45 research outputs found
Ancient volcanism on the Moon: Insights from Pb isotopes in the MIL 13317 and Kalahari 009 lunar meteorites
Lunar meteorites provide a potential opportunity to expand the study of ancient (>4000 Ma) basaltic volcanism on the Moon, of which there are only a few examples in the Apollo sample collection. Secondary Ion Mass Spectrometry (SIMS) was used to determine the Pb isotopic compositions of multiple mineral phases (Ca-phosphates, baddeleyite K-feldspar, K-rich glass and plagioclase) in two lunar meteorites, Miller Range (MIL) 13317 and Kalahari (Kal) 009. These data were used to calculate crystallisation ages of 4332 ±2Ma (95% confidence level) for basaltic clasts in MIL 13317, and 4369 ±7Ma (95% confidence level) for the monomict basaltic breccia Kal 009. From the analyses of the MIL 13317 basaltic clasts, it was possible to determine an initial Pb isotopic composition of the protolith from which the clasts originated, and infer a 238U/204Pb ratio (ÎŒ-value) of 850 ±130(2Ï uncertainty) for the magmatic source of this basalt. This is lower than ÎŒ-values determined previously for KREEP-rich (an acronym for K, Rare Earth Elements and P) basalts, although analyses of other lithological components in the meteorite suggest the presence of a KREEP component in the regolith from which the breccia was formed and, therefore, a more probable origin for the meteorite on the lunar nearside. It was not possible to determine a similar initial Pb isotopic composition from the Kal 009 data, but previous studies of the meteorite have highlighted the very low concentrations of incompatible trace elements and proposed an origin on the farside of the Moon. Taken together, the data from these two meteorites provide more compelling evidence for widespread ancient volcanism on the Moon. Furthermore, the compositional differences between the basaltic materials in the meteorites provide evidence that this volcanism was not an isolated or localised occurrence, but happened in multiple locations on the Moon and at distinct times. In light of previous studies into early lunar magmatic evolution, these data also imply that basaltic volcanism commenced almost immediately after Lunar Magma Ocean (LMO) crystallisation, as defined by Nd, Hf and Pb model ages at about 4370Ma
Non-extremal Black Holes, Harmonic Functions, and Attractor Equations
We present a method which allows to deform extremal black hole solutions into
non-extremal solutions, for a large class of supersymmetric and
non-supersymmetric Einstein-Vector-Scalar type theories. The deformation is
shown to be largely independent of the details of the matter sector. While the
line element is dressed with an additional harmonic function, the attractor
equations for the scalars remain unmodified in suitable coordinates, and the
values of the scalar fields on the outer and inner horizon are obtained from
their fixed point values by making specific substitutions for the charges. For
a subclass of models, which includes the five-dimensional STU-model, we find
explicit solutions.Comment: 33 page
Recommended from our members
Science objectives of the NOMAD spectrometer on ExoMars Trace Gas Orbiter
The "Nadir and Occultation for MArs Discovery" (NOMAD) instrument on ESA and NASA's ExoMars Trace Gas Orbiter (EMTGO) will conduct a spectroscopic survey of the Martian atmosphere in the infrared (IR) and UV/visible spectral regions, both in solar occultation and nadir looking modes (see: Vandaele, A.C., same session). In the IR wavelength domain, the spectral resolution (~0.15 cm-1) surpasses those of previous surveys of Mars by more than an order of magnitude, this channel's heritage derives from the SOIR instrument with proven success on ESA's Venus Express mission [1]. An additional light-weight channel UVIS extends the survey to UV and visible wavelengths with a 1-2 nm resolution. NOMAD will search for active geology, volcanism and life by looking for the atmospheric markers of these processes on Mars, confining the source regions, and providing crucial information on the nature of the processes involved. NOMAD will also extend the survey of major climatology cycles of Mars
OPTIMIZATION OF A HIGH-PRESSURE STEAM TURBINE STAGE FOR A WIDE FLOW COEFFICIENT RANGE
In this paper a multi-objective, aerodynamic optimization of
a high-pressure steam turbine stage is presented. The overall optimization strategy relies on a neural-network-based approach,
aimed at maximizing the stageâs efficiency, while at the same
time increasing the stage loading. The stage under investigation
is composed of prismatic blades, usually employed in a repeating
stage environment and in a wide range of operating conditions.
