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1

Digitale Medien

Fluid infiltration during contact metamorphism of interbedded marble and calc-silicate hornfels, Twin Lakes area, central Sierra Nevada, California (1993)

DAVIS, S. R. ; FERRY, J. M.

Oxford, UK : Blackwell Publishing Ltd

Journal of metamorphic geology 11 (1993), S. 0

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ISSN: 1525-1314

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: Abstract In the Twin Lakes area, central Sierra Nevada, California, most contact metamorphosed marbles contain calcite + dolomite + forsterite ± diopside ± phlogopite ± tremolite, and most calc-silicate hornfelses contain calcite + diopside + wollastonite + quartz ± anorthite ± K-feldspar ± grossular ± titanite. Mineral-fluid equilibria involving calcite + dolomite + tremolite + diopside + forsterite in two marble samples and wollastonite + anorthite + quartz + grossular in three hornfels samples record P± 3 kbar and T± 630° C. Various isobaric univariant assemblages record CO2-H2O fluid compositions of χCO2= 0.61–0.74 in the marbles and χCO2= 0.11 in the hornfelses. Assuming a siliceous dolomitic limestone protolith consisting of dolomite + quartz ° Calcite ± K-feldspar ± muscovite ± rutile, all plausible prograde reaction pathways were deduced for marble and hornfels on isobaric T-XCO2 diagrams in the model system K2O-CaO-MgO-Al2O3-SiO2-H2O-CO2. Progress of the prograde reactions was estimated from measured modes and mass-balance calculations. Time-integrated fluxes of reactive fluid which infiltrated samples were computed for a temperature gradient of 150 °C/km along the fluid flow path, calculated fluid compositions, and estimated reaction progress using the mass-continuity equation. Marbles and hornfelses record values in the range 0.1–3.6 × 104 cm3/cm2 and 4.8–12.9 × 104 cm3/cm2, respectively. For an estimated duration of metamorphism of 105 years, average in situ metamorphic rock permeabilities, calculated from Darcy's Law, are 0.1–8 × 10−6 D in the marbles and 10–27 × 10−6 D in the hornfelses. Reactive metamorphic fluids flowed up-temperature, and were preferentially channellized in hornfelses relative to the marbles. These results appear to give a general characterization of hydrothermal activity during contact metamorphism of small pendants and screens (dimensions ± 1 km or less) associated with emplacement of the Sierra Nevada batholith.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1525-1314.1993.tb00132.x

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2

Digitale Medien

GROUND-PENETRATING RADAR FOR HIGH-RESOLUTION MAPPING OF SOIL AND ROCK STRATIGRAPHY (1989)

DAVIS, J. L. ; ANNAN, A. P.

Oxford, UK : Blackwell Publishing Ltd

Geophysical prospecting 37 (1989), S. 0

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ISSN: 1365-2478

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie , Physik

Notizen: Ground-penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions. The need to better understanding overburden conditions for activities such as geochemical sampling, geotechnical investigations, and placer exploration, as well as the factors controlling groundwater flow, has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible.The areas of application for ground-penetrating radar are diverse. The method has been used successfully to map ice thickness, water depth in lakes, bedrock depth, soil stratigraphy, and water table depth. It is also used to delineate rock fabric, detect voids and identify karst features. The effective application of the radar for the high-resolution definition of soil stratigraphy and fractures in bedrock is highlighted.The basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories. One example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m. Two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine. Another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination. The corroboration of the radar results by borehole investigations demonstrates the power and utility of the high-resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes. With the advent of new instrumentation and field procedures, the routine application of the radar method is becoming economically viable and the method will see expanded use in the future.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-2478.1989.tb02221.x

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3

Digitale Medien

Atrazine in a Stream-Aquifer System: Estimation of Aquifer Properties from Atrazine Concentration Profiles (1993)

Davis, Ralph K. ; Pederson, Darryll T. ; Blum, Darryl A. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Ground water monitoring & remediation 13 (1993), S. 0

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ISSN: 1745-6592

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Energietechnik , Geologie und Paläontologie

