空间最近目标查找算法分析及其高性能Web实现   总被引：1，自引：1，他引：0  

田锋  蒋许锋 《测绘与空间地理信息》2009,32(3):108-109,113

讨论了空间最近目标查找的基本算法和相关的空间索引机制,简单地比较了几种算法和索引机制的优缺点.详细地介绍了在Windows IIS和.Net下,建立多级空间格网索引,实现空间最近目标查找的实现方法.  相似文献   

Primary production and implications for metabolic balance in Hawaiian lee eddies     

Patricia M. McAndrew  Robert R. Bidigare  David M. Karl 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1300

Recent discrepancies between geochemical and biological approaches for determining whether ocean ecosystems are net heterotrophic or net autotrophic have led to uncertainty in the net metabolic state of open ocean ecosystems. Geochemical approaches indicate that the oceans are net positive autotrophic, but direct observations based on short-term incubation techniques suggest that the ocean is in a state of net heterotrophy. One hypothesis for the apparent discrepancy is that net autotrophic production occurs in aperiodic “bursts,” which are superimposed on a more constant background state of net heterotrophy. Mixing events, which introduce new nutrients to the surface ocean, provide one mechanism for fueling such aperiodic bursts of net production. In conjunction with the Eddy Flux (E-Flux) program in the lee of the Hawaiian Islands during winter 2004–2005, we examined the relationship between photosynthesis and irradiance (P vs. E) in surface waters inside and outside of two cold-core, cyclonic eddies, and conducted five incubation experiments to examine the metabolic response of mixed-layer plankton communities to nutrient-rich deep-sea water additions. Our results showed that in the mixed layer, maximum rates of light-saturated photosynthesis, derived from photosynthesis–irradiance experiments were not significantly different inside vs. outside the eddies (p=0.35 and 0.44 for E-Flux I and E-Flux III, respectively). Addition of nutrients to mixed-layer water showed that (1) gross primary production (GPP) became decoupled from a more constant rate of respiration and (2) net system metabolism shifted from approximate balance, or slight net heterotrophy, to a demonstrably net autotrophic system. From these results, we determined that the threshold GPP for net autotrophic production for the mixed layer of the study region was 1.65 mmol O₂ m⁻³ d⁻¹, which is consistent with previous estimates for the oligotrophic open ocean.  相似文献   

基于WebGIS的城市地下管线信息系统的建立   总被引：1，自引：0，他引：1       下载免费PDF全文

陈兴华  石金锋  丛日盛 《海洋测绘》2008,28(1):68-71

城市地下管线是城市的重要基础设施,传统单机模式的城市地下管线信息系统已经不能满足城市管理的需求,随着城市生活的日益复杂化,城市地下管线信息系统功能的改进势在必行。针对上述问题,以北京市为例,基于B／S架构,以AreGIS Server和．Net为核心技术开发WebGIS,建立了网络化的地下管线信息系统。建成的北京数字市政地下管线信息系统在满足大众化和网络化需求的同时,其采用AreGIS Server技术开发WebGIS的方式,能够充分发挥ArcObjects强大的网络分析和空间分析功能,可为综合决策提供全面、准确的信息依据。  相似文献   

利用叶绿素资料计算初级生产力   总被引：1，自引：0，他引：1  

费尊乐  C．C．Trees  李宝华 《海洋科学进展》1997,(1)

海水中浮游植物叶绿素浓度是海洋生物调查中的一个重要观测参数。它不仅是表征浮游植物生物量的一个指标，而且利用它与浮游植物光合作用之间的相互关系还可以估算水域初级生产力。目前许多学者正致力于利用叶绿素资料计算初级生产力的研究．本文阐述了根据叶绿素浓度计算初级生产力的方法：Ryther－Yentsch模式、生态学数理模式和遥感模式。文章对方法应用中的一些问题作出了分析讨论。  相似文献   

夏热冬暖地区住宅户式中央空调的能耗比较     

林小闹  王弘  叶盛权 《广东海洋大学学报》2005,25(3):56-59

针对夏热冬暖地区住宅空调的特点,结合广东省液化天然气一体化试点项目,对比不同形式户式中央空调额定工况一次能源利用率和全年平均一次能源利用率。结果表明:天然气应用于户式中央空调中,电制冷户式中央空调的能源利用效率比较高,尤以多联空调为最高。  相似文献   

Model analysis of grazing effect on above-ground biomass and above-ground net primary production of a Mongolian grassland ecosystem     

Yuxiang Chen  Gilzae Lee  Takehisa Oikawa 《Journal of Hydrology》2007,333(1):155-164

