DSpace Community:
http://hdl.handle.net/10773/5695
Fri, 17 Jan 2020 04:22:21 GMT2020-01-17T04:22:21ZInjective edge coloring of graphs
http://hdl.handle.net/10773/27299
Title: Injective edge coloring of graphs
Author: Cardoso, Domingos M.; Cerdeira, J. Orestes; Dominic, Charles; Cruz, J. Pedro
Abstract: Three edges $e_{1}, e_{2}$ and $e_{3}$ in a graph $G$ are consecutive if they form a path (in this order) or a cycle of lengths three. An injective edge coloring of a graph $G = (V,E)$ is a coloring $c$ of the edges of $G$ such that if $e_{1}, e_{2}$ and $e_{3}$ are consecutive edges in $G$, then $c(e_{1})\neq c(e_3)$. The injective edge coloring number $\chi_{i}^{'}(G)$ is the minimum number of colors permitted in such a coloring. In this paper, exact values of $\chi_{i}^{'}(G)$ for several classes of graphs are obtained, upper and lower bounds for $\chi_{i}^{'}(G)$ are introduced and it is proven that checking whether $\chi_{i}^{'}(G)= k$ is NP-complete.Sun, 01 Dec 2019 00:00:00 GMThttp://hdl.handle.net/10773/272992019-12-01T00:00:00ZAsymptotically at spinning scalar, Dirac and Proca stars
http://hdl.handle.net/10773/27247
Title: Asymptotically at spinning scalar, Dirac and Proca stars
Author: Herdeiro, C.; Perapechka, I.; Radu, E.; Shnir, Ya.
Abstract: Einstein's gravity minimally coupled to free, massive, classical fundamental fields admits particle-like solutions. These are asymptotically flat, everywhere non-singular configurations that realise Wheeler's concept of a geon: a localised lump of self-gravitating energy whose existence is anchored on the non-linearities of general relativity, trivialising in the flat spacetime limit. In [1] the key properties for the existence of these solutions (also referred to as stars or self-gravitating solitons) were discussed – which include a harmonic time dependence in the matter field –, and a comparative analysis of the stars arising in the Einstein-Klein-Gordon, Einstein-Dirac and Einstein-Proca models was performed, for the particular case of static, spherically symmetric spacetimes. In the present work we generalise this analysis for spinning solutions. In particular, the spinning Einstein-Dirac stars are reported here for the first time. Our analysis shows that the high degree of universality observed in the spherical case remains when angular momentum is allowed. Thus, as classical field theory solutions, these self-gravitating solitons are rather insensitive to the fundamental fermionic or bosonic nature of the corresponding field, displaying similar features. We describe some physical properties and, in particular, we observe that the angular momentum of the spinning stars satisfies the quantisation condition , for all models, where N is the particle number and m is an integer for the bosonic fields and a half-integer for the Dirac field. The way in which this quantisation condition arises, however, is more subtle for the non-zero spin fields.Thu, 10 Oct 2019 00:00:00 GMThttp://hdl.handle.net/10773/272472019-10-10T00:00:00ZMixed integer formulations for a routing problem with information collection in wireless networks
http://hdl.handle.net/10773/27246
Title: Mixed integer formulations for a routing problem with information collection in wireless networks
Author: Flores-Luyo, Luis; Agra, Agostinho; Figueiredo, Rosa; Ocaña, Eladio
Abstract: We study a routing-collecting problem where a system of stations is considered. A vehicle is responsible for collecting information generated continuously in the stations and to deliver it to a base station. The objective is to determine the vehicle route and the collection operations, both physical and wireless, in order to maximize the amount of information collected during a time horizon. Three mixed integer programming models are introduced and a computational study is reported to compare the performance of a solver based on each one of the models.Thu, 16 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10773/272462020-01-16T00:00:00ZRegional enlarged observability of Caputo fractional differential equations
http://hdl.handle.net/10773/27243
Title: Regional enlarged observability of Caputo fractional differential equations
Author: Zouiten, Hayat; Boutoulout, Ali; Torres, Delfim F. M.
Abstract: We consider the regional enlarged observability problem for fractional
evolution differential equations involving Caputo derivatives. Using the
Hilbert Uniqueness Method, we show that it is possible to rebuild the initial
state between two prescribed functions only in an internal subregion of the
whole domain. Finally, an example is provided to illustrate the theory.Sun, 01 Mar 2020 00:00:00 GMThttp://hdl.handle.net/10773/272432020-03-01T00:00:00ZSmart grid topology designs
http://hdl.handle.net/10773/27231
Title: Smart grid topology designs
Author: Carroll, Paula; Requejo, Cristina
Abstract: This paper addresses supports for evolving design demands of electricity low voltage networks in urban areas. Innovations in how electricity is generated and supplied are required to support transformation of energy systems in response to climate change. We describe a MIP model to support grid upgrade decisions in the context of an energy community in an existing urban setting. We evaluate the MIP model on an adaption of an IEEE radial network benchmark instance augmented with geographic data. We present interesting computational results which suggest additional arcs to be added. Our results highlight potential research opportunities for the network optimisation community to facilitate the desired energy systems transformation challenge.Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10773/272312019-01-01T00:00:00Z