37 research outputs found
Anomalies of Density, Stresses, and the Gravitational Field in the Interior of Mars
We determined the possible compensation depths for relief harmonics of
different degrees and orders. The relief is shown to be completely compensated
within the depth range of 0 to 1400 km. The lateral distributions of
compensation masses are determined at these depths and the maps are
constructed. The possible nonisostatic vertical stresses in the crust and
mantle of Mars are estimated to be 64 MPa in compression and 20 MPa in tension.
The relief anomalies of the Tharsis volcanic plateau and symmetric feature in
the eastern hemisphere could have arisen and been maintained dynamically due to
two plumes in the mantle substance that are enriched with fluids. The plumes
that originate at the core of Mars can arise and be maintained by the anomalies
of the inner gravitational field achieving +800 mGal in the region of plume
formation, - 1200 mGal above the lower mantle-core transition layer, and -1400
mGal at the crust.Comment: 9 pages, 5 figure
The boundary integral method for magnetic billiards
We introduce a boundary integral method for two-dimensional quantum billiards
subjected to a constant magnetic field. It allows to calculate spectra and wave
functions, in particular at strong fields and semiclassical values of the
magnetic length. The method is presented for interior and exterior problems
with general boundary conditions. We explain why the magnetic analogues of the
field-free single and double layer equations exhibit an infinity of spurious
solutions and how these can be eliminated at the expense of dealing with
(hyper-)singular operators. The high efficiency of the method is demonstrated
by numerical calculations in the extreme semiclassical regime.Comment: 28 pages, 12 figure
Averaging method in the motion stability problem for a rotating body suspended on a long rigid string
Mapping the Agulhas Current from space: An assessment of ASAR surface current velocities
Over 2 years of surface current information collected in the Agulhas Current region and derived from the Doppler centroid anomalies of Envisat's advanced synthetic aperture radar (ASAR) are examined. The sources of errors and potential use of ASAR surface current velocities for oceanographic research are assessed. ASAR surface current velocities are compared to surface drifter data and merged altimetry observations. Maps of sea surface temperature are used to establish the ASAR's capacity to capture the synoptic circulation. Discrepancies between observed and predicted ASAR velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 degrees. Occasionally observed wind-induced outliers cause a bias in the estimated ASAR velocities but do not affect the ability of the ASAR to systematically image regions of strong surface current flow and shear. Time-averaged maps of ASAR-derived surface current velocity seem able to accurately capture the position as well as the intensity of the Agulhas Current. The ability of the ASAR to pick up the smaller features of the circulation along the shelf break also shows that variability along the Agulhas Bank is of the same order of magnitude as that observed in the Agulhas retroflection. ASAR surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved. The quasi-synoptic nature of ASAR acquisitions combined with the relatively high resolution of ASAR surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics