Influence of redox conditions on the intensity of Mars crustal magnetic anomalies          下载免费PDF全文

Stefanie Brachfeld  Deepa Shah  Emily First  Julia Hammer  Julie Bowles 《Meteoritics & planetary science》2015,50(10):1703-1717

We evaluate the relationship between the intensity of remanent magnetization and fO₂ in natural and synthetic Mars meteorites. The olivine‐phyric shergottite meteorite Yamato 980459 (Y‐980459) and a sulfur‐free synthetic analog (Y‐98*) of identical major element composition were analyzed to explore the rock magnetic and remanence properties of a basalt crystallized from a primitive melt, and to explore the role of magmatic and alteration environment fO₂ on Mars crustal anomalies. The reducing conditions under which Y‐980459 is estimated to have formed (QFM‐2.5; Shearer et al. 2006) were replicated during the synthesis of Y‐98*. Y‐980459 contains pyrrhotite and chromite. Chromite is the only magnetic phase in Y‐98*. The remanence‐carrying capacity of Y‐980459 is comparable to other shergottites that formed in the fO₂ range of QFM‐3 to QFM‐1. The remanence‐carrying capacity of these low fO₂ basalts is 1–2 orders of magnitude too weak to account for the intense crustal anomalies observed in Mars's southern cratered highlands. Moderately oxidizing conditions of >QFM‐1, which are more commonly observed in nakhlites and Noachian breccias, are key to generating either a primary igneous assemblage or secondary alteration assemblage capable of acquiring an intense remanent magnetization, regardless of the basalt character or thermal history. This suggests that if igneous rocks are responsible for the intensely magnetized crust, these oxidizing conditions must have existed in the magmatic plumbing systems of early Mars or must have existed in the crust during secondary processes that led to acquisition of a chemical remanent magnetization.  相似文献   

Photochemistry of methane-water ices     

Robert Hodyss  Paul V. Johnson  Julie V. Stern  Jay D. Goguen  Isik Kanik 《Icarus》2009,200(1):338-156

We report a study on the broadband ultraviolet photolysis of methane-water ice mixtures, at low methane concentrations and temperatures relevant to the icy satellites of the outer Solar System. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products. This implies that, given sufficient exposure time, the methane will eventually be completely oxidized to carbon dioxide. The presence of methane inhibits the formation of hydrogen peroxide by serving as a trap for hydroxyl radicals. The distribution of photochemical products is broadly similar to that previously conducted using ion and electron sources, with some differences possibly attributable to the difference in radiation source. The results are applicable to a variety of icy bodies in the Solar System. On Enceladus, where methane mixed with water is measured in the plumes, methane in the surface ices is subject to oxidation and will eventually be converted to CO₂. The CH stretch feature detected in the VIMS spectra of the Enceladus surface ice suggests that methane is currently being supplied to the surface ice, likely from re-condensation of the plume gas.  相似文献   

Dynamics of planets in retrograde mean motion resonance     

Julie Gayon  Eric Bois  Hans Scholl 《Celestial Mechanics and Dynamical Astronomy》2009,103(3):267-279

In a previous paper (Gayon and Bois 2008a), we have shown the general efficiency of retrograde resonances for stabilizing compact planetary systems. Such retrograde resonances can be found when two-planets of a three-body planetary system are both in mean motion resonance and revolve in opposite directions. For a particular two-planet system, we have also obtained a new orbital fit involving such a counter-revolving configuration and consistent with the observational data. In the present paper, we analytically investigate the three-body problem in this particular case of retrograde resonances. We therefore define a new set of canonical variables allowing to express correctly the resonance angles and obtain the Hamiltonian of a system harboring planets revolving in opposite directions. The acquiring of an analytical “rail” may notably contribute to a deeper understanding of our numerical investigation and provides the major structures related to the stability properties. A comparison between our analytical and numerical results is also carried out.  相似文献   

Environmental conservation and the production of new territories: the example of French départements     

Pech Pierre  Dizière Sophie  Gillet Anne-Gabrielle  Mamder Julie  Tichit Marion 《GeoJournal》2010,75(2):149-161

Very important initiatives have been taken and policies have been adopted in the European Union to protect areas of great importance for threatened species and habitats. Protected areas differ broadly in terms of category, natural conditions and administrative organisation, from international initiative such as Biosphere Reserves, European ones with Natura 2000 network until the institution of national and regional protected areas. In France, the administrative subdivisions known as “départements” were created with the French Revolution in the end of the eighteenth century; in 1985 an original and autonomous procedure to establish special protected areas, called “Sensitive Natural Spaces” (SNS) was devolved to them. The scope of this paper is to present an overview of these devolved powers which enable French départements to create protected areas and to levy a departmental tax on sensitive natural spaces (DTSNS). We statistically studied some parameters by multivariate methods in order to explain the choices of this policy by the départements. The huge variations in the way these powers are implemented prove the development of new environmental territories.  相似文献   

Climate policies as a hedge against the uncertainty on future oil supply   总被引：2，自引：2，他引：0  

Julie Rozenberg  Stéphane Hallegatte  Adrien Vogt-Schilb  Olivier Sassi  Céline Guivarch  Henri Waisman  Jean-Charles Hourcade 《Climatic change》2010,101(3-4):663-668

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Modern Sphagnumδ13C signatures follow a surface moisture gradient in two boreal peat bogs,James Bay lowlands,Québec     

