The rotating disk cavity is an important part of the cooling-air system of the aero engine,and it has obviously significance to study the internal flow and heat transfer characteristics of the disc cavity,which will b...The rotating disk cavity is an important part of the cooling-air system of the aero engine,and it has obviously significance to study the internal flow and heat transfer characteristics of the disc cavity,which will be helpful to improve the efficiency of the aero engine.This paper summarizes the existing research results of domestic and overseas.The present work considers the test methods and calculation methods of the flow and heat transfer characteristics of the rotating disc cavity of the aircraft engine.It points out that,the main factors which affect the heat transfer characteristics are the disc chamber speed,the intake volume,the design of the disc cavity pre-rotation/despin structure,and the type of disc cavity system.The influence of these factors on the characteristics of flow heat transfer is summarized.Based on these factors,the disc cavity structure can be optimized and designed,which provides suggestions for reducing the weight of the turbine,improving the thrust-to-weight ratio of the aero engine,and improving the cooling efficiency.展开更多
China’s infrastructure construction has been continuously improving in recent years,especially its highway construction,which spans from north to south and connects east to west.Some special areas are also interconne...China’s infrastructure construction has been continuously improving in recent years,especially its highway construction,which spans from north to south and connects east to west.Some special areas are also interconnected through bridges,but constructing highway bridges through complex terrains or across valleys and mountain gullies presents significant challenges,requiring an increase in the height of bridge piers.These bridge piers generally reach tens or even hundreds of meters in height.Furthermore,the construction of these high-pier bridges is becoming increasingly widespread.Not only do they pose greater construction challenges,but they also have higher requirements for seismic resistance.This article primarily analyzes the characteristics of high-pier bridges and proposes seismic design schemes,calculation methods,and design strategies to enhance the construction quality of high-pier bridges.展开更多
Previous results show that the floating reference theory(FRT)is an effective tool to reduce the infuence of interference factors on noninvasive blood glucose sensing by near infrared spectros-copy(NIRS).It is the key ...Previous results show that the floating reference theory(FRT)is an effective tool to reduce the infuence of interference factors on noninvasive blood glucose sensing by near infrared spectros-copy(NIRS).It is the key to measure the floating reference point(FRP)precisely for the application of FRT.Monte Carlo(MC)simulation has been introduced to quantitatively in-vestigate the effects of positioning errors and light source drifts on measuring FRP.In this article,thinning and calculating method(TCM)is proposed to quantify the positioning error.Mean-while,the normalization process(NP)is developed to significantly reduce the error induced by light source drift.The results according to TCM show that 7 purm deviations in positioning can generate about 10.63%relative error in FRP.It is more noticeable that 1%fluctuation in light source intensity may lead to 12.21%relative errors.Gratifyingly,the proposed NP model can effectively reduce the error caused by light source drift.Therefore,the measurement system for FRPs must meet that the positioning error is less than 7 purm,and the light source drift is kept within 1%.Furthermore,an improvement for measurement system is proposed in order to take advantage of the NP model.展开更多
According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears...According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears is researched, and computing formulas of power and rotation speed for equivalent gears are deduced. A numerical simulation of contact stress for non-circular gears has also been conducted based on the finite element method. By the comparison of fitting curves, the feasibility of using equivalent gears instead of non-circular gears to calculate the contact stress is testified.展开更多
Reference crop evapotranspiration (ET_0) is a critical part in water cycle and water balance of ecosystem, which is greatly important to effective utilization of agricultural water resources and for making reasonable ...Reference crop evapotranspiration (ET_0) is a critical part in water cycle and water balance of ecosystem, which is greatly important to effective utilization of agricultural water resources and for making reasonable irrigation system. In order to propose a suitable method for computing ET_0 in North Xinjiang, based on daily meteorological data from May 1 to September30, 2010 provided by Weather Station of Fuhai County, we used FAO56 Penman-Monteith as the standard formula to compute ET_0, compared the differences and relations between such the method and other 4 calculation formulas, and analyzed the cause of the deviation, finally evaluated the applicability of computational method in North Xinjiang. The results showed that the calculation results by FA056 PM Method was approximate to that by FAO Penman method and IA method, of which the relative error was 9.26% and 13.51% respectively, the ET_0 results calculated by PT method and HS method were generally greater than the results by FAO56 PM, and their deviation was very obvious.展开更多
Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing ...Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing waves or currents in the ocean. By analyzing the domestic and international norms, this study <span style="letter-spacing:0.1pt;font-family:Verdana;font-size:12px;">pre</span><span style="font-family:Verdana;font-size:12px;">sents a review of calculation methods of wind load on ocean platforms, which </span><span style="letter-spacing:-0.15pt;font-family:Verdana;font-size:12px;">belongs to large-scale non-entity structure used in the open sea while sur</span><span style="font-family:Verdana;font-size:12px;">round</span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">ing wind has no fixed direction. Current computations according to the</span><span style="font-family:Verdana;font-size:12px;"> norms are not accurate, which even not takes the force of the wind against the surf</span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">ace perpendicular to the structure into consideration. Additionally, thi</span><span style="font-family:Verdana;font-size:12px;">s study also introduces and compares the lift model of platforms based on different </span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">theories, such as vortex-excitation and vibration, engineering structure dy</span><span style="font-family:Verdana;font-size:12px;">namics, gas flow pressure theory, analyzing their applicability, advantages, and disadvantages. This paper analyzes the limitations and applicable conditions of the existing calculation method itself, such as the lift model is suitable for the existence of stable vortex wake;the calculation method of the structural dynamics of marine engineering must be combined with the wind tunnel test and consider the mistakes caused by the position relationship;the numerical simulation method is accurate but tedious. This study provides an insight into the calculation methods of lift in designing ocean platforms, including the </span><span style="letter-spacing:0.1pt;font-family:Verdana;font-size:12px;">finite element method for simulating fluid force and updating formulas in</span><span style="font-family:Verdana;font-size:12px;"> Chinese norms.</span>展开更多
Because of my carelessness,Eq.(1)in the paper "An approximate method for calculating the fluid force and response of a circular cylinder at lock-in"(China Ocean Engineering,22(3),2008,pp.373)should be ...Because of my carelessness,Eq.(1)in the paper "An approximate method for calculating the fluid force and response of a circular cylinder at lock-in"(China Ocean Engineering,22(3),2008,pp.373)should be f’-1.0/U’-5.0=f’<sub>lower</sub>-1.0/5.75f’<sub>lower</sub>-5.0,not f’=U’/5.75. My apology is hereby given.展开更多
In the present paper the analytical formulas for calculating the equivalent deterministictransients for multivariable cross correlated random processes are developed.The formulaspermit the determination of the Root-me...In the present paper the analytical formulas for calculating the equivalent deterministictransients for multivariable cross correlated random processes are developed.The formulaspermit the determination of the Root-mean-square of the responses of a lineartime-invariant system to stationary multiple random inputs in the time domain.The methodis applicable in the study of flight of airplanes in atmospheric turbulence and is also usefulfor general engineering applications of stochastc processes control.展开更多
In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy sec...In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy security. In order to improve the quality of water injection in the oilfield and gradually achieve efficient and stable production, Bohai Oilfield has launched a water injection well pressure optimization project, focusing on improving the efficiency and quality of water injection in the water injection wells, in order to achieve the optimal water injection plan. In practical work, P Oilfield continues to promote the development of water injection well pressure optimization projects, emphasizing practical exploration and continuous optimization of work plans. However, during the project implementation process, there were some problems, one of which was that the statistics of cumulative injection volume were not scientific enough, resulting in a more comprehensive and accurate presentation of the actual results of pressure optimization work. In the context of continuous improvement work, after careful analysis and research, P Oilfield has decided to optimize the cumulative injection rate algorithm to guide the oilfield’s water injection work in a more refined way, ensuring sufficient and good water injection, and enhancing the oilfield’s production efficiency and comprehensive competitiveness.展开更多
