Estimating fish length and age at 50% maturity using a logistic type model   总被引：3，自引：0，他引：3  

Y. Chen  J. E. Paloheimo 《Aquatic Sciences - Research Across Boundaries》1994,56(3):206-219

We propose a two-parameter logistic type model for estimating fish length and age at 50% maturity using the nonlinear least-squares method. The independent and dependent variables in the model are length (or age) and the corresponding arcsin-square-root transformed proportion of mature fish (P_i). The two parameters in the model are length (or age) at 50% maturity (L50 or A50) and instantaneous rate of maturation (K). A simulation study was conducted to examine the statistical behaviour of the proposed model in estimating L50 and K. The L50 was well estimated with a small bias (<1%) using the proposed model in all simulation cases. The K was well estimated (bias < 1%) when its true value and the variance in P_i were small. The proposed model was found to have relatively smaller bias than the probit and Lysack's methods in estimating L50 (or A50). To examine whether there are significant differences in maturation patterns between different groups of fish, we propose fitting the maturation data to the proposed model, and then conducting an analysis of residuals sum of squares to test whether there are significant differences in the fitted models.  相似文献   

Determination of unit hydrographs by multiple storm analysis     

B. Zhao  Y. -K. Tung  J. -C. Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(4):269-280

This paper discusses the derivation of a unit hydrograph by multiple storm analysis using least squares methods. Variations of least squares method was generalized using the framework of weighted ridge analysis. The paper also shows two theorems to support using multi-storm analysis to derive UH. In addition, an issue was addressed on the scaling effect in the conventional multi-storm analysis which could create potential bias toward large storms in deriving a multi-storm UH. For that, a simple scaling procedure was proposed to reduce such potential bias problem. Numerical investigations were conducted to examine the performance of the scaling procedure by comparing with the conventional multi-storm analysis (without scaling) and the HEC-1 weighing procedures. Based on various performance criteria using a total of 39 storms from three watersheds, the proposed scaling procedure was found to produce a quite desirable UH.  相似文献   

Selectivity of diamond- and square-mesh codends in the deepwater crustacean trawl fishery off the Balearic Islands (western Mediterranean)   总被引：3，自引：2，他引：3  

Guijarro  Beatriz; Massuti  Enric 《ICES Journal of Marine Science》2006,63(1):52-67

  相似文献   

估计海表温度的1种简便方法   总被引：1，自引：0，他引：1  

李云芳  郭佩芳  周慧 《中国海洋大学学报(自然科学版)》2006,36(1):127-130

依据随机过程线性均方估计的正交原理,可由水文站获得的海洋要素估计工程点的海洋要素。利用1984~2003年的卫星海表温度(SST)数据将该方法用于估计海表温度,并对该方法产生的误差进行了分析,结果表明该方法比传统方法更能有效地减小误差;其意义在于可在陆地台站和工程点进行一段时间的同步观测,找出两者之间的相关系数,之后便可长期由台站气温估计工程点的海表温度。  相似文献   

Calibration and modification of energy dissipation models for irregular wave breaking     

Winyu Rattanapitikon   《Ocean Engineering》2007,34(11-12):1592-1601

This study is undertaken to recalibrate eight existing energy dissipation models and find out the suitable models, which can be used to compute H_rms for a wide range of experimental conditions. The examination shows that the coefficients in the existing models are not the optimal values for a wide range of experimental conditions. Using the new calibrated coefficients, all existing models can be used for computing H_rms and the model of Battjes, J.A., Stive, M.J.F. [1985. Calibration and verification of a dissipation model for random breaking waves. Journal of Geophysical Research 90 (C5), 9159–9167] gives the best predictions. The existing models are also modified by changing the breaker height formulas in the dissipation models. The accuracy of most existing models is improved significantly by using the suitable breaker height formula.  相似文献   

基于积分方程法的大地电磁三维反演   总被引：1，自引：0，他引：1  

徐凯军  李桐林  刘展 《物探化探计算技术》2009,31(6):564-567

采用积分方程法计算均匀半空间中三维异常体的大地电磁响应,然后利用阻尼最小二乘法反演得到地下三维异常体电阻率分布。在计算灵敏度矩阵时,将灵敏度矩阵分为线性项和体现反演过程非线性的偏微分项进行求解,提高了计算精度。理论模型反演结果表明,反演较准确,对初值依赖性小,且只针对异常体剖分单元进行反演,反演效率较高。  相似文献   

浅析基桩完整性检测的工程实例     

姜凡  冯晓明  张德新  关鹏 《吉林地质》2009,28(3):71-73,82

随着我们基本建设事业的发展,桩基工程已成为一种重要的基础形式,其中以混凝土预制方桩和混凝土灌注桩应用较广泛。  相似文献   

基于均方差-模糊综合评判复合模型的地下水水质评价   总被引：1，自引：0，他引：1  

斯蔼  杜关记  王爽  李晓华  刘方 《地下水》2009,31(1)

首次运用均方差-模糊综合评判复合模型,选取地下水水质的主要影响因子,通过评价因子的选取及评价集的建立、隶属函数及单因子隶属度的确定、评价指标权重的确定和综合隶属度的确定四个步骤,对天津蓟县官庄地区深层地下水水质行了综合评价.评价结果表明,研究区采样点水质总体级别为I级,说明该区地下水水质较好,而局部点位硝酸盐超标是导致水质污染的主要原因,这一结论与该区其它研究成果评价结果相一致.  相似文献   

基于MATLAB的地下水流量与水位降深关系的一种优化计算方法     

李继超  桑有明  邓宇  袁章均 《地下水》2009,31(2):20-22,79

相比理论公式法,基于最小二乘法原理及其计算方法,结合MATLAB数值分析软件对抽水试验数据进行曲线拟合,求得拟合公式,同时得Q—sw关系曲线的计算和绘制转化为计算机来处理,避免了手工绘制和计算求解时存在的各种人为缺陷;公式能够对勘探孔的Q—sw关系进行定性定量的分析,降低误差因素影响,提高预报流量的可信度。  相似文献   

小比例尺数码航摄资料在城市规划中的应用     

傅长刚 《安徽地质》2009,19(3):231-233

对利用小比例尺数码航摄资料进行控制,获取应用于城市规划设计前期1：1000地形图资料的方法进行探讨和实践,进行理论分析和实际应用结果分析,提出满足了我们规划用图的需要。这种方法可为今后一些局部地区急需用图,测绘作为借鉴。  相似文献