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101.
A model that emphasizes possible alternative sequences of events that occur over time is presented in this article. Representing alternative or branching events captures additional semantics unrealized by linear or non‐branching approaches. Two basic elements of branching, divergence and convergence are discussed. From these elements, many complex branching models can be built capturing a perspective of events that will take place in the future or have occurred in the past. This produces likely sequences of events that a user may compare and analyze using spatial or temporal criteria. The branching events model is especially useful for spatiotemporal decision support systems, as decision‐makers are able to identify alternative locations and times of events and, depending on the context, also identify regions of multiple possible events. A branching events viewer application is presented illustrating a case study based on a tornado response. 相似文献
102.
Assessing potential repositories for geologic sequestration of carbon dioxide using numerical models can be complicated, costly,
and time-consuming, especially when faced with the challenge of selecting a repository from a multitude of potential repositories.
This paper presents a set of simple analytical equations (model), based on the work of previous researchers, that could be
used to evaluate the suitability of candidate repositories for subsurface sequestration of carbon dioxide. We considered the
injection of carbon dioxide at a constant rate into a confined saline aquifer via a fully perforated vertical injection well.
The validity of the analytical model was assessed via comparison with the TOUGH2 numerical model. The metrics used in comparing
the two models include (1) spatial variations in formation pressure and (2) vertically integrated brine saturation profile.
The analytical model and TOUGH2 show excellent agreement in their results when similar input conditions and assumptions are
applied in both. The analytical model neglects capillary pressure and the pressure dependence of fluid properties. However,
simulations in TOUGH2 indicate that little error is introduced by these simplifications. Sensitivity studies indicate that
the agreement between the analytical model and TOUGH2 depends strongly on (1) the residual brine saturation, (2) the difference
in density between carbon dioxide and resident brine (buoyancy), and (3) the relationship between relative permeability and
brine saturation. The results achieved suggest that the analytical model is valid when the relationship between relative permeability
and brine saturation is linear or quasi-linear and when the irreducible saturation of brine is zero or very small. 相似文献
103.
A. J. Stewart 《Australian Journal of Earth Sciences》2013,60(2):175-184
The basal unit of the Amadeus Basin sequence is the Heavitree Quartzite, and this formation usually forms a single east‐west ridge along the northern side of the MacDonnell Ranges. However, at Alice Springs there are two such ridges. Basement rocks crop out on the northern side of each ridge, and dolomite and shale of the Bitter Springs Formation crop out on their southern sides. The northern outcrop of dolomite and shale is tightly folded, and is separated from the southern outcrop of basement by a major fault. The bedding of the sediments, the axial plane of the fold, and the fault all dip south at about 45°. Inverted facings on parasitic folds indicate that the northern outcrop of quartzite and dolomite plus shale is an antiform in inverted rocks. Hence the southern outcrop of basement and quartzite is synformal, and is interpreted as the frontal part of a fold nappe. The nappe started as a recumbent anticline whose middle limb of quartzite sheared out as the anticline travelled several kilometres southwards relative to the dolomite and shale below, which formed a tight recumbent syncline. Later monoclinal uplift of the northern half of the area tilted the nappe into its present south‐dipping attitude, thus converting the recumbent anticline into a synform and the recumbent syncline into an antiform. 相似文献
104.
A. J. Stewart 《Australian Journal of Earth Sciences》2013,60(2):205-211
Twenty‐four mineral separates from the Arunta Complex, four from the metamorphosed Heavitree Quartzite (White Range Quartzite), and one whole rock sample of metamorphosed Bitter Springs Formation, all from the western part of the White Range Nappe of the Arltunga Nappe Complex, and two samples from the autochthonous basement west of the nappe have been dated by the K‐Ar method. The samples from the basement rocks form two groups. Those in the southern or frontal part of the nappe are of Middle Proterozoic (Carpentarian) age (1660–1368 m.y.), determined on hornblende, biotite, and muscovite. In the northern or rear part of the nappe, all but one of the muscovite samples and two biotites are of Middle Silurian to Early Carboniferous age (431–345 m.y.); the remainder of the biotite dates range from 1775 to 548 m.y. (including the two samples from the autochthon), and two hornblendes gave dates of 1639 and 2132 m.y. respectively. All the muscovite samples from the Heavitree Quartzite, and the whole rock sample from the Bitter Springs Formation gave Early to Middle Carboniferous dates (358–322 m.y.). The findings support the identification of the White Range Quartzite as the metamorphosed part of the Heavitree Quartzite, which in turn supports the interpretation of the structure of the area as a large, basement‐cored fold nappe. In addition, they date the time of the Alice Springs Orogeny as pre‐Late Carboniferous, which agrees with fossil evidence from elsewhere in the area. The Alice Springs Orogeny was accompanied by widespread greenschist facies meta‐morphism that progressively metamorphosed the Heavitree Quartzite and Bitter Springs Formation, and retrogressively metamorphosed the Arunta Complex. However, the basement rocks in the southern part of the nappe escaped this metamorphism and retain a Middle Proterozoic age, thus dating the time of the Arunta Orogeny in this region as Carpentarian or older. 相似文献
105.
