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The periphery graph of a median graph
Boštjan Brešar, Manoj Changat, Ajitha R. Subhamathi, Aleksandra Tepeh, 2010, izvirni znanstveni članek

Opis: The periphery graph of a median graph is the intersection graph of its peripheral subgraphs. We show that every graph without a universal vertex can be realized as the periphery graph of a median graph. We characterize those median graphs whose periphery graph is the join of two graphs and show that they are precisely Cartesian products of median graphs. Path-like median graphs are introduced as the graphs whose periphery graph has independence number 2, and it is proved that there are path-like median graphs with arbitrarily large geodetic number. Peripheral expansion with respect to periphery graph is also considered, and connections with the concept of crossing graph are established.
Ključne besede: mathematics, graph theory, median graph, Cartesian product, geodesic, periphery, peripheral expansion
Objavljeno: 31.03.2017; Ogledov: 492; Prenosov: 184
.pdf Celotno besedilo (145,86 KB)
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Weak k-reconstruction of Cartesian products
Wilfried Imrich, Blaž Zmazek, Janez Žerovnik, 2003, izvirni znanstveni članek

Opis: By Ulam's conjecture every finite graph ▫$G$▫ can be reconstructed from its deck of vertex deleted subgraphs. The conjecture is still open, but many special cases have been settled. In particular, one can reconstruct Cartesian products. We consider the case of ▫$k$▫-vertex deleted subgraphs of Cartesian products and prove that one can decide whether a graph ▫$H$▫ is a ▫$k$▫-vertex deleted subgraph of a Cartesian product ▫$G$▫ with at least ▫$k+1$▫ prime factors on at least ▫$k+1$▫ vertices each, and that ▫$H$▫ uniquely determines ▫$G$▫. This extends previous works of the authors and Sims. This paper also contains a counterexample to a conjecture of MacAvaney.
Ključne besede: mathematics, graph theory, reconstruction problem, Cartesian product, composite graphs
Objavljeno: 31.03.2017; Ogledov: 511; Prenosov: 181
.pdf Celotno besedilo (197,33 KB)
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Harold Pinter in Slovene translations
Darja Darinka Hribar, 2004, izvirni znanstveni članek

Opis: This article examines the translation of Harold Pinter's most notable stylistic peculiarities into Slovene, illustrating its main points with examples taken from his play The Homecoming. The findings demonstrate above all a marked degree of non-observance of the special verbal pattern (special cohesion) of the originals, a failure to convey Pinter's special configuration of meaning (special coherence), and a disregard for internal unifying coincidences. It argues that the Slovene translations of Pinter rely mostly on traditional theories of meaning and of language norms, thus preventing the reproduction of those emotional and psychological actions of Pinter's characters which are usually not expressed by means of the rhetorical, informative elements of his dialogue, but by its form and sonority, i. e. the length, strength, and level of articulation of verbal expression. This blurs Pinter's famous logic of emotion, narrows the proverbial openness and conceptual uncertainty of his plays, and limits their potential vitality in translation. Taking into account current drama and theatre translation practices in Slovenia, i.e. the rarity of published drama translation and the depedence on a translated performance text for subsequent theatrical productions, the article argues that in such cases the drama translation should be retrospective, i.e. aiming at a maximum reconstruction of all relevant linguistic, stylistic, and textual properties of the original, leaving expressly subjective interventions in the text to the theatre practitioners.
Ključne besede: English literature, drama, translation, theory of translation, translation of beletristics, cohesion, coherence, comparative analyses, drama translations
Objavljeno: 16.05.2017; Ogledov: 417; Prenosov: 40
.pdf Celotno besedilo (165,85 KB)
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Application of Mawhin’s coincidence degree and matrix spectral theory to a delayed system
Yong-Hui Xia, Xiang Gu, Patricia Wong J. Y., Syed Abbas, 2012, izvirni znanstveni članek

Opis: This paper gives an application of Mawhin’s coincidence degree and matrix spectral theory to a predator-prey model with M-predators and N-preys. The method is different from that used in the previous work. Some new sufficient conditions are obtained for the existence and global asymptotic stability of the periodic solution. The existence and stability conditions are given in terms of spectral radius of explicit matrices which are much different from the conditions given by the algebraic inequalities. Finally, an example is given to show the feasibility of our results.
Ključne besede: coincidence degree, Jean Mawhin, predator-prey model, spectral theory
Objavljeno: 12.06.2017; Ogledov: 419; Prenosov: 99
.pdf Celotno besedilo (2,05 MB)

