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71.
It is often presumed that salt marshes provide a predation refuge for small fishes, but predation risks have rarely been compared in intertidal and subtidal habitats, making the importance of salt marshes as a predation refuge speculative. We measured relative survival of tethered mummichog (Fundulus heteroclitus) in four habitats in a salt marsh?Ctidal creek system: unvegetated and vegetated intertidal areas and the subtidal creek at high and low tide. At high tide, mummichog in the intertidal zone had significantly higher survival than in the subtidal creek in June through August. Survival rates in unvegetated and vegetated intertidal habitats were not significantly different, suggesting that higher intertidal survival was due to less abundant predators compared with the creek, rather than predators being less effective in vegetation. The lower predation risk experienced by mummichog in the intertidal marsh suggests that access to intertidal habitats will be important for production of small estuarine fishes. 相似文献
72.
Erica X.Y. Yap 《Singapore journal of tropical geography》2013,34(3):390-406
From Shanghai's Pudong to Dubai's Marina, waterfront developments are increasingly popular urban forms worldwide. Drawing on the literature on urban assemblages, I explore how urban waterfronts are produced out of the transnational assembling of models, knowledge and expertise. My case study here is Marina Bay, Singapore, a landscape that like much of the rest of Singapore is a product of talent and ideas from elsewhere. In this paper, two strategies employed by Singapore's urban authorities to court global expertise for Marina Bay's development are examined – their formation of an international panel of experts in the fields of urban planning, policy and design, and their launching of international competitions to attract top design firms. Like transfer agents that enable policies to travel, I argue that these individuals and firms are situated within wider knowledge circuits that straddle the globe, and are thus well placed to filter and channel ideas from elsewhere to Singapore. Drawing on selected developments within Marina Bay, I trace the routes taken by these ideas, the changes they underwent as they travelled, as well as their relationships with the actors that facilitated their journeys. In doing so, I hope to demonstrate the usefulness of understanding the urban as more‐than‐territorial in both theory and practice. 相似文献
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74.
G. D. Fleishman 《Astronomy Letters》2004,30(9):603-614
We studied the spectral properties of the electron cyclotron maser emission generated by anisotropic distributions of fast electrons with power-law magnitude distributions in solar flares. The natural bandwidth of the generated spectral line depends significantly on the angle between the direction of the wave emission and the direction of the magnetic field in the source. In addition, the line bandwidth depends on the parameters of the momentum and pitch-angle distribution functions for fast electrons. The typical spectral bandwidths are shown to lie within the range 0.1–0.4%, in agreement with the minimum observable bandwidths of millisecond solar radio spikes. 相似文献
75.
Larisa Fleishman 《Geoforum》2008,39(2):1021-1043
The Green Line constituted the armistice line between Israel and Jordan during the period 1949-1967. This paper discusses the familiarity of Israeli students with the nature and geographical location of the Green Line by restructuring and analyzing their mental maps. The findings of this study show that students who are men, long-term residents, identify themselves on the left end of the political spectrum, and professional geographers, show better knowledge concerning the issue of borders. However, most students revealed a certain vagueness and even ignorance concerning both spatial perception of the Green Line and its essence. The reasons for the revealed phenomenon are also discussed in this paper, as well as the behavioral implications of the familiarity with the Green Line, both in spatial and political contexts. 相似文献
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Stephanie Stainbank Silvia Spezzaferri Dick Kroon Erica S. de Leau Andres Rüggeberg 《Swiss Journal of Geoscience》2018,111(3):511-522
Here we define a new morphospecies of planktonic foraminifera Globigerinoides eoconglobatus n. sp., identified from International Ocean Discovery Program (IODP) expedition 359 samples from drift deposits of the Maldives, Inner Sea. Through biostratigraphic analysis, we infer it may be the direct ancestor of Globigerinoides conglobatus evolving from Globigerinoides obliquus in the Late Miocene (Subzone M13a). Globigerinoides eoconglobatus n. sp. can be distinguished from G. conglobatus through both its morphological traits and stable isotopic signature (δ18O and δ13C) in pre-adult and adult specimens. The most defining characteristic being its aperture height (AH). A variance in adult stable isotopic signals shows a possible difference in life strategies, possibly related to symbionts (presence/absence or concentration) and/or depth habitat. This work also tentatively shows G. eoconglobatus n. sp. and G. conglobatus abundances are linked to glacial–interglacial stages. Its low abundances and similarities to its descendent Globigerinoides conglobatus has likely accounted for it being unreported, until present, in both modern and fossil studies. 相似文献
78.
