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811.
We propose an automatic and robust approach to detect, segment and classify urban objects from 3D point clouds. Processing is carried out using elevation images and the result is reprojected onto the 3D point cloud. First, the ground is segmented and objects are detected as discontinuities on the ground. Then, connected objects are segmented using a watershed approach. Finally, objects are classified using SVM with geometrical and contextual features. Our methodology is evaluated on databases from Ohio (USA) and Paris (France). In the former, our method detects 98% of the objects, 78% of them are correctly segmented and 82% of the well-segmented objects are correctly classified. In the latter, our method leads to an improvement of about 15% on the classification step with respect to previous works. Quantitative results prove that our method not only provides a good performance but is also faster than other works reported in the literature. 相似文献
812.
813.
Microalgal-based indicators were used to assess terrestrial influence on Shiraho coral reef of Ishigaki Island (Okinawa, Japan). A typhoon occurred on 4-5 August 2005 and sampling were made on three occasions thereafter (6, 8, and 11 August). Pre-typhoon sampling was conducted on 26 July. The typhoon-enhanced terrestrial discharges increased reef nutrient levels (e.g. average NO(3)(-)-N: 0.088mg/L pre-typhoon to 0.817mg/L post-typhoon). This elevated chlorophyll-a concentrations by four times and shifted phytoplankton composition (spectral class-based) from an initial dominance of diatoms and green microalgae to the dominance of bluegreen microalgae (cyanobacteria) and cryptophytes. Cyanobacteria later increased by more than 200% and accounted for as much as 80% of total chl-a ( approximately 0.29microg/L), possibly assisted by favorable nutrient availability. In outer reef waters, diatoms and green microalgae predominated whereas cyanobacteria and cryptophytes were nearly undetectable. Due to detrital decomposition and river discharge, the CDOM was much higher in the inner reef than in the outer reef. Benthic bluegreen microalgae were relatively more abundant in areas close to the river mouth and coastal agricultural fields. At these locations, nutrient concentrations were much higher due to river discharge and potentially significant groundwater discharge. Thus, phytoplankton and benthic microalgae can serve as indicators of terrestrial influence on coral reefs. 相似文献
814.
随着地理信息系统(Geograph ic Information System,简称G IS)的飞速发展和数字地球的提出,空间数据在诸如航空、遥感、测绘、交通、水电等不同领域展现出日益强大的生命力。空间数据采集的手段有很多,纸制图的数字化是G IS中空间数据采集的主要手段之一。结合广州市白云区和海珠区自来水管网矢量化生产实践,介绍了用ArcG IS完成自来水管线图扫描矢量化的整个过程,包括图象处理、配准、数字化、检查、图形接边等各个工序的实现方法,其中着重介绍了符号库的制作和地图接边及检查等技术问题。实践表明,该方法是一种简便、实用的扫描矢量化方法。 相似文献
815.
P. van Thienen N.J. Vlaar A.P. van den Berg 《Physics of the Earth and Planetary Interiors》2005,150(4):287-315
Geophysical arguments against plate tectonics in a hotter Earth, based on buoyancy considerations, require an alternative means of cooling the planet from its original hot state to the present situation. Such an alternative could be extensive flood volcanism in a more stagnant-lid like setting. Starting from the notion that all heat output of the Earth is through its surface, we have constructed two parametric models to evaluate the cooling characteristics of these two mechanisms: plate tectonics and basalt extrusion/flood volcanism. Our model results show that for a steadily (exponentially) cooling Earth, plate tectonics is capable of removing all the required heat at a rate of operation comparable to or even lower than its current rate of operation, contrary to earlier speculations. The extrusion mechanism may have been an important cooling agent in the early Earth, but requires global eruption rates two orders of magnitude greater than those of known Phanerozoic flood basalt provinces. This may not be a problem, since geological observations indicate that flood volcanism was both stronger and more ubiquitous in the early Earth. Because of its smaller size, Mars is capable of cooling conductively through its lithosphere at significant rates, and as a result may have cooled without an additional cooling mechanism. Venus, on the other hand, has required the operation of an additional cooling agent for probably every cooling phase of its possibly episodic history, with rates of activity comparable to those of the Earth. 相似文献
816.
