Generalized thin sheet analysis in magnetotellurics: an extension of Price's analysis   总被引：1，自引：0，他引：1  

Rambabu P. Ranganayaki  Theodore R. Madden 《Geophysical Journal International》1980,60(3):445-457

Summary. Price's thin sheet analysis for electromagnetic fields has been extended in order to model the effects of crustal resistivity and conductivity variations on magnetotelluric fields. These extensions allow for a general layered medium below the crust and also account for the vertical resistance of the crust as well as its horizontal conductance. An important parameter emerges from the analysis which determines the distance it takes for the crustal current levels to readjust to changes in the crustal conductance. This adjustment distance is given by the square root of the conductivity thickness product multiplied by the resistivity thickness product. Approximate analytical solutions were developed for two-dimensional geometries in order to demonstrate these effects as well as the modifications produced by finite source wavelengths.  相似文献   

Theme issue “Visualization and exploration of geospatial data”     

Jochen Schiewe  Marguerite Madden 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(3):255

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Application of polypyrrole actuators: feasibility of variable camber foils     

Madden  J.D.W. Schmid  B. Hechinger  M. Lafontaine  S.R. Madden  P.G.A. Hover  F.S. Kimball  R. Hunter  I.W. 《Oceanic Engineering, IEEE Journal of》2004,29(3):738-749

A decade of research into electroactive polymer actuators is leading to the exploration of applications. These technologies are not ready to compete with the internal combustion engine and electric motors in high power propulsion systems but are suitable for intermittent or aperiodic applications with moderate cycle life requirements, providing an alternative to solenoids and direct drive electric motors. Polypyrrole, an emerging actuator material, is applied to drive hydrodynamic control surfaces and in particular to change the camber of a foil. The foil is intended for use in the propeller blade of an autonomous underwater vehicle. A scaled prototype is constructed which employs polypyrrole actuators imbedded within the blade itself to vary camber. The kinematics required to generate camber change are demonstrated, with >30/spl deg/ deflections of the trailing edge being observed from both bending bilayer and linear actuator designs. Forces developed in still conditions are five times lower than the 3.5 N estimated to be required to implement variable camber. The observed 70 kJ/m/sup 3/ polypyrrole work density however is more than sufficient to produce the desired actuation from within the limited blade volume, enabling an application that is not feasible using direct drive electric motors. A key challenge with the polypyrrole actuators is to increase force without sacrificing speed of actuation.  相似文献   

Mid-Infrared properties of Early-type galaxies     

E.M. Xilouris  S.C. Madden  L. Vigroux 《Astrophysics and Space Science》2004,289(3-4):415-418

We have conducted a survey of early-type galaxies using the ISOCAMinstrument on board the Infrared Space Observatory (ISO)in order to probe their dustcontent. We present Mid-Infrared photometric properties for a sampleof 20 galaxies observed at 4.5, 7 and 15 μ$m. Using diagnosticcolor-color diagrams, we can delineate the different Mid-Infrared emissioncontribution from evolved stars, non-thermal emission from AGNs/radiosources, and dust.Detailed modelling of the Spectral Energy Distribution (SED)is performed showing that even though theemission from the evolved stellar population may account for a large part of the Mid-Infrared output, emission from the hot dust and the aromatic hydrocarbon bands (e.g. PAHs) is the main contributorin many cases. Modelling of the surface brightness distribution is alsomade, showing that most of the galaxies follow a de Vaucouleurs profile.The physical nature and spatial distribution of the dust that we findfrom our studies of early-type galaxies will help to constrainthe origin of the dust in those galaxies.  相似文献   

A separable potential in triaxially ellipsoidal coordinates satisfying the laplace equation     

Stephen J. Madden Jr. 《Celestial Mechanics and Dynamical Astronomy》1970,2(2):217-227

This paper derives the most general potential function which allows separation of the hamilton-Jacobi equation in orthogonal coordinates and which satisfies the Laplace equation. The resulting potential is then specialized to the case of interest for near-Earth satellites, where the proper behavior of the potential at infinity is obtained and singularities in the region of interest are eliminated. The Vinti potential is found as a special case.This paper was prepared under the sponsorship of the Electronics Research Center of the National Aeronautics and Space Administration through NASA Grant NGR-22-009-262.  相似文献   

The effects of boundary condition asymmetries on the interplanetary magnetic field-moon interaction     

A. Colbert Reisz  Donald L. Paul  Theodore R. Madden 《Earth, Moon, and Planets》1972,4(1-2):134-140

Boundary condition asymmetries inherent in the solar wind flow past the Moon are included in a cylindrical model of the interplanetary magnetic field - Moon interaction. Numerical examinations of the sunward side response of this model are compared in the frequency domain with those of symmetrically excited spherical and cylindrical models and two characteristic differences are observed: the response of the asymmetric model is depressed at low frequencies due to magnetic diffusion around a conducting core, and is flattened at high frequencies because of the finite application time of the incident interplanetary magnetic field. The diffusion of field lines around the core is also evident in the time response of the model in the anti-solar cavity. The above features of the lunar response resulting from boundary condition asymmetries are shown to be evident in observational measurements.  相似文献   

Reply to 'Comment on "Generalized thin sheet analysis in magnetotellurics: an extension of Price's analysis"     

R. P. Ranganayaki  T. R. Madden  Malcolm J. Drury  R. P. Ranganayaki  T. R. Madden 《Geophysical Journal International》1981,65(1):239-240

