Two serendipitous low-mass LMC clusters discovered with HST1     

Basílio X. Santiago  Rebecca A. W. Elson  Steinn Sigurdsson  & Gerard F. Gilmore 《Monthly notices of the Royal Astronomical Society》1998,295(4):860-868

We present V and I photometry of two open clusters in the LMC down to V ∼26. The clusters were imaged with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope ( HST ), as part of the Medium Deep Survey Key Project. Both are low-luminosity ( M_V ∼−3.5), low-mass ( M ∼10³ M⊙) systems. The chance discovery of these two clusters in two parallel WFPC2 fields suggests a significant incompleteness in the LMC cluster census near the bar. One of the clusters is roughly elliptical and compact, with a steep light profile, a central surface brightness μ _V (0)∼20.2 mag arcsec⁻², a half-light radius r _hl∼0.9 pc (total visual major diameter D ∼3 pc) and an estimated mass M ∼1500 M⊙. From the colour–magnitude diagram and isochrone fits we estimate its age as τ∼(2–5)×10⁸ yr. Its mass function has a fitted slope of Γ=Δlogφ( M )/Δlog M =−1.8±0.7 in the range probed (0.9≲ M /M⊙≲4.5). The other cluster is more irregular and sparse, having shallower density and surface brightness profiles. We obtain Γ=−1.2±0.4, and estimate its mass as M ∼400 M⊙. A derived upper limit for its age is τ≲5×10⁸ yr. Both clusters have mass functions with slopes similar to that of R136, a massive LMC cluster, for which HST results indicate Γ∼−1.2. They also seem to be relaxed in their cores and well contained in their tidal radii.  相似文献   

Multiwavelength monitoring of GRS 1915+105     

Bandyopadhyay  Martini  Gerard  Charles  Wagner  Shrader  Shahbaz  & Mirabel 《Monthly notices of the Royal Astronomical Society》1998,295(3):623-631

Since its discovery in 1992, the superluminal X-ray transient GRS 1915+105 has been extensively observed in an attempt to understand its behaviour. We present here first results from a multiwavelength campaign undertaken from 1996 July to September. This study includes X-ray data from the RXTE All Sky Monitor and BATSE , two-frequency data from the Nançay radio telescope, and infrared photometry from the 1.8-m Perkins telescope at Lowell Observatory. The first long-term, well-sampled infrared light curve of GRS 1915+105 is presented herein; it is consistent with the interpretation of this source as a long-period binary. We compare the various light curves, searching for correlations in the behaviour of the source at differing wavelengths and for possible periodicities.  相似文献   

Upscaling of Hooke's Law for Imperfectly Layered Rocks     

Rijpsma  Gerard  Zijl  Wouter 《Mathematical Geosciences》1998,30(8):943-969

In this paper, we consider the upscaling of Hooke's law and its parameters on the fine scale, to a similar law with upscaled parameters on a larger scale. It is assumed that the fine scale material properties of the rock are imperfectly layered. In the governing equations, the deviations from perfect layering introduce a small parameter that can be used in perturbation series expansions for the stress, the strain, and the displacement. In the approximation of order zero the upscaled compliance matrix contains the well-known Backus parameters; this approximation holds exactly for a perfect layering. However, many natural rock types are imperfectly layered and in that case the approximation of order zero may not be sufficiently accurate. Therefore, we consider also the first order corrections. The derivation and results are presented both for the most general case and for the much simpler case in which the fine scale Poisson ratio may be assumed constant. From thermodynamic principles, it follows that the compliance tensor is symmetric on the fine scale. However, it is shown that the argument for symmetry cannot be extended to upscaled rigidities. One of the most important conclusions is that upscaled compliance tensors are nonsymmetric when there are trends in the deviations from perfect layering.  相似文献   

Letter from the Guest Editors: The GPS Wireless Special Issue     

Gerard Lachapelle  Jinling Wang 《GPS Solutions》2002,6(3):137-137

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An attempted pollution abatement in the Gulf of La Napoule (Cannes,France)     

Gerard L. Bellan 《Marine pollution bulletin》1979,10(6):163-166

A benthic survey was carried out in 1973 at the servicing of a 1285 m long submarine pipe designed to achieve pollution abatement in the Gulf of La Napoule (Cannes, French Mediterranean coast) and repeated 4 years later (1977). This last survey points to a good recovery of benthic communities in the eastern part of the Gulf (off Cannes) but a severe change in the western part of the Gulf with the appearance, in a deposition area, of the species Scolelepis fuliginosa and Capitella capitata which are highly characteristic of polluted areas and which had not been sampled during the first survey.  相似文献   

