Plant diversity and community structure of Brazilian <Emphasis Type="Italic">Páramos</Emphasis>     

Prímula Viana Campos  Pedro Manuel Villa  Jaquelina Alves Nunes  Carlos E.G.R. Schaefer  Stefan Porembski  Andreza Viana Neri 《山地科学学报》2018,15(6):1186-1198

In Eastern South America, high altitude grasslands represent a mountain system that has a high number of endemic species. However, studies on the ecology of plant communities in these environments remain scarce. We aimed to evaluate the patterns of biodiversity and structure of plant communities from rocky outcrops in high altitude grasslands of three areas at the Caparaó National Park, southeastern Brazil, by sampling 300 randomly distributed plots. Then, we compared the floristic composition, relative abundance, and biological and vegetation spectra among areas. We classified species as endemic and non-endemic and verified the occurrence of endangered species. Species richness was evaluated by rarefaction analysis on the sampling units. The importance value and species abundance distribution (SAD) models were assessed. We also performed an indicator species analysis. We sampled 58 species belonging to 49 genera and 32 families. The number of species decreased with increasing altitude, with significant differences being observed among areas regarding richness, abundance, and cover. Of the total number of species, 10 are endemic to the Caparaó National Park and 17 are listed on the Brazilian Red List of endangered species. The dominant families on all peaks were Asteraceae and Poaceae. The SAD models showed lognormal and geometric distributions, corroborating the fact that 10 species that were common to all three areas were also the most dominant ones in the communities and showed the highest importance values, which ranged between 35% and 60%. Indicator species analysis revealed that 28 species (48.27%) were indicators. Of these, 42.85% had maximum specificity, meaning that they occurred only in one area. Thus, the number of species per life form ratio was similar among areas, yet vegetation spectra differed, especially for hemicryptophytes. The altimetric difference among the areas showed to be a very important driver in the community assembly, influencing the evaluated variables, however, other drivers as soil depth, slope and water could also influence the community structure on a smaller and local spatial scale.  相似文献   

A focal plane detector design for a wide-band Laue-lens telescope     

Ezio Caroli  Natalia Auricchio  Lorenzo Amati  Yuriy Bezsmolnyy  Carl Budtz-JøRgensen  Rui M. Curado da Silva  Filippo Frontera  Alessandro Pisa  Stefano Del Sordo  John B. Stephen  Giulio Ventura 《Experimental Astronomy》2005,20(1-3):341-351

The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy. Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies.  相似文献   

Microwave and hard X-Ray observations of a solar flare with a time resolution better than 100 ms     

P. Kaufmann  F. M. Strauss  J. E. R. Costa  B. R. Dennis  A. Kiplinger  K. J. Frost  L. E. Orwig 《Solar physics》1983,84(1-2):311-319

Simultaneous microwave and X-ray observations are presented for a solar flare detected on May 8, 1980 starting at 19:37 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28–490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms, respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive peaks in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240 ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5 s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model.  相似文献   

Quick-look assessments to identify optimal CO2 EOR storage sites   总被引：1，自引：0，他引：1  

Vanessa Núñez-López  Mark H. Holtz  Derek J. Wood  William A. Ambrose  Susan D. Hovorka 《Environmental Geology》2008,54(8):1695-1706

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.  相似文献   

Constraining the origin and evolution of confined turbidite systems: southern Cretan margin,Eastern Mediterranean Sea (34°30–36°N)     

Tiago M. Alves  Vasilios Lykousis  Dimitris Sakellariou  Stamatina Alexandri  Paraskevi Nomikou 《Geo-Marine Letters》2007,27(1):41-61

Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises >100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms (TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently, topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic and eustatic episodes affecting the Eastern Mediterranean.  相似文献   

Variability in the nutritional value of the major copepods in Cape Cod Bay (Massachusetts, USA) with implications for right whales     

Amy DeLorenzo Costa  Edward G. Durbin  & Charles A. Mayo 《Marine Ecology》2006,27(2):109-123

The North Atlantic right whale, a seriously endangered species, is found in Cape Cod Bay (Massachusetts, USA) during the winter and early spring. During their residency in these waters, these whales are frequently observed feeding. This study evaluated spatial and temporal changes in the chemical composition (carbon weight and C/N ratio) of the food resource targeted by the right whales in Cape Cod Bay. The three taxa measured (Centropages typicus, Pseudocalanus spp., and Calanus finmarchicus) had highly variable chemical compositions resulting from the different life strategies and from fluctuations in their surrounding environment. The impact of seasonal variability in the energy densities of the food resource of right whales was calculated and compared to the energetic requirements of these whales. Calculations indicated that differences in the nutritional content of the zooplankton prey in Cape Cod Bay could have a considerable effect on the nutrition available to the right whales. Therefore, it is likely that using more precise estimates of the energetic densities of the prey of right whales would lead to a re‐evaluation of the adequacy of the food resource available to these whales in the North Atlantic.  相似文献   

