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Simulation Analysis and Optimization of Rolling Process of Steel Rim 认领
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作者 Wenhua Lv Mao Pang +1 位作者 Shunping Li Miaolong Cao 《力学国际期刊(英文)》 2021年第3期34-51,共18页
In order to solve the problems of rolling forming accuracy and fillet thinning of alloy steel rim, a three-dimensional model of three pass rolling process was established, and the influence of different process parame... In order to solve the problems of rolling forming accuracy and fillet thinning of alloy steel rim, a three-dimensional model of three pass rolling process was established, and the influence of different process parameters on forming quality was analyzed by using the finite element software, and the optimal process parameter combination was obtained. On this basis, the simulation results of wheel rim stress and strain for each pass rolling are analyzed, and the particle tracking technology is introduced to analyze the variation rule of stress in each incremental step. Finally, the simulation and experimental results show that the simulation thickness is basically consistent with the actual thickness, which improves the accuracy of rim rolling forming, and further verifies the correctness of rolling process simulation. 展开更多
关键词 Roll Forming Parameter Optimization Simulation Analysis Thickness Verification
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Covariance Matrix Learning Differential Evolution Algorithm Based on Correlation 认领
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作者 Sainan Yuan Quanxi Feng 《智能科学国际期刊(英文)》 2021年第1期17-30,共14页
Differential evolution algorithm based on the covariance matrix learning can adjust the coordinate system according to the characteristics of the population, which make<span style="font-family:Verdana;"&g... Differential evolution algorithm based on the covariance matrix learning can adjust the coordinate system according to the characteristics of the population, which make<span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> the search move in a more favorable direction. In order to obtain more accurate information about the function shape, this paper propose</span><span style="font-family:Verdana;">s</span><span style="font-family:;" "=""> <span style="font-family:Verdana;">covariance</span><span style="font-family:Verdana;"> matrix learning differential evolution algorithm based on correlation (denoted as RCLDE)</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">to improve the search efficiency of the algorithm. First, a hybrid mutation strategy is designed to balance the diversity and convergence of the population;secondly, the covariance learning matrix is constructed by selecting the individual with the less correlation;then, a comprehensive learning mechanism is comprehensively designed by two covariance matrix learning mechanisms based on the principle of probability. Finally,</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">the algorithm is tested on the CEC2005, and the experimental results are compared with other effective differential evolution algorithms. The experimental results show that the algorithm proposed in this paper is </span><span style="font-family:Verdana;">an effective algorithm</span><span style="font-family:Verdana;">.</span></span> 展开更多
关键词 Differential Evolution Algorithm CORRELATION Covariance Matrix Parameter Self-Adaptive Technique
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Estimation of Infiltration Models’ Parameters Using Regression Analysis in Irrigation Fields of Northern Ghana 认领
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作者 Abdallah Salifu Felix. K. Abagale Gordana Kranjac-Berisavljevic 《土壤科学期刊(英文)》 2021年第3期164-176,共13页
