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1.
Scaling and multivariate analysis of medium to large landslide events: Haida Gwaii, British Columbia
Gimbarzevsky (1988) collected an exceptional landsliding inventory for Haida Gwaii, British Columbia that included over 8,000 landsliding vectors
covering an area of approximately 10,000 km2. This database was never published in the referred literature, despite its regional significance. It was collected prior
to widespread application of GIS technologies in landsliding studies, limiting the analyses undertaken at the time. Gimbarzevsky
identified landslides using 1:50,000 aerial photographs, and transferred the information to NTS map sheets. In our study,
we digitized the landslide vectors from these original map sheets and connected each landslide to a digital elevation model.
Lengths of landslide vectors are compared to the landsliding inventory for Haida Gwaii analyzed in Rood (1984), Martin Y et al. BC Can J Earth Sci 39:289–305 (2002); the latter inventory is based on larger-scale aerial photographs (~1:12,000). Rood’s database contains a more complete
record of smaller landslides, while the inventory of Gimbarzevsky provides improved statistical representation of less frequent,
medium to large landslides. It is suggested that combined landslide delineation at different scales could provide a more complete
landslide record. Discriminant analysis was undertaken to assess which of nine predictor variables, chosen on the basis of
mechanical theory, best predict failed versus unfailed locations. Seven of the nine variables were found to be statistically
significant in discriminating amongst failed and unfailed locations. Results show that 81.7% of original grouped cases were
correctly classified. 相似文献
2.
Crystal size distributions (CSDs) are a standard method of describing populations of crystals within magmatic rocks. Olivine
is the dominant phase in kimberlite (∼40–50% by volume) and features a diverse range of sizes, shapes and origins. CSDs of
olivine provide a logical means of semi-quantitatively characterising kimberlite. The CSDs can then be used to distinguish
or correlate between kimberlite bodies or to investigate processes related to ascent, emplacement and eruption. In this paper,
we present an automatic image analysis technique that provides efficient quantification of olivine CSDs within digital images
of polished slabs of kimberlite. This technique relies on a combination of algorithms for detecting regions of interest (ROI)
and for segmentation of ROIs in order to identify individual olivine crystals that are used for size distribution datasets.
The detection process identifies regions expected to be olivine using a model-based colour detection technique using Mahalanobis
distance combined with texture analysis based on local standard deviation and greyscale foreground enhancement techniques.
The segmentation process separates adjacent domains to identify individual crystals using an iterative marker-based watershed
algorithm to separate adjoined structures of varying sizes. We demonstrate the utility of automatic image analysis by comparing
CSDs for olivine derived from this method versus results from manual digitisation of olivine grains. The automatic detection
system correctly identified ∼86% of the manually detected olivine domains; ∼88% of the automatically detected regions correctly
correlate to manually defined olivine grains. Discrepancies between the two methods are mostly the result of oversimplification
of crystal margins (i.e. rounding) by manual tracing whereas automatic boundary recognition shows clear advantages in identifying
irregularities in crystal edges. Closer examination of the results shows that both methods suffer from under-representation
of smaller crystals due to: (1) human subjectivity and error in manual tracing and (2) noise removal processes in automatic
detection. Automatic detection of olivine grains is much more efficient than conventional manual tracing; manual detection
requires ∼6 h per sample versus ∼1 min for automatic analysis of the same sample. 相似文献
3.
The combined use of both (1) low-flow purging and sampling and (2) trace-metal clean techniques provides more representative
measurements of trace-element concentrations in groundwater than results derived with standard techniques. The use of low-flow
purging and sampling provides relatively undisturbed groundwater samples that are more representative of in situ conditions,
and the use of trace-element clean techniques limits the inadvertent introduction of contaminants during sampling, storage,
and analysis. When these techniques are applied, resultant trace-element concentrations are likely to be markedly lower than
results based on standard sampling techniques. In a comparison of data derived from contaminated and control groundwater wells
at a site in California, USA, trace-element concentrations from this study were 2–1000 times lower than those determined by
the conventional techniques used in sampling of the same wells prior to (5 months) and subsequent to (1 month) the collections
for this study. Specifically, the cadmium and chromium concentrations derived using standard sampling techniques exceed the
California Maximum Contaminant Levels (MCL), whereas in this investigation concentrations of both of those elements are substantially
below their MCLs. Consequently, the combined use of low-flow and trace-metal clean techniques may preclude erroneous reports
of trace-element contamination in groundwater.
