BASIC: Baltic Sea cyanobacteria. An investigation of the structure and dynamics of water blooms of cyanobacteria in the Baltic Sea—responses to a changing environment     

Lucas J. Stal  Patrizia Albertano  Birgitta Bergman  Klaus von Brckel  John R. Gallon  Paul K. Hayes  Kaarina Sivonen  Anthony E. Walsby 《Continental Shelf Research》2003,23(17-19):1695

The blooms of cyanobacteria that develop each summer in the Baltic Sea are composed of two functional groups, namely the small-sized picocyanobacteria (Synechococcus sp.) and the larger, colony-forming, filamentous N₂-fixing cyanobacteria. The former encompassed both red (phycoerythrin-rich) and blue-green (phycocyanin-rich) species. The majority of the picocyanobacteria measured less than 1 μm and this size fraction comprised as much as 80% of the total cyanobacterial biomass and contributed as much as 50% of the total primary production of a cyanobacterial bloom. The picocyanobacteria are incapable of fixing N₂, do not possess gas vesicles and are not toxic. However, a small filamentous Pseudanabaena sp. that could potentially fix N₂ was isolated from the picocyanobacteria fraction. The larger cyanobacteria may form surface scums because they possess gas vesicles that make them buoyant. Although their biomass was less than the picocyanobacteria, they therefore form the more conspicuous and nuisance-forming part of the bloom. The larger cyanobacteria were composed mainly of three different species: Nodularia spumigena, Aphanizomenon flos-aquae and Anabaena sp. These all belong to the heterocystous, N₂-fixing cyanobacteria. N. spumigena and A. flos-aquae were the dominant species; only N. spumigena was toxic. Although individual Nodularia filaments showed a range of different phenotypes, they all belong to one species as judged from 16S rDNA sequencing. Through determination of the genotypes of many individual Nodularia filaments, it was shown that this population was not clonal and that horizontal exchange of genetic information occurs. N. spumigena and A. flos-aquae were different with respect to their photosynthetic and N₂-fixing potentials. Depending on prevailing environmental conditions, these differences would promote the proliferation of one species over the other and hence would determine overall the toxicity of a bloom. Daily integrals of photon irradiance rather than temperature determined the onset of bloom formation. During a bloom, the diazotrophic cyanobacteria fixed N₂ at a rate that was 10–20% in excess of their own demand for N. Picocyanobacteria assimilated most of this excess N as shown by ¹⁵N incorporation. During bloom conditions, the diazotrophic cyanobacteria met about 50% of the N demand of the total cyanobacterial community. The picocyanobacteria were predominantly N-limited while the diazotrophic cyanobacteria were probably iron limited. These findings allow us to understand the formation of toxic cyanobacterial blooms and also to develop tools to predict bloom formation.  相似文献   

Automatic Surface Reconstruction Based on the Fusion of Fuzzy Logic and Robust Estimation Techniques     

Farhad Samadzadegan  Ali Azizi  Caro Lucas  & Michael Hahn 《The Photogrammetric Record》2002,17(100):651-674

Automatic surface reconstruction by means of digital image matching essentially involves computation in both image and object spaces. In image space, image matching is performed according to certain radiometric and geometric similarity criteria for conjugate point determination. The matching operations may therefore be regarded as decision–making processes. In practice, however, the similarity criteria for conjugate point determination demonstrate non–deterministic behaviour. Thus, the nature of these decision–making processes is more compatible with fuzzy reasoning concepts. In object space, on the other hand, surface reconstruction procedures, which operate on the basis of previously determined conjugate points, are essentially deterministic in nature and hence demand rigorous geometric modelling. In this paper, a new approach for automatic surface modelling is proposed, based on two different mathematical treatments: a fuzzy logic reasoning method for the conjugate point determination in image space; and a robust finite elements approach for the surface modelling in object space. Tests carried out on real data demonstrate the high potential of the strategy proposed.  相似文献   

A very cool brown dwarf in UKIDSS DR1     

S. J. Warren  D. J. Mortlock  S. K. Leggett  D. J. Pinfield  D. Homeier  S. Dye  R. F. Jameson  N. Lodieu  P. W. Lucas  A. J. Adamson  F. Allard  D. Barrado y Navascués  M. Casali  K. Chiu  N. C. Hambly  P. C. Hewett  P. Hirst  M. J. Irwin  A. Lawrence  M. C. Liu †  E. L. Martín  R. L. Smart  L. Valdivielso  B. P. Venemans 《Monthly notices of the Royal Astronomical Society》2007,381(4):1400-1412

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Total mercury and methylmercury in sediments near offshore drilling sites in the Gulf of Mexico     

John H. Trefry  Robert P. Trocine  Michelle L. McElvaine  Robert D. Rember  Lucas T. Hawkins 《Environmental Geology》2007,53(2):375-385

Concentrations of total Hg in sediments near six drilling sites in the Gulf of Mexico were elevated well above average background values of 40–80 ng/g. The excess Hg was associated with barite from discharged drilling mud. In contrast with total Hg, concentrations of methylmercury (MeHg) in these sediments did not vary significantly at nearfield (<100 m) versus farfield (>3 km) distances from the drilling sites. Observed variability in concentrations of MeHg were related to local differences in redox state in the top 10 cm of sediment. Low to non-detectable concentrations of MeHg were found in nearfield sediments that were anoxic, highly reducing and contained abundant H₂S. At most drilling sites, nearfield samples with high concentrations of total Hg (>200 ng/g) had similar or lower amounts of MeHg than found at background (farfield) stations. Higher values of MeHg were found in a few nearfield sediments at one site where concentrations of TOC were higher and where sediments were anoxic and moderately reducing. Overall, results from this study support the conclusion that elevated concentrations of MeHg in sediments around drilling sites are not a common phenomenon in the Gulf of Mexico.  相似文献   

