Effects of model sensitivity and nonlinearity on nonlinear regression of ground water flow   总被引：1，自引：0，他引：1  

Yager RM 《Ground water》2004,42(3):390-400

Nonlinear regression is increasingly applied to the calibration of hydrologic models through the use of perturbation methods to compute the Jacobian or sensitivity matrix required by the Gauss-Newton optimization method. Sensitivities obtained by perturbation methods can be less accurate than those obtained by direct differentiation, however, and concern has arisen that the optimal parameter values and the associated parameter covariance matrix computed by perturbation could also be less accurate. Sensitivities computed by both perturbation and direct differentiation were applied in nonlinear regression calibration of seven ground water flow models. The two methods gave virtually identical optimum parameter values and covariances for the three models that were relatively linear and two of the models that were relatively nonlinear, but gave widely differing results for two other nonlinear models. The perturbation method performed better than direct differentiation in some regressions with the nonlinear models, apparently because approximate sensitivities computed for an interval yielded better search directions than did more accurately computed sensitivities for a point. The method selected to avoid overshooting minima on the error surface when updating parameter values with the Gauss-Newton procedure appears for nonlinear models to be more important than the method of sensitivity calculation in controlling regression convergence.  相似文献   

Assessment of polycyclic aromatic hydrocarbon input to urban wetlands in relation to adjacent land use   总被引：2，自引：0，他引：2  

Kimbrough KL  Dickhut RM 《Marine pollution bulletin》2006,52(11):1355-1363

The relationship between polycyclic aromatic hydrocarbons (PAHs) in wetland surface sediments and adjacent land use was assessed in the Elizabeth River, VA, an urbanized sub-estuary of the Chesapeake Bay. Significant differences (p<0.05) in surface sediment PAH concentration between sites indicated adjacent land use had a substantial influence on PAH concentration in wetland sediments. Wetlands adjacent to parking lots and petroleum industrial sites exhibited the highest PAH concentrations of all wetlands examined. Overall, commercial land uses had the highest PAH concentrations and automotive sources dominated (52-69%) PAH input to wetland surface sediments irrespective of adjacent land use.  相似文献   

Effects of multiple perturbations on the survivorship of fragments of three coral species     

Dizon RM  Yap HT 《Marine pollution bulletin》2006,52(8):928-934

Fist-sized fragments of Porites cylindrica, Porites rus and Pavona frondifera were deployed in single-species (P. cylindrica) and mixed-species (all three) plots in a shallow reef area in the northwestern Philippines. After 6 months, the corals in half of the plots were broken into smaller pieces to simulate an episodic physical disturbance. The survival of all corals was monitored from March 2000 to July 2001 during which the corals experienced 2 typhoons and episodes of algal overgrowth. For both intact and broken treatments, there was significantly higher survival in the mixed-species plots than in the single-species treatments. Fragment mortality varied between disturbances of varying frequencies and magnitudes, namely: one-time fragmentation stress, seasonal overgrowth by cyanobacteria and macroalgae, short-term (1 day) and long-term (more than 1 week) burial. The mixed-species assemblages had higher fragment survivorship than the monospecific assemblages during small-scale perturbations (e.g., algal overgrowth), but not in the face of subsequent, larger scale disturbances. This study emphasizes that coral responses to disturbance are both species- and context-specific.  相似文献   

Microbial community of cyanobacteria mats in the intertidal zone of oil-polluted coast of Saudi Arabia     

Al-Thukair AA  Abed RM  Mohamed L 《Marine pollution bulletin》2007,54(2):173-179

Cyanobacterial mats are found at various locations along the coast of the Eastern Province of Saudi Arabia. Those mats were affected by severe oil pollution following 1991 oil spill. In this study, samples from Abu Ali Island were collected at three selected sampling sites across the intertidal zone (Lower, Middle, and Upper) in order to understand the effect of extreme environmental conditions of high salinity, temperature and desiccation on distribution of cyanobacteria along the oil polluted intertidal zone. Our investigation of composition of cyanobacteria and diatoms was carried out using light microscopy, and Denaturant Gradient Gel Electrophoresis (DGGE) technique. Light microscopy identification revealed dominant cyanobacteria to be affiliated with genera Phormidium, Microcoleus, and Schizothrix, and to a lesser extent with Oscillatoria, Halothece, and various diatom species. The analysis of DGGE of PCR-amplified 16S rRNA fragments showed that the diversity of cyanobacteria decreases as we proceed from the lower to the upper intertidal zone. Accordingly, the tidal regime, salinity, elevated ambient air temperature, and desiccation periods have a great influence on the distribution of cyanobacterial community in the oil polluted intertidal zone of Abu Ali Island.  相似文献   

实时近景三维非接触测量体积和运动     

Wilson  R 李小鹏 《武测译文》1992,(3):9-13,42

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Structure of microbial communities and hydrocarbon-dependent sulfate reduction in the anoxic layer of a polluted microbial mat     

Abed RM  Musat N  Musat F  Mussmann M 《Marine pollution bulletin》2011,62(3):539-546

The bacterial communities in the anoxic layer of a heavily polluted microbial mat and their growth on hydrocarbons under sulfate-reducing conditions were investigated. Microbial communities were dominated by members of Alphaproteobacteria (27% of the total rRNA), Planctomycetes (21.1%) and sulfate-reducing bacteria (SRB: 17.5%). 16S rRNA cloning revealed sequences beloning to the same bacterial groups with SRB affiliated to the genera Desulfobulbus, Desulfocapsa, Desulfomicrobium, Desulfobacterium and Desulfosarcina/Desulfococcus. The derived enrichment cultures on crude oil, hexadecane and toluene were dominated by SRB. While most SRB sequences of the toluene and hexadecane cultures were related to the sequence of Desulfotignum toluolica, the crude oil enrichment showed a more diverse bacterial community with sequences from the genera Desulfotignum, Desulfobacter, Desulfatibacillus, Desulfosalina, and Desulfococcus. We conclude that the anoxic layer of the studied mats contains a diverse community of anaerobic bacteria, dominated by SRB, some of which are able to grow on hydrocarbons.  相似文献   

水平井重力泄油     

Butl.  RM 刘建华 《国外石油地质》1992,(3):67-79

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与金矿化共生的有机质的硫化作用多米尼加Pueblo Viejo矿区实例     

Kett.  RM 胡明安 《地质科学译丛》1991,8(3):68-74

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气候变化对共水系统可靠性,回弹性,脆弱性影响的区域评价     

Vogel  RM 李中平 《水文科技信息》1997,14(A00):42-58

研究气候变化对水资源系统的影响通常是建立详细的月水文、气候和水库运行模型来对特定的供水系统进行模拟。这些研究结果只适用于被研究的供水系统。本文旨在建立一个区域水文气候评价模型，并研究该模型所带来的巨大潜力。这样的模型适用于在更大的地理范围内确定气候变化对供水特性的影响情况。  相似文献   

以电子经纬仪为传感器的无接触三维精密定位测量系统   总被引：4，自引：0，他引：4  

李小鹏 《测绘工程》1995,(1)

无接触三维精密定位测量系统,测量速度快、精度高、通用性强,不受测量物体大小和形状的限制。近十几年来,在工业测量领域中得到了较广泛的应用。本文介绍了以电子经纬仪为传感器的此类系统的组成、原理,详细地讨论了摄影测量中的光束平差法用于处理经纬仪方向观测值的问题。  相似文献