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Insights for size-dependent reactivity of hematite nanomineral surfaces through Cu sorption     

Andrew S. Madden  Michael F. Hochella Jr. 《Geochimica et cosmochimica acta》2006,70(16):4095-4104

Macroscopic sorption edges for Cu²⁺ were measured on hematite nanoparticles with average diameters of 7 nm, 25 nm, and 88 nm in 0.1 M NaNO₃. The pH edges for the 7 nm hematite were shifted approximately 0.6 pH units lower than that for the 25 nm and 88 nm samples, demonstrating an affinity sequence of 7 nm > 25 nm = 88 nm. Although, zeta potential data suggest increased proton accumulation at the 7 nm hematite surfaces, changes in surface structure are most likely responsible for the preference of Cu²⁺ for the smallest particles. As Cu²⁺ preferentially binds to sites which accommodate the Jahn-Teller distortion of its coordination to oxygen, this indicates the relative importance of distorted binding environments on the 7 nm hematite relative to the 25 nm and 88 nm particles. This work highlights the uniqueness of surface reactivity for crystalline iron oxide particles with decreasing nanoparticle diameter.  相似文献   

Inorganic phosphorus uptake in a carbonate-dominated seagrass ecosystem     

Ole I. Nielsen  Marguerite S. Koch  Christopher J. Madden 《Estuaries and Coasts》2007,30(5):827-839

Seasonal phosphate (Pi) uptake kinetics were determined using chambers encompassing the water column, sediment and the entire system (water column + sediment + seagrass/epiphyte) in Florida Bay (FB) during 2003–2006 and on the Little Bahama Bank (LBB) during a cruise June, 2004. Pi uptake was a linear function of concentration at low Pi levels (< 2 μmo11^-1). Applying the Pi system rate constant (S_p) from western (177 ±50 x 10^-6 m s^-1) and eastern (272 ±66 x 10^-6 m s^-1) bay sites, and using Pi measured during the study (0.02 to 0.177 μmol Pi 1^-1), we calculated a Pi uptake rate of 0.30 to 2.62 mmol Pi m^-2 d^-1 for western and 0.47 to 4.16 mmol Pi m^-2 d^-1 for eastern bay sites which includes phytoplankton uptake (0.455 m height). During non-bloom conditions, phytoplankton dominated Pi uptake in the east (46%) and both phytoplankton and the seagrass-epiphyte consortium in the west (32 and 52%, respectively), with a smaller contribution by the sediment (15–20%). On LBB interior sites, the water column always dominated (≽94%) Pi uptake with a higher S_p (573-881 x 10^-6 m s^-1) than FB. During cyanobacterial blooms in FB (chla 17 μg 1^-1), the water column dominated Pi uptake (100%) and S_p was the highest (>2,800 x 10^-6 m s^-1) measured. Phytoplankton accounted for 88% of this sequestered Pi with only 12% in the acid extractable fraction, likely as calcium bound and/or adsorbed P, and only 1% attributable to small heterotrophs. When chl α levels declined (2 μg I^-1) Pi uptake was still dominated by phytoplankton (77%), the acid extractable pool increased (18%) and the heterotrophic community became more important (22%). In carbonate-dominated seagrass systems, Pi is primarily taken up by the water column biota and is subsequently remineralized/hydrolyzed in the water column or settles to the benthos where it becomes available to benthic primary producers.  相似文献   

Ecosystem model of an estuarine submersed plant community: Calibration and simulation of eutrophication responses   总被引：1，自引：0，他引：1  

Christopher J. Madden  W. Michael Kemp 《Estuaries and Coasts》1996,19(2):457-474

As water quality in the Chesapeake Bay has declined over recent decades, formely healthy submersed plant communities have disappeared from littoral areas of the mesohaline estuary. A dynamic simulation model of shallow regions of bay tributaries (<1 m) was developed to investigate growth responses of submersed vascular plants to eutrophication and habitat degradation. Our objectives were to elucidate mechanisms responsible for the decline and to evaluate conditions required for plant restoration and survival. State varibles in the model are plant leaves, roots, phytoplankton, epiphytes, and detrital material. The model calculates biomass pools and biogeochemical rate processes over annual cycles with a time step of 6 h. Simulations were performed to investigate the influence of phytoplankton and epiphytes on the underwater light environment, how the balance of limiting resources (light and nutrients) controls growth and productivity of submersed plants, and conditions necessary, for the restoration of submersed vegetation. Model output for submersed plants was calibrated to baseline data from the mid 1970s (r²=0.86); simulations reproduced declines in plant biomass with increasing nutrient enrichment. Model experiments showed, that by increasing nutrient inputs 40% above levels observed in the 1960s, submersed plants disappeared within 1–2 yr due to enhanced growth of phytoplankton and epiphytes, which reduced light below required levels. Epiphytes were more important than were phytoplankton in attenuating light. The relationship between nutrient enrichment and plant loss rate was complex, as epiphyte density on leaf surfaces was not linearly related to nutrient levels. Relatively small nutrient increases could have a large effect on submersed plants because epiphyte density on leaves increased exponentially as leaf surface area decreased. Exchanges of organic carbon and nutrients between leaf and root compartments were seasonally variable and were critical for survival of submersed plants. The amount of root-rhizome material available for regrowth could control the outcome of nutrient reduction strategies. Consequently, model predictions of plant restoration success were highly dependent on initial conditions. The model is being used successfully as a research tool to interpret ecological relationships in the ongoing re-evaluation of management alternatives for submersed plant restoration.  相似文献