Black hole thermodynamics from a variational principle: asymptotically conical backgrounds
Song-ok An, Mirjam Cvetič, Ioannis Papadimitriou, 2016, izvirni znanstveni članek

Opis: The variational problem of gravity theories is directly related to black hole thermodynamics. For asymptotically locally AdS backgrounds it is known that holographic renormalization results in a variational principle in terms of equivalence classes of boundary data under the local asymptotic symmetries of the theory, which automatically leads to finite conserved charges satisfying the first law of thermodynamics. We show that this connection holds well beyond asymptotically AdS black holes. In particular, we formulate the variational problem for N = 2 STU supergravity in four dimensions with boundary conditions corresponding to those obeyed by the so called 'subtracted geometries'. We show that such boundary conditions can be imposed covariantly in terms of a set of asymptotic second class constraints, and we derive the appropriate boundary terms that render the variational problem well posed in two different duality frames of the STU model. This allows us to define finite conserved charges associated with any asymptotic Killing vector and to demonstrate that these charges satisfy the Smarr formula and the first law of thermodynamics. Moreover, by uplifting the theory to five dimensions and then reducing on a 2-sphere, we provide a precise map between the thermodynamic observables of the subtracted geometries and those of the BTZ black hole. Surface terms play a crucial role in this identification.
Ključne besede: M-Theory, Black Holes, String Theory, Gauge-gravity correspondence
Objavljeno: 27.06.2017; Ogledov: 303; Prenosov: 185
.pdf Celotno besedilo (834,82 KB)
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Black holes with intrinsic spin
Mirjam Cvetič, Finn Larsen, 2014, izvirni znanstveni članek

Opis: We analyze the general black hole solutions to the four dimensional STU model recently constructed by Chow and Compere. We define a dilute gas limit where the black holes can be interpreted as excited states of an extremal ground state. In this limit we express the black hole entropy and the excitation energy in terms of physical quantities with no need for parametric charges. We discuss a dual microscopic CFT description that incorporates all electric and magnetic charges. This description is recovered geometrically by identification of a near horizon BTZ region. We construct the subtracted geometry with no restrictions on charges by analyzing the scalar wave equation in the full geometry. We determine the matter sources that support the subtracted geometry by studying a scaling limit and show that the general geometry permits a dilute gas description with parameters that we specify.
Ključne besede: black holes, string theory, conformal field models, string duality
Objavljeno: 27.06.2017; Ogledov: 341; Prenosov: 184
.pdf Celotno besedilo (598,59 KB)
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Chiral four-dimensional F-theory compactifications with SU(5) and multiple U(1)-factors
Mirjam Cvetič, Antonella Grassi, Denis Klevers, Hernan Piragua, 2014, izvirni znanstveni članek

Opis: We develop geometric techniques to determine the spectrum and the chiral indices of matter multiplets for four-dimensional F-theory compactifications on elliptic Calabi-Yau fourfolds with rank two Mordell-Weil group. The general elliptic fiber is the Calabi-Yau onefold in dP(2). We classify its resolved elliptic fibrations over a general base B. The study of singularities of these fibrations leads to explicit matter representations, that we determine both for U(1) xU(1) and SU(5) x U(1) x U(1) constructions. We determine for the first time certain matter curves and surfaces using techniques involving prime ideals. The vertical cohomology ring of these fourfolds is calculated for both cases and general formulas for the Euler numbers are derived. Explicit calculations are presented for a specific base B = P-3. We determine the general G(4)-flux that belongs to H-V((2,2)) of the resolved Calabi-Yau fourfolds. As a by-product, we derive for the first time all conditions on G(4)-flux in general F-theory compactifications with a non-holomorphic zero section. These conditions have to be formulated after a circle reduction in terms of Chern-Simons terms on the 3D Coulomb branch and invoke M-theory/F-theory duality. New ChernSimons terms are generated by Kaluza-Klein states of the circle compactification. We explicitly perform the relevant field theory computations, that yield non-vanishing results precisely for fourfolds with a non-holomorphic zero section. Taking into account the new Chern-Simons terms, all 4D matter chiralities are determined via 3D M-theory/F-theory duality. We independently check these chiralities using the subset of matter surfaces we determined. The presented techniques are general and do not rely on toric data.
Ključne besede: flux compactifications, F-theory
Objavljeno: 27.06.2017; Ogledov: 223; Prenosov: 216
.pdf Celotno besedilo (1,75 MB)
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Compactifications of deformed conifolds, branes and the geometry of qubits
Mirjam Cvetič, G. W. Gibbons, Christopher N. Pope, 2016, izvirni znanstveni članek

