Can catch share fisheries better track management targets?

Fisheries management based on catch shares – divisions of annual fleet‐wide quotas among individuals or groups – has been strongly supported for their economic benefits, but biological consequences have not been rigorously quantified. We used a global meta‐analysis of 345 stocks to assess whether fisheries under catch shares were more likely to track management targets set for sustainable harvest than fisheries managed only by fleet‐wide quota caps or effort controls. We examined three ratios: catch‐to‐quota, current exploitation rate to target exploitation rate and current biomass to target biomass. For each, we calculated the mean response, variation around the target and the frequency of undesirable outcomes with respect to these targets. Regional effects were stronger than any other explanatory variable we examined. After accounting for region, we found the effects of catch shares primarily on catch‐to‐quota ratios: these ratios were less variable over time than in other fisheries. Over‐exploitation occurred in only 9% of stocks under catch shares compared to 13% of stocks under fleet‐wide quota caps. Additionally, over‐exploitation occurred in 41% of stocks under effort controls, suggesting a substantial benefit of quota caps alone. In contrast, there was no evidence for a response in the biomass of exploited populations because of either fleet‐wide quota caps or individual catch shares. Thus, for many fisheries, management controls improve under catch shares in terms of reduced variation in catch around quota targets, but ecological benefits in terms of increased biomass may not be realized by catch shares alone.     

基于邻域直方图的玉米田绿色植物图像分割方法

为了准确分割绿色植物与土壤背景,克服田间环境的复杂性,比如植物阴影、残渣的存在和光照强度变化等外界因素带来的影响,采用图像处理和支持向量机方法,以超绿特征(2G-R-B)灰度图像为研究对象,以像素点邻域组成的灰度直方图特征作为输入特征向量,通过试验选出最佳训练参数和最优邻域窗口模型。实验表明,该方法适应不同光照强度,并且可以减小噪声、植物阴影和残渣对图像分割带来的影响,得到完整的分割图像。     

犬血型与安全输血研究进展

综述了犬血型系统、血型鉴定、交叉配血、供血犬选择以及输血反应等与安全输血相关的各方面的研究进展,系统探讨了临床上如何对犬进行安全、有效输血以及当前存在问题。     

精准配比料药一体化生猪饲喂器设计与试验

针对向生猪饲料中添加颗粒药物时药物分布不均导致的药物利用率低的问题,设计了一种精准配比料药一体化饲喂器,以计量式斜槽轮为排料装置,并对排料斜槽轮、排药斜槽轮、饲料分流刀等关键部件进行了设计和仿真,实现给定质量比范围内的实时精准加药。用离散元分析软件EDEM进行排料稳定性分析,得出转速为40～60 r/min时排料槽轮的稳定性较好,根据(100～250)∶1的料药质量配比确定排药槽轮转速为10～20 r/min。用力链分析饲料颗粒和药物颗粒在斜槽轮排料装置工作时的受力情况,可知饲料颗粒和药物颗粒所受的外力小于破碎力,两种颗粒在整个运动过程中所受的外力不会造成颗粒破碎。通过样机试验测得在给定转速范围内,可实现的料药质量配比范围为(93.4～251.8)∶1,给定的料药质量配比在此范围内;进行料药配比混合台架试验,试验结果表明精准配比料药一体化饲喂器能实现向饲料中实时精准加药,解决了小粒径小流量的药物颗粒在大粒径大流量的饲料颗粒中分布不均匀问题。     

农村学生高等教育选择的个体异质性影响及长期收入回报研究

高等教育进入大众化阶段,但高校中农村学生比例偏低。利用CFPS 2012年的调查数据,采用Logit回归方法,从个体特征、家庭特征和区位特征三个维度系统分析个体异质性对农村学生高等教育选择的影响,进而在控制个体差异的基础上,采用PSM方法测度农村高等教育的收入回报,设定不同的年龄分组,研究高等教育的长期收入回报,并分析东中西部农村高等教育的长期收入回报是否存在区域上的差异。结果表明,健康状况、医疗保险、智力、理解能力、外貌、父母学历和家庭地位等特征显著影响农村学生是否接受高等教育的选择;接受高等教育的农村个人收入要高于不接受高等教育时的收入;从长期来看,接受高等教育和没有接受高等教育的农村个人之间的收入差异随着年龄的增长呈现不断上升的趋势;西部地区高等教育对农村个人收入的长期影响显现得最早,中部地区次之,东部地区最晚。在此基础上,为缩小教育差距、实现高等教育公平,提出教育资源投入向农村落后地区倾斜、高校针对农村贫困学生制定合理的教育补助规模、农村家庭转变传统封闭的教育观念鼓励子女接受高等教育的政策建议。     