Notizen: Lincolns municipal wellfield consists of 44 wells developed in an alluvial aquifer adjacent to the Platte River near Ashland, Nebraska Induced recharge from the river is the primary source of water for the wellfield. Wafer samples were collected on a periodic basis from the Platte River arid two transects of monitoring wells. These samples were analyzed for the herbicide atrazine, which was used as a tracer of induced recharge in this stream-aquifer system. Atrazine concentrations in the river and aquifer were much less than 1.0 ppb during late fall and winter, but increased to as high as 18.9 ppb during spring and summer, associated with runoff from upgradient agricultural lands. There was approximately a 21-day lag time from the first detection of increasing atrazine concentration in the river to the first detection in monitoring wells immediately adjacent to the river. This lag time was relatively constant throughout the year and from one year to the next, even with major fluctuations of river stage and wellfield production. This consistency of lag time indicated that the travel times from the river to the first set of monitoring wells immediately adjacent to the river were fairly constant.Paths of preferential flow were identified in the aquifer at a depth of 25 to 35 feet below land surface. This aquifer zone appeared to play a significant role in movement of water from beneath the river into the wellfield.Aquifer dispersivity was calculated using a method described by Hoehn and Santschi (1987). Macrodispersivity (AL) was shown to increase linearly over the scale of the wellfield. Calculated values of AL were within limits of other reported values for this type of aquifer material and agreed well with values reported by Hoehn and Santschi (1987); These findings will be extremely beneficial for planning and management of the municipal wellfield.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1745-6592.1993.tb00445.x

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4

Digitale Medien

WHAT IS HYDROGEOLOGY? (1989)

Davis, Stanley N.

Oxford, UK : Blackwell Publishing Ltd

Ground water 27 (1989), S. 0

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ISSN: 1745-6584

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Energietechnik , Geologie und Paläontologie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1745-6584.1989.tb00433.x

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5

Digitale Medien

Impact of the Proposed Qattara Reservoir on the Moghra Aquifer of Northwestern Egypt (1991)

Rizk, Zein S. ; Davis, Arden D.

Oxford, UK : Blackwell Publishing Ltd

Ground water 29 (1991), S. 0

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ISSN: 1745-6584

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Energietechnik , Geologie und Paläontologie

Notizen: This paper examines hydrogeologie effects of proposed diversion of water from the Mediterranean Sea to the Qattara Depression for generation of electricity in northwestern Egypt. The Lower Miocene Moghra aquifer directly underlies the Qattara Depression, extending to the east and dipping beneath younger formations to the north. The Qattara Depression is a sink for ground-water flow from the Nile Delta aquifer in the east, the Mediterranean Sea in the north, and the Nubian artesian aquifer in the south. In this study, a two-dimensional finite-difference model was used in conjunction with available meteorologie, geologic, and hydrologie data to characterize the present ground-water conditions in this aquifer and to make predictions about the water-table rise which could occur as a result of the proposed Qattara Reservoir. Model predictions indicate that creation of the reservoir could cause a 30-meter rise of the Moghra aquifer's water table in the central part of the Qattara Depression. This water-table rise decreases to the north and east. Transient simulations indicate that steady-state conditions in the modeled area of the Moghra aquifer are not likely to be reached during the expected 100-year lifetime of the reservoir.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1745-6584.1991.tb00515.x

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6

Digitale Medien

The dipping antiplane crack (1991)

Davis, Paul M. ; Knopoff, Leon

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 106 (1991), S. 0

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ISSN: 1365-246X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: We derive the elastostatic field arising from the introduction of a 2-D dipping antiplane crack at the surface of an elastic half-space having a pre-existing uniform field. The problem is equivalent to that of two identical, joined, antiplane cracks in an infinite, uniformly strained medium; each crack is inclined by the same amount from the axis of symmetry, giving rise to a bent crack. For cracks with the same depth of crack tip beneath the surface, the amount of elastic energy released increases with the angle from the vertical. However, the rate of energy release with increasing angle is less than the rate of increase of surface energy. Plane, vertical cracks are favoured energetically in infinite, homogeneous media, while bent cracks are favoured in heterogeneous media where a crack must deviate from straight line growth in order to bypass a high-strength barrier. We compare the trade-offs in total energy of bent cracks with barrier energies.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb06331.x

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7

Digitale Medien

Single-Link Cluster Analysis, Synthetic Earthquake Catalogues, and Aftershock Identification (1991)

