178,200 research outputs found
pail
No full textpailA bucket, usually enamel, with a cover, used to contain human waste. "She carried the pail down to the bank"R. Hollett MAY 1973JH MAY 1973Not usedNot usedWithdraw
Screened pail for sifting bottom-fauna samples
Get PDFArticle by Calvin R. Fremling, in the January 1961 issue (volume 6, number 1) of Limnology and Oceanography, published quarterly by the American Society of Limnology and Oceanography. Journal issue is incomplete (title page and article only.) The article describes a modified version of Donald S. Rawson\u27s screened sample pail, used for sifting and retrieving biological samples from lake, pond, and river bottoms. Includes an image of the modified pail. 2 pages. Part of the Cal R. Fremling Collection.https://openriver.winona.edu/calfremlingpapers/1012/thumbnail.jp
Uncertainty budget of solid Earth data reductions to global gravity models
Get PDFSolid Earth applications of satellite gravity models commonly involve some type of data reduction - i.e. forward
modelling the gravity effect of known mass distributions to isolate an anomaly from the observed field, which is
then attributed to the enquired phenomenon. The adopted "known masses" suffer from the uncertainties arising
from the non-modelled variance in the shape of geological bodies and the density distribution therein. These
uncertainties are propagated to the reduced gravity field, superimposed to the formal errors provided with the
gravity model. Given the different origin between formal errors of satellite global gravity models (GGM), arising
from observation and noise models, and the contribution of geophysical data reductions, we aimed at assessing
the comprehensive error characteristics of reduced-GGMs.
In order to do so, we computed a set of common reductions (topography, crustal layers, mantle inhomogeneities)
using a combination of spectral- and space-domain forward modelling. Uncertainties in the input
quantities (depths and densities) were propagated trough Monte Carlo methods.
Geometries were constrained by a topography-bedrock-ice model (Earth2014), by a global layered model of the
lithosphere (LITHO1.0), and by local higher detail models of the crust and sediments, where available. Depth
uncertainties, if not provided with the input data, were assigned according to method-specific assumptions. Estimates of density and its variance come from probability distributions fitted to literature data, from petrophysical
relationships (e.g. velocity-composition-temperature) and from worst-case assumptions where no sufficient data is
available.
We report the outcome of a set of global models, at a resolution and spectral content coherent with the
currently available satellite-only GGMs. We resort to global uncertainty maps and to the familiar representations
employed in GGM sensitivity assessments (e.g. degree error curves). Different combinations of data reductions
were applied, simulating the interest in different anomalies (e.g. by correcting either for the crust or the mantle)
Uncertainity of satellite – gravity – derived Moho estimates : Contribution of data reductions
Get PDFIn the last years, the unparalleled spatial homogeneity provided by satellite-only global gravity models has been successfully exploited to obtain estimates on mass distribution in the solid Earth. Among these, the depth of the crust-mantle boundary (Mohorovicic discontinuity), has been a successful target of regional and global studies. Even when simplified to a sharp density discontinuity surface, its knowledge enables a reliable infill between terrestrial data, chiefly from seismic methods, and can be applied to the evaluation and comparison of different crustal models, at similar spatial scales.
Owing to the high degrees of GOCE-based GGMs, the theoretical resolving power can be estimated on the order of 0.1 km depth-wise, at less than 1 arc-degree of horizontal resolution. Such estimate assumes a perfectly isolated signal, i.e. no unmodelled masses in the data reductions, in a correctly constrained inversion (no unknown a-priori parameters, e.g. crust-mantle density contrast).
The Moho depth can be estimated from gravity data by solving the inverse problem relating the relief of a density discontinuity to the observed gravity field. This problem requires two input parameters, a density contrast and a reference depth; it is also necessary to isolate the signal due to Moho relief from all other contributions to the gravity field.
Input parameters are usually constrained by seismic data. Data reductions, applied to isolate a "residual anomaly", commonly consists in the forward-modelled effect of topography, of masses both above (e.g. sediments, upper crustal boundaries), and below the crust-mantle boundary (e.g. lateral density variations in the mantle).
Any variance in the input densities and geometries used in the data reduction, if not accounted for, and any uncertainty in the adopted constraints, is mapped in the inversion results, and thus propagated in any subsequent modelling that makes use of crustal thickness (e.g. temperature, rheology, velocity corrections). An uncertainty estimate is now commonly distributed alongside Moho depth models.
Starting from the theoretical Moho depth-error estimate, obtained from formal errors in the global gravity model, we compute the uncertainty effect that each data reduction step adds to this estimate. The gravity uncertainty is then propagated to a depth estimate using a reference inversion operator. This provides a quantitative assessment of the suitability of satellite-only GGMs in detecting Moho features, at different wavelengths, in a realistic geophysical framework. It also highlights where improvement in critical parameters would be more rewarding in terms of uncertainty reduction.
