The masses, radii and luminosities of the components of U Geminorum     

T. Naylor  A. Allan  K. S. Long 《Monthly notices of the Royal Astronomical Society》2005,361(3):1091-1101

We present a phase-resolved spectroscopic study of the secondary star in the cataclysmic variable (CV) U Gem. We use our data to measure the radial velocity semi-amplitude, systemic velocity and rotational velocity of the secondary star. Combining this with literature data allows us to determine masses and radii for both the secondary star and white dwarf, which are independent of any assumptions about their structure. We use these to compare their properties to those of field stars and find that both components follow field mass–radius relationships. The secondary star has the mass, radius, luminosity and photometric temperature of an M2 star, but a spectroscopic temperature of M4. The latter may well be due to a high metallicity. There is a troubling inconsistency between the radius of the white dwarf inferred from its gravitational redshift and inclination and that inferred from its temperature, flux and astrometric distance.
We find that there are two fundamental limits to the accuracy of the parameters we can derive. First, the radial velocity curve of the secondary star deviates from a sinusoid, in part because of its asphericity (which can be modelled) and in part because the line flux is not evenly distributed over its surface. Secondly, we cannot be certain which spectral type is the best match for the lines of the secondary star, and the derived rotational velocity is a function of the spectral type of the template star used.  相似文献   

High resolution polarimetric radar scattering measurements of lowgrazing angle sea clutter     

McLaughlin  D.J. Allan  N. Twarog  E.M. Trizna  D.B. 《Oceanic Engineering, IEEE Journal of》1995,20(3):166-178

This paper presents fully polarimetric radar scattering measurements of low grazing angle sea clutter. The measurements were obtained at a three degree grazing angle using a high range resolution (1.5 m) X-Band polarimetric radar operated from a shore site overlooking the Chesapeake Bay. The radar employs pulse-to-pulse switching between orthogonal transmitted polarizations and simultaneously measures two orthogonally polarized components of the backscattered wave to obtain full polarimetric information about the scattering process. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to obtain polarization signatures and to determine the polarization dependence of the clutter. Sea spike echoes are shown to be weakly polarized and to exhibit polarization signatures indicative of multiple independent scattering mechanisms. Clutter echoes in the absence of sea spikes are shown to be highly polarized and to exhibit polarization signatures indicative of a single dominant scattering mechanism  相似文献   

In vitro growth of iron sulphide chimneys: possible culture chambers for origin-of-life experiments     

Michael J. Russell  Allan J. Hall  Dugald Turner 《地学学报》1989,1(3):238-241

Iron monosulphide globules and tubes grown in the laboratory have similar morphologies to the fossil pyrite botryoids and chimneys found in the Silvermines exhalative sedimentary ore-body of Carboniferous age in Ireland. We envisage analogous fine structures growing at hot springs (100–200°C) in the earliest oceans as having provided the culture chambers and flow reactors for life to originate by phosphorylation and growth of organic molecules on the iron sulphide surfaces. Such sulphide structures grown in the laboratory could be used in origin-of-life experiments.  相似文献   

The role of stochastic hydrogeological modeling in real-world engineering applications     

R. Allan Freeze 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(4):286-289

  相似文献   

Transmissivity estimation for highly heterogeneous aquifers: comparison of three methods applied to the Edwards Aquifer,Texas, USA     

Scott L. Painter  Allan D. Woodbury  Yefang Jiang 《Hydrogeology Journal》2007,15(2):315-331

Obtaining reliable hydrological input parameters is a key challenge in groundwater modeling. Although many quantitative characterization techniques exist, experience applying these techniques to highly heterogeneous real-world aquifers is limited. Three geostatistical characterization techniques are applied to the Edwards Aquifer, a limestone aquifer in south-central Texas, USA, for the purposes of quantifying the performance in an 88,000-cell groundwater model. The first method is a simple kriging of existing hydraulic conductivity data developed primarily from single-well tests. The second method involves numerical upscaling to the grid-block scale, followed by cokriging the grid-block conductivity. In the third method, the results of the second method are used to establish the prior distribution for a Bayesian updating calculation. Results of kriging alone are biased towards low values and fail to reproduce hydraulic heads or spring flows. The upscaling/cokriging approach removes most of the systematic bias. The Bayesian update reduced the mean residual by more than a factor of 10, to 6 m, approximately 2.5% of the total head variation in the aquifer. This agreement demonstrates the utility of automatic calibration techniques based on formal statistical approaches and lends further support for using the Bayesian updating approach for highly heterogeneous aquifers.  相似文献   

