Use of nuclear magnetic resonance microscopy for noninvasive observations of root-soil water relations     

J. M. Brown  P. J. Kramer  G. P. Cofer  G. A. Johnson 《Theoretical and Applied Climatology》1990,42(4):229-236

Summary As part of our strategy to study root-soil water relationships, it was necessary to develop a nondestructive technique to detect small changes in water distribution in and near the root. Nuclear magnetic resonance imaging (MRI), clinically used to nondestructively and noninvasively acquire anatomical information, can also be used to observe water distribution in roots, soils and other plant tissues. In MRI, a sample is placed in a strong magnetic field and a sequence of radio frequency (rf) pulses and magnetic field gradients is used to measure the concentration and relaxation properties of protons, chiefly those associated with water. This information is then reconstructed into a digital image representing the spatial distribution of water in plant tissues and soil. Today, intact roots less than 1 mm in diameter growing in soil or synthetic media can be clearly imaged in less than 4 minutes at resolutions typically less than 30µm. This permits rapid production of images that simultaneously distinguish temporal changes in water distribution in root tissue, the rhizosphere and the adjacent soil at microscopic levels. Applications of this technique for investigating plant-soil water relationships will be discussed.With 3 Figures  相似文献   

Rock mechanics applied to shaft pillar mining     

J. C. Johnson  S. A. Orr 《Geotechnical and Geological Engineering》1990,8(4):385-392

Summary The Bureau of Mines is investigating methods for evaluating and optimizing shaft designs for deep metal mines. This paper describes one such project at the Homestake Mine in Lead, SD. To determine a safe approach for the extraction of ore from the Ross Shaft pillar at Homestake, a basic rock mechanics approach has been taken that involves laboratory testing, field measurements, and computer modelling. The results of the study show that ore bodies in the Ross pillar can be mined safely and that the shaft will remain in elastic rock. On the basis of this work, other mines can develop finite-element modelling to evaluate the stability of mine openings and increase resource recovery.  相似文献   

Simulation of surface urban heat islands under ‘IDEAL’ conditions at night part 1: Theory and tests against field data   总被引：1，自引：0，他引：1  

G. T. Johnson  T. R. Oke  T. J. Lyons  D. G. Steyn  I. D. Watson  J. A. Voogt 《Boundary-Layer Meteorology》1991,56(3):275-294

Observations show that the urban heat island in the atmospheric layer below roof level is most strongly developed during calm, cloudless conditions at night. This paper outlines two versions of a numerical model to describe the cooling of rural and street canyon surfaces under these conditions using surface thermal and radiative properties and the radiative geometry of the canyons. One version uses a full system of differential equations and the other the simpler force-restore approach. The two approaches are shown to be in general agreement and the output of the simpler model is shown to give a faithful representation of cooling of rural and urban surfaces, and therefore heat islands, when compared with field observations.  相似文献   

Nonlinear western boundary current flow near a corner     

Michael A. Page  E. R. Johnson 《Dynamics of Atmospheres and Oceans》1991,15(6)

This paper analyses a western boundary current striking a solid boundary. Interest is concentrated on the case where inertial effects are sufficient to modify the flow from its ‘Stommel-layer’ form with Ekman friction relatively unimportant in the interior. It is shown that, beyond a critical inflow speed, a complicated system of four asymptotic regions forms near the corner, turning some of the flow along the blocking boundary and then returning it westwards to rejoin the western boundary current. A comparison with the results of a simple ocean model shows that many of the features in that flow can be explained through the asymptotic theory.  相似文献   

