Scientific Reports
The preprint collection of the Department of Mathematics.
Full-text generally not available for preprints prior to may 2006.
Found 866 products
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QDD143 - 01/11/2013
Gazzola, F.
Hexagonal design for stiffening trusses | Abstract | | We consider the problem of choosing the best design for stiffening trusses of plates, such as bridges. We suggest to cover the plate with regular hexagons which fit side to side. We show that this design has some important advantages when compared with alternative designs. |
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QDD142 - 11/30/2012
Terracini, S.; Verzini, G.; Zilio, A.
Uniform Holder bounds for strongly competing systems involving the square root of the laplacian | Abstract | | For a class of competition-diffusion nonlinear systems involving the square root of the Laplacian, including the fractional Gross-Pitaevskii system, we prove that uniform boundedness implies Holder boundedness for every exponent less than 1/2, uniformly as the interspecific competition parameter diverges. Moreover we prove that the limiting profile is Holder continuous of exponent 1/2. This system arises, for instance, in the relativistic Hartree-Fock approximation theory for mixtures of Bose-Einstein condensates in different hyperfine states. |
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QDD141 - 11/15/2012
Hartshorne, R.; Lella, P.; Schlesinger, E:
Smooth curves specialize to extremal curves | Abstract | | Let H_{d,g} denote the Hilbert scheme of locally Cohen-Macaulay curves of degree d and genus g in projective three space. We show that, given a smooth irreducible curve C of degree d and genus g, there is a rational curve {[C_t]} in H_{d,g} such that C_t for t neq 0 is projectively equivalent to C, while the special fibre C_0 is an extremal curve. It follows that smooth curves lie in a unique connected component of H_{d,g}. We also determine necessary and sufficient conditions for a locally Cohen-Macaulay curve to admit such a specialization to an extremal curve. |
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QDD138 - 11/12/2012
Baccarin, S; Marazzina, D.
Optimal impulse control of a portfolio with a fixed transaction cost | Abstract | | The aim of this work is to investigate a portfolio optimization problem in presence of fixed transaction costs. We consider an economy with two assets, one risky and one risk-free, and an agent fully described by its power utility function. We show how fixed transaction costs influence the agent s behavior, showing when it is optimal to recalibrate his/her portfolio, paying the transaction costs. |
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QDD139 - 11/12/2012
Berchio, E.; Ferrero, A.; Grillo, G.
Stability and qualitative properties of radial solutions of the Lane-Emden-Fowler equation on Riemannian models | Abstract | | We study existence, uniqueness and stability of radial solutions of the Lane-Emden-Fowler equation - Delta_g u=|u|^{p-1}u in a class of Riemannian models (M,g) of dimension n>2 which includes the classical hyperbolic space H^n as well as manifolds with sectional curvatures unbounded below. Sign properties and asymptotic behavior of solutions are influenced by the critical Sobolev exponent while the so-called Joseph-Lundgren exponent is involved in the stability of solutions. |
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QDD140 - 11/12/2012
Berchio, E.
A family of Hardy-Rellich type inequalities involving the L^2-norm of the Hessian matrices | Abstract | | We derive a family of Hardy-Rellich type inequalities in H^2( Omega) cap H_0^1( Omega) involving the scalar product between Hessian matrices. The constants found are optimal and the existence of a boundary remainder term is discussed. |
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QDD137 - 10/30/2012
Grillo, G.; Kovarik, H.
Weighted dispersive estimates for two-dimensional Schroedinger operators with Aharonov-Bohm magnetic field | Abstract | | We consider two-dimensional Schroedinger operators with Aharonov-Bohm magnetic field and an additional electric potential.
We obtain an explicit leading term of the asymptotic expansion of the unitary group associated to H for large times in weighted L^2 spaces. In particular, we show that the magnetic field improves the decay of the unitary group with respect to the unitary group generated by non-magnetic Schroedinger operators, and that the decay rate in time is determined by the magnetic flux. |
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QDD135 - 10/29/2012
Bertacchi, D.; Zucca, F.
Strong local survival of branching random walks is not monotone | Abstract | | The aim of this paper is the study of the strong local survival property for discrete-time and continuous-time branching random walks. We study this property by means of an infinite dimensional generating function G and a maximum principle which, we prove, is satisfied by every fixed point of G.
We give results about the existence of a strong local survival regime and we prove that, unlike local and global survival, in continuous time, strong local survival is not a monotone property in the general case (though it is monotone if the branching random walk is quasi transitive).
We provide an example of an irreducible branching random walk
where the strong local property depends on the starting site of the process.
By means of other counterexamples we show that the existence of a pure global phase is not equivalent to nonamenability of the process, and that even a branching random walk with the same branching law at each site may not exhibit strong local survival.
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