Localized multi-scale energy and vorticity analysis: II. Finite-amplitude instability theory and validation     

X. San Liang  Allan R. Robinson 《Dynamics of Atmospheres and Oceans》2007

A novel localized finite-amplitude hydrodynamic stability analysis is established in a unified treatment for the study of real oceanic and atmospheric processes, which are in general highly nonlinear, and intermittent in space and time. We first re-state the classical definition using the multi-scale energy and vorticity analysis (MS-EVA) developed in Liang and Robinson [Liang, X.S., Robinson, A.R., 2005. Localized multiscale energy and vorticity analysis. I. Fundamentals. Dyn. Atmos. Oceans 38, 195–230], and then manipulate certain global operators to achieve the temporal and spatial localization. The key of the spatial localization is transfer-transport separation, which is made precise with the concept of perfect transfer, while relaxation of marginalization leads to the localization of time. In doing so the information of transfer lost in the averages is retrieved and an easy-to-use instability metric is obtained. The resulting metric is field-like (Eulerian), conceptually generalizing the classical formalism, a bulk notion over the whole system. In this framework, an instability has a structure, which is of particular use for open flow processes. We check the structure of baroclinic instability with the benchmark Eady model solution, and the Iceland–Faeroe Frontal (IFF) intrusion, a highly localized and nonlinear process occurring frequently in the region between Iceland and Faeroe Islands. A clear isolated baroclinic instability is identified around the intrusion, which is further found to be characterized by the transition from a spatially growing mode to a temporally growing mode. We also check the consistency of the MS-EVA dynamics with the barotropic Kuo model. An observation is that a local perturbation burst does not necessarily imply an instability: the perturbation energy could be transported from other processes occurring elsewhere. We find that our analysis yields a Kuo theorem-consistent mean–eddy interaction, which is not seen in a conventional Reynolds stress framework. Using the techniques of marginalization and localization, this work sets up an example for the generalization of certain geophysical fluid dynamics theories for more generic purposes.  相似文献   

The effects of climatic variability on estimates of recharge from temperature profiles   总被引：1，自引：0，他引：1  

Ferguson G  Woodbury AD 《Ground water》2005,43(6):837-842

Using heat as a tracer allows for estimation of ground water recharge rates based on subsurface temperature measurements. While possible in theory, it may be difficult in practice to discriminate the effects of climate from the effects of ground water advection. This study uses synthetic simulations to determine the influence of variability of ground surface temperature (GST) on the ability to estimate vertical specific discharge from temperature profiles. Results suggest that in cases where temperature measurements are sufficiently deep and specific discharge is sufficiently high, estimates of specific discharges will be reasonably accurate. Increasing the number of times temperatures are measured, or producing models that incorporate variations in GST, will increase the reliability of any studies using temperatures to estimate specific discharge. Furthermore, inversions of temperature measurements should be combined with other methods of estimating recharge rates to improve the reliability of recharge estimates.  相似文献   

An attempt at an unambiguous scheme to code the geometry of bedding planes     

Allan D. Griesemer  Donald F. Costello 《Mathematical Geology》1972,4(4):345-351

  相似文献   

Theory of the Excitation and Propagation of Lamb's Atmospheric Edge Mode from Nuclear Explosions     

Allan D. Pierce  Joe W. Posey 《Geophysical Journal International》1971,26(1-4):341-368

  相似文献   

Is Convection Towards or Away from the Continents?     

D. W. Allan  W. B. Thompson 《Geophysical Journal International》1967,14(1-4):449-450

  相似文献