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71.
72.
E. E. Ferguson F. C. Fehsenfeld D. B. Dunkin A. L. Schmeltekopf H. I. Schjff 《Planetary and Space Science》1964,12(12):1169-1171
Preliminary measurements of reaction rates for loss of thermal helium ions in reaction with molecular oxygen and nitrogen establish rather conclusively that the helium ions in the ionosphere will be lost in reaction with molecular nitrogen rather than molecular oxygen in contrast to previous assumptions based on theoretical considerations. The rate of thermal He+ loss in reaction with N2 is measured to be 1·2 ± 0·3 times the rate for reaction with O2. This conclusion is of considerable significance to atmospheric physics because the oxygen loss process contained the possibility of leading to terrestrial helium escape and therefore the possibility of a steady state helium atmosphere. The nitrogen loss process does not have this possibility so that no satisfactory mechanism has yet been proposed which will allow a steady state helium atmosphere. The interpretation of recent atmospheric helium ion profiles obtained by rocket borne mass spectrometers appear to be inconsistent with the laboratory loss rate constants and current atmospheric theory. 相似文献
73.
Several organic contaminants in sewage effluent have been shown to elicit an estrogenic response in juvenile fish. Comparatively little emphasis has been placed on assessing these effects in marine invertebrates, particularly benthic organisms inhabiting sediment where lipophilic contaminants tend to persist. The present study examined reproductive effects in the benthic crustacean Leptocheirus plumulosus exposed to sewage-impacted sediment from Jamaica Bay, New York. Data from chronic 28-day tests showed a 50% reduction in the average number of young (juveniles + embryos) produced per surviving female in exposures to sediment from Jamaica Bay (JB). Nonylphenol ethoxylate ('NPEO) concentrations at this site were measured at 44.2 microg/g dw, concentrations two orders of magnitude higher than reference site concentrations in central Long Island Sound (CLIS). Dose-response studies with nonylphenol (NP) amended reference sediment, however, did not significantly affect reproduction suggesting that other contaminants may have contributed to the effects observed. 相似文献
74.
Sarah J. Kelloway Steven Craven Mark Pecha William R. Dickinson Martin Gibbs Timothy Ferguson Michael D. Glascock 《Geoarchaeology》2014,29(1):47-60
We present U‐Pb ages of zircons extracted from olive jars recovered from two sites associated with Alvaro de Mendaña y Neyra's colonising expedition to the Solomon Islands, c. 1595–1596 A.D. The olive jars were previously associated with Panamanian and Peruvian origins based on petrological and geochemical studies. To further define provenance, 143 zircons were extracted from five olive jar sherds, analyzed and dated. The resultant U‐Pb ages range from the Archaean to the Cenozoic (2977.2 ± 29.0–3.2 ± 4.0 Ma), but the dominance of Cretaceous and Palaeogene ages (∼ 90% of the total age population is between ∼ 145 and 23 Ma) supports a Peruvian origin based on comparative geology, with the Coastal Batholith of Peru a prime candidate area of ceramic production. These results are significant for the characterization of 16th Century Peruvian‐made pottery and our understanding of its production and trade. 相似文献
75.
76.
A. P. Huxor N. R. Tanvir M. J. Irwin R. Ibata J. L. Collett A. M. N. Ferguson T. Bridges G. F. Lewis 《Monthly notices of the Royal Astronomical Society》2005,360(3):1007-1012
We present three new clusters discovered in the halo of M31 which, although having globular-like colours and luminosities, have unusually large half-light radii, ∼30 pc. They lie at projected galactocentric distances of ≈15 to ≈35 kpc. These objects begin to fill the gap in parameter space between globular clusters and dwarf spheroidals, and are unlike any clusters found in the Milky Way, or elsewhere to date. Colour–magnitude diagrams, integrated photometric properties and derived King profile fit parameters are given, and we discuss possible origins of these clusters and their relationships to other populations. 相似文献
77.
78.
M.D. Gregg M.J. Drinkwater M.J. Hilker Steven Phillipps J. Bryn Jones Henry C. Ferguson 《Astrophysics and Space Science》2003,285(1):113-117
We have discovered a new type of galaxy in the Fornax Cluster: `ultra-compact' dwarfs (UCDs). The UCDs are unresolved in ground-based
imaging and have spectra typical of old stellar systems. Although the UCDs resemble overgrown globular clusters, based on
VLT UVES echelle spectroscopy, they appear to be dynamically distinct systems with higher internal velocity dispersions and
M/L ratios for a given luminosity than Milky Way or M31 globulars. Our preferred explanation for their origin is that they
are the remnant nuclei of dwarf elliptical galaxies which have been tidally stripped, or `threshed' by repeated encounters
with the central cluster galaxy, NGC1399. If correct, then tidal stripping of nucleated dwarfs to form UCDs may, over a Hubble
time, be an important source of the plentiful globular cluster population in the halo of NGC1399, and, by implication, other
cD galaxies. In this picture, the dwarf elliptical halo contents, up to 99% of the original dwarf luminosity, contribute a
significant fraction of the populations of intergalactic stars, globulars, and gas in galaxy clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
The effects of both small perturbations and large deformations to the array's shape on both conventional and adaptive beamformers are shown for two frequencies: the spatial Nyquist frequency (or design frequency) of the array and a frequency about three times greater. Large shape deformations lead to a decrease in the conventional beamformer's output power for a beam steered in the direction of the signal source, together with an increase in the sidelobe levels (or secondary maxima), while small perturbations in the array shape have little effect. Signal suppression is observed to be far greater for the adaptive beamformer because it is very sensitive to system errors. The imposition of a weight norm constraint on the adaptive beamformer reduces the signal suppression only for small shape perturbations array shape estimation techniques are needed to reduce signal suppression for large shape deformations. The adverse effects of a nonlinear array shape on both conventional and adaptive beamforming are shown to be substantially reduced by applying techniques that estimate the coordinates of the hydrophones prior to beamforming 相似文献
80.