QUEST on DASI: a South Pole CMB polarization experiment

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.     

Modelling larval dispersal of the king scallop (Pecten maximus) in the English Channel: examples from the bay of Saint-Brieuc and the bay of Seine

The king scallop (Pecten maximus) is one of the most important benthic species of the English Channel as it constitutes the first fishery in terms of landings in this area. To support strategies of spatial fishery management, we develop a high-resolution biophysical model to study scallop dispersal in two bays along the French coasts of the English Channel (i.e. the bay of Saint-Brieuc and the bay of Seine) and to quantify the relative roles of local hydrodynamic processes, temperature-dependent planktonic larval duration (PLD) and active swimming behaviour (SB). The two bays are chosen for three reasons: (1) the distribution of the scallop stocks in these areas is well known from annual scallop stock surveys, (2) these two bays harbour important fisheries and (3) scallops in these two areas present some differences in terms of reproductive cycle and spawning duration. The English Channel currents and temperature are simulated for 10 years (2000–2010) with the MARS-3D code and then used by the Lagrangian module of MARS-3D to model the transport. Results were analysed in terms of larval distribution at settlement and connectivity rates. While larval transport in the two bays depended both on the tidal residual circulation and the wind-induced currents, the relative role of these two hydrodynamic processes varied among bays. In the bay of Saint-Brieuc, the main patterns of larval dispersal were due to tides, the wind being only a source of variability in the extent of larval patch and the local retention rate. Conversely, in the bay of Seine, wind-induced currents altered both the direction and the extent of larval transport. The main effect of a variable PLD in relation to the thermal history of each larva was to reduce the spread of dispersal and consequently increase the local retention by about 10 % on average. Although swimming behaviour could influence larval dispersal during the first days of the PLD when larvae are mainly located in surface waters, it has a minor role on larval distribution at settlement and retention rates. The analysis of the connectivity between subpopulations within each bay allows identifying the main sources of larvae which depend on both the characteristics of local hydrodynamics and the spatial heterogeneity in the reproductive outputs.     

The French experience in low level radioactive waste management

The Radioactive Waste Management Agency (ANDRA-FRANCE) is now operating a new facility in the eastern part of the Paris basin which is designed to dispose of one million cubic meters of waste.

The safety of the waste disposal is based on a multibarrier concept including waste packages, concrete disposal modules, site and closure operations.

Under normal conditions, confinement is guaranteed by the waste packages and the disposal modules, as they prevent the waste from being leached by rainfall or underground water over a certain period of time.

The site must bring an additional guarantee concerning the isolation of waste from water. Consequently, the chosen site must be located in an area where no natural disasters (landslides, earthquakes, etc.) can harm the isolating barriers. The geological, hydrogeological and chemical characteristics must allow us to minimize and control the transport of radionuclides within the ground. Finally, the chosen site must be in an area where it is easy to implement a system to monitor the environment.

A set of criteria guides the choice of site. The criteria include such factors as low seismicity, geotechnical stability, a hydrogeology that is simple to model, a location sufficiently above the water table and safe from the threat of flooding, good radionuclide sorption and the absence of any mineral or other natural resources of economic interest.

At the time of the closure of the disposal facility, the entire collection of modules will be covered by an impervious cap composed of clayey layers interbedded by sandy layers and overlain by humus to promote the growth of grass. The facility will then look like a succession of undulating green mounds.

A 300-year monitoring period will follow the closure. During this period, the water collecting networks and cap will be maintained and radioactivity in underground and stream water will be controlled.

We have selected the AUBE site as a case study to illustrate the French waste management experience. We will report on how the site characterization program has been calTied out, including the hydrogeological modelling which is being applied to both the operating and post-closure periods.     

Production of carbonate and silica nano-particles in stirred bead milling

This paper presents the experimental results of the mechanical production of silica and carbonate colloidal particles below 100 nm using two types of stirred bead mills (i.e., DCP Superflow 12 and PML H/V). It is shown that the stirred bead mill with very small beads can be used as an efficient equipment for the production of the colloidal particles in nanoscale from the feed materials of several microns in sizes at high energy consumptions. The DCP Superflow mill with high power densities is superior for the effective size reduction and production rate, compared to the conventional PML H/V mill with lower power densities. The smaller particles could be produced by the DCP Superflow mill at the same level of high energy inputs as from the PML H/V mill. The “grinding limit” for the processes in the mills has been discussed.     

Unique isoprene oxidation products demonstrate chlorine atom chemistry occurs in the Houston,Texas urban area

As part of the 2000 Texas Air Quality Study (TexAQS), we studied the isoprene oxidation process under ambient conditions to discern the presence of chlorine atom (Cl) chemistry in the Houston, Texas urban area. By measuring chloromethylbutenone (CMBO) and an isomer of chloromethylbutenal (CMBA), we clearly observed sixteen episodes of active Cl chemistry during the 24-day experiment. Estimated median Cl concentration during each of these episodes was between the detection limit of ~10² atoms cm⁻³ and 50 _{- 30} ^{+ 70} ×10⁴ 50_{ - 30}^{ + 70} \times {10^4} atoms cm⁻³. Cl concentration during all the episodes averaged 7.6 _{- 2.0} ^{+ 4.7} ×10⁴ 7.6_{ - 2.0}^{ + 4.7} \times {10^4} atoms cm⁻³ and thus amounted to less than 3% of the OH concentration during the same periods. During the episodes, the fraction of oxidation chemistry initiated by Cl ranged from 3–43% and was strongly dependent on the quantity and type of hydrocarbons present in the atmosphere. Because of its intermittent presence and low concentration, Cl is not a broadly influential oxidant in the Houston, Texas urban area.     

