Optimization of Harvesting Return from Age-Structured Population

Synopsis Maximization of the net profit from harvesting in a one-species age-structured population is analyzed. One of the control functions is the age of harvested individuals. The constructed mathematical model is similar to vintage capital models used in economics for optimal capital replacement. The optimization technique developed by authors for the capital replacement is disseminated to the formulated problem. A qualitative analysis of the problem is provided and the interpretation of results is given. Such economic topics as a zero-investment period, optimal balanced growth, and turnpike properties are discussed.     

Optimal harvesting of a spatial renewable resource

In this paper we investigate the optimal harvesting of a renewable natural resource. While in most standard approaches the resource is located at a single point, we allow the resource to be distributed spatially. Consequently, an agent who exploits the resource has to travel from one location to another. For a fixed planning horizon, we investigate the speed and the path of harvesting chosen by the agent. We show that the agent adjusts this speed so as to visit each location only once, even in the absence of travelling cost. Since the agent does not return to any location for a second harvest, it is optimal to fully deplete the resource upon arrival. A similar type of bang–bang solution results when we drop the assumption of a constant harvesting rate: allowing for a variable harvesting rate, the agent chooses to fully exploit the resource either in the last or in the first travelling period. A society interested in conserving some of the resource thus has to take measures to limit the exploitative behaviour of the agent.     

Impact of contracts in high yielding varieties seed production on profits and yield: The case of Nepal

Nepal’s population continues to grow, but the agricultural sector’s performance remains almost stagnant. This has led to a decline in the per capita availability of food. Increasing agricultural productivity is the key to agricultural growth, and one strategy for increasing agricultural productivity is to use improved seeds. This study investigates the impact of contract farming (CF) in high yielding varieties (HYV) of paddy seed production on costs, yield, and profits of smallholder farms in Nepal. Using farm-level data and a non-parametric propensity score matching estimator, the study finds a significant positive impact of contract HYV seed farming on revenues, profits, and yield, and a significant negative impact on total costs of production. Additionally, very small farms (⩽0.43 ha) with CF in HYV paddy seeds tend to gain the most when it comes to yield per hectare. Our estimates reveal that the average smallholder household in Nepal engaged in CF with input conditions receives higher profits. However, farmers engaged in CF with output conditions tend to have higher yields but smaller profits. Finally, farmers engaged in CF in HYV paddy seeds with both input and output conditions have the highest yield gains and significantly higher profits.     

Fine-scale conservation planning outside of reserves: Cost-effective selection of retention patches at final harvest

Retaining forest patches at final harvest is a key conservation measure in boreal forests, but guidelines for how to increase its cost-effectiveness are lacking. In a study in boreal Sweden, we compared the cost-effectiveness of three different approaches a forest owner may use to select patches: selection based on the conservation value of patches alone, economic cost alone or both of them combined. We also compared the cost-effectiveness of six different common types of patches. Conservation value was measured as species richness of bryophytes and lichens and as structural characteristics of patches. Compared to the selection approach in which both conservation value and cost were used, cost-effectiveness was 5-14% lower when only conservation value was used, depending on how conservation value was measured. On the contrary, using only the economic cost decreased the cost-effectiveness by only 1-2%. Among the patch types, swamp forest areas and deciduous tree groups were cost-effective types to retain. However, the patch types were complementary in their species composition and all hosted unique species. We argue that, ideally, assessments of both conservation values and economic costs of retaining patches should be made prior to harvest to enable planners to make well-informed and cost-effective decisions.     

