velocity,distribution of thermal gradient and stray grain.Based on the research methods proposed in this work,any substrate crystallographic orientation can be studied,and predicted stray grains distribution can be visualized.
文摘A single column model (SCM) is constructed by extracting the physical subroutines from the NCAR Community Climate Model version 1 (CCM1).Simulated data are generated by CCM1 and used to validate the SCM and to study the sensitivity of the SCM to errors in its input data.It is found that the SCM temperature predictions are moderately sensitive to errors in the input horizontal temperature flux convergence and moisture flux convergence.Two types of error are concerned in this study,random errors due to insufficient data resolution,and errors due to insufficient data area coverage.While the first type of error can be reduced by filtering and/or increasing the data resolution,it is shown that the second type of error can be reduced by enlarging the data area coverage and using a suitable method to compute the input flux convergence terms.
文摘<span style="font-family:Verdana;">A successful single parameter model has be</span><span style="font-family:Verdana;">en </span><span style="font-family:Verdana;">formulated to match the observations of photons from type 1a supernovae which were previously used to corroborate the standard </span><span style="font-family:Verdana;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">𝛬</span></span></span><span style="font-family:;" "=""><span style="font-family:Verdana;"> cold dark matter model. The new single parameter model extrapolates all the way back to the cosmic background radiation (CMB) without requiring a separate model to describe inflation of the space dimensions after the Big Bang. This single parameter model assumes that spacetime forms a finite symmetrical manifold with positive curvature. For the spacetime manifold to be finite, the time dimension must also have positive curvature. This model was formulated to consider whether the curvature of the time dimension may be related to the curvature of the space dimensions. This possibility is not considered in the more complex models previously used to fit the available redshift data. The geometry for the finite spacetime manifold was selected to be compatible with the Friedmann equation with positive curvature. The manifold shape was motivated by an assumption that there exists a matter hemisphere (when considering time together with a single space dimension) and an antimatter hemisphere to give a symmetrical and spherical overall spacetime manifold. Hence, the space dimension expands from a pole to the equator, at a maximum value for the time dimension. This is analogous to the expansion of a circle of latitude on a globe from a pole to the equator. The three space dimensions are identical so that any arbitrary single space direction may be selected. The initial intention was to modify the assumed geometry for the spacetime manifold to account for the presence of matter. It was surprisingly found that, within the error of the reported measurements, no further modification was necessary to fit the data. The Friedmann equation reduces to the Schwarzschild equation at the equator so this can be used to predict the total amount of mass in the Universe. The resulting prediction is of the order of 10</span><sup><span style="font-family:Verdana;">51</span></sup><span style="font-family:Verdana;"> kg. The corresponding density of matter at the current time is approxima</span></span><span style="font-family:;" "=""><span style="font-family:Verdana;">tely 1.6 × 10</span><sup><span style="font-family:Verdana;">-28</span></sup><span style="font-family:Verdana;"> kg<span style="color:#636363;"><span style="font-size:13.3333px;"><span style="white-space:nowrap;">·</span></span></span>m</span><sup><span style="font-family:Verdana;">-3</span></sup><span style="font-family:Verdana;">.</span></span>
文摘Current research focuses on the performance degradation of photovoltaic(PV)modules,examining both crystalline silicon(p-Si and m-Si)and thin-film technologies,including a-Si/μc-Si,HIT,CdTe and CIGS.These modules were operated outdoors in two distinct climatic zones in the United States(US)over a period of three years.The degradation analysis includes the study of various quantities,such as the decrease in peak power,the reduction in current and voltage,and the variation in the fill factor.The annual degradation rate(DR)of PV modules is obtained by a linear fit of the effective maximum power evolution over time.The results indicate that m-Si and p-Si modules experienced a slight decrease in performance,with DRs of−0.83%and−1.07%,respectively.Subsequently,the HIT module exhibited a DR of−1.75%,while CdTe and CIGS modules demonstrated DRs of−2.03%and−2.45%,respectively.The a-Si/μc-Si module showed the highest DR at−3.26%.Using the Single Diode Model(SDM),we monitored the temporal evolution of physical parameters as well as changes in the shape of the I-V and P-V curves over time.We found that the key points of the I-V curve degrade over time,as do the I-V and P-V characteristics between two days approximately 30 months apart.
基金The National Science Foundation of China(No.2157604921576050)the Fundamental Research Funds for the Central Universities(No.2242014K10025)
文摘A comprehensive single particle model which includes the mesoscale and microscale models was developed to study the influence of particle diameter on mass and heat transfer occurring within a ferrite catalyst during the oxidative dehydrogenation of butene to butadiene process. The verified model can be used to investigate the influence of catalyst diameter on the flow distribution inside the particle. The simulation results demonstrate that the mass fraction gradients of all species, temperature gradient and pressure gradient increase with the increase of the particle diameter. It means that there is a high intraparticle transfer resistance and strong diffusion when applying the large catalysts. The external particle mass transfer resistance is nearly constant under different particle diameters so that the effect of particle diameter at external diffusion can be ignored. A large particle diameter can lead to a high surface temperature, which indicates the external heat transfer resistance. Moreover, the selectivity of reaction may be changed with a variety of particle diameters so that choosing appropriate particle size can enhance the production of butadiene and optimize the reaction process.
