Is the present stellar birthrate really determined by gas density?     

David C. Black  Sanford A. Kellman 《Astrophysics and Space Science》1974,26(1):107-109

Observed supernovae rates in Sb and Sc galaxies, and a recent re-examination of the mean gas density in these galactic types, implies that if the clumpiness of gas in the disks of Sb and Sc galaxies is similar, the gas density isnot the primary factor in determining the overall present stellar birthrate.  相似文献   

Integrated Approaches to Explore the Biosphere Inhabiting the Deep Subsurface of the Illinois Basin, USA     

Yiran Dong  Liang Shi  Robert A. Sanfor  Bruce W. Fouke 《《地质学报》英文版》2018,92(Z1):201-201

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Influence of Shoreline Stabilization Structures on the Nearshore Sedimentary Environment in Mesohaline Chesapeake Bay     

Cindy M. Palinkas  Lawrence P. Sanford  Evamaria W. Koch 《Estuaries and Coasts》2018,41(4):952-965

Shorelines around many estuaries and coastal embayments are rapidly eroding (approximately several meters/year), with more rapid erosion rates expected in the future due to natural and anthropogenic stressors. In response, a variety of techniques have been used to stabilize shorelines, but there are limited quantitative, long-term data available about their effects on the sedimentary environment immediately adjacent to them (i.e., the nearshore). This study evaluated changes in sediment characteristics (mud and organic content) and accumulation rates associated with installation of breakwaters, riprap, and living shorelines with (“hybrid”) and without (“soft”) a structural component. ²¹⁰Pb (half-life 22.3 years) geochronologies were used to identify horizons in core profiles that corresponded to years when structures were built. Sites with naturally eroding shorelines (i.e., no structures) were used as a control group at which any sedimentary changes represent broad environmental trends, in contrast to changes at the protected sites that also include the influence of structures. Observations were placed within the context of modeled wave climate, shoreline-erosion rates, land use, dominant sediment source, and the apparent effect on submersed aquatic vegetation (SAV) inhabiting the nearshore sedimentary environment. The main conclusion of this study is that there was no “one size fits all” answer to anticipated impacts of structures on nearshore sedimentary environments. Instead, specific changes associated with structures depended on individual site characteristics, but could be predicted with multiple linear regression models that included structure type, shoreline-erosion rate, dominant sediment source, and land use. Riprap or breakwater installation had either positive or no obvious impact on SAV at six of seven sites but negatively impacted SAV at one riprapped site. No obvious impacts on SAV were observed at living shoreline sites.  相似文献