Up to degree and order 280, the cumulative reduction uncertainty can exceed 200 mGal, in terms of gravity anomaly. This results in local Moho depth uncertainties in the order of 10 km. A 10 points percent simulated improvement in the sediment thickness error improves the Moho depth uncertainty range by up to 1 km. This indicates that even slight improvements, such as the harmonisation of existing near-surface data, can pay off in terms of quality of gravity inversion estimates
Error Characteristics of Satellite-only Global Gravity Models after Solid Earth Data Reductions
Get PDFThe spatial homogeneity provided by satellite-only gravity models has been successfully exploited to probe the lithosphere density structure and its related quantities (e.g. composition and temperature). Compared with other observables, these models provide an unparalleled spatial coverage, which comes with the price of lower resolution.
Geophysical applications of gravity products start with data reduction, stripping the gravity effect of "known masses" to isolate an anomalous field. Uncertainties in the reductions, which rely on a-priori data, accumulate in the anomaly and are non-trivially propagated to the inversion results. The static spatial distribution of mass in the lithosphere is responsible for a large part of the observed signal, well above the sensitivity of the products. At the same time, the uncertainties in reductions can reach the same magnitude as the enquired source.
We aimed at providing an error estimate for solid Earth applications, in the form of error curves "after reduction", in the spectral domain, and maps of the spatial distribution of uncertainty. We computed a set of reductions for crustal and mantle inhomogeneities. Uncertainties in the input quantities were propagated trough Monte Carlo methods. Depth uncertainties, if not provided with the input data, were assigned according to method-specific assumptions. Estimates of density and its variance come from distributions fitted to literature data, from petrophysics, and from worst-case assumptions where no data is available. We report the results of these tests globally. Simulated improvements in the input data show how slight improvements in quality would pay off in terms of error reduction
On the combination of global and local data in collocation theory
No full textDue to the successful operation of dedicated satellite gravity missions, nowadays highaccuracy global gravity field models have become available. This triggers the challenge to optimally combine this long to medium wavelength gravity field information derived from space-borne data with high-resolution terrestrial gravity data. In this paper, the least squares collocation concept is revised with the attempt to consistently unify the combination procedure in such a way that the full information contained in both data sets is merged. For example, in local or regional geoid determination the remove-restore method is usually applied only partially taking into account the accuracy of the global model coefficients used for the long-wavelength reduction. The key advantage of the extended formulation is the fact that it automatically accounts for the error covariance of all data types involved. The applicability, feasibility and performance of the proposed method is investigated in the frame of numerical closed-loop simulations. The two main fields of application, i.e., the improvement of a global gravity field model by terrestrial gravity field data, and, vice versa, the support to a regional geoid solution by the incorporation of a global gravity field model, have been analyzed and assessed. Although applied under simplified conditions, it could be shown that the method works and is practically applicable
Male Student Seated on Couch with Feet in Metal Pail
No full textThis unidentified male was a student at Jacksonville State College (now Jacksonville State University) in 1963-1964. He is seated inside on a couch with both feet in a metal pail on the floor.https://digitalcommons.jsu.edu/lib-ac-histimg/30384/thumbnail.jp
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Satellite gravimetry: Methods, products, applications, and future trends
No full textThe gravitational field of the Earth reflects Earth's surface mass redistribution and its inner structure and dynamics. Satellite gravimetry techniques have been used to observe the Earth's external gravitational field and its temporal variations on a global scale. The global gravitational models from satellite gravimetry, typically in terms of spherical harmonic coefficients, are crucial in geodetic, geodynamic, geophysical, hydrological, glaciological, oceanographic, and many other geoscience applications. In this paper, we provide a comprehensive overview of theoretical definitions describing relationships between the spherical harmonic coefficients and different satellite gravimetry observables such as orbital perturbations in terms of satellite positions, velocities, and accelerations; satellite-to-satellite range rates; and gravitational gradients. Products and applications of the Earth's static global gravitational models are presented and discussed in the context of determination of the gravimetric geoid and physical heights, gravimetric and isostatic crustal thickness, bathymetric depths, glacier bedrock relief, sediment thickness, geostrophic and eddy currents, Earth's inertia tensor and dipole, precession and nutation parameters of the Earth's rotation, and prediction of the satellite orbital geometry. Furthermore, applications and advances of the Earth's time-variable gravitational models for monitoring large earthquakes, hydrological mass transport, Earth's rotation parameters, and vertical crustal motions (due to the glacial isostatic adjustment and other phenomena) are presented. Finally, future trends and prospects in the satellite gravimetry are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
Get PDFBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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