Mauro Celussi Alessandro Paoli Erica Crevatin Andrea Bergamasco Francesca Margiotta Vincenzo Saggiomo Serena Fonda Umani Paola Del Negro 《Estuarine, Coastal and Shelf Science》2009,81(4):491-500
During the 2006 Italian Antarctic expedition a diel sampling was performed close to Cape Hallett (Ross Sea) during the Austral summer. Under-ice seawater samples (4 m) were collected every 2 h for 28 h in order to estimate prokaryotic processes' variability and community structure dynamics. Prokaryotic and viral abundances, exoenzymatic activities (β-glucosidase, chitinase, lipase, alkaline phosphatase and leucine aminopeptidase), prokaryotic carbon production (3H-leucine incorporation) and community structure (Denaturing Gradient Gel Electrophoresis – DGGE fingerprints) were analysed. Results showed that the diel variability of the prokaryotic activity followed a variation in salinity, probably as a consequence of the periodical thawing of sea ice (driven by solar radiation and air temperature cycles), while negligible variation in viral and prokaryotic abundances occurred. The Bacterial and Archaeal community structures underwent an Operational Taxonomic Units (OTUs) temporal shift from the beginning to the end of the sampling, while Flavobacteria-specific primers highlighted high variations in this group possibly related to sea ice melting and substrate release. 相似文献
79.
High-time-resolution observations of an unusual event of 1991 November 17, 07:04 UT at 2.5 and 2.85 GHz are presented. The event demonstrates sophisticated tine time structure including sudden reductions and quasi-periodic pulsations about various zero levels. It is shown that the sudden reductions (30–100 ms) can be produced with upward-injected > 100 keV electron beams filling the loss-cone. In such a case the acceleration is proceeding in a dense plasma layer with number densityn > 2.5 × 1010 cm–3. The shortest time scale of the fragmented injection is
inj
min
30 ms. Several different pulsating regimes arising due to the wave-particle and wave-wave interactions are considered. A theoretical mechanism with the nonlinear oscillations of Langmuir waves at the different steady-state levels provides the best agreement with the observed pulsations. The reduced steady-state level of the second train of pulsations is connected with the long (quasi-continuous) injection of electrons filling the loss-cone, which reduced the wave energy level. Physical parameters of the radio source were obtained. On the other hand, ECM nonlinear pulsations seem to be responsible for the radio pulsations observed in dMe stars. 相似文献
80.
Determining Biogenic Silica in Marine Samples by Tracking Silicate and Aluminium Concentrations in Alkaline Leaching Solutions 总被引：5，自引：0，他引：5
This study introduces an alkaline leaching technique for the simultaneous analysis of biogenic silica and aluminium in sediments. Measuring aluminium facilitates the discrimination between silica from the biogenic (BSiO2) and the non-biogenic fraction, because it originates almost solely from the lithogenic phase. The method was tested using fine-grained silicagel, standard clay minerals, artificial sediments, and natural samples ranging from fresh diatoms to aged sediment from different depositional settings. To determine the BSiO2 content, four different models each describing the dissolution curves, but of increasing complexity, were applied and for each different type of sample the optimum model was selected on the basis of F-test statistics. For mixtures of silicagel and clay minerals, the contribution of Si from the dissolution of clay was negligible compared to Si originating from silicagel. For natural samples with high clay content, complex dissolution curves were observed and single-phase first order dissolution was the exception. This deviation from `ideal' behavior could only be recognized because of high-resolution sampling, especially in the first 20 minutes of the experiment. For most of the samples, the distinction between the biogenic silica fraction and the silica originating from dissolution of clays could be made on the basis of the Si/Al ratios and reactivity constants of the dissolving phases calculated with the models. Clay minerals typically dissolve slowly at a Si/Al ratio close to 1–2, depending on the type of clay mineral. In contrast, biogenic silica displays a wide range of reactivities and Si/Al ratios. Fresh biogenic silica from the water column usually has a high reactivity and a low Al content. Aged biogenic silica from the sediments has a lower reactivity, but Si/Al ratios as low as 5 were found. The method as described here therefore presents an accurate method to analyze biogenic silica in marine sediments with a relatively high clay mineral content. 相似文献