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31.
32.
—?We test how well low-magnitude (m bLg 1.8 to 2.6), 25-ton chemical explosions at Balapan, Kazakhstan, can be located using IMS stations and standard earth models, relying on precisely determined relative arrival times of nearly similar, regional and teleseismic waveforms. Three 1997 Balapan explosions were recorded by a number of currently reporting and surrogate IMS stations. Three regional stations and two teleseismic arrays yielded consistent waveforms appropriate for relative picking. Master-event locations based on the AK135 model and ground-truth information from the first, shallowest and best-recorded explosion, fell under 1 km from known locations, for depths constrained to that of the master event. The resulting 90% confidence ellipses covered 12–13?km2 and contained the true locations; however, results for depth constrained to true depth were slightly less satisf actory. From predictions based on ground truth, we found a P g -coda phase at Makanchi, Kazakhstan to be misidentified and poorly modeled. After accounting for this, 90% ellipses shrank to 2–3?km2 and true-depth mislocation vectors became more consistent with confidence-ellipse orientations. These results suggest that a high level of precision could be provided by a tripartite array of calibration shots in cases where models are poorly known. We hope that the successful relocation of these small Balapan shots will support the role of calibration explosions in verification monitoring and special event studies, including on-site inspection. 相似文献
33.
Pieter Hoekstra Raye Lahti Jim Hild C. Richard Bates David Phillips 《Ground Water Monitoring & Remediation》1992,12(4):110-117
Time domain electromagnetic (TDEM) soundings were utilized in site assessment studies for the purpose of accomplishing two objectives: (1) measuring the migration of brines from oil and gas field evaporation pits, and (2) mapping the continuity of clay strata. Both case histories are representative of common objectives in site assessment. The data for both examples were analyzed by one-dimensional ridge regression inversions.
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity. 相似文献
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity. 相似文献
34.
Jonathan D. Phillips 《地球表面变化过程与地形》1992,17(7):699-709
Extensive storage of upper-basin Piedmont sediment and apparent low sediment supply to streams in lower-basin Coastal Plain areas generates questions as to the source of alluvium in lower reaches of rivers of the U.S. Atlantic drainage. This was investigated on the Neuse River, North Carolina, using a mineralogical indicator of sediment source areas. The utility of mica flakes for discriminating between Piedmont and non-Piedmont sources of sediment in the lower Coastal Plain reaches of the Neuse was established on the basis of an examination of the U.S. National Soils Database and of 26 soil surveys of the North Carolina Coastal Plain. From the Neuse River estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments. Mica flakes become more common upstream. This suggests that a very small proportion of the sediment eroded in the Piedmont portion of the watershed is delivered to the river mouth. The small amounts which presumably do reach the lower Coastal Plain are so diluted by Coastal Plain-derived alluvium that no Piedmont origin can be discerned. This demonstrates a dominantly Coastal Plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems. More importantly, results suggest that upper- and lower-basin sediment dynamics are not only non-linearly related, but may be virtually decoupled. 相似文献
35.
Multiple linear regression analysis has been applied to the geometric and chemical variables in sodic plagioclases in order to determine their relative effects on individual T-O bond lengths in the Al1+xSi3?xO8 tetrahedral framework. Using data from crystal structure analyses of low and high albite, An16 and An28, and assuming that low albite is completely ordered, 1 $$\begin{gathered} {\text{T}} - {\text{O = 1}}{\text{.568}} + {\text{[(0}}{\text{.122) x (Al content of the T site)]}} \hfill \\ {\text{ }} - {\text{[(0}}{\text{.037) x (}}\Delta {\text{{\rm A}l}}_{{\text{br}}} )] + [0.063){\text{ x }}(\Sigma {\text{[}}q{\text{/(Na,Ca}} - {\text{O)}}^{\text{2}} ])] \hfill \\ {\text{ }} + {\text{[(0}}{\text{.029) x (}} - {\text{1/cosT}} - {\text{O}} - {\text{T)]}} \hfill \\ \end{gathered}$$ where the Al content of a particular tetrahedral (T) site can be estimated from empirically-derived determinative curves, where Δ Albr is a linkage factor to account for the Al content of adjacent tetrahedral sites, where the formal charge on the (Na1?xCax) atom is q=1+x, and where T-O-T is the inter-tetrahedral angle involving the T-O bond. For sodic plagioclases it is essential to know only the anorthite content and the 2Θ131-2Θ1¯31 spacing (CuK α radiation) in order to determine the independent variables in this equation and thus to evaluate the individual T-O distances. The 64 individual T-O distances predicted for the four sodic plagioclases by this equation agree well with the observed T-O bond lengths (σ=0.004 Å; r=0.994), and the method has been used by way of example to rationalize the T-O bond lengths in analcime (cf. Ferraris, Jones and Yerkess, 1972). 相似文献
36.
