Evolution of the Martian atmosphere and hydrosphere: Solar wind erosion studied by ASPERA-3 on Mars Express     

Rickard Lundin  Stanislav Barabash 《Planetary and Space Science》2004,52(11):1059-1071

The evolution of the Martian atmosphere and the potential existence of a past hydrosphere is a scientific issue of great interest in planetary research. Although the first missions to Mars had a focus on surface features and atmospheric properties, some of the missions (e.g., The Soviet Mars 2, 3 and 5) also carried instruments addressing the solar wind interaction with the Martian atmosphere and ionosphere and the potential existence of an intrinsic magnetic field on Mars. However, it took until 1989 before a spacecraft, Phobos-2, was able to carry out a more detailed investigation of the solar wind interaction with Mars. Phobos-2 gave valuable data on the Solar wind interaction with Mars during about 2 months of operations, leading to a better understanding of the solar wind impact on a weakly magnetized planet. However, Phobos-2 also raised a number of critical issues that has left science without adequate data since 1989.Investigations planned for Mars Express will cast new light on important aspects of the solar wind interaction with Mars. ASPERA-3 (Analyzer of Space Plasma and Energetic Atoms) on Mars Express will focus on the overall plasma outflow and monitor remotely the outflow and inflow of energetic neutral atoms produced by charge exchange processes. This report will discuss some of the unsolved issues about the solar wind interaction with Mars and how we plan to address these issues with Mars Express.  相似文献   

Rocket observations of electron spectral and angular characteristics in an “inverted V” event     

Rickard Lundin 《Planetary and Space Science》1976,24(5):499-514

Energy spectra and pitch angle distributions of auroral electrons in the energy range 2.5–11 keV observed on a rocket flight launched from Andøya on 13 November 1970 are presented. Strong rapidly fluctuating fluxes during the first part of the flight were succeeded by fluxes below or close to the level of detectability. Before the rocket passed through the northern precipitation boundary two spectral events of “inverted V” character occurred. Both events were associated with field aligned pitch angle distributions. While anisotropies with the flux peaked near 0° were in general associated with the spectral peak energy, isotropy over the upper hemisphere was the dominant distribution for other energies. The observations made during these events provide strong support for the theory of a parallel potential drop close to the ionosphere as an important accelerating mechanism for auroral electrons in connection with “inverted V” events.  相似文献   

On the Use of Computational Fluid Dynamics to Investigate Aerosol Dispersion in an Industrial Environment: A Case Study     

H. E. Fossum  B. A. Pettersson Reif  M. Tutkun  T. Gjesdal 《Boundary-Layer Meteorology》2012,144(1):21-40

Aerosol dispersion in the area surrounding an existing biological treatment facility is investigated using large-eddy simulation, with the objective to investigate the applicability of computational fluid dynamics to complex real-life problems. The aerosol sources consist of two large aeration ponds that slowly diffuse aerosols into the atmosphere. These sources are modelled as dilute concentrations of a non-buoyant non-reacting pollutant diffusing from two horizontal surfaces. The time frame of the aerosol release is restricted to the order of minutes, justifying a statistically steady inlet boundary condition. The numerical results are compared to wind-tunnel experiments for validation. The wind-tunnel flow characteristics resemble neutral atmospheric conditions with a Reynolds number, based on the boundary-layer thickness, of Re _δ ≈ 2 × 10⁵. The numerical inflow conditions are based upon the wind-tunnel flow field. The predicted decay of both the mean and root-mean-square concentrations are in good agreement with experimental data; at 3 m from the ground, the plume mean concentration 200 m downwind of the source is approximately 2% of the source strength. The numerical data in the near-surface layer (0–50 m from the ground) correspond particularly well with the wind-tunnel data. Tentative deposition simulations suggest that there seems to be little difference in the deposition rates of large (1.8 × 10⁻⁵ m) and small (3 × 10⁻⁶ m) particles in the near-field under the flow conditions considered.  相似文献   

Peter Deines (1936–2009)     

David Rickard 《Chemical Geology》2009,266(3-4)

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European Phanerozoic metallogenesis     

D. Rickard 《Mineralium Deposita》1999,34(5-6):417-421

Phanerozoic metallogenesis in Europe displays divergent characteristics which may be related to the variable nature of the three great European Phanerozoic orogens: Caledonian, Variscan and Alpine. These reflect different geodynamic processes. The Caledonian orogen resulted from the interaction of essentially oceanic with continental lithosphere, whilst the Variscan and Alpine orogens evolved mainly from continent-continent collisions with the involvement of a series of smaller oceanic basins. Each major stage of the orogenic processes is characterised by a typical metallogeny. The occurrence of subduction-related processes in the Caledonian orogeny gave rise to extensive VHMS deposition with characteristic Zn:Cu ratio signatures. The relative lack of abundance of metal-rich, Andean-type porphyry-type mineralisation remains unexplained, unless present erosional levels have prevented the preservation of such deposits. Continent-continent collisions do not appear to result in extensive mineralisation unless elevated heat flows result, possibly as a result of lithospheric delamination at the peak collisional stage. The development of late stage and peri-orogenic sedimentary basins are characterised by extensive Pb-Zn-Ba-F mineralisation as expressions of basinal fluid flow of regional dimensions.  相似文献   

