| 1. |
- McLennan, S.M., et al.
(författare)
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Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars
- 2014
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 343:6169
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine–rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.
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| 2. |
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| 3. |
- Cousin, A., et al.
(författare)
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Compositions of coarse and fine particles in martian soils at gale: A window into the production of soils
- 2015
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 249, s. 22-42
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Tidskriftsartikel (refereegranskat)abstract
- The ChemCam instrument onboard the Curiosity rover provides for the first time an opportunity to study martian soils at a sub-millimeter resolution. In this work, we analyzed 24 soil targets probed by ChemCam during the first 250 sols on Mars. Using the depth profile capability of the ChemCam LIBS (Laser-Induced Breakdown Spectroscopy) technique, we found that 45% of the soils contained coarse grains (>500 μm). Three distinct clusters have been detected: Cluster 1 shows a low SiO2 content; Cluster 2 corresponds to coarse grains with a felsic composition, whereas Cluster 3 presents a typical basaltic composition. Coarse grains from Cluster 2 have been mostly observed exposed in the vicinity of the landing site, whereas coarse grains from Clusters 1 and 3 have been detected mostly buried, and were found all along the rover traverse. The possible origin of these coarse grains was investigated. Felsic (Cluster 2) coarse grains have the same origin as the felsic rocks encountered near the landing site, whereas the origin of the coarse grains from Clusters 1 and 3 seems to be more global. Fine-grained soils (particle size < laser beam diameter which is between 300 and 500 μm) show a homogeneous composition all along the traverse, different from the composition of the rocks encountered at Gale. Although they contain a certain amount of hydrated amorphous component depleted in SiO2, possibly present as a surface coating, their overall chemical homogeneity and their close-to-basaltic composition suggest limited, or isochemical alteration, and a limited interaction with liquid water. Fine particles and coarse grains from Cluster 1 have a similar composition, and the former could derive from weathering of the latter. Overall martian soils have a bulk composition between that of fine particles and coarse grains. This work shows that the ChemCam instrument provides a means to study the variability of soil composition at a scale not achievable by bulk chemical analyses.
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| 4. |
- Melikechi, N., et al.
(författare)
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Correcting for variable laser-target distances of laser-induced breakdown spectroscopy measurements with ChemCam using emission lines of Martian dust spectra
- 2014
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Ingår i: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier BV. - 0584-8547 .- 1873-3565. ; 96, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- As part of the Mars Science Laboratory, the ChemCam instrument acquires remote laser induced breakdown spectra at distances that vary between 1.56 m and 7 m. This variation in distance affects the intensities of the measured LIBS emission lines in non-trivial ways. To determine the behavior of a LIBS emission line with distance, it is necessary to separate the effects of many parameters such as laser energy, laser spot size, target homogeneity, and optical collection efficiency. These parameters may be controlled in a laboratory on Earth but for field applications or in space this is a challenge. In this paper, we show that carefully selected ChemCam LIBS emission lines acquired from the Martian dust can be used to build an internal proxy spectroscopic standard. This in turn, allows for a direct measurement of the effects of the distance of various LIBS emission lines and hence can be used to correct ChemCam LIBS spectra for distance variations. When tested on pre-launch LIBS calibration data acquired under Martian-like conditions and with controlled and well-calibrated targets, this approach yields much improved agreement between targets observed at various distances. This work lays the foundation for future implementation of automated routines to correct ChemCam spectra for differences caused by variable distance.
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| 5. |
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| 6. |
- Dyar, O J, et al.
(författare)
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ESCMID generic competencies in antimicrobial prescribing and stewardship : towards a European consensus.
- 2019
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Ingår i: Clinical Microbiology and Infection. - : Elsevier. - 1198-743X .- 1469-0691. ; 25:1, s. 13-19
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To develop a consensus-based set of generic competencies in antimicrobial prescribing and stewardship for European prescribers through a structured consensus procedure.METHODS: The RAND-modified Delphi procedure comprised two online questionnaire rounds, a face-to-face meeting between rounds, and a final review. Our departure point was a set of competencies agreed previously by consensus among a UK multi-disciplinary panel, and which had been subsequently revised through consultation with ESCMID Study Group representatives. The 46 draft competency points were reviewed by an expert panel consisting of specialists in infectious diseases and clinical microbiology, and pharmacists. Each proposed competency was assessed using a nine-point Likert scale, for relevance as a minimum standard for all independent prescribers in all European countries.RESULTS: A total of 65 expert panel members participated, from 24 European countries (one to six experts per country). There was very high satisfaction (98%) with the final competencies set, which included 35 competency points, in three sections: core concepts in microbiology, pathogenesis and diagnosing infections (11 points); antimicrobial prescribing (20 points); and antimicrobial stewardship (4 points).CONCLUSIONS: The consensus achieved enabled the production of generic antimicrobial prescribing and stewardship competencies for all European independent prescribers, and of possible global utility. These can be used for training and can be further adapted to the needs of specific professional groups.
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