Refined parameter and uncertainty estimation when both variables are subject to error. Case study: estimation of Si consumption and regeneration rates in a marine environment

The problem of estimating parameters and their uncertainty from experimental measurements in marine ecosystems is a common task and often necessitates solving nonlinear equations. If the measurements are subject to individually varying errors (i.e., heteroscedastic data), the parameters are often estimated using a Weighted Least Squares (WLS) method. For estimating the parameter uncertainties, a linearized expression for the covariance matrix exists. Yet, both methods assume that the errors on the independent variable, also called “input”, is negligible, which is often not true. For instance, in order to determine uptake and regeneration rates of silicic acid by phytoplankton, concentration and isotopic abundance measurements are performed at the beginning (input) and at the end (output) of an incubation experiment. Here, the so-called input and output are measurements of the same quantities, i.e., determined in exactly the same way, only differing by the time at which the measurements were performed. Clearly, there is no reason to assume that the input measurements are subject to less error than the output measurements. We propose a refinement of the two abovementioned estimation methods which enlarges their applicability to cases where input noise is not negligible. The refined methods are evaluated on the uptake and regeneration processes of silicic acid and compared to the original procedures using Monte-Carlo simulations. The results reveal a smaller bias for the refined WLS estimator compared with the original one. An additional advantage of using the refined WLS cost function is that its residual value can be interpreted as a sample from a χ² distribution. This property is especially useful because it enables an internal quality control of the results. In addition, the parameter uncertainty estimation is significantly improved. By neglecting the effect of the input noise, a (potentially) important origin of the parameter variation is simply ignored. Therefore, without the refinement, the parameter uncertainties are systematically underestimated. Using the refined method, this systematic error disappears and on the whole, the parameter standard deviations are accurately estimated.     

天安门广场改建工程

本文记述了天安门广场改建工程 ,包括广场铺装改建、广场照明改建、金水河喷泉改造、广场扩声系统改造、广场地下管线及配套设施等工程内容     

上海轨道交通人民广场枢纽站大客流组织对策研究

上海轨道交通人民广场枢纽站是上海最大的公交枢纽与人员集散地之一。由于历史原因,该枢纽中的3条轨道交通线的站台不是一次规划建成的,因此在换乘通道、站台通行能力、收费区布局等方面均暴露出运营规模与客流总量不相适宜之处,给乘客的通行带来了安全隐患。因此,针对目前现状,以人民广场站为例,开展了大客流组织对策研究,通过行人仿真方案模型模拟,确定了8号线站台改善方案;提出了缓解换乘客流在1号线北侧站厅和2号线站厅通往大三角区域通道上对冲的措施,为今后轨道交通枢纽大客流站的运营管理提供参考。     

利用DOA和TOA对运动辐射源的单舰无源定位

采用最优加权最小二乘估计和卡尔曼滤波算法,讨论了利用目标到达角和到达时间测量数据对运动目标进行单舰无源定位与跟踪的方法,经计算机仿真证明,该方法在无源定位系统中有一定的参考价值。     

简便实用的最小二乘预测算式

本文推导了在等间隔观测条件下的最小二乘预测的简例实用的预测算式，它可以利用前四点历史数据直接计算出下一观测点的预测值，因此能更加方便地在实时控制及其它领域中直接应用，对各种数据的动态趋势进行预测分析。     

汽车悬架参数优化的一种新方法研究

研究利用最优控制理论和最小二乘法对汽车悬架系统参数进行优化设计的方法,并利用该方法对某汽车的悬架参数进行优化。研究了悬架参数优化后的汽车对标准路面激励的响应。研究结果表明,利用该方法,可以得到兼顾各方面性能且能使某方面性能显著提高的悬架系统参数。     

A unified seakeeping and maneuvering analysis of ships in regular waves

The behavior of a ship in regular waves during maneuvering was studied by using a two-time scale model. The maneuvering analysis was based on Söding’s (Schiffstechnik 1982; 29:3–29) nonlinear slender-body theory generalized to account for heel. Forces and moments due to rudder, propeller, and viscous cross-flow follow from the state-of-the-art procedures. The developed unified theory of seakeeping and maneuvering was verified and validated for calm water by comparing it with experimental and calculated zigzag and circle maneuvers. Linear wave-induced motions and loads were determined by generalizing the Salvesen-Tuck-Faltinsen (Trans SNAME 1970; 78:250–287) strip theory. The mean second-order wave loads in incident regular deep water waves in oblique sea conditions were estimated by the potential flow theories of Faltinsen et al. (Proc 13th Symp Naval Hydrody 1980), Salvesen (Proc Intl Symp Dynam Mar Vehicl Struct Wave 1974), and Loukakis and Sclavounos (J Ship Res 1978; 22:1–19). The considered theories cover the whole range of important wavelengths. Comparisons between the different mean second-order wave load theories and available experimental data were carried out for different ship hull forms when the ship was advancing forward on a straight course. The mentioned methods have been incorporated into the maneuvering model. Their applicability from the perspective of the maneuvering ability of the selected types of ships was investigated in given wave environments. The wave conditions are valid for realistic maneuvering cases in open coastal areas. It was demonstrated that the incident waves may have an important influence on the maneuvering behavior of a ship. The added resistance, mean second-order transverse force, and yaw moment also play important roles.     

道路改造纵断面计算机自动设计

对适用于道路改造纵断面计算机自动设计的数学模型、计算机实现方法进行了探讨,采用最小二乘曲线拟合法拟和出最贴近原地面线的纵断面曲线,达到工程量最小的目的。利用ObjectARX与MFC混合编程的方法编制了应用程序,通过相应的工程项目的实践,并与手工拉坡及定坡相比较,达到了技术性与经济性双重优化的目的。     

成都天府广场的综合开发

介绍成都市中心商务区的核心--天府广场,指出不仅要通过它展现成都市的文化特征,还要体现完备的商业和交通价值;提出将天府广场打造成城市综合广场--地上有文化广场,地下集交通和商业为一体,与周边城市公共设施尤其是与城市地下空间形成完好的互联互通.阐述新的设计思路与方案,通过综合开发与改造,顺利实现文化广场和轨道交通及公共设...     

Analysis of S–N data for new and corroded mooring chains at varying mean load levels using a hierarchical linear model

Results from full scale fatigue tests of offshore mooring chains are analyzed. The data set includes new and used chains, tested at a variety of mean load levels. The used chains have been retrieved after operation offshore and include samples with varying surface conditions, ranging from as-new to heavily corroded. Based on a parameterized S–N curve intercept parameter, the effects of mean load and chain condition are estimated empirically by regression analysis. A hierarchical linear model is used, to account for and quantify correlations within subsets of the data. The choice of grouping criterion for the hierarchical model is discussed, and assessed based on the current data. Results show that the mean load and corrosion effects are both significant. Differences in the fatigue performance of new versus used chains are quantified and discussed.