考虑农产品绿色度的农业生产经营主体治污策略选择研究     

王梦丹  杜建国  许玲燕 《科技管理研究》2020,(16)

在消费者具有绿色选择偏好和政府提供绿色补贴情况下,考虑农产品绿色度对农业生产经营效益的影响,建立农业生产经营主体在非合作与合作情形下的农业面源污染治理微分博弈模型,基于HJB方程求得博弈均衡解。研究发现：无论是非合作还是协同合作情形,消费者的绿色偏好和政府的绿色补贴越高,主体产生的污染量越少、治污努力程度越高;政府补贴激励作用在非合作情形下失效,但在合作情形时效果显著;从非合作情形到合作情形,当政府补贴系数一定时,农业生产经营主体的治污努力及个体收益和总收益、农产品绿色度均实现了帕累托改进  相似文献   

Sexual dimorphism in bone–muscle relationship in young adults     

Vera Zymbal  Kathleen F. Janz  Fátima Baptista 《Journal of sports sciences》2017,35(24):2433-2438

The purpose of this study was to analyse associations between lean soft tissue (LST), a surrogate of skeletal muscle mass and key fracture-related geometric characteristics of the proximal femur. Moreover, we examined the role that muscle played on the proximal femur geometry in response to physical activity (PA). Participants were 83 young adults. Leg LST (exposure) was assessed by dual energy X-ray absorptiometry (DXA). Proximal femur geometry was derived from a left hip DXA scan. Geometric variables (outcomes) included the femoral neck axis length (FNAL), the femoral neck width (FNW), the neck–shaft angle and FNW|FNAL (an index of robustness). PA was evaluated by accelerometry. Linear regression was used to analyse relationships. Additional exposure variables included body height and mass. In males, leg LST explained 17.4% of variation in FNAL (P < 0.001) and 15% in FNW (P = 0.015). In females, it explained 8.8% of the variance in FNAL (P = 0.020). Associations remained significant in males, but not in females, when vigorous PA was added to the models. These results suggest that public health approaches to promote PA may be particularly important in females since vigorous PA seems to convey advantages in femur geometry and consequently in bone strength.  相似文献   

Evaluating the Comparability of Paper‐ and Computer‐Based Science Tests Across Sex and SES Subgroups     

Jennifer Randall  Stephen Sireci  Xueming Li  Leah Kaira 《Educational Measurement》2012,31(4):2-12

As access and reliance on technology continue to increase, so does the use of computerized testing for admissions, licensure/certification, and accountability exams. Nonetheless, full computer‐based test (CBT) implementation can be difficult due to limited resources. As a result, some testing programs offer both CBT and paper‐based test (PBT) administration formats. In such situations, evidence that scores obtained from different formats are comparable must be gathered. In this study, we illustrate how contemporary statistical methods can be used to provide evidence regarding the comparability of CBT and PBT scores at the total test score and item levels. Specifically, we looked at the invariance of test structure and item functioning across test administration mode across subgroups of students defined by SES and sex. Multiple replications of both confirmatory factor analysis and Rasch differential item functioning analyses were used to assess invariance at the factorial and item levels. Results revealed a unidimensional construct with moderate statistical support for strong factorial‐level invariance across SES subgroups, and moderate support of invariance across sex. Issues involved in applying these analyses to future evaluations of the comparability of scores from different versions of a test are discussed.  相似文献   

"三线共点"的常用证明方法     

王贵军 《天水师范学院学报》2002,22(2):56-58

从仿射几何学与射影几何学的基本方法出发,简述了"三线共点"问题的一些基本的证明方法.  相似文献   

General and Specific Factors in Reading Comprehension     

A. Sterl Artley 《Journal of Experimental Education》2013,81(3):181-186

One explanation for why many students routinely choose to do their homework with a radio or TV operating is that this distraction facilitates studying. To investigate the validity of this explanation, the authors carried out two experiments with sixth-grade students who worked on two difficulty levels of individualized mathematics assignments (N = 12) and reading assignments (N = 9) under three distraction conditions: quiet; self-selected, self-regulated radio; and self-selected, self-regulated TV. The data yielded no evidence of sizable distractor effects on students' time spent studying, computational accuracy, reading comprehension, or reading rate. These results generally are consistent with the theoretical conceptualization of attention as flexible and adaptable.  相似文献   

差异统一中的质量互变与否定之否定     

刘国章 《贵阳学院学报(社会科学版)》2004,(4)

随着中国现代化的进程 ,以及经济全球化的不断推进 ,使人们越加感到要理解和把握现代社会 ,具备唯物辩证的认识方法和思维方法已经成为实现这一目的必要条件。然而 ,现有教科书关于辩证法的论述却不能准确反映现实世界的存在状态。所以 ,从现实世界差异统一的存在状态出发 ,进一步深化对唯物辩证法及其规律的思考就显得迫切而重要 ,其现实意义也是显而易见的。  相似文献   

一阶中立型微分方程的振动性     

刘玉记 《怀化学院学报》2000,(2)

研究变系数中立型泛函微分方程的解的振动性问题 分别获得了保证两类中立型方程的所有解振动的充分条件 ,改进了已有的部分结果 ,而且在某种程度上 ,我们的结果是不可改进的。  相似文献   

一阶常微分方程比较定理的高阶推广     

梁淼 《苏州市职业大学学报》2007,18(4):87-89

比较定理是研究常微分方程解的属性的基本工具。但对于高阶的情况,现有的结论只给出了类似把解作为向量范数之间的比较。我们将一阶常微分方程的比较定理推广到高阶,从而给出了高阶常微分方程的解自身的大小的比较定理。  相似文献   

微分在微积分课程中的作用     

罗贤新 《贵阳金筑大学学报》2007,(2)

微分是微积分中的一个基本的重要概念,它是微分学转向积分学的枢纽。其概念和运算在微积分课程中有广泛的应用。如果能从多方面了解这些应用,就会进一步明确微分教学的目的性和重要性,并可使有关内容的教学取得更好的效果。将微分与导数、不定积分、定积分的关系作一定探讨,用以体现微分在微积分课程中的作用。  相似文献   

一阶泛函微分方程变号周期解的存在性     

康淑瑰 《雁北师范学院学报》2014,(1):1-3,7

利用不动点理论，讨论如下方程y（t）=-a（t）y（t）＋f（t,y（t-τ（t）））变号周期解的存在性，给出方程三个非零变号周期解的存在性，其中一个是正的，一个是负的，另一个是变号的。  相似文献