中国生猪耗粮系数时空演变特征

当代中国,生猪饲料粮的生产与消费已经逐渐成为影响我国粮食安全保障的重要问题。耗粮系数是合理测算饲料粮需求量的核心,厘清其时空演变特征对准确测算饲料粮数量具有重要意义。通过着重测算2000—2018年中国不同规模饲养生猪耗粮系数,探讨其时空演变特征及可能原因,得到以下主要结论：（1）近年来我国生猪耗粮系数呈现出明显的上升趋势,由2000年的2.39上升至2018年的2.76,年均增长0.023。（2）不同规模饲养生猪耗粮系数的差距逐渐缩小,主要受到饲养过程中使用的精饲料占比变化趋同的影响。（3）大规模饲养生猪的粮食转化效率和时间效率均高于其他规模。（4）散养生猪的耗粮系数在空间上呈现“南北高,中部低”,其他规模则呈现“北高南低,中部高东西低”的格局。从提高粮食利用效率的角度,我国生猪养殖宜继续推动大规模饲养。     

云南喀斯特山区国土空间优化分区与管控

国土空间的协调发展是区域可持续发展的前提,如何优化国土空间结构并构建合理的管控模式成为亟需解决的重要问题之一。以云南喀斯特典型山区文山市为例,探讨基于"双评价"的国土空间优化方法及冲突区的修正规则,对喀斯特山区国土空间进行优化分区,并提出国土空间分区及石漠化分区的管控模式。研究发现:(1)云南喀斯特山区国土空间优化后可划分为城镇开发边界区、城镇预留区、永久基本农田区、一般农业区、生态保护红线区和一般生态区六种类型,其中,生态保护红线区面积最大,城镇开发边界区面积最小;(2)城镇开发边界区和城镇预留区主要分布于东部和东南部,永久基本农田区和一般农业区主要分布于北部和南部,一般生态区主要分布于西北部和西南部,生态保护红线区主要分布于西部、南部、东部和东北部,其中东部和东北部主要为石漠化区;(3)从各国土空间类型的发展潜力和趋势对国土空间分区提出了管控措施和模式;从轻度石漠化区、中度石漠化区以及重度石漠化区角度对城镇、农业和生态三类空间,提出了石漠化区开发和保护的路径和方法。研究结果可为云南喀斯特山区国土空间的合理发展和石漠化的治理提供决策支持,研究方法和思路为国土空间优化和管控提供参考。     

大气臭氧浓度升高对丛枝菌根(AM)及其功能的影响

通过模拟大气O₃浓度(0.02μL·L^-1、0.1μL·L^-1和0.2μL·L^-1)升高,观察其对丛枝菌根(AM)及功能的影响.结果表明,大气O₃浓度升高对菌根侵染率影响较小,但对孢子和外生菌丝影响显著,高浓度O₃时的孢子数比自然O₃浓度时增加1倍,低、高浓度O₃分别使AM外生菌丝量比自然浓度时下降48.7%和85.6%.随着O相似文献   

超级钢闪光对焊电热耦合过程温度场分布的有限元分析

为研究超级钢闪光对焊闪光阶段焊件的温度场分布 ,建立了轴对称有限元模型。运用单元死活技术解决闪光时液体过梁爆破引起物质烧损的模拟问题 ,提出了闪光焊过程中电热耦合作用的模拟方法。考虑单元死活的有限元分析结果与试验结果更加吻合 ,为选择和优化闪光焊焊接参数以及为闪光焊过程顶锻阶段的热力耦合过程的模拟提供了有效的分析手段     

Optimization of C/N ratio for preparation of protein-rich and multi-enzymes feed thallus through synergic fermentation of mixed distillers'grains

A new procedure of determining optimal C/N (the rate of carbon source to nitrogen source) of mixed distillers' grains for combined bacteria synergic fermentation is established. At the same time an improved method evaluating bacteria growth, called method of dry cell weighing by filtering is developed. For each combination of C and N , their initial and residual contents before and after fermentation respectively are determined. Then followed the calculation of utilization of C and N sources by the compound bacteria. The optimal C/N is finally located from among the utilization of C and N of several combinations and the weight of produced mass of oven-dried thallus The conditions of fermentation are: inoculum size 10%, temperature 30.0℃, rotational speed 170 r/min, shake culture time 48h. The best results obtained from orthogonal experiments are: maximum mass of oven dried thallus is 14.693g in a liter liquid medium, maximum utilization rate of carbon source is 98.13% and maximum utilization rate of nitrogen is 78.14%. Optimal C/N is 5.1.     

Kinetic and thermodynamic studies on partitioning of polychlorinated biphenyls (PCBs) between aqueous solution and modeled individual soil particle grain sizes

The significance of soil mineral properties and secondary environmental conditions such as pH, temperature, ionic strength and time in the partitioning of eight selected polychlorinated biphenyl(PCB) congeners between aqueous solution and soil particles with different grain sizes was studied. The mineral properties of a model soil sample were determined, and Brunauer–Emmett–Teller(BET) adsorption–desorption isotherms were employed to observe the surface characteristics of the individual modeled soil particles.Batch adsorption experiments were conducted to determine the sorption of PCBs onto soil particles of different sizes. The results revealed that the sorption of PCB congeners onto the soil was dependent on the amount of soil organic matter, surface area, and pore size distribution of the various individual soil particles. Low pH favored the sorption of PCBs,with maximum sorption occurring between pH 6.5 and 7.5 with an equilibration period of 8 hr.Changes in the ionic strength were found to be less significant. Low temperature favored the sorption of PCBs onto the soil compared to high temperatures. Thermodynamic studies showed that the partition coefficient(K_d) decreased with increasing temperature, and negative and low values of ΔH° indicated an exothermic physisorption process. The data generated is critical and will help in further understanding remediation and cleanup strategies for polluted water.     