The quantification of soil infiltration is necessary for the estimation of water accessibility in soils for plant growth and development. Field infiltration tests runs were conducted on agricultural soils in three irr... The quantification of soil infiltration is necessary for the estimation of water accessibility in soils for plant growth and development. Field infiltration tests runs were conducted on agricultural soils in three irrigation sites of Northern Ghana. The field data were fitted into Green and Ampt, Kostiakov, Philip, Holtan, Soil Conservation Service and Horton infiltration models for the determination of the unknown model parameters. Regression analysis at 95% confidence level using GraphPad Prism 8. Laboratory and field data on infiltration were used for the model fitting and the unknown parameters were determined using the calibrated models. The <i>k</i> and <i>n</i> parameters of Kostiakov model at Bontanga study site were found to be <i>k</i> = 28.0027 and <i>n</i> = 0.5902, <i>k</i> = 17.0294 and <i>n</i> = 0.4504 for Golinga and <i>k</i> = 23.0356 and <i>n</i> = 0.6339 for Libga. For all the models, the coefficient of determination ranged from 0.7612 to 0.9876 indicating strong relationships. Only Holtan model gave different values at all the three study sites. The parameter <i>GIa</i> and <i>i<sub>c</sub></i><i> </i>of the Holtan model drawn from hydrologic soil group were the same at all the study sites because of the same vegetative cover and surface conditions. The study observed the values of the parameters to have influenced the models’ performance. 展开更多
关键词 PARAMETER Infiltration Model Regression SORPTIVITY TRANSMISSIVITY
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A New Approach for the DFT NIST Test Applicable for Non-Stationary Input Sequences 认领
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作者 Yehonatan Avraham Monika Pinchas 《信号与信息处理(英文)》 2021年第1期1-41,共41页
The National Institute of Standards and Technology (NIST) document is a list of fifteen tests for estimating the probability of signal randomness degree. <span style="font-family:Verdana;">Test number ... The National Institute of Standards and Technology (NIST) document is a list of fifteen tests for estimating the probability of signal randomness degree. <span style="font-family:Verdana;">Test number six in the NIST document is the Discrete Fourier Transform</span><span style="font-family:Verdana;"> (DFT) test suitable for stationary incoming sequences. But, for cases where the input sequence is not stationary, the DFT test provides inaccurate results. For these cases, test number seven and eight (the Non-overlapping Template Matching Test and the Overlapping Template Matching Test) of the NIST document were designed to classify those non-stationary sequences. But, even with test number seven and eight of the NIST document, the results are not always accurate. Thus, the NIST test does not give a proper answer for the non-stationary input sequence case. In this paper, we offer a new algorithm </span><span style="font-family:Verdana;">or test, which may replace the NIST tests number six, seven and eight. The</span> <span style="font-family:Verdana;">proposed test is applicable also for non-stationary sequences and supplies</span><span style="font-family:Verdana;"> more </span><span style="font-family:Verdana;">accurate results than the existing tests (NIST tests number six, seven and</span><span style="font-family:Verdana;"> eight), for non-stationary sequences. The new proposed test is based on the Wigner function and on the Generalized Gaussian Distribution (GGD). In addition, </span><span style="font-family:Verdana;">this new proposed algorithm alarms and indicates on suspicious places of</span><span style="font-family:Verdana;"> cyclic </span><span style="font-family:Verdana;">sections in the tested sequence. Thus, it gives us the option to repair or to</span><span style="font-family:Verdana;"> remove the suspicious places of cyclic sections</span><span><span><span><span></span><span></span><b><span style="font-family:;" "=""><span></span><span></span> </span></b></span></span></span><span><span><span><span></ 展开更多
关键词 Wigner Distribution Shape Parameter Generalized Gaussian Distribution Random Number Generator True Random Number Generator Pseudo Random Number Generator
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A Model Effective Mass Quantum Anharmonic Oscillator and Its Thermodynamic Characterization 认领
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作者 M. Vubangsi F. B. Migueu +3 位作者 B. F. Kamsu L. S. Yonya Tchapda M. Tchoffo L. C. Fai 《应用数学与应用物理(英文)》 2021年第2期306-316,共11页
