1,723,742 research outputs found
The development of a simulation model of the surface water response of a catchment
No full textBased on the physics of flow through porous media, on the dynamic equations of De Saint-Venant and on the kinematic wave approach a numerical model which links groundwater motion through an unconfined aquifer to stream and overland flows has been developed. Galerkin's method has been used to discretize the partial differential equations over the space domain, whereas finite difference schemes have been utilized to approximate the set of nonlinear ordinary differential equations into a set of difference equations which have been solved iteratively by Newton-Raphson's method by means of Gauss substitution of each time step.It has been suggested that the use of two-dimensional models to simulate nonlinear aquifer motions by means of Dupuit's assumption has been the main cause of senseless numerical transient fluctuations on the water table levels. The fact that the accuracy of the solutions near the sinks is constrained to the magnitude of the pumping rates has been shown to be another consequence of having assumed the hydraulic gradient to be equal to the slope of the free surface.A new approach to solve complex channel networks by means of penalty functions over the depths of flow in order to simulate abrupt cross-section width augmentation at the junctions has been presented. Stage-discharge rating functions which take the slope of free surface into account have been used as open downstream boundary conditions to allow the simulation of hysteresis even in these boundaries of the channel networks. It has been shown that approximation of natural cross-sections to asymmetric trapezia can minimize the errors of the main geometric elements of these natural channel cross-sections.Several unsuccessful attempts to model surface runoff as shallow two-dimensional flow have led to the conclusion that it cannot be modelled using fixed boundaries.</p
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
New species and records of the supertribe Stomatosematidi (Diptera: Cecidomyiidae) in Brazil
No full textCarmo-Neto, Antonio Marcelino Do, Lamas, Carlos José Einicker, Urso-Guimarães, Maria Virginia (2019): New species and records of the supertribe Stomatosematidi (Diptera: Cecidomyiidae) in Brazil. Zootaxa 4608 (1): 119-130, DOI: https://doi.org/10.11646/zootaxa.4608.1.
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
The tadpole of Hypsiboas guentheri (Boulenger) (Anura: Hylidae)
No full textAlmeida-Silva, Diego, Neto, Antonio Mollo, Mendes, Humberto Fonseca, Verdade, Vanessa Kruth (2016): The tadpole of Hypsiboas guentheri (Boulenger) (Anura: Hylidae). Zootaxa 4179 (1): 139-143, DOI: http://doi.org/10.11646/zootaxa.4179.1.1
Formulação variacional para o eletromagnetismo e suas aplicações
Get PDFThe variational calculus is directly related to the energetic modeling of
physical systems in general. The advantage of such approach in relation to
the classical approaches (Newtonians) is that a system can be subdivided in
many sub-systems whose modeling can be simpler than the one of the
whole. As the total energy of a system is the sum of the energy of the parts,
it is possible to obtain a global result from the partial results. Nevertheless,
in the classic methods, based on force, such flexibility does not exist, the
most possible way is to apply the effect superposition method. However,
this method does not apply to non-linear systems. In general, the
engineering applications are always linked to the solution of a set of
descriptive equations of the phenomena. Starting in these equations and
reaching a functional, which represent them, is the inverse problem of the
variational calculus. This paper presents a description of the methods which
have been employed for the solution of this problem. Morever, this paper
generalize the Vainberg theorem, which was the starting point for all these
methods. From this theorem, this paper proposes methods that apply to a
more general class of problems, such as, for example, the variational
formulation of Navier-Stokes equations. This work approaches, principally,
the variational formulation of Maxwell, including the quaternionic
formulation, which takes to the langrangian classic electromagnetic field
added of a complex term, which allows the functional, when varied, to
result in the four Maxwell equations. Finally, the formulation of Maxwell
equations by means of differential forms is presented. The advantage of the
energetic method on the weak formulation is that the former provides
superior and inferior quotes to the numeric solution of the problems.O cálculo variacional está diretamente relacionado à modelagem energética
dos sistemas físicos em geral. A vantagem desta abordagem sobre as
abordagens clássicas (Newtonianas), é que um sistema pode ser
subdividido em vários sub-sistemas cuja modelagem pode ser mais simples
que a do todo. Como a energia total de um sistema é a soma das energias
das partes, é possível obter-se um resultado global a partir dos resultados
parciais. Já nos métodos clássicos, baseados na força, não existe esta
flexibilidade, quando muito é possível a aplicação do método da
superposição de efeitos. Contudo, este método não se aplica aos sistemas
não lineares. Em geral, as aplicações de engenharia estão sempre ligadas à
solução de um conjunto de equações descritivas dos fenômenos. Partir
dessas equações e chegar a um funcional, que as represente, é o problema
inverso do cálculo variacional. Este trabalho apresenta uma descrição dos
métodos que têm sido empregados para a solução deste problema, bem
como generaliza o teorema de Vainberg, que foi o ponto de partida para
todos esses métodos. A partir desse teorema este trabalho propõe métodos
que se aplicam a uma classe mais geral de problemas, como por exemplo a
formulação variacional das equações de Navier-Stokes. Este trabalho
aborda, principalmente, a formulação variacional das equações de
Maxwell, inclusive a formulação quaterniônica, que conduz ao lagrangeano
eletromagnético clássico acrescido de um termo complexo, o qual permite
que o funcional ao ser variado resulte nas quatro equações de Maxwell.
Finalmente apresenta-se a formulação das equações de Maxwell por
intermédio de formas diferenciais. A vantagem do método energético sobre
a formulação fraca é que o primeiro fornece cotas superior e inferior para a
solução numérica dos problemas
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