Adsorption of Benzoic Acid and Related Carboxylic Acids onto FeOOH(Goethite): The Low Ionic Strength Regime     

Charles F. Whitehead  Richard F. Carbonaro  Alan T. Stone 《Aquatic Geochemistry》2015,21(2-4):99-121

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Influence of climate factors on spatial distribution of Texas cattle breeds     

Yuquan W. Zhang  Amy D. Hagerman  Bruce A. McCarl 《Climatic change》2013,118(2):183-195

This paper investigates the spatial distribution of cattle breeders in Texas to quantify how climate factors influence cattle breed selection. A multivariate probit model is employed to examine the county-level binary choices of Bos taurus, Bos indicus and composite breeds derived from cattle breed association membership data. The estimation results suggest that summer heat stress is a significant factor for breed selection: positive for Bos indicus and negative for Bos taurus and composite breeds, with the average marginal effects on breed membership probability being 9.7 %, ?26.5 % and ?7.9 %, respectively. The intensity of the summer heat impacts can lead to noteworthy changes in spatial distributions of Texas cattle breeds in the event of climate change.  相似文献   

The High-Resolution Coronal Imager (Hi-C)     

Ken Kobayashi  Jonathan Cirtain  Amy R. Winebarger  Kelly Korreck  Leon Golub  Robert W. Walsh  Bart De Pontieu  Craig DeForest  Alan Title  Sergey Kuzin  Sabrina Savage  Dyana Beabout  Brent Beabout  William Podgorski  David Caldwell  Kenneth McCracken  Mark Ordway  Henry Bergner  Richard Gates  Sean McKillop  Peter Cheimets  Simon Platt  Nick Mitchell  David Windt 《Solar physics》2014,289(11):4393-4412

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈?0.3?–?0.4′′), high-cadence (≈?5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′?pixel^?1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.  相似文献   

The relative importance of tropical variability forced from the North Pacific through ocean pathways     

Amy Solomon  Sang-Ik Shin  Michael A. Alexander  Julian P. McCreary 《Climate Dynamics》2008,31(2-3):315-331

To what extent is tropical variability forced from the North Pacific through ocean pathways relative to locally generated variability and variability forced through the atmosphere? To address this question, in this study we use an anomaly-coupled model, consisting of a global, atmospheric general circulation model and a 4½-layer, reduced-gravity, Pacific-Ocean model. Three solutions are obtained; with coupling over the entire basin (CNT), with coupling confined to the tropics and wind stress and heat fluxes in the North and South Pacific specified by climatology (TP), and with coupling confined to the Tropics and wind stress and heat fluxes in the North Pacific specified by output from CNT (NPF). It is found that there are two distinct signals forced in the North Pacific that can impact the tropics through ocean pathways. These two signals are forced by wind stress and surface heat flux anomalies in the subtropical North Pacific. The first signal is relatively fast, impacts tropical variability less than a year after forcing, is triggered from November to March, and propagates as a first-mode baroclinic Rossby wave. The second signal is only triggered during springtime when buoyancy forcing can effectively generate higher-order baroclinic modes through subduction anomalies into the permanent thermocline, and it reaches the equator 4–5 years after forcing. The slow signal is found to initiate tropical variability more efficiently than the fast signal with one standard deviation in subtropical zonal wind stress forcing tropical SST anomalies centered on the equator at 135°W of approximately 0.5°C. Allowing extratropically forced tropical variability is found to shift primarily 2-year ENSO variability in a tropics-alone simulation to a more realistic range of 2–6 years.  相似文献   

Sub-micron scale distributions of trace elements in zircon   总被引：2，自引：1，他引：1  

Amy E. Hofmann  John W. Valley  E. Bruce Watson  Aaron J. Cavosie  John M. Eiler 《Contributions to Mineralogy and Petrology》2009,158(3):317-335