Using a model anharmonic oscillator with asymptotically decreasing effective mass to study the effect of compositional grading on the quantum mechanical properties of a semiconductor heterostructure, we determine the ... Using a model anharmonic oscillator with asymptotically decreasing effective mass to study the effect of compositional grading on the quantum mechanical properties of a semiconductor heterostructure, we determine the exact bound states and spectral values of the system. Furthermore, we show that ordering ambiguity only brings about a spectral shift on the quantum anharmonic oscillator with spatially varying effective mass. A study of thermodynamic properties of the system reveals a resonance condition dependent on the magnitude of the anharmonicity parameter. This resonance condition is seen to set a critical value on the said parameter beyond which a complex valued entropy which is discussed, emerges. 展开更多
关键词 Ordering Ambiguity Anharmonicity Parameter Variable Mass Anharmonic Oscillator Thermodynamic Resonance Complex Entropy Quantum Harmonic Oscillator
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High Purity Hydrogen Production by Metal Hydride System:A Parametric Study Based on the Lumped Parameter Model 认领
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作者 KOUA Koua Alain Jesus TONG Liang +1 位作者 杨天麒 XIAO Jinsheng 《武汉理工大学学报:材料科学英文版》 SCIE EI CAS 2021年第1期127-135,共9页
The simulation of hydrogen purification in a mixture gas of hydrogen/carbon dioxide (H2/CO2) by metal hydride system was reported.The lumped parameter model was developed and validated.The validated model was implemen... The simulation of hydrogen purification in a mixture gas of hydrogen/carbon dioxide (H2/CO2) by metal hydride system was reported.The lumped parameter model was developed and validated.The validated model was implemented on the software Matlab/Simulink to simulate the present investigation.The simulation results demonstrate that the purification efficiency depends on the external pressure and the venting time.An increase in the external pressure and enough venting time makes it possible to effectively remove the impurities from the tank during the venting process and allows to desorb pure hydrogen.The impurities are partially removed from the tank for low external pressure and venting time during the venting process and the desorbed hydrogen is contaminated.Other parameters such as the overall heat transfer coefficient,solid material mass,supply pressure,and the ambient temperature influence the purification system in terms of the hydrogen recovery rate.An increase in the overall heat transfer coefficient,solid material mass,and supply pressure improves the hydrogen recovery rate while a decrease in the ambient temperature enhances the recovery rate. 展开更多
关键词 hydrogen production hydrogen purification carbon dioxide metal hydride lumped parameter parametric study
Design optimization of a wind turbine gear transmission based on fatigue reliability sensitivity 认领
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作者 Genshen LIU Huaiju LIU +2 位作者 Caichao ZHU Tianyu MAO Gang HU 《机械工程前沿:英文版》 SCIE CSCD 2021年第1期61-79,共19页
Fatigue failure of gear transmission is one of the key factors that restrict the performance and service life of wind turbines.One of the major concerns in gear transmission under random loading conditions is the disr... Fatigue failure of gear transmission is one of the key factors that restrict the performance and service life of wind turbines.One of the major concerns in gear transmission under random loading conditions is the disregard of dynamic fatigue reliability in conventional design methods.Various issues,such as overweight structure or insufficient fatigue reliability,require continuous improvements in the reliability-based design optimization(RBDO)methodology.In this work,a novel gear transmission optimization model based on dynamic fatigue reliability sensitivity is developed to predict the optimal structural parameters of a wind turbine gear transmission.In the model,the dynamic fatigue reliability of the gear transmission is evaluated based on stress–strength interference theory.Design variables are determined based on the reliability sensitivity and correlation coefficient of the initial design parameters.The optimal structural parameters with the minimum volume are identified using the genetic algorithm in consideration of the dynamic fatigue reliability constraints.Comparison of the initial and optimized structures shows that the volume decreases by 3.58%while ensuring fatigue reliability.This work provides new insights into the RBDO of transmission systems from the perspective of reliability sensitivity. 展开更多