Opis: We present three families of exact, cohomogeneity-one Einstein metrics in (2n + 2) dimensions, which are generalizations of the Stenzel construction of Ricci-flat metrics to those with a positive cosmological constant. The first family of solutions are Fubini-Study metrics on the complex projective spaces CPn+1, written in a Stenzel form, whose principal orbits are the Stiefel manifolds V-2(Rn+2) = SO(n+2)/SO(n) divided by Z(2). The second family are also Einstein-Kahler metrics, now on the Grassmannian manifolds G(2)(Rn+3) = SO(n+3)/((SO(n+1)xSO(2)), whose principal orbits are the Stiefel manifolds V-2(Rn+2) (with no Z(2) factoring in this case). The third family are Einstein metrics on the product manifolds Sn+1 x Sn+1, and are Kahler only for n = 1. Some of these metrics are believed to play a role in studies of consistent string theory compactifications and in the context of the AdS/CFT correspondence. We also elaborate on the geometric approach to quantum mechanics based on the Kahler geometry of Fubini-Study metrics on CPn+1, and we apply the formalism to study the quantum entanglement of qubits.
Ključne besede: conformal field models, string theory, models of quantum gravity, differential geometry, algebraic geometry
Objavljeno: 27.06.2017; Ogledov: 283; Prenosov: 195
.pdf Celotno besedilo (586,14 KB)
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Electrodynamics of black holes in STU supergravity
Mirjam Cvetič, G. W. Gibbons, Christopher N. Pope, Zain H. Saleem, 2014, izvirni znanstveni članek

Opis: External magnetic fields can probe the composite structure of black holes in string theory. With this motivation we study magnetised four-charge black holes in the STU model, a consistent truncation of maximally supersymmetric supergravity with four types of electromagnetic fields. We employ solution generating techniques to obtain Melvin backgrounds, and black holes in these backgrounds. For an initially electrically charged static black hole immersed in magnetic fields, we calculate the resultant angular momenta and analyse their global structure. Examples are given for which the ergoregion does not extend to infinity. We calculate magnetic moments and gyromagnetic ratios via Larmor's formula. Our results are consistent with earlier special cases. A scaling limit and associated subtracted geometry in a single surviving magnetic field is shown to lift to AdS(3) x S-2. Magnetizing magnetically charged black holes give static solutions with conical singularities representing strings or struts holding the black holes against magnetic forces. In some cases it is possible to balance these magnetic forces.
Ključne besede: black holes, supergravity, string theory, conformal field models, string duality
Objavljeno: 27.06.2017; Ogledov: 286; Prenosov: 189
.pdf Celotno besedilo (563,26 KB)
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Elliptic fibrations with rank three Mordell-Weilgroup
Mirjam Cvetič, Denis Klevers, Hernan Piragua, Peng Song, 2014, izvirni znanstveni članek

Opis: We analyze general F-theory compactifications with U(1)xU(1)xU(1) Abelian gauge symmetry by constructing the general elliptically fibered Calabi-Yau manifolds with a rank three Mordell-Weil group of rational sections. The general elliptic fiber is shown to be a complete intersection of two non-generic quadrics in P-3 and resolved elliptic fibrations are obtained by embedding the fiber as the generic Calabi-Yau complete intersection into Bl(3)P(3), the blow-up of P-3 at three points. For a fixed base B, there are finitely many Calabi-Yau elliptic fibrations. Thus, F-theory compactifications on these Calabi-Yau manifolds are shown to be labeled by integral points in reflexive polytopes constructed from the nef-partition of Bl(3)P(3). We determine all 14 massless matter representations to six and four dimensions by an explicit study of the codimension two singularities of the elliptic fibration. We obtain three matter representations charged under all three U(1)-factors, most notably a tri-fundamental representation. The existence of these representations, which are not present in generic perturbative Type II compactifications, signifies an intriguing universal structure of codimension two singularities of the elliptic fibrations with higher rank Mordell-Weil groups. We also compute explicitly the corresponding 14 multiplicities of massless hypermultiplets of a six-dimensional F-theory compactification for a general base B.
Ključne besede: flux compactifications, F-theory, superstring vacua, D-branes
Objavljeno: 27.06.2017; Ogledov: 253; Prenosov: 60
.pdf Celotno besedilo (840,88 KB)
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