931 research outputs found
Progress in geophysical aspects of the rotation of the earth
The geophysical causes and consequences of the Earth's rotation are reviewed. Specific topics covered include: (1) the motion of the rotation axis in space, precession and nutation; (2) the motion of the rotation axis relative to the Earth, polar motion; and (3) the rate of rotation about this axis, or changes in the length of day. Secular decrease in obliquity and evolution of the Earth-Moon system are also discussed
Probability of recording satellite images optically
Probability of recording and tracking satellite images opticall
Effect of random atmospheric refraction on optical satellite observations
Random atmospheric refraction effects on optical satellite observation
The earths gravity field to 16th degree and station coordinates from satellite and terrestrial data
Geodetic parameters of earth gravity field and satellite tracking station positions in geocentric reference fram
Optimum station-satellite configurations for simultaneous observations to satellites
Formula derivation for optimum satellite station configurations for simultaneous direction observations to satellite
Tidal Heating of Extra-Solar Planets
Extra-solar planets close to their host stars have likely undergone
significant tidal evolution since the time of their formation. Tides probably
dominated their orbital evolution once the dust and gas had cleared away, and
as the orbits evolved there was substantial tidal heating within the planets.
The tidal heating history of each planet may have contributed significantly to
the thermal budget that governed the planet's physical properties, including
its radius, which in many cases may be measured by observing transit events.
Typically, tidal heating increases as a planet moves inward toward its star and
then decreases as its orbit circularizes. Here we compute the plausible heating
histories for several planets with measured radii, using the same tidal
parameters for the star and planet that had been shown to reconcile the
eccentricity distribution of close-in planets with other extra-solar planets.
Several planets are discussed, including for example HD 209458 b, which may
have undergone substantial tidal heating during the past billion years, perhaps
enough to explain its large measured radius. Our models also show that GJ 876 d
may have experienced tremendous heating and is probably not a solid, rocky
planet. Theoretical models should include the role of tidal heating, which is
large, but time-varying.Comment: Accepted for publication to Ap
Changes in wave climate over the northwest European shelf seas during the last 12,000 years
Because of the depth attenuation of wave orbital velocity, wave-induced bed shear stress is much more sensitive to changes in total water depth than tidal-induced bed shear stress. The ratio between wave- and tidal-induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment. In order to capture the high-frequency nature of wind events, a two-dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka BP to present using paleobathymetries of the NW European shelf seas. By contrasting paleowave climates and bed shear stress distributions with present-day conditions, the model results demonstrate that, in regions of the shelf seas that remained wet continuously over the last 12,000 years, annual root-mean-square (rms) and peak wave heights increased from 12 ka BP to present. This increase in wave height was accompanied by a large reduction in the annual rms wave- induced bed shear stress, primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level. In regions of the shelf seas which remained wet over the last 12,000 years, the annual mean ratio of wave- to (M-2) tidal-induced bed shear stress decreased from 1 (at 12 ka BP) to its present-day value of 0.5. Therefore compared to present- day conditions, waves had a more important contribution to large-scale sediment transport processes in the Celtic Sea and the northwestern North Sea at 12 ka BP
Tolerance and application of polarization independent waveguide for communication devices
A polarization independent optical waveguide structure has been developed and optimized towards minimized dependence on deviations in the processing parameters and very low processing complexity. The tolerance analysis was based on typical parameters of the silicon oxynitride technology. The optimized waveguide structure meets the criterion of a channel birefringence within 5x10-5 taking the processing tolerance into account. Moreover, it was found that the channel birefringence is thickness independent (within the 10-5 criterion) over a range of up to 200 nm. The optimized waveguide, fulfilling also the remaining demands of the application, has been applied for the realization of a passband flattened add-drop multiplexing device with 0.4 nm free spectral range and 0.03 nm TE-TM shift
SEA LEVEL CHANGE ALONG THE TYRRHENIAN COAST FROM EARLY HOLOCENE TO THE PRESENT
In any discussion of the evolution of a river basin, the history of sealevel
change is important since river gradients and delta developments are
strongly influenced by local sea level. Also, sea level provides a reference
for inferring past vertical tectonic stability from the geological record.
Hence it is appropriate that the discussion on the Tiber basin starts with sea
level change along the Tyrrhenian coast during the Holocene.
The past evidence for sea level comes from inferences of the position of
the sea surface with respect to the present. Hence it is a relative measure; a
function of both the changing position of the ocean surface and of the land
surface or an integrated measure of changes in ocean volume, land movement
and redistribution of water within the ocean basins. The observation
therefore contains information on all the processes that change these surfaces:
on geophysical, glaciological and oceanographic processes
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