Received: October 1997 Revised: May 1998 Accepted: December 1998 相似文献
4.
Fluid inclusion microthermometric data are often reported as homogenization temperature frequency histograms. Interpretation
of such histograms for a single fluid inclusion assemblage (FIA) of non-reequilibrated fluid inclusions is usually straightforward
and provides an accurate determination of the original density (Th) of that FIA. However, interpretation of such histograms for reequilibrated inclusions is more problematic. Decompression
experiments using synthetic inclusions in natural quartz and conducted at 2–5 kbar and 600–700 °C with a maximum internal
overpressure of 2 kbar indicate that histogram shape reflects the sample's P-T history. Our results further indicate that the mean, mode, range, standard deviation, extreme values, etc., all have a significance
with respect to the P-T history of the sample. Thus, a mound-shaped, unimodal histogram with low range is indicative of a nearly isochoric cooling
P-T path. A unimodal histogram that is slightly skewed to the right, and with a low standard deviation but high range, results
from inclusion deformation in the plastic regime (high temperature/low strain rates). Fluid inclusions deformed plastically
show no correlation between size and density. Histogram outliers should not be ignored and may be used to determine an isochore
that passes close to the conditions of entrapment (minimum Th) or close to the final reequilibration conditions (maximum Th). The histogram mean Th value corresponds to an isochore that represents the internal overpressure (about 1 kbar) that can be maintained over geologic
time by a majority of reequilibrated fluid inclusions. A multimodal histogram with high range and high standard deviation
indicates inclusion brittle deformation (low temperature/high strain environments). Fluid inclusions deformed in a brittle
manner show strong positive correlation between size and density. Histograms produced in the laboratory show many similarities
to histograms for natural samples, offering the hope that laboratory results may be used to interpret P-T histories of natural samples.
Received: 20 May 1997 / Accepted: 3 April 1998 相似文献
5.
Zoltán Zajacz Werner Halter Wim J. Malfait Olivier Bachmann Robert J. Bodnar Marc M. Hirschmann Charles W. Mandeville Yann Morizet Othmar Müntener Peter Ulmer James D. Webster 《Contributions to Mineralogy and Petrology》2005,150(6):631-642
A new approach was developed to measure the water content of silicate glasses using Raman spectroscopy, which is independent
of the glass matrix composition and structure. Contrary to previous studies, the compositional range of our studied silicate
glasses was not restricted to rhyolites, but included andesitic, basaltic and phonolitic glasses. We used 21 glasses with
known water contents for calibration. To reduce the uncertainties caused by the baseline removal and correct for the influence
of the glass composition on the spectra, we developed the following strategy: (1) application of a frequency-dependent intensity
correction of the Raman spectra; (2) normalization of the water peak using the broad T–O and T–O–T vibration band at 850–1250 cm−1 wavenumbers (instead of the low wavenumber T–O–T broad band, which appeared to be highly sensitive to the FeO content and
the degree of polymerization of the melt); (3) normalization of the integrated Si-O band area by the total number of tetrahedral
cations and the position of the band maximum. The calibration line shows a ±0.4 wt% uncertainty at one relative standard deviation
in the range of 0.8–9.5 wt% water and a wide range of natural melt compositions. This method provides a simple, quick, broadly
available and cost-effective way for a quantitative determination of the water content of silicate glasses. Application to
silicate melt inclusions yielded data in good agreement with SIMS data. 相似文献
6.