Julie Loisel  Michelle Garneau  Jean‐François Hélie 《第四纪科学杂志》2009,24(3):209-214

Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat‐based climatic studies since a relationship between Sphagnum δ¹³C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum δ¹³C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P < 0.0001) was found between Sphagnum δ¹³C values and their position along the surface moisture gradient. Results show that ¹³C‐depleted values are related to low water table depths (WTD), while ¹³C‐enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO₂ diffusion is an important fractionation process that is observed in bulk Sphagnum δ¹³C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Intelligent Transportation Systems and Travel Behavior in Connecticut     

Julie M. Annino  Robert Cromley 《The Professional geographer》2005,57(1):106-114

In the past decade, there has been significant investment in Intelligent Transportation Systems (ITS) technologies that provide information to both en‐route and pre‐trip travelers. However, there is no definitive evidence that en‐route travelers actually use the information and alter their travel patterns. Previous research employed surveys that relied on motorists' written or spoken responses to questions involving travel information and hypothetical roadway scenarios. This research examines travel behavior on freeways equipped with ITS technologies in Connecticut using collected real‐time traffic count data from the diversionary roadways. Results find that more travel is occurring on the diversionary routes during periods of variable message sign (VMS) messages than during equivalent periods having no messages, indicating a motorist travel response to these messages.  相似文献   

Constructing quality: The multinational histories of chocolate   总被引：1，自引：0，他引：1  

Julie L. Cidell  Heike C. Alberts 《Geoforum》2006,37(6):999-1007

Geographic research on food quality, while considering many of the ways in which quality is socially constructed, has largely focused on the place-based aspects of the raw materials of food production. Here, we use French convention theory to look at a highly processed food in order to show how place associations in the social construction of food quality extend to manufacturing. For chocolate, quality is based on material characteristics whose relative importance in determining quality depends on the country in which different stages of economic innovation took place. Struggles over the definition of quality chocolate, as exemplified by the “European Chocolate War,” show how quality issues are connected to geographies of manufacturing and innovation.  相似文献   

Going to the Extremes   总被引：8，自引：1，他引：8  

Claudia Tebaldi  Katharinec Hayhoe  Julie M. Arblaster  Gerald A. Meehl 《Climatic change》2006,79(3-4):185-211

Projections of changes in climate extremes are critical to assessing the potential impacts of climate change on human and natural systems. Modeling advances now provide the opportunity of utilizing global general circulation models (GCMs) for projections of extreme temperature and precipitation indicators. We analyze historical and future simulations of ten such indicators as derived from an ensemble of 9 GCMs contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), under a range of emissions scenarios. Our focus is on the consensus from the GCM ensemble, in terms of direction and significance of the changes, at the global average and geographical scale. The climate extremes described by the ten indices range from heat-wave frequency to frost-day occurrence, from dry-spell length to heavy rainfall amounts. Historical trends generally agree with previous observational studies, providing a basic sense of reliability for the GCM simulations. Individual model projections for the 21st century across the three scenarios examined are in agreement in showing greater temperature extremes consistent with a warmer climate. For any specific temperature index, minor differences appear in the spatial distribution of the changes across models and across scenarios, while substantial differences appear in the relative magnitude of the trends under different emissions rates. Depictions of a wetter world and greater precipitation intensity emerge unequivocally in the global averages of most of the precipitation indices. However, consensus and significance are less strong when regional patterns are considered. This analysis provides a first overview of projected changes in climate extremes from the IPCC-AR4 model ensemble, and has significant implications with regard to climate projections for impact assessments. An erratum to this article is available at . An erratum to this article can be found at  相似文献   

On the vertical structure of the Rhine region of freshwater influence   总被引：1，自引：0，他引：1  

Gerben J. de Boer  Julie D. Pietrzak  Johan C. Winterwerp 《Ocean Dynamics》2006,56(3-4):198-216

An idealised three-dimensional numerical model of the Rhine region of fresh water influence (ROFI) was set up to explore the effect of stratification on the vertical structure of the tidal currents. Prandle’s dynamic Ekman layer model, in the case of zero-depth-averaged, cross-shore velocities, was first used to validate the response of the numerical model in the case of barotropic tidal flow. Prandle’s model predicted rectilinear tidal currents with an ellipse veering of up to 2%. The behaviour of the Rhine ROFI in response to both a neap and a spring tide was then investigated. For the given numerical specifications, the Rhine plume region was well mixed over the vertical on spring tide and stratified on neap tide. During spring conditions, rectilinear tidal surface currents were found along the Dutch coast. In contrast, during neap conditions, significant cross-shore currents and tidal straining were observed. Prandle’s model predicted ellipse veering of 50%, and was found to be a good indicator of ellipticity magnitude as a function of bulk vertical eddy viscosity. The modelled tidal ellipses showed that surface currents rotated anti-cyclonically whereas bottom currents rotated cyclonically. This caused a semi-diurnal cross-shore velocity shearing which was 90° out of phase with the alongshore currents. This cross-shore shear subsequently acted on the horizontal density gradient in the plume, thereby causing a semi-diurnal stratification pattern, with maximum stratification around high water. The same behaviour was exhibited in simulations of a complete spring–neap tidal cycle. This showed a pattern of recurring stratification on neaps and de-stratification on springs, in accordance with observations collected from field campaigns in the 1990’s. To understand the increase in ellipticities to 30% during neaps and the precise shape of the vertical ellipse structure, stratification has to be taken into account. Here, a full three-dimensional numerical model was employed, and was found to represent the effect of de-coupling of the upper and lower layers due to a reduction of mixing at the pycnocline.  相似文献