排序方式： 共有32条查询结果，搜索用时 203 毫秒
11.
12.
模拟退火法系一种非线性整体搜索算法，本文用以反演远震Ｐ波波速慢度和方位数据，求解地壳速度结构。综合试验表明，用模拟退火法能够以合理的精度确定Ｐ波低速带的空间位置，并能使近７０％的目标速度扰动得以再现。实验表明，用少至两个台的资料便可得到明显的结果。 相似文献
13.
Fecal indicator bacteria (FIB) were measured approximately 5 days a week in ankle-depth water at 19 surfzone stations along Huntington Beach and Newport Beach, California, from 1998 to the end of 2003. These sampling periods span the time before and after treated sewage effluent, discharged into the coastal ocean from the local outfall, was disinfected. Bacterial samples were also taken in the vicinity of the outfall during the pre- and post-disinfection periods. Our analysis of the results from both data sets suggest that land-based sources, rather than the local outfall, were the source of the FIB responsible for the frequent closures and postings of local beaches in the summers of 2001 and 2002. Because the annual cycle is the dominant frequency in the fecal and total coliform data sets at most sampling stations, we infer that sources associated with local runoff were responsible for the majority of coliform contamination along wide stretches of the beach. The dominant fortnightly cycle in enterococci at many surfzone sampling stations suggests that the source for these relatively frequent bacteria contamination events in summer is related to the wetting and draining of the land due to the large tidal excursions found during spring tides. Along the most frequently closed section of the beach at stations 3N-15N, the fortnightly cycle is dominant in all FIBs. The strikingly different spatial and spectral patterns found in coliform and in enterococci suggest the presence of different sources, at least for large sections of beach. The presence of a relatively large enterococci fortnightly cycle along the beaches near Newport Harbor indicates that contamination sources similar to those found off Huntington Beach are present, though not at high enough levels to close the Newport beaches. 相似文献
14.
15.
Stige LC Ottersen G Hjermann DØ Dalpadado P Jensen LK Stenseth NC 《Marine pollution bulletin》2011,62(2):395-398
Two factors determine whether pollution is likely to affect a population indirectly through loss of prey: firstly, the sensitivity of the prey to the pollutants, and secondly, the sensitivity of the predator population to loss of prey at the given life stage. We here apply a statistical recruitment model for Northeast Arctic cod to evaluate the sensitivity of cod cohorts to loss of zooplankton prey, for example following an oil spill. The calculations show that cod cohorts are highly sensitive to possible zooplankton biomass reductions in the distribution area of the cod larvae, and point to a need for more knowledge about oil-effects on zooplankton. Our study illustrates how knowledge about population dynamics may guide which indirect effects to consider in environmental impact studies. 相似文献
16.
Vulnerability indicators of sea water intrusion 总被引：5，自引：0，他引：5
In this paper, simple indicators of the propensity for sea water intrusion (SWI) to occur (referred to as "SWI vulnerability indicators") are devised. The analysis is based on an existing analytical solution for the steady-state position of a sharp fresh water-salt water interface. Interface characteristics, that is, the wedge toe location and sea water volume, are used in quantifying SWI in both confined and unconfined aquifers. Rates-of-change (partial derivatives of the analytical solution) in the wedge toe or sea water volume are used to quantify the aquifer vulnerability to various stress situations, including (1) sea-level rise; (2) change in recharge (e.g., due to climate change); and (3) change in seaward discharge. A selection of coastal aquifer cases is used to apply the SWI vulnerability indicators, and the proposed methodology produces interpretations of SWI vulnerability that are broadly consistent with more comprehensive investigations. Several inferences regarding SWI vulnerability arise from the analysis, including: (1) sea-level rise impacts are more extensive in aquifers with head-controlled rather than flux-controlled inland boundaries, whereas the opposite is true for recharge change impacts; (2) sea-level rise does not induce SWI in constant-discharge confined aquifers; (3) SWI vulnerability varies depending on the causal factor, and therefore vulnerability composites are needed that differentiate vulnerability to such threats as sea-level rise, climate change, and changes in seaward groundwater discharge. We contend that the approach is an improvement over existing methods for characterizing SWI vulnerability, because the method has theoretical underpinnings and yet calculations are simple, although the coastal aquifer conceptualization is highly idealized. 相似文献
17.
18.
19.
20.
介绍了一种用于估计地震台阵数据到时残差的多信道处理的新方法。该方法综合了3种传统台阵处理方法的特点：频率域波束形成、时间域波束形成和主成分分析。首先对数据进行多子波变换，从而产生一组窄频带地震图。我们利用多子波变换替代加窗的傅里叶变换，以控制时间和频率的分辨率。我们还使用了一种波速形成程序，对转换过的、按时间排齐的数据进行主成分分析。主成分矢量值和成对数值被用来计算衡量波外形相似的相干性。主成分矢量的相差可作为数据与平面波模型拟合偏差的一种量度。相位差可以直接转换成时间差，但它们只有分辩一部分波长。因此，我们的方法是从较低的分析频带移至较高的分析频带的逐步分析法。我们提供了两个实例来说明这种方法在很宽的时空尺度范围均可采用。第一，1994年的玻利维亚深源地震期间，我们测定了一组覆盖南加利福尼亚大部分地区的宽频带地震台的时间残差。时间残差的范围为2s，将它们消除后，我们可以在1.0Hz上把数据叠加。第二，我们研究了在土库曼斯坦的直径不足1km的地震台阵的高频传感器记录的地方震数据。我们发现，时间残差范围只有0．02s，将其消除后，我们显著地改善了信号的主频数据的叠加。 相似文献