关键词 gear transmission fatigue reliability reliabi-lity sensitivity parameter optimization
System Design and Signal Processing for Frequency Diverse Array Radar 认领
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作者 Jingwei Xu Lan Lan +4 位作者 Xiongpeng He Shengqi Zhu Cao Zeng Guisheng Liao Yuhong Zhang 《北京理工大学学报:英文版》 EI CAS 2021年第1期1-19,共19页
Frequency diverse array(FDA)radar has been studied for more than 15 years and has attracted a lot of attention due to its potential advantages over the well-known phased array radar.The representative feature of FDA i... Frequency diverse array(FDA)radar has been studied for more than 15 years and has attracted a lot of attention due to its potential advantages over the well-known phased array radar.The representative feature of FDA is range-angle-time-dependent transmit beampattern and its underlying properties are continuously revealed in the research.The formulation and exploitation of the transmit diversity with a frequency increment is the fundamental principle,which brings extra degrees-of-freedom(DOFs)in the transmit dimension.As the FDA radar carries additional information in range,it provides more flexibility in signal processing and also brings in new technical issues.This article overviews the state-of-the-art in FDA radar area and its applications,mainly based on the progress in our group.There are two main catalogs in FDA radar area,namely coherent FDA and FDA-MIMO(multiple-input multiple-output)radars.Potential applications including target parameter estimation,ambiguous clutter suppression,and deceptive jammer suppression are discussed. 展开更多
关键词 frequency diverse array(FDA) range-angle-time-dependent transmit beampattern parameter estimation ambiguous clutter suppression deceptive jammer suppression
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熔接结构与工艺对PMMA双色注塑熔接状态的影响 认领
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作者 吴晓兰 黄继忠 +1 位作者 颜许 黄园林 《工程塑料应用》 CAS CSCD 北大核心 2021年第3期47-52,共6页
利用具有不同末端熔接夹角的聚甲基丙烯酸甲酯(PMMA)双色注塑拉伸试样模具,通过实时监测成型过程中第二次注塑的末端熔体温度、末端熔体压力、末端模具温度等重要注塑工艺参数,分别分析了末端熔接夹角、末端熔体温度、末端熔体压力、末... 利用具有不同末端熔接夹角的聚甲基丙烯酸甲酯(PMMA)双色注塑拉伸试样模具,通过实时监测成型过程中第二次注塑的末端熔体温度、末端熔体压力、末端模具温度等重要注塑工艺参数,分别分析了末端熔接夹角、末端熔体温度、末端熔体压力、末端模具温度对PMMA双色注塑试样熔接状态的影响。结果表明,在末端熔接夹角为70°、末端模具温度不低于80℃的工艺条件下,提高注塑温度,确保第二次注塑的末端熔体温度不低于250℃,或者末端熔体压力控制在63 MPa左右,此时PMMA双色注塑试样熔接强度处于较佳状态,而且可以避免PMMA双色注塑试样熔接处溶剂应力开裂的风险。 展开更多
关键词 双色注塑 熔接状态 工艺参数 应力开裂
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Quantile Regression for Thinning-based INAR(1)Models of Time Series of Counts 认领
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作者 Dan-shu SHENG De-hui WANG +1 位作者 Kai YANG Zi-ang WU 《应用数学学报:英文版》 SCIE CSCD 2021年第2期264-277,共14页
In this paper,we develop the quantile regression(QR)estimation for the first-order integer-valued autoregressive(INAR(1))models by defining the smoothing INAR(1)process.Jittering method is used to derive the QR estima... In this paper,we develop the quantile regression(QR)estimation for the first-order integer-valued autoregressive(INAR(1))models by defining the smoothing INAR(1)process.Jittering method is used to derive the QR estimators for the autoregressive coefficient and the quantile of innovations.The consistency and asymptotic normality of the proposed estimators are established.The performances of the proposed estimation procedures are evaluated by Monte Carlo simulations.The results show that the proposed procedures perform well for simulations and a real data application. 展开更多
关键词 INAR(1)process quantile regression parameter estimation jittering
Human resource allocation for multiple scientific research projects via improved pigeon-inspired optimization algorithm 认领
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作者 LIU ChuanBin MA YongHong +1 位作者 YIN Hang YU LeAn 《中国科学:技术科学英文版》 SCIE EI CAS CSCD 2021年第1期139-147,共9页
