Temporal trends in abundance of fish in the tidal Delaware River     

Stephen B. Weisberg  Peter Himchak  Tom Baum  Harold T. Wilson  Russell Allen 《Estuaries and Coasts》1996,19(3):723-729

Water quality in the tidal Delaware River has improved dramatically over the last several decades. Areas near Philadelphia that were once anoxic and formed a pollution block to migratory fish passage now rarely experience dissolved oxygen concentrations less than 3 ppm. To assess whether these improvements in water quality led to increased abundance of juvenile fishes, data from a beach seine survey conducted annually since 1980 were examined. The number of species captured increased throughout the tidal river, but the increase was greatest in the areas downstream of Philadelphia, wheare water quality has improved the most. Abundance of juvenile striped bass and American shad, two important game species in the river whose migratory patterns make them susceptible to water quality problems, both increased more than, 1,000-fold during the last decade. Correlatations between the temporal abundance patterns of these species in the tidal Delaware River and in other East Coast systems were poor, suggesting that increases in their numbers were related more closely to improving conditions within the Delaware than to factors affecting coastal stocks.  相似文献   

Navigating Space Vehicles Using Signals From NAVSTAR GPS Satellites     

Tom Logsdon 《GPS Solutions》1995,1(2):86-87

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The geology and geophysics of the ambrym caldera,New Hebrides     

G. J. H. McCall  R. W. LeMaitre  A. Malahoff  G. P. Robinson  P. J. Stephenson 《Bulletin of Volcanology》1970,34(3):681-696

Ambrym Island has an unusually large, well-preserved basaltic caldera 13 km across. The caldera occurs in the central region of an early broad composite cone, which formed a north-south line with three smailer volcanoes. Alter the caldera was formed volcanism occurred within it and along fissure lines running nearly east-west. Two volcanic cones are active almost continuously and historic fissure cruptions have been recorded. The caldera formed by quiet subsidence, or by subsidence accompanied by eruption of scoria lappili similar to that erupted prior and subsequent to caldera formation. The collapse was at least 600 metres and radiocarbon dating suggests it took place less than 2000 years ago. The caldera is detined by gravity anomalies 10 to 14 milligals lower than those at its rim suggesting predominantly ash infilling. Aeromagnetic anomalies show a prominent. nearly east-west lineation, with normally magnetised bipole anomalies over the centre of the caldera and over fissure lines east of it. The source of the present volcanic activity is believed to be located along dyke fissures, with a perched magma chamber beneath the caldera. The geophysical evidence on Ambrym, together with that of regional east trending magnetic anomalies and recent bathymetric results, suggests that the volcanic activity is localised by the intersection of an east-west fracture zone with the axis of the New Hebrides island are.  相似文献   

Accelerograph calibration and accelerogram correction     

R. I. Skinner  W. R. Stephenson 《地震工程与结构动力学》1973,2(1):71-86

When measured earthquake accelerations are used as a basis for structural design, then acceleration errors of a few per cent are usually acceptable. However a number of tasks in structural design, and in earthquake engineering research, require measured accelerations with errors limited to a few parts per thousand. Such tasks include those which call for the calculation of angular accelerations, the comparison of acceleration spectra or the calculation of relative displacement Accurate accelerations may be obtained from existing accelerographs by applying the results of an accurate static calibration to an accelerogram, and then applying corrections for the effects of accelerometer resonance. This paper concentrates attention on the correction of static errors, including sensing direction errors and cross-axis interaction errors. For completeness there is a brief discussion of dynamic errors, which depend on accelerometer periods and dampings. It is concluded that earthquake accelerations may be obtained with errors of not much more than 0·001 g, the resolution of a typical accelerograph, at least for periods greater than 0·2 sec. When the accelerations have shorter periods, larger errors may arise due to the limited accuracy of the corrections for dynamic errors The static calibration of accelerographs, and the corresponding record correction procedures, are illustrated by application to the M.O.2 accelerograph.  相似文献   

Synthetic and natural chlorine-bearing apatite     

Tom K. Ekström 《Contributions to Mineralogy and Petrology》1973,38(4):329-338

Hydrothermal syntheses of chlor-hydroxyapatite have been carried out between 300 and 700° C at a constant pressure of 1000 bar. The substitution of OH for Cl varies as a function of the amount of added CaCl₂, temperature, and pH. In the main reaction the incorporation of Cl is negligible at 300° C but increases to over 40 mole percent Cl-apatite at 700° C. A simple X-ray method for determining the Cl/Cl+OH ratio has been developed and this is also extended to fluorine-bearing chlor-hydroxyapatites. A number of natural chlor-fluorhydroxyapatites are discussed in the light of the X-ray method and the result of the synthesis.  相似文献   

