Movement of logperch—the obligate host fish for endangered snuffbox mussels: implications for mussel dispersal     

Astrid N. Schwalb  Mark S. Poos  Josef D. Ackerman 《Aquatic Sciences - Research Across Boundaries》2011,73(2):223-231

Unionid mussels are highly imperiled and the survival of their local populations is linked to the availability and dispersal potential of their host fish. We examined the displacement distance of logperch (Percina caprodes), which are obligate host fish for endangered snuffbox mussels (Epioblasma triquetra), to determine the dispersal potential by fish. Logperch in the Sydenham River, Ontario, Canada, were electrofished and marked with visible implant elastomer on five sampling dates during the gravid period of E. triquetra. The majority of all recaptures (82%) of P. caprodes occurred within 30 m of their original capture location, with a mean displacement distance of 13 ± 3 m (mean ± standard error, n = 28). These results were consistent with a review of movement studies of small benthic host fish (i.e., darters and sculpins), which revealed average fish displacement distances of 37 ± 19 m (n = 14 species; range: 4–275 m). However, significantly greater movement distances were also found and the maximum displacement distance increased significantly with the spatial extent of the study and with the duration of the study. These results indicate that many P. caprodes remain in a small area, which could restrict the dispersal and (re)colonization potential of E. triquetra. Further studies are needed to determine the dispersal potential of mussels via host fish, which may be important for maintaining the connectivity among unionid populations.  相似文献   

Optimization of interpolation parameters when deriving DEM from contour lines   总被引：1，自引：0，他引：1  

Stanislav Bek  Josef Je?ek 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1049-1055

Digital elevation models (DEMs) are still an important and current source of information for digital soil mapping and the modeling of soil processes. The grid DEM is often interpolated from contour lines. The contour sampling step becomes an additional interpolation parameter which can play an important role. The objective of this paper is to optimize the interpolation parameters of the Regularized spline with tension (RST) method, in order to prepare a DEM suitable as an input for erosion modeling. Two contrasting cases, with and without a reference DEM, were investigated. If a reference DEM was available, good results of interpolation were reached both by small and larger sampling steps. In the second case, it was found that small sampling steps should be avoided. The influence of the sampling was demonstrated by topographic potential for erosion and deposition.  相似文献   

Microbial community and activity shifts after soil transplantation in a glacier forefield     

Anita Zumsteg  Stefano M. Bernasconi  Josef Zeyer  Beat Frey 《Applied Geochemistry》2011

The majority of Alpine glaciers are currently receding because of global warming. Their forefields have become interesting sites to study primary microbial colonisation and microbial adaptation. Here, the structure and enzyme activity of microbial communities in exposed rock substrates and their changes in a gradient of temperature and soil moisture conditions within the forefield of the Damma glacier in the Swiss Central Alps are discussed. The temperature at the sites differed in the course of a day and also showed differing mean temperatures over the summer. Distinct bacterial communities inhabit the differing sites at the beginning of the experiment and even after transplantation they stay distinct. But a seasonal shift in the communities could be observed, which followed the same pattern for all the samples. Interestingly, microbial enzyme activity was highest at the site with the smallest temperature shifts.  相似文献   

Synthetic Spectra for Carbon Stars from Dynamica Model Atmospheres     

Rita Loidl  Josef Hron  Bernhard Aringer  Susanne Höfner  Uffe G. Jφrgensen 《Astrophysics and Space Science》1997,255(1-2):289-290

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Dust Features of Visually Bright AGB Variables as Seen by ISO and IRAS     

Josef Hron  Rita Loidl  Franz Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):211-214

ISO-SWS spectra of two Mira variables (R Cas and T Dra), taken at two different pulsational phases, are presented. We describe the reduction of the data and the encountered problems. The dust features observed by ISO at different phases and with the Low Resolution Spectrometer of IRAS are compared. We briefly discuss the results in terms of current models for the circumstellar dust shells of AGB variables. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Observations of Jet Diameter, Density and Dynamics     

Francesca Bacciotti  Thomas P. Ray  Jochen Eislöffel  Jens Woitas  Josef Solf  Reinhard Mundt  Christopher J. Davis 《Astrophysics and Space Science》2003,287(1-4):3-13

Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow.  相似文献   

Synthetic radii and visibilities for pulsating red giants     

Josef Hron  Walter Nowotny  Rita Gautschy-Loidl  Susanne Höfner 《Astrophysics and Space Science》2003,286(1-2):213-218

We present synthetic radii and visibilities in the IR, based on hydrostatic and dynamic model atmospheres of carbon stars. The differences between these two sets of input models and to uniform disc models are discussed and compared to the expected capabilities of the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Effect of the Screen on the Mass, Momentum, and Energy Exchange Rates of a Uniform Crop Situated in an Extensive Screenhouse   总被引：2，自引：2，他引：0  

Mario B. Siqueira  Gabriel G. Katul  Josef Tanny 《Boundary-Layer Meteorology》2012,142(3):339-363

The area of crops cultivated in extensive screenhouses is rapidly growing, especially in semi-arid and arid regions. Water vapour, carbon dioxide, and sensible heat released or taken up by crops within such protected environments can substantially alter the immediate micro-environment, which in turn, affects these fluxes. This amplified interaction between plants and their microclimate challenges simple assessments on how partially covering the crop by a screen modifies plant water uptake and photosynthesis. Via a newly proposed higher-order closure model, the effects of a screen on the mean flow field, turbulent stresses, radiative and energy fluxes, as well as scalar sources, sinks, fluxes, and mean scalar concentration within screenhouses are explored. As a starting point, an extensive screenhouse is assumed thereby reducing the sensitivity of the model results to the precise geometric configuration of the screenhouse. The model findings for the screenhouse are presented and referenced against their open field counterpart. The radiation modulation and changes to turbulent transport due to the presence of the screen are investigated. In general, the presence of a screen results in a warmer and more humid environment inside the screenhouse, promoting reductions in both canopy photosynthesis and transpiration. However, the overall effect of the screen is to enhance water-use efficiency thereby resulting in water savings for the same amount of gross primary production.  相似文献   

Comparative Study of the Spherical Downward Continuation     

Josef Sebera  Martin Pitoňák  Eliška Hamáčková  Pavel Novák 《Surveys in Geophysics》2015,36(2):253-267

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克鲁格曼的新经济地理研究及其意义   总被引：11，自引：0，他引：11  

段学军  虞孝感  陆大道  Josef Nipper 《地理学报》2010,65(2):131-138

克鲁格曼在借鉴经典区位理论的基础上,引入了世界贸易、新经济增长理论的最新研究成果,改造并创新了传统区位理论,在此基础上构造出一套新的空间区位理论-称之为新经济地理学。克鲁格曼以在该领域及此前在国际贸易和世界经济形势预测方面的贡献,获得了2008年度诺贝尔经济学奖。克鲁格曼新经济地理学是经济地理学在新形势下取得的新成果,解决了许多传统区位理论未能解决的难题,而且使经典区位理论获得了新的发展动力。但是,长期以来克鲁格曼新经济地理学被认为与地理界所研究的经济地理学关系不大,未引起地理学界的足够重视。本文从地理学的角度对克鲁格曼所研究的新经济地理学的内涵、研究意义及其与传统区位论的关系等方面,重新解读和审视克鲁格曼的新经济地理学,分析该理论对经济地理学发展的影响,以期对中国经济地理学的创新研究和制订区域科学发展路线图提供参考。  相似文献