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131.
We generalize previous studies of Alfvénic oscillations in the solar atmosphere to geometries in which the background magnetic field is not parallel to the gravitational acceleration. A uniform but inclined field produces only subtle changes in the mathematics, and virtually no changes to the coronal energy flux, over previous vertical field studies. We show that simple, two-layer models agree remarkably well with more sophisticated, multi-layer calculations. In addition, we derive several useful and accurate analytic results with which we highlight many features and parameter dependences. We also study a model with a spreading field geometry. For low magnetic fields (- 10 G) the corona still appears WKB to the oscillations and we do not find any significant deviations from the uniform field calculations. This is not the case for higher magnetic fields in active regions (- 3000 G) where we confirm previous results which suggest an order of magnitude increase in the coronal flux. Again, we derive useful analytic approximations.Now at: Mathematics Department, Monash University, Clayton, Victoria, Australia. 相似文献
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134.
Nicole Limondin‐Lozouet Richard C. Preece Pierre Antoine 《Boreas: An International Journal of Quaternary Research》2013,42(3):650-663
One of the thickest and most extensive tufa deposits in northern France occurs at Daours, about 8 km upstream of Amiens at the confluence of the River Somme and its tributary the Hallue. It covers an area of about 80 ha and reaches 10 m above the level of the present valley, probably owing to the construction of a tufa barrage, which caused periodic damming of the valley. The molluscan succession from a 4‐m section through the Daours tufa provides an unusually detailed record of environmental change during the Holocene. The faunal record, supported by four radiocarbon dates, indicates that the tufa sequence at this location does not extend back to the early Holocene but began c. 7340 cal. a BP and ceased to form shortly after c. 4938 cal. a BP, consistent with the notion of a NW European ‘late Holocene tufa decline’. The molluscan record is divisible into six zones that define three aquatic phases separated by three terrestrial episodes, when the tufa surface dried out sufficiently to allow colonization by dry‐ground species, including some shade‐demanding elements. These events are also reflected by differences in the lithology of the tufa. The earliest aquatic phase at the base of the sequence represents the most stable and permanent water‐body. The two subsequent aquatic phases appear to represent smaller, more ephemeral, water‐bodies surrounded by marsh. The land snail assemblages show ecological changes within each terrestrial episode, as well as faunal differences between them. These events, which reflect changes in the local hydrology, were short‐lived, each lasting for only a few hundred years. The tufa at Daours has also yielded flint artefacts and pottery, but it seems unlikely that the dynamic environmental record of the site results from anthropogenic activity. 相似文献
135.
This study analyzes pro-wind, “anti-environmental” discourses prevalent among key stakeholders in Nolan County, Texas, the epicenter of US wind power. We draw upon interviews conducted within a Q-method study to examine environmental views held by key actors in wind-farm development. We frame our analysis within the theoretical field that engages the formation of environmental subjects, defined as the process through which individuals and communities align their environmental practices with state ends. We argue that this is a process that can be incomplete or in tension with other subject positions, which together may lead to unexpected environmental views. We introduce “environmental skepticism,” defined as a rejection of ecological science steeped in deep anthropocentrism and possessive individualism, as a dominant counter-narrative informing certain environmental subjectivities. The remainder of the paper describes Texas wind stakeholders’ views or subject positions on energy and the environment and reveals how environmental skepticism is not overturned even as renewable energy supports the local economy. We analyze wind stakeholders’ environmental subjectivity in terms of emergent subject positions as “reflexive environmental skepticism,” a view that accepts the economic products, processes, and policy innovations advocated by ecological modernization without accepting the core claim that innovations are required to adapt to environmental change. 相似文献
136.
