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61.
62.
A.W. Jones R.J. Davis A. Wilkinson G. Giardino S.J. Melhuish H. Asareh R.D. Davies A.N. Lasenby 《Monthly notices of the Royal Astronomical Society》2001,327(2):545-551
We present the joint analysis of two 5-GHz interferometric surveys of the northern sky, taken with different baselines. The two surveys were carried out on the Jodrell Bank 5-GHz interferometer based at Manchester. The Maximum Entropy Method is used to check the consistency of the two surveys and the final two-dimensional maps are used, together with low-frequency full sky surveys, to put constraints on the Galactic spectral index. It is found that synchrotron emission is the dominant process at high Galactic latitudes below 5 GHz. 相似文献
63.
H. L. Davies J. B. Keene K. Hashimoto M. Joshima J. E. Stuart D. L. Tiffin 《Geo-Marine Letters》1987,6(4):181-191
The floor of the western Solomon Sea (for new bathymetric map see inside back cover of this issue) is dominated by the arched and ridged basement of the Solomon Sea Basin, the partly-sediment-filled New Britain Trench, and a more completely filled trench, the Trobriand Trough. There is a deep basin where the trenches join (149° Embayment), and a silled basin west of the New Britain Trench (Finsch Deep). Submarine canyons descend from the west and south to the 149° Embayment. Abyssal fans and plains are structurally defined and locally disturbed by young faults. Probable submerged pinnacle reefs stand in water depths as great as 1,200 m. 相似文献
64.
A non-linear three-dimensional unstructured grid model of the M2 tide in the shelf edge area off the west coast of Scotland is used to examine the spatial distribution of the M2 internal tide and its higher harmonics in the region. In addition, the spatial variability of the tidally induced turbulent
kinetic energy and associated mixing in the area are considered. Initial calculations involve only tidal forcing, although
subsequent calculations are performed with up-welling and down-welling favourable winds to examine how these influence the
tidal distribution (particularly the higher harmonics) and mixing in the region. Both short- and long-duration winds are used
in these calculations. Tidal calculations show that there is significant small-scale spatial variability particularly in the
higher harmonics of the internal tide in the region. In addition, turbulence energy and mixing exhibit appreciable spatial
variability in regions of rapidly changing topography, with increased mixing occurring above seamounts. Wind effects significantly
change the distribution of the M2 internal tide and its higher harmonics, with appreciable differences found between up- and down-welling winds and long- and
short-duration winds because of differences in mixing and the presence of wind-induced flows. The implications for model validation,
particularly in terms of energy transfer to higher harmonics, and mixing are briefly discussed. 相似文献
65.
A cross-sectional non-hydrostatic model with idealized topography was used to examine the processes influencing tidal mixing
in the region of sills. Initial calculations with appropriate parameters for the sill at the entrance to Loch Etive showed
that the model could reproduce the main features of the observed mixing in the region. In particular, the hydraulic jump in
the sill region was reproduced, as was an intense mid-water jet that was observed to separate from the lee side of the sill.
Shear instabilities associated with the jet appeared to be a source of mixing within the thermocline. In addition, internal
lee waves were generated on the lee side of the sill, with the observed amplification because of trapping during the flood
stage. Their magnitude and hence the mixing increased with increasing Froude number (F
r). In the case of vertically varying buoyancy frequency, its value near the sill top determined the F
r number, with its value below influencing internal waves magnitude at depth. At high F
r values particularly with strong currents, short waves and overturning occurred. 相似文献
66.
Melvyn B. Davies Richard Blackwell Vernon C. Bailey & Steinn Sigurdsson 《Monthly notices of the Royal Astronomical Society》1998,301(3):745-753
We consider the destructive effects of encounters between binaries and red giant stars in the Galactic Centre. Such encounters may explain the observed depletion of luminous red giants within the central 0.2 pc of the galaxy. We consider encounters involving 2- and 8-M⊙ red giants, and thus span the range of stellar masses contributing to the most luminous red giants observed in the Galactic Centre. To explore the phase space of encounters thoroughly, we simulate 18 × 103 encounters using a modified four-body code in which the red giant core and components of the binary are treated as point masses, and where the envelope configuration is assumed to remain static throughout the encounter. We then rerun a small number of encounters with a smoothed particle hydrodynamics (SPH) code to confirm the reliability of conclusions drawn from the four-body runs. We see two possible pathways to red giant destruction. A large fraction of encounters lead to the formation of common-envelope systems, where two compact objects (drawn from the red giant core and the components of the original binary) form a binary within a common gaseous envelope, whilst the third body is ejected. The destruction of the red giant will then follow when the envelope is ejected as the binary hardens. In a smaller number of encounters, the intruding binary passes through the star and ejects the red giant core from the envelope. The red giant envelope will then disperse on short time-scales. We compute the time-scales for both of these processes to occur in the Galactic Centre for a variety of binary populations. 相似文献
67.
Ian A. Bonnell & Melvyn B. Davies 《Monthly notices of the Royal Astronomical Society》1998,295(3):691-698
We investigate the evolutionary effect of dynamical mass segregation in young stellar clusters. Dynamical mass segregation acts on a time-scale of order the relaxation time of a cluster. Although some degree of mass segregation occurs earlier, the position of massive stars in rich young clusters generally reflects the cluster's initial conditions. In particular, the positions of the massive stars in the Trapezium cluster in Orion cannot be due to dynamical mass segregation, but indicate that they formed in, or near, the centre of the cluster. Implications of this for cluster formation and for the formation of high-mass stars are discussed. 相似文献
68.
J. I. Davies P. Alton S. Bianchi & M. Trewhella 《Monthly notices of the Royal Astronomical Society》1998,300(4):1006-1014
We have constructed a numerical model of a galaxy that consists of a stellar, gas and dust disc imbedded within a dark halo. We have used this model to assess the radiation, gravitational and viscous forces on dust grains and to trace their motion through the interstellar medium over a period of 109 yr. We conclude that the disc opacity is a crucial factor in understanding the motion of the grains. Large grains (≈0.1 μm) with low disc opacity will lead to dust expulsion from the stellar disc, while high opacity leads to dust retention. Reasonable disc opacities lead to the recycling of the larger grains from the outer to the inner regions of the galaxy. The larger grains travel at higher velocities than small grains (0.01−0.001 μm), and so the smaller grains remain relatively close to their formation sites. Dust can 'leak' out over the entire surface of the disc because of the imbalance of radiation and gravitational forces. The dust is dynamically coupled to the gas and so although the gas lags behind the dust it is carried along with it. This explains the close correlation between the far-infrared emission from dust and the gas column density. We use a simple analytical model to show how the dust mass of a galaxy may evolve with time and how a significant fraction (90 per cent) of the total dust mass produced may have been expelled into the intergalactic medium. 相似文献
69.
70.
M. Nonino J. P. Henry C. Fanti R. Fanti & J. Davies 《Monthly notices of the Royal Astronomical Society》1998,299(2):332-340
We report on new optical, infrared and radio observations of the Seyfert galaxy Markarian 315. We confirm the detection at all wavelengths of a secondary peak of emission, which lies ≈ 2 arcsec east of the Seyfert nucleus. Moreover, we detect a chain-like structure which surrounds the active nucleus, with peculiar behaviour westward of the nucleus. We consider different interpretations for the origin of the secondary peak emission. 相似文献