Prediction of the calcium carbonate budget in a sedimentary basin: A “source-to-sink” approach applied to Great Salt Lake,Utah, USA

Most source-to-sink studies typically focus on the dynamics of clastic sediments and consider erosion, transport and deposition of sediment particles as the sole contributors. Although often neglected, dissolved solids produced by weathering processes contribute significantly in the sedimentary dynamics of basins, supporting chemical and/or biological precipitation. Calcium ions are usually a major dissolved constituent of water drained through the watershed and may facilitate the precipitation of calcium carbonate when supersaturating conditions are reached. The high mobility of Ca²⁺ ions may cause outflow from an open system and consequently loss. In contrast, in closed basins, all dissolved (i.e. non-volatile) inputs converge at the lowest point of the basin. The endoreic Great Salt Lake basin constitutes an excellent natural laboratory to study the dynamics of calcium on a basin scale, from the erosion and transport through the watershed to the sink, including sedimentation in lake's waterbody. The current investigation focused on the Holocene epoch. Despite successive lake level fluctuations (amplitude around 10 m), the average water level seems to have not been affected by any significant long-term change (i.e. no increasing or decreasing trend, but fairly stable across the Holocene). Weathering of calcium-rich minerals in the watershed mobilizes Ca²⁺ ions that are transported by surface streams and subsurface flow to the Great Salt Lake (GSL). Monitoring data of these flows was corrected for recent anthropogenic activity (river management) and combined with direct precipitation (i.e. rain and snow) and atmospheric dust income into the lake, allowing estimating the amount of calcium delivered to the GSL. These values were then extrapolated through the Holocene period and compared to the estimated amount of calcium stored in GSL water column, porewater and sediments (using hydrochemical, mapping, coring and petrophysical estimates). The similar estimate of calcium delivered (4.88 Gt) and calcium stored (3.94 Gt) is consistent with the premise of the source-to-sink approach: a mass balance between eroded and transported compounds and the sinks. The amount of calcium deposited in the basin can therefore be predicted indirectly from the different inputs, which can be assessed with more confidence. When monitoring is unavailable (e.g. in the fossil record), the geodynamic context, the average lithology of the watershed and the bioclimatic classification of an endoreic basin are alternative properties that may be used to estimate the inputs. We show that this approach is sufficiently accurate to predict the amount of calcium captured in a basin and can be extended to the whole fossil record and inform on the storage of calcium.     

Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States

Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites are generally calc-alkaline, magnesian, oxidized, wet, cool (<850°C), Sr-and Al-rich, and Fe-poor. These silicic rocks are interpreted to have been derived from mafic parent magmas generated by dehydration of oceanic lithosphere and melting in the mantle wedge above a subduction zone. Plagioclase fractionation was minimized by the high water fugacity and oxide precipitation was enhanced by high oxygen fugacity. This resulted in the formation of Si-, Al-, and Sr-rich differentiates with low Fe/Mg ratios, relatively low temperatures, and declining densities. Magma mixing, large proportions of crustal assimilation, and polybaric crystal fractionation were all important processes in generating this Oligocene suite. In contrast, most of the rhyolites of the Snake River Plain are alkaline to calc-alkaline, ferroan, reduced, dry, hot (830–1,050°C), Sr-and Al-poor, and Nb-and Fe-rich. They are part of a distinctly bimodal sequence with tholeiitic basalt. These characteristics were largely imposed by their derivation from parental basalt (with low fH₂O and low fO₂) which formed by partial melting in or above a mantle plume. The differences in intensive parameters caused early precipitation of plagioclase and retarded crystallization of Fe–Ti oxides. Fractionation led to higher density magmas and mid-crustal entrapment. Renewed intrusion of mafic magma caused partial melting of the intrusive complex. Varying degrees of partial melting, fractionation, and minor assimilation of older crust led to the array of rhyolite compositions. Only very small volumes of distinctive rhyolite were derived by fractional crystallization of Fe-rich intermediate magmas like those of the Craters of the Moon-Cedar Butte trend. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

AN HISTORICAL APPROACH TO MOBILITY RESEARCH *

Most existing work on residential mobility has assumed that the household relocation decision is an intrinsically significant object of inquiry. In contrast, we argue that mobility derives its significance primarily from the particular historical and locational contexts within which it occurs. We suggest, therefore, that future mobility research should be directed away from the development of a theory of mobility per se and toward a more explicit articulation of mobility studies to existing theories of urbanization and social change.