本文介绍了在CT引导下,利用激光对原发性肝癌局部进行光动力学疗法(以下简称PDT),治疗半月后,进行CT复查,所有病人肿块中心均出现大小不等的液化坏死区,液化坏死区最大直径3.7cm,CT值下降7—49HU,经组织学检查治疗区,表明细胞膜严重受损,并可见大量坏死组织,经PDT治疗后的病人生存超过半年者达92.3%,所有随访病例均未发现肿块增大及其它部位转移,有肝区疼痛者,治疗后疼痛消失,同时食欲明显增加,体重有所增长。 相似文献
817.
砂岩型铀矿中铀的平均含量为635μg/g,而铼的含量仅为0.3~1.9μg/g,由于铼的含量低,准确测定高含量铀矿样中的低含量铼仍是分析化学的一个难题。本文建立了电感耦合等离子体质谱法测定砂岩型铀矿中痕量铼的方法。样品经过氧化镁烧结,热水浸提以及采用103Rh作内标元素等方式消除了铀、钼及其他基体元素对测定铼的干扰。在最佳条件下,痕量铼的检出限可低至0.12 ng/g,回收率达99.8%。本方法通过多种标准样品验证,铼的测定值与标准值吻合,对铼含量在0.06~180.57μg/g范围内的实际样品进行测定,相对标准偏差均小于1.5%,能够满足砂岩型铀矿等高含量铀矿中痕量铼的测定需求。 相似文献
818.
The Organyà Basin, south–central Spanish Pyrenees, developed as a marginal depocenter during a rapid extensional phase of anticlockwise rotation of the Iberian plate. As a result of increased subsidence, an important change in sedimentation occurred from the late Barremian to the Aptian leading to unusually high sediment accumulation rates. Approximately 1000 m of hemipelagic marls and limestones accumulated during this time interval.Here we studied the basal 85 m of the hemipelagic facies of the El Pui section, Organyà Basin, that are characterized by alternating 15 cm – ∼3 m thick beds of limestone and marls. Geochemical analyses indicate high total inorganic carbon (TIC) values (average 70%) suggesting enhanced CaCO3 production and deposition. SEM analyses of the samples indicate high abundance of calcareous nannofossils, which together with the absence of shallow water taxa characteristic of the Urgonian Carbonate platform of Organyà, and the lack of sedimentary facies attributable to carbonate platform components point to nannofossils as the main source for the elevated TIC. Organic-rich levels (total organic carbon (TOC) up to 1.74%) concurrent with positive excursions up to 2‰ in δ13Corg, imply enhanced preservation of organic matter (OM) in the basin. In addition, pronounced peaks of δ13Corg higher than the global average suggest superimposed local factors related to intensified 12C removal due to primary productivity. Biomarker analyses and the δ13Corg profile suggest an autochthonous origin of the OM from phytoplankton and possible additional contributions from microbial communities.X-ray diffraction (XRD) results attest for sustained terrestrial fluxes as the source of nutrients to the basin because of a 30% average non-carbonate bulk mineral content in the sediment. The non-carbonate fraction is dominated by quartz (average, 14%) whereas the clay mineral assemblages are characterized by high illite content (>73 relative%) with minor concentrations of kaolinite (<5%), illite /smectite mixed layers (<17%) and chlorite (<15%), consistent with a provenance from the Paleozoic metamorphic terranes adjacent to the Organyà Basin.The integrated results suggest a high sediment accumulation rate (5 cm/ky–7.5 cm/ky) and enhanced carbon burial during the latest Barremian–earliest Aptian in the hemipelagic setting of the El Pui section. 相似文献
819.
820.
Nitrogen is an important gas-phase element in geological fluid,and normally hosted in mineralizing fluid,in which the content is very low.Nearly 100% mol pure nitrogen inclusion was discovered in copper-bearing quartz vein from Xikuangshan copper deposit,Dongchuan,Yunnan Province in this research.It is between 3 and 5 μm,in shape of ellipse,occurring in group or independence without obvious orientation,and co-existed with primary gas-liquid inclusions.Inclusion analysis by using laser Raman spectroscopy shows its composition is dominated by nitrogen with minor H2O.High concentration of N2 may be the necessary and sufficient condition for forming this kind of inclusion.It is suggested that there are two genesis modes of pure N2 inclusion in the deposit,oxida-tion-devolativation of mantle matter and trap of metasomatic fluid in organic matter decomposition in Luoxue For-mation dolomite.In conclusion,pure N2 inclusion hardly presents in the ore-forming fluids,which providing a new evidence for the genesis of Xikuangshan type copper deposit. 相似文献