基于图像受噪程度的改进模糊加权均值滤波

根据高斯噪声密度大、噪声强度的波动范围宽,其污染图像不仅每一个像素灰度级都会受影响,而且即使是同一灰度级受污染的程度也会不同的特点和传统的图像模糊滤波算法在图像细节保护方面上的不足,提出基于图像受噪程度的改进模糊加权均值滤波算法,该算法根据图像各像素点的受噪程度,得到首次滤波图像和原图像估计直方图,根据该直方图确定模糊隶属度函数,然后对首次滤波图像中灰度小于25的像素点进行模糊加权均值滤波,该算法在不需要期望图像和高斯噪声方差的情况下能有效地去除噪声,同时能够很好地保护图像细节信息。     

隐马尔可夫模型下基于SIFT特征的局部遮挡目标识别

提出一种利用隐马尔可夫模型建立目标特征匹配库来识别图像中局部遮挡目标的新方法。该方法首先通过SIFT算法提取目标SIFT特征,然后采用隐马尔可夫模型对目标所有的SIFT特征进行训练,得到目标SIFT特征对应的模型输出概率范围,将该概率范围作为目标特征匹配库。在对图像中的目标进行识别时,利用目标特征匹配库可以把目标特征从图像所有特征中识别出来,即使目标遮挡比例为60%时,该方法仍能识别出目标。实验结果表明,新方法可以精准地识别出图像中被遮挡目标,能够很好地解决遮挡情况下的目标识别问题。与现有局部遮挡目标识别算法相比,新方法所取得的目标识别率均有所提高。     

云制造环境下设计需求与服务匹配模式算法

针对云制造环境下设计需求与设计服务的特性,构建含有属性集、关系集和操作集的设计需求与设计服务数据结构。建立一种云制造环境下的设计需求与设计服务输入、分解、组合和输出匹配模式,研究了该模型的原子匹配、扩展匹配和产品匹配。针对匹配过程中输入、分解、组合和输出量化问题,采用语义概念相似度和循环递归设计结构匹配算法实现设计需求与设计服务智能匹配。最后,通过实验验证,表明该模式与算法的有效性和可行性。     

Deciduous forest mapping using change detection of multi-temporal canopy height models from aerial images acquired at leaf-on and leaf-off conditions

Discrimination of deciduous trees using spectral information from aerial images has only been partly successfully due to the complexity of the reflectance at different view angles, times of acquisition, phenology of the trees and inter-tree radiance. Therefore, the objective was to evaluate the accuracy of estimating the proportion of deciduous stem volume (P) utilizing change detection between canopy height models (CHMs) generated by digital photogrammetry from leaf-on and leaf-off aerial images instead of using spectral information. The study was conducted at a hemi-boreal study area in Sweden. Using aerial images from three seasons, CHMs with a resolution of approximately 0.5?m were generated using semi-global matching. For training plots, metrics describing the change between leaf-on and leaf-off conditions were calculated and used to model the continuous variable P, using the Random Forest approach. Validated at sub-stands, the estimation accuracy of P in terms of root mean square error and bias was found to be 18% and ?6%, respectively. The overall classification accuracy, using four equally wide classes, was 83% with a kappa value of 0.68. The validation plots in classes of high proportion of coniferous or deciduous stem volume were well classified, whereas the mixed forest classes showed lower classification accuracies.     

浅谈居住区绿化适地适树

文章通过归纳适合植物生长的各种生态因子和植物的种植株距来为适地适树规划提供依据。