A. A. Adepelumi A. A. Solanke O. B. Sanusi A. M. Shallangwa 《Environmental Geology》2006,50(8):1221-1233
A modeling tank time-lapse 2D electrical resistivity experiment was undertaken to model the leakage of petroleum products from underground pipelines into a clayey-sand aquifer. Numerical modeling was employed to simulate the electrode arrays that would resolve the post-leakage subsurface image most efficiently. Of the four arrays tested, the dipole–dipole array proved most effective and was adopted for the laboratory studies. Pre-injection surveys were conducted to assist in discriminating between features caused by hydrocarbon accumulation and those due to natural geologic variability. Subsequently, controlled injection of diesel–oil into the model tank was undertaken at regular intervals over a period of 3 days. Experimental evidence obtained from the studies indicates that high resistivity build up few hours after injection is directly related to hydrocarbon accumulation. Rather than biodegradation of the hydrocarbon, a more probable explanation for the observed decrease in resistivity observed a few hours after injection is simply that the hydrocarbons drained to a deeper level after pooling temporarily at a shallow level. 相似文献
7.
Application of remote-sensing data to groundwater exploration: A case study of the Cross River State, southeastern Nigeria 总被引:12,自引:2,他引:10
The Cross River State, Nigeria, is underlain by the Precambrian-age crystalline basement complex and by rocks of Cretaceous
to Tertiary age. The exploration for groundwater in this area requires a systematic technique in order to obtain optimum results,
but the non-availability of funds and facilities has made it extremely difficult to carry out site investigations prior to
the drilling of water wells. Therefore, the failure rate is as high as 80%. In order to delineate areas that are expected
to be suitable for future groundwater development, black and white radar imagery and aerial photographs were used to define
some hydrological and hydrogeological features in parts of the study area. Lineament and drainage patterns were analysed using
length density and frequency. Lineament-length density ranges from 0.04–1.52; lineament frequency is 0.11–5.09; drainage-length
density is 0.17–0.94, and the drainage frequency is 0.16–1.53. These range of values reflect the differences in the probability
of groundwater potentials. Results were then used to delineate areas of high, medium, and low groundwater potential. Study
results also indicate that correlations exist between lineament and drainage patterns, lithology, water temperature, water
conductivity, well yield, transmissivity, longitudinal conductance, and the occurrence of groundwater.
Received, August 1994 · Revised, March 1996, June 1996 · Accepted, October 1996 相似文献
8.
M. F. Grasso R. Clocchiatti F. Carrot C. Deschamps F. Vurro 《Environmental Geology》1999,37(3):207-217
The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic
activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano
Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and
Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material,
and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover,
the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows
different geochemical trends on Mt. Etna and Vulcano.
Received: 20 April 1998 · Accepted: 4 July 1998 相似文献
9.
Large tank experiment on nitrate fate and transport: the role of permeability distribution 总被引:2,自引:1,他引:1
M. Mastrocicco N. Colombani S. Palpacelli G. Castaldelli 《Environmental Earth Sciences》2011,63(5):903-914
A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted
within a large tank (4 × 8 × 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m3), used to fill the tank, were excavated from an unconfined alluvial aquifer near Ferrara (Northern Italy); the field site
was connected to a pit lake located in a former agricultural field. To evaluate spatial heterogeneity, the tank’s filling
material was characterized via slug tests and grain-size distribution analysis. The investigated sediments were characterized
by a large spectrum of textures and a heterogeneous hydraulic conductivity (k) field. Initial tank pore water composition exhibited high concentration of nitrate (NO3
−) sulfate (SO4
2−) calcium (Ca2+), and magnesium (Mg2+), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO3
− and SO4
2− was heterogeneous and not related to the finer grain-size content (<63 μm). The tank’s material was flushed with purified
tap water for 800 days in steady-state conditions; out flowing water was regularly sampled to monitor the migration rate of
fertilizer by-products. Complete removal of NO3
− and SO4
2− took 500 and 600 days, respectively. Results emphasized organic substrate availability and spatial heterogeneities as the
most important constraints to denitrification and nitrogen removal, which increase the time required to achieve remediation
targets. Finally, the obtained clean-up time was compared with a previous column experiment filled with the same sediments. 相似文献
10.