Aiming at the complex and restrictive characteristics of human resource allocation in multiple scientific university research projects, an improved pigeon-inspired optimization(IPIO) algorithm is proposed wherein loss... Aiming at the complex and restrictive characteristics of human resource allocation in multiple scientific university research projects, an improved pigeon-inspired optimization(IPIO) algorithm is proposed wherein loss minimization and the shortest project delay time are considered as optimization goals. Firstly, mathematical modelling of the problem is carried out, and the multi-objective optimization problem is transformed into a single-objective optimization problem by means of a weighted solution. In the second step, the traditional pigeon-inspired optimization(PIO) algorithm is discretized, and an adaptive parameter strategy is adopted to improve the shortcomings of the algorithm itself. Finally, by comparing the simulation results with the original algorithm and the genetic algorithm in the optimization of human resource allocation in multiple projects, the feasibility and superiority of the proposed algorithm in the optimization of human resource allocation in multi-scientific research projects is verified. 展开更多
关键词 human resource allocation multiple scientific research projects improved pigeon-inspired optimization(IPIO)algorithm parameter adaptation
Evaluation of controlled attenuation parameter in assessing hepatic steatosis in patients with autoimmune liver diseases 认领
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作者 Xi-Xi Ni Min Lian +9 位作者 Hui-Min Wu Xiao-Yun Li Li Sheng Han Bao Qi Miao Xiao Xiao Can-Jie Guo Hai Li Xiong Ma Jing Hua 《世界胃肠病学杂志:英文版》 SCIE CAS 2021年第1期80-91,共12页
BACKGROUND Hepatic steatosis commonly occurs in some chronic liver diseases and may affect disease progression.AIM To investigate the performance of controlled attenuation parameter(CAP)for the diagnosis of hepatic st... BACKGROUND Hepatic steatosis commonly occurs in some chronic liver diseases and may affect disease progression.AIM To investigate the performance of controlled attenuation parameter(CAP)for the diagnosis of hepatic steatosis in patients with autoimmune liver diseases(AILDs).METHODS Patients who were suspected of having AILDs and underwent liver biopsy were consistently enrolled.Liver stiffness measurement(LSM)and CAP were performed by transient elastography.The area under the receiver operating characteristic(AUROC)curve was used to evaluate the performance of CAP for diagnosing hepatic steatosis compared with biopsy.RESULTS Among 190 patients with biopsy-proven hepatic steatosis,69 were diagnosed with autoimmune hepatitis(AIH),18 with primary biliary cholangitis(PBC),and 27 with AIH-PBC overlap syndrome.The AUROCs of CAP for the diagnosis of steatosis in AILDS were 0.878(0.791-0.965)for S1,0.764(0.676-0.853)for S2,and 0.821(0.716-0.926)for S3.The CAP value was significantly related to hepatic steatosis grade(P<0.001).Among 69 patients with AIH,the median CAP score was 205.63±47.36 dB/m for S0,258.41±42.83 dB/m for S1,293.00±37.18 dB/m for S2,and 313.60±27.89 dB/m for S3.Compared with patients with nonalcoholic fatty liver disease(NAFLD)presenting with autoimmune markers,patients with AIH concomitant with NAFLD were much older and had higher serum IgG levels and LSM values.CONCLUSION CAP can be used as a noninvasive diagnostic method to evaluate hepatic steatosis in patients with AILDs.Determination of LSM combined with CAP may help to identify patients with AIH concomitant with NAFLD from those with NAFLD with autoimmune phenomena. 展开更多
关键词 Controlled attenuation parameter Hepatic steatosis Autoimmune liver diseases Nonalcoholic fatty liver disease Liver stiffness measurement Autoimmune hepatitis
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模型驱动的土地调查要素符号库设计与实现 认领
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作者 戴劲松 杨明 《城市勘测》 2021年第1期79-83,共5页
土地调查的工作性质与目的会产生多种需求,除去存储工作中海量的成果数据,还需提高数据的组织、利用效率,如准确的数据表达、节省数据存储空间、优化数据检索速度等。针对这种需求,本文结合实际生产需要,研究基于矢量数据库的符号化表... 土地调查的工作性质与目的会产生多种需求,除去存储工作中海量的成果数据,还需提高数据的组织、利用效率,如准确的数据表达、节省数据存储空间、优化数据检索速度等。针对这种需求,本文结合实际生产需要,研究基于矢量数据库的符号化表达机制,研发符合土地调查数据制图标准的符号化机制和实现方法。按照土地调查数据制图的相关标准,提取规定的符号图元与参数,使用矢量图元的方式制作要素符号,实现土地数据要素符号的标准化,形成完整的土地调查要素符号库。设计并研发通用符号库访问接口,为不同的制图软件使用符号库提供途径,实现符号共享与符号库的跨平台应用。 展开更多