Davis, Scott D. ; Frohlich, Cliff

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 104 (1991), S. 0

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ISSN: 1365-246X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: This paper investigates several aspects of synthetic catalogue generation and aftershock identification schemes. First, we introduce a method for generating synthetic catalogues of earthquakes. This method produces a catalogue which has the geographic appearance of an actual catalogue when the hypocentres are plotted in map view, but allows us to vary the spatial and temporal relationships between pairs of close events. Second, we discuss six statistics to measure certain characteristics of synthetic and actual catalogues. These include four new statistics So, Bo, S1 and B1 which evaluate the distributions of link lengths between events in space and space-time as computed by single-link cluster analysis (SLC). Third, we develop a new scheme for identifying aftershocks in which a group of events forms an aftershock sequence if each event is within a space-time distance D of at least one other event in the group. We define the space-time separation of events by dst=√(d2+C2τ2), where d is the spatial separation of events, τ is the time separation, and C= 1km day-1. Our experience with several synthetic catalogues suggests that an appropriate trial value for D is 9.4 km1/2 (√S1) - 25.2 km. Here, S1, is the median link length using SLC with the metric dsT. Fourth, we generate synthetic catalogues resembling both teleseismic and local network catalogues to evaluate the validity and reliability of this aftershock identification scheme, as well as other schemes proposed by Gardner & Knopoff (1974), Shlien & Toksöz (1974), Knopoff, Kagan & Knopoff (1982), and Reasenberg (1985). Using a simple scoring method, we find that the SLC method compares favourably with other aftershock identification algorithms described in the literature.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb02512.x

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8

Digitale Medien

Aetiology of stem canker diseases of pigeonpea in Fiji (1989)

DAVIS, R. I. ; OGLE, H. ; HAYWARD, A. C. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Plant pathology 38 (1989), S. 0

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ISSN: 1365-3059

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Xanthomonas campestris pv. cajani is reported for the first time from Fiji as the cause of potentially serious pustular stem lesions of pigeonpea. Cultivars and breeding lines differed in susceptibility. The cause of another stem canker disease, characterized by smooth lesions, remains undetermined.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-3059.1989.tb02165.x

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9

Digitale Medien

Selection of a new set of homogeneously reacting bean (Phaseolus vulgaris) differentials to differentiate races of Colletotrichum lindemuthianum (1989)

DRIJFHOUT, E. ; DAVIS, J. H. C.

Oxford, UK : Blackwell Publishing Ltd

Plant pathology 38 (1989), S. 0

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ISSN: 1365-3059

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Twenty-two cultivars of Phaseolus vulgaris, mentioned in the literature as differential cultivars or sources of resistance, were screened with isolates representing 10 races of Colletotrichum lindemuthianum, to test their suitability as differentials. Single-plant selections from eight cultivars were chosen, with genetic uniformity for resistance and with clear positive or negative reactions following inoculation with all 10 individual races. These differentials are proposed as a standard set for international use, to make the identification of C. lindemuthianum races internationally more comparable. The criteria for a set of differentials, and the influence of cultivar, fungus race and environment on the host-pathogen reaction are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-3059.1989.tb02158.x

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10

Digitale Medien

Fat Concentration Affects Sweetness and Sensory Profiles of Sucrose, Sucralose, and Aspartame (1993)

WIET, STEPHAN G. ; KETELSEN, SANDRA M. ; DAVIS, THOMAS R. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Journal of food science 58 (1993), S. 0

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ISSN: 1750-3841

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: The sensory characteristics of sucralose, aspartame, and sucrose were studied in an unflavored lipid model system varying in fat levels. One study investigated the effects of fat on the potencies (vs. sucrose) of sucralose and aspartame. We also examined absolute changes in all three sweeteners in taste, temporal, and mouthfeel properties at fiied concentrations across a wide fat range. Results indicated a modest decrease in the potencies of sucralose and aspartame across fat concentrations, especially at lower sweetness levels. All sweeteners responded similarly to changes in fat concentration. Independent of fat level, sucralose was perceived more similar to aspartame in onset, bitterness, and aftertaste, than to sucrose.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-2621.1993.tb04333.x

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