1,721,031 research outputs found
Distributional curvature of time dependent cosmic strings
No full textColombeau's theory of generalized functions is used to calculate the contributions, at the rotation axis, to the distributional curvature for a time-dependent radiating cosmic string, and hence the mass per unit length of the string source. This mass per unit length is compared with the mass at null infinity, giving evidence for a global energy conservation law
Generalised hyperbolicity in spacetimes with conical singularities
No full textA well posed initial value problem for the scalar wave equation (The existence and uniqueness of an H1 solution) provides a concept of hyperbolicity for many space-times with weak singularities which violate cosmic censorship. A discussion of the extent to which the conical singularity, which describes a thin cosmic string, is hyperbolic in this sense is presented
Invariance of the distributional curvature of the cone under smooth diffeomorphisms
No full textAn explicit calculation is carried out to show that the distributional curvature of a 2-cone, calculated by Clarke et al (Clarke C J S, Vickers J A and Wilson J P 1996 Class. Quantum Grav. 13 2485-98), using Colombeau's new generalized functions is invariant under nonlinear Coo coordinate transformations
Generalised hyperbolicity in conical spacetimes
No full textSolutions of the wave equation in a spacetime containing a thin cosmic string are examined in the context of nonlinear generalized functions. Existence and uniqueness of solutions to the wave equation in the Colombeau algebra is established for a conical spacetime and this solution is shown to be associated with a distributional solution. A concept of generalized hyperbolicity, based on test fields, can be defined for such singular spacetimes and it is shown that a conical spacetime is -hyperboli
'Elementary flatness' on a symmetry axis
No full textThe conditions of elementary flatness, trivial behaviour under parallel propagation of frames, and regularity to various degrees of differentiability, are given precise definitions and related to practical criteria. As an example, their relations are explored in the case of cylindrically symmetrical stationary dust
Generalised hyperbolicity in singular space-times
No full textIt is shown that a unique solution exists to the wave equation in certain singular, but physically plausible, space-times such as those containing thin cosmic strings or shells of matter. One can therefore define a notion of hyperbolicity in such space-times
Generalised functions and distributional curvature of cosmic strings
No full textA new method is presented for assigning distributional curvature, in an invariant manner, to a spacetime of low differentiability, using the techniques of Colombeau's 'new generalized functions'. The method is applied to show that the scalar curvature density of a cone is equivalent to a delta function. The same is true under small enough perturbations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
- …