关键词 土地调查 符号库 图元 参数
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Adaptive Output-Feedback Stabilization for PDE-ODE Cascaded Systems with Unknown Control Coefficient and Spatially Varying Parameter 认领
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作者 LI Xia LIU Yungang +1 位作者 LI Jian XU Zaihua 《系统科学与复杂性学报:英文版》 SCIE EI CSCD 2021年第1期298-313,共16页
This paper investigates the adaptive stabilization for a class of uncertain PDE-ODE cascaded systems. Remarkably, the PDE subsystem allows unknown control coefficient and spatially varying parameter, and only its one ... This paper investigates the adaptive stabilization for a class of uncertain PDE-ODE cascaded systems. Remarkably, the PDE subsystem allows unknown control coefficient and spatially varying parameter, and only its one boundary value is measurable. This renders the system in question more general and practical, and the control problem more challenging. To solve the problem,an invertible transformation is first introduced to change the system into an observer canonical form,from which a couple of filters are constructed to estimate the unmeasurable states. Then, by adaptive technique and infinite-dimensional backstepping method, an adaptive controller is constructed which guarantees that all states of the resulting closed-loop system are bounded while the original system states converging to zero. Finally, a numerical simulation is provided to illustrate the effectiveness of the proposed method. 展开更多
关键词 Adaptive stabilization OUTPUT-FEEDBACK PDE-ODE cascaded systems unknown control coefficient unknown spatially varying parameter
银杏叶有效成分超临界提取技术 认领
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作者 刘可福 《海峡药学》 2021年第3期49-52,共4页
目的为解决银杏叶有效成分常规提取技术的弊端,使我国银杏制品达到国际指标要求,提高产品质量。方法本研究探索超临界流体技术在银杏叶有效成分提取上的应用,设置16组提取参数,并通过测定不同参数下提取物有效成分的含量,来确定银杏有... 目的为解决银杏叶有效成分常规提取技术的弊端,使我国银杏制品达到国际指标要求,提高产品质量。方法本研究探索超临界流体技术在银杏叶有效成分提取上的应用,设置16组提取参数,并通过测定不同参数下提取物有效成分的含量,来确定银杏有效成分的提纯技术的最佳技术参数。结果不同萃取参数条件下,萃取物中黄酮、内酯含量不同,各试验组银杏提取物中黄酮含量均大于24%,内酯含量均大于6%,达到国际产品质量标准;与传统的提取方法相比,能源消耗降低66.7%,生产成本降低20%,产量提高185%,产值提高218%,经济效益明显。综合分析药理药效和萃取工艺成本,3号和11号工艺为最佳萃取参数。结论银杏叶有效成分超临界提取技术最佳参数的确定,既能提高有效成分的含量,又能降低生产成本,提高我国银杏叶提取物在国际市场的竞争能力,具有广阔的应用前景和推广价值。 展开更多
关键词 银杏叶提取物 超临界流体技术 参数
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Parameter regionalization of the FLEX-Global hydrological model 认领
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作者 Jingjing WANG Hongkai GAO +4 位作者 Min LIU Yongjian DING Yan WANG Fang ZHAO Jun XIA 《中国科学:地球科学英文版》 SCIE EI CSCD 2021年第4期571-588,共18页
Global hydrological models(GHMs) are important tools for addressing worldwide change-related water resource problems from a global perspective. However, the development of these models has long been hindered by their ... Global hydrological models(GHMs) are important tools for addressing worldwide change-related water resource problems from a global perspective. However, the development of these models has long been hindered by their low accuracy. In order to improve the streamflow simulation accuracy of GHMs, we developed a GHM—the FLEX-Global—based on the regionalization of hydrological model parameters. The FLEX-Global model is primarily based on the framework of the FLEX hydrological model coupled with the HAND-based Storage Capacity curve(HSC) runoff generation module to calculate net rainfall, and uses the global river-routing Ca Ma-Flood model to calculate river network routing. This new model allows for streamflow simulation at a spatial resolution of 0.5°×0.5° and a temporal resolution of 1 day in global catchments. To validate FLEX-Global accuracy, the FLEX-Global-simulated streamflow of 26 major rivers distributed in five different climate zones was compared with the observed data from the Global Runoff Data Center(GRDC). Next, the model performance of FLEXGlobal was further verified by comparing it with that of seven existing GHMs with varying accuracy in the five climate zones.Multi-metric evaluation indicated that the streamflow simulation accuracy was improved by the FLEX-Global model with regionalized parameters, especially in the tropical and dry climate zones. This newly-developed GHM with regionalized parameters can provide scientific support for the assessment of climate change impact, optimization of global water resource mangement, simulation of Earth's multi-sphere coupling, and implementation of the Inter-Sectoral Impact Model Intercomparison Project(ISIMIP). 展开更多
