Some basic difference equations of Schrodinger boundary value problemsAndreas Ruffing
, Maria Meiler
, Andrea Bruder
, 2009, izvirni znanstveni članek
Opis: We consider special basic difference equations which are related to discretizations of Schrödinger equations on time scales with special symmetry properties, namely, so-called basic discrete grids. These grids are of an adaptive grid type. Solving the boundary value problem of suitable Schrödinger equations on these grids leads to completely new and unexpected analytic properties of the underlying function spaces. Some of them are presented in this work.
Ključne besede: differential equations, discretization, Schrödinger equations, value problems
Objavljeno: 26.06.2017; Ogledov: 110; Prenosov: 43
Celotno besedilo (278,92 KB)
Oscillatory difference equations and moment problemsJosé M. Ferreira
, Sandra Pinelas
, Andreas Ruffing
, 2014, izvirni znanstveni članek
Opis: In this paper, we first consider some new oscillatory results with respect to the discrete Hermite polynomials of type I, respectively, type II and the Heim-Lorek polynomials. In the second part, we investigate the oscillatory and boundedness properties of the related orthogonality measures and the functions representing them. The polynomials considered so far in this article are closely related to the concept of theWess-Ruffing discretization.
Ključne besede: difference equations, Hermite polynomials, polynomials, discretization
Objavljeno: 26.06.2017; Ogledov: 118; Prenosov: 49
Celotno besedilo (331,56 KB)
, G. W. Gibbons
, Christopher N. Pope
, 2015, izvirni znanstveni članek
Opis: We present explicit solutions of the time-symmetric initial value constraints, expressed in terms of freely specifiable harmonic functions for examples of supergravity theories, which emerge as effective theories of compactified string theory. These results are a prerequisite for the study of the time-evolution of topologically non-trivial initial data for supergravity theories, thus generalising the "Geometrodynamics" program of Einstein-Maxwell theory to that of supergravity theories. Specifically, we focus on examples of multiple electric Maxwell and scalar fields, and analyse the initial data problem for the general Einstein-Maxwell-Dilaton theory both with one and two Maxwell fields, and the STU model. The solutions are given in terms of up to eight arbitrary harmonic functions in the STU model. As a by-product, in order compare our results with known static solutions, the metric in isotropic coordinates and all the sources of the non-extremal black holes are expressed entirely in terms of harmonic functions. We also comment on generalizations to time-nonsymmetric initial data and their relation to cosmological solutions of gauged so-called fake supergravities with positive cosmological constant.
Ključne besede: black holes, supergravity, string theory, conformal field models, string duality
Objavljeno: 14.06.2017; Ogledov: 177; Prenosov: 32
Celotno besedilo (581,40 KB)
Entanglement entropy of subtracted geometry black holesMirjam Cvetič
, Zain H. Saleem
, Alejandro Satz
, 2015, polemika, diskusijski prispevek, komentar
Opis: We compute the entanglement entropy of minimally coupled scalar fields on subtracted geometry black hole backgrounds, focusing on the logarithmic corrections. We notice that matching between the entanglement entropy of original black holes and their subtracted counterparts is only at the order of the area term. The logarithmic correction term is not only different but also, in general, changes sign in the subtracted case. We apply Harrison transformations to the original black holes and find out the choice of the Harrison parameters for which the logarithmic corrections vanish.
Ključne besede: black holes, string theory
Objavljeno: 14.06.2017; Ogledov: 122; Prenosov: 26
Celotno besedilo (378,41 KB)
Gradivo ima več datotek! Več...
General U(1) x U(1) F-theory compactifications and beyond: geometry of unHiggsings and novel matter structureMirjam Cvetič
, Denis Klevers
, Hernan Piragua
, Washington Taylor
, 2015, izvirni znanstveni članek
Opis: We construct the general form of an F-theory compactification with two U(1) factors based on a general elliptically fibered Calabi-Yau manifold with Mordell-Weil group of rank two. This construction produces broad classes of models with diverse matter spectra, including many that are not realized in earlier F-theory constructions with U(1) x U(1) gauge symmetry. Generic U(1) x U(1) models can be related to a Higgsed non-Abelian model with gauge group SU(2) x SU(2) x SU(3), SU(2)(3) x SU(3), or a subgroup thereof. The nonlocal horizontal divisors of the Mordell-Weil group are replaced with local vertical divisors associated with the Cartan generators of non-Abelian gauge groups from Kodaira singularities. We give a global resolution of codimension two singularities of the Abelian model; we identify the full anomaly free matter content, and match it to the unHiggsed non-Abelian model. The non-Abelian Weierstrass model exhibits a new algebraic description of the singularities in the fibration that results in the first explicit construction of matter in the symmetric representation of SU(3). This matter is realized on double point singularities of the discriminant locus. The construction suggests a generalization to U(1)(k) factors with k > 2, which can be studied by Higgsing theories with larger non-Abelian gauge groups.
Ključne besede: F-theory, differential geometry, algebraic geometry, gauge symmetry
Objavljeno: 14.06.2017; Ogledov: 176; Prenosov: 39
Celotno besedilo (1,36 MB)
Application of Mawhin’s coincidence degree and matrix spectral theory to a delayed systemYong-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: 280; Prenosov: 6
Celotno besedilo (2,05 MB)
Obolenja prebavil in nujna stanja v obdobju novorojenčkaSilva Burja
, Dušanka Mičetić-Turk
, 2012, pregledni znanstveni članek
Opis: V skupini novorojenčkov z običajnimi prebavnimi težavami je tudi pomembna skupina otrok z zelo resnimi obolenji prebavil s kirurškimi diagnozami. Prispevek je osredotočen na tiste, ki jih najpogosteje srečamo v praksi in razpravlja o nekaterih potencialno ogrožajočih prirojenih anomalijah in drugih obolenjih prebavil, ki se pojavijo že v obdobju novorojenčka. Naš namen je bil poglobiti razpravo o tej problematiki s poudarki na pomembnosti hitrega in pravilnega ukrepanja v vsakodnevni praksi.
Ključne besede: Dojenček, novorojenček, Emergencies, Gastrointestinal Diseases, Gastrointestinalne bolezni, Infant, Newborn, novorojenčki, Nujna stanja, prebavila
Objavljeno: 30.12.2015; Ogledov: 360; Prenosov: 19
Celotno besedilo (0,00 KB)