Sub-micron scale zoning of Ti concentrations and correlations between concentrations of Ti and other trace elements (P, Ce, and Y) and cathodoluminescent (CL) banding is observed in natural zircons. Ion images were made using the Caltech Microanalysis Center’s CAMECA NanoSIMS 50L with an O⁻ primary beam focused to ~300 nm on the sample surface. The high spatial resolution of this technique allows for interrogation of chemical variations at or below the scale of CL banding in natural zircons. Images produced in this manner display two types of correlations among Ti, P, Ce, and Y (which appears to be a proxy for CL intensity): strong (correlation coefficients >0.8) and subtle (correlation coefficients ~0.15–0.4). Strongly correlated images, which display Ti variations of ca. a factor of 3 between adjacent CL bands and overall elevated trace element concentrations in CL-dark bands, were found within an oscillatory-zoned, trace element enriched sector of a CL sector-zoned zircon. Three possible causes for such correlations include: temperature-dependent equilibrium partitioning, trace element partitioning limited by diffusion in the host melt and surface-controlled, non-equilibrium growth. Comparison of our data with the expected results of these processes suggests that: (1) Ti partitioning in zircon is dependent upon non-equilibrium effects in addition to temperature and/or (2) the incorporation of elements that co-vary with Ti in zircon (e.g., Y, P and Ce) is also temperature-dependent. Sub-micron scale, high-Ti regions are also found within Proterozoic Adirondack and >4 Ga Jack Hills zircons as well as trace element enrichments (including Ti) along cracks within Jack Hills zircons.  相似文献   

Aerial electromagnetic sounding of the lithosphere of Venus     

Robert E. Grimm  Amy C. Barr  Keith P. Harrison  David E. Stillman  Kerry L. Neal  Michael A. Vincent  Gregory T. Delory 《Icarus》2012,217(2):462-473

Electromagnetic (EM) investigation depths are larger on Venus than Earth due to the dearth of water in rocks, in spite of higher temperatures. Whistlers detected by Venus Express proved that lightning is present, so the Schumann resonances ～10–40 Hz may provide a global source of electromagnetic energy that penetrates ～10–100 km. Electrical conductivity will be sensitive at these depths to temperature structure and hence thermal lithospheric thickness. Using 1D analytic and 2D numerical models, we demonstrate that the Schumann resonances—transverse EM waves in the ground-ionosphere waveguide—remain sensitive at all altitudes to the properties of the boundaries. This is in marked contrast to other EM methods in which sensitivity to the ground falls off sharply with altitude. We develop a 1D analytical model for aerial EM sounding that treats the electrical properties of the subsurface (thermal gradient, water content, and presence of conductive crust) and ionosphere, and the effects of both random errors and biases that can influence the measurements. We initially consider specified 1D lithospheric thicknesses 100–500 km, but we turn to 2D convection models with Newtonian temperature-dependent viscosity to provide representative vertical and lateral temperature variations. We invert for the conductivity-depth structure and then temperature gradient. For a dry Venus, we find that the error on temperature gradient obtained from any single local measurement is ～100%—perhaps enough to distinguish “thick” vs. “thin” lithospheres. When averaging over thousands of kilometers, however, the standard deviation of the recovered thermal gradient is within the natural variability of the convection models, <25%. A “wet” interior (hundreds of ppm H₂O) limits EM sounding depths using the Schumann resonances to <20 km, and errors are too large to estimate lithospheric properties. A 30-km conductive crust has little influence on the dry-interior models because the Schumann penetration depths are significantly larger. We conclude that EM sounding of the interior of Venus is feasible from a 55-km high balloon. Lithospheric thickness can be measured if the upper-mantle water content is low. If H₂O at hundreds of ppm is present, the deeper, temperature-sensitive structure is screened, but the “wet” nature of the upper mantle, as well as structure of the upper crust, is revealed.  相似文献   