The normal distribution, which has a symmetric and middle-tailed profile, is one of the most important distributions in probability theory, parametric inference, and description of quantitative variables. However, the...The normal distribution, which has a symmetric and middle-tailed profile, is one of the most important distributions in probability theory, parametric inference, and description of quantitative variables. However, there are many non-normal distributions and knowledge of a non-zero bias allows their identification and decision making regarding the use of techniques and corrections. Pearson’s skewness coefficient defined as the standardized signed distance from the arithmetic mean to the median is very simple to calculate and clear to interpret from the normal distribution model, making it an excellent measure to evaluate this assumption, complemented with the visual inspection by means of a histogram and a box-and-whisker plot. From its variant without tripling the numerator or Yule’s skewness coefficient, the objective of this methodological article is to facilitate the use of this latter measure, presenting how to obtain asymptotic and bootstrap confidence intervals for its interpretation. Not only are the formulas shown, but they are applied with an example using R program. A general rule of interpretation of ∓0.1 has been suggested, but this can only become relevant when contextualized in relation to sample size and a measure of skewness with a population or parametric value of zero. For this purpose, intervals with confidence levels of 90%, 95% and 99% were estimated with 10,000 draws at random with replacement from 57 normally distributed samples-population with different sample sizes. The article closes with suggestions for the use of this measure of skewness.展开更多
A simple analytic modified embedded atom method (M EAM ) Inciuding a modified term for hcp metals has been developed from the MEAM applied to the fcc and bcc metals. The enthalpiesof formation of all binary alloy syst...A simple analytic modified embedded atom method (M EAM ) Inciuding a modified term for hcp metals has been developed from the MEAM applied to the fcc and bcc metals. The enthalpiesof formation of all binary alloy systems for eight transition hcp metals are calculated with theMEAM. The calculations are in agreement with the experimental data avallable and resultscalculated from the Miedema theory. One can conclude that our MEAM is also effective toapply to the hcp metals and their alloys.展开更多
At present,research on hydraulic mounts has mainly focused on the prediction of the dynamic stiffness and loss angle.Compared to the traditional finite element analysis method,the programming method can be used to ana...At present,research on hydraulic mounts has mainly focused on the prediction of the dynamic stiffness and loss angle.Compared to the traditional finite element analysis method,the programming method can be used to analyze hydraulic mounts for a rapid and accurate understanding of the influence of the different mounting parameters on the dynamic stiffness and loss angle.The aims of this study were to investigate the nonlinear dynamic characteristics of a hydraulic mount,and to identify the parameters that affect the dynamic stiffness and loss angle using MATLAB software programs to obtain the influence curves of the parameters,so as to use suitable parameters as the basis for vibration analysis.A nonlinear mechanical model of a hydraulic mount was established according to the basic principles of fluid dynamics.The dynamic stiffness and loss angle of the dimensionless expression were proposed.A numerical calculation method for the dynamic performance evaluation index of the hydraulic mount was derived.A one-to-one correspondence was established between the structural parameters and peak frequency of the evaluation index.The accuracy and applicability of the mechanical model were verified by the test results.The results demonstrated the accuracy of the nonlinear mechanical model of the hydraulic mount,and the vehicle driving comfort was greatly improved by the optimization of the structural parameters.展开更多
The aerodynamic noise of high-speed trains passing through a tunnel has gradually become an important issue.Numerical approaches for predicting the aerodynamic noise sources of high-speed trains running in tunnels are...The aerodynamic noise of high-speed trains passing through a tunnel has gradually become an important issue.Numerical approaches for predicting the aerodynamic noise sources of high-speed trains running in tunnels are the key to alleviating aerodynamic noise issues.In this paper,two typical numerical methods are used to calculate the aerodynamic noise of high-speed trains.These are the static method combined with non-reflective boundary conditions and the dynamic mesh method combined with adaptive mesh.The fluctuating pressure,flow field and aerodynamic noise source are numerically simulated using the abovemethods.The results showthat the fluctuating pressure,flow field structure and noise source characteristics obtained using different methods,are basically consistent.Compared to the dynamic mesh method,the pressure,vortex size and noise source radiation intensity,obtained by the static method,are larger.The differences are in the tail car and its wake.The two calculation methods show that the spectral characteristics of the surface noise source are consistent.The maximum difference in the sound pressure level is 1.9 dBA.The static method is more efficient and more suitable for engineering applications.展开更多
