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101.
Jack C. Parker Ungtae Kim Alyson Fortune Steffen Griepke James P. Galligan Amber Bonarrigo 《Ground Water Monitoring & Remediation》2017,37(1):51-66
The objective of in situ thermal treatment is typically to reduce the contaminant mass or average soil concentration below a specified value. Evaluation of whether the objective has been met is usually made by averaging soil concentrations from a limited number of soil samples. Results from several field sites indicate large performance uncertainty using this approach, even when the number of samples is large. We propose a method to estimate average soil concentration by fitting a log normal probability model to thermal mass recovery data. A statistical approach is presented for making termination decisions from mass recovery data, soil sample data, or both for an entire treatment volume or for subregions that explicitly considers estimation uncertainty which is coupled to a stochastic optimization algorithm to identify monitoring strategies to meet objectives with minimum expected cost. Early termination of heating in regions that reach cleanup targets sooner enables operating costs to be reduced while ensuring a high likelihood of meeting remediation objectives. Results for an example problem demonstrate that significant performance improvement and cost reductions can be achieved using this approach. 相似文献
102.
Simon G. Lewis 《第四纪科学杂志》2002,17(8):799-800
103.
"This paper establishes and discusses briefly regional patterns and trends in crude birth, death, and natural increase rates in Russia and the USSR from the turn of the century to 1989. The study is based on a comparable regional framework and placed in the context of the demographic transition theory. It discusses sources, collection, and quality of data, as well as necessary estimating procedures. An attempt also is made to examine briefly regional age-standardized rates." 相似文献
104.
Migrating magmatism in the northern US Cordillera: in situ U–Pb geochronology of the Idaho batholith
Richard M. Gaschnig Jeffrey D. Vervoort Reed S. Lewis William C. McClelland 《Contributions to Mineralogy and Petrology》2010,159(6):863-883
New in situ laser ablation-inductively coupled plasma-mass spectrometry and sensitive high-resolution ion microprobe U–Pb
geochronology of zircons from the Idaho batholith and spatially overlapping Challis intrusions reveals a series of discrete
magmatic belts of different ages and compositions. Following the accretion of the Blue Mountains province to North America
along the Salmon River suture zone, two compositionally diverse belts of metaluminous plutons formed both adjacent to the
suture and well inboard of it. These were constructed from ~100 to 85 Ma and were followed by a voluminous pulse of peraluminous
magmatism, forming the bulk of the Atlanta lobe and largest fraction of the batholith between ~80 and 67 Ma. Around 70 Ma,
a later and more spatially restricted suite of metaluminous plutons formed around the Bitterroot lobe of the batholith. This
was followed by another pulse of voluminous peraluminous magmatism in the Bitterroot lobe, lasting from ~66 to 54 Ma. The
changes from low volume metaluminous to high volume peraluminous magmatism may reflect a combination of changes in the angle
and segmentation of the subducting Farallon plate and over thickening of the continental lithosphere. All of these features
were then cut by plutons and dikes associated with the Challis volcanic field, lasting from ~51 to 43 Ma. Inherited components
are pervasive in zircons from most phases of the batholith. While Precambrian components are very common, zircons also often
contain cores or mantles that are 5–20 million years older than their rims. This suggests that the early phases of the batholith
were repeatedly cannibalized by subsequent magmas. This also implies that the older suites may have been originally more aerially
extensive than their currently exposed forms. 相似文献
105.
Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and
silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative
of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation,
mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin
using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels
to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the
western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with
the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection
with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley
via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide
lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no
outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small
isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral
habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario
above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels
continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern
Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived
from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario. 相似文献
106.
Detailed analysis is presented of a conformable succession of Early Miocene conglomerates and sandstones lying between massive marine mudstones. The coarse sediments reflect deposition by a spectrum of subaqueous debris-flow mechanisms during an early pulse of tectonism that ultimately resulted in Plio-Pleistocene eversion of the Kaikoura Mountains.Sparse pebbly mudstones and rare sandy conglomerates show disoriented clasts and reflect high-viscosity flows and slurry-creep flow mechanisms. Other deposits have little mud matrix, hence appear to reflect low-viscosity flow processes. The largest clasts in these have a preferred planar orientation, probably reflecting dispersive grain pressure, and a preferred long-axis orientation parallel to flow direction. Common sorted sandstones and some conglomeratic sandstones show diffuse parallel lamination; with rare exceptions neither grading nor traction structures are present. Other conglomeratic sandstones show trough cross-bedding which we attribute to entrained bedload movement during intersurge episodes of debris flow.Microfossil data from the mudstones indicate sedimentation in an environment of outer neritic to upper bathyal aspect. Most detritus is abraded, suggesting derivation from terrestrial or inner neritic sources, but angular calcilutitic clasts and irregular sandstone and mudstone clasts and rafts were probably derived from submarine erosion between the emergent source area and the site of accumulation. Deposits generally appear to infill broad shallow channels. Paleocurrent and fabric analysis indicate a markedly uniform flow direction throughout succession, and suggest that the locus of channeling remained relatively fixed in space throughout accumulation of hundreds of metres of superimposed, commonly amalgamated debris-flow deposits. Although lateral control away from the measured sequence is limited, we infer that the locus of deposition lay shoreward of any submarine canyon or fan. 相似文献
107.