Ice grain size and the rheology of the martian polar deposits     

Amy C. Barr  Sarah M. Milkovich 《Icarus》2008,194(2):513-518

The history and dynamics of the martian polar deposits (MPD), the largest known water reservoirs on Mars, are of great interest, but estimates of ice grain size are required before detailed modeling can be performed. We clarify the microphysical processes that may control grain size in the MPD. If the MPD are ∼2% dust by mass, the maximum ice grain size is ∼1 mm due to grain boundary pinning by silicate microparticles. Relatively dusty layers in the MPD will have smaller grain sizes. If MPD ice has a very low impurity content and has experienced a significant amount of strain, grains may reach a steady state size of ∼1.5 to 3 mm due to dynamic recrystallization, wherein a steady state grain size is maintained due to the balance of grain growth and destruction during flow. If the near-bed ice in the MPD is warmed close to its melting point and has been extensively sheared, grain sizes at its base may be between 10 and 40 mm, by analogy with warm, dirty, near-bed ice in terrestrial ice sheets.  相似文献   

Global travertine deposition modulated by oscillations in climate   总被引：1，自引：0，他引：1  

Jason W. Ricketts  Lin Ma  Amy E. Wagler  Victor H. Garcia 《第四纪科学杂志》2019,34(7):558-568

Travertine deposits are important records of past fluid flow in the Earth's crust, and document fluid migration through both tectonic activity and changes in climate. While many studies hint at possible relationships between travertine formation and global climate, none have investigated these connections on a global scale. Here we compile 1649 published travertine ages from six continents to test the hypothesis that global and/or regional changes in climate regulate travertine deposition. Peaks in bedded travertine ages occur with main frequencies that correspond to 100‐kyr changes in global climate, where most peaks occur during glacial terminations or interglacial periods, including a large peak that coincides with the Early Holocene climatic optimum. Time–series analysis also suggests a possible connection with 41‐kyr obliquity cycles. At regional scales, many peaks also correspond with local times of high precipitation or wet conditions. This can be attributed to higher groundwater recharge rates, providing the necessary water to form travertine. Many bedded travertine‐depositing systems may therefore be water‐limiting and sufficient CO₂ may be present even during times of no travertine deposition. Exceptions to this conclusion are banded vein travertine deposits, which typically form during times of dry climate when water tables are low. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

Prograded coastal barriers provide paleoenvironmental records of storms and sea level during late Quaternary highstands          下载免费PDF全文

Amy J. Dougherty 《第四纪科学杂志》2018,33(5):501-517

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Verification of tropical cyclone deposits with oxygen isotope analyses of coeval ostracod valves     

Chad S. Lane  Brooklyn Hildebrandt  Lisa M. Kennedy  Allison LeBlanc  Kam-Biu Liu  Amy J. Wagner  Andrea D. Hawkes 《Journal of Paleolimnology》2017,57(3):245-255

Reconstruction of prehistoric tropical cyclone (TC) activity often relies on the identification of distinctive overwash deposits (tempestites) in coastal lagoon sediments. Similar sediment deposits, however, can result from high-energy events other than TCs. In this study we assessed the utility of using the geochemistry of ostracod valves, specifically their stable oxygen isotope composition (δ¹⁸O), as a potential validation variable that could reduce the chances of misidentifying an overwash deposit as having been generated by a TC, when in fact it formed from another high-energy depositional process (type 1 error). We applied this technique to a sediment core recovered from Laguna Alejandro, Dominican Republic, which had already been analyzed for other sedimentary TC proxies. Negative δ¹⁸O anomalies identified in the ostracod valve stable isotope record are associated with TC deposits and are most easily explained by large influxes of ¹⁸O-depleted meteoric waters typical of intense tropical storms. There is potential for this technique to be used to identify TC landfalls that are not represented by overwash deposits. We, however, propose a more conservative approach and suggest this technique be used to validate the origin of a storm deposit and reduce the odds of a type 1 error.  相似文献