W.J. Phillips 《Lithos》1973,6(3):235-244
Attention is drawn to the nomenclature of spheroidal structures, and the textures are interpreted in terms of central, marginal or disseminated crystal nucleation. The essential physical characteristics of the nucleation and growth of crystals, bubbles of a low density gaseous phase, and globules of liquid with a density comparable with that of the magma are described. It seems likely that crystallization within an immiscible liquid fraction would proceed from disseminated nuclei thus producing a rock texture, rather than a cavity filling texture developed from marginal nucleation which is a characteristics of crystallization within gas cavities. Structures of mineralogical features which clearly indicate early liquid immiscibility or subsequent retrograde boiling are rarely preserved because of the nature of the processes, but it is suggested that both processes play a greater part in the formation of certain igneous rocks than in generally realized. 相似文献
37.
Fluoride replacement of oxygens in the GaO4Al12(OH)24(H2O)127+(aq) molecule [GaAl12] was studied via 19F nuclear magnetic resonance (NMR) at 4 < pH < 5 and 278 K in order to elucidate similar reactions at the surfaces of clays. Peaks are identified in the 19F-NMR spectra that correspond to both terminal and bridging fluorides on the GaAl12 molecule, with relative peak positions similar to those previously identified in fluoridated aluminum (hydr)oxide mineral surfaces (Nordin, J. P., Sullivan, D. J., Phillips, B. L., and Casey, W. H. [1999], “Mechanisms for fluoride-promoted dissolution of bayerite [β-Al(OH)3(s)] and boehmite [γ-AlOOH(s)]-19F-NMR spectroscopy and aqueous surface chemistry,” Geochim. Cosmochim. Acta63, 3513-3524). Fluoride substitutes for oxygen at three different sites in the GaAl12 molecule, but at dramatically different rates.The kinetics of fluoride substitution follow a rate law that includes parallel and reversible transfer of fluoride from nonbridging sites to the two bridging sites. The essential features of the rate law are as follows: (1) fluoride replaces bound water molecules (η-OH2) within minutes at 278 K at rates that are quantitatively similar to fluoride uptake by Al(H2O)63+(aq) to form AlF2+(aq) at similar conditions; (2) fluoride substitutes onto the two topologically distinct μ2-OH sites at different rates, as was previously observed for oxygen exchange, but here, the reaction is complete in hours to days at 278 K. Most importantly, rates of fluoride substitution onto μ2-OH sites are 102 times more rapid than the corresponding rates of oxygen exchange with bulk waters, indicating that fluoride considerably labilizes the molecule, as is also observed at the surfaces of minerals. The largest cause of this labilization is the reduced molecular charge on the GaAl12 upon replacement of bound waters by fluoride, which for mineral surfaces corresponds to a reduction in surface charge density. 相似文献
38.
