A context for recruitment correlations: why marine fisheries biologists should still look for them

In many cases when ecologists want to investigate a process, they often look for the best system on which to conduct the research, "best" meaning that the possibility of discovering mechanisms is optimized or made easier in some way. In fisheries we do it backwards. The species and system are given to us by economics, and we then fly in the face of the difficult circumstances to find mechanisms that are elusive anyway. These difficult circumstances constitute in some sense the first set of statistical problems. Using examples from the Northeast Pacific, I review the characteristics of cohort time series that make some species more tractable; propose a conscious process of conceptualization to assist in the formulation of clear, germane hypotheses; highlight the contrast between modeling in the sense of statistical fitting versus simulation models of processes; explore how the first round of models integrates with the second round of planning for new data collection at sea and in the lab; and, finally, propose how to judge success in terms of an operational approach.     

Evaluation of two N cycle models for the prediction of N mineralization from grassland soils in the UK

Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.     

刺槐单株生物量动态研究

本文依据420株刺槐生物量及23株树干解析资料,应用灰色Verhulst模型,对太行山坡地刺槐林单株干、枝、叶、根生物量动态进行了研究,分别建立了预测模型,预测了各器官生长的速生期和停止生长林龄,为实现刺槐林的多目标经营提供决策依据。     

设施园艺电驱移动平台轮毂电机设计及其磁-热耦合性能

针对设施园艺作业场景下电驱移动平台的低速大扭矩牵引作业需求,该研究设计了一种减速内转子轴向磁通轮毂电机,建立电机的电磁有限元模型并分析其电磁和损耗特性。考虑到绕组电阻率受温度变化影响,构建基于热网络法的轮毂电机磁-热耦合改进模型。与台架试验结果相比,基于改进模型获得的转矩预测值较传统模型的精度提高了5.33%,验证了模型的正确性。利用改进模型分析了温度和相电流对电机转矩特性的影响,仿真结果表明,输出转矩随电机温度增加而降低;在0～20 A,电机平均输出转矩与相电流呈线性关系。试验结果表明,轮毂电机功率随转速增加而增大,峰值功率可达4.59 kW,而转矩基本保持恒定;在转速450～900 r/min、转矩300～600 N·m时,电机效率高达93.2%。研究结果可为轴向磁通电机初步设计与多场耦合影响下电机性能分析提供思路。     

贝类养殖容量研究进展

近年来国内的贝类养殖产业出现大规模的病害事故,就其本质看是由于养殖区域生态环境平衡遭到破坏。本文从生态学角度出发,归纳国内外对于养殖容量概念的发展,比较各种概念的适用情况;对于养殖容量数学模型的建立和估算,介绍了目前国内外相对成熟,应用较广的模型,并且评价各种模型的优缺点。     

基于分形理论的汽油机富氧燃烧模型

阐述了湍流的分形特征,应用分形理论计算了湍流燃烧速度和质量燃烧率,分析了富氧燃烧时未燃混合气密度的计算方法。借助VB语言编制计算程序,进行了计算与实验对比分析。探讨了将分形理论应用到发动机富氧燃烧模型中的可行性。     

Model uncertainty in the ecosystem approach to fisheries

Fisheries scientists habitually consider uncertainty in parameter values, but often neglect uncertainty about model structure, an issue of increasing importance as ecosystem models are devised to support the move to an ecosystem approach to fisheries (EAF). This paper sets out pragmatic approaches with which to account for uncertainties in model structure and we review current ways of dealing with this issue in fisheries and other disciplines. All involve considering a set of alternative models representing different structural assumptions, but differ in how those models are used. The models can be asked to identify bounds on possible outcomes, find management actions that will perform adequately irrespective of the true model, find management actions that best achieve one or more objectives given weights assigned to each model, or formalize hypotheses for evaluation through experimentation. Data availability is likely to limit the use of approaches that involve weighting alternative models in an ecosystem setting, and the cost of experimentation is likely to limit its use. Practical implementation of an EAF should therefore be based on management approaches that acknowledge the uncertainty inherent in model predictions and are robust to it. Model results must be presented in ways that represent the risks and trade‐offs associated with alternative actions and the degree of uncertainty in predictions. This presentation should not disguise the fact that, in many cases, estimates of model uncertainty may be based on subjective criteria. The problem of model uncertainty is far from unique to fisheries, and a dialogue among fisheries modellers and modellers from other scientific communities will therefore be helpful.     

草地净第一性生产力估算的研究进展

草地净第一性生产力(NPP)是全球变化与陆地生态系统研究的核心内容之一。草地NPP的模拟方法从站点实测法、统计模型发展到了机理性的过程模型,NPP的站点实测数据为统计模型和过程模型模拟结果提供参考。统计模型通过NPP和温度、降雨等气候因子或者直接与遥感获得的植被指数建立统计关系计算NPP;过程模型从机理上对植物的生物生理过程进行模拟并能够对NPP的影响因子进行分析,主要过程包括了光合作用、生长和维持呼吸、蒸散、氮吸收和释放、光合物质分配与分解,和季相变化等。遥感过程模型通过遥感手段获得地表覆盖状况、植被冠层结构变量值(如LAI)、地表反射率、地表辐射温度及土壤水分状况等作为重要参数应用到模型中,改善了模拟结果的时空精度,成为当前草地生产力模型的主要研究方向。最后对遥感监测草地NPP研究中存在的问题进行了分析并提出了展望。     

基于GF-6/WFV卫星遥感的大田冬小麦叶片氮素含量估测

为对大田冬小麦叶片氮素含量（LNC）进行快速、准确及无损监测,通过在江苏省泰州泰兴市、盐城大丰区和南通如皋市布设冬小麦遥感监测大田试验,在获取试验样点冬小麦冠层红光波段反射率（RED_ref）、近红外波段反射率（NIR_ref）和计算的十个光谱指数（RVI、NDVI、DVI、SAVI、OSAVI、MSR、RDVI、EVI2、NLI和SVI）基础上,将12个遥感光谱指标与冬小麦LNC进行相关分析,选出与LNC相关性较好的作为模型输入变量,构建基于BP神经网络的冬小麦LNC估测模型, 并利用GF-6/WFV卫星遥感影像对县域冬小麦LNC的空间分布开展监测。结果表明,12个遥感光谱指标与冬小麦LNC之间存在不同程度的相关性,其中NDVI、RVI、MSR、OSAVI和NLI与冬小麦LNC的相关性较好（相关系数不低于0.65）。将优选的5个遥感光谱指标作为模型输入变量,构建基于BP神经网络的冬小麦LNC估测模型（LNC-BPEM）,模型的估测精度r²=0.866,RMSE=0.246%,ARE=12.9%。将冬小麦LNC-BPEM估测模型和GF-6/WFV影像结合对县域冬小麦LNC的空间信息监测,获得了如皋县域冬小麦LNC的空间分布特征,该区域冬小麦LNC范围在0.9%~2.0%（长势正常）的种植面积为29 693.3 hm²,占冬小麦总种植面积的74%。这说明利用GF-6/WFV卫星的多个遥感光谱指标与神经网络结合建模可有效估测县域大田冬小麦叶片氮素含量。     

油管式传感器车辆行驶称重系统算法研究

在分析油管式车辆动态称重系统工作原理和特性的基础上,建立了相应的称重系统称量数学模型;利用非线性最小二乘优化算法获得最小平方误差意义上的静载参数估计,同时根据前后油管信号的相关性实现了车速的精确测量和计算;并通过实车试验,验证该算法是可行的,且达到了较好的精度,为车辆超载检测提供了一种经济有效的手段。