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.     

Temperature-dependent stock-recruitment model for walleye pollock (Theragra chalcogramma) around northern Japan

Changes in fish year‐class strength have been attributed to year‐to‐year variability in environmental conditions and spawning stock biomass (SSB). In particular, sea temperature has been shown to be linked to fish recruitment. In the present study, I examined the relationship between sea surface temperature (SST), SSB and recruitment for two stocks of walleye pollock (Theragra chalcogramma) around northern Japan [Japanese Pacific stock (JPS) and northern Japan Sea stock (JSS)] using a temperature‐dependent stock‐recruitment model (TDSRM). The recruitment fluctuation of JPS was successfully reproduced by the TDSRM with February and April SSTs, and February SST was a better environmental predictor than April SST. In addition, the JPS recruitment was positively related to February SST and negatively to April SST. The JSS recruitment modeled by the TDSRM incorporating February SST was also consistent with the observation, whereas the relationship between recruitment and February SST was negative, that is the opposite trend to JPS. These findings suggest that SST in February is important as a predictor of recruitment for both stocks, and that higher and lower SSTs in February act favorably on the recruitment of JPS and JSS respectively. Furthermore, Ricker‐type TDSRM was not selected for either of the stocks, suggesting that the strong density‐dependent effect as in the Ricker model does not exist for JPS and JSS. I formulate hypotheses to explain the links between SST and recruitment, and note that these relationships should be considered in any future attempts to understand the recruitment dynamics of JPS and JSS.     

全子叶生物活性豆腐凝胶特性的研究

通过因子筛选实验,确定了接种量、微生物转谷氨酰胺酶(MTG)用量和水豆比是影响全子叶生物活性豆腐凝胶特性的关键因子。在此基础上,采用响应曲面法(Response SurfaceMethodology,RSM)分别建立了豆腐硬度和持水率的二次多项数学模型,验证了模型的有效性并探讨了上述3个因子的交互作用。从产品成本和凝胶特性综合考虑,选择出最佳配比,即乳酸菌接种量为105cfu/mL,MTG用量为347 U/L,水豆比为8.5,其硬度和持水率实测值分别为44.8g和89.2%,可生产出富含乳酸菌和几乎全部大豆营养的健康豆腐。     

细河污染物在地下水中运移规律的模拟研究

为了研究河水中污染物在地下水中运移规律,分析了细河污染对地下水的影响,根据细河水文地质条件建立了污染物在地下水中运移的2区动力学模型,对河水中氨氮、总硬度等组分在地下水中的运移规律进行了模拟研究。结果表明,随运移距离的增加,污染物浓度逐渐降低;地下含水层对河流中部分污染物具有较强的去除能力,如对氨氮、耗氧量的去除率可达98%以上;水分蒸发对部分污染物具有浓缩作用,地下水中总硬度等组分浓度逐渐升高,并高于污染源浓度。     

农村小额信贷的国际考察与借鉴

该文介绍了国际农村小额信贷的多种模式及成功经验;分析了我国现行小额信贷的现状,探讨了如何因地制宜,通过制度供给的方式,推进我国小额信贷发展的建议。     

不同生态区玉米自交系苞叶与穗轴同步发育特性研究

2022-2023年在河南和海南以玉米自交系驻85、驻136、ZM3358为试验材料,研究自交系苞叶与穗轴同步发育特性。结果表明,河南苞叶驻85第1～7 d伸长迅速,速增期与ZM3358一致,低于驻136;穗轴,驻85第1～11 d急剧伸长。海南苞叶ZM3358伸长速增期为13 d,比驻85、驻136延长2～3 d;穗轴ZM3358伸长渐增期最长为19 d,显著高于驻85、驻136。河南苞叶驻85宽度持续变宽,驻136苞叶宽度第11 d开始增幅变缓,ZM3358苞叶宽度速增期最短为7 d;穗轴粗度驻136第1～17 d持续变粗,第19 d稍有下降。海南ZM3358苞叶宽度速增期为13 d,驻85、驻136苞叶宽度速增期均为9 d;驻85穗轴粗度速增期最长为19 d,苞叶与穗轴可保持同步发育特性。     

含运动副间隙汽车摆振系统非线性动力学建模

机构运动副间隙对系统动力学响应有重要影响,有必要将转向机构运动副间隙引入汽车摆振系统动力学分析。基于非线性系统动力学,应用拉格朗日方程建立了考虑转向机构运动副间隙的六自由度摆振动力学模型。通过仿真分析讨论了车速对前轮摆振的影响,结果表明在特定车速范围内前轮会发生自激摆振,这与实际情况吻合,验证了模型的正确性。     

用于车辆紧急制动仿真的动态轮胎模型

提出一种可用于车辆紧急制动仿真的动态轮胎模型——LuGre轮胎模型。该动态模型不仅具有与经典稳态模型（如魔术公式）相似的稳态特性,可以方便地通过试验数据进行参数拟合和在线整定,而且能够精确捕捉汽车紧急制动过程中的瞬态特性,又由于采用微分方程形式来描述,更有利于开发高性能的电子制动控制系统来提高汽车的行驶安全性。得到了LuGre轮胎模型的基本特性,并分析了其在车辆紧急制动仿真中的稳态特性和动态特性。     

基于混沌的超声物位检测系统的研究

物位检测技术在现代化工业控制中占有重要地位。由于现场具体的安装环境不同,被测介质种类和状态不同,情况异常复杂,因此必须根据具体的现场工况,合理地选择物位检测的方法和产品。为此,提出了一种基于混沌理论的超声波物位检测系统,并论述了信号处理方法,从而能准确识别噪声干扰与超声波回波信号,提高了物位检测精度。     

内燃机燃烧模型的发展现状

利用CFD技术对内燃机燃烧过程进行数值模拟已成为内燃机研究的重要工具。选用恰当的燃烧模型对准确预测内燃机燃烧过程具有重要意义。内燃机CFD燃烧模型主要针对自燃、预混燃烧和非预混燃烧3种燃烧模式,其中有些模型可以同时模拟2种模式或3种模式。内燃机新的燃烧系统的不断出现促进了燃烧模型的发展。本文以STAR—CD和FIRE软件为出发点,介绍了内燃机燃烧模型的发展现状。