Phillips K.J.H. Read P.D. Gallagher P.T. Keenan F.P. Rudawy P. Rompolt B. Berlicki A. Buczylko A. Diego F. Barnsley R. Smartt R.N. Pasachoff J.M. Babcock B.A. 《Solar physics》2000,193(1-2):259-271
The Solar Eclipse Coronal Imaging System (SECIS) is an instrument designed to search for short-period modulations in the solar corona seen either during a total eclipse or with a coronagraph. The CCD cameras used in SECIS have the capability of imaging the corona at a rate of up to 70 frames a second, with the intensities in each pixel digitised in 12-bit levels. The data are captured and stored on a modified PC. With suitable optics it is thus possible to search for fast changes or short-period wave motions in the corona that will have important implications for the coronal heating mechanism. The equipment has been successfully tested using the Evans Solar Facility coronagraph at National Solar Observatory/Sacramento Peak and during the 11 August 1999 eclipse at a site in north-eastern Bulgaria. The instrument is described and preliminary results are outlined. 相似文献
39.
Gallagher Peter T. Williams David R. Phillips Kenneth J.H. Mathioudakis Mihalis Smartt Raymond N. Keenan Francis P. 《Solar physics》2000,195(2):367-380
We report on observations of a large eruptive event associated with a flare that occurred on 27 September 1998 made with the Richard B. Dunn Solar Telescope at Sacramento Peak Observatory (several wave bands including off-line-center H), in soft and hard X-rays (GOES and BATSE), and in several TRACE wave bands (including Feix/x 171 Å, Fexii 195 Å, and Civ 1550 Å). The flare initiation is signaled by two H foot-point brightenings which are closely followed by a hard X-ray burst and a subsequent gradual increase in other wavelengths. The flare light curves show a complicated, three-component structure which includes two minor maxima before the main GOES class C5.2 peak after which there is a characteristic exponential decline. During the initial stages, a large spray event is observed within seconds of the hard X-ray burst which can be directly associated with a two-ribbon flare in H. The emission returns to pre-flare levels after about 35 min, by which time a set of bright post-flare loops have begun to form at temperatures of about 1.0–1.5 MK. Part of the flare plasma also intrudes into the penumbra of a large sunspot, generally a characteristic of very powerful flares, but the flare importance in GOES soft X-rays is in fact relatively modest. Much of the energy appears to be in the form of a second ejection which is observed in optical and ultraviolet bands, traveling out via several magnetic flux tubes from the main flare site (about 60° from Sun center) to beyond the limb. 相似文献
40.
Summary Daily precipitation totals for five consecutive winters (1995–99) were obtained for 127 stations in Devon and Cornwall to
explore spatial variations in rainfall. This dataset was assembled with the explicit aim of assessing the appropriateness
of current arrangements for daily rainfall forecasts in the SW Peninsula of England. Firstly, the extent to which fundamental
geographic variables determine precipitation was investigated by correlating each station’s mean wet day amount (WDA) and
percentage of wet days (PERWET) with altitude, latitude, longitude and distance from the coast. Altitude emerged as the most
important control on precipitation, with a two-variable multiple linear regression model containing altitude and latitude
being able to explain 39.3% (29.8%) of the variance in WDA (PERWET) values. The main spatial modes of variability in the region’s
precipitation field were identified by using S mode principal components analysis (PCA). Six PCs were statistically significant
and explained 83.4% of the geographic variance in precipitation over Devon and Cornwall. The components were interpreted physically
by examining the synoptic flow environment (pressure and wind anomalies) on days with high positive and negative PC scores.
Explaining 25.1% of the variance, the most important pattern (PC1) depicts a location’s degree of exposure or shelter in a
moist, unstable W–NW airflow. The higher PCs describe modes of variability that accentuate rainfall in East Devon (PC2), Cornwall
(PC3), Dartmoor and Bodmin Moor (PC4), South Devon (PC5), and North Cornwall and NW Devon (PC6) relative to other areas of
the Peninsula. Finally, a winter precipitation regionalisation was derived by applying agglomerative hierarchical cluster
analysis to the PC loadings of the significant components. In most cases, the six coherent precipitation regions do not reflect
the familiar administrative or topographic areas used for forecasting, suggesting that forecasts issued on such a basis are
likely to be insufficiently detailed and misleading. 相似文献