FeS-Induced Radical Formation and Its Effect on Plasmid DNA     

D. Rickard  B. Hatton  D. M. Murphy  I. B. Butler  A. Oldroyd  A. Hann 《Aquatic Geochemistry》2011,17(4-5):545-566

Plasmid DNA was incubated at 25°C with aqueous solutions of dissolved Fe(II), S(-II), and nanoparticulate FeS with a mackinawite structure, FeS_m. At ??0.1 mM total dissolved Fe(II) and S(-II), an increase in the proportion of the relaxed plasmid DNA occurs, through scission of the DNA backbone. In solutions where FeS_m was precipitated, nanoparticulate FeS_m binds to the DNA molecules. In solutions with concentrations below the FeS_m solubility product, nicking of supercoiled pDNA occurs. Plasmid DNA appears to be a sensitive proxy for radical reactions. The reactant is proposed to be a sulfur-based radical produced from the iron-catalyzed decomposition of bisulfide, in a manner analogous to the Fenton reaction. This is further supported by experiments that suggest that sulfide free radicals are produced during the photolysis of aqueous solutions of polysulfides. Supercoiling of DNA affects nearly all DNA?Cprotein transactions so the observation of relaxation of supercoiled forms through reaction with FeS solutions has direct implications to biochemistry. The results of this experimentation suggest that genotoxicity in FeS-rich systems is a further contributory factor to the limited survival of organisms in sulfidic environments. Mutations resulting from the interactions of organisms and mobile elements, such as plasmids, in sediments will also be affected in sulfide-rich environments.  相似文献   

On a new method of preparing peat for the purposes of fuel and gas-making     

W.T. Rickard 《Proceedings of the Geologists' Association. Geologists' Association》1862,1(8):197-199

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Scandinavian metallogenesis     

D. T. Rickard Dr. 《GeoJournal》1979,3(3):235-252

The Baltic shield broadly evolved by successive accretions of younger rocks in a SW direction. The Archaean (>2.5 Ga) basement is situated in the NE of the area and is mantled to the SW by a broad belt of early Proterozoic supracrustals of the Svecokarelian orogen. Over 80% of mined sulfide ores and known reserves in Finland occur on the NE side of a major NW-SE suture, that limits the Archaean basement complex in the SW. These ores, which include the Kotalahti Ni-Cu zone, the Vihanti Zn-Cu-Pb zone and the Outokumpu Cu-Co zone, are emplaced in early Proterozoic epicontinental rocks and obducted ophiolitic slices. The early Proterozoic marine complexes on the SW side of the Archaean continent include the ore districts of the Skellefte field and the Central Province of Sweden and Finland. These ores include complex massive and bedded Pb-Zn-Cu ores, often with pyrite, in island arc settings. The Bergslagen district of the Central Province also includes a large number of small, exhalative-sedimentary iron and manganese ores.Mid-Proterozoic evolution in Scandinavia mostly occurred through vertical movements and the emplacement of late- and an-orogenic granite suites with associated porphyry effusives and continental sandstones. The Kiruna-type iron ores, which accounted for six % of global iron ore production in 1969, probably originated in association with these events.Phanerozoic evolution in Scandinavia was dominated by the formation of the Caledonide orogen. The complex Pb-Cu-Zn ores of the Caledonide Province were formed mainly in an island arc setting during the Ordovician. These units were obducted onto the continental margin, where they suffered complex folding, metamorphism, intrusion and further nappe development during mid-Silurian or early-Devonian times.Intraformational brines, generated in the thick back-arc sedimentary pile during the Ordovician and Silurian, were mobilized in advance of the eastward translation of the Caledonide nappes. Lead and zinc, leached from sediments, were deposited as sulfide ores in sulfidic sandstone aquifers along the E margin of the Caledonide orogen.  相似文献   

Stress configurations in conjugate quartz-vein arrays     

M.J. Rickard  L.K. Rixon 《Journal of Structural Geology》1983,5(6):573-578

Arrays of quartz gash-veins in small angle (40°), conjugate shear zones (type 1 arrays of Beach) are well-developed in the Upper Devonian Merrimbula sandstone of the south coast region of New South Wales, Australia. We argue that vein and cleavage geometry support an origin of the veins as tension fractures in a rotated secondary stress field rather than a primary shear origin as advocated by Beach. We also conclude that the veins develop in dilational shear zones under high fluid pressure.  相似文献   

Surface chemistry of disordered mackinawite (FeS)   总被引：1，自引：0，他引：1  

Mariëtte Wolthers  Laurent Charlet  David Rickard 《Geochimica et cosmochimica acta》2005,69(14):3469-3481

Disordered mackinawite, FeS, is the first formed iron sulfide in ambient sulfidic environments and has a highly reactive surface. In this study, the solubility and surface chemistry of FeS is described. Its solubility in the neutral pH range can be described by K_s^app = {Fe²⁺} · {H₂S(aq)} · {H⁺}⁻² = 10^+4.87±0.27. Acid-base titrations show that the point of zero charge (PZC) of disordered mackinawite lies at pH ∼7.5. The hydrated disordered mackinawite surface can be best described by strongly acidic mono-coordinated and weakly acidic tricoordinated sulfurs. The mono-coordinated sulfur site determines the acid-base properties at pH < PZC and has a concentration of 1.2 × 10⁻³ mol/g FeS. At higher pH, the tricoordinated sulfur, which has a concentration of 1.2 × 10⁻³ mol/g FeS, determines surface charge changes. Total site density is 4 sites nm⁻². The acid-base titration data are used to develop a surface complexation model for the surface chemistry of FeS.  相似文献