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   

MAXIPOL: a balloon-borne experiment for measuring the polarization anisotropy of the cosmic microwave background radiation     

B. R. Johnson  M. E. Abroe  P. Ade  J. Bock  J. Borrill  J. S. Collins  P. Ferreira  S. Hanany  A. H. Jaffe  T. Jones  A. T. Lee  L. Levinson  T. Matsumura  B. Rabii  T. Renbarger  P. L. Richards  G. F. Smoot  R. Stompor  H. T. Tran  C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067

We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10^′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress.  相似文献   

Calcium isotope (δCa) fractionation along hydrothermal pathways, Logatchev field (Mid-Atlantic Ridge, 14°45′N)     

Marghaleray Amini  Anton Eisenhauer  Florian Böhm  Wolfgang Bach  Martin Rosner  Barbara Bock  Folkmar Hauff 《Geochimica et cosmochimica acta》2008,72(16):4107-4122

We investigate the Logatchev Hydrothermal Field at the Mid-Atlantic Ridge, 14°45′N to constrain the calcium isotope hydrothermal flux into the ocean. During the transformation of seawater to a hydrothermal solution, the Ca concentration of pristine seawater ([Ca]_SW) increases from about 10 mM to about 32 mM in the hydrothermal fluid endmember ([Ca]_HydEnd) and thereby adopts a δ^44/40Ca_HydEnd of −0.95 ± 0.07‰ relative to seawater (SW) and a ⁸⁷Sr/⁸⁶Sr isotope ratio of 0.7034(4). We demonstrate that δ^44/40Ca_HydEnd is higher than that of the bedrock at the Logatchev field. From mass balance calculations, we deduce a δ^44/40Ca of −1.17 ± 0.04‰ (SW) for the host-rocks in the reaction zone and −1.45 ± 0.05‰ (SW) for the isotopic composition of the entire hydrothermal cell of the Logatchev field. The values are isotopically lighter than the currently assumed δ^44/40Ca for Bulk Earth of −0.92 ± 0.18‰ (SW) [Skulan J., DePaolo D. J. and Owens T. L. (1997) Biological control of calcium isotopic abundances in the global calcium cycle. Geochim. Cosmochim. Acta61,(12) 2505-2510] and challenge previous assumptions of no Ca isotope fractionation between hydrothermal fluid and the oceanic crust [Zhu P. and Macdougall J. D. (1998) Calcium isotopes in the marine environment and the oceanic calcium cycle. Geochim. Cosmochim. Acta62,(10) 1691-1698; Schmitt A. -D., Chabeaux F. and Stille P. (2003) The calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance. Earth Planet. Sci. Lett. 6731, 1-16]. Here we propose that Ca isotope fractionation along the fluid flow pathway of the Logatchev field occurs during the precipitation of anhydrite. Two anhydrite samples from the Logatchev Hydrothermal Field show an average fractionation of about Δ^44/40Ca = −0.5‰ relative to their assumed parental solutions. Ca isotope ratios in aragonites from carbonate veins from ODP drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average δ^44/40Ca of −1.54 ± 0.08‰ (SW). The relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine Ca isotope budget, in particular with regard to ocean crust alteration.  相似文献   

Conflicting imaginations: Archaeology, anthropology and geomorphology on Leskernick Hill, Bodmin Moor, southwest Britain     

Sue Hamilton  Barbara Bender 《Geoforum》2008,39(2):602-615

In this paper we view the different practices of archaeology, anthropology, environmental reconstruction and geomorphology through the lens of fieldwork on the clitter fields and Bronze Age settlement patterns on Leskernick Hill, Bodmin Moor, southwest Britain. The moor forms one of the best preserved fossil prehistoric landscapes of Europe and has undergone repeated periglacial episodes during the Quaternary. We show that the characterisation of patterned ground by archaeologists and anthropologists can be very different from that generated by geomorphology, particularly with respect to the spatial scales at which culture/nature questions are posed. We argue that the research project at Leskernick is a good example of how multi-disciplinary work is often more fruitful than mono-disciplinary and provides an example of how conversations across the divides of disciplinary practice can be held.  相似文献   

Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem     

Laurence P. Madin  Stephen M. Bollens  Erich Horgan  Mari Butler  Jeffrey Runge  Barbara K. Sullivan  Grace Klein-Macphee  Edward Durbin  Ann G. Durbin  Donna Van Keuren  Stphane Plourde  Ann Bucklin  M. Elizabeth Clarke 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)

Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank.  相似文献   

Primodial retention of carbon by the terrestrial planets     

John S. Lewis  Stephen S. Barshay  Barbara Noyes 《Icarus》1979,37(1):190-206

Chemical equilibrium calculations on the stability of pure and dissolved graphite and cohenite (Fe₃C), several other carbides, and several carbonates have been carried out for a system with solar elemental abundances over a very wide range of temperature and pressure. The calculated abundances of condensed carbon compounds are similar to the observed inventories on Earth and Venus, but fully 10 times smaller than the minimum carbon abundance found in ordinary chondrites. The total carbon content of most iron meteorites is compatible with their origin as a cooling FeNiCSP solution which was saturated with dissolved carbon at the solidus, such as would be produced by melting an ordinary chondrite, not by direct condensation from or equilibrium with the primitive solar nebula. It is argued that the carbon content of Mars need not be appreciably greater than that of the Earth. Material with even lower formation temperatures than Mars, such as the primitive material in the asteroid belt, may retain substantially more carbon as disequilibrium polymeric organic matter, possibly by the Fischer-Tropsch mechanism favored by Anders. Carbonates are not found as equilibrium products in a solar-composition system, and are probably secondary alteration products. CaCO₃ might, however, persist in a solar-composition gas at temperatures below 460°K and pressures below 10^?6.6 bar. The most stable condensed carbon compounds are found to be graphite, Fe₃C, and possibly TiC, all in solid solution in the metal phase.  相似文献   

Monazite U-Pb dating of staurolite grade metamorphism in pelitic schists   总被引：1，自引：1，他引：0  

Harold A. Smith  Barbara Barreiro 《Contributions to Mineralogy and Petrology》1990,105(5):602-615

A study of the occurrence of and relations between rare-earth element (REE) minerals in pelitic schists indicates that monazite forms at or near the P and T of the staurolite isograd. Samples at staurolite grade from the Silurian Perry Mountain Formation in the Rumford quadrangle of Maine yield monazite in sufficient quantities to permit accurate dating of the metamorphic events forming the monazites. The bulk chemistry of the metapelites, as seen in the major element abundances and REE patterns, does not vary significantly across the study area. Thus the appearance and disappearance of REE phases is assumed to reflect changes in metamorphic grade. In a sample from the biotite zone, scanning electron microscope and microprobe studies show allanite and monazite intimately associated on a 10 m scale. The texture suggest that metastable detrital monazite breaks down, distributing its REE components to allanite. From samples below staurolite grade in which monazite is not present, our observations suggest that REEs are partitioned into allanite. At or near the staurolite isograd monazite forms as a metamorphic mineral, initiating its role as a geochronometer. Garnet-biotite geothermometry on samples at this grade from this and other studies places constraints on the minimum temperature necessary to form monazite: 525° C±25°C at 3.1±0.25 kbar. A total of 15 separates from nine schist samples ranging up to sillimanite grade have been dated. Each date is remarkably concordant, even though petrologic and textural studies by previous workers have shown that the rocks in the area have been affected by at least three metamorphic episodes. Calculations indicate insignificant Th disequilibrium in these monazites. The conditions associated with the metamorphic events suggest that monazite remains closed to lead loss provided that subsequent metamorphisms are at or below sillimanite grade. Two distinct metamorphic events are resolved, one at around 400 Ma and one at about 370 Ma. The latter was due to thermal effects of a nearby pluton that yields concordant monazite ages of 363 Ma. This work suggests that in addition to dating plutonism and high-grade metamorphism, monazite should be viewed as a reliable geochronometer for moderate metamorphism of pelitic schists.  相似文献   