森林采伐管理面临的问题与对策探讨——基于江西省的调查

总结回顾了江西省十一五期间森林采伐管理历程,江西省坚持森林采伐限额不突破,确保林农合法权益得到落实,惩处乱砍滥伐行为,加强林业部门能力建设。通过对全省11个设区市及26个县的调查认为:现行森林采伐管理政策滞后,受采伐限额制约经营者林木处置权难以落实,林木采伐管理对象多监管难以到位。为此提出了做好今后5年森林采伐管理工作的对策措施。     

球形锐钛矿TiO_2合成及晶种对TiO_2形貌的影响

成功地采用水解法制备了球形锐钛矿TiO2,研究了空白实验(未引入晶种)、引入10 nm TiO2晶种及菌体晶种对锐钛矿TiO2形貌的影响。结果表明随着引入晶种的颗粒逐渐变大,合成的锐钛矿型TiO2颗粒也在逐渐增大:空白实验中TiO2的颗粒平均直径约为0.5μm,10 nm TiO2晶种中TiO2的颗粒平均直径约为0.6~0.7μm,菌体中TiO2的颗粒平均直径约为0.8~0.9μm;加入晶种的颗粒越大,合成的锐钛矿型TiO2颗粒粒度越均匀,球形越完整、团聚现象越少。     

不同培养时间对决明子芽菜生物学产量和黄酮含量的影响

本文使用控温豆芽机恒温20℃培养决明子芽菜,研究不同培养时间(5 d、7 d、9 d、11 d和13 d)对决明子芽菜生物学产量和黄酮含量的影响。结果表明,决明子芽菜的胚根长度、子叶长度、胚轴长度、单株鲜重和单株净菜重在培养7 d采收时均高于5 d采收,且差异显著,7 d后各指标数值虽呈增加趋势,但是差异不显著。黄酮含量随生长期增加不断增加,但在5 d、7 d、9 d和11 d之间差异不显著,13 d时采收黄酮含量最高为16.17 mg·g^-1,且与之前不同生长期差异显著。综合生物学产量、黄酮含量及时间成本决明子芽菜培养7 d即可以进行采收。     

甘肃省杂粮种业现状、存在问题与发展策略探讨

[目的]甘肃省农业气候资源丰富,适宜种植的杂粮作物品种较多,但其杂粮种业发展存在诸多与现代农业不相适应的问题,严重制约了杂粮产业的发展,因此急需提出针对甘肃省特色杂粮种业发展的策略。[方法]文章通过实地调研与文献分析,全面系统地分析了杂粮种业的特点和存在问题,并提出了甘肃省特色杂粮种业的发展策略。[结果]调研发现,甘肃省杂粮种子产值高达2亿元以上,其种子研发体系正在完善,商业化速度逐步加快,市场前景广阔。但仍存在杂粮种业缺乏长远规划,杂粮作物种子市场尚不健全,缺乏育繁推一体化的种子企业,种子信息网络及监管机制不健全;育种创新能力有待提高,品种布局不尽合理;杂粮作物品种保护意识不强,对知识产权重视程度不够等诸多问题。因此需要充分发挥甘肃省自然气候生态特点,挖掘优势特色杂粮作物,整合资源,构建杂粮作物育种创新技术体系;建立健全杂粮种子质量监控体制机制;培育现代杂粮种业龙头企业和现代化销售网络等发展策略。[结论]甘肃杂粮作物种业具有广阔的发展空间。     

森林采伐限额制度对林农经营行为的影响因素分析——基于浙江省农户调研数据的实证

通过农户问卷调查和关键信息人访谈等方法,了解浙江省景宁县木材采伐管理政策状况;运用计量经济方法分析影响农户木材采伐行为的主要因素。结果显示:受教育程度、办理采伐许可证的时间和费用、乡镇差异对木材采伐行为具有显著影响。因此,提出要加强农户营林培训力度、加大补贴力度、增加县级预留采伐限额指标等加快景宁县林业经济发展的建议。     

基于Nutch的物流信息平台网页资源定向采集系统

针对物流信息平台中信息资源采集系统建设的不足,提出建立基于Nutch的网页资源定向采集系统,并对中文分词、主题相关度分析、结果排序、正文解析等关键模块进行重点探讨。最后在一定条件下进行了实验,并分析了实验结果。