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61.
62.
Veronica Della Dora 《Geographical review》2015,105(2):251-255
63.
Daniela Veronica Ghica 《Journal of Seismology》2011,15(3):487-506
Data recorded with the Bucovina Romanian Seismic Array (BURAR) seismic array between January 2005 and December 2008 were analyzed
to verify the monitoring capabilities of regional and distant seismicity. For this time interval, nearly 35,000 events detected
by BURAR and identified in seismic bulletins (Preliminary Determination of Epicenters and Romanian Earthquake Catalogue) were
investigated using parameters as backazimuth, epicentral distance and magnitude. A remarkably detection capability is emphasized
for teleseismic observations (Δ > 20°). BURAR onsets could be associated to almost 60% of all events in the teleseismic distance,
with a magnitude detection threshold of 4.5 (mb). When no threshold magnitude is applied, the full detection capability of
BURAR is in the same order as the performance of GERES array, which is one of the most sensitive stations in Central Europe.
For regional events, detection capability decreases to about 16% of all events within regional distance range. The site conditions
(crustal structure and high frequency cultural noise) as well as array dimension, affect the signal coherency and reduce the
array detection capability for regional events. For both teleseismic and regional distances, a monthly variation of BURAR
detection capabilities has been found; the number of events detected during the summer time is diminished by the specific
seasonal human activity and atmospheric conditions (thunderstorms). To prove the good detection capability of the BURAR for
teleseismic distances, a comparison with the observations of the Romanian Real Time Network in terms of magnitude and epicentral
distance was carried out. The higher signal detection capability of BURAR is due to the array techniques applied in data processing,
which enhance the signal-to-noise ratio. The monitoring performed by the BURAR seismic array provides a good azimuthal coverage
of the regional and distant seismicity, in a large range of epicentral distances. 相似文献
64.
Cyprinid fish have pharyngeal teeth that mash ingested food. Here we show that roach (Rutilus rutilus L.), a common cyprinid in Swedish boreal lakes, often break the mandibles of ingested Chaoborus larvae into smaller fragments. The presence/absence of roach in historic fish communities could therefore possibly be determined
from the proportion of fragmented Chaoborus mandibles in lake sediments, which we assessed using the following three approaches. (1) Roach that were fed Chaoborus larvae in laboratory aquaria evacuated a significantly higher fraction of fragmented prey mandibles than perch (Perca fluviatilis L.). (2) Surface sediments from lakes in an acidified region in southwestern Sweden showed significantly higher proportions
of fragmented mandibles for lakes containing roach compared to lakes devoid of cyprinid fish. (3) A paleo-study in Lake Lysevatten,
into which roach were introduced in the 1880s and were extirpated in the 1960s, showed significantly higher proportions of
fragmented mandibles in sediment layers from the roach period. We conclude that mandible fragmentation was related to roach
presence, and propose that the proportion of fragmented Chaoborus mandibles in lake sediments may provide important information when historical cyprinid alterations are of interest, as in
paleo-studies on acidification, eutrophication, or fish introductions. 相似文献
65.
Veronica Rossi Giulia Barbieri Stefano Claudio Vaiani Marco Cacciari Luigi Bruno Bruno Campo Marco Marchesini Silvia Marvelli Alessandro Amorosi 《第四纪科学杂志》2021,36(6):961-979
Framed into a robust stratigraphic context, multivariate analyses on the Holocene palaeobiological record (pollen, benthic foraminifers, ostracods) of the Po coastal plain (NE Italy) allowed the investigation of microtidal ecosystems variability and driving parameters along a 35-km-long land–sea transect. Millennial-scale ecosystem shifts are documented by coeval changes in the meiofauna, reflecting variations in organic matter–water depth (shallow-marine environments) and degree of confinement-salinity (back-barrier settings). In-phase shifts of vegetation communities track unsteady water-table levels and river dynamics in freshwater palustrine areas. Five environmental–ecological stages followed one another crossing four tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. At the culmination of Mediterranean RSL rise, after the 8200 event, remarkable growth of peatlands took place in the Po estuary, while low accumulation rates typified the shelf. At the transgressive–regressive turnaround (~7000 cal a bp ), the estuary turned into a delta plain with tidally influenced interdistributary embayments. River flow regime oscillations after the Climate Optimum (post-5000 cal a bp ) favoured isolation of the bays and the development of brackish wetlands surrounded by wooded peatlands. The youngest threshold (~800 cal a bp ), which led to the establishment of the modern delta, reflects a major avulsion of the Po River. 相似文献
66.