Gas maturity and alteration systematics across the Western Canada Sedimentary Basin from four mud gas isotope depth profiles   总被引：1，自引：0，他引：1  

Barbara Tilley  Karlis Muehlenbachs 《Organic Geochemistry》2006,37(12):1857

Carbon isotope and molecular compositions of Mississippian to Upper Cretaceous mud gases have been examined from four depth profiles across the Western Canada Sedimentary Basin (WCSB). The profiles range from the shallow oil sands in the east (R₀ = 0.25) to the very mature sediments in the overthrust zone to the west (R₀ = 2.5). In the undisturbed WCSB, δ¹³C₁–δ¹³C₂ and δ¹³C₂–δ¹³C₃ cross-plots show three maturity and alteration trends: (1) pre-Cretaceous gas sourced from type II kerogen; (2) Cretaceous Colorado Group gas; and (3) Lower Cretaceous Mannville Group biodegraded gas. A fourth set of distinctly different maturity trends is recognized for Lower Cretaceous gas sourced from type III kerogen in the disturbed belt of the WCSB. Displacement of these latter maturity trends to high δ¹³C₂ values suggests that the sampled gas was trapped after earlier formed gas escaped, probably as a result of overthrusting. Unusually ¹³C-enriched gas (δ¹³C₁ = −34‰, δ¹³C₂ = −13‰, and δ¹³C₃ = 0‰), from the Gething Formation in the disturbed belt, is the result of late stage gas cracking in a closed system. In general, gas maturity is consistent with the maturity of the host sediments in the WCSB, suggesting that migration and mixing of gases was not pervasive on a broad regional and stratigraphic scale. The ‘Deep Basin’ portion of the WCSB is an exception. Here extensive cross-formational homogenization of gases has occurred, in addition to updip migration along the most permeable stratigraphic units.  相似文献   

Laboratory Studies Of Wind Stress Over Surface Waves   总被引：4，自引：0，他引：4  

B. Mete Uz  Mark A. Donelan  Tetsu Hara  Erik J. Bock 《Boundary-Layer Meteorology》2002,102(2):301-331

Simultaneous laboratory observations of wind speed, wind stress, and surfacewind-wave spectra are made under a variety of wind forcing patterns using cleanwater as well as water containing an artificial surfactant. Under typical experimentalconditions, more than half of the total stress is supported by the wave-induced stressrather than by the surface viscous stress. When the surfactant reduces the shortwind-wave spectra, the wind stress also decreases by as much as 20–30% at agiven wind speed. When the wind forcing is modulated in time, the wind stresstends to be higher under decreasing wind than under increasing wind at a givenwind speed, mainly because the response of short wind-wave spectra to varyingwind forcing is delayed in time. These examples clearly demonstrate that therelationship between the wind speed and the wind stress can be significantlymodified if the surface wave field is not in equilibrium with the wind forcing.Next, we examine whether the wind stress is estimated accurately if the wave-inducedstress by all surface wave components is explicitly evaluated by linear superpositionand is added to the surface viscous stress. It is assumed that the surface viscous stressis uniquely related to the wind speed, and that the wind input rate is determined by thelocal, reduced turbulent stress rather than the total stress. Our wind stress estimatesincluding the wave contributions agree well with observed wind stress values, evenif the surface wave field is away from its equilibrium with the wind in the presenceof surface films and/or under time-transient wind forcing. These observations stronglysuggest that the wind stress is accurately evaluated as a sum of the wave-induced stressand the surface viscous stress. At very high winds, our stress estimates tend to be lowerthan the observations. We suspect that this is because of the enhancement of wind stressover very steep (or breaking) short wind-waves.  相似文献   

Contrasting sources for lead in Cu-polymetallic and Zn–Pb mineralisation in Ireland: constraints from lead isotopes     

Judith A. Kinnaird  Robert A. Ixer  Barbara Barreiro  Paul A. Nex 《Mineralium Deposita》2002,37(5):495-511

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