基金Projects (50821003,50405014) supported by the National Natural Science Foundation of ChinaProjects (10QH1401400,10520705000,10JC1407300) supported by Shanghai Committee of Science and Technology,China+1 种基金Project (NCET-07-0545) supported by Program for New Century Excellent Talents in University,ChinaProject supported by Ford University Research Program
文摘Two alternative formulations of single crystal plasticity model were introduced respectively and two schemes were implemented in the explicit FE code with software ABAQUS/Explicit by writing the user subroutine VUMAT.Meshes containing material data were created with solid elements.Each element represented an individual grain,and the grain orientations were explicitly stored and updated at each increment.Tangential modulus method was employed to calculate the plastic shear strain increment of deformation systems in combination with a hardening law to describe the hardening responses.Both two developed subroutines were applied to simulate the texture evolution during the uniaxial tension of copper（FCC）,cold rolling of IF steel（BCC） and uniaxial compression of AZ31 magnesium alloy（HCP）.The predicted texture distributions are in qualitative agreement with the experimental results.
基金supported by the National Key Technologies Research and Development Program(Grant No.2006BAC02B02)Key International S&T Cooperation Projects(Grant No. 2008DFA22180)European Commission(Call FP7ENV -2007-1 Grant nr.212921) as part of the CEOPAEGIS project(http://www.ceop-aegis.org) coordinated by the University of Strasbourg.
文摘A Single Column Model(SCM) for Global and Regional Atmospheric Prediction Enhanced System (GRAPES) is constructed for the purpose of evaluating physical process parameterizations.Two observational datasets including Wangara and the third Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study(GABLS-3) SCM field observations have been applied to evaluate this SCM.By these two numerical experiments,the GRAPESSCM is verified to be correctly constructed.Furthermore, the interaction between the land surface process and atmospheric boundary layer(ABL) is discussed through the second experiment.It is found that CASE3(CoLM land surface scheme coupled with ABL scheme) simulates less sensible heat fluxes and smaller surface temperature which corresponds with its lower potential temperature at the bottom of the ABL.Moreover,CASE3 simulates turbulence that is weaker during the daytime and stronger during nighttime,corresponding with its wind speed at 200 m which is bigger during daytime and smaller during nighttime.However,they are generally opposite in CASE2(SLAB coupled with ABL).The initial profile of the water vapor mixing ratio is artificially increased by the experiment setup which results in the simulated water vapor mixing becoming wetter than actually observed.CASE1 (observed surface temperature taken as lower thermal forcing) and CASE2 have no soil moisture prediction and simulate a similar water vapor mixing ratio,while CASE3 has a soil moisture prediction and simulates wetter.It is also shown that the time step may affect the stabilization of the ABL when the vertical levels of the SCM are fixed.
基金supported by National Natural Science Foundation for Young Scientists of China(Grant Nos.11101397,11201108)the Humanities and Social Sciences Project from Ministry of Education of China(Grant No.12YJC910007)+1 种基金Anhui Provincial Natural Science Foundation(Grant No.1208085QA12)the National Statistical Research Plan Project(Grant No.2012LZ009)
文摘This paper considers the problem of change point in single index models.In order to obtain asymptotically valid confidence intervals for the estimation of the change point,the convergence rate and asymptotic distribution of the change point estimate is studied.Some simulation results are presented which show that the numerical performance of our estimator is satisfactory.
文摘Tests for nonparametric parts on partially linear single index models are considered in this paper.Based on the estimates obtained by the local linear method,the generalized likelihood ratio tests for the models are established.Under the null hypotheses the normalized tests follow asymptotically theχ2-distribution with the scale constants and the degrees of freedom being independent of the nuisance parameters,which is called the Wilks phenomenon.A simulated example is used to evaluate the performances of the testing procedures empirically.
基金This work is supported by the National Natural Science Foundation (50005016) and the foundation of Yangtze River Scholarship. Although all the calculation was carried out in China, the researching experience of ZFY in Cambridge University is acknowledged
文摘A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.
基金the National Natural Science Foundation of China (Grant Nos. 10471136, 10671189)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX3-SYW-S02)
文摘Single index models are widely used in medicine, econometrics and some other fields. In this paper, we consider the inference of a change point problem in single index models. Based on density-weighted average derivative estimation (ADE) method, we propose a statistic to test whether a change point exists or not. The null distribution of the test statistic is obtained using a permutation technique. The permuted statistic is rigorously shown to have the same distribution in the limiting sense under both null and alternative hypotheses. After the null hypothesis of no change point is rejected, an ADE-based estimate of the change point is proposed under assumption that the change point is unique. A simulation study confirms the theoretical results.
基金the National Key Research and Development Program of China(Grant No.2018YFB0904200).
文摘To ensure the safety and stability of power grids with photovoltaic(PV)gen eration integrati on,it is necessary to predict the output perform a nee of PV modules un der varyi ng operating con ditions.In this paper,an improved artificial neural network(ANN)method is proposed to predict the electrical characteristics of a PV module by combining several neural networks under different environmental conditions.To study the dependenee of the output performance on the solar irradianee and temperature,the proposed neural network model is composed of four neural networks,it called multineural network(MANN).Each neural network consists of three layers,in which the input is solar radiation,and the module temperature and output are five physical parameters of the single diode model.The experimental data were divided into four groups and used for training the neural networks.The electrical properties of PV modules,including l-V curves,PV curves,and normalized root mean square error,were obtained and discussed.The effectiveness and accuracy of this method is verified by the experimental data for d iff ere nt types of PV modules.Compared with the traditional single-ANN(SANN)method,the proposed method shows be社er accuracy under different operating conditions.
基金provided by the National Natural Science Foundation of China Youth Found of China (No.41102169)the doctoral foundation of Henan Polytechnic University of China (No. B2014-056)
文摘The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.