Spawning of the red drum in Mosquito Lagoon,East-Central Florida     

Darlene R. Johnson  Nicholas A. Funicelli 《Estuaries and Coasts》1991,14(1):74-79

A study was carried out in fall 1987 to determine if red drum (Sciaenops ocellatus) spawned in the southern portion of Mosquito Lagoon, Florida, 30 km from the nearest tidal pass. Weekly plankton tows were taken from mid-September to mid-November. Floating sciaenid eggs were removed from the samples and incubated 16–36 h: 329 red drun eggs were hatched. Viable red drum eggs were collected from October 27 to November 18 at salinities of 29‰ to 32‰ and water temperatures of 21°C to 23°C. The largest number of eggs was collected on November 4, during a full moon. This is the first documentation of red drum spawning in an estuary. The physiography and high salinity (which are more characteristic of marine than estuarine waters) of Mosquito Lagoon were probable factors in producing this phenomenon.  相似文献   

Parallel, similar and constrained folds   总被引：1，自引：0，他引：1  

Arvid M. Johnson  Virginia J. Pfaff   《Engineering Geology》1989,27(1-4):115-180

Theoretical analysis of folding of viscous multilayers with free slip or bonding at layer contacts indicates that folds in such multilayers can be described in terms of three end-members:parallel, in which orthogonal thicknesses of layers are largely constant;similar, in which vertical thicknesses of layers and shapes of successive interfaces are essentially constant; andconstrained, in which amplitudes of anticlines and synclines decrease to zero at upper and lower boundaries. Constrained,internal folds form if the multilayer is confined by rigid media; parallel,concentric-like folds form if the multilayer is confined by soft media, provided soft interbeds are sufficiently thin for the stiff layers to fold as an ensemble. Similar,sinusoidal orchevron folds form throughout much of the thickness of a multilayer, for any stiffness of confining media, provided wavelengths of folds are short relative to the thickness of the multilayer or soft interbeds are sufficiently soft and thick for the stiff layers to act independently. The analysis shows that multilayer folds may have the same form regardless of whether the layer contacts are freely slipping or bonded.

The forms of folds in multilayers confined by media with different viscosities above and below depend on the viscosity contrast of the media. For no medium above and a rigid medium below, the forms are concentric-like in the upper part and internal in the lower part of the multilayer. For no medium above and a soft medium below, the folds are concentric-like throughout the multilayer.

The theory indicates that a useful way to analyze forms of folds in rocks or in experiments is in terms of component waveforms, as defined, for example, by Fourier series. The distributions of amplitudes of component waveforms throughout the multilayer appears to be diagnostic, reflecting contrasts in properties of the multilayer and its confining media. Analysis of a large fold in the central Appalachians, Pennsylvania, and of a smaller fold in the Huasna syncline, California, indicates that at least three component waveforms are required to produce the gross forms of those folds.

The theory closely predicts wavelengths and shapes of folds produced in analogous elastic multilayers, indicating that nonlinearities in material behavior, which are inherent in the elastic material but are absent in the viscous material, are less significant than nonlinearities in the boundary conditions, which are the same in elastic and viscous materials.  相似文献   

The solubility of SO2 and the dissociation of H2SO3 in NaCl solutions     

Frank J. Millero  J. Beter Hershey  George Johnson  Jia-Zhong Zhang 《Journal of Atmospheric Chemistry》1989,8(4):377-389

The pK ₁ ^* and pK ₂ ^* of H₂SO₃ have been determined in NaCl solutions as a function of ionic strength (0.1 to 6 m) and temperature (5 and 25 °C). The extrapolated values in water were found to be in good agreement with literature data. The experimental results have been used to determine the Pitzer interaction parameters for SO₂, HSO ₃ ^- and SO ₃ ^- in NaCl solutions. The resultant parameters for NaHSO₃ and Na₂SO₃ were found to be in reasonable agreement with the values for NaHSO₄ and Na₂SO₄. It, thus, seems reasonable to assume that the interactions of Mg²⁺ and Ca²⁺ with HSO ₃ ^- and SO ₃ ^- can be estimated from the values with HSO ₄ ^- and SO ₄ ^- until experimental values are available. Measurements of pK ₁ ^* and pK ₂ ^* in artificial seawater were found to be in good agreement with the calculated values using the derived Pitzer parameters. It is, thus, possible to make reasonable estimates of the activity coefficients of HSO ₃ ^- and SO ₃ ^- ions and pK ₁ ^* and pK ₂ ^* for the ionization of H₂SO₃ in marine aerosols.  相似文献   

