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1.
Daniel Lane Colin P.R. McCarter Murray Richardson Chris McConnell Tim Field Huaxia Yao George Arhonditsis Carl P.J. Mitchell 《水文研究》2020,34(3):598-614
The estimation of hydrologic transit times in a catchment provides insights into the integrated effects of water storage, mixing dynamics, and runoff generation processes. There has been limited effort to estimate transit times in southern boreal Precambrian Shield landscapes, which are characteristically heterogeneous with surface cover including till, thin soils, bedrock outcrops, and depressional wetland features that play contrasting hydrologic roles. This study presents approximately 3.5 years of precipitation and streamflow water isotope data and estimates mean transit times (MTTs) and the young water fraction (py) across six small catchments in the Muskoka-Haliburton region of south-central Ontario. The main objectives were to define a typical range of MTTs for headwater catchments in this region and to identify landscape variables that best explain differences in MTTs/py using airborne light detection and ranging and digital terrain analysis. Of the transit time distributions, the two parallel linear reservoir and gamma distributions best describe the hydrology of these catchments, particularly because of their ability to capture more extreme changes related to events such as snowmelt. The estimated MTTs, regardless of the modelling approach or distribution used, are positively associated with the percent wetland area and negatively with mean slope in the catchments. In this landscape, low-gradient features such as wetlands increase catchment scale water storage when antecedent conditions are dryer and decrease transit times when there is a moisture surplus, which plausibly explains the increases in MTTs and mean annual runoff from catchments with significant coverage of these landscape features. 相似文献
2.
George Saklatvala Michael P. Hobson Stafford Withington 《Monthly notices of the Royal Astronomical Society》2006,367(3):1194-1200
We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
3.
Sarah Church Peter Ade James Bock Melanie Bowden John Carlstrom Ken Ganga Walter Gear James Hinderks Wayne Hu Brian Keating John Kovac Andrew Lange Eric Leitch Olivier Mallie Simon Melhuish Anthony Murphy Ben Rusholme Creidhe OSullivan Lucio Piccirillo Clem Pryke Andy Taylor Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083
QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓmax2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005. 相似文献
4.
For monoparametric familiesf(x,y)=c of planar orbits, created by a planar potentialV(x,y), we introduce the notion of the family boundary curves (FBC). All members of the familyf(x,y)=c are traced in an allowable region of thexy plane, defined by the corresponding FBC, with total energyE=E(c) varying along the family. Family boundary curves are also found for two-parametric familiesf(x,y,b)=c. The relation of equilibrium points and asymptotic orbits, possibly possessed by the potentialV(x,y), to be FBC is studied. 相似文献
5.
Almudena Alonso-Herrero Marcia J. Rieke George H. Rieke Douglas M. Kelly 《Astrophysics and Space Science》2001,276(2-4):1109-1120
The irregular galaxy M82 is known as the archetypal starburst galaxy. Its proximity (3.5 Mpc) makes this galaxy an ideal laboratory
for studying the properties of its starburst. The detailed morphology of the [FeII] 1.644 μm and emission Paα (at 1.87 μm) is revealed by the NICMOS images. The peak of the 2.2 μm continuum brightness(evolved population) lies very
close to the dynamical centre. Most of the Paα emission (which traces the young population) is distributed in a ring of star formation (with a `hole' lacking line emission
at the centre of the galaxy). These observations support the scenario in which the starburst in M82 is propagating outwards.
It has long been suggested that the [FeII] emission in starburst galaxies can be used as a measure of supernova (SN) activity.
