Soft X-ray Focusing Telescope Aboard AstroSat: Design,Characteristics and Performance     

K. P. Singh  G. C. Stewart  N. J. Westergaard  S. Bhattacharayya  S. Chandra  V. R. Chitnis  G. C. Dewangan  A. T. Kothare  I. M. Mirza  K. Mukerjee  V. Navalkar  H. Shah  A. F. Abbey  A. P. Beardmore  S. Kotak  N. Kamble  S. Vishwakarama  D. P. Pathare  V. M. Risbud  J. P. Koyande  T. Stevenson  C. Bicknell  T. Crawford  G. Hansford  G. Peters  J. Sykes  P. Agarwal  M. Sebastian  A. Rajarajan  G. Nagesh  S. Narendra  M. Ramesh  R. Rai  K. H. Navalgund  K. S. Sarma  R. Pandiyan  K. Subbarao  T. Gupta  N. Thakkar  A. K. Singh  A. Bajpai 《Journal of Astrophysics and Astronomy》2017,38(2):29

The Soft X-ray focusing Telescope (SXT), India’s first X-ray telescope based on the principle of grazing incidence, was launched aboard the AstroSat and made operational on October 26, 2015. X-rays in the energy band of 0.3–8.0 keV are focussed on to a cooled charge coupled device thus providing medium resolution X-ray spectroscopy of cosmic X-ray sources of various types. It is the most sensitive X-ray instrument aboard the AstroSat. In its first year of operation, SXT has been used to observe objects ranging from active stars, compact binaries, supernova remnants, active galactic nuclei and clusters of galaxies in order to study its performance and quantify its characteriztics. Here, we present an overview of its design, mechanical hardware, electronics, data modes, observational constraints, pipeline processing and its in-orbit performance based on preliminary results from its characterization during the performance verification phase.  相似文献   

Multidecadal biological monitoring and abatement program\ assessing human impacts on aquatic ecosystems within the Oak Ridge Reservation in eastern Tennessee,USA     

Paul G. Matson  Louise M. Stevenson  Natalie A. Griffiths  Christopher R. DeRolph  R. Trent Jett  Allison M. Fortner  Michael W. Jones  Nikki J. Jones  Teresa J. Mathews 《水文研究》2021,35(9):e14340

Human activities can be powerful drivers of ecosystem change within catchments. While most long-term catchment studies have been conducted at pristine sites, such studies are less common from sites more impacted by human activity. The Oak Ridge National Laboratory's Biological Monitoring and Abatement Program (BMAP) was developed in the mid-1980s to (1) assess compliance with environmental regulations, (2) identify causes of adverse ecological impacts, (3) provide data for human and ecological risk assessments, and (4) evaluate the effectiveness of remedial actions taken to mitigate the impacts of contaminants in soils, groundwater, and surface water by documenting ecological recovery on the Oak Ridge Reservation (ORR), a federally owned 33 476-acre site in eastern Tennessee, managed by the US Department of Energy. The ORR is composed of multiple watersheds containing many small to mid-size streams. BMAP uses an integrated approach for determining stream health; its databases include long-term seasonal records of contaminant concentrations in water and biota, data from aquatic toxicity testing, and surveys of macroinvertebrate and fish assemblages from impacted and reference streams. These long-term data provide valuable records of degradation and recovery in catchment ecosystems. Our objective here is to describe our study system and data series in order to increase awareness of the availability of these long-term data to the catchment science community.  相似文献   

Entrainment from a bed of particles by thermal convection     

Viatcheslav S. Solomatov  Peter Olson  David J. Stevenson 《Earth and Planetary Science Letters》1993,120(3-4):387-393

Differentiation in magma chambers, in the Earth's core and in the partially molten early Earth is a competitive process between sedimentation and re-entrainment of crystals in the presence of convection. Previous studies show that the particles suspended in convective layers eventually settle and do so almost as fast as in the absence of convection. However, the nature and magnitude of the competing entrainment has remained unclear. Here we provide a simple theory and experimental evidence showing that entrainment occurs at the crests of dunes created in the particle bed at the base of a convecting fluid. In both laminar and turbulent regimes, the dune formation and entrainment are driven by viscous stresses produced by thermal plumes. At sufficiently high Rayleigh numbers the particles are probably entrained by Reynolds stresses. Entrainment in the Earth's core is hardly possible because it requires unreasonably small crystals. Entrainment of 10⁻²–10⁻¹ cm diameter crystals is very likely in magma oceans. For magma chambers entrainment requires large viscosities (> 10⁶ P) and even when it occurs, the total amount of the suspended solid fraction is very small.  相似文献   

The presence and possible ecological significance of mycorrhizae of the submersed macrophyte,Vallisneria americana     