The water and bed-sediment pollution status of the Padma River was determined by analysis of representative samples for selected
metals and ions. Water and bed-sediment samples were collected at a T-dam, Rajshahi, Bangladesh, for 7 months. Water and silt-metal
content analysis was performed using atomic absorption spectrophotometry or other analytical methods. The data showed the
variation of the metal ion-levels in water as follows: Ca 17.11–48.37 ppm, Na 17.51–20.09 ppm, K 1.00–3.60 ppm, Cr 2.80–7.00 ppm,
and SO4 4.17–5.48 ppm; in bed sediment, the levels were Cr 35–1050 ppm and Pb 12–48 ppm. The occurrence of Na, K and Ca was in the
normal range (US EPA permissible limit), but the levels of Cr in water were much higher than the permissible limit. The SO4 ion content was well below the pollution level. The concentration of Pb in the bed sediment was within the permissible limit
for the standard International Atomic Energy Agency (IAEA) Soil-5a, but the concentration of Cr in the bed sediment was significantly
higher than the permissible limit for the standard IAEA Soil-5a. Thus the Padma river water was polluted with Cr. The occurrence
of some ions showed a monthly variation.
Received: 19 August 1999 · Accepted: 12 October 1999 相似文献
11.
Doug V. Prose 《Environmental Geology》1985,7(3):163-170
Soil compaction and substrate modification produced during large-scale armored military maneuvers in the early 1940s were
examined in 1981 at seven sites in California’s eastern Mojave Desert Recording penetrometer measurements show that tracks
left by a single pass of an M3 “medium” tank have average soil resistance values that are 50% greater than those of the surrounding
untracked soil in the upper 20 cm At one site, measurements made along short segments of track that have been visually eliminated
by erosion and deposition processes show a 73% increase in penetrometer resistance over adjacent, undisturbed soils Dirt roadways
at three former base camp locations could not be penetrated below 5–10 cm because of extreme compaction Soil bulk density
was not as sensitive an indicator of soil compaction as was penetrometer resistance Density values in the upper 10 cm of soil
are not significantly different between tank tracks and undisturbed soils at most sites, and roadways at two base camps show
an average increase in bulk density of only 12% over adjacent soils. Trench excavations across tank tracks show that physical
modifications of the substrate can extend vertically beneath a track to a depth of 25 cm and outward from a track’s edge to
50 cm These soil disturbances are probably major factors that encourage accelerated soil erosion throughout the manuever area
and also retard or prevent the return of vegetation to pre-disturbance conditions 相似文献
12.
A. Grzechnik Hans D. Zimmermann P. L. King Paul F. McMillan R. L. Hervig 《Contributions to Mineralogy and Petrology》1996,125(4):311-318
Infrared spectroscopy provides a reliable method for rapid, non-destructive quantitative analysis of volatile species in
silicate glasses, with applications to geochemistry and volcanology. The technique has been extensively calibrated for transmission
measurements, in which the species concentration present is correlated with the height or area of characteristic absorption
peaks, for doubly polished samples of known thickness. There are several drawbacks associated with this method, including
the need for double polishing of parallel faces on thin samples, the errors associated with sample thickness measurement,
and total absorption of the IR beam intensity for samples with high volatile content. We have tested an alternative method
for quantitative IR determination of volatile concentrations in silicate glasses, based on analysis of the IR reflectivity
signal. The reflectivity method requires preparation of a single polished glass surface, and no thickness measurement of the
sample is necessary. The technique is applied easily as a microbeam technique using apertures as small as a few μm in diameter.
The method should be particularly useful for volatile analysis of glass inclusions in phenocrystals, or standard samples in
thin section. We have developed the methodology for the technique using a series of basanite and leucitite glasses with high
carbonate contents (>1 wt% CO2), which could not be easily analyzed via IR transmission. We have used SIMS to standardize the technique. Two features observed
in the reflectance spectra near 1400 cm–1 and 1500 cm–1 are due to resonance of the infrared beam with the asymmetric stretching vibrations of carbonate groups. The contribution
of these species to the total reflectivity is directly correlated with the carbon abundance in the samples. This forms the
basis for an empirical quantitative analysis. The optical constants, including the IR absorption coefficients associated with
the CO3
2– stretching vibrations, have been extracted by Kramers-Kronig analysis of the reflectivity data. The molar extinction coefficients
are 1119 ± 138 L mol–1 cm–1 and 1198 ± 145 L mol–1 cm–1 for the 1400 and 1500 cm–1 bands, respectively, in excellent agreement with results of previous transmission studies, after orientation effects are
taken into account.