The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based...The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based on density functional theory(DFT),we systematically research the electronic structure and optical properties of dopedα-Ga2O3 by GGA+U calculation method.The results show that Ge atoms and F atoms are effective n-type dopants.For Ge-dopedα-Ga2O3,it is probably obtained under O-poor conditions.However,for F-dopedα-Ga2O3,it is probably obtained under O-rich conditions.The doping system of F element is more stable due to the lower formation energy.In this investigation,it is found that two kinds of doping can reduce theα-Ga2O3 band gap and improve the conductivity.What is more,it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region.Through the whole scale of comparison,Ge doping is more suitable for the application of transmittance materials,yet F doping is more appropriate for the application of deep ultraviolet devices.We expect that our research can provide guidance and reference for preparation ofα-Ga2O3 thin films and photoelectric devices.展开更多
Objective Traditional oil and gas theory considers that hydrocarbon generation process is a hydrodeoxygenation reaction of organic matter(OM).Thus,the supply condition of hydrogen controls the hydrocarbon generation a...Objective Traditional oil and gas theory considers that hydrocarbon generation process is a hydrodeoxygenation reaction of organic matter(OM).Thus,the supply condition of hydrogen controls the hydrocarbon generation ability of OM.Those factors of TOC and hydrogen index(I_H)are playing important roles for calculating展开更多
A new method of 3 D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination(METCE) are derived under the assumption of magnetic quasi static approximation, especiall...A new method of 3 D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination(METCE) are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a3 D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.展开更多
At present, greenhouse effect has become a severe challenge of international society. In order to cope with this challenge, countries all over the world reached an agreement to develop low-carbon economy and create lo...At present, greenhouse effect has become a severe challenge of international society. In order to cope with this challenge, countries all over the world reached an agreement to develop low-carbon economy and create low-carbon society. As a new concept, "carbon footprint" emerged with the vigorous development of low-carbon economy, and its calculation method is related to the evaluation system of low carbon economy. In order to calculate "carbon footprint", "carbon subject" in the study was divided into energy consumption account, soil respiration account and biological resources account, and the calculation formula of "carbon footprint" was defined, as well as CO2 emission from various accounts, namely the calculation method of "carbon footprint" was discussed preliminarily from quantitative evaluation index.展开更多
Derivation of bulk transport coefficients helps solving land surface processes. A similarity-based method for determining the turbulent transfer (including the flux exchange, the vertical distribution of wind and pote...Derivation of bulk transport coefficients helps solving land surface processes. A similarity-based method for determining the turbulent transfer (including the flux exchange, the vertical distribution of wind and potential temperature) in the atmospheric surface layer is presented. Comparisons with iterative schemes (Businger, 1971) are given to demonstrate the advantages of the calculation methods.展开更多
文摘The rotating disk cavity is an important part of the cooling-air system of the aero engine,and it has obviously significance to study the internal flow and heat transfer characteristics of the disc cavity,which will be helpful to improve the efficiency of the aero engine.This paper summarizes the existing research results of domestic and overseas.The present work considers the test methods and calculation methods of the flow and heat transfer characteristics of the rotating disc cavity of the aircraft engine.It points out that,the main factors which affect the heat transfer characteristics are the disc chamber speed,the intake volume,the design of the disc cavity pre-rotation/despin structure,and the type of disc cavity system.The influence of these factors on the characteristics of flow heat transfer is summarized.Based on these factors,the disc cavity structure can be optimized and designed,which provides suggestions for reducing the weight of the turbine,improving the thrust-to-weight ratio of the aero engine,and improving the cooling efficiency.
文摘China’s infrastructure construction has been continuously improving in recent years,especially its highway construction,which spans from north to south and connects east to west.Some special areas are also interconnected through bridges,but constructing highway bridges through complex terrains or across valleys and mountain gullies presents significant challenges,requiring an increase in the height of bridge piers.These bridge piers generally reach tens or even hundreds of meters in height.Furthermore,the construction of these high-pier bridges is becoming increasingly widespread.Not only do they pose greater construction challenges,but they also have higher requirements for seismic resistance.This article primarily analyzes the characteristics of high-pier bridges and proposes seismic design schemes,calculation methods,and design strategies to enhance the construction quality of high-pier bridges.
基金the National High Technology Research and Development Program of China(863 Program:2012AA022602)the 111 Project(B07014)and Tianjin Natural Science Foundation(No.16JCZDJC31200).