For this reason, two different optimizations are carried
out, at high and low flow coefficients. The optimized geometries
are chosen taking into account aerodynamic constraints, such as
limitation of the pressure recovery in the uncovered part of the
suction side, as well as mechanical constraints, such as root tensile
stress and dynamic behavior. As a result, an optimum airfoil
is selected and its performance are characterized over the whole
range of operating conditions. Parallel to the numerical activity,
both optimized and original geometries are tested in a linear
cascade, and experimental results are available for comparison
purposes in terms of loading distributions and loss coefficients.
Comparisons between measurements and calculations are presented
and discussed for a number of incidence angles and expansion
ratios
Martian surface mineralogy from Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité on board the Mars Express spacecraft (OMEGA/MEx): Global mineral maps
International audienceAfter 2 years of operation the Observatoire pour la MinĂ©ralogie, l'Eau, les Glaces et l'ActivitĂ© (OMEGA) imaging spectrometer on board Mars Express has acquired data coverage of the Martian surface with spatial resolution varying between 300 m and 4.8 km, depending on the pericenter altitude of the spacecraft's elliptical orbit. We report the global surface distributions of some minerals using the OMEGA observations in the visible and near infrared (VNIR) wavelength domains (0.35â2.5 ÎŒ m). Global maps of ferric phases, mafic minerals (pyroxenes and olivines), and hydrated minerals have been derived from spectral parameters. The limits of detection in terms of abundance for some minerals of different grain size distributions are given. The distribution of pyroxenes is in general agreement with the mineral maps of previous telescopic and space observations. The Fe 3+ absorption feature in the visible wavelength region is present everywhere on the surface. The spectra of the bright regions compare with anhydrous nanophase ferric oxides. Terrains with waterâbearing minerals cover a very small fraction of the Martian surface. Olivine (Mgârich compositions) is detected in more extensive regions of the pyroxeneârich zones than previously reported. Olivine with higher iron content and/or larger grain size (>100 ÎŒ m) is only detected in isolated areas. The mineralogy of the northern lowâalbedo regions is discussed in the light of these mineral maps. Chemical alteration or oxidation during extrusion producing a coating or varnish of anhydrous ferric phases over a dark basaltic surface best accounts for the VNIR spectral properties of these regions, although a glassy composition resulting from impact is also considered
Magnesium deficiency results in an increased formation of osteoclasts
Magnesium (Mg2+) deficiency is a frequently occurring disorder that leads to loss of bone mass, abnormal bone growth and skeletal weakness. It is not clear whether Mg2+ deficiency affects the formation and/or activity of osteoclasts. We evaluated the effect of Mg2+ restriction on these parameters. Bone marrow cells from long bone and jaw of mice were seeded on plastic and on bone in medium containing different concentrations of Mg2+ (0.8 mM which is 100% of the normal value, 0.4, 0.08 and 0 mM). The effect of Mg2+ deficiency was evaluated on osteoclast precursors for their viability after 3 days and proliferation rate after 3 and 6 days, as was mRNA expression of osteoclastogenesis-related genes and Mg2+-related genes. After 6 days of incubation, the number of tartrate resistant acid phosphatase-positive (TRACP+) multinucleated cells was determined, and the TRACP activity of the medium was measured. Osteoclastic activity was assessed at 8 days by resorption pit analysis. Mg2+ deficiency resulted in increased numbers of osteoclast-like cells, a phenomenon found for both types of marrow. Mg2+ deficiency had no effect on cell viability and proliferation. Increased osteoclastogenesis due to Mg2+ deficiency was reflected in higher expression of osteoclast-related genes. However, resorption per osteoclast and TRACP activity were lower in the absence of Mg2+. In conclusion, Mg2+ deficiency augmented osteoclastogenesis but appeared to inhibit the activity of these cells. Together, our in vitro data suggest that altered osteoclast numbers and activity may contribute to the skeletal phenotype as seen in Mg2+ deficient patients. © 2012 Elsevier Inc. All rights reserved