• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 7894
  • 3170
  • 1596
  • 831
  • 748
  • 716
  • 218
  • 177
  • 149
  • 109
  • 106
  • 106
  • 106
  • 106
  • 106
  • Tagged with
  • 19228
  • 2591
  • 2094
  • 1860
  • 1768
  • 1694
  • 1513
  • 1496
  • 1470
  • 1440
  • 1388
  • 1351
  • 1244
  • 1218
  • 1166
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Estimating ground-level PM2.5 in Texas from remote sensing satellite data with interpolation and regression methods

Jiang, Xiaoyan 2009 August 1900 (has links)
The integration of remote sensing satellite data in air quality monitoring system at a regional scale is an important method to provide high spatial / temporal resolution information. This work focuses on estimating high spatial / temporal resolution ground-level information about particulate matter with aerodynamic diameters less than 2.5 um (PM2.5), with the utilization of MODIS aerosol optical thickness (AOT) data and meteorological data. Several missing data reconstruction techniques including Bayesian inversion, regularization and prediction-error filter are employed to estimate PM2.5 from satellite data. The results show that several direct missing data interpolation methods have the capability to estimate some distinctive features on the basis of available ground-based measurements, while the PEF method tends to generate more information with the aid of satellite AOT information. In addition to interpolation methods, general linear regression methods are used to predict ground-level PM2.5 with the consideration of other factors that have been shown to play an important role in predictions. Ordinary Least Square (OLS) method, when natural log taken on dependent and independent variables, is able to reduce the violation of homoscedasticity. The scatterplot of predicted and measured PM2.5 shows a strong correlation over the validation region, indicating the ability of the regression model to predict PM2.5. Weighted Least Square (WLS) method also has advantage in improving homoscedasticity. The predicted and measured PM2.5 has a relatively high correlation. / text

Preconditioning of discontinuous Galerkin methods for second order elliptic problems

Dobrev, Veselin Asenov 15 May 2009 (has links)
We consider algorithms for preconditioning of two discontinuous Galerkin (DG) methods for second order elliptic problems, namely the symmetric interior penalty (SIPG) method and the method of Baumann and Oden. For the SIPG method we first consider two-level preconditioners using coarse spaces of either continuous piecewise polynomial functions or piecewise constant (discontinuous) functions. We show that both choices give rise to uniform, with respect to the mesh size, preconditioners. We also consider multilevel preconditioners based on the same two types of coarse spaces. In the case when continuous coarse spaces are used, we prove that a variable V-cycle multigrid algorithm is a uniform preconditioner. We present numerical experiments illustrating the behavior of the considered preconditioners when applied to various test problems in three spatial dimensions. The numerical results confirm our theoretical results and in the cases not covered by the theory show the efficiency of the proposed algorithms. Another approach for preconditioning the SIPG method that we consider is an algebraic multigrid algorithm using coarsening based on element agglomeration which is suitable for unstructured meshes. We also consider an improved version of the algorithm using a smoothed aggregation technique. We present numerical experiments using the proposed algorithms which show their efficiency as uniform preconditioners. For the method of Baumann and Oden we construct a preconditioner based on an orthogonal splitting of the discrete space into piecewise constant functions and functions with zero average over each element. We show that the preconditioner is uniformly spectrally equivalent to an appropriate symmetrization of the discrete equations when quadratic or higher order finite elements are used. In the case of linear elements we give a characterization of the kernel of the discrete system and present numerical evidence that the method has optimal convergence rates in both L2 and H1 norms. We present numerical experiments which show that the convergence of the proposed preconditioning technique is independent of the mesh size.

