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51.
D. G. Victor 《Climatic change》1992,20(2):113-141
A model of the U.S. automobile market is used to test the role that natural gas vehicles (NGVs) might play in reducing greenhouse-gas emissions. Since natural gas (primarily methane) emits less CO2 per unit of energy than petroleum products, NGVs are an obvious pathway to lower CO2 emissions. High-and low-demand scenarios are used to forecast the emissions from unrestricted growth and a modest program of conservation, respectively. Based on these scenarios, a reference scenario is developed that projects a possible future path of automobile use and efficiency. It is found that without a dramatic increase in automobile use, fuel consumption and greenhouse-gas emissions from automobiles in the United States will probably decrease in the future, provided that efficiency continues to improve at modest rates. In theory, NGVs can help shift emissions even further down.A second objective is to quantify the role that leaking methane might play in offsetting some of the greenhouse advantages of NGVs. To do this, a simple atmospheric chemistry model is applied to the reference scenario; several leak rates and feedback factors are used to test the sensitivity of the projected green-house forcing from now until 2050. Committed warming beyond 2050 is not included, and the results should be interpreted with that in mind.It is highly unlikely that switching automobiles from gasoline to natural gas will appreciably lower future greenhouse forcing. Constraints on vehicle miles travelled as well as continued improvements in vehicle efficiency will make a much larger contribution towards controlling global warming. 相似文献
52.
In a basin developed on a stream table, effluent subsurface flow supported a channel network that evolved by a combination of headward growth, lateral widening and divide decay. The area occupied by the developing network increased with time. Circularity was used to characterize network evolution which occurred in three phases (initiation, extension and abstraction). Basin sediment discharge declined exponentially with time. Pronounced quasi-cyclic variability was superimposed upon this general trend. Some of the variability was directly linked to changes in the amount of sediment supplied to the channel. The variation of mean network sediment yield (mean sediment discharge scaled by network area) with time adequately described the general decline in sediment discharge as the network evolved. 相似文献
53.
Raymond M. Valente Donald C. Rhoads Joseph D. Germano Victor J. Cabelli 《Estuaries and Coasts》1992,15(1):1-17
A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats. 相似文献
54.
55.
Victor P. Starr 《Pure and Applied Geophysics》1973,110(1):2108-2129
Summary The problem of the gross nature of the Jovian atmospheric circulation is examined from the viewpoint of the following previous findings of the writer and others. 1) The equatorial acceleration cannot be accounted for by axisymmetric motions. 2) The departures from symmetry in a rotating system having an equatorial acceleration must impart angular momentum selectively to those particles moving toward the jet maximum and abstract it from those moving away. 3) These selective (pressure) torques and associated sorting processes arise spontaneously in the presence of a vertical convection mode involving motions not independent of longitude, if the cell sizes and other conditions are right.Since there is evidence that Jovian dark spots have statistical maxima of occurrence along the tropical shear lines flanking the equator, these are assumed to be vertical convective systems forming, in effect,convective vortex sheets which generate the high angular momentum of the equatorial zone. Various additional concepts are discussed, and many comparisons with conditions in the sun and in the earth's atmosphere are made. 相似文献
56.
57.
Episodes of late Holocene aridity recorded by stalagmites from Devil's Icebox Cave, central Missouri, USA 总被引:1,自引:0,他引:1
Rhawn F. Denniston Michelle DuPree Jeffrey A. Dorale Victor J. Polyak 《Quaternary Research》2007,68(1):45-52
Two stalagmites from Devil's Icebox Cave, central Missouri, display similar δ13C and δ18O values and trends during the late Holocene. Positive δ13C excursions at 3.5-2.6 ka and 1.2-0.9 ka are interpreted to reflect drier conditions. These elevated stalagmite δ13C values could have plausibly been driven by increasing C4 plant abundances over the cave or an increased contribution of bedrock carbon, both of which could reflect decreased effective moisture. A lack of corresponding oxygen isotopic anomalies during these intervals suggests that neither mean annual temperature nor the seasonality of precipitation changed concomitantly with dryness. Both of the δ13C excursions identified in our stalagmite record are roughly coincident with dry intervals from a number of sites located across the Great Plains. 相似文献
58.
Younger Dryas to mid-Holocene environmental history of the lowlands of NW Transylvania, Romania 总被引:2,自引:1,他引:2
Angelica Feurdean Volker Mosbrugger Bogdan P. Onac Victor Polyak Daniel Veres 《Quaternary Research》2007,68(3):364-378
Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS 14C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed. 相似文献
59.
The biology, ecology, biogeography, phylogeny, and evolution of sand-dwelling scorpions are reviewed. We present general features of sand that form the ecological theatre on which psammophiles have evolved. Sand scorpions, compared to those that live off sand, are not very diverse in any one local habitat, although they are often relatively abundant. Worldwide, they are represented by 29 genera, 11 of which exist exclusively in sand. Endemic genera belong to non-related families, suggesting that psammophilic adaptations evolvedin situin different sand deserts of the world. 相似文献
60.
Victor B. MAGLAMBAYAN † Daizo ISHIYAMA Toshio MIZUTA Akira IMAI Yohei ISHIKAWA 《Resource Geology》1998,48(2):87-104
Abstract: The Bulawan deposit is located in the porphyry copper belt of southwest Negros island, Philippines. Propylitic, K–feldspar, sericitic, and carbonate alteration types can be distinguished in the deposit. Propylite alteration occurs mainly in Cretaceous-Eocene andesitic lavas and agglomerates while K–feldspar, sericite and carbonate alteration types occur mostly in the Middle Miocene dacite porphyry breccia pipes and stocks which were intruded into the andesites. K-feldspar zones occur in the inner parts of the sericitized zone. Sericite alteration overprinted the propylitized and K-feldspar alteration zones, at lower temperature than epidote and chlorite in the propylitized zone. Carbonate alteration is associated with the mineralization in the center of the breccia pipes and along faults. Mineralization consists of gold-silver telluride ores that are hosted by the carbonate– and sericite-altered dacite porphyry breccia pipes. The Bulawan ores occur mainly as disseminations, but unlike many epithermal gold deposits, lack classical epithermal colloform and crustiform quartz veins. The ore minerals are sphalerite, galena, chalcopyrite, pyrite and tetrahedite-tennantite with minor amounts of electrum, calaverite, petzite, sylvanite, hessite, tellurobismuthite, coloradoite, altaite, and rucklidgeite. Electrum and telluride minerals are associated mostly with calcite and dolomite-ankerite minerals. Fluid inclusions in quartz and calcite in clasts of propylitized andesite in the breccia pipes homogenize from about 300° to 400°C while fluid inclusions in quartz, calcite and sphalerite within the dacite porphyry breccia pipes homogenize between 300° to 310°C. The ores were formed around 300°C from hydrothermal solutions with salinity of about 6. 6 wt % NaCl equivalent. The presence of sylvanite and calaverite as intergrowths with each other, and the Ag content of calaverite are consistent with the above temperature estimate. Based on paragenesis, the Bulawan deposit formed in a pyrite-stable environment, with pH between 3. 4 and 5. 5, fO2 between 10-32 to 10-30 atm, fS2 between 10-9.8 to 10-7.8 atm, fTe2 between 10-8.9 to 10-6.5 atm, and total sulfur content about 10-2.8 molal. The dominant reduced sulfur species in the ore solutions may have been H2S(aq), and the likely aqueous tellurium species were H2Te(aq) and H2TeO3(aq). The ore minerals in the Bulawan deposit were probably formed by mixing of slightly saline and low salinity fluids. 相似文献