Rayleigh wave magnitude scaleM s     

P. D. Marshall  P. W. Basham 《Pure and Applied Geophysics》1973,103(1):406-414

Summary TheM _s Rayleigh wave magnitude formula is revised for purposes of eliminating the variable effects of near distances and propagation pats on the values computed from standard long period seismograms. The improved formulation employs a revised distance correction function and period dependent path correction that normalisesM _s to large teleseismic distance, 20 second values. The method for computing the path corrections is described. The magnitude scale presented here givesM _s values which are within ±0.1 magnitude units of the Gutenberg and Prague magnitude formulae.  相似文献   

Ion balance,acid-base regulation,and chloride cell function in the common killifish,Fundulus heteroclitus—a euryhaline estuarine teleost     

Chris M. Wood  William S. Marshall 《Estuaries and Coasts》1994,17(1):34-52

The common killifish,Fundulus heteroclitus, is a euryhaline teleost common throughout estuaries of eastern North America. This symposium paper reviews the important contributions of the killifish to our present understanding of ionoregulation in seawater (SW) fish and their mechanisms of euryhalinity, and presents new data developing the killifish as a freshwater (FW) model system. Experiments on killifish have characterized (i) drinking in SW and its reduction in FW; (ii) the adaptive roles of the kidney to SW and FW conditions; (iii) the instantaneous (Phase I) and delayed (Phase II) reductions in Na⁺ outflux that occur upon transfer from SW to FW; (iv) the importance of prolactin secretion in the Phase II effect; (v) the cortisol-stimulated induction of branchial Na⁺, K⁺-ATPase that occurs upon transfer from FW to SW; (vi) the accompanying changes in morphology of the mitochondria-rich (MR) or “chloride cells” on the gills; (vii) the localization of this Na⁺, K⁺-ATPase activity to the basolateral membrane of chloride cells; and (viii) the NaCl-secretory function of these cells in SW. The opercular epithelium, which is rich in chloride cells, has been used as an in vitro model to characterize the mechanisms and control of NaCl secretion in SW fish. Much less is known about gill function in fresh water (inward NaCl transport), primarily due to the absence of a comparable freshwater model. Here we show that killifish acclimated to dilute FW ([NaCl] = 1 mmol I^?1) possess large numbers of MR cells on the opercular epithelium. When mounted in vitro with FW on the outside, the preparation develops a large inside negative transepithelial potential (TEP) that is a Na⁺ diffusion potential. By the Ussing flux ratio criterion, Na⁺ fluxes are passive, but a small active influx of Cl^? occurs, an observation that supports the involvement of MR cells in active Cl^? uptake. This FW opercular epithelium if bathed with isotonic saline on both sides does not secrete Cl^?, indicating that the MR cells indeed are of the FW type. In vivo, the fish exhibits a high rate of Na⁺ influx and outflux; Cl^? outflux is much lower, and there is no detectable Cl^? influx. Experimental variation of FW [NaCl] reveals a saturable, low affinity Na⁺ uptake mechanism, a Cl^? influx mechanism that is activated only at much higher concentrations, and no evidence of exchange diffusion. Acid-base disturbance appears to be corrected by differential regulation of the outflux components only. Hence, the FW killifish ionoregulates somewhat differently from the few other FW teleosts that have been examined, and its opercular epithelium will serve as a very useful model system.  相似文献   

An improved snow hydrology for GCMs. Part 1: snow cover fraction,albedo, grain size,and age     

