Diatoms on Earth, Comets, Europa and in Interstellar Space     

Richard B. Hoover  Fred Hoyle  N.C. Wickramasinghe  Miriam J. Hoover  S. Al-Mufti 《Astrophysics and Space Science》1999,268(1-3):197-224

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of acosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.  相似文献   

A multi-envelope vertical coordinate system for numerical ocean modelling     

Diego Bruciaferri  Georgy I. Shapiro  Fred Wobus 《Ocean Dynamics》2018,68(10):1239-1258

A multi-envelope generalised coordinate system for numerical ocean modelling is introduced. In this system, computational levels are curved and adjusted to multiple ‘virtual bottoms’ (aka envelopes) rather than following geopotential levels or the actual bathymetry. This allows defining computational levels which are optimised to best represent different physical processes in different sub-domains of the model. In particular, we show how it can be used to improve the representation of tracer advection in the ocean interior. The new vertical system is compared with a widely used z-partial step scheme. The modelling skill of the models is assessed by comparison with the analytical solutions or results produced by a model with a very high-resolution z-level grid. Three idealised process-oriented numerical experiments are carried out. Experiments show that numerical errors produced by the new scheme are much smaller than those produced by the standard z-partial step scheme at a comparable vertical resolution. In particular, the new scheme shows superiority in simulating the formation of a cold intermediate layer in the ocean interior and in representing dense water cascading down a steep topography.  相似文献   

The fate of suspended sediment and particulate organic carbon in transit through the channels of a river catchment          下载免费PDF全文

Fred Worrall  Tim P. Burt  Nicholas J.K. Howden  Gregory R. Hancock  John Wainwright 《水文研究》2018,32(1):146-159

Particulate organic matter (POM) transiting through rivers could be lost to overbank storage, stored in‐channel, added to by erosion or autochthonous production, or turned over to release greenhouse gases to the atmosphere (either while in the water column or while stored in the channel). In the UK, a net loss of POM across catchments has been recorded, and the aim here was to investigate the balances of processes acting on the POM. This study considered records of suspended sediment and POM flux in comparison to stream flow, velocity, stream power, and residence time for the River Trent (English Midlands, 8,231 km²). We show that for the lower two thirds (106 km) of the River Trent, 2% is lost to overbank storage; 10% is lost to the atmosphere in the water column; and 31% is turned over while in temporary storage. Permanent in‐channel storage is negligible, and for the lower course of the river, material stored in‐channel will have a residence time of the order of hundreds of days between the last flood hydrograph of one winter and the first winter storm of the next winter (usually in the same calendar year). When considered at the scale of the UK, 1% POM in transit would be lost to overbank sedimentation; 5% turned over in the water column, and 14% turned over while in temporary storage. In the upper third of the study river channel, there is insufficient stream power to transport sediment and so in‐channel storage or in‐channel turnover over to the atmosphere dominate. The in‐channel processes of the River Trent do not conform to that expected for river channels as the headwaters are not eroding or transporting sediment. Therefore, the source of sediment must be lower down the channel network.  相似文献   

Changes in Projected Spatial and Seasonal Groundwater Recharge in the Upper Colorado River Basin          下载免费PDF全文

Fred D Tillman  Subhrendu Gangopadhyay  Tom Pruitt 《Ground water》2017,55(4):506-518

The Colorado River is an important source of water in the western United States, supplying the needs of more than 38 million people in the United States and Mexico. Groundwater discharge to streams has been shown to be a critical component of streamflow in the Upper Colorado River Basin (UCRB), particularly during low‐flow periods. Understanding impacts on groundwater in the basin from projected climate change will assist water managers in the region in planning for potential changes in the river and groundwater system. A previous study on changes in basin‐wide groundwater recharge in the UCRB under projected climate change found substantial increases in temperature, moderate increases in precipitation, and mostly periods of stable or slight increases in simulated groundwater recharge through 2099. This study quantifies projected spatial and seasonal changes in groundwater recharge within the UCRB from recent historical (1950 to 2015) through future (2016 to 2099) time periods, using a distributed‐parameter groundwater recharge model with downscaled climate data from 97 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections. Simulation results indicate that projected increases in basin‐wide recharge of up to 15% are not distributed uniformly within the basin or throughout the year. Northernmost subregions within the UCRB are projected an increase in groundwater recharge, while recharge in other mainly southern subregions will decline. Seasonal changes in recharge also are projected within the UCRB, with decreases of 50% or more in summer months and increases of 50% or more in winter months for all subregions, and increases of 10% or more in spring months for many subregions.  相似文献   

An Introduction to Water Well Hydrofracturing          下载免费PDF全文

Fred Rothauge 《Ground water》2018,56(3):360-360

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Thermal pulse induced by emplacement of Ramba leucogranites in southern Tibet     

Xu Chu  Ozan Akça  Fred Gaidies  Ivano Gennaro  Weiqiang Ji 《Journal of Metamorphic Geology》2023,41(1):121-141

The thermal histories of Himalayan leucogranites provide critical information for unravelling the post-collisional geodynamics of the Himalayas. The Ramba Dome is located at the intersection of the Tethyan Himalayan leucogranite belt with the Yadong–Gulu Rift and hosts several generations of granitic intrusions. Of these intrusions, the 8-Ma two-mica granites and garnet leucogranite dykes are the youngest of Himalayan leucogranites. In this study, we focus on the carbonaceous staurolite schist located ~1.3 km from the intrusion to constrain the thermal history of the aureole that marked the cessation of leucogranite magmatism. The schist contains euhedral garnet and staurolite porphyroblasts in a foliated matrix of muscovite + biotite + chlorite + plagioclase + quartz + graphite. The staurolite shows minor compositional variations from the inclusion-free core to the inclusion-rich rim. By contrast, the garnet features a distinctive bell-shaped Mn profile and increasing Mg# from the garnet core to rims. In a graphite-bearing equilibrium phase diagram for a modified bulk composition with garnet cores removed, the garnet rim composition suggests a peak temperature of ~550°C, consistent with an independent thermometer based on the Raman spectra of carbonaceous materials (RSCM; 548 ± 9°C). The P–T condition lies within the narrow low-variance field bracketed by the staurolite-in and chlorite-out boundaries, indicating minimal overstepping of staurolite nucleation and growth. On the other hand, the garnet core composition indicates 520°C at 2.5 kbar, about 40°C higher than the predicted garnet-in boundary (~480°C). This apparent temperature overstep corresponds to a small chemical affinity (<5 kJ/mol 12 O) for garnet nucleation, comparable to previous estimates. The sharp boundaries of the high-Ca sector zoning in the core indicate limited diffusion modification (~1.5 Ma if at the peak temperature). The short thermal pulse involves advective heat transfer by leucogranite emplacement, followed by rapid cooling toward the end of Himalayan magmatism and rapid exhumation likely facilitated by the Yadong–Gulu Rift.  相似文献