  相似文献   

Long-term comparisons of net radiation calculation schemes   总被引：1，自引：0，他引：1  

J. H. Kjaersgaard  R. H. Cuenca  F. L. Plauborg  S. Hansen 《Boundary-Layer Meteorology》2007,123(3):417-431

Six commonly used models for calculating daily net radiation were tested against measured net radiation. Meteorological data from 32 and 7 consecutive years obtained at two temperate sites were used. The extensive duration of the datasets ensured that all weather conditions and extreme events were captured. A set of statistical procedures was used to evaluate the performance of the models. The mean bias errors ranged from 0.0 W m⁻² to 24.8 W m⁻² and 0.1–24.7 W m⁻² and root mean square error from 11.0 W m⁻² to 28.1 W m⁻² and 10.0–27.9 W m⁻² at the two sites respectively, for days without snow cover on the ground. The best agreement was found when locally calibrated model coefficients were used. Only negligible differences in model performances were found between the two sites and the differences were lower than the inaccuracies of the net radiation instruments used. Including days with snow cover in the analysis lead to a slight increase in the bias and scatter of the predictions. Model performances were in general better during summertime than wintertime. Altered albedo values during winter caused by generally low sun angles were likely the cause of this. Analysis showed that at least 5 years of data were needed to obtain stable calibration coefficients for local calibration of the models. Based on the results from this study, and due to their physical background, two physical based models were recommended for calculating daily values of net radiation under temperate climate regimes. A simple adjustment of the calibration coefficients based on climate regime was suggested for these models.  相似文献   

大亚湾网箱养殖区生物-化学特性与营养状况的周日变化     

黄洪辉  王寓平 《广东海洋大学学报》2001,21(2):35-43

根据1998年11月对大亚湾大鹏澳网箱养殖区进行的定点24h连续水质监测资料,分析并讨论了该养殖区海水生物-化学各要素的垂直分布和周日变化规律,并用单项指标评价法和改进的营养状态质量指数(NQI)法,参照营养指数(E)对该网箱养殖区海水的营养状况进行了评价和研究.结果表明,各项要素的平均值大都是表层＞中层＞底层;周日变化主要受潮汐运动和海水中生物的节律性生理活动的综合影响;表层海水的富营养化率明显高于中层海水,其各单项指标处于中度一富营养状态,而中层和底层海水则分别处于贫一中度和贫-富营养状态;PO4-P相对较贫乏,为养殖区富营养化的最关键限制因素.  相似文献   

Electron density distribution and bond critical point properties for forsterite, Mg2 SiO4, determined with synchrotron single crystal X-ray diffraction data     

A. Kirfel  T. Lippmann  P. Blaha  K. Schwarz  D. F. Cox  K. M. Rosso  G. V. Gibbs 《Physics and Chemistry of Minerals》2005,32(4):301-313

A generalized X-ray scattering factor model experimental electron density distribution has been generated for the orthosilicate forsterite, using an essentially extinction and absorption free set of single crystal diffraction data recorded with intense, high energy synchrotron X-ray radiation (E=100.6 keV). A refinement of the model converged with an R(F)=0.0061. An evaluation of the bond critical point, bcp, properties of the distribution at the (3, –1) stationary points for the SiO and MgO bonded interactions, yielded values that agree typically within ~5%, on average, with theoretical values generated with quantum chemical computational strategies, using relatively robust basis sets. On the basis of this result, the modeling of the experimental distribution is considered to be adequate. As the bcp properties increase in magnitude, the MgO and SiO bonds decrease in length as calculated for a number of rock forming silicates. As asserted by Coppens (X-ray charge densities and chemical bonding. Oxford University Press, Oxford, 1997), large negative ²(r_c) values, characteristic of shared interactions involving first row atoms, may not be characteristic of closed shell covalent bonded interactions involving second row Si, P and S atoms bonded to O. This study adds new evidence to the overall relatively good agreement between theoretical bcp properties generated with computational quantum strategies, on the one hand, and experimental properties generated with single crystal high energy synchrotron diffraction data on the other. The similarity of results not only provides a basis for using computational strategies for studying and modeling structures, defects and the reactivity of representative structures, but it also provides a basis for improving our understanding of the crystal chemistry of earth materials and the character of the SiO bonded interaction.  相似文献   

Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia     

Levings CD  Varela DE  Mehlenbacher NM  Barry KL  Piercey GE  Guo M  Harrison PJ 《Marine pollution bulletin》2005,50(12):158-1594

We investigated the effect of acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (Howe Sound, BC, Canada) on primary productivity and chlorophyll a levels in the receiving waters of Howe Sound before, during, and after freshet from the Squamish River. Elevated concentrations of copper (integrated average through the water column >0.050 mg l⁻¹) in nearshore waters indicated that under some conditions a small gyre near the mouth of Britannia Creek may have retained the AMD from Britannia Creek and from a 30-m deep water outfall close to shore. Regression and correlation analyses indicated that copper negatively affected primary productivity during April (pre-freshet) and November (post-freshet). Negative effects of copper on primary productivity were not supported statistically for July (freshet), possibly because of additional effects such as turbidity from the Squamish River. Depth-integrated average and surface chlorophyll a were correlated to copper concentrations in April. During this short study we demonstrated that copper concentrations from the AMD discharge can negatively affect both primary productivity and the standing stock of primary producers in Howe Sound.  相似文献