1,720,977 research outputs found
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
Quiver vacua geometry and fermions on branes
Get PDFThis thesis explores two topics from the intersection between string theory, quantum field theory, and geometry. While the two topics share some overarching themes, for practical purposes they are distinct areas of research. Therefore this work is presented in two parts, treated separately.
Quiver vacua geometry
Supersymmetric quantum fields theories with eight supercharges are intimately related with numerous topics in geometry. Theories living in three dimensions and enjoying N=4 supersymmetry are perhaps the most accessible such theories. The fields in these theories are arranged into hyper- and vector multiplets, both containing scalar fields. The field-content and symmetries of these theories may be denoted using a quiver, a type of graph in which edges and nodes have specific interpretations in terms of multiplets and symmetries. The possible lowest energy states (vacua) for these theories are associated to vacuum expectation values (VEVs) of the scalar fields. These possible vacua can be organised as an affine variety wherein each point corresponds to a particular set of scalar VEVs. This variety is called the moduli space of vacua for the theory in question. For the class of linear quivers, these varieties are known to be nilpotent varieties in sl_n. In Part I of this thesis, after introducing the necessary machinery, we explore the geometry of the moduli space of vacua of two sets of quiver gauge theories which appear as natural generalisations of the linear case. These are circular quiver gauge theories and D-type Dynkin quiver gauge theories. A central tool in our work is the Kraft-Procesi transition which can be thought of as a physical interpretation of the singularity structure of the affine variety associated to the possible vacua for a given theory.
Fermions on branes
In Part II we make a detailed study of the fermionic fields living on brane worldvolumes. In string phenomenology many of the most promising candidates for the construction of a small, positive cosmological constant in a string theoretic setting rely on ingredients in which the fermionic couplings of fields living on brane worldvolumes play a critical role. We use the superspace formulation of supergravity in eleven and ten dimensions to compute fermion couplings on the M2-brane and on Dp-branes. Fermionic couplings arise naturally from the expansion of the superfields in orders of the fermionic coordinates of superspace. The techniques we use and develop can be applied to determine the fermionic couplings to background fields up to arbitrary fermionic order. We start with the superspace formulation of 11-dimensional supergravity and use a geometric technique known as the normal coordinate method to obtain the -expansion of the M2-brane action. We then present a method which allows the translation of knowledge of fermionic couplings on the M2-brane to knowledge of such couplings on the D2-brane, and then to any Dp-brane. This method is based on superspace generalizations of both the compactification taking 11-dimensional supergravity to type IIA supergravity and the T-duality rules connecting the type IIA and type IIB supergravities
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
The r-map, c-map and black hole solutions
No full textWe consider various geometrical and physical aspects of the r-map and c-map, which are two maps induced by the dimensional reduction of 5d and 4d, N = 2 supergravity coupled to vector multiplets respectively. We treat reduction over a spacelike or timelike dimension on an equal footing, and prove, for the first time, that the target manifold in the image of the timelike c-map is para-quaternion Kahler. In order to do this we provide a new formulation of projective special Kahler geometry based on real Darboux coordinates, which is useful both mathematically and physically in its own right.
As an application we investigate how the r-map and c-map can be used to generate new stationary black hole solutions. In four dimensions we construct new extremal non-BPS solutions, and in both four and five dimensions we construct new non-extremal solutions. We also take the first steps towards constructing new rotating solutions, though at this stage we only recover known solutions.
The systematic and geometrical nature of these constructions allows us to gain a deeper understanding of many familiar properties of black holes in supergravity, such as the attractor mechanism and the transformation of BPS into non-BPS black holes using a field rotation matrix. We also observe an interesting and novel feature relating to non-extremal black holes: in order for solutions to correspond to non-extremal black holes with finite scalar fields we find that the number of integration constants must reduce by half. This suggests that non-extremal black holes always satisfy first order equations similar to their extremal counterparts. For STU-like models all calculations are performed explicitly
Aspects of F-theory GUTs
No full textWe explicitly construct an SO(10) GUT using a global description of the geometry and find two interesting properties: first, at the point of expected E7 enhancement where the Yukawa interaction is generated, we see that there are not enough irreducible compo- nents in the resolved singular fiber to yield an E7 structure; second, upon constructing the G-flux for this GUT, we see that it is not possible, in general, to satisfy the quan- tization condition. This leads to a set of extra conditions on the geometry to allow for the required quantization. We then look at an E7 GUT using a similar construction
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