55 research outputs found
Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D" layer
The Earth's lower mantle is believed to be composed mainly of (Mg,Fe)SiO3
perovskite, with lesser amounts of (Mg,Fe)O and CaSiO3). But it has not been
possible to explain many unusual properties of the lowermost 150 km of the
mantle (the D" layer) with this mineralogy. Here, using ab initio simulations
and high-pressure experiments, we show that at pressures and temperatures of
the D" layer, MgSiO3 transforms from perovskite into a layered CaIrO3-type
post-perovskite phase. The elastic properties of the post-perovskite phase and
its stability field explain several observed puzzling properties of the D"
layer: its seismic anisotropy, the strongly undulating shear-wave discontinuity
at its top and possibly the anticorrelation between shear and bulk sound
velocities.Comment: PUBLISHED IN Nature 430, 445-448 (2004
Lambda hyperons produced in central nucleus-nucleus interactions at 4.5 GeV/c momentum per incident nucleon
Transverse momenta and rapidities of Lambda 's produced in central nucleus-nucleus collisions at 4.5 GeV/c·u (C-C,...,O-Pb) were studied and compared with those from inelastic He-Li interactions at the same incident momentum. Polarization of the Lambda hyperons was found to be consistent with zero ( alpha P=-0.06=0.11 for Lambda 's from central collisions). An upper limit of the Lambda -bar / Lambda production ratio was estimated to be less than 4.5 x 10-3. The experiment was performed in a triggered streamer chamber
Creation of the precision magnetic spectrometer SCAN-3
The new JINR project [1] is aimed at studies of highly excited nuclear matter created in nuclei by a high-energy deuteron beam. The matter is studied through observation of its particular decay products - pairs of energetic particles with a wide opening angle, close to 180°. The new precision hybrid magnetic spectrometer SCAN-3 is to be built for detecting charged (π±, K±, p) and neutral (n) particles produced at the JINR Nuclotron internal target in dA collisions. One of the main and complex tasks is a study of low-energy ηA interaction and a search for η-bound states (η-mesic nuclei). Basic elements of the spectrometer and its characteristics are discussed in the article
DAMIT: a database of asteroid models
Context. Apart from a few targets that were directly imaged by spacecraft, remote sensing techniques are the main
source of information about the basic physical properties of asteroids, such as the size, the spin state, or the spectral type.
The most widely used observing technique –
time-resolved photometry – provides us with data that can be used for deriving asteroid shapes and spin states. In the past decade, inversion of
asteroid lightcurves has led to more than a hundred asteroid models. In the next decade, when data from all-sky surveys are available, the
number of asteroid models will increase. Combining
photometry with, e.g., adaptive optics data produces more detailed models.
Aims. We created the Database of Asteroid Models from Inversion Techniques (DAMIT) with the aim of
providing the astronomical community access to reliable and up-to-date physical models of asteroids – i.e., their shapes, rotation periods,
and spin axis directions.
Models from DAMIT can be used for further detailed studies of individual objects, as well as for statistical studies of the whole set.
Methods. Most DAMIT models were derived from photometric data by the lightcurve inversion method. Some of them have been further refined or scaled using
adaptive optics images, infrared observations, or occultation data. A substantial number of the models were derived also using sparse photometric data
from astrometric databases.
Results. At present, the database contains models of more than one hundred asteroids.
For each asteroid, DAMIT provides the polyhedral shape model, the sidereal rotation period, the spin axis direction, and the photometric data used for the inversion. The database
is updated when new models are available or when already published models are updated or refined.
We have also released the C source code for the lightcurve inversion and for the direct problem (updates and extensions will follow)
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