Methods in Percolation

Lee, Michael James January 2008 (has links)
Algorithms are presented for the computationally efficient manipulation of graphs. These are subsequently used as the basis of a Monte Carlo method for sampling from the microcanonical ensemble of lattice configurations of a percolation model within a neighbourhood of the critical point. This new method arbitrarily increments and decrements the number of occupied lattice sites, and is shown to be a generalisation of several earlier, purely incremental, methods. As demonstrations of capability, the method was used to construct a phase diagram for exciton transport on a disordered surface, and to study finite size effects upon the incipient spanning cluster. Application of the method to the classical site percolation model on the two-dimensional square lattice resulted in an exceptionally precise estimate of the critical threshold. Although this estimate is not in agreement with earlier results, its accuracy was established through an application specific test of randomness, which is also introduced here. The same test suggests that many earlier results have been systematically biased due to the use of deficient pseudorandom number generators. The estimate made here has since been independently confirmed.

Sparse ordinary graphs

Kalk, Jonathan W. January 2005 (has links)
Ordinary graphs are directed graphs that can be viewed as generalizations of symmetric block designs. They were introduced by Fossorier, Jezek, Nation and Pogel in [2] in an attempt to construct new finite projective planes. In this thesis we investigate some special cases of ordinary graphs, most prominently the case where nonadjacent vertices have no common neighbors. We determine all connected graphs of this type that exist. / vii, 65 leaves, bound ; 29 cm. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2005.

On variance estimation and a goodness-of-fit test using the bootstrap method /

Amiri, Saeid, January 2009 (has links) (PDF)
Lic.-avh. Uppsala : Sveriges lantbruksuniversitet, 2009. / Härtill 2 uppsatser.

Analysis of the discontinuous galerkin method applied to collisionless plasma physics

Heath, Ross Evan, 1976- 28 August 2008 (has links)
Not available / text

The Rep Test and Other Sorting Tasks in ILS Research

Edwards, Phillip, VanScoy, Amy 01 1900 (has links)
How people make sense of the world around them via the categories they use is a question that social science researchers frequently attempt to address through their investigations (e.g., Spradley, 1970). One prevalent approach in organizational research is the rep grid method (Reger, 1990). This technique, based upon Kelly's (1955) role construct repertory test, asks participants to sort items (e.g., people, recent events, or artifacts) within a three-member group into subgroups based on participant-defined similarity and dissimilarity. The researcher's main task, therefore, is to inquire about the characteristics or conditions that each participant uses to sort these itemsâ what is similar among the paired items and what makes the pair different from the item that is excluded. Reger (1990) remarks that such an approach creates conditions in which "the researcher's frame of reference and worldview would not be imposed upon the respondent" (301). In information and library science (ILS) research, individuals' uses of categories for sense-making are viewed as being closely coupled to their interactions with available information resources, services, or systems. Sorting tasks are one general class of methods used to uncover the categories that users employ during these interactions. In information systems research, Tan and Hunter (2002) discuss qualitative and quantitative applications of the rep grid method. While other sorting tasks in ILS research do not explicitly share the same intellectual lineage as the rep grid method, the general approaches and outcomes are largely consistent. Kwasnik (1991) studied how users classify personal documents based on criteria other than document attributes. She asked participants to provide a 'guided tour' of an office location along with a document sorting process, and, in reflection, she notes that "people are able to articulate the process by which...decisions were made, and the data produced by this articulation lend themselves to analysis at a level which can yield general rules about the behaviour" (389). The qualitative analysis from Kwasnik's (1991) study can be contrasted with quantitative analyses of sort data used for guidance in the design of information displays (Carlyle, 2001) and interoperable metadata schema (Tennis, 2003).The rep grip method and other sorting tasks represent alternative approaches to direct questioning through standard qualitative interviewing. In this presentation, the authors will review various ways in which sorting techniques have been employed in ILS research, highlight how these methods are applied in their research (e.g., Edwards, forthcoming), suggest strategies for the inclusion of these tasks in study designs, and describe unique challenges encountered during data collection and analysis.

A beginning method for B♭ cornet

Brewer, Leslie Odell, 1907- January 1941 (has links)
No description available.

Utility of flight data in calibrating engagement simulations

Mathiasmeier, Kenneth James 12 1900 (has links)
No description available.

Local structure in graph classes

Muller, John H. January 1987 (has links)
No description available.

Page generated in 0.0403 seconds