Susan Marshall  Robert J. Oglesby 《Climate Dynamics》1994,10(1-2):21-38

A new, physically-based snow hydrology has been implemented into the NCAR CCM1. The snow albedo is based on snow depth, solar zenith angle, snow cover pollutants, cloudiness, and a new parameter, the snow grain size. Snow grain size in turn depends on temperature and snow age. An improved expression is used for fractional snow cover which relates it to surface roughness and to snow depth. Each component of the new snow hydrology was implemented separately and then combined to make a new control run integrated for ten seasonal cycles. With the new snow hydrology, springtime snow melt occurs more rapidly, leading to a more reasonable late spring and summer distribution of snow cover. Little impact is seen on winter snow cover, since the new hydrology affects snow melt directly, but snowfall only indirectly, if at all. The influence of the variable grain size appears more important when snow packs are relatively deep while variable fractional snow cover becomes increasingly important as the snow pack thins. Variable surface roughness affects the snow cover fraction directly, but shows little effect on the seasonal cycle of the snow line. As an applicaion of the new snow hydrology, we have rerun simulations involving Antarctic and Northern Hemisphere glaciation; these simulations were previously made with CCM1 and the old snow hydrology. Relatively little difference is seen for Antarctica, but a profound difference occurs for the Northern Hemisphere. In particular, ice sheets computed using net snow accumulations from the GCM are more numerous and larger in extent with the new snow hydrology. The new snow hydrology leads to a better simulation of the seasonal cycle of snow cover, however, our primary goal in implementing it into the GCM is to improve the predictive capabilities of the model. Since the snow hydrology is based on fundamental physical processes, and has well-defined parameters, it should enable model simulations of climatic change in which we have increased confidence.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil  相似文献   

Deformation mechanisms in experimentally deformed plagioclase feldspars     

D. B. Marshall  A. C. McLaren 《Physics and Chemistry of Minerals》1977,1(4):351-370

Optical and transmission electron microscopy have been used to study the microstructures in a series of plagioclase feldspars which had been experimentally deformed in compression. The observations show that deformation takes place by three mechanisms: (1) brittle fracture, (2) twinning and (3) slip due to the generation and motion of dislocations. Optical “deformation lamellae” are shown to be due to bunches of microfractures and to walls of tangled dislocations. Twins and fractures are often intimately associated and dislocations are often generated at fracture steps or voids. Moving dislocations apparently always generate a strip of fault in the slip plane. This, together with structural considerations as well as the visibility of dislocations (under various diffracting conditions) and the orientation of the applied stress, has made it possible to determine the slip systems which have operated in the deformed specimens.  相似文献   

Interpretation of pyroclast surface features using sem images   总被引：1，自引：0，他引：1  

Michael F. Sheridan  John R. Marshall 《Journal of Volcanology and Geothermal Research》1983,16(1-2)

  相似文献   

Precise age determinations and petrogenetic studies using the KCa method     

B.D. Marshall  D.J. DePaolo 《Geochimica et cosmochimica acta》1982,46(12):2537-2545

High precision mass spectrometric determination of calcium isotope ratios allows the ⁴⁰K → ⁴⁰Ca radioactive decay to be used for dating a much broader range of geologic materials than is suggested by previous work. ${}^{40}\text{Ca}{}^{42}\text{Ca}$ is used to monitor enrichments in ⁴⁰Ca and can be measured to ±0.01% (2σ) using an exponential mass discrimination correction (Russell et al., 1978) and large ion currents. The earth's mantle has such a low $\text{K}\text{Ca}$ (～0.01) that it has retained “primordial” ${}^{40}\text{Ca}{}^{42}\text{Ca}\text{= 151.016}$ ± 0.011 (normalized to ${}^{42}\text{Ca}{}^{44}\text{Ca}\text{= 0.31221}$), as determined by measurements on two meteorites, pyroxene from an ultramafic nodule, metabasalt, and carbonatite. ${}^{40}\text{Ca}{}^{42}\text{Ca}$ ratios can be conveniently expressed relative to this value as ?_Ca in units of 10^?4. To test the method for age dating, a mineral isochron has been obtained on a sample of Pikes Peak granite, which has been shown to have concordant KAr, RbSr, and UPb ages. Plagioclase, K-feldspar, biotite, and whole rock yield an age of 1041 ± 32 m.y. (2σ) in agreement with previous age determinations (λ_K = 0.5543 b.y.^?1, $\text{λ}{}_{\mathrm{\beta ?}}\text{λ}{}_{\mathrm{<mtext>K</mtext>}}\text{= 0.8952}$, ⁴⁰K = 0.01167%). The initial ${}^{40}\text{Ca}{}^{42}\text{Ca}$ of 151.024 ± 0.016 (?_Ca = +0.5 ± 1.0), indicates that assimilation of high K/Ca crust was insufficient to affect calcium isotopes. Measurements on two-mica granite from eastern Nevada indicate that the magma sources had K/Ca ≈ 1, similar to intermediate-composition crustal rocks. These results show that the KCa system can be used as a precise geochromometer for common felsic igneous and metamorphic rocks, and may prove applicable to sedimentary rocks containing authigenic K minerals. The relatively short half-life of ⁴⁰K, the non-volatile daughter, and the fact that potassium and calcium are stoichiometric constituents of many minerals, make the KCa system complementary to other dating methods, and potentially applicable to a variety of geologic problems.  相似文献   