Geochemical effects of oxidation products and framboidal pyrite oxidation in acid mine drainage prediction techniques 总被引:1,自引:0,他引:1
P. A. Weber W. A. Stewart W. M. Skinner C. G. Weisener J. E. Thomas R. St. C. Smart 《Applied Geochemistry》2004,19(12):1953-1974
Acid mine drainage predictive testwork associated with the Australian Mineral Industries Research Association (AMIRA) P387A Project: Prediction and Kinetic Control of Acid Mine Drainage (AMD) has critically examined static acid assessment and kinetic information from acid–base accounting techniques, including net acid production potential (NAPP), net acid generation (NAG) and column leach tests. This paper compares results on two waste rock samples that were obtained from the Kaltim Prima Coal mine (KPC) containing significant quantities of fine-grained framboidal pyrite. In agreement with other research, the authors' results indicated that framboidal pyrite is more reactive than euhedral forms due to the greater specific surface area of framboidal pyrite. This is evidenced by optical microscopy of reacted samples. Importantly, the results showed that NAPP testing is biased by the rapid acid generating oxidation of framboidal pyrite prior to, and during the acid neutralisation capacity (ANC) test. This can result in negative ANC values for samples containing significant framboidal pyrite (often “corrected” to zero kg H2SO4/t) when significant ANC is actually present in the sample. NAG testing using H2O2 indicated that samples containing a significant quantity of framboidal pyrite can result in the catalytic decomposition of the H2O2 prior to complete oxidation of the sulfide minerals present, requiring sequential addition of H2O2 for completion. A benefit of the NAG test, however, is that it assesses the net acid generation capacity of the sample without bias towards acid generation as is observed using NAPP methods. The kinetic NAG test also gives information on the reaction sequence of framboidal and euhedral pyrite. Periodic (kinetic) analysis of sub-samples from column leach tests indicated rapid oxidation of the framboidal pyrite compared to the euhedral pyrite, which was correlated with the greater framboidal pyrite surface area.Calculations to determine the sulfide/sulfate acidity derived from the oxidation of framboidal pyrite prior to; and during the ANC test have been developed to provide a better indication of the actual ANC (ANCActual) of the sample. Paste pH values of <pH 4–5 may be one suitable trigger mechanism for the implementation of this new method. This has led to an improved NAPP estimation of total acid production. Together with NAG and column leach testing this improved methodology has resulted in accurate AMD characterisation of samples containing acidic oxidation products and framboidal pyrite. 相似文献
106.
DiDonato GT Stewart JR Sanger DM Robinson BJ Thompson BC Holland AF Van Dolah RF 《Marine pollution bulletin》2009,58(1):97-106
Population growth along the southeastern United States coast has precipitated the conversion of forested watersheds to suburban and urban ones. This study sampled creeks representing forested, suburban, and urban watersheds along a longitudinal gradient for indicators of water quality, including traditional indicator bacteria (fecal coliforms and enterococci) and alternative viral indicators (male-specific and somatic coliphages). Tested microorganisms were generally distributed with highest concentrations in creek headwaters and in more developed watersheds. The headwaters also showed the strongest predictive relationship between indicator concentrations and urbanization as measured by impervious cover. A seasonal pattern was observed for indicator bacteria but not for indicator viruses. Coliphage typing indicated the likely source of contamination was nonhuman. Results suggest that headwater creeks can serve as sentinel habitat, signaling early warning of public health concerns from land-based anthropogenic activities. This study also implies the potential to eventually forecast indicator concentrations under land use change scenarios. 相似文献
107.
