共查询到20条相似文献，搜索用时 109 毫秒
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Alejandra Piñón-Gimate María Julia Ochoa-Izaguirre Federico Páez-Osuna 《Marine pollution bulletin》2009,58(8):1144-74
Macroalgae blooms of Gracilaria vermiculophylla, Hypnea spinella and Spyridia filamentosa have been found in coastal lagoons in the SE Gulf of California. Agriculture, livestock, shrimp and poultry farms and sewage contribute anthropogenic nitrogen to the systems. The δ15N of these sources, water column and macroalgae were studied in order to identify the N supply for macroalgae blooms. δ15N of three species of macroalgae (4.3-13.6‰) were enriched compared to the water column ( 3.7-6.8‰), probably because of fractioning from the macroalgae. δ15N of POM (1.4-10.3‰) was similar to the water column but the relationship was unclear. Depending on the site, macroalgae showed different δ15N values since some sites receive more or less influence from one given source of the associated watershed, which is reflected in the different δ15N values of the macroalgae of the same system and in the relative contributions of the sources. 相似文献
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Amundsen I Iosjpe M Reistad O Lind B Gussgaard K Strand P Borghuis S Sickel M Dowdall M 《Marine pollution bulletin》2002,44(6):459-468
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Robert F. Benson 《Journal of Atmospheric and Solar》1997,59(18):2281-2293
Ionospheric topside sounders can be considered to act as mobile ionospheric heating facilities. They stimulate a wide variety of plasma phenomena that suggests that significant plasma heating can be produced in the vicinity of the spacecraft following the short duration (0.1 ms) high-power (hundreds of watts) sounder pulse. Most of these phenomena are sensitive to the ambient plasma conditions, particularly to the ratio of the plasma frequency to the gyro frequency . Certain stimulated phenomena only occur, or are greatly enhanced, when where n is an integer. One example is a diffuse signal return that appears at a frequency just above the Z mode wave cutoff frequency (the L = 0 condition in the notation of Stix). This signal, which is the subject of the present paper, is present only for moderately large near-integer values for (e.g., n > 3). It is a relatively short-duration echo—usually less than about 10 ms. These characteristics are quite different from the Z mode echoes often observed between or (whichever is greater) and the upper hybrid frequency . These latter echoes occur for smaller values (not necessarily near-integer values) of and are received during the entire 30 ms listening time period following the sounder pulse. They have been attributed to the scattering of sounder Z mode signals from naturally occurring electron density fieldaligned irregularities (FAI). The short-duration echoes observed just above , on the other hand, are here attributed to the ducting of sounder-generated Z mode waves in sounder-stimulated (or sounderenhanced) FAI. These FAI are believed to be generated (or enhanced) on a very short time scale (? 1 s) by the efficient absorption of sounder energy when the plasma/gyro frequency ratio is nearly an integer value significantly greater than one. The most likely generation process is the filamentation instability driven by the ponderomotive force due to the high-power sounder pulse. 相似文献
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Yu Nishihara Toru Shinmei Shun-ichiro Karato 《Physics of the Earth and Planetary Interiors》2006,154(1):30-43
Grain-growth kinetics in wadsleyite was investigated using a multianvil high-pressure apparatus. Fine-grained wadsleyite aggregates were synthesized by isostatic hot-pressing and were subsequently annealed under high pressure and temperature in a controlled chemical environment. Wadsleyite samples show normal grain-growth characterized by a log-normal grain-size distribution following the relation, where n is a constant, L the grain-size at time t, L0 the grain-size at time t = 0 and k is a rate constant that depends on temperature T and chemical environments (fO2: oxygen fugacity in Pa, COH: water content in H/106Si) as:
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Source parameters and scaling relationships in the Friuli-Venezia Giulia (Northeastern Italy) region
Gianlorenzo Franceschina Stefano Kravanja 《Physics of the Earth and Planetary Interiors》2006,154(2):148-167
We estimated the source parameters of 53 local earthquakes (2.0<ML<5.7) of the Friuli-Venezia Giulia (Northeastern Italy) area, recorded by the short-period local seismic network of the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS), in the period 1995-2003. Data were selected on the basis of high quality locations and focal mechanisms. Standard H/V spectral ratios (HVRS) of the three-component stations of the network were performed in order to assess local amplifications, and only stations showing HVRS not exceeding two were considered for the source parameters estimation. Both velocity and acceleration data were used to compute the SH-wave spectra. Observed spectra were corrected for attenuation effects using an independent regional estimate of the quality factor Q and a station dependent estimate of the spectral decay parameter k. Only earthquakes with ML>3.0 recorded with a sampling rate of 125 cps were used to compute k, thus allowing to visualize a linear trend of the high frequency acceleration spectrum up to 40-50 Hz. SH-wave spectra, corrected for attenuation, showed an ω−2 shape allowing a good fit with the Brune model. Seismic moments and Brune radii ranged between 1.5×1012 and 1.1×1017 N m and between 0.1 and 2.7 km respectively. We obtained Mo=1.1×1017 N m for the seismic moment of the Kobarid (SLO) main shock, in good agreement with the Harvard CMT solution (Mo=3.5×1017 N m). Brune stress drops were confined to the range from 0.07 to 5.31 MPa, with an average value of 0.73 MPa and seem to be approximately constant over five orders of magnitude of seismic moment. Radiated seismic energy computed from two nearby stations scales with seismic moment according to , and apparent stress values are between 0.02 and 4.26 MPa. The observed scatter of Brune stress drop data allowed to hypothesize a scaling relation between seismic moment and corner frequency in order to accommodate both Brune stress drop and apparent stress scalings. No systematic differences are evidenced between stress parameters of earthquakes with different focal mechanisms. As a consequence, a relation of the seismic stress release with the strength of rocks can be hypothesized. A high correlation (r>0.9) of Brune stress drop is found with both apparent stress and RMS stress drop, according to and respectively. 相似文献
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