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  • Authors: Nikolaos S., Papageorgiou; Calogero, Vetro; Francesca, Vetro;  Advisor: -;  Co-Author: - (2023)

    We consider a Dirichlet problem driven by the anisotropic (p(z), q(z))-Laplacian, with a parametric reaction exhibiting the combined effects of singular and concave-convex nonlinearities. The superlinear term may change sign. Using variational tools together with truncation and comparison techniques, we prove a global (for the parameter λ>0 ) existence and multiplicity theorem (a bifurcation-type theorem).

  • Authors: Ján, Terpák;  Advisor: -;  Co-Author: - (2023)

    This paper deals with the analysis of the time-fractional diffusion-wave equation as one-dimensional problem in a large plane wall, long cylinder, and sphere. The result of the analysis is the proposal of one general mathematical model that describes various geometries and different processes. Finite difference method for solving the time-fractional diffusion-wave equation using Grünwald-Letnikov definition for homogeneous or inhomogeneous material and for homogeneous or inhomogeneous boundary conditions is described. Dirichlet, Neumann and Robin boundary conditions are considered. Implementation of numerical methods for explicit, implicit, and Crank-Nicolson scheme were realised in MATLAB. Finally, illustrative examples of simulations using the developed toolbox are presented.

  • Authors: Jack, Robles;  Advisor: -;  Co-Author: - (2023)

    We present an evolutionary model which allows us to study the impact relationship-specific investment has on bargaining. Agents are matched to play an investment and bargaining game. During bargaining, agents have an outside option to form a new relationship, but in exercising this option loses their current investment. We find that the stochastically stable post-investment bargaining convention is dependent on the cost of investment. In particular, the larger the cost of investment, the lower is the share of gross surplus that is received. This stands in contrast with previous studies. In addition, we find that there is under-investment. We disentangle the forces which lead to these two results.

  • Authors: W. A., Mulder;  Advisor: -;  Co-Author: - (2023)

    Finite elements with polynomial basis functions on the simplex with a symmetric distribution of nodes should have a unique polynomial representation. Unisolvence not only requires that the number of nodes equals the number of independent polynomials spanning a polynomial space of a given degree, but also that the Vandermonde matrix controlling their mapping to the Lagrange interpolating polynomials can be inverted. Here, a necessary condition for unisolvence is presented for polynomial spaces that have non-decreasing degrees when going from the edges and the various faces to the interior of the simplex.

  • Authors: Theresa, Lange;  Advisor: -;  Co-Author: - (2023)

    In Tao 2016, the author constructs an averaged version of the deterministic three-dimensional Navier–Stokes equations (3D NSE) which experiences blow-up in finite time. In the last decades, various works have studied suitable perturbations of ill-behaved deterministic PDEs in order to prevent or delay such behavior. A promising example is given by a particular choice of stochastic transport noise closely studied in Flandoli et al. 2021. We analyze the model in Tao 2016 in view of these results and discuss the regularization skills of this noise in the context of the averaged 3D NSE.

  • Authors: Karsten, Kruse; Christian, Seifert;  Advisor: -;  Co-Author: - (2023)

    We consider final state observability estimates for bi-continuous semigroups on Banach spaces, i.e. for every initial value, estimating the state at a final time T>0 by taking into account the orbit of the initial value under the semigroup for t∈[0,T], measured in a suitable norm. We state a sufficient criterion based on an uncertainty relation and a dissipation estimate and provide two examples of bi-continuous semigroups which share a final state observability estimate, namely the Gauß–Weierstraß semigroup and the Ornstein–Uhlenbeck semigroup on the space of bounded continuous functions.

  • Authors: Krzysztof, Stempak;  Advisor: -;  Co-Author: - (2023)

    In this paper, we propose a treatment of some class of differential–difference operators in dimension one from the spectral theory point of view. These operators emerge as symmetrizations of differential operators on (0, b), 0

  • Authors: Jens, Marklof; Matthew, Welsh;  Advisor: -;  Co-Author: - (2023)

    Theta sums are finite exponential sums with a quadratic form in the oscillatory phase. This paper establishes new upper bounds for theta sums in the case of smooth and box truncations. This generalises a classic 1977 result of Fiedler, Jurkat and Körner for one-variable theta sums and, in the multi-variable case, improves previous estimates obtained by Cosentino and Flaminio in 2015. Key steps in our approach are the automorphic representation of theta functions and their growth in the cusps of the underlying homogeneous space.

  • Authors: Oskar, Riedler;  Advisor: -;  Co-Author: - (2023)

    In this article, we show the existence of closed embedded self-shrinkers in Rn+1 that are topologically of type S1×M, where M⊂Sn is any isoparametric hypersurface in Sn for which the multiplicities of the principle curvatures agree. This yields new examples of closed self-shrinkers, for example self-shrinkers of topological type S1×Sk×Sk⊂R2k+2 for any k. If the number of distinct principle curvatures of M is one, the resulting self-shrinker is topologically S1×Sn−1 and the construction recovers Angenent’s shrinking doughnut (Angenent in Shrinking doughnuts, Birkhäuser, Boston, pp 21–38).

  • Authors: Petros, Galanopoulos; Daniel, Girela; Alejandro, Mas;  Advisor: -;  Co-Author: - (2023)

    These are natural generalizations of the classical Hilbert and Cesàro operators. A good amount of work has been devoted recently to study the action of these operators on distinct spaces of analytic functions in D . In this paper we study the action of the operators Hμ and Cμ on the Dirichlet space D and, more generally, on the analytic Besov spaces Bp (1≤p<∞).