Received: 29 September 1995 / Accepted: 17 May 1996 相似文献
13.
Computer models are commonly used by regulators and managers to make predictions regarding groundwater flow and contaminant
concentrations at various locations and times. However, the uncertainty associated with those predictions is often overlooked,
despite the fact that an assessment of such uncertainty is critical in the formulation of policy decisions. One method of
quantifying the uncertainty of model predictions, based on the collective uncertainties of the model parameter input values,
is to use an approximation of the three-point Gauss–Hermite quadrature formula. The Gauss–Hermite approximation is a convenient
substitute for simple Monte Carlo sampling, because it requires fewer model runs and provides an immediate sensitivity analysis
of parameter main effects and two-way interactions. For example, a model with four parameters, each with its own associated
uncertainty, needs to be run only 33 times to complete the Gauss–Hermite analysis. For an application to a contaminant-transport
model, the Gauss–Hermite approximation compares well to the full method, with considerable savings in computing effort. By
comparison, Latin hypercube sampling can be more flexible, but it is more complex to use in some circumstances and cannot
as easily generate the detailed sensitivity analysis that the Gauss–Hermite approach offers.
Received, October 1997 Revised, August 1998 Accepted, August 1998 相似文献
14.
Heavy metals in sediments of a large, turbid tropical lake affected by anthropogenic discharges 总被引:2,自引:0,他引:2
Bottom-water data and trace metal concentration of Cu, Cr, Ni, Pb, Co, Zn, and organic matter in surficial sediment samples
from 13 sampling stations of Lake Chapala in Mexico were studied. The lake is turbid with a great amount of flocculated sediments
as a result of wind mixing, sediment re-suspension, and Lerma River discharges. Al distribution pattern in sediments was used
as an indicator of the Lerma River discharges into Lake Chapala. The highest values of Cu (33.27 ppm), Cr (81.94 ppm), Pb
(99.8 ppm), and Zn (149.7 ppm) were detected in sediments near the lake outlet. The bioavailable metal fraction is low for
all metals except Pb, which shows 65–93% of the total metal concentration in bioavailable form. The minimum energy zone in
the lake was related to organic matter concentration and was located in the SE part of the lake. An analysis of the studied
parameters shows two zones: eastern zone (fluvio-deltaic) and central-western zone (lacustrine).
Received: 9 September 1998 · Accepted: 16 November 1998 相似文献
15.
The nature of OH species in natural clear quartz was investigated by means of in-situ IR measurements over the temperature
range –185 to 1000 °C. Reversible thermal behavior of OH species was examined for a sample pre-heated to 1000 °C for 1 hour.
At room temperature, the IR spectrum of the quartz sample examined includes an intense absorption peak at 3379 cm–1 which has been assigned to an OH stretching vibration associated with Al substituting for Si (OH(Al)). The major spectral
changes of the OH(Al) bond involve a systematic shift of its peak position and a decrease in its integral absorbance with
temperature. A quasi-linear increase of the peak position from –185 to 400 °C is interpreted to be due to the change in the
vibrational frequency of OH(Al) with hydrogen bond (H bond) distance. At higher temperatures, the IR frequency shows only
a slight change, indicating a small influence of the H bond. On the other hand, the gradual decrease of the integral absorbance
of OH(Al) with temperature indicates a decrease of this defect’s molar absorptivity without any reduction in defect concentration.
This is interpreted to result from a decrease in dipole moment of OH(Al) with temperature. A sudden shift of the vibrational
frequency from 3396 to 3386 cm–1 between 550 and 560 °C and a constant value of the integral absorbance from 535 to 570 °C were considered to be related to
the change in H bond distance during the structural transformation of α-quartz to its β-form. The local environment of OH(Al)
begins to change at temperatures below 570 °C, where the crystallographic α–β transition occurs.