“Where is home?” Here and there: transnational experiences of home among Canadian migrants in the United States     

Susan Lucas  Bandana Purkayastha 《GeoJournal》2007,68(2-3):243-251

Using structured telephone interviews this research focuses on how Canadian migrants living in the United States experience and describe home. We argue that the globalisation of peoples’ lives, transnationalism and the concomitant creation of transnational social spaces have greatly affected the meaning of home for migrants. The understandings of home that result reflect the reality of living in social worlds that span two countries and the development of decentred multiple attachments and feelings of belonging in more than one place. In response to these circumstances Canadian migrants experience home as multi-dimensional, pluri-local, and characterized by regular movement across the U.S.–Canada border. When asked specifically about feeling at home upon re-entry to the U.S. many respondents answered yes. However, many interviewees qualified their answers by describing home in different ways and associating different aspects of their lives with each country. Canada as home was most often described in terms of family, while home in the U.S. was associated with work. Respondents also differentiated between feeling at home once they reached their residence as opposed to feeling unwelcome at the U.S. border.  相似文献   

Snow process monitoring in montane forests with time‐lapse photography          下载免费PDF全文

Chunyu Dong  Lucas Menzel 《水文研究》2017,31(16):2872-2886

A camera network with hourly resolution was used to monitor the complex snow processes in montane forest environments. We developed a semi‐automatic procedure to interpret snow depths from the digital images, which exhibited high consistency with manual measurements and station‐based recordings. To extract snow interception dynamics, six binary classification methods were compared. The MaxEntropy classifier demonstrated better performance than the other methods under conditions of varying illumination and was therefore selected as the method used for quantifying snow in tree canopies. Snow accumulation and ablation on the ground, as well as snow loading and unloading in the forest canopies, were investigated using snow parameters derived from the time‐lapse photography monitoring. The influences of meteorologic conditions, forest cover, and elevation on the snow processes were also considered. Time‐lapse photography proved to be an effective and low‐cost approach for collecting useful information on snow processes and facilitating the set‐up of hydrological models.  相似文献   

The planet formation imager     

John D. Monnier  Stefan Kraus  Michael J. Ireland  Fabien Baron  Amelia Bayo  Jean-Philippe Berger  Michelle Creech-Eakman  Ruobing Dong  Gaspard Duchêne  Catherine Espaillat  Chris Haniff  Sebastian Hönig  Andrea Isella  Attila Juhasz  Lucas Labadie  Sylvestre Lacour  Stephanie Leifer  Antoine Merand  Ernest Michael  Stefano Minardi  Christoph Mordasini  David Mozurkewich  Johan Olofsson  Claudia Paladini  Romain Petrov  Jörg-Uwe Pott  Stephen Ridgway  Stephen Rinehart  Keivan Stassun  Jean Surdej  Theo ten Brummelaar  Neal Turner  Peter Tuthill  Kerry Vahala  Gerard van Belle  Gautam Vasisht  Ed Wishnow  John Young  Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.  相似文献   

Evaluation of remotely sensed data for estimating recharge to an outcrop zone of the Guarani Aquifer System (South America)   总被引：1，自引：0，他引：1  

Murilo Lucas  Paulo T. S. Oliveira  Davi C. D. Melo  Edson Wendland 《Hydrogeology Journal》2015,23(5):961-969

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Airborne LiDAR and Terrestrial Laser Scanning Derived Vegetation Obstruction Factors for Visibility Models     

Jayson Murgoitio  Rupesh Shrestha  Nancy Glenn  Lucas Spaete 《Transactions in GIS》2014,18(1):147-160

Research presented here explores the feasibility of leveraging vegetation data derived from airborne light detection and ranging (LiDAR) and terrestrial laser scanning (TLS) for visibility modeling. Using LiDAR and TLS datasets of a lodgepole pine (Pinus contorta) dominant ecosystem, tree canopy and trunk obstructions were isolated relevant to a discrete visibility beam in a short‐range line‐of‐sight model. Cumulative obstruction factors from vegetation were compared with reference visibility values from digital photographs along sightline paths. LiDAR‐derived tree factors were augmented with single‐scan TLS data for obstruction prediction. Good correlation between datasets was found up to 10 m from the terrestrial scanner, but fine scale visibility modeling was problematic at longer distances. Analysis of correlation and regression results reveal the influence of obstruction shadowing inherent to discrete LiDAR and TLS, potentially limiting the feasibility of modeling visibility over large areas with similar technology. However, the results support the potential for TLS‐derived subcanopy metrics for augmenting large amounts of aerial LiDAR data to significantly improve models of forest structure. Subtle LiDAR processing improvements, including more accurate tree delineation through higher point density aerial data, combined with better vegetation quantification processes for TLS data, will advance the feasibility and accuracy of data integration.  相似文献   

Infrared spectroscopy of substellar objects in Orion     

P.W. Lucas  P.F. Roche  France Allard  P.H. Hauschildt 《Monthly notices of the Royal Astronomical Society》2001,326(2):695-721

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