Michael B. Turner Shane J. Cronin Ian E. Smith Robert B. Stewart Vince E. Neall 《Journal of Volcanology and Geothermal Research》2008
Eruption episodes, where a series of eruption events are generically related, can include the eruption of a wide spectrum of volcanic activity over decadal periods. This paper concentrates on the opening phases of an eruption episode which occurred approximately 1800 yrs BP from Mt Taranaki, New Zealand. These events spanned the eruption of differing bulk compositions and styles from two distinct vent locations; an andesitic sub-plinian eruption from the summit vent and a scoria cone-building eruption of basaltic magma from a satellite vent. Compositional profiles and zoning textures of plagioclase, amphibole and clinopyroxene phenocrysts from the opening andesitic event show evidence of magma mixing and subsequent crystallisation just prior to the initiation of the eruption episode. Titanomagnetite grain morphology and Ti variation suggest that the magma mixing event occurred within a few days to weeks before the eruption acting as a trigger for it. We present a magmatic model which is constrained by the petrological observations and eruptions of the episode. In this model magma differentiation at depth causes its rise and recharging of a mid-crustal magma storage area at 5–7 km. Although the recharging magma differed slightly in oxygen fugacity and temperature, it was compositionally and physically similar enough to the residing andesitic magma to allow efficient mixing. The petrological characteristics described here can be readily observed and enable identification of mixing events in other recent eruption episodes. 相似文献
108.
Polarization analysis of multi-component seismic data is used in both exploration seismology and earthquake seismology. In
single-station polarization processing, it is generally assumed that any noise present in the window of analysis is incoherent,
i.e., does not correlate between components. This assumption is often violated in practice because several overlapping seismic
events may be present in the data. The additional arrival(s) to that of interest can be viewed as coherent noise. This paper
quantifies the error because of coherent noise interference. We first give a general theoretical analysis of the problem.
A simple mathematical wavelet is then used to obtain a closed-form solution to the principal direction estimated for a transient
incident signal superposed with a time-shifted, unequal amplitude version of itself, arriving at an arbitrary angle to the
first wavelet. The effects of relative amplitude, arrival angle, and the time delay of the two wavelets on directional estimates
are investigated. Even for small differences in angle of arrival, there may be significant error (>10°) in the azimuth estimate. 相似文献
109.
Michael B. Turner Mark S. Bebbington Shane J. Cronin Robert B. Stewart 《Bulletin of Volcanology》2009,71(8):903-918
Acquiring detailed eruption frequency datasets for a volcano system is essential for realistic eruption forecasts. However,
accurate datasets are inherently difficult to compile, even if one or more well-dated eruption records are available. A single
record typically under-represents the eruption frequency, while combining two or more records may result in an overrepresentation.
Although glass compositions have proven to be successful in tephrochronological studies of dominantly rhyolitic tephras; microlitic
growth and thin glass shards inhibit their application to andesitic tephras. A method consisting of a combination of two techniques
for correlating syn-eruptive deposits is demonstrated on data from the typical andesitic stratovolcano of Mt. Taranaki, New
Zealand. Firstly, tentative matches are identified using the radiocarbon age and associated error of each event. Secondly,
the compositions of titanomagnetite micro-phenocrysts are used as an independent check, and shown to be a useful correlation
tool where age data is available. Using two lake-core records containing tephra layers in an overlapping time-frame, the radiocarbon
age-correlation procedure suggested 31 tephra matches. Geochemistry data were available for 15 of these pairs. In three of
these cases, the titanomagnetite compositions did not match. Hence, these “paired” tephras were from compositionally distinct
magmas and therefore likely represent separate events. An additional three matches were reassigned within the temporal uncertainty
limits of the dating procedure, based on better geochemical pairing. The final combined dataset suggests that there have been
at least 138 separate ash fall-producing eruptions between 96 and 10 150 years B.P. from Taranaki. Using the combined dataset
the mixture of Weibulls renewal model forecasts a probability of 0.52 for an eruption occurring in the next 50 years at this
volcano. The present annual eruption probability is estimated at 1.6%. This likelihood is almost double that obtained when
relying on a single stratigraphic record. 相似文献
110.