1,721,027 research outputs found
Upscaling for unsaturated flow including connectivity of the soil structure
No full textModelling of flow processes in the unsaturated zone on a large scale requires often
upscaling of the flow problem. The soil parameter distribution is mostly not known,
so that the upscaled problem is based on a characterization of the soil
heterogeneity, which is obtained from local measurements. Effective flow parameters
are therefore often derived in a stochastic framework, where the heterogeneity of a
field is quantified by its second order stochastic properties (the mean, variance
and a two-point covariance model with an integral scale and anisotropy parameters).
A field has to be Gaussian to be quantified completely by these parameters. However,
soil structure resembles rarely Gaussian fields. It has connected and isolated
structures of different material types. The connectedness of material has a large
influence on the upscaled models, yet these properties can in general not be derived
from second order stochastic field parameters. Therefore upscaling methods are
needed which take connectivity into account.
In this contribution we first discuss how soil connectivity can be quantified from
local data in a reasonable way. We then discuss how the information about
connectivity can be taken into account into the upscaled models. This is done here
by applying different effective medium approaches to derive unsaturated effective
permeability. The methods are all derived assuming capillary equilibrium on the
small scale. Effective parameters are obtained using the self-consistent approach,
the Maxwell approach, the differential effective medium approach and a generalized
percolation approach. We compare the methods and discuss their advantages and
limits. The results obtained for different test fields are compared to the exact
solution for the effective parameters, derived by homogenization theory.Presenters:
name: Neuweiler, Insa
affiliation: Institute of Hydraulic Engineering, University of Stuttgar
Skalenabhängigkeit von Strömungs- und Transportparametern in porösen Medien
No full textThe study discusses the problem of the influence of spatial scales on modeling of flow and transport processes in porous media. As soil and rock formations are usually heterogeneous, this problem is strongly coupled to the question as to how information about structure is transported over length scales. On different length scales different driving forces determine flow and transport processes. In order to derive an appropriate model for a certain scale of interest it is crucial to include information about the impact of structure on smaller scales into the model. The transfer from a detailed heterogeneous model to an equivalent model on a larger scale, where averaged properties are described, is called upscaling.
To derive an upscaled model the following questions have to be addressed:
• What are the relevant time scales and length scales?
• What are the relevant processes on the scale, where heterogeneities are resolved?
• How does the upscaled model look like?
• What are the effective parameters for the upscaled model?
As detailed information about the parameter distribution in the heterogeneous model is in most cases not known or it is not possible to deal with the exact distribution, further questions have to be addressed:
• How can the effective parameters be approximated based on incomplete knowledge
about the parameter distribution?
• What are the relevant quantities to characterize the heterogeneous distribution and how can they be taken into account?
Upscaling for different two-phase flow problems in porous media is discussed in the study.In dieser Arbeit wird das Problem der Skalenabhängigkeit von Modellen für Strömungs- und Transportprozessen in porösen Medien untersucht. Da Boden und Felsformationen in der Regel heterogene Strukturen aufweisen, ist dieses Problem mit der Frage verknüpft, wie Information über relevante Struktureigenschaften über verschiedene Skalen transferiert wird. Auf unterschiedlichen Skalen bestimmen unterschiedliche Kräfte und Mechanismen die Strömungs- und Transportprozesse. Um ein adäquates Modell für eine bestimmte Längenskala zu entwickeln, ist es daher notwendig, Information über die nicht-aufgelösten Strukturen auf kleineren Skalen zu integrieren. Der Übergang von einem detaillierten Modell, in dem kleinskalige Details aufgelöst werden, zu einem äquivalenten homogenen Modell auf einer größeren Skala, in dem gemittelte Größen beschrieben werden, wird uspcaling genannt.
Um ein hochskaliertes Modell zu entwickeln, müssen folgende Fragen diskutiert werden:
• Was sind die relevanten Zeit- und Längenskalen?
• Was sind die relevanten Prozesse auf der Skala, auf der Heterogenitäten aufgelöst werden?
• Wie sieht das hochskalierte Modell aus?
• Was sind die effektiven Parameter für das hochskalierte Modell?
Da detaillierte Information über die Parameterverteilungen im heterogenen Modell meist nicht gut bekannt ist, oder weil die benötigte kleinskalige Modellierung zu viel Rechenaufwand bedeutet, müssen weitere Fragen gestellt werden:
• Wie können effektive Parameter genähert werden, basierend auf unvollständiger Information über die kleinskalige Parameterverteilung?
• Was sind die relevanten Eigenschaften, die Heterogenität charakterisieren und wie können sie in ein hochskaliertes Modell integriert werden?
In dieser Arbeit werden diese Fragen für verschiedene Zwei-Phasen Strömungsprobleme in porösen Medien diskutiert und hochsaklierte Modelle mit effektiven Parametern abgeleitet
Modellierung von Strömung und Transport in terrestrischen Hydrosystemen – Das Wasser im Untergrund
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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
Data driven real-time prediction of urban floods with spatial and temporal distribution
Get PDFThe increase in extreme rainfall events due to climate change, combined with urbanisation, leads to increased risks to urban infrastructure and human life. Physically based urban flood models capable of producing water depth maps with sufficient spatial and temporal resolution are generally too slow for decision makers to react in time during an extreme event. We present a surrogate model with high temporal and spatial resolution for real-time prediction of water levels during a pluvial urban flood. We used machine learning techniques to achieve short computation times. The recursive approach used in this work combines convolutional and fully coupled multilayer architectures. The database for the machine learning was pre-simulated results from a physically based urban flood model. The forcing input of the prediction is precipitation and the output is water level maps with a temporal resolution of 5 min and a spatial resolution of 6 x 6 meters. The prediction performance can be considered promising for testing the model in real operational applications
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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