文摘Previous results show that the floating reference theory(FRT)is an effective tool to reduce the infuence of interference factors on noninvasive blood glucose sensing by near infrared spectros-copy(NIRS).It is the key to measure the floating reference point(FRP)precisely for the application of FRT.Monte Carlo(MC)simulation has been introduced to quantitatively in-vestigate the effects of positioning errors and light source drifts on measuring FRP.In this article,thinning and calculating method(TCM)is proposed to quantify the positioning error.Mean-while,the normalization process(NP)is developed to significantly reduce the error induced by light source drift.The results according to TCM show that 7 purm deviations in positioning can generate about 10.63%relative error in FRP.It is more noticeable that 1%fluctuation in light source intensity may lead to 12.21%relative errors.Gratifyingly,the proposed NP model can effectively reduce the error caused by light source drift.Therefore,the measurement system for FRPs must meet that the positioning error is less than 7 purm,and the light source drift is kept within 1%.Furthermore,an improvement for measurement system is proposed in order to take advantage of the NP model.
文摘According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears is researched, and computing formulas of power and rotation speed for equivalent gears are deduced. A numerical simulation of contact stress for non-circular gears has also been conducted based on the finite element method. By the comparison of fitting curves, the feasibility of using equivalent gears instead of non-circular gears to calculate the contact stress is testified.
基金Supported by Key Scientific and Technological Research and Development Program of Xinjiang(201531115)Special Fund for Scientific Research of China Institute of Water Resources and Hydropower Research(MK2016J10)
文摘Reference crop evapotranspiration (ET_0) is a critical part in water cycle and water balance of ecosystem, which is greatly important to effective utilization of agricultural water resources and for making reasonable irrigation system. In order to propose a suitable method for computing ET_0 in North Xinjiang, based on daily meteorological data from May 1 to September30, 2010 provided by Weather Station of Fuhai County, we used FAO56 Penman-Monteith as the standard formula to compute ET_0, compared the differences and relations between such the method and other 4 calculation formulas, and analyzed the cause of the deviation, finally evaluated the applicability of computational method in North Xinjiang. The results showed that the calculation results by FA056 PM Method was approximate to that by FAO Penman method and IA method, of which the relative error was 9.26% and 13.51% respectively, the ET_0 results calculated by PT method and HS method were generally greater than the results by FAO56 PM, and their deviation was very obvious.
文摘Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing waves or currents in the ocean. By analyzing the domestic and international norms, this study <span style="letter-spacing:0.1pt;font-family:Verdana;font-size:12px;">pre</span><span style="font-family:Verdana;font-size:12px;">sents a review of calculation methods of wind load on ocean platforms, which </span><span style="letter-spacing:-0.15pt;font-family:Verdana;font-size:12px;">belongs to large-scale non-entity structure used in the open sea while sur</span><span style="font-family:Verdana;font-size:12px;">round</span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">ing wind has no fixed direction. Current computations according to the</span><span style="font-family:Verdana;font-size:12px;"> norms are not accurate, which even not takes the force of the wind against the surf</span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">ace perpendicular to the structure into consideration. Additionally, thi</span><span style="font-family:Verdana;font-size:12px;">s study also introduces and compares the lift model of platforms based on different </span><span style="letter-spacing:-0.1pt;font-family:Verdana;font-size:12px;">theories, such as vortex-excitation and vibration, engineering structure dy</span><span style="font-family:Verdana;font-size:12px;">namics, gas flow pressure theory, analyzing their applicability, advantages, and disadvantages. This paper analyzes the limitations and applicable conditions of the existing calculation method itself, such as the lift model is suitable for the existence of stable vortex wake;the calculation method of the structural dynamics of marine engineering must be combined with the wind tunnel test and consider the mistakes caused by the position relationship;the numerical simulation method is accurate but tedious. This study provides an insight into the calculation methods of lift in designing ocean platforms, including the </span><span style="letter-spacing:0.1pt;font-family:Verdana;font-size:12px;">finite element method for simulating fluid force and updating formulas in</span><span style="font-family:Verdana;font-size:12px;"> Chinese norms.</span>
文摘Because of my carelessness,Eq.(1)in the paper "An approximate method for calculating the fluid force and response of a circular cylinder at lock-in"(China Ocean Engineering,22(3),2008,pp.373)should be f’-1.0/U’-5.0=f’<sub>lower</sub>-1.0/5.75f’<sub>lower</sub>-5.0,not f’=U’/5.75. My apology is hereby given.
