QUEST on DASI: a South Pole CMB polarization experiment     

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 O&#x;Sullivan  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 (ℓ_max2500) 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   

Melting in the martian mantle: Shergottite formation and implications for present‐day mantle convection on Mars     

Walter S. KIEFER 《Meteoritics & planetary science》2003,38(12):1815-1832

Abstract— Radiometric age dating of the shergottite meteorites and cratering studies of lava flows in Tharsis and Elysium both demonstrate that volcanic activity has occurred on Mars in the geologically recent past. This implies that adiabatic decompression melting and upwelling convective flow in the mantle remains important on Mars at present. I present a series of numerical simulations of mantle convection and magma generation on Mars. These models test the effects of the total radioactive heating budget and of the partitioning of radioactivity between crust and mantle on the production of magma. In these models, melting is restricted to the heads of hot mantle plumes that rise from the core‐mantle boundary, consistent with the spatially localized distribution of recent volcanism on Mars. For magma production to occur on present‐day Mars, the minimum average radioactive heating rate in the martian mantle is 1.6 times 10^?12 W/kg, which corresponds to 39% of the Wanke and Dreibus (1994) radioactivity abundance. If the mantle heating rate is lower than this, the mean mantle temperature is low, and the mantle plumes experience large amounts of cooling as they rise from the base of the mantle to the surface and are, thus, unable to melt. Models with mantle radioactive heating rates of 1.8 to 2.1 times 10 ^?12 W/kg can satisfy both the present‐day volcanic resurfacing rate on Mars and the typical melt fraction observed in the shergottites. This corresponds to 43–50% of the Wanke and Dreibus radioactivity remaining in the mantle, which is geochemically reasonable for a 50 km thick crust formed by about 10% partial melting. Plausible changes to either the assumed solidus temperature or to the assumed core‐mantle boundary temperature would require a larger amount of mantle radioactivity to permit present‐day magmatism. These heating rates are slightly higher than inferred for the nakhlite source region and significantly higher than inferred from depleted shergottites such as QUE 94201. The geophysical estimate of mantle radioactivity inferred here is a global average value, while values inferred from the martian meteorites are for particular points in the martian mantle. Evidently, the martian mantle has several isotopically distinct compositions, possibly including a radioactively enriched source that has not yet been sampled by the martian meteorites. The minimum mantle heating rate corresponds to a minimum thermal Rayleigh number of 2 times 10⁶, implying that mantle convection remains moderately vigorous on present‐day Mars. The basic convective pattern on Mars appears to have been stable for most of martian history, which has prevented the mantle flow from destroying the isotopic heterogeneity.  相似文献   

A high-resolution rotation curve of NGC 6822: a test-case for cold dark matter     

D. T. F. Weldrake  W. J. G. de Blok †  F. Walter 《Monthly notices of the Royal Astronomical Society》2003,340(1):12-28

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Getting SMARTS on Novae: Highlights of the Early Evolution of Nova V475 Sct     

Guy S. Stringfellow  Frederich M. Walter 《Astrophysics and Space Science》2006,304(1-4):401-403

There is a disconcerting global trend of retiring telescopes of modest aperture, supplanting them instead with fewer expensive telescopes of quite large aperture. As a consequence, the available time and feasibility of following transient objects in astrophysics is diminishing. We show the utility of having a suite of small to moderate aperture telescopes capable of conducting imaging and spectroscopic observations in a service queue mode. The example we provide is the high-cadence early observations of the classical nova V475 Scuti (2003) carried out with the SMARTS suite of telescopes located at CTIO.  相似文献   

Neutrino Tomography – Learning About The Earth’s Interior Using The Propagation Of Neutrinos     

Walter Winter 《Earth, Moon, and Planets》2006,99(1-4):285-307

Because the propagation of neutrinos is affected by the presence of Earth matter, it opens new possibilities to probe the Earth’s interior. Different approaches range from techniques based upon the interaction of high energy (above TeV) neutrinos with Earth matter, to methods using the MSW effect on the oscillations of low energy (MeV to GeV) neutrinos. In principle, neutrinos from many different sources (sun, atmosphere, supernovae, beams etc.) can be used. In this talk, we summarize and compare different approaches with an emphasis on more recent developments. In addition, we point out other geophysical aspects relevant for neutrino oscillations.  相似文献   

Experimental petrology of the basaltic shergottite Yamato‐980459: Implications for the thermal structure of the Martian mantle     