Cathleen Wigand  J. Court Stevenson 《Estuaries and Coasts》1994,17(1):206-215

Atypical fungal vesicles and arbuscules were found within the roots of the submersed macrophyteVallisneria americana collected at the tidal fresh headwaters of the Chesapeake Bay (Susquehanna flats) in July 1991 and 1992, suggesting the presence of a myocrrhizal association. In order to determine whether the presence of the fungus facilitates phosphorus uptake and plant growth,V. americana cores were placed in separate pots in an aquatic greenhouse and were given one of the following treatments: control, fungicide (Captan) application, or fungicide plus phosphate enrichment. Fungicide addition resulted in significantly decreased shoot elongation rates and chlorophylla production; phosphate enrichment plus fungicide restored plant growth to control levels. Low nitrogen in plant tissues of fungicide treatment groups suggests nitrogen uptake may also be promoted by the fungal association. A second laboratory experiment withV. americana grown from turions demonstrated the negative effects of the fungicide are only evident on plant growth when fungal infection is present, indicating the fungicide was not directly toxic to the macrophyte, but acted by disrupting a mycorrhizal relationship. This study supports the hypothesis that mycorrhizae are important in nutrient acquisition and growth ofVallisneria in an estuarine environment.  相似文献   

New insights into the deformation of a Middle Pleistocene glaciotectonised sequence in Norfolk,England through magnetic and structural analysis     

Edward J. Fleming  Carl T.E. Stevenson  Michael S. Petronis 《Proceedings of the Geologists' Association. Geologists' Association》2013

North Norfolk is a classic area for the study of glacial sediments with a complex glaciotectonic deformational history, but the processes leading to the formation of some structures can be ambiguous. Anisotropy of magnetic susceptibility (AMS) analyses, providing quantitative fabric data, have been combined with the analysis of visible structures and applied to the Bacton Green Till Member, exposed at Bacton, Norfolk. Thermomagnetic curves, low temperature susceptibility and acquisition of isothermal remanent magnetism (IRM) reveal that the magnetic mineralogy is dominated by paramagnetic phases. The magnetic foliation is parallel to fold axial planes and weakly inclined to bedding, whilst the magnetic lineation is orientated parallel to stretching, indicated by the presence of stretching lineations and the trend of sheath folds. Variations in the orientation of the magnetic lineation suggest that the Bacton section has been subject to polyphase deformation. After subaqueous deposition, the sequence was overridden by ice and glaciotectonically deformed which involved stretching initially north–south, then east–west. These results show that AMS can be used to detect strain in three dimensions through a glaciotectonite where paramagnetic mineralogy is dominant. This approach therefore provides further support to the use of AMS as a fast, objective and accurate method of examining strain within deformed glacial sediments.  相似文献   

A geophysically constrained multi-scale litho-structural analysis of the Trans-Tanami Fault,Granites-Tanami Orogen,Western Australia     

D. B. Stevenson  L. Bagas  A. R. A. Aitken  T. C. McCuaig 《Australian Journal of Earth Sciences》2013,60(8):745-768

The Trans-Tanami Fault in the poorly exposed Paleoproterozoic Granites-Tanami Orogen of Western Australia is an ～100 km long curvilinear structure with ～6 km right lateral displacement. Multi-scale integration and analysis of aeromagnetic, gravimetric, reflection seismic and remote sensing data have constrained the relative timing and architectural relationship of this structure. Interpretation of regional scale long-wavelength potential field (gravity and magnetic) anomalies, which are commonly used to define first-order structures, show that the fault is not a terrane boundary. Structural interpretation of short-wavelength potential field data illustrates that the structural domains on either side of the fault represent the products of a non-homogeneous stress regime developed between rigid granitic plutons. Additionally, 2D joint forward modelling of gravity and magnetic data and interpretation of reflection seismic data confirms the vertical displacement across this fault to be negligible indicating a predominant lateral displacement. The lateral displacement along a portion of this structure has exploited a pre-existing plane of a north-dipping thrust fault. Where this early thrust fault terminates, the Trans-Tanami Fault displaces previously unfaulted rock as a wrench fault step-over. These observations differ from previous findings in the area by constraining the absolute displacement of this structure and through the recognition of a wrench fault system that includes lateral step-overs between re-activated early thrust fault planes.  相似文献   

Multiple-input-multiple-output coherent time reversal communications in a shallow-water acoustic channel     

Song  H.C. Roux  P. Hodgkiss  W.S. Kuperman  W.A. Akal  T. Stevenson  M. 《Oceanic Engineering, IEEE Journal of》2006,31(1):170-178

A recent time reversal (TR) experiment demonstrated that multiple foci can be projected from an array of sources to the same range but at different depths. This multiple input/multiple output process can potentially increase the information data rate. This paper presents experimental results of coherent TR communications (binary phase-shift keying, quaternary phase-shift keying, and 8-quadratic-amplitude modulation) at 3.5 kHz with a 1-kHz bandwidth where different messages were sent simultaneously to either two or three different depths at an 8.6-km range in a 105-m-deep water.  相似文献   

ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir     

W. J. Feline  V. S. Dhillon  T. R. Marsh  M. J. Stevenson  C. A. Watson  C. S. Brinkworth 《Monthly notices of the Royal Astronomical Society》2004,347(4):1173-1179

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The masses of the cataclysmic variables AC Cancri and V363 Aurigae     

T. D. Thoroughgood  V. S. Dhillon  C. A. Watson  D. A. H. Buckley  D. Steeghs  M. J. Stevenson 《Monthly notices of the Royal Astronomical Society》2004,353(4):1135-1150

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Erratum: ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir     

W. J. Feline  V. S. Dhillon  T. R. Marsh  M. J. Stevenson  C. A. Watson  C. S. Brinkworth 《Monthly notices of the Royal Astronomical Society》2004,354(4):1279-1279

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