19,019 research outputs found
The delineation and interpretation of the Earth's gravity field
The observed changes in velocity with time are reduced relative to the well-determined low degree and order GEM field model and accelerations are found by analytical differentiation of the range rates. This new map is essentially identical to the first map and we have produced a composite map by combining all 90 passes of SST data. The resolution of the map is at worst about 5 deg and much better in most places. A comparison of this map with conventional GEM models shows very good agreement. A reduction of the SEASAT altimeter data has also been carried out for an additional comparison. Although the SEASAT geoid contains much more high frequency information, it agrees very well with both the SST and GEM fields. The maps are dominated (especially in the east) by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. A further comparison with regional bathymetric data shows a remarkably close correlation with plate age
Lithospheric structure in the Pacific geoid
In order that sub-lithospheric density variations be revealed with the geoid, the regional geoid anomalies associated with bathymetric variations must first be removed. Spectral techniques were used to generate a synthetic geoid by filtering the residual bathymetry assuming an Airy-type isostatic compensation model. An unbiased estimated of the admittances show that for region under study, no single compensation mechanism will explain all of the power in the geoid. Nevertheless, because topographic features are mainly coherent with the geoid, to first order an isostationally compensated lithosphere cut by major E-W fracture zones accounts for most of the power in the high degree and other SEASAT geoid in the Pacific
On gravity from SST, geoid from Seasat, and plate age and fracture zones in the Pacific
A composite map produced by combining 90 passes of SST data show good agreement with conventional GEM models. The SEASAT altimeter data were deduced and found to agree with both the SST and GEM fields. The maps are dominated (especially in the east) by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. Comparison with regional bathymetric data shows a remarkedly close correlation with plate age. Most anomalies in the east half of the Pacific could be partly caused by regional differences in plate age. The amplitude of these geoid or gravity anomalies caused by age differences should decrease with absolute plate age, and large anomalies (approximately 3 m) over old, smooth sea floor may indicate a further deeper source within or perhaps below the lithosphere. The possible plume size and ascent velocity necessary to supply deep mantle material to the upper mantle without complete thermal equilibration was considered. A plume emanating from a buoyant layer 100 km thick and 10,000 times less viscous than the surrounding mantle should have a diameter of about 400 km and must ascend at about 10 cm/yr to arrive still anomalously hot in the uppermost mantle
Selectivity of interaction of spin-labelled lipids with peripheral proteins bound to dimyristoylphosphatidylglycerol bilayers, as determined by ESR spectroscopy.
The selectivity of interaction between spin-labelled lipids and the peripheral proteins, apocytochrome c, cytochrome c, lysozyme and polylysine has been studied using ESR spectroscopy. Derivatives of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylinositol (PI), diphosphatidylglycerol (CL) and diacylglycerol (DG) spin-labelled at the 5-C atom position of the sn-2 chain were used to study the association of these proteins with bilayers of dimyristoylphosphatidylglycero. Binding of the proteins increased the outer hyperfine splitting in the ESR spectra of the lipid spin labees to an extent which depended both on the spin-labelled lipid species involved and on the particular protein. The order of selectivity for apocytochrome c follows the sequence: PIā>CLāāDG PSā>PCĀ±>PGā>PEĀ±. The selectivity pattern for cytochrome c is: PIā>PGā>CLā>DG PSāāPCĀ±>PEĀ±; for lysozyme is: CLā>PGā>DG PEā>PCĀ±PSā>PIā; and that for polylysine is: CLā>PSāā©¾PGā>PIā>PCĀ±>DG PE+-. The overall strength of interaction is in the order lysozyme>cytochrome c>apcoytochrome c, for equivalent binding, and the spread of the selectivity for the different proteins is in the reverse order. Assuming fast exchange for the ESR spectra of the 5-C atom labelled lipids, the relative association constants of the different labels with the different proteins have been estimated
Reasonableness, Murder, and Modern Science
Originally titled āIs It Murder in Tennessee to Kill a Chimpanzee,ā this article argues in some detail that typical legal definitions of āmurderā as involving the intentional killing of āa reasonable beingā would require classifying the intentional killing of chimpanzees as murder
Petrologic and geophysical sources of long-wavelength crustal magnetic anomalies
The magnetic mineralogy and magnetic properties of the deep crust are studied as they pertain to the interpretation of long wavelength, or regional, crustal magnetic anomalies in satellite magnetic data and near surface magnetic data. The conclusions have relevance to the understanding of regional magnetic anomalies in magnetic field measuring satellite missions data. There are two separable studies: (1) a synthesis of available information of regional magnetic anomalies and the magnetization of metamorphic and igneous rocks, and (2) a detailed field, analytical, and experimental study of in situ and laboratory specimens from a terrain that offers exposures of high grade granlite facies rocks that have associated regional magnetic and gravity anomalies
Lithospheric structure in the Pacific geoid
The high degree and order SEASAT geoid in the central Pacific correlates closely with the structure of the cooling lithosphere. Relative changes in plate age across major fracture zones in relatively young seafloor frame the east-west trending pattern formed by the geoid anomalies. The field removal in bathymetry corresponds to removal of some of the low degree and order geoidal components, the step like structure across fracture zones is also removed. The regional thermal subsidence was removed from the bathymetry by subtracting a mean subsidence surface from the observed bathymetry. This produces a residual bathymetry map analogous to the usual residual depth anomaly maps. The residual bathymetry obtained in this way contains shallow depths for young seafloor, and larger depths for older seafloor, thus retaining the structure of the lithosphere while removing the subsidence of the lithosphere
Evaluation of the Goddard range and range rate system at Rosman by intercomparison with GEOS 1 long-arc orbital solutions
Evaluation of Goddard range and range rate system at Rosman by intercomparison with GEOS 1 long-arc orbital solution
Gravity model comparison using Geos-1 long arc orbital solutions
Gravity model comparison using Geos-1 long arc orbital solution
The Future is Now: the Formation of Single Low Mass White Dwarfs in the Solar Neighborhood
Low mass helium-core white dwarfs (M < 0.45 Msun) can be produced from
interacting binary systems, and traditionally all of them have been attributed
to this channel. However, a low mass white dwarf could also result from a
single star that experiences severe mass loss on the first ascent giant branch.
A large population of low mass He-core white dwarfs has been discovered in the
old metal-rich cluster NGC 6791. There is therefore a mechanism in clusters to
produce low mass white dwarfs without requiring binary star interactions, and
we search for evidence of a similar population in field white dwarfs. We argue
that there is a significant field population (of order half of the detected
systems) that arises from old metal rich stars which truncate their evolution
prior to the helium flash from severe mass loss. There is a consistent absence
of evidence for nearby companions in a large fraction of low mass white dwarfs.
The number of old metal-rich field dwarfs is also comparable with the
apparently single low mass white dwarf population, and our revised estimate for
the space density of low mass white dwarfs produced from binary interactions is
also compatible with theoretical expectations. This indicates that this channel
of stellar evolution, hitherto thought hypothetical only, has been in operation
in our own Galaxy for many billions of years. One strong implication of our
model is that single low mass white dwarfs should be good targets for planet
searches because they are likely to arise from metal-rich progenitors. We also
discuss other observational tests and implications, including the potential
impact on SN Ia rates and the frequency of planetary nebulae.Comment: ApJ published versio
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