Autoxidation of N(III), S(IV), and other Species in Frozen Solution – A Possible Pathway for Enhanced Chemical Transformation in Freezing Systems     

Eric A. Betterton  Darcy J. Anderson 《Journal of Atmospheric Chemistry》2001,40(2):171-189

The chemistry of glycolaldehyde (hydroxyacetaldehyde) relevant to the troposphere has been investigated using UV absorption spectrometry and FTIR absorption spectrometry in an environmental chamber. Quantitative UV absorption spectra have been obtained for the first time. The UV spectrum peaks at 277 nm with a maximum cross section of (5.5± 0.7)×10^–20 cm² molecule^–1. Studies of the ultraviolet photolysis of glycolaldehyde ( = 285 ± 25 nm) indicated that the overall quantum yield is > 0.5 in one bar of air, with the major products being CH₂OH and HCO radicals. Rate coefficients for the reactions of Cl atoms and OH radicals with glycolaldehyde have been determined to be (7.6± 1.5)×10^–11 and (1.1± 0.3)×10^–11 cm³ molecule^–1 s^–1, respectively, in good agreement with the only previous study. The lifetime of glycolaldehyde in the atmosphere is about 1.0 day for reaction with OH, and > 2.5 days for photolysis, although both wet and dry deposition should also be considered in future modeling studies.  相似文献   

Bioterrorism: A ‘New’ Global Environmental Health Threat     

Eric K. Noji 《Global Change & Human Health》2001,2(1):46-53

Biological weapons represent a unique "environmental" hazard. The pathogens involved are natural in the sense that they are risks that naturally occur in our environment. However they are unnatural in the way in which they are inflicted upon society. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Detection Time for Plausible Changes in Annual Precipitation, Evapotranspiration, and Streamflow in Three Mississippi River Sub-Basins     

Alan D. Ziegler  Edwin P. Maurer  Justin Sheffield  Bart Nijssen  Eric F. Wood  Dennis P. Lettenmaier 《Climatic change》2005,72(1-2):17-36

We use diagnostic studies of off-line variable infiltration capacity (VIC) model simulations of terrestrial water budgets and 21st-century climate change simulations using the parallel climate model (PCM) to estimate the time required to detect predicted changes in annual precipitation (P), evapotranspiration (E), and discharge (Q) in three sub-basins of the Mississippi River Basin. Time series lengths on the order of 50–350 years are required to detect plausible P, E, and Q trends in the Missouri, Ohio, and Upper Mississippi River basins. Approximately 80–160, 50, and 140–350 years, respectively, are needed to detect the predicted P, E, and Q trends with a high degree of statistical confidence. These detection time estimates are based on conservative statistical criteria (α = 0.05 and β = 0.10) associated with low probability of both detecting a trend when it is not occurring (Type I error) and not detecting a trend when it is occurring (Type II error). The long detection times suggest that global-warming-induced changes in annual basin-wide hydro-climatic variables that may already be occurring in the three basins probably cannot yet be detected at this level of confidence. Furthermore, changes for some variables that may occur within the 21st century might not be detectable for many decades or until the following century – this may or may not be the case for individual recording station data. The long detection times for streamflow result from comparatively low signal-to-noise ratios in the annual time series. Finally, initial estimates suggest that faster detection of acceleration in the hydrological cycle may be possible using seasonal time series of appropriate hydro-climatic variables, rather than annual time series.  相似文献   

Inverted-polarity electrical structures in thunderstorms in the Severe Thunderstorm Electrification and Precipitation Study (STEPS)     

W. David Rust  Donald R. MacGorman  Eric C. Bruning  Stephanie A. Weiss  Paul R. Krehbiel  Ronald J. Thomas  William Rison  Timothy Hamlin  Jeremiah Harlin 《Atmospheric Research》2005,76(1-4):247

Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures.  相似文献   

Global change and the intensification of agriculture in the tropics   总被引：3，自引：2，他引：3  

Eric Keys  William J. McConnell 《Global Environmental Change》2005,15(4):320-337

Bridging understanding of local environmental change with regional and global patterns of land-use and land-cover change (LUCC) remains a key goal and challenge for our understanding of global environmental change. This meta-analysis attempts to bridge local and regional scales of LUCC by demonstrating the ways in which previously published case studies can be compared and used for a broader regional synthesis in the tropics. In addition to providing results from a meta-analysis, this paper suggests ways to make future case studies more widely comparable.  相似文献   

Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation?     

Yongjun Gao  Jochen Hoefs  Eric Hellebrand  Anette von der Handt  Jonathan E. Snow 《Contributions to Mineralogy and Petrology》2007,153(4):429-442

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.  相似文献   

Permanganate Treatment of an Emplaced DNAPL Source     

Neil R. Thomson  Eric D. Hood  Grahame J. Farquhar 《Ground Water Monitoring & Remediation》2007,27(4):74-85

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The Effect of Concentrated Electron Donors on the Solubility of Trichloroethene     

Eric Hood  David Major  Greg Driedger 《Ground Water Monitoring & Remediation》2007,27(4):93-98

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Unstructured,anisotropic mesh generation for the Northwestern European continental shelf,the continental slope and the neighbouring ocean     

Sébastien Legrand  Eric Deleersnijder  Eric Delhez  Vincent Legat 《Continental Shelf Research》2007

A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective is to demonstrate the ability of anisotropic unstructured meshes to adequately address the challenge of simulating the hydrodynamics occurring in these three regions within a unique mesh. The refinement criteria blend several hydrodynamic considerations as the tidal wave propagation on the continental shelf and the hydrostatic consistency condition in steep areas. Several meshes illustrate both the validity and the efficiency of the refinement strategy. The selection of the refinement parameters is discussed. Finally, an attempt is made to take into account tidal ellipses, providing another cause for anisotropy in the mesh.  相似文献   

First comparisons of precipitable water vapor estimation using GPS and water vapor radiometers at the Royal Observatory of Belgium     

Eric Pottiaux  René Warnant 《GPS Solutions》2002,6(1-2):11-17

We compare precipitable water vapor (PWV) time series measured by water vapor radiometers (WVRs) to PWV time series estimated using global positioning system (GPS) observations in a regional network of stations in western Europe. Inside this network, we focus on the baseline Brussels – Wettzell which presents the advantage to have the collocation of a GPS receiver and a WVR at both endpoints. The comparison between our GPS and WVR estimations of precipitable water vapor shows an agreement at the millimeter level. In addition, we show that the zenith total delay (ZTD) estimations computed with our GPS processing strategy agrees with the GPS estimations of ZTD done by the CODE analysis center at the millimeter level. Electronic Publication  相似文献