Donald S. Mussel White  Heather A. Dalton  Walter S. Kiefer  Allan H. Treiman 《Meteoritics & planetary science》2006,41(9):1271-1290

Abstract— The Martian meteorite Yamato (Y‐) 980459 is an olivine‐phyric shergottite. It has a very primitive character and may be a primary melt of the Martian mantle. We have conducted crystallization experiments on a synthetic Y‐980459 composition at Martian upper mantle conditions in order to test the primary mantle melt hypothesis. Results of these experiments indicate that the cores of the olivine megacrysts in Y‐980459 are in equilibrium with a melt of bulk rock composition, suggesting that these megacrysts are in fact phenocrysts that grew from a magma of the bulk rock composition. Multiple saturation of the melt with olivine and a low‐calcium pyroxene occurs at approximately 12 ± 0.5 kbar and 1540 ± 10°C, suggesting that the meteorite represents a primary melt that separated from its mantle source at a depth of ?100 km. Several lines of evidence suggest that the Y‐980459 source underwent extensive melting prior to and/or during the magmatic event that produced the Y‐980459 parent magma. When factored into convective models of the Martian interior, the high temperature indicated for the upper Martian mantle and possibly high melt fraction for the Y‐980459 magmatic event suggests a significantly higher temperature at the core‐mantle boundary than previously estimated.  相似文献   

A Chandra X-ray survey of nearby dwarf starburst galaxies – II. Starburst properties and outflows     

Jürgen Ott †  Fabian Walter  Elias Brinks † 《Monthly notices of the Royal Astronomical Society》2005,358(4):1453-1471

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Refined conceptualization of TOPMODEL for shallow subsurface flows     

M. Todd Walter  Tammo S. Steenhuis  Vishal K. Mehta  Dominique Thongs  Mark Zion  Elliot Schneiderman 《水文研究》2002,16(10):2041-2046

The TOPMODEL framework was used to derive expressions that account for saturated and unsaturated flow through shallow soil on a hillslope. The resulting equations were the basis for a shallow‐soil TOPMODEL (STOPMODEL). The common TOPMODEL theory implicitly assumes a water table below the entire watershed and this does not conceptually apply to systems hydrologically controlled by shallow interflow of perched groundwater. STOPMODEL provides an approach for extending TOPMODEL's conceptualization to apply to shallow, interflow‐driven watersheds by using soil moisture deficit instead of water table depth as the state variable. Deriving STOPMODEL by using a hydraulic conductivity function that changes exponentially with soil moisture content results in equations that look very similar to those commonly associated with TOPMODEL. This alternative way of conceptualizing TOPMODEL makes the modelling approach available to researchers, planners, and engineers who work in areas where TOPMODEL was previously believed to be unsuited, such as the New York City Watershed in the Catskills region of New York State. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign     

Josef Gochermann  Walter F. Wargau  Claus Tappert  Theodor Schmidt-Kaler  Robert S. Stobie  Fred Marang  Greg Roberts  Francois G. van Wyk  Peter Rucks 《Experimental Astronomy》1999,9(1):1-15

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.  相似文献   

The carbon cycle and biogeochemical dynamics in lake sediments   总被引：30，自引：3，他引：27  

Walter E. Dean 《Journal of Paleolimnology》1999,21(4):375-393

The concentrations of organic carbon (OC) and CaCO3 in lake sediments are often inversely related. This relation occurs in surface sediments from different locations in the same lake, surface sediments from different lakes, and with depth in Holocene sediments. Where data on accumulation rates are available, the relation holds for organic carbon and CaCO3 accumulation rates as well. An increase of several percent OC is accompanied by a decrease of several tens of percent CaCO3 indicating that the inverse relation is not due to simple dilution of one component by another. It appears from core data that once the OC concentration in the sediments becomes greater than about 12%, the CO2 produced by decomposition of that OC and production of organic acids lowers the pH of anoxic pore waters enough to dissolve any CaCO3 that reaches the sediment-water interface. In a lake with a seasonally anoxic hypolimnion, processes in the water column also can produce an inverse relation between OC and CaCO3 over time. If productivity of the lake increases, the rain rate of OC from the epilimnion increases. Biogenic removal of CO2 and accompanying increase in pH also may increase the production of CaCO3. However, the decomposition of organic matter in the hypolimnion will decrease the pH of the hypolimnion causing greater dissolution of CaCO3 and therefore a decrease in the rain rate of CaCO3 to the sediment-water interface.  相似文献