Population‐level effects of egg predation on a native planktivore in a large freshwater lake     

David B. Bunnell  Justin G. Mychek‐Londer  Charles P. Madenjian 《Ecology of Freshwater Fish》2014,23(4):604-614

Using a 37‐year recruitment time series, we uncovered a field pattern revealing a strong, inverse relationship between bloater Coregonus hoyi recruitment success and slimy sculpin Cottus cognatus biomass in Lake Michigan (United States), one of the largest freshwater lakes of the world. Given that slimy sculpins (and deepwater sculpin Myoxocephalus thompsonii) are known egg predators that spatiotemporally overlap with incubating bloater eggs, we used recently published data on sculpin diets and daily ration to model annual bloater egg consumption by sculpins for the 1973–2010 year‐classes. Although several strong year‐classes were produced in the late 1980s when the proportion of eggs consumed by slimy sculpins was extremely low (i.e., <0.001) and several weak year‐classes were produced when the proportion of bloater eggs consumed was at its highest (i.e., >0.10–1.0), egg predation failed to explain why recruitment was weak for the 1995–2005 year‐classes when the proportion consumed was also low (i.e., <0.02). We concluded that egg predation by slimy and deepwater sculpins could have limited bloater recruitment in some years, but that some undetermined factor was more important in many other years. Given that slimy sculpin densities are influenced by piscivorous lake trout Salvelinus namaycush, the restoration of which in Lake Michigan has lagged behind those in lakes Superior and Huron, our study highlights the importance of an ecosystem perspective when considering population dynamics of fishes.  相似文献   

Rectangular Cover System of Manifold Method and Its Auto Mesh Algorithm   总被引：2，自引：0，他引：2  

CAI Yong chang  ZHANG Xiang wei 《保鲜与加工》2001,(1):42-46

In contrast to the finite element method, another form of numerical method which is based on the using of rectangular math covers in manifold method is proposed. In this method, the element data is not a necessary in the input data files and it can be incorporated with the CAD technology conveniently. The theory and application of the method are discussed and the auto mesh algorithm of the cover system is also given in this paper. The numerical examples indicate that the method and the algorithm are accurate and effective.  相似文献   

Application of Multivector Algebra in Real Space-time to Set Pair Analysis     

DUAN Shao-guang 《保鲜与加工》2004,(11):66-70

The contact number is an important mathematical tool of systems theory and methods in the monograph Set Pair Analysis and Its Preliminary Applications written by Zhao Keqin for unitizedly processing the uncertainties due to the fuzzy, stochastic, intermediate and information uncomplete about something. The article applies the multivector algebra which is isomorphism with the real Dirac algebra in the real space-time adopted by Venzo de Sabbata to the contact number of set pair analysis, and consequently, the contact number is generalized correspondingly.  相似文献   

THE EXISTENCE OF APPROXIMATE EXTREME POIKTS OF CONSTRAINED OPTIMIZATION     

Yang Wannjan Zhang Shiqing 《保鲜与加工》1988,(4)

According to the theories o?Riemannian manifolds and variational principles, two theorems about the existence of approximate extreme point of constrained optimization are given in this paper.  相似文献   

Complexity of indica-japonica varietal differentiation in Bangladesh rice landraces revealed by microsatellite markers     

Mumu Wang  Zuofeng Zhu  Lubin Tan  Fengxia Liu  Yongcai Fu  Chuanqing Sun  Hongwei Cai 《Breeding Science》2013,63(2):227-232

To understand the genetic diversity and indica-japonica differentiation in Bangladesh rice varieties, a total of 151 accessions of rice varieties mostly Bangladesh traditional varieties including Aus, Boro, broadcast Aman, transplant Aman and Rayada varietal groups were genotyped using 47 rice nuclear SSRs. As a result, three distinct groups were detected by cluster analysis, corresponding to indica, Aus and japonica rice. Among deepwater rice varieties analyzed some having particular morphological features that mainly corresponded to the japonica varietal group. Some small seeded and aromatic varieties from Bangladesh also corresponded to the japonica varietal group. This research for the first time establishes that the japonica varietal group is a prominent component of traditional varieties in Bangladesh, particularly in deepwater areas.  相似文献   

正交全局-局部判别映射应用于植物叶片分类   总被引：2，自引：2，他引：0  

张善文  巨春飞 《农业工程学报》2010,26(10):162-166

提出了一种正交全局-局部判别映射的维数约简方法,并应用于植物叶片分类中。对于给定点的邻域点集,首先建立能够描述数据点之间关系的权重矩阵;然后,充分利用数据的类别信息和局部信息来构建类间散度矩阵和局部结构矩阵,使得映射后类内数据点之间的距离减小,而类间数据点之间的距离增大,这一性质有利于数据分类;最后,构造正交优化目标函数,通过Lagrange数乘法求解该目标函数。植物叶片图像分类的试验结果表明,该方法是有效、可行的。  相似文献   

基于FLUENT的歧管式催化器流场仿真分析     

丁柏群  李明扬 《森林工程》2011,27(3):33-37

通过数值模拟和试验验证,分析岐管式催化器内部气流的速度场、压力场和气流分布状态。结果表明,随入口流量的增大,岐管式催化器内部气流流速增大、压力损失增大、径向分布的均匀性降低;气流的径向分布不同于常规催化器集中于轴线的轴对称形式,而是呈多中心分散状态,均匀性较常规催化器提高。  相似文献   

某发动机排气歧管流场分析与结构优化   总被引：1，自引：0，他引：1  

黄泽好  张浩亮  孙章栋  董腾鲜 《西南大学学报(自然科学版)》2011,33(1)

首先建立某发动机排气歧管的三维模型,利用有限元前处理软件Hypermesh划分网格,用有限元方法分析各缸对应支管的单管流速分布和三元催化剂前端截面的流速分布,并根据分析结果对排气歧管进行结构优化,改进后的排气歧管在各缸流量均匀性、减小流通阻力、漩涡消失、气流噪声和能量损失方面取得较明显的效果.  相似文献   

Finsler 流形的 Cartan 型1形式的一些性质     

宋佩  李明 《西南大学学报》2014,(10)

给出了 Cartan 型1形式的外微分与 Bott 陈联络的曲率之间的关系，探讨了其与畸变、 S 曲率之间的关系，证明了 Berwald 流形的 Cartan 型1形式为恰当形式。利用 Cartan 型1形式构造了 Finsler 流形的射影球丛上的一个 Randers 度量，证明该度量为 Landsberg 度量的充要条件是底流形为 Riemann 流形。证明了 Cartan 型1形式及Cartan 1形式的对偶向量场为共型向量场的充要条件是底流形为 Riemman 流形。  相似文献   

歧管式高压射流水下洗网机的设计     

张小明  郭根喜  陶启友  黄小华  胡昱 《南方水产》2010,6(3):46-51

文章针对深水网箱养殖过程中岸电供应不便而给网衣的水下清洗带来极大困难的问题,研制了歧管式高压射流水下洗网机,克服了高压仓式洗网机水头损失大的缺点。通过水力学计算得到歧管式高压射流水下洗网机射流压力P=5．57MPa、喷嘴孔径d=2．6mm、射流速度v=104．1m·s。和射流功率P=12．3kW、射流反冲力F=234．96N。水下洗网机的海上清洗试验表明,在工作泵满足工作压力和设计流量条件下,歧管式高压水射流水下洗网机的综合性能达到了设计要求。  相似文献