Summary The basic concept of synoptic statistical methods for construction of prognostic charts was outlined by the author in a previous paper. As a result of these investigations it was found that a high correlation exists between time and space means of contourheights of an isobaric surface (850 mb surface). As it has been shown later byPichler this result may be interpreted by assuming that the geopotential fields obeys a numerical solution of the second order homogenous differential equation for wave propagation (hyperbolic equation) provided the phase velocity is given by
. SinceReuter has used for s=666 km and for t=24 hours the conclusion may be drawn that the phase velocity of the wave propagation has an order of magnitude of 5 m/sec. Actually for long waves in the westerlies such a value can be found on an average. The same method can be used for extended forecast procedures if the wave equation is set down for 5 days mean values. Theoretical considerations lead then to a prognostic formula for a 5 days mean chart (8a). This formula can be applied for a sufficient number of grid points in order to construct prognostic charts. The underlying assumption, namely that the mean geopotential field satisfies also a solution of the wave equation turns out to be quite accurate even if only average values of the phase velocity were used for the computation. The usefullness of the method is illustrated for two cases.
Vortrag gehalten am 7. April 1961 auf der 9. Allgemeinversammlung der «Società Italiana di Geofisica e Meteorologia» (Genova, 6.8. April 1961). 相似文献
Vortrag gehalten am 7. April 1961 auf der 9. Allgemeinversammlung der «Società Italiana di Geofisica e Meteorologia» (Genova, 6.8. April 1961). 相似文献
67.
Rates of pelagic nitrification, measured using N-Serve-sensitive [14C]bicarbonate uptake, varied by as much as an order-of-magnitude among three sites along the salinity gradient of Narragansett Bay (Rhode Island, United States). Rates were always higher at the Providence River estuary site (0.04–11.2 μmol N I?1 d?1) than at either the lower Narragansett Bay site (0.02–0.98 μmol N I?1d?1) or the freshwater Blackstone River site (0.04–1.7 μmol N I?1d?1). Although temperature was the most important variable regulating the annual cycle of nitrification, ammonium concentrations were most likely responsible for the large differences in rates among the three sites in summer. At the levels found in this estuarine system, salinity and concentrations of oxygen or total suspended matter did not appear to have a direct measurable effect on nitrification and pH did only occasionally. Nitrification played an important role in the nitrogen cycle at all three sites. In Narragansett Bay, nitrification contributed 55% of the NO2 ? and NO3 ? entering annually, and was the major source during spring and summer. Water from offshore was the only other large source of NO2 ? and NO3 ?, contributing 34%. High summer rates of nitrification could support much of the phytoplankton uptake of NO2 ? and NO3 ?. In the Providence River estuary, the largest annual input of NO2 ? and NO3 ? was from rivers (54%), although nitrification (28%) and water from lower portions of the bay (11%) also made large contributions. Again, nitrification was most important in the summer. The high rates of nitrification in the Providence River estuary during summer were also likely to be important in terms of oxygen demand, and the production of nitric and nitrous oxides. In the Blackstone River, NO2 ? and NO3 ? concentrations increased as the river flowed through Rhode Island, and nitrification was a possible source. 相似文献
68.
Distribution and seasonal variation of concentrations of particulate carbohydrates and uronic acids in the northern Indian Ocean 总被引:3,自引:0,他引:3
Vishwas B. Khodse Loreta Fernandes V.V. Gopalkrishna Narayan B. Bhosle Veronica Fernandes S.G. Prabhu Matondkar Ravi Bhushan 《Marine Chemistry》2007,103(3-4):327-346
Suspended particulate matter (SPM) samples were collected from the surface seawaters at 31 stations, and from various depths (2 to 1000 m) at 9 locations in the northern Indian Ocean during various seasons. SPM samples were analyzed for total particulate carbohydrate (TPCHO), total particulate uronic acid (TPURA) and total particulate neutral carbohydrate (TPNCHO) concentrations and composition. Strong spatial, temporal and depth related variations were evident in the distribution of these compounds. In surface waters, concentrations of TPCHO, TPNCHO, and TPURA varied from 0.57 to 3.58 μM C, 0.11 to 2.34 μM C, and from 0.01 to 0.31 μM C, respectively, and accounted for 2.6 to 34.6%, 2 to 24.5%, and 0.2 to 6.3% of POC, respectively, whereas the TPURA accounted for 4.7 to 22.7% of TPCHO. Concentrations and yields of both TPNCHO and TPURA decreased rapidly in the upper 100 m of the water column suggesting their utilization by heterotrophic organisms. Glucose was the most abundant constituent of the TPNCHO. Glucose mole fraction decreased while that of other monosaccharides, especially galactose, arabinose, mannose, rhamnose and fucose increased in the upper 100 m water. Below this depth, mole fraction of glucose increased while that of other sugars decreased with the increasing water depth. Generally, high C:N ratios were associated with low yields of carbohydrates and uronic acids. Inverse correlation between the mole fractions of arabinose plus xylose and rhamnose plus fucose indicates the importance of biogenic and terrestrial organic matter input to the Bay of Bengal. TPURA are surface-active in nature and thus may play an important role in coagulation of particles and macromolecules. The observed spatial and seasonal variations of these compounds may be due to differences in phytoplankton biomass, nutrient status, and the influence of terrestrial material. 相似文献
69.
70.