Towards the production of a reproducible aerosol by radiolytic methods     

Gerard McGreevy 《Pure and Applied Geophysics》1968,71(1):190-197

Summary A convenient constant reproducible aerosol has been a long-felt need for satisfactory research and development purposes in the field of Aitken nucleus studies. An account is given of a recent attempt to produce such an aerosol by radiolytic methods. It consists of the introduction of -particle sources of different activities into nucleus-free air in aerosol containers. Condensation nuclei in the Aitken size-range are produced by radiolytic reactions in the air. The concentration, size and size-distribution of the particles have been measured for sources of various activities and the results are sufficiently consistent to allow us to state that radiolytic production seems a promising approach to the problem of providing aerosols of particles lying in the lower Aitken nucleus size range.  相似文献   

Episodic mesozoic volcanism in Namibia and Brazil: A K—Ar Isochron study bearing on the opening of the south atlantic     

Gerard Siedner  John G. Mitchell 《Earth and Planetary Science Letters》1976,30(2):292-302

An attempt is made to find a more objective and precise basis for the correlation of volcanics from southwestern Africa and South America than is possible by frequency diagrams of individual K—Ar ages. This leads to a critical appraisal of conventionally calculated K—Ar ages with the conclusion thata priori assumption regarding the isotopic composition of non-radiogenic argon and, hence, the standard atmospheric correction, are no longer tenable.K—Ar isotoopic data on Mesozoic basalts and dolerites from Namibia and Brazil are presented in terms of an isochron model. Plots for cogenetic rocks are unacceptably scattered on a “radiogenic”⁴⁰Ar vs. K diagram, but show a high degree of collinearity on⁴⁰Ar/³⁶Ar diagrams0K/³⁶Ar diagrams. Using the latter plots, a number of isochrons are generated which indicate that Mesozoic volcanism in these regions occured as several discrete episodes of fairly short duration. Effusion of the extensive Serra Geral basalts of Brazil and the Kaoko basalts of Namibia is shown to have occured simultaneeously at 121 m.y.B.P. Basalts from a series of boreholes along the central Parana Basin, as well as a group of dykes from Sao Paulo, yield isochrons of 128 m.y., which coincides with the postulated onset of separation of Africa and South America based on marine magnetic anomalies. Linear dyke swarms along the Namibian seaboard, interpreted as an expression of the earliest rift phase, have an isochron age of 134 m.y. Sills and dykes, mainly from southern Namibia, with isochron ages of 183 m.y. are considered to be the westernmost manifestation of Stormberg volcanism, not necessarily related to rifting. Most of the igneous suites examined have initial⁴⁰Ar/³⁶Ar ratios significantly different from the modern atmospheric value.  相似文献   

American beach law and policies     

Gerard J. Mangone 《Ocean & Coastal Management》2010,53(8):454-467

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Evaluation of the Relationship Between Coral Damage and Tsunami Dynamics; Case Study: 2009 Samoa Tsunami     

Derya I. Dilmen  Vasily V. Titov  Gerard H. Roe 《Pure and Applied Geophysics》2015,172(12):3557-3572

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Interferometric interpolation of sparse marine data     

Sherif M. Hanafy  Gerard T. Schuster 《Geophysical Prospecting》2014,62(1):1-16

We present the theory and numerical results for interferometrically interpolating 2D and 3D marine surface seismic profiles data. For the interpolation of seismic data we use the combination of a recorded Green's function and a model‐based Green's function for a water‐layer model. Synthetic (2D and 3D) and field (2D) results show that the seismic data with sparse receiver intervals can be accurately interpolated to smaller intervals using multiples in the data. An up‐ and downgoing separation of both recorded and model‐based Green's functions can help in minimizing artefacts in a virtual shot gather. If the up‐ and downgoing separation is not possible, noticeable artefacts will be generated in the virtual shot gather. As a partial remedy we iteratively use a non‐stationary 1D multi‐channel matching filter with the interpolated data. Results suggest that a sparse marine seismic survey can yield more information about reflectors if traces are interpolated by interferometry. Comparing our results to those of f‐k interpolation shows that the synthetic example gives comparable results while the field example shows better interpolation quality for the interferometric method.  相似文献