关键词 Global hydrological model Model performance Parameter regionalization
Seismic wave equations in tight oil/gas sandstone media 认领
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作者 Jinghuai GAO Weimin HAN +4 位作者 Yanbin HE Haixia ZHAO Hui LI Yijie ZHANG Zongben XU 《中国科学:地球科学英文版》 SCIE EI CSCD 2021年第3期377-387,共11页
Tight oil/gas medium is a special porous medium,which plays a significant role in oil and gas exploration.This paper is devoted to the derivation of wave equations in such a media,which take a much simpler form compar... Tight oil/gas medium is a special porous medium,which plays a significant role in oil and gas exploration.This paper is devoted to the derivation of wave equations in such a media,which take a much simpler form compared to the general equations in the poroelasticity theory and can be employed for parameter inversion from seismic data.We start with the fluid and solid motion equations at a pore scale,and deduce the complete Biot’s equations by applying the volume averaging technique.The underlying assumptions are carefully clarified.Moreover,time dependence of the permeability in tight oil/gas media is discussed based on available results from rock physical experiments.Leveraging the Kozeny-Carman equation,time dependence of the porosity is theoretically investigated.We derive the wave equations in tight oil/gas media based on the complete Biot’s equations under some reasonable assumptions on the media.The derived wave equations have the similar form as the diffusiveviscous wave equations.A comparison of the two sets of wave equations reveals explicit relations between the coefficients in diffusive-viscous wave equations and the measurable parameters for the tight oil/gas media.The derived equations are validated by numerical results.Based on the derived equations,reflection and transmission properties for a single tight interlayer are investigated.The numerical results demonstrate that the reflection and transmission of the seismic waves are affected by the thickness and attenuation of the interlayer,which is of great significance for the exploration of oil and gas. 展开更多
关键词 Tight oil/gas Wave equation POROSITY PERMEABILITY Physical parameter Complete Biot’s equations Volume-averaging technique
Systematic comparison of epidemic growth patterns using two different estimation approaches 认领
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作者 Yiseul Lee Kimberlyn Roosa Gerardo Chowell 《传染病建模》 2021年第1期5-14,共10页
Background:Different estimation approaches are frequently used to calibrate mathematical models to epidemiological data,particularly for analyzing infectious disease outbreaks.Here,we use two common methods to estimat... Background:Different estimation approaches are frequently used to calibrate mathematical models to epidemiological data,particularly for analyzing infectious disease outbreaks.Here,we use two common methods to estimate parameters that characterize growth patterns using the generalized growth model(GGM)calibrated to real outbreak datasets.Materials and methods:Data from 31 outbreaks are used to fit the GGM to the ascending phase of each outbreak and estimate the parameters using both least squares(LSQ)and maximum likelihood estimation(MLE)methods.We utilize parametric bootstrapping to construct confidence intervals for parameter estimates.We compare the results including RMSE,Anscombe residual,and 95%prediction interval coverage.We also evaluate the correlation between the estimates from both methods.Results:Comparing LSQ and MLE estimates,most outbreaks have similar parameter estimates,RMSE,Anscombe,and 95%prediction interval coverage.Parameter estimates do not differ across methods when the model yields a good fit to the early growth phase.However,for two outbreaks,there are systematic deviations in model fit to the data that explain differences in parameter estimates(e.g.,residuals represent random error rather than systematic deviation).Conclusion:Our findings indicate that utilizing LSQ and MLE methods produce similar results in the context of characterizing epidemic growth patterns with the GGM,provided that the model yields a good fit to the data. 展开更多