Hugues Lantuit Pier Paul Overduin Nicole Couture Sebastian Wetterich Felix Aré David Atkinson Jerry Brown Georgy Cherkashov Dmitry Drozdov Donald Lawrence Forbes Allison Graves-Gaylord Mikhail Grigoriev Hans-Wolfgang Hubberten James Jordan Torre Jorgenson Rune Strand ?deg?rd Stanislav Ogorodov Wayne H. Pollard Volker Rachold Sergey Sedenko Steve Solomon Frits Steenhuisen Irina Streletskaya Alexander Vasiliev 《Estuaries and Coasts》2012,35(2):383-400
Arctic permafrost coasts are sensitive to changing climate. The lengthening open water season and the increasing open water area are likely to induce greater erosion and threaten community and industry infrastructure as well as dramatically change nutrient pathways in the near-shore zone. The shallow, mediterranean Arctic Ocean is likely to be strongly affected by changes in currently poorly observed arctic coastal dynamics. We present a geomorphological classification scheme for the arctic coast, with 101,447?km of coastline in 1,315 segments. The average rate of erosion for the arctic coast is 0.5?m? year?1 with high local and regional variability. Highest rates are observed in the Laptev, East Siberian, and Beaufort Seas. Strong spatial variability in associated database bluff height, ground carbon and ice content, and coastline movement highlights the need to estimate the relative importance of shifting coastal fluxes to the Arctic Ocean at multiple spatial scales. 相似文献
137.
Jason Timmons Young Min Cho Timothy Townsend Nicole Berge Debra Reinhart 《Geotechnical and Geological Engineering》2012,30(1):95-105
Commercially available hydraulic total overburden pressure cells were installed in the sand drainage layer of a municipal
solid waste landfill and monitored for a period of 3,110 days. Both overburden pressure and temperature were measured in the
landfill as it was filled with compacted waste. Topographic surveys of the landfill were periodically conducted to measure
the height of waste above the pressure cells and to determine the landfill volume for indirect unit weight estimation. The
average ratio of measured to theoretically-predicted overburden pressure was 0.6, indicating that on average the pressure
cells underestimated the load. The overburden pressure measured near the toe of the landfill was greater than that predicted
by the unit weight of landfilled material, while most of the overburden pressure measurements further inside the landfill
were less than predicted. Several possible causes for this phenomenon are discussed, including the uneven distribution of
forces resulting from the heterogeneous nature of the waste and cover soil. The earth pressure cells were capable of detecting
the placement of individual waste lifts. 相似文献
138.
Fouad Sahraoui Melvyn L. Goldstein Alain Roux Patrick Canu Nicole Cornilleau-Wehrlin Thierry Dudok De Wit Khurom Kiyani 《Planetary and Space Science》2011,59(7):585-591
Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the k-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross-Scale mission. 相似文献
139.
Joshua Mukwakwami Bruno Lafrance C. Michael Lesher Douglas K. Tinkham Nicole M. Rayner Doreen E. Ames 《Mineralium Deposita》2014,49(2):175-198
The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D1 shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D2 at mid-greenschist facies metamorphism. Syn-D2 metamorphic titanite yields an age of 1,849?±?6 Ma, suggesting that D1 and D2 occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L1 and L2 mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D1 and D2. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D2 quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D1 and D2, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D2. Metamorphic pentlandite overgrows a S1 ferrotschermakite foliation in D1 deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D1, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S2 chlorite foliation in D2 shear zones. Pyrrhotite recrystallized and was flattened during D2 deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D1 deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D1 and continued to deform as a monosulfide solid solution during D2. 相似文献
140.
Starburst galaxies are extremely luminous objects with an abundance of young massive stars and a disturbed optical morphology.
Famous examples such as the Antennae, involve major mergers, but the starburst phenomenon can also be triggered in a more
gentle, minor merger. Such an event disturbs but does not disrupt the primary galaxy (i.e. the primary will recover from the
interaction without a drastic jump along the Hubble sequence). In such an interaction a significant number of super-star clusters
(SSCs) are formed,which may be the progenitors of present-day globular clusters. The ubiquity of globular cluster systems
among a wide range of galaxy types suggests that these interactions play a significant role in the evolution of ‘normal’ galaxies.
Therefore to understand the formation and evolution of galaxies, it is essential to understand such processes. Here we present
a HST WFPC2 broad-band study of three starburst galaxies with different merger histories.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献