Effects of water-borne copper on metallothionein and lipid peroxidation in the marine amphipod Gammarus locusta   总被引：1，自引：0，他引：1  

Correi AD  Livingstone DR  Costa MH 《Marine environmental research》2002,54(3-5):357-360

The aim of the current work was to determine over 10 days the effects of water-borne exposure of the marine amphipod Gammarus locusta to 4 microgCu l(-1) on the metallothionein (MT; measured by differential pulse polarography) protection system and lipid peroxidation (LP: thiobarbituric acid-reactive malondialdehyde equivalents) as a measure of oxidative damage. MT levels in exposed animals increased significantly at day 2 (36% > control; P < 0.001) and remained high at days 6 and 10 (55 and 38%, respectively, P < 0.001). The maximum level of MT at day 6 coincided with the highest Cu body-burden. LP increased within I day of exposure, indicative of Cu as an oxidative stressor. However, in contrast to MT, the highest LP level was seen at day 4 (68% > control, P < 0.001) before returning to control values by day 6, indicating a protective role of MT against the pro-oxidant effects of Cu.  相似文献   

冲绳海槽轴线地质特征   总被引：10，自引：2，他引：10  

杨文达  王振宇  曾久岭 《海洋地质与第四纪地质》2001,21(2):1-6

冲绳海槽位于东海大陆架与琉球岛弧之间，海槽中发育着一系列平行轴向延伸的地堑型正断层。穿越海槽的地震剖面证实了海槽扩张中心的存在，扩张轴沿海槽轴线方向延伸。由于地堑构造中心的扩张速率较大，由某引起的海槽中心下陷的速率大于沉积作用的补偿速率，使海槽中心海底出现明显的下陷。在轴线的大陆坡一侧，陆源沉积占绝对优势；轴线的岛坡一侧，以火山坡碎屑、浮岩、有孔虫软泥为沉积特征。  相似文献   

Sample treatment with focused ultrasound and bath sonication as a powerful tool for the evaluation of cadmium pollution in estuarine waters     

R. Agapito  S. Alves  J.L. Capelo  M.L. Gonalves  A.M. Mota 《Marine Chemistry》2006,98(2-4):286-294

A new sample treatment was developed for the determination of dissolved cadmium in Tagus estuarine waters, based on focused ultrasound in conjunction with small volumes in the extraction steps for Cd pre-concentration. Cadmium was first pre-concentrated using a classical approach (APDC as the complexing agent and MIBK as the organic phase) and then back-extracted into HNO₃ with the aid of focused ultrasound, which reduced the acid concentration by more than one order of magnitude (from 4 to 0.1 mol L^− 3). This sample treatment was accomplished in less than 5 min, using low sample volume (20 mL), and low-volume, low-concentration reagents. The pre-concentration factor used in this work was 25, but different sample/organic volume ratios may be used in order to increase that value. The limit of detection and the limit of quantification in Tagus water samples were 0.03 nmol L^− 1 and 0.1 nmol L^− 3, respectively. Recoveries from spiked Tagus water were higher than 90%. The procedure was validated using the reference estuarine water NRC-SLEW-3. In the solubilization of Cd particulate, bath ultrasonication was used in conjunction with HNO₃ + HCl, followed by H₂O₂, which took about 2 instead of the usual 12 h (cooling included) when high-pressure microwave digestion is used.  相似文献   

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: II. Organism and population-level endpoints     

Costa FO  Neuparth T  Correia AD  Costa MH 《Marine environmental research》2005,60(1):93-110

This study aimed to test the performance of the amphipod Gammarus locusta (L.) in chronic sediment toxicity tests. It constitutes part of a multi-level assessment of chronic toxicity of estuarine sediments, integrating organism and population-level endpoints with biochemical markers responses. Here we account for organism and population-level effects, while biomarker responses were reported in a companion article. Five moderately contaminated sediments from Sado and Tagus estuaries were tested, comprising 3 muddy and 2 sandy sediments. These sediments either did not show acute toxicity or were diluted with control sediment as much as required to remove acute toxicity. Subsequent chronic tests consisted of 28-day exposures with survival, individual growth and reproductive traits as endpoints. Two of the muddy sediments induced higher growth rates in the amphipods, and improved reproductive traits. This was understood to be a consequence of the amount of organic matter in the sediment, which was nutritionally beneficial to the amphipods, while concurrently decreasing contaminant bioavailability. Biomarker responses did not reveal toxicant-induced stress in amphipods exposed to these sediments. One of the sandy sediments was acutely toxic at 50% dilution, but in contrast stimulated amphipod growth when diluted 75%. This was presumed to be an indication of a hormetic response. Finally the two remaining contaminated sediments showed pronounced chronic toxicity, affecting survival and reproduction. The sex ratio of survivors was highly biased towards females, and offspring production was severely impaired. The particulars of the responses of this amphipod were examined, as well as strengths versus limitations of the sediment test. This study illustrates the utility of this chronic test for toxicity assessment of contaminated estuarine sediments, with potential application all along Atlantic Europe.  相似文献