关键词 Parameter estimation Generalized growth model Least squares estimation Maximum likelihood estimation Epidemiological models
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Dynamic crossover in [VIO2+][Tf2N-]2 ionic liquid 认领
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作者 任淦 《中国物理B:英文版》 SCIE EI CAS CSCD 2021年第1期374-379,共6页
Ionic liquids usually behave as fragile liquids,and the temperature dependence of their dynamic properties obeys supper-Arrhenius law.In this work,a dynamic crossover is observed in([VIO2+][Tf2N-]2) ionic liq... Ionic liquids usually behave as fragile liquids,and the temperature dependence of their dynamic properties obeys supper-Arrhenius law.In this work,a dynamic crossover is observed in([VIO2+][Tf2N-]2) ionic liquid at the temperature of 240-800 K.The diffusion coefficient does not obey a single Arrhenius law or a Vogel-Fulcher-Tammann(VFT) relation,but can be well fitted by three Arrhenius laws or a combination of a VFT relation and an Arrhenius law.The origin of the dynamic crossover is analyzed from correlation,structure,and thermodynamics.Ion gets a stronger backward correlation at a lower temperature,as shown by the fractal dimension of the random walk.The temperature dependence function of fractal dimension,heterogeneity order parameter,and thermodynamic data can be separated into three regions similar to that observed in the diffusion coefficient.The two crossover temperatures observed in the three types of data are almost the same as that in diffusion coefficient fitted by three Arrhenius laws.The results indicate that the dynamic crossover of[VIO2+][Tf2 N-]2 is attributed to the heterogeneous structure when it undergoes cooling. 展开更多
关键词 ionic liquids dynamic crossover heterogeneity order parameter fractal dimension fragile
Analysis of effects of operating parameters on rate of penetration in drilling process with air down-the-hole hammer 认领
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作者 HO Yinchol PAK Kumdol +3 位作者 PENG Jianming RI Jaemyong KIM Yongnam CHOE Cholho 《世界地质:英文版》 2021年第1期64-70,共7页
Air down-the-hole(DTH)hammer drilling has long been recognized to have the potential of drilling faster than conventional rotary drill,especially in some hard rocks such as granite,sandstone,limestone,dolomite,etc.wit... Air down-the-hole(DTH)hammer drilling has long been recognized to have the potential of drilling faster than conventional rotary drill,especially in some hard rocks such as granite,sandstone,limestone,dolomite,etc.with the same weight on bit(WOB)and rotations per minute(RPM).So,it has been widely used in many drilling fields including mineral resource exploration drilling,oil and gas drilling and geothermal drilling.In order to reduce drilling cost by selecting optimal drilling parameters,rate of penetration(ROP)should be estimated accurately and the effects of different factors on ROP should be analyzed.In this research,ANN model with several multi-layer perception back propagation(BP)networks for predicting ROP of air DTH hammer drilling was developed using controllable parameters such as impact energy,impact frequency,WOB,RPM and bit operating time for the formations with a certain drillability index of rock.Several BP neural networks with the different neurons in hidden layers were developed and compared for selecting optimal architecture of ANN.The effects of the drilling parameters such as impact energy,impacting frequency,WOB,RPM and bit operating time on the ROP of air DTH hammer drilling were investigated by trained ANN.From the analyses,the optimum range of drilling parameters for providing high ROP were determined and analyzed for a formation with a certain drillability index of rock.The methodology proposed in this study can be used in many mathematical problems for optimization of drilling process with air DTH hammer. 展开更多
关键词 ROP air DTH hammer drilling drilling parameter artificial neural network optimization
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