文摘In the present paper the analytical formulas for calculating the equivalent deterministictransients for multivariable cross correlated random processes are developed.The formulaspermit the determination of the Root-mean-square of the responses of a lineartime-invariant system to stationary multiple random inputs in the time domain.The methodis applicable in the study of flight of airplanes in atmospheric turbulence and is also usefulfor general engineering applications of stochastc processes control.
文摘In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy security. In order to improve the quality of water injection in the oilfield and gradually achieve efficient and stable production, Bohai Oilfield has launched a water injection well pressure optimization project, focusing on improving the efficiency and quality of water injection in the water injection wells, in order to achieve the optimal water injection plan. In practical work, P Oilfield continues to promote the development of water injection well pressure optimization projects, emphasizing practical exploration and continuous optimization of work plans. However, during the project implementation process, there were some problems, one of which was that the statistics of cumulative injection volume were not scientific enough, resulting in a more comprehensive and accurate presentation of the actual results of pressure optimization work. In the context of continuous improvement work, after careful analysis and research, P Oilfield has decided to optimize the cumulative injection rate algorithm to guide the oilfield’s water injection work in a more refined way, ensuring sufficient and good water injection, and enhancing the oilfield’s production efficiency and comprehensive competitiveness.
文摘The normal distribution, which has a symmetric and middle-tailed profile, is one of the most important distributions in probability theory, parametric inference, and description of quantitative variables. However, there are many non-normal distributions and knowledge of a non-zero bias allows their identification and decision making regarding the use of techniques and corrections. Pearson’s skewness coefficient defined as the standardized signed distance from the arithmetic mean to the median is very simple to calculate and clear to interpret from the normal distribution model, making it an excellent measure to evaluate this assumption, complemented with the visual inspection by means of a histogram and a box-and-whisker plot. From its variant without tripling the numerator or Yule’s skewness coefficient, the objective of this methodological article is to facilitate the use of this latter measure, presenting how to obtain asymptotic and bootstrap confidence intervals for its interpretation. Not only are the formulas shown, but they are applied with an example using R program. A general rule of interpretation of ∓0.1 has been suggested, but this can only become relevant when contextualized in relation to sample size and a measure of skewness with a population or parametric value of zero. For this purpose, intervals with confidence levels of 90%, 95% and 99% were estimated with 10,000 draws at random with replacement from 57 normally distributed samples-population with different sample sizes. The article closes with suggestions for the use of this measure of skewness.
文摘A simple analytic modified embedded atom method (M EAM ) Inciuding a modified term for hcp metals has been developed from the MEAM applied to the fcc and bcc metals. The enthalpiesof formation of all binary alloy systems for eight transition hcp metals are calculated with theMEAM. The calculations are in agreement with the experimental data avallable and resultscalculated from the Miedema theory. One can conclude that our MEAM is also effective toapply to the hcp metals and their alloys.
文摘At present,research on hydraulic mounts has mainly focused on the prediction of the dynamic stiffness and loss angle.Compared to the traditional finite element analysis method,the programming method can be used to analyze hydraulic mounts for a rapid and accurate understanding of the influence of the different mounting parameters on the dynamic stiffness and loss angle.The aims of this study were to investigate the nonlinear dynamic characteristics of a hydraulic mount,and to identify the parameters that affect the dynamic stiffness and loss angle using MATLAB software programs to obtain the influence curves of the parameters,so as to use suitable parameters as the basis for vibration analysis.A nonlinear mechanical model of a hydraulic mount was established according to the basic principles of fluid dynamics.The dynamic stiffness and loss angle of the dimensionless expression were proposed.A numerical calculation method for the dynamic performance evaluation index of the hydraulic mount was derived.A one-to-one correspondence was established between the structural parameters and peak frequency of the evaluation index.The accuracy and applicability of the mechanical model were verified by the test results.The results demonstrated the accuracy of the nonlinear mechanical model of the hydraulic mount,and the vehicle driving comfort was greatly improved by the optimization of the structural parameters.