基于随机森林的耕地利用效率测度模型构建及其应用

构建合适的量化分析模型是科学把握耕地利用状况及利用效率的基础性工作,可为制定合理有效的耕地资源管控政策,实现耕地利用与生态环境的协调发展提供决策依据。为了更准确地反映耕地利用系统的复杂性、动态性及差异性等特征,鉴于随机森林的基本思想,运用随机抽样Bootstrap法在合理构建分类树的基础上,构造了耕地利用效率测度的RF模型,进而以中国粮食主产区172个城市为例训练该模型并将其运用至2003-2015年的耕地利用效率测度中,同时将BP神经网络和熵权法作为对比验证其一致性、代表性和优越性。结果表明：（1）耕地利用效率测度的RF模型不受量纲限制,运行所需参数少,运算过程简化,能够较为精确地模拟各评价指标间的复杂联系,科学量化各评价指标对耕地利用效率的贡献。（2）对同一空间单元的效率值而言,RF>BPNN>EW,RF与BPNN所得效率值的总体分布格局相似,且均与EW的测度结果存在较大差异。（3）从评价结果与现实的匹配度和精度表征参数来看,RF的测度结果与自然和社会经济发展等客观事实更相符,具有较高的适用性与可靠性。同时,与其余两种常用模型相比,RF能够降低计算复杂度,提高训练效率,其测度结果的相关系数R为0.8685,M_RPD为2.3533,且具有最小M_MSE0.0174和M_MAE0.0211,更适用于复杂非线性特征的耕地利用效率研究。     

基于市域尺度的中国化肥施用与粮食产量的时空耦合关系

化肥施用是一把双刃剑,在促进粮食产量增加、保障粮食安全的同时,导致了生态环境退化,当前亟需辨明化肥施用与粮食生产之间的时空耦合关系,以便为维护粮食安全与生态安全提供有效的对策。以中国336个地级行政区为研究单元,分析2005-2015年中国粮食产量与化肥施用量的时空格局变化特征、化肥施用量与粮食产量的时空耦合关系及其动态变化过程。研究发现：（1）2005-2015年中国化肥施用量与粮食产量均呈上升趋势,化肥施用量的区内差异呈“粮食主产区—产销平衡区—粮食主销区”递减态势;而粮食产量的区域差异总体趋于增大,且呈“粮食主产区—产销平衡区—粮食主销区”递增态势。（2）化肥施用量增幅大致呈“东—中—西”阶梯式递增的趋势,而粮食产量增幅呈明显的南北分异特征。（3）从空间分布来看,胡焕庸线以东地区以“双高区”为主,胡焕庸线以西地区以“双低区”为主,且“低效施肥区”收缩,“他因素影响区”扩张。（4）期间,粮肥耦合关系以“双增型”为主,其他类型为辅,粮肥耦合关系主要向“双增型”与“他因素影响型”转变。     

Control of TAME reactive distillation using Non-Dominated Sorting Genetic Algorithm-II

The control system performs poor in characteristics and even it becomes unstable, if improper values of the controller tuning constants are used. So it becomes necessary to tune the controller parameters to achieve good control performance with the proper choice of tuning constants. Many control problems involve simultaneous optimization of multiple variables that competing with each other. In this paper, the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) has been successfully applied to optimization of dynamic state of t-amyl-methyl-ether (TAME) reactive distillation process. This paper presents the tuning of Proportional-Integral-Derivative (PID) controllers by minimizing of two objective functions (overshoot and Integral of Absolute Error (IAE)) through the NSGA-II. Results show that genetic algorithm is more suitable method for optimal control of the TAME reactive distillation columns than traditional methods such as Tyreus-Luyben.     

Empirical analysis on the influence of the Shaanxi fruit industry on regional food security

As part of its development policy to relieve rural poverty in west China, the Chinese government has introduced measures such as agricultural tax exemptions, agricultural subsidies, and scientific, technological and restructuring improvements to agriculture. Following these actions, farmers’ incomes have increased greatly and the economy in poor areas of west China has seen rapid improvements. However, agricultural restructuring, infrastructure construction and ecological restoration projects have reduced the area of land under arable farming, restricting opportunities for increasing total grain yield. Regional food security is therefore threatened and an imbalance between economic development and food security is created. Shaanxi is a representative province in west China where agricultural restructuring has resulted in large areas of arable land being converted into orchards that produce higher economic returns. This study randomly surveyed 1430 farm households in three counties in the apple-producing region of Shaanxi Province (Luochuan, Changwu and Baishui). The standard of living and household income of farmers in the fruit production areas were higher than in grain-producing areas, thus discouraging grain production. Land under agriculture in the counties studied comprised 59% orchards and 39% arable, with 2% under other uses. Per capita, 204.3 kg of grain was produced, 51% of that required for self-sufficiency. Other staple foods produced amounted to only 13.9% of that needed for self-sufficiency. As a result, nearly half of the grain needed by the community was purchased from outside, resulting in very poor regional food security. Clearly, fruit production in this region seriously affects regional food security. Coordination of relationships between rural economic development and regional food security is key for sustainable development of the regional agriculture and economy of west China.