Received: 18 February 1998/ Accepted: 10 July 1998 相似文献
16.
Dynamics of transparent exopolymeric particles (TEP) and particle-associated carbohydrates in the Dona Paula bay, west coast of India 总被引:1,自引:0,他引:1
Surface seawater samples were collected over a period of 27 months at a shallow water station in Dona Paula bay from 1998–2000.
The samples were analyzed to assess the seasonal variations, inter-annual variability and the contributions of:
A distinct inter-annual variability was observed with an increase in the bacterial abundance, chlorophylla (Chl a), TEP and Sal-PCHO and their greater contribution to particulate organic carbon during May 1998–1999 than in June
1999–July 2000. Overall, there was no statistically significant correlation of TEP with phytoplankton biomass (Chl a), Sal-PCHO,
CPCHO and hydrodynamic conditions. A weak inverse correlation was observed between TEP and TBA (r = −0.397;p < 0.05) but the role of TEP as a C-source for bacteria was not evident. Both Sal-PCHO and CPCHO appeared to be two distinct
forms of carbohydrates. Unlike CPCHO, Sal-PCHO concentrations showed a positive trend with Chla and significant linear correlation with bacterial abundance (r = 0.44,p < 0.007,n = 48), indicating that Sal-PCHO as carbon source might have supported bacterioplankton abundance. The mean %TEP-C contribution
to the annual average organic carbon for 1998–2000 was 6.9% ± 5.8%, next only to phytoplankton-C (33.1 ± 22.1%) and greater
than bacterial-C (4.6% ± 4.6%) or carbohydrate-C (< 3.8%). Despite its greater contribution to the organic carbon pool, the
contribution of TEP-C to the benthic carbon demand and its fate in the study area could not be ascertained in this study. 相似文献
– | •transparent exopolymeric particles (TEP) concentration, |
– | •two forms of particle-associated carbohydrates — 1.5 M NaCl/saline extracted (Sal-PCHO) and 10 mM EDTA-extracted (CPCHO) and |
– | •total bacterial abundance (TBA) to particulate organic carbon pool. |
17.
Xiaodong Zou Tao Yuan Ying Zhu Xiaodong Zhang Suping Feng Zhemin Shen Wenhua Wang 《Environmental Geology》2007,51(5):813-820
The copper (Cu) distributions and speciation in the surface sediment collected from Nansi Lake (NL) (China) were investigated
by chemical and physical fractionation methods. Sediment was first fractionated into four grain size fractions (< 63, 78–163,
163–280, and > 280 μm) in wet condition. Each fraction was then further divided into two density sub-fractions (low and heavy)
by flotation in sodium-polytungstate solution (ρ = 2.0 g/cm3). In addition, a three-stage extraction procedure following the European Communities Bureau of Reference (BCR) protocol was
applied to study the speciation distribution of Cu among grain size fractions. It was found that the speciation distributions
of Cu among different grain size fractions were quite close to each other, although the total Cu concentrations were different
in the individual fractions. Moreover, Cu mainly occurred in the coarser, low density, OC-rich fractions. Extractable Cu,
which was dominated by reducible and oxidizable parts, occupied almost 80% of the total Cu concentration. Total Cu concentrations
in grain size fractions and density sub-fractions ranged from 29.6 to 72.9 and from 21.4 to 156 mg/kg dw, respectively. It
was noted that low-density fractions had 4–7 times higher Cu concentrations and 5–12 times higher organic carbon (OC) content
than those in high-density fractions. The results demonstrated that OC was a main factor influencing Cu distributions in either
grain size or density fractionated sediment. This study suggests that the role of the Cu-rich fraction should be considered
when conducting the remediation of Cu contamination in NL. 相似文献
18.