GPS/GNSS Current Bibliography     

Tomás?SolerEmail author 《GPS Solutions》2003,7(3):206-208

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A note on frame transformations with applications to geodetic datums   总被引：1，自引：0，他引：1  

Tomás?SolerEmail author  John?Marshall 《GPS Solutions》2003,7(1):23-32

Rigorous equations in compact symbolic matrix notation are introduced to transform coordinates and velocities between ITRF frames and modern GPS-based geocentric geodetic datums. The theory is general but, after neglecting higher than second-order terms, it is shown that the equations revert to the formulation currently applied in most major continental datums. We discuss several examples: the North American Datum of 1983 (NAD83), the European Terrestrial Reference System of 1989 (ETRS89), the Geodetic Datum of Australia of 1994 (GDA94), and the South American Geocentric Reference System (SIRGAS). Electronic Publication  相似文献   

Automatic Location of Swarm Earthquakes from Local Network Data     

Fischer  Tomáš 《Studia Geophysica et Geodaetica》2003,47(1):83-98

An advanced method of automated seismic phase picking and exact location and magnitude determination of swarm micro-earthquakes from local network data is presented. The phase picker is applied in two steps: first, S-wave groups are identified using a polarisation detector, and then corresponding P-wave groups are searched for. The times of maximum P- and S-amplitudes are then used as starting points for the determination of accurate P- and S-arrival times. The maximum S-wave amplitudes are utilised for determining local magnitudes. The whole procedure is checked by simultaneous preliminary hypocentre location providing estimates of local magnitudes and a compatibility check of the candidate P- and S-phases. The closest station to the earthquake cluster is used as a master, and the phase search at the remaining stations is governed by the P- and S-phases identified at the master station. Thanks to the use of apriori information on the approximate position of hypocentres, the procedure is also capable of picking the individual P- and S-phases of sequences of overlapping swarm events. The performance of the procedure was tested by comparison of the automatically and interactively created catalogues of the January 1997 NW-Bohemia micro-earthquake swarm. With stations located at epicentral distances between 0 and 20 km, the difference between hypocentre coordinates obtained by automatic and interactive processing did not exceed 80 m for 86% events. All events above magnitude 0.5 were identified, and the automatically determined polarity of first P-wave motion proved to be correct in 89% of them.  相似文献   

Köppen Climate Types in Observed and Simulated Climates     

Kalvová  Jaroslava  Halenka  Tomáš  Bezpalcová  Klára  Nemešová  Ivana 《Studia Geophysica et Geodaetica》2003,47(1):185-202

The Köppen climate classification was applied to the observed gridded climatological sets and the outputs of four general circulation models (GCMs) over the continents of the Earth. All data had been acquired via the Data Distribution Centre established by the Intergovernmental Panel on Climate Change. The ability of the GCMs to simulate the Köppen climate zones identified in the real data was explored and possible future (global warming) changes in the climate types' distribution for each GCM were assessed. Differences in the area distributions derived from the GCMs' recent climate simulations give evidence about uncertainties generally involved in climate models. As to the global warming simulations, all GCM projections of warming climate (horizon 2050) show that the zones representing tropical rain climates and dry climates become larger, and the zones identified with boreal forest and snow climates together with the polar climates are smaller.  相似文献   

On the Integrability of Limited-Area Numerical Weather Prediction Model ALADIN over Extended Time Periods     

Huth  Radan  Mládek  Richard  Metelka  Ladislav  Sedlák  Pavel  Huthová  Zuzana  Kliegrová  Stanislava  Kyselý  Jan  Pokorná  Lucie  Halenka  Tomáš  Janoušek  Martin 《Studia Geophysica et Geodaetica》2003,47(4):863-873

This note summarizes results of the first integration of regional numerical weather prediction model ALADIN in a climate mode. The ALADIN model, developed in an international cooperation led by Météo France, is operationally used for weather prediction. The grid step of the model is 12 km; the integration domain covers a major part of Europe. A one-month-long run has been performed with this model on observed boundary conditions (represented by assimilations by the global model ARPEGE). It is demonstrated that no excessive error is generated and accumulated in the model during the integration; hence the model is integrable for extended time periods and may serve a basis for a development towards a regional climate model.  相似文献