基金This work is supported by the National Key Research and Development Program of China(2020YFA0710902)Sichuan Science and Technology Program(2021YFG0214,2019YJ0227)+1 种基金Fundamental Research Funds for the Central Universities(2682021ZTPY124)State Key Laboratory of Traction Power(2019TPL_T02).
文摘The aerodynamic noise of high-speed trains passing through a tunnel has gradually become an important issue.Numerical approaches for predicting the aerodynamic noise sources of high-speed trains running in tunnels are the key to alleviating aerodynamic noise issues.In this paper,two typical numerical methods are used to calculate the aerodynamic noise of high-speed trains.These are the static method combined with non-reflective boundary conditions and the dynamic mesh method combined with adaptive mesh.The fluctuating pressure,flow field and aerodynamic noise source are numerically simulated using the abovemethods.The results showthat the fluctuating pressure,flow field structure and noise source characteristics obtained using different methods,are basically consistent.Compared to the dynamic mesh method,the pressure,vortex size and noise source radiation intensity,obtained by the static method,are larger.The differences are in the tail car and its wake.The two calculation methods show that the spectral characteristics of the surface noise source are consistent.The maximum difference in the sound pressure level is 1.9 dBA.The static method is more efficient and more suitable for engineering applications.
基金Project supported by the National Natural Science Foundation of China(Grant No.51302215)the Natural Science Basic Research Program of Shaanxi Province,China(Grant Nos.2018JQ6084 and 2019JQ-860).
文摘The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based on density functional theory(DFT),we systematically research the electronic structure and optical properties of dopedα-Ga2O3 by GGA+U calculation method.The results show that Ge atoms and F atoms are effective n-type dopants.For Ge-dopedα-Ga2O3,it is probably obtained under O-poor conditions.However,for F-dopedα-Ga2O3,it is probably obtained under O-rich conditions.The doping system of F element is more stable due to the lower formation energy.In this investigation,it is found that two kinds of doping can reduce theα-Ga2O3 band gap and improve the conductivity.What is more,it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region.Through the whole scale of comparison,Ge doping is more suitable for the application of transmittance materials,yet F doping is more appropriate for the application of deep ultraviolet devices.We expect that our research can provide guidance and reference for preparation ofα-Ga2O3 thin films and photoelectric devices.
基金sponsored by National Science Foundation of China (grants No.41541019, 41230312 and 41102075)Strategic Priority Research Program of the Chinese Academy of Sciences (grant No.XDA14010404)Liu Baojun Geological Youth Foundation Project (grant No.DMSM2017053)
文摘Objective Traditional oil and gas theory considers that hydrocarbon generation process is a hydrodeoxygenation reaction of organic matter(OM).Thus,the supply condition of hydrogen controls the hydrocarbon generation ability of OM.Those factors of TOC and hydrogen index(I_H)are playing important roles for calculating
基金Supported by the National Natural Science Foundation of China under Grant Nos 51137004,61427806 and 51577184the Equipment Development Project of Chinese Academy of Sciences under Grant No YZ201507
文摘A new method of 3 D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination(METCE) are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a3 D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.
文摘At present, greenhouse effect has become a severe challenge of international society. In order to cope with this challenge, countries all over the world reached an agreement to develop low-carbon economy and create low-carbon society. As a new concept, "carbon footprint" emerged with the vigorous development of low-carbon economy, and its calculation method is related to the evaluation system of low carbon economy. In order to calculate "carbon footprint", "carbon subject" in the study was divided into energy consumption account, soil respiration account and biological resources account, and the calculation formula of "carbon footprint" was defined, as well as CO2 emission from various accounts, namely the calculation method of "carbon footprint" was discussed preliminarily from quantitative evaluation index.
基金Key National Scientific Project for the"9^(th)-five year"economic plan(No.96-908-02-04-2)
文摘Derivation of bulk transport coefficients helps solving land surface processes. A similarity-based method for determining the turbulent transfer (including the flux exchange, the vertical distribution of wind and potential temperature) in the atmospheric surface layer is presented. Comparisons with iterative schemes (Businger, 1971) are given to demonstrate the advantages of the calculation methods.