Magma genesis in the New Britain island-arc: Constraints from Nd and Sr isotopes and trace-element patterns     

D. J. DePaolo  R. W. Johnson 《Contributions to Mineralogy and Petrology》1979,70(4):367-379

A selected suite of fresh volcanic rocks from the New Britain island arc has been analyzed for ¹⁴³Nd/¹⁴⁴Nd, ⁸⁷Sr/⁸⁶Sr, major and trace elements to investigate relationships between isotopes, trace elements and petrology, and depth to the underlying Benioff zone. From these relationships inferences about magma generation are made utilizing Nd and Sr isotope systematics in possible source materials. Lavas ranging in composition from basalt to rhyolite show minimal variation of ¹⁴³Nd/¹⁴⁴Nd. Small variations in ⁸⁷Sr/⁸⁶Sr do not correlate with depth to the Benioff zone, but are related to magma type. Nd-Sr isotopes suggest that island arc lavas in general are derived from a mixture of suboceanic mantle and hydrothermally altered mid-ocean ridge-type basalt, but the New Britain magma source appears homogeneous with little indication of either the involvement of oceanic crust or mantle inhomogeneity. Trace element patterns in New Britain lavas are not consistent with Nd isotope data for currently accepted petrologic and trace element models of magma genesis. Mafic lavas from New Britain and other island arcs have anomalously high Sr/Nd, possibly due to components derived from subducted oceanic crust.  相似文献   

REE-fractionated trachytes and dacites from Papua New Guinea and their relationship to andesite petrogenesis   总被引：1，自引：0，他引：1  

I. E. M. Smith  S. R. Taylor  R. W. Johnson 《Contributions to Mineralogy and Petrology》1979,69(3):227-233

Minor trachyte and dacite temporally associated with, but spatially separated from, arc-trench type volcanoes in Papua New Guinea have distinctive REE abundances similar to experimentally produced and theoretically predicted partial melts of eclogite. However, modelling based on small amounts of equilibrium partial melting indicates that only fractionation involving a garnet-dominated residuum can account for the observed REE patterns if the source rock was subducted oceanic basalt. If the source was geochemically evolved, other mineral phases (e.g., amphibole) are possible in the residuum, and there is no necessity to postulate that the downgoing slab was the source for these magmas. The REE fractionated trachytes and dacites appear to be a part of the nearby late Cenozoic volcanic provinces, and possibly represent minor partial melts which only in unusual tectonic situations arrive unmodified at the Earth's surface.  相似文献   

Stable isotope compositions of olivine and dolomite in peridotites formed by deserpentinization,Darrington area,North Cascades,Washington     

Michael Johnson  Michael A Dungan  Joseph A Vance 《Geochimica et cosmochimica acta》1977,41(3):431-435

Oxygen isotope analyses of five olivines from the Darrington peridotite, Washington, yield δO¹⁸ values of +7.3 to +8.9%. which are consistent with derivation of these rocks from a serpentinite precursor. The isotopic data are compatible with mineralogical, textural and chemical evidence that most of the Darrington peridotites have formed by deserpentinization. Olivine from a single, petro-graphically distinct peridotite sample has a δO¹⁸-value of +5.2%. which is within the field of high-temperature olivines. The isotopic and textural evidence indicate that this is a partially recrystallized peridotite tectonite.Oxygen and carbon isotope analyses of dolomites from olivine-carbonate rocks indicate that they could have originated by introduction of atmospheric CO₂ via meteoric waters during the formation of ophidolomites or ophicalcites. Subsequent metamorphism and reequilibration have modified the δO¹⁸-values.  相似文献