In deltaic marshes, mineral sediment promotes positive elevation change and counters subsidence and sea level rise. In many
such marshes sediment deficits result in wetland loss. One new way to address sediment deficiency is to supply marshes with
sediments in a slurry that deposits the sediment in a thin layer over a large area. The long-term effects of this strategy
are poorly understood. In a rapidly submerging,Spartina alterniflora salt marsh, we tested how different amounts of sediment ameliorated the effects of sea level rise and subsidence over 7 yr
(1992–1998). Sediment slurry enrichment likely affected plants and soils by two mechanisms. It increased elevation and soil
bulk density, leading to increased plant vigor and soil condition. These effects were long lasting, such that by 1998 areas
receiving moderate amounts of sediment (5–12 cm relative elevation) had better plant vigor and soil condition compared to
areas not receiving sediment (55% cover versus 20%; bulk densities of 0.4–1.0 g cm−3 versus 0.2 g cm−3; 0 mM hydrogen sulfide versus > 1.0 mM). The sediment slurry also had high nutrient content, which resulted in a pulse of
growth, especially in areas receiving the most sediment (areas > 12 cm relative elevation initially had >90% cover and canopy
heights >1.6 m). This nutrient-induced growth spurt was short lived and faded after 3 yr, at which point the long lasting
effects of increased elevation probably became the dominant factor promoting plant vigor and soil condition. Moderate levels
of sediment generated the most beneficial and long lasting effects to the vegetation and soils. This degree of sediment slurry
addition countered the effects of subsidence and sea level rise, but not so much as to surpass the intertidal position to
whichS. alterniflora is best adapted. 相似文献
19.
G. V. Gibbs A. F. Wallace R. T. Downs N. L. Ross D. F. Cox K. M. Rosso 《Physics and Chemistry of Minerals》2011,38(4):267-291
Electron density distributions, bond paths, Laplacian and local-energy density properties have been calculated for a number
of As4S
n
(n = 3, 4 and 5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As–S and As–As interactions
classify as shared bonded interactions, and the intermolecular As–S, As–As and S–S interactions classify as closed-shell van
der Waals (vdW) bonded interactions. The bulk of the intermolecular As–S bond paths link regions of locally concentrated electron
density (Lewis-base regions) with aligned regions of locally depleted electron density (Lewis-acid regions) on adjacent molecules.
The paths are comparable with intermolecular paths reported for several other molecular crystals that link aligned Lewis base
and acid regions in a key–lock fashion, interactions that classified as long-range Lewis acid–base-directed vdW interactions.
As the bulk of the intermolecular As–S bond paths (~70%) link Lewis acid–base regions on adjacent molecules, it appears that
molecules adopt an arrangement that maximizes the number of As–S Lewis acid–base intermolecular bonded interactions. The maximization
of the number of Lewis acid–base interactions appears to be connected with the close-packed array adopted by molecules: distorted
cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal
close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from
aqueous species that maximizes the number of long-range Lewis acid–base vdW As–S bonded interactions with the resulting directed
bond paths structuralizing the molecules as a molecular crystal. 相似文献
20.
Ryuji Tateyama Eiji Ohtani Hidenori Terasaki Keisuke Nishida Yuki Shibazaki Akio Suzuki Takumi Kikegawa 《Physics and Chemistry of Minerals》2011,38(10):801-807
The compositional dependence on the density of liquid Fe alloys under high pressure is important for estimating the amount
of light elements in the Earth’s outer core. Here, we report on the density of liquid Fe–Si at 4 GPa and 1,923 K measured
using the sink–float method and our investigation on the effect of the Si content on the density of the liquid. Our experiments
show that the density of liquid Fe–Si decreases from 7.43 to 2.71 g/cm3 non-linearly with increasing Si content (0–100 at%). The molar volume of liquid Fe–Si calculated from the measured density
gradually decreases in the compositional range 0–50 at% Si, and increases in the range 50–100 at% Si. It should be noted that
the estimated molar volume of the alloys shows a negative volume of mixing between Fe and Si. This behaviour is similar to
Fe–S liquid (Nishida et al. in Phys Chem Miner 35:417–423, 2008). However, the excess molar volume of mixing for the liquid Fe–Si is smaller than that of liquid Fe–S. The light element
contents in the outer core estimated previously may be an underestimation if we take into account the possible negative value
of the excess mixing volume of iron–light element alloys in the outer core. 相似文献