设施蔬菜发展制约因素与对策建议——基于武汉市新建设施蔬菜基地的调研

为确保蔬菜均衡供应,平抑物价,武汉市2013年新建成七万亩集中连片的设施蔬菜基地。基于武汉市新建七万亩设施蔬菜基地的调研结果表明,目前设施蔬菜发展的制约因素主要表现为:基础设施建设滞后、基地管理技术人员缺乏、用工难、投入成本较高、风险大、比较效益低、病虫害及自然灾害严重、技术推广不到位、区域化特色不明显、销售渠道不畅等,设施蔬菜的发展仍然需要政府及农业主管部门的通力合作。     

Groundnut (Arachis hypogaea L.) improvement in sub-Saharan Africa: a review

Groundnut (Arachis hypogaea L.) is a multi-purpose legume crop widely cultivated in sub-Saharan Africa (SSA). However, yield levels of the crop has remained relatively low in SSA owing to a range of biotic, abiotic and socio-economic constraints. A dedicated groundnut improvement programme integrating new tools and methodologies to breed varieties suitable for current and emerging agro-ecologies and market needs is essential for enhanced and sustainable groundnut production in SSA. The objective of this review is to highlight breeding progress, opportunities and challenges on groundnut improvement with regard to cultivar development and deployment in SSA in order to guide future improvement of the crop. The review analysed the role of new tools in breeding such as, high-throughput and automated phenotyping techniques, rapid generation advancement, single seed descent approach, marker-assisted selection, genomic selection, next-generation sequencing, genetic engineering and genome editing for accelerated breeding and cultivar development of groundnut.     

乡村振兴背景下农产品直播营销模式及其优化路径研究

【目的】研究农产品直播营销模式及其优化路径,为农产品直播营销的应用和发展提供理论依据。【方法】从农产品直播营销模式的类型开始着手,采用文献研究法对农产品直播营销模式现状的相关资料进行整理分析。【结果】制约农产品直播营销可持续发展的主要因素为农产品供应基础服务设施不健全、农产品缺少品牌经营、农产品直播营销人才匮乏、农产品直播内容缺乏亮点四个方面。【结论】从完善农产品供应基础服务设施、打造优质农产品品牌、加大人才培养与专业团队建设、优化直播营销内容四个方面提出针对性优化策略,使农产品线上直播营销成为推进乡村振兴战略实施高效、有力的重要手段,对推动传统农业转型升级,促进农村现代化建设以及实施乡村振兴战略具有重要意义。     

Vacco变分下的Noether对称性

利用条件变分法研究有限维约束力学系统在Ｖａｃｏ变分下的对称性问题．当系统沿Ｖａｃｏ方程的解曲线运动时,系统的Ｎｏｅｔｈｅｒ对称性给出一种守恒量,它在一定条件下过渡到经典守恒量．     

Tropical spiny lobster (Panulirus ornatus) farming in Vietnam – bioeconomics and perceived constraints to development

This paper presents bioeconomic data on lobster farming in Vietnam, and perceived constraints to the development of the industry. The farms were found to be profitable, with an average benefit cost ratio of 1.44 and an average net revenue of 262 million VND year^?1 (or just under US$15 000 year^?1). Investment in the enterprise is high compared with other enterprises in the region. However, disease has the potential to devastate lobster crops and there is little information available to lobster farmers about disease prevention and management. Hence, the lobster enterprise is a high‐risk high‐return industry. The predominant perceived constraints to the development of lobster operations include water quality and temperature issues, insufficient access to credit, good‐quality affordable feed and accurate information about technology improvements in lobster farming. It seems that improving the livelihood of lobster farmers in Vietnam is dependent on reducing their dependence on wild stocks for seed and feed, improving access to credit and improving technical and market information flows. Such improvements are likely to lead to higher profitability, given high export demand and hence sustained high prices for their lobster product.     

Cluster analysis of linear model coefficients under contiguity constraints for identifying spatial and temporal fishing effort patterns

For fisheries management purposes, it is essential to take into account spatial and seasonal characteristics of fishing activities to allow a reliable assessment of fishing impact on resource. This paper presents a novel technique for describing spatial and temporal patterns in fishing effort. The spatial and seasonal fishing activity patterns of the French trawler fleet in the Celtic Sea during the period 1991–1998 were analysed by modelling fishing effort (fishing time) with generalised linear models. The linear model for fishing effort included fixed effects for both spatial (statistical rectangles) and temporal units (months). In addition, spatial correlations in any given month were modelled by an exponentially decreasing function. Temporal correlations were included using the previous month's fishing effort for a given spatial unit as predictor. A method based on cluster analysis of estimated model coefficients of spatial or temporal fixed effects is proposed for identifying groups of similar spatial and temporal units. A contiguity constraint is imposed in the clustering algorithm, ensuring that only neighbouring spatial units or consecutive temporal units are grouped. The cluster analysis identified 22 spatial and 9 temporal groups. Winter and spring months stood out as being more variable than the remaining months. Spatial groups were of varying size, and generally larger offshore. The proposed method is generic and could for example be used to analyse temporal and spatial patterns in catch or catch rate data.     

认知语境的构建

本文在关联理论的框架下讨论发话人怎在认知环境中选择并延伸认知语境。     

计算机组装与维护课程实训平台的建设

计算机组装与维护课程在计算机维护专业的重要性决定了该课程的实践教学的高要求。作为该课程的实践教学环节之一的实训过程,在充分弥补了原有实验教学不足的同时,大大提高了学生的技术水平并在一定程度上促进了就业工作的进行。所以,构建起完整、有效的实训平台是为学校、企业、学生的搭建的共赢平台。在这里,我们就该课程的定位、大纲的规划制定、实训平台的构建思路进行了实践性详细的讨论。     

农业女性化促进了农业机械服务外包吗?

从农业机械服务外包现象入手,基于相关理论分析,使用中国劳动力动态调查(CLDS)2016年数据,采用普通最小二乘(OLS)、两阶段最小二乘法(2SLS)、广义矩估计(GMM)等计量方法,分析农业女性化对农业机械服务外包的影响及其影响机制.结果表明:(1)农业女性化程度加深会明显促进农户选择农业机械服务外包.(2)当户主...     

Descending Dimension Algorithm for Convex Nonlinear Programming Problem with Equality Constraints

This paper deals with the nonlinear system of equations algorithm for convex nonlinear programming problems with equality constraints.We use the optimatily conditions for programming problem with equality constraints and then estabish a nonlinear system of equations.Finally we solve these to get optimal solution of nonlinear programming problems.