A number of processes may modify the noble gas composition of silicate liquids so that the composition of noble gases observed in glassy margins of deep-sea basalts is not that of the upper mantle. Differential solubility enhances the light noble gases relative to the heavier gases; however, we demonstrate that the observed abundance pattern cannot be attributed to solubility of noble gases with atmospheric proportions. Partial melting and fractional crystallization increase the noble gas content of all species relative to mantle concentrations, but do not fractionate their relative abundances. Noble gases may be lost from an ascending magma in various ways, the most important, however, may be exclusion of gas from crystals forming at the time of solidification, which is shown to result in marked loss of gas from the basalt. Small amounts of low-temperature alteration of solidified basalt can produce dramatic changes in the noble gas abundance pattern, since the adsorption coefficients for the different noble gas favor uptake of heavy species relative to the light species. Atmospheric contamination can account for observed variations in the 40Ar/36Ar ratio of oceanic basalts. The degree of crystallinity of glassy margins of deep-sea basalts may control the helium abundance of these samples; however, the uniform 3He/4He values reported apparently reflect a relatively constant proportion of radiogenic and primordial helium in the mantle. 相似文献
108.
The conditional spectrum (CS, with mean and variability) is a target response spectrum that links nonlinear dynamic analysis back to probabilistic seismic hazard analysis for ground motion selection. The CS is computed on the basis of a specified conditioning period, whereas structures under consideration may be sensitive to response spectral amplitudes at multiple periods of excitation. Questions remain regarding the appropriate choice of conditioning period when utilizing the CS as the target spectrum. This paper focuses on risk‐based assessments, which estimate the annual rate of exceeding a specified structural response amplitude. Seismic hazard analysis, ground motion selection, and nonlinear dynamic analysis are performed, using the conditional spectra with varying conditioning periods, to assess the performance of a 20‐story reinforced concrete frame structure. It is shown here that risk‐based assessments are relatively insensitive to the choice of conditioning period when the ground motions are carefully selected to ensure hazard consistency. This observed insensitivity to the conditioning period comes from the fact that, when CS‐based ground motion selection is used, the distributions of response spectra of the selected ground motions are consistent with the site ground motion hazard curves at all relevant periods; this consistency with the site hazard curves is independent of the conditioning period. The importance of an exact CS (which incorporates multiple causal earthquakes and ground motion prediction models) to achieve the appropriate spectral variability at periods away from the conditioning period is also highlighted. The findings of this paper are expected theoretically but have not been empirically demonstrated previously. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
109.
Late Quaternary slip across the Cañada David detachment has produced an extensive array of Quaternary scarps cutting alluvial-fans along nearly the entire length (~ 60 km) of the range-bounding detachment. Eight regional alluvial-fan surfaces (Q1 [youngest] to Q8 [oldest]) are defined and mapped along the entire Sierra el Mayor range-front. Terrestrial cosmogenic nuclide 10Be concentrations from individual boulders on alluvial-fan surfaces Q4 and Q7 yield surface exposure ages of 15.5 ± 2.2 ka and 204 ± 11 ka, respectively. Formation of the fans is probably tectonic, but their evolution is strongly moderated by climate, with surfaces developing as the hydrological conditions have changed in response to climate change on Milankovitch timescales. Systematic mapping reveals that the fault scarp array along active range-bounding faults in Sierras Cucapa and El Mayor can be divided into individual rupture zones, based on cross-cutting relationships with alluvial-fans. Quantitative morphological ages of the Laguna Salada fault-scarps, derived from linear diffusive degradation modeling, are consistent with the age of the scarps based on cross-cutting relationships. The weighted means of the maximum mass diffusivity constant for all scarps with offsets < 4 m is 0.051 and 0.066 m2/ka for the infinite and finite-slope solutions of the diffusion equation, respectively. This estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of Laguna Salada. 相似文献
110.
Earlier studies of quiescent prominences claim that there is a systematic downward directed motion of the small-scale structure.
Disk observations, on the other hand, have detected mass motions both upwards and downwards. The earlier high-resolution observations
of limb prominences have been re-examined using local cross-correlation techniques for measurements of motion perpendicular
to the line of sight. The new measurements reveal flow speeds and directions that are in good agreement with current Doppler
measurements on the disk. 相似文献