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Eriksson, Mattias
Publications (2 of 2) Show all publications
Lennerstad, H. & Eriksson, M. (2018). List graphs and distance-consistent node labelings. Electronic Journal of Graph Theory and Applications, 6(1), 152-165
Open this publication in new window or tab >>List graphs and distance-consistent node labelings
2018 (English)In: Electronic Journal of Graph Theory and Applications, ISSN 2338-2287, Vol. 6, no 1, p. 152-165Article in journal (Refereed) Published
Abstract [en]

In this paper we consider node labelings c of an undirected connected graph G = (V,E) with labels (1, 2, ...,|V|), which induce a list distance c(u, v) = |c(v) - c(u)| besides the usual graph distance d(u, v). Our main aim is to find a labeling c so c(u; v) is as close to d(u, v) as possible. For any graph we specify algorithms to find a distance-consistent labeling, which is a labeling c that minimize Σ u,vεV (c(u, v) - d(u, v))2. Such labeliings may provide structure for very large graphs. Furthermore, we define a labeling c fulfilling d(u1, v1) < d(u2, v2) ) c(u1, v1) ⇒ c(u2, v2) for all node pairs u1; v1 and u2; v2 as a list labeling, and a graph that has a list labeling is a list graph. We prove that list graphs exist for all n = |V| and all k = |E|: n - 1 ≤ k ≤ n(n - 1)/2, and establish basic properties. List graphs are Hamiltonian, and show weak versions of properties of path graphs. © 2018 Indonesian Combinatorics Society.

Place, publisher, year, edition, pages
Extremal combinatorics, Graph distance, Graph labeling
National Category
urn:nbn:se:bth-16110 (URN)10.5614/ejgta.2018.6.1.11 (DOI)000437328400011 ()2-s2.0-85045005282 (Scopus ID)
Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2018-08-20Bibliographically approved
Eriksson, M. (2012). Radiation processes in the Seyfert galaxy NGC 4151. Astronomy and Astrophysics, 547
Open this publication in new window or tab >>Radiation processes in the Seyfert galaxy NGC 4151
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 547Article in journal (Refereed) Published
Abstract [en]

Aims. The main aim of this work was to investigate if the radiative process photoexcitation by accidental resonance (PAR) is producing Fe II lines in the UV region of NGC 4151. At the same time I searched for collisionally excited Fe II emission. While doing so, the broad line region (BLR), intermediate line region (ILR) and narrow line region (NLR) contributions to the Mg II resonance doublet were also investigated. Methods. The focus was on the 2000 to 3000 Å wavelength region, in which decay from both the collisionally and PAR excited Fe II levels would form emission lines. I examined three archived Space Telescope Imaging Spectrograph (STIS) spectra of NGC 4151. Theoretical spectra based on calculated ranges for possible fluxes of the collisionally excited lines and pumping rates through the Fe II channels were then fitted to the observed spectra Results. I show that the UV region is influenced by PAR and that the Fe II fluorescence lines are clearly needed to explain the spectrum between 2000 to 3000 Å. The best fit of the theoretical spectra to the STIS spectra was obtained by assuming a similar radiation power of Fe+ ions and Mg+ ions. Conclusions. The PAR is active in the BLR of NGC 4151 and the total power of the Fe II fluorescence is a significant fraction of the total emission in the 2000 to 3000 wavelength region. Therefore it is important to incorporate this in models of NGC 4151 and possibly also in models of other active galactic nuclei. There are also many collisionally excited Fe II lines that are blended by each other and are therefore not individually observable in the NGC 4151 spectra.

Place, publisher, year, edition, pages
Springer, 2012
atomic processes, line formation, active galaxies, NGC4151
National Category
Mathematical Analysis
urn:nbn:se:bth-7033 (URN)10.1051/0004-6361/201220248 (DOI) (Local ID) (Archive number) (OAI)
Available from: 2013-01-17 Created: 2013-01-16 Last updated: 2017-12-04Bibliographically approved

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