Periodicities in blue crab population of Chesapeake Bay     

Paul R. Hurt  Leona Marshall Libby  Louis J. Pandolfi  Lawrence H. Levine  W. A. Van Engel 《Climatic change》1979,2(1):75-78

Analysis of the annual blue crab catch in Chesapeake Bay for the years 1922–1976 shows that there are variations with periods of 18.0, 10.7, and 8.6 years. Analysis of Philadelphia air temperatures shows periods of 17.5, 9.8, and 7.4 years. The periods of 18.0 and 17.5 years agree with the 18.6 year period of the Earth-Moon-Sun tidal force, and the periods of 8.6 and 7.4 years agree with the 8.8 year period of the Earth-Moon-Sun tidal force, within experimental error. The periods of 9.8 and 10.7 years, for the temperatures and crabs, respectively, are probably related to the 10.5 year sunspot cycle within experimental error.  相似文献   

Accretionary unit formats in subduction complexes: examples from the Franciscan and Miura-Boso complexes     

Loren A. Raymond  Yujiro Ogawa  Marshall E. Maddock 《International Geology Review》2020,62(12):1581-1609

  相似文献   

The effect of the Jessica grounding on subtidal invertebrate and plant communities at the Galápagos wreck site     

Marshall PA  Edgar GJ 《Marine pollution bulletin》2003,47(7-8):284-295

Impacts of the grounding of the oil tanker Jessica off San Cristóbal island, Galápagos, included both effects of oil on biota and also mechanical effects associated with a shallow furrow 50 m x 30 m gouged across the rocky seafloor and wreckage strewn over 7500 m(2). The wreckage represented a minor but potentially chronic source of pollution to the surrounding environment through delayed releases of oil, antifouling compounds and other toxic chemicals, and a possible source of exotic marine taxa. Investigation at the wreck site indicated that impacts on subtidal plant and macro-invertebrate communities were largely confined within 100 m of the wreck site itself. Observed population effects included significant increases in cover of opportunistic algae (filamentous green algae, filamentous red algae and Ulva sp.) and the hydroid Ectopleura media adjacent to the wreck, while densities of the green sea urchin Lytechinus semituberculatus significantly decreased from 0.3 m(-2) adjacent to the wreck to 11 m(-2) at 100 m distance.  相似文献   

Geochemical and C, O, Sr, and U-series isotopic evidence for the meteoric origin of calcrete at Solitario Wash, Crater Flat, Nevada, USA     

L. A. Neymark  J. B. Paces  B. D. Marshall  Z. E. Peterman  J. F. Whelan 《Environmental Geology》2005,48(4-5):450-465

Calcite-rich soils (calcrete) in alluvium and colluvium at Solitario Wash, Crater Flat, Nevada, USA, contain pedogenic calcite and opaline silica similar to soils present elsewhere in the semi-arid southwestern United States. Nevertheless, a ground-water discharge origin for the Solitario Wash soil deposits was proposed in a series of publications proposing elevation-dependent variations of carbon and oxygen isotopes in calcrete samples. Discharge of ground water in the past would raise the possibility of future flooding in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository. New geochemical and carbon, oxygen, strontium, and uranium-series isotopic data disprove the presence of systematic elevation-isotopic composition relations, which are the main justification given for a proposed ground-water discharge origin of the calcrete deposits at Solitario Wash. Values of δ¹³C (−4.1 to −7.8 per mil [‰]), δ¹⁸O (23.8–17.2‰), ⁸⁷Sr/⁸⁶Sr (0.71270–0.71146), and initial ²³⁴U/²³⁸U activity ratios of about 1.6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits at Yucca Mountain and are incompatible with a ground-water origin for the calcrete. Variations in carbon and oxygen isotopes in Solitario Wash calcrete likely are caused by pedogenic deposition from meteoric water under varying Quaternary climatic conditions over hundreds of thousands of years.  相似文献