M82 shows a large number of radio supernova remnants (SNRs), approximately 50, lying in the plane of the galaxy. The comparison
of the positions of the bright compact [FeII] emitting regions with the location of the radio SNRs shows that there is no one-to-one spatial correspondence between
the two emissions, suggesting that the radio and [FeII] emissions trace two populations of SNRs with different ages. Young
(a few hundred years) SNRs are best traced by their radio emission, whereas the [FeII] stage lasts for at least a few 104 yr. The compact [FeII] sources contribute only some 20 % of the total [FeII] emission observed in M82. However, much of the remaining unresolved
[FeII] emission in the plane of the galaxy may arise from SNRs that expanded and merged into a general interstellar medium
within a few 104 yr. Presumably, as much as 70% of the total extinction-corrected [FeII]1.644 μm in M82 is associated with SNRs. The extended
and diffuse [FeII] component in M82 seems to be related with the superwind above and below the disc of the galaxy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
7.
Jeremy Allington-Smith Graham Murray Robert Content George Dodsworth Bryan W. Miller James Turner Inger Jorgensen Isobel Hook 《Experimental Astronomy》2002,13(1):1-37
We describe the integral field unit (IFU) which converts the Gemini Multiobject Spectrograph (GMOS) installed on the Gemini-North telescope to an integral field spectrograph,which produces spectra over a contiguous field of view of 7 × 5 arcsec with spatial sampling of 0.2 arcsecover the wavelength range 0.4-1.0 μm.GMOS is converted to this mode by the remote insertion of the IFU into thebeam in place of the masks used for the multiobject mode. A separate fieldof half the area of the main field, but otherwise identical, is alsoprovided to improve background subtraction. The IFU contains 1500lenslet-coupled fibres and was the first facility of any type for integralfield spectroscopy employed on an 8/10 m telescope.We describe the design, construction and testing of the GMOS IFU and present measurements of the throughput both in the laboratory and at the telescope. We compare these with a theoretical prediction made before construction started. All are in good agreement with each other, with the on-telescope throughput exceeding 60% (averaged over wavelength). Finallywe show an example of data obtained during commissioning to illustrate the power of the device. 相似文献
8.
9.
George L. Withbroe 《Solar physics》1985,99(1-2):145-158
EUV observations of two subflares and associated surges have been analyzed. At maximum brightness the emission measures and radiative outputs of the subflares were approximately 20% of the corresponding values for the active region. Multiple EUV surges were observed during and following each subflare, with surge material being ejected in a variety of directions, including toward a coronal bright point located outside of the active region. The total energy of the surges appears to be comparable to that radiated by the subflares, a few times 1028 erg. As reported in previous studies of surges, we find that there was no significant emission from these features in spectral lines formed at temperatures T>106K. The ejection of surges in several different directions and nearly simultaneous flaring of various areas of the active region suggest that the primary site of the subflares was magnetically connected to a variety of different areas in the active region and the surrounding quiet region. 相似文献
10.
Olivier Harifidy Ralison Alberto Vieira Borges Frank Dehairs J.J. Middelburg Steven Bouillon 《Organic Geochemistry》2008,39(12):1649
Madagascar’s largest estuary (Betsiboka) was sampled along the salinity gradient during the dry season to document the distribution and sources of particulate and dissolved organic carbon (POC, DOC) as well as dissolved inorganic carbon (DIC). The Betsiboka was characterized by a relatively high suspended matter load, and in line with this, low DOC/POC ratios (0.4–2.5). The partial pressure of CO2 (pCO2) was generally above atmospheric equilibrium (270–1530 ppm), but relatively low in comparison to other tropical and subtropical estuaries, resulting in low average CO2 emission to the atmosphere (9.1 ± 14.2 mmol m−2 d−1). Despite the fact that C4 vegetation is reported to cover >80% of the catchment area, stable isotope data on DOC and POC suggest that C4 derived material comprises only 30% of both pools in the freshwater zone, increasing to 60–70% and 50–60%, respectively, in the oligohaline zone due to additional lateral inputs. Sediments from intertidal mangroves in the estuary showed low organic carbon concentrations (<1%) and δ13C values (average −19.8‰) consistent with important inputs of riverine imported C4 material. This contribution was reflected in δ13C signatures of bacterial phospholipid derived fatty acids (i + a15:0), suggesting the potential importance of terrestrial organic matter sources for mineralization and secondary production in coastal ecosystems. 相似文献