10-µm images and spectra of T Tauri stars     

J. E. Van Cleve  T. L. Hayward  J. W. Miles  G. E. Gull  J. Schoenwald  J. R. Houck 《Astrophysics and Space Science》1994,212(1-2):231-238

T Tauri stars are young stars usually surrounded by dusty disks similar to the one from which we believe our own Solar System formed. Most T Tauri stars exhibit a broad emission or absorption band between 7.5 and 13.5µm which is attributed to silicate grains in the circumstellar environment. We imaged three spatially resolved T Tauri binaries through a set of broadband filters which include the spectral region occupied by the silicate band. Two of these objects (T Tauri and Haro 6–10) are infrared companion systems in which one component is optically much fainter but contributes strongly in the infrared. Both infrared companions exhibit a deep silicate absorption which is not present in their primaries, indicating that they suffer very strong local extinction which may be due to an edge-on circumstellar disk or to a dense shell. We also took low resolution spectra of the silicate feature of two unresolved T Tauris to look for narrow features in the silicate band which would indicate the presence of specific minerals such as olivine. We observed GK Tau, for which Cohen and Witteborn (1985) reported a narrow emission feature at 9.7µm, but do not find evidence for this feature, and conclude that it is either time-dependent or an artifact of absorption by telluric ozone.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

Gaseous electron multiplier gain characteristics using low-pressure Ar/CO<Subscript>2</Subscript>     

T. Rogers  R. McEntaffer  T. Schultz  J. McCoy  D. Miles  J. Tutt 《Experimental Astronomy》2017,43(2):201-210

Gaseous Electron Multiplier detectors, or GEMs, show promise for use on space-based X-ray missions. Operating pressure strongly affects the gain of the detector and must be optimized for best performance. We have measured the gain characteristics of a GEM detector at various pressures below atmosphere using a mixture of Ar:CO₂ with the goal of maximizing gain to push GEM capabilities to the lowest energies possible. This paper discusses our tests, results, and their implications for choosing a detector pressure. We found that at any operating pressure the detector voltage can be adjusted to achieve roughly the same maximum gain prior to the onset of electrical discharges. We also find that the gain varies substantially by spatial location across the detector, but this variation is insensitive to changes in pressure allowing it to be calibrated and corrected if necessary. The detector pressure can therefore be optimized in the interest of other performance parameters such as leak rate, window stress, power requirements, or quantum efficiency without concern for negatively affecting the gain. These results can inform the choice of operating pressure and voltage for GEMs used onboard future space missions.  相似文献   

Characterizing beach intertidal bar systems using multi-annual LiDAR data     

Andrew Miles  Suzana Ilic  Duncan Whyatt  Mike R. James 《地球表面变化过程与地形》2019,44(8):1572-1583

Intertidal bars are common in mesotidal/macrotidal low-to-moderate energy coastal environments and an understanding of their morphodynamics is important from the perspective of both coastal scientists and managers. However, previous studies have typically been limited by considering bar systems two-dimensionally, or with very limited alongshore resolution. This article presents the first multi-annual study of intertidal alongshore bars and troughs in a macrotidal environment using airborne LiDAR (light detection and ranging) data to extract three-dimensional (3D) bar morphology at high resolution. Bar and trough positions are mapped along a 17.5 km stretch of coastline in the northwest of England on the eastern Irish Sea, using eight complete, and one partial, LiDAR surveys spanning 17 years. Typically, 3–4 bars are present, with significant obliquity identified in their orientation. This orientation mirrors the alignment of waves from the dominant south-westerly direction of wave approach, undergoing refraction as they approach the shoreline. Bars also become narrower and steeper as they migrate onshore, in a pattern reminiscent of wave shoaling. This suggests that the configuration of the bars is being influenced by overlying wave activity. Net onshore migration is present for the entire coastline, though rates vary alongshore, and periods of offshore migration may occur locally, with greatest variability between northern and southern regions of the coastline. This work highlights the need to consider intertidal bar systems as 3D, particularly on coastlines with complex configurations and bathymetry, as localized studies of bar migration can overlook 3D behaviour. Furthermore, the wider potential of LiDAR data in enabling high-resolution morphodynamic studies is clear, both within the coastal domain and beyond. © 2019 John Wiley & Sons, Ltd.  相似文献   

一种新的土壤冻融特征曲线模型   总被引：1，自引：0，他引：1  

付子腾  吴青柏  Miles DYCK  何海龙 《冰川冻土》2021,43(2):437-452

土壤冻融特征曲线(SFTC)可以描述冻融过程中未冻水含量随负温的变化关系.准确刻画土壤冻融特征曲线对土壤的冻融过程及相关的水热耦合运移研究至关重要.以往研究中土壤冻融特征曲线适用范围较窄,无法满足实际需要.通过类比水分特征曲线,考虑初始含水量和溶质浓度对未冻水含量的影响,提出了一种新的冻融特征曲线模型,经广泛的文献数据...  相似文献   

An assessment of the effect of urban development on groundwater levels in a chalk aquifer     

J. C. Miles  J. W. Lloyd  J. A. J. Witt 《Environmental Geology》1989,14(3):187-194

Underlying the site of a proposed development is a chalk aquifer, groundwater levels are close to the surface. The storm water from the development is to be drained into a lake in the center of the development. Because of the high groundwater levels the effect of this lake has been studied by means of a simple localized mathematical model. It is shown that such a model can give results of sufficient accuracy with regard to probable changes in groundwater levels caused by the development.  相似文献   

Development and parameterisation of a complex hydrogeological model based on high-resolution direct-push data     

B. Miles  T. Kalbacher  O. Kolditz  C. Chen  J. Gronewold  W. Wang  A. Peter 《Environmental Geology》2007,52(7):1399-1412

Ongoing developments in geological and hydrogeological investigation techniques, especially direct-push methods, have led to an increase in the quality, density and spatial resolution of data available from such investigations. This has created new challenges in the development of numerical models in terms of accurately and efficiently translating detailed and complex conceptual models into effective numerical models. Suitable geometrical and numerical modelling tools are essential in order to meet these challenges. This paper describes the development of a three-dimensional hydrogeological flow model for a contaminated site near Berlin, Germany, based on high-resolution geological data obtained principally using direct-push methods. The available data were first interpreted to construct a detailed GIS-based geological model, which formed the basis of the conceptual site model. The conceptual model was then translated into a geometrical model, which was used to create a finite element numerical model. An innovative geometry object-based approach enabled the complex structural details of the conceptual model to be accurately reproduced in the numerical model domain. The resulting three-dimensional steady-state unconfined flow model was successfully calibrated using external automated calibration software, whereby parameter values for groundwater recharge and hydraulic conductivity were determined.  相似文献   

Plankton: A guide to their ecology and monitoring for water quality, 2nd edition     

Miles Lamare 《新西兰海洋与淡水研究杂志》2019,53(3)

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The group evolution multiwavelength study: the near-infrared luminosity function of nearby galaxy groups     

Trevor A. Miles  Somak Raychaudhury  Paul A. Russell 《Monthly notices of the Royal Astronomical Society》2006,373(4):1461-1469

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First results of the XI Groups Project: studying an unbiased sample of galaxy groups     

Jesper Rasmussen  Trevor J. Ponman  John S. Mulchaey  Trevor A. Miles  Somak Raychaudhury 《Monthly notices of the Royal Astronomical Society》2006,373(2):653-665

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Water quality in the inshore Great Barrier Reef lagoon: Implications for long-term monitoring and management     

Schaffelke B  Carleton J  Skuza M  Zagorskis I  Furnas MJ 《Marine pollution bulletin》2012,65(4-9):249-260

Coastal and inshore areas of the Great Barrier Reef lagoon receive substantial amounts of material from adjacent developed catchments, which can affect the ecological integrity of coral reefs and other inshore ecosystems. A 5-year water quality monitoring dataset provides a 'base range' of water quality conditions for the inshore GBR lagoon and illustrates the considerable temporal and spatial variability in this system. Typical at many sites were high turbidity levels and elevated chlorophyll a and phosphorus concentrations, especially close to river mouths. Water quality variability was mainly driven by seasonal processes such as river floods and sporadic wind-driven resuspension as well as by regional differences such as land use. Extreme events, such as floods, caused large and sustained increases in water quality variables. Given the highly variable climate in the GBR region, long